GNU Emacs Lisp Reference Manual
For Emacs Version 29.1.90

by Bil Lewis, Dan LaLiberte, Richard Stallman,
the GNU Manual Group, et al.

This is the GNU Emacs Lisp Reference Manual corresponding to Emacs version 29.1.90.
Copyright c 1990–1996, 1998–2024 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.3 or any later
version published by the Free Software Foundation; with the Invariant Sections
being “GNU General Public License,” with the Front-Cover Texts being “A
GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of thelicense is included in the section entitled “GNU Free Documentation License.”(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify
this GNU manual. Buying copies from the FSF supports it in developing GNU
and promoting software freedom.”

Published by the Free Software Foundation
51 Franklin St, Fifth Floor
Boston, MA 02110-1301
USAISBN 1-882114-74-4

Cover art by Etienne Suvasa.

iShort Contents
1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2

Lisp Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

45Strings and Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

6

Sequences, Arrays, and Vectors . . . . . . . . . . . . . . . . . . . . . . . . 102

7

Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

8
9Hash Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

10 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
11 Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
12 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
13 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
14 Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
15 Customization Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
16 Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
17 Byte Compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
18 Compilation of Lisp to Native Code . . . . . . . . . . . . . . . . . . . . . 327
19 Debugging Lisp Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
20 Reading and Printing Lisp Objects . . . . . . . . . . . . . . . . . . . . . 371
21 Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
22 Command Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
23 Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
24 Major and Minor Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
25 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
26 Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
27 Backups and Auto-Saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
28 Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
29 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
30 Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
31 Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
32 Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
33 Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878

ii

34 Non-ASCII Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
35 Searching and Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
36 Syntax Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
37 Parsing Program Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1039
38 Abbrevs and Abbrev Expansion . . . . . . . . . . . . . . . . . . . . . . . 1066
39 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
40 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
41 Emacs Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
42 Operating System Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . 1255
43 Preparing Lisp code for distribution . . . . . . . . . . . . . . . . . . . . 1303
A

Emacs 28 Antinews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1309

B

GNU Free Documentation License . . . . . . . . . . . . . . . . . . . . . 1312

CD

GNU General Public License . . . . . . . . . . . . . . . . . . . . . . . . . 1320
Tips and Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331

E

GNU Emacs Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346

F

Standard Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1390

G
H

Standard Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395
Standard Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1398

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1402

iii

Table of Contents
1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1
1.2
1.3

Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Lisp History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3.1 Some Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3.2 nil and t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3.3 Evaluation Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.4 Printing Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.5 Error Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.6 Buffer Text Notation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.7 Format of Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.7.1 A Sample Function Description . . . . . . . . . . . . . . . . . . . . . . . 4
1.3.7.2 A Sample Variable Description . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Version Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2

Lisp Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1
2.2
2.3
2.4

Printed Representation and Read Syntax. . . . . . . . . . . . . . . . . . . . . . . . 8
Special Read Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Comments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Programming Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.1 Integer Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.2 Floating-Point Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.3 Character Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.3.1 Basic Char Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.3.2 General Escape Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4.3.3 Control-Character Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.3.4 Meta-Character Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.3.5 Other Character Modifier Bits . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.4 Symbol Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.5 Sequence Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.6 Cons Cell and List Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.6.1 Drawing Lists as Box Diagrams . . . . . . . . . . . . . . . . . . . . . . 16
2.4.6.2 Dotted Pair Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.6.3 Association List Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4.7 Array Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.4.8 String Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.8.1 Syntax for Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.8.2 Non-ASCII Characters in Strings . . . . . . . . . . . . . . . . . . . . . 20
2.4.8.3 Nonprinting Characters in Strings . . . . . . . . . . . . . . . . . . . . 21
2.4.8.4 Text Properties in Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.9 Vector Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.10 Char-Table Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

iv

2.4.11 Bool-Vector Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.12 Hash Table Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.13 Function Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.14 Macro Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.15 Primitive Function Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.16 Byte-Code Function Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.17 Record Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.18 Type Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.19 Autoload Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.20 Finalizer Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.5 Editing Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.5.1 Buffer Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.2 Marker Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5.3 Window Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.4 Frame Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.5 Terminal Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.6 Window Configuration Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.7 Frame Configuration Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.8 Process Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.9 Thread Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.10 Mutex Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.11 Condition Variable Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.12 Stream Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5.13 Keymap Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5.14 Overlay Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5.15 Font Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5.16 Xwidget Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6 Read Syntax for Circular Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.7 Type Predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.8 Equality Predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.9 Mutability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3

Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.1 Integer Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2 Floating-Point Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 Type Predicates for Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 Comparison of Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.5 Numeric Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.6 Arithmetic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.7 Rounding Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.8 Bitwise Operations on Integers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.9 Standard Mathematical Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.10 Random Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

v

4

Strings and Characters . . . . . . . . . . . . . . . . . . . . . . . . 54
4.1 String and Character Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.2 Predicates for Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.3 Creating Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4 Modifying Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.5 Comparison of Characters and Strings . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.6 Conversion of Characters and Strings . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.7 Formatting Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.8 Custom Format Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.9 Case Conversion in Lisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.10 The Case Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

5

Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.1
5.2
5.3
5.4
5.5
5.6

Lists and Cons Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Predicates on Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Accessing Elements of Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Building Cons Cells and Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Modifying List Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Modifying Existing List Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.6.1 Altering List Elements with setcar . . . . . . . . . . . . . . . . . . . . . . . 88
5.6.2 Altering the CDR of a List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.6.3 Functions that Rearrange Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.7 Using Lists as Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.8 Association Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.9 Property Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
5.9.1 Property Lists and Association Lists . . . . . . . . . . . . . . . . . . . . . 100
5.9.2 Property Lists Outside Symbols . . . . . . . . . . . . . . . . . . . . . . . . . 100

6Sequences, Arrays, and Vectors. . . . . . . . . . . . . . 102
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8

7

Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Functions that Operate on Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Vectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Functions for Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Char-Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Bool-vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Managing a Fixed-Size Ring of Objects . . . . . . . . . . . . . . . . . . . . . . . 123

Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.1
7.2

Record Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Backward Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

vi

8

Hash Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
8.1
8.2
8.3
8.4

9

Creating Hash Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Hash Table Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Defining Hash Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Other Hash Table Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
9.1
9.2
9.3
9.4

Symbol Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Defining Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Creating and Interning Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Symbol Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
9.4.1 Accessing Symbol Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
9.4.2 Standard Symbol Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
9.5 Shorthands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
9.5.1 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
9.6 Symbols with Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

10

Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

10.1 Kinds of Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
10.1.1 Self-Evaluating Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
10.1.2 Symbol Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
10.1.3 Classification of List Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
10.1.4 Symbol Function Indirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
10.1.5 Evaluation of Function Forms. . . . . . . . . . . . . . . . . . . . . . . . . . . 148
10.1.6 Lisp Macro Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
10.1.7 Special Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
10.1.8 Autoloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
10.2 Quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
10.3 Backquote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
10.4 Eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
10.5 Deferred and Lazy Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

11

Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 158

11.1 Sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
11.2 Conditionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
11.3 Constructs for Combining Conditions . . . . . . . . . . . . . . . . . . . . . . . . 162
11.4 Pattern-Matching Conditional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
11.4.1 The pcase macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
11.4.2 Extending pcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
11.4.3 Backquote-Style Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
11.4.4 Destructuring with pcase Patterns . . . . . . . . . . . . . . . . . . . . . 172
11.5 Iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
11.6 Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
11.7 Nonlocal Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
11.7.1 Explicit Nonlocal Exits: catch and throw . . . . . . . . . . . . . . 177

vii

11.7.2 Examples of catch and throw . . . . . . . . . . . . . . . . . . . . . . . . . . 178
11.7.3 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
11.7.3.1 How to Signal an Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
11.7.3.2 How Emacs Processes Errors. . . . . . . . . . . . . . . . . . . . . . . 181
11.7.3.3 Writing Code to Handle Errors . . . . . . . . . . . . . . . . . . . . 182
11.7.3.4 Error Symbols and Condition Names . . . . . . . . . . . . . . . 186
11.7.4 Cleaning Up from Nonlocal Exits . . . . . . . . . . . . . . . . . . . . . . . 187

12

Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

12.1 Global Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
12.2 Variables that Never Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
12.3 Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
12.4 When a Variable is Void . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
12.5 Defining Global Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
12.6 Tips for Defining Variables Robustly. . . . . . . . . . . . . . . . . . . . . . . . . 196
12.7 Accessing Variable Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
12.8 Setting Variable Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
12.9 Running a function when a variable is changed. . . . . . . . . . . . . . . 200
12.9.1 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
12.10 Scoping Rules for Variable Bindings . . . . . . . . . . . . . . . . . . . . . . . . 201
12.10.1 Dynamic Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
12.10.2 Proper Use of Dynamic Binding . . . . . . . . . . . . . . . . . . . . . . . 202
12.10.3 Lexical Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
12.10.4 Using Lexical Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
12.10.5 Converting to Lexical Binding . . . . . . . . . . . . . . . . . . . . . . . . . 206
12.11 Buffer-Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
12.11.1 Introduction to Buffer-Local Variables . . . . . . . . . . . . . . . . . 207
12.11.2 Creating and Deleting Buffer-Local Bindings . . . . . . . . . . . 208
12.11.3 The Default Value of a Buffer-Local Variable . . . . . . . . . . 211
12.12 File Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
12.13 Directory Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
12.14 Connection Local Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
12.14.1 Connection Local Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
12.14.2 Applying Connection Local Variables . . . . . . . . . . . . . . . . . . 220
12.15 Variable Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
12.16 Variables with Restricted Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
12.17 Generalized Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.17.1 The setf Macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.17.2 Defining new setf forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
12.18 Multisession Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

viii

13

Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

13.1 What Is a Function? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
13.2 Lambda Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
13.2.1 Components of a Lambda Expression . . . . . . . . . . . . . . . . . . . 232
13.2.2 A Simple Lambda Expression Example . . . . . . . . . . . . . . . . . 233
13.2.3 Features of Argument Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
13.2.4 Documentation Strings of Functions . . . . . . . . . . . . . . . . . . . . 235
13.3 Naming a Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
13.4 Defining Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
13.5 Calling Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
13.6 Mapping Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
13.7 Anonymous Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
13.8 Generic Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
13.9 Accessing Function Cell Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
13.10 Closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
13.11 Open Closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
13.12 Advising Emacs Lisp Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
13.12.1 Primitives to manipulate advices . . . . . . . . . . . . . . . . . . . . . . 253
13.12.2 Advising Named Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
13.12.3 Ways to compose advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
13.12.4 Adapting code using the old defadvice . . . . . . . . . . . . . . . . . 258
13.12.5 Advice and Byte Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
13.13 Declaring Functions Obsolete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
13.14 Inline Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
13.15 The declare Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
13.16 Telling the Compiler that a Function is Defined . . . . . . . . . . . . . 265
13.17 Determining whether a Function is Safe to Call . . . . . . . . . . . . . 266
13.18 Other Topics Related to Functions . . . . . . . . . . . . . . . . . . . . . . . . . 267

14

Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

14.1 A Simple Example of a Macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
14.2 Expansion of a Macro Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
14.3 Macros and Byte Compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
14.4 Defining Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
14.5 Common Problems Using Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
14.5.1 Wrong Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
14.5.2 Evaluating Macro Arguments Repeatedly . . . . . . . . . . . . . . . 271
14.5.3 Local Variables in Macro Expansions . . . . . . . . . . . . . . . . . . . 273
14.5.4 Evaluating Macro Arguments in Expansion . . . . . . . . . . . . . 273
14.5.5 How Many Times is the Macro Expanded? . . . . . . . . . . . . . . 274
14.6 Indenting Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

ix

15

Customization Settings . . . . . . . . . . . . . . . . . . . . . 277

15.1 Common Item Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
15.2 Defining Customization Groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
15.3 Defining Customization Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
15.4 Customization Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
15.4.1 Simple Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
15.4.2 Composite Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
15.4.3 Splicing into Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
15.4.4 Type Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
15.4.5 Defining New Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
15.5 Applying Customizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
15.6 Custom Themes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

16

Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

16.1 How Programs Do Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
16.2 Load Suffixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
16.3 Library Search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
16.4 Loading Non-ASCII Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
16.5 Autoload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
16.5.1 Autoload by Prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
16.5.2 When to Use Autoload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
16.6 Repeated Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
16.7 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
16.8 Which File Defined a Certain Symbol. . . . . . . . . . . . . . . . . . . . . . . . 311
16.9 Unloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
16.10 Hooks for Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
16.11 Emacs Dynamic Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

17

Byte Compilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

17.1
17.2
17.3
17.4
17.5
17.6
17.7
17.8

18

Performance of Byte-Compiled Code. . . . . . . . . . . . . . . . . . . . . . . . . 316
Byte-Compilation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
Documentation Strings and Compilation . . . . . . . . . . . . . . . . . . . . . 319
Dynamic Loading of Individual Functions . . . . . . . . . . . . . . . . . . . . 319
Evaluation During Compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
Compiler Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Byte-Code Function Objects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
Disassembled Byte-Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

Compilation of Lisp to Native Code . . . . . . . 327

18.1
18.2

Native-Compilation Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Native-Compilation Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

x

19

Debugging Lisp Programs . . . . . . . . . . . . . . . . . . 333

19.1 The Lisp Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
19.1.1 Entering the Debugger on an Error . . . . . . . . . . . . . . . . . . . . . 333
19.1.2 Debugging Redisplay Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
19.1.3 Debugging Infinite Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
19.1.4 Entering the Debugger on a Function Call . . . . . . . . . . . . . . 336
19.1.5 Entering the debugger when a variable is modified . . . . . . 337
19.1.6 Explicit Entry to the Debugger . . . . . . . . . . . . . . . . . . . . . . . . . 337
19.1.7 Using the Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
19.1.8 Backtraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
19.1.9 Debugger Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
19.1.10 Invoking the Debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
19.1.11 Internals of the Debugger. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
19.2 Edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
19.2.1 Using Edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
19.2.2 Instrumenting for Edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
19.2.3 Edebug Execution Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
19.2.4 Jumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
19.2.5 Miscellaneous Edebug Commands . . . . . . . . . . . . . . . . . . . . . . 349
19.2.6 Breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
19.2.6.1 Edebug Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
19.2.6.2 Global Break Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
19.2.6.3 Source Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
19.2.7 Trapping Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
19.2.8 Edebug Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
19.2.9 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
19.2.10 Evaluation List Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
19.2.11 Printing in Edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
19.2.12 Trace Buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
19.2.13 Coverage Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
19.2.14 The Outside Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
19.2.14.1 Checking Whether to Stop . . . . . . . . . . . . . . . . . . . . . . . . 357
19.2.14.2 Edebug Display Update . . . . . . . . . . . . . . . . . . . . . . . . . . 357
19.2.14.3 Edebug Recursive Edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
19.2.15 Edebug and Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
19.2.15.1 Instrumenting Macro Calls . . . . . . . . . . . . . . . . . . . . . . . 358
19.2.15.2 Specification List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
19.2.15.3 Backtracking in Specifications . . . . . . . . . . . . . . . . . . . . 363
19.2.15.4 Specification Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
19.2.16 Edebug Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
19.3 Debugging Invalid Lisp Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
19.3.1 Excess Open Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
19.3.2 Excess Close Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
19.4 Test Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
19.5 Profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

xi

20

Reading and Printing Lisp Objects . . . . . . . . 371

20.1
20.2
20.3
20.4
20.5
20.6
20.7

21

Introduction to Reading and Printing . . . . . . . . . . . . . . . . . . . . . . . . 371
Input Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
Input Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
Output Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Output Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
Variables Affecting Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
Overriding Output Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385

21.1 Introduction to Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
21.2 Reading Text Strings with the Minibuffer . . . . . . . . . . . . . . . . . . . . 386
21.3 Reading Lisp Objects with the Minibuffer . . . . . . . . . . . . . . . . . . . 391
21.4 Minibuffer History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
21.5 Initial Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
21.6 Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
21.6.1 Basic Completion Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
21.6.2 Completion and the Minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . 398
21.6.3 Minibuffer Commands that Do Completion . . . . . . . . . . . . . 400
21.6.4 High-Level Completion Functions . . . . . . . . . . . . . . . . . . . . . . . 402
21.6.5 Reading File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
21.6.6 Completion Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
21.6.7 Programmed Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
21.6.8 Completion in Ordinary Buffers . . . . . . . . . . . . . . . . . . . . . . . . 411
21.7 Yes-or-No Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
21.8 Asking Multiple-Choice Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9 Reading a Password . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
21.10 Minibuffer Commands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
21.11 Minibuffer Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
21.12 Minibuffer Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
21.13 Recursive Minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
21.14 Inhibiting Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
21.15 Minibuffer Miscellany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421

22

Command Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

22.1 Command Loop Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
22.2 Defining Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.2.1 Using interactive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.2.2 Code Characters for interactive . . . . . . . . . . . . . . . . . . . . . . 427
22.2.3 Examples of Using interactive . . . . . . . . . . . . . . . . . . . . . . . . 430
22.2.4 Specifying Modes For Commands . . . . . . . . . . . . . . . . . . . . . . . 430
22.2.5 Select among Command Alternatives . . . . . . . . . . . . . . . . . . . 431
22.3 Interactive Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
22.4 Distinguish Interactive Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
22.5 Information from the Command Loop . . . . . . . . . . . . . . . . . . . . . . . 436

xii

22.6 Adjusting Point After Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
22.7 Input Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
22.7.1 Keyboard Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
22.7.2 Function Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
22.7.3 Mouse Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
22.7.4 Click Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
22.7.5 Drag Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
22.7.6 Button-Down Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
22.7.7 Repeat Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
22.7.8 Motion Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
22.7.9 Touchscreen Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
22.7.10 Focus Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
22.7.11 Xwidget events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
22.7.12 Miscellaneous System Events . . . . . . . . . . . . . . . . . . . . . . . . . . 450
22.7.13 Event Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
22.7.14 Classifying Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
22.7.15 Accessing Mouse Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
22.7.16 Accessing Scroll Bar Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
22.7.17 Putting Keyboard Events in Strings . . . . . . . . . . . . . . . . . . . 459
22.8 Reading Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
22.8.1 Key Sequence Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
22.8.2 Reading One Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
22.8.3 Modifying and Translating Input Events . . . . . . . . . . . . . . . . 466
22.8.4 Invoking the Input Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
22.8.5 Quoted Character Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
22.8.6 Miscellaneous Event Input Features . . . . . . . . . . . . . . . . . . . . . 468
22.9 Special Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
22.10 Waiting for Elapsed Time or Input . . . . . . . . . . . . . . . . . . . . . . . . . 470
22.11 Quitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
22.12 Prefix Command Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
22.13 Recursive Editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
22.14 Disabling Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
22.15 Command History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
22.16 Keyboard Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

23

Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

23.1 Key Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
23.2 Keymap Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
23.3 Format of Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
23.4 Creating Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
23.5 Inheritance and Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
23.6 Prefix Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
23.7 Active Keymaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
23.8 Searching the Active Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
23.9 Controlling the Active Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
23.10 Key Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

xiii

23.11 Functions for Key Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
23.12 Changing Key Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
23.13 Low-Level Key Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
23.14 Remapping Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
23.15 Keymaps for Translating Sequences of Events . . . . . . . . . . . . . . . 504
23.15.1 Interaction with normal keymaps . . . . . . . . . . . . . . . . . . . . . . 506
23.16 Commands for Binding Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506
23.17 Scanning Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
23.18 Menu Keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
23.18.1 Defining Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
23.18.1.1 Simple Menu Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
23.18.1.2 Extended Menu Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
23.18.1.3 Menu Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
23.18.1.4 Alias Menu Items. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
23.18.2 Menus and the Mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
23.18.3 Menus and the Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
23.18.4 Menu Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
23.18.5 The Menu Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
23.18.6 Tool bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
23.18.7 Modifying Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
23.18.8 Easy Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521

24

Major and Minor Modes . . . . . . . . . . . . . . . . . . . . 524

24.1 Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
24.1.1 Running Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
24.1.2 Setting Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
24.2 Major Modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
24.2.1 Major Mode Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
24.2.2 How Emacs Chooses a Major Mode . . . . . . . . . . . . . . . . . . . . . 531
24.2.3 Getting Help about a Major Mode . . . . . . . . . . . . . . . . . . . . . . 534
24.2.4 Defining Derived Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
24.2.5 Basic Major Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
24.2.6 Mode Hooks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
24.2.7 Tabulated List mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
24.2.8 Generic Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
24.2.9 Major Mode Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
24.3 Minor Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
24.3.1 Conventions for Writing Minor Modes . . . . . . . . . . . . . . . . . . 544
24.3.2 Keymaps and Minor Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
24.3.3 Defining Minor Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
24.4 Mode Line Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
24.4.1 Mode Line Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
24.4.2 The Data Structure of the Mode Line . . . . . . . . . . . . . . . . . . . 551
24.4.3 The Top Level of Mode Line Control . . . . . . . . . . . . . . . . . . . 552
24.4.4 Variables Used in the Mode Line . . . . . . . . . . . . . . . . . . . . . . . 554
24.4.5 %-Constructs in the Mode Line. . . . . . . . . . . . . . . . . . . . . . . . . . 556

xiv

24.4.6 Properties in the Mode Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
24.4.7 Window Header Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
24.4.8 Emulating Mode Line Formatting . . . . . . . . . . . . . . . . . . . . . . . 560
24.5 Imenu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
24.6 Font Lock Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
24.6.1 Font Lock Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
24.6.2 Search-based Fontification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
24.6.3 Customizing Search-Based Fontification . . . . . . . . . . . . . . . . . 569
24.6.4 Other Font Lock Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
24.6.5 Levels of Font Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
24.6.6 Precalculated Fontification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
24.6.7 Faces for Font Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
24.6.8 Syntactic Font Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575
24.6.9 Multiline Font Lock Constructs . . . . . . . . . . . . . . . . . . . . . . . . . 576
24.6.9.1 Font Lock Multiline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
24.6.9.2 Region to Fontify after a Buffer Change . . . . . . . . . . . . 578
24.6.10 Parser-based Font Lock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578
24.7 Automatic Indentation of code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
24.7.1 Simple Minded Indentation Engine . . . . . . . . . . . . . . . . . . . . . 581
24.7.1.1 SMIE Setup and Features . . . . . . . . . . . . . . . . . . . . . . . . . . 582
24.7.1.2 Operator Precedence Grammars . . . . . . . . . . . . . . . . . . . 582
24.7.1.3 Defining the Grammar of a Language . . . . . . . . . . . . . . 584
24.7.1.4 Defining Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
24.7.1.5 Living With a Weak Parser . . . . . . . . . . . . . . . . . . . . . . . . 585
24.7.1.6 Specifying Indentation Rules . . . . . . . . . . . . . . . . . . . . . . . 587
24.7.1.7 Helper Functions for Indentation Rules. . . . . . . . . . . . . 588
24.7.1.8 Sample Indentation Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 589
24.7.1.9 Customizing Indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
24.7.2 Parser-based Indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
24.8 Desktop Save Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594

25

Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

25.1
25.2
25.3
25.4
25.5
25.6
25.7

26

Documentation Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
Access to Documentation Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
Substituting Key Bindings in Documentation . . . . . . . . . . . . . . . . 598
Text Quoting Style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600
Describing Characters for Help Messages . . . . . . . . . . . . . . . . . . . . 601
Help Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602
Documentation Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605

Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608

26.1 Visiting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
26.1.1 Functions for Visiting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
26.1.2 Subroutines of Visiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
26.2 Saving Buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612
26.3 Reading from Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614

xv

26.4 Writing to Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616
26.5 File Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
26.6 Information about Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
26.6.1 Testing Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
26.6.2 Distinguishing Kinds of Files . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
26.6.3 Truenames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
26.6.4 File Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
26.6.5 Extended File Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
26.6.6 Locating Files in Standard Places . . . . . . . . . . . . . . . . . . . . . . . 628
26.7 Changing File Names and Attributes . . . . . . . . . . . . . . . . . . . . . . . . 629
26.8 Files and Secondary Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
26.9 File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
26.9.1 File Name Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
26.9.2 Absolute and Relative File Names . . . . . . . . . . . . . . . . . . . . . . 637
26.9.3 Directory Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
26.9.4 Functions that Expand Filenames. . . . . . . . . . . . . . . . . . . . . . . 639
26.9.5 Generating Unique File Names . . . . . . . . . . . . . . . . . . . . . . . . . 641
26.9.6 File Name Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
26.9.7 Standard File Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
26.10 Contents of Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
26.11 Creating, Copying and Deleting Directories . . . . . . . . . . . . . . . . . 648
26.12 Making Certain File Names “Magic” . . . . . . . . . . . . . . . . . . . . . . . 649
26.13 File Format Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
26.13.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
26.13.2 Round-Trip Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
26.13.3 Piecemeal Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657

27

Backups and Auto-Saving. . . . . . . . . . . . . . . . . . . 659

27.1 Backup Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
27.1.1 Making Backup Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
27.1.2 Backup by Renaming or by Copying? . . . . . . . . . . . . . . . . . . . 661
27.1.3 Making and Deleting Numbered Backup Files . . . . . . . . . . . 662
27.1.4 Naming Backup Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
27.2 Auto-Saving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
27.3 Reverting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667

28

Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671

28.1
28.2
28.3
28.4
28.5
28.6
28.7
28.8
28.9

Buffer Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
The Current Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
Buffer Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
Buffer File Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
Buffer Modification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677
Buffer Modification Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678
Read-Only Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
The Buffer List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681
Creating Buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684

xvi

28.10
28.11
28.12
28.13

29

Killing Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
Indirect Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687
Swapping Text Between Two Buffers . . . . . . . . . . . . . . . . . . . . . . . 688
The Buffer Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688

Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690

29.1 Basic Concepts of Emacs Windows . . . . . . . . . . . . . . . . . . . . . . . . . . 690
29.2 Windows and Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
29.3 Selecting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
29.4 Window Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
29.5 Resizing Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
29.6 Preserving Window Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
29.7 Splitting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
29.8 Deleting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
29.9 Recombining Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712
29.10 Cyclic Ordering of Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
29.11 Buffers and Windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
29.12 Switching to a Buffer in a Window . . . . . . . . . . . . . . . . . . . . . . . . . 721
29.13 Displaying a Buffer in a Suitable Window . . . . . . . . . . . . . . . . . . 724
29.13.1 Choosing a Window for Displaying a Buffer . . . . . . . . . . . . 724
29.13.2 Action Functions for Buffer Display. . . . . . . . . . . . . . . . . . . . 726
29.13.3 Action Alists for Buffer Display. . . . . . . . . . . . . . . . . . . . . . . . 730
29.13.4 Additional Options for Displaying Buffers. . . . . . . . . . . . . . 736
29.13.5 Precedence of Action Functions . . . . . . . . . . . . . . . . . . . . . . . . 738
29.13.6 The Zen of Buffer Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
29.14 Window History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746
29.15 Dedicated Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749
29.16 Quitting Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749
29.17 Side Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
29.17.1 Displaying Buffers in Side Windows . . . . . . . . . . . . . . . . . . . 752
29.17.2 Side Window Options and Functions. . . . . . . . . . . . . . . . . . . 753
29.17.3 Frame Layouts with Side Windows . . . . . . . . . . . . . . . . . . . . 754
29.18 Atomic Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
29.19 Windows and Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
29.20 The Window Start and End Positions . . . . . . . . . . . . . . . . . . . . . . 759
29.21 Textual Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
29.22 Vertical Fractional Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766
29.23 Horizontal Scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 767
29.24 Coordinates and Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
29.25 Mouse Window Auto-selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
29.26 Window Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
29.27 Window Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
29.28 Hooks for Window Scrolling and Changes. . . . . . . . . . . . . . . . . . . 779

xvii

30

Frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785

30.1 Creating Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786
30.2 Multiple Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
30.3 Frame Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
30.3.1 Frame Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
30.3.2 Frame Font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
30.3.3 Frame Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798
30.3.4 Frame Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
30.3.5 Implied Frame Resizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
30.4 Frame Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802
30.4.1 Access to Frame Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803
30.4.2 Initial Frame Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804
30.4.3 Window Frame Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
30.4.3.1 Basic Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
30.4.3.2 Position Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
30.4.3.3 Size Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808
30.4.3.4 Layout Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
30.4.3.5 Buffer Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 812
30.4.3.6 Frame Interaction Parameters. . . . . . . . . . . . . . . . . . . . . . 812
30.4.3.7 Mouse Dragging Parameters . . . . . . . . . . . . . . . . . . . . . . . 813
30.4.3.8 Window Management Parameters . . . . . . . . . . . . . . . . . . 814
30.4.3.9 Cursor Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
30.4.3.10 Font and Color Parameters . . . . . . . . . . . . . . . . . . . . . . . 818
30.4.4 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
30.5 Terminal Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
30.6 Frame Titles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821
30.7 Deleting Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
30.8 Finding All Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
30.9 Minibuffers and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824
30.10 Input Focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824
30.11 Visibility of Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
30.12 Raising, Lowering and Restacking Frames . . . . . . . . . . . . . . . . . . 829
30.13 Frame Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
30.14 Child Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
30.15 Mouse Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
30.16 Mouse Position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
30.17 Pop-Up Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
30.18 Dialog Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
30.19 Pointer Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
30.20 Window System Selections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
30.21 Yanking Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
30.22 Drag and Drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
30.23 Color Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
30.24 Text Terminal Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
30.25 X Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
30.26 Display Feature Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849

xviii31

Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853

31.1 Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
31.2 Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
31.2.1 Motion by Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
31.2.2 Motion by Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
31.2.3 Motion to an End of the Buffer . . . . . . . . . . . . . . . . . . . . . . . . . 856
31.2.4 Motion by Text Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856
31.2.5 Motion by Screen Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
31.2.6 Moving over Balanced Expressions . . . . . . . . . . . . . . . . . . . . . . 861
31.2.7 Skipping Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863
31.3 Excursions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
31.4 Narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865

32

Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869

32.1
32.2
32.3
32.4
32.5
32.6
32.7
32.8

33

Overview of Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
Predicates on Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
Functions that Create Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
Information from Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872
Marker Insertion Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872
Moving Marker Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
The Mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
The Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877

Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878

33.1 Examining Text Near Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
33.2 Examining Buffer Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
33.3 Comparing Text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882
33.4 Inserting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882
33.5 User-Level Insertion Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884
33.6 Deleting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
33.7 User-Level Deletion Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887
33.8 The Kill Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
33.8.1 Kill Ring Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
33.8.2 Functions for Killing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890
33.8.3 Yanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 891
33.8.4 Functions for Yanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892
33.8.5 Low-Level Kill Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893
33.8.6 Internals of the Kill Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
33.9 Undo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
33.10 Maintaining Undo Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898
33.11 Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
33.12 Margins for Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902
33.13 Adaptive Fill Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904
33.14 Auto Filling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905
33.15 Sorting Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906

xix

33.16 Counting Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
33.17 Indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
33.17.1 Indentation Primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
33.17.2 Indentation Controlled by Major Mode . . . . . . . . . . . . . . . . 911
33.17.3 Indenting an Entire Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913
33.17.4 Indentation Relative to Previous Lines . . . . . . . . . . . . . . . . . 914
33.17.5 Adjustable Tab Stops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915
33.17.6 Indentation-Based Motion Commands . . . . . . . . . . . . . . . . . 915
33.18 Case Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
33.19 Text Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
33.19.1 Examining Text Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
33.19.2 Changing Text Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
33.19.3 Text Property Search Functions . . . . . . . . . . . . . . . . . . . . . . . 921
33.19.4 Properties with Special Meanings . . . . . . . . . . . . . . . . . . . . . . 924
33.19.5 Formatted Text Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932
33.19.6 Stickiness of Text Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . 932
33.19.7 Lazy Computation of Text Properties . . . . . . . . . . . . . . . . . . 933
33.19.8 Defining Clickable Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934
33.19.9 Defining and Using Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 936
33.19.10 Why Text Properties are not Intervals . . . . . . . . . . . . . . . . 938
33.20 Substituting for a Character Code . . . . . . . . . . . . . . . . . . . . . . . . . . 939
33.21 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
33.22 Transposition of Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
33.23 Replacing Buffer Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
33.24 Dealing With Compressed Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942
33.25 Base 64 Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943
33.26 Checksum/Hash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944
33.27 Suspicious Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
33.28 GnuTLS Cryptography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
33.28.1 Format of GnuTLS Cryptography Inputs . . . . . . . . . . . . . . 947
33.28.2 GnuTLS Cryptographic Functions . . . . . . . . . . . . . . . . . . . . . 947
33.29 Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
33.30 Parsing HTML and XML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
33.30.1 Document Object Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
33.31 Parsing and generating JSON values. . . . . . . . . . . . . . . . . . . . . . . . 955
33.32 JSONRPC communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
33.32.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
33.32.2 Process-based JSONRPC connections. . . . . . . . . . . . . . . . . . 958
33.32.3 JSONRPC JSON object format . . . . . . . . . . . . . . . . . . . . . . . 958
33.32.4 Deferred JSONRPC requests . . . . . . . . . . . . . . . . . . . . . . . . . . 959
33.33 Atomic Change Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959
33.34 Change Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961

xx

34

Non-ASCII Characters . . . . . . . . . . . . . . . . . . . . . . 963

34.1 Text Representations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
34.2 Disabling Multibyte Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
34.3 Converting Text Representations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
34.4 Selecting a Representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
34.5 Character Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967
34.6 Character Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
34.7 Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
34.8 Scanning for Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974
34.9 Translation of Characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975
34.10 Coding Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976
34.10.1 Basic Concepts of Coding Systems . . . . . . . . . . . . . . . . . . . . . 977
34.10.2 Encoding and I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97834.10.3 Coding Systems in Lisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979
34.10.4 User-Chosen Coding Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 982
34.10.5 Default Coding Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 983
34.10.6 Specifying a Coding System for One Operation . . . . . . . . 986
34.10.7 Explicit Encoding and Decoding . . . . . . . . . . . . . . . . . . . . . . . 988
34.10.8 Terminal I/O Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 990
34.11 Input Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 990
34.12 Locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991

35

Searching and Matching . . . . . . . . . . . . . . . . . . . . 993

35.1 Searching for Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
35.2 Searching and Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
35.3 Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
35.3.1 Syntax of Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . 996
35.3.1.1 Special Characters in Regular Expressions . . . . . . . . . 996
35.3.1.2 Character Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000
35.3.1.3 Backslash Constructs in Regular Expressions . . . . . . 1001
35.3.2 Complex Regexp Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005
35.3.3 Regular Expression Functions . . . . . . . . . . . . . . . . . . . . . . . . . 1005
35.3.4 Problems with Regular Expressions . . . . . . . . . . . . . . . . . . . . 1007
35.4 Regular Expression Searching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1008
35.5 POSIX Regular Expression Searching. . . . . . . . . . . . . . . . . . . . . . . 1011
35.6 The Match Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1011
35.6.1 Replacing the Text that Matched . . . . . . . . . . . . . . . . . . . . . . 1012
35.6.2 Simple Match Data Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1013
35.6.3 Accessing the Entire Match Data . . . . . . . . . . . . . . . . . . . . . . 1015
35.6.4 Saving and Restoring the Match Data . . . . . . . . . . . . . . . . . 1016
35.7 Search and Replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016
35.8 Standard Regular Expressions Used in Editing . . . . . . . . . . . . . . 1020

xxi

36

Syntax Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022

36.1 Syntax Table Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
36.2 Syntax Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023
36.2.1 Table of Syntax Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023
36.2.2 Syntax Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026
36.3 Syntax Table Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027
36.4 Syntax Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1029
36.5 Motion and Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1030
36.6 Parsing Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1030
36.6.1 Motion Commands Based on Parsing . . . . . . . . . . . . . . . . . . 1031
36.6.2 Finding the Parse State for a Position . . . . . . . . . . . . . . . . . 1032
36.6.3 Parser State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1032
36.6.4 Low-Level Parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033
36.6.5 Parameters to Control Parsing . . . . . . . . . . . . . . . . . . . . . . . . . 1034
36.7 Syntax Table Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1034
36.8 Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1036

37

Parsing Program Source . . . . . . . . . . . . . . . . . . . 1039

37.1
37.2
37.3
37.4
37.5
37.6
37.7
37.8

38

Abbrevs and Abbrev Expansion . . . . . . . . . . 1066

38.1
38.2
38.3
38.4
38.5
38.6
38.7

39

Tree-sitter Language Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1039
Using Tree-sitter Parser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043
Retrieving Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1045
Accessing Node Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051
Pattern Matching Tree-sitter Nodes . . . . . . . . . . . . . . . . . . . . . . . . 1052
Parsing Text in Multiple Languages . . . . . . . . . . . . . . . . . . . . . . . . 1057
Developing major modes with tree-sitter . . . . . . . . . . . . . . . . . . . . 1061
Tree-sitter C API Correspondence . . . . . . . . . . . . . . . . . . . . . . . . . . 1063

Abbrev Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
Defining Abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067
Saving Abbrevs in Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
Looking Up and Expanding Abbreviations . . . . . . . . . . . . . . . . . . 1069
Standard Abbrev Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
Abbrev Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
Abbrev Table Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072

Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073

39.1
39.2
39.3
39.4

Basic Thread Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
Mutexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
Condition Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
The Thread List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076

xxii

40

Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078

40.1 Functions that Create Subprocesses . . . . . . . . . . . . . . . . . . . . . . . . 1078
40.2 Shell Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080
40.3 Creating a Synchronous Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1081
40.4 Creating an Asynchronous Process . . . . . . . . . . . . . . . . . . . . . . . . . 1086
40.5 Deleting Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1091
40.6 Process Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
40.7 Sending Input to Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096
40.8 Sending Signals to Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
40.9 Receiving Output from Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099
40.9.1 Process Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099
40.9.2 Process Filter Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1101
40.9.3 Decoding Process Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103
40.9.4 Accepting Output from Processes . . . . . . . . . . . . . . . . . . . . . . 1104
40.9.5 Processes and Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105
40.10 Sentinels: Detecting Process Status Changes. . . . . . . . . . . . . . . 1105
40.11 Querying Before Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1107
40.12 Accessing Other Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108
40.13 Transaction Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110
40.14 Network Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1111
40.15 Network Servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114
40.16 Datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114
40.17 Low-Level Network Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115
40.17.1 make-network-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115
40.17.2 Network Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1118
40.17.3 Testing Availability of Network Features . . . . . . . . . . . . . . 1119
40.18 Misc Network Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1119
40.19 Communicating with Serial Ports. . . . . . . . . . . . . . . . . . . . . . . . . . 1122
40.20 Packing and Unpacking Byte Arrays . . . . . . . . . . . . . . . . . . . . . . 1124
40.20.1 Describing Data Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1125
40.20.2 Functions to Unpack and Pack Bytes . . . . . . . . . . . . . . . . . 1127
40.20.3 Advanced data layout specifications . . . . . . . . . . . . . . . . . . 1127

41

Emacs Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129

41.1 Refreshing the Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
41.2 Forcing Redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
41.3 Truncation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130
41.4 The Echo Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
41.4.1 Displaying Messages in the Echo Area . . . . . . . . . . . . . . . . . 1131
41.4.2 Reporting Operation Progress . . . . . . . . . . . . . . . . . . . . . . . . . 1134
41.4.3 Logging Messages in *Messages* . . . . . . . . . . . . . . . . . . . . . . 1137
41.4.4 Echo Area Customization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
41.5 Reporting Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
41.5.1 Warning Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
41.5.2 Warning Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139
41.5.3 Warning Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1141

xxiii41.5.4 Delayed Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
41.6 Invisible Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
41.7 Selective Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1145
41.8 Temporary Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1146
41.9 Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
41.9.1 Managing Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
41.9.2 Overlay Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
41.9.3 Searching for Overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1157
41.10 Size of Displayed Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1157
41.11 Line Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162
41.12 Faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
41.12.1 Face Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
41.12.2 Defining Faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
41.12.3 Face Attribute Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1171
41.12.4 Displaying Faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
41.12.5 Face Remapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1175
41.12.6 Functions for Working with Faces . . . . . . . . . . . . . . . . . . . . 1177
41.12.7 Automatic Face Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . 1178
41.12.8 Basic Faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1178
41.12.9 Font Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180
41.12.10 Looking Up Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1181
41.12.11 Fontsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182
41.12.12 Low-Level Font Representation . . . . . . . . . . . . . . . . . . . . . . 1184
41.13 Fringes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1189
41.13.1 Fringe Size and Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1189
41.13.2 Fringe Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1190
41.13.3 Fringe Cursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
41.13.4 Fringe Bitmaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
41.13.5 Customizing Fringe Bitmaps . . . . . . . . . . . . . . . . . . . . . . . . . 1194
41.13.6 The Overlay Arrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1194
41.14 Scroll Bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1195
41.15 Window Dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
41.16 The display Property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
41.16.1 Display Specs That Replace The Text . . . . . . . . . . . . . . . . 1199
41.16.2 Specified Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200
41.16.3 Pixel Specification for Spaces . . . . . . . . . . . . . . . . . . . . . . . . . 1201
41.16.4 Other Display Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 1203
41.16.5 Displaying in the Margins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1205
41.17 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
41.17.1 Image Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
41.17.2 Image Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207
41.17.3 XBM Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
41.17.4 XPM Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212
41.17.5 ImageMagick Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212
41.17.6 SVG Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1213
41.17.7 Other Image Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220
41.17.8 Defining Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220

xxiv

41.17.9 Showing Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222
41.17.10 Multi-Frame Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
41.17.11 Image Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225
41.18 Icons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1226
41.19 Embedded Native Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
41.20 Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232
41.20.1 Button Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232
41.20.2 Button Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233
41.20.3 Making Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233
41.20.4 Manipulating Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
41.20.5 Button Buffer Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
41.21 Abstract Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
41.21.1 Abstract Display Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
41.21.2 Abstract Display Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239
41.22 Blinking Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1241
41.23 Character Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1242
41.23.1 Usual Display Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1242
41.23.2 Display Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1243
41.23.3 Active Display Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1244
41.23.4 Glyphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
41.23.5 Glyphless Character Display. . . . . . . . . . . . . . . . . . . . . . . . . . 1245
41.24 Beeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1247
41.25 Window Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
41.26 Tooltips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
41.27 Bidirectional Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250

42

Operating System Interface . . . . . . . . . . . . . . . 1255

42.1 Starting Up Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1255
42.1.1 Summary: Sequence of Actions at Startup . . . . . . . . . . . . . 1255
42.1.2 The Init File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258
42.1.3 Terminal-Specific Initialization . . . . . . . . . . . . . . . . . . . . . . . . 1260
42.1.4 Command-Line Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261
42.2 Getting Out of Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
42.2.1 Killing Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
42.2.2 Suspending Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
42.3 Operating System Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1265
42.4 User Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
42.5 Time of Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
42.6 Time Zone Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
42.7 Time Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273
42.8 Parsing and Formatting Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
42.9 Processor Run time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
42.10 Time Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
42.11 Timers for Delayed Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
42.12 Idle Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284
42.13 Terminal Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1285

xxv

42.13.1 Input Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1285
42.13.2 Recording Input. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1286
42.14 Terminal Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
42.15 Sound Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
42.16 Operating on X11 Keysyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
42.17 Batch Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
42.18 Session Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1290
42.19 Desktop Notifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1291
42.20 Notifications on File Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1296
42.21 Dynamically Loaded Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1299
42.22 Security Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1300

43

Preparing Lisp code for distribution . . . . . . 1303

43.1
43.2
43.3
43.4
43.5

Packaging Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
Simple Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
Multi-file Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1305
Creating and Maintaining Package Archives . . . . . . . . . . . . . . . . 1307
Interfacing to an archive web server . . . . . . . . . . . . . . . . . . . . . . . . 1308

Appendix A

Emacs 28 Antinews . . . . . . . . . . . . . 1309

Appendix B GNU Free
Documentation License . . . . . . . . . . . . . . . . . . . . . . . 1312
Appendix C

GNU General Public License . . . 1320

Appendix D Tips and Conventions . . . . . . . . . . . 1331
D.1
D.2
D.3
D.4
D.5
D.6
D.7
D.8

Emacs Lisp Coding Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331
Key Binding Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334
Emacs Programming Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1335
Tips for Making Compiled Code Fast . . . . . . . . . . . . . . . . . . . . . . . 1336
Tips for Avoiding Compiler Warnings . . . . . . . . . . . . . . . . . . . . . . . 1337
Tips for Documentation Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1337
Tips on Writing Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1341
Conventional Headers for Emacs Libraries . . . . . . . . . . . . . . . . . . . 1343

xxvi

Appendix E

GNU Emacs Internals. . . . . . . . . . . 1346

E.1 Building Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
E.2 Pure Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349
E.3 Garbage Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1350
E.4 Stack-allocated Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
E.5 Memory Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
E.6 C Dialect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
E.7 Writing Emacs Primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1356
E.8 Writing Dynamically-Loaded Modules . . . . . . . . . . . . . . . . . . . . . . . 1361
E.8.1 Module Initialization Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1361
E.8.2 Writing Module Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1363
E.8.3 Conversion Between Lisp and Module Values . . . . . . . . . . . 1366
E.8.4 Miscellaneous Convenience Functions for Modules . . . . . . 1373
E.8.5 Nonlocal Exits in Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375
E.9 Object Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1377
E.9.1 Buffer Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1378
E.9.2 Window Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1382
E.9.3 Process Internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1387
E.10 C Integer Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1388

Appendix F

Standard Errors . . . . . . . . . . . . . . . . . 1390

Appendix G Standard Keymaps . . . . . . . . . . . . . . 1395
Appendix H Standard Hooks . . . . . . . . . . . . . . . . . 1398
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1402

1

1 Introduction
Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp.
You can write new code in Emacs Lisp and install it as an extension to the editor. However,Emacs Lisp is more than a mere extension language; it is a full computer programming
language in its own right. You can use it as you would any other programming language.
Because Emacs Lisp is designed for use in an editor, it has special features for scanningand parsing text as well as features for handling files, buffers, displays, subprocesses, andso on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands
are functions that can also conveniently be called from Lisp programs, and parameters forcustomization are ordinary Lisp variables.
This manual attempts to be a full description of Emacs Lisp. For a beginner’s introduction
to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also
published by the Free Software Foundation. This manual presumes considerable familiarity
with the use of Emacs for editing; see The GNU Emacs Manual for this basic information.
Generally speaking, the earlier chapters describe features of Emacs Lisp that havecounterparts in many programming languages, and later chapters describe features that are
peculiar to Emacs Lisp or relate specifically to editing.
This is the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 29.1.90.

1.1 Caveats
This manual has gone through numerous drafts. It is nearly complete but not flawless.
There are a few topics that are not covered, either because we consider them secondary(such as most of the individual modes) or because they are yet to be written. Because weare not able to deal with them completely, we have left out several parts intentionally.
The manual should be fully correct in what it does cover, and it is therefore open to
criticism on anything it says—from specific examples and descriptive text, to the orderingof chapters and sections. If something is confusing, or you find that you have to look at
the sources or experiment to learn something not covered in the manual, then perhaps the
manual should be fixed. Please let us know.
As you use this manual, we ask that you mark pages with corrections so you can later
look them up and send them to us. If you think of a simple, real-life example for a function
or group of functions, please make an effort to write it up and send it in. Please reference
any comments to the chapter name, section name, and function name, as appropriate, since
page numbers and chapter and section numbers will change and we may have trouble finding
the text you are talking about. Also state the version of the edition you are criticizing.
Please send comments and corrections using M-x report-emacs-bug. For more details,
See Section “Reporting Bugs” in The GNU Emacs Manual.

1.2 Lisp History
Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts
Institute of Technology for research in artificial intelligence. The great power of the Lisp
language makes it ideal for other purposes as well, such as writing editing commands.

Chapter 1: Introduction

2

Dozens of Lisp implementations have been built over the years, each with its own
idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960s
at MIT’s Project MAC. Eventually the implementers of the descendants of Maclisp came
together and developed a standard for Lisp systems, called Common Lisp. In the meantime,
Gerry Sussman and Guy Steele at MIT developed a simplified but very powerful dialect ofLisp, called Scheme.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you
know Common Lisp, you will notice many similarities. However, many features of Common
Lisp have been omitted or simplified in order to reduce the memory requirements of GNU
Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might bevery confused. We will occasionally point out how GNU Emacs Lisp differs from Common
Lisp. If you don’t know Common Lisp, don’t worry about it; this manual is self-contained.
A certain amount of Common Lisp emulation is available via the cl-lib library. See
Section “Overview” in Common Lisp Extensions.
Emacs Lisp is not at all influenced by Scheme; but the GNU project has an implementationof Scheme, called Guile. We use it in all new GNU software that calls for extensibility.

1.3 Conventions
This section explains the notational conventions that are used in this manual. You may
want to skip this section and refer back to it later.

1.3.1 Some Terms
Throughout this manual, the phrases “the Lisp reader” and “the Lisp printer” refer to thoseroutines in Lisp that convert textual representations of Lisp objects into actual Lisp objects,
and vice versa. See Section 2.1 [Printed Representation], page 8, for more details. You, theperson reading this manual, are thought of as the programmer and are addressed as “you”.
The user is the person who uses Lisp programs, including those you write.
Examples of Lisp code are formatted like this: (list 1 2 3). Names that represent
metasyntactic variables, or arguments to a function being described, are formatted like this:first-number.

1.3.2 nil and t
In Emacs Lisp, the symbol nil has three separate meanings: it is a symbol with the name‘nil’; it is the logical truth value false; and it is the empty list—the list of zero elements.
When used as a variable, nil always has the value nil.
As far as the Lisp reader is concerned, ‘()’ and ‘nil’ are identical: they stand for thesame object, the symbol nil. The different ways of writing the symbol are intended entirely
for human readers. After the Lisp reader has read either ‘()’ or ‘nil’, there is no way todetermine which representation was actually written by the programmer.
In this manual, we write () when we wish to emphasize that it means the empty list,
and we write nil when we wish to emphasize that it means the truth value false. That is agood convention to use in Lisp programs also.
(cons 'foo ())(setq foo-flag nil)

; Emphasize the empty list
; Emphasize the truth value false

Chapter 1: Introduction

3

In contexts where a truth value is expected, any non-nil value is considered to be true.
However, t is the preferred way to represent the truth value true. When you need to choose
a value that represents true, and there is no other basis for choosing, use t. The symbol t
always has the value t.
In Emacs Lisp, nil and t are special symbols that always evaluate to themselves. This is
so that you do not need to quote them to use them as constants in a program. An attempt
to change their values results in a setting-constant error. See Section 12.2 [ConstantVariables], page 189.

booleanp object[Function]
Return non-nil if object is one of the two canonical boolean values: t or nil.

1.3.3 Evaluation Notation
A Lisp expression that you can evaluate is called a form. Evaluating a form always produces
a result, which is a Lisp object. In the examples in this manual, this is indicated with ‘⇒’:(car '(1 2))⇒ 1
You can read this as “(car '(1 2)) evaluates to 1”.
When a form is a macro call, it expands into a new form for Lisp to evaluate. We show
the result of the expansion with ‘7→’. We may or may not show the result of the evaluationof the expanded form.
(third '(a b c))
7→ (car (cdr (cdr '(a b c))))⇒ c
To help describe one form, we sometimes show another form that produces identicalresults. The exact equivalence of two forms is indicated with ‘ ≡ ’.
(make-sparse-keymap) ≡ (list 'keymap)

1.3.4 Printing Notation
Many of the examples in this manual print text when they are evaluated. If you execute
example code in a Lisp Interaction buffer (such as the buffer *scratch*) by typing C-j after
the closing parenthesis of the example, the printed text is inserted into the buffer. If you
execute the example by other means (such as by evaluating the function eval-region), theprinted text is displayed in the echo area.
Examples in this manual indicate printed text with ‘ a ’, irrespective of where that text
goes. The value returned by evaluating the form follows on a separate line with ‘⇒’.
(progn (prin1 'foo) (princ "\n") (prin1 'bar))
a foo
a bar
⇒ bar

1.3.5 Error Messages
Some examples signal errors. This normally displays an error message in the echo area. We
show the error message on a line starting with ‘ error ’. Note that ‘ error ’ itself does notappear in the echo area.
(+ 23 'x)

Chapter 1: Introduction

error

4

Wrong type argument: number-or-marker-p, x

1.3.6 Buffer Text Notation
Some examples describe modifications to the contents of a buffer, by showing the before
and after versions of the text. These examples show the contents of the buffer in question
between two lines of dashes containing the buffer name. In addition, ‘?’ indicates the locationof point. (The symbol for point, of course, is not part of the text in the buffer; it indicatesthe place between two characters where point is currently located.)---------- Buffer: foo ---------This is the ?contents of foo.
---------- Buffer: foo ---------(insert "changed ")⇒ nil---------- Buffer: foo ---------This is the changed ?contents of foo.
---------- Buffer: foo ----------

1.3.7 Format of Descriptions
Functions, variables, macros, commands, user options, and special forms are described inthis manual in a uniform format. The first line of a description contains the name of theitem followed by its arguments, if any. The category—function, variable, or whatever—isprinted next to the right margin. The description follows on succeeding lines, sometimes
with examples.

1.3.7.1 A Sample Function Description
In a function description, the name of the function being described appears first. It isfollowed on the same line by a list of argument names. These names are also used in the
body of the description, to stand for the values of the arguments.
The appearance of the keyword &optional in the argument list indicates that thesubsequent arguments may be omitted (omitted arguments default to nil). Do not write&optional when you call the function.
The keyword &rest (which must be followed by a single argument name) indicates thatany number of arguments can follow. The single argument name following &rest receives, as
its value, a list of all the remaining arguments passed to the function. Do not write &rest
when you call the function.
Here is a description of an imaginary function foo:

foo integer1 &optional integer2 &rest integers[Function]
The function foo subtracts integer1 from integer2, then adds all the rest of thearguments to the result. If integer2 is not supplied, then the number 19 is used bydefault.
(foo 1 5 3 9)
⇒ 16
(foo 5)⇒ 14

Chapter 1: Introduction

5

More generally,(foo w x y...)≡(+ (- x w) y...)By convention, any argument whose name contains the name of a type (e.g., integer,
integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers)
often means a list of objects of that type. An argument named object may be of any type.
(For a list of Emacs object types, see Chapter 2 [Lisp Data Types], page 8.) An argumentwith any other sort of name (e.g., new-file) is specific to the function; if the function has adocumentation string, the type of the argument should be described there (see Chapter 25[Documentation], page 595).
See Section 13.2 [Lambda Expressions], page 232, for a more complete description ofarguments modified by &optional and &rest.
Command, macro, and special form descriptions have the same format, but the word
‘Function’ is replaced by ‘Command’, ‘Macro’, or ‘Special Form’, respectively. Commands are
simply functions that may be called interactively; macros process their arguments differently
from functions (the arguments are not evaluated), but are presented the same way.
The descriptions of macros and special forms use a more complex notation to specify
optional and repeated arguments, because they can break the argument list down into
separate arguments in more complicated ways. ‘[optional-arg]’ means that optional-arg
is optional and ‘repeated-args...’ stands for zero or more arguments. Parentheses areused when several arguments are grouped into additional levels of list structure. Here is an
example:count-loop (var [from to [inc]]) body. . .

[Special Form]
This imaginary special form implements a loop that executes the body forms and thenincrements the variable var on each iteration. On the first iteration, the variable has
the value from; on subsequent iterations, it is incremented by one (or by inc if that isgiven). The loop exits before executing body if var equals to. Here is an example:(count-loop (i 0 10)(prin1 i) (princ " ")(prin1 (aref vector i))(terpri))
If from and to are omitted, var is bound to nil before the loop begins, and the loop
exits if var is non-nil at the beginning of an iteration. Here is an example:(count-loop (done)(if (pending)(fixit)(setq done t)))In this special form, the arguments from and to are optional, but must both be present
or both absent. If they are present, inc may optionally be specified as well. Thesearguments are grouped with the argument var into a list, to distinguish them frombody, which includes all remaining elements of the form.

Chapter 1: Introduction

6

1.3.7.2 A Sample Variable Description
A variable is a name that can be bound (or set) to an object. The object to which a variable
is bound is called a value; we say also that variable holds that value. Although nearly all
variables can be set by the user, certain variables exist specifically so that users can change
them; these are called user options. Ordinary variables and user options are described using
a format like that for functions, except that there are no arguments.
Here is a description of the imaginary electric-future-map variable.
[Variable]
The value of this variable is a full keymap used by Electric Command Future mode.
The functions in this map allow you to edit commands you have not yet thought about
executing.

electric-future-map

User option descriptions have the same format, but ‘Variable’ is replaced by ‘User
Option’.

1.4 Version Information
These facilities provide information about which version of Emacs is in use.

emacs-version &optional here

[Command]This function returns a string describing the version of Emacs that is running. It isuseful to include this string in bug reports.
(emacs-version)⇒ "GNU Emacs 26.1 (build 1, x86_64-unknown-linux-gnu,
GTK+ Version 3.16) of 2017-06-01"

If here is non-nil, it inserts the text in the buffer before point, and returns nil. When
this function is called interactively, it prints the same information in the echo area,
but giving a prefix argument makes here non-nil.
[Variable]
The value of this variable indicates the time at which Emacs was built. It uses thestyle of current-time (see Section 42.5 [Time of Day], page 1270), or is nil if theinformation is not available.

emacs-build-time

emacs-build-time⇒ (25194 55894 8547 617000)(This timestamp is (1651169878008547617 . 1000000000) if current-time-list
was nil when Emacs was built.)[Variable]
The value of this variable is the version of Emacs being run. It is a string such as "26.1".
A value with three numeric components, such as "26.0.91", indicates an unreleased
test version. (Prior to Emacs 26.1, the string includes an extra final component with
the integer that is now stored in emacs-build-number; e.g., "25.1.1".)

emacs-version[Variable]
The major version number of Emacs, as an integer. For Emacs version 23.1, the value
is 23.

emacs-major-version

Chapter 1: Introduction

7[Variable]
The minor version number of Emacs, as an integer. For Emacs version 23.1, the valueis 1.

emacs-minor-version[Variable]
An integer that increments each time Emacs is built in the same directory (withoutcleaning). This is only of relevance when developing Emacs.

emacs-build-number[Variable]
A string that gives the repository revision from which Emacs was built. If Emacs wasbuilt outside revision control, the value is nil.

emacs-repository-version[Variable]
A string that gives the repository branch from which Emacs was built. In the mostcases this is "master". If Emacs was built outside revision control, the value is nil.

emacs-repository-branch

1.5 Acknowledgments
This manual was originally written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M.
Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending
over several years. Robert J. Chassell helped to review and edit the manual, with thesupport of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged
by Warren A. Hunt, Jr. of Computational Logic, Inc. Additional sections have since been
written by Miles Bader, Lars Brinkhoff, Chong Yidong, Kenichi Handa, Lute Kamstra, Juri
Linkov, Glenn Morris, Thien-Thi Nguyen, Dan Nicolaescu, Martin Rudalics, Kim F. Storm,
Luc Teirlinck, and Eli Zaretskii, and others.
Corrections were supplied by Drew Adams, Juanma Barranquero, Karl Berry, Jim Blandy,
Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R.
Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp,
Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, Jesper Harder,
George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten,
Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland
McGrath, Stefan Monnier, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson,
Francesco Potortı̀, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Jason Rumney,
Per Starbäck, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard
Westman, Jean White, Eduard Wiebe, Matthew Wilding, Carl Witty, Dale Worley, Rusty
Wright, and David D. Zuhn.
For a more complete list of contributors, please see the relevant change log entries in the
Emacs source repository.

8

2 Lisp Data Types
A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes,a type or data type is a set of possible objects.
Every object belongs to at least one type. Objects of the same type have similar structuresand may usually be used in the same contexts. Types can overlap, and objects can belong
to two or more types. Consequently, we can ask whether an object belongs to a particular
type, but not for the type of an object.
A few fundamental object types are built into Emacs. These, from which all othertypes are constructed, are called primitive types. Each object belongs to one and only one
primitive type. These types include integer, float, cons, symbol, string, vector, hash-table,
subr, byte-code function, and record, plus several special types, such as buffer, that are
related to editing. (See Section 2.5 [Editing Types], page 25.)
Each primitive type has a corresponding Lisp function that checks whether an object is amember of that type.
Lisp is unlike many other languages in that its objects are self-typing: the primitive typeof each object is implicit in the object itself. For example, if an object is a vector, nothing
can treat it as a number; Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each variable, and thetype is known by the compiler but not represented in the data. Such type declarations do notexist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatevervalue you store in it, type and all. (Actually, a small number of Emacs Lisp variables canonly take on values of a certain type. See Section 12.16 [Variables with Restricted Values],
page 223.)
This chapter describes the purpose, printed representation, and read syntax of each of
the standard types in GNU Emacs Lisp. Details on how to use these types can be found inlater chapters.

2.1 Printed Representation and Read Syntax
The printed representation of an object is the format of the output generated by the
Lisp printer (the function prin1) for that object. Every data type has a unique printed
representation. The read syntax of an object is the format of the input accepted by the Lisp
reader (the function read) for that object. This is not necessarily unique; many kinds ofobject have more than one syntax. See Chapter 20 [Read and Print], page 371.
In most cases, an object’s printed representation is also a read syntax for the object.
However, some types have no read syntax, since it does not make sense to enter objectsof these types as constants in a Lisp program. These objects are printed in hash notation,
which consists of the characters ‘#<’, a descriptive string (typically the type name followedby the name of the object), and a closing ‘>’. (This is called “hash notation” because it
begins with the ‘#’ character, known as “hash” or “number sign”). For example:(current-buffer)⇒ #<buffer objects.texi>
Hash notation cannot be read at all, so the Lisp reader signals the error invalid-readsyntax whenever it encounters ‘#<’.

Chapter 2: Lisp Data Types

9

We describe the read syntax and the printed representation of each Lisp data type where
we describe that data type, in the following sections of this chapter. For example, see
Section 2.4.8 [String Type], page 20, and its subsections for the read syntax and printed
representation of strings; see Section 2.4.9 [Vector Type], page 22, for the same information
about vectors; etc.
In other languages, an expression is text; it has no other form. In Lisp, an expression is
primarily a Lisp object and only secondarily the text that is the object’s read syntax. Often
there is no need to emphasize this distinction, but you must keep it in the back of yourmind, or you will occasionally be very confused.
When you evaluate an expression interactively, the Lisp interpreter first reads the textual
representation of it, producing a Lisp object, and then evaluates that object (see Chapter 10[Evaluation], page 145). However, evaluation and reading are separate activities. Reading
returns the Lisp object represented by the text that is read; the object may or may not be
evaluated later. See Section 20.3 [Input Functions], page 374, for a description of read, thebasic function for reading objects.

2.2 Special Read Syntax
Emacs Lisp represents many special objects and constructs via special hash notations.
‘#<...>’

Objects that have no read syntax are presented like this (see Section 2.1 [Printed
Representation], page 8).

‘##’

The printed representation of an interned symbol whose name is an empty string(see Section 2.4.4 [Symbol Type], page 14).

‘#'’This is a shortcut for function, see Section 13.7 [Anonymous Functions],
page 243.

‘#:’

The printed representation of an uninterned symbol whose name is foo is ‘#:foo’(see Section 2.4.4 [Symbol Type], page 14).

‘#N’

When printing circular structures, this construct is used to represent where thestructure loops back onto itself, and ‘N’ is the starting list count:(let ((a (list 1)))
(setcdr a a))=> (1 . #0)

‘#N=’
‘#N#’

‘#N=’ gives the name to an object, and ‘#N#’ represents that object, so whenreading back the object, they will be the same object instead of copies (seeSection 2.6 [Circular Objects], page 30).

‘#xN’

‘N’ represented as a hexadecimal number (‘#x2a’).

‘#oN’‘N’ represented as an octal number (‘#o52’).

‘#bN’‘N’ represented as a binary number (‘#b101010’).

‘#(...)’

String text properties (see Section 2.4.8.4 [Text Props and Strings], page 22).

‘#^’

A char table (see Section 2.4.10 [Char-Table Type], page 22).

Chapter 2: Lisp Data Types10‘#s(hash-table ...)’A hash table (see Section 2.4.12 [Hash Table Type], page 23).
‘?C’

A character (see Section 2.4.3.1 [Basic Char Syntax], page 11).

‘#$’

The current file name in byte-compiled files (see Section 17.3 [Docs and Compilation], page 319). This is not meant to be used in Emacs Lisp source files.

‘#@N’

Skip the next ‘N’ characters (see Section 2.3 [Comments], page 10). This is used
in byte-compiled files, and is not meant to be used in Emacs Lisp source files.

‘#f’

Indicates that the following form isn’t readable by the Emacs Lisp reader. This is
only in text for display purposes (when that would look prettier than alternative
ways of indicating an unreadable form) and will never appear in any Lisp file.

2.3 Comments
A comment is text that is written in a program only for the sake of humans that read theprogram, and that has no effect on the meaning of the program. In Lisp, an unescaped
semicolon (‘;’) starts a comment if it is not within a string or character constant. The
comment continues to the end of line. The Lisp reader discards comments; they do not
become part of the Lisp objects which represent the program within the Lisp system.
The ‘#@count’ construct, which skips the next count characters, is useful for programgenerated comments containing binary data. The Emacs Lisp byte compiler uses this in its
output files (see Chapter 17 [Byte Compilation], page 316). It isn’t meant for source files,
however.
See Section D.7 [Comment Tips], page 1341, for conventions for formatting comments.

2.4 Programming Types
There are two general categories of types in Emacs Lisp: those having to do with Lisp
programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.

2.4.1 Integer Type
Under the hood, there are two kinds of integers—small integers, called fixnums, and large
integers, called bignums.
The range of values for a fixnum depends on the machine. The minimum range is−536,870,912 to 536,870,911 (30 bits; i.e., −229 to 229 − 1) but many machines provide awider range.
Bignums can have arbitrary precision. Operations that overflow a fixnum will return abignum instead.
All numbers can be compared with eql or =; fixnums can also be compared with eq. To
test whether an integer is a fixnum or a bignum, you can compare it to most-negativefixnum and most-positive-fixnum, or you can use the convenience predicates fixnump
and bignump on any object.
The read syntax for integers is a sequence of (base ten) digits with an optional sign atthe beginning and an optional period at the end. The printed representation produced by
the Lisp interpreter never has a leading ‘+’ or a final ‘.’.

Chapter 2: Lisp Data Types

-1
1
1.
+1

11

; The integer −1.
; The integer 1.
; Also the integer 1.
; Also the integer 1.

See Chapter 3 [Numbers], page 38, for more information.

2.4.2 Floating-Point Type
Floating-point numbers are the computer equivalent of scientific notation; you can think ofa floating-point number as a fraction together with a power of ten. The precise number ofsignificant figures and the range of possible exponents is machine-specific; Emacs uses the C
data type double to store the value, and internally this records a power of 2 rather than apower of 10.
The printed representation for floating-point numbers requires either a decimal point(with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘+15e2’,‘15.0e+2’, ‘+1500000e-3’, and ‘.15e4’ are five ways of writing a floating-point number whose
value is 1500. They are all equivalent.
See Chapter 3 [Numbers], page 38, for more information.

2.4.3 Character TypeA character in Emacs Lisp is nothing more than an integer. In other words, characters are
represented by their character codes. For example, the character A is represented as theinteger 65. That is also their usual printed representation; see Section 2.4.3.1 [Basic Char
Syntax], page 11.
Individual characters are used occasionally in programs, but it is more common to workwith strings, which are sequences composed of characters. See Section 2.4.8 [String Type],
page 20.
Characters in strings and buffers are currently limited to the range of 0 to 4194303—
twenty two bits (see Section 34.5 [Character Codes], page 967). Codes 0 through 127 are
ASCII codes; the rest are non-ASCII (see Chapter 34 [Non-ASCII Characters], page 963).
Characters that represent keyboard input have a much wider range, to encode modifier keys
such as Control, Meta and Shift.
There are special functions for producing a human-readable textual description of acharacter for the sake of messages. See Section 25.5 [Describing Characters], page 601.

2.4.3.1 Basic Char Syntax
Since characters are really integers, the printed representation of a character is a decimal
number. This is also a possible read syntax for a character, but writing characters that way
in Lisp programs is not clear programming. You should always use the special read syntax
formats that Emacs Lisp provides for characters. These syntax formats start with a question
mark.
The usual read syntax for alphanumeric characters is a question mark followed by thecharacter; thus, ‘?A’ for the character A, ‘?B’ for the character B, and ‘?a’ for the character a.
For example:?Q ⇒ 81?q ⇒ 113

Chapter 2: Lisp Data Types

12

You can use the same syntax for punctuation characters. However, if the punctuation
character has a special syntactic meaning in Lisp, you must quote it with a ‘\’. For example,‘?\(’ is the way to write the open-paren character. Likewise, if the character is ‘\’, you mustuse a second ‘\’ to quote it: ‘?\\’.
You can express the characters control-g, backspace, tab, newline, vertical tab, formfeed,
space, return, del, and escape as ‘?\a’, ‘?\b’, ‘?\t’, ‘?\n’, ‘?\v’, ‘?\f’, ‘?\s’, ‘?\r’, ‘?\d’,and ‘?\e’, respectively. (‘?\s’ followed by a dash has a different meaning—it applies theSuper modifier to the following character.) Thus,?\a ⇒ 7?\b ⇒ 8?\t ⇒ 9?\n ⇒ 10?\v ⇒ 11?\f ⇒ 12?\r ⇒ 13?\e ⇒ 27?\s ⇒ 32?\\ ⇒ 92?\d ⇒ 127

; control-g, C-g; backspace, BS, C-h; tab, TAB, C-i; newline, C-j; vertical tab, C-k; formfeed character, C-l; carriage return, RET, C-m; escape character, ESC, C-[; space character, SPC; backslash character, \; delete character, DEL

These sequences which start with backslash are also known as escape sequences, because
backslash plays the role of an escape character; this has nothing to do with the character
ESC. ‘\s’ is meant for use in character constants; in string constants, just write the space.
A backslash is allowed, and harmless, preceding any character without a special escapemeaning; thus, ‘?\+’ is equivalent to ‘?+’. There is no reason to add a backslash before mostcharacters. However, you must add a backslash before any of the characters ‘()[]\;"’, andyou should add a backslash before any of the characters ‘|'`#.,’ to avoid confusing theEmacs commands for editing Lisp code. You should also add a backslash before Unicodecharacters which resemble the previously mentioned ASCII ones, to avoid confusing people
reading your code. Emacs will highlight some non-escaped commonly confused characterssuch as ‘‘’ to encourage this. You can also add a backslash before whitespace characterssuch as space, tab, newline and formfeed. However, it is cleaner to use one of the easilyreadable escape sequences, such as ‘\t’ or ‘\s’, instead of an actual whitespace charactersuch as a tab or a space. (If you do write backslash followed by a space, you should write an
extra space after the character constant to separate it from the following text.)

2.4.3.2 General Escape Syntax
In addition to the specific escape sequences for special important control characters, Emacs
provides several types of escape syntax that you can use to specify non-ASCII text characters.
1. You can specify characters by their Unicode names, if any. ?\N{NAME} represents theUnicode character named NAME. Thus, ‘?\N{LATIN SMALL LETTER A WITH GRAVE}’ isequivalent to ?à and denotes the Unicode character U+00E0. To simplify entering
multi-line strings, you can replace spaces in the names by non-empty sequences ofwhitespace (e.g., newlines).
2. You can specify characters by their Unicode values. ?\N{U+X} represents a characterwith Unicode code point X, where X is a hexadecimal number. Also, ?\uxxxx andChapter 2: Lisp Data Types

13?\Uxxxxxxxx represent code points xxxx and xxxxxxxx, respectively, where each x isa single hexadecimal digit. For example, ?\N{U+E0}, ?\u00e0 and ?\U000000E0 are
all equivalent to ?à and to ‘?\N{LATIN SMALL LETTER A WITH GRAVE}’. The UnicodeStandard defines code points only up to ‘U+10ffff’, so if you specify a code point higher
than that, Emacs signals an error.
3. You can specify characters by their hexadecimal character codes. A hexadecimal escapesequence consists of a backslash, ‘x’, and the hexadecimal character code. Thus, ‘?\x41’
is the character A, ‘?\x1’ is the character C-a, and ?\xe0 is the character à (a withgrave accent). You can use one or more hex digits after ‘x’, so you can represent any
character code in this way.
4. You can specify characters by their character code in octal. An octal escape sequence
consists of a backslash followed by up to three octal digits; thus, ‘?\101’ for the characterA, ‘?\001’ for the character C-a, and ?\002 for the character C-b. Only characters up
to octal code 777 can be specified this way.
These escape sequences may also be used in strings. See Section 2.4.8.2 [Non-ASCII in
Strings], page 20.

2.4.3.3 Control-Character Syntax
Control characters can be represented using yet another read syntax. This consists of aquestion mark followed by a backslash, caret, and the corresponding non-control character,in either upper or lower case. For example, both ‘?\^I’ and ‘?\^i’ are valid read syntax forthe character C-i, the character whose value is 9.
Instead of the ‘^’, you can use ‘C-’; thus, ‘?\C-i’ is equivalent to ‘?\^I’ and to ‘?\^i’:?\^I ⇒ 9?\C-I ⇒ 9
In strings and buffers, the only control characters allowed are those that exist in ASCII;
but for keyboard input purposes, you can turn any character into a control character with
‘C-’. The character codes for these non-ASCII control characters include the 226 bit as wellas the code for the corresponding non-control character. Not all text terminals can generate
non-ASCII control characters, but it is straightforward to generate them using X and otherwindow systems.
For historical reasons, Emacs treats the DEL character as the control equivalent of ?:?\^? ⇒ 127?\C-? ⇒ 127
As a result, it is currently not possible to represent the character Control-?, which is ameaningful input character under X, using ‘\C-’. It is not easy to change this, as various
Lisp files refer to DEL in this way.
For representing control characters to be found in files or strings, we recommend the ‘^’syntax; for control characters in keyboard input, we prefer the ‘C-’ syntax. Which one you
use does not affect the meaning of the program, but may guide the understanding of people
who read it.

2.4.3.4 Meta-Character Syntax
A meta character is a character typed with the META modifier key. The integer that represents
such a character has the 227 bit set. We use high bits for this and other modifiers to makepossible a wide range of basic character codes.

Chapter 2: Lisp Data Types

14

In a string, the 27 bit attached to an ASCII character indicates a meta character; thus,
the meta characters that can fit in a string have codes in the range from 128 to 255, and are
the meta versions of the ordinary ASCII characters. See Section 22.7.17 [Strings of Events],
page 459, for details about META-handling in strings.
The read syntax for meta characters uses ‘\M-’. For example, ‘?\M-A’ stands for M-A.
You can use ‘\M-’ together with octal character codes (see below), with ‘\C-’, or with anyother syntax for a character. Thus, you can write M-A as ‘?\M-A’, or as ‘?\M-\101’. Likewise,
you can write C-M-b as ‘?\M-\C-b’, ‘?\C-\M-b’, or ‘?\M-\002’.

2.4.3.5 Other Character Modifier Bits
The case of a graphic character is indicated by its character code; for example, ASCII
distinguishes between the characters ‘a’ and ‘A’. But ASCII has no way to represent whether
a control character is upper case or lower case. Emacs uses the 225 bit to indicate thatthe shift key was used in typing a control character. This distinction is possible only on agraphical display such as a GUI display on X; text terminals do not report the distinction.
The Lisp syntax for the shift bit is ‘\S-’; thus, ‘?\C-\S-o’ or ‘?\C-\S-O’ represents theshifted-control-o character.
The X Window System defines three other modifier bits that can be set in a character:
hyper, super and alt. The syntaxes for these bits are ‘\H-’, ‘\s-’ and ‘\A-’. (Case issignificant in these prefixes.) Thus, ‘?\H-\M-\A-x’ represents Alt-Hyper-Meta-x. (Notethat ‘\s’ with no following ‘-’ represents the space character.) Numerically, the bit values
are 222 for alt, 223 for super and 224 for hyper.

2.4.4 Symbol TypeA symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as theprinted representation of the symbol. In ordinary Lisp use, with one single obarray (seeSection 9.3 [Creating Symbols], page 135), a symbol’s name is unique—no two symbols havethe same name.
A symbol can serve as a variable, as a function name, or to hold a property list. Or
it may serve only to be distinct from all other Lisp objects, so that its presence in a data
structure may be recognized reliably. In a given context, usually only one of these uses isintended. But you can use one symbol in all of these ways, independently.
A symbol whose name starts with a colon (‘:’) is called a keyword symbol. These symbols
automatically act as constants, and are normally used only by comparing an unknown
symbol with a few specific alternatives. See Section 12.2 [Constant Variables], page 189.
A symbol name can contain any characters whatever. Most symbol names are writtenwith letters, digits, and the punctuation characters ‘-+=*/’. Such names require no special
punctuation; the characters of the name suffice as long as the name does not look like anumber. (If it does, write a ‘\’ at the beginning of the name to force interpretation as asymbol.) The characters ‘_~!@$%^&:<>{}?’ are less often used but also require no special
punctuation. Any other characters may be included in a symbol’s name by escaping themwith a backslash. In contrast to its use in strings, however, a backslash in the name of asymbol simply quotes the single character that follows the backslash. For example, in astring, ‘\t’ represents a tab character; in the name of a symbol, however, ‘\t’ merely quotes
the letter ‘t’. To have a symbol with a tab character in its name, you must actually use atab (preceded with a backslash). But it’s rare to do such a thing.

Chapter 2: Lisp Data Types

15

Common Lisp note: In Common Lisp, lower case letters are always folded toupper case, unless they are explicitly escaped. In Emacs Lisp, upper case andlower case letters are distinct.
Here are several examples of symbol names. Note that the ‘+’ in the fourth example
is escaped to prevent it from being read as a number. This is not necessary in the sixth
example because the rest of the name makes it invalid as a number.
foo
FOO
1+
\+1
\(*\ 1\ 2\)+-*/_~!@$%^&=:<>{}; A symbol named ‘foo’.
; A symbol named ‘FOO’, different from ‘foo’.
; A symbol named ‘1+’;
(not ‘+1’, which is an integer).
; A symbol named ‘+1’;
(not a very readable name).
; A symbol named ‘(* 1 2)’ (a worse name).
; A symbol named ‘+-*/_~!@$%^&=:<>{}’.
;
These characters need not be escaped.

As an exception to the rule that a symbol’s name serves as its printed representation,‘##’ is the printed representation for an interned symbol whose name is an empty string.
Furthermore, ‘#:foo’ is the printed representation for an uninterned symbol whose nameis foo. (Normally, the Lisp reader interns all symbols; see Section 9.3 [Creating Symbols],
page 135.)

2.4.5 Sequence Types
A sequence is a Lisp object that represents an ordered set of elements. There are two kindsof sequence in Emacs Lisp: lists and arrays.
Lists are the most commonly-used sequences. A list can hold elements of any type, andits length can be easily changed by adding or removing elements. See the next subsection
for more about lists.
Arrays are fixed-length sequences. They are further subdivided into strings, vectors,
char-tables and bool-vectors. Vectors can hold elements of any type, whereas string elements
must be characters, and bool-vector elements must be t or nil. Char-tables are like vectors
except that they are indexed by any valid character code. The characters in a string can havetext properties like characters in a buffer (see Section 33.19 [Text Properties], page 917), but
vectors do not support text properties, even when their elements happen to be characters.
Lists, strings and the other array types also share important similarities. For example,
all have a length l, and all have elements which can be indexed from zero to l minus one.
Several functions, called sequence functions, accept any kind of sequence. For example,
the function length reports the length of any kind of sequence. See Chapter 6 [Sequences
Arrays Vectors], page 102.
It is generally impossible to read the same sequence twice, since sequences are always
created anew upon reading. If you read the read syntax for a sequence twice, you get two
sequences with equal contents. There is one exception: the empty list () always stands forthe same object, nil.

Chapter 2: Lisp Data Types

16

2.4.6 Cons Cell and List Types
A cons cell is an object that consists of two slots, called the car slot and the cdr slot. Eachslot can hold any Lisp object. We also say that the car of this cons cell is whatever object
its car slot currently holds, and likewise for the cdr.
A list is a series of cons cells, linked together so that the cdr slot of each cons cell holds
either the next cons cell or the empty list. The empty list is actually the symbol nil. See
Chapter 5 [Lists], page 77, for details. Because most cons cells are used as part of lists, werefer to any structure made out of cons cells as a list structure.
A note to C programmers: a Lisp list thus works as a linked list built up ofcons cells. Because pointers in Lisp are implicit, we do not distinguish between
a cons cell slot holding a value versus pointing to the value.
Because cons cells are so central to Lisp, we also have a word for an object which is nota cons cell. These objects are called atoms.
The read syntax and printed representation for lists are identical, and consist of a leftparenthesis, an arbitrary number of elements, and a right parenthesis. Here are examples oflists:(A 2 "A")()nil("A ()")(A ())(A nil)((A B C)); A list of three elements.
; A list of no elements (the empty list).
; A list of no elements (the empty list).
; A list of one element: the string "A ()".
; A list of two elements: A and the empty list.
; Equivalent to the previous.
; A list of one element;(which is a list of three elements).

Upon reading, each object inside the parentheses becomes an element of the list. That is,a cons cell is made for each element. The car slot of the cons cell holds the element, andits cdr slot refers to the next cons cell of the list, which holds the next element in the list.
The cdr slot of the last cons cell is set to hold nil.
The names car and cdr derive from the history of Lisp. The original Lisp implementation
ran on an IBM 704 computer which divided words into two parts, the address and thedecrement; car was an instruction to extract the contents of the address part of a register,and cdr an instruction to extract the contents of the decrement. By contrast, cons cells are
named for the function cons that creates them, which in turn was named for its purpose,the construction of cells.

2.4.6.1 Drawing Lists as Box Diagrams
A list can be illustrated by a diagram in which the cons cells are shown as pairs of boxes,
like dominoes. (The Lisp reader cannot read such an illustration; unlike the textual notation,
which can be understood by both humans and computers, the box illustrations can beunderstood only by humans.) This picture represents the three-element list (rose violet
buttercup):Chapter 2: Lisp Data Types

17--- ----- ----- --|||--> |||--> |||--> nil--- ----- ----- --|
|
|
|
|
|
--> rose--> violet--> buttercup
In this diagram, each box represents a slot that can hold or refer to any Lisp object.
Each pair of boxes represents a cons cell. Each arrow represents a reference to a Lisp object,either an atom or another cons cell.
In this example, the first box, which holds the car of the first cons cell, refers to or holds
rose (a symbol). The second box, holding the cdr of the first cons cell, refers to the next
pair of boxes, the second cons cell. The car of the second cons cell is violet, and its cdr
is the third cons cell. The cdr of the third (and last) cons cell is nil.
Here is another diagram of the same list, (rose violet buttercup), sketched in adifferent manner:-----------------------------------------------| car
| cdr
|
| car
| cdr
|
| car
| cdr
|
| rose |o-------->| violet |o-------->| buttercup | nil |
|
|
|
|
|
|
|
|
|
------------------------------------------------

A list with no elements in it is the empty list; it is identical to the symbol nil. In otherwords, nil is both a symbol and a list.
Here is the list (A ()), or equivalently (A nil), depicted with boxes and arrows:--- ----- --|||--> |||--> nil--- ----- --|
|
|
|
--> A
--> nil
Here is a more complex illustration, showing the three-element list, ((pine needles)
oak maple), the first element of which is a two-element list:--- ----- ----- --|||--> |||--> |||--> nil--- ----- ----- --|
|
|
|
|
|
|
--> oak--> maple||--- ----- ----> |||--> |||--> nil--- ----- --||||--> pine--> needles
The same list represented in the second box notation looks like this:Chapter 2: Lisp Data Types

18---------------------------------------| car| cdr |
| car
| cdr |
| car
| cdr ||o|o------->| oak|o------->| maple | nil |
|
|
|
|
|
|
|
|
|
|
-- | ----------------------------------|||----------------------------|| car| cdr |
| car
| cdr |------>| pine |o------->| needles | nil |
|
|
|
|
|
|
-----------------------------

2.4.6.2 Dotted Pair Notation
Dotted pair notation is a general syntax for cons cells that represents the car and cdr
explicitly. In this syntax, (a . b) stands for a cons cell whose car is the object a and whose
cdr is the object b. Dotted pair notation is more general than list syntax because the cdr
does not have to be a list. However, it is more cumbersome in cases where list syntax would
work. In dotted pair notation, the list ‘(1 2 3)’ is written as ‘(1 . (2 . (3 . nil)))’. For
nil-terminated lists, you can use either notation, but list notation is usually clearer andmore convenient. When printing a list, the dotted pair notation is only used if the cdr of acons cell is not a list.
Here’s an example using boxes to illustrate dotted pair notation. This example shows
the pair (rose . violet):--- --|||--> violet--- --||--> rose
You can combine dotted pair notation with list notation to represent conveniently achain of cons cells with a non-nil final cdr. You write a dot after the last element of thelist, followed by the cdr of the final cons cell. For example, (rose violet . buttercup) is
equivalent to (rose . (violet . buttercup)). The object looks like this:--- ----- --|||--> |||--> buttercup--- ----- --||||--> rose--> violet
The syntax (rose . violet . buttercup) is invalid because there is nothing that it
could mean. If anything, it would say to put buttercup in the cdr of a cons cell whose
cdr is already used for violet.
The list (rose violet) is equivalent to (rose . (violet)), and looks like this:Chapter 2: Lisp Data Types

19--- ----- --|||--> |||--> nil--- ----- --||||--> rose--> violet
Similarly, the three-element list (rose violet buttercup) is equivalent to (rose .
(violet . (buttercup))).

2.4.6.3 Association List TypeAn association list or alist is a specially-constructed list whose elements are cons cells. In
each element, the car is considered a key, and the cdr is considered an associated value.
(In some cases, the associated value is stored in the car of the cdr.) Association lists areoften used as stacks, since it is easy to add or remove associations at the front of the list.
For example,(setq alist-of-colors'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable alist-of-colors to an alist of three elements. In the first element, roseis the key and red is the value.
See Section 5.8 [Association Lists], page 95, for a further explanation of alists and forfunctions that work on alists. See Chapter 8 [Hash Tables], page 127, for another kind of
lookup table, which is much faster for handling a large number of keys.

2.4.7 Array TypeAn array is composed of an arbitrary number of slots for holding or referring to other Lisp
objects, arranged in a contiguous block of memory. Accessing any element of an array takes
approximately the same amount of time. In contrast, accessing an element of a list requires
time proportional to the position of the element in the list. (Elements at the end of a list
take longer to access than elements at the beginning of a list.)
Emacs defines four types of array: strings, vectors, bool-vectors, and char-tables.
A string is an array of characters and a vector is an array of arbitrary objects. A
bool-vector can hold only t or nil. These kinds of array may have any length up to thelargest fixnum, subject to system architecture limits and available memory. Char-tables aresparse arrays indexed by any valid character code; they can hold arbitrary objects.
The first element of an array has index zero, the second element has index 1, and so on.
This is called zero-origin indexing. For example, an array of four elements has indices 0, 1,
2, and 3. The largest possible index value is one less than the length of the array. Once anarray is created, its length is fixed.
All Emacs Lisp arrays are one-dimensional. (Most other programming languages support
multidimensional arrays, but they are not essential; you can get the same effect with nested
one-dimensional arrays.) Each type of array has its own read syntax; see the following
sections for details.
The array type is a subset of the sequence type, and contains the string type, the vector
type, the bool-vector type, and the char-table type.

Chapter 2: Lisp Data Types

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2.4.8 String TypeA string is an array of characters. Strings are used for many purposes in Emacs, as can be
expected in a text editor; for example, as the names of Lisp symbols, as messages for theuser, and to represent text extracted from buffers. Strings in Lisp are constants: evaluationof a string returns the same string.
See Chapter 4 [Strings and Characters], page 54, for functions that operate on strings.

2.4.8.1 Syntax for Strings
The read syntax for a string is a double-quote, an arbitrary number of characters, andanother double-quote, "like this". To include a double-quote in a string, precede it witha backslash; thus, "\"" is a string containing just one double-quote character. Likewise, you
can include a backslash by preceding it with another backslash, like this: "this \\ is asingle embedded backslash".
Since a string is an array of characters, you can specify the string characters using theread syntax of characters, but without the leading question mark. This is useful for including
in string constants characters that don’t stand for themselves. Thus, control characters canbe specified as escape sequences that start with a backslash; for example, "foo\r" yields‘foo’ followed by the carriage return character. See Section 2.4.3.1 [Basic Char Syntax],
page 11, for escape sequences of other control characters. Similarly, you can use the special
read syntax for control characters (see Section 2.4.3.3 [Ctl-Char Syntax], page 13), as in"foo\^Ibar", which produces a tab character embedded within a string. You can also use
the escape sequences for non-ASCII characters described in Section 2.4.3.2 [General Escape
Syntax], page 12, as in "\N{LATIN SMALL LETTER A WITH GRAVE}" and "\u00e0" (however,see a caveat with non-ASCII characters in Section 2.4.8.2 [Non-ASCII in Strings], page 20).
The newline character is not special in the read syntax for strings; if you write a newline between the double-quotes, it becomes a character in the string. But an escaped
newline—one that is preceded by ‘\’—does not become part of the string; i.e., the Lisp
reader ignores an escaped newline while reading a string. An escaped space ‘\ ’ is likewise
ignored.
"It is useful to include newlines
in documentation strings,
but the newline is \ignored if escaped."⇒ "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."

2.4.8.2 Non-ASCII Characters in Strings
There are two text representations for non-ASCII characters in Emacs strings: multibyte
and unibyte (see Section 34.1 [Text Representations], page 963). Roughly speaking, unibyte
strings store raw bytes, while multibyte strings store human-readable text. Each characterin a unibyte string is a byte, i.e., its value is between 0 and 255. By contrast, each characterin a multibyte string may have a value between 0 to 4194303 (see Section 2.4.3 [Character
Type], page 11). In both cases, characters above 127 are non-ASCII.

Chapter 2: Lisp Data Types

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You can include a non-ASCII character in a string constant by writing it literally. If thestring constant is read from a multibyte source, such as a multibyte buffer or string, or afile that would be visited as multibyte, then Emacs reads each non-ASCII character as amultibyte character and automatically makes the string a multibyte string. If the string
constant is read from a unibyte source, then Emacs reads the non-ASCII character as unibyte,
and makes the string unibyte.
Instead of writing a character literally into a multibyte string, you can write it as its
character code using an escape sequence. See Section 2.4.3.2 [General Escape Syntax],
page 12, for details about escape sequences.
If you use any Unicode-style escape sequence ‘\uNNNN’ or ‘\U00NNNNNN’ in a string constant(even for an ASCII character), Emacs automatically assumes that it is multibyte.
You can also use hexadecimal escape sequences (‘\xn’) and octal escape sequences (‘\n’)in string constants. But beware: If a string constant contains octal escape sequences or oneor two-digit hexadecimal escape sequences, and these escape sequences all specify unibyte
characters (i.e., codepoints less than 256), and there are no other literal non-ASCII characters
or Unicode-style escape sequences in the string, then Emacs automatically assumes that it
is a unibyte string. That is to say, it assumes that all non-ASCII characters occurring in thestring are 8-bit raw bytes.
In hexadecimal and octal escape sequences, the escaped character code may contain avariable number of digits, so the first subsequent character which is not a valid hexadecimalor octal digit terminates the escape sequence. If the next character in a string could beinterpreted as a hexadecimal or octal digit, write ‘\ ’ (backslash and space) to terminate theescape sequence. For example, ‘\xe0\ ’ represents one character, ‘a’ with grave accent. ‘\ ’in a string constant is just like backslash-newline; it does not contribute any character tothe string, but it does terminate any preceding hex escape.

2.4.8.3 Nonprinting Characters in Strings
You can use the same backslash escape-sequences in a string constant as in character literals(but do not use the question mark that begins a character constant). For example, you canwrite a string containing the nonprinting characters tab and C-a, with commas and spaces
between them, like this: "\t, \C-a". See Section 2.4.3 [Character Type], page 11, and its
subsections for a description of the various kinds of read syntax for characters.
However, not all of the characters you can write with backslash escape-sequences arevalid in strings. The only control characters that a string can hold are the ASCII control
characters. Strings do not distinguish case in ASCII control characters.
Properly speaking, strings cannot hold meta characters; but when a string is to be used asa key sequence, there is a special convention that provides a way to represent meta versionsof ASCII characters in a string. If you use the ‘\M-’ syntax to indicate a meta character ina string constant, this sets the 27 bit of the character in the string. If the string is usedin define-key or lookup-key, this numeric code is translated into the equivalent metacharacter. See Section 2.4.3 [Character Type], page 11.
Strings cannot hold characters that have the hyper, super, or alt modifiers.

Chapter 2: Lisp Data Types

22

2.4.8.4 Text Properties in Strings
A string can hold properties for the characters it contains, in addition to the charactersthemselves. This enables programs that copy text between strings and buffers to copy the
text’s properties with no special effort. See Section 33.19 [Text Properties], page 917, for an
explanation of what text properties mean. Strings with text properties use a special readand print syntax:#("characters" property-data...)where property-data consists of zero or more elements, in groups of three as follows:
beg end plist
The elements beg and end are integers, and together specify a range of indices in the string;plist is the property list for that range. For example,#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
represents a string whose textual contents are ‘foo bar’, in which the first three charactershave a face property with value bold, and the last three have a face property with value
italic. (The fourth character has no text properties, so its property list is nil. It is not
actually necessary to mention ranges with nil as the property list, since any characters not
mentioned in any range will default to having no properties.)

2.4.9 Vector TypeA vector is a one-dimensional array of elements of any type. It takes a constant amount oftime to access any element of a vector. (In a list, the access time of an element is proportional
to the distance of the element from the beginning of the list.)
The printed representation of a vector consists of a left square bracket, the elements, anda right square bracket. This is also the read syntax. Like numbers and strings, vectors are
considered constants for evaluation.
[1 "two" (three)]; A vector of three elements.
⇒ [1 "two" (three)]See Section 6.4 [Vectors], page 117, for functions that work with vectors.

2.4.10 Char-Table TypeA char-table is a one-dimensional array of elements of any type, indexed by character codes.
Char-tables have certain extra features to make them more useful for many jobs that involve
assigning information to character codes—for example, a char-table can have a parent toinherit from, a default value, and a small number of extra slots to use for special purposes.
A char-table can also specify a single value for a whole character set.
The printed representation of a char-table is like a vector except that there is an extra‘#^’ at the beginning.1
See Section 6.6 [Char-Tables], page 119, for special functions to operate on char-tables.
Uses of char-tables include:• Case tables (see Section 4.10 [Case Tables], page 74).
• Character category tables (see Section 36.8 [Categories], page 1036).
1

You may also encounter ‘#^^’, used for sub-char-tables.

Chapter 2: Lisp Data Types

23• Display tables (see Section 41.23.2 [Display Tables], page 1243).
• Syntax tables (see Chapter 36 [Syntax Tables], page 1022).

2.4.11 Bool-Vector TypeA bool-vector is a one-dimensional array whose elements must be t or nil.
The printed representation of a bool-vector is like a string, except that it begins with ‘#&’followed by the length. The string constant that follows actually specifies the contents ofthe bool-vector as a bitmap—each character in the string contains 8 bits, which specify thenext 8 elements of the bool-vector (1 stands for t, and 0 for nil). The least significant bitsof the character correspond to the lowest indices in the bool-vector.
(make-bool-vector 3 t)
⇒ #&3"^G"(make-bool-vector 3 nil)
⇒ #&3"^@"
These results make sense, because the binary code for ‘C-g’ is 111 and ‘C-@’ is the characterwith code 0.
If the length is not a multiple of 8, the printed representation shows extra elements,
but these extras really make no difference. For instance, in the next example, the twobool-vectors are equal, because only the first 3 bits are used:(equal #&3"\377" #&3"\007")⇒ t

2.4.12 Hash Table TypeA hash table is a very fast kind of lookup table, somewhat like an alist in that it maps
keys to corresponding values, but much faster. The printed representation of a hash tablespecifies its properties and contents, like this:(make-hash-table)⇒ #s(hash-table size 65 test eql rehash-size 1.5
rehash-threshold 0.8125 data ())
See Chapter 8 [Hash Tables], page 127, for more information about hash tables.

2.4.13 Function Type
Lisp functions are executable code, just like functions in other programming languages. In
Lisp, unlike most languages, functions are also Lisp objects. A non-compiled function in
Lisp is a lambda expression: that is, a list whose first element is the symbol lambda (seeSection 13.2 [Lambda Expressions], page 232).
In most programming languages, it is impossible to have a function without a name. In
Lisp, a function has no intrinsic name. A lambda expression can be called as a function
even though it has no name; to emphasize this, we also call it an anonymous function (seeSection 13.7 [Anonymous Functions], page 243). A named function in Lisp is just a symbolwith a valid function in its function cell (see Section 13.4 [Defining Functions], page 237).
Most of the time, functions are called when their names are written in Lisp expressions in
Lisp programs. However, you can construct or obtain a function object at run time and thencall it with the primitive functions funcall and apply. See Section 13.5 [Calling Functions],
page 239.

Chapter 2: Lisp Data Types

24

2.4.14 Macro TypeA Lisp macro is a user-defined construct that extends the Lisp language. It is represented
as an object much like a function, but with different argument-passing semantics. A Lisp
macro has the form of a list whose first element is the symbol macro and whose cdr is a
Lisp function object, including the lambda symbol.
Lisp macro objects are usually defined with the built-in defmacro macro, but any listthat begins with macro is a macro as far as Emacs is concerned. See Chapter 14 [Macros],
page 268, for an explanation of how to write a macro.
Warning: Lisp macros and keyboard macros (see Section 22.16 [Keyboard Macros],
page 478) are entirely different things. When we use the word “macro” without qualification,
we mean a Lisp macro, not a keyboard macro.

2.4.15 Primitive Function TypeA primitive function is a function callable from Lisp but written in the C programming
language. Primitive functions are also called subrs or built-in functions. (The word “subr”
is derived from “subroutine”.) Most primitive functions evaluate all their arguments when
they are called. A primitive function that does not evaluate all its arguments is called a
special form (see Section 10.1.7 [Special Forms], page 149).
It does not matter to the caller of a function whether the function is primitive. However,this does matter if you try to redefine a primitive with a function written in Lisp. The reason
is that the primitive function may be called directly from C code. Calls to the redefined
function from Lisp will use the new definition, but calls from C code may still use the built-in
definition. Therefore, we discourage redefinition of primitive functions.
The term function refers to all Emacs functions, whether written in Lisp or C. See
Section 2.4.13 [Function Type], page 23, for information about the functions written in Lisp.
Primitive functions have no read syntax and print in hash notation with the name of thesubroutine.
(symbol-function 'car); Access the function cell;of the symbol.
⇒ #<subr car>(subrp (symbol-function 'car)) ; Is this a primitive function?
⇒ t; Yes.

2.4.16 Byte-Code Function Type
Byte-code function objects are produced by byte-compiling Lisp code (see Chapter 17 [ByteCompilation], page 316). Internally, a byte-code function object is much like a vector;
however, the evaluator handles this data type specially when it appears in a function call.
See Section 17.7 [Byte-Code Objects], page 323.
The printed representation and read syntax for a byte-code function object is like thatfor a vector, with an additional ‘#’ before the opening ‘[’.

2.4.17 Record TypeA record is much like a vector. However, the first element is used to hold its type as
returned by type-of. The purpose of records is to allow programmers to create objects
with new types that are not built into Emacs.

Chapter 2: Lisp Data Types

25

See Chapter 7 [Records], page 125, for functions that work with records.

2.4.18 Type Descriptors
A type descriptor is a record which holds information about a type. Slot 1 in the record
must be a symbol naming the type, and type-of relies on this to return the type of record
objects. No other type descriptor slot is used by Emacs; they are free for use by Lisp
extensions.
An example of a type descriptor is any instance of cl-structure-class.

2.4.19 Autoload TypeAn autoload object is a list whose first element is the symbol autoload. It is stored as thefunction definition of a symbol, where it serves as a placeholder for the real definition. The
autoload object says that the real definition is found in a file of Lisp code that should be
loaded when necessary. It contains the name of the file, plus some other information about
the real definition.
After the file has been loaded, the symbol should have a new function definition that is
not an autoload object. The new definition is then called as if it had been there to begin
with. From the user’s point of view, the function call works as expected, using the function
definition in the loaded file.
An autoload object is usually created with the function autoload, which stores the object
in the function cell of a symbol. See Section 16.5 [Autoload], page 304, for more details.

2.4.20 Finalizer TypeA finalizer object helps Lisp code clean up after objects that are no longer needed. A
finalizer holds a Lisp function object. When a finalizer object becomes unreachable aftera garbage collection pass, Emacs calls the finalizer’s associated function object. When
deciding whether a finalizer is reachable, Emacs does not count references from finalizer
objects themselves, allowing you to use finalizers without having to worry about accidentally
capturing references to finalized objects themselves.
Errors in finalizers are printed to *Messages*. Emacs runs a given finalizer object’s
associated function exactly once, even if that function fails.

make-finalizer function[Function]
Make a finalizer that will run function. function will be called after garbage collection
when the returned finalizer object becomes unreachable. If the finalizer object isreachable only through references from finalizer objects, it does not count as reachable
for the purpose of deciding whether to run function. function will be run once per
finalizer object.

2.5 Editing Types
The types in the previous section are used for general programming purposes, and most ofthem are common to most Lisp dialects. Emacs Lisp provides several additional data types
for purposes connected with editing.

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2.5.1 Buffer TypeA buffer is an object that holds text that can be edited (see Chapter 28 [Buffers], page 671).
Most buffers hold the contents of a disk file (see Chapter 26 [Files], page 608) so they canbe edited, but some are used for other purposes. Most buffers are also meant to be seen by
the user, and therefore displayed, at some time, in a window (see Chapter 29 [Windows],
page 690). But a buffer need not be displayed in any window. Each buffer has a designatedposition called point (see Chapter 31 [Positions], page 853); most editing commands act on
the contents of the current buffer in the neighborhood of point. At any time, one buffer isthe current buffer.
The contents of a buffer are much like a string, but buffers are not used like strings in
Emacs Lisp, and the available operations are different. For example, you can insert text
efficiently into an existing buffer, altering the buffer’s contents, whereas inserting text into astring requires concatenating substrings, and the result is an entirely new string object.
Many of the standard Emacs functions manipulate or test the characters in the current
buffer; a whole chapter in this manual is devoted to describing these functions (see Chapter 33[Text], page 878).
Several other data structures are associated with each buffer:• a local syntax table (see Chapter 36 [Syntax Tables], page 1022);• a local keymap (see Chapter 23 [Keymaps], page 480); and,• a list of buffer-local variable bindings (see Section 12.11 [Buffer-Local Variables],page 207).
• overlays (see Section 41.9 [Overlays], page 1150).
• text properties for the text in the buffer (see Section 33.19 [Text Properties], page 917).
The local keymap and variable list contain entries that individually override global bindings
or values. These are used to customize the behavior of programs in different buffers, without
actually changing the programs.
A buffer may be indirect, which means it shares the text of another buffer, but presents
it differently. See Section 28.11 [Indirect Buffers], page 687.
Buffers have no read syntax. They print in hash notation, showing the buffer name.
(current-buffer)⇒ #<buffer objects.texi>

2.5.2 Marker TypeA marker denotes a position in a specific buffer. Markers therefore have two components:
one for the buffer, and one for the position. Changes in the buffer’s text automaticallyrelocate the position value as necessary to ensure that the marker always points between
the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the current character
position and the name of the buffer.
(point-marker)⇒ #<marker at 10779 in objects.texi>
See Chapter 32 [Markers], page 869, for information on how to test, create, copy, andmove markers.

Chapter 2: Lisp Data Types

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2.5.3 Window TypeA window describes the portion of the screen that Emacs uses to display buffers. Everylive window (see Section 29.1 [Basic Windows], page 690) has one associated buffer, whose
contents appear in that window. By contrast, a given buffer may appear in one window, no
window, or several windows. Windows are grouped on the screen into frames; each window
belongs to one and only one frame. See Section 2.5.4 [Frame Type], page 27.
Though many windows may exist simultaneously, at any time one window is designatedthe selected window (see Section 29.3 [Selecting Windows], page 696). This is the window
where the cursor is (usually) displayed when Emacs is ready for a command. The selected
window usually displays the current buffer (see Section 28.2 [Current Buffer], page 671), but
this is not necessarily the case.
Windows have no read syntax. They print in hash notation, giving the window number
and the name of the buffer being displayed. The window numbers exist to identify windows
uniquely, since the buffer displayed in any given window can change frequently.
(selected-window)⇒ #<window 1 on objects.texi>
See Chapter 29 [Windows], page 690, for a description of the functions that work on
windows.

2.5.4 Frame TypeA frame is a screen area that contains one or more Emacs windows; we also use the term
“frame” to refer to the Lisp object that Emacs uses to refer to the screen area.
Frames have no read syntax. They print in hash notation, giving the frame’s title, plus
its address in core (useful to identify the frame uniquely).
(selected-frame)⇒ #<frame emacs@psilocin.gnu.org 0xdac80>
See Chapter 30 [Frames], page 785, for a description of the functions that work on frames.

2.5.5 Terminal TypeA terminal is a device capable of displaying one or more Emacs frames (see Section 2.5.4[Frame Type], page 27).
Terminals have no read syntax. They print in hash notation giving the terminal’s ordinal
number and its TTY device file name.
(get-device-terminal nil)
⇒ #<terminal 1 on /dev/tty>

2.5.6 Window Configuration TypeA window configuration stores information about the positions, sizes, and contents of thewindows in a frame, so you can recreate the same arrangement of windows later.
Window configurations do not have a read syntax; their print syntax looks like‘#<window-configuration>’. See Section 29.26 [Window Configurations], page 774, for a
description of several functions related to window configurations.

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2.5.7 Frame Configuration TypeA frame configuration stores information about the positions, sizes, and contents of thewindows in all frames. It is not a primitive type—it is actually a list whose car isframe-configuration and whose cdr is an alist. Each alist element describes one frame,
which appears as the car of that element.
See Section 30.13 [Frame Configurations], page 831, for a description of several functions
related to frame configurations.

2.5.8 Process TypeThe word process usually means a running program. Emacs itself runs in a process of
this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocesscreated by the Emacs process. Programs such as shells, GDB, ftp, and compilers, runningin subprocesses of Emacs, extend the capabilities of Emacs. An Emacs subprocess takes
textual input from Emacs and returns textual output to Emacs for further manipulation.
Emacs can also send signals to the subprocess.
Process objects have no read syntax. They print in hash notation, giving the name ofthe process:(process-list)⇒ (#<process shell>)See Chapter 40 [Processes], page 1078, for information about functions that create, delete,return information about, send input or signals to, and receive output from processes.

2.5.9 Thread TypeA thread in Emacs represents a separate thread of Emacs Lisp execution. It runs its own Lisp
program, has its own current buffer, and can have subprocesses locked to it, i.e. subprocesses
whose output only this thread can accept. See Chapter 39 [Threads], page 1073.
Thread objects have no read syntax. They print in hash notation, giving the name of thethread (if it has been given a name) or its address in core:(all-threads)⇒ (#<thread 0176fc40>)

2.5.10 Mutex TypeA mutex is an exclusive lock that threads can own and disown, in order to synchronize
between them. See Section 39.2 [Mutexes], page 1075.
Mutex objects have no read syntax. They print in hash notation, giving the name of the
mutex (if it has been given a name) or its address in core:(make-mutex "my-mutex")⇒ #<mutex my-mutex>(make-mutex)⇒ #<mutex 01c7e4e0>

2.5.11 Condition Variable TypeA condition variable is a device for a more complex thread synchronization than the one
supported by a mutex. A thread can wait on a condition variable, to be woken up whensome other thread notifies the condition.

Chapter 2: Lisp Data Types

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Condition variable objects have no read syntax. They print in hash notation, giving thename of the condition variable (if it has been given a name) or its address in core:(make-condition-variable (make-mutex))⇒ #<condvar 01c45ae8>

2.5.12 Stream TypeA stream is an object that can be used as a source or sink for characters—either to supply
characters for input or to accept them as output. Many different types can be used thisway: markers, buffers, strings, and functions. Most often, input streams (character sources)
obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks)
send characters to a buffer, such as a *Help* buffer, or to the echo area.
The object nil, in addition to its other meanings, may be used as a stream. It stands
for the value of the variable standard-input or standard-output. Also, the object t asa stream specifies input using the minibuffer (see Chapter 21 [Minibuffers], page 385) or
output in the echo area (see Section 41.4 [The Echo Area], page 1131).
Streams have no special printed representation or read syntax, and print as whatever
primitive type they are.
See Chapter 20 [Read and Print], page 371, for a description of functions related to
streams, including parsing and printing functions.

2.5.13 Keymap TypeA keymap maps keys typed by the user to commands. This mapping controls how the user’scommand input is executed. A keymap is actually a list whose car is the symbol keymap.
See Chapter 23 [Keymaps], page 480, for information about creating keymaps, handlingprefix keys, local as well as global keymaps, and changing key bindings.

2.5.14 Overlay TypeAn overlay specifies properties that apply to a part of a buffer. Each overlay applies toa specified range of the buffer, and contains a property list (a list whose elements arealternating property names and values). Overlay properties are used to present parts of thebuffer temporarily in a different display style. Overlays have no read syntax, and print inhash notation, giving the buffer name and range of positions.
See Section 41.9 [Overlays], page 1150, for information on how you can create and use
overlays.

2.5.15 Font TypeA font specifies how to display text on a graphical terminal. There are actually three separate
font types—font objects, font specs, and font entities—each of which has slightly different
properties. None of them have a read syntax; their print syntax looks like ‘#<font-object>’,‘#<font-spec>’, and ‘#<font-entity>’ respectively. See Section 41.12.12 [Low-Level Font],
page 1184, for a description of these Lisp objects.

2.5.16 Xwidget TypeAn xwidget is a special display element, such as a web browser, that can be embedded insidea buffer. Each window that displays an xwidget will also have an xwidget view, which on
X-Windows corresponds to a single X window used to display the widget.

Chapter 2: Lisp Data Types30

Neither of these objects are readable; their print syntaxes look like ‘#<xwidget>’ and‘#<xwidget-view>’, respectively. See Section 41.19 [Xwidgets], page 1228, for a more detailed
description of xwidgets.

2.6 Read Syntax for Circular Objects
To represent shared or circular structures within a complex of Lisp objects, you can use thereader constructs ‘#n=’ and ‘#n#’.
Use #n= before an object to label it for later reference; subsequently, you can use #n# torefer the same object in another place. Here, n is some integer. For example, here is how tomake a list in which the first element recurs as the third element:(#1=(a) b #1#)
This differs from ordinary syntax such as this((a) b (a))
which would result in a list whose first and third elements look alike but are not the same
Lisp object. This shows the difference:(prog1 nil(setq x '(#1=(a) b #1#)))(eq (nth 0 x) (nth 2 x))⇒ t(setq x '((a) b (a)))(eq (nth 0 x) (nth 2 x))⇒ nil
You can also use the same syntax to make a circular structure, which appears as anelement within itself. Here is an example:#1=(a #1#)
This makes a list whose second element is the list itself. Here’s how you can see that it really
works:(prog1 nil(setq x '#1=(a #1#)))(eq x (cadr x))⇒ t
The Lisp printer can produce this syntax to record circular and shared structure in a
Lisp object, if you bind the variable print-circle to a non-nil value. See Section 20.6
[Output Variables], page 380.

2.7 Type Predicates
The Emacs Lisp interpreter itself does not perform type checking on the actual arguments
passed to functions when they are called. It could not do so, since function arguments in
Lisp do not have declared data types, as they do in other programming languages. It istherefore up to the individual function to test whether each actual argument belongs to a
type that the function can use.

Chapter 2: Lisp Data Types

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All built-in functions do check the types of their actual arguments when appropriate,and signal a wrong-type-argument error if an argument is of the wrong type. For example,
here is what happens if you pass an argument to + that it cannot handle:(+ 2 'a)error Wrong type argument: number-or-marker-p, a
If you want your program to handle different types differently, you must do explicit
type checking. The most common way to check the type of an object is to call a typepredicate function. Emacs has a type predicate for each type, as well as some predicates for
combinations of types.
A type predicate function takes one argument; it returns t if the argument belongs tothe appropriate type, and nil otherwise. Following a general Lisp convention for predicate
functions, most type predicates’ names end with ‘p’.
Here is an example which uses the predicates listp to check for a list and symbolp tocheck for a symbol.
(defun add-on (x)(cond ((symbolp x);; If X is a symbol, put it on LIST.
(setq list (cons x list)))((listp x);; If X is a list, add its elements to LIST.
(setq list (append x list)))(t;; We handle only symbols and lists.
(error "Invalid argument %s in add-on" x))))Here is a table of predefined type predicates, in alphabetical order, with references tofurther information.
atom

See Section 5.2 [List-related Predicates], page 78.

arraypSee Section 6.3 [Array Functions], page 116.

bignump

See Section 3.3 [Predicates on Numbers], page 41.

bool-vector-p
See Section 6.7 [Bool-Vectors], page 121.
booleanp

See Section 1.3.2 [nil and t], page 2.

bufferpSee Section 28.1 [Buffer Basics], page 671.

byte-code-function-p
See Section 2.4.16 [Byte-Code Type], page 24.
compiled-function-p
See Section 2.4.16 [Byte-Code Type], page 24.
case-table-p
See Section 4.10 [Case Tables], page 74.
char-or-string-p
See Section 4.2 [Predicates for Strings], page 55.

Chapter 2: Lisp Data Types

char-table-p
See Section 6.6 [Char-Tables], page 119.
commandp

See Section 22.3 [Interactive Call], page 432.

condition-variable-p
See Section 39.3 [Condition Variables], page 1075.
consp

See Section 5.2 [List-related Predicates], page 78.

custom-variable-p
See Section 15.3 [Variable Definitions], page 280.
fixnump

See Section 3.3 [Predicates on Numbers], page 41.

floatpSee Section 3.3 [Predicates on Numbers], page 41.

fontp

See Section 41.12.12 [Low-Level Font], page 1184.

frame-configuration-p
See Section 30.13 [Frame Configurations], page 831.
frame-live-p
See Section 30.7 [Deleting Frames], page 822.
framepSee Chapter 30 [Frames], page 785.

functionp
See Chapter 13 [Functions], page 230.
hash-table-p
See Section 8.4 [Other Hash], page 131.
integer-or-marker-p
See Section 32.2 [Predicates on Markers], page 870.
integerp

See Section 3.3 [Predicates on Numbers], page 41.

keymappSee Section 23.4 [Creating Keymaps], page 483.

keywordp

See Section 12.2 [Constant Variables], page 189.

listp

See Section 5.2 [List-related Predicates], page 78.

markerpSee Section 32.2 [Predicates on Markers], page 870.

mutexpSee Section 39.2 [Mutexes], page 1075.

nlistpSee Section 5.2 [List-related Predicates], page 78.

number-or-marker-p
See Section 32.2 [Predicates on Markers], page 870.
numberpSee Section 3.3 [Predicates on Numbers], page 41.

overlaypSee Section 41.9 [Overlays], page 1150.

processp

See Chapter 40 [Processes], page 1078.

recordp

See Section 2.4.17 [Record Type], page 24.

32

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sequencep
See Section 6.1 [Sequence Functions], page 102.
string-or-null-p
See Section 4.2 [Predicates for Strings], page 55.
stringp

See Section 4.2 [Predicates for Strings], page 55.

subrp

See Section 13.9 [Function Cells], page 248.

symbolp

See Chapter 9 [Symbols], page 133.

syntax-table-p
See Chapter 36 [Syntax Tables], page 1022.
threadp

See Section 39.1 [Basic Thread Functions], page 1073.

vectorpSee Section 6.4 [Vectors], page 117.

wholenump
See Section 3.3 [Predicates on Numbers], page 41.
window-configuration-p
See Section 29.26 [Window Configurations], page 774.
window-live-p
See Section 29.8 [Deleting Windows], page 711.
windowp

See Section 29.1 [Basic Windows], page 690.

The most general way to check the type of an object is to call the function type-of. Recall
that each object belongs to one and only one primitive type; type-of tells you which one(see Chapter 2 [Lisp Data Types], page 8). But type-of knows nothing about non-primitive
types. In most cases, it is more convenient to use type predicates than type-of.

type-of object[Function]
This function returns a symbol naming the primitive type of object. The value
is one of the symbols bool-vector, buffer, char-table, compiled-function,
condition-variable, cons, finalizer, float, font-entity, font-object,
font-spec, frame, hash-table, integer, marker, mutex, overlay, process,string, subr, symbol, thread, vector, window, or window-configuration.
However, if object is a record, the type specified by its first slot is returned; Chapter 7[Records], page 125.
(type-of 1)⇒ integer(type-of 'nil)⇒ symbol(type-of '())
; () is nil.
⇒ symbol(type-of '(x))⇒ cons(type-of (record 'foo))⇒ foo

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2.8 Equality Predicates
Here we describe functions that test for equality between two objects. Other functions test
equality of contents between objects of specific types, e.g., strings. For these predicates, see
the appropriate chapter describing the data type.

eq object1 object2[Function]
This function returns t if object1 and object2 are the same object, and nil otherwise.
If object1 and object2 are symbols with the same name, they are normally the same
object—but see Section 9.3 [Creating Symbols], page 135, for exceptions. For othernon-numeric types (e.g., lists, vectors, strings), two arguments with the same contents
or elements are not necessarily eq to each other: they are eq only if they are the same
object, meaning that a change in the contents of one will be reflected by the samechange in the contents of the other.
If object1 and object2 are numbers with differing types or values, then they cannot
be the same object and eq returns nil. If they are fixnums with the same value, thenthey are the same object and eq returns t. If they were computed separately but
happen to have the same value and the same non-fixnum numeric type, then theymight or might not be the same object, and eq returns t or nil depending on whether
the Lisp interpreter created one object or two.
(eq 'foo 'foo)⇒ t(eq ?A ?A)⇒ t(eq 3.0 3.0)
⇒ t or nil;; Equal floats may or may not be the same object.
(eq (make-string 3 ?A) (make-string 3 ?A))⇒ nil
(eq "asdf" "asdf")⇒ t or nil;; Equal string constants or may not be the same object.
(eq '(1 (2 (3))) '(1 (2 (3))))⇒ nil(setq foo '(1 (2 (3))))⇒ (1 (2 (3)))(eq foo foo)⇒ t
(eq foo '(1 (2 (3))))⇒ nil

Chapter 2: Lisp Data Types35(eq [(1 2) 3] [(1 2) 3])⇒ nil(eq (point-marker) (point-marker))⇒ nil
The make-symbol function returns an uninterned symbol, distinct from the symbolthat is used if you write the name in a Lisp expression. Distinct symbols with thesame name are not eq. See Section 9.3 [Creating Symbols], page 135.
(eq (make-symbol "foo") 'foo)⇒ nil
The Emacs Lisp byte compiler may collapse identical literal objects, such as literal
strings, into references to the same object, with the effect that the byte-compiled code
will compare such objects as eq, while the interpreted version of the same code will
not. Therefore, your code should never rely on objects with the same literal contents
being either eq or not eq, it should instead use functions that compare object contentssuch as equal, described below. Similarly, your code should not modify literal objects(e.g., put text properties on literal strings), since doing that might affect other literalobjects of the same contents, if the byte compiler collapses them.

equal object1 object2[Function]
This function returns t if object1 and object2 have equal components, and nil
otherwise. Whereas eq tests if its arguments are the same object, equal looks inside
nonidentical arguments to see if their elements or contents are the same. So, if two
objects are eq, they are equal, but the converse is not always true.
(equal 'foo 'foo)⇒ t(equal 456 456)
⇒ t(equal "asdf" "asdf")⇒ t(eq "asdf" "asdf")⇒ nil(equal '(1 (2 (3))) '(1 (2 (3))))⇒ t(eq '(1 (2 (3))) '(1 (2 (3))))⇒ nil(equal [(1 2) 3] [(1 2) 3])⇒ t(eq [(1 2) 3] [(1 2) 3])⇒ nil(equal (point-marker) (point-marker))⇒ tChapter 2: Lisp Data Types36(eq (point-marker) (point-marker))⇒ nilComparison of strings is case-sensitive, but does not take account of text properties—
it compares only the characters in the strings. See Section 33.19 [Text Properties],
page 917. Use equal-including-properties to also compare text properties. For
technical reasons, a unibyte string and a multibyte string are equal if and only if they
contain the same sequence of character codes and all these codes are in the range 0
through 127 (ASCII).
(equal "asdf" "ASDF")⇒ nil
The equal function recursively compares the contents of objects if they are integers,
strings, markers, vectors, bool-vectors, byte-code function objects, char-tables, records,
or font objects. Other objects are considered equal only if they are eq. For example,
two distinct buffers are never considered equal, even if their textual contents are thesame.
For equal, equality is defined recursively; for example, given two cons cells x and y,(equal x y) returns t if and only if both the expressions below return t:(equal (car x) (car y))(equal (cdr x) (cdr y))Comparing circular lists may therefore cause deep recursion that leads to an error, andthis may result in counterintuitive behavior such as (equal a b) returning t whereas (equalb a) signals an error.

equal-including-properties object1 object2[Function]
This function behaves like equal in all cases but also requires that for two strings tobe equal, they have the same text properties.
(equal "asdf" (propertize "asdf" 'asdf t))⇒ t(equal-including-properties "asdf"(propertize "asdf" 'asdf t))⇒ nil

2.9 Mutability
Some Lisp objects should never change. For example, the Lisp expression "aaa" yields
a string, but you should not change its contents. And some objects cannot be changed;
for example, although you can create a new number by calculating one, Lisp provides nooperation to change the value of an existing number.
Other Lisp objects are mutable: it is safe to change their values via destructive operations
involving side effects. For example, an existing marker can be changed by moving the marker
to point to somewhere else.
Although numbers never change and all markers are mutable, some types have members
some of which are mutable and others not. These types include conses, vectors, and strings.
For example, although "cons" and (symbol-name 'cons) both yield strings that should notChapter 2: Lisp Data Types37

be changed, (copy-sequence "cons") and (make-string 3 ?a) both yield mutable strings
that can be changed via later calls to aset.
A mutable object stops being mutable if it is part of an expression that is evaluated. For
example:(let* ((x (list 0.5))(y (eval (list 'quote x))))(setcar x 1.5) ;; The program should not do this.
y)Although the list (0.5) was mutable when it was created, it should not have been changed
via setcar because it was given to eval. The reverse does not occur: an object that should
not be changed never becomes mutable afterwards.
If a program attempts to change objects that should not be changed, the resulting
behavior is undefined: the Lisp interpreter might signal an error, or it might crash or behave
unpredictably in other ways.2
When similar constants occur as parts of a program, the Lisp interpreter might savetime or space by reusing existing constants or their components. For example, (eq "abc""abc") returns t if the interpreter creates only one instance of the string literal "abc", andreturns nil if it creates two instances. Lisp programs should be written so that they work
regardless of whether this optimization is in use.

2

This is the behavior specified for languages like Common Lisp and C for constants, and this differs fromlanguages like JavaScript and Python where an interpreter is required to signal an error if a programattempts to change an immutable object. Ideally the Emacs Lisp interpreter will evolve in latter direction.

38

3 Numbers
GNU Emacs supports two numeric data types: integers and floating-point numbers. Integers
are whole numbers such as −3, 0, 7, 13, and 511. Floating-point numbers are numbers withfractional parts, such as −4.5, 0.0, and 2.71828. They can also be expressed in exponential
notation: ‘1.5e2’ is the same as ‘150.0’; here, ‘e2’ stands for ten to the second power, andthat is multiplied by 1.5. Integer computations are exact. Floating-point computations often
involve rounding errors, as the numbers have a fixed amount of precision.

3.1 Integer Basics
The Lisp reader reads an integer as a nonempty sequence of decimal digits with optional
initial sign and optional final period.
1; The integer 1.
1.
; The integer 1.
+1; Also the integer 1.
-1; The integer −1.
0; The integer 0.
-0; The integer 0.
The syntax for integers in bases other than 10 consists of ‘#’ followed by a radix indication
followed by one or more digits. The radix indications are ‘b’ for binary, ‘o’ for octal, ‘x’
for hex, and ‘radixr’ for radix radix. Thus, ‘#binteger’ reads integer in binary, and‘#radixrinteger’ reads integer in radix radix. Allowed values of radix run from 2 to 36,
and allowed digits are the first radix characters taken from ‘0’–‘9’, ‘A’–‘Z’. Letter case isignored and there is no initial sign or final period. For example:#b101100 ⇒ 44
#o54 ⇒ 44#x2c ⇒ 44#24r1k ⇒ 44
To understand how various functions work on integers, especially the bitwise operators(see Section 3.8 [Bitwise Operations], page 48), it is often helpful to view the numbers intheir binary form.
In binary, the decimal integer 5 looks like this:...000101(The ellipsis ‘...’ stands for a conceptually infinite number of bits that match the leading
bit; here, an infinite number of 0 bits. Later examples also use this ‘...’ notation.)
The integer −1 looks like this:...111111−1 is represented as all ones. (This is called two’s complement notation.)
Subtracting 4 from −1 returns the negative integer −5. In binary, the decimal integer 4
is 100. Consequently, −5 looks like this:...111011
Many of the functions described in this chapter accept markers for arguments in placeof numbers. (See Chapter 32 [Markers], page 869.) Since the actual arguments to such

Chapter 3: Numbers39functions may be either numbers or markers, we often give these arguments the namenumber-or-marker. When the argument value is a marker, its position value is used and its
buffer is ignored.
In Emacs Lisp, text characters are represented by integers. Any integer between zero andthe value of (max-char), inclusive, is considered to be valid as a character. See Section 34.5
[Character Codes], page 967.
Integers in Emacs Lisp are not limited to the machine word size. Under the hood, though,there are two kinds of integers: smaller ones, called fixnums, and larger ones, called bignums.
Although Emacs Lisp code ordinarily should not depend on whether an integer is a fixnum
or a bignum, older Emacs versions support only fixnums, some functions in Emacs still
accept only fixnums, and older Emacs Lisp code may have trouble when given bignums. For
example, while older Emacs Lisp code could safely compare integers for numeric equality
with eq, the presence of bignums means that equality predicates like eql and = should now
be used to compare integers.
The range of values for bignums is limited by the amount of main memory, by machine
characteristics such as the size of the word used to represent a bignum’s exponent, and by
the integer-width variable. These limits are typically much more generous than the limits
for fixnums. A bignum is never numerically equal to a fixnum; Emacs always represents an
integer in fixnum range as a fixnum, not a bignum.
The range of values for a fixnum depends on the machine. The minimum range is−536,870,912 to 536,870,911 (30 bits; i.e., −229 to 229 − 1), but many machines provide awider range.
[Variable]
The value of this variable is the greatest “small” integer that Emacs Lisp can handle.
Typical values are 229 − 1 on 32-bit and 261 − 1 on 64-bit platforms.

most-positive-fixnum[Variable]
The value of this variable is the numerically least “small” integer that Emacs Lisp canhandle. It is negative. Typical values are −229 on 32-bit and −261 on 64-bit platforms.

most-negative-fixnum[Variable]
The value of this variable is a nonnegative integer that controls whether Emacs signals
a range error when a large integer would be calculated. Integers with absolute values
less than 2n , where n is this variable’s value, do not signal a range error. Attempts tocreate larger integers typically signal a range error, although there might be no signal
if a larger integer can be created cheaply. Setting this variable to a large number canbe costly if a computation creates huge integers.

integer-width

3.2 Floating-Point Basics
Floating-point numbers are useful for representing numbers that are not integral. The
range of floating-point numbers is the same as the range of the C data type double on
the machine you are using. On almost all computers supported by Emacs, this is IEEEbinary64 floating point format, which is standardized by IEEE Std 754-2019 and is discussed further in David Goldberg’s paper “What Every Computer Scientist Should Know
About Floating-Point Arithmetic (https://docs.oracle.com/cd/E19957-01/806-3568/

Chapter 3: Numbers

40

ncg_goldberg.html)”. On modern platforms, floating-point operations follow the IEEE-754
standard closely; however, results are not always rounded correctly on some systems, notably
32-bit x86.
On some old computer systems, Emacs may not use IEEE floating-point. We know of
one such system on which Emacs runs correctly, but does not follow IEEE-754: the VAX
running NetBSD using GCC 10.4.0, where the VAX ‘D_Floating’ format is used instead.
IBM System/370-derived mainframes and their XL/C compiler are also capable of utilizing ahexadecimal floating point format, but Emacs has not yet been built in such a configuration.
The read syntax for floating-point numbers requires either a decimal point, an exponent,or both. Optional signs (‘+’ or ‘-’) precede the number and its exponent. For example,‘1500.0’, ‘+15e2’, ‘15.0e+2’, ‘+1500000e-3’, and ‘.15e4’ are five ways of writing a floatingpoint number whose value is 1500. They are all equivalent. Like Common Lisp, Emacs Lisp
requires at least one digit after a decimal point in a floating-point number that does nothave an exponent; ‘1500.’ is an integer, not a floating-point number.
Emacs Lisp treats -0.0 as numerically equal to ordinary zero with respect to numericcomparisons like =. This follows the IEEE floating-point standard, which says -0.0 and 0.0
are numerically equal even though other operations can distinguish them.
The IEEE floating-point standard supports positive infinity and negative infinity as
floating-point values. It also provides for a class of values called NaN, or “not a number”;
numerical functions return such values in cases where there is no correct answer. For example,(/ 0.0 0.0) returns a NaN. A NaN is never numerically equal to any value, not even to
itself. NaNs carry a sign and a significand, and non-numeric functions treat two NaNs as
equal when their signs and significands agree. Significands of NaNs are machine-dependent,
as are the digits in their string representation.
NaNs are not available on systems which do not use IEEE floating-point arithmetic; if
the read syntax for a NaN is used on a VAX, for example, the reader signals an error.
When NaNs and signed zeros are involved, non-numeric functions like eql, equal,
sxhash-eql, sxhash-equal and gethash determine whether values are indistinguishable,
not whether they are numerically equal. For example, when x and y are the same NaN,
(equal x y) returns t whereas (= x y) uses numeric comparison and returns nil; conversely,(equal 0.0 -0.0) returns nil whereas (= 0.0 -0.0) returns t.
Here are read syntaxes for these special floating-point values:
infinity‘1.0e+INF’ and ‘-1.0e+INF’

not-a-number‘0.0e+NaN’ and ‘-0.0e+NaN’
The following functions are specialized for handling floating-point numbers:

isnan x

[Function]
This predicate returns t if its floating-point argument is a NaN, nil otherwise.

frexp x

[Function]
This function returns a cons cell (s . e), where s and e are respectively the significand
and exponent of the floating-point number x.

Chapter 3: Numbers

41

If x is finite, then s is a floating-point number between 0.5 (inclusive) and 1.0 (exclusive),
e is an integer, and x = s2e . If x is zero or infinity, then s is the same as x. If x is a
NaN, then s is also a NaN. If x is zero, then e is 0.

ldexp s e

[Function]
Given a numeric significand s and an integer exponent e, this function returns thefloating point number s2e .

copysign x1 x2[Function]
This function copies the sign of x2 to the value of x1, and returns the result. x1 andx2 must be floating point.

logb x[Function]
This function returns the binary exponent of x. More precisely, if x is finite andnonzero, the value is the logarithm base 2 of |x|, rounded down to an integer. If x iszero or infinite, the value is infinity; if x is a NaN, the value is a NaN.
(logb 10)⇒ 3(logb 10.0e20)⇒ 69(logb 0)⇒ -1.0e+INF

3.3 Type Predicates for Numbers
The functions in this section test for numbers, or for a specific type of number. The functions
integerp and floatp can take any type of Lisp object as argument (they would not be ofmuch use otherwise), but the zerop predicate requires a number as its argument. See also
integer-or-marker-p and number-or-marker-p, in Section 32.2 [Predicates on Markers],
page 870.

bignump object[Function]
This predicate tests whether its argument is a large integer, and returns t if so, nilotherwise. Unlike small integers, large integers can be = or eql even if they are not eq.

fixnump object[Function]
This predicate tests whether its argument is a small integer, and returns t if so, nilotherwise. Small integers can be compared with eq.

floatp object[Function]
This predicate tests whether its argument is floating point and returns t if so, nilotherwise.

integerp object[Function]
This predicate tests whether its argument is an integer, and returns t if so, nilotherwise.

numberp object[Function]
This predicate tests whether its argument is a number (either integer or floating point),
and returns t if so, nil otherwise.

Chapter 3: Numbers

42

natnump object[Function]
This predicate (whose name comes from the phrase “natural number”) tests to see
whether its argument is a nonnegative integer, and returns t if so, nil otherwise. 0 is
considered non-negative.
wholenump is a synonym for natnump.

zerop number[Function]
This predicate tests whether its argument is zero, and returns t if so, nil otherwise.
The argument must be a number.
(zerop x) is equivalent to (= x 0).

3.4 Comparison of Numbers
To test numbers for numerical equality, you should normally use = instead of non-numericcomparison predicates like eq, eql and equal. Distinct floating-point and large integer
objects can be numerically equal. If you use eq to compare them, you test whether they are
the same object; if you use eql or equal, you test whether their values are indistinguishable.
In contrast, = uses numeric comparison, and sometimes returns t when a non-numericcomparison would return nil and vice versa. See Section 3.2 [Float Basics], page 39.
In Emacs Lisp, if two fixnums are numerically equal, they are the same Lisp object. Thatis, eq is equivalent to = on fixnums. It is sometimes convenient to use eq for comparing an
unknown value with a fixnum, because eq does not report an error if the unknown value
is not a number—it accepts arguments of any type. By contrast, = signals an error if thearguments are not numbers or markers. However, it is better programming practice to use =if you can, even for comparing integers.
Sometimes it is useful to compare numbers with eql or equal, which treat two numbers
as equal if they have the same data type (both integers, or both floating point) and thesame value. By contrast, = can treat an integer and a floating-point number as equal. See
Section 2.8 [Equality Predicates], page 34.
There is another wrinkle: because floating-point arithmetic is not exact, it is often a bad
idea to check for equality of floating-point values. Usually it is better to test for approximate
equality. Here’s a function to do this:(defvar fuzz-factor 1.0e-6)(defun approx-equal (x y)(or (= x y)(< (/ (abs (- x y))(max (abs x) (abs y)))fuzz-factor)))= number-or-marker &rest number-or-markers[Function]
This function tests whether all its arguments are numerically equal, and returns t if
so, nil otherwise.

eql value1 value2[Function]
This function acts like eq except when both arguments are numbers. It compares
numbers by type and numeric value, so that (eql 1.0 1) returns nil, but (eql 1.0
1.0) and (eql 1 1) both return t. This can be used to compare large integers as well

Chapter 3: Numbers

43

as small ones. Floating-point values with the same sign, exponent and fraction areeql. This differs from numeric comparison: (eql 0.0 -0.0) returns nil and (eql
0.0e+NaN 0.0e+NaN) returns t, whereas = does the opposite.

/= number-or-marker1 number-or-marker2[Function]
This function tests whether its arguments are numerically equal, and returns t if they
are not, and nil if they are.

< number-or-marker &rest number-or-markers[Function]
This function tests whether each argument is strictly less than the following argument.
It returns t if so, nil otherwise.

<= number-or-marker &rest number-or-markers[Function]
This function tests whether each argument is less than or equal to the following
argument. It returns t if so, nil otherwise.

> number-or-marker &rest number-or-markers[Function]
This function tests whether each argument is strictly greater than the following
argument. It returns t if so, nil otherwise.

>= number-or-marker &rest number-or-markers[Function]
This function tests whether each argument is greater than or equal to the following
argument. It returns t if so, nil otherwise.

max number-or-marker &rest numbers-or-markers[Function]

This function returns the largest of its arguments.
(max 20)⇒ 20(max 1 2.5)
⇒ 2.5
(max 1 3 2.5)
⇒ 3

min number-or-marker &rest numbers-or-markers[Function]

This function returns the smallest of its arguments.
(min -4 1)⇒ -4

abs number[Function]

This function returns the absolute value of number.

3.5 Numeric Conversions
To convert an integer to floating point, use the function float.

float number[Function]
This returns number converted to floating point. If number is already floating point,
float returns it unchanged.

Chapter 3: Numbers

44

There are four functions to convert floating-point numbers to integers; they differ in
how they round. All accept an argument number and an optional argument divisor. Botharguments may be integers or floating-point numbers. divisor may also be nil. If divisor isnil or omitted, these functions convert number to an integer, or return it unchanged if italready is an integer. If divisor is non-nil, they divide number by divisor and convert theresult to an integer. If divisor is zero (whether integer or floating point), Emacs signals anarith-error error.

truncate number &optional divisor[Function]

This returns number, converted to an integer by rounding towards zero.
(truncate 1.2)
⇒ 1
(truncate 1.7)
⇒ 1
(truncate -1.2)⇒ -1(truncate -1.7)⇒ -1

floor number &optional divisor[Function]
This returns number, converted to an integer by rounding downward (towards negative
infinity).
If divisor is specified, this uses the kind of division operation that corresponds to mod,rounding downward.
(floor 1.2)
⇒ 1
(floor 1.7)
⇒ 1
(floor -1.2)⇒ -2(floor -1.7)⇒ -2(floor 5.99 3)⇒ 1

ceiling number &optional divisor[Function]
This returns number, converted to an integer by rounding upward (towards positive
infinity).
(ceiling 1.2)
⇒ 2
(ceiling 1.7)
⇒ 2(ceiling -1.2)⇒ -1(ceiling -1.7)⇒ -1

Chapter 3: Numbers

45round number &optional divisor[Function]
This returns number, converted to an integer by rounding towards the nearest integer.
Rounding a value equidistant between two integers returns the even integer.
(round 1.2)
⇒ 1
(round 1.7)
⇒ 2
(round -1.2)⇒ -1(round -1.7)⇒ -2

3.6 Arithmetic Operations
Emacs Lisp provides the traditional four arithmetic operations (addition, subtraction,
multiplication, and division), as well as remainder and modulus functions, and functions
to add or subtract 1. Except for %, each of these functions accepts both integer andfloating-point arguments, and returns a floating-point number if any argument is floating
point.

1+ number-or-marker[Function]

This function returns number-or-marker plus 1. For example,(setq foo 4)⇒ 4(1+ foo)⇒ 5This function is not analogous to the C operator ++—it does not increment a variable.
It just computes a sum. Thus, if we continue,foo⇒ 4
If you want to increment the variable, you must use setq, like this:(setq foo (1+ foo))⇒ 5

1- number-or-marker[Function]

This function returns number-or-marker minus 1.

+ &rest numbers-or-markers[Function]
This function adds its arguments together. When given no arguments, + returns 0.
(+)
⇒ 0
(+ 1)
⇒ 1
(+ 1 2 3 4)
⇒ 10

Chapter 3: Numbers

46- &optional number-or-marker &rest more-numbers-or-markers[Function]
The - function serves two purposes: negation and subtraction. When - has a single
argument, the value is the negative of the argument. When there are multiple
arguments, - subtracts each of the more-numbers-or-markers from number-or-marker,
cumulatively. If there are no arguments, the result is 0.
(- 10 1 2 3 4)
⇒ 0(- 10)
⇒ -10
(-)
⇒ 0

* &rest numbers-or-markers[Function]
This function multiplies its arguments together, and returns the product. When given
no arguments, * returns 1.
(*)
⇒ 1
(* 1)
⇒ 1
(* 1 2 3 4)
⇒ 24

/ number &rest divisors[Function]
With one or more divisors, this function divides number by each divisor in divisors inturn, and returns the quotient. With no divisors, this function returns 1/number, i.e.,the multiplicative inverse of number. Each argument may be a number or a marker.
If all the arguments are integers, the result is an integer, obtained by rounding thequotient towards zero after each division.
(/ 6 2)⇒ 3(/ 5 2)⇒ 2(/ 5.0 2)⇒ 2.5(/ 5 2.0)⇒ 2.5(/ 5.0 2.0)
⇒ 2.5(/ 4.0)⇒ 0.25(/ 4)⇒ 0(/ 25 3 2)
⇒ 4(/ -17 6)⇒ -2

Chapter 3: Numbers

47

If you divide an integer by the integer 0, Emacs signals an arith-error error (seeSection 11.7.3 [Errors], page 179). On systems using IEEE-754 floating-point, floatingpoint division of a nonzero number by zero yields either positive or negative infinity(see Section 3.2 [Float Basics], page 39); otherwise, an arith-error is signaled as
usual.

% dividend divisor[Function]
This function returns the integer remainder after division of dividend by divisor. The
arguments must be integers or markers.
For any two integers dividend and divisor,(+ (% dividend divisor)(* (/ dividend divisor) divisor))always equals dividend if divisor is nonzero.
(% 9 4)⇒ 1(% -9 4)⇒ -1(% 9 -4)⇒ 1(% -9 -4)
⇒ -1

mod dividend divisor[Function]
This function returns the value of dividend modulo divisor; in other words, theremainder after division of dividend by divisor, but with the same sign as divisor. The
arguments must be numbers or markers.
Unlike %, mod permits floating-point arguments; it rounds the quotient downward(towards minus infinity) to an integer, and uses that quotient to compute the remainder.
If divisor is zero, mod signals an arith-error error if both arguments are integers,
and returns a NaN otherwise.
(mod 9 4)⇒ 1(mod -9 4)⇒ 3(mod 9 -4)⇒ -3(mod -9 -4)⇒ -1(mod 5.5 2.5)
⇒ .5
For any two numbers dividend and divisor,(+ (mod dividend divisor)(* (floor dividend divisor) divisor))always equals dividend, subject to rounding error if either argument is floating point
and to an arith-error if dividend is an integer and divisor is 0. For floor, see
Section 3.5 [Numeric Conversions], page 43.

Chapter 3: Numbers

48

3.7 Rounding Operations
The functions ffloor, fceiling, fround, and ftruncate take a floating-point argument
and return a floating-point result whose value is a nearby integer. ffloor returns the nearest
integer below; fceiling, the nearest integer above; ftruncate, the nearest integer in the
direction towards zero; fround, the nearest integer.

ffloor float[Function]
This function rounds float to the next lower integral value, and returns that value asa floating-point number.

fceiling float[Function]
This function rounds float to the next higher integral value, and returns that value asa floating-point number.

ftruncate float[Function]
This function rounds float towards zero to an integral value, and returns that value asa floating-point number.

fround float[Function]
This function rounds float to the nearest integral value, and returns that value as afloating-point number. Rounding a value equidistant between two integers returns theeven integer.

3.8 Bitwise Operations on Integers
In a computer, an integer is represented as a binary number, a sequence of bits (digits
which are either zero or one). Conceptually the bit sequence is infinite on the left, with themost-significant bits being all zeros or all ones. A bitwise operation acts on the individual
bits of such a sequence. For example, shifting moves the whole sequence left or right one ormore places, reproducing the same pattern moved over.
The bitwise operations in Emacs Lisp apply only to integers.

ash integer1 count[Function]ash (arithmetic shift) shifts the bits in integer1 to the left count places, or to the right
if count is negative. Left shifts introduce zero bits on the right; right shifts discard
the rightmost bits. Considered as an integer operation, ash multiplies integer1 by
2count , and then converts the result to an integer by rounding downward, toward minus
infinity.
Here are examples of ash, shifting a pattern of bits one place to the left and to theright. These examples show only the low-order bits of the binary pattern; leading
bits all agree with the highest-order bit shown. As you can see, shifting left by one
is equivalent to multiplying by two, whereas shifting right by one is equivalent todividing by two and then rounding toward minus infinity.
(ash 7 1) ⇒ 14;; Decimal 7 becomes decimal 14.
...000111⇒...001110

Chapter 3: Numbers

49(ash 7 -1) ⇒ 3...000111⇒...000011(ash -7 1) ⇒ -14...111001⇒...110010(ash -7 -1) ⇒ -4...111001⇒...111100
Here are examples of shifting left or right by two bits:(ash 5 2)⇒ 20(ash -5 2)⇒ -20(ash 5 -2)⇒ 1(ash -5 -2)
⇒ -2

;
;
5
;
; -5
;

binary values= . . . 000101= . . . 010100= . . . 111011= . . . 101100;=. . . 000001;=. . . 111110

lsh integer1 count[Function]lsh, which is an abbreviation for logical shift, shifts the bits in integer1 to the left
count places, or to the right if count is negative, bringing zeros into the vacated bits. If
count is negative, then integer1 must be either a fixnum or a positive bignum, and lsh
treats a negative fixnum as if it were unsigned by subtracting twice most-negativefixnum before shifting, producing a nonnegative result. This quirky behavior dates
back to when Emacs supported only fixnums; nowadays ash is a better choice.
As lsh behaves like ash except when integer1 and count1 are both negative, thefollowing examples focus on these exceptional cases. These examples assume 30-bit
fixnums.
;binary values(ash -7 -1); -7 = . . . 111111111111111111111111111001⇒ -4;= . . . 111111111111111111111111111100(lsh -7 -1)⇒ 536870908 ;= . . . 011111111111111111111111111100(ash -5 -2); -5 = . . . 111111111111111111111111111011⇒ -2;= . . . 111111111111111111111111111110(lsh -5 -2)⇒ 268435454 ;= . . . 001111111111111111111111111110

logand &rest ints-or-markers[Function]
This function returns the bitwise AND of the arguments: the nth bit is 1 in the result
if, and only if, the nth bit is 1 in all the arguments.
For example, using 4-bit binary numbers, the bitwise AND of 13 and 12 is 12: 1101
combined with 1100 produces 1100. In both the binary numbers, the leftmost two

Chapter 3: Numbers

50

bits are both 1 so the leftmost two bits of the returned value are both 1. However, forthe rightmost two bits, each is 0 in at least one of the arguments, so the rightmost
two bits of the returned value are both 0.
Therefore,(logand 13 12)⇒ 12
If logand is not passed any argument, it returns a value of −1. This number is an
identity element for logand because its binary representation consists entirely of ones.
If logand is passed just one argument, it returns that argument.
;

binary values

; 14
; 13
; 12

=
=
=

. . . 001110. . . 001101. . . 001100

⇒ 4

; 14
; 13
; 4
; 4

=
=
=
=

. . . 001110. . . 001101. . . 000100. . . 000100(logand)
⇒ -1

; -1

=

. . . 111111(logand 14 13)⇒ 12(logand 14 13 4)

logior &rest ints-or-markers[Function]
This function returns the bitwise inclusive OR of its arguments: the nth bit is 1 in
the result if, and only if, the nth bit is 1 in at least one of the arguments. If there
are no arguments, the result is 0, which is an identity element for this operation. If
logior is passed just one argument, it returns that argument.
(logior 12 5)⇒ 13(logior 12 5 7)

⇒ 15

;

binary values

; 12
; 5
; 13

=
=
=

. . . 001100. . . 000101. . . 001101

; 12
; 5
; 7
; 15

=
=
=
=

. . . 001100. . . 000101. . . 000111. . . 001111

logxor &rest ints-or-markers[Function]
This function returns the bitwise exclusive OR of its arguments: the nth bit is 1 in
the result if, and only if, the nth bit is 1 in an odd number of the arguments. If there
are no arguments, the result is 0, which is an identity element for this operation. If
logxor is passed just one argument, it returns that argument.
(logxor 12 5)⇒ 9(logxor 12 5 7)

⇒ 14

;

binary values

; 12
; 5
; 9

=
=
=

. . . 001100. . . 000101. . . 001001

; 12
; 5
; 7
; 14

=
=
=
=

. . . 001100. . . 000101. . . 000111. . . 001110

Chapter 3: Numbers

51

lognot integer[Function]
This function returns the bitwise complement of its argument: the nth bit is one in
the result if, and only if, the nth bit is zero in integer, and vice-versa. The result
equals −1 − integer.
(lognot 5)⇒ -6;; 5 = . . . 000101;; becomes;; -6 = . . . 111010

logcount integer[Function]
This function returns the Hamming weight of integer: the number of ones in thebinary representation of integer. If integer is negative, it returns the number of zero
bits in its two’s complement binary representation. The result is always nonnegative.
(logcount 43)⇒ 4(logcount -43)
⇒ 3;

43 = . . . 000101011; -43 = . . . 111010101

3.9 Standard Mathematical Functions
These mathematical functions allow integers as well as floating-point numbers as arguments.

sin argcos argtan arg[Function][Function][Function]
These are the basic trigonometric functions, with argument arg measured in radians.

asin arg[Function]
The value of (asin arg) is a number between −π/2 and π/2 (inclusive) whose sine isarg. If arg is out of range (outside [−1, 1]), asin returns a NaN.

acos arg[Function]
The value of (acos arg) is a number between 0 and π (inclusive) whose cosine is arg.
If arg is out of range (outside [−1, 1]), acos returns a NaN.

atan y &optional x[Function]
The value of (atan y) is a number between −π/2 and π/2 (exclusive) whose tangent
is y. If the optional second argument x is given, the value of (atan y x) is the angle
in radians between the vector [x, y] and the X axis.

exp arg[Function]

This is the exponential function; it returns e to the power arg.

log arg &optional base

[Function]
This function returns the logarithm of arg, with base base. If you don’t specify base,the natural base e is used. If arg or base is negative, log returns a NaN.

Chapter 3: Numbers

52

expt x y[Function]
This function returns x raised to power y. If both arguments are integers and y isnonnegative, the result is an integer; in this case, overflow signals an error, so watch
out. If x is a finite negative number and y is a finite non-integer, expt returns a NaN.

sqrt arg[Function]
This returns the square root of arg. If arg is finite and less than zero, sqrt returns a
NaN.

In addition, Emacs defines the following common mathematical constants:

float-e[Variable]

The mathematical constant e (2.71828. . . ).

float-pi[Variable]

The mathematical constant pi (3.14159. . . ).

3.10 Random Numbers
A deterministic computer program cannot generate true random numbers. For most purposes,
pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a
deterministic fashion. The numbers are not truly random, but they have certain properties
that mimic a random series. For example, all possible values occur equally often in a
pseudo-random series.
Pseudo-random numbers are generated from a seed value. Starting from any given seed,
the random function always generates the same sequence of numbers. By default, Emacs
initializes the random seed at startup, in such a way that the sequence of values of random(with overwhelming likelihood) differs in each Emacs run. The random seed is typicallyinitialized from system entropy; however, on obsolescent platforms lacking entropy pools,
the seed is taken from less-random volatile data such as the current time.
Sometimes you want the random number sequence to be repeatable. For example, when
debugging a program whose behavior depends on the random number sequence, it is helpful
to get the same behavior in each program run. To make the sequence repeat, execute(random ""). This sets the seed to a constant value for your particular Emacs executable(though it may differ for other Emacs builds). You can use other strings to choose various
seed values.

random &optional limit[Function]
This function returns a pseudo-random integer. Repeated calls return a series ofpseudo-random integers.
If limit is a positive integer, the value is chosen to be nonnegative and less than limit.
Otherwise, the value might be any fixnum, i.e., any integer from most-negativefixnum through most-positive-fixnum (see Section 3.1 [Integer Basics], page 38).
If limit is a string, it means to choose a new seed based on the string’s contents. This
causes later calls to random to return a reproducible sequence of results.
If limit is t, it means to choose a new seed as if Emacs were restarting. This causes
later calls to random to return an unpredictable sequence of results.

Chapter 3: Numbers

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If you need a random nonce for cryptographic purposes, using random is typically not
the best approach, for several reasons:• Although you can use (random t) to consult system entropy, doing so can adversely
affect other parts of your program that benefit from reproducible results.
• The system-dependent pseudo-random number generator (PRNG) used by random is
not necessarily suitable for cryptography.
• A call to (random t) does not give direct access to system entropy; the entropy is
passed through the system-dependent PRNG, thus possibly biasing the results.
• On typical platforms the random seed contains only 32 bits, which is typically narrower
than an Emacs fixnum, and is not nearly enough for cryptographic purposes.
• A (random t) call leaves information about the nonce scattered about Emacs’s internal
state, increasing the size of the internal attack surface.
• On obsolescent platforms lacking entropy pools, (random t) is seeded from a cryptographically weak source.

54

4 Strings and Characters
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings
are used as names of symbols, buffers, and files; to send messages to users; to hold text being
copied between buffers; and for many other purposes. Because strings are so important,Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use
strings more often than individual characters.
See Section 22.7.17 [Strings of Events], page 459, for special considerations for strings ofkeyboard character events.

4.1 String and Character Basics
A character is a Lisp object which represents a single character of text. In Emacs Lisp,
characters are simply integers; whether an integer is a character or not is determined only
by how it is used. See Section 34.5 [Character Codes], page 967, for details about character
representation in Emacs.
A string is a fixed sequence of characters. It is a type of sequence called an array,meaning that its length is fixed and cannot be altered once it is created (see Chapter 6[Sequences Arrays Vectors], page 102). Unlike in C, Emacs Lisp strings are not terminatedby a distinguished character code.
Since strings are arrays, and therefore sequences as well, you can operate on them with thegeneral array and sequence functions documented in Chapter 6 [Sequences Arrays Vectors],
page 102. For example, you can access individual characters in a string using the function
aref (see Section 6.3 [Array Functions], page 116).
There are two text representations for non-ASCII characters in Emacs strings (and in
buffers): unibyte and multibyte. For most Lisp programming, you don’t need to be concernedwith these two representations. See Section 34.1 [Text Representations], page 963, for details.
Sometimes key sequences are represented as unibyte strings. When a unibyte string isa key sequence, string elements in the range 128 to 255 represent meta characters (which
are large integers) rather than character codes in the range 128 to 255. Strings cannot
hold characters that have the hyper, super or alt modifiers; they can hold ASCII control
characters, but no other control characters. They do not distinguish case in ASCII control
characters. If you want to store such characters in a sequence, such as a key sequence, youmust use a vector instead of a string. See Section 2.4.3 [Character Type], page 11, for more
information about keyboard input characters.
Strings are useful for holding regular expressions. You can also match regular expressions
against strings with string-match (see Section 35.4 [Regexp Search], page 1008). The functions match-string (see Section 35.6.2 [Simple Match Data], page 1013) and replace-match(see Section 35.6.1 [Replacing Match], page 1012) are useful for decomposing and modifying
strings after matching regular expressions against them.
Like a buffer, a string can contain text properties for the characters in it, as well as
the characters themselves. See Section 33.19 [Text Properties], page 917. All the Lisp
primitives that copy text from strings to buffers or other strings also copy the properties of
the characters being copied.
See Chapter 33 [Text], page 878, for information about functions that display strings or
copy them into buffers. See Section 2.4.3 [Character Type], page 11, and Section 2.4.8 [StringChapter 4: Strings and Characters

55

Type], page 20, for information about the syntax of characters and strings. See Chapter 34[Non-ASCII Characters], page 963, for functions to convert between text representations
and to encode and decode character codes. Also, note that length should not be used forcomputing the width of a string on display; use string-width (see Section 41.10 [Size of
Displayed Text], page 1157) instead.

4.2 Predicates for Strings
For more information about general sequence and array predicates, see Chapter 6 [Sequences
Arrays Vectors], page 102, and Section 6.2 [Arrays], page 115.

stringp object[Function]

This function returns t if object is a string, nil otherwise.

string-or-null-p object[Function]
This function returns t if object is a string or nil. It returns nil otherwise.

char-or-string-p object[Function]
This function returns t if object is a string or a character (i.e., an integer), nilotherwise.

4.3 Creating Strings
The following functions create strings, either from scratch, or by putting strings together, orby taking them apart. (For functions that create strings based on the modified contents
of other strings, like string-replace and replace-regexp-in-string, see Section 35.7
[Search and Replace], page 1016.)

make-string count character &optional multibyte[Function]
This function returns a string made up of count repetitions of character. If count isnegative, an error is signaled.
(make-string 5 ?x)⇒ "xxxxx"(make-string 0 ?x)⇒ ""Normally, if character is an ASCII character, the result is a unibyte string. But if theoptional argument multibyte is non-nil, the function will produce a multibyte string
instead. This is useful when you later need to concatenate the result with non-ASCII
strings or replace some of its characters with non-ASCII characters.
Other functions to compare with this one include make-vector (see Section 6.4[Vectors], page 117) and make-list (see Section 5.4 [Building Lists], page 82).

string &rest characters
This returns a string containing the characters characters.
(string ?a ?b ?c)⇒ "abc"[Function]

Chapter 4: Strings and Characters

56

substring string &optional start end[Function]
This function returns a new string which consists of those characters from string in therange from (and including) the character at the index start up to (but excluding) the
character at the index end. The first character is at index zero. With one argument,
this function just copies string.
(substring "abcdefg" 0 3)
⇒ "abc"In the above example, the index for ‘a’ is 0, the index for ‘b’ is 1, and the index for ‘c’
is 2. The index 3—which is the fourth character in the string—marks the character
position up to which the substring is copied. Thus, ‘abc’ is copied from the string"abcdefg".

A negative number counts from the end of the string, so that −1 signifies the index of
the last character of the string. For example:(substring "abcdefg" -3 -1)⇒ "ef"In this example, the index for ‘e’ is −3, the index for ‘f’ is −2, and the index for ‘g’ is−1. Therefore, ‘e’ and ‘f’ are included, and ‘g’ is excluded.
When nil is used for end, it stands for the length of the string. Thus,(substring "abcdefg" -3 nil)⇒ "efg"Omitting the argument end is equivalent to specifying nil. It follows that (substring
string 0) returns a copy of all of string.
(substring "abcdefg" 0)⇒ "abcdefg"
But we recommend copy-sequence for this purpose (see Section 6.1 [Sequence Functions], page 102).
If the characters copied from string have text properties, the properties are copied
into the new string also. See Section 33.19 [Text Properties], page 917.
substring also accepts a vector for the first argument. For example:(substring [a b (c) "d"] 1 3)
⇒ [b (c)]A wrong-type-argument error is signaled if start is not an integer or if end is neither
an integer nor nil. An args-out-of-range error is signaled if start indicates acharacter following end, or if either integer is out of range for string.
Contrast this function with buffer-substring (see Section 33.2 [Buffer Contents],
page 879), which returns a string containing a portion of the text in the current buffer.
The beginning of a string is at index 0, but the beginning of a buffer is at index 1.

substring-no-properties string &optional start end[Function]
This works like substring but discards all text properties from the value.
Also, start may be omitted or nil, which is equivalent to 0.
Thus,(substring-no-properties string) returns a copy of string, with all text
properties removed.

Chapter 4: Strings and Characters

57

concat &rest sequences[Function]
This function returns a string consisting of the characters in the arguments passed toit (along with their text properties, if any). The arguments may be strings, lists ofnumbers, or vectors of numbers; they are not themselves changed. If concat receives
no arguments, it returns an empty string.
(concat "abc" "-def")⇒ "abc-def"(concat "abc" (list 120 121) [122])⇒ "abcxyz";; nil is an empty sequence.
(concat "abc" nil "-def")⇒ "abc-def"(concat "The " "quick brown " "fox.")⇒ "The quick brown fox."(concat)⇒ ""This function does not always allocate a new string. Callers are advised not rely on
the result being a new string nor on it being eq to an existing string.
In particular, mutating the returned value may inadvertently change another string,alter a constant string in the program, or even raise an error. To obtain a string thatyou can safely mutate, use copy-sequence on the result.
For information about other concatenation functions, see the description of mapconcat
in Section 13.6 [Mapping Functions], page 241, vconcat in Section 6.5 [Vector Functions], page 118, and append in Section 5.4 [Building Lists], page 82. For concatenating
individual command-line arguments into a string to be used as a shell command, see
Section 40.2 [Shell Arguments], page 1080.

split-string string &optional separators omit-nulls trim

[Function]
This function splits string into substrings based on the regular expression separators(see Section 35.3 [Regular Expressions], page 995). Each match for separators defines
a splitting point; the substrings between splitting points are made into a list, which isreturned.
If separators is nil (or omitted), the default is the value of split-string-defaultseparators and the function behaves as if omit-nulls were t.
If omit-nulls is nil (or omitted), the result contains null strings whenever there are
two consecutive matches for separators, or a match is adjacent to the beginning or
end of string. If omit-nulls is t, these null strings are omitted from the result.
If the optional argument trim is non-nil, it should be a regular expression to matchtext to trim from the beginning and end of each substring. If trimming makes thesubstring empty, it is treated as null.
If you need to split a string into a list of individual command-line arguments suitablefor call-process or start-process, see Section 40.2 [Shell Arguments], page 1080.
Examples:(split-string " two words ")⇒ ("two" "words")

Chapter 4: Strings and Characters

58

The result is not ("" "two" "words" ""), which would rarely be useful. If you needsuch a result, use an explicit value for separators:(split-string " two words "split-string-default-separators)⇒ ("" "two" "words" "")(split-string "Soup is good food" "o")⇒ ("S" "up is g" "" "d f" "" "d")(split-string "Soup is good food" "o" t)⇒ ("S" "up is g" "d f" "d")(split-string "Soup is good food" "o+")⇒ ("S" "up is g" "d f" "d")Empty matches do count, except that split-string will not look for a final empty
match when it already reached the end of the string using a non-empty match or when
string is empty:(split-string "aooob" "o*")⇒ ("" "a" "" "b" "")(split-string "ooaboo" "o*")⇒ ("" "" "a" "b" "")(split-string "" "")⇒ ("")
However, when separators can match the empty string, omit-nulls is usually t, so thatthe subtleties in the three previous examples are rarely relevant:(split-string "Soup is good food" "o*" t)⇒ ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d")(split-string "Nice doggy!" "" t)⇒ ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!")
(split-string "" "" t)⇒ nil
Somewhat odd, but predictable, behavior can occur for certain “non-greedy” valuesof separators that can prefer empty matches over non-empty matches. Again, suchvalues rarely occur in practice:(split-string "ooo" "o*" t)⇒ nil(split-string "ooo" "\\|o+" t)⇒ ("o" "o" "o")split-string-default-separators
The default value of separators for split-string.
"[ \f\t\n\r\v]+".

string-clean-whitespace string[Variable]
Its usual value is[Function]
Clean up the whitespace in string by collapsing stretches of whitespace to a single
space character, as well as removing all whitespace from the start and the end ofstring.

Chapter 4: Strings and Characters

59

string-trim-left string &optional regexp[Function]
Remove the leading text that matches regexp from string. regexp defaults to ‘[\t\n\r]+’.

string-trim-right string &optional regexp[Function]
Remove the trailing text that matches regexp from string. regexp defaults to ‘[\t\n\r]+’.

string-trim string &optional trim-left trim-right[Function]
Remove the leading text that matches trim-left and trailing text that matches trimright from string. Both regexps default to ‘[ \t\n\r]+’.

string-fill string length[Function]
Attempt to Word-wrap string so that no lines are longer than length. Filling is doneon whitespace boundaries only. If there are individual words that are longer thanlength, these will not be shortened.

string-limit string length &optional end coding-system[Function]
If string is shorter than length characters, string is returned as is. Otherwise, returna substring of string consisting of the first length characters. If the optional end
parameter is given, return a string of the length last characters instead.
If coding-system is non-nil, string will be encoded before limiting, and the result will
be a unibyte string that’s shorter than length bytes. If string contains charactersthat are encoded into several bytes (for instance, when using utf-8), the resulting
unibyte string is never truncated in the middle of a character representation.

This function measures the string length in characters or bytes, and thus isgenerally inappropriate if you need to shorten strings for display purposes; usetruncate-string-to-width or window-text-pixel-size or string-glyph-split
instead (see Section 41.10 [Size of Displayed Text], page 1157).

string-lines string &optional omit-nulls keep-newlines[Function]
Split string into a list of strings on newline boundaries. If the optional argument
omit-nulls is non-nil, remove empty lines from the results. If the optional argumentkeep-newlines is non-nil, don’t remove the trailing newlines from the result strings.

string-pad string length &optional padding start[Function]
Pad string to be of the given length using padding as the padding character. padding
defaults to the space character. If string is longer than length, no padding is done. If
start is nil or omitted, the padding is appended to the characters of string, and if it’s
non-nil, the padding is prepended to string’s characters.

string-chop-newline string[Function]

Remove the final newline, if any, from string.

4.4 Modifying Strings
You can alter the contents of a mutable string via operations described in this section. See
Section 2.9 [Mutability], page 36.

Chapter 4: Strings and Characters

60

The most basic way to alter the contents of an existing string is with aset (see Section 6.3[Array Functions], page 116). (aset string idx char) stores char into string at character
index idx. It will automatically convert a pure-ASCII string to a multibyte string (seeSection 34.1 [Text Representations], page 963) if needed, but we recommend to always makesure string is multibyte (e.g., by using string-to-multibyte, see Section 34.3 [Converting
Representations], page 965), if char is a non-ASCII character, not a raw byte.
A more powerful function is store-substring:

store-substring string idx obj[Function]
This function alters part of the contents of the specified string, by storing obj startingat character index idx. The argument obj may be either a character (in which case thefunction behaves exactly as aset) or a (smaller) string. If obj is a multibyte string,
we recommend to make sure string is also multibyte, even if it’s pure-ASCII.
Since it is impossible to change the number of characters in an existing string, it is anerror if obj consists of more characters than would fit in string starting at character
index idx.

To clear out a string that contained a password, use clear-string:clear-string string[Function]
This makes string a unibyte string and clears its contents to zeros. It may also change
string’s length.

4.5 Comparison of Characters and Strings
char-equal character1 character2[Function]
This function returns t if the arguments represent the same character, nil otherwise.
This function ignores differences in case if case-fold-search is non-nil.
(char-equal ?x ?x)⇒ t(let ((case-fold-search nil))(char-equal ?x ?X))⇒ nilstring= string1 string2[Function]
This function returns t if the characters of the two strings match exactly. Symbols arealso allowed as arguments, in which case the symbol names are used. Case is always
significant, regardless of case-fold-search.
This function is equivalent to equal for comparing two strings (see Section 2.8 [Equality
Predicates], page 34). In particular, the text properties of the two strings are ignored;
use equal-including-properties if you need to distinguish between strings thatdiffer only in their text properties. However, unlike equal, if either argument is not astring or symbol, string= signals an error.
(string= "abc" "abc")⇒ t(string= "abc" "ABC")⇒ nil

Chapter 4: Strings and Characters

61(string= "ab" "ABC")⇒ nil
A unibyte and a multibyte string are equal in the sense of string= if and only if they
contain the same sequence of character codes all being in the range 0–127 (ASCII).
See Section 34.1 [Text Representations], page 963.

string-equal string1 string2[Function]

string-equal is another name for string=.

string-equal-ignore-case string1 string2[Function]
string-equal-ignore-case compares strings ignoring case differences, likechar-equal when case-fold-search is t.

string-collate-equalp string1 string2 &optional locale ignore-case[Function]
This function returns t if string1 and string2 are equal with respect to the collation
rules of the specified locale, which defaults to your current system locale. A collation
rule is not only determined by the lexicographic order of the characters contained instring1 and string2, but also by further rules about relations between these characters.
Usually, it is defined by the locale environment with which Emacs is running and by
the Standard C library against which Emacs was linked1 .
For example, characters with different code points but the same meaning, like different
grave accent Unicode characters, might, in some locales, be considered as equal:(string-collate-equalp (string ?\uFF40) (string ?\u1FEF))⇒ t
The optional argument locale, a string, overrides the setting of your current locale
identifier for collation. The value is system dependent; a locale "en_US.UTF-8"
is applicable on POSIX systems, while it would be, e.g., "enu_USA.1252" on MSWindows systems.
If ignore-case is non-nil, characters are compared case-insensitively, by convertingthem to lower-case. However, if the underlying system library doesn’t provide localespecific collation rules, this function falls back to string-equal, in which case theignore-case argument is ignored, and the comparison will always be case-sensitive.
To emulate Unicode-compliant collation on MS-Windows systems, bind w32-collateignore-punctuation to a non-nil value, since the codeset part of the locale cannot
be "UTF-8" on MS-Windows.
If your system does not support a locale environment, this function behaves likestring-equal.
Do not use this function to compare file names for equality, as filesystems generally
don’t honor linguistic equivalence of strings that collation implements.

string< string1 string2[Function]
This function compares two strings a character at a time. It scans both the strings at
the same time to find the first pair of corresponding characters that do not match. If

1

For more information about collation rules and their locale dependencies, see The Unicode Collation
Algorithm (https://unicode.org/reports/tr10/). Some Standard C libraries, such as the GNU C
Library (a.k.a. glibc) implement large portions of the Unicode Collation Algorithm and use the associatedlocale data, Common Locale Data Repository, or CLDR.

Chapter 4: Strings and Characters62

the lesser character of these two is the character from string1, then string1 is less, andthis function returns t. If the lesser character is the one from string2, then string1 isgreater, and this function returns nil. If the two strings match entirely, the value isnil.
Pairs of characters are compared according to their character codes. Keep in mind
that lower case letters have higher numeric values in the ASCII character set thantheir upper case counterparts; digits and many punctuation characters have a lower
numeric value than upper case letters. An ASCII character is less than any non-ASCII
character; a unibyte non-ASCII character is always less than any multibyte non-ASCII
character (see Section 34.1 [Text Representations], page 963).
(string< "abc" "abd")⇒ t(string< "abd" "abc")⇒ nil(string< "123" "abc")⇒ tWhen the strings have different lengths, and they match up to the length of string1,
then the result is t. If they match up to the length of string2, the result is nil. A
string of no characters is less than any other string.
(string< "" "abc")⇒ t(string< "ab" "abc")⇒ t(string< "abc" "")⇒ nil(string< "abc" "ab")⇒ nil(string< "" "")⇒ nil
Symbols are also allowed as arguments, in which case their print names are compared.

string-lessp string1 string2[Function]

string-lessp is another name for string<.

string-greaterp string1 string2[Function]
This function returns the result of comparing string1 and string2 in the opposite order,i.e., it is equivalent to calling (string-lessp string2 string1).

string-collate-lessp string1 string2 &optional locale ignore-case[Function]
This function returns t if string1 is less than string2 in collation order of the specified
locale, which defaults to your current system locale. A collation order is not only
determined by the lexicographic order of the characters contained in string1 andstring2, but also by further rules about relations between these characters. Usually,
it is defined by the locale environment with which Emacs is running, and by theStandard C library against which Emacs was linked.
For example, punctuation and whitespace characters might be ignored for sorting (seeSection 6.1 [Sequence Functions], page 102):

Chapter 4: Strings and Characters

63(sort (list "11" "12" "1 1" "1 2" "1.1" "1.2") 'string-collate-lessp)⇒ ("11" "1 1" "1.1" "12" "1 2" "1.2")
This behavior is system-dependent; e.g., punctuation and whitespace are never ignored
on Cygwin, regardless of locale.
The optional argument locale, a string, overrides the setting of your current locale
identifier for collation. The value is system dependent; a locale "en_US.UTF-8"
is applicable on POSIX systems, while it would be, e.g., "enu_USA.1252" on MSWindows systems. The locale value of "POSIX" or "C" lets string-collate-lessp
behave like string-lessp:(sort (list "11" "12" "1 1" "1 2" "1.1" "1.2")(lambda (s1 s2) (string-collate-lessp s1 s2 "POSIX")))⇒ ("1 1" "1 2" "1.1" "1.2" "11" "12")
If ignore-case is non-nil, characters are compared case-insensitively, by convertingthem to lower-case. However, if the underlying system library doesn’t provide localespecific collation rules, this function falls back to string-lessp, in which case theignore-case argument is ignored, and the comparison will always be case-sensitive.
To emulate Unicode-compliant collation on MS-Windows systems, bind w32-collateignore-punctuation to a non-nil value, since the codeset part of the locale cannot
be "UTF-8" on MS-Windows.
If your system does not support a locale environment, this function behaves likestring-lessp.

string-version-lessp string1 string2[Function]
This function compares strings lexicographically, except it treats sequences of numericalcharacters as if they comprised a base-ten number, and then compares the numbers.
So ‘foo2.png’ is “smaller” than ‘foo12.png’ according to this predicate, even if ‘12’is lexicographically “smaller” than ‘2’.

string-prefix-p string1 string2 &optional ignore-case[Function]
This function returns non-nil if string1 is a prefix of string2; i.e., if string2 starts
with string1. If the optional argument ignore-case is non-nil, the comparison ignorescase differences.

string-suffix-p suffix string &optional ignore-case[Function]
This function returns non-nil if suffix is a suffix of string; i.e., if string ends with
suffix. If the optional argument ignore-case is non-nil, the comparison ignores casedifferences.

string-search needle haystack &optional start-pos[Function]
Return the position of the first instance of needle in haystack, both of which are strings.
If start-pos is non-nil, start searching from that position in haystack. Return nil if
no match was found. This function only considers the characters in the strings when
doing the comparison; text properties are ignored. Matching is always case-sensitive.

compare-strings string1 start1 end1 string2 start2 end2 &optional
ignore-case[Function]

This function compares a specified part of string1 with a specified part of string2.
The specified part of string1 runs from index start1 (inclusive) up to index end1

Chapter 4: Strings and Characters64(exclusive); nil for start1 means the start of the string, while nil for end1 means thelength of the string. Likewise, the specified part of string2 runs from index start2 up
to index end2.
The strings are compared by the numeric values of their characters. For instance, str1
is considered less than str2 if its first differing character has a smaller numeric value.
If ignore-case is non-nil, characters are converted to upper-case, using the current
buffer’s case-table (see Section 4.10 [Case Tables], page 74), before comparing them.
Unibyte strings are converted to multibyte for comparison (see Section 34.1 [Text
Representations], page 963), so that a unibyte string and its conversion to multibyte
are always regarded as equal.
If the specified portions of the two strings match, the value is t. Otherwise, the value
is an integer which indicates how many leading characters agree, and which string isless. Its absolute value is one plus the number of characters that agree at the beginningof the two strings. The sign is negative if string1 (or its specified portion) is less.

string-distance string1 string2 &optional bytecompare[Function]
This function returns the Levenshtein distance between the source string string1 andthe target string string2. The Levenshtein distance is the number of single-characterchanges—deletions, insertions, or replacements—required to transform the source
string into the target string; it is one possible definition of the edit distance between
strings.
Letter-case of the strings is significant for the computed distance, but their text
properties are ignored. If the optional argument bytecompare is non-nil, the function
calculates the distance in terms of bytes instead of characters. The byte-wise comparison uses the internal Emacs representation of characters, so it will produce inaccurate
results for multibyte strings that include raw bytes (see Section 34.1 [Text Representations], page 963); make the strings unibyte by encoding them (see Section 34.10.7[Explicit Encoding], page 988) if you need accurate results with raw bytes.

assoc-string key alist &optional case-fold[Function]
This function works like assoc, except that key must be a string or symbol, andcomparison is done using compare-strings. Symbols are converted to strings before
testing. If case-fold is non-nil, key and the elements of alist are converted to uppercase before comparison. Unlike assoc, this function can also match elements of thealist that are strings or symbols rather than conses. In particular, alist can be a listof strings or symbols rather than an actual alist. See Section 5.8 [Association Lists],
page 95.

See also the function compare-buffer-substrings in Section 33.3 [Comparing Text],
page 882, for a way to compare text in buffers. The function string-match, which matchesa regular expression against a string, can be used for a kind of string comparison; see
Section 35.4 [Regexp Search], page 1008.

4.6 Conversion of Characters and Strings
This section describes functions for converting between characters, strings and integers.
format (see Section 4.7 [Formatting Strings], page 66) and prin1-to-string (seeSection 20.5 [Output Functions], page 377) can also convert Lisp objects into strings.

Chapter 4: Strings and Characters65

read-from-string (see Section 20.3 [Input Functions], page 374) can convert a string
representation of a Lisp object into an object. The functions string-to-multibyte
and string-to-unibyte convert the text representation of a string (see Section 34.3
[Converting Representations], page 965).
See Chapter 25 [Documentation], page 595, for functions that produce textual descriptionsof text characters and general input events (single-key-description and text-chardescription). These are used primarily for making help messages.

number-to-string number[Function]
This function returns a string consisting of the printed base-ten representation of
number. The returned value starts with a minus sign if the argument is negative.
(number-to-string 256)
⇒ "256"(number-to-string -23)
⇒ "-23"(number-to-string -23.5)⇒ "-23.5"
int-to-string is a semi-obsolete alias for this function.
See also the function format in Section 4.7 [Formatting Strings], page 66.

string-to-number string &optional base

[Function]
This function returns the numeric value of the characters in string. If base is non-nil,
it must be an integer between 2 and 16 (inclusive), and integers are converted in thatbase. If base is nil, then base ten is used. Floating-point conversion only works inbase ten; we have not implemented other radices for floating-point numbers, becausethat would be much more work and does not seem useful.
The parsing skips spaces and tabs at the beginning of string, then reads as much ofstring as it can interpret as a number in the given base. (On some systems it ignores
other whitespace at the beginning, not just spaces and tabs.) If string cannot beinterpreted as a number, this function returns 0.
(string-to-number "256")⇒ 256(string-to-number "25 is a perfect square.")⇒ 25(string-to-number "X256")⇒ 0(string-to-number "-4.5")⇒ -4.5(string-to-number "1e5")⇒ 100000.0
string-to-int is an obsolete alias for this function.

char-to-string character[Function]
This function returns a new string containing one character, character. This function
is semi-obsolete because the function string is more general. See Section 4.3 [Creating
Strings], page 55.

Chapter 4: Strings and Characters

66

string-to-char string[Function]
This function returns the first character in string. This is mostly identical to(aref string 0), except that it returns 0 if the string is empty. (The value isalso 0 when the first character of string is the null character, ASCII code 0.) Thisfunction may be eliminated in the future if it does not seem useful enough to retain.

Here are some other functions that can convert to or from a string:
concatThis function converts a vector or a list into a string. See Section 4.3 [Creating
Strings], page 55.

vconcatThis function converts a string into a vector. See Section 6.5 [Vector Functions],
page 118.

appendThis function converts a string into a list. See Section 5.4 [Building Lists],
page 82.

byte-to-string
This function converts a byte of character data into a unibyte string. See
Section 34.3 [Converting Representations], page 965.

4.7 Formatting Strings
Formatting means constructing a string by substituting computed values at various places
in a constant string. This constant string controls how the other values are printed, as wellas where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In fact, the functions
message and error provide the same formatting feature described here; they differ fromformat-message only in how they use the result of formatting.

format string &rest objects[Function]
This function returns a string equal to string, replacing any format specifications withencodings of the corresponding objects. The arguments objects are the computed
values to be formatted.
The characters in string, other than the format specifications, are copied directly
into the output, including their text properties, if any. Any text properties of theformat specifications are copied to the produced string representations of the argument
objects.
The output string need not be newly-allocated. For example, if x is the string "foo",
the expressions (eq x (format x)) and (eq x (format "%s" x)) might both yield t.

format-message string &rest objects[Function]
This function acts like format, except it also converts any grave accents (‘) andapostrophes (’) in string as per the value of text-quoting-style.
Typically grave accent and apostrophe in the format translate to matching curved
quotes, e.g., "Missing ‘%s’" might result in "Missing ‘foo’". See Section 25.4
[Text Quoting Style], page 600, for how to influence or inhibit this translation.

Chapter 4: Strings and Characters

67

A format specification is a sequence of characters beginning with a ‘%’. Thus, if there isa ‘%d’ in string, the format function replaces it with the printed representation of one of thevalues to be formatted (one of the arguments objects). For example:(format "The value of fill-column is %d." fill-column)⇒ "The value of fill-column is 72."
Since format interprets ‘%’ characters as format specifications, you should never pass anarbitrary string as the first argument. This is particularly true when the string is generated
by some Lisp code. Unless the string is known to never include any ‘%’ characters, pass"%s", described below, as the first argument, and the string as the second, like this:(format "%s" arbitrary-string)
Certain format specifications require values of particular types. If you supply a valuethat doesn’t fit the requirements, an error is signaled.
Here is a table of valid format specifications:‘%s’

Replace the specification with the printed representation of the object, madewithout quoting (that is, using princ, not prin1—see Section 20.5 [Output
Functions], page 377). Thus, strings are represented by their contents alone,with no ‘"’ characters, and symbols appear without ‘\’ characters.
If the object is a string, its text properties are copied into the output. The text
properties of the ‘%s’ itself are also copied, but those of the object take priority.

‘%S’

Replace the specification with the printed representation of the object, made withquoting (that is, using prin1—see Section 20.5 [Output Functions], page 377).
Thus, strings are enclosed in ‘"’ characters, and ‘\’ characters appear where
necessary before special characters.

‘%o’Replace the specification with the base-eight representation of an integer. Negative integers are formatted in a platform-dependent way. The object can also bea floating-point number that is formatted as an integer, dropping any fraction.

‘%d’

Replace the specification with the base-ten representation of a signed integer.
The object can also be a floating-point number that is formatted as an integer,
dropping any fraction.

‘%x’
‘%X’

Replace the specification with the base-sixteen representation of an integer.
Negative integers are formatted in a platform-dependent way. ‘%x’ uses lower
case and ‘%X’ uses upper case. The object can also be a floating-point numberthat is formatted as an integer, dropping any fraction.

‘%c’

Replace the specification with the character which is the value given.

‘%e’

Replace the specification with the exponential notation for a floating-point
number.

‘%f’

Replace the specification with the decimal-point notation for a floating-point
number.

‘%g’

Replace the specification with notation for a floating-point number, using either
exponential notation or decimal-point notation. The exponential notation isChapter 4: Strings and Characters68

used if the exponent would be less than −4 or greater than or equal to theprecision (default: 6). By default, trailing zeros are removed from the fractional
portion of the result and a decimal-point character appears only if it is followed
by a digit.
‘%%’

Replace the specification with a single ‘%’. This format specification is unusualin that its only form is plain ‘%%’ and that it does not use a value. For example,(format "%% %d" 30) returns "% 30".

Any other format character results in an ‘Invalid format operation’ error.
Here are several examples, which assume the typical text-quoting-style settings:(format "The octal value of %d is %o,and the hex value is %x." 18 18 18)⇒ "The octal value of 18 is 22,
and the hex value is 12."
(format-message"The name of this buffer is ‘%s’." (buffer-name))⇒ "The name of this buffer is ‘strings.texi’."(format-message"The buffer object prints as `%s'." (current-buffer))⇒ "The buffer object prints as ‘strings.texi’."
By default, format specifications correspond to successive values from objects. Thus, thefirst format specification in string uses the first such value, the second format specification
uses the second such value, and so on. Any extra format specifications (those for which there
are no corresponding values) cause an error. Any extra values to be formatted are ignored.
A format specification can have a field number, which is a decimal number immediately
after the initial ‘%’, followed by a literal dollar sign ‘$’. It causes the format specification toconvert the argument with the given number instead of the next argument. Field numbers
start at 1. A format can contain either numbered or unnumbered format specifications but
not both, except that ‘%%’ can be mixed with numbered specifications.
(format "%2$s, %3$s, %%, %1$s" "x" "y" "z")⇒ "y, z, %, x"
After the ‘%’ and any field number, you can put certain flag characters.
The flag ‘+’ inserts a plus sign before a nonnegative number, so that it always has asign. A space character as flag inserts a space before a nonnegative number. (Otherwise,
nonnegative numbers start with the first digit.) These flags are useful for ensuring that
nonnegative and negative numbers use the same number of columns. They are ignored
except for ‘%d’, ‘%e’, ‘%f’, ‘%g’, and if both flags are used, ‘+’ takes precedence.
The flag ‘#’ specifies an alternate form which depends on the format in use. For ‘%o’, it
ensures that the result begins with a ‘0’. For ‘%x’ and ‘%X’, it prefixes nonzero results with‘0x’ or ‘0X’. For ‘%e’ and ‘%f’, the ‘#’ flag means include a decimal point even if the precision
is zero. For ‘%g’, it always includes a decimal point, and also forces any trailing zeros after
the decimal point to be left in place where they would otherwise be removed.

Chapter 4: Strings and Characters

69

The flag ‘0’ ensures that the padding consists of ‘0’ characters instead of spaces. This
flag is ignored for non-numerical specification characters like ‘%s’, ‘%S’ and ‘%c’. These
specification characters accept the ‘0’ flag, but still pad with spaces.
The flag ‘-’ causes any padding inserted by the width, if specified, to be inserted on theright rather than the left. If both ‘-’ and ‘0’ are present, the ‘0’ flag is ignored.
(format "%06d is padded on the left with zeros" 123)
⇒ "000123 is padded on the left with zeros"(format "'%-6d' is padded on the right" 123)⇒ "'123' is padded on the right"(format "The word '%-7s' actually has %d letters in it.""foo" (length "foo"))⇒ "The word 'foo
' actually has 3 letters in it."A specification can have a width, which is a decimal number that appears after any field
number and flags. If the printed representation of the object contains fewer characters than
this width, format extends it with padding. Any padding introduced by the width normallyconsists of spaces inserted on the left:(format "%5d is padded on the left with spaces" 123)⇒ " 123 is padded on the left with spaces"
If the width is too small, format does not truncate the object’s printed representation. Thus,
you can use a width to specify a minimum spacing between columns with no risk of losing
information. In the following two examples, ‘%7s’ specifies a minimum width of 7. In thefirst case, the string inserted in place of ‘%7s’ has only 3 letters, and needs 4 blank spaces
as padding. In the second case, the string "specification" is 13 letters wide but is nottruncated.
(format "The word '%7s' has %d letters in it.""foo" (length "foo"))⇒ "The word 'foo' has 3 letters in it."(format "The word '%7s' has %d letters in it."
"specification" (length "specification"))⇒ "The word 'specification' has 13 letters in it."All the specification characters allow an optional precision after the field number, flags
and width, if present. The precision is a decimal-point ‘.’ followed by a digit-string. For
the floating-point specifications (‘%e’ and ‘%f’), the precision specifies how many digits
following the decimal point to show; if zero, the decimal-point itself is also omitted. For ‘%g’,
the precision specifies how many significant digits to show (significant digits are the first
digit before the decimal point and all the digits after it). If the precision of %g is zero or
unspecified, it is treated as 1. For ‘%s’ and ‘%S’, the precision truncates the string to thegiven width, so ‘%.3s’ shows only the first three characters of the representation for object.
For other specification characters, the effect of precision is what the local library functionsof the printf family produce.
If you plan to use read later on the formatted string to retrieve a copy of the formatted
value, use a specification that lets read reconstruct the value. To format numbers in thisreversible way you can use ‘%s’ and ‘%S’, to format just integers you can also use ‘%d’, and toChapter 4: Strings and Characters70

format just nonnegative integers you can also use ‘#x%x’ and ‘#o%o’. Other formats may beproblematic; for example, ‘%d’ and ‘%g’ can mishandle NaNs and can lose precision and type,and ‘#x%x’ and ‘#o%o’ can mishandle negative integers. See Section 20.3 [Input Functions],
page 374.
The functions described in this section accept a fixed set of specification characters.
The next section describes a function format-spec which can accept custom specification
characters, such as ‘%a’ or ‘%z’.

4.8 Custom Format Strings
Sometimes it is useful to allow users and Lisp programs alike to control how certain text
is generated via custom format control strings. For example, a format string could control
how to display someone’s forename, surname, and email address. Using the function format
described in the previous section, the format string could be something like "%s %s <%s>".
This approach quickly becomes impractical, however, as it can be unclear which specification
character corresponds to which piece of information.
A more convenient format string for such cases would be something like "%f %l <%e>",where each specification character carries more semantic information and can easily berearranged relative to other specification characters, making such format strings more easily
customizable by the user.
The function format-spec described in this section performs a similar function to format,
except it operates on format control strings that use arbitrary specification characters.

format-spec template spec-alist &optional ignore-missing split[Function]
This function returns a string produced from the format string template according
to conversions specified in spec-alist, which is an alist (see Section 5.8 [Association
Lists], page 95) of the form (letter . replacement). Each specification %letter intemplate will be replaced by replacement when formatting the resulting string.
The characters in template, other than the format specifications, are copied directly
into the output, including their text properties, if any. Any text properties of theformat specifications are copied to their replacements.
Using an alist to specify conversions gives rise to some useful properties:• If spec-alist contains more unique letter keys than there are unique specification
characters in template, the unused keys are simply ignored.
• If spec-alist contains more than one association with the same letter, the closest
one to the start of the list is used.
• If template contains the same specification character more than once, then thesame replacement found in spec-alist is used as a basis for all of that character’s
substitutions.
• The order of specifications in template need not correspond to the order ofassociations in spec-alist.
REPLACEMENT can also be a function taking no arguments, and returning a string
to be used for the replacement. It will only be called when the corresponding LETTER
is used in the TEMPLATE. This is useful, for example, to avoid prompting for input
unless it is needed.

Chapter 4: Strings and Characters71

The optional argument ignore-missing indicates how to handle specification charactersin template that are not found in spec-alist. If it is nil or omitted, the function signals
an error; if it is ignore, those format specifications are left verbatim in the output,
including their text properties, if any; if it is delete, those format specifications are
removed from the output; any other non-nil value is handled like ignore, but any
occurrences of ‘%%’ are also left verbatim in the output.
If the optional argument split is non-nil, instead of returning a single string,format-spec will split the result into a list of strings, based on where thesubstitutions were performed. For instance:(format-spec "foo %b bar" '((?b . "zot")) nil t)⇒ ("foo " "zot" " bar")
The syntax of format specifications accepted by format-spec is similar, but not identical,
to that accepted by format. In both cases, a format specification is a sequence of charactersbeginning with ‘%’ and ending with an alphabetic letter such as ‘s’.
Unlike format, which assigns specific meanings to a fixed set of specification characters,
format-spec accepts arbitrary specification characters and treats them all equally. For
example:(setq my-site-info(list (cons ?s system-name)(cons ?t (symbol-name system-type))(cons ?c system-configuration)(cons ?v emacs-version)(cons ?e invocation-name)(cons ?p (number-to-string (emacs-pid)))(cons ?a user-mail-address)(cons ?n user-full-name)))(format-spec "%e %v (%c)" my-site-info)⇒ "emacs 27.1 (x86_64-pc-linux-gnu)"(format-spec "%n <%a>" my-site-info)⇒ "Emacs Developers <emacs-devel@gnu.org>"
A format specification can include any number of the following flag characters immediately
after the ‘%’ to modify aspects of the substitution.
‘0’This flag causes any padding specified by the width to consist of ‘0’ charactersinstead of spaces.

‘-’

This flag causes any padding specified by the width to be inserted on the rightrather than the left.

‘<’

This flag causes the substitution to be truncated on the left to the given widthand precision, if specified.

‘>’This flag causes the substitution to be truncated on the right to the given widthand precision, if specified.

Chapter 4: Strings and Characters

‘^’

72

This flag converts the substituted text to upper case (see Section 4.9 [CaseConversion], page 72).

‘_ (underscore)’This flag converts the substituted text to lower case (see Section 4.9 [CaseConversion], page 72).
The result of using contradictory flags (for instance, both upper and lower case) is
undefined.
As is the case with format, a format specification can include a width, which is a decimal
number that appears after any flags, and a precision, which is a decimal-point ‘.’ followed
by a decimal number that appears after any flags and width.
If a substitution contains fewer characters than its specified width, it is padded on theleft:(format-spec "%8a is padded on the left with spaces"'((?a . "alpha")))⇒ "alpha is padded on the left with spaces"
If a substitution contains more characters than its specified precision, it is truncated on
the right:(format-spec "%.2a is truncated on the right"'((?a . "alpha")))⇒ "al is truncated on the right"
Here is a more complicated example that combines several aforementioned features:(setq my-battery-info(list (cons ?p "73"); Percentage(cons ?L "Battery") ; Status(cons ?t "2:23"); Remaining time(cons ?c "24330"); Capacity(cons ?r "10.6"))) ; Rate of discharge(format-spec "%>^-3L : %3p%% (%05t left)" my-battery-info)⇒ "BAT : 73% (02:23 left)"(format-spec "%>^-3L : %3p%% (%05t left)"(cons (cons ?L "AC")my-battery-info))⇒ "AC : 73% (02:23 left)"
As the examples in this section illustrate, format-spec is often used for selectively
formatting an assortment of different pieces of information. This is useful in programs thatprovide user-customizable format strings, as the user can choose to format with a regularsyntax and in any desired order only a subset of the information that the program makes
available.

4.9 Case Conversion in Lisp
The character case functions change the case of single characters or of the contents of strings.
The functions normally convert only alphabetic characters (the letters ‘A’ through ‘Z’ and ‘a’Chapter 4: Strings and Characters73

through ‘z’, as well as non-ASCII letters); other characters are not altered. You can specify adifferent case conversion mapping by specifying a case table (see Section 4.10 [Case Tables],page 74).
These functions do not modify the strings that are passed to them as arguments.
The examples below use the characters ‘X’ and ‘x’ which have ASCII codes 88 and 120
respectively.

downcase string-or-char[Function]
This function converts string-or-char, which should be either a character or a string,
to lower case.
When string-or-char is a string, this function returns a new string in which each letterin the argument that is upper case is converted to lower case. When string-or-char isa character, this function returns the corresponding lower case character (an integer);if the original character is lower case, or is not a letter, the return value is equal tothe original character.
(downcase "The cat in the hat")⇒ "the cat in the hat"(downcase ?X)⇒ 120

upcase string-or-char[Function]
This function converts string-or-char, which should be either a character or a string,
to upper case.
When string-or-char is a string, this function returns a new string in which each letterin the argument that is lower case is converted to upper case. When string-or-char isa character, this function returns the corresponding upper case character (an integer);if the original character is upper case, or is not a letter, the return value is equal tothe original character.
(upcase "The cat in the hat")⇒ "THE CAT IN THE HAT"
(upcase ?x)⇒ 88

capitalize string-or-char[Function]
This function capitalizes strings or characters. If string-or-char is a string, the function
returns a new string whose contents are a copy of string-or-char in which each word
has been capitalized. This means that the first character of each word is converted toupper case, and the rest are converted to lower case.
The definition of a word is any sequence of consecutive characters that are assigned
to the word constituent syntax class in the current syntax table (see Section 36.2.1[Syntax Class Table], page 1023).
When string-or-char is a character, this function does the same thing as upcase.
(capitalize "The cat in the hat")⇒ "The Cat In The Hat"

Chapter 4: Strings and Characters74(capitalize "THE 77TH-HATTED CAT")⇒ "The 77th-Hatted Cat"(capitalize ?x)⇒ 88

upcase-initials string-or-char[Function]
If string-or-char is a string, this function capitalizes the initials of the words in stringor-char, without altering any letters other than the initials. It returns a new string
whose contents are a copy of string-or-char, in which each word has had its initialletter converted to upper case.
The definition of a word is any sequence of consecutive characters that are assigned
to the word constituent syntax class in the current syntax table (see Section 36.2.1[Syntax Class Table], page 1023).
When the argument to upcase-initials is a character, upcase-initials has thesame result as upcase.
(upcase-initials "The CAT in the hAt")⇒ "The CAT In The HAt"

Note that case conversion is not a one-to-one mapping of codepoints and length of theresult may differ from length of the argument. Furthermore, because passing a character
forces return type to be a character, functions are unable to perform proper substitution
and result may differ compared to treating a one-character string. For example:(upcase "fi") ; note: single character, ligature "fi"⇒ "FI"(upcase ?fi)
⇒ 64257 ; i.e. ?fi
To avoid this, a character must first be converted into a string, using string function,
before being passed to one of the casing functions. Of course, no assumptions on the lengthof the result may be made.
Mapping for such special cases are taken from special-uppercase, special-lowercase
and special-titlecase See Section 34.6 [Character Properties], page 968.
See Section 4.5 [Text Comparison], page 60, for functions that compare strings; some ofthem ignore case differences, or can optionally ignore case differences.

4.10 The Case Table
You can customize case conversion by installing a special case table. A case table specifies
the mapping between upper case and lower case letters. It affects both the case conversion
functions for Lisp objects (see the previous section) and those that apply to text in thebuffer (see Section 33.18 [Case Changes], page 916). Each buffer has a case table; there isalso a standard case table which is used to initialize the case table of new buffers.
A case table is a char-table (see Section 6.6 [Char-Tables], page 119) whose subtype
is case-table. This char-table maps each character into the corresponding lower casecharacter. It has three extra slots, which hold related tables:

Chapter 4: Strings and Characters

upcase75

The upcase table maps each character into the corresponding upper case character.

canonicalize
The canonicalize table maps all of a set of case-related characters into a particularmember of that set.
equivalences
The equivalences table maps each one of a set of case-related characters into
the next character in that set.
In simple cases, all you need to specify is the mapping to lower-case; the three related
tables will be calculated automatically from that one.
For some languages, upper and lower case letters are not in one-to-one correspondence.
There may be two different lower case letters with the same upper case equivalent. In thesecases, you need to specify the maps for both lower case and upper case.
The extra table canonicalize maps each character to a canonical equivalent; any two
characters that are related by case-conversion have the same canonical equivalent character.
For example, since ‘a’ and ‘A’ are related by case-conversion, they should have the same
canonical equivalent character (which should be either ‘a’ for both of them, or ‘A’ for bothof them).
The extra table equivalences is a map that cyclically permutes each equivalence class(of characters with the same canonical equivalent). (For ordinary ASCII, this would map ‘a’into ‘A’ and ‘A’ into ‘a’, and likewise for each set of equivalent characters.)
When constructing a case table, you can provide nil for canonicalize; then Emacs fills
in this slot from the lower case and upper case mappings. You can also provide nil forequivalences; then Emacs fills in this slot from canonicalize. In a case table that is actuallyin use, those components are non-nil. Do not try to specify equivalences without also
specifying canonicalize.
Here are the functions for working with case tables:

case-table-p object[Function]

This predicate returns non-nil if object is a valid case table.

set-standard-case-table table[Function]
This function makes table the standard case table, so that it will be used in any buffers
created subsequently.

standard-case-table[Function]

This returns the standard case table.

current-case-table[Function]

This function returns the current buffer’s case table.

set-case-table table[Function]

This sets the current buffer’s case table to table.

with-case-table table body. . .

[Macro]The with-case-table macro saves the current case table, makes table the current
case table, evaluates the body forms, and finally restores the case table. The return

Chapter 4: Strings and Characters

76

value is the value of the last form in body. The case table is restored even in case ofan abnormal exit via throw or error (see Section 11.7 [Nonlocal Exits], page 177).
Some language environments modify the case conversions of ASCII characters; for example,
in the Turkish language environment, the ASCII capital I is downcased into a Turkish dotlessi (‘ı’). This can interfere with code that requires ordinary ASCII case conversion, such as
implementations of ASCII-based network protocols. In that case, use the with-case-table
macro with the variable ascii-case-table, which stores the unmodified case table for the
ASCII character set.
[Variable]
The case table for the ASCII character set. This should not be modified by any
language environment settings.

ascii-case-table

The following three functions are convenient subroutines for packages that define nonASCII character sets. They modify the specified case table case-table; they also modify thestandard syntax table. See Chapter 36 [Syntax Tables], page 1022. Normally you would use
these functions to change the standard case table.

set-case-syntax-pair uc lc case-table[Function]
This function specifies a pair of corresponding letters, one upper case and one lower
case.

set-case-syntax-delims l r case-table[Function]
This function makes characters l and r a matching pair of case-invariant delimiters.

set-case-syntax char syntax case-table[Function]

This function makes char case-invariant, with syntax syntax.
[Command]This command displays a description of the contents of the current buffer’s case table.

describe-buffer-case-table

77

5 Lists
A list represents a sequence of zero or more elements (which may be any Lisp objects). The
important difference between lists and vectors is that two or more lists can share part oftheir structure; in addition, you can insert or delete elements in a list without copying thewhole list.

5.1 Lists and Cons Cells
Lists in Lisp are not a primitive data type; they are built up from cons cells (see Section 2.4.6[Cons Cell Type], page 16). A cons cell is a data object that represents an ordered pair.
That is, it has two slots, and each slot holds, or refers to, some Lisp object. One slot is
known as the car, and the other is known as the cdr. (These names are traditional; see
Section 2.4.6 [Cons Cell Type], page 16.) cdr is pronounced “could-er”.
We say that “the car of this cons cell is” whatever object its car slot currently holds,
and likewise for the cdr.
A list is a series of cons cells chained together, so that each cell refers to the next one.
There is one cons cell for each element of the list. By convention, the cars of the cons
cells hold the elements of the list, and the cdrs are used to chain the list (this asymmetry
between car and cdr is entirely a matter of convention; at the level of cons cells, the car
and cdr slots have similar properties). Hence, the cdr slot of each cons cell in a list refers
to the following cons cell.
Also by convention, the cdr of the last cons cell in a list is nil. We call such a nilterminated structure a proper list1 . In Emacs Lisp, the symbol nil is both a symbol and alist with no elements. For convenience, the symbol nil is considered to have nil as its cdr(and also as its car).
Hence, the cdr of a proper list is always a proper list. The cdr of a nonempty proper
list is a proper list containing all the elements except the first.
If the cdr of a list’s last cons cell is some value other than nil, we call the structure adotted list, since its printed representation would use dotted pair notation (see Section 2.4.6.2[Dotted Pair Notation], page 18). There is one other possibility: some cons cell’s cdr could
point to one of the previous cons cells in the list. We call that structure a circular list.
For some purposes, it does not matter whether a list is proper, circular or dotted. If a
program doesn’t look far enough down the list to see the cdr of the final cons cell, it won’t
care. However, some functions that operate on lists demand proper lists and signal errors if
given a dotted list. Most functions that try to find the end of a list enter infinite loops if
given a circular list. You can use the function proper-list-p, described in the next section(see Section 5.2 [List-related Predicates], page 78), to determine whether a list is a properone.
Because most cons cells are used as part of lists, we refer to any structure made out ofcons cells as a list structure.
1

It is sometimes also referred to as a true list, but we generally do not use this terminology in this manual.

Chapter 5: Lists

78

5.2 Predicates on Lists
The following predicates test whether a Lisp object is an atom, whether it is a cons cell or
is a list, or whether it is the distinguished object nil. (Many of these predicates can be
defined in terms of the others, but they are used so often that it is worth having them.)

consp object[Function]
This function returns t if object is a cons cell, nil otherwise. nil is not a cons cell,although it is a list.

atom object[Function]
This function returns t if object is an atom, nil otherwise. All objects except cons
cells are atoms. The symbol nil is an atom and is also a list; it is the only Lisp object
that is both.
(atom object) ≡ (not (consp object))

listp object[Function]
This function returns t if object is a cons cell or nil. Otherwise, it returns nil.
(listp '(1))⇒ t(listp '())⇒ tnlistp object[Function]
This function is the opposite of listp: it returns t if object is not a list. Otherwise,
it returns nil.
(listp object) ≡ (not (nlistp object))null object[Function]
This function returns t if object is nil, and returns nil otherwise. This function
is identical to not, but as a matter of clarity we use not when object is considereda truth value (see not in Section 11.3 [Combining Conditions], page 162) and null
otherwise.
(null '(1))⇒ nil(null '())⇒ tproper-list-p object[Function]
This function returns the length of object if it is a proper list, nil otherwise (seeSection 5.1 [Cons Cells], page 77). In addition to satisfying listp, a proper list isneither circular nor dotted.
(proper-list-p '(a b c))⇒ 3(proper-list-p '(a b . c))⇒ nilChapter 5: Lists

79

5.3 Accessing Elements of Lists
car cons-cell[Function]
This function returns the value referred to by the first slot of the cons cell cons-cell.
In other words, it returns the car of cons-cell.
As a special case, if cons-cell is nil, this function returns nil. Therefore, any list is avalid argument. An error is signaled if the argument is not a cons cell or nil.
(car '(a b c))⇒ a(car '())⇒ nil

cdr cons-cell[Function]
This function returns the value referred to by the second slot of the cons cell cons-cell.
In other words, it returns the cdr of cons-cell.
As a special case, if cons-cell is nil, this function returns nil; therefore, any list is avalid argument. An error is signaled if the argument is not a cons cell or nil.
(cdr '(a b c))⇒ (b c)(cdr '())⇒ nil

car-safe object[Function]
This function lets you take the car of a cons cell while avoiding errors for other datatypes. It returns the car of object if object is a cons cell, nil otherwise. This is incontrast to car, which signals an error if object is not a list.
(car-safe object)≡(let ((x object))(if (consp x)(car x)nil))

cdr-safe object[Function]
This function lets you take the cdr of a cons cell while avoiding errors for other datatypes. It returns the cdr of object if object is a cons cell, nil otherwise. This is incontrast to cdr, which signals an error if object is not a list.
(cdr-safe object)≡(let ((x object))(if (consp x)(cdr x)nil))

pop listname[Macro]This macro provides a convenient way to examine the car of a list, and take it off thelist, all at once. It operates on the list stored in listname. It removes the first elementfrom the list, saves the cdr into listname, then returns the removed element.

Chapter 5: Lists

80

In the simplest case, listname is an unquoted symbol naming a list; in that case, thismacro is equivalent to (prog1 (car listname) (setq listname (cdr listname))).
x⇒ (a b c)(pop x)⇒ ax⇒ (b c)More generally, listname can be a generalized variable. In that case, this macro saves
into listname using setf. See Section 12.17 [Generalized Variables], page 224.
For the push macro, which adds an element to a list, See Section 5.5 [List Variables],page 85.

nth n list

[Function]
This function returns the nth element of list. Elements are numbered starting withzero, so the car of list is element number zero. If the length of list is n or less, thevalue is nil.
(nth 2 '(1 2 3 4))⇒ 3(nth 10 '(1 2 3 4))⇒ nil(nth n x) ≡ (car (nthcdr n x))
The function elt is similar, but applies to any kind of sequence. For historical reasons,it takes its arguments in the opposite order. See Section 6.1 [Sequence Functions],
page 102.

nthcdr n list

[Function]
This function returns the nth cdr of list. In other words, it skips past the first n linksof list and returns what follows.
If n is zero, nthcdr returns all of list. If the length of list is n or less, nthcdr returns
nil.
(nthcdr 1 '(1 2 3 4))⇒ (2 3 4)(nthcdr 10 '(1 2 3 4))⇒ nil(nthcdr 0 '(1 2 3 4))⇒ (1 2 3 4)

take n list

[Function]
This function returns the n first elements of list. Essentially, it returns the part of listthat nthcdr skips.
take returns list if shorter than n elements; it returns nil if n is zero or negative.
(take 3 '(a b c d))⇒ (a b c)

Chapter 5: Lists

81(take 10 '(a b c d))⇒ (a b c d)(take 0 '(a b c d))⇒ nilntake n list

[Function]
This is a version of take that works by destructively modifying the list structure of
the argument. That makes it faster, but the original value of list may be lost.
ntake returns list unmodified if shorter than n elements; it returns nil if n is zero or
negative. Otherwise, it returns list truncated to its first n elements.
This means that it is usually a good idea to use the return value and not just rely on
the truncation effect unless n is known to be positive.

last list &optional n[Function]
This function returns the last link of list. The car of this link is the list’s last element.
If list is null, nil is returned. If n is non-nil, the nth-to-last link is returned instead,or the whole of list if n is bigger than list’s length.

safe-length list

[Function]
This function returns the length of list, with no risk of either an error or an infinite
loop. It generally returns the number of distinct cons cells in the list. However, forcircular lists, the value is just an upper bound; it is often too large.
If list is not nil or a cons cell, safe-length returns 0.

The most common way to compute the length of a list, when you are not worried that it
may be circular, is with length. See Section 6.1 [Sequence Functions], page 102.

caar cons-cell[Function]

This is the same as (car (car cons-cell)).

cadr cons-cell[Function]

This is the same as (car (cdr cons-cell)) or (nth 1 cons-cell).

cdar cons-cell[Function]

This is the same as (cdr (car cons-cell)).

cddr cons-cell[Function]

This is the same as (cdr (cdr cons-cell)) or (nthcdr 2 cons-cell).
In addition to the above, 24 additional compositions of car and cdr are defined as
cxxxr and cxxxxr, where each x is either a or d. cadr, caddr, and cadddr pick out thesecond, third or fourth elements of a list, respectively. cl-lib provides the same under thenames cl-second, cl-third, and cl-fourth. See Section “List Functions” in Common
Lisp Extensions.

butlast x &optional n[Function]
This function returns the list x with the last element, or the last n elements, removed.
If n is greater than zero it makes a copy of the list so as not to damage the originallist. In general, (append (butlast x n) (last x n)) will return a list equal to x.

Chapter 5: Lists

82

nbutlast x &optional n[Function]
This is a version of butlast that works by destructively modifying the cdr of theappropriate element, rather than making a copy of the list.

5.4 Building Cons Cells and Lists
Many functions build lists, as lists reside at the very heart of Lisp. cons is the fundamental
list-building function; however, it is interesting to note that list is used more times in thesource code for Emacs than cons.

cons object1 object2[Function]
This function is the most basic function for building new list structure. It creates a
new cons cell, making object1 the car, and object2 the cdr. It then returns the newcons cell. The arguments object1 and object2 may be any Lisp objects, but mostoften object2 is a list.
(cons 1 '(2))⇒ (1 2)(cons 1 '())⇒ (1)(cons 1 2)
⇒ (1 . 2)cons is often used to add a single element to the front of a list. This is called consing
the element onto the list.2 For example:(setq list (cons newelt list))
Note that there is no conflict between the variable named list used in this example
and the function named list described below; any symbol can serve both purposes.

list &rest objects[Function]
This function creates a list with objects as its elements. The resulting list is always
nil-terminated. If no objects are given, the empty list is returned.
(list 1 2 3 4 5)
⇒ (1 2 3 4 5)
(list 1 2 '(3 4 5) 'foo)⇒ (1 2 (3 4 5) foo)
(list)⇒ nil

make-list length object[Function]
This function creates a list of length elements, in which each element is object. Compare
make-list with make-string (see Section 4.3 [Creating Strings], page 55).
(make-list 3 'pigs)⇒ (pigs pigs pigs)

2

There is no strictly equivalent way to add an element to the end of a list. You can use (append listname(list newelt)), which creates a whole new list by copying listname and adding newelt to its end. Or
you can use (nconc listname (list newelt)), which modifies listname by following all the cdrs andthen replacing the terminating nil. Compare this to adding an element to the beginning of a list withcons, which neither copies nor modifies the list.

Chapter 5: Lists

83(make-list 0 'pigs)⇒ nil(setq l (make-list 3 '(a b)))⇒ ((a b) (a b) (a b))(eq (car l) (cadr l))⇒ tappend &rest sequences[Function]
This function returns a list containing all the elements of sequences. The sequences
may be lists, vectors, bool-vectors, or strings, but the last one should usually be alist. All arguments except the last one are copied, so none of the arguments is altered.
(See nconc in Section 5.6.3 [Rearrangement], page 90, for a way to join lists with no
copying.)
More generally, the final argument to append may be any Lisp object. The final
argument is not copied or converted; it becomes the cdr of the last cons cell in the
new list. If the final argument is itself a list, then its elements become in effect elementsof the result list. If the final element is not a list, the result is a dotted list since its
final cdr is not nil as required in a proper list (see Section 5.1 [Cons Cells], page 77).

Here is an example of using append:(setq trees '(pine oak))⇒ (pine oak)(setq more-trees (append '(maple birch) trees))⇒ (maple birch pine oak)trees
⇒ (pine oak)more-trees⇒ (maple birch pine oak)(eq trees (cdr (cdr more-trees)))⇒ t
You can see how append works by looking at a box diagram. The variable trees is set tothe list (pine oak) and then the variable more-trees is set to the list (maple birch pineoak). However, the variable trees continues to refer to the original list:
more-trees
trees
|
|
|
--- ----- ---> --- ----- ----> |||--> |||--> |||--> |||--> nil--- ----- ----- ----- --|
|
|
|
|
|
|
|
--> maple-->birch--> pine--> oak

An empty sequence contributes nothing to the value returned by append. As a consequenceof this, a final nil argument forces a copy of the previous argument:trees⇒ (pine oak)(setq wood (append trees nil))⇒ (pine oak)Chapter 5: Lists

84

wood
⇒ (pine oak)(eq wood trees)⇒ nilThis once was the usual way to copy a list, before the function copy-sequence was invented.
See Chapter 6 [Sequences Arrays Vectors], page 102.
Here we show the use of vectors and strings as arguments to append:(append [a b] "cd" nil)
⇒ (a b 99 100)
With the help of apply (see Section 13.5 [Calling Functions], page 239), we can append
all the lists in a list of lists:(apply 'append '((a b c) nil (x y z) nil))⇒ (a b c x y z)
If no sequences are given, nil is returned:(append)⇒ nil
Here are some examples where the final argument is not a list:(append '(x y) 'z)⇒ (x y . z)
(append '(x y) [z])⇒ (x y . [z])The second example shows that when the final argument is a sequence but not a list, thesequence’s elements do not become elements of the resulting list. Instead, the sequence
becomes the final cdr, like any other non-list final argument.

copy-tree tree &optional vecp

[Function]
This function returns a copy of the tree tree. If tree is a cons cell, this makes a newcons cell with the same car and cdr, then recursively copies the car and cdr in thesame way.
Normally, when tree is anything other than a cons cell, copy-tree simply returns
tree. However, if vecp is non-nil, it copies vectors too (and operates recursively on
their elements).

flatten-tree tree

[Function]
This function returns a “flattened” copy of tree, that is, a list containing all the
non-nil terminal nodes, or leaves, of the tree of cons cells rooted at tree. Leaves in
the returned list are in the same order as in tree.
(flatten-tree '(1 (2 . 3) nil (4 5 (6)) 7))⇒(1 2 3 4 5 6 7)

ensure-list object[Function]
This function returns object as a list. If object is already a list, the function returns
it; otherwise, the function returns a one-element list containing object.

Chapter 5: Lists

85

This is usually useful if you have a variable that may or may not be a list, and you
can then say, for instance:(dolist (elem (ensure-list foo))(princ elem))number-sequence from &optional to separation[Function]
This function returns a list of numbers starting with from and incrementing byseparation, and ending at or just before to. separation can be positive or negative anddefaults to 1. If to is nil or numerically equal to from, the value is the one-element
list (from). If to is less than from with a positive separation, or greater than fromwith a negative separation, the value is nil because those arguments specify an empty
sequence.
If separation is 0 and to is neither nil nor numerically equal to from, number-sequencesignals an error, since those arguments specify an infinite sequence.

All arguments are numbers. Floating-point arguments can be tricky, because floatingpoint arithmetic is inexact. For instance, depending on the machine, it may quite
well happen that (number-sequence 0.4 0.6 0.2) returns the one element list (0.4),
whereas (number-sequence 0.4 0.8 0.2) returns a list with three elements. The nthelement of the list is computed by the exact formula (+ from (* n separation)).
Thus, if one wants to make sure that to is included in the list, one can pass an
expression of this exact type for to. Alternatively, one can replace to with a slightly
larger value (or a slightly more negative value if separation is negative).
Some examples:(number-sequence 4 9)
⇒ (4 5 6 7 8 9)
(number-sequence 9 4 -1)⇒ (9 8 7 6 5 4)
(number-sequence 9 4 -2)⇒ (9 7 5)(number-sequence 8)⇒ (8)(number-sequence 8 5)
⇒ nil(number-sequence 5 8 -1)⇒ nil(number-sequence 1.5 6 2)
⇒ (1.5 3.5 5.5)

5.5 Modifying List Variables
These functions, and one macro, provide convenient ways to modify a list which is stored ina variable.

push element listname[Macro]This macro creates a new list whose car is element and whose cdr is the list
specified by listname, and saves that list in listname. In the simplest case,Chapter 5: Lists

86

listname is an unquoted symbol naming a list, and this macro is equivalent to(setq listname (cons element listname)).
(setq l '(a b))⇒ (a b)(push 'c l)⇒ (c a b)l⇒ (c a b)
More generally, listname can be a generalized variable. In that case, this macro does
the equivalent of (setf listname (cons element listname)). See Section 12.17[Generalized Variables], page 224.
For the pop macro, which removes the first element from a list, See Section 5.3 [ListElements], page 79.
Two functions modify lists that are the values of variables.

add-to-list symbol element &optional append compare-fn[Function]
This function sets the variable symbol by consing element onto the old value, if element
is not already a member of that value. It returns the resulting list, whether updated
or not. The value of symbol had better be a list already before the call. add-to-list
uses compare-fn to compare element against existing list members; if compare-fn isnil, it uses equal.
Normally, if element is added, it is added to the front of symbol, but if the optional
argument append is non-nil, it is added at the end.
The argument symbol is not implicitly quoted; add-to-list is an ordinary function,
like set and unlike setq. Quote the argument yourself if that is what you want.
Do not use this function when symbol refers to a lexical variable.

Here’s a scenario showing how to use add-to-list:(setq foo '(a b))⇒ (a b)(add-to-list 'foo 'c)⇒ (c a b);; Add c.

(add-to-list 'foo 'b)⇒ (c a b);; No effect.

foo;; foo was changed.
⇒ (c a b)

An equivalent expression for (add-to-list 'var value) is this:(if (member value var)
var
(setq var (cons value var)))Chapter 5: Lists

87

add-to-ordered-list symbol element &optional order[Function]
This function sets the variable symbol by inserting element into the old value, whichmust be a list, at the position specified by order. If element is already a member ofthe list, its position in the list is adjusted according to order. Membership is tested
using eq. This function returns the resulting list, whether updated or not.
The order is typically a number (integer or float), and the elements of the list aresorted in non-decreasing numerical order.
order may also be omitted or nil. Then the numeric order of element stays unchanged
if it already has one; otherwise, element has no numeric order. Elements without anumeric list order are placed at the end of the list, in no particular order.

Any other value for order removes the numeric order of element if it already has one;otherwise, it is equivalent to nil.
The argument symbol is not implicitly quoted; add-to-ordered-list is an ordinary
function, like set and unlike setq. Quote the argument yourself if necessary.
The ordering information is stored in a hash table on symbol’s list-order property.
symbol cannot refer to a lexical variable.
Here’s a scenario showing how to use add-to-ordered-list:(setq foo '())⇒ nil
(add-to-ordered-list 'foo 'a 1)⇒ (a);; Add a.

(add-to-ordered-list 'foo 'c 3)⇒ (a c);; Add c.

(add-to-ordered-list 'foo 'b 2)⇒ (a b c);; Add b.

(add-to-ordered-list 'foo 'b 4)⇒ (a c b);; Move b.

(add-to-ordered-list 'foo 'd)⇒ (a c b d);; Append d.

(add-to-ordered-list 'foo 'e)⇒ (a c b e d);; Add e.

;; foo was changed.

foo⇒ (a c b e d)

5.6 Modifying Existing List Structure
You can modify the car and cdr contents of a cons cell with the primitives setcar
and setcdr. These are destructive operations because they change existing list structure.

Chapter 5: Lists

88

Destructive operations should be applied only to mutable lists, that is, lists constructed
via cons, list or similar operations. Lists created by quoting are part of the program andshould not be changed by destructive operations. See Section 2.9 [Mutability], page 36.
Common Lisp note: Common Lisp uses functions rplaca and rplacd to alter
list structure; they change structure the same way as setcar and setcdr, but
the Common Lisp functions return the cons cell while setcar and setcdr returnthe new car or cdr.

5.6.1 Altering List Elements with setcar
Changing the car of a cons cell is done with setcar. When used on a list, setcar replaces
one element of a list with a different element.

setcar cons object[Function]
This function stores object as the new car of cons, replacing its previous car. In
other words, it changes the car slot of cons to refer to object. It returns the value
object. For example:(setq x (list 1 2))⇒ (1 2)(setcar x 4)⇒ 4x⇒ (4 2)

When a cons cell is part of the shared structure of several lists, storing a new car into
the cons changes one element of each of these lists. Here is an example:;; Create two lists that are partly shared.
(setq x1 (list 'a 'b 'c))⇒ (a b c)(setq x2 (cons 'z (cdr x1)))⇒ (z b c);; Replace the car of a shared link.
(setcar (cdr x1) 'foo)⇒ foo
x1; Both lists are changed.
⇒ (a foo c)x2⇒ (z foo c);; Replace the car of a link that is not shared.
(setcar x1 'baz)⇒ baz
x1; Only one list is changed.
⇒ (baz foo c)x2⇒ (z foo c)Chapter 5: Lists

89

Here is a graphical depiction of the shared structure of the two lists in the variables x1
and x2, showing why replacing b changes them both:--- ----- ----- --x1---> |||----> |||--> |||--> nil--- ----- ----- --|
-->
|
|
|
|
|
|
--> a |
--> b
--> c
|
--- --|
x2--> |||---- --||--> z
Here is an alternative form of box diagram, showing the same relationship:x1:---------------------------------------| car| cdr |
| car
| cdr |
| car
| cdr ||a|o------->|b|o------->|c| nil |||
| -->||||||-------------- |--------------------------|x2:|-------------- || car| cdr | |
|
z
|
o---|
|
|
--------------

5.6.2 Altering the CDR of a List
The lowest-level primitive for modifying a cdr is setcdr:

setcdr cons object[Function]
This function stores object as the new cdr of cons, replacing its previous cdr. In
other words, it changes the cdr slot of cons to refer to object. It returns the value
object.

Here is an example of replacing the cdr of a list with a different list. All but the firstelement of the list are removed in favor of a different sequence of elements. The first element
is unchanged, because it resides in the car of the list, and is not reached via the cdr.
(setq x (list 1 2 3))⇒ (1 2 3)(setcdr x '(4))⇒ (4)x⇒ (1 4)

Chapter 5: Lists

90

You can delete elements from the middle of a list by altering the cdrs of the cons cells
in the list. For example, here we delete the second element, b, from the list (a b c), bychanging the cdr of the first cons cell:(setq x1 (list 'a 'b 'c))⇒ (a b c)(setcdr x1 (cdr (cdr x1)))⇒ (c)x1⇒ (a c)Here is the result in box notation:-------------------||-------------|-------------|-------------| car| cdr | | | car| cdr |-->| car| cdr ||a|o----|b|o-------->|c| nil |
|
|
|
|
|
|
|
|
|
----------------------------------------The second cons cell, which previously held the element b, still exists and its car is still b,
but it no longer forms part of this list.
It is equally easy to insert a new element by changing cdrs:(setq x1 (list 'a 'b 'c))⇒ (a b c)(setcdr x1 (cons 'd (cdr x1)))⇒ (d b c)
x1⇒ (a d b c)
Here is this result in box notation:-------------------------------------| car | cdr|| car | cdr || car | cdr |
|
a |
o
|
-->|
b |
o------->|
c | nil |
|
|
|
| |
|
|
|
|
|
|
--------- | -|------------------------||-----------|||--------------|
|
| car
| cdr
| |
-->|
d
|
o-----|||---------------

5.6.3 Functions that Rearrange Lists
Here are some functions that rearrange lists destructively by modifying the cdrs of theircomponent cons cells. These functions are destructive because they chew up the originallists passed to them as arguments, relinking their cons cells to form a new list that is thereturned value.
The function delq in the following section is another example of destructive list manipulation.

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nconc &rest lists[Function]
This function returns a list containing all the elements of lists. Unlike append (seeSection 5.4 [Building Lists], page 82), the lists are not copied. Instead, the last cdr
of each of the lists is changed to refer to the following list. The last of the lists is notaltered. For example:(setq x (list 1 2 3))⇒ (1 2 3)(nconc x '(4 5))⇒ (1 2 3 4 5)x
⇒ (1 2 3 4 5)
Since the last argument of nconc is not itself modified, it is reasonable to use a constantlist, such as '(4 5), as in the above example. For the same reason, the last argument
need not be a list:(setq x (list 1 2 3))⇒ (1 2 3)(nconc x 'z)⇒ (1 2 3 . z)x
⇒ (1 2 3 . z)
However, the other arguments (all but the last) should be mutable lists.

A common pitfall is to use a constant list as a non-last argument to nconc. If you do
this, the resulting behavior is undefined (see Section 10.1.1 [Self-Evaluating Forms],
page 146). It is possible that your program will change each time you run it! Here iswhat might happen (though this is not guaranteed to happen):(defun add-foo (x)(nconc '(foo) x)); We want this function to add;
foo to the front of its arg.

(symbol-function 'add-foo)⇒ (lambda (x) (nconc '(foo) x))(setq xx (add-foo '(1 2)))⇒ (foo 1 2)
(setq xy (add-foo '(3 4)))⇒ (foo 1 2 3 4)
(eq xx xy)⇒ t; It seems to work.
; What happened?

(symbol-function 'add-foo)⇒ (lambda (x) (nconc '(foo 1 2 3 4) x))

5.7 Using Lists as Sets
A list can represent an unordered mathematical set—simply consider a value an elementof a set if it appears in the list, and ignore the order of the list. To form the union of two
sets, use append (as long as you don’t mind having duplicate elements). You can remove
equal duplicates using delete-dups or seq-uniq. Other useful functions for sets include
memq and delq, and their equal versions, member and delete.

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Common Lisp note: Common Lisp has functions union (which avoids duplicate
elements) and intersection for set operations. In Emacs Lisp, variants ofthese facilities are provided by the cl-lib library. See Section “Lists as Sets”
in Common Lisp Extensions.

memq object list

[Function]
This function tests to see whether object is a member of list. If it is, memq returns alist starting with the first occurrence of object. Otherwise, it returns nil. The letter‘q’ in memq says that it uses eq to compare object against the elements of the list. For
example:(memq 'b '(a b c b a))⇒ (b c b a)(memq '(2) '((1) (2))); The two (2)s need not be eq.
⇒ Unspecified; might be nil or ((2)).

delq object list

[Function]
This function destructively removes all elements eq to object from list, and returns
the resulting list. The letter ‘q’ in delq says that it uses eq to compare object against
the elements of the list, like memq and remq.
Typically, when you invoke delq, you should use the return value by assigning it to
the variable which held the original list. The reason for this is explained below.

The delq function deletes elements from the front of the list by simply advancing down
the list, and returning a sublist that starts after those elements. For example:(delq 'a '(a b c)) ≡ (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involveschanging the cdrs (see Section 5.6.2 [Setcdr], page 89).
(setq sample-list (list 'a 'b 'c '(4)))⇒ (a b c (4))(delq 'a sample-list)⇒ (b c (4))
sample-list⇒ (a b c (4))(delq 'c sample-list)⇒ (a b (4))
sample-list⇒ (a b (4))
Note that (delq 'c sample-list) modifies sample-list to splice out the third element,but (delq 'a sample-list) does not splice anything—it just returns a shorter list. Don’t
assume that a variable which formerly held the argument list now has fewer elements, orthat it still holds the original list! Instead, save the result of delq and use that. Most often
we store the result back into the variable that held the original list:(setq flowers (delq 'rose flowers))
In the following example, the (list 4) that delq attempts to match and the (4) in thesample-list are equal but not eq:(delq (list 4) sample-list)⇒ (a c (4))

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If you want to delete elements that are equal to a given value, use delete (see below).

remq object list

[Function]
This function returns a copy of list, with all elements removed which are eq to object.
The letter ‘q’ in remq says that it uses eq to compare object against the elements oflist.
(setq sample-list (list 'a 'b 'c 'a 'b 'c))⇒ (a b c a b c)(remq 'a sample-list)⇒ (b c b c)sample-list⇒ (a b c a b c)

memql object list

[Function]
The function memql tests to see whether object is a member of list, comparing memberswith object using eql, so floating-point elements are compared by value. If object is amember, memql returns a list starting with its first occurrence in list. Otherwise, it
returns nil.
Compare this with memq:(memql 1.2 '(1.1 1.2 1.3)) ; 1.2 and 1.2 are eql.
⇒ (1.2 1.3)
(memq 1.2 '(1.1 1.2 1.3)) ; The two 1.2s need not be eq.
⇒ Unspecified; might be nil or (1.2 1.3).

The following three functions are like memq, delq and remq, but use equal rather thaneq to compare elements. See Section 2.8 [Equality Predicates], page 34.

member object list

[Function]
The function member tests to see whether object is a member of list, comparing
members with object using equal. If object is a member, member returns a list
starting with its first occurrence in list. Otherwise, it returns nil.
Compare this with memq:(member '(2) '((1) (2))) ; (2) and (2) are equal.
⇒ ((2))(memq '(2) '((1) (2))); The two (2)s need not be eq.
⇒ Unspecified; might be nil or (2).
;; Two strings with the same contents are equal.
(member "foo" '("foo" "bar"))⇒ ("foo" "bar")delete object sequence[Function]
This function removes all elements equal to object from sequence, and returns theresulting sequence.
If sequence is a list, delete is to delq as member is to memq: it uses equal to compare
elements with object, like member; when it finds an element that matches, it cuts theelement out just as delq would. As with delq, you should typically use the return
value by assigning it to the variable which held the original list.

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If sequence is a vector or string, delete returns a copy of sequence with all elements
equal to object removed.
For example:(setq l (list '(2) '(1) '(2)))(delete '(2) l)⇒ ((1))l⇒ ((2) (1));; If you want to change l reliably,;; write (setq l (delete '(2) l)).
(setq l (list '(2) '(1) '(2)))(delete '(1) l)⇒ ((2) (2))
l⇒ ((2) (2));; In this case, it makes no difference whether you set l,;; but you should do so for the sake of the other case.
(delete '(2) [(2) (1) (2)])⇒ [(1)]

remove object sequence[Function]
This function is the non-destructive counterpart of delete. It returns a copy ofsequence, a list, vector, or string, with elements equal to object removed. For
example:(remove '(2) '((2) (1) (2)))⇒ ((1))(remove '(2) [(2) (1) (2)])⇒ [(1)]
Common Lisp note: The functions member, delete and remove in GNU Emacs
Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions
do not use equal to compare elements.

member-ignore-case object list

[Function]
This function is like member, except that object should be a string and that it ignores
differences in letter-case and text representation: upper-case and lower-case letters aretreated as equal, and unibyte strings are converted to multibyte prior to comparison.

delete-dups list

[Function]
This function destructively removes all equal duplicates from list, stores the result in
list and returns it. Of several equal occurrences of an element in list, delete-dups
keeps the first one. See seq-uniq for non-destructive operation (see Section 6.1[Sequence Functions], page 102).

See also the function add-to-list, in Section 5.5 [List Variables], page 85, for a way to
add an element to a list stored in a variable and used as a set.

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5.8 Association Lists
An association list, or alist for short, records a mapping from keys to values. It is a listof cons cells called associations: the car of each cons cell is the key, and the cdr is theassociated value.3
Here is an example of an alist. The key pine is associated with the value cones; the key
oak is associated with acorns; and the key maple is associated with seeds.
((pine . cones)(oak . acorns)(maple . seeds))
Both the values and the keys in an alist may be any Lisp objects. For example, in thefollowing alist, the symbol a is associated with the number 1, and the string "b" is associatedwith the list (2 3), which is the cdr of the alist element:((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the car of the
cdr of the element. Here is an example of such an alist:((rose red) (lily white) (buttercup yellow))
Here we regard red as the value associated with rose. One advantage of this kind of alistis that you can store other related information—even a list of other items—in the cdr ofthe cdr. One disadvantage is that you cannot use rassq (see below) to find the element
containing a given value. When neither of these considerations is important, the choice is amatter of taste, as long as you are consistent about it for any given alist.
The same alist shown above could be regarded as having the associated value in the cdrof the element; the value associated with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on astack, since new associations may be added easily to the front of the list. When searching an
association list for an association with a given key, the first one found is returned, if there ismore than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell.
The alist search functions simply ignore such elements. Many other versions of Lisp signal
errors in such cases.
Note that property lists are similar to association lists in several respects. A property
list behaves like an association list in which each key can occur only once. See Section 5.9[Property Lists], page 99, for a comparison of property lists and association lists.

assoc key alist &optional testfn[Function]
This function returns the first association for key in alist, comparing key against thealist elements using testfn if it is a function, and equal otherwise (see Section 2.8[Equality Predicates], page 34). If testfn is a function, it is called with two arguments:
the car of an element from alist and key. The function returns nil if no associationin alist has a car equal to key, as tested by testfn. For example:(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))⇒ ((pine . cones) (oak . acorns) (maple . seeds))

3

This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item
in a table. In this case, the table is the alist, and the alist associations are the items.

Chapter 5: Lists

96(assoc 'oak trees)⇒ (oak . acorns)(cdr (assoc 'oak trees))⇒ acorns(assoc 'birch trees)⇒ nil

Here is another example, in which the keys and values are not symbols:(setq needles-per-cluster'((2 "Austrian Pine" "Red Pine")(3 "Pitch Pine")(5 "White Pine")))(cdr (assoc 3 needles-per-cluster))⇒ ("Pitch Pine")(cdr (assoc 2 needles-per-cluster))⇒ ("Austrian Pine" "Red Pine")

The function assoc-string is much like assoc except that it ignores certain differences
between strings. See Section 4.5 [Text Comparison], page 60.

rassoc value alist[Function]
This function returns the first association with value value in alist. It returns nil if
no association in alist has a cdr equal to value.
rassoc is like assoc except that it compares the cdr of each alist association insteadof the car. You can think of this as reverse assoc, finding the key for a given value.

assq key alist[Function]
This function is like assoc in that it returns the first association for key in alist, but it
makes the comparison using eq. assq returns nil if no association in alist has a car
eq to key. This function is used more often than assoc, since eq is faster than equaland most alists use symbols as keys. See Section 2.8 [Equality Predicates], page 34.
(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))⇒ ((pine . cones) (oak . acorns) (maple . seeds))(assq 'pine trees)⇒ (pine . cones)

On the other hand, assq is not usually useful in alists where the keys may not be
symbols:(setq leaves'(("simple leaves" . oak)("compound leaves" . horsechestnut)))(assq "simple leaves" leaves)⇒ Unspecified; might be nil or ("simple leaves" . oak).
(assoc "simple leaves" leaves)⇒ ("simple leaves" . oak)alist-get key alist &optional default remove testfn[Function]
This function is similar to assq. It finds the first association (key . value) bycomparing key with alist elements, and, if found, returns the value of that association.
If no association is found, the function returns default. Comparison of key against
alist elements uses the function specified by testfn, defaulting to eq.

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This is a generalized variable (see Section 12.17 [Generalized Variables], page 224)
that can be used to change a value with setf. When using it to set a value, optional
argument remove non-nil means to remove key’s association from alist if the newvalue is eql to default.

rassq value alist[Function]
This function returns the first association with value value in alist. It returns nil if
no association in alist has a cdr eq to value.
rassq is like assq except that it compares the cdr of each alist association instead of
the car. You can think of this as reverse assq, finding the key for a given value.
For example:(setq trees '((pine . cones) (oak . acorns) (maple . seeds)))(rassq 'acorns trees)⇒ (oak . acorns)(rassq 'spores trees)⇒ nilrassq cannot search for a value stored in the car of the cdr of an element:(setq colors '((rose red) (lily white) (buttercup yellow)))(rassq 'white colors)⇒ nil

In this case, the cdr of the association (lily white) is not the symbol white, butrather the list (white). This becomes clearer if the association is written in dottedpair notation:(lily white) ≡ (lily . (white))

assoc-default key alist &optional test default[Function]
This function searches alist for a match for key. For each element of alist, it compares
the element (if it is an atom) or the element’s car (if it is a cons) against key, by
calling test with two arguments: the element or its car, and key. The arguments are
passed in that order so that you can get useful results using string-match with analist that contains regular expressions (see Section 35.4 [Regexp Search], page 1008).
If test is omitted or nil, equal is used for comparison.
If an alist element matches key by this criterion, then assoc-default returns a value
based on this element. If the element is a cons, then the value is the element’s cdr.
Otherwise, the return value is default.
If no alist element matches key, assoc-default returns nil.

copy-alist alist[Function]
This function returns a two-level deep copy of alist: it creates a new copy of eachassociation, so that you can alter the associations of the new alist without changing
the old one.
(setq needles-per-cluster'((2 . ("Austrian Pine" "Red Pine"))(3 . ("Pitch Pine"))(5 . ("White Pine"))))⇒((2 "Austrian Pine" "Red Pine")Chapter 5: Lists

98(3 "Pitch Pine")(5 "White Pine"))(setq copy (copy-alist needles-per-cluster))⇒((2 "Austrian Pine" "Red Pine")(3 "Pitch Pine")(5 "White Pine"))(eq needles-per-cluster copy)⇒ nil(equal needles-per-cluster copy)⇒ t(eq (car needles-per-cluster) (car copy))⇒ nil(cdr (car (cdr needles-per-cluster)))⇒ ("Pitch Pine")(eq (cdr (car (cdr needles-per-cluster)))(cdr (car (cdr copy))))⇒ tThis example shows how copy-alist makes it possible to change the associations of
one copy without affecting the other:(setcdr (assq 3 copy) '("Martian Vacuum Pine"))(cdr (assq 3 needles-per-cluster))⇒ ("Pitch Pine")

assq-delete-all key alist[Function]
This function deletes from alist all the elements whose car is eq to key, much as
if you used delq to delete each such element one by one. It returns the shortened
alist, and often modifies the original list structure of alist. For correct results, use thereturn value of assq-delete-all rather than looking at the saved value of alist.
(setq alist (list '(foo 1) '(bar 2) '(foo 3) '(lose 4)))⇒ ((foo 1) (bar 2) (foo 3) (lose 4))(assq-delete-all 'foo alist)⇒ ((bar 2) (lose 4))alist⇒ ((foo 1) (bar 2) (lose 4))

assoc-delete-all key alist &optional test

[Function]
This function is like assq-delete-all except that it accepts an optional argument
test, a predicate function to compare the keys in alist. If omitted or nil, test defaults
to equal. As assq-delete-all, this function often modifies the original list structureof alist.

rassq-delete-all value alist[Function]
This function deletes from alist all the elements whose cdr is eq to value. It returns theshortened alist, and often modifies the original list structure of alist. rassq-deleteall is like assq-delete-all except that it compares the cdr of each alist association
instead of the car.

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let-alist alist body

[Macro]Creates a binding for each symbol used as keys the association list alist, prefixed withdot. This can be useful when accessing several items in the same association list, andit’s best understood through a simple example:(setq colors '((rose . red) (lily . white) (buttercup . yellow)))(let-alist colors(if (eq .rose 'red).lily))⇒ whiteThe body is inspected at compilation time, and only the symbols that appear in bodywith a ‘.’ as the first character in the symbol name will be bound. Finding the keys isdone with assq, and the cdr of the return value of this assq is assigned as the value
for the binding.
Nested association lists is supported:(setq colors '((rose . red) (lily (belladonna . yellow) (brindisi . pink))))(let-alist colors(if (eq .rose 'red).lily.belladonna))⇒ yellow
Nesting let-alist inside each other is allowed, but the code in the inner let-alist
can’t access the variables bound by the outer let-alist.

5.9 Property Lists
A property list (plist for short) is a list of paired elements. Each of the pairs associates aproperty name (usually a symbol) with a property or value. Here is an example of a property
list:(pine cones numbers (1 2 3) color "blue")
This property list associates pine with cones, numbers with (1 2 3), and color with"blue". The property names and values can be any Lisp objects, but the names are usuallysymbols (as they are in this example).
Property lists are used in several contexts. For instance, the function put-text-property
takes an argument which is a property list, specifying text properties and associated values
which are to be applied to text in a string or buffer. See Section 33.19 [Text Properties],
page 917.
Another prominent use of property lists is for storing symbol properties. Every symbol
possesses a list of properties, used to record miscellaneous information about the symbol;
these properties are stored in the form of a property list. See Section 9.4 [Symbol Properties],
page 138.

plistp object
This predicate function returns non-nil if object is a valid property list.

[Function]

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5.9.1 Property Lists and Association Lists
Association lists (see Section 5.8 [Association Lists], page 95) are very similar to property
lists. In contrast to association lists, the order of the pairs in the property list is not
significant, since the property names must be distinct.
Property lists are better than association lists for attaching information to various Lisp
function names or variables. If your program keeps all such information in one association
list, it will typically need to search that entire list each time it checks for an association for aparticular Lisp function name or variable, which could be slow. By contrast, if you keep thesame information in the property lists of the function names or variables themselves, eachsearch will scan only the length of one property list, which is usually short. This is why the
documentation for a variable is recorded in a property named variable-documentation.
The byte compiler likewise uses properties to record those functions needing special treatment.
However, association lists have their own advantages. Depending on your application,
it may be faster to add an association to the front of an association list than to updatea property. All properties for a symbol are stored in the same property list, so there isa possibility of a conflict between different uses of a property name. (For this reason, it
is a good idea to choose property names that are probably unique, such as by beginningthe property name with the program’s usual name-prefix for variables and functions.) An
association list may be used like a stack where associations are pushed on the front of thelist and later discarded; this is not possible with a property list.

5.9.2 Property Lists Outside Symbols
The following functions can be used to manipulate property lists. They all default tocomparing property names using eq.

plist-get plist property &optional predicate[Function]
This returns the value of the property property stored in the property list plist.
Comparisons are done with predicate, which defaults to eq. It accepts a malformed
plist argument. If property is not found in the plist, it returns nil. For example,(plist-get '(foo 4) 'foo)⇒ 4(plist-get '(foo 4 bad) 'foo)⇒ 4(plist-get '(foo 4 bad) 'bad)⇒ nil(plist-get '(foo 4 bad) 'bar)⇒ nilplist-put plist property value &optional predicate[Function]
This stores value as the value of the property property in the property list plist.
Comparisons are done with predicate, which defaults to eq. It may modify plist
destructively, or it may construct a new list structure without altering the old. The
function returns the modified property list, so you can store that back in the place
where you got plist. For example,(setq my-plist (list 'bar t 'foo 4))⇒ (bar t foo 4)

Chapter 5: Lists

101(setq my-plist (plist-put my-plist 'foo 69))⇒ (bar t foo 69)(setq my-plist (plist-put my-plist 'quux '(a)))⇒ (bar t foo 69 quux (a))

lax-plist-get plist property[Function]
This obsolete function is like plist-get except that it compares properties using
equal instead of eq.

lax-plist-put plist property value[Function]
This obsolete function is like plist-put except that it compares properties using
equal instead of eq.

plist-member plist property &optional predicate[Function]
This returns non-nil if plist contains the given property. Comparisons are done withpredicate, which defaults to eq. Unlike plist-get, this allows you to distinguishbetween a missing property and a property with the value nil. The value is actually
the tail of plist whose car is property.

102

6 Sequences, Arrays, and Vectors
The sequence type is the union of two other Lisp types: lists and arrays. In other words,
any list is a sequence, and any array is a sequence. The common property that all sequences
have is that each is an ordered collection of elements.
An array is a fixed-length object with a slot for each of its elements. All the elements
are accessible in constant time. The four types of arrays are strings, vectors, char-tables andbool-vectors.
A list is a sequence of elements, but it is not a single primitive object; it is made of cons
cells, one cell per element. Finding the nth element requires looking through n cons cells, soelements farther from the beginning of the list take longer to access. But it is possible to
add elements to the list, or remove elements.
The following diagram shows the relationship between these types:_____________________________________________|||
Sequence|| ______________________________________ |
| |
| |
| |
| | List | |
Array
| |
| |
| |
________________| || |______| |
|
|
|
|
| |
|
|
| Vector || String || ||||________||________|| ||| _________________________ | |
|
| |
| |
| | |
|
| | Char-table | | Bool-vector | | ||| |____________| |_____________| | |||________________________________| ||_____________________________________________|

6.1 Sequences
This section describes functions that accept any kind of sequence.

sequencep object[Function]
This function returns t if object is a list, vector, string, bool-vector, or char-table, nilotherwise. See also seqp below.

length sequence[Function]
This function returns the number of elements in sequence. The function signals thewrong-type-argument error if the argument is not a sequence or is a dotted list; itsignals the circular-list error if the argument is a circular list. For a char-table,
the value returned is always one more than the maximum Emacs character code.
See [Definition of safe-length], page 81, for the related function safe-length.
(length '(1 2 3))⇒ 3

Chapter 6: Sequences, Arrays, and Vectors

103(length ())⇒ 0(length "foobar")⇒ 6(length [1 2 3])⇒ 3(length (make-bool-vector 5 nil))⇒ 5
See also string-bytes, in Section 34.1 [Text Representations], page 963.
If you need to compute the width of a string on display, you should use string-width(see Section 41.10 [Size of Displayed Text], page 1157), not length, since length only counts
the number of characters, but does not account for the display width of each character.

length< sequence length[Function]
Return non-nil if sequence is shorter than length. This may be more efficient thancomputing the length of sequence if sequence is a long list.

length> sequence length[Function]

Return non-nil if sequence is longer than length.

length= sequence length[Function]

Return non-nil if the length of sequence is equal to length.

elt sequence index[Function]
This function returns the element of sequence indexed by index. Legitimate valuesof index are integers ranging from 0 up to one less than the length of sequence. If
sequence is a list, out-of-range values behave as for nth. See [Definition of nth], page 80.
Otherwise, out-of-range values trigger an args-out-of-range error.
(elt [1 2 3 4] 2)⇒ 3(elt '(1 2 3 4) 2)⇒ 3;; We use string to show clearly which character elt returns.
(string (elt "1234" 2))⇒ "3"(elt [1 2 3 4] 4)
error Args out of range: [1 2 3 4], 4(elt [1 2 3 4] -1)
error Args out of range: [1 2 3 4], -1This function generalizes aref (see Section 6.3 [Array Functions], page 116) and nth(see [Definition of nth], page 80).

copy-sequence seqr

[Function]
This function returns a copy of seqr, which should be either a sequence or a record.
The copy is the same type of object as the original, and it has the same elements inthe same order. However, if seqr is empty, like a string or a vector of zero length, thevalue returned by this function might not be a copy, but an empty object of the same
type and identical to seqr.

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Storing a new element into the copy does not affect the original seqr, and vice versa.
However, the elements of the copy are not copies; they are identical (eq) to theelements of the original. Therefore, changes made within these elements, as found via
the copy, are also visible in the original.
If the argument is a string with text properties, the property list in the copy is itself acopy, not shared with the original’s property list. However, the actual values of theproperties are shared. See Section 33.19 [Text Properties], page 917.
This function does not work for dotted lists. Trying to copy a circular list may cause
an infinite loop.
See also append in Section 5.4 [Building Lists], page 82, concat in Section 4.3 [Creating
Strings], page 55, and vconcat in Section 6.5 [Vector Functions], page 118, for otherways to copy sequences.
(setq bar (list 1 2))⇒ (1 2)(setq x (vector 'foo bar))⇒ [foo (1 2)](setq y (copy-sequence x))⇒ [foo (1 2)](eq x y)⇒ nil(equal x y)⇒ t(eq (elt x 1) (elt y 1))⇒ t;; Replacing an element of one sequence.
(aset x 0 'quux)x ⇒ [quux (1 2)]y ⇒ [foo (1 2)];; Modifying the inside of a shared element.
(setcar (aref x 1) 69)
x ⇒ [quux (69 2)]y ⇒ [foo (69 2)]

reverse sequence[Function]
This function creates a new sequence whose elements are the elements of sequence, but
in reverse order. The original argument sequence is not altered. Note that char-tables
cannot be reversed.
(setq x '(1 2 3 4))⇒ (1 2 3 4)
(reverse x)⇒ (4 3 2 1)x
⇒ (1 2 3 4)

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105(setq x [1 2 3 4])⇒ [1 2 3 4]
(reverse x)⇒ [4 3 2 1]x
⇒ [1 2 3 4]
(setq x "xyzzy")⇒ "xyzzy"(reverse x)⇒ "yzzyx"x⇒ "xyzzy"

nreverse sequence[Function]
This function reverses the order of the elements of sequence. Unlike reverse theoriginal sequence may be modified.
For example:(setq x (list 'a 'b 'c))⇒ (a b c)x⇒ (a b c)(nreverse x)⇒ (c b a);; The cons cell that was first is now last.
x⇒ (a)To avoid confusion, we usually store the result of nreverse back in the same variablewhich held the original list:(setq x (nreverse x))
Here is the nreverse of our favorite example, (a b c), presented graphically:
Original list head:
Reversed list:-----------------------------------| car | cdr || car | cdr || car | cdr ||a | nil |<-|b |o |<-|
c |
o |
|
|
|
| |
|
| |
| |
|
| |
------------|--------- | |-------- | ||||------------------------For the vector, it is even simpler because you don’t need setq:(setq x (copy-sequence [1 2 3 4]))
⇒ [1 2 3 4]
(nreverse x)⇒ [4 3 2 1]x
⇒ [4 3 2 1]

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106

Note that unlike reverse, this function doesn’t work with strings. Although you canalter string data by using aset, it is strongly encouraged to treat strings as immutableeven when they are mutable. See Section 2.9 [Mutability], page 36.

sort sequence predicate[Function]
This function sorts sequence stably. Note that this function doesn’t work for all
sequences; it may be used only for lists and vectors. If sequence is a list, it is modified
destructively. This functions returns the sorted sequence and compares elements using
predicate. A stable sort is one in which elements with equal sort keys maintain theirrelative order before and after the sort. Stability is important when successive sorts
are used to order elements according to different criteria.
The argument predicate must be a function that accepts two arguments. It is calledwith two elements of sequence. To get an increasing order sort, the predicate should
return non-nil if the first element is “less” than the second, or nil if not.
The comparison function predicate must give reliable results for any given pair ofarguments, at least within a single call to sort. It must be antisymmetric; that is,
if a is less than b, b must not be less than a. It must be transitive—that is, if a isless than b, and b is less than c, then a must be less than c. If you use a comparison
function which does not meet these requirements, the result of sort is unpredictable.
The destructive aspect of sort for lists is that it reuses the cons cells forming sequenceby changing their contents, possibly rearranging them in a different order. This meansthat the value of the input list is undefined after sorting; only the list returned bysort has a well-defined value. Example:(setq nums (list 2 1 4 3 0))(sort nums #'<)⇒ (0 1 2 3 4)
; nums is unpredictable at this point
Most often we store the result back into the variable that held the original list:(setq nums (sort nums #'<))
If you wish to make a sorted copy without destroying the original, copy it first andthen sort:(setq nums (list 2 1 4 3 0))(sort (copy-sequence nums) #'<)⇒ (0 1 2 3 4)nums
⇒ (2 1 4 3 0)
For the better understanding of what stable sort is, consider the following vector
example. After sorting, all items whose car is 8 are grouped at the beginning ofvector, but their relative order is preserved. All items whose car is 9 are grouped at
the end of vector, but their relative order is also preserved:(setq
vector(vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz")'(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff")))⇒ [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz")(9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")]

Chapter 6: Sequences, Arrays, and Vectors

107(sort vector (lambda (x y) (< (car x) (car y))))⇒ [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee")(9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]
See Section 33.15 [Sorting], page 906, for more functions that perform sorting. See
documentation in Section 25.2 [Accessing Documentation], page 596, for a usefulexample of sort.
The seq.el library provides the following additional sequence manipulation macros andfunctions, prefixed with seq-.
All functions defined in this library are free of side-effects; i.e., they do not modify any
sequence (list, vector, or string) that you pass as an argument. Unless otherwise stated, theresult is a sequence of the same type as the input. For those functions that take a predicate,
this should be a function of one argument.
The seq.el library can be extended to work with additional types of sequential datastructures. For that purpose, all functions are defined using cl-defgeneric. See Section 13.8
[Generic Functions], page 245, for more details about using cl-defgeneric for adding
extensions.

seq-elt sequence index[Function]
This function returns the element of sequence at the specified index, which is an
integer whose valid value range is zero to one less than the length of sequence. For
out-of-range values on built-in sequence types, seq-elt behaves like elt. For thedetails, see [Definition of elt], page 103.
(seq-elt [1 2 3 4] 2)⇒ 3
seq-elt returns places settable using setf (see Section 12.17.1 [Setting Generalized
Variables], page 224).
(setq vec [1 2 3 4])(setf (seq-elt vec 2) 5)
vec⇒ [1 2 5 4]

seq-length sequence[Function]
This function returns the number of elements in sequence. For built-in sequence types,
seq-length behaves like length. See [Definition of length], page 102.

seqp object[Function]
This function returns non-nil if object is a sequence (a list or array), or any additional
type of sequence defined via seq.el generic functions. This is an extensible variant of
sequencep.
(seqp [1 2])⇒ t(seqp 2)⇒ nil

seq-drop sequence n[Function]
This function returns all but the first n (an integer) elements of sequence. If n is
negative or zero, the result is sequence.

Chapter 6: Sequences, Arrays, and Vectors

108(seq-drop [1 2 3 4 5 6] 3)⇒ [4 5 6](seq-drop "hello world" -4)⇒ "hello world"

seq-take sequence n[Function]
This function returns the first n (an integer) elements of sequence. If n is negative orzero, the result is nil.
(seq-take '(1 2 3 4) 3)⇒ (1 2 3)(seq-take [1 2 3 4] 0)⇒ []seq-take-while predicate sequence[Function]
This function returns the members of sequence in order, stopping before the first one
for which predicate returns nil.
(seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
⇒ (1 2 3)(seq-take-while (lambda (elt) (> elt 0)) [-1 4 6])⇒ []seq-drop-while predicate sequence[Function]
This function returns the members of sequence in order, starting from the first one forwhich predicate returns nil.
(seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2))
⇒ (-1 -2)
(seq-drop-while (lambda (elt) (< elt 0)) [1 4 6])⇒ [1 4 6]

seq-split sequence length[Function]
This function returns a list consisting of sub-sequences of sequence of (at most) length
length. (The final element may be shorter than length if the length of sequence isn’t amultiple of length.
(seq-split [0 1 2 3 4] 2)⇒ ([0 1] [2 3] [4])seq-do function sequence[Function]
This function applies function to each element of sequence in turn (presumably forside effects), and returns sequence.

seq-map function sequence[Function]
This function returns the result of applying function to each element of sequence. The
returned value is a list.
(seq-map #'1+ '(2 4 6))⇒ (3 5 7)(seq-map #'symbol-name [foo bar])⇒ ("foo" "bar")Chapter 6: Sequences, Arrays, and Vectors

109

seq-map-indexed function sequence[Function]
This function returns the result of applying function to each element of sequence andits index within seq. The returned value is a list.
(seq-map-indexed (lambda (elt idx)
(list idx elt))'(a b c))⇒ ((0 a) (1 b) (2 c))

seq-mapn function &rest sequences[Function]
This function returns the result of applying function to each element of sequences.
The arity (see Section 13.1 [What Is a Function], page 230) of function must matchthe number of sequences. Mapping stops at the end of the shortest sequence, and thereturned value is a list.
(seq-mapn #'+ '(2 4 6) '(20 40 60))
⇒ (22 44 66)(seq-mapn #'concat '("moskito" "bite") ["bee" "sting"])⇒ ("moskitobee" "bitesting")

seq-filter predicate sequence[Function]
This function returns a list of all the elements in sequence for which predicate returns
non-nil.
(seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5])⇒ (1 3 5)(seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5))
⇒ nil

seq-remove predicate sequence[Function]
This function returns a list of all the elements in sequence for which predicate returns
nil.
(seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5])⇒ (-1 -3)(seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5))
⇒ nil

seq-remove-at-position sequence n[Function]
This function returns a copy of sequence where the element at (zero-based) index n
got removed. The result is a sequence of the same type as sequence.
(seq-remove-at-position [1 -1 3 -3 5] 0)⇒ [-1 3 -3 5](seq-remove-at-position [1 -1 3 -3 5] 3)⇒ [1 -1 3 5]

seq-keep function sequence[Function]
This function returns a list of all non-nil results from calling function on the elements
in sequence.
(seq-keep #'cl-digit-char-p '(?6 ?a ?7))
⇒ (6 7)

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110

seq-reduce function sequence initial-value[Function]
This function returns the result of calling function with initial-value and the firstelement of sequence, then calling function with that result and the second elementof sequence, then with that result and the third element of sequence, etc. function
should be a function of two arguments.
function is called with two arguments. initial-value (and then the accumulated value)is used as the first argument, and the elements in sequence are used for the second
argument.
If sequence is empty, this returns initial-value without calling function.
(seq-reduce #'+ [1 2 3 4] 0)⇒ 10(seq-reduce #'+ '(1 2 3 4) 5)⇒ 15(seq-reduce #'+ '() 3)⇒ 3

seq-some predicate sequence[Function]
This function returns the first non-nil value returned by applying predicate to eachelement of sequence in turn.
(seq-some #'numberp ["abc" 1 nil])⇒ t(seq-some #'numberp ["abc" "def"])⇒ nil(seq-some #'null ["abc" 1 nil])⇒ t(seq-some #'1+ [2 4 6])⇒ 3

seq-find predicate sequence &optional default[Function]
This function returns the first element in sequence for which predicate returns non-nil.
If no element matches predicate, the function returns default.
Note that this function has an ambiguity if the found element is identical to default,
as in that case it cannot be known whether an element was found or not.
(seq-find #'numberp ["abc" 1 nil])⇒ 1(seq-find #'numberp ["abc" "def"])⇒ nil

seq-every-p predicate sequence[Function]
This function returns non-nil if applying predicate to every element of sequence
returns non-nil.
(seq-every-p #'numberp [2 4 6])⇒ t(seq-every-p #'numberp [2 4 "6"])⇒ nil

Chapter 6: Sequences, Arrays, and Vectors

seq-empty-p sequence

111[Function]

This function returns non-nil if sequence is empty.
(seq-empty-p "not empty")⇒ nil(seq-empty-p "")⇒ t

seq-count predicate sequence[Function]
This function returns the number of elements in sequence for which predicate returns
non-nil.
(seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2])
⇒ 2

seq-sort function sequence[Function]
This function returns a copy of sequence that is sorted according to function, a functionof two arguments that returns non-nil if the first argument should sort before thesecond.

seq-sort-by function predicate sequence[Function]
This function is similar to seq-sort, but the elements of sequence are transformed byapplying function on them before being sorted. function is a function of one argument.
(seq-sort-by #'seq-length #'> ["a" "ab" "abc"])⇒ ["abc" "ab" "a"]seq-contains-p sequence elt &optional function[Function]
This function returns non-nil if at least one element in sequence is equal to elt. If
the optional argument function is non-nil, it is a function of two arguments to use
instead of the default equal.
(seq-contains-p '(symbol1 symbol2) 'symbol1)⇒ t(seq-contains-p '(symbol1 symbol2) 'symbol3)⇒ nil

seq-set-equal-p sequence1 sequence2 &optional testfn[Function]
This function checks whether sequence1 and sequence2 contain the same elements,
regardless of the order. If the optional argument testfn is non-nil, it is a function of
two arguments to use instead of the default equal.
(seq-set-equal-p '(a b c) '(c b a))⇒ t(seq-set-equal-p '(a b c) '(c b))⇒ nil(seq-set-equal-p '("a" "b" "c") '("c" "b" "a"))⇒ t(seq-set-equal-p '("a" "b" "c") '("c" "b" "a") #'eq)⇒ nilChapter 6: Sequences, Arrays, and Vectors

112

seq-position sequence elt &optional function[Function]
This function returns the (zero-based) index of the first element in sequence that isequal to elt. If the optional argument function is non-nil, it is a function of twoarguments to use instead of the default equal.
(seq-position '(a b c) 'b)⇒ 1(seq-position '(a b c) 'd)⇒ nil

seq-positions sequence elt &optional testfn[Function]
This function returns a list of the (zero-based) indices of the elements in sequence forwhich testfn returns non-nil when passed the element and elt as arguments. testfn
defaults to equal.
(seq-positions '(a b c a d) 'a)⇒ (0 3)(seq-positions '(a b c a d) 'z)⇒ nil(seq-positions '(11 5 7 12 9 15) 10 #'>=)⇒ (0 3 5)

seq-uniq sequence &optional function[Function]
This function returns a list of the elements of sequence with duplicates removed. If
the optional argument function is non-nil, it is a function of two arguments to use
instead of the default equal.
(seq-uniq '(1 2 2 1 3))⇒ (1 2 3)(seq-uniq '(1 2 2.0 1.0) #'=)⇒ (1 2)

seq-subseq sequence start &optional end[Function]
This function returns a subset of sequence from start to end, both integers (enddefaults to the last element). If start or end is negative, it counts from the end of
sequence.
(seq-subseq '(1 2 3 4 5) 1)⇒ (2 3 4 5)
(seq-subseq '[1 2 3 4 5] 1 3)
⇒ [2 3](seq-subseq '[1 2 3 4 5] -3 -1)⇒ [3 4]

seq-concatenate type &rest sequences[Function]
This function returns a sequence of type type made of the concatenation of sequences.
type may be: vector, list or string.
(seq-concatenate 'list '(1 2) '(3 4) [5 6])⇒ (1 2 3 4 5 6)
(seq-concatenate 'string "Hello " "world")⇒ "Hello world"Chapter 6: Sequences, Arrays, and Vectors

113

seq-mapcat function sequence &optional type

[Function]
This function returns the result of applying seq-concatenate to the result of applying
function to each element of sequence. The result is a sequence of type type, or a list if
type is nil.
(seq-mapcat #'seq-reverse '((3 2 1) (6 5 4)))⇒ (1 2 3 4 5 6)

seq-partition sequence n[Function]
This function returns a list of the elements of sequence grouped into sub-sequences oflength n. The last sequence may contain less elements than n. n must be an integer.
If n is a negative integer or 0, the return value is nil.
(seq-partition '(0 1 2 3 4 5 6 7) 3)⇒ ((0 1 2) (3 4 5) (6 7))

seq-union sequence1 sequence2 &optional function[Function]
This function returns a list of the elements that appear either in sequence1 or sequence2.
The elements of the returned list are all unique, in the sense that no two elements
there will compare equal. If the optional argument function is non-nil, it should be afunction of two arguments to use to compare elements, instead of the default equal.
(seq-union [1 2 3] [3 5])⇒ (1 2 3 5)

seq-intersection sequence1 sequence2 &optional function[Function]
This function returns a list of the elements that appear both in sequence1 andsequence2. If the optional argument function is non-nil, it is a function of twoarguments to use to compare elements instead of the default equal.
(seq-intersection [2 3 4 5] [1 3 5 6 7])⇒ (3 5)

seq-difference sequence1 sequence2 &optional function[Function]
This function returns a list of the elements that appear in sequence1 but not insequence2. If the optional argument function is non-nil, it is a function of twoarguments to use to compare elements instead of the default equal.
(seq-difference '(2 3 4 5) [1 3 5 6 7])⇒ (2 4)

seq-group-by function sequence[Function]
This function separates the elements of sequence into an alist whose keys are the resultof applying function to each element of sequence. Keys are compared using equal.
(seq-group-by #'integerp '(1 2.1 3 2 3.2))⇒ ((t 1 3 2) (nil 2.1 3.2))(seq-group-by #'car '((a 1) (b 2) (a 3) (c 4)))⇒ ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))

seq-into sequence type

[Function]
This function converts the sequence sequence into a sequence of type type. type canbe one of the following symbols: vector, string or list.
(seq-into [1 2 3] 'list)⇒ (1 2 3)

Chapter 6: Sequences, Arrays, and Vectors

114(seq-into nil 'vector)⇒ [](seq-into "hello" 'vector)⇒ [104 101 108 108 111]

seq-min sequence[Function]
This function returns the smallest element of sequence. The elements of sequencemust be numbers or markers (see Chapter 32 [Markers], page 869).
(seq-min [3 1 2])⇒ 1(seq-min "Hello")⇒ 72

seq-max sequence[Function]
This function returns the largest element of sequence. The elements of sequence mustbe numbers or markers.
(seq-max [1 3 2])⇒ 3(seq-max "Hello")⇒ 111

seq-doseq (var sequence) body. . .

[Macro]This macro is like dolist (see Section 11.5 [Iteration], page 174), except that sequencecan be a list, vector or string. This is primarily useful for side-effects.

seq-let var-sequence val-sequence body. . .

[Macro]This macro binds the variables defined in var-sequence to the values that are thecorresponding elements of val-sequence. This is known as destructuring binding.
The elements of var-sequence can themselves include sequences, allowing for nested
destructuring.
The var-sequence sequence can also include the &rest marker followed by a variablename to be bound to the rest of val-sequence.
(seq-let [first second] [1 2 3 4]
(list first second))⇒ (1 2)(seq-let (_ a _ b) '(1 2 3 4)
(list a b))⇒ (2 4)(seq-let [a [b [c]]] [1 [2 [3]]](list a b c))⇒ (1 2 3)(seq-let [a b &rest others] [1 2 3 4]others)⇒ [3 4]The pcase patterns provide an alternative facility for destructuring binding, see
Section 11.4.4 [Destructuring with pcase Patterns], page 172.

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115

seq-setq var-sequence val-sequence[Macro]This macro works similarly to seq-let, except that values are assigned to variables
as if by setq instead of as in a let binding.
(let ((a nil)(b nil))(seq-setq (_ a _ b) '(1 2 3 4))(list a b))⇒ (2 4)

seq-random-elt sequence[Function]

This function returns an element of sequence taken at random.
(seq-random-elt [1 2 3 4])⇒ 3(seq-random-elt [1 2 3 4])⇒ 2(seq-random-elt [1 2 3 4])⇒ 4(seq-random-elt [1 2 3 4])⇒ 2(seq-random-elt [1 2 3 4])⇒ 1
If sequence is empty, this function signals an error.

6.2 Arrays
An array object has slots that hold a number of other Lisp objects, called the elements of
the array. Any element of an array may be accessed in constant time. In contrast, the timeto access an element of a list is proportional to the position of that element in the list.
Emacs defines four types of array, all one-dimensional: strings (see Section 2.4.8 [StringType], page 20), vectors (see Section 2.4.9 [Vector Type], page 22), bool-vectors (seeSection 2.4.11 [Bool-Vector Type], page 23), and char-tables (see Section 2.4.10 [Char-TableType], page 22). Vectors and char-tables can hold elements of any type, but strings can only
hold characters, and bool-vectors can only hold t and nil.
All four kinds of array share these characteristics:• The first element of an array has index zero, the second element has index 1, and so on.
This is called zero-origin indexing. For example, an array of four elements has indices 0,
1, 2, and 3.
• The length of the array is fixed once you create it; you cannot change the length of an
existing array.
• For purposes of evaluation, the array is a constant—i.e., it evaluates to itself.
• The elements of an array may be referenced or changed with the functions aref andaset, respectively (see Section 6.3 [Array Functions], page 116).
When you create an array, other than a char-table, you must specify its length. You
cannot specify the length of a char-table, because that is determined by the range of charactercodes.

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116

In principle, if you want an array of text characters, you could use either a string or avector. In practice, we always choose strings for such applications, for four reasons:• They occupy one-fourth the space of a vector of the same elements.
• Strings are printed in a way that shows the contents more clearly as text.
• Strings can hold text properties. See Section 33.19 [Text Properties], page 917.
• Many of the specialized editing and I/O facilities of Emacs accept only strings. For
example, you cannot insert a vector of characters into a buffer the way you can insert astring. See Chapter 4 [Strings and Characters], page 54.
By contrast, for an array of keyboard input characters (such as a key sequence), a vector
may be necessary, because many keyboard input characters are outside the range that will
fit in a string. See Section 22.8.1 [Key Sequence Input], page 461.

6.3 Functions that Operate on Arrays
In this section, we describe the functions that accept all types of arrays.

arrayp object[Function]
This function returns t if object is an array (i.e., a vector, a string, a bool-vector or achar-table).
(arrayp [a])⇒ t(arrayp "asdf")⇒ t(arrayp (syntax-table));; A char-table.
⇒ taref arr index[Function]
This function returns the indexth element of the array or record arr. The first element
is at index zero.
(setq primes [2 3 5 7 11 13])
⇒ [2 3 5 7 11 13](aref primes 4)⇒ 11(aref "abcdefg" 1)⇒ 98; ‘b’ is ASCII code 98.
See also the function elt, in Section 6.1 [Sequence Functions], page 102.

aset array index object[Function]
This function sets the indexth element of array to be object. It returns object.
(setq w (vector 'foo 'bar 'baz))⇒ [foo bar baz](aset w 0 'fu)
⇒ fu
w
⇒ [fu bar baz]

Chapter 6: Sequences, Arrays, and Vectors

117;; copy-sequence copies the string to be modified later.
(setq x (copy-sequence "asdfasfd"))⇒ "asdfasfd"(aset x 3 ?Z)⇒ 90
x⇒ "asdZasfd"
The array should be mutable. See Section 2.9 [Mutability], page 36.
If array is a string and object is not a character, a wrong-type-argument error results.
The function converts a unibyte string to multibyte if necessary to insert a character.

fillarray array object[Function]
This function fills the array array with object, so that each element of array is object.
It returns array.
(setq a (copy-sequence [a b c d e f g]))⇒ [a b c d e f g]
(fillarray a 0)
⇒ [0 0 0 0 0 0 0]a
⇒ [0 0 0 0 0 0 0]
(setq s (copy-sequence "When in the course"))⇒ "When in the course"(fillarray s ?-)⇒ "------------------"
If array is a string and object is not a character, a wrong-type-argument error results.

The general sequence functions copy-sequence and length are often useful for objects
known to be arrays. See Section 6.1 [Sequence Functions], page 102.

6.4 Vectors
A vector is a general-purpose array whose elements can be any Lisp objects. (By contrast,
the elements of a string can only be characters. See Chapter 4 [Strings and Characters],
page 54.) Vectors are used in Emacs for many purposes: as key sequences (see Section 23.1
[Key Sequences], page 480), as symbol-lookup tables (see Section 9.3 [Creating Symbols],
page 135), as part of the representation of a byte-compiled function (see Chapter 17 [ByteCompilation], page 316), and more.
Like other arrays, vectors use zero-origin indexing: the first element has index 0.
Vectors are printed with square brackets surrounding the elements. Thus, a vector whose
elements are the symbols a, b and a is printed as [a b a]. You can write vectors in the sameway in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of
evaluating it is the same vector. This does not evaluate or even examine the elements of thevector. See Section 10.1.1 [Self-Evaluating Forms], page 146. Vectors written with square
brackets should not be modified via aset or other destructive operations. See Section 2.9[Mutability], page 36.

Chapter 6: Sequences, Arrays, and Vectors

118

Here are examples illustrating these principles:(setq avector [1 two '(three) "four" [five]])⇒ [1 two '(three) "four" [five]](eval avector)⇒ [1 two '(three) "four" [five]](eq avector (eval avector))⇒ t

6.5 Functions for Vectors
Here are some functions that relate to vectors:

vectorp object[Function]

This function returns t if object is a vector.
(vectorp [a])⇒ t(vectorp "asdf")⇒ nilvector &rest objects[Function]
This function creates and returns a vector whose elements are the arguments, objects.
(vector 'foo 23 [bar baz] "rats")⇒ [foo 23 [bar baz] "rats"](vector)⇒ []make-vector length object[Function]
This function returns a new vector consisting of length elements, each initialized toobject.
(setq sleepy (make-vector 9 'Z))
⇒ [Z Z Z Z Z Z Z Z Z]

vconcat &rest sequences[Function]
This function returns a new vector containing all the elements of sequences. The
arguments sequences may be proper lists, vectors, strings or bool-vectors. If nosequences are given, the empty vector is returned.
The value is either the empty vector, or is a newly constructed nonempty vector thatis not eq to any existing vector.
(setq a (vconcat '(A B C) '(D E F)))
⇒ [A B C D E F]
(eq a (vconcat a))⇒ nil(vconcat)⇒ [](vconcat [A B C] "aa" '(foo (6 7)))
⇒ [A B C 97 97 foo (6 7)]

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The vconcat function also allows byte-code function objects as arguments. This is a
special feature to make it easy to access the entire contents of a byte-code function
object. See Section 17.7 [Byte-Code Objects], page 323.
For other concatenation functions, see mapconcat in Section 13.6 [Mapping Functions],
page 241, concat in Section 4.3 [Creating Strings], page 55, and append in Section 5.4[Building Lists], page 82.
The append function also provides a way to convert a vector into a list with the sameelements:(setq avector [1 two (quote (three)) "four" [five]])⇒ [1 two '(three) "four" [five]](append avector nil)
⇒ (1 two '(three) "four" [five])

6.6 Char-Tables
A char-table is much like a vector, except that it is indexed by character codes. Any validcharacter code, without modifiers, can be used as an index in a char-table. You can access achar-table’s elements with aref and aset, as with any array. In addition, a char-table canhave extra slots to hold additional data not associated with particular character codes. Like
vectors, char-tables are constants when evaluated, and can hold elements of any type.
Each char-table has a subtype, a symbol, which serves two purposes:• The subtype provides an easy way to tell what the char-table is for. For instance,
display tables are char-tables with display-table as the subtype, and syntax tables
are char-tables with syntax-table as the subtype. The subtype can be queried using
the function char-table-subtype, described below.
• The subtype controls the number of extra slots in the char-table. This number is
specified by the subtype’s char-table-extra-slots symbol property (see Section 9.4[Symbol Properties], page 138), whose value should be an integer between 0 and 10. If
the subtype has no such symbol property, the char-table has no extra slots.
A char-table can have a parent, which is another char-table. If it does, then wheneverthe char-table specifies nil for a particular character c, it inherits the value specified in
the parent. In other words, (aref char-table c) returns the value from the parent ofchar-table if char-table itself specifies nil.
A char-table can also have a default value. If so, then (aref char-table c) returns thedefault value whenever the char-table does not specify any other non-nil value.

make-char-table subtype &optional init

[Function]
Return a newly-created char-table, with subtype subtype (a symbol). Each element isinitialized to init, which defaults to nil. You cannot alter the subtype of a char-table
after the char-table is created.

There is no argument to specify the length of the char-table, because all char-tables
have room for any valid character code as an index.
If subtype has the char-table-extra-slots symbol property, that specifies thenumber of extra slots in the char-table. This should be an integer between 0 and 10;

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otherwise, make-char-table raises an error. If subtype has no char-table-extraslots symbol property (see Section 5.9 [Property Lists], page 99), the char-table has
no extra slots.

char-table-p object[Function]

This function returns t if object is a char-table, and nil otherwise.

char-table-subtype char-table[Function]

This function returns the subtype symbol of char-table.
There is no special function to access default values in a char-table. To do that, usechar-table-range (see below).

char-table-parent char-table[Function]
This function returns the parent of char-table. The parent is always either nil oranother char-table.

set-char-table-parent char-table new-parent[Function]

This function sets the parent of char-table to new-parent.

char-table-extra-slot char-table n[Function]
This function returns the contents of extra slot n (zero based) of char-table. The
number of extra slots in a char-table is determined by its subtype.

set-char-table-extra-slot char-table n value[Function]

This function stores value in extra slot n (zero based) of char-table.
A char-table can specify an element value for a single character code; it can also specify
a value for an entire character set.

char-table-range char-table range[Function]
This returns the value specified in char-table for a range of characters range. Here are
the possibilities for range:
nil

Refers to the default value.

char

Refers to the element for character char (supposing char is a valid charactercode).

(from . to)
A cons cell refers to all the characters in the inclusive range ‘[from..to]’.
In this case, the function returns the value for the character specified byfrom.

set-char-table-range char-table range value[Function]
This function sets the value in char-table for a range of characters range. Here are thepossibilities for range:
nil

Refers to the default value.

tRefers to the whole range of character codes.

char

Refers to the element for character char (supposing char is a valid charactercode).

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A cons cell refers to all the characters in the inclusive range ‘[from..to]’.

map-char-table function char-table[Function]
This function calls its argument function for each element of char-table that has a
non-nil value. The call to function is with two arguments, a key and a value. The
key is a possible range argument for char-table-range—either a valid character ora cons cell (from . to), specifying a range of characters that share the same value.
The value is what (char-table-range char-table key) returns.
Overall, the key-value pairs passed to function describe all the values stored in chartable.
The return value is always nil; to make calls to map-char-table useful, function
should have side effects. For example, here is how to examine the elements of thesyntax table:(let (accumulator)(map-char-table(lambda (key value)(setq accumulator(cons (list(if (consp key)(list (car key) (cdr key))
key)
value)
accumulator)))(syntax-table))accumulator)⇒(((2597602 4194303) (2)) ((2597523 2597601) (3))... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1))... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))

6.7 Bool-vectors
A bool-vector is much like a vector, except that it stores only the values t and nil. If you
try to store any non-nil value into an element of the bool-vector, the effect is to store t
there. As with all arrays, bool-vector indices start from 0, and the length cannot be changed
once the bool-vector is created. Bool-vectors are constants when evaluated.
Several functions work specifically with bool-vectors; aside from that, you manipulatethem with same functions used for other kinds of arrays.

make-bool-vector length initial[Function]
Return a new bool-vector of length elements, each one initialized to initial.

bool-vector &rest objects[Function]
This function creates and returns a bool-vector whose elements are the arguments,
objects.

Chapter 6: Sequences, Arrays, and Vectors

bool-vector-p object

122[Function]

This returns t if object is a bool-vector, and nil otherwise.
There are also some bool-vector set operation functions, described below:bool-vector-exclusive-or a b &optional c[Function]
Return bitwise exclusive or of bool vectors a and b. If optional argument c is given,
the result of this operation is stored into c. All arguments should be bool vectors of
the same length.

bool-vector-union a b &optional c[Function]
Return bitwise or of bool vectors a and b. If optional argument c is given, the resultof this operation is stored into c. All arguments should be bool vectors of the samelength.

bool-vector-intersection a b &optional c[Function]
Return bitwise and of bool vectors a and b. If optional argument c is given, the resultof this operation is stored into c. All arguments should be bool vectors of the samelength.

bool-vector-set-difference a b &optional c[Function]
Return set difference of bool vectors a and b. If optional argument c is given, theresult of this operation is stored into c. All arguments should be bool vectors of thesame length.

bool-vector-not a &optional b[Function]
Return set complement of bool vector a. If optional argument b is given, the resultof this operation is stored into b. All arguments should be bool vectors of the samelength.

bool-vector-subsetp a b[Function]
Return t if every t value in a is also t in b, nil otherwise. All arguments should bebool vectors of the same length.

bool-vector-count-consecutive a b i[Function]
Return the number of consecutive elements in a equal b starting at i. a is a bool
vector, b is t or nil, and i is an index into a.

bool-vector-count-population a
Return the number of elements that are t in bool vector a.
The printed form represents up to 8 boolean values as a single character:(bool-vector t nil t nil)
⇒ #&4"^E"(bool-vector)⇒ #&0""
You can use vconcat to print a bool-vector like other vectors:(vconcat (bool-vector nil t nil t))⇒ [nil t nil t][Function]

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Here is another example of creating, examining, and updating a bool-vector:(setq bv (make-bool-vector 5 t))⇒ #&5"^_"(aref bv 1)⇒ t(aset bv 3 nil)
⇒ nilbv
⇒ #&5"^W"
These results make sense because the binary codes for control- and control-W are 11111
and 10111, respectively.

6.8 Managing a Fixed-Size Ring of Objects
A ring is a fixed-size data structure that supports insertion, deletion, rotation, and moduloindexed reference and traversal. An efficient ring data structure is implemented by the ringpackage. It provides the functions listed in this section.
Note that several rings in Emacs, like the kill ring and the mark ring, are actually
implemented as simple lists, not using the ring package; thus the following functions won’t
work on them.

make-ring size

[Function]
This returns a new ring capable of holding size objects. size should be an integer.

ring-p object[Function]

This returns t if object is a ring, nil otherwise.

ring-size ring

[Function]

This returns the maximum capacity of the ring.

ring-length ring

[Function]
This returns the number of objects that ring currently contains. The value will neverexceed that returned by ring-size.

ring-elements ring

[Function]

This returns a list of the objects in ring, in order, newest first.

ring-copy ring

[Function]
This returns a new ring which is a copy of ring. The new ring contains the same (eq)objects as ring.

ring-empty-p ring

[Function]

This returns t if ring is empty, nil otherwise.
The newest element in the ring always has index 0. Higher indices correspond to older
elements. Indices are computed modulo the ring length. Index −1 corresponds to the oldest
element, −2 to the next-oldest, and so forth.

ring-ref ring index[Function]
This returns the object in ring found at index index. index may be negative or greaterthan the ring length. If ring is empty, ring-ref signals an error.

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ring-insert ring object[Function]
This inserts object into ring, making it the newest element, and returns object.
If the ring is full, insertion removes the oldest element to make room for the newelement.

ring-remove ring &optional index[Function]
Remove an object from ring, and return that object. The argument index specifies
which item to remove; if it is nil, that means to remove the oldest item. If ring is
empty, ring-remove signals an error.

ring-insert-at-beginning ring object[Function]
This inserts object into ring, treating it as the oldest element. The return value is not
significant.
If the ring is full, this function removes the newest element to make room for theinserted element.

ring-resize ring size

[Function]
Set the size of ring to size. If the new size is smaller, then the oldest items in the ringare discarded.

If you are careful not to exceed the ring size, you can use the ring as a first-in-first-out
queue. For example:(let ((fifo (make-ring 5)))
(mapc (lambda (obj) (ring-insert fifo obj))'(0 one "two"))(list (ring-remove fifo) t(ring-remove fifo) t(ring-remove fifo)))⇒ (0 t one t "two")125

7 Records
The purpose of records is to allow programmers to create objects with new types that are
not built into Emacs. They are used as the underlying representation of cl-defstruct anddefclass instances.
Internally, a record object is much like a vector; its slots can be accessed using aref andit can be copied using copy-sequence. However, the first slot is used to hold its type as
returned by type-of. Also, in the current implementation records can have at most 4096
slots, whereas vectors can be much larger. Like arrays, records use zero-origin indexing: thefirst slot has index 0.
The type slot should be a symbol or a type descriptor. If it’s a type descriptor, thesymbol naming its type will be returned; Section 2.4.18 [Type Descriptors], page 25. Anyother kind of object is returned as-is.
The printed representation of records is ‘#s’ followed by a list specifying the contents.
The first list element must be the record type. The following elements are the record slots.
To avoid conflicts with other type names, Lisp programs that define new types of records
should normally use the naming conventions of the package where these record types are
introduced for the names of the types. Note that the names of the types which could possibly
conflict might not be known at the time the package defining a record type is loaded; they
could be loaded at some future point in time.
A record is considered a constant for evaluation: the result of evaluating it is the same
record. This does not evaluate or even examine the slots. See Section 10.1.1 [Self-Evaluating
Forms], page 146.

7.1 Record Functions
recordp object[Function]

This function returns t if object is a record.
(recordp #s(a))⇒ trecord type &rest objects[Function]
This function creates and returns a record whose type is type and remaining slots are
the rest of the arguments, objects.
(record 'foo 23 [bar baz] "rats")⇒ #s(foo 23 [bar baz] "rats")

make-record type length object[Function]
This function returns a new record with type type and length more slots, each initialized
to object.
(setq sleepy (make-record 'foo 9 'Z))
⇒ #s(foo Z Z Z Z Z Z Z Z Z)

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7.2 Backward Compatibility
Code compiled with older versions of cl-defstruct that doesn’t use records may run
into problems when used in a new Emacs. To alleviate this, Emacs detects when an old
cl-defstruct is used, and enables a mode in which type-of handles old struct objects as
if they were records.

cl-old-struct-compat-mode arg
If arg is positive, enable backward compatibility with old-style structs.

[Function]

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8 Hash Tables
A hash table is a very fast kind of lookup table, somewhat like an alist (see Section 5.8[Association Lists], page 95) in that it maps keys to corresponding values. It differs from analist in these ways:• Lookup in a hash table is extremely fast for large tables—in fact, the time required
is essentially independent of how many elements are stored in the table. For smaller
tables (a few tens of elements) alists may still be faster because hash tables have amore-or-less constant overhead.
• The correspondences in a hash table are in no particular order.
• There is no way to share structure between two hash tables, the way two alists canshare a common tail.
Emacs Lisp provides a general-purpose hash table data type, along with a series offunctions for operating on them. Hash tables have a special printed representation, which
consists of ‘#s’ followed by a list specifying the hash table properties and contents. See
Section 8.1 [Creating Hash], page 127. (Hash notation, the initial ‘#’ character used in theprinted representations of objects with no read representation, has nothing to do with hashtables. See Section 2.1 [Printed Representation], page 8.)
Obarrays are also a kind of hash table, but they are a different type of object and areused only for recording interned symbols (see Section 9.3 [Creating Symbols], page 135).

8.1 Creating Hash Tables
The principal function for creating a hash table is make-hash-table.

make-hash-table &rest keyword-args[Function]
This function creates a new hash table according to the specified arguments. The
arguments should consist of alternating keywords (particular symbols recognizedspecially) and values corresponding to them.
Several keywords make sense in make-hash-table, but the only two that you reallyneed to know about are :test and :weakness.
:test test
This specifies the method of key lookup for this hash table. The default
is eql; eq and equal are other alternatives:eql

Keys which are numbers are the same if they are equal, thatis, if they are equal in value and either both are integers orboth are floating point; otherwise, two distinct objects arenever the same.

eq

Any two distinct Lisp objects are different as keys.

equal

Two Lisp objects are the same, as keys, if they are equal
according to equal.

You can use define-hash-table-test (see Section 8.3 [Defining Hash],page 130) to define additional possibilities for test.

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128:weakness weak
The weakness of a hash table specifies whether the presence of a key orvalue in the hash table preserves it from garbage collection.
The value, weak, must be one of nil, key, value, key-or-value,
key-and-value, or t which is an alias for key-and-value. If weak is
key then the hash table does not prevent its keys from being collected as
garbage (if they are not referenced anywhere else); if a particular key
does get collected, the corresponding association is removed from thehash table.
If weak is value, then the hash table does not prevent values frombeing collected as garbage (if they are not referenced anywhere else); if
a particular value does get collected, the corresponding association isremoved from the hash table.
If weak is key-and-value or t, both the key and the value must be live
in order to preserve the association. Thus, the hash table does not protect
either keys or values from garbage collection; if either one is collected as
garbage, that removes the association.
If weak is key-or-value, either the key or the value can preserve theassociation. Thus, associations are removed from the hash table when boththeir key and value would be collected as garbage (if not for referencesfrom weak hash tables).
The default for weak is nil, so that all keys and values referenced in thehash table are preserved from garbage collection.
:size size
This specifies a hint for how many associations you plan to store in thehash table. If you know the approximate number, you can make things
a little more efficient by specifying it this way. If you specify too smalla size, the hash table will grow automatically when necessary, but doingthat takes some extra time.
The default size is 65.
:rehash-size rehash-size
When you add an association to a hash table and the table is full, it grows
automatically. This value specifies how to make the hash table larger, atthat time.
If rehash-size is an integer, it should be positive, and the hash table grows
by adding approximately that much to the nominal size. If rehash-size is
floating point, it had better be greater than 1, and the hash table grows
by multiplying the old size by approximately that number.
The default value is 1.5.
:rehash-threshold threshold
This specifies the criterion for when the hash table is full (so it should bemade larger). The value, threshold, should be a positive floating-point
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129

number of entries exceeds the nominal size multiplied by an approximation
to this value. The default for threshold is 0.8125.
You can also create a hash table using the printed representation for hash tables. The
Lisp reader can read this printed representation, provided each element in the specified
hash table has a valid read syntax (see Section 2.1 [Printed Representation], page 8). For
instance, the following specifies a hash table containing the keys key1 and key2 (bothsymbols) associated with val1 (a symbol) and 300 (a number) respectively.
#s(hash-table size 30 data (key1 val1 key2 300))
Note, however, that when using this in Emacs Lisp code, it’s undefined whether thiscreates a new hash table or not. If you want to create a new hash table, you should always
use make-hash-table (see Section 10.1.1 [Self-Evaluating Forms], page 146).
The printed representation for a hash table consists of ‘#s’ followed by a list beginningwith ‘hash-table’. The rest of the list should consist of zero or more property-value pairs
specifying the hash table’s properties and initial contents. The properties and values are read
literally. Valid property names are size, test, weakness, rehash-size, rehash-threshold,and data. The data property should be a list of key-value pairs for the initial contents;
the other properties have the same meanings as the matching make-hash-table keywords(:size, :test, etc.), described above.
Note that you cannot specify a hash table whose initial contents include objects thathave no read syntax, such as buffers and frames. Such objects may be added to the hashtable after it is created.

8.2 Hash Table AccessThis section describes the functions for accessing and storing associations in a hash table. In
general, any Lisp object can be used as a hash key, unless the comparison method imposes
limits. Any Lisp object can also be used as the value.

gethash key table &optional default[Function]
This function looks up key in table, and returns its associated value—or default, if
key has no association in table.

puthash key value table[Function]
This function enters an association for key in table, with value value. If key alreadyhas an association in table, value replaces the old associated value. This function
always returns value.

remhash key table[Function]
This function removes the association for key from table, if there is one. If key has no
association, remhash does nothing.
Common Lisp note: In Common Lisp, remhash returns non-nil if it actually removed
an association and nil otherwise. In Emacs Lisp, remhash always returns nil.

clrhash table[Function]
This function removes all the associations from hash table table, so that it becomes
empty. This is also called clearing the hash table. clrhash returns the empty table.

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maphash function table[Function]
This function calls function once for each of the associations in table. The function
function should accept two arguments—a key listed in table, and its associated value.
maphash returns nil.

8.3 Defining Hash Comparisons
You can define new methods of key lookup by means of define-hash-table-test. In order
to use this feature, you need to understand how hash tables work, and what a hash codemeans.
You can think of a hash table conceptually as a large array of many slots, each capableof holding one association. To look up a key, gethash first computes an integer, the hashcode, from the key. It can reduce this integer modulo the length of the array, to produce anindex in the array. Then it looks in that slot, and if necessary in other nearby slots, to see if
it has found the key being sought.
Thus, to define a new method of key lookup, you need to specify both a function tocompute the hash code from a key, and a function to compare two keys directly. The twofunctions should be consistent with each other: that is, two keys’ hash codes should be thesame if the keys compare as equal. Also, since the two functions can be called at any time(such as by the garbage collector), the functions should be free of side effects and should
return quickly, and their behavior should depend on only on properties of the keys that do
not change.

define-hash-table-test name test-fn hash-fn[Function]

This function defines a new hash table test, named name.
After defining name in this way, you can use it as the test argument in make-hashtable. When you do that, the hash table will use test-fn to compare key values, andhash-fn to compute a hash code from a key value.
The function test-fn should accept two arguments, two keys, and return non-nil ifthey are considered the same.
The function hash-fn should accept one argument, a key, and return an integer that is
the hash code of that key. For good results, the function should use the whole rangeof fixnums for hash codes, including negative fixnums.
The specified functions are stored in the property list of name under the property
hash-table-test; the property value’s form is (test-fn hash-fn).

sxhash-equal obj[Function]
This function returns a hash code for Lisp object obj. This is an integer that reflects
the contents of obj and the other Lisp objects it points to.
If two objects obj1 and obj2 are equal, then (sxhash-equal obj1) and(sxhash-equal obj2) are the same integer.
If the two objects are not equal, the values returned by sxhash-equal are usuallydifferent, but not always. sxhash-equal is designed to be reasonably fast (since it’sused for indexing hash tables) so it won’t recurse deeply into nested structures. In
addition; once in a rare while, by luck, you will encounter two distinct-looking simple

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objects that give the same result from sxhash-equal. So you can’t, in general, use
sxhash-equal to check whether an object has changed.
Common Lisp note: In Common Lisp a similar function is called sxhash. Emacs
provides this name as a compatibility alias for sxhash-equal.

sxhash-eq obj[Function]
This function returns a hash code for Lisp object obj. Its result reflects identity ofobj, but not its contents.
If two objects obj1 and obj2 are eq, then (sxhash-eq obj1) and (sxhash-eq obj2)
are the same integer.

sxhash-eql obj[Function]
This function returns a hash code for Lisp object obj suitable for eql comparison. I.e.
it reflects identity of obj except for the case where the object is a bignum or a float
number, in which case a hash code is generated for the value.
If two objects obj1 and obj2 are eql, then (sxhash-eql obj1) and (sxhash-eqlobj2) are the same integer.

This example creates a hash table whose keys are strings that are compared caseinsensitively.
(defun string-hash-ignore-case (a)(sxhash-equal (upcase a)))(define-hash-table-test 'ignore-case'string-equal-ignore-case 'string-hash-ignore-case)(make-hash-table :test 'ignore-case)
Here is how you could define a hash table test equivalent to the predefined test value
equal. The keys can be any Lisp object, and equal-looking objects are considered the samekey.
(define-hash-table-test 'contents-hash 'equal 'sxhash-equal)(make-hash-table :test 'contents-hash)
Lisp programs should not rely on hash codes being preserved between Emacs sessions, as
the implementation of the hash functions uses some details of the object storage that canchange between sessions and between different architectures.

8.4 Other Hash Table Functions
Here are some other functions for working with hash tables.

hash-table-p table[Function]

This returns non-nil if table is a hash table object.

copy-hash-table table[Function]
This function creates and returns a copy of table. Only the table itself is copied—thekeys and values are shared.

Chapter 8: Hash Tables

hash-table-count table

132[Function]

This function returns the actual number of entries in table.

hash-table-test table[Function]
This returns the test value that was given when table was created, to specify how
to hash and compare keys. See make-hash-table (see Section 8.1 [Creating Hash],page 127).

hash-table-weakness table[Function]
This function returns the weak value that was specified for hash table table.

hash-table-rehash-size table[Function]

This returns the rehash size of table.

hash-table-rehash-threshold table[Function]

This returns the rehash threshold of table.

hash-table-size table
This returns the current nominal size of table.

[Function]

133

9 Symbols
A symbol is an object with a unique name. This chapter describes symbols, their components,
their property lists, and how they are created and interned. Separate chapters describe theuse of symbols as variables and as function names; see Chapter 12 [Variables], page 189, andChapter 13 [Functions], page 230. For the precise read syntax for symbols, see Section 2.4.4[Symbol Type], page 14.
You can test whether an arbitrary Lisp object is a symbol with symbolp:

symbolp object[Function]

This function returns t if object is a symbol, nil otherwise.

9.1 Symbol Components
Each symbol has four components (or “cells”), each of which references another object:
Print name
The symbol’s name.
Value

The symbol’s current value as a variable.

Function

The symbol’s function definition. It can also hold a symbol, a keymap, or a
keyboard macro.

Property list
The symbol’s property list.
The print name cell always holds a string, and cannot be changed. Each of the other threecells can be set to any Lisp object.
The print name cell holds the string that is the name of a symbol. Since symbols are
represented textually by their names, it is important not to have two symbols with the same
name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing
symbol with the specified name before it creates a new one. To get a symbol’s name, use thefunction symbol-name (see Section 9.3 [Creating Symbols], page 135). However, althougheach symbol has only one unique print name, it is nevertheless possible to refer to thatsame symbol via different alias names called “shorthands” (see Section 9.5 [Shorthands],
page 142).
The value cell holds a symbol’s value as a variable, which is what you get if the symbol
itself is evaluated as a Lisp expression. See Chapter 12 [Variables], page 189, for details
about how values are set and retrieved, including complications such as local bindings andscoping rules. Most symbols can have any Lisp object as a value, but certain special symbols
have values that cannot be changed; these include nil and t, and any symbol whose namestarts with ‘:’ (those are called keywords). See Section 12.2 [Constant Variables], page 189.
The function cell holds a symbol’s function definition. Often, we refer to “the functionfoo” when we really mean the function stored in the function cell of foo; we make thedistinction explicit only when necessary. Typically, the function cell is used to hold a function(see Chapter 13 [Functions], page 230) or a macro (see Chapter 14 [Macros], page 268).
However, it can also be used to hold a symbol (see Section 10.1.4 [Function Indirection],
page 147), keyboard macro (see Section 22.16 [Keyboard Macros], page 478), keymap (seeChapter 9: Symbols

134

Chapter 23 [Keymaps], page 480), or autoload object (see Section 10.1.8 [Autoloading],
page 150). To get the contents of a symbol’s function cell, use the function symbol-function(see Section 13.9 [Function Cells], page 248).
The property list cell normally should hold a correctly formatted property list. To get asymbol’s property list, use the function symbol-plist. See Section 9.4 [Symbol Properties],
page 138.
The function cell or the value cell may be void, which means that the cell does notreference any object. (This is not the same thing as holding the symbol void, nor the same
as holding the symbol nil.) Examining a function or value cell that is void results in anerror, such as ‘Symbol's value as variable is void’.
Because each symbol has separate value and function cells, variables names and function
names do not conflict. For example, the symbol buffer-file-name has a value (the nameof the file being visited in the current buffer) as well as a function definition (a primitive
function that returns the name of the file):
buffer-file-name⇒ "/gnu/elisp/symbols.texi"(symbol-function 'buffer-file-name)⇒ #<subr buffer-file-name>

9.2 Defining Symbols
A definition is a special kind of Lisp expression that announces your intention to use asymbol in a particular way. It typically specifies a value or meaning for the symbol for
one kind of use, plus documentation for its meaning when used in this way. Thus, when
you define a symbol as a variable, you can supply an initial value for the variable, plus
documentation for the variable.
defvar and defconst are special forms that define a symbol as a global variable—avariable that can be accessed at any point in a Lisp program. See Chapter 12 [Variables],page 189, for details about variables. To define a customizable variable, use the defcustom
macro, which also calls defvar as a subroutine (see Chapter 15 [Customization], page 277).
In principle, you can assign a variable value to any symbol with setq, whether or notit has first been defined as a variable. However, you ought to write a variable definition
for each global variable that you want to use; otherwise, your Lisp program may not act
correctly if it is evaluated with lexical scoping enabled (see Section 12.10 [Variable Scoping],
page 201).
defun defines a symbol as a function, creating a lambda expression and storing it in thefunction cell of the symbol. This lambda expression thus becomes the function definition of
the symbol. (The term “function definition”, meaning the contents of the function cell, isderived from the idea that defun gives the symbol its definition as a function.) defsubst anddefalias are two other ways of defining a function. See Chapter 13 [Functions], page 230.
defmacro defines a symbol as a macro. It creates a macro object and stores it in thefunction cell of the symbol. Note that a given symbol can be a macro or a function, but
not both at once, because both macro and function definitions are kept in the function cell,and that cell can hold only one Lisp object at any given time. See Chapter 14 [Macros],
page 268.

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As previously noted, Emacs Lisp allows the same symbol to be defined both as a variable(e.g., with defvar) and as a function or macro (e.g., with defun). Such definitions do notconflict.
These definitions also act as guides for programming tools. For example, the C-h f and
C-h v commands create help buffers containing links to the relevant variable, function, or
macro definitions. See Section “Name Help” in The GNU Emacs Manual.

9.3 Creating and Interning Symbols
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads
them. Lisp must ensure that it finds the same symbol every time it reads the same sequenceof characters in the same context. Failure to do so would cause complete confusion.
When the Lisp reader encounters a name that references a symbol in the source code,
it reads all the characters of that name. Then it looks up that name in a table called anobarray to find the symbol that the programmer meant. The technique used in this lookup
is called “hashing”, an efficient method of looking something up by converting a sequenceof characters to a number, known as a “hash code”. For example, instead of searching atelephone book cover to cover when looking up Jan Jones, you start with the J’s and gofrom there. That is a simple version of hashing. Each element of the obarray is a bucket
which holds all the symbols with a given hash code; to look for a given name, it is sufficient
to look through all the symbols in the bucket for that name’s hash code. (The same idea isused for general Emacs hash tables, but they are a different data type; see Chapter 8 [HashTables], page 127.)
When looking up names, the Lisp reader also considers “shorthands”. If the programmer
supplied them, this allows the reader to find a symbol even if its name isn’t present in its
full form in the source code. Of course, the reader needs to be aware of some pre-establishedcontext about such shorthands, much as one needs context to be to able to refer uniquely to
Jan Jones by just the name “Jan”: it’s probably fine when amongst the Joneses, or when
Jan has been mentioned recently, but very ambiguous in any other situation. See Section 9.5[Shorthands], page 142.
If a symbol with the desired name is found, the reader uses that symbol. If the obarraydoes not contain a symbol with that name, the reader makes a new symbol and adds it tothe obarray. Finding or adding a symbol with a certain name is called interning it, and thesymbol is then called an interned symbol.
Interning ensures that each obarray has just one symbol with any particular name. Other
like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same
symbols for the same names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes other programs
may want to do it. For example, after the M-x command obtains the command name as astring using the minibuffer, it then interns the string, to get the interned symbol with thatname. As another example, a hypothetical telephone book program could intern the nameof each looked up person’s name as a symbol, even if the obarray did not contain it, so thatit could attach information to that new symbol, such as the last time someone looked it up.
No obarray contains all symbols; in fact, some symbols are not in any obarray. They arecalled uninterned symbols. An uninterned symbol has the same four cells as other symbols;
however, the only way to gain access to it is by finding it in some other object or as theChapter 9: Symbols

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value of a variable. Uninterned symbols are sometimes useful in generating Lisp code, see
below.
In Emacs Lisp, an obarray is actually a vector. Each element of the vector is a bucket;
its value is either an interned symbol whose name hashes to that bucket, or 0 if the bucket is
empty. Each interned symbol has an internal link (invisible to the user) to the next symbolin the bucket. Because these links are invisible, there is no way to find all the symbols in an
obarray except using mapatoms (below). The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, so you can create an obarray with (make-vector
length 0). This is the only valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also good.
Do not try to put symbols in an obarray yourself. This does not work—only intern canenter a symbol in an obarray properly.
Common Lisp note: Unlike Common Lisp, Emacs Lisp does not provide forinterning the same name in several different “packages”, thus creating multiple
symbols with the same name but different packages. Emacs Lisp provides adifferent namespacing system called “shorthands” (see Section 9.5 [Shorthands],
page 142).
Most of the functions below take a name and sometimes an obarray as arguments. A
wrong-type-argument error is signaled if the name is not a string, or if the obarray is nota vector.

symbol-name symbol[Function]

This function returns the string that is symbol’s name. For example:(symbol-name 'foo)⇒ "foo"Warning: Never alter the string returned by that function. Doing that might makeEmacs dysfunctional, and might even crash Emacs.
Creating an uninterned symbol is useful in generating Lisp code, because an uninterned
symbol used as a variable in the code you generate cannot clash with any variables used inother Lisp programs.

make-symbol name

[Function]
This function returns a newly-allocated, uninterned symbol whose name is name(which must be a string). Its value and function definition are void, and its property
list is nil. In the example below, the value of sym is not eq to foo because it is adistinct uninterned symbol whose name is also ‘foo’.
(setq sym (make-symbol "foo"))⇒ foo(eq sym 'foo)⇒ nilgensym &optional prefix[Function]
This function returns a symbol using make-symbol, whose name is made by appending
gensym-counter to prefix and incrementing that counter, guaranteeing that no twocalls to this function will generate a symbol with the same name. The prefix defaults
to "g".

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To avoid problems when accidentally interning printed representation of generated code
(see Section 2.1 [Printed Representation], page 8), it is recommended to use gensym insteadof make-symbol.

intern name &optional obarray[Function]
This function returns the interned symbol whose name is name. If there is no such
symbol in the obarray obarray, intern creates a new one, adds it to the obarray, andreturns it. If obarray is omitted, the value of the global variable obarray is used.
(setq sym (intern "foo"))⇒ foo(eq sym 'foo)⇒ t(setq sym1 (intern "foo" other-obarray))⇒ foo(eq sym1 'foo)⇒ nilCommon Lisp note: In Common Lisp, you can intern an existing symbol in an
obarray. In Emacs Lisp, you cannot do this, because the argument to internmust be a string, not a symbol.

intern-soft name &optional obarray[Function]
This function returns the symbol in obarray whose name is name, or nil if obarrayhas no symbol with that name. Therefore, you can use intern-soft to test whether
a symbol with a given name is already interned. If obarray is omitted, the value ofthe global variable obarray is used.
The argument name may also be a symbol; in that case, the function returns name ifname is interned in the specified obarray, and otherwise nil.
(intern-soft "frazzle"); No such symbol exists.
⇒ nil(make-symbol "frazzle"); Create an uninterned one.
⇒ frazzle(intern-soft "frazzle"); That one cannot be found.
⇒ nil(setq sym (intern "frazzle")) ; Create an interned one.
⇒ frazzle(intern-soft "frazzle"); That one can be found!
⇒ frazzle(eq sym 'frazzle); And it is the same one.
⇒ tobarray[Variable]

This variable is the standard obarray for use by intern and read.

mapatoms function &optional obarray[Function]
This function calls function once with each symbol in the obarray obarray. Then it
returns nil. If obarray is omitted, it defaults to the value of obarray, the standard
obarray for ordinary symbols.

Chapter 9: Symbols

138(setq count 0)⇒ 0(defun count-syms (s)(setq count (1+ count)))⇒ count-syms(mapatoms 'count-syms)
⇒ nil
count
⇒ 1871
See documentation in Section 25.2 [Accessing Documentation], page 596, for anotherexample using mapatoms.

unintern symbol obarray[Function]
This function deletes symbol from the obarray obarray. If symbol is not actually inthe obarray, unintern does nothing. If obarray is nil, the current obarray is used.
If you provide a string instead of a symbol as symbol, it stands for a symbol name.
Then unintern deletes the symbol (if any) in the obarray which has that name. If
there is no such symbol, unintern does nothing.
If unintern does delete a symbol, it returns t. Otherwise it returns nil.

9.4 Symbol Properties
A symbol may possess any number of symbol properties, which can be used to record miscellaneous information about the symbol. For example, when a symbol has a risky-localvariable property with a non-nil value, that means the variable which the symbol names
is a risky file-local variable (see Section 12.12 [File Local Variables], page 213).
Each symbol’s properties and property values are stored in the symbol’s property list
cell (see Section 9.1 [Symbol Components], page 133), in the form of a property list (seeSection 5.9 [Property Lists], page 99).

9.4.1 Accessing Symbol Properties
The following functions can be used to access symbol properties.

get symbol property[Function]
This function returns the value of the property named property in symbol’s property
list. If there is no such property, it returns nil. Thus, there is no distinction between
a value of nil and the absence of the property.
The name property is compared with the existing property names using eq, so any
object is a legitimate property.
See put for an example.

put symbol property value[Function]
This function puts value onto symbol’s property list under the property name property,
replacing any previous property value. The put function returns value.
(put 'fly 'verb 'transitive)⇒'transitiveChapter 9: Symbols

139(put 'fly 'noun '(a buzzing little bug))⇒ (a buzzing little bug)(get 'fly 'verb)⇒ transitive(symbol-plist 'fly)⇒ (verb transitive noun (a buzzing little bug))symbol-plist symbol[Function]

This function returns the property list of symbol.

setplist symbol plist[Function]
This function sets symbol’s property list to plist. Normally, plist should be a wellformed property list, but this is not enforced. The return value is plist.
(setplist 'foo '(a 1 b (2 3) c nil))⇒ (a 1 b (2 3) c nil)(symbol-plist 'foo)⇒ (a 1 b (2 3) c nil)
For symbols in special obarrays, which are not used for ordinary purposes, it may
make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev
mechanism does so (see Chapter 38 [Abbrevs], page 1066).

You could define put in terms of setplist and plist-put, as follows:(defun put (symbol prop value)(setplist symbol(plist-put (symbol-plist symbol) prop value)))function-get symbol property &optional autoload[Function]
This function is identical to get, except that if symbol is the name of a function alias,
it looks in the property list of the symbol naming the actual function. See Section 13.4
[Defining Functions], page 237. If the optional argument autoload is non-nil, andsymbol is auto-loaded, this function will try to autoload it, since autoloading might set
property of symbol. If autoload is the symbol macro, only try autoloading if symbol
is an auto-loaded macro.

function-put function property value[Function]
This function sets property of function to value. function should be a symbol. Thisfunction is preferred to calling put for setting properties of a function, because it willallow us some day to implement remapping of old properties to new ones.

9.4.2 Standard Symbol Properties
Here, we list the symbol properties which are used for special purposes in Emacs. In thefollowing table, whenever we say “the named function”, that means the function whosename is the relevant symbol; similarly for “the named variable” etc.
:advertised-binding
This property value specifies the preferred key binding, when showing documentation, for the named function. See Section 25.3 [Keys in Documentation],
page 598.

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char-table-extra-slots
The value, if non-nil, specifies the number of extra slots in the named char-table
type. See Section 6.6 [Char-Tables], page 119.
customized-faceface-defface-spec
saved-facetheme-face
These properties are used to record a face’s standard, saved, customized, andthemed face specs. Do not set them directly; they are managed by defface andrelated functions. See Section 41.12.2 [Defining Faces], page 1168.
customized-value
saved-value
standard-value
theme-value
These properties are used to record a customizable variable’s standard value,
saved value, customized-but-unsaved value, and themed values. Do not set them
directly; they are managed by defcustom and related functions. See Section 15.3
[Variable Definitions], page 280.
definition-nameThis property is used to find the definition of a symbol in the source code,when it might be hard to find the definition by textual search of the source
file. For example, a define-derived-mode (see Section 24.2.4 [Derived Modes],page 534) might define a mode-specific function or a variable implicitly; or
your Lisp program might generate a run-time call to defun to define a function(see Section 13.4 [Defining Functions], page 237). In these and similar cases,
the definition-name property of the symbol should be another symbol whose
definition can be found by textual search and whose code defines the original
symbol. In the example with define-derived-mode, the value of this propertyof the functions and variables it defines should be the mode symbol. The Emacs
Help commands such as C-h f (see Section “Help” in The GNU Emacs Manual)
use this property to show the definition of a symbol via a button in the *Help*
buffer where the symbol’s documentation is shown.
disabled

If the value is non-nil, the named function is disabled as a command. See
Section 22.14 [Disabling Commands], page 476.

face-documentation
The value stores the documentation string of the named face. This is set
automatically by defface. See Section 41.12.2 [Defining Faces], page 1168.
history-length
The value, if non-nil, specifies the maximum minibuffer history length for thenamed history list variable. See Section 21.4 [Minibuffer History], page 392.
interactive-form
The value is an interactive form for the named function. Normally, you should
not set this directly; use the interactive special form instead. See Section 22.3
[Interactive Call], page 432.

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menu-enable
The value is an expression for determining whether the named menu item should
be enabled in menus. See Section 23.18.1.1 [Simple Menu Items], page 510.
mode-class
If the value is special, the named major mode is special. See Section 24.2.1[Major Mode Conventions], page 528.
permanent-local
If the value is non-nil, the named variable is a buffer-local variable whose value
should not be reset when changing major modes. See Section 12.11.2 [Creating
Buffer-Local], page 208.
permanent-local-hook
If the value is non-nil, the named function should not be deleted from thelocal value of a hook variable when changing major modes. See Section 24.1.2[Setting Hooks], page 525.
pure

If the value is non-nil, the named function is considered to be pure (seeSection 13.1 [What Is a Function], page 230). Calls with constant arguments
can be evaluated at compile time. This may shift run time errors to compile
time. Not to be confused with pure storage (see Section E.2 [Pure Storage],
page 1349).

risky-local-variable
If the value is non-nil, the named variable is considered risky as a file-local
variable. See Section 12.12 [File Local Variables], page 213.
safe-function
If the value is non-nil, the named function is considered generally safe for
evaluation. See Section 13.17 [Function Safety], page 266.
safe-local-eval-function
If the value is non-nil, the named function is safe to call in file-local evaluation
forms. See Section 12.12 [File Local Variables], page 213.
safe-local-variable
The value specifies a function for determining safe file-local values for the named
variable. See Section 12.12 [File Local Variables], page 213. Since this value isconsulted when loading files, the function should be efficient and should ideally
not lead to loading any libraries to determine the safeness (e.g., it should not
be an autoloaded function).
side-effect-free
A non-nil value indicates that the named function is free of side effects (seeSection 13.1 [What Is a Function], page 230), so the byte compiler may ignore
a call whose value is unused. If the property’s value is error-free, the byte
compiler may even delete such unused calls. In addition to byte compiler
optimizations, this property is also used for determining function safety (seeSection 13.17 [Function Safety], page 266).

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undo-inhibit-region
If non-nil, the named function prevents the undo operation from being restricted
to the active region, if undo is invoked immediately after the function. See
Section 33.9 [Undo], page 895.
variable-documentation
If non-nil, this specifies the named variable’s documentation string. This is set
automatically by defvar and related functions. See Section 41.12.2 [Defining
Faces], page 1168.

9.5 Shorthands
The symbol shorthands, sometimes known as “renamed symbols”, are symbolic forms foundin Lisp source. They’re just like regular symbolic forms, except that when the Lisp reader
encounters them, it produces symbols which have a different and usually longer print name(see Section 9.1 [Symbol Components], page 133).
It is useful to think of shorthands as abbreviating the full names of intended symbols.
Despite this, do not confuse shorthands with the Abbrev system (see Chapter 38 [Abbrevs],
page 1066).
Shorthands make Emacs Lisp’s namespacing etiquette easier to work with. Since all
symbols are stored in a single obarray (see Section 9.3 [Creating Symbols], page 135), programmers commonly prefix each symbol name with the name of the library where it originates.
For example, the functions text-property-search-forward and text-property-searchbackward both belong to the text-property-search.el library (see Chapter 16 [Loading],
page 298). By properly prefixing symbol names, one effectively prevents clashes between
similarly named symbols which belong to different libraries and thus do different things.
However, this practice commonly originates very long symbols names, which are inconvenient
to type and read after a while. Shorthands solve these issues in a clean way.
[Variable]
This variable’s value is an alist whose elements have the form (shorthand-prefix. longhand-prefix). Each element instructs the Lisp reader to read every symbol
form which starts with shorthand-prefix as if it started with longhand-prefix instead.

read-symbol-shorthandsThis variable may only be set in file-local variables (see Section “Local Variables inFiles” in The GNU Emacs Manual).
Here’s an example of shorthands usage in a hypothetical string manipulating librarysome-nice-string-utils.el.
(defun some-nice-string-utils-split (separator s &optional omit-nulls)"A match-data saving variant of `split-string'."(save-match-data (split-string s separator omit-nulls)))(defun some-nice-string-utils-lines (s)"Split string S at newline characters into a list of strings."(some-nice-string-utils-split "\\(\r\n\\|[\n\r]\\)" s))As can be seen, it’s quite tedious to read or develop this code since the symbol names totype are so long. We can use shorthands to alleviate that.
(defun snu-split (separator s &optional omit-nulls)

Chapter 9: Symbols

143"A match-data saving variation on `split-string'."(save-match-data (split-string s separator omit-nulls)))(defun snu-lines (s)"Split string S into a list of strings on newline characters."(snu-split "\\(\r\n\\|[\n\r]\\)" s));; Local Variables:;; read-symbol-shorthands: (("snu-" . "some-nice-string-utils-"));; End:Even though the two excerpts look different, they are quite identical after the Lisp reader
processes them. Both will lead to the very same symbols being interned (see Section 9.3[Creating Symbols], page 135). Thus loading or byte-compiling any of the two files has
equivalent results. The shorthands snu-split and snu-lines used in the second version
are not interned in the obarray. This is easily seen by moving point to the location where
the shorthands are used and waiting for ElDoc (see Section “Local Variables in Files” in
The GNU Emacs Manual) to hint at the true full name of the symbol under point in theecho area.
Since read-symbol-shorthands is a file-local variable, it is possible that multiple libraries
depending on some-nice-string-utils-lines.el refer to the same symbols under different
shorthands, or not using shorthands at all. In the next example, the my-tricks.el libraryrefers to the symbol some-nice-string-utils-lines using the sns- prefix instead of snu-.
(defun t-reverse-lines (s) (string-join (reverse (sns-lines s)) "\n");; Local Variables:;; read-symbol-shorthands: (("t-" . "my-tricks-");;("sns-" . "some-nice-string-utils-"));; End:9.5.1 Exceptions
There are two exceptions to rules governing Shorthand transformations:• Symbol forms comprised entirely of characters in the Emacs Lisp symbol constituent
class (see Section 36.2.1 [Syntax Class Table], page 1023) are not transformed. For
example, it’s possible to use - or /= as shorthand prefixes, but that won’t shadow thearithmetic functions of those names.
• Symbol forms whose names start with ‘#_’ are not transformed.

9.6 Symbols with Position
A symbol with position is a symbol, the bare symbol, together with an unsigned integer
called the position. These objects are intended for use by the byte compiler, which records
in them the position of each symbol occurrence and uses those positions in warning anderror messages.
The printed representation of a symbol with position uses the hash notation outlined in
Section 2.1 [Printed Representation], page 8. It looks like ‘#<symbol foo at 12345>’. It has
no read syntax. You can cause just the bare symbol to be printed by binding the variableChapter 9: Symbols

144

print-symbols-bare to non-nil around the print operation. The byte compiler does thisbefore writing its output to the compiled Lisp file.
For most purposes, when the flag variable symbols-with-pos-enabled is non-nil, symbols with positions behave just as bare symbols do. For example, ‘(eq #<symbol foo at
12345> foo)’ has a value t when that variable is set (but nil when it isn’t set). Most of
the time in Emacs this variable is nil, but the byte compiler binds it to t when it runs.
Typically, symbols with position are created by the byte compiler calling the reader
function read-positioning-symbols (see Section 20.3 [Input Functions], page 374). One
can also be created with the function position-symbol.
[Variable]
When this variable is non-nil, symbols with position behave like the contained baresymbol. Emacs runs a little more slowly in this case.

symbols-with-pos-enabled[Variable]
When bound to non-nil, the Lisp printer prints only the bare symbol of a symbolwith position, ignoring the position.

print-symbols-baresymbol-with-pos-p symbol.

[Function]
This function returns t if symbol is a symbol with position, nil otherwise.

bare-symbol symbol[Function]
This function returns the bare symbol contained in symbol, or symbol itself if it isalready a bare symbol. For any other type of object, it signals an error.

symbol-with-pos-pos symbol[Function]
This function returns the position, a number, from a symbol with position. For any
other type of object, it signals an error.

position-symbol sym pos[Function]
Make a new symbol with position. sym is either a bare symbol or a symbol withposition, and supplies the symbol part of the new object. pos is either an integer
which becomes the number part of the new object, or a symbol with position whose
position is used. Emacs signals an error if either argument is invalid.

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10 Evaluation
The evaluation of expressions in Emacs Lisp is performed by the Lisp interpreter—a programthat receives a Lisp object as input and computes its value as an expression. How it does
this depends on the data type of the object, according to rules described in this chapter.
The interpreter runs automatically to evaluate portions of your program, but can also becalled explicitly via the Lisp primitive function eval.
A Lisp object that is intended for evaluation is called a form or expression1 . The fact that
forms are data objects and not merely text is one of the fundamental differences between
Lisp-like languages and typical programming languages. Any object can be evaluated, but
in practice only numbers, symbols, lists and strings are evaluated very often.
In subsequent sections, we will describe the details of what evaluation means for eachkind of form.
It is very common to read a Lisp form and then evaluate the form, but reading andevaluation are separate activities, and either can be performed alone. Reading per se does
not evaluate anything; it converts the printed representation of a Lisp object to the object
itself. It is up to the caller of read to specify whether this object is a form to be evaluated,or serves some entirely different purpose. See Section 20.3 [Input Functions], page 374.
Evaluation is a recursive process, and evaluating a form often involves evaluating parts
within that form. For instance, when you evaluate a function call form such as (car x),
Emacs first evaluates the argument (the subform x). After evaluating the argument, Emacs
executes the function (car), and if the function is written in Lisp, execution works byevaluating the body of the function (in this example, however, car is not a Lisp function; it
is a primitive function implemented in C). See Chapter 13 [Functions], page 230, for more
information about functions and function calls.
Evaluation takes place in a context called the environment, which consists of the current
values and bindings of all Lisp variables (see Chapter 12 [Variables], page 189).2 Whenevera form refers to a variable without creating a new binding for it, the variable evaluates tothe value given by the current environment. Evaluating a form may also temporarily alter
the environment by binding variables (see Section 12.3 [Local Variables], page 190).
Evaluating a form may also make changes that persist; these changes are called side
effects. An example of a form that produces a side effect is (setq foo 1).
Do not confuse evaluation with command key interpretation. The editor command looptranslates keyboard input into a command (an interactively callable function) using theactive keymaps, and then uses call-interactively to execute that command. Executing
the command usually involves evaluation, if the command is written in Lisp; however, thisstep is not considered a part of command key interpretation. See Chapter 22 [Command
Loop], page 423.
1

It is sometimes also referred to as an S-expression or sexp, but we generally do not use this terminology
in this manual.
2This definition of “environment” is specifically not intended to include all the data that can affect theresult of a program.

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146

10.1 Kinds of Forms
A Lisp object that is intended to be evaluated is called a form (or an expression). How
Emacs evaluates a form depends on its data type. Emacs has three different kinds of form
that are evaluated differently: symbols, lists, and all other types. This section describes all
three kinds, one by one, starting with the other types, which are self-evaluating forms.

10.1.1 Self-Evaluating Forms
A self-evaluating form is any form that is not a list or symbol. Self-evaluating forms evaluate
to themselves: the result of evaluation is the same object that was evaluated. Thus, thenumber 25 evaluates to 25, and the string "foo" evaluates to the string "foo". Likewise,
evaluating a vector does not cause evaluation of the elements of the vector—it returns thesame vector with its contents unchanged.
; A number, shown without evaluation.

'123
⇒ 123
123

; Evaluated as usual—result is the same.

⇒ 123(eval '123); Evaluated "by hand"—result is the same.
⇒ 123(eval (eval '123)) ; Evaluating twice changes nothing.
⇒ 123
A self-evaluating form yields a value that becomes part of the program, and you should
not try to modify it via setcar, aset or similar operations. The Lisp interpreter might
unify the constants yielded by your program’s self-evaluating forms, so that these constants
might share structure. See Section 2.9 [Mutability], page 36.
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking
advantage of the fact that they self-evaluate. However, it is quite unusual to do this fortypes that lack a read syntax, because there’s no way to write them textually. It is possible
to construct Lisp expressions containing these types by means of a Lisp program. Here is an
example:;; Build an expression containing a buffer object.
(setq print-exp (list 'print (current-buffer)))⇒ (print #<buffer eval.texi>);; Evaluate it.
(eval print-exp)
a #<buffer eval.texi>⇒ #<buffer eval.texi>

10.1.2 Symbol Forms
When a symbol is evaluated, it is treated as a variable. The result is the variable’s value, if
it has one. If the symbol has no value as a variable, the Lisp interpreter signals an error.
For more information on the use of variables, see Chapter 12 [Variables], page 189.
In the following example, we set the value of a symbol with setq. Then we evaluate thesymbol, and get back the value that setq stored.
(setq a 123)
⇒ 123

Chapter 10: Evaluation

147(eval 'a)
⇒ 123
a
⇒ 123
The symbols nil and t are treated specially, so that the value of nil is always nil, andthe value of t is always t; you cannot set or bind them to any other values. Thus, these two
symbols act like self-evaluating forms, even though eval treats them like any other symbol.
A symbol whose name starts with ‘:’ also self-evaluates in the same way; likewise, its value
ordinarily cannot be changed. See Section 12.2 [Constant Variables], page 189.

10.1.3 Classification of List Forms
A form that is a nonempty list is either a function call, a macro call, or a special form,
according to its first element. These three kinds of forms are evaluated in different ways,
described below. The remaining list elements constitute the arguments for the function,
macro, or special form.
The first step in evaluating a nonempty list is to examine its first element. This element
alone determines what kind of form the list is and how the rest of the list is to be processed.
The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.

10.1.4 Symbol Function Indirection
If the first element of the list is a symbol then evaluation examines the symbol’s function
cell, and uses its contents instead of the original symbol. If the contents are another symbol,
this process, called symbol function indirection, is repeated until it obtains a non-symbol.
See Section 13.3 [Function Names], page 236, for more information about symbol function
indirection.
One possible consequence of this process is an infinite loop, in the event that a symbol’sfunction cell refers to the same symbol. Otherwise, we eventually obtain a non-symbol,
which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda expression), a byte-code
function, a primitive function, a Lisp macro, a special form, or an autoload object. Each ofthese types is a case described in one of the following sections. If the object is not one ofthese types, Emacs signals an invalid-function error.
The following example illustrates the symbol indirection process. We use fset to set
the function cell of a symbol and symbol-function to get the function cell contents (seeSection 13.9 [Function Cells], page 248). Specifically, we store the symbol car into thefunction cell of first, and the symbol first into the function cell of erste.
;; Build this function cell linkage:;;----------------------------;; | #<subr car> | <-- | car | <-- | first | <-- | erste |;;----------------------------(symbol-function 'car)⇒ #<subr car>(fset 'first 'car)⇒ car(fset 'erste 'first)⇒ firstChapter 10: Evaluation

148(erste '(1 2 3)); Call the function referenced by erste.
⇒ 1
By contrast, the following example calls a function without any symbol function indirection,
because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))'(1 2 3))
⇒ 1
Executing the function itself evaluates its body; this does involve symbol function indirection
when calling erste.
This form is rarely used and is now deprecated. Instead, you should write it as:(funcall (lambda (arg) (erste arg))'(1 2 3))or just(let ((arg '(1 2 3))) (erste arg))
The built-in function indirect-function provides an easy way to perform symbol
function indirection explicitly.

indirect-function function &optional noerror[Function]
This function returns the meaning of function as a function. If function is a symbol,
then it finds function’s function definition and starts over with that value. If function
is not a symbol, then it returns function itself.
This function returns nil if the final symbol is unbound.
It signals acyclic-function-indirection error if there is a loop in the chain of symbols.
The optional argument noerror is obsolete, kept for backward compatibility, and has
no effect.
Here is how you could define indirect-function in Lisp:(defun indirect-function (function)(if (and function(symbolp function))(indirect-function (symbol-function function))function))

10.1.5 Evaluation of Function Forms
If the first element of a list being evaluated is a Lisp function object, byte-code object orprimitive function object, then that list is a function call. For example, here is a call to thefunction +:(+ 1 x)
The first step in evaluating a function call is to evaluate the remaining elements of the list
from left to right. The results are the actual argument values, one value for each list element.
The next step is to call the function with this list of arguments, effectively using the function
apply (see Section 13.5 [Calling Functions], page 239). If the function is written in Lisp,the arguments are used to bind the argument variables of the function (see Section 13.2
[Lambda Expressions], page 232); then the forms in the function body are evaluated in order,
and the value of the last body form becomes the value of the function call.

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10.1.6 Lisp Macro Evaluation
If the first element of a list being evaluated is a macro object, then the list is a macro call.
When a macro call is evaluated, the elements of the rest of the list are not initially evaluated.
Instead, these elements themselves are used as the arguments of the macro. The macrodefinition computes a replacement form, called the expansion of the macro, to be evaluatedin place of the original form. The expansion may be any sort of form: a self-evaluating
constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion
repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the expansion. However, themacro expansion is not necessarily evaluated right away, or at all, because other programs
also expand macro calls, and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of computing the macro
expansion, but instead appear as part of the expansion, so they are computed when the
expansion is evaluated.
For example, given a macro defined as follows:(defmacro cadr (x)(list 'car (list 'cdr x)))an expression such as (cadr (assq 'handler list)) is a macro call, and its expansion is:(car (cdr (assq 'handler list)))Note that the argument (assq 'handler list) appears in the expansion.
See Chapter 14 [Macros], page 268, for a complete description of Emacs Lisp macros.

10.1.7 Special Forms
A special form is a primitive specially marked so that its arguments are not all evaluated.
Most special forms define control structures or perform variable bindings—things whichfunctions cannot do.
Each special form has its own rules for which arguments are evaluated and which areused without evaluation. Whether a particular argument is evaluated may depend on the
results of evaluating other arguments.
If an expression’s first symbol is that of a special form, the expression should follow therules of that special form; otherwise, Emacs’s behavior is not well-defined (though it will
not crash). For example, ((lambda (x) x . 3) 4) contains a subexpression that begins withlambda but is not a well-formed lambda expression, so Emacs may signal an error, or may
return 3 or 4 or nil, or may behave in other ways.

special-form-p object[Function]
This predicate tests whether its argument is a special form, and returns t if so, nilotherwise.

Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with areference to where each is described.
andsee Section 11.3 [Combining Conditions], page 162,

catch

see Section 11.7.1 [Catch and Throw], page 177,

cond

see Section 11.2 [Conditionals], page 159,

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condition-casesee Section 11.7.3.3 [Handling Errors], page 182,
defconst

see Section 12.5 [Defining Variables], page 194,

defvarsee Section 12.5 [Defining Variables], page 194,functionsee Section 13.7 [Anonymous Functions], page 243,

if

see Section 11.2 [Conditionals], page 159,

interactive
see Section 22.3 [Interactive Call], page 432,
lambdasee Section 13.2 [Lambda Expressions], page 232,

let
let*

see Section 12.3 [Local Variables], page 190,

or

see Section 11.3 [Combining Conditions], page 162,

prog1
prog2
progn

see Section 11.1 [Sequencing], page 158,

quote

see Section 10.2 [Quoting], page 151,

save-current-buffer
see Section 28.2 [Current Buffer], page 671,
save-excursion
see Section 31.3 [Excursions], page 864,
save-restriction
see Section 31.4 [Narrowing], page 865,
see Section 12.8 [Setting Variables], page 198,

setq

setq-default
see Section 12.11.2 [Creating Buffer-Local], page 208,
unwind-protect
see Section 11.7 [Nonlocal Exits], page 177,
while

see Section 11.5 [Iteration], page 174,

Common Lisp note: Here are some comparisons of special forms in GNU Emacs
Lisp and Common Lisp. setq, if, and catch are special forms in both Emacs
Lisp and Common Lisp. save-excursion is a special form in Emacs Lisp, butdoesn’t exist in Common Lisp. throw is a special form in Common Lisp (because
it must be able to throw multiple values), but it is a function in Emacs Lisp
(which doesn’t have multiple values).

10.1.8 Autoloading
The autoload feature allows you to call a function or macro whose function definition has
not yet been loaded into Emacs. It specifies which file contains the definition. When an
autoload object appears as a symbol’s function definition, calling that symbol as a function

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automatically loads the specified file; then it calls the real definition loaded from that file.
The way to arrange for an autoload object to appear as a symbol’s function definition is
described in Section 16.5 [Autoload], page 304.

10.2 Quoting
The special form quote returns its single argument, as written, without evaluating it. This
provides a way to include constant symbols and lists, which are not self-evaluating objects,
in a program. (It is not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)quote object[Special Form]
This special form returns object, without evaluating it. The returned value might
be shared and should not be modified. See Section 10.1.1 [Self-Evaluating Forms],
page 146.

Because quote is used so often in programs, Lisp provides a convenient read syntax for
it. An apostrophe character (‘'’) followed by a Lisp object (in read syntax) expands to alist whose first element is quote, and whose second element is the object. Thus, the readsyntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:(quote (+ 1 2))⇒ (+ 1 2)(quote foo)
⇒ foo
'foo
⇒ foo
''foo
⇒ 'foo'(quote foo)
⇒ 'foo['foo]⇒ ['foo]
Although the expressions (list '+ 1 2) and '(+ 1 2) both yield lists equal to (+ 1 2),
the former yields a freshly-minted mutable list whereas the latter yields a list built fromconses that might be shared and should not be modified. See Section 10.1.1 [Self-Evaluating
Forms], page 146.
Other quoting constructs include function (see Section 13.7 [Anonymous Functions],
page 243), which causes an anonymous lambda expression written in Lisp to be compiled,and ‘`’ (see Section 10.3 [Backquote], page 151), which is used to quote only part of a list,
while computing and substituting other parts.

10.3 Backquote
Backquote constructs allow you to quote a list, but selectively evaluate elements of that list.
In the simplest case, it is identical to the special form quote. For example, these two forms
yield identical results:

Chapter 10: Evaluation

152`(a list of (+ 2 3) elements)⇒ (a list of (+ 2 3) elements)'(a list of (+ 2 3) elements)⇒ (a list of (+ 2 3) elements)
The special marker ‘,’ inside of the argument to backquote indicates a value that isn’t
constant. The Emacs Lisp evaluator evaluates the argument of ‘,’, and puts the value inthe list structure:`(a list of ,(+ 2 3) elements)⇒ (a list of 5 elements)
Substitution with ‘,’ is allowed at deeper levels of the list structure also. For example:`(1 2 (3 ,(+ 4 5)))⇒ (1 2 (3 9))You can also splice an evaluated value into the resulting list, using the special marker‘,@’. The elements of the spliced list become elements at the same level as the other elementsof the resulting list. The equivalent code without using ‘`’ is often unreadable. Here aresome examples:(setq some-list '(2 3))⇒ (2 3)(cons 1 (append some-list '(4) some-list))⇒ (1 2 3 4 2 3)`(1 ,@some-list 4 ,@some-list)⇒ (1 2 3 4 2 3)
(setq list '(hack foo bar))⇒ (hack foo bar)(cons 'use(cons 'the(cons 'words (append (cdr list) '(as elements)))))⇒ (use the words foo bar as elements)`(use the words ,@(cdr list) as elements)⇒ (use the words foo bar as elements)
If a subexpression of a backquote construct has no substitutions or splices, it acts likequote in that it yields conses, vectors and strings that might be shared and should not be
modified. See Section 10.1.1 [Self-Evaluating Forms], page 146.

10.4 Eval
Most often, forms are evaluated automatically, by virtue of their occurrence in a program
being run. On rare occasions, you may need to write code that evaluates a form that iscomputed at run time, such as after reading a form from text being edited or getting one
from a property list. On these occasions, use the eval function. Often eval is not needed
and something else should be used instead. For example, to get the value of a variable, whileeval works, symbol-value is preferable; or rather than store expressions in a property listthat then need to go through eval, it is better to store functions instead that are thenpassed to funcall.

Chapter 10: Evaluation

153

The functions and variables described in this section evaluate forms, specify limits to theevaluation process, or record recently returned values. Loading a file also does evaluation(see Chapter 16 [Loading], page 298).
It is generally cleaner and more flexible to store a function in a data structure, and callit with funcall or apply, than to store an expression in the data structure and evaluate it.
Using functions provides the ability to pass information to them as arguments.

eval form &optional lexical[Function]
This is the basic function for evaluating an expression. It evaluates form in the current
environment, and returns the result. The type of the form object determines how it isevaluated. See Section 10.1 [Forms], page 146.
The argument lexical specifies the scoping rule for local variables (see Section 12.10[Variable Scoping], page 201). If it is omitted or nil, that means to evaluate form
using the default dynamic scoping rule. If it is t, that means to use the lexical scoping
rule. The value of lexical can also be a non-empty alist specifying a particular lexical
environment for lexical bindings; however, this feature is only useful for specializedpurposes, such as in Emacs Lisp debuggers. See Section 12.10.3 [Lexical Binding],
page 203.
Since eval is a function, the argument expression that appears in a call to eval isevaluated twice: once as preparation before eval is called, and again by the evalfunction itself. Here is an example:(setq foo 'bar)⇒ bar(setq bar 'baz)⇒ baz;; Here eval receives argument foo(eval 'foo)⇒ bar;; Here eval receives argument bar, which is the value of foo(eval foo)⇒ baz
The number of currently active calls to eval is limited to max-lisp-eval-depth (seebelow).

eval-region start end &optional stream read-function[Command]This function evaluates the forms in the current buffer in the region defined by the
positions start and end. It reads forms from the region and calls eval on them until
the end of the region is reached, or until an error is signaled and not handled.
By default, eval-region does not produce any output. However, if stream is nonnil, any output produced by output functions (see Section 20.5 [Output Functions],
page 377), as well as the values that result from evaluating the expressions in theregion are printed using stream. See Section 20.4 [Output Streams], page 375.
If read-function is non-nil, it should be a function, which is used instead of read toread expressions one by one. This function is called with one argument, the stream
for reading input. You can also use the variable load-read-function (see [How

Chapter 10: Evaluation

154

Programs Do Loading], page 300) to specify this function, but it is more robust to use
the read-function argument.
eval-region does not move point. It always returns nil.

eval-buffer &optional buffer-or-name stream filename unibyte
print[Command]This is similar to eval-region, but the arguments provide different optional features.
eval-buffer operates on the entire accessible portion of buffer buffer-or-name (seeSection “Narrowing” in The GNU Emacs Manual). buffer-or-name can be a buffer, abuffer name (a string), or nil (or omitted), which means to use the current buffer.
stream is used as in eval-region, unless stream is nil and print non-nil. In thatcase, values that result from evaluating the expressions are still discarded, but theoutput of the output functions is printed in the echo area. filename is the file nameto use for load-history (see Section 16.9 [Unloading], page 313), and defaults tobuffer-file-name (see Section 28.4 [Buffer File Name], page 675). If unibyte is
non-nil, read converts strings to unibyte whenever possible.
[User Option]
This variable defines the maximum depth allowed in calls to eval, apply, and funcall
before an error is signaled (with error message "Lisp nesting exceeds max-lispeval-depth").

max-lisp-eval-depthThis limit, with the associated error when it is exceeded, is how Emacs Lisp avoids
infinite recursion on an ill-defined function. If you increase the value of max-lispeval-depth too much, such code can cause stack overflow instead. On some systems,
this overflow can be handled. In that case, normal Lisp evaluation is interrupted andcontrol is transferred back to the top level command loop (top-level). Note that
there is no way to enter Emacs Lisp debugger in this situation. See Section 19.1.1[Error Debugging], page 333.
The depth limit counts internal uses of eval, apply, and funcall, such as for callingthe functions mentioned in Lisp expressions, and recursive evaluation of function callarguments and function body forms, as well as explicit calls in Lisp code.
The default value of this variable is 1600. If you set it to a value less than 100, Lisp
will reset it to 100 if the given value is reached. Entry to the Lisp debugger increases
the value, if there is little room left, to make sure the debugger itself has room to
execute.
[Variable]
The value of this variable is a list of the values returned by all the expressions that were
read, evaluated, and printed from buffers (including the minibuffer) by the standard
Emacs commands which do this. (Note that this does not include evaluation in*ielm* buffers, nor evaluation using C-j, C-x C-e, and similar evaluation commands
in lisp-interaction-mode.)valuesThis variable is obsolete, and will be removed in a future version, since it constantly
enlarges the memory footprint of the Emacs process. For that reason, we recommend
against using it.
The elements of values are ordered most recent first.

Chapter 10: Evaluation

155(setq x 1)
⇒ 1
(list 'A (1+ 2) auto-save-default)⇒ (A 3 t)values⇒ ((A 3 t) 1 ...)
This variable could be useful for referring back to values of forms recently evaluated.
It is generally a bad idea to print the value of values itself, since this may be very
long. Instead, examine particular elements, like this:;; Refer to the most recent evaluation result.
(nth 0 values)⇒ (A 3 t);; That put a new element on,;;
so all elements move back one.
(nth 1 values)⇒ (A 3 t);; This gets the element that was next-to-most-recent;;
before this example.
(nth 3 values)⇒ 1

10.5 Deferred and Lazy Evaluation
Sometimes it is useful to delay the evaluation of an expression, for example if you want toavoid performing a time-consuming calculation if it turns out that the result is not neededin the future of the program. The thunk library provides the following functions and macros
to support such deferred evaluation:

thunk-delay forms. . .

[Macro]Return a thunk for evaluating the forms. A thunk is a closure (see Section 13.10[Closures], page 249) that inherits the lexical environment of the thunk-delay call.
Using this macro requires lexical-binding.

thunk-force thunk[Function]
Force thunk to perform the evaluation of the forms specified in the thunk-delay thatcreated the thunk. The result of the evaluation of the last form is returned. The thunkalso “remembers” that it has been forced: Any further calls of thunk-force with thesame thunk will just return the same result without evaluating the forms again.

thunk-let (bindings. . . ) forms. . .

[Macro]This macro is analogous to let but creates “lazy” variable bindings. Any binding
has the form (symbol value-form). Unlike let, the evaluation of any value-form
is deferred until the binding of the according symbol is used for the first time whenevaluating the forms. Any value-form is evaluated at most once. Using this macro
requires lexical-binding.

Example:Chapter 10: Evaluation

156(defun f (number)(thunk-let ((derived-number(progn (message "Calculating 1 plus 2 times %d" number)(1+ (* 2 number)))))(if (> number 10)
derived-number
number)))(f 5)⇒ 5(f 12)a Calculating 1 plus 2 times 12⇒ 25
Because of the special nature of lazily bound variables, it is an error to set them (e.g.
with setq).

thunk-let* (bindings. . . ) forms. . .

[Macro]This is like thunk-let but any expression in bindings is allowed to refer to precedingbindings in this thunk-let* form. Using this macro requires lexical-binding.
(thunk-let* ((x (prog2 (message "Calculating x...")(+ 1 1)(message "Finished calculating x")))(y (prog2 (message "Calculating y...")(+ x 1)(message "Finished calculating y")))(z (prog2 (message "Calculating z...")(+ y 1)(message "Finished calculating z")))(a (prog2 (message "Calculating a...")(+ z 1)(message "Finished calculating a"))))(* z x))a Calculating z...
a Calculating y...
a Calculating x...
a Finished calculating x
a Finished calculating ya Finished calculating z⇒ 8thunk-let and thunk-let* use thunks implicitly: their expansion creates helper symbols
and binds them to thunks wrapping the binding expressions. All references to the originalvariables in the body forms are then replaced by an expression that calls thunk-force with

Chapter 10: Evaluation157

the according helper variable as the argument. So, any code using thunk-let or thunk-let*could be rewritten to use thunks, but in many cases using these macros results in nicer code
than using thunks explicitly.

158

11 Control Structures
A Lisp program consists of a set of expressions, or forms (see Section 10.1 [Forms], page 146).
We control the order of execution of these forms by enclosing them in control structures.
Control structures are special forms which control when, whether, or how many times to
execute the forms they contain.
The simplest order of execution is sequential execution: first form a, then form b, andso on. This is what happens when you write several forms in succession in the body of afunction, or at top level in a file of Lisp code—the forms are executed in the order written.
We call this textual order. For example, if a function body consists of two forms a and b,
evaluation of the function evaluates first a and then b. The result of evaluating b becomesthe value of the function.
Explicit control structures make possible an order of execution other than sequential.
Emacs Lisp provides several kinds of control structure, including other varieties ofsequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in
control structures are special forms since their subforms are not necessarily evaluated or not
evaluated sequentially. You can use macros to define your own control structure constructs(see Chapter 14 [Macros], page 268).

11.1 Sequencing
Evaluating forms in the order they appear is the most common way control passes from one
form to another. In some contexts, such as in a function body, this happens automatically.
Elsewhere you must use a control structure construct to do this: progn, the simplest control
construct of Lisp.
A progn special form looks like this:(progn a b c ...)and it says to execute the forms a, b, c, and so on, in that order. These forms are called the
body of the progn form. The value of the last form in the body becomes the value of theentire progn. (progn) returns nil.
In the early days of Lisp, progn was the only way to execute two or more forms insuccession and use the value of the last of them. But programmers found they often needed
to use a progn in the body of a function, where (at that time) only one form was allowed.
So the body of a function was made into an implicit progn: several forms are allowed just as
in the body of an actual progn. Many other control structures likewise contain an implicit
progn. As a result, progn is not used as much as it was many years ago. It is needed now
most often inside an unwind-protect, and, or, or in the then-part of an if.

progn forms. . .

[Special Form]
This special form evaluates all of the forms, in textual order, returning the result of
the final form.

Chapter 11: Control Structures

159(progn (print "The first form")(print "The second form")(print "The third form"))a "The first form"a "The second form"a "The third form"⇒ "The third form"
Two other constructs likewise evaluate a series of forms but return different values:

prog1 form1 forms. . .

[Special Form]
This special form evaluates form1 and all of the forms, in textual order, returning theresult of form1.
(prog1 (print "The first form")(print "The second form")(print "The third form"))a "The first form"a "The second form"a "The third form"⇒ "The first form"
Here is a way to remove the first element from a list in the variable x, then return thevalue of that former element:(prog1 (car x) (setq x (cdr x)))prog2 form1 form2 forms. . .

[Special Form]
This special form evaluates form1, form2, and all of the following forms, in textual
order, returning the result of form2.
(prog2 (print "The first form")(print "The second form")(print "The third form"))a "The first form"a "The second form"a "The third form"⇒ "The second form"

11.2 Conditionals
Conditional control structures choose among alternatives. Emacs Lisp has five conditional
forms: if, which is much the same as in other languages; when and unless, which are variants
of if; cond, which is a generalized case statement; and pcase, which is a generalization ofcond (see Section 11.4 [Pattern-Matching Conditional], page 163).

if condition then-form else-forms. . .

[Special Form]if chooses between the then-form and the else-forms based on the value of condition.
If the evaluated condition is non-nil, then-form is evaluated and the result returned.
Otherwise, the else-forms are evaluated in textual order, and the value of the last one
is returned. (The else part of if is an example of an implicit progn. See Section 11.1
[Sequencing], page 158.)

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160

If condition has the value nil, and no else-forms are given, if returns nil.
if is a special form because the branch that is not selected is never evaluated—it isignored. Thus, in this example, true is not printed because print is never called:(if nil(print 'true)'very-false)⇒ very-false

when condition then-forms. . .

[Macro]This is a variant of if where there are no else-forms, and possibly several then-forms.
In particular,(when condition a b c)is entirely equivalent to(if condition (progn a b c) nil)unless condition forms. . .

[Macro]This is a variant of if where there is no then-form:(unless condition a b c)is entirely equivalent to(if condition nil
a b c)

cond clause. . .

[Special Form]
cond chooses among an arbitrary number of alternatives. Each clause in the cond
must be a list. The car of this list is the condition; the remaining elements, if any,
the body-forms. Thus, a clause looks like this:(condition body-forms...)cond tries the clauses in textual order, by evaluating the condition of each clause.
If the value of condition is non-nil, the clause succeeds; then cond evaluates its
body-forms, and returns the value of the last of body-forms. Any remaining clauses
are ignored.
If the value of condition is nil, the clause fails, so the cond moves on to the following
clause, trying its condition.
A clause may also look like this:(condition)
Then, if condition is non-nil when tested, the cond form returns the value of condition.
If every condition evaluates to nil, so that every clause fails, cond returns nil.
The following example has four clauses, which test for the cases where the value of x
is a number, string, buffer and symbol, respectively:(cond ((numberp x) x)((stringp x) x)((bufferp x)(setq temporary-hack x) ; multiple body-forms(buffer-name x)); in one clause((symbolp x) (symbol-value x)))Chapter 11: Control Structures

161

Often we want to execute the last clause whenever none of the previous clauses was
successful. To do this, we use t as the condition of the last clause, like this: (tbody-forms). The form t evaluates to t, which is never nil, so this clause never fails,
provided the cond gets to it at all. For example:(setq a 5)
(cond ((eq a 'hack) 'foo)(t "default"))⇒ "default"This cond expression returns foo if the value of a is hack, and returns the string"default" otherwise.
Any conditional construct can be expressed with cond or with if. Therefore, the choice
between them is a matter of style. For example:(if a b c)≡(cond (a b) (t c))
It can be convenient to bind variables in conjunction with using a conditional. It’s often
the case that you compute a value, and then want to do something with that value if it’s
non-nil. The straightforward way to do that is to just write, for instance:(let ((result1 (do-computation)))(when result1(let ((result2 (do-more result1)))(when result2(do-something result2)))))
Since this is a very common pattern, Emacs provides a number of macros to make thiseasier and more readable. The above can be written the following way instead:(when-let ((result1 (do-computation))(result2 (do-more result1)))(do-something result2))
There’s a number of variations on this theme, and they’re briefly described below.

if-let spec then-form else-forms...

[Macro]Evaluate each binding in spec in turn, like in let* (see Section 12.3 [Local Variables],page 190), stopping if a binding value is nil. If all are non-nil, return the value ofthen-form, otherwise the last form in else-forms.

when-let spec then-forms...

[Macro]Like if-let, but without else-forms.

while-let spec then-forms...

[Macro]Like when-let, but repeat until a binding in spec is nil. The return value is always
nil.

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11.3 Constructs for Combining Conditions
This section describes constructs that are often used together with if and cond to express
complicated conditions. The constructs and and or can also be used individually as kinds ofmultiple conditional constructs.

not condition[Function]
This function tests for the falsehood of condition. It returns t if condition is nil, andnil otherwise. The function not is identical to null, and we recommend using thename null if you are testing for an empty list or nil value.

and conditions. . .

[Special Form]
The and special form tests whether all the conditions are true. It works by evaluating
the conditions one by one in the order written.
If any of the conditions evaluates to nil, then the result of the and must be nil
regardless of the remaining conditions; so and returns nil right away, ignoring theremaining conditions.
If all the conditions turn out non-nil, then the value of the last of them becomes thevalue of the and form. Just (and), with no conditions, returns t, appropriate because
all the conditions turned out non-nil. (Think about it; which one did not?)Here is an example. The first condition returns the integer 1, which is not nil.
Similarly, the second condition returns the integer 2, which is not nil. The third
condition is nil, so the remaining condition is never evaluated.
(and (print 1) (print 2) nil (print 3))
a 1
a 2
⇒ nil
Here is a more realistic example of using and:(if (and (consp foo) (eq (car foo) 'x))
(message "foo is a list starting with x"))
Note that (car foo) is not executed if (consp foo) returns nil, thus avoiding anerror.
and expressions can also be written using either if or cond. Here’s how:(and arg1 arg2 arg3)≡(if arg1 (if arg2 arg3))≡(cond (arg1 (cond (arg2 arg3))))or conditions. . .

[Special Form]
The or special form tests whether at least one of the conditions is true. It works byevaluating all the conditions one by one in the order written.
If any of the conditions evaluates to a non-nil value, then the result of the or must
be non-nil; so or returns right away, ignoring the remaining conditions. The value it
returns is the non-nil value of the condition just evaluated.

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If all the conditions turn out nil, then the or expression returns nil. Just (or), withno conditions, returns nil, appropriate because all the conditions turned out nil.
(Think about it; which one did not?)For example, this expression tests whether x is either nil or the integer zero:(or (eq x nil) (eq x 0))
Like the and construct, or can be written in terms of cond. For example:(or arg1 arg2 arg3)≡(cond (arg1)(arg2)(arg3))
You could almost write or in terms of if, but not quite:(if arg1 arg1
(if arg2 arg2arg3))
This is not completely equivalent because it can evaluate arg1 or arg2 twice. By
contrast, (or arg1 arg2 arg3) never evaluates any argument more than once.

xor condition1 condition2[Function]
This function returns the boolean exclusive-or of condition1 and condition2. That is,
xor returns nil if either both arguments are nil, or both are non-nil. Otherwise, it
returns the value of that argument which is non-nil.
Note that in contrast to or, both arguments are always evaluated.

11.4 Pattern-Matching Conditional
Aside from the four basic conditional forms, Emacs Lisp also has a pattern-matchingconditional form, the pcase macro, a hybrid of cond and cl-case (see Section “Conditionals”
in Common Lisp Extensions) that overcomes their limitations and introduces the patternmatching programming style. The limitations that pcase overcomes are:
• The cond form chooses among alternatives by evaluating the predicate condition ofeach of its clauses (see Section 11.2 [Conditionals], page 159). The primary limitation isthat variables let-bound in condition are not available to the clause’s body-forms.
Another annoyance (more an inconvenience than a limitation) is that when a series ofcondition predicates implement equality tests, there is a lot of repeated code. (cl-casesolves this inconvenience.)• The cl-case macro chooses among alternatives by evaluating the equality of its firstargument against a set of specific values.
Its limitations are two-fold:
1. The equality tests use eql.
2. The values must be known and written in advance.
These render cl-case unsuitable for strings or compound data structures (e.g., lists or
vectors). (cond doesn’t have these limitations, but it has others, see above.)Chapter 11: Control Structures

164

Conceptually, the pcase macro borrows the first-arg focus of cl-case and the clauseprocessing flow of cond, replacing condition with a generalization of the equality test which
is a variant of pattern matching, and adding facilities so that you can concisely express
a clause’s predicate, and arrange to share let-bindings between a clause’s predicate andbody-forms.
The concise expression of a predicate is known as a pattern. When the predicate, calledon the value of the first arg, returns non-nil, we say that “the pattern matches the value”(or sometimes “the value matches the pattern”).

11.4.1 The pcase macro
For background, See Section 11.4 [Pattern-Matching Conditional], page 163.

pcase expression &rest clauses[Macro]Each clause in clauses has the form: (pattern body-forms...).
Evaluate expression to determine its value, expval. Find the first clause in clauses
whose pattern matches expval and pass control to that clause’s body-forms.
If there is a match, the value of pcase is the value of the last of body-forms in the
successful clause. Otherwise, pcase evaluates to nil.

Each pattern has to be a pcase pattern, which can use either one of the core patterns
defined below, or one of the patterns defined via pcase-defmacro (see Section 11.4.2[Extending pcase], page 170).
The rest of this subsection describes different forms of core patterns, presents someexamples, and concludes with important caveats on using the let-binding facility provided
by some pattern forms. A core pattern can have the following forms:_ (underscore)
Matches any expval. This is also known as don’t care or wildcard.
'val
keywordintegerstringMatches if expval equals val. The comparison is done as if by equal (seeSection 2.8 [Equality Predicates], page 34).

Matches if expval equals the literal object. This is a special case of 'val, above,
possible because literal objects of these types are self-quoting.

symbolMatches any expval, and additionally let-binds symbol to expval, such that
this binding is available to body-forms (see Section 12.10.1 [Dynamic Binding],
page 201).
If symbol is part of a sequencing pattern seqpat (e.g., by using and, below), thebinding is also available to the portion of seqpat following the appearance ofsymbol. This usage has some caveats, see [caveats], page 168.
Two symbols to avoid are t, which behaves like _ (above) and is deprecated,and nil, which signals an error. Likewise, it makes no sense to bind keyword
symbols (see Section 12.2 [Constant Variables], page 189).

`qpat

A backquote-style pattern. See Section 11.4.3 [Backquote Patterns], page 171,
for the details.

Chapter 11: Control Structures165(cl-type type)
Matches if expval is of type type, which is a type descriptor as accepted bycl-typep (see Section “Type Predicates” in Common Lisp Extensions). Examples:(cl-type integer)(cl-type (integer 0 10))(pred function)
Matches if the predicate function returns non-nil when called on expval. The
test can be negated with the syntax (pred (not function)). The predicate
function can have one of the following forms:
function name (a symbol)
Call the named function with one argument, expval.
Example: integerp
lambda expression
Call the anonymous function with one argument, expval (seeSection 13.2 [Lambda Expressions], page 232).
Example: (lambda (n) (= 42 n))function call with n args
Call the function (the first element of the function call) with narguments (the other elements) and an additional n+1-th argumentthat is expval.
Example: (= 42)
In this example, the function is =, n is one, and the actual function
call becomes: (= 42 expval).
(app function pattern)
Matches if function called on expval returns a value that matches pattern.
function can take one of the forms described for pred, above. Unlike pred,however, app tests the result against pattern, rather than against a boolean
truth value.
(guard boolean-expression)
Matches if boolean-expression evaluates to non-nil.
(let pattern expr)
Evaluates expr to get exprval and matches if exprval matches pattern. (It iscalled let because pattern can bind symbols to values using symbol.)
A sequencing pattern (also known as seqpat) is a pattern that processes its sub-patternarguments in sequence. There are two for pcase: and and or. They behave in a similarmanner to the special forms that share their name (see Section 11.3 [Combining Conditions],
page 162), but instead of processing values, they process sub-patterns.
(and pattern1...)
Attempts to match pattern1 . . . , in order, until one of them fails to match. Inthat case, and likewise fails to match, and the rest of the sub-patterns are nottested. If all sub-patterns match, and matches.

Chapter 11: Control Structures

166(or pattern1 pattern2...)
Attempts to match pattern1, pattern2, . . . , in order, until one of them succeeds.
In that case, or likewise matches, and the rest of the sub-patterns are not tested.
To present a consistent environment to body-forms (thus avoiding an evaluation
error on match), the set of variables bound by the pattern is the union of
the variables bound by each sub-pattern. If a variable is not bound by the
sub-pattern that matched, then it is bound to nil.

Example: Advantage Over cl-caseHere’s an example that highlights some advantages pcase has over cl-case (see Section“Conditionals” in Common Lisp Extensions).
(pcase (get-return-code x);; string((and (pred stringp) msg)
(message "%s" msg));; symbol('success(message "Done!"))('would-block(message "Sorry, can't do it now"))('read-only(message "The schmilblick is read-only"))('access-denied (message "You do not have the needed rights"));; default(code(message "Unknown return code %S" code)))With cl-case, you would need to explicitly declare a local variable code to hold the return
value of get-return-code. Also cl-case is difficult to use with strings because it uses eql
for comparison.

Example: Using and
A common idiom is to write a pattern starting with and, with one or more symbol subpatterns providing bindings to the sub-patterns that follow (as well as to the body forms).
For example, the following pattern matches single-digit integers.
(and(pred integerp)n(guard (<= -9 n 9))); bind n to expval

First, pred matches if (integerp expval) evaluates to non-nil. Next, n is a symbol patternthat matches anything and binds n to expval. Lastly, guard matches if the boolean expression(<= -9 n 9) (note the reference to n) evaluates to non-nil. If all these sub-patterns match,and matches.

Example: Reformulation with pcase
Here is another example that shows how to reformulate a simple matching task from its
traditional implementation (function grok/traditional) to one using pcase (function
grok/pcase). The docstring for both these functions is: “If OBJ is a string of the form
"key:NUMBER", return NUMBER (a string). Otherwise, return the list ("149" default).”
First, the traditional implementation (see Section 35.3 [Regular Expressions], page 995):

Chapter 11: Control Structures

167(defun grok/traditional (obj)(if (and (stringp obj)
(string-match "^key:\\([[:digit:]]+\\)$" obj))(match-string 1 obj)
(list "149" 'default)))⇒ "0"(grok/traditional "key:0")(grok/traditional "key:149") ⇒ "149"(grok/traditional 'monolith) ⇒ ("149" default)
The reformulation demonstrates symbol binding as well as or, and, pred, app and let.
(defun grok/pcase (obj)(pcase obj
((or
(and
(pred stringp)(pred (string-match"^key:\\([[:digit:]]+\\)$"))(app (match-string 1)
val))(let val (list "149" 'default)))val))); line 1; line 2; line 3; line 4; line 5; line 6; line 7; line 8; line 9⇒ "0"(grok/pcase "key:0")(grok/pcase "key:149") ⇒ "149"(grok/pcase 'monolith) ⇒ ("149" default)
The bulk of grok/pcase is a single clause of a pcase form, the pattern on lines 1-8, the(single) body form on line 9. The pattern is or, which tries to match in turn its argument
sub-patterns, first and (lines 2-7), then let (line 8), until one of them succeeds.
As in the previous example (see [Example 1], page 166), and begins with a pred subpattern to ensure the following sub-patterns work with an object of the correct type (string,in this case). If (stringp expval) returns nil, pred fails, and thus and fails, too.
The next pred (lines 4-5) evaluates (string-match RX expval) and matches if the result
is non-nil, which means that expval has the desired form: key:NUMBER. Again, failing this,pred fails and and, too.
Lastly (in this series of and sub-patterns), app evaluates (match-string 1 expval) (line6) to get a temporary value tmp (i.e., the “NUMBER” substring) and tries to match tmp
against pattern val (line 7). Since that is a symbol pattern, it matches unconditionally andadditionally binds val to tmp.
Now that app has matched, all and sub-patterns have matched, and so and matches.
Likewise, once and has matched, or matches and does not proceed to try sub-pattern let(line 8).
Let’s consider the situation where obj is not a string, or it is a string but has the wrong
form. In this case, one of the pred (lines 3-5) fails to match, thus and (line 2) fails to match,thus or (line 1) proceeds to try sub-pattern let (line 8).

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First, let evaluates (list "149" 'default) to get ("149" default), the exprval, andthen tries to match exprval against pattern val. Since that is a symbol pattern, it matches
unconditionally and additionally binds val to exprval. Now that let has matched, ormatches.
Note how both and and let sub-patterns finish in the same way: by trying (always
successfully) to match against the symbol pattern val, in the process binding val. Thus,or always matches and control always passes to the body form (line 9). Because that is thelast body form in a successfully matched pcase clause, it is the value of pcase and likewise
the return value of grok/pcase (see Section 13.1 [What Is a Function], page 230).

Caveats for symbol in Sequencing Patterns
The preceding examples all use sequencing patterns which include the symbol sub-patternin some way. Here are some important details about that usage.
1. When symbol occurs more than once in seqpat, the second and subsequent occurrences
do not expand to re-binding, but instead expand to an equality test using eq.
The following example features a pcase form with two clauses and two seqpat, A and
B. Both A and B first check that expval is a pair (using pred), and then bind symbols
to the car and cdr of expval (using one app each).
For A, because symbol st is mentioned twice, the second mention becomes an equality
test using eq. On the other hand, B uses two separate symbols, s1 and s2, both ofwhich become independent bindings.
(defun grok (object)(pcase object((and (pred consp)(app car st)(app cdr st))(list 'eq st))((and (pred consp)(app car s1)(app cdr s2))
(list 'not-eq s1 s2)))); seqpat A; first mention: st; second mention: st; seqpat B; first mention: s1; first mention: s2(let ((s "yow!"))⇒ (eq "yow!")(grok (cons s s)))(grok (cons "yo!" "yo!")) ⇒ (not-eq "yo!" "yo!")⇒ (not-eq 4 (2))(grok '(4 2))
2. Side-effecting code referencing symbol is undefined. Avoid. For example, here are twosimilar functions. Both use and, symbol and guard:(defun square-double-digit-p/CLEAN (integer)(pcase (* integer integer)((and n (guard (< 9 n 100))) (list 'yes n))(sorry (list 'no sorry))))(square-double-digit-p/CLEAN 9) ⇒ (yes 81)(square-double-digit-p/CLEAN 3) ⇒ (no 9)

Chapter 11: Control Structures

169(defun square-double-digit-p/MAYBE (integer)(pcase (* integer integer)((and n (guard (< 9 (incf n) 100))) (list 'yes n))(sorry (list 'no sorry))))(square-double-digit-p/MAYBE 9) ⇒ (yes 81)(square-double-digit-p/MAYBE 3) ⇒ (yes 9) ; WRONG!
The difference is in boolean-expression in guard: CLEAN references n simply and directly,
while MAYBE references n with a side-effect, in the expression (incf n). When integer
is 3, here’s what happens:• The first n binds it to expval, i.e., the result of evaluating (* 3 3), or 9.
• boolean-expression is evaluated:start:(< 9 (incf n)
100)
becomes: (< 9 (setq n (1+ n)) 100)
becomes: (< 9 (setq n (1+ 9)) 100)
becomes: (< 9 (setq n 10)
100)
becomes: (< 9becomes: (< 9becomes: tn10; side-effect here!
100) ; n now bound to 10
100)• Because the result of the evaluation is non-nil, guard matches, and matches, andcontrol passes to that clause’s body forms.
Aside from the mathematical incorrectness of asserting that 9 is a double-digit integer,
there is another problem with MAYBE. The body form references n once more, yet we donot see the updated value—10—at all. What happened to it?
To sum up, it’s best to avoid side-effecting references to symbol patterns entirely, notonly in boolean-expression (in guard), but also in expr (in let) and function (in predand app).
3. On match, the clause’s body forms can reference the set of symbols the pattern let-binds.
When seqpat is and, this set is the union of all the symbols each of its sub-patterns
let-binds. This makes sense because, for and to match, all the sub-patterns must match.
When seqpat is or, things are different: or matches at the first sub-pattern that matches;
the rest of the sub-patterns are ignored. It makes no sense for each sub-pattern tolet-bind a different set of symbols because the body forms have no way to distinguishwhich sub-pattern matched and choose among the different sets. For example, thefollowing is invalid:(require 'cl-lib)(pcase (read-number "Enter an integer: ")((or (and (pred cl-evenp)
e-num); bind e-num to expval
o-num); bind o-num to expval(list e-num o-num)))

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Enter an integer: 42
error Symbol’s value as variable is void: o-numEnter an integer: 149
error Symbol’s value as variable is void: e-num
Evaluating body form (list e-num o-num) signals error. To distinguish between subpatterns, you can use another symbol, identical in name in all sub-patterns but differingin value. Reworking the above example:(require 'cl-lib)(pcase (read-number "Enter an integer: ")((and num(or (and (pred cl-evenp)(let spin 'even))(let spin 'odd)))(list spin num))); line 1; line 2; line 3; line 4; line 5

Enter an integer: 42⇒ (even 42)
Enter an integer: 149⇒ (odd 149)
Line 1 “factors out” the expval binding with and and symbol (in this case, num). On
line 2, or begins in the same way as before, but instead of binding different symbols,
uses let twice (lines 3-4) to bind the same symbol spin in both sub-patterns. The
value of spin distinguishes the sub-patterns. The body form references both symbols(line 5).

11.4.2 Extending pcase
The pcase macro supports several kinds of patterns (see Section 11.4 [Pattern-Matching
Conditional], page 163). You can add support for other kinds of patterns using thepcase-defmacro macro.

pcase-defmacro name args [doc] &rest body

[Macro]Define a new kind of pattern for pcase, to be invoked as (name actual-args). The
pcase macro expands this into a function call that evaluates body, whose job it is torewrite the invoked pattern into some other pattern, in an environment where args
are bound to actual-args.

Additionally, arrange to display doc along with the docstring of pcase. By convention,
doc should use EXPVAL to stand for the result of evaluating expression (first arg topcase).
Typically, body rewrites the invoked pattern to use more basic patterns. Although all
patterns eventually reduce to core patterns, body need not use core patterns straight away.
The following example defines two patterns, named less-than and integer-less-than.
(pcase-defmacro less-than (n)"Matches if EXPVAL is a number less than N."`(pred (> ,n)))Chapter 11: Control Structures

171(pcase-defmacro integer-less-than (n)"Matches if EXPVAL is an integer less than N."`(and (pred integerp)(less-than ,n)))Note that the docstrings mention args (in this case, only one: n) in the usual way, andalso mention EXPVAL by convention. The first rewrite (i.e., body for less-than) uses one
core pattern: pred. The second uses two core patterns: and and pred, as well as the
newly-defined pattern less-than. Both use a single backquote construct (see Section 10.3
[Backquote], page 151).

11.4.3 Backquote-Style Patterns
This subsection describes backquote-style patterns, a set of builtin patterns that eases
structural matching. For background, see Section 11.4 [Pattern-Matching Conditional],
page 163.
Backquote-style patterns are a powerful set of pcase pattern extensions (created using
pcase-defmacro) that make it easy to match expval against specifications of its structure.
For example, to match expval that must be a list of two elements whose first element is a
specific string and the second element is any value, you can write a core pattern:(and (pred listp)
ls(guard (= 2 (length ls)))(guard (string= "first" (car ls)))(let second-elem (cadr ls)))or you can write the equivalent backquote-style pattern:`("first" ,second-elem)
The backquote-style pattern is more concise, resembles the structure of expval, and avoids
binding ls.
A backquote-style pattern has the form `qpat where qpat can have the following forms:(qpat1 . qpat2)
Matches if expval is a cons cell whose car matches qpat1 and whose cdr matches
qpat2. This readily generalizes to lists as in (qpat1 qpat2 ...).
[qpat1 qpat2 ... qpatm]
Matches if expval is a vector of length m whose 0..(m-1)th elements match
qpat1, qpat2 . . . qpatm, respectively.
symbolkeywordnumberstring,pattern

Matches if the corresponding element of expval is equal to the specified literalobject.
Matches if the corresponding element of expval matches pattern. Note that pattern is any kind that pcase supports. (In the example above, second-elem is asymbol core pattern; it therefore matches anything, and let-binds second-elem.)Chapter 11: Control Structures

172

The corresponding element is the portion of expval that is in the same structural position
as the structural position of qpat in the backquote-style pattern. (In the example above, thecorresponding element of second-elem is the second element of expval.)
Here is an example of using pcase to implement a simple interpreter for a little expression
language (note that this requires lexical binding for the lambda expression in the fn clauseto properly capture body and arg (see Section 12.10.3 [Lexical Binding], page 203):(defun evaluate (form env)
(pcase form(`(add ,x ,y)(+ (evaluate x env)
(evaluate y env)))(`(call ,fun ,arg) (funcall (evaluate fun env)
(evaluate arg env)))(`(fn ,arg ,body)(lambda (val)(evaluate body (cons (cons arg val)env))))((pred numberp)
form)((pred symbolp)(cdr (assq form env)))(_(error "Syntax error: %S" form))))The first three clauses use backquote-style patterns. `(add ,x ,y) is a pattern that checks
that form is a three-element list starting with the literal symbol add, then extracts thesecond and third elements and binds them to symbols x and y, respectively. This is known
as destructuring, see Section 11.4.4 [Destructuring with pcase Patterns], page 172. The
clause body evaluates x and y and adds the results. Similarly, the call clause implements afunction call, and the fn clause implements an anonymous function definition.
The remaining clauses use core patterns. (pred numberp) matches if form is a number.
On match, the body evaluates it. (pred symbolp) matches if form is a symbol. On match,the body looks up the symbol in env and returns its association. Finally, _ is the catch-all
pattern that matches anything, so it’s suitable for reporting syntax errors.
Here are some sample programs in this small language, including their evaluation results:⇒ 3(evaluate '(add 1 2) nil)(evaluate '(add x y) '((x . 1) (y . 2))) ⇒ 3(evaluate '(call (fn x (add 1 x)) 2) nil) ⇒ 3⇒ error(evaluate '(sub 1 2) nil)

11.4.4 Destructuring with pcase Patterns
Pcase patterns not only express a condition on the form of the objects they can match, butthey can also extract sub-fields of those objects. For example we can extract 2 elementsfrom a list that is the value of the variable my-list with the following code:(pcase my-list(`(add ,x ,y) (message "Contains %S and %S" x y)))This will not only extract x and y but will additionally test that my-list is a list
containing exactly 3 elements and whose first element is the symbol add. If any of thosetests fail, pcase will immediately return nil without calling message.
Extraction of multiple values stored in an object is known as destructuring. Using pcase
patterns allows to perform destructuring binding, which is similar to a local binding (seeChapter 11: Control Structures

173

Section 12.3 [Local Variables], page 190), but gives values to multiple elements of a variable
by extracting those values from an object of compatible structure.
The macros described in this section use pcase patterns to perform destructuring binding.
The condition of the object to be of compatible structure means that the object must match
the pattern, because only then the object’s subfields can be extracted. For example:(pcase-let ((`(add ,x ,y) my-list))(message "Contains %S and %S" x y))
does the same as the previous example, except that it directly tries to extract x and y frommy-list without first verifying if my-list is a list which has the right number of elements
and has add as its first element. The precise behavior when the object does not actuallymatch the pattern is undefined, although the body will not be silently skipped: either anerror is signaled or the body is run with some of the variables potentially bound to arbitraryvalues like nil.
The pcase patterns that are useful for destructuring bindings are generally those describedin Section 11.4.3 [Backquote Patterns], page 171, since they express a specification of thestructure of objects that will match.
For an alternative facility for destructuring binding, see [seq-let], page 114.

pcase-let bindings body. . .

[Macro]Perform destructuring binding of variables according to bindings, and then evaluate
body.
bindings is a list of bindings of the form (pattern exp), where exp is an expression
to evaluate and pattern is a pcase pattern.

All exps are evaluated first, after which they are matched against their respective
pattern, introducing new variable bindings that can then be used inside body. The
variable bindings are produced by destructuring binding of elements of pattern to thevalues of the corresponding elements of the evaluated exp.
Here’s a trivial example:(pcase-let ((`(,major ,minor)(split-string "image/png" "/")))
minor)⇒ "png"pcase-let* bindings body. . .

[Macro]Perform destructuring binding of variables according to bindings, and then evaluate
body.
bindings is a list of bindings of the form (pattern exp), where exp is an expression
to evaluate and pattern is a pcase pattern. The variable bindings are produced
by destructuring binding of elements of pattern to the values of the corresponding
elements of the evaluated exp.
Unlike pcase-let, but similarly to let*, each exp is matched against its corresponding
pattern before processing the next element of bindings, so the variable bindings
introduced in each one of the bindings are available in the exps of the bindings that
follow it, additionally to being available in body.

Chapter 11: Control Structures174

pcase-dolist (pattern list) body. . .

[Macro]Execute body once for each element of list, on each iteration performing a destructuringbinding of variables in pattern to the values of the corresponding subfields of theelement of list. The bindings are performed as if by pcase-let. When pattern is a
simple variable, this ends up being equivalent to dolist (see Section 11.5 [Iteration],
page 174).

pcase-setq pattern value. . .

[Macro]Assign values to variables in a setq form, destructuring each value according to its
respective pattern.

pcase-lambda lambda-list &rest body

[Macro]This is like lambda, but allows each argument to be a pattern. For instance, here’s asimple function that takes a cons cell as the argument:(setq fun(pcase-lambda (`(,key . ,val))(vector key (* val 10))))(funcall fun '(foo . 2))⇒ [foo 20]

11.5 Iteration
Iteration means executing part of a program repetitively. For example, you might want torepeat some computation once for each element of a list, or once for each integer from 0 to
n. You can do this in Emacs Lisp with the special form while:

while condition forms. . .

[Special Form]
while first evaluates condition. If the result is non-nil, it evaluates forms in textual
order. Then it reevaluates condition, and if the result is non-nil, it evaluates forms
again. This process repeats until condition evaluates to nil.
There is no limit on the number of iterations that may occur. The loop will continue
until either condition evaluates to nil or until an error or throw jumps out of it (seeSection 11.7 [Nonlocal Exits], page 177).
The value of a while form is always nil.
(setq num 0)⇒ 0(while (< num 4)(princ (format "Iteration %d." num))(setq num (1+ num)))a Iteration 0.
a Iteration 1.
a Iteration 2.
a Iteration 3.
⇒ nil
To write a repeat-until loop, which will execute something on each iteration and thendo the end-test, put the body followed by the end-test in a progn as the first argumentof while, as shown here:Chapter 11: Control Structures

175(while (progn(forward-line 1)(not (looking-at "^$"))))
This moves forward one line and continues moving by lines until it reaches an empty
line. It is peculiar in that the while has no body, just the end test (which also does
the real work of moving point).
The dolist and dotimes macros provide convenient ways to write two common kinds ofloops.

dolist (var list [result]) body. . .

[Macro]This construct executes body once for each element of list, binding the variable var
locally to hold the current element. Then it returns the value of evaluating result, or
nil if result is omitted. For example, here is how you could use dolist to define thereverse function:(defun reverse (list)(let (value)(dolist (elt list value)(setq value (cons elt value)))))

dotimes (var count [result]) body. . .

[Macro]This construct executes body once for each integer from 0 (inclusive) to count (exclusive), binding the variable var to the integer for the current iteration. Then it returns
the value of evaluating result, or nil if result is omitted. Use of result is deprecated.
Here is an example of using dotimes to do something 100 times:(dotimes (i 100)
(insert "I will not obey absurd orders\n"))11.6 Generators
A generator is a function that produces a potentially-infinite stream of values. Each time
the function produces a value, it suspends itself and waits for a caller to request the next
value.

iter-defun name args [doc] [declare] [interactive] body. . .

[Macro]iter-defun defines a generator function. A generator function has the same signature
as a normal function, but works differently. Instead of executing body when called, agenerator function returns an iterator object. That iterator runs body to generatevalues, emitting a value and pausing where iter-yield or iter-yield-from appears.
When body returns normally, iter-next signals iter-end-of-sequence with body’s
result as its condition data.
Any kind of Lisp code is valid inside body, but iter-yield and iter-yield-fromcannot appear inside unwind-protect forms.

iter-lambda args [doc] [interactive] body. . .

[Macro]iter-lambda produces an unnamed generator function that works just like a generator
function produced with iter-defun.

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iter-yield value[Macro]When it appears inside a generator function, iter-yield indicates that the current
iterator should pause and return value from iter-next. iter-yield evaluates to thevalue parameter of next call to iter-next.

iter-yield-from iterator[Macro]iter-yield-from yields all the values that iterator produces and evaluates to thevalue that iterator’s generator function returns normally. While it has control, iterator
receives values sent to the iterator using iter-next.

To use a generator function, first call it normally, producing a iterator object. An
iterator is a specific instance of a generator. Then use iter-next to retrieve values fromthis iterator. When there are no more values to pull from an iterator, iter-next raises aniter-end-of-sequence condition with the iterator’s final value.
It’s important to note that generator function bodies only execute inside calls toiter-next. A call to a function defined with iter-defun produces an iterator; you must
drive this iterator with iter-next for anything interesting to happen. Each call to a
generator function produces a different iterator, each with its own state.

iter-next iterator &optional value[Function]
Retrieve the next value from iterator. If there are no more values to be generated(because iterator’s generator function returned), iter-next signals the iter-endof-sequence condition; the data value associated with this condition is the value withwhich iterator’s generator function returned.
value is sent into the iterator and becomes the value to which iter-yield evaluates.
value is ignored for the first iter-next call to a given iterator, since at the start ofiterator’s generator function, the generator function is not evaluating any iter-yieldform.

iter-close iterator[Function]
If iterator is suspended inside an unwind-protect’s bodyform and becomes unreachable, Emacs will eventually run unwind handlers after a garbage collection pass. (Notethat iter-yield is illegal inside an unwind-protect’s unwindforms.) To ensure thatthese handlers are run before then, use iter-close.

Some convenience functions are provided to make working with iterators easier:iter-do (var iterator) body . . .

[Macro]Run body with var bound to each value that iterator produces.
The Common Lisp loop facility also contains features for working with iterators. See
Section “Loop Facility” in Common Lisp Extensions.
The following piece of code demonstrates some important principles of working with
iterators.
(require 'generator)(iter-defun my-iter (x)(iter-yield (1+ (iter-yield (1+ x))));; Return normallyChapter 11: Control Structures

177

-1)
(let* ((iter (my-iter 5))(iter2 (my-iter 0)));; Prints 6(print (iter-next iter));; Prints 9(print (iter-next iter 8));; Prints 1; iter and iter2 have distinct states(print (iter-next iter2 nil));; We expect the iter sequence to end now(condition-case x(iter-next iter)(iter-end-of-sequence;; Prints -1, which my-iter returned normally(print (cdr x)))))

11.7 Nonlocal Exits
A nonlocal exit is a transfer of control from one point in a program to another remote point.
Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under
explicit control. Nonlocal exits unbind all variable bindings made by the constructs being
exited.

11.7.1 Explicit Nonlocal Exits: catch and throw
Most control constructs affect only the flow of control within the construct itself. The
function throw is the exception to this rule of normal program execution: it performs a
nonlocal exit on request. (There are other exceptions, but they are for error handling only.)
throw is used inside a catch, and jumps back to that catch. For example:(defun foo-outer ()(catch 'foo
(foo-inner)))(defun foo-inner ()
...
(if x
(throw 'foo t))...)
The throw form, if executed, transfers control straight back to the corresponding catch,which returns immediately. The code following the throw is not executed. The second
argument of throw is used as the return value of the catch.
The function throw finds the matching catch based on the first argument: it searches fora catch whose first argument is eq to the one specified in the throw. If there is more than
one applicable catch, the innermost one takes precedence. Thus, in the above example, thethrow specifies foo, and the catch in foo-outer specifies the same symbol, so that catchis the applicable one (assuming there is no other matching catch in between).

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Executing throw exits all Lisp constructs up to the matching catch, including function
calls. When binding constructs such as let or function calls are exited in this way, thebindings are unbound, just as they are when these constructs exit normally (see Section 12.3
[Local Variables], page 190). Likewise, throw restores the buffer and position saved bysave-excursion (see Section 31.3 [Excursions], page 864), and the narrowing status savedby save-restriction. It also runs any cleanups established with the unwind-protect
special form when it exits that form (see Section 11.7.4 [Cleanups], page 187).
The throw need not appear lexically within the catch that it jumps to. It can equallywell be called from another function called within the catch. As long as the throw takes
place chronologically after entry to the catch, and chronologically before exit from it, it hasaccess to that catch. This is why throw can be used in commands such as exit-recursiveedit that throw back to the editor command loop (see Section 22.13 [Recursive Editing],
page 475).
Common Lisp note: Most other versions of Lisp, including Common Lisp, haveseveral ways of transferring control nonsequentially: return, return-from, andgo, for example. Emacs Lisp has only throw. The cl-lib library provides
versions of some of these. See Section “Blocks and Exits” in Common Lisp
Extensions.

catch tag body. . .

[Special Form]catch establishes a return point for the throw function. The return point is distinguished from other such return points by tag, which may be any Lisp object except
nil. The argument tag is evaluated normally before the return point is established.

With the return point in effect, catch evaluates the forms of the body in textual order.
If the forms execute normally (without error or nonlocal exit) the value of the last
body form is returned from the catch.
If a throw is executed during the execution of body, specifying the same value tag,the catch form exits immediately; the value it returns is whatever was specified as
the second argument of throw.

throw tag value[Function]
The purpose of throw is to return from a return point previously established withcatch. The argument tag is used to choose among the various existing return points;
it must be eq to the value specified in the catch. If multiple return points match tag,the innermost one is used.

The argument value is used as the value to return from that catch.
If no return point is in effect with tag tag, then a no-catch error is signaled with data(tag value).

11.7.2 Examples of catch and throw
One way to use catch and throw is to exit from a doubly nested loop. (In most languages,
this would be done with a goto.) Here we compute (foo i j) for i and j varying from 0 to
9:

Chapter 11: Control Structures

179(defun search-foo ()(catch 'loop(let ((i 0))(while (< i 10)(let ((j 0))(while (< j 10)(if (foo i j)(throw 'loop (list i j)))(setq j (1+ j))))(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a list of i and j. If foo always
returns nil, the catch returns normally, and the value is nil, since that is the result of thewhile.
Here are two tricky examples, slightly different, showing two return points at once. First,
two return points with the same tag, hack:(defun catch2 (tag)(catch tag(throw 'hack 'yes)))⇒ catch2(catch 'hack(print (catch2 'hack))
'no)
a yes
⇒ no
Since both return points have tags that match the throw, it goes to the inner one, the one
established in catch2. Therefore, catch2 returns normally with value yes, and this value isprinted. Finally the second body form in the outer catch, which is 'no, is evaluated andreturned from the outer catch.
Now let’s change the argument given to catch2:(catch 'hack(print (catch2 'quux))
'no)
⇒ yes
We still have two return points, but this time only the outer one has the tag hack; the inner
one has the tag quux instead. Therefore, throw makes the outer catch return the value yes.
The function print is never called, and the body-form 'no is never evaluated.

11.7.3 Errors
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated,
it signals an error.
When an error is signaled, Emacs’s default reaction is to print an error message andterminate execution of the current command. This is the right thing to do in most cases,
such as if you type C-f at the end of the buffer.

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In complicated programs, simple termination may not be what you want. For example,
the program may have made temporary changes in data structures, or created temporary
buffers that should be deleted before the program is finished. In such cases, you would
use unwind-protect to establish cleanup expressions to be evaluated in case of error. (See
Section 11.7.4 [Cleanups], page 187.) Occasionally, you may wish the program to continue
execution despite an error in a subroutine. In these cases, you would use condition-caseto establish error handlers to recover control in case of error.
For reporting problems without terminating the execution of the current command,consider issuing a warning instead. See Section 41.5 [Warnings], page 1138.
Resist the temptation to use error handling to transfer control from one part of the
program to another; use catch and throw instead. See Section 11.7.1 [Catch and Throw],
page 177.

11.7.3.1 How to Signal an Error
Signaling an error means beginning error processing. Error processing normally aborts allor part of the running program and returns to a point that is set up to handle the error (seeSection 11.7.3.2 [Processing of Errors], page 181). Here we describe how to signal an error.
Most errors are signaled automatically within Lisp primitives which you call for otherpurposes, such as if you try to take the car of an integer or move forward a character at theend of the buffer. You can also signal errors explicitly with the functions error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it ishandled almost like an error. See Section 22.11 [Quitting], page 471.
Every error specifies an error message, one way or another. The message should state
what is wrong (“File does not exist”), not how things ought to be (“File must exist”). The
convention in Emacs Lisp is that error messages should start with a capital letter, but should
not end with any sort of punctuation.

error format-string &rest args

[Function]
This function signals an error with an error message constructed by applying
format-message (see Section 4.7 [Formatting Strings], page 66) to format-string and
args.
These examples show typical uses of error:(error "That is an error -- try something else")
error That is an error -- try something else
(error "Invalid name `%s'" "A%%B")error Invalid name ‘A%%B’error works by calling signal with two arguments: the error symbol error, and alist containing the string returned by format-message.
Typically grave accent and apostrophe in the format translate to matching curved
quotes, e.g., "Missing ‘%s’" might result in "Missing ‘foo’". See Section 25.4
[Text Quoting Style], page 600, for how to influence or inhibit this translation.
Warning: If you want to use your own string as an error message verbatim, don’t justwrite (error string). If string string contains ‘%’, ‘`’, or ‘'’ it may be reformatted,
with undesirable results. Instead, use (error "%s" string).

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When noninteractive is non-nil (see Section 42.17 [Batch Mode], page 1289), thisfunction kills Emacs if the signaled error has no handler.

signal error-symbol data

[Function]
This function signals an error named by error-symbol. The argument data is a list ofadditional Lisp objects relevant to the circumstances of the error.
The argument error-symbol must be an error symbol—a symbol defined withdefine-error. This is how Emacs Lisp classifies different sorts of errors. See
Section 11.7.3.4 [Error Symbols], page 186, for a description of error symbols, error
conditions and condition names.
If the error is not handled, the two arguments are used in printing the error message.
Normally, this error message is provided by the error-message property of errorsymbol. If data is non-nil, this is followed by a colon and a comma separated list of
the unevaluated elements of data. For error, the error message is the car of data(that must be a string). Subcategories of file-error are handled specially.
The number and significance of the objects in data depends on error-symbol. For
example, with a wrong-type-argument error, there should be two objects in the list:a predicate that describes the type that was expected, and the object that failed to fitthat type.
Both error-symbol and data are available to any error handlers that handle the error:
condition-case binds a local variable to a list of the form (error-symbol . data)(see Section 11.7.3.3 [Handling Errors], page 182).
The function signal never returns. If the error error-symbol has no handler, andnoninteractive is non-nil (see Section 42.17 [Batch Mode], page 1289), this function
eventually kills Emacs.
(signal 'wrong-number-of-arguments '(x y))error Wrong number of arguments: x, y(signal 'no-such-error '("My unknown error condition"))error peculiar error: "My unknown error condition"user-error format-string &rest args

[Function]
This function behaves exactly like error, except that it uses the error symboluser-error rather than error. As the name suggests, this is intended to report
errors on the part of the user, rather than errors in the code itself. For example, if
you try to use the command Info-history-back (l) to move back beyond the startof your Info browsing history, Emacs signals a user-error. Such errors do not cause
entry to the debugger, even when debug-on-error is non-nil. See Section 19.1.1[Error Debugging], page 333.
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept ofcontinuable errors.

11.7.3.2 How Emacs Processes Errors
When an error is signaled, signal searches for an active handler for the error. A handler
is a sequence of Lisp expressions designated to be executed if an error happens in part

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of the Lisp program. If the error has an applicable handler, the handler is executed, andcontrol resumes following the handler. The handler executes in the environment of thecondition-case that established it; all functions called within that condition-case havealready been exited, and the handler cannot return to them.
If there is no applicable handler for the error, it terminates the current command andreturns control to the editor command loop. (The command loop has an implicit handler for
all kinds of errors.) The command loop’s handler uses the error symbol and associated data
to print an error message. You can use the variable command-error-function to control
how this is done:[Variable]
This variable, if non-nil, specifies a function to use to handle errors that return control
to the Emacs command loop. The function should take three arguments: data, a listof the same form that condition-case would bind to its variable; context, a string
describing the situation in which the error occurred, or (more often) nil; and caller,
the Lisp function which called the primitive that signaled the error.

command-error-function

An error that has no explicit handler may call the Lisp debugger (see Section 19.1.10[Invoking the Debugger], page 340). The debugger is enabled if the variable debug-on-error(see Section 19.1.1 [Error Debugging], page 333) is non-nil. Unlike error handlers, thedebugger runs in the environment of the error, so that you can examine values of variablesprecisely as they were at the time of the error. In batch mode (see Section 42.17 [BatchMode], page 1289), the Emacs process then normally exits with a non-zero exit status.

11.7.3.3 Writing Code to Handle Errors
The usual effect of signaling an error is to terminate the command that is running andreturn immediately to the Emacs editor command loop. You can arrange to trap errors
occurring in a part of your program by establishing an error handler, with the special form
condition-case. A simple example looks like this:(condition-case nil(delete-file filename)(error nil))This deletes the file named filename, catching any error and returning nil if an error occurs.
(You can use the macro ignore-errors for a simple case like this; see below.)
The condition-case construct is often used to trap errors that are predictable, such as
failure to open a file in a call to insert-file-contents. It is also used to trap errors thatare totally unpredictable, such as when the program evaluates an expression read from theuser.
The second argument of condition-case is called the protected form. (In the example
above, the protected form is a call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns. They remain in effectfor all the intervening time. In particular, they are in effect during the execution of functions
called by this form, in their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including signal and error) calledby the protected form, not by the protected form itself.
The arguments after the protected form are handlers. Each handler lists one or morecondition names (which are symbols) to specify which errors it will handle. The error symbolChapter 11: Control Structures

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specified when an error is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example above, there is one
handler, and it specifies one condition name, error, which covers all errors.
The search for an applicable handler checks all the established handlers starting with themost recently established one. Thus, if two nested condition-case forms offer to handle
the same error, the inner of the two gets to handle it.
If an error is handled by some condition-case form, this ordinarily prevents the debugger
from being run, even if debug-on-error says this error should invoke the debugger.
If you want to be able to debug errors that are caught by a condition-case, set thevariable debug-on-signal to a non-nil value. You can also specify that a particular handler
should let the debugger run first, by writing debug among the conditions, like this:(condition-case nil(delete-file filename)((debug error) nil))
The effect of debug here is only to prevent condition-case from suppressing the call to the
debugger. Any given error will invoke the debugger only if debug-on-error and the otherusual filtering mechanisms say it should. See Section 19.1.1 [Error Debugging], page 333.

condition-case-unless-debug var protected-form handlers. . .

[Macro]The macro condition-case-unless-debug provides another way to handle debugging
of such forms. It behaves exactly like condition-case, unless the variable debug-onerror is non-nil, in which case it does not handle any errors at all.

Once Emacs decides that a certain handler handles the error, it returns control to that
handler. To do so, Emacs unbinds all variable bindings made by binding constructs that are
being exited, and executes the cleanups of all unwind-protect forms that are being exited.
Once control arrives at the handler, the body of the handler executes normally.
After execution of the handler body, execution returns from the condition-case form.
Because the protected form is exited completely before execution of the handler, the handler
cannot resume execution at the point of the error, nor can it examine variable bindings thatwere made within the protected form. All it can do is clean up and proceed.
Error signaling and handling have some resemblance to throw and catch (seeSection 11.7.1 [Catch and Throw], page 177), but they are entirely separate facilities. An
error cannot be caught by a catch, and a throw cannot be handled by an error handler(though using throw when there is no suitable catch signals an error that can be handled).

condition-case var protected-form handlers. . .

[Special Form]
This special form establishes the error handlers handlers around the execution ofprotected-form. If protected-form executes without error, the value it returns becomesthe value of the condition-case form (in the absence of a success handler; see below).
In this case, the condition-case has no effect. The condition-case form makes adifference when an error occurs during protected-form.
Each of the handlers is a list of the form (conditions body...). Here conditions
is an error condition name to be handled, or a list of condition names (which can
include debug to allow the debugger to run before the handler). A condition name ofChapter 11: Control Structures184

t matches any condition. body is one or more Lisp expressions to be executed when
this handler handles an error. Here are examples of handlers:(error nil)(arith-error (message "Division by zero"))((arith-error file-error)(message"Either division by zero or failure to open a file"))Each error that occurs has an error symbol that describes what kind of error it
is, and which describes also a list of condition names (see Section 11.7.3.4 [Error
Symbols], page 186). Emacs searches all the active condition-case forms for ahandler that specifies one or more of these condition names; the innermost matchingcondition-case handles the error. Within this condition-case, the first applicablehandler handles the error.
After executing the body of the handler, the condition-case returns normally, using
the value of the last form in the handler body as the overall value.
The argument var is a variable. condition-case does not bind this variable when
executing the protected-form, only when it handles an error. At that time, it binds
var locally to an error description, which is a list giving the particulars of the error.
The error description has the form (error-symbol . data). The handler can refer tothis list to decide what to do. For example, if the error is for failure opening a file, thefile name is the second element of data—the third element of the error description.
If var is nil, that means no variable is bound. Then the error symbol and associateddata are not available to the handler.
As a special case, one of the handlers can be a list of the form (:success body...),
where body is executed with var (if non-nil) bound to the return value of protectedform when that expression terminates without error.
Sometimes it is necessary to re-throw a signal caught by condition-case, for someouter-level handler to catch. Here’s how to do that:(signal (car err) (cdr err))
where err is the error description variable, the first argument to condition-casewhose error condition you want to re-throw. See [Definition of signal], page 181.

error-message-string error-descriptor[Function]
This function returns the error message string for a given error descriptor. It is useful
if you want to handle an error by printing the usual error message for that error. See[Definition of signal], page 181.

Here is an example of using condition-case to handle the error that results from
dividing by zero. The handler displays the error message (but without a beep), then returns
a very large number.
(defun safe-divide (dividend divisor)(condition-case err;; Protected form.
(/ dividend divisor)

Chapter 11: Control Structures

185;; The handler.
(arith-error; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))⇒ safe-divide(safe-divide 5 0)
a Arithmetic error: (arith-error)⇒ 1000000
The handler specifies condition name arith-error so that it will handle only division-by-zeroerrors. Other kinds of errors will not be handled (by this condition-case). Thus:(safe-divide nil 3)
error Wrong type argument: number-or-marker-p, nil
Here is a condition-case that catches all kinds of errors, including those from error:(setq baz 34)⇒ 34(condition-case err(if (eq baz 35)t;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35" 'baz baz));; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))2))
a The error was: (error "Rats! The variable baz was 34, not 35")
⇒ 2

ignore-errors body. . .

[Macro]This construct executes body, ignoring any errors that occur during its execution. If
the execution is without error, ignore-errors returns the value of the last form inbody; otherwise, it returns nil.
Here’s the example at the beginning of this subsection rewritten using ignore-errors:(ignore-errors(delete-file filename))

ignore-error condition body. . .

[Macro]This macro is like ignore-errors, but will only ignore the specific error condition
specified.
(ignore-error end-of-file(read ""))
condition can also be a list of error conditions.

with-demoted-errors format body. . .

[Macro]This macro is like a milder version of ignore-errors. Rather than suppressing
errors altogether, it converts them into messages. It uses the string format to format

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the message. format should contain a single ‘%’-sequence; e.g., "Error: %S". Use
with-demoted-errors around code that is not expected to signal errors, but should berobust if one does occur. Note that this macro uses condition-case-unless-debug
rather than condition-case.

11.7.3.4 Error Symbols and Condition Names
When you signal an error, you specify an error symbol to specify the kind of error you havein mind. Each error has one and only one error symbol to categorize it. This is the finest
classification of errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider classes called error
conditions, identified by condition names. The narrowest such classes belong to the error
symbols themselves: each error symbol is also a condition name. There are also condition
names for more extensive classes, up to the condition name error which takes in all kindsof errors (but not quit). Thus, each error has one or more condition names: error, theerror symbol if that is distinct from error, and perhaps some intermediate classifications.

define-error name message &optional parent[Function]
In order for a symbol to be an error symbol, it must be defined with define-error
which takes a parent condition (defaults to error). This parent defines the conditions
that this kind of error belongs to. The transitive set of parents always includes theerror symbol itself, and the symbol error. Because quitting is not considered an error,
the set of parents of quit is just (quit).

In addition to its parents, the error symbol has a message which is a string to be printed
when that error is signaled but not handled. If that message is not valid, the error message‘peculiar error’ is used. See [Definition of signal], page 181.
Internally, the set of parents is stored in the error-conditions property of the error
symbol and the message is stored in the error-message property of the error symbol.
Here is how we define a new error symbol, new-error:(define-error 'new-error "A new error" 'my-own-errors)
This error has several condition names: new-error, the narrowest classification; my-ownerrors, which we imagine is a wider classification; and all the conditions of my-own-errors
which should include error, which is the widest of all.
The error string should start with a capital letter but it should not end with a period.
This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal new-error on its own; only an explicit call to signal(see [Definition of signal], page 181) in your code can do this:(signal 'new-error '(x y))error A new error: x, yThis error can be handled through any of its condition names. This example handles
new-error and any other errors in the class my-own-errors:(condition-case foo(bar nil t)(my-own-errors nil))Chapter 11: Control Structures

187

The significant way that errors are classified is by their condition names—the names used
to match errors with handlers. An error symbol serves only as a convenient way to specify
the intended error message and list of condition names. It would be cumbersome to give
signal a list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would seriously decrease
the power of condition-case. Condition names make it possible to categorize errors at
various levels of generality when you write an error handler. Using error symbols alone
would eliminate all but the narrowest level of classification.
See Appendix F [Standard Errors], page 1390, for a list of the main error symbols andtheir conditions.

11.7.4 Cleaning Up from Nonlocal Exits
The unwind-protect construct is essential whenever you temporarily put a data structure
in an inconsistent state; it permits you to make the data consistent again in the event of anerror or throw. (Another more specific cleanup construct that is used only for changes inbuffer contents is the atomic change group; Section 33.33 [Atomic Changes], page 959.)

unwind-protect body-form cleanup-forms. . .

[Special Form]
unwind-protect executes body-form with a guarantee that the cleanup-forms will be
evaluated if control leaves body-form, no matter how that happens. body-form maycomplete normally, or execute a throw out of the unwind-protect, or cause an error;
in all cases, the cleanup-forms will be evaluated.
If body-form finishes normally, unwind-protect returns the value of body-form, after
it evaluates the cleanup-forms. If body-form does not finish, unwind-protect does
not return any value in the normal sense.
Only body-form is protected by the unwind-protect. If any of the cleanup-forms
themselves exits nonlocally (via a throw or an error), unwind-protect is not guaranteed to evaluate the rest of them. If the failure of one of the cleanup-forms has thepotential to cause trouble, then protect it with another unwind-protect around thatform.

For example, here we make an invisible buffer for temporary use, and make sure to kill it
before finishing:(let ((buffer (get-buffer-create " *temp*")))(with-current-buffer buffer(unwind-protect
body-form(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer (current-buffer)) anddispense with the variable buffer. However, the way shown above is safer, if body-form
happens to get an error after switching to a different buffer! (Alternatively, you could writea save-current-buffer around body-form, to ensure that the temporary buffer becomescurrent again in time to kill it.)
Emacs includes a standard macro called with-temp-buffer which expands into more orless the code shown above (see [Current Buffer], page 673). Several of the macros defined inthis manual use unwind-protect in this way.

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Here is an actual example derived from an FTP package. It creates a process (seeChapter 40 [Processes], page 1078) to try to establish a connection to a remote machine.
As the function ftp-login is highly susceptible to numerous problems that the writer ofthe function cannot anticipate, it is protected with a form that guarantees deletion of theprocess in the event of failure. Otherwise, Emacs might fill up with useless subprocesses.
(let ((win nil))(unwind-protect(progn(setq process (ftp-setup-buffer host file))(if (setq win (ftp-login process host user password))(message "Logged in")(error "Ftp login failed")))(or win (and process (delete-process process)))))
This example has a small bug: if the user types C-g to quit, and the quit happens
immediately after the function ftp-setup-buffer returns but before the variable process
is set, the process will not be killed. There is no easy way to fix this bug, but at least it isvery unlikely.

189

12 Variables
A variable is a name used in a program to stand for a value. In Lisp, each variable isrepresented by a Lisp symbol (see Chapter 9 [Symbols], page 133). The variable name issimply the symbol’s name, and the variable’s value is stored in the symbol’s value cell1 .
See Section 9.1 [Symbol Components], page 133. In Emacs Lisp, the use of a symbol as avariable is independent of its use as a function name.
As previously noted in this manual, a Lisp program is represented primarily by Lisp
objects, and only secondarily as text. The textual form of a Lisp program is given by theread syntax of the Lisp objects that constitute the program. Hence, the textual form of avariable in a Lisp program is written using the read syntax for the symbol representing thevariable.

12.1 Global Variables
The simplest way to use a variable is globally. This means that the variable has just one
value at a time, and this value is in effect (at least for the moment) throughout the Lisp
system. The value remains in effect until you specify a new one. When a new value replaces
the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,(setq x '(a b))
gives the variable x the value (a b). Note that setq is a special form (see Section 10.1.7[Special Forms], page 149); it does not evaluate its first argument, the name of the variable,
but it does evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol itself as an
expression. Thus,x ⇒ (a b)
assuming the setq form shown above has already been executed.
If you do set the same variable again, the new value replaces the old one:x
⇒ (a b)(setq x 4)
⇒ 4
x
⇒ 4

12.2 Variables that Never Change
In Emacs Lisp, certain symbols normally evaluate to themselves. These include nil and t,
as well as any symbol whose name starts with ‘:’ (these are called keywords). These symbols
cannot be rebound, nor can their values be changed. Any attempt to set or bind nil or tsignals a setting-constant error. The same is true for a keyword (a symbol whose name1

To be precise, under the default dynamic scoping rule, the value cell always holds the variable’s current
value, but this is not the case under the lexical scoping rule. See Section 12.10 [Variable Scoping],
page 201, for details.

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starts with ‘:’), if it is interned in the standard obarray, except that setting such a symbol
to itself is not an error.
nil ≡ 'nil
⇒ nil(setq nil 500)
error Attempt to set constant symbol: nil

keywordp object[Function]function returns t if object is a symbol whose name starts with ‘:’, interned in thestandard obarray, and returns nil otherwise.

These constants are fundamentally different from the constants defined using the defconst
special form (see Section 12.5 [Defining Variables], page 194). A defconst form serves toinform human readers that you do not intend to change the value of a variable, but Emacs
does not raise an error if you actually change it.
A small number of additional symbols are made read-only for various practical reasons.
These include enable-multibyte-characters, most-positive-fixnum, most-negativefixnum, and a few others. Any attempt to set or bind these also signals a setting-constanterror.

12.3 Local Variables
Global variables have values that last until explicitly superseded with new values. Sometimes
it is useful to give a variable a local value—a value that takes effect only within a certain
part of a Lisp program. When a variable has a local value, we say that it is locally bound tothat value, and that it is a local variable.
For example, when a function is called, its argument variables receive local values, which
are the actual arguments supplied to the function call; these local bindings take effect within
the body of the function. To take another example, the let special form explicitly establishes
local bindings for specific variables, which take effect only within the body of the let form.
We also speak of the global binding, which is where (conceptually) the global value is
kept.
Establishing a local binding saves away the variable’s previous value (or lack of one). We
say that the previous value is shadowed. Both global and local values may be shadowed. If
a local binding is in effect, using setq on the local variable stores the specified value in thelocal binding. When that local binding is no longer in effect, the previously shadowed value(or lack of one) comes back.
A variable can have more than one local binding at a time (e.g., if there are nested let
forms that bind the variable). The current binding is the local binding that is actually ineffect. It determines the value returned by evaluating the variable symbol, and it is thebinding acted on by setq.
For most purposes, you can think of the current binding as the innermost local binding,or the global binding if there is no local binding. To be more precise, a rule called thescoping rule determines where in a program a local binding takes effect. The default scoping
rule in Emacs Lisp is called dynamic scoping, which simply states that the current binding at
any given point in the execution of a program is the most recently-created binding for that

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variable that still exists. For details about dynamic scoping, and an alternative scoping rulecalled lexical scoping, see Section 12.10 [Variable Scoping], page 201. Lately Emacs is moving
towards using lexical binding in more and more places, with the goal of eventually making
lexical binding the default. In particular, all Emacs Lisp source files and the *scratch*buffer use lexical scoping.
The special forms let and let* exist to create local bindings:

let (bindings. . . ) forms. . .

[Special Form]
This special form sets up local bindings for a certain set of variables, as specified bybindings, and then evaluates all of the forms in textual order. Its return value is thevalue of the last form in forms. The local bindings set up by let will be in effect only
within the body of forms.
Each of the bindings is either (i) a symbol, in which case that symbol is locally boundto nil; or (ii) a list of the form (symbol value-form), in which case symbol is locallybound to the result of evaluating value-form. If value-form is omitted, nil is used.
All of the value-forms in bindings are evaluated in the order they appear and before
binding any of the symbols to them. Here is an example of this: z is bound to the oldvalue of y, which is 2, not the new value of y, which is 1.
(setq y 2)
⇒ 2(let ((y 1)(z y))(list y z))⇒ (1 2)On the other hand, the order of bindings is unspecified: in the following example,
either 1 or 2 might be printed.
(let ((x 1)(x 2))(print x))
Therefore, avoid binding a variable more than once in a single let form.

let* (bindings. . . ) forms. . .

[Special Form]
This special form is like let, but it binds each variable right after computing its local
value, before computing the local value for the next variable. Therefore, an expression
in bindings can refer to the preceding symbols bound in this let* form. Compare thefollowing example with the example above for let.
(setq y 2)
⇒ 2
(let* ((y 1)(z y)); Use the just-established value of y.
(list y z))⇒ (1 1)
Basically, the let* binding of x and y in the previous example is equivalent to using
nested let bindings:

Chapter 12: Variables

192(let ((y 1))(let ((z y))(list y z)))letrec (bindings. . . ) forms. . .

[Special Form]
This special form is like let*, but all the variables are bound before any of the local
values are computed. The values are then assigned to the locally bound variables.
This is only useful when lexical binding is in effect, and you want to create closuresthat refer to bindings that would otherwise not yet be in effect when using let*.
For instance, here’s a closure that removes itself from a hook after being run once:(letrec ((hookfun (lambda ()(message "Run once")(remove-hook 'post-command-hook hookfun))))(add-hook 'post-command-hook hookfun))dlet (bindings. . . ) forms. . .

[Special Form]
This special form is like let, but it binds all variables dynamically. This is rarely
useful—you usually want to bind normal variables lexically, and special variables (i.e.,variables that are defined with defvar) dynamically, and this is what let does.
dlet can be useful when interfacing with old code that assumes that certain variables
are dynamically bound (see Section 12.10.1 [Dynamic Binding], page 201), but it’s
impractical to defvar these variables. dlet will temporarily make the bound variables
special, execute the forms, and then make the variables non-special again.

named-let name bindings &rest body[Special Form]
This special form is a looping construct inspired from the Scheme language. It issimilar to let: It binds the variables in bindings, and then evaluates body. However,named-let also binds name to a local function whose formal arguments are the variables
in bindings and whose body is body. This allows body to call itself recursively bycalling name, where the arguments passed to name are used as the new values of thebound variables in the recursive invocation.
Example of a loop summing a list of numbers:(named-let sum ((numbers '(1 2 3 4))(running-sum 0))(if numbers(sum (cdr numbers) (+ running-sum (car numbers)))
running-sum))⇒ 10
Recursive calls to name that occur in tail positions in body are guaranteed to be
optimized as tail calls, which means that they will not consume any additional stackspace no matter how deeply the recursion runs. Such recursive calls will effectively
jump to the top of the loop with new values for the variables.
A function call is in the tail position if it’s the very last thing done so that the value
returned by the call is the value of body itself, as is the case in the recursive call tosum above.
Warning: named-let works as expected only when lexical-binding is enabled. See
Section 12.10.3 [Lexical Binding], page 203.

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Here is a complete list of the other facilities that create local bindings:• Function calls (see Chapter 13 [Functions], page 230).
• Macro calls (see Chapter 14 [Macros], page 268).
• condition-case (see Section 11.7.3 [Errors], page 179).
Variables can also have buffer-local bindings (see Section 12.11 [Buffer-Local Variables],page 207); a few variables have terminal-local bindings (see Section 30.2 [Multiple Terminals],
page 787). These kinds of bindings work somewhat like ordinary local bindings, but they
are localized depending on where you are in Emacs.

12.4 When a Variable is Void
We say that a variable is void if its symbol has an unassigned value cell (see Section 9.1[Symbol Components], page 133).
Under Emacs Lisp’s default dynamic scoping rule (see Section 12.10 [Variable Scoping],
page 201), the value cell stores the variable’s current (local or global) value. Note that an
unassigned value cell is not the same as having nil in the value cell. The symbol nil is a
Lisp object and can be the value of a variable, just as any other object can be; but it is stilla value. If a variable is void, trying to evaluate the variable signals a void-variable error,
instead of returning a value.
Under the optional lexical scoping rule, the value cell only holds the variable’s global
value—the value outside of any lexical binding construct. When a variable is lexically bound,the local value is determined by the lexical environment; hence, variables can have local
values even if their symbols’ value cells are unassigned.

makunbound symbol[Function]
This function empties out the value cell of symbol, making the variable void. It returns
symbol.
If symbol has a dynamic local binding, makunbound voids the current binding, and thisvoidness lasts only as long as the local binding is in effect. Afterwards, the previously
shadowed local or global binding is reexposed; then the variable will no longer be void,
unless the reexposed binding is void too.
Here are some examples (assuming dynamic binding is in effect):(setq x 1)
; Put a value in the global binding.
⇒ 1(let ((x 2)); Locally bind it.
(makunbound 'x); Void the local binding.
x)
error Symbol's value as variable is void: xx; The global binding is unchanged.
⇒ 1(let ((x 2)); Locally bind it.
(let ((x 3)); And again.
(makunbound 'x); Void the innermost-local binding.
x)); And refer: it’s void.
error Symbol's value as variable is void: x

Chapter 12: Variables(let ((x 2))(let ((x 3))(makunbound 'x))
x)
⇒ 2

194

; Void inner binding, then remove it.
; Now outer let binding is visible.

boundp variable[Function]
This function returns t if variable (a symbol) is not void, and nil if it is void.
Here are some examples (assuming dynamic binding is in effect):(boundp 'abracadabra)⇒ nil(let ((abracadabra 5))(boundp 'abracadabra))⇒ t(boundp 'abracadabra)⇒ nil(setq abracadabra 5)⇒ 5(boundp 'abracadabra)⇒ t; Starts out void.
; Locally bind it.

; Still globally void.
; Make it globally nonvoid.

12.5 Defining Global Variables
A variable definition is a construct that announces your intention to use a symbol as a global
variable. It uses the special forms defvar or defconst, which are documented below.
A variable definition serves three purposes. First, it informs people who read the codethat the symbol is intended to be used a certain way (as a variable). Second, it informs the
Lisp system of this, optionally supplying an initial value and a documentation string. Third,
it provides information to programming tools such as etags, allowing them to find wherethe variable was defined.
The difference between defconst and defvar is mainly a matter of intent, serving to
inform human readers of whether the value should ever change. Emacs Lisp does not actually
prevent you from changing the value of a variable defined with defconst. One notabledifference between the two forms is that defconst unconditionally initializes the variable,
whereas defvar initializes it only if it is originally void.
To define a customizable variable, you should use defcustom (which calls defvar as a
subroutine). See Section 15.3 [Variable Definitions], page 280.

defvar symbol [value [doc-string]][Special Form]
This special form defines symbol as a variable. Note that symbol is not evaluated;
the symbol to be defined should appear explicitly in the defvar form. The variable
is marked as special, meaning that it should always be dynamically bound (seeSection 12.10 [Variable Scoping], page 201).
If value is specified, and symbol is void (i.e., it has no dynamically bound value; see
Section 12.4 [Void Variables], page 193), then value is evaluated and symbol is set to
the result. But if symbol is not void, value is not evaluated, and symbol’s value is left
unchanged. If value is omitted, the value of symbol is not changed in any case.

Note that specifying a value, even nil, marks the variable as special permanently.
Whereas if value is omitted then the variable is only marked special locally (i.e. withinChapter 12: Variables

195

the current lexical scope, or file if at the top-level). This can be useful for suppressing
byte compilation warnings, see Section 17.6 [Compiler Errors], page 321.
If symbol has a buffer-local binding in the current buffer, defvar acts on the default
value, which is buffer-independent, rather than the buffer-local binding. It sets thedefault value if the default value is void. See Section 12.11 [Buffer-Local Variables],page 207.
If symbol is already let bound (e.g., if the defvar form occurs in a let form), thendefvar sets the toplevel default value, like set-default-toplevel-value. The letbinding remains in effect until its binding construct exits. See Section 12.10 [Variable
Scoping], page 201.
When you evaluate a top-level defvar form with C-M-x (eval-defun) or with C-x
C-e (eval-last-sexp) in Emacs Lisp mode, a special feature of these two commands
arranges to set the variable unconditionally, without testing whether its value is void.
If the doc-string argument is supplied, it specifies the documentation string for thevariable (stored in the symbol’s variable-documentation property). See Chapter 25[Documentation], page 595.
Here are some examples. This form defines foo but does not initialize it:(defvar foo)
⇒ foo
This example initializes the value of bar to 23, and gives it a documentation string:(defvar bar 23"The normal weight of a bar.")⇒ bar
The defvar form returns symbol, but it is normally used at top level in a file where
its value does not matter.
For a more elaborate example of using defvar without a value, see [Local defvar
example], page 205.

defconst symbol value [doc-string][Special Form]
This special form defines symbol as a value and initializes it. It informs a person
reading your code that symbol has a standard global value, established here, thatshould not be changed by the user or by other programs. Note that symbol is notevaluated; the symbol to be defined must appear explicitly in the defconst.
The defconst form, like defvar, marks the variable as special, meaning that it should
always be dynamically bound (see Section 12.10 [Variable Scoping], page 201). In
addition, it marks the variable as risky (see Section 12.12 [File Local Variables],page 213).
defconst always evaluates value, and sets the value of symbol to the result. If symbol
does have a buffer-local binding in the current buffer, defconst sets the default value,
not the buffer-local value. (But you should not be making buffer-local bindings for a
symbol that is defined with defconst.)

An example of the use of defconst is Emacs’s definition of float-pi—the mathematical constant pi, which ought not to be changed by anyone (attempts by the Indiana

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State Legislature notwithstanding). As the second form illustrates, however, defconst
is only advisory.
(defconst float-pi 3.141592653589793 "The value of Pi.")⇒ float-pi(setq float-pi 3)⇒ float-pi
float-pi⇒ 3
Warning: If you use a defconst or defvar special form while the variable has a local
binding (made with let, or a function argument), it sets the local binding rather than the
global binding. This is not what you usually want. To prevent this, use these special forms
at top level in a file, where normally no local binding is in effect, and make sure to load thefile before making a local binding for the variable.

12.6 Tips for Defining Variables Robustly
When you define a variable whose value is a function, or a list of functions, use a name that
ends in ‘-function’ or ‘-functions’, respectively.
There are several other variable name conventions; here is a complete list:‘...-hook’
The variable is a normal hook (see Section 24.1 [Hooks], page 524).
‘...-function’The value is a function.
‘...-functions’
The value is a list of functions.
‘...-form’
The value is a form (an expression).
‘...-forms’
The value is a list of forms (expressions).
‘...-predicate’
The value is a predicate—a function of one argument that returns non-nil for
success and nil for failure.
‘...-flag’The value is significant only as to whether it is nil or not. Since such variables
often end up acquiring more values over time, this convention is not strongly
recommended.
‘...-program’
The value is a program name.
‘...-command’
The value is a whole shell command.
‘...-switches’
The value specifies options for a command.

Chapter 12: Variables

197‘prefix--...’The variable is intended for internal use and is defined in the file prefix.el.
(Emacs code contributed before 2018 may follow other conventions, which arebeing phased out.)‘...-internal’
The variable is intended for internal use and is defined in C code. (Emacs code
contributed before 2018 may follow other conventions, which are being phased
out.)
When you define a variable, always consider whether you should mark it as safe or risky;
see Section 12.12 [File Local Variables], page 213.
When defining and initializing a variable that holds a complicated value (such as a syntax
table for a major mode), it’s best to put the entire computation of the value into the defvar,
like this:(defvar my-major-mode-syntax-table(let ((table (make-syntax-table)))(modify-syntax-entry ?# "<" table)...
table)
docstring)This method has several benefits. First, if the user quits while loading the file, the variable
is either still uninitialized or initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the file once the variable
is initialized will not alter it; that is important if the user has changed its value. Third,
evaluating the defvar form with C-M-x will reinitialize the variable completely.

12.7 Accessing Variable Values
The usual way to reference a variable is to write the symbol which names it. See Section 10.1.2[Symbol Forms], page 146.
Occasionally, you may want to reference a variable which is only determined at run time.
In that case, you cannot specify the variable name in the text of the program. You can use
the symbol-value function to extract the value.

symbol-value symbol[Function]
This function returns the value stored in symbol’s value cell. This is where thevariable’s current (dynamic) value is stored. If the variable has no local binding, thisis simply its global value. If the variable is void, a void-variable error is signaled.
If the variable is lexically bound, the value reported by symbol-value is not necessarily
the same as the variable’s lexical value, which is determined by the lexical environment
rather than the symbol’s value cell. See Section 12.10 [Variable Scoping], page 201.
(setq abracadabra 5)⇒ 5(setq foo 9)⇒ 9

Chapter 12: Variables

198;; Here the symbol abracadabra;;
is the symbol whose value is examined.
(let ((abracadabra 'foo))(symbol-value 'abracadabra))⇒ foo;; Here, the value of abracadabra,;;
which is foo,;;is the symbol whose value is examined.
(let ((abracadabra 'foo))(symbol-value abracadabra))⇒ 9(symbol-value 'abracadabra)⇒ 5

12.8 Setting Variable Values
The usual way to change the value of a variable is with the special form setq. When you
need to compute the choice of variable at run time, use the function set.

setq [symbol form]. . .

[Special Form]
This special form is the most common method of changing a variable’s value. Eachsymbol is given a new value, which is the result of evaluating the corresponding form.
The current binding of the symbol is changed.
setq does not evaluate symbol; it sets the symbol that you write. We say that thisargument is automatically quoted. The ‘q’ in setq stands for “quoted”.

The value of the setq form is the value of the last form.
(setq x (1+ 2))
⇒ 3
x
⇒ 3
(let ((x 5))(setq x 6)
x)
⇒ 6
x
⇒ 3

; x now has a global value.

; The local binding of x is set.

; The global value is unchanged.

Note that the first form is evaluated, then the first symbol is set, then the second
form is evaluated, then the second symbol is set, and so on:(setq x 10
y (1+ x))⇒ 11

; Notice that x is set before;
the value of y is computed.

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set symbol value[Function]
This function puts value in the value cell of symbol. Since it is a function rather thana special form, the expression written for symbol is evaluated to obtain the symbol toset. The return value is value.

When dynamic variable binding is in effect (the default), set has the same effect as
setq, apart from the fact that set evaluates its symbol argument whereas setq doesnot. But when a variable is lexically bound, set affects its dynamic value, whereas
setq affects its current (lexical) value. See Section 12.10 [Variable Scoping], page 201.
(set one 1)
error Symbol's value as variable is void: one(set 'one 1)⇒ 1(set 'two 'one)⇒ one(set two 2); two evaluates to symbol one.
⇒ 2
one
; So it is one that was set.
⇒ 2
(let ((one 1)); This binding of one is set,
(set 'one 3);
not the global value.
one)
⇒ 3
one
⇒ 2
If symbol is not actually a symbol, a wrong-type-argument error is signaled.
(set '(x y) 'z)
error Wrong type argument: symbolp, (x y)setopt [symbol form]. . .

[Macro]This is like setq (see above), but meant for user options. This macro uses the
Customize machinery to set the variable(s) (see Section 15.3 [Variable Definitions],
page 280). In particular, setopt will run the setter function associated with thevariable. For instance, if you have:(defcustom my-var 1"My var.":type 'number:set (lambda (var val)
(set-default var val)(message "We set %s to %s" var val)))then the following, in addition to setting my-var to ‘2’, will also issue a message:(setopt my-var 2)
setopt also checks whether the value is valid for the user option. For instance, using
setopt to set a user option defined with a number type to a string will signal an error.
Unlike defcustom and related customization commands, such as customize-variable,
setopt is meant for non-interactive use, in particular in the user init file. For that

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reason, it doesn’t record the standard, saved, and user-set values, and doesn’t markthe variable as candidate for saving in the custom file.
The setopt macro can be used on regular, non-user option variables, but is much lessefficient than setq. The main use case for this macro is setting user options in theuser’s init file.

12.9 Running a function when a variable is changed.
It is sometimes useful to take some action when a variable changes its value. The variable
watchpoint facility provides the means to do so. Some possible uses for this feature include
keeping display in sync with variable settings, and invoking the debugger to track down
unexpected changes to variables (see Section 19.1.5 [Variable Debugging], page 337).
The following functions may be used to manipulate and query the watch functions for avariable.

add-variable-watcher symbol watch-function[Function]
This function arranges for watch-function to be called whenever symbol is modified.
Modifications through aliases (see Section 12.15 [Variable Aliases], page 222) will havethe same effect.
watch-function will be called, just before changing the value of symbol, with 4 arguments: symbol, newval, operation, and where. symbol is the variable being changed.
newval is the value it will be changed to. (The old value is available to watch-function
as the value of symbol, since it was not yet changed to newval.) operation is asymbol representing the kind of change, one of: set, let, unlet, makunbound, or
defvaralias. where is a buffer if the buffer-local value of the variable is being changed,
nil otherwise.

remove-variable-watcher symbol watch-function[Function]

This function removes watch-function from symbol’s list of watchers.

get-variable-watchers symbol[Function]

This function returns the list of symbol’s active watcher functions.

12.9.1 Limitations
There are a couple of ways in which a variable could be modified (or at least appear to bemodified) without triggering a watchpoint.
Since watchpoints are attached to symbols, modification to the objects contained withinvariables (e.g., by a list modification function see Section 5.6 [Modifying Lists], page 87) is
not caught by this mechanism.
Additionally, C code can modify the value of variables directly, bypassing the watchpointmechanism.
A minor limitation of this feature, again because it targets symbols, is that only variablesof dynamic scope may be watched. This poses little difficulty, since modifications to lexical
variables can be discovered easily by inspecting the code within the scope of the variable(unlike dynamic variables, which can be modified by any code at all, see Section 12.10[Variable Scoping], page 201).

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12.10 Scoping Rules for Variable Bindings
When you create a local binding for a variable, that binding takes effect only within a limited
portion of the program (see Section 12.3 [Local Variables], page 190). This section describes
exactly what this means.
Each local binding has a certain scope and extent. Scope refers to where in the textual
source code the binding can be accessed. Extent refers to when, as the program is executing,the binding exists.
By default, the local bindings that Emacs creates are dynamic bindings. Such a binding
has dynamic scope, meaning that any part of the program can potentially access the variablebinding. It also has dynamic extent, meaning that the binding lasts only while the binding
construct (such as the body of a let form) is being executed.
Emacs can optionally create lexical bindings. A lexical binding has lexical scope, meaningthat any reference to the variable must be located textually within the binding construct2 .
It also has indefinite extent, meaning that under some circumstances the binding can live oneven after the binding construct has finished executing, by means of special objects called
closures.
The dynamic binding was (and still is) the default in Emacs for many years, but lately
Emacs is moving towards using lexical binding in more and more places, with the goal ofeventually making that the default.
The following subsections describe dynamic binding and lexical binding in greater detail,and how to enable lexical binding in Emacs Lisp programs.

12.10.1 Dynamic Binding
By default, the local variable bindings made by Emacs are dynamic bindings. When avariable is dynamically bound, its current binding at any point in the execution of the Lisp
program is simply the most recently-created dynamic local binding for that symbol, or the
global binding if there is no such local binding.
Dynamic bindings have dynamic scope and extent, as shown by the following example:(defvar x -99)

; x receives an initial value of −99.

(defun getx ()x); x is used free in this function.

(let ((x 1))(getx))⇒ 1; x is dynamically bound.

;; After the let form finishes, x reverts to its;; previous value, which is −99.
(getx)⇒ -99
2

With some exceptions; for instance, a lexical binding can also be accessed from the Lisp debugger.

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The function getx refers to x. This is a free reference, in the sense that there is no binding
for x within that defun construct itself. When we call getx from within a let form in which
x is (dynamically) bound, it retrieves the local value (i.e., 1). But when we call getx outside
the let form, it retrieves the global value (i.e., −99).
Here is another example, which illustrates setting a dynamically bound variable using
setq:(defvar x -99)

; x receives an initial value of −99.

(defun addx ()(setq x (1+ x))); Add 1 to x and return its new value.

(let ((x 1))(addx)(addx))⇒ 3; The two addx calls add to x twice.

;; After the let form finishes, x reverts to its;; previous value, which is −99.
(addx)⇒ -98
Dynamic binding is implemented in Emacs Lisp in a simple way. Each symbol has avalue cell, which specifies its current dynamic value (or absence of value). See Section 9.1[Symbol Components], page 133. When a symbol is given a dynamic local binding, Emacs
records the contents of the value cell (or absence thereof) in a stack, and stores the new
local value in the value cell. When the binding construct finishes executing, Emacs pops theold value off the stack, and puts it in the value cell.
Note that when code using Dynamic Binding is native compiled the native compiler will
not perform any Lisp specific optimization.

12.10.2 Proper Use of Dynamic Binding
Dynamic binding is a powerful feature, as it allows programs to refer to variables that are
not defined within their local textual scope. However, if used without restraint, this canalso make programs hard to understand. There are two clean ways to use this technique:• If a variable has no global definition, use it as a local variable only within a binding
construct, such as the body of the let form where the variable was bound. If thisconvention is followed consistently throughout a program, the value of the variable will
not affect, nor be affected by, any uses of the same variable symbol elsewhere in the
program.
• Otherwise, define the variable with defvar, defconst (see Section 12.5 [Defining
Variables], page 194), or defcustom (see Section 15.3 [Variable Definitions], page 280).
Usually, the definition should be at top-level in an Emacs Lisp file. As far as possible,
it should include a documentation string which explains the meaning and purpose of
the variable. You should also choose the variable’s name to avoid name conflicts (seeSection D.1 [Coding Conventions], page 1331).

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Then you can bind the variable anywhere in a program, knowing reliably what theeffect will be. Wherever you encounter the variable, it will be easy to refer back to
the definition, e.g., via the C-h v command (provided the variable definition has been
loaded into Emacs). See Section “Name Help” in The GNU Emacs Manual.
For example, it is common to use local bindings for customizable variables like
case-fold-search:(defun search-for-abc ()"Search for the string \"abc\", ignoring case differences."(let ((case-fold-search t))(re-search-forward "abc")))12.10.3 Lexical Binding
Lexical binding was introduced to Emacs, as an optional feature, in version 24.1. We expect
its importance to increase with time. Lexical binding opens up many more opportunities for
optimization, so programs using it are likely to run faster in future Emacs versions. Lexicalbinding is also more compatible with concurrency, which was added to Emacs in version
26.1.
A lexically-bound variable has lexical scope, meaning that any reference to the variablemust be located textually within the binding construct. Here is an example (see the next
subsection, for how to actually enable lexical binding):(let ((x 1))(+ x 3))⇒ 4(defun getx ()x); x is lexically bound.

; x is used free in this function.

(let ((x 1)); x is lexically bound.
(getx))
error Symbol's value as variable is void: x
Here, the variable x has no global value. When it is lexically bound within a let form, it
can be used in the textual confines of that let form. But it can not be used from within agetx function called from the let form, since the function definition of getx occurs outside
the let form itself.
Here is how lexical binding works. Each binding construct defines a lexical environment,
specifying the variables that are bound within the construct and their local values. When the
Lisp evaluator wants the current value of a variable, it looks first in the lexical environment;
if the variable is not specified in there, it looks in the symbol’s value cell, where the dynamic
value is stored.
(Internally, the lexical environment is a list whose members are usually cons cells thatare symbol-value pairs, but some of its members can be symbols rather than cons cells. A
symbol in the list means the lexical environment declared that symbol’s variable as locallyconsidered to be dynamically bound. This list can be passed as the second argument to
the eval function, in order to specify a lexical environment in which to evaluate a form.

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See Section 10.4 [Eval], page 152. Most Emacs Lisp programs, however, should not interact
directly with lexical environments in this way; only specialized programs like debuggers.)
Lexical bindings have indefinite extent. Even after a binding construct has finishedexecuting, its lexical environment can be “kept around” in Lisp objects called closures. A
closure is created when you define a named or anonymous function with lexical binding
enabled. See Section 13.10 [Closures], page 249, for details.
When a closure is called as a function, any lexical variable references within its definition
use the retained lexical environment. Here is an example:(defvar my-ticker nil)

; We will use this dynamically bound; variable to store a closure.

(let ((x 0)); x is lexically bound.
(setq my-ticker (lambda ()(setq x (1+ x)))))⇒ (closure ((x . 0)) ()(setq x (1+ x)))(funcall my-ticker)⇒ 1(funcall my-ticker)⇒ 2(funcall my-ticker)
⇒ 3
x
error

; Note that x has no global value.
Symbol's value as variable is void: x

The let binding defines a lexical environment in which the variable x is locally bound to 0.
Within this binding construct, we define a lambda expression which increments x by one
and returns the incremented value. This lambda expression is automatically turned into a
closure, in which the lexical environment lives on even after the let binding construct has
exited. Each time we evaluate the closure, it increments x, using the binding of x in that
lexical environment.
Note that unlike dynamic variables which are tied to the symbol object itself, therelationship between lexical variables and symbols is only present in the interpreter (orcompiler). Therefore, functions which take a symbol argument (like symbol-value, boundp,
and set) can only retrieve or modify a variable’s dynamic binding (i.e., the contents of its
symbol’s value cell).

12.10.4 Using Lexical Binding
When loading an Emacs Lisp file or evaluating a Lisp buffer, lexical binding is enabled if
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205[Variable]
If this buffer-local variable is non-nil, Emacs Lisp files and buffers are evaluatedusing lexical binding instead of dynamic binding. (However, special variables are still
dynamically bound; see below.) If nil, dynamic binding is used for all local variables.
This variable is typically set for a whole Emacs Lisp file, as a file local variable (seeSection 12.12 [File Local Variables], page 213). Note that unlike other such variables,
this one must be set in the first line of a file.

lexical-binding

When evaluating Emacs Lisp code directly using an eval call, lexical binding is enabled if
the lexical argument to eval is non-nil. See Section 10.4 [Eval], page 152.
Lexical binding is also enabled in Lisp Interaction and IELM mode, used in the *scratch*and *ielm* buffers, and also when evaluating expressions via M-: (eval-expression) andwhen processing the --eval command-line options of Emacs (see Section “Action Arguments”
in The GNU Emacs Manual) and emacsclient (see Section “emacsclient Options” in The
GNU Emacs Manual).
Even when lexical binding is enabled, certain variables will continue to be dynamicallybound. These are called special variables. Every variable that has been defined with defvar,
defcustom or defconst is a special variable (see Section 12.5 [Defining Variables], page 194).
All other variables are subject to lexical binding.
Using defvar without a value, it is possible to bind a variable dynamically just in one
file, or in just one part of a file while still binding it lexically elsewhere. For example:(let (_)(defvar x); Let-bindings of x will be dynamic within this let.
(let ((x -99)) ; This is a dynamic binding of x.
(defun get-dynamic-x ()x)))(let ((x 'lexical)) ; This is a lexical binding of x.
(defun get-lexical-x ()x))(let (_)(defvar x)(let ((x 'dynamic))(list (get-lexical-x)(get-dynamic-x))))⇒ (lexical dynamic)

special-variable-p symbol[Function]
This function returns non-nil if symbol is a special variable (i.e., it has a defvar,
defcustom, or defconst variable definition). Otherwise, the return value is nil.
Note that since this is a function, it can only return non-nil for variables which arepermanently special, but not for those that are only special in the current lexicalscope.

The use of a special variable as a formal argument in a function is not supported.

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12.10.5 Converting to Lexical Binding
Converting an Emacs Lisp program to lexical binding is easy. First, add a file-local variablesetting of lexical-binding to t in the header line of the Emacs Lisp source file (seeSection 12.12 [File Local Variables], page 213). Second, check that every variable in the
program which needs to be dynamically bound has a variable definition, so that it is not
inadvertently bound lexically.
A simple way to find out which variables need a variable definition is to byte-compile
the source file. See Chapter 17 [Byte Compilation], page 316. If a non-special variable
is used outside of a let form, the byte-compiler will warn about reference or assignment
to a free variable. If a non-special variable is bound but not used within a let form, thebyte-compiler will warn about an unused lexical variable. The byte-compiler will also issue
a warning if you use a special variable as a function argument.
A warning about a reference or an assignment to a free variable is usually a clear sign thatthat variable should be marked as dynamically scoped, so you need to add an appropriate
defvar before the first use of that variable.
A warning about an unused variable may be a good hint that the variable was intended
to be dynamically scoped (because it is actually used, but in another function), but it may
also be an indication that the variable is simply really not used and could simply be removed.
So you need to find out which case it is, and based on that, either add a defvar or remove
the variable altogether. If removal is not possible or not desirable (typically because it is aformal argument and that we cannot or don’t want to change all the callers), you can also
add a leading underscore to the variable’s name to indicate to the compiler that this is avariable known not to be used.)

Cross-file variable checking
Caution: This is an experimental feature that may change or disappear without prior notice.
The byte-compiler can also warn about lexical variables that are special in other Emacs
Lisp files, often indicating a missing defvar declaration. This useful but somewhat specialized
check requires three steps:
1. Byte-compile all files whose special variable declarations may be of interest, with theenvironment variable EMACS_GENERATE_DYNVARS set to a nonempty string. These are
typically all the files in the same package or related packages or Emacs subsystems.
The process will generate a file whose name ends in .dynvars for each compiled Emacs
Lisp file.
2. Concatenate the .dynvars files into a single file.
3. Byte-compile the files that need to be checked, this time with the environment variable
EMACS_DYNVARS_FILE set to the name of the aggregated file created in step 2.
Here is an example illustrating how this could be done, assuming that a Unix shell andmake are used for byte-compilation:$ rm *.elc$ EMACS_GENERATE_DYNVARS=1 make$ cat *.dynvars > ~/my-dynvars$ rm *.elc$ EMACS_DYNVARS_FILE=~/my-dynvars make# force recompilation# generate .dynvars# combine .dynvars# force recompilation# perform checks

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12.11 Buffer-Local Variables
Global and local variable bindings are found in most programming languages in one formor another. Emacs, however, also supports additional, unusual kinds of variable binding,such as buffer-local bindings, which apply only in one buffer. Having different values for avariable in different buffers is an important customization method. (Variables can also havebindings that are local to each terminal. See Section 30.2 [Multiple Terminals], page 787.)

12.11.1 Introduction to Buffer-Local Variables
A buffer-local variable has a buffer-local binding associated with a particular buffer. The
binding is in effect when that buffer is current; otherwise, it is not in effect. If you set thevariable while a buffer-local binding is in effect, the new value goes in that binding, so its
other bindings are unchanged. This means that the change is visible only in the buffer where
you made it.
The variable’s ordinary binding, which is not associated with any specific buffer, is called
the default binding. In most cases, this is the global binding.
A variable can have buffer-local bindings in some buffers but not in other buffers. The
default binding is shared by all the buffers that don’t have their own bindings for the variable.
(This includes all newly-created buffers.) If you set the variable in a buffer that does nothave a buffer-local binding for it, this sets the default binding, so the new value is visible inall the buffers that see the default binding.
The most common use of buffer-local bindings is for major modes to change variables
that control the behavior of commands. For example, C mode and Lisp mode both set thevariable paragraph-start to specify that only blank lines separate paragraphs. They dothis by making the variable buffer-local in the buffer that is being put into C mode or Lisp
mode, and then setting it to the new value for that mode. See Section 24.2 [Major Modes],page 526.
The usual way to make a buffer-local binding is with make-local-variable, which iswhat major mode commands typically use. This affects just the current buffer; all otherbuffers (including those yet to be created) will continue to share the default value unlessthey are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the variable local in all
buffers, even those yet to be created. More precisely, the effect is that setting the variable
automatically makes the variable local to the current buffer if it is not already so. All buffers
start out by sharing the default value of the variable as usual, but setting the variable createsa buffer-local binding for the current buffer. The new value is stored in the buffer-local
binding, leaving the default binding untouched. This means that the default value cannot
be changed with setq in any buffer; the only way to change it is with setq-default.
Warning: When a variable has buffer-local bindings in one or more buffers, let rebinds
the binding that’s currently in effect. For instance, if the current buffer has a buffer-local
value, let temporarily rebinds that. If no buffer-local bindings are in effect, let rebinds
the default value. If inside the let you then change to a different current buffer in which a
different binding is in effect, you won’t see the let binding any more. And if you exit thelet while still in the other buffer, you won’t see the unbinding occur (though it will occur
properly). Here is an example to illustrate:

Chapter 12: Variables

208(setq foo 'g)(set-buffer "a")(make-local-variable 'foo)(setq foo 'a)(let ((foo 'temp));; foo ⇒ 'temp ; let binding in buffer ‘a’(set-buffer "b");; foo ⇒ 'g
; the global value since foo is not local in ‘b’body...)
foo ⇒ 'g
; exiting restored the local value in buffer ‘a’,; but we don’t see that in buffer ‘b’(set-buffer "a") ; verify the local value was restored
foo ⇒ 'aNote that references to foo in body access the buffer-local binding of buffer ‘b’.
When a file specifies local variable values, these become buffer-local values when you
visit the file. See Section “File Variables” in The GNU Emacs Manual.
A buffer-local variable cannot be made terminal-local (see Section 30.2 [Multiple Terminals], page 787).

12.11.2 Creating and Deleting Buffer-Local Bindings
make-local-variable variable[Command]This function creates a buffer-local binding in the current buffer for variable (a symbol).
Other buffers are not affected. The value returned is variable.
The buffer-local value of variable starts out as the same value variable previously had.
If variable was void, it remains void.
;; In buffer ‘b1’:(setq foo 5); Affects all buffers.
⇒ 5(make-local-variable 'foo) ; Now it is local in ‘b1’.
⇒ foo
foo
; That did not change⇒ 5;
the value.
(setq foo 6); Change the value⇒ 6;in ‘b1’.
foo⇒ 6;; In buffer ‘b2’, the value hasn’t changed.
(with-current-buffer "b2"foo)
⇒ 5
Making a variable buffer-local within a let-binding for that variable does not work
reliably, unless the buffer in which you do this is not current either on entry to orexit from the let. This is because let does not distinguish between different kinds ofbindings; it knows only which variable the binding was made for.

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It is an error to make a constant or a read-only variable buffer-local. See Section 12.2
[Constant Variables], page 189.
If the variable is terminal-local (see Section 30.2 [Multiple Terminals], page 787), thisfunction signals an error. Such variables cannot have buffer-local bindings as well.
Warning: do not use make-local-variable for a hook variable. The hook variables
are automatically made buffer-local as needed if you use the local argument to
add-hook or remove-hook.

setq-local &rest pairs[Macro]pairs is a list of variable and value pairs. This macro creates a buffer-local binding in
the current buffer for each of the variables, and gives them a buffer-local value. It isequivalent to calling make-local-variable followed by setq for each of the variables.
The variables should be unquoted symbols.
(setq-local var1 "value1"
var2 "value2")

make-variable-buffer-local variable[Command]This function marks variable (a symbol) automatically buffer-local, so that any
subsequent attempt to set it will make it local to the current buffer at the time. Unlike
make-local-variable, with which it is often confused, this cannot be undone, andaffects the behavior of the variable in all buffers.

A peculiar wrinkle of this feature is that binding the variable (with let or otherbinding constructs) does not create a buffer-local binding for it. Only setting thevariable (with set or setq), while the variable does not have a let-style binding thatwas made in the current buffer, does so.
If variable does not have a default value, then calling this command will give it a default
value of nil. If variable already has a default value, that value remains unchanged.
Subsequently calling makunbound on variable will result in a void buffer-local value
and leave the default value unaffected.
The value returned is variable.
It is an error to make a constant or a read-only variable buffer-local. See Section 12.2
[Constant Variables], page 189.
Warning: Don’t assume that you should use make-variable-buffer-local for useroption variables, simply because users might want to customize them differently in
different buffers. Users can make any variable local, when they wish to. It is better toleave the choice to them.
The time to use make-variable-buffer-local is when it is crucial that no two
buffers ever share the same binding. For example, when a variable is used for internal
purposes in a Lisp program which depends on having separate values in separate
buffers, then using make-variable-buffer-local can be the best solution.

defvar-local variable value &optional docstring[Macro]This macro defines variable as a variable with initial value value and docstring, andmarks it as automatically buffer-local. It is equivalent to calling defvar followed by
make-variable-buffer-local. variable should be an unquoted symbol.

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local-variable-p variable &optional buffer[Function]
This returns t if variable is buffer-local in buffer buffer (which defaults to the current
buffer); otherwise, nil.

local-variable-if-set-p variable &optional buffer[Function]
This returns t if variable either has a buffer-local value in buffer buffer, or is automatically buffer-local. Otherwise, it returns nil. If omitted or nil, buffer defaults to thecurrent buffer.

buffer-local-value variable buffer[Function]
This function returns the buffer-local binding of variable (a symbol) in buffer buffer.
If variable does not have a buffer-local binding in buffer buffer, it returns the default
value (see Section 12.11.3 [Default Value], page 211) of variable instead.

buffer-local-boundp variable buffer[Function]
This returns non-nil if there’s either a buffer-local binding of variable (a symbol) in
buffer buffer, or variable has a global binding.

buffer-local-variables &optional buffer[Function]
This function returns a list describing the buffer-local variables in buffer buffer. (Ifbuffer is omitted, the current buffer is used.) Normally, each list element has the form
(sym . val), where sym is a buffer-local variable (a symbol) and val is its buffer-local
value. But when a variable’s buffer-local binding in buffer is void, its list element isjust sym.
(make-local-variable 'foobar)(makunbound 'foobar)(make-local-variable 'bind-me)(setq bind-me 69)(setq lcl (buffer-local-variables));; First, built-in variables local in all buffers:⇒ ((mark-active . nil)(buffer-undo-list . nil)(mode-name . "Fundamental")...
;; Next, non-built-in buffer-local variables.
;; This one is buffer-local and void:
foobar;; This one is buffer-local and nonvoid:(bind-me . 69))
Note that storing new values into the cdrs of cons cells in this list does not change
the buffer-local values of the variables.

kill-local-variable variable[Command]This function deletes the buffer-local binding (if any) for variable (a symbol) in thecurrent buffer. As a result, the default binding of variable becomes visible in thisbuffer. This typically results in a change in the value of variable, since the default
value is usually different from the buffer-local value just eliminated.

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If you kill the buffer-local binding of a variable that automatically becomes buffer-local
when set, this makes the default value visible in the current buffer. However, if you
set the variable again, that will once again create a buffer-local binding for it.
kill-local-variable returns variable.
This function is a command because it is sometimes useful to kill one buffer-local
variable interactively, just as it is useful to create buffer-local variables interactively.

kill-all-local-variables &optional kill-permanent[Function]
This function eliminates all the buffer-local variable bindings of the current buffer.
As a result, the buffer will see the default values of most variables. By default,
for variables marked as permanent and local hook functions that have a non-nil
permanent-local-hook property (see Section 24.1.2 [Setting Hooks], page 525) won’t
be killed, but if the optional kill-permanent argument is non-nil, even these variables
will be killed.
This function also resets certain other information pertaining to the buffer: it sets
the local keymap to nil, the syntax table to the value of (standard-syntax-table),the case table to (standard-case-table), and the abbrev table to the value offundamental-mode-abbrev-table.
The very first thing this function does is run the normal hook change-major-modehook (see below).
Every major mode command begins by calling this function, which has the effect ofswitching to Fundamental mode and erasing most of the effects of the previous major
mode. To ensure that this does its job, the variables that major modes set should not
be marked permanent.
kill-all-local-variables returns nil.
[Variable]
The function kill-all-local-variables runs this normal hook before it does anything else. This gives major modes a way to arrange for something special to be done
if the user switches to a different major mode. It is also useful for buffer-specific minor
modes that should be forgotten if the user changes the major mode.

change-major-mode-hook

For best results, make this variable buffer-local, so that it will disappear after doing its
job and will not interfere with the subsequent major mode. See Section 24.1 [Hooks],
page 524.
A buffer-local variable is permanent if the variable name (a symbol) has apermanent-local property that is non-nil.
Such variables are unaffected bykill-all-local-variables, and their local bindings are therefore not cleared by changing
major modes. Permanent locals are appropriate for data pertaining to where the file camefrom or how to save it, rather than with how to edit the contents.

12.11.3 The Default Value of a Buffer-Local Variable
The global value of a variable with buffer-local bindings is also called the default value,
because it is the value that is in effect whenever neither the current buffer nor the selected
frame has its own binding for the variable.

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The functions default-value and setq-default access and change a variable’s default
value regardless of whether the current buffer has a buffer-local binding. For example, you
could use setq-default to change the default setting of paragraph-start for most buffers;
and this would work even when you are in a C or Lisp mode buffer that has a buffer-local
value for this variable.
The special forms defvar and defconst also set the default value (if they set the variable
at all), rather than any buffer-local value.

default-value symbol[Function]
This function returns symbol’s default value. This is the value that is seen in buffers
and frames that do not have their own values for this variable. If symbol is notbuffer-local, this is equivalent to symbol-value (see Section 12.7 [Accessing Variables],page 197).

default-boundp symbol[Function]
The function default-boundp tells you whether symbol’s default value is nonvoid.
If (default-boundp 'foo) returns nil, then (default-value 'foo) would get anerror.
default-boundp is to default-value as boundp is to symbol-value.

setq-default [symbol form]. . .

[Special Form]
This special form gives each symbol a new default value, which is the result of
evaluating the corresponding form. It does not evaluate symbol, but does evaluate
form. The value of the setq-default form is the value of the last form.
If a symbol is not buffer-local for the current buffer, and is not marked automaticallybuffer-local, setq-default has the same effect as setq. If symbol is buffer-local forthe current buffer, then this changes the value that other buffers will see (as long as
they don’t have a buffer-local value), but not the value that the current buffer sees.
;; In buffer ‘foo’:(make-local-variable 'buffer-local)⇒ buffer-local(setq buffer-local 'value-in-foo)⇒ value-in-foo(setq-default buffer-local 'new-default)⇒ new-default
buffer-local⇒ value-in-foo(default-value 'buffer-local)⇒ new-default;; In (the new) buffer ‘bar’:buffer-local⇒ new-default(default-value 'buffer-local)⇒ new-default(setq buffer-local 'another-default)⇒ another-default

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213(default-value 'buffer-local)⇒ another-default;; Back in buffer ‘foo’:
buffer-local⇒ value-in-foo(default-value 'buffer-local)⇒ another-default

set-default symbol value[Function]
This function is like setq-default, except that symbol is an ordinary evaluatedargument.
(set-default (car '(a b c)) 23)⇒ 23(default-value 'a)⇒ 23

A variable can be let-bound (see Section 12.3 [Local Variables], page 190) to a value. This
makes its global value shadowed by the binding; default-value will then return the value
from that binding, not the global value, and set-default will be prevented from setting
the global value (it will change the let-bound value instead). The following two functions
allow to reference the global value even if it’s shadowed by a let-binding.

default-toplevel-value symbol[Function]
This function returns the top-level default value of symbol, which is its value outsideof any let-binding.
(defvar variable 'global-value)⇒ variable(let ((variable 'let-binding))(default-value 'variable))⇒ let-binding(let ((variable 'let-binding))(default-toplevel-value 'variable))⇒ global-value

set-default-toplevel-value symbol value[Function]
This function sets the top-level default value of symbol to the specified value. This
comes in handy when you want to set the global value of symbol regardless of whether
your code runs in the context of symbol’s let-binding.

12.12 File Local Variables
A file can specify local variable values; Emacs uses these to create buffer-local bindings for
those variables in the buffer visiting that file. See Section “Local Variables in Files” in The
GNU Emacs Manual, for basic information about file-local variables. This section describes
the functions and variables that affect how file-local variables are processed.
If a file-local variable could specify an arbitrary function or Lisp expression that would
be called later, visiting a file could take over your Emacs. Emacs protects against this by

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automatically setting only those file-local variables whose specified values are known to besafe. Other file-local variables are set only if the user agrees.
For additional safety, read-circle is temporarily bound to nil when Emacs reads filelocal variables (see Section 20.3 [Input Functions], page 374). This prevents the Lisp reader
from recognizing circular and shared Lisp structures (see Section 2.6 [Circular Objects],
page 30).
[User Option]
This variable controls whether to process file-local variables. The possible values are:enable-local-variablest (the default)
Set the safe variables, and query (once) about any unsafe variables.
:safe

Set only the safe variables and do not query.

:all

Set all the variables and do not query.

nil

Don’t set any variables.

anything else
Query (once) about all the variables.
[Variable]
This is a list of regular expressions. If a file has a name matching an element of thislist, then it is not scanned for any form of file-local variable. For examples of why you
might want to use this, see Section 24.2.2 [Auto Major Mode], page 531.

inhibit-local-variables-regexps[Variable]
Some local variable settings will, by default, be heeded even if enable-localvariables is nil. By default, this is only the case for the lexical-binding local
variable setting, but this can be controlled by using this variable, which is a list ofsymbols.

permanently-enabled-local-variables

hack-local-variables &optional handle-mode[Function]
This function parses, and binds or evaluates as appropriate, any local variables specified
by the contents of the current buffer. The variable enable-local-variables has
its effect here. However, this function does not look for the ‘mode:’ local variable inthe ‘-*-’ line. set-auto-mode does that, also taking enable-local-variables into
account (see Section 24.2.2 [Auto Major Mode], page 531).
This function works by walking the alist stored in file-local-variables-alist andapplying each local variable in turn. It calls before-hack-local-variables-hookand hack-local-variables-hook before and after applying the variables, respectively.
It only calls the before-hook if the alist is non-nil; it always calls the other hook. Thisfunction ignores a ‘mode’ element if it specifies the same major mode as the buffer
already has.
If the optional argument handle-mode is t, then all this function does is return asymbol specifying the major mode, if the ‘-*-’ line or the local variables list specifies
one, and nil otherwise. It does not set the mode or any other file-local variable. If
handle-mode has any value other than nil or t, any settings of ‘mode’ in the ‘-*-’line or the local variables list are ignored, and the other settings are applied. If
handle-mode is nil, all the file local variables are set.

Chapter 12: Variables

215[Variable]
This buffer-local variable holds the alist of file-local variable settings. Each element of
the alist is of the form (var . value), where var is a symbol of the local variable andvalue is its value. When Emacs visits a file, it first collects all the file-local variables
into this alist, and then the hack-local-variables function applies them one byone.

file-local-variables-alist[Variable]
Emacs calls this hook immediately before applying file-local variables stored infile-local-variables-alist.

before-hack-local-variables-hook[Variable]
Emacs calls this hook immediately after it finishes applying file-local variables storedin file-local-variables-alist.

hack-local-variables-hook

You can specify safe values for a variable with a safe-local-variable property. The
property has to be a function of one argument; any value is safe if the function returns
non-nil given that value. Many commonly-encountered file variables have safe-localvariable properties; these include fill-column, fill-prefix, and indent-tabs-mode.
For boolean-valued variables that are safe, use booleanp as the property value.
If you want to define safe-local-variable properties for variables defined in C source
code, add the names and the properties of those variables to the list in the “Safe local
variables” section of files.el.
When defining a user option using defcustom, you can set its safe-local-variable
property by adding the arguments :safe function to defcustom (see Section 15.3 [Variable
Definitions], page 280). However, a safety predicate defined using :safe will only be known
once the package that contains the defcustom is loaded, which is often too late. As analternative, you can use the autoload cookie (see Section 16.5 [Autoload], page 304) to assign
the option its safety predicate, like this:;;;###autoload (put 'var 'safe-local-variable 'pred)
The safe value definitions specified with autoload are copied into the package’s autoloads
file (loaddefs.el for most packages bundled with Emacs), and are known to Emacs since
the beginning of a session.
[User Option]
This variable provides another way to mark some variable values as safe. It is a list ofcons cells (var . val), where var is a variable name and val is a value which is safefor that variable.

safe-local-variable-values

When Emacs asks the user whether or not to obey a set of file-local variable specifications, the user can choose to mark them as safe. Doing so adds those variable/value
pairs to safe-local-variable-values, and saves it to the user’s custom file.
[User Option]
If there are some values of particular local variables that you always want to ignore
completely, you can use this variable. Its value has the same form as safe-localvariable-values; a file-local variable setting to the value that appears in the list will
always be ignored when processing the local variables specified by the file. As withignored-local-variable-values

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that variable, when Emacs queries the user about whether to obey file-local variables,
the user can choose to ignore their particular values permanently, and that will alter
this variable and save it to the user’s custom file. Variable-value pairs that appear inthis variable take precedence over the same pairs in safe-local-variable-values.

safe-local-variable-p sym val[Function]
This function returns non-nil if it is safe to give sym the value val, based on theabove criteria.

Some variables are considered risky. If a variable is risky, it is never entered automaticallyinto safe-local-variable-values; Emacs always queries before setting a risky variable,
unless the user explicitly allows a value by customizing safe-local-variable-values
directly.
Any variable whose name has a non-nil risky-local-variable property is
considered risky. When you define a user option using defcustom, you can set its
risky-local-variable property by adding the arguments :risky value to defcustom(see Section 15.3 [Variable Definitions], page 280). In addition, any variable whosename ends in any of ‘-command’, ‘-frame-alist’, ‘-function’, ‘-functions’, ‘-hook’,‘-hooks’, ‘-form’, ‘-forms’, ‘-map’, ‘-map-alist’, ‘-mode-alist’, ‘-program’, or‘-predicate’ is automatically considered risky. The variables ‘font-lock-keywords’,‘font-lock-keywords’ followed by a digit, and ‘font-lock-syntactic-keywords’ are also
considered risky.

risky-local-variable-p sym[Function]
This function returns non-nil if sym is a risky variable, based on the above criteria.

[Variable]
This variable holds a list of variables that should not be given local values by files.
Any value specified for one of these variables is completely ignored.

ignored-local-variables

The ‘Eval:’ “variable” is also a potential loophole, so Emacs normally asks for confirmation before handling it.
[User Option]
This variable controls processing of ‘Eval:’ in ‘-*-’ lines or local variables lists in files
being visited. A value of t means process them unconditionally; nil means ignore
them; anything else means ask the user what to do for each file. The default value ismaybe.

enable-local-eval[User Option]
This variable holds a list of expressions that are safe to evaluate when found in the‘Eval:’ “variable” in a file local variables list.

safe-local-eval-forms

If the expression is a function call and the function has a safe-local-eval-function
property, the property value determines whether the expression is safe to evaluate. The
property value can be a predicate to call to test the expression, a list of such predicates (it’ssafe if any predicate succeeds), or t (always safe provided the arguments are constant).
Text properties are also potential loopholes, since their values could include functions tocall. So Emacs discards all text properties from string values specified for file-local variables.

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12.13 Directory Local Variables
A directory can specify local variable values common to all files in that directory; Emacs
uses these to create buffer-local bindings for those variables in buffers visiting any file inthat directory. This is useful when the files in the directory belong to some project andtherefore share the same local variables.
There are two different methods for specifying directory local variables: by putting themin a special file, or by defining a project class for that directory.
[Constant]
This constant is the name of the file where Emacs expects to find the directorylocal variables. The name of the file is .dir-locals.el3 . A file by that name in a
directory causes Emacs to apply its settings to any file in that directory or any of
its subdirectories (optionally, you can exclude subdirectories; see below). If someof the subdirectories have their own .dir-locals.el files, Emacs uses the settingsfrom the deepest file it finds starting from the file’s directory and moving up thedirectory tree. This constant is also used to derive the name of a second dir-locals
file .dir-locals-2.el. If this second dir-locals file is present, then that is loaded inaddition to .dir-locals.el. This is useful when .dir-locals.el is under version
control in a shared repository and cannot be used for personal customizations. The
file specifies local variables as a specially formatted list; see Section “Per-directory
Local Variables” in The GNU Emacs Manual, for more details.

dir-locals-file[Function]
This function reads the .dir-locals.el file and stores the directory-local variables in file-local-variables-alist that is local to the buffer visiting any file inthe directory, without applying them. It also stores the directory-local settings in
dir-locals-class-alist, where it defines a special class for the directory in which.dir-locals.el file was found. This function works by calling dir-locals-setclass-variables and dir-locals-set-directory-class, described below.

hack-dir-local-variables[Function]
This function looks for directory-local variables, and immediately applies them inthe current buffer. It is intended to be called in the mode commands for non-filebuffers, such as Dired buffers, to let them obey directory-local variable settings. For
non-file buffers, Emacs looks for directory-local variables in default-directory andits parent directories.

hack-dir-local-variables-non-file-buffer

dir-locals-set-class-variables class variables[Function]
This function defines a set of variable settings for the named class, which is a symbol.
You can later assign the class to one or more directories, and Emacs will apply thosevariable settings to all files in those directories. The list in variables can be of one of
the two forms: (major-mode . alist) or (directory . list). With the first form, if
the file’s buffer turns on a mode that is derived from major-mode, then all the variablesin the associated alist are applied; alist should be of the form (name . value). A
special value nil for major-mode means the settings are applicable to any mode. In

3

The MS-DOS version of Emacs uses _dir-locals.el instead, due to limitations of the DOS filesystems.

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alist, you can use a special name: subdirs. If the associated value is nil, the alist is
only applied to files in the relevant directory, not to those in any subdirectories.
With the second form of variables, if directory is the initial substring of the file’s
directory, then list is applied recursively by following the above rules; list should be of
one of the two forms accepted by this function in variables.

dir-locals-set-directory-class directory class &optional mtime[Function]
This function assigns class to all the files in directory and its subdirectories. Thereafter, all the variable settings specified for class will be applied to any visited file indirectory and its children. class must have been already defined by dir-locals-setclass-variables.
Emacs uses this function internally when it loads directory variables from a.dir-locals.el file. In that case, the optional argument mtime holds the filemodification time (as returned by file-attributes). Emacs uses this time to checkstored local variables are still valid. If you are assigning a class directly, not via a file,
this argument should be nil.
[Variable]
This alist holds the class symbols and the associated variable settings. It is updated
by dir-locals-set-class-variables.

dir-locals-class-alist[Variable]
This alist holds directory names, their assigned class names, and modification times of
the associated directory local variables file (if there is one). The function dir-localsset-directory-class updates this list.

dir-locals-directory-cache[Variable]
If nil, directory-local variables are ignored. This variable may be useful for modes
that want to ignore directory-locals while still respecting file-local variables (seeSection 12.12 [File Local Variables], page 213).

enable-dir-local-variables

12.14 Connection Local Variables
Connection-local variables provide a general mechanism for different variable settings inbuffers with a remote connection (see Section “Remote Files” in The GNU Emacs Manual).
They are bound and set depending on the remote connection a buffer is dedicated to.

12.14.1 Connection Local Profiles
Emacs uses connection-local profiles to store the variable settings to apply to particularconnections. You can then associate these with remote connections by defining the criteria
when they should apply, using connection-local-set-profiles.

connection-local-set-profile-variables profile variables[Function]
This function defines a set of variable settings for the connection profile, which is asymbol. You can later assign the connection profile to one or more remote connections,and Emacs will apply those variable settings to all process buffers for those connections.
The list in variables is an alist of the form (name . value). Example:

Chapter 12: Variables219(connection-local-set-profile-variables'remote-bash'((shell-file-name . "/bin/bash")(shell-command-switch . "-c")(shell-interactive-switch . "-i")(shell-login-switch . "-l")))(connection-local-set-profile-variables'remote-ksh'((shell-file-name . "/bin/ksh")(shell-command-switch . "-c")(shell-interactive-switch . "-i")(shell-login-switch . "-l")))(connection-local-set-profile-variables'remote-null-device'((null-device . "/dev/null")))If you want to append variable settings to an existing profile, you could use the function
connection-local-get-profile-variables in order to retrieve the existing settings,
like(connection-local-set-profile-variables'remote-bash(append(connection-local-get-profile-variables 'remote-bash)'((shell-command-dont-erase-buffer . t))))[User Option]
This alist holds the connection profile symbols and the associated variable settings. It
is updated by connection-local-set-profile-variables.

connection-local-profile-alist

connection-local-set-profiles criteria &rest profiles[Function]
This function assigns profiles, which are symbols, to all remote connections identified
by criteria. criteria is a plist identifying a connection and the application using
this connection. Property names might be :application, :protocol, :user and:machine. The property value of :application is a symbol, all other property values
are strings. All properties are optional; if criteria is nil, it always applies. Example:(connection-local-set-profiles'(:application tramp :protocol "ssh" :machine "localhost")'remote-bash 'remote-null-device)(connection-local-set-profiles'(:application tramp :protocol "sudo":user "root" :machine "localhost")'remote-ksh 'remote-null-device)If criteria is nil, it applies for all remote connections. Therefore, the example above
would be equivalent toChapter 12: Variables

220(connection-local-set-profiles'(:application tramp :protocol "ssh" :machine "localhost")'remote-bash)(connection-local-set-profiles'(:application tramp :protocol "sudo":user "root" :machine "localhost")'remote-ksh)(connection-local-set-profiles
nil 'remote-null-device)
Any connection profile of profiles must have been already defined byconnection-local-set-profile-variables.
[User Option]
This alist contains connection criteria and their assigned profile names. The function
connection-local-set-profiles updates this list.

connection-local-criteria-alist

12.14.2 Applying Connection Local Variables
When writing connection-aware code, you’ll need to collect, and possibly apply, any
connection-local variables. There are several ways to do this, as described below.

hack-connection-local-variables criteria[Function]
This function collects applicable connection-local variables associated with criteria in
connection-local-variables-alist, without applying them. Example:(hack-connection-local-variables'(:application tramp :protocol "ssh" :machine "localhost"))connection-local-variables-alist⇒ ((null-device . "/dev/null")(shell-login-switch . "-l")(shell-interactive-switch . "-i")(shell-command-switch . "-c")(shell-file-name . "/bin/bash"))hack-connection-local-variables-apply criteria[Function]
This function looks for connection-local variables according to criteria, and immediately
applies them in the current buffer.

with-connection-local-application-variables application &rest
body[Macro]Apply all connection-local variables for application, which are specified bydefault-directory.
After that, body is executed, and the connection-local variables are unwound. Example:(connection-local-set-profile-variables'my-remote-perl'((perl-command-name . "/usr/local/bin/perl5")(perl-command-switch . "-e %s")))Chapter 12: Variables

221(connection-local-set-profiles'(:application my-app :protocol "ssh" :machine "remotehost")'my-remote-perl)(let ((default-directory "/ssh:remotehost:/working/dir/"))(with-connection-local-application-variables 'my-app
do something useful))[Variable]
The default application, a symbol, to be applied in with-connection-localvariables. It defaults to tramp, but you can let-bind it to change the application
temporarily (see Section 12.3 [Local Variables], page 190).
This variable must not be changed globally.

connection-local-default-application

with-connection-local-variables &rest body

[Macro]This is equivalent to with-connection-local-application-variables, but uses
connection-local-default-application for the application.

setq-connection-local [symbol form]. . .

[Macro]This macro sets each symbol connection-locally to the result of evaluating the corresponding form, using the connection-local profile specified in connection-localprofile-name-for-setq; if the profile name is nil, this macro will just set thevariables normally, as with setq (see Section 12.8 [Setting Variables], page 198).
For example, you can use this macro in combination with with-connection-localvariables or with-connection-local-application-variables to lazily initialize
connection-local settings:(defvar my-app-variable nil)(connection-local-set-profile-variables'my-app-connection-default-profile'((my-app-variable . nil)))(connection-local-set-profiles'(:application my-app)'my-app-connection-default-profile)(defun my-app-get-variable ()(with-connection-local-application-variables 'my-app(or my-app-variable(setq-connection-local my-app-variable
do something useful))))[Variable]
The connection-local profile name, a symbol, to use when setting variables via
setq-connection-local. This is let-bound in the body of with-connection-localvariables, but you can also let-bind it yourself if you’d like to set variables on adifferent profile.

connection-local-profile-name-for-setq

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This variable must not be changed globally.
[Variable]
If nil, connection-local variables are ignored. This variable shall be changed temporarily only in special modes.

enable-connection-local-variables

12.15 Variable Aliases
It is sometimes useful to make two variables synonyms, so that both variables always havethe same value, and changing either one also changes the other. Whenever you change thename of a variable—either because you realize its old name was not well chosen, or because
its meaning has partly changed—it can be useful to keep the old name as an alias of the
new one for compatibility. You can do this with defvaralias.

defvaralias new-alias base-variable &optional docstring[Function]
This function defines the symbol new-alias as a variable alias for symbol base-variable.
This means that retrieving the value of new-alias returns the value of base-variable,
and changing the value of new-alias changes the value of base-variable. The two aliased
variable names always share the same value and the same bindings.
If the docstring argument is non-nil, it specifies the documentation for new-alias;
otherwise, the alias gets the same documentation as base-variable has, if any, unlessbase-variable is itself an alias, in which case new-alias gets the documentation of thevariable at the end of the chain of aliases.
This function returns base-variable.

Variable aliases are convenient for replacing an old name for a variable with a new name.
make-obsolete-variable declares that the old name is obsolete and therefore that it may
be removed at some stage in the future.

make-obsolete-variable obsolete-name current-name when
&optional access-type[Function]

This function makes the byte compiler warn that the variable obsolete-name is obsolete.
If current-name is a symbol, it is the variable’s new name; then the warning message
says to use current-name instead of obsolete-name. If current-name is a string, this is
the message and there is no replacement variable. when should be a string indicatingwhen the variable was first made obsolete (usually a version number string).
The optional argument access-type, if non-nil, should specify the kind of access thatwill trigger obsolescence warnings; it can be either get or set.
You can make two variables synonyms and declare one obsolete at the same time using
the macro define-obsolete-variable-alias.

define-obsolete-variable-alias obsolete-name current-name when
&optional docstring[Macro]This macro marks the variable obsolete-name as obsolete and also makes it an alias
for the variable current-name. It is equivalent to the following:(defvaralias obsolete-name current-name docstring)(make-obsolete-variable obsolete-name current-name when)Chapter 12: Variables

223

This macro evaluates all its parameters, and both obsolete-name and current-nameshould be symbols, so a typical usage would look like:(define-obsolete-variable-alias 'foo-thing 'bar-thing "27.1")

indirect-variable variable[Function]
This function returns the variable at the end of the chain of aliases of variable. Ifvariable is not a symbol, or if variable is not defined as an alias, the function returns
variable.
This function signals a cyclic-variable-indirection error if there is a loop in the
chain of symbols.
(defvaralias 'foo 'bar)(indirect-variable 'foo)⇒ bar(indirect-variable 'bar)⇒ bar(setq bar 2)
bar
⇒ 2
foo
⇒ 2
(setq foo 0)
bar
⇒ 0
foo
⇒ 0

12.16 Variables with Restricted Values
Ordinary Lisp variables can be assigned any value that is a valid Lisp object. However,certain Lisp variables are not defined in Lisp, but in C. Most of these variables aredefined in the C code using DEFVAR_LISP. Like variables defined in Lisp, these can takeon any value. However, some variables are defined using DEFVAR_INT or DEFVAR_BOOL. See[Writing Emacs Primitives], page 1358, in particular the description of functions of the typesyms_of_filename, for a brief discussion of the C implementation.
Variables of type DEFVAR_BOOL can only take on the values nil or t. Attempting toassign them any other value will set them to t:(let ((display-hourglass 5))
display-hourglass)⇒ tbyte-boolean-vars[Variable]

This variable holds a list of all variables of type DEFVAR_BOOL.
Variables of type DEFVAR_INT can take on only integer values. Attempting to assign
them any other value will result in an error:(setq undo-limit 1000.0)
error Wrong type argument: integerp, 1000.0

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12.17 Generalized Variables
A generalized variable or place form is one of the many places in Lisp memory where values
can be stored using the setf macro (see Section 12.17.1 [Setting Generalized Variables],page 224). The simplest place form is a regular Lisp variable. But the cars and cdrs oflists, elements of arrays, properties of symbols, and many other locations are also places
where Lisp values get stored.
Generalized variables are analogous to lvalues in the C language, where ‘x = a[i]’ gets
an element from an array and ‘a[i] = x’ stores an element using the same notation. Just as
certain forms like a[i] can be lvalues in C, there is a set of forms that can be generalized
variables in Lisp.

12.17.1 The setf Macro
The setf macro is the most basic way to operate on generalized variables. The setf form
is like setq, except that it accepts arbitrary place forms in the first (left) argument of eachpair rather than just symbols. For example, (setf (car a) b) sets the car of a to b, doing
the same operation as (setcar a b), but without you having to use two separate functions
for setting and accessing this type of place.

setf [place form]. . .

[Macro]This macro evaluates form and stores its value in place, which must be a valid
generalized variable form. If there are several place and form pairs, the assignments
are done sequentially just as with setq. setf returns the value of the last form.

The following Lisp forms are the forms in Emacs that will work as generalized variables,and so may appear in the place argument of setf:• A symbol. In other words, (setf x y) is exactly equivalent to (setq x y), and setq
itself is strictly speaking redundant given that setf exists. Most programmers willcontinue to prefer setq for setting simple variables, though, for stylistic and historical reasons. The macro (setf x y) actually expands to (setq x y), so there is no
performance penalty for using it in compiled code.
• A call to any of the following standard Lisp functions:
aref
car
caar
cadr
cdr
cdar

cddr
elt
get
gethashnthnthcdrsymbol-function
symbol-plist
symbol-value• A call to any of the following Emacs-specific functions:alist-getdefault-value
face-backgroundface-fontface-foregroundface-stipple
face-underline-p
file-modes
frame-parameter
frame-parameters
get-register

overlay-start
overlay-get
process-buffer
process-filter
process-get
process-sentinelterminal-parameter
window-buffer
window-dedicated-p
window-display-tablewindow-hscroll

Chapter 12: Variables

getenvkeymap-parent
match-data
overlay-end

225window-parameter
window-point
window-start• A call of the form (substring subplace n [m]), where subplace is itself a valid generalized variable whose current value is a string, and where the value stored is also astring. The new string is spliced into the specified part of the destination string. For
example:(setq a (list "hello" "world"))⇒ ("hello" "world")(cadr a)⇒ "world"(substring (cadr a) 2 4)
⇒ "rl"(setf (substring (cadr a) 2 4) "o")⇒ "o"(cadr a)⇒ "wood"a⇒ ("hello" "wood")• The if and cond conditionals will work as generalized variables. For instance, this will
set either the foo or the bar variable to zot:
(setf (if (zerop (random 2))
foo
bar)
'zot)
setf signals an error if you pass a place form that it does not know how to handle.
Note that for nthcdr, the list argument of the function must itself be a valid place form.
For example, (setf (nthcdr 0 foo) 7) will set foo itself to 7.
The macros push (see Section 5.5 [List Variables], page 85) and pop (see Section 5.3[List Elements], page 79) can manipulate generalized variables, not just lists. (pop place)removes and returns the first element of the list stored in place. It is analogous to (prog1(car place) (setf place (cdr place))), except that it takes care to evaluate all subforms
only once. (push x place) inserts x at the front of the list stored in place. It is analogous
to (setf place (cons x place)), except for evaluation of the subforms. Note that pushand pop on an nthcdr place can be used to insert or delete at any position in a list.
The cl-lib library defines various extensions for generalized variables, including additional setf places. See Section “Generalized Variables” in Common Lisp Extensions.

12.17.2 Defining new setf forms
This section describes how to define new forms that setf can operate on.

gv-define-simple-setter name setter &optional fix-return[Macro]This macro enables you to easily define setf methods for simple cases. name is thename of a function, macro, or special form. You can use this macro whenever name has

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a directly corresponding setter function that updates it, e.g., (gv-define-simplesetter car setcar).
This macro translates a call of the form
(setf (name args...) value)
into(setter args... value)
Such a setf call is documented to return value. This is no problem with, e.g., car andsetcar, because setcar returns the value that it set. If your setter function does not
return value, use a non-nil value for the fix-return argument of gv-define-simplesetter. This expands into something equivalent to(let ((temp value))(setter args... temp)
temp)
so ensuring that it returns the correct result.

gv-define-setter name arglist &rest body

[Macro]This macro allows for more complex setf expansions than the previous form. You
may need to use this form, for example, if there is no simple setter function to call, or
if there is one but it requires different arguments to the place form.
This macro expands the form (setf (name args...) value) by first binding thesetf argument forms (value args...) according to arglist, and then executing body.
body should return a Lisp form that does the assignment, and finally returns thevalue that was set. An example of using this macro is:(gv-define-setter caar (val x) `(setcar (car ,x) ,val))

gv-define-expander name handler[Macro]For more control over the expansion, the gv-define-expander macro can be used.
For instance, a settable substring could be implemented this way:
(gv-define-expander substring(lambda (do place from &optional to)(gv-letplace (getter setter) place(macroexp-let2* (from to)(funcall do `(substring ,getter ,from ,to)(lambda (v)(macroexp-let2* (v)`(progn,(funcall setter `(cl--set-substring,getter ,from ,to ,v)),v))))))))

gv-letplace (getter setter) place &rest body

[Macro]The macro gv-letplace can be useful in defining macros that perform similarly tosetf; for example, the incf macro of Common Lisp could be implemented this way:
(defmacro incf (place &optional n)(gv-letplace (getter setter) place

Chapter 12: Variables

227(macroexp-let2* ((v (or n 1)))
(funcall setter `(+ ,v ,getter)))))
getter will be bound to a copyable expression that returns the value of place. setter
will be bound to a function that takes an expression v and returns a new expressionthat sets place to v. body should return a Emacs Lisp expression manipulating place
via getter and setter.
Consult the source file gv.el for more details.

make-obsolete-generalized-variable obsolete-name current-namewhen[Function]

This function makes the byte compiler warn that the generalized variable obsoletename is obsolete. If current-name is a symbol, then the warning message says to use
current-name instead of obsolete-name. If current-name is a string, this is the message.
when should be a string indicating when the variable was first made obsolete (usuallya version number string).
Common Lisp note: Common Lisp defines another way to specify the setf
behavior of a function, namely setf functions, whose names are lists (setfname) rather than symbols. For example, (defun (setf foo) ...) defines thefunction that is used when setf is applied to foo. Emacs does not support this.
It is a compile-time error to use setf on a form that has not already had anappropriate expansion defined. In Common Lisp, this is not an error since thefunction (setf func) might be defined later.

12.18 Multisession Variables
When you set a variable to a value and then close Emacs and restart it, that value won’t
be automatically restored. Users usually set normal variables in their startup files, or use
Customize (see Chapter 15 [Customization], page 277) to set user options permanently,
and various packages have various files where they store the data (e.g., Gnus stores this in.newsrc.eld and the URL library stores cookies in ~/.emacs.d/url/cookies).
For things in between these two extremes (i.e., configuration which goes in the startup
file, and massive application state that goes into separate files), Emacs provides a facility
to replicate data between sessions called multisession variables. (This facility may not be
available on all systems.) To give you an idea of how these are meant to be used, here’s asmall example:(define-multisession-variable foo 0)(defun my-adder (num)(interactive "nAdd number: ")(setf (multisession-value foo)(+ (multisession-value foo) num))(message "The new number is: %s" (multisession-value foo)))This defines the variable foo and binds it to a special multisession object which is initializedwith the value ‘0’ (if the variable doesn’t already exist from a previous session). The
my-adder command queries the user for a number, adds this to the old (possibly savedvalue), and then saves the new value.

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This facility isn’t meant to be used for huge data structures, but should be performant
for most values.

define-multisession-variable name initial-value &optional doc&rest args

[Macro]This macro defines name as a multisession variable, and gives it the initial-value if
this variable hasn’t been assigned a value earlier. doc is the doc string, and several
keyword arguments can be used in args::package package-symbolThis keyword says that a multisession variable belongs to the package
specified by package-symbol. The combination of package-symbol andname has to be unique. If package-symbol isn’t given, this will default tothe first “segment” of the name symbol’s name, which is the part of its
name up to and excluding the first ‘-’. For instance, if name is foo andpackage-symbol isn’t given, package-symbol will default to foo.
:synchronized bool
Multisession variables can be synchronized if bool is non-nil. This meansthat if there’re two concurrent Emacs instances running, and the otherEmacs changes the multisession variable foo, the current Emacs instancewill retrieve that modified data when accessing the value. If synchronizedis nil or missing, this won’t happen, and the values in all Emacs sessions
using the variable will be independent of each other.
:storage storage
Use the specified storage method. This can be either sqlite (in Emacs
compiled with SQLite support) or files. If not given, this defaults tothe value of the multisession-storage variable, described below.

multisession-value variable[Function]
This function returns the current value of variable. If this variable hasn’t been accessed
before in this Emacs session, or if it’s changed externally, it will be read in fromexternal storage. If not, the current value in this session is returned as is. It is anerror to call this function for a variable that is not a multisession variable.
Values retrieved via multisession-value may or may not be eq to each other, butthey will always be equal.
This is a generalized variable (see Section 12.17 [Generalized Variables], page 224), so
the way to update such a variable is to say, for instance:(setf (multisession-value foo-bar) 'zot)
Only Emacs Lisp values that have a readable print syntax (see Section 2.1 [Printed
Representation], page 8) can be saved this way.
If the multisession variable is synchronized, setting it may update the value first. For
instance:(cl-incf (multisession-value foo-bar))
This first checks whether the value has changed in a different Emacs instance, retrieves
that value, and then adds 1 to that value and stores it. But note that this is done
without locking, so if many instances are updating the value at the same time, it’sunpredictable which instance “wins”.

Chapter 12: Variables

multisession-delete object

229[Function]

This function deletes object and its value from its persistent storage.
[Function]
You can also make persistent values that aren’t tied to a specific variable, but are tied
to an explicit package and key.
(setq foo (make-multisession :package "mail":key "friends"))(setf (multisession-value foo) 'everybody)This supports the same keywords as define-multisession-variable, but also supports a :initial-value keyword, which specifies the default value.

make-multisession[User Option]
This variable controls how the multisession variables are stored. It value defaults
to files, which means that the values are stored in a one-file-per-variable structure
inside the directory specified by multisession-directory. If this value is sqlite
instead, the values are stored in an SQLite database; this is only available if Emacs
was built with SQLite support.

multisession-storage[User Option]
The multisession variables are stored under this directory, which defaults tomultisession/ subdirectory of the user-emacs-directory, which is typically~/.emacs.d/multisession/.

multisession-directory[Command]This command pops up a buffer listing all the multisession variables, and enters a
special mode multisession-edit-mode which allows you to delete them and edit
their values.

list-multisession-values

230

13 Functions
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions
are, how they accept arguments, and how to define them.

13.1 What Is a Function?
In a general sense, a function is a rule for carrying out a computation given input values
called arguments. The result of the computation is called the value or return value of thefunction. The computation can also have side effects, such as lasting changes in the valuesof variables or the contents of data structures (see [Definition of side effect], page 145). A
pure function is a function which, in addition to having no side effects, always returns thesame value for the same combination of arguments, regardless of external factors such asmachine type or system state.
In most computer languages, every function has a name. But in Lisp, a function in thestrictest sense has no name: it is an object which can optionally be associated with a symbol(e.g., car) that serves as the function name. See Section 13.3 [Function Names], page 236.
When a function has been given a name, we usually also refer to that symbol as a “function”(e.g., we refer to “the function car”). In this manual, the distinction between a function
name and the function object itself is usually unimportant, but we will take note wherever
it is relevant.
Certain function-like objects, called special forms and macros, also accept arguments tocarry out computations. However, as explained below, these are not considered functions in
Emacs Lisp.
Here are important terms for functions and function-like objects:
lambda expression
A function (in the strict sense, i.e., a function object) which is written in Lisp.
These are described in the following section.
primitive

A function which is callable from Lisp but is actually written in C. Primitives
are also called built-in functions, or subrs. Examples include functions like
car and append. In addition, all special forms (see below) are also consideredprimitives.
Usually, a function is implemented as a primitive because it is a fundamental
part of Lisp (e.g., car), or because it provides a low-level interface to operating
system services, or because it needs to run fast. Unlike functions defined in
Lisp, primitives can be modified or added only by changing the C sources andrecompiling Emacs. See Section E.7 [Writing Emacs Primitives], page 1356.

special form
A primitive that is like a function but does not evaluate all of its arguments inthe usual way. It may evaluate only some of the arguments, or may evaluate
them in an unusual order, or several times. Examples include if, and, andwhile. See Section 10.1.7 [Special Forms], page 149.
macro

A construct defined in Lisp, which differs from a function in that it translates a
Lisp expression into another expression which is to be evaluated instead of theChapter 13: Functions

231

original expression. Macros enable Lisp programmers to do the sorts of things
that special forms can do. See Chapter 14 [Macros], page 268.
command

An object which can be invoked via the command-execute primitive, usually due
to the user typing in a key sequence bound to that command. See Section 22.3
[Interactive Call], page 432. A command is usually a function; if the function
is written in Lisp, it is made into a command by an interactive form in thefunction definition (see Section 22.2 [Defining Commands], page 424). Commands
that are functions can also be called from Lisp expressions, just like otherfunctions.
Keyboard macros (strings and vectors) are commands also, even though they
are not functions. See Section 22.16 [Keyboard Macros], page 478. We say thata symbol is a command if its function cell contains a command (see Section 9.1[Symbol Components], page 133); such a named command can be invoked with
M-x.

closureA function object that is much like a lambda expression, except that it also
encloses an environment of lexical variable bindings. See Section 13.10 [Closures],page 249.

byte-code function
A function that has been compiled by the byte compiler. See Section 2.4.16[Byte-Code Type], page 24.
autoload object
A place-holder for a real function. If the autoload object is called, Emacs loads
the file containing the definition of the real function, and then calls the realfunction. See Section 16.5 [Autoload], page 304.
You can use the function functionp to test if an object is a function:functionp object[Function]
This function returns t if object is any kind of function, i.e., can be passed to funcall.
Note that functionp returns t for symbols that are function names, and returns nil
for symbols that are macros or special forms.
If object is not a function, this function ordinarily returns nil. However, the representation of function objects is complicated, and for efficiency reasons in rare cases thisfunction can return t even when object is not a function.

It is also possible to find out how many arguments an arbitrary function expects:

func-arity function[Function]
This function provides information about the argument list of the specified function.
The returned value is a cons cell of the form (min . max), where min is the minimum
number of arguments, and max is either the maximum number of arguments, or thesymbol many for functions with &rest arguments, or the symbol unevalled if function
is a special form.
Note that this function might return inaccurate results in some situations, such as thefollowing:− Functions defined using apply-partially (see Section 13.5 [Calling Functions],
page 239).

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232− Functions that are advised using advice-add (see Section 13.12.2 [Advising
Named Functions], page 255).
− Functions that determine the argument list dynamically, as part of their code.
Unlike functionp, the next three functions do not treat a symbol as its function definition.

subrp object[Function]
This function returns t if object is a built-in function (i.e., a Lisp primitive).
(subrp 'message); message is a symbol,⇒ nil;
not a subr object.
(subrp (symbol-function 'message))⇒ tbyte-code-function-p object[Function]

This function returns t if object is a byte-code function. For example:(byte-code-function-p (symbol-function 'next-line))⇒ tcompiled-function-p object[Function]
This function returns t if object is a function object that is not in the form of ELisp
source code but something like machine code or byte code instead. More specificallyit returns t if the function is built-in (a.k.a. “primitive”, see Section 13.1 [What Is a
Function], page 230), or byte-compiled (see Chapter 17 [Byte Compilation], page 316),
or natively-compiled (see Chapter 18 [Native Compilation], page 327), or a function
loaded from a dynamic module (see Section 16.11 [Dynamic Modules], page 314).

subr-arity subr

[Function]
This works like func-arity, but only for built-in functions and without symbol
indirection. It signals an error for non-built-in functions. We recommend to use
func-arity instead.

13.2 Lambda Expressions
A lambda expression is a function object written in Lisp. Here is an example:(lambda (x)"Return the hyperbolic cosine of X."(* 0.5 (+ (exp x) (exp (- x)))))In Emacs Lisp, such a list is a valid expression which evaluates to a function object.
A lambda expression, by itself, has no name; it is an anonymous function. Although
lambda expressions can be used this way (see Section 13.7 [Anonymous Functions], page 243),
they are more commonly associated with symbols to make named functions (see Section 13.3
[Function Names], page 236). Before going into these details, the following subsections
describe the components of a lambda expression and what they do.

13.2.1 Components of a Lambda Expression
A lambda expression is a list that looks like this:(lambda (arg-variables...)Chapter 13: Functions

233[documentation-string][interactive-declaration]body-forms...)
The first element of a lambda expression is always the symbol lambda. This indicatesthat the list represents a function. The reason functions are defined to start with lambda isso that other lists, intended for other uses, will not accidentally be valid as functions.
The second element is a list of symbols—the argument variable names (see Section 13.2.3[Argument List], page 234). This is called the lambda list. When a Lisp function is called,
the argument values are matched up against the variables in the lambda list, which are given
local bindings with the values provided. See Section 12.3 [Local Variables], page 190.
The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See Section 13.2.4 [Function
Documentation], page 235.
The interactive declaration is a list of the form (interactive code-string). Thisdeclares how to provide arguments if the function is used interactively. Functions withthis declaration are called commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive declarations. See
Section 22.2 [Defining Commands], page 424, for how to write an interactive declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of
the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The
value returned by the function is the value returned by the last element of the body.

13.2.2 A Simple Lambda Expression Example
Consider the following example:(lambda (a b c) (+ a b c))
We can call this function by passing it to funcall, like this:(funcall (lambda (a b c) (+ a b c))
1 2 3)
This call evaluates the body of the lambda expression with the variable a bound to 1, b
bound to 2, and c bound to 3. Evaluation of the body adds these three numbers, producing
the result 6; therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:(funcall (lambda (a b c) (+ a b c))
1 (* 2 3) (- 5 4))This evaluates the arguments 1, (* 2 3), and (- 5 4) from left to right. Then it applies thelambda expression to the argument values 1, 6 and 1 to produce the value 8.
As these examples show, you can use a form with a lambda expression as its car to
make local variables and give them values. In the old days of Lisp, this technique was the
only way to bind and initialize local variables. But nowadays, it is clearer to use the special
form let for this purpose (see Section 12.3 [Local Variables], page 190). Lambda expressions
are mainly used as anonymous functions for passing as arguments to other functions (seeSection 13.7 [Anonymous Functions], page 243), or stored as symbol function definitions to
produce named functions (see Section 13.3 [Function Names], page 236).

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13.2.3 Features of Argument Lists
Our simple sample function, (lambda (a b c) (+ a b c)), specifies three argument variables,
so it must be called with three arguments: if you try to call it with only two arguments orfour arguments, you get a wrong-number-of-arguments error (see Section 11.7.3 [Errors],
page 179).
It is often convenient to write a function that allows certain arguments to be omitted.
For example, the function substring accepts three arguments—a string, the start index
and the end index—but the third argument defaults to the length of the string if you omit
it. It is also convenient for certain functions to accept an indefinite number of arguments, as
the functions list and + do.
To specify optional arguments that may be omitted when a function is called, simply
include the keyword &optional before the optional arguments. To specify a list of zero or
more extra arguments, include the keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:(required-vars...
[&optional [optional-vars...]][&rest rest-var])
The square brackets indicate that the &optional and &rest clauses, and the variables that
follow them, are optional.
A call to the function requires one actual argument for each of the required-vars. Theremay be actual arguments for zero or more of the optional-vars, and there cannot be any
actual arguments beyond that unless the lambda list uses &rest. In that case, there may be
any number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted, then they always
default to nil. There is no way for the function to distinguish between an explicit argumentof nil and an omitted argument. However, the body of the function is free to consider nil
an abbreviation for some other meaningful value. This is what substring does; nil as thethird argument to substring means to use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what default
value to use when an optional argument is omitted; Emacs Lisp always uses
nil. Emacs Lisp does not support supplied-p variables that tell you whether
an argument was explicitly passed.
For example, an argument list that looks like this:(a b &optional c d &rest e)binds a and b to the first two actual arguments, which are required. If one or two morearguments are provided, c and d are bound to them respectively; any arguments after the
first four are collected into a list and e is bound to that list. Thus, if there are only twoarguments, c, d and e are nil; if two or three arguments, d and e are nil; if four arguments
or fewer, e is nil. Note that exactly five arguments with an explicit nil argument provided
for e will cause that nil argument to be passed as a list with one element, (nil), as withany other single value for e.
There is no way to have required arguments following optional ones—it would not makesense. To see why this must be so, suppose that c in the example were optional and dwere required. Suppose three actual arguments are given; which variable would the third

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argument be for? Would it be used for the c, or for d? One can argue for both possibilities.
Similarly, it makes no sense to have any more arguments (either required or optional) after
a &rest argument.
Here are some examples of argument lists and proper calls:(funcall (lambda (n) (1+ n)); One required:1); requires exactly one argument.
⇒ 2(funcall (lambda (n &optional n1); One required and one optional:(if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments.
1 2)⇒ 3(funcall (lambda (n &rest ns); One required and one rest:(+ n (apply '+ ns))); 1 or more arguments.
1 2 3 4 5)
⇒ 15

13.2.4 Documentation Strings of Functions
A lambda expression may optionally have a documentation string just after the lambda
list. This string does not affect execution of the function; it is a kind of comment, but asystematized comment which actually appears inside the Lisp world and can be used by theEmacs help facilities. See Chapter 25 [Documentation], page 595, for how the documentation
string is accessed.
It is a good idea to provide documentation strings for all the functions in your program,even those that are called only from within your program. Documentation strings are likecomments, except that they are easier to access.
The first line of the documentation string should stand on its own, because apropos
displays just this first line. It should consist of one or two complete sentences that summarize
the function’s purpose.
The start of the documentation string is usually indented in the source file, but sincethese spaces come before the starting double-quote, they are not part of the string. Somepeople make a practice of indenting any additional lines of the string so that the text lines
up in the program source. That is a mistake. The indentation of the following lines is inside
the string; what looks nice in the source code will look ugly when displayed by the help
commands.
You may wonder how the documentation string could be optional, since there are requiredcomponents of the function that follow it (the body). Since evaluation of a string returns thatstring, without any side effects, it has no effect if it is not the last form in the body. Thus,in practice, there is no confusion between the first form of the body and the documentation
string; if the only body form is a string then it serves both as the return value and as the
documentation.
The last line of the documentation string can specify calling conventions different fromthe actual function arguments. Write text like this:\(fn arglist)
following a blank line, at the beginning of the line, with no newline following it inside thedocumentation string. (The ‘\’ is used to avoid confusing the Emacs motion commands.)

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The calling convention specified in this way appears in help messages in place of the one
derived from the actual arguments of the function.
This feature is particularly useful for macro definitions, since the arguments written in amacro definition often do not correspond to the way users think of the parts of the macrocall.
Do not use this feature if you want to deprecate the calling convention and favor the one
you advertise by the above specification. Instead, use the advertised-calling-convention
declaration (see Section 13.15 [Declare Form], page 263) or set-advertised-callingconvention (see Section 13.13 [Obsolete Functions], page 260), because these two will cause
the byte compiler emit a warning message when it compiles Lisp programs which use thedeprecated calling convention.
Documentation strings are usually static, but occasionally it can be necessary to generatethem dynamically. In some cases you can do so by writing a macro which generates atcompile time the code of the function, including the desired documentation string. But you
can also generate the docstring dynamically by writing (:documentation form) instead ofthe documentation string. This will evaluate form at run-time when the function is definedand use it as the documentation string1 . You can also compute the documentation stringon the fly when it is requested, by setting the function-documentation property of thefunction’s symbol to a Lisp form that evaluates to a string.
For example:(defun adder (x)(lambda (y)(:documentation (format "Add %S to the argument Y." x))(+ x y)))(defalias 'adder5 (adder 5))(documentation 'adder5)⇒ "Add 5 to the argument Y."(put 'adder5 'function-documentation'(concat (documentation (symbol-function 'adder5) 'raw)" Consulted at " (format-time-string "%H:%M:%S")))(documentation 'adder5)⇒ "Add 5 to the argument Y. Consulted at 15:52:13"(documentation 'adder5)⇒ "Add 5 to the argument Y. Consulted at 15:52:18"

13.3 Naming a Function
A symbol can serve as the name of a function. This happens when the symbol’s function
cell (see Section 9.1 [Symbol Components], page 133) contains a function object (e.g., alambda expression). Then the symbol itself becomes a valid, callable function, equivalent to
the function object in its function cell.
The contents of the function cell are also called the symbol’s function definition. The
procedure of using a symbol’s function definition in place of the symbol is called symbol
1This only works in code using lexical-binding.

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function indirection; see Section 10.1.4 [Function Indirection], page 147. If you have notgiven a symbol a function definition, its function cell is said to be void, and it cannot be
used as a function.
In practice, nearly all functions have names, and are referred to by their names. You cancreate a named Lisp function by defining a lambda expression and putting it in a function
cell (see Section 13.9 [Function Cells], page 248). However, it is more common to use thedefun macro, described in the next section.
We give functions names because it is convenient to refer to them by their names in
Lisp expressions. Also, a named Lisp function can easily refer to itself—it can be recursive.
Furthermore, primitives can only be referred to textually by their names, since primitive
function objects (see Section 2.4.15 [Primitive Function Type], page 24) have no read syntax.
A function need not have a unique name. A given function object usually appears in
the function cell of only one symbol, but this is just a convention. It is easy to store it inseveral symbols using fset; then each of the symbols is a valid name for the same function.
Note that a symbol used as a function name may also be used as a variable; these twouses of a symbol are independent and do not conflict. (This is not the case in some dialectsof Lisp, like Scheme.)
By convention, if a function’s symbol consists of two names separated by ‘--’, the function
is intended for internal use and the first part names the file defining the function. For example,
a function named vc-git--rev-parse is an internal function defined in vc-git.el. Internaluse functions written in C have names ending in ‘-internal’, e.g., bury-buffer-internal.
Emacs code contributed before 2018 may follow other internal-use naming conventions,which are being phased out.

13.4 Defining Functions
We usually give a name to a function when it is first created. This is called defining afunction, and we usually do it with the defun macro. This section also describes other ways
to define a function.

defun name args [doc] [declare] [interactive] body. . .

[Macro]defun is the usual way to define new Lisp functions. It defines the symbol name as afunction with argument list args (see Section 13.2.3 [Argument List], page 234) andbody forms given by body. Neither name nor args should be quoted.

doc, if present, should be a string specifying the function’s documentation string(see Section 13.2.4 [Function Documentation], page 235). declare, if present, should
be a declare form specifying function metadata (see Section 13.15 [Declare Form],
page 263). interactive, if present, should be an interactive form specifying how thefunction is to be called interactively (see Section 22.3 [Interactive Call], page 432).
The return value of defun is undefined.
Here are some examples:(defun foo () 5)
(foo)
⇒ 5

Chapter 13: Functions

238(defun bar (a &optional b &rest c)(list a b c))(bar 1 2 3 4 5)
⇒ (1 2 (3 4 5))(bar 1)⇒ (1 nil nil)(bar)error Wrong number of arguments.
(defun capitalize-backwards ()"Upcase the last letter of the word at point."(interactive)(backward-word 1)(forward-word 1)(backward-char 1)(capitalize-word 1))
Most Emacs functions are part of the source code of Lisp programs, and are definedwhen the Emacs Lisp reader reads the program source before executing it. However,you can also define functions dynamically at run time, e.g., by generating defun calls
when your program’s code is executed. If you do this, be aware that Emacs’s Help
commands, such as C-h f, which present in the *Help* buffer a button to jump to thefunction’s definition, might be unable to find the source code because generating afunction dynamically usually looks very different from the usual static calls to defun.
You can make the job of finding the code which generates such functions easier by using
the definition-name property, see Section 9.4.2 [Standard Properties], page 139.
Be careful not to redefine existing functions unintentionally. defun redefines evenprimitive functions such as car without any hesitation or notification. Emacs does
not prevent you from doing this, because redefining a function is sometimes done deliberately, and there is no way to distinguish deliberate redefinition from unintentional
redefinition.

defalias name definition &optional doc[Function]
This function defines the symbol name as a function, with definition definition.
definition can be any valid Lisp function or macro, or a special form (see Section 10.1.7[Special Forms], page 149), or a keymap (see Chapter 23 [Keymaps], page 480), or avector or string (a keyboard macro). The return value of defalias is undefined.
If doc is non-nil, it becomes the function documentation of name. Otherwise, any
documentation provided by definition is used.
Internally, defalias normally uses fset to set the definition. If name has adefalias-fset-function property, however, the associated value is used as afunction to call in place of fset.
The proper place to use defalias is where a specific function or macro name is being
defined—especially where that name appears explicitly in the source file being loaded.
This is because defalias records which file defined the function, just like defun (seeSection 16.9 [Unloading], page 313).

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By contrast, in programs that manipulate function definitions for other purposes, it
is better to use fset, which does not keep such records. See Section 13.9 [Function
Cells], page 248.

function-alias-p object &optional noerror[Function]
Checks whether object is a function alias. If it is, it returns a list of symbols representing
the function alias chain, else nil. For instance, if a is an alias for b, and b is an alias
for c:(function-alias-p 'a)⇒ (b c)If there’s a loop in the definitions, an error will be signaled. If noerror is non-nil, thenon-looping parts of the chain is returned instead.

You cannot create a new primitive function with defun or defalias, but you can use
them to change the function definition of any symbol, even one such as car or x-popup-menu
whose normal definition is a primitive. However, this is risky: for instance, it is next to
impossible to redefine car without breaking Lisp completely. Redefining an obscure function
such as x-popup-menu is less dangerous, but it still may not work as you expect. If there
are calls to the primitive from C code, they call the primitive’s C definition directly, sochanging the symbol’s definition will have no effect on them.
See also defsubst, which defines a function like defun and tells the Lisp compiler toperform inline expansion on it. See Section 13.14 [Inline Functions], page 261.
To undefine a function name, use fmakunbound. See Section 13.9 [Function Cells],
page 248.

13.5 Calling Functions
Defining functions is only half the battle. Functions don’t do anything until you call them,i.e., tell them to run. Calling a function is also known as invocation.
The most common way of invoking a function is by evaluating a list. For example,
evaluating the list (concat "a" "b") calls the function concat with arguments "a" and"b". See Chapter 10 [Evaluation], page 145, for a description of evaluation.
When you write a list as an expression in your program, you specify which function tocall, and how many arguments to give it, in the text of the program. Usually that’s justwhat you want. Occasionally you need to compute at run time which function to call. To
do that, use the function funcall. When you also need to determine at run time how manyarguments to pass, use apply.

funcall function &rest arguments[Function]
funcall calls function with arguments, and returns whatever function returns.

Since funcall is a function, all of its arguments, including function, are evaluatedbefore funcall is called. This means that you can use any expression to obtainthe function to be called. It also means that funcall does not see the expressions
you write for the arguments, only their values. These values are not evaluated asecond time in the act of calling function; the operation of funcall is like the normal
procedure for calling a function, once its arguments have already been evaluated.

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The argument function must be either a Lisp function or a primitive function. Special
forms and macros are not allowed, because they make sense only when given theunevaluated argument expressions. funcall cannot provide these because, as we saw
above, it never knows them in the first place.
If you need to use funcall to call a command and make it behave as if invoked interactively, use funcall-interactively (see Section 22.3 [Interactive Call], page 432).
(setq f 'list)⇒ list(funcall f 'x 'y 'z)⇒ (x y z)(funcall f 'x 'y '(z))⇒ (x y (z))(funcall 'and t nil)error Invalid function: #<subr and>Compare these examples with the examples of apply.

apply function &rest arguments[Function]
apply calls function with arguments, just like funcall but with one difference: the lastof arguments is a list of objects, which are passed to function as separate arguments,
rather than a single list. We say that apply spreads this list so that each individual
element becomes an argument.
apply with a single argument is special: the first element of the argument, which must
be a non-empty list, is called as a function with the remaining elements as individualarguments. Passing two or more arguments will be faster.
apply returns the result of calling function. As with funcall, function must either bea Lisp function or a primitive function; special forms and macros do not make sense
in apply.
(setq f 'list)⇒ list(apply f 'x 'y 'z)
error Wrong type argument: listp, z(apply '+ 1 2 '(3 4))⇒ 10(apply '+ '(1 2 3 4))⇒ 10(apply 'append '((a b c) nil (x y z) nil))⇒ (a b c x y z)
(apply '(+ 3 4))⇒ 7

For an interesting example of using apply, see [Definition of mapcar], page 242.
Sometimes it is useful to fix some of the function’s arguments at certain values, andleave the rest of arguments for when the function is actually called. The act of fixing some

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241of the function’s arguments is called partial application of the function2 . The result is a
new function that accepts the rest of arguments and calls the original function with all thearguments combined.
Here’s how to do partial application in Emacs Lisp:

apply-partially func &rest args

[Function]
This function returns a new function which, when called, will call func with the listof arguments composed from args and additional arguments specified at the time of
the call. If func accepts n arguments, then a call to apply-partially with m <= narguments will produce a new function of n - m arguments3 .
Here’s how we could define the built-in function 1+, if it didn’t exist, using
apply-partially and +, another built-in function4 :(defalias '1+ (apply-partially '+ 1)"Increment argument by one.")(1+ 10)⇒ 11

It is common for Lisp functions to accept functions as arguments or find them in data
structures (especially in hook variables and property lists) and call them using funcall orapply. Functions that accept function arguments are often called functionals.
Sometimes, when you call a functional, it is useful to supply a no-op function as theargument. Here are three different kinds of no-op functions:

identity argument[Function]

This function returns argument and has no side effects.

ignore &rest arguments[Function]

This function ignores any arguments and returns nil.

always &rest arguments[Function]

This function ignores any arguments and returns t.
Some functions are user-visible commands, which can be called interactively (usually by
a key sequence). It is possible to invoke such a command exactly as though it was calledinteractively, by using the call-interactively function. See Section 22.3 [Interactive Call],page 432.

13.6 Mapping Functions
A mapping function applies a given function (not a special form or macro) to each elementof a list or other collection. Emacs Lisp has several such functions; this section describes
mapcar, mapc, mapconcat, and mapcan, which map over a list. See [Definition of mapatoms],
2

This is related to, but different from currying, which transforms a function that takes multiple arguments
in such a way that it can be called as a chain of functions, each one with a single argument.
3
If the number of arguments that func can accept is unlimited, then the new function will also accept
an unlimited number of arguments, so in that case apply-partially doesn’t reduce the number ofarguments that the new function could accept.
4Note that unlike the built-in function, this version accepts any number of arguments.

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page 137, for the function mapatoms which maps over the symbols in an obarray. See[Definition of maphash], page 130, for the function maphash which maps over key/value
associations in a hash table.
These mapping functions do not allow char-tables because a char-table is a sparse array
whose nominal range of indices is very large. To map over a char-table in a way that
deals properly with its sparse nature, use the function map-char-table (see Section 6.6[Char-Tables], page 119).

mapcar function sequence[Function]
mapcar applies function to each element of sequence in turn, and returns a list of theresults.

The argument sequence can be any kind of sequence except a char-table; that is, alist, a vector, a bool-vector, or a string. The result is always a list. The length of theresult is the same as the length of sequence. For example:(mapcar #'car '((a b) (c d) (e f)))⇒ (a c e)(mapcar #'1+ [1 2 3])⇒ (2 3 4)(mapcar #'string "abc")⇒ ("a" "b" "c");; Call each function in my-hooks.
(mapcar 'funcall my-hooks)(defun mapcar* (function &rest args)"Apply FUNCTION to successive cars of all ARGS.
Return the list of results.";; If no list is exhausted,(if (not (memq nil args));; apply function to cars.
(cons (apply function (mapcar #'car args))(apply #'mapcar* function;; Recurse for rest of elements.
(mapcar #'cdr args)))))(mapcar* #'cons '(a b c) '(1 2 3 4))⇒ ((a . 1) (b . 2) (c . 3))

mapcan function sequence[Function]
This function applies function to each element of sequence, like mapcar, but insteadof collecting the results into a list, it returns a single list with all the elements of theresults (which must be lists), by altering the results (using nconc; see Section 5.6.3[Rearrangement], page 90). Like with mapcar, sequence can be of any type except achar-table.

Chapter 13: Functions

243;; Contrast this:(mapcar #'list '(a b c d))⇒ ((a) (b) (c) (d));; with this:(mapcan #'list '(a b c d))⇒ (a b c d)mapc function sequence[Function]
mapc is like mapcar except that function is used for side-effects only—the values it
returns are ignored, not collected into a list. mapc always returns sequence.

mapconcat function sequence &optional separator[Function]
mapconcat applies function to each element of sequence; the results, which must
be sequences of characters (strings, vectors, or lists), are concatenated into a single
string return value. Between each pair of result sequences, mapconcat inserts thecharacters from separator, which also must be a string, or a vector or list of characters;
a nil value is treated as the empty string. See Chapter 6 [Sequences Arrays Vectors],
page 102.

The argument function must be a function that can take one argument and returns asequence of characters: a string, a vector, or a list. The argument sequence can be any
kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat #'symbol-name'(The cat in the hat)
" ")⇒ "The cat in the hat"
(mapconcat (lambda (x) (format "%c" (1+ x)))
"HAL-8000")⇒ "IBM.9111"

13.7 Anonymous Functions
Although functions are usually defined with defun and given names at the same time, it
is sometimes convenient to use an explicit lambda expression—an anonymous function.
Anonymous functions are valid wherever function names are. They are often assigned as
variable values, or as arguments to functions; for instance, you might pass one as the function
argument to mapcar, which applies that function to each element of a list (see Section 13.6
[Mapping Functions], page 241). See [describe-symbols example], page 597, for a realistic
example of this.
When defining a lambda expression that is to be used as an anonymous function, you canin principle use any method to construct the list. But typically you should use the lambda
macro, or the function special form, or the #' read syntax:

lambda args [doc] [interactive] body. . .

[Macro]This macro returns an anonymous function with argument list args, documentation
string doc (if any), interactive spec interactive (if any), and body forms given by body.

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Under dynamic binding, this macro effectively makes lambda forms self-quoting:evaluating a form whose car is lambda yields the form itself:(lambda (x) (* x x))⇒ (lambda (x) (* x x))
Note that when evaluating under lexical binding the result is a closure object (seeSection 13.10 [Closures], page 249).
The lambda form has one other effect: it tells the Emacs evaluator and byte-compiler
that its argument is a function, by using function as a subroutine (see below).

function function-object[Special Form]
This special form returns function-object without evaluating it. In this, it is similar
to quote (see Section 10.2 [Quoting], page 151). But unlike quote, it also serves as anote to the Emacs evaluator and byte-compiler that function-object is intended to be
used as a function. Assuming function-object is a valid lambda expression, this has
two effects:• When the code is byte-compiled, function-object is compiled into a byte-code
function object (see Chapter 17 [Byte Compilation], page 316).
• When lexical binding is enabled, function-object is converted into a closure. See
Section 13.10 [Closures], page 249.

When function-object is a symbol and the code is byte compiled, the byte-compiler
will warn if that function is not defined or might not be known at run time.
The read syntax #' is a short-hand for using function. The following forms are all
equivalent:(lambda (x) (* x x))(function (lambda (x) (* x x)))#'(lambda (x) (* x x))
In the following example, we define a change-property function that takes a function as its third argument, followed by a double-property function that makes use ofchange-property by passing it an anonymous function:(defun change-property (symbol prop function)(let ((value (get symbol prop)))(put symbol prop (funcall function value))))(defun double-property (symbol prop)(change-property symbol prop (lambda (x) (* 2 x))))
Note that we do not quote the lambda form.
If you compile the above code, the anonymous function is also compiled. This would not
happen if, say, you had constructed the anonymous function by quoting it as a list:(defun double-property (symbol prop)(change-property symbol prop '(lambda (x) (* 2 x))))In that case, the anonymous function is kept as a lambda expression in the compiled code.
The byte-compiler cannot assume this list is a function, even though it looks like one, since
it does not know that change-property intends to use it as a function.

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13.8 Generic Functions
Functions defined using defun have a hard-coded set of assumptions about the types andexpected values of their arguments. For example, a function that was designed to handle
values of its argument that are either numbers or lists of numbers will fail or signal an error
if called with a value of any other type, such as a vector or a string. This happens because
the implementation of the function is not prepared to deal with types other than thoseassumed during the design.
By contrast, object-oriented programs use polymorphic functions: a set of specialized
functions having the same name, each one of which was written for a certain specific set ofargument types. Which of the functions is actually called is decided at run time based on
the types of the actual arguments.
Emacs provides support for polymorphism. Like other Lisp environments, notably
Common Lisp and its Common Lisp Object System (CLOS), this support is based on genericfunctions. The Emacs generic functions closely follow CLOS, including use of similar names,
so if you have experience with CLOS, the rest of this section will sound very familiar.
A generic function specifies an abstract operation, by defining its name and list ofarguments, but (usually) no implementation. The actual implementation for several specificclasses of arguments is provided by methods, which should be defined separately. Eachmethod that implements a generic function has the same name as the generic function, but
the method’s definition indicates what kinds of arguments it can handle by specializing thearguments defined by the generic function. These argument specializers can be more orless specific; for example, a string type is more specific than a more general type, such as
sequence.
Note that, unlike in message-based OO languages, such as C++ and Simula, methods
that implement generic functions don’t belong to a class, they belong to the generic function
they implement.
When a generic function is invoked, it selects the applicable methods by comparing theactual arguments passed by the caller with the argument specializers of each method. A
method is applicable if the actual arguments of the call are compatible with the method’s
specializers. If more than one method is applicable, they are combined using certain rules,
described below, and the combination then handles the call.

cl-defgeneric name arguments [documentation][options-and-methods. . . ] &rest body

[Macro]This macro defines a generic function with the specified name and arguments. If bodyis present, it provides the default implementation. If documentation is present (itshould always be), it specifies the documentation string for the generic function, in
the form (:documentation docstring). The optional options-and-methods can beone of the following forms:(declare declarations)
A declare form, as described in Section 13.15 [Declare Form], page 263.
(:argument-precedence-order &rest args)
This form affects the sorting order for combining applicable methods.
Normally, when two methods are compared during combination, method
arguments are examined left to right, and the first method whose argument

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specializer is more specific will come before the other one. The orderdefined by this form overrides that, and the arguments are examinedaccording to their order in this form, and not left to right.
(:method [qualifiers...] args &rest body)This form defines a method like cl-defmethod does.

cl-defmethod name [extra] [qualifier] arguments [&context (expr
spec) . . . ] &rest [docstring] body

[Macro]This macro defines a particular implementation for the generic function called name.
The implementation code is given by body. If present, docstring is the documentation
string for the method. The arguments list, which must be identical in all the methods
that implement a generic function, and must match the argument list of that function,
provides argument specializers of the form (arg spec), where arg is the argumentname as specified in the cl-defgeneric call, and spec is one of the following specializer
forms:
type

This specializer requires the argument to be of the given type, one of thetypes from the type hierarchy described below.

(eql object)This specializer requires the argument be eql to the given object.
(head object)
The argument must be a cons cell whose car is eql to object.
struct-type
The argument must be an instance of a class named struct-type definedwith cl-defstruct (see Section “Structures” in Common Lisp Extensionsfor GNU Emacs Lisp), or of one of its child classes.
Method definitions can make use of a new argument-list keyword, &context, which
introduces extra specializers that test the environment at the time the method isrun. This keyword should appear after the list of required arguments, but before
any &rest or &optional keywords. The &context specializers look much like regularargument specializers—(expr spec)—except that expr is an expression to be evaluatedin the current context, and the spec is a value to compare against. For example,&context (overwrite-mode (eql t)) will make the method applicable only whenoverwrite-mode is turned on. The &context keyword can be followed by any numberof context specializers. Because the context specializers are not part of the genericfunction’s argument signature, they may be omitted in methods that don’t requirethem.
The type specializer, (arg type), can specify one of the system types in the following
list. When a parent type is specified, an argument whose type is any of its more
specific child types, as well as grand-children, grand-grand-children, etc. will also becompatible.
integer

Parent type: number.

numbernull

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symbolstringParent type: array.

array

Parent type: sequence.

cons

Parent type: list.

list

Parent type: sequence.

markeroverlay
float

Parent type: number.

window-configuration
process
window
subr
compiled-function
bufferchar-table
Parent type: array.
bool-vector
Parent type: array.
vectorParent type: array.

frame
hash-tablefont-spec
font-entity
font-object
The optional extra element, expressed as ‘:extra string’, allows you to add moremethods, distinguished by string, for the same specializers and qualifiers.
The optional qualifier allows combining several applicable methods. If it is not present,
the defined method is a primary method, responsible for providing the primary
implementation of the generic function for the specialized arguments. You can also
define auxiliary methods, by using one of the following values as qualifier::beforeThis auxiliary method will run before the primary method. More accurately, all the :before methods will run before the primary, in the
most-specific-first order.

:afterThis auxiliary method will run after the primary method. More accurately,
all such methods will run after the primary, in the most-specific-last order.

:aroundThis auxiliary method will run instead of the primary method. The most
specific of such methods will be run before any other method. Suchmethods normally use cl-call-next-method, described below, to invoke
the other auxiliary or primary methods.

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Functions defined using cl-defmethod cannot be made interactive, i.e. commands (seeSection 22.2 [Defining Commands], page 424), by adding the interactive form tothem. If you need a polymorphic command, we recommend defining a normal commandthat calls a polymorphic function defined via cl-defgeneric and cl-defmethod.
Each time a generic function is called, it builds the effective method which will handle
this invocation by combining the applicable methods defined for the function. The processof finding the applicable methods and producing the effective method is called dispatch.
The applicable methods are those all of whose specializers are compatible with the actualarguments of the call. Since all of the arguments must be compatible with the specializers,
they all determine whether a method is applicable. Methods that explicitly specialize morethan one argument are called multiple-dispatch methods.
The applicable methods are sorted into the order in which they will be combined. The
method whose left-most argument specializer is the most specific one will come first in theorder. (Specifying :argument-precedence-order as part of cl-defmethod overrides that,as described above.) If the method body calls cl-call-next-method, the next most-specificmethod will run. If there are applicable :around methods, the most-specific of them will run
first; it should call cl-call-next-method to run any of the less specific :around methods.
Next, the :before methods run in the order of their specificity, followed by the primarymethod, and lastly the :after methods in the reverse order of their specificity.

cl-call-next-method &rest args

[Function]
When invoked from within the lexical body of a primary or an :around auxiliary
method, call the next applicable method for the same generic function. Normally, it
is called with no arguments, which means to call the next applicable method withthe same arguments that the calling method was invoked. Otherwise, the specified
arguments are used instead.
[Function]
This function, when called from within the lexical body of a primary or an :aroundauxiliary method, returns non-nil if there is a next method to call.

cl-next-method-p13.9 Accessing Function Cell Contents
The function definition of a symbol is the object stored in the function cell of the symbol.
The functions described here access, test, and set the function cell of symbols.
See also the function indirect-function. See [Definition of indirect-function], page 148.

symbol-function symbol[Function]
This returns the object in the function cell of symbol. It does not check that thereturned object is a legitimate function.
If the function cell is void, the return value is nil. To distinguish between a function
cell that is void and one set to nil, use fboundp (see below).
(defun bar (n) (+ n 2))(symbol-function 'bar)⇒ (lambda (n) (+ n 2))(fset 'baz 'bar)⇒ bar

Chapter 13: Functions

249(symbol-function 'baz)⇒ bar
If you have never given a symbol any function definition, we say that that symbol’sfunction cell is void. In other words, the function cell does not have any Lisp object in it. If
you try to call the symbol as a function, Emacs signals a void-function error.
Note that void is not the same as nil or the symbol void. The symbols nil and void
are Lisp objects, and can be stored into a function cell just as any other object can be (andvoid can be a valid function if you define it with defun). A void function cell contains noobject whatsoever.
You can test the voidness of a symbol’s function definition with fboundp. After you havegiven a symbol a function definition, you can make it void once more using fmakunbound.

fboundp symbol[Function]
This function returns t if the symbol has an object in its function cell, nil otherwise.
It does not check that the object is a legitimate function.

fmakunbound symbol[Function]
This function makes symbol’s function cell void, so that a subsequent attempt to accessthis cell will cause a void-function error. It returns symbol. (See also makunbound,in Section 12.4 [Void Variables], page 193.)(defun foo (x) x)(foo 1)⇒1(fmakunbound 'foo)⇒ foo(foo 1)error Symbol's function definition is void: foofset symbol definition[Function]
This function stores definition in the function cell of symbol. The result is definition.
Normally definition should be a function or the name of a function, but this is notchecked. The argument symbol is an ordinary evaluated argument.
The primary use of this function is as a subroutine by constructs that define or alterfunctions, like defun or advice-add (see Section 13.12 [Advising Functions], page 252).
You can also use it to give a symbol a function definition that is not a function, e.g., akeyboard macro (see Section 22.16 [Keyboard Macros], page 478):;; Define a named keyboard macro.
(fset 'kill-two-lines "\^u2\^k")⇒ "\^u2\^k"If you wish to use fset to make an alternate name for a function, consider using
defalias instead. See [Definition of defalias], page 238.

13.10 Closures
As explained in Section 12.10 [Variable Scoping], page 201, Emacs can optionally enable
lexical binding of variables. When lexical binding is enabled, any named function that youChapter 13: Functions

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create (e.g., with defun), as well as any anonymous function that you create using thelambda macro or the function special form or the #' syntax (see Section 13.7 [Anonymous
Functions], page 243), is automatically converted into a closure.
A closure is a function that also carries a record of the lexical environment that existed
when the function was defined. When it is invoked, any lexical variable references within
its definition use the retained lexical environment. In all other respects, closures behavemuch like ordinary functions; in particular, they can be called in the same way as ordinary
functions.
See Section 12.10.3 [Lexical Binding], page 203, for an example of using a closure.
Currently, an Emacs Lisp closure object is represented by a list with the symbol closure
as the first element, a list representing the lexical environment as the second element, andthe argument list and body forms as the remaining elements:;; lexical binding is enabled.
(lambda (x) (* x x))⇒ (closure (t) (x) (* x x))
However, the fact that the internal structure of a closure is exposed to the rest of the Lisp
world is considered an internal implementation detail. For this reason, we recommend against
directly examining or altering the structure of closure objects.

13.11 Open Closures
Traditionally, functions are opaque objects which offer no other functionality but to callthem. (Emacs Lisp functions aren’t fully opaque since you can extract some info out ofthem such as their docstring, their arglist, or their interactive spec, but they are still mostly
opaque.) This is usually what we want, but occasionally we need functions to expose a bit
more information about themselves.
Open closures, or OClosures for short, are function objects which carry additional type
information and expose some information about themselves in the form of slots which you
can access via accessor functions.
OClosures are defined in two steps: first you use oclosure-define to define a new
OClosure type by specifying the slots carried by the OClosures of this type, and then you
use oclosure-lambda to create an OClosure object of a given type.
Let’s say we want to define keyboard macros, i.e. interactive functions which re-executea sequence of key events (see Section 22.16 [Keyboard Macros], page 478). You could do itwith a plain function as follows:(defun kbd-macro (key-sequence)(lambda (&optional arg)
(interactive "P")(execute-kbd-macro key-sequence arg)))
But with such a definition there is no easy way to extract the key-sequence from thatfunction, for example to print it.
We can solve this problem using OClosures as follows. First we define the type of our
keyboard macros (to which we decided to add a counter slot while at it):(oclosure-define kbd-macroChapter 13: Functions

251"Keyboard macro."keys (counter :mutable t))
After which we can rewrite our kbd-macro function:(defun kbd-macro (key-sequence)(oclosure-lambda (kbd-macro (keys key-sequence) (counter 0))(&optional arg)
(interactive "P")(execute-kbd-macro keys arg)
(setq counter (1+ counter))))As you can see, the keys and counter slots of the OClosure can be accessed as local variablesfrom within the body of the OClosure. But we can now also access them from outside of the
body of the OClosure, for example to describe a keyboard macro:(defun describe-kbd-macro (km)(if (not (eq 'kbd-macro (oclosure-type km)))(message "Not a keyboard macro")(let ((keys(kbd-macro--keys km))(counter (kbd-macro--counter km)))(message "Keys=%S, called %d times" keys counter))))
Where kbd-macro--keys and kbd-macro--counter are accessor functions generated by theoclosure-define macro for oclosures whose type is kbd-macro.

oclosure-define oname &optional docstring &rest slots[Macro]This macro defines a new OClosure type along with accessor functions for its
slots. oname can be a symbol (the name of the new type), or a list of the form
(oname . type-props), in which case type-props is a list of additional properties ofthis oclosure type. slots is a list of slot descriptions where each slot can be either asymbol (the name of the slot) or it can be of the form (slot-name . slot-props),
where slot-props is a property list of the corresponding slot slot-name. The OClosure
type’s properties specified by type-props can include the following:(:predicate pred-name)
This requests creation of a predicate function named pred-name. Thisfunction will be used to recognize OClosures of the type oname. If thistype property is not specified, oclosure-define will generate a default
name for the predicate.
(:parent otype)This makes type otype of OClosures be the parent of the type oname.
The OClosures of type oname inherit the slots defined by their parent
type.
(:copier copier-name copier-args)
This causes the definition of a functional update function, knows as the
copier, which takes an OClosure of type oname as its first argument
and returns a copy of it with the slots named in copier-args modified tocontain the value passed in the corresponding argument in the actual callto copier-name.

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For each slot in slots, the oclosure-define macro creates an accessor function named
oname--slot-name; these can be used to access the values of the slots. The slot
definitions in slots can specify the following properties of the slots::mutable val
By default, slots are immutable, but if you specify the :mutable property
with a non-nil value, the slot can be mutated, for example with setf
(see Section 12.17.1 [Setting Generalized Variables], page 224).
:type val-type
This specifies the type of the values expected to appear in the slot.

oclosure-lambda (type . slots) arglist &rest body

[Macro]This macro creates an anonymous OClosure of type type, which should have been
defined with oclosure-define. slots should be a list of elements of the form
(slot-name expr). At run time, each expr is evaluated, in order, after which the
OClosure is created with its slots initialized with the resulting values.

When called as a function (see Section 13.5 [Calling Functions], page 239), the OClosure
created by this macro will accept arguments according to arglist and will execute thecode in body. body can refer to the value of any of its slot directly as if it were a local
variable that had been captured by static scoping.

oclosure-type object[Function]
This function returns the OClosure type (a symbol) of object if it is an OClosure, andnil otherwise.

One other function related to OClosures is oclosure-interactive-form, which allows
some types of OClosures to compute their interactive forms dynamically. See Section 22.2.1[Using Interactive], page 424.

13.12 Advising Emacs Lisp Functions
When you need to modify a function defined in another library, or when you need to modify
a hook like foo-function, a process filter, or basically any variable or object field whichholds a function value, you can use the appropriate setter function, such as fset or defun
for named functions, setq for hook variables, or set-process-filter for process filters,
but those are often too blunt, completely throwing away the previous value.
The advice feature lets you add to the existing definition of a function, by advising thefunction. This is a cleaner method than redefining the whole function.
Emacs’s advice system provides two sets of primitives for that: the core set, for function values held in variables and object fields (with the corresponding primitives being
add-function and remove-function) and another set layered on top of it for named
functions (with the main primitives being advice-add and advice-remove).
As a trivial example, here’s how to add advice that’ll modify the return value of a function
every time it’s called:(defun my-double (x)(* x 2))(defun my-increase (x)Chapter 13: Functions

253(+ x 1))(advice-add 'my-double :filter-return #'my-increase)
After adding this advice, if you call my-double with ‘3’, the return value will be ‘7’. To
remove this advice, say(advice-remove 'my-double #'my-increase)
A more advanced example would be to trace the calls to the process filter of a processproc:(defun my-tracing-function (proc string)(message "Proc %S received %S" proc string))(add-function :before (process-filter proc) #'my-tracing-function)
This will cause the process’s output to be passed to my-tracing-function before being
passed to the original process filter. my-tracing-function receives the same arguments as
the original function. When you’re done with it, you can revert to the untraced behavior
with:(remove-function (process-filter proc) #'my-tracing-function)
Similarly, if you want to trace the execution of the function named display-buffer, you
could use:
(defun his-tracing-function (orig-fun &rest args)(message "display-buffer called with args %S" args)(let ((res (apply orig-fun args)))(message "display-buffer returned %S" res)res))
(advice-add 'display-buffer :around #'his-tracing-function)
Here, his-tracing-function is called instead of the original function and receives theoriginal function (additionally to that function’s arguments) as argument, so it can call it
if and when it needs to. When you’re tired of seeing this output, you can revert to theuntraced behavior with:(advice-remove 'display-buffer #'his-tracing-function)
The arguments :before and :around used in the above examples specify how the twofunctions are composed, since there are many different ways to do it. The added function is
also called a piece of advice.

13.12.1 Primitives to manipulate advices
add-function where place function &optional props[Macro]This macro is the handy way to add the advice function to the function stored inplace (see Section 12.17 [Generalized Variables], page 224).
where determines how function is composed with the existing function, e.g., whether
function should be called before, or after the original function. See Section 13.12.3[Advice Combinators], page 257, for the list of available ways to compose the twofunctions.
When modifying a variable (whose name will usually end with -function), you canchoose whether function is used globally or only in the current buffer: if place is just

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a symbol, then function is added to the global value of place. Whereas if place is of
the form (local symbol), where symbol is an expression which returns the variable
name, then function will only be added in the current buffer. Finally, if you want tomodify a lexical variable, you will have to use (var variable).
Every function added with add-function can be accompanied by an association listof properties props. Currently only two of those properties have a special meaning:
nameThis gives a name to the advice, which remove-function can use to
identify which function to remove. Typically used when function is ananonymous function.

depthThis specifies how to order the advice, should several pieces of advice be
present. By default, the depth is 0. A depth of 100 indicates that thispiece of advice should be kept as deep as possible, whereas a depth of−100 indicates that it should stay as the outermost piece. When twopieces of advice specify the same depth, the most recently added one will
be outermost.
For :before advice, being outermost means that this advice will be run
first, before any other advice, whereas being innermost means that it will
run right before the original function, with no other advice run between
itself and the original function. Similarly, for :after advice innermost
means that it will run right after the original function, with no otheradvice run in between, whereas outermost means that it will be run rightat the end after all other advice. An innermost :override piece of advice
will only override the original function and other pieces of advice will
apply to it, whereas an outermost :override piece of advice will override
not only the original function but all other advice applied to it as well.

If function is not interactive, then the combined function will inherit the interactive
spec, if any, of the original function. Else, the combined function will be interactive
and will use the interactive spec of function. One exception: if the interactive spec offunction is a function (i.e., a lambda expression or an fbound symbol rather than an
expression or a string), then the interactive spec of the combined function will be acall to that function with the interactive spec of the original function as sole argument.
To interpret the spec received as argument, use advice-eval-interactive-spec.
Note: The interactive spec of function will apply to the combined function and should
hence obey the calling convention of the combined function rather than that of function.
In many cases, it makes no difference since they are identical, but it does matter
for :around, :filter-args, and :filter-return, where function receives different
arguments than the original function stored in place.

remove-function place function[Macro]This macro removes function from the function stored in place. This only works iffunction was added to place using add-function.
function is compared with functions added to place using equal, to try and make itwork also with lambda expressions. It is additionally compared also with the nameproperty of the functions added to place, which can be more reliable than comparing
lambda expressions using equal.

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advice-function-member-p advice function-def[Function]
Return non-nil if advice is already in function-def. Like for remove-function above,instead of advice being the actual function, it can also be the name of the piece ofadvice.

advice-function-mapc f function-def[Function]
Call the function f for every piece of advice that was added to function-def. f is calledwith two arguments: the advice function and its properties.

advice-eval-interactive-spec spec

[Function]
Evaluate the interactive spec just like an interactive call to a function with sucha spec would, and then return the corresponding list of arguments that was built.
E.g., (advice-eval-interactive-spec "r\nP") will return a list of three elements,
containing the boundaries of the region and the current prefix argument.

For instance, if you want to make the C-x m (compose-mail) command prompt for a‘From:’ header, you could say something like this:(defun my-compose-mail-advice (orig &rest args)"Read From: address interactively."(interactive(lambda (spec)(let* ((user-mail-address(completing-read "From: "'("one.address@example.net""alternative.address@example.net")))(from (message-make-from user-full-nameuser-mail-address))(spec (advice-eval-interactive-spec spec)));; Put the From header into the OTHER-HEADERS argument.
(push (cons 'From from) (nth 2 spec))spec)))(apply orig args))(advice-add 'compose-mail :around #'my-compose-mail-advice)13.12.2 Advising Named Functions
A common use of advice is for named functions and macros. You could just use add-function
as in:(add-function :around (symbol-function 'fun) #'his-tracing-function)
But you should use advice-add and advice-remove for that instead. This separate set offunctions to manipulate pieces of advice applied to named functions, offers the following extra
features compared to add-function: they know how to deal with macros and autoloadedfunctions, they let describe-function preserve the original docstring as well as document
the added advice, and they let you add and remove advice before a function is even defined.
advice-add can be useful for altering the behavior of existing calls to an existing function
without having to redefine the whole function. However, it can be a source of bugs, since
existing callers to the function may assume the old behavior, and work incorrectly when theChapter 13: Functions

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behavior is changed by advice. Advice can also cause confusion in debugging, if the person
doing the debugging does not notice or remember that the function has been modified byadvice.
For these reasons, advice should be reserved for the cases where you cannot modify afunction’s behavior in any other way. If it is possible to do the same thing via a hook, thatis preferable (see Section 24.1 [Hooks], page 524). If you simply want to change what a
particular key does, it may be better to write a new command, and remap the old command’s
key bindings to the new one (see Section 23.14 [Remapping Commands], page 503).
If you are writing code for release, for others to use, try to avoid including advice in it.
If the function you want to advise has no hook to do the job, please talk with the Emacs
developers about adding a suitable hook. Especially, Emacs’s own source files should not
put advice on functions in Emacs. (There are currently a few exceptions to this convention,
but we aim to correct them.) It is generally cleaner to create a new hook in foo, and makebar use the hook, than to have bar put advice in foo.
Special forms (see Section 10.1.7 [Special Forms], page 149) cannot be advised, however
macros can be advised, in much the same way as functions. Of course, this will not affectcode that has already been macro-expanded, so you need to make sure the advice is installed
before the macro is expanded.
It is possible to advise a primitive (see Section 13.1 [What Is a Function], page 230), but
one should typically not do so, for two reasons. Firstly, some primitives are used by theadvice mechanism, and advising them could cause an infinite recursion. Secondly, many
primitives are called directly from C, and such calls ignore advice; hence, one ends up in a
confusing situation where some calls (occurring from Lisp code) obey the advice and othercalls (from C code) do not.

define-advice symbol (where lambda-list &optional name depth)&rest body

[Macro]This macro defines a piece of advice and adds it to the function named symbol. The
advice is an anonymous function if name is nil or a function named symbol@name.
See advice-add for explanation of other arguments.

advice-add symbol where function &optional props[Function]
Add the advice function to the named function symbol. where and props have thesame meaning as for add-function (see Section 13.12.1 [Core Advising Primitives],
page 253).

advice-remove symbol function[Function]
Remove the advice function from the named function symbol. function can also be
the name of a piece of advice.

advice-member-p function symbol[Function]
Return non-nil if the advice function is already in the named function symbol.
function can also be the name of a piece of advice.

advice-mapc function symbol[Function]
Call function for every piece of advice that was added to the named function symbol.
function is called with two arguments: the advice function and its properties.

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13.12.3 Ways to compose advice
Here are the different possible values for the where argument of add-function andadvice-add, specifying how the advice function and the original function should becomposed.
:beforeCall function before the old function. Both functions receive the same arguments,
and the return value of the composition is the return value of the old function.
More specifically, the composition of the two functions behaves like:(lambda (&rest r) (apply function r) (apply oldfun r))(add-function :before funvar function) is comparable for single-function
hooks to (add-hook 'hookvar function) for normal hooks.

:afterCall function after the old function. Both functions receive the same arguments,
and the return value of the composition is the return value of the old function.
More specifically, the composition of the two functions behaves like:(lambda (&rest r) (prog1 (apply oldfun r) (apply function r)))(add-function :after funvar function) is comparable for single-function
hooks to (add-hook 'hookvar function 'append) for normal hooks.

:overrideThis completely replaces the old function with the new one. The old function
can of course be recovered if you later call remove-function.
:aroundCall function instead of the old function, but provide the old function as an
extra argument to function. This is the most flexible composition. For example,
it lets you call the old function with different arguments, or many times, orwithin a let-binding, or you can sometimes delegate the work to the old function
and sometimes override it completely. More specifically, the composition of thetwo functions behaves like:(lambda (&rest r) (apply function oldfun r)):before-while
Call function before the old function and don’t call the old function if function
returns nil. Both functions receive the same arguments, and the return valueof the composition is the return value of the old function. More specifically, thecomposition of the two functions behaves like:(lambda (&rest r) (and (apply function r) (apply oldfun r)))(add-function :before-while funvar function)iscomparableforsingle-function hooks to (add-hook 'hookvar function) when hookvar is run
via run-hook-with-args-until-failure.
:before-until
Call function before the old function and only call the old function if function
returns nil. More specifically, the composition of the two functions behaves
like:(lambda (&rest r) (or (apply function r) (apply oldfun r)))(add-function :before-until funvar function)iscomparableforsingle-function hooks to (add-hook 'hookvar function) when hookvar is run
via run-hook-with-args-until-success.

Chapter 13: Functions

258:after-while
Call function after the old function and only if the old function returned nonnil. Both functions receive the same arguments, and the return value of thecomposition is the return value of function. More specifically, the compositionof the two functions behaves like:(lambda (&rest r) (and (apply oldfun r) (apply function r)))iscomparablefor(add-function :after-while funvar function)
single-function hooks to (add-hook 'hookvar function 'append) whenhookvar is run via run-hook-with-args-until-failure.
:after-until
Call function after the old function and only if the old function returned nil.
More specifically, the composition of the two functions behaves like:(lambda (&rest r) (or (apply oldfun r) (apply function r)))(add-function :after-until funvar function)iscomparableforsingle-function hooks to (add-hook 'hookvar function 'append) whenhookvar is run via run-hook-with-args-until-success.
:filter-args
Call function first and use the result (which should be a list) as the newarguments to pass to the old function. More specifically, the composition of thetwo functions behaves like:(lambda (&rest r) (apply oldfun (funcall function r))):filter-return
Call the old function first and pass the result to function. More specifically, thecomposition of the two functions behaves like:(lambda (&rest r) (funcall function (apply oldfun r)))13.12.4 Adapting code using the old defadvice
A lot of code uses the old defadvice mechanism, which is largely made obsolete by the newadvice-add, whose implementation and semantics is significantly simpler.
An old piece of advice such as:(defadvice previous-line (before next-line-at-end(&optional arg try-vscroll))"Insert an empty line when moving up from the top line."(if (and next-line-add-newlines (= arg 1)(save-excursion (beginning-of-line) (bobp)))(progn(beginning-of-line)(newline))))could be translated in the new advice mechanism into a plain function:(defun previous-line--next-line-at-end (&optional arg try-vscroll)"Insert an empty line when moving up from the top line."(if (and next-line-add-newlines (= arg 1)(save-excursion (beginning-of-line) (bobp)))

Chapter 13: Functions

259(progn(beginning-of-line)(newline))))Obviously, this does not actually modify previous-line. For that the old advice needed:(ad-activate 'previous-line)
whereas the new advice mechanism needs:(advice-add 'previous-line :before #'previous-line--next-line-at-end)
Note that ad-activate had a global effect: it activated all pieces of advice enabled forthat specified function. If you wanted to only activate or deactivate a particular piece, youneeded to enable or disable it with ad-enable-advice and ad-disable-advice. The newmechanism does away with this distinction.
Around advice such as:(defadvice foo (around foo-around)"Ignore case in `foo'."(let ((case-fold-search t))
ad-do-it))(ad-activate 'foo)
could translate into:(defun foo--foo-around (orig-fun &rest args)"Ignore case in `foo'."(let ((case-fold-search t))(apply orig-fun args)))(advice-add 'foo :around #'foo--foo-around)
Regarding the advice’s class, note that the new :before is not quite equivalent to theold before, because in the old advice you could modify the function’s arguments (e.g.,with ad-set-arg), and that would affect the argument values seen by the original function,
whereas in the new :before, modifying an argument via setq in the advice has no effect on
the arguments seen by the original function. When porting before advice which relied on
this behavior, you’ll need to turn it into new :around or :filter-args advice instead.
Similarly old after advice could modify the returned value by changing ad-returnvalue, whereas new :after advice cannot, so when porting such old after advice, you’ll
need to turn it into new :around or :filter-return advice instead.

13.12.5 Advice and Byte CodeNot all functions can be reliably advised. The byte compiler may choose to replace a call toa function with a sequence of instructions that doesn’t call the function you were interested
in altering.
This usually happens due to one of the three following mechanisms:
byte-compile properties
If a function’s symbol has a byte-compile property, that property will be
used instead of the symbol’s function definition. See Section 17.2 [Compilation
Functions], page 316.

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byte-optimize properties
If a function’s symbol has a byte-optimize property, the byte compiler may
rewrite the function arguments, or decide to use a different function altogether.
compiler-macro declare forms
A function can have a special compiler-macro declare form in its definition(see Section 13.15 [Declare Form], page 263) that defines an expander to callwhen compiling the function. The expander could then cause the produced
byte-code not to call the original function.

13.13 Declaring Functions Obsolete
You can mark a named function as obsolete, meaning that it may be removed at somepoint in the future. This causes Emacs to warn that the function is obsolete whenever it
byte-compiles code containing that function, and whenever it displays the documentation
for that function. In all other respects, an obsolete function behaves like any other function.
The easiest way to mark a function as obsolete is to put a (declare (obsolete ...))
form in the function’s defun definition. See Section 13.15 [Declare Form], page 263. Alternatively, you can use the make-obsolete function, described below.
A macro (see Chapter 14 [Macros], page 268) can also be marked obsolete withmake-obsolete; this has the same effects as for a function. An alias for a function or macro
can also be marked as obsolete; this makes the alias itself obsolete, not the function or
macro which it resolves to.

make-obsolete obsolete-name current-name when

[Function]
This function marks obsolete-name as obsolete. obsolete-name should be a symbol
naming a function or macro, or an alias for a function or macro.
If current-name is a symbol, the warning message says to use current-name instead ofobsolete-name. current-name does not need to be an alias for obsolete-name; it canbe a different function with similar functionality. current-name can also be a string,which serves as the warning message. The message should begin in lower case, andend with a period. It can also be nil, in which case the warning message provides noadditional details.
The argument when should be a string indicating when the function was first madeobsolete—for example, a date or a release number.

define-obsolete-function-alias obsolete-name current-name when
&optional doc[Macro]This convenience macro marks the function obsolete-name obsolete and also defines it
as an alias for the function current-name. It is equivalent to the following:(defalias obsolete-name current-name doc)
(make-obsolete obsolete-name current-name when)
In addition, you can mark a particular calling convention for a function as obsolete:set-advertised-calling-convention function signature when

[Function]
This function specifies the argument list signature as the correct way to call function.
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Emacs Lisp program that calls function any other way (however, it will still allow thecode to be byte compiled). when should be a string indicating when the variable was
first made obsolete (usually a version number string).
For instance, in old versions of Emacs the sit-for function accepted three arguments,
like this(sit-for seconds milliseconds nodisp)
However, calling sit-for this way is considered obsolete (see Section 22.10 [Waiting],
page 470). The old calling convention is deprecated like this:(set-advertised-calling-convention'sit-for '(seconds &optional nodisp) "22.1")
The alternative to using this function is the advertised-calling-convention
declare spec, see Section 13.15 [Declare Form], page 263.

13.14 Inline Functions
An inline function is a function that works just like an ordinary function, except for one
thing: when you byte-compile a call to the function (see Chapter 17 [Byte Compilation],
page 316), the function’s definition is expanded into the caller.
The simple way to define an inline function, is to write defsubst instead of defun. The
rest of the definition looks just the same, but using defsubst says to make it inline for byte
compilation.

defsubst name args [doc] [declare] [interactive] body. . .

[Macro]This macro defines an inline function. Its syntax is exactly the same as defun (seeSection 13.4 [Defining Functions], page 237).

Making a function inline often makes its function calls run faster. But it also has
disadvantages. For one thing, it reduces flexibility; if you change the definition of thefunction, calls already inlined still use the old definition until you recompile them.
Another disadvantage is that making a large function inline can increase the size ofcompiled code both in files and in memory. Since the speed advantage of inline functions isgreatest for small functions, you generally should not make large functions inline.
Also, inline functions do not behave well with respect to debugging, tracing, and advising(see Section 13.12 [Advising Functions], page 252). Since ease of debugging and the flexibilityof redefining functions are important features of Emacs, you should not make a function
inline, even if it’s small, unless its speed is really crucial, and you’ve timed the code to verify
that using defun actually has performance problems.
After an inline function is defined, its inline expansion can be performed later on in thesame file, just like macros.
It’s possible to use defmacro to define a macro to expand into the same code that an
inline function would execute (see Chapter 14 [Macros], page 268). But the macro would be
limited to direct use in expressions—a macro cannot be called with apply, mapcar and soon. Also, it takes some work to convert an ordinary function into a macro. To convert it
into an inline function is easy; just replace defun with defsubst. Since each argument of
an inline function is evaluated exactly once, you needn’t worry about how many times the
body uses the arguments, as you do for macros.

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Alternatively, you can define a function by providing the code which will inline it as acompiler macro (see Section 13.15 [Declare Form], page 263). The following macros makethis possible.

define-inline name args [doc] [declare] body. . .

[Macro]Define a function name by providing code that does its inlining, as a compiler macro.
The function will accept the argument list args and will have the specified body.
If present, doc should be the function’s documentation string (see Section 13.2.4[Function Documentation], page 235); declare, if present, should be a declare form
(see Section 13.15 [Declare Form], page 263) specifying the function’s metadata.

Functions defined via define-inline have several advantages with respect to macros
defined by defsubst or defmacro:− They can be passed to mapcar (see Section 13.6 [Mapping Functions], page 241).
− They are more efficient.
− They can be used as place forms to store values (see Section 12.17 [Generalized Variables],page 224).
− They behave in a more predictable way than cl-defsubst (see Section “Argument
Lists” in Common Lisp Extensions for GNU Emacs Lisp).
Like defmacro, a function inlined with define-inline inherits the scoping rules, either
dynamic or lexical, from the call site. See Section 12.10 [Variable Scoping], page 201.
The following macros should be used in the body of a function defined by define-inline.

inline-quote expression[Macro]Quote expression for define-inline. This is similar to the backquote (see Section 10.3
[Backquote], page 151), but quotes code and accepts only ,, not ,@.

inline-letevals (bindings. . . ) body. . .

[Macro]This provides a convenient way to ensure that the arguments to an inlined function
are evaluated exactly once, as well as to create local variables.
It’s similar to let (see Section 12.3 [Local Variables], page 190): It sets up local
variables as specified by bindings, and then evaluates body with those bindings ineffect.
Each element of bindings should be either a symbol or a list of the form (var expr);
the result is to evaluate expr and bind var to the result. However, when an elementof bindings is just a symbol var, the result of evaluating var is re-bound to var (whichis quite different from the way let works).
The tail of bindings can be either nil or a symbol which should hold a list of arguments,
in which case each argument is evaluated, and the symbol is bound to the resulting
list.

inline-const-p expression[Macro]Return non-nil if the value of expression is already known.

inline-const-val expression
Return the value of expression.

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inline-error format &rest args

263

[Macro]Signal an error, formatting args according to format.
Here’s an example of using define-inline:(define-inline myaccessor (obj)(inline-letevals (obj)(inline-quote (if (foo-p ,obj) (aref (cdr ,obj) 3) (aref ,obj 2)))))
This is equivalent to(defsubst myaccessor (obj)(if (foo-p obj) (aref (cdr obj) 3) (aref obj 2)))13.15 The declare Formdeclare is a special macro which can be used to add meta properties to a function or macro:for example, marking it as obsolete, or giving its forms a special TAB indentation convention
in Emacs Lisp mode.

declare specs. . .

[Macro]This macro ignores its arguments and evaluates to nil; it has no run-time effect.
However, when a declare form occurs in the declare argument of a defun or defsubst
function definition (see Section 13.4 [Defining Functions], page 237) or a defmacro
macro definition (see Section 14.4 [Defining Macros], page 270), it appends theproperties specified by specs to the function or macro. This work is specially performed
by defun, defsubst, and defmacro.
Each element in specs should have the form (property args...), which should not
be quoted. These have the following effects:(advertised-calling-convention signature when)This acts like a call to set-advertised-calling-convention (seeSection 13.13 [Obsolete Functions], page 260); signature specifies thecorrect argument list for calling the function or macro, and when should
be a string indicating when the old argument list was first made obsolete.
(debug edebug-form-spec)
This is valid for macros only. When stepping through the macro with
Edebug, use edebug-form-spec. See Section 19.2.15.1 [Instrumenting
Macro Calls], page 358.
(doc-string n)This is used when defining a function or macro which itself will be used
to define entities like functions, macros, or variables. It indicates that thenth argument, if any, should be considered as a documentation string.
(indent indent-spec)
Indent calls to this function or macro according to indent-spec. Thisis typically used for macros, though it works for functions too. See
Section 14.6 [Indenting Macros], page 275.
(interactive-only value)
Set the function’s interactive-only property to value.
interactive-only property], page 424.

See [TheChapter 13: Functions

264(obsolete current-name when)
Mark the function or macro as obsolete, similar to a call to make-obsolete(see Section 13.13 [Obsolete Functions], page 260). current-name should
be a symbol (in which case the warning message says to use that instead), a
string (specifying the warning message), or nil (in which case the warning
message gives no extra details). when should be a string indicating when
the function or macro was first made obsolete.
(compiler-macro expander)This can only be used for functions, and tells the compiler to use expander
as an optimization function. When encountering a call to the function,of the form (function args...), the macro expander will call expanderwith that form as well as with args . . . , and expander can either return a
new expression to use instead of the function call, or it can return just theform unchanged, to indicate that the function call should be left alone.
When expander is a lambda form it should be written with a single
argument (i.e., be of the form (lambda (arg) body)) because the function’s formal arguments are automatically added to the lambda’s list ofarguments for you.
(gv-expander expander)
Declare expander to be the function to handle calls to the macro (orfunction) as a generalized variable, similarly to gv-define-expander.
expander can be a symbol or it can be of the form (lambda (arg) body)in which case that function will additionally have access to the macro (orfunction)’s arguments.
(gv-setter setter)
Declare setter to be the function to handle calls to the macro (or function)
as a generalized variable. setter can be a symbol in which case it will bepassed to gv-define-simple-setter, or it can be of the form (lambda(arg) body) in which case that function will additionally have access tothe macro (or function)’s arguments and it will be passed to gv-definesetter.
(completion completion-predicate)
Declare completion-predicate as a function to determine whether to include
a function’s symbol in the list of functions when asking for completions in
M-x. This predicate function will only be called when read-extendedcommand-predicate is customized to command-completion-defaultinclude-p; by default the value of read-extended-command-predicate
is nil (see Section 22.3 [Interactive Call], page 432). The predicatecompletion-predicate is called with two arguments: the function’s symbol
and the current buffer.
(modes modes)
Specify that this command is meant to be applicable only to specified
modes. See Section 22.2.4 [Command Modes], page 430.

Chapter 13: Functions

265(interactive-args arg ...)
Specify the arguments that should be stored for repeat-command. Eacharg is on the form argument-name form.
(pure val)
If val is non-nil, this function is pure (see Section 13.1 [What Is a
Function], page 230). This is the same as the pure property of thefunction’s symbol (see Section 9.4.2 [Standard Properties], page 139).
(side-effect-free val)
If val is non-nil, this function is free of side effects, so the byte compiler can ignore calls whose value is ignored. This is the same as the
side-effect-free property of the function’s symbol, see Section 9.4.2[Standard Properties], page 139.
(speed n) Specify the value of native-comp-speed in effect for native compilation ofthis function (see Section 18.2 [Native-Compilation Variables], page 330).
This allows function-level control of the optimization level used for nativecode emitted for the function. In particular, if n is −1, native compilationof the function will emit bytecode instead of native code for the function.
no-font-lock-keyword
This is valid for macros only. Macros with this declaration are highlighted
by font-lock (see Section 24.6 [Font Lock Mode], page 563) as normal
functions, not specially as macros.

13.16 Telling the Compiler that a Function is Defined
Byte-compiling a file often produces warnings about functions that the compiler doesn’tknow about (see Section 17.6 [Compiler Errors], page 321). Sometimes this indicates a real
problem, but usually the functions in question are defined in other files which would be
loaded if that code is run. For example, byte-compiling simple.el used to warn:
simple.el:8727:1:Warning: the function ‘shell-mode’ is not known to be
defined.
In fact, shell-mode is used only in a function that executes (require 'shell) before
calling shell-mode, so shell-mode will be defined properly at run-time. When you knowthat such a warning does not indicate a real problem, it is good to suppress the warning.
That makes new warnings which might mean real problems more visible. You do that withdeclare-function.
All you need to do is add a declare-function statement before the first use of thefunction in question:(declare-function shell-mode "shell" ())
This says that shell-mode is defined in shell.el (the ‘.el’ can be omitted). The
compiler takes for granted that that file really defines the function, and does not check.
The optional third argument specifies the argument list of shell-mode. In this case, ittakes no arguments (nil is different from not specifying a value). In other cases, this might
be something like (file &optional overwrite). You don’t have to specify the argument
list, but if you do the byte compiler can check that the calls match the declaration.

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declare-function function file &optional arglist fileonly[Macro]Tell the byte compiler to assume that function is defined in the file file. The optional
third argument arglist is either t, meaning the argument list is unspecified, or a list offormal parameters in the same style as defun (including the parentheses). An omitted
arglist defaults to t, not nil; this is atypical behavior for omitted arguments, andit means that to supply a fourth but not third argument one must specify t for thethird-argument placeholder instead of the usual nil. The optional fourth argument
fileonly non-nil means check only that file exists, not that it actually defines function.

To verify that these functions really are declared where declare-function says they
are, use check-declare-file to check all declare-function calls in one source file, or use
check-declare-directory check all the files in and under a certain directory.
These commands find the file that ought to contain a function’s definition using
locate-library; if that finds no file, they expand the definition file name relative to thedirectory of the file that contains the declare-function call.
You can also say that a function is a primitive by specifying a file name ending in ‘.c’ or‘.m’. This is useful only when you call a primitive that is defined only on certain systems.
Most primitives are always defined, so they will never give you a warning.
Sometimes a file will optionally use functions from an external package. If you prefix
the filename in the declare-function statement with ‘ext:’, then it will be checked if it isfound, otherwise skipped without error.
There are some function definitions that ‘check-declare’ does not understand (e.g.,
defstruct and some other macros). In such cases, you can pass a non-nil fileonly argument
to declare-function, meaning to only check that the file exists, not that it actually defines
the function. Note that to do this without having to specify an argument list, you should
set the arglist argument to t (because nil means an empty argument list, as opposed to anunspecified one).

13.17 Determining whether a Function is Safe to Call
Some major modes, such as SES, call functions that are stored in user files. (See ses,
for more information on SES.) User files sometimes have poor pedigrees—you can get a
spreadsheet from someone you’ve just met, or you can get one through email from someone
you’ve never met. So it is risky to call a function whose source code is stored in a user fileuntil you have determined that it is safe.

unsafep form &optional unsafep-vars[Function]
Returns nil if form is a safe Lisp expression, or returns a list that describes why
it might be unsafe. The argument unsafep-vars is a list of symbols known to have
temporary bindings at this point; it is mainly used for internal recursive calls. The
current buffer is an implicit argument, which provides a list of buffer-local bindings.

Being quick and simple, unsafep does a very light analysis and rejects many Lisp
expressions that are actually safe. There are no known cases where unsafep returns nil foran unsafe expression. However, a safe Lisp expression can return a string with a display
property, containing an associated Lisp expression to be executed after the string is inserted
into a buffer. This associated expression can be a virus. In order to be safe, you must delete
properties from all strings calculated by user code before inserting them into buffers.

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13.18 Other Topics Related to Functions
Here is a table of several functions that do things related to function calling and function
definitions. They are documented elsewhere, but we provide cross references here.
apply

See Section 13.5 [Calling Functions], page 239.

autoload

See Section 16.5 [Autoload], page 304.

call-interactively
See Section 22.3 [Interactive Call], page 432.
called-interactively-p
See Section 22.4 [Distinguish Interactive], page 435.
commandp

See Section 22.3 [Interactive Call], page 432.

documentation
See Section 25.2 [Accessing Documentation], page 596.
eval

See Section 10.4 [Eval], page 152.

funcallSee Section 13.5 [Calling Functions], page 239.

function

See Section 13.7 [Anonymous Functions], page 243.

ignoreSee Section 13.5 [Calling Functions], page 239.

indirect-function
See Section 10.1.4 [Function Indirection], page 147.
interactive
See Section 22.2.1 [Using Interactive], page 424.
interactive-p
See Section 22.4 [Distinguish Interactive], page 435.
mapatoms

See Section 9.3 [Creating Symbols], page 135.

mapcarSee Section 13.6 [Mapping Functions], page 241.

map-char-table
See Section 6.6 [Char-Tables], page 119.
mapconcat
See Section 13.6 [Mapping Functions], page 241.
undefined
See Section 23.11 [Functions for Key Lookup], page 495.

268

14 Macros
Macros enable you to define new control constructs and other language features. A macrois defined much like a function, but instead of telling how to compute a value, it tells how
to compute another Lisp expression which will in turn compute the value. We call thisexpression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments,
not on the argument values as functions do. They can therefore construct an expansion
containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for thesake of speed, consider using an inline function instead. See Section 13.14 [Inline Functions],
page 261.

14.1 A Simple Example of a Macro
Suppose we would like to define a Lisp construct to increment a variable value, much likethe ++ operator in C. We would like to write (inc x) and have the effect of (setq x (1+x)). Here’s a macro definition that does the job:(defmacro inc (var)(list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var is the symbol x—not the value of x,
as it would be in a function. The body of the macro uses this to construct the expansion,
which is (setq x (1+ x)). Once the macro definition returns this expansion, Lisp proceeds
to evaluate it, thus incrementing x.

macrop object[Function]
This predicate tests whether its argument is a macro, and returns t if so, nil otherwise.

14.2 Expansion of a Macro Call
A macro call looks just like a function call in that it is a list which starts with the name of
the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial
difference: the macro arguments are the actual expressions appearing in the macro call.
They are not evaluated before they are given to the macro definition. By contrast, thearguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just as a function
is invoked. The argument variables of the macro are bound to the argument values fromthe macro call, or to a list of them in the case of a &rest argument. And the macro body
executes and returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by
the macro body is an alternate Lisp expression, also known as the expansion of the macro.
The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from themacro.
Since the expansion is evaluated in the normal manner, it may contain calls to othermacros. It may even be a call to the same macro, though this is unusual.

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Note that Emacs tries to expand macros when loading an uncompiled Lisp file. This is
not always possible, but if it is, it speeds up subsequent execution. See Section 16.1 [HowPrograms Do Loading], page 298.
You can see the expansion of a given macro call by calling macroexpand.

macroexpand form &optional environment[Function]
This function expands form, if it is a macro call. If the result is another macro call,
it is expanded in turn, until something which is not a macro call results. That isthe value returned by macroexpand. If form is not a macro call to begin with, it isreturned as given.
Note that macroexpand does not look at the subexpressions of form (although somemacro definitions may do so). Even if they are macro calls themselves, macroexpand
does not expand them.
The function macroexpand does not expand calls to inline functions. Normally there
is no need for that, since a call to an inline function is no harder to understand than acall to an ordinary function.
If environment is provided, it specifies an alist of macro definitions that shadow thecurrently defined macros. Byte compilation uses this feature.
(defmacro inc (var)(list 'setq var (list '1+ var)))(macroexpand '(inc r))⇒ (setq r (1+ r))(defmacro inc2 (var1 var2)(list 'progn (list 'inc var1) (list 'inc var2)))(macroexpand '(inc2 r s))⇒ (progn (inc r) (inc s)); inc not expanded here.

macroexpand-all form &optional environment[Function]
macroexpand-all expands macros like macroexpand, but will look for and expand all
macros in form, not just at the top-level. If no macros are expanded, the return value
is eq to form.
Repeating the example used for macroexpand above with macroexpand-all, we seethat macroexpand-all does expand the embedded calls to inc:(macroexpand-all '(inc2 r s))⇒ (progn (setq r (1+ r)) (setq s (1+ s)))macroexpand-1 form &optional environment[Function]
This function expands macros like macroexpand, but it only performs one step of the
expansion: if the result is another macro call, macroexpand-1 will not expand it.

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14.3 Macros and Byte Compilation
You might ask why we take the trouble to compute an expansion for a macro and thenevaluate the expansion. Why not have the macro body produce the desired results directly?
The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls
the macro definition just as the interpreter would, and receives an expansion. But instead ofevaluating this expansion, it compiles the expansion as if it had appeared directly in the
program. As a result, the compiled code produces the value and side effects intended forthe macro, but executes at full compiled speed. This would not work if the macro bodycomputed the value and side effects itself—they would be computed at compile time, which
is not useful.
In order for compilation of macro calls to work, the macros must already be defined in
Lisp when the calls to them are compiled. The compiler has a special feature to help you do
this: if a file being compiled contains a defmacro form, the macro is defined temporarily forthe rest of the compilation of that file.
Byte-compiling a file also executes any require calls at top-level in the file, so you canensure that necessary macro definitions are available during compilation by requiring thefiles that define them (see Section 16.7 [Named Features], page 309). To avoid loading themacro definition files when someone runs the compiled program, write eval-when-compile
around the require calls (see Section 17.5 [Eval During Compile], page 320).

14.4 Defining Macros
A Lisp macro object is a list whose car is macro, and whose cdr is a function. Expansion of
the macro works by applying the function (with apply) to the list of unevaluated argumentsfrom the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous function, but thisis never done, because it does not make sense to pass an anonymous macro to functionals
such as mapcar. In practice, all Lisp macros have names, and they are almost always definedwith the defmacro macro.

defmacro name args [doc] [declare] body. . .

[Macro]defmacro defines the symbol name (which should not be quoted) as a macro thatlooks like this:(macro lambda args . body)(Note that the cdr of this list is a lambda expression.) This macro object is stored
in the function cell of name. The meaning of args is the same as in a function, andthe keywords &rest and &optional may be used (see Section 13.2.3 [Argument List],
page 234). Neither name nor args should be quoted. The return value of defmacro isundefined.
doc, if present, should be a string specifying the macro’s documentation string.
declare, if present, should be a declare form specifying metadata for the macro (seeSection 13.15 [Declare Form], page 263). Note that macros cannot have interactive
declarations, since they cannot be called interactively.

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271

Macros often need to construct large list structures from a mixture of constants andnonconstant parts. To make this easier, use the ‘`’ syntax (see Section 10.3 [Backquote],
page 151). For example:(defmacro t-becomes-nil (variable)`(if (eq ,variable t)(setq ,variable nil)))(t-becomes-nil foo)
≡ (if (eq foo t) (setq foo nil))

14.5 Common Problems Using Macros
Macro expansion can have counterintuitive consequences. This section describes some
important consequences that can lead to trouble, and rules to follow to avoid trouble.

14.5.1 Wrong TimeThe most common problem in writing macros is doing some of the real work prematurely—
while expanding the macro, rather than in the expansion itself. For instance, one real
package had this macro definition:(defmacro my-set-buffer-multibyte (arg)(if (fboundp 'set-buffer-multibyte)(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when interpreted but failed
when compiled. This macro definition called set-buffer-multibyte during compilation,
which was wrong, and then did nothing when the compiled package was run. The definition
that the programmer really wanted was this:(defmacro my-set-buffer-multibyte (arg)(if (fboundp 'set-buffer-multibyte)`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to set-buffer-multibyte that will be
executed when the compiled program is actually run.

14.5.2 Evaluating Macro Arguments Repeatedly
When defining a macro you must pay attention to the number of times the arguments will be
evaluated when the expansion is executed. The following macro (used to facilitate iteration)
illustrates the problem. This macro allows us to write a for-loop construct.
(defmacro for (var from init to final do &rest body)"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."(list 'let (list (list var init))(cons 'while(cons (list '<= var final)(append body (list (list 'inc var)))))))

Chapter 14: Macros

272(for i from 1 to 3 do
(setq square (* i i))(princ (format "\n%d %d" i square)))7→(let ((i 1))(while (<= i 3)
(setq square (* i i))(princ (format "\n%d %d" i square))(inc i)))
a1
a2
a3
⇒ nil

1
4
9

The arguments from, to, and do in this macro are syntactic sugar; they are entirely ignored.
The idea is that you will write noise words (such as from, to, and do) in those positions in
the macro call.
Here’s an equivalent definition simplified through use of backquote:(defmacro for (var from init to final do &rest body)"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."`(let ((,var ,init))(while (<= ,var ,final),@body(inc ,var))))Both forms of this definition (with backquote and without) suffer from the defect that
final is evaluated on every iteration. If final is a constant, this is not a problem. If it is amore complex form, say (long-complex-calculation x), this can slow down the execution
significantly. If final has side effects, executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by producing an
expansion that evaluates the argument expressions exactly once unless repeated evaluation
is part of the intended purpose of the macro. Here is a correct expansion for the for macro:(let ((i 1)(max 3))(while (<= i max)
(setq square (* i i))(princ (format "%d(inc i)))%d" i square))Here is a macro definition that creates this expansion:

Chapter 14: Macros273(defmacro for (var from init to final do &rest body)"Execute a simple for loop: (for i from 1 to 10 do (print i))."`(let ((,var ,init)(max ,final))(while (<= ,var max),@body(inc ,var))))Unfortunately, this fix introduces another problem, described in the following section.

14.5.3 Local Variables in Macro Expansions
The new definition of for has a new problem: it introduces a local variable named max
which the user does not expect. This causes trouble in examples such as the following:(let ((max 0))(for x from 0 to 10 do(let ((this (frob x)))(if (< max this)(setq max this)))))The references to max inside the body of the for, which are supposed to refer to the user’s
binding of max, really access the binding made by for.
The way to correct this is to use an uninterned symbol instead of max (see Section 9.3[Creating Symbols], page 135). The uninterned symbol can be bound and referred to justlike any other symbol, but since it is created by for, we know that it cannot already appear
in the user’s program. Since it is not interned, there is no way the user can put it into theprogram later. It will never appear anywhere except where put by for. Here is a definitionof for that works this way:
(defmacro for (var from init to final do &rest body)"Execute a simple for loop: (for i from 1 to 10 do (print i))."(let ((tempvar (make-symbol "max")))`(let ((,var ,init)(,tempvar ,final))(while (<= ,var ,tempvar),@body(inc ,var)))))
This creates an uninterned symbol named max and puts it in the expansion instead of theusual interned symbol max that appears in expressions ordinarily.

14.5.4 Evaluating Macro Arguments in Expansion
Another problem can happen if the macro definition itself evaluates any of the macroargument expressions, such as by calling eval (see Section 10.4 [Eval], page 152). You haveto take into account that macro expansion may take place long before the code is executed,
when the context of the caller (where the macro expansion will be evaluated) is not yet
accessible.
Also, if your macro definition does not use lexical-binding, its formal arguments may
hide the user’s variables of the same name. Inside the macro body, the macro argument

Chapter 14: Macros274

binding is the most local binding of such variable, so any references inside the form being
evaluated do refer to it. Here is an example:(defmacro foo (a)(list 'setq (eval a) t))(setq x 'b)(foo x) 7→ (setq b t)
⇒ t
; and b has been set.
;; but(setq a 'c)(foo a) 7→ (setq a t)
⇒ t
; but this set a, not c.
It makes a difference whether the user’s variable is named a or x, because a conflicts
with the macro argument variable a.
Also, the expansion of (foo x) above will return something different or signal an error
when the code is compiled, since in that case (foo x) is expanded during compilation,
whereas the execution of (setq x 'b) will only take place later when the code is executed.
To avoid these problems, don’t evaluate an argument expression while computing themacro expansion. Instead, substitute the expression into the macro expansion, so that its
value will be computed as part of executing the expansion. This is how the other examples
in this chapter work.

14.5.5 How Many Times is the Macro Expanded?
Occasionally problems result from the fact that a macro call is expanded each time it isevaluated in an interpreted function, but is expanded only once (during compilation) for
a compiled function. If the macro definition has side effects, they will work differently
depending on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro expansion, unless
you really know what you are doing.
One special kind of side effect can’t be avoided: constructing Lisp objects. Almost all
macro expansions include constructed lists; that is the whole point of most macros. This is
usually safe; there is just one case where you must be careful: when the object you construct
is part of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object is constructed justonce, during compilation. But in interpreted execution, the macro is expanded each timethe macro call runs, and this means a new object is constructed each time.
In most clean Lisp code, this difference won’t matter. It can matter only if you perform
side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid
side effects on objects constructed by macro definitions. Here is an example of how suchside effects can get you into trouble:(defmacro empty-object ()(list 'quote (cons nil nil)))Chapter 14: Macros

275(defun initialize (condition)(let ((object (empty-object)))(if condition(setcar object condition))
object))If initialize is interpreted, a new list (nil) is constructed each time initialize is called.
Thus, no side effect survives between calls. If initialize is compiled, then the macro
empty-object is expanded during compilation, producing a single constant (nil) that isreused and altered each time initialize is called.
One way to avoid pathological cases like this is to think of empty-object as a funny kindof constant, not as a memory allocation construct. You wouldn’t use setcar on a constantsuch as '(nil), so naturally you won’t use it on (empty-object) either.

14.6 Indenting Macros
Within a macro definition, you can use the declare form (see Section 14.4 [Defining Macros],
page 270) to specify how TAB should indent calls to the macro. An indentation specification
is written like this:(declare (indent indent-spec))
This results in the lisp-indent-function property being set on the macro name.
Here are the possibilities for indent-spec:
nilThis is the same as no property—use the standard indentation pattern.

defun

Handle this function like a ‘def’ construct: treat the second line as the start ofa body.

an integer, number
The first number arguments of the function are distinguished arguments; therest are considered the body of the expression. A line in the expression isindented according to whether the first argument on it is distinguished or not.
If the argument is part of the body, the line is indented lisp-body-indent
more columns than the open-parenthesis starting the containing expression. If
the argument is distinguished and is either the first or second argument, it isindented twice that many extra columns. If the argument is distinguished andnot the first or second argument, the line uses the standard pattern.
a symbol, symbol
symbol should be a function name; that function is called to calculate theindentation of a line within this expression. The function receives two arguments:
pos

The position at which the line being indented begins.

state

The value returned by parse-partial-sexp (a Lisp primitive forindentation and nesting computation) when it parses up to thebeginning of this line.

It should return either a number, which is the number of columns of indentation
for that line, or a list whose car is such a number. The difference between
returning a number and returning a list is that a number says that all following

Chapter 14: Macros276

lines at the same nesting level should be indented just like this one; a list saysthat following lines might call for different indentations. This makes a difference
when the indentation is being computed by C-M-q; if the value is a number,
C-M-q need not recalculate indentation for the following lines until the end of
the list.

277

15 Customization Settings
Users of Emacs can customize variables and faces without writing Lisp code, by using theCustomize interface. See Section “Easy Customization” in The GNU Emacs Manual. This
chapter describes how to define customization items that users can interact with throughthe Customize interface.
Customization items include customizable variables, which are defined with thedefcustom macro; customizable faces, which are defined with defface (described separately
in Section 41.12.2 [Defining Faces], page 1168); and customization groups, defined with
defgroup, which act as containers for groups of related customization items.

15.1 Common Item Keywords
The customization declarations that we will describe in the next few sections—defcustom,
defgroup, etc.—all accept keyword arguments (see Section 12.2 [Constant Variables],page 189) for specifying various information. This section describes keywords that apply to all types of customization declarations.
All of these keywords, except :tag, can be used more than once in a given item. Eachuse of the keyword has an independent effect. The keyword :tag is an exception because
any given item can only display one name.
:tag label
Use label, a string, instead of the item’s name, to label the item in customization
menus and buffers. Don’t use a tag which is substantially different from theitem’s real name; that would cause confusion.
:group group
Put this customization item in group group. If this keyword is missing from acustomization item, it’ll be placed in the same group that was last defined (inthe current file).
When you use :group in a defgroup, it makes the new group a subgroup ofgroup.
If you use this keyword more than once, you can put a single item into morethan one group. Displaying any of those groups will show this item. Please
don’t overdo this, since the result would be annoying.
:link link-data
Include an external link after the documentation string for this item. This is asentence containing a button that references some other documentation.
There are several alternatives you can use for link-data:(custom-manual info-node)
Link to an Info node; info-node is a string which specifies the node
name, as in "(emacs)Top". The link appears as ‘[Manual]’ in thecustomization buffer and enters the built-in Info reader on info-node.
(info-link info-node)
Like custom-manual except that the link appears in the customization buffer with the Info node name.

Chapter 15: Customization Settings

278(url-link url)
Link to a web page; url is a string which specifies the URL. The link
appears in the customization buffer as url and invokes the WWW
browser specified by browse-url-browser-function.
(emacs-commentary-link library)
Link to the commentary section of a library; library is a string
which specifies the library name. See Section D.8 [Library Headers],
page 1343.
(emacs-library-link library)
Link to an Emacs Lisp library file; library is a string which specifies
the library name.
(file-link file)
Link to a file; file is a string which specifies the name of the file tovisit with find-file when the user invokes this link.
(function-link function)
Link to the documentation of a function; function is a string
which specifies the name of the function to describe withdescribe-function when the user invokes this link.
(variable-link variable)
Link to the documentation of a variable; variable is a string
which specifies the name of the variable to describe withdescribe-variable when the user invokes this link.
(face-link face)
Link to the documentation of a face; face is a string which specifies
the name of the face to describe with describe-face when the user
invokes this link.
(custom-group-link group)
Link to another customization group. Invoking it creates a newcustomization buffer for group.
You can specify the text to use in the customization buffer by adding :tag nameafter the first element of the link-data; for example, (info-link :tag "foo""(emacs)Top") makes a link to the Emacs manual which appears in the buffer
as ‘foo’.
You can use this keyword more than once, to add multiple links.
:load file
Load file file (a string) before displaying this customization item (see Chapter 16[Loading], page 298). Loading is done with load, and only if the file is notalready loaded.
:require feature
Execute (require 'feature) when your saved customizations set the value of
this item. feature should be a symbol.

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279

The most common reason to use :require is when a variable enables a featuresuch as a minor mode, and just setting the variable won’t have any effect unlessthe code which implements the mode is loaded.
:version version
This keyword specifies that the item was first introduced in Emacs version
version, or that its default value was changed in that version. The value version
must be a string.
:package-version '(package . version)
This keyword specifies that the item was first introduced in package version
version, or that its meaning or default value was changed in that version. This
keyword takes priority over :version.
package should be the official name of the package, as a symbol (e.g., MH-E).
version should be a string. If the package package is released as part of Emacs,
package and version should appear in the value of customize-package-emacsversion-alist.
Packages distributed as part of Emacs that use the :package-version keyword mustalso update the customize-package-emacs-version-alist variable.
[Variable]
This alist provides a mapping for the versions of Emacs that are associated withversions of a package listed in the :package-version keyword. Its elements are:(package (pversion . eversion)...)For each package, which is a symbol, there are one or more elements that contain apackage version pversion with an associated Emacs version eversion. These versions
are strings. For example, the MH-E package updates this alist with the following:

customize-package-emacs-version-alist(add-to-list 'customize-package-emacs-version-alist'(MH-E ("6.0" . "22.1") ("6.1" . "22.1") ("7.0" . "22.1")("7.1" . "22.1") ("7.2" . "22.1") ("7.3" . "22.1")("7.4" . "22.1") ("8.0" . "22.1")))The value of package needs to be unique and it needs to match the package value
appearing in the :package-version keyword. Since the user might see the value inan error message, a good choice is the official name of the package, such as MH-E or
Gnus.

15.2 Defining Customization Groups
Each Emacs Lisp package should have one main customization group which contains all theoptions, faces and other groups in the package. If the package has a small number of options
and faces, use just one group and put everything in it. When there are more than twenty or
so options and faces, then you should structure them into subgroups, and put the subgroups
under the package’s main customization group. It is OK to put some of the options andfaces in the package’s main group alongside the subgroups.
The package’s main or only group should be a member of one or more of the standard
customization groups. (To display the full list of them, use M-x customize.) Choose one ormore of them (but not too many), and add your group to each of them using the :group
keyword.

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The way to declare new customization groups is with defgroup.

defgroup group members doc [keyword value]. . .

[Macro]Declare group as a customization group containing members. Do not quote the symbolgroup. The argument doc specifies the documentation string for the group.
The argument members is a list specifying an initial set of customization items to
be members of the group. However, most often members is nil, and you specify thegroup’s members by using the :group keyword when defining those members.
If you want to specify group members through members, each element should have theform (name widget). Here name is a symbol, and widget is a widget type for editingthat symbol. Useful widgets are custom-variable for a variable, custom-face for aface, and custom-group for a group.
When you introduce a new group into Emacs, use the :version keyword in thedefgroup; then you need not use it for the individual members of the group.
In addition to the common keywords (see Section 15.1 [Common Keywords], page 277),
you can also use this keyword in defgroup::prefix prefix
If the name of an item in the group starts with prefix, and the customizablevariable custom-unlispify-remove-prefixes is non-nil, the item’s tag
will omit prefix. A group can have any number of prefixes.
The variables, faces, and subgroups of a group are stored in the custom-group propertyof the group’s symbol. See Section 9.4.1 [Symbol Plists], page 138. The value ofthat property is a list of pairs whose car is the symbol of the variable or the faceor the subgroup, and the cdr is one of the corresponding symbols custom-variable,
custom-face, or custom-group.
[User Option]
If this variable is non-nil, the prefixes specified by a group’s :prefix keyword areomitted from tag names, whenever the user customizes the group.
The default value is nil, i.e., the prefix-discarding feature is disabled. This is because
discarding prefixes often leads to confusing names for options and faces.

custom-unlispify-remove-prefixes

15.3 Defining Customization Variables
Customizable variables, also called user options, are global Lisp variables whose values canbe set through the Customize interface. Unlike other global variables, which are defined withdefvar (see Section 12.5 [Defining Variables], page 194), customizable variables are definedusing the defcustom macro. In addition to calling defvar as a subroutine, defcustom states
how the variable should be displayed in the Customize interface, the values it is allowed totake, etc.

defcustom option standard doc [keyword value]. . .

[Macro]This macro declares option as a user option (i.e., a customizable variable). You should
not quote option.
The argument standard is an expression that specifies the standard value for option.
Evaluating the defcustom form evaluates standard, but does not necessarily bind theChapter 15: Customization Settings281

option to that value. If option already has a default value, it is left unchanged. If
the user has already saved a customization for option, the user’s customized value isinstalled as the default value. Otherwise, the result of evaluating standard is installed
as the default value.
Like defvar, this macro marks option as a special variable, meaning that it should
always be dynamically bound. If option is already lexically bound, that lexical binding
remains in effect until the binding construct exits. See Section 12.10 [Variable Scoping],
page 201.
The expression standard can be evaluated at various other times, too—whenever thecustomization facility needs to know option’s standard value. So be sure to use an
expression which is harmless to evaluate at any time.
The argument doc specifies the documentation string for the variable.
If a defcustom does not specify any :group, the last group defined with defgroup in
the same file will be used. This way, most defcustom do not need an explicit :group.
When you evaluate a defcustom form with C-M-x in Emacs Lisp mode (eval-defun),a special feature of eval-defun arranges to set the variable unconditionally, without
testing whether its value is void. (The same feature applies to defvar, see Section 12.5
[Defining Variables], page 194.) Using eval-defun on a defcustom that is alreadydefined calls the :set function (see below), if there is one.
If you put a defcustom in a pre-loaded Emacs Lisp file (see Section E.1 [Building
Emacs], page 1346), the standard value installed at dump time might be incorrect,
e.g., because another variable that it depends on has not been assigned the right value
yet. In that case, use custom-reevaluate-setting, described below, to re-evaluate
the standard value after Emacs starts up.
In addition to the keywords listed in Section 15.1 [Common Keywords], page 277, thismacro accepts the following keywords::type type
Use type as the data type for this option. It specifies which values are legitimate,and how to display the value (see Section 15.4 [Customization Types], page 284).
Every defcustom should specify a value for this keyword.
:options value-list
Specify the list of reasonable values for use in this option. The user is not
restricted to using only these values, but they are offered as convenient alternatives.
This is meaningful only for certain types, currently including hook, plist andalist. See the definition of the individual types for a description of how to use:options.
Re-evaluating a defcustom form with a different :options value does not clear
the values added by previous evaluations, or added by calls to custom-addfrequent-value (see below).
:set setfunction
Specify setfunction as the way to change the value of this option when using
the Customize interface. The function setfunction should take two arguments,

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a symbol (the option name) and the new value, and should do whatever isnecessary to update the value properly for this option (which may not mean
simply setting the option as a Lisp variable); preferably, though, it should
not modify its value argument destructively. The default for setfunction is
set-default-toplevel-value.
If defined, setfunction will also be called when evaluating a defcustom form
with C-M-x in Emacs Lisp mode and when the option’s value is changed via thesetopt macro (see Section 12.8 [Setting Variables], page 198).
If you specify this keyword, the variable’s documentation string should describe
how to do the same job in hand-written Lisp code, either by invoking setfunction
directly or by using setopt.
:get getfunction
Specify getfunction as the way to extract the value of this option. The function
getfunction should take one argument, a symbol, and should return whatevercustomize should use as the current value for that symbol (which need not be
the symbol’s Lisp value). The default is default-toplevel-value.
You have to really understand the workings of Custom to use :get correctly. It
is meant for values that are treated in Custom as variables but are not actuallystored in Lisp variables. It is almost surely a mistake to specify getfunction fora value that really is stored in a Lisp variable.
:initialize function
function should be a function used to initialize the variable when the defcustom
is evaluated. It should take two arguments, the option name (a symbol) andthe value. Here are some predefined functions meant for use in this way:
custom-initialize-set
Use the variable’s :set function to initialize the variable, but do
not reinitialize it if it is already non-void.
custom-initialize-default
Like custom-initialize-set, but use the function set-defaulttoplevel-value to set the variable, instead of the variable’s :setfunction. This is the usual choice for a variable whose :set function
enables or disables a minor mode; with this choice, defining thevariable will not call the minor mode function, but customizing thevariable will do so.
custom-initialize-reset
Always use the :set function to initialize the variable. If the variable
is already non-void, reset it by calling the :set function using thecurrent value (returned by the :get method). This is the default:initialize function.
custom-initialize-changed
Use the :set function to initialize the variable, if it is already set or
has been customized; otherwise, just use set-default-toplevelvalue.

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custom-initialize-delayThis function behaves like custom-initialize-set, but it delays
the actual initialization to the next Emacs start. This should be
used in files that are preloaded (or for autoloaded variables), so thatthe initialization is done in the run-time context rather than thebuild-time context. This also has the side-effect that the (delayed)
initialization is performed with the :set function. See Section E.1[Building Emacs], page 1346.
:local value
If the value is t, mark option as automatically buffer-local; if the value ispermanent, also set options permanent-local property to t. See Section 12.11.2[Creating Buffer-Local], page 208.
:risky value
Set the variable’s risky-local-variable property to value (see Section 12.12[File Local Variables], page 213).
:safe function
Set the variable’s safe-local-variable property to function (see Section 12.12[File Local Variables], page 213).
:set-after variables
When setting variables according to saved customizations, make sure to set thevariables variables before this one; i.e., delay setting this variable until after
those others have been handled. Use :set-after if setting this variable won’t
work properly unless those other variables already have their intended values.
It is useful to specify the :require keyword for an option that turns on a certain feature.
This causes Emacs to load the feature, if it is not already loaded, whenever the option is set.
See Section 15.1 [Common Keywords], page 277. Here is an example:(defcustom frobnicate-automatically nil"Non-nil means automatically frobnicate all buffers.":type 'boolean:require 'frobnicate-mode:group 'frobnicate)
If a customization item has a type such as hook or alist, which supports :options,
you can add additional values to the list from outside the defcustom declaration by calling custom-add-frequent-value. For example, if you define a function my-lisp-modeinitialization intended to be called from emacs-lisp-mode-hook, you might want to
add that to the list of reasonable values for emacs-lisp-mode-hook, but not by editing its
definition. You can do it thus:(custom-add-frequent-value 'emacs-lisp-mode-hook'my-lisp-mode-initialization)custom-add-frequent-value symbol value[Function]
For the customization option symbol, add value to the list of reasonable values.
The precise effect of adding a value depends on the customization type of symbol.
Since evaluating a defcustom form does not clear values added previously, Lisp
programs can use this function to add values for user options not yet defined.

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Internally, defcustom uses the symbol property standard-value to record the expression for the standard value, saved-value to record the value saved by the user with thecustomization buffer, and customized-value to record the value set by the user with thecustomization buffer, but not saved. See Section 9.4 [Symbol Properties], page 138. In
addition, there’s themed-value, which is used to record the value set by a theme (seeSection 15.6 [Custom Themes], page 295). These properties are lists, the car of which is anexpression that evaluates to the value.

custom-reevaluate-setting symbol[Function]
This function re-evaluates the standard value of symbol, which should be a user option
declared via defcustom. If the variable was customized, this function re-evaluates the
saved value instead. Then it sets the user option to that value (using the option’s:set property if that is defined).
This is useful for customizable options that are defined before their value could becomputed correctly. For example, during startup Emacs calls this function for someuser options that were defined in pre-loaded Emacs Lisp files, but whose initial values
depend on information available only at run-time.

custom-variable-p arg[Function]
This function returns non-nil if arg is a customizable variable. A customizablevariable is either a variable that has a standard-value or custom-autoload property(usually meaning it was declared with defcustom), or an alias for another customizablevariable.

15.4 Customization Types
When you define a user option with defcustom, you must specify its customization type.
That is a Lisp object which describes (1) which values are legitimate and (2) how to display
the value in the customization buffer for editing.
You specify the customization type in defcustom with the :type keyword. The argumentof :type is evaluated, but only once when the defcustom is executed, so it isn’t useful forthe value to vary. Normally we use a quoted constant. For example:(defcustom diff-command "diff""The command to use to run diff.":type '(string):group 'diff)
In general, a customization type is a list whose first element is a symbol, one of thecustomization type names defined in the following sections. After this symbol come a numberof arguments, depending on the symbol. Between the type symbol and its arguments, you
can optionally write keyword-value pairs (see Section 15.4.4 [Type Keywords], page 291).
Some type symbols do not use any arguments; those are called simple types. For a simple
type, if you do not use any keyword-value pairs, you can omit the parentheses around thetype symbol. For example just string as a customization type is equivalent to (string).
All customization types are implemented as widgets; see Section “Introduction” in The
Emacs Widget Library, for details.

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15.4.1 Simple Types
This section describes all the simple customization types. For several of these customization
types, the customization widget provides inline completion with C-M-i or M-TAB.
sexp

The value may be any Lisp object that can be printed and read back. You can
use sexp as a fall-back for any option, if you don’t want to take the time towork out a more specific type to use.

integer

The value must be an integer.

natnumThe value must be a nonnegative integer.

number

The value must be a number (floating point or integer).

float

The value must be floating point.

string

The value must be a string. The customization buffer shows the string without
delimiting ‘"’ characters or ‘\’ quotes.

regexpLike string except that the string must be a valid regular expression.

character
The value must be a character code. A character code is actually an integer,
but this type shows the value by inserting the character in the buffer, rather
than by showing the number.
file

The value must be a file name. The widget provides completion.

(file :must-match t)
The value must be a file name for an existing file. The widget provides completion.
directory
The value must be a directory. The widget provides completion.
hook

The value must be a list of functions. This customization type is used for hookvariables. You can use the :options keyword in a hook variable’s defcustom
to specify a list of functions recommended for use in the hook; See Section 15.3
[Variable Definitions], page 280.

symbol

The value must be a symbol. It appears in the customization buffer as the
symbol name. The widget provides completion.

function

The value must be either a lambda expression or a function name. The widget
provides completion for function names.

variable

The value must be a variable name. The widget provides completion.

face

The value must be a symbol which is a face name. The widget provides
completion.

boolean

The value is boolean—either nil or t. Note that by using choice and const
together (see the next section), you can specify that the value must be nil or t,
but also specify the text to describe each value in a way that fits the specificmeaning of the alternative.

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The value is a valid key according to key-valid-p, and suitable for use with,for example keymap-set.

key-sequence
The value is a key sequence. The customization buffer shows the key sequence
using the same syntax as the kbd function. See Section 23.1 [Key Sequences],
page 480. This is a legacy type; use key instead.
coding-system
The value must be a coding-system name, and you can do completion with
M-TAB.
color

The value must be a valid color name. The widget provides completion for color
names, as well as a sample and a button for selecting a color name from a listof color names shown in a *Colors* buffer.

fringe-bitmap
The value must be a valid fringe bitmap name. The widget provides completion.

15.4.2 Composite Types
When none of the simple types is appropriate, you can use composite types, which build
new types from other types or from specified data. The specified types or data are called
the arguments of the composite type. The composite type normally looks like this:(constructor arguments...)but you can also add keyword-value pairs before the arguments, like this:(constructor {keyword value}... arguments...)Here is a table of constructors and how to use them to write composite types:(cons car-type cdr-type)The value must be a cons cell, its car must fit car-type, and its cdr must fit
cdr-type. For example, (cons string symbol) is a customization type whichmatches values such as ("foo" . foo).
In the customization buffer, the car and cdr are displayed and edited separately,each according to their specified type.
(list element-types...)The value must be a list with exactly as many elements as the element-types
given; and each element must fit the corresponding element-type.
For example, (list integer string function) describes a list of three elements; the first element must be an integer, the second a string, and the third afunction.
In the customization buffer, each element is displayed and edited separately,according to the type specified for it.
(group element-types...)This works like list except for the formatting of text in the Custom buffer.
list labels each element value with its tag; group does not.
(vector element-types...)Like list except that the value must be a vector instead of a list. The elements
work the same as in list.

Chapter 15: Customization Settings

287(alist :key-type key-type :value-type value-type)The value must be a list of cons-cells, the car of each cell representing a key ofcustomization type key-type, and the cdr of the same cell representing a valueof customization type value-type. The user can add and delete key/value pairs,
and edit both the key and the value of each pair.
If omitted, key-type and value-type default to sexp.
The user can add any key matching the specified key type, but you can givesome keys a preferential treatment by specifying them with the :options (seeSection 15.3 [Variable Definitions], page 280). The specified keys will always be
shown in the customize buffer (together with a suitable value), with a checkbox
to include or exclude or disable the key/value pair from the alist. The user will
not be able to edit the keys specified by the :options keyword argument.
The argument to the :options keywords should be a list of specifications forreasonable keys in the alist. Ordinarily, they are simply atoms, which stand forthemselves. For example::options '("foo" "bar" "baz")specifies that there are three known keys, namely "foo", "bar" and "baz",which will always be shown first.
You may want to restrict the value type for specific keys, for example, the value
associated with the "bar" key can only be an integer. You can specify this byusing a list instead of an atom in the list. The first element will specify the key,
like before, while the second element will specify the value type. For example::options '("foo" ("bar" integer) "baz")
Finally, you may want to change how the key is presented. By default, thekey is simply shown as a const, since the user cannot change the special keys
specified with the :options keyword. However, you may want to use a more
specialized type for presenting the key, like function-item if you know it is asymbol with a function binding. This is done by using a customization typespecification instead of a symbol for the key.
:options '("foo"((function-item some-function) integer)"baz")
Many alists use lists with two elements, instead of cons cells. For example,(defcustom list-alist'(("foo" 1) ("bar" 2) ("baz" 3))"Each element is a list of the form (KEY VALUE).")
instead of(defcustom cons-alist'(("foo" . 1) ("bar" . 2) ("baz" . 3))"Each element is a cons-cell (KEY . VALUE).")
Because of the way lists are implemented on top of cons cells, you can treat
list-alist in the example above as a cons cell alist, where the value type is alist with a single element containing the real value.
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))Chapter 15: Customization Settings

288"Each element is a list of the form (KEY VALUE).":type '(alist :value-type (group integer)))
The group widget is used here instead of list only because the formatting isbetter suited for the purpose.
Similarly, you can have alists with more values associated with each key, using
variations of this trick:(defcustom person-data '(("brian" 50 t)("dorith" 55 nil)("ken"
52 t))"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG).":type '(alist :value-type (group integer boolean)))(plist :key-type key-type :value-type value-type)This customization type is similar to alist (see above), except that (i) the
information is stored as a property list, (see Section 5.9 [Property Lists], page 99),
and (ii) key-type, if omitted, defaults to symbol rather than sexp.
(choice alternative-types...)The value must fit one of alternative-types. For example, (choice integer
string) allows either an integer or a string.
In the customization buffer, the user selects an alternative using a menu, andcan then edit the value in the usual way for that alternative.
Normally the strings in this menu are determined automatically from the choices;
however, you can specify different strings for the menu by including the :tagkeyword in the alternatives. For example, if an integer stands for a number of
spaces, while a string is text to use verbatim, you might write the customization
type this way,(choice (integer :tag "Number of spaces")(string :tag "Literal text"))
so that the menu offers ‘Number of spaces’ and ‘Literal text’.
In any alternative for which nil is not a valid value, other than a const, you
should specify a valid default for that alternative using the :value keyword.
See Section 15.4.4 [Type Keywords], page 291.
If some values are covered by more than one of the alternatives, customize will
choose the first alternative that the value fits. This means you should always
list the most specific types first, and the most general last. Here’s an example
of proper usage:(choice (const :tag "Off" nil)symbol (sexp :tag "Other"))This way, the special value nil is not treated like other symbols, and symbols
are not treated like other Lisp expressions.
(radio element-types...)This is similar to choice, except that the choices are displayed using radio
buttons rather than a menu. This has the advantage of displaying documentation

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for the choices when applicable and so is often a good choice for a choice between
constant functions (function-item customization types).
(const value)
The value must be value—nothing else is allowed.
The main use of const is inside of choice. For example, (choice integer(const nil)) allows either an integer or nil.
:tag is often used with const, inside of choice. For example,(choice (const :tag "Yes" t)(const :tag "No" nil)(const :tag "Ask" foo))
describes a variable for which t means yes, nil means no, and foo means “ask”.
(other value)
This alternative can match any Lisp value, but if the user chooses this alternative,that selects the value value.
The main use of other is as the last element of choice. For example,(choice (const :tag "Yes" t)(const :tag "No" nil)(other :tag "Ask" foo))
describes a variable for which t means yes, nil means no, and anything elsemeans “ask”. If the user chooses ‘Ask’ from the menu of alternatives, thatspecifies the value foo; but any other value (not t, nil or foo) displays as ‘Ask’,
just like foo.
(function-item function)
Like const, but used for values which are functions. This displays the documentation string as well as the function name. The documentation string is either
the one you specify with :doc, or function’s own documentation string.
(variable-item variable)
Like const, but used for values which are variable names. This displays the
documentation string as well as the variable name. The documentation string iseither the one you specify with :doc, or variable’s own documentation string.
(set types...)The value must be a list, and each element of the list must match one of thetypes specified.
This appears in the customization buffer as a checklist, so that each of types may
have either one corresponding element or none. It is not possible to specify two
different elements that match the same one of types. For example, (set integer
symbol) allows one integer and/or one symbol in the list; it does not allow
multiple integers or multiple symbols. As a result, it is rare to use nonspecifictypes such as integer in a set.
Most often, the types in a set are const types, as shown here:(set (const :bold) (const :italic))
Sometimes they describe possible elements in an alist:(set (cons :tag "Height" (const height) integer)

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290(cons :tag "Width" (const width) integer))That lets the user specify a height value optionally and a width value optionally.
(repeat element-type)The value must be a list and each element of the list must fit the type elementtype. This appears in the customization buffer as a list of elements, with ‘[INS]’and ‘[DEL]’ buttons for adding more elements or removing elements.
(restricted-sexp :match-alternatives criteria)
This is the most general composite type construct. The value may be any Lisp
object that satisfies one of criteria. criteria should be a list, and each element
should be one of these possibilities:• A predicate—that is, a function of one argument that returns either nil or
non-nil according to the argument. Using a predicate in the list says that
objects for which the predicate returns non-nil are acceptable.
• A quoted constant—that is, 'object. This sort of element in the list saysthat object itself is an acceptable value.
For example,(restricted-sexp :match-alternatives(integerp 't 'nil))allows integers, t and nil as legitimate values.
The customization buffer shows all legitimate values using their read syntax,
and the user edits them textually.
Here is a table of the keywords you can use in keyword-value pairs in a composite type::tag tag

Use tag as the name of this alternative, for user communication purposes. Thisis useful for a type that appears inside of a choice.

:match-alternatives criteria
Use criteria to match possible values. This is used only in restricted-sexp.
:args argument-list
Use the elements of argument-list as the arguments of the type construct.
For instance, (const :args (foo)) is equivalent to (const foo). You rarely
need to write :args explicitly, because normally the arguments are recognizedautomatically as whatever follows the last keyword-value pair.

15.4.3 Splicing into Lists
The :inline feature lets you splice a variable number of elements into the middle of a list
or vector customization type. You use it by adding :inline t to a type specification whichis contained in a list or vector specification.
Normally, each entry in a list or vector type specification describes a single element
type. But when an entry contains :inline t, the value it matches is merged directly into
the containing sequence. For example, if the entry matches a list with three elements, thosebecome three elements of the overall sequence. This is analogous to ‘,@’ in a backquoteconstruct (see Section 10.3 [Backquote], page 151).

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For example, to specify a list whose first element must be baz and whose remainingarguments should be zero or more of foo and bar, use this customization type:(list (const baz) (set :inline t (const foo) (const bar)))This matches values such as (baz), (baz foo), (baz bar) and (baz foo bar).
When the element-type is a choice, you use :inline not in the choice itself, but in(some of) the alternatives of the choice. For example, to match a list which must startwith a file name, followed either by the symbol t or two strings, use this customization type:(list file(choice (const t)(list :inline t string string)))
If the user chooses the first alternative in the choice, then the overall list has two elements
and the second element is t. If the user chooses the second alternative, then the overall list
has three elements and the second and third must be strings.
The widgets can specify predicates to say whether an inline value matches the widget
with the :match-inline element.

15.4.4 Type Keywords
You can specify keyword-argument pairs in a customization type after the type name symbol.
Here are the keywords you can use, and their meanings::value default
Provide a default value.
If nil is not a valid value for the alternative, then it is essential to specify avalid default with :value.
If you use this for a type that appears as an alternative inside of choice; it
specifies the default value to use, at first, if and when the user selects thisalternative with the menu in the customization buffer.
Of course, if the actual value of the option fits this alternative, it will appear
showing the actual value, not default.
:format format-string
This string will be inserted in the buffer to represent the value corresponding to
the type. The following ‘%’ escapes are available for use in format-string:‘%[button%]’
Display the text button marked as a button. The :action attribute
specifies what the button will do if the user invokes it; its value is afunction which takes two arguments—the widget which the button
appears in, and the event.
There is no way to specify two different buttons with different
actions.
‘%{sample%}’Show sample in a special face specified by :sample-face.
‘%v’

Substitute the item’s value. How the value is represented depends
on the kind of item, and (for variables) on the customization type.

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‘%d’

Substitute the item’s documentation string.

‘%h’

Like ‘%d’, but if the documentation string is more than one line, add
a button to control whether to show all of it or just the first line.

‘%t’

Substitute the tag here. You specify the tag with the :tag keyword.

‘%%’

Display a literal ‘%’.

:action action
Perform action if the user clicks on a button.
:button-face face
Use the face face (a face name or a list of face names) for button text displayedwith ‘%[...%]’.
:button-prefix prefix:button-suffix suffix
These specify the text to display before and after a button. Each can be:nil

No text is inserted.

a string

The string is inserted literally.

a symbol

The symbol’s value is used.

:tag tag

Use tag (a string) as the tag for the value (or part of the value) that corresponds
to this type.

:doc doc

Use doc as the documentation string for this value (or part of the value) that
corresponds to this type. In order for this to work, you must specify a value for:format, and use ‘%d’ or ‘%h’ in that value.
The usual reason to specify a documentation string for a type is to provide
more information about the meanings of alternatives inside a choice type or
the parts of some other composite type.

:help-echo motion-doc
When you move to this item with widget-forward or widget-backward, it
will display the string motion-doc in the echo area. In addition, motion-doc isused as the mouse help-echo string and may actually be a function or form
evaluated to yield a help string. If it is a function, it is called with one argument,
the widget.
:match function
Specify how to decide whether a value matches the type. The corresponding
value, function, should be a function that accepts two arguments, a widget anda value; it should return non-nil if the value is acceptable.
:match-inline function
Specify how to decide whether an inline value matches the type. The corresponding value, function, should be a function that accepts two arguments, awidget and an inline value; it should return non-nil if the value is acceptable.
See Section 15.4.3 [Splicing into Lists], page 290, for more information about
inline values.

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Specify a validation function for input. function takes a widget as an argument,
and should return nil if the widget’s current value is valid for the widget.
Otherwise, it should return the widget containing the invalid data, and set thatwidget’s :error property to a string explaining the error.
:type-error string
string should be a string that describes why a value doesn’t match the type,as determined by the :match function. When the :match function returns nil,
the widget’s :error property will be set to string.

15.4.5 Defining New Types
In the previous sections we have described how to construct elaborate type specifications
for defcustom. In some cases you may want to give such a type specification a name. The
obvious case is when you are using the same type for many user options: rather than repeat
the specification for each option, you can give the type specification a name, and use thatname each defcustom. The other case is when a user option’s value is a recursive data
structure. To make it possible for a datatype to refer to itself, it needs to have a name.
Since custom types are implemented as widgets, the way to define a new customize type
is to define a new widget. We are not going to describe the widget interface here in details,
see Section “Introduction” in The Emacs Widget Library, for that. Instead we are going todemonstrate the minimal functionality needed for defining new customize types by a simple
example.
(define-widget 'binary-tree-of-string 'lazy"A binary tree made of cons-cells and strings.":offset 4:tag "Node":type '(choice (string :tag "Leaf" :value "")(cons :tag "Interior":value ("" . "")binary-tree-of-stringbinary-tree-of-string)))(defcustom foo-bar """Sample variable holding a binary tree of strings.":type 'binary-tree-of-string)
The function to define a new widget is called define-widget. The first argument is the
symbol we want to make a new widget type. The second argument is a symbol representing
an existing widget, the new widget is going to be defined in terms of difference from theexisting widget. For the purpose of defining new customization types, the lazy widget isperfect, because it accepts a :type keyword argument with the same syntax as the keyword
argument to defcustom with the same name. The third argument is a documentation string
for the new widget. You will be able to see that string with the M-x widget-browse RET
binary-tree-of-string RET command.
After these mandatory arguments follow the keyword arguments. The most important
is :type, which describes the data type we want to match with this widget. Here aChapter 15: Customization Settings294

binary-tree-of-string is described as being either a string, or a cons-cell whose car andcdr are themselves both binary-tree-of-string. Note the reference to the widget type weare currently in the process of defining. The :tag attribute is a string to name the widget
in the user interface, and the :offset argument is there to ensure that child nodes areindented four spaces relative to the parent node, making the tree structure apparent in thecustomization buffer.
The defcustom shows how the new widget can be used as an ordinary customization
type.
The reason for the name lazy is that the other composite widgets convert their inferiorwidgets to internal form when the widget is instantiated in a buffer. This conversion isrecursive, so the inferior widgets will convert their inferior widgets. If the data structure
is itself recursive, this conversion is an infinite recursion. The lazy widget prevents therecursion: it convert its :type argument only when needed.

15.5 Applying Customizations
The following functions are responsible for installing the user’s customization settings forvariables and faces, respectively. When the user invokes ‘Save for future sessions’ in
the Customize interface, that takes effect by writing a custom-set-variables and/or acustom-set-faces form into the custom file, to be evaluated the next time Emacs starts.

custom-set-variables &rest args

[Function]
This function installs the variable customizations specified by args. Each argument inargs should have the form
(var expression [now [request [comment]]])var is a variable name (a symbol), and expression is an expression which evaluates tothe desired customized value.
If the defcustom form for var has been evaluated prior to this custom-set-variables
call, expression is immediately evaluated, and the variable’s value is set to the result.
Otherwise, expression is stored into the variable’s saved-value property, to be evaluated when the relevant defcustom is called (usually when the library defining thatvariable is loaded into Emacs).
The now, request, and comment entries are for internal use only, and may be omitted.
now, if non-nil, means to set the variable’s value now, even if the variable’s defcustom
form has not been evaluated. request is a list of features to be loaded immediately(see Section 16.7 [Named Features], page 309). comment is a string describing thecustomization.

custom-set-faces &rest args

[Function]
This function installs the face customizations specified by args. Each argument inargs should have the form
(face spec [now [comment]])
face is a face name (a symbol), and spec is the customized face specification for thatface (see Section 41.12.2 [Defining Faces], page 1168).
The now and comment entries are for internal use only, and may be omitted. now, if
non-nil, means to install the face specification now, even if the defface form has notbeen evaluated. comment is a string describing the customization.

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15.6 Custom Themes
Custom themes are collections of settings that can be enabled or disabled as a unit. See
Section “Custom Themes” in The GNU Emacs Manual. Each Custom theme is defined by
an Emacs Lisp source file, which should follow the conventions described in this section.
(Instead of writing a Custom theme by hand, you can also create one using a Customize-likeinterface; see Section “Creating Custom Themes” in The GNU Emacs Manual.)
A Custom theme file should be named foo-theme.el, where foo is the theme name. The
first Lisp form in the file should be a call to deftheme, and the last form should be a call toprovide-theme.

deftheme theme &optional doc &rest properties[Macro]This macro declares theme (a symbol) as the name of a Custom theme. The optional
argument doc should be a string describing the theme; this is the description shown
when the user invokes the describe-theme command or types ? in the ‘*Custom
Themes*’ buffer. The remaining arguments properties are used pass a property list
with theme attributes.
The following attributes are supported::family

A symbol designating what “family” a theme belongs to. A family of
themes is a set of similar themes that differ by minor aspects, such as facecolors that are meant for the light vs dark background of the frame.

:kind

A symbol. If a theme is enabled and this property has the value
color-scheme, then the theme-choose-variant command will look forother available themes that belong to the same family in order to switch
the themes. Other values are currently unspecified and should not be
used.

:background-mode
A symbol, either light or dark. This attribute is currently unused, butshould still be specified.
Two special theme names are disallowed (using them causes an error): user is adummy theme that stores the user’s direct customization settings, and changed is adummy theme that stores changes made outside of the Customize system.

provide-theme theme[Macro]This macro declares that the theme named theme has been fully specified.
In between deftheme and provide-theme are Lisp forms specifying the theme settings:
usually a call to custom-theme-set-variables and/or a call to custom-theme-set-faces.

custom-theme-set-variables theme &rest args

[Function]
This function specifies the Custom theme theme’s variable settings. theme should bea symbol. Each argument in args should be a list of the form
(var expression [now [request [comment]]])where the list entries have the same meanings as in custom-set-variables. See
Section 15.5 [Applying Customizations], page 294.

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custom-theme-set-faces theme &rest args

[Function]
This function specifies the Custom theme theme’s face settings. theme should be asymbol. Each argument in args should be a list of the form
(face spec [now [comment]])
where the list entries have the same meanings as in custom-set-faces.
Section 15.5 [Applying Customizations], page 294.

See

In theory, a theme file can also contain other Lisp forms, which would be evaluated whenloading the theme, but that is bad form. To protect against loading themes containing
malicious code, Emacs displays the source file and asks for confirmation from the user
before loading any non-built-in theme for the first time. As such, themes are not ordinarily
byte-compiled, and source files usually take precedence when Emacs is looking for a theme
to load.
The following functions are useful for programmatically enabling and disabling themes:

custom-theme-p theme[Function]
This function return a non-nil value if theme (a symbol) is the name of a Custom
theme (i.e., a Custom theme which has been loaded into Emacs, whether or not thetheme is enabled). Otherwise, it returns nil.
[Variable]
The value of this variable is a list of themes loaded into Emacs. Each theme isrepresented by a Lisp symbol (the theme name). The default value of this variable
is a list containing two dummy themes: (user changed). The changed theme stores
settings made before any Custom themes are applied (e.g., variables set outside ofCustomize). The user theme stores settings the user has customized and saved. Any
additional themes declared with the deftheme macro are added to the front of thislist.

custom-known-themes

load-theme theme &optional no-confirm no-enable[Command]This function loads the Custom theme named theme from its source file, looking forthe source file in the directories specified by the variable custom-theme-load-path.
See Section “Custom Themes” in The GNU Emacs Manual. It also enables the theme(unless the optional argument no-enable is non-nil), causing its variable and facesettings to take effect. It prompts the user for confirmation before loading the theme,
unless the optional argument no-confirm is non-nil.

require-theme feature &optional noerror[Function]
This function searches custom-theme-load-path for a file that provides feature andthen loads it. This is like the function require (see Section 16.7 [Named Features],page 309), except it searches custom-theme-load-path instead of load-path (seeSection 16.3 [Library Search], page 301). This can be useful in Custom themes thatneed to load supporting Lisp files when require is unsuitable for that.
If feature, which should be a symbol, is not already present in the current Emacs
session according to featurep, then require-theme searches for a file named feature
with an added ‘.elc’ or ‘.el’ suffix, in that order, in the directories specified bycustom-theme-load-path.

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If a file providing feature is successfully found and loaded, then require-theme returns
feature. The optional argument noerror determines what happens if the search or
loading fails. If it is nil, the function signals an error; otherwise, it returns nil. If
the file loads successfully but does not provide feature, then require-theme signals
an error; this cannot be suppressed.

enable-theme theme[Command]This function enables the Custom theme named theme. It signals an error if no suchtheme has been loaded.

disable-theme theme[Command]This function disables the Custom theme named theme. The theme remains loaded,
so that a subsequent call to enable-theme will re-enable it.

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16 Loading
Loading a file of Lisp code means bringing its contents into the Lisp environment in theform of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form,
and then closes the file. Such a file is also called a Lisp library.
The load functions evaluate all the expressions in a file just as the eval-buffer function
evaluates all the expressions in a buffer. The difference is that the load functions read andevaluate the text in the file as found on disk, not the text in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or as byte-compiled
code. Each form in the file is called a top-level form. There is no special format for the forms
in a loadable file; any form in a file may equally well be typed directly into a buffer andevaluated there. (Indeed, most code is tested this way.) Most often, the forms are function
definitions and variable definitions.
Emacs can also load compiled dynamic modules: shared libraries that provide additional
functionality for use in Emacs Lisp programs, just like a package written in Emacs Lisp
would. When a dynamic module is loaded, Emacs calls a specially-named initialization
function which the module needs to implement, and which exposes the additional functionsand variables to Emacs Lisp programs.
For on-demand loading of external libraries which are known in advance to be requiredby certain Emacs primitives, see Section 42.21 [Dynamic Libraries], page 1299.

16.1 How Programs Do Loading
Emacs Lisp has several interfaces for loading. For example, autoload creates a placeholder
object for a function defined in a file; trying to call the autoloading function loads the file toget the function’s real definition (see Section 16.5 [Autoload], page 304). require loads afile if it isn’t already loaded (see Section 16.7 [Named Features], page 309). Ultimately, allthese facilities call the load function to do the work.

load filename &optional missing-ok nomessage nosuffix must-suffix[Function]
This function finds and opens a file of Lisp code, evaluates all the forms in it, andcloses the file.
To find the file, load first looks for a file named filename.elc, that is, for a file whosename is filename with the extension ‘.elc’ appended. If such a file exists, and Emacs
was compiled with native-compilation support (see Chapter 18 [Native Compilation],
page 327), load attempts to find a corresponding ‘.eln’ file, and if found, loads it
instead of filename.elc. Otherwise, it loads filename.elc (and starts a backgroundnative compilation to produce the missing ‘.eln’ file, followed by loading that file).
If there is no filename.elc, then load looks for a file named filename.el. If thatfile exists, it is loaded. If Emacs was compiled with support for dynamic modules(see Section 16.11 [Dynamic Modules], page 314), load next looks for a file named
filename.ext, where ext is a system-dependent file-name extension of shared libraries(‘.so’ on GNU and Unix systems). Finally, if neither of those names is found, load
looks for a file named filename with nothing appended, and loads it if it exists. (Theload function is not clever about looking at filename. In the perverse case of a file
named foo.el.el, evaluation of (load "foo.el") will indeed find it.)

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If Auto Compression mode is enabled, as it is by default, then if load can not find afile, it searches for a compressed version of the file before trying other file names. It
decompresses and loads it if it exists. It looks for compressed versions by appending
each of the suffixes in jka-compr-load-suffixes to the file name. The value of thisvariable must be a list of strings. Its standard value is (".gz").
If the optional argument nosuffix is non-nil, then load does not try the suffixes ‘.elc’and ‘.el’. In this case, you must specify the precise file name you want, except that, if
Auto Compression mode is enabled, load will still use jka-compr-load-suffixes tofind compressed versions. By specifying the precise file name and using t for nosuffix,
you can prevent file names like foo.el.el from being tried.
If the optional argument must-suffix is non-nil, then load insists that the file nameused must end in either ‘.el’ or ‘.elc’ (possibly extended with a compression suffix)
or the shared-library extension, unless it contains an explicit directory name.
If the option load-prefer-newer is non-nil, then when searching suffixes, load
selects whichever version of a file (‘.elc’, ‘.el’, etc.) has been modified most recently.
In this case, load doesn’t load the ‘.eln’ natively-compiled file even if it exists.
If filename is a relative file name, such as foo or baz/foo.bar, load searches for the
file using the variable load-path. It appends filename to each of the directories listed
in load-path, and loads the first file it finds whose name matches. The current default
directory is tried only if it is specified in load-path, where nil stands for the default
directory. load tries all three possible suffixes in the first directory in load-path,then all three suffixes in the second directory, and so on. See Section 16.3 [Library
Search], page 301.
Whatever the name under which the file is eventually found, and the directory whereEmacs found it, Emacs sets the value of the variable load-file-name to that file’s
name.
If you get a warning that foo.elc is older than foo.el, it means you should consider
recompiling foo.el. See Chapter 17 [Byte Compilation], page 316.
When loading a source file (not compiled), load performs character set translation
just as Emacs would do when visiting the file. See Section 34.10 [Coding Systems],
page 976.
When loading an uncompiled file, Emacs tries to expand any macros that the filecontains (see Chapter 14 [Macros], page 268). We refer to this as eager macro
expansion. Doing this (rather than deferring the expansion until the relevant coderuns) can significantly speed up the execution of uncompiled code. Sometimes, thismacro expansion cannot be done, owing to a cyclic dependency. In the simplest
example of this, the file you are loading refers to a macro defined in another file, andthat file in turn requires the file you are loading. Emacs will issue an error about(‘Eager macro-expansion skipped due to cycle...’) giving details of the problem.
You have to restructure your code so that this does not happen. Loading a compiled
file does not cause macroexpansion, because this should already have happened duringcompilation. See Section 14.3 [Compiling Macros], page 270.
Messages like ‘Loading foo...’ and ‘Loading foo...done’ appear in the echo area
during loading unless nomessage is non-nil. If a natively-compiled ‘.eln’ file is loaded,
the message says so.

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Any unhandled errors while loading a file terminate loading. If the load was done forthe sake of autoload, any function definitions made during the loading are undone.
If load can’t find the file to load, then normally it signals a file-error (with ‘Cannot
open load file filename’). But if missing-ok is non-nil, then load just returns
nil.
You can use the variable load-read-function to specify a function for load to use
instead of read for reading expressions. See below.
load returns t if the file loads successfully.

load-file filename[Command]This command loads the file filename. If filename is a relative file name, then thecurrent default directory is assumed. This command does not use load-path, anddoes not append suffixes. However, it does look for compressed versions (if Auto
Compression Mode is enabled). Use this command if you wish to specify precisely thefile name to load.

load-library library[Command]This command loads the library named library. It is equivalent to load, except for
the way it reads its argument interactively. See Section “Lisp Libraries” in The GNU
Emacs Manual.
[Variable]
This variable is non-nil if Emacs is in the process of loading a file, and it is nilotherwise.

load-in-progress[Variable]
When Emacs is in the process of loading a file, this variable’s value is the name ofthat file, as Emacs found it during the search described earlier in this section.

load-file-name[Variable]
This variable specifies an alternate expression-reading function for load andeval-region to use instead of read. The function should accept one argument, justas read does.
By default, this variable’s value is read. See Section 20.3 [Input Functions], page 374.
Instead of using this variable, it is cleaner to use another, newer feature: to pass thefunction as the read-function argument to eval-region. See [Eval], page 153.

load-read-function

For information about how load is used in building Emacs, see Section E.1 [Building
Emacs], page 1346.

16.2 Load Suffixes
We now describe some technical details about the exact suffixes that load tries.
[Variable]
This is a list of suffixes indicating (compiled or source) Emacs Lisp files. It should
not include the empty string. load uses these suffixes in order when it appends
Lisp suffixes to the specified file name. The standard value is (".elc" ".el") which
produces the behavior described in the previous section.

load-suffixes

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301[Variable]
This is a list of suffixes that indicate representations of the same file. This list should
normally start with the empty string. When load searches for a file it appends thesuffixes in this list, in order, to the file name, before searching for another file.
Enabling Auto Compression mode appends the suffixes in jka-compr-load-suffixes
to this list and disabling Auto Compression mode removes them again. The standard
value of load-file-rep-suffixes if Auto Compression mode is disabled is ("").
Given that the standard value of jka-compr-load-suffixes is (".gz"), the standard value of load-file-rep-suffixes if Auto Compression mode is enabled is (""".gz").

load-file-rep-suffixes[Function]
This function returns the list of all suffixes that load should try, in order, when its
must-suffix argument is non-nil. This takes both load-suffixes and load-filerep-suffixes into account. If load-suffixes, jka-compr-load-suffixes andload-file-rep-suffixes all have their standard values, this function returns(".elc" ".elc.gz" ".el" ".el.gz") if Auto Compression mode is enabled and(".elc" ".el") if Auto Compression mode is disabled.

get-load-suffixes

To summarize, load normally first tries the suffixes in the value of (get-load-suffixes)
and then those in load-file-rep-suffixes. If nosuffix is non-nil, it skips the formergroup, and if must-suffix is non-nil, it skips the latter group.
[User Option]
If this option is non-nil, then rather than stopping at the first suffix that exists, load
tests them all, and uses whichever file is the newest.

load-prefer-newer

16.3 Library Search
When Emacs loads a Lisp library, it searches for the library in a list of directories specified
by the variable load-path.
[Variable]
The value of this variable is a list of directories to search when loading files with load.
Each element is a string (which must be a directory) or nil (which stands for thecurrent working directory).

load-path

When Emacs starts up, it sets up the value of load-path in several steps. First, it looks
for the directory containing its own Lisp files, using default locations set when Emacs wascompiled. It saves this directory in lisp-directory. Normally, this is a directory where
the *.elc files are installed, something like"/usr/local/share/emacs/version/lisp"
where version is the Emacs version. (In this and the following examples, replace /usr/local
with the prefix appropriate for your Emacs installation.) This directory and its subdirectories
contain the standard Lisp files that come with Emacs. If Emacs cannot find its own Lisp
files, it will not start correctly.
If you run Emacs from the directory where it was built—that is, an executable that has notbeen installed yet—Emacs instead initializes lisp-directory using the lisp subdirectoryof the directory containing the sources from which it was built.

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Emacs then initializes load-path with this lisp-directory. If you built Emacs in a
separate directory from the sources, it also adds the lisp subdirectory of the build directory.
All of these directories are stored in the above two variables as absolute file names.
Unless you start Emacs with the --no-site-lisp option, it then adds two moresite-lisp directories to the front of load-path. These are intended for locally installed
Lisp files, and are normally of the form:"/usr/local/share/emacs/version/site-lisp"
and"/usr/local/share/emacs/site-lisp"
The first one is for locally installed files for the current Emacs version; the second is for
locally installed files meant for use with any installed Emacs version. (If Emacs is running
uninstalled, it also adds site-lisp subdirectories from the source and build directories, if
they exist. However, normally the source and build directories do not contain site-lisp
subdirectories.)
If the environment variable EMACSLOADPATH is set, it modifies the above initialization
procedure. Emacs initializes load-path based on the value of the environment variable.
The syntax of EMACSLOADPATH is the same as used for PATH; directories are separated by‘:’ (or ‘;’, on some operating systems). Here is an example of how to set EMACSLOADPATH
variable (from a sh-style shell):export EMACSLOADPATH=/home/foo/.emacs.d/lisp:
An empty element in the value of the environment variable, whether trailing (as in theabove example, note the trailing ‘:’), leading, or embedded, is replaced by the default valueof load-path as determined by the standard initialization procedure. If there are no such
empty elements, then EMACSLOADPATH specifies the entire load-path. You must include
either an empty element, or the explicit path to the directory containing the standard Lisp
files, else Emacs will not function. (Another way to modify load-path is to use the -L
command-line option when starting Emacs; see below.)
For each directory in load-path, Emacs then checks to see if it contains a file subdirs.el,and if so, loads it. The subdirs.el file is created when Emacs is built/installed, and contains
code that causes Emacs to add any subdirectories of those directories to load-path. Both
immediate subdirectories and subdirectories multiple levels down are added. But it excludes
subdirectories whose names do not start with a letter or digit, and subdirectories named
RCS or CVS, and subdirectories containing a file named .nosearch.
Next, Emacs adds any extra load directories that you specify using the -L command-line
option (see Section “Action Arguments” in The GNU Emacs Manual). It also adds the
directories where optional packages are installed, if any (see Section 43.1 [Packaging Basics],
page 1303).
It is common to add code to one’s init file (see Section 42.1.2 [Init File], page 1258) to
add one or more directories to load-path. For example:(push "~/.emacs.d/lisp" load-path)
See Section 5.5 [List Variables], page 85, for the description of push.
Dumping Emacs uses a special value of load-path. If you use a site-load.el orsite-init.el file to customize the dumped Emacs (see Section E.1 [Building Emacs],
page 1346), any changes to load-path that these files make will be lost after dumping.

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303[Variable]
This variable holds a string naming the directory which holds Emacs’s own *.eland *.elc files. This is usually the place where those files are located in the Emacs
installation tree, unless Emacs is run from its build directory in which case it points
to the lisp subdirectory in the source directory from which Emacs was built.

lisp-directory

locate-library library &optional nosuffix path interactive-call[Command]This command finds the precise file name for library library. It searches for the libraryin the same way load does, and the argument nosuffix has the same meaning as inload: don’t add suffixes ‘.elc’ or ‘.el’ to the specified name library.
If the path is non-nil, that list of directories is used instead of load-path.

When locate-library is called from a program, it returns the file name as a string.
When the user runs locate-library interactively, the argument interactive-call is t,
and this tells locate-library to display the file name in the echo area.

list-load-path-shadows &optional stringp[Command]This command shows a list of shadowed Emacs Lisp files. A shadowed file is one thatwill not normally be loaded, despite being in a directory on load-path, due to theexistence of another similarly-named file in a directory earlier on load-path.
For instance, suppose load-path is set to("/opt/emacs/site-lisp" "/usr/share/emacs/29.1/lisp")
and that both these directories contain a file named foo.el. Then (require 'foo)
never loads the file in the second directory. Such a situation might indicate a problem
in the way Emacs was installed.

When called from Lisp, this function prints a message listing the shadowed files, insteadof displaying them in a buffer. If the optional argument stringp is non-nil, it instead
returns the shadowed files as a string.
If Emacs was compiled with support for native compilation (see Chapter 18 [Native
Compilation], page 327), then when a ‘.elc’ byte-compiled file is found by searchingload-path, Emacs will try to look for a corresponding ‘.eln’ file holding the corresponding
natively-compiled code. The natively-compiled files are looked up in the directories listed by
the native-comp-eln-load-path.
[Variable]
This variable holds a list of directories where Emacs looks for natively-compiled‘.eln’ files. File names in the list that are not absolute are interpreted as relative to
invocation-directory (see Section 42.3 [System Environment], page 1265). The last
directory in the list is the system directory, i.e. the directory with ‘.eln’ files installedby the Emacs build and installation procedure. In each of the directories in the list,
Emacs looks for ‘.eln’ files in a subdirectory whose name is constructed from the Emacs
version and an 8-character hash that depends on the current native-compilation ABI;
the name of this subdirectory is stored in the variable comp-native-version-dir.

native-comp-eln-load-path

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16.4 Loading Non-ASCII Characters
When Emacs Lisp programs contain string constants with non-ASCII characters, these can be
represented within Emacs either as unibyte strings or as multibyte strings (see Section 34.1
[Text Representations], page 963). Which representation is used depends on how the fileis read into Emacs. If it is read with decoding into multibyte representation, the text of
the Lisp program will be multibyte text, and its string constants will be multibyte strings.
If a file containing Latin-1 characters (for example) is read without decoding, the text ofthe program will be unibyte text, and its string constants will be unibyte strings. See
Section 34.10 [Coding Systems], page 976.
In most Emacs Lisp programs, the fact that non-ASCII strings are multibyte strings
should not be noticeable, since inserting them in unibyte buffers converts them to unibyte
automatically. However, if this does make a difference, you can force a particular Lisp file to
be interpreted as unibyte by writing ‘coding: raw-text’ in a local variables section. With
that designator, the file will unconditionally be interpreted as unibyte. This can matter
when making key bindings to non-ASCII characters written as ?vliteral.

16.5 Autoload
The autoload facility lets you register the existence of a function or macro, but put off
loading the file that defines it. The first call to the function automatically loads the proper
library, in order to install the real definition and other associated code, then runs the real
definition as if it had been loaded all along. Autoloading can also be triggered by looking
up the documentation of the function or macro (see Section 25.1 [Documentation Basics],
page 595), and completion of variable and function names (see Section 16.5.1 [Autoload by
Prefix], page 307, below).
There are two ways to set up an autoloaded function: by calling autoload, and by
writing a “magic” comment in the source before the real definition. autoload is the low-level
primitive for autoloading; any Lisp program can call autoload at any time. Magic comments
are the most convenient way to make a function autoload, for packages installed along with
Emacs. These comments do nothing on their own, but they serve as a guide for the command
loaddefs-generate, which constructs calls to autoload and arranges to execute them when
Emacs is built.

autoload function filename &optional docstring interactive type

[Function]
This function defines the function (or macro) named function so as to load automaticallyfrom filename. The string filename specifies the file to load to get the real definitionof function.
If filename does not contain either a directory name, or the suffix .el or .elc, thisfunction insists on adding one of these suffixes, and it will not load from a file whosename is just filename with no added suffix. (The variable load-suffixes specifies
the exact required suffixes.)
The argument docstring is the documentation string for the function. Specifying
the documentation string in the call to autoload makes it possible to look at the
documentation without loading the function’s real definition. Normally, this should
be identical to the documentation string in the function definition itself. If it isn’t,
the function definition’s documentation string takes effect when it is loaded.

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If interactive is non-nil, that says function can be called interactively. This lets
completion in M-x work without loading function’s real definition. The complete
interactive specification is not given here; it’s not needed unless the user actually calls
function, and when that happens, it’s time to load the real definition.
If interactive is a list, it is interpreted as a list of modes this command is applicablefor.
You can autoload macros and keymaps as well as ordinary functions. Specify typeas macro if function is really a macro. Specify type as keymap if function is really akeymap. Various parts of Emacs need to know this information without loading thereal definition.
An autoloaded keymap loads automatically during key lookup when a prefix key’s
binding is the symbol function. Autoloading does not occur for other kinds of access to
the keymap. In particular, it does not happen when a Lisp program gets the keymap
from the value of a variable and calls keymap-set; not even if the variable name isthe same symbol function.
If function already has a non-void function definition that is not an autoload object,
this function does nothing and returns nil. Otherwise, it constructs an autoload
object (see Section 2.4.19 [Autoload Type], page 25), and stores it as the function
definition for function. The autoload object has this form:(autoload filename docstring interactive type)For example,(symbol-function 'run-prolog)⇒ (autoload "prolog" 169681 t nil)
In this case, "prolog" is the name of the file to load, 169681 refers to the documentation
string in the emacs/etc/DOC file (see Section 25.1 [Documentation Basics], page 595),
t means the function is interactive, and nil that it is not a macro or a keymap.

autoloadp object[Function]
This function returns non-nil if object is an autoload object. For example, to checkif run-prolog is defined as an autoloaded function, evaluate(autoloadp (symbol-function 'run-prolog))

The autoloaded file usually contains other definitions and may require or provide one
or more features. If the file is not completely loaded (due to an error in the evaluation of
its contents), any function definitions or provide calls that occurred during the load areundone. This is to ensure that the next attempt to call any function autoloading from thisfile will try again to load the file. If not for this, then some of the functions in the file might
be defined by the aborted load, but fail to work properly for the lack of certain subroutines
not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or macro, then an error issignaled with data "Autoloading failed to define function function-name".
A magic autoload comment (often called an autoload cookie) consists of ‘;;;###autoload’,
on a line by itself, just before the real definition of the function in its autoloadable source file.
The function loaddefs-generate writes a corresponding autoload call into loaddefs.el.
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loaddefs-generate can be changed from the above defaults, see below.) Building Emacs
loads loaddefs.el and thus calls autoload.
The same magic comment can copy any kind of form into loaddefs.el. The form
following the magic comment is copied verbatim, except if it is one of the forms which theautoload facility handles specially (e.g., by conversion into an autoload call). The forms
which are not copied verbatim are the following:
Definitions for function or function-like objects:
defun and defmacro; also cl-defun and cl-defmacro (see Section “Argument
Lists” in Common Lisp Extensions), and define-overloadable-function (seethe commentary in mode-local.el).
Definitions for major or minor modes:
define-minor-mode, define-globalized-minor-mode, define-genericmode,
define-derived-mode,easy-mmode-define-minor-mode,easy-mmode-define-global-mode,
define-compilation-mode,
anddefine-global-minor-mode.
Other definition types:
defcustom,
defgroup,
deftheme,define-skeleton (see Autotyping).

defclass(see

EIEIO),

andYou can also use a magic comment to execute a form at build time without executing
it when the file itself is loaded. To do this, write the form on the same line as the magiccomment. Since it is in a comment, it does nothing when you load the source file; but
loaddefs-generate copies it to loaddefs.el, where it is executed while building Emacs.
The following example shows how doctor is prepared for autoloading with a magiccomment:;;;###autoload(defun doctor ()"Switch to *doctor* buffer and start giving psychotherapy."(interactive)(switch-to-buffer "*doctor*")(doctor-mode))
Here’s what that produces in loaddefs.el:(autoload 'doctor "doctor" "\Switch to *doctor* buffer and start giving psychotherapy.
\(fn)" t nil)
While the loaddefs.el isn’t for editing, we try to keep it somewhat readable for people.
For instance, control characters in defvar values are escaped, and we insert a backslash andnewline immediately following the double-quote of the doc string to keep the line length
down. ‘(fn)’ in the usage part of the documentation string is replaced with the function’sname when the various help functions (see Section 25.6 [Help Functions], page 602) display
it.
If you write a function definition with an unusual macro that is not one of the known
and recognized function definition methods, use of an ordinary magic autoload comment

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would copy the whole definition into loaddefs.el. That is not desirable. You can put thedesired autoload call into loaddefs.el instead by writing this:;;;###autoload (autoload 'foo "myfile")(mydefunmacro foo...)
You can use a non-default string as the autoload cookie and have the corresponding
autoload calls written into a file whose name is different from the default loaddefs.el.
Emacs provides two variables to control this:[Variable]
The value of this constant is a regexp that matches autoload cookies.
loaddefs-generate copies the Lisp form that follows the cookie into the
autoload file it generates. This will match comments like ‘;;;###autoload’ and‘;;;###calc-autoload’.

lisp-mode-autoload-regexp[Variable]
The value of this variable names an Emacs Lisp file where the autoload calls should
go. The default value is loaddefs.el, but you can override that, e.g., in the local
variables section of a .el file (see Section 12.12 [File Local Variables], page 213). The
autoload file is assumed to contain a trailer starting with a formfeed character.

generated-autoload-file

The following function may be used to explicitly load the library specified by an autoload
object:autoload-do-load autoload &optional name macro-only[Function]
This function performs the loading specified by autoload, which should be an autoload
object. The optional argument name, if non-nil, should be a symbol whose function
value is autoload; in that case, the return value of this function is the symbol’s new
function value. If the value of the optional argument macro-only is macro, this function
avoids loading a function, only a macro.

16.5.1 Autoload by Prefix
During completion for the commands describe-variable and describe-function,
Emacs will try to load files which may contain definitions matching the prefix being
completed. The variable definition-prefixes holds a hashtable which maps a prefix tothe corresponding list of files to load for it. Entries to this mapping are added by calls
to register-definition-prefixes which are generated by loaddefs-generate (seeSection 16.5 [Autoload], page 304). Files which don’t contain any definitions worth loading(test files, for example), should set autoload-compute-prefixes to nil as a file-local
variable.

16.5.2 When to Use Autoload
Do not add an autoload comment unless it is really necessary. Autoloading code means it isalways globally visible. Once an item is autoloaded, there is no compatible way to transition
back to it not being autoloaded (after people become accustomed to being able to use it
without an explicit load).
• The most common items to autoload are the interactive entry points to a library. For
example, if python.el is a library defining a major-mode for editing Python code,

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autoload the definition of the python-mode function, so that people can simply use M-x
python-mode to load the library.
• Variables usually don’t need to be autoloaded. An exception is if the variable on its
own is generally useful without the whole defining library being loaded. (An example ofthis might be something like find-exec-terminator.)• Don’t autoload a user option just so that a user can set it.
• Never add an autoload comment to silence a compiler warning in another file. In the filethat produces the warning, use (defvar foo) to silence an undefined variable warning,and declare-function (see Section 13.16 [Declaring Functions], page 265) to silence an
undefined function warning; or require the relevant library; or use an explicit autoloadstatement.

16.6 Repeated Loading
You can load a given file more than once in an Emacs session. For example, after you haverewritten and reinstalled a function definition by editing it in a buffer, you may wish to
return to the original version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the load and load-library functions
automatically load a byte-compiled file rather than a non-compiled file of similar name.
If you rewrite a file that you intend to save and reinstall, you need to byte-compile thenew version; otherwise Emacs will load the older, byte-compiled file instead of your newer,
non-compiled file! If that happens, the message displayed when loading the file includes,‘(compiled; note, source is newer)’, to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the file might be loaded
more than once. For example, think about whether each variable should be reinitialized
when you reload the library; defvar does not change the value if the variable is alreadyinitialized. (See Section 12.5 [Defining Variables], page 194.)
The simplest way to add an element to an alist is like this:(push '(leif-mode " Leif") minor-mode-alist)
But this would add multiple elements if the library is reloaded. To avoid the problem, use
add-to-list (see Section 5.5 [List Variables], page 85):(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Occasionally you will want to test explicitly whether a library has already been loaded.
If the library uses provide to provide a named feature, you can use featurep earlier in thefile to test whether the provide call has been executed before (see Section 16.7 [Named
Features], page 309). Alternatively, you could use something like this:(defvar foo-was-loaded nil)(unless foo-was-loaded
execute-first-time-only(setq foo-was-loaded t))

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16.7 Features
provide and require are an alternative to autoload for loading files automatically. They
work in terms of named features. Autoloading is triggered by calling a specific function, but
a feature is loaded the first time another program asks for it by name.
A feature name is a symbol that stands for a collection of functions, variables, etc. The
file that defines them should provide the feature. Another program that uses them may
ensure they are defined by requiring the feature. This loads the file of definitions if it hasn’t
been loaded already.
To require the presence of a feature, call require with the feature name as argument.
require looks in the global variable features to see whether the desired feature has been
provided already. If not, it loads the feature from the appropriate file. This file should callprovide at the top level to add the feature to features; if it fails to do so, require signals
an error.
For example, in idlwave.el, the definition for idlwave-complete-filename includes
the following code:(defun idlwave-complete-filename ()"Use the comint stuff to complete a file name."(require 'comint)(let* ((comint-file-name-chars "~/A-Za-z0-9+@:_.$#%={}\\-")(comint-completion-addsuffix nil)...)(comint-dynamic-complete-filename)))
The expression (require 'comint) loads the file comint.el if it has not yet been loaded, ensuring that comint-dynamic-complete-filename is defined. Features are normally named
after the files that provide them, so that require need not be given the file name. (Notethat it is important that the require statement be outside the body of the let. Loading
a library while its variables are let-bound can have unintended consequences, namely thevariables becoming unbound after the let exits.)
The comint.el file contains the following top-level expression:(provide 'comint)
This adds comint to the global features list, so that (require 'comint) will henceforthknow that nothing needs to be done.
When require is used at top level in a file, it takes effect when you byte-compile thatfile (see Chapter 17 [Byte Compilation], page 316) as well as when you load it. This is incase the required package contains macros that the byte compiler must know about. It also
avoids byte compiler warnings for functions and variables defined in the file loaded withrequire.
Although top-level calls to require are evaluated during byte compilation, provide calls
are not. Therefore, you can ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same feature, as in the following
example.
(provide 'my-feature) ; Ignored by byte compiler,;
evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.

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The compiler ignores the provide, then processes the require by loading the file in question.
Loading the file does execute the provide call, so the subsequent require call does nothing
when the file is loaded.

provide feature &optional subfeatures[Function]
This function announces that feature is now loaded, or being loaded, into the current
Emacs session. This means that the facilities associated with feature are or will beavailable for other Lisp programs.
The direct effect of calling provide is to add feature to the front of features if it
is not already in that list and call any eval-after-load code waiting for it (seeSection 16.10 [Hooks for Loading], page 313). The argument feature must be a symbol.
provide returns feature.
If provided, subfeatures should be a list of symbols indicating a set of specific subfeatures provided by this version of feature. You can test the presence of a subfeatureusing featurep. The idea of subfeatures is that you use them when a package (which
is one feature) is complex enough to make it useful to give names to various partsor functionalities of the package, which might or might not be loaded, or might or
might not be present in a given version. See Section 40.17.3 [Network Feature Testing],
page 1119, for an example.
features⇒ (bar bish)(provide 'foo)⇒ foofeatures⇒ (foo bar bish)
When a file is loaded to satisfy an autoload, and it stops due to an error in theevaluation of its contents, any function definitions or provide calls that occurred
during the load are undone. See Section 16.5 [Autoload], page 304.

require feature &optional filename noerror[Function]
This function checks whether feature is present in the current Emacs session (using(featurep feature); see below). The argument feature must be a symbol.
If the feature is not present, then require loads filename with load. If filename is
not supplied, then the name of the symbol feature is used as the base file name toload. However, in this case, require insists on finding feature with an added ‘.el’ or‘.elc’ suffix (possibly extended with a compression suffix); a file whose name is justfeature won’t be used. (The variable load-suffixes specifies the exact required Lisp
suffixes.)
If noerror is non-nil, that suppresses errors from actual loading of the file. In thatcase, require returns nil if loading the file fails. Normally, require returns feature.
If loading the file succeeds but does not provide feature, require signals an error
about the missing feature.

featurep feature &optional subfeature[Function]
This function returns t if feature has been provided in the current Emacs session(i.e., if feature is a member of features.) If subfeature is non-nil, then the function

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returns t only if that subfeature is provided as well (i.e., if subfeature is a member ofthe subfeature property of the feature symbol.)[Variable]
The value of this variable is a list of symbols that are the features loaded in the current
Emacs session. Each symbol was put in this list with a call to provide. The order ofthe elements in the features list is not significant.

features

The use-package macro provides a convenient way of loading a feature and configuring it
for use. It provides a means to combine requiring a feature, like require does, with code to be
run when the feature is actually loaded, similar to load-time hooks (see Section 16.10 [Hooks
for Loading], page 313). The declarative syntax of use-package makes it exceptionally easy
to use in user init files.

use-package feature &rest args

[Macro]This macro specifies how to load the named feature and how to configure and customize
it for use. The arguments args are keyword-value pairs. Some of the important
keywords and their values are::init forms
Specifies forms to execute before feature is loaded.
:config forms
Specifies forms to execute after loading feature.
:defer condition
If condition is non-nil, it specifies to defer loading feature until any of the
autoloaded commands or variables of feature are first used. If condition
is a number n, it specifies that feature should be loaded after n seconds ofidle time.
:commands commands...
Specifies commands of feature to be autoloaded.
:bind keybindings...
Specifies the keybindings for features commands. Each binding has theform(key-sequence . command)or(:map keymap (key-sequence . command))
where key-sequence is in the form accepted by the kbd macro (seeSection 23.1 [Key Sequences], page 480).
For more details about use-package, see use-package User Manual.

16.8 Which File Defined a Certain Symbol
symbol-file symbol &optional type native-p[Function]
This function returns the name of the file that defined symbol. If type is nil, then any
kind of definition is acceptable. If type is defun, defvar, or defface, that specifies
function definition, variable definition, or face definition only.

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The value is normally an absolute file name. It can also be nil, if the definition is not
associated with any file. If symbol specifies an autoloaded function, the value can bea relative file name without extension.
If the optional third argument native-p is non-nil, and Emacs was built with native
compilation support (see Chapter 18 [Native Compilation], page 327), this function
will try to find the .eln file that defined symbol, instead of the .elc or .el file. Ifsuch a .eln file is found and is not outdated, the function will return its absolute filename; otherwise it will report the name of either the source or the byte-compiled file.
The basis for symbol-file is the data in the variable load-history.
[Variable]
The value of this variable is an alist that associates the names of loaded library files
with the names of the functions and variables they defined, as well as the features
they provided or required.
Each element in this alist describes one loaded library (including libraries that are
preloaded at startup). It is a list whose car is the absolute file name of the library (astring). The rest of the list elements have these forms:

load-historyvar

The symbol var was defined as a variable.

(defun . fun)The function fun was defined. (defun . fun), which represents defining
fun as a function.
(defface . face)
The face face was defined.
(require . feature)
The feature feature was required.
(provide . feature)
The feature feature was provided.
(cl-defmethod method specializers)
The named method was defined by using cl-defmethod, with specializers
as its specializers.
(define-type . type)
The type type was defined.
The value of load-history may have one element whose car is nil. This element
describes definitions made with eval-buffer on a buffer that is not visiting a file.
The command eval-region updates load-history, but does so by adding the symbols
defined to the element for the file being visited, rather than replacing that element. See
Section 10.4 [Eval], page 152.
In addition to load-history, every function keeps track of its own history in the symbol
property function-history. The reason why functions are treated specially in this respectis that it is common for functions to be defined in two steps in two different files (typically,
one of them is an autoload), so in order to be able to properly unload a file, we need toknow more precisely what that file did to the function definition.

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The symbol property function-history holds a list of the form (file1 def2 file2 def3 ...),
where file1 is the last file that changed the definition and def2 was the definition before file1,
set by file2, etc. Logically this list should end with the name of the first file that defined
this function, but to save space this last element is usually omitted.

16.9 Unloading
You can discard the functions and variables loaded by a library to reclaim memory for other
Lisp objects. To do this, use the function unload-feature:

unload-feature feature &optional force[Command]This command unloads the library that provided feature feature. It undefines all functions, macros, and variables defined in that library with defun, defalias, defsubst,
defmacro, defconst, defvar, and defcustom. It then restores any autoloads formerly associated with those symbols. (Loading saves these in the function-history
property of the symbol.)
Before restoring the previous definitions, unload-feature runs remove-hook to remove functions defined by the library from certain hooks. These hooks include variables
whose names end in ‘-hook’ (or the deprecated suffix ‘-hooks’), plus those listed in
unload-feature-special-hooks, as well as auto-mode-alist. This is to prevent
Emacs from ceasing to function because important hooks refer to functions that are
no longer defined.
Standard unloading activities also undo ELP profiling of functions in that library,
unprovides any features provided by the library, and cancels timers held in variables
defined by the library.
If these measures are not sufficient to prevent malfunction, a library can define an
explicit unloader named feature-unload-function. If that symbol is defined as afunction, unload-feature calls it with no arguments before doing anything else. It can
do whatever is appropriate to unload the library. If it returns nil, unload-featureproceeds to take the normal unload actions. Otherwise it considers the job to be done.
Ordinarily, unload-feature refuses to unload a library on which other loaded libraries
depend. (A library a depends on library b if a contains a require for b.) If theoptional argument force is non-nil, dependencies are ignored and you can unload any
library.

The unload-feature function is written in Lisp; its actions are based on the variableload-history.
[Variable]
This variable holds a list of hooks to be scanned before unloading a library, to remove
functions defined in the library.

unload-feature-special-hooks

16.10 Hooks for Loading
You can ask for code to be executed each time Emacs loads a library, by using the variable
after-load-functions:Chapter 16: Loading

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This abnormal hook is run after loading a file. Each function in the hook is calledwith a single argument, the absolute filename of the file that was just loaded.

after-load-functions

If you want code to be executed when a particular library is loaded, use the macro
with-eval-after-load:

with-eval-after-load library body. . .

[Macro]This macro arranges to evaluate body at the end of loading the file library, each time
library is loaded. If library is already loaded, it evaluates body right away.

You don’t need to give a directory or extension in the file name library. Normally, youjust give a bare file name, like this:(with-eval-after-load "js" (keymap-set js-mode-map "C-c C-c" 'js-eval))
To restrict which files can trigger the evaluation, include a directory or an extension
or both in library. Only a file whose absolute true name (i.e., the name with all
symbolic links chased out) matches all the given name components will match. In thefollowing example, my_inst.elc or my_inst.elc.gz in some directory ..../foo/bar
will trigger the evaluation, but not my_inst.el:(with-eval-after-load "foo/bar/my_inst.elc" ...)
library can also be a feature (i.e., a symbol), in which case body is evaluated at theend of any file where (provide library) is called.
An error in body does not undo the load, but does prevent execution of the rest of
body.
Normally, well-designed Lisp programs should not use with-eval-after-load. If you
need to examine and set the variables defined in another library (those meant for outsideuse), you can do it immediately—there is no need to wait until the library is loaded. If you
need to call functions defined by that library, you should load the library, preferably withrequire (see Section 16.7 [Named Features], page 309).

16.11 Emacs Dynamic Modules
A dynamic Emacs module is a shared library that provides additional functionality for use
in Emacs Lisp programs, just like a package written in Emacs Lisp would.
Functions that load Emacs Lisp packages can also load dynamic modules. They recognize
dynamic modules by looking at their file-name extension, a.k.a. “suffix”. This suffix is
platform-dependent.
[Variable]
This variable holds the system-dependent value of the file-name extension of the module
files. Its value is .so on POSIX hosts, .dylib on macOS, and .dll on MS-Windows.

module-file-suffix

On macOS, dynamic modules can also have the suffix .so in addition to .dylib.
Every dynamic module should export a C-callable function named emacs_module_init,
which Emacs will call as part of the call to load or require which loads the module. It
should also export a symbol named plugin_is_GPL_compatible to indicate that its code isChapter 16: Loading315

released under the GPL or compatible license; Emacs will signal an error if your program
tries to load modules that don’t export such a symbol.
If a module needs to call Emacs functions, it should do so through the API (Application
Programming Interface) defined and documented in the header file emacs-module.h that ispart of the Emacs distribution. See Section E.8 [Writing Dynamic Modules], page 1361, fordetails of using that API when writing your own modules.
Modules can create user-ptr Lisp objects that embed pointers to C struct’s defined by
the module. This is useful for keeping around complex data structures created by a module,
to be passed back to the module’s functions. User-ptr objects can also have associated
finalizers – functions to be run when the object is GC’ed; this is useful for freeing any
resources allocated for the underlying data structure, such as memory, open file descriptors,
etc. See Section E.8.3 [Module Values], page 1366.

user-ptrp object[Function]

This function returns t if its argument is a user-ptr object.

module-load file

[Function]
Emacs calls this low-level primitive to load a module from the specified file andperform the necessary initialization of the module. This is the primitive which makes
sure the module exports the plugin_is_GPL_compatible symbol, calls the module’s
emacs_module_init function, and signals an error if that function returns an error
indication, or if the user typed C-g during the initialization. If the initialization
succeeds, module-load returns t. Note that file must already have the proper filename extension, as this function doesn’t try looking for files with known extensions,unlike load.
Unlike load, module-load doesn’t record the module in load-history, doesn’t print
any messages, and doesn’t protect against recursive loads. Most users should therefore
use load, load-file, load-library, or require instead of module-load.

Loadable modules in Emacs are enabled by using the --with-modules option at configure
time.

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17 Byte Compilation
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp
function definitions with byte-code. When a byte-code function is called, its definition isevaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead ofbeing executed directly by the machine’s hardware (as true compiled code is), byte-code iscompletely transportable from machine to machine without recompilation. It is not, however,as fast as true compiled code.
In general, any version of Emacs can run byte-compiled code produced by recent earlier
versions of Emacs, but the reverse is not true.
If you do not want a Lisp file to be compiled, ever, put a file-local variable binding forno-byte-compile into it, like this:;; -*-no-byte-compile: t; -*-17.1 Performance of Byte-Compiled CodeA byte-compiled function is not as efficient as a primitive function written in C, but runs
much faster than the version written in Lisp. Here is an example:(defun silly-loop (n)"Return the time, in seconds, to run N iterations of a loop."(let ((t1 (float-time)))(while (> (setq n (1- n)) 0))(- (float-time) t1)))⇒ silly-loop(silly-loop 50000000)⇒ 5.200886011123657(byte-compile 'silly-loop)⇒ [Compiled code not shown](silly-loop 50000000)⇒ 0.6239290237426758
In this example, the interpreted code required more than 5 seconds to run, whereas thebyte-compiled code required less than 1 second. These results are representative, but actual
results may vary.

17.2 Byte-Compilation Functions
You can byte-compile an individual function or macro definition with the byte-compile
function. You can compile a whole file with byte-compile-file, or several files withbyte-recompile-directory or batch-byte-compile.
Sometimes, the byte compiler produces warning and/or error messages (see Section 17.6
[Compiler Errors], page 321, for details). These messages are normally recorded in a bufferChapter 17: Byte Compilation

317

called *Compile-Log*, which uses Compilation mode. See Section “Compilation Mode” in
The GNU Emacs Manual. However, if the variable byte-compile-debug is non-nil, error
messages will be signaled as Lisp errors instead (see Section 11.7.3 [Errors], page 179).
Be careful when writing macro calls in files that you intend to byte-compile. Since macro
calls are expanded when they are compiled, the macros need to be loaded into Emacs or thebyte compiler will not do the right thing. The usual way to handle this is with require forms
which specify the files containing the needed macro definitions (see Section 16.7 [Named
Features], page 309). Normally, the byte compiler does not evaluate the code that it iscompiling, but it handles require forms specially, by loading the specified libraries. To
avoid loading the macro definition files when someone runs the compiled program, write
eval-when-compile around the require calls (see Section 17.5 [Eval During Compile],
page 320). For more details, See Section 14.3 [Compiling Macros], page 270.
Inline (defsubst) functions are less troublesome; if you compile a call to such a function
before its definition is known, the call will still work right, it will just run slower.

byte-compile symbol[Function]
This function byte-compiles the function definition of symbol, replacing the previous
definition with the compiled one. The function definition of symbol must be the actual
code for the function; byte-compile does not handle function indirection. The return
value is the byte-code function object which is the compiled definition of symbol (seeSection 17.7 [Byte-Code Objects], page 323).
(defun factorial (integer)"Compute factorial of INTEGER."(if (= 1 integer) 1(* integer (factorial (1- integer)))))⇒ factorial(byte-compile 'factorial)⇒#[257"\211\300U\203^H^@\300\207\211\301^BS!_\207"[1 factorial] 4"Compute factorial of INTEGER.\n\n(fn INTEGER)"]If symbol’s definition is a byte-code function object, byte-compile does nothing andreturns nil. It does not compile the symbol’s definition again, since the original(non-compiled) code has already been replaced in the symbol’s function cell by thebyte-compiled code.
The argument to byte-compile can also be a lambda expression. In that case, thefunction returns the corresponding compiled code but does not store it anywhere.

compile-defun &optional arg[Command]This command reads the defun containing point, compiles it, and evaluates the result.
If you use this on a defun that is actually a function definition, the effect is to install
a compiled version of that function.
compile-defun normally displays the result of evaluation in the echo area, but if arg
is non-nil, it inserts the result in the current buffer after the form it has compiled.

Chapter 17: Byte Compilation318

byte-compile-file filename[Command]This function compiles a file of Lisp code named filename into a file of byte-code. The
output file’s name is made by changing the ‘.el’ suffix into ‘.elc’; if filename does
not end in ‘.el’, it adds ‘.elc’ to the end of filename.
Compilation works by reading the input file one form at a time. If it is a definition ofa function or macro, the compiled function or macro definition is written out. Other
forms are batched together, then each batch is compiled, and written so that its
compiled code will be executed when the file is read. All comments are discarded
when the input file is read.
This command returns t if there were no errors and nil otherwise. When calledinteractively, it prompts for the file name.
$ ls -l push*-rw-r--r-- 1 lewis lewis 791 Oct 5 20:31 push.el(byte-compile-file "~/emacs/push.el")⇒ t$ ls -l push*-rw-r--r-- 1 lewis lewis 791 Oct-rw-rw-rw- 1 lewis lewis 638 Oct

5 20:31 push.el
8 20:25 push.elc

byte-recompile-directory directory &optional flag force
follow-symlinks[Command]This command recompiles every ‘.el’ file in directory (or its subdirectories) thatneeds recompilation. A file needs recompilation if a ‘.elc’ file exists but is older thanthe ‘.el’ file.
When a ‘.el’ file has no corresponding ‘.elc’ file, flag says what to do. If it is nil,this command ignores these files. If flag is 0, it compiles them. If it is neither nil nor
0, it asks the user whether to compile each such file, and asks about each subdirectoryas well.
Interactively, byte-recompile-directory prompts for directory and flag is the prefix
argument.
If force is non-nil, this command recompiles every ‘.el’ file that has a ‘.elc’ file.
This command will normally not compile ‘.el’ files that are symlinked. If the optional
follow-symlink parameter is non-nil, symlinked ‘.el’ will also be compiled.
The returned value is unpredictable.

batch-byte-compile &optional noforce[Function]
This function runs byte-compile-file on files specified on the command line. Thisfunction must be used only in a batch execution of Emacs, as it kills Emacs oncompletion. An error in one file does not prevent processing of subsequent files, but
no output file will be generated for it, and the Emacs process will terminate with anonzero status code.
If noforce is non-nil, this function does not recompile files that have an up-to-date‘.elc’ file.
$ emacs -batch -f batch-byte-compile *.el

Chapter 17: Byte Compilation319

17.3 Documentation Strings and Compilation
When Emacs loads functions and variables from a byte-compiled file, it normally does notload their documentation strings into memory. Each documentation string is dynamicallyloaded from the byte-compiled file only when needed. This saves memory, and speeds up
loading by skipping the processing of the documentation strings.
This feature has a drawback: if you delete, move, or alter the compiled file (such as bycompiling a new version), Emacs may no longer be able to access the documentation stringof previously-loaded functions or variables. Such a problem normally only occurs if you
build Emacs yourself, and happen to edit and/or recompile the Lisp source files. To solve it,just reload each file after recompilation.
Dynamic loading of documentation strings from byte-compiled files is determined, atcompile time, for each byte-compiled file. It can be disabled via the option byte-compiledynamic-docstrings.
[User Option]
If this is non-nil, the byte compiler generates compiled files that are set up for
dynamic loading of documentation strings.

byte-compile-dynamic-docstrings

To disable the dynamic loading feature for a specific file, set this option to nil in its
header line (see Section “Local Variables in Files” in The GNU Emacs Manual), likethis:-*-byte-compile-dynamic-docstrings: nil;-*-This is useful mainly if you expect to change the file, and you want Emacs sessions
that have already loaded it to keep working when the file changes.
Internally, the dynamic loading of documentation strings is accomplished by writing
compiled files with a special Lisp reader construct, ‘#@count’. This construct skips the next
count characters. It also uses the ‘#$’ construct, which stands for the name of this file, as astring. Do not use these constructs in Lisp source files; they are not designed to be clear tohumans reading the file.

17.4 Dynamic Loading of Individual Functions
When you compile a file, you can optionally enable the dynamic function loading feature(also known as lazy loading). With dynamic function loading, loading the file doesn’t
fully read the function definitions in the file. Instead, each function definition contains aplace-holder which refers to the file. The first time each function is called, it reads the fulldefinition from the file, to replace the place-holder.
The advantage of dynamic function loading is that loading the file should become faster.
This is a good thing for a file which contains many separate user-callable functions, if using
one of them does not imply you will probably also use the rest. A specialized mode which
provides many keyboard commands often has that usage pattern: a user may invoke themode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:• If you delete or move the compiled file after loading it, Emacs can no longer load theremaining function definitions not already loaded.

Chapter 17: Byte Compilation

320• If you alter the compiled file (such as by compiling a new version), then trying to load
any function not already loaded will usually yield nonsense results.
These problems will never happen in normal circumstances with installed Emacs files.
But they are quite likely to happen with Lisp files that you are changing. The easiest
way to prevent these problems is to reload the new compiled file immediately after each
recompilation.
Experience shows that using dynamic function loading provides benefits that are hardly
measurable, so this feature is deprecated since Emacs 27.1.
The byte compiler uses the dynamic function loading feature if the variablebyte-compile-dynamic is non-nil at compilation time. Do not set this variable globally,
since dynamic loading is desirable only for certain files. Instead, enable the feature for
specific source files with file-local variable bindings. For example, you could do it by writing
this text in the source file’s first line:-*-byte-compile-dynamic: t;-*[Variable]
If this is non-nil, the byte compiler generates compiled files that are set up for
dynamic function loading.

byte-compile-dynamic

fetch-bytecode function[Function]
If function is a byte-code function object, this immediately finishes loading the byte
code of function from its byte-compiled file, if it is not fully loaded already. Otherwise,
it does nothing. It always returns function.

17.5 Evaluation During Compilation
These features permit you to write code to be evaluated during compilation of a program.

eval-and-compile body. . .

[Macro]This form marks body to be evaluated both when you compile the containing code
and when you run it (whether compiled or not).

You can get a similar result by putting body in a separate file and referring to thatfile with require. That method is preferable when body is large. Effectively requireis automatically eval-and-compile, the package is loaded both when compiling andexecuting.
autoload is also effectively eval-and-compile too. It’s recognized when compiling,so uses of such a function don’t produce “not known to be defined” warnings.
Most uses of eval-and-compile are fairly sophisticated.
If a macro has a helper function to build its result, and that macro is used both locallyand outside the package, then eval-and-compile should be used to get the helper
both when compiling and then later when running.
If functions are defined programmatically (with fset say), then eval-and-compile
can be used to have that done at compile-time as well as run-time, so calls to thosefunctions are checked (and warnings about “not known to be defined” suppressed).

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eval-when-compile body. . .

[Macro]This form marks body to be evaluated at compile time but not when the compiled
program is loaded. The result of evaluation by the compiler becomes a constant whichappears in the compiled program. If you load the source file, rather than compiling it,
body is evaluated normally.
If you have a constant that needs some calculation to produce, eval-when-compile
can do that at compile-time. For example,(defvar my-regexp(eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))
If you’re using another package, but only need macros from it (the byte compiler will
expand those), then eval-when-compile can be used to load it for compiling, but not
executing. For example,(eval-when-compile(require 'my-macro-package))
The same sort of thing goes for macros and defsubst functions defined locally andonly for use within the file. They are needed for compiling the file, but in most cases
they are not needed for execution of the compiled file. For example,(eval-when-compile(unless (fboundp 'some-new-thing)(defmacro some-new-thing ()(compatibility code))))This is often good for code that’s only a fallback for compatibility with other versionsof Emacs.
Common Lisp Note: At top level, eval-when-compile is analogous to the Common
Lisp idiom (eval-when (compile eval) ...). Elsewhere, the Common Lisp ‘#.’reader macro (but not when interpreting) is closer to what eval-when-compile does.

17.6 Compiler Errors
Error and warning messages from byte compilation are printed in a buffer named*Compile-Log*. These messages include file names and line numbers identifying thelocation of the problem. The usual Emacs commands for operating on compiler output canbe used on these messages.
When an error is due to invalid syntax in the program, the byte compiler might get
confused about the error’s exact location. One way to investigate is to switch to the buffer*Compiler Input*. (This buffer name starts with a space, so it does not show up in the
Buffer Menu.) This buffer contains the program being compiled, and point shows how far
the byte compiler was able to read; the cause of the error might be nearby. See Section 19.3
[Syntax Errors], page 367, for some tips for locating syntax errors.
A common type of warning issued by the byte compiler is for functions and variables
that were used but not defined. Such warnings report the line number for the end of the file,
not the locations where the missing functions or variables were used; to find these, you mustsearch the file manually.
If you are sure that a warning message about a missing function or variable is unjustified,there are several ways to suppress it:Chapter 17: Byte Compilation

322• You can suppress the warning for a specific call to a function func by conditionalizing
it on an fboundp test, like this:(if (fboundp 'func) ...(func ...)...)
The call to func must be in the then-form of the if, and func must appear quoted in
the call to fboundp. (This feature operates for cond as well.)• Likewise, you can suppress the warning for a specific use of a variable variable byconditionalizing it on a boundp test:(if (boundp 'variable) ...variable...)The reference to variable must be in the then-form of the if, and variable must appear
quoted in the call to boundp.
• You can tell the compiler that a function is defined using declare-function. See
Section 13.16 [Declaring Functions], page 265.
• Likewise, you can tell the compiler that a variable is defined using defvar with no
initial value. (Note that this marks the variable as special, i.e. dynamically bound, but
only within the current lexical scope, or file if at top-level.) See Section 12.5 [Defining
Variables], page 194.
You can also suppress compiler warnings within a certain expression using thewith-suppressed-warnings macro:with-suppressed-warnings warnings body. . .

[Special Form]
In execution, this is equivalent to (progn body...), but the compiler does not issue
warnings for the specified conditions in body. warnings is an association list of warning
symbols and function/variable symbols they apply to. For instance, if you wish to callan obsolete function called foo, but want to suppress the compilation warning, say:(with-suppressed-warnings ((obsolete foo))(foo ...))For more coarse-grained suppression of compiler warnings, you can use the with-nowarnings construct:

with-no-warnings body. . .

[Special Form]
In execution, this is equivalent to (progn body...), but the compiler does not issue
warnings for anything that occurs inside body.

We recommend that you use with-suppressed-warnings instead, but if you do use
this construct, that you use it around the smallest possible piece of code to avoid
missing possible warnings other than one you intend to suppress.
Byte compiler warnings can be controlled more precisely by setting the variablebyte-compile-warnings. See its documentation string for details.
Sometimes you may wish the byte-compiler warnings to be reported using error. If so,
set byte-compile-error-on-warn to a non-nil value.

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17.7 Byte-Code Function Objects
Byte-compiled functions have a special data type: they are byte-code function objects.
Whenever such an object appears as a function to be called, Emacs uses the byte-code
interpreter to execute the byte-code.
Internally, a byte-code function object is much like a vector; its elements can be accessedusing aref. Its printed representation is like that for a vector, with an additional ‘#’ before
the opening ‘[’. It must have at least four elements; there is no maximum number, but only
the first six elements have any normal use. They are:argdesc

The descriptor of the arguments. This can either be a list of arguments, as
described in Section 13.2.3 [Argument List], page 234, or an integer encoding
the required number of arguments. In the latter case, the value of the descriptor
specifies the minimum number of arguments in the bits zero to 6, and the
maximum number of arguments in bits 8 to 14. If the argument list uses &rest,
then bit 7 is set; otherwise it’s cleared.
If argdesc is a list, the arguments will be dynamically bound before executing
the byte code. If argdesc is an integer, the arguments will be instead pushed
onto the stack of the byte-code interpreter, before executing the code.

byte-code

The string containing the byte-code instructions.

constants

The vector of Lisp objects referenced by the byte code. These include symbols
used as function names and variable names.

stacksize

The maximum stack size this function needs.

docstring

The documentation string (if any); otherwise, nil. The value may be a number
or a list, in case the documentation string is stored in a file. Use the function
documentation to get the real documentation string (see Section 25.2 [Accessing
Documentation], page 596).

interactive
The interactive spec (if any). This can be a string or a Lisp expression. It isnil for a function that isn’t interactive.
Here’s an example of a byte-code function object, in printed representation. It is thedefinition of the command backward-sexp.
#[256"\211\204^G^@\300\262^A\301^A[!\207"[1 forward-sexp]
3
1793299"^p"]
The primitive way to create a byte-code object is with make-byte-code:

make-byte-code &rest elements[Function]
This function constructs and returns a byte-code function object with elements as its
elements.

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324

You should not try to come up with the elements for a byte-code function yourself,
because if they are inconsistent, Emacs may crash when you call the function. Always leaveit to the byte compiler to create these objects; it makes the elements consistent (we hope).

17.8 Disassembled Byte-CodePeople do not write byte-code; that job is left to the byte compiler. But we provide a
disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled
code into human-readable form.
The byte-code interpreter is implemented as a simple stack machine. It pushes values
onto a stack of its own, then pops them off to use them in calculations whose results arethemselves pushed back on the stack. When a byte-code function returns, it pops a value
off the stack and returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables,by transferring values between variables and the stack.

disassemble object &optional buffer-or-name[Command]This command displays the disassembled code for object. In interactive use, or if
buffer-or-name is nil or omitted, the output goes in a buffer named *Disassemble*.
If buffer-or-name is non-nil, it must be a buffer or the name of an existing buffer.
Then the output goes there, at point, and point is left before the output.
The argument object can be a function name, a lambda expression (see Section 13.2
[Lambda Expressions], page 232), or a byte-code object (see Section 17.7 [Byte-Code
Objects], page 323). If it is a lambda expression, disassemble compiles it anddisassembles the resulting compiled code.

Here are two examples of using the disassemble function. We have added explanatory
comments to help you relate the byte-code to the Lisp source; these do not appear in the
output of disassemble.
(defun factorial (integer)"Compute factorial of an integer."(if (= 1 integer) 1(* integer (factorial (1- integer)))))⇒ factorial(factorial 4)⇒ 24(disassemble 'factorial)
a byte-code for factorial:
doc: Compute factorial of an integer.
args: (arg1)
0

dup

1
2

constant 1
eqlsign; Get the value of integer and;push it onto the stack.
; Push 1 onto stack.
; Pop top two values off stack, compare;
them, and push result onto stack.

Chapter 17: Byte Compilation

3

goto-if-nil 1

6constant 1
7
return8:1 dup9
constant factorial
10 stack-ref 2
11 sub1
12

call

13

mult

14

return

1

325; Pop and test top of stack;;if nil, go to 1, else continue.
; Push 1 onto top of stack.
; Return the top element of the stack.
; Push value of integer onto stack.
; Push factorial onto stack.
; Push value of integer onto stack.
; Pop integer, decrement value,;
push new value onto stack.
; Call function factorial using first;(i.e., top) stack element as argument;;
push returned value onto stack.
; Pop top two values off stack, multiply;
them, and push result onto stack.
; Return the top element of the stack.

The silly-loop function is somewhat more complex:(defun silly-loop (n)"Return time before and after N iterations of a loop."(let ((t1 (current-time-string)))(while (> (setq n (1- n))0))(list t1 (current-time-string))))⇒ silly-loop(disassemble 'silly-loop)
a byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (arg1); Push current-time-string;
onto top of stack.
; Call current-time-string with no;argument, push result onto stack as t1.
; Get value of the argument n;
and push the value on the stack.
; Subtract 1 from top of stack.
; Duplicate top of stack; i.e., copy the top;of the stack and push copy onto stack.
; Pop the top of the stack,;and set n to the value.

0

constant current-time-string

1

call

0

2:1 stack-ref 1
3
4

sub1
dup

5

stack-set 3;; (In effect, the sequence dup stack-set copies the top of;; the stack into the value of n without popping it.)

Chapter 17: Byte Compilation

7
8

9

12
13
14
15
16

; Push 0 onto stack.
; Pop top two values off stack,;test if n is greater than 0;
and push result onto stack.
goto-if-not-nil 1; Goto 1 if n > 0;(this continues the while loop);
else continue.
dup; Push value of t1 onto stack.
constant current-time-string ; Push current-time-string;
onto the top of the stack.
call
0; Call current-time-string again.
list2; Pop top two elements off stack, create a;list of them, and push it onto stack.
return; Return value of the top of stack.
constant 0
gtr

326

327

18 Compilation of Lisp to Native CodeIn addition to the byte-compilation, described in Chapter 17 [Byte Compilation], page 316,
Emacs can also optionally compile Lisp function definitions into a true compiled code,
known as native code. This feature uses the libgccjit library, which is part of the GCC
distribution, and requires that Emacs be built with support for using that library. It also
requires to have GCC and Binutils (the assembler and linker) available on your system foryou to be able to native-compile Lisp code.
To determine whether the current Emacs process can produce and load natively-compiled
Lisp code, call native-comp-available-p (see Section 18.1 [Native-Compilation Functions],
page 328).
Unlike byte-compiled code, natively-compiled Lisp code is executed directly by themachine’s hardware, and therefore runs at full speed that the host CPU can provide. The
resulting speedup generally depends on what the Lisp code does, but is usually 2.5 to 5
times faster than the corresponding byte-compiled code.
Since native code is generally incompatible between different systems, the nativelycompiled code is not transportable from one machine to another, it can only be used on thesame machine where it was produced or on very similar ones (having the same CPU andrun-time libraries). The transportability of natively-compiled code is the same as that ofshared libraries (.so or .dll files).
Libraries of natively-compiled code include crucial dependencies on Emacs Lisp primitives(see Section 13.1 [What Is a Function], page 230) and their calling conventions, and thus
Emacs usually won’t load natively-compiled code produced by earlier or later Emacs versions;
native compilation of the same Lisp code by a different Emacs version will usually produce
a natively-compiled library under a unique file name that only that version of Emacs will beable to load. However, the use of unique file names allows to have in the same directory
several versions of the same Lisp library natively-compiled by several different versions ofEmacs.
A non-nil file-local variable binding of no-byte-compile (see Chapter 17 [Byte Compilation], page 316) also disables the native compilation of that file. In addition, a similar variable no-native-compile disables just the native compilation of the file. If bothno-byte-compile and no-native-compile are specified, the former takes precedence.
Sometimes there could be a need to prevent the native compilation from writing its
results, the *.eln files, into a subdirectory of user-emacs-directory (see Section 42.1.2[Init File], page 1258). You can do that by either changing the value of native-comp-elnload-path (see Section 18.2 [Native-Compilation Variables], page 330) or by temporarily
pointing the HOME environment variable to a non-existing directory. Note that the latter
technique might still produce a small number of *.eln files if Emacs needs to generate
trampolines, which are used if Lisp primitives are advised or redefined in your Lisp codethat is being natively compiled. See Section 18.2 [Native-Compilation Variables], page 330.
Alternatively, you can specify that the *.eln files are written to a non-default directoryusing the startup-redirect-eln-cache function; see Section 18.1 [Native-Compilation
Functions], page 328.

Chapter 18: Compilation of Lisp to Native Code328

18.1 Native-Compilation Functions
Native-Compilation is implemented as a side effect of byte-compilation (see Chapter 17 [ByteCompilation], page 316). Thus, compiling Lisp code natively always produces its byte code
as well, and therefore all the rules and caveats of preparing Lisp code for byte compilation(see Section 17.2 [Compilation Functions], page 316) are valid for native-compilation as well.
You can natively-compile either a single function or macro definition, or a whole file ofLisp code, with the native-compile function. Natively-compiling a file will produce the.eln file with native code.
Native compilation might produce warning or error messages; these are normally recordedin the buffer called *Native-compile-Log*. In interactive sessions, it uses the special
LIMPLE mode (native-comp-limple-mode), which sets up font-lock as appropriate forthis log, and is otherwise the same as Fundamental mode. Logging of messages resulting from
native-compilation can be controlled by the native-comp-verbose variable (see Section 18.2
[Native-Compilation Variables], page 330).
When Emacs is run non-interactively, messages produced by native-compilation arereported by calling message (see Section 41.4.1 [Displaying Messages], page 1131), andare usually displayed on the standard error stream of the terminal from which Emacs was
invoked.

native-compile function-or-file &optional output[Function]
This function compiles function-or-file into native code. The argument function-or-filecan be a function symbol, a Lisp form, or a name (a string) of the file which contains
the Emacs Lisp source code to compile. If the optional argument output is provided,
it must be a string specifying the name of the file to write the compiled code into.
Otherwise, if function-or-file is a function or a Lisp form, this function returns thecompiled object, and if function-or-file is a file name, the function returns the fullabsolute name of the file it created for the compiled code. The output file is by default
given the .eln extension.
This function runs the final phase of the native compilation, which invokes GCC via
libgccjit, in a separate subprocess, which invokes the same Emacs executable as
the process that called this function.

batch-native-compile &optional for-tarball[Function]
This function runs native-compilation on files specified on the Emacs command line inbatch mode. It must be used only in a batch execution of Emacs, as it kills Emacs
upon completion of the compilation. If one or more of the files fail to compile, theEmacs process will attempt to compile all the other files, and will terminate with a
non-zero status code. The optional argument for-tarball, if non-nil, tells the function
to place the resulting .eln files in the last directory mentioned in native-comp-elnload-path (see Section 16.3 [Library Search], page 301); this is meant to be used aspart of building an Emacs source tarball for the first time, when the natively-compiled
files, which are absent from the source tarball, should be generated in the build tree
instead of the user’s cache directory.

Native compilation can be run entirely asynchronously, in a subprocess of the main
Emacs process. This leaves the main Emacs process free to use while the compilation

Chapter 18: Compilation of Lisp to Native Code329

runs in the background. This is the method used by Emacs to natively-compile any Lisp
file or byte-compiled Lisp file that is loaded into Emacs, when no natively-compiled filefor it is available. Note that because of this use of a subprocess, native compilation may
produce warning and errors which byte-compilation does not, and Lisp code may thus need
to be modified to work correctly. See native-comp-async-report-warnings-errors in
see Section 18.2 [Native-Compilation Variables], page 330, for more details.

native-compile-async files &optional recursively load selector[Function]
This function compiles the named files asynchronously. The argument files should bea single file name (a string) or a list of one or more file and/or directory names. If
directories are present in the list, the optional argument recursively should be non-nil
to cause the compilation to recurse into those directories. If load is non-nil, Emacs
will load each file that it succeeded to compile. The optional argument selector allows
control of which of files will be compiled; it can have one of the following values:
nil or omitted
Select all the files and directories in files.
a regular expression string
Select the files and directories whose names match the regexp.
a function A predicate function, which will be called with each file and directoryin files, and should return non-nil if the file or the directory should beselected for compilation.

On systems with multiple CPU execution units, when files names more than one file,
this function will normally start several compilation subprocesses in parallel, under thecontrol of native-comp-async-jobs-number (see Section 18.2 [Native-Compilation
Variables], page 330).
[Command]This command compiles the file visited by the current buffer into native code, if thefile was changed since the last time it was natively-compiled.

emacs-lisp-native-compile[Command]This command compiles the file visited by the current buffer into native code, likeemacs-lisp-native-compile, but it also loads the native code when the compilation
finishes.

emacs-lisp-native-compile-and-load

The following function allows Lisp programs to test whether native-compilation is available
at runtime.
[Function]
This function returns non-nil if the running Emacs process has the native-compilation
support compiled into it. On systems that load libgccjit dynamically, it also makes
sure that library is available and can be loaded. Lisp programs that need to know up
front whether native-compilation is available should use this predicate.

native-comp-available-p

By default, asynchronous native compilation writes the *.eln files it produces to a
subdirectory of the first writable directory specified by the native-comp-eln-load-pathvariable (see Section 18.2 [Native-Compilation Variables], page 330). You can change thisby using the following function in your startup files:

Chapter 18: Compilation of Lisp to Native Code330

startup-redirect-eln-cache cache-directory[Function]
This function arranges for the asynchronous native compilation to write the produced*.eln files to cache-directory, which must be a single directory, a string. It also
destructively modifies native-comp-eln-load-path such that its first element iscache-directory. If cache-directory is not an absolute file name, it is interpreted
relative to user-emacs-directory (see Section 42.1.2 [Init File], page 1258).

18.2 Native-Compilation Variables
This section documents the variables that control native-compilation.
[User Option]
This variable specifies the optimization level for native compilation. Its value should
be a number between −1 and 3. Values between 0 and 3 specify the optimizationlevels equivalent to the corresponding compiler -O0, -O1, etc. command-line optionsof the compiler. The value −1 means disable native-compilation: functions and files
will be only byte-compiled; however, the *.eln files will still be produced, they will
just contain the compiled code in bytecode form. (This can be achieved at function
granularity by using the (declare (speed -1)) form, see Section 13.15 [Declare Form],
page 263.) The default value is 2.

native-comp-speed[User Option]
This variable specifies the level of debugging information produced by nativecompilation. Its value should be a number between zero and 3, with the following
meaning:

native-comp-debug0

No debugging output. This is the default.

1

Emit debugging symbols with the native code. This allows easier debugging
of the native code with debuggers such as gdb.

2

Like 1, and in addition dump pseudo-C code.

3

Like 2, and in addition dump the GCC intermediate passes and libgccjit
log file.

[User Option]
This variable controls the verbosity of native-compilation by suppressing some or all of
the log messages emitted by it. If its value is zero, the default, all of the log messages
are suppressed. Setting it to a value between 1 and 3 will allow logging of the messages
whose level is above the value. The values have the following interpretations:

native-comp-verbose

0

No logging. This is the default.

1

Log the final LIMPLE representation of the code.

2

Log the LAP, the final LIMPLE, and some additional pass info.

3

Maximum verbosity: log everything.

[User Option]
This variable determines the maximum number of native-compilation subprocesses
that will be started simultaneously. It should be a non-negative number. The default
value is zero, which means use half the number of the CPU execution units, or 1 if the
CPU has only one execution unit.

native-comp-async-jobs-numberChapter 18: Compilation of Lisp to Native Code331

[User Option]
If this variable’s value is non-nil, warnings and errors from asynchronous nativecompilation subprocesses are reported in the main Emacs session in a buffer named*Warnings*. The default value t means display the resulting buffer. To log warnings
without popping up the *Warnings* buffer, set this variable to silent.
A common cause for asynchronous native-compilation to produce warnings is compilinga file that is missing some require of a necessary feature. The feature may be loaded
into the main emacs, but because native compilation always starts from a subprocesswith a pristine environment, that may not be true for the subprocess.

native-comp-async-report-warnings-errors[User Option]
If this variable’s value is non-nil, Emacs will query upon exiting whether to exit andkill any asynchronous native-compilation subprocesses that are still running, thus
preventing the corresponding .eln files from being written. If the value is nil, thedefault, Emacs will kill these subprocesses without querying.

native-comp-async-query-on-exit

The variable native-comp-eln-load-path holds the list of directories where Emacs
looks for the *.eln files (see Section 16.3 [Library Search], page 301); in that role it isthe equivalent of load-path used to look for *.el and *.elc files. The directories in thislist are also used for writing the *.eln files produced by asynchronous native-compilation;
specifically, Emacs will write these files into the first writable directory in the list. Thus,
you can control where native-compilation stores the results by changing the value of thisvariable.
[Variable]
This variable, if non-nil, enables asynchronous (a.k.a. just-in-time, or JIT) native
compilation of the *.elc files loaded by Emacs for which the corresponding *.eln
files do not already exist. This JIT compilation uses separate Emacs sub-processes
running in batch mode, according to the value of native-comp-async-jobs-number.
When the JIT compilation of a Lisp file finishes successfully, the resulting .eln file isloaded and its code replaces the definition of functions provided by the .elc file.

native-comp-jit-compilation

Setting the value of native-comp-jit-compilation to nil disables JIT native compilation. However, even when JIT native compilation is disabled, Emacs might still need tostart asynchronous native compilation subprocesses to produce trampolines. To control this,use a separate variable, described below.
[Variable]
This variable controls generation of trampolines. A trampoline is a small piece of nativecode required to allow calling Lisp primitives, which were advised or redefined, from
Lisp code that was natively-compiled with native-comp-speed set to 2 or greater.
Emacs stores the generated trampolines on separate *.eln files. By default, thisvariable’s value is t, which enables the generation of trampoline files; setting it to nil
disables the generation of trampolines. Note that if a trampoline needed for advising or
redefining a primitive is not available and cannot be generated, calls to that primitivefrom natively-compiled Lisp will ignore redefinitions and advices, and will behave as if
the primitive was called directly from C. Therefore, we don’t recommend disabling
the trampoline generation, unless you know that all the trampolines needed by yourLisp programs are already compiled and accessible to Emacs.

native-comp-enable-subr-trampolines

Chapter 18: Compilation of Lisp to Native Code332

The value of this variable can also be a string, in which case it specifies the name of adirectory in which to store the generated trampoline *.eln files, overriding the directories in native-comp-eln-load-path. This is useful if you want the trampolines to begenerated as needed, but don’t want to store them under the user’s HOME directory or in
the other public directories where *.eln files are kept. However, unlike with directories
in native-comp-eln-load-path, the trampolines will be stored in the directory givenby the value of this variable, not in its version-specific subdirectory. If the name ofthis directory is not absolute, it is interpreted relative to invocation-directory (seeSection 42.3 [System Environment], page 1265)
If this variable is non-nil, and Emacs needs to produce a trampoline, but it cannot find
any writable directory to store the trampoline, it will store it inside temporary-filedirectory (see Section 26.9.5 [Unique File Names], page 641).
Trampolines produced when no writable directory is found to store them, or when
this variable is a string, will only be available for the duration of the current Emacs
session, because Emacs doesn’t look for trampolines in either of these places.

333

19 Debugging Lisp Programs
There are several ways to find and investigate problems in an Emacs Lisp program.
• If a problem occurs when you run the program, you can use the built-in Emacs Lisp
debugger (see Section 19.1 [Debugger], page 333) to suspend the Lisp evaluator, andexamine and/or alter its internal state.
• You can use Edebug, a source-level debugger for Emacs Lisp. See Section 19.2 [Edebug],page 344.
• You can trace the execution of functions involved in the problem using the tracing
facilities provided by the trace.el package. This package provides the functions
trace-function-foreground and trace-function-background for tracing function
calls, and trace-values for adding values of select variables to the trace. For thedetails, see the documentation of these facilities in trace.el.
• If a syntactic problem is preventing Lisp from even reading the program, you can locate
it using Lisp editing commands.
• You can look at the error and warning messages produced by the byte compiler when itcompiles the program. See Section 17.6 [Compiler Errors], page 321.
• You can use the Testcover package to perform coverage testing on the program.
• You can use the ERT package to write regression tests for the program. See ERT:
Emacs Lisp Regression Testing.
• You can profile the program to get hints about how to make it more efficient. See
Section 19.5 [Profiling], page 369.
Other useful tools for debugging input and output problems are the dribble file (seeSection 42.13 [Terminal Input], page 1285) and the open-termscript function (seeSection 42.14 [Terminal Output], page 1287).

19.1 The Lisp Debugger
The ordinary Lisp debugger provides the ability to suspend evaluation of a form. Whileevaluation is suspended (a state that is commonly known as a break), you may examine therun time stack, examine the values of local or global variables, or change those values. Sincea break is a recursive edit, all the usual editing facilities of Emacs are available; you caneven run programs that will enter the debugger recursively. See Section 22.13 [Recursive
Editing], page 475.

19.1.1 Entering the Debugger on an Error
The most important time to enter the debugger is when a Lisp error happens. This allows
you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an error. Many commands
signal Lisp errors when invoked inappropriately, and during ordinary editing it would be very
inconvenient to enter the debugger each time this happens. So if you want errors to enter
the debugger, set the variable debug-on-error to non-nil. (The command toggle-debugon-error provides an easy way to do this.)

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Note that, for technical reasons, you cannot use the facilities defined in this subsection
to debug errors in Lisp that the redisplay code has invoked. See Section 19.1.2 [Debugging
Redisplay], page 335, for help with these.
[User Option]
This variable determines whether the debugger is called when an error is signaled andnot handled. If debug-on-error is t, all kinds of errors call the debugger, except thoselisted in debug-ignored-errors (see below). If it is nil, none call the debugger.
The value can also be a list of error conditions (see Section 11.7.3.1 [Signaling Errors],
page 180). Then the debugger is called only for error conditions in this list (except
those also listed in debug-ignored-errors). For example, if you set debug-on-error
to the list (void-variable), the debugger is only called for errors about a variable
that has no value.
Note that eval-expression-debug-on-error overrides this variable in some cases;
see below.
When this variable is non-nil, Emacs does not create an error handler around processfilter functions and sentinels. Therefore, errors in these functions also invoke thedebugger. See Chapter 40 [Processes], page 1078.

debug-on-error[User Option]
This variable specifies errors which should not enter the debugger, regardless of thevalue of debug-on-error. Its value is a list of error condition symbols and/or regularexpressions. If the error has any of those condition symbols, or if the error message
matches any of the regular expressions, then that error does not enter the debugger.
The normal value of this variable includes user-error, as well as several errors that
happen often during editing but rarely result from bugs in Lisp programs. However,“rarely” is not “never”; if your program fails with an error that matches this list,
you may try changing this list to debug the error. The easiest way is usually to set
debug-ignored-errors to nil.

debug-ignored-errors[User Option]
If this variable has a non-nil value (the default), running the commandeval-expression causes debug-on-error to be temporarily bound to t. See Section“Evaluating Emacs Lisp Expressions” in The GNU Emacs Manual.
If eval-expression-debug-on-error is nil, then the value of debug-on-error is
not changed during eval-expression.

eval-expression-debug-on-error[User Option]
Normally, errors caught by condition-case never invoke the debugger. The
condition-case gets a chance to handle the error before the debugger gets a chance.
If you change debug-on-signal to a non-nil value, the debugger gets the firstchance at every error, regardless of the presence of condition-case. (To invoke thedebugger, the error must still fulfill the criteria specified by debug-on-error anddebug-ignored-errors.)
For example, setting this variable is useful to get a backtrace from code evaluated byemacsclient’s --eval option. If Lisp code evaluated by emacsclient signals an error
while this variable is non-nil, the backtrace will popup in the running Emacs.

debug-on-signal

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Warning: Setting this variable to non-nil may have annoying effects. Various partsof Emacs catch errors in the normal course of affairs, and you may not even realizethat errors happen there. If you need to debug code wrapped in condition-case,consider using condition-case-unless-debug (see Section 11.7.3.3 [Handling Errors],
page 182).
[User Option]
If you set debug-on-event to a special event (see Section 22.9 [Special Events],
page 470), Emacs will try to enter the debugger as soon as it receives this event,bypassing special-event-map. At present, the only supported values correspondto the signals SIGUSR1 and SIGUSR2 (this is the default). This can be helpful when
inhibit-quit is set and Emacs is not otherwise responding.

debug-on-event[Variable]
If you set debug-on-message to a regular expression, Emacs will enter the debugger
if it displays a matching message in the echo area. For example, this can be usefulwhen trying to find the cause of a particular message.

debug-on-message[Variable]
You can evaluate forms in the current stack frame in the ‘*Backtrace*’ buffer withthe e command, and while edebugging you can use the e and C-x C-e commands
to do something similar. By default, the debugger is inhibited by these commands(because (re-)entering the debugger at this point will usually take you out of the
debugging context you’re in). Set debug-allow-recursive-debug to a non-nil value
to allow these commands to enter the debugger recursively.

debug-allow-recursive-debug

To debug an error that happens during loading of the init file, use the option‘--debug-init’. This binds debug-on-error to t while loading the init file, and bypasses
the condition-case which normally catches errors in the init file.

19.1.2 Debugging Redisplay Errors
When an error occurs in Lisp code which redisplay has invoked, Emacs’s usual debugging
mechanisms are unusable, for technical reasons. This subsection describes how to get abacktrace from such an error, which should be helpful in debugging it.
These directions apply to Lisp forms used, for example, in :eval mode line constructs(see Section 24.4.2 [Mode Line Data], page 551), and in all hooks invoked from redisplay,such as:• fontification-functions (see Section 41.12.7 [Auto Faces], page 1178).
• window-scroll-functions (see Section 29.28 [Window Hooks], page 779).
Note that if you have had an error in a hook function called from redisplay, the error
handling might have removed this function from the hook. You will thus need to reinitializethat hook somehow, perhaps with add-hook, to be able to replay the bug.
To generate a backtrace in these circumstances, set the variable backtrace-onredisplay-error to non-nil. When the error occurs, Emacs will dump the backtrace tothe buffer *Redisplay-trace*, but won’t automatically display it in a window. This is to
avoid needlessly corrupting the redisplay you are debugging. You will thus need to display
the buffer yourself, with a command such as switch-to-buffer-other-frame C-x 5 b.

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336[Variable]
Set this variable to non-nil to enable the generation of a backtrace when an error
occurs in any Lisp called from redisplay.

backtrace-on-redisplay-error

19.1.3 Debugging Infinite Loops
When a program loops infinitely and fails to return, your first problem is to stop the loop.
On most operating systems, you can do this with C-g, which causes a quit. See Section 22.11[Quitting], page 471.
Ordinary quitting gives no information about why the program was looping. To get
more information, you can set the variable debug-on-quit to non-nil. Once you have thedebugger running in the middle of the infinite loop, you can proceed from the debugger
using the stepping commands. If you step through the entire loop, you may get enoughinformation to solve the problem.
Quitting with C-g is not considered an error, and debug-on-error has no effect on thehandling of C-g. Likewise, debug-on-quit has no effect on errors.
[User Option]
This variable determines whether the debugger is called when quit is signaled andnot handled. If debug-on-quit is non-nil, then the debugger is called whenever you
quit (that is, type C-g). If debug-on-quit is nil (the default), then the debugger is
not called when you quit.

debug-on-quit

19.1.4 Entering the Debugger on a Function Call
To investigate a problem that happens in the middle of a program, one useful technique isto enter the debugger whenever a certain function is called. You can do this to the functionin which the problem occurs, and then step through the function, or you can do this to afunction called shortly before the problem, step quickly over the call to that function, andthen step through its caller.

debug-on-entry function-name[Command]This function requests function-name to invoke the debugger each time it is called.
Any function or macro defined as Lisp code may be set to break on entry, regardlessof whether it is interpreted code or compiled code. If the function is a command, it
will enter the debugger when called from Lisp and when called interactively (after thereading of the arguments). You can also set debug-on-entry for primitive functions(i.e., those written in C) this way, but it only takes effect when the primitive is calledfrom Lisp code. Debug-on-entry is not allowed for special forms.
When debug-on-entry is called interactively, it prompts for function-name in theminibuffer. If the function is already set up to invoke the debugger on entry, debug-onentry does nothing. debug-on-entry always returns function-name.
Here’s an example to illustrate use of this function:(defun fact (n)(if (zerop n) 1(* n (fact (1- n)))))⇒ fact(debug-on-entry 'fact)⇒ factChapter 19: Debugging Lisp Programs

337(fact 3)------ Buffer: *Backtrace* -----Debugger entered--entering a function:* fact(3)eval((fact 3))eval-last-sexp-1(nil)eval-last-sexp(nil)call-interactively(eval-last-sexp)------ Buffer: *Backtrace* ------

cancel-debug-on-entry &optional function-name[Command]This function undoes the effect of debug-on-entry on function-name. When calledinteractively, it prompts for function-name in the minibuffer. If function-name isomitted or nil, it cancels break-on-entry for all functions. Calling cancel-debugon-entry does nothing to a function which is not currently set up to break on entry.

19.1.5 Entering the debugger when a variable is modified
Sometimes a problem with a function is due to a wrong setting of a variable. Setting up the
debugger to trigger whenever the variable is changed is a quick way to find the origin of thesetting.

debug-on-variable-change variable[Command]This function arranges for the debugger to be called whenever variable is modified.
It is implemented using the watchpoint mechanism, so it inherits the same characteristics and limitations: all aliases of variable will be watched together, only dynamic
variables can be watched, and changes to the objects referenced by variables are notdetected. For details, see Section 12.9 [Watching Variables], page 200.

cancel-debug-on-variable-change &optional variable[Command]This function undoes the effect of debug-on-variable-change on variable. Whencalled interactively, it prompts for variable in the minibuffer. If variable is omitted ornil, it cancels break-on-change for all variables. Calling cancel-debug-on-variablechange does nothing to a variable which is not currently set up to break on change.

19.1.6 Explicit Entry to the Debugger
You can cause the debugger to be called at a certain point in your program by writing theexpression (debug) at that point. To do this, visit the source file, insert the text ‘(debug)’at the proper place, and type C-M-x (eval-defun, a Lisp mode key binding). Warning: if
you do this for temporary debugging purposes, be sure to undo this insertion before you
save the file!
The place where you insert ‘(debug)’ must be a place where an additional form canbe evaluated and its value ignored. (If the value of (debug) isn’t ignored, it will alter the
execution of the program!) The most common suitable places are inside a progn or an
implicit progn (see Section 11.1 [Sequencing], page 158).

Chapter 19: Debugging Lisp Programs338

If you don’t know exactly where in the source code you want to put the debug statement,
but you want to display a backtrace when a certain message is displayed, you can set
debug-on-message to a regular expression matching the desired message.

19.1.7 Using the Debugger
When the debugger is entered, it displays the previously selected buffer in one window anda buffer named *Backtrace* in another window. The backtrace buffer contains one line foreach level of Lisp function execution currently going on. At the beginning of this buffer is amessage describing the reason that the debugger was invoked (such as the error message
and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode, Debugger mode, inwhich letters are defined as debugger commands. The usual Emacs editing commands areavailable; thus, you can switch windows to examine the buffer that was being edited at thetime of the error, switch buffers, visit files, or do any other sort of editing. However, thedebugger is a recursive editing level (see Section 22.13 [Recursive Editing], page 475) and
it is wise to go back to the backtrace buffer and exit the debugger (with the q command)when you are finished with it. Exiting the debugger gets out of the recursive edit and buries
the backtrace buffer. (You can customize what the q command does with the backtrace
buffer by setting the variable debugger-bury-or-kill. For example, set it to kill if you
prefer to kill the buffer rather than bury it. Consult the variable’s documentation for more
possibilities.)
When the debugger has been entered, the debug-on-error variable is temporarily
set according to eval-expression-debug-on-error. If the latter variable is non-nil,debug-on-error will temporarily be set to t. However, further errors that occur while
debugging won’t (by default) trigger another debugger, because inhibit-debugger will also
be bound to non-nil.
The debugger itself must be run byte-compiled, since it makes assumptions about the stateof the Lisp interpreter. These assumptions are false if the debugger is running interpreted.

19.1.8 Backtraces
Debugger mode is derived from Backtrace mode, which is also used to show backtraces by
Edebug and ERT. (see Section 19.2 [Edebug], page 344, and ERT: Emacs Lisp Regression
Testing.)
The backtrace buffer shows you the functions that are executing and their argument
values. When a backtrace buffer is created, it shows each stack frame on one, possibly very
long, line. (A stack frame is the place where the Lisp interpreter records information abouta particular invocation of a function.) The most recently called function will be at the top.
In a backtrace you can specify a stack frame by moving point to a line describing thatframe. The frame whose line point is on is considered the current frame.
If a function name is underlined, that means Emacs knows where its source code islocated. You can click with the mouse on that name, or move to it and type RET, to visit
the source code. You can also type RET while point is on any name of a function or variablewhich is not underlined, to see help information for that symbol in a help buffer, if any exists.
The xref-find-definitions command, bound to M-., can also be used on any identifier
in a backtrace (see Section “Looking Up Identifiers” in The GNU Emacs Manual).

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In backtraces, the tails of long lists and the ends of long strings, vectors or structures, aswell as objects which are deeply nested, will be printed as underlined “...”. You can clickwith the mouse on a “...”, or type RET while point is on it, to show the part of the object thatwas hidden. To control how much abbreviation is done, customize backtrace-line-length.
Here is a list of commands for navigating and viewing backtraces:v

Toggle the display of local variables of the current stack frame.

pMove to the beginning of the frame, or to the beginning of the previous frame.

nMove to the beginning of the next frame.

+

Add line breaks and indentation to the top-level Lisp form at point to make it
more readable.

-

Collapse the top-level Lisp form at point back to a single line.

#

Toggle print-circle for the frame at point.

:

Toggle print-gensym for the frame at point.

.

Expand all the forms abbreviated with “...” in the frame at point.

19.1.9 Debugger Commands
The debugger buffer (in Debugger mode) provides special commands in addition to theusual Emacs commands and to the Backtrace mode commands described in the previous
section. The most important use of debugger commands is for stepping through code, sothat you can see how control flows. The debugger can step through the control structures ofan interpreted function, but cannot do so in a byte-compiled function. If you would like tostep through a byte-compiled function, replace it with an interpreted definition of the samefunction. (To do this, visit the source for the function and type C-M-x on its definition.)
You cannot use the Lisp debugger to step through a primitive function.
Some of the debugger commands operate on the current frame. If a frame starts witha star, that means that exiting that frame will call the debugger again. This is useful for
examining the return value of a function.
Here is a list of Debugger mode commands:cExit the debugger and continue execution. This resumes execution of the
program as if the debugger had never been entered (aside from any side-effects
that you caused by changing variable values or data structures while inside thedebugger).

dContinue execution, but enter the debugger the next time any Lisp function
is called. This allows you to step through the subexpressions of an expression,seeing what values the subexpressions compute, and what else they do.
The stack frame made for the function call which enters the debugger in thisway will be flagged automatically so that the debugger will be called again when
the frame is exited. You can use the u command to cancel this flag.

b

Flag the current frame so that the debugger will be entered when the frame
is exited. Frames flagged in this way are marked with stars in the backtrace
buffer.

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uDon’t enter the debugger when the current frame is exited. This cancels a b
command on that frame. The visible effect is to remove the star from the linein the backtrace buffer.

jFlag the current frame like b. Then continue execution like c, but temporarily
disable break-on-entry for all functions that are set up to do so by debug-onentry.

eRead a Lisp expression in the minibuffer, evaluate it (with the relevant lexical
environment, if applicable), and print the value in the echo area. The debugger
alters certain important variables, and the current buffer, as part of its operation;e temporarily restores their values from outside the debugger, so you can examineand change them. This makes the debugger more transparent. By contrast, M-:does nothing special in the debugger; it shows you the variable values within the
debugger. By default, this command suppresses the debugger during evaluation,
so that an error in the evaluated expression won’t add a new error on top of theexisting one. Set the debug-allow-recursive-debug user option to a non-nil
value to override this.

R

Like e, but also save the result of evaluation in the buffer *Debugger-record*.

q

Terminate the program being debugged; return to top-level Emacs commandexecution.
If the debugger was entered due to a C-g but you really want to quit, and not
debug, use the q command.

r

Return a value from the debugger. The value is computed by reading an
expression with the minibuffer and evaluating it.
The r command is useful when the debugger was invoked due to exit from a
Lisp call frame (as requested with b or by entering the frame with d); then thevalue specified in the r command is used as the value of that frame. It is also
useful if you call debug and use its return value. Otherwise, r has the same
effect as c, and the specified return value does not matter.
You can’t use r when the debugger was entered due to an error.

l

Display a list of functions that will invoke the debugger when called. This is alist of functions that are set to break on entry by means of debug-on-entry.

19.1.10 Invoking the Debugger
Here we describe in full detail the function debug that is used to invoke the debugger.

debug &rest debugger-args[Command]This function enters the debugger. In interactive sessions, it switches to a buffer named*Backtrace* (or *Backtrace*<2> if it is the second recursive entry to the debugger,etc.), and fills it with information about the stack of Lisp function calls. It then entersa recursive edit, showing the backtrace buffer in Debugger mode. In batch mode
(more generally, when noninteractive is non-nil, see Section 42.17 [Batch Mode],
page 1289), this function shows the Lisp backtrace on the standard error stream,
and then kills Emacs, causing it to exit with a non-zero exit code (see Section 42.2.1

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341[Killing Emacs], page 1262). Binding backtrace-on-error-noninteractive to nil
suppresses the backtrace in batch mode, see below.
The Debugger mode c, d, j, and r commands exit the recursive edit; then debug
switches back to the previous buffer and returns to whatever called debug. This is the
only way the function debug can return to its caller.
The use of the debugger-args is that debug displays the rest of its arguments at the
top of the *Backtrace* buffer, so that the user can see them. Except as described
below, this is the only way these arguments are used.
However, certain values for first argument to debug have a special significance. (Normally, these values are used only by the internals of Emacs, and not by programmers
calling debug.) Here is a table of these special values:
lambdaA first argument of lambda means debug was called because of entry to afunction when debug-on-next-call was non-nil. The debugger displays‘Debugger entered--entering a function:’ as a line of text at the topof the buffer.

debug

debug as first argument means debug was called because of entry to afunction that was set to debug on entry. The debugger displays the string‘Debugger entered--entering a function:’, just as in the lambda case.
It also marks the stack frame for that function so that it will invoke thedebugger when exited.

t

When the first argument is t, this indicates a call to debug due toevaluation of a function call form when debug-on-next-call is non-nil.
The debugger displays ‘Debugger entered--beginning evaluation offunction call form:’ as the top line in the buffer.

exit

When the first argument is exit, it indicates the exit of a stack frame
previously marked to invoke the debugger on exit. The second argument
given to debug in this case is the value being returned from the frame.
The debugger displays ‘Debugger entered--returning value:’ in the
top line of the buffer, followed by the value being returned.

error

When the first argument is error, the debugger indicates that it isbeing entered because an error or quit was signaled and not handled,by displaying ‘Debugger entered--Lisp error:’ followed by the error
signaled and any arguments to signal. For example,(let ((debug-on-error t))(/ 1 0))------ Buffer: *Backtrace* -----Debugger entered--Lisp error: (arith-error)/(1 0)...
------ Buffer: *Backtrace* -----If an error was signaled, presumably the variable debug-on-error is nonnil. If quit was signaled, then presumably the variable debug-on-quit
is non-nil.

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Use nil as the first of the debugger-args when you want to enter the
debugger explicitly. The rest of the debugger-args are printed on the
top line of the buffer. You can use this feature to display messages—for
example, to remind yourself of the conditions under which debug is called.

[Variable]
If this variable is non-nil, the default, entering the debugger in batch mode shows
the backtrace of Lisp functions calls. Binding the variable to the nil value suppresses
the backtrace and shows only the error message.

backtrace-on-error-noninteractive

19.1.11 Internals of the Debugger
This section describes functions and variables used internally by the debugger.
[Variable]
The value of this variable is the function to call to invoke the debugger. Its value must
be a function of any number of arguments, or, more typically, the name of a function.
This function should invoke some kind of debugger. The default value of the variable
is debug.

debugger

The first argument that Lisp hands to the function indicates why it was called. The
convention for arguments is detailed in the description of debug (see Section 19.1.10[Invoking the Debugger], page 340).
[Function]
This function prints a trace of Lisp function calls currently active. The trace is
identical to the one that debug would show in the *Backtrace* buffer. The return
value is always nil.

backtrace

In the following example, a Lisp expression calls backtrace explicitly. This prints
the backtrace to the stream standard-output, which, in this case, is the buffer‘backtrace-output’.
Each line of the backtrace represents one function call. The line shows the function
followed by a list of the values of the function’s arguments if they are all known; if
they are still being computed, the line consists of a list containing the function and its
unevaluated arguments. Long lists or deeply nested structures may be elided.
(with-output-to-temp-buffer "backtrace-output"(let ((var 1))(save-excursion(setq var (eval '(progn(1+ var)(list 'testing (backtrace))))))))⇒ (testing nil)----------- Buffer: backtrace-output -----------backtrace()(list 'testing (backtrace))(progn ...)eval((progn (1+ var) (list 'testing (backtrace))))(setq ...)
(save-excursion ...)
(let ...)

Chapter 19: Debugging Lisp Programs343(with-output-to-temp-buffer ...)eval((with-output-to-temp-buffer ...))
eval-last-sexp-1(nil)eval-last-sexp(nil)call-interactively(eval-last-sexp)----------- Buffer: backtrace-output ------------[User Option]
If this variable is non-nil, every stack frame of the backtrace is displayed as a list.
This aims at improving the backtrace readability at the cost of special forms no longer
being visually different from regular function calls.

debugger-stack-frame-as-list

With debugger-stack-frame-as-list non-nil, the above example would look as
follows:----------- Buffer: backtrace-output -----------(backtrace)(list 'testing (backtrace))(progn ...)
(eval (progn (1+ var) (list 'testing (backtrace))))(setq ...)
(save-excursion ...)
(let ...)(with-output-to-temp-buffer ...)
(eval (with-output-to-temp-buffer ...))(eval-last-sexp-1 nil)(eval-last-sexp nil)(call-interactively eval-last-sexp)----------- Buffer: backtrace-output ------------[Variable]
If this variable is non-nil, it says to call the debugger before the next eval, apply or
funcall. Entering the debugger sets debug-on-next-call to nil.

debug-on-next-call

The d command in the debugger works by setting this variable.

backtrace-debug level flag

[Function]
This function sets the debug-on-exit flag of the stack frame level levels down the stack,giving it the value flag. If flag is non-nil, this will cause the debugger to be enteredwhen that frame later exits. Even a nonlocal exit through that frame will enter the
debugger.

This function is used only by the debugger.
[Variable]
This variable records the debugging status of the current interactive command. Eachtime a command is called interactively, this variable is bound to nil. The debugger
can set this variable to leave information for future debugger invocations during thesame command invocation.

command-debug-status

The advantage of using this variable rather than an ordinary global variable is thatthe data will never carry over to a subsequent command invocation.
This variable is obsolete and will be removed in future versions.

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backtrace-frame frame-number &optional base

[Function]
The function backtrace-frame is intended for use in Lisp debuggers. It returns
information about what computation is happening in the stack frame frame-number
levels down.
If that frame has not evaluated the arguments yet, or is a special form, the value is(nil function arg-forms...).
If that frame has evaluated its arguments and called its function already, the return
value is (t function arg-values...).
In the return value, function is whatever was supplied as the car of the evaluatedlist, or a lambda expression in the case of a macro call. If the function has a &rest
argument, that is represented as the tail of the list arg-values.
If base is specified, frame-number counts relative to the topmost frame whose function
is base.
If frame-number is out of range, backtrace-frame returns nil.

mapbacktrace function &optional base

[Function]
The function mapbacktrace calls function once for each frame in the backtrace, startingat the first frame whose function is base (or from the top if base is omitted or nil).
function is called with four arguments: evald, func, args, and flags.
If a frame has not evaluated its arguments yet or is a special form, evald is nil andargs is a list of forms.
If a frame has evaluated its arguments and called its function already, evald is t andargs is a list of values. flags is a plist of properties of the current frame: currently,
the only supported property is :debug-on-exit, which is t if the stack frame’s
debug-on-exit flag is set.

19.2 Edebug
Edebug is a source-level debugger for Emacs Lisp programs, with which you can:• Step through evaluation, stopping before and after each expression.
• Set conditional or unconditional breakpoints.
• Stop when a specified condition is true (the global break event).
• Trace slow or fast, stopping briefly at each stop point, or at each breakpoint.
• Display expression results and evaluate expressions as if outside of Edebug.
• Automatically re-evaluate a list of expressions and display their results each time Edebug
updates the display.
• Output trace information on function calls and returns.
• Stop when an error occurs.
• Display a backtrace, omitting Edebug’s own frames.
• Specify argument evaluation for macros and defining forms.
• Obtain rudimentary coverage testing and frequency counts.
The first three sections below should tell you enough about Edebug to start using it.

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19.2.1 Using Edebug
To debug a Lisp program with Edebug, you must first instrument the Lisp code that you
want to debug. A simple way to do this is to first move point into the definition of a function
or macro and then do C-u C-M-x (eval-defun with a prefix argument). See Section 19.2.2[Instrumenting], page 346, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates Edebug. Dependingon which Edebug execution mode you have selected, activating Edebug may stop execution
and let you step through the function, or it may update the display and continue execution
while checking for debugging commands. The default execution mode is step, which stops
execution. See Section 19.2.3 [Edebug Execution Modes], page 347.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp
code you are debugging. This is referred to as the source code buffer, and it is temporarily
read-only.
An arrow in the left fringe indicates the line where the function is executing. Point
initially shows where within the line the function is executing, but this ceases to be true if
you move point yourself.
If you instrument the definition of fac (shown below) and then execute (fac 3), here iswhat you would normally see. Point is at the open-parenthesis before if.
(defun fac (n)=>?(if (< 0 n)(* n (fac (1- n)))1))
The places within a function where Edebug can stop execution are called stop points.
These occur both before and after each subexpression that is a list, and also after eachvariable reference. Here we use periods to show the stop points in the function fac:
(defun fac (n).(if .(< 0 n.).
.(* n. .(fac .(1- n.).).).
1).)
The special commands of Edebug are available in the source code buffer in addition to
the commands of Emacs Lisp mode. For example, you can type the Edebug command SPC
to execute until the next stop point. If you type SPC once after entry to fac, here is thedisplay you will see:(defun fac (n)=>(if ?(< 0 n)(* n (fac (1- n)))1))
When Edebug stops execution after an expression, it displays the expression’s value inthe echo area.
Other frequently used commands are b to set a breakpoint at a stop point, g to execute
until a breakpoint is reached, and q to exit Edebug and return to the top-level command
loop. Type ? to display a list of all Edebug commands.

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19.2.2 Instrumenting for Edebug
In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting
code inserts additional code into it, to invoke Edebug at the proper places.
When you invoke command C-M-x (eval-defun) with a prefix argument on a function
definition, it instruments the definition before evaluating it. (This does not modify the sourcecode itself.) If the variable edebug-all-defs is non-nil, that inverts the meaning of theprefix argument: in this case, C-M-x instruments the definition unless it has a prefix argument.
The default value of edebug-all-defs is nil. The command M-x edebug-all-defs toggles
the value of the variable edebug-all-defs.
If edebug-all-defs is non-nil, then the commands eval-region, and eval-buffer
also instrument any definitions they evaluate. Similarly, edebug-all-forms controls whether
eval-region should instrument any form, even non-defining forms. This doesn’t apply toloading or evaluations in the minibuffer. The command M-x edebug-all-forms toggles thisoption.
Another command, M-x edebug-eval-top-level-form, is available to instrument
any top-level form regardless of the values of edebug-all-defs and edebug-all-forms.
edebug-defun is an alias for edebug-eval-top-level-form.
While Edebug is active, the command I (edebug-instrument-callee) instruments thedefinition of the function or macro called by the list form after point, if it is not already
instrumented. This is possible only if Edebug knows where to find the source for that function;
for this reason, after loading Edebug, eval-region records the position of every definition it
evaluates, even if not instrumenting it. See also the i command (see Section 19.2.4 [Jumping],
page 348), which steps into the call after instrumenting the function.
Edebug knows how to instrument all the standard special forms, interactive forms
with an expression argument, anonymous lambda expressions, and other defining forms.
However, Edebug cannot determine on its own what a user-defined macro will do with thearguments of a macro call, so you must provide that information using Edebug specifications;for details, see Section 19.2.15 [Edebug and Macros], page 358.
When Edebug is about to instrument code for the first time in a session, it runs the hook
edebug-setup-hook, then sets it to nil. You can use this to load Edebug specifications
associated with a package you are using, but only when you use Edebug.
If Edebug detects a syntax error while instrumenting, it leaves point at the erroneouscode and signals an invalid-read-syntax error. Example:
error

Invalid read syntax: "Expected lambda expression"

One potential reason for such a failure to instrument is that some macro definitions are
not yet known to Emacs. To work around this, load the file which defines the function you
are about to instrument.
To remove instrumentation from a definition, simply re-evaluate its definition in a waythat does not instrument. There are two ways of evaluating forms that never instrument
them: from a file with load, and from the minibuffer with eval-expression (M-:).
A different way to remove the instrumentation from a definition is to use theedebug-remove-instrumentation command. It also allows removing the instrumentationfrom everything that has been instrumented.

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See Section 19.2.9 [Edebug Eval], page 352, for other evaluation functions available insideof Edebug.

19.2.3 Edebug Execution Modes
Edebug supports several execution modes for running the program you are debugging. We
call these alternatives Edebug execution modes; do not confuse them with major or minor
modes. The current Edebug execution mode determines how far Edebug continues execution
before stopping—whether it stops at each stop point, or continues to the next breakpoint,
for example—and how much Edebug displays the progress of the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command to continue
the program in a certain mode. Here is a table of these commands; all except for S resume
execution of the program, at least for a certain distance.
S

Stop: don’t execute any more of the program, but wait for more Edebug
commands (edebug-stop).

SPC

Step: stop at the next stop point encountered (edebug-step-mode).

n

Next: stop at the next stop point encountered after an expression (edebug-nextmode). Also see edebug-forward-sexp in Section 19.2.4 [Jumping], page 348.

t

Trace: pause (normally one second) at each Edebug stop point (edebug-tracemode).

T

Rapid trace: update the display at each stop point, but don’t actually pause(edebug-Trace-fast-mode).

g

Go: run until the next breakpoint (edebug-go-mode). See Section 19.2.6.1[Breakpoints], page 350.

c

Continue: pause one second at each breakpoint, and then continue(edebug-continue-mode).

C

Rapid continue:
move point to each breakpoint,(edebug-Continue-fast-mode).

G

Go non-stop: ignore breakpoints (edebug-Go-nonstop-mode). You can still
stop the program by typing S, or any editing command.

but don’t pause

In general, the execution modes earlier in the above list run the program more slowly orstop sooner than the modes later in the list.
When you enter a new Edebug level, Edebug will normally stop at the first instrumented
function it encounters. If you prefer to stop only at a break point, or not at all (for example,
when gathering coverage data), change the value of edebug-initial-mode from its default
step to go, or Go-nonstop, or one of its other values (see Section 19.2.16 [Edebug Options],
page 364). You can do this readily with C-x C-a C-m (edebug-set-initial-mode):[Command]This command, bound to C-x C-a C-m, sets edebug-initial-mode. It prompts you
for a key to indicate the mode. You should enter one of the eight keys listed above,
which sets the corresponding mode.

edebug-set-initial-mode

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Note that you may reenter the same Edebug level several times if, for example, an
instrumented function is called several times from one command.
While executing or tracing, you can interrupt the execution by typing any Edebug
command. Edebug stops the program at the next stop point and then executes the command
you typed. For example, typing t during execution switches to trace mode at the next stop
point. You can use S to stop execution without doing anything else.
If your function happens to read input, a character you type intending to interrupt
execution may be read by the function instead. You can avoid such unintended results bypaying attention to when your program wants input.
Keyboard macros containing the commands in this section do not completely work:
exiting from Edebug, to resume the program, loses track of the keyboard macro. This is noteasy to fix. Also, defining or executing a keyboard macro outside of Edebug does not affectcommands inside Edebug. This is usually an advantage. See also the edebug-continuekbd-macro option in Section 19.2.16 [Edebug Options], page 364.
[User Option]
This option specifies how many seconds to wait between execution steps in trace modeor continue mode. The default is 1 second.

edebug-sit-for-seconds

19.2.4 Jumping
The commands described in this section execute until they reach a specified location. All
except i make a temporary breakpoint to establish the place to stop, then switch to go
mode. Any other breakpoint reached before the intended stop point will also stop execution.
See Section 19.2.6.1 [Breakpoints], page 350, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit, as that can bypass
the temporary breakpoint where you expected the program to stop.
h

Proceed to the stop point near where point is (edebug-goto-here).

f

Run the program for one expression (edebug-forward-sexp).

o

Run the program until the end of the containing sexp (edebug-step-out).

i

Step into the function or macro called by the form after point (edebug-step-in).

The h command proceeds to the stop point at or after the current location of point, using
a temporary breakpoint.
The f command runs the program forward over one expression. More precisely, it sets a
temporary breakpoint at the position that forward-sexp would reach, then executes in gomode so that the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If
the containing list ends before n more elements, then the place to stop is after the containing
expression.
You must check that the position forward-sexp finds is a place that the program will
really get to. In cond, for example, this may not be true.
For flexibility, the f command does forward-sexp starting at point, rather than at thestop point. If you want to execute one expression from the current stop point, first type w(edebug-where) to move point there, and then type f.

Chapter 19: Debugging Lisp Programs349

The o command continues out of an expression. It places a temporary breakpoint at
the end of the sexp containing point. If the containing sexp is a function definition itself, ocontinues until just before the last sexp in the definition. If that is where you are now, it
returns from the function and then stops. In other words, this command does not exit thecurrently executing function unless you are positioned after the last sexp.
Normally, the h, f, and o commands display “Break” and pause for edebug-sit-forseconds before showing the result of the form just evaluated. You can avoid this pause by
setting edebug-sit-on-break to nil. See Section 19.2.16 [Edebug Options], page 364.
The i command steps into the function or macro called by the list form after point, andstops at its first stop point. Note that the form need not be the one about to be evaluated.
But if the form is a function call about to be evaluated, remember to use this command
before any of the arguments are evaluated, since otherwise it will be too late.
The i command instruments the function or macro it’s supposed to step into, if it isn’t
instrumented already. This is convenient, but keep in mind that the function or macroremains instrumented unless you explicitly arrange to deinstrument it.

19.2.5 Miscellaneous Edebug Commands
Some miscellaneous Edebug commands are described here.
?

Display the help message for Edebug (edebug-help).

aC-]

Abort one level back to the previous command level (abort-recursive-edit).

q

Return to the top level editor command loop (top-level). This exits all recursive editing levels, including all levels of Edebug activity. However, instrumented
code protected with unwind-protect or condition-case forms may resume
debugging.

Q

Like q, but don’t stop even for protected code (edebug-top-level-nonstop).

r

Redisplay the most recently known expression result in the echo area
(edebug-previous-result).

dDisplay a backtrace, excluding Edebug’s own functions for clarity (edebug-popto-backtrace).
See Section 19.1.8 [Backtraces], page 338, for a description of backtraces andthe commands which work on them.
If you would like to see Edebug’s functions in the backtrace, use M-x edebugbacktrace-show-instrumentation. To hide them again use M-x edebugbacktrace-hide-instrumentation.
If a backtrace frame starts with ‘>’ that means that Edebug knows where thesource code for the frame is located. Use s to jump to the source code for thecurrent frame.
The backtrace buffer is killed automatically when you continue execution.

You can invoke commands from Edebug that activate Edebug again recursively. Whenever
Edebug is active, you can quit to the top level with q or abort one recursive edit level with
C-]. You can display a backtrace of all the pending evaluations with d.

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19.2.6 Breaks
Edebug’s step mode stops execution when the next stop point is reached. There are threeother ways to stop Edebug execution once it has started: breakpoints, the global breakcondition, and source breakpoints.

19.2.6.1 Edebug Breakpoints
While using Edebug, you can specify breakpoints in the program you are testing: these areplaces where execution should stop. You can set a breakpoint at any stop point, as definedin Section 19.2.1 [Using Edebug], page 345. For setting and unsetting breakpoints, the stop
point that is affected is the first one at or after point in the source code buffer. Here are the
Edebug commands for breakpoints:b

Set a breakpoint at the stop point at or after point (edebug-set-breakpoint).
If you use a prefix argument, the breakpoint is temporary—it turns off the firsttime it stops the program. An overlay with the edebug-enabled-breakpointor edebug-disabled-breakpoint faces is put at the breakpoint.

u

Unset the breakpoint (if any) at the stop point at or after point (edebug-unsetbreakpoint).

U

Unset any breakpoints in the current form (edebug-unset-breakpoints).

D

Toggle whether to disable the breakpoint near point (edebug-toggle-disablebreakpoint). This command is mostly useful if the breakpoint is conditional
and it would take some work to recreate the condition.

x condition RET
Set a conditional breakpoint which stops the program only if evaluating condition
produces a non-nil value (edebug-set-conditional-breakpoint). With aprefix argument, the breakpoint is temporary.
B

Move point to the next breakpoint in the current definition (edebug-nextbreakpoint).

While in Edebug, you can set a breakpoint with b and unset one with u. First movepoint to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint
there. Unsetting a breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition removes all of its previous breakpoints.
A conditional breakpoint tests a condition each time the program gets there. Any errorsthat occur as a result of evaluating the condition are ignored, as if the result were nil. To
set a conditional breakpoint, use x, and specify the condition expression in the minibuffer.
Setting a conditional breakpoint at a stop point that has a previously established conditional
breakpoint puts the previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint temporary by using a prefix
argument with the command to set the breakpoint. When a temporary breakpoint stops
the program, it is automatically unset.
Edebug always stops or pauses at a breakpoint, except when the Edebug mode is
Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to thenext breakpoint following point, within the same function, or to the first breakpoint if thereChapter 19: Debugging Lisp Programs351

are no following breakpoints. This command does not continue execution—it just moves
point in the buffer.

19.2.6.2 Global Break Condition
A global break condition stops execution when a specified condition is satisfied, no matter
where that may occur. Edebug evaluates the global break condition at every stop point; if it
evaluates to a non-nil value, then execution stops or pauses depending on the executionmode, as if a breakpoint had been hit. If evaluating the condition gets an error, execution
does not stop.
The condition expression is stored in edebug-global-break-condition. You can specify
a new expression using the X command from the source code buffer while Edebug is active,
or using C-x X X from any buffer at any time, as long as Edebug is loaded (edebug-setglobal-break-condition).
The global break condition is the simplest way to find where in your code some event
occurs, but it makes code run much more slowly. So you should reset the condition to nil
when not using it.

19.2.6.3 Source Breakpoints
All breakpoints in a definition are forgotten each time you reinstrument it. If you wish to
make a breakpoint that won’t be forgotten, you can write a source breakpoint, which issimply a call to the function edebug in your source code. You can, of course, make such acall conditional. For example, in the fac function, you can insert the first line as shown
below, to stop when the argument reaches zero:(defun fac (n)(if (= n 0) (edebug))(if (< 0 n)(* n (fac (1- n)))1))
When the fac definition is instrumented and the function is called, the call to edebug
acts as a breakpoint. Depending on the execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when edebug is called, that function calls
debug.

19.2.7 Trapping Errors
Emacs normally displays an error message when an error is signaled and not handled withcondition-case. While Edebug is active and executing instrumented code, it normally
responds to all unhandled errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see Section 19.2.16 [Edebug Options], page 364.
When Edebug responds to an error, it shows the last stop point encountered before theerror. This may be the location of a call to a function which was not instrumented, andwithin which the error actually occurred. For an unbound variable error, the last known
stop point might be quite distant from the offending variable reference. In that case, you
might want to display a full backtrace (see Section 19.2.5 [Edebug Misc], page 349).

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If you change debug-on-error or debug-on-quit while Edebug is active, these changes
will be forgotten when Edebug becomes inactive. Furthermore, during Edebug’s recursive
edit, these variables are bound to the values they had outside of Edebug.

19.2.8 Edebug Views
These Edebug commands let you view aspects of the buffer and window status as they were
before entry to Edebug. The outside window configuration is the collection of windows andcontents that were in effect outside of Edebug.
Pv

Switch to viewing the outside window configuration (edebug-view-outside).
Type C-x X w to return to Edebug.

pTemporarily display the outside current buffer with point at its outside position(edebug-bounce-point), pausing for one second before returning to Edebug.
With a prefix argument n, pause for n seconds instead.

w

Move point back to the current stop point in the source code buffer(edebug-where).
If you use this command in a different window displaying the same buffer, thatwindow will be used instead to display the current definition in the future.

W

Toggle whether Edebug saves and restores the outside window configuration(edebug-toggle-save-windows).
With a prefix argument, W only toggles saving and restoring of the selected
window. To specify a window that is not displaying the source code buffer, youmust use C-x X W from the global keymap.

You can view the outside window configuration with v or just bounce to the point in thecurrent buffer with p, even if it is not normally displayed.
After moving point, you may wish to jump back to the stop point. You can do that withw from a source code buffer. You can jump back to the stop point in the source code bufferfrom any buffer using C-x X w.
Each time you use W to turn saving off, Edebug forgets the saved outside window
configuration—so that even if you turn saving back on, the current window configuration
remains unchanged when you next exit Edebug (by continuing the program). However, theautomatic redisplay of *edebug* and *edebug-trace* may conflict with the buffers you
wish to see unless you have enough windows open.

19.2.9 Evaluation
While within Edebug, you can evaluate expressions as if Edebug were not running. Edebug
tries to be invisible to the expression’s evaluation and printing. Evaluation of expressions thatcause side effects will work as expected, except for changes to data that Edebug explicitly
saves and restores. See Section 19.2.14 [The Outside Context], page 357, for details on thisprocess.
e exp RET Evaluate expression exp in the context outside of Edebug (edebug-evalexpression). That is, Edebug tries to minimize its interference with theChapter 19: Debugging Lisp Programs

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evaluation. The result is shown in the echo area, or, if this command is given a
prefix, pop up a new buffer and pretty-print the result there.
By default, this command suppresses the debugger during evaluation, so that anerror in the evaluated expression won’t add a new error on top of the existingone. Set the debug-allow-recursive-debug user option to a non-nil value tooverride this.
M-: exp RET
Evaluate expression exp in the context of Edebug itself (eval-expression).
C-x C-e

Evaluate the expression before point, in the context outside of Edebug(edebug-eval-last-sexp). With the prefix argument of zero (C-u 0 C-x C-e),
don’t shorten long items (like strings and lists). Any other prefix will result inthe value being pretty-printed in a separate buffer.

Edebug supports evaluation of expressions containing references to lexically boundsymbols created by the following constructs in cl.el: lexical-let, macrolet, andsymbol-macrolet.

19.2.10 Evaluation List Buffer
You can use the evaluation list buffer, called *edebug*, to evaluate expressions interactively.
You can also set up the evaluation list of expressions to be evaluated automatically eachtime Edebug updates the display.
E

Switch to the evaluation list buffer *edebug* (edebug-visit-eval-list).

In the *edebug* buffer you can use the commands of Lisp Interaction mode (see Section“Lisp Interaction” in The GNU Emacs Manual) as well as these special commands:
C-j

Evaluate the expression before point, in the outside context, and insert the value
in the buffer (edebug-eval-print-last-sexp). With prefix argument of zero(C-u 0 C-j), don’t shorten long items (like strings and lists).

C-x C-e

Evaluate the expression before point, in the context outside of Edebug(edebug-eval-last-sexp).

C-c C-u

Build a new evaluation list from the contents of the buffer (edebug-updateeval-list).

C-c C-d

Delete the evaluation list group that point is in (edebug-delete-eval-item).

C-c C-w

Switch back to the source code buffer at the current stop point (edebug-where).

You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as
you would in *scratch*; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue
execution; but you can set up an evaluation list consisting of expressions to be evaluatedeach time execution stops.
To do this, write one or more evaluation list groups in the evaluation list buffer. An
evaluation list group consists of one or more Lisp expressions. Groups are separated bycomment lines.

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The command C-c C-u (edebug-update-eval-list) rebuilds the evaluation list, scanning the buffer and using the first expression of each group. (The idea is that the second
expression of the group is the value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each expression in thebuffer, followed by its current value. It also inserts comment lines so that each expression
becomes its own group. Thus, if you type C-c C-u again without changing the buffer text,
the evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the error message isdisplayed in a string as if it were the result. Therefore, expressions using variables that are
not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions
have been added to it:(current-buffer)#<buffer *scratch*>;--------------------------------------------------------------(selected-window)#<window 16 on *scratch*>;--------------------------------------------------------------(point)196;--------------------------------------------------------------bad-var"Symbol's value as variable is void: bad-var";--------------------------------------------------------------(recursion-depth)0;--------------------------------------------------------------this-commandeval-last-sexp;---------------------------------------------------------------

To delete a group, move point into it and type C-c C-d, or simply delete the text for
the group and update the evaluation list with C-c C-u. To add a new expression to theevaluation list, insert the expression at a suitable place, insert a new comment line, thentype C-c C-u. You need not insert dashes in the comment line—its contents don’t matter.
After selecting *edebug*, you can return to the source code buffer with C-c C-w. The*edebug* buffer is killed when you continue execution, and recreated next time it is needed.

19.2.11 Printing in Edebug
If an expression in your program produces a value containing circular list structure, you
may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set print-length or print-level totruncate the printing. Edebug does this for you; it binds print-length and print-levelto the values of the variables edebug-print-length and edebug-print-level (so long as
they have non-nil values). See Section 20.6 [Output Variables], page 380.
[User Option]
If non-nil, Edebug binds print-length to this value while printing results. The
default value is 50.

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355[User Option]
If non-nil, Edebug binds print-level to this value while printing results. The
default value is 50.

edebug-print-level

You can also print circular structures and structures that share elements more informatively by binding print-circle to a non-nil value.
Here is an example of code that creates a circular structure:(setq a (list 'x 'y))(setcar a a)If print-circle is non-nil, printing functions (e.g., prin1) will print a as ‘#1=(#1# y)’.
The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’
notation references the previously labeled structure. This notation is used for any sharedelements of lists or vectors.
[User Option]
If non-nil, Edebug binds print-circle to this value while printing results. The
default value is t.

edebug-print-circle

For further details about how printing can be customized, see see Section 20.5 [Output
Functions], page 377.

19.2.12 Trace Buffer
Edebug can record an execution trace, storing it in a buffer named *edebug-trace*. Thisis a log of function calls and returns, showing the function names and their arguments andvalues. To enable trace recording, set edebug-trace to a non-nil value.
Making a trace buffer is not the same thing as using trace execution mode (seeSection 19.2.3 [Edebug Execution Modes], page 347).
When trace recording is enabled, each function entry and exit adds lines to the trace
buffer. A function entry record consists of ‘::::{’, followed by the function name andargument values. A function exit record consists of ‘::::}’, followed by the function nameand result of the function.
The number of ‘:’s in an entry shows its recursion depth. You can use the braces in the
trace buffer to find the matching beginning or end of function calls.
You can customize trace recording for function entry and exit by redefining the functions
edebug-print-trace-before and edebug-print-trace-after.

edebug-tracing string body. . .

[Macro]This macro requests additional trace information around the execution of the bodyforms. The argument string specifies text to put in the trace buffer, after the ‘{’ or‘}’. All the arguments are evaluated, and edebug-tracing returns the value of thelast form in body.

edebug-trace format-string &rest format-args[Function]
This function inserts text in the trace buffer. It computes the text with (apply 'format
format-string format-args). It also appends a newline to separate entries.

edebug-tracing and edebug-trace insert lines in the trace buffer whenever they arecalled, even if Edebug is not active. Adding text to the trace buffer also scrolls its window
to show the last lines inserted.

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19.2.13 Coverage Testing
Edebug provides rudimentary coverage testing and display of execution frequency.
Coverage testing works by comparing the result of each expression with the previous
result; each form in the program is considered covered if it has returned two different values
since you began testing coverage in the current Emacs session. Thus, to do coverage testingon your program, execute it under various conditions and note whether it behaves correctly;
Edebug will tell you when you have tried enough different conditions that each form has
returned two different values.
Coverage testing makes execution slower, so it is only done if edebug-test-coverage is
non-nil. Frequency counting is performed for all executions of an instrumented function,even if the execution mode is Go-nonstop, and regardless of whether coverage testing isenabled.
Use C-x X = (edebug-display-freq-count) to display both the coverage informationand the frequency counts for a definition. Just = (edebug-temp-display-freq-count)displays the same information temporarily, only until you type another key.
[Command]This command displays the frequency count data for each line of the current definition.

edebug-display-freq-count

It inserts frequency counts as comment lines after each line of code. You can undo
all insertions with one undo command. The counts appear under the ‘(’ before an
expression or the ‘)’ after an expression, or on the last character of a variable. To
simplify the display, a count is not shown if it is equal to the count of an earlier
expression on the same line.
The character ‘=’ following the count for an expression says that the expression has
returned the same value each time it was evaluated. In other words, it is not yet
covered for coverage testing purposes.
To clear the frequency count and coverage data for a definition, simply reinstrument
it with eval-defun.
For example, after evaluating (fac 5) with a source breakpoint, and setting
edebug-test-coverage to t, when the breakpoint is reached, the frequency data looks likethis:(defun fac (n)(if (= n 0) (edebug))
;#6
1
= =5
(if (< 0 n);#5=(* n (fac (1- n)))
;#
5
0
1))
;#
0
The comment lines show that fac was called 6 times. The first if statement returned 5times with the same result each time; the same is true of the condition on the second if.
The recursive call of fac did not return at all.

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19.2.14 The Outside Context
Edebug tries to be transparent to the program you are debugging, but it does not succeed
completely. Edebug also tries to be transparent when you evaluate expressions with e orwith the evaluation list buffer, by temporarily restoring the outside context. This section
explains precisely what context Edebug restores, and how Edebug fails to be completelytransparent.

19.2.14.1 Checking Whether to Stop
Whenever Edebug is entered, it needs to save and restore certain data before even deciding
whether to make trace information or stop the program.
• max-lisp-eval-depth (see Section 10.4 [Eval], page 152) is increased to reduce Edebug’s
impact on the stack. You could, however, still run out of stack space when using Edebug.
You can also enlarge the value of edebug-max-depth if Edebug reaches the limit ofrecursion depth instrumenting code that contains very large quoted lists.
• The state of keyboard macro execution is saved and restored. While Edebug is active,
executing-kbd-macro is bound to nil unless edebug-continue-kbd-macro is nonnil.

19.2.14.2 Edebug Display Update
When Edebug needs to display something (e.g., in trace mode), it saves the current window
configuration from outside Edebug (see Section 29.26 [Window Configurations], page 774).
When you exit Edebug, it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program
re-enters Edebug at a breakpoint or after stepping, without pausing or reading input inbetween. In such cases, Emacs never gets a chance to redisplay the outside configuration.
Consequently, what you see is the same window configuration as the last time Edebug was
active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data
(though some of them are deliberately not restored if an error or quit signal occurs).
• Which buffer is current, and the positions of point and the mark in the current buffer,
are saved and restored.
• The outside window configuration is saved and restored if edebug-save-windows is
non-nil (see Section 19.2.16 [Edebug Options], page 364). If the value of edebug-savewindows is a list, only the listed windows are saved and restored.
The window configuration is not restored on error or quit, but the outside selected
window is reselected even on error or quit in case a save-excursion is active.
The window start and horizontal scrolling of the source code buffer are not restored,
however, so that the display remains coherent within Edebug.
Saving and restoring the outside window configuration can sometimes change thepositions of point in the buffers on which the Lisp program you are debugging operates,
especially if your program moves point. If this happens and interferes with yourdebugging, we recommend to set edebug-save-windows to nil (see Section 19.2.16[Edebug Options], page 364).
• The value of point in each displayed buffer is saved and restored if edebug-savedisplayed-buffer-points is non-nil.

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358• The variables overlay-arrow-position and overlay-arrow-string are saved andrestored, so you can safely invoke Edebug from the recursive edit elsewhere in the same
buffer.
• cursor-in-echo-area is locally bound to nil so that the cursor shows up in thewindow.

19.2.14.3 Edebug Recursive Edit
When Edebug is entered and actually reads commands from the user, it saves (and later
restores) these additional data:• The current match data. See Section 35.6 [Match Data], page 1011.
• The variables last-command, this-command, last-command-event, last-inputevent, last-event-frame, last-nonmenu-event, and track-mouse. Commands in
Edebug do not affect these variables outside of Edebug.
Executing commands within Edebug can change the key sequence that would be returnedby this-command-keys, and there is no way to reset the key sequence from Lisp.
Edebug cannot save and restore the value of unread-command-events. Entering Edebug
while this variable has a nontrivial value can interfere with execution of the program
you are debugging.
• Complex commands executed while in Edebug are added to the variablecommand-history. In rare cases this can alter execution.
• Within Edebug, the recursion depth appears one deeper than the recursion depth
outside Edebug. This is not true of the automatically updated evaluation list window.
• standard-output and standard-input are bound to nil by the recursive-edit, but
Edebug temporarily restores them during evaluations.
• The state of keyboard macro definition is saved and restored. While Edebug is active,
defining-kbd-macro is bound to edebug-continue-kbd-macro.

19.2.15 Edebug and Macros
To make Edebug properly instrument expressions that call macros, some extra care is needed.
This subsection explains the details.

19.2.15.1 Instrumenting Macro Calls
When Edebug instruments an expression that calls a Lisp macro, it needs additional
information about the macro to do the job properly. This is because there is no a-priori
way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation
may occur explicitly in the macro body, or when the resulting expansion is evaluated, or
any time later.)
Therefore, you must define an Edebug specification for each macro that Edebug willencounter, to explain the format of calls to that macro. To do this, add a debug declaration
to the macro definition. Here is a simple example that shows the specification for the forexample macro (see Section 14.5.2 [Argument Evaluation], page 271).
(defmacro for (var from init to final do &rest body)"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."(declare (debug (symbolp "from" form "to" form "do" &rest form)))

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...)

The Edebug specification says which parts of a call to the macro are forms to be evaluated.
For simple macros, the specification often looks very similar to the formal argument list of
the macro definition, but specifications are much more general than macro arguments. See
Section 14.4 [Defining Macros], page 270, for more explanation of the declare form.
Take care to ensure that the specifications are known to Edebug when you instrument
code. If you are instrumenting a function which uses a macro defined in another file, you
may first need to either evaluate the require forms in the file containing your function,
or explicitly load the file containing the macro. If the definition of a macro is wrapped byeval-when-compile, you may need to evaluate it.
You can also define an edebug specification for a macro separately from the macro definition with def-edebug-spec. Adding debug declarations is preferred, and more convenient,
for macro definitions in Lisp, but def-edebug-spec makes it possible to define Edebug
specifications for special forms implemented in C.

def-edebug-spec macro specification[Macro]Specify which expressions of a call to macro macro are forms to be evaluated. specification should be the Edebug specification. Neither argument is evaluated.
The macro argument can actually be any symbol, not just a macro name.

Here is a table of the possibilities for specification and how each directs processing ofarguments.
t

All arguments are instrumented for evaluation. This is short for (body).

a symbol

The symbol must have an Edebug specification, which is used instead. This
indirection is repeated until another kind of specification is found. This allows
you to inherit the specification from another macro.

a list

The elements of the list describe the types of the arguments of a calling form. The
possible elements of a specification list are described in the following sections.

If a macro has no Edebug specification, neither through a debug declaration nor througha def-edebug-spec call, the variable edebug-eval-macro-args comes into play.
[User Option]
This controls the way Edebug treats macro arguments with no explicit Edebug
specification. If it is nil (the default), none of the arguments is instrumented forevaluation. Otherwise, all arguments are instrumented.

edebug-eval-macro-args

19.2.15.2 Specification List
A specification list is required for an Edebug specification if some arguments of a macro callare evaluated while others are not. Some elements in a specification list match one or morearguments, but others modify the processing of all following elements. The latter, called
specification keywords, are symbols beginning with ‘&’ (such as &optional).
A specification list may contain sublists, which match arguments that are themselves
lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide
the specification list into a hierarchy of levels. Specification keywords apply only to theremainder of the sublist or group they are contained in.

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When a specification list involves alternatives or repetition, matching it against an actual
macro call may require backtracking. For more details, see Section 19.2.15.3 [Backtracking],
page 363.
Edebug specifications provide the power of regular expression matching, plus some contextfree grammar constructs: the matching of sublists with balanced parentheses, recursive
processing of forms, and recursion via indirect specifications.
Here’s a table of the possible elements of a specification list, with their meanings (seeSection 19.2.15.4 [Specification Examples], page 363, for the referenced examples):sexp

A single unevaluated Lisp object, which is not instrumented.

form

A single evaluated expression, which is instrumented. If your macro wraps
the expression with lambda before it is evaluated, use def-form instead. See
def-form below.

place

A generalized variable. See Section 12.17 [Generalized Variables], page 224.

body

Short for &rest form. See &rest below. If your macro wraps its body of codewith lambda before it is evaluated, use def-body instead. See def-body below.

lambda-expr
A lambda expression with no quoting.
&optional
All following elements in the specification list are optional; as soon as one does
not match, Edebug stops matching at this level.
To make just a few elements optional, followed by non-optional elements, use[&optional specs...]. To specify that several elements must all match ornone, use &optional [specs...]. See the defun example.
&rest

All following elements in the specification list are repeated zero or more times.
In the last repetition, however, it is not a problem if the expression runs out
before matching all of the elements of the specification list.
To repeat only a few elements, use [&rest specs...]. To specify several
elements that must all match on every repetition, use &rest [specs...].

&orEach of the following elements in the specification list is an alternative. One of
the alternatives must match, or the &or specification fails.
Each list element following &or is a single alternative. To group two or more
list elements as a single alternative, enclose them in [...].

&notEach of the following elements is matched as alternatives as if by using &or, but
if any of them match, the specification fails. If none of them match, nothing ismatched, but the &not specification succeeds.

&defineIndicates that the specification is for a defining form. Edebug’s definition of adefining form is a form containing one or more code forms which are saved andexecuted later, after the execution of the defining form.
The defining form itself is not instrumented (that is, Edebug does not stop before
and after the defining form), but forms inside it typically will be instrumented.
The &define keyword should be the first element in a list specification.

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nil

This is successful when there are no more arguments to match at the current
argument list level; otherwise it fails. See sublist specifications and the backquote
example.

gate

No argument is matched but backtracking through the gate is disabled while
matching the remainder of the specifications at this level. This is primarily
used to generate more specific syntax error messages. See Section 19.2.15.3[Backtracking], page 363, for more details. Also see the let example.

&error&error should be followed by a string, an error message, in the edebug-spec; itaborts the instrumentation, displaying the message in the minibuffer.

&interpose
Lets a function control the parsing of the remaining code. It takes the form
&interpose spec fun args... and means that Edebug will first match spec
against the code and then call fun with the code that matched spec, a parsing
function pf, and finally args.... The parsing function expects a single argument
indicating the specification list to use to parse the remaining code. It should becalled exactly once and returns the instrumented code that fun is expected toreturn. For example (&interpose symbolp pcase--match-pat-args) matches
sexps whose first element is a symbol and then lets pcase--match-pat-args
lookup the specs associated with that head symbol according to pcase--matchpat-args and pass them to the pf it received as argument.
other-symbol
Any other symbol in a specification list may be a predicate or an indirect
specification.
If the symbol has an Edebug specification, this indirect specification shouldbe either a list specification that is used in place of the symbol, or a functionthat is called to process the arguments. The specification may be defined with
def-edebug-elem-spec:

def-edebug-elem-spec element specification[Function]
Define the specification to use in place of the symbol element. specification
has to be a list.

Otherwise, the symbol should be a predicate. The predicate is called withthe argument, and if the predicate returns nil, the specification fails and theargument is not instrumented.
Some suitable predicates include symbolp, integerp, stringp, vectorp, andatom.
[elements...]A vector of elements groups the elements into a single group specification. Its
meaning has nothing to do with vectors.
"string"

The argument should be a symbol named string. This specification is equivalent
to the quoted symbol, 'symbol, where the name of symbol is the string, but
the string form is preferred.

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362(vector elements...)
The argument should be a vector whose elements must match the elements inthe specification. See the backquote example.
(elements...)Any other list is a sublist specification and the argument must be a list whose
elements match the specification elements.
A sublist specification may be a dotted list and the corresponding list argument
may then be a dotted list. Alternatively, the last cdr of a dotted list specification
may be another sublist specification (via a grouping or an indirect specification,e.g., (spec . [(more specs...)])) whose elements match the non-dotted list
arguments. This is useful in recursive specifications such as in the backquote
example. Also see the description of a nil specification above for terminatingsuch recursion.
Note that a sublist specification written as (specs . nil) is equivalent to(specs), and (specs . (sublist-elements...)) is equivalent to (specs
sublist-elements...).
Here is a list of additional specifications that may appear only after &define. See thedefun example.
&nameExtracts the name of the current defining form from the code. It takes the form
&name [prestring] spec [poststring] fun args... and means that Edebug
will match spec against the code and then call fun with the concatenation of thecurrent name, args..., prestring, the code that matched spec, and poststring. If
fun is absent, it defaults to a function that concatenates the arguments (withan @ between the previous name and the new).

name

The argument, a symbol, is the name of the defining form. Shorthand for [&namesymbolp].
A defining form is not required to have a name field; and it may have multiple
name fields.

arg

The argument, a symbol, is the name of an argument of the defining form.
However, lambda-list keywords (symbols starting with ‘&’) are not allowed.

lambda-list
This matches a lambda list—the argument list of a lambda expression.
def-body

The argument is the body of code in a definition. This is like body, describedabove, but a definition body must be instrumented with a different Edebug callthat looks up information associated with the definition. Use def-body for thehighest level list of forms within the definition.

def-form

The argument is a single, highest-level form in a definition. This is like def-body,
except it is used to match a single form rather than a list of forms. As a specialcase, def-form also means that tracing information is not output when the form
is executed. See the interactive example.

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19.2.15.3 Backtracking in Specifications
If a specification fails to match at some point, this does not necessarily mean a syntax
error will be signaled; instead, backtracking will take place until all alternatives have been
exhausted. Eventually every element of the argument list must be matched by some elementin the specification, and every required element in the specification must match someargument.
When a syntax error is detected, it might not be reported until much later, after higherlevel alternatives have been exhausted, and with the point positioned further from the realerror. But if backtracking is disabled when an error occurs, it can be reported immediately.
Note that backtracking is also reenabled automatically in several situations; when a newalternative is established by &optional, &rest, or &or, or at the start of processing a sublist,
group, or indirect specification. The effect of enabling or disabling backtracking is limited
to the remainder of the level currently being processed and lower levels.
Backtracking is disabled while matching any of the form specifications (that is, form,
body, def-form, and def-body). These specifications will match any form so any error must
be in the form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted symbol, string specification, or &define keyword, since this usually indicates a recognized construct. But if you
have a set of alternative constructs that all begin with the same symbol, you can usuallywork around this constraint by factoring the symbol out of the alternatives, e.g., ["foo"&or [first case] [second case] ...].
Most needs are satisfied by these two ways that backtracking is automatically disabled,
but occasionally it is useful to explicitly disable backtracking by using the gate specification.
This is useful when you know that no higher alternatives could apply. See the example ofthe let specification.

19.2.15.4 Specification Examples
It may be easier to understand Edebug specifications by studying the examples provided
here.
Consider a hypothetical macro my-test-generator that runs tests on supplied lists ofdata. Although it is Edebug’s default behavior to not instrument arguments as code, as
controlled by edebug-eval-macro-args (see Section 19.2.15.1 [Instrumenting Macro Calls],
page 358), it can be useful to explicitly document that the arguments are data:(def-edebug-spec my-test-generator (&rest sexp))
A let special form has a sequence of bindings and a body. Each of the bindings is either
a symbol or a sublist with a symbol and optional expression. In the specification below,
notice the gate inside of the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let((&rest&or symbolp (gate symbolp &optional form))body))
Edebug uses the following specifications for defun and the associated argument list andinteractive specifications. It is necessary to handle interactive forms specially since anChapter 19: Debugging Lisp Programs

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expression argument is actually evaluated outside of the function body. (The specification
for defmacro is very similar to that for defun, but allows for the declare statement.)(def-edebug-spec defun(&define name lambda-list[&optional stringp]; Match the doc string, if present.
[&optional ("interactive" interactive)]def-body))(def-edebug-elem-spec 'lambda-list'(([&rest arg][&optional ["&optional" arg &rest arg]]&optional ["&rest" arg])))
(def-edebug-elem-spec 'interactive'(&optional &or stringp def-form)); Notice: def-form

The specification for backquote below illustrates how to match dotted lists and use nil
to terminate recursion. It also illustrates how components of a vector may be matched. (Theactual specification defined by Edebug is a little different, and does not support dotted lists
because doing so causes very deep recursion that could fail.)(def-edebug-spec \` (backquote-form)); Alias just for clarity.

(def-edebug-elem-spec 'backquote-form'(&or ([&or "," ",@"] &or ("quote" backquote-form) form)(backquote-form . [&or nil backquote-form])(vector &rest backquote-form)sexp))

19.2.16 Edebug Options
These options affect the behavior of Edebug:[User Option]
Functions to call before Edebug is used. Each time it is set to a new value, Edebug
will call those functions once and then reset edebug-setup-hook to nil. You could
use this to load up Edebug specifications associated with a package you are using, but
only when you also use Edebug. See Section 19.2.2 [Instrumenting], page 346.

edebug-setup-hook[User Option]
If this is non-nil, normal evaluation of defining forms such as defun and defmacro
instruments them for Edebug. This applies to eval-defun, eval-region andeval-buffer.

edebug-all-defs

Use the command M-x edebug-all-defs to toggle the value of this option. See
Section 19.2.2 [Instrumenting], page 346.
[User Option]
If this is non-nil, the commands eval-defun, eval-region and eval-buffer instrument all forms, even those that don’t define anything. This doesn’t apply to loadingor evaluations in the minibuffer.

edebug-all-forms

Use the command M-x edebug-all-forms to toggle the value of this option. See
Section 19.2.2 [Instrumenting], page 346.

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365[User Option]
When this is non-nil, all macro arguments will be instrumented in the generated
code. For any macro, the debug declaration overrides this option. So to specify
exceptions for macros that have some arguments evaluated and some not, use thedebug declaration specify an Edebug form specification.

edebug-eval-macro-args[User Option]
If this is non-nil, Edebug saves and restores the window configuration. That takessome time, so if your program does not care what happens to the window configurations,
it is better to set this variable to nil. We also recommend to set this to nil if thedefault value causes Edebug to overwrite the positions of point in buffers that are
involved in the program you are debugging, as result of saving and restoring thewindow configuration; this could happen if your program moves point in one or moreof those buffers. Another option to try to customize in this case is edebug-savedisplayed-buffer-points, described below.

edebug-save-windows

If the value of edebug-save-windows is a list, only the listed windows are saved andrestored.
You can use the W command in Edebug to change this variable interactively. See
Section 19.2.14.2 [Edebug Display Update], page 357.
[User Option]
If this is non-nil, Edebug saves and restores point in all displayed buffers.

edebug-save-displayed-buffer-points

Saving and restoring point in other buffers is necessary if you are debugging code thatchanges the point of a buffer that is displayed in a non-selected window. If Edebug or
the user then selects the window, point in that buffer will move to the window’s valueof point.
Saving and restoring point in all buffers is expensive, since it requires selecting eachwindow twice, so enable this only if you need it. See Section 19.2.14.2 [Edebug Display
Update], page 357.
[User Option]
If this variable is non-nil, it specifies the initial execution mode for Edebug when it isfirst activated. Possible values are step, next, go, Go-nonstop, trace, Trace-fast,
continue, and Continue-fast.

edebug-initial-mode

The default value is step. This variable can be set interactively with C-x C-a C-m(edebug-set-initial-mode). See Section 19.2.3 [Edebug Execution Modes], page 347.
[User Option]
If this is non-nil, trace each function entry and exit. Tracing output is displayed in abuffer named *edebug-trace*, one function entry or exit per line, indented by therecursion level.

edebug-trace

Also see edebug-tracing, in Section 19.2.12 [Trace Buffer], page 355.
[User Option]
If non-nil, Edebug tests coverage of all expressions debugged. See Section 19.2.13[Coverage Testing], page 356.

edebug-test-coverageChapter 19: Debugging Lisp Programs

366[User Option]
If non-nil, continue defining or executing any keyboard macro that is executing
outside of Edebug. Use this with caution since it is not debugged. See Section 19.2.3[Edebug Execution Modes], page 347.

edebug-continue-kbd-macro[User Option]
If non-nil, the default value of print-length for printing results in Edebug. See
Section 20.6 [Output Variables], page 380.

edebug-print-length[User Option]
If non-nil, the default value of print-level for printing results in Edebug. See
Section 20.6 [Output Variables], page 380.

edebug-print-level[User Option]
If non-nil, the default value of print-circle for printing results in Edebug. See
Section 20.6 [Output Variables], page 380.

edebug-print-circle[User Option]
If non-nil, Edebug tries to remove any of its own instrumentation when showing theresults of expressions. This is relevant when debugging macros where the results ofexpressions are themselves instrumented expressions. As a very artificial example,
suppose that the example function fac has been instrumented, and consider a macroof the form:

edebug-unwrap-results(defmacro test () "Edebug example."(if (symbol-function 'fac)...))

If you instrument the test macro and step through it, then by default the result of
the symbol-function call has numerous edebug-after and edebug-before forms,
which can make it difficult to see the actual result. If edebug-unwrap-results is
non-nil, Edebug tries to remove these forms from the result.
[User Option]
Edebug binds debug-on-error to this value, if debug-on-error was previously nil.
See Section 19.2.7 [Trapping Errors], page 351.

edebug-on-error[User Option]
Edebug binds debug-on-quit to this value, if debug-on-quit was previously nil.
See Section 19.2.7 [Trapping Errors], page 351.

edebug-on-quit

If you change the values of edebug-on-error or edebug-on-quit while Edebug is active,
their values won’t be used until the next time Edebug is invoked via a new command.
[User Option]
If non-nil, an expression to test for at every stop point. If the result is non-nil, thenbreak. Errors are ignored. See Section 19.2.6.2 [Global Break Condition], page 351.

edebug-global-break-condition[User Option]
Number of seconds to pause when a breakpoint is reached and the execution mode istrace or continue. See Section 19.2.3 [Edebug Execution Modes], page 347.

edebug-sit-for-seconds

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367[User Option]
Whether or not to pause for edebug-sit-for-seconds on reaching a breakpoint. Set
to nil to prevent the pause, non-nil to allow it.

edebug-sit-on-break[User Option]
By default, this alist contains one entry with the key edebug and a list of three functions,which are the default implementations of the functions inserted in instrumented code:
edebug-enter, edebug-before and edebug-after. To change Edebug’s behavior
globally, modify the default entry.

edebug-behavior-alist

Edebug’s behavior may also be changed on a per-definition basis by adding an entry tothis alist, with a key of your choice and three functions. Then set the edebug-behavior
symbol property of an instrumented definition to the key of the new entry, and Edebug
will call the new functions in place of its own for that definition.
[User Option]
A function run by Edebug after it wraps the body of a definition or closure. After
Edebug has initialized its own data, this function is called with one argument, thesymbol associated with the definition, which may be the actual symbol defined or one
generated by Edebug. This function may be used to set the edebug-behavior symbol
property of each definition instrumented by Edebug.

edebug-new-definition-function[User Option]
To inspect or modify Edebug’s instrumentation before it is used, set this variable toa function which takes one argument, an instrumented top-level form, and returns
either the same or a replacement form, which Edebug will then use as the final resultof instrumentation.

edebug-after-instrumentation-function

19.3 Debugging Invalid Lisp Syntax
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For
example, the error ‘End of file during parsing’ in evaluating an expression indicates anexcess of open parentheses (or square brackets). The reader detects this imbalance atthe end of the file, but it cannot figure out where the close parenthesis should have been.
Likewise, ‘Invalid read syntax: ")"’ indicates an excess close parenthesis or missing open
parenthesis, but does not say where the missing parenthesis belongs. How, then, to findwhat to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try
C-M-e (end-of-defun, see Section “Moving by Defuns” in The GNU Emacs Manual) at the
beginning of each defun, and see if it goes to the place where that defun appears to end. If
it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we
can give further advice for those cases. (In addition, just moving point through the codewith Show Paren mode enabled might find the mismatch.)

19.3.1 Excess Open Parentheses
The first step is to find the defun that is unbalanced. If there is an excess open parenthesis,
the way to do this is to go to the end of the file and type C-u C-M-u (backward-up-list,

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see Section “Moving by Parens” in The GNU Emacs Manual). This will move you to thebeginning of the first defun that is unbalanced.
The next step is to determine precisely what is wrong. There is no way to be sure of thisexcept by studying the program, but often the existing indentation is a clue to where theparentheses should have been. The easiest way to use this clue is to reindent with C-M-q(indent-pp-sexp, see Section “Multi-line Indent” in The GNU Emacs Manual) and see
what moves. But don’t do this yet! Keep reading, first.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q
will get an error, or will reindent all the rest of the file until the end. So move to the end of
the defun and insert a close parenthesis there. Don’t use C-M-e (end-of-defun) to move
there, since that too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type C-M-q. Usually all the lines froma certain point to the end of the function will shift to the right. There is probably a missing
close parenthesis, or a superfluous open parenthesis, near that point. (However, don’t assume
this is true; study the code to make sure.) Once you have found the discrepancy, undo the
C-M-q with C-_ (undo), since the old indentation is probably appropriate to the intended
parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation
actually fit the intended nesting of parentheses, and you have put back those parentheses,
C-M-q should not change anything.

19.3.2 Excess Close Parentheses
To deal with an excess close parenthesis, first go to the beginning of the file, then type C-u -1
C-M-u (backward-up-list with an argument of −1) to find the end of the first unbalanced
defun.
Then find the actual matching close parenthesis by typing C-M-f (forward-sexp, see
Section “Expressions” in The GNU Emacs Manual) at the beginning of that defun. This
will leave you somewhere short of the place where the defun ought to end. It is possible thatyou will find a spurious close parenthesis in that vicinity.
If you don’t see a problem at that point, the next thing to do is to type C-M-q (indent-ppsexp) at the beginning of the defun. A range of lines will probably shift left; if so, themissing open parenthesis or spurious close parenthesis is probably near the first of those lines.
(However, don’t assume this is true; study the code to make sure.) Once you have foundthe discrepancy, undo the C-M-q with C-_ (undo), since the old indentation is probably
appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation
actually fits the intended nesting of parentheses, and you have put back those parentheses,
C-M-q should not change anything.

19.4 Test Coverage
You can do coverage testing for a file of Lisp code by loading the testcover library and using
the command M-x testcover-start RET file RET to instrument the code. Then test yourcode by calling it one or more times. Then use the command M-x testcover-mark-all to
display colored highlights on the code to show where coverage is insufficient. The commandM-x testcover-next-mark will move point forward to the next highlighted spot.

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Normally, a red highlight indicates the form was never completely evaluated; a brownhighlight means it always evaluated to the same value (meaning there has been little testingof what is done with the result). However, the red highlight is skipped for forms that can’t
possibly complete their evaluation, such as error. The brown highlight is skipped for forms
that are expected to always evaluate to the same value, such as (setq x 14).
For difficult cases, you can add do-nothing macros to your code to give advice to the test
coverage tool.

1value form

[Macro]Evaluate form and return its value, but inform coverage testing that form’s value
should always be the same.

noreturn form

[Macro]Evaluate form, informing coverage testing that form should never return. If it everdoes return, you get a run-time error.

Edebug also has a coverage testing feature (see Section 19.2.13 [Coverage Testing],
page 356). These features partly duplicate each other, and it would be cleaner to combine
them.

19.5 Profiling
If your program is working correctly, but not fast enough, and you want to make it run
more quickly or efficiently, the first thing to do is profile your code so that you know where
it spends most of the execution time. If you find that one particular function is responsible
for a significant portion of the execution time, you can start looking for ways to optimizethat piece.
Emacs has built-in support for this. To begin profiling, type M-x profiler-start. You
can choose to sample CPU usage periodically (cpu), when memory is allocated (memory), or
both. Then run the code you’d like to speed up. After that, type M-x profiler-report
to display a summary buffer for CPU usage sampled by each type (cpu and memory)that you chose to profile. The names of the report buffers include the times at which
the reports were generated, so you can generate another report later on without erasing
previous results. When you have finished profiling, type M-x profiler-stop (there is asmall overhead associated with profiling, so we don’t recommend leaving it active except
when you are actually running the code you want to examine).
The profiler report buffer shows, on each line, a function that was called, preceded by
how much CPU resources it used in absolute and percentage terms since profiling started. If
a given line has a ‘+’ symbol to the left of the function name, you can expand that line bytyping RET, in order to see the function(s) called by the higher-level function. Use a prefix
argument (C-u RET) to see the whole call tree below a function. Pressing RET again will
collapse back to the original state.
Press j (profiler-report-find-entry) or mouse-2 to jump to the definition of afunction at point. Press d (profiler-report-describe-entry) to view a function’s
documentation. You can save a profile to a file using C-x C-w (profiler-reportwrite-profile) and read a saved profile with M-x profiler-find-profile orM-x profiler-find-profile-other-window. You can compare two profiles using =(profiler-report-compare-profile).

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The elp library offers an alternative approach, which is useful when you know inadvance which Lisp function(s) you want to profile. Using that library, you begin by setting
elp-function-list to the list of function symbols—those are the functions you want toprofile. Then type M-x elp-instrument-list RET nil RET to arrange for profiling thosefunctions. After running the code you want to profile, invoke M-x elp-results to display
the current results. See the file elp.el for more detailed instructions. This approach islimited to profiling functions written in Lisp, it cannot profile Emacs primitives.
You can measure the time it takes to evaluate individual Emacs Lisp forms using thebenchmark library. See the function benchmark-call as well as the macros benchmark-run,benchmark-run-compiled, and benchmark-progn in benchmark.el. You can also use thebenchmark command for timing forms interactively.

371

20 Reading and Printing Lisp Objects
Printing and reading are the operations of converting Lisp objects to textual form and viceversa. They use the printed representations and read syntax described in Chapter 2 [Lisp
Data Types], page 8.
This chapter describes the Lisp functions for reading and printing. It also describes
streams, which specify where to get the text (if reading) or where to put it (if printing).

20.1 Introduction to Reading and Printing
Reading a Lisp object means parsing a Lisp expression in textual form and producing acorresponding Lisp object. This is how Lisp programs get into Lisp from files of Lisp code.
We call the text the read syntax of the object. For example, the text ‘(a . 5)’ is the readsyntax for a cons cell whose car is a and whose cdr is the number 5.
Printing a Lisp object means producing text that represents that object—converting
the object to its printed representation (see Section 2.1 [Printed Representation], page 8).
Printing the cons cell described above produces the text ‘(a . 5)’.
Reading and printing are more or less inverse operations: printing the object that resultsfrom reading a given piece of text often produces the same text, and reading the text that
results from printing an object usually produces a similar-looking object. For example,
printing the symbol foo produces the text ‘foo’, and reading that text returns the symbol
foo. Printing a list whose elements are a and b produces the text ‘(a b)’, and reading thattext produces a list (but not the same list) with elements a and b.
However, these two operations are not precisely inverse to each other. There are threekinds of exceptions:• Printing can produce text that cannot be read. For example, buffers, windows, frames,
subprocesses and markers print as text that starts with ‘#’; if you try to read this text,
you get an error. There is no way to read those data types.
• One object can have multiple textual representations. For example, ‘1’ and ‘01’ represent
the same integer, and ‘(a b)’ and ‘(a . (b))’ represent the same list. Reading will
accept any of the alternatives, but printing must choose one of them.
• Comments can appear at certain points in the middle of an object’s read sequence
without affecting the result of reading it.

20.2 Input Streams
Most of the Lisp functions for reading text take an input stream as an argument. The input
stream specifies where or how to get the characters of the text to be read. Here are thepossible types of input stream:
buffer

The input characters are read from buffer, starting with the character directly
after point. Point advances as characters are read.

marker

The input characters are read from the buffer that marker is in, starting with thecharacter directly after the marker. The marker position advances as characters
are read. The value of point in the buffer has no effect when the stream is amarker.

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string

The input characters are taken from string, starting at the first character in thestring and using as many characters as required.

function

The input characters are generated by function, which must support two kindsof calls:• When it is called with no arguments, it should return the next character.
• When it is called with one argument (always a character), function shouldsave the argument and arrange to return it on the next call. This iscalled unreading the character; it happens when the Lisp reader reads one
character too many and wants to put it back where it came from. In thiscase, it makes no difference what value function returns.
t used as a stream means that the input is read from the minibuffer. In fact,
the minibuffer is invoked once and the text given by the user is made into astring that is then used as the input stream. If Emacs is running in batch mode(see Section 42.17 [Batch Mode], page 1289), standard input is used instead ofthe minibuffer. For example,t(message "%s" (read t))
will in batch mode read a Lisp expression from standard input and print theresult to standard output.
nil

nil supplied as an input stream means to use the value of standard-input
instead; that value is the default input stream, and must be a non-nil input
stream.

symbol

A symbol as input stream is equivalent to the symbol’s function definition (ifany).

Here is an example of reading from a stream that is a buffer, showing where point islocated before and after:---------- Buffer: foo ---------This? is the contents of foo.
---------- Buffer: foo ---------(read (get-buffer "foo"))⇒ is(read (get-buffer "foo"))⇒ the---------- Buffer: foo ---------This is the? contents of foo.
---------- Buffer: foo ---------Note that the first read skips a space. Reading skips any amount of whitespace preceding
the significant text.
Here is an example of reading from a stream that is a marker, initially positioned at the
beginning of the buffer shown. The value read is the symbol This.

Chapter 20: Reading and Printing Lisp Objects373---------- Buffer: foo ---------This is the contents of foo.
---------- Buffer: foo ---------(setq m (set-marker (make-marker) 1 (get-buffer "foo")))⇒ #<marker at 1 in foo>
(read m)⇒ Thism⇒ #<marker at 5 in foo>;; Before the first space.
Here we read from the contents of a string:(read "(When in) the course")⇒ (When in)
The following example reads from the minibuffer. The prompt is: ‘Lisp expression: ’.
(That is always the prompt used when you read from the stream t.) The user’s input isshown following the prompt.
(read t)⇒ 23---------- Buffer: Minibuffer ---------Lisp expression: 23 RET---------- Buffer: Minibuffer ---------Finally, here is an example of a stream that is a function, named useless-stream. Before
we use the stream, we initialize the variable useless-list to a list of characters. Theneach call to the function useless-stream obtains the next character in the list or unreadsa character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))⇒ (88 89 40 41)(defun useless-stream (&optional unread)(if unread(setq useless-list (cons unread useless-list))(prog1 (car useless-list)(setq useless-list (cdr useless-list)))))⇒ useless-stream
Now we read using the stream thus constructed:(read 'useless-stream)⇒ XY
useless-list⇒ (40 41)
Note that the open and close parentheses remain in the list. The Lisp reader encountered
the open parenthesis, decided that it ended the input, and unread it. Another attempt toread from the stream at this point would read ‘()’ and return nil.

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20.3 Input Functions
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see the previous section). If
stream is nil or omitted, it defaults to the value of standard-input.
An end-of-file error is signaled if reading encounters an unterminated list, vector, or
string.

read &optional stream[Function]
This function reads one textual Lisp expression from stream, returning it as a Lisp
object. This is the basic Lisp input function.

read-from-string string &optional start end[Function]
This function reads the first textual Lisp expression from the text in string. It returns
a cons cell whose car is that expression, and whose cdr is an integer giving theposition of the next remaining character in the string (i.e., the first one not read).
If start is supplied, then reading begins at index start in the string (where the firstcharacter is at index 0). If you specify end, then reading is forced to stop just before
that index, as if the rest of the string were not there.
For example:(read-from-string "(setq x 55) (setq y 5)")⇒ ((setq x 55) . 11)(read-from-string "\"A short string\"")⇒ ("A short string" . 16);; Read starting at the first character.
(read-from-string "(list 112)" 0)⇒ ((list 112) . 10);; Read starting at the second character.
(read-from-string "(list 112)" 1)⇒ (list . 5);; Read starting at the seventh character,;;and stopping at the ninth.
(read-from-string "(list 112)" 6 8)
⇒ (11 . 8)

read-positioning-symbols &optional stream[Function]
This function reads one textual expression from stream, like read does, but additionally
positions the read symbols to the positions in stream where they occurred. Only thesymbol nil is not positioned, this for efficiency reasons. See Section 9.6 [Symbols with
Position], page 143. This function is used by the byte compiler.
[Variable]
This variable holds the default input stream—the stream that read uses when thestream argument is nil. The default is t, meaning use the minibuffer.

standard-input[Variable]
If non-nil, this variable enables the reading of circular and shared structures. See
Section 2.6 [Circular Objects], page 30. Its default value is t.

read-circle

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When reading or writing from the standard input/output streams of the Emacs process
in batch mode, it is sometimes required to make sure any arbitrary binary data will beread/written verbatim, and/or that no translation of newlines to or from CR-LF pairs is
performed. This issue does not exist on POSIX hosts, only on MS-Windows and MS-DOS.
The following function allows you to control the I/O mode of any standard stream of theEmacs process.

set-binary-mode stream mode

[Function]
Switch stream into binary or text I/O mode. If mode is non-nil, switch to binarymode, otherwise switch to text mode. The value of stream can be one of stdin,
stdout, or stderr. This function flushes any pending output data of stream as a side
effect, and returns the previous value of I/O mode for stream. On POSIX hosts, it
always returns a non-nil value and does nothing except flushing pending output.

readablep object[Function]
This predicate says whether object has readable syntax, i.e., it can be written out
and then read back by the Emacs Lisp reader. If it can’t, this function returns nil;
if it can, this function returns a printed representation (via prin1, see Section 20.5
[Output Functions], page 377) of object.

20.4 Output Streams
An output stream specifies what to do with the characters produced by printing. Most printfunctions accept an output stream as an optional argument. Here are the possible types of
output stream:
buffer

The output characters are inserted into buffer at point. Point advances ascharacters are inserted.

marker

The output characters are inserted into the buffer that marker points into, at
the marker position. The marker position advances as characters are inserted.
The value of point in the buffer has no effect on printing when the stream is amarker, and this kind of printing does not move point (except that if the marker
points at or before the position of point, point advances with the surrounding
text, as usual).

function

The output characters are passed to function, which is responsible for storingthem away. It is called with a single character as argument, as many times as
there are characters to be output, and is responsible for storing the characterswherever you want to put them.

t

The output characters are displayed in the echo area. If Emacs is running inbatch mode (see Section 42.17 [Batch Mode], page 1289), the output is written
to the standard output descriptor instead.

nil

nil specified as an output stream means to use the value of the standard-output
variable instead; that value is the default output stream, and must not be nil.

symbol

A symbol as output stream is equivalent to the symbol’s function definition (ifany).

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Many of the valid output streams are also valid as input streams. The difference between
input and output streams is therefore more a matter of how you use a Lisp object, than ofdifferent types of object.
Here is an example of a buffer used as an output stream. Point is initially located asshown immediately before the ‘h’ in ‘the’. At the end, point is located directly before thatsame ‘h’.
---------- Buffer: foo ---------This is t?he contents of foo.
---------- Buffer: foo ---------(print "This is the output" (get-buffer "foo"))⇒ "This is the output"---------- Buffer: foo ---------This is t
"This is the output"?he contents of foo.
---------- Buffer: foo ---------Now we show a use of a marker as an output stream. Initially, the marker is in buffer foo,
between the ‘t’ and the ‘h’ in the word ‘the’. At the end, the marker has advanced over theinserted text so that it remains positioned before the same ‘h’. Note that the location ofpoint, shown in the usual fashion, has no effect.
---------- Buffer: foo ---------This is the ?output---------- Buffer: foo ---------(setq m (copy-marker 10))
⇒ #<marker at 10 in foo>(print "More output for foo." m)⇒ "More output for foo."---------- Buffer: foo ---------This is t"More output for foo."
he ?output---------- Buffer: foo ---------m⇒ #<marker at 34 in foo>
The following example shows output to the echo area:(print "Echo Area output" t)⇒ "Echo Area output"---------- Echo Area ---------"Echo Area output"---------- Echo Area ----------

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Finally, we show the use of a function as an output stream. The function eat-output
takes each character that it is given and conses it onto the front of the list last-output(see Section 5.4 [Building Lists], page 82). At the end, the list contains all the characters
output, but in reverse order.
(setq last-output nil)⇒ nil(defun eat-output (c)(setq last-output (cons c last-output)))⇒ eat-output(print "This is the output" #'eat-output)⇒ "This is the output"
last-output⇒ (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:(concat (nreverse last-output))⇒ "\"This is the output\""
Calling concat converts the list to a string so you can see its contents more clearly.

external-debugging-output character[Function]
This function can be useful as an output stream when debugging. It writes characterto the standard error stream.
For example(print "This is the output" #'external-debugging-output)a This is the output⇒ "This is the output"

20.5 Output Functions
This section describes the Lisp functions for printing Lisp objects—converting objects into
their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary
so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguishstrings from symbols, and prevent punctuation characters in strings and symbols from being
taken as delimiters when reading. See Section 2.1 [Printed Representation], page 8, for fulldetails. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting charactersto avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp
programmer. However, if the purpose of the output is to look nice for humans, then it isusually better to print without quoting.

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Lisp objects can refer to themselves. Printing a self-referential object in the normal way
would require an infinite amount of text, and the attempt could cause infinite recursion.
Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object
already being printed. For example, here ‘#0’ indicates a recursive reference to the object at
level 0 of the current print operation:(setq foo (list nil))⇒ (nil)(setcar foo foo)
⇒ (#0)In the functions below, stream stands for an output stream. (See the previous section
for a description of output streams. Also See [external-debugging-output], page 377, a
useful stream value for debugging.) If stream is nil or omitted, it defaults to the value ofstandard-output.

print object &optional stream[Function]
The print function is a convenient way of printing. It outputs the printed representation of object to stream, printing in addition one newline before object and anotherafter it. Quoting characters are used. print returns object. For example:(progn (print 'The\ cat\ in)(print "the hat")(print " came back"))aa The\ cat\ inaa "the hat"aa " came back"⇒ " came back"prin1 object &optional stream overrides[Function]
This function outputs the printed representation of object to stream. It does not print
newlines to separate output as print does, but it does use quoting characters justlike print. It returns object.
(progn (prin1 'The\ cat\ in)(prin1 "the hat")(prin1 " came back"))a The\ cat\ in"the hat"" came back"⇒ " came back"If overrides is non-nil, it should either be t (which tells prin1 to use the defaults for
all printer related variables), or a list of settings. See Section 20.7 [Output Overrides],page 383, for details.

princ object &optional stream[Function]
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people, not by read, so
it doesn’t insert quoting characters and doesn’t put double-quotes around the contentsof strings. It does not add any spacing between calls.

Chapter 20: Reading and Printing Lisp Objects

379(progn(princ 'The\ cat)(princ " in the \"hat\""))
a The cat in the "hat"⇒ " in the \"hat\""terpri &optional stream ensure[Function]
This function outputs a newline to stream. The name stands for “terminate print”. If
ensure is non-nil no newline is printed if stream is already at the beginning of a line.
Note in this case stream can not be a function and an error is signaled if it is. Thisfunction returns t if a newline is printed.

write-char character &optional stream[Function]

This function outputs character to stream. It returns character.
[Function]
If you have Emacs-based batch scripts that send output to the terminal, Emacs
will automatically display the output whenever you write a newline characters tostandard-output. This function allows you to flush to standard-output without
sending a newline character first, which enables you to display incomplete lines.

flush-standard-output

prin1-to-string object &optional noescape overrides[Function]
This function returns a string containing the text that prin1 would have printed forthe same argument.
(prin1-to-string 'foo)⇒ "foo"(prin1-to-string (mark-marker))⇒ "#<marker at 2773 in strings.texi>"
If overrides is non-nil, it should either be t(which tells prin1 to use the defaults for all printer related
variables), or a list of settings. See Section 20.7 [Output Overrides], page 383, for details.
If noescape is non-nil, that inhibits use of quoting characters in the output. (Thisargument is supported in Emacs versions 19 and later.)(prin1-to-string "foo")⇒ "\"foo\""(prin1-to-string "foo" t)⇒ "foo"See format, in Section 4.7 [Formatting Strings], page 66, for other ways to obtain theprinted representation of a Lisp object as a string.

with-output-to-string body. . .

[Macro]This macro executes the body forms with standard-output set up to feed output
into a string. Then it returns that string.
For example, if the current buffer name is ‘foo’,(with-output-to-stringChapter 20: Reading and Printing Lisp Objects

380(princ "The buffer is ")(princ (buffer-name)))returns "The buffer is foo".

pp object &optional stream[Function]
This function outputs object to stream, just like prin1, but does it in a prettier way.
That is, it’ll indent and fill the object to make it more readable for humans.

If you need to use binary I/O in batch mode, e.g., use the functions described in thissection to write out arbitrary binary data or avoid conversion of newlines on non-POSIX
hosts, see Section 20.3 [Input Functions], page 374.

20.6 Variables Affecting Output[Variable]
The value of this variable is the default output stream—the stream that print functions
use when the stream argument is nil. The default is t, meaning display in the echo
area.

standard-output[Variable]
If this is non-nil, that means to print quoted forms using abbreviated reader syntax,e.g., (quote foo) prints as 'foo, and (function foo) as #'foo. The default is t.

print-quoted[Variable]
If this variable is non-nil, then newline characters in strings are printed as ‘\n’ andformfeeds are printed as ‘\f’. Normally these characters are printed as actual newlines
and formfeeds.
This variable affects the print functions prin1 and print that print with quoting. It
does not affect princ. Here is an example using prin1:(prin1 "a\nb")
a "a
a b"
⇒ "a
b"

print-escape-newlines(let ((print-escape-newlines t))(prin1 "a\nb"))a "a\nb"⇒ "ab"
In the second expression, the local binding of print-escape-newlines is in effectduring the call to prin1, but not during the printing of the result.
[Variable]
If this variable is non-nil, control characters in strings are printed as backslash
sequences by the print functions prin1 and print that print with quoting. If thisvariable and print-escape-newlines are both non-nil, the latter takes precedences
for newlines and formfeeds.

print-escape-control-charactersChapter 20: Reading and Printing Lisp Objects

381[Variable]
If this variable is non-nil, then unibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functions prin1 and print thatprint with quoting.
Those functions also use backslash sequences for unibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a multibyte buffer or amarker pointing into one.

print-escape-nonascii[Variable]
If this variable is non-nil, then multibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functions prin1 and print thatprint with quoting.
Those functions also use backslash sequences for multibyte non-ASCII characters,
regardless of the value of this variable, when the output stream is a unibyte buffer ora marker pointing into one.

print-escape-multibyte[Variable]
This variable controls printing of ‘charset’ text property on printing a string. The
value should be nil, t, or default.
If the value is nil, charset text properties are never printed. If t, they are always
printed.
If the value is default, only print charset text properties if there is an “unexpected” charset property. For ascii characters, all charsets are considered “expected”.
Otherwise, the expected charset property of a character is given by char-charset.

print-charset-text-property[Variable]
The value of this variable is the maximum number of elements to print in any list,
vector or bool-vector. If an object being printed has more than this many elements, it
is abbreviated with an ellipsis.
If the value is nil (the default), then there is no limit.
(setq print-length 2)⇒ 2(print '(1 2 3 4 5))
a (1 2 ...)⇒ (1 2 ...)

print-length[Variable]
The value of this variable is the maximum depth of nesting of parentheses and brackets
when printed. Any list or vector at a depth exceeding this limit is abbreviated with
an ellipsis. A value of nil (which is the default) means no limit.

print-level[User Option][User Option]
These are the values for print-length and print-level used by eval-expression,and thus, indirectly, by many interactive evaluation commands (see Section “Evaluating
Emacs Lisp Expressions” in The GNU Emacs Manual).

eval-expression-print-lengtheval-expression-print-level

These variables are used for detecting and reporting circular and shared structure:

Chapter 20: Reading and Printing Lisp Objects

382[Variable]
If non-nil, this variable enables detection of circular and shared structure in printing.
See Section 2.6 [Circular Objects], page 30.

print-circle

print-unreadable-function[Variable]

By default, Emacs prints unreadable objects as ‘#<...>"’. For instance:(prin1-to-string (make-marker))⇒ "#<marker in no buffer>"If this variable is non-nil, it should be a function that will be called to handle printingof these objects. The function will be called with two arguments: the object and thenoescape flag used by the printing functions (see Section 20.5 [Output Functions],
page 377).
The function should return either nil (print the object as usual), or a string (which
will be printed), or any other object (don’t print the object). For instance:(let ((print-unreadable-function(lambda (object escape) "hello")))(prin1-to-string (make-marker)))⇒ "hello"[Variable]
If non-nil, this variable enables detection of uninterned symbols (see Section 9.3[Creating Symbols], page 135) in printing. When this is enabled, uninterned symbols
print with the prefix ‘#:’, which tells the Lisp reader to produce an uninterned symbol.

print-gensym[Variable]
If non-nil, that means number continuously across print calls. This affects thenumbers printed for ‘#n=’ labels and ‘#m#’ references. Don’t set this variable with
setq; you should only bind it temporarily to t with let. When you do that, you
should also bind print-number-table to nil.

print-continuous-numbering[Variable]
This variable holds a vector used internally by printing to implement theprint-circle feature. You should not use it except to bind it to nil when you bind
print-continuous-numbering.

print-number-table[Variable]
This variable specifies how to print floating-point numbers. The default is nil, meaning
use the shortest output that represents the number without losing information.

float-output-format

To control output format more precisely, you can put a string in this variable. The
string should hold a ‘%’-specification to be used in the C function sprintf. For further
restrictions on what you can use, see the variable’s documentation string.
[Variable]
When this variable is non-nil, integers that represent graphic base characters will be
printed using Lisp character syntax (see Section 2.4.3.1 [Basic Char Syntax], page 11).
Other numbers are printed the usual way. For example, the list (4 65 -1 10) would
be printed as ‘(4 ?A -1 ?\n)’.

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383

More precisely, values printed in character syntax are those representing charactersbelonging to the Unicode general categories Letter, Number, Punctuation, Symbol
and Private-use (see Section 34.6 [Character Properties], page 968), as well as thecontrol characters having their own escape syntax such as newline.

20.7 Overriding Output Variables
The previous section (see Section 20.6 [Output Variables], page 380) lists the numerous
variables that control how the Emacs Lisp printer formats data for outputs. These are
generally available for users to change, but sometimes you want to output data in the default
format, or override the user settings in some other way. For instance, if you’re storing Emacs
Lisp data in a file, you don’t want that data to be shortened by a print-length setting.
The prin1 and prin1-to-string functions therefore have an optional overrides argument.
This argument can either be t (which means that all printing variables should be reset tothe default values), or a list of settings for some of the variables. Each element in the list
can be either t (which means “reset to defaults”, and will usually be the first element of thelist), or a pair whose car is a symbol that stands for an output variable and whose cdr isthe value for that variable.
For instance, this prints using nothing but defaults:(prin1 object nil t)
This prints object using the current printing settings, but overrides the value of
print-length to be 5:(prin1 object nil '((length . 5)))
And finally, this prints object using only default settings, but with print-length boundto 5:(prin1 object nil '(t (length . 5)))
Below is a list of symbols that can be used, and which variables they map to:lengthThis overrides print-length.

levelThis overrides print-level.

circleThis overrides print-circle.

quotedThis overrides print-quoted.

escape-newlines
This overrides print-escape-newlines.
escape-control-characters
This overrides print-escape-control-characters.
escape-nonascii
This overrides print-escape-nonascii.
escape-multibyte
This overrides print-escape-multibyte.
charset-text-property
This overrides print-charset-text-property.

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384

unreadeable-function
This overrides print-unreadable-function.
gensymThis overrides print-gensym.

continuous-numbering
This overrides print-continuous-numbering.
number-table
This overrides print-number-table.
float-format
This overrides float-output-format.
integers-as-characters
This overrides print-integers-as-characters.
In the future, more overrides may be offered that do not map directly to a variable, but
can only be used via this parameter.

385

21 Minibuffers
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer
names, and command names (as in M-x). The minibuffer is displayed on the bottom line of
the frame, in the same place as the echo area (see Section 41.4 [The Echo Area], page 1131),but only while it is in use for reading an argument.

21.1 Introduction to Minibuffers
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer,such as editing commands, work normally in a minibuffer. However, many operations for
managing buffers do not apply to minibuffers. The name of a minibuffer always has theform ‘ *Minibuf-number*’, and it cannot be changed. Minibuffers are displayed only in
special windows used only for minibuffers; these windows always appear at the bottom ofa frame. (Sometimes frames have no minibuffer window, and sometimes a special kind offrame contains nothing but a minibuffer window; see Section 30.9 [Minibuffers and Frames],
page 824.)
The text in the minibuffer always starts with the prompt string, the text that was specified
by the program that is using the minibuffer to tell the user what sort of input to type. This
text is marked read-only so you won’t accidentally delete or change it. It is also marked asa field (see Section 33.19.9 [Fields], page 936), so that certain motion functions, including
beginning-of-line, forward-word, forward-sentence, and forward-paragraph, stop at
the boundary between the prompt and the actual text.
The minibuffer’s window is normally a single line; it grows automatically if the contents
require more space. Whilst the minibuffer is active, you can explicitly resize its window
temporarily with the window sizing commands; the window reverts to its normal size whenthe minibuffer is exited. When the minibuffer is not active, you can resize its window
permanently by using the window sizing commands in the frame’s other window, or dragging
the mode line with the mouse. (Due to details of the current implementation, for this towork resize-mini-windows must be nil.) If the frame contains just a minibuffer window,
you can change its size by changing the frame’s size.
Use of the minibuffer reads input events, and that alters the values of variables such as
this-command and last-command (see Section 22.5 [Command Loop Info], page 436). Your
program should bind them around the code that uses the minibuffer, if you do not wantthat to change them.
Under some circumstances, a command can use a minibuffer even if there is an active
minibuffer; such a minibuffer is called a recursive minibuffer. The first minibuffer is named‘ *Minibuf-1*’. Recursive minibuffers are named by incrementing the number at the endof the name. (The names begin with a space so that they won’t show up in normal buffer
lists.) Of several recursive minibuffers, the innermost (or most recently entered) is theactive minibuffer–it is the one you can terminate by typing RET (exit-minibuffer) in. We
usually call this the minibuffer. You can permit or forbid recursive minibuffers by setting
the variable enable-recursive-minibuffers, or by putting properties of that name oncommand symbols (See Section 21.13 [Recursive Mini], page 420.)

Chapter 21: Minibuffers

386

Like other buffers, a minibuffer uses a local keymap (see Chapter 23 [Keymaps], page 480)
to specify special key bindings. The function that invokes the minibuffer also sets up its
local map according to the job to be done. See Section 21.2 [Text from Minibuffer], page 386,
for the non-completion minibuffer local maps. See Section 21.6.3 [Completion Commands],
page 400, for the minibuffer local maps for completion.
An active minibuffer usually has major mode minibuffer-mode. This is an Emacs
internal mode without any special features. To customize the setup of minibuffers, wesuggest you use minibuffer-setup-hook (see Section 21.15 [Minibuffer Misc], page 421)
rather than minibuffer-mode-hook, since the former is run later, after the minibuffer has
been fully initialized.
When a minibuffer is inactive, its major mode is minibuffer-inactive-mode, withkeymap minibuffer-inactive-mode-map. This is only really useful if the minibuffer is ina separate frame. See Section 30.9 [Minibuffers and Frames], page 824.
When Emacs is running in batch mode, any request to read from the minibuffer actuallyreads a line from the standard input descriptor that was supplied when Emacs was started.
This supports only basic input: none of the special minibuffer features (history, completion,etc.) are available in batch mode.

21.2 Reading Text Strings with the Minibuffer
The most basic primitive for minibuffer input is read-from-minibuffer, which can be used
to read either a string or a Lisp object in textual form. The function read-regexp is used
for reading regular expressions (see Section 35.3 [Regular Expressions], page 995), which area special kind of string. There are also specialized functions for reading commands, variables,
file names, etc. (see Section 21.6 [Completion], page 395).
In most cases, you should not call minibuffer input functions in the middle of a Lisp
function. Instead, do all minibuffer input as part of reading the arguments for a command,in the interactive specification. See Section 22.2 [Defining Commands], page 424.

read-from-minibuffer prompt &optional initial keymap readhistory default inherit-input-method[Function]

This function is the most general way to get input from the minibuffer. By default, it
accepts arbitrary text and returns it as a string; however, if read is non-nil, then it
uses read to convert the text into a Lisp object (see Section 20.3 [Input Functions],
page 374).
The first thing this function does is to activate a minibuffer and display it with prompt(which must be a string) as the prompt. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer, read-from-minibuffer
constructs the return value from the text in the minibuffer. Normally it returns astring containing that text. However, if read is non-nil, read-from-minibuffer
reads the text and returns the resulting Lisp object, unevaluated. (See Section 20.3
[Input Functions], page 374, for information about reading.)
The argument default specifies default values to make available through the history
commands. It should be a string, a list of strings, or nil. The string or strings become
the minibuffer’s “future history”, available to the user with M-n. In addition, if thecall provides completion (e.g., via the keymap argument), the completion candidates

Chapter 21: Minibuffers387

are added to the “future history” when the values in default are exhausted by M-n;see Section 21.4 [minibuffer-default-add-function], page 392.
If read is non-nil, then default is also used as the input to read, if the user enters
empty input. If default is a list of strings, the first string is used as the input. If
default is nil, empty input results in an end-of-file error. However, in the usualcase (where read is nil), read-from-minibuffer ignores default when the user enters
empty input and returns an empty string, "". In this respect, it differs from all theother minibuffer input functions in this chapter.
If keymap is non-nil, that keymap is the local keymap to use in the minibuffer. If
keymap is omitted or nil, the value of minibuffer-local-map is used as the keymap.
Specifying a keymap is the most important way to customize the minibuffer for various
applications such as completion.
The argument history specifies a history list variable to use for saving the input andfor history commands used in the minibuffer. It defaults to minibuffer-history. If
history is the symbol t, history is not recorded. You can optionally specify a starting
position in the history list as well. See Section 21.4 [Minibuffer History], page 392.
If the variable minibuffer-allow-text-properties is non-nil, then the string thatis returned includes whatever text properties were present in the minibuffer. Otherwise
all the text properties are stripped when the value is returned. (By default this variable
is nil.)The text properties in minibuffer-prompt-properties are applied to the prompt.
By default, this property list defines a face to use for the prompt. This face, if present,
is applied to the end of the face list and merged before display.
If the user wants to completely control the look of the prompt, the most convenient
way to do that is to specify the default face at the end of all face lists. For instance:(read-from-minibuffer(concat(propertize "Bold" 'face '(bold default))(propertize " and normal: " 'face '(default))))If the argument inherit-input-method is non-nil, then the minibuffer inherits thecurrent input method (see Section 34.11 [Input Methods], page 990) and the setting of
enable-multibyte-characters (see Section 34.1 [Text Representations], page 963)
from whichever buffer was current before entering the minibuffer.
Use of initial is mostly deprecated; we recommend using a non-nil value only in
conjunction with specifying a cons cell for history. See Section 21.5 [Initial Input],
page 394.

read-string prompt &optional initial history default
inherit-input-method[Function]

This function reads a string from the minibuffer and returns it. The arguments prompt,
initial, history and inherit-input-method are used as in read-from-minibuffer. The
keymap used is minibuffer-local-map.
The optional argument default is used as in read-from-minibuffer, except that, if
non-nil, it also specifies a default value to return if the user enters null input. As
in read-from-minibuffer it should be a string, a list of strings, or nil, which isChapter 21: Minibuffers388

equivalent to an empty string. When default is a string, that string is the default
value. When it is a list of strings, the first string is the default value. (All these strings
are available to the user in the “future minibuffer history”.)
This function works by calling the read-from-minibuffer function:(read-string prompt initial history default inherit)≡(let ((value(read-from-minibuffer prompt initial nil nil
history default inherit)))(if (and (equal value "") default)(if (consp default) (car default) default)
value))

If you have a long string (for instance, one that is several lines long) that you wish toedit, using read-string may not be ideal. In that case, popping to a new, normal
buffer where the user can edit the string may be more convenient, and you can use
the read-string-from-buffer function to do that.

read-regexp prompt &optional defaults history[Function]
This function reads a regular expression as a string from the minibuffer and returns
it. If the minibuffer prompt string prompt does not end in ‘:’ (followed by optional
whitespace), the function adds ‘: ’ to the end, preceded by the default return value(see below), if that is non-empty.
The optional argument defaults controls the default value to return if the user enters
null input, and should be one of: a string; nil, which is equivalent to an empty string;a list of strings; or a symbol.
If defaults is a symbol, read-regexp consults the value of the variable read-regexpdefaults-function (see below), and if that is non-nil uses it in preference to defaults.
The value in this case should be either:− regexp-history-last, which means to use the first element of the appropriate
minibuffer history list (see below).
− A function of no arguments, whose return value (which should be nil, a string,or a list of strings) becomes the value of defaults.
read-regexp now ensures that the result of processing defaults is a list (i.e., if thevalue is nil or a string, it converts it to a list of one element). To this list, read-regexp
then appends a few potentially useful candidates for input. These are:
− The word or symbol at point.
− The last regexp used in an incremental search.
− The last string used in an incremental search.
− The last string or pattern used in query-replace commands.

The function now has a list of regular expressions that it passes to read-fromminibuffer to obtain the user’s input. The first element of the list is the default
result in case of empty input. All elements of the list are available to the user as the“future minibuffer history” list (see Section “Minibuffer History” in The GNU Emacs
Manual).

Chapter 21: Minibuffers389

The optional argument history, if non-nil, is a symbol specifying a minibuffer history
list to use (see Section 21.4 [Minibuffer History], page 392). If it is omitted or nil,
the history list defaults to regexp-history.
The user can use the M-s c command to indicate whether case folding should be on
or off. If the user has used this command, the returned string will have the text
property case-fold set to either fold or inhibit-fold. It is up to the caller ofread-regexp to actually use this value, and the convenience function read-regexpcase-fold-search is provided for that. A typical usage pattern here might looklike:(let* ((regexp (read-regexp "Search for: "))(case-fold-search (read-regexp-case-fold-search regexp)))(re-search-forward regexp))[User Option]
The function read-regexp may use the value of this variable to determine its list ofdefault regular expressions. If non-nil, the value of this variable should be either:− The symbol regexp-history-last.
− A function of no arguments that returns either nil, a string, or a list of strings.

read-regexp-defaults-function

See read-regexp above for details of how these values are used.
[Variable]
If this variable is nil, the default, then read-from-minibuffer and read-string strip
all text properties from the minibuffer input before returning it. However, read-noblanks-input (see below), as well as read-minibuffer and related functions (seeSection 21.3 [Reading Lisp Objects With the Minibuffer], page 391), and all functions
that do minibuffer input with completion, remove the face property unconditionally,
regardless of the value of this variable.
If this variable is non-nil, most text properties on strings from the completion table
are preserved—but only on the part of the strings that were completed.
(let ((minibuffer-allow-text-properties t))(completing-read "String: " (list (propertize "foobar" 'data 'zot))))=> #("foobar" 3 6 (data zot))In this example, the user typed ‘foo’ and then hit the TAB key, so the text properties
are only preserved on the last three characters.

minibuffer-allow-text-properties[Variable]
This is the default local keymap for reading from the minibuffer. By default, it makes
the following bindings:

minibuffer-local-map

C-jexit-minibuffer

RET

exit-minibufferM-<minibuffer-beginning-of-buffer

C-gabort-recursive-edit

M-n
DOWN

next-history-element

Chapter 21: Minibuffers

M-pUP

previous-history-elementM-snext-matching-history-element

M-rprevious-matching-history-element390

The variable minibuffer-mode-map is an alias for this variable.

read-no-blanks-input prompt &optional initialinherit-input-method[Function]

This function reads a string from the minibuffer, but does not allow whitespacecharacters as part of the input: instead, those characters terminate the input. The
arguments prompt, initial, and inherit-input-method are used as in read-fromminibuffer.
This is a simplified interface to the read-from-minibuffer function, and passes thevalue of the minibuffer-local-ns-map keymap as the keymap argument for thatfunction. Since the keymap minibuffer-local-ns-map does not rebind C-q, it ispossible to put a space into the string, by quoting it.
This function discards text properties, regardless of the value of minibuffer-allowtext-properties.
(read-no-blanks-input prompt initial)≡(let (minibuffer-allow-text-properties)(read-from-minibuffer prompt initial minibuffer-local-ns-map))[Variable]
This built-in variable is the keymap used as the minibuffer local keymap in the function
read-no-blanks-input. By default, it makes the following bindings, in addition to
those of minibuffer-local-map:

minibuffer-local-ns-map

SPC

exit-minibuffer

TAB

exit-minibuffer?

self-insert-and-exit

format-prompt prompt default &rest format-args[Function]
Format prompt with default value default according to the minibuffer-defaultprompt-format variable.
minibuffer-default-prompt-format is a format string (defaulting to ‘" (default%s)"’ that says how the “default” bit in prompts like ‘"Local filename (default
somefile): "’ are to be formatted.
To allow the users to customize how this is displayed, code that prompts the user fora value (and has a default) should look something along the lines of this code snippet:(read-file-name(format-prompt "Local filename" file)nil file)
If format-args is nil, prompt is used as a literal string. If format-args is non-nil,prompt is used as a format control string, and prompt and format-args are passed toformat (see Section 4.7 [Formatting Strings], page 66).

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minibuffer-default-prompt-format can be ‘""’, in which case no default values
are displayed.
If default is nil, there is no default value, and therefore no “default value” string is
included in the result value. If default is a non-nil list, the first element of the list is
used in the prompt.
Both prompt and minibuffer-default-prompt-format are run throughsubstitute-command-keys (see Section 25.3 [Keys in Documentation], page 598).
[Variable]
If this option is non-nil (the default), getting input from the minibuffer will restore,
on exit, the window configurations of the frame where the minibuffer was entered from
and, if it is different, the frame that owns the minibuffer window. This means that if,
for example, a user splits a window while getting input from the minibuffer on thesame frame, that split will be undone when exiting the minibuffer.

read-minibuffer-restore-windows

If this option is nil, no such restorations are done. Hence, the window split mentioned
above will persist after exiting the minibuffer.

21.3 Reading Lisp Objects with the MinibufferThis section describes functions for reading Lisp objects with the minibuffer.

read-minibuffer prompt &optional initial[Function]
This function reads a Lisp object using the minibuffer, and returns it without evaluating
it. The arguments prompt and initial are used as in read-from-minibuffer.
This is a simplified interface to the read-from-minibuffer function:(read-minibuffer prompt initial)≡(let (minibuffer-allow-text-properties)(read-from-minibuffer prompt initial nil t))

Here is an example in which we supply the string "(testing)" as initial input:(read-minibuffer"Enter an expression: " (format "%s" '(testing)));; Here is how the minibuffer is displayed:---------- Buffer: Minibuffer ---------Enter an expression: (testing)?
---------- Buffer: Minibuffer ----------The user can type RET immediately to use the initial input as a default, or can edit
the input.

eval-minibuffer prompt &optional initial[Function]
This function reads a Lisp expression using the minibuffer, evaluates it, then returns
the result. The arguments prompt and initial are used as in read-from-minibuffer.
This function simply evaluates the result of a call to read-minibuffer:(eval-minibuffer prompt initial)≡(eval (read-minibuffer prompt initial))Chapter 21: Minibuffers392

edit-and-eval-command prompt form

[Function]
This function reads a Lisp expression in the minibuffer, evaluates it, then returns
the result. The difference between this command and eval-minibuffer is that here
the initial form is not optional and it is treated as a Lisp object to be converted toprinted representation rather than as a string of text. It is printed with prin1, so if it
is a string, double-quote characters (‘"’) appear in the initial text. See Section 20.5
[Output Functions], page 377.
In the following example, we offer the user an expression with initial text that isalready a valid form:(edit-and-eval-command "Please edit: " '(forward-word 1));; After evaluation of the preceding expression,;;
the following appears in the minibuffer:---------- Buffer: Minibuffer ---------Please edit: (forward-word 1)?
---------- Buffer: Minibuffer ----------

Typing RET right away would exit the minibuffer and evaluate the expression, thus
moving point forward one word.

21.4 Minibuffer History
A minibuffer history list records previous minibuffer inputs so the user can reuse themconveniently. It is a variable whose value is a list of strings (previous inputs), most recent
first.
There are many separate minibuffer history lists, used for different kinds of inputs. It’s
the Lisp programmer’s job to specify the right history list for each use of the minibuffer.
You specify a minibuffer history list with the optional history argument to read-fromminibuffer or completing-read. Here are the possible values for it:
variableUse variable (a symbol) as the history list.

(variable . startpos)
Use variable (a symbol) as the history list, and assume that the initial history
position is startpos (a nonnegative integer).
Specifying 0 for startpos is equivalent to just specifying the symbol variable.
previous-history-element will display the most recent element of the history
list in the minibuffer. If you specify a positive startpos, the minibuffer history
functions behave as if (elt variable (1- startpos)) were the history element
currently shown in the minibuffer.
For consistency, you should also specify that element of the history as the initial
minibuffer contents, using the initial argument to the minibuffer input function(see Section 21.5 [Initial Input], page 394).
If you don’t specify history, then the default history list minibuffer-history is used.
For other standard history lists, see below. You can also create your own history list variable;
just initialize it to nil before the first use. If the variable is buffer local, then each buffer
will have its own input history list.

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Both read-from-minibuffer and completing-read add new elements to the history
list automatically, and provide commands to allow the user to reuse items on the list (seeSection 21.10 [Minibuffer Commands], page 417). The only thing your program needs to do
to use a history list is to initialize it and to pass its name to the input functions when you
wish. But it is safe to modify the list by hand when the minibuffer input functions are notusing it.
By default, when M-n (next-history-element, see Section 21.10 [next-history-element],
page 417) reaches the end of the list of default values provided by the command which
initiated reading input from the minibuffer, M-n adds all of the completion candidates, as
specified by minibuffer-completion-table (see Section 21.6.3 [Completion Commands],
page 400), to the list of defaults, so that all those candidates are available as “future history”.
Your program can control that via the variable minibuffer-default-add-function: if its
value is not a function, this automatic addition is disabled, and you can also set this variable
to your own function which adds only some candidates, or some other values, to the “future
history”.
Emacs functions that add a new element to a history list can also delete old elements
if the list gets too long. The variable history-length specifies the maximum length formost history lists. To specify a different maximum length for a particular history list,
put the length in the history-length property of the history list symbol. The variable
history-delete-duplicates specifies whether to delete duplicates in history.

add-to-history history-var newelt &optional maxelt keep-all[Function]
This function adds a new element newelt, if it isn’t the empty string, to the history list
stored in the variable history-var, and returns the updated history list. It limits the list
length to the value of maxelt (if non-nil) or history-length (described below). The
possible values of maxelt have the same meaning as the values of history-length.
history-var cannot refer to a lexical variable.
Normally, add-to-history removes duplicate members from the history list if
history-delete-duplicates is non-nil. However, if keep-all is non-nil, that says
not to remove duplicates, and to add newelt to the list even if it is empty.
[Variable]
If the value of this variable is nil, standard functions that read from the minibuffer
don’t add new elements to the history list. This lets Lisp programs explicitly manage
input history by using add-to-history. The default value is t.

history-add-new-input[User Option]
The value of this variable specifies the maximum length for all history lists that
don’t specify their own maximum lengths. If the value is t, that means there is no
maximum (don’t delete old elements). If a history list variable’s symbol has a non-nil
history-length property, it overrides this variable for that particular history list.

history-length[User Option]
If the value of this variable is t, that means when adding a new history element, allprevious identical elements are deleted.

history-delete-duplicates

Here are some of the standard minibuffer history list variables:

Chapter 21: Minibuffers394

minibuffer-history[Variable]

The default history list for minibuffer history input.
[Variable]
A history list for arguments to query-replace (and similar arguments to othercommands).

query-replace-history

file-name-history[Variable]

A history list for file-name arguments.

buffer-name-history[Variable]

A history list for buffer-name arguments.

regexp-history[Variable]

A history list for regular expression arguments.

extended-command-history[Variable]

A history list for arguments that are names of extended commands.

shell-command-history[Variable]

A history list for arguments that are shell commands.

read-expression-history[Variable]

A history list for arguments that are Lisp expressions to evaluate.

face-name-history[Variable]

A history list for arguments that are faces.

custom-variable-history[Variable]

A history list for variable-name arguments read by read-variable.

read-number-history[Variable]

A history list for numbers read by read-number.
[Variable]
A history list for arguments to goto-line. This variable can be made local in every
buffer by customizing the user option goto-line-history-local.

goto-line-history

21.5 Initial Input
Several of the functions for minibuffer input have an argument called initial. This is amostly-deprecated feature for specifying that the minibuffer should start out with certain
text, instead of empty as usual.
If initial is a string, the minibuffer starts out containing the text of the string, with pointat the end, when the user starts to edit the text. If the user simply types RET to exit theminibuffer, it will use the initial input string to determine the value to return.
We discourage use of a non-nil value for initial, because initial input is an intrusive
interface. History lists and default values provide a much more convenient method to offer
useful default inputs to the user.

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There is just one situation where you should specify a string for an initial argument.
This is when you specify a cons cell for the history argument. See Section 21.4 [Minibuffer
History], page 392.
initial can also be a cons cell of the form (string . position). This means to insert
string in the minibuffer but put point at position within the string’s text.
As a historical accident, position was implemented inconsistently in different functions. In
completing-read, position’s value is interpreted as origin-zero; that is, a value of 0 means
the beginning of the string, 1 means after the first character, etc. In read-minibuffer, andthe other non-completion minibuffer input functions that support this argument, 1 means
the beginning of the string, 2 means after the first character, etc.
Use of a cons cell as the value for initial arguments is deprecated.

21.6 Completion
Completion is a feature that fills in the rest of a name starting from an abbreviation for
it. Completion works by comparing the user’s input against a list of valid names anddetermining how much of the name is determined uniquely by what the user has typed. For
example, when you type C-x b (switch-to-buffer) and then type the first few letters of thename of the buffer to which you wish to switch, and then type TAB (minibuffer-complete),
Emacs extends the name as far as it can.
Standard Emacs commands offer completion for names of symbols, files, buffers, andprocesses; with the functions in this section, you can implement completion for other kindsof names.
The try-completion function is the basic primitive for completion: it returns the longest
determined completion of a given initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface for completion. A callto completing-read specifies how to determine the list of valid names. The function thenactivates the minibuffer with a local keymap that binds a few keys to commands useful forcompletion. Other functions provide convenient simple interfaces for reading certain kindsof names with completion.

21.6.1 Basic Completion Functions
The following completion functions have nothing in themselves to do with minibuffers. We
describe them here to keep them near the higher-level completion features that do use theminibuffer.

try-completion string collection &optional predicate[Function]
This function returns the longest common substring of all possible completions ofstring in collection.
collection is called the completion table. Its value must be a list of strings or cons
cells, an obarray, a hash table, or a completion function.
try-completion compares string against each of the permissible completions specified
by the completion table. If no permissible completions match, it returns nil. If there
is just one matching completion, and the match is exact, it returns t. Otherwise, it
returns the longest initial sequence common to all possible matching completions.

Chapter 21: Minibuffers396

If collection is a list, the permissible completions are specified by the elements of thelist, each of which should be either a string, or a cons cell whose car is either a stringor a symbol (a symbol is converted to a string using symbol-name). If the list contains
elements of any other type, those are ignored.
If collection is an obarray (see Section 9.3 [Creating Symbols], page 135), the namesof all symbols in the obarray form the set of permissible completions.
If collection is a hash table, then the keys that are strings or symbols are the possible
completions. Other keys are ignored.
You can also use a function as collection. Then the function is solely responsible for
performing completion; try-completion returns whatever this function returns. The
function is called with three arguments: string, predicate and nil (the third argument
is so that the same function can be used in all-completions and do the appropriate
thing in either case). See Section 21.6.7 [Programmed Completion], page 409.
If the argument predicate is non-nil, then it must be a function of one argument,
unless collection is a hash table, in which case it should be a function of two arguments.
It is used to test each possible match, and the match is accepted only if predicate
returns non-nil. The argument given to predicate is either a string or a cons cell(the car of which is a string) from the alist, or a symbol (not a symbol name) fromthe obarray. If collection is a hash table, predicate is called with two arguments, thestring key and the associated value.
In addition, to be acceptable, a completion must also match all the regular expressions
in completion-regexp-list. (Unless collection is a function, in which case thatfunction has to handle completion-regexp-list itself.)
In the first of the following examples, the string ‘foo’ is matched by three of the alistcars. All of the matches begin with the characters ‘fooba’, so that is the result. In
the second example, there is only one possible match, and it is exact, so the return
value is t.
(try-completion"foo"'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)))⇒ "fooba"(try-completion "foo" '(("barfoo" 2) ("foo" 3)))⇒ t

In the following example, numerous symbols begin with the characters ‘forw’, and allof them begin with the word ‘forward’. In most of the symbols, this is followed witha ‘-’, but not in all, so no more than ‘forward’ can be completed.
(try-completion "forw" obarray)⇒ "forward"

Finally, in the following example, only two of the three possible matches pass thepredicate test (the string ‘foobaz’ is too short). Both of those begin with the string‘foobar’.
(defun test (s)(> (length (car s)) 6))⇒ testChapter 21: Minibuffers397(try-completion"foo"'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))'test)⇒ "foobar"

all-completions string collection &optional predicate[Function]
This function returns a list of all possible completions of string. The arguments to thisfunction are the same as those of try-completion, and it uses completion-regexplist in the same way that try-completion does.
If collection is a function, it is called with three arguments: string, predicate andt; then all-completions returns whatever the function returns. See Section 21.6.7[Programmed Completion], page 409.
Here is an example, using the function test shown in the example for try-completion:(defun test (s)(> (length (car s)) 6))⇒ test(all-completions"foo"'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))'test)⇒ ("foobar1" "foobar2")

test-completion string collection &optional predicate[Function]
This function returns non-nil if string is a valid completion alternative specified bycollection and predicate. The arguments are the same as in try-completion. For
instance, if collection is a list of strings, this is true if string appears in the list andpredicate is satisfied.
This function uses completion-regexp-list in the same way that try-completion
does.
If predicate is non-nil and if collection contains several strings that are equal to eachother, as determined by compare-strings according to completion-ignore-case,then predicate should accept either all or none of them. Otherwise, the return valueof test-completion is essentially unpredictable.
If collection is a function, it is called with three arguments, the values string, predicate
and lambda; whatever it returns, test-completion returns in turn.

completion-boundaries string collection predicate suffix[Function]
This function returns the boundaries of the field on which collection will operate,
assuming that string holds the text before point and suffix holds the text after point.
Normally completion operates on the whole string, so for all normal collections, thiswill always return (0 . (length suffix)). But more complex completion, such ascompletion on files, is done one field at a time. For example, completion of "/usr/sh"
will include "/usr/share/" but not "/usr/share/doc" even if "/usr/share/doc"
exists. Also all-completions on "/usr/sh" will not include "/usr/share/" but only
"share/". So if string is "/usr/sh" and suffix is "e/doc", completion-boundaries
will return (5 . 1) which tells us that the collection will only return completion information that pertains to the area after "/usr/" and before "/doc". try-completion

Chapter 21: Minibuffers398

is not affected by nontrivial boundaries; e.g., try-completion on "/usr/sh" might
still return "/usr/share/", not "share/".
If you store a completion alist in a variable, you should mark the variable as risky
by giving it a non-nil risky-local-variable property. See Section 12.12 [File Local
Variables], page 213.
[Variable]
If the value of this variable is non-nil, case is not considered significant in completion.
Within read-file-name, this variable is overridden by read-file-name-completionignore-case (see Section 21.6.5 [Reading File Names], page 404); within read-buffer,
it is overridden by read-buffer-completion-ignore-case (see Section 21.6.4 [HighLevel Completion], page 402).

completion-ignore-case[Variable]
This is a list of regular expressions. The completion functions only consider a completion acceptable if it matches all regular expressions in this list, with case-foldsearch (see Section 35.2 [Searching and Case], page 995) bound to the value ofcompletion-ignore-case.
Do not set this variable to a non-nil value globally, as that is not safe and willprobably cause errors in completion commands. This variable should be only letbound to non-nil values around calls to basic completion functions: try-completion,
test-completion, and all-completions.

completion-regexp-list

lazy-completion-table var fun[Macro]This macro provides a way to initialize the variable var as a collection for completionin a lazy way, not computing its actual contents until they are first needed. You use
this macro to produce a value that you store in var. The actual computation of theproper value is done the first time you do completion using var. It is done by calling
fun with no arguments. The value fun returns becomes the permanent value of var.
Here is an example:(defvar foo (lazy-completion-table foo make-my-alist))

There are several functions that take an existing completion table and returna modified version. completion-table-case-fold returns a case-insensitive table.
completion-table-in-turn and completion-table-merge combine multiple input
tables in different ways. completion-table-subvert alters a table to use a different
initial prefix. completion-table-with-quoting returns a table suitable for operating on
quoted text. completion-table-with-predicate filters a table with a predicate function.
completion-table-with-terminator adds a terminating string.

21.6.2 Completion and the MinibufferThis section describes the basic interface for reading from the minibuffer with completion.

completing-read prompt collection &optional predicate
require-match initial history default inherit-input-method[Function]

This function reads a string in the minibuffer, assisting the user by providing completion.
It activates the minibuffer with prompt prompt, which must be a string.

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The actual completion is done by passing the completion table collection and the completion predicate predicate to the function try-completion (see Section 21.6.1 [Basic
Completion], page 395). This happens in certain commands bound in the local keymaps
used for completion. Some of these commands also call test-completion. Thus, if
predicate is non-nil, it should be compatible with collection and completion-ignorecase. See [Definition of test-completion], page 397.
See Section 21.6.7 [Programmed Completion], page 409, for detailed requirements
when collection is a function.
The value of the optional argument require-match determines how the user may exit
the minibuffer:• If nil, the usual minibuffer exit commands work regardless of the input in theminibuffer.
• If t, the usual minibuffer exit commands won’t exit unless the input completes toan element of collection.
• If confirm, the user can exit with any input, but is asked for confirmation if the
input is not an element of collection.
• If confirm-after-completion, the user can exit with any input, but is asked
for confirmation if the preceding command was a completion command (i.e., oneof the commands in minibuffer-confirm-exit-commands) and the resulting
input is not an element of collection. See Section 21.6.3 [Completion Commands],
page 400.
• If a function, it is called with the input as the only argument. The function
should return a non-nil value if the input is acceptable.
• Any other value of require-match behaves like t, except that the exit commands
won’t exit if it performs completion.
However, empty input is always permitted, regardless of the value of require-match;in that case, completing-read returns the first element of default, if it is a list; "",if default is nil; or default. The string or strings in default are also available tothe user through the history commands (see Section 21.10 [Minibuffer Commands],
page 417). In addition, the completion candidates are added to the “future history”
when the values in default are exhausted by M-n; see Section 21.4 [minibuffer-defaultadd-function], page 392.
The function completing-read uses minibuffer-local-completion-map as the
keymap if require-match is nil, and uses minibuffer-local-must-match-map if
require-match is non-nil. See Section 21.6.3 [Completion Commands], page 400.
The argument history specifies which history list variable to use for saving the input
and for minibuffer history commands. It defaults to minibuffer-history. If historyis the symbol t, history is not recorded. See Section 21.4 [Minibuffer History], page 392.
The argument initial is mostly deprecated; we recommend using a non-nil value onlyin conjunction with specifying a cons cell for history. See Section 21.5 [Initial Input],
page 394. For default input, use default instead.
If the argument inherit-input-method is non-nil, then the minibuffer inherits thecurrent input method (see Section 34.11 [Input Methods], page 990) and the setting ofChapter 21: Minibuffers

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enable-multibyte-characters (see Section 34.1 [Text Representations], page 963)
from whichever buffer was current before entering the minibuffer.
If the variable completion-ignore-case is non-nil, completion ignores case whencomparing the input against the possible matches. See Section 21.6.1 [Basic Completion], page 395. In this mode of operation, predicate must also ignore case, or you
will get surprising results.
Here’s an example of using completing-read:(completing-read"Complete a foo: "'(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))nil t "fo");; After evaluation of the preceding expression,;;
the following appears in the minibuffer:---------- Buffer: Minibuffer ---------Complete a foo: fo?
---------- Buffer: Minibuffer ----------

If the user then types DEL DEL b RET, completing-read returns barfoo.
The completing-read function binds variables to pass information to the commands
that actually do completion. They are described in the following section.
[Variable]
The value of this variable must be a function, which is called by completing-read toactually do its work. It should accept the same arguments as completing-read. Thiscan be bound to a different function to completely override the normal behavior ofcompleting-read.

completing-read-function

21.6.3 Minibuffer Commands that Do Completion
This section describes the keymaps, commands and user options used in the minibuffer to
do completion.
[Variable]
The value of this variable is the completion table (see Section 21.6.1 [Basic Completion],
page 395) used for completion in the minibuffer. This is the buffer-local variable that
contains what completing-read passes to try-completion. It is used by minibuffer
completion commands such as minibuffer-complete.

minibuffer-completion-table[Variable]
This variable’s value is the predicate that completing-read passes to try-completion.
The variable is also used by the other minibuffer completion functions.

minibuffer-completion-predicate[Variable]
This variable determines whether Emacs asks for confirmation before exiting the minibuffer; completing-read sets this variable, and the function minibuffer-completeand-exit checks the value before exiting. If the value is nil, confirmation is not
required. If the value is confirm, the user may exit with an input that is nota valid completion alternative, but Emacs asks for confirmation. If the value isminibuffer-completion-confirm

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confirm-after-completion, the user may exit with an input that is not a valid completion alternative, but Emacs asks for confirmation if the user submitted the input
right after any of the completion commands in minibuffer-confirm-exit-commands.
[Variable]
This variable holds a list of commands that cause Emacs to ask for confirmation
before exiting the minibuffer, if the require-match argument to completing-read isconfirm-after-completion. The confirmation is requested if the user attempts toexit the minibuffer immediately after calling any command in this list.

minibuffer-confirm-exit-commands[Command]This function completes the minibuffer contents by at most a single word. Even if
the minibuffer contents have only one completion, minibuffer-complete-word does
not add any characters beyond the first character that is not a word constituent. See
Chapter 36 [Syntax Tables], page 1022.

minibuffer-complete-wordminibuffer-complete[Command]This function completes the minibuffer contents as far as possible.
[Command]This function completes the minibuffer contents, and exits if confirmation is not
required, i.e., if minibuffer-completion-confirm is nil. If confirmation is required,
it is given by repeating this command immediately—the command is programmed towork without confirmation when run twice in succession.

minibuffer-complete-and-exit[Command]This function creates a list of the possible completions of the current minibuffer contents. It works by calling all-completions using the value of the variable minibuffer-completion-table as the collection argument, and the value ofminibuffer-completion-predicate as the predicate argument. The list of completions is displayed as text in a buffer named *Completions*.

minibuffer-completion-help

display-completion-list completions[Function]
This function displays completions to the stream in standard-output, usually abuffer. (See Chapter 20 [Read and Print], page 371, for more information about
streams.) The argument completions is normally a list of completions just returnedby all-completions, but it does not have to be. Each element may be a symbol or astring, either of which is simply printed. It can also be a list of two strings, which isprinted as if the strings were concatenated. The first of the two strings is the actual
completion, the second string serves as annotation.
This function is called by minibuffer-completion-help. A common way to use it istogether with with-output-to-temp-buffer, like this:(with-output-to-temp-buffer "*Completions*"(display-completion-list(all-completions (buffer-string) my-alist)))[User Option]
If this variable is non-nil, the completion commands automatically display a list of
possible completions whenever nothing can be completed because the next characteris not uniquely determined.

completion-auto-help

Chapter 21: Minibuffers

402[Variable]
completing-read uses this value as the local keymap when an exact match of one of
the completions is not required. By default, this keymap makes the following bindings:

minibuffer-local-completion-map?

minibuffer-completion-help

SPC

minibuffer-complete-word

TAB

minibuffer-complete

and uses minibuffer-local-map as its parent keymap (see [Definition of minibufferlocal-map], page 389).
[Variable]
completing-read uses this value as the local keymap when an exact match of one of
the completions is required. Therefore, no keys are bound to exit-minibuffer, thecommand that exits the minibuffer unconditionally. By default, this keymap makes
the following bindings:

minibuffer-local-must-match-map

C-jminibuffer-complete-and-exit

RET

minibuffer-complete-and-exit

and uses minibuffer-local-completion-map as its parent keymap.
[Variable]
This is a sparse keymap that simply unbinds SPC; because filenames can contain spaces.
The function read-file-name combines this keymap with either minibuffer-localcompletion-map or minibuffer-local-must-match-map.

minibuffer-local-filename-completion-map[Variable]
If non-nil, the M-< command will move to the end of the prompt if point is after theend of the prompt. If point is at or before the end of the prompt, move to the start ofthe buffer. If this variable is nil, the command behaves like beginning-of-buffer.

minibuffer-beginning-of-buffer-movement

21.6.4 High-Level Completion Functions
This section describes the higher-level convenience functions for reading certain sorts ofnames with completion.
In most cases, you should not call these functions in the middle of a Lisp function. Whenpossible, do all minibuffer input as part of reading the arguments for a command, in theinteractive specification. See Section 22.2 [Defining Commands], page 424.

read-buffer prompt &optional default require-match predicate[Function]
This function reads the name of a buffer and returns it as a string. It prompts withprompt. The argument default is the default name to use, the value to return if
the user exits with an empty minibuffer. If non-nil, it should be a string, a list of
strings, or a buffer. If it is a list, the default value is the first element of this list. It is
mentioned in the prompt, but is not inserted in the minibuffer as initial input.
The argument prompt should be a string ending with a colon and a space. If default
is non-nil, the function inserts it in prompt before the colon to follow the convention
for reading from the minibuffer with a default value (see Section D.3 [ProgrammingTips], page 1335).

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The optional argument require-match has the same meaning as in completing-read.
See Section 21.6.2 [Minibuffer Completion], page 398.
The optional argument predicate, if non-nil, specifies a function to filter the buffersthat should be considered: the function will be called with every potential candidate
as its argument, and should return nil to reject the candidate, non-nil to accept it.
In the following example, the user enters ‘minibuffer.t’, and then types RET. The
argument require-match is t, and the only buffer name starting with the given input
is ‘minibuffer.texi’, so that name is the value.
(read-buffer "Buffer name: " "foo" t);; After evaluation of the preceding expression,;;
the following prompt appears,;;
with an empty minibuffer:---------- Buffer: Minibuffer ---------Buffer name (default foo): ?
---------- Buffer: Minibuffer ---------;; The user types minibuffer.t RET.
⇒ "minibuffer.texi"[User Option]
This variable, if non-nil, specifies a function for reading buffer names. read-buffer
calls this function instead of doing its usual work, with the same arguments passed toread-buffer.

read-buffer-function[User Option]
If this variable is non-nil, read-buffer ignores case when performing completion
while reading the buffer name.

read-buffer-completion-ignore-caseread-command prompt &optional default[Function]
This function reads the name of a command and returns it as a Lisp symbol. The
argument prompt is used as in read-from-minibuffer. Recall that a command isanything for which commandp returns t, and a command name is a symbol for which
commandp returns t. See Section 22.3 [Interactive Call], page 432.
The argument default specifies what to return if the user enters null input. It can bea symbol, a string or a list of strings. If it is a string, read-command interns it before
returning it. If it is a list, read-command interns the first element of this list. If default
is nil, that means no default has been specified; then if the user enters null input, thereturn value is (intern ""), that is, a symbol whose name is an empty string, andwhose printed representation is ## (see Section 2.4.4 [Symbol Type], page 14).
(read-command "Command name? ");; After evaluation of the preceding expression,;;
the following prompt appears with an empty minibuffer:---------- Buffer: Minibuffer ---------Command name?
---------- Buffer: Minibuffer ----------

Chapter 21: Minibuffers404

If the user types forward-c RET, then this function returns forward-char.
The read-command function is a simplified interface to completing-read. It uses thevariable obarray so as to complete in the set of extant Lisp symbols, and it uses thecommandp predicate so as to accept only command names:(read-command prompt)≡(intern (completing-read prompt obarray'commandp t nil))read-variable prompt &optional default[Function]
This function reads the name of a customizable variable and returns it as a symbol. Its arguments have the same form as those of read-command. It behaves justlike read-command, except that it uses the predicate custom-variable-p instead ofcommandp.

read-color &optional prompt convert allow-empty display[Command]This function reads a string that is a color specification, either the color’s name or an
RGB hex value such as #RRRGGGBBB. It prompts with prompt (default: "Color (nameor #RGB triplet):") and provides completion for color names, but not for hex RGB
values. In addition to names of standard colors, completion candidates include theforeground and background colors at point.

Valid RGB values are described in Section 30.23 [Color Names], page 846.
The function’s return value is the string typed by the user in the minibuffer. However,when called interactively or if the optional argument convert is non-nil, it converts
any input color name into the corresponding RGB value string and instead returns
that. This function requires a valid color specification to be input. Empty color names
are allowed when allow-empty is non-nil and the user enters null input.
Interactively, or when display is non-nil, the return value is also displayed in the echo
area.
See also the functions read-coding-system and read-non-nil-coding-system, in
Section 34.10.4 [User-Chosen Coding Systems], page 982, and read-input-method-name, in
Section 34.11 [Input Methods], page 990.

21.6.5 Reading File Names
The high-level completion functions read-file-name, read-directory-name, andread-shell-command are designed to read file names, directory names, and shell commands,
respectively. They provide special features, including automatic insertion of the default
directory.

read-file-name prompt &optional directory default require-match
initial predicate[Function]

This function reads a file name, prompting with prompt and providing completion.
As an exception, this function reads a file name using a graphical file dialog instead ofthe minibuffer, if all of the following are true:
1. It is invoked via a mouse command.

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2. The selected frame is on a graphical display supporting such dialogs.
3. The variable use-dialog-box is non-nil. See Section “Dialog Boxes” in The
GNU Emacs Manual.
4. The directory argument, described below, does not specify a remote file. See
Section “Remote Files” in The GNU Emacs Manual.
The exact behavior when using a graphical file dialog is platform-dependent. Here, we
simply document the behavior when using the minibuffer.
read-file-name does not automatically expand the returned file name. You can call
expand-file-name yourself if an absolute file name is required.
The optional argument require-match has the same meaning as in completing-read.
See Section 21.6.2 [Minibuffer Completion], page 398.
The argument directory specifies the directory to use for completing relative file names.
It should be an absolute directory name. If the variable insert-default-directoryis non-nil, directory is also inserted in the minibuffer as initial input. It defaults tothe current buffer’s value of default-directory.
If you specify initial, that is an initial file name to insert in the buffer (after directory,
if that is inserted). In this case, point goes at the beginning of initial. The default for
initial is nil—don’t insert any file name. To see what initial does, try the command
C-x C-v in a buffer visiting a file. Please note: we recommend using default rather
than initial in most cases.
If default is non-nil, then the function returns default if the user exits the minibuffer
with the same non-empty contents that read-file-name inserted initially. The initial
minibuffer contents are always non-empty if insert-default-directory is non-nil,
as it is by default. default is not checked for validity, regardless of the value of requirematch. However, if require-match is non-nil, the initial minibuffer contents should
be a valid file (or directory) name. Otherwise read-file-name attempts completion
if the user exits without any editing, and does not return default. default is alsoavailable through the history commands.
If default is nil, read-file-name tries to find a substitute default to use in its place,which it treats in exactly the same way as if it had been specified explicitly. If default
is nil, but initial is non-nil, then the default is the absolute file name obtained fromdirectory and initial. If both default and initial are nil and the buffer is visiting a file,read-file-name uses the absolute file name of that file as default. If the buffer is not
visiting a file, then there is no default. In that case, if the user types RET without any
editing, read-file-name simply returns the pre-inserted contents of the minibuffer.
If the user types RET in an empty minibuffer, this function returns an empty string,
regardless of the value of require-match. This is, for instance, how the user can makethe current buffer visit no file using M-x set-visited-file-name.
If predicate is non-nil, it specifies a function of one argument that decides which filenames are acceptable completion alternatives. A file name is an acceptable value if
predicate returns non-nil for it.
Here is an example of using read-file-name:Chapter 21: Minibuffers

406(read-file-name "The file is ");; After evaluation of the preceding expression,;;
the following appears in the minibuffer:---------- Buffer: Minibuffer ---------The file is /gp/gnu/elisp/?
---------- Buffer: Minibuffer ---------Typing manual TAB results in the following:---------- Buffer: Minibuffer ---------The file is /gp/gnu/elisp/manual.texi?
---------- Buffer: Minibuffer ---------If the user types RET, read-file-name returns the file name as the string"/gp/gnu/elisp/manual.texi".
[Variable]
If non-nil, this should be a function that accepts the same arguments as read-filename. When read-file-name is called, it calls this function with the supplied arguments instead of doing its usual work.

read-file-name-function[User Option]
If this variable is non-nil, read-file-name ignores case when performing completion.

read-file-name-completion-ignore-caseread-directory-name prompt &optional directory default
require-match initial[Function]

This function is like read-file-name but allows only directory names as completion
alternatives.
If default is nil and initial is non-nil, read-directory-name constructs a substitutedefault by combining directory (or the current buffer’s default directory if directory isnil) and initial. If both default and initial are nil, this function uses directory as
substitute default, or the current buffer’s default directory if directory is nil.
[User Option]
This variable is used by read-file-name, and thus, indirectly, by most commands
reading file names. (This includes all commands that use the code letters ‘f’ or ‘F’ intheir interactive form. See Section 22.2.2 [Code Characters for interactive], page 427.)
Its value controls whether read-file-name starts by placing the name of the default
directory in the minibuffer, plus the initial file name, if any. If the value of this variable
is nil, then read-file-name does not place any initial input in the minibuffer (unless
you specify initial input with the initial argument). In that case, the default directoryis still used for completion of relative file names, but is not displayed.

insert-default-directory

If this variable is nil and the initial minibuffer contents are empty, the user may haveto explicitly fetch the next history element to access a default value. If the variable isnon-nil, the initial minibuffer contents are always non-empty and the user can always
request a default value by immediately typing RET in an unedited minibuffer. (Seeabove.)

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For example:;; Here the minibuffer starts out with the default directory.
(let ((insert-default-directory t))(read-file-name "The file is "))---------- Buffer: Minibuffer ---------The file is ~lewis/manual/?
---------- Buffer: Minibuffer ---------;; Here the minibuffer is empty and only the prompt;;
appears on its line.
(let ((insert-default-directory nil))(read-file-name "The file is "))---------- Buffer: Minibuffer ---------The file is ?
---------- Buffer: Minibuffer ----------

read-shell-command prompt &optional initial history &rest args

[Function]
This function reads a shell command from the minibuffer, prompting with prompt andproviding intelligent completion. It completes the first word of the command using
candidates that are appropriate for command names, and the rest of the commandwords as file names.
This function uses minibuffer-local-shell-command-map as the keymap for minibuffer input. The history argument specifies the history list to use; if is omitted ornil, it defaults to shell-command-history (see Section 21.4 [Minibuffer History],
page 392). The optional argument initial specifies the initial content of the minibuffer(see Section 21.5 [Initial Input], page 394). The rest of args, if present, are usedas the default and inherit-input-method arguments in read-from-minibuffer (seeSection 21.2 [Text from Minibuffer], page 386).
[Variable]
This keymap is used by read-shell-command for completing command and file namesthat are part of a shell command. It uses minibuffer-local-map as its parent keymap,
and binds TAB to completion-at-point.

minibuffer-local-shell-command-map

21.6.6 Completion Variables
Here are some variables that can be used to alter the default completion behavior.
[User Option]
The value of this variable is a list of completion style (symbols) to use for performing
completion. A completion style is a set of rules for generating completions. Eachsymbol occurring this list must have a corresponding entry in completion-stylesalist.

completion-styles[Variable]
This variable stores a list of available completion styles. Each element in the list has
the formcompletion-styles-alist

Chapter 21: Minibuffers408(style try-completion all-completions doc)
Here, style is the name of the completion style (a symbol), which may be used in thecompletion-styles variable to refer to this style; try-completion is the function that
does the completion; all-completions is the function that lists the completions; anddoc is a string describing the completion style.
The try-completion and all-completions functions should each accept four arguments:
string, collection, predicate, and point. The string, collection, and predicate arguments
have the same meanings as in try-completion (see Section 21.6.1 [Basic Completion],
page 395), and the point argument is the position of point within string. Each function
should return a non-nil value if it performed its job, and nil if it did not (e.g., if
there is no way to complete string according to the completion style).
When the user calls a completion command like minibuffer-complete (seeSection 21.6.3 [Completion Commands], page 400), Emacs looks for the firststyle listed in completion-styles and calls its try-completion function. If thisfunction returns nil, Emacs moves to the next listed completion style and calls
its try-completion function, and so on until one of the try-completion functions
successfully performs completion and returns a non-nil value. A similar procedure isused for listing completions, via the all-completions functions.
See Section “Completion Styles” in The GNU Emacs Manual, for a description of theavailable completion styles.
[User Option]
This variable specifies special completion styles and other completion behaviors to use
when completing certain types of text. Its value should be an alist with elements of theform (category . alist). category is a symbol describing what is being completed;currently, the buffer, file, and unicode-name categories are defined, but others
can be defined via specialized completion functions (see Section 21.6.7 [Programmed
Completion], page 409). alist is an association list describing how completion should
behave for the corresponding category. The following alist keys are supported:

completion-category-overrides

stylesThe value should be a list of completion styles (symbols).

cycle

The value should be a value for completion-cycle-threshold (seeSection “Completion Options” in The GNU Emacs Manual) for thiscategory.

Additional alist entries may be defined in the future.
[Variable]
This variable is used to specify extra properties of the current completion command.
It is intended to be let-bound by specialized completion commands. Its value should
be a list of property and value pairs. The following properties are supported:

completion-extra-properties:annotation-function
The value should be a function to add annotations in the completions
buffer. This function must accept one argument, a completion, and should
either return nil or a string to be displayed next to the completion.
Unless this function puts own face on the annotation suffix string, thecompletions-annotations face is added by default to that string.

Chapter 21: Minibuffers409:affixation-function
The value should be a function to add prefixes and suffixes to completions.
This function must accept one argument, a list of completions, and should
return a list of annotated completions. Each element of the returned list
must be a three-element list, the completion, a prefix string, and a suffix
string. This function takes priority over :annotation-function.
:exit-function
The value should be a function to run after performing completion. The
function should accept two arguments, string and status, where stringis the text to which the field was completed, and status indicates whatkind of operation happened: finished if text is now complete, sole if
the text cannot be further completed but completion is not finished, orexact if the text is a valid completion but may be further completed.

21.6.7 Programmed Completion
Sometimes it is not possible or convenient to create an alist or an obarray containing all
the intended possible completions ahead of time. In such a case, you can supply your ownfunction to compute the completion of a given string. This is called programmed completion.
Emacs uses programmed completion when completing file names (see Section 26.9.6 [FileName Completion], page 643), among many other cases.
To use this feature, pass a function as the collection argument to completing-read.
The function completing-read arranges to pass your completion function along totry-completion, all-completions, and other basic completion functions, which will thenlet your function do all the work.
The completion function should accept three arguments:• The string to be completed.
• A predicate function with which to filter possible matches, or nil if none. The function
should call the predicate for each possible match, and ignore the match if the predicate
returns nil.
• A flag specifying the type of completion operation to perform; see Section 21.6.1 [Basic
Completion], page 395, for the details of those operations. This flag may be one of thefollowing values.
nilThis specifies a try-completion operation. The function should returnnil if there are no matches; it should return t if the specified string is aunique and exact match; and it should return the longest common prefix
substring of all matches otherwise.

tThis specifies an all-completions operation. The function should returna list of all possible completions of the specified string.

lambdaThis specifies a test-completion operation. The function should return t
if the specified string is an exact match for some completion alternative;
nil otherwise.

(boundaries . suffix)
This specifies a completion-boundaries operation. The function should
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ning boundary in the specified string, and end is the position of the end
boundary in suffix.
If a Lisp program returns nontrivial boundaries, it should make sure thatthe all-completions operation is consistent with them. The completions
returned by all-completions should only pertain to the piece of the prefix
and suffix covered by the completion boundaries. See Section 21.6.1 [Basic
Completion], page 395, for the precise expected semantics of completion
boundaries.
metadata

This specifies a request for information about the state of the current
completion. The return value should have the form (metadata . alist),
where alist is an alist whose elements are described below.

If the flag has any other value, the completion function should return nil.
The following is a list of metadata entries that a completion function may return in
response to a metadata flag argument:
category

The value should be a symbol describing what kind of text the completionfunction is trying to complete. If the symbol matches one of the keys incompletion-category-overrides, the usual completion behavior is overridden.
See Section 21.6.6 [Completion Variables], page 407.

annotation-function
The value should be a function for annotating completions. The function shouldtake one argument, string, which is a possible completion. It should return astring, which is displayed after the completion string in the *Completions*buffer. Unless this function puts own face on the annotation suffix string, thecompletions-annotations face is added by default to that string.
affixation-function
The value should be a function for adding prefixes and suffixes to completions.
The function should take one argument, completions, which is a list of possible
completions. It should return such a list of completions where each element
contains a list of three elements: a completion, a prefix which is displayed before
the completion string in the *Completions* buffer, and a suffix displayed after
the completion string. This function takes priority over annotation-function.
group-function
The value should be a function for grouping the completion candidates. The
function must take two arguments, completion, which is a completion candidate
and transform, which is a boolean flag. If transform is nil, the function must
return the group title of the group to which the candidate belongs. The returned
title can also be nil. Otherwise the function must return the transformed
candidate. The transformation can for example remove a redundant prefix,
which is displayed in the group title.
display-sort-function
The value should be a function for sorting completions. The function should takeone argument, a list of completion strings, and return a sorted list of completion
strings. It is allowed to alter the input list destructively.

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cycle-sort-function
The value should be a function for sorting completions, whencompletion-cycle-threshold is non-nil and the user is cycling throughcompletion alternatives. See Section “Completion Options” in The GNU
Emacs Manual. Its argument list and return value are the same as fordisplay-sort-function.

completion-table-dynamic function &optional switch-buffer[Function]
This function is a convenient way to write a function that can act as a programmed
completion function. The argument function should be a function that takes one
argument, a string, and returns a completion table (see Section 21.6.1 [Basic Completion], page 395) containing all the possible completions. The table returned byfunction can also include elements that don’t match the string argument; they areautomatically filtered out by completion-table-dynamic. In particular, function canignore its argument and return a full list of all possible completions. You can think ofcompletion-table-dynamic as a transducer between function and the interface forprogrammed completion functions.
If the optional argument switch-buffer is non-nil, and completion is performed in theminibuffer, function will be called with current buffer set to the buffer from which theminibuffer was entered.
The return value of completion-table-dynamic is a function that can be used as the
2nd argument to try-completion and all-completions. Note that this function
will always return empty metadata and trivial boundaries.

completion-table-with-cache function &optional ignore-case[Function]
This is a wrapper for completion-table-dynamic that saves the last argument-result
pair. This means that multiple lookups with the same argument only need to callfunction once. This can be useful when a slow operation is involved, such as callingan external process.

21.6.8 Completion in Ordinary Buffers
Although completion is usually done in the minibuffer, the completion facility can also be
used on the text in ordinary Emacs buffers. In many major modes, in-buffer completion is
performed by the C-M-i or M-TAB command, bound to completion-at-point. See Section“Symbol Completion” in The GNU Emacs Manual. This command uses the abnormal hookvariable completion-at-point-functions:[Variable]
The value of this abnormal hook should be a list of functions, which are used tocompute a completion table (see Section 21.6.1 [Basic Completion], page 395) forcompleting the text at point. It can be used by major modes to provide mode-specificcompletion tables (see Section 24.2.1 [Major Mode Conventions], page 528).
When the command completion-at-point runs, it calls the functions in the list one
by one, without any argument. Each function should return nil unless it can andwants to take responsibility for the completion data for the text at point. Otherwise
it should return a list of the following form:(start end collection . props)

completion-at-point-functions

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start and end delimit the text to complete (which should enclose point). collection is acompletion table for completing that text, in a form suitable for passing as the second
argument to try-completion (see Section 21.6.1 [Basic Completion], page 395); completion alternatives will be generated from this completion table in the usual way, via
the completion styles defined in completion-styles (see Section 21.6.6 [Completion
Variables], page 407). props is a property list for additional information; any ofthe properties in completion-extra-properties are recognized (see Section 21.6.6[Completion Variables], page 407), as well as the following additional ones::predicate
The value should be a predicate that completion candidates need to satisfy.
:exclusive
If the value is no, then if the completion table fails to match the text
at point, completion-at-point moves on to the next function incompletion-at-point-functions instead of reporting a completion
failure.
The functions on this hook should generally return quickly, since they may be calledvery often (e.g., from post-command-hook). Supplying a function for collection isstrongly recommended if generating the list of completions is an expensive operation.
Emacs may internally call functions in completion-at-point-functions many times,
but care about the value of collection for only some of these calls. By supplying afunction for collection, Emacs can defer generating completions until necessary. You
can use completion-table-dynamic to create a wrapper function:;; Avoid this pattern.
(let ((beg ...) (end ...) (my-completions (my-make-completions)))(list beg end my-completions));; Use this instead.
(let ((beg ...) (end ...))(list beg
end(completion-table-dynamic(lambda (_)(my-make-completions)))))

Additionally, the collection should generally not be pre-filtered based on the current text between start and end, because that is the responsibility of the caller ofcompletion-at-point-functions to do that according to the completion styles it
decides to use.
A function in completion-at-point-functions may also return a function insteadof a list as described above. In that case, that returned function is called, with noargument, and it is entirely responsible for performing the completion. We discourage
this usage; it is only intended to help convert old code to using completion-at-point.
The first function in completion-at-point-functions to return a non-nil value
is used by completion-at-point. The remaining functions are not called. The
exception to this is when there is an :exclusive specification, as described above.
The following function provides a convenient way to perform completion on an arbitrary
stretch of text in an Emacs buffer:Chapter 21: Minibuffers

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completion-in-region start end collection &optional predicate[Function]
This function completes the text in the current buffer between the positions startand end, using collection. The argument collection has the same meaning as intry-completion (see Section 21.6.1 [Basic Completion], page 395).
This function inserts the completion text directly into the current buffer. Unlike
completing-read (see Section 21.6.2 [Minibuffer Completion], page 398), it does not
activate the minibuffer.
For this function to work, point must be somewhere between start and end.

21.7 Yes-or-No QueriesThis section describes functions used to ask the user a yes-or-no question. The function
y-or-n-p can be answered with a single character; it is useful for questions where an
inadvertent wrong answer will not have serious consequences. yes-or-no-p is suitable formore momentous questions, since it requires three or four characters to answer.
If either of these functions is called in a command that was invoked using the mouse orsome other window-system gesture, or in a command invoked via a menu, then they use a
dialog box or pop-up menu to ask the question if dialog boxes are supported. Otherwise,
they use keyboard input. You can force use either of the mouse or of keyboard input bybinding last-nonmenu-event to a suitable value around the call—bind it to t to force
keyboard interaction, and to a list to force dialog boxes.
Both yes-or-no-p and y-or-n-p use the minibuffer.

y-or-n-p prompt[Function]
This function asks the user a question, expecting input in the minibuffer. It returns t
if the user types y, nil if the user types n. This function also accepts SPC to mean yes
and DEL to mean no. It accepts C-] and C-g to quit, because the question uses theminibuffer and for that reason the user might try to use C-] to get out. The answer
is a single character, with no RET needed to terminate it. Upper and lower case are
equivalent.

“Asking the question” means printing prompt in the minibuffer, followed by the string‘(y or n) ’. If the input is not one of the expected answers (y, n, SPC, DEL, or somethingthat quits), the function responds ‘Please answer y or n.’, and repeats the request.
This function actually uses the minibuffer, but does not allow editing of the answer.
The cursor moves to the minibuffer while the question is being asked.
The answers and their meanings, even ‘y’ and ‘n’, are not hardwired, and are specified by
the keymap query-replace-map (see Section 35.7 [Search and Replace], page 1016). In
particular, if the user enters the special responses recenter, scroll-up, scroll-down,
scroll-other-window, or scroll-other-window-down (respectively bound to C-l,
C-v, M-v, C-M-v and C-M-S-v in query-replace-map), this function performs the
specified window recentering or scrolling operation, and poses the question again.
If you bind help-form (see Section 25.6 [Help Functions], page 602) to a non-nil value
while calling y-or-n-p, then pressing help-char causes it to evaluate help-form anddisplay the result. help-char is automatically added to prompt.

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y-or-n-p-with-timeout prompt seconds default[Function]
Like y-or-n-p, except that if the user fails to answer within seconds seconds, thisfunction stops waiting and returns default. It works by setting up a timer; see
Section 42.11 [Timers], page 1281. The argument seconds should be a number.

yes-or-no-p prompt[Function]
This function asks the user a question, expecting input in the minibuffer. It returns t
if the user enters ‘yes’, nil if the user types ‘no’. The user must type RET to finalize
the response. Upper and lower case are equivalent.

yes-or-no-p starts by displaying prompt in the minibuffer, followed by ‘(yes or no) ’.
The user must type one of the expected responses; otherwise, the function responds‘Please answer yes or no.’, waits about two seconds and repeats the request.
yes-or-no-p requires more work from the user than y-or-n-p and is appropriate formore crucial decisions.
Here is an example:(yes-or-no-p "Do you really want to remove everything? ");; After evaluation of the preceding expression,;;
the following prompt appears,;;
with an empty minibuffer:---------- Buffer: minibuffer ---------Do you really want to remove everything? (yes or no)---------- Buffer: minibuffer ----------

If the user first types y RET, which is invalid because this function demands the entire
word ‘yes’, it responds by displaying these prompts, with a brief pause between them:---------- Buffer: minibuffer ---------Please answer yes or no.
Do you really want to remove everything? (yes or no)---------- Buffer: minibuffer ----------

21.8 Asking Multiple-Choice Questions
This section describes facilities for asking the user more complex questions or several similar
questions.
When you have a series of similar questions to ask, such as “Do you want to savethis buffer?” for each buffer in turn, you should use map-y-or-n-p to ask the collectionof questions, rather than asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at once.

map-y-or-n-p prompter actor list &optional help action-alist
no-cursor-in-echo-area[Function]

This function asks the user a series of questions, reading a single-character answer inthe echo area for each one.
The value of list specifies the objects to ask questions about. It should be either alist of objects or a generator function. If it is a function, it will be called with noarguments, and should return either the next object to ask about, or nil, meaning tostop asking questions.

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The argument prompter specifies how to ask each question. If prompter is a string,the question text is computed like this:(format prompter object)
where object is the next object to ask about (as obtained from list). See Section 4.7[Formatting Strings], page 66, for more information about format.
If prompter is not a string, it should be a function of one argument (the object to
ask about) and should return the question text for that object. If the value prompter
returns is a string, that is the question to ask the user. The function can also return t,
meaning to act on this object without asking the user, or nil, which means to silently
ignore this object.
The argument actor says how to act on the objects for which the user answers yes. It
should be a function of one argument, and will be called with each object from list for
which the user answers yes.
If the argument help is given, it should be a list of this form:(singular plural action)
where singular is a string containing a singular noun that describes a single object tobe acted on, plural is the corresponding plural noun, and action is a transitive verb
describing what actor does with the objects.
If you don’t specify help, it defaults to the list ("object" "objects" "act on").
Each time a question is asked, the user can answer as follows:y, Y, or SPC
act on the object
n, N, or DEL
skip the object!

act on all the following objects

ESC or q

exit (skip all following objects). (period) act on the object and then exitC-h

get help

These are the same answers that query-replace accepts.
The keymap
query-replace-map defines their meaning for map-y-or-n-p as well as forquery-replace; see Section 35.7 [Search and Replace], page 1016.
You can use action-alist to specify additional possible answers and what theymean. If provided, action-alist should be an alist whose elements are of the form(char function help). Each of the alist elements defines one additional answer.
In each element, char is a character (the answer); function is a function of one
argument (an object from list); and help is a string. When the user responds withchar, map-y-or-n-p calls function. If it returns non-nil, the object is considered tohave been acted upon, and map-y-or-n-p advances to the next object in list. If it
returns nil, the prompt is repeated for the same object. If the user requests help, thetext in help is used to describe these additional answers.
Normally, map-y-or-n-p binds cursor-in-echo-area while prompting. But if nocursor-in-echo-area is non-nil, it does not do that.

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If map-y-or-n-p is called in a command that was invoked using the mouse or someother window-system gesture, or a command invoked via a menu, then it uses a dialog
box or pop-up menu to ask the question if dialog boxes are supported. In this case, itdoes not use keyboard input or the echo area. You can force use either of the mouseor of keyboard input by binding last-nonmenu-event to a suitable value around thecall—bind it to t to force keyboard interaction, and to a list to force dialog boxes.
The return value of map-y-or-n-p is the number of objects acted on.
If you need to ask the user a question that might have more than just 2 answers, use
read-answer.

read-answer question answers[Function]
This function prompts the user with text in question, which should end in the ‘SPC’character. The function includes in the prompt the possible responses in answers
by appending them to the end of question. The possible responses are provided inanswers as an alist whose elements are of the following form:(long-answer short-answer help-message)
where long-answer is the complete text of the user response, a string; short-answer is a
short form of the same response, a single character or a function key; and help-message
is the text that describes the meaning of the answer. If the variable read-answershort is non-nil, the prompt will show the short variants of the possible answers andthe user is expected to type the single characters/keys shown in the prompt; otherwise
the prompt will show the long variants of the answers, and the user is expected totype the full text of one of the answers and end by pressing RET. If use-dialog-box is
non-nil, and this function was invoked by mouse events, the question and the answers
will be displayed in a GUI dialog box.
The function returns the text of the long-answer selected by the user, regardless ofwhether long or short answers were shown in the prompt and typed by the user.
Here is an example of using this function:(let ((read-answer-short t))(read-answer "Foo "'(("yes" ?y "perform the action")("no"?n "skip to the next")("all" ?! "perform for the rest without more questions")("help" ?h "show help")("quit" ?q "exit"))))

read-char-from-minibuffer prompt &optional chars history[Function]
This function uses the minibuffer to read and return a single character. Optionally, itignores any input that is not a member of chars, a list of accepted characters. The
history argument specifies the history list symbol to use; if it is omitted or nil, thisfunction doesn’t use the history.
If you bind help-form (see Section 25.6 [Help Functions], page 602) to a non-nil
value while calling read-char-from-minibuffer, then pressing help-char causes it
to evaluate help-form and display the result.

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21.9 Reading a Password
To read a password to pass to another program, you can use the function read-passwd.

read-passwd prompt &optional confirm default[Function]
This function reads a password, prompting with prompt. It does not echo the password
as the user types it; instead, it echoes ‘*’ for each character in the password. If you want
to apply another character to hide the password, let-bind the variable read-hide-charwith that character.
The optional argument confirm, if non-nil, says to read the password twice and insist
it must be the same both times. If it isn’t the same, the user has to type it over andover until the last two times match.
The optional argument default specifies the default password to return if the user
enters empty input. If default is nil, then read-passwd returns the null string inthat case.

21.10 Minibuffer Commands
This section describes some commands meant for use in the minibuffer.
[Command]This command exits the active minibuffer. It is normally bound to keys in minibuffer
local keymaps. The command throws an error if the current buffer is a minibuffer,
but not the active minibuffer.

exit-minibuffer[Command]This command exits the active minibuffer after inserting the last character typed on
the keyboard (found in last-command-event; see Section 22.5 [Command Loop Info],
page 436).

self-insert-and-exit

previous-history-element n[Command]This command replaces the minibuffer contents with the value of the nth previous(older) history element.

next-history-element n[Command]This command replaces the minibuffer contents with the value of the nth more recent
history element. The position in the history can go beyond the current position andinvoke “future history” (see Section 21.2 [Text from Minibuffer], page 386).

previous-matching-history-element pattern n[Command]This command replaces the minibuffer contents with the value of the nth previous(older) history element that matches pattern (a regular expression).

next-matching-history-element pattern n[Command]This command replaces the minibuffer contents with the value of the nth next (newer)
history element that matches pattern (a regular expression).

previous-complete-history-element n[Command]This command replaces the minibuffer contents with the value of the nth previous(older) history element that completes the current contents of the minibuffer before
the point.

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next-complete-history-element n[Command]This command replaces the minibuffer contents with the value of the nth next (newer)
history element that completes the current contents of the minibuffer before the point.

goto-history-element nabs

[Command]This function puts element of the minibuffer history in the minibuffer. The argument
nabs specifies the absolute history position in descending order, where 0 means the current element and a positive number n means the nth previous element. NABS being anegative number -n means the nth entry of “future history”. When this function reaches
the end of the default values provided by read-from-minibuffer (see Section 21.2
[Text from Minibuffer], page 386) and completing-read (see Section 21.6.2 [Minibuffer Completion], page 398), it adds the completion candidates to “future history”, see
Section 21.4 [minibuffer-default-add-function], page 392.

21.11 Minibuffer Windows
These functions access and select minibuffer windows, test whether they are active andcontrol how they get resized.

minibuffer-window &optional frame[Function]
This function returns the minibuffer window used for frame frame. If frame is nil,that stands for the selected frame.
Note that the minibuffer window used by a frame need not be part of that frame—aframe that has no minibuffer of its own necessarily uses some other frame’s minibuffer
window. The minibuffer window of a minibuffer-less frame can be changed by settingthat frame’s minibuffer frame parameter (see Section 30.4.3.5 [Buffer Parameters],
page 812).

set-minibuffer-window window[Function]
This function specifies window as the minibuffer window to use. This affects where
the minibuffer is displayed if you put text in it without invoking the usual minibuffer
commands. It has no effect on the usual minibuffer input functions because they all
start by choosing the minibuffer window according to the selected frame.

window-minibuffer-p &optional window[Function]
This function returns t if window is a minibuffer window. window defaults to theselected window.

The following function returns the window showing the currently active minibuffer.
[Function]
This function returns the window of the currently active minibuffer, or nil if there isno active minibuffer.

active-minibuffer-window

It is not sufficient to determine whether a given window shows the currently active
minibuffer by comparing it with the result of (minibuffer-window), because there can be
more than one minibuffer window if there is more than one frame.

minibuffer-window-active-p window[Function]
This function returns non-nil if window shows the currently active minibuffer.

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The following two options control whether minibuffer windows are resized automaticallyand how large they can get in the process.
[User Option]
This option specifies whether minibuffer windows are resized automatically. The
default value is grow-only, which means that a minibuffer window by default expands
automatically to accommodate the text it displays and shrinks back to one line assoon as the minibuffer gets empty. If the value is t, Emacs will always try to fit theheight of a minibuffer window to the text it displays (with a minimum of one line). If
the value is nil, a minibuffer window never changes size automatically. In that casethe window resizing commands (see Section 29.5 [Resizing Windows], page 703) canbe used to adjust its height.

resize-mini-windows[User Option]
This option provides a maximum height for resizing minibuffer windows automatically.
A floating-point number specifies the maximum height as a fraction of the frame’sheight; an integer specifies the maximum height in units of the frame’s canonicalcharacter height (see Section 30.3.2 [Frame Font], page 797). The default value is 0.25.

max-mini-window-height

Note that the values of the above two variables take effect at display time, so let-binding
them around code which produces echo-area messages will not work. If you want to prevent
resizing of minibuffer windows when displaying long messages, bind the message-truncatelines variable instead (see Section 41.4.4 [Echo Area Customization], page 1138).
The option resize-mini-windows does not affect the behavior of minibuffer-only frames(see Section 30.3.1 [Frame Layout], page 791). The following option allows to automatically
resize such frames as well.
[User Option]
If this is nil, minibuffer-only frames are never resized automatically.
If this is a function, that function is called with the minibuffer-only frame to be resized
as sole argument. At the time this function is called, the buffer of the minibuffer
window of that frame is the buffer whose contents will be shown the next time thatwindow is redisplayed. The function is expected to fit the frame to the buffer in someappropriate way.
Any other non-nil value means to resize minibuffer-only frames by calling
fit-mini-frame-to-buffer, a function that behaves like fit-frame-to-buffer(see Section 29.5 [Resizing Windows], page 703) but does not strip leading or trailing
empty lines from the buffer text.

resize-mini-frames

21.12 Minibuffer Contents
These functions access the minibuffer prompt and contents.
[Function]
This function returns the prompt string of the currently active minibuffer. If nominibuffer is active, it returns nil.

minibuffer-prompt[Function]
This function returns the current position of the end of the minibuffer prompt, if aminibuffer is current. Otherwise, it returns the minimum valid buffer position.

minibuffer-prompt-end

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This function returns the current display-width of the minibuffer prompt, if a minibuffer
is current. Otherwise, it returns zero.

minibuffer-prompt-width[Function]
This function returns the editable contents of the minibuffer (that is, everything except
the prompt) as a string, if a minibuffer is current. Otherwise, it returns the entire
contents of the current buffer.

minibuffer-contents[Function]
This is like minibuffer-contents, except that it does not copy text properties, justthe characters themselves. See Section 33.19 [Text Properties], page 917.

minibuffer-contents-no-properties[Command]This command erases the editable contents of the minibuffer (that is, everything except
the prompt), if a minibuffer is current. Otherwise, it erases the entire current buffer.

delete-minibuffer-contents

21.13 Recursive Minibuffers
These functions and variables deal with recursive minibuffers (see Section 22.13 [Recursive
Editing], page 475):[Function]
This function returns the current depth of activations of the minibuffer, a nonnegative
integer. If no minibuffers are active, it returns zero.

minibuffer-depth[User Option]
If this variable is non-nil, you can invoke commands (such as find-file) that use
minibuffers even while the minibuffer is active. Such invocation produces a recursive
editing level for a new minibuffer. By default, the outer-level minibuffer is invisible
while you are editing the inner one. If you have minibuffer-follows-selectedframe set to nil, you can have minibuffers visible on several frames at the same time.
See Section “Basic Minibuffer” in emacs.
If this variable is nil, you cannot invoke minibuffer commands when the minibuffer isactive, not even if you switch to another window to do it.

enable-recursive-minibuffers

If a command name has a property enable-recursive-minibuffers that is non-nil,then the command can use the minibuffer to read arguments even if it is invoked from theminibuffer. A command can also achieve this by binding enable-recursive-minibuffers
to t in the interactive declaration (see Section 22.2.1 [Using Interactive], page 424). The
minibuffer command next-matching-history-element (normally M-s in the minibuffer)does the latter.

21.14 Inhibiting Interaction
It’s sometimes useful to be able to run Emacs as a headless server process that responds tocommands given over a network connection. However, Emacs is primarily a platform forinteractive usage, so many commands prompt the user for feedback in certain anomalous
situations. This makes this use case more difficult, since the server process will just hangwaiting for user input.

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Binding the inhibit-interaction variable to something non-nil makes Emacs signal ainhibited-interaction error instead of prompting, which can then be used by the server
process to handle these situations.
Here’s a typical use case:(let ((inhibit-interaction t))(respond-to-client(condition-case err(my-client-handling-function)(inhibited-interaction err))))If my-client-handling-function ends up calling something that asks the user for something (via y-or-n-p or read-from-minibuffer or the like), an inhibited-interaction
error is signaled instead. The server code then catches that error and reports it to the client.

21.15 Minibuffer Miscellanyminibufferp &optional buffer-or-name live

[Function]
This function returns non-nil if buffer-or-name is a minibuffer. If buffer-or-name isomitted or nil, it tests the current buffer. When live is non-nil, the function returns
non-nil only when buffer-or-name is an active minibuffer.
[Variable]
This is a normal hook that is run whenever a minibuffer is entered. See Section 24.1
[Hooks], page 524.

minibuffer-setup-hookminibuffer-with-setup-hook function &rest body

[Macro]This macro executes body after arranging for the specified function to be called via
minibuffer-setup-hook. By default, function is called before the other functions in
the minibuffer-setup-hook list, but if function is of the form (:append func), func
will be called after the other hook functions.
The body forms should not use the minibuffer more than once. If the minibuffer isre-entered recursively, function will only be called once, for the outermost use of theminibuffer.
[Variable]
This is a normal hook that is run whenever a minibuffer is exited. See Section 24.1
[Hooks], page 524.

minibuffer-exit-hook[Variable]
The current value of this variable is used to rebind help-form locally inside theminibuffer (see Section 25.6 [Help Functions], page 602).

minibuffer-help-form[Variable]
If the value of this variable is non-nil, it should be a window object. When thefunction scroll-other-window is called in the minibuffer, it scrolls this window (seeSection 29.21 [Textual Scrolling], page 763).

minibuffer-scroll-window[Function]
This function returns the window that was selected just before the minibuffer window
was selected. If the selected window is not a minibuffer window, it returns nil.

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minibuffer-message string &rest args

[Function]
This function is like message (see Section 41.4.1 [Displaying Messages], page 1131),but it displays the messages specially when the user types in the minibuffer, typicallybecause Emacs prompted the user for some input. When the minibuffer is the current
buffer, this function displays the message specified by string temporarily at the endof the minibuffer text, and thus avoids hiding the minibuffer text by the echo-areadisplay of the message. It leaves the message on display for a few seconds, or until thenext input event arrives, whichever comes first. The variable minibuffer-messagetimeout specifies the number of seconds to wait in the absence of input. It defaults
to 2. If args is non-nil, the actual message is obtained by passing string and args
through format-message. See Section 4.7 [Formatting Strings], page 66.
If called when the minibuffer is not the current buffer, this function just calls message,
and thus string will be shown in the echo-area.
[Command]This is the major mode used in inactive minibuffers.
It uses keymap
minibuffer-inactive-mode-map. This can be useful if the minibuffer is in a
separate frame. See Section 30.9 [Minibuffers and Frames], page 824.

minibuffer-inactive-mode

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22 Command Loop
When you run Emacs, it enters the editor command loop almost immediately. This loop
reads key sequences, executes their definitions, and displays the results. In this chapter, we
describe how these things are done, and the subroutines that allow Lisp programs to dothem.

22.1 Command Loop Overview
The first thing the command loop must do is read a key sequence, which is a sequence of
input events that translates into a command. It does this by calling the function read-keysequence. Lisp programs can also call this function (see Section 22.8.1 [Key Sequence Input],
page 461). They can also read input at a lower level with read-key or read-event (seeSection 22.8.2 [Reading One Event], page 462), or discard pending input with discard-input(see Section 22.8.6 [Event Input Misc], page 468).
The key sequence is translated into a command through the currently active keymaps.
See Section 23.10 [Key Lookup], page 494, for information on how this is done. The result
should be a keyboard macro or an interactively callable function. If the key is M-x, thenit reads the name of another command, which it then calls. This is done by the commandexecute-extended-command (see Section 22.3 [Interactive Call], page 432).
Prior to executing the command, Emacs runs undo-boundary to create an undo boundary.
See Section 33.10 [Maintaining Undo], page 898.
To execute a command, Emacs first reads its arguments by calling command-execute (seeSection 22.3 [Interactive Call], page 432). For commands written in Lisp, the interactive
specification says how to read the arguments. This may use the prefix argument (seeSection 22.12 [Prefix Command Arguments], page 473) or may read with prompting in theminibuffer (see Chapter 21 [Minibuffers], page 385). For example, the command find-filehas an interactive specification which says to read a file name using the minibuffer. The
function body of find-file does not use the minibuffer, so if you call find-file as afunction from Lisp code, you must supply the file name string as an ordinary Lisp function
argument.
If the command is a keyboard macro (i.e., a string or vector), Emacs executes it using
execute-kbd-macro (see Section 22.16 [Keyboard Macros], page 478).
[Variable]
This normal hook is run by the editor command loop before it executes each command. At that time, this-command contains the command that is about to run, andlast-command describes the previous command. See Section 22.5 [Command LoopInfo], page 436.

pre-command-hook[Variable]
This normal hook is run by the editor command loop after it executes each command(including commands terminated prematurely by quitting or by errors). At that time,
this-command refers to the command that just ran, and last-command refers to thecommand before that.
This hook is also run when Emacs first enters the command loop (at which point
this-command and last-command are both nil).

post-command-hook

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Quitting is suppressed while running pre-command-hook and post-command-hook. If anerror happens while executing one of these hooks, it does not terminate execution of thehook; instead the error is silenced and the function in which the error occurred is removed
from the hook.
A request coming into the Emacs server (see Section “Emacs Server” in The GNU Emacs
Manual) runs these two hooks just as a keyboard command does.
Note that, when the buffer text includes very long lines, these two hooks are called asif they were in a with-restriction form (see Section 31.4 [Narrowing], page 865), witha long-line-optimizations-in-command-hooks label and with the buffer narrowed to a
portion around point.

22.2 Defining Commands
The special form interactive turns a Lisp function into a command. The interactive
form must be located at top-level in the function body, usually as the first form in thebody; this applies to both lambda expressions (see Section 13.2 [Lambda Expressions],
page 232) and defun forms (see Section 13.4 [Defining Functions], page 237). This form
does nothing during the actual execution of the function; its presence serves as a flag, telling
the Emacs command loop that the function can be called interactively. The argument of
the interactive form specifies how the arguments for an interactive call should be read.
Alternatively, an interactive form may be specified in a function symbol’sinteractive-form property. A non-nil value for this property takes precedence over any
interactive form in the function body itself. This feature is seldom used.
Sometimes, a function is only intended to be called interactively, never directly from Lisp.
In that case, give the function a non-nil interactive-only property, either directly or via
declare (see Section 13.15 [Declare Form], page 263). This causes the byte compiler towarn if the command is called from Lisp. The output of describe-function will include
similar information. The value of the property can be: a string, which the byte-compiler
will use directly in its warning (it should end with a period, and not start with a capital,
e.g., "use (system-name) instead."); t; any other symbol, which should be an alternative
function to use in Lisp code.
Generic functions (see Section 13.8 [Generic Functions], page 245) cannot be turned into
commands by adding the interactive form to them.

22.2.1 Using interactive
This section describes how to write the interactive form that makes a Lisp function aninteractively-callable command, and how to examine a command’s interactive form.

interactive &optional arg-descriptor &rest modes[Special Form]
This special form declares that a function is a command, and that it may therefore becalled interactively (via M-x or by entering a key sequence bound to it). The argument
arg-descriptor declares how to compute the arguments to the command when thecommand is called interactively.

A command may be called from Lisp programs like any other function, but then thecaller supplies the arguments and arg-descriptor has no effect.

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The interactive form must be located at top-level in the function body, or in thefunction symbol’s interactive-form property (see Section 9.4 [Symbol Properties],
page 138). It has its effect because the command loop looks for it before calling thefunction (see Section 22.3 [Interactive Call], page 432). Once the function is called, allits body forms are executed; at this time, if the interactive form occurs within thebody, the form simply returns nil without even evaluating its argument.
The modes list allows specifying which modes the command is meant to be used in.
See Section 22.2.4 [Command Modes], page 430, for more details about the effect ofspecifying modes, and when to use it.
By convention, you should put the interactive form in the function body, as the first
top-level form. If there is an interactive form in both the interactive-form symbol
property and the function body, the former takes precedence. The interactive-form
symbol property can be used to add an interactive form to an existing function, orchange how its arguments are processed interactively, without redefining the function.
There are three possibilities for the argument arg-descriptor:• It may be omitted or nil; then the command is called with no arguments. This leads
quickly to an error if the command requires one or more arguments.
• It may be a string; its contents are a sequence of elements separated by newlines, one foreach argument1 . Each element consists of a code character (see Section 22.2.2 [Interactive
Codes], page 427) optionally followed by a prompt (which some code characters use
and some ignore). Here is an example:(interactive "P\nbFrobnicate buffer: ")The code letter ‘P’ sets the command’s first argument to the raw command prefix(see Section 22.12 [Prefix Command Arguments], page 473). ‘bFrobnicate buffer: ’prompts the user with ‘Frobnicate buffer: ’ to enter the name of an existing buffer,
which becomes the second and final argument.
The prompt string can use ‘%’ to include previous argument values (starting with thefirst argument) in the prompt. This is done using format-message (see Section 4.7[Formatting Strings], page 66). For example, here is how you could read the name of an
existing buffer followed by a new name to give to that buffer:(interactive "bBuffer to rename: \nsRename buffer %s to: ")If ‘*’ appears at the beginning of the string, then an error is signaled if the buffer isread-only.
If ‘@’ appears at the beginning of the string, and if the key sequence used to invoke thecommand includes any mouse events, then the window associated with the first of those
events is selected before the command is run.
If ‘^’ appears at the beginning of the string, and if the command was invoked throughshift-translation, set the mark and activate the region temporarily, or extend an alreadyactive region, before the command is run. If the command was invoked without
shift-translation, and the region is temporarily active, deactivate the region before thecommand is run. Shift-translation is controlled on the user level by shift-select-mode;see Section “Shift Selection” in The GNU Emacs Manual.
1

Some elements actually supply two arguments.

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You can use ‘*’, ‘@’, and ^ together; the order does not matter. Actual reading ofarguments is controlled by the rest of the prompt string (starting with the first character
that is not ‘*’, ‘@’, or ‘^’).
• It may be a Lisp expression that is not a string; then it should be a form that isevaluated to get a list of arguments to pass to the command. Usually this form willcall various functions to read input from the user, most often through the minibuffer(see Chapter 21 [Minibuffers], page 385) or directly from the keyboard (see Section 22.8
[Reading Input], page 460).
Providing point or the mark as an argument value is also common, but if you do thisand read input (whether using the minibuffer or not), be sure to get the integer valuesof point or the mark after reading. The current buffer may be receiving subprocess
output; if subprocess output arrives while the command is waiting for input, it could
relocate point and the mark.
Here’s an example of what not to do:(interactive(list (region-beginning) (region-end)(read-string "Foo: " nil 'my-history)))

Here’s how to avoid the problem, by examining point and the mark after reading the
keyboard input:(interactive(let ((string (read-string "Foo: " nil 'my-history)))(list (region-beginning) (region-end) string)))

Warning: the argument values should not include any data types that can’t be printed
and then read. Some facilities save command-history in a file to be read in thesubsequent sessions; if a command’s arguments contain a data type that prints using‘#<...>’ syntax, those facilities won’t work.
There are, however, a few exceptions: it is ok to use a limited set of expressions such as(point), (mark), (region-beginning), and (region-end), because Emacs recognizes
them specially and puts the expression (rather than its value) into the command history.
To see whether the expression you wrote is one of these exceptions, run the command,then examine (car command-history).

interactive-form function[Function]
This function returns the interactive form of function. If function is an interactively
callable function (see Section 22.3 [Interactive Call], page 432), the value is thecommand’s interactive form (interactive spec), which specifies how to computeits arguments. Otherwise, the value is nil. If function is a symbol, its function
definition is used. When called on an OClosure, the work is delegated to the genericfunction oclosure-interactive-form.

oclosure-interactive-form function[Function]
Just like interactive-form, this function takes a command and returns its interactive
form. The difference is that it is a generic function and it is only called when function
is an OClosure (see Section 13.11 [OClosures], page 250). The purpose is to makeit possible for some OClosure types to compute their interactive forms dynamicallyinstead of carrying it in one of their slots.

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This is used for example for kmacro functions in order to reduce their memory size,
since they all share the same interactive form. It is also used for advice functions,where the interactive form is computed from the interactive forms of its components,
so as to make this computation more lazily and to correctly adjust the interactive
form when one of its component’s is redefined.

22.2.2 Code Characters for interactive
The code character descriptions below contain a number of key words, defined here as
follows:
Completion
Provide completion. TAB, SPC, and RET perform name completion because
the argument is read using completing-read (see Section 21.6 [Completion],
page 395). ? displays a list of possible completions.
Existing

Require the name of an existing object. An invalid name is not accepted; thecommands to exit the minibuffer do not exit if the current input is not valid.

Default

A default value of some sort is used if the user enters no text in the minibuffer.
The default depends on the code character.

No I/OThis code letter computes an argument without reading any input. Therefore,
it does not use a prompt string, and any prompt string you supply is ignored.
Even though the code letter doesn’t use a prompt string, you must follow itwith a newline if it is not the last code character in the string.

PromptA prompt immediately follows the code character. The prompt ends either withthe end of the string or with a newline.

SpecialThis code character is meaningful only at the beginning of the interactive string,and it does not look for a prompt or a newline. It is a single, isolated character.

Here are the code character descriptions for use with interactive:‘*’

Signal an error if the current buffer is read-only. Special.

‘@’

Select the window mentioned in the first mouse event in the key sequence thatinvoked this command. Special.

‘^’

If the command was invoked through shift-translation, set the mark and activate
the region temporarily, or extend an already active region, before the commandis run. If the command was invoked without shift-translation, and the region is
temporarily active, deactivate the region before the command is run. Special.

‘a’

A function name (i.e., a symbol satisfying fboundp). Existing, Completion,
Prompt.

‘b’

The name of an existing buffer. By default, uses the name of the current buffer(see Chapter 28 [Buffers], page 671). Existing, Completion, Default, Prompt.

‘B’

A buffer name. The buffer need not exist. By default, uses the name of a recently
used buffer other than the current buffer. Completion, Default, Prompt.

‘c’

A character. The cursor does not move into the echo area. Prompt.

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‘C’

A command name (i.e., a symbol satisfying commandp). Existing, Completion,
Prompt.

‘d’

The position of point, as an integer (see Section 31.1 [Point], page 853). No I/O.

‘D’

A directory. The default is the current default directory of the current buffer,
default-directory (see Section 26.9.4 [File Name Expansion], page 639).
Existing, Completion, Default, Prompt.

‘e’The first or next non-keyboard event in the key sequence that invoked thecommand. More precisely, ‘e’ gets events that are lists, so you can look at thedata in the lists. See Section 22.7 [Input Events], page 440. No I/O.
You use ‘e’ for mouse events and for special system events (see Section 22.7.12[Misc Events], page 450). The event list that the command receives depends onthe event. See Section 22.7 [Input Events], page 440, which describes the formsof the list for each event in the corresponding subsections.
You can use ‘e’ more than once in a single command’s interactive specification.
If the key sequence that invoked the command has n events that are lists, thenth ‘e’ provides the nth such event. Events that are not lists, such as function
keys and ASCII characters, do not count where ‘e’ is concerned.

‘f’

A file name of an existing file (see Section 26.9 [File Names], page 634). See
Section 21.6.5 [Reading File Names], page 404, for details about default values.
Existing, Completion, Default, Prompt.

‘F’

A file name. The file need not exist. Completion, Default, Prompt.

‘G’

A file name. The file need not exist. If the user enters just a directory name,then the value is just that directory name, with no file name within the directory
added. Completion, Default, Prompt.

‘i’

An irrelevant argument. This code always supplies nil as the argument’s value.
No I/O.

‘k’

A key sequence (see Section 23.1 [Key Sequences], page 480). This keeps reading
events until a command (or undefined command) is found in the current key
maps. The key sequence argument is represented as a string or vector. The
cursor does not move into the echo area. Prompt.
If ‘k’ reads a key sequence that ends with a down-event, it also reads and discards
the following up-event. You can get access to that up-event with the ‘U’ codecharacter.
This kind of input is used by commands such as describe-key andkeymap-global-set.

‘K’

A key sequence on a form that can be used as input to functions like keymap-set.
This works like ‘k’, except that it suppresses, for the last input event in the key
sequence, the conversions that are normally used (when necessary) to convert
an undefined key into a defined one (see Section 22.8.1 [Key Sequence Input],
page 461), so this form is usually used when prompting for a new key sequencethat is to be bound to a command.

‘m’

The position of the mark, as an integer. No I/O.

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‘M’

Arbitrary text, read in the minibuffer using the current buffer’s input method,
and returned as a string (see Section “Input Methods” in The GNU Emacs
Manual). Prompt.

‘n’

A number, read with the minibuffer. If the input is not a number, the user has
to try again. ‘n’ never uses the prefix argument. Prompt.

‘N’

The numeric prefix argument; but if there is no prefix argument, read a number
as with n. The value is always a number. See Section 22.12 [Prefix Command
Arguments], page 473. Prompt.

‘p’

The numeric prefix argument. (Note that this ‘p’ is lower case.) No I/O.

‘P’

The raw prefix argument. (Note that this ‘P’ is upper case.) No I/O.

‘r’

Point and the mark, as two numeric arguments, smallest first. This is the only
code letter that specifies two successive arguments rather than one. This will
signal an error if the mark is not set in the buffer which is current when thecommand is invoked. If Transient Mark mode is turned on (see Section 32.7
[The Mark], page 873) — as it is by default — and user option mark-evenif-inactive is nil, Emacs will signal an error even if the mark is set, but isinactive. No I/O.

‘s’

Arbitrary text, read in the minibuffer and returned as a string (see Section 21.2
[Text from Minibuffer], page 386). Terminate the input with either C-j or RET.
(C-q may be used to include either of these characters in the input.) Prompt.

‘S’

An interned symbol whose name is read in the minibuffer. Terminate the input
with either C-j or RET. Other characters that normally terminate a symbol (e.g.,
whitespace, parentheses and brackets) do not do so here. Prompt.

‘U’

A key sequence or nil. Can be used after a ‘k’ or ‘K’ argument to get the
up-event that was discarded (if any) after ‘k’ or ‘K’ read a down-event. If no
up-event has been discarded, ‘U’ provides nil as the argument. No I/O.

‘v’

A variable declared to be a user option (i.e., satisfying the predicate
custom-variable-p). This reads the variable using read-variable. See[Definition of read-variable], page 404. Existing, Completion, Prompt.

‘x’

A Lisp object, specified with its read syntax, terminated with a C-j or RET. The
object is not evaluated. See Section 21.3 [Object from Minibuffer], page 391.
Prompt.

‘X’

A Lisp form’s value. ‘X’ reads as ‘x’ does, then evaluates the form so that its
value becomes the argument for the command. Prompt.

‘z’

A coding system name (a symbol). If the user enters null input, the argument
value is nil. See Section 34.10 [Coding Systems], page 976. Completion, Existing,
Prompt.

‘Z’

A coding system name (a symbol)—but only if this command has a prefix
argument. With no prefix argument, ‘Z’ provides nil as the argument value.
Completion, Existing, Prompt.

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22.2.3 Examples of Using interactive
Here are some examples of interactive:(defun foo1 ()(interactive)(forward-word 2))⇒ foo1; foo1 takes no arguments,;
just moves forward two words.

(defun foo2 (n)(interactive "^p"); foo2 takes one argument,;
which is the numeric prefix.
; under shift-select-mode,;
will activate or extend region.

(forward-word (* 2 n)))⇒ foo2(defun foo3 (n); foo3 takes one argument,(interactive "nCount:") ;which is read with the Minibuffer.
(forward-word (* 2 n)))⇒ foo3(defun three-b (b1 b2 b3)"Select three existing buffers.
Put them into three windows, selecting the last one."(interactive "bBuffer1:\nbBuffer2:\nbBuffer3:")(delete-other-windows)(split-window (selected-window) 8)(switch-to-buffer b1)(other-window 1)(split-window (selected-window) 8)(switch-to-buffer b2)(other-window 1)(switch-to-buffer b3))
⇒ three-b(three-b "*scratch*" "declarations.texi" "*mail*")⇒ nil

22.2.4 Specifying Modes For Commands
Many commands in Emacs are general, and not tied to any specific mode. For instance, M-x
kill-region can be used in pretty much any mode that has editable text, and commands
that display information (like M-x list-buffers) can be used in pretty much any context.
Many other commands, however, are specifically tied to a mode, and make no sense
outside of that context. For instance, M-x dired-diff will just signal an error if used outsideof a Dired buffer.
Emacs therefore has a mechanism for specifying what mode (or modes) a command“belongs” to:(defun dired-diff (...)

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...
(interactive "p" dired-mode)...)This will mark the command as applicable to dired-mode only (or any modes that arederived from dired-mode). Any number of modes can be added to the interactive form.
Specifying modes affects command completion in M-S-x (execute-extended-commandfor-buffer, see Section 22.3 [Interactive Call], page 432). It may also affect completion in
M-x, depending on the value of read-extended-command-predicate.
For instance, when using the command-completion-default-include-p predicate as
the value of read-extended-command-predicate, M-x won’t list commands that have beenmarked as being applicable to a specific mode (unless you are in a buffer that uses thatmode, of course). This goes for both major and minor modes. (By contrast, M-S-x always
omits inapplicable commands from the completion candidates.)
By default, read-extended-command-predicate is nil, and completion in M-x lists all
the commands that match what the user has typed, whether those commands are or aren’tmarked as applicable to the current buffer’s mode.
Marking commands to be applicable to a mode will also make C-h m list these commands(if they aren’t bound to any keys).
If using this extended interactive form isn’t convenient (because the code is supposed
to work in older versions of Emacs that don’t support the extended interactive form), thefollowing equivalent declaration (see Section 13.15 [Declare Form], page 263) can be usedinstead:(declare (modes dired-mode))
Which commands to tag with modes is to some degree a matter of taste, but commands
that clearly do not work outside of the mode should be tagged. This includes commands thatwill signal an error if called from somewhere else, but also commands that are destructive
when called from an unexpected mode. (This usually includes most of the commands thatare written for special (i.e., non-editing) modes.)Some commands may be harmless, and “work” when called from other modes, but shouldstill be tagged with a mode if they don’t actually make much sense to use elsewhere. For
instance, many special modes have commands to exit the buffer bound to q, and may not doanything but issue a message like "Goodbye from this mode" and then call kill-buffer.
This command will “work” from any mode, but it is highly unlikely that anybody would
actually want to use the command outside the context of this special mode.
Many modes have a set of different commands that start the mode in different ways
(e.g., eww-open-in-new-buffer and eww-open-file). Commands like that should never
be tagged as mode-specific, as they can be issued by the user from pretty much any context.

22.2.5 Select among Command Alternatives
Sometimes it is useful to define a command that serves as a “generic dispatcher” capableof invoking one of a set of commands according to the user’s needs. For example, imagine
that you want to define a command named ‘open’ that can “open” and display several
different types of objects. Or you could have a command named ‘mua’ (which stands for
Mail User Agent) that can read and send email using one of several email backends, such

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as Rmail, Gnus, or MH-E. The macro define-alternatives can be used to define suchgeneric commands. A generic command is an interactive function whose implementation
can be selected from several alternatives, as a matter of user preference.

define-alternatives command &rest customizations[Macro]This macro defines the new generic command, which can have several alternative
implementations. The argument command should be an unquoted symbol.

When invoked, the macro creates an interactive Lisp closure (see Section 13.10[Closures], page 249). When the user runs M-x command RET for the first time, Emacs
asks to select one of the alternative implementations of command, offering completion
for the names of these alternatives. These names come from the user option whosename is command-alternatives, which the macro creates (if it didn’t exist before).
To be useful, this variable’s value should be an alist whose elements have the form
(alt-name . alt-func), where alt-name is the name of the alternative and alt-func is
the interactive function to be called if this alternative is selected. When the user selects
an alternative, Emacs remembers the selection, and will thereafter automatically callthat selected alternative without prompting when the user invokes M-x command again.
To choose a different alternative, type C-u M-x command RET–then Emacs will again
prompt for one of the alternatives, and the selection will override the previous one.
The variable command-alternatives can be created before callingdefine-alternatives, with the appropriate values; otherwise the macro
creates the variable with a nil value, and it should then be populated with theassociations describing the alternatives. Packages that wish to provide their own
implementation of an existing generic command can use autoload cookies (seeSection 16.5 [Autoload], page 304) to add to the alist, for example:;;;###autoload (push '("My name" . my-foo-symbol) foo-alternatives
If the optional argument customizations is non-nil, it should consist of alternating
defcustom keywords (typically :group and :version) and values to add to thedefinition of the defcustom command-alternatives.
Here is an example of a simple generic dispatcher command named open with 3
alternative implementations:(define-alternatives open
:group 'files:version "42.1")(setq open-alternatives'(("file" . find-file)("directory" . dired)("hexl" . hexl-find-file)))22.3 Interactive Call
After the command loop has translated a key sequence into a command, it invokes that command using the function command-execute. If the command is a function, command-execute
calls call-interactively, which reads the arguments and calls the command. You canalso call these functions yourself.

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Note that the term “command”, in this context, refers to an interactively callable function(or function-like object), or a keyboard macro. It does not refer to the key sequence used to
invoke a command (see Chapter 23 [Keymaps], page 480).

commandp object &optional for-call-interactively[Function]

This function returns t if object is a command. Otherwise, it returns nil.
Commands include strings and vectors (which are treated as keyboard macros),lambda expressions that contain a top-level interactive form (see Section 22.2.1[Using Interactive], page 424), byte-code function objects made from such lambda
expressions, autoload objects that are declared as interactive (non-nil fourth argument
to autoload), and some primitive functions. Also, a symbol is considered a command
if it has a non-nil interactive-form property, or if its function definition satisfies
commandp.
If for-call-interactively is non-nil, then commandp returns t only for objects thatcall-interactively could call—thus, not for keyboard macros.
See documentation in Section 25.2 [Accessing Documentation], page 596, for a realistic
example of using commandp.

call-interactively command &optional record-flag keys

[Function]
This function calls the interactively callable function command, providing arguments
according to its interactive calling specifications. It returns whatever command returns.
If, for instance, you have a function with the following signature:(defun foo (begin end)
(interactive "r")...)then saying(call-interactively 'foo)

will call foo with the region (point and mark) as the arguments.
An error is signaled if command is not a function or if it cannot be called interactively(i.e., is not a command). Note that keyboard macros (strings and vectors) are notaccepted, even though they are considered commands, because they are not functions.
If command is a symbol, then call-interactively uses its function definition.
If record-flag is non-nil, then this command and its arguments are unconditionallyadded to the list command-history. Otherwise, the command is added only if it uses
the minibuffer to read an argument. See Section 22.15 [Command History], page 477.
The argument keys, if given, should be a vector which specifies the sequence of events
to supply if the command inquires which events were used to invoke it. If keys isomitted or nil, the default is the return value of this-command-keys-vector. See[Definition of this-command-keys-vector], page 437.

funcall-interactively function &rest arguments[Function]
This function works like funcall (see Section 13.5 [Calling Functions], page 239), but
it makes the call look like an interactive invocation: a call to called-interactivelyp inside function will return t. If function is not a command, it is called without
signaling an error.

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command-execute command &optional record-flag keys special[Function]
This function executes command. The argument command must satisfy the commandp
predicate; i.e., it must be an interactively callable function or a keyboard macro.
A string or vector as command is executed with execute-kbd-macro. A function
is passed to call-interactively (see above), along with the record-flag and keys
arguments.
If command is a symbol, its function definition is used in its place. A symbol with anautoload definition counts as a command if it was declared to stand for an interactively
callable function. Such a definition is handled by loading the specified library andthen rechecking the definition of the symbol.
The argument special, if given, means to ignore the prefix argument and not clear it.
This is used for executing special events (see Section 22.9 [Special Events], page 470).

execute-extended-command prefix-argument[Command]This function reads a command name from the minibuffer using completing-read(see Section 21.6 [Completion], page 395). Then it uses command-execute to callthe specified command. Whatever that command returns becomes the value of
execute-extended-command.
If the command asks for a prefix argument, it receives the value prefix-argument. If
execute-extended-command is called interactively, the current raw prefix argument
is used for prefix-argument, and thus passed on to whatever command is run.
execute-extended-command is the normal definition of M-x, so it uses the string ‘M-x ’
as a prompt. (It would be better to take the prompt from the events used to invoke
execute-extended-command, but that is painful to implement.) A description of thevalue of the prefix argument, if any, also becomes part of the prompt.
(execute-extended-command 3)---------- Buffer: Minibuffer ---------3 M-x forward-word RET---------- Buffer: Minibuffer ---------⇒ t
This command heeds the read-extended-command-predicate variable, which
can filter out commands that are not applicable to the current major mode(or enabled minor modes). By default, the value of this variable is nil, andno commands are filtered out. However, customizing it to invoke the functioncommand-completion-default-include-p will perform mode-dependent filtering.
read-extended-command-predicate can be any predicate function; it will be calledwith two parameters: the command’s symbol and the current buffer. If should return
non-nil if the command is to be included when completing in that buffer.

execute-extended-command-for-buffer prefix-argument[Command]This is like execute-extended-command, but limits the commands offered for completion to those commands that are of particular relevance to the current major mode(and enabled minor modes). This includes commands that are tagged with the modes(see Section 22.2.1 [Using Interactive], page 424), and also commands that are boundto locally active keymaps. This command is the normal definition of M-S-x (that’s“meta shift x”).

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Both these commands prompt for a command name, but with different completion rules.
You can toggle between these two modes by using the M-S-x command while being prompted.

22.4 Distinguish Interactive Calls
Sometimes a command should display additional visual feedback (such as an informative
message in the echo area) for interactive calls only. There are three ways to do this. The
recommended way to test whether the function was called using call-interactively is
to give it an optional argument print-message and use the interactive spec to make it
non-nil in interactive calls. Here’s an example:(defun foo (&optional print-message)(interactive "p")(when print-message(message "foo")))We use "p" because the numeric prefix argument is never nil. Defined in this way, thefunction does display the message when called from a keyboard macro.
The above method with the additional argument is usually best, because it allows
callers to say “treat this call as interactive”. But you can also do the job by testing
called-interactively-p.

called-interactively-p kindThis function returns
call-interactively.

t

when

the

callingfunctionwas[Function]
called using

The argument kind should be either the symbol interactive or the symbol any. If it
is interactive, then called-interactively-p returns t only if the call was madedirectly by the user—e.g., if the user typed a key sequence bound to the calling function,
but not if the user ran a keyboard macro that called the function (see Section 22.16[Keyboard Macros], page 478). If kind is any, called-interactively-p returns t
for any kind of interactive call, including keyboard macros.
If in doubt, use any; the only known proper use of interactive is if you need todecide whether to display a helpful message while a function is running.
A function is never considered to be called interactively if it was called via Lisp
evaluation (or with apply or funcall).
Here is an example of using called-interactively-p:(defun foo ()(interactive)(when (called-interactively-p 'any)(message "Interactive!")'foo-called-interactively));; Type M-x foo.
a Interactive!
(foo)
⇒ nil

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Here is another example that contrasts direct and indirect calls to called-interactively-p.
(defun bar ()(interactive)(message "%s" (list (foo) (called-interactively-p 'any))));; Type M-x bar.
a (nil t)

22.5 Information from the Command Loop
The editor command loop sets several Lisp variables to keep status records for itself andfor commands that are run. With the exception of this-command and last-command it’s
generally a bad idea to change any of these variables in a Lisp program.
[Variable]
This variable records the name of the previous command executed by the command
loop (the one before the current command). Normally the value is a symbol with afunction definition, but this is not guaranteed.

last-command

The value is copied from this-command when a command returns to the command
loop, except when the command has specified a prefix argument for the following
command.
This variable is always local to the current terminal and cannot be buffer-local. See
Section 30.2 [Multiple Terminals], page 787.
[Variable]
This variable is set up by Emacs just like last-command, but never altered by Lisp
programs.

real-last-command[Variable]
This variable stores the most recently executed command that was not part of an
input event. This is the command repeat will try to repeat, See Section “Repeating”
in The GNU Emacs Manual.

last-repeatable-command[Variable]
This variable records the name of the command now being executed by the editor
command loop. Like last-command, it is normally a symbol with a function definition.

this-command

The command loop sets this variable just before running a command, and copies its
value into last-command when the command finishes (unless the command specified
a prefix argument for the following command).
Some commands set this variable during their execution, as a flag for whatevercommand runs next. In particular, the functions for killing text set this-command tokill-region so that any kill commands immediately following will know to append
the killed text to the previous kill.
If you do not want a particular command to be recognized as the previous command in
the case where it got an error, you must code that command to prevent this. One way is toChapter 22: Command Loop437

set this-command to t at the beginning of the command, and set this-command back to its
proper value at the end, like this:(defun foo (args...)(interactive ...)
(let ((old-this-command this-command))(setq this-command t). . . do the work. . .
(setq this-command old-this-command)))
We do not bind this-command with let because that would restore the old value in case oferror—a feature of let which in this case does precisely what we want to avoid.
[Variable]
This has the same value as this-command except when command remapping occurs(see Section 23.14 [Remapping Commands], page 503). In that case, this-commandgives the command actually run (the result of remapping), and this-originalcommand gives the command that was specified to run but remapped into anothercommand.

this-original-command[Variable]
This has the same value as this-command, but is bound recursively when entering aminibuffer. This variable can be used from minibuffer hooks and the like to determine
what command opened the current minibuffer session.

current-minibuffer-command[Function]
This function returns a string or vector containing the key sequence that invoked thepresent command. Any events read by the command using read-event without atimeout get tacked on to the end.

this-command-keys

However, if the command has called read-key-sequence, it returns the last read key
sequence. See Section 22.8.1 [Key Sequence Input], page 461. The value is a string if
all events in the sequence were characters that fit in a string. See Section 22.7 [Input
Events], page 440.
(this-command-keys);; Now use C-u C-x C-e to evaluate that.
⇒ "^X^E"[Function]
Like this-command-keys, except that it always returns the events in a vector, so
you don’t need to deal with the complexities of storing input events in a string (seeSection 22.7.17 [Strings of Events], page 459).

this-command-keys-vector

clear-this-command-keys &optional keep-record[Function]
This function empties out the table of events for this-command-keys to return. Unlesskeep-record is non-nil, it also empties the records that the function recent-keys(see Section 42.13.2 [Recording Input], page 1286) will subsequently return. This isuseful after reading a password, to prevent the password from echoing inadvertently
as part of the next command in certain cases.

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[Variable]
This variable holds the last input event read as part of a key sequence, not counting
events resulting from mouse menus.

last-nonmenu-event

One use of this variable is for telling x-popup-menu where to pop up a menu. It isalso used internally by y-or-n-p (see Section 21.7 [Yes-or-No Queries], page 413).
[Variable]
This variable is set to the last input event that was read by the command loop as
part of a command. The principal use of this variable is in self-insert-command,
which uses it to decide which character to insert, and in post-self-insert-hook(see Section 33.5 [Commands for Insertion], page 884), which uses it to access thecharacter that was just inserted.

last-command-eventlast-command-event;; Now use C-u C-x C-e to evaluate that.
⇒ 5
The value is 5 because that is the ASCII code for C-e.
[Variable]
This variable records which frame the last input event was directed to. Usually thisis the frame that was selected when the event was generated, but if that frame has
redirected input focus to another frame, the value is the frame to which the event was
redirected. See Section 30.10 [Input Focus], page 824.

last-event-frame

If the last event came from a keyboard macro, the value is macro.
Input events must come from somewhere; sometimes, that is a keyboard macro, asignal, or ‘unread-command-events’, but it is usually a physical input device connected to acomputer that is controlled by the user. Those devices are referred to as input devices, andEmacs associates each input event with the input device from which it originated. They are
identified by a name that is unique to each input device.
The ability to determine the precise input device used depends on the details of eachsystem. When that information is unavailable, Emacs reports keyboard events as originatingfrom the ‘"Virtual core keyboard"’, and other events as originating from the ‘"Virtual
core pointer"’. (These values are used on every platform because the X server reports
them when detailed device information is not known.)[Variable]
This variable records the name of the input device from which the last input event
read was generated. It is nil if no such device exists, i.e., the last input event wasread from unread-command-events, or it came from a keyboard macro.

last-event-device

When the X Input Extension is being used on X Windows, the device name is astring that is unique to each physical keyboard, pointing device and touchscreen
attached to the X server. Otherwise, it is either the string ‘"Virtual core pointer"’or ‘"Virtual core keyboard"’, depending on whether the event was generated by apointing device (such as a mouse) or a keyboard.

Chapter 22: Command Loop439

device-class frame name

[Function]
There are various different types of devices, which can be determined from their names.
This function can be used to determined the correct type of the device name for an
event originating from frame.

The return value is one of the following symbols (“device classes”):
core-keyboard
The core keyboard; this is means the device is a keyboard-like device, but
no other characteristics are unknown.
core-pointerThe core pointer; this means the device is a pointing device, but no othercharacteristics are known.
mouse

A computer mouse.

trackpoint
A trackpoint or joystick (or other similar control.)eraser

The other end of a stylus on a graphics tablet, or a standalone eraser.

pen

The pointed end of a pen on a graphics tablet, a stylus, or some othersimilar device.

puck

A device that looks like a computer mouse, but reports absolute coordinates relative to some other surface.

power-button
A power button or volume button (or other similar control.)keyboard

A computer keyboard.

touchscreen
A computer touchpad.
pad

A collection of sensitive buttons, rings, and strips commonly found arounda drawing tablet.

touchpadAn indirect touch device such as a touchpad.

piano

A musical instrument such as an electronic keyboard.

test

A device used by the XTEST extension to report input.

22.6 Adjusting Point After Commands
Emacs cannot display the cursor when point is in the middle of a sequence of text thathas the display or composition property, or is invisible. Therefore, after a commandfinishes and returns to the command loop, if point is within such a sequence, the command
loop normally moves point to the edge of the sequence, making this sequence effectively
intangible.
A command can inhibit this feature by setting the variable disable-point-adjustment:Chapter 22: Command Loop

440

[Variable]
If this variable is non-nil when a command returns to the command loop, then thecommand loop does not check for those text properties, and does not move point outof sequences that have them.
The command loop sets this variable to nil before each command, so if a commandsets it, the effect applies only to that command.

disable-point-adjustment[Variable]
If you set this variable to a non-nil value, the feature of moving point out of thesesequences is completely turned off.

global-disable-point-adjustment

22.7 Input EventsThe Emacs command loop reads a sequence of input events that represent keyboard or mouse
activity, or system events sent to Emacs. The events for keyboard activity are charactersor symbols; other events are always lists. This section describes the representation andmeaning of input events in detail.

eventp object[Function]

This function returns non-nil if object is an input event or event type.
Note that any non-nil symbol might be used as an event or an event type; eventp
cannot distinguish whether a symbol is intended by Lisp code to be used as an event.

22.7.1 Keyboard Events
There are two kinds of input you can get from the keyboard: ordinary keys, and function
keys. Ordinary keys correspond to (possibly modified) characters; the events they generate
are represented in Lisp as characters. The event type of a character event is the character
itself (an integer), which might have some modifier bits set; see Section 22.7.14 [Classifying
Events], page 455.
An input character event consists of a basic code between 0 and 524287, plus any or allof these modifier bits:
meta

The 227 bit in the character code indicates a character typed with the meta key
held down.

control

The 226 bit in the character code indicates a non-ASCII control character.
ascii control characters such as C-a have special basic codes of their own, so
Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1.
But if you type a control combination not in ASCII, such as % with the control
key, the numeric value you get is the code for % plus 226 (assuming the terminal
supports non-ASCII control characters), i.e. with the 27th bit set.

shift

The 225 bit (the 26th bit) in the character event code indicates an ASCII control
character typed with the shift key held down.
For letters, the basic code itself indicates upper versus lower case; for digits andpunctuation, the shift key selects an entirely different character with a different
basic code. In order to keep within the ASCII character set whenever possible,
Emacs avoids using the 225 bit for those character events.

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However, ASCII provides no way to distinguish C-A from C-a, so Emacs uses
the 225 bit in C-A and not in C-a.
hyper

The 224 bit in the character event code indicates a character typed with thehyper key held down.

super

The 223 bit in the character event code indicates a character typed with thesuper key held down.

alt

The 222 bit in the character event code indicates a character typed with the alt
key held down. (The key labeled Alt on most keyboards is actually treated as
the meta key, not this.)

It is best to avoid mentioning specific bit numbers in your program. To test the modifierbits of a character, use the function event-modifiers (see Section 22.7.14 [Classifying
Events], page 455). When making key bindings with keymap-set, you specify these eventsusing strings like ‘C-H-x’ instead (for “control hyper x”) (see Section 23.12 [Changing Key
Bindings], page 497).

22.7.2 Function Keys
Most keyboards also have function keys—keys that have names or symbols that are notcharacters. Function keys are represented in Emacs Lisp as symbols; the symbol’s name isthe function key’s label, in lower case. For example, pressing a key labeled F1 generates aninput event represented by the symbol f1.
The event type of a function key event is the event symbol itself. See Section 22.7.14[Classifying Events], page 455.
Here are a few special cases in the symbol-naming convention for function keys:
backspace, tab, newline, return, delete
These keys correspond to common ASCII control characters that have special
keys on most keyboards.
In ASCII, C-i and TAB are the same character. If the terminal can distinguishbetween them, Emacs conveys the distinction to Lisp programs by representing
the former as the integer 9, and the latter as the symbol tab.
Most of the time, it’s not useful to distinguish the two. So normally
local-function-key-map (see Section 23.15 [Translation Keymaps], page 504)
is set up to map tab into 9. Thus, a key binding for character code 9 (thecharacter C-i) also applies to tab. Likewise for the other symbols in this group.
The function read-char likewise converts these events into characters.
In ASCII, BS is really C-h. But backspace converts into the character code 127(DEL), not into code 8 (BS). This is what most users prefer.
left, up, right, down
Cursor arrow keys
kp-add, kp-decimal, kp-divide, . . .
Keypad keys (to the right of the regular keyboard).
kp-0, kp-1, . . .
Keypad keys with digits.

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kp-f1, kp-f2, kp-f3, kp-f4
Keypad PF keys.
kp-home, kp-left, kp-up, kp-right, kp-down
Keypad arrow keys. Emacs normally translates these into the corresponding
non-keypad keys home, left, . . .
kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-delete
Additional keypad duplicates of keys ordinarily found elsewhere. Emacs normallytranslates these into the like-named non-keypad keys.
You can use the modifier keys ALT, CTRL, HYPER, META, SHIFT, and SUPER with function
keys. The way to represent them is with prefixes in the symbol name:‘A-’

The alt modifier.

‘C-’

The control modifier.

‘H-’

The hyper modifier.

‘M-’

The meta modifier.

‘S-’

The shift modifier.

‘s-’

The super modifier.

Thus, the symbol for the key F3 with META held down is M-f3. When you use more than
one prefix, we recommend you write them in alphabetical order; but the order does notmatter in arguments to the key-binding lookup and modification functions.

22.7.3 Mouse Events
Emacs supports four kinds of mouse events: click events, drag events, button-down events,and motion events. All mouse events are represented as lists. The car of the list is the event
type; this says which mouse button was involved, and which modifier keys were used with
it. The event type can also distinguish double or triple button presses (see Section 22.7.7[Repeat Events], page 446). The rest of the list elements give position and time information.
For key lookup, only the event type matters: two events of the same type necessarily run
the same command. The command can access the full values of these events using the ‘e’interactive code. See Section 22.2.2 [Interactive Codes], page 427.
A key sequence that starts with a mouse event is read using the keymaps of the buffer
in the window that the mouse was in, not the current buffer. This does not imply thatclicking in a window selects that window or its buffer—that is entirely under the control of
the command binding of the key sequence.

22.7.4 Click Events
When the user presses a mouse button and releases it at the same location, that generates aclick event. Depending on how your window-system reports mouse-wheel events, turning
the mouse wheel can generate either a mouse click or a mouse-wheel event. All mouse event
share the same format:(event-type position click-count)
event-type This is a symbol that indicates which mouse button was used. It is one of thesymbols mouse-1, mouse-2, . . . , where the buttons are numbered left to right.
For mouse-wheel event, it can be wheel-up or wheel-down.

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You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’, ‘S-’ and ‘s-’ for modifiers alt,
control, hyper, meta, shift and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings describe
events by their types; thus, if there is a key binding for mouse-1, that binding
would apply to all events whose event-type is mouse-1.
position

This is a mouse position list specifying where the mouse event occurred; seebelow for details.

click-countThis is the number of rapid repeated presses so far of the same mouse button or
the number of repeated turns of the wheel. See Section 22.7.7 [Repeat Events],
page 446.
To access the contents of a mouse position list in the position slot of a mouse event,you should typically use the functions documented in Section 22.7.15 [Accessing Mouse],
page 456.
The explicit format of the list depends on where the event occurred. For clicks in the
text area, mode line, header line, tab line, or in the fringe or marginal areas, the mouseposition list has the form
(window pos-or-area (x . y) timestamp
object text-pos (col . row)
image (dx . dy) (width . height))
The meanings of these list elements are as follows:
window

The window in which the mouse event occurred.

pos-or-area
The buffer position of the character clicked on in the text area; or, if the event
was outside the text area, the window area where it occurred. It is one of thesymbols mode-line, header-line, tab-line, vertical-line, left-margin,
right-margin, left-fringe, or right-fringe.
In one special case, pos-or-area is a list containing a symbol (one of the symbols
listed above) instead of just the symbol. This happens after the imaginary prefixkeys for the event are registered by Emacs. See Section 22.8.1 [Key Sequence
Input], page 461.
x, y

The relative pixel coordinates of the event. For events in the text area of awindow, the coordinate origin (0 . 0) is taken to be the top left corner of thetext area. See Section 29.4 [Window Sizes], page 699. For events in a mode line,
header line or tab line, the coordinate origin is the top left corner of the window
itself. For fringes, margins, and the vertical border, x does not have meaningful
data. For fringes and margins, y is relative to the bottom edge of the headerline. In all cases, the x and y coordinates increase rightward and downward
respectively.

timestamp
The time at which the event occurred, as an integer number of milliseconds
since a system-dependent initial time.

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object444

Either nil, which means the event occurred on buffer text, or a cons cell of theform (string . string-pos) if there is a string from a text property or an overlay
at the event position.
string

The string which was clicked on, including any properties.

string-pos The position in the string where the click occurred.
text-pos

For clicks on a marginal area or on a fringe, this is the buffer position of thefirst visible character in the corresponding line in the window. For clicks on themode line, the header line or the tab line, this is nil. For other events, it is thebuffer position closest to the click.

col, row

These are the actual column and row coordinate numbers of the glyph under
the x, y position. If x lies beyond the last column of actual text on its line, colis reported by adding fictional extra columns that have the default character
width. Row 0 is taken to be the header line if the window has one, or Row 1 if
the window also has the tab line, or the topmost row of the text area otherwise.
Column 0 is taken to be the leftmost column of the text area for clicks on awindow text area, or the leftmost mode line or header line column for clicks
there. For clicks on fringes or vertical borders, these have no meaningful data.
For clicks on margins, col is measured from the left edge of the margin area androw is measured from the top of the margin area.

image

If there is an image at the click location, this is the image object as returned byfind-image (see Section 41.17.8 [Defining Images], page 1220); otherwise thisis nil.

dx, dyThese are the pixel offsets of the click relative to the top left corner of theobject’s glyph that is the nearest one to the click. The relevant objects can beeither a buffer, or a string, or an image, see above. If object is nil or a string,the coordinates are relative to the top left corner of the character glyph clickedon. Note that the offsets are always zero on text-mode frames, when object isnil, since each glyph there is considered to have exactly 1x1 pixel dimensions.

width, height
If the click is on a character, either from buffer text or from overlay or display
string, these are the pixel width and height of that character’s glyph; otherwise
they are dimensions of object clicked on.
For clicks on a scroll bar, position has this form:(window area (portion . whole) timestamp part)
window

The window whose scroll bar was clicked on.

area

This is the symbol vertical-scroll-bar.

portion

The number of pixels from the top of the scroll bar to the click position. On
some toolkits, including GTK+, Emacs cannot extract this data, so the value isalways 0.

whole

The total length, in pixels, of the scroll bar. On some toolkits, including GTK+,
Emacs cannot extract this data, so the value is always 0.

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timestamp
The time at which the event occurred, in milliseconds. On some toolkits,
including GTK+, Emacs cannot extract this data, so the value is always 0.
part

The part of the scroll bar on which the click occurred. It is one of the symbols
handle (the scroll bar handle), above-handle (the area above the handle),
below-handle (the area below the handle), up (the up arrow at one end of thescroll bar), or down (the down arrow at one end of the scroll bar).

For clicks on the frame’s internal border (see Section 30.3.1 [Frame Layout], page 791),
the frame’s tool bar (see Section 23.18.6 [Tool Bar], page 517) or tab bar, position has thisform:
(frame part (X . Y) timestamp)
frame

The frame whose internal border or tool bar or tab bar was clicked on.

part

The part of the frame which was clicked on. This can be one of the following:
tool-bar

The frame has a tool bar, and the event was in the tool-bar area.

tab-bar

The frame has a tab bar, and the event was in the tab-bar area.

left-edge
top-edge
right-edge
bottom-edge
The click was on the corresponding border at an offset of at least
one canonical character from the border’s nearest corner.
top-left-corner
top-right-corner
bottom-right-corner
bottom-left-corner
The click was on the corresponding corner of the internal border.
nil

The frame does not have an internal border, and the event was noton the tab bar or the tool bar. This usually happens on text-mode
frames. This can also happen on GUI frames with internal border if
the frame doesn’t have its drag-internal-border parameter (seeSection 30.4.3.7 [Mouse Dragging Parameters], page 813) set to a
non-nil value.

22.7.5 Drag Events
With Emacs, you can have a drag event without even changing your clothes. A dragevent happens every time the user presses a mouse button and then moves the mouse to adifferent character position before releasing the button. Like all mouse events, drag events
are represented in Lisp as lists. The lists record both the starting mouse position and thefinal position, like this:(event-type(window1 START-POSITION)(window2 END-POSITION))

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For a drag event, the name of the symbol event-type contains the prefix ‘drag-’. For
example, dragging the mouse with button 2 held down generates a drag-mouse-2 event.
The second and third elements of the event give the starting and ending position of thedrag, as mouse position lists (see Section 22.7.4 [Click Events], page 442). You can accessthe second element of any mouse event in the same way. However, the drag event may
end outside the boundaries of the frame that was initially selected. In that case, the third
element’s position list contains that frame in place of a window.
The ‘drag-’ prefix follows the modifier key prefixes such as ‘C-’ and ‘M-’.
If read-key-sequence receives a drag event that has no key binding, and the corresponding click event does have a binding, it changes the drag event into a click event at the drag’s
starting position. This means that you don’t have to distinguish between click and dragevents unless you want to.

22.7.6 Button-Down Events
Click and drag events happen when the user releases a mouse button. They cannot happen
earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down
events.2 These occur as soon as a button is pressed. They are represented by lists thatlook exactly like click events (see Section 22.7.4 [Click Events], page 442), except that theevent-type symbol name contains the prefix ‘down-’. The ‘down-’ prefix follows modifier key
prefixes such as ‘C-’ and ‘M-’.
The function read-key-sequence ignores any button-down events that don’t have command bindings; therefore, the Emacs command loop ignores them too. This means that you
need not worry about defining button-down events unless you want them to do something.
The usual reason to define a button-down event is so that you can track mouse motion (byreading motion events) until the button is released. See Section 22.7.8 [Motion Events],
page 447.

22.7.7 Repeat Events
If you press the same mouse button more than once in quick succession without moving themouse, Emacs generates special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click
event when you click a button twice; the event happens when you release the button (as isnormal for all click events).
The event type of a double-click event contains the prefix ‘double-’. Thus, a double
click on the second mouse button with meta held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the binding of the corresponding
ordinary click event is used to execute it. Thus, you need not pay attention to the double
click feature unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, andthen a double-click event. Therefore, you must design the command binding of the double
click event to assume that the single-click command has already run. It must produce thedesired results of a double click, starting from the results of a single click.
2

Button-down is the conservative antithesis of drag.

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This is convenient, if the meaning of a double click somehow builds on the meaning of asingle click—which is recommended user interface design practice for double clicks.
If you click a button, then press it down again and start moving the mouse with the
button held down, then you get a double-drag event when you ultimately release the button.
Its event type contains ‘double-drag’ instead of just ‘drag’. If a double-drag event has nobinding, Emacs looks for an alternate binding as if the event were an ordinary drag.
Before the double-click or double-drag event, Emacs generates a double-down event when
the user presses the button down for the second time. Its event type contains ‘double-down’
instead of just ‘down’. If a double-down event has no binding, Emacs looks for an alternate
binding as if the event were an ordinary button-down event. If it finds no binding that way
either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs
generates a down event and a click event for the first click, a double-down event when youpress the button again, and finally either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick succession, Emacs generates
a triple-down event, followed by either a triple-click or a triple-drag. The event types ofthese events contain ‘triple’ instead of ‘double’. If any triple event has no binding, Emacs
uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for thepresses beyond the third are all triple events. Emacs does not have separate event types
for quadruple, quintuple, etc. events. However, you can look at the event list to find out
precisely how many times the button was pressed.

event-click-count event[Function]
This function returns the number of consecutive button presses that led up to event.
If event is a double-down, double-click or double-drag event, the value is 2. If event isa triple event, the value is 3 or greater. If event is an ordinary mouse event (not arepeat event), the value is 1.

[User Option]
To generate repeat events, successive mouse button presses must be at approximately
the same screen position. The value of double-click-fuzz specifies the maximum
number of pixels the mouse may be moved (horizontally or vertically) between two
successive clicks to make a double-click.
This variable is also the threshold for motion of the mouse to count as a drag.

double-click-fuzz[User Option]
To generate repeat events, the number of milliseconds between successive buttonpresses must be less than the value of double-click-time. Setting double-clicktime to nil disables multi-click detection entirely. Setting it to t removes the time
limit; Emacs then detects multi-clicks by position only.

double-click-time

22.7.8 Motion Events
Emacs sometimes generates mouse motion events to describe motion of the mouse without
any button activity. Mouse motion events are represented by lists that look like this:(mouse-movement POSITION)

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position is a mouse position list (see Section 22.7.4 [Click Events], page 442), specifying thecurrent position of the mouse cursor. As with the end-position of a drag event, this position
list may represent a location outside the boundaries of the initially selected frame, in whichcase the list contains that frame in place of a window.
The track-mouse macro enables generation of motion events within its body. Outsideof track-mouse body, Emacs does not generate events for mere motion of the mouse, andthese events do not appear. See Section 30.15 [Mouse Tracking], page 835.
[Variable]
When non-nil, mouse motion events are generated even for very small movements.
Otherwise, motion events are not generated as long as the mouse cursor remains
pointing to the same glyph in the text.

mouse-fine-grained-tracking

22.7.9 Touchscreen Events
Some window systems provide support for input devices that react to the user’s touching
the screen and moving fingers while touching the screen. These input devices are known as
touchscreens, and Emacs reports the events they generate as touchscreen events.
Most individual events generated by a touchscreen only have meaning as part of a larger
sequence of other events: for instance, the simple operation of tapping the touchscreen
involves the user placing and raising a finger on the touchscreen, and swiping the display toscroll it involves placing a finger, moving it many times upwards or downwards, and thenraising the finger.
While a simplistic model consisting of one finger is adequate for taps and scrolling, more
complicated gestures require support for keeping track of multiple fingers, where the positionof each finger is represented by a touch point. For example, a “pinch to zoom” gesture might
consist of the user placing two fingers and moving them individually in opposite directions,where the distance between the positions of their individual points determine the amountby which to zoom the display, and the center of an imaginary line between those positions
determines where to pan the display after zooming.
The low-level touchscreen events described below can be used to implement all the touchsequences described above. In those events, each point is represented by a cons of anarbitrary number identifying the point and a mouse position list (see Section 22.7.4 [Click
Events], page 442) specifying the position of the finger when the event occurred.
(touchscreen-begin point)
This event is sent when point is created by the user pressing a finger against
the touchscreen.
(touchscreen-update points)
This event is sent when a point on the touchscreen has changed position. points
is a list of touch points containing the up-to-date positions of each touch point
currently on the touchscreen.
(touchscreen-end point)
This event is sent when point is no longer present on the display, because
another program took the grab, or because the user raised the finger from thetouchscreen.

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22.7.10 Focus Events
Window systems provide general ways for the user to control which window gets keyboard
input. This choice of window is called the focus. When the user does something to switch
between Emacs frames, that generates a focus event. The normal definition of a focus event,in the global keymap, is to select a new frame within Emacs, as the user would expect. See
Section 30.10 [Input Focus], page 824, which also describes hooks related to focus events.
Focus events are represented in Lisp as lists that look like this:(switch-frame new-frame)
where new-frame is the frame switched to.
Some X window managers are set up so that just moving the mouse into a window isenough to set the focus there. Usually, there is no need for a Lisp program to know about
the focus change until some other kind of input arrives. Emacs generates a focus event only
when the user actually types a keyboard key or presses a mouse button in the new frame;
just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs
never generates a focus event in the middle of a key sequence. If the user changes focus in
the middle of a key sequence—that is, after a prefix key—then Emacs reorders the eventsso that the focus event comes either before or after the multi-event key sequence, and notwithin it.

22.7.11 Xwidget events
Xwidgets (see Section 41.19 [Xwidgets], page 1228) can send events to update Lisp programson their status. These events are dubbed xwidget-events, and contain various data
describing the nature of the change.
(xwidget-event kind xwidget arg)
This event is sent whenever some kind of update occurs in xwidget. There areseveral types of updates, identified by their kind.
It is a special event (see Section 22.9 [Special Events], page 470), which should be
handled by adding a callback to an xwidget that is called whenever an xwidget
event for xwidget is received.
You can add a callback by setting the callback of an xwidget’s property list,
which should be a function that accepts xwidget and kind as arguments.
load-changed
This xwidget event indicates that the xwidget has reached a particular point of the page-loading process. When these events aresent, arg will contain a string that further describes the status of
the widget:‘load-started’
This means the widget has begun a page-loading operation.
‘load-finished’
This means the xwidget has finished processing whatever page-loading operation that it was previously performing.

Chapter 22: Command Loop450‘load-redirected’This means the xwidget has encountered and followed
a redirect during the page-loading operation.
‘load-committed’This means the xwidget has committed to a given URL
during the page-loading operation, i.e. the URL is the
final URL that will be rendered by xwidget during thecurrent page-loading operation.
download-callback
This event indicates that a download of some kind has been completed.
In the above events, there can be arguments after arg, which itself indicates
the URL from which the download file was retrieved: the first argument afterarg indicates the MIME type of the download, as a string, while the second
argument contains the full file name of the downloaded file.
download-started
This event indicates that a download has been started. In these
events, arg contains the URL of the file that is currently being
downloaded.
javascript-callback
This event contains JavaScript callback data. These events are usedinternally by xwidget-webkit-execute-script.
(xwidget-display-event xwidget source)This event is sent whenever an xwidget requests that another xwidget bedisplayed. xwidget is the xwidget that should be displayed, and source is thexwidget that asked to display xwidget.
It is also a special event which should be handled through callbacks. You can
add such a callback by setting the display-callback of source’s property list,
which should be a function that accepts xwidget and source as arguments.
xwidget’s buffer will be set to a temporary buffer. When displaying the widget,
care should be taken to replace the buffer with the buffer in which the xwidget
will be displayed, using set-xwidget-buffer (see Section 41.19 [Xwidgets],page 1228).

22.7.12 Miscellaneous System Events
A few other event types represent occurrences within the system.
(delete-frame (frame))
This kind of event indicates that the user gave the window manager a command
to delete a particular window, which happens to be an Emacs frame.
The standard definition of the delete-frame event is to delete frame.
(iconify-frame (frame))
This kind of event indicates that the user iconified frame using the window
manager. Its standard definition is ignore; since the frame has already been

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iconified, Emacs has no work to do. The purpose of this event type is so thatyou can keep track of such events if you want to.
(make-frame-visible (frame))
This kind of event indicates that the user deiconified frame using the window
manager. Its standard definition is ignore; since the frame has already been
made visible, Emacs has no work to do.
(touch-end (position))
This kind of event indicates that the user’s finger moved off the mouse wheel orthe touchpad. The position element is a mouse position list (see Section 22.7.4[Click Events], page 442), specifying the position of the mouse cursor when thefinger moved off the mouse wheel.
(wheel-up position clicks lines pixel-delta)(wheel-down position clicks lines pixel-delta)
These events are generated by moving a mouse wheel. The position element is amouse position list (see Section 22.7.4 [Click Events], page 442), specifying theposition of the mouse cursor when the event occurred.
clicks, if present, is the number of times that the wheel was moved in quick
succession. See Section 22.7.7 [Repeat Events], page 446. lines, if present andnot nil, is the positive number of screen lines that should be scrolled (either up,
when the event is wheel-up, or down when the event is wheel-down). pixel-delta,
if present, is a cons cell of the form (x . y), where x and y are the numbers of
pixels by which to scroll in each axis, a.k.a. pixelwise deltas. Usually, only oneof the two will be non-zero, the other will be either zero or very close to zero;
the larger number indicates the axis to scroll the window. When the variable
mwheel-coalesce-scroll-events is nil, the scroll commands ignore the lines
element, even if it’s non-nil, and use the pixel-delta data instead; in that case,the direction of scrolling is determined by the sign of the pixelwise deltas, andthe direction (up or down) implied by the event kind is ignored.
You can use these x and y pixelwise deltas to determine how much the mousewheel has actually moved at pixel resolution. For example, the pixelwise deltas
could be used to scroll the display at pixel resolution, exactly according to theuser’s turning the mouse wheel. This pixelwise scrolling is possible only whenmwheel-coalesce-scroll-events is nil, and in general the pixel-delta data
is not generated when that variable is non-nil.
The wheel-up and wheel-down events are generated only on some kinds ofsystems. On other systems, mouse-4 and mouse-5 are used instead. For portablecode, use the variables mouse-wheel-up-event, mouse-wheel-up-alternateevent, mouse-wheel-down-event and mouse-wheel-down-alternate-event
defined in mwheel.el to determine what event types to expect from the mousewheel.
Similarly, some mice can generate mouse-wheel-left-event and mouse-wheelright-event and can be used to scroll if mouse-wheel-tilt-scroll is non-nil.
However, some mice also generate other events at the same time as they’regenerating these scroll events which may get in the way. The way to fix this isChapter 22: Command Loop452

generally to unbind these events (for instance, mouse-6 or mouse-7, but this isvery hardware and operating system dependent).
(pinch position dx dy scale angle)
This kind of event is generated by the user performing a “pinch” gesture byplacing two fingers on a touchpad and moving them towards or away fromeach other. position is a mouse position list (see Section 22.7.4 [Click Events],
page 442) that provides the position of the mouse pointer when the event
occurred, dx is the change in the horizontal distance between the fingers since
the last event in the same sequence, dy is the vertical movement of the fingers
since the last event in the same sequence, scale is the ratio of the current distance
between the fingers to that distance at the start of the sequence, and angle isthe angular difference in degrees between the direction of the line connecting
the fingers in this event and the direction of that line in the last event of thesame sequence.
As pinch events are only sent at the beginning or during a pinch sequence, they
do not report gestures where the user moves two fingers on a touchpad in arotating fashion without pinching the fingers.
All arguments after position are floating point numbers.
This event is usually sent as part of a sequence, which begins with the user
placing two fingers on the touchpad, and ends with the user removing those
fingers. dx, dy, and angle will be 0.0 in the first event of a sequence; subsequent
events will report non-zero values for these members of the event structure.
dx and dy are reported in imaginary relative units, in which 1.0 is the widthand height of the touchpad respectively. They are usually interpreted as being
relative to the size of the object beneath the gesture: image, window, etc.
(preedit-text arg)
This event is sent when a system input method tells Emacs to display some text
to indicate to the user what will be inserted. The contents of arg are dependent
on the window system being used.
On X, arg is a string describing some text to place behind the cursor. It can benil, which means to remove any text previously displayed.
On PGTK frames (see Chapter 30 [Frames], page 785), arg is a list of strings
with information about their color and underline attributes. It has the following
form:((string1(ul . underline-color)(bg . background-color)(fg . foreground-color))(string2(ul . underline-color)(bg . background-color)(fg . foreground-color))...
)

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Color information can be omitted, leaving just the text of the strings. underlinecolor can be t, meaning underlined text with default underline color, or it canbe a string, the name of the color to draw the underline.
This is a special event (see Section 22.9 [Special Events], page 470), which
normally should not be bound by the user to any command. Emacs will
typically display the text contained in the event in an overlay behind point when
it is received.
(drag-n-drop position files)
This kind of event is generated when a group of files is selected in an application
outside of Emacs, and then dragged and dropped onto an Emacs frame.
The element position is a list describing the position of the event, in the sameformat as used in a mouse-click event (see Section 22.7.4 [Click Events], page 442),
and files is the list of file names that were dragged and dropped. The usual way
to handle this event is by visiting these files.
This kind of event is generated, at present, only on some kinds of systems.
help-echoThis kind of event is generated when a mouse pointer moves onto a portion of
buffer text which has a help-echo text property. The generated event has thisform:
(help-echo frame help window object pos)
The precise meaning of the event parameters and the way these parameters areused to display the help-echo text are described in [Text help-echo], page 926.
sigusr1
sigusr2

These events are generated when the Emacs process receives the signals SIGUSR1and SIGUSR2. They contain no additional data because signals do not carryadditional information. They can be useful for debugging (see Section 19.1.1[Error Debugging], page 333).
To catch a user signal, bind the corresponding event to an interactive command in
the special-event-map (see Section 23.9 [Controlling Active Maps], page 491).
The command is called with no arguments, and the specific signal event isavailable in last-input-event (see Section 22.8.6 [Event Input Misc], page 468.
For example:(defun sigusr-handler ()(interactive)(message "Caught signal %S" last-input-event))(keymap-set special-event-map "<sigusr1>" 'sigusr-handler)

To test the signal handler, you can make Emacs send a signal to itself:(signal-process (emacs-pid) 'sigusr1)

language-changeThis kind of event is generated on MS-Windows when the input language haschanged. This typically means that the keyboard keys will send to Emacs
characters from a different language. The generated event has this form:(language-change frame codepage language-id)

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Here frame is the frame which was current when the input language changed;
codepage is the new codepage number; and language-id is the numerical ID of
the new input language. The coding-system (see Section 34.10 [Coding Systems],
page 976) that corresponds to codepage is cpcodepage or windows-codepage.
To convert language-id to a string (e.g., to use it for various language-dependentfeatures, such as set-language-environment), use the w32-get-locale-info
function, like this:;; Get the abbreviated language name, such as "ENU" for English(w32-get-locale-info language-id);; Get the full English name of the language,;; such as "English (United States)"(w32-get-locale-info language-id 4097);; Get the full localized name of the language(w32-get-locale-info language-id t)

end-session
This event is generated on MS-Windows when the operating system informs
Emacs that the user terminated the interactive session, or that the system isshutting down. The standard definition of this event is to invoke the kill-emacs
command (see Section 42.2.1 [Killing Emacs], page 1262) so as to shut down
Emacs in an orderly fashion; if there are unsaved changes, this will produce
auto-save files (see Section 27.2 [Auto-Saving], page 664) that the user can use
after restarting the session to restore the unsaved edits.
If one of these events arrives in the middle of a key sequence—that is, after a prefix
key—then Emacs reorders the events so that this event comes either before or after themulti-event key sequence, not within it.
Some of these special events, such as delete-frame, invoke Emacs commands by default;
others are not bound. If you want to arrange for a special event to invoke a command, you
can do that via special-event-map. The command you bind to a function key in that map
can then examine the full event which invoked it in last-input-event. See Section 22.9
[Special Events], page 470.

22.7.13 Event Examples
If the user presses and releases the left mouse button over the same location, that generates
a sequence of events like this:(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))(mouse-1(#<window 18 on NEWS> 2613 (0 . 38) -864180))

While holding the control key down, the user might hold down the second mouse button,and drag the mouse from one line to the next. That produces two events, as shown here:(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)(#<window 18 on NEWS> 3510 (0 . 28) -729648))

While holding down the meta and shift keys, the user might press the second mousebutton on the window’s mode line, and then drag the mouse into another window. That
produces a pair of events like these:(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)

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-453816))

The frame with input focus might not take up the entire screen, and the user might movethe mouse outside the scope of the frame. Inside the track-mouse macro, that produces anevent like this:(mouse-movement (#<frame *ielm* 0x102849a30> nil (563 . 205) 532301936))

22.7.14 Classifying Events
Every event has an event type, which classifies the event for key binding purposes. For a
keyboard event, the event type equals the event value; thus, the event type for a character isthe character, and the event type for a function key symbol is the symbol itself. For events
that are lists, the event type is the symbol in the car of the list. Thus, the event type isalways a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they
always run the same command. That does not necessarily mean they do the same things,
however, as some commands look at the whole event to decide what to do. For example,
some commands use the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example, you might want to
ask whether an event involved the META key, regardless of which other key or mouse button
was used.
The functions event-modifiers and event-basic-type are provided to get such information conveniently.

event-modifiers event[Function]
This function returns a list of the modifiers that event has. The modifiers are symbols;
they include shift, control, meta, alt, hyper and super. In addition, the modifiers
list of a mouse event symbol always contains one of click, drag, and down. For double
or triple events, it also contains double or triple.
The argument event may be an entire event object, or just an event type. If event is asymbol that has never been used in an event that has been read as input in the current
Emacs session, then event-modifiers can return nil, even when event actually has
modifiers.
Here are some examples:(event-modifiers ?a)⇒ nil(event-modifiers ?A)⇒ (shift)(event-modifiers ?\C-a)⇒ (control)(event-modifiers ?\C-%)⇒ (control)(event-modifiers ?\C-\S-a)⇒ (control shift)(event-modifiers 'f5)
⇒ nil(event-modifiers 's-f5)

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⇒ (super)(event-modifiers 'M-S-f5)⇒ (meta shift)(event-modifiers 'mouse-1)⇒ (click)(event-modifiers 'down-mouse-1)⇒ (down)
The modifiers list for a click event explicitly contains click, but the event symbolname itself does not contain ‘click’. Similarly, the modifiers list for an ASCII control
character, such as ‘C-a’, contains control, even though reading such an event via
read-char will return the value 1 with the control modifier bit removed.

event-basic-type event[Function]
This function returns the key or mouse button that event describes, with all modifiers
removed. The event argument is as in event-modifiers. For example:(event-basic-type ?a)⇒ 97(event-basic-type ?A)⇒ 97(event-basic-type ?\C-a)⇒ 97(event-basic-type ?\C-\S-a)⇒ 97(event-basic-type 'f5)
⇒ f5(event-basic-type 's-f5)⇒ f5(event-basic-type 'M-S-f5)⇒ f5(event-basic-type 'down-mouse-1)⇒ mouse-1

mouse-movement-p object[Function]
This function returns non-nil if object is a mouse movement event. See Section 22.7.8[Motion Events], page 447.

22.7.15 Accessing Mouse Events
This section describes convenient functions for accessing the data in a mouse button or
motion event. Keyboard event data can be accessed using the same functions, but data
elements that aren’t applicable to keyboard events are zero or nil.
The following two functions return a mouse position list (see Section 22.7.4 [Click Events],
page 442), specifying the position of a mouse event.

event-start event[Function]
This returns the starting position of event.
If event is a click or button-down event, this returns the location of the event. If event
is a drag event, this returns the drag’s starting position.

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event-end event

457[Function]

This returns the ending position of event.
If event is a drag event, this returns the position where the user released the mousebutton. If event is a click or button-down event, the value is actually the starting
position, which is the only position such events have.

posnp object[Function]
This function returns non-nil if object is a mouse position list, in the format documented in Section 22.7.4 [Click Events], page 442); and nil otherwise.

These functions take a mouse position list as argument, and return various parts of it:

posn-window position[Function]
Return the window that position is in. If position represents a location outside theframe where the event was initiated, return that frame instead.

posn-area position[Function]
Return the window area recorded in position. It returns nil when the event occurredin the text area of the window; otherwise, it is a symbol identifying the area in which
the event occurred.

posn-point position[Function]
Return the buffer position in position. When the event occurred in the text area of
the window, in a marginal area, or on a fringe, this is an integer specifying a buffer
position. Otherwise, the value is undefined.

posn-x-y position[Function]
Return the pixel-based x and y coordinates in position, as a cons cell (x . y). These
coordinates are relative to the window given by posn-window.

This example shows how to convert the window-relative coordinates in the text areaof a window into frame-relative coordinates:(defun frame-relative-coordinates (position)"Return frame-relative coordinates from POSITION.
POSITION is assumed to lie in a window text area."(let* ((x-y (posn-x-y position))(window (posn-window position))(edges (window-inside-pixel-edges window)))(cons (+ (car x-y) (car edges))(+ (cdr x-y) (cadr edges)))))

posn-col-row position &optional use-window[Function]
This function returns a cons cell (col . row), containing the estimated column androw corresponding to buffer position described by position. The return value is given
in units of the frame’s default character width and default line height (including
spacing), as computed from the x and y values corresponding to position. (So, if theactual characters have non-default sizes, the actual row and column may differ fromthese computed values.) If the optional window argument is non-nil, use the default
character width in the window indicated by position instead of the frame. (This makes

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a difference if that window is showing a buffer with a non-default zooming level, forinstance.)
Note that row is counted from the top of the text area. If the window given by position
possesses a header line (see Section 24.4.7 [Header Lines], page 559) or a tab line, they
are not included in the row count.

posn-actual-col-row position[Function]
Return the actual row and column in position, as a cons cell (col . row). The
values are the actual row and column numbers in the window given by position. See
Section 22.7.4 [Click Events], page 442, for details. The function returns nil if position
does not include actual position values; in that case posn-col-row can be used to getapproximate values.
Note that this function doesn’t account for the visual width of characters on display,
like the number of visual columns taken by a tab character or an image. If you need
the coordinates in canonical character units, use posn-col-row instead.

posn-string position[Function]
Return the string object described by position, either nil (which means position
describes buffer text), or a cons cell (string . string-pos).

posn-image position[Function]
Return the image object in position, either nil (if there’s no image at position), or animage spec (image ...).

posn-object position[Function]
Return the image or string object described by position, either nil (whichmeans position describes buffer text), an image (image ...), or a cons cell(string . string-pos).

posn-object-x-y position[Function]
Return the pixel-based x and y coordinates relative to the upper left corner of theobject described by position, as a cons cell (dx . dy). If the position describes buffer
text, return the relative coordinates of the buffer-text character closest to that position.

posn-object-width-height position[Function]
Return the pixel width and height of the object described by position, as a cons cell
(width . height). If the position describes a buffer position, return the size of thecharacter at that position.

posn-timestamp position[Function]
Return the timestamp in position. This is the time at which the event occurred, inmilliseconds. Such a timestamp is reported relative to an arbitrary starting time thatvaries according to the window system in use. On the X Window System, for example,
it is the number of milliseconds since the X server was started.

These functions compute a position list given particular buffer position or screen position.
You can access the data in this position list with the functions described above.

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posn-at-point &optional pos window[Function]
This function returns a position list for position pos in window. pos defaults to point
in window; window defaults to the selected window.
posn-at-point returns nil if pos is not visible in window.

posn-at-x-y x y &optional frame-or-window whole[Function]
This function returns position information corresponding to pixel coordinates x andy in a specified frame or window, frame-or-window, which defaults to the selected
window. The coordinates x and y are relative to the text area of the selected window.
If whole is non-nil, the x coordinate is relative to the entire window area including
scroll bars, margins and fringes.

22.7.16 Accessing Scroll Bar Events
These functions are useful for decoding scroll bar events.

scroll-bar-event-ratio event[Function]
This function returns the fractional vertical position of a scroll bar event within thescroll bar. The value is a cons cell (portion . whole) containing two integers whose
ratio is the fractional position.

scroll-bar-scale ratio total[Function]
This function multiplies (in effect) ratio by total, rounding the result to an integer.
The argument ratio is not a number, but rather a pair (num . denom)—typically avalue returned by scroll-bar-event-ratio.
This function is handy for scaling a position on a scroll bar into a buffer position.
Here’s how to do that:(+ (point-min)(scroll-bar-scale(posn-x-y (event-start event))(- (point-max) (point-min))))Recall that scroll bar events have two integers forming a ratio, in place of a pair of x
and y coordinates.

22.7.17 Putting Keyboard Events in Strings
In most of the places where strings are used, we conceptualize the string as containing text
characters—the same kind of characters found in buffers or files. Occasionally Lisp programs
use strings that conceptually contain keyboard characters; for example, they may be key
sequences or keyboard macro definitions. However, storing keyboard characters in a string
is a complex matter, for reasons of historical compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities by not storing
keyboard events in strings containing control characters or the like, but instead store themin the common Emacs format as understood by key-valid-p.
If you read a key sequence with read-key-sequence-vector (or read-key-sequence),or access a key sequence with this-command-keys-vector (or this-command-keys), you
can transform this to the recommended format by using key-description.

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The complexities stem from the modifier bits that keyboard input characters can include.
Aside from the Meta modifier, none of these modifier bits can be included in a string, andthe Meta modifier is allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes in the range of
128 to 255. At that time, the basic character codes ranged from 0 to 127, so all keyboard
character codes did fit in a string. Many Lisp programs used ‘\M-’ in string constants tostand for meta characters, especially in arguments to define-key and similar functions, andkey sequences and sequences of events were always represented as strings.
When we added support for larger basic character codes beyond 127, and additional
modifier bits, we had to change the representation of meta characters. Now the flag that
represents the Meta modifier in a character is 227 and such numbers cannot be included in astring.
To support programs with ‘\M-’ in string constants, there are special rules for including
certain meta characters in a string. Here are the rules for interpreting a string as a sequenceof input characters:• If the keyboard character value is in the range of 0 to 127, it can go in the stringunchanged.
• The meta variants of those characters, with codes in the range of 227 to 227 + 127, canalso go in the string, but you must change their numeric values. You must set the 27 bit
instead of the 227 bit, resulting in a value between 128 and 255. Only a unibyte string
can include these codes.
• Non-ASCII characters above 256 can be included in a multibyte string.
• Other keyboard character events cannot fit in a string. This includes keyboard eventsin the range of 128 to 255.
Functions such as read-key-sequence that construct strings of keyboard input characters
follow these rules: they construct vectors instead of strings, when the events won’t fit in astring.
When you use the read syntax ‘\M-’ in a string, it produces a code in the range of 128 to
255—the same code that you get if you modify the corresponding keyboard event to put itin the string. Thus, meta events in strings work consistently regardless of how they get into
the strings.
However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section.

22.8 Reading Input
The editor command loop reads key sequences using the function read-key-sequence, whichuses read-event. These and other functions for event input are also available for use in
Lisp programs. See also momentary-string-display in Section 41.8 [Temporary Displays],
page 1146, and sit-for in Section 22.10 [Waiting], page 470. See Section 42.13 [Terminal
Input], page 1285, for functions and variables for controlling terminal input modes anddebugging terminal input.
For higher-level input facilities, see Chapter 21 [Minibuffers], page 385.

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22.8.1 Key Sequence Input
The command loop reads input a key sequence at a time, by calling read-key-sequence.
Lisp programs can also call this function; for example, describe-key uses it to read the
key to describe.

read-key-sequence prompt &optional continue-echo
dont-downcase-last switch-frame-ok command-loop[Function]

This function reads a key sequence and returns it as a string or vector. It keeps reading
events until it has accumulated a complete key sequence; that is, enough to specify
a non-prefix command using the currently active keymaps. (Remember that a key
sequence that starts with a mouse event is read using the keymaps of the buffer in thewindow that the mouse was in, not the current buffer.)If the events are all characters and all can fit in a string, then read-key-sequence
returns a string (see Section 22.7.17 [Strings of Events], page 459). Otherwise, it
returns a vector, since a vector can hold all kinds of events—characters, symbols, andlists. The elements of the string or vector are the events in the key sequence.
Reading a key sequence includes translating the events in various ways. See
Section 23.15 [Translation Keymaps], page 504.
The argument prompt is either a string to be displayed in the echo area as a prompt,
or nil, meaning not to display a prompt. The argument continue-echo, if non-nil,means to echo this key as a continuation of the previous key.
Normally any upper case event is converted to lower case if the original event isundefined and the lower case equivalent is defined. The argument dont-downcase-last,
if non-nil, means do not convert the last event to lower case. This is appropriate forreading a key sequence to be defined.
The argument switch-frame-ok, if non-nil, means that this function should process aswitch-frame event if the user switches frames before typing anything. If the user
switches frames in the middle of a key sequence, or at the start of the sequence but
switch-frame-ok is nil, then the event will be put off until after the current key
sequence.
The argument command-loop, if non-nil, means that this key sequence is being readby something that will read commands one after another. It should be nil if the caller
will read just one key sequence.
In the following example, Emacs displays the prompt ‘?’ in the echo area, and thenthe user types C-x C-f.
(read-key-sequence "?")---------- Echo Area ---------?C-x C-f---------- Echo Area ---------⇒ "^X^F"
The function read-key-sequence suppresses quitting: C-g typed while reading withthis function works like any other character, and does not set quit-flag. See
Section 22.11 [Quitting], page 471.

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read-key-sequence-vector prompt &optional continue-echo
dont-downcase-last switch-frame-ok command-loop

462[Function]

This is like read-key-sequence except that it always returns the key sequence as avector, never as a string. See Section 22.7.17 [Strings of Events], page 459.
If an input character is upper-case (or has the shift modifier) and has no key binding, but
its lower-case equivalent has one, then read-key-sequence converts the character to lower
case. (This behavior can be disabled by setting the translate-upper-case-key-bindings
user option to nil.) Note that lookup-key does not perform case conversion in this way.
When reading input results in such a shift-translation, Emacs sets the variable
this-command-keys-shift-translated to a non-nil value. Lisp programs can examine
this variable if they need to modify their behavior when invoked by shift-translated keys.
For example, the function handle-shift-selection examines the value of this variable todetermine how to activate or deactivate the region (see Section 32.7 [The Mark], page 873).
The function read-key-sequence also transforms some mouse events. It converts unbound drag events into click events, and discards unbound button-down events entirely. It
also reshuffles focus events and miscellaneous window events so that they never appear in a
key sequence with any other events.
When mouse events occur in special parts of a window or frame, such as a mode line or ascroll bar, the event type shows nothing special—it is the same symbol that would normallyrepresent that combination of mouse button and modifier keys. The information about thewindow part is kept elsewhere in the event—in the coordinates. But read-key-sequencetranslates this information into imaginary prefix keys, all of which are symbols: tab-line,
header-line, horizontal-scroll-bar, menu-bar, tab-bar, mode-line, vertical-line,
vertical-scroll-bar, left-margin, right-margin, left-fringe, right-fringe,
right-divider, and bottom-divider. You can define meanings for mouse clicks in special
window parts by defining key sequences using these imaginary prefix keys.
For example, if you call read-key-sequence and then click the mouse on the window’s
mode line, you get two events, like this:(read-key-sequence "Click on the mode line: ")⇒ [mode-line(mouse-1(#<window 6 on NEWS> mode-line(40 . 63) 5959987))][Variable]
This variable’s value is the number of key sequences processed so far in this Emacs
session. This includes key sequences read from the terminal and key sequences readfrom keyboard macros being executed.

num-input-keys

22.8.2 Reading One Event
The lowest level functions for command input are read-event, read-char, and read-charexclusive.
If you need a function to read a character using the minibuffer, use read-char-fromminibuffer (see Section 21.8 [Multiple Queries], page 414).

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read-event &optional prompt inherit-input-method seconds[Function]
This function reads and returns the next event of command input, waiting if necessary
until an event is available.
The returned event may come directly from the user, or from a keyboard macro. It is
not decoded by the keyboard’s input coding system (see Section 34.10.8 [Terminal
I/O Encoding], page 990).
If the optional argument prompt is non-nil, it should be a string to display in theecho area as a prompt. If prompt is nil or the string ‘""’, read-event does not
display any message to indicate it is waiting for input; instead, it prompts by echoing:
it displays descriptions of the events that led to or were read by the current command.
See Section 41.4 [The Echo Area], page 1131.
If inherit-input-method is non-nil, then the current input method (if any) is employed
to make it possible to enter a non-ASCII character. Otherwise, input method handlingis disabled for reading this event.
If cursor-in-echo-area is non-nil, then read-event moves the cursor temporarily
to the echo area, to the end of any message displayed there. Otherwise read-event
does not move the cursor.
If seconds is non-nil, it should be a number specifying the maximum time to wait
for input, in seconds. If no input arrives within that time, read-event stops waiting
and returns nil. A floating point seconds means to wait for a fractional number of
seconds. Some systems support only a whole number of seconds; on these systems,
seconds is rounded down. If seconds is nil, read-event waits as long as necessary
for input to arrive.
If seconds is nil, Emacs is considered idle while waiting for user input to arrive. Idle
timers—those created with run-with-idle-timer (see Section 42.12 [Idle Timers],
page 1284)—can run during this period. However, if seconds is non-nil, the stateof idleness remains unchanged. If Emacs is non-idle when read-event is called, it
remains non-idle throughout the operation of read-event; if Emacs is idle (which canhappen if the call happens inside an idle timer), it remains idle.
If read-event gets an event that is defined as a help character, then in some cases
read-event processes the event directly without returning. See Section 25.6 [HelpFunctions], page 602. Certain other events, called special events, are also processed
directly within read-event (see Section 22.9 [Special Events], page 470).
Here is what happens if you call read-event and then press the right-arrow function
key:(read-event)⇒ right

read-char &optional prompt inherit-input-method seconds[Function]
This function reads and returns a character input event. If the user generates an event
which is not a character (i.e., a mouse click or function key event), read-char signals
an error. The arguments work as in read-event.
If the event has modifiers, Emacs attempts to resolve them and return the code of
the corresponding character. For example, if the user types C-a, the function returns
1, which is the ASCII code of the ‘C-a’ character. If some of the modifiers cannotChapter 22: Command Loop464

be reflected in the character code, read-char leaves the unresolved modifier bits set
in the returned event. For example, if the user types C-M-a, the function returns
134217729, 8000001 in hex, i.e. ‘C-a’ with the Meta modifier bit set. This value is nota valid character code: it fails the characterp test (see Section 34.5 [Character Codes],page 967). Use event-basic-type (see Section 22.7.14 [Classifying Events], page 455)
to recover the character code with the modifier bits removed; use event-modifiers
to test for modifiers in the character event returned by read-char.
In the first example below, the user types the character 1 (ASCII code 49). The second
example shows a keyboard macro definition that calls read-char from the minibufferusing eval-expression. read-char reads the keyboard macro’s very next character,which is 1. Then eval-expression displays its return value in the echo area.
(read-char)⇒ 49;; We assume here you use M-: to evaluate this.
(symbol-function 'foo)⇒ "^[:(read-char)^M1"(execute-kbd-macro 'foo)
a 49
⇒ nil

read-char-exclusive &optional prompt inherit-input-method
seconds[Function]

This function reads and returns a character input event. If the user generates an event
which is not a character event, read-char-exclusive ignores it and reads anotherevent, until it gets a character. The arguments work as in read-event. The returned
value may include modifier bits, as with read-char.
None of the above functions suppress quitting.
[Variable]
This variable holds the total number of input events received so far from the terminal—
not counting those generated by keyboard macros.

num-nonmacro-input-events

We emphasize that, unlike read-key-sequence, the functions read-event, read-char,and read-char-exclusive do not perform the translations described in Section 23.15[Translation Keymaps], page 504. If you wish to read a single key taking these translations
into account (for example, to read Section 22.7.2 [Function Keys], page 441, in a terminal
or Section 22.7.3 [Mouse Events], page 442, from xterm-mouse-mode), use the function
read-key:read-key &optional prompt disable-fallbacks[Function]
This function reads a single key. It is intermediate between read-key-sequence andread-event. Unlike the former, it reads a single key, not a key sequence. Unlike
the latter, it does not return a raw event, but decodes and translates the user input
according to input-decode-map, local-function-key-map, and key-translationmap (see Section 23.15 [Translation Keymaps], page 504).

Chapter 22: Command Loop465

The argument prompt is either a string to be displayed in the echo area as a prompt,
or nil, meaning not to display a prompt.
If argument disable-fallbacks is non-nil then the usual fallback logic for unboundkeys in read-key-sequence is not applied. This means that mouse button-down
and multi-click events will not be discarded and local-function-key-map andkey-translation-map will not get applied. If nil or unspecified, the only fallback
disabled is downcasing of the last event.

read-char-choice prompt chars &optional inhibit-quit[Function]
This function uses read-from-minibuffer to read and return a single character thatis a member of chars, which should be a list of single characters. It discards any input
characters that are not members of chars, and shows a message to that effect.
The optional argument inhibit-quit is by default ignored, but if the variable read-charchoice-use-read-key is non-nil, this function uses read-key instead of read-fromminibuffer, and in that case inhibit-quit non-nil means ignore keyboard-quit events
while waiting for valid input. In addition, if read-char-choice-use-read-key is
non-nil, binding help-form (see Section 25.6 [Help Functions], page 602) to a non-nil
value while calling this function causes it to evaluate help-form and display the result
when the user presses help-char; it then continues to wait for a valid input character,or for keyboard-quit.

read-multiple-choice prompt choices &optional help-string
show-help long-form[Function]

Ask user a multiple choice question. prompt should be a string that will be displayed
as the prompt.
choices is an alist where the first element in each entry is a character to be entered,
the second element is a short name for the entry to be displayed while prompting(if there’s room, it might be shortened), and the third, optional entry is a longer
explanation that will be displayed in a help buffer if the user requests more help.
If optional argument help-string is non-nil, it should be a string with a more detailed
description of all choices. It will be displayed in a help buffer instead of the default
auto-generated description when the user types ?.
If optional argument show-help is non-nil, the help buffer will be displayed immediately,
before any user input. If it is a string, use it as the name of the help buffer.
If optional argument long-form is non-nil, the user will have to type in long-form
answers (using completing-read) instead of hitting a single key. The answers mustbe among the second elements of the values in the choices list.
The return value is the matching value from choices.
(read-multiple-choice"Continue connecting?"'((?a "always" "Accept certificate for this and future sessions.")(?s "session only" "Accept certificate this session only.")(?n "no" "Refuse to use certificate, close connection.")))The read-multiple-choice-face face is used to highlight the matching charactersin the name string on graphical terminals.

Chapter 22: Command Loop466

22.8.3 Modifying and Translating Input Events
Emacs modifies every event it reads according to extra-keyboard-modifiers, thentranslates it through keyboard-translate-table (if applicable), before returning it fromread-event.
[Variable]
This variable lets Lisp programs “press” the modifier keys on the keyboard. The
value is a character. Only the modifiers of the character matter. Each time the user
types a keyboard key, it is altered as if those modifier keys were held down. For
instance, if you bind extra-keyboard-modifiers to ?\C-\M-a, then all keyboard
input characters typed during the scope of the binding will have the control and meta
modifiers applied to them. The character ?\C-@, equivalent to the integer 0, does notcount as a control character for this purpose, but as a character with no modifiers.
Thus, setting extra-keyboard-modifiers to zero cancels any modification.

extra-keyboard-modifiers

When using a window system, the program can press any of the modifier keys in thisway. Otherwise, only the CTL and META keys can be virtually pressed.
Note that this variable applies only to events that really come from the keyboard, andhas no effect on mouse events or any other events.
[Variable]
This terminal-local variable is the translate table for keyboard characters. It lets you
reshuffle the keys on the keyboard without changing any command bindings. Its value
is normally a char-table, or else nil. (It can also be a string or vector, but this isconsidered obsolete.)keyboard-translate-tableIf keyboard-translate-table is a char-table (see Section 6.6 [Char-Tables], page 119),then each character read from the keyboard is looked up in this char-table. If thevalue found there is non-nil, then it is used instead of the actual input character.
Note that this translation is the first thing that happens to a character after it is readfrom the terminal. Record-keeping features such as recent-keys and dribble files
record the characters after translation.
Note also that this translation is done before the characters are supplied to input
methods (see Section 34.11 [Input Methods], page 990). Use translation-tablefor-input (see Section 34.9 [Translation of Characters], page 975), if you want totranslate characters after input methods operate.

key-translate from to[Function]
This function modifies keyboard-translate-table to translate character code from
into character code to. It creates the keyboard translate table if necessary.

Here’s an example of using the keyboard-translate-table to make C-x, C-c and C-v
perform the cut, copy and paste operations:(key-translate "C-x" "<control-x>")(key-translate "C-c" "<control-c>")(key-translate "C-v" "<control-v>")(keymap-global-set "<control-x>" 'kill-region)(keymap-global-set "<control-c>" 'kill-ring-save)Chapter 22: Command Loop467

(keymap-global-set "<control-v>" 'yank)On a graphical terminal that supports extended ASCII input, you can still get the standard
Emacs meanings of one of those characters by typing it with the shift key. That makes it adifferent character as far as keyboard translation is concerned, but it has the same usual
meaning.
See Section 23.15 [Translation Keymaps], page 504, for mechanisms that translate event
sequences at the level of read-key-sequence. If you need to translate input events that are
not characters (i.e., characterp returns nil for them), you must use the event translation
mechanism described there.

22.8.4 Invoking the Input Method
The event-reading functions invoke the current input method, if any (see Section 34.11[Input Methods], page 990). If the value of input-method-function is non-nil, it should
be a function; when read-event reads a printing character (including SPC) with no modifier
bits, it calls that function, passing the character as an argument.

input-method-function[Variable]

If this is non-nil, its value specifies the current input method function.
Warning: don’t bind this variable with let. It is often buffer-local, and if you bind it
around reading input (which is exactly when you would bind it), switching buffers
asynchronously while Emacs is waiting will cause the value to be restored in the wrong
buffer.
The input method function should return a list of events which should be used as input.
(If the list is nil, that means there is no input, so read-event waits for another event.)
These events are processed before the events in unread-command-events (see Section 22.8.6[Event Input Misc], page 468). Events returned by the input method function are not passed
to the input method function again, even if they are printing characters with no modifier
bits.
If the input method function calls read-event or read-key-sequence, it should bind
input-method-function to nil first, to prevent recursion.
The input method function is not called when reading the second and subsequent
events of a key sequence. Thus, these characters are not subject to input method processing. The input method function should test the values of overriding-local-map andoverriding-terminal-local-map; if either of these variables is non-nil, the input methodshould put its argument into a list and return that list with no further processing.

22.8.5 Quoted Character Input
You can use the function read-quoted-char to ask the user to specify a character, andallow the user to specify a control or meta character conveniently, either literally or as anoctal character code. The command quoted-insert uses this function.

read-quoted-char &optional prompt[Function]
This function is like read-char, except that if the first character read is an octal
digit (0–7), it reads any number of octal digits (but stopping if a non-octal digit isfound), and returns the character represented by that numeric character code. If theChapter 22: Command Loop

468

character that terminates the sequence of octal digits is RET, it is discarded. Anyother terminating character is used as input after this function returns.
Quitting is suppressed when the first character is read, so that the user can enter a
C-g. See Section 22.11 [Quitting], page 471.
If prompt is supplied, it specifies a string for prompting the user. The prompt stringis always displayed in the echo area, followed by a single ‘-’.
In the following example, the user types in the octal number 177 (which is 127 indecimal).
(read-quoted-char "What character")---------- Echo Area ---------What character 1 7 7---------- Echo Area ---------⇒ 127

22.8.6 Miscellaneous Event Input Features
This section describes how to peek ahead at events without using them up, how to check forpending input, and how to discard pending input. See also the function read-passwd (seeSection 21.9 [Reading a Password], page 417).
[Variable]
This variable holds a list of events waiting to be read as command input. The eventsare used in the order they appear in the list, and removed one by one as they are used.

unread-command-events

The variable is needed because in some cases a function reads an event and thendecides not to use it. Storing the event in this variable causes it to be processed
normally, by the command loop or by the functions to read command input.
For example, the function that implements numeric prefix arguments reads any numberof digits. When it finds a non-digit event, it must unread the event so that it can beread normally by the command loop. Likewise, incremental search uses this feature to
unread events with no special meaning in a search, because these events should exit
the search and then execute normally.
The reliable and easy way to extract events from a key sequence so as to put them in
unread-command-events is to use listify-key-sequence (see below).
Normally you add events to the front of this list, so that the events most recently
unread will be reread first.
Events read from this list are not normally added to the current command’s key
sequence (as returned by, e.g., this-command-keys), as the events will already havebeen added once as they were read for the first time. An element of the form(t . event) forces event to be added to the current command’s key sequence.
Elements read from this list are normally recorded by the record-keeping features (seeSection 42.13.2 [Recording Input], page 1286) and while defining a keyboard macro(see Section 22.16 [Keyboard Macros], page 478). However, an element of the form
(no-record . event) causes event to be processed normally without recording it.

Chapter 22: Command Loop469

listify-key-sequence key[Function]
This function converts the string or vector key to a list of individual events, which
you can put in unread-command-events.

input-pending-p &optional check-timers[Function]
This function determines whether any command input is currently available to beread. It returns immediately, with value t if there is available input, nil otherwise.
On rare occasions it may return t when no input is available.
If the optional argument check-timers is non-nil, then if no input is available, Emacs
runs any timers which are ready. See Section 42.11 [Timers], page 1281.
[Variable]
This variable records the last terminal input event read, whether as part of a commandor explicitly by a Lisp program.
In the example below, the Lisp program reads the character 1, ASCII code 49. It
becomes the value of last-input-event, while C-e (we assume C-x C-e command isused to evaluate this expression) remains the value of last-command-event.
(progn (print (read-char))(print last-command-event)last-input-event)
a 49
a 5
⇒ 49

last-input-event

while-no-input body. . .

[Macro]This construct runs the body forms and returns the value of the last one—but only
if no input arrives. If any input arrives during the execution of the body forms, it
aborts them (working much like a quit). The while-no-input form returns nil if
aborted by a real quit, and returns t if aborted by arrival of other input.
If a part of body binds inhibit-quit to non-nil, arrival of input during those parts
won’t cause an abort until the end of that part.
If you want to be able to distinguish all possible values computed by body from bothkinds of abort conditions, write the code like this:(while-no-input(list(progn . body)))[Variable]
This variable allow setting which special events while-no-input should ignore. It isa list of event symbols (see Section 22.7.13 [Event Examples], page 454).

while-no-input-ignore-events[Function]
This function discards the contents of the terminal input buffer and cancels any
keyboard macro that might be in the process of definition. It returns nil.
In the following example, the user may type a number of characters right after starting
the evaluation of the form. After the sleep-for finishes sleeping, discard-input
discards any characters typed during the sleep.
(progn (sleep-for 2)

discard-inputChapter 22: Command Loop470

(discard-input))⇒ nil

22.9 Special Events
Certain special events are handled at a very low level—as soon as they are read. The
read-event function processes these events itself, and never returns them. Instead, it keeps
waiting for the first event that is not special and returns that one.
Special events do not echo, they are never grouped into key sequences, and they neverappear in the value of last-command-event or (this-command-keys). They do not discard
a numeric argument, they cannot be unread with unread-command-events, they may notappear in a keyboard macro, and they are not recorded in a keyboard macro while you are
defining one.
Special events do, however, appear in last-input-event immediately after they are
read, and this is the way for the event’s definition to find the actual event.
The events types iconify-frame, make-frame-visible, delete-frame, drag-n-drop,
language-change, and user signals like sigusr1 are normally handled in this way. The
keymap which defines how to handle special events—and which events are special—is in thevariable special-event-map (see Section 23.9 [Controlling Active Maps], page 491).

22.10 Waiting for Elapsed Time or Input
The wait functions are designed to wait for a certain amount of time to pass or until there is
input. For example, you may wish to pause in the middle of a computation to allow the user
time to view the display. sit-for pauses and updates the screen, and returns immediately
if input comes in, while sleep-for pauses without updating the screen.

sit-for seconds &optional nodisp[Function]
This function performs redisplay (provided there is no pending input from the user),then waits seconds seconds, or until input is available. The usual purpose of sit-for
is to give the user time to read text that you display. The value is t if sit-for waited
the full time with no input arriving (see Section 22.8.6 [Event Input Misc], page 468).
Otherwise, the value is nil.
The argument seconds need not be an integer. If it is floating point, sit-for waits
for a fractional number of seconds. Some systems support only a whole number of
seconds; on these systems, seconds is rounded down.
The expression (sit-for 0) is equivalent to (redisplay), i.e., it requests a redisplay,without any delay, if there is no pending input. See Section 41.2 [Forcing Redisplay],
page 1129.
If nodisp is non-nil, then sit-for does not redisplay, but it still returns as soon as
input is available (or when the timeout elapses).
In batch mode (see Section 42.17 [Batch Mode], page 1289), sit-for cannot beinterrupted, even by input from the standard input descriptor. It is thus equivalent tosleep-for, which is described below.
It is also possible to call sit-for with three arguments, as (sit-for seconds millisec nodisp), but that is considered obsolete.

Chapter 22: Command Loop471

sleep-for seconds &optional millisec[Function]
This function simply pauses for seconds seconds without updating the display. It pays
no attention to available input. It returns nil.
The argument seconds need not be an integer. If it is floating point, sleep-for waits
for a fractional number of seconds. Some systems support only a whole number of
seconds; on these systems, seconds is rounded down.
The optional argument millisec specifies an additional waiting period measured inmilliseconds. This adds to the period specified by seconds. If the system doesn’t
support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use sleep-for when you wish to guarantee a delay.

See Section 42.5 [Time of Day], page 1270, for functions to get the current time.

22.11 Quitting
Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. Thismeans that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input does not cause a quit;
it acts as an ordinary input character. In the simplest case, you cannot tell the difference,
because C-g normally runs the command keyboard-quit, whose effect is to quit. However,when C-g follows a prefix key, they combine to form an undefined key. The effect is to cancel
the prefix key as well as any prefix argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. Thismeans, in effect, that it exits the minibuffer and then quits. (Simply quitting would returnto the command loop within the minibuffer.) The reason why C-g does not quit directly
when the command reader is reading input is so that its meaning can be redefined in theminibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it
has its normal effect of canceling the prefix key and prefix argument. This too would not be
possible if C-g always quit directly.
When C-g does directly quit, it does so by setting the variable quit-flag to t. Emacs
checks this variable at appropriate times and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only at the special places
that check quit-flag. The reason for this is that quitting at other places might leavean inconsistency in Emacs’s internal state. Because quitting is delayed until a safe place,quitting cannot make Emacs crash.
Certain functions such as read-key-sequence or read-quoted-char prevent quitting
entirely even though they wait for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring about the special behaviorof C-g in the command loop. In the case of read-quoted-char, this is so that C-q can beused to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding the variableinhibit-quit to a non-nil value. Then, although C-g still sets quit-flag to t as usual,the usual result of this—a quit—is prevented. Eventually, inhibit-quit will become nil
again, such as when its binding is unwound at the end of a let form. At that time, if

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quit-flag is still non-nil, the requested quit happens immediately. This behavior is ideal
when you wish to make sure that quitting does not happen within a critical section of the
program.
In some functions (such as read-quoted-char), C-g is handled in a special way that
does not involve quitting. This is done by reading the input with inhibit-quit bound tot, and setting quit-flag to nil before inhibit-quit becomes nil again. This excerpt
from the definition of read-quoted-char shows how this is done; it also shows that normal
quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)"...documentation..."(let ((message-log-max nil) done (first t) (code 0) char)(while (not done)(let ((inhibit-quit first)...)(and prompt (message "%s-" prompt))(setq char (read-event))(if inhibit-quit (setq quit-flag nil))). . . set the variable code. . . )code))[Variable]
If this variable is non-nil, then Emacs quits immediately, unless inhibit-quit isnon-nil. Typing C-g ordinarily sets quit-flag non-nil, regardless of inhibit-quit.

quit-flag[Variable]
This variable determines whether Emacs should quit when quit-flag is set to a value
other than nil. If inhibit-quit is non-nil, then quit-flag has no special effect.

inhibit-quit

with-local-quit body. . .

[Macro]This macro executes body forms in sequence, but allows quitting, at least locally,
within body even if inhibit-quit was non-nil outside this construct. It returns thevalue of the last form in body, unless exited by quitting, in which case it returns nil.
If inhibit-quit is nil on entry to with-local-quit, it only executes the body, andsetting quit-flag causes a normal quit. However, if inhibit-quit is non-nil sothat ordinary quitting is delayed, a non-nil quit-flag triggers a special kind of local
quit. This ends the execution of body and exits the with-local-quit body with
quit-flag still non-nil, so that another (ordinary) quit will happen as soon as thatis allowed. If quit-flag is already non-nil at the beginning of body, the local quit
happens immediately and the body doesn’t execute at all.
This macro is mainly useful in functions that can be called from timers, process filters,
process sentinels, pre-command-hook, post-command-hook, and other places where
inhibit-quit is normally bound to t.
[Command]This function signals the quit condition with (signal 'quit nil). This is the samething that quitting does. (See signal in Section 11.7.3 [Errors], page 179.)

keyboard-quitChapter 22: Command Loop473

To quit without aborting a keyboard macro definition or execution, you can signal theminibuffer-quit condition. This has almost the same effect as the quit condition exceptthat the error handling in the command loop handles it without exiting keyboard macrodefinition or execution.
You can specify a character other than C-g to use for quitting. See the function
set-input-mode in Section 42.13.1 [Input Modes], page 1285.

22.12 Prefix Command Arguments
Most Emacs commands can use a prefix argument, a number specified before the command
itself. (Don’t confuse prefix arguments with prefix keys.) The prefix argument is at all times
represented by a value, which may be nil, meaning there is currently no prefix argument.
Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: raw and numeric. The editor
command loop uses the raw representation internally, and so do the Lisp variables that store
the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:• nil, meaning there is no prefix argument. Its numeric value is 1, but numerous
commands make a distinction between nil and the integer 1.
• An integer, which stands for itself.
• A list of one element, which is an integer. This form of prefix argument results fromone or a succession of C-us with no digits. The numeric value is the integer in the list,
but some commands make a distinction between such a list and an integer alone.
• The symbol -. This indicates that M-- or C-u - was typed, without following digits.
The equivalent numeric value is −1, but some commands make a distinction between
the integer −1 and the symbol -.
We illustrate these possibilities by calling the following function with various prefixes:(defun display-prefix (arg)"Display the value of the raw prefix arg."(interactive "P")(message "%s" arg))
Here are the results of calling display-prefix with various raw prefix arguments:
M-x display-prefixa nil

M-x display-prefixa (4)C-u C-u M-x display-prefixa (16)

C-u 3

M-x display-prefix

a 3

M-3

M-x display-prefix

a 3

C-u -

M-x display-prefix

a -

C-u

; (Same as C-u 3.)

Chapter 22: Command Loop474

M-x display-prefixa -C-u - 7 M-x display-prefix

a -7

M--

; (Same as C-u -.)M-- 7
M-x display-prefix a -7
; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument: prefix-arg and current-prefixarg. Commands such as universal-argument that set up prefix arguments for othercommands store them in prefix-arg. In contrast, current-prefix-arg conveys the prefix
argument to the current command, so setting it has no effect on the prefix arguments for
future commands.
Normally, commands specify which representation to use for the prefix argument, either
numeric or raw, in the interactive specification. (See Section 22.2.1 [Using Interactive],
page 424.) Alternatively, functions may look at the value of the prefix argument directly inthe variable current-prefix-arg, but this is less clean.

prefix-numeric-value arg[Function]
This function returns the numeric meaning of a valid raw prefix argument value, arg.
The argument may be a symbol, a number, or a list. If it is nil, the value 1 is returned;
if it is -, the value −1 is returned; if it is a number, that number is returned; if it is alist, the car of that list (which should be a number) is returned.
[Variable]
This variable holds the raw prefix argument for the current command. Commands
may examine it directly, but the usual method for accessing it is with (interactive"P").

current-prefix-arg[Variable]
The value of this variable is the raw prefix argument for the next editing command.
Commands such as universal-argument that specify prefix arguments for the following command work by setting this variable.

prefix-arg

last-prefix-arg[Variable]

The raw prefix argument value used by the previous command.
The following commands exist to set up prefix arguments for the following command.
Do not call them for any other reason.
[Command]This command reads input and specifies a prefix argument for the following command.
Don’t call this command yourself unless you know what you are doing.

universal-argument

digit-argument arg[Command]This command adds to the prefix argument for the following command. The argument
arg is the raw prefix argument as it was before this command; it is used to computethe updated prefix argument. Don’t call this command yourself unless you know what
you are doing.

negative-argument arg[Command]This command adds to the numeric argument for the next command. The argument
arg is the raw prefix argument as it was before this command; its value is negatedChapter 22: Command Loop475

to form the new prefix argument. Don’t call this command yourself unless you knowwhat you are doing.

22.13 Recursive Editing
The Emacs command loop is entered automatically when Emacs starts up. This top-levelinvocation of the command loop never exits; it keeps running as long as Emacs does. Lisp
programs can also invoke the command loop. Since this makes more than one activation of
the command loop, we call it recursive editing. A recursive editing level has the effect ofsuspending whatever command invoked it and permitting the user to do arbitrary editing
before resuming that command.
The commands available during recursive editing are the same ones available in the
top-level editing loop and defined in the keymaps. Only a few special commands exit therecursive editing level; the others return to the recursive editing level when they finish.
(The special commands for exiting are always available, but they do nothing when recursive
editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that anerror in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, suchas enabling display of the minibuffer and the minibuffer window, but fewer than you might
suppose. Certain keys behave differently in the minibuffer, but that is only because of theminibuffer’s local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function recursive-edit. This function
contains the command loop; it also contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit (see Section 11.7.1 [Catchand Throw], page 177). Throwing a t value causes recursive-edit to quit, so that control
returns to the command loop one level up. This is called aborting, and is done by C-](abort-recursive-edit). Similarly, you can throw a string value to make recursive-edit
signal an error, printing this string as the message. If you throw a function, recursive-edit
will call it without arguments before returning. Throwing any other value, will makerecursive-edit return normally to the function that called it. The command C-M-c(exit-recursive-edit) does this.
Most applications should not use recursive editing, except as part of using the minibuffer.
Usually it is more convenient for the user if you change the major mode of the current
buffer temporarily to a special major mode, which should have a command to go back to
the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to givethe user different text to edit recursively, create and select a new buffer in a special mode.
In this mode, define a command to complete the processing and go back to the previous
buffer. (The m command in Rmail does this.)Recursive edits are useful in debugging. You can insert a call to debug into a function
definition as a sort of breakpoint, so that you can look around when the function gets there.
debug invokes a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in query-replace or use C-x q(kbd-macro-query).

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[Command]This function invokes the editor command loop. It is called automatically by the
initialization of Emacs, to let the user begin editing. When called from a Lisp program,it enters a recursive editing level.
If the current buffer is not the same as the selected window’s buffer, recursive-edit
saves and restores the current buffer. Otherwise, if you switch buffers, the buffer you
switched to is current after recursive-edit returns.
In the following example, the function simple-rec first advances point one word, thenenters a recursive edit, printing out a message in the echo area. The user can then doany editing desired, and then type C-M-c to exit and continue executing simple-rec.
(defun simple-rec ()(forward-word 1)(message "Recursive edit in progress")(recursive-edit)(forward-word 1))⇒ simple-rec(simple-rec)⇒ nil

recursive-edit[Command]This function exits from the innermost recursive edit (including minibuffer input). Its
definition is effectively (throw 'exit nil).

exit-recursive-edit[Command]This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling quit after exiting the recursive edit. Its definitionis effectively (throw 'exit t). See Section 22.11 [Quitting], page 471.

abort-recursive-edit[Command]This function exits all recursive editing levels; it does not return a value, as it jumps
completely out of any computation directly back to the main command loop.

top-level[Function]
This function returns the current depth of recursive edits. When no recursive edit isactive, it returns 0.

recursion-depth

22.14 Disabling Commands
Disabling a command marks the command as requiring user confirmation before it can be
executed. Disabling is used for commands which might be confusing to beginning users, toprevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a non-nil disabled propertyon the Lisp symbol for the command. These properties are normally set up by the user’s
init file (see Section 42.1.2 [Init File], page 1258) with Lisp expressions such as this:(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default (you can remove them in yourinit file if you wish).

Chapter 22: Command Loop477

If the value of the disabled property is a string, the message saying the command isdisabled includes that string. For example:(put 'delete-region 'disabled"Text deleted this way cannot be yanked back!\n")
See Section “Disabling” in The GNU Emacs Manual, for the details on what happens
when a disabled command is invoked interactively. Disabling a command has no effect on
calling it as a function from Lisp programs.
The value of the disabled property can also be a list where the first element is the
symbol query. In that case, the user will be queried whether to execute the command. The
second element in the list should be nil or non-nil to say whether to use y-or-n-p or
yes-or-no-p, respectively, and the third element is the question to use. The command-query
convenience function should be used to enable querying for a command.

enable-command command[Command]
Allow command (a symbol) to be executed without special confirmation from now on,
and alter the user’s init file (see Section 42.1.2 [Init File], page 1258) so that this will
apply to future sessions.

disable-command command[Command]Require special confirmation to execute command from now on, and alter the user’s
init file so that this will apply to future sessions.

[Variable]
The value of this variable should be a function. When the user invokes a disabledcommand interactively, this function is called instead of the disabled command. It
can use this-command-keys to determine what the user typed to run the command,and thus find the command itself.

disabled-command-function

The value may also be nil. Then all commands work normally, even disabled ones.
By default, the value is a function that asks the user whether to proceed.

22.15 Command History
The command loop keeps a history of the complex commands that have been executed, tomake it convenient to repeat these commands. A complex command is one for which theinteractive argument reading uses the minibuffer. This includes any M-x command, any M-:
command, and any command whose interactive specification reads an argument from theminibuffer. Explicit use of the minibuffer during the execution of the command itself does
not cause the command to be considered complex.
[Variable]
This variable’s value is a list of recent complex commands, each represented as a form
to evaluate. It continues to accumulate all complex commands for the duration of theediting session, but when it reaches the maximum size (see Section 21.4 [Minibuffer
History], page 392), the oldest elements are deleted as new ones are added.

command-history

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command-history⇒ ((switch-to-buffer "chistory.texi")(describe-key "^X^[")(visit-tags-table "~/emacs/src/")(find-tag "repeat-complex-command"))This history list is actually a special case of minibuffer history (see Section 21.4 [Minibuffer
History], page 392), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of previous commands.
The commands repeat-complex-command, and list-command-history are described in theuser manual (see Section “Repetition” in The GNU Emacs Manual). Within the minibuffer,
the usual minibuffer history commands are available.

22.16 Keyboard Macros
A keyboard macro is a canned sequence of input events that can be considered a commandand made the definition of a key. The Lisp representation of a keyboard macro is a stringor vector containing the events. Don’t confuse keyboard macros with Lisp macros (seeChapter 14 [Macros], page 268).

execute-kbd-macro kbdmacro &optional count loopfunc[Function]
This function executes kbdmacro as a sequence of events. If kbdmacro is a string or
vector, then the events in it are executed exactly as if they had been input by the user.
The sequence is not expected to be a single key sequence; normally a keyboard macrodefinition consists of several key sequences concatenated.
If kbdmacro is a symbol, then its function definition is used in place of kbdmacro. If
that is another symbol, this process repeats. Eventually the result should be a stringor vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; kbdmacro is executed that many times. If
count is omitted or nil, kbdmacro is executed once. If it is 0, kbdmacro is executedover and over until it encounters an error or a failing search.
If loopfunc is non-nil, it is a function that is called, without arguments, prior to each
iteration of the macro. If loopfunc returns nil, then this stops execution of the macro.
See Section 22.8.2 [Reading One Event], page 462, for an example of using
execute-kbd-macro.
[Variable]
This variable contains the string or vector that defines the keyboard macro that iscurrently executing. It is nil if no macro is currently executing. A command can test
this variable so as to behave differently when run from an executing macro. Do not
set this variable yourself.

executing-kbd-macro[Variable]
This variable is non-nil if and only if a keyboard macro is being defined. A command
can test this variable so as to behave differently while a macro is being defined. The
value is append while appending to the definition of an existing macro. The commands
start-kbd-macro, kmacro-start-macro and end-kbd-macro set this variable—do
not set it yourself.

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The variable is always local to the current terminal and cannot be buffer-local. See
Section 30.2 [Multiple Terminals], page 787.
[Variable]
This variable is the definition of the most recently defined keyboard macro. Its value
is a string or vector, or nil.
The variable is always local to the current terminal and cannot be buffer-local. See
Section 30.2 [Multiple Terminals], page 787.

last-kbd-macro[Variable]
This normal hook is run when a keyboard macro terminates, regardless of whatcaused it to terminate (reaching the macro end or an error which ended the macroprematurely).

kbd-macro-termination-hook

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23 Keymaps
The command bindings of input events are recorded in data structures called keymaps. Each
entry in a keymap associates (or binds) an individual event type, either to another keymap
or to a command. When an event type is bound to a keymap, that keymap is used to lookup the next input event; this continues until a command is found. The whole process iscalled key lookup.

23.1 Key Sequences
A key sequence, or key for short, is a sequence of one or more input events that form a unit.
Input events include characters, function keys, mouse actions, or system events external to
Emacs, such as iconify-frame (see Section 22.7 [Input Events], page 440). The Emacs Lisp
representation for a key sequence is a string or vector. Unless otherwise stated, any Emacs
Lisp function that accepts a key sequence as an argument can handle both representations.
In the string representation, alphanumeric characters ordinarily stand for themselves; forexample, "a" represents a and "2" represents 2. Control character events are prefixed by thesubstring "\C-", and meta characters by "\M-"; for example, "\C-x" represents the key C-x.
In addition, the TAB, RET, ESC, and DEL events are represented by "\t", "\r", "\e", and"\d" respectively. The string representation of a complete key sequence is the concatenationof the string representations of the constituent events; thus, "\C-xl" represents the key
sequence C-x l.
Key sequences containing function keys, mouse button events, system events, or nonASCII characters such as C-= or H-a cannot be represented as strings; they have to be

represented as vectors.
In the vector representation, each element of the vector represents an input event, in its
Lisp form. See Section 22.7 [Input Events], page 440. For example, the vector [?\C-x ?l]represents the key sequence C-x l.
For examples of key sequences written in string and vector representations, Section “Init
Rebinding” in The GNU Emacs Manual.

kbd keyseq-text[Function]
This function converts the text keyseq-text (a string constant) into a key sequence (astring or vector constant). The contents of keyseq-text should use the same syntax as in
the buffer invoked by the C-x C-k RET (kmacro-edit-macro) command; in particular,
you must surround function key names with ‘<...>’. See Section “Edit Keyboard
Macro” in The GNU Emacs Manual.
(kbd "C-x") ⇒ "\C-x"(kbd "C-x C-f") ⇒ "\C-x\C-f"(kbd "C-x 4 C-f") ⇒ "\C-x4\C-f"(kbd "X") ⇒ "X"(kbd "RET") ⇒ "^M"(kbd "C-c SPC") ⇒ "\C-c "(kbd "<f1> SPC") ⇒ [f1 32](kbd "C-M-<down>") ⇒ [C-M-down]Chapter 23: Keymaps

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The kbd function is very permissive, and will try to return something sensible even if
the syntax used isn’t completely conforming. To check whether the syntax is actuallyvalid, use the key-valid-p function.

23.2 Keymap Basics
A keymap is a Lisp data structure that specifies key bindings for various key sequences.
A single keymap directly specifies definitions for individual events. When a key sequence
consists of a single event, its binding in a keymap is the keymap’s definition for that event.
The binding of a longer key sequence is found by an iterative process: first find the definitionof the first event (which must itself be a keymap); then find the second event’s definition inthat keymap, and so on until all the events in the key sequence have been processed.
If the binding of a key sequence is a keymap, we call the key sequence a prefix key.
Otherwise, we call it a complete key (because no more events can be added to it). If thebinding is nil, we call the key undefined. Examples of prefix keys are C-c, C-x, and C-x
4. Examples of defined complete keys are X, RET, and C-x 4 C-f. Examples of undefinedcomplete keys are C-x C-g, and C-c 3. See Section 23.6 [Prefix Keys], page 488, for moredetails.
The rule for finding the binding of a key sequence assumes that the intermediate bindings(found for the events before the last) are all keymaps; if this is not so, the sequence of events
does not form a unit—it is not really one key sequence. In other words, removing one ormore events from the end of any valid key sequence must always yield a prefix key. For
example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence startingwith C-f cannot be a key sequence.
The set of possible multi-event key sequences depends on the bindings for prefix keys;
therefore, it can be different for different keymaps, and can change when bindings arechanged. However, a one-event sequence is always a key sequence, because it does notdepend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active—that is, in use for finding key bindings.
These are the global map, which is shared by all buffers; the local keymap, which is usuallyassociated with a specific major mode; and zero or more minor mode keymaps, which belong
to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap
bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor
mode keymaps shadow both local and global keymaps. See Section 23.7 [Active Keymaps],
page 489, for details.

23.3 Format of Keymaps
Each keymap is a list whose car is the symbol keymap. The remaining elements of the list
define the key bindings of the keymap. A symbol whose function definition is a keymap isalso a keymap. Use the function keymapp (see below) to test whether an object is a keymap.
Several kinds of elements may appear in a keymap, after the symbol keymap that begins
it:(type . binding)This specifies one binding, for events of type type. Each ordinary binding applies
to events of a particular event type, which is always a character or a symbol. See

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Section 22.7.14 [Classifying Events], page 455. In this kind of binding, binding
is a command.
(type item-name . binding)This specifies a binding which is also a simple menu item that displays as
item-name in the menu. See Section 23.18.1.1 [Simple Menu Items], page 510.
(type item-name help-string . binding)This is a simple menu item with help string help-string.
(type menu-item . details)
This specifies a binding which is also an extended menu item. This allows useof other features. See Section 23.18.1.2 [Extended Menu Items], page 511.
(t . binding)This specifies a default key binding; any event not bound by other elements of
the keymap is given binding as its binding. Default bindings allow a keymap
to bind all possible event types without having to enumerate all of them. A
keymap that has a default binding completely masks any lower-precedence
keymap, except for events explicitly bound to nil (see below).
char-table
If an element of a keymap is a char-table, it counts as holding bindings for all
character events with no modifier bits (see [modifier bits], page 14): the element
whose index is c is the binding for the character c. This is a compact way torecord lots of bindings. A keymap with such a char-table is called a full keymap.
Other keymaps are called sparse keymaps.
vectorThis kind of element is similar to a char-table: the element whose index is c
is the binding for the character c. Since the range of characters that can bebound this way is limited by the vector size, and vector creation allocates space
for all character codes from 0 up, this format should not be used except for
creating menu keymaps (see Section 23.18 [Menu Keymaps], page 510), where
the bindings themselves don’t matter.

stringAside from elements that specify bindings for keys, a keymap can also havea string as an element. This is called the overall prompt string and makes it
possible to use the keymap as a menu. See Section 23.18.1 [Defining Menus],
page 510.

(keymap ...)
If an element of a keymap is itself a keymap, it counts as if this inner keymap
were inlined in the outer keymap. This is used for multiple-inheritance, such as
in make-composed-keymap.
When the binding is nil, it doesn’t constitute a definition but it does take precedence
over a default binding or a binding in the parent keymap. On the other hand, a binding of
nil does not override lower-precedence keymaps; thus, if the local map gives a binding ofnil, Emacs uses the binding from the global map.
Keymaps do not directly record bindings for the meta characters. Instead, meta characters
are regarded for purposes of key lookup as sequences of two characters, the first of which
is ESC (or whatever is currently the value of meta-prefix-char). Thus, the key M-a isChapter 23: Keymaps

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internally represented as ESC a, and its global binding is found at the slot for a in esc-map(see Section 23.6 [Prefix Keys], page 488).
This conversion applies only to characters, not to function keys or other input events;
thus, M-end has nothing to do with ESC end.
Here as an example is the local keymap for Lisp mode, a sparse keymap. It definesbindings for DEL, C-c C-z, C-M-q, and C-M-x (the actual value also contains a menu binding,which is omitted here for the sake of brevity).
lisp-mode-map⇒(keymap(3 keymap;; C-c C-z(26 . run-lisp))(27 keymap;; C-M-x, treated as ESC C-x(24 . lisp-send-defun));; This part is inherited from lisp-mode-shared-map.
keymap;; DEL(127 . backward-delete-char-untabify)(27 keymap;; C-M-q, treated as ESC C-q(17 . indent-sexp)))

keymapp object[Function]
This function returns t if object is a keymap, nil otherwise. More precisely, thisfunction tests for a list whose car is keymap, or for a symbol whose function definition
satisfies keymapp.
(keymapp '(keymap))⇒ t(fset 'foo '(keymap))(keymapp 'foo)⇒ t(keymapp (current-global-map))⇒ t

23.4 Creating Keymaps
Here we describe the functions for creating keymaps.

make-sparse-keymap &optional prompt[Function]
This function creates and returns a new sparse keymap with no entries. (A sparsekeymap is the kind of keymap you usually want.) The new keymap does not containa char-table, unlike make-keymap, and does not bind any events.
(make-sparse-keymap)⇒ (keymap)

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If you specify prompt, that becomes the overall prompt string for the keymap. You
should specify this only for menu keymaps (see Section 23.18.1 [Defining Menus],
page 510). A keymap with an overall prompt string will always present a mouse menu
or a keyboard menu if it is active for looking up the next input event. Don’t specify
an overall prompt string for the main map of a major or minor mode, because thatwould cause the command loop to present a keyboard menu every time.

make-keymap &optional prompt[Function]
This function creates and returns a new full keymap. That keymap contains a chartable (see Section 6.6 [Char-Tables], page 119) with slots for all characters without
modifiers. The new keymap initially binds all these characters to nil, and does notbind any other kind of event. The argument prompt specifies a prompt string, as in
make-sparse-keymap.
(make-keymap)⇒ (keymap #^[nil nil keymap nil nil nil ...])

A full keymap is more efficient than a sparse keymap when it holds lots of bindings;
for just a few, the sparse keymap is better.

define-keymap &key options... &rest pairs...

[Function]
You can create a keymap with the functions described above, and then use keymap-set(see Section 23.12 [Changing Key Bindings], page 497) to specify key bindings in that
map. When writing modes, however, you frequently have to bind a large numberof keys at once, and using keymap-set on them all can be tedious and error-prone.
Instead you can use define-keymap, which creates a keymap and binds a number ofkeys. Here’s a very basic example:(define-keymap"n" #'forward-line"f" #'previous-line"C-c C-c" #'quit-window)
This function creates a new sparse keymap, defines the keystrokes in pairs, and returns
the new keymap. It signals an error if there are duplicate key bindings in pairs.
pairs is a list of alternating key bindings and key definitions, as accepted by keymap-set.
In addition, the key can be the special symbol :menu, in which case the definition
should be a menu definition as accepted by easy-menu-define (see Section 23.18.8[Easy Menu], page 521). Here’s a brief example of this usage:(define-keymap :full t"g" #'eww-reload:menu '("Eww"["Exit" quit-window t]["Reload" eww-reload t]))A number of keywords can be used before the key/definition pairs to change featuresof the new keymap. If any of the feature keywords is missing from the define-keymap
call, the default value for that feature is nil. Here’s a list of the available feature
keywords:

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:full

If non-nil, create a char-table keymap (as from make-keymap) instead of asparse keymap (as from make-sparse-keymap (see Section 23.4 [Creating
Keymaps], page 483). A sparse keymap is the default.

:parent

If non-nil, the value should be a keymap to use as the parent (seeSection 23.5 [Inheritance and Keymaps], page 487).

:keymap

If non-nil, the value should be a keymap. Instead of creating a new
keymap, the specified keymap is modified instead.

:suppress
If non-nil, the keymap will be suppressed with suppress-keymap (seeSection 23.12 [Changing Key Bindings], page 497). By default, digits andthe minus sign are exempt from suppressing, but if the value is nodigits,
this suppresses digits and minus-sign like it does with other characters.
:name

If non-nil, the value should be a string to use as the menu for the keymap
if you use it as a menu with x-popup-menu (see Section 30.17 [Pop-Up
Menus], page 837).

:prefix

If non-nil, the value should be a symbol to be used as a prefix command(see Section 23.6 [Prefix Keys], page 488). If this is the case, this symbol
is returned by define-keymap instead of the map itself.

defvar-keymap name &key options... &rest pairs...

[Macro]By far, the most common thing to do with a keymap is to bind it to a variable. This
is what virtually all modes do—a mode called foo almost always has a variable called
foo-mode-map.
This macro defines name as a variable, passes options and pairs to define-keymap,
and uses the result as the default value for the variable. It signals an error if there are
duplicate key bindings in pairs.
options is like the keywords in define-keymap, but there’s an additional :doc keyword
that provides the doc string for the defined variable.
Here’s an example:(defvar-keymap eww-textarea-map:parent text-mode-map:doc "Keymap for the eww text area.""RET" #'forward-line"TAB" #'shr-next-link)
Each command in the keymap can be marked as ‘repeatable’, i.e. usable inrepeat-mode, by putting a repeat-map property on it, e.g.
(put 'undo 'repeat-map 'undo-repeat-map)
where the value of the property is the map to be used by repeat-mode.
To avoid repetitive invocations of put, defvar-keymap also has a :repeat keyword, which can be used to specify which commands in the keymap are usable
by repeat-mode. The following values are available:tThis means all the commands in the keymap are repeatable, and is themost common usage.

Chapter 23: Keymaps

486(:enter (commands ...) :exit (commands ...))
This specifies that the commands in the :enter list enter repeat-mode,and the commands in the :exit list exit repeat mode.
If the :enter list is empty, then all commands in the map enter
repeat-mode. Specifying one or more commands in this list is useful if
there is a command which doesn’t exist in the map being defined, butwhich should have the repeat-map property.
If the :exit list is empty then no commands in the map exit repeat-mode.
Specifying one or more commands in this list is useful if the keymap
being defined contains a command that should not have the repeat-map
property.
In order to make e.g. u repeat the undo command, the following two stanzas areequivalent:(defvar-keymap undo-repeat-map"u" #'undo)(put 'undo 'repeat-map 'undo-repeat-map)
and(defvar-keymap undo-repeat-map:repeat t"u" #'undo)
The latter is preferred when there are many commands in the map, all of which should
be repeatable.

copy-keymap keymap[Function]
This function returns a copy of keymap. This is almost never needed. If you want akeymap that’s like another yet with a few changes, you should use map inheritancerather than copying. I.e., something like:(let ((map (make-sparse-keymap)))(set-keymap-parent map <theirmap>)(keymap-set map ...)...)
When performing copy-keymap, any keymaps that appear directly as bindings inkeymap are also copied recursively, and so on to any number of levels. However,recursive copying does not take place when the definition of a character is a symbol
whose function definition is a keymap; the same symbol appears in the new copy.
(setq map (copy-keymap (current-local-map)))⇒ (keymap;; (This implements meta characters.)(27 keymap(83 . center-paragraph)(115 . center-line))(9 . tab-to-tab-stop))(eq map (current-local-map))⇒ nilChapter 23: Keymaps

487(equal map (current-local-map))⇒ t

23.5 Inheritance and Keymaps
A keymap can inherit the bindings of another keymap, which we call the parent keymap.
Such a keymap looks like this:(keymap elements... . parent-keymap)
The effect is that this keymap inherits all the bindings of parent-keymap, whatever they
may be at the time a key is looked up, but can add to them or override them with elements.
If you change the bindings in parent-keymap using keymap-set or other key-binding
functions, these changed bindings are visible in the inheriting keymap, unless shadowed by
the bindings made by elements. The converse is not true: if you use keymap-set to changebindings in the inheriting keymap, these changes are recorded in elements, but have no effecton parent-keymap.
The proper way to construct a keymap with a parent is to use set-keymap-parent; if
you have code that directly constructs a keymap with a parent, please convert the program
to use set-keymap-parent instead.

keymap-parent keymap[Function]
This returns the parent keymap of keymap. If keymap has no parent, keymap-parent
returns nil.

set-keymap-parent keymap parent[Function]
This sets the parent keymap of keymap to parent, and returns parent. If parent isnil, this function gives keymap no parent at all.
If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps
that reflect what parent specifies for those prefix keys.

Here is an example showing how to make a keymap that inherits from text-mode-map:(let ((map (make-sparse-keymap)))(set-keymap-parent map text-mode-map)
map)
A non-sparse keymap can have a parent too, but this is not very useful. A non-sparsekeymap always specifies something as the binding for every numeric character code without
modifier bits, even if it is nil, so these character’s bindings are never inherited from theparent keymap.
Sometimes you want to make a keymap that inherits from more than one map. You can
use the function make-composed-keymap for this.

make-composed-keymap maps &optional parent[Function]
This function returns a new keymap composed of the existing keymap(s) maps, andoptionally inheriting from a parent keymap parent. maps can be a single keymap or
a list of more than one. When looking up a key in the resulting new map, Emacs
searches in each of the maps in turn, and then in parent, stopping at the first match.
A nil binding in any one of maps overrides any binding in parent, but it does notoverride any non-nil binding in any other of the maps.

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For example, here is how Emacs sets the parent of help-mode-map, such that it inherits
from both button-buffer-map and special-mode-map:(defvar-keymap help-mode-map:parent (make-composed-keymap button-buffer-map
special-mode-map)...)

23.6 Prefix Keys
A prefix key is a key sequence whose binding is a keymap. The keymap defines what to dowith key sequences that extend the prefix key. For example, C-x is a prefix key, and it uses
a keymap that is also stored in the variable ctl-x-map. This keymap defines bindings forkey sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:• esc-map is the global keymap for the ESC prefix key. Thus, the global definitions of allmeta characters are actually found here. This map is also the function definition of
ESC-prefix.
• help-map is the global keymap for the C-h prefix key.
• mode-specific-map is the global keymap for the prefix key C-c. This map is actually
global, not mode-specific, but its name provides useful information about C-c in the
output of C-h b (display-bindings), since the main use of this prefix key is formode-specific bindings.
• ctl-x-map is the global keymap used for the C-x prefix key. This map is found via thefunction cell of the symbol Control-X-prefix.
• mule-keymap is the global keymap used for the C-x RET prefix key.
• ctl-x-4-map is the global keymap used for the C-x 4 prefix key.
• ctl-x-5-map is the global keymap used for the C-x 5 prefix key.
• 2C-mode-map is the global keymap used for the C-x 6 prefix key.
• tab-prefix-map is the global keymap used for the C-x t prefix key.
• vc-prefix-map is the global keymap used for the C-x v prefix key.
• goto-map is the global keymap used for the M-g prefix key.
• search-map is the global keymap used for the M-s prefix key.
• The other Emacs prefix keys are C-x @, C-x a i, C-x ESC and ESC ESC. They use
keymaps that have no special names.
The keymap binding of a prefix key is used for looking up the event that follows theprefix key. (It may instead be a symbol whose function definition is a keymap. The effect isthe same, but the symbol serves as a name for the prefix key.) Thus, the binding of C-x isthe symbol Control-X-prefix, whose function cell holds the keymap for C-x commands.
(The same keymap is also the value of ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-hand ESC as prefix keys appear in the global map, so these prefix keys are always available.
Major and minor modes can redefine a key as a prefix by putting a prefix key definition for
it in the local map or the minor mode’s map. See Section 23.7 [Active Keymaps], page 489.

Chapter 23: Keymaps489

If a key is defined as a prefix in more than one active map, then its various definitions
are in effect merged: the commands defined in the minor mode keymaps come first, followedby those in the local map’s prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local keymap, in such a waythat C-p is identical to C-x. Then the binding for C-p C-f is the function find-file, justlike C-x C-f. By contrast, the key sequence C-p 9 is not found in any active keymap.
(use-local-map (make-sparse-keymap))⇒ nil(keymap-local-set "C-p" ctl-x-map)⇒ (keymap #^[nil nil keymap ...
(keymap-lookup nil "C-p C-f")⇒ find-file(keymap-lookup nil "C-p 9")⇒ nildefine-prefix-command symbol &optional mapvar prompt[Function]
This function prepares symbol for use as a prefix key’s binding: it creates a sparsekeymap and stores it as symbol’s function definition. Subsequently binding a key
sequence to symbol will make that key sequence into a prefix key. The return value issymbol.
This function also sets symbol as a variable, with the keymap as its value. But if
mapvar is non-nil, it sets mapvar as a variable instead.
If prompt is non-nil, that becomes the overall prompt string for the keymap. The
prompt string should be given for menu keymaps (see Section 23.18.1 [Defining Menus],
page 510).

23.7 Active Keymaps
Emacs contains many keymaps, but at any time only a few keymaps are active. When Emacs
receives user input, it translates the input event (see Section 23.15 [Translation Keymaps],
page 504), and looks for a key binding in the active keymaps.
Usually, the active keymaps are: (i) the keymap specified by the keymap property, (ii) the
keymaps of enabled minor modes, (iii) the current buffer’s local keymap, and (iv) the global
keymap, in that order. Emacs searches for each input key sequence in all these keymaps.
Of these usual keymaps, the highest-precedence one is specified by the keymap text oroverlay property at point, if any. (For a mouse input event, Emacs uses the event position
instead of point; see the next section for details.)
Next in precedence are keymaps specified by enabled minor modes. These keymaps, if any,
are specified by the variables emulation-mode-map-alists, minor-mode-overriding-mapalist, and minor-mode-map-alist. See Section 23.9 [Controlling Active Maps], page 491.
Next in precedence is the buffer’s local keymap, containing key bindings specific to thebuffer. The minibuffer also has a local keymap (see Section 21.1 [Intro to Minibuffers],
page 385). If there is a local-map text or overlay property at point, that specifies the local
keymap to use, in place of the buffer’s default local keymap.
The local keymap is normally set by the buffer’s major mode, and every buffer with thesame major mode shares the same local keymap. Hence, if you call keymap-local-set (seeChapter 23: Keymaps

490

Section 23.16 [Key Binding Commands], page 506) to change the local keymap in one buffer,that also affects the local keymaps in other buffers with the same major mode.
Finally, the global keymap contains key bindings that are defined regardless of the current
buffer, such as C-f. It is always active, and is bound to the variable global-map.
Apart from the above usual keymaps, Emacs provides special ways for programs to makeother keymaps active. Firstly, the variable overriding-local-map specifies a keymap that
replaces the usual active keymaps, except for the global keymap. Secondly, the terminal-local
variable overriding-terminal-local-map specifies a keymap that takes precedence over allother keymaps (including overriding-local-map); this is normally used for modal/transient
key bindings (the function set-transient-map provides a convenient interface for this).
See Section 23.9 [Controlling Active Maps], page 491, for details.
Making keymaps active is not the only way to use them. Keymaps are also used inother ways, such as for translating events within read-key-sequence. See Section 23.15[Translation Keymaps], page 504.
See Appendix G [Standard Keymaps], page 1395, for a list of some standard keymaps.

current-active-maps &optional olp position[Function]
This returns the list of active keymaps that would be used by the command loop
in the current circumstances to look up a key sequence. Normally it ignores
overriding-local-map and overriding-terminal-local-map, but if olp is
non-nil then it pays attention to them. position can optionally be either an event
position as returned by event-start or a buffer position, and may change thekeymaps as described for keymap-lookup (see Section 23.11 [Functions for Key
Lookup], page 495).

23.8 Searching the Active Keymaps
Here is a pseudo-Lisp summary of how Emacs searches the active keymaps:(or (if overriding-terminal-local-map(find-in overriding-terminal-local-map))(if overriding-local-map(find-in overriding-local-map)(or (find-in (get-char-property (point) 'keymap))(find-in-any emulation-mode-map-alists)(find-in-any minor-mode-overriding-map-alist)(find-in-any minor-mode-map-alist)(if (get-char-property (point) 'local-map)(find-in (get-char-property (point) 'local-map))(find-in (current-local-map)))))(find-in (current-global-map)))
Here, find-in and find-in-any are pseudo functions that search in one keymap and in analist of keymaps, respectively. Note that the set-transient-map function works by setting
overriding-terminal-local-map (see Section 23.9 [Controlling Active Maps], page 491).
In the above pseudo-code, if a key sequence starts with a mouse event (see Section 22.7.3[Mouse Events], page 442), that event’s position is used instead of point, and the event’s
buffer is used instead of the current buffer. In particular, this affects how the keymap

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491

and local-map properties are looked up. If a mouse event occurs on a string embeddedwith a display, before-string, or after-string property (see Section 33.19.4 [Special
Properties], page 924), and the string has a non-nil keymap or local-map property, that
overrides the corresponding property in the underlying buffer text (i.e., the property specified
by the underlying text is ignored).
When a key binding is found in one of the active keymaps, and that binding is a command,the search is over—the command is executed. However, if the binding is a symbol witha value or a string, Emacs replaces the input key sequences with the variable’s value or
the string, and restarts the search of the active keymaps. See Section 23.10 [Key Lookup],
page 494.
The command which is finally found might also be remapped. See Section 23.14 [Remapping Commands], page 503.

23.9 Controlling the Active Keymaps[Variable]
This variable contains the default global keymap that maps Emacs keyboard input tocommands. The global keymap is normally this keymap. The default global keymap
is a full keymap that binds self-insert-command to all of the printing characters.

global-map

It is normal practice to change the bindings in the global keymap, but you should not
assign this variable any value other than the keymap it starts out with.
[Function]
This function returns the current global keymap. This is the same as the value of
global-map unless you change one or the other. The return value is a reference, nota copy; if you use keymap-set or other functions on it you will alter global bindings.

current-global-map(current-global-map)⇒ (keymap [set-mark-command beginning-of-line ...
delete-backward-char])[Function]
This function returns the current buffer’s local keymap, or nil if it has none. In
the following example, the keymap for the *scratch* buffer (using Lisp Interactionmode) is a sparse keymap in which the entry for ESC, ASCII code 27, is another sparsekeymap.

current-local-map(current-local-map)⇒ (keymap(10 . eval-print-last-sexp)(9 . lisp-indent-line)(127 . backward-delete-char-untabify)(27 keymap(24 . eval-defun)(17 . indent-sexp)))
current-local-map returns a reference to the local keymap, not a copy of it; if you use
keymap-set or other functions on it you will alter local bindings.

Chapter 23: Keymaps

492[Function]
This function returns a list of the keymaps of currently enabled minor modes.

current-minor-mode-maps
use-global-map keymap[Function]
This function makes keymap the new current global keymap. It returns nil.
It is very unusual to change the global keymap.

use-local-map keymap[Function]
This function makes keymap the new local keymap of the current buffer. If keymap isnil, then the buffer has no local keymap. use-local-map returns nil. Most major
mode commands use this function.
[Variable]
This variable is an alist describing keymaps that may or may not be active according
to the values of certain variables. Its elements look like this:minor-mode-map-alist(variable . keymap)
The keymap keymap is active whenever variable has a non-nil value. Typicallyvariable is the variable that enables or disables a minor mode. See Section 24.3.2[Keymaps and Minor Modes], page 546.
Note that elements of minor-mode-map-alist do not have the same structure as
elements of minor-mode-alist. The map must be the cdr of the element; a list withthe map as the second element will not do. The cdr can be either a keymap (a list)
or a symbol whose function definition is a keymap.
When more than one minor mode keymap is active, the earlier one in minor-modemap-alist takes priority. But you should design minor modes so that they don’tinterfere with each other. If you do this properly, the order will not matter.
See Section 24.3.2 [Keymaps and Minor Modes], page 546, for more information aboutminor modes. See also minor-mode-key-binding (see Section 23.11 [Functions for
Key Lookup], page 495).
[Variable]
This variable allows major modes to override the key bindings for particular minor
modes. The elements of this alist look like the elements of minor-mode-map-alist:(variable . keymap).

minor-mode-overriding-map-alist

If a variable appears as an element of minor-mode-overriding-map-alist, the map
specified by that element totally replaces any map specified for the same variable inminor-mode-map-alist.
minor-mode-overriding-map-alist is automatically buffer-local in all buffers.
[Variable]
If non-nil, this variable holds a keymap to use instead of the buffer’s local keymap,
any text property or overlay keymaps, and any minor mode keymaps. This keymap, if
specified, overrides all other maps that would have been active, except for the current
global map.

overriding-local-map

Chapter 23: Keymaps

493[Variable]
If non-nil, this variable holds a keymap to use instead of overriding-local-map,the buffer’s local keymap, text property or overlay keymaps, and all the minor mode
keymaps.

overriding-terminal-local-map

This variable is always local to the current terminal and cannot be buffer-local. See
Section 30.2 [Multiple Terminals], page 787. It is used to implement incremental
search mode.
[Variable]
If this variable is non-nil, the value of overriding-local-map oroverriding-terminal-local-map can affect the display of the menu bar.
The default value is nil, so those map variables have no effect on the menu bar.

overriding-local-map-menu-flag

Note that these two map variables do affect the execution of key sequences enteredusing the menu bar, even if they do not affect the menu bar display. So if a menu bar
key sequence comes in, you should clear the variables before looking up and executingthat key sequence. Modes that use the variables would typically do this anyway;normally they respond to events that they do not handle by “unreading” them andexiting.
[Variable]
This variable holds a keymap for special events. If an event type has a binding in thiskeymap, then it is special, and the binding for the event is run directly by read-event.
See Section 22.9 [Special Events], page 470.

special-event-map[Variable]
This variable holds a list of keymap alists to use for emulation modes. It is intended
for modes or packages using multiple minor-mode keymaps. Each element is a keymap
alist which has the same format and meaning as minor-mode-map-alist, or a symbolwith a variable binding which is such an alist. The active keymaps in each alist areused before minor-mode-map-alist and minor-mode-overriding-map-alist.

emulation-mode-map-alists

set-transient-map keymap &optional keep-pred on-exit[Function]
This function adds keymap as a transient keymap, which takes precedence over otherkeymaps for one (or more) subsequent keys.
Normally, keymap is used just once, to look up the very next key. If the optional
argument keep-pred is t, the map stays active as long as the user types keys definedin keymap; when the user types a key that is not in keymap, the transient keymap isdeactivated and normal key lookup continues for that key.
The keep-pred argument can also be a function. In that case, the function is calledwith no arguments, prior to running each command, while keymap is active; it should
return non-nil if keymap should stay active.
The optional argument on-exit, if non-nil, specifies a function that is called, with noarguments, after keymap is deactivated.

The optional argument message specifies the message to display after activating thetransient map. If message is a string, it is the format string for the message, and any‘%k’ specifier in that string is replaced with the list of keys from the transient map.

Chapter 23: Keymaps494

Any other non-nil value of message stands for the default message format ‘Repeat
with %k’.
If the optional argument timeout is non-nil, it should be a number that specifies
how many seconds of idle time to wait before deactivating keymap. The value ofthe variable set-transient-map-timeout, if non-nil, overrides the value of thisargument.
This function works by adding and removing keymap from the variable
overriding-terminal-local-map, which takes precedence over all other active
keymaps (see Section 23.8 [Searching Keymaps], page 490).

23.10 Key Lookup
Key lookup is the process of finding the binding of a key sequence from a given keymap.
The execution or use of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key sequence; the rest of theevent is ignored. In fact, a key sequence used for key lookup may designate a mouse eventwith just its types (a symbol) instead of the entire event (a list). See Section 22.7 [Input
Events], page 440. Such a key sequence is insufficient for command-execute to run, but it issufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup processes the events
sequentially: the binding of the first event is found, and must be a keymap; then the second
event’s binding is found in that keymap, and so on until all the events in the key sequence
are used up. (The binding thus found for the last event may or may not be a keymap.)Thus, the process of key lookup is defined in terms of a simpler process for looking up asingle event in a keymap. How that is done depends on the type of object associated withthe event in that keymap.
Let’s use the term keymap entry to describe the value found by looking up an event typein a keymap. (This doesn’t include the item string and other extra elements in a keymap
element for a menu item, because keymap-lookup and other key lookup functions don’t
include them in the returned value.) While any Lisp object may be stored in a keymap as a
keymap entry, not all make sense for key lookup. Here is a table of the meaningful types ofkeymap entries:
nil

nil means that the events used so far in the lookup form an undefined key.
When a keymap fails to mention an event type at all, and has no default binding,that is equivalent to a binding of nil for that event type.

command

The events used so far in the lookup form a complete key, and command is its
binding. See Section 13.1 [What Is a Function], page 230.

array

The array (either a string or a vector) is a keyboard macro. The events used
so far in the lookup form a complete key, and the array is its binding. See
Section 22.16 [Keyboard Macros], page 478, for more information.

keymap

The events used so far in the lookup form a prefix key. The next event of the
key sequence is looked up in keymap.

list

The meaning of a list depends on what it contains:• If the car of list is the symbol keymap, then the list is a keymap, and istreated as a keymap (see above).

Chapter 23: Keymaps495• If the car of list is lambda, then the list is a lambda expression. This ispresumed to be a function, and is treated as such (see above). In order
to execute properly as a key binding, this function must be a command—
it must have an interactive specification. See Section 22.2 [Defining
Commands], page 424.
symbolThe function definition of symbol is used in place of symbol. If that too is asymbol, then this process is repeated, any number of times. Ultimately thisshould lead to an object that is a keymap, a command, or a keyboard macro.
Note that keymaps and keyboard macros (strings and vectors) are not validfunctions, so a symbol with a keymap, string, or vector as its function definition is invalid as a function. It is, however, valid as a key binding. If thedefinition is a keyboard macro, then the symbol is also valid as an argument tocommand-execute (see Section 22.3 [Interactive Call], page 432).
The symbol undefined is worth special mention: it means to treat the key as
undefined. Strictly speaking, the key is defined, and its binding is the command
undefined; but that command does the same thing that is done automaticallyfor an undefined key: it rings the bell (by calling ding) but does not signal anerror.
undefined is used in local keymaps to override a global key binding and makethe key undefined locally. A local binding of nil would fail to do this because
it would not override the global binding.

anything else
If any other type of object is found, the events used so far in the lookup form acomplete key, and the object is its binding, but the binding is not executable asa command.
In short, a keymap entry may be a keymap, a command, a keyboard macro, a symbolthat leads to one of them, or nil.

23.11 Functions for Key Lookup
Here are the functions and variables pertaining to key lookup.

keymap-lookup keymap key &optional accept-defaults no-remap
position[Function]

This function returns the definition of key in keymap. All the other functions describedin this chapter that look up keys use keymap-lookup. Here are examples:(keymap-lookup (current-global-map) "C-x C-f")⇒ find-file(keymap-lookup (current-global-map) "C-x C-f 1 2 3 4 5")⇒ 2
If the string or vector key is not a valid key sequence according to the prefix keys
specified in keymap, it must be too long and have extra events at the end that do not
fit into a single key sequence. Then the value is a number, the number of events at
the front of key that compose a complete key.

Chapter 23: Keymaps496

If accept-defaults is non-nil, then keymap-lookup considers default bindings as wellas bindings for the specific events in key. Otherwise, keymap-lookup reports onlybindings for the specific sequence key, ignoring default bindings except when you
explicitly ask about them. (To do this, supply t as an element of key; see Section 23.3
[Format of Keymaps], page 481.)
If key contains a meta character (not a function key), that character is implicitly
replaced by a two-character sequence: the value of meta-prefix-char, followed by
the corresponding non-meta character. Thus, the first example below is handled byconversion into the second example.
(keymap-lookup (current-global-map) "M-f")⇒ forward-word(keymap-lookup (current-global-map) "ESC f")⇒ forward-word
The keymap argument can be nil, meaning to look up key in the current keymaps (asreturned by current-active-maps, see Section 23.7 [Active Keymaps], page 489); or
it can be a keymap or a list of keymaps, meaning to look up key only in the specified
keymaps.
Unlike read-key-sequence, this function does not modify the specified events in waysthat discard information (see Section 22.8.1 [Key Sequence Input], page 461). In
particular, it does not convert letters to lower case and it does not change drag events
to clicks.
Like the normal command loop, keymap-lookup will remap the command resulting
from looking up key by looking up the command in the current keymaps. However,if the optional third argument no-remap is non-nil, keymap-lookup returns thecommand without remapping.
If the optional argument position is non-nil, it specifies a mouse position as returnedby event-start and event-end, and the lookup occurs in the keymaps associatedwith that position, instead of in keymap. position can also be a number or a marker,
in which case it is interpreted as a buffer position, and the function uses the keymap
properties at that position instead of at point.
[Command]
Used in keymaps to undefine keys. It calls ding, but does not cause an error.

undefined

keymap-local-lookup key &optional accept-defaults[Function]
This function returns the binding for key in the current local keymap, or nil if it isundefined there.
The argument accept-defaults controls checking for default bindings, as in
keymap-lookup (above).

keymap-global-lookup key &optional accept-defaults[Function]
This function returns the binding for command key in the current global keymap, or
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings, as in
keymap-lookup (above).

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497

minor-mode-key-binding key &optional accept-defaults[Function]
This function returns a list of all the active minor mode bindings of key. More precisely,
it returns an alist of pairs (modename . binding), where modename is the variable
that enables the minor mode, and binding is key’s binding in that mode. If key has
no minor-mode bindings, the value is nil.
If the first binding found is not a prefix definition (a keymap or a symbol defined
as a keymap), all subsequent bindings from other minor modes are omitted, since
they would be completely shadowed. Similarly, the list omits non-prefix bindings that
follow prefix bindings.
The argument accept-defaults controls checking for default bindings, as in
keymap-lookup (above).

[User Option]
This variable is the meta-prefix character code. It is used for translating a metacharacter to a two-character sequence so it can be looked up in a keymap. For useful
results, the value should be a prefix event (see Section 23.6 [Prefix Keys], page 488).
The default value is 27, which is the ASCII code for ESC.
As long as the value of meta-prefix-char remains 27, key lookup translates M-b into
ESC b, which is normally defined as the backward-word command. However, if you
were to set meta-prefix-char to 24, the code for C-x, then Emacs will translate
M-b into C-x b, whose standard binding is the switch-to-buffer command. (Don’t
actually do this!) Here is an illustration of what would happen:meta-prefix-charmeta-prefix-char⇒ 27(key-binding "\M-b")⇒ backward-word
?\C-x
⇒ 24
(setq meta-prefix-char 24)⇒ 24(key-binding "\M-b")⇒ switch-to-buffer(setq meta-prefix-char 27)⇒ 27; The default value.

; The print representation;of a character.

; Now, typing M-b is;like typing C-x b.
; Avoid confusion!
; Restore the default value!

This translation of one event into two happens only for characters, not for other kindsof input events. Thus, M-F1, a function key, is not converted into ESC F1.

23.12 Changing Key Bindings
The way to rebind a key is to change its entry in a keymap. If you change a binding in the
global keymap, the change is effective in all buffers (though it has no direct effect in buffersthat shadow the global binding with a local one). If you change the current buffer’s local map,that usually affects all buffers using the same major mode. The keymap-global-set andkeymap-local-set functions are convenient interfaces for these operations (see Section 23.16[Key Binding Commands], page 506). You can also use keymap-set, a more general function;then you must explicitly specify the map to change.
When choosing the key sequences for Lisp programs to rebind, please follow the Emacs
conventions for use of various keys (see Section D.2 [Key Binding Conventions], page 1334).

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498

The functions below signal an error if keymap is not a keymap, or if key is not a valid
key.
key is a string representing a single key or a series of key strokes, and must satisfy
key-valid-p. Key strokes are separated by a single space character.
Each key stroke is either a single character, or the name of an event, surrounded by angle
brackets. In addition, any key stroke may be preceded by one or more modifier keys. Finally,a limited number of characters have a special shorthand syntax. Here’s some example key
sequences:f

The key f.

Som

A three key sequence of the keys S, o and m.

C-c o

A two key sequence of the keys c with the control modifier and then the key o

H-<left>

The key named left with the hyper modifier.

M-RET

The return key with a meta modifier.

C-M-<space>
The space key with both the control and meta modifiers.
The only keys that have a special shorthand syntax are NUL, RET, TAB, LFD, ESC, SPC andDEL.
The modifiers have to be specified in alphabetical order: ‘A-C-H-M-S-s’, which is‘Alt-Control-Hyper-Meta-Shift-super’.

keymap-set keymap key binding[Function]
This function sets the binding for key in keymap. (If key is more than one event long,the change is actually made in another keymap reached from keymap.) The argumentbinding can be any Lisp object, but only certain types are meaningful. (For a list of
meaningful types, see Section 23.10 [Key Lookup], page 494.) The value returned by
keymap-set is binding.
If key is <t>, this sets the default binding in keymap. When an event has no bindingof its own, the Emacs command loop uses the keymap’s default binding, if there isone.
Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined;
otherwise an error is signaled. If some prefix of key is undefined, then keymap-set
defines it as a prefix key so that the rest of key can be defined as specified.
If there was previously no binding for key in keymap, the new binding is added at
the beginning of keymap. The order of bindings in a keymap makes no difference
for keyboard input, but it does matter for menu keymaps (see Section 23.18 [MenuKeymaps], page 510).

keymap-unset keymap key &optional remove[Function]
This function is the inverse of keymap-set, it unsets the binding for key in keymap,
which is the same as setting the binding to nil. In order to instead remove the binding
completely, specify remove as non-nil. This only makes a difference if keymap has aparent keymap: if you just unset a key in a child map, it will still shadow the same key
in the parent keymap; using remove instead will allow the key in the parent keymap
to be used.

Chapter 23: Keymaps499

Note: using keymap-unset with remove non-nil is intended for users to put in their init
file; Emacs packages should avoid using it if possible, since they have complete control overtheir own keymaps anyway, and they should not be altering other packages’ keymaps.
This example creates a sparse keymap and makes a number of bindings in it:(setq map (make-sparse-keymap))⇒ (keymap)(keymap-set map "C-f" 'forward-char)⇒ forward-charmap⇒ (keymap (6 . forward-char));; Build sparse submap for C-x and bind f in that.
(keymap-set map "C-x f" 'forward-word)⇒ forward-wordmap⇒ (keymap(24 keymap; C-x(102 . forward-word)) ;f(6 . forward-char)); C-f;; Bind C-p to the ctl-x-map.
(keymap-set map "C-p" ctl-x-map);; ctl-x-map⇒ [nil ... find-file ... backward-kill-sentence];; Bind C-f to foo in the ctl-x-map.
(keymap-set map "C-p C-f" 'foo)⇒ 'foomap⇒ (keymap; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])(24 keymap(102 . forward-word))(6 . forward-char))

Note that storing a new binding for C-p C-f actually works by changing an entry in ctl-xmap, and this has the effect of changing the bindings of both C-p C-f and C-x C-f in thedefault global map.
keymap-set is the general work horse for defining a key in a keymap. When writing
modes, however, you frequently have to bind a large number of keys at once, and using
keymap-set on them all can be tedious and error-prone. Instead you can use define-keymap,
which creates a keymap and binds a number of keys. See Section 23.4 [Creating Keymaps],
page 483, for details.
The function substitute-key-definition scans a keymap for keys that have a certain
binding and rebinds them with a different binding. Another feature which is cleaner and canoften produce the same results is to remap one command into another (see Section 23.14[Remapping Commands], page 503).

substitute-key-definition olddef newdef keymap &optional
oldmap[Function]

This function replaces olddef with newdef for any keys in keymap that were boundto olddef. In other words, olddef is replaced with newdef wherever it appears. The
function returns nil.

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For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:(substitute-key-definition'find-file 'find-file-read-only (current-global-map))

If oldmap is non-nil, that changes the behavior of substitute-key-definition: thebindings in oldmap determine which keys to rebind. The rebindings still happen in
keymap, not in oldmap. Thus, you can change one map under the control of thebindings in another. For example,(substitute-key-definition'delete-backward-char 'my-funny-delete
my-map global-map)

puts the special deletion command in my-map for whichever keys are globally boundto the standard deletion command.
Here is an example showing a keymap before and after substitution:(setq map (list 'keymap(cons ?1 olddef-1)(cons ?2 olddef-2)(cons ?3 olddef-1)))⇒ (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1))(substitute-key-definition 'olddef-1 'newdef map)
⇒ nil
map
⇒ (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))

suppress-keymap keymap &optional nodigits[Function]
This function changes the contents of the full keymap keymap by remapping
self-insert-command to the command undefined (see Section 23.14 [Remapping
Commands], page 503). This has the effect of undefining all printing characters, thus
making ordinary insertion of text impossible. suppress-keymap returns nil.
If nodigits is nil, then suppress-keymap defines digits to run digit-argument, and- to run negative-argument. Otherwise it makes them undefined like the rest of theprinting characters.
The suppress-keymap function does not make it impossible to modify a buffer, as
it does not suppress commands such as yank and quoted-insert. To prevent any
modification of a buffer, make it read-only (see Section 28.7 [Read Only Buffers],
page 680).
Since this function modifies keymap, you would normally use it on a newly createdkeymap. Operating on an existing keymap that is used for some other purpose is likely
to cause trouble; for example, suppressing global-map would make it impossible touse most of Emacs.
This function can be used to initialize the local keymap of a major mode for whichinsertion of text is not desirable. But usually such a mode should be derived from
special-mode (see Section 24.2.5 [Basic Major Modes], page 536); then its keymap
will automatically inherit from special-mode-map, which is already suppressed. Hereis how special-mode-map is defined:Chapter 23: Keymaps

501(defvar special-mode-map(let ((map (make-sparse-keymap)))(suppress-keymap map)
(keymap-set map "q" 'quit-window)
...
map))

23.13 Low-Level Key Binding
Historically, Emacs has supported a number of different syntaxes for defining keys. The
documented way to bind a key today is to use the syntax supported by key-valid-p,
which is what all the functions like keymap-set and keymap-lookup supports. This section
documents the old-style syntax and interface functions; they should not be used in new code.
define-key (and other low-level functions that are used to rebind keys) understand anumber of different syntaxes for the keys.
A vector containing lists of keys.
You can use a list containing modifier names plus one base event (a characteror function key name). For example, [(control ?a) (meta b)] is equivalent to
C-a M-b and [(hyper control left)] is equivalent to C-H-left.
A string of characters with modifiersInternally, key sequences are often represented as strings using the special escapesequences for shift, control and meta modifiers (see Section 2.4.8 [String Type],
page 20), but this representation can also be used by users when rebinding
keys. A string like "\M-x" is read as containing a single M-x, "\C-f" is readas containing a single C-f, and "\M-\C-x" and "\C-\M-x" are both read ascontaining a single C-M-x.
A vector of characters and key symbols
This is the other internal representation of key sequences. It supports a fuller
range of modifiers than the string representation, and also support function
keys. An example is ‘[?\C-\H-x home]’, which represents the C-H-x home key
sequence. See Section 2.4.3 [Character Type], page 11.

define-key keymap key binding &optional remove[Function]
This function is like keymap-set (see Section 23.12 [Changing Key Bindings], page 497,
but understands only the legacy key syntaxes.
In addition, this function also has a remove argument. If it is non-nil, the definition
will be removed. This is almost the same as setting the definition to nil, but makesa difference if the keymap has a parent, and key is shadowing the same binding in
the parent. With remove, subsequent lookups will return the binding in the parent,
whereas with a nil definition the lookups will return nil.

Here are other legacy key definition functions and commands, with the equivalent modern
function to use instead in new code.

global-set-key key binding[Command]This function sets the binding of key in the current global map to binding. Use
keymap-global-set instead.

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global-unset-key key[Command]This function removes the binding of key from the current global map. Use
keymap-global-unset instead.

local-set-key key binding[Command]This function sets the binding of key in the current local keymap to binding. Use
keymap-local-set instead.

local-unset-key key[Command]This function removes the binding of key from the current local map. Use
keymap-local-unset instead.

substitute-key-definition olddef newdef keymap &optional
oldmap[Function]

This function replaces olddef with newdef for any keys in keymap that were boundto olddef. In other words, olddef is replaced with newdef wherever it appears. The
function returns nil. Use keymap-substitute instead.

define-key-after map key binding &optional after[Function]
Define a binding in map for key, with value binding, just like define-key, but position
the binding in map after the binding for the event after. The argument key should beof length one—a vector or string with just one element. But after should be a single
event type—a symbol or a character, not a sequence. The new binding goes after thebinding for after. If after is t or is omitted, then the new binding goes last, at theend of the keymap. However, new bindings are added before any inherited keymap.
Use keymap-set-after instead of this function.

keyboard-translate from to[Function]
This function modifies keyboard-translate-table to translate character code from
into character code to. It creates the keyboard translate table if necessary. Use
key-translate instead.

key-binding key &optional accept-defaults no-remap position[Function]
This function returns the binding for key according to the current active keymaps.
The result is nil if key is undefined in the keymaps. The argument accept-defaults
controls checking for default bindings, as in lookup-key (see Section 23.11 [Functions
for Key Lookup], page 495). If no-remap is non-nil, key-binding ignores command
remappings (see Section 23.14 [Remapping Commands], page 503) and returns thebinding directly specified for key. The optional argument position should be either abuffer position or an event position like the value of event-start; it tells the function
to consult the maps determined based on that position.
Emacs signals an error if key is not a string or a vector.
Use keymap-lookup instead of this function.

lookup-key keymap key &optional accept-defaults[Function]
This function returns the definition of key in keymap. If the string or vector key is
not a valid key sequence according to the prefix keys specified in keymap, it must be
too long and have extra events at the end that do not fit into a single key sequence.

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Then the value is a number, the number of events at the front of key that compose acomplete key.
If accept-defaults is non-nil, then lookup-key considers default bindings as well asbindings for the specific events in key. Otherwise, lookup-key reports only bindings
for the specific sequence key, ignoring default bindings except when you explicitly ask
about them.
Use keymap-lookup instead of this function.

local-key-binding key &optional accept-defaults[Function]
This function returns the binding for key in the current local keymap, or nil if it isundefined there.
The argument accept-defaults controls checking for default bindings, as in lookup-key(above).

global-key-binding key &optional accept-defaults[Function]
This function returns the binding for command key in the current global keymap, or
nil if it is undefined there.
The argument accept-defaults controls checking for default bindings, as in lookup-key(above).

event-convert-list list

[Function]
This function converts a list of modifier names and a basic event type to an event typewhich specifies all of them. The basic event type must be the last element of the list.
For example,(event-convert-list '(control ?a))⇒ 1(event-convert-list '(control meta ?a))⇒ -134217727(event-convert-list '(control super f1))
⇒ C-s-f1

23.14 Remapping Commands
A special kind of key binding can be used to remap one command to another, without
having to refer to the key sequence(s) bound to the original command. To use this feature,
make a key binding for a key sequence that starts with the dummy event remap, followed by
the command name you want to remap; for the binding, specify the new definition (usually
a command name, but possibly any other valid definition for a key binding).
For example, suppose My mode provides a special command my-kill-line, which should
be invoked instead of kill-line. To establish this, its mode keymap should contain thefollowing remapping:(keymap-set my-mode-map "<remap> <kill-line>" 'my-kill-line)

Then, whenever my-mode-map is active, if the user types C-k (the default global key sequencefor kill-line) Emacs will instead run my-kill-line.
Note that remapping only takes place through active keymaps; for example, putting a
remapping in a prefix keymap like ctl-x-map typically has no effect, as such keymaps areChapter 23: Keymaps

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not themselves active. In addition, remapping only works through a single level; in thefollowing example,(keymap-set my-mode-map "<remap> <kill-line>" 'my-kill-line)(keymap-set my-mode-map "<remap> <my-kill-line>" 'my-other-kill-line)

kill-line is not remapped to my-other-kill-line. Instead, if an ordinary key binding
specifies kill-line, it is remapped to my-kill-line; if an ordinary binding specifies
my-kill-line, it is remapped to my-other-kill-line.
To undo the remapping of a command, remap it to nil; e.g.,(keymap-set my-mode-map "<remap> <kill-line>" nil)command-remapping command &optional position keymaps[Function]
This function returns the remapping for command (a symbol), given the current active
keymaps. If command is not remapped (which is the usual situation), or not a symbol,
the function returns nil. position can optionally specify a buffer position or an
event position to determine the keymaps to use, as in key-binding.
If the optional argument keymaps is non-nil, it specifies a list of keymaps to search
in. This argument is ignored if position is non-nil.

23.15 Keymaps for Translating Sequences of Events
When the read-key-sequence function reads a key sequence (see Section 22.8.1 [KeySequence Input], page 461), it uses translation keymaps to translate certain event sequences
into others. The translation keymaps are input-decode-map, local-function-key-map,and key-translation-map (in order of priority).
Translation keymaps have the same structure as other keymaps, but are used differently:
they specify translations to make while reading key sequences, rather than bindings forcomplete key sequences. As each key sequence is read, it is checked against each translation
keymap. If one of the translation keymaps binds k to a vector v, then whenever k appears
as a sub-sequence anywhere in a key sequence, that sub-sequence is replaced with the events
in v.
For example, VT100 terminals send ESC O P when the keypad key PF1 is pressed. On suchterminals, Emacs must translate that sequence of events into a single event pf1. This is done
by binding ESC O P to [pf1] in input-decode-map. Thus, when you type C-c PF1 on theterminal, the terminal emits the character sequence C-c ESC O P, and read-key-sequencetranslates this back into C-c PF1 and returns it as the vector [?\C-c pf1].
Translation keymaps take effect only after Emacs has decoded the keyboard input (via the
input coding system specified by keyboard-coding-system). See Section 34.10.8 [Terminal
I/O Encoding], page 990.
[Variable]
This variable holds a keymap that describes the character sequences sent by function
keys on an ordinary character terminal.
The value of input-decode-map is usually set up automatically according to theterminal’s Terminfo or Termcap entry, but sometimes those need help from terminalspecific Lisp files. Emacs comes with terminal-specific files for many common terminals;
their main purpose is to make entries in input-decode-map beyond those that can be
deduced from Termcap and Terminfo. See Section 42.1.3 [Terminal-Specific], page 1260.

input-decode-map

Chapter 23: Keymaps

505[Variable]
This variable holds a keymap similar to input-decode-map except that it describes
key sequences which should be translated to alternative interpretations that are usually
preferred. It applies after input-decode-map and before key-translation-map.

local-function-key-map

Entries in local-function-key-map are ignored if they conflict with bindings madein the minor mode, local, or global keymaps. I.e., the remapping only applies if theoriginal key sequence would otherwise not have any binding.
local-function-key-map inherits from function-key-map. The latter should only
be altered if you want the binding to apply in all terminals, so using the former isalmost always preferred.

[Variable]
This variable is another keymap used just like input-decode-map to translate input
events into other events. It differs from input-decode-map in that it goes to work
after local-function-key-map is finished rather than before; it receives the resultsof translation by local-function-key-map.

key-translation-map

Just like input-decode-map, but unlike local-function-key-map, this keymap is applied regardless of whether the input key-sequence has a normal binding. Note howeverthat actual key bindings can have an effect on key-translation-map, even though
they are overridden by it. Indeed, actual key bindings override local-functionkey-map and thus may alter the key sequence that key-translation-map receives.
Clearly, it is better to avoid this type of situation.
The intent of key-translation-map is for users to map one character set to another,including ordinary characters normally bound to self-insert-command.

You can use input-decode-map, local-function-key-map, and key-translation-map
for more than simple aliases, by using a function, instead of a key sequence, as the translationof a key. Then this function is called to compute the translation of that key.
The key translation function receives one argument, which is the prompt that was specified
in read-key-sequence—or nil if the key sequence is being read by the editor command
loop. In most cases you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering the event that follows.
For example, here’s how to define C-c h to turn the character that follows into a Hypercharacter:Chapter 23: Keymaps

506(defun hyperify (prompt)(let ((e (read-event)))(vector (if (numberp e)(logior (ash 1 24) e)(if (memq 'hyper (event-modifiers e))e(add-event-modifier "H-" e))))))(defun add-event-modifier (string e)(let ((symbol (if (symbolp e) e (car e))))(setq symbol (intern (concat string(symbol-name symbol))))(if (symbolp e)
symbol(cons symbol (cdr e)))))(keymap-set local-function-key-map "C-c h" 'hyperify)

23.15.1 Interaction with normal keymaps
The end of a key sequence is detected when that key sequence either is bound to a command,or when Emacs determines that no additional event can lead to a sequence that is bound to
a command.
This means that, while input-decode-map and key-translation-map apply regardlessof whether the original key sequence would have a binding, the presence of such a binding
can still prevent translation from taking place. For example, let us return to our VT100
example above and add a binding for C-c ESC to the global map; now when the user hits
C-c PF1 Emacs will fail to decode C-c ESC O P into C-c PF1 because it will stop reading
keys right after C-c ESC, leaving O P for later. This is in case the user really hit C-c ESC, inwhich case Emacs should not sit there waiting for the next key to decide whether the user
really pressed ESC or PF1.
For that reason, it is better to avoid binding commands to key sequences where the end of
the key sequence is a prefix of a key translation. The main such problematic suffixes/prefixes
are ESC, M-O (which is really ESC O) and M-[ (which is really ESC [).

23.16 Commands for Binding Keys
This section describes some convenient interactive interfaces for changing key bindings. They
work by calling keymap-set (see Section 23.12 [Changing Key Bindings], page 497). In
interactive use, these commands prompt for the argument key and expect the user to type avalid key sequence; they also prompt for the binding of the key sequence, and expect thename of a command (i.e., a symbol that satisfies commandp, see Section 22.3 [InteractiveCall], page 432). When called from Lisp, these commands expect key to be a string thatsatisfies key-valid-p (see Section 23.1 [Key Sequences], page 480), and binding to be any
Lisp object that is meaningful in a keymap (see Section 23.10 [Key Lookup], page 494).
People often use keymap-global-set in their init files (see Section 42.1.2 [Init File],
page 1258) for simple customization. For example,(keymap-global-set "C-x C-\\" 'next-line)

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redefines C-x C-\ to move down a line.
(keymap-global-set "M-<mouse-1>" 'mouse-set-point)

redefines the first (leftmost) mouse button, entered with the Meta key, to set point where
you click.
Be careful when using non-ASCII text characters in Lisp specifications of keys to bind.
If these are read as multibyte text, as they usually will be in a Lisp file (see Section 16.4
[Loading Non-ASCII], page 304), you must type the keys as multibyte too. For instance, if
you use this:(keymap-global-set "ö" 'my-function) ; bind o-umlaut

and your language environment is multibyte Latin-1, these commands actually bind themultibyte character with code 246, not the byte code 246 (M-v) sent by a Latin-1 terminal.
In order to use this binding, you need to teach Emacs how to decode the keyboard by using
an appropriate input method (see Section “Input Methods” in The GNU Emacs Manual).

keymap-global-set key binding[Command]This function sets the binding of key in the current global map to binding.
(keymap-global-set key binding)≡(keymap-set (current-global-map) key binding)keymap-global-unset key[Command]This function removes the binding of key from the current global map.
One use of this function is in preparation for defining a longer key that uses key as aprefix—which would not be allowed if key has a non-prefix binding. For example:(keymap-global-unset "C-l")⇒ nil(keymap-global-set "C-l C-l" 'redraw-display)⇒ nilkeymap-local-set key binding[Command]This function sets the binding of key in the current local keymap to binding.
(keymap-local-set key binding)≡(keymap-set (current-local-map) key binding)keymap-local-unset key[Command]This function removes the binding of key from the current local map.

23.17 Scanning Keymaps
This section describes functions used to scan all the current keymaps for the sake ofprinting help information. To display the bindings in a particular keymap, you can use
the describe-keymap command (see Section “Other Help Commands” in The GNU Emacs
Manual)accessible-keymaps keymap &optional prefix[Function]
This function returns a list of all the keymaps that can be reached (via zero or more
prefix keys) from keymap. The value is an association list with elements of the form
(key . map), where key is a prefix key whose definition in keymap is map.

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The elements of the alist are ordered so that the key increases in length. The firstelement is always ([] . keymap), because the specified keymap is accessible from itself
with a prefix of no events.
If prefix is given, it should be a prefix key sequence; then accessible-keymaps
includes only the submaps whose prefixes start with prefix. These elements look justas they do in the value of (accessible-keymaps); the only difference is that someelements are omitted.
In the example below, the returned alist indicates that the key ESC, which is displayed as ‘^[’, is a prefix key whose definition is the sparse keymap (keymap (83 .
center-paragraph) (115 . foo)).
(accessible-keymaps (current-local-map))⇒(([] keymap(27 keymap; Note this keymap for ESC is repeated below.
(83 . center-paragraph)(115 . center-line))(9 . tab-to-tab-stop))("^[" keymap(83 . center-paragraph)(115 . foo)))In the following example, C-h is a prefix key that uses a sparse keymap starting with(keymap (118 . describe-variable)...). Another prefix, C-x 4, uses a keymap
which is also the value of the variable ctl-x-4-map. The event mode-line is one ofseveral dummy events used as prefixes for mouse actions in special parts of a window.
(accessible-keymaps (current-global-map))⇒ (([] keymap [set-mark-command beginning-of-line ...
delete-backward-char])("^H" keymap (118 . describe-variable) ...
(8 . help-for-help))("^X" keymap [x-flush-mouse-queue ...
backward-kill-sentence])("^[" keymap [mark-sexp backward-sexp ...
backward-kill-word])("^X4" keymap (15 . display-buffer) ...)([mode-line] keymap(S-mouse-2 . mouse-split-window-horizontally) ...))

These are not all the keymaps you would see in actuality.

map-keymap function keymap[Function]
The function map-keymap calls function once for each binding in keymap. It passes
two arguments, the event type and the value of the binding. If keymap has a parent,
the parent’s bindings are included as well. This works recursively: if the parent has
itself a parent, then the grandparent’s bindings are also included and so on.

This function is the cleanest way to examine all the bindings in a keymap.

where-is-internal command &optional keymap firstonly noindirect
no-remap[Function]

This function is a subroutine used by the where-is command (see Section “Help” in
The GNU Emacs Manual). It returns a list of all key sequences (of any length) thatare bound to command in a set of keymaps.

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The argument command can be any object; it is compared with all keymap entries
using eq.
If keymap is nil, then the maps used are the current active keymaps, disregarding
overriding-local-map (that is, pretending its value is nil). If keymap is a keymap,
then the maps searched are keymap and the global keymap. If keymap is a list of
keymaps, only those keymaps are searched.
Usually it’s best to use overriding-local-map as the expression for keymap. Then
where-is-internal searches precisely the keymaps that are active. To search only
the global map, pass the value (keymap) (an empty keymap) as keymap.
If firstonly is non-ascii, then the value is a single vector representing the first key
sequence found, rather than a list of all possible key sequences. If firstonly is t, thenthe value is the first key sequence, except that key sequences consisting entirely of
ASCII characters (or meta variants of ASCII characters) are preferred to all other key
sequences and that the return value can never be a menu binding.
If noindirect is non-nil, where-is-internal doesn’t look inside menu-items to findtheir commands. This makes it possible to search for a menu-item itself.
The fifth argument, no-remap, determines how this function treats command remappings (see Section 23.14 [Remapping Commands], page 503). There are two cases ofinterest:
If a command other-command is remapped to command:
If no-remap is nil, find the bindings for other-command and treat themas though they are also bindings for command. If no-remap is non-nil,include the vector [remap other-command] in the list of possible key
sequences, instead of finding those bindings.
If command is remapped to other-command:
If no-remap is nil, return the bindings for other-command rather thancommand. If no-remap is non-nil, return the bindings for command,
ignoring the fact that it is remapped.
If a command maps to a key binding like [some-event], and some-event has a symbol
plist containing a non-nil non-key-event property, then that binding is ignored bywhere-is-internal.

describe-bindings &optional prefix buffer-or-name[Command]This function creates a listing of all current key bindings, and displays it in a buffer
named *Help*. The text is grouped by modes—minor modes first, then the majormode, then global bindings.
If prefix is non-nil, it should be a prefix key; then the listing includes only keys thatstart with prefix.
When several characters with consecutive ASCII codes have the same definition, they
are shown together, as ‘firstchar..lastchar’. In this instance, you need to know
the ASCII codes to understand which characters this means. For example, in thedefault global map, the characters ‘SPC .. ~’ are described by a single line. SPC is
ASCII 32, ~ is ASCII 126, and the characters between them include all the normal
printing characters, (e.g., letters, digits, punctuation, etc.); all these characters arebound to self-insert-command.

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If buffer-or-name is non-nil, it should be a buffer or a buffer name. Then
describe-bindings lists that buffer’s bindings, instead of the current buffer’s.

23.18 Menu Keymaps
A keymap can operate as a menu as well as defining bindings for keyboard keys and mousebuttons. Menus are usually actuated with the mouse, but they can function with the
keyboard also. If a menu keymap is active for the next input event, that activates the
keyboard menu feature.

23.18.1 Defining Menus
A keymap acts as a menu if it has an overall prompt string, which is a string that appears
as an element of the keymap. (See Section 23.3 [Format of Keymaps], page 481.) The string
should describe the purpose of the menu’s commands. Emacs displays the overall prompt
string as the menu title in some cases, depending on the toolkit (if any) used for displaying
menus.1 Keyboard menus also display the overall prompt string.
The easiest way to construct a keymap with a prompt string is to specify the string as
an argument when you call make-keymap, make-sparse-keymap (see Section 23.4 [Creating
Keymaps], page 483), or define-prefix-command (see [Definition of define-prefix-command],page 489). If you do not want the keymap to operate as a menu, don’t specify a prompt
string for it.

keymap-prompt keymap[Function]
This function returns the overall prompt string of keymap, or nil if it has none.

The menu’s items are the bindings in the keymap. Each binding associates an event typeto a definition, but the event types have no significance for the menu appearance. (Usually
we use pseudo-events, symbols that the keyboard cannot generate, as the event types formenu item bindings.) The menu is generated entirely from the bindings that correspond in
the keymap to these events.
The order of items in the menu is the same as the order of bindings in the keymap. Since
define-key puts new bindings at the front, you should define the menu items starting at thebottom of the menu and moving to the top, if you care about the order. When you add anitem to an existing menu, you can specify its position in the menu using keymap-set-after(see Section 23.18.7 [Modifying Menus], page 521).

23.18.1.1 Simple Menu Items
The simpler (and original) way to define a menu item is to bind some event type (it doesn’t
matter what event type) to a binding like this:(item-string . real-binding)
The car, item-string, is the string to be displayed in the menu. It should be short—preferably
one to three words. It should describe the action of the command it corresponds to. Notethat not all graphical toolkits can display non-ASCII text in menus (it will work for keyboard
menus and will work to a large extent with the GTK+ toolkit).
1

It is required for menus which do not use a toolkit, e.g., on a text terminal.

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You can also supply a second string, called the help string, as follows:(item-string help . real-binding)help specifies a help-echo string to display while the mouse is on that item in the same way
as help-echo text properties (see [Help display], page 931).
As far as define-key is concerned, item-string and help-string are part of the event’s
binding. However, lookup-key returns just real-binding, and only real-binding is used forexecuting the key.
If real-binding is nil, then item-string appears in the menu but cannot be selected.
If real-binding is a symbol and has a non-nil menu-enable property, that property is anexpression that controls whether the menu item is enabled. Every time the keymap is used
to display a menu, Emacs evaluates the expression, and it enables the menu item only if
the expression’s value is non-nil. When a menu item is disabled, it is displayed in a fuzzy
fashion, and cannot be selected.
The menu bar does not recalculate which items are enabled every time you look at amenu. This is because the X toolkit requires the whole tree of menus in advance. To force
recalculation of the menu bar, call force-mode-line-update (see Section 24.4 [Mode Line
Format], page 550).

23.18.1.2 Extended Menu Items
An extended-format menu item is a more flexible and also cleaner alternative to the simple
format. You define an event type with a binding that’s a list starting with the symbol
menu-item. For a non-selectable string, the binding looks like this:(menu-item item-name)
A string starting with two or more dashes specifies a separator line; see Section 23.18.1.3[Menu Separators], page 513.
To define a real menu item which can be selected, the extended format binding looks likethis:(menu-item item-name real-binding. item-property-list)
Here, item-name is an expression which evaluates to the menu item string. Thus, the stringneed not be a constant.
The third element, real-binding, can be the command to execute (in which case you
get a normal menu item). It can also be a keymap, which will result in a submenu, anditem-name is used as the submenu name. Finally, it can be nil, in which case you will get a
non-selectable menu item. This is mostly useful when creating separator lines and the like.
The tail of the list, item-property-list, has the form of a property list (see Section 5.9[Property Lists], page 99) which contains other information.
Here is a table of the properties that are supported::enable form
The result of evaluating form determines whether the item is enabled (non-nil
means yes). If the item is not enabled, you can’t really click on it.

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512:visible form
The result of evaluating form determines whether the item should actuallyappear in the menu (non-nil means yes). If the item does not appear, then themenu is displayed as if this item were not defined at all.
:help help
The value of this property, help, specifies a help-echo string to display while themouse is on that item. This is displayed in the same way as help-echo text
properties (see [Help display], page 931). Note that this must be a constantstring, unlike the help-echo property for text and overlays.
:button (type . selected)
This property provides a way to define radio buttons and toggle buttons. The
car, type, says which: it should be :toggle or :radio. The cdr, selected,
should be a form; the result of evaluating it says whether this button is currently
selected.
A toggle is a menu item which is labeled as either on or off according to thevalue of selected. The command itself should toggle selected, setting it to t
if it is nil, and to nil if it is t. Here is how the menu item to toggle thedebug-on-error flag is defined:(menu-item "Debug on Error" toggle-debug-on-error:button (:toggle. (and (boundp 'debug-on-error)
debug-on-error)))This works because toggle-debug-on-error is defined as a command which
toggles the variable debug-on-error.
Radio buttons are a group of menu items, in which at any time one and only one
is selected. There should be a variable whose value says which one is selected at
any time. The selected form for each radio button in the group should check
whether the variable has the right value for selecting that button. Clicking on
the button should set the variable so that the button you clicked on becomesselected.
:key-sequence key-sequenceThis property specifies which key sequence to display as keyboard equivalent.
Before Emacs displays key-sequence in the menu, it verifies that key-sequenceis really equivalent to this menu item, so it only has an effect if you specify
a correct key sequence. Specifying nil for key-sequence is equivalent to the:key-sequence attribute being absent.
:keys string
This property specifies that string is the string to display as the keyboard
equivalent for this menu item. You can use the ‘\\[...]’ documentation
construct in string.
This property can also be a function (which will be called with no arguments).
This function should return a string. This function will be called every time themenu is computed, so using a function that takes a lot of time to compute is
not a good idea, and it should expect to be called from any context.

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513:filter filter-fn
This property provides a way to compute the menu item dynamically. The
property value filter-fn should be a function of one argument; when it is called,
its argument will be real-binding. The function should return the binding touse instead.
Emacs can call this function at any time that it does redisplay or operates onmenu data structures, so you should write it so it can safely be called at any
time.

23.18.1.3 Menu Separators
A menu separator is a kind of menu item that doesn’t display any text—instead, it divides
the menu into subparts with a horizontal line. A separator looks like this in the menu
keymap:(menu-item separator-type)where separator-type is a string starting with two or more dashes.
In the simplest case, separator-type consists of only dashes. That specifies the default
kind of separator. (For compatibility, "" and - also count as separators.)
Certain other values of separator-type specify a different style of separator. Here is atable of them:"--no-line""--space"
An extra vertical space, with no actual line.
"--single-line"
A single line in the menu’s foreground color.
"--double-line"
A double line in the menu’s foreground color.
"--single-dashed-line"
A single dashed line in the menu’s foreground color.
"--double-dashed-line"
A double dashed line in the menu’s foreground color.
"--shadow-etched-in"
A single line with a 3D sunken appearance. This is the default, used separators
consisting of dashes only.
"--shadow-etched-out"
A single line with a 3D raised appearance.
"--shadow-etched-in-dash"
A single dashed line with a 3D sunken appearance.
"--shadow-etched-out-dash"
A single dashed line with a 3D raised appearance.
"--shadow-double-etched-in"
Two lines with a 3D sunken appearance.

Chapter 23: Keymaps

514"--shadow-double-etched-out"
Two lines with a 3D raised appearance.
"--shadow-double-etched-in-dash"Two dashed lines with a 3D sunken appearance.
"--shadow-double-etched-out-dash"Two dashed lines with a 3D raised appearance.
You can also give these names in another style, adding a colon after the double-dash andreplacing each single dash with capitalization of the following word. Thus, "--:singleLine",
is equivalent to "--single-line".
You can use a longer form to specify keywords such as :enable and :visible for a menu
separator:(menu-item separator-type nil . item-property-list)
For example:(menu-item "--" nil :visible (boundp 'foo))
Some systems and display toolkits don’t really handle all of these separator types. If
you use a type that isn’t supported, the menu displays a similar kind of separator that is
supported.

23.18.1.4 Alias Menu Items
Sometimes it is useful to make menu items that use the same command but with different
enable conditions. The best way to do this in Emacs now is with extended menu items;
before that feature existed, it could be done by defining alias commands and using them inmenu items. Here’s an example that makes two aliases for read-only-mode and gives themdifferent enable conditions:(defalias 'make-read-only 'read-only-mode)(put 'make-read-only 'menu-enable '(not buffer-read-only))(defalias 'make-writable 'read-only-mode)(put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the equivalent key bindings forthe real command name, not the aliases (which typically don’t have any key bindings except
for the menu itself). To request this, give the alias symbol a non-nil menu-alias property.
Thus,(put 'make-read-only 'menu-alias t)(put 'make-writable 'menu-alias t)causes menu items for make-read-only and make-writable to show the keyboard bindings
for read-only-mode.

23.18.2 Menus and the Mouse
The usual way to make a menu keymap produce a menu is to make it the definition of aprefix key. (A Lisp program can explicitly pop up a menu and receive the user’s choice—see
Section 30.17 [Pop-Up Menus], page 837.)
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping
up a visible menu, so that the user can select a choice with the mouse. When the user clicks

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on a menu item, the event generated is whatever character or symbol has the binding thatbrought about that menu item. (A menu item may generate a series of events if the menu
has multiple levels or comes from the menu bar.)It’s often best to use a button-down event to trigger the menu. Then the user can selecta menu item by releasing the button.
If the menu keymap contains a binding to a nested keymap, the nested keymap specifies
a submenu. There will be a menu item, labeled by the nested keymap’s item string, andclicking on this item automatically pops up the specified submenu. As a special exception,
if the menu keymap contains a single nested keymap and no other menu items, the menu
shows the contents of the nested keymap directly, not as a submenu.
However, if Emacs is compiled without X toolkit support, or on text terminals, submenus
are not supported. Each nested keymap is shown as a menu item, but clicking on it does not
automatically pop up the submenu. If you wish to imitate the effect of submenus, you cando that by giving a nested keymap an item string which starts with ‘@’. This causes Emacs
to display the nested keymap using a separate menu pane; the rest of the item string afterthe ‘@’ is the pane label. If Emacs is compiled without X toolkit support, or if a menu isdisplayed on a text terminal, menu panes are not used; in that case, a ‘@’ at the beginningof an item string is omitted when the menu label is displayed, and has no other effect.

23.18.3 Menus and the Keyboard
When a prefix key ending with a keyboard event (a character or function key) has a definition
that is a menu keymap, the keymap operates as a keyboard menu; the user specifies thenext event by choosing a menu item with the keyboard.
Emacs displays the keyboard menu with the map’s overall prompt string, followed by
the alternatives (the item strings of the map’s bindings), in the echo area. If the bindings
don’t all fit at once, the user can type SPC to see the next line of alternatives. Successive
uses of SPC eventually get to the end of the menu and then cycle around to the beginning.
(The variable menu-prompt-more-char specifies which character is used for this; SPC is thedefault.)
When the user has found the desired alternative from the menu, he or she should typethe corresponding character—the one whose binding is that alternative.
[Variable]
This variable specifies the character to use to ask to see the next line of a menu. Its
initial value is 32, the code for SPC.

menu-prompt-more-char

23.18.4 Menu Example
Here is a complete example of defining a menu keymap. It is the definition of the ‘Replace’submenu in the ‘Edit’ menu in the menu bar, and it uses the extended menu item format(see Section 23.18.1.2 [Extended Menu Items], page 511). First we create the keymap, andgive it a name:(defvar menu-bar-replace-menu (make-sparse-keymap "Replace"))

Next we define the menu items:(define-key menu-bar-replace-menu [tags-repl-continue]'(menu-item "Continue Replace" multifile-continue:help "Continue last tags replace operation"))Chapter 23: Keymaps

516(define-key menu-bar-replace-menu [tags-repl]'(menu-item "Replace in tagged files" tags-query-replace:help "Interactively replace a regexp in all tagged files"))(define-key menu-bar-replace-menu [separator-replace-tags]'(menu-item "--"));; . . .

Note the symbols which the bindings are made for; these appear inside square brackets, inthe key sequence being defined. In some cases, this symbol is the same as the command
name; sometimes it is different. These symbols are treated as function keys, but they are
not real function keys on the keyboard. They do not affect the functioning of the menu
itself, but they are echoed in the echo area when the user selects from the menu, and they
appear in the output of where-is and apropos.
The menu in this example is intended for use with the mouse. If a menu is intended
for use with the keyboard, that is, if it is bound to a key sequence ending with a keyboard
event, then the menu items should be bound to characters or real function keys, that can be
typed with the keyboard.
The binding whose definition is ("--") is a separator line. Like a real menu item, theseparator has a key symbol, in this case separator-replace-tags. If one menu has two
separators, they must have two different key symbols.
Here is how we make this menu appear as an item in the parent menu:(define-key menu-bar-edit-menu [replace](list 'menu-item "Replace" menu-bar-replace-menu))
Note that this incorporates the submenu keymap, which is the value of the variable menu-barreplace-menu, rather than the symbol menu-bar-replace-menu itself. Using that symbolin the parent menu item would be meaningless because menu-bar-replace-menu is not acommand.
If you wanted to attach the same replace menu to a mouse click, you can do it this way:
(define-key global-map [C-S-down-mouse-1]
menu-bar-replace-menu)

23.18.5 The Menu Bar
Emacs usually shows a menu bar at the top of each frame. See Section “Menu Bars” in The
GNU Emacs Manual. Menu bar items are subcommands of the fake function key MENU-BAR,
as defined in the active keymaps.
To add an item to the menu bar, invent a fake function key of your own (let’s call itkey), and make a binding for the key sequence [menu-bar key]. Most often, the binding isa menu keymap, so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same function key for the menu bar,
the item appears just once. If the user clicks on that menu bar item, it brings up a single,
combined menu containing all the subcommands of that item—the global subcommands,
the local subcommands, and the minor mode subcommands.
The variable overriding-local-map is normally ignored when determining the menu
bar contents. That is, the menu bar is computed from the keymaps that would be active if
overriding-local-map were nil. See Section 23.7 [Active Keymaps], page 489.

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517

Here’s an example of setting up a menu bar item:;; Make a menu keymap (with a prompt string);; and make it the menu bar item’s definition.
(define-key global-map [menu-bar words](cons "Words" (make-sparse-keymap "Words")));; Define specific subcommands in this menu.
(define-key global-map[menu-bar words forward]'("Forward word" . forward-word))(define-key global-map[menu-bar words backward]'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by rebinding
the same fake function key with undefined as the binding. For example, this is how Dired
suppresses the ‘Edit’ menu bar item:(define-key dired-mode-map [menu-bar edit] 'undefined)
Here, edit is the symbol produced by a fake function key, it is used by the global map forthe ‘Edit’ menu bar item. The main reason to suppress a global menu bar item is to regain
space for mode-specific items.
[Variable]
Normally the menu bar shows global items followed by items defined by the local
maps.
This variable holds a list of fake function keys for items to display at the end of themenu bar rather than in normal sequence. The default value is (help-menu); thus,
the ‘Help’ menu item normally appears at the end of the menu bar, following local
menu items.

menu-bar-final-items[Variable]
This normal hook is run by redisplay to update the menu bar contents, before
redisplaying the menu bar. You can use it to update menus whose contents shouldvary. Since this hook is run frequently, we advise you to ensure that the functions it
calls do not take much time in the usual case.

menu-bar-update-hook

Next to every menu bar item, Emacs displays a key binding that runs the same command(if such a key binding exists). This serves as a convenient hint for users who do not know
the key binding. If a command has multiple bindings, Emacs normally displays the first one
it finds. You can specify one particular key binding by assigning an :advertised-binding
symbol property to the command. See Section 25.3 [Keys in Documentation], page 598.

23.18.6 Tool bars
A tool bar is a row of clickable icons at the top of a frame, just below the menu bar. See
Section “Tool Bars” in The GNU Emacs Manual. Emacs normally shows a tool bar ongraphical displays.
On each frame, the frame parameter tool-bar-lines controls how many lines’ worthof height to reserve for the tool bar. A zero value suppresses the tool bar. If the value

Chapter 23: Keymaps518

is nonzero, and auto-resize-tool-bars is non-nil, the tool bar expands and contracts
automatically as needed to hold the specified contents. If the value is grow-only, the tool
bar expands automatically, but does not contract automatically.
The tool bar contents are controlled by a menu keymap attached to a fake function key
called TOOL-BAR (much like the way the menu bar is controlled). So you define a tool bar
item using define-key, like this:(define-key global-map [tool-bar key] item)
where key is a fake function key to distinguish this item from other items, and item is amenu item key binding (see Section 23.18.1.2 [Extended Menu Items], page 511), which says
how to display this item and how it behaves.
The usual menu keymap item properties, :visible, :enable, :button, and :filter,
are useful in tool bar bindings and have their normal meanings. The real-binding in theitem must be a command, not a keymap; in other words, it does not work to define a tool
bar icon as a prefix key.
The :help property specifies a help-echo string to display while the mouse is on that
item. This is displayed in the same way as help-echo text properties (see [Help display],
page 931).
In addition, you should use the :image property; this is how you specify the image todisplay in the tool bar:
:image image
image is either a single image specification (see Section 41.17 [Images], page 1206)
or a vector of four image specifications. If you use a vector of four, one of themis used, depending on circumstances:
item 0Used when the item is enabled and selected.

item 1

Used when the item is enabled and deselected.

item 2

Used when the item is disabled and selected.

item 3

Used when the item is disabled and deselected.

The GTK+ and NS versions of Emacs ignores items 1 to 3, because disabled and/or
deselected images are autocomputed from item 0.
If image is a single image specification, Emacs draws the tool bar button in disabledstate by applying an edge-detection algorithm to the image.
The :rtl property specifies an alternative image to use for right-to-left languages. Only
the GTK+ version of Emacs supports this at present.
Some toolkits display both an image and a text in the toolbar. If you want to force using
only the image, use a :vert-only non-nil property.
Like the menu bar, the tool bar can display separators (see Section 23.18.1.3 [MenuSeparators], page 513). Tool bar separators are vertical rather than horizontal, though, andonly a single style is supported. They are represented in the tool bar keymap by (menu-item"--") entries; properties like :visible are not supported for tool bar separators. Separators
are rendered natively in GTK+ and Nextstep tool bars; in the other cases, they are renderedusing an image of a vertical line.

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The default tool bar is defined so that items specific to editing do not appear for major
modes whose command symbol has a mode-class property of special (see Section 24.2.1[Major Mode Conventions], page 528). Major modes may add items to the global bar bybinding [tool-bar foo] in their local map. It makes sense for some major modes to replace
the default tool bar items completely, since not many can be accommodated conveniently,
and the default bindings make this easy by using an indirection through tool-bar-map.
[Variable]
By default, the global map binds [tool-bar] as follows:(keymap-global-set "<tool-bar>"`(menu-item ,(purecopy "tool bar") ignore:filter tool-bar-make-keymap))
The function tool-bar-make-keymap, in turn, derives the actual tool bar map dynamically from the value of the variable tool-bar-map. Hence, you should normally adjust
the default (global) tool bar by changing that map. Some major modes, such as Infomode, completely replace the global tool bar by making tool-bar-map buffer-local
and setting it to a different keymap.

tool-bar-map

There are two convenience functions for defining tool bar items, as follows.

tool-bar-add-item icon def key &rest props[Function]
This function adds an item to the tool bar by modifying tool-bar-map. The image
to use is defined by icon, which is the base name of an XPM, XBM or PBM image file
to be located by find-image. Given a value ‘"exit"’, say, exit.xpm, exit.pbm andexit.xbm would be searched for in that order on a color display. On a monochrome
display, the search order is ‘.pbm’, ‘.xbm’ and ‘.xpm’. The binding to use is thecommand def, and key is the fake function key symbol in the prefix keymap. The
remaining arguments props are additional property list elements to add to the menu
item specification.
To define items in some local map, bind tool-bar-map with let around calls of thisfunction:(defvar foo-tool-bar-map(let ((tool-bar-map (make-sparse-keymap)))(tool-bar-add-item ...)...
tool-bar-map))

tool-bar-add-item-from-menu command icon &optional map &rest
props[Function]

This function is a convenience for defining tool bar items which are consistent withexisting menu bar bindings. The binding of command is looked up in the menu bar inmap (default global-map) and modified to add an image specification for icon, which
is found in the same way as by tool-bar-add-item. The resulting binding is thenplaced in tool-bar-map, so use this function only for global tool bar items.
map must contain an appropriate keymap bound to [menu-bar]. The remainingarguments props are additional property list elements to add to the menu item
specification.

Chapter 23: Keymaps

tool-bar-local-item-from-menu command icon in-map &optional
from-map &rest props

520[Function]

This function is used for making non-global tool bar items. Use it like tool-bar-additem-from-menu except that in-map specifies the local map to make the definition in.
The argument from-map is like the map argument of tool-bar-add-item-from-menu.
[Variable]
If this variable is non-nil, the tool bar automatically resizes to show all defined tool
bar items—but not larger than a quarter of the frame’s height.
If the value is grow-only, the tool bar expands automatically, but does not contract
automatically. To contract the tool bar, the user has to redraw the frame by entering
C-l.
If Emacs is built with GTK+ or Nextstep, the tool bar can only show one line, so thisvariable has no effect.

auto-resize-tool-bars[Variable]
If this variable is non-nil, tool bar items display in raised form when the mouse moves
over them.

auto-raise-tool-bar-buttons[Variable]
This variable specifies an extra margin to add around tool bar items. The value is an
integer, a number of pixels. The default is 4.

tool-bar-button-margin[Variable]
This variable specifies the shadow width for tool bar items. The value is an integer, anumber of pixels. The default is 1.

tool-bar-button-relief[Variable]
This variable specifies the height of the border drawn below the tool bar area. An
integer specifies height as a number of pixels. If the value is one of internal-borderwidth (the default) or border-width, the tool bar border height corresponds to thecorresponding frame parameter.

tool-bar-border

You can define a special meaning for clicking on a tool bar item with the shift, control,
meta, etc., modifiers. You do this by setting up additional items that relate to the originalitem through the fake function keys. Specifically, the additional items should use the modified
versions of the same fake function key used to name the original item.
Thus, if the original item was defined this way,
(define-key global-map [tool-bar shell]'(menu-item "Shell" shell:image (image :type xpm :file "shell.xpm")))then here is how you can define clicking on the same tool bar image with the shift modifier:(define-key global-map [tool-bar S-shell] 'some-command)
See Section 22.7.2 [Function Keys], page 441, for more information about how to add
modifiers to function keys.
If you have functions that change whether a tool bar item is enabled or not, this status
is not necessarily updated visually immediately. To force recalculation of the tool bar, callforce-mode-line-update (see Section 24.4 [Mode Line Format], page 550).

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23.18.7 Modifying Menus
When you insert a new item in an existing menu, you probably want to put it in a particularplace among the menu’s existing items. If you use define-key to add the item, it normallygoes at the front of the menu. To put it elsewhere in the menu, use keymap-set-after:

keymap-set-after map key binding &optional after[Function]
Define a binding in map for key, with value binding, just like keymap-set (seeSection 23.12 [Changing Key Bindings], page 497), but position the binding in map
after the binding for the event after. The argument key should represent a single
menu item or key, and should satisfy key-valid-p (see Section 23.1 [Key Sequences],
page 480). after should be a single event type—a symbol or a character, not a sequence.
The new binding goes after the binding for after. If after is t or is omitted, then the
new binding goes last, at the end of the keymap. However, new bindings are added
before any inherited keymap.
Here is an example:(keymap-set-after my-menu "<drink>"'("Drink" . drink-command) 'eat)
makes a binding for the fake function key DRINK and puts it right after the binding
for EAT.
Here is how to insert an item called ‘Work’ in the ‘Signals’ menu of Shell mode, after
the item break:(keymap-set-after shell-mode-map "<menu-bar> <signals> <work>"'("Work" . work-command) 'break)23.18.8 Easy Menu
The following macro provides a convenient way to define pop-up menus and/or menu bar
menus.

easy-menu-define symbol maps doc menu

[Macro]This macro defines a pop-up menu and/or menu bar submenu, whose contents are
given by menu.
If symbol is non-nil, it should be a symbol; then this macro defines symbol as afunction for popping up the menu (see Section 30.17 [Pop-Up Menus], page 837), withdoc as its documentation string. symbol should not be quoted.
Regardless of the value of symbol, if maps is a keymap, the menu is added to that
keymap, as a top-level menu for the menu bar (see Section 23.18.5 [Menu Bar],
page 516). It can also be a list of keymaps, in which case the menu is added separately
to each of those keymaps.
The first element of menu must be a string, which serves as the menu label. It may befollowed by any number of the following keyword-argument pairs::filter function
function must be a function which, if called with one argument—the listof the other menu items—returns the actual items to be displayed in themenu.

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522:visible include
include is an expression; if it evaluates to nil, the menu is made invisible.
:included is an alias for :visible.
:active enableenable is an expression; if it evaluates to nil, the menu is not selectable.
:enable is an alias for :active.
The remaining elements in menu are menu items.
A menu item can be a vector of three elements, [name callback enable]. name is
the menu item name (a string). callback is a command to run, or an expression toevaluate, when the item is chosen. enable is an expression; if it evaluates to nil, theitem is disabled for selection.
Alternatively, a menu item may have the form:[ name callback [ keyword arg ]... ]where name and callback have the same meanings as above, and each optional keyword
and arg pair should be one of the following::keys keys
keys is a string to display as keyboard equivalent to the menu item. This isnormally not needed, as keyboard equivalents are computed automatically.
keys is expanded with substitute-command-keys before it is displayed(see Section 25.3 [Keys in Documentation], page 598).
:key-sequence keys
keys is a hint indicating which key sequence to display as keyboard
equivalent, in case the command is bound to several key sequences. It has
no effect if keys is not bound to same command as this menu item.
:active enableenable is an expression; if it evaluates to nil, the item is made unselectable.
:enable is an alias for :active.
:visible include
include is an expression; if it evaluates to nil, the item is made invisible.
:included is an alias for :visible.
:label form
form is an expression that is evaluated to obtain a value which serves as
the menu item’s label (the default is name).
:suffix form
form is an expression that is dynamically evaluated and whose value isconcatenated with the menu entry’s label.
:style style
style is a symbol describing the type of menu item; it should be toggle(a checkbox), or radio (a radio button), or anything else (meaning an
ordinary menu item).
:selected selected
selected is an expression; the checkbox or radio button is selected whenever
the expression’s value is non-nil.

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523:help help
help is a string describing the menu item.
Alternatively, a menu item can be a string. Then that string appears in the menu
as unselectable text. A string consisting of dashes is displayed as a separator (seeSection 23.18.1.3 [Menu Separators], page 513).
Alternatively, a menu item can be a list with the same format as menu. This is a
submenu.
Here is an example of using easy-menu-define to define a menu similar to the one
defined in the example in Section 23.18.5 [Menu Bar], page 516:
(easy-menu-define words-menu global-map"Menu for word navigation commands."'("Words"["Forward word" forward-word]["Backward word" backward-word]))524

24 Major and Minor Modes
A mode is a set of definitions that customize Emacs behavior in useful ways. There are
two varieties of modes: minor modes, which provide features that users can turn on and off
while editing; and major modes, which are used for editing or interacting with a particularkind of text. Each buffer has exactly one major mode at a time.
This chapter describes how to write both major and minor modes, how to indicate themin the mode line, and how they run hooks supplied by the user. For related topics such as
keymaps and syntax tables, see Chapter 23 [Keymaps], page 480, and Chapter 36 [Syntax
Tables], page 1022.

24.1 Hooks
A hook is a variable where you can store a function or functions (see Section 13.1 [What Is
a Function], page 230) to be called on a particular occasion by an existing program. Emacs
provides hooks for the sake of customization. Most often, hooks are set up in the init file (seeSection 42.1.2 [Init File], page 1258), but Lisp programs can set them also. See Appendix H[Standard Hooks], page 1398, for a list of some standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions
to be called with no arguments. By convention, whenever the hook name ends in ‘-hook’,that tells you it is normal. We try to make all hooks normal, as much as possible, so thatyou can use them in a uniform way.
Every major mode command is supposed to run a normal hook called the mode hook as
one of the last steps of initialization. This makes it easy for a user to customize the behaviorof the mode, by overriding the buffer-local variable assignments already made by the mode.
Most minor mode functions also run a mode hook at the end. But hooks are used in othercontexts too. For example, the hook suspend-hook runs just before Emacs suspends itself(see Section 42.2.2 [Suspending Emacs], page 1263).
If the hook variable’s name does not end with ‘-hook’, that indicates it is probably anabnormal hook. These differ from normal hooks in two ways: they can be called with one ormore arguments, and their return values can be used in some way. The hook’s documentation
says how the functions are called and how their return values are used. Any functions added
to an abnormal hook must follow the hook’s calling convention. By convention, abnormal
hook names end in ‘-functions’.
If the name of the variable ends in ‘-predicate’ or ‘-function’ (singular) then its value
must be a function, not a list of functions. As with abnormal hooks, the expected arguments
and meaning of the return value vary across such single function hooks. The details are
explained in each variable’s docstring.
Since hooks (both multi and single function) are variables, their values can be modified
with setq or temporarily with let. However, it is often useful to add or remove a particularfunction from a hook while preserving any other functions it might have. For multifunction hooks, the recommended way of doing this is with add-hook and remove-hook (seeSection 24.1.2 [Setting Hooks], page 525). Most normal hook variables are initially void;
add-hook knows how to deal with this. You can add hooks either globally or buffer-locallywith add-hook. For hooks which hold only a single function, add-hook is not appropriate,
but you can use add-function (see Section 13.12 [Advising Functions], page 252) to combine

Chapter 24: Major and Minor Modes

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new functions with the hook. Note that some single function hooks may be nil which
add-function cannot deal with, so you must check for that before calling add-function.

24.1.1 Running Hooks
In this section, we document the run-hooks function, which is used to run a normal hook.
We also document the functions for running various kinds of abnormal hooks.

run-hooks &rest hookvars[Function]
This function takes one or more normal hook variable names as arguments, and runs
each hook in turn. Each argument should be a symbol that is a normal hook variable.
These arguments are processed in the order specified.
If a hook variable has a non-nil value, that value should be a list of functions.
run-hooks calls all the functions, one by one, with no arguments.
The hook variable’s value can also be a single function—either a lambda expression
or a symbol with a function definition—which run-hooks calls. But this usage isobsolete.
If the hook variable is buffer-local, the buffer-local variable will be used instead of the
global variable. However, if the buffer-local variable contains the element t, the global
hook variable will be run as well.

run-hook-with-args hook &rest args

[Function]
This function runs an abnormal hook by calling all the hook functions in hook, passing
each one the arguments args.

run-hook-with-args-until-failure hook &rest args

[Function]
This function runs an abnormal hook by calling each hook function in turn, stopping
if one of them fails by returning nil. Each hook function is passed the arguments
args. If this function stops because one of the hook functions fails, it returns nil;otherwise it returns a non-nil value.

run-hook-with-args-until-success hook &rest args

[Function]
This function runs an abnormal hook by calling each hook function, stopping if oneof them succeeds by returning a non-nil value. Each hook function is passed thearguments args. If this function stops because one of the hook functions returns a
non-nil value, it returns that value; otherwise it returns nil.

24.1.2 Setting Hooks
Here’s an example that adds a function to a mode hook to turn on Auto Fill mode when in
Lisp Interaction mode:(add-hook 'lisp-interaction-mode-hook 'auto-fill-mode)
The value of a hook variable should be a list of functions. You can manipulate that list
using the normal Lisp facilities, but the modular way is to use the functions add-hook andremove-hook, defined below. They take care to handle some unusual situations and avoid
problems.
It works to put a lambda-expression function on a hook, but we recommend avoiding thisbecause it can lead to confusion. If you add the same lambda-expression a second time but
write it slightly differently, you will get two equivalent but distinct functions on the hook. If
you then remove one of them, the other will still be on it.

Chapter 24: Major and Minor Modes526

add-hook hook function &optional depth local[Function]
This function is the handy way to add function function to hook variable hook. You
can use it for abnormal hooks as well as for normal hooks. function can be any Lisp
function that can accept the proper number of arguments for hook. For example,(add-hook 'text-mode-hook 'my-text-hook-function)
adds my-text-hook-function to the hook called text-mode-hook.
If function is already present in hook (comparing using equal), then add-hook does
not add it a second time.
If function has a non-nil property permanent-local-hook, then kill-all-localvariables (or changing major modes) won’t delete it from the hook variable’s local
value.
For a normal hook, hook functions should be designed so that the order in which they
are executed does not matter. Any dependence on the order is asking for trouble.
However, the order is predictable: normally, function goes at the front of the hook list,
so it is executed first (barring another add-hook call).
In some cases, it is important to control the relative ordering of functions on the hook.
The optional argument depth lets you indicate where the function should be inserted
in the list: it should then be a number between -100 and 100 where the higher thevalue, the closer to the end of the list the function should go. The depth defaults to 0
and for backward compatibility when depth is a non-nil symbol it is interpreted as adepth of 90. Furthermore, when depth is strictly greater than 0 the function is added
after rather than before functions of the same depth. One should never use a depthof 100 (or -100), because one can never be sure that no other function will ever needto come before (or after) us.
add-hook can handle the cases where hook is void or its value is a single function; it
sets or changes the value to a list of functions.
If local is non-nil, that says to add function to the buffer-local hook list instead of to
the global hook list. This makes the hook buffer-local and adds t to the buffer-local
value. The latter acts as a flag to run the hook functions in the default value as wellas in the local value.

remove-hook hook function &optional local[Function]
This function removes function from the hook variable hook. It compares function withelements of hook using equal, so it works for both symbols and lambda expressions.
If local is non-nil, that says to remove function from the buffer-local hook list insteadof from the global hook list.

24.2 Major Modes
Major modes specialize Emacs for editing or interacting with particular kinds of text. Eachbuffer has exactly one major mode at a time. Every major mode is associated with a major
mode command, whose name should end in ‘-mode’. This command takes care of switching
to that mode in the current buffer, by setting various buffer-local variables such as a local
keymap. See Section 24.2.1 [Major Mode Conventions], page 528. Note that unlike minor
modes there is no way to “turn off” a major mode, instead the buffer must be switched to a

Chapter 24: Major and Minor Modes

527

different one. However, you can temporarily suspend a major mode and later restore thesuspended mode, see below.
The least specialized major mode is called Fundamental mode, which has no mode-specificdefinitions or variable settings.
[Command]This is the major mode command for Fundamental mode. Unlike other mode commands, it does not run any mode hooks (see Section 24.2.1 [Major Mode Conventions],
page 528), since you are not supposed to customize this mode.

fundamental-mode[Function]
This function works like fundamental-mode, in that it kills all buffer-local variables,
but it also records the major mode in effect, so that it could subsequently be restored.
This function and major-mode-restore (described next) are useful when you need to
put a buffer under some specialized mode other than the one Emacs chooses for it
automatically (see Section 24.2.2 [Auto Major Mode], page 531), but would also liketo be able to switch back to the original mode later.

major-mode-suspend

major-mode-restore &optional avoided-modes[Function]
This function restores the major mode recorded by major-mode-suspend. If no major
mode was recorded, this function calls normal-mode (see Section 24.2.2 [Auto MajorMode], page 531), but tries to force it not to choose any modes in avoided-modes, if
that argument is non-nil.
[Function]
Changing the major mode clears out most local variables, but it doesn’t remove
all artifacts in the buffer (like text properties and overlays). It’s rare to change abuffer from one major mode to another (except from fundamental-mode to everythingelse), so this is usually not a concern. It can sometimes be convenient (mostly when
debugging a problem in a buffer) to do a “full reset” of the buffer, and that’s what theclean-mode major mode offers. It will kill all local variables (even the permanently
local ones), and also removes all overlays and text properties.

clean-mode

The easiest way to write a major mode is to use the macro define-derived-mode, whichsets up the new mode as a variant of an existing major mode. See Section 24.2.4 [Derived
Modes], page 534. We recommend using define-derived-mode even if the new mode is not
an obvious derivative of another mode, as it automatically enforces many coding conventions
for you. See Section 24.2.5 [Basic Major Modes], page 536, for common modes to derivefrom.
The standard GNU Emacs Lisp directory tree contains the code for several major modes,
in files such as text-mode.el, texinfo.el, lisp-mode.el, and rmail.el. You can study
these libraries to see how modes are written.
[User Option]
The buffer-local value of this variable holds the symbol for the current major mode.
Its default value holds the default major mode for new buffers. The standard default
value is fundamental-mode.
If the default value is nil, then whenever Emacs creates a new buffer via a commandsuch as C-x b (switch-to-buffer), the new buffer is put in the major mode of the

major-mode

Chapter 24: Major and Minor Modes

528

previously current buffer. As an exception, if the major mode of the previous buffer
has a mode-class symbol property with value special, the new buffer is put inFundamental mode (see Section 24.2.1 [Major Mode Conventions], page 528).

24.2.1 Major Mode Conventions
The code for every major mode should follow various coding conventions, including conventions for local keymap and syntax table initialization, function and variable names, andhooks.
If you use the define-derived-mode macro, it will take care of many of these conventions
automatically. See Section 24.2.4 [Derived Modes], page 534. Note also that Fundamental
mode is an exception to many of these conventions, because it represents the default stateof Emacs.
The following list of conventions is only partial. Each major mode should aim forconsistency in general with other Emacs major modes, as this makes Emacs as a whole more
coherent. It is impossible to list here all the possible points where this issue might come up;
if the Emacs developers point out an area where your major mode deviates from the usual
conventions, please make it compatible.
• Define a major mode command whose name ends in ‘-mode’. When called with noarguments, this command should switch to the new mode in the current buffer by
setting up the keymap, syntax table, and buffer-local variables in an existing buffer. It
should not change the buffer’s contents.
• Write a documentation string for this command that describes the special commands
available in this mode. See Section 24.2.3 [Mode Help], page 534.
The documentation string may include the special documentation substrings,‘\[command]’, ‘\{keymap}’, and ‘\<keymap>’, which allow the help display to adapt
automatically to the user’s own key bindings. See Section 25.3 [Keys in Documentation],
page 598.
• The major mode command should start by calling kill-all-local-variables. Thisruns the normal hook change-major-mode-hook, then gets rid of the buffer-local
variables of the major mode previously in effect. See Section 12.11.2 [Creating BufferLocal], page 208.
• The major mode command should set the variable major-mode to the major mode
command symbol. This is how describe-mode discovers which documentation to print.
• The major mode command should set the variable mode-name to the “pretty” nameof the mode, usually a string (but see Section 24.4.2 [Mode Line Data], page 551, forother possible forms). The name of the mode appears in the mode line.
• Calling the major mode command twice in direct succession should not fail and should
do the same thing as calling the command only once. In other words, the major mode
command should be idempotent.
• Since all global names are in the same name space, all the global variables, constants,
and functions that are part of the mode should have names that start with the major
mode name (or with an abbreviation of it if the name is long). See Section D.1 [Coding
Conventions], page 1331.
• In a major mode for editing some kind of structured text, such as a programming
language, indentation of text according to structure is probably useful. So the modeChapter 24: Major and Minor Modes

529

should set indent-line-function to a suitable function, and probably customize othervariables for indentation. See Section 24.7 [Auto-Indentation], page 581.
• The major mode should usually have its own keymap, which is used as the local keymap
in all buffers in that mode. The major mode command should call use-local-map
to install this local map. See Section 23.7 [Active Keymaps], page 489, for more
information.
This keymap should be stored permanently in a global variable named modename-modemap. Normally the library that defines the mode sets this variable.
See Section 12.6 [Tips for Defining], page 196, for advice about how to write the code
to set up the mode’s keymap variable.
• The key sequences bound in a major mode keymap should usually start with C-c,followed by a control character, a digit, or {, }, <, >, : or ;. The other punctuation
characters are reserved for minor modes, and ordinary letters are reserved for users.
A major mode can also rebind the keys M-n, M-p and M-s. The bindings for M-n andM-p should normally be some kind of moving forward and backward, but this does notnecessarily mean cursor motion.
It is legitimate for a major mode to rebind a standard key sequence if it provides acommand that does the same job in a way better suited to the text this mode is used
for. For example, a major mode for editing a programming language might redefine
C-M-a to move to the beginning of a function in a way that works better for that
language. The recommended way of tailoring C-M-a to the needs of a major mode is
to set beginning-of-defun-function (see Section 31.2.6 [List Motion], page 861) toinvoke the function specific to the mode.
It is also legitimate for a major mode to rebind a standard key sequence whose standard
meaning is rarely useful in that mode. For instance, minibuffer modes rebind M-r, whose
standard meaning is rarely of any use in the minibuffer. Major modes such as Dired or
Rmail that do not allow self-insertion of text can reasonably redefine letters and otherprinting characters as special commands.
• Major modes for editing text should not define RET to do anything other than insert a
newline. However, it is ok for specialized modes for text that users don’t directly edit,
such as Dired and Info modes, to redefine RET to do something entirely different.
• Major modes should not alter options that are primarily a matter of user preference,such as whether Auto-Fill mode is enabled. Leave this to each user to decide. However,a major mode should customize other variables so that Auto-Fill mode will work usefully
if the user decides to use it.
• The mode may have its own syntax table or may share one with other related modes.
If it has its own syntax table, it should store this in a variable named modename-modesyntax-table. See Chapter 36 [Syntax Tables], page 1022.
• If the mode handles a language that has a syntax for comments, it should set thevariables that define the comment syntax. See Section “Options Controlling Comments”
in The GNU Emacs Manual.
• The mode may have its own abbrev table or may share one with other related modes.
If it has its own abbrev table, it should store this in a variable named modename-modeabbrev-table. If the major mode command defines any abbrevs itself, it should pass t

Chapter 24: Major and Minor Modes530

for the system-flag argument to define-abbrev. See Section 38.2 [Defining Abbrevs],
page 1067.
• The mode should specify how to do highlighting for Font Lock mode, by setting up abuffer-local value for the variable font-lock-defaults (see Section 24.6 [Font LockMode], page 563).
• Each face that the mode defines should, if possible, inherit from an existing Emacs face.
See Section 41.12.8 [Basic Faces], page 1178, and Section 24.6.7 [Faces for Font Lock],
page 573.
• Consider adding a mode-specific menu to the menu bar. This should preferably include the most important menu-specific settings and commands that will allow users
discovering the main features quickly and efficiently.
• Consider adding mode-specific context menus for the mode, to be used if and whenusers activate the context-menu-mode (see Section “Menu Mouse Clicks” in The Emacs
Manual). To this end, define a mode-specific function which builds one or more menus
depending on the location of the mouse-3 click in the buffer, and then add that function
to the buffer-local value of context-menu-functions.
• The mode should specify how Imenu should find the definitions or sections of a buffer, bysetting up a buffer-local value for the variable imenu-generic-expression, for the twovariables imenu-prev-index-position-function and imenu-extract-index-namefunction, or for the variable imenu-create-index-function (see Section 24.5 [Imenu],
page 561).
• The mode can tell ElDoc mode how to retrieve different types of documentation forwhatever is at point, by adding one or more buffer-local entries to the special hookeldoc-documentation-functions.
• The mode can specify how to complete various keywords by adding one or more bufferlocal entries to the special hook completion-at-point-functions. See Section 21.6.8[Completion in Buffers], page 411.
• To make a buffer-local binding for an Emacs customization variable, use make-localvariable in the major mode command, not make-variable-buffer-local. The latterfunction would make the variable local to every buffer in which it is subsequently set,
which would affect buffers that do not use this mode. It is undesirable for a mode tohave such global effects. See Section 12.11 [Buffer-Local Variables], page 207.
With rare exceptions, the only reasonable way to use make-variable-buffer-local
in a Lisp package is for a variable which is used only within that package. Using it on avariable used by other packages would interfere with them.
• Each major mode should have a normal mode hook named modename-mode-hook. Thevery last thing the major mode command should do is to call run-mode-hooks. This runs
the normal hook change-major-mode-after-body-hook, the mode hook, the function
hack-local-variables (when the buffer is visiting a file), and then the normal hookafter-change-major-mode-hook. See Section 24.2.6 [Mode Hooks], page 537.
• The major mode command may start by calling some other major mode command (called
the parent mode) and then alter some of its settings. A mode that does this is calleda derived mode. The recommended way to define one is to use the define-derivedmode macro, but this is not required. Such a mode should call the parent mode
command inside a delay-mode-hooks form. (Using define-derived-mode does thisChapter 24: Major and Minor Modes

531

automatically.) See Section 24.2.4 [Derived Modes], page 534, and Section 24.2.6 [ModeHooks], page 537.
• If something special should be done if the user switches a buffer from this mode to any
other major mode, this mode can set up a buffer-local value for change-major-modehook (see Section 12.11.2 [Creating Buffer-Local], page 208).
• If this mode is appropriate only for specially-prepared text produced by the mode itself(rather than by the user typing at the keyboard or by an external file), then the major
mode command symbol should have a property named mode-class with value special,
put on as follows:(put 'funny-mode 'mode-class 'special)This tells Emacs that new buffers created while the current buffer is in Funny mode
should not be put in Funny mode, even though the default value of major-mode is nil.
By default, the value of nil for major-mode means to use the current buffer’s major
mode when creating new buffers (see Section 24.2.2 [Auto Major Mode], page 531), butwith such special modes, Fundamental mode is used instead. Modes such as Dired,
Rmail, and Buffer List use this feature.
The function view-buffer does not enable View mode in buffers whose mode-class is
special, because such modes usually provide their own View-like bindings.
The define-derived-mode macro automatically marks the derived mode as special
if the parent mode is special. Special mode is a convenient parent for such modes toinherit from; See Section 24.2.5 [Basic Major Modes], page 536.
• If you want to make the new mode the default for files with certain recognizable
names, add an element to auto-mode-alist to select the mode for those file names(see Section 24.2.2 [Auto Major Mode], page 531). If you define the mode command toautoload, you should add this element in the same file that calls autoload. If you use
an autoload cookie for the mode command, you can also use an autoload cookie for theform that adds the element (see [autoload cookie], page 305). If you do not autoload
the mode command, it is sufficient to add the element in the file that contains the mode
definition.
• The top-level forms in the file defining the mode should be written so that they may
be evaluated more than once without adverse consequences. For instance, use defvar
or defcustom to set mode-related variables, so that they are not reinitialized if they
already have a value (see Section 12.5 [Defining Variables], page 194).

24.2.2 How Emacs Chooses a Major Mode
When Emacs visits a file, it automatically selects a major mode for the buffer based on
information in the file name or in the file itself. It also processes local variables specified in
the file text.

normal-mode &optional find-file[Command]This function establishes the proper major mode and buffer-local variable bindings
for the current buffer. It calls set-auto-mode (see below). As of Emacs 26.1, it nolonger runs hack-local-variables, this now being done in run-mode-hooks at theinitialization of major modes (see Section 24.2.6 [Mode Hooks], page 537).
If the find-file argument to normal-mode is non-nil, normal-mode assumes that thefind-file function is calling it. In this case, it may process local variables in theChapter 24: Major and Minor Modes

532‘-*-’ line or at the end of the file. The variable enable-local-variables controls
whether to do so. See Section “Local Variables in Files” in The GNU Emacs Manual,for the syntax of the local variables section of a file.
If you run normal-mode interactively, the argument find-file is normally nil. In thiscase, normal-mode unconditionally processes any file local variables.
The function calls set-auto-mode to choose and set a major mode. If this does not
specify a mode, the buffer stays in the major mode determined by the default value ofmajor-mode (see below).
normal-mode uses condition-case around the call to the major mode command, so
errors are caught and reported as a ‘File mode specification error’, followed by
the original error message.

set-auto-mode &optional keep-mode-if-same[Function]
This function selects and sets the major mode that is appropriate for the current
buffer. It bases its decision (in order of precedence) on the ‘-*-’ line, on any ‘mode:’
local variable near the end of a file, on the ‘#!’ line (using interpreter-modealist), on the text at the beginning of the buffer (using magic-mode-alist), andfinally on the visited file name (using auto-mode-alist). See Section “How Major
Modes are Chosen” in The GNU Emacs Manual. If enable-local-variables is nil,set-auto-mode does not check the ‘-*-’ line, or near the end of the file, for any modetag.

There are some file types where it is not appropriate to scan the file contents fora mode specifier. For example, a tar archive may happen to contain, near the endof the file, a member file that has a local variables section specifying a mode forthat particular file. This should not be applied to the containing tar file. Similarly,
a tiff image file might just happen to contain a first line that seems to match the‘-*-’ pattern. For these reasons, both these file extensions are members of the list
inhibit-local-variables-regexps. Add patterns to this list to prevent Emacs
searching them for local variables of any kind (not just mode specifiers).
If keep-mode-if-same is non-nil, this function does not call the mode command if thebuffer is already in the proper major mode. For instance, set-visited-file-namesets this to t to avoid killing buffer local variables that the user may have set.

set-buffer-major-mode buffer[Function]
This function sets the major mode of buffer to the default value of major-mode; if thatis nil, it uses the current buffer’s major mode (if that is suitable). As an exception, if
buffer’s name is *scratch*, it sets the mode to initial-major-mode.
The low-level primitives for creating buffers do not use this function, but medium-levelcommands such as switch-to-buffer and find-file-noselect use it whenever theycreate buffers.
[User Option]
The value of this variable determines the major mode of the initial *scratch* buffer.
The value should be a symbol that is a major mode command. The default value is
lisp-interaction-mode.

initial-major-mode

Chapter 24: Major and Minor Modes

533[Variable]
This variable specifies major modes to use for scripts that specify a command interpreterin a ‘#!’ line. Its value is an alist with elements of the form (regexp . mode); thissays to use mode mode if the file specifies an interpreter which matches \\`regexp\\'.
For example, one of the default elements is ("python[0-9.]*" . python-mode).

interpreter-mode-alist[Variable]
This variable’s value is an alist with elements of the form (regexp . function), where
regexp is a regular expression and function is a function or nil. After visiting a file,
set-auto-mode calls function if the text at the beginning of the buffer matches regexp
and function is non-nil; if function is nil, auto-mode-alist gets to decide the mode.

magic-mode-alist[Variable]
This works like magic-mode-alist, except that it is handled only if auto-mode-alist
does not specify a mode for this file.

magic-fallback-mode-alist[Variable]
This variable contains an association list of file name patterns (regular expressions)and corresponding major mode commands. Usually, the file name patterns test forsuffixes, such as ‘.el’ and ‘.c’, but this need not be the case. An ordinary element of
the alist looks like (regexp . mode-function).

auto-mode-alist

For example,(("\\`/tmp/fol/" . text-mode)("\\.texinfo\\'" . texinfo-mode)("\\.texi\\'" . texinfo-mode)("\\.el\\'" . emacs-lisp-mode)("\\.c\\'" . c-mode)("\\.h\\'" . c-mode)...)

When you visit a file whose expanded file name (see Section 26.9.4 [File Name
Expansion], page 639), with version numbers and backup suffixes removed using
file-name-sans-versions (see Section 26.9.1 [File Name Components], page 634),
matches a regexp, set-auto-mode calls the corresponding mode-function. This featureenables Emacs to select the proper major mode for most files.
If an element of auto-mode-alist has the form (regexp function t), then after calling function, Emacs searches auto-mode-alist again for a match against the portionof the file name that did not match before. This feature is useful for uncompression
packages: an entry of the form ("\\.gz\\'" function t) can uncompress the fileand then put the uncompressed file in the proper mode according to the name sans‘.gz’.
If auto-mode-alist has more than one element whose regexp matches the file name,Emacs will use the first match.
Here is an example of how to prepend several pattern pairs to auto-mode-alist.
(You might use this sort of expression in your init file.)Chapter 24: Major and Minor Modes

534(setq auto-mode-alist(append;; File name (within directory) starts with a dot.
'(("/\\.[^/]*\\'" . fundamental-mode);; File name has no dot.
("/[^\\./]*\\'" . fundamental-mode);; File name ends in ‘.C’.
("\\.C\\'" . c++-mode))
auto-mode-alist))

24.2.3 Getting Help about a Major Mode
The describe-mode function provides information about major modes. It is normally boundto C-h m. It uses the value of the variable major-mode (see Section 24.2 [Major Modes],page 526), which is why every major mode command needs to set that variable.

describe-mode &optional buffer[Command]This command displays the documentation of the current buffer’s major mode andminor modes. It uses the documentation function to retrieve the documentation stringsof the major and minor mode commands (see Section 25.2 [Accessing Documentation],
page 596).
If called from Lisp with a non-nil buffer argument, this function displays the documentation for that buffer’s major and minor modes, rather than those of the current
buffer.

24.2.4 Defining Derived Modes
The recommended way to define a new major mode is to derive it from an existing one using
define-derived-mode. If there is no closely related mode, you should inherit from either
text-mode, special-mode, or prog-mode. See Section 24.2.5 [Basic Major Modes], page 536.
If none of these are suitable, you can inherit from fundamental-mode (see Section 24.2
[Major Modes], page 526).

define-derived-mode variant parent name docstring keyword-args. . .
body. . .

[Macro]This macro defines variant as a major mode command, using name as the string formof the mode name. variant and parent should be unquoted symbols.
The new command variant is defined to call the function parent, then override certain
aspects of that parent mode:• The new mode has its own sparse keymap, named variant-map.
define-derived-mode makes the parent mode’s keymap the parent of the newmap, unless variant-map is already set and already has a parent.
• The new mode has its own syntax table, kept in the variable variant-syntaxtable, unless you override this using the :syntax-table keyword (see below).
define-derived-mode makes the parent mode’s syntax-table the parent ofvariant-syntax-table, unless the latter is already set and already has a parent
different from the standard syntax table.
• The new mode has its own abbrev table, kept in the variable variant-abbrevtable, unless you override this using the :abbrev-table keyword (see below).

Chapter 24: Major and Minor Modes

535• The new mode has its own mode hook, variant-hook. It runs this hook, after
running the hooks of its ancestor modes, with run-mode-hooks, as the last thing
it does, apart from running any :after-hook form it may have. See Section 24.2.6[Mode Hooks], page 537.
In addition, you can specify how to override other aspects of parent with body. The
command variant evaluates the forms in body after setting up all its usual overrides,
just before running the mode hooks.
If parent has a non-nil mode-class symbol property, then define-derived-mode
sets the mode-class property of variant to the same value. This ensures, for example,
that if parent is a special mode, then variant is also a special mode (see Section 24.2.1[Major Mode Conventions], page 528).
You can also specify nil for parent. This gives the new mode no parent. Thendefine-derived-mode behaves as described above, but, of course, omits all actions
connected with parent.
The argument docstring specifies the documentation string for the new mode.
define-derived-mode adds some general information about the mode’s hook,followed by the mode’s keymap, at the end of this documentation string. If you omit
docstring, define-derived-mode generates a documentation string.
The keyword-args are pairs of keywords and values. The values, except for:after-hook’s, are evaluated. The following keywords are currently supported::syntax-table
You can use this to explicitly specify a syntax table for the new mode.
If you specify a nil value, the new mode uses the same syntax table asparent, or the standard syntax table if parent is nil. (Note that this does
not follow the convention used for non-keyword arguments that a nil
value is equivalent with not specifying the argument.):abbrev-table
You can use this to explicitly specify an abbrev table for the new mode.
If you specify a nil value, the new mode uses the same abbrev table asparent, or fundamental-mode-abbrev-table if parent is nil. (Again, anil value is not equivalent to not specifying this keyword.):interactive
Modes are interactive commands by default. If you specify a nil value,
the mode defined here won’t be interactive. This is useful for modes thatare never meant to be activated by users manually, but are only supposed
to be used in some specially-formatted buffer.
:groupIf this is specified, the value should be the customization group for thismode. (Not all major modes have one.) The command customize-mode
uses this. define-derived-mode does not automatically define the specified customization group.

:after-hook
This optional keyword specifies a single Lisp form to evaluate as the final
act of the mode function, after the mode hooks have been run. It should

Chapter 24: Major and Minor Modes536

not be quoted. Since the form might be evaluated after the mode function
has terminated, it should not access any element of the mode function’s
local state. An :after-hook form is useful for setting up aspects of themode which depend on the user’s settings, which in turn may have beenchanged in a mode hook.
Here is a hypothetical example:(defvar-keymap hypertext-mode-map"<down-mouse-3>" #'do-hyper-link)(define-derived-mode hypertext-mode
text-mode "Hypertext""Major mode for hypertext."(setq-local case-fold-search nil))
Do not write an interactive spec in the definition; define-derived-mode does that
automatically.

derived-mode-p &rest modes[Function]
This function returns non-nil if the current major mode is derived from any of the
major modes given by the symbols modes.

24.2.5 Basic Major Modes
Apart from Fundamental mode, there are three major modes that other major modes
commonly derive from: Text mode, Prog mode, and Special mode. While Text mode isuseful in its own right (e.g., for editing files ending in .txt), Prog mode and Special mode
exist mainly to let other modes derive from them.
As far as possible, new major modes should be derived, either directly or indirectly, fromone of these three modes. One reason is that this allows users to customize a single mode
hook (e.g., prog-mode-hook) for an entire family of relevant modes (e.g., all programming
language modes).
[Command]
Text mode is a major mode for editing human languages. It defines the ‘"’ and ‘\’
characters as having punctuation syntax (see Section 36.2.1 [Syntax Class Table],
page 1023), and binds M-TAB to ispell-complete-word (see Section “Spelling” in
The GNU Emacs Manual).

text-mode

An example of a major mode derived from Text mode is HTML mode. See Section“SGML and HTML Modes” in The GNU Emacs Manual.
[Command]Prog mode is a basic major mode for buffers containing programming language sourcecode. Most of the programming language major modes built into Emacs are derived
from it.

prog-mode

Prog mode binds parse-sexp-ignore-comments to t (see Section 36.6.1 [Motion
via Parsing], page 1031) and bidi-paragraph-direction to left-to-right (seeSection 41.27 [Bidirectional Display], page 1250).

Chapter 24: Major and Minor Modes

537[Command]Special mode is a basic major mode for buffers containing text that is produced
specially by Emacs, rather than directly from a file. Major modes derived from Special
mode are given a mode-class property of special (see Section 24.2.1 [Major Mode
Conventions], page 528).

special-mode

Special mode sets the buffer to read-only. Its keymap defines several common bindings,
including q for quit-window and g for revert-buffer (see Section 27.3 [Reverting],
page 667).
An example of a major mode derived from Special mode is Buffer Menu mode, which
is used by the *Buffer List* buffer. See Section “Listing Existing Buffers” in The
GNU Emacs Manual.
In addition, modes for buffers of tabulated data can inherit from Tabulated List mode,
which is in turn derived from Special mode. See Section 24.2.7 [Tabulated List Mode],
page 538.

24.2.6 Mode Hooks
Every major mode command should finish by running the mode-independent normal
hook change-major-mode-after-body-hook, its mode hook, and the normal hookafter-change-major-mode-hook. It does this by calling run-mode-hooks. If the major
mode is a derived mode, that is if it calls another major mode (the parent mode) in its
body, it should do this inside delay-mode-hooks so that the parent won’t run these hooks
itself. Instead, the derived mode’s call to run-mode-hooks runs the parent’s mode hook too.
See Section 24.2.1 [Major Mode Conventions], page 528.
Emacs versions before Emacs 22 did not have delay-mode-hooks. Versions before 24 did
not have change-major-mode-after-body-hook. When user-implemented major modes do
not use run-mode-hooks and have not been updated to use these newer features, they won’t
entirely follow these conventions: they may run the parent’s mode hook too early, or fail torun after-change-major-mode-hook. If you encounter such a major mode, please correct
it to follow these conventions.
When you define a major mode using define-derived-mode, it automatically makes
sure these conventions are followed. If you define a major mode “by hand”, not using
define-derived-mode, use the following functions to handle these conventions automatically.

run-mode-hooks &rest hookvars[Function]
Major modes should run their mode hook using this function. It is similar to
run-hooks (see Section 24.1 [Hooks], page 524), but it also runs change-majormode-after-body-hook, hack-local-variables (when the buffer is visiting a file)(see Section 12.12 [File Local Variables], page 213), and after-change-major-modehook. The last thing it does is to evaluate any :after-hook forms declared by parent
modes (see Section 24.2.4 [Derived Modes], page 534).

When this function is called during the execution of a delay-mode-hooks form, it
does not run the hooks or hack-local-variables or evaluate the forms immediately.
Instead, it arranges for the next call to run-mode-hooks to run them.

Chapter 24: Major and Minor Modes

538

delay-mode-hooks body. . .

[Macro]When one major mode command calls another, it should do so inside of delay-modehooks.
This macro executes body, but tells all run-mode-hooks calls during the execution ofbody to delay running their hooks. The hooks will actually run during the next callto run-mode-hooks after the end of the delay-mode-hooks construct.
[Variable]
This is a normal hook run by run-mode-hooks. It is run before the mode hooks.

change-major-mode-after-body-hook[Variable]
This is a normal hook run by run-mode-hooks. It is run at the very end of every
properly-written major mode command.

after-change-major-mode-hook

24.2.7 Tabulated List mode
Tabulated List mode is a major mode for displaying tabulated data, i.e., data consistingof entries, each entry occupying one row of text with its contents divided into columns.
Tabulated List mode provides facilities for pretty-printing rows and columns, and sorting
the rows according to the values in each column. It is derived from Special mode (seeSection 24.2.5 [Basic Major Modes], page 536).
Tabulated List mode is geared towards displaying text using monospaced fonts, using asingle font and text size. If you want to display a table using variable pitch fonts or images,
make-vtable can be used instead. vtable also support having more than a single table in abuffer, or having a buffer that contains both a table and additional text in it. See Section“Introduction” in vtable, for more information.
Tabulated List mode is intended to be used as a parent mode by a more specialized
major mode. Examples include Process Menu mode (see Section 40.6 [Process Information],
page 1092) and Package Menu mode (see Section “Package Menu” in The GNU Emacs
Manual).
Such a derived mode should use define-derived-mode in the usual way, specifying tabulated-list-mode as the second argument (see Section 24.2.4 [Derived Modes],page 534). The body of the define-derived-mode form should specify the format of thetabulated data, by assigning values to the variables documented below; optionally, it canthen call the function tabulated-list-init-header, which will populate a header with
the names of the columns.
The derived mode should also define a listing command. This, not the mode command,is what the user calls (e.g., M-x list-processes). The listing command should create or
switch to a buffer, turn on the derived mode, specify the tabulated data, and finally calltabulated-list-print to populate the buffer.
[User Option]
This variable specifies the character to be used on GUI frames as an indication thatthe column is sorted in the ascending order.

tabulated-list-gui-sort-indicator-asc

Whenever you change the sort direction in Tabulated List buffers, this indicator toggles
between ascending (“asc”) and descending (“desc”).

Chapter 24: Major and Minor Modes

539[User Option]
Like tabulated-list-gui-sort-indicator-asc, but used when the column is sorted
in the descending order.

tabulated-list-gui-sort-indicator-desc[User Option]
Like tabulated-list-gui-sort-indicator-asc, but used for text-mode frames.

tabulated-list-tty-sort-indicator-asc[User Option]
Like tabulated-list-tty-sort-indicator-asc, but used when the column is sorted
in the descending order.

tabulated-list-tty-sort-indicator-desc[Variable]
This buffer-local variable specifies the format of the Tabulated List data. Its value
should be a vector. Each element of the vector represents a data column, and should
be a list (name width sort . props), wheretabulated-list-format• name is the column’s name (a string).
• width is the width to reserve for the column (an integer). This is meaningless forthe last column, which runs to the end of each line.
• sort specifies how to sort entries by the column. If nil, the column cannot be
used for sorting. If t, the column is sorted by comparing string values. Otherwise,
this should be a predicate function for sort (see Section 5.6.3 [Rearrangement],
page 90), which accepts two arguments with the same form as the elements of
tabulated-list-entries (see below).
• props is a plist (see Section 5.9 [Property Lists], page 99) of additional column
properties. If the value of the property :right-align is non-nil then the column
should be right-aligned. And the property :pad-right specifies the number of
additional padding spaces to the right of the column (by default 1 if omitted).
[Variable]
This buffer-local variable specifies the entries displayed in the Tabulated List buffer.
Its value should be either a list, or a function.

tabulated-list-entries

If the value is a list, each list element corresponds to one entry, and should have theform (id contents), where• id is either nil, or a Lisp object that identifies the entry. If the latter, the cursor
stays on the same entry when re-sorting entries. Comparison is done with equal.
• contents is a vector with the same number of elements as tabulated-listformat. Each vector element is either a string, which is inserted into the buffer
as-is; an image descriptor, which is used to insert an image (see Section 41.17.2[Image Descriptors], page 1207); or a list (label . properties), which means
to insert a text button by calling insert-text-button with label and properties
as arguments (see Section 41.20.3 [Making Buttons], page 1233).
There should be no newlines in any of these strings.
Otherwise, the value should be a function which returns a list of the above form whencalled with no arguments.

Chapter 24: Major and Minor Modes

540[Variable]
This normal hook is run prior to reverting a Tabulated List buffer. A derived mode
can add a function to this hook to recompute tabulated-list-entries.

tabulated-list-revert-hook[Variable]
The value of this variable is the function called to insert an entry at point, including
its terminating newline. The function should accept two arguments, id and contents,
having the same meanings as in tabulated-list-entries. The default value is afunction which inserts an entry in a straightforward way; a mode which uses Tabulated
List mode in a more complex way can specify another function.

tabulated-list-printer[Variable]
The value of this variable specifies the current sort key for the Tabulated List buffer. If
it is nil, no sorting is done. Otherwise, it should have the form (name . flip), wherename is a string matching one of the column names in tabulated-list-format, andflip, if non-nil, means to invert the sort order.

tabulated-list-sort-key[Function]
This function computes and sets header-line-format for the Tabulated List buffer(see Section 24.4.7 [Header Lines], page 559), and assigns a keymap to the header line
to allow sorting entries by clicking on column headers.

tabulated-list-init-header

Modes derived from Tabulated List mode should call this after setting the above
variables (in particular, only after setting tabulated-list-format).

tabulated-list-print &optional remember-pos update[Function]
This function populates the current buffer with entries. It should be called by thelisting command. It erases the buffer, sorts the entries specified by tabulated-listentries according to tabulated-list-sort-key, then calls the function specified
by tabulated-list-printer to insert each entry.
If the optional argument remember-pos is non-nil, this function looks for the id
element on the current line, if any, and tries to move to that entry after all the entries
are (re)inserted.
If the optional argument update is non-nil, this function will only erase or add entries
that have changed since the last print. This is several times faster if most entries
haven’t changed since the last time this function was called. The only difference inoutcome is that tags placed via tabulated-list-put-tag will not be removed fromentries that haven’t changed (normally all tags are removed).

tabulated-list-delete-entry[Function]

This function deletes the entry at point.
It returns a list (id cols), where id is the ID of the deleted entry and cols is a vector
of its column descriptors. It moves point to the beginning of the current line. It
returns nil if there is no entry at point.
Note that this function only changes the buffer contents; it does not alter
tabulated-list-entries.

Chapter 24: Major and Minor Modes

541

tabulated-list-get-id &optional pos[Function]
This defsubst returns the ID object from tabulated-list-entries (if that is a list)
or from the list returned by tabulated-list-entries (if it is a function). If omitted
or nil, pos defaults to point.

tabulated-list-get-entry &optional pos[Function]
This defsubst returns the entry object from tabulated-list-entries (if that is alist) or from the list returned by tabulated-list-entries (if it is a function). This
will be a vector for the ID at pos. If there is no entry at pos, then the function returns
nil.

tabulated-list-header-overlay-p &optional POS[Function]
This defsubst returns non-nil if there is a fake header at pos. A fake header isused if tabulated-list-use-header-line is nil to put the column names at the
beginning of the buffer. If omitted or nil, pos defaults to point-min.

tabulated-list-put-tag tag &optional advance[Function]
This function puts tag in the padding area of the current line. The padding area
can be empty space at the beginning of the line, the width of which is governed bytabulated-list-padding. tag should be a string, with a length less than or equal
to tabulated-list-padding. If advance is non-nil, this function advances point by
one line.

tabulated-list-clear-all-tags[Function]

This function clears all tags from the padding area in the current buffer.

tabulated-list-set-col col desc &optional change-entry-data[Function]
This function changes the tabulated list entry at point, setting col to desc. col is thecolumn number to change, or the name of the column to change. desc is the newcolumn descriptor, which is inserted via tabulated-list-print-col.
If change-entry-data is non-nil, this function modifies the underlying data (usually
the column descriptor in the list tabulated-list-entries) by setting the column
descriptor of the vector to desc.

24.2.8 Generic Modes
Generic modes are simple major modes with basic support for comment syntax and Font
Lock mode. To define a generic mode, use the macro define-generic-mode. See the file
generic-x.el for some examples of the use of define-generic-mode.

define-generic-mode mode comment-list keyword-list font-lock-list
auto-mode-list function-list &optional docstring[Macro]This macro defines a generic mode command named mode (a symbol, not quoted).
The optional argument docstring is the documentation for the mode command. If you
do not supply it, define-generic-mode generates one by default.
The argument comment-list is a list in which each element is either a character, astring of one or two characters, or a cons cell. A character or a string is set up in themode’s syntax table as a comment starter. If the entry is a cons cell, the car is set up
as a comment starter and the cdr as a comment ender. (Use nil for the latter if youChapter 24: Major and Minor Modes

542

want comments to end at the end of the line.) Note that the syntax table mechanism
has limitations about what comment starters and enders are actually possible. See
Chapter 36 [Syntax Tables], page 1022.
The argument keyword-list is a list of keywords to highlight with font-lock-keywordface. Each keyword should be a string. Meanwhile, font-lock-list is a list of additional
expressions to highlight. Each element of this list should have the same form as
an element of font-lock-keywords. See Section 24.6.2 [Search-based Fontification],
page 565.
The argument auto-mode-list is a list of regular expressions to add to the variable
auto-mode-alist. They are added by the execution of the define-generic-mode
form, not by expanding the macro call.
Finally, function-list is a list of functions for the mode command to call for additional
setup. It calls these functions just before it runs the mode hook variable mode-hook.

24.2.9 Major Mode Examples
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts fromtext-mode.el that illustrate many of the conventions listed above:;; Create the syntax table for this mode.
(defvar text-mode-syntax-table(let ((st (make-syntax-table)))(modify-syntax-entry ?\" ".
" st)(modify-syntax-entry ?\\ ".
" st);; Add 'p' so M-c on 'hello' leads to 'Hello', not 'hello'.
(modify-syntax-entry ?' "w p" st)...
st)"Syntax table used while in `text-mode'.");; Create the keymap for this mode.
(defvar-keymap text-mode-map:doc "Keymap for `text-mode'.
Many other modes, such as `mail-mode' and `outline-mode', inherit all
the commands defined in this map.""C-M-i" #'ispell-complete-word)

Here is how the actual mode command is defined now:
(define-derived-mode text-mode nil "Text""Major mode for editing text written for humans to read.
In this mode, paragraphs are delimited only by blank or white lines.
You can thus get the full benefit of adaptive filling(see the variable `adaptive-fill-mode').
\\{text-mode-map}
Turning on Text mode runs the normal hook `text-mode-hook'."(setq-local text-mode-variant t)(setq-local require-final-newline mode-require-final-newline))

The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) havemore features than Text mode and the code is correspondingly more complicated. Here are
excerpts from lisp-mode.el that illustrate how these modes are written.
Here is how the Lisp mode syntax and abbrev tables are defined:Chapter 24: Major and Minor Modes

543;; Create mode-specific table variables.
(define-abbrev-table 'lisp-mode-abbrev-table ()"Abbrev table for Lisp mode.")(defvar lisp-mode-syntax-table(let ((table (make-syntax-table lisp--mode-syntax-table)))(modify-syntax-entry ?\[ "_" table)(modify-syntax-entry ?\] "_" table)(modify-syntax-entry ?# "' 14" table)(modify-syntax-entry ?| "\" 23bn" table)table)"Syntax table used in `lisp-mode'.")

The three modes for Lisp share much of their code. For instance, Lisp mode and Emacs
Lisp mode inherit from Lisp Data mode and Lisp Interaction Mode inherits from Emacs
Lisp mode.
Amongst other things, Lisp Data mode sets up the comment-start variable to handle Lisp
comments:(setq-local comment-start ";")...

Each of the different Lisp modes has a slightly different keymap. For example, Lisp mode
binds C-c C-z to run-lisp, but the other Lisp modes do not. However, all Lisp modes havesome commands in common. The following code sets up the common commands:(defvar-keymap lisp-mode-shared-map:parent prog-mode-map:doc "Keymap for commands shared by all sorts of Lisp modes.""C-M-q" #'indent-sexp"DEL" #'backward-delete-char-untabify)

And here is the code to set up the keymap for Lisp mode:(defvar-keymap lisp-mode-map:doc "Keymap for ordinary Lisp mode.
All commands in `lisp-mode-shared-map' are inherited by this map.":parent lisp-mode-shared-map"C-M-x" #'lisp-eval-defun"C-c C-z" #'run-lisp)

Finally, here is the major mode command for Lisp mode:(define-derived-mode lisp-mode lisp-data-mode "Lisp""Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one."(setq-local find-tag-default-function 'lisp-find-tag-default)(setq-local comment-start-skip"\\(\\(^\\|[^\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")(setq imenu-case-fold-search t))

24.3 Minor Modes
A minor mode provides optional features that users may enable or disable independently of
the choice of major mode. Minor modes can be enabled individually or in combination.

Chapter 24: Major and Minor Modes

544

Most minor modes implement features that are independent of the major mode, and canthus be used with most major modes. For example, Auto Fill mode works with any major
mode that permits text insertion. A few minor modes, however, are specific to a particularmajor mode. For example, Diff Auto Refine mode is a minor mode that is intended to be
used only with Diff mode.
Ideally, a minor mode should have its desired effect regardless of the other minor modes
in effect. It should be possible to activate and deactivate minor modes in any order.
[Variable]
This buffer-local variable lists the currently enabled minor modes in the current buffer,and is a list of symbols.

local-minor-modes[Variable]
This variable lists the currently enabled global minor modes, and is a list of symbols.

global-minor-modes
minor-mode-list[Variable]

The value of this variable is a list of all minor mode commands.

24.3.1 Conventions for Writing Minor Modes
There are conventions for writing minor modes just as there are for major modes (seeSection 24.2 [Major Modes], page 526). These conventions are described below. The easiest
way to follow them is to use the macro define-minor-mode. See Section 24.3.3 [Defining
Minor Modes], page 546.
• Define a variable whose name ends in ‘-mode’. We call this the mode variable. The
minor mode command should set this variable. The value will be nil if the mode isdisabled, and non-nil if the mode is enabled. The variable should be buffer-local if theminor mode is buffer-local.
This variable is used in conjunction with the minor-mode-alist to display the minor
mode name in the mode line. It also determines whether the minor mode keymap
is active, via minor-mode-map-alist (see Section 23.9 [Controlling Active Maps],
page 491). Individual commands or hooks can also check its value.
• Define a command, called the mode command, whose name is the same as the mode
variable. Its job is to set the value of the mode variable, plus anything else that needs
to be done to actually enable or disable the mode’s features.
The mode command should accept one optional argument. If called interactively withno prefix argument, it should toggle the mode (i.e., enable if it is disabled, and disable
if it is enabled). If called interactively with a prefix argument, it should enable themode if the argument is positive and disable it otherwise.
If the mode command is called from Lisp (i.e., non-interactively), it should enable themode if the argument is omitted or nil; it should toggle the mode if the argument is
the symbol toggle; otherwise it should treat the argument in the same way as for aninteractive call with a numeric prefix argument, as described above.
The following example shows how to implement this behavior (it is similar to the code
generated by the define-minor-mode macro):(interactive (list (or current-prefix-arg 'toggle)))(let ((enableChapter 24: Major and Minor Modes

545(if (eq arg 'toggle)(not foo-mode) ; this is the mode’s mode variable(> (prefix-numeric-value arg) 0))))(if enable
do-enable
do-disable))
The reason for this somewhat complex behavior is that it lets users easily toggle theminor mode interactively, and also lets the minor mode be easily enabled in a mode
hook, like this:(add-hook 'text-mode-hook 'foo-mode)This behaves correctly whether or not foo-mode was already enabled, since the foo-mode
mode command unconditionally enables the minor mode when it is called from Lisp
with no argument. Disabling a minor mode in a mode hook is a little uglier:(add-hook 'text-mode-hook (lambda () (foo-mode -1)))
However, this is not very commonly done.
Enabling or disabling a minor mode twice in direct succession should not fail and should
do the same thing as enabling or disabling it only once. In other words, the minor mode
command should be idempotent.
• Add an element to minor-mode-alist for each minor mode (see [Definition of minormode-alist], page 556), if you want to indicate the minor mode in the mode line. Thiselement should be a list of the following form:(mode-variable string)

Here mode-variable is the variable that controls enabling of the minor mode, and string
is a short string, starting with a space, to represent the mode in the mode line. These
strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist, use assq to check for an existingelement, to avoid duplication. For example:(unless (assq 'leif-mode minor-mode-alist)(push '(leif-mode " Leif") minor-mode-alist))

or like this, using add-to-list (see Section 5.5 [List Variables], page 85):(add-to-list 'minor-mode-alist '(leif-mode " Leif"))

In addition, several major mode conventions (see Section 24.2.1 [Major Mode Conventions],
page 528) apply to minor modes as well: those regarding the names of global symbols, theuse of a hook at the end of the initialization function, and the use of keymaps and othertables.
The minor mode should, if possible, support enabling and disabling via Custom (seeChapter 15 [Customization], page 277). To do this, the mode variable should be defined with
defcustom, usually with :type 'boolean. If just setting the variable is not sufficient toenable the mode, you should also specify a :set method which enables the mode by invoking
the mode command. Note in the variable’s documentation string that setting the variable
other than via Custom may not take effect. Also, mark the definition with an autoload
cookie (see [autoload cookie], page 305), and specify a :require so that customizing thevariable will load the library that defines the mode. For example:

Chapter 24: Major and Minor Modes

546;;;###autoload(defcustom msb-mode nil"Toggle msb-mode.
Setting this variable directly does not take effect;use either \\[customize] or the function `msb-mode'.":set 'custom-set-minor-mode:initialize 'custom-initialize-default:version "20.4":type'boolean:group'msb:require 'msb)

24.3.2 Keymaps and Minor Modes
Each minor mode can have its own keymap, which is active when the mode is enabled. To
set up a keymap for a minor mode, add an element to the alist minor-mode-map-alist.
See [Definition of minor-mode-map-alist], page 492.
One use of minor mode keymaps is to modify the behavior of certain self-inserting
characters so that they do something else as well as self-insert. (Another way to customize
self-insert-command is through post-self-insert-hook, see Section 33.5 [Commands
for Insertion], page 884. Apart from this, the facilities for customizing self-insert-command
are limited to special cases, designed for abbrevs and Auto Fill mode. Do not try substituting
your own definition of self-insert-command for the standard one. The editor command
loop handles this function specially.)
Minor modes may bind commands to key sequences consisting of C-c followed by apunctuation character. However, sequences consisting of C-c followed by one of {}<>:;, ora control character or digit, are reserved for major modes. Also, C-c letter is reserved forusers. See Section D.2 [Key Binding Conventions], page 1334.

24.3.3 Defining Minor Modes
The macro define-minor-mode offers a convenient way of implementing a mode in one
self-contained definition.

define-minor-mode mode doc keyword-args. . . body. . .

[Macro]This macro defines a new minor mode whose name is mode (a symbol). It defines
a command named mode to toggle the minor mode, with doc as its documentation
string.
The toggle command takes one optional (prefix) argument. If called interactively
with no argument it toggles the mode on or off. A positive prefix argument enables
the mode, any other prefix argument disables it. From Lisp, an argument of toggle
toggles the mode, whereas an omitted or nil argument enables the mode. This makes
it easy to enable the minor mode in a major mode hook, for example. If doc is nil,
the macro supplies a default documentation string explaining the above.
By default, it also defines a variable named mode, which is set to t or nil by enablingor disabling the mode.
The keyword-args consist of keywords followed by corresponding values. A few
keywords have special meanings:

Chapter 24: Major and Minor Modes

547:global global
If non-nil, this specifies that the minor mode should be global rather
than buffer-local. It defaults to nil.
One of the effects of making a minor mode global is that the mode variable
becomes a customization variable. Toggling it through the Customize
interface turns the mode on and off, and its value can be saved for future
Emacs sessions (see Section “Saving Customizations” in The GNU Emacs
Manual. For the saved variable to work, you should ensure that the minor
mode function is available each time Emacs starts; usually this is done bymarking the define-minor-mode form as autoloaded.
:init-value init-value
This is the value to which the mode variable is initialized. Except inunusual circumstances (see below), this value must be nil.
:lighter lighter
The string lighter says what to display in the mode line when the mode isenabled; if it is nil, the mode is not displayed in the mode line.
:keymap keymap
The optional argument keymap specifies the keymap for the minor mode.
If non-nil, it should be a variable name (whose value is a keymap), a
keymap, or an alist of the form
(key-sequence . definition)
where each key-sequence and definition are arguments suitable for passing
to define-key (see Section 23.12 [Changing Key Bindings], page 497). If
keymap is a keymap or an alist, this also defines the variable mode-map.
:variable place
This replaces the default variable mode, used to store the state of themode. If you specify this, the mode variable is not defined, and any
init-value argument is unused. place can be a different named variable(which you must define yourself), or anything that can be used with thesetf function (see Section 12.17 [Generalized Variables], page 224). place
can also be a cons (get . set), where get is an expression that returns
the current state, and set is a function of one argument (a state) whichshould be assigned to place.
:after-hook after-hook
This defines a single Lisp form which is evaluated after the mode hooks
have run. It should not be quoted.
:interactive value
Minor modes are interactive commands by default. If value is nil, this isinhibited. If value is a list of symbols, it’s used to say which major modes
this minor mode is useful in.
Any other keyword arguments are passed directly to the defcustom generated for thevariable mode. See Section 15.3 [Variable Definitions], page 280, for the description of
those keywords and their values.

Chapter 24: Major and Minor Modes

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The command named mode first performs the standard actions such as setting thevariable named mode and then executes the body forms, if any. It then runs the mode
hook variable mode-hook and finishes by evaluating any form in :after-hook. (Notethat all of this, including running the hook, is done both when the mode is enabled
and disabled.)
The initial value must be nil except in cases where (1) the mode is preloaded in Emacs,or (2) it is painless for loading to enable the mode even though the user did not request it.
For instance, if the mode has no effect unless something else is enabled, and will always beloaded by that time, enabling it by default is harmless. But these are unusual circumstances.
Normally, the initial value must be nil.
The name easy-mmode-define-minor-mode is an alias for this macro.
Here is an example of using define-minor-mode:(define-minor-mode hungry-mode"Toggle Hungry mode.
Interactively with no argument, this command toggles the mode.
A positive prefix argument enables the mode, any other prefix
argument disables it. From Lisp, argument omitted or nil enables
the mode, `toggle' toggles the state.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete].";; The initial value.
nil;; The indicator for the mode line.
" Hungry";; The minor mode bindings.
'(([C-backspace] . hungry-electric-delete)))This defines a minor mode named “Hungry mode”, a command named hungry-mode totoggle it, a variable named hungry-mode which indicates whether the mode is enabled, anda variable named hungry-mode-map which holds the keymap that is active when the modeis enabled. It initializes the keymap with a key binding for C-DEL. There are no bodyforms—many minor modes don’t need any.
Here’s an equivalent way to write it:(define-minor-mode hungry-mode"Toggle Hungry mode.
...rest of documentation as before...";; The initial value.
:init-value nil;; The indicator for the mode line.
:lighter " Hungry";; The minor mode bindings.
:keymap'(([C-backspace] . hungry-electric-delete)([C-M-backspace]. (lambda ()(interactive)(hungry-electric-delete t)))))

Chapter 24: Major and Minor Modes

define-globalized-minor-mode global-mode mode turn-on
keyword-args. . . body. . .

549[Macro]This defines a global toggle named global-mode whose meaning is to enable or disable
the buffer-local minor mode mode in all (or some; see below) buffers. It also executes
the body forms. To turn on the minor mode in a buffer, it uses the function turn-on;
to turn off the minor mode, it calls mode with −1 as argument. (The function turn-on
is a separate function so it could determine whether to enable the minor mode or not
when it is not a priori clear that it should always be enabled.)
Globally enabling the mode also affects buffers subsequently created by visiting files,
and buffers that use a major mode other than Fundamental mode; but it does notdetect the creation of a new buffer in Fundamental mode.
This macro defines the customization option global-mode (see Chapter 15 [Customization], page 277), which can be toggled via the Customize interface to turnthe minor mode on and off. As with define-minor-mode, you should ensure thatthe define-globalized-minor-mode form is evaluated each time Emacs starts, forexample by providing a :require keyword.
Use :group group in keyword-args to specify the custom group for the mode variableof the global minor mode.
By default, the buffer-local minor mode variable that says whether the mode is switchedon or off is the same as the name of the mode itself. Use :variable variable if that’s
not the case–some minor modes use a different variable to store this state information.
Generally speaking, when you define a globalized minor mode, you should also define a
non-globalized version, so that people could use it (or disable it) in individual buffers.
This also allows them to disable a globally enabled minor mode in a specific majormode, by using that mode’s hook.
If the macro is given a :predicate keyword, it will create a user option called thesame as the global mode variable, but with -modes instead of -mode at the end, i.e.
global-modes. This variable will be used in a predicate function that determines
whether the minor mode should be activated in a particular major mode, and users cancustomize the value of the variable to control the modes in which the minor mode will
be switched on. Valid values of :predicate (and thus valid values of the user option
it creates) include t (use in all major modes), nil (don’t use in any major modes),or a list of mode names, optionally preceded with not (as in (not mode-name ...)).
These elements can be mixed, as shown in the following examples.
(c-mode (not mail-mode message-mode) text-mode)This means “use in modes derived from c-mode, and not in modes derived frommessage-mode or mail-mode, but do use in modes derived from text-mode, andotherwise no other modes”.
((not c-mode) t)
This means “don’t use in modes derived from c-mode, but do use everywhere else”.
(text-mode)This means “use in modes derived from text-mode, but nowhere else”. (There’s animplicit nil element at the end.)

Chapter 24: Major and Minor Modes

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buffer-local-set-state variable value...

[Macro]Minor modes often set buffer-local variables that affect some features in Emacs. Whena minor mode is switched off, the mode is expected to restore the previous state ofthese variables. This convenience macro helps with doing that: It works much like
setq-local, but returns an object that can be used to restore these values back totheir previous values/states (using the companion function buffer-local-restorestate).

24.4 Mode Line Format
Each Emacs window (aside from minibuffer windows) typically has a mode line at thebottom, which displays status information about the buffer displayed in the window. The
mode line contains information about the buffer, such as its name, associated file, depthof recursive editing, and major and minor modes. A window can also have a header line,
which is much like the mode line but appears at the top of the window.
This section describes how to control the contents of the mode line and header line. We
include it in this chapter because much of the information displayed in the mode line relates
to the enabled major and minor modes.

24.4.1 Mode Line Basics
The contents of each mode line are specified by the buffer-local variable mode-line-format(see Section 24.4.3 [Mode Line Top], page 552). This variable holds a mode line construct: atemplate that controls what is displayed on the buffer’s mode line. The value of header-lineformat specifies the buffer’s header line in the same way. All windows for the same buffer
use the same mode-line-format and header-line-format unless a mode-line-format
or header-line-format parameter has been specified for that window (see Section 29.27[Window Parameters], page 776).
For efficiency, Emacs does not continuously recompute each window’s mode line andheader line. It does so when circumstances appear to call for it—for instance, if you change
the window configuration, switch buffers, narrow or widen the buffer, scroll, or modify the
buffer. If you alter any of the variables referenced by mode-line-format or header-lineformat (see Section 24.4.4 [Mode Line Variables], page 554), or any other data structuresthat affect how text is displayed (see Chapter 41 [Display], page 1129), you should use thefunction force-mode-line-update to update the display.

force-mode-line-update &optional all[Function]
This function forces Emacs to update the current buffer’s mode line and header line,
based on the latest values of all relevant variables, during its next redisplay cycle. If
the optional argument all is non-nil, it forces an update for all mode lines and headerlines.

This function also forces an update of the menu bar and frame title.
The selected window’s mode line is usually displayed in a different color using the facemode-line-active. Other windows’ mode lines appear in the face mode-line-inactive
instead. See Section 41.12 [Faces], page 1164.

Chapter 24: Major and Minor Modes

551[Function]
If you want to have more extensive differences between the mode lines in selected andnon-selected windows, you can use this predicate in an :eval construct. For instance,
if you want to display the buffer name in bold in selected windows, but in italics inthe other windows, you can say something like:(setq-default
mode-line-buffer-identification'(:eval (propertize "%12b"'face (if (mode-line-window-selected-p)'bold'italic))))mode-line-window-selected-p

Some modes put a lot of data in the mode line, pushing elements at the end of themode line off to the right. Emacs can “compress” the mode line if the mode-line-compact
variable is non-nil by turning stretches of spaces into a single space. If this variable is long,
this is only done when the mode line is wider than the currently selected window. (Thiscomputation is approximate, based on the number of characters, and not their displayed
width.) This variable can be buffer-local to only compress mode-lines in certain buffers.

24.4.2 The Data Structure of the Mode LineThe mode line contents are controlled by a data structure called a mode line construct, madeup of lists, strings, symbols, and numbers kept in buffer-local variables. Each data typehas a specific meaning for the mode line appearance, as described below. The same data
structure is used for constructing frame titles (see Section 30.6 [Frame Titles], page 821)
and header lines (see Section 24.4.7 [Header Lines], page 559).
A mode line construct may be as simple as a fixed string of text, but it usually specifies
how to combine fixed strings with variables’ values to construct the text. Many of thesevariables are themselves defined to have mode line constructs as their values.
Here are the meanings of various data types as mode line constructs:
stringA string as a mode line construct appears verbatim except for %-constructs in it.
These stand for substitution of other data; see Section 24.4.5 [%-Constructs],
page 556.
If parts of the string have face properties, they control display of the text justas they would text in the buffer. Any characters which have no face propertiesare displayed, by default, in the face mode-line or mode-line-inactive (seeSection “Standard Faces” in The GNU Emacs Manual). The help-echo andkeymap properties in string have special meanings. See Section 24.4.6 [Properties
in Mode], page 558.

symbol

A symbol as a mode line construct stands for its value. The value of symbol isused as a mode line construct, in place of symbol. However, the symbols t andnil are ignored, as is any symbol whose value is void.
There is one exception: if the value of symbol is a string, it is displayed verbatim:
the %-constructs are not recognized.
Unless symbol is marked as risky (i.e., it has a non-nil risky-local-variable
property), all text properties specified in symbol’s value are ignored. This

Chapter 24: Major and Minor Modes

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includes the text properties of strings in symbol’s value, as well as all :eval and:propertize forms in it. (The reason for this is security: non-risky variables
could be set automatically from file variables without prompting the user.)(string rest...)(list rest...)A list whose first element is a string or list means to process all the elements
recursively and concatenate the results. This is the most common form of modeline construct. (Note that text properties are handled specially (for reasons ofefficiency) when displaying strings in the mode line: Only the text property on
the first character of the string are considered, and they are then used over theentire string. If you need a string with different text properties, you have to use
the special :propertize mode line construct.)(:eval form)
A list whose first element is the symbol :eval says to evaluate form, and use
the result as a string to display. Make sure this evaluation cannot load any files,
as doing so could cause infinite recursion.
(:propertize elt props...)A list whose first element is the symbol :propertize says to process the modeline construct elt recursively, then add the text properties specified by props tothe result. The argument props should consist of zero or more pairs text-property
value. If elt is or produces a string with text properties, all the characters ofthat string should have the same properties, or else some of them might beremoved by :propertize.
(symbol then else)
A list whose first element is a symbol that is not a keyword specifies a conditional.
Its meaning depends on the value of symbol. If symbol has a non-nil value,
the second element, then, is processed recursively as a mode line construct.
Otherwise, the third element, else, is processed recursively. You may omit else;then the mode line construct displays nothing if the value of symbol is nil orvoid.
(width rest...)A list whose first element is an integer specifies truncation or padding of theresults of rest. The remaining elements rest are processed recursively as modeline constructs and concatenated together. When width is positive, the result isspace filled on the right if its width is less than width. When width is negative,
the result is truncated on the right to −width columns if its width exceeds−width.
For example, the usual way to show what percentage of a buffer is above the
top of the window is to use a list like this: (-3 "%p").

24.4.3 The Top Level of Mode Line Control
The variable in overall control of the mode line is mode-line-format.

Chapter 24: Major and Minor Modes

553[User Option]
The value of this variable is a mode line construct that controls the contents of themode-line. It is always buffer-local in all buffers.

mode-line-format

If you set this variable to nil in a buffer, that buffer does not have a mode line. (Awindow that is just one line tall also does not display a mode line.)
The default value of mode-line-format is designed to use the values of other variables
such as mode-line-position and mode-line-modes (which in turn incorporates the values of the variables mode-name and minor-mode-alist). Very few modes need to alter
mode-line-format itself. For most purposes, it is sufficient to alter some of the variables
that mode-line-format either directly or indirectly refers to.
If you do alter mode-line-format itself, the new value should use the same variables
that appear in the default value (see Section 24.4.4 [Mode Line Variables], page 554), rather
than duplicating their contents or displaying the information in another fashion. This way,
customizations made by the user or by Lisp programs (such as display-time and major
modes) via changes to those variables remain effective.
Here is a hypothetical example of a mode-line-format that might be useful for Shellmode (in reality, Shell mode does not set mode-line-format):(setq mode-line-format(list "-"
'mode-line-mule-info'mode-line-modified'mode-line-frame-identification"%b--";; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")":"'default-directory""'global-mode-string"%[("'(:eval (format-time-string "%F"))'mode-line-process'minor-mode-alist"%n"")%]--"'(which-function-mode ("" which-func-format "--"))'(line-number-mode "L%l--")'(column-number-mode "C%c--")'(-3 "%p")))(The variables line-number-mode, column-number-mode and which-function-mode enable
particular minor modes; as usual, these variable names are also the minor mode command
names.)

Chapter 24: Major and Minor Modes

554

24.4.4 Variables Used in the Mode Line
This section describes variables incorporated by the standard value of mode-line-format
into the text of the mode line. There is nothing inherently special about these variables;
any other variables could have the same effects on the mode line if the value of mode-lineformat is changed to use them. However, various parts of Emacs set these variables on theunderstanding that they will control parts of the mode line; therefore, practically speaking,it is essential for the mode line to use them. Also see Section “Optional Mode Line” in The
GNU Emacs Manual.
[Variable]
This variable holds the value of the mode line construct that displays information
about the language environment, buffer coding system, and current input method.
See Chapter 34 [Non-ASCII Characters], page 963.

mode-line-mule-info[Variable]
This variable holds the value of the mode line construct that displays whether thecurrent buffer is modified. Its default value displays ‘**’ if the buffer is modified, ‘--’if the buffer is not modified, ‘%%’ if the buffer is read only, and ‘%*’ if the buffer is read
only and modified.
Changing this variable does not force an update of the mode line.

mode-line-modified[Variable]
This variable identifies the current frame. Its default value displays " " if you areusing a window system which can show multiple frames, or "-%F " on an ordinary
terminal which shows only one frame at a time.

mode-line-frame-identification[Variable]
This variable identifies the buffer being displayed in the window. Its default value
displays the buffer name, padded with spaces to at least 12 columns.

mode-line-buffer-identification[Variable]
This variable indicates the position in the buffer. Its default value displays the buffer
percentage and, optionally, the buffer size, the line number and the column number.

mode-line-position[User Option]
This option is used in mode-line-position. Its value specifies both the buffer
percentage to display (one of nil, "%o", "%p", "%P" or "%q", see Section 24.4.5 [%Constructs], page 556) and a width to space-fill or truncate to. You are recommended
to set this option with the customize-variable facility.

mode-line-percent-position[Variable]
The variable vc-mode, buffer-local in each buffer, records whether the buffer’s visited
file is maintained with version control, and, if so, which kind. Its value is a string thatappears in the mode line, or nil for no version control.

vc-mode[Variable]
This variable displays the buffer’s major and minor modes. Its default value also
displays the recursive editing level, information on the process status, and whether
narrowing is in effect.

mode-line-modes

Chapter 24: Major and Minor Modes

555[Variable]
This variable is used to show whether default-directory for the current buffer isremote.

mode-line-remotemode-line-client[Variable]

This variable is used to identify emacsclient frames.
The following three variables are used in mode-line-modes:[Variable]
This buffer-local variable holds the “pretty” name of the current buffer’s major mode.
Each major mode should set this variable so that the mode name will appear in
the mode line. The value does not have to be a string, but can use any of thedata types valid in a mode-line construct (see Section 24.4.2 [Mode Line Data],
page 551). To compute the string that will identify the mode name in the mode line,
use format-mode-line (see Section 24.4.8 [Emulating Mode Line], page 560).

mode-name[Variable]
This buffer-local variable contains the mode line information on process status in modes
used for communicating with subprocesses. It is displayed immediately following the
major mode name, with no intervening space. For example, its value in the *shell*
buffer is (":%s"), which allows the shell to display its status along with the major
mode as: ‘(Shell:run)’. Normally this variable is nil.

mode-line-process[Variable]
This variable is displayed at the front of the mode line. By default, this construct isdisplayed right at the beginning of the mode line, except that if there is a memory-fullmessage, it is displayed first.

mode-line-front-spacemode-line-end-spaces[Variable]

This variable is displayed at the end of the mode line.
[Variable]
Mode line construct for miscellaneous information. By default, this shows the information specified by global-mode-string.

mode-line-misc-info[Variable]
The format used to display line numbers when line-number-mode (see Section “Optional Mode Line” in The GNU Emacs Manual) is switched on. ‘%l’ in the format
will be replaced with the line number.

mode-line-position-line-format[Variable]
The format used to display column numbers when column-number-mode (see Section“Optional Mode Line” in The GNU Emacs Manual) is switched on. ‘%c’ in the format
will be replaced with a zero-based column number, and ‘%C’ will be replaced with a
one-based column number.

mode-line-position-column-format[Variable]
The format used to display column numbers when both line-number-mode andcolumn-number-mode are switched on. See the previous two variables for the meaningof the ‘%l’, ‘%c’ and ‘%C’ format specs.

mode-line-position-column-line-format

Chapter 24: Major and Minor Modes

556[Variable]
This variable holds an association list whose elements specify how the mode line should
indicate that a minor mode is active. Each element of the minor-mode-alist should
be a two-element list:

minor-mode-alist(minor-mode-variable mode-line-string)More generally, mode-line-string can be any mode line construct. It appears in themode line when the value of minor-mode-variable is non-nil, and not otherwise. These
strings should begin with spaces so that they don’t run together. Conventionally, theminor-mode-variable for a specific mode is set to a non-nil value when that minor
mode is activated.
minor-mode-alist itself is not buffer-local. Each variable mentioned in the alist
should be buffer-local if its minor mode can be enabled separately in each buffer.
[Variable]
This variable holds a mode line construct that, by default, appears in the mode line
as part of mode-line-misc-info, just after the which-function-mode information ifthat minor mode is enabled, else after mode-line-modes. Elements that are added tothis construct should normally end in a space (to ensure that consecutive global-modestring elements display properly). For instance, the command display-time sets
global-mode-string to refer to the variable display-time-string, which holds astring containing the time and load information.

global-mode-string

The ‘%M’ construct substitutes the value of global-mode-string. This construct is not
used by the default mode line, as the variable itself is used in mode-line-misc-info.
Here is a simplified version of the default value of mode-line-format. The real default
value also specifies addition of text properties.
("-"
mode-line-mule-infomode-line-modified
mode-line-frame-identification
mode-line-buffer-identification""
mode-line-position(vc-mode vc-mode)""
mode-line-modes(which-function-mode ("" which-func-format "--"))(global-mode-string ("--" global-mode-string))"-%-")

24.4.5 %-Constructs in the Mode Line
Strings used as mode line constructs can use certain %-constructs to substitute various kindsof data. The following is a list of the defined %-constructs, and what they mean.
In any construct except ‘%%’, you can add a decimal integer after the ‘%’ to specify aminimum field width. If the width is less, the field is padded to that width. Purely numericChapter 24: Major and Minor Modes

557

constructs (‘c’, ‘i’, ‘I’, and ‘l’) are padded by inserting spaces to the left, and others arepadded by inserting spaces to the right.
%b

The current buffer name, obtained with the buffer-name function.
Section 28.3 [Buffer Names], page 674.

See

%c

The current column number of point, counting from zero starting at the left
margin of the window.

%C

The current column number of point, counting from one starting at the left
margin of the window.

%eWhen Emacs is nearly out of memory for Lisp objects, a brief message saying
so. Otherwise, this is empty.

%f

The visited file name, obtained with the buffer-file-name function. See
Section 28.4 [Buffer File Name], page 675.

%F

The title (only on a window system) or the name of the selected frame. See
Section 30.4.3.1 [Basic Parameters], page 805.

%i

The size of the accessible part of the current buffer; basically (- (point-max)(point-min)).

%I

Like ‘%i’, but the size is printed in a more readable way by using ‘k’ for 10^3,‘M’ for 10^6, ‘G’ for 10^9, etc., to abbreviate.

%l

The current line number of point, counting within the accessible portion of thebuffer.

%M

The value of global-mode-string (which is part of mode-line-misc-info bydefault).

%n‘Narrow’ when narrowing is in effect; nothing otherwise (see narrow-to-regionin Section 31.4 [Narrowing], page 865).

%o

The degree of travel of the window through (the visible portion of) the buffer,i.e. the size of the text above the top of the window expressed as a percentage
of all the text outside the window, or ‘Top’, ‘Bottom’ or ‘All’.

%p

The percentage of the buffer text above the top of window, or ‘Top’, ‘Bottom’or ‘All’. Note that the default mode line construct truncates this to threecharacters.

%P

The percentage of the buffer text that is above the bottom of the window (which
includes the text visible in the window, as well as the text above the top), plus
‘Top’ if the top of the buffer is visible on screen; or ‘Bottom’ or ‘All’.

%q

The percentages of text above both the top and the bottom of the window,
separated by ‘-’, or ‘All’.

%s

The status of the subprocess belonging to the current buffer, obtained withprocess-status. See Section 40.6 [Process Information], page 1092.

%z

The mnemonics of keyboard, terminal, and buffer coding systems.

%Z

Like ‘%z’, but including the end-of-line format.

Chapter 24: Major and Minor Modes

558

%*

‘%’ if the buffer is read only (see buffer-read-only);‘*’ if the buffer is modified (see buffer-modified-p);‘-’ otherwise. See Section 28.5 [Buffer Modification], page 677.

%+‘*’ if the buffer is modified (see buffer-modified-p);‘%’ if the buffer is read only (see buffer-read-only);‘-’ otherwise. This differs from ‘%*’ only for a modified read-only buffer. See
Section 28.5 [Buffer Modification], page 677.

%&‘*’ if the buffer is modified, and ‘-’ otherwise.

%@‘@’ if the buffer’s default-directory (see Section 26.9.4 [File Name Expansion],
page 639) is on a remote machine, and ‘-’ otherwise.

%[

An indication of the depth of recursive editing levels (not counting minibuffer
levels): one ‘[’ for each editing level. See Section 22.13 [Recursive Editing],
page 475.

%]

One ‘]’ for each recursive editing level (not counting minibuffer levels).

%-

Dashes sufficient to fill the remainder of the mode line.

%%

The character ‘%’—this is how to include a literal ‘%’ in a string in which%-constructs are allowed.

Obsolete %-Constructs
The following constructs should no longer be used.
%m

Obsolete; use the mode-name variable instead. The %m construct is inadequate, as
it produces an empty string if the value of mode-name is a non-string mode-line
construct (as in emacs-lisp-mode, for example).

24.4.6 Properties in the Mode Line
Certain text properties are meaningful in the mode line. The face property affects theappearance of text; the help-echo property associates help strings with the text, and keymap
can make the text mouse-sensitive.
There are four ways to specify text properties for text in the mode line:
1. Put a string with a text property directly into the mode line data structure, but see
Section 24.4.2 [Mode Line Data], page 551, for caveats for that.
2. Put a text property on a mode line %-construct such as ‘%12b’; then the expansion of
the %-construct will have that same text property.
3. Use a (:propertize elt props...) construct to give elt a text property specified byprops.
4. Use a list containing :eval form in the mode line data structure, and make form
evaluate to a string that has a text property.
You can use the keymap property to specify a keymap. This keymap only takes realeffect for mouse clicks; binding character keys and function keys to it has no effect, since it
is impossible to move point into the mode line.
When the mode line refers to a variable which does not have a non-nil risky-localvariable property, any text properties given or specified within that variable’s values areChapter 24: Major and Minor Modes

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ignored. This is because such properties could otherwise specify functions to be called, andthose functions could come from file local variables.

24.4.7 Window Header Lines
A window can have a header line at the top, just as it can have a mode line at the bottom.
The header line feature works just like the mode line feature, except that it’s controlled byheader-line-format:[Variable]
This variable, local in every buffer, specifies how to display the header line, for windows
displaying the buffer. The format of the value is the same as for mode-line-format(see Section 24.4.2 [Mode Line Data], page 551). It is normally nil, so that ordinary
buffers have no header line.

header-line-format

If display-line-numbers-mode is turned on in a buffer (see Section “Display Custom”
in The GNU Emacs Manual), the buffer text is indented on display by the amount ofscreen space needed to show the line numbers. By contrast, text of the header line is not
automatically indented, because a header line never displays a line number, and because thetext of the header line is not necessarily directly related to buffer text below it. If a Lisp
program needs the header-line text to be aligned with buffer text (for example, if the buffer
displays columnar data, like tabulated-list-mode does, see Section 24.2.7 [Tabulated ListMode], page 538), it should turn on the minor mode header-line-indent-mode.
[Command]This buffer-local minor mode tracks the changes of the width of the line-number
display on screen (which may vary depending on the range of line numbers shownin the window), and allows Lisp programs to arrange that header-line text is alwaysaligned with buffer text when the line-number width changes. Such Lisp programs
should turn on this mode in the buffer, and use the variables header-line-indentand header-line-indent-width in the header-line-format to ensure it is adjusted
to the text indentation at all times.

header-line-indent-mode[Variable]
This variable’s value is a whitespace string whose width is kept equal to the current
width of line-numbers on display, provided that header-line-indent-mode is turnedon in the buffer shown in the window. The number of spaces is calculated under theassumption that the face of the header-line text uses the same font, including size, as
the frame’s default font; if that assumption is false, use header-line-indent-width,
described below, instead. This variable is intended to be used in simple situations
where the header-line text needs to be indented as a whole to be realigned with buffer
text, by prepending this variable’s value to the actual header-line text. For example,
the following definition of header-line-format:

header-line-indent(setq header-line-format`("" header-line-indent ,my-header-line))
where my-header-line is the format string that produces the actual text of the headerline, will make sure the header-line text is always indented like the buffer text belowit.

Chapter 24: Major and Minor Modes

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This variable’s value is kept updated to provide the current width, in units of theframe’s canonical character width, used for displaying the line numbers, provided thatheader-line-indent-mode is turned on in the buffer shown in the window. It can beused for aligning the header-line text with the buffer text when header-line-indent
is not flexible enough. For example, if the header line uses a font whose metrics isdifferent from the default face’s font, your Lisp program can calculate the width ofline-number display in pixels, by multiplying the value of this variable by the value
returned by frame-char-width (see Section 30.3.2 [Frame Font], page 797), and thenuse the result to align header-line text using the :align-to display property spec(see Section 41.16.2 [Specified Space], page 1200) in pixels on the relevant parts ofheader-line-format.

header-line-indent-width

window-header-line-height &optional window[Function]
This function returns the height in pixels of window’s header line. window must be alive window, and defaults to the selected window.

A window that is just one line tall never displays a header line. A window that is twolines tall cannot display both a mode line and a header line at once; if it has a mode line,
then it does not display a header line.

24.4.8 Emulating Mode Line Formatting
You can use the function format-mode-line to compute the text that would appear in amode line or header line based on a certain mode line construct.

format-mode-line format &optional face window buffer[Function]
This function formats a line of text according to format as if it were generating themode line for window, but it also returns the text as a string. The argument window
defaults to the selected window. If buffer is non-nil, all the information used is takenfrom buffer; by default, it comes from window’s buffer.
The value string normally has text properties that correspond to the faces, keymaps,
etc., that the mode line would have. Any character for which no face property is
specified by format gets a default value determined by face. If face is t, that stands
for either mode-line if window is selected, otherwise mode-line-inactive. If faceis nil or omitted, that stands for the default face. If face is an integer, the value
returned by this function will have no text properties.
You can also specify other valid faces as the value of face. If specified, that faceprovides the face property for characters whose face is not specified by format.
Note that using mode-line, mode-line-inactive, or header-line as face will actually redisplay the mode line or the header line, respectively, using the current
definitions of the corresponding face, in addition to returning the formatted string.
(Other faces do not cause redisplay.)
For example, (format-mode-line header-line-format) returns the text that would
appear in the selected window’s header line ("" if it has no header line). (format-modeline header-line-format 'header-line) returns the same text, with each character
carrying the face that it will have in the header line itself, and also redraws the header
line.

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24.5 Imenu
Imenu is a feature that lets users select a definition or section in the buffer, from a menu
which lists all of them, to go directly to that location in the buffer. Imenu works byconstructing a buffer index which lists the names and buffer positions of the definitions, orother named portions of the buffer; then the user can choose one of them and move point to
it. Major modes can add a menu bar item to use Imenu using imenu-add-to-menubar.

imenu-add-to-menubar name[Command]This function defines a local menu bar item named name to run Imenu.
The user-level commands for using Imenu are described in the Emacs Manual (see Section“Imenu” in the Emacs Manual). This section explains how to customize Imenu’s method offinding definitions or buffer portions for a particular major mode.
The usual and simplest way is to set the variable imenu-generic-expression:[Variable]
This variable, if non-nil, is a list that specifies regular expressions for finding definitions
for Imenu. Simple elements of imenu-generic-expression look like this:(menu-title regexp index)
Here, if menu-title is non-nil, it says that the matches for this element should go ina submenu of the buffer index; menu-title itself specifies the name for the submenu.
If menu-title is nil, the matches for this element go directly in the top level of thebuffer index.
The second item in the list, regexp, is a regular expression (see Section 35.3 [Regular
Expressions], page 995); anything in the buffer that it matches is considered a definition,
something to mention in the buffer index. The third item, index, is a non-negative
integer that indicates which subexpression in regexp matches the definition’s name.
An element can also look like this:(menu-title regexp index function arguments...)Each match for this element creates an index item, and when the index item is selectedby the user, it calls function with arguments consisting of the item name, the buffer
position, and arguments.
For Emacs Lisp mode, imenu-generic-expression could look like this:((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\\\s-+\\([-A-Za-z0-9+]+\\)" 2)("*Vars*" "^\\s-*(def\\(var\\|const\\)\\\s-+\\([-A-Za-z0-9+]+\\)" 2)("*Types*""^\\s-*\(def\\(type\\|struct\\|class\\|ine-condition\\)\\\s-+\\([-A-Za-z0-9+]+\\)" 2))
Setting this variable makes it buffer-local in the current buffer.

imenu-generic-expression[Variable]
This variable controls whether matching against the regular expressions in the value of
imenu-generic-expression is case-sensitive: t, the default, means matching should
ignore case.

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Setting this variable makes it buffer-local in the current buffer.
[Variable]
This variable is an alist of syntax table modifiers to use while processing
imenu-generic-expression, to override the syntax table of the current buffer. Eachelement should have this form:

imenu-syntax-alist(characters . syntax-description)
The car, characters, can be either a character or a string. The element says to givethat character or characters the syntax specified by syntax-description, which is passed
to modify-syntax-entry (see Section 36.3 [Syntax Table Functions], page 1027).
This feature is typically used to give word syntax to characters which normally
have symbol syntax, and thus to simplify imenu-generic-expression and speed up
matching. For example, Fortran mode uses it this way:
(setq imenu-syntax-alist '(("_$" . "w")))
The imenu-generic-expression regular expressions can then use ‘\\sw+’ instead of‘\\(\\sw\\|\\s_\\)+’. Note that this technique may be inconvenient when the modeneeds to limit the initial character of a name to a smaller set of characters than are
allowed in the rest of a name.
Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the variables imenu-previndex-position-function and imenu-extract-index-name-function:[Variable]
If this variable is non-nil, its value should be a function that finds the next definition
to put in the buffer index, scanning backward in the buffer from point. It should
return nil if it doesn’t find another definition before point. Otherwise it should leave
point at the place it finds a definition and return any non-nil value.

imenu-prev-index-position-function

Setting this variable makes it buffer-local in the current buffer.
[Variable]
If this variable is non-nil, its value should be a function to return the name for adefinition, assuming point is in that definition as the imenu-prev-index-positionfunction function would leave it.

imenu-extract-index-name-function

Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the variable imenu-createindex-function:[Variable]
This variable specifies the function to use for creating a buffer index. The function
should take no arguments, and return an index alist for the current buffer. It is called
within save-excursion, so where it leaves point makes no difference.

imenu-create-index-function

The index alist can have three types of elements. Simple elements look like this:(index-name . index-position)

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Selecting a simple element has the effect of moving to position index-position in thebuffer. Special elements look like this:(index-name index-position function arguments...)Selecting a special element performs:(funcall function
index-name index-position arguments...)A nested sub-alist element looks like this:(menu-title . sub-alist)
It creates the submenu menu-title specified by sub-alist.
The default value of imenu-create-index-function is imenu-default-createindex-function. This function calls the value of imenu-prev-index-positionfunction and the value of imenu-extract-index-name-function to produce theindex alist. However, if either of these two variables is nil, the default function uses
imenu-generic-expression instead.
Setting this variable makes it buffer-local in the current buffer.
If built with tree-sitter, Emacs can automatically generate an Imenu index if the major
mode sets relevant variables.
[Variable]
This variable instructs Emacs how to generate Imenu indexes. It should be a list of(category regexp pred name-fn).
category should be the name of a category, like "Function", "Class", etc. regexp
should be a regexp matching the type of nodes that belong to category. pred should beeither nil or a function that takes a node as the argument. It should return non-nil
if the node is a valid node for category, or nil if not.
category could also be nil, in which case the entries matched by regexp and pred are
not grouped under category.
name-fn should be either nil or a function that takes a defun node and returns thename of that defun, e.g., the function name for a function definition. If name-fn isnil, treesit-defun-name (see Section 37.7 [Tree-sitter Major Modes], page 1061) isused instead.
treesit-major-mode-setup (see Section 37.7 [Tree-sitter Major Modes], page 1061)
automatically sets up Imenu if this variable is non-nil.

treesit-simple-imenu-settings

24.6 Font Lock Mode
Font Lock mode is a buffer-local minor mode that automatically attaches face properties tocertain parts of the buffer based on their syntactic role. How it parses the buffer depends onthe major mode; most major modes define syntactic criteria for which faces to use in which
contexts. This section explains how to customize Font Lock for a particular major mode.
Font Lock mode finds text to highlight in three ways: through parsing based on a fullblown parser (usually, via an external library or program), through syntactic parsing basedon the Emacs’s built-in syntax table, or through searching (usually for regular expressions).
If enabled, parser-based fontification happens first (see Section 24.6.10 [Parser-based Font

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Lock], page 578). Syntactic fontification happens next; it finds comments and string constants
and highlights them. Search-based fontification happens last.

24.6.1 Font Lock Basics
The Font Lock functionality is based on several basic functions. Each of these calls thefunction specified by the corresponding variable. This indirection allows major and minor
modes to modify the way fontification works in the buffers of that mode, and even use theFont Lock mechanisms for features that have nothing to do with fontification. (This is why
the description below says “should” when it describes what the functions do: the modecan customize the values of the corresponding variables to do something entirely different.)
The variables mentioned below are described in Section 24.6.4 [Other Font Lock Variables],page 571.
font-lock-fontify-bufferThis function should fontify the current buffer’s accessible portion, by callingthe function specified by font-lock-fontify-buffer-function.
font-lock-unfontify-buffer
Used when turning Font Lock off to remove the fontification. Calls the function
specified by font-lock-unfontify-buffer-function.
font-lock-fontify-region beg end &optional loudly
Should fontify the region between beg and end. If loudly is non-nil, should display status messages while fontifying. Calls the function specified by font-lockfontify-region-function.
font-lock-unfontify-region beg end
Should remove fontification from the region between beg and end. Calls thefunction specified by font-lock-unfontify-region-function.
font-lock-flush &optional beg end
This function should mark the fontification of the region between beg and end
as outdated. If not specified or nil, beg and end default to the beginningand end of the buffer’s accessible portion. Calls the function specified by
font-lock-flush-function.
font-lock-ensure &optional beg end
This function should make sure the region between beg and end has beenfontified. The optional arguments beg and end default to the beginning and theend of the buffer’s accessible portion. Calls the function specified by font-lockensure-function.
font-lock-debug-fontify
This is a convenience command meant to be used when developing font locking
for a mode, and should not be called from Lisp code. It recomputes all the
relevant variables and then calls font-lock-fontify-region on the entire
buffer.
There are several variables that control how Font Lock mode highlights text. But major
modes should not set any of these variables directly. Instead, they should set font-lockdefaults as a buffer-local variable. The value assigned to this variable is used, if and when
Font Lock mode is enabled, to set all the other variables.

Chapter 24: Major and Minor Modes

565[Variable]
This variable is set by modes to specify how to fontify text in that mode. It automatically becomes buffer-local when set. If its value is nil, Font Lock mode does
no highlighting, and you can use the ‘Faces’ menu (under ‘Edit’ and then ‘Text
Properties’ in the menu bar) to assign faces explicitly to text in the buffer.
If non-nil, the value should look like this:(keywords [keywords-only [case-fold[syntax-alist other-vars...]]])
The first element, keywords, indirectly specifies the value of font-lock-keywords
which directs search-based fontification. It can be a symbol, a variable or a function
whose value is the list to use for font-lock-keywords. It can also be a list of several
such symbols, one for each possible level of fontification. The first symbol specifies the‘mode default’ level of fontification, the next symbol level 1 fontification, the nextlevel 2, and so on. The ‘mode default’ level is normally the same as level 1. It is used
when font-lock-maximum-decoration has a nil value. See Section 24.6.5 [Levels of
Font Lock], page 572.
The second element, keywords-only, specifies the value of the variable font-lockkeywords-only. If this is omitted or nil, syntactic fontification (of strings andcomments) is also performed. If this is non-nil, syntactic fontification is not performed.
See Section 24.6.8 [Syntactic Font Lock], page 575.
The third element, case-fold, specifies the value of font-lock-keywords-case-foldsearch. If it is non-nil, Font Lock mode ignores case during search-based fontification.
If the fourth element, syntax-alist, is non-nil, it should be a list of cons cells of the form(char-or-string . string). These are used to set up a syntax table for syntactic
fontification; the resulting syntax table is stored in font-lock-syntax-table. If
syntax-alist is omitted or nil, syntactic fontification uses the syntax table returnedby the syntax-table function. See Section 36.3 [Syntax Table Functions], page 1027.
All the remaining elements (if any) are collectively called other-vars. Each of theseelements should have the form (variable . value)—which means, make variablebuffer-local and then set it to value. You can use these other-vars to set other variables
that affect fontification, aside from those you can control with the first five elements.
See Section 24.6.4 [Other Font Lock Variables], page 571.

font-lock-defaults

If your mode fontifies text explicitly by adding font-lock-face properties, it can specify(nil t) for font-lock-defaults to turn off all automatic fontification. However, this is
not required; it is possible to fontify some things using font-lock-face properties and set
up automatic fontification for other parts of the text.

24.6.2 Search-based Fontification
The variable which directly controls search-based fontification is font-lock-keywords,
which is typically specified via the keywords element in font-lock-defaults.
[Variable]
The value of this variable is a list of the keywords to highlight. Lisp programs should not
set this variable directly. Normally, the value is automatically set by Font Lock mode,using the keywords element in font-lock-defaults. The value can also be altered

font-lock-keywords

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using the functions font-lock-add-keywords and font-lock-remove-keywords (seeSection 24.6.3 [Customizing Keywords], page 569).
Each element of font-lock-keywords specifies how to find certain cases of text, and how
to highlight those cases. Font Lock mode processes the elements of font-lock-keywords
one by one, and for each element, it finds and handles all matches. Ordinarily, once partof the text has been fontified already, this cannot be overridden by a subsequent matchin the same text; but you can specify different behavior using the override element of asubexp-highlighter.
Each element of font-lock-keywords should have one of these forms:
regexpHighlight all matches for regexp using font-lock-keyword-face. For example,;; Highlight occurrences of the word ‘foo’;; using font-lock-keyword-face.
"\\<foo\\>"Be careful when composing these regular expressions; a poorly written pattern
can dramatically slow things down! The function regexp-opt (see Section 35.3.3[Regexp Functions], page 1005) is useful for calculating optimal regular expressions to match several keywords.

function

Find text by calling function, and highlight the matches it finds using
font-lock-keyword-face.
When function is called, it receives one argument, the limit of the search; itshould begin searching at point, and not search beyond the limit. It should
return non-nil if it succeeds, and set the match data to describe the match thatwas found. Returning nil indicates failure of the search.
Fontification will call function repeatedly with the same limit, and with point
where the previous invocation left it, until function fails. On failure, functionneed not reset point in any particular way.

(matcher . subexp)
In this kind of element, matcher is either a regular expression or a function, as
described above. The cdr, subexp, specifies which subexpression of matcher
should be highlighted (instead of the entire text that matcher matched).
;; Highlight the ‘bar’ in each occurrence of ‘fubar’,;; using font-lock-keyword-face.
("fu\\(bar\\)" . 1)
(matcher . facespec)
In this kind of element, facespec is an expression whose value specifies the face touse for highlighting. In the simplest case, facespec is a Lisp variable (a symbol)
whose value is a face name.
;; Highlight occurrences of ‘fubar’,;; using the face which is the value of fubar-face.
("fubar" . fubar-face)
However, facespec can also evaluate to a list of this form:(subexp

Chapter 24: Major and Minor Modes

567(face face prop1 val1 prop2 val2...))
to specify the face face and various additional text properties to put on the
text that matches. If you do this, be sure to add the other text property
names that you set in this way to the value of font-lock-extra-managedprops so that the properties will also be cleared out when they are no longer
appropriate. Alternatively, you can set the variable font-lock-unfontifyregion-function to a function that clears these properties. See Section 24.6.4[Other Font Lock Variables], page 571.
(matcher . subexp-highlighter)In this kind of element, subexp-highlighter is a list which specifies how tohighlight matches found by matcher. It has the form:(subexp facespec [override [laxmatch]])The car, subexp, is an integer specifying which subexpression of the match tofontify (0 means the entire matching text). The second subelement, facespec, isan expression whose value specifies the face, as described above.
The last two values in subexp-highlighter, override and laxmatch, are optionalflags. If override is t, this element can override existing fontification made byprevious elements of font-lock-keywords. If it is keep, then each character
is fontified if it has not been fontified already by some other element. If it
is prepend, the face specified by facespec is added to the beginning of the
font-lock-face property. If it is append, the face is added to the end of the
font-lock-face property.
If laxmatch is non-nil, it means there should be no error if there is no subexpression numbered subexp in matcher. Obviously, fontification of the subexpression
numbered subexp will not occur. However, fontification of other subexpressions(and other regexps) will continue. If laxmatch is nil, and the specified subexpression is missing, then an error is signaled which terminates search-based
fontification.
Here are some examples of elements of this kind, and what they do:;; Highlight occurrences of either ‘foo’ or ‘bar’, using;; foo-bar-face, even if they have already been highlighted.
;; foo-bar-face should be a variable whose value is a face.
("foo\\|bar" 0 foo-bar-face t);; Highlight the first subexpression within each occurrence;; that the function fubar-match finds,;; using the face which is the value of fubar-face.
(fubar-match 1 fubar-face)(matcher . anchored-highlighter)In this kind of element, anchored-highlighter specifies how to highlight textthat follows a match found by matcher. So a match found by matcher acts
as the anchor for further searches specified by anchored-highlighter. anchoredhighlighter is a list of the following form:(anchored-matcher pre-form post-form subexp-highlighters...)Here, anchored-matcher, like matcher, is either a regular expression or a function.
After a match of matcher is found, point is at the end of the match. Now, Font

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Lock evaluates the form pre-form. Then it searches for matches of anchoredmatcher and uses subexp-highlighters to highlight these. A subexp-highlighter
is as described above. Finally, Font Lock evaluates post-form.
The forms pre-form and post-form can be used to initialize before, and cleanup
after, anchored-matcher is used. Typically, pre-form is used to move point tosome position relative to the match of matcher, before starting with anchoredmatcher. post-form might be used to move back, before resuming with matcher.
After Font Lock evaluates pre-form, it does not search for anchored-matcher
beyond the end of the line. However, if pre-form returns a buffer position that isgreater than the position of point after pre-form is evaluated, then the position
returned by pre-form is used as the limit of the search instead. It is generally abad idea to return a position greater than the end of the line; in other words,
the anchored-matcher search should not span lines.
For example,;; Highlight occurrences of the word ‘item’ following;; an occurrence of the word ‘anchor’ (on the same line);; in the value of item-face.
("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face))

Here, pre-form and post-form are nil. Therefore searching for ‘item’ starts
at the end of the match of ‘anchor’, and searching for subsequent instances of‘anchor’ resumes from where searching for ‘item’ concluded.
(matcher highlighters...)This sort of element specifies several highlighter lists for a single matcher. A
highlighter list can be of the type subexp-highlighter or anchored-highlighter as
described above.
For example,;; Highlight occurrences of the word ‘anchor’ in the value;; of anchor-face, and subsequent occurrences of the word;; ‘item’ (on the same line) in the value of item-face.
("\\<anchor\\>" (0 anchor-face)("\\<item\\>" nil nil (0 item-face)))(eval . form)
Here form is an expression to be evaluated the first time this value of font-lockkeywords is used in a buffer. Its value should have one of the forms describedin this table.
Warning: Do not design an element of font-lock-keywords to match text which spanslines; this does not work reliably. For details, see Section 24.6.9 [Multiline Font Lock],
page 576.
You can use case-fold in font-lock-defaults to specify the value of font-lockkeywords-case-fold-search which says whether search-based fontification should be caseinsensitive.
[Variable]
Non-nil means that regular expression matching for the sake of font-lock-keywords
should be case-insensitive.

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24.6.3 Customizing Search-Based Fontification
You can use font-lock-add-keywords to add additional search-based fontification rules toa major mode, and font-lock-remove-keywords to remove rules. You can also customize
the font-lock-ignore option to selectively disable fontification rules for keywords thatmatch certain criteria.

font-lock-add-keywords mode keywords &optional how[Function]
This function adds highlighting keywords, for the current buffer or for major mode
mode. The argument keywords should be a list with the same format as the variable
font-lock-keywords.
If mode is a symbol which is a major mode command name, such as c-mode, the effectis that enabling Font Lock mode in mode will add keywords to font-lock-keywords.
Calling with a non-nil value of mode is correct only in your ~/.emacs file.
If mode is nil, this function adds keywords to font-lock-keywords in the current
buffer. This way of calling font-lock-add-keywords is usually used in mode hookfunctions.
By default, keywords are added at the beginning of font-lock-keywords. If theoptional argument how is set, they are used to replace the value of font-lockkeywords. If how is any other non-nil value, they are added at the end of font-lockkeywords.
Some modes provide specialized support you can use in additional highlighting patterns. See the variables c-font-lock-extra-types, c++-font-lock-extra-types,
and java-font-lock-extra-types, for example.
Warning: Major mode commands must not call font-lock-add-keywords under any
circumstances, either directly or indirectly, except through their mode hooks. (Doingso would lead to incorrect behavior for some minor modes.) They should set up theirrules for search-based fontification by setting font-lock-keywords.

font-lock-remove-keywords mode keywords[Function]
This function removes keywords from font-lock-keywords for the current buffer orfor major mode mode. As in font-lock-add-keywords, mode should be a major
mode command name or nil. All the caveats and requirements for font-lock-addkeywords apply here too. The argument keywords must exactly match the one usedby the corresponding font-lock-add-keywords.

For example, the following code adds two fontification patterns for C mode: one to fontify
the word ‘FIXME’, even in comments, and another to fontify the words ‘and’, ‘or’ and ‘not’
as keywords.
(font-lock-add-keywords 'c-mode'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))This example affects only C mode proper. To add the same patterns to C mode and allmodes derived from it, do this instead:(add-hook 'c-mode-hook(lambda ()(font-lock-add-keywords nil'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)Chapter 24: Major and Minor Modes

570("\\<\\(and\\|or\\|not\\)\\>" .
font-lock-keyword-face)))))[User Option]
This option defines conditions for selectively disabling fontifications due to certain
Font Lock keywords. If non-nil, its value is a list of elements of the following form:(symbol condition ...)
Here, symbol is a symbol, usually a major or minor mode. The subsequent conditionsof a symbol’s list element will be in effect if symbol is bound and its value is non-nil.
For a mode’s symbol, it means that the current major mode is derived from thatmode, or that minor mode is enabled in the buffer. When a condition is in effect, any
fontifications caused by font-lock-keywords elements that match the condition will
be disabled.
Each condition can be one of the following:font-lock-ignore

a symbolThis condition matches any element of Font Lock keywords that references
the symbol. This is usually a face, but can be any symbol referenced
by an element of the font-lock-keywords list. The symbol can containwildcards: * matches any string in the symbol’ss name, ? matches a single
character, and [char-set], where char-set is a string of one or morecharacters, matches a single character from the set.

a string

This condition matches any element of Font Lock keywords whose matcher
is a regexp which matches the string. In other words, this condition
matches a Font Lock rule which highlights the string. Thus, the string
could be a specific program keyword whose highlighting you want todisable.

(pred function)
This condition matches any element of Font Lock keywords for whichfunction, when called with the element as the argument, returns non-nil.
(not condition)
This matches if condition doesn’t.
(and condition ...)
This matches if each of the conditions matches.
(or condition ...)
This matches if at least one of the conditions matches.
(except condition)
This condition can only be used at top level or inside an or clause. It
undoes the effect of a previously matching condition on the same level.
As an example, consider the following setting:(setq font-lock-ignore'((prog-mode font-lock-*-face(except help-echo))(emacs-lisp-mode (except ";;;###autoload)")(whitespace-mode whitespace-empty-at-bob-regexp)(makefile-mode (except *))))

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Line by line, this does the following:
1. In all programming modes, disable fontifications due to all font-lock keywords that
apply one of the standard font-lock faces (excluding strings and comments, which arecovered by syntactic Font Lock).
2. However, keep any keywords that add a help-echo text property.
3. In Emacs Lisp mode, also keep the highlighting of autoload cookies, which would havebeen excluded by the first condition.
4. When whitespace-mode (a minor mode) is enabled, also don’t highlight an empty line
at beginning of buffer.
5. Finally, in Makefile mode, don’t apply any conditions.

24.6.4 Other Font Lock Variables
This section describes additional variables that a major mode can set by means of other-vars
in font-lock-defaults (see Section 24.6.1 [Font Lock Basics], page 564).
[Variable]
If this variable is non-nil, it should be a function that is called with no arguments, tochoose an enclosing range of text for refontification for the command M-x font-lockfontify-block.
The function should report its choice by placing the region around it. A good choice
is a range of text large enough to give proper results, but not too large so thatrefontification becomes slow. Typical values are mark-defun for programming modes
or mark-paragraph for textual modes.

font-lock-mark-block-function[Variable]
This variable specifies additional properties (other than font-lock-face) that are
being managed by Font Lock mode. It is used by font-lock-default-unfontifyregion, which normally only manages the font-lock-face property. If you want
Font Lock to manage other properties as well, you must specify them in a facespec in
font-lock-keywords as well as add them to this list. See Section 24.6.2 [Search-based
Fontification], page 565.

font-lock-extra-managed-props[Variable]
Function to use for fontifying the buffer. The default value is font-lock-defaultfontify-buffer.

font-lock-fontify-buffer-function[Variable]
Function to use for unfontifying the buffer. This is used when turning off Font Lockmode. The default value is font-lock-default-unfontify-buffer.

font-lock-unfontify-buffer-function[Variable]
Function to use for fontifying a region. It should take two arguments, the beginningand end of the region, and an optional third argument verbose. If verbose is non-nil,the function should print status messages. The default value is font-lock-defaultfontify-region.

font-lock-fontify-region-function[Variable]
Function to use for unfontifying a region. It should take two arguments, the beginningand end of the region. The default value is font-lock-default-unfontify-region.

font-lock-unfontify-region-function

Chapter 24: Major and Minor Modes

572[Variable]
Function to use for declaring that a region’s fontification is out of date. It takes twoarguments, the beginning and end of the region. The default value of this variable isfont-lock-after-change-function.

font-lock-flush-function[Variable]
Function to use for making sure a region of the current buffer has been fontified. It iscalled with two arguments, the beginning and end of the region. The default valueof this variable is a function that calls font-lock-default-fontify-buffer if thebuffer is not fontified; the effect is to make sure the entire accessible portion of thebuffer is fontified.

font-lock-ensure-function

jit-lock-register function &optional contextual[Function]
This function tells Font Lock mode to run the Lisp function function any time it
has to fontify or refontify part of the current buffer. It calls function before callingthe default fontification functions, and gives it two arguments, start and end, which
specify the region to be fontified or refontified. If function performs fontifications, it
can return a list of the form (jit-lock-bounds beg . end), to indicate the boundsof the region it actually fontified; Just-In-Time (a.k.a. “JIT”) font-lock will use thisinformation to optimize subsequent redisplay cycles and regions of buffer text it willpass to future calls to function.
The optional argument contextual, if non-nil, forces Font Lock mode to always
refontify a syntactically relevant part of the buffer, and not just the modified lines.
This argument can usually be omitted.

When Font Lock is activated in a buffer, it calls this function with a non-nil value ofcontextual if the value of font-lock-keywords-only (see Section 24.6.8 [Syntactic
Font Lock], page 575) is nil.

jit-lock-unregister function[Function]
If function was previously registered as a fontification function using jit-lockregister, this function unregisters it.

jit-lock-debug-mode &optional arg[Command]This is a minor mode whose purpose is to help in debugging code that is run by
JIT font-lock. When this mode is enabled, most of the code that JIT font-locknormally runs during redisplay cycles, where Lisp errors are suppressed, is instead
run by a timer. Thus, this mode allows using debugging aids such as debug-onerror (see Section 19.1.1 [Error Debugging], page 333) and Edebug (see Section 19.2
[Edebug], page 344) for finding and fixing problems in font-lock code and any othercode run by JIT font-lock. Another command that could be useful when developing
and debugging font-lock is font-lock-debug-fontify, see Section 24.6.1 [Font Lock
Basics], page 564.

24.6.5 Levels of Font Lock
Some major modes offer three different levels of fontification. You can define multiple levels
by using a list of symbols for keywords in font-lock-defaults. Each symbol specifies one
level of fontification; it is up to the user to choose one of these levels, normally by setting

Chapter 24: Major and Minor Modes

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font-lock-maximum-decoration (see Section “Font Lock” in the GNU Emacs Manual).
The chosen level’s symbol value is used to initialize font-lock-keywords.
Here are the conventions for how to define the levels of fontification:• Level 1: highlight function declarations, file directives (such as include or importdirectives), strings and comments. The idea is speed, so only the most important andtop-level components are fontified.
• Level 2: in addition to level 1, highlight all language keywords, including type namesthat act like keywords, as well as named constant values. The idea is that all keywords(either syntactic or semantic) should be fontified appropriately.
• Level 3: in addition to level 2, highlight the symbols being defined in function andvariable declarations, and all builtin function names, wherever they appear.

24.6.6 Precalculated Fontification
Some major modes such as list-buffers and occur construct the buffer text programmatically. The easiest way for them to support Font Lock mode is to specify the faces of text
when they insert the text in the buffer.
The way to do this is to specify the faces in the text with the special text property
font-lock-face (see Section 33.19.4 [Special Properties], page 924). When Font Lock modeis enabled, this property controls the display, just like the face property. When Font Lockmode is disabled, font-lock-face has no effect on the display.
It is ok for a mode to use font-lock-face for some text and also use the normal Font
Lock machinery. But if the mode does not use the normal Font Lock machinery, it should not
set the variable font-lock-defaults. In this case the face property will not be overridden,
so using the face property could work too. However, using font-lock-face is generally
preferable as it allows the user to control the fontification by toggling font-lock-mode, andlets the code work regardless of whether the mode uses Font Lock machinery or not.

24.6.7 Faces for Font Lock
Font Lock mode can highlight using any face, but Emacs defines several faces specificallyfor Font Lock to use to highlight text. These Font Lock faces are listed below. They canalso be used by major modes for syntactic highlighting outside of Font Lock mode (seeSection 24.2.1 [Major Mode Conventions], page 528).
Each of these symbols is both a face name, and a variable whose default value is the symbol
itself. Thus, the default value of font-lock-comment-face is font-lock-comment-face.
The faces are listed with descriptions of their typical usage, and in order of greater tolesser prominence. If a mode’s syntactic categories do not fit well with the usage descriptions,the faces can be assigned using the ordering as a guide.
font-lock-warning-facefor a construct that is peculiar (e.g., an unescaped confusable quote in an Emacs
Lisp symbol like ‘‘foo’), or that greatly changes the meaning of other text, like‘;;;###autoload’ in Emacs Lisp and ‘#error’ in C.
font-lock-function-name-face
for the name of a function being defined or declared.

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font-lock-function-call-face
for the name of a function being called. This face inherits, by default, from
font-lock-function-name-face.
font-lock-variable-name-face
for the name of a variable being defined or declared.
font-lock-variable-use-face
for the name of a variable being referenced. This face inherits, by default, from
font-lock-variable-name-face.
font-lock-keyword-facefor a keyword with special syntactic significance, like ‘for’ and ‘if’ in C.
font-lock-comment-facefor comments.
font-lock-comment-delimiter-facefor comments delimiters, like ‘/*’ and ‘*/’ in C. On most terminals, this inherits
from font-lock-comment-face.
font-lock-type-face
for the names of user-defined data types.
font-lock-constant-face
for the names of constants, like ‘NULL’ in C.
font-lock-builtin-face
for the names of built-in functions.
font-lock-preprocessor-facefor preprocessor commands.
builtin-face.

This inherits, by default, from font-lock-font-lock-string-facefor string constants.
font-lock-doc-facefor documentation embedded in program code inside specially-formed comments
or strings. This face inherits, by default, from font-lock-string-face.
font-lock-doc-markup-facefor mark-up elements in text using font-lock-doc-face. It is typically used forthe mark-up constructs in documentation embedded in program code, following
conventions such as Haddock, Javadoc or Doxygen. This face inherits, by default,
from font-lock-constant-face.
font-lock-negation-char-facefor easily-overlooked negation characters.
font-lock-escape-facefor escape sequences in strings. This face inherits, by default, from font-lockregexp-grouping-backslash.
Here is an example in Python, where the escape sequence \n is used:
print('Hello world!\n')Chapter 24: Major and Minor Modes

575

font-lock-number-facefor numbers.
font-lock-operator-facefor operators.
font-lock-property-name-facefor properties of an object, such as the declaration of fields in a struct. This
face inherits, by default, from font-lock-variable-name-face.
font-lock-property-use-facefor properties of an object, such as use of fields in a struct. This face inherits,
by default, from font-lock-property-name-face.
For example,
typedef struct{
int prop;//^ property} obj;
int main(){obj o;
o.prop = 3;// ^ property}

font-lock-punctuation-facefor punctuation such as brackets and delimiters.
font-lock-bracket-facefor brackets (e.g., (), [], {}). This face inherits, by default, from font-lockpunctuation-face.
font-lock-delimiter-facefor delimiters (e.g., ;, :, ,). This face inherits, by default, from font-lockpunctuation-face.
font-lock-misc-punctuation-facefor punctuation that is not a bracket or delimiter. This face inherits, by default,
from font-lock-punctuation-face.

24.6.8 Syntactic Font Lock
Syntactic fontification uses a syntax table (see Chapter 36 [Syntax Tables], page 1022) to findand highlight syntactically relevant text. If enabled, it runs prior to search-based fontification.
The variable font-lock-syntactic-face-function, documented below, determines whichsyntactic constructs to highlight. There are several variables that affect syntactic fontification;
you should set them by means of font-lock-defaults (see Section 24.6.1 [Font Lock Basics],
page 564).
Whenever Font Lock mode performs syntactic fontification on a stretch of text, it first
calls the function specified by syntax-propertize-function. Major modes can use this to
apply syntax-table text properties to override the buffer’s syntax table in special cases.
See Section 36.4 [Syntax Properties], page 1029.

Chapter 24: Major and Minor Modes

576[Variable]
If the value of this variable is non-nil, Font Lock does not do syntactic fontification,
only search-based fontification based on font-lock-keywords. It is normally set by
Font Lock mode based on the keywords-only element in font-lock-defaults. If
the value is nil, Font Lock will call jit-lock-register (see Section 24.6.4 [Other
Font Lock Variables], page 571) to set up for automatic refontification of buffer text
following a modified line to reflect the new syntactic context due to the change.
To use only syntactic fontification, this variable should be non-nil, while font-lockkeywords should be set to nil (see Section 24.6.1 [Font Lock Basics], page 564).

font-lock-keywords-only[Variable]
This variable holds the syntax table to use for fontification of comments and strings.
It is normally set by Font Lock mode based on the syntax-alist element in font-lockdefaults. If this value is nil, syntactic fontification uses the buffer’s syntax table(the value returned by the function syntax-table; see Section 36.3 [Syntax Table
Functions], page 1027).

font-lock-syntax-table[Variable]
If this variable is non-nil, it should be a function to determine which face to use for agiven syntactic element (a string or a comment).
The function is called with one argument, the parse state at point returned
by parse-partial-sexp, and should return a face. The default value returns
font-lock-comment-face for comments and font-lock-string-face for strings(see Section 24.6.7 [Faces for Font Lock], page 573).
This variable is normally set through the “other” elements in font-lock-defaults:(setq-local font-lock-defaults`(,python-font-lock-keywords
nil nil nil nil(font-lock-syntactic-face-function. python-font-lock-syntactic-face-function)))font-lock-syntactic-face-function

24.6.9 Multiline Font Lock Constructs
Normally, elements of font-lock-keywords should not match across multiple lines; that
doesn’t work reliably, because Font Lock usually scans just part of the buffer, and it canmiss a multi-line construct that crosses the line boundary where the scan starts. (The scan
normally starts at the beginning of a line.)
Making elements that match multiline constructs work properly has two aspects: correct
identification and correct rehighlighting. The first means that Font Lock finds all multiline
constructs. The second means that Font Lock will correctly rehighlight all the relevant text
when a multiline construct is changed—for example, if some of the text that was previously
part of a multiline construct ceases to be part of it. The two aspects are closely related, andoften getting one of them to work will appear to make the other also work. However, forreliable results you must attend explicitly to both aspects.
There are three ways to ensure correct identification of multiline constructs:• Add a function to font-lock-extend-region-functions that does the identificationand extends the scan so that the scanned text never starts or ends in the middle of amultiline construct.

Chapter 24: Major and Minor Modes

577• Use the font-lock-fontify-region-function hook similarly to extend the scan sothat the scanned text never starts or ends in the middle of a multiline construct.
• Somehow identify the multiline construct right when it gets inserted into the buffer (orat any point after that but before font-lock tries to highlight it), and mark it with afont-lock-multiline which will instruct font-lock not to start or end the scan in the
middle of the construct.
There are several ways to do rehighlighting of multiline constructs:• Place a font-lock-multiline property on the construct. This will rehighlight thewhole construct if any part of it is changed. In some cases you can do this automaticallyby setting the font-lock-multiline variable, which see.
• Make sure jit-lock-contextually is set and rely on it doing its job. This will only
rehighlight the part of the construct that follows the actual change, and will do it after
a short delay. This only works if the highlighting of the various parts of your multiline
construct never depends on text in subsequent lines. Since jit-lock-contextually is
activated by default, this can be an attractive solution.
• Place a jit-lock-defer-multiline property on the construct. This works only if
jit-lock-contextually is used, and with the same delay before rehighlighting, butlike font-lock-multiline, it also handles the case where highlighting depends on
subsequent lines.
• If parsing the syntax of a construct depends on it being parsed in one single chunk, you
can add the syntax-multiline text property over the construct in question. The mostcommon use for this is when the syntax property to apply to ‘FOO’ depend on some latertext ‘BAR’: By placing this text property over the whole of ‘FOO...BAR’, you make surethat any change of ‘BAR’ will also cause the syntax property of ‘FOO’ to be recomputed.
Note: For this to work, the mode needs to add syntax-propertize-multiline tosyntax-propertize-extend-region-functions.

24.6.9.1 Font Lock Multiline
One way to ensure reliable rehighlighting of multiline Font Lock constructs is to put onthem the text property font-lock-multiline. It should be present and non-nil for textthat is part of a multiline construct.
When Font Lock is about to highlight a range of text, it first extends the boundaries of
the range as necessary so that they do not fall within text marked with the font-lockmultiline property. Then it removes any font-lock-multiline properties from the range,and highlights it. The highlighting specification (mostly font-lock-keywords) must reinstall
this property each time, whenever it is appropriate.
Warning: don’t use the font-lock-multiline property on large ranges of text, becausethat will make rehighlighting slow.
[Variable]
If the font-lock-multiline variable is set to t, Font Lock will try to add the
font-lock-multiline property automatically on multiline constructs. This is nota universal solution, however, since it slows down Font Lock somewhat. It can misssome multiline constructs, or make the property larger or smaller than necessary.

font-lock-multiline

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For elements whose matcher is a function, the function should ensure that submatch
0 covers the whole relevant multiline construct, even if only a small subpart will behighlighted. It is often just as easy to add the font-lock-multiline property by
hand.
The font-lock-multiline property is meant to ensure proper refontification; it does
not automatically identify new multiline constructs. Identifying them requires that Font
Lock mode operate on large enough chunks at a time. This will happen by accident on
many cases, which may give the impression that multiline constructs magically work. If you
set the font-lock-multiline variable non-nil, this impression will be even stronger, since
the highlighting of those constructs which are found will be properly updated from then on.
But that does not work reliably.
To find multiline constructs reliably, you must either manually place the font-lockmultiline property on the text before Font Lock mode looks at it, or use font-lockfontify-region-function.

24.6.9.2 Region to Fontify after a Buffer Change
When a buffer is changed, the region that Font Lock refontifies is by default the smallest
sequence of whole lines that spans the change. While this works well most of the time,sometimes it doesn’t—for example, when a change alters the syntactic meaning of text onan earlier line.
You can enlarge (or even reduce) the region to refontify by setting the following variable:[Variable]
This buffer-local variable is either nil or a function for Font Lock mode to call todetermine the region to scan and fontify.

font-lock-extend-after-change-region-function

The function is given three parameters, the standard beg, end, and old-len fromafter-change-functions (see Section 33.34 [Change Hooks], page 961). It should
return either a cons of the beginning and end buffer positions (in that order) of theregion to fontify, or nil (which means choose the region in the standard way). Thisfunction needs to preserve point, the match-data, and the current restriction. The
region it returns may start or end in the middle of a line.
Since this function is called after every buffer change, it should be reasonably fast.

24.6.10 Parser-based Font Lock
Besides simple syntactic font lock and regexp-based font lock, Emacs also provides complete
syntactic font lock with the help of a parser. Currently, Emacs uses the tree-sitter library(see Chapter 37 [Parsing Program Source], page 1039) for this purpose.
Parser-based font lock and other font lock mechanisms are not mutually exclusive. Bydefault, if enabled, parser-based font lock runs first, replacing syntactic font lock, followedby regexp-based font lock.
Although parser-based font lock doesn’t share the same customization variables withregexp-based font lock, it uses similar customization schemes. The tree-sitter counterpart offont-lock-keywords is treesit-font-lock-settings.
In general, tree-sitter fontification works as follows:Chapter 24: Major and Minor Modes

579• A Lisp program (usually, part of a major mode) provides a query consisting of patterns,
each pattern associated with a capture name.
• The tree-sitter library finds the nodes in the parse tree that match these patterns, tags
the nodes with the corresponding capture names, and returns them to the Lisp program.
• The Lisp program uses the returned nodes to highlight the portions of buffer text
corresponding to each node as appropriate, using the tagged capture names of the nodes
to determine the correct fontification. For example, a node tagged font-lock-keyword
would be highlighted in font-lock-keyword face.
For more information about queries, patterns, and capture names, see Section 37.5
[Pattern Matching], page 1052.
To set up tree-sitter fontification, a major mode should first set treesit-font-locksettings with the output of treesit-font-lock-rules, then call treesit-major-modesetup.

treesit-font-lock-rules &rest query-specs[Function]
This function is used to set treesit-font-lock-settings. It takes care of compiling
queries and other post-processing, and outputs a value that treesit-font-locksettings accepts. Here’s an example:(treesit-font-lock-rules:language 'javascript:feature 'constant:override t'((true) @font-lock-constant-face(false) @font-lock-constant-face):language 'html:feature 'script"(script_element) @font-lock-builtin-face")
This function takes a series of query-specs, where each query-spec is a query precededby one or more keyword/value pairs. Each query is a tree-sitter query in either thestring, s-expression, or compiled form.
For each query, the keyword/value pairs that precede it add meta information to it. The:language keyword declares query’s language. The :feature keyword sets the featurename of query. Users can control which features are enabled with treesit-fontlock-level and treesit-font-lock-feature-list (described below). These two
keywords are mandatory.
Other keywords are optional:
KeywordValue
Description:overridenil
If the region already has a face, discard the newfacet
Always apply the new faceappendAppend the new face to existing ones
prependPrepend the new face to existing ones
keepFill-in regions without an existing face
Lisp programs mark patterns in query with capture names (names that start with@), and tree-sitter will return matched nodes tagged with those same capture names.

Chapter 24: Major and Minor Modes580

For the purpose of fontification, capture names in query should be face names like
font-lock-keyword-face. The captured node will be fontified with that face.
A capture name can also be a function name, in which case the function is called with
4 arguments: node and override, start and end, where node is the node itself, overrideis the :override property of the rule which captured this node, and start and end
limit the region which this function should fontify. (If this function wants to respect
the override argument, it can use treesit-fontify-with-override.)
Beyond the 4 arguments presented, this function should accept more arguments as
optional arguments for future extensibility.
If a capture name is both a face and a function, the face takes priority. If a capture
name is neither a face nor a function, it is ignored.
[Variable]
This is a list of lists of feature symbols. Each element of the list is a list that represents
a decoration level. treesit-font-lock-level controls which levels are activated.
Each element of the list is a list of the form (feature ...), where each featurecorresponds to the :feature value of a query defined in treesit-font-lock-rules.
Removing a feature symbol from this list disables the corresponding query duringfont-lock.
Common feature names, for many programming languages, include definition, type,assignment, builtin, constant, keyword, string-interpolation, comment, doc,
string, operator, preprocessor, escape-sequence, and key. Major modes are free
to subdivide or extend these common features.
Some of these features warrant some explanation: definition highlights whateveris being defined, e.g., the function name in a function definition, the struct name ina struct definition, the variable name in a variable definition; assignment highlights
whatever is being assigned to, e.g., the variable or field in an assignment statement;
key highlights keys in key-value pairs, e.g., keys in a JSON object or Python dictionary;
doc highlights docstrings or doc-comments.
For example, the value of this variable could be:((comment string doc) ; level 1(function-name keyword type builtin constant) ; level 2(variable-name string-interpolation key)) ; level 3
Major modes should set this variable before calling treesit-major-mode-setup.
For this variable to take effect, a Lisp program should call treesit-font-lockrecompute-features (which resets treesit-font-lock-settings accordingly),or treesit-major-mode-setup (which calls treesit-font-lock-recomputefeatures).

treesit-font-lock-feature-list[Variable]
A list of settings for tree-sitter based font lock. The exact format of each setting is
considered internal. One should always use treesit-font-lock-rules to set thisvariable.

treesit-font-lock-settings

Multi-language major modes should provide range functions in treesit-rangefunctions, and Emacs will set the ranges accordingly before fontifing a region (seeSection 37.6 [Multiple Languages], page 1057).

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24.7 Automatic Indentation of code
For programming languages, an important feature of a major mode is to provide automaticindentation. There are two parts: one is to decide what is the right indentation of a line,
and the other is to decide when to reindent a line. By default, Emacs reindents a line
whenever you type a character in electric-indent-chars, which by default only includes
Newline. Major modes can add chars to electric-indent-chars according to the syntaxof the language.
Deciding what is the right indentation is controlled in Emacs by indent-line-function(see Section 33.17.2 [Mode-Specific Indent], page 911). For some modes, the right indentation
cannot be known reliably, typically because indentation is significant so several indentations
are valid but with different meanings. In that case, the mode should set electric-indentinhibit to make sure the line is not constantly re-indented against the user’s wishes.
Writing a good indentation function can be difficult and to a large extent it is still a
black art. Many major mode authors will start by writing a simple indentation functionthat works for simple cases, for example by comparing with the indentation of the previous
text line. For most programming languages that are not really line-based, this tends to scalevery poorly: improving such a function to let it handle more diverse situations tends tobecome more and more difficult, resulting in the end with a large, complex, unmaintainable
indentation function which nobody dares to touch.
A good indentation function will usually need to actually parse the text, according to
the syntax of the language. Luckily, it is not necessary to parse the text in as much detailas would be needed for a compiler, but on the other hand, the parser embedded in the
indentation code will want to be somewhat friendly to syntactically incorrect code.
Good maintainable indentation functions usually fall into two categories: either parsing
forward from some safe starting point until the position of interest, or parsing backward fromthe position of interest. Neither of the two is a clearly better choice than the other: parsing
backward is often more difficult than parsing forward because programming languages aredesigned to be parsed forward, but for the purpose of indentation it has the advantage of
not needing to guess a safe starting point, and it generally enjoys the property that only aminimum of text will be analyzed to decide the indentation of a line, so indentation willtend to be less affected by syntax errors in some earlier unrelated piece of code. Parsing
forward on the other hand is usually easier and has the advantage of making it possible toreindent efficiently a whole region at a time, with a single parse.
Rather than write your own indentation function from scratch, it is often preferable totry and reuse some existing ones or to rely on a generic indentation engine. There are sadly
few such engines. The CC-mode indentation code (used with C, C++, Java, Awk and a few
other such modes) has been made more generic over the years, so if your language seems
somewhat similar to one of those languages, you might try to use that engine. Anotherone is SMIE which takes an approach in the spirit of Lisp sexps and adapts it to non-Lisp
languages. Yet another one is to rely on a full-blown parser, for example, the tree-sitter
library.

24.7.1 Simple Minded Indentation Engine
SMIE is a package that provides a generic navigation and indentation engine. Based on avery simple parser using an operator precedence grammar, it lets major modes extend theChapter 24: Major and Minor Modes582

sexp-based navigation of Lisp to non-Lisp languages as well as provide a simple to use but
reliable auto-indentation.
Operator precedence grammar is a very primitive technology for parsing compared tosome of the more common techniques used in compilers. It has the following characteristics:
its parsing power is very limited, and it is largely unable to detect syntax errors, but it has
the advantage of being algorithmically efficient and able to parse forward just as well as
backward. In practice that means that SMIE can use it for indentation based on backward
parsing, that it can provide both forward-sexp and backward-sexp functionality, and that
it will naturally work on syntactically incorrect code without any extra effort. The downsideis that it also means that most programming languages cannot be parsed correctly using
SMIE, at least not without resorting to some special tricks (see Section 24.7.1.5 [SMIE
Tricks], page 585).

24.7.1.1 SMIE Setup and Features
SMIE is meant to be a one-stop shop for structural navigation and various other features
which rely on the syntactic structure of code, in particular automatic indentation. The
main entry point is smie-setup which is a function typically called while setting up a majormode.

smie-setup grammar rules-function &rest keywords[Function]
Setup SMIE navigation and indentation. grammar is a grammar table generatedby smie-prec2->grammar. rules-function is a set of indentation rules for use onsmie-rules-function. keywords are additional arguments, which can include thefollowing keywords:• :forward-token fun: Specify the forward lexer to use.
• :backward-token fun: Specify the backward lexer to use.

Calling this function is sufficient to make commands such as forward-sexp,
backward-sexp, and transpose-sexps be able to properly handle structural elements
other than just the paired parentheses already handled by syntax tables. For example, if theprovided grammar is precise enough, transpose-sexps can correctly transpose the twoarguments of a + operator, taking into account the precedence rules of the language.
Calling smie-setup is also sufficient to make TAB indentation work in the expected way,
extends blink-matching-paren to apply to elements like begin...end, and provides somecommands that you can bind in the major mode keymap.
[Command]This command closes the most recently opened (and not yet closed) block.

smie-close-blocksmie-down-list &optional arg[Command]This command is like down-list but it also pays attention to nesting of tokens otherthan parentheses, such as begin...end.

24.7.1.2 Operator Precedence Grammars
SMIE’s precedence grammars simply give to each token a pair of precedences: the leftprecedence and the right-precedence. We say T1 < T2 if the right-precedence of token T1 isless than the left-precedence of token T2. A good way to read this < is as a kind of parenthesis:

Chapter 24: Major and Minor Modes583

if we find ... T1 something T2 ... then that should be parsed as ... T1 (something T2... rather than as ... T1 something) T2 .... The latter interpretation would be the case
if we had T1 > T2. If we have T1 = T2, it means that token T2 follows token T1 in the same
syntactic construction, so typically we have "begin" = "end". Such pairs of precedences
are sufficient to express left-associativity or right-associativity of infix operators, nesting of
tokens like parentheses and many other cases.

smie-prec2->grammar table[Function]
This function takes a prec2 grammar table and returns an alist suitable for use insmie-setup. The prec2 table is itself meant to be built by one of the functions below.

smie-merge-prec2s &rest tables[Function]
This function takes several prec2 tables and merges them into a new prec2 table.

smie-precs->prec2 precs[Function]
This function builds a prec2 table from a table of precedences precs. precs should bea list, sorted by precedence (for example "+" will come before "*"), of elements of theform (assoc op ...), where each op is a token that acts as an operator; assoc is theirassociativity, which can be either left, right, assoc, or nonassoc. All operators ina given element share the same precedence level and associativity.

smie-bnf->prec2 bnf &rest resolvers[Function]
This function lets you specify the grammar using a BNF notation. It accepts a bnf
description of the grammar along with a set of conflict resolution rules resolvers, andreturns a prec2 table.
bnf is a list of nonterminal definitions of the form (nonterm rhs1 rhs2 ...) where
each rhs is a (non-empty) list of terminals (aka tokens) or non-terminals.
Not all grammars are accepted:• An rhs cannot be an empty list (an empty list is never needed, since SMIE allows
all non-terminals to match the empty string anyway).
• An rhs cannot have 2 consecutive non-terminals: each pair of non-terminals needs
to be separated by a terminal (aka token). This is a fundamental limitation ofoperator precedence grammars.

Additionally, conflicts can occur:• The returned prec2 table holds constraints between pairs of tokens, and for any
given pair only one constraint can be present: T1 < T2, T1 = T2, or T1 > T2.
• A token can be an opener (something similar to an open-paren), a closer (likea close-paren), or neither of the two (e.g., an infix operator, or an inner token
like "else").
Precedence conflicts can be resolved via resolvers, which is a list of precs tables (seesmie-precs->prec2): for each precedence conflict, if those precs tables specify aparticular constraint, then the conflict is resolved by using this constraint instead, else
a conflict is reported and one of the conflicting constraints is picked arbitrarily andthe others are simply ignored.

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24.7.1.3 Defining the Grammar of a Language
The usual way to define the SMIE grammar of a language is by defining a new global variable
that holds the precedence table by giving a set of BNF rules. For example, the grammar
definition for a small Pascal-like language could look like:(require 'smie)(defvar sample-smie-grammar(smie-prec2->grammar(smie-bnf->prec2'((id)(inst ("begin" insts "end")("if" exp "then" inst "else" inst)(id ":=" exp)(exp))(insts (insts ";" insts) (inst))(exp (exp "+" exp)
(exp "*" exp)("(" exps ")"))(exps (exps "," exps) (exp)))'((assoc ";"))'((assoc ","))'((assoc "+") (assoc "*")))))
A few things to note:• The above grammar does not explicitly mention the syntax of function calls: SMIE willautomatically allow any sequence of sexps, such as identifiers, balanced parentheses, or
begin ... end blocks to appear anywhere anyway.
• The grammar category id has no right hand side: this does not mean that it can match
only the empty string, since as mentioned any sequence of sexps can appear anywhere
anyway.
• Because non terminals cannot appear consecutively in the BNF grammar, it is difficult
to correctly handle tokens that act as terminators, so the above grammar treats ";" asa statement separator instead, which SMIE can handle very well.
• Separators used in sequences (such as "," and ";" above) are best defined with BNF
rules such as (foo (foo "separator" foo) ...) which generate precedence conflicts
which are then resolved by giving them an explicit (assoc "separator").
• The ("(" exps ")") rule was not needed to pair up parens, since SMIE will pair up
any characters that are marked as having paren syntax in the syntax table. What thisrule does instead (together with the definition of exps) is to make it clear that ","should not appear outside of parentheses.
• Rather than have a single precs table to resolve conflicts, it is preferable to have several
tables, so as to let the BNF part of the grammar specify relative precedences where
possible.
• Unless there is a very good reason to prefer left or right, it is usually preferable tomark operators as associative, using assoc. For that reason "+" and "*" are defined
above as assoc, although the language defines them formally as left associative.

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24.7.1.4 Defining Tokens
SMIE comes with a predefined lexical analyzer which uses syntax tables in the following
way: any sequence of characters that have word or symbol syntax is considered a token, andso is any sequence of characters that have punctuation syntax. This default lexer is often agood starting point but is rarely actually correct for any given language. For example, itwill consider "2,+3" to be composed of 3 tokens: "2", ",+", and "3".
To describe the lexing rules of your language to SMIE, you need 2 functions, one to fetch
the next token, and another to fetch the previous token. Those functions will usually firstskip whitespace and comments and then look at the next chunk of text to see if it is a special
token. If so it should skip the token and return a description of this token. Usually this issimply the string extracted from the buffer, but it can be anything you want. For example:(defvar sample-keywords-regexp(regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "=")))(defun sample-smie-forward-token ()(forward-comment (point-max))(cond((looking-at sample-keywords-regexp)(goto-char (match-end 0))(match-string-no-properties 0))(t (buffer-substring-no-properties(point)(progn (skip-syntax-forward "w_")(point))))))(defun sample-smie-backward-token ()(forward-comment (- (point)))(cond((looking-back sample-keywords-regexp (- (point) 2) t)(goto-char (match-beginning 0))(match-string-no-properties 0))(t (buffer-substring-no-properties(point)(progn (skip-syntax-backward "w_")(point))))))
Notice how those lexers return the empty string when in front of parentheses. Thisis because SMIE automatically takes care of the parentheses defined in the syntax table.
More specifically if the lexer returns nil or an empty string, SMIE tries to handle thecorresponding text as a sexp according to syntax tables.

24.7.1.5 Living With a Weak Parser
The parsing technique used by SMIE does not allow tokens to behave differently in different
contexts. For most programming languages, this manifests itself by precedence conflicts
when converting the BNF grammar.
Sometimes, those conflicts can be worked around by expressing the grammar slightly
differently. For example, for Modula-2 it might seem natural to have a BNF grammar thatlooks like this:Chapter 24: Major and Minor Modes

586

...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")("CASE" exp "OF" cases "END")...)(cases (cases "|" cases)(caselabel ":" insts)("ELSE" insts))...
But this will create conflicts for "ELSE": on the one hand, the IF rule implies (among
many other things) that "ELSE" = "END"; but on the other hand, since "ELSE" appears
within cases, which appears left of "END", we also have "ELSE" > "END". We can solve theconflict either by using:...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")("CASE" exp "OF" cases "END")("CASE" exp "OF" cases "ELSE" insts "END")...)(cases (cases "|" cases) (caselabel ":" insts))
...
or
...
(inst ("IF" exp "THEN" else "END")("CASE" exp "OF" cases "END")...)(else (insts "ELSE" insts))(cases (cases "|" cases) (caselabel ":" insts) (else))...
Reworking the grammar to try and solve conflicts has its downsides, tho, because SMIE
assumes that the grammar reflects the logical structure of the code, so it is preferable tokeep the BNF closer to the intended abstract syntax tree.
Other times, after careful consideration you may conclude that those conflicts are notserious and simply resolve them via the resolvers argument of smie-bnf->prec2. Usually
this is because the grammar is simply ambiguous: the conflict does not affect the set ofprograms described by the grammar, but only the way those programs are parsed. This is
typically the case for separators and associative infix operators, where you want to add aresolver like '((assoc "|")). Another case where this can happen is for the classic dangling
else problem, where you will use '((assoc "else" "then")). It can also happen for cases
where the conflict is real and cannot really be resolved, but it is unlikely to pose a problem
in practice.
Finally, in many cases some conflicts will remain despite all efforts to restructure thegrammar. Do not despair: while the parser cannot be made more clever, you can makethe lexer as smart as you want. So, the solution is then to look at the tokens involvedin the conflict and to split one of those tokens into 2 (or more) different tokens. E.g., if
the grammar needs to distinguish between two incompatible uses of the token "begin",make the lexer return different tokens (say "begin-fun" and "begin-plain") dependingChapter 24: Major and Minor Modes587

on which kind of "begin" it finds. This pushes the work of distinguishing the different cases
to the lexer, which will thus have to look at the surrounding text to find ad-hoc clues.

24.7.1.6 Specifying Indentation Rules
Based on the provided grammar, SMIE will be able to provide automatic indentation without
any extra effort. But in practice, this default indentation style will probably not be goodenough. You will want to tweak it in many different cases.
SMIE indentation is based on the idea that indentation rules should be as local as possible.
To this end, it relies on the idea of virtual indentation, which is the indentation that a
particular program point would have if it were at the beginning of a line. Of course, if
that program point is indeed at the beginning of a line, its virtual indentation is its current
indentation. But if not, then SMIE uses the indentation algorithm to compute the virtualindentation of that point. Now in practice, the virtual indentation of a program point does
not have to be identical to the indentation it would have if we inserted a newline before it.
To see how this works, the SMIE rule for indentation after a { in C does not care whether
the { is standing on a line of its own or is at the end of the preceding line. Instead, thesedifferent cases are handled in the indentation rule that decides how to indent before a {.
Another important concept is the notion of parent: The parent of a token, is the head
token of the nearest enclosing syntactic construct. For example, the parent of an elseis the if to which it belongs, and the parent of an if, in turn, is the lead token of thesurrounding construct. The command backward-sexp jumps from a token to its parent,
but there are some caveats: for openers (tokens which start a construct, like if), you needto start with point before the token, while for others you need to start with point after thetoken. backward-sexp stops with point before the parent token if that is the opener of thetoken of interest, and otherwise it stops with point after the parent token.
SMIE indentation rules are specified using a function that takes two arguments method
and arg where the meaning of arg and the expected return value depend on method.
method can be:• :after, in which case arg is a token and the function should return the offset to use
for indentation after arg.
• :before, in which case arg is a token and the function should return the offset to use
to indent arg itself.
• :elem, in which case the function should return either the offset to use to indent function
arguments (if arg is the symbol arg) or the basic indentation step (if arg is the symbol
basic).
• :list-intro, in which case arg is a token and the function should return non-nil if
the token is followed by a list of expressions (not separated by any token) rather thanan expression.
When arg is a token, the function is called with point just before that token. A return
value of nil always means to fallback on the default behavior, so the function should return
nil for arguments it does not expect.
offset can be:• nil: use the default indentation rule.
• (column . column): indent to column column.

Chapter 24: Major and Minor Modes588• number: offset by number, relative to a base token which is the current token for :afterand its parent for :before.

24.7.1.7 Helper Functions for Indentation Rules
SMIE provides various functions designed specifically for use in the indentation rules function(several of those functions break if used in another context). These functions all start withthe prefix smie-rule-.

smie-rule-bolp[Function]

Return non-nil if the current token is the first on the line.
[Function]
Return non-nil if the current token is hanging. A token is hanging if it is the last
token on the line and if it is preceded by other tokens: a lone token on a line is nothanging.

smie-rule-hanging-p

smie-rule-next-p &rest tokens[Function]

Return non-nil if the next token is among tokens.

smie-rule-prev-p &rest tokens[Function]

Return non-nil if the previous token is among tokens.

smie-rule-parent-p &rest parents[Function]

Return non-nil if the current token’s parent is among parents.
[Function]
Return non-nil if the current token’s parent is actually a sibling. This is the case forexample when the parent of a "," is just the previous ",".

smie-rule-sibling-p

smie-rule-parent &optional offset[Function]
Return the proper offset to align the current token with the parent. If non-nil, offset
should be an integer giving an additional offset to apply.

smie-rule-separator method[Function]

Indent current token as a separator.
By separator, we mean here a token whose sole purpose is to separate various elements
within some enclosing syntactic construct, and which does not have any semantic
significance in itself (i.e., it would typically not exist as a node in an abstract syntaxtree).
Such a token is expected to have an associative syntax and be closely tied to its
syntactic parent. Typical examples are "," in lists of arguments (enclosed inside
parentheses), or ";" in sequences of instructions (enclosed in a {...} or begin...end
block).
method should be the method name that was passed to smie-rules-function.

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24.7.1.8 Sample Indentation Rules
Here is an example of an indentation function:(defun sample-smie-rules (kind token)(pcase (cons kind token)(`(:elem . basic) sample-indent-basic)(`(,_ . ",") (smie-rule-separator kind))(`(:after . ":=") sample-indent-basic)(`(:before . ,(or `"begin" `"(" `"{"))(if (smie-rule-hanging-p) (smie-rule-parent)))(`(:before . "if")(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")(smie-rule-parent)))))
A few things to note:• The first case indicates the basic indentation increment to use. If sample-indent-basic
is nil, then SMIE uses the global setting smie-indent-basic. The major mode could
have set smie-indent-basic buffer-locally instead, but that is discouraged.
• The rule for the token "," make SMIE try to be more clever when the comma separatoris placed at the beginning of lines. It tries to outdent the separator so as to align thecode after the comma; for example:
x = longfunctionname (arg1, arg2);• The rule for indentation after ":=" exists because otherwise SMIE would treat ":=" asan infix operator and would align the right argument with the left one.
• The rule for indentation before "begin" is an example of the use of virtual indentation:
This rule is used only when "begin" is hanging, which can happen only when "begin"
is not at the beginning of a line. So this is not used when indenting "begin" itself but
only when indenting something relative to this "begin". Concretely, this rule changes
the indentation from:
if x > 0 then begin
dosomething(x);endtoif x > 0 then begin
dosomething(x);end• The rule for indentation before "if" is similar to the one for "begin", but where thepurpose is to treat "else if" as a single unit, so as to align a sequence of tests rather
than indent each test further to the right. This function does this only in the casewhere the "if" is not placed on a separate line, hence the smie-rule-bolp test.
If we know that the "else" is always aligned with its "if" and is always at the beginningof a line, we can use a more efficient rule:((equal token "if")Chapter 24: Major and Minor Modes

590(and (not (smie-rule-bolp))(smie-rule-prev-p "else")(save-excursion(sample-smie-backward-token)(cons 'column (current-column)))))
The advantage of this formulation is that it reuses the indentation of the previous"else", rather than going all the way back to the first "if" of the sequence.

24.7.1.9 Customizing Indentation
If you are using a mode whose indentation is provided by SMIE, you can customize theindentation to suit your preferences. You can do this on a per-mode basis (using the optionsmie-config), or a per-file basis (using the function smie-config-local in a file-local
variable specification).
[User Option]
This option lets you customize indentation on a per-mode basis. It is an alist withelements of the form (mode . rules). For the precise form of rules, see the variable’s
documentation; but you may find it easier to use the command smie-config-guess.

smie-config[Command]This command tries to work out appropriate settings to produce your preferred styleof indentation. Simply call the command while visiting a file that is indented withyour style.

smie-config-guess[Command]Call this command after using smie-config-guess, to save your settings for futuresessions.

smie-config-savesmie-config-show-indent &optional move[Command]This command displays the rules that are used to indent the current line.

[Command]This command adds a local rule to adjust the indentation of the current line.

smie-config-set-indentsmie-config-local rules[Function]
This function adds rules as indentation rules for the current buffer. These add to any
mode-specific rules defined by the smie-config option. To specify custom indentation
rules for a specific file, add an entry to the file’s local variables of the form: eval:(smie-config-local '(rules)).

24.7.2 Parser-based Indentation
When built with the tree-sitter library (see Chapter 37 [Parsing Program Source], page 1039),
Emacs is capable of parsing the program source and producing a syntax tree. This syntax
tree can be used for guiding the program source indentation commands. For maximum
flexibility, it is possible to write a custom indentation function that queries the syntax tree
and indents accordingly for each language, but that is a lot of work. It is more convenient to
use the simple indentation engine described below: then the major mode needs only write
some indentation rules, and the engine takes care of the rest.

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To enable the parser-based indentation engine, either set treesit-simple-indentrules and call treesit-major-mode-setup, or equivalently, set the value of indent-linefunction to treesit-indent.
[Variable]
This variable stores the actual function called by treesit-indent. By default, itsvalue is treesit-simple-indent. In the future we might add other, more complex
indentation engines.

treesit-indent-function

Writing indentation rules[Variable]
This local variable stores indentation rules for every language. It is an alist withelements of the form (language . rules), where language is a language symbol, andrules is a list with elements of the form (matcher anchor offset).
First, Emacs passes the smallest tree-sitter node at the beginning of the current line
to matcher; if it returns non-nil, this rule is applicable. Then Emacs passes the nodeto anchor, which returns a buffer position. Emacs takes the column number of that
position, adds offset to it, and the result is the indentation column for the current line.
The matcher and anchor are functions, and Emacs provides convenient defaults forthem.
Each matcher or anchor is a function that takes three arguments: node, parent, andbol. The argument bol is the buffer position whose indentation is required: theposition of the first non-whitespace character after the beginning of the line. The
argument node is the largest node that starts at that position (and is not a root node);and parent is the parent of node. However, when that position is in a whitespace orinside a multi-line string, no node can start at that position, so node is nil. In thatcase, parent would be the smallest node that spans that position.
matcher should return non-nil if the rule is applicable, and anchor should return abuffer position.
offset can be an integer, a variable whose value is an integer, or a function that returns
an integer. If it is a function, it is passed node, parent, and bol, like matchers andanchors.

treesit-simple-indent-rules[Variable]
This is a list of defaults for matchers and anchors in treesit-simple-indent-rules.
Each of them represents a function that takes 3 arguments: node, parent, and bol.
The available default functions are:treesit-simple-indent-presets

no-nodeThis matcher is a function that is called with 3 arguments: node, parent,
and bol. It returns non-nil, indicating a match, if node is nil, i.e., there
is no node that starts at bol. This is the case when bol is on an empty
line or inside a multi-line string, etc.

parent-is
This matcher is a function of one argument, type; it returns a function thatis called with 3 arguments: node, parent, and bol, and returns non-nil(i.e., a match) if parent’s type matches regexp type.

Chapter 24: Major and Minor Modes592

node-isThis matcher is a function of one argument, type; it returns a function thatis called with 3 arguments: node, parent, and bol, and returns non-nil if
node’s type matches regexp type.

field-isThis matcher is a function of one argument, name; it returns a functionthat is called with 3 arguments: node, parent, and bol, and returns
non-nil if node’s field name in parent matches regexp name.

query

This matcher is a function of one argument, query; it returns a functionthat is called with 3 arguments: node, parent, and bol, and returns nonnil if querying parent with query captures node (see Section 37.5 [Pattern
Matching], page 1052).

match

This matcher is a function of 5 arguments: node-type, parent-type, nodefield, node-index-min, and node-index-max). It returns a function thatis called with 3 arguments: node, parent, and bol, and returns non-nil
if node’s type matches regexp node-type, parent’s type matches regexp
parent-type, node’s field name in parent matches regexp node-field, andnode’s index among its siblings is between node-index-min and nodeindex-max. If the value of an argument is nil, this matcher doesn’t checkthat argument. For example, to match the first child where parent isargument_list, use(match nil "argument_list" nil 0 0)
In addition, node-type can be a special value null, which matches whenthe value of node is nil.

n-p-gp

Short for “node-parent-grandparent”, this matcher is a function of 3arguments: node-type, parent-type, and grandparent-type. It returns
a function that is called with 3 arguments: node, parent, and bol, andreturns non-nil if: (1) node-type matches node’s type, and (2) parenttype matches parent’s type, and (3) grandparent-type matches parent’s
parent’s type. If any of node-type, parent-type, and grandparent-type isnil, this function doesn’t check for it.

comment-end
This matcher is a function that is called with 3 arguments: node, parent,
and bol, and returns non-nil if point is before a comment-ending token.
Comment-ending tokens are defined by regexp comment-end-skip.
catch-all
This matcher is a function that is called with 3 arguments: node, parent,
and bol. It always returns non-nil, indicating a match.
first-sibling
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of the first child of parent.
nth-sibling
This anchor is a function of two arguments: n, and an optional argument
named. It returns a function that is called with 3 arguments: node, parent,
and bol, and returns the start of the nth child of parent. If named isChapter 24: Major and Minor Modes

593

non-nil, only named children are counted (see [tree-sitter named node],
page 1041).
parentThis anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of parent.

grand-parent
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of parent’s parent.
great-grand-parent
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of parent’s parent’s parent.
parent-bol
This anchor is a function that is called with 3 arguments: node, parent, andbol, and returns the first non-space character on the line which parent’s
start is on.
standalone-parent
This anchor is a function that is called with 3 arguments: node, parent,
and bol. It finds the first ancestor node (parent, grandparent, etc.) of nodethat starts on its own line, and return the start of that node. “Startingon its own line” means there is only whitespace character before the nodeon the line which the node’s start is on.
prev-sibling
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of the previous sibling of node.
no-indent
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the start of node.
prev-line
This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the first non-whitespace character on the previous
line.
column-0This anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the beginning of the current line, which is at column
0.

comment-startThis anchor is a function that is called with 3 arguments: node, parent,
and bol, and returns the position after the comment-start token. Commentstart tokens are defined by regular expression comment-start-skip. Thisfunction assumes parent is the comment node.
prev-adaptive-prefix
This anchor is a function that is called with 3 arguments: node, parent, andbol. It tries to match adaptive-fill-regexp to the text at the beginningof the previous non-empty line. If there is a match, this function returns

Chapter 24: Major and Minor Modes594

the end of the match, otherwise it returns nil. However, if the current
line begins with a prefix (e.g., ‘-’), return the beginning of the prefix ofthe previous line instead, so that the two prefixes align. This anchor isuseful for an indent-relative-like indent behavior for block comments.

Indentation utilities
Here are some utility functions that can help writing parser-based indentation rules.

treesit-check-indent mode[Command]This command checks the current buffer’s indentation against major mode mode. It
indents the current buffer according to mode and compares the results with the current
indentation. Then it pops up a buffer showing the differences. Correct indentation(target) is shown in green color, current indentation is shown in red color.

It is also helpful to use treesit-inspect-mode (see Section 37.1 [Language Grammar],page 1039) when writing indentation rules.

24.8 Desktop Save Mode
Desktop Save Mode is a feature to save the state of Emacs from one session to another. The
user-level commands for using Desktop Save Mode are described in the GNU Emacs Manual(see Section “Saving Emacs Sessions” in the GNU Emacs Manual). Modes whose buffers
visit a file, don’t have to do anything to use this feature.
For buffers not visiting a file to have their state saved, the major mode must bind thebuffer local variable desktop-save-buffer to a non-nil value.
[Variable]
If this buffer-local variable is non-nil, the buffer will have its state saved in thedesktop file at desktop save. If the value is a function, it is called at desktop save withargument desktop-dirname, and its value is saved in the desktop file along with thestate of the buffer for which it was called. When file names are returned as part of
the auxiliary information, they should be formatted using the call(desktop-file-name file-name desktop-dirname)desktop-save-buffer

For buffers not visiting a file to be restored, the major mode must define a function to
do the job, and that function must be listed in the alist desktop-buffer-mode-handlers.

desktop-buffer-mode-handlers[Variable]

Alist with elements(major-mode . restore-buffer-function)
The function restore-buffer-function will be called with argument list
(buffer-file-name buffer-name desktop-buffer-misc)and it should return the restored buffer. Here desktop-buffer-misc is the value returnedby the function optionally bound to desktop-save-buffer.

595

25 Documentation
GNU Emacs has convenient built-in help facilities, most of which derive their informationfrom documentation strings associated with functions and variables. This chapter describes
how to access documentation strings in Lisp programs.
The contents of a documentation string should follow certain conventions. In particular,
its first line should be a complete sentence (or two complete sentences) that briefly describes
what the function or variable does. See Section D.6 [Documentation Tips], page 1337, for
how to write good documentation strings.
Note that the documentation strings for Emacs are not the same thing as the Emacs
manual. Manuals have their own source files, written in the Texinfo language; documentation
strings are specified in the definitions of the functions and variables they apply to. A collectionof documentation strings is not sufficient as a manual because a good manual is not organizedin that fashion; it is organized in terms of topics of discussion.
For commands to display documentation strings, see Section “Help” in The GNU Emacs
Manual.

25.1 Documentation Basics
A documentation string is written using the Lisp syntax for strings, with double-quotecharacters surrounding the text. It is, in fact, an actual Lisp string. When the string appears
in the proper place in a function or variable definition, it serves as the function’s or variable’s
documentation.
In a function definition (a lambda or defun form), the documentation string is specified after the argument list, and is normally stored directly in the function object. See
Section 13.2.4 [Function Documentation], page 235. You can also put function documentationin the function-documentation property of a function name (see Section 25.2 [Accessing
Documentation], page 596).
In a variable definition (a defvar form), the documentation string is specified after the
initial value. See Section 12.5 [Defining Variables], page 194. The string is stored in thevariable’s variable-documentation property.
Sometimes, Emacs does not keep documentation strings in memory. There are two suchcircumstances. Firstly, to save memory, the documentation for primitive functions (seeSection 13.1 [What Is a Function], page 230) and built-in variables is kept in a file named DOC,
in the directory specified by doc-directory (see Section 25.2 [Accessing Documentation],
page 596). Secondly, when a function or variable is loaded from a byte-compiled file, Emacs
avoids loading its documentation string (see Section 17.3 [Docs and Compilation], page 319).
In both cases, Emacs looks up the documentation string from the file only when needed,such as when the user calls C-h f (describe-function) for a function.
Documentation strings can contain special key substitution sequences, referring to keybindings which are looked up only when the user views the documentation. This allows thehelp commands to display the correct keys even if a user rearranges the default key bindings.
See Section 25.3 [Keys in Documentation], page 598.
In the documentation string of an autoloaded command (see Section 16.5 [Autoload],
page 304), these key-substitution sequences have an additional special effect: they cause

Chapter 25: Documentation

596

C-h f on the command to trigger autoloading. (This is needed for correctly setting up thehyperlinks in the *Help* buffer.)

25.2 Access to Documentation Strings
documentation-property symbol property &optional verbatim[Function]
This function returns the documentation string recorded in symbol’s property list
under property property. It is most often used to look up the documentation stringsof variables, for which property is variable-documentation. However, it can also be
used to look up other kinds of documentation, such as for customization groups (butfor function documentation, use the documentation function, below).
If the property value refers to a documentation string stored in the DOC file or abyte-compiled file, this function looks up that string and returns it.
If the property value isn’t nil, isn’t a string, and doesn’t refer to text in a file, then it
is evaluated as a Lisp expression to obtain a string.
Finally, this function passes the string through substitute-command-keys to substitute key bindings (see Section 25.3 [Keys in Documentation], page 598). It skips thisstep if verbatim is non-nil.
(documentation-property 'command-line-processed'variable-documentation)⇒ "Non-nil once command line has been processed"(symbol-plist 'command-line-processed)⇒ (variable-documentation 188902)(documentation-property 'emacs 'group-documentation)⇒ "Customization of the One True Editor."

documentation function &optional verbatim[Function]
This function returns the documentation string of function. It handles macros, named
keyboard macros, and special forms, as well as ordinary functions.
If function is a symbol, this function first looks for the function-documentation
property of that symbol; if that has a non-nil value, the documentation comes fromthat value (if the value is not a string, it is evaluated).
If function is not a symbol, or if it has no function-documentation property, thendocumentation extracts the documentation string from the actual function definition,
reading it from a file if called for.
Finally, unless verbatim is non-nil, this function calls substitute-command-keys.
The result is the documentation string to return.
The documentation function signals a void-function error if function has no function
definition. However, it is OK if the function definition has no documentation string.
In that case, documentation returns nil.

function-documentation function[Function]
Generic function used by documentation to extract the raw docstring from a function
object. You can specify how to get the docstring of a specific function type by adding
a corresponding method to it.

face-documentation faceThis function returns the documentation string of face as a face.

[Function]

Chapter 25: Documentation

Here is an example of
documentation-property, tosymbols in a *Help* buffer.

597

using the two functions,display the documentation

documentation andstrings for several(defun describe-symbols (pattern)"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are describedin the *Help* buffer."(interactive "sDescribe symbols matching: ")(let ((describe-func(lambda (s);; Print description of symbol.
(if (fboundp s); It is a function.
(princ(format "%s\t%s\n%s\n\n" s(if (commandp s)(let ((keys (where-is-internal s)))(if keys(concat"Keys: "(mapconcat 'key-description
keys " "))"Keys: none"))"Function")(or (documentation s)"not documented"))))(if (boundp s); It is a variable.
(princ(format "%s\t%s\n%s\n\n" s(if (custom-variable-p s)"Option " "Variable")(or (documentation-propertys 'variable-documentation)"not documented"))))))
sym-list);; Build a list of symbols that match pattern.
(mapatoms (lambda (sym)(if (string-match pattern (symbol-name sym))(setq sym-list (cons sym sym-list)))));; Display the data.
(help-setup-xref (list 'describe-symbols pattern)(called-interactively-p 'interactive))(with-help-window (help-buffer)(mapcar describe-func (sort sym-list 'string<)))))The describe-symbols function works like apropos, but provides more information.
(describe-symbols "goal")---------- Buffer: *Help* ---------goal-column
OptionSemipermanent goal column for vertical motion, as set by ...
minibuffer-temporary-goal-position
not documented

VariableChapter 25: Documentation

598

set-goal-column Keys: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved torather than trying to keep the same horizontal position.
With a non-nil argument ARG, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable ‘goal-column’.
(fn ARG)
temporary-goal-column
Variable
Current goal column for vertical motion.
It is the column where point was at the start of the current runof vertical motion commands.
When moving by visual lines via the function ‘line-move-visual’, it is a cons
cell (COL . HSCROLL), where COL is the x-position, in pixels,
divided by the default column width, and HSCROLL is the number ofcolumns by which window is scrolled from left margin.
When the ‘track-eol’ feature is doing its job, the value is‘most-positive-fixnum’.
---------- Buffer: *Help* ----------

Snarf-documentation filename[Function]
This function is used when building Emacs, just before the runnable Emacs is dumped.
It finds the positions of the documentation strings stored in the file filename, andrecords those positions into memory in the function definitions and variable property
lists. See Section E.1 [Building Emacs], page 1346.
Emacs reads the file filename from the emacs/etc directory. When the dumped Emacs
is later executed, the same file will be looked for in the directory doc-directory.
Usually filename is "DOC".
[Variable]
This variable holds the name of the directory which should contain the file "DOC" that
contains documentation strings for built-in functions and variables.

doc-directory

In most cases, this is the same as data-directory. They may be different when you
run Emacs from the directory where you built it, without actually installing it. See[Definition of data-directory], page 604.

25.3 Substituting Key Bindings in Documentation
When documentation strings refer to key sequences, they should use the current, actual key
bindings. They can do so using certain special text sequences described below. Accessing
documentation strings in the usual way substitutes current key binding information for these
special sequences. This works by calling substitute-command-keys. You can also call thatfunction yourself.
Here is a list of the special sequences and what they mean:\[command]
stands for a key sequence that will invoke command, or ‘M-x command’ if command has no key bindings.

Chapter 25: Documentation

599\{mapvar}stands for a summary of the keymap which is the value of the variablemapvar. The summary is made using describe-bindings. The summary
will normally exclude meny bindings, but if the include-menus argument tosubstitute-command-keys is non-nil, the menu bindings will be included.
\<mapvar>stands for no text itself. It is used only for a side effect: it specifies mapvar’s value
as the keymap for any following ‘\[command]’ sequences in this documentation
string.
\`KEYSEQ'
stands for a key sequence KEYSEQ, which will use the same face as a commandsubstitution. This should be used only when a key sequence has no corresponding
command, for example when it is read directly with read-key-sequence. It
must be a valid key sequence according to key-valid-p. It can also be usedwith command names, like ‘\`M-x foo'’, where you want this to be fontified likea keyboard sequence, but you want to inhibit translating it into a key sequence
like ‘\[foo]’ does.
`(grave accent) stands for a left quote. This generates a left single quotation mark,an apostrophe, or a grave accent depending on the value of text-quoting-style.
See Section 25.4 [Text Quoting Style], page 600.

'

(apostrophe) stands for a right quote. This generates a right single quotation
mark or an apostrophe depending on the value of text-quoting-style.

\=quotes the following character and is discarded; thus, ‘\=`’ puts ‘`’ into the
output, ‘\=\[’ puts ‘\[’ into the output, and ‘\=\=’ puts ‘\=’ into the output.

\+

This indicates that the symbol directly following should not be marked as linkin the *Help* buffer.
Please note: Each ‘\’ must be doubled when written in a string in Emacs Lisp.

substitute-command-keys string &optional no-face include-menus[Function]
This function scans string for the above special sequences and replaces them by what
they stand for, returning the result as a string. This permits display of documentationthat refers accurately to the user’s own customized key bindings. By default, the key
bindings are given a special face help-key-binding, but if the optional argument
no-face is non-nil, the function doesn’t add this face to the produced string.
If a command has multiple bindings, this function normally uses the first one it finds.
You can specify one particular key binding by assigning an :advertised-binding
symbol property to the command, like this:(put 'undo :advertised-binding [?\C-/])The :advertised-binding property also affects the binding shown in menu items(see Section 23.18.5 [Menu Bar], page 516). The property is ignored if it specifies a
key binding that the command does not actually have.
Here are examples of the special sequences:(substitute-command-keys"To abort recursive edit, type `\\[abort-recursive-edit]'.")⇒ "To abort recursive edit, type ‘C-]’."

Chapter 25: Documentation

600(substitute-command-keys"The keys that are defined for the minibuffer here are:\\{minibuffer-local-must-match-map}")⇒ "The keys that are defined for the minibuffer here are:
?
SPC
TAB
C-j
RET
C-g
"

minibuffer-completion-help
minibuffer-complete-wordminibuffer-complete
minibuffer-complete-and-exit
minibuffer-complete-and-exit
abort-recursive-edit

The keymap description will normally exclude menu items, but if
include-menus is non-nil, include them.
(substitute-command-keys"To abort a recursive edit from the minibuffer, type \`\\<minibuffer-local-must-match-map>\\[abort-recursive-edit]'.")⇒ "To abort a recursive edit from the minibuffer, type ‘C-g’."substitute-quotes string[Function]
This function works like substitute-command-keys, but only replaces quote characters.

There are other special conventions for the text in documentation strings—for instance,
you can refer to functions, variables, and sections of this manual. See Section D.6 [Documentation Tips], page 1337, for details.

25.4 Text Quoting Style
Typically, grave accents and apostrophes are treated specially in documentation stringsand diagnostic messages, and translate to matching single quotation marks (also called“curved quotes”). For example, the documentation string "Alias for ‘foo’." and thefunction call (message "Alias for `foo'.") both translate to "Alias for ‘foo’.". Less
commonly, Emacs displays grave accents and apostrophes as themselves, or as apostrophes
only (e.g., "Alias for ’foo’."). Documentation strings and message formats should be
written so that they display well with any of these styles. For example, the documentation
string "Alias for ’foo’." is probably not what you want, as it can display as "Alias
for ’foo’.", an unusual style in English.
Sometimes you may need to display a grave accent or apostrophe without translation,
regardless of text quoting style. In a documentation string, you can do this with escapes. For
example, in the documentation string "\\=‘(a ,(sin 0)) ==> (a 0.0)" the grave accentis intended to denote Lisp code, so it is escaped and displays as itself regardless of quoting
style. In a call to message or error, you can avoid translation by using a format "%s" withan argument that is a call to format. For example, (message "%s" (format "`(a ,(sin%S)) ==> (a %S)" x (sin x))) displays a message that starts with grave accent regardlessof text quoting style.
[User Option]
The value of this user option is a symbol that specifies the style Emacs should use
for single quotes in the wording of help and messages. If the option’s value is curve,

text-quoting-style

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601

the style is ‘like this’ with curved single quotes. If the value is straight, thestyle is ’like this’ with straight apostrophes. If the value is grave, quotes are
not translated and the style is ‘like this’ with grave accent and apostrophe, thestandard style before Emacs version 25. The default value nil acts like curve if
curved single quotes seem to be displayable, and like grave otherwise.
This option is useful on platforms that have problems with curved quotes. You cancustomize it freely according to your personal preference.
[Function]
You should not read the value of the variable text-quoting-style directly. Instead,use this function with the same name to dynamically compute the correct quoting
style on the current terminal in the nil case described above.

text-quoting-style

25.5 Describing Characters for Help Messages
These functions convert events, key sequences, or characters to textual descriptions. These
descriptions are useful for including arbitrary text characters or key sequences in messages,
because they convert non-printing and whitespace characters to sequences of printing
characters. The description of a non-whitespace printing character is the character itself.

key-description sequence &optional prefix[Function]
This function returns a string containing the Emacs standard notation for the input
events in sequence. If prefix is non-nil, it is a sequence of input events leading up to
sequence and is included in the return value. Both arguments may be strings, vectors
or lists. See Section 22.7 [Input Events], page 440, for more information about valid
events.
(key-description [?\M-3 delete])⇒ "M-3 <delete>"(key-description [delete] "\M-3")⇒ "M-3 <delete>"

See also the examples for single-key-description, below.

single-key-description event &optional no-angles[Function]
This function returns a string describing event in the standard Emacs notation for
keyboard input. A normal printing character appears as itself, but a control character
turns into a string starting with ‘C-’, a meta character turns into a string startingwith ‘M-’, and space, tab, etc., appear as ‘SPC’, ‘TAB’, etc. A function key symbol
appears inside angle brackets ‘<...>’. An event that is a list appears as the name ofthe symbol in the car of the list, inside angle brackets.
If the optional argument no-angles is non-nil, the angle brackets around function keys
and event symbols are omitted; this is for compatibility with old versions of Emacs
which didn’t use the brackets.
(single-key-description ?\C-x)⇒ "C-x"(key-description "\C-x \M-y \n \t \r \f123")⇒ "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3"
(single-key-description 'delete)⇒ "<delete>"(single-key-description 'C-mouse-1)⇒ "C-<mouse-1>"

Chapter 25: Documentation

602(single-key-description 'C-mouse-1 t)⇒ "C-mouse-1"

text-char-description character[Function]
This function returns a string describing character in the standard Emacs notation
for characters that can appear in text—similar to single-key-description, exceptthat the argument must be a valid character code that passes a characterp test (seeSection 34.5 [Character Codes], page 967). The function produces descriptions ofcontrol characters with a leading caret (which is how Emacs usually displays control
characters in buffers). Characters with modifier bits will cause this function to signal
an error (ASCII characters with the Control modifier are an exception, they are
represented as control characters).
(text-char-description ?\C-c)⇒ "^C"(text-char-description ?\M-m)error Wrong type argument: characterp, 134217837

read-kbd-macro string &optional need-vector[Command]This function is used mainly for operating on keyboard macros, but it can also be
used as a rough inverse for key-description. You call it with a string containing
key descriptions, separated by spaces; it returns a string or vector containing thecorresponding events. (This may or may not be a single valid key sequence, dependingon what events you use; see Section 23.1 [Key Sequences], page 480.) If need-vector is
non-nil, the return value is always a vector.

25.6 Help Functions
Emacs provides a variety of built-in help functions, all accessible to the user as subcommandsof the prefix C-h. For more information about them, see Section “Help” in The GNU Emacs
Manual. Here we describe some program-level interfaces to the same information.

apropos pattern &optional do-all[Command]This function finds all meaningful symbols whose names contain a match for the
apropos pattern pattern. An apropos pattern is either a word to match, a spaceseparated list of words of which at least two must match, or a regular expression (ifany special regular expression characters occur). A symbol is meaningful if it has adefinition as a function, variable, or face, or has properties.
The function returns a list of elements that look like this:(symbol score function-doc variable-doc
plist-doc widget-doc face-doc group-doc)
Here, score is an integer measure of how important the symbol seems to be as a match.
Each of the remaining elements is a documentation string, or nil, for symbol as afunction, variable, etc.
It also displays the symbols in a buffer named *Apropos*, each with a one-line
description taken from the beginning of its documentation string.
If do-all is non-nil, or if the user option apropos-do-all is non-nil, then apropos
also shows key bindings for the functions that are found; it also shows all interned
symbols, not just meaningful ones (and it lists them in the return value as well).

Chapter 25: Documentation

603[Variable]
The value of this variable is a local keymap for characters following the Help key, C-h.

help-map[Prefix Command]
This symbol is not a function; its function definition cell holds the keymap known as
help-map. It is defined in help.el as follows:

help-command(keymap-set global-map (key-description (string help-char)) 'help-command)(fset 'help-command help-map)[User Option]
The value of this variable is the help character—the character that Emacs recognizes
as meaning Help. By default, its value is 8, which stands for C-h. When Emacs reads
this character, if help-form is a non-nil Lisp expression, it evaluates that expression,and displays the result in a window if it is a string.
Usually the value of help-form is nil. Then the help character has no special meaningat the level of command input, and it becomes part of a key sequence in the normal
way. The standard key binding of C-h is a prefix key for several general-purpose help
features.
The help character is special after prefix keys, too. If it has no binding as a subcommandof the prefix key, it runs describe-prefix-bindings, which displays a list of all thesubcommands of the prefix key.

help-char[User Option]
The value of this variable is a list of event types that serve as alternative help characters.
These events are handled just like the event specified by help-char.

help-event-list[Variable]
If this variable is non-nil, its value is a form to evaluate whenever the character
help-char is read. If evaluating the form produces a string, that string is displayed.
A command that calls read-event, read-char-choice, read-char, read-charfrom-minibuffer, or y-or-n-p probably should bind help-form to a non-nil expression while it does input. (The time when you should not do this is when C-h has someother meaning.) Evaluating this expression should result in a string that explains
what the input is for and how to enter it properly.
Entry to the minibuffer binds this variable to the value of minibuffer-help-form(see [Definition of minibuffer-help-form], page 421).

help-form[Variable]
This variable holds a function to print help for a prefix key. The function is called when
the user types a prefix key followed by the help character, and the help character has nobinding after that prefix. The variable’s default value is describe-prefix-bindings.

prefix-help-command[Command]This function calls describe-bindings to display a list of all the subcommands of theprefix key of the most recent key sequence. The prefix described consists of all but thelast event of that key sequence. (The last event is, presumably, the help character.)

describe-prefix-bindings

The following two functions are meant for modes that want to provide help without
relinquishing control, such as the electric modes. Their names begin with ‘Helper’ todistinguish them from the ordinary help functions.

Chapter 25: Documentation

604[Command]This command pops up a window displaying a help buffer containing a listing of allof the key bindings from both the local and global keymaps. It works by calling
describe-bindings.

Helper-describe-bindings[Command]This command provides help for the current mode. It prompts the user in the minibuffer
with the message ‘Help (Type ? for further options)’, and then provides assistancein finding out what the key bindings are, and what the mode is intended for. It returns
nil.
This can be customized by changing the map Helper-help-map.

Helper-help[Variable]
This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs.

data-directory[Function]
This function returns the name of the help buffer, which is normally *Help*; if such abuffer does not exist, it is first created.

help-buffer

with-help-window buffer-or-name body. . .

[Macro]This macro evaluates body like with-output-to-temp-buffer (see Section 41.8
[Temporary Displays], page 1146), inserting any output produced by its forms intoa buffer specified by buffer-or-name, which can be a buffer or the name of a buffer.
(Frequently, buffer-or-name is the value returned by the function help-buffer.) This
macro puts the specified buffer into Help mode and displays a message telling the user
how to quit and scroll the help window. It selects the help window if the current valueof the user option help-window-select has been set accordingly. It returns the lastvalue in body.

help-setup-xref item interactive-p[Function]
This function updates the cross reference data in the *Help* buffer, which is used
to regenerate the help information when the user clicks on the ‘Back’ or ‘Forward’
buttons. Most commands that use the *Help* buffer should invoke this function
before clearing the buffer. The item argument should have the form (function .
args), where function is a function to call, with argument list args, to regenerate
the help buffer. The interactive-p argument is non-nil if the calling command was
invoked interactively; in that case, the stack of items for the *Help* buffer’s ‘Back’
buttons is cleared.

See [describe-symbols example], page 597, for an example of using help-buffer,with-help-window, and help-setup-xref.

make-help-screen fname help-line help-text help-map[Macro]This macro defines a help command named fname that acts like a prefix key thatshows a list of the subcommands it offers.
When invoked, fname displays help-text in a window, then reads and executes a key
sequence according to help-map. The string help-text should describe the bindings
available in help-map.

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605

The command fname is defined to handle a few events itself, by scrolling the displayof help-text. When fname reads one of those special events, it does the scrolling andthen reads another event. When it reads an event that is not one of those few, andwhich has a binding in help-map, it executes that key’s binding and then returns.
The argument help-line should be a single-line summary of the alternatives in help-map.
In the current version of Emacs, this argument is used only if you set the option
three-step-help to t.
This macro is used in the command help-for-help which is the binding of C-h C-h.
[User Option]
If this variable is non-nil, commands defined with make-help-screen display their
help-line strings in the echo area at first, and display the longer help-text strings only
if the user types the help character again.

three-step-help

25.7 Documentation Groups
Emacs can list functions based on various groupings. For instance, string-trim andmapconcat are “string” functions, so M-x shortdoc RET string RET will give an overview
of functions that operate on strings.
The documentation groups are created with the define-short-documentation-group
macro.

define-short-documentation-group group &rest functions[Macro]Define group as a group of functions, and provide short summaries of using thosefunctions. The optional argument functions is a list whose elements are of the form:(func [keyword val]...)

The following keywords are recognized::eval

The value should be a form that has no side effect when evaluated. The
form will be used in the documentation by printing it with prin1 (seeSection 20.5 [Output Functions], page 377). However, if the form is astring, it will be inserted as-is, and the string will then be read to yield
the form. In any case, the form will then be evaluated, and the result
used. For instance::eval (concat "foo" "bar" "zot"):eval "(make-string 5 ?x)"
will result in:(concat "foo" "bar" "zot")⇒ "foobarzot"(make-string 5 ?x)⇒ "xxxxx"(The reason for allowing both Lisp forms and strings here is so thatprinting could be controlled in the few cases where a certain presentationof the form is wished for. In the example, ‘?x’ would otherwise have been
printed as ‘120’ if it hadn’t been included in a string.)

Chapter 25: Documentation606:no-evalThis is like :eval, except that the form will not be evaluated. In thesecases, a :result element of some kind (see below) should be included.
:no-eval (file-symlink-p "/tmp/foo"):eg-result t:no-eval*
Like :no-eval, but always inserts ‘[it depends]’ as the result. For
instance::no-eval* (buffer-string)
will result in:(buffer-string)→ [it depends]:no-value
Like :no-eval, but is used when the function in question has no welldefined return value, and is used for side effect only.
Used to output the result from non-evaluating example forms.

:result:no-eval (setcar list 'c):result c:eg-result
Used to output an example result from non-evaluating example forms.
For instance::no-eval (looking-at "f[0-9]"):eg-result t
will result in:(looking-at "f[0-9]")eg. → t:result-string:eg-result-string
These two are the same as :result and :eg-result, respectively, but
are inserted as is. This is useful when the result is unreadable or should
be of a particular form::no-eval (find-file "/tmp/foo"):eg-result-string "#<buffer foo>":no-eval (default-file-modes):eg-result-string "#o755":no-manual
Indicates that this function is not documented in the manual.
:args

By default, the function’s actual argument list is shown. If :args ispresent, they are used instead.
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Here’s a very short example:(define-short-documentation-group string"Creating Strings"(substring:eval (substring "foobar" 0 3)
:eval (substring "foobar" 3))(concat:eval (concat "foo" "bar" "zot")))
The first argument is the name of the group to be defined, and then follows any
number of function descriptions.
A function can belong to any number of documentation groups.
In addition to function descriptions, the list can also have string elements, which areused to divide a documentation group into sections.

shortdoc-add-function group section elem

[Function]
Lisp packages can add functions to groups with this function. Each elem should be afunction description, as described above. group is the function group, and section iswhat section in the function group to insert the function into.
If group doesn’t exist, it will be created. If section doesn’t exist, it will be added tothe end of the function group.

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26 FilesThis chapter describes the Emacs Lisp functions and variables to find, create, view, save, andotherwise work with files and directories. A few other file-related functions are described in
Chapter 28 [Buffers], page 671, and those related to backups and auto-saving are describedin Chapter 27 [Backups and Auto-Saving], page 659.
Many of the file functions take one or more arguments that are file names. A filename is a string. Most of these functions expand file name arguments using the function
expand-file-name, so that ~ is handled correctly, as are relative file names (including ../and the empty string). See Section 26.9.4 [File Name Expansion], page 639.
In addition, certain magic file names are handled specially. For example, when a remote
file name is specified, Emacs accesses the file over the network via an appropriate protocol.
See Section “Remote Files” in The GNU Emacs Manual. This handling is done at a very low
level, so you may assume that all the functions described in this chapter accept magic filenames as file name arguments, except where noted. See Section 26.12 [Magic File Names],
page 649, for details.
When file I/O functions signal Lisp errors, they usually use the condition file-error (seeSection 11.7.3.3 [Handling Errors], page 182). The error message is in most cases obtained
from the operating system, according to locale system-messages-locale, and decodedusing coding system locale-coding-system (see Section 34.12 [Locales], page 991).

26.1 Visiting Files
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer isvisiting that file, and call the file the visited file of the buffer.
A file and a buffer are two different things. A file is information recorded permanently inthe computer (unless you delete it). A buffer, on the other hand, is information inside ofEmacs that will vanish at the end of the editing session (or when you kill the buffer). Whena buffer is visiting a file, it contains information copied from the file. The copy in the buffer
is what you modify with editing commands. Changes to the buffer do not change the file; tomake the changes permanent, you must save the buffer, which means copying the alteredbuffer contents back into the file.
Despite the distinction between files and buffers, people often refer to a file when theymean a buffer and vice-versa. Indeed, we say, “I am editing a file”, rather than, “I amediting a buffer that I will soon save as a file of the same name”. Humans do not usuallyneed to make the distinction explicit. When dealing with a computer program, however, it
is good to keep the distinction in mind.

26.1.1 Functions for Visiting Files
This section describes the functions normally used to visit files. For historical reasons, thesefunctions have names starting with ‘find-’ rather than ‘visit-’. See Section 28.4 [Buffer
File Name], page 675, for functions and variables that access the visited file name of a buffer
or that find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but not alter it, thefastest way is to use insert-file-contents in a temporary buffer. Visiting the file is notnecessary and takes longer. See Section 26.3 [Reading from Files], page 614.

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find-file filename &optional wildcards[Command]This command selects a buffer visiting the file filename, using an existing buffer if
there is one, and otherwise creating a new buffer and reading the file into it. It also
returns that buffer.

Aside from some technical details, the body of the find-file function is basicallyequivalent to:(switch-to-buffer (find-file-noselect filename nil nil wildcards))(See switch-to-buffer in Section 29.12 [Switching Buffers], page 721.)
If wildcards is non-nil, which is always true in an interactive call, then find-file
expands wildcard characters in filename and visits all the matching files.
When find-file is called interactively, it prompts for filename in the minibuffer.

find-file-literally filename[Command]This command visits filename, like find-file does, but it does not perform any
format conversions (see Section 26.13 [Format Conversion], page 654), character code
conversions (see Section 34.10 [Coding Systems], page 976), or end-of-line conversions(see Section 34.10.1 [Coding System Basics], page 977). The buffer visiting the file ismade unibyte, and its major mode is Fundamental mode, regardless of the file name.
File local variable specifications in the file (see Section 12.12 [File Local Variables],page 213) are ignored, and automatic decompression and adding a newline at the endof the file due to require-final-newline (see Section 26.2 [Saving Buffers], page 612)
are also disabled.
Note that if Emacs already has a buffer visiting the same file non-literally, it will not
visit the same file literally, but instead just switch to the existing buffer. If you want
to be sure of accessing a file’s contents literally, you should create a temporary buffer
and then read the file contents into it using insert-file-contents-literally (seeSection 26.3 [Reading from Files], page 614).

find-file-noselect filename &optional nowarn rawfile wildcards[Function]
This function is the guts of all the file-visiting functions. It returns a buffer visiting
the file filename. You may make the buffer current or display it in a window if you
wish, but this function does not do so.
The function returns an existing buffer if there is one; otherwise it creates a new buffer
and reads the file into it. When find-file-noselect uses an existing buffer, it first
verifies that the file has not changed since it was last visited or saved in that buffer. If
the file has changed, this function asks the user whether to reread the changed file. If
the user says ‘yes’, any edits previously made in the buffer are lost.
Reading the file involves decoding the file’s contents (see Section 34.10 [Coding Systems],
page 976), including end-of-line conversion, and format conversion (see Section 26.13[Format Conversion], page 654). If wildcards is non-nil, then find-file-noselectexpands wildcard characters in filename and visits all the matching files.
This function displays warning or advisory messages in various peculiar cases, unlessthe optional argument nowarn is non-nil. For example, if it needs to create a buffer,and there is no file named filename, it displays the message ‘(New file)’ in the echo
area, and leaves the buffer empty.

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The find-file-noselect function normally calls after-find-file after reading thefile (see Section 26.1.2 [Subroutines of Visiting], page 611). That function sets thebuffer major mode, parses local variables, warns the user if there exists an auto-save
file more recent than the file just visited, and finishes by running the functions infind-file-hook.
If the optional argument rawfile is non-nil, then after-find-file is not called, andthe find-file-not-found-functions are not run in case of failure. What’s more, a
non-nil rawfile value suppresses coding system conversion and format conversion.
The find-file-noselect function usually returns the buffer that is visiting the file
filename. But, if wildcards are actually used and expanded, it returns a list of buffersthat are visiting the various files.
(find-file-noselect "/etc/fstab")⇒ #<buffer fstab>find-file-other-window filename &optional wildcards[Command]This command selects a buffer visiting the file filename, but does so in a window otherthan the selected window. It may use another existing window or split a window; see
Section 29.12 [Switching Buffers], page 721.

When this command is called interactively, it prompts for filename.

find-file-read-only filename &optional wildcards[Command]This command selects a buffer visiting the file filename, like find-file, but it marks
the buffer as read-only. See Section 28.7 [Read Only Buffers], page 680, for related
functions and variables.

When this command is called interactively, it prompts for filename.
[User Option]
If this variable is non-nil, then the various find-file commands check for wildcard
characters and visit all the files that match them (when invoked interactively or when
their wildcards argument is non-nil). If this option is nil, then the find-filecommands ignore their wildcards argument and never treat wildcard characters
specially.

find-file-wildcards[User Option]
The value of this variable is a list of functions to be called after a file is visited. The
file’s local-variables specification (if any) will have been processed before the hooks
are run. The buffer visiting the file is current when the hook functions are run.

find-file-hook

This variable is a normal hook. See Section 24.1 [Hooks], page 524.
[Variable]
The value of this variable is a list of functions to be called when find-file orfind-file-noselect is passed a nonexistent file name. find-file-noselect calls
these functions as soon as it detects a nonexistent file. It calls them in the order ofthe list, until one of them returns non-nil. buffer-file-name is already set up.

find-file-not-found-functions

This is not a normal hook because the values of the functions are used, and in manycases only some of the functions are called.

Chapter 26: Files

611[Variable]
This buffer-local variable, if set to a non-nil value, makes save-buffer behave as
if the buffer were visiting its file literally, i.e., without conversions of any kind. The
command find-file-literally sets this variable’s local value, but other equivalentfunctions and commands can do that as well, e.g., to avoid automatic addition of a
newline at the end of the file. This variable is permanent local, so it is unaffected bychanges of major modes.

find-file-literally

26.1.2 Subroutines of Visiting
The find-file-noselect function uses two important subroutines which are sometimes
useful in user Lisp code: create-file-buffer and after-find-file. This section explains
how to use them.

create-file-buffer filename[Function]
This function creates a suitably named buffer for visiting filename, and returns it. It
uses filename (sans directory) as the name if that name is free; otherwise, it appends
a string such as ‘<2>’ to get an unused name. See also Section 28.9 [Creating Buffers],
page 684. Note that the uniquify library affects the result of this function. See
Section “Uniquify” in The GNU Emacs Manual.
Please note: create-file-buffer does not associate the new buffer with a file anddoes not select the buffer. It also does not use the default major mode.
(create-file-buffer "foo")⇒ #<buffer foo>(create-file-buffer "foo")⇒ #<buffer foo<2>>(create-file-buffer "foo")⇒ #<buffer foo<3>>This function is used by find-file-noselect. It uses generate-new-buffer (seeSection 28.9 [Creating Buffers], page 684).

after-find-file &optional error warn noauto
after-find-file-from-revert-buffer nomodes[Function]

This function sets the buffer major mode, and parses local variables (see Section 24.2.2[Auto Major Mode], page 531). It is called by find-file-noselect and by the default
revert function (see Section 27.3 [Reverting], page 667).
If reading the file got an error because the file does not exist, but its directory does
exist, the caller should pass a non-nil value for error. In that case, after-find-fileissues a warning: ‘(New file)’. For more serious errors, the caller should usually notcall after-find-file.
If warn is non-nil, then this function issues a warning if an auto-save file exists andis more recent than the visited file.
If noauto is non-nil, that says not to enable or disable Auto-Save mode. The moderemains enabled if it was enabled before.
If after-find-file-from-revert-buffer is non-nil, that means this call was fromrevert-buffer. This has no direct effect, but some mode functions and hookfunctions check the value of this variable.

Chapter 26: Files612

If nomodes is non-nil, that means don’t alter the buffer’s major mode, don’t process
local variables specifications in the file, and don’t run find-file-hook. This featureis used by revert-buffer in some cases.
The last thing after-find-file does is call all the functions in the list find-filehook.

26.2 Saving Buffers
When you edit a file in Emacs, you are actually working on a buffer that is visiting that
file—that is, the contents of the file are copied into the buffer and the copy is what you
edit. Changes to the buffer do not change the file until you save the buffer, which means
copying the contents of the buffer into the file. Buffers which are not visiting a file can stillbe “saved”, in a sense, using functions in the buffer-local write-contents-functions hook.

save-buffer &optional backup-option[Command]This function saves the contents of the current buffer in its visited file if the buffer has
been modified since it was last visited or saved. Otherwise it does nothing.
save-buffer is responsible for making backup files. Normally, backup-option is nil,and save-buffer makes a backup file only if this is the first save since visiting thefile. Other values for backup-option request the making of backup files in othercircumstances:• With an argument of 4 or 64, reflecting 1 or 3 C-u’s, the save-buffer function
marks this version of the file to be backed up when the buffer is next saved.
• With an argument of 16 or 64, reflecting 2 or 3 C-u’s, the save-buffer function
unconditionally backs up the previous version of the file before saving it.
• With an argument of 0, unconditionally do not make any backup file.

save-some-buffers &optional save-silently-p pred[Command]This command saves some modified file-visiting buffers. Normally it asks the user
about each buffer. But if save-silently-p is non-nil, it saves all the file-visiting buffers
without querying the user.
The optional pred argument provides a predicate that controls which buffers to ask
about (or to save silently if save-silently-p is non-nil). If pred is nil, that means
to use the value of save-some-buffers-default-predicate instead of pred. If theresult is nil, it means ask only about file-visiting buffers. If it is t, that means alsooffer to save certain other non-file buffers—those that have a non-nil buffer-local
value of buffer-offer-save (see Section 28.10 [Killing Buffers], page 685). A user
who says ‘yes’ to saving a non-file buffer is asked to specify the file name to use. The
save-buffers-kill-emacs function passes the value t for pred.
If the predicate is neither t nor nil, then it should be a function of no arguments. It
will be called in each buffer to decide whether to offer to save that buffer. If it returns
a non-nil value in a certain buffer, that means do offer to save that buffer.

write-file filename &optional confirm[Command]This function writes the current buffer into file filename, makes the buffer visit that file,and marks it not modified. Then it renames the buffer based on filename, appending astring like ‘<2>’ if necessary to make a unique buffer name. It does most of this workChapter 26: Files613

by calling set-visited-file-name (see Section 28.4 [Buffer File Name], page 675)
and save-buffer.
If confirm is non-nil, that means to ask for confirmation before overwriting an existing
file. Interactively, confirmation is required, unless the user supplies a prefix argument.
If filename is a directory name (see Section 26.9.3 [Directory Names], page 637),
write-file uses the name of the visited file, in directory filename. If the buffer is
not visiting a file, it uses the buffer name instead.
Saving a buffer runs several hooks. It also performs format conversion (see Section 26.13[Format Conversion], page 654). Note that these hooks, described below, are only run bysave-buffer, they are not run by other primitives and functions that write buffer text tofiles, and in particular auto-saving (see Section 27.2 [Auto-Saving], page 664) doesn’t run
these hooks.
[Variable]
The value of this variable is a list of functions to be called before writing out a buffer
to its visited file. If one of them returns non-nil, the file is considered already written
and the rest of the functions are not called, nor is the usual code for writing the file
executed.

write-file-functions

If a function in write-file-functions returns non-nil, it is responsible for making
a backup file (if that is appropriate). To do so, execute the following code:(or buffer-backed-up (backup-buffer))
You might wish to save the file modes value returned by backup-buffer and use that
(if non-nil) to set the mode bits of the file that you write. This is what save-buffer
normally does. See Section 27.1.1 [Making Backup Files], page 659.
The hook functions in write-file-functions are also responsible for encoding thedata (if desired): they must choose a suitable coding system and end-of-line conversion(see Section 34.10.3 [Lisp and Coding Systems], page 979), perform the encoding (seeSection 34.10.7 [Explicit Encoding], page 988), and set last-coding-system-used tothe coding system that was used (see Section 34.10.2 [Encoding and I/O], page 978).
If you set this hook locally in a buffer, it is assumed to be associated with the file or
the way the contents of the buffer were obtained. Thus the variable is marked as apermanent local, so that changing the major mode does not alter a buffer-local value.
On the other hand, calling set-visited-file-name will reset it. If this is not what
you want, you might like to use write-contents-functions instead.
Even though this is not a normal hook, you can use add-hook and remove-hook tomanipulate the list. See Section 24.1 [Hooks], page 524.
[Variable]
This works just like write-file-functions, but it is intended for hooks that pertain
to the buffer’s contents, not to the particular visited file or its location, and can beused to create arbitrary save processes for buffers that aren’t visiting files at all. Suchhooks are usually set up by major modes, as buffer-local bindings for this variable.
This variable automatically becomes buffer-local whenever it is set; switching to a new
major mode always resets this variable, but calling set-visited-file-name does not.

write-contents-functions

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If any of the functions in this hook returns non-nil, the file is considered already written
and the rest are not called and neither are the functions in write-file-functions.
When using this hook to save buffers that are not visiting files (for instance, specialmode buffers), keep in mind that, if the function fails to save correctly and returns a
nil value, save-buffer will go on to prompt the user for a file to save the buffer in.
If this is undesirable, consider having the function fail by raising an error.
[User Option]
This normal hook runs before a buffer is saved in its visited file, regardless of whether
that is done normally or by one of the hooks described above. For instance, thecopyright.el program uses this hook to make sure the file you are saving has thecurrent year in its copyright notice.

before-save-hookafter-save-hook[User Option]

This normal hook runs after a buffer has been saved in its visited file.
[User Option]
If this variable is non-nil, then save-buffer protects against I/O errors while saving
by writing the new file to a temporary name instead of the name it is supposed tohave, and then renaming it to the intended name after it is clear there are no errors.
This procedure prevents problems such as a lack of disk space from resulting in an
invalid file.
As a side effect, backups are necessarily made by copying. See Section 27.1.2 [Rename
or Copy], page 661. Yet, at the same time, saving a precious file always breaks all
hard links between the file you save and other file names.
Some modes give this variable a non-nil buffer-local value in particular buffers.

file-precious-flag[User Option]
This variable determines whether files may be written out that do not end with anewline. If the value of the variable is t, then save-buffer silently adds a newline at
the end of the buffer whenever it does not already end in one. If the value is visit,
Emacs adds a missing newline just after it visits the file. If the value is visit-save,Emacs adds a missing newline both on visiting and on saving. For any other non-nil
value, save-buffer asks the user whether to add a newline each time the case arises.
If the value of the variable is nil, then save-buffer doesn’t add newlines at all. nil
is the default value, but a few major modes set it to t in particular buffers.

require-final-newline

See also the function set-visited-file-name (see Section 28.4 [Buffer File Name],
page 675).

26.3 Reading from Files
To copy the contents of a file into a buffer, use the function insert-file-contents. (Don’t
use the command insert-file in a Lisp program, as that sets the mark.)

insert-file-contents filename &optional visit beg end replace[Function]
This function inserts the contents of file filename into the current buffer after point.
It returns a list of the absolute file name and the length of the data inserted. An error
is signaled if filename is not the name of a file that can be read.

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This function checks the file contents against the defined file formats, and converts
the file contents if appropriate and also calls the functions in the list after-insertfile-functions. See Section 26.13 [Format Conversion], page 654. Normally, oneof the functions in the after-insert-file-functions list determines the coding
system (see Section 34.10 [Coding Systems], page 976) used for decoding the file’s
contents, including end-of-line conversion. However, if the file contains null bytes, it isby default visited without any code conversions. See Section 34.10.3 [Lisp and Coding
Systems], page 979.
If visit is non-nil, this function additionally marks the buffer as unmodified and sets
up various fields in the buffer so that it is visiting the file filename: these include
the buffer’s visited file name and its last save file modtime. This feature is used byfind-file-noselect and you probably should not use it yourself.
If beg and end are non-nil, they should be numbers that are byte offsets specifying
the portion of the file to insert. In this case, visit must be nil. For example,(insert-file-contents filename nil 0 500)
inserts the characters coded by the first 500 bytes of a file.
If beg or end happens to be in the middle of a character’s multibyte sequence, Emacs’s
character code conversion will insert one or more eight-bit characters (a.k.a. “rawbytes”) (see Section 34.7 [Character Sets], page 973) into the buffer. If you want toread part of a file this way, we recommend to bind coding-system-for-read to asuitable value around the call to this function (see Section 34.10.6 [Specifying Coding
Systems], page 986), and to write Lisp code which will check for raw bytes at theboundaries, read the entire sequence of these bytes, and convert them back to validcharacters.
If the argument replace is non-nil, it means to replace the contents of the buffer(actually, just the accessible portion) with the contents of the file. This is better
than simply deleting the buffer contents and inserting the whole file, because (1) it
preserves some marker positions and (2) it puts less data in the undo list.
It is possible to read a special file (such as a FIFO or an I/O device) with insert-filecontents, as long as replace, and visit and beg are nil. However, you should normallyuse an end argument for these files to avoid inserting (potentially) unlimited data into
the buffer (for instance, when inserting data from /dev/urandom).

insert-file-contents-literally filename &optional visit beg end
replace[Function]

This function works like insert-file-contents except that each byte in the file ishandled separately, being converted into an eight-bit character if needed. It does
not run after-insert-file-functions, and does not do format decoding, charactercode conversion, automatic uncompression, and so on.
If you want to pass a file name to another process so that another program can read thefile, use the function file-local-copy; see Section 26.12 [Magic File Names], page 649.

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26.4 Writing to Files
You can write the contents of a buffer, or part of a buffer, directly to a file on disk using theappend-to-file and write-region functions. Don’t use these functions to write to files
that are being visited; that could cause confusion in the mechanisms for visiting.

append-to-file start end filename[Command]This function appends the contents of the region delimited by start and end in thecurrent buffer to the end of file filename. If that file does not exist, it is created. Thisfunction returns nil.

An error is signaled if you cannot write or create filename.
When called from Lisp, this function is completely equivalent to:(write-region start end filename t)write-region start end filename &optional append visit lockname
mustbenew[Command]This function writes the region delimited by start and end in the current buffer into
the file specified by filename.
If start is nil, then the command writes the entire buffer contents (not just theaccessible portion) to the file and ignores end.
If start is a string, then write-region writes or appends that string, rather than text
from the buffer. end is ignored in this case.
If append is non-nil, then the specified text is appended to the existing file contents(if any). If append is a number, write-region seeks to that byte offset from the startof the file and writes the data from there.
If mustbenew is non-nil, then write-region asks for confirmation if filename names
an existing file. If mustbenew is the symbol excl, then write-region does not ask for
confirmation, but instead it signals an error file-already-exists if the file alreadyexists. Although write-region normally follows a symbolic link and creates thepointed-to file if the symbolic link is dangling, it does not follow symbolic links if
mustbenew is excl.
The test for an existing file, when mustbenew is excl, uses a special system feature.
At least for files on a local disk, there is no chance that some other program could
create a file of the same name before Emacs does, without Emacs’s noticing.
If visit is t, then Emacs establishes an association between the buffer and the file:the buffer is then visiting that file. It also sets the last file modification time for thecurrent buffer to filename’s modtime, and marks the buffer as not modified. Thisfeature is used by save-buffer, but you probably should not use it yourself.
If visit is a string, it specifies the file name to visit. This way, you can write the data
to one file (filename) while recording the buffer as visiting another file (visit). The
argument visit is used in the echo area message and also for file locking; visit is stored
in buffer-file-name. This feature is used to implement file-precious-flag; don’t
use it yourself unless you really know what you’re doing.
The optional argument lockname, if non-nil, specifies the file name to use for purposesof locking and unlocking, overriding filename and visit for that purpose.

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The function write-region converts the data which it writes to the appropriate
file formats specified by buffer-file-format and also calls the functions in thelist write-region-annotate-functions. See Section 26.13 [Format Conversion],
page 654.
Normally, write-region displays the message ‘Wrote filename’ in the echo area.
This message is inhibited if visit is neither t nor nil nor a string, or if Emacs is
operating in batch mode (see Section 42.17 [Batch Mode], page 1289). This feature isuseful for programs that use files for internal purposes, files that the user does notneed to know about.
[Variable]
If this variable’s value is nil, write-region uses the fsync system call after writing
a file. Although this slows Emacs down, it lessens the risk of data loss after power
failure. If the value is t, Emacs does not use fsync. The default value is nil when
Emacs is interactive, and t when Emacs runs in batch mode. See Section 26.8 [Filesand Storage], page 634.

write-region-inhibit-fsync

with-temp-file file body. . .

[Macro]The with-temp-file macro evaluates the body forms with a temporary buffer as
the current buffer; then, at the end, it writes the buffer contents into file file. It kills
the temporary buffer when finished, restoring the buffer that was current before thewith-temp-file form. Then it returns the value of the last form in body.
The current buffer is restored even in case of an abnormal exit via throw or error (seeSection 11.7 [Nonlocal Exits], page 177).
Like with-temp-buffer (see [Current Buffer], page 673), the temporary buffer usedby this macro does not run the hooks kill-buffer-hook, kill-buffer-queryfunctions (see Section 28.10 [Killing Buffers], page 685), and buffer-list-updatehook (see Section 28.8 [Buffer List], page 681).

26.5 File Locks
When two users edit the same file at the same time, they are likely to interfere with eachother. Emacs tries to prevent this situation from arising by recording a file lock when afile is being modified. Emacs can then detect the first attempt to modify a buffer visiting
a file that is locked by another Emacs job, and ask the user what to do. The file lock isreally a file, a symbolic link with a special name, stored in the same directory as the file youare editing. The name is constructed by prepending .# to the file name of the buffer. The
target of the symbolic link will be of the form user@host.pid:boot, where user is replacedwith the current username (from user-login-name), host with the name of the host whereEmacs is running (from system-name), pid with Emacs’s process id, and boot with the timesince the last reboot. :boot is omitted if the boot time is unavailable. (On file systems
that do not support symbolic links, a regular file is used instead, with contents of the form
user@host.pid:boot.)
When you access files using NFS, there may be a small probability that you and anotheruser will both lock the same file simultaneously. If this happens, it is possible for the twousers to make changes simultaneously, but Emacs will still warn the user who saves second.

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Also, the detection of modification of a buffer visiting a file changed on disk catches somecases of simultaneous editing; see Section 28.6 [Modification Time], page 678.

file-locked-p filename[Function]
This function returns nil if the file filename is not locked. It returns t if it is locked
by this Emacs process, and it returns the name of the user who has locked it if it islocked by some other job.
(file-locked-p "foo")⇒ nillock-buffer &optional filename[Function]
This function locks the file filename, if the current buffer is modified. The argument
filename defaults to the current buffer’s visited file. Nothing is done if the current
buffer is not visiting a file, or is not modified, or if the option create-lockfiles isnil.
[Function]
This function unlocks the file being visited in the current buffer, if the buffer is modified.
If the buffer is not modified, then the file should not be locked, so this function doesnothing. It also does nothing if the current buffer is not visiting a file, or is not locked.
This function handles file system errors by calling display-warning and otherwise
ignores the error.

unlock-buffer

create-lockfiles[User Option]

If this variable is nil, Emacs does not lock files.
[User Option]
By default, Emacs creates the lock files in the same directory as the files that are being
locked. This can be changed by customizing this variable. Is has the same syntax as
auto-save-file-name-transforms (see Section 27.2 [Auto-Saving], page 664). For
instance, to make Emacs write all the lock files to /var/tmp/, you could say somethinglike:(setq lock-file-name-transforms'(("\\`/.*/\\([^/]+\\)\\'" "/var/tmp/\\1" t)))lock-file-name-transforms

ask-user-about-lock file other-user[Function]
This function is called when the user tries to modify file, but it is locked by anotheruser named other-user. The default definition of this function asks the user to say
what to do. The value this function returns determines what Emacs does next:• A value of t says to grab the lock on the file. Then this user may edit the fileand other-user loses the lock.
• A value of nil says to ignore the lock and let this user edit the file anyway.
• This function may instead signal a file-locked error, in which case the changethat the user was about to make does not take place.
The error message for this error looks like this:error File is locked: file other-user
where file is the name of the file and other-user is the name of the user who has
locked the file.

Chapter 26: Files619

If you wish, you can replace the ask-user-about-lock function with your own version
that makes the decision in another way.
[User Option]
You can prevent the creation of remote lock files by setting the variable remote-filename-inhibit-locks to t.

remote-file-name-inhibit-locks[Command]This command, called interactively, toggles the local value of create-lockfiles in
the current buffer.

lock-file-mode

26.6 Information about Files
This section describes the functions for retrieving various types of information about files(or directories or symbolic links), such as whether a file is readable or writable, and its
size. These functions all take arguments which are file names. Except where noted, thesearguments need to specify existing files, or an error is signaled.
Be careful with file names that end in spaces. On some filesystems (notably, MS-Windows),
trailing whitespace characters in file names are silently and automatically ignored.

26.6.1 Testing Accessibility
These functions test for permission to access a file for reading, writing, or execution. Unlessexplicitly stated otherwise, they follow symbolic links. See Section 26.6.2 [Kinds of Files],page 621.
On some operating systems, more complex sets of access permissions can be specified, via
mechanisms such as Access Control Lists (ACLs). See Section 26.6.5 [Extended Attributes],
page 627, for how to query and set those permissions.

file-exists-p filename[Function]
This function returns t if a file named filename appears to exist. This does not mean
you can necessarily read the file, only that you can probably find out its attributes.
(On GNU and other POSIX-like systems, this is true if the file exists and you haveexecute permission on the containing directories, regardless of the permissions of thefile itself.)
If the file does not exist, or if there was trouble determining whether the file exists,
this function returns nil.
Since a file name that is an empty string is interpreted relative to the current
buffer’s default directory (see Section 26.9.2 [Relative File Names], page 637), callingfile-exists-p with an argument that is an empty string will report about the buffer’s
default directory.
Directories are files, so file-exists-p can return t when given a directory. However, because file-exists-p follows symbolic links, it returns t for a symbolic linkname only if the target of the link exists; if your Lisp program needs to consider
dangling symlinks whose target doesn’t exist as existing files, use file-attributes(see Section 26.6.4 [File Attributes], page 624) instead of file-exists-p.

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file-readable-p filename[Function]
This function returns t if a file named filename exists and you can read it. It returns
nil otherwise.

file-executable-p filename[Function]
This function returns t if a file named filename exists and you can execute it. It
returns nil otherwise. On GNU and other POSIX-like systems, if the file is a directory,
execute permission means you can check the existence and attributes of files insidethe directory, and open those files if their modes permit.

file-writable-p filename[Function]
This function returns t if the file filename can be written or created by you, and nil
otherwise. A file is writable if the file exists and you can write it. It is creatable if it
does not exist, but its parent directory does exist and you can write in that directory.
In the example below, foo is not writable because the parent directory does not exist,
even though the user could create such a directory.
(file-writable-p "~/no-such-dir/foo")⇒ nil

file-accessible-directory-p dirname[Function]
This function returns t if you have permission to open existing files in the directory
whose name as a file is dirname; otherwise (e.g., if there is no such directory), it
returns nil. The value of dirname may be either a directory name (such as /foo/) or
the file name of a file which is a directory (such as /foo, without the final slash).
For example, from the following we deduce that any attempt to read a file in /foo/
will give an error:(file-accessible-directory-p "/foo")⇒ nil

with-existing-directory body. . .

[Macro]This macro ensures that default-directory is bound to an existing directory before
executing body. If default-directory already exists, that’s preferred, and otherwisesome other directory is used. This macro can be useful, for instance, when callingan external command that requires that it’s running in a directory that exists. The
chosen directory is not guaranteed to be writable.

access-file filename string[Function]
If you can read filename this function returns nil; otherwise it signals an error using
string as the error message text.

file-ownership-preserved-p filename &optional group[Function]
This function returns t if deleting the file filename and then creating it anew would
keep the file’s owner unchanged. It also returns t for nonexistent files.
If the optional argument group is non-nil, this function also checks that the file’s
group would be unchanged.

This function does not follow symbolic links.

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621

file-modes filename &optional flag

[Function]
This function returns the mode bits of filename—an integer summarizing its read,
write, and execution permissions. This function follows symbolic links. If the file does
not exist, the return value is nil.
See Section “File permissions” in The gnu Coreutils Manual, for a description ofmode bits. For example, if the low-order bit is 1, the file is executable by all users;
if the second-lowest-order bit is 1, the file is writable by all users; etc. The highest
possible value is 4095 (7777 octal), meaning that everyone has read, write, and executepermission, the SUID bit is set for both others and group, and the sticky bit is set.
By default this function follows symbolic links. However, if the optional argument flagis the symbol nofollow, this function does not follow filename if it is a symbolic link;
this can help prevent inadvertently obtaining the mode bits of a file somewhere else,and is more consistent with file-attributes (see Section 26.6.4 [File Attributes],
page 624).
See Section 26.7 [Changing Files], page 629, for the set-file-modes function, which
can be used to set these permissions.
(file-modes "~/junk/diffs" 'nofollow)⇒ 492; Decimal integer.
(format "%o" 492)
⇒ "754"; Convert to octal.
(set-file-modes "~/junk/diffs" #o666 'nofollow)⇒ nil$ ls -l diffs-rw-rw-rw- 1 lewis lewis 3063 Oct 30 16:00 diffs
MS-DOS note: On MS-DOS, there is no such thing as an executable file mode bit.
So file-modes considers a file executable if its name ends in one of the standard
executable extensions, such as .com, .bat, .exe, and some others. Files that begin with
the POSIX-standard ‘#!’ signature, such as shell and Perl scripts, are also considered
executable. Directories are also reported as executable, for compatibility with POSIX.
These conventions are also followed by file-attributes (see Section 26.6.4 [FileAttributes], page 624).

26.6.2 Distinguishing Kinds of Files
This section describes how to distinguish various kinds of files, such as directories, symbolic
links, and ordinary files.
Symbolic links are ordinarily followed wherever they appear. For example, to interpret thefile name a/b/c, any of a, a/b, and a/b/c can be symbolic links that are followed, possibly
recursively if the link targets are themselves symbolic links. However, a few functions do
not follow symbolic links at the end of a file name (a/b/c in this example). Such a function
is said to not follow symbolic links.

file-symlink-p filename[Function]
If the file filename is a symbolic link, this function does not follow it and instead
returns its link target as a string. (The link target string is not necessarily the fullChapter 26: Files622

absolute file name of the target; determining the full file name that the link points tois nontrivial, see below.)
If the file filename is not a symbolic link, or does not exist, or if there is trouble
determining whether it is a symbolic link, file-symlink-p returns nil.
Here are a few examples of using this function:(file-symlink-p "not-a-symlink")⇒ nil(file-symlink-p "sym-link")⇒ "not-a-symlink"(file-symlink-p "sym-link2")⇒ "sym-link"(file-symlink-p "/bin")⇒ "/pub/bin"Note that in the third example, the function returned sym-link, but did not proceed
to resolve it, although that file is itself a symbolic link. That is because this function
does not follow symbolic links—the process of following the symbolic links does not
apply to the last component of the file name.
The string that this function returns is what is recorded in the symbolic link; it may
or may not include any leading directories. This function does not expand the linktarget to produce a fully-qualified file name, and in particular does not use the leading
directories, if any, of the filename argument if the link target is not an absolute file
name. Here’s an example:(file-symlink-p "/foo/bar/baz")⇒ "some-file"
Here, although /foo/bar/baz was given as a fully-qualified file name, the result is
not, and in fact does not have any leading directories at all. And since some-filemight itself be a symbolic link, you cannot simply prepend leading directories to it,
nor even naively use expand-file-name (see Section 26.9.4 [File Name Expansion],
page 639) to produce its absolute file name.
For this reason, this function is seldom useful if you need to determine more than justthe fact that a file is or isn’t a symbolic link. If you actually need the file name of
the link target, use file-chase-links or file-truename, described in Section 26.6.3[Truenames], page 623.

file-directory-p filename[Function]
This function returns t if filename is the name of an existing directory. It returns nil
if filename does not name a directory, or if there is trouble determining whether it isa directory. This function follows symbolic links.
(file-directory-p "~rms")⇒ t(file-directory-p "~rms/lewis/files.texi")⇒ nil(file-directory-p "~rms/lewis/no-such-file")⇒ nil(file-directory-p "$HOME")⇒ nil

Chapter 26: Files

623(file-directory-p(substitute-in-file-name "$HOME"))⇒ tfile-regular-p filename[Function]
This function returns t if the file filename exists and is a regular file (not a directory,
named pipe, terminal, or other I/O device). It returns nil if filename does not exist
or is not a regular file, or if there is trouble determining whether it is a regular file.
This function follows symbolic links.

26.6.3 Truenames
The truename of a file is the name that you get by following symbolic links at all levels until
none remain, then simplifying away ‘.’ and ‘..’ appearing as name components. This results
in a sort of canonical name for the file. A file does not always have a unique truename;the number of distinct truenames a file has is equal to the number of hard links to the file.
However, truenames are useful because they eliminate symbolic links as a cause of namevariation.

file-truename filename[Function]
This function returns the truename of the file filename. If the argument is not an
absolute file name, this function first expands it against default-directory.
This function does not expand environment variables. Only substitute-in-filename does that. See [Definition of substitute-in-file-name], page 640.
If you may need to follow symbolic links preceding ‘..’ appearing as a name component, call file-truename without prior direct or indirect calls to expand-file-name.
Otherwise, the file name component immediately preceding ‘..’ will be simplified away
before file-truename is called. To eliminate the need for a call to expand-file-name,file-truename handles ‘~’ in the same way that expand-file-name does.
If the target of a symbolic links has remote file name syntax, file-truename returns
it quoted. See Section 26.9.4 [Functions that Expand Filenames], page 639.

file-chase-links filename &optional limit[Function]
This function follows symbolic links, starting with filename, until it finds a file namewhich is not the name of a symbolic link. Then it returns that file name. This function
does not follow symbolic links at the level of parent directories.
If you specify a number for limit, then after chasing through that many links, thefunction just returns what it has even if that is still a symbolic link.

To illustrate the difference between file-chase-links and file-truename, supposethat /usr/foo is a symbolic link to the directory /home/foo, and /home/foo/hello is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then we would have:(file-chase-links "/usr/foo/hello");; This does not follow the links in the parent directories.
⇒ "/usr/foo/hello"(file-truename "/usr/foo/hello");; Assuming that /home is not a symbolic link.
⇒ "/home/foo/hello"Chapter 26: Files

624

file-equal-p file1 file2[Function]
This function returns t if the files file1 and file2 name the same file. This is similar
to comparing their truenames, except that remote file names are also handled in an
appropriate manner. If file1 or file2 does not exist, the return value is unspecified.

file-name-case-insensitive-p filename[Function]
Sometimes file names or their parts need to be compared as strings, in which case it’s
important to know whether the underlying filesystem is case-insensitive. This function
returns t if file filename is on a case-insensitive filesystem. It always returns t on
MS-DOS and MS-Windows. On Cygwin and macOS, filesystems may or may not becase-insensitive, and the function tries to determine case-sensitivity by a runtime test.
If the test is inconclusive, the function returns t on Cygwin and nil on macOS.

Currently this function always returns nil on platforms other than MS-DOS, MSWindows, Cygwin, and macOS. It does not detect case-insensitivity of mounted
filesystems, such as Samba shares or NFS-mounted Windows volumes. On remote
hosts, it assumes t for the ‘smb’ method. For all other connection methods, runtime
tests are performed.

vc-responsible-backend file

[Function]
This function determines the responsible VC backend of the given file. For example,
if emacs.c is a file tracked by Git, (vc-responsible-backend "emacs.c") returns‘Git’. Note that if file is a symbolic link, vc-responsible-backend will not resolve
it—the backend of the symbolic link file itself is reported. To get the backend VC ofthe file to which file refers, wrap file with a symbolic link resolving function such as
file-chase-links:(vc-responsible-backend (file-chase-links "emacs.c"))26.6.4 File Attributes
This section describes the functions for getting detailed information about a file, including
the owner and group numbers, the number of names, the inode number, the size, and thetimes of access and modification.

file-newer-than-file-p filename1 filename2[Function]
This function returns t if the file filename1 is newer than file filename2. If filename1
does not exist, it returns nil. If filename1 does exist, but filename2 does not, it
returns t.
In the following example, assume that the file aug-19 was written on the 19th, aug-20
was written on the 20th, and the file no-file doesn’t exist at all.
(file-newer-than-file-p "aug-19" "aug-20")⇒ nil(file-newer-than-file-p "aug-20" "aug-19")⇒ t(file-newer-than-file-p "aug-19" "no-file")⇒ t(file-newer-than-file-p "no-file" "aug-19")⇒ nil

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625

file-has-changed-p filename tag[Function]
This function returns non-nil if the time stamp of filename has changed since the lastcall. When called for the first time for some filename, it records the last modification
time and size of the file, and returns non-nil when filename exists. Thereafter, whencalled for the same filename, it compares the current time stamp and size with therecorded ones, and returns non-nil only if either the time stamp or the size (or both)are different. This is useful when a Lisp program wants to re-read a file wheneverit changes. With an optional argument tag, which must be a symbol, the size andmodification time comparisons are limited to calls with the same tag.

file-attributes filename &optional id-format[Function]
This function returns a list of attributes of file filename. If the specified file does
not exist, it returns nil. This function does not follow symbolic links. The optionalparameter id-format specifies the preferred format of attributes UID and GID (seebelow)—the valid values are 'string and 'integer. The latter is the default, but weplan to change that, so you should specify a non-nil value for id-format if you use
the returned UID or GID.
On GNU platforms when operating on a local file, this function is atomic: if thefilesystem is simultaneously being changed by some other process, this function returns
the file’s attributes either before or after the change. Otherwise this function is not
atomic, and might return nil if it detects the race condition, or might return ahodgepodge of the previous and current file attributes.
Accessor functions are provided to access the elements in this list. The accessors are
mentioned along with the descriptions of the elements below.
The elements of the list, in order, are:0. t for a directory, a string for a symbolic link (the name linked to), or nil for atext file (file-attribute-type).
1. The number of names the file has (file-attribute-link-number). Alternatenames, also known as hard links, can be created by using the add-name-to-filefunction (see Section 26.7 [Changing Files], page 629).
2. The file’s UID, normally as a string (file-attribute-user-id). However, if it
does not correspond to a named user, the value is an integer.
3. The file’s GID, likewise (file-attribute-group-id).
4. The time of last access as a Lisp timestamp (file-attribute-access-time).
The timestamp is in the style of current-time (see Section 42.5 [Time of Day],
page 1270) and is truncated to that of the filesystem’s timestamp resolution; forexample, on some FAT-based filesystems, only the date of last access is recorded,
so this time will always hold the midnight of the day of the last access.
5. The time of last modification as a Lisp timestamp (file-attributemodification-time). This is the last time when the file’s contents weremodified.
6. The time of last status change as a Lisp timestamp (file-attribute-statuschange-time). This is the time of the last change to the file’s access mode bits,
its owner and group, and other information recorded in the filesystem for the file,
beyond the file’s contents.

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626

7. The size of the file in bytes (file-attribute-size).
8. The file’s modes, as a string of ten letters or dashes, as in ‘ls -l’(file-attribute-modes).
9. An unspecified value, present for backward compatibility.
10. The file’s inode number (file-attribute-inode-number), a nonnegative integer.
11. The filesystem’s identifier of the device that the file is on (file-attributedevice-number), an integer or a cons cell of two integers. The latter is sometimes
used by remote files, in order to distinguish remote filesystems from local ones.
The file’s inode and device together give enough information to distinguish any two
files on the system—no two files can have the same values for both of these attributes.
This tuple that uniquely identifies the file is returned by file-attribute-fileidentifier.
For example, here are the file attributes for files.texi:(file-attributes "files.texi" 'string)⇒ (nil 1 "lh" "users"(20614 64019 50040 152000)(20000 23 0 0)(20614 64555 902289 872000)
122295 "-rw-rw-rw-"
t 6473924464520138
1014478468)
and here is how the result is interpreted:nil

is neither a directory nor a symbolic link.

1

has only one name (the name files.texi in the current default directory).

"lh"

is owned by the user with name ‘lh’.

"users"is in the group with name ‘users’.

(20614 64019 50040 152000)
was last accessed on October 23, 2012, at 20:12:03.050040152 UTC. (Thistimestamp is (1351023123050040152 . 1000000000) if current-timelist is nil.)(20000 23 0 0)
was last modified on July 15, 2001, at 08:53:43.000000000 UTC. (Thistimestamp is (1310720023000000000 . 1000000000) if current-timelist is nil.)(20614 64555 902289 872000)
last had its status changed on October 23, 2012, at 20:20:59.902289872
UTC. (This timestamp is (1351023659902289872 . 1000000000) if
current-time-list is nil.)
122295is 122295 bytes long. (It may not contain 122295 characters, though, ifsome of the bytes belong to multibyte sequences, and also if the end-of-line
format is CR-LF.)

Chapter 26: Files

627"-rw-rw-rw-"
has a mode of read and write access for the owner, group, and world.
is merely a placeholder; it carries no information.

t6473924464520138
has an inode number of 6473924464520138.
1014478468
is on the file-system device whose number is 1014478468.

file-nlinks filename[Function]
This function returns the number of names (i.e., hard links) that file filename has. If
the file does not exist, this function returns nil. Note that symbolic links have noeffect on this function, because they are not considered to be names of the files theylink to. This function does not follow symbolic links.
$ ls -l foo*-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1
(file-nlinks "foo")⇒ 2(file-nlinks "doesnt-exist")⇒ nil

26.6.5 Extended File Attributes
On some operating systems, each file can be associated with arbitrary extended file attributes.
At present, Emacs supports querying and setting two specific sets of extended file attributes:
Access Control Lists (ACLs) and SELinux contexts. These extended file attributes are used,on some systems, to impose more sophisticated file access controls than the basic Unix-stylepermissions discussed in the previous sections.
A detailed explanation of ACLs and SELinux is beyond the scope of this manual. For
our purposes, each file can be associated with an ACL, which specifies its properties underan ACL-based file control system, and/or an SELinux context, which specifies its properties
under the SELinux system.

file-acl filename[Function]
This function returns the ACL for the file filename. The exact Lisp representation of
the ACL is unspecified (and may change in future Emacs versions), but it is the sameas what set-file-acl takes for its acl argument (see Section 26.7 [Changing Files],page 629).
The underlying ACL implementation is platform-specific; on GNU/Linux and BSD,
Emacs uses the POSIX ACL interface, while on MS-Windows Emacs emulates the
POSIX ACL interface with native file security APIs.
If ACLs are not supported or the file does not exist, then the return value is nil.

file-selinux-context filename[Function]
This function returns the SELinux context of the file filename, as a list of the form
(user role type range). The list elements are the context’s user, role, type, andChapter 26: Files

628

range respectively, as Lisp strings; see the SELinux documentation for details about
what these actually mean. The return value has the same form as what set-fileselinux-context takes for its context argument (see Section 26.7 [Changing Files],page 629).
If SELinux is not supported or the file does not exist, then the return value is (nilnil nil nil).

file-extended-attributes filename[Function]
This function returns an alist of the Emacs-recognized extended attributes of file
filename. Currently, it serves as a convenient way to retrieve both the ACL and
SELinux context; you can then call the function set-file-extended-attributes,
with the returned alist as its second argument, to apply the same file access attributes
to another file (see Section 26.7 [Changing Files], page 629).
One of the elements is (acl . acl), where acl has the same form returned by file-acl.
Another element is (selinux-context . context), where context is the SELinux
context, in the same form returned by file-selinux-context.

26.6.6 Locating Files in Standard Places
This section explains how to search for a file in a list of directories (a path), or for an
executable file in the standard list of executable file directories.
To search for a user-specific configuration file, See Section 26.9.7 [Standard File Names],
page 645, for the locate-user-emacs-file function.

locate-file filename path &optional suffixes predicate[Function]
This function searches for a file whose name is filename in a list of directories given bypath, trying the suffixes in suffixes. If it finds such a file, it returns the file’s absolute
file name (see Section 26.9.2 [Relative File Names], page 637); otherwise it returns
nil.
The optional argument suffixes gives the list of file-name suffixes to append to filename
when searching. locate-file tries each possible directory with each of these suffixes.
If suffixes is nil, or (""), then there are no suffixes, and filename is used only as-is.
Typical values of suffixes are exec-suffixes (see Section 40.1 [Subprocess Creation],
page 1078), load-suffixes, load-file-rep-suffixes and the return value of thefunction get-load-suffixes (see Section 16.2 [Load Suffixes], page 300).
Typical values for path are exec-path (see Section 40.1 [Subprocess Creation],
page 1078) when looking for executable programs, or load-path (see Section 16.3
[Library Search], page 301) when looking for Lisp files. If filename is absolute, pathhas no effect, but the suffixes in suffixes are still tried.
The optional argument predicate, if non-nil, specifies a predicate function for testingwhether a candidate file is suitable. The predicate is passed the candidate file name asits single argument. If predicate is nil or omitted, locate-file uses file-readablep as the predicate. See Section 26.6.2 [Kinds of Files], page 621, for other usefulpredicates, e.g., file-executable-p and file-directory-p.
This function will normally skip directories, so if you want it to find directories, makesure the predicate function returns dir-ok for them. For example:(locate-file "html" '("/var/www" "/srv") nil

Chapter 26: Files

629(lambda (f) (if (file-directory-p f) 'dir-ok)))
For compatibility, predicate can also be one of the symbols executable, readable,
writable, exists, or a list of one or more of these symbols.

executable-find program &optional remote[Function]
This function searches for the executable file of the named program and returns theabsolute file name of the executable, including its file-name extensions, if any. It
returns nil if the file is not found. The function searches in all the directories in
exec-path, and tries all the file-name extensions in exec-suffixes (see Section 40.1
[Subprocess Creation], page 1078).
If remote is non-nil, and default-directory is a remote directory, program issearched on the respective remote host.

26.7 Changing File Names and Attributes
The functions in this section rename, copy, delete, link, and set the modes (permissions)of files. Typically, they signal a file-error error if they fail to perform their function,
reporting the system-dependent error message that describes the reason for the failure. Ifthey fail because a file is missing, they signal a file-missing error instead.
For performance, the operating system may cache or alias changes made by thesefunctions instead of writing them immediately to secondary storage. See Section 26.8 [Filesand Storage], page 634.
In the functions that have an argument newname, if this argument is a directory nameit is treated as if the nondirectory part of the source name were appended. Typically, a
directory name is one that ends in ‘/’ (see Section 26.9.3 [Directory Names], page 637). For
example, if the old name is a/b/c, the newname d/e/f/ is treated as if it were d/e/f/c.
This special treatment does not apply if newname is not a directory name but names a filethat is a directory; for example, the newname d/e/f is left as-is even if d/e/f happens to
be a directory.
In the functions that have an argument newname, if a file by the name of newname
already exists, the actions taken depend on the value of the argument ok-if-already-exists:• Signal a file-already-exists error if ok-if-already-exists is nil.
• Request confirmation if ok-if-already-exists is a number.
• Replace the old file without confirmation if ok-if-already-exists is any other value.

add-name-to-file oldname newname &optional ok-if-already-exists[Command]This function gives the file named oldname the additional name newname. This meansthat newname becomes a new hard link to oldname.
If newname is a symbolic link, its directory entry is replaced, not the directory entry
it points to. If oldname is a symbolic link, this function might or might not follow
the link; it does not follow the link on GNU platforms. If oldname is a directory, thisfunction typically fails, although for the superuser on a few old-fashioned non-GNU
platforms it can succeed and create a filesystem that is not tree-structured.
In the first part of the following example, we list two files, foo and foo3.
$ ls -li fo*
81908 -rw-rw-rw- 1 rms rms 29 Aug 18 20:32 foo
84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3

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Now we create a hard link, by calling add-name-to-file, then list the files again.
This shows two names for one file, foo and foo2.
(add-name-to-file "foo" "foo2")⇒ nil$ ls -li fo*
81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo2
84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3
Finally, we evaluate the following:(add-name-to-file "foo" "foo3" t)and list the files again. Now there are three names for one file: foo, foo2, and foo3.
The old contents of foo3 are lost.
(add-name-to-file "foo1" "foo3")⇒ nil$ ls -li fo*
81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo
81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo2
81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo3
This function is meaningless on operating systems where multiple names for one file
are not allowed. Some systems implement multiple names by copying the file instead.
See also file-nlinks in Section 26.6.4 [File Attributes], page 624.

rename-file filename newname &optional ok-if-already-exists[Command]This command renames the file filename as newname.
If filename has additional names aside from filename, it continues to have thosenames. In fact, adding the name newname with add-name-to-file and then deleting
filename has the same effect as renaming, aside from momentary intermediate states
and treatment of errors, directories and symbolic links.
This command does not follow symbolic links. If filename is a symbolic link, thiscommand renames the symbolic link, not the file it points to. If newname is a symbolic
link, its directory entry is replaced, not the directory entry it points to.
This command does nothing if filename and newname are the same directory entry,i.e., if they refer to the same parent directory and give the same name within that
directory. Otherwise, if filename and newname name the same file, this command doesnothing on POSIX-conforming systems, and removes filename on some non-POSIX
systems.
If newname exists, then it must be an empty directory if oldname is a directory and anon-directory otherwise.

copy-file oldname newname &optional ok-if-already-exists timepreserve-uid-gid preserve-permissions[Command]This command copies the file oldname to newname. An error is signaled if oldname is
not a regular file. If newname names a directory, it copies oldname into that directory,
preserving its final name component.

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This function follows symbolic links, except that it does not follow a dangling symbolic
link to create newname.
If time is non-nil, then this function gives the new file the same last-modified timethat the old one has. (This works on only some operating systems.) If setting the time
gets an error, copy-file signals a file-date-error error. In an interactive call, aprefix argument specifies a non-nil value for time.
If argument preserve-uid-gid is nil, we let the operating system decide the user andgroup ownership of the new file (this is usually set to the user running Emacs). If
preserve-uid-gid is non-nil, we attempt to copy the user and group ownership of the
file. This works only on some operating systems, and only if you have the correct
permissions to do so.
If the optional argument preserve-permissions is non-nil, this function copies the filemodes (or “permissions”) of oldname to newname, as well as the Access Control Listand SELinux context (if any). See Section 26.6 [Information about Files], page 619.
Otherwise, the file modes of newname are left unchanged if it is an existing file, andset to those of oldname, masked by the default file permissions (see set-defaultfile-modes below), if newname is to be newly created. The Access Control List or
SELinux context are not copied over in either case.

make-symbolic-link target linkname &optional ok-if-already-exists[Command]This command makes a symbolic link to target, named linkname. This is like theshell command ‘ln -s target linkname’. The target argument is treated only as astring; it need not name an existing file. If ok-if-already-exists is an integer, indicatinginteractive use, then leading ‘~’ is expanded and leading ‘/:’ is stripped in the target
string.
If target is a relative file name, the resulting symbolic link is interpreted relative tothe directory containing the symbolic link. See Section 26.9.2 [Relative File Names],
page 637.
If both target and linkname have remote file name syntax, and if both remote
identifications are equal, the symbolic link points to the local file name part of target.
This function is not available on systems that don’t support symbolic links.

delete-file filename &optional trash[Command]This command deletes the file filename. If the file has multiple names, it continues toexist under the other names. If filename is a symbolic link, delete-file deletes only
the symbolic link and not its target.
The command signals a suitable kind of file-error error if filename cannot bedeleted. (On GNU and other POSIX-like systems, a file can be deleted if its directoryis writable.) If the file does not exist, this command will not signal any error.

If the optional argument trash is non-nil and the variable delete-by-moving-totrash is non-nil, this command moves the file into the system Trash instead ofdeleting it. See Section “Miscellaneous File Operations” in The GNU Emacs Manual.
When called interactively, trash is t if no prefix argument is given, and nil otherwise.
See also delete-directory in Section 26.11 [Create/Delete Dirs], page 648.

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set-file-modes filename mode &optional flag

632

[Command]This function sets the file mode (or permissions) of filename to mode.
By default this function follows symbolic links. However, if the optional argument
flag is the symbol nofollow, this function does not follow filename if it is a symbolic
link; this can help prevent inadvertently changing the mode bits of a file somewhere
else. On platforms that do not support changing mode bits on a symbolic link, thisfunction signals an error when filename is a symbolic link and flag is nofollow.
If called non-interactively, mode must be an integer. Only the lowest 12 bits of theinteger are used; on most systems, only the lowest 9 bits are meaningful. You can use
the Lisp construct for octal numbers to enter mode. For example,(set-file-modes "myfile" #o644 'nofollow)
specifies that the file should be readable and writable for its owner, readable for groupmembers, and readable for all other users. See Section “File permissions” in The gnu
Coreutils Manual, for a description of mode bit specifications.
Interactively, mode is read from the minibuffer using read-file-modes (see below),which lets the user type in either an integer or a string representing the permissions
symbolically.
See Section 26.6.1 [Testing Accessibility], page 619, for the function file-modes, which
returns the permissions of a file.

set-default-file-modes mode

[Function]
This function sets the default permissions for new files created by Emacs and its
subprocesses. Every file created with Emacs initially has these permissions, or a subsetof them (write-region will not grant execute permissions even if the default filepermissions allow execution). On GNU and other POSIX-like systems, the default
permissions are given by the bitwise complement of the ‘umask’ value, i.e. each bitthat is set in the argument mode will be reset in the default permissions with which
Emacs creates files.
The argument mode should be an integer which specifies the permissions, similar to
set-file-modes above. Only the lowest 9 bits are meaningful.
The default file permissions have no effect when you save a modified version of an
existing file; saving a file preserves its existing permissions.

with-file-modes mode body. . .

[Macro]This macro evaluates the body forms with the default permissions for new files
temporarily set to modes (whose value is as for set-file-modes above). When
finished, it restores the original default file permissions, and returns the value of thelast form in body.
This is useful for creating private files, for example.

default-file-modes[Function]

This function returns the default file permissions, as an integer.

read-file-modes &optional prompt base-file[Function]
This function reads a set of file mode bits from the minibuffer. The first optional
argument prompt specifies a non-default prompt. Second second optional argument

Chapter 26: Files633

base-file is the name of a file on whose permissions to base the mode bits that thisfunction returns, if what the user types specifies mode bits relative to permissions ofan existing file.
If user input represents an octal number, this function returns that number. If it is acomplete symbolic specification of mode bits, as in "u=rwx", the function converts it to
the equivalent numeric value using file-modes-symbolic-to-number and returns theresult. If the specification is relative, as in "o+g", then the permissions on which thespecification is based are taken from the mode bits of base-file. If base-file is omitted ornil, the function uses 0 as the base mode bits. The complete and relative specifications
can be combined, as in "u+r,g+rx,o+r,g-w". See Section “File permissions” in The
gnu Coreutils Manual, for a description of file mode specifications.

file-modes-symbolic-to-number modes &optional base-modes[Function]
This function converts a symbolic file mode specification in modes into the equivalent
integer. If the symbolic specification is based on an existing file, that file’s mode bits
are taken from the optional argument base-modes; if that argument is omitted or nil,
it defaults to 0, i.e., no access rights at all.

file-modes-number-to-symbolic modes[Function]
This function converts a numeric file mode specification in modes into the equivalentstring form. The string which this function returns is in the same format produced by
the shell command ls -l and by file-attributes, not the symbolic form acceptedby file-modes-symbolic-to-number and the chmod shell command.

set-file-times filename &optional time flag

[Function]
This function sets the access and modification times of filename to time. The return
value is t if the times are successfully set, otherwise it is nil. time defaults to thecurrent time and must be a time value (see Section 42.5 [Time of Day], page 1270).
By default this function follows symbolic links. However, if the optional argument
flag is the symbol nofollow, this function does not follow filename if it is a symbolic
link; this can help prevent inadvertently changing the times of a file somewhere else.
On platforms that do not support changing times on a symbolic link, this function
signals an error when filename is a symbolic link and flag is nofollow.

set-file-extended-attributes filename attribute-alist[Function]
This function sets the Emacs-recognized extended file attributes for filename. The
second argument attribute-alist should be an alist of the same form returned by
file-extended-attributes. The return value is t if the attributes are successfully
set, otherwise it is nil. See Section 26.6.5 [Extended Attributes], page 627.

set-file-selinux-context filename context[Function]
This function sets the SELinux security context for filename to context. The context
argument should be a list (user role type range), where each element is a string.
See Section 26.6.5 [Extended Attributes], page 627.
The function returns t if it succeeds in setting the SELinux context of filename. It
returns nil if the context was not set (e.g., if SELinux is disabled, or if Emacs wascompiled without SELinux support).

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set-file-acl filename acl[Function]
This function sets the Access Control List for filename to acl. The acl argument
should have the same form returned by the function file-acl. See Section 26.6.5[Extended Attributes], page 627.
The function returns t if it successfully sets the ACL of filename, nil otherwise.

26.8 Files and Secondary Storage
After Emacs changes a file, there are two reasons the changes might not survive later failuresof power or media, both having to do with efficiency. First, the operating system might
alias written data with data already stored elsewhere on secondary storage until one file or
the other is later modified; this will lose both files if the only copy on secondary storage islost due to media failure. Second, the operating system might not write data to secondary
storage immediately, which will lose the data if power is lost.
Although both sorts of failures can largely be avoided by a suitably configured file system,
such systems are typically more expensive or less efficient. In more-typical systems, tosurvive media failure you can copy the file to a different device, and to survive a power failure
you can use the write-region function with the write-region-inhibit-fsync variable
set to nil. See Section 26.4 [Writing to Files], page 616.

26.9 File Names
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs
are represented as strings. The functions that operate on a file all expect a file nameargument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate
on file names; i.e., to take them apart and to use part of a name to construct related filenames. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on filenames that do not refer to an existing file or directory.
On MS-DOS and MS-Windows, these functions (like the function that actually operate
on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate thecomponents, as well as POSIX syntax; but they always return POSIX syntax. This enables
Lisp programs to specify file names in POSIX syntax and work properly on all systems
without change.1

26.9.1 File Name Components
The operating system groups files into directories. To specify a file, you must specify the
directory and the file’s name within that directory. Therefore, Emacs considers a file nameas having two main parts: the directory name part, and the nondirectory part (or file namewithin the directory). Either part may be empty. Concatenating these two parts reproduces
the original file name.2
1

In MS-Windows versions of Emacs compiled for the Cygwin environment, you can use the functions
cygwin-convert-file-name-to-windows and cygwin-convert-file-name-from-windows to convert between the two file-name syntaxes.
2
Emacs follows the GNU convention to use the term file name instead of the term pathname. We use theterm path only for search paths, which are lists of directory names.

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On most systems, the directory part is everything up to and including the last slash(backslash is also allowed in input on MS-DOS or MS-Windows); the nondirectory part is
the rest.
For some purposes, the nondirectory part is further subdivided into the name properand the version number. On most systems, only backup files have version numbers in theirnames.

file-name-directory filename[Function]
This function returns the directory part of filename, as a directory name (seeSection 26.9.3 [Directory Names], page 637), or nil if filename does not include a
directory part.
On GNU and other POSIX-like systems, a string returned by this function always
ends in a slash. On MS-DOS it can also end in a colon.
(file-name-directory "lewis/foo") ; GNU example⇒ "lewis/"(file-name-directory "foo"); GNU example⇒ nilfile-name-nondirectory filename[Function]

This function returns the nondirectory part of filename.
(file-name-nondirectory "lewis/foo")⇒ "foo"(file-name-nondirectory "foo")⇒ "foo"(file-name-nondirectory "lewis/")⇒ ""file-name-sans-versions filename &optional keep-backup-version[Function]
This function returns filename with any file version numbers, backup version numbers,
or trailing tildes discarded.
If keep-backup-version is non-nil, then true file version numbers understood as suchby the file system are discarded from the return value, but backup version numbers
are kept.
(file-name-sans-versions "~rms/foo.~1~")⇒ "~rms/foo"(file-name-sans-versions "~rms/foo~")⇒ "~rms/foo"(file-name-sans-versions "~rms/foo")⇒ "~rms/foo"

file-name-extension filename &optional period[Function]
This function returns filename’s final extension, if any, after applying file-namesans-versions to remove any version/backup part. The extension, in a file name, isthe part that follows the last ‘.’ in the last name component (minus any version/backuppart).
This function returns nil for extensionless file names such as foo. It returns "" fornull extensions, as in foo.. If the last component of a file name begins with a ‘.’, that

Chapter 26: Files

636‘.’ doesn’t count as the beginning of an extension. Thus, .emacs’s extension is nil,
not ‘.emacs’.
If period is non-nil, then the returned value includes the period that delimits theextension, and if filename has no extension, the value is "".

file-name-with-extension filename extension[Function]
This function returns filename with its extension set to extension. A single leading
dot in the extension will be stripped if there is one. For example:(file-name-with-extension "file" "el")⇒ "file.el"(file-name-with-extension "file" ".el")⇒ "file.el"(file-name-with-extension "file.c" "el")⇒ "file.el"
Note that this function will error if filename or extension are empty, or if the filename
is shaped like a directory (i.e., if directory-name-p returns non-nil).

file-name-sans-extension filename[Function]
This function returns filename minus its extension, if any. The version/backup part, if
present, is only removed if the file has an extension. For example,(file-name-sans-extension "foo.lose.c")⇒ "foo.lose"(file-name-sans-extension "big.hack/foo")⇒ "big.hack/foo"(file-name-sans-extension "/my/home/.emacs")⇒ "/my/home/.emacs"(file-name-sans-extension "/my/home/.emacs.el")⇒ "/my/home/.emacs"(file-name-sans-extension "~/foo.el.~3~")⇒ "~/foo"(file-name-sans-extension "~/foo.~3~")⇒ "~/foo.~3~"
Note that the ‘.~3~’ in the two last examples is the backup part, not an extension.

file-name-base filename[Function]
This function is the composition of file-name-sans-extension and file-namenondirectory. For example,(file-name-base "/my/home/foo.c")⇒ "foo"file-name-split filename[Function]
This function splits a file name into its components, and can be thought of as theinverse of string-join with the appropriate directory separator. For example,(file-name-split "/tmp/foo.txt")⇒ ("" "tmp" "foo.txt")(string-join (file-name-split "/tmp/foo.txt") "/")
⇒ "/tmp/foo.txt"

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26.9.2 Absolute and Relative File Names
All the directories in the file system form a tree starting at the root directory. A file namecan specify all the directory names starting from the root of the tree; then it is called
an absolute file name. Or it can specify the position of the file in the tree relative to adefault directory; then it is called a relative file name. On GNU and other POSIX-likesystems, after any leading ‘~’ has been expanded, an absolute file name starts with a ‘/’ (see[abbreviate-file-name], page 639), and a relative one does not. On MS-DOS and MS-Windows,
an absolute file name starts with a slash or a backslash, or with a drive specification ‘x:/’,where x is the drive letter.

file-name-absolute-p filename[Function]
This function returns t if file filename is an absolute file name, nil otherwise. A filename is considered to be absolute if its first component is ‘~’, or is ‘~user’ where user
is a valid login name. In the following examples, assume that there is a user named‘rms’ but no user named ‘nosuchuser’.
(file-name-absolute-p "~rms/foo")⇒ t(file-name-absolute-p "~nosuchuser/foo")⇒ nil(file-name-absolute-p "rms/foo")⇒ nil(file-name-absolute-p "/user/rms/foo")⇒ t

Given a possibly relative file name, you can expand any leading ‘~’ and convert the result
to an absolute name using expand-file-name (see Section 26.9.4 [File Name Expansion],
page 639). This function converts absolute file names to relative names:

file-relative-name filename &optional directory[Function]
This function tries to return a relative name that is equivalent to filename, assuming
the result will be interpreted relative to directory (an absolute directory name or
directory file name). If directory is omitted or nil, it defaults to the current buffer’s
default directory.
On some operating systems, an absolute file name begins with a device name. On
such systems, filename has no relative equivalent based on directory if they start withtwo different device names. In this case, file-relative-name returns filename inabsolute form.
(file-relative-name "/foo/bar" "/foo/")⇒ "bar"(file-relative-name "/foo/bar" "/hack/")⇒ "../foo/bar"

A file name that is an empty string stands for the current buffer’s default directory.

26.9.3 Directory Names
A directory name is a string that must name a directory if it names any file at all. A
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which is related to the directory name but is typically not identical. (This is not quite thesame as the usual POSIX terminology.) These two names for the same entity are related
by a syntactic transformation. On GNU and other POSIX-like systems, this is simple: toobtain a directory name, append a ‘/’ to a directory file name that does not already end in‘/’. On MS-DOS the relationship is more complicated.
The difference between a directory name and a directory file name is subtle but crucial.
When an Emacs variable or function argument is described as being a directory name, a
directory file name is not acceptable. When file-name-directory returns a string, that isalways a directory name.
The following two functions convert between directory names and directory file names.
They do nothing special with environment variable substitutions such as ‘$HOME’, and theconstructs ‘~’, ‘.’ and ‘..’.

file-name-as-directory filename[Function]
This function returns a string representing filename in a form that the operating
system will interpret as the name of a directory (a directory name). On most systems,
this means appending a slash to the string (if it does not already end in one).
(file-name-as-directory "~rms/lewis")⇒ "~rms/lewis/"

directory-name-p filename[Function]
This function returns non-nil if filename ends with a directory separator character.
This is the forward slash ‘/’ on GNU and other POSIX-like systems; MS-Windows
and MS-DOS recognize both the forward slash and the backslash ‘\’ as directory
separators.

directory-file-name dirname[Function]
This function returns a string representing dirname in a form that the operating
system will interpret as the name of a file (a directory file name). On most systems,
this means removing the final directory separators from the string, unless the string
consists entirely of directory separators.
(directory-file-name "~lewis/")⇒ "~lewis"

file-name-concat directory &rest components[Function]
Concatenate components to directory, inserting a slash before the components if
directory or the preceding component didn’t end with a slash.
(file-name-concat "/tmp" "foo")⇒ "/tmp/foo"

A directory or components that are nil or the empty string are ignored—they arefiltered out first and do not affect the results in any way.
This is almost the same as using concat, but dirname (and the non-final components)
may or may not end with slash characters, and this function will not double thosecharacters.
To convert a directory name to its abbreviation, use this function:

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639

abbreviate-file-name filename[Function]
This function returns an abbreviated form of filename. It applies the abbreviations
specified in directory-abbrev-alist (see Section “File Aliases” in The GNU Emacs
Manual), then substitutes ‘~’ for the user’s home directory if the argument names afile in the home directory or one of its subdirectories. If the home directory is a root
directory, it is not replaced with ‘~’, because this does not make the result shorter onmany systems.
You can use this function for directory names and for file names, because it recognizes
abbreviations even as part of the name.

file-name-parent-directory filename[Function]
This function returns the directory name of the parent directory of filename. If
filename is at the root directory of the filesystem, it returns nil. A relative filename
is assumed to be relative to default-directory, and the return value will also be
relative in that case. If the return value is non-nil, it ends in a slash.

26.9.4 Functions that Expand Filenames
Expanding a file name means converting a relative file name to an absolute one. Since thisis done relative to a default directory, you must specify the default directory as well as thefile name to be expanded. It also involves expanding abbreviations like ~/ and eliminating
redundancies like ./ and name/../.

expand-file-name filename &optional directory[Function]
This function converts filename to an absolute file name. If directory is supplied,
it is the default directory to start with if filename is relative and does not startwith ‘~’. (The value of directory should itself be an absolute directory name or
directory file name; it may start with ‘~’.) Otherwise, the current buffer’s value of
default-directory is used. For example:(expand-file-name "foo")⇒ "/xcssun/users/rms/lewis/foo"(expand-file-name "../foo")⇒ "/xcssun/users/rms/foo"(expand-file-name "foo" "/usr/spool/")⇒ "/usr/spool/foo"
If the part of filename before the first slash is ‘~’, it expands to your home directory,
which is typically specified by the value of the HOME environment variable (see Section“General Variables” in The GNU Emacs Manual). If the part before the first slash is‘~user’ and if user is a valid login name, it expands to user’s home directory. If you
do not want this expansion for a relative filename that might begin with a literal ‘~’,you can use (concat (file-name-as-directory directory) filename) instead of(expand-file-name filename directory).
File names containing ‘.’ or ‘..’ are simplified to their canonical form:(expand-file-name "bar/../foo")⇒ "/xcssun/users/rms/lewis/foo"
In some cases, a leading ‘..’ component can remain in the output:(expand-file-name "../home" "/")
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This is for the sake of filesystems that have the concept of a superroot above the root
directory /. On other filesystems, /../ is interpreted exactly the same as /.
Expanding . or the empty string returns the default directory:(expand-file-name "." "/usr/spool/")⇒ "/usr/spool"(expand-file-name "" "/usr/spool/")⇒ "/usr/spool"
Note that expand-file-name does not expand environment variables; only
substitute-in-file-name does that:(expand-file-name "$HOME/foo")⇒ "/xcssun/users/rms/lewis/$HOME/foo"
Note also that expand-file-name does not follow symbolic links at any level. This
results in a difference between the way file-truename and expand-file-name treat‘..’. Assuming that ‘/tmp/bar’ is a symbolic link to the directory ‘/tmp/foo/bar’ we
get:(file-truename "/tmp/bar/../myfile")⇒ "/tmp/foo/myfile"(expand-file-name "/tmp/bar/../myfile")⇒ "/tmp/myfile"If you may need to follow symbolic links preceding ‘..’, you should make sure tocall file-truename without prior direct or indirect calls to expand-file-name. See
Section 26.6.3 [Truenames], page 623.
[Variable]
The value of this buffer-local variable is the default directory for the current buffer.
It should be an absolute directory name; it may start with ‘~’. This variable isbuffer-local in every buffer.

default-directory

expand-file-name uses the default directory when its second argument is nil.
The value is always a string ending with a slash.
default-directory⇒ "/user/lewis/manual/"

substitute-in-file-name filename[Function]
This function replaces environment variable references in filename with the environment
variable values. Following standard Unix shell syntax, ‘$’ is the prefix to substitutean environment variable value. If the input contains ‘$$’, that is converted to ‘$’; thisgives the user a way to quote a ‘$’.
The environment variable name is the series of alphanumeric characters (including
underscores) that follow the ‘$’. If the character following the ‘$’ is a ‘{’, then thevariable name is everything up to the matching ‘}’.
Calling substitute-in-file-name on output produced by substitute-in-filename tends to give incorrect results. For instance, use of ‘$$’ to quote a single ‘$’
won’t work properly, and ‘$’ in an environment variable’s value could lead to repeatedsubstitution. Therefore, programs that call this function and put the output where itChapter 26: Files

641

will be passed to this function need to double all ‘$’ characters to prevent subsequent
incorrect results.
Here we assume that the environment variable HOME, which holds the user’s home
directory, has value ‘/xcssun/users/rms’.
(substitute-in-file-name "$HOME/foo")⇒ "/xcssun/users/rms/foo"
After substitution, if a ‘~’ or a ‘/’ appears immediately after another ‘/’, the function
discards everything before it (up through the immediately preceding ‘/’).
(substitute-in-file-name "bar/~/foo")⇒ "~/foo"(substitute-in-file-name "/usr/local/$HOME/foo")⇒ "/xcssun/users/rms/foo";; /usr/local/ has been discarded.
Sometimes, it is not desired to expand file names. In such cases, the file name can bequoted to suppress the expansion, and to handle the file name literally. Quoting happens by
prefixing the file name with ‘/:’.

file-name-quote name[Macro]This macro adds the quotation prefix ‘/:’ to the file name. For a local file name, it
prefixes name with ‘/:’. If name is a remote file name, the local part of name (seeSection 26.12 [Magic File Names], page 649) is quoted. If name is already a quoted
file name, name is returned unchanged.
(substitute-in-file-name (file-name-quote "bar/~/foo"))⇒ "/:bar/~/foo"(substitute-in-file-name (file-name-quote "/ssh:host:bar/~/foo"))⇒ "/ssh:host:/:bar/~/foo"
The macro cannot be used to suppress file name handlers from magic file names (seeSection 26.12 [Magic File Names], page 649).

file-name-unquote name[Macro]This macro removes the quotation prefix ‘/:’ from the file name, if any. If name is aremote file name, the local part of name is unquoted.

file-name-quoted-p name[Macro]This macro returns non-nil, when name is quoted with the prefix ‘/:’. If name is aremote file name, the local part of name is checked.

26.9.5 Generating Unique File Names
Some programs need to write temporary files. Here is the usual way to construct a name forsuch a file:(make-temp-file name-of-application)
The job of make-temp-file is to prevent two different users or two different jobs from trying
to use the exact same file name.

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make-temp-file prefix &optional dir-flag suffix text

[Function]
This function creates a temporary file and returns its name. Emacs creates the
temporary file’s name by adding to prefix some random characters that are different
in each Emacs job. The result is guaranteed to be a newly created file, containing
text if that’s given as a string and empty otherwise. On MS-DOS, this function cantruncate prefix to fit into the 8+3 file-name limits. If prefix is a relative file name, it
is expanded against temporary-file-directory.
(make-temp-file "foo")⇒ "/tmp/foo232J6v"
When make-temp-file returns, the file has been created and is empty. At that point,
you should write the intended contents into the file.
If dir-flag is non-nil, make-temp-file creates an empty directory instead of anempty file. It returns the file name, not the directory name, of that directory. See
Section 26.9.3 [Directory Names], page 637.
If suffix is non-nil, make-temp-file adds it at the end of the file name.
If text is a string, make-temp-file inserts it in the file.
To prevent conflicts among different libraries running in the same Emacs, each Lisp
program that uses make-temp-file should have its own prefix. The number added
to the end of prefix distinguishes between the same application running in different
Emacs jobs. Additional added characters permit a large number of distinct names
even in one Emacs job.

The default directory for temporary files is controlled by the variable temporary-filedirectory. This variable gives the user a uniform way to specify the directory for all
temporary files. Some programs use small-temporary-file-directory instead, if that is
non-nil. To use it, you should expand the prefix against the proper directory before calling
make-temp-file.
[User Option]
This variable specifies the directory name for creating temporary files. Its value should
be a directory name (see Section 26.9.3 [Directory Names], page 637), but it is goodfor Lisp programs to cope if the value is a directory’s file name instead. Using thevalue as the second argument to expand-file-name is a good way to achieve that.
The default value is determined in a reasonable way for your operating system; itis based on the TMPDIR, TMP and TEMP environment variables, with a fall-back to asystem-dependent name if none of these variables is defined.
Even if you do not use make-temp-file to create the temporary file, you should still
use this variable to decide which directory to put the file in. However, if you expect
the file to be small, you should use small-temporary-file-directory first if that is
non-nil.

temporary-file-directory[User Option]
This variable specifies the directory name for creating certain temporary files, which
are likely to be small.
If you want to write a temporary file which is likely to be small, you should computethe directory like this:(make-temp-filesmall-temporary-file-directoryChapter 26: Files

643(expand-file-name prefix(or small-temporary-file-directory
temporary-file-directory)))

make-temp-name base-name[Function]
This function generates a string that might be a unique file name. The name starts
with base-name, and has several random characters appended to it, which are different
in each Emacs job. It is like make-temp-file except that (i) it just constructs a nameand does not create a file, (ii) base-name should be an absolute file name that is not
magic, and (iii) if the returned file name is magic, it might name an existing file. See
Section 26.12 [Magic File Names], page 649.
Warning: In most cases, you should not use this function; use make-temp-file instead!
This function is susceptible to a race condition, between the make-temp-name call andthe creation of the file, which in some cases may cause a security hole.

Sometimes, it is necessary to create a temporary file on a remote host or a mounted
directory. The following two functions support this.

make-nearby-temp-file prefix &optional dir-flag suffix[Function]
This function is similar to make-temp-file, but it creates a temporary file asclose as possible to default-directory. If prefix is a relative file name, anddefault-directory is a remote file name or located on a mounted file systems, thetemporary file is created in the directory returned by the function temporary-filedirectory. Otherwise, the function make-temp-file is used. prefix, dir-flag andsuffix have the same meaning as in make-temp-file.
(let ((default-directory "/ssh:remotehost:"))(make-nearby-temp-file "foo"))⇒ "/ssh:remotehost:/tmp/foo232J6v"[Function]
The directory for writing temporary files via make-nearby-temp-file. In case of aremote default-directory, this is a directory for temporary files on that remotehost. If such a directory does not exist, or default-directory ought to be located on a mounted file system (see mounted-file-systems), the function returns
default-directory. For a non-remote and non-mounted default-directory, thevalue of the variable temporary-file-directory is returned.

temporary-file-directory

In order to extract the local part of the file’s name of a temporary file, use file-localname (see Section 26.12 [Magic File Names], page 649).

26.9.6 File Name Completion
This section describes low-level subroutines for completing a file name. For higher level
functions, see Section 21.6.5 [Reading File Names], page 404.

file-name-all-completions partial-filename directory[Function]
This function returns a list of all possible completions for a file whose name starts
with partial-filename in directory directory. The order of the completions is the orderof the files in the directory, which is unpredictable and conveys no useful information.

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The argument partial-filename must be a file name containing no directory part andno slash (or backslash on some systems). The current buffer’s default directory isprepended to directory, if directory is not absolute.
In the following example, suppose that ~rms/lewis is the current default directory,
and has five files whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, andfile.c.~2~.
(file-name-all-completions "f" "")⇒ ("foo" "file~" "file.c.~2~""file.c.~1~" "file.c")(file-name-all-completions "fo" "")⇒ ("foo")file-name-completion filename directory &optional predicate[Function]
This function completes the file name filename in directory directory. It returns thelongest prefix common to all file names in directory directory that start with filename.
If predicate is non-nil then it ignores possible completions that don’t satisfy predicate,after calling that function with one argument, the expanded absolute file name.
If only one match exists and filename matches it exactly, the function returns t. The
function returns nil if directory directory contains no name starting with filename.
In the following example, suppose that the current default directory has five files
whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-completion "fi" "")⇒ "file"(file-name-completion "file.c.~1" "")⇒ "file.c.~1~"(file-name-completion "file.c.~1~" "")⇒ t(file-name-completion "file.c.~3" "")⇒ nil[User Option]
file-name-completion usually ignores file names that end in any string in this list.
It does not ignore them when all the possible completions end in one of these suffixes.
This variable has no effect on file-name-all-completions.

completion-ignored-extensions

A typical value might look like this:completion-ignored-extensions⇒ (".o" ".elc" "~" ".dvi")
If an element of completion-ignored-extensions ends in a slash ‘/’, it signals a
directory. The elements which do not end in a slash will never match a directory; thus,
the above value will not filter out a directory named foo.elc.

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26.9.7 Standard File Names
Sometimes, an Emacs Lisp program needs to specify a standard file name for a particular
use—typically, to hold configuration data specified by the current user. Usually, such files
should be located in the directory specified by user-emacs-directory, which is typically~/.config/emacs/ or ~/.emacs.d/ by default (see Section “How Emacs Finds Your Init
File” in The GNU Emacs Manual). For example, abbrev definitions are stored by default in~/.config/emacs/abbrev_defs or ~/.emacs.d/abbrev_defs. The easiest way to specify
such a file name is to use the function locate-user-emacs-file.

locate-user-emacs-file base-name &optional old-name[Function]
This function returns an absolute file name for an Emacs-specific configuration or data
file. The argument base-name should be a relative file name. The return value is theabsolute name of a file in the directory specified by user-emacs-directory; if that
directory does not exist, this function creates it.
If the optional argument old-name is non-nil, it specifies a file in the user’s home
directory, ~/old-name. If such a file exists, the return value is the absolute nameof that file, instead of the file specified by base-name. This argument is intended
to be used by Emacs packages to provide backward compatibility. For instance,
prior to the introduction of user-emacs-directory, the abbrev file was located in~/.abbrev_defs. Here is the definition of abbrev-file-name:(defcustom abbrev-file-name(locate-user-emacs-file "abbrev_defs" ".abbrev_defs")"Default name of file from which to read abbrevs."...
:type 'file)

A lower-level function for standardizing file names, which locate-user-emacs-file uses
as a subroutine, is convert-standard-filename.

convert-standard-filename filename[Function]
This function returns a file name based on filename, which fits the conventions of thecurrent operating system.
On GNU and other POSIX-like systems, this simply returns filename. On otheroperating systems, it may enforce system-specific file name conventions; for example,
on MS-DOS this function performs a variety of changes to enforce MS-DOS filename limitations, including converting any leading ‘.’ to ‘_’ and truncating to threecharacters after the ‘.’.
The recommended way to use this function is to specify a name which fits theconventions of GNU and Unix systems, and pass it to convert-standard-filename.

26.10 Contents of Directories
A directory is a kind of file that contains other files entered under various names. Directories
are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list, or display the names ina buffer using the ls shell command. In the latter case, it can optionally display information
about each file, depending on the options passed to the ls command.

Chapter 26: Files

directory-files directory &optional full-name match-regexp nosort
count

646

[Function]

This function returns a list of the names of the files in the directory directory. Bydefault, the list is in alphabetical order.
If full-name is non-nil, the function returns the files’ absolute file names. Otherwise,
it returns the names relative to the specified directory.
If match-regexp is non-nil, this function returns only those file names whose nondirectory part contain a match for that regular expression—the other file names are
excluded from the list. On case-insensitive filesystems, the regular expression matchingis case-insensitive.
If nosort is non-nil, directory-files does not sort the list, so you get the file names
in no particular order. Use this if you want the utmost possible speed and don’t carewhat order the files are processed in. If the order of processing is visible to the user,
then the user will probably be happier if you do sort the names.
If count is non-nil, the function will return names of first count number of files, ornames of all files, whichever occurs first. count has to be an integer greater than zero.
(directory-files "~lewis")⇒ ("#foo#" "#foo.el#" "." ".."
"dired-mods.el" "files.texi""files.texi.~1~")
An error is signaled if directory is not the name of a directory that can be read.

directory-empty-p directory[Function]
This utility function returns t if given directory is an accessible directory and it does
not contain any files, i.e., is an empty directory. It will ignore ‘.’ and ‘..’ on systems
that return them as files in a directory.
Symbolic links to directories count as directories. See file-symlink-p to distinguishsymlinks.

directory-files-recursively directory regexp &optional
include-directories predicate follow-symlinks[Function]

Return all files under directory whose names match regexp. This function searches
the specified directory and its sub-directories, recursively, for files whose basenames(i.e., without the leading directories) match the specified regexp, and returns a list of
the absolute file names of the matching files (see Section 26.9.2 [Relative File Names],
page 637). The file names are returned in depth-first order, meaning that files insome sub-directory are returned before the files in its parent directory. In addition,
matching files found in each subdirectory are sorted alphabetically by their basenames.
By default, directories whose names match regexp are omitted from the list, but if
the optional argument include-directories is non-nil, they are included.
By default, all subdirectories are descended into. If predicate is t, errors when trying
to descend into a subdirectory (for instance, if it’s not readable by this user) are
ignored. If it’s neither nil nor t, it should be a function that takes one parameter(the subdirectory name) and should return non-nil if the directory is to be descended
into.

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Symbolic links to subdirectories are not followed by default, but if follow-symlinks is
non-nil, they are followed.

locate-dominating-file file name

[Function]
Starting at file, go up the directory tree hierarchy looking for the first directory where
name, a string, exists, and return that directory. If file is a file, its directory willserve as the starting point for the search; otherwise file should be a directory fromwhich to start. The function looks in the starting directory, then in its parent, thenin its parent’s parent, etc., until it either finds a directory with name or reaches theroot directory of the filesystem without finding name – in the latter case the function
returns nil.
The argument name can also be a predicate function. The predicate is called for every
directory examined by the function, starting from file (even if file is not a directory).
It is called with one argument (the file or directory) and should return non-nil if that
directory is the one it is looking for.

file-in-directory-p file dir[Function]
This function returns t if file is a file in directory dir, or in a subdirectory of dir. It
also returns t if file and dir are the same directory. It compares the truenames of thetwo directories. If dir does not name an existing directory, the return value is nil.

directory-files-and-attributes directory &optional full-namematch-regexp nosort id-format count[Function]

This is similar to directory-files in deciding which files to report on and how toreport their names. However, instead of returning a list of file names, it returns foreach file a list (filename . attributes), where attributes is what file-attributes
returns for that file. The optional argument id-format has the same meaning as
the corresponding argument to file-attributes (see [Definition of file-attributes],
page 625).
[Constant]
This regular expression matches any file name except ‘.’ and ‘..’. More precisely, it
matches parts of any nonempty string except those two. It is useful as the match-regexp
argument to directory-files and directory-files-and-attributes:(directory-files "/foo" nil directory-files-no-dot-files-regexp)
returns nil, if directory ‘/foo’ is empty.

directory-files-no-dot-files-regexp

file-expand-wildcards pattern &optional full regexp[Function]
This function expands the wildcard pattern pattern, returning a list of file names thatmatch it.
pattern is, by default, a “glob”/wildcard string, e.g., ‘"/tmp/*.png"’ or‘"/*/*/foo.png"’, but can also be a regular expression if the optional regexp
parameter is non-nil. In any case, the matches are applied per sub-directory, so amatch can’t span a parent/sub directory.
If pattern is written as an absolute file name, the values are absolute also.
If pattern is written as a relative file name, it is interpreted relative to the current
default directory. The file names returned are normally also relative to the current
default directory. However, if full is non-nil, they are absolute.

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insert-directory file switches &optional wildcard full-directory-p[Function]
This function inserts (in the current buffer) a directory listing for directory file,formatted with ls according to switches. It leaves point after the inserted text.
switches may be a string of options, or a list of strings representing individual options.
The argument file may be either a directory or a file specification including wildcard
characters. If wildcard is non-nil, that means treat file as a file specification withwildcards.
If full-directory-p is non-nil, that means the directory listing is expected to show thefull contents of a directory. You should specify t when file is a directory and switches
do not contain ‘-d’. (The ‘-d’ option to ls says to describe a directory itself as a file,rather than showing its contents.)
On most systems, this function works by running a directory listing program whosename is in the variable insert-directory-program. If wildcard is non-nil, it also
runs the shell specified by shell-file-name, to expand the wildcards.
MS-DOS and MS-Windows systems usually lack the standard Unix program ls, so
this function emulates the standard Unix program ls with Lisp code.

As a technical detail, when switches contains the long ‘--dired’ option,
insert-directory treats it specially, for the sake of dired. However, the normallyequivalent short ‘-D’ option is just passed on to insert-directory-program, as anyother option.
[Variable]
This variable’s value is the program to run to generate a directory listing for thefunction insert-directory. It is ignored on systems which generate the listing with
Lisp code.

insert-directory-program

26.11 Creating, Copying and Deleting Directories
Most Emacs Lisp file-manipulation functions get errors when used on files that are directories.
For example, you cannot delete a directory with delete-file. These special functions exist
to create and delete directories.

make-directory dirname &optional parents[Command]This command creates a directory named dirname. If parents is non-nil, as is always
the case in an interactive call, that means to create the parent directories first, if
they don’t already exist. As a function, make-directory returns non-nil if dirname
already exists as a directory and parents is non-nil, and returns nil if it successfully
created dirname. mkdir is an alias for this.

make-empty-file filename &optional parents[Command]This command creates an empty file named filename. As make-directory, thiscommand creates parent directories if parents is non-nil. If filename already exists,
this command signals an error.

Chapter 26: Files

copy-directory dirname newname &optional keep-time parents
copy-contents

649[Command]This command copies the directory named dirname to newname. If newname is adirectory name, dirname will be copied to a subdirectory there. See Section 26.9.3[Directory Names], page 637.
It always sets the file modes of the copied files to match the corresponding original file.
The third argument keep-time non-nil means to preserve the modification time of
the copied files. A prefix arg makes keep-time non-nil.
The fourth argument parents says whether to create parent directories if they don’t
exist. Interactively, this happens by default.
The fifth argument copy-contents, if non-nil, means to copy the contents of dirname
directly into newname if the latter is a directory name, instead of copying dirname
into it as a subdirectory.

delete-directory dirname &optional recursive trash[Command]This command deletes the directory named dirname. The function delete-file does
not work for files that are directories; you must use delete-directory for them. If
recursive is nil, and the directory contains any files, delete-directory signals anerror. If recursive is non-nil, there is no error merely because the directory or its files
are deleted by some other process before delete-directory gets to them.
delete-directory only follows symbolic links at the level of parent directories.

If the optional argument trash is non-nil and the variable delete-by-moving-totrash is non-nil, this command moves the file into the system Trash instead ofdeleting it. See Section “Miscellaneous File Operations” in The GNU Emacs Manual.
When called interactively, trash is t if no prefix argument is given, and nil otherwise.

26.12 Making Certain File Names “Magic”
You can implement special handling for certain file names. This is called making thosenames magic. The principal use for this feature is in implementing access to remote files(see Section “Remote Files” in The GNU Emacs Manual).
To define a kind of magic file name, you must supply a regular expression to define theclass of names (all those that match the regular expression), plus a handler that implements
all the primitive Emacs file operations for file names that match.
The variable file-name-handler-alist holds a list of handlers, together with regularexpressions that determine when to apply each handler. Each element has this form:(regexp . handler)
All the Emacs primitives for file access and file name transformation check the given filename against file-name-handler-alist. If the file name matches regexp, the primitives
handle that file by calling handler.
The first argument given to handler is the name of the primitive, as a symbol; theremaining arguments are the arguments that were passed to that primitive. (The first ofthese arguments is most often the file name itself.) For example, if you do this:(file-exists-p filename)Chapter 26: Files

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and filename has handler handler, then handler is called like this:(funcall handler 'file-exists-p filename)
When a function takes two or more arguments that must be file names, it checks each of
those names for a handler. For example, if you do this:(expand-file-name filename dirname)then it checks for a handler for filename and then for a handler for dirname. In either case,the handler is called like this:(funcall handler 'expand-file-name filename dirname)
The handler then needs to figure out whether to handle filename or dirname.
If the specified file name matches more than one handler, the one whose match starts
last in the file name gets precedence. This rule is chosen so that handlers for jobs such as
uncompression are handled first, before handlers for jobs such as remote file access.
Here are the operations that a magic file name handler gets to handle:
abbreviate-file-name, access-file,add-name-to-file,byte-compiler-base-file-name,copy-directory, copy-file,delete-directory, delete-file,
diff-latest-backup-file,
directory-file-name,directory-files,
directory-files-and-attributes,
dired-compress-file, dired-uncache,exec-path, expand-file-name,file-accessible-directory-p,
file-acl,
file-attributes,
file-directory-p,
file-equal-p,
file-executable-p, file-exists-p,
file-in-directory-p,
file-local-copy, file-locked-p,
file-modes, file-name-all-completions,file-name-as-directory,
file-name-case-insensitive-p,
file-name-completion,
file-name-directory,
file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-notify-add-watch, file-notify-rm-watch,file-notify-valid-p,
file-ownership-preserved-p,
file-readable-p, file-regular-p,
file-remote-p, file-selinux-context,
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file-truename, file-writable-p,find-backup-file-name,get-file-buffer,insert-directory,
insert-file-contents,
list-system-processes,
load, lock-file,make-auto-save-file-name,make-directory,
make-lock-file-name,make-nearby-temp-file,make-process,make-symbolic-link,
memory-info, process-attributes, process-file,rename-file, set-file-acl, set-file-modes,
set-file-selinux-context, set-file-times,
set-visited-file-modtime, shell-command,
start-file-process,substitute-in-file-name,temporary-file-directory,
unhandled-file-name-directory,
unlock-file,vc-registered,verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the buffer’s modified flag,with (set-buffer-modified-p nil), if the visit argument is non-nil. This also has theeffect of unlocking the buffer if it is locked.
The handler function must handle all of the above operations, and possibly others to be
added in the future. It need not implement all these operations itself—when it has nothing
special to do for a certain operation, it can reinvoke the primitive, to handle the operation in
the usual way. It should always reinvoke the primitive for an operation it does not recognize.
Here’s one way to do this:(defun my-file-handler (operation &rest args);; First check for the specific operations;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)((eq operation 'write-region) ...)...
;; Handle any operation we don’t know about.
(t (let ((inhibit-file-name-handlers(cons 'my-file-handler(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))(inhibit-file-name-operation operation))(apply operation args)))))

When a handler function decides to call the ordinary Emacs primitive for the operation
at hand, it needs to prevent the primitive from calling the same handler once again, thus
leading to an infinite recursion. The example above shows how to do this, with the variables

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inhibit-file-name-handlers and inhibit-file-name-operation. Be careful to usethem exactly as shown above; the details are crucial for proper behavior in the case ofmultiple handlers, and for operations that have two file names that may each have handlers.
Handlers that don’t really do anything special for actual access to the file—such as theones that implement completion of host names for remote file names—should have a non-nil
safe-magic property. For instance, Emacs normally protects directory names it finds in
PATH from becoming magic, if they look like magic file names, by prefixing them with ‘/:’.
But if the handler that would be used for them has a non-nil safe-magic property, the‘/:’ is not added.
A file name handler can have an operations property to declare which operations it
handles in a nontrivial way. If this property has a non-nil value, it should be a list ofoperations; then only those operations will call the handler. This avoids inefficiency, but its
main purpose is for autoloaded handler functions, so that they won’t be loaded except when
they have real work to do.
Simply deferring all operations to the usual primitives does not work. For instance, if
the file name handler applies to file-exists-p, then it must handle load itself, because
the usual load code won’t work properly in that case. However, if the handler uses theoperations property to say it doesn’t handle file-exists-p, then it need not handle load
nontrivially.
[Variable]
This variable holds a list of handlers whose use is presently inhibited for a certain
operation.

inhibit-file-name-handlers

inhibit-file-name-operation[Variable]

The operation for which certain handlers are presently inhibited.

find-file-name-handler file operation[Function]
This function returns the handler function for file name file, or nil if there is none.
The argument operation should be the operation to be performed on the file—the value
you will pass to the handler as its first argument when you call it. If operation equals
inhibit-file-name-operation, or if it is not found in the operations property of
the handler, this function returns nil.

file-local-copy filename[Function]
This function copies file filename to an ordinary non-magic file on the local machine, if
it isn’t on the local machine already. Magic file names should handle the file-localcopy operation if they refer to files on other machines. A magic file name that is used
for other purposes than remote file access should not handle file-local-copy; thenthis function will treat the file as local.
If filename is local, whether magic or not, this function does nothing and returns nil.
Otherwise it returns the file name of the local copy file.

file-remote-p filename &optional identification connected[Function]
This function tests whether filename is a remote file. If filename is local (not remote),
the return value is nil. If filename is indeed remote, the return value is a string that
identifies the remote system.

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This identifier string can include a host name and a user name, as well as charactersdesignating the method used to access the remote system. For example, the remote
identifier string for the file name /sudo::/some/file is /sudo:root@localhost:.
If file-remote-p returns the same identifier for two different file names, that means
they are stored on the same file system and can be accessed locally with respect toeach other. This means, for example, that it is possible to start a remote processaccessing both files at the same time. Implementers of file name handlers need toensure this principle is valid.
identification specifies which part of the identifier shall be returned as string. identification can be the symbol method, user or host; any other value is handled like nil
and means to return the complete identifier string. In the example above, the remoteuser identifier string would be root.
If connected is non-nil, this function returns nil even if filename is remote, if Emacs
has no network connection to its host. This is useful when you want to avoid the delayof making connections when they don’t exist.

unhandled-file-name-directory filename[Function]
This function returns the name of a directory that is not magic. For a non-magic
filename it returns the corresponding directory name (see Section 26.9.3 [DirectoryNames], page 637). For a magic filename, it invokes the file name handler, which
therefore decides what value to return. If filename is not accessible from a local
process, then the file name handler should indicate that by returning nil.
This is useful for running a subprocess; every subprocess must have a non-magic
directory to serve as its current directory, and this function is a good way to come up
with one.

file-local-name filename[Function]
This function returns the local part of filename. This is the part of the file’s namethat identifies it on the remote host, and is typically obtained by removing from theremote file name the parts that specify the remote host and the method of accessing
it. For example:(file-local-name "/ssh:user@host:/foo/bar")⇒ "/foo/bar"

For a remote filename, this function returns a file name which could be used directly as
an argument of a remote process (see Section 40.4 [Asynchronous Processes], page 1086,
and see Section 40.3 [Synchronous Processes], page 1081), and as the program to run
on the remote host. If filename is local, this function returns it unchanged.
[User Option]
The attributes of remote files can be cached for better performance. If they arechanged outside of Emacs’s control, the cached values become invalid, and must be
reread.

remote-file-name-inhibit-cache

When this variable is set to nil, cached values are never expired. Use this settingwith caution, only if you are sure nothing other than Emacs ever changes the remote
files. If it is set to t, cached values are never used. This is the safest value, but could
result in performance degradation.

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A compromise is to set it to a positive number. This means that cached values areused for that amount of seconds since they were cached. If a remote file is checked
regularly, it might be a good idea to let-bind this variable to a value less than thetime period between consecutive checks. For example:(defun display-time-file-nonempty-p (file)(let ((remote-file-name-inhibit-cache(- display-time-interval 5)))(and (file-exists-p file)(< 0 (file-attribute-size(file-attributes(file-chase-links file)))))))

26.13 File Format Conversion
Emacs performs several steps to convert the data in a buffer (text, text properties, andpossibly other information) to and from a representation suitable for storing into a file. Thissection describes the fundamental functions that perform this format conversion, namely
insert-file-contents for reading a file into a buffer, and write-region for writing abuffer into a file.

26.13.1 Overview
The function insert-file-contents:• initially, inserts bytes from the file into the buffer;• decodes bytes to characters as appropriate;• processes formats as defined by entries in format-alist; and• calls functions in after-insert-file-functions.
The function write-region:• initially, calls functions in write-region-annotate-functions;• processes formats as defined by entries in format-alist;• encodes characters to bytes as appropriate; and• modifies the file with the bytes.
This shows the symmetry of the lowest-level operations; reading and writing handle
things in opposite order. The rest of this section describes the two facilities surrounding
the three variables named above, as well as some related functions. Section 34.10 [Coding
Systems], page 976, for details on character encoding and decoding.

26.13.2 Round-Trip Specification
The most general of the two facilities is controlled by the variable format-alist, a list of
file format specifications, which describe textual representations used in files for the data in
an Emacs buffer. The descriptions for reading and writing are paired, which is why we callthis “round-trip” specification (see Section 26.13.3 [Format Conversion Piecemeal], page 657,
for non-paired specification).

Chapter 26: Files

655[Variable]
This list contains one format definition for each defined file format. Each format
definition is a list of this form:(name doc-string regexp from-fn to-fn modify mode-fn preserve)

format-alist

Here is what the elements in a format definition mean:
name

The name of this format.

doc-string A documentation string for the format.
regexpA regular expression which is used to recognize files represented in this format.
If nil, the format is never applied automatically.

from-fn

A shell command or function to decode data in this format (to convert file data
into the usual Emacs data representation).
A shell command is represented as a string; Emacs runs the command as a filter
to perform the conversion.
If from-fn is a function, it is called with two arguments, begin and end, which
specify the part of the buffer it should convert. It should convert the text byediting it in place. Since this can change the length of the text, from-fn should
return the modified end position.
One responsibility of from-fn is to make sure that the beginning of the file nolonger matches regexp. Otherwise it is likely to get called again. Also, from-fn
must not involve buffers or files other than the one being decoded, otherwise
the internal buffer used for formatting might be overwritten.

to-fn

A shell command or function to encode data in this format—that is, to convert
the usual Emacs data representation into this format.
If to-fn is a string, it is a shell command; Emacs runs the command as a filter
to perform the conversion.
If to-fn is a function, it is called with three arguments: begin and end, which
specify the part of the buffer it should convert, and buffer, which specifies whichbuffer. There are two ways it can do the conversion:• By editing the buffer in place. In this case, to-fn should return the endposition of the range of text, as modified.
• By returning a list of annotations. This is a list of elements of the form
(position . string), where position is an integer specifying the relative
position in the text to be written, and string is the annotation to add there.
The list must be sorted in order of position when to-fn returns it.
When write-region actually writes the text from the buffer to the file, itintermixes the specified annotations at the corresponding positions. All
this takes place without modifying the buffer.
to-fn must not involve buffers or files other than the one being encoded, otherwise
the internal buffer used for formatting might be overwritten.

modifyA flag, t if the encoding function modifies the buffer, and nil if it works byreturning a list of annotations.

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mode-fn

A minor-mode function to call after visiting a file converted from this format.
The function is called with one argument, the integer 1; that tells a minor-mode
function to enable the mode.

preserve

A flag, t if format-write-file should not remove this format from
buffer-file-format.

The function insert-file-contents automatically recognizes file formats when it reads
the specified file. It checks the text of the beginning of the file against the regular expressionsof the format definitions, and if it finds a match, it calls the decoding function for thatformat. Then it checks all the known formats over again. It keeps checking them until noneof them is applicable.
Visiting a file, with find-file-noselect or the commands that use it, performs conversion likewise (because it calls insert-file-contents); it also calls the mode function foreach format that it decodes. It stores a list of the format names in the buffer-local variablebuffer-file-format.
[Variable]
This variable states the format of the visited file. More precisely, this is a list of thefile format names that were decoded in the course of visiting the current buffer’s file.
It is always buffer-local in all buffers.

buffer-file-format

When write-region writes data into a file, it first calls the encoding functions for theformats listed in buffer-file-format, in the order of appearance in the list.

format-write-file file format &optional confirm[Command]This command writes the current buffer contents into the file file in a format based onformat, which is a list of format names. It constructs the actual format starting fromformat, then appending any elements from the value of buffer-file-format with a
non-nil preserve flag (see above), if they are not already present in format. It thenupdates buffer-file-format with this format, making it the default for future saves.
Except for the format argument, this command is similar to write-file. In particular,
confirm has the same meaning and interactive treatment as the corresponding argument
to write-file. See [Definition of write-file], page 612.

format-find-file file format[Command]This command finds the file file, converting it according to format format. It also
makes format the default if the buffer is saved later.
The argument format is a list of format names. If format is nil, no conversion takes
place. Interactively, typing just RET for format specifies nil.

format-insert-file file format &optional beg end[Command]This command inserts the contents of file file, converting it according to format
format. If beg and end are non-nil, they specify which part of the file to read, as ininsert-file-contents (see Section 26.3 [Reading from Files], page 614).
The return value is like what insert-file-contents returns: a list of the absolute
file name and the length of the data inserted (after conversion).
The argument format is a list of format names. If format is nil, no conversion takes
place. Interactively, typing just RET for format specifies nil.

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657[Variable]
This variable specifies the format to use for auto-saving. Its value is a list of format
names, just like the value of buffer-file-format; however, it is used instead of
buffer-file-format for writing auto-save files. If the value is t, the default, autosaving uses the same format as a regular save in the same buffer. This variable isalways buffer-local in all buffers.

buffer-auto-save-file-format

26.13.3 Piecemeal Specification
In contrast to the round-trip specification described in the previous subsection (seeSection 26.13.2 [Format Conversion Round-Trip], page 654), you can use the variables
after-insert-file-functions and write-region-annotate-functions to separately
control the respective reading and writing conversions.
Conversion starts with one representation and produces another representation. When
there is only one conversion to do, there is no conflict about what to start with. However,when there are multiple conversions involved, conflict may arise when two conversions needto start with the same data.
This situation is best understood in the context of converting text properties during
write-region. For example, the character at position 42 in a buffer is ‘X’ with a text
property foo. If the conversion for foo is done by inserting into the buffer, say, ‘FOO:’, thenthat changes the character at position 42 from ‘X’ to ‘F’. The next conversion will start withthe wrong data straight away.
To avoid conflict, cooperative conversions do not modify the buffer, but instead specify
annotations, a list of elements of the form (position . string), sorted in order of increasing
position.
If there is more than one conversion, write-region merges their annotations destructively
into one sorted list. Later, when the text from the buffer is actually written to the file, itintermixes the specified annotations at the corresponding positions. All this takes place
without modifying the buffer.
In contrast, when reading, the annotations intermixed with the text are handled immediately. insert-file-contents sets point to the beginning of some text to be converted,
then calls the conversion functions with the length of that text. These functions should
always return with point at the beginning of the inserted text. This approach makes sense
for reading because annotations removed by the first converter can’t be mistakenly processedby a later converter. Each conversion function should scan for the annotations it recognizes,
remove the annotation, modify the buffer text (to set a text property, for example), andreturn the updated length of the text, as it stands after those changes. The value returned
by one function becomes the argument to the next function.
[Variable]
A list of functions for write-region to call. Each function in the list is called with
two arguments: the start and end of the region to be written. These functions should
not alter the contents of the buffer. Instead, they should return annotations.

write-region-annotate-functions

As a special case, a function may return with a different buffer current. Emacs takes
this to mean that the current buffer contains altered text to be output. It thereforechanges the start and end arguments of the write-region call, giving them the values

Chapter 26: Files658

of point-min and point-max in the new buffer, respectively. It also discards all
previous annotations, because they should have been dealt with by this function.
[Variable]
The value of this variable, if non-nil, should be a function. This function is called,with no arguments, after write-region has completed.
If any function in write-region-annotate-functions returns with a different buffer
current, Emacs calls write-region-post-annotation-function more than once.
Emacs calls it with the last buffer that was current, and again with the buffer before
that, and so on back to the original buffer.
Thus, a function in write-region-annotate-functions can create a buffer, give thisvariable the local value of kill-buffer in that buffer, set up the buffer with altered
text, and make the buffer current. The buffer will be killed after write-region is
done.

write-region-post-annotation-function[Variable]
Each function in this list is called by insert-file-contents with one argument, thenumber of characters inserted, and with point at the beginning of the inserted text.
Each function should leave point unchanged, and return the new character countdescribing the inserted text as modified by the function.

after-insert-file-functions

We invite users to write Lisp programs to store and retrieve text properties in files,
using these hooks, and thus to experiment with various data formats and find good ones.
Eventually we hope users will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property names or values—
because a program that general is probably difficult to write, and slow. Instead, choose a
set of possible data types that are reasonably flexible, and not too hard to encode.

659

27 Backups and Auto-Saving
Backup files and auto-save files are two methods by which Emacs tries to protect the userfrom the consequences of crashes or of the user’s own errors. Auto-saving preserves the text
from earlier in the current editing session; backup files preserve file contents prior to thecurrent session.

27.1 Backup Files
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup
file the first time you save a buffer into its visited file. Thus, normally, the backup filecontains the contents of the file as it was before the current editing session. The contents ofthe backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you
can specify that backup files should be made by copying the visited file. This choice makesa difference for files with multiple names; it also can affect whether the edited file remains
owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively
request numbered backups; then each new backup file gets a new name. You can delete
old numbered backups when you don’t want them any more, or Emacs can delete them
automatically.
For performance, the operating system may not write the backup file’s contents tosecondary storage immediately, or may alias the backup data with the original until one or
the other is later modified. See Section 26.8 [Files and Storage], page 634.

27.1.1 Making Backup Files[Function]
This function makes a backup of the file visited by the current buffer, if appropriate.
It is called by save-buffer before saving the buffer the first time.

backup-buffer

If a backup was made by renaming, the return value is a cons cell of the form (modes
extra-alist backupname), where modes are the mode bits of the original file, as returned
by file-modes (see Section 26.6.1 [Testing Accessibility], page 619), extra-alist is analist describing the original file’s extended attributes, as returned by file-extendedattributes (see Section 26.6.5 [Extended Attributes], page 627), and backupname isthe name of the backup.
In all other cases (i.e., if a backup was made by copying or if no backup was made),
this function returns nil.
[Variable]
This buffer-local variable says whether this buffer’s file has been backed up on accountof this buffer. If it is non-nil, the backup file has been written. Otherwise, thefile should be backed up when it is next saved (if backups are enabled). This is apermanent local; kill-all-local-variables does not alter it.

buffer-backed-up

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660[User Option]
This variable determines whether or not to make backup files. If it is non-nil, thenEmacs creates a backup of each file when it is saved for the first time—provided thatbackup-inhibited is nil (see below).
The following example shows how to change the make-backup-files variable only in
the Rmail buffers and not elsewhere. Setting it nil stops Emacs from making backupsof these files, which may save disk space. (You would put this code in your init file.)

make-backup-files(add-hook 'rmail-mode-hook(lambda () (setq-local make-backup-files nil)))[Variable]
This variable’s value is a function to be called on certain occasions to decide whether
a file should have backup files. The function receives one argument, an absolute
file name to consider. If the function returns nil, backups are disabled for that file.
Otherwise, the other variables in this section say whether and how to make backups.
The default value is normal-backup-enable-predicate, which checks for files in
temporary-file-directory and small-temporary-file-directory.

backup-enable-predicate[Variable]
If this variable is non-nil, backups are inhibited. It records the result of testing
backup-enable-predicate on the visited file name. It can also coherently be usedby other mechanisms that inhibit backups based on which file is visited. For example,
VC sets this variable non-nil to prevent making backups for files managed with aversion control system.
This is a permanent local, so that changing the major mode does not lose its value.
Major modes should not set this variable—they should set make-backup-files instead.

backup-inhibited[User Option]
This variable’s value is an alist of filename patterns and backup directories. Eachelement looks likebackup-directory-alist(regexp . directory)

Backups of files with names matching regexp will be made in directory. directory may
be relative or absolute. If it is absolute, so that all matching files are backed up into
the same directory, the file names in this directory will be the full name of the file
backed up with all directory separators changed to ‘!’ to prevent clashes. This will
not work correctly if your filesystem truncates the resulting name.
For the common case of all backups going into one directory, the alist should containa single element pairing ‘"."’ with the appropriate directory.
If this variable is nil (the default), or it fails to match a filename, the backup is madein the original file’s directory.
On MS-DOS filesystems without long names this variable is always ignored.
[User Option]
This variable’s value is a function to use for making backup file names. The function
make-backup-file-name calls it. See Section 27.1.4 [Naming Backup Files], page 662.
This could be buffer-local to do something special for specific files. If you change it,
you may need to change backup-file-name-p and file-name-sans-versions too.

make-backup-file-name-function

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27.1.2 Backup by Renaming or by Copying?
There are two ways that Emacs can make a backup file:• Emacs can rename the original file so that it becomes a backup file, and then write thebuffer being saved into a new file. After this procedure, any other names (i.e., hard
links) of the original file now refer to the backup file. The new file is owned by the user
doing the editing, and its group is the default for new files written by the user in that
directory.
• Emacs can copy the original file into a backup file, and then overwrite the original
file with new contents. After this procedure, any other names (i.e., hard links) of theoriginal file continue to refer to the current (updated) version of the file. The file’sowner and group will be unchanged.
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use the second method, whichis to copy the original file and overwrite it with the new buffer contents. The variable
file-precious-flag, if non-nil, also has this effect (as a sideline of its main significance).
See Section 26.2 [Saving Buffers], page 612.
[User Option]
If this variable is non-nil, Emacs always makes backup files by copying. The default
is nil.

backup-by-copying

The following three variables, when non-nil, cause the second method to be used incertain special cases. They have no effect on the treatment of files that don’t fall into thespecial cases.
[User Option]
If this variable is non-nil, Emacs makes backups by copying for files with multiple
names (hard links). The default is nil.
This variable is significant only if backup-by-copying is nil, since copying is always
used when that variable is non-nil.

backup-by-copying-when-linked[User Option]
If this variable is non-nil (the default), Emacs makes backups by copying in cases
where renaming would change either the owner or the group of the file.
The value has no effect when renaming would not alter the owner or group of the file;that is, for files which are owned by the user and whose group matches the default for
a new file created there by the user.
This variable is significant only if backup-by-copying is nil, since copying is always
used when that variable is non-nil.

backup-by-copying-when-mismatch[User Option]
This variable, if non-nil, specifies the same behavior as backup-by-copying-whenmismatch, but only for certain user-id and group-id values: namely, those less than orequal to a certain number. You set this variable to that number.
Thus, if you set backup-by-copying-when-privileged-mismatch to 0, backup by
copying is done for the superuser and group 0 only, when necessary to prevent a change
in the owner of the file.

backup-by-copying-when-privileged-mismatch

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The default is 200.

27.1.3 Making and Deleting Numbered Backup Files
If a file’s name is foo, the names of its numbered backup versions are foo.~v~, for various
integers v, like this: foo.~1~, foo.~2~, foo.~3~, . . . , foo.~259~, and so on.
[User Option]
This variable controls whether to make a single non-numbered backup file or multiple
numbered backups.

version-control

nil

Make numbered backups if the visited file already has numbered backups;
otherwise, do not. This is the default.

never

Do not make numbered backups.

anything else
Make numbered backups.
The use of numbered backups ultimately leads to a large number of backup versions,which must then be deleted. Emacs can do this automatically or it can ask the user whether
to delete them.
[User Option]
The value of this variable is the number of newest versions to keep when a newnumbered backup is made. The newly made backup is included in the count. The
default value is 2.

kept-new-versions[User Option]
The value of this variable is the number of oldest versions to keep when a new numbered
backup is made. The default value is 2.

kept-old-versions

If there are backups numbered 1, 2, 3, 5, and 7, and both of these variables have the value
2, then the backups numbered 1 and 2 are kept as old versions and those numbered 5 and 7
are kept as new versions; backup version 3 is excess. The function find-backup-file-name(see Section 27.1.4 [Backup Names], page 662) is responsible for determining which backup
versions to delete, but does not delete them itself.
[User Option]
If this variable is t, then saving a file deletes excess backup versions silently. If it isnil, that means to ask for confirmation before deleting excess backups. Otherwise,
they are not deleted at all.

delete-old-versions[User Option]
This variable specifies how many of the newest backup versions to keep in the Diredcommand . (dired-clean-directory). That’s the same thing kept-new-versions
specifies when you make a new backup file. The default is 2.

dired-kept-versions

27.1.4 Naming Backup Files
The functions in this section are documented mainly because you can customize the naming
conventions for backup files by redefining them. If you change one, you probably need tochange the rest.

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backup-file-name-p filename[Function]
This function returns a non-nil value if filename is a possible name for a backup file.
It just checks the name, not whether a file with the name filename exists.
(backup-file-name-p "foo")⇒ nil(backup-file-name-p "foo~")⇒ 3

The standard definition of this function is as follows:(defun backup-file-name-p (file)"Return non-nil if FILE is a backup file \name (numeric or not)..."(string-match "~\\'" file))

Thus, the function returns a non-nil value if the file name ends with a ‘~’. (We use abackslash to split the documentation string’s first line into two lines in the text, but
produce just one line in the string itself.)
This simple expression is placed in a separate function to make it easy to redefine forcustomization.

make-backup-file-name filename[Function]
This function returns a string that is the name to use for a non-numbered backup filefor file filename. On Unix, this is just filename with a tilde appended.

The standard definition of this function, on most operating systems, is as follows:(defun make-backup-file-name (file)"Create the non-numeric backup file name for FILE..."(concat file "~"))

You can change the backup-file naming convention by redefining this function. The
following example redefines make-backup-file-name to prepend a ‘.’ in addition toappending a tilde:(defun make-backup-file-name (filename)(expand-file-name(concat "." (file-name-nondirectory filename) "~")
(file-name-directory filename)))(make-backup-file-name "backups.texi")⇒ ".backups.texi~"

Some parts of Emacs, including some Dired commands, assume that backup file names
end with ‘~’. If you do not follow that convention, it will not cause serious problems,
but these commands may give less-than-desirable results.

find-backup-file-name filename[Function]
This function computes the file name for a new backup file for filename. It may also
propose certain existing backup files for deletion. find-backup-file-name returns alist whose car is the name for the new backup file and whose cdr is a list of backup
files whose deletion is proposed. The value can also be nil, which means not to makea backup.
Two variables, kept-old-versions and kept-new-versions, determine which backup
versions should be kept. This function keeps those versions by excluding them fromthe cdr of the value. See Section 27.1.3 [Numbered Backups], page 662.

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In this example, the value says that ~rms/foo.~5~ is the name to use for the new
backup file, and ~rms/foo.~3~ is an excess version that the caller should consider
deleting now.
(find-backup-file-name "~rms/foo")⇒ ("~rms/foo.~5~" "~rms/foo.~3~")file-backup-file-names filename[Function]
This function returns a list of all the backup file names for filename, or nil if there arenone. The files are sorted by modification time, descending, so that the most recent
files are first.

file-newest-backup filename[Function]
This function returns the first element of the list returned by file-backup-filenames.
Some file comparison commands use this function so that they can automaticallycompare a file with its most recent backup.

27.2 Auto-Saving
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving
prevents you from losing more than a limited amount of work if the system crashes. By
default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time.
See Section “Auto-Saving: Protection Against Disasters” in The GNU Emacs Manual, for
information on auto-save for users. Here we describe the functions used to implement
auto-saving and the variables that control them.
[Variable]
This buffer-local variable is the name of the file used for auto-saving the current buffer.
It is nil if the buffer should not be auto-saved.
buffer-auto-save-file-name⇒ "/xcssun/users/rms/lewis/#backups.texi#"

buffer-auto-save-file-nameauto-save-mode arg[Command]This is the mode command for Auto Save mode, a buffer-local minor mode. When Auto
Save mode is enabled, auto-saving is enabled in the buffer. The calling convention
is the same as for other minor mode commands (see Section 24.3.1 [Minor Mode
Conventions], page 544).
Unlike most minor modes, there is no auto-save-mode variable. Auto Save modeis enabled if buffer-auto-save-file-name is non-nil and buffer-saved-size (seebelow) is non-zero.
[Variable]
This variable lists transforms to apply to buffer’s file name before making the auto-save
file name.
Each transform is a list of the form (regexp replacement [uniquify]). regexp isa regular expression to match against the file name; if it matches, replace-match isused to replace the matching part with replacement. If the optional element uniquify
is non-nil, the auto-save file name is constructed by concatenating the directory

auto-save-file-name-transforms

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part of the transformed file name with the buffer’s file name in which all directory
separators were changed to ‘!’ to prevent clashes. (This will not work correctly if yourfilesystem truncates the resulting name.)
If uniquify is one of the members of secure-hash-algorithms, Emacs constructs thenondirectory part of the auto-save file name by applying that secure-hash to thebuffer file name. This avoids any risk of excessively long file names.
All the transforms in the list are tried, in the order they are listed. When one transform
applies, its result is final; no further transforms are tried.
The default value is set up to put the auto-save files of remote files into the temporary
directory (see Section 26.9.5 [Unique File Names], page 641).
On MS-DOS filesystems without long names this variable is always ignored.

auto-save-file-name-p filename[Function]
This function returns a non-nil value if filename is a string that could be the name ofan auto-save file. It assumes the usual naming convention for auto-save files: a namethat begins and ends with hash marks (‘#’) is a possible auto-save file name. The
argument filename should not contain a directory part.
(make-auto-save-file-name)⇒ "/xcssun/users/rms/lewis/#backups.texi#"(auto-save-file-name-p "#backups.texi#")⇒ 0(auto-save-file-name-p "backups.texi")⇒ nil[Function]
This function returns the file name to use for auto-saving the current buffer. Thisis just the file name with hash marks (‘#’) prepended and appended to it. Thisfunction does not look at the variable auto-save-visited-file-name (described
below); callers of this function should check that variable first.

make-auto-save-file-name(make-auto-save-file-name)⇒ "/xcssun/users/rms/lewis/#backups.texi#"[User Option]
If this variable is non-nil, Emacs auto-saves buffers in the files they are visiting. Thatis, the auto-save is done in the same file that you are editing. Normally, this variable
is nil, so auto-save files have distinct names that are created by make-auto-savefile-name.

auto-save-visited-file-name

When you change the value of this variable, the new value does not take effect inan existing buffer until the next time auto-save mode is reenabled in it. If autosave mode is already enabled, auto-saves continue to go in the same file name until
auto-save-mode is called again.
Note that setting this variable to a non-nil value does not change the fact that
auto-saving is different from saving the buffer; e.g., the hooks described in Section 26.2
[Saving Buffers], page 612, are not run when a buffer is auto-saved.

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666[Function]
This function returns t if the current buffer has been auto-saved since the last time it
was read in or saved.

recent-auto-save-p[Function]
This function marks the current buffer as auto-saved. The buffer will not be auto-saved
again until the buffer text is changed again. The function returns nil.

set-buffer-auto-saved[User Option]
The value of this variable specifies how often to do auto-saving, in terms of numberof input events. Each time this many additional input events are read, Emacs does
auto-saving for all buffers in which that is enabled. Setting this to zero disables
autosaving based on the number of characters typed.

auto-save-interval[User Option]
The value of this variable is the number of seconds of idle time that should cause
auto-saving. Each time the user pauses for this long, Emacs does auto-saving for all
buffers in which that is enabled. (If the current buffer is large, the specified timeout ismultiplied by a factor that increases as the size increases; for a million-byte buffer,
the factor is almost 4.)

auto-save-timeout

If the value is zero or nil, then auto-saving is not done as a result of idleness, only
after a certain number of input events as specified by auto-save-interval.

auto-save-hook[Variable]

This normal hook is run whenever an auto-save is about to happen.
[User Option]
If this variable is non-nil, buffers that are visiting files have auto-saving enabled bydefault. Otherwise, they do not.

auto-save-default

do-auto-save &optional no-message current-only[Command]This function auto-saves all buffers that need to be auto-saved. It saves all buffers forwhich auto-saving is enabled and that have been changed since the previous auto-save.

If any buffers are auto-saved, do-auto-save normally displays a message saying‘Auto-saving...’ in the echo area while auto-saving is going on. However, if nomessage is non-nil, the message is inhibited.
If current-only is non-nil, only the current buffer is auto-saved.

delete-auto-save-file-if-necessary &optional force[Function]
This function deletes the current buffer’s auto-save file if delete-auto-save-files
is non-nil. It is called every time a buffer is saved.
Unless force is non-nil, this function only deletes the file if it was written by thecurrent Emacs session since the last true save.
[User Option]
This variable is used by the function delete-auto-save-file-if-necessary. If it
is non-nil, Emacs deletes auto-save files when a true save is done (in the visited file).
This saves disk space and unclutters your directory.

delete-auto-save-files

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667[Function]
This function adjusts the current buffer’s auto-save file name if the visited file namehas changed. It also renames an existing auto-save file, if it was made in the current
Emacs session. If the visited file name has not changed, this function does nothing.

rename-auto-save-file[Variable]
The value of this buffer-local variable is the length of the current buffer, when it waslast read in, saved, or auto-saved. This is used to detect a substantial decrease in size,
and turn off auto-saving in response.

buffer-saved-size

If it is −1, that means auto-saving is temporarily shut off in this buffer due to a
substantial decrease in size. Explicitly saving the buffer stores a positive value in thisvariable, thus reenabling auto-saving. Turning auto-save mode off or on also updates
this variable, so that the substantial decrease in size is forgotten.
If it is −2, that means this buffer should disregard changes in buffer size; in particular,
it should not shut off auto-saving temporarily due to changes in buffer size.
[Variable]
This variable (if non-nil) specifies a file for recording the names of all the auto-savefiles. Each time Emacs does auto-saving, it writes two lines into this file for eachbuffer that has auto-saving enabled. The first line gives the name of the visited file(it’s empty if the buffer has none), and the second gives the name of the auto-save file.

auto-save-list-file-name

When Emacs exits normally, it deletes this file; if Emacs crashes, you can look in thefile to find all the auto-save files that might contain work that was otherwise lost. The
recover-session command uses this file to find them.
The default name for this file specifies your home directory and starts with ‘.saves-’.
It also contains the Emacs process ID and the host name.
[User Option]
After Emacs reads your init file, it initializes auto-save-list-file-name (if you
have not already set it non-nil) based on this prefix, adding the host name andprocess ID. If you set this to nil in your init file, then Emacs does not initialize
auto-save-list-file-name.

auto-save-list-file-prefix

27.3 Reverting
If you have made extensive changes to a file and then change your mind about them, you
can get rid of them by reading in the previous version of the file with the revert-buffer
command. See Section “Reverting a Buffer” in The GNU Emacs Manual.

revert-buffer &optional ignore-auto noconfirm preserve-modes[Command]This command replaces the buffer text with the text of the visited file on disk. Thisaction undoes all changes since the file was visited or saved.
By default, if the latest auto-save file is more recent than the visited file, and theargument ignore-auto is nil, revert-buffer asks the user whether to use that autosave instead. When you invoke this command interactively, ignore-auto is t if there isno numeric prefix argument; thus, the interactive default is not to check the auto-savefile.

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Normally, revert-buffer asks for confirmation before it changes the buffer; but if
the argument noconfirm is non-nil, revert-buffer does not ask for confirmation.
Normally, this command reinitializes the buffer’s major and minor modes using
normal-mode. But if preserve-modes is non-nil, the modes remain unchanged.
Reverting tries to preserve marker positions in the buffer by using the replacement
feature of insert-file-contents. If the buffer contents and the file contents are
identical before the revert operation, reverting preserves all the markers. If they are
not identical, reverting does change the buffer; in that case, it preserves the markers
in the unchanged text (if any) at the beginning and end of the buffer. Preserving any
additional markers would be problematic.
When reverting from non-file sources, markers are usually not preserved, but this is
up to the specific revert-buffer-function implementation.

revert-buffer-in-progress-p[Variable]

revert-buffer binds this variable to a non-nil value while it is working.
You can customize how revert-buffer does its work by setting the variables describedin the rest of this section.
[User Option]
This variable holds a list of files that should be reverted without query. The value
is a list of regular expressions. If the visited file name matches one of these regularexpressions, and the file has changed on disk but the buffer is not modified, thenrevert-buffer reverts the file without asking the user for confirmation.

revert-without-query

Some major modes customize revert-buffer by making buffer-local bindings for thesevariables:[Variable]
The value of this variable is the function to use to revert this buffer. It should bea function with two optional arguments to do the work of reverting. The two optional arguments, ignore-auto and noconfirm, are the arguments that revert-buffer
received.
Modes such as Dired mode, in which the text being edited does not consist of afile’s contents but can be regenerated in some other fashion, can give this variable abuffer-local value that is a special function to regenerate the contents.

revert-buffer-function[Variable]
The value of this variable specifies the function to use to insert the updated contents
when reverting this buffer. The function receives two arguments: first the file name touse; second, t if the user has asked to read the auto-save file.
The reason for a mode to change this variable instead of revert-buffer-function
is to avoid duplicating or replacing the rest of what revert-buffer does: asking for
confirmation, clearing the undo list, deciding the proper major mode, and running thehooks listed below.

revert-buffer-insert-file-contents-function[Variable]
This normal hook is run by the default revert-buffer-function before inserting
the modified contents. A custom revert-buffer-function may or may not run thishook.

before-revert-hook

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This normal hook is run by the default revert-buffer-function after inserting themodified contents. A custom revert-buffer-function may or may not run thishook.

after-revert-hook

Emacs can revert buffers automatically. It does that by default for buffers visiting files.
The following describes how to add support for auto-reverting new types of buffers.
First, such buffers must have a suitable revert-buffer-function and buffer-stalefunction defined.
[Variable]
The value of this variable specifies a function to call to check whether a buffer needs
reverting. The default value only handles buffers that are visiting files, by checking
their modification time. Buffers that are not visiting files require a custom function of
one optional argument noconfirm. The function should return non-nil if the buffer
should be reverted. The buffer is current when this function is called.
While this function is mainly intended for use in auto-reverting, it could be used forother purposes as well. For instance, if auto-reverting is not enabled, it could be
used to warn the user that the buffer needs reverting. The idea behind the noconfirm
argument is that it should be t if the buffer is going to be reverted without asking theuser and nil if the function is just going to be used to warn the user that the buffer
is out of date. In particular, for use in auto-reverting, noconfirm is t. If the function
is only going to be used for auto-reverting, you can ignore the noconfirm argument.
If you just want to automatically auto-revert every auto-revert-interval seconds(like the Buffer Menu), use:
(setq-local buffer-stale-function(lambda (&optional noconfirm) 'fast))in the buffer’s mode function.
The special return value ‘fast’ tells the caller that the need for reverting was notchecked, but that reverting the buffer is fast. It also tells Auto Revert not to print
any revert messages, even if auto-revert-verbose is non-nil. This is important, as
getting revert messages every auto-revert-interval seconds can be very annoying.
The information provided by this return value could also be useful if the function isconsulted for purposes other than auto-reverting.

buffer-stale-function

Once the buffer has a suitable revert-buffer-function and buffer-stale-function,
several problems usually remain.
The buffer will only auto-revert if it is marked unmodified. Hence, you will have to makesure that various functions mark the buffer modified if and only if either the buffer contains
information that might be lost by reverting, or there is reason to believe that the user might
be inconvenienced by auto-reverting, because he is actively working on the buffer. The user
can always override this by manually adjusting the modified status of the buffer. To support
this, calling the revert-buffer-function on a buffer that is marked unmodified should
always keep the buffer marked unmodified.
It is important to assure that point does not continuously jump around as a consequenceof auto-reverting. Of course, moving point might be inevitable if the buffer radically changes.

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You should make sure that the revert-buffer-function does not print messages that
unnecessarily duplicate Auto Revert’s own messages, displayed if auto-revert-verbose ist, and effectively override a nil value for auto-revert-verbose. Hence, adapting a mode
for auto-reverting often involves getting rid of such messages. This is especially importantfor buffers that automatically revert every auto-revert-interval seconds.
If the new auto-reverting is part of Emacs, you should mention it in the documentation
string of global-auto-revert-non-file-buffers.
Similarly, you should document the additions in the Emacs manual.

671

28 Buffers
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents
of files that are being visited; there may also be buffers that are not visiting files. While
several buffers may exist at one time, only one buffer is designated the current buffer at
any time. Most editing commands act on the contents of the current buffer. Each buffer,including the current buffer, may or may not be displayed in any windows.

28.1 Buffer Basics
Buffers in Emacs editing are objects that have distinct names and hold text that can beedited. Buffers appear to Lisp programs as a special data type. You can think of the contents
of a buffer as a string that you can extend; insertions and deletions may occur in any partof the buffer. See Chapter 33 [Text], page 878.
A Lisp buffer object contains numerous pieces of information. Some of this information is
directly accessible to the programmer through variables, while other information is accessible
only through special-purpose functions. For example, the visited file name is directly
accessible through a variable, while the value of point is accessible only through a primitive
function.
Buffer-specific information that is directly accessible is stored in buffer-local variablebindings, which are variable values that are effective only in a particular buffer. This featureallows each buffer to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this way. For more information about
buffer-local variables and functions related to them, see Section 12.11 [Buffer-Local Variables],page 207.
For functions and variables related to visiting files in buffers, see Section 26.1 [Visiting
Files], page 608, and Section 26.2 [Saving Buffers], page 612. For functions and variables
related to the display of buffers in windows, see Section 29.11 [Buffers and Windows],
page 720.

bufferp object[Function]

This function returns t if object is a buffer, nil otherwise.

28.2 The Current Buffer
There are, in general, many buffers in an Emacs session. At any time, one of them isdesignated the current buffer—the buffer in which most editing takes place. Most of theprimitives for examining or changing text operate implicitly on the current buffer (seeChapter 33 [Text], page 878).
Normally, the buffer displayed in the selected window (see Section 29.3 [Selecting Windows], page 696) is the current buffer, but this is not always so: a Lisp program cantemporarily designate any buffer as current in order to operate on its contents, withoutchanging what is displayed on the screen. The most basic function for designating a current
buffer is set-buffer.

current-bufferThis function returns the current buffer.

[Function]

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672(current-buffer)⇒ #<buffer buffers.texi>

set-buffer buffer-or-name[Function]
This function makes buffer-or-name the current buffer. buffer-or-name must be an
existing buffer or the name of an existing buffer. The return value is the buffer madecurrent.
This function does not display the buffer in any window, so the user cannot necessarily
see the buffer. But Lisp programs will now operate on it.

When an editing command returns to the editor command loop, Emacs automatically
calls set-buffer on the buffer shown in the selected window (see Section 29.3 [Selecting
Windows], page 696). This is to prevent confusion: it ensures that the buffer that the cursor
is in, when Emacs reads a command, is the buffer to which that command applies (seeChapter 22 [Command Loop], page 423). Thus, you should not use set-buffer to switch
visibly to a different buffer; for that, use the functions described in Section 29.12 [Switching
Buffers], page 721.
When writing a Lisp function, do not rely on this behavior of the command loop to
restore the current buffer after an operation. Editing commands can also be called as Lisp
functions by other programs, not just from the command loop; it is convenient for the caller
if the subroutine does not change which buffer is current (unless, of course, that is thesubroutine’s purpose).
To operate temporarily on another buffer, put the set-buffer within a save-currentbuffer form. Here, as an example, is a simplified version of the command append-tobuffer:(defun append-to-buffer (buffer start end)
"Append the text of the region to BUFFER."(interactive "BAppend to buffer: \nr")(let ((oldbuf (current-buffer)))(save-current-buffer(set-buffer (get-buffer-create buffer))(insert-buffer-substring oldbuf start end))))Here, we bind a local variable to record the current buffer, and then save-current-buffer
arranges to make it current again later. Next, set-buffer makes the specified buffer current,
and insert-buffer-substring copies the string from the original buffer to the specified(and now current) buffer.
Alternatively, we can use the with-current-buffer macro:(defun append-to-buffer (buffer start end)
"Append the text of the region to BUFFER."(interactive "BAppend to buffer: \nr")(let ((oldbuf (current-buffer)))(with-current-buffer (get-buffer-create buffer)(insert-buffer-substring oldbuf start end))))In either case, if the buffer appended to happens to be displayed in some window, thenext redisplay will show how its text has changed. If it is not displayed in any window,

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you will not see the change immediately on the screen. The command causes the buffer tobecome current temporarily, but does not cause it to be displayed.
If you make local bindings (with let or function arguments) for a variable that may also
have buffer-local bindings, make sure that the same buffer is current at the beginning and at
the end of the local binding’s scope. Otherwise you might bind it in one buffer and unbind
it in another!
Do not rely on using set-buffer to change the current buffer back, because that won’t
do the job if a quit happens while the wrong buffer is current. For instance, in the previous
example, it would have been wrong to do this:(let ((oldbuf (current-buffer)))(set-buffer (get-buffer-create buffer))(insert-buffer-substring oldbuf start end)
(set-buffer oldbuf))
Using save-current-buffer or with-current-buffer, as we did, correctly handles quitting, errors, and throw, as well as ordinary evaluation.

save-current-buffer body. . .

[Special Form]
The save-current-buffer special form saves the identity of the current buffer,evaluates the body forms, and finally restores that buffer as current. The return value
is the value of the last form in body. The current buffer is restored even in case of anabnormal exit via throw or error (see Section 11.7 [Nonlocal Exits], page 177).
If the buffer that used to be current has been killed by the time of exit fromsave-current-buffer, then it is not made current again, of course. Instead, whichever
buffer was current just before exit remains current.

with-current-buffer buffer-or-name body. . .

[Macro]The with-current-buffer macro saves the identity of the current buffer, makes
buffer-or-name current, evaluates the body forms, and finally restores the current
buffer. buffer-or-name must specify an existing buffer or the name of an existing
buffer.
The return value is the value of the last form in body. The current buffer is restored
even in case of an abnormal exit via throw or error (see Section 11.7 [Nonlocal Exits],
page 177).

with-temp-buffer body. . .

[Macro]The with-temp-buffer macro evaluates the body forms with a temporary buffer as
the current buffer. It saves the identity of the current buffer, creates a temporary
buffer and makes it current, evaluates the body forms, and finally restores the previous
current buffer while killing the temporary buffer.
By default, undo information (see Section 33.9 [Undo], page 895) is not recordedin the buffer created by this macro (but body can enable that, if needed). The
temporary buffer also does not run the hooks kill-buffer-hook, kill-bufferquery-functions (see Section 28.10 [Killing Buffers], page 685), and buffer-listupdate-hook (see Section 28.8 [Buffer List], page 681).
The return value is the value of the last form in body. You can return the contents ofthe temporary buffer by using (buffer-string) as the last form.

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The current buffer is restored even in case of an abnormal exit via throw or error (seeSection 11.7 [Nonlocal Exits], page 177).
See also with-temp-file in [Writing to Files], page 617.

28.3 Buffer Names
Each buffer has a unique name, which is a string. Many of the functions that work on buffers
accept either a buffer or a buffer name as an argument. Any argument called buffer-or-nameis of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument
called buffer must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user have names startingwith a space, so that the list-buffers and buffer-menu commands don’t mention them(but if such a buffer visits a file, it is mentioned). A name starting with space also initiallydisables recording undo information; see Section 33.9 [Undo], page 895.

buffer-name &optional buffer[Function]
This function returns the name of buffer as a string. buffer defaults to the current
buffer.
If buffer-name returns nil, it means that buffer has been killed. See Section 28.10[Killing Buffers], page 685.
(buffer-name)⇒ "buffers.texi"(setq foo (get-buffer "temp"))⇒ #<buffer temp>(kill-buffer foo)⇒ nil(buffer-name foo)
⇒ nil
foo
⇒ #<killed buffer>rename-buffer newname &optional unique[Command]This function renames the current buffer to newname. An error is signaled if newname
is not a string.
Ordinarily, rename-buffer signals an error if newname is already in use. However, if
unique is non-nil, it modifies newname to make a name that is not in use. Interactively,
you can make unique non-nil with a numeric prefix argument. (This is how thecommand rename-uniquely is implemented.)
This function returns the name actually given to the buffer.

get-buffer buffer-or-name[Function]
This function returns the buffer specified by buffer-or-name. If buffer-or-name is astring and there is no buffer with that name, the value is nil. If buffer-or-name is abuffer, it is returned as given; that is not very useful, so the argument is usually aname. For example:(setq b (get-buffer "lewis"))⇒ #<buffer lewis>

Chapter 28: Buffers

675(get-buffer b)⇒ #<buffer lewis>(get-buffer "Frazzle-nots")⇒ nil
See also the function get-buffer-create in Section 28.9 [Creating Buffers], page 684.

generate-new-buffer-name starting-name &optional ignore[Function]
This function returns a name that would be unique for a new buffer—but does notcreate the buffer. It starts with starting-name, and produces a name not currently inuse for any buffer by appending a number inside of ‘<...>’. It starts at 2 and keeps
incrementing the number until it is not the name of an existing buffer.
If the optional second argument ignore is non-nil, it should be a string, a potential
buffer name. It means to consider that potential buffer acceptable, if it is tried, even
if it is the name of an existing buffer (which would normally be rejected). Thus, if
buffers named ‘foo’, ‘foo<2>’, ‘foo<3>’ and ‘foo<4>’ exist,(generate-new-buffer-name "foo")⇒ "foo<5>"(generate-new-buffer-name "foo" "foo<3>")⇒ "foo<3>"(generate-new-buffer-name "foo" "foo<6>")⇒ "foo<5>"
See the related function generate-new-buffer in Section 28.9 [Creating Buffers],
page 684.

28.4 Buffer File Name
The buffer file name is the name of the file that is visited in that buffer. When a buffer
is not visiting a file, its buffer file name is nil. Most of the time, the buffer name is thesame as the nondirectory part of the buffer file name, but the buffer file name and the buffername are distinct and can be set independently. See Section 26.1 [Visiting Files], page 608.

buffer-file-name &optional buffer[Function]
This function returns the absolute file name of the file that buffer is visiting. If buffer
is not visiting any file, buffer-file-name returns nil. If buffer is not supplied, it
defaults to the current buffer.
(buffer-file-name (other-buffer))⇒ "/usr/user/lewis/manual/files.texi"[Variable]
This buffer-local variable contains the name of the file being visited in the current
buffer, or nil if it is not visiting a file. It is a permanent local variable, unaffected bykill-all-local-variables.
buffer-file-name⇒ "/usr/user/lewis/manual/buffers.texi"
It is risky to change this variable’s value without doing various other things. Normally
it is better to use set-visited-file-name (see below); some of the things done there,
such as changing the buffer name, are not strictly necessary, but others are essential
to avoid confusing Emacs.

buffer-file-nameChapter 28: Buffers

676[Variable]
This buffer-local variable holds the abbreviated truename of the file visited in the current buffer, or nil if no file is visited. It is a permanent local, unaffected by kill-alllocal-variables. See Section 26.6.3 [Truenames], page 623, and [abbreviate-filename], page 639.

buffer-file-truename[Variable]
This buffer-local variable holds the inode number and device identifier of the file visitedin the current buffer, or nil if no file or a nonexistent file is visited. It is a permanent
local, unaffected by kill-all-local-variables.

buffer-file-number

The value is normally a list of the form (inodenum device). This tuple uniquely identifies the file among all files accessible on the system. See the function file-attributes,
in Section 26.6.4 [File Attributes], page 624, for more information about them.
If buffer-file-name is the name of a symbolic link, then both inodenum and device
refer to the recursive target of the link.

get-file-buffer filename[Function]
This function returns the buffer visiting file filename. If there is no such buffer,
it returns nil. The argument filename, which must be a string, is expanded (seeSection 26.9.4 [File Name Expansion], page 639), then compared against the visited
file names of all live buffers. Note that the buffer’s buffer-file-name must matchthe expansion of filename exactly. This function will not recognize other names forthe same file.
(get-file-buffer "buffers.texi")⇒ #<buffer buffers.texi>
In unusual circumstances, there can be more than one buffer visiting the same file
name. In such cases, this function returns the first such buffer in the buffer list.

find-buffer-visiting filename &optional predicate[Function]
This is like get-file-buffer, except that it can return any buffer visiting the filepossibly under a different name. That is, the buffer’s buffer-file-name does notneed to match the expansion of filename exactly, it only needs to refer to the same
file. If predicate is non-nil, it should be a function of one argument, a buffer visiting
filename. The buffer is only considered a suitable return value if predicate returns
non-nil. If it can not find a suitable buffer to return, find-buffer-visiting returns
nil.

set-visited-file-name filename &optional no-queryalong-with-file[Command]If filename is a non-empty string, this function changes the name of the file visited in
the current buffer to filename. (If the buffer had no visited file, this gives it one.) The
next time the buffer is saved it will go in the newly-specified file.
This command marks the buffer as modified, since it does not (as far as Emacs knows)
match the contents of filename, even if it matched the former visited file. It alsorenames the buffer to correspond to the new file name, unless the new name is alreadyin use.

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If filename is nil or the empty string, that stands for “no visited file”. In this case,set-visited-file-name marks the buffer as having no visited file, without changing
the buffer’s modified flag.
Normally, this function asks the user for confirmation if there already is a buffer
visiting filename. If no-query is non-nil, that prevents asking this question. If there
already is a buffer visiting filename, and the user confirms or no-query is non-nil,this function makes the new buffer name unique by appending a number inside of‘<...>’ to filename.
If along-with-file is non-nil, that means to assume that the former visited file has
been renamed to filename. In this case, the command does not change the buffer’s
modified flag, nor the buffer’s recorded last file modification time as reported byvisited-file-modtime (see Section 28.6 [Modification Time], page 678). If alongwith-file is nil, this function clears the recorded last file modification time, after
which visited-file-modtime returns zero.
When the function set-visited-file-name is called interactively, it prompts forfilename in the minibuffer.
[Variable]
This buffer-local variable specifies a string to display in a buffer listing where thevisited file name would go, for buffers that don’t have a visited file name. Dired buffers
use this variable.

list-buffers-directory

28.5 Buffer Modification
Emacs keeps a flag called the modified flag for each buffer, to record whether you havechanged the text of the buffer. This flag is set to t whenever you alter the contents of thebuffer, and cleared to nil when you save it. Thus, the flag shows whether there are unsavedchanges. The flag value is normally shown in the mode line (see Section 24.4.4 [Mode Line
Variables], page 554), and controls saving (see Section 26.2 [Saving Buffers], page 612) andauto-saving (see Section 27.2 [Auto-Saving], page 664).
Some Lisp programs set the flag explicitly. For example, the function set-visitedfile-name sets the flag to t, because the text does not match the newly-visited file, even if
it is unchanged from the file formerly visited.
The functions that modify the contents of buffers are described in Chapter 33 [Text],
page 878.

buffer-modified-p &optional buffer[Function]
This function returns non-nil if buffer has been modified since it was last read infrom a file or saved, or nil otherwise. If buffer has been auto-saved since the time
it was last modified, this function returns the symbol autosaved. If buffer is nil oromitted, it defaults to the current buffer.

set-buffer-modified-p flag

[Function]
This function marks the current buffer as modified if flag is non-nil, or as unmodified
if the flag is nil.

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Another effect of calling this function is to cause unconditional redisplay of the modeline for the current buffer. In fact, the function force-mode-line-update works bydoing this:(set-buffer-modified-p (buffer-modified-p))

restore-buffer-modified-p flag

[Function]
Like set-buffer-modified-p, but does not force redisplay of mode lines. Thisfunction also allows flag’s value to be the symbol autosaved, which marks the buffer
as modified and auto-saved after the last modification.

not-modified &optional arg[Command]This command marks the current buffer as unmodified, and not needing to be saved.
If arg is non-nil, it marks the buffer as modified, so that it will be saved at the next
suitable occasion. Interactively, arg is the prefix argument.
Don’t use this function in programs, since it prints a message in the echo area; use
set-buffer-modified-p (above) instead.

buffer-modified-tick &optional buffer[Function]
This function returns buffer’s modification-count. This is a counter that increments
every time the buffer is modified. If buffer is nil (or omitted), the current buffer isused.

buffer-chars-modified-tick &optional buffer[Function]
This function returns buffer’s character-change modification-count. Changes to text
properties leave this counter unchanged; however, each time text is inserted or removed from the buffer, the counter is reset to the value that would be returned bybuffer-modified-tick. By comparing the values returned by two buffer-charsmodified-tick calls, you can tell whether a character change occurred in that buffer
in between the calls. If buffer is nil (or omitted), the current buffer is used.

Sometimes there’s a need for modifying buffer in a way that doesn’t really change
its text, like if only its text properties are changed. If your program needs to modify abuffer without triggering any hooks and features that react to buffer modifications, use thewith-silent-modifications macro.

with-silent-modifications body. . .

[Macro]Execute body pretending it does not modify the buffer. This includes checking whether
the buffer’s file is locked (see Section 26.5 [File Locks], page 617), running buffer
modification hooks (see Section 33.34 [Change Hooks], page 961), etc. Note that if
body actually modifies the buffer text (as opposed to its text properties), its undodata may become corrupted.

28.6 Buffer Modification Time
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself ischanged on disk. At this point, saving the buffer would overwrite the changes in the file.
Occasionally this may be what you want, but usually it would lose valuable information.
Emacs therefore checks the file’s modification time using the functions described below
before saving the file. (See Section 26.6.4 [File Attributes], page 624, for how to examine afile’s modification time.)

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verify-visited-file-modtime &optional buffer[Function]
This function compares what buffer (by default, the current-buffer) has recorded forthe modification time of its visited file against the actual modification time of the file
as recorded by the operating system. The two should be the same unless some otherprocess has written the file since Emacs visited or saved it.
The function returns t if the last actual modification time and Emacs’s recorded
modification time are the same, nil otherwise. It also returns t if the buffer has norecorded last modification time, that is if visited-file-modtime would return zero.
It always returns t for buffers that are not visiting a file, even if visited-filemodtime returns a non-zero value. For instance, it always returns t for dired buffers.
It returns t for buffers that are visiting a file that does not exist and never existed,
but nil for file-visiting buffers whose file has been deleted.
[Function]
This function clears out the record of the last modification time of the file being
visited by the current buffer. As a result, the next attempt to save this buffer will notcomplain of a discrepancy in file modification times.

clear-visited-file-modtime

This function is called in set-visited-file-name and other exceptional places where
the usual test to avoid overwriting a changed file should not be done.
[Function]
This function returns the current buffer’s recorded last file modification time, as a
Lisp timestamp (see Section 42.5 [Time of Day], page 1270).

visited-file-modtime

If the buffer has no recorded last modification time, this function returns zero. Thiscase occurs, for instance, if the buffer is not visiting a file or if the time has been explicitly cleared by clear-visited-file-modtime. Note, however, that visited-filemodtime returns a timestamp for some non-file buffers too. For instance, in a Diredbuffer listing a directory, it returns the last modification time of that directory, as
recorded by Dired.
If the buffer is visiting a file that doesn’t exist, this function returns −1.

set-visited-file-modtime &optional time

[Function]
This function updates the buffer’s record of the last modification time of the visited file,to the value specified by time if time is not nil, and otherwise to the last modification
time of the visited file.
If time is neither nil nor an integer flag returned by visited-file-modtime, it
should be a Lisp time value (see Section 42.5 [Time of Day], page 1270).
This function is useful if the buffer was not read from the file normally, or if the fileitself has been changed for some known benign reason.

ask-user-about-supersession-threat filename[Function]
This function is used to ask a user how to proceed after an attempt to modify a buffer
visiting file filename when the file is newer than the buffer text. Emacs detects thisbecause the modification time of the file on disk is newer than the last save-time andits contents have changed. This means some other program has probably altered thefile.

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Depending on the user’s answer, the function may return normally, in which case themodification of the buffer proceeds, or it may signal a file-supersession error withdata (filename), in which case the proposed buffer modification is not allowed.
This function is called automatically by Emacs on the proper occasions. It exists so
you can customize Emacs by redefining it. See the file userlock.el for the standard
definition.
See also the file locking mechanism in Section 26.5 [File Locks], page 617.

28.7 Read-Only Buffers
If a buffer is read-only, then you cannot change its contents, although you may change yourview of the contents by scrolling and narrowing.
Read-only buffers are used in two kinds of situations:• A buffer visiting a write-protected file is normally read-only.
Here, the purpose is to inform the user that editing the buffer with the aim of saving itin the file may be futile or undesirable. The user who wants to change the buffer text
despite this can do so after clearing the read-only flag with C-x C-q.
• Modes such as Dired and Rmail make buffers read-only when altering the contents withthe usual editing commands would probably be a mistake.
The special commands of these modes bind buffer-read-only to nil (with let) orbind inhibit-read-only to t around the places where they themselves change thetext.
[Variable]
This buffer-local variable specifies whether the buffer is read-only. The buffer is readonly if this variable is non-nil. However, characters that have the inhibit-read-only
text property can still be modified. See Section 33.19.4 [Special Properties], page 924.

buffer-read-only[Variable]
If this variable is non-nil, then read-only buffers and, depending on the actual value,
some or all read-only characters may be modified. Read-only characters in a buffer
are those that have a non-nil read-only text property. See Section 33.19.4 [Special
Properties], page 924, for more information about text properties.
If inhibit-read-only is t, all read-only character properties have no effect. If
inhibit-read-only is a list, then read-only character properties have no effect ifthey are members of the list (comparison is done with eq).

inhibit-read-only

read-only-mode &optional arg[Command]This is the mode command for Read Only minor mode, a buffer-local minor mode.
When the mode is enabled, buffer-read-only is non-nil in the buffer; when disabled,buffer-read-only is nil in the buffer. The calling convention is the same as forother minor mode commands (see Section 24.3.1 [Minor Mode Conventions], page 544).
This minor mode mainly serves as a wrapper for buffer-read-only; unlike mostminor modes, there is no separate read-only-mode variable. Even when Read Only
mode is disabled, characters with non-nil read-only text properties remain read-only.
To temporarily ignore all read-only states, bind inhibit-read-only, as describedabove.

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When enabling Read Only mode, this mode command also enables View mode if theoption view-read-only is non-nil. See Section “Miscellaneous Buffer Operations”
in The GNU Emacs Manual. When disabling Read Only mode, it disables View mode
if View mode was enabled.

barf-if-buffer-read-only &optional position[Function]
This function signals a buffer-read-only error if the current buffer is read-only.
If the text at position (which defaults to point) has the inhibit-read-only text
property set, the error will not be raised.
See Section 22.2.1 [Using Interactive], page 424, for another way to signal an error if
the current buffer is read-only.

28.8 The Buffer List
The buffer list is a list of all live buffers. The order of the buffers in this list is based
primarily on how recently each buffer has been displayed in a window. Several functions,notably other-buffer, use this ordering. A buffer list displayed for the user also follows
this order.
Creating a buffer adds it to the end of the buffer list, and killing a buffer removes it fromthat list. A buffer moves to the front of this list whenever it is chosen for display in a window(see Section 29.12 [Switching Buffers], page 721) or a window displaying it is selected (seeSection 29.3 [Selecting Windows], page 696). A buffer moves to the end of the list when it isburied (see bury-buffer, below). There are no functions available to the Lisp programmer
which directly manipulate the buffer list.
In addition to the fundamental buffer list just described, Emacs maintains a local buffer
list for each frame, in which the buffers that have been displayed (or had their windows
selected) in that frame come first. (This order is recorded in the frame’s buffer-list frame
parameter; see Section 30.4.3.5 [Buffer Parameters], page 812.) Buffers never displayed inthat frame come afterward, ordered according to the fundamental buffer list.

buffer-list &optional frame[Function]
This function returns the buffer list, including all buffers, even those whose names
begin with a space. The elements are actual buffers, not their names.
If frame is a frame, this returns frame’s local buffer list. If frame is nil or omitted,
the fundamental buffer list is used: the buffers appear in order of most recent display
or selection, regardless of which frames they were displayed on.
(buffer-list)⇒ (#<buffer buffers.texi>#<buffer *Minibuf-1*> #<buffer buffer.c>#<buffer *Help*> #<buffer TAGS>);; Note that the name of the minibuffer;;
begins with a space!
(mapcar #'buffer-name (buffer-list))⇒ ("buffers.texi" " *Minibuf-1*""buffer.c" "*Help*" "TAGS")

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The list returned by buffer-list is constructed specifically; it is not an internal Emacs
data structure, and modifying it has no effect on the order of buffers. If you want to change
the order of buffers in the fundamental buffer list, here is an easy way:
(defun reorder-buffer-list (new-list)(while new-list(bury-buffer (car new-list))(setq new-list (cdr new-list))))With this method, you can specify any order for the list, but there is no danger of losing
a buffer or adding something that is not a valid live buffer.
To change the order or value of a specific frame’s buffer list, set that frame’s
buffer-list parameter with modify-frame-parameters (see Section 30.4.1 [Parameter
Access], page 803).

other-buffer &optional buffer visible-ok frame[Function]
This function returns the first buffer in the buffer list other than buffer. Usually, this isthe buffer appearing in the most recently selected window (in frame frame or else theselected frame, see Section 30.10 [Input Focus], page 824), aside from buffer. Buffers
whose names start with a space are not considered at all.
If buffer is not supplied (or if it is not a live buffer), then other-buffer returns thefirst buffer in the selected frame’s local buffer list. (If frame is non-nil, it returns thefirst buffer in frame’s local buffer list instead.)
If frame has a non-nil buffer-predicate parameter, then other-buffer uses thatpredicate to decide which buffers to consider. It calls the predicate once for each buffer,and if the value is nil, that buffer is ignored. See Section 30.4.3.5 [Buffer Parameters],
page 812.
If visible-ok is nil, other-buffer avoids returning a buffer visible in any window on
any visible frame, except as a last resort. If visible-ok is non-nil, then it does notmatter whether a buffer is displayed somewhere or not.
If no suitable buffer exists, the buffer *scratch* is returned (and created, if necessary).

last-buffer &optional buffer visible-ok frame[Function]
This function returns the last buffer in frame’s buffer list other than buffer. If frame
is omitted or nil, it uses the selected frame’s buffer list.
The argument visible-ok is handled as with other-buffer, see above. If no suitablebuffer can be found, the buffer *scratch* is returned.

bury-buffer &optional buffer-or-name[Command]This command puts buffer-or-name at the end of the buffer list, without changing theorder of any of the other buffers on the list. This buffer therefore becomes the least
desirable candidate for other-buffer to return. The argument can be either a buffer
itself or the name of one.
This function operates on each frame’s buffer-list parameter as well as the fundamental buffer list; therefore, the buffer that you bury will come last in the value of(buffer-list frame) and in the value of (buffer-list). In addition, it also puts
the buffer at the end of the list of buffers of the selected window (see Section 29.14[Window History], page 746) provided it is shown in that window.

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If buffer-or-name is nil or omitted, this means to bury the current buffer. In addition,
if the current buffer is displayed in the selected window (see Section 29.3 [Selecting
Windows], page 696), this makes sure that the window is either deleted or another buffer
is shown in it. More precisely, if the selected window is dedicated (see Section 29.15[Dedicated Windows], page 749) and there are other windows on its frame, the window
is deleted. If it is the only window on its frame and that frame is not the only frame on
its terminal, the frame is dismissed by calling the function specified by frame-autohide-function (see Section 29.16 [Quitting Windows], page 749). Otherwise, it calls
switch-to-prev-buffer (see Section 29.14 [Window History], page 746) to show
another buffer in that window. If buffer-or-name is displayed in some other window,
it remains displayed there.
To replace a buffer in all the windows that display it, use replace-buffer-in-windows,
See Section 29.11 [Buffers and Windows], page 720.
[Command]This command switches to the last buffer in the local buffer list of the selected frame.
More precisely, it calls the function switch-to-buffer (see Section 29.12 [Switching
Buffers], page 721), to display the buffer returned by last-buffer (see above), in theselected window.

unbury-buffer[Variable]
This is a normal hook run whenever the buffer list changes. Functions (implicitly)
running this hook are get-buffer-create (see Section 28.9 [Creating Buffers],
page 684), rename-buffer (see Section 28.3 [Buffer Names], page 674), kill-buffer(see Section 28.10 [Killing Buffers], page 685), bury-buffer (see above), andselect-window (see Section 29.3 [Selecting Windows], page 696). This hook
is not run for internal or temporary buffers created by get-buffer-create or
generate-new-buffer with a non-nil argument inhibit-buffer-hooks.

buffer-list-update-hook

Functions run by this hook should avoid calling select-window with a nil norecord
argument since this may lead to infinite recursion.

buffer-match-p condition buffer-or-name &optional arg[Function]
This function checks if a buffer designated by buffer-or-name satisfies the specified
condition. Optional third argument arg is passed to the predicate function in condition.
A valid condition can be one of the following:• A string, interpreted as a regular expression. The buffer satisfies the condition if
the regular expression matches the buffer name.
• A predicate function, which should return non-nil if the buffer matches. If thefunction expects one argument, it is called with buffer-or-name as the argument;
if it expects 2 arguments, the first argument is buffer-or-name and the second isarg (or nil if arg is omitted).
• A cons-cell (oper . expr) where oper is one of(not cond)
Satisfied if cond doesn’t satisfy buffer-match-p with the same buffer
and arg.

Chapter 28: Buffers684(or conds...)Satisfied if any condition in conds satisfies buffer-match-p, withthe same buffer and arg.
(and conds...)Satisfied if all the conditions in conds satisfy buffer-match-p, withthe same buffer and arg.
derived-mode
Satisfied if the buffer’s major mode derives from expr. Note that thiscondition might fail to report a match if buffer-match-p is invoked
before the major mode of the buffer has been established.
major-mode
Satisfied if the buffer’s major mode is equal to expr. Prefer using
derived-mode instead, when both can work. Note that this condition
might fail to report a match if buffer-match-p is invoked before themajor mode of the buffer has been established.
• t Satisfied by any buffer. A convenient alternative to "" (empty string) or (and)(empty conjunction).

match-buffers condition &optional buffer-list arg[Function]
This function returns a list of all buffers that satisfy the condition. If no buffers match,the function returns nil. The argument condition is as defined in buffer-match-p
above. By default, all the buffers are considered, but this can be restricted via theoptional argument buffer-list, which should be a list of buffers to consider. Optional
third argument arg will be passed to condition in the same way as buffer-match-p
does.

28.9 Creating Buffers
This section describes the two primitives for creating buffers. get-buffer-create creates abuffer if it finds no existing buffer with the specified name; generate-new-buffer always
creates a new buffer and gives it a unique name.
Both functions accept an optional argument inhibit-buffer-hooks. If it is non-nil,the buffer they create does not run the hooks kill-buffer-hook, kill-buffer-queryfunctions (see Section 28.10 [Killing Buffers], page 685), and buffer-list-update-hook(see Section 28.8 [Buffer List], page 681). This avoids slowing down internal or temporary
buffers that are never presented to users or passed on to other applications.
Other functions you can use to create buffers include with-output-to-temp-buffer (seeSection 41.8 [Temporary Displays], page 1146) and create-file-buffer (see Section 26.1
[Visiting Files], page 608). Starting a subprocess can also create a buffer (see Chapter 40[Processes], page 1078).

get-buffer-create buffer-or-name &optional inhibit-buffer-hooks[Function]
This function returns a buffer named buffer-or-name. The buffer returned does not
become the current buffer—this function does not change which buffer is current.
buffer-or-name must be either a string or an existing buffer. If it is a string and a live
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such buffer exists, it creates a new buffer. If buffer-or-name is a buffer instead of astring, it is returned as given, even if it is dead.
(get-buffer-create "foo")⇒ #<buffer foo>
The major mode for a newly created buffer is set to Fundamental mode. (The default
value of the variable major-mode is handled at a higher level; see Section 24.2.2 [AutoMajor Mode], page 531.) If the name begins with a space, the buffer initially disables
undo information recording (see Section 33.9 [Undo], page 895).

generate-new-buffer name &optional inhibit-buffer-hooks[Function]
This function returns a newly created, empty buffer, but does not make it current.
The name of the buffer is generated by passing name to the function generate-newbuffer-name (see Section 28.3 [Buffer Names], page 674). Thus, if there is no buffer
named name, then that is the name of the new buffer; if that name is in use, a suffixof the form ‘<n>’, where n is an integer, is appended to name.

An error is signaled if name is not a string.
(generate-new-buffer "bar")⇒ #<buffer bar>
(generate-new-buffer "bar")⇒ #<buffer bar<2>>(generate-new-buffer "bar")⇒ #<buffer bar<3>>
The major mode for the new buffer is set to Fundamental mode. The default value ofthe variable major-mode is handled at a higher level. See Section 24.2.2 [Auto MajorMode], page 531.

28.10 Killing Buffers
Killing a buffer makes its name unknown to Emacs and makes the memory space it occupied
available for other use.
The buffer object for the buffer that has been killed remains in existence as long as
anything refers to it, but it is specially marked so that you cannot make it current or display
it. Killed buffers retain their identity, however; if you kill two distinct buffers, they remain
distinct according to eq although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects
or displays some other buffer instead. This means that killing a buffer can change the current
buffer. Therefore, when you kill a buffer, you should also take the precautions associatedwith changing the current buffer (unless you happen to know that the buffer being killed
isn’t current). See Section 28.2 [Current Buffer], page 671.
If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect
buffers are automatically killed as well.
The buffer-name of a buffer is nil if, and only if, the buffer is killed. A buffer thathas not been killed is called a live buffer. To test whether a buffer is live or killed, use thefunction buffer-live-p (see below).

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kill-buffer &optional buffer-or-name[Command]This function kills the buffer buffer-or-name, freeing all its memory for other uses orto be returned to the operating system. If buffer-or-name is nil or omitted, it kills
the current buffer.
Any processes that have this buffer as the process-buffer are sent the SIGHUP(hangup) signal, which normally causes them to terminate. See Section 40.8 [Signals
to Processes], page 1097.
If the buffer is visiting a file and contains unsaved changes, kill-buffer asks the user
to confirm before the buffer is killed. It does this even if not called interactively. To
prevent the request for confirmation, clear the modified flag before calling kill-buffer.
See Section 28.5 [Buffer Modification], page 677.
This function calls replace-buffer-in-windows for cleaning up all windows currently
displaying the buffer to be killed.
Killing a buffer that is already dead has no effect.
This function returns t if it actually killed the buffer. It returns nil if the user refuses
to confirm or if buffer-or-name was already dead.
(kill-buffer "foo.unchanged")⇒ t(kill-buffer "foo.changed")---------- Buffer: Minibuffer ---------Buffer foo.changed modified; kill anyway? (yes or no) yes---------- Buffer: Minibuffer ---------⇒ t[Variable]
Before confirming unsaved changes, kill-buffer calls the functions in the list
kill-buffer-query-functions, in order of appearance, with no arguments. The
buffer being killed is the current buffer when they are called. The idea of this featureis that these functions will ask for confirmation from the user. If any of them returns
nil, kill-buffer spares the buffer’s life.
This hook is not run for internal or temporary buffers created by get-buffer-create
or generate-new-buffer with a non-nil argument inhibit-buffer-hooks.

kill-buffer-query-functions[Variable]
This is a normal hook run by kill-buffer after asking all the questions it is going toask, just before actually killing the buffer. The buffer to be killed is current when thehook functions run. See Section 24.1 [Hooks], page 524. This variable is a permanent
local, so its local binding is not cleared by changing major modes.
This hook is not run for internal or temporary buffers created by get-buffer-create
or generate-new-buffer with a non-nil argument inhibit-buffer-hooks.

kill-buffer-hook[User Option]
This variable, if non-nil in a particular buffer, tells save-buffers-kill-emacs to offer
to save that buffer, just as it offers to save file-visiting buffers. If save-some-buffers
is called with the second optional argument set to t, it will also offer to save the buffer.
Lastly, if this variable is set to the symbol always, both save-buffers-kill-emacs

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and save-some-buffers will always offer to save. See [Definition of save-some-buffers],
page 612. The variable buffer-offer-save automatically becomes buffer-local when
set for any reason. See Section 12.11 [Buffer-Local Variables], page 207.
[Variable]
This variable, if non-nil in a particular buffer, tells save-buffers-kill-emacs andsave-some-buffers to save this buffer (if it’s modified) without asking the user. The
variable automatically becomes buffer-local when set for any reason.

buffer-save-without-query

buffer-live-p object[Function]
This function returns t if object is a live buffer (a buffer which has not been killed),
nil otherwise.

28.11 Indirect Buffers
An indirect buffer shares the text of some other buffer, which is called the base buffer of theindirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files.
The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes
made by editing either one are visible immediately in the other. This includes the text
properties as well as the characters themselves.
In all other respects, the indirect buffer and its base buffer are completely separate. They
have different names, independent values of point, independent narrowing, independent
markers and overlays (though inserting or deleting text in either buffer relocates the markers
and overlays for both), independent major modes, and independent buffer-local variablebindings.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save theindirect buffer, that actually saves the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively
kills the indirect buffer in that it cannot ever again be the current buffer.

make-indirect-buffer base-buffer name &optional clone
inhibit-buffer-hooks[Command]This creates and returns an indirect buffer named name whose base buffer is basebuffer. The argument base-buffer may be a live buffer or the name (a string) of an
existing buffer. If name is the name of an existing buffer, an error is signaled.
If clone is non-nil, then the indirect buffer originally shares the state of base-buffer
such as major mode, minor modes, buffer local variables and so on. If clone is omitted
or nil the indirect buffer’s state is set to the default state for new buffers.
If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer.
If, in addition, clone is non-nil, the initial state is copied from the actual base buffer,
not from base-buffer.
See Section 28.9 [Creating Buffers], page 684, for the meaning of inhibit-buffer-hooks.

clone-indirect-buffer newname display-flag &optional norecord[Command]This function creates and returns a new indirect buffer that shares the current buffer’sbase buffer and copies the rest of the current buffer’s attributes. (If the current buffer
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If display-flag is non-nil, as it always is in interactive calls, that means to display the
new buffer by calling pop-to-buffer. If norecord is non-nil, that means not to put
the new buffer to the front of the buffer list.

buffer-base-buffer &optional buffer[Function]
This function returns the base buffer of buffer, which defaults to the current buffer. If
buffer is not indirect, the value is nil. Otherwise, the value is another buffer, which
is never an indirect buffer.

28.12 Swapping Text Between Two Buffers
Specialized modes sometimes need to let the user access from the same buffer several vastlydifferent types of text. For example, you may need to display a summary of the buffer text,
in addition to letting the user access the text itself.
This could be implemented with multiple buffers (kept in sync when the user edits thetext), or with narrowing (see Section 31.4 [Narrowing], page 865). But these alternatives
might sometimes become tedious or prohibitively expensive, especially if each type of text
requires expensive buffer-global operations in order to provide correct display and editing
commands.
Emacs provides another facility for such modes: you can quickly swap buffer text between
two buffers with buffer-swap-text. This function is very fast because it doesn’t move any
text, it only changes the internal data structures of the buffer object to point to a different
chunk of text. Using it, you can pretend that a group of two or more buffers are actually asingle virtual buffer that holds the contents of all the individual buffers together.

buffer-swap-text buffer[Function]
This function swaps the text of the current buffer and that of its argument buffer.
It signals an error if one of the two buffers is an indirect buffer (see Section 28.11[Indirect Buffers], page 687) or is a base buffer of an indirect buffer.
All the buffer properties that are related to the buffer text are swapped as well: thepositions of point and mark, all the markers, the overlays, the text properties, theundo list, the value of the enable-multibyte-characters flag (see Section 34.1 [Text
Representations], page 963), etc.
Warning: If this function is called from within a save-excursion form, the current buffer will be set to buffer upon leaving the form, since the marker used bysave-excursion to save the position and buffer will be swapped as well.

If you use buffer-swap-text on a file-visiting buffer, you should set up a hook to savethe buffer’s original text rather than what it was swapped with. write-region-annotatefunctions works for this purpose. You should probably set buffer-saved-size to −2 inthe buffer, so that changes in the text it is swapped with will not interfere with auto-saving.

28.13 The Buffer Gap
Emacs buffers are implemented using an invisible gap to make insertion and deletion faster.
Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, thismeans that the gap must first be moved to the locus of the insertion or deletion. Emacs
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in one part of a large buffer, after previously editing in another far-away part, sometimes
involves a noticeable delay.
This mechanism works invisibly, and Lisp code should never be affected by the gap’s
current location, but these functions are available for getting information about the gap
status.

gap-position[Function]

This function returns the current gap position in the current buffer.

gap-sizeThis function returns the current gap size of the current buffer.

[Function]

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29 Windows
This chapter describes the functions and variables related to Emacs windows. See Chapter 30[Frames], page 785, for how windows are assigned an area of screen available for Emacs
to use. See Chapter 41 [Display], page 1129, for information on how text is displayed inwindows.

29.1 Basic Concepts of Emacs Windows
A window is an area of the screen that can be used to display a buffer (see Chapter 28[Buffers], page 671). Windows are grouped into frames (see Chapter 30 [Frames], page 785).
Each frame contains at least one window; the user can subdivide a frame into multiple,
non-overlapping windows to view several buffers at once. Lisp programs can use multiple
windows for a variety of purposes. In Rmail, for example, you can view a summary of
message titles in one window, and the contents of the selected message in another window.
Emacs uses the term “window” with a different meaning than in graphical desktop
environments and window systems, such as the X Window System. When Emacs is run onX, each graphical X window owned by the Emacs process corresponds to one Emacs frame.
When Emacs is run on a text terminal, each Emacs frame fills the entire terminal screen. In
either case, the frame may contain one or more Emacs windows. For disambiguation, we use
the term window-system window when we mean the window-system window corresponding
to an Emacs frame.
Unlike X windows, Emacs windows are tiled; they never overlap within the area of theirframe. When a window is created, resized, or deleted, the change in window space is takenfrom or given to other windows on the same frame, so that the total area of the frame isunchanged.
In Emacs Lisp, windows are represented by a special Lisp object type (see Section 2.5.3[Window Type], page 27).

windowp object[Function]
This function returns t if object is a window (whether or not it displays a buffer).
Otherwise, it returns nil.

A live window is one that is actually displaying a buffer in a frame.

window-live-p object[Function]
This function returns t if object is a live window and nil otherwise. A live window is
one that displays a buffer.

The windows in each frame are organized into a window tree. See Section 29.2 [Windows
and Frames], page 692. The leaf nodes of each window tree are live windows—the ones
actually displaying buffers. The internal nodes of the window tree are internal windows,
which are not live.
A valid window is one that is either live or internal. A valid window can be deleted, i.e.,removed from its frame (see Section 29.8 [Deleting Windows], page 711); then it is no longer
valid, but the Lisp object representing it might be still referenced from other Lisp objects.
A deleted window may be made valid again by restoring a saved window configuration (seeSection 29.26 [Window Configurations], page 774).
You can distinguish valid windows from deleted windows with window-valid-p.

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window-valid-p object[Function]
This function returns t if object is a live window, or an internal window in a window
tree. Otherwise, it returns nil, including for the case where object is a deleted window.

The following schematic shows the structure of a live window:____________________________________________|________________ Tab Line _______________|RD| ^|______________ Header Line ______________| | |^ |LS|LM|LF||RF|RM|RS| | || | | | || | | | | |Window | | | || | | | | Window
Body | | | | |Window Body
| | | | | Total
Height | | | || | | | | Height| | | | |<- Window Body Width ->| | | | | |v |__|__|__|_______________________|__|__|__| | ||_________ Horizontal Scroll Bar _________| | ||_______________ Mode Line _______________|__| ||_____________ Bottom Divider _______________| v<---------- Window Total Width ------------>At the center of that window is the body, where the buffer text is displayed. The bodycan be surrounded by a series of optional areas which we will call window decorations. On
the left and right, from innermost to outermost, these are the left and right fringes, denotedby LF and RF (see Section 41.13 [Fringes], page 1189); the left and right margins, denoted
by LM and RM in the schematic (see Section 41.16.5 [Display Margins], page 1205); theleft or right vertical scroll bar, only one of which is present at any time, denoted by LS andRS (see Section 41.14 [Scroll Bars], page 1195); and the right divider, denoted by RD (seeSection 41.15 [Window Dividers], page 1198). Together these are the window’s left and rightdecorations.
At the top of the window are the tab line and the header line (see Section 24.4.7 [Header
Lines], page 559). The text area of the window includes the header line and the tab line,
if they are present in the window. At the bottom of the window are the horizontal scrollbar (see Section 41.14 [Scroll Bars], page 1195); the mode line (see Section 24.4 [ModeLine Format], page 550); and the bottom divider (see Section 41.15 [Window Dividers],
page 1198). Together these form the window’s top and bottom decorations.
There are two special areas omitted in the schematic:• When any of the fringes is missing, the display engine may use one character cell in its
place for showing a continuation or truncation glyph provided a text line doesn’t fit ina window.
• When both, the vertical scroll bar and the right divider are missing, the display engine
usurps one pixel for drawing a vertical divider line between this window and the window
on its right, provided such a window exists. On a text terminal, this divider always
occupies an entire character cell.
In either case, the resulting artifact is considered part of the window’s body although its
screen space cannot be used for displaying buffer text.
Note also, that line numbers (and their surrounding whitespace) as displayed bydisplay-line-numbers-mode (see Section “Display Custom” in The GNU Emacs Manual)
do not count as decorations either; they are part of the window’s body too.

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Internal windows neither show any text nor do they have decorations. Hence, the conceptof “body” does not make sense for them. In fact, most functions operating on the body of awindow will yield an error when applied to an internal window.
By default, an Emacs frame exhibits one special live window that is used for displaying
messages and accepting user input—the minibuffer window (see Section 21.11 [Minibuffer
Windows], page 418). Since the minibuffer window is used for displaying text, it has a body
but it does not have a tab or header line or any margins. Finally, a tooltip window which isused for displaying a tooltip in a tooltip frame (see Section 41.26 [Tooltips], page 1249) hasa body too but no decorations at all.

29.2 Windows and Frames
Each window belongs to exactly one frame (see Chapter 30 [Frames], page 785). For all
windows belonging to a specific frame, we sometimes also say that these windows are ownedby that frame or simply that they are on that frame.

window-frame &optional window[Function]
This function returns the specified window’s frame—the frame that window belongs
to. If window is omitted or nil, it defaults to the selected window (see Section 29.3
[Selecting Windows], page 696).

window-list &optional frame minibuffer window[Function]
This function returns a list of all live windows owned by the specified frame. If frame
is omitted or nil, it defaults to the selected frame (see Section 30.10 [Input Focus],
page 824).
The optional argument minibuffer specifies whether to include the minibuffer window(see Section 21.11 [Minibuffer Windows], page 418) in that list. If minibuffer is t, theminibuffer window is included. If nil or omitted, the minibuffer window is included
only if it is active. If minibuffer is neither nil nor t, the minibuffer window is neverincluded.
The optional argument window, if non-nil, must be a live window on the specified
frame; then window will be the first element in the returned list. If window is omitted
or nil, the window selected within frame (see Section 29.3 [Selecting Windows],
page 696) is the first element.

Windows on the same frame are organized into a window tree, whose leaf nodes are thelive windows. The internal nodes of a window tree are not live; they exist for the purposeof organizing the relationships between live windows. The root node of a window tree iscalled the root window. It is either a live window or an internal window. If it is a live
window, then the frame has just one window besides the minibuffer window, or the frame isa minibuffer-only frame, see Section 30.3.1 [Frame Layout], page 791.
A minibuffer window (see Section 21.11 [Minibuffer Windows], page 418) that is not alone
on its frame does not have a parent window, so it strictly speaking is not part of its frame’s
window tree. Nonetheless, it is a sibling window of the frame’s root window, and thus canbe reached from the root window via window-next-sibling, see below. Also, the function
window-tree described at the end of this section lists the minibuffer window alongside theactual window tree.

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frame-root-window &optional frame-or-window[Function]
This function returns the root window for frame-or-window. The argument frame-orwindow should be either a window or a frame; if omitted or nil, it defaults to theselected frame. If frame-or-window is a window, the return value is the root windowof that window’s frame.

When a live window is split (see Section 29.7 [Splitting Windows], page 708), there are
two live windows where previously there was one. One of these is represented by the same
Lisp window object as the original window, and the other is represented by a newly-created
Lisp window object. Both of these live windows become leaf nodes of the window tree, as
child windows of a single internal window. If necessary, Emacs automatically creates thisinternal window, which is also called the parent window, and assigns it to the appropriate
position in the window tree. The set of windows that share the same parent are called
siblings.

window-parent &optional window[Function]
This function returns the parent window of window. If window is omitted or nil, it
defaults to the selected window. The return value is nil if window has no parent (i.e.,
it is a minibuffer window or the root window of its frame).

A parent window always has at least two child windows. If this number were to fall to
one as a result of window deletion (see Section 29.8 [Deleting Windows], page 711), Emacs
automatically deletes the parent window too, and its sole remaining child window takes its
place in the window tree.
A child window can be either a live window, or an internal window (which in turn would
have its own child windows). Therefore, each internal window can be thought of as occupyinga certain rectangular screen area—the union of the areas occupied by the live windows thatare ultimately descended from it.
For each internal window, the screen areas of the immediate children are arranged either
vertically or horizontally (never both). If the child windows are arranged one above theother, they are said to form a vertical combination; if they are arranged side by side, they
are said to form a horizontal combination. Consider the following example:______________________________________| ______ ____________________________ ||||| __________________________ ||
||
|||
|||
||
|||
|||
||
|||
|||
||
|||____________W4____________||||||| __________________________ ||
||
|||
|||
||
|||
|||
||
|||____________W5____________|||||__W2__||_____________W3_____________ ||__________________W1__________________|The root window of this frame is an internal window, W1. Its child windows form a horizontal
combination, consisting of the live window W2 and the internal window W3. The childwindows of W3 form a vertical combination, consisting of the live windows W4 and W5.
Hence, the live windows in this window tree are W2, W4, and W5.

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The following functions can be used to retrieve a child window of an internal window,
and the siblings of a child window. Their window argument always defaults to the selected
window (see Section 29.3 [Selecting Windows], page 696).

window-top-child &optional window[Function]
This function returns the topmost child window of window, if window is an internal
window whose children form a vertical combination. For any other type of window,
the return value is nil.

window-left-child &optional window[Function]
This function returns the leftmost child window of window, if window is an internal
window whose children form a horizontal combination. For any other type of window,
the return value is nil.

window-child window[Function]
This function returns the first child window of the internal window window—the
topmost child window for a vertical combination, or the leftmost child window for ahorizontal combination. If window is a live window, the return value is nil.

window-combined-p &optional window horizontal[Function]
This function returns a non-nil value if and only if window is part of a vertical
combination.
If the optional argument horizontal is non-nil, this means to return non-nil if andonly if window is part of a horizontal combination.

window-next-sibling &optional window[Function]
This function returns the next sibling of the specified window. The return value isnil if window is the last child of its parent.

window-prev-sibling &optional window[Function]
This function returns the previous sibling of the specified window. The return value isnil if window is the first child of its parent.

The functions window-next-sibling and window-prev-sibling should not be confusedwith the functions next-window and previous-window, which return the next and previous
window in the cyclic ordering of windows (see Section 29.10 [Cyclic Window Ordering],
page 717).
The following functions can be useful to locate a window within its frame.

frame-first-window &optional frame-or-window[Function]
This function returns the live window at the upper left corner of the frame specified
by frame-or-window. The argument frame-or-window must denote a window or a live
frame and defaults to the selected frame. If frame-or-window specifies a window, thisfunction returns the first window on that window’s frame. Under the assumption thatthe frame from our canonical example is selected (frame-first-window) returns W2.

window-at-side-p &optional window side

[Function]
This function returns t if window is located at side of its containing frame. The
argument window must be a valid window and defaults to the selected one. The

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argument side can be any of the symbols left, top, right or bottom. The default
value nil is handled like bottom.
Note that this function disregards the minibuffer window (see Section 21.11 [Minibuffer
Windows], page 418). Hence, with side equal to bottom it may return t also whenthe minibuffer window appears right below window.

window-in-direction direction &optional window ignore sign wrap
minibuf[Function]

This function returns the nearest live window in direction direction as seen from theposition of window-point in window window. The argument direction must be oneof above, below, left or right. The optional argument window must denote a live
window and defaults to the selected one.
This function does not return a window whose no-other-window parameter is nonnil (see Section 29.27 [Window Parameters], page 776). If the nearest window’s
no-other-window parameter is non-nil, this function tries to find another window
in the indicated direction whose no-other-window parameter is nil. If the optional
argument ignore is non-nil, a window may be returned even if its no-other-window
parameter is non-nil.
If the optional argument sign is a negative number, it means to use the right or bottomedge of window as reference position instead of window-point. If sign is a positive
number, it means to use the left or top edge of window as reference position.
If the optional argument wrap is non-nil, this means to wrap direction around frame
borders. For example, if window is at the top of the frame and direction is above,
then this function usually returns the frame’s minibuffer window if it’s active and awindow at the bottom of the frame otherwise.
If the optional argument minibuf is t, this function may return the minibuffer window
even when it’s not active. If the optional argument minibuf is nil, this means toreturn the minibuffer window if and only if it is currently active. If minibuf is neither
nil nor t, this function never returns the minibuffer window. However, if wrap is
non-nil, it always acts as if minibuf were nil.
If it doesn’t find a suitable window, this function returns nil.
Don’t use this function to check whether there is no window in direction. Calling
window-at-side-p described above is a much more efficient way to do that.
The following function retrieves the entire window tree of a frame:

window-tree &optional frame[Function]
This function returns a list representing the window tree for frame frame. If frame isomitted or nil, it defaults to the selected frame.
The return value is a list of the form (root mini), where root represents the window
tree of the frame’s root window, and mini is the frame’s minibuffer window.
If the root window is live, root is that window itself. Otherwise, root is a list (diredges w1 w2 ...) where dir is nil for a horizontal combination and t for a vertical
combination, edges gives the size and position of the combination, and the remaining
elements are the child windows. Each child window may again be a window object(for a live window) or a list with the same format as above (for an internal window).

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The edges element is a list (left top right bottom), similar to the value returned
by window-edges (see Section 29.24 [Coordinates and Windows], page 769).

29.3 Selecting Windows
In each frame, at any time, exactly one Emacs window is designated as selected within
the frame. For the selected frame, that window is called the selected window—the one inwhich most editing takes place, and in which the cursor for selected windows appears (seeSection 30.4.3.9 [Cursor Parameters], page 817). Keyboard input that inserts or deletes text
is also normally directed to this window. The selected window’s buffer is usually also thecurrent buffer, except when set-buffer has been used (see Section 28.2 [Current Buffer],
page 671). As for non-selected frames, the window selected within the frame becomes theselected window if the frame is ever selected.
[Function]
This function returns the selected window (which is always a live window).

selected-window

The following function explicitly selects a window and its frame.

select-window window &optional norecord[Function]
This function makes window the selected window and the window selected within
its frame, and selects that frame. It also makes window’s buffer (see Section 29.11[Buffers and Windows], page 720) current and sets that buffer’s value of point tothe value of window-point (see Section 29.19 [Window Point], page 758) in window.
window must be a live window. The return value is window.
By default, this function also moves window’s buffer to the front of the buffer list (seeSection 28.8 [Buffer List], page 681) and makes window the most recently selected
window. If the optional argument norecord is non-nil, these additional actions areomitted.
In addition, this function by default also tells the display engine to update the displayof window when its frame gets redisplayed the next time. If norecord is non-nil,such updates are usually not performed. If, however, norecord equals the special
symbol mark-for-redisplay, the additional actions mentioned above are omitted
but window’s display will be nevertheless updated.
Note that sometimes selecting a window is not enough to show it, or make its frame
the top-most frame on display: you may also need to raise the frame or make sure
input focus is directed to that frame. See Section 30.10 [Input Focus], page 824.

For historical reasons, Emacs does not run a separate hook whenever a window getsselected. Applications and internal routines often temporarily select a window to performa few actions on it. They do that either to simplify coding—because many functions bydefault operate on the selected window when no window argument is specified—or becausesome functions did not (and still do not) take a window as argument and always operate(d)on the selected window instead. Running a hook every time a window gets selected for ashort time and once more when the previously selected window gets restored is not useful.
However, when its norecord argument is nil, select-window updates the buffer list andthus indirectly runs the normal hook buffer-list-update-hook (see Section 28.8 [BufferChapter 29: Windows

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List], page 681). Consequently, that hook provides one way to run a function whenever awindow gets selected more “permanently”.
Since buffer-list-update-hook is also run by functions that are not related to window
management, it will usually make sense to save the value of the selected window somewhere
and compare it with the value of selected-window while running that hook. Also, toavoid false positives when using buffer-list-update-hook, it is good practice that every
select-window call supposed to select a window only temporarily passes a non-nil norecord
argument. If possible, the macro with-selected-window (see below) should be used insuch cases.
Emacs also runs the hook window-selection-change-functions whenever the redisplay
routine detects that another window has been selected since last redisplay. See Section 29.28[Window Hooks], page 779, for a detailed explanation. window-state-change-functions(described in the same section) is another abnormal hook run after a different window has
been selected but is triggered by other window changes as well.
The sequence of calls to select-window with a non-nil norecord argument determines anordering of windows by their selection or use time, see below. The function get-lru-window,
for example, can then be used to retrieve the least recently selected window (see Section 29.10[Cyclic Window Ordering], page 717).

frame-selected-window &optional frame[Function]
This function returns the window on frame that is selected within that frame. frame
should be a live frame; if omitted or nil, it defaults to the selected frame.

set-frame-selected-window frame window &optional norecord[Function]
This function makes window the window selected within the frame frame. frame
should be a live frame; if nil, it defaults to the selected frame. window must denotea live window.
If frame is the selected frame, this makes window the selected window.
If the optional argument norecord is non-nil, this function does not alter the orderingof the most recently selected windows, nor the buffer list.

The following macros are useful to temporarily select a window without affecting theordering of recently selected windows or the buffer list.

save-selected-window forms. . .

[Macro]This macro records the selected frame, as well as the selected window of each frame,
executes forms in sequence, then restores the earlier selected frame and windows. It
also saves and restores the current buffer. It returns the value of the last form informs.
This macro does not save or restore anything about the sizes, arrangement or contentsof windows; therefore, if forms change them, the change persists. If the previously
selected window of some frame is no longer live at the time of exit from forms, thatframe’s selected window is left alone. If the previously selected window is no longer
live, then whatever window is selected at the end of forms remains selected. The
current buffer is restored if and only if it is still live when exiting forms.
This macro changes neither the ordering of recently selected windows nor the buffer
list.

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with-selected-window window forms. . .

[Macro]This macro selects window, executes forms in sequence, then restores the previously
selected window and current buffer. The ordering of recently selected windows and thebuffer list remain unchanged unless you deliberately change them within forms; forexample, by calling select-window with argument norecord nil. Hence, this macrois the preferred way to temporarily work with window as the selected window without
needlessly running buffer-list-update-hook.
Note that this macro temporarily puts the window management code in an unstablestate. In particular, the most recently used window (see below) will not necessarily
match the selected one. Hence, functions like get-lru-window and get-mru-window
may return unexpected results when called from the body of this macro.

with-selected-frame frame forms. . .

[Macro]This macro executes forms with frame as the selected frame. The value returned isthe value of the last form in forms. This macro saves and restores the selected frame,and changes the order of neither the recently selected windows nor the buffers in thebuffer list.

window-use-time &optional window[Function]
This function returns the use time of window window. window must be a live window
and defaults to the selected one.
The use time of a window is not really a time value, but an integer that does increase
monotonically with each call of select-window with a nil norecord argument. The
window with the lowest use time is usually called the least recently used window.
The window with the highest use time is called the most recently used one (seeSection 29.10 [Cyclic Window Ordering], page 717) and is usually the selected window
unless with-selected-window has been used.

window-bump-use-time &optional window[Function]
This function marks window as being the second most recently used one (after theselected window). It does nothing if window is the selected window or the selected
window does not have the highest use time among all windows which may happen
within the scope of with-selected-window.

Sometimes several windows collectively and cooperatively display a buffer, for example,
under the management of Follow Mode (see Section “Follow Mode” in emacs), where thewindows together display a bigger portion of the buffer than one window could alone. It is
often useful to consider such a window group as a single entity. Several functions such as
window-group-start (see Section 29.20 [Window Start and End], page 759) allow you to
do this by supplying, as an argument, one of the windows as a stand-in for the whole group.
[Function]
When the selected window is a member of a group of windows, this function returns
a list of the windows in the group, ordered such that the first window in the list isdisplaying the earliest part of the buffer, and so on. Otherwise the function returns alist containing just the selected window.
The selected window is considered part of a group when the buffer local
variable selected-window-group-function is set to a function. In this case,selected-window-groupChapter 29: Windows699

selected-window-group calls it with no arguments and returns its result (whichshould be the list of windows in the group).

29.4 Window Sizes
Emacs provides miscellaneous functions for finding the height and width of a window. The
return value of many of these functions can be specified either in units of pixels or inunits of lines and columns. On a graphical display, the latter actually correspond to theheight and width of a default character specified by the frame’s default font as returned byframe-char-height and frame-char-width (see Section 30.3.2 [Frame Font], page 797).
Thus, if a window is displaying text with a different font or size, the reported line height andcolumn width for that window may differ from the actual number of text lines or columns
displayed within it.
The total height of a window is the number of lines comprising its body and its top andbottom decorations (see Section 29.1 [Basic Windows], page 690).

window-total-height &optional window round[Function]
This function returns the total height, in lines, of the window window. If window isomitted or nil, it defaults to the selected window. If window is an internal window,
the return value is the total height occupied by its descendant windows.
If a window’s pixel height is not an integral multiple of its frame’s default characterheight, the number of lines occupied by the window is rounded internally. This is donein a way such that, if the window is a parent window, the sum of the total heights of
all its child windows internally equals the total height of their parent. This meansthat although two windows have the same pixel height, their internal total heights
may differ by one line. This means also, that if window is vertically combined and has
a next sibling, the topmost row of that sibling can be calculated as the sum of thiswindow’s topmost row and total height (see Section 29.24 [Coordinates and Windows],
page 769)
If the optional argument round is ceiling, this function returns the smallest integer
larger than window’s pixel height divided by the character height of its frame; if it isfloor, it returns the largest integer smaller than said value; with any other round it
returns the internal value of windows’s total height.

The total width of a window is the number of columns comprising its body and its left
and right decorations (see Section 29.1 [Basic Windows], page 690).

window-total-width &optional window round[Function]
This function returns the total width, in columns, of the window window. If window
is omitted or nil, it defaults to the selected window. If window is internal, the return
value is the total width occupied by its descendant windows.
If a window’s pixel width is not an integral multiple of its frame’s character width,
the number of columns occupied by the window is rounded internally. This is donein a way such that, if the window is a parent window, the sum of the total widthsof all its children internally equals the total width of their parent. This means that
although two windows have the same pixel width, their internal total widths may
differ by one column. This means also, that if this window is horizontally combined

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and has a next sibling, the leftmost column of that sibling can be calculated as thesum of this window’s leftmost column and total width (see Section 29.24 [Coordinatesand Windows], page 769). The optional argument round behaves as it does forwindow-total-height.

window-total-size &optional window horizontal round[Function]
This function returns either the total height in lines or the total width in columnsof the window window. If horizontal is omitted or nil, this is equivalent to calling
window-total-height for window; otherwise it is equivalent to calling window-totalwidth for window. The optional argument round behaves as it does for window-totalheight.

The following two functions can be used to return the total size of a window in units ofpixels.

window-pixel-height &optional window[Function]
This function returns the total height of window window in pixels. window must be avalid window and defaults to the selected one.
The return value includes the heights of window’s top and bottom decorations. If
window is an internal window, its pixel height is the pixel height of the screen areas
spanned by its children.

window-pixel-width &optional window[Function]
This function returns the width of window window in pixels. window must be a valid
window and defaults to the selected one.
The return value includes the widths of window’s left and right decorations. If window
is an internal window, its pixel width is the width of the screen areas spanned by its
children.

The following functions can be used to determine whether a given window has any
adjacent windows.

window-full-height-p &optional window[Function]
This function returns non-nil if window has no other window above or below it in its
frame. More precisely, this means that the total height of window equals the totalheight of the root window on that frame. The minibuffer window does not count inthis regard. If window is omitted or nil, it defaults to the selected window.

window-full-width-p &optional window[Function]
This function returns non-nil if window has no other window to the left or right inits frame, i.e., its total width equals that of the root window on that frame. If window
is omitted or nil, it defaults to the selected window.

The body height of a window is the height of its body, which does not include any of its
top or bottom decorations (see Section 29.1 [Basic Windows], page 690).

window-body-height &optional window pixelwise[Function]
This function returns the height, in lines, of the body of window window. If window isomitted or nil, it defaults to the selected window; otherwise it must be a live window.

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The optional argument pixelwise defines the units to use for the height. If nil, returnthe body height of window in characters, rounded down to the nearest integer, if
necessary. This means that if a line at the bottom of the text area is only partiallyvisible, that line is not counted. It also means that the height of a window’s body cannever exceed its total height as returned by window-total-height.
If pixelwise is remap and the default face is remapped (see Section 41.12.5 [FaceRemapping], page 1175), use the remapped face to determine the character height.
For any other non-nil value, return the height in pixels.
The body width of a window is the width of its body and of the text area, which does
not include any of its left or right decorations (see Section 29.1 [Basic Windows], page 690).
Note that when one or both fringes are removed (by setting their width to zero), thedisplay engine reserves two character cells, one on each side of the window, for displaying
the continuation and truncation glyphs, which leaves 2 columns less for text display. (Thefunction window-max-chars-per-line, described below, takes this peculiarity into account.)

window-body-width &optional window pixelwise[Function]
This function returns the width, in columns, of the body of window window. If window
is omitted or nil, it defaults to the selected window; otherwise it must be a live
window.
The optional argument pixelwise defines the units to use for the width. If nil, returnthe body width of window in characters, rounded down to the nearest integer, if
necessary. This means that if a column on the right of the text area is only partiallyvisible, that column is not counted. It also means that the width of a window’s bodycan never exceed its total width as returned by window-total-width.
If pixelwise is remap and the default face is remapped (see Section 41.12.5 [FaceRemapping], page 1175), use the remapped face to determine the character width.
For any other non-nil value, return the width in pixels.

window-body-size &optional window horizontal pixelwise[Function]
This function returns the body height or body width of window. If horizontal isomitted or nil, it is equivalent to calling window-body-height for window; otherwise
it is equivalent to calling window-body-width. In either case, the optional argument
pixelwise is passed to the function called.

The pixel heights of a window’s mode, tab and header line can be retrieved with thefunctions given below. Their return value is usually accurate unless the window has notbeen displayed before: In that case, the return value is based on an estimate of the font used
for the window’s frame.

window-mode-line-height &optional window[Function]
This function returns the height in pixels of window’s mode line. window must be alive window and defaults to the selected one. If window has no mode line, the return
value is zero.

window-tab-line-height &optional window[Function]
This function returns the height in pixels of window’s tab line. window must be a live
window and defaults to the selected one. If window has no tab line, the return value
is zero.

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window-header-line-height &optional window[Function]
This function returns the height in pixels of window’s header line. window must be alive window and defaults to the selected one. If window has no header line, the return
value is zero.

Functions for retrieving the height and/or width of window dividers (see Section 41.15[Window Dividers], page 1198), fringes (see Section 41.13 [Fringes], page 1189), scroll bars
(see Section 41.14 [Scroll Bars], page 1195), and display margins (see Section 41.16.5 [Display
Margins], page 1205) are described in the corresponding sections.
If your Lisp program needs to make layout decisions, you will find the following function
useful:window-max-chars-per-line &optional window face

[Function]
This function returns the number of characters displayed in the specified face face inthe specified window window (which must be a live window). If face was remapped(see Section 41.12.5 [Face Remapping], page 1175), the information is returned forthe remapped face. If omitted or nil, face defaults to the default face, and window
defaults to the selected window.
Unlike window-body-width, this function accounts for the actual size of face’s font,instead of working in units of the canonical character width of window’s frame(see Section 30.3.2 [Frame Font], page 797). It also accounts for space used by thecontinuation glyph, if window lacks one or both of its fringes.

Commands that change the size of windows (see Section 29.5 [Resizing Windows],
page 703), or split them (see Section 29.7 [Splitting Windows], page 708), obey the variables
window-min-height and window-min-width, which specify the smallest allowable window
height and width. They also obey the variable window-size-fixed, with which a window
can be fixed in size (see Section 29.6 [Preserving Window Sizes], page 707).
[User Option]
This option specifies the minimum total height, in lines, of any window. Its value has
to accommodate at least one text line and any top or bottom decorations.

window-min-height[User Option]
This option specifies the minimum total width, in columns, of any window. Its value
has to accommodate at least two text columns and any left or right decorations.

window-min-width

The following function tells how small a specific window can get taking into accountthe sizes of its areas and the values of window-min-height, window-min-width andwindow-size-fixed (see Section 29.6 [Preserving Window Sizes], page 707).

window-min-size &optional window horizontal ignore pixelwise[Function]
This function returns the minimum size of window. window must be a valid window
and defaults to the selected one. The optional argument horizontal non-nil means toreturn the minimum number of columns of window; otherwise return the minimum
number of window’s lines.

The return value makes sure that all components of window remain fully visible ifwindow’s size were actually set to it. With horizontal nil it includes any top orChapter 29: Windows

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bottom decorations. With horizontal non-nil it includes any left or right decorationsof window.
The optional argument ignore, if non-nil, means ignore restrictions imposed by
fixed size windows, window-min-height or window-min-width settings. If ignore
equals safe, live windows may get as small as window-safe-min-height lines andwindow-safe-min-width columns. If ignore is a window, ignore restrictions for thatwindow only. Any other non-nil value means ignore all of the above restrictions for
all windows.
The optional argument pixelwise non-nil means to return the minimum size of window
counted in pixels.

29.5 Resizing Windows
This section describes functions for resizing a window without changing the size of its frame.
Because live windows do not overlap, these functions are meaningful only on frames that
contain two or more windows: resizing a window also changes the size of at least one otherwindow. If there is just one window on a frame, its size cannot be changed except by resizing
the frame (see Section 30.3.4 [Frame Size], page 799).
Except where noted, these functions also accept internal windows as arguments. Resizing
an internal window causes its child windows to be resized to fit the same space.

window-resizable window delta &optional horizontal ignore
pixelwise[Function]

This function returns delta if the size of window can be changed vertically by deltalines. If the optional argument horizontal is non-nil, it instead returns delta if window
can be resized horizontally by delta columns. It does not actually change the window
size.
If window is nil, it defaults to the selected window.
A positive value of delta means to check whether the window can be enlarged by that
number of lines or columns; a negative value of delta means to check whether thewindow can be shrunk by that many lines or columns. If delta is non-zero, a return
value of 0 means that the window cannot be resized.
Normally, the variables window-min-height and window-min-width specify the smallest allowable window size (see Section 29.4 [Window Sizes], page 699). However, if
the optional argument ignore is non-nil, this function ignores window-min-height
and window-min-width, as well as window-size-fixed. Instead, it considers theminimum height of a window as the sum of its top and bottom decorations plus the
text of one line; and its minimum width as the sum of its left and right decorations
plus text that takes two columns.
If the optional argument pixelwise is non-nil, delta is interpreted as pixels.

window-resize window delta &optional horizontal ignore pixelwise[Function]
This function resizes window by delta increments. If horizontal is nil, it changes theheight by delta lines; otherwise, it changes the width by delta columns. A positivedelta means to enlarge the window, and a negative delta means to shrink it.
If window is nil, it defaults to the selected window. If the window cannot be resized
as demanded, an error is signaled.

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The optional argument ignore has the same meaning as for the function
window-resizable above.
If the optional argument pixelwise is non-nil, delta will be interpreted as pixels.
The choice of which window edges this function alters depends on the values ofthe option window-combination-resize and the combination limits of the involved
windows; in some cases, it may alter both edges. See Section 29.9 [Recombining
Windows], page 712. To resize by moving only the bottom or right edge of a window,
use the function adjust-window-trailing-edge.

adjust-window-trailing-edge window delta &optional horizontal
pixelwise[Function]

This function moves window’s bottom edge by delta lines. If optional argument
horizontal is non-nil, it instead moves the right edge by delta columns. If window isnil, it defaults to the selected window.
If the optional argument pixelwise is non-nil, delta is interpreted as pixels.
A positive delta moves the edge downwards or to the right; a negative delta moves it
upwards or to the left. If the edge cannot be moved as far as specified by delta, thisfunction moves it as far as possible but does not signal an error.
This function tries to resize windows adjacent to the edge that is moved. If this is
not possible for some reason (e.g., if that adjacent window is fixed-size), it may resize
other windows.
[User Option]
If the value of this option is non-nil, Emacs resizes windows in units of pixels.
This currently affects functions like split-window (see Section 29.7 [Splitting
Windows], page 708), maximize-window, minimize-window, fit-window-to-buffer,
fit-frame-to-buffer and shrink-window-if-larger-than-buffer (all listed
below).

window-resize-pixelwise

Note that when a frame’s pixel size is not a multiple of its character size, at least one
window may get resized pixelwise even if this option is nil. The default value is nil.
The following commands resize windows in more specific ways. When called interactively,
they act on the selected window.

fit-window-to-buffer &optional window max-height min-heightmax-width min-width preserve-size[Command]This command adjusts the height or width of window to fit the text in it. It returns
non-nil if it was able to resize window, and nil otherwise. If window is omitted ornil, it defaults to the selected window. Otherwise, it should be a live window.
If window is part of a vertical combination, this function adjusts window’s height.
The new height is calculated from the actual height of the accessible portion of its
buffer. The optional argument max-height, if non-nil, specifies the maximum totalheight that this function can give window. The optional argument min-height, if
non-nil, specifies the minimum total height that it can give, which overrides thevariable window-min-height. Both max-height and min-height are specified in lines
and include any top or bottom decorations of window.

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If window is part of a horizontal combination and the value of the option fit-windowto-buffer-horizontally (see below) is non-nil, this function adjusts window’s
width. The new width of window is calculated from the maximum length of its buffer’slines that follow the current start position of window. The optional argument maxwidth specifies a maximum width and defaults to the width of window’s frame. The
optional argument min-width specifies a minimum width and defaults to window-minwidth. Both max-width and min-width are specified in columns and include any leftor right decorations of window.
The optional argument preserve-size, if non-nil, will install a parameter to preserve thesize of window during future resize operations (see Section 29.6 [Preserving Window
Sizes], page 707).
If the option fit-frame-to-buffer (see below) is non-nil, this function will try to
resize the frame of window to fit its contents by calling fit-frame-to-buffer (seebelow).
[User Option]
If this is non-nil, fit-window-to-buffer can resize windows horizontally. If this isnil (the default) fit-window-to-buffer never resizes windows horizontally. If thisis only, it can resize windows horizontally only. Any other value means fit-windowto-buffer can resize windows in both dimensions.

fit-window-to-buffer-horizontally[User Option]
If this option is non-nil, fit-window-to-buffer can fit a frame to its buffer. A
frame is fit if and only if its root window is a live window and this option is non-nil.
If this is horizontally, frames are fit horizontally only. If this is vertically, frames
are fit vertically only. Any other non-nil value means frames can be resized in bothdimensions.

fit-frame-to-buffer

If you have a frame that displays only one window, you can fit that frame to its bufferusing the command fit-frame-to-buffer.

fit-frame-to-buffer &optional frame max-height min-heightmax-width min-width only

[Command]This command adjusts the size of frame to display the contents of its buffer exactly.
frame can be any live frame and defaults to the selected one. Fitting is done only ifframe’s root window is live.
The arguments max-height, min-height, max-width and min-width, if non-nil, specify
bounds on the new body size of frame’s root window. A non-nil value specified
by any of these arguments overrides the corresponding value specified by the option
fit-frame-to-buffer-sizes described below.
If the optional argument only is vertically, this function may resize the frame
vertically only. If only is horizontally, it may resize the frame horizontally only.
The behavior of fit-frame-to-buffer can be controlled with the help of the two options
listed next.

Chapter 29: Windows

706[User Option]
This option can be used to specify margins around frames to be fit by fit-frameto-buffer. Such margins can be useful to avoid, for example, that the resized frame
overlaps the taskbar or parts of its parent frame.

fit-frame-to-buffer-margins

It specifies the numbers of pixels to be left free on the left, above, the right, andbelow a frame that shall be fit. The default specifies nil for each which means to use
no margins. The value specified here can be overridden for a specific frame by thatframe’s fit-frame-to-buffer-margins parameter, if present.
[User Option]
This option specifies size boundaries for fit-frame-to-buffer. It specifies the
maximum and minimum lines and maximum and minimum columns of the root
window’s body of any frame that shall be fit to its buffer. Any value this option
specifies will be overridden by the corresponding argument of fit-frame-to-buffer,
if non-nil.

fit-frame-to-buffer-sizes

shrink-window-if-larger-than-buffer &optional window[Command]This command attempts to reduce window’s height as much as possible while still
showing its full buffer, but no less than window-min-height lines. The return value
is non-nil if the window was resized, and nil otherwise. If window is omitted or nil,
it defaults to the selected window. Otherwise, it should be a live window.
This command does nothing if the window is already too short to display all of its
buffer, or if any of the buffer is scrolled off-screen, or if the window is the only live
window in its frame.
This command calls fit-window-to-buffer (see above) to do its work.

balance-windows &optional window-or-frame[Command]This function balances windows in a way that gives more space to full-width and/or
full-height windows. If window-or-frame specifies a frame, it balances all windows onthat frame. If window-or-frame specifies a window, it balances only that window andits siblings (see Section 29.2 [Windows and Frames], page 692).
[Command]This function attempts to give all windows on the selected frame approximately thesame share of the screen area. Full-width or full-height windows are not given more
space than other windows.

balance-windows-area

maximize-window &optional window[Command]This function attempts to make window as large as possible, in both dimensions,
without resizing its frame or deleting other windows. If window is omitted or nil, it
defaults to the selected window.

minimize-window &optional window[Command]This function attempts to make window as small as possible, in both dimensions,
without deleting it or resizing its frame. If window is omitted or nil, it defaults tothe selected window.

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29.6 Preserving Window Sizes
A window can get resized explicitly by using one of the functions from the preceding section
or implicitly, for example, when resizing an adjacent window, when splitting or deleting awindow (see Section 29.7 [Splitting Windows], page 708, see Section 29.8 [Deleting Windows],
page 711) or when resizing the window’s frame (see Section 30.3.4 [Frame Size], page 799).
It is possible to avoid implicit resizing of a specific window when there are one or moreother resizable windows on the same frame. For this purpose, Emacs must be advised topreserve the size of that window. There are two basic ways to do that.
[Variable]
If this buffer-local variable is non-nil, the size of any window displaying the buffer
cannot normally be changed. Deleting a window or changing the frame’s size may stillchange the window’s size, if there is no choice.
If the value is height, then only the window’s height is fixed; if the value is width,then only the window’s width is fixed. Any other non-nil value fixes both the width
and the height.
If this variable is nil, this does not necessarily mean that any window showing thebuffer can be resized in the desired direction. To determine that, use the function
window-resizable. See Section 29.5 [Resizing Windows], page 703.

window-size-fixed

Often window-size-fixed is overly aggressive because it inhibits any attempt to explicitly
resize or split an affected window as well. This may even happen after the window has been
resized implicitly, for example, when deleting an adjacent window or resizing the window’s
frame. The following function tries hard to never disallow resizing such a window explicitly:

window-preserve-size &optional window horizontal preserve[Function]
This function (un-)marks the height of window window as preserved for future resize
operations. window must be a live window and defaults to the selected one. If
the optional argument horizontal is non-nil, it (un-)marks the width of window aspreserved.
If the optional argument preserve is t, this means to preserve the current height/widthof window’s body. The height/width of window will change only if Emacs has no
better choice. Resizing a window whose height/width is preserved by this function
never throws an error.
If preserve is nil, this means to stop preserving the height/width of window, lifting any respective restraint induced by a previous call of this function for window.
Calling enlarge-window, shrink-window or fit-window-to-buffer with window asargument may also remove the respective restraint.

window-preserve-size is currently invoked by the following functions:fit-window-to-buffer
If the optional argument preserve-size of that function (see Section 29.5 [Resizing
Windows], page 703) is non-nil, the size established by that function is preserved.
display-buffer
If the alist argument of that function (see Section 29.13.1 [Choosing Window],
page 724) contains a preserve-size entry, the size of the window produced bythat function is preserved.

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window-preserve-size installs a window parameter (see Section 29.27 [Window Parameters], page 776) called window-preserved-size which is consulted by the window resizing
functions. This parameter will not prevent resizing the window when the window shows
another buffer than the one when window-preserve-size was invoked or if its size haschanged since then.
The following function can be used to check whether the height of a particular window ispreserved:

window-preserved-size &optional window horizontal[Function]
This function returns the preserved height of window window in pixels. window must
be a live window and defaults to the selected one. If the optional argument horizontal
is non-nil, it returns the preserved width of window. It returns nil if the size ofwindow is not preserved.

29.7 Splitting Windows
This section describes functions for creating a new window by splitting an existing one.
Note that some windows are special in the sense that these functions may fail to split themas described here. Examples of such windows are side windows (see Section 29.17 [SideWindows], page 752) and atomic windows (see Section 29.18 [Atomic Windows], page 756).

split-window &optional window size side pixelwise[Function]
This function creates a new live window next to the window window. If window isomitted or nil, it defaults to the selected window. That window is split, and reducedin size. The space is taken up by the new window, which is returned.
The optional second argument size determines the sizes of window and/or the new
window. If it is omitted or nil, both windows are given equal sizes; if there is an oddline, it is allocated to the new window. If size is a positive number, window is given
size lines (or columns, depending on the value of side). If size is a negative number,the new window is given −size lines (or columns).
If size is nil, this function obeys the variables window-min-height and window-minwidth (see Section 29.4 [Window Sizes], page 699). Thus, it signals an error if splitting
would result in making a window smaller than those variables specify. However, anon-nil value for size causes those variables to be ignored; in that case, the smallest
allowable window is considered to be one that has space for a text that is one line talland/or two columns wide.
Hence, if size is specified, it’s the caller’s responsibility to check whether the emanating
windows are large enough to encompass all of their decorations like a mode line or ascroll bar. The function window-min-size (see Section 29.4 [Window Sizes], page 699)
can be used to determine the minimum requirements of window in this regard. Since
the new window usually inherits areas like the mode line or the scroll bar from window,that function is also a good guess for the minimum size of the new window. The
caller should specify a smaller size only if it correspondingly removes an inherited area
before the next redisplay.
The optional third argument side determines the position of the new window relative
to window. If it is nil or below, the new window is placed below window. If it isChapter 29: Windows

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above, the new window is placed above window. In both these cases, size specifies a
total window height, in lines.
If side is t or right, the new window is placed on the right of window. If side is left,
the new window is placed on the left of window. In both these cases, size specifies a
total window width, in columns.
The optional fourth argument pixelwise, if non-nil, means to interpret size in unitsof pixels, instead of lines and columns.
If window is a live window, the new window inherits various properties from it,
including margins and scroll bars. If window is an internal window, the new window
inherits the properties of the window selected within window’s frame.
The behavior of this function may be altered by the window parameters of window,
so long as the variable ignore-window-parameters is nil. If the value of the
split-window window parameter is t, this function ignores all other window parameters. Otherwise, if the value of the split-window window parameter is a function, thatfunction is called with the arguments window, size, and side, in lieu of the usual actionof split-window. Otherwise, this function obeys the window-atom or window-side
window parameter, if any. See Section 29.27 [Window Parameters], page 776.

As an example, here is a sequence of split-window calls that yields the window configuration discussed in Section 29.2 [Windows and Frames], page 692. This example demonstrates
splitting a live window as well as splitting an internal window. We begin with a frame containing a single window (a live root window), which we denote by W4. Calling (split-window
W4) yields this window configuration:______________________________________| ____________________________________ |
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||_________________W5_________________|||__________________W3__________________|The split-window call has created a new live window, denoted by W5. It has also createda new internal window, denoted by W3, which becomes the root window and the parent ofboth W4 and W5.
Next, we call (split-window W3 nil 'left), passing the internal window W3 as theargument. The result:Chapter 29: Windows710______________________________________| ______ ____________________________ ||||| __________________________ ||
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|||____________W5____________|||||__W2__||_____________W3_____________ ||__________________W1__________________|A new live window W2 is created, to the left of the internal window W3. A new internal
window W1 is created, becoming the new root window.
For interactive use, Emacs provides two commands which always split the selected window.
These call split-window internally.

split-window-right &optional size window-to-split[Command]This function splits the window window-to-split into two side-by-side windows, putting
window-to-split on the left. window-to-split defaults to the selected window. If size ispositive, the left window gets size columns; if size is negative, the right window gets−size columns.

split-window-below &optional size window-to-split[Command]This function splits the window window-to-split into two windows, one above theother, leaving the upper window selected. window-to-split defaults to the selected
window. If size is positive, the upper window gets size lines; if size is negative, thelower window gets −size lines.

split-root-window-below &optional size

[Command]This function splits the whole frame in two. The current window configuration isretained on the top, and a new window is created below, taking up the whole width of
the frame. size is treated as by split-window-below.

split-root-window-right &optional size

[Command]This function splits the whole frame in two. The current window configuration isretained on the left, and a new window is created on the right, taking up the wholeheight of the frame. size is treated as by split-window-right.
[User Option]
If the value of this variable is non-nil (the default), split-window-below behaves as
described above.

split-window-keep-point

If it is nil, split-window-below adjusts point in each of the two windows to minimize
redisplay. (This is useful on slow terminals.) It selects whichever window contains thescreen line that point was previously on. Note that this only affects split-windowbelow, not the lower-level split-window function.

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29.8 Deleting Windows
Deleting a window removes it from the frame’s window tree. If the window is a live window,
it disappears from the screen. If the window is an internal window, its child windows aredeleted too.
Even after a window is deleted, it continues to exist as a Lisp object, until there are
no more references to it. Window deletion can be reversed, by restoring a saved window
configuration (see Section 29.26 [Window Configurations], page 774).

delete-window &optional window[Command]This function removes window from display and returns nil. If window is omitted ornil, it defaults to the selected window.
If deleting the window would leave no more windows in the window tree (e.g., if it is
the only live window in the frame) or all remaining windows on window’s frame areside windows (see Section 29.17 [Side Windows], page 752), an error is signaled. If
window is part of an atomic window (see Section 29.18 [Atomic Windows], page 756),
this function tries to delete the root of that atomic window instead.
By default, the space taken up by window is given to one of its adjacent sibling
windows, if any. However, if the variable window-combination-resize is non-nil,the space is proportionally distributed among any remaining windows in the same
window combination. See Section 29.9 [Recombining Windows], page 712.
The behavior of this function may be altered by the window parameters of window,
so long as the variable ignore-window-parameters is nil. If the value of thedelete-window window parameter is t, this function ignores all other window parameters. Otherwise, if the value of the delete-window window parameter is a function,that function is called with the argument window, in lieu of the usual action ofdelete-window. See Section 29.27 [Window Parameters], page 776.

When delete-window deletes the selected window of its frame, it has to make anotherwindow the new selected window of that frame. The following option allows configuring
which window is chosen.
[User Option]
This option allows specifying which window should become a frame’s selected window
after delete-window has deleted the previously selected one. Possible choices are• mru (the default) choose the most recently used window on that frame.
• pos choose the window comprising the frame coordinates of point of the previously
selected window on that frame.
• nil choose the first window (the window returned by frame-first-window) onthat frame.

delete-window-choose-selected

A window with a non-nil no-other-window parameter is chosen only if all otherwindows on that frame have that parameter set to a non-nil value too.

delete-other-windows &optional window[Command]This function makes window fill its frame, deleting other windows as necessary. If
window is omitted or nil, it defaults to the selected window. An error is signaled if
window is a side window (see Section 29.17 [Side Windows], page 752). If windowChapter 29: Windows712

is part of an atomic window (see Section 29.18 [Atomic Windows], page 756), thisfunction tries to make the root of that atomic window fill its frame. The return value
is nil.
The behavior of this function may be altered by the window parameters of window,
so long as the variable ignore-window-parameters is nil. If the value of thedelete-other-windows window parameter is t, this function ignores all other window
parameters. Otherwise, if the value of the delete-other-windows window parameteris a function, that function is called with the argument window, in lieu of the usual
action of delete-other-windows. See Section 29.27 [Window Parameters], page 776.
Also, if ignore-window-parameters is nil, this function does not delete any window
whose no-delete-other-windows parameter is non-nil.

delete-windows-on &optional buffer-or-name frame[Command]This function deletes all windows showing buffer-or-name, by calling delete-window
on those windows. buffer-or-name should be a buffer, or the name of a buffer; ifomitted or nil, it defaults to the current buffer. If there are no windows showing thespecified buffer, this function does nothing. If the specified buffer is a minibuffer, anerror is signaled.
If there is a dedicated window showing the buffer, and that window is the only one
on its frame, this function also deletes that frame if it is not the only frame on theterminal.

The optional argument frame specifies which frames to operate on:• nil means operate on all frames.
• t means operate on the selected frame.
• visible means operate on all visible frames.
• 0 means operate on all visible or iconified frames.
• A frame means operate on that frame.
Note that this argument does not have the same meaning as in other functions
which scan all live windows (see Section 29.10 [Cyclic Window Ordering], page 717).
Specifically, the meanings of t and nil here are the opposite of what they are in thoseother functions.

29.9 Recombining Windows
When deleting the last sibling of a window W, its parent window is deleted too, with
W replacing it in the window tree. This means that W must be recombined with its
parent’s siblings to form a new window combination (see Section 29.2 [Windows and Frames],
page 692). In some occasions, deleting a live window may even entail the deletion of two
internal windows.

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Deleting W5 in this configuration normally causes the deletion of W3 and W4. The remaining
live windows W2, W6 and W7 are recombined to form a new horizontal combination withparent W1.
Sometimes, however, it makes sense to not delete a parent window like W4. In particular,a parent window should not be removed when it was used to preserve a combination
embedded in a combination of the same type. Such embeddings make sense to assure thatwhen you split a window and subsequently delete the new window, Emacs reestablishes thelayout of the associated frame as it existed before the splitting.
Consider a scenario starting with two live windows W2 and W3 and their parent W1.
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Split W2 to make a new window W4 as follows.
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Now, when enlarging a window vertically, Emacs tries to obtain the corresponding spacefrom its lower sibling, provided such a window exists. In our scenario, enlarging W4 will
steal space from W3.
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Deleting W4 will now give its entire space to W2, including the space earlier stolen from
W3.
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This can be counterintuitive, in particular if W4 were used for displaying a buffer only
temporarily (see Section 41.8 [Temporary Displays], page 1146), and you want to continue
working with the initial layout.
The behavior can be fixed by making a new parent window when splitting W2. The
variable described next allows that to be done.
[User Option]
This variable controls whether splitting a window shall make a new parent window.
The following values are recognized:

window-combination-limit

nilThis means that the new live window is allowed to share the existing
parent window, if one exists, provided the split occurs in the same direction
as the existing window combination (otherwise, a new internal window iscreated anyway).

window-sizeThis means that display-buffer makes a new parent window when it
splits a window and is passed a window-height or window-width entry inChapter 29: Windows

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the alist argument (see Section 29.13.2 [Buffer Display Action Functions],
page 726). Otherwise, window splitting behaves as for a value of nil.
temp-buffer-resize
In this case with-temp-buffer-window makes a new parent window
when it splits a window and temp-buffer-resize-mode is enabled (seeSection 41.8 [Temporary Displays], page 1146). Otherwise, window splitting behaves as for nil.
temp-buffer
In this case with-temp-buffer-window always makes a new parent window when it splits an existing window (see Section 41.8 [Temporary
Displays], page 1146). Otherwise, window splitting behaves as for nil.
display-bufferThis means that when display-buffer (see Section 29.13.1 [Choosing
Window], page 724) splits a window it always makes a new parent window.
Otherwise, window splitting behaves as for nil.
tThis means that splitting a window always creates a new parent window.
Thus, if the value of this variable is at all times t, then at all times every
window tree is a binary tree (a tree where each window except the root
window has exactly one sibling).

The default is window-size. Other values are reserved for future use.
If, as a consequence of this variable’s setting, split-window makes a new parent
window, it also calls set-window-combination-limit (see below) on the newlycreated internal window. This affects how the window tree is rearranged when thechild windows are deleted (see below).
If window-combination-limit is t, splitting W2 in the initial configuration of ourscenario would have produced this:______________________________________| ____________________________________ ||| __________________________________ |||||||||||________________W2________________||||| __________________________________ |||||||||||________________W4________________|||||_________________W5_________________||| ____________________________________ |
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W4. Now, W2 is the only sibling of W4, so enlarging W4 will try to shrink W2, leaving W3
unaffected. Observe that W5 represents a vertical combination of two windows embeddedin the vertical combination W1.

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set-window-combination-limit window limit[Function]
This function sets the combination limit of the window window to limit. This value canbe retrieved via the function window-combination-limit. See below for its effects;
note that it is only meaningful for internal windows. The split-window function
automatically calls this function, passing it t as limit, provided the value of thevariable window-combination-limit is t when it is called.

window-combination-limit window[Function]
This function returns the combination limit for window.
The combination limit is meaningful only for an internal window. If it is nil, thenEmacs is allowed to automatically delete window, in response to a window deletion,in order to group the child windows of window with its sibling windows to form a new
window combination. If the combination limit is t, the child windows of window arenever automatically recombined with its siblings.
If, in the configuration shown at the beginning of this section, the combination limitof W4 (the parent window of W6 and W7) is t, deleting W5 will not implicitly delete
W4 too.

Alternatively, the problems sketched above can be avoided by always resizing all windows
in the same combination whenever one of its windows is split or deleted. This also permits
splitting windows that would be otherwise too small for such an operation.
[User Option]
If this variable is nil, split-window can only split a window (denoted by window) if
window’s screen area is large enough to accommodate both itself and the new window.
If this variable is t, split-window tries to resize all windows that are part of thesame combination as window, in order to accommodate the new window. In particular,
this may allow split-window to succeed even if window is a fixed-size window or too
small to ordinarily split. Furthermore, subsequently resizing or deleting window may
resize all other windows in its combination.
The default is nil. Other values are reserved for future use. A specific split operation may ignore the value of this variable if it is affected by a non-nil value of
window-combination-limit.

window-combination-resize

To illustrate the effect of window-combination-resize, consider the following framelayout.
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If window-combination-resize is nil, splitting window W3 leaves the size of W2 unchanged:______________________________________| ____________________________________ |
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If window-combination-resize is t, splitting W3 instead leaves all three live windows withapproximately the same height:______________________________________| ____________________________________ |
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Deleting any of the live windows W2, W3 or W4 will distribute its space proportionallyamong the two remaining live windows.

29.10 Cyclic Ordering of Windows
When you use the command C-x o (other-window) to select some other window, it moves
through live windows in a specific order. For any given configuration of windows, this ordernever varies. It is called the cyclic ordering of windows.
The ordering is determined by a depth-first traversal of each frame’s window tree,
retrieving the live windows which are the leaf nodes of the tree (see Section 29.2 [Windows
and Frames], page 692). If the minibuffer is active, the minibuffer window is included too.
The ordering is cyclic, so the last window in the sequence is followed by the first one.

next-window &optional window minibuf all-frames[Function]
This function returns a live window, the one following window in the cyclic orderingof windows. window should be a live window; if omitted or nil, it defaults to theselected window.
The optional argument minibuf specifies whether minibuffer windows should be
included in the cyclic ordering. Normally, when minibuf is nil, a minibuffer windowChapter 29: Windows718

is included only if it is currently active; this matches the behavior of C-x o. (Notethat a minibuffer window is active as long as its minibuffer is in use; see Chapter 21[Minibuffers], page 385).
If minibuf is t, the cyclic ordering includes all minibuffer windows. If minibuf isneither t nor nil, minibuffer windows are not included even if they are active.
The optional argument all-frames specifies which frames to consider:• nil means to consider windows on window’s frame. If the minibuffer window is
considered (as specified by the minibuf argument), then frames that share theminibuffer window are considered too.
• t means to consider windows on all existing frames.
• visible means to consider windows on all visible frames.
• 0 means to consider windows on all visible or iconified frames.
• A frame means to consider windows on that specific frame.
• Anything else means to consider windows on window’s frame, and no others.
If more than one frame is considered, the cyclic ordering is obtained by appending
the orderings for those frames, in the same order as the list of all live frames (seeSection 30.8 [Finding All Frames], page 823).

previous-window &optional window minibuf all-frames[Function]
This function returns a live window, the one preceding window in the cyclic orderingof windows. The other arguments are handled like in next-window.

other-window count &optional all-frames[Command]This function selects a live window, one count places from the selected window inthe cyclic ordering of windows. If count is a positive number, it skips count windows
forwards; if count is negative, it skips −count windows backwards; if count is zero,that simply re-selects the selected window. When called interactively, count is thenumeric prefix argument.
The optional argument all-frames has the same meaning as in next-window, like a
nil minibuf argument to next-window.
This function does not select a window that has a non-nil no-other-window window parameter (see Section 29.27 [Window Parameters], page 776), provided that
ignore-window-parameters is nil.
If the other-window parameter of the selected window is a function, andignore-window-parameters is nil, that function will be called with the arguments
count and all-frames instead of the normal operation of this function.

walk-windows fun &optional minibuf all-frames[Function]
This function calls the function fun once for each live window, with the window as theargument.
It follows the cyclic ordering of windows. The optional arguments minibuf andall-frames specify the set of windows included; these have the same arguments asin next-window. If all-frames specifies a frame, the first window walked is the firstwindow on that frame (the one returned by frame-first-window), not necessarily
the selected window.

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If fun changes the window configuration by splitting or deleting windows, that does
not alter the set of windows walked, which is determined prior to calling fun for the
first time.

one-window-p &optional no-mini all-frames[Function]
This function returns t if the selected window is the only live window, and nil
otherwise.
If the minibuffer window is active, it is normally considered (so that this function
returns nil). However, if the optional argument no-mini is non-nil, the minibuffer
window is ignored even if active. The optional argument all-frames has the same
meaning as for next-window.

The following functions return a window which satisfies some criterion, without selecting
it:get-lru-window &optional all-frames dedicated not-selected no-other[Function]
This function returns a live window which is heuristically the least recently used one.
The least recently used window is the least recently selected one—the window whose
use time is less than the use time of all other live windows (see Section 29.3 [Selecting
Windows], page 696). The optional argument all-frames has the same meaning as innext-window.
If any full-width windows are present, only those windows are considered. A minibuffer
window is never a candidate. A dedicated window (see Section 29.15 [Dedicated
Windows], page 749) is never a candidate unless the optional argument dedicatedis non-nil. The selected window is never returned, unless it is the only candidate.
However, if the optional argument not-selected is non-nil, this function returns nil
in that case. The optional argument no-other, if non-nil, means to never return awindow whose no-other-window parameter is non-nil.

get-mru-window &optional all-frames dedicated not-selected no-other[Function]
This function is like get-lru-window, but it returns the most recently used window
instead. The most recently used window is the most recently selected one—thewindow whose use time exceeds the use time of all other live windows (see Section 29.3
[Selecting Windows], page 696). The meaning of the arguments is the same as for
get-lru-window.
Since in practice the most recently used window is always the selected one, it usually
makes sense to call this function with a non-nil not-selected argument only.

get-largest-window &optional all-frames dedicated not-selected
no-other[Function]

This function returns the window with the largest area (height times width). If there
are two candidate windows of the same size, it prefers the one that comes first in thecyclic ordering of windows, starting from the selected window. The meaning of thearguments is the same as for get-lru-window.

get-window-with-predicate predicate &optional minibuf all-frames
default[Function]

This function calls the function predicate for each of the windows in the cyclic orderof windows in turn, passing it the window as an argument. If the predicate returns

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non-nil for any window, this function stops and returns that window. If no such
window is found, the return value is default (which defaults to nil).
The optional arguments minibuf and all-frames specify the windows to search, andhave the same meanings as in next-window.

29.11 Buffers and Windows
This section describes low-level functions for examining and setting the contents of windows.
See Section 29.12 [Switching Buffers], page 721, for higher-level functions for displaying a
specific buffer in a window.

window-buffer &optional window[Function]
This function returns the buffer that window is displaying. If window is omitted or
nil it defaults to the selected window. If window is an internal window, this function
returns nil.

set-window-buffer window buffer-or-name &optional keep-margins[Function]
This function makes window display buffer-or-name. window should be a live window;
if nil, it defaults to the selected window. buffer-or-name should be a buffer, or thename of an existing buffer. This function does not change which window is selected,
nor does it directly change which buffer is current (see Section 28.2 [Current Buffer],
page 671). Its return value is nil.
If window is strongly dedicated to a buffer and buffer-or-name does not specify thatbuffer, this function signals an error. See Section 29.15 [Dedicated Windows], page 749.
By default, this function resets window’s position, display margins, fringe widths, andscroll bar settings, based on the local variables in the specified buffer. However, if
the optional argument keep-margins is non-nil, it leaves window’s display margins,fringes and scroll bar settings alone.
When writing an application, you should normally use display-buffer (seeSection 29.13.1 [Choosing Window], page 724) or the higher-level functions describedin Section 29.12 [Switching Buffers], page 721, instead of calling set-window-buffer
directly.
This runs window-scroll-functions, followed by window-configuration-changehook. See Section 29.28 [Window Hooks], page 779.
[Variable]
This buffer-local variable records the number of times a buffer has been displayed in awindow. It is incremented each time set-window-buffer is called for the buffer.

buffer-display-count[Variable]
This buffer-local variable records the time at which a buffer was last displayed ina window. The value is nil if the buffer has never been displayed. It is updated
each time set-window-buffer is called for the buffer, with the value returned bycurrent-time (see Section 42.5 [Time of Day], page 1270).

buffer-display-time

get-buffer-window &optional buffer-or-name all-frames[Function]
This function returns the first window displaying buffer-or-name in the cyclic orderingof windows, starting from the selected window (see Section 29.10 [Cyclic Window
Ordering], page 717). If no such window exists, the return value is nil.

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buffer-or-name should be a buffer or the name of a buffer; if omitted or nil, it defaults
to the current buffer. The optional argument all-frames specifies which windows to
consider:• t means consider windows on all existing frames.
• visible means consider windows on all visible frames.
• 0 means consider windows on all visible or iconified frames.
• A frame means consider windows on that frame only.
• Any other value means consider windows on the selected frame.
Note that these meanings differ slightly from those of the all-frames argument to
next-window (see Section 29.10 [Cyclic Window Ordering], page 717). This function
may be changed in a future version of Emacs to eliminate this discrepancy.

get-buffer-window-list &optional buffer-or-name minibuf
all-frames[Function]

This function returns a list of all windows currently displaying buffer-or-name. bufferor-name should be a buffer or the name of an existing buffer. If omitted or nil, it
defaults to the current buffer. If the currently selected window displays buffer-or-name,it will be the first in the list returned by this function.
The arguments minibuf and all-frames have the same meanings as in the function
next-window (see Section 29.10 [Cyclic Window Ordering], page 717). Note that the
all-frames argument does not behave exactly like in get-buffer-window.

replace-buffer-in-windows &optional buffer-or-name[Command]This command replaces buffer-or-name with some other buffer, in all windows displaying it. buffer-or-name should be a buffer, or the name of an existing buffer; if omitted
or nil, it defaults to the current buffer.
The replacement buffer in each window is chosen via switch-to-prev-buffer (seeSection 29.14 [Window History], page 746). With the exception of side windows (seeSection 29.17 [Side Windows], page 752), any dedicated window displaying buffer-orname is deleted if possible (see Section 29.15 [Dedicated Windows], page 749). If sucha window is the only window on its frame and there are other frames on the same
terminal, the frame is deleted as well. If the dedicated window is the only window on
the only frame on its terminal, the buffer is replaced anyway.

29.12 Switching to a Buffer in a Window
This section describes high-level functions for switching to a specified buffer in some window.
In general, “switching to a buffer” means to (1) show the buffer in some window, (2) makethat window the selected window (and its frame the selected frame), and (3) make the buffer
the current buffer.
Do not use these functions to make a buffer temporarily current just so a Lisp program
can access or modify it. They have side-effects, such as changing window histories (seeSection 29.14 [Window History], page 746), which will surprise the user if used that way.
If you want to make a buffer current to modify it in Lisp, use with-current-buffer,save-current-buffer, or set-buffer. See Section 28.2 [Current Buffer], page 671.

Chapter 29: Windows

switch-to-buffer buffer-or-name &optional norecord
force-same-window

722[Command]This command attempts to display buffer-or-name in the selected window and makeit the current buffer. It is often used interactively (as the binding of C-x b), as well as
in Lisp programs. The return value is the buffer switched to.
If buffer-or-name is nil, it defaults to the buffer returned by other-buffer (seeSection 28.8 [Buffer List], page 681). If buffer-or-name is a string that is not thename of any existing buffer, this function creates a new buffer with that name; thenew buffer’s major mode is determined by the variable major-mode (see Section 24.2
[Major Modes], page 526).
Normally, the specified buffer is put at the front of the buffer list—both the global
buffer list and the selected frame’s buffer list (see Section 28.8 [Buffer List], page 681).
However, this is not done if the optional argument norecord is non-nil.
Sometimes, the selected window may not be suitable for displaying the buffer. This
happens if the selected window is a minibuffer window, or if the selected window isstrongly dedicated to its buffer (see Section 29.15 [Dedicated Windows], page 749). In
such cases, the command normally tries to display the buffer in some other window,
by invoking pop-to-buffer (see below).
If the optional argument force-same-window is non-nil and the selected window is
not suitable for displaying the buffer, this function always signals an error when called
non-interactively. In interactive use, if the selected window is a minibuffer window,
this function will try to use some other window instead. If the selected window isstrongly dedicated to its buffer, the option switch-to-buffer-in-dedicated-window
described next can be used to proceed.
[User Option]
This option, if non-nil, allows switch-to-buffer to proceed when called interactively
and the selected window is strongly dedicated to its buffer.
The following values are respected:

switch-to-buffer-in-dedicated-window

nil

Disallows switching and signals an error as in non-interactive use.

promptPrompts the user whether to allow switching.

pop

Invokes pop-to-buffer to proceed.

tMarks the selected window as non-dedicated and proceeds.

This option does not affect non-interactive calls of switch-to-buffer.
By default, switch-to-buffer tries to preserve window-point. This behavior can betuned using the following option.
[User Option]
If this variable is nil, switch-to-buffer displays the buffer specified by buffer-orname at the position of that buffer’s point. If this variable is already-displayed, it
tries to display the buffer at its previous position in the selected window, provided thebuffer is currently displayed in some other window on any visible or iconified frame. If
this variable is t, switch-to-buffer unconditionally tries to display the buffer at its
previous position in the selected window.

switch-to-buffer-preserve-window-point

Chapter 29: Windows

723

This variable is ignored if the buffer is already displayed in the selected window ornever appeared in it before, or if switch-to-buffer calls pop-to-buffer to display
the buffer.
[User Option]
If this variable is non-nil, switch-to-buffer respects display actions specified bydisplay-buffer-overriding-action, display-buffer-alist and other display related variables.

switch-to-buffer-obey-display-actions

The next two commands are similar to switch-to-buffer, except for the describedfeatures.

switch-to-buffer-other-window buffer-or-name &optional
norecord[Command]This function displays the buffer specified by buffer-or-name in some window otherthan the selected window. It uses the function pop-to-buffer internally (see below).
If the selected window already displays the specified buffer, it continues to do so, butanother window is nonetheless found to display it as well.
The buffer-or-name and norecord arguments have the same meanings as in switch-tobuffer.

switch-to-buffer-other-frame buffer-or-name &optional
norecord[Command]This function displays the buffer specified by buffer-or-name in a new frame. It uses
the function pop-to-buffer internally (see below).
If the specified buffer is already displayed in another window, in any frame on thecurrent terminal, this switches to that window instead of creating a new frame.
However, the selected window is never used for this.
The buffer-or-name and norecord arguments have the same meanings as in switch-tobuffer.
The above commands use the function pop-to-buffer, which flexibly displays a buffer
in some window and selects that window for editing. In turn, pop-to-buffer uses
display-buffer for displaying the buffer. Hence, all the variables affecting display-buffer
will affect it as well. See Section 29.13.1 [Choosing Window], page 724, for the documentationof display-buffer.

pop-to-buffer buffer-or-name &optional action norecord[Command]This function makes buffer-or-name the current buffer and displays it in some window,
preferably not the window currently selected. It then selects the displaying window.
If that window is on a different graphical frame, that frame is given input focus if
possible (see Section 30.10 [Input Focus], page 824).
If buffer-or-name is nil, it defaults to the buffer returned by other-buffer (seeSection 28.8 [Buffer List], page 681). If buffer-or-name is a string that is not thename of any existing buffer, this function creates a new buffer with that name; thenew buffer’s major mode is determined by the variable major-mode (see Section 24.2
[Major Modes], page 526). In any case, that buffer is made current and returned, evenwhen no suitable window was found to display it.

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If action is non-nil, it should be a display action to pass to display-buffer (seeSection 29.13.1 [Choosing Window], page 724). Alternatively, a non-nil, non-list valuemeans to pop to a window other than the selected one—even if the buffer is alreadydisplayed in the selected window.
Like switch-to-buffer, this function updates the buffer list unless norecord is nonnil.

29.13 Displaying a Buffer in a Suitable Window
This section describes lower-level functions Emacs uses to find or create a window for
displaying a specified buffer. The common workhorse of these functions is display-buffer
which eventually handles all incoming requests for buffer display (see Section 29.13.1[Choosing Window], page 724).
display-buffer delegates the task of finding a suitable window to so-called action
functions (see Section 29.13.2 [Buffer Display Action Functions], page 726). First,
display-buffer compiles a so-called action alist—a special association list that action
functions can use to fine-tune their behavior. Then it passes that alist on to each action
function it calls (see Section 29.13.3 [Buffer Display Action Alists], page 730).
The behavior of display-buffer is highly customizable. To understand how customizations are used in practice, you may wish to study examples illustrating the order of precedence
which display-buffer uses to call action functions (see Section 29.13.5 [Precedence of Action Functions], page 738). To avoid conflicts between Lisp programs calling display-buffer
and user customizations of its behavior, it may make sense to follow a number of guidelines
which are sketched in the final part of this section (see Section 29.13.6 [The Zen of Buffer
Display], page 743).

29.13.1 Choosing a Window for Displaying a Buffer
The command display-buffer flexibly chooses a window for display, and displays a specified
buffer in that window. It can be called interactively, via the key binding C-x 4 C-o. It isalso used as a subroutine by many functions and commands, including switch-to-buffer
and pop-to-buffer (see Section 29.12 [Switching Buffers], page 721).
This command performs several complex steps to find a window to display in. These steps
are described by means of display actions, which have the form (functions . alist). Here,functions is either a single function or a list of functions, referred to as “action functions”(see Section 29.13.2 [Buffer Display Action Functions], page 726); and alist is an association
list, referred to as “action alist” (see Section 29.13.3 [Buffer Display Action Alists], page 730).
See Section 29.13.6 [The Zen of Buffer Display], page 743, for samples of display actions.
An action function accepts two arguments: the buffer to display and an action alist. It
attempts to display the buffer in some window, picking or creating a window according to
its own criteria. If successful, it returns the window; otherwise, it returns nil.
display-buffer works by combining display actions from several sources, and callingthe action functions in turn, until one of them manages to display the buffer and returns a
non-nil value.

display-buffer buffer-or-name &optional action frame[Command]This command makes buffer-or-name appear in some window, without selecting thewindow or making the buffer current. The argument buffer-or-name must be a bufferChapter 29: Windows

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or the name of an existing buffer. The return value is the window chosen to display
the buffer, or nil if no suitable window was found.
The optional argument action, if non-nil, should normally be a display action (described above). display-buffer builds a list of action functions and an action alist,by consolidating display actions from the following sources (in order of their precedence,from highest to lowest):• The variable display-buffer-overriding-action.
• The user option display-buffer-alist.
• The action argument.
• The user option display-buffer-base-action.
• The constant display-buffer-fallback-action.
In practice this means that display-buffer builds a list of all action functions specified
by these display actions. The first element of this list is the first action function specified
by display-buffer-overriding-action, if any. Its last element is display-bufferpop-up-frame—the last action function specified by display-buffer-fallbackaction. Duplicates are not removed from this list—hence one and the same action
function may be called multiple times during one call of display-buffer.
display-buffer calls the action functions specified by this list in turn, passing thebuffer as the first argument and the combined action alist as the second argument,
until one of the functions returns non-nil. See Section 29.13.5 [Precedence of Action
Functions], page 738, for examples how display actions specified by different sources
are processed by display-buffer.
Note that the second argument is always the list of all action alist entries specified
by the sources named above. Hence, the first element of that list is the first action
alist entry specified by display-buffer-overriding-action, if any. Its last element
is the last alist entry of display-buffer-base-action, if any (the action alist of
display-buffer-fallback-action is empty).
Note also, that the combined action alist may contain duplicate entries and entries forthe same key with different values. As a rule, action functions always use the first
association of a key they find. Hence, the association an action function uses is notnecessarily the association provided by the display action that specified that action
function,
The argument action can also have a non-nil, non-list value. This has the special
meaning that the buffer should be displayed in a window other than the selected one,even if the selected window is already displaying it. If called interactively with a prefix
argument, action is t. Lisp programs should always supply a list value.
The optional argument frame, if non-nil, specifies which frames to check when
deciding whether the buffer is already displayed. It is equivalent to adding an element(reusable-frames . frame) to the action alist of action (see Section 29.13.3 [Buffer
Display Action Alists], page 730). The frame argument is provided for compatibility
reasons, Lisp programs should not use it.

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726[Variable]
The value of this variable should be a display action, which is treated with thehighest priority by display-buffer. The default value is an empty display action,i.e., (nil . nil).

display-buffer-overriding-action[User Option]
The value of this option is an alist mapping conditions to display actions. Eachcondition is passed to buffer-match-p (see Section 28.8 [Buffer List], page 681),
along with the buffer name and the action argument passed to display-buffer. If it
returns a non-nil value, then display-buffer uses the corresponding display action
to display the buffer. Caveat: if you use derived-mode or major-mode as condition,buffer-match-p could fail to report a match if display-buffer is called before themajor mode of the buffer is set.

display-buffer-alist[User Option]
The value of this option should be a display action. This option can be used to definea standard display action for calls to display-buffer.

display-buffer-base-action[Constant]
This display action specifies the fallback behavior for display-buffer if no otherdisplay actions are given.

display-buffer-fallback-action

29.13.2 Action Functions for Buffer Display
An action function is a function display-buffer calls for choosing a window to display
a buffer. Action functions take two arguments: buffer, the buffer to display, and alist, anaction alist (see Section 29.13.3 [Buffer Display Action Alists], page 730). They are supposed
to return a window displaying buffer if they succeed and nil if they fail.
The following basic action functions are defined in Emacs.

display-buffer-same-window buffer alist[Function]
This function tries to display buffer in the selected window. It fails if the selected
window is a minibuffer window or is dedicated to another buffer (see Section 29.15[Dedicated Windows], page 749). It also fails if alist has a non-nil inhibit-samewindow entry.

display-buffer-reuse-window buffer alist[Function]
This function tries to display buffer by finding a window that is already displaying it.
Windows on the selected frame are preferred to windows on other frames.
If alist has a non-nil inhibit-same-window entry, the selected window is not eligible
for reuse. The set of frames to search for a window already displaying buffer can be
specified with the help of the reusable-frames action alist entry. If alist contains no
reusable-frames entry, this function searches just the selected frame.
If this function chooses a window on another frame, it makes that frame visible and,
unless alist contains an inhibit-switch-frame entry, raises that frame if necessary.

display-buffer-reuse-mode-window buffer alist[Function]
This function tries to display buffer by finding a window that is displaying a buffer ina given mode.

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If alist contains a mode entry, its value specifies a major mode (a symbol) or a listof major modes. If alist contains no mode entry, the current major mode of buffer isused instead. A window is a candidate if it displays a buffer whose mode derives fromone of the modes specified thusly.
The behavior is also controlled by alist entries for inhibit-same-window,
reusable-frames and inhibit-switch-frame, like display-buffer-reusewindow does.

display-buffer-pop-up-window buffer alist[Function]
This function tries to display buffer by splitting the largest or least recently-usedwindow (usually located on the selected frame). It actually performs the split by callingthe function specified by split-window-preferred-function (see Section 29.13.4[Choosing Window Options], page 736).
The size of the new window can be adjusted by supplying window-height andwindow-width entries in alist. If alist contains a preserve-size entry, Emacs will
also try to preserve the size of the new window during future resize operations (seeSection 29.6 [Preserving Window Sizes], page 707).
This function fails if no window can be split. More often than not, this happens because
no window is large enough to allow splitting. Setting split-height-threshold or
split-width-threshold to lower values may help in this regard. Splitting also fails
when the selected frame has an unsplittable frame parameter; see Section 30.4.3.5[Buffer Parameters], page 812.

display-buffer-in-previous-window buffer alist[Function]
This function tries to display buffer in a window where it was displayed previously.
If alist contains a non-nil inhibit-same-window entry, the selected window is not
eligible for use. A dedicated window is usable only if it already shows buffer. If alist
contains a previous-window entry, the window specified by that entry is usable even
if it never showed buffer before.
If alist contains a reusable-frames entry (see Section 29.13.3 [Buffer Display Action
Alists], page 730), its value determines which frames to search for a suitable window. If
alist contains no reusable-frames entry, this function searches just the selected frame
if display-buffer-reuse-frames and pop-up-frames are both nil; it searches all
frames on the current terminal if either of those variables is non-nil.
If more than one window qualifies as usable according to these rules, this function
makes a choice in the following order of preference:• The window specified by any previous-window alist entry, provided it is not the
selected window.
• A window that showed buffer before, provided it is not the selected window.
• The selected window if it is either specified by a previous-window alist entry or
showed buffer before.

display-buffer-use-some-window buffer alist[Function]
This function tries to display buffer by choosing an existing window and displaying thebuffer in that window. It first tries to find a window that has not been used recently(see Section 29.10 [Cyclic Window Ordering], page 717) on any frame specified by a

Chapter 29: Windows728

lru-frames alist entry, falling back to the selected frame if no such entry exists. It
also prefers windows that satisfy the constraints specified by window-min-width andwindow-min-height alist entries; preferring full-width windows if no window-minwidth entry is found. Finally, it will not return a window whose use time is higher
than that specified by any lru-time entry provided by alist.
If no less recently used window is found, this function will try to use some otherwindow, preferably a large window on some visible frame. It can fail if all windows
are dedicated to other buffers (see Section 29.15 [Dedicated Windows], page 749).

display-buffer-use-least-recent-window buffer alist[Function]
This function is similar to display-buffer-use-some-window, but will try harder to
not use the a recently used window. In particular, it does not use the selected window.
In addition, it will first try to reuse a window that shows buffer already, base thedecision whether it should use a window showing another buffer on that window’s use
time alone and pop up a new window if no usable window is found.
Finally, this function will bump the use time (see Section 29.3 [Selecting Windows],
page 696) of any window it returns in order to avoid that further invocations will
use that window for showing another buffer. An application that wants to display
several buffers in a row can help this function by providing a lru-time alist entry it
has initially set to the value of the selected window’s use time. Each invocation ofthis function will then bump the use time of the window returned to a value higher
than that and a subsequent invocation will inhibit this function to use a window it
returned earlier.

display-buffer-in-direction buffer alist[Function]
This function tries to display buffer at a location specified by alist. For this purpose,
alist should contain a direction entry whose value is one of left, above (or up),right and below (or down). Other values are usually interpreted as below.
If alist also contains a window entry, its value specifies a reference window. Thatvalue can be a special symbol like main which stands for the selected frame’s main
window (see Section 29.17.2 [Side Window Options and Functions], page 753) or root
standing for the selected frame’s root window (see Section 29.2 [Windows and Frames],
page 692). It can also specify an arbitrary valid window. Any other value (or omitting
the window entry entirely) means to use the selected window as reference window.
This function first tries to reuse a window in the specified direction that alreadyshows buffer. If no such window exists, it tries to split the reference window in orderto produce a new window in the specified direction. If this fails as well, it will try
to display buffer in an existing window in the specified direction. In either case,the window chosen will appear on the side of the reference window specified by the
direction entry, sharing at least one edge with the reference window.
If the reference window is live, the edge the chosen window will share with it isalways the opposite of the one specified by the direction entry. For example, if thevalue of the direction entry is left, the chosen window’s right edge coordinate (seeSection 29.24 [Coordinates and Windows], page 769) will equal the reference window’s
left edge coordinate.
If the reference window is internal, a reused window must share with it the edge
specified by the direction entry. Hence if, for example, the reference window is theChapter 29: Windows

729

frame’s root window and the value of the direction entry is left, a reused window
must be on the left of the frame. This means that the left edge coordinate of thechosen window and that of the reference window are the same.
A new window, however, will be created by splitting the reference window such that thechosen window will share the opposite edge with the reference window. In our example,
a new root window would be created with a new live window and the reference window
as its children. The chosen window’s right edge coordinate would then equal the leftedge coordinate of the reference window. Its left edge coordinate would equal the leftedge coordinate of the frame’s new root window.
Four special values for direction entries allow to implicitly specify the selected frame’s
main window as the reference window: leftmost, top, rightmost and bottom. Thismeans that instead of, for example, (direction . left) (window . main) one canjust specify (direction . leftmost). An existing window alist entry is ignored insuch cases.

display-buffer-below-selected buffer alist[Function]
This function tries to display buffer in a window below the selected window. If there
is a window below the selected one and that window already displays buffer, it reusesthat window.
If there is no such window, this function tries to create a new window by splitting theselected one, and displays buffer there. It will also try to adjust that window’s size
provided alist contains a suitable window-height or window-width entry, see above.
If splitting the selected window fails and there is a non-dedicated window below theselected one showing some other buffer, this function tries to use that window for
showing buffer.
If alist contains a window-min-height entry, this function ensures that the windowused is or can become at least as high as specified by that entry’s value. Note that
this is only a guarantee. In order to actually resize the window used, alist must also
provide an appropriate window-height entry.

display-buffer-at-bottom buffer alist[Function]
This function tries to display buffer in a window at the bottom of the selected frame.
This either tries to split the window at the bottom of the frame or the frame’s root
window, or to reuse an existing window at the bottom of the selected frame.

display-buffer-pop-up-frame buffer alist[Function]
This function creates a new frame, and displays the buffer in that frame’s window.
It actually performs the frame creation by calling the function specified in pop-upframe-function (see Section 29.13.4 [Choosing Window Options], page 736). If alist
contains a pop-up-frame-parameters entry, the associated value is added to the
newly created frame’s parameters.

display-buffer-full-frame buffer alist[Function]
This function displays the buffer on the current frame, deleting all other windows sothat it takes up the full frame.

Chapter 29: Windows730

display-buffer-in-child-frame buffer alist[Function]
This function tries to display buffer in a child frame (see Section 30.14 [Child Frames],
page 831) of the selected frame, either reusing an existing child frame or by making a
new one. If alist has a non-nil child-frame-parameters entry, the corresponding
value is an alist of frame parameters to give the new frame. A parent-frame parameter
specifying the selected frame is provided by default. If the child frame should become
the child of another frame, a corresponding entry must be added to alist.
The appearance of child frames is largely dependent on the parameters provided via
alist. It is advisable to use at least ratios to specify the size (see Section 30.4.3.3 [SizeParameters], page 808) and the position (see Section 30.4.3.2 [Position Parameters],
page 805) of the child frame, and to add a keep-ratio parameter (see Section 30.4.3.6[Frame Interaction Parameters], page 812), in order to make sure that the child frame
remains visible. For other parameters that should be considered see Section 30.14[Child Frames], page 831.

display-buffer-use-some-frame buffer alist[Function]
This function tries to display buffer by finding a frame that meets a predicate (bydefault any frame other than the selected frame).
If this function chooses a window on another frame, it makes that frame visible and,
unless alist contains an inhibit-switch-frame entry, raises that frame if necessary.
If alist has a non-nil frame-predicate entry, its value is a function taking one
argument (a frame), returning non-nil if the frame is a candidate; this function
replaces the default predicate.
If alist has a non-nil inhibit-same-window entry, the selected window is not used;thus if the selected frame has a single window, it is not used.

display-buffer-no-window buffer alist[Function]
If alist has a non-nil allow-no-window entry, then this function does not display
buffer and returns the symbol fail. This constitutes the only exception to theconvention that an action function returns either nil or a window showing buffer. If
alist has no such allow-no-window entry, this function returns nil.

If this function returns fail, display-buffer will skip the execution of any further display actions and return nil immediately. If this function returns nil, display-buffer
will continue with the next display action, if any.
It is assumed that when a caller of display-buffer specifies a non-nil allow-nowindow entry, it is also able to handle a nil return value.
Two other action functions are described in their proper sections—display-bufferin-side-window (see Section 29.17.1 [Displaying Buffers in Side Windows], page 752) anddisplay-buffer-in-atom-window (see Section 29.18 [Atomic Windows], page 756).

29.13.3 Action Alists for Buffer Display
An action alist is an association list mapping predefined symbols recognized by action
functions to values these functions are supposed to interpret accordingly. In each call,display-buffer constructs a new, possibly empty action alist and passes that entire list on
to any action function it calls.

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By design, action functions are free in their interpretation of action alist entries. In fact,some entries like allow-no-window or previous-window have a meaning only for one or a
few action functions, and are ignored by the rest. Other entries, like inhibit-same-window
or window-parameters, are supposed to be respected by most action functions, including
those provided by application programs and external packages.
In the previous subsection we have described in detail how individual action functions
interpret the action alist entries they care about. Here we give a reference list of all
known action alist entries according to their symbols, together with their values and action
functions (see Section 29.13.2 [Buffer Display Action Functions], page 726) that recognize
them. Throughout this list, the terms “buffer” will refer to the buffer display-buffer is
supposed to display, and “value” refers to the entry’s value.
inhibit-same-window
If the value is non-nil, this signals that the selected window must not be used
for displaying the buffer. All action functions that (re-)use an existing window
should respect this entry.
previous-window
The value must specify a window that may have displayed the buffer previously.
display-buffer-in-previous-window will give preference to such a window
provided it is still live and not dedicated to another buffer.
mode

The value is either a major mode or a list of major modes. display-bufferreuse-mode-window may reuse a window whenever the value specified by thisentry matches the major mode of that window’s buffer. Other action functions
ignore such entries.

frame-predicate
The value must be a function taking one argument (a frame), supposed to return
non-nil if that frame is a candidate for displaying the buffer. This entry is usedby display-buffer-use-some-frame.
reusable-frames
The value specifies the set of frames to search for a window that can be reused
because it already displays the buffer. It can be set as follows:• nil means consider only windows on the selected frame. (Actually, the last
frame used that is not a minibuffer-only frame.)• visible means consider windows on all visible frames.
• 0 means consider windows on all visible or iconified frames.
• A frame means consider windows on that frame only.
• t means consider windows on all frames. (Note that this value is rarely theright thing to use—it might also return a tooltip frame.)
Note that the meaning of nil differs slightly from that of the all-frames argument
to next-window (see Section 29.10 [Cyclic Window Ordering], page 717).
A major client of this is display-buffer-reuse-window, but all other action
functions that try to reuse a window are affected as well. display-bufferin-previous-window consults it when searching for a window that previously
displayed the buffer on another frame.

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inhibit-switch-frame
A non-nil value prevents another frame from being raised or selected, if the window chosen by display-buffer is displayed there. Primarily affected by this are
display-buffer-use-some-frame and display-buffer-reuse-window. Ideally, display-buffer-pop-up-frame should be affected as well, but there is no
guarantee that the window manager will comply.
window-parameters
The value specifies an alist of window parameters to give the chosen window.
All action functions that choose a window should process this entry.
window-min-width
The value specifies a minimum width of the window used, in canonical frame
columns. The special value full-width means the chosen window should be
one that has no other windows on the left or right of it in its frame.
This entry is currently honored by display-buffer-use-some-window anddisplay-buffer-use-least-recent-window, which try hard to avoid returning a less recently used window that does not satisfy the entry.
Note that providing such an entry alone does not necessarily make the window
as wide as specified by its value. To actually resize an existing window or makea new window as wide as specified by this entry’s value, a window-width entry
specifying that value should be provided as well. Such a window-width entry
can, however, specify a completely different value, or ask the window width tofit that of its buffer, in which case the window-min-width entry provides theguaranteed minimum width of the window.
window-min-height
The value specifies a minimum height of the window used, in canonical framelines. The special value full-height means the chosen window should be afull-height window, one that has no other windows above or below it in its frame.
This entry is currently honored by display-buffer-below-selected which
does not use a window that is not as high as specified by this entry. It’s also honored by display-buffer-use-some-window and display-buffer-use-leastrecent-window which try hard to avoid returning a less recently used window
if it does not satisfy this constraint.
Note that providing such an entry alone does not necessarily make the window astall as specified by its value. To actually resize an existing window or make a new
window as tall as specified by that value, a window-height entry specifying thatvalue should be provided as well. Such a window-height entry can, however,specify a completely different value or ask the window height to be fit to that ofits buffer in which case the window-min-height entry provides the guaranteed
minimum height of the window used.
window-height
The value specifies whether and how to adjust the height of the chosen window
and can be one of the following:• nil means to leave the height of the chosen window alone.

Chapter 29: Windows733• An integer number specifies the desired total height of the chosen window
in lines.
• A floating-point number specifies the fraction of the chosen window’s desired
total height with respect to the total height of its frame’s root window.
• A cons cell whose car is body-lines and whose cdr is an integer thatspecifies the height of the chosen window’s body in frame lines.
• If the value specifies a function, that function is called with one argument—
the chosen window. The function is supposed to adjust the height of thewindow; its return value is ignored. Suitable functions are fit-windowto-buffer and shrink-window-if-larger-than-buffer, see Section 29.5
[Resizing Windows], page 703.
By convention, the height of the chosen window is adjusted only if the window ispart of a vertical combination (see Section 29.2 [Windows and Frames], page 692)
to avoid changing the height of other, unrelated windows. Also, this entry should
be processed only under certain conditions which are specified right below thislist.
window-widthThis entry is similar to the window-height entry described before, but used toadjust the chosen window’s width instead. The value can be one of the following:• nil means to leave the width of the chosen window alone.
• An integer specifies the desired total width of the chosen window in columns.
• A floating-point number specifies the fraction of the chosen window’s desired
total width with respect to the total width of the frame’s root window.
• A cons cell whose car is body-columns and whose cdr is an integer thatspecifies the width of the chosen window’s body in frame columns.
• If the value specifies a function, that function is called with one argument—
the chosen window. The function is supposed to adjust the width of thewindow; its return value is ignored.
window-sizeThis entry is a combination of the two preceding ones and can be used to adjust
the chosen window’s height and width. Since windows can be resized in one
direction only without affecting other windows, window-size is effective only
to set up the size of a window appearing alone on a frame. The value can beone of the following:• nil means to leave the size of the chosen window alone.
• A cons cell of two integers specifies the desired total width and height ofthe chosen window in lines and columns. It’s effect is to adjust the size ofthe frame accordingly.
• A cons cell whose car equals body-chars and whose cdr is a cons cellof two integers—the desired body width and height of the chosen window
in frame columns and lines. It’s effect is to adjust the size of the frame
accordingly.

Chapter 29: Windows734• If the value specifies a function, that function is called with one argument—
the chosen window. The function is supposed to adjust the size of thewindow’s frame; its return value is ignored.
This entry should be processed under only certain conditions which are specified
right below this list.
dedicated
If non-nil, such an entry tells display-buffer to mark any window it createsas dedicated to its buffer (see Section 29.15 [Dedicated Windows], page 749).
It does that by calling set-window-dedicated-p with the chosen window as
first argument and the entry’s value as second. Side windows are by default
dedicated with the value side (see Section 29.17.2 [Side Window Options andFunctions], page 753).
preserve-size
If non-nil such an entry tells Emacs to preserve the size of the window chosen(see Section 29.6 [Preserving Window Sizes], page 707). The value should beeither (t . nil) to preserve the width of the window, (nil . t) to preserve itsheight or (t . t) to preserve both, its width and its height. This entry should
be processed only under certain conditions which are specified right after thislist.
lru-frames
The value specifies the set of frames to search for a window that can be used
to display the buffer. It is honored by display-buffer-use-some-window anddisplay-buffer-use-least-recent-window when trying to find a less recently
used window showing some other buffer. Its values are the same as for thereusable-frames entry described above.
lru-time

The value is supposed to specify a use time (see Section 29.3 [Selecting Windows],
page 696). This entry is honored by display-buffer-use-some-window anddisplay-buffer-use-least-recent-window when trying to find a less recently
used window showing some other buffer. If a window’s use time is higher thanthe value specified by this option, these action functions will not consider sucha window for displaying the buffer.

bump-use-time
If non-nil, such an entry will cause display-buffer to bump the use time(see Section 29.3 [Selecting Windows], page 696) of the window it uses. Thisshould avoid later use of this window by action functions like display-bufferuse-some-window and display-buffer-use-least-recent-window for showing another buffer.
There is a fine difference between using this entry and using the action function
display-buffer-use-least-recent-window. Calling the latter means to only
bump the use times of windows that function uses for displaying the buffer. The
entry described here will cause display-buffer to bump the use time of any
window used for displaying a buffer.

Chapter 29: Windows735

pop-up-frame-parameters
The value specifies an alist of frame parameters to give a new frame, if one iscreated. display-buffer-pop-up-frame is its one and only addressee.
parent-frame
The value specifies the parent frame to be used when the buffer is displayed ona child frame. This entry is used only by display-buffer-in-child-frame.
child-frame-parameters
The value specifies an alist of frame parameters to use when the buffer is displayedon a child frame. This entry is used only by display-buffer-in-child-frame.
side

The value denotes the side of the frame or window where a new window displaying
the buffer shall be created. This entry is used by display-buffer-in-sidewindow to indicate the side of the frame where a new side window shall be placed(see Section 29.17.1 [Displaying Buffers in Side Windows], page 752). It is also
used by display-buffer-in-atom-window to indicate the side of an existing
window where the new window shall be located (see Section 29.18 [Atomic
Windows], page 756).

slot

If non-nil, the value specifies the slot of the side window supposed to display
the buffer. This entry is used only by display-buffer-in-side-window.

direction
The value specifies a direction which, together with a window entry, allows
display-buffer-in-direction to determine the location of the window todisplay the buffer.
window

The value specifies a window that is in some way related to the window chosen bydisplay-buffer. This entry is currently used by display-buffer-in-atomwindow to indicate the window on whose side the new window shall be created. It
is also used by display-buffer-in-direction to specify the reference window
on whose side the resulting window shall appear.

allow-no-window
If the value is non-nil, display-buffer does not necessarily have to display
the buffer and the caller is prepared to accept that. This entry is not intended
for user customizations, since there is no guarantee that an arbitrary caller ofdisplay-buffer will be able to handle the case that no window will display
the buffer. display-buffer-no-window is the only action function that cares
about this entry.
body-function
The value must be a function taking one argument (a displayed window). Thisfunction can be used to fill the displayed window’s body with some contents
that might depend on dimensions of the displayed window. It is called after the
buffer is displayed, and before the entries window-height, window-width andpreserve-size are applied that could resize the window to fit it to the inserted
contents.
By convention, the entries window-height, window-width and preserve-size are applied after the chosen window’s buffer has been set up and if and only if that window neverChapter 29: Windows736

showed another buffer before. More precisely, the latter means that the window must havebeen either created by the current display-buffer call or the window was created earlier
by display-buffer to show the buffer and never was used to show another buffer until it
was reused by the current invocation of display-buffer.
If no window-height, window-width or window-size entry was specified, the window
may still be resized automatically when the buffer is temporary and temp-buffer-resizemode has been enabled, Section 41.8 [Temporary Displays], page 1146. In that case, the cdr
of a window-height, window-width or window-size entry can be used to inhibit or override
the default behavior of temp-buffer-resize-mode for specific buffers or invocations ofdisplay-buffer.

29.13.4 Additional Options for Displaying Buffers
The behavior of buffer display actions (see Section 29.13.1 [Choosing Window], page 724)
can be further modified by the following user options.
[User Option]
If the value of this variable is non-nil, display-buffer is allowed to split an existing
window to make a new window for displaying in. This is the default.

pop-up-windows

This variable is provided for backward compatibility only. It is obeyed bydisplay-buffer via a special mechanism in display-buffer-fallback-action,
which calls the action function display-buffer-pop-up-window (see Section 29.13.2[Buffer Display Action Functions], page 726) when the value of this option is non-nil.
It is not consulted by display-buffer-pop-up-window itself, which the user may
specify directly in display-buffer-alist etc.
[User Option]
This variable specifies a function for splitting a window, in order to make a new
window for displaying a buffer. It is used by the display-buffer-pop-up-window
action function to actually split the window.

split-window-preferred-function

The value must be a function that takes one argument, a window, and returns either a
new window (which will be used to display the desired buffer) or nil (which means the
splitting failed). The default value is split-window-sensibly, which is documented
next.

split-window-sensibly &optional window[Function]
This function tries to split window and return the newly created window. If window
cannot be split, it returns nil. If window is omitted or nil, it defaults to the selected
window.
This function obeys the usual rules that determine when a window may be split (seeSection 29.7 [Splitting Windows], page 708). It first tries to split by placing the new
window below, subject to the restriction imposed by split-height-threshold (seebelow), in addition to any other restrictions. If that fails, it tries to split by placing
the new window to the right, subject to split-width-threshold (see below). If that
also fails, and the window is the only window on its frame, this function again tries
to split and place the new window below, disregarding split-height-threshold. If
this fails as well, this function gives up and returns nil.

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737[User Option]
This variable specifies whether split-window-sensibly is allowed to split the window
placing the new window below. If it is an integer, that means to split only if theoriginal window has at least that many lines. If it is nil, that means not to split thisway.

split-height-threshold[User Option]
This variable specifies whether split-window-sensibly is allowed to split the window
placing the new window to the right. If the value is an integer, that means to split
only if the original window has at least that many columns. If the value is nil, thatmeans not to split this way.

split-width-threshold[User Option]
This variable, if non-nil, causes display-buffer to even window sizes whenever itreuses an existing window, and that window is adjacent to the selected one.
If its value is width-only, sizes are evened only if the reused window is on the left or
right of the selected one and the selected window is wider than the reused one. If its
value is height-only sizes are evened only if the reused window is above or beneaththe selected window and the selected window is higher than the reused one. Any othernon-nil value means to even sizes in any of these cases provided the selected window
is larger than the reused one in the sense of their combination.

even-window-sizes[User Option]
If the value of this variable is non-nil, that means display-buffer may display
buffers by making new frames. The default is nil.
A non-nil value also means that when display-buffer is looking for a window
already displaying buffer-or-name, it can search any visible or iconified frame, not justthe selected frame.
This variable is provided mainly for backward compatibility. It is obeyed bydisplay-buffer via a special mechanism in display-buffer-fallback-action,
which calls the action function display-buffer-pop-up-frame (see Section 29.13.2[Buffer Display Action Functions], page 726) if the value is non-nil. (This isdone before attempting to split a window.) This variable is not consulted bydisplay-buffer-pop-up-frame itself, which the user may specify directly indisplay-buffer-alist etc.

pop-up-frames[User Option]
This variable specifies a function for creating a new frame, in order to make a new
window for displaying a buffer. It is used by the display-buffer-pop-up-frame
action function.
The value should be a function that takes no arguments and returns a frame, or nil if
no frame could be created. The default value is a function that creates a frame using
the parameters specified by pop-up-frame-alist (see below).

pop-up-frame-function[User Option]
This variable holds an alist of frame parameters (see Section 30.4 [Frame Parameters],
page 802), which is used by the function specified by pop-up-frame-function to
make a new frame. The default is nil.

pop-up-frame-alist

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This option is provided for backward compatibility only. Note, that whendisplay-buffer-pop-up-frame calls the function specified by pop-up-framefunction, it prepends the value of all pop-up-frame-parameters action alist
entries to pop-up-frame-alist so that the values specified by the action alist entry
effectively override any corresponding values of pop-up-frame-alist.
Hence, users should set up a pop-up-frame-parameters action alist entry indisplay-buffer-alist instead of customizing pop-up-frame-alist. Only this will
guarantee that the value of a parameter specified by the user overrides the value ofthat parameter specified by the caller of display-buffer.
Many efforts in the design of display-buffer have been given to maintain compatibility
with code that uses older options like pop-up-windows, pop-up-frames, pop-up-framealist, same-window-buffer-names and same-window-regexps. Lisp Programs and users
should refrain from using these options. Above we already warned against customizing
pop-up-frame-alist. Here we describe how to convert the remaining options to use display
actions instead.
pop-up-windows
This variable is t by default. Instead of customizing it to nil and thus telling
display-buffer what not to do, it’s much better to list in display-bufferbase-action the action functions it should try instead as, for example:(setopt
display-buffer-base-action'((display-buffer-reuse-window display-buffer-same-window
display-buffer-in-previous-window
display-buffer-use-some-window)))
pop-up-frames
Instead of customizing this variable to t, customize display-buffer-baseaction, for example, as follows:(setopt
display-buffer-base-action'((display-buffer-reuse-window display-buffer-pop-up-frame)(reusable-frames . 0)))same-window-buffer-namessame-window-regexps
Instead of adding a buffer name or a regular expression to one of these options
use a display-buffer-alist entry for that buffer specifying the action function
display-buffer-same-window.
(setopt
display-buffer-alist(cons '("\\*foo\\*" (display-buffer-same-window))
display-buffer-alist))

29.13.5 Precedence of Action Functions
From the past subsections we already know that display-buffer must be supplied witha number of display actions (see Section 29.13.1 [Choosing Window], page 724) in orderChapter 29: Windows739

to display a buffer. In a completely uncustomized Emacs, these actions are specified bydisplay-buffer-fallback-action in the following order of precedence: Reuse a window,
pop up a new window on the same frame, use a window previously showing the buffer,use some window and pop up a new frame. (Note that the remaining actions named bydisplay-buffer-fallback-action are void in an uncustomized Emacs).
Consider the following form:(display-buffer (get-buffer-create "*foo*"))Evaluating this form in the buffer *scratch* of an uncustomized Emacs session will usually
fail to reuse a window that shows *foo* already, but succeed in popping up a new window.
Evaluating the same form again will now not cause any visible changes—display-buffer
reused the window already showing *foo* because that action was applicable and had thehighest precedence among all applicable actions.
Popping up a new window will fail if there is not enough space on the selected frame. In
an uncustomized Emacs it typically fails when there are already two windows on a frame.
For example, if you now type C-x 1 followed by C-x 2 and evaluate the form once more,*foo* should show up in the lower window—display-buffer just used “some” window.
If, before typing C-x 2 you had typed C-x o, *foo* would have been shown in the upper
window because “some” window stands for the “least recently used” window and the selected
window has been least recently used if and only if it is alone on its frame.
Let’s assume you did not type C-x o and *foo* is shown in the lower window. TypeC-x o to get there followed by C-x left and evaluate the form again. This should display*foo* in the same, lower window because that window had already shown *foo* previously
and was therefore chosen instead of some other window.
So far we have only observed the default behavior in an uncustomized Emacs session.
To see how this behavior can be customized, let’s consider the option display-bufferbase-action. It provides a very coarse customization which conceptually affects the displayof any buffer. It can be used to supplement the actions supplied by display-bufferfallback-action by reordering them or by adding actions that are not present there but fit
more closely the user’s editing practice. However, it can also be used to change the default
behavior in a more profound way.
Let’s consider a user who, as a rule, prefers to display buffers on another frame. Such auser might provide the following customization:(setopt
display-buffer-base-action'((display-buffer-reuse-window display-buffer-pop-up-frame)(reusable-frames . 0)))This setting will cause display-buffer to first try to find a window showing the buffer on avisible or iconified frame and, if no such frame exists, pop up a new frame. You can observe
this behavior on a graphical system by typing C-x 1 in the window showing *scratch* andevaluating our canonical display-buffer form. This will usually create (and give focus to)a new frame whose root window shows *foo*. Iconify that frame and evaluate the canonicalform again: display-buffer will reuse the window on the new frame (usually raising theframe and giving it focus too).
Only if creating a new frame fails, display-buffer will apply the actions supplied bydisplay-buffer-fallback-action which means to again try reusing a window, poppingChapter 29: Windows

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up a new window and so on. A trivial way to make frame creation fail is supplied by thefollowing form:(let ((pop-up-frame-function 'ignore))(display-buffer (get-buffer-create "*foo*")))
We will forget about that form immediately after observing that it fails to create a newframe and uses a fallback action instead.
Note that display-buffer-reuse-window appears redundant in the customization of
display-buffer-base-action because it is already part of display-buffer-fallbackaction and should be tried there anyway. However, that would fail because due to theprecedence of display-buffer-base-action over display-buffer-fallback-action, atthat time display-buffer-pop-up-frame would have already won the race. In fact, this:(setopt
display-buffer-base-action'(display-buffer-pop-up-frame (reusable-frames . 0)))would cause display-buffer to always pop up a new frame which is probably not what
our user wants.
So far, we have only shown how users can customize the default behavior
of display-buffer. Let us now see how applications can change the course ofdisplay-buffer. The canonical way to do that is to use the action argument of
display-buffer or a function that calls it, like, for example, pop-to-buffer (seeSection 29.12 [Switching Buffers], page 721).
Suppose an application wants to display *foo* preferably below the selected window(to immediately attract the attention of the user to the new window) or, if that fails, in awindow at the bottom of the frame. It could do that with a call like this:(display-buffer(get-buffer-create "*foo*")'((display-buffer-below-selected display-buffer-at-bottom)))
In order to see how this new, modified form works, delete any frame showing *foo*, typeC-x 1 followed by C-x 2 in the window showing *scratch*, and subsequently evaluate that
form. display-buffer should split the upper window, and show *foo* in the new window.
Alternatively, if after C-x 2 you had typed C-x o, display-buffer would have split thewindow at the bottom instead.
Suppose now that, before evaluating the new form, you have made the selected window
as small as possible, for example, by evaluating the form (fit-window-to-buffer) in thatwindow. In that case, display-buffer would have failed to split the selected window andwould have split the frame’s root window instead, effectively displaying *foo* at the bottomof the frame.
In either case, evaluating the new form a second time should reuse the window alreadyshowing *foo* since both functions supplied by the action argument try to reuse such awindow first.
By setting the action argument, an application effectively overrules any customization of
display-buffer-base-action. Our user can now either accept the choice of the application,or redouble by customizing the option display-buffer-alist as follows:Chapter 29: Windows

741(setopt
display-buffer-alist'(("\\*foo\\*"(display-buffer-reuse-window display-buffer-pop-up-frame))))Trying this with the new, modified form above in a configuration that does not show *foo*
anywhere, will display *foo* on a separate frame, completely ignoring the action argumentof display-buffer.
Note that we didn’t care to specify a reusable-frames action alist entry in our specification of display-buffer-alist. display-buffer always takes the first one it finds—in ourcase the one specified by display-buffer-base-action. If we wanted to use a different
specification, for example, to exclude iconified frames showing *foo* from the list of reusable
ones, we would have to specify that separately, however:(setopt
display-buffer-alist'(("\\*foo\\*"(display-buffer-reuse-window display-buffer-pop-up-frame)(reusable-frames . visible))))If you try this, you will notice that repeated attempts to display *foo* will succeed to reusea frame only if that frame is visible.
The above example would allow the conclusion that users customize display-bufferalist for the sole purpose to overrule the action argument chosen by applications. Such a
conclusion would be incorrect. display-buffer-alist is the standard option for users to
direct the course of display of specific buffers in a preferred way regardless of whether the
display is also guided by an action argument.
We can, however, reasonably conclude that customizing display-buffer-alist differsfrom customizing display-buffer-base-action in two major aspects: it is stronger because
it overrides the action argument of display-buffer, and it allows to explicitly specify theaffected buffers. In fact, displaying other buffers is not affected in any way by a customization
for *foo*. For example,(display-buffer (get-buffer-create "*bar*"))continues being governed by the settings of display-buffer-base-action anddisplay-buffer-fallback-action only.
We could stop with our examples here but Lisp programs still have an ace up their sleeves
which they can use to overrule any customization of display-buffer-alist. It’s the variabledisplay-buffer-overriding-action which they can bind around display-buffer calls
as follows:(let ((display-buffer-overriding-action'((display-buffer-same-window))))(display-buffer(get-buffer-create "*foo*")'((display-buffer-below-selected display-buffer-at-bottom))))Evaluating this form will usually display *foo* in the selected window regardless of theaction argument and any user customizations. (Usually, an application will not botherto also provide an action argument. Here it just serves to illustrate the fact that it gets
overridden.)Chapter 29: Windows742

It might be illustrative to look at the list of action functions display-buffer would
have tried to display *foo* with the customizations we provided here. The list (includingcomments explaining who added this and the subsequent elements) is:(display-buffer-same-window ;; `display-buffer-overriding-action'
display-buffer-reuse-window ;; `display-buffer-alist'
display-buffer-pop-up-frame
display-buffer-below-selected ;; ACTION argument
display-buffer-at-bottom
display-buffer-reuse-window ;; `display-buffer-base-action'
display-buffer-pop-up-frame
display-buffer--maybe-same-window ;; `display-buffer-fallback-action'
display-buffer-reuse-window
display-buffer--maybe-pop-up-frame-or-window
display-buffer-in-previous-window
display-buffer-use-some-window
display-buffer-pop-up-frame)
Note that among the internal functions listed here, display-buffer--maybe-same-window
is effectively ignored while display-buffer--maybe-pop-up-frame-or-window actuallyruns display-buffer-pop-up-window.
The action alist passed in each function call is:((reusable-frames . visible)(reusable-frames . 0))
which shows that we have used the second specification of display-buffer-alist above,overriding the specification supplied by display-buffer-base-action. Suppose our user
had written that as(setopt
display-buffer-alist'(("\\*foo\\*"(display-buffer-reuse-window display-buffer-pop-up-frame)(inhibit-same-window . t)(reusable-frames . visible))))In this case the inhibit-same-window alist entry will successfully invalidate thedisplay-buffer-same-window specification from display-buffer-overriding-action
and display-buffer will show *foo* on another frame. To make display-bufferoverriding-action more robust in this regard, the application would have to specify anappropriate inhibit-same-window entry too, for example, as follows:(let ((display-buffer-overriding-action'(display-buffer-same-window (inhibit-same-window . nil))))(display-buffer (get-buffer-create "*foo*")))
This last example shows that while the precedence order of action functions is fixed, as
described in Section 29.13.1 [Choosing Window], page 724, an action alist entry specified
by a display action ranked lower in that order can affect the execution of a higher ranked
display action.

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29.13.6 The Zen of Buffer Display
In its most simplistic form, a frame accommodates always one single window that can beused for displaying a buffer. As a consequence, it is always the latest call of display-bufferthat will have succeeded in placing its buffer there.
Since working with such a frame is not very practical, Emacs by default allows formore complex frame layouts controlled by the default values of the frame size and thesplit-height-threshold and split-width-threshold options. Displaying a buffer not
yet shown on a frame then either splits the single window on that frame or (re-)uses one ofits two windows.
The default behavior is abandoned as soon as the user customizes one of these thresholds
or manually changes the frame’s layout. The default behavior is also abandoned when calling
display-buffer with a non-nil action argument or the user customizes one of the options
mentioned in the previous subsections. Mastering display-buffer soon may become afrustrating experience due to the plethora of applicable display actions and the resulting
frame layouts.
However, refraining from using buffer display functions and falling back on a split &delete windows metaphor is not a good idea either. Buffer display functions give Lisp
programs and users a framework to reconcile their different needs; no comparable framework
exists for splitting and deleting windows. Buffer display functions also allow to at least
partially restore the layout of a frame when removing a buffer from it later (see Section 29.16[Quitting Windows], page 749).
Below we will give a number of guidelines to redeem the frustration mentioned above
and thus to avoid literally losing buffers in-between the windows of a frame.
Write display actions without stressWriting display actions can be a pain because one has to lump together action
functions and action alists in one huge list. (Historical reasons prevented us
from having display-buffer support separate arguments for these.) It might
help to memorize some basic forms like the ones listed below:'(nil (inhibit-same-window . t))
specifies an action alist entry only and no action function. Its sole purpose is
to inhibit a display-buffer-same-window function specified elsewhere fromshowing the buffer in the same window, see also the last example of the preceding
subsection.
'(display-buffer-below-selected)
on the other hand, specifies one action function and an empty action alist. To
combine the effects of the above two specifications one would write the form'(display-buffer-below-selected (inhibit-same-window . t))
to add another action function one would write'((display-buffer-below-selected display-buffer-at-bottom)(inhibit-same-window . t))
and to add another alist entry one would write'((display-buffer-below-selected display-buffer-at-bottom)(inhibit-same-window . t)(window-height . fit-window-to-buffer))Chapter 29: Windows

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That last form can be used as action argument of display-buffer in thefollowing way:(display-buffer(get-buffer-create "*foo*")'((display-buffer-below-selected display-buffer-at-bottom)(inhibit-same-window . t)(window-height . fit-window-to-buffer)))
In a customization of display-buffer-alist it would be used as follows:(setopt
display-buffer-alist'(("\\*foo\\*"(display-buffer-below-selected display-buffer-at-bottom)(inhibit-same-window . t)(window-height . fit-window-to-buffer))))To add a customization for a second buffer one would then write:(setopt
display-buffer-alist'(("\\*foo\\*"(display-buffer-below-selected display-buffer-at-bottom)(inhibit-same-window . t)(window-height . fit-window-to-buffer))("\\*bar\\*"(display-buffer-reuse-window display-buffer-pop-up-frame)(reusable-frames . visible))))Treat each other with respect
display-buffer-alist and display-buffer-base-action are user options—
Lisp programs must never set or rebind them. display-buffer-overridingaction, on the other hand, is reserved for applications—who seldom use that
option and if they use it, then with utmost care.
Older implementations of display-buffer frequently caused users and applications to fight over the settings of user options like pop-up-frames andpop-up-windows (see Section 29.13.4 [Choosing Window Options], page 736).
This was one major reason for redesigning display-buffer—to provide a clear
framework specifying what users and applications should be allowed to do.
Lisp programs must be prepared that user customizations may cause buffers
to get displayed in an unexpected way. They should never assume in theirsubsequent behavior, that the buffer has been shown precisely the way they
asked for in the action argument of display-buffer.
Users should not pose too many and too severe restrictions on how arbitrary
buffers get displayed. Otherwise, they will risk to lose the characteristics ofshowing a buffer for a certain purpose. Suppose a Lisp program has been written
to compare different versions of a buffer in two windows side-by-side. If thecustomization of display-buffer-alist prescribes that any such buffer shouldbe always shown in or below the selected window, the program will have a hardtime to set up the desired window configuration via display-buffer.

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To specify a preference for showing an arbitrary buffer, users should customize
display-buffer-base-action. An example of how users who prefer working with multiple frames would do that was given in the previous subsection.
display-buffer-alist should be reserved for displaying specific buffers in a
specific way.
Consider reusing a window that already shows the buffer
Generally, it’s always a good idea for users and Lisp programmers to be prepared
for the case that a window already shows the buffer in question and to reusethat window. In the preceding subsection we have shown that failing to doso properly may cause display-buffer to continuously pop up a new frame
although a frame showing that buffer existed already. In a few cases only, it
might be undesirable to reuse a window, for example, when a different portionof the buffer should be shown in that window.
Hence, display-buffer-reuse-window is one action function that should be
used as often as possible, both in action arguments and customizations. An
inhibit-same-window entry in the action argument usually takes care of themost common case where reusing a window showing the buffer should be
avoided—that where the window in question is the selected one.
Attract focus to the window chosen
This is a no-brainer for people working with multiple frames—the frame
showing the buffer will automatically raise and get focus unless aninhibit-switch-frame entry forbids it. For single frame users this task can
be considerably more difficult. In particular, display-buffer-pop-up-window
and display-buffer-use-some-window can become obtrusive in this regard.
They split or use a seemingly arbitrary (often the largest or least recently used)window, distracting the user’s attention.
Some Lisp programs therefore try to choose a window at the bottom of theframe, for example, in order to display the buffer in vicinity of the minibuffer
window where the user is expected to answer a question related to the new window. For non-input related actions display-buffer-below-selected might bepreferable because the selected window usually already has the user’s attention.
Take care which window is selected
Many applications call display-buffer from within window excursions
produced by with-selected-window or select-window calls with a non-nil
norecord argument. This is almost always a bad idea because the window
selected within such an excursion is usually not the window selected in theconfiguration presented to the user.
If, for example, a user had added an inhibit-same-window alist entry, thatentry would have avoided the window selected within the scope of the excursion
and not the window selected in the resulting configuration. Even if no suchentry has been added, the resulting behavior might be strange. While in a frame
containing one live window, evaluating the following form
(progn(split-window)(display-buffer "*Messages*"))Chapter 29: Windows

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will display a window showing the *Messages* buffer at the bottom and leave
the other window selected. Evaluating the next form
(with-selected-window (split-window)(display-buffer "*Messages*"))will display *Messages* in a window on the top and select it which is usually
not what display-buffer is supposed to do.
On the other hand, while evaluating the following form
(progn(split-window)(pop-to-buffer "*Messages*"))will correctly select the *Messages* buffer, the next form
(progn(split-window)(with-selected-window (selected-window)(pop-to-buffer "*Messages*")))
will not.
Also, invocations of action functions like display-buffer-use-some-window
and display-buffer-use-least-recent-window that expect the selected window to have the highest use time among all windows, may fail to produce awindow according to their specifications.
Hence, an application that relies on using a window excursion should try to
postpone the display-buffer call until after the excursion has terminated.

29.14 Window History
Each window remembers in a list the buffers it has previously displayed, and the order in whichthese buffers were removed from it. This history is used, for example, by replace-bufferin-windows (see Section 29.11 [Buffers and Windows], page 720), and when quitting windows(see Section 29.16 [Quitting Windows], page 749). The list is automatically maintained byEmacs, but you can use the following functions to explicitly inspect or alter it:

window-prev-buffers &optional window[Function]
This function returns a list specifying the previous contents of window. The optional
argument window should be a live window and defaults to the selected one.
Each list element has the form (buffer window-start window-pos), where buffer isa buffer previously shown in the window, window-start is the window start position(see Section 29.20 [Window Start and End], page 759) when that buffer was last shown,and window-pos is the point position (see Section 29.19 [Window Point], page 758)
when that buffer was last shown in window.
The list is ordered so that earlier elements correspond to more recently-shown buffers,
and the first element usually corresponds to the buffer most recently removed fromthe window.

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set-window-prev-buffers window prev-buffers[Function]
This function sets window’s previous buffers to the value of prev-buffers. The argument
window must be a live window and defaults to the selected one. The argument prevbuffers should be a list of the same form as that returned by window-prev-buffers.

In addition, each window maintains a list of next buffers, which is a list of buffers
re-shown by switch-to-prev-buffer (see below). This list is mainly used by switch-toprev-buffer and switch-to-next-buffer for choosing buffers to switch to.

window-next-buffers &optional window[Function]
This function returns the list of buffers recently re-shown in window via switch-toprev-buffer. The window argument must denote a live window or nil (meaning theselected window).

set-window-next-buffers window next-buffers[Function]
This function sets the next buffer list of window to next-buffers. The window argument
should be a live window or nil (meaning the selected window). The argument nextbuffers should be a list of buffers.

The following commands can be used to cycle through the global buffer list, much likebury-buffer and unbury-buffer. However, they cycle according to the specified window’s
history list, rather than the global buffer list. In addition, they restore window-specificwindow start and point positions, and may show a buffer even if it is already shownin another window. The switch-to-prev-buffer command, in particular, is used byreplace-buffer-in-windows, bury-buffer and quit-window to find a replacement buffer
for a window.

switch-to-prev-buffer &optional window bury-or-kill[Command]This command displays the previous buffer in window. The argument window should
be a live window or nil (meaning the selected window). If the optional argumentbury-or-kill is non-nil, this means that the buffer currently shown in window is about
to be buried or killed and consequently should not be switched to in future invocationsof this command.
The previous buffer is usually the buffer shown before the buffer currently shownin window. However, a buffer that has been buried or killed, or has been alreadyshown by a recent invocation of switch-to-prev-buffer, does not qualify as previous
buffer.
If repeated invocations of this command have already shown all buffers previously
shown in window, further invocations will show buffers from the buffer list of theframe window appears on (see Section 28.8 [Buffer List], page 681).
The option switch-to-prev-buffer-skip described below can be used to inhibit
switching to certain buffers, for example, to those already shown in another window.
Also, if window’s frame has a buffer-predicate parameter (see Section 30.4.3.5[Buffer Parameters], page 812), that predicate may inhibit switching to certain buffers.

switch-to-next-buffer &optional window[Command]This command switches to the next buffer in window, thus undoing the effect of thelast switch-to-prev-buffer command in window. The argument window must be alive window and defaults to the selected one.

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If there is no recent invocation of switch-to-prev-buffer that can be undone, thisfunction tries to show a buffer from the buffer list of the frame window appears on(see Section 28.8 [Buffer List], page 681).
The option switch-to-prev-buffer-skip and the buffer-predicate (seeSection 30.4.3.5 [Buffer Parameters], page 812) of window’s frame affect this commandas they do for switch-to-prev-buffer.
By default switch-to-prev-buffer and switch-to-next-buffer can switch to a bufferthat is already shown in another window. The following option can be used to override thisbehavior.
[User Option]
If this variable is nil, switch-to-prev-buffer may switch to any buffer, including
those already shown in other windows.

switch-to-prev-buffer-skip

If this variable is non-nil, switch-to-prev-buffer will refrain from switching tocertain buffers. The following values can be used:• this means do not switch to a buffer shown on the frame that hosts the window
switch-to-prev-buffer is acting upon.
• visible means do not switch to a buffer shown on any visible frame.
• 0 (the number zero) means do not switch to a buffer shown on any visible or
iconified frame.
• t means do not switch to a buffer shown on any live frame.
• A function that takes three arguments—the window argument of switch-toprev-buffer, a buffer switch-to-prev-buffer intends to switch to and thebury-or-kill argument of switch-to-prev-buffer. If that function returns nonnil, switch-to-prev-buffer will refrain from switching to the buffer specified
by the second argument.
The command switch-to-next-buffer obeys this option in a similar way. If thisoption specifies a function, switch-to-next-buffer will call that function with thethird argument always nil.
Note that since switch-to-prev-buffer is called by bury-buffer, replace-bufferin-windows and quit-restore-window as well, customizing this option may also
affect the behavior of Emacs when a window is quit or a buffer gets buried or killed.
Note also that under certain circumstances switch-to-prev-buffer and switch-tonext-buffer may ignore this option, for example, when there is only one buffer leftthese functions can switch to.
[User Option]
This user option should be either a regular expression or a list of regular expressions.
Buffers whose names match one of those regular expressions will be ignored byswitch-to-prev-buffer and switch-to-next-buffer (except when there’s no otherbuffer to switch to).

switch-to-prev-buffer-skip-regexp

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29.15 Dedicated Windows
Functions for displaying a buffer can be told to not use specific windows by marking thesewindows as dedicated to their buffers. display-buffer (see Section 29.13.1 [Choosing
Window], page 724) never uses a dedicated window for displaying another buffer in it.
get-lru-window and get-largest-window (see Section 29.10 [Cyclic Window Ordering],
page 717) do not consider dedicated windows as candidates when their dedicated argument
is non-nil. The behavior of set-window-buffer (see Section 29.11 [Buffers and Windows],
page 720) with respect to dedicated windows is slightly different, see below.
Functions supposed to remove a buffer from a window or a window from a frame canbehave specially when a window they operate on is dedicated. We will distinguish four basic
cases, namely where (1) the window is not the only window on its frame, (2) the window is
the only window on its frame but there are other frames on the same terminal left, (3) thewindow is the only window on the only frame on the same terminal, and (4) the dedication’svalue is side (see Section 29.17.1 [Displaying Buffers in Side Windows], page 752).
In particular, delete-windows-on (see Section 29.8 [Deleting Windows], page 711) handles case (2) by deleting the associated frame and cases (3) and (4) by showing another buffer
in that frame’s only window. The function replace-buffer-in-windows (see Section 29.11[Buffers and Windows], page 720) which is called when a buffer gets killed, deletes thewindow in case (1) and behaves like delete-windows-on otherwise.
When bury-buffer (see Section 28.8 [Buffer List], page 681) operates on the selected window (which shows the buffer that shall be buried), it handles case (2) by calling frame-autohide-function (see Section 29.16 [Quitting Windows], page 749) to deal with the selected
frame. The other two cases are handled as with replace-buffer-in-windows.

window-dedicated-p &optional window[Function]
This function returns non-nil if window is dedicated to its buffer and nil otherwise.
More precisely, the return value is the value assigned by the last call of set-windowdedicated-p for window, or nil if that function was never called with window as its
argument. The default for window is the selected window.

set-window-dedicated-p window flag

[Function]
This function marks window as dedicated to its buffer if flag is non-nil, and nondedicated otherwise.

As a special case, if flag is t, window becomes strongly dedicated to its buffer.
set-window-buffer signals an error when the window it acts upon is strongly dedicated to its buffer and does not already display the buffer it is asked to display. Other
functions do not treat t differently from any non-nil value.
You can also tell display-buffer to mark a window it creates as dedicated to its buffer
by providing a suitable dedicated action alist entry (see Section 29.13.3 [Buffer Display
Action Alists], page 730).

29.16 Quitting Windows
After a command uses display-buffer to put a buffer on the screen, the user may decideto hide it and return to the previous configuration of the Emacs display. We call that

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quitting the window. The way to do this is to call quit-window while the window used bydisplay-buffer is the selected window.
The right way to restore the previous configuration of the display depends on what wasdone to the window where the buffer now appears. It might be right to delete that window,
or delete its frame, or just display another buffer in that window. One complication is thatthe user may have changed the window configuration since the act of displaying that buffer,and it would be undesirable to undo the user’s explicitly requested changes.
To enable quit-window to do the right thing, display-buffer saves information about
what it did in the window’s quit-restore parameter (see Section 29.27 [Window Parameters],
page 776).

quit-window &optional kill window[Command]This command quits window and buries its buffer. The argument window must be alive window and defaults to the selected one. With prefix argument kill non-nil, it
kills the buffer instead of burying it.
The function quit-window first runs quit-window-hook. Then it calls the function
quit-restore-window, described next, which does the hard work.

You can get more control by calling quit-restore-window instead.

quit-restore-window &optional window bury-or-kill[Function]
This function handles window and its buffer after quitting. The optional argument
window must be a live window and defaults to the selected one. The function takes
account of the window’s quit-restore parameter.
The optional argument bury-or-kill specifies how to deal with window’s buffer. The
following values are meaningful:nilThis means to not deal with the buffer in any particular way. As aconsequence, if window is not deleted, invoking switch-to-prev-buffer
will usually show the buffer again.

appendThis means that if window is not deleted, its buffer is moved to the endof window’s list of previous buffers (see Section 29.14 [Window History],
page 746), so it’s less likely that future invocations of switch-to-prevbuffer will switch to it. Also, it moves the buffer to the end of the frame’s
buffer list (see Section 28.8 [Buffer List], page 681).

buryThis means that if window is not deleted, its buffer is removed from
window’s list of previous buffers. Also, it moves the buffer to the end of
the frame’s buffer list. This is the most reliable way to prevent switch-toprev-buffer from switching to this buffer again, short of killing the buffer.

killThis means to kill window’s buffer.

The argument bury-or-kill also specifies what to do with window’s frame when window
should be deleted, if it is the only window on its frame, and there are other frameson that frame’s terminal. If bury-or-kill equals kill, it means to delete the frame.
Otherwise, the fate of the frame is determined by calling frame-auto-hide-function(see below) with that frame as sole argument.
This function always sets window’s quit-restore parameter to nil unless it deletes
the window.

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The window window’s quit-restore parameter (see Section 29.27 [Window Parameters],
page 776) should be nil or a list of four elements:(method obuffer owindow this-buffer)
The first element, method, is one of the four symbols window, frame, same and other.
frame and window control how to delete window, while same and other control displaying
some other buffer in it.
Specifically, window means that the window has been specially created bydisplay-buffer; frame means that a separate frame has been created; same, that thewindow has only ever displayed this buffer; other, that the window showed another buffer
before.
The second element, obuffer, is either one of the symbols window or frame, or a list of
the form(prev-buffer prev-window-start prev-window-point height)
which says which buffer was shown in window before, that buffer’s window start (seeSection 29.20 [Window Start and End], page 759) and window point (see Section 29.19[Window Point], page 758) positions at that time, and window’s height at that time. If
prev-buffer is still live when quitting window, quitting the window may reuse window todisplay prev-buffer.
The third element, owindow, is the window that was selected just before the displaying
was done. If quitting deletes window, it tries to select owindow.
The fourth element, this-buffer, is the buffer whose displaying set the quit-restore
parameter. Quitting window may delete that window only if it still shows that buffer.
Quitting window tries to delete it if and only if (1) method is either window or frame, (2)the window has no history of previously-displayed buffers and (3) this-buffer equals the buffer
currently displayed in window. If window is part of an atomic window (see Section 29.18[Atomic Windows], page 756), quitting will try to delete the root of that atomic window
instead. In either case, it tries to avoid signaling an error when window cannot be deleted.
If obuffer is a list, and prev-buffer is still live, quitting displays prev-buffer in window
according to the rest of the elements of obuffer. This includes resizing the window to height
if it was temporarily resized to display this-buffer.
Otherwise, if window was previously used for displaying other buffers (see Section 29.14[Window History], page 746), the most recent buffer in that history will be displayed.
The following option specifies a function to do the right thing with a frame containing
one window when quitting that window.
[User Option]
The function specified by this option is called to automatically hide frames. Thisfunction is called with one argument—a frame.

frame-auto-hide-function

The function specified here is called by bury-buffer (see Section 28.8 [Buffer List],
page 681) when the selected window is dedicated and shows the buffer to bury. It isalso called by quit-restore-window (see above) when the frame of the window toquit has been specially created for displaying that window’s buffer and the buffer is
not killed.

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The default is to call iconify-frame (see Section 30.11 [Visibility of Frames], page 828).
Alternatively, you may specify either delete-frame (see Section 30.7 [Deleting Frames],
page 822) to remove the frame from its display, make-frame-invisible to make theframe invisible, ignore to leave the frame unchanged, or any other function that cantake a frame as its sole argument.
Note that the function specified by this option is called only if the specified frame
contains just one live window and there is at least one other frame on the same
terminal.
For a particular frame, the value specified here may be overridden by that frame’s
auto-hide-function frame parameter (see Section 30.4.3.6 [Frame Interaction Parameters], page 812).

29.17 Side Windows
Side windows are special windows positioned at any of the four sides of a frame’s root
window (see Section 29.2 [Windows and Frames], page 692). In practice, this means thatthe area of the frame’s root window is subdivided into a main window and a number of side
windows surrounding that main window. The main window is either a “normal” live windowor specifies the area containing all the normal windows.
In their most simple form of use, side windows allow to display specific buffers always in thesame area of a frame. Hence they can be regarded as a generalization of the concept provided
by display-buffer-at-bottom (see Section 29.13.2 [Buffer Display Action Functions],
page 726) to the remaining sides of a frame. With suitable customizations, however, side
windows can be also used to provide frame layouts similar to those found in so-called
integrated development environments (IDEs).

29.17.1 Displaying Buffers in Side Windows
The following action function for display-buffer (see Section 29.13.2 [Buffer Display
Action Functions], page 726) creates or reuses a side window for displaying the specified
buffer.

display-buffer-in-side-window buffer alist[Function]
This function displays buffer in a side window of the selected frame. It returns thewindow used for displaying buffer, nil if no such window can be found or created.
alist is an association list of symbols and values as for display-buffer. The following
symbols in alist are special for this function:side

Denotes the side of the frame where the window shall be located. Validvalues are left, top, right and bottom. If unspecified, the window islocated at the bottom of the frame.

slot

Denotes a slot at the specified side where to locate the window. A valueof zero means to preferably position the window in the middle of thespecified side. A negative value means to use a slot preceding (that is,above or on the left of) the middle slot. A positive value means to use aslot following (that is, below or on the right of) the middle slot. Hence, allwindows on a specific side are ordered by their slot value. If unspecified,
the window is located in the middle of the specified side.

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dedicated
The dedicated flag (see Section 29.15 [Dedicated Windows], page 749) has aslightly different meaning for side windows. When a side window is created,that flag is set to the value side to prevent display-buffer to use thewindow in other action functions. Its value persists across invocations ofquit-window, kill-buffer, previous-buffer and next-buffer.
In particular, these commands will refrain from showing, in a side window,
buffers that have not been displayed in that window before. They will
also refrain from having a normal, non-side window show a buffer thathas been already displayed in a side window. A notable exception to thelatter rule occurs when an application, after displaying a buffer, resets thatbuffer’s local variables. To override these rules and always delete a side
window with quit-window or kill-buffer, and eventually prevent theuse of previous-buffer and next-buffer, set this value to t or specify
a value via display-buffer-mark-dedicated.
If you specify the same slot on the same side for two or more different buffers, thebuffer displayed last is shown in the corresponding window. Hence, slots can be used
for sharing the same side window between buffers.
This function installs the window-side and window-slot parameters (seeSection 29.27 [Window Parameters], page 776) and makes them persistent. It does
not install any other window parameters unless they have been explicitly provided via
a window-parameters entry in alist.
By default, side windows cannot be split via split-window (see Section 29.7 [Splitting
Windows], page 708). Also, a side window is not reused or split by any buffer display
action (see Section 29.13.2 [Buffer Display Action Functions], page 726) unless it is explicitly
specified as target of that action. Note also that delete-other-windows cannot make aside window the only window on its frame (see Section 29.8 [Deleting Windows], page 711).

29.17.2 Side Window Options and Functions
The following options provide additional control over the placement of side windows.
[User Option]
If non-nil, the side windows on the left and right of a frame occupy the frame’s fullheight. Otherwise, the side windows on the top and bottom of the frame occupy theframe’s full width.

window-sides-vertical[User Option]
This option specifies the maximum number of side windows on each side of a frame.
The value is a list of four elements specifying the number of side window slots on (inthis order) the left, top, right and bottom of each frame. If an element is a number, itmeans to display at most that many windows on the corresponding side. If an element
is nil, it means there’s no bound on the number of slots on that side.

window-sides-slots

If any of the specified values is zero, no window can be created on the corresponding
side. display-buffer-in-side-window will not signal an error in that case, but will
return nil. If a specified value just forbids the creation of an additional side window,

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the most suitable window on that side is reused and may have its window-slot
parameter changed accordingly.
[User Option]
This option specifies whether top/bottom side windows should appear in reverse order.
When this is nil, side windows on the top and bottom of a frame are always drawn
from left to right with increasing slot values. When this is t, the drawing order isreversed and side windows on the top and bottom of a frame are drawn from right toleft with increasing slot values.
When this is bidi, the drawing order is reversed if and only if the value ofbidi-paragraph-direction (see Section 41.27 [Bidirectional Display], page 1250) is
right-to-left in the buffer displayed in the window most recently selected within
the main window area of this frame. Sometimes that window may be hard to find,so heuristics are used to avoid that the drawing order changes inadvertently whenanother window gets selected.
The layout of side windows on the left or right of a frame is not affected by the valueof this variable.

window-sides-reversed

When a frame has side windows, the following function returns the main window of thatframe.

window-main-window &optional frame[Function]
This function returns the main window of the specified frame. The optional argument
frame must be a live frame and defaults to the selected one.
If frame has no side windows, it returns frame’s root window. Otherwise, it returns
either an internal non-side window such that all other non-side windows on frame
descend from it, or the single live non-side window of frame. Note that the main
window of a frame cannot be deleted via delete-window.

The following command is handy to toggle the appearance of all side windows on a
specified frame.

window-toggle-side-windows &optional frame[Command]This command toggles side windows on the specified frame. The optional argument
frame must be a live frame and defaults to the selected one.
If frame has at least one side window, this command saves the state of frame’s root
window in the frame’s window-state frame parameter and deletes all side windows
on frame afterwards.
If frame has no side windows, but does have a window-state parameter, this command
uses that parameter’s value to restore the side windows on frame leaving frame’s main
window alone.
An error is signaled if frame has no side windows and no saved state is found for it.

29.17.3 Frame Layouts with Side Windows
Side windows can be used to create more complex frame layouts like those provided byintegrated development environments (IDEs). In such layouts, the area of the main window
is where the normal editing activities take place. Side windows are not conceived for editingChapter 29: Windows

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in the usual sense. Rather, they are supposed to display information complementary to thecurrent editing activity, like lists of files, tags or buffers, help information, search or grep
results or shell output.
The layout of such a frame might appear as follows:___________________________________|*Buffer List*||___________________________________|
|
|
|
|
| * |
| * |
| d |
| T |
| i |
| a |
| r |
Main Window Area
| g |
| e |
| s |
| d |
| * |
| * |
|
|
|_____|_______________________|_____|| *help*/*grep*/ | *shell*/|| *Completions*| *compilation* ||_________________|_________________||
Echo Area||___________________________________|

The following example illustrates how window parameters (see Section 29.27 [Window Parameters], page 776) can be used with display-buffer-in-side-window (see Section 29.17.1[Displaying Buffers in Side Windows], page 752) to set up code for producing the framelayout sketched above.
(defvar parameters'(window-parameters . ((no-other-window . t)
(no-delete-other-windows . t))))(setq fit-window-to-buffer-horizontally t)(setq window-resize-pixelwise t)(setq
display-buffer-alist`(("\\*Buffer List\\*" display-buffer-in-side-window(side . top) (slot . 0) (window-height . fit-window-to-buffer)(preserve-size . (nil . t)) ,parameters)("\\*Tags List\\*" display-buffer-in-side-window(side . right) (slot . 0) (window-width . fit-window-to-buffer)(preserve-size . (t . nil)) ,parameters)("\\*\\(?:help\\|grep\\|Completions\\)\\*"
display-buffer-in-side-window(side . bottom) (slot . -1) (preserve-size . (nil . t)),parameters)("\\*\\(?:shell\\|compilation\\)\\*" display-buffer-in-side-window(side . bottom) (slot . 1) (preserve-size . (nil . t)),parameters)))

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This specifies display-buffer-alist entries (see Section 29.13.1 [Choosing Window],
page 724) for buffers with fixed names. In particular, it asks for showing *Buffer List*
with adjustable height at the top of the frame and *Tags List* with adjustable width on
the frame’s right. It also asks for having the *help*, *grep* and *Completions* buffers
share a window on the bottom left side of the frame and the *shell* and *compilation*buffers appear in a window on the bottom right side of the frame.
Note that the option fit-window-to-buffer-horizontally must have a non-nil value
in order to allow horizontal adjustment of windows. Entries are also added that ask forpreserving the height of side windows at the top and bottom of the frame and the widthof side windows at the left or right of the frame. To assure that side windows retain theirrespective sizes when maximizing the frame, the variable window-resize-pixelwise is set
to a non-nil value. See Section 29.5 [Resizing Windows], page 703.
The last form also makes sure that none of the created side windows are accessible
via C-x o by installing the no-other-window parameter for each of these windows. In
addition, it makes sure that side windows are not deleted via C-x 1 by installing the
no-delete-other-windows parameter for each of these windows.
Since dired buffers have no fixed names, we use a special function dired-defaultdirectory-on-left in order to display a lean directory buffer on the left side of the frame.
(defun dired-default-directory-on-left ()"Display `default-directory' in side window on left, hiding details."(interactive)(let ((buffer (dired-noselect default-directory)))(with-current-buffer buffer (dired-hide-details-mode t))(display-buffer-in-side-windowbuffer `((side . left) (slot . 0)
(window-width . fit-window-to-buffer)(preserve-size . (t . nil)) ,parameters))))
Evaluating the preceding forms and typing, in any order, M-x list-buffers, C-h f,
M-x shell, M-x list-tags, and M-x dired-default-directory-on-left should now reproduce the frame layout sketched above.

29.18 Atomic Windows
Atomic windows are rectangular compositions of at least two live windows. They have thefollowing distinctive characteristics:• The function split-window (see Section 29.7 [Splitting Windows], page 708), whenapplied to a constituent of an atomic window, will try to create the new window outsideof the atomic window.
• The function delete-window (see Section 29.8 [Deleting Windows], page 711), whenapplied to a constituent of an atomic window, will try to delete the entire atomic window
instead.
• The function delete-other-windows (see Section 29.8 [Deleting Windows], page 711),
when applied to a constituent of an atomic window, will try to make the atomic window
fill its frame or main window (see Section 29.17 [Side Windows], page 752).

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This means that the basic groups of functions that alter the window structure treat an
atomic window like a live one, thus preserving the internal structure of the atomic window.
Atomic windows are useful to construct and preserve window layouts that are meaningful
only when all involved buffers are shown simultaneously in a specific manner, such as when
showing differences between file revisions, or the same text in different languages or markups.
They can also be used to permanently display information pertinent to a specific window inbars on that window’s sides.
Atomic windows are implemented with the help of the reserved window-atom window
parameter (see Section 29.27 [Window Parameters], page 776) and an internal window (seeSection 29.1 [Basic Windows], page 690) called the root window of the atomic window. All
windows that are part of the same atomic window have this root window as their common
ancestor and are assigned a non-nil window-atom parameter.
The following function returns the root of the atomic window a specified window is partof:window-atom-root &optional window[Function]
This functions returns the root of the atomic window window is a part of. The
specified window must be a valid window and defaults to the selected one. It returns
nil if window is not part of an atomic window.

The most simple approach to make a new atomic window is to take an existing internal
window and apply the following function:

window-make-atom window[Function]
This function converts window into an atomic window. The specified window must
be an internal window. All this function does is to set the window-atom parameter of
each descendant of window to t.

To create a new atomic window from an existing live window or to add a new window to
an existing atomic window, the following buffer display action function (see Section 29.13.2[Buffer Display Action Functions], page 726) can be used:display-buffer-in-atom-window buffer alist[Function]
This function tries to display buffer in a new window that will be combined with anexisting window to form an atomic window. If the existing window is already part ofan atomic window, it adds the new window to that atomic window.
The specified alist is an association list of symbols and values. The following symbols
have a special meaning:
window

The value of such an element specifies an existing window the new window
shall be combined with. If it specifies an internal window, all childrenof that window become part of the atomic window too. If no window is
specified, the new window becomes a sibling of the selected window. The
window-atom parameter of the existing window is set to main provided
that window is live and its window-atom parameter was not already set.

side

The value of such an element denotes the side of the existing window
where the new window shall be located. Valid values are below, right,
above and left. The default is below. The window-atom parameter ofthe new window is set to this value.

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The return value is the new window, nil when creating that window failed.
Note that the value of the window-atom parameter does not really matter as long as
it is non-nil. The values assigned by display-buffer-in-atom-window just allow foreasy retrieval of the original and the new window after that function has been applied.
Note also that the window-atom parameter is the only window parameter assigned bydisplay-buffer-in-atom-window. Further parameters have to be set by the application
explicitly via a window-parameters entry in alist.
Atomic windows automatically cease to exist when one of their constituents gets
deleted. To dissolve an atomic window manually, reset the window-atom parameter of
its constituents—the root of the atomic window and all its descendants.
The following code snippet, when applied to a single-window frame, first splits the selected
window and makes the selected and the new window constituents of an atomic window with
their parent as root. It then displays the buffer *Messages* in a new window at the frame’sbottom and makes that new window part of the atomic window just created.
(let ((window (split-window-right)))(window-make-atom (window-parent window))(display-buffer-in-atom-window(get-buffer-create "*Messages*")`((window . ,(window-parent window)) (window-height . 5))))At this moment typing C-x 2 in any window of that frame produces a new window atthe bottom of the frame. Typing C-x 3 instead will put the new window at the frame’sright. In either case, typing now C-x 1 in any window of the atomic window will remove the
new window only. Typing C-x 0 in any window of the atomic window will make that new
window fill the frame.

29.19 Windows and Point
Each window has its own value of point (see Section 31.1 [Point], page 853), independent of
the value of point in other windows displaying the same buffer. This makes it useful to havemultiple windows showing one buffer.
• The window point is established when a window is first created; it is initialized fromthe buffer’s point, or from the window point of another window opened on the buffer ifsuch a window exists.
• Selecting a window sets the value of point in its buffer from the window’s value of point.
Conversely, deselecting a window sets the window’s value of point from that of thebuffer. Thus, when you switch between windows that display a given buffer, the pointvalue for the selected window is in effect in the buffer, while the point values for theother windows are stored in those windows.
• As long as the selected window displays the current buffer, the window’s point and thebuffer’s point always move together; they remain equal.
Emacs displays the cursor, by default as a rectangular block, in each window at theposition of that window’s point. When the user switches to another buffer in a window,
Emacs moves that window’s cursor to where point is in that buffer. If the exact position ofpoint is hidden behind some display element, such as a display string or an image, Emacs
displays the cursor immediately before or after that display element.

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window-point &optional window[Function]
This function returns the current position of point in window. For a nonselected
window, this is the value point would have (in that window’s buffer) if that window
were selected. The default for window is the selected window.

When window is the selected window, the value returned is the value of point in thatwindow’s buffer. Strictly speaking, it would be more correct to return the top-levelvalue of point, outside of any save-excursion forms. But that value is hard to find.

set-window-point window position[Function]
This function positions point in window at position position in window’s buffer. It
returns position.
If window is selected, this simply does goto-char in window’s buffer.
[Variable]
This variable specifies the marker insertion type (see Section 32.5 [Marker Insertion
Types], page 872) of window-point. The default is nil, so window-point will staybehind text inserted there.

window-point-insertion-type

29.20 The Window Start and End Positions
Each window maintains a marker used to keep track of a buffer position that specifies wherein the buffer display should start. This position is called the display-start position of thewindow (or just the start). The character after this position is the one that appears at theupper left corner of the window. It is usually, but not inevitably, at the beginning of a text
line.
After switching windows or buffers, and in some other cases, if the window start is in the
middle of a line, Emacs adjusts the window start to the start of a line. This prevents certain
operations from leaving the window start at a meaningless point within a line. This feature
may interfere with testing some Lisp code by executing it using the commands of Lisp mode,
because they trigger this readjustment. To test such code, put it into a command and bindthe command to a key.

window-start &optional window[Function]
This function returns the display-start position of window window. If window is nil,
the selected window is used.

When you create a window, or display a different buffer in it, the display-start positionis set to a display-start position recently used for the same buffer, or to point-min if
the buffer doesn’t have any.
Redisplay updates the window-start position (if you have not specified it explicitly
since the previous redisplay)—to make sure point appears on the screen. Nothing
except redisplay automatically changes the window-start position; if you move point,
do not expect the window-start position to change in response until after the next
redisplay.

window-group-start &optional window[Function]
This function is like window-start, except that when window is a part of a groupof windows (see [Window Group], page 698), window-group-start returns the startChapter 29: Windows

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position of the entire group. This condition holds when the buffer local variablewindow-group-start-function is set to a function. In this case, window-groupstart calls the function with the single argument window, then returns its result.

window-end &optional window update[Function]
This function returns the position where display of its buffer ends in window. The
default for window is the selected window.
Simply changing the buffer text or moving point does not update the value thatwindow-end returns. The value is updated only when Emacs redisplays and redisplay
completes without being preempted.
If the last redisplay of window was preempted, and did not finish, Emacs does notknow the position of the end of display in that window. In that case, this function
returns nil.
If update is non-nil, window-end always returns an up-to-date value for where display
ends, based on the current window-start value. If a previously saved value of that
position is still valid, window-end returns that value; otherwise it computes the correct
value by scanning the buffer text.
Even if update is non-nil, window-end does not attempt to scroll the display if point
has moved off the screen, the way real redisplay would do. It does not alter thewindow-start value. In effect, it reports where the displayed text will end if scrollingis not required. Note that the position it returns might be only partially visible.

window-group-end &optional window update[Function]
This function is like window-end, except that when window is a part of a groupof windows (see [Window Group], page 698), window-group-end returns the end
position of the entire group. This condition holds when the buffer local variablewindow-group-end-function is set to a function. In this case, window-group-end
calls the function with the two arguments window and update, then returns its result.
The argument update has the same meaning as in window-end.

set-window-start window position &optional noforce[Function]
This function sets the display-start position of window to position in window’s buffer.
It returns position.
The display routines insist that the position of point be visible when a buffer isdisplayed. Normally, they select the display-start position according to their internal
logic (and scroll the window if necessary) to make point visible. However, if you
specify the start position with this function using nil for noforce, it means you wantdisplay to start at position even if that would put the location of point off the screen.
If this does place point off screen, the display routines attempt to move point to theleft margin on the middle line in the window.
For example, if point is 1 and you set the start of the window to 37, the start of
the next line, point will be above the top of the window. The display routines willautomatically move point if it is still 1 when redisplay occurs. Here is an example:;; Here is what ‘foo’ looks like before executing;;
the set-window-start expression.

Chapter 29: Windows761---------- Buffer: foo ---------?This is the contents of buffer foo.
2
3
4
5
6
---------- Buffer: foo ---------(set-window-start(selected-window)(save-excursion(goto-char 1)(forward-line 1)(point)))⇒ 37;; Here is what ‘foo’ looks like after executing;;
the set-window-start expression.
---------- Buffer: foo ---------23?456---------- Buffer: foo ---------If the attempt to make point visible (i.e., in a fully-visible screen line) fails, the display
routines will disregard the requested window-start position and compute a new one
anyway. Thus, for reliable results Lisp programs that call this function should always
move point to be inside the window whose display starts at position.
If noforce is non-nil, and position would place point off screen at the next redisplay,then redisplay computes a new window-start position that works well with point, andthus position is not used.

set-window-group-start window position &optional noforce[Function]
This function is like set-window-start, except that when window is a part of a groupof windows (see [Window Group], page 698), set-window-group-start sets the start
position of the entire group. This condition holds when the buffer local variable
set-window-group-start-function is set to a function. In this case, set-windowgroup-start calls the function with the three arguments window, position, andnoforce, then returns its result. The arguments position and noforce in this function
have the same meaning as in set-window-start.

pos-visible-in-window-p &optional position window partially[Function]
This function returns non-nil if position is within the range of text currently visibleon the screen in window. It returns nil if position is scrolled vertically out of view.
Locations that are partially obscured are not considered visible unless partially isChapter 29: Windows762

non-nil. The argument position defaults to the current position of point in window;
window defaults to the selected window. If position is t, that means to check either
the first visible position of the last screen line in window, or the end-of-buffer position,
whichever comes first.
This function considers only vertical scrolling. If position is out of view only because
window has been scrolled horizontally, pos-visible-in-window-p returns non-nil
anyway. See Section 29.23 [Horizontal Scrolling], page 767.
If position is visible, pos-visible-in-window-p returns t if partially is nil; if
partially is non-nil, and the character following position is fully visible, it returns
a list of the form (x y), where x and y are the pixel coordinates relative to the top
left corner of the window; otherwise it returns an extended list of the form (x y rtop
rbot rowh vpos), where rtop and rbot specify the number of off-window pixels at the
top and bottom of the row at position, rowh specifies the visible height of that row,and vpos specifies the vertical position (zero-based row number) of that row.
Here is an example:;; If point is off the screen now, recenter it now.
(or (pos-visible-in-window-p(point) (selected-window))(recenter 0))

pos-visible-in-window-group-p &optional position window
partially[Function]

This function is like pos-visible-in-window-p, except that when window is a partof a group of windows (see [Window Group], page 698), pos-visible-in-windowgroup-p tests the visibility of pos in the entire group, not just in the single window.
This condition holds when the buffer local variable pos-visible-in-window-groupp-function is set to a function. In this case pos-visible-in-window-group-p
calls the function with the three arguments position, window, and partially, thenreturns its result. The arguments position and partially have the same meaning as in
pos-visible-in-window-p.

window-line-height &optional line window[Function]
This function returns the height of text line line in window. If line is one ofheader-line or mode-line, window-line-height returns information about thecorresponding line of the window. Otherwise, line is a text line number starting from
0. A negative number counts from the end of the window. The default for line is thecurrent line in window; the default for window is the selected window.
If the display is not up to date, window-line-height returns nil. In that case,pos-visible-in-window-p may be used to obtain related information.
If there is no line corresponding to the specified line, window-line-height returns
nil. Otherwise, it returns a list (height vpos ypos offbot), where height is theheight in pixels of the visible part of the line, vpos and ypos are the vertical positionin lines and pixels of the line relative to the top of the first text line, and offbot is thenumber of off-window pixels at the bottom of the text line. If there are off-window
pixels at the top of the (first) text line, ypos is negative.

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29.21 Textual Scrolling
Textual scrolling means moving the text up or down through a window. It works by changing
the window’s display-start location. It may also change the value of window-point to keep
point on the screen (see Section 29.19 [Window Point], page 758).
The basic textual scrolling functions are scroll-up (which scrolls forward) andscroll-down (which scrolls backward). In these function names, “up” and “down” refer tothe direction of motion of the buffer text relative to the window. Imagine that the text iswritten on a long roll of paper and that the scrolling commands move the paper up anddown. Thus, if you are looking at the middle of a buffer and repeatedly call scroll-down,
you will eventually see the beginning of the buffer.
Unfortunately, this sometimes causes confusion, because some people tend to think interms of the opposite convention: they imagine the window moving over text that remains
in place, so that “down” commands take you to the end of the buffer. This convention isconsistent with fact that such a command is bound to a key named PageDown on modern
keyboards.
Textual scrolling functions (aside from scroll-other-window) have unpredictable results
if the current buffer is not the one displayed in the selected window. See Section 28.2 [Current
Buffer], page 671.
If the window contains a row taller than the height of the window (for example in thepresence of a large image), the scroll functions will adjust the window’s vertical scroll position
to scroll the partially visible row. Lisp callers can disable this feature by binding the variable
auto-window-vscroll to nil (see Section 29.22 [Vertical Scrolling], page 766).

scroll-up &optional count[Command]This function scrolls forward by count lines in the selected window.
If count is negative, it scrolls backward instead. If count is nil (or omitted), thedistance scrolled is next-screen-context-lines lines less than the height of thewindow’s body.
If the selected window cannot be scrolled any further, this function signals an error.
Otherwise, it returns nil.

scroll-down &optional count[Command]This function scrolls backward by count lines in the selected window.
If count is negative, it scrolls forward instead. In other respects, it behaves the same
way as scroll-up does.

scroll-up-command &optional count[Command]This behaves like scroll-up, except that if the selected window cannot be scrolled
any further and the value of the variable scroll-error-top-bottom is t, it tries tomove to the end of the buffer instead. If point is already there, it signals an error.

scroll-down-command &optional count[Command]This behaves like scroll-down, except that if the selected window cannot be scrolled
any further and the value of the variable scroll-error-top-bottom is t, it tries tomove to the beginning of the buffer instead. If point is already there, it signals anerror.

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scroll-other-window &optional count[Command]This function scrolls the text in another window upward count lines. Negative valuesof count, or nil, are handled as in scroll-up.

You can specify which buffer to scroll by setting the variable other-window-scrollbuffer to a buffer. If that buffer isn’t already displayed, scroll-other-window
displays it in some window.
When the selected window is the minibuffer, the next window is normally the leftmost
one immediately above it. You can specify a different window to scroll, when theminibuffer is selected, by setting the variable minibuffer-scroll-window. Thisvariable has no effect when any other window is selected. When it is non-nil and theminibuffer is selected, it takes precedence over other-window-scroll-buffer. See[Definition of minibuffer-scroll-window], page 421.

scroll-other-window-down &optional count[Command]This function scrolls the text in another window downward count lines. Negativevalues of count, or nil, are handled as in scroll-down. In other respects, it behaves
the same way as scroll-other-window does.
[Variable]
If this variable is non-nil, it tells scroll-other-window which buffer’s window toscroll.

other-window-scroll-buffer[User Option]
This option specifies the size of the scroll margin—a minimum number of lines between
point and the top or bottom of a window. Whenever point gets within this manylines of the top or bottom of the window, redisplay scrolls the text automatically (ifpossible) to move point out of the margin, closer to the center of the window.

scroll-margin[User Option]
This variable limits the effective value of scroll-margin to a fraction of the current window line height. For example, if the current window has 20 lines andmaximum-scroll-margin is 0.1, then the scroll margins will never be larger than
2 lines, no matter how big scroll-margin is.

maximum-scroll-margin

maximum-scroll-margin itself has a maximum value of 0.5, which allows setting
margins large to keep the cursor at the middle line of the window (or two middle lines
if the window has an even number of lines). If it’s set to a larger value (or any value
other than a float between 0.0 and 0.5) then the default value of 0.25 will be usedinstead.
[User Option]
This variable controls how scrolling is done automatically when point moves off thescreen (or into the scroll margin). If the value is a positive integer n, then redisplay
scrolls the text up to n lines in either direction, if that will bring point back into properview. This behavior is called conservative scrolling. Otherwise, scrolling happens in
the usual way, under the control of other variables such as scroll-up-aggressively
and scroll-down-aggressively.

scroll-conservatively

The default value is zero, which means that conservative scrolling never happens.

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765[User Option]
The value of this variable should be either nil or a fraction f between 0 and 1. If it isa fraction, that specifies where on the screen to put point when scrolling down. Moreprecisely, when a window scrolls down because point is above the window start, the
new start position is chosen to put point f part of the window height from the top.
The larger f, the more aggressive the scrolling.
A value of nil is equivalent to .5, since its effect is to center point. This variable
automatically becomes buffer-local when set in any fashion.

scroll-down-aggressively[User Option]
Likewise, for scrolling up. The value, f, specifies how far point should be placed fromthe bottom of the window; thus, as with scroll-down-aggressively, a larger value
scrolls more aggressively.

scroll-up-aggressively[User Option]
This variable is an older variant of scroll-conservatively. The difference is that if
its value is n, that permits scrolling only by precisely n lines, not a smaller number.
This feature does not work with scroll-margin. The default value is zero.

scroll-step[User Option]
If this option is t, whenever a scrolling command moves point off-window, Emacs tries
to adjust point to keep the cursor at its old vertical position in the window, rather
than the window edge.
If the value is non-nil and not t, Emacs adjusts point to keep the cursor at the samevertical position, even if the scrolling command didn’t move point off-window.
This option affects all scroll commands that have a non-nil scroll-command symbol
property.

scroll-preserve-screen-position[User Option]
The value of this variable is the number of lines of continuity to retain when scrollingby full screens. For example, scroll-up with an argument of nil scrolls so that thismany lines at the bottom of the window appear instead at the top. The default valueis 2.

next-screen-context-lines[User Option]
If this option is nil (the default), scroll-up-command and scroll-down-command
simply signal an error when no more scrolling is possible.
If the value is t, these commands instead move point to the beginning or end of thebuffer (depending on scrolling direction); only if point is already on that position dothey signal an error.

scroll-error-top-bottom

recenter &optional count redisplay[Command]This function scrolls the text in the selected window so that point is displayed at a
specified vertical position within the window. It does not move point with respect tothe text.
If count is a non-negative number, that puts the line containing point count lines downfrom the top of the window. If count is a negative number, then it counts upward fromthe bottom of the window, so that −1 stands for the last usable line in the window.

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If count is nil (or a non-nil list), recenter puts the line containing point in the
middle of the window. If count is nil and redisplay is non-nil, this function may
redraw the frame, according to the value of recenter-redisplay. Thus, omitting
the second argument can be used to countermand the effect of recenter-redisplay
being non-nil. Interactive calls pass non-nil for redisplay.
When recenter is called interactively, count is the raw prefix argument. Thus, typing
C-u as the prefix sets the count to a non-nil list, while typing C-u 4 sets count to 4,
which positions the current line four lines from the top.
With an argument of zero, recenter positions the current line at the top of the window.
The command recenter-top-bottom offers a more convenient way to achieve this.

recenter-window-group &optional count[Function]
This function is like recenter, except that when the selected window is part of a groupof windows (see [Window Group], page 698), recenter-window-group scrolls the entire
group. This condition holds when the buffer local variable recenter-window-groupfunction is set to a function. In this case, recenter-window-group calls the function
with the argument count, then returns its result. The argument count has the same
meaning as in recenter, but with respect to the entire window group.
[User Option]
If this variable is non-nil, calling recenter with a nil count argument and non-nil
redisplay argument redraws the frame. The default value is tty, which means only
redraw the frame if it is a tty frame.

recenter-redisplay

recenter-top-bottom &optional count[Command]This command, which is the default binding for C-l, acts like recenter, except if
called with no argument. In that case, successive calls place point according to thecycling order defined by the variable recenter-positions.
[User Option]
This variable controls how recenter-top-bottom behaves when called with no argument. The default value is (middle top bottom), which means that successive calls ofrecenter-top-bottom with no argument cycle between placing point at the middle,
top, and bottom of the window.

recenter-positions

29.22 Vertical Fractional Scrolling
Vertical fractional scrolling means shifting text in a window up or down by a specified
multiple or fraction of a line. Emacs uses it, for example, on images and screen lines which
are taller than the window. Each window has a vertical scroll position, which is a number,never less than zero. It specifies how far to raise the contents of the window when displaying
them. Raising the window contents generally makes all or part of some lines disappear off
the top, and all or part of some other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line height, which is theheight of the default font. Thus, if the value is .5, that means the window contents will be
scrolled up half the normal line height. If it is 3.3, that means the window contents arescrolled up somewhat over three times the normal line height.

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What fraction of a line the vertical scrolling covers, or how many lines, depends on what
the lines contain. A value of .5 could scroll a line whose height is very short off the screen,
while a value of 3.3 could scroll just part of the way through a tall line or an image.

window-vscroll &optional window pixels-p[Function]
This function returns the current vertical scroll position of window. The default forwindow is the selected window. If pixels-p is non-nil, the return value is measured inpixels, rather than in units of the normal line height.
(window-vscroll)⇒ 0

set-window-vscroll window lines &optional pixels-ppreserve-vscroll-p[Function]

This function sets window’s vertical scroll position to lines. If window is nil, theselected window is used. The argument lines should be zero or positive; if not, it istaken as zero.
The actual vertical scroll position must always correspond to an integral number ofpixels, so the value you specify is rounded accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2)
⇒ 1.13
If pixels-p is non-nil, lines specifies a number of pixels. In this case, the return value
is lines.
Normally, the vscroll does not take effect on windows that aren’t theminibuffer-scroll-window or the selected window when the mini-window is resized(see Section 21.11 [Minibuffer Windows], page 418). This “frozen” behavior isdisabled when the preserve-vscroll-p parameter is non-nil, which means to set the
vscroll as usual.
[Variable]
If this variable is non-nil, the line-move, scroll-up, and scroll-down functions
will automatically modify the vertical scroll position to scroll through display rowsthat are taller than the height of the window, for example in the presence of large
images.

auto-window-vscroll

29.23 Horizontal Scrolling
Horizontal scrolling means shifting the image in the window left or right by a specified
multiple of the normal character width. Each window has a horizontal scroll position, which
is a number, never less than zero. It specifies how far to shift the contents left. Shifting thewindow contents left generally makes all or part of some characters disappear off the left,
and all or part of some other characters appear at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal character width, whichis the width of space in the default font. Thus, if the value is 5, that means the window
contents are scrolled left by 5 times the normal character width. How many characters
actually disappear off to the left depends on their width, and could vary from line to line.

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Because we read from side to side in the inner loop, and from top to bottom in the outerloop, the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual
scrolling involves selection of a portion of text to display, and vertical scrolling moves thewindow contents contiguously; but horizontal scrolling causes part of each line to go off
screen.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of
the window. In this state, scrolling to the right is meaningless, since there is no data to theleft of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it
scrolls the first columns of text off the edge of the window and can reveal additional columnson the right that were truncated before. Once a window has a nonzero amount of leftward
horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net
horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all
the text will disappear off the left edge.
If auto-hscroll-mode is set, redisplay automatically alters the horizontal scrolling ofa window as necessary to ensure that point is always visible. However, you can still set
the horizontal scrolling value explicitly. The value you specify serves as a lower bound forautomatic scrolling, i.e., automatic scrolling will not scroll a window to a column less than
the specified one.
The default value of auto-hscroll-mode is t; setting it to current-line activatesa variant of automatic horizontal scrolling whereby only the line showing the cursor ishorizontally scrolled to make point visible, the rest of the window is left either unscrolled, orat the minimum scroll amount set by scroll-left and scroll-right, see below.

scroll-left &optional count set-minimum[Command]This function scrolls the selected window count columns to the left (or to the right if
count is negative). The default for count is the window width, minus 2.
The return value is the total amount of leftward horizontal scrolling in effect after thechange—just like the value returned by window-hscroll (below).
Note that text in paragraphs whose base direction is right-to-left (see Section 41.27[Bidirectional Display], page 1250) moves in the opposite direction: e.g., it moves tothe right when scroll-left is invoked with a positive value of count.
Once you scroll a window as far right as it can go, back to its normal position where
the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
If set-minimum is non-nil, the new scroll amount becomes the lower bound forautomatic scrolling; that is, automatic scrolling will not scroll a window to a column
less than the value returned by this function. Interactive calls pass non-nil for
set-minimum.

scroll-right &optional count set-minimum[Command]This function scrolls the selected window count columns to the right (or to the left if
count is negative). The default for count is the window width, minus 2. Aside fromthe direction of scrolling, this works just like scroll-left.

window-hscroll &optional window[Function]
This function returns the total leftward horizontal scrolling of window—the numberof columns by which the text in window is scrolled left past the left margin. (In right-

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to-left paragraphs, the value is the total amount of the rightward scrolling instead.)
The default for window is the selected window.
The return value is never negative. It is zero when no horizontal scrolling has been
done in window (which is usually the case).
(window-hscroll)⇒ 0(scroll-left 5)⇒ 5(window-hscroll)⇒ 5

set-window-hscroll window columns[Function]
This function sets horizontal scrolling of window. The value of columns specifies
the amount of scrolling, in terms of columns from the left margin (right margin inright-to-left paragraphs). The argument columns should be zero or positive; if not, it
is taken as zero. Fractional values of columns are not supported at present.
Note that set-window-hscroll may appear not to work if you test it by evaluating acall with M-: in a simple way. What happens is that the function sets the horizontal
scroll value and returns, but then redisplay adjusts the horizontal scrolling to makepoint visible, and this overrides what the function did. You can observe the function’s
effect if you call it while point is sufficiently far from the left margin that it will remain
visible.
The value returned is columns.
(set-window-hscroll (selected-window) 10)⇒ 10

Here is how you can determine whether a given position position is off the screen due tohorizontal scrolling:(defun hscroll-on-screen (window position)(save-excursion(goto-char position)(and(>= (- (current-column) (window-hscroll window)) 0)(< (- (current-column) (window-hscroll window))(window-width window)))))

29.24 Coordinates and Windows
This section describes functions that report positions of and within a window. Most of thesefunctions report positions relative to an origin at the native position of the window’s frame(see Section 30.3 [Frame Geometry], page 791). Some functions report positions relative tothe origin of the display of the window’s frame. In any case, the origin has the coordinates(0, 0) and X and Y coordinates increase rightward and downward respectively.
For the following functions, X and Y coordinates are reported in integer character units,i.e., numbers of lines and columns respectively. On a graphical display, each “line” and“column” corresponds to the height and width of the default character specified by the frame’s
default font (see Section 30.3.2 [Frame Font], page 797).

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window-edges &optional window body absolute pixelwise[Function]
This function returns a list of the edge coordinates of window. If window is omitted
or nil, it defaults to the selected window.

The return value has the form (left top right bottom). These list elements are,respectively, the X coordinate of the leftmost column occupied by the window, theY coordinate of the topmost row, the X coordinate one column to the right of therightmost column, and the Y coordinate one row down from the bottommost row.
Note that these are the actual outer edges of the window, including any of its
decorations. On a text terminal, if the window has a neighbor on its right, its rightedge includes the separator line between the window and its neighbor.
If the optional argument body is nil, this means to return the edges corresponding to
the total size of window. body non-nil means to return the edges of window’s body.
If body is non-nil, window must specify a live window.
If the optional argument absolute is nil, this means to return edges relative to thenative position of window’s frame. absolute non-nil means to return coordinates
relative to the origin (0, 0) of window’s display. On non-graphical systems thisargument has no effect.
If the optional argument pixelwise is nil, this means to return the coordinates interms of the default character width and height of window’s frame (see Section 30.3.2[Frame Font], page 797), rounded if necessary. pixelwise non-nil means to return thecoordinates in pixels. Note that the pixel specified by right and bottom is immediately
outside of these edges. If absolute is non-nil, pixelwise is implicitly non-nil too.

window-body-edges &optional window[Function]
This function returns the edges of window’s body (see Section 29.4 [Window
Sizes], page 699). Calling (window-body-edges window) is equivalent to calling(window-edges window t), see above.

The following functions can be used to relate a set of frame-relative coordinates to awindow:window-at x y &optional frame[Function]
This function returns the live window at the coordinates x and y given in default
character sizes (see Section 30.3.2 [Frame Font], page 797) relative to the native
position of frame (see Section 30.3 [Frame Geometry], page 791).
If there is no window at that position, the return value is nil. If frame is omitted ornil, it defaults to the selected frame.

coordinates-in-window-p coordinates window[Function]
This function checks whether a window window occupies the frame relative coordinates
coordinates, and if so, which part of the window that is. window should be a live
window.
coordinates should be a cons cell of the form (x . y), where x and y are given indefault character sizes (see Section 30.3.2 [Frame Font], page 797) relative to thenative position of window’s frame (see Section 30.3 [Frame Geometry], page 791).

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If there is no window at the specified position, the return value is nil . Otherwise,
the return value is one of the following:(relx . rely)
The coordinates are inside window. The numbers relx and rely are theequivalent window-relative coordinates for the specified position, counting
from 0 at the top left corner of the window.
mode-line
The coordinates are in the mode line of window.
header-line
The coordinates are in the header line of window.
tab-line

The coordinates are in the tab line of window.

right-divider
The coordinates are in the divider separating window from a window on
the right.
bottom-divider
The coordinates are in the divider separating window from a window
beneath.
vertical-line
The coordinates are in the vertical line between window and its neighborto the right. This value occurs only if the window doesn’t have a scroll
bar; positions in a scroll bar are considered outside the window for these
purposes.
left-fringe
right-fringe
The coordinates are in the left or right fringe of the window.
left-margin
right-margin
The coordinates are in the left or right margin of the window.
nil

The coordinates are not in any part of window.

The function coordinates-in-window-p does not require a frame as argument because
it always uses the frame that window is on.
The following functions return window positions in pixels, rather than character units.
Though mostly useful on graphical displays, they can also be called on text terminals, where
the screen area of each text character is taken to be one pixel.

window-pixel-edges &optional window[Function]
This function returns a list of pixel coordinates for the edges of window. Calling(window-pixel-edges window) is equivalent to calling (window-edges window nil
nil t), see above.

window-body-pixel-edges &optional window[Function]
This function returns the pixel edges of window’s body. Calling (window-bodypixel-edges window) is equivalent to calling (window-edges window t nil t), seeabove.

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The following functions return window positions in pixels, relative to the origin of thedisplay screen rather than that of the frame:

window-absolute-pixel-edges &optional window[Function]
This function returns the pixel coordinates of window relative to an origin at (0,0) of the display of window’s frame. Calling (window-absolute-pixel-edges) is
equivalent to calling (window-edges window nil t t), see above.

window-absolute-body-pixel-edges &optional window[Function]
This function returns the pixel coordinates of window’s body relative to an origin at (0,0) of the display of window’s frame. Calling (window-absolute-body-pixel-edges
window) is equivalent to calling (window-edges window t t t), see above.
Combined with set-mouse-absolute-pixel-position, this function can be used tomove the mouse pointer to an arbitrary buffer position visible in some window:(let ((edges (window-absolute-body-pixel-edges))(position (pos-visible-in-window-p nil nil t)))(set-mouse-absolute-pixel-position(+ (nth 0 edges) (nth 0 position))(+ (nth 1 edges) (nth 1 position))))On a graphical terminal this form “warps” the mouse cursor to the upper left cornerof the glyph at the selected window’s point. A position calculated this way can bealso used to show a tooltip window there.

The following function returns the screen coordinates of a buffer position visible in awindow:window-absolute-pixel-position &optional position window[Function]
If the buffer position position is visible in window window, this function returns thedisplay coordinates of the upper/left corner of the glyph at position. The return value
is a cons of the X- and Y-coordinates of that corner, relative to an origin at (0, 0) of
window’s display. It returns nil if position is not visible in window.
window must be a live window and defaults to the selected window. position defaults
to the value of window-point of window.

This means that in order to move the mouse pointer to the position of point in theselected window, it’s sufficient to write:(let ((position (window-absolute-pixel-position)))(set-mouse-absolute-pixel-position(car position) (cdr position)))The following function returns the largest rectangle that can be inscribed in a window
without covering text displayed in that window.

window-largest-empty-rectangle &optional window countmin-width min-height positions left

[Function]

This function calculates the dimensions of the largest empty rectangle that can be
inscribed in the specified window’s text area. window must be a live window anddefaults to the selected one.

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The return value is a triple of the width and the start and end y-coordinates of thelargest rectangle that can be inscribed into the empty space (space not displaying anytext) of the text area of window. No x-coordinates are returned by this function—any
such rectangle is assumed to end at the right edge of window’s text area. If no empty
space can be found, the return value is nil.
The optional argument count, if non-nil, specifies a maximum number of rectangles
to return. This means that the return value is a list of triples specifying rectangles
with the largest rectangle first. count can be also a cons cell whose car specifies thenumber of rectangles to return and whose cdr, if non-nil, states that all rectangles
returned must be disjoint.
The optional arguments min-width and min-height, if non-nil, specify the minimum
width and height of any rectangle returned.
The optional argument positions, if non-nil, is a cons cell whose car specifies theuppermost and whose cdr specifies the lowermost pixel position that must be coveredby any rectangle returned. These positions measure from the start of the text area of
window.
The optional argument left, if non-nil, means to return values suitable for buffers
displaying right to left text. In that case, any rectangle returned is assumed to startat the left edge of window’s text area.
Note that this function has to retrieve the dimensions of each line of window’s glyph
matrix via window-lines-pixel-dimensions (see Section 41.10 [Size of Displayed
Text], page 1157). Hence, this function may also return nil when the current glyph
matrix of window is not up-to-date.

29.25 Mouse Window Auto-selection
The following option allows to automatically select the window under the mouse pointer.
This accomplishes a policy similar to that of window managers that give focus to a frame (andthus trigger its subsequent selection) whenever the mouse pointer enters its window-systemwindow (see Section 30.10 [Input Focus], page 824).
[User Option]
If this variable is non-nil, Emacs will try to automatically select the window underthe mouse pointer. The following values are meaningful:mouse-autoselect-window

A positive numberThis specifies a delay in seconds after which auto-selection triggers. The
window under the mouse pointer is selected after the mouse has remainedin it for the entire duration of the delay.
A negative number
A negative number has a similar effect as a positive number, but selects
the window under the mouse pointer only after the mouse pointer has
remained in it for the entire duration of the absolute value of that number
and in addition has stopped moving.
Other value
Any other non-nil value means to select a window instantaneously assoon as the mouse pointer enters it.

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In either case, the mouse pointer must enter the text area of a window in order totrigger its selection. Dragging the scroll bar slider or the mode line of a window
conceptually should not cause its auto-selection.
Mouse auto-selection selects the minibuffer window only if it is active, and neverdeselects the active minibuffer window.
Mouse auto-selection can be used to emulate a focus follows mouse policy for child frames(see Section 30.14 [Child Frames], page 831) which usually are not tracked by the window
manager. This requires to set the value of focus-follows-mouse (see Section 30.10 [Input
Focus], page 824) to a non-nil value. If the value of focus-follows-mouse is auto-raise,entering a child frame with the mouse will raise it automatically above all other child framesof that frame’s parent frame.

29.26 Window Configurations
A window configuration records the entire layout of one frame—all windows, their sizes,
their decorations, which buffers they contain, how those buffers are scrolled, and their valueof point, It also includes the value of minibuffer-scroll-window. As a special exception,
the window configuration does not record the value of point in the selected window for thecurrent buffer.
You can bring back an entire frame layout by restoring a previously saved window
configuration. If you want to record the layout of all frames instead of just one, use a frame
configuration instead of a window configuration. See Section 30.13 [Frame Configurations],
page 831.

current-window-configuration &optional frame[Function]
This function returns a new object representing frame’s current window configuration.
The default for frame is the selected frame. The variable window-persistentparameters specifies which window parameters (if any) are saved by this function.
See Section 29.27 [Window Parameters], page 776.

set-window-configuration configuration &optional dont-set-frame
dont-set-miniwindow[Function]

This function restores the configuration of windows and buffers as specified byconfiguration, for the frame that configuration was created for, regardless of whether
that frame is selected or not. The argument configuration must be a value that waspreviously returned by current-window-configuration for that frame. Normallythe function also selects the frame which is recorded in the configuration, but if
dont-set-frame is non-nil, it leaves selected the frame which was already selected at
the start of the function.
Normally the function restores the saved minibuffer (if any), but if dont-set-miniwindow
is non-nil, the minibuffer current at the start of the function (if any) remains in themini-window.
If the frame from which configuration was saved is dead, all this function does is torestore the value of the variable minibuffer-scroll-window and to adjust the value
returned by minibuffer-selected-window. In this case, the function returns nil.
Otherwise, it returns t.

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If the buffer of a window of configuration has been killed since configuration was made,that window is, as a rule, removed from the restored configuration. However, if thatwindow is the last window remaining in the restored configuration, another live buffer
is shown in it.
Here is a way of using this function to get the same effect as save-window-excursion:(let ((config (current-window-configuration)))(unwind-protect(progn (split-window-below nil)...)(set-window-configuration config)))save-window-excursion forms. . .

[Macro]This macro records the window configuration of the selected frame, executes forms
in sequence, then restores the earlier window configuration. The return value is thevalue of the final form in forms.
Most Lisp code should not use this macro; save-selected-window is typically sufficient. In particular, this macro cannot reliably prevent the code in forms from
opening new windows, because new windows might be opened in other frames (seeSection 29.13.1 [Choosing Window], page 724), and save-window-excursion only
saves and restores the window configuration on the current frame.

window-configuration-p object[Function]

This function returns t if object is a window configuration.

window-configuration-equal-p config1 config2[Function]
This function says whether two window configurations have the same window layout,
but ignores the values of point and the saved scrolling positions—it can return t even
if those aspects differ.

window-configuration-frame config[Function]
This function returns the frame for which the window configuration config was made.

Other primitives to look inside of window configurations would make sense, but are
not implemented because we did not need them. See the file winner.el for some more
operations on windows configurations.
The objects returned by current-window-configuration die together with the Emacs
process. In order to store a window configuration on disk and read it back in another Emacs
session, you can use the functions described next. These functions are also useful to clone
the state of a frame into an arbitrary live window (set-window-configuration effectively
clones the windows of a frame into the root window of that very frame only).

window-state-get &optional window writable[Function]
This function returns the state of window as a Lisp object. The argument window
must be a valid window and defaults to the root window of the selected frame.
If the optional argument writable is non-nil, this means to not use markers forsampling positions like window-point or window-start. This argument should be
non-nil when the state will be written to disk and read back in another session.

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Together, the argument writable and the variable window-persistent-parametersspecify which window parameters are saved by this function. See Section 29.27[Window Parameters], page 776.
The value returned by window-state-get can be used in the same session to make aclone of a window in another window. It can be also written to disk and read back in anothersession. In either case, use the following function to restore the state of the window.

window-state-put state &optional window ignore[Function]
This function puts the window state state into window. The argument state shouldbe the state of a window returned by an earlier invocation of window-state-get, seeabove. The optional argument window can be either a live window or an internal
window (see Section 29.2 [Windows and Frames], page 692). If window is not a live
window, it is replaced by a new live window created on the same frame before putting
state into it. If window is nil, it puts the window state into a new window.
If the optional argument ignore is non-nil, it means to ignore minimum window sizes
and fixed-size restrictions. If ignore is safe, this means windows can get as small as
one line and/or two columns.

The functions window-state-get and window-state-put also allow to exchange thecontents of two live windows. The following function does precisely that:window-swap-states &optional window-1 window-2 size

[Command]This command swaps the states of the two live windows window-1 and window-2.
window-1 must specify a live window and defaults to the selected one. window-2 mustspecify a live window and defaults to the window following window-1 in the cyclic
ordering of windows, excluding minibuffer windows and including live windows on all
visible frames.
Optional argument size non-nil means to try swapping the sizes of window-1 andwindow-2 as well. A value of height means to swap heights only, a value of widthmeans to swap widths only, while t means to swap both widths and heights, if possible.
Frames are not resized by this function.

29.27 Window Parameters
This section describes the window parameters that can be used to associate additional
information with windows.

window-parameter window parameter[Function]
This function returns window’s value for parameter. The default for window is theselected window. If window has no setting for parameter, this function returns nil.

window-parameters &optional window[Function]
This function returns all parameters of window and their values. The default forwindow is the selected window. The return value is either nil, or an association list
whose elements have the form (parameter . value).

set-window-parameter window parameter value[Function]
This function sets window’s value of parameter to value and returns value. The default
for window is the selected window.

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By default, the functions that save and restore window configurations or the states ofwindows (see Section 29.26 [Window Configurations], page 774) do not care about window
parameters. This means that when you change the value of a parameter within the bodyof a save-window-excursion, the previous value is not restored when that macro exits. It
also means that when you restore via window-state-put a window state saved earlier bywindow-state-get, all cloned windows have their parameters reset to nil. The following
variable allows you to override the standard behavior:[Variable]
This variable is an alist specifying which parameters get saved by current-windowconfiguration and window-state-get, and subsequently restored by set-windowconfiguration and window-state-put. See Section 29.26 [Window Configurations],
page 774.
The car of each entry of this alist is a symbol specifying the parameter. The cdr
should be one of the following:

window-persistent-parameters

nilThis value means the parameter is saved neither by window-state-get
nor by current-window-configuration.

tThis value specifies that the parameter is saved by current-windowconfiguration and (provided its writable argument is nil) bywindow-state-get.

writableThis means that the parameter is saved unconditionally by bothcurrent-window-configuration and window-state-get. This value
should not be used for parameters whose values do not have a readsyntax. Otherwise, invoking window-state-put in another session may
fail with an invalid-read-syntax error.

Some functions (notably delete-window, delete-other-windows and split-window),
may behave specially when the window specified by their window argument has a parameter
whose name is equal to the function’s name. You can override such special behavior bybinding the following variable to a non-nil value:[Variable]
If this variable is non-nil, some standard functions do not process window parameters. The functions currently affected by this are split-window, delete-window,
delete-other-windows, and other-window.
An application can bind this variable to a non-nil value around calls to these functions.
If it does so, the application is fully responsible for correctly assigning the parametersof all involved windows when exiting that function.

ignore-window-parameters

The following parameters are currently used by the window management code:
delete-window
This parameter affects the execution of delete-window (see Section 29.8 [Deleting Windows], page 711).
delete-other-windows
This parameter affects the execution of delete-other-windows (see Section 29.8
[Deleting Windows], page 711).

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no-delete-other-windows
This parameter marks the window as not deletable by delete-other-windows(see Section 29.8 [Deleting Windows], page 711).
split-window
This parameter affects the execution of split-window (see Section 29.7 [Splitting
Windows], page 708).
other-window
This parameter affects the execution of other-window (see Section 29.10 [Cyclic
Window Ordering], page 717).
no-other-window
This parameter marks the window as not selectable by other-window (seeSection 29.10 [Cyclic Window Ordering], page 717).
clone-ofThis parameter specifies the window that this one has been cloned from. It
is installed by window-state-get (see Section 29.26 [Window Configurations],
page 774).

window-preserved-sizeThis parameter specifies a buffer, a direction where nil means vertical and thorizontal, and a size in pixels. If this window displays the specified buffer andits size in the indicated direction equals the size specified by this parameter,
then Emacs will try to preserve the size of this window in the indicated direction.
This parameter is installed and updated by the function window-preserve-size(see Section 29.6 [Preserving Window Sizes], page 707).
quit-restore
This parameter is installed by the buffer display functions (see Section 29.13.1[Choosing Window], page 724) and consulted by quit-restore-window (seeSection 29.16 [Quitting Windows], page 749). It is a list of four elements, see
the description of quit-restore-window in Section 29.16 [Quitting Windows],
page 749, for details.
window-side
window-slot
These parameters are used internally for implementing side windows (seeSection 29.17 [Side Windows], page 752).
window-atomThis parameter is used internally for implementing atomic windows, see
Section 29.18 [Atomic Windows], page 756.
mode-line-format
This parameter replaces the value of the buffer-local variable mode-line-format(see Section 24.4.1 [Mode Line Basics], page 550) of this window’s buffer wheneverthis window is displayed. The symbol none means to suppress display of a modeline for this window. Display and contents of the mode line on other windows
showing this buffer are not affected.

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header-line-format
This parameter replaces the value of the buffer-local variable header-lineformat (see Section 24.4.1 [Mode Line Basics], page 550) of this window’s buffer
whenever this window is displayed. The symbol none means to suppress displayof a header line for this window. Display and contents of the header line onother windows showing this buffer are not affected.
tab-line-format
This parameter replaces the value of the buffer-local variable tab-line-format(see Section 24.4.1 [Mode Line Basics], page 550) of this window’s buffer wheneverthis window is displayed. The symbol none means to suppress display of a tabline for this window. Display and contents of the tab line on other windows
showing this buffer are not affected.
min-margins
The value of this parameter is a cons cell whose car and cdr, if non-nil, specify
the minimum values (in columns) for the left and right margin of this window(see Section 41.16.5 [Display Margins], page 1205. When present, Emacs will
use these values instead of the actual margin widths for determining whether awindow can be split or shrunk horizontally.
Emacs never auto-adjusts the margins of any window after splitting or resizing
it. It is the sole responsibility of any application setting this parameter to adjust
the margins of this window as well as those of any new window that inherits
this window’s margins due to a split. Both window-configuration-changehook and window-size-change-functions (see Section 29.28 [Window Hooks],
page 779) should be employed for this purpose.
This parameter was introduced in Emacs version 25.1 to support applications
that use large margins to center buffer text within a window and should be used,with due care, exclusively by those applications. It might be replaced by an
improved solution in future versions of Emacs.

29.28 Hooks for Window Scrolling and Changes
This section describes how Lisp programs can take action after a window has been scrolled
or other window modifications occurred. We first consider the case where a window shows adifferent part of its buffer.
[Variable]
This variable holds a list of functions that Emacs should call before redisplaying awindow with scrolling. Displaying a different buffer in a window and making a new
window also call these functions.
This variable is not a normal hook, because each function is called with two arguments:
the window, and its new display-start position. At the time of the call, the display-start
position of the argument window is already set to its new value, and the buffer to be
displayed in the window is set as the current buffer.
These functions must take care when using window-end (see Section 29.20 [Window
Start and End], page 759); if you need an up-to-date value, you must use the update
argument to ensure you get it.

window-scroll-functions

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Warning: don’t use this feature to alter the way the window is scrolled. It’s notdesigned for that, and such use probably won’t work.
In addition, you can use jit-lock-register to register a Font Lock fontification function,
which will be called whenever parts of a buffer are (re)fontified because a window was scrolled
or its size changed. See Section 24.6.4 [Other Font Lock Variables], page 571.
The remainder of this section covers six hooks that are called during redisplay provided asignificant, non-scrolling change of a window has been detected. For simplicity, these hooks
and the functions they call will be collectively referred to as window change functions. As
any hook, these hooks can be set either globally or buffer-locally via the local argument of
add-hook (see Section 24.1.2 [Setting Hooks], page 525) when the hook is installed.
The first of these hooks is run after a window buffer change is detected, which meansthat a window was created, deleted or assigned another buffer.
[Variable]
This variable specifies functions called during redisplay when window buffers havechanged. The value should be a list of functions that take one argument.

window-buffer-change-functions

Functions specified buffer-locally are called for any window showing the corresponding
buffer if that window has been created or assigned that buffer since the last time
window change functions were run. In this case the window is passed as argument.
Functions specified by the default value are called for a frame if at least one window
on that frame has been added, deleted or assigned another buffer since the last time
window change functions were run. In this case the frame is passed as argument.
The second of these hooks is run when a window size change has been detected whichmeans that a window was created, assigned another buffer, or changed its total size or thatof its text area.
[Variable]
This variable specifies functions called during redisplay when a window size change
occurred. The value should be a list of functions that take one argument.

window-size-change-functions

Functions specified buffer-locally are called for any window showing the corresponding
buffer if that window has been added or assigned another buffer or changed its total
or body size since the last time window change functions were run. In this case thewindow is passed as argument.
Functions specified by the default value are called for a frame if at least one window
on that frame has been added or assigned another buffer or changed its total or bodysize since the last time window change functions were run. In this case the frame ispassed as argument.
The third of these hooks is run when a window selection change has selected anotherwindow since the last redisplay.
[Variable]
This variable specifies functions called during redisplay when the selected window ora frame’s selected window has changed. The value should be a list of functions thattake one argument.

window-selection-change-functions

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Functions specified buffer-locally are called for any window showing the corresponding
buffer if that window has been selected or deselected (among all windows or among
all windows on its frame) since the last time window change functions were run. In
this case the window is passed as argument.
Functions specified by the default value are called for a frame if that frame has been
selected or deselected or the frame’s selected window has changed since the last time
window change functions were run. In this case the frame is passed as argument.
The fourth of these hooks is run when a window state change has been detected, whichmeans that at least one of the three preceding window changes has occurred.
[Variable]
This variable specifies functions called during redisplay when a window buffer or sizechange occurred or the selected window or a frame’s selected window has changed.
The value should be a list of functions that take one argument.

window-state-change-functions

Functions specified buffer-locally are called for any window showing the corresponding
buffer if that window has been added or assigned another buffer, changed its total or
body size or has been selected or deselected (among all windows or among all windows
on its frame) since the last time window change functions were run. In this case thewindow is passed as argument.
Functions specified by the default value are called for a frame if at least one window
on that frame has been added, deleted or assigned another buffer, changed its total or
body size or that frame has been selected or deselected or the frame’s selected window
has changed since the last time window change functions were run. In this case theframe is passed as argument.
Functions specified by the default value are also run for a frame when that frame’s
window state change flag (see below) has been set since last redisplay.
The fifth of these hooks is run when a window configuration change has been detectedwhich means that either the buffer or the size of a window changed. It differs from the four
preceding hooks in the way it is run.
[Variable]
This variable specifies functions called during redisplay when either the buffer or thesize of a window has changed. The value should be a list of functions that take noargument.

window-configuration-change-hook

Functions specified buffer-locally are called for any window showing the corresponding
buffer if at least one window on that frame has been added, deleted or assigned anotherbuffer or changed its total or body size since the last time window change functions
were run. Each call is performed with the window showing the buffer temporarily
selected and its buffer current.
Functions specified by the default value are called for each frame if at least one window
on that frame has been added, deleted or assigned another buffer or changed its
total or body size since the last time window change functions were run. Each callis performed with the frame temporarily selected and the selected window’s buffer
current.

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Finally, Emacs runs a normal hook that generalizes the behavior of window-statechange-functions.
[Variable]
The default value of this variable specifies functions called during redisplay when awindow state change has been detected or the window state change flag has been set
on at least one frame. The value should be a list of functions that take no argument.
Applications should put a function on this hook only if they want to react to changes
that happened on (or have been signaled for) two or more frames since last redisplay.
In every other case, putting the function on window-state-change-functions should
be preferred.

window-state-change-hook

Window change functions are called during redisplay for each frame as follows: First, any
buffer-local window buffer change function, window size change function, selected windowchange and window state change functions are called in this order. Next, the default values
for these functions are called in the same order. Then any buffer-local window configuration
change functions are called followed by functions specified by the default value of thosefunctions. Finally, functions on window-state-change-hook are run.
Window change functions are run for a specific frame only if a corresponding change wasregistered for that frame earlier. Such changes include the creation or deletion of a windowor the assignment of another buffer or size to a window. Note that even when such a change
has been registered, this does not mean that any of the hooks described above is run. If, forexample, a change was registered within the scope of a window excursion (see Section 29.26[Window Configurations], page 774), this will trigger a call of window change functions only
if that excursion still persists at the time change functions are run. If it is exited earlier,hooks will be run only if registered by a change outside the scope of that excursion.
The window state change flag of a frame, if set, will cause the default values ofwindow-state-change-functions (for that frame) and window-state-change-hook to
be run during next redisplay regardless of whether a window state change actually occurred
for that frame or not. After running any functions on these hooks, the flag is reset for eachframe. Applications can set that flag and inspect its value using the following functions.

set-frame-window-state-change &optional frame arg[Function]
This function sets frame’s window state change flag if arg is non-nil and resets itotherwise. frame must be a live frame and defaults to the selected one.

frame-window-state-change &optional frame[Function]
This functions returns t if frame’s window state change flag is set and nil otherwise.
frame must be a live frame and defaults to the selected one.

While window change functions are run, the functions described next can be called to get
more insight into what has changed for a specific window or frame since the last redisplay.
All these functions take a live window as single, optional argument, defaulting to the selected
window.

window-old-buffer &optional window[Function]
This function returns the buffer shown in window at the last time window change
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after that. If it returns t, window was not shown at that time but has been restoredfrom a previously saved window configuration afterwards. Otherwise, the return value
is the buffer shown by window at that time.

window-old-pixel-width &optional window[Function]
This function returns the total pixel width of window the last time window change
functions found window live on its frame. It is zero if window was created after that.

window-old-pixel-height &optional window[Function]
This function returns the total pixel height of window the last time window change
functions found window live on its frame. It is zero if window was created after that.

window-old-body-pixel-width &optional window[Function]
This function returns the pixel width of window’s text area the last time windowchange functions found window live on its frame. It is zero if window was createdafter that.

window-old-body-pixel-height &optional window[Function]
This function returns the pixel height of window’s text area the last time windowchange functions found window live on its frame. It is zero if window was createdafter that.

In order to find out which window or frame was selected the last time window change
functions were run, the following functions can be used:frame-old-selected-window &optional frame[Function]
This function returns the selected window of frame at the last time window change
functions were run. If omitted or nil frame defaults to the selected frame.
[Function]
This function returns the selected window at the last time window change functions
were run.

old-selected-window[Function]
This function returns the selected frame at the last time window change functions
were run.

old-selected-frame

Note that window change functions provide no information about which windows havebeen deleted since the last time they were run. If necessary, applications should remember
any window showing a specific buffer in a local variable of that buffer and update it in afunction run by the default values of any of the hooks that are run when a window bufferchange was detected.
The following caveats should be considered when adding a function to window change
functions:• Some operations will not trigger a call of window change functions. These include
showing another buffer in a minibuffer window or any change of a tooltip window.
• Window change functions should not create or delete windows or change the buffer, sizeor selection status of any window because there is no guarantee that the information
about such a change will be propagated to other window change functions. If at all, any

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such change should be executed only by the last function listed by the default value of
window-state-change-hook.
• Macros like save-window-excursion, with-selected-window or with-currentbuffer can be used when running window change functions.
• Running window change functions does not save and restore match data. Unless runningwindow-configuration-change-hook it does not save or restore the selected window
or frame or the current buffer either.
• Any redisplay triggering the run of window change functions may be aborted. If theabort occurs before window change functions have run to their completion, they will be
run again with the previous values, that is, as if redisplay had not been performed. If
aborted later, they will be run with the new values, that is, as if redisplay had been
actually performed.

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30 Frames
A frame is a screen object that contains one or more Emacs windows (see Chapter 29[Windows], page 690). It is the kind of object called a “window” in the terminology ofgraphical environments; but we can’t call it a “window” here, because Emacs uses that word
in a different way. In Emacs Lisp, a frame object is a Lisp object that represents a frame on
the screen. See Section 2.5.4 [Frame Type], page 27.
A frame initially contains a single main window and/or a minibuffer window; you can
subdivide the main window vertically or horizontally into smaller windows. See Section 29.7
[Splitting Windows], page 708.
A terminal is a display device capable of displaying one or more Emacs frames. In
Emacs Lisp, a terminal object is a Lisp object that represents a terminal. See Section 2.5.5[Terminal Type], page 27.
There are two classes of terminals: text terminals and graphical terminals. Text terminals
are non-graphics-capable displays, including xterm and other terminal emulators. On a text
terminal, each Emacs frame occupies the terminal’s entire screen; although you can create
additional frames and switch between them, the terminal only shows one frame at a time.
Graphical terminals, on the other hand, are managed by graphical display systems such as
the X Window System, which allow Emacs to show multiple frames simultaneously on thesame display.
On GNU and Unix systems, you can create additional frames on any available terminal,
within a single Emacs session, regardless of whether Emacs was started on a text or graphicalterminal. Emacs can display on both graphical and text terminals simultaneously. This
comes in handy, for instance, when you connect to the same session from several remotelocations. See Section 30.2 [Multiple Terminals], page 787.

framep object[Function]
This predicate returns a non-nil value if object is a frame, and nil otherwise. For aframe, the value indicates which kind of display the frame uses:t

The frame is displayed on a text terminal.

x

The frame is displayed on an X graphical terminal.

w32

The frame is displayed on a MS-Windows graphical terminal.

ns

The frame is displayed on a GNUstep or Macintosh Cocoa graphicalterminal.

pc

The frame is displayed on an MS-DOS terminal.

pgtk

The frame is displayed using pure GTK facilities.

frame-terminal &optional frame[Function]
This function returns the terminal object that displays frame. If frame is nil orunspecified, it defaults to the selected frame.

terminal-live-p object[Function]
This predicate returns a non-nil value if object is a terminal that is live (i.e., notdeleted), and nil otherwise. For live terminals, the return value indicates what kindof frames are displayed on that terminal; the list of possible values is the same as forframep above.

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On a graphical terminal we distinguish two types of frames: A normal top-level frame isa frame whose window-system window is a child of the window-system’s root window forthat terminal. A child frame is a frame whose window-system window is the child of thewindow-system window of another Emacs frame. See Section 30.14 [Child Frames], page 831.

30.1 Creating Frames
To create a new frame, call the function make-frame.

make-frame &optional parameters[Command]This function creates and returns a new frame, displaying the current buffer.
The parameters argument is an alist that specifies frame parameters for the new frame.
See Section 30.4 [Frame Parameters], page 802. If you specify the terminal parameterin parameters, the new frame is created on that terminal. Otherwise, if you specify thewindow-system frame parameter in parameters, that determines whether the frame
should be displayed on a text terminal or a graphical terminal. See Section 41.25[Window Systems], page 1248. If neither is specified, the new frame is created in thesame terminal as the selected frame.
Any parameters not mentioned in parameters default to the values in the alist
default-frame-alist (see Section 30.4.2 [Initial Parameters], page 804); parameters
not specified there default from the X resources or its equivalent on your operating
system (see Section “X Resources” in The GNU Emacs Manual). After the frame is created, this function applies any parameters specified in frame-inherited-parameters(see below) it has no assigned yet, taking the values from the frame that was selected
when make-frame was called.
Note that on multi-monitor displays (see Section 30.2 [Multiple Terminals], page 787),
the window manager might position the frame differently than specified by the positional parameters in parameters (see Section 30.4.3.2 [Position Parameters], page 805).
For example, some window managers have a policy of displaying the frame on themonitor that contains the largest part of the window (a.k.a. the dominating monitor).
This function itself does not make the new frame the selected frame. See Section 30.10[Input Focus], page 824. The previously selected frame remains selected. On graphicalterminals, however, the window system may select the new frame for its own reasons.

before-make-frame-hook[Variable]

A normal hook run by make-frame before it creates the frame.
[Variable]
An abnormal hook run by make-frame after it created the frame. Each function inafter-make-frame-functions receives one argument, the frame just created.

after-make-frame-functions

Note that any functions added to these hooks by your initial file are usually not run for
the initial frame, since Emacs reads the initial file only after creating that frame. However, if
the initial frame is specified to use a separate minibuffer frame (see Section 30.9 [Minibuffers
and Frames], page 824), the functions will be run for both, the minibuffer-less and theminibuffer frame. Alternatively, you can add functions to these hooks in your “early init
file” (see Section 42.1.2 [Init File], page 1258), in which case they will be in effect for the
initial frame as well.

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This variable specifies the list of frame parameters that a newly created frame inherits
from the currently selected frame. For each parameter (a symbol) that is an element inthis list and has not been assigned earlier when processing make-frame, the function
sets the value of that parameter in the created frame to its value in the selected frame.

frame-inherited-parameters[User Option]
A normal hook run when the Emacs server starts using a client frame. When thishook is called, the client frame is the selected one. Note that, depending on how
emacsclient was invoked (see Section “Invoking emacsclient” in The GNU Emacs
Manual), this client frame could be a new frame created for the client, or it could
be an existing frame that the server reused for handling the client commands. See
Section “Emacs Server” in The GNU Emacs Manual.

server-after-make-frame-hook

30.2 Multiple Terminals
Emacs represents each terminal as a terminal object data type (see Section 2.5.5 [Terminal
Type], page 27). On GNU and Unix systems, Emacs can use multiple terminals simultaneously in each session. On other systems, it can only use a single terminal. Each terminal
object has the following attributes:• The name of the device used by the terminal (e.g., ‘:0.0’ or /dev/tty).
• The terminal and keyboard coding systems used on the terminal. See Section 34.10.8[Terminal I/O Encoding], page 990.
• The kind of display associated with the terminal. This is the symbol returned by thefunction terminal-live-p (i.e., x, t, w32, ns, pc, haiku, or pgtk). See Chapter 30[Frames], page 785.
• A list of terminal parameters. See Section 30.5 [Terminal Parameters], page 820.
There is no primitive for creating terminal objects. Emacs creates them as needed, suchas when you call make-frame-on-display (described below).

terminal-name &optional terminal[Function]
This function returns the file name of the device used by terminal. If terminal isomitted or nil, it defaults to the selected frame’s terminal. terminal can also be aframe, meaning that frame’s terminal.

terminal-list[Function]

This function returns a list of all live terminal objects.

get-device-terminal device[Function]
This function returns a terminal whose device name is given by device. If device is astring, it can be either the file name of a terminal device, or the name of an X displayof the form ‘host:server.screen’. If device is a frame, this function returns thatframe’s terminal; nil means the selected frame. Finally, if device is a terminal object
that represents a live terminal, that terminal is returned. The function signals anerror if its argument is none of the above.

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delete-terminal &optional terminal force[Function]
This function deletes all frames on terminal and frees the resources used by it. It runs
the abnormal hook delete-terminal-functions, passing terminal as the argument
to each function.
If terminal is omitted or nil, it defaults to the selected frame’s terminal. terminal
can also be a frame, meaning that frame’s terminal.
Normally, this function signals an error if you attempt to delete the sole active terminal,
but if force is non-nil, you are allowed to do so. Emacs automatically calls thisfunction when the last frame on a terminal is deleted (see Section 30.7 [Deleting
Frames], page 822).

[Variable]
An abnormal hook run by delete-terminal. Each function receives one argument,
the terminal argument passed to delete-terminal. Due to technical details, thefunctions may be called either just before the terminal is deleted, or just afterwards.

delete-terminal-functions

A few Lisp variables are terminal-local; that is, they have a separate binding for each terminal. The binding in effect at any time is the one for the terminal that the currently selected
frame belongs to. These variables include default-minibuffer-frame, defining-kbdmacro, last-kbd-macro, and system-key-alist. They are always terminal-local, and cannever be buffer-local (see Section 12.11 [Buffer-Local Variables], page 207).
On GNU and Unix systems, each X display is a separate graphical terminal. When
Emacs is started from within the X window system, it uses the X display specified by the
DISPLAY environment variable, or by the ‘--display’ option (see Section “Initial Options”
in The GNU Emacs Manual). Emacs can connect to other X displays via the command
make-frame-on-display. Each X display has its own selected frame and its own minibuffer
windows; however, only one of those frames is the selected frame at any given moment (seeSection 30.10 [Input Focus], page 824). Emacs can even connect to other text terminals,
by interacting with the emacsclient program. See Section “Emacs Server” in The GNU
Emacs Manual.
A single X server can handle more than one display. Each X display has a three-part name,‘hostname:displaynumber.screennumber’. The first part, hostname, specifies the name of
the machine to which the display is physically connected. The second part, displaynumber,is a zero-based number that identifies one or more monitors connected to that machinethat share a common keyboard and pointing device (mouse, tablet, etc.). The third part,
screennumber, identifies a zero-based screen number (a separate monitor) that is part of asingle monitor collection on that X server. When you use two or more screens belonging to
one server, Emacs knows by the similarity in their names that they share a single keyboard.
Systems that don’t use the X window system, such as MS-Windows, don’t support
the notion of X displays, and have only one display on each host. The display name onthese systems doesn’t follow the above 3-part format; for example, the display name on
MS-Windows systems is a constant string ‘w32’, and exists for compatibility, so that you
could pass it to functions that expect a display name.

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make-frame-on-display display &optional parameters[Command]This function creates and returns a new frame on display, taking the other frame
parameters from the alist parameters. display should be the name of an X display (astring).
Before creating the frame, this function ensures that Emacs is set up to display
graphics. For instance, if Emacs has not processed X resources (e.g., if it was started
on a text terminal), it does so at this time. In all other respects, this function behaves
like make-frame (see Section 30.1 [Creating Frames], page 786).
[Function]
This function returns a list that indicates which X displays Emacs has a connection
to. The elements of the list are strings, and each one is a display name.

x-display-list

x-open-connection display &optional xrm-string must-succeed[Function]
This function opens a connection to the X display display, without creating a frameon that display. Normally, Emacs Lisp programs need not call this function, as
make-frame-on-display calls it automatically. The only reason for calling it is tocheck whether communication can be established with a given X display.
The optional argument xrm-string, if not nil, is a string of resource names and values,in the same format used in the .Xresources file. See Section “X Resources” in The
GNU Emacs Manual. These values apply to all Emacs frames created on this display,overriding the resource values recorded in the X server. Here’s an example of what
this string might look like:"*BorderWidth: 3\n*InternalBorder: 2\n"If must-succeed is non-nil, failure to open the connection terminates Emacs. Otherwise,
it is an ordinary Lisp error.

x-close-connection display[Function]
This function closes the connection to display display. Before you can do this, you mustfirst delete all the frames that were open on that display (see Section 30.7 [Deleting
Frames], page 822).

On some multi-monitor setups, a single X display outputs to more than one physical monitor. You can use the functions display-monitor-attributes-list and frame-monitorattributes to obtain information about such setups.

display-monitor-attributes-list &optional display[Function]
This function returns a list of physical monitor attributes on display, which can be adisplay name (a string), a terminal, or a frame; if omitted or nil, it defaults to theselected frame’s display. Each element of the list is an association list, representing
the attributes of a physical monitor. The first element corresponds to the primarymonitor. The attribute keys and values are:‘geometry’Position of the top-left corner of the monitor’s screen and its size, in pixels,as ‘(x y width height)’. Note that, if the monitor is not the primarymonitor, some of the coordinates might be negative.

Chapter 30: Frames

790‘workarea’
Position of the top-left corner and size of the work area (usable space) in
pixels as ‘(x y width height)’. This may be different from ‘geometry’ inthat space occupied by various window manager features (docks, taskbars,etc.) may be excluded from the work area. Whether or not such features
actually subtract from the work area depends on the platform and environment. Again, if the monitor is not the primary monitor, some of thecoordinates might be negative.
‘mm-size’

Width and height in millimeters as ‘(width height)’‘frames’

List of frames that this physical monitor dominates (see below).

‘name’Name of the physical monitor as string.

‘source’

Source of the multi-monitor information as string; e.g., ‘XRandR 1.5’,‘XRandr’ or ‘Xinerama’.

x, y, width, and height are integers. ‘name’ and ‘source’ may be absent.
A frame is dominated by a physical monitor when either the largest area of the frame
resides in that monitor, or (if the frame does not intersect any physical monitors) thatmonitor is the closest to the frame. Every (non-tooltip) frame (whether visible or not)in a graphical display is dominated by exactly one physical monitor at a time, though
the frame can span multiple (or no) physical monitors.
Here’s an example of the data produced by this function on a 2-monitor display:(display-monitor-attributes-list)⇒(((geometry 0 0 1920 1080) ;; Left-hand, primary monitor(workarea 0 0 1920 1050) ;; A taskbar occupies some of the height(mm-size 677 381)
(name . "DISPLAY1")(frames #<frame emacs@host *Messages* 0x11578c0>#<frame emacs@host *scratch* 0x114b838>))((geometry 1920 0 1680 1050) ;; Right-hand monitor(workarea 1920 0 1680 1050) ;; Whole screen can be used
(mm-size 593 370)
(name . "DISPLAY2")(frames)))frame-monitor-attributes &optional frame[Function]
This function returns the attributes of the physical monitor dominating (see above)
frame, which defaults to the selected frame.

On multi-monitor displays it is possible to use the command make-frame-on-monitor
to make frames on the specified monitor.

make-frame-on-monitor monitor &optional display parameters[Command]This function creates and returns a new frame on monitor located on display, taking
the other frame parameters from the alist parameters. monitor should be the name ofChapter 30: Frames

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the physical monitor, the same string as returned by the function display-monitorattributes-list in the attribute name. display should be the name of an X display(a string).
[Variable]
This variable is an abnormal hook run when the monitor configuration changes, which
can happen if a monitor is rotated, moved, added or removed from a multiple-monitor
setup, if the primary monitor changes, or if the resolution of a monitor changes. It
is called with a single argument consisting of the terminal on which the monitor
configuration changed. Programs should call display-monitor-attributes-list
with the terminal as the argument to retrieve the new monitor configuration on thatterminal.

display-monitors-changed-functions

30.3 Frame Geometry
The geometry of a frame depends on the toolkit that was used to build this instance ofEmacs and the terminal that displays the frame. This chapter describes these dependencies
and some of the functions to deal with them. Note that the frame argument of all of thesefunctions has to specify a live frame (see Section 30.7 [Deleting Frames], page 822). If
omitted or nil, it specifies the selected frame (see Section 30.10 [Input Focus], page 824).

30.3.1 Frame Layout
A visible frame occupies a rectangular area on its terminal’s display. This area may containa number of nested rectangles, each serving a different purpose. The drawing below sketches
the layout of a frame on a graphical terminal:<------------ Outer Frame Width ----------->____________________________________________^(0) ________ External/Outer Border _______|| | |_____________ Title Bar ______________| || | (1)_____________ Menu Bar ______________| | ^| | (2)_____________ Tool Bar ______________| | ^| | (3)_____________ Tab Bar _______________| | ^| | | _________ Internal Border ________ | | ^| | | |^
| | | |
| | | ||
| | | |
Outer | | | Inner| | | Native
Frame | | | Frame| | | Frame
Height | | | Height| | | Height| | | ||
| | | |
| | | |<--+--- Inner Frame Width ------->| | | || | | ||
| | | |
| | | |___v______________________________| | | || | |___________ Internal Border __________| | v
v |___________ External/Outer Border __________|<-------- Native Frame Width -------->

In practice not all of the areas shown in the drawing will or may be present. The meaningof these areas is described below.

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Outer Frame
The outer frame is a rectangle comprising all areas shown in the drawing. The
edges of that rectangle are called the outer edges of the frame. Together, theouter width and outer height of the frame specify the outer size of that rectangle.
Knowing the outer size of a frame is useful for fitting a frame into the working
area of its display (see Section 30.2 [Multiple Terminals], page 787) or for placing
two frames adjacent to each other on the screen. Usually, the outer size ofa frame is available only after the frame has been mapped (made visible, see
Section 30.11 [Visibility of Frames], page 828) at least once. For the initial frame
or a frame that has not been created yet, the outer size can be only estimatedor must be calculated from the window-system’s or window manager’s defaults.
One workaround is to obtain the differences of the outer and native (see below)
sizes of a mapped frame and use them for calculating the outer size of the newframe.
The position of the upper left corner of the outer frame (indicated by ‘(0)’ in
the drawing above) is the outer position of the frame. The outer position ofa graphical frame is also referred to as “the position” of the frame because it
usually remains unchanged on its display whenever the frame is resized or its
layout is changed.
The outer position is specified by and can be set via the left and top frame
parameters (see Section 30.4.3.2 [Position Parameters], page 805). For a normal,
top-level frame these parameters usually represent its absolute position (seebelow) with respect to its display’s origin. For a child frame (see Section 30.14[Child Frames], page 831) these parameters represent its position relative to thenative position (see below) of its parent frame. For frames on text terminals thevalues of these parameters are meaningless and always zero.
External Border
The external border is part of the decorations supplied by the window manager.
It is typically used for resizing the frame with the mouse and is therefore
not shown on “fullboth” and maximized frames (see Section 30.4.3.3 [SizeParameters], page 808). Its width is determined by the window manager andcannot be changed by Emacs’ functions.
External borders don’t exist on text terminal frames. For graphical frames, theirdisplay can be suppressed by setting the override-redirect or undecorated
frame parameter (see Section 30.4.3.8 [Management Parameters], page 814).
Outer Border
The outer border is a separate border whose width can be specified withthe border-width frame parameter (see Section 30.4.3.4 [Layout Parameters],
page 810). In practice, either the external or the outer border of a frame
are displayed but never both at the same time. Usually, the outer borderis shown only for special frames that are not (fully) controlled by the window manager like tooltip frames (see Section 41.26 [Tooltips], page 1249),
child frames (see Section 30.14 [Child Frames], page 831) and undecorated
or override-redirect frames (see Section 30.4.3.8 [Management Parameters],
page 814).

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Outer borders are never shown on text terminal frames and on frames generated
by GTK+ routines. On MS-Windows, the outer border is emulated with the helpof a one pixel wide external border. Non-toolkit builds on X allow to change
the color of the outer border by setting the border-color frame parameter (seeSection 30.4.3.4 [Layout Parameters], page 810).
Title Bar

The title bar, a.k.a. caption bar, is also part of the window manager’s decorations and typically displays the title of the frame (see Section 30.6 [Frame
Titles], page 821) as well as buttons for minimizing, maximizing and deleting the frame. It can be also used for dragging the frame with the mouse.
The title bar is usually not displayed for fullboth (see Section 30.4.3.3 [SizeParameters], page 808), tooltip (see Section 41.26 [Tooltips], page 1249) andchild frames (see Section 30.14 [Child Frames], page 831) and doesn’t exist
for terminal frames. Display of the title bar can be suppressed by setting theoverride-redirect or the undecorated frame parameters (see Section 30.4.3.8[Management Parameters], page 814).

Menu Bar The menu bar (see Section 23.18.5 [Menu Bar], page 516) can be either internal(drawn by Emacs itself) or external (drawn by the toolkit). Most builds (GTK+,
Lucid, Motif and MS-Windows) rely on an external menu bar. NS also uses
an external menu bar which, however, is not part of the outer frame. Nontoolkit builds can provide an internal menu bar. On text terminal frames, themenu bar is part of the frame’s root window (see Section 29.2 [Windows andFrames], page 692). As a rule, menu bars are never shown on child frames(see Section 30.14 [Child Frames], page 831). Display of the menu bar canbe suppressed by setting the menu-bar-lines parameter (see Section 30.4.3.4[Layout Parameters], page 810) to zero.
Whether the menu bar is wrapped or truncated whenever its width becomes
too large to fit on its frame depends on the toolkit . Usually, only Motif and
MS-Windows builds can wrap the menu bar. When they (un-)wrap the menubar, they try to keep the outer height of the frame unchanged, so the native
height of the frame (see below) will change instead.
Tool Bar

Like the menu bar, the tool bar (see Section 23.18.6 [Tool Bar], page 517) canbe either internal (drawn by Emacs itself) or external (drawn by a toolkit). The
GTK+ and NS builds have the tool bar drawn by the toolkit. The remaining
builds use internal tool bars. With GTK+ the tool bar can be located oneither side of the frame, immediately outside the internal border, see below.
Tool bars are usually not shown for child frames (see Section 30.14 [Child
Frames], page 831). Display of the tool bar can be suppressed by setting thetool-bar-lines parameter (see Section 30.4.3.4 [Layout Parameters], page 810)
to zero.
If the variable auto-resize-tool-bars is non-nil, Emacs wraps the internal
tool bar when its width becomes too large for its frame. If and when Emacs(un-)wraps the internal tool bar, it by default keeps the outer height of the frame
unchanged, so the native height of the frame (see below) will change instead.
Emacs built with GTK+, on the other hand, never wraps the tool bar but may

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automatically increase the outer width of a frame in order to accommodate an
overlong tool bar.
Tab Bar

The tab bar (see Section “Tab Bars” in The GNU Emacs Manual) is always
drawn by Emacs itself. The tab bar appears above the tool bar in Emacs builtwith an internal tool bar, and below the tool bar in builds with an external tool
bar. Display of the tab bar can be suppressed by setting the tab-bar-lines
parameter (see Section 30.4.3.4 [Layout Parameters], page 810) to zero.

Native Frame
The native frame is a rectangle located entirely within the outer frame. It
excludes the areas occupied by an external or outer border, the title bar andany external menu or tool bar. The edges of the native frame are called thenative edges of the frame. Together, the native width and native height of aframe specify the native size of the frame.
The native size of a frame is the size Emacs passes to the window-system orwindow manager when creating or resizing the frame from within Emacs. It
is also the size Emacs receives from the window-system or window manager
whenever these resize the frame’s window-system window, for example, after
maximizing the frame by clicking on the corresponding button in the title baror when dragging its external border with the mouse.
The position of the top left corner of the native frame specifies the native positionof the frame. (1)–(3) in the drawing above indicate that position for the various
builds:(1) non-toolkit, Haiku, and terminal frames(2) Lucid, Motif, and MS-Windows frames(3) GTK+ and NS frames
Accordingly, the native height of a frame may include the height of the tool bar
but not that of the menu bar (Lucid, Motif, MS-Windows) or those of the menu
bar and the tool bar (non-toolkit and text terminal frames).
The native position of a frame is the reference position for functions thatset or return the current position of the mouse (see Section 30.16 [Mouse
Position], page 835) and for functions dealing with the position of windows likewindow-edges, window-at or coordinates-in-window-p (see Section 29.24[Coordinates and Windows], page 769). It also specifies the (0, 0) origin forlocating and positioning child frames within this frame (see Section 30.14 [Child
Frames], page 831).
Note also that the native position of a frame usually remains unaltered on its
display when removing or adding the window manager decorations by changing
the frame’s override-redirect or undecorated parameter (see Section 30.4.3.8[Management Parameters], page 814).
Internal Border
The internal border is a border drawn by Emacs around the inner frame (seebelow). The specification of its appearance depends on whether or not the given
frame is a child frame (see Section 30.14 [Child Frames], page 831).

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For normal frames its width is specified by the internal-border-width frame
parameter (see Section 30.4.3.4 [Layout Parameters], page 810), and its color is
specified by the background of the internal-border face.
For child frames its width is specified by the child-frame-border-width frame
parameter (but will use the internal-border-width parameter as fallback),
and its color is specified by the background of the child-frame-border face.
Inner Frame
The inner frame is the rectangle reserved for the frame’s windows. It’s enclosedby the internal border which, however, is not part of the inner frame. Its edges
are called the inner edges of the frame. The inner width and inner height specify
the inner size of the rectangle. The inner frame is sometimes also referred to as
the display area of the frame.
As a rule, the inner frame is subdivided into the frame’s root window (seeSection 29.2 [Windows and Frames], page 692) and the frame’s minibuffer
window (see Section 21.11 [Minibuffer Windows], page 418). There are two
notable exceptions to this rule: A minibuffer-less frame contains a root window
only and does not contain a minibuffer window. A minibuffer-only frame contains
only a minibuffer window which also serves as that frame’s root window. See
Section 30.4.2 [Initial Parameters], page 804, for how to create such frame
configurations.
Text Area The text area of a frame is a somewhat fictitious area that can be embeddedin the native frame. Its position is unspecified. Its width can be obtained byremoving from that of the native width the widths of the internal border, one
vertical scroll bar, and one left and one right fringe if they are specified for thisframe, see Section 30.4.3.4 [Layout Parameters], page 810. Its height can beobtained by removing from that of the native height the widths of the internalborder and the heights of the frame’s internal menu and tool bars, the tab bar
and one horizontal scroll bar if specified for this frame.
The absolute position of a frame is given as a pair (X, Y) of horizontal and vertical pixel
offsets relative to an origin (0, 0) of the frame’s display. Correspondingly, the absolute edges
of a frame are given as pixel offsets from that origin.
Note that with multiple monitors, the origin of the display does not necessarily coincidewith the top-left corner of the entire usable display area of the terminal. Hence the absolute
position of a frame can be negative in such an environment even when that frame is completely
visible.
By convention, vertical offsets increase “downwards”. This means that the height of aframe is obtained by subtracting the offset of its top edge from that of its bottom edge.
Horizontal offsets increase “rightwards”, as expected, so a frame’s width is calculated bysubtracting the offset of its left edge from that of its right edge.
For a frame on a graphical terminal the following function returns the sizes of the areas
described above:

frame-geometry &optional frame[Function]
This function returns geometric attributes of frame. The return value is an association
list of the attributes listed below. All coordinate, height and width values are integers

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counting pixels. Note that if frame has not been mapped yet, (see Section 30.11[Visibility of Frames], page 828) some of the return values may only represent approximations of the actual values—those that can be seen after the frame has been
mapped.
outer-position
A cons representing the absolute position of the outer frame, relative tothe origin at position (0, 0) of frame’s display.
outer-size
A cons of the outer width and height of frame.
external-border-size
A cons of the horizontal and vertical width of frame’s external borders as
supplied by the window manager. If the window manager doesn’t supply
these values, Emacs will try to guess them from the coordinates of theouter and inner frame.
outer-border-width
The width of the outer border of frame. The value is meaningful for
non-GTK+ X builds only.
title-bar-size
A cons of the width and height of the title bar of frame as supplied by
the window manager or operating system. If both of them are zero, theframe has no title bar. If only the width is zero, Emacs was not able toretrieve the width information.
menu-bar-external
If non-nil, this means the menu bar is external (not part of the native
frame of frame).
menu-bar-size
A cons of the width and height of the menu bar of frame.
tool-bar-external
If non-nil, this means the tool bar is external (not part of the native
frame of frame).
tool-bar-position
This tells on which side the tool bar on frame is and can be one of left,
top, right or bottom. The only toolkit that currently supports a value
other than top is GTK+.
tool-bar-size
A cons of the width and height of the tool bar of frame.
internal-border-width
The width of the internal border of frame.
The following function can be used to retrieve the edges of the outer, native and inner
frame.

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frame-edges &optional frame type

[Function]
This function returns the absolute edges of the outer, native or inner frame of frame.
frame must be a live frame and defaults to the selected one. The returned list has theform (left top right bottom) where all values are in pixels relative to the origin offrame’s display. For terminal frames the values returned for left and top are always
zero.
Optional argument type specifies the type of the edges to return: outer-edges means
to return the outer edges of frame, native-edges (or nil) means to return its nativeedges and inner-edges means to return its inner edges.
By convention, the pixels of the display at the values returned for left and top are
considered to be inside (part of) frame. Hence, if left and top are both zero, the pixel
at the display’s origin is part of frame. The pixels at bottom and right, on the other
hand, are considered to lie immediately outside frame. This means that if you have,for example, two side-by-side frames positioned such that the right outer edge of theframe on the left equals the left outer edge of the frame on the right, the pixels atthat edge show a part of the frame on the right.

30.3.2 Frame Font
Each frame has a default font which specifies the default character size for that frame. Thissize is meant when retrieving or changing the size of a frame in terms of columns or lines (seeSection 30.4.3.3 [Size Parameters], page 808). It is also used when resizing (see Section 29.4
[Window Sizes], page 699) or splitting (see Section 29.7 [Splitting Windows], page 708)
windows.
The terms line height and canonical character height are sometimes used instead of“default character height”. Similarly, the terms column width and canonical character width
are used instead of “default character width”.

frame-char-height &optional frame
frame-char-width &optional frame[Function][Function]
These functions return the default height and width of a character in frame, measured
in pixels. Together, these values establish the size of the default font on frame. The
values depend on the choice of font for frame, see Section 30.4.3.10 [Font and Color
Parameters], page 818.

The default font can be also set directly with the following function:

set-frame-font font &optional keep-size frames[Command]This sets the default font to font. When called interactively, it prompts for the nameof a font, and uses that font on the selected frame. When called from Lisp, font should
be a font name (a string), a font object, font entity, or a font spec.
If the optional argument keep-size is nil, this keeps the number of frame lines andcolumns fixed. (If non-nil, the option frame-inhibit-implied-resize described in
the next section will override this.) If keep-size is non-nil (or with a prefix argument),
it tries to keep the size of the display area of the current frame fixed by adjusting thenumber of lines and columns.

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If the optional argument frames is nil, this applies the font to the selected frame
only. If frames is non-nil, it should be a list of frames to act upon, or t meaning all
existing and all future graphical frames.

30.3.3 Frame Position
On graphical systems, the position of a normal top-level frame is specified as the absolute
position of its outer frame (see Section 30.3 [Frame Geometry], page 791). The position of achild frame (see Section 30.14 [Child Frames], page 831) is specified via pixel offsets of its
outer edges relative to the native position of its parent frame.
You can access or change the position of a frame using the frame parameters left andtop (see Section 30.4.3.2 [Position Parameters], page 805). Here are two additional functions
for working with the positions of an existing, visible frame. For both functions, the argument
frame must denote a live frame and defaults to the selected frame.

frame-position &optional frame[Function]
For a normal, non-child frame this function returns a cons of the pixel coordinatesof its outer position (see Section 30.3.1 [Frame Layout], page 791) with respect tothe origin (0, 0) of its display. For a child frame (see Section 30.14 [Child Frames],
page 831) this function returns the pixel coordinates of its outer position with respect
to an origin (0, 0) at the native position of frame’s parent.
Negative values never indicate an offset from the right or bottom edge of frame’s
display or parent frame. Rather, they mean that frame’s outer position is on the left
and/or above the origin of its display or the native position of its parent frame. This
usually means that frame is only partially visible (or completely invisible). However,on systems where the display’s origin does not coincide with its top-left corner, theframe may be visible on a secondary monitor.
On a text terminal frame both values are zero.

set-frame-position frame x y[Function]
This function sets the outer frame position of frame to (x, y). The latter arguments
specify pixels and normally count from the origin at the position (0, 0) of frame’s
display. For child frames, they count from the native position of frame’s parent frame.
Negative parameter values position the right edge of the outer frame by -x pixels leftfrom the right edge of the screen (or the parent frame’s native rectangle) and thebottom edge by -y pixels up from the bottom edge of the screen (or the parent frame’s
native rectangle).
Note that negative values do not permit to align the right or bottom edge of frame
exactly at the right or bottom edge of its display or parent frame. Neither do they
allow to specify a position that does not lie within the edges of the display or parent
frame. The frame parameters left and top (see Section 30.4.3.2 [Position Parameters],
page 805) allow to do that, but may still fail to provide good results for the initial ora new frame.
This function has no effect on text terminal frames.
[Variable]
This hook specifies the functions that are run when an Emacs frame is moved (assigned
a new position) by the window-system or window manager. The functions are run

move-frame-functions

Chapter 30: Frames

799with one argument, the frame that moved. For a child frame (see Section 30.14 [Child
Frames], page 831), the functions are run only when the position of the frame changes
in relation to that of its parent frame.

30.3.4 Frame Size
The canonical way to specify the size of a frame from within Emacs is by specifying its text
size—a tuple of the width and height of the frame’s text area (see Section 30.3.1 [Frame
Layout], page 791). It can be measured either in pixels or in terms of the frame’s canonicalcharacter size (see Section 30.3.2 [Frame Font], page 797).
For frames with an internal menu or tool bar, the frame’s native height cannot be told
exactly before the frame has been actually drawn. This means that in general you cannot
use the native size to specify the initial size of a frame. As soon as you know the native
size of a visible frame, you can calculate its outer size (see Section 30.3.1 [Frame Layout],
page 791) by adding in the remaining components from the return value of frame-geometry.
For invisible frames or for frames that have yet to be created, however, the outer size canonly be estimated. This also means that calculating an exact initial position of a frame
specified via offsets from the right or bottom edge of the screen (see Section 30.3.3 [Frame
Position], page 798) is impossible.
The text size of any frame can be set and retrieved with the help of the height andwidth frame parameters (see Section 30.4.3.3 [Size Parameters], page 808). The text sizeof the initial frame can be also set with the help of an X-style geometry specification. See
Section “Command Line Arguments for Emacs Invocation” in The GNU Emacs Manual.
Below we list some functions to access and set the size of an existing, visible frame, by
default the selected one.

frame-height &optional frame
frame-width &optional frame[Function][Function]
These functions return the height and width of the text area of frame, measured inunits of the default font height and width of frame (see Section 30.3.2 [Frame Font],
page 797). These functions are plain shorthands for writing (frame-parameter frame'height) and (frame-parameter frame 'width).
If the text area of frame measured in pixels is not a multiple of its default font size,
the values returned by these functions are rounded down to the number of charactersof the default font that fully fit into the text area.

The functions following next return the pixel widths and heights of the native, outer andinner frame and the text area (see Section 30.3.1 [Frame Layout], page 791) of a given frame.
For a text terminal, the results are in characters rather than pixels.

frame-outer-width &optional frame
frame-outer-height &optional frame[Function][Function]

These functions return the outer width and height of frame in pixels.

frame-native-height &optional frame
frame-native-width &optional frame
These functions return the native width and height of frame in pixels.

[Function][Function]

Chapter 30: Frames

frame-inner-width &optional frame
frame-inner-height &optional frame

800[Function][Function]

These functions return the inner width and height of frame in pixels.

frame-text-width &optional frame
frame-text-height &optional frame[Function][Function]
These functions return the width and height of the text area of frame in pixels.

On window systems that support it, Emacs tries by default to make the text size of aframe measured in pixels a multiple of the frame’s character size. This, however, usuallymeans that a frame can be resized only in character size increments when dragging its
external borders. It also may break attempts to truly maximize the frame or making it“fullheight” or “fullwidth” (see Section 30.4.3.3 [Size Parameters], page 808) leaving someempty space below and/or on the right of the frame. The following option may help in thatcase.
[User Option]
If this option is nil (the default), a frame’s text pixel size is usually rounded to a
multiple of the current values of that frame’s frame-char-height and frame-charwidth whenever the frame is resized. If this is non-nil, no rounding occurs, hence
frame sizes can increase/decrease by one pixel.

frame-resize-pixelwise

Setting this variable usually causes the next resize operation to pass the corresponding
size hints to the window manager. This means that this variable should be set only ina user’s initial file; applications should never bind it temporarily.
The precise meaning of a value of nil for this option depends on the toolkit used.
Dragging the external border with the mouse is done character-wise provided thewindow manager is willing to process the corresponding size hints. Calling set-framesize (see below) with arguments that do not specify the frame size as an integer
multiple of its character size, however, may: be ignored, cause a rounding (GTK+), or
be accepted (Lucid, Motif, MS-Windows).
With some window managers you may have to set this to non-nil in order to make aframe appear truly maximized or full-screen.

set-frame-size frame width height &optional pixelwise[Function]
This function sets the size of the text area of frame, measured in terms of the canonicalheight and width of a character on frame (see Section 30.3.2 [Frame Font], page 797).
The optional argument pixelwise non-nil means to measure the new width and heightin units of pixels instead. Note that if frame-resize-pixelwise is nil, some toolkits
may refuse to truly honor the request if it does not increase/decrease the frame size
to a multiple of its character size.

set-frame-height frame height &optional pretend pixelwise[Function]
This function resizes the text area of frame to a height of height lines. The sizes ofexisting windows in frame are altered proportionally to fit.
If pretend is non-nil, then Emacs displays height lines of output in frame, but does
not change its value for the actual height of the frame. This is only useful on text
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801

to reproduce behavior observed on a smaller screen, or if the terminal malfunctions
when using its whole screen. Setting the frame height directly does not always work,
because knowing the correct actual size may be necessary for correct cursor positioning
on text terminals.
The optional fourth argument pixelwise non-nil means that frame should be heightpixels high. Note that if frame-resize-pixelwise is nil, some window managers
may refuse to truly honor the request if it does not increase/decrease the frame height
to a multiple of its character height.
When used interactively, this command will ask the user for the number of lines to
set the height of the currently selected frame. You can also provide this value with anumeric prefix.

set-frame-width frame width &optional pretend pixelwise[Function]
This function sets the width of the text area of frame, measured in characters. The
argument pretend has the same meaning as in set-frame-height.
The optional fourth argument pixelwise non-nil means that frame should be width
pixels wide. Note that if frame-resize-pixelwise is nil, some window managers
may refuse to fully honor the request if it does not increase/decrease the frame width
to a multiple of its character width.

When used interactively, this command will ask the user for the number of columns to
set the width of the currently selected frame. You can also provide this value with anumeric prefix.
None of these three functions will make a frame smaller than needed to display all of its
windows together with their scroll bars, fringes, margins, dividers, mode and header lines.
This contrasts with requests by the window manager triggered, for example, by dragging theexternal border of a frame with the mouse. Such requests are always honored by clipping, if
necessary, portions that cannot be displayed at the right, bottom corner of the frame. The
parameters min-width and min-height (see Section 30.4.3.3 [Size Parameters], page 808)
can be used to obtain a similar behavior when changing the frame size from within Emacs.
The abnormal hook window-size-change-functions (see Section 29.28 [Window Hooks],
page 779) tracks all changes of the inner size of a frame including those induced by requestof the window-system or window manager. To rule out false positives that might occur whenchanging only the sizes of a frame’s windows without actually changing the size of the inner
frame, use the following function.

frame-size-changed-p &optional frame[Function]
This function returns non-nil when the inner width or height of frame has changed
since window-size-change-functions was run the last time for frame. It always
returns nil immediately after running window-size-change-functions for frame.

30.3.5 Implied Frame Resizing
By default, Emacs tries to keep the number of lines and columns of a frame’s text area
unaltered when, for example, toggling its menu or tool bar, changing its default font or
setting the width of any of its scroll bars. This means that in such case Emacs must ask thewindow manager to resize the frame’s window in order to accommodate the size change.

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Occasionally, such implied frame resizing may be unwanted, for example, when a frame
has been maximized or made full-screen (where it’s turned off by default). In general, users
can disable implied resizing with the following option:[User Option]
If this option is nil, changing a frame’s font, menu bar, tool bar, internal borders,fringes or scroll bars may resize its outer frame in order to keep the number of columns
or lines of its text area unaltered. If this option is t, no such resizing is done.

frame-inhibit-implied-resize

The value of this option can be also a list of frame parameters. In that case, implied
resizing is inhibited for the change of a parameter that appears in this list. Parameterscurrently handled by this option are font, font-backend, internal-border-width,menu-bar-lines and tool-bar-lines.
Changing any of the scroll-bar-width, scroll-bar-height, vertical-scrollbars, horizontal-scroll-bars, left-fringe and right-fringe frame parametersis handled as if the frame contained just one live window. This means, for example, thatremoving vertical scroll bars on a frame containing several side by side windows will
shrink the outer frame width by the width of one scroll bar provided this option is nil
and keep it unchanged if this option is t or a list containing vertical-scroll-bars.
The default value is (tab-bar-lines tool-bar-lines) for Lucid, Motif and MSWindows (which means that adding/removing a tool or tab bar there does not change
the outer frame height), (tab-bar-lines) on all other window systems including
GTK+ (which means that changing any of the parameters listed above with the
exception of tab-bar-lines may change the size of the outer frame), and t otherwise(which means the outer frame size never changes implicitly when there’s no window
system support).
Note that when a frame is not large enough to accommodate a change of any of theparameters listed above, Emacs may try to enlarge the frame even if this option is
non-nil.
Note also that window managers usually do not ask for resizing a frame when theychange the number of lines occupied by an external menu or tool bar. Typically, such“wrappings” occur when a user shrinks a frame horizontally, making it impossible todisplay all elements of its menu or tool bar. They may also result from a change of the
major mode altering the number of items of a menu or tool bar. Any such wrappings
may implicitly alter the number of lines of a frame’s text area and are unaffected by
the setting of this option.

30.4 Frame Parameters
A frame has many parameters that control its appearance and behavior. Just what parameters
a frame has depends on what display mechanism it uses.
Frame parameters exist mostly for the sake of graphical displays. Most frame parameters have no effect when applied to a frame on a text terminal; only the height,
width, name, title, menu-bar-lines, buffer-list and buffer-predicate parameters
do something special. If the terminal supports colors, the parameters foreground-color,background-color, background-mode and display-type are also meaningful. If the terminal supports frame transparency, the parameter alpha is also meaningful.

Chapter 30: Frames803

By default, frame parameters are saved and restored by the desktop library functions (seeSection 24.8 [Desktop Save Mode], page 594) when the variable desktop-restore-frames
is non-nil. It’s the responsibility of applications that their parameters are included inframeset-persistent-filter-alist to avoid that they get meaningless or even harmful
values in restored sessions.

30.4.1 Access to Frame Parameters
These functions let you read and change the parameter values of a frame.

frame-parameter frame parameter[Function]
This function returns the value of the parameter parameter (a symbol) of frame. Ifframe is nil, it returns the selected frame’s parameter. If frame has no setting forparameter, this function returns nil.

frame-parameters &optional frame[Function]
The function frame-parameters returns an alist listing all the parameters of frame andtheir values. If frame is nil or omitted, this returns the selected frame’s parametersmodify-frame-parameters frame alist[Function]
This function alters the frame frame based on the elements of alist. Each element ofalist has the form (parm . value), where parm is a symbol naming a parameter. If
you don’t mention a parameter in alist, its value doesn’t change. If frame is nil, it
defaults to the selected frame.
Some parameters are only meaningful for frames on certain kinds of display (seeChapter 30 [Frames], page 785). If alist includes parameters that are not meaningful
for the frame’s display, this function will change its value in the frame’s parameter
list, but will otherwise ignore it.
When alist specifies more than one parameter whose value can affect the new size offrame, the final size of the frame may differ according to the toolkit used. For example,
specifying that a frame should from now on have a menu and/or tool bar instead ofnone and simultaneously specifying the new height of the frame will inevitably lead toa recalculation of the frame’s height. Conceptually, in such case, this function will try
to have the explicit height specification prevail. It cannot be excluded, however, thatthe addition (or removal) of the menu or tool bar, when eventually performed by thetoolkit, will defeat this intention.
Sometimes, binding frame-inhibit-implied-resize (see Section 30.3.5 [Implied
Frame Resizing], page 801) to a non-nil value around calls to this function may fix
the problem sketched here. Sometimes, however, exactly such binding may be hit by
the problem.

set-frame-parameter frame parm value[Function]
This function sets the frame parameter parm to the specified value. If frame is nil, it
defaults to the selected frame.

modify-all-frames-parameters alist[Function]
This function alters the frame parameters of all existing frames according to alist, thenmodifies default-frame-alist (and, if necessary, initial-frame-alist) to apply
the same parameter values to frames that will be created henceforth.

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30.4.2 Initial Frame Parameters
You can specify the parameters for the initial startup frame by setting initial-frame-alist
in your init file (see Section 42.1.2 [Init File], page 1258).
[User Option]
This variable’s value is an alist of parameter values used when creating the initialframe. You can set this variable to specify the appearance of the initial frame without
altering subsequent frames. Each element has the form:

initial-frame-alist(parameter . value)
Emacs creates the initial frame before it reads your init file. After reading that
file, Emacs checks initial-frame-alist, and applies the parameter settings in thealtered value to the already created initial frame.
If these settings affect the frame geometry and appearance, you’ll see the frame appear
with the wrong ones and then change to the specified ones. If that bothers you, you
can specify the same geometry and appearance with X resources; those do take effectbefore the frame is created. See Section “X Resources” in The GNU Emacs Manual.
X resource settings typically apply to all frames. If you want to specify some X
resources solely for the sake of the initial frame, and you don’t want them to apply tosubsequent frames, here’s how to achieve this. Specify parameters in default-framealist to override the X resources for subsequent frames; then, to prevent these from
affecting the initial frame, specify the same parameters in initial-frame-alist withvalues that match the X resources.
If these parameters include (minibuffer . nil), that indicates that the initial frame
should have no minibuffer. In this case, Emacs creates a separate minibuffer-only frame as
well.
[User Option]
This variable’s value is an alist of parameter values used when creating an initial minibuffer-only frame (i.e., the minibuffer-only frame that Emacs creates if
initial-frame-alist specifies a frame with no minibuffer).

minibuffer-frame-alist[User Option]
This is an alist specifying default values of frame parameters for all Emacs frames—thefirst frame, and subsequent frames. When using the X Window System, you can get
the same results by means of X resources in many cases.

default-frame-alist

Setting this variable does not affect existing frames. Furthermore, functions that
display a buffer in a separate frame may override the default parameters by supplying
their own parameters.
If you invoke Emacs with command-line options that specify frame appearance, those
options take effect by adding elements to either initial-frame-alist or default-framealist. Options which affect just the initial frame, such as ‘--geometry’ and ‘--maximized’,
add to initial-frame-alist; the others add to default-frame-alist. see Section “Command Line Arguments for Emacs Invocation” in The GNU Emacs Manual.

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30.4.3 Window Frame Parameters
Just what parameters a frame has depends on what display mechanism it uses. This section
describes the parameters that have special meanings on some or all kinds of terminals. Of
these, name, title, height, width, buffer-list and buffer-predicate provide meaningful information in terminal frames, and tty-color-mode is meaningful only for frames on
text terminals.

30.4.3.1 Basic Parameters
These frame parameters give the most basic information about the frame. title and nameare meaningful on all terminals.
display

The display on which to open this frame. It should be a string of the form
‘host:dpy.screen’, just like the DISPLAY environment variable. See Section 30.2
[Multiple Terminals], page 787, for more details about display names.

display-type
This parameter describes the range of possible colors that can be used in thisframe. Its value is color, grayscale or mono.
title

If a frame has a non-nil title, that title appears in the window system’s title barat the top of the frame, and also in the mode line of windows in that frame if
mode-line-frame-identification uses ‘%F’ (see Section 24.4.5 [%-Constructs],
page 556). This is normally the case when Emacs is not using a window system,
and can only display one frame at a time. When Emacs is using a window
system, this parameter, if non-nil, overrides the title determined by the nameparameter and the implicit title calculated according to frame-title-format.
It also overrides the title determined by icon-title-format for iconified frames.
See Section 30.6 [Frame Titles], page 821.

name

The name of the frame. If you don’t specify a name via this parameter, Emacs
sets the frame name automatically, as specified by frame-title-format andicon-title-format, and that is the frame’s title that will appear on display
when Emacs uses a window system (unless the title parameter overrides it).
If you specify the frame name explicitly when you create the frame, the nameis also used (instead of the name of the Emacs executable) when looking up X
resources for the frame.

explicit-name
If the frame name was specified explicitly when the frame was created, thisparameter will be that name. If the frame wasn’t explicitly named, this parameter
will be nil.

30.4.3.2 Position Parameters
Parameters describing the X- and Y-offsets of a frame are always measured in pixels. For anormal, non-child frame they specify the frame’s outer position (see Section 30.3 [Frame
Geometry], page 791) relative to its display’s origin. For a child frame (see Section 30.14[Child Frames], page 831) they specify the frame’s outer position relative to the native
position of the frame’s parent frame. (Note that none of these parameters is meaningful on
TTY frames.)

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left

806

The position, in pixels, of the left outer edge of the frame with respect to theleft edge of the frame’s display or parent frame. It can be specified in one of thefollowing ways.
an integer A positive integer always relates the left edge of the frame to the leftedge of its display or parent frame. A negative integer relates theright frame edge to the right edge of the display or parent frame.
(+ pos)This specifies the position of the left frame edge relative to the leftedge of its display or parent frame. The integer pos may be positiveor negative; a negative value specifies a position outside the screen
or parent frame or on a monitor other than the primary one (formulti-monitor displays).

(- pos)This specifies the position of the right frame edge relative to theright edge of the display or parent frame. The integer pos may bepositive or negative; a negative value specifies a position outside thescreen or parent frame or on a monitor other than the primary one(for multi-monitor displays).

a floating-point value
A floating-point value in the range 0.0 to 1.0 specifies the left edge’s
offset via the left position ratio of the frame—the ratio of the leftedge of its outer frame to the width of the frame’s workarea (seeSection 30.2 [Multiple Terminals], page 787) or its parent’s native
frame (see Section 30.14 [Child Frames], page 831) minus the widthof the outer frame. Thus, a left position ratio of 0.0 flushes a frameto the left, a ratio of 0.5 centers it and a ratio of 1.0 flushes it to
the right of its display or parent frame. Similarly, the top position
ratio of a frame is the ratio of the frame’s top position to the heightof its workarea or parent frame minus the height of the frame.
Emacs will try to keep the position ratios of a child frame unaltered if that frame has a non-nil keep-ratio parameter (seeSection 30.4.3.6 [Frame Interaction Parameters], page 812) and its
parent frame is resized.
Since the outer size of a frame (see Section 30.3 [Frame Geometry],
page 791) is usually unavailable before a frame has been madevisible, it is generally not advisable to use floating-point values
when creating decorated frames. Floating-point values are moresuited for ensuring that an (undecorated) child frame is positioned
nicely within the area of its parent frame.
Some window managers ignore program-specified positions. If you want to be
sure the position you specify is not ignored, specify a non-nil value for theuser-position parameter as in the following example:(modify-frame-parameters
nil '((user-position . t) (left . (+ -4))))
In general, it is not a good idea to position a frame relative to the right orbottom edge of its display. Positioning the initial or a new frame is either notChapter 30: Frames

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accurate (because the size of the outer frame is not yet fully known before theframe has been made visible) or will cause additional flicker (if the frame has tobe repositioned after becoming visible).
Note also, that positions specified relative to the right/bottom edge of a display,
workarea or parent frame as well as floating-point offsets are stored internallyas integer offsets relative to the left/top edge of the display, workarea or parent
frame edge. They are also returned as such by functions like frame-parameters
and restored as such by the desktop saving routines.
top

The screen position of the top (or bottom) edge, in pixels, with respect to the
top (or bottom) edge of the display or parent frame. It works just like left,
except vertically instead of horizontally.

icon-left
The screen position of the left edge of the frame’s icon, in pixels, counting fromthe left edge of the screen. This takes effect when the frame is iconified, if thewindow manager supports this feature. If you specify a value for this parameter,
then you must also specify a value for icon-top and vice versa.
icon-top

The screen position of the top edge of the frame’s icon, in pixels, counting fromthe top edge of the screen. This takes effect when the frame is iconified, if thewindow manager supports this feature.

user-position
When you create a frame and specify its screen position with the left andtop parameters, use this parameter to say whether the specified position wasuser-specified (explicitly requested in some way by a human user) or merely
program-specified (chosen by a program). A non-nil value says the position
was user-specified.
Window managers generally heed user-specified positions, and some heed
program-specified positions too. But many ignore program-specified positions,placing the window in a default fashion or letting the user place it with themouse. Some window managers, including twm, let the user specify whether toobey program-specified positions or ignore them.
When you call make-frame, you should specify a non-nil value for this parameter if the values of the left and top parameters represent the user’s statedpreference; otherwise, use nil.
z-groupThis parameter specifies a relative position of the frame’s window-system window
in the stacking (Z-) order of the frame’s display.
If this is above, the window-system will display the window that corresponds tothe frame above all other window-system windows that do not have the above
property set. If this is nil, the frame’s window is displayed below all windowsthat have the above property set and above all windows that have the below
property set. If this is below, the frame’s window is displayed below all windowsthat do not have the below property set.
To position the frame above or below a specific other frame use the function
frame-restack (see Section 30.12 [Raising and Lowering], page 829).

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30.4.3.3 Size Parameters
Frame parameters usually specify frame sizes in character units. On graphical displays, thedefault face determines the actual pixel sizes of these character units (see Section 41.12.1[Face Attributes], page 1164).
widthThis parameter specifies the width of the frame. It can be specified as in thefollowing ways:
an integer A positive integer specifies the width of the frame’s text area (seeSection 30.3 [Frame Geometry], page 791) in characters.
a cons cell If this is a cons cell with the symbol text-pixels in its car, thecdr of that cell specifies the width of the frame’s text area in pixels.
a floating-point value
A floating-point number between 0.0 and 1.0 can be used to specify
the width of a frame via its width ratio—the ratio of its outer width(see Section 30.3 [Frame Geometry], page 791) to the width of theframe’s workarea (see Section 30.2 [Multiple Terminals], page 787)
or its parent frame’s (see Section 30.14 [Child Frames], page 831)
native frame. Thus, a value of 0.5 makes the frame occupy half of
the width of its workarea or parent frame, a value of 1.0 the full
width. Similarly, the height ratio of a frame is the ratio of its outerheight to the height of its workarea or its parent’s native frame.
Emacs will try to keep the width and height ratio of a child frame
unaltered if that frame has a non-nil keep-ratio parameter (seeSection 30.4.3.6 [Frame Interaction Parameters], page 812) and its
parent frame is resized.
Since the outer size of a frame is usually unavailable before a frame
has been made visible, it is generally not advisable to use floatingpoint values when creating decorated frames. Floating-point values
are more suited to ensure that a child frame always fits within
the area of its parent frame as, for example, when customizing
display-buffer-alist (see Section 29.13.1 [Choosing Window],
page 724) via display-buffer-in-child-frame.
Regardless of how this parameter was specified, functions reporting the value of
this parameter like frame-parameters always report the width of the frame’s
text area in characters as an integer rounded, if necessary, to a multiple of theframe’s default character width. That value is also used by the desktop saving
routines.

heightThis parameter specifies the height of the frame. It works just like width, except
vertically instead of horizontally.

user-size
This does for the size parameters height and width what the user-position
parameter (see Section 30.4.3.2 [Position Parameters], page 805) does for the
position parameters top and left.

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min-width
This parameter specifies the minimum native width (see Section 30.3 [Frame
Geometry], page 791) of the frame, in characters. Normally, the functions that
establish a frame’s initial width or resize a frame horizontally make sure that all
the frame’s windows, vertical scroll bars, fringes, margins and vertical dividers
can be displayed. This parameter, if non-nil allows to make a frame narrower
than that with the consequence that any components that do not fit will beclipped by the window manager.
min-heightThis parameter specifies the minimum native height (see Section 30.3 [Frame
Geometry], page 791) of the frame, in characters. Normally, the functions that
establish a frame’s initial size or resize a frame make sure that all the frame’s
windows, horizontal scroll bars and dividers, mode and header lines, the echoarea and the internal menu and tool bar can be displayed. This parameter, if
non-nil allows to make a frame smaller than that with the consequence thatany components that do not fit will be clipped by the window manager.
fullscreen
This parameter specifies whether to maximize the frame’s width, height orboth. Its value can be fullwidth, fullheight, fullboth, or maximized.1 A
fullwidth frame is as wide as possible, a fullheight frame is as tall as possible,
and a fullboth frame is both as wide and as tall as possible. A maximized frame
is like a “fullboth” frame, except that it usually keeps its title bar and the
buttons for resizing and closing the frame. Also, maximized frames typically
avoid hiding any task bar or panels displayed on the desktop. A “fullboth”
frame, on the other hand, usually omits the title bar and occupies the entire
available screen space.
Full-height and full-width frames are more similar to maximized frames in thisregard. However, these typically display an external border which might beabsent with maximized frames. Hence the heights of maximized and full-heightframes and the widths of maximized and full-width frames often differ by a few
pixels.
With some window managers you may have to customize the variable
frame-resize-pixelwise (see Section 30.3.4 [Frame Size], page 799) inorder to make a frame truly appear maximized or full-screen. Moreover,some window managers might not support smooth transition between
the various full-screen or maximization states. Customizing the variable
x-frame-normalize-before-maximize can help to overcome that.
Full-screen on macOS hides both the tool-bar and the menu-bar, however bothwill be displayed if the mouse pointer is moved to the top of the screen.
fullscreen-restore
This parameter specifies the desired fullscreen state of the frame after invoking
the toggle-frame-fullscreen command (see Section “Frame Commands” in
The GNU Emacs Manual) in the “fullboth” state. Normally this parameter is1

On PGTK frames, setting the values fullheight and fullwidth has no effect.

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installed automatically by that command when toggling the state to fullboth.
If, however, you start Emacs in the “fullboth” state, you have to specify thedesired behavior in your initial file as, for example(setq default-frame-alist'((fullscreen . fullboth)(fullscreen-restore . fullheight)))
This will give a new frame full height after typing in it F11 for the first time.
fit-frame-to-buffer-margins
This parameter allows to override the value of the option fit-frame-to-buffermargins when fitting this frame to the buffer of its root window with fit-frameto-buffer (see Section 29.5 [Resizing Windows], page 703).
fit-frame-to-buffer-sizes
This parameter allows to override the value of the option fit-frame-to-buffersizes when fitting this frame to the buffer of its root window with fit-frameto-buffer (see Section 29.5 [Resizing Windows], page 703).

30.4.3.4 Layout Parameters
These frame parameters enable or disable various parts of the frame, or control their sizes.
border-width
The width in pixels of the frame’s outer border (see Section 30.3 [Frame Geometry], page 791).
internal-border-width
The width in pixels of the frame’s internal border (see Section 30.3 [Frame
Geometry], page 791).
child-frame-border-width
The width in pixels of the frame’s internal border (see Section 30.3 [Frame
Geometry], page 791) if the given frame is a child frame (see Section 30.14 [Child
Frames], page 831). If this is nil, the value specified by the internal-borderwidth parameter is used instead.
vertical-scroll-bars
Whether the frame has scroll bars (see Section 41.14 [Scroll Bars], page 1195) for
vertical scrolling, and which side of the frame they should be on. The possible
values are left, right, and nil for no scroll bars.
horizontal-scroll-bars
Whether the frame has scroll bars for horizontal scrolling (t and bottom meanyes, nil means no).
scroll-bar-width
The width of vertical scroll bars, in pixels, or nil meaning to use the default
width.
scroll-bar-height
The height of horizontal scroll bars, in pixels, or nil meaning to use the default
height.

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left-fringe
right-fringe
The default width of the left and right fringes of windows in this frame (seeSection 41.13 [Fringes], page 1189). If either of these is zero, that effectively
removes the corresponding fringe.
When you use frame-parameter to query the value of either of these two frame
parameters, the return value is always an integer. When using set-frameparameter, passing a nil value imposes an actual default value of 8 pixels.
right-divider-width
The width (thickness) reserved for the right divider (see Section 41.15 [Window
Dividers], page 1198) of any window on the frame, in pixels. A value of zeromeans to not draw right dividers.
bottom-divider-width
The width (thickness) reserved for the bottom divider (see Section 41.15 [Window
Dividers], page 1198) of any window on the frame, in pixels. A value of zeromeans to not draw bottom dividers.
menu-bar-lines
The number of lines to allocate at the top of the frame for a menu bar (seeSection 23.18.5 [Menu Bar], page 516). The default is one if Menu Bar modeis enabled and zero otherwise. See Section “Menu Bars” in The GNU Emacs
Manual. For an external menu bar (see Section 30.3.1 [Frame Layout], page 791),
this value remains unchanged even when the menu bar wraps to two or morelines. In that case, the menu-bar-size value returned by frame-geometry (seeSection 30.3 [Frame Geometry], page 791) allows to derive whether the menu
bar actually occupies one or more lines.
tool-bar-lines
The number of lines to use for the tool bar (see Section 23.18.6 [Tool Bar],
page 517). The default is one if Tool Bar mode is enabled and zero otherwise.
See Section “Tool Bars” in The GNU Emacs Manual. This value may change
whenever the tool bar wraps (see Section 30.3.1 [Frame Layout], page 791).
tool-bar-position
The position of the tool bar when Emacs was built with GTK+. Its value canbe one of top, bottom left, right. The default is top.
tab-bar-lines
The number of lines to use for the tab bar (see Section “Tab Bars” in The
GNU Emacs Manual). The default is one if Tab Bar mode is enabled and zerootherwise. This value may change whenever the tab bar wraps (see Section 30.3.1[Frame Layout], page 791).
line-spacing
Additional space to leave below each text line, in pixels (a positive integer). See
Section 41.11 [Line Height], page 1162, for more information.
no-special-glyphs
If this is non-nil, it suppresses the display of any truncation (see Section 41.3
[Truncation], page 1130) and continuation glyphs for all the buffers displayed

Chapter 30: Frames812

by this frame. This is useful to eliminate such glyphs when fitting a frame
to its buffer via fit-frame-to-buffer (see Section 29.5 [Resizing Windows],
page 703). This frame parameter has effect only for GUI frames shown ongraphical displays, and only if the fringes are disabled. This parameter isintended as a purely-presentation feature, and in particular should not be used
for frames where the user can interactively insert text, or more generally where
the cursor is shown. A notable example of frames where this is used is tooltip
frames (see Section 41.26 [Tooltips], page 1249).

30.4.3.5 Buffer Parameters
These frame parameters, meaningful on all kinds of terminals, deal with which buffers havebeen, or should, be displayed in the frame.
minibuffer
Whether this frame has its own minibuffer. The value t means yes, nil meansno, only means this frame is just a minibuffer. If the value is a minibuffer
window (in some other frame), the frame uses that minibuffer.
This parameter takes effect when the frame is created. If specified as nil, Emacs
will try to set it to the minibuffer window of default-minibuffer-frame (seeSection 30.9 [Minibuffers and Frames], page 824). For an existing frame, thisparameter can be used exclusively to specify another minibuffer window. It is
not allowed to change it from a minibuffer window to t and vice-versa, or fromt to nil. If the parameter specifies a minibuffer window already, setting it tonil has no effect.
The special value child-frame means to make a minibuffer-only child frame(see Section 30.14 [Child Frames], page 831) whose parent becomes the frame
created. As if specified as nil, Emacs will set this parameter to the minibuffer
window of the child frame but will not select the child frame after its creation.
buffer-predicate
The buffer-predicate function for this frame. The function other-buffer uses
this predicate (from the selected frame) to decide which buffers it should consider,
if the predicate is not nil. It calls the predicate with one argument, a buffer,once for each buffer; if the predicate returns a non-nil value, it considers thatbuffer.
buffer-list
A list of buffers that have been selected in this frame, ordered most-recentlyselected first.
unsplittable
If non-nil, this frame’s window is never split automatically.

30.4.3.6 Frame Interaction Parameters
These parameters supply forms of interactions between different frames.
parent-frame
If non-nil, this means that this frame is a child frame (see Section 30.14 [Child
Frames], page 831), and this parameter specifies its parent frame. If nil, thismeans that this frame is a normal, top-level frame.

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delete-before
If non-nil, this parameter specifies another frame whose deletion will automatically trigger the deletion of this frame. See Section 30.7 [Deleting Frames],
page 822.
mouse-wheel-frame
If non-nil, this parameter specifies the frame whose windows will be scrolled
whenever the mouse wheel is scrolled with the mouse pointer hovering over thisframe, see Section “Mouse Commands” in The GNU Emacs Manual.
no-other-frame
If this is non-nil, then this frame is not eligible as candidate for the functions
next-frame, previous-frame (see Section 30.8 [Finding All Frames], page 823)
and other-frame, see Section “Frame Commands” in The GNU Emacs Manual.
auto-hide-function
When this parameter specifies a function, that function will be called instead of
the function specified by the variable frame-auto-hide-function when quitting
the frame’s only window (see Section 29.16 [Quitting Windows], page 749) andthere are other frames left.
minibuffer-exit
When this parameter is non-nil, Emacs will by default make this frame invisible
whenever the minibuffer (see Chapter 21 [Minibuffers], page 385) is exited.
Alternatively, it can specify the functions iconify-frame and delete-frame.
This parameter is useful to make a child frame disappear automatically (similar
to how Emacs deals with a window) when exiting the minibuffer.
keep-ratio
This parameter is currently meaningful for child frames (see Section 30.14 [Child
Frames], page 831) only. If it is non-nil, then Emacs will try to keep theframe’s size (width and height) ratios (see Section 30.4.3.3 [Size Parameters],
page 808) as well as its left and right position ratios (see Section 30.4.3.2 [Position
Parameters], page 805) unaltered whenever its parent frame is resized.
If the value of this parameter is nil, the frame’s position and size remain
unaltered when the parent frame is resized, so the position and size ratios maychange. If the value of this parameter is t, Emacs will try to preserve the frame’s
size and position ratios, hence the frame’s size and position relative to its parent
frame may change.
More individual control is possible by using a cons cell: In that case the frame’s
width ratio is preserved if the car of the cell is either t or width-only. The
height ratio is preserved if the car of the cell is either t or height-only. The
left position ratio is preserved if the cdr of the cell is either t or left-only.
The top position ratio is preserved if the cdr of the cell is either t or top-only.

30.4.3.7 Mouse Dragging Parameters
The parameters described below provide support for resizing a frame by dragging its internalborders with the mouse. They also allow moving a frame with the mouse by dragging theheader or tab line of its topmost or the mode line of its bottommost window.

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These parameters are mostly useful for child frames (see Section 30.14 [Child Frames],
page 831) that come without window manager decorations. If necessary, they can be used
for undecorated top-level frames as well.
drag-internal-border
If non-nil, the frame can be resized by dragging its internal borders, if present,with the mouse.
drag-with-header-line
If non-nil, the frame can be moved with the mouse by dragging the header lineof its topmost window.
drag-with-tab-line
If non-nil, the frame can be moved with the mouse by dragging the tab line ofits topmost window.
drag-with-mode-line
If non-nil, the frame can be moved with the mouse by dragging the mode lineof its bottommost window. Note that such a frame is not allowed to have its
own minibuffer window.
snap-width
A frame that is moved with the mouse will “snap” at the border(s) of the display
or its parent frame whenever it is dragged as near to such an edge as the numberof pixels specified by this parameter.
top-visible
If this parameter is a number, the top edge of the frame never appears above
the top edge of its display or parent frame. Moreover, as many pixels of theframe as specified by that number will remain visible when the frame is moved
against any of the remaining edges of its display or parent frame. Setting thisparameter is useful to guard against dragging a child frame with a non-nil
drag-with-header-line parameter completely out of the area of its parent
frame.
bottom-visible
If this parameter is a number, the bottom edge of the frame never appears below
the bottom edge of its display or parent frame. Moreover, as many pixels of
the frame as specified by that number will remain visible when the frame is
moved against any of the remaining edges of its display or parent frame. Setting
this parameter is useful to guard against dragging a child frame with a non-nil
drag-with-mode-line parameter completely out of the area of its parent frame.

30.4.3.8 Window Management Parameters
The following frame parameters control various aspects of the frame’s interaction with thewindow manager or window system. They have no effect on text terminals.
visibility
The state of visibility of the frame. There are three possibilities: nil for invisible,t for visible, and icon for iconified. See Section 30.11 [Visibility of Frames],
page 828.

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auto-raise
If non-nil, Emacs automatically raises the frame when it is selected. Somewindow managers do not allow this.
auto-lower
If non-nil, Emacs automatically lowers the frame when it is deselected. Somewindow managers do not allow this.
icon-type
The type of icon to use for this frame. If the value is a string, that specifies afile containing a bitmap to use; nil specifies no icon (in which case the window
manager decides what to show); any other non-nil value specifies the default
Emacs icon.
icon-name
The name to use in the icon for this frame, when and if the icon appears. If thisis nil, the frame’s title is used.
window-id
The ID number which the graphical display uses for this frame. Emacs assigns
this parameter when the frame is created; changing the parameter has no effecton the actual ID number.
outer-window-id
The ID number of the outermost window-system window in which the frame
exists. As with window-id, changing this parameter has no actual effect.
wait-for-wm
If non-nil, tell Xt to wait for the window manager to confirm geometry changes.
Some window managers, including versions of Fvwm2 and KDE, fail to confirm,
so Xt hangs. Set this to nil to prevent hanging with those window managers.
stickyIf non-nil, the frame is visible on all virtual desktops on systems with virtual
desktops.

shadedIf non-nil, tell the window manager to display the frame in a way that its
contents are hidden, leaving only the title bar.

use-frame-synchronization
If non-nil, synchronize the frame redisplay with the refresh rate of the monitor
to avoid graphics tearing. At present, this is only implemented on Haiku and the
X window system inside no-toolkit and X toolkit builds, does not work correctlywith toolkit scroll bars, and requires a compositing manager supporting therelevant display synchronization protocols. The synchronizeResize X resourcemust also be set to the string "extended".
inhibit-double-buffering
If non-nil, the frame is drawn to the screen without double buffering. Emacs
normally attempts to use double buffering, where available, to reduce flicker.
Set this property if you experience display bugs or pine for that retro, flicker-y
feeling.

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skip-taskbar
If non-nil, this tells the window manager to remove the frame’s icon from thetaskbar associated with the frame’s display and inhibit switching to the frame’s
window via the combination Alt-TAB. On MS-Windows, iconifying such a frame
will "roll in" its window-system window at the bottom of the desktop. Somewindow managers may not honor this parameter.
no-focus-on-map
If non-nil, this means that the frame does not want to receive input focus when
it is mapped (see Section 30.11 [Visibility of Frames], page 828). Some window
managers may not honor this parameter.
no-accept-focus
If non-nil, this means that the frame does not want to receive input focus via explicit mouse clicks or when moving the mouse into it either via focus-followsmouse (see Section 30.10 [Input Focus], page 824) or mouse-autoselect-window(see Section 29.25 [Mouse Window Auto-selection], page 773). This may havethe unwanted side-effect that a user cannot scroll a non-selected frame with themouse. Some window managers may not honor this parameter. On Haiku, italso has the side-effect that the window will not be able to receive any keyboard
input from the user, not even if the user switches to the frame using the key
combination Alt-TAB.
undecorated
If non-nil, this frame’s window-system window is drawn without decorations,like the title, minimize/maximize boxes and external borders. This usuallymeans that the window cannot be dragged, resized, iconified, maximized ordeleted with the mouse. If nil, the frame’s window is usually drawn with all
the elements listed above unless their display has been suspended via window
manager settings.
Under X, Emacs uses the Motif window manager hints to turn off decorations.
Some window managers may not honor these hints.
NS builds consider the tool bar to be a decoration, and therefore hide it on an
undecorated frame.
override-redirect
If non-nil, this means that this is an override redirect frame—a frame nothandled by window managers under X. Override redirect frames have no window
manager decorations, can be positioned and resized only via Emacs’ positioning
and resizing functions and are usually drawn on top of all other frames. Setting
this parameter has no effect on MS-Windows.
ns-appearance
Only available on macOS, if set to dark draw this frame’s window-systemwindow using the “vibrant dark” theme, and if set to light use the “aqua”
theme, otherwise use the system default. The “vibrant dark” theme can be used
to set the toolbar and scrollbars to a dark appearance when using an Emacs
theme with a dark background.

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ns-transparent-titlebar
Only available on macOS, if non-nil, set the titlebar and toolbar to be transparent. This effectively sets the background color of both to match the Emacs
background color.

30.4.3.9 Cursor Parameters
This frame parameter controls the way the cursor looks.
cursor-type
How to display the cursor. Legitimate values are:box

Display a filled box. (This is the default.)(box . size)
Display a filled box. However, display it as a hollow box if point isunder masked image larger than size pixels in either dimension.
hollow

Display a hollow box.

nil

Don’t display a cursor.

bar

Display a vertical bar between characters.

(bar . width)
Display a vertical bar width pixels wide between characters.
hbar

Display a horizontal bar.

(hbar . height)
Display a horizontal bar height pixels high.
The cursor-type frame parameter may be overridden by the variables cursor-type
and cursor-in-non-selected-windows:[User Option]
This buffer-local variable controls how the cursor looks in a selected window showing
the buffer. If its value is t, that means to use the cursor specified by the cursor-type
frame parameter. Otherwise, the value should be one of the cursor types listed above,and it overrides the cursor-type frame parameter.

cursor-type[User Option]
This buffer-local variable controls how the cursor looks in a window that is not selected.
It supports the same values as the cursor-type frame parameter; also, nil means
don’t display a cursor in nonselected windows, and t (the default) means use a standard
modification of the usual cursor type (solid box becomes hollow box, and bar becomesa narrower bar).

cursor-in-non-selected-windows[User Option]
This variable controls the width of the block cursor displayed on extra-wide glyphs
such as a tab or a stretch of white space. By default, the block cursor is only as wide
as the font’s default character, and will not cover all of the width of the glyph under
it if that glyph is extra-wide. A non-nil value of this variable means draw the block
cursor as wide as the glyph under it. The default value is nil.
This variable has no effect on text-mode frames, since the text-mode cursor is drawn
by the terminal out of Emacs’s control.

x-stretch-cursor

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818[User Option]
This variable specifies how to blink the cursor. Each element has the form (on-state. off-state). Whenever the cursor type equals on-state (comparing using equal),
the corresponding off-state specifies what the cursor looks like when it blinks off. Bothon-state and off-state should be suitable values for the cursor-type frame parameter.
There are various defaults for how to blink each type of cursor, if the type is not
mentioned as an on-state here. Changes in this variable do not take effect immediately,
only when you specify the cursor-type frame parameter.

blink-cursor-alist

30.4.3.10 Font and Color Parameters
These frame parameters control the use of fonts and colors.
font-backend
A list of symbols, specifying the font backends to use for drawing characterson the frame, in order of priority. In Emacs built without Cairo drawing on X,
there are currently three potentially available font backends: x (the X core fontdriver), xft (the Xft font driver), and xfthb (the Xft font driver with HarfBuzz
text shaping). If built with Cairo drawing, there are also three potentiallyavailable font backends on X: x, ftcr (the FreeType font driver on Cairo), andftcrhb (the FreeType font driver on Cairo with HarfBuzz text shaping). When
Emacs is built with HarfBuzz, the default font driver is ftcrhb, although useof the ftcr driver is still possible, but not recommended. On MS-Windows,
there are currently three available font backends: gdi (the core MS-Windows
font driver), uniscribe (font driver for OTF and TTF fonts with text shaping
by the Uniscribe engine), and harfbuzz (font driver for OTF and TTF fontswith HarfBuzz text shaping) (see Section “Windows Fonts” in The GNU Emacs
Manual). The harfbuzz driver is similarly recommended. On Haiku, there canbe several font drivers (see Section “Haiku Fonts” in The GNU Emacs Manual).
On other systems, there is only one available font backend, so it does not makesense to modify this frame parameter.
background-mode
This parameter is either dark or light, according to whether the backgroundcolor is a light one or a dark one.
tty-color-mode
This parameter overrides the terminal’s color support as given by the system’s
terminal capabilities database in that this parameter’s value specifies the color
mode to use on a text terminal. The value can be either a symbol or a number.
A number specifies the number of colors to use (and, indirectly, what commands
to issue to produce each color). For example, (tty-color-mode . 8) specifies
use of the ANSI escape sequences for 8 standard text colors. A value of −1
turns off color support.
If the parameter’s value is a symbol, it specifies a number through the value of
tty-color-mode-alist, and the associated number is used instead.
screen-gamma
If this is a number, Emacs performs gamma correction which adjusts thebrightness of all colors. The value should be the screen gamma of your display.

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Usual PC monitors have a screen gamma of 2.2, so color values in Emacs, and in
X windows generally, are calibrated to display properly on a monitor with that
gamma value. If you specify 2.2 for screen-gamma, that means no correction isneeded. Other values request correction, designed to make the corrected colors
appear on your screen the way they would have appeared without correction on
an ordinary monitor with a gamma value of 2.2.
If your monitor displays colors too light, you should specify a screen-gamma
value smaller than 2.2. This requests correction that makes colors darker. A
screen gamma value of 1.5 may give good results for LCD color displays.
alphaThis parameter specifies the opacity of the frame, on graphical displays that
support variable opacity. It should be an integer between 0 and 100, where 0means completely transparent and 100 means completely opaque. It can also
have a nil value, which tells Emacs not to set the frame opacity (leaving it to
the window manager).
To prevent the frame from disappearing completely from view, the variable
frame-alpha-lower-limit defines a lower opacity limit. If the value of theframe parameter is less than the value of this variable, Emacs uses the latter.
By default, frame-alpha-lower-limit is 20.
The alpha frame parameter can also be a cons cell (active . inactive), where
active is the opacity of the frame when it is selected, and inactive is the opacity
when it is not selected.
Some window systems do not support the alpha parameter for child frames (seeSection 30.14 [Child Frames], page 831).

alpha-background
Sets the background transparency of the frame. Unlike the alpha frame parameter, this only controls the transparency of the background while keeping
foreground elements such as text fully opaque. It should be an integer between
0 and 100, where 0 means completely transparent and 100 means completely
opaque (default).
The following frame parameters are semi-obsolete in that they are automatically equivalent
to particular face attributes of particular faces (see Section “Standard Faces” in The Emacs
Manual):font

The name of the font for displaying text in the frame. This is a string, either a valid font name for your system or the name of an Emacs fontset (seeSection 41.12.11 [Fontsets], page 1182). It is equivalent to the font attribute ofthe default face.

foreground-color
The color to use for characters. It is equivalent to the :foreground attribute ofthe default face.
background-color
The color to use for the background of characters. It is equivalent to the:background attribute of the default face.

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mouse-color
The color for the mouse pointer. It is equivalent to the :background attributeof the mouse face.
cursor-color
The color for the cursor that shows point. It is equivalent to the :background
attribute of the cursor face.
border-color
The color for the border of the frame. It is equivalent to the :background
attribute of the border face.
scroll-bar-foregroundIf non-nil, the color for the foreground of scroll bars. It is equivalent to the:foreground attribute of the scroll-bar face.
scroll-bar-backgroundIf non-nil, the color for the background of scroll bars. It is equivalent to the:background attribute of the scroll-bar face.

30.4.4 Geometry
Here’s how to examine the data in an X-style window geometry specification:

x-parse-geometry geom

[Function]
The function x-parse-geometry converts a standard X window geometry string toan alist that you can use as part of the argument to make-frame.
The alist describes which parameters were specified in geom, and gives the values
specified for them. Each element looks like (parameter . value). The possible
parameter values are left, top, width, and height.
For the size parameters, the value must be an integer. The position parameter names
left and top are not totally accurate, because some values indicate the position of theright or bottom edges instead. The value possibilities for the position parameters are:an integer, a list (+ pos), or a list (- pos); as previously described (see Section 30.4.3.2[Position Parameters], page 805).
Here is an example:(x-parse-geometry "35x70+0-0")⇒ ((height . 70) (width . 35)(top - 0) (left . 0))

30.5 Terminal Parameters
Each terminal has a list of associated parameters. These terminal parameters are mostly aconvenient way of storage for terminal-local variables, but some terminal parameters have a
special meaning.
This section describes functions to read and change the parameter values of a terminal.
They all accept as their argument either a terminal or a frame; the latter means use thatframe’s terminal. An argument of nil means the selected frame’s terminal.

terminal-parameters &optional terminal[Function]
This function returns an alist listing all the parameters of terminal and their values.

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terminal-parameter terminal parameter[Function]
This function returns the value of the parameter parameter (a symbol) of terminal. If
terminal has no setting for parameter, this function returns nil.

set-terminal-parameter terminal parameter value[Function]
This function sets the parameter parameter of terminal to the specified value, andreturns the previous value of that parameter.

Here’s a list of a few terminal parameters that have a special meaning:background-mode
The classification of the terminal’s background color, either light or dark.
normal-erase-is-backspace
Value is either 1 or 0, depending on whether normal-erase-is-backspacemode is turned on or off on this terminal. See Section “DEL Does Not Delete”
in The Emacs Manual.
terminal-initted
After the terminal is initialized, this is set to the terminal-specific initialization
function.
tty-mode-set-strings
When present, a list of strings containing escape sequences that Emacs will
output while configuring a tty for rendering. Emacs emits these strings only
when configuring a terminal: if you want to enable a mode on a terminal thatis already active (for example, while in tty-setup-hook), explicitly output
the necessary escape sequence using send-string-to-terminal in addition toadding the sequence to tty-mode-set-strings.
tty-mode-reset-strings
When present, a list of strings that undo the effects of the strings in tty-modeset-strings. Emacs emits these strings when exiting, deleting a terminal, or
suspending itself.

30.6 Frame Titles
Every frame has a name parameter; this serves as the default for the frame title whichwindow systems typically display at the top of the frame. You can specify a name explicitly
by setting the name frame property.
Normally you don’t specify the name explicitly, and Emacs computes the frame nameautomatically based on a template stored in the variable frame-title-format. Emacs
recomputes the name each time the frame is redisplayed.
[Variable]
This variable specifies how to compute a name for a frame when you have not explicitly
specified one (via the frame’s parameters; see Section 30.4.3.1 [Basic Parameters],
page 805). The variable’s value is actually a mode line construct, just like mode-lineformat, except that the ‘%c’, ‘%C’, and ‘%l’ constructs are ignored. See Section 24.4.2[Mode Line Data], page 551.

frame-title-format

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822[Variable]
This variable specifies how to compute the name for an iconified frame when you havenot explicitly specified the frame’s name via the frame’s parameters. The resulting
title appears in the frame’s icon itself. If the value is a string, is should be a mode line
construct like that of frame-title-format. The value can also be t, which means touse frame-title-format instead; this avoids problems with some window managers
and desktop environments, where a change in a frame’s title (when a frame is iconified)is interpreted as a request to raise the frame and/or give it input focus. It is also useful
if you want the frame’s title to be the same no matter if the frame is iconified or not.
The default value is a string identical to the default value of frame-title-format.

icon-title-format[Variable]
This variable is set automatically by Emacs. Its value is t when there are two or more
frames (not counting minibuffer-only frames or invisible frames). The default valueof frame-title-format uses multiple-frames so as to put the buffer name in theframe title only when there is more than one frame.
The value of this variable is not guaranteed to be accurate except while processing
frame-title-format or icon-title-format.

multiple-frames

30.7 Deleting Frames
A live frame is one that has not been deleted. When a frame is deleted, it is removed fromits terminal display, although it may continue to exist as a Lisp object until there are no
more references to it.

delete-frame &optional frame force[Command]This function deletes the frame frame. The argument frame must specify a live frame(see below) and defaults to the selected frame.
It first deletes any child frame of frame (see Section 30.14 [Child Frames], page 831)
and any frame whose delete-before frame parameter (see Section 30.4.3.6 [Frame
Interaction Parameters], page 812) specifies frame. All such deletions are performed
recursively; so this step makes sure that no other frames with frame as their ancestor will exist. Then, unless frame specifies a tooltip, this function runs the hookdelete-frame-functions (each function getting one argument, frame) before actually killing the frame. After actually killing the frame and removing the frame fromthe frame list, delete-frame runs after-delete-frame-functions.
Note that a frame cannot be deleted as long as its minibuffer serves as surrogate
minibuffer for another frame (see Section 30.9 [Minibuffers and Frames], page 824).
Normally, you cannot delete a frame if all other frames are invisible, but if force is
non-nil, then you are allowed to do so.

frame-live-p frame[Function]
This function returns non-nil if the frame frame has not been deleted. The possible
non-nil return values are like those of framep. See Chapter 30 [Frames], page 785.

Some window managers provide a command to delete a window. These work by sending
a special message to the program that operates the window. When Emacs gets one of thesecommands, it generates a delete-frame event, whose normal definition is a command that
calls the function delete-frame. See Section 22.7.12 [Misc Events], page 450.

Chapter 30: Frames823

delete-other-frames &optional frame iconify[Command]This command deletes all frames on frame’s terminal, except frame. If frame uses
another frame’s minibuffer, that minibuffer frame is left untouched. The argument
frame must specify a live frame and defaults to the selected frame. Internally, thiscommand works by calling delete-frame with force nil for all frames that shall bedeleted.
This function does not delete any of frame’s child frames (see Section 30.14 [Child
Frames], page 831). If frame is a child frame, it deletes frame’s siblings only.

With the prefix argument iconify, the frames are iconified rather than deleted.

30.8 Finding All Frames[Function]
This function returns a list of all the live frames, i.e., those that have not been deleted.
It is analogous to buffer-list for buffers, and includes frames on all terminals. The
list that you get is newly created, so modifying the list doesn’t have any effect on theinternals of Emacs.

frame-list[Function]
This function returns a list of just the currently visible frames. See Section 30.11[Visibility of Frames], page 828. Frames on text terminals always count as visible,
even though only the selected one is actually displayed.

visible-frame-list

frame-list-z-order &optional display[Function]
This function returns a list of Emacs’ frames, in Z (stacking) order (see Section 30.12[Raising and Lowering], page 829). The optional argument display specifies whichdisplay to poll. display should be either a frame or a display name (a string). If
omitted or nil, that stands for the selected frame’s display. It returns nil if display
contains no Emacs frame.
Frames are listed from topmost (first) to bottommost (last). As a special case, if
display is non-nil and specifies a live frame, it returns the child frames of that framein Z (stacking) order.

This function is not meaningful on text terminals.

next-frame &optional frame minibuf[Function]
This function lets you cycle conveniently through all the frames on a specific terminalfrom an arbitrary starting point. It returns the frame following frame, in the list of
all live frames, on frame’s terminal. The argument frame must specify a live frameand defaults to the selected frame. It never returns a frame whose no-other-frame
parameter (see Section 30.4.3.6 [Frame Interaction Parameters], page 812) is non-nil.
The second argument, minibuf, says which frames to consider when deciding what thenext frame should be:nil

Consider all frames except minibuffer-only frames.

visibleConsider only visible frames.

0Consider only visible or iconified frames.

Chapter 30: Frames

a window

824

Consider only the frames using that particular window as their minibuffer
window.

anything else
Consider all frames.

previous-frame &optional frame minibuf[Function]

Like next-frame, but cycles through all frames in the opposite direction.
See also next-window and previous-window, in Section 29.10 [Cyclic Window Ordering],
page 717.
Some Lisp programs need to find one or more frames that satisfy a given criteria. The
function filtered-frame-list is provided for this purpose.

filtered-frame-list predicate[Function]
This function returns the list of all the live frames which satisfy the specified predicate.
The argument predicate must be a function of one argument, a frame to be tested
against the filtering criteria, and should return non-nil if the frame satisfies thecriteria.

30.9 Minibuffers and Frames
Normally, each frame has its own minibuffer window at the bottom, which is used wheneverthat frame is selected. You can get that window with the function minibuffer-window (seeSection 21.11 [Minibuffer Windows], page 418).
However, you can also create a frame without a minibuffer. Such a frame must use theminibuffer window of some other frame. That other frame will serve as surrogate minibuffer
frame for this frame and cannot be deleted via delete-frame (see Section 30.7 [Deleting
Frames], page 822) as long as this frame is live.
When you create the frame, you can explicitly specify its minibuffer window (in someother frame) with the minibuffer frame parameter (see Section 30.4.3.5 [Buffer Parameters],
page 812). If you don’t, then the minibuffer is found in the frame which is the value ofthe variable default-minibuffer-frame. Its value should be a frame that does have aminibuffer.
If you use a minibuffer-only frame, you might want that frame to raise when you enter theminibuffer. If so, set the variable minibuffer-auto-raise to t. See Section 30.12 [Raisingand Lowering], page 829.
[Variable]
This variable specifies the frame to use for the minibuffer window, by default. It does
not affect existing frames. It is always local to the current terminal and cannot bebuffer-local. See Section 30.2 [Multiple Terminals], page 787.

default-minibuffer-frame

30.10 Input Focus
At any time, one frame in Emacs is the selected frame. The selected window (see Section 29.3
[Selecting Windows], page 696) always resides on the selected frame.
When Emacs displays its frames on several terminals (see Section 30.2 [Multiple Terminals],
page 787), each terminal has its own selected frame. But only one of these is the selected

Chapter 30: Frames825

frame: it’s the frame that belongs to the terminal from which the most recent input came.
That is, when Emacs runs a command that came from a certain terminal, the selected frame
is the one of that terminal. Since Emacs runs only a single command at any given time, itneeds to consider only one selected frame at a time; this frame is what we call the selected
frame in this manual. The display on which the selected frame is shown is the selected
frame’s display.

selected-frame[Function]

This function returns the selected frame.
Some window systems and window managers direct keyboard input to the window object
that the mouse is in; others require explicit clicks or commands to shift the focus to various
window objects. Either way, Emacs automatically keeps track of which frames have focus.
To explicitly switch to a different frame from a Lisp function, call select-frame-setinput-focus.
The plural “frames” in the previous paragraph is deliberate: while Emacs itself has
only one selected frame, Emacs can have frames on many different terminals (recall that aconnection to a window system counts as a terminal), and each terminal has its own idea of
which frame has input focus. Under the X Window System, where user input is organized
into individual “seats” of input, each seat in turn can have its own specific input focus.
When you set the input focus to a frame, you set the focus for that frame’s terminal on thelast seat which interacted with Emacs, but frames on other terminals and seats may still
remain focused.
If the input focus is set before any user interaction has occurred on the specified terminal,
then the X server picks a random seat (normally the one with the lowest number) and sets
the input focus there.
Lisp programs can switch frames temporarily by calling the function select-frame. This
does not alter the window system’s concept of focus; rather, it escapes from the window
manager’s control until that control is somehow reasserted.
When using a text terminal, only one frame can be displayed at a time on the terminal,
so after a call to select-frame, the next redisplay actually displays the newly selected
frame. This frame remains selected until a subsequent call to select-frame. Each frameon a text terminal has a number which appears in the mode line before the buffer name (seeSection 24.4.4 [Mode Line Variables], page 554).

select-frame-set-input-focus frame &optional norecord[Function]
This function selects frame, raises it (should it happen to be obscured by other frames)
and tries to give it the window system’s focus. On a text terminal, the next redisplay
displays the new frame on the entire terminal screen. The optional argument norecord
has the same meaning as for select-frame (see below). The return value of thisfunction is not significant.

Ideally, the function described next should focus a frame without also raising it above
other frames. Unfortunately, many window-systems or window managers may refuse tocomply.

x-focus-frame frame &optional noactivate[Function]
This function gives frame the focus of the X server without necessarily raising it. frame
nil means use the selected frame. Under X, the optional argument noactivate, if

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non-nil, means to avoid making frame’s window-system window the “active” window
which should insist a bit more on avoiding to raise frame above other frames.
On MS-Windows the noactivate argument has no effect. However, if frame is a childframe (see Section 30.14 [Child Frames], page 831), this function usually focuses frame
without raising it above other child frames.
If there is no window system support, this function does nothing.

select-frame frame &optional norecord[Command]This function selects frame frame, temporarily disregarding the focus of the X server
if any. The selection of frame lasts until the next time the user does something toselect a different frame, or until the next time this function is called. (If you are using
a window system, the previously selected frame may be restored as the selected frame
after return to the command loop, because it still may have the window system’s input
focus.)The specified frame becomes the selected frame, and its terminal becomes the selected
terminal. This function then calls select-window as a subroutine, passing the window
selected within frame as its first argument and norecord as its second argument (hence,
if norecord is non-nil, this avoids changing the order of recently selected windows
and the buffer list). See Section 29.3 [Selecting Windows], page 696.
This function returns frame, or nil if frame has been deleted.
In general, you should never use select-frame in a way that could switch to a different
terminal without switching back when you’re done.

Emacs cooperates with the window system by arranging to select frames as the server
and window manager request. When a window system informs Emacs that one of its
frames has been selected, Emacs internally generates a focus-in event. When an Emacs
frame is displayed on a text-terminal emulator, such as xterm, which supports reporting of
focus-change notification, the focus-in and focus-out events are available even for text-mode
frames. Focus events are normally handled by handle-focus-in.

handle-focus-in event[Command]This function handles focus-in events from window systems and terminals that support
explicit focus notifications. It updates the per-frame focus flags that frame-focusstate queries and calls after-focus-change-function. In addition, it generates aswitch-frame event in order to switch the Emacs notion of the selected frame to theframe most recently focused in some terminal. It’s important to note that this switchingof the Emacs selected frame to the most recently focused frame does not mean that
other frames do not continue to have the focus in their respective terminals. Do notinvoke this function yourself: instead, attach logic to after-focus-change-function.

handle-switch-frame frame[Command]This function handles a switch-frame event, which Emacs generates for itself upon focus
notification or under various other circumstances involving an input event arriving at
a different frame from the last event. Do not invoke this function yourself.

redirect-frame-focus frame &optional focus-frame[Function]
This function redirects focus from frame to focus-frame. This means that focus-frame
will receive subsequent keystrokes and events intended for frame. After such anChapter 30: Frames

827

event, the value of last-event-frame will be focus-frame. Also, switch-frame events
specifying frame will instead select focus-frame.
If focus-frame is omitted or nil, that cancels any existing redirection for frame, which
therefore once again receives its own events.
One use of focus redirection is for frames that don’t have minibuffers. These frames
use minibuffers on other frames. Activating a minibuffer on another frame redirects
focus to that frame. This puts the focus on the minibuffer’s frame, where it belongs,
even though the mouse remains in the frame that activated the minibuffer.
Selecting a frame can also change focus redirections. Selecting frame bar, when foo
had been selected, changes any redirections pointing to foo so that they point to bar
instead. This allows focus redirection to work properly when the user switches fromone frame to another using select-window.
This means that a frame whose focus is redirected to itself is treated differently froma frame whose focus is not redirected. select-frame affects the former but not thelatter.
The redirection lasts until redirect-frame-focus is called to change it.

frame-focus-state frame[Function]

This function retrieves the last known focus state of frame.
It returns nil if the frame is known not to be focused, t if the frame is known to befocused, or unknown if Emacs does not know the focus state of the frame. (You may
see this last state in TTY frames running on terminals that do not support explicit
focus notifications.)[Variable]
This function is called with no arguments when Emacs notices that a frame may
have gotten or lost focus. Focus events are delivered asynchronously, and may not bedelivered in the expected order, so code that wants to do something depending on thestate of focused frames have go through all the frames and check.

after-focus-change-function

For instance, here’s a simple example function that sets the background color basedon whether the frame has focus or not:(add-function :after after-focus-change-function#'my-change-background)(defun my-change-background ()(dolist (frame (frame-list))(pcase (frame-focus-state frame)(`t (set-face-background 'default "black" frame))(`nil (set-face-background 'default "#404040" frame)))))
Multiple frames may appear to have input focus simultaneously due to focus event
delivery differences, the presence of multiple Emacs terminals, and other factors, andcode should be robust in the face of this situation.
Depending on window system, focus events may also be delivered repeatedly and withdifferent focus states before settling to the expected values. Code relying on focus
notifications should “debounce” any user-visible updates arising from focus changes,
perhaps by deferring work until redisplay.

Chapter 30: Frames

828This function may be called in arbitrary contexts, including from inside read-event,so take the same care as you might when writing a process filter.
[User Option]
This option informs Emacs whether and how the window manager transfers focus
when you move the mouse pointer into a frame. It can have three meaningful values:

focus-follows-mousenil

The default value nil should be used when your window manager follows
a “click-to-focus” policy where you have to click the mouse inside of aframe in order for that frame to gain focus.

t

The value t should be used when your window manager has the focus
automatically follow the position of the mouse pointer but a frame thatgains focus is not raised automatically and may even remain occluded byother window-system windows.

auto-raise
The value auto-raise should be used when your window manager has
the focus automatically follow the position of the mouse pointer and aframe that gains focus is raised automatically.
If this option is non-nil, Emacs moves the mouse pointer to the frame selected by
select-frame-set-input-focus. That function is used by a number of commands
like, for example, other-frame and pop-to-buffer.
The distinction between the values t and auto-raise is not needed for “normal”
frames because the window manager usually takes care of raising them. It is useful
to automatically raise child frames via mouse-autoselect-window (see Section 29.25[Mouse Window Auto-selection], page 773).
Note that this option does not distinguish “sloppy” focus (where the frame that
previously had focus retains focus as long as the mouse pointer does not move intoanother window-system window) from “strict” focus (where a frame immediately loses
focus when it’s left by the mouse pointer). Neither does it recognize whether yourwindow manager supports delayed focusing or auto-raising where you can explicitly
specify the time until a new frame gets focus or is auto-raised.
You can supply a “focus follows mouse” policy for individual Emacs windows by customizing the variable mouse-autoselect-window (see Section 29.25 [Mouse Window
Auto-selection], page 773).

30.11 Visibility of Frames
A frame on a graphical display may be visible, invisible, or iconified. If it is visible, its
contents are displayed in the usual manner. If it is iconified, its contents are not displayed,
but there is a little icon somewhere to bring the frame back into view (some window managers
refer to this state as minimized rather than iconified, but from Emacs’ point of view they
are the same thing). If a frame is invisible, it is not displayed at all.
The concept of visibility is strongly related to that of (un-)mapped frames. A frame (or,more precisely, its window-system window) is and becomes mapped when it is displayed forthe first time and whenever it changes its state of visibility from iconified or invisible

Chapter 30: Frames829

to visible. Conversely, a frame is and becomes unmapped whenever it changes its statusfrom visible to iconified or invisible.
Visibility is meaningless on text terminals, since only the selected frame is actuallydisplayed in any case.

frame-visible-p frame[Function]
This function returns the visibility status of frame frame. The value is t if frame isvisible, nil if it is invisible, and icon if it is iconified.
On a text terminal, all frames are considered visible for the purposes of this function,even though only one frame is displayed. See Section 30.12 [Raising and Lowering],
page 829.

iconify-frame &optional frame[Command]This function iconifies frame frame. If you omit frame, it iconifies the selected frame.
This usually makes all child frames of frame (and their descendants) invisible (seeSection 30.14 [Child Frames], page 831).

make-frame-visible &optional frame[Command]This function makes frame frame visible. If you omit frame, it makes the selected
frame visible. This does not raise the frame, but you can do that with raise-frame
if you wish (see Section 30.12 [Raising and Lowering], page 829).
Making a frame visible usually makes all its child frames (and their descendants)
visible as well (see Section 30.14 [Child Frames], page 831).

make-frame-invisible &optional frame force[Command]This function makes frame frame invisible. If you omit frame, it makes the selected
frame invisible. Usually, this makes all child frames of frame (and their descendants)
invisible too (see Section 30.14 [Child Frames], page 831).
Unless force is non-nil, this function refuses to make frame invisible if all other frames
are invisible.

The visibility status of a frame is also available as a frame parameter. You can read orchange it as such. See Section 30.4.3.8 [Management Parameters], page 814. The user canalso iconify and deiconify frames with the window manager. This happens below the levelat which Emacs can exert any control, but Emacs does provide events that you can use to
keep track of such changes. See Section 22.7.12 [Misc Events], page 450.

x-double-buffered-p &optional frame[Function]
This function returns non-nil if frame is currently being rendered with double buffering.
frame defaults to the selected frame.

30.12 Raising, Lowering and Restacking Frames
Most window systems use a desktop metaphor. Part of this metaphor is the idea thatsystem-level windows (representing, e.g., Emacs frames) are stacked in a notional third
dimension perpendicular to the screen surface. The order induced by stacking is total andusually referred to as stacking (or Z-) order. Where the areas of two windows overlap, theone higher up in that order will (partially) cover the one underneath.

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You can raise a frame to the top of that order or lower a frame to its bottom by using
the functions raise-frame and lower-frame. You can restack a frame directly above or
below another frame using the function frame-restack.
Note that all functions described below will respect the adherence of frames (and allother window-system windows) to their respective z-group (see Section 30.4.3.2 [Position
Parameters], page 805). For example, you usually cannot lower a frame below that of thedesktop window and you cannot raise a frame whose z-group parameter is nil above thewindow-system’s taskbar or tooltip window.

raise-frame &optional frame[Command]This function raises frame frame (default, the selected frame) above all other framesbelonging to the same or a lower z-group as frame. If frame is invisible or iconified,
this makes it visible. If frame is a child frame (see Section 30.14 [Child Frames],
page 831), this raises frame above all other child frames of its parent.

lower-frame &optional frame[Command]This function lowers frame frame (default, the selected frame) below all other framesbelonging to the same or a higher z-group as frame. If frame is a child frame (seeSection 30.14 [Child Frames], page 831), this lowers frame below all other child framesof its parent.

frame-restack frame1 frame2 &optional above[Function]
This function restacks frame1 below frame2. This implies that if both frames arevisible and their display areas overlap, frame2 will (partially) obscure frame1. If theoptional third argument above is non-nil, this function restacks frame1 above frame2.
This means that if both frames are visible and their display areas overlap, frame1 will(partially) obscure frame2.
Technically, this function may be thought of as an atomic action performed in two
steps: The first step removes frame1’s window-system window from the display. The
second step reinserts frame1’s window into the display below (above if above is true)that of frame2. Hence the position of frame2 in its display’s Z (stacking) order relative
to all other frames excluding frame1 remains unaltered.
Some window managers may refuse to restack windows.

Note that the effect of restacking will only hold as long as neither of the involved frames
is iconified or made invisible. You can use the z-group (see Section 30.4.3.2 [Position
Parameters], page 805) frame parameter to add a frame to a group of frames permanently
shown above or below other frames. As long as a frame belongs to one of these groups,
restacking it will only affect its relative stacking position within that group. The effect ofrestacking frames belonging to different z-groups is undefined. You can list frames in theircurrent stacking order with the function frame-list-z-order (see Section 30.8 [Finding
All Frames], page 823).
[User Option]
If this is non-nil, activation of the minibuffer raises the frame that the minibuffer
window is in.

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831

On window systems, you can also enable auto-raising (on frame selection) or autolowering (on frame deselection) using frame parameters. See Section 30.4.3.8 [Management
Parameters], page 814.
The concept of raising and lowering frames also applies to text terminal frames. On eachtext terminal, only the top frame is displayed at any one time.

tty-top-frame &optional terminal[Function]
This function returns the top frame on terminal. terminal should be a terminal
object, a frame (meaning that frame’s terminal), or nil (meaning the selected frame’s
terminal). If it does not refer to a text terminal, the return value is nil.

30.13 Frame Configurations
A frame configuration records the current arrangement of frames, all their properties, and thewindow configuration of each one. (See Section 29.26 [Window Configurations], page 774.)[Function]
This function returns a frame configuration list that describes the current arrangementof frames and their contents.

current-frame-configuration

set-frame-configuration configuration &optional nodelete[Function]
This function restores the state of frames described in configuration. However, thisfunction does not restore deleted frames.
Ordinarily, this function deletes all existing frames not listed in configuration. But if
nodelete is non-nil, the unwanted frames are iconified instead.

30.14 Child FramesChild frames are objects halfway between windows (see Chapter 29 [Windows], page 690)
and “normal” frames. Like windows, they are attached to an owning frame. Unlike windows,
they may overlap each other—changing the size or position of one child frame does notchange the size or position of any of its sibling child frames.
By design, operations to make or modify child frames are implemented with the help offrame parameters (see Section 30.4 [Frame Parameters], page 802) without any specialized
functions or customizable variables. Note that child frames are meaningful on graphicalterminals only.
To create a new child frame or to convert a normal frame into a child frame, set thatframe’s parent-frame parameter (see Section 30.4.3.6 [Frame Interaction Parameters],
page 812) to that of an already existing frame. The frame specified by that parameter
will then be the frame’s parent frame as long as the parameter is not changed or reset.
Technically, this makes the child frame’s window-system window a child window of theparent frame’s window-system window.
The parent-frame parameter can be changed at any time. Setting it to another frame
reparents the child frame. Setting it to another child frame makes the frame a nested childframe. Setting it to nil restores the frame’s status as a top-level frame—a frame whose
window-system window is a child of its display’s root window.2
2

On Haiku, child frames are only visible when a parent frame is active, owing to a limitation of the Haiku
windowing system. Owing to the same limitation, child frames are only guaranteed to appear above

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Since child frames can be arbitrarily nested, a frame can be both a child and a parent
frame. Also, the relative roles of child and parent frame may be reversed at any time (though
it’s usually a good idea to keep the size of a child frame sufficiently smaller than that of its
parent). An error will be signaled for the attempt to make a frame an ancestor of itself.
Most window-systems clip a child frame at the native edges (see Section 30.3 [Frame
Geometry], page 791) of its parent frame—everything outside these edges is usually invisible.
A child frame’s left and top parameters specify a position relative to the top-left corner of its
parent’s native frame. When the parent frame is resized, this position remains conceptuallyunaltered.
NS builds do not clip child frames at the parent frame’s edges, allowing them to bepositioned so they do not obscure the parent frame while still being visible themselves.
Usually, moving a parent frame moves along all its child frames and their descendants aswell, keeping their relative positions unaltered. Note that the hook move-frame-functions(see Section 30.3.3 [Frame Position], page 798) is run for a child frame only when the positionof the child frame relative to its parent frame changes.
When a parent frame is resized, its child frames conceptually retain their previous sizes
and their positions relative to the left upper corner of the parent. This means that achild frame may become (partially) invisible when its parent frame shrinks. The parameter
keep-ratio (see Section 30.4.3.6 [Frame Interaction Parameters], page 812) can be used toresize and reposition a child frame proportionally whenever its parent frame is resized. This
may avoid obscuring parts of a frame when its parent frame is shrunk.
A visible child frame always appears on top of its parent frame thus obscuring parts of it,
except on NS builds where it may be positioned beneath the parent. This is comparable
to the window-system window of a top-level frame which also always appears on top of
its parent window—the desktop’s root window. When a parent frame is iconified or madeinvisible (see Section 30.11 [Visibility of Frames], page 828), its child frames are madeinvisible. When a parent frame is deiconified or made visible, its child frames are madevisible.
When a parent frame is about to be deleted (see Section 30.7 [Deleting Frames], page 822),
its child frames are recursively deleted before it. There is one exception to this rule: Whenthe child frame serves as a surrogate minibuffer frame (see Section 30.9 [Minibuffers andFrames], page 824) for another frame, it is retained until the parent frame has been deleted.
If, at this time, no remaining frame uses the child frame as its minibuffer frame, Emacs will
try to delete the child frame too. If that deletion fails for whatever reason, the child frame
is made a top-level frame.
Whether a child frame can have a menu or tool bar is window-system or window manager
dependent. Most window-systems explicitly disallow menu bars for child frames. It seems
advisable to disable both, menu and tool bars, via the frame’s initial parameters settings.
Usually, child frames do not exhibit window manager decorations like a title bar orexternal borders (see Section 30.3 [Frame Geometry], page 791). When the child frame does
not show a menu or tool bar, any other of the frame’s borders (see Section 30.4.3.4 [Layout
Parameters], page 810) can be used instead of the external borders.
their top-level parent; that is to say, the top-most frame in the hierarchy, which does not have a parent
frame.

Chapter 30: Frames833

In particular, under X (but not when building with GTK+), the frame’s outer border canbe used. On MS-Windows, specifying a non-zero outer border width will show a one-pixel
wide external border. Under all window-systems, the internal border can be used. In
either case, it’s advisable to disable a child frame’s window manager decorations with theundecorated frame parameter (see Section 30.4.3.8 [Management Parameters], page 814).
To resize or move an undecorated child frame with the mouse, special frame parameters(see Section 30.4.3.7 [Mouse Dragging Parameters], page 813) have to be used. The internalborder of a child frame, if present, can be used to resize the frame with the mouse, provided
that frame has a non-nil drag-internal-border parameter. If set, the snap-widthparameter indicates the number of pixels where the frame snaps at the respective edge or
corner of its parent frame.
There are two ways to drag an entire child frame with the mouse: The drag-withmode-line parameter, if non-nil, allows to drag a frame without minibuffer window (seeSection 21.11 [Minibuffer Windows], page 418) via the mode line area of its bottommost
window. The drag-with-header-line parameter, if non-nil, allows to drag the frame via
the header line area of its topmost window.
In order to give a child frame a draggable header or mode line, the window parameters mode-line-format and header-line-format are handy (see Section 29.27 [Window
Parameters], page 776). These allow to remove an unwanted mode line (when drag-withheader-line is chosen) and to remove mouse-sensitive areas which might interfere withframe dragging.
When the user drags a frame with a mouse and overshoots, it’s easy to drag a frame out of
the screen area of its parent. Retrieving such a frame can be hairy once the mouse button has
been released. To prevent such a situation, it is advisable to set the frame’s top-visible orbottom-visible parameter (see Section 30.4.3.7 [Mouse Dragging Parameters], page 813).
Set the top-visible parameter of a child frame to a number when you intend toallow the user dragging that frame by its header line. Setting top-visible to a number
inhibits dragging the top edge of the child frame above the top edge of its parent. Set thebottom-visible parameter to a number when you intend to drag that frame via its modeline; this inhibits dragging the bottom edge of the child frame beneath the bottom edge of
its parent. In either case, that number also specifies width and height (in pixels) of the areaof the child frame that remains visible during dragging.
When a child frame is used for displaying a buffer via display-buffer-in-child-frame(see Section 29.13.2 [Buffer Display Action Functions], page 726), the frame’s auto-hidefunction parameter (see Section 30.4.3.6 [Frame Interaction Parameters], page 812) can be
set to a function, in order to appropriately deal with the frame when the window displaying
the buffer shall be quit.
When a child frame is used during minibuffer interaction, for example, to display
completions in a separate window, the minibuffer-exit parameter (see Section 30.4.3.6[Frame Interaction Parameters], page 812) is useful in order to deal with the frame whenthe minibuffer is exited.
The behavior of child frames deviates from that of top-level frames in a number of otherways as well. Here we sketch a few of them:• The semantics of maximizing and iconifying child frames is highly window-systemdependent. As a rule, applications should never invoke these operations on child frames.

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By default, invoking iconify-frame on a child frame will try to iconify the top-level
frame corresponding to that child frame instead. To obtain a different behavior, users
may customize the option iconify-child-frame described below.
• Raising, lowering and restacking child frames (see Section 30.12 [Raising and Lowering],
page 829) or changing the z-group (see Section 30.4.3.2 [Position Parameters], page 805)
of a child frame changes only the stacking order of child frames with the same parent.
• Many window-systems are not able to change the opacity (see Section 30.4.3.10 [Fontand Color Parameters], page 818) of child frames.
• Transferring focus from a child frame to an ancestor that is not its parent by clicking withthe mouse in a visible part of that ancestor’s window may fail with some window-systems.
You may have to click into the direct parent’s window-system window first.
• Window managers might not bother to extend their focus follows mouse policy tochild frames. Customizing mouse-autoselect-window can help in this regard (seeSection 29.25 [Mouse Window Auto-selection], page 773).
• Dropping (see Section 30.22 [Drag and Drop], page 841) on child frames is not guaranteed
to work on all window-systems. Some will drop the object on the parent frame or onsome ancestor instead.
The following two functions can be useful when working with child and parent frames:

frame-parent &optional frame[Function]
This function returns the parent frame of frame. The parent frame of frame is theEmacs frame whose window-system window is the parent window of frame’s windowsystem window. If such a frame exists, frame is considered a child frame of thatframe.
This function returns nil if frame has no parent frame.

frame-ancestor-p ancestor descendant[Function]
This functions returns non-nil if ancestor is an ancestor of descendant. ancestor is anancestor of descendant when it is either descendant’s parent frame or it is an ancestorof descendant’s parent frame. Both, ancestor and descendant must specify live frames.

Note also the function window-largest-empty-rectangle (see Section 29.24 [Coordinates and Windows], page 769) which can be used to inscribe a child frame in the largest
empty area of an existing window. This can be useful to avoid that a child frame obscures
any text shown in that window.
Customizing the following option can be useful to tweak the behavior of iconify-frame
for child frames.
[User Option]
This option tells Emacs how to proceed when it is asked to iconify a child frame.
If it is nil, iconify-frame will do nothing when invoked on a child frame. If it is
iconify-top-level, Emacs will try to iconify the top-level frame that is the ancestorof this child frame instead. If it is make-invisible, Emacs will try to make this childframe invisible instead of iconifying it.
Any other value means to try iconifying the child frame. Since such an attempt may
not be honored by all window managers and can even lead to making the child frame
unresponsive to user actions, the default is to iconify the top level frame instead.

iconify-child-frame

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30.15 Mouse Tracking
Sometimes it is useful to track the mouse, which means to display something to indicate
where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking,you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion.
Then you can wait for motion by waiting for an event. In addition, you can easily handle
any other sorts of events that may occur. That is useful, because normally you don’t want
to track the mouse forever—only until some other event, such as the release of a button.

track-mouse body. . .

[Macro]This macro executes body, with generation of mouse motion events enabled. Typically,
body would use read-event to read the motion events and modify the display
accordingly. See Section 22.7.8 [Motion Events], page 447, for the format of mouse
motion events.
The value of track-mouse is that of the last form in body. You should design body toreturn when it sees the up-event that indicates the release of the button, or whatever
kind of event means it is time to stop tracking. Its value also controls how mouse events
are reported while a mouse button is held down: if it is dropping or drag-source,
the motion events are reported relative to the frame underneath the pointer. If there
is no such frame, the events will be reported relative to the frame the mouse buttons
were first pressed on. In addition, the posn-window of the mouse position list will be
nil if the value is drag-source. This is useful to determine if a frame is not directly
visible underneath the mouse pointer.
The track-mouse macro causes Emacs to generate mouse motion events by binding
the variable track-mouse to a non-nil value. If that variable has the special value
dragging, it additionally instructs the display engine to refrain from changing theshape of the mouse pointer. This is desirable in Lisp programs that require mousedragging across large portions of Emacs display, which might otherwise cause themouse pointer to change its shape according to the display portion it hovers on (seeSection 30.19 [Pointer Shape], page 839). Therefore, Lisp programs that need themouse pointer to retain its original shape during dragging should bind track-mouseto the value dragging at the beginning of their body.

The usual purpose of tracking mouse motion is to indicate on the screen the consequencesof pushing or releasing a button at the current position.
In many cases, you can avoid the need to track the mouse by using the mouse-face text
property (see Section 33.19.4 [Special Properties], page 924). That works at a much lower
level and runs more smoothly than Lisp-level mouse tracking.

30.16 Mouse Position
The functions mouse-position and set-mouse-position give access to the current positionof the mouse.
[Function]
This function returns a description of the position of the mouse. The value looks
like (frame x . y), where x and y are integers giving the (possibly rounded) position

mouse-position

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in multiples of the default character size of frame (see Section 30.3.2 [Frame Font],
page 797) relative to the native position of frame (see Section 30.3 [Frame Geometry],
page 791).
[Variable]
If non-nil, the value of this variable is a function for mouse-position to call.
mouse-position calls this function just before returning, with its normal return
value as the sole argument, and it returns whatever this function returns to it.
This abnormal hook exists for the benefit of packages like xt-mouse.el that need to
do mouse handling at the Lisp level.

mouse-position-function[Variable]
If non-nil, TTY menus will call mouse-position-function as described above. This
exists for cases where mouse-position-function is not safe to be called by the TTY
menus, such as if it could trigger redisplay.

tty-menu-calls-mouse-position-function

set-mouse-position frame x y[Function]
This function warps the mouse to position x, y in frame frame. The arguments x andy are integers, giving the position in multiples of the default character size of frame(see Section 30.3.2 [Frame Font], page 797) relative to the native position of frame(see Section 30.3 [Frame Geometry], page 791).
The resulting mouse position is constrained to the native frame of frame. If frame is
not visible, this function does nothing. The return value is not significant.
[Function]
This function is like mouse-position except that it returns coordinates in units ofpixels rather than units of characters.

mouse-pixel-position

set-mouse-pixel-position frame x y[Function]
This function warps the mouse like set-mouse-position except that x and y are inunits of pixels rather than units of characters.
The resulting mouse position is not constrained to the native frame of frame. If frame
is not visible, this function does nothing. The return value is not significant.

On a graphical terminal the following two functions allow the absolute position of themouse cursor to be retrieved and set.
[Function]
This function returns a cons cell (x . y) of the coordinates of the mouse cursor positionin pixels, relative to a position (0, 0) of the selected frame’s display.

mouse-absolute-pixel-position

set-mouse-absolute-pixel-position x y[Function]
This function moves the mouse cursor to the position (x, y). The coordinates x and y
are interpreted in pixels relative to a position (0, 0) of the selected frame’s display.

The following function can tell whether the mouse cursor is currently visible on a frame:frame-pointer-visible-p &optional frame[Function]
This predicate function returns non-nil if the mouse pointer displayed on frame isvisible; otherwise it returns nil. frame omitted or nil means the selected frame.
This is useful when make-pointer-invisible is set to t: it allows you to know if thepointer has been hidden. See Section “Mouse Avoidance” in The Emacs Manual.

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30.17 Pop-Up Menus
A Lisp program can pop up a menu so that the user can choose an alternative with themouse. On a text terminal, if the mouse is not available, the user can choose an alternative
using the keyboard motion keys—C-n, C-p, or up- and down-arrow keys.

x-popup-menu position menu

[Function]
This function displays a pop-up menu and returns an indication of what selection theuser makes.
The argument position specifies where on the screen to put the top left corner of themenu. It can be either a mouse button event (which says to put the menu where theuser actuated the button) or a list of this form:((xoffset yoffset) window)
where xoffset and yoffset are coordinates, measured in pixels, counting from the top
left corner of window. window may be a window or a frame.
If position is t, it means to use the current mouse position (or the top-left corner ofthe frame if the mouse is not available on a text terminal). If position is nil, it means
to precompute the key binding equivalents for the keymaps specified in menu, without
actually displaying or popping up the menu.
The argument menu says what to display in the menu. It can be a keymap or a listof keymaps (see Section 23.18 [Menu Keymaps], page 510). In this case, the return
value is the list of events corresponding to the user’s choice. This list has more than
one element if the choice occurred in a submenu. (Note that x-popup-menu does not
actually execute the command bound to that sequence of events.) On text terminals
and toolkits that support menu titles, the title is taken from the prompt string ofmenu if menu is a keymap, or from the prompt string of the first keymap in menu if it
is a list of keymaps (see Section 23.18.1 [Defining Menus], page 510).

Alternatively, menu can have the following form:(title pane1 pane2...)where each pane is a list of form
(title item1 item2...)Each item should be a cons cell, (line . value), where line is a string and value
is the value to return if that line is chosen. Unlike in a menu keymap, a nil value
does not make the menu item non-selectable. Alternatively, each item can be a string
rather than a cons cell; this makes a non-selectable menu item.
If the user gets rid of the menu without making a valid choice, for instance by clicking
the mouse away from a valid choice or by typing C-g, then this normally results ina quit and x-popup-menu does not return. But if position is a mouse button event(indicating that the user invoked the menu with the mouse) then no quit occurs andx-popup-menu returns nil.
Usage note: Don’t use x-popup-menu to display a menu if you could do the job with aprefix key defined with a menu keymap. If you use a menu keymap to implement a menu,
C-h c and C-h a can see the individual items in that menu and provide help for them. If
instead you implement the menu by defining a command that calls x-popup-menu, the help

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facilities cannot know what happens inside that command, so they cannot give any help forthe menu’s items.
The menu bar mechanism, which lets you switch between submenus by moving the mouse,cannot look within the definition of a command to see that it calls x-popup-menu. Therefore,
if you try to implement a submenu using x-popup-menu, it cannot work with the menu bar
in an integrated fashion. This is why all menu bar submenus are implemented with menu
keymaps within the parent menu, and never with x-popup-menu. See Section 23.18.5 [MenuBar], page 516.
If you want a menu bar submenu to have contents that vary, you should still use a menu
keymap to implement it. To make the contents vary, add a hook function to menu-barupdate-hook to update the contents of the menu keymap as necessary.
[Variable]
A normal hook run immediately before a pop-up menu is displayed, either directly bycalling x-popup-menu, or through a menu keymap. It won’t be called if x-popup-menu
returns for some other reason without displaying a pop-up menu.

x-pre-popup-menu-hook

30.18 Dialog Boxes
A dialog box is a variant of a pop-up menu—it looks a little different, it always appears
in the center of a frame, and it has just one level and one or more buttons. The main useof dialog boxes is for asking questions that the user can answer with “yes”, “no”, and a
few other alternatives. With a single button, they can also force the user to acknowledge
important information. The functions y-or-n-p and yes-or-no-p use dialog boxes insteadof the keyboard, when called from commands invoked by mouse clicks.

x-popup-dialog position contents &optional header[Function]
This function displays a pop-up dialog box and returns an indication of what selection
the user makes. The argument contents specifies the alternatives to offer; it has thisformat:(title (string . value)...)

which looks like the list that specifies a single pane for x-popup-menu.
The return value is value from the chosen alternative.
As for x-popup-menu, an element of the list may be just a string instead of a cons cell(string . value). That makes a box that cannot be selected.
If nil appears in the list, it separates the left-hand items from the right-hand items;
items that precede the nil appear on the left, and items that follow the nil appear
on the right. If you don’t include a nil in the list, then approximately half the items
appear on each side.
Dialog boxes always appear in the center of a frame; the argument position specifies
which frame. The possible values are as in x-popup-menu, but the precise coordinatesor the individual window don’t matter; only the frame matters.
If header is non-nil, the frame title for the box is ‘Information’, otherwise it is‘Question’. The former is used for message-box (see [message-box], page 1134). (Ontext terminals, the box title is not displayed.)Chapter 30: Frames839

In some configurations, Emacs cannot display a real dialog box; so instead it displays
the same items in a pop-up menu in the center of the frame.
If the user gets rid of the dialog box without making a valid choice, for instance using
the window manager, then this produces a quit and x-popup-dialog does not return.

30.19 Pointer ShapeYou can specify the mouse pointer style for particular text or images using the pointer text
property, and for images with the :pointer and :map image properties. The values you canuse in these properties are in the table below. The actual shapes may vary between systems;
the descriptions are examples.
text
nil

The usual mouse pointer style used over text (an “I”-like shape).

arrow
vdrag
modeline

An arrow that points north-west.

hand

A hand that points upwards.

hdrag

A right-left arrow.

nhdragAn up-down arrow.

hourglassA rotating ring.
Over void parts of the window (parts that do not correspond to any of the buffer contents),
the mouse pointer usually uses the arrow style, but you can specify a different style (one ofthose above) by setting void-text-area-pointer.
[User Option]
This variable specifies the mouse pointer style for void text areas. These include theareas after the end of a line or below the last line in the buffer. The default is to use
the arrow (non-text) pointer style.

void-text-area-pointerWhen using some window systems, you can specify what the text pointer style really
looks like by setting the variable x-pointer-shape.
[Variable]
This variable specifies the pointer shape to use ordinarily in the Emacs frame, for the
text pointer style.

x-pointer-shape[Variable]
This variable specifies the pointer shape to use when the mouse is over mouse-sensitivetext.

x-sensitive-text-pointer-shape

These variables affect newly created frames. They do not normally affect existing frames;
however, if you set the mouse color of a frame, that also installs the current value of those
two variables. See Section 30.4.3.10 [Font and Color Parameters], page 818.
The values you can use, to specify either of these pointer shapes, are defined in the file
lisp/term/x-win.el. Use M-x apropos RET x-pointer RET to see a list of them.

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30.20 Window System Selections
In window systems, such as X, data can be transferred between different applications bymeans of selections. X defines an arbitrary number of selection types, each of which canstore its own data; however, only three are commonly used: the clipboard, primary selection,and secondary selection. Other window systems support only the clipboard. See Section“Cut and Paste” in The GNU Emacs Manual, for Emacs commands that make use of
these selections. This section documents the low-level functions for reading and setting
window-system selections.

gui-set-selection type data

[Command]This function sets a window-system selection. It takes two arguments: a selection typetype, and the value to assign to it, data.
type should be a symbol; it is usually one of PRIMARY, SECONDARY or CLIPBOARD. These
are symbols with upper-case names, in accord with X Window System conventions. If
type is nil, that stands for PRIMARY.
If data is nil, it means to clear out the selection. Otherwise, data may be a string, asymbol, an integer, an overlay, or a cons of two markers pointing to the same buffer.
An overlay or a pair of markers stands for text in the overlay or between the markers.
The argument data may also be a vector of valid non-vector selection values.
If data is a string, then its text properties can specify values used for individual datatypes. For example, if data has a property named text/uri-list, then a call to
gui-get-selection with the data type text/uri-list will result in the value ofthat property being used instead of data itself.
This function returns data.

gui-get-selection &optional type data-type[Function]
This function accesses selections set up by Emacs or by other programs. It takes two
optional arguments, type and data-type. The default for type, the selection type, is
PRIMARY.
The data-type argument specifies the form of data conversion to use, to convert the raw
data obtained from another program into Lisp data. Meaningful values include TEXT,STRING, UTF8_STRING, TARGETS, LENGTH, DELETE, FILE_NAME, CHARACTER_POSITION,
NAME, LINE_NUMBER, COLUMN_NUMBER, OWNER_OS, HOST_NAME, USER, CLASS, ATOM, andINTEGER. (These are symbols with upper-case names in accord with X conventions.)
The default for data-type is STRING. Window systems other than X usually support
only a small subset of these types, in addition to STRING.

[User Option]
This variable specifies the coding system to use when reading and writing selectionsor the clipboard. See Section 34.10 [Coding Systems], page 976. The default iscompound-text-with-extensions, which converts to the text representation that
X11 normally uses.

selection-coding-system

When Emacs runs on MS-Windows, it does not implement X selections in general, but it
does support the clipboard. gui-get-selection and gui-set-selection on MS-Windows
support the text data type only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty. The supported data type is STRING.

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For backward compatibility, there are obsolete aliases x-get-selection and x-setselection, which were the names of gui-get-selection and gui-set-selection before
Emacs 25.1.

30.21 Yanking MediaIf you choose, for instance, “Copy Image” in a web browser, that image is put onto the
clipboard, and Emacs can access it via gui-get-selection. But in general, inserting image
data into an arbitrary buffer isn’t very useful—you can’t really do much with it by default.
So Emacs has a system to let modes register handlers for these “complicated” selections.

yank-media-handler types handler[Function]
types can be a MIME media type symbol, a regexp to match these, or a list of thesesymbols and regexps. For instance:(yank-media-handler 'text/html #'my-html-handler)(yank-media-handler "image/.*" #'my-image-handler)
A mode can register as many handlers as required.
The handler function is called with two parameters: The MIME media type symbol
and the data (as a string). The handler should then insert the object into the buffer,or save it, or do whatever is appropriate for the mode.

The yank-media command will consult the registered handlers in the current buffer,compare that with the available media types on the clipboard, and then pass on the matching
selection to the handler (if any). If there’s more than one matching selection, the user isqueried first.
The yank-media-types command can be used to explore the clipboard/primary selection.
It lists all the media types that are currently available, and can be handy when creating
handlers—to see what data is actually available. Some applications put a surprising amountof different data types on the clipboard.

30.22 Drag and Drop
When the user drops something from another application over Emacs, Emacs will try toinsert any text and open any URL that was dropped. If text was dropped, then it will always
be inserted at the location of the mouse pointer where the drop happened, or saved in the killring if insertion failed, which could happen if the buffer was read-only. If a URL was dropped
instead, then Emacs will first try to call an appropriate handler function by matching
the URL against regexps defined in the variable dnd-protocol-alist, and then against
those defined in the variables browse-url-handlers and browse-url-default-handlers.
Should no suitable handler be located, Emacs will fall back to inserting the URL as plain
text.
[Variable]
This variable is a list of cons cells of the form (pattern . action). pattern is a regexp
that URLs are matched against after being dropped. action is a function that is calledwith two arguments, should a URL being dropped match pattern: the URL being
dropped, and the action being performed for the drop, which is one of the symbols
copy, move, link, private or ask.

dnd-protocol-alist

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If action is private, then it means the program that initiated the drop wants Emacs toperform an unspecified action with the URL; a reasonable action to perform in thatcase is to open the URL or copy its contents into the current buffer. Otherwise, action
has the same meaning as the action argument to dnd-begin-file-drag.
Emacs implements receiving text and URLs individually for each window system, anddoes not by default support receiving other kinds of data as drops. To support receiving
other kinds of data, use the X-specific interface described below.
When a user drags something from another application over Emacs under the X Window
System, that other application expects Emacs to tell it if Emacs understands the data being
dragged. The function in the variable x-dnd-test-function is called by Emacs to determine
what to reply to any such inquiry. The default value is x-dnd-default-test-function,
which accepts drops if the type of the data to be dropped is present in x-dnd-known-types.
Changing the variables x-dnd-test-function and x-dnd-known-types can make Emacs
accept or reject drops based on some other criteria.
If you want to change the way Emacs receives drops of different data types, or you wantto enable it to understand a new type, change the variable x-dnd-types-alist. Doing socorrectly requires detailed knowledge of what data types other applications use for drag anddrop.
These data types are typically implemented as special data types that can be obtained
from an X selection provided by the other application. In most cases, they are either
the same data types that are typically accepted by gui-set-selection, or MIME types,
depending on the specific drag-and-drop protocol being used. For example, the data typeused for plain text may be either "STRING" or "text/plain".
When Emacs runs on X window system, it supports the X Direct Save (XDS) protocol,
which allows users to save a file by dragging and dropping it onto an Emacs window, suchas a Dired window. To comply with the unique requirements of XDS, these drag-and-drop
requests are processed specially: instead of being handled according to x-dnd-types-alist,
they are handled by the direct-save function that is the value of the variable x-dnd-directsave-function. The value should be a function of two arguments, need-name and filename.
The XDS protocol uses a two-step procedure for dragging files:
1. The application from which the file is dragged asks Emacs to provide the full file nameunder which to save the file. For this purpose, the direct-save function is called with
its first argument need-name non-nil, and the second argument filename set to thebasename of the file to be saved. It should return the fully-expanded absolute file nameunder which to save the file. For example, if a file is dragged to a Dired window, thenatural directory for the file is the directory of the file shown at location of the drop. If
saving the file is not possible for some reason, the function should return nil, which
will cancel the drag-and-drop operation.
2. The application from which the file is dragged saves the file under the name returned by
the first call to the direct-save function. If it succeeds in saving the file, the direct-save
function is called again, this time with the first argument need-name set to nil and thesecond argument filename set to the full absolute name of the saved file. The function isthen expected to do whatever is needed given the fact that file was saved. For example,
Dired should update the directory on display by showing the new file there.
The default value of x-dnd-direct-save-function is x-dnd-save-direct.

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x-dnd-save-direct need-name filename[Function]
When called with the need-name argument non-nil, this function prompts the user
for the absolute file name under which it should be saved. If the specified file alreadyexists, it additionally asks the user whether to overwrite it, and returns the absolute
file name only if the user confirms the overwriting.
When called with the need-name argument nil, it reverts the Dired listing if thecurrent buffer is in Dired mode or one of its descendants, and otherwise visits the fileby calling find-file (see Section 26.1.1 [Visiting Functions], page 608).

x-dnd-save-direct-immediately need-name filename[Function]
This function works like x-dnd-save-direct, but when called with its need-nameargument non-nil, it doesn’t prompt the user for the full name of the file to be
saved; instead, it returns its argument filename expanded against the current buffer’s
default directory (see Section 26.9.4 [File Name Expansion], page 639). (It still asks
for confirmation if a file by that name already exists in the default directory.)

On capable window systems, Emacs also supports dragging contents from its frames towindows of other applications.

dnd-begin-text-drag text &optional frame action allow-same-frame[Function]
This function begins dragging text from frame to another program (known as the drop
target), and returns the result of drag-and-drop operation when the text is dropped
or the drag-and-drop operation is canceled. text is the text that will be inserted by
the drop target.
action must be one of the symbols copy or move, where copy means that text should
be inserted by the drop target, and move means the same as copy, but in addition thecaller may have to delete text from its source as explained below.
frame is the frame where the mouse is currently held down, or nil, which means to
use the selected frame. This function may return immediately if no mouse buttons areheld down, so it should be only called immediately after a down-mouse-1 or similar
event (see Section 22.7.3 [Mouse Events], page 442), with frame set to the frame wherethat event was generated (see Section 22.7.4 [Click Events], page 442).
allow-same-frame specifies whether or not drops on top of frame itself are to beignored.
The return value specifies the action that the drop target actually performed, andoptionally what the caller should do. It can be one of the following symbols:
copy

The drop target inserted the dropped text.

move

The drop target inserted the dropped text, but in addition the caller
should delete text from wherever it originated, such as its buffer.

privateThe drop target performed some other unspecified action.

nil

The drag-and-drop operation was canceled.

dnd-begin-file-drag file &optional frame action allow-same-frame[Function]
This function begins dragging file from frame to another program, and returns theresult of the drag-and-drop operation when the file is dropped or the drag-and-drop
operation is canceled.

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If file is a remote file, then a temporary copy will be made.
action must be one of the symbols copy, move or link, where copy means that fileshould be opened or copied by the drop target, move means the drop target should
move the file to another location, and link means the drop target should create asymbolic link to file. It is an error to specify link as the action if file is a remote file.
frame and allow-same-frame have the same meaning as in dnd-begin-text-drag.
The return value is the action that the drop target actually performed, which can beone of the following symbols:
copy

The drop target opened or copied file to a different location.

move

The drop target moved file to a different location.

link

The drop target (usually a file manager) created a symbolic link to file.

privateThe drop target performed some other unspecified action.

nil

The drag-and-drop operation was canceled.

dnd-begin-drag-files files &optional frame action
allow-same-frame[Function]

This function is like dnd-begin-file-drag, except that files is a list of files. If thedrop target doesn’t support dropping multiple files, then the first file will be usedinstead.

dnd-direct-save file name &optional frame allow-same-frame[Function]
This function is similar to dnd-begin-file-drag (with the default action of copy),
but instead of specifying the action you specify the name of the copy created by thetarget program in name.

The high-level interfaces described above are implemented on top of a lower-level primitive.
If you need to drag content other than files or text, use the low-level interface x-begin-draginstead. However, using it will require detailed knowledge of the data types and actions
used by the programs to transfer content via drag-and-drop on each platform you want tosupport.

x-begin-drag targets &optional action frame return-frame
allow-current-frame follow-tooltip[Function]

This function begins a drag from frame, and returns when the drag-and-drop operation
ends, either because the drop was successful, or because the drop was rejected. The
drop occurs when all mouse buttons are released on top of an X window other thanframe (the drop target), or any X window if allow-current-frame is non-nil. If nomouse buttons are held down when the drag-and-drop operation begins, this function
may immediately return nil.
targets is a list of strings describing selection targets, much like the data-type argument
to gui-get-selection, that the drop target can request from Emacs (see Section 30.20[Window System Selections], page 840).
action is a symbol describing the action recommended to the target. It can either be
XdndActionCopy, which means to copy the contents of the selection XdndSelection
to the drop target; or XdndActionMove, which means copy as with XdndActionCopy,Chapter 30: Frames

845

and in addition the caller should delete whatever was stored in that selection after
copying it.
action may also be an alist which associates between symbols describing the available
actions, and strings that the drop target is expected to present to the user to choose
between the available actions.
If return-frame is non-nil and the mouse moves over an Emacs frame after first moving
out of frame, then the frame to which the mouse moves will be returned immediately.
If return-frame is the symbol now, then any frame underneath the mouse pointer will
be returned without waiting for the mouse to first move out of frame. return-frame isuseful when you want to treat dragging content from one frame to another specially,
while also being able to drag content to other programs, but it is not guaranteed towork on all systems and with all window managers.
If follow-tooltip is non-nil, the position of any tooltip (such as one shown bytooltip-show) will follow the location of the mouse pointer whenever it moves
during the drag-and-drop operation. The tooltip will be hidden once all mouse buttons
are released.
If the drop was rejected or no drop target was found, this function returns nil.
Otherwise, it returns a symbol describing the action the target chose to perform, which
can differ from action if that isn’t supported by the drop target. XdndActionPrivate
is also a valid return value in addition to XdndActionCopy and XdndActionMove; itmeans that the drop target chose to perform an unspecified action, and no further
processing is required by the caller.
The caller must cooperate with the target to fully perform the action chosen by thetarget. For example, callers should delete the buffer text that was dragged if thisfunction returns XdndActionMove.
On X Windows, several different drag-and-drop protocols are supported by x-begin-drag.
When dragging content that is known to not be supported by a specific drag-and-drop
protocol, it might be desirable to turn that protocol off, by changing the values of thefollowing variables:[Variable]
When this is non-nil, the Motif drag and drop protocols are disabled, and dropping
onto programs that only understand them will not work.

x-dnd-disable-motif-protocol[Variable]
When this is nil, the OffiX (old KDE) drag and drop protocol is disabled. When thisis the symbol files, the OffiX protocol will only be used if "FILE_NAME" is one of
the targets given to x-begin-drag. Any other value means to use the OffiX protocol
to drop all supported content.

x-dnd-use-offix-drop[Variable]
When one of the "STRING", "UTF8_STRING", "COMPOUND_TEXT" or "TEXT" targets ispresent in the list given to x-begin-drag, Emacs will try to use synthesized mouse
events and the primary selection to insert the text if the drop target doesn’t support
any drag-and-drop protocol at all.

x-dnd-use-unsupported-drop

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A side effect is that Emacs will become the owner of the primary selection upon sucha drop. If that is not desired, then the drop emulation can be disabled by setting thisvariable to nil.

30.23 Color Names
A color name is text (usually in a string) that specifies a color. Symbolic names suchas ‘black’, ‘white’, ‘red’, etc., are allowed; use M-x list-colors-display to see a listof defined names. You can also specify colors numerically in forms such as ‘#rgb’ and‘RGB:r/g/b’, where r specifies the red level, g specifies the green level, and b specifies theblue level. You can use either one, two, three, or four hex digits for r; then you must use
the same number of hex digits for all g and b as well, making either 3, 6, 9 or 12 hex digits
in all. (See the documentation of the X Window System for more details about numerical
RGB specification of colors.)
These functions provide a way to determine which color names are valid, and what theylook like. In some cases, the value depends on the selected frame, as described below; see
Section 30.10 [Input Focus], page 824, for the meaning of the term “selected frame”.
To read user input of color names with completion, use read-color (see Section 21.6.4[High-Level Completion], page 402).

color-defined-p color &optional frame[Function]
This function reports whether a color name is meaningful. It returns t if so; otherwise,nil. The argument frame says which frame’s display to ask about; if frame is omitted
or nil, the selected frame is used.
Note that this does not tell you whether the display you are using really supportsthat color. When using X, you can ask for any defined color on any kind of display,and you will get some result—typically, the closest it can do. To determine whether aframe can really display a certain color, use color-supported-p (see below).
This function used to be called x-color-defined-p, and that name is still supported
as an alias.

defined-colors &optional frame[Function]
This function returns a list of the color names that are defined and supported on frame
frame (default, the selected frame). If frame does not support colors, the value is nil.
This function used to be called x-defined-colors, and that name is still supported
as an alias.

color-supported-p color &optional frame background-p[Function]
This returns t if frame can really display the color color (or at least something close
to it). If frame is omitted or nil, the question applies to the selected frame.
Some terminals support a different set of colors for foreground and background. If
background-p is non-nil, that means you are asking whether color can be used as a
background; otherwise you are asking whether it can be used as a foreground.

The argument color must be a valid color name.

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847

color-gray-p color &optional frame[Function]
This returns t if color is a shade of gray, as defined on frame’s display. If frame isomitted or nil, the question applies to the selected frame. If color is not a valid color
name, this function returns nil.

color-values color &optional frame[Function]
This function returns a value that describes what color should ideally look like onframe. If color is defined, the value is a list of three integers, which give the amountof red, the amount of green, and the amount of blue. Each integer ranges in principle
from 0 to 65535, but some displays may not use the full range. This three-element list
is called the rgb values of the color.
If color is not defined, the value is nil.
(color-values "black")⇒ (0 0 0)(color-values "white")⇒ (65535 65535 65535)(color-values "red")⇒ (65535 0 0)
(color-values "pink")⇒ (65535 49344 52171)(color-values "hungry")⇒ nil
The color values are returned for frame’s display. If frame is omitted or nil, theinformation is returned for the selected frame’s display. If the frame cannot display
colors, the value is nil.
This function used to be called x-color-values, and that name is still supported as
an alias.

color-name-to-rgb color &optional frame[Function]
This function does the same as color-values, but it returns color values as floatingpoint numbers between 0.0 and 1.0 inclusive.

color-dark-p rgb[Function]
This function returns non-nil if the color described by its RGB triplet rgb is morereadable against white background than against dark background. The argument rgb
should be a list of the form (r g b), with each component a floating-point number inthe range 0.0 to 1.0 inclusive. You can use color-name-to-rgb to convert a color’sname to such a list.

30.24 Text Terminal Colors
Text terminals usually support only a small number of colors, and the computer uses small
integers to select colors on the terminal. This means that the computer cannot reliably tellwhat the selected color looks like; instead, you have to inform your application which small
integers correspond to which colors. However, Emacs does know the standard set of colors
and will try to use them automatically.
The functions described in this section control how terminal colors are used by Emacs.

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Several of these functions use or return rgb values, described in Section 30.23 [Color
Names], page 846.
These functions accept a display (either a frame or the name of a terminal) as an optional
argument. We hope in the future to make Emacs support different colors on different text
terminals; then this argument will specify which terminal to operate on (the default being
the selected frame’s terminal; see Section 30.10 [Input Focus], page 824). At present, though,the frame argument has no effect.

tty-color-define name number &optional rgb frame[Function]
This function associates the color name name with color number number on theterminal.
The optional argument rgb, if specified, is an rgb value, a list of three numbers thatspecify what the color actually looks like. If you do not specify rgb, then this color
cannot be used by tty-color-approximate to approximate other colors, because
Emacs will not know what it looks like.

tty-color-clear &optional frame[Function]

This function clears the table of defined colors for a text terminal.

tty-color-alist &optional frame[Function]
This function returns an alist recording the known colors supported by a text terminal.
Each element has the form (name number . rgb) or (name number). Here, name isthe color name, number is the number used to specify it to the terminal. If present,
rgb is a list of three color values (for red, green, and blue) that says what the color
actually looks like.

tty-color-approximate rgb &optional frame[Function]
This function finds the closest color, among the known colors supported for display,
to that described by the rgb value rgb (a list of color values). The return value is anelement of tty-color-alist.

tty-color-translate color &optional frame[Function]
This function finds the closest color to color among the known colors supported for
display and returns its index (an integer). If the name color is not defined, the value
is nil.

30.25 X Resources
This section describes some of the functions and variables for querying and using X resources,or their equivalent on your operating system. See Section “X Resources” in The GNU Emacs
Manual, for more information about X resources.

x-get-resource attribute class &optional component subclass[Function]
The function x-get-resource retrieves a resource value from the X Window defaults
database.
Resources are indexed by a combination of a key and a class. This function searches
using a key of the form ‘instance.attribute’ (where instance is the name underwhich Emacs was invoked), and using ‘Emacs.class’ as the class.

Chapter 30: Frames849

The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is‘instance.component.attribute’, and the class is ‘Emacs.class.subclass’.
[Variable]
This variable specifies the application name that x-get-resource should look up.
The default value is "Emacs". You can examine X resources for other application
names by binding this variable to some other string, around a call to x-get-resource.

x-resource-class[Variable]
This variable specifies the instance name that x-get-resource should look up. The
default value is the name Emacs was invoked with, or the value specified with the‘-name’ or ‘-rn’ switches.

x-resource-name

To illustrate some of the above, suppose that you have the line:
xterm.vt100.background: yellow
in your X resources file (whose name is usually ~/.Xdefaults or ~/.Xresources). Then:(let ((x-resource-class "XTerm") (x-resource-name "xterm"))(x-get-resource "vt100.background" "VT100.Background"))⇒ "yellow"(let ((x-resource-class "XTerm") (x-resource-name "xterm"))(x-get-resource "background" "VT100" "vt100" "Background"))⇒ "yellow"[Variable]
If this variable is non-nil, Emacs does not look up X resources, and X resources do
not have any effect when creating new frames.

inhibit-x-resources

30.26 Display Feature Testing
The functions in this section describe the basic capabilities of a particular display. Lisp
programs can use them to adapt their behavior to what the display can do. For example, aprogram that ordinarily uses a popup menu could use the minibuffer if popup menus are
not supported.
The optional argument display in these functions specifies which display to ask thequestion about. It can be a display name, a frame (which designates the display that frame
is on), or nil (which refers to the selected frame’s display, see Section 30.10 [Input Focus],
page 824).
See Section 30.23 [Color Names], page 846, Section 30.24 [Text Terminal Colors], page 847,
for other functions to obtain information about displays.

display-popup-menus-p &optional display[Function]
This function returns t if popup menus are supported on display, nil if not. Support
for popup menus requires that the mouse be available, since the menu is popped up
by clicking the mouse on some portion of the Emacs display.

display-graphic-p &optional display[Function]
This function returns t if display is a graphic display capable of displaying several
frames and several different fonts at once. This is true for displays that use a window
system such as X, and false for text terminals.

Chapter 30: Frames

display-mouse-p &optional display

850[Function]

This function returns t if display has a mouse available, nil if not.

display-color-p &optional display[Function]
This function returns t if the screen is a color screen. It used to be called x-displaycolor-p, and that name is still supported as an alias.

display-grayscale-p &optional display[Function]
This function returns t if the screen can display shades of gray. (All color displays
can do this.)

display-supports-face-attributes-p attributes &optional display[Function]
This function returns non-nil if all the face attributes in attributes are supported(see Section 41.12.1 [Face Attributes], page 1164).
The definition of “supported” is somewhat heuristic, but basically means that a facecontaining all the attributes in attributes, when merged with the default face fordisplay, can be represented in a way that’s
1. different in appearance than the default face, and2. close in spirit to what the attributes specify, if not exact.
Point (2) implies that a :weight black attribute will be satisfied by any display thatcan display bold, as will :foreground "yellow" as long as some yellowish color can bedisplayed, but :slant italic will not be satisfied by the tty display code’s automatic
substitution of a dim face for italic.

display-selections-p &optional display[Function]
This function returns t if display supports selections. Windowed displays normallysupport selections, but they may also be supported in some other cases.

display-images-p &optional display[Function]
This function returns t if display can display images. Windowed displays ought inprinciple to handle images, but some systems lack the support for that. On a displaythat does not support images, Emacs cannot display a tool bar.

display-screens &optional display[Function]

This function returns the number of screens associated with the display.

display-pixel-height &optional display[Function]
This function returns the height of the screen in pixels. On a character terminal, it
gives the height in characters.
For graphical terminals, note that on multi-monitor setups this refers to the pixel
height for all physical monitors associated with display. See Section 30.2 [Multiple
Terminals], page 787.

display-pixel-width &optional display[Function]
This function returns the width of the screen in pixels. On a character terminal, it
gives the width in characters.
For graphical terminals, note that on multi-monitor setups this refers to the pixel
width for all physical monitors associated with display. See Section 30.2 [Multiple
Terminals], page 787.

Chapter 30: Frames851

display-mm-height &optional display[Function]
This function returns the height of the screen in millimeters, or nil if Emacs cannot
get that information.
For graphical terminals, note that on multi-monitor setups this refers to the height for
all physical monitors associated with display. See Section 30.2 [Multiple Terminals],
page 787.

display-mm-width &optional display[Function]
This function returns the width of the screen in millimeters, or nil if Emacs cannot
get that information.
For graphical terminals, note that on multi-monitor setups this refers to the width for
all physical monitors associated with display. See Section 30.2 [Multiple Terminals],
page 787.
[User Option]
This variable allows the user to specify the dimensions of graphical displays returnedby display-mm-height and display-mm-width in case the system provides incorrect
values.

display-mm-dimensions-alist

display-backing-store &optional display[Function]
This function returns the backing store capability of the display. Backing store means
recording the pixels of windows (and parts of windows) that are not exposed, so thatwhen exposed they can be displayed very quickly.

Values can be the symbols always, when-mapped, or not-useful. The function canalso return nil when the question is inapplicable to a certain kind of display.

display-save-under &optional display[Function]
This function returns non-nil if the display supports the SaveUnder feature. Thatfeature is used by pop-up windows to save the pixels they obscure, so that they can
pop down quickly.

display-planes &optional display[Function]
This function returns the number of planes the display supports. This is typicallythe number of bits per pixel. For a tty display, it is log to base two of the number ofcolors supported.

display-visual-class &optional display[Function]
This function returns the visual class for the screen. The value is one of the symbols
static-gray (a limited, unchangeable number of grays), gray-scale (a full range ofgrays), static-color (a limited, unchangeable number of colors), pseudo-color (alimited number of colors), true-color (a full range of colors), and direct-color (afull range of colors).

display-color-cells &optional display[Function]

This function returns the number of color cells the screen supports.
These functions obtain additional information about the window system in use whereEmacs shows the specified display. (Their names begin with x- for historical reasons.)

Chapter 30: Frames852

x-server-version &optional display[Function]
This function returns the list of version numbers of the GUI window system runningon display, such as the X server on GNU and Unix systems. The value is a list of three
integers: the major and minor version numbers of the protocol, and the distributorspecific release number of the window system software itself. On GNU and Unix
systems, these are normally the version of the X protocol and the distributor-specificrelease number of the X server software. On MS-Windows, this is the version of theWindows OS.

x-server-vendor &optional display[Function]
This function returns the vendor that provided the window system software (as astring). On GNU and Unix systems this really means whoever distributes the X server.
On MS-Windows this is the vendor ID string of the Windows OS (Microsoft).
When the developers of X labeled software distributors as “vendors”, they showed
their false assumption that no system could ever be developed and distributed noncommercially.

853

31 Positions
A position is the index of a character in the text of a buffer. More precisely, a position
identifies the place between two characters (or before the first character, or after the last
character), so we can speak of the character before or after a given position. However, we
often speak of the character “at” a position, meaning the character after that position.
Positions are usually represented as integers starting from 1, but can also be represented
as markers—special objects that relocate automatically when text is inserted or deleted
so they stay with the surrounding characters. Functions that expect an argument to be aposition (an integer), but accept a marker as a substitute, normally ignore which buffer themarker points into; they convert the marker to an integer, and use that integer, exactly as if
you had passed the integer as the argument, even if the marker points to the wrong buffer.
A marker that points nowhere cannot convert to an integer; using it instead of an integer
causes an error. See Chapter 32 [Markers], page 869.
See also the field feature (see Section 33.19.9 [Fields], page 936), which provides functions
that are used by many cursor-motion commands.

31.1 Point
Point is a special buffer position used by many editing commands, including the self-inserting
typed characters and text insertion functions. Other commands move point through thetext to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the firstcharacter, or after the last character), rather than a particular character. Usually terminals
display the cursor over the character that immediately follows point; point is actually before
the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than the buffer size plus 1.
If narrowing is in effect (see Section 31.4 [Narrowing], page 865), then point is constrained
to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point inother buffers. Each window also has a value of point, which is independent of the value ofpoint in other windows on the same buffer. This is why point can have different values invarious windows that display the same buffer. When a buffer appears in only one window,
the buffer’s point and the window’s point normally have the same value, so the distinction
is rarely important. See Section 29.19 [Window Point], page 758, for more details.
[Function]
This function returns the value of point in the current buffer, as an integer.

point(point)⇒ 175[Function]
This function returns the minimum accessible value of point in the current buffer.
This is normally 1, but if narrowing is in effect, it is the position of the start of theregion that you narrowed to. (See Section 31.4 [Narrowing], page 865.)

point-minChapter 31: Positions

854[Function]
This function returns the maximum accessible value of point in the current buffer.
This is (1+ (buffer-size)), unless narrowing is in effect, in which case it is the
position of the end of the region that you narrowed to. (See Section 31.4 [Narrowing],
page 865.)

point-max

buffer-end flag

[Function]
This function returns (point-max) if flag is greater than 0, (point-min) otherwise.
The argument flag must be a number.

buffer-size &optional buffer[Function]
This function returns the total number of characters in the current buffer. In theabsence of any narrowing (see Section 31.4 [Narrowing], page 865), point-max returns
a value one larger than this.
If you specify a buffer, buffer, then the value is the size of buffer.
(buffer-size)⇒ 35(point-max)⇒ 36

31.2 Motion
Motion functions change the value of point, either relative to the current value of point,
relative to the beginning or end of the buffer, or relative to the edges of the selected window.
See Section 31.1 [Point], page 853.

31.2.1 Motion by Characters
These functions move point based on a count of characters. goto-char is the fundamental
primitive; the other functions use that.

goto-char position[Command]This function sets point in the current buffer to the value position.
If narrowing is in effect, position still counts from the beginning of the buffer, but
point cannot go outside the accessible portion. If position is out of range, goto-char
moves point to the beginning or the end of the accessible portion.
When this function is called interactively, position is the numeric prefix argument, if
provided; otherwise it is read from the minibuffer.
goto-char returns position.

forward-char &optional count[Command]This function moves point count characters forward, towards the end of the buffer (orbackward, towards the beginning of the buffer, if count is negative). If count is nil,the default is 1.
If this attempts to move past the beginning or end of the buffer (or the limits of theaccessible portion, when narrowing is in effect), it signals an error with error symbol
beginning-of-buffer or end-of-buffer.
In an interactive call, count is the numeric prefix argument.

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backward-char &optional count[Command]This is just like forward-char except that it moves in the opposite direction.

31.2.2 Motion by Words
The functions for parsing words described below use the syntax table and char-scripttable to decide whether a given character is part of a word. See Chapter 36 [Syntax Tables],page 1022, and see Section 34.6 [Character Properties], page 968.

forward-word &optional count[Command]This function moves point forward count words (or backward if count is negative). If
count is omitted or nil, it defaults to 1. In an interactive call, count is specified by
the numeric prefix argument.
“Moving one word” means moving until point crosses a word-constituent character,which indicates the beginning of a word, and then continue moving until the word ends.
By default, characters that begin and end words, known as word boundaries, are definedby the current buffer’s syntax table (see Section 36.2.1 [Syntax Class Table], page 1023),
but modes can override that by setting up a suitable find-word-boundary-functiontable, described below. Characters that belong to different scripts (as definedby char-script-table), also define a word boundary (see Section 34.6 [Character
Properties], page 968). In any case, this function cannot move point past the boundaryof the accessible portion of the buffer, or across a field boundary (see Section 33.19.9[Fields], page 936). The most common case of a field boundary is the end of theprompt in the minibuffer.
If it is possible to move count words, without being stopped prematurely by the bufferboundary or a field boundary, the value is t. Otherwise, the return value is nil andpoint stops at the buffer boundary or field boundary.
If inhibit-field-text-motion is non-nil, this function ignores field boundaries.

backward-word &optional count[Command]This function is just like forward-word, except that it moves backward until encountering the front of a word, rather than forward.
[User Option]
This variable affects the behavior of forward-word and backward-word, and everything that uses them. If it is non-nil, then characters in the escape and character-quote
syntax classes count as part of words. Otherwise, they do not.

words-include-escapes[Variable]
If this variable is non-nil, certain motion functions including forward-word,
forward-sentence, and forward-paragraph ignore field boundaries.

inhibit-field-text-motion[Variable]
This variable affects the behavior of forward-word and backward-word, and everything that uses them. Its value is a char-table (see Section 6.6 [Char-Tables], page 119)of functions to search for word boundaries. If a character has a non-nil entry inthis table, then when a word starts or ends with that character, the corresponding
function will be called with 2 arguments: pos and limit. The function should return
the position of the other word boundary. Specifically, if pos is smaller than limit, thenfind-word-boundary-function-table

Chapter 31: Positions856

pos is at the beginning of a word, and the function should return the position after
the last character of the word; otherwise, pos is at the last character of a word, andthe function should return the position of that word’s first character.

forward-word-strictly &optional count[Function]
This function is like forward-word, but it is not affected by find-word-boundaryfunction-table. Lisp programs that should not change behavior when word movement is modified by modes which set that table, such as subword-mode, should use
this function instead of forward-word.

backward-word-strictly &optional count[Function]
This function is like backward-word, but it is not affected by find-word-boundaryfunction-table. Like with forward-word-strictly, use this function instead of
backward-word when movement by words should only consider syntax tables.

31.2.3 Motion to an End of the Buffer
To move point to the beginning of the buffer, write:(goto-char (point-min))
Likewise, to move to the end of the buffer, use:(goto-char (point-max))
Here are two commands that users use to do these things. They are documented here to
warn you not to use them in Lisp programs, because they set the mark and display messages
in the echo area.

beginning-of-buffer &optional n[Command]This function moves point to the beginning of the buffer (or the limits of the accessible
portion, when narrowing is in effect), setting the mark at the previous position (except
in Transient Mark mode, if the mark is already active, it does not set the mark.)
If n is non-nil, then it puts point n tenths of the way from the beginning of theaccessible portion of the buffer. In an interactive call, n is the numeric prefix argument,
if provided; otherwise n defaults to nil.
Warning: Don’t use this function in Lisp programs!

end-of-buffer &optional n[Command]This function moves point to the end of the buffer (or the limits of the accessible
portion, when narrowing is in effect), setting the mark at the previous position (except
in Transient Mark mode when the mark is already active). If n is non-nil, then it
puts point n tenths of the way from the end of the accessible portion of the buffer.
In an interactive call, n is the numeric prefix argument, if provided; otherwise ndefaults to nil.
Warning: Don’t use this function in Lisp programs!

31.2.4 Motion by Text Lines
Text lines are portions of the buffer delimited by newline characters, which are regarded aspart of the previous line. The first text line begins at the beginning of the buffer, and thelast text line ends at the end of the buffer whether or not the last character is a newline.

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The division of the buffer into text lines is not affected by the width of the window, by line
continuation in display, or by how tabs and control characters are displayed.

beginning-of-line &optional count[Command]This function moves point to the beginning of the current line. With an argument
count not nil or 1, it moves forward count−1 lines and then to the beginning of theline.
This function does not move point across a field boundary (see Section 33.19.9 [Fields],
page 936) unless doing so would move beyond there to a different line; therefore, if
count is nil or 1, and point starts at a field boundary, point does not move. To
ignore field boundaries, either bind inhibit-field-text-motion to t, or use theforward-line function instead. For instance, (forward-line 0) does the same thingas (beginning-of-line), except that it ignores field boundaries.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing
is in effect), it positions point there. No error is signaled.

line-beginning-position &optional count[Function]

Return the position that (beginning-of-line count) would move to.

end-of-line &optional count[Command]This function moves point to the end of the current line. With an argument count notnil or 1, it moves forward count−1 lines and then to the end of the line.
This function does not move point across a field boundary (see Section 33.19.9 [Fields],
page 936) unless doing so would move beyond there to a different line; therefore, if
count is nil or 1, and point starts at a field boundary, point does not move. To ignore
field boundaries, bind inhibit-field-text-motion to t.
If this function reaches the end of the buffer (or of the accessible portion, if narrowing
is in effect), it positions point there. No error is signaled.

line-end-position &optional count[Function]

Return the position that (end-of-line count) would move to.

pos-bol &optional count[Function]

Like line-beginning-position, but ignores fields (and is more efficient).

pos-eol &optional count[Function]

Like line-end-position, but ignores fields (and is more efficient).

forward-line &optional count[Command]This function moves point forward count lines, to the beginning of the line following
that. If count is negative, it moves point −count lines backward, to the beginning ofa line preceding that. If count is zero, it moves point to the beginning of the current
line. If count is nil, that means 1.
If forward-line encounters the beginning or end of the buffer (or of the accessible
portion) before finding that many lines, it sets point there. No error is signaled.
forward-line returns the difference between count and the number of lines actually
moved. If you attempt to move down five lines from the beginning of a buffer that has
only three lines, point stops at the end of the last line, and the value will be 2. As an

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explicit exception, if the last accessible line is non-empty, but has no newline (e.g., if
the buffer ends without a newline), the function sets point to the end of that line, andthe value returned by the function counts that line as one line successfully moved.
In an interactive call, count is the numeric prefix argument.

count-lines start end &optional ignore-invisible-lines[Function]
This function returns the number of lines between the positions start and end in thecurrent buffer. If start and end are equal, then it returns 0. Otherwise it returns atleast 1, even if start and end are on the same line. This is because the text between
them, considered in isolation, must contain at least one line unless it is empty.
If the optional ignore-invisible-lines is non-nil, invisible lines will not be included in
the count.

count-words start end[Command]This function returns the number of words between the positions start and end in thecurrent buffer.
This function can also be called interactively. In that case, it prints a message reporting
the number of lines, words, and characters in the buffer, or in the region if the regionis active.

line-number-at-pos &optional pos absolute[Function]
This function returns the line number in the current buffer corresponding to the buffer
position pos. If pos is nil or omitted, the current buffer position is used. If absoluteis nil, the default, counting starts at (point-min), so the value refers to the contentsof the accessible portion of the (potentially narrowed) buffer. If absolute is non-nil,
ignore any narrowing and return the absolute line number.

Also see the functions bolp and eolp in Section 33.1 [Near Point], page 878. These
functions do not move point, but test whether it is already at the beginning or end of a line.

31.2.5 Motion by Screen Lines
The line functions in the previous section count text lines, delimited only by newline
characters. By contrast, these functions count screen lines, which are defined by the way the
text appears on the screen. A text line is a single screen line if it is short enough to fit thewidth of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than continued onto additional
screen lines. In these cases, vertical-motion moves point much like forward-line. See
Section 41.3 [Truncation], page 1130.
Because the width of a given string depends on the flags that control the appearance of
certain characters, vertical-motion behaves differently, for a given piece of text, dependingon the buffer it is in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). See Section 41.23.1 [Usual Display],
page 1242.
These functions scan text to determine where screen lines break, and thus take time
proportional to the distance scanned.

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vertical-motion count &optional window cur-col[Function]
This function moves point to the start of the screen line count screen lines down fromthe screen line containing point. If count is negative, it moves up instead. If count iszero, point moves to the visual start of the current screen line.
The count argument can be a cons cell, (cols . lines), instead of an integer. Thenthe function moves by lines screen lines, as described for count above, and puts pointcols columns from the visual start of that screen line. The value of cols can be a float,
and is interpreted in units of the frame’s canonical character width (see Section 30.3.2[Frame Font], page 797); this allows specifying accurate horizontal position of point
when the target screen line uses variable fonts. Note that cols are counted fromthe visual start of the line; if the window is scrolled horizontally (see Section 29.23[Horizontal Scrolling], page 767), the column where point will end is in addition to thenumber of columns by which the text is scrolled, and if the target line is a continuationline, its leftmost column is considered column zero (unlike column-oriented functions,
see Section 33.16 [Columns], page 909).
The return value is the number of screen lines over which point was moved. The value
may be less in absolute value than count if the beginning or end of the buffer was
reached.
The window window is used for obtaining parameters such as the width, the horizontal
scrolling, and the display table. But vertical-motion always operates on the current
buffer, even if window currently displays some other buffer.
The optional argument cur-col specifies the current column when the function is called.
This is the window-relative horizontal coordinate of point, measured in units of font
width of the frame’s default face. Providing it speeds up the function, especially invery long lines, because the function doesn’t have to go back in the buffer in order todetermine the current column. Note that cur-col is also counted from the visual startof the line.

count-screen-lines &optional beg end count-final-newline window[Function]
This function returns the number of screen lines in the text from beg to end. The
number of screen lines may be different from the number of actual lines, due to line
continuation, the display table, etc. If beg and end are nil or omitted, they default
to the beginning and end of the accessible portion of the buffer.
If the region ends with a newline, that is ignored unless the optional third argument
count-final-newline is non-nil.
The optional fourth argument window specifies the window for obtaining parameterssuch as width, horizontal scrolling, and so on. The default is to use the selected
window’s parameters.
Like vertical-motion, count-screen-lines always uses the current buffer, regardless of which buffer is displayed in window. This makes possible to use count-screenlines in any buffer, whether or not it is currently displayed in some window.

move-to-window-line count[Command]This function moves point with respect to the text currently displayed in the selected
window. It moves point to the beginning of the screen line count screen lines from the
top of the window; zero means the topmost line. If count is negative, that specifies a

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position −count lines from the bottom (or the last line of the buffer, if the buffer ends
above the specified screen position); thus, count of −1 specifies the last fully visible
screen line of the window.
If count is nil, then point moves to the beginning of the line in the middle of thewindow. If the absolute value of count is greater than the size of the window, thenpoint moves to the place that would appear on that screen line if the window were tallenough. This will probably cause the next redisplay to scroll to bring that location
onto the screen.
In an interactive call, count is the numeric prefix argument.
The value returned is the screen line number point has moved to, relative to the top
line of the window.

move-to-window-group-line count[Function]
This function is like move-to-window-line, except that when the selected window
is a part of a group of windows (see [Window Group], page 698), move-to-windowgroup-line will move to a position with respect to the entire group, not just the single
window. This condition holds when the buffer local variable move-to-window-groupline-function is set to a function. In this case, move-to-window-group-line calls
the function with the argument count, then returns its result.

compute-motion from frompos to topos width offsets window[Function]
This function scans the current buffer, calculating screen positions. It scans the buffer
forward from position from, assuming that is at screen coordinates frompos, to position
to or coordinates topos, whichever comes first. It returns the ending buffer positionand screen coordinates.
The coordinate arguments frompos and topos are cons cells of the form (hpos .
vpos).
The argument width is the number of columns available to display text; this affects
handling of continuation lines. nil means the actual number of usable text columns
in the window, which is equivalent to the value returned by (window-width window).
The argument offsets is either nil or a cons cell of the form (hscroll . tab-offset).
Here hscroll is the number of columns not being displayed at the left margin; mostcallers get this by calling window-hscroll. Meanwhile, tab-offset is the offset between
column numbers on the screen and column numbers in the buffer. This can be nonzero
in a continuation line, when the previous screen lines’ widths do not add up to a
multiple of tab-width. It is always zero in a non-continuation line.
The window window serves only to specify which display table to use. compute-motion
always operates on the current buffer, regardless of what buffer is displayed in window.
The return value is a list of five elements:(pos hpos vpos prevhpos contin)
Here pos is the buffer position where the scan stopped, vpos is the vertical screen
position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back from pos. The resultcontin is t if the last line was continued after (or within) the previous character.

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For example, to find the buffer position of column col of screen line line of a certain
window, pass the window’s display start location as from and the window’s upper-leftcoordinates as frompos. Pass the buffer’s (point-max) as to, to limit the scan to theend of the accessible portion of the buffer, and pass line and col as topos. Here’s afunction that does this:(defun coordinates-of-position (col line)(car (compute-motion (window-start)'(0 . 0)(point-max)(cons col line)(window-width)(cons (window-hscroll) 0)(selected-window))))
When you use compute-motion for the minibuffer, you need to use
minibuffer-prompt-width to get the horizontal position of the beginning of the firstscreen line. See Section 21.12 [Minibuffer Contents], page 419.

31.2.6 Moving over Balanced Expressions
Here are several functions concerned with balanced-parenthesis expressions (also called
sexps in connection with moving across them in Emacs). The syntax table controls how
these functions interpret various characters; see Chapter 36 [Syntax Tables], page 1022.
See Section 36.6 [Parsing Expressions], page 1030, for lower-level primitives for scanningsexps or parts of sexps. For user-level commands, see Section “Commands for Editing with
Parentheses” in The GNU Emacs Manual.

forward-list &optional arg[Command]This function moves forward across arg (default 1) balanced groups of parentheses.
(Other syntactic entities such as words or paired string quotes are ignored.)

backward-list &optional arg[Command]This function moves backward across arg (default 1) balanced groups of parentheses.
(Other syntactic entities such as words or paired string quotes are ignored.)

up-list &optional arg escape-strings no-syntax-crossing[Command]This function moves forward out of arg (default 1) levels of parentheses. A negativeargument means move backward but still to a less deep spot. If escape-strings is nonnil (as it is interactively), move out of enclosing strings as well. If no-syntax-crossing
is non-nil (as it is interactively), prefer to break out of any enclosing string insteadof moving to the start of a list broken across multiple strings. On error, location ofpoint is unspecified.

backward-up-list &optional arg escape-strings no-syntax-crossing[Command]This function is just like up-list, but with a negated argument.

down-list &optional arg[Command]This function moves forward into arg (default 1) levels of parentheses. A negativeargument means move backward but still go deeper in parentheses (−arg levels).

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forward-sexp &optional arg[Command]This function moves forward across arg (default 1) balanced expressions. Balanced
expressions include both those delimited by parentheses and other kinds, such as words
and string constants. See Section 36.6 [Parsing Expressions], page 1030. For example,---------- Buffer: foo ---------(concat? "foo " (car x) y z)---------- Buffer: foo ---------(forward-sexp 3)⇒ nil---------- Buffer: foo ---------(concat "foo " (car x) y? z)---------- Buffer: foo ----------

backward-sexp &optional arg[Command]This function moves backward across arg (default 1) balanced expressions.

beginning-of-defun &optional arg[Command]This function moves back to the argth beginning of a defun. If arg is negative, thisactually moves forward, but it still moves to the beginning of a defun, not to the endof one. arg defaults to 1.

end-of-defun &optional arg[Command]This function moves forward to the argth end of a defun. If arg is negative, thisactually moves backward, but it still moves to the end of a defun, not to the beginningof one. arg defaults to 1.
[User Option]
If non-nil, this buffer-local variable holds a regular expression that specifies what text
can appear before the open-parenthesis that starts a defun. That is to say, a defun
begins on a line that starts with a match for this regular expression, followed by acharacter with open-parenthesis syntax.

defun-prompt-regexp[User Option]
If this variable’s value is non-nil, an open parenthesis in column 0 is considered tobe the start of a defun. If it is nil, an open parenthesis in column 0 has no special
meaning. The default is t. If a string literal happens to have a parenthesis in column
0, escape it with a backslash to avoid a false positive.

open-paren-in-column-0-is-defun-start[Variable]
If non-nil, this variable holds a function for finding the beginning of a defun. The
function beginning-of-defun calls this function instead of using its normal method,
passing it its optional argument. If the argument is non-nil, the function should moveback by that many functions, like beginning-of-defun does.

beginning-of-defun-function[Variable]
If non-nil, this variable holds a function for finding the end of a defun. The function
end-of-defun calls this function instead of using its normal method.

end-of-defun-function

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If Emacs is compiled with tree-sitter, it can use the tree-sitter parser information to moveacross syntax constructs. Since what exactly is considered a defun varies between languages,
a major mode should set treesit-defun-type-regexp to determine that. Then the modecan get navigation-by-defun functionality for free, by using treesit-beginning-of-defun
and treesit-end-of-defun.
[Variable]
This variable determines which nodes are considered defuns by Emacs. It can bea regexp that matches the type of defun nodes. (For “node” and “node type”, see
Chapter 37 [Parsing Program Source], page 1039.)

treesit-defun-type-regexp

For example, python-mode sets this variable to a regexp that matches either‘function_definition’ or ‘class_definition’.
Sometimes not all nodes matched by the regexp are valid defuns. Therefore, thisvariable can also be a cons cell of the form (regexp . pred), where pred should be afunction that takes a node as its argument, and returns non-nil if the node is a valid
defun, or nil if it is not valid.
[Variable]
This variable determines how Emacs treats nested defuns. If the value is top-level,navigation functions only move across top-level defuns. If the value is nested, navigation functions recognize nested defuns.

treesit-defun-tactic

31.2.7 Skipping Characters
The following two functions move point over a specified set of characters. For example,
they are often used to skip whitespace. For related functions, see Section 36.5 [Motion and
Syntax], page 1030.
These functions convert the set string to multibyte if the buffer is multibyte, and they
convert it to unibyte if the buffer is unibyte, as the search functions do (see Chapter 35[Searching and Matching], page 993).

skip-chars-forward character-set &optional limit[Function]
This function moves point in the current buffer forward, skipping over a given setof characters. It examines the character following point, then advances point if thecharacter matches character-set. This continues until it reaches a character that does
not match. The function returns the number of characters moved over.
The argument character-set is a string, like the inside of a ‘[...]’ in a regularexpression except that ‘]’ does not terminate it, and ‘\’ quotes ‘^’, ‘-’ or ‘\’. Thus,"a-zA-Z" skips over all letters, stopping before the first nonletter, and "^a-zA-Z"
skips nonletters stopping before the first letter (see Section 35.3 [Regular Expressions],
page 995). Character classes can also be used, e.g., "[:alnum:]" (see Section 35.3.1.2[Char Classes], page 1000).
If limit is supplied (it must be a number or a marker), it specifies the maximum
position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the ‘T’. After theform is evaluated, point is located at the end of that line (between the ‘t’ of ‘hat’ andthe newline). The function skips all letters and spaces, but not newlines.

Chapter 31: Positions

864---------- Buffer: foo ---------I read "?The cat in the hatcomes back" twice.
---------- Buffer: foo ---------(skip-chars-forward "a-zA-Z ")⇒ 18---------- Buffer: foo ---------I read "The cat in the hat?
comes back" twice.
---------- Buffer: foo ----------

skip-chars-backward character-set &optional limit[Function]
This function moves point backward, skipping characters that match character-set,
until limit. It is just like skip-chars-forward except for the direction of motion.
The return value indicates the distance traveled. It is an integer that is zero or less.

31.3 Excursions
It is often useful to move point temporarily within a localized portion of the program. Thisis called an excursion, and it is done with the save-excursion special form. This constructremembers the initial identity of the current buffer, and its value of point, and restores themafter the excursion completes. It is the standard way to move point within one part of aprogram and avoid affecting the rest of the program, and is used thousands of times in the
Lisp sources of Emacs.
If you only need to save and restore the identity of the current buffer, use save-currentbuffer or with-current-buffer instead (see Section 28.2 [Current Buffer], page 671). If
you need to save or restore window configurations, see the forms described in Section 29.26[Window Configurations], page 774, and in Section 30.13 [Frame Configurations], page 831.

save-excursion body. . .

[Special Form]
This special form saves the identity of the current buffer and the value of point in
it, evaluates body, and finally restores the buffer and its saved value of point. Bothsaved values are restored even in case of an abnormal exit via throw or error (seeSection 11.7 [Nonlocal Exits], page 177).
The value returned by save-excursion is the result of the last form in body, or nil
if no body forms were given.

Because save-excursion only saves point for the buffer that was current at the start ofthe excursion, any changes made to point in other buffers, during the excursion, will remainin effect afterward. This frequently leads to unintended consequences, so the byte compiler
warns if you call set-buffer during an excursion:
Warning: Use ‘with-current-buffer’ rather thansave-excursion+set-buffer
To avoid such problems, you should call save-excursion only after setting the desired
current buffer, as in the following example:

Chapter 31: Positions

865(defun append-string-to-buffer (string buffer)"Append STRING to the end of BUFFER."(with-current-buffer buffer(save-excursion(goto-char (point-max))(insert string))))Likewise, save-excursion does not restore window-buffer correspondences altered byfunctions such as switch-to-buffer.
Warning: Ordinary insertion of text adjacent to the saved point value relocates the savedvalue, just as it relocates all markers. More precisely, the saved value is a marker withinsertion type nil. See Section 32.5 [Marker Insertion Types], page 872. Therefore, when
the saved point value is restored, it normally comes before the inserted text.

save-mark-and-excursion body. . .

[Macro]This macro is like save-excursion, but also saves and restores the mark location andmark-active. This macro does what save-excursion did before Emacs 25.1.

31.4 Narrowing
Narrowing means limiting the text addressable by Emacs editing commands to a limited
range of characters in a buffer. The text that remains addressable is called the accessible
portion of the buffer.
Narrowing is specified with two buffer positions, which become the beginning and end of
the accessible portion. For most editing commands and primitives, these positions replace
the values of the beginning and end of the buffer. While narrowing is in effect, no text
outside the accessible portion is displayed, and point cannot move outside the accessible
portion. Note that narrowing does not alter actual buffer positions (see Section 31.1 [Point],
page 853); it only determines which positions are considered the accessible portion of thebuffer. Most functions refuse to operate on text that is outside the accessible portion.
Commands for saving buffers are unaffected by narrowing; they save the entire buffer
regardless of any narrowing.
If you need to display in a single buffer several very different types of text, consider using
an alternative facility described in Section 28.12 [Swapping Text], page 688.

narrow-to-region start end[Command]This function sets the accessible portion of the current buffer to start at start and end
at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point
and the mark, with the smallest first).
However, when the narrowing has been set by with-restriction with a label argument (see below), narrow-to-region can be used only within the limits of thatnarrowing. If start or end are outside these limits, the corresponding limit set bywith-restriction is used instead. To gain access to other portions of the buffer, use
without-restriction with the same label.

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narrow-to-page &optional move-count[Command]This function sets the accessible portion of the current buffer to include just thecurrent page. An optional first argument move-count non-nil means to move forward or backward by move-count pages and then narrow to one page. The variable
page-delimiter specifies where pages start and end (see Section 35.8 [Standard
Regexps], page 1020).
In an interactive call, move-count is set to the numeric prefix argument.
[Command]This function cancels any narrowing in the current buffer, so that the entire contents
are accessible. This is called widening. It is equivalent to the following expression:(narrow-to-region 1 (1+ (buffer-size)))
However, when a narrowing has been set by with-restriction with a label argument(see below), the limits set by with-restriction are restored, instead of canceling thenarrowing. To gain access to other portions of the buffer, use without-restriction
with the same label.

widen[Function]
This function returns non-nil if the buffer is narrowed, and nil otherwise.

buffer-narrowed-p

save-restriction body. . .

[Special Form]
This special form saves the current bounds of the accessible portion, evaluates the bodyforms, and finally restores the saved bounds, thus restoring the same state of narrowing(or absence thereof) formerly in effect. The state of narrowing is restored even in
the event of an abnormal exit via throw or error (see Section 11.7 [Nonlocal Exits],
page 177). Therefore, this construct is a clean way to narrow a buffer temporarily.
This construct also saves and restores the narrowings that were set bywith-restriction with a label argument (see below).
The value returned by save-restriction is that returned by the last form in body,or nil if no body forms were given.
Caution: it is easy to make a mistake when using the save-restriction construct.
Read the entire description here before you try it.
If body changes the current buffer, save-restriction still restores the restrictions
on the original buffer (the buffer whose restrictions it saved from), but it does notrestore the identity of the current buffer.
save-restriction does not restore point; use save-excursion for that. If you
use both save-restriction and save-excursion together, save-excursion shouldcome first (on the outside). Otherwise, the old point value would be restored withtemporary narrowing still in effect. If the old point value were outside the limits ofthe temporary narrowing, this would fail to restore it accurately.
Here is a simple example of correct use of save-restriction:---------- Buffer: foo ---------This is the contents of foo
This is the contents of foo
This is the contents of foo?
---------- Buffer: foo ----------

Chapter 31: Positions867(save-excursion(save-restriction(goto-char 1)(forward-line 2)(narrow-to-region 1 (point))(goto-char (point-min))(replace-string "foo" "bar")))---------- Buffer: foo ---------This is the contents of bar
This is the contents of bar
This is the contents of foo?
---------- Buffer: foo ----------

with-restriction start end [:label label] body[Special Form]
This special form saves the current bounds of the accessible portion of the buffer, sets
the accessible portion to start at start and end at end, evaluates the body forms, andrestores the saved bounds. In that case it is equivalent to(save-restriction(narrow-to-region start end)
body)

When the optional argument label, which is evaluated to get the label to use and mustyield a non-nil value, is present, the narrowing is labeled. A labeled narrowing differsfrom a non-labeled one in several ways:• During the evaluation of the body form, narrow-to-region and widen can beused only within the start and end limits.
• To lift the restriction introduced by with-restriction and gain access to otherportions of the buffer, use without-restriction with the same label argument.
(Another way to gain access to other portions of the buffer is to use an indirect
buffer (see Section 28.11 [Indirect Buffers], page 687).)• Labeled narrowings can be nested.
• Labeled narrowings can only be used in Lisp programs: they are never visible on
display, and never interfere with narrowings set by the user.
If you use with-restriction with the optional label argument, we recommend
documenting the label in the doc strings of the functions which use it, so that other
Lisp programs your code calls could lift the labeled narrowing if and when it needs.

without-restriction [:label label] body[Special Form]
This special form saves the current bounds of the accessible portion of the buffer,
widens the buffer, evaluates the body forms, and restores the saved bounds. In thatcase it is equivalent to(save-restriction(widen)body)

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When the optional argument label is present, the narrowing set by with-restriction
with the same label argument is lifted.

869

32 Markers
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding
text. A marker changes its offset from the beginning of the buffer automatically whenevertext is inserted or deleted, so that it stays with the two characters on either side of it.

32.1 Overview of Markers
A marker specifies a buffer and a position in that buffer. A marker can be used to represent
a position in functions that require one, just as an integer could be used. In that case, themarker’s buffer is normally ignored. Of course, a marker used in this way usually points toa position in the buffer that the function operates on, but that is entirely the programmer’s
responsibility. See Chapter 31 [Positions], page 853, for a complete description of positions.
A marker has three attributes: the marker position, the marker buffer, and the insertion
type. The marker position is an integer that is equivalent (at a given time) to the marker
as a position in that buffer. But the marker’s position value can change during the life of
the marker, and often does. Insertion and deletion of text in the buffer relocate the marker.
The idea is that a marker positioned between two characters remains between those two
characters despite insertion and deletion elsewhere in the buffer. Relocation changes theinteger equivalent of the marker.
Deleting text around a marker’s position leaves the marker between the characters
immediately before and after the deleted text. Inserting text at the position of a marker
normally leaves the marker either in front of or after the new text, depending on the marker’s
insertion type (see Section 32.5 [Marker Insertion Types], page 872)—unless the insertion isdone with insert-before-markers (see Section 33.4 [Insertion], page 882).
Insertion and deletion in a buffer must check all the markers and relocate them if necessary.
This slows processing in a buffer with a large number of markers. For this reason, it isa good idea to make a marker point nowhere if you are sure you don’t need it any more.
Markers that can no longer be accessed are eventually removed (see Section E.3 [Garbage
Collection], page 1350).
Because it is common to perform arithmetic operations on a marker position, most ofthese operations (including + and -) accept markers as arguments. In such cases, the marker
stands for its current position.
Here are examples of creating markers, setting markers, and moving point to markers:;; Make a new marker that initially does not point anywhere:(setq m1 (make-marker))⇒ #<marker in no buffer>;; Set m1 to point between the 99th and 100th characters;;in the current buffer:(set-marker m1 100)
⇒ #<marker at 100 in markers.texi>Chapter 32: Markers

870;; Now insert one character at the beginning of the buffer:(goto-char (point-min))⇒ 1(insert "Q")⇒ nil;; m1 is updated appropriately.
m1⇒ #<marker at 101 in markers.texi>;; Two markers that point to the same position;;
are not eq, but they are equal.
(setq m2 (copy-marker m1))
⇒ #<marker at 101 in markers.texi>(eq m1 m2)⇒ nil(equal m1 m2)⇒ t;; When you are finished using a marker, make it point nowhere.
(set-marker m1 nil)
⇒ #<marker in no buffer>32.2 Predicates on Markers
You can test an object to see whether it is a marker, or whether it is either an integer or amarker. The latter test is useful in connection with the arithmetic functions that work withboth markers and integers.

markerp object[Function]
This function returns t if object is a marker, nil otherwise. Note that integers are
not markers, even though many functions will accept either a marker or an integer.

integer-or-marker-p object[Function]

This function returns t if object is an integer or a marker, nil otherwise.

number-or-marker-p object[Function]
This function returns t if object is a number (either integer or floating point) or amarker, nil otherwise.

32.3 Functions that Create Markers
When you create a new marker, you can make it point nowhere, or point to the present
position of point, or to the beginning or end of the accessible portion of the buffer, or to thesame place as another given marker.
The next four functions all return markers with insertion type nil. See Section 32.5
[Marker Insertion Types], page 872.

Chapter 32: Markers

871[Function]
This function returns a newly created marker that does not point anywhere.

make-marker(make-marker)⇒ #<marker in no buffer>[Function]
This function returns a new marker that points to the present position of point in thecurrent buffer. See Section 31.1 [Point], page 853. For an example, see copy-marker,
below.

point-marker[Function]
This function returns a new marker that points to the beginning of the accessible
portion of the buffer. This will be the beginning of the buffer unless narrowing is ineffect. See Section 31.4 [Narrowing], page 865.

point-min-marker[Function]
This function returns a new marker that points to the end of the accessible portionof the buffer. This will be the end of the buffer unless narrowing is in effect. See
Section 31.4 [Narrowing], page 865.

point-max-marker

Here are examples of this function and point-min-marker, shown in a buffer containing
a version of the source file for the text of this chapter.
(point-min-marker)⇒ #<marker at 1 in markers.texi>(point-max-marker)⇒ #<marker at 24080 in markers.texi>(narrow-to-region 100 200)
⇒ nil(point-min-marker)⇒ #<marker at 100 in markers.texi>(point-max-marker)⇒ #<marker at 200 in markers.texi>

copy-marker &optional marker-or-integer insertion-type[Function]
If passed a marker as its argument, copy-marker returns a new marker that points tothe same place and the same buffer as does marker-or-integer. If passed an integer as its
argument, copy-marker returns a new marker that points to position marker-or-integer
in the current buffer.

The new marker’s insertion type is specified by the argument insertion-type. See
Section 32.5 [Marker Insertion Types], page 872.
(copy-marker 0)⇒ #<marker at 1 in markers.texi>(copy-marker 90000)⇒ #<marker at 24080 in markers.texi>
An error is signaled if marker is neither a marker nor an integer.

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Two distinct markers are considered equal (even though not eq) to each other if they
have the same position and buffer, or if they both point nowhere.
(setq p (point-marker))⇒ #<marker at 2139 in markers.texi>(setq q (copy-marker p))⇒ #<marker at 2139 in markers.texi>(eq p q)⇒ nil(equal p q)
⇒ t32.4 Information from Markers
This section describes the functions for accessing the components of a marker object.

marker-position marker[Function]
This function returns the position that marker points to, or nil if it points nowhere.

marker-buffer marker[Function]
This function returns the buffer that marker points into, or nil if it points nowhere.
(setq m (make-marker))⇒ #<marker in no buffer>(marker-position m)⇒ nil(marker-buffer m)⇒ nil(set-marker m 3770 (current-buffer))⇒ #<marker at 3770 in markers.texi>(marker-buffer m)⇒ #<buffer markers.texi>(marker-position m)⇒ 377032.5 Marker Insertion Types
When you insert text directly at the place where a marker points, there are two possible
ways to relocate that marker: it can point before the inserted text, or point after it. You
can specify which one a given marker should do by setting its insertion type. Note that useof insert-before-markers ignores markers’ insertion types, always relocating a marker topoint after the inserted text.

set-marker-insertion-type marker type

[Function]
This function sets the insertion type of marker marker to type. If type is t, marker
will advance when text is inserted at its position. If type is nil, marker does notadvance when text is inserted there.

Chapter 32: Markers

marker-insertion-type marker

873[Function]

This function reports the current insertion type of marker.
All functions that create markers without accepting an argument that specifies theinsertion type, create them with insertion type nil (see Section 32.3 [Creating Markers],
page 870). Also, the mark has, by default, insertion type nil.

32.6 Moving Marker Positions
This section describes how to change the position of an existing marker. When you do this,be sure you know whether the marker is used outside of your program, and, if so, what
effects will result from moving it—otherwise, confusing things may happen in other parts ofEmacs.

set-marker marker position &optional buffer[Function]
This function moves marker to position in buffer. If buffer is not provided, it defaults
to the current buffer.
If position is nil or a marker that points nowhere, then marker is set to point nowhere.
The value returned is marker.
(setq m (point-marker))⇒ #<marker at 4714 in markers.texi>(set-marker m 55)⇒ #<marker at 55 in markers.texi>(setq b (get-buffer "foo"))⇒ #<buffer foo>
(set-marker m 0 b)
⇒ #<marker at 1 in foo>

move-marker marker position &optional buffer[Function]

This is another name for set-marker.

32.7 The Mark
Each buffer has a special marker, which is designated the mark. When a buffer is newly
created, this marker exists but does not point anywhere; this means that the mark doesn’t
exist in that buffer yet. Subsequent commands can set the mark.
The mark specifies a position to bound a range of text for many commands, such as
kill-region and indent-rigidly. These commands typically act on the text between
point and the mark, which is called the region. If you are writing a command that operates
on the region, don’t examine the mark directly; instead, use interactive with the ‘r’specification. This provides the values of point and the mark as arguments to the commandin an interactive call, but permits other Lisp programs to specify arguments explicitly. See
Section 22.2.2 [Interactive Codes], page 427.
Some commands set the mark as a side-effect. Commands should do this only if it has
a potential use to the user, and never for their own internal purposes. For example, thereplace-regexp command sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after the replace is finished.

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Once the mark exists in a buffer, it normally never ceases to exist. However, it may become
inactive, if Transient Mark mode is enabled. The buffer-local variable mark-active, if nonnil, means that the mark is active. A command can call the function deactivate-mark todeactivate the mark directly, or it can request deactivation of the mark upon return to theeditor command loop by setting the variable deactivate-mark to a non-nil value.
If Transient Mark mode is enabled, certain editing commands that normally apply to textnear point, apply instead to the region when the mark is active. This is the main motivation
for using Transient Mark mode. (Another is that this enables highlighting of the region
when the mark is active. See Chapter 41 [Display], page 1129.)
In addition to the mark, each buffer has a mark ring which is a list of markers containing
previous values of the mark. When editing commands change the mark, they should normallysave the old value of the mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this long, adding a newelement deletes the last element.
There is also a separate global mark ring, but that is used only in a few particularuser-level commands, and is not relevant to Lisp programming. So we do not describe ithere.

mark &optional force[Function]
This function returns the current buffer’s mark position as an integer, or nil if nomark has ever been set in this buffer.
If Transient Mark mode is enabled, and mark-even-if-inactive is nil, mark signals
an error if the mark is inactive. However, if force is non-nil, then mark disregards
inactivity of the mark, and returns the mark position (or nil) anyway.
[Function]
This function returns the marker that represents the current buffer’s mark. It is not a
copy, it is the marker used internally. Therefore, changing this marker’s position will
directly affect the buffer’s mark. Don’t do that unless that is the effect you want.

mark-marker(setq m (mark-marker))⇒ #<marker at 3420 in markers.texi>(set-marker m 100)
⇒ #<marker at 100 in markers.texi>(mark-marker)⇒ #<marker at 100 in markers.texi>
Like any marker, this marker can be set to point at any buffer you like. If you make itpoint at any buffer other than the one of which it is the mark, it will yield perfectly
consistent, but rather odd, results. We recommend that you not do it!

set-mark position[Function]
This function sets the mark to position, and activates the mark. The old value of themark is not pushed onto the mark ring.
Please note: Use this function only if you want the user to see that the mark has
moved, and you want the previous mark position to be lost. Normally, when a newmark is set, the old one should go on the mark-ring. For this reason, most applications
should use push-mark and pop-mark, not set-mark.

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Novice Emacs Lisp programmers often try to use the mark for the wrong purposes.
The mark saves a location for the user’s convenience. An editing command should
not alter the mark unless altering the mark is part of the user-level functionality of
the command. (And, in that case, this effect should be documented.) To remember alocation for internal use in the Lisp program, store it in a Lisp variable. For example:(let ((beg (point)))(forward-line 1)(delete-region beg (point))).

push-mark &optional position nomsg activate[Function]
This function sets the current buffer’s mark to position, and pushes a copy of theprevious mark onto mark-ring. If position is nil, then the value of point is used.
The function push-mark normally does not activate the mark. To do that, specify t
for the argument activate.

A ‘Mark set’ message is displayed unless nomsg is non-nil.
[Function]
This function pops off the top element of mark-ring and makes that mark become
the buffer’s actual mark. This does not move point in the buffer, and it does nothing
if mark-ring is empty. It deactivates the mark.

pop-mark[User Option]
This variable, if non-nil, enables Transient Mark mode. In Transient Mark mode,
every buffer-modifying primitive sets deactivate-mark. As a consequence, mostcommands that modify the buffer also deactivate the mark.

transient-mark-mode

When Transient Mark mode is enabled and the mark is active, many commands that
normally apply to the text near point instead apply to the region. Such commands
should use the function use-region-p to test whether they should operate on theregion. See Section 32.8 [The Region], page 877.
Lisp programs can set transient-mark-mode to non-nil, non-t values to enable
Transient Mark mode temporarily. If the value is lambda, Transient Mark mode is
automatically turned off after any action, such as buffer modification, that would
normally deactivate the mark. If the value is (only . oldval), then transient-markmode is set to the value oldval after any subsequent command that moves point and is
not shift-translated (see Section 22.8.1 [Key Sequence Input], page 461), or after any
other action that would normally deactivate the mark. (Marking a region with themouse will temporarily enable transient-mark-mode in this way.)[User Option]
If this is non-nil, Lisp programs and the Emacs user can use the mark even when it isinactive. This option affects the behavior of Transient Mark mode. When the option
is non-nil, deactivation of the mark turns off region highlighting, but commands that
use the mark behave as if the mark were still active.

mark-even-if-inactive[Variable]
If an editor command sets this variable non-nil, then the editor command loop
deactivates the mark after the command returns (if Transient Mark mode is enabled).

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All the primitives that change the buffer set deactivate-mark, to deactivate the markwhen the command is finished. Setting this variable makes it buffer-local.
To write Lisp code that modifies the buffer without causing deactivation of the markat the end of the command, bind deactivate-mark to nil around the code that does
the modification. For example:(let (deactivate-mark)(insert " "))deactivate-mark &optional force[Function]
If Transient Mark mode is enabled or force is non-nil, this function deactivates themark and runs the normal hook deactivate-mark-hook. Otherwise, it does nothing.

[Variable]
The mark is active when this variable is non-nil. This variable is always buffer-local
in each buffer. Do not use the value of this variable to decide whether a commandthat normally operates on text near point should operate on the region instead. Use
the function use-region-p for that (see Section 32.8 [The Region], page 877).

mark-active[Variable][Variable]
These normal hooks are run, respectively, when the mark becomes active and when
it becomes inactive. The hook activate-mark-hook is also run when the region isreactivated, for instance after using a command that switches back to a buffer thathas an active mark.

activate-mark-hookdeactivate-mark-hook[Function]
This function implements the shift-selection behavior of point-motion commands. See
Section “Shift Selection” in The GNU Emacs Manual. It is called automatically by theEmacs command loop whenever a command with a ‘^’ character in its interactive
spec is invoked, before the command itself is executed (see Section 22.2.2 [Interactive
Codes], page 427).

handle-shift-selection

If shift-select-mode is non-nil and the current command was invoked via shifttranslation (see Section 22.8.1 [Key Sequence Input], page 461), this function sets themark and temporarily activates the region, unless the region was already temporarily
activated in this way. Otherwise, if the region has been activated temporarily, it
deactivates the mark and restores the variable transient-mark-mode to its earlier
value.
[Variable]
The value of this buffer-local variable is the list of saved former marks of the current
buffer, most recent first.

mark-ringmark-ring⇒ (#<marker at 11050 in markers.texi>#<marker at 10832 in markers.texi>...)Chapter 32: Markers

877[User Option]
The value of this variable is the maximum size of mark-ring. If more marks than thisare pushed onto the mark-ring, push-mark discards an old mark when it adds a newone.

mark-ring-max

When Delete Selection mode (see Section “Using Region” in The GNU Emacs Manual) is enabled, commands that operate on the active region (a.k.a. “selection”) behaveslightly differently. This works by adding the function delete-selection-pre-hook to thepre-command-hook (see Section 22.1 [Command Overview], page 423). That function callsdelete-selection-helper to delete the selection as appropriate for the command. If you
want to adapt a command to Delete Selection mode, put the delete-selection propertyon the function’s symbol (see Section 9.4.1 [Symbol Plists], page 138); commands that don’t
have this property on their symbol won’t delete the selection. This property can have one ofseveral values to tailor the behavior to what the command is supposed to do; see the doc
strings of delete-selection-pre-hook and delete-selection-helper for the details.

32.8 The Region
The text between point and the mark is known as the region. Various functions operate on
text delimited by point and the mark, but only those functions specifically related to theregion itself are described here.
The next two functions signal an error if the mark does not point anywhere. If TransientMark mode is enabled and mark-even-if-inactive is nil, they also signal an error if themark is inactive.
[Function]
This function returns the position of the beginning of the region (as an integer). Thisis the position of either point or the mark, whichever is smaller.

region-beginning[Function]
This function returns the position of the end of the region (as an integer). This is the
position of either point or the mark, whichever is larger.

region-end

Instead of using region-beginning and region-end, a command designed to operate
on a region should normally use interactive with the ‘r’ specification to find the beginningand end of the region. This lets other Lisp programs specify the bounds explicitly asarguments. See Section 22.2.2 [Interactive Codes], page 427.
[Function]
This function returns t if Transient Mark mode is enabled, the mark is active, andthere is a valid region in the buffer. This function is intended to be used by commands
that operate on the region, instead of on text near point, when the mark is active.
A region is valid if it has a non-zero size, or if the user option use-empty-activeregion is non-nil (by default, it is nil). The function region-active-p is similar
to use-region-p, but considers all regions as valid. In most cases, you should not use
region-active-p, since if the region is empty it is often more appropriate to operateon point.

use-region-p

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33 Text
This chapter describes the functions that deal with the text in a buffer. Most examine,
insert, or delete text in the current buffer, often operating at point or on text adjacent topoint. Many are interactive. All the functions that change the text provide for undoing thechanges (see Section 33.9 [Undo], page 895).
Many text-related functions operate on a region of text defined by two buffer positions
passed in arguments named start and end. These arguments should be either markers (seeChapter 32 [Markers], page 869) or numeric character positions (see Chapter 31 [Positions],
page 853). The order of these arguments does not matter; it is all right for start to be
the end of the region and end the beginning. For example, (delete-region 1 10) and(delete-region 10 1) are equivalent. An args-out-of-range error is signaled if either
start or end is outside the accessible portion of the buffer. In an interactive call, point andthe mark are used for these arguments.
Throughout this chapter, “text” refers to the characters in the buffer, together with theirproperties (when relevant). Keep in mind that point is always between two characters, andthe cursor appears on the character after point.

33.1 Examining Text Near Point
Many functions are provided to look at the characters around point. Several simple functions
are described here. See also looking-at in Section 35.4 [Regexp Search], page 1008.
In the following four functions, “beginning” or “end” of buffer refers to the beginning or
end of the accessible portion.

char-after &optional position[Function]
This function returns the character in the current buffer at (i.e., immediately after)
position position. If position is out of range for this purpose, either before the beginningof the buffer, or at or beyond the end, then the value is nil. The default for positionis point.
In the following example, assume that the first character in the buffer is ‘@’:(string (char-after 1))⇒ "@"char-before &optional position[Function]
This function returns the character in the current buffer immediately before position
position. If position is out of range for this purpose, either at or before the beginningof the buffer, or beyond the end, then the value is nil. The default for position ispoint.
[Function]
This function returns the character following point in the current buffer. This issimilar to (char-after (point)). However, if point is at the end of the buffer, thenfollowing-char returns 0.
Remember that point is always between characters, and the cursor normally appears over the character following point. Therefore, the character returned byfollowing-char is the character the cursor is over.

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In this example, point is between the ‘a’ and the ‘c’.
---------- Buffer: foo ---------Gentlemen may cry ``Pea?ce! Peace!,''but there is no peace.
---------- Buffer: foo ---------(string (preceding-char))⇒ "a"(string (following-char))⇒ "c"[Function]
This function returns the character preceding point in the current buffer. See above,
under following-char, for an example. If point is at the beginning of the buffer,preceding-char returns 0.

preceding-char

bobp[Function]
This function returns t if point is at the beginning of the buffer. If narrowing isin effect, this means the beginning of the accessible portion of the text. See also
point-min in Section 31.1 [Point], page 853.

eobp

[Function]
This function returns t if point is at the end of the buffer. If narrowing is in effect, thismeans the end of accessible portion of the text. See also point-max in See Section 31.1
[Point], page 853.

bolp

[Function]
This function returns t if point is at the beginning of a line. See Section 31.2.4 [TextLines], page 856. The beginning of the buffer (or of its accessible portion) always
counts as the beginning of a line.

eolp[Function]
This function returns t if point is at the end of a line. The end of the buffer (or of its
accessible portion) is always considered the end of a line.

33.2 Examining Buffer Contents
This section describes functions that allow a Lisp program to convert any portion of thetext in the buffer into a string.

buffer-substring start end[Function]
This function returns a string containing a copy of the text of the region defined bypositions start and end in the current buffer. If the arguments are not positions in theaccessible portion of the buffer, buffer-substring signals an args-out-of-range
error.
Here’s an example which assumes Font-Lock mode is not enabled:---------- Buffer: foo ---------This is the contents of buffer foo---------- Buffer: foo ----------

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(buffer-substring 1 10)⇒ "This is t"(buffer-substring (point-max) 10)⇒ "he contents of buffer foo\n"If the text being copied has any text properties, these are copied into the string alongwith the characters they belong to. See Section 33.19 [Text Properties], page 917.
However, overlays (see Section 41.9 [Overlays], page 1150) in the buffer and theirproperties are ignored, not copied.
For example, if Font-Lock mode is enabled, you might get results like these:(buffer-substring 1 10)⇒ #("This is t" 0 1 (fontified t) 1 9 (fontified t))

buffer-substring-no-properties start end[Function]
This is like buffer-substring, except that it does not copy text properties, just thecharacters themselves. See Section 33.19 [Text Properties], page 917.
[Function]
This function returns the contents of the entire accessible portion of the current buffer,
as a string. If the text being copied has any text properties, these are copied into thestring along with the characters they belong to.

buffer-string

If you need to make sure the resulting string, when copied to a different location,
will not change its visual appearance due to reordering of bidirectional text, use thebuffer-substring-with-bidi-context function (see Section 41.27 [Bidirectional Display],
page 1250).

filter-buffer-substring start end &optional delete[Function]
This function filters the buffer text between start and end using a function specified
by the variable filter-buffer-substring-function, and returns the result.
The default filter function consults the obsolete wrapper hook filter-buffersubstring-functions (see the documentation string of the macro with-wrapperhook for the details about this obsolete facility). If it is nil, it returns the unaltered
text from the buffer, i.e., what buffer-substring would return.
If delete is non-nil, the function deletes the text between start and end after copying
it, like delete-and-extract-region.
Lisp code should use this function instead of buffer-substring, buffer-substringno-properties, or delete-and-extract-region when copying into user-accessible
data structures such as the kill-ring, X clipboard, and registers. Major and minor
modes can modify filter-buffer-substring-function to alter such text as it iscopied out of the buffer.
[Variable]
The value of this variable is a function that filter-buffer-substring will call todo the actual work. The function receives three arguments, the same as those offilter-buffer-substring, which it should treat as per the documentation of thatfunction. It should return the filtered text (and optionally delete the source text).

filter-buffer-substring-function

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The following two variables are obsoleted by filter-buffer-substring-function, but are
still supported for backward compatibility.
[Variable]
This obsolete variable is a wrapper hook, whose members should be functions that
accept four arguments: fun, start, end, and delete. fun is a function that takes threearguments (start, end, and delete), and returns a string. In both cases, the start, end,
and delete arguments are the same as those of filter-buffer-substring.

filter-buffer-substring-functions

The first hook function is passed a fun that is equivalent to the default operationof filter-buffer-substring, i.e., it returns the buffer-substring between start andend and optionally deletes the original text from the buffer. In most cases, the hookfunction will call fun once, and then do its own processing of the result. The next
hook function receives a fun equivalent to this, and so on. The actual return value isthe result of all the hook functions acting in sequence.

current-word &optional strict really-word[Function]
This function returns the symbol (or word) at or near point, as a string. The return
value includes no text properties.
If the optional argument really-word is non-nil, it finds a word; otherwise, it finds a
symbol (which includes both word characters and symbol constituent characters).
If the optional argument strict is non-nil, then point must be in or next to the symbol
or word—if no symbol or word is there, the function returns nil. Otherwise, a nearby
symbol or word on the same line is acceptable.

thing-at-point thing &optional no-properties[Function]

Return the thing around or next to point, as a string.
The argument thing is a symbol which specifies a kind of syntactic entity. Possibilities include symbol, list, sexp, defun, filename, existing-filename, url, word,
sentence, whitespace, line, page, string, and others.
When the optional argument no-properties is non-nil, this function strips text properties from the return value.
---------- Buffer: foo ---------Gentlemen may cry ``Pea?ce! Peace!,''but there is no peace.
---------- Buffer: foo ---------(thing-at-point 'word)⇒ "Peace"(thing-at-point 'line)⇒ "Gentlemen may cry ``Peace! Peace!,''\n"(thing-at-point 'whitespace)⇒ nil[Variable]
This variable allows users and modes to tweak how thing-at-point works.
It’s an association list of things and functions (called with zero parameters) tothing-at-point-provider-alist

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return that thing. Entries for thing will be evaluated in turn until a non-nil
result is returned.
For instance, a major mode could say:(setq-local thing-at-point-provider-alist(append thing-at-point-provider-alist'((url . my-mode--url-at-point))))If no providers have a non-nil return, the thing will be computed the standard
way.

33.3 Comparing Text
This function lets you compare portions of the text in a buffer, without copying them into
strings first.

compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2

[Function]
This function lets you compare two substrings of the same buffer or two different
buffers. The first three arguments specify one substring, giving a buffer (or a buffername) and two positions within the buffer. The last three arguments specify the othersubstring in the same way. You can use nil for buffer1, buffer2, or both to stand forthe current buffer.
The value is negative if the first substring is less, positive if the first is greater, andzero if they are equal. The absolute value of the result is one plus the index of thefirst differing characters within the substrings.
This function ignores case when comparing characters if case-fold-search is non-nil.
It always ignores text properties.
Suppose you have the text ‘foobarbar haha!rara!’ in the current buffer; then in thisexample the two substrings are ‘rbar ’ and ‘rara!’. The value is 2 because the first
substring is greater at the second character.
(compare-buffer-substrings nil 6 11 nil 16 21)⇒ 2

33.4 Inserting Text
Insertion means adding new text to a buffer. The inserted text goes at point—between thecharacter before point and the character after point. Some insertion functions leave point
before the inserted text, while other functions leave it after. We call the former insertion
after point and the latter insertion before point.
Insertion moves markers located at positions after the insertion point, so that they staywith the surrounding text (see Chapter 32 [Markers], page 869). When a marker points
at the place of insertion, insertion may or may not relocate the marker, depending on themarker’s insertion type (see Section 32.5 [Marker Insertion Types], page 872). Certain
special functions such as insert-before-markers relocate all such markers to point after
the inserted text, regardless of the markers’ insertion type.
Insertion functions signal an error if the current buffer is read-only (see Section 28.7
[Read Only Buffers], page 680) or if they insert within read-only text (see Section 33.19.4[Special Properties], page 924).

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These functions copy text characters from strings and buffers along with their properties.
The inserted characters have exactly the same properties as the characters they were copied
from. By contrast, characters specified as separate arguments, not part of a string or buffer,inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in order to insert in a
multibyte buffer, and vice versa—if the text comes from a string or from a buffer. However,they do not convert unibyte character codes 128 through 255 to multibyte characters, noteven if the current buffer is a multibyte buffer. See Section 34.3 [Converting Representations],
page 965.

insert &rest args

[Function]
This function inserts the strings and/or characters args into the current buffer, atpoint, moving point forward. In other words, it inserts the text before point. An error
is signaled unless all args are either strings or characters. The value is nil.

insert-before-markers &rest args

[Function]
This function inserts the strings and/or characters args into the current buffer, atpoint, moving point forward. An error is signaled unless all args are either strings orcharacters. The value is nil.
This function is unlike the other insertion functions in that it relocates markers initiallypointing at the insertion point, to point after the inserted text. If an overlay begins at
the insertion point, the inserted text falls outside the overlay; if a nonempty overlay
ends at the insertion point, the inserted text falls inside that overlay.

insert-char character &optional count inherit[Command]This command inserts count instances of character into the current buffer before point.
The argument count must be an integer, and character must be a character.
If called interactively, this command prompts for character using its Unicode name orits code point. See Section “Inserting Text” in The GNU Emacs Manual.
This function does not convert unibyte character codes 128 through 255 to multibyte
characters, not even if the current buffer is a multibyte buffer. See Section 34.3
[Converting Representations], page 965.
If inherit is non-nil, the inserted characters inherit sticky text properties from the two
characters before and after the insertion point. See Section 33.19.6 [Sticky Properties],
page 932.

insert-buffer-substring from-buffer-or-name &optional start end[Function]
This function inserts a portion of buffer from-buffer-or-name into the current buffer
before point. The text inserted is the region between start (inclusive) and end(exclusive). (These arguments default to the beginning and end of the accessible
portion of that buffer.) This function returns nil.
In this example, the form is executed with buffer ‘bar’ as the current buffer. We
assume that buffer ‘bar’ is initially empty.
---------- Buffer: foo ---------We hold these truths to be self-evident, that all---------- Buffer: foo ----------

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(insert-buffer-substring "foo" 1 20)⇒ nil---------- Buffer: bar ---------We hold these truth?
---------- Buffer: bar ----------

insert-buffer-substring-no-properties from-buffer-or-name&optional start end[Function]

This is like insert-buffer-substring except that it does not copy any text properties.

insert-into-buffer to-buffer &optional start end[Function]
This is like insert-buffer-substring, but works in the opposite direction: The text
is copied from the current buffer into to-buffer. The block of text is copied to thecurrent point in to-buffer, and point (in that buffer) is advanced to after the end of thecopied text. Is start/end is nil, the entire text in the current buffer is copied over.

See Section 33.19.6 [Sticky Properties], page 932, for other insertion functions that inherit
text properties from the nearby text in addition to inserting it. Whitespace inserted byindentation functions also inherits text properties.

33.5 User-Level Insertion Commands
This section describes higher-level commands for inserting text, commands intended primarily
for the user but useful also in Lisp programs.

insert-buffer from-buffer-or-name[Command]This command inserts the entire accessible contents of from-buffer-or-name (whichmust exist) into the current buffer after point. It leaves the mark after the inserted
text. The value is nil.

self-insert-command count &optional char[Command]This command inserts the character char (the last character typed); it does so counttimes, before point, and returns nil. Most printing characters are bound to thiscommand. In routine use, self-insert-command is the most frequently called functionin Emacs, but programs rarely use it except to install it on a keymap.
In an interactive call, count is the numeric prefix argument.
Self-insertion translates the input character through translation-table-for-input.
See Section 34.9 [Translation of Characters], page 975.
This command calls auto-fill-function whenever that is non-nil and the character
inserted is in the table auto-fill-chars (see Section 33.14 [Auto Filling], page 905).
This command performs abbrev expansion if Abbrev mode is enabled and the inserted
character does not have word-constituent syntax. (See Chapter 38 [Abbrevs], page 1066,
and Section 36.2.1 [Syntax Class Table], page 1023.) It is also responsible for calling
blink-paren-function when the inserted character has close parenthesis syntax (seeSection 41.22 [Blinking], page 1241).

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The final thing this command does is to run the hook post-self-insert-hook. You
could use this to automatically reindent text as it is typed, for example. The functions
on this hook can use last-command-event (see Section 22.5 [Command Loop Info],
page 436) to access the character just inserted.
If any function on this hook needs to act on the region (see Section 32.8 [The Region],
page 877), it should make sure Delete Selection mode (see Section “Using Region”
in The GNU Emacs Manual) doesn’t delete the region before post-self-inserthook functions are invoked. The way to do so is to add a function that returns nil
to self-insert-uses-region-functions, a special hook that tells Delete Selection
mode it should not delete the region.
Do not try substituting your own definition of self-insert-command for the standard
one. The editor command loop handles this function specially.

newline &optional number-of-newlines interactive[Command]This command inserts newlines into the current buffer before point. If number-ofnewlines is supplied, that many newline characters are inserted. In an interactive call,number-of-newlines is the numeric prefix argument.
This command calls self-insert-command to insert newlines, which may subsequently
break the preceding line by calling auto-fill-function (see Section 33.14 [AutoFilling], page 905). Typically what auto-fill-function does is insert a newline;
thus, the overall result in this case is to insert two newlines at different places: one atpoint, and another earlier in the line. newline does not auto-fill if number-of-newlines
is non-nil.
This command does not run the hook post-self-insert-hook unless called interactively or interactive is non-nil.
This command indents to the left margin if that is not zero. See Section 33.12 [Margins],
page 902.

The value returned is nil.

ensure-empty-lines &optional number-of-empty-lines[Command]This command can be used to ensure that you have a specific number of empty lines
before point. (An “empty line” is here defined as a line with no characters on it—aline with space characters isn’t an empty line.) It defaults to ensuring that there’s asingle empty line before point.
If point isn’t at the beginning of a line, a newline character is inserted first. If there’s
more empty lines before point than specified, the number of empty lines is reduced.
Otherwise it’s increased to the specified number.
[Variable]
This variable controls whether overwrite mode is in effect. The value should beoverwrite-mode-textual, overwrite-mode-binary, or nil. overwrite-modetextual specifies textual overwrite mode (treats newlines and tabs specially), andoverwrite-mode-binary specifies binary overwrite mode (treats newlines and tabs
like any other characters).

overwrite-mode

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33.6 Deleting Text
Deletion means removing part of the text in a buffer, without saving it in the kill ring (seeSection 33.8 [The Kill Ring], page 889). Deleted text can’t be yanked, but can be reinserted
using the undo mechanism (see Section 33.9 [Undo], page 895). Some deletion functions dosave text in the kill ring in some special cases.
All of the deletion functions operate on the current buffer.
[Command]This function deletes the entire text of the current buffer (not just the accessible
portion), leaving it empty. If the buffer is read-only, it signals a buffer-readonly error; if some of the text in it is read-only, it signals a text-read-only error.
Otherwise, it deletes the text without asking for any confirmation. It returns nil.

erase-buffer

Normally, deleting a large amount of text from a buffer inhibits further auto-saving ofthat buffer because it has shrunk. However, erase-buffer does not do this, the idea
being that the future text is not really related to the former text, and its size should
not be compared with that of the former text.

delete-region start end[Command]This command deletes the text between positions start and end in the current buffer,and returns nil. If point was inside the deleted region, its value afterward is start.
Otherwise, point relocates with the surrounding text, as markers do.

delete-and-extract-region start end[Function]
This function deletes the text between positions start and end in the current buffer,and returns a string containing the text just deleted.
If point was inside the deleted region, its value afterward is start. Otherwise, point
relocates with the surrounding text, as markers do.

delete-char count &optional killp[Command]This command deletes count characters directly after point, or before point if count isnegative. If killp is non-nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed
prefix argument. Therefore, if a prefix argument is supplied, the text is saved in thekill ring. If no prefix argument is supplied, then one character is deleted, but not
saved in the kill ring.

The value returned is always nil.

delete-backward-char count &optional killp[Command]This command deletes count characters directly before point, or after point if count isnegative. If killp is non-nil, then it saves the deleted characters in the kill ring.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed
prefix argument. Therefore, if a prefix argument is supplied, the text is saved in thekill ring. If no prefix argument is supplied, then one character is deleted, but not
saved in the kill ring.

The value returned is always nil.

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backward-delete-char-untabify count &optional killp[Command]This command deletes count characters backward, changing tabs into spaces. Whenthe next character to be deleted is a tab, it is first replaced with the proper number of
spaces to preserve alignment and then one of those spaces is deleted instead of the tab.
If killp is non-nil, then the command saves the deleted characters in the kill ring.
Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly−count characters after point are deleted.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed
prefix argument. Therefore, if a prefix argument is supplied, the text is saved in thekill ring. If no prefix argument is supplied, then one character is deleted, but not
saved in the kill ring.
The value returned is always nil.
[User Option]
This option specifies how backward-delete-char-untabify should deal with whitespace. Possible values include untabify, the default, meaning convert a tab to many
spaces and delete one; hungry, meaning delete all tabs and spaces before point with
one command; all meaning delete all tabs, spaces and newlines before point, and nil,meaning do nothing special for whitespace characters.

backward-delete-char-untabify-method33.7 User-Level Deletion Commands
This section describes higher-level commands for deleting text, commands intended primarily
for the user but useful also in Lisp programs.

delete-horizontal-space &optional backward-only[Command]This function deletes all spaces and tabs around point. It returns nil.
If backward-only is non-nil, the function deletes spaces and tabs before point, but
not after point.
In the following examples, we call delete-horizontal-space four times, once oneach line, with point between the second and third characters on the line each time.
---------- Buffer: foo ---------I ?thoughtI ?
thought
We? thought
Yo?u thought---------- Buffer: foo ---------(delete-horizontal-space)⇒ nil; Four times.

---------- Buffer: foo ---------Ithought
Ithought
Wethought
You thought---------- Buffer: foo ----------

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delete-indentation &optional join-following-p beg end[Command]This function joins the line point is on to the previous line, deleting any whitespace atthe join and in some cases replacing it with one space. If join-following-p is non-nil,delete-indentation joins this line to the following line instead. Otherwise, if beg
and end are non-nil, this function joins all lines in the region they define.
In an interactive call, join-following-p is the prefix argument, and beg and end are,respectively, the start and end of the region if it is active, else nil. The function
returns nil.
If there is a fill prefix, and the second of the lines being joined starts with theprefix, then delete-indentation deletes the fill prefix before joining the lines. See
Section 33.12 [Margins], page 902.
In the example below, point is located on the line starting ‘events’, and it makes nodifference if there are trailing spaces in the preceding line.
---------- Buffer: foo ---------When in the course of human?
events, it becomes necessary---------- Buffer: foo ---------(delete-indentation)⇒ nil---------- Buffer: foo ---------When in the course of human? events, it becomes necessary---------- Buffer: foo ----------

After the lines are joined, the function fixup-whitespace is responsible for deciding
whether to leave a space at the junction.
[Command]This function replaces all the horizontal whitespace surrounding point with either one
space or no space, according to the context. It returns nil.
At the beginning or end of a line, the appropriate amount of space is none. Before acharacter with close parenthesis syntax, or after a character with open parenthesisor expression-prefix syntax, no space is also appropriate. Otherwise, one space isappropriate. See Section 36.2.1 [Syntax Class Table], page 1023.
In the example below, fixup-whitespace is called the first time with point before
the word ‘spaces’ in the first line. For the second invocation, point is directly afterthe ‘(’.

fixup-whitespace---------- Buffer: foo ---------This has too many?spacesThis has too many spaces at the start of (?
---------- Buffer: foo ----------

this list)(fixup-whitespace)⇒ nil(fixup-whitespace)⇒ nil---------- Buffer: foo ---------This has too many spaces
This has too many spaces at the start of (this list)---------- Buffer: foo ----------

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just-one-space &optional n[Command]This command replaces any spaces and tabs around point with a single space, or nspaces if n is specified. It returns nil.

[Command]This function deletes blank lines surrounding point. If point is on a blank line with
one or more blank lines before or after it, then all but one of them are deleted. If
point is on an isolated blank line, then it is deleted. If point is on a nonblank line, thecommand deletes all blank lines immediately following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-lines returns nil.

delete-blank-lines

delete-trailing-whitespace &optional start end[Command]
Delete trailing whitespace in the region defined by start and end.
This command deletes whitespace characters after the last non-whitespace characterin each line in the region.
If this command acts on the entire buffer (i.e., if called interactively with the markinactive, or called from Lisp with end nil), it also deletes all trailing lines at the endof the buffer if the variable delete-trailing-lines is non-nil.

33.8 The Kill Ring
Kill functions delete text like the deletion functions, but save it so that the user can reinsert
it by yanking. Most of these functions have ‘kill-’ in their name. By contrast, the functions
whose names start with ‘delete-’ normally do not save text for yanking (though they canstill be undone); these are deletion functions.
Most of the kill commands are primarily for interactive use, and are not described here.
What we do describe are the functions provided for use in writing such commands. You can
use these functions to write commands for killing text. When you need to delete text forinternal purposes within a Lisp function, you should normally use deletion functions, so as
not to disturb the kill ring contents. See Section 33.6 [Deletion], page 886.
Killed text is saved for later yanking in the kill ring. This is a list that holds a numberof recent kills, not just the last text kill. We call this a “ring” because yanking treats it as
having elements in a cyclic order. The list is kept in the variable kill-ring, and can be
operated on with the usual functions for lists; there are also specialized functions, describedin this section, that treat it as a ring.
Some people think this use of the word “kill” is unfortunate, since it refers to operations
that specifically do not destroy the entities killed. This is in sharp contrast to ordinary life,in which death is permanent and killed entities do not come back to life. Therefore, othermetaphors have been proposed. For example, the term “cut ring” makes sense to people
who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts.
However, it would be difficult to change the terminology now.

33.8.1 Kill Ring Concepts
The kill ring records killed text as strings in a list, most recent first. A short kill ring, forexample, might look like this:("some text" "a different piece of text" "even older text")

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When the list reaches kill-ring-max entries in length, adding a new entry automaticallydeletes the last entry.
When kill commands are interwoven with other commands, each kill command makesa new entry in the kill ring. Multiple kill commands in succession build up a single killring entry, which would be yanked as a unit; the second and subsequent consecutive killcommands add text to the entry made by the first one.
For yanking, one entry in the kill ring is designated the front of the ring. Some yankcommands rotate the ring by designating a different element as the front. But this virtual
rotation doesn’t change the list itself—the most recent entry always comes first in the list.

33.8.2 Functions for Killing
kill-region is the usual subroutine for killing text. Any command that calls this function
is a kill command (and should probably have ‘kill’ in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or adds it to the mostrecent element. It determines automatically (using last-command) whether the previous
command was a kill command, and if so appends the killed text to the most recent entry.
The commands described below can filter the killed text before they save it in the killring. They call filter-buffer-substring (see Section 33.2 [Buffer Contents], page 879)
to perform the filtering. By default, there’s no filtering, but major and minor modes andhook functions can set up filtering, so that text saved in the kill ring is different from what
was in the buffer.

kill-region start end &optional region[Command]This function kills the stretch of text between start and end; but if the optional
argument region is non-nil, it ignores start and end, and kills the text in the current
region instead. The text is deleted but saved in the kill ring, along with its text
properties. The value is always nil.
In an interactive call, start and end are point and the mark, and region is always
non-nil, so the command always kills the text in the current region.
If the buffer or text is read-only, kill-region modifies the kill ring just the same,then signals an error without modifying the buffer. This is convenient because it lets
the user use a series of kill commands to copy text from a read-only buffer into thekill ring.
[User Option]
If this option is non-nil, kill-region does not signal an error if the buffer or text
is read-only. Instead, it simply returns, updating the kill ring but not changing thebuffer.

kill-read-only-ok

copy-region-as-kill start end &optional region[Command]This function saves the stretch of text between start and end on the kill ring (including
text properties), but does not delete the text from the buffer. However, if the optional
argument region is non-nil, the function ignores start and end, and saves the current
region instead. It always returns nil.
In an interactive call, start and end are point and the mark, and region is always
non-nil, so the command always saves the text in the current region.

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The command does not set this-command to kill-region, so a subsequent killcommand does not append to the same kill ring entry.

33.8.3 Yanking
Yanking means inserting text from the kill ring, but it does not insert the text blindly. The
yank command, and related commands, use insert-for-yank to perform special processing
on the text before it is inserted.

insert-for-yank string[Function]
This function works like insert, except that it processes the text in string according to
the yank-handler text property, as well as the variables yank-handled-properties
and yank-excluded-properties (see below), before inserting the result into thecurrent buffer.
string will be run through yank-transform-functions (see below) before inserting.

insert-buffer-substring-as-yank buf &optional start end[Function]
This function resembles insert-buffer-substring, except that it processes the text
according to yank-handled-properties and yank-excluded-properties. (It does
not handle the yank-handler property, which does not normally occur in buffer text
anyway.)If you put a yank-handler text property on all or part of a string, that alters
how insert-for-yank inserts the string. If different parts of the string have different
yank-handler values (comparison being done with eq), each substring is handled separately.
The property value must be a list of one to four elements, with the following format (where
elements after the first may be omitted):(function param noexclude undo)
Here is what the elements do:function

When function is non-nil, it is called instead of insert to insert the string,with one argument—the string to insert.

param

If param is present and non-nil, it replaces string (or the substring of string
being processed) as the object passed to function (or insert). For example,
if function is yank-rectangle, param should be a list of strings to insert as arectangle.

noexclude If noexclude is present and non-nil, that disables the normal action of
yank-handled-properties and yank-excluded-properties on the inserted
string.
undo

If undo is present and non-nil, it is a function that will be called by yank-pop
to undo the insertion of the current object. It is called with two arguments, thestart and end of the current region. function can set yank-undo-function to
override the undo value.
[User Option]
This variable specifies special text property handling conditions for yanked text. It
takes effect after the text has been inserted (either normally, or via the yank-handler
property), and prior to yank-excluded-properties taking effect.

yank-handled-properties

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The value should be an alist of elements (prop . fun). Each alist element is handled
in order. The inserted text is scanned for stretches of text having text properties eq
to prop; for each such stretch, fun is called with three arguments: the value of theproperty, and the start and end positions of the text.
[User Option]
The value of this variable is the list of properties to remove from inserted text. Its
default value contains properties that might lead to annoying results, such as causing
the text to respond to the mouse or specifying key bindings. It takes effect after
yank-handled-properties.

yank-excluded-properties[Variable]
This variable is a list of functions. Each function is called (in order) with the string to
be yanked as the argument, and should return a (possibly transformed) string. Thisvariable can be set globally, but can also be used to create new commands that arevariations on yank. For instance, to create a command that works like yank, butcleans up whitespace before inserting, you could say something like:(defun yank-with-clean-whitespace ()(interactive)(let ((yank-transform-functions'(string-clean-whitespace)))(call-interactively #'yank)))

yank-transform-functions

33.8.4 Functions for Yanking
This section describes higher-level commands for yanking, which are intended primarily for the user but useful also in Lisp programs. Both yank and yank-pop honor theyank-excluded-properties variable and yank-handler text property (see Section 33.8.3[Yanking], page 891).

yank &optional arg[Command]This command inserts before point the text at the front of the kill ring. It sets themark at the beginning of that text, using push-mark (see Section 32.7 [The Mark],
page 873), and puts point at the end.
If arg is a non-nil list (which occurs interactively when the user types C-u with nodigits), then yank inserts the text as described above, but puts point before the yanked
text and sets the mark after it.
If arg is a number, then yank inserts the argth most recently killed text—the argth
element of the kill ring list, counted cyclically from the front, which is considered thefirst element for this purpose.
yank does not alter the contents of the kill ring, unless it used text provided by anotherprogram, in which case it pushes that text onto the kill ring. However if arg is an
integer different from one, it rotates the kill ring to place the yanked string at thefront.
yank returns nil.

yank-pop &optional arg[Command]
When invoked immediately after a yank or another yank-pop, this command replaces
the just-yanked entry from the kill ring with a different entry from the kill ring. When

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this command is invoked like that, the region contains text that was just inserted byanother yank command. yank-pop deletes that text and inserts in its place a different
piece of killed text. It does not add the deleted text to the kill ring, since it is alreadyin the kill ring somewhere. It does however rotate the kill ring to place the newly
yanked string at the front.
If arg is nil, then the replacement text is the previous element of the kill ring. If arg
is numeric, the replacement is the argth previous kill. If arg is negative, a more recent
kill is the replacement.
The sequence of kills in the kill ring wraps around, so if yank-pop is invoked repeatedly
and reaches the oldest kill, the one that comes after it is the newest one, and the one
before the newest one is the oldest one.
This command can also be invoked after a command that is not a yank command. Inthat case, it prompts in the minibuffer for a kill-ring entry, with completion, and uses
the kill ring elements as the minibuffer history (see Section 21.4 [Minibuffer History],
page 392). This allows the user to interactively select one of the previous kills recordedin the kill ring.
The return value is always nil.
[Variable]
If this variable is non-nil, the function yank-pop uses its value instead ofdelete-region to delete the text inserted by the previous yank or yank-pop
command. The value must be a function of two arguments, the start and end of thecurrent region.
The function insert-for-yank automatically sets this variable according to the undo
element of the yank-handler text property, if there is one.

yank-undo-function

33.8.5 Low-Level Kill Ring
These functions and variables provide access to the kill ring at a lower level, but are still
convenient for use in Lisp programs, because they take care of interaction with window
system selections (see Section 30.20 [Window System Selections], page 840).

current-kill n &optional do-not-move[Function]
The function current-kill rotates the yanking pointer, which designates the frontof the kill ring, by n places (from newer kills to older ones), and returns the text atthat place in the ring.
If the optional second argument do-not-move is non-nil, then current-kill doesn’talter the yanking pointer; it just returns the nth kill, counting from the current yanking
pointer.
If n is zero, indicating a request for the latest kill, current-kill calls the value ofinterprogram-paste-function (documented below) before consulting the kill ring.
If that value is a function and calling it returns a string or a list of several strings,
current-kill pushes the strings onto the kill ring and returns the first string. It also
sets the yanking pointer to point to the kill-ring entry of the first string returned byinterprogram-paste-function, regardless of the value of do-not-move. Otherwise,
current-kill does not treat a zero value for n specially: it returns the entry pointed
at by the yanking pointer and does not move the yanking pointer.

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kill-new string &optional replace[Function]
This function pushes the text string onto the kill ring and makes the yanking pointerpoint to it. It discards the oldest entry if appropriate. It also invokes the valuesof interprogram-paste-function (subject to the user option save-interprogrampaste-before-kill) and interprogram-cut-function (see below).
If replace is non-nil, then kill-new replaces the first element of the kill ring withstring, rather than pushing string onto the kill ring.

kill-append string before-p[Function]
This function appends the text string to the first entry in the kill ring and makes
the yanking pointer point to the combined entry. Normally string goes at the endof the entry, but if before-p is non-nil, it goes at the beginning. This function calls
kill-new as a subroutine, thus causing the values of interprogram-cut-function
and possibly interprogram-paste-function (see below) to be invoked by extension.
[Variable]
This variable provides a way of transferring killed text from other programs, when you
are using a window system. Its value should be nil or a function of no arguments.
If the value is a function, current-kill calls it to get the most recent kill. If thefunction returns a non-nil value, then that value is used as the most recent kill. If it
returns nil, then the front of the kill ring is used.
To facilitate support for window systems that support multiple selections, this function
may also return a list of strings. In that case, the first string is used as the mostrecent kill, and all the other strings are pushed onto the kill ring, for easy access byyank-pop.
The normal use of this function is to get the window system’s clipboard as the mostrecent kill, even if the selection belongs to another application. See Section 30.20[Window System Selections], page 840. However, if the clipboard contents come fromthe current Emacs session, this function should return nil.

interprogram-paste-function[Variable]
This variable provides a way of communicating killed text to other programs, when
you are using a window system. Its value should be nil or a function of one required
argument.
If the value is a function, kill-new and kill-append call it with the new first elementof the kill ring as the argument.
The normal use of this function is to put newly killed text in the window system’s
clipboard. See Section 30.20 [Window System Selections], page 840.

interprogram-cut-function

33.8.6 Internals of the Kill Ring
The variable kill-ring holds the kill ring contents, in the form of a list of strings. The
most recent kill is always at the front of the list.
The kill-ring-yank-pointer variable points to a link in the kill ring list, whose car
is the text to yank next. We say it identifies the front of the ring. Moving kill-ringyank-pointer to a different link is called rotating the kill ring. We call the kill ring a “ring”
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the beginning, or vice-versa. Rotation of the kill ring is virtual; it does not change the valueof kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp variables whose values arenormally lists. The word “pointer” in the name of the kill-ring-yank-pointer indicatesthat the variable’s purpose is to identify one element of the list for use by the next yankcommand.
The value of kill-ring-yank-pointer is always eq to one of the links in the kill ring
list. The element it identifies is the car of that link. Kill commands, which change the killring, also set this variable to the value of kill-ring. The effect is to rotate the ring so thatthe newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer pointing to the second entry in the kill ring ("some text" "a different piece of text" "yet older text").
kill-ring---- kill-ring-yank-pointer
|
|
|
v
|
--- ----- ----- ----> |||------> |||--> |||--> nil--- ----- ----- --|
|
|
|
|
|
|
|
-->"yet older text"|||--> "a different piece of text"|--> "some text"
This state of affairs might occur after C-y (yank) immediately followed by M-y (yank-pop).
[Variable]
This variable holds the list of killed text sequences, most recently killed first.

kill-ring[Variable]
This variable’s value indicates which element of the kill ring is at the front of the ringfor yanking. More precisely, the value is a tail of the value of kill-ring, and its car
is the kill string that C-y should yank.

kill-ring-yank-pointer[User Option]
The value of this variable is the maximum length to which the kill ring can grow,before elements are thrown away at the end. The default value for kill-ring-max is120.

kill-ring-max

33.9 Undo
Most buffers have an undo list, which records all changes made to the buffer’s text so thatthey can be undone. (The buffers that don’t have one are usually special-purpose buffers
for which Emacs assumes that undoing is not useful. In particular, any buffer whose namebegins with a space has its undo recording off by default; see Section 28.3 [Buffer Names],
page 674.) All the primitives that modify the text in the buffer automatically add elements
to the front of the undo list, which is in the variable buffer-undo-list.

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[Variable]
This buffer-local variable’s value is the undo list of the current buffer. A value of t
disables the recording of undo information.

buffer-undo-list

Here are the kinds of elements an undo list can have:position

This kind of element records a previous value of point; undoing this element
moves point to position. Ordinary cursor motion does not make any sort ofundo record, but deletion operations use these entries to record where point was
before the command.

(beg . end)
This kind of element indicates how to delete text that was inserted. Upon
insertion, the text occupied the range beg–end in the buffer.
(text . position)
This kind of element indicates how to reinsert text that was deleted. The deleted
text itself is the string text. The place to reinsert it is (abs position). If
position is positive, point was at the beginning of the deleted text, otherwise it
was at the end. Zero or more (marker . adjustment) elements follow immediately
after this element.
(t . time-flag)
This kind of element indicates that an unmodified buffer became modified.
A time-flag that is a non-integer Lisp timestamp represents the visited file’s
modification time as of when it was previously visited or saved, using the sameformat as current-time; see Section 42.5 [Time of Day], page 1270. A time-flagof 0 means the buffer does not correspond to any file; −1 means the visited
file previously did not exist. primitive-undo uses these values to determine
whether to mark the buffer as unmodified once again; it does so only if the file’s
status matches that of time-flag.
(nil property value beg . end)
This kind of element records a change in a text property. Here’s how you mightundo the change:(put-text-property beg end property value)(marker . adjustment)This kind of element records the fact that the marker marker was relocated
due to deletion of surrounding text, and that it moved adjustment character
positions. If the marker’s location is consistent with the (text . position)
element preceding it in the undo list, then undoing this element moves marker− adjustment characters.
(apply funname . args)
This is an extensible undo item, which is undone by calling funname witharguments args.
(apply delta beg end funname . args)
This is an extensible undo item, which records a change limited to the range beg
to end, which increased the size of the buffer by delta characters. It is undone
by calling funname with arguments args.

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This kind of element enables undo limited to a region to determine whether theelement pertains to that region.
nilThis element is a boundary. The elements between two boundaries are calleda change group; normally, each change group corresponds to one keyboard
command, and undo commands normally undo an entire group as a unit.
[Function]
This function places a boundary element in the undo list. The undo command stops atsuch a boundary, and successive undo commands undo to earlier and earlier boundaries.
This function returns nil.
Calling this function explicitly is useful for splitting the effects of a command into
more than one unit. For example, query-replace calls undo-boundary after eachreplacement, so that the user can undo individual replacements one by one.
Mostly, however, this function is called automatically at an appropriate time.

undo-boundary[Function]
The editor command loop automatically calls undo-boundary just before executing
each key sequence, so that each undo normally undoes the effects of one command. A
few exceptional commands are amalgamating: these commands generally cause smallchanges to buffers, so with these a boundary is inserted only every 20th command, allowing the changes to be undone as a group. By default, the commands self-insertcommand, which produces self-inserting input characters (see Section 33.5 [Commands
for Insertion], page 884), and delete-char, which deletes characters (see Section 33.6
[Deletion], page 886), are amalgamating. Where a command affects the contents ofseveral buffers, as may happen, for example, when a function on the post-commandhook affects a buffer other than the current-buffer, then undo-boundary will becalled in each of the affected buffers.
This function can be called before an amalgamating command. It removes the previous
undo-boundary if a series of such calls have been made.
The maximum number of changes that can be amalgamated is controlled by theamalgamating-undo-limit variable. If this variable is 1, no changes are amalgamated.

undo-auto-amalgamate

A Lisp program can amalgamate a series of changes into a single change group by callingundo-amalgamate-change-group (see Section 33.33 [Atomic Changes], page 959). Notethat amalgamating-undo-limit has no effect on the groups produced by that function.
[Variable]
Some buffers, such as process buffers, can change even when no commands are
executing. In these cases, undo-boundary is normally called periodically by the timer
in this variable. Setting this variable to non-nil prevents this behavior.

undo-auto-current-boundary-timer[Variable]
This variable is normally nil, but the undo commands bind it to t. This is so thatvarious kinds of change hooks can tell when they’re being called for the sake of undoing.

undo-in-progressprimitive-undo count list

[Function]
This is the basic function for undoing elements of an undo list. It undoes the first
count elements of list, returning the rest of list.

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primitive-undo adds elements to the buffer’s undo list when it changes the buffer.
Undo commands avoid confusion by saving the undo list value at the beginning ofa sequence of undo operations. Then the undo operations use and update the savedvalue. The new elements added by undoing are not part of this saved value, so they
don’t interfere with continuing to undo.
This function does not bind undo-in-progress.

with-undo-amalgamate body. . .

[Macro]This macro removes all the undo boundaries inserted during the execution of body sothat it can be undone as a single step.

Some commands leave the region active after execution in such a way that it interfereswith selective undo of that command. To make undo ignore the active region when invoked immediately after such a command, set the property undo-inhibit-region of thecommand’s function symbol to a non-nil value. See Section 9.4.2 [Standard Properties],
page 139.

33.10 Maintaining Undo Lists
This section describes how to enable and disable undo information for a given buffer. It also
explains how the undo list is truncated automatically so it doesn’t get too big.
Recording of undo information in a newly created buffer is normally enabled to start
with; but if the buffer name starts with a space, the undo recording is initially disabled.
You can explicitly enable or disable undo recording with the following two functions, or by
setting buffer-undo-list yourself.

buffer-enable-undo &optional buffer-or-name[Command]This command enables recording undo information for buffer buffer-or-name, so that
subsequent changes can be undone. If no argument is supplied, then the current buffer
is used. This function does nothing if undo recording is already enabled in the buffer.
It returns nil.
In an interactive call, buffer-or-name is the current buffer. You cannot specify anyother buffer.

buffer-disable-undo &optional buffer-or-name[Command]This function discards the undo list of buffer-or-name, and disables further recording of
undo information. As a result, it is no longer possible to undo either previous changes
or any subsequent changes. If the undo list of buffer-or-name is already disabled, thisfunction has no effect.
In an interactive call, BUFFER-OR-NAME is the current buffer. You cannot specify
any other buffer. This function returns nil.

As editing continues, undo lists get longer and longer. To prevent them from using up all
available memory space, garbage collection trims them back to size limits you can set. (Forthis purpose, the size of an undo list measures the cons cells that make up the list, plus thestrings of deleted text.) Three variables control the range of acceptable sizes: undo-limit,
undo-strong-limit and undo-outer-limit. In these variables, size is counted as thenumber of bytes occupied, which includes both saved text and other data.

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[User Option]
This is the soft limit for the acceptable size of an undo list. The change group at
which this size is exceeded is the last one kept.

undo-limit[User Option]
This is the upper limit for the acceptable size of an undo list. The change group at
which this size is exceeded is discarded itself (along with all older change groups).
There is one exception: the very latest change group is only discarded if it exceeds
undo-outer-limit.

undo-strong-limit[User Option]
If at garbage collection time the undo info for the current command exceeds this limit,
Emacs discards the info and displays a warning. This is a last ditch limit to prevent
memory overflow.

undo-outer-limit[User Option]
If this variable is non-nil, when the undo info exceeds undo-outer-limit, Emacs
asks in the echo area whether to discard the info. The default value is nil, whichmeans to discard it automatically.
This option is mainly intended for debugging. Garbage collection is inhibited while
the question is asked, which means that Emacs might leak memory if the user waits
too long before answering the question.

undo-ask-before-discard

33.11 Filling
Filling means adjusting the lengths of lines (by moving the line breaks) so that they arenearly (but no greater than) a specified maximum width. Additionally, lines can be justified,
which means inserting spaces to make the left and/or right margins line up precisely. The
width is controlled by the variable fill-column. For ease of reading, lines should be nolonger than 70 or so columns.
You can use Auto Fill mode (see Section 33.14 [Auto Filling], page 905) to fill text
automatically as you insert it, but changes to existing text may leave it improperly filled.
Then you must fill the text explicitly.
Most of the commands in this section return values that are not meaningful. All thefunctions that do filling take note of the current left margin, current right margin, andcurrent justification style (see Section 33.12 [Margins], page 902). If the current justificationstyle is none, the filling functions don’t actually do anything.
Several of the filling functions have an argument justify. If it is non-nil, that requests
some kind of justification. It can be left, right, full, or center, to request a specificstyle of justification. If it is t, that means to use the current justification style for this partof the text (see current-justification, below). Any other value is treated as full.
When you call the filling functions interactively, using a prefix argument implies thevalue full for justify.

fill-paragraph &optional justify region[Command]This command fills the paragraph at or after point. If justify is non-nil, each line isjustified as well. It uses the ordinary paragraph motion commands to find paragraphboundaries. See Section “Paragraphs” in The GNU Emacs Manual.

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When region is non-nil, then if Transient Mark mode is enabled and the mark is active,
this command calls fill-region to fill all the paragraphs in the region, instead offilling only the current paragraph. When this command is called interactively, region
is t.

fill-region start end &optional justify nosqueeze to-eop[Command]This command fills each of the paragraphs in the region from start to end. It justifies
as well if justify is non-nil.
If nosqueeze is non-nil, that means to leave whitespace other than line breaks
untouched. If to-eop is non-nil, that means to keep filling to the end of the paragraph—or the next hard newline, if use-hard-newlines is enabled (see below).
The variable paragraph-separate controls how to distinguish paragraphs. See
Section 35.8 [Standard Regexps], page 1020.

pixel-fill-region start end pixel-width[Function]
Most Emacs buffers use monospaced text, so all the filling functions (like fill-region)
work based on the number of characters and char-width. However, Emacs can renderother types of things, like text that contains images and using proportional fonts, andthe pixel-fill-region exists to handle that. It fills the region of text between startand end at pixel granularity, so text using variable-pitch fonts or several different fonts
looks filled regardless of different character sizes. The argument pixel-width specifies
the maximum pixel width a line is allowed to have after filling; it is the pixel-resolution
equivalent of the fill-column in fill-region. For instance, this Lisp snippet willinsert text using a proportional font, and then fill this to be no wider than 300 pixels:(insert (propertize"This is a sentence that's ends here."'face 'variable-pitch))(pixel-fill-region (point) (point-max) 300)
If start isn’t at the start of a line, the horizontal position of start, converted to pixel
units, will be used as the indentation prefix on subsequent lines.
The pixel-fill-width helper function can be used to compute the pixel width touse. If given no arguments, it’ll return a value slightly less than the width of thecurrent window. The first optional value, columns, specifies the number of columns
using the standard, monospaced fonts, e.g. fill-column. The second optional value
is the window to use. You’d typically use it like this:(pixel-fill-region
start end (pixel-fill-width fill-column))

fill-individual-paragraphs start end &optional justify
citation-regexp[Command]This command fills each paragraph in the region according to its individual fill prefix.
Thus, if the lines of a paragraph were indented with spaces, the filled paragraph willremain indented in the same fashion.
The first two arguments, start and end, are the beginning and end of the region to be
filled. The third and fourth arguments, justify and citation-regexp, are optional. If
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non-nil, it means the function is operating on a mail message and therefore should
not fill the header lines. If citation-regexp is a string, it is used as a regular expression;
if it matches the beginning of a line, that line is treated as a citation marker.
Ordinarily, fill-individual-paragraphs regards each change in indentation as
starting a new paragraph. If fill-individual-varying-indent is non-nil, then
only separator lines separate paragraphs. That mode can handle indented paragraphswith additional indentation on the first line.
[User Option]
This variable alters the action of fill-individual-paragraphs as described above.

fill-individual-varying-indent

fill-region-as-paragraph start end &optional justify nosqueeze
squeeze-after[Command]This command considers a region of text as a single paragraph and fills it. If the region
was made up of many paragraphs, the blank lines between paragraphs are removed.
This function justifies as well as filling when justify is non-nil.
If nosqueeze is non-nil, that means to leave whitespace other than line breaks
untouched. If squeeze-after is non-nil, it specifies a position in the region, and meansthat whitespace other than line breaks should be left untouched before that position.
In Adaptive Fill mode, this command calls fill-context-prefix to choose a fill
prefix by default. See Section 33.13 [Adaptive Fill], page 904.

justify-current-line &optional how eop nosqueeze[Command]This command inserts spaces between the words of the current line so that the line
ends exactly at fill-column. It returns nil.
The argument how, if non-nil specifies explicitly the style of justification. It can beleft, right, full, center, or none. If it is t, that means to follow specified justification style (see current-justification, below). nil means to do full justification.
If eop is non-nil, that means do only left-justification if current-justification
specifies full justification. This is used for the last line of a paragraph; even if theparagraph as a whole is fully justified, the last line should not be.
If nosqueeze is non-nil, that means do not change interior whitespace.
[User Option]
This variable’s value specifies the style of justification to use for text that doesn’t
specify a style with a text property. The possible values are left, right, full, center,or none. The default value is left.

default-justification[Function]
This function returns the proper justification style to use for filling the text aroundpoint.
This returns the value of the justification text property at point, or the variable
default-justification if there is no such text property. However, it returns nil
rather than none to mean “don’t justify”.

current-justification[User Option]
If this variable is non-nil, a period followed by just one space does not count as theend of a sentence, and the filling functions avoid breaking the line at such a place.

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[User Option]
If this variable is non-nil, a sentence can end without a period. This is used for
languages like Thai, where sentences end with a double space but without a period.

sentence-end-without-period[User Option]
If this variable is non-nil, it should be a string of characters that can end a sentence
without following spaces.

sentence-end-without-space[User Option]
If this variable is non-nil, two words of different kind (e.g., English and CJK) will beseparated with a space when concatenating one that is in the end of a line and theother that is in the beginning of the next line for filling.

fill-separate-heterogeneous-words-with-space[Variable]
This variable provides a way to override the filling of paragraphs. If its value is
non-nil, fill-paragraph calls this function to do the work. If the function returns
a non-nil value, fill-paragraph assumes the job is done, and immediately returns
that value.

fill-paragraph-function

The usual use of this feature is to fill comments in programming language modes. If
the function needs to fill a paragraph in the usual way, it can do so as follows:(let ((fill-paragraph-function nil))(fill-paragraph arg))[Variable]
This variable provides a way to override how the filling functions, such as fill-region
and fill-paragraph, move forward to the next paragraph. Its value should be afunction, which is called with a single argument n, the number of paragraphs to
move, and should return the difference between n and the number of paragraphs
actually moved. The default value of this variable is forward-paragraph. See Section“Paragraphs” in The GNU Emacs Manual.

fill-forward-paragraph-function[Variable]
If this variable is non-nil, the filling functions do not delete newlines that have thehard text property. These hard newlines act as paragraph separators. See Section“Hard and Soft Newlines” in The GNU Emacs Manual.

use-hard-newlines

33.12 Margins for Filling[User Option]
This buffer-local variable, if non-nil, specifies a string of text that appears at the
beginning of normal text lines and should be disregarded when filling them. Any linethat fails to start with the fill prefix is considered the start of a paragraph; so is any
line that starts with the fill prefix followed by additional whitespace. Lines that startwith the fill prefix but no additional whitespace are ordinary text lines that can be
filled together. The resulting filled lines also start with the fill prefix.

fill-prefix

The fill prefix follows the left margin whitespace, if any.

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[User Option]
This buffer-local variable specifies the maximum width of filled lines. Its value should
be an integer, which is a number of columns. All the filling, justification, and centeringcommands are affected by this variable, including Auto Fill mode (see Section 33.14[Auto Filling], page 905).

fill-column

As a practical matter, if you are writing text for other people to read, you should set
fill-column to no more than 70. Otherwise the line will be too long for people toread comfortably, and this can make the text seem clumsy.
The default value for fill-column is 70. To disable Auto Fill mode in a specific mode,
you could say something like:(add-hook 'foo-mode-hook (lambda () (auto-fill-mode -1))

set-left-margin from to margin[Command]This sets the left-margin property on the text from from to to to the value margin.
If Auto Fill mode is enabled, this command also refills the region to fit the new margin.

set-right-margin from to margin[Command]This sets the right-margin property on the text from from to to to the value margin.
If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
[Function]
This function returns the proper left margin value to use for filling the text aroundpoint. The value is the sum of the left-margin property of the character at the startof the current line (or zero if none), and the value of the variable left-margin.

current-left-margin[Function]
This function returns the proper fill column value to use for filling the text aroundpoint. The value is the value of the fill-column variable, minus the value of theright-margin property of the character after point.

current-fill-column

move-to-left-margin &optional n force[Command]This function moves point to the left margin of the current line. The column moved
to is determined by calling the function current-left-margin. If the argument n is
non-nil, move-to-left-margin moves forward n−1 lines first.
If force is non-nil, that says to fix the line’s indentation if that doesn’t match the left
margin value.

delete-to-left-margin &optional from to[Function]
This function removes left margin indentation from the text between from and to.
The amount of indentation to delete is determined by calling current-left-margin.
In no case does this function delete non-whitespace. If from and to are omitted, theydefault to the whole buffer.
[Function]
This function adjusts the indentation at the beginning of the current line to the value
specified by the variable left-margin. (That may involve either inserting or deleting
whitespace.) This function is value of indent-line-function in Paragraph-Indent
Text mode.

indent-to-left-margin

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[User Option]
This variable specifies the base left margin column. In Fundamental mode, RET indents
to this column. This variable automatically becomes buffer-local when set in any
fashion.

left-margin[User Option]
This variable gives major modes a way to specify not to break a line at certain places.
Its value should be a list of functions. Whenever filling considers breaking the line ata certain place in the buffer, it calls each of these functions with no arguments andwith point located at that place. If any of the functions returns non-nil, then theline won’t be broken there.

fill-nobreak-predicate

33.13 Adaptive Fill Mode
When Adaptive Fill Mode is enabled, Emacs determines the fill prefix automatically fromthe text in each paragraph being filled rather than using a predetermined value. During
filling, this fill prefix gets inserted at the start of the second and subsequent lines of theparagraph as described in Section 33.11 [Filling], page 899, and in Section 33.14 [AutoFilling], page 905.
[User Option]
Adaptive Fill mode is enabled when this variable is non-nil. It is t by default.

adaptive-fill-mode

fill-context-prefix from to[Function]
This function implements the heart of Adaptive Fill mode; it chooses a fill prefix basedon the text between from and to, typically the start and end of a paragraph. It does
this by looking at the first two lines of the paragraph, based on the variables described
below.
Usually, this function returns the fill prefix, a string. However, before doing this,the function makes a final check (not specially mentioned in the following) that aline starting with this prefix wouldn’t look like the start of a paragraph. Should thishappen, the function signals the anomaly by returning nil instead.
In detail, fill-context-prefix does this:
1. It takes a candidate for the fill prefix from the first line—it tries first the function in
adaptive-fill-function (if any), then the regular expression adaptive-fillregexp (see below). The first non-nil result of these, or the empty string ifthey’re both nil, becomes the first line’s candidate.
2. If the paragraph has as yet only one line, the function tests the validity of theprefix candidate just found. The function then returns the candidate if it’s valid,or a string of spaces otherwise. (see the description of adaptive-fill-firstline-regexp below).
3. When the paragraph already has two lines, the function next looks for a prefix
candidate on the second line, in just the same way it did for the first line. If it
doesn’t find one, it returns nil.
4. The function now compares the two candidate prefixes heuristically: if the nonwhitespace characters in the line 2 candidate occur in the same order in the line
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largest initial substring which is common to both candidates (which might be theempty string).
[User Option]
Adaptive Fill mode matches this regular expression against the text starting after
the left margin whitespace (if any) on a line; the characters it matches are that line’s
candidate for the fill prefix.
The default value matches whitespace with certain punctuation characters intermingled.

adaptive-fill-regexp[User Option]
Used only in one-line paragraphs, this regular expression acts as an additional checkof the validity of the one available candidate fill prefix: the candidate must match
this regular expression, or match comment-start-skip. If it doesn’t, fill-contextprefix replaces the candidate with a string of spaces of the same width as it.
The default value of this variable is "\\`[ \t]*\\'", which matches only a stringof whitespace. The effect of this default is to force the fill prefixes found in one-line
paragraphs always to be pure whitespace.

adaptive-fill-first-line-regexp[User Option]
You can specify more complex ways of choosing a fill prefix automatically by setting
this variable to a function. The function is called with point after the left margin (ifany) of a line, and it must preserve point. It should return either that line’s fill prefix
or nil, meaning it has failed to determine a prefix.

adaptive-fill-function

33.14 Auto Filling
Auto Fill mode is a minor mode that fills lines automatically as text is inserted. See Section“Auto Fill” in The GNU Emacs Manual. This section describes some variables used byAuto Fill mode. For a description of functions that you can call explicitly to fill and justify
existing text, see Section 33.11 [Filling], page 899.
Auto Fill mode also enables the functions that change the margins and justification style
to refill portions of the text. See Section 33.12 [Margins], page 902.
[Variable]
The value of this buffer-local variable should be a function (of no arguments) to becalled after self-inserting a character from the table auto-fill-chars, see below. It
may be nil, in which case nothing special is done in that case.
The value of auto-fill-function is do-auto-fill when Auto Fill mode is enabled.
That is a function whose sole purpose is to implement the usual strategy for breaking
a line.

auto-fill-function[Variable]
This variable specifies the function to use for auto-fill-function, if and when Auto
Fill is turned on. Major modes can set buffer-local values for this variable to alter
how Auto Fill works.

normal-auto-fill-function[Variable]
A char table of characters which invoke auto-fill-function when self-inserted—
space and newline in most language environments. They have an entry t in thetable.

auto-fill-chars

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[User Option]
This variable, if non-nil, means to fill lines automatically within comments only. Moreprecisely, this means that if a comment syntax was defined for the current buffer, thenself-inserting a character outside of a comment will not call auto-fill-function.

comment-auto-fill-only-comments

33.15 Sorting Text
The sorting functions described in this section all rearrange text in a buffer. This is incontrast to the function sort, which rearranges the order of the elements of a list (seeSection 5.6.3 [Rearrangement], page 90). The values returned by these functions are notmeaningful.

sort-subr reverse nextrecfun endrecfun &optional startkeyfun
endkeyfun predicate[Function]

This function is the general text-sorting routine that subdivides a buffer into records
and then sorts them. Most of the commands in this section use this function.
To understand how sort-subr works, consider the whole accessible portion of thebuffer as being divided into disjoint pieces called sort records. The records may or
may not be contiguous, but they must not overlap. A portion of each sort record(perhaps all of it) is designated as the sort key. Sorting rearranges the records in orderby their sort keys.
Usually, the records are rearranged in order of ascending sort key. If the first argument
to the sort-subr function, reverse, is non-nil, the sort records are rearranged inorder of descending sort key.
The next four arguments to sort-subr are functions that are called to move point
across a sort record. They are called many times from within sort-subr.
1. nextrecfun is called with point at the end of a record. This function moves point
to the start of the next record. The first record is assumed to start at the positionof point when sort-subr is called. Therefore, you should usually move point tothe beginning of the buffer before calling sort-subr.
This function can indicate there are no more sort records by leaving point at theend of the buffer.
2. endrecfun is called with point within a record. It moves point to the end of therecord.
3. startkeyfun is called to move point from the start of a record to the start of thesort key. This argument is optional; if it is omitted, the whole record is the sort
key. If supplied, the function should either return a non-nil value to be used as
the sort key, or return nil to indicate that the sort key is in the buffer startingat point. In the latter case, endkeyfun is called to find the end of the sort key.
4. endkeyfun is called to move point from the start of the sort key to the end of thesort key. This argument is optional. If startkeyfun returns nil and this argument
is omitted (or nil), then the sort key extends to the end of the record. There isno need for endkeyfun if startkeyfun returns a non-nil value.
The argument predicate is the function to use to compare keys. It is called with twoarguments, the keys to compare, and should return non-nil if the first key should

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come before the second in the sorting order. What exactly are the key arguments
depends on what startkeyfun and endkeyfun return. If predicate is omitted or nil, it
defaults to < if the keys are numbers, to compare-buffer-substrings if the keys arecons cells (whose car and cdr are start and end buffer positions of the key), and tostring< otherwise (with keys assumed to be strings).
As an example of sort-subr, here is the complete function definition for sort-lines:;; Note that the first two lines of doc string;; are effectively one line when viewed by a user.
(defun sort-lines (reverse beg end)
"Sort lines in region alphabetically;\
argument means descending order.
Called from a program, there are three arguments:
REVERSE (non-nil means reverse order),\
BEG and END (region to sort).
The variable `sort-fold-case' determines\
whether alphabetic case affects
the sort order."(interactive "P\nr")(save-excursion(save-restriction(narrow-to-region beg end)
(goto-char (point-min))(let ((inhibit-field-text-motion t))(sort-subr reverse 'forward-line 'end-of-line)))))
Here forward-line moves point to the start of the next record, and end-of-line
moves point to the end of record. We do not pass the arguments startkeyfun andendkeyfun, because the entire record is used as the sort key.
The sort-paragraphs function is very much the same, except that its sort-subr calllooks like this:(sort-subr reverse(lambda ()(while (and (not (eobp))(looking-at paragraph-separate))(forward-line 1)))
'forward-paragraph)Markers pointing into any sort records are left with no useful position after sort-subr
returns.
[User Option]
If this variable is non-nil, sort-subr and the other buffer sorting functions ignore
case when comparing strings.

sort-fold-casesort-regexp-fields reverse record-regexp key-regexp start end[Command]This command sorts the region between start and end alphabetically as specified byrecord-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse
order.

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Alphabetical sorting means that two sort keys are compared by comparing the firstcharacters of each, the second characters of each, and so on. If a mismatch is found,it means that the sort keys are unequal; the sort key whose character is less at the
point of first mismatch is the lesser sort key. The individual characters are comparedaccording to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide the buffer into sort
records. At the end of each record, a search is done for this regular expression, and thetext that matches it is taken as the next record. For example, the regular expression‘^.+$’, which matches lines with at least one character besides a newline, would makeeach such line into a sort record. See Section 35.3 [Regular Expressions], page 995, fora description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is the sort
key. The key-regexp could match the whole record, or only a part. In the latter case,the rest of the record has no effect on the sorted order of records, but it is carriedalong when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of recordregexp, or it can be a regular expression on its own.
If key-regexp is:‘\digit’

then the text matched by the digitth ‘\(...\)’ parenthesis grouping inrecord-regexp is the sort key.

‘\&’then the whole record is the sort key.

a regular expression
then sort-regexp-fields searches for a match for the regular expression
within the record. If such a match is found, it is the sort key. If there
is no match for key-regexp within a record then that record is ignored,
which means its position in the buffer is not changed. (The other records
may move around it.)For example, if you plan to sort all the lines in the region by the first word on each line
starting with the letter ‘f’, you should set record-regexp to ‘^.*$’ and set key-regexp
to ‘\<f\w*\>’. The resulting expression looks like this:(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>"(region-beginning)(region-end))
If you call sort-regexp-fields interactively, it prompts for record-regexp and keyregexp in the minibuffer.

sort-lines reverse start end[Command]This command alphabetically sorts lines in the region between start and end. If reverse
is non-nil, the sort is in reverse order.

sort-paragraphs reverse start end[Command]This command alphabetically sorts paragraphs in the region between start and end.
If reverse is non-nil, the sort is in reverse order.

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sort-pages reverse start end[Command]This command alphabetically sorts pages in the region between start and end. If
reverse is non-nil, the sort is in reverse order.

sort-fields field start end[Command]This command sorts lines in the region between start and end, comparing themalphabetically by the fieldth field of each line. Fields are separated by whitespace andnumbered starting from 1. If field is negative, sorting is by the −fieldth field from theend of the line. This command is useful for sorting tables.

sort-numeric-fields field start end[Command]This command sorts lines in the region between start and end, comparing them
numerically by the fieldth field of each line. Fields are separated by whitespace andnumbered starting from 1. The specified field must contain a number in each line of
the region. Numbers starting with 0 are treated as octal, and numbers starting with‘0x’ are treated as hexadecimal.
If field is negative, sorting is by the −fieldth field from the end of the line. This
command is useful for sorting tables.
[User Option]
This variable specifies the default radix for sort-numeric-fields to parse numbers.

sort-numeric-basesort-columns reverse &optional beg end[Command]This command sorts the lines in the region between beg and end, comparing themalphabetically by a certain range of columns. The column positions of beg and end
bound the range of columns to sort on.
If reverse is non-nil, the sort is in reverse order.
One unusual thing about this command is that the entire line containing position beg,
and the entire line containing position end, are included in the region sorted.
Note that sort-columns rejects text that contains tabs, because tabs could be split
across the specified columns. Use M-x untabify to convert tabs to spaces before
sorting.
When possible, this command actually works by calling the sort utility program.

33.16 Counting Columns
The column functions convert between a character position (counting characters from the
beginning of the buffer) and a column position (counting screen characters from the beginningof a line).
These functions count each character according to the number of columns it occupies on
the screen. This means control characters count as occupying 2 or 4 columns, depending
upon the value of ctl-arrow, and tabs count as occupying a number of columns that depends
on the value of tab-width and on the column where the tab begins. See Section 41.23.1[Usual Display], page 1242.
Column number computations ignore the width of the window and the amount ofhorizontal scrolling. Consequently, a column value can be arbitrarily high. The first (orleftmost) column is numbered 0. They also ignore overlays and text properties, aside from

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invisibility. Invisible text is considered as having zero width, unless buffer-invisibilityspec specifies that invisible text should be displayed as ellipsis (see Section 41.6 [Invisible
Text], page 1142).
[Function]
This function returns the horizontal position of point, measured in columns, counting
from 0 at the left margin. The column position is the sum of the widths of all thedisplayed representations of the characters between the start of the current line andpoint.

current-column

move-to-column column &optional force[Command]This function moves point to column in the current line. The calculation of column
takes into account the widths of the displayed representations of the characters between
the start of the line and point.

When called interactively, column is the value of prefix numeric argument. If column
is not an integer, an error is signaled.
If it is impossible to move to column column because that is in the middle of amulticolumn character such as a tab, point moves to the end of that character.
However, if force is non-nil, and column is in the middle of a tab, then move-tocolumn either converts the tab into spaces (when indent-tabs-mode is nil), or inserts
enough spaces before it (otherwise), so that point can move precisely to column column.
Other multicolumn characters can cause anomalies despite force, since there is no way
to split them.
The argument force also has an effect if the line isn’t long enough to reach column
column; if it is t, that means to add whitespace at the end of the line to reach thatcolumn.
The return value is the column number actually moved to.

33.17 Indentation
The indentation functions are used to examine, move to, and change whitespace that is at
the beginning of a line. Some of the functions can also change whitespace elsewhere on aline. Columns and indentation count from zero at the left margin.

33.17.1 Indentation Primitives
This section describes the primitive functions used to count and insert indentation. The
functions in the following sections use these primitives. See Section 41.10 [Size of Displayed
Text], page 1157, for related functions.
[Function]
This function returns the indentation of the current line, which is the horizontal
position of the first nonblank character. If the contents are entirely blank, then this is
the horizontal position of the end of the line.

current-indentation

This function considers invisible text as having zero width, unlessbuffer-invisibility-spec specifies that invisible text should be displayed as
ellipsis. See Section 41.6 [Invisible Text], page 1142.

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indent-to column &optional minimum[Command]This function indents from point with tabs and spaces until column is reached. If
minimum is specified and non-nil, then at least that many spaces are inserted even if
this requires going beyond column. Otherwise the function does nothing if point isalready beyond column. The value is the column at which the inserted indentation
ends.
The inserted whitespace characters inherit text properties from the surrounding
text (usually, from the preceding text only). See Section 33.19.6 [Sticky Properties],
page 932.
[User Option]
If this variable is non-nil, indentation functions can insert tabs as well as spaces.
Otherwise, they insert only spaces. Setting this variable automatically makes it
buffer-local in the current buffer.

indent-tabs-mode

33.17.2 Indentation Controlled by Major Mode
An important function of each major mode is to customize the TAB key to indent properly
for the language being edited. This section describes the mechanism of the TAB key and how
to control it. The functions in this section return unpredictable values.

indent-for-tab-command &optional rigid[Command]This is the command bound to TAB in most editing modes. Its usual action is to indent
the current line, but it can alternatively insert a tab character or indent a region.
Here is what it does:• First, it checks whether Transient Mark mode is enabled and the region is active. If
so, it calls indent-region to indent all the text in the region (see Section 33.17.3[Region Indent], page 913).
• Otherwise, if the indentation function in indent-line-function is indent-toleft-margin (a trivial command that inserts a tab character), or if the variabletab-always-indent specifies that a tab character ought to be inserted (see below),then it inserts a tab character.
• Otherwise, it indents the current line; this is done by calling the function
in indent-line-function. If the line is already indented, and the value of
tab-always-indent is complete (see below), it tries completing the text at
point.
If rigid is non-nil (interactively, with a prefix argument), then after this commandindents a line or inserts a tab, it also rigidly indents the entire balanced expression
which starts at the beginning of the current line, in order to reflect the new indentation.
This argument is ignored if the command indents the region.
[Variable]
This variable’s value is the function to be used by indent-for-tab-command, andvarious other indentation commands, to indent the current line. It is usually assignedby the major mode; for instance, Lisp mode sets it to lisp-indent-line, C modesets it to c-indent-line, and so on. The default value is indent-relative. See
Section 24.7 [Auto-Indentation], page 581.

indent-line-function

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[Command]This command calls the function in indent-line-function to indent the current line
in a way appropriate for the current major mode.

indent-according-to-mode[Command]This function inserts a newline, then indents the new line (the one following thenewline just inserted) according to the major mode. It does indentation by callingindent-according-to-mode.

newline-and-indent[Command]This command reindents the current line, inserts a newline at point, and then indents
the new line (the one following the newline just inserted). It does indentation on bothlines by calling indent-according-to-mode.

reindent-then-newline-and-indent[User Option]
This variable can be used to customize the behavior of the TAB (indent-for-tabcommand) command. If the value is t (the default), the command normally just indents
the current line. If the value is nil, the command indents the current line only if point
is at the left margin or in the line’s indentation; otherwise, it inserts a tab character.
If the value is complete, the command first tries to indent the current line, and if
the line was already indented, it calls completion-at-point to complete the text at
point (see Section 21.6.8 [Completion in Buffers], page 411).

tab-always-indent[User Option]
If tab-always-indent is complete, whether to expand or indent can be further
customized via the tab-first-completion variable. The following values can beused:tab-first-completion

eol

Only complete if point is at the end of a line.

wordComplete unless the next character has word syntax.

word-or-paren
Complete unless the next character has word syntax or is a parenthesis.
word-or-paren-or-punct
Complete unless the next character has word syntax, or is a parenthesis,
or is punctuation.
In any case, typing TAB a second time always results in completion.
Some major modes need to support embedded regions of text whose syntax belongs toa different major mode. Examples include literate programming source files that combine
documentation and snippets of source code, Yacc/Bison programs that include snippets of
Python or JS code, etc. To correctly indent the embedded chunks, the primary mode needs
to delegate the indentation to another mode’s indentation engine (e.g., call js-indent-line
for JS code or python-indent-line for Python), while providing it with some context toguide the indentation. Major modes, for their part, should avoid calling widen in theirindentation code and obey prog-first-column.

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[Variable]
This variable, when non-nil, holds the indentation context for the sub-mode’s indentation engine provided by the superior major mode. The value should be a list of theform (first-column . rest. The members of the list have the following meaning:prog-indentation-context

first-column
The column to be used for top-level constructs. This replaces the default
value of the top-level column used by the sub-mode, usually zero.
restThis value is currently unused.

The following convenience function should be used by major mode’s indentation engine
in support of invocations as sub-modes of another major mode.
[Function]
Call this function instead of using a literal value (usually, zero) of the column number
for indenting top-level program constructs. The function’s value is the column number
to use for top-level constructs. When no superior mode is in effect, this function
returns zero.

prog-first-column

33.17.3 Indenting an Entire Region
This section describes commands that indent all the lines in the region. They return
unpredictable values.

indent-region start end &optional to-column[Command]This command indents each nonblank line starting between start (inclusive) and end(exclusive). If to-column is nil, indent-region indents each nonblank line by callingthe current mode’s indentation function, the value of indent-line-function.
If to-column is non-nil, it should be an integer specifying the number of columnsof indentation; then this function gives each line exactly that much indentation, byeither adding or deleting whitespace.
If there is a fill prefix, indent-region indents each line by making it start with thefill prefix.

[Variable]
The value of this variable is a function that can be used by indent-region as a shortcut. It should take two arguments, the start and end of the region. You should design
the function so that it will produce the same results as indenting the lines of the region
one by one, but presumably faster.
If the value is nil, there is no short cut, and indent-region actually works line byline.
A short-cut function is useful in modes such as C mode and Lisp mode, where theindent-line-function must scan from the beginning of the function definition:
applying it to each line would be quadratic in time. The short cut can update thescan information as it moves through the lines indenting them; this takes linear time.
In a mode where indenting a line individually is fast, there is no need for a short cut.
indent-region with a non-nil argument to-column has a different meaning and does
not use this variable.

indent-region-function

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indent-rigidly start end count[Command]This function indents all lines starting between start (inclusive) and end (exclusive)
sideways by count columns. This preserves the shape of the affected region, moving it
as a rigid unit.
This is useful not only for indenting regions of unindented text, but also for indenting
regions of formatted code. For example, if count is 3, this command adds 3 columnsof indentation to every line that begins in the specified region.
If called interactively with no prefix argument, this command invokes a transient mode
for adjusting indentation rigidly. See Section “Indentation Commands” in The GNU
Emacs Manual.

indent-code-rigidly start end columns &optional
nochange-regexp[Command]This is like indent-rigidly, except that it doesn’t alter lines that start within strings
or comments.
In addition, it doesn’t alter a line if nochange-regexp matches at the beginning of theline (if nochange-regexp is non-nil).

33.17.4 Indentation Relative to Previous Lines
This section describes two commands that indent the current line based on the contents ofprevious lines.

indent-relative &optional first-only unindented-ok[Command]This command inserts whitespace at point, extending to the same column as thenext indent point of the previous nonblank line. An indent point is a non-whitespacecharacter following whitespace. The next indent point is the first one at a column
greater than the current column of point. For example, if point is underneath and to
the left of the first non-blank character of a line of text, it moves to that column byinserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at a great enoughcolumn position), indent-relative either does nothing (if unindented-ok is non-nil)or calls tab-to-tab-stop. Thus, if point is underneath and to the right of the lastcolumn of a short line of text, this command ordinarily moves point to the next tab
stop by inserting whitespace.
If first-only is non-nil, only the first indent point is considered.
The return value of indent-relative is unpredictable.
In the following example, point is at the beginning of the second line:
This line is indented twelve spaces.
?The quick brown fox jumped.
Evaluation of the expression (indent-relative nil) produces the following:This line is indented twelve spaces.
?The quick brown fox jumped.
In this next example, point is between the ‘m’ and ‘p’ of ‘jumped’:
This line is indented twelve spaces.
The quick brown fox jum?ped.

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Evaluation of the expression (indent-relative nil) produces the following:This line is indented twelve spaces.
The quick brown fox jum ?ped.
[Command]This command indents the current line like the previous nonblank line, by callingindent-relative with t as the first-only argument. The return value is unpredictable.

indent-relative-first-indent-point

If the previous nonblank line has no indent points beyond the current column, thiscommand does nothing.

33.17.5 Adjustable Tab Stops
This section explains the mechanism for user-specified tab stops and the mechanisms thatuse and set them. The name “tab stops” is used because the feature is similar to that of thetab stops on a typewriter. The feature works by inserting an appropriate number of spaces
and tab characters to reach the next tab stop column; it does not affect the display of tab
characters in the buffer (see Section 41.23.1 [Usual Display], page 1242). Note that the TAB
character as input uses this tab stop feature only in a few major modes, such as Text mode.
See Section “Tab Stops” in The GNU Emacs Manual.
[Command]This command inserts spaces or tabs before point, up to the next tab stop column
defined by tab-stop-list.

tab-to-tab-stop[User Option]
This variable defines the tab stop columns used by tab-to-tab-stop. It should beeither nil, or a list of increasing integers, which need not be evenly spaced. The list
is implicitly extended to infinity through repetition of the interval between the lastand penultimate elements (or tab-width if the list has fewer than two elements). A
value of nil means a tab stop every tab-width columns.

tab-stop-list

Use M-x edit-tab-stops to edit the location of tab stops interactively.

33.17.6 Indentation-Based Motion Commands
These commands, primarily for interactive use, act based on the indentation in the text.
[Command]This command moves point to the first non-whitespace character in the current line
(which is the line in which point is located).

back-to-indentation

backward-to-indentation &optional arg[Command]This command moves point backward arg lines and then to the first nonblank characteron that line. If arg is omitted or nil, it defaults to 1.

forward-to-indentation &optional arg[Command]This command moves point forward arg lines and then to the first nonblank characteron that line. If arg is omitted or nil, it defaults to 1.

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33.18 Case Changes
The case change commands described here work on text in the current buffer. See Section 4.9[Case Conversion], page 72, for case conversion functions that work on strings and characters.
See Section 4.10 [Case Tables], page 74, for how to customize which characters are upper orlower case and how to convert them.

capitalize-region start end[Command]This function capitalizes all words in the region defined by start and end. To capitalizemeans to convert each word’s first character to upper case and convert the rest ofeach word to lower case. The function returns nil.
If one end of the region is in the middle of a word, the part of the word within theregion is treated as an entire word.
When capitalize-region is called interactively, start and end are point and themark, with the smallest first.
---------- Buffer: foo ---------This is the contents of the 5th foo.
---------- Buffer: foo ---------(capitalize-region 1 37)⇒ nil---------- Buffer: foo ---------This Is The Contents Of The 5th Foo.
---------- Buffer: foo ----------

downcase-region start end[Command]This function converts all of the letters in the region defined by start and end to lower
case. The function returns nil.
When downcase-region is called interactively, start and end are point and the mark,with the smallest first.

upcase-region start end[Command]This function converts all of the letters in the region defined by start and end to upper
case. The function returns nil.
When upcase-region is called interactively, start and end are point and the mark,with the smallest first.

capitalize-word count[Command]This function capitalizes count words after point, moving point over as it does. To
capitalize means to convert each word’s first character to upper case and convert
the rest of each word to lower case. If count is negative, the function capitalizes the−count previous words but does not move point. The value is nil.
If point is in the middle of a word, the part of the word before point is ignored whenmoving forward. The rest is treated as an entire word.
When capitalize-word is called interactively, count is set to the numeric prefix
argument.

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downcase-word count[Command]This function converts the count words after point to all lower case, moving point overas it does. If count is negative, it converts the −count previous words but does not
move point. The value is nil.
When downcase-word is called interactively, count is set to the numeric prefix argument.

upcase-word count[Command]This function converts the count words after point to all upper case, moving point
over as it does. If count is negative, it converts the −count previous words but does
not move point. The value is nil.
When upcase-word is called interactively, count is set to the numeric prefix argument.

33.19 Text Properties
Each character position in a buffer or a string can have a text property list, much like theproperty list of a symbol (see Section 5.9 [Property Lists], page 99). The properties belong
to a particular character at a particular place, such as, the letter ‘T’ at the beginning of thissentence or the first ‘o’ in ‘foo’—if the same character occurs in two different places, thetwo occurrences in general have different properties.
Each property has a name and a value. Both of these can be any Lisp object, but thename is normally a symbol. Typically each property name symbol is used for a particularpurpose; for instance, the text property face specifies the faces for displaying the character(see Section 33.19.4 [Special Properties], page 924). The usual way to access the property
list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the property category of the character.
It should be a symbol. The properties of the symbol serve as defaults for the properties of
the character.
Copying text between strings and buffers preserves the properties along with the characters;
this includes such diverse functions as substring, insert, and buffer-substring. Killing
and then yanking text (see Section 33.8 [The Kill Ring], page 889) also preserves theproperties, except that some properties are handled specially and might be removed whentext is yanked; see Section 33.8.3 [Yanking], page 891.

33.19.1 Examining Text Properties
The simplest way to examine text properties is to ask for the value of a particular property
of a particular character. For that, use get-text-property. Use text-properties-at to
get the entire property list of a character. See Section 33.19.3 [Property Search], page 921,
for functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string
start from 0, whereas positions in a buffer start from 1. Passing a buffer other than thecurrent buffer may be slow.

get-text-property pos prop &optional object[Function]
This function returns the value of the prop property of the character after position
pos in object (a buffer or string). The argument object is optional and defaults to thecurrent buffer.

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If position is at the end of object, the value is nil, but note that buffer narrowing does
not affect the value. That is, if object is a buffer or nil, and the buffer is narrowed
and position is at the end of the narrowed buffer, the result may be non-nil.
If there is no prop property strictly speaking, but the character has a property categorythat is a symbol, then get-text-property returns the prop property of that symbol.

get-char-property position prop &optional object[Function]
This function is like get-text-property, except that it checks overlays first and thentext properties. See Section 41.9 [Overlays], page 1150.
The argument object may be a string, a buffer, or a window. If it is a window, thenthe buffer displayed in that window is used for text properties and overlays, but only
the overlays active for that window are considered. If object is a buffer, then overlays
in that buffer are considered first, in order of decreasing priority, followed by the text
properties. If object is a string, only text properties are considered, since strings never
have overlays.

get-pos-property position prop &optional object[Function]
This function is like get-char-property, except that it pays attention to properties’
stickiness and overlays’ advancement settings instead of the property of the characterat (i.e., right after) position.

get-char-property-and-overlay position prop &optional object[Function]
This is like get-char-property, but gives extra information about the overlay thatthe property value comes from.
Its value is a cons cell whose car is the property value, the same value get-charproperty would return with the same arguments. Its cdr is the overlay in which theproperty was found, or nil, if it was found as a text property or not found at all.
If position is at the end of object, both the car and the cdr of the value are nil.
[Variable]
This variable holds an alist which maps property names to a list of alternative
property names. If a character does not specify a direct value for a property, thealternative property names are consulted in order; the first non-nil value is used. Thisvariable takes precedence over default-text-properties, and category properties
take precedence over this variable.

char-property-alias-alist

text-properties-at position &optional object[Function]
This function returns the entire property list of the character at position in the stringor buffer object. If object is nil, it defaults to the current buffer.
If position is at the end of object, the value is nil, but note that buffer narrowing does
not affect the value. That is, if object is a buffer or nil, and the buffer is narrowed
and position is at the end of the narrowed buffer, the result may be non-nil.
[Variable]
This variable holds a property list giving default values for text properties. Whenevera character does not specify a value for a property, neither directly, through a category

default-text-properties

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symbol, or through char-property-alias-alist, the value stored in this list is usedinstead. Here is an example:(setq default-text-properties '(foo 69)
char-property-alias-alist nil);; Make sure character 1 has no properties of its own.
(set-text-properties 1 2 nil);; What we get, when we ask, is the default value.
(get-text-property 1 'foo)⇒ 69

object-intervals OBJECT[Function]
This function returns a copy of the intervals (i.e., text properties) in object as a list ofintervals. object must be a string or a buffer. Altering the structure of this list does
not change the intervals in the object.
(object-intervals (propertize "foo" 'face 'bold))⇒ ((0 3 (face bold)))
Each element in the returned list represents one interval. Each interval has three parts:
The first is the start, the second is the end, and the third part is the text property
itself.

33.19.2 Changing Text Properties
The primitives for changing properties apply to a specified range of text in a buffer or string.
The function set-text-properties (see end of section) sets the entire property list of thetext in that range; more often, it is useful to add, change, or delete just certain properties
specified by name.
Since text properties are considered part of the contents of the buffer (or string), andcan affect how a buffer looks on the screen, any change in buffer text properties marks thebuffer as modified. Buffer text property changes are undoable also (see Section 33.9 [Undo],
page 895). Positions in a string start from 0, whereas positions in a buffer start from 1.

put-text-property start end prop value &optional object[Function]
This function sets the prop property to value for the text between start and end in
the string or buffer object. If object is nil, it defaults to the current buffer.

add-text-properties start end props &optional object[Function]
This function adds or overrides text properties for the text between start and end in
the string or buffer object. If object is nil, it defaults to the current buffer.
The argument props specifies which properties to add. It should have the form of aproperty list (see Section 5.9 [Property Lists], page 99): a list whose elements include
the property names followed alternately by the corresponding values.
The return value is t if the function actually changed some property’s value; nilotherwise (if props is nil or its values agree with those in the text).
For example, here is how to set the comment and face properties of a range of text:(add-text-properties start end'(comment t face highlight))

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remove-text-properties start end props &optional object[Function]
This function deletes specified text properties from the text between start and end in
the string or buffer object. If object is nil, it defaults to the current buffer.
The argument props specifies which properties to delete. It should have the form ofa property list (see Section 5.9 [Property Lists], page 99): a list whose elements areproperty names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here’s how to remove theface property.
(remove-text-properties start end '(face nil))
The return value is t if the function actually changed some property’s value; nilotherwise (if props is nil or if no character in the specified text had any of those
properties).
To remove all text properties from certain text, use set-text-properties and specify
nil for the new property list.

remove-list-of-text-properties start end list-of-properties&optional object[Function]

Like remove-text-properties except that list-of-properties is a list of property
names only, not an alternating list of property names and values.

set-text-properties start end props &optional object[Function]
This function completely replaces the text property list for the text between start andend in the string or buffer object. If object is nil, it defaults to the current buffer.
The argument props is the new property list. It should be a list whose elements areproperty names alternating with corresponding values.
After set-text-properties returns, all the characters in the specified range haveidentical properties.
If props is nil, the effect is to get rid of all properties from the specified range of text.
Here’s an example:(set-text-properties start end nil)
Do not rely on the return value of this function.

add-face-text-property start end face &optional appendp object[Function]
This function acts on the text between start and end, adding the face face to the facetext property. face should be a valid value for the face property (see Section 33.19.4[Special Properties], page 924), such as a face name or an anonymous face (seeSection 41.12 [Faces], page 1164).
If any text in the region already has a non-nil face property, those face(s) are retained.
This function sets the face property to a list of faces, with face as the first element(by default) and the pre-existing faces as the remaining elements. If the optional
argument appendp is non-nil, face is appended to the end of the list instead. Notethat in a face list, the first occurring value for each attribute takes precedence.
For example, the following code would assign an italicized green face to the text
between start and end:
(add-face-text-property start end 'italic)

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(add-face-text-property start end '(:foreground "red"))(add-face-text-property start end '(:foreground "green"))
The optional argument object, if non-nil, specifies a buffer or string to act on, rather
than the current buffer. If object is a string, then start and end are zero-based indicesinto the string.
The easiest way to make a string with text properties is with propertize:

propertize string &rest properties[Function]
This function returns a copy of string with the text properties properties added. These
properties apply to all the characters in the string that is returned. Here is an example
that constructs a string with a face property and a mouse-face property:(propertize "foo" 'face 'italic'mouse-face 'bold-italic)⇒ #("foo" 0 3 (mouse-face bold-italic face italic))

To put different properties on various parts of a string, you can construct each partwith propertize and then combine them with concat:(concat(propertize "foo" 'face 'italic'mouse-face 'bold-italic)" and "
(propertize "bar" 'face 'italic'mouse-face 'bold-italic))⇒ #("foo and bar"
0 3 (face italic mouse-face bold-italic)
3 8 nil
8 11 (face italic mouse-face bold-italic))

See Section 33.2 [Buffer Contents], page 879, for the function buffer-substring-noproperties, which copies text from the buffer but does not copy its properties.
If you wish to add text properties to a buffer or remove them without marking the buffer
as modified, you can wrap the calls above in the with-silent-modifications macro. See
Section 28.5 [Buffer Modification], page 677.

33.19.3 Text Property Search Functions
In typical use of text properties, most of the time several or many consecutive characters havethe same value for a property. Rather than writing your programs to examine characters
one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for comparing property values.
In all cases, object defaults to the current buffer.
For good performance, it’s very important to use the limit argument to these functions,especially the ones that search for a single property—otherwise, they may spend a long timescanning to the end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or nil). Rememberthat a position is always between two characters; the position returned by these functions is
between two characters with different properties.

next-property-change pos &optional object limit[Function]
The function scans the text forward from position pos in the string or buffer object
until it finds a change in some text property, then returns the position of the change. In

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other words, it returns the position of the first character beyond pos whose properties
are not identical to those of the character just after pos.
If limit is non-nil, then the scan ends at position limit. If there is no property change
before that point, this function returns limit.
The value is nil if the properties remain unchanged all the way to the end of object
and limit is nil. If the value is non-nil, it is a position greater than or equal to pos.
The value equals pos only when limit equals pos.
Here is an example of how to scan the buffer by chunks of text within which allproperties are constant:(while (not (eobp))(let ((plist (text-properties-at (point)))(next-change(or (next-property-change (point) (current-buffer))(point-max))))
Process text from point to next-change . . .
(goto-char next-change)))previous-property-change pos &optional object limit[Function]
This is like next-property-change, but scans back from pos instead of forward. If
the value is non-nil, it is a position less than or equal to pos; it equals pos only if
limit equals pos.

next-single-property-change pos prop &optional object limit[Function]
The function scans text for a change in the prop property, then returns the positionof the change. The scan goes forward from position pos in the string or buffer object.
In other words, this function returns the position of the first character beyond pos
whose prop property differs from that of the character just after pos.
If limit is non-nil, then the scan ends at position limit. If there is no property change
before that point, next-single-property-change returns limit.
The value is nil if the property remains unchanged all the way to the end of object
and limit is nil. If the value is non-nil, it is a position greater than or equal to pos;it equals pos only if limit equals pos.

previous-single-property-change pos prop &optional object limit[Function]
This is like next-single-property-change, but scans back from pos instead offorward. If the value is non-nil, it is a position less than or equal to pos; it equals
pos only if limit equals pos.

next-char-property-change pos &optional limit[Function]
This is like next-property-change except that it considers overlay properties as wellas text properties, and if no change is found before the end of the buffer, it returns the
maximum buffer position rather than nil (in this sense, it resembles the corresponding
overlay function next-overlay-change, rather than next-property-change). Thereis no object operand because this function operates only on the current buffer. It
returns the next address at which either kind of property changes.

previous-char-property-change pos &optional limit[Function]
This is like next-char-property-change, but scans back from pos instead of forward,
and returns the minimum buffer position if no change is found.

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limit

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[Function]

This is like next-single-property-change except that it considers overlay properties
as well as text properties, and if no change is found before the end of the object, it
returns the maximum valid position in object rather than nil. Unlike next-charproperty-change, this function does have an object operand; if object is not a buffer,
only text-properties are considered.

previous-single-char-property-change pos prop &optional
object limit[Function]

This is like next-single-char-property-change, but scans back from pos insteadof forward, and returns the minimum valid position in object if no change is found.

text-property-any start end prop value &optional object[Function]
This function returns non-nil if at least one character between start and end has aproperty prop whose value is value. More precisely, it returns the position of the firstsuch character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions
are relative to object. The default for object is the current buffer.

text-property-not-all start end prop value &optional object[Function]
This function returns non-nil if at least one character between start and end does
not have a property prop with value value. More precisely, it returns the position of
the first such character. Otherwise, it returns nil.
The optional fifth argument, object, specifies the string or buffer to scan. Positions
are relative to object. The default for object is the current buffer.

text-property-search-forward prop &optional value predicate
not-current[Function]

Search for the next region of text whose property prop is a match for value (which
defaults to nil), according to predicate.
This function is modeled after search-forward (see Section 35.1 [String Search],
page 993) and friends, in that it moves point, but it also returns a structure that
describes the match instead of returning it in match-beginning and friends.
If the text property whose value is a match can’t be found, the function returns nil. If
it’s found, point is placed at the end of the region that has this matching text property,
and the function returns a prop-match structure with information about the match.
predicate can either be t (which is a synonym for equal), nil (which means “notequal”), or a predicate that will be called with two arguments: value and the value ofthe text property prop at the buffer position that is a candidate for a match. The
function should return non-nil if there’s a match, nil otherwise.
If not-current is non-nil, then if point is already in a region where we have a property
match, skip past that region and find the next region instead.
The prop-match structure has the following accessor functions: prop-matchbeginning (the start of the match), prop-match-end (the end of the match), andprop-match-value (the value of property at the start of the match).

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In the examples below, we use a buffer whose contents is:This is a bold and here’s bolditalic and this is the end.
That is, the “bold” words are the bold face, and the “italic” word is in the italic
face.
With point at the start:(while (setq match (text-property-search-forward 'face 'bold t))(push (buffer-substring (prop-match-beginning match)(prop-match-end match))words))
This will pick out all the words that use the bold face.
(while (setq match (text-property-search-forward 'face nil t))(push (buffer-substring (prop-match-beginning match)(prop-match-end match))words))
This will pick out all the bits that have no face properties, which will result in the list‘("This is a " "and here's " "and this is the end")’ (only in reverse order, since
we used push, see Section 5.5 [List Variables], page 85).
(while (setq match (text-property-search-forward 'face nil nil))(push (buffer-substring (prop-match-beginning match)(prop-match-end match))words))
This will pick out all the regions where face is set to something, but this is split up into
where the properties change, so the result here will be ‘("bold" "bold" "italic")’.
For a more realistic example where you might use this, consider that you have a buffer
where certain sections represent URLs, and these are tagged with shr-url.
(while (setq match (text-property-search-forward 'shr-url nil nil))(push (prop-match-value match) urls))
This will give you a list of all those URLs.

text-property-search-backward prop &optional value predicate
not-current[Function]

This is just like text-property-search-forward, but searches backward instead, andif a match is found, point is placed at the beginning of the matched region instead ofthe end.

33.19.4 Properties with Special Meanings
Here is a table of text property names that have special built-in meanings. The following
sections list a few additional special property names that control filling and property
inheritance. All other names have no standard meaning, and you can use them as you like.
Note: the properties composition, display, invisible and intangible can also cause
point to move to an acceptable place, after each Emacs command. See Section 22.6 [Adjusting
Point], page 439.
category

If a character has a category property, we call it the property category of thecharacter. It should be a symbol. The properties of this symbol serve as defaults
for the properties of the character.

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The face property controls the appearance of the character (see Section 41.12[Faces], page 1164). The value of the property can be the following:• A face name (a symbol or string).
• An anonymous face: a property list of the form (keyword value ...),
where each keyword is a face attribute name and value is a value for that
attribute.
• A list of faces. Each list element should be either a face name or an
anonymous face. This specifies a face which is an aggregate of the attributesof each of the listed faces. Faces occurring earlier in the list have higher
priority.
• A cons cell of the form (foreground-color . color-name) or(background-color . color-name). This specifies the foreground or
background color, similar to (:foreground color-name) or (:backgroundcolor-name). This form is supported for backward compatibility only, andshould be avoided.
• A cons cell of the form (:filtered filter face-spec), that specifies theface given by face-spec, but only if filter matches when the face is used for
display. The face-spec can use any of the forms mentioned above. The filter
should be of the form (:window param value), which matches for windows
whose parameter param is eq to value. If the variable face-filtersalways-match is non-nil, all face filters are deemed to have matched.
Font Lock mode (see Section 24.6 [Font Lock Mode], page 563) works in mostbuffers by dynamically updating the face property of characters based on thecontext.
The add-face-text-property function provides a convenient way to set thistext property. See Section 33.19.2 [Changing Properties], page 919.

font-lock-faceThis property specifies a value for the face property that Font Lock mode
should apply to the underlying text. It is one of the fontification methods usedby Font Lock mode, and is useful for special modes that implement their own
highlighting. See Section 24.6.6 [Precalculated Fontification], page 573. When
Font Lock mode is disabled, font-lock-face has no effect.
mouse-faceThis property is used instead of face when the mouse pointer hovers over the
text which has this property. When this happens, the entire stretch of textthat has the same mouse-face property value, not just the character under themouse, is highlighted.
Emacs ignores all face attributes from the mouse-face property that alter the
text size (e.g., :height, :weight, and :slant). Those attributes are always
the same as for the unhighlighted text.
cursor-faceThis property is similar to mouse-face, but it is used when point (not themouse) is inside text that has this property. The highlighting happens only
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cursor-face-highlight-nonselected-window is non-nil, the text withthis face is highlighted even if the window is not selected, similarly to what
highlight-nonselected-windows does for the region (see Section “The Markand the Region” in The GNU Emacs Manual).
fontifiedThis property says whether the text is ready for display. If nil, Emacs’s redisplay
routine calls the functions in fontification-functions (see Section 41.12.7[Auto Faces], page 1178) to prepare this part of the buffer before it is displayed.
It is used internally by the just-in-time font locking code.
displayThis property activates various features that change the way text is displayed.
For example, it can make text appear taller or shorter, higher or lower, wider
or narrow, or replaced with an image. See Section 41.16 [Display Property],
page 1198.

help-echo
If text has a string as its help-echo property, then when you move the mouseonto that text, Emacs displays that string in the echo area, or in the tooltip
window (see Section 41.26 [Tooltips], page 1249), after passing it throughsubstitute-command-keys.
If the value of the help-echo property is a function, that function is calledwith three arguments, window, object and pos and should return a help stringor nil for none. The first argument, window is the window in which the help
was found. The second, object, is the buffer, overlay or string which had thehelp-echo property. The pos argument is as follows:• If object is a buffer, pos is the position in the buffer.
• If object is an overlay, that overlay has a help-echo property, and pos is
the position in the overlay’s buffer.
• If object is a string (an overlay string or a string displayed with the display
property), pos is the position in that string.
If the value of the help-echo property is neither a function nor a string, it isevaluated to obtain a help string.
You can alter the way help text is displayed by setting the variable show-helpfunction (see [Help display], page 931).
This feature is used in the mode line and for other active text.
help-echo-inhibit-substitution
If the first character of a help-echo string has a non-nil help-echo-inhibitsubstitution property, then it is displayed as-is by show-help-function,
without being passed through substitute-command-keys.
keymap

The keymap property specifies an additional keymap for commands. When thiskeymap applies, it is used for key lookup before the minor mode keymaps andbefore the buffer’s local map. See Section 23.7 [Active Keymaps], page 489. If
the property value is a symbol, the symbol’s function definition is used as the
keymap.

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The property’s value for the character before point applies if it is non-nil andrear-sticky, and the property’s value for the character after point applies if it
is non-nil and front-sticky. (For mouse clicks, the position of the click is usedinstead of the position of point.)
local-map
This property works like keymap except that it specifies a keymap to use insteadof the buffer’s local map. For most purposes (perhaps all purposes), it is better
to use the keymap property.
syntax-table
The syntax-table property overrides what the syntax table says about thisparticular character. See Section 36.4 [Syntax Properties], page 1029.
read-only
If a character has the property read-only, then modifying that character is notallowed. Any command that would do so gets an error, text-read-only. If theproperty value is a string, that string is used as the error message.
Insertion next to a read-only character is an error if inserting ordinary text
there would inherit the read-only property due to stickiness. Thus, you cancontrol permission to insert next to read-only text by controlling the stickiness.
See Section 33.19.6 [Sticky Properties], page 932.
Since changing properties counts as modifying the buffer, it is not possible
to remove a read-only property unless you know the special trick: bindinhibit-read-only to a non-nil value and then remove the property. See
Section 28.7 [Read Only Buffers], page 680.
inhibit-read-only
Characters that have the property inhibit-read-only can be edited even inread-only buffers. See Section 28.7 [Read Only Buffers], page 680.
invisible
A non-nil invisible property can make a character invisible on the screen.
See Section 41.6 [Invisible Text], page 1142, for details.
inhibit-isearch
A non-nil inhibit-isearch property will make isearch skip the text.
intangible
If a group of consecutive characters have equal and non-nil intangible properties, then you cannot place point between them. If you try to move point
forward into the group, point actually moves to the end of the group. If you try
to move point backward into the group, point actually moves to the start of thegroup.
If consecutive characters have unequal non-nil intangible properties, they
belong to separate groups; each group is separately treated as described above.
When the variable inhibit-point-motion-hooks is non-nil (as it is by default),
the intangible property is ignored.
Beware: this property operates at a very low level, and affects a lot of codein unexpected ways. So use it with extreme caution. A common misuse is toChapter 33: Text

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put an intangible property on invisible text, which is actually unnecessary since
the command loop will move point outside of the invisible text at the end ofeach command anyway. See Section 22.6 [Adjusting Point], page 439. For thesereasons, this property is obsolete; use the cursor-intangible property instead.
cursor-intangible
When the minor mode cursor-intangible-mode is turned on, point is moved
away from any position that has a non-nil cursor-intangible property, just before redisplay happens. Note that “stickiness” of the property (see Section 33.19.6[Sticky Properties], page 932) is taken into account when computing allowed
cursor positions, so (for instance) to insert a stretch of five ‘x’ characters into
which the cursor can’t enter, you should do something like:(insert(propertize "xxxx" 'cursor-intangible t)(propertize "x" 'cursor-intangible t 'rear-nonsticky t))Whenthevariablecursor-sensor-inhibit
isnon-nil,thecursor-intangible
property
andthecursor-sensor-functions
property (described below) are ignored.
field

Consecutive characters with the same field property constitute a field. Somemotion functions including forward-word and beginning-of-line stop moving
at a field boundary. See Section 33.19.9 [Fields], page 936.

cursorNormally, the cursor is displayed at the beginning or the end of any overlay andtext property strings that “hide” (i.e., are displayed instead of) the current buffer
position. You can instead tell Emacs to place the cursor on any desired characterof these strings by giving that character a non-nil cursor text property. In
addition, if the value of the cursor property is an integer, it specifies the numberof buffer’s character positions, starting with the position where the overlay or
the display property begins, for which the cursor should be displayed on thatcharacter. Specifically, if the value of the cursor property of a character is thenumber n, the cursor will be displayed on this character for any buffer positionin the range [ovpos..ovpos+n), where ovpos is the overlay’s starting position
given by overlay-start (see Section 41.9.1 [Managing Overlays], page 1150),or the position where the display text property begins in the buffer.
In other words, the string character with the cursor property of any non-nil
value is the character where to display the cursor when the overlay or display
string make point not visible on display. The value of the property says forwhich buffer positions to display the cursor there. If the value is an integer n, thecursor is displayed there when point is anywhere between the beginning of theoverlay or display property and n positions after that. If the value is anythingelse and non-nil, the cursor is displayed there only when point is at the buffer
position that is the beginning of the display property, or at overlay-start ifthat position is not visible on display. Note that an integer value of the cursor
property could mean that the cursor is displayed on that character even whenpoint is visible on display.
One subtlety of this property is that it doesn’t work to put this property on a
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newline doesn’t have a graphic representation on the screen for Emacs to findwhen it looks for a character on display with that cursor property.
When the buffer has many overlay strings (e.g., see Section 41.9.2 [Overlay
Properties], page 1153) that conceal some of the buffer text or display properties
that are strings, it is a good idea to use the cursor property on these strings tocue the Emacs display about the places where to put the cursor while traversing
these strings. This directly communicates to the display engine where the Lisp
program wants to put the cursor, or where the user would expect the cursor,
when point is located on some buffer position that is “covered” by the display
or overlay string.
pointerThis specifies a specific pointer shape when the mouse pointer is over this text orimage. See Section 30.19 [Pointer Shape], page 839, for possible pointer shapes.

line-spacing
A newline can have a line-spacing text or overlay property that controls theheight of the display line ending with that newline. The property value overrides
the default frame line spacing and the buffer local line-spacing variable. See
Section 41.11 [Line Height], page 1162.
line-height
A newline can have a line-height text or overlay property that controls thetotal height of the display line ending in that newline. See Section 41.11 [LineHeight], page 1162.
wrap-prefix
If text has a wrap-prefix property, the prefix it defines will be added at display
time to the beginning of every continuation line due to text wrapping (so iflines are truncated, the wrap-prefix is never used). It may be a string or animage (see Section 41.16.4 [Other Display Specs], page 1203), or a stretch ofwhitespace such as specified by the :width or :align-to display properties (seeSection 41.16.2 [Specified Space], page 1200).
A wrap-prefix may also be specified for an entire buffer using the wrap-prefixbuffer-local variable (however, a wrap-prefix text-property takes precedence
over the value of the wrap-prefix variable). See Section 41.3 [Truncation],
page 1130.
line-prefix
If text has a line-prefix property, the prefix it defines will be added at display
time to the beginning of every non-continuation line. It may be a string or animage (see Section 41.16.4 [Other Display Specs], page 1203), or a stretch ofwhitespace such as specified by the :width or :align-to display properties (seeSection 41.16.2 [Specified Space], page 1200).
A line-prefix may also be specified for an entire buffer using the line-prefixbuffer-local variable (however, a line-prefix text-property takes precedence
over the value of the line-prefix variable). See Section 41.3 [Truncation],
page 1130.

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modification-hooks
If a character has the property modification-hooks, then its value should bea list of functions; modifying that character calls all of those functions before
the actual modification. Each function receives two arguments: the beginningand end of the part of the buffer being modified. Note that if a particularmodification hook function appears on several characters being modified by asingle primitive, you can’t predict how many times the function will be called.
Furthermore, insertion will not modify any existing character, so this hook will
only be run when removing some characters, replacing them with others, orchanging their text-properties.
Unlike with other similar hooks, when Emacs calls these functions,inhibit-modification-hooks does not get bound to non-nil. If the functions
modify the buffer, you should consider binding this variable to non-nil toprevent any buffer changes running the change hooks. Otherwise, you must be
prepared for recursive calls. See Section 33.34 [Change Hooks], page 961.
Overlays also support the modification-hooks property, but the details are
somewhat different (see Section 41.9.2 [Overlay Properties], page 1153).
insert-in-front-hooks
insert-behind-hooks
The operation of inserting text in a buffer also calls the functions listed in
the insert-in-front-hooks property of the following character and in theinsert-behind-hooks property of the preceding character. These functions
receive two arguments, the beginning and end of the inserted text. The functions
are called after the actual insertion takes place.
When these functions are called, inhibit-modification-hooks is boundto non-nil. If the functions modify the buffer, you might want to bindinhibit-modification-hooks to nil, so as to cause the change hooks to run
for these modifications. However, doing this may call your own change hookrecursively, so be sure to prepare for that.
See also Section 33.34 [Change Hooks], page 961, for other hooks that are called
when you change text in a buffer.
point-enteredpoint-left
The special properties point-entered and point-left record hook functions
that report motion of point. Each time point moves, Emacs compares these two
property values:• the point-left property of the character after the old location, and• the point-entered property of the character after the new location.
If these two values differ, each of them is called (if not nil) with two arguments:
the old value of point, and the new one.
The same comparison is made for the characters before the old and new locations.
The result may be to execute two point-left functions (which may be thesame function) and/or two point-entered functions (which may be the samefunction). In any case, all the point-left functions are called first, followed by
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It is possible to use char-after to examine characters at various buffer positions
without moving point to those positions. Only an actual change in the value ofpoint runs these hook functions.
The variable inhibit-point-motion-hooks by default inhibits running thepoint-left and point-entered hooks, see [Inhibit point motion hooks],
page 931.
These properties are obsolete; please use cursor-sensor-functions instead.
cursor-sensor-functions
This special property records a list of functions that react to cursor motion.
Each function in the list is called, just before redisplay, with 3 arguments: theaffected window, the previous known position of the cursor, and one of thesymbols entered or left, depending on whether the cursor is entering the textthat has this property or leaving it. The functions are called only when theminor mode cursor-sensor-mode is turned on.
When the variable cursor-sensor-inhibit is non-nil, the cursor-sensorfunctions property is ignored.
composition
This text property is used to display a sequence of characters as a single glyph
composed from components. But the value of the property itself is completelyinternal to Emacs and should not be manipulated directly by, for instance,
put-text-property.
minibuffer-message
This text property tells where to display temporary messages in an active
minibuffer. Specifically, the first character of the minibuffer text which has thisproperty will have the temporary message displayed before it. The default is todisplay temporary messages at the end of the minibuffer text. This text property
is used by the function that is the default value of set-message-function (seeSection 41.4.1 [Displaying Messages], page 1131).
[Variable]
When this obsolete variable is non-nil, point-left and point-entered hooks are
not run, and the intangible property has no effect. Do not set this variable globally;bind it with let. Since the affected properties are obsolete, this variable’s default
value is t, to effectively disable them.

inhibit-point-motion-hooks[Variable]
If this variable is non-nil, it specifies a function called to display help strings. Thesemay be help-echo properties, menu help strings (see Section 23.18.1.1 [Simple Menu
Items], page 510, see Section 23.18.1.2 [Extended Menu Items], page 511), or tool
bar help strings (see Section 23.18.6 [Tool Bar], page 517). The specified function
is called with one argument, the help string to display, which is passed throughsubstitute-command-keys before being given to the function, unless the help string
has a non-nil help-echo-inhibit-substitution property on its first character; see
Section 25.3 [Keys in Documentation], page 598. See the code of Tooltip mode (seeSection “Tooltips” in The GNU Emacs Manual) for an example of a mode that uses
show-help-function.

show-help-function

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[Variable]
If this variable is non-nil, face filters that specify attributes applied only when certain
conditions are met will be deemed to match always.

face-filters-always-match

33.19.5 Formatted Text Properties
These text properties affect the behavior of the fill commands. They are used for representing
formatted text. See Section 33.11 [Filling], page 899, and Section 33.12 [Margins], page 902.
hard

If a newline character has this property, it is a “hard” newline. The fill commands
do not alter hard newlines and do not move words across them. However, thisproperty takes effect only if the use-hard-newlines minor mode is enabled.
See Section “Hard and Soft Newlines” in The GNU Emacs Manual.

right-margin
This property specifies an extra right margin for filling this part of the text.
left-margin
This property specifies an extra left margin for filling this part of the text.
justification
This property specifies the style of justification for filling this part of the text.

33.19.6 Stickiness of Text Properties
Self-inserting characters, the ones that get inserted into a buffer when the user types them(see Section 33.5 [Commands for Insertion], page 884), normally take on the same properties
as the preceding character. This is called inheritance of properties.
By contrast, a Lisp program can do insertion with inheritance or without, depending on
the choice of insertion primitive. The ordinary text insertion functions, such as insert, do
not inherit any properties. They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text from one context toanother—for example, into or out of the kill ring. To insert with inheritance, use the special
primitives described in this section. Self-inserting characters inherit properties because theywork using these primitives.
When you do insertion with inheritance, which properties are inherited, and from where,
depends on which properties are sticky. Insertion after a character inherits those of its
properties that are rear-sticky. Insertion before a character inherits those of its properties
that are front-sticky. When both sides offer different sticky values for the same property,
the previous character’s value takes precedence.
By default, a text property is rear-sticky but not front-sticky; thus, the default is toinherit all the properties of the preceding character, and nothing from the following character.
You can control the stickiness of various text properties with two specific text properties, front-sticky and rear-nonsticky, and with the variable text-property-defaultnonsticky. You can use the variable to specify a different default for a given property. You
can use those two text properties to make any specific properties sticky or nonsticky in any
particular part of the text.
If a character’s front-sticky property is t, then all its properties are front-sticky. If thefront-sticky property is a list, then the sticky properties of the character are those whosenames are in the list. For example, if a character has a front-sticky property whose value

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is (face read-only), then insertion before the character can inherit its face property andits read-only property, but no others.
The rear-nonsticky property works the opposite way. Most properties are rear-sticky
by default, so the rear-nonsticky property says which properties are not rear-sticky. If acharacter’s rear-nonsticky property is t, then none of its properties are rear-sticky. If therear-nonsticky property is a list, properties are rear-sticky unless their names are in thelist.
[Variable]
This variable holds an alist which defines the default rear-stickiness of various text
properties. Each element has the form (property . nonstickiness), and it defines
the stickiness of a particular text property, property.
If nonstickiness is non-nil, this means that the property property is rear-nonsticky
by default. Since all properties are front-nonsticky by default, this makes property
nonsticky in both directions by default.
The text properties front-sticky and rear-nonsticky, when used, take precedence
over the default nonstickiness specified in text-property-default-nonsticky.

text-property-default-nonsticky

Here are the functions that insert text with inheritance of properties:

insert-and-inherit &rest strings[Function]
Insert the strings strings, just like the function insert, but inherit any sticky properties
from the adjoining text.

insert-before-markers-and-inherit &rest strings[Function]
Insert the strings strings, just like the function insert-before-markers, but inherit
any sticky properties from the adjoining text.

See Section 33.4 [Insertion], page 882, for the ordinary insertion functions which do notinherit.

33.19.7 Lazy Computation of Text Properties
Instead of computing text properties for all the text in the buffer, you can arrange tocompute the text properties for parts of the text when and if something depends on them.
The primitive that extracts text from the buffer along with its properties isbuffer-substring. Before examining the properties, this function runs the abnormal hookbuffer-access-fontify-functions.
[Variable]
This variable holds a list of functions for computing text properties. Before
buffer-substring copies the text and text properties for a portion of the buffer, itcalls all the functions in this list. Each of the functions receives two arguments thatspecify the range of the buffer being accessed. (The buffer itself is always the current
buffer.)buffer-access-fontify-functions

The function buffer-substring-no-properties does not call these functions, since itignores text properties anyway.
In order to prevent the hook functions from being called more than once for the same
part of the buffer, you can use the variable buffer-access-fontified-property.

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[Variable]
If this variable’s value is non-nil, it is a symbol which is used as a text property
name. A non-nil value for that text property means the other text properties for thischaracter have already been computed.

buffer-access-fontified-property

If all the characters in the range specified for buffer-substring have a non-nil value
for this property, buffer-substring does not call the buffer-access-fontifyfunctions functions. It assumes these characters already have the right text properties,
and just copies the properties they already have.
The normal way to use this feature is that the buffer-access-fontify-functions
functions add this property, as well as others, to the characters they operate on. Thatway, they avoid being called over and over for the same text.

33.19.8 Defining Clickable Text
Clickable text is text that can be clicked, with either the mouse or via a keyboard command, toproduce some result. Many major modes use clickable text to implement textual hyper-links,
or links for short.
The easiest way to insert and manipulate links is to use the button package. See
Section 41.20 [Buttons], page 1232. In this section, we will explain how to manually set up
clickable text in a buffer, using text properties. For simplicity, we will refer to the clickabletext as a link.
Implementing a link involves three separate steps: (1) indicating clickability when themouse moves over the link; (2) making RET or mouse-2 on that link do something; and (3)setting up a follow-link condition so that the link obeys mouse-1-click-follows-link.
To indicate clickability, add the mouse-face text property to the text of the link; thenEmacs will highlight the link when the mouse moves over it. In addition, you should define
a tooltip or echo area message, using the help-echo text property. See Section 33.19.4[Special Properties], page 924. For instance, here is how Dired indicates that file names areclickable:(if (dired-move-to-filename)(add-text-properties(point)(save-excursion(dired-move-to-end-of-filename)(point))'(mouse-face highlight
help-echo "mouse-2: visit this file in other window")))

To make the link clickable, bind RET and mouse-2 to commands that perform the desired
action. Each command should check to see whether it was called on a link, and act accordingly.
For instance, Dired’s major mode keymap binds mouse-2 to the following command:(defun dired-mouse-find-file-other-window (event)"In Dired, visit the file or directory name you click on."(interactive "e")(let ((window (posn-window (event-end event)))(pos (posn-point (event-end event)))
file)(if (not (windowp window))(error "No file chosen"))(with-current-buffer (window-buffer window)

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(goto-char pos)(setq file (dired-get-file-for-visit)))(if (file-directory-p file)(or (and (cdr dired-subdir-alist)(dired-goto-subdir file))(progn(select-window window)(dired-other-window file)))(select-window window)(find-file-other-window (file-name-sans-versions file t)))))

This command uses the functions posn-window and posn-point to determine where theclick occurred, and dired-get-file-for-visit to determine which file to visit.
Instead of binding the mouse command in a major mode keymap, you can bind it within
the link text, using the keymap text property (see Section 33.19.4 [Special Properties],
page 924). For instance:(let ((map (make-sparse-keymap)))(define-key map [mouse-2] 'operate-this-button)(put-text-property link-start link-end 'keymap map))
With this method, you can easily define different commands for different links. Furthermore,
the global definition of RET and mouse-2 remain available for the rest of the text in thebuffer.
The basic Emacs command for clicking on links is mouse-2. However, for compatibility
with other graphical applications, Emacs also recognizes mouse-1 clicks on links, provided
the user clicks on the link quickly without moving the mouse. This behavior is controlled
by the user option mouse-1-click-follows-link. See Section “Mouse References” in The
GNU Emacs Manual.
To set up the link so that it obeys mouse-1-click-follows-link, you must either (1)apply a follow-link text or overlay property to the link text, or (2) bind the follow-link
event to a keymap (which can be a major mode keymap or a local keymap specified via
the keymap text property). The value of the follow-link property, or the binding for thefollow-link event, acts as a condition for the link action. This condition tells Emacs twothings: the circumstances under which a mouse-1 click should be regarded as occurringinside the link, and how to compute an action code that says what to translate the mouse-1
click into. The link action condition can be one of the following:mouse-face
If the condition is the symbol mouse-face, a position is inside a link if there isa non-nil mouse-face property at that position. The action code is always t.
For example, here is how Info mode handles mouse-1:(keymap-set Info-mode-map "<follow-link>" 'mouse-face)a function If the condition is a function, func, then a position pos is inside a link if (funcpos) evaluates to non-nil. The value returned by func serves as the actioncode.
For example, here is how pcvs enables mouse-1 to follow links on file names
only:(keymap-set map "<follow-link>"(lambda (pos)(eq (get-char-property pos 'face) 'cvs-filename-face)))Chapter 33: Text

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anything else
If the condition value is anything else, then the position is inside a link andthe condition itself is the action code. Clearly, you should specify this kind of
condition only when applying the condition via a text or overlay property on
the link text (so that it does not apply to the entire buffer).
The action code tells mouse-1 how to follow the link:a string or vector
If the action code is a string or vector, the mouse-1 event is translated into thefirst element of the string or vector; i.e., the action of the mouse-1 click is the
local or global binding of that character or symbol. Thus, if the action code is"foo", mouse-1 translates into f. If it is [foo], mouse-1 translates into foo.
anything else
For any other non-nil action code, the mouse-1 event is translated into amouse-2 event at the same position.
To define mouse-1 to activate a button defined with define-button-type, give thebutton a follow-link property. The property value should be a link action condition, as
described above. See Section 41.20 [Buttons], page 1232. For example, here is how Helpmode handles mouse-1:(define-button-type 'help-xref'follow-link t'action #'help-button-action)

To define mouse-1 on a widget defined with define-widget, give the widget a:follow-link property. The property value should be a link action condition, as describedabove. For example, here is how the link widget specifies that a mouse-1 click shall betranslated to RET:
(define-widget 'link 'item"An embedded link.":button-prefix 'widget-link-prefix:button-suffix 'widget-link-suffix:follow-link "\C-m":help-echo "Follow the link.":format "%[%t%]")mouse-on-link-p pos[Function]
This function returns non-nil if position pos in the current buffer is on a link. pos
can also be a mouse event location, as returned by event-start (see Section 22.7.15[Accessing Mouse], page 456).

33.19.9 Defining and Using Fields
A field is a range of consecutive characters in the buffer that are identified by having thesame value (comparing with eq) of the field property (either a text-property or an overlay
property). This section describes special functions that are available for operating on fields.
You specify a field with a buffer position, pos. We think of each field as containing a
range of buffer positions, so the position you specify stands for the field containing that
position.
When the characters before and after pos are part of the same field, there is no doubt
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between fields, which field it belongs to depends on the stickiness of the field properties of
the two surrounding characters (see Section 33.19.6 [Sticky Properties], page 932). The field
whose property would be inherited by text inserted at pos is the field that contains pos.
There is an anomalous case where newly inserted text at pos would not inherit the field
property from either side. This happens if the previous character’s field property is notrear-sticky, and the following character’s field property is not front-sticky. In this case,pos belongs to neither the preceding field nor the following field; the field functions treat it
as belonging to an empty field whose beginning and end are both at pos.
In all of these functions, if pos is omitted or nil, the value of point is used by default. If
narrowing is in effect, then pos should fall within the accessible portion. See Section 31.4
[Narrowing], page 865.

field-beginning &optional pos escape-from-edge limit[Function]

This function returns the beginning of the field specified by pos.
If pos is at the beginning of its field, and escape-from-edge is non-nil, then the return
value is always the beginning of the preceding field that ends at pos, regardless of the
stickiness of the field properties around pos.
If limit is non-nil, it is a buffer position; if the beginning of the field is before limit,
then limit will be returned instead.

field-end &optional pos escape-from-edge limit[Function]

This function returns the end of the field specified by pos.
If pos is at the end of its field, and escape-from-edge is non-nil, then the return value
is always the end of the following field that begins at pos, regardless of the stickinessof the field properties around pos.
If limit is non-nil, it is a buffer position; if the end of the field is after limit, thenlimit will be returned instead.

field-string &optional pos[Function]
This function returns the contents of the field specified by pos, as a string.

field-string-no-properties &optional pos[Function]
This function returns the contents of the field specified by pos, as a string, discarding
text properties.

delete-field &optional pos[Function]

This function deletes the text of the field specified by pos.

constrain-to-field new-pos old-pos &optional escape-from-edge
only-in-line inhibit-capture-property[Function]

This function constrains new-pos to the field that old-pos belongs to—in other words,
it returns the position closest to new-pos that is in the same field as old-pos.
If new-pos is nil, then constrain-to-field uses the value of point instead, andmoves point to the resulting position in addition to returning that position.
If old-pos is at the boundary of two fields, then the acceptable final positions dependon the argument escape-from-edge. If escape-from-edge is nil, then new-pos must
be in the field whose field property equals what new characters inserted at old-pos

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would inherit. (This depends on the stickiness of the field property for the characters
before and after old-pos.) If escape-from-edge is non-nil, new-pos can be anywhere in
the two adjacent fields. Additionally, if two fields are separated by another field withthe special value boundary, then any point within this special field is also considered
to be on the boundary.
Commands like C-a with no argument, that normally move backward to a specific kindof location and stay there once there, probably should specify nil for escape-from-edge.
Other motion commands that check fields should probably pass t.
If the optional argument only-in-line is non-nil, and constraining new-pos in theusual way would move it to a different line, new-pos is returned unconstrained. This
used in commands that move by line, such as next-line and beginning-of-line, sothat they respect field boundaries only in the case where they can still move to theright line.
If the optional argument inhibit-capture-property is non-nil, and old-pos has a
non-nil property of that name, then any field boundaries are ignored.
You can cause constrain-to-field to ignore all field boundaries (and so neverconstrain anything) by binding the variable inhibit-field-text-motion to a nonnil value.

33.19.10 Why Text Properties are not Intervals
Some editors that support adding attributes to text in the buffer do so by letting the user
specify intervals within the text, and adding the properties to the intervals. Those editors
permit the user or the programmer to determine where individual intervals start and end. We
deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical
behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguishbetween a buffer that is just one interval with a certain property, and a buffer containing
the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text
remaining in the buffer is one interval, and the copy in the kill ring (and the undo list)
becomes a separate interval. Then if you yank back the killed text, you get two intervals withthe same properties. Thus, editing does not preserve the distinction between one interval
and two.
Suppose we attempt to fix this problem by coalescing the two intervals when the text isinserted. That works fine if the buffer originally was a single interval. But suppose insteadthat we have two adjacent intervals with the same properties, and we kill the text of one
interval and yank it back. The same interval-coalescence feature that rescues the other casecauses trouble in this one: after yanking, we have just one interval. Once again, editing does
not preserve the distinction between one interval and two.
Insertion of text at the border between intervals also raises questions that have nosatisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form,“What are the properties of text at this buffer or string position?” So we have decided these
are the only questions that make sense; we have not implemented asking questions about
where intervals start or end.

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In practice, you can usually use the text property search functions in place of explicit
interval boundaries. You can think of them as finding the boundaries of intervals, assumingthat intervals are always coalesced whenever possible. See Section 33.19.3 [Property Search],
page 921.
Emacs also provides explicit intervals as a presentation feature; see Section 41.9 [Overlays],
page 1150.

33.20 Substituting for a Character CodeThe following functions replace characters within a specified region based on their charactercodes.

subst-char-in-region start end old-char new-char &optional
noundo[Function]

This function replaces all occurrences of the character old-char with the character
new-char in the region of the current buffer defined by start and end. Both charactersmust have the same length of their multibyte form.
If noundo is non-nil, then subst-char-in-region does not record the change forundo and does not mark the buffer as modified. This was useful for controlling theold selective display feature (see Section 41.7 [Selective Display], page 1145).
subst-char-in-region does not move point and returns nil.
---------- Buffer: foo ---------This is the contents of the buffer before.
---------- Buffer: foo ---------(subst-char-in-region 1 20 ?i ?X)⇒ nil---------- Buffer: foo ---------ThXs Xs the contents of the buffer before.
---------- Buffer: foo ----------

subst-char-in-string fromchar tochar string &optional inplace[Function]
This function replaces all occurrences of the character fromchar with tochar in string.
By default, substitution occurs in a copy of string, but if the optional argument inplaceis non-nil, the function modifies the string itself. In any case, the function returns
the resulting string.

translate-region start end table[Command]This function applies a translation table to the characters in the buffer between
positions start and end.
The translation table table is a string or a char-table; (aref table ochar) gives thetranslated character corresponding to ochar. If table is a string, any characters withcodes larger than the length of table are not altered by the translation.
The return value of translate-region is the number of characters that were actuallychanged by the translation. This does not count characters that were mapped into
themselves in the translation table.

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33.21 Registers
A register is a sort of variable used in Emacs editing that can hold a variety of different
kinds of values. Each register is named by a single character. All ASCII characters and theirmeta variants (but with the exception of C-g) can be used to name registers. Thus, there
are 255 possible registers. A register is designated in Emacs Lisp by the character that is its
name.
[Variable]
This variable is an alist of elements of the form (name . contents). Normally, there
is one element for each Emacs register that has been used.

register-alist

The object name is a character (an integer) identifying the register.
The contents of a register can have several possible types:
a number

A number stands for itself. If insert-register finds a number in the register,
it converts the number to decimal.

a markerA marker represents a buffer position to jump to.

a string

A string is text saved in the register.

a rectangle
A rectangle is represented by a list of strings.
(window-configuration position)
This represents a window configuration to restore in one frame, and a position
to jump to in the current buffer.
(frame-configuration position)
This represents a frame configuration to restore, and a position to jump to in
the current buffer. Frame configurations are also known as framesets.
(file filename)
This represents a file to visit; jumping to this value visits file filename.
(file-query filename position)
This represents a file to visit and a position in it; jumping to this value visits
file filename and goes to buffer position position. Restoring this type of position
asks the user for confirmation first.
(buffer buffer-name)
This represents a buffer; jumping to this value switches to buffer buffer-name.
The functions in this section return unpredictable values unless otherwise stated.

get-register reg[Function]
This function returns the contents of the register reg, or nil if it has no contents.

set-register reg value[Function]
This function sets the contents of register reg to value. A register can be set to any
value, but the other register functions expect only certain data types. The return
value is value.

Chapter 33: Text

view-register reg

941[Command]This command displays what is contained in register reg.

insert-register reg &optional beforep[Command]This command inserts contents of register reg into the current buffer.
Normally, this command puts point before the inserted text, and the mark after it.
However, if the optional second argument beforep is non-nil, it puts the mark before
and point after.
When called interactively, the command defaults to putting point after text, and aprefix argument inverts this behavior.
If the register contains a rectangle, then the rectangle is inserted with its upper left
corner at point. This means that text is inserted in the current line and underneath iton successive lines.
If the register contains something other than saved text (a string) or a rectangle (alist), currently useless things happen. This may be changed in the future.

register-read-with-preview prompt[Function]
This function reads and returns a register name, prompting with prompt and possibly
showing a preview of the existing registers and their contents. The preview is shown ina temporary window, after the delay specified by the user option register-previewdelay, if its value and register-alist are both non-nil. The preview is also shown
if the user requests help (e.g., by typing the help character). We recommend that allinteractive commands which read register names use this function.

33.22 Transposition of Text
This function can be used to transpose stretches of text:transpose-regions start1 end1 start2 end2 &optional leave-markers[Function]
This function exchanges two nonoverlapping portions of the buffer (if they overlap,
the function signals an error). Arguments start1 and end1 specify the bounds of one
portion and arguments start2 and end2 specify the bounds of the other portion.
Normally, transpose-regions relocates markers with the transposed text; a marker
previously positioned within one of the two transposed portions moves along withthat portion, thus remaining between the same two characters in their new position.
However, if leave-markers is non-nil, transpose-regions does not do this—it leaves
all markers unrelocated.

33.23 Replacing Buffer Text
You can use the following function to replace the text of one buffer with the text of anotherbuffer:replace-buffer-contents source &optional max-secs max-costs[Command]This function replaces the accessible portion of the current buffer with the accessible
portion of the buffer source. source may either be a buffer object or the name of abuffer. When replace-buffer-contents succeeds, the text of the accessible portion

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of the current buffer will be equal to the text of the accessible portion of the source
buffer.
This function attempts to keep point, markers, text properties, and overlays in thecurrent buffer intact. One potential case where this behavior is useful is external
code formatting programs: they typically write the reformatted text into a temporary
buffer or file, and using delete-region and insert-buffer-substring would destroy
these properties. However, the latter combination is typically faster (See Section 33.6
[Deletion], page 886, and Section 33.4 [Insertion], page 882).
For its working, replace-buffer-contents needs to compare the contents of theoriginal buffer with that of source which is a costly operation if the buffers arehuge and there is a high number of differences between them. In order to keep
replace-buffer-contents’s runtime in bounds, it has two optional arguments.
max-secs defines a hard boundary in terms of seconds. If given and exceeded, it will
fall back to delete-region and insert-buffer-substring.
max-costs defines the quality of the difference computation. If the actual costs exceed
this limit, heuristics are used to provide a faster but suboptimal solution. The default
value is 1000000.
replace-buffer-contents returns t if a non-destructive replacement could be performed. Otherwise, i.e., if max-secs was exceeded, it returns nil.

replace-region-contents beg end replace-fn &optional max-secs
max-costs[Function]

This function replaces the region between beg and end using the given replace-fn. The
function replace-fn is run in the current buffer narrowed to the specified region and it
should return either a string or a buffer replacing the region.
The replacement is performed using replace-buffer-contents (see above) which
also describes the max-secs and max-costs arguments and the return value.
Note: If the replacement is a string, it will be placed in a temporary buffer sothat replace-buffer-contents can operate on it. Therefore, if you already havethe replacement in a buffer, it makes no sense to convert it to a string using
buffer-substring or similar.

33.24 Dealing With Compressed Data
When auto-compression-mode is enabled, Emacs automatically uncompresses compressed
files when you visit them, and automatically recompresses them if you alter and save them.
See Section “Compressed Files” in The GNU Emacs Manual.
The above feature works by calling an external executable (e.g., gzip). Emacs can also
be compiled with support for built-in decompression using the zlib library, which is fasterthan calling an external program.

zlib-available-p[Function]

This function returns non-nil if built-in zlib decompression is available.

zlib-decompress-region start end &optional allow-partial[Function]
This function decompresses the region between start and end, using built-in zlib
decompression. The region should contain data that were compressed with gzip or zlib.

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On success, the function replaces the contents of the region with the decompressed
data. If allow-partial is nil or omitted, then on failure, the function leaves the region
unchanged and returns nil. Otherwise, it returns the number of bytes that were
not decompressed and replaces the region text by whatever data was successfully
decompressed. This function can be called only in unibyte buffers.

33.25 Base 64 Encoding
Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of
ASCII graphic characters. It is defined in Internet RFC1 2045 and also in RFC 4648. Thissection describes the functions for converting to and from this code.

base64-encode-region beg end &optional no-line-break[Command]This function converts the region from beg to end into base 64 code. It returns thelength of the encoded text. An error is signaled if a character in the region is multibyte,i.e., in a multibyte buffer the region must contain only ASCII characters or raw bytes.
Normally, this function inserts newline characters into the encoded text, to avoid
overlong lines. However, if the optional argument no-line-break is non-nil, these
newlines are not added, so the output is just one long line.

base64url-encode-region beg end &optional no-pad[Command]This function is like base64-encode-region, but it implements the URL variant ofbase 64 encoding, per RFC 4648, and it doesn’t insert newline characters into theencoded text, so the output is just one long line.
If the optional argument no-pad is non-nil then this function doesn’t generate thepadding (=).

base64-encode-string string &optional no-line-break[Function]
This function converts the string string into base 64 code. It returns a string containing
the encoded text. As for base64-encode-region, an error is signaled if a characterin the string is multibyte.
Normally, this function inserts newline characters into the encoded text, to avoid
overlong lines. However, if the optional argument no-line-break is non-nil, these
newlines are not added, so the result string is just one long line.

base64url-encode-string string &optional no-pad[Function]
Like base64-encode-string, but generates the URL variant of base 64, and doesn’t
insert newline characters into the encoded text, so the result is just one long line.
If the optional argument no-pad is non-nil then this function doesn’t generate thepadding.

base64-decode-region beg end &optional base64url ignore-invalid[Command]This function converts the region from beg to end from base 64 code into the corresponding decoded text. It returns the length of the decoded text.

1

An RFC, an acronym for Request for Comments, is a numbered Internet informational document
describing a standard. RFCs are usually written by technical experts acting on their own initiative, andare traditionally written in a pragmatic, experience-driven manner.

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The decoding functions ignore newline characters in the encoded text.
If optional argument base64url is non-nil, then padding is optional, and the URL
variant of base 64 encoding is used. If optional argument ignore-invalid is non-nil,then any unrecognized characters are ignored.

base64-decode-string string &optional base64url ignore-invalid[Function]
This function converts the string string from base 64 code into the corresponding
decoded text. It returns a unibyte string containing the decoded text.
The decoding functions ignore newline characters in the encoded text.
If optional argument base64url is non-nil, then padding is optional, and the URL
variant of base 64 encoding is used. If optional argument ignore-invalid is non-nil,then any unrecognized characters are ignored.

33.26 Checksum/Hash
Emacs has built-in support for computing cryptographic hashes. A cryptographic hash, orchecksum, is a digital fingerprint of a piece of data (e.g., a block of text) which can be used
to check that you have an unaltered copy of that data.
Emacs supports several common cryptographic hash algorithms: MD5, SHA-1, SHA-2,
SHA-224, SHA-256, SHA-384 and SHA-512. MD5 is the oldest of these algorithms, andis commonly used in message digests to check the integrity of messages transmitted overa network. MD5 and SHA-1 are not collision resistant (i.e., it is possible to deliberately
design different pieces of data which have the same MD5 or SHA-1 hash), so you should not
use them for anything security-related. For security-related applications you should use theother hash types, such as SHA-2 (e.g. sha256 or sha512).
[Function]
This function returns a list of symbols representing algorithms that secure-hash canuse.

secure-hash-algorithms

secure-hash algorithm object &optional start end binary[Function]
This function returns a hash for object. The argument algorithm is a symbol stating
which hash to compute: one of md5, sha1, sha224, sha256, sha384 or sha512. The
argument object should be a buffer or a string.
The optional arguments start and end are character positions specifying the portionof object to compute the message digest for. If they are nil or omitted, the hash iscomputed for the whole of object.
If the argument binary is omitted or nil, the function returns the text form of thehash, as an ordinary Lisp string. If binary is non-nil, it returns the hash in binary
form, as a sequence of bytes stored in a unibyte string. The length of the returned
string depends on algorithm:• For md5: 32 characters (32 bytes if binary is non-nil).
• For sha1: 40 characters (40 bytes if binary is non-nil).
• For sha224: 56 characters (56 bytes if binary is non-nil).
• For sha256: 64 characters (64 bytes if binary is non-nil).
• For sha384: 96 characters (96 bytes if binary is non-nil).

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• For sha512: 128 characters (128 bytes if binary is non-nil).
This function does not compute the hash directly from the internal representation of
object’s text (see Section 34.1 [Text Representations], page 963). Instead, it encodes
the text using a coding system (see Section 34.10 [Coding Systems], page 976), andcomputes the hash from that encoded text. If object is a buffer, the coding systemused is the one which would be chosen by default for writing the text of that buffer
into a file. If object is a string, the user’s preferred coding system is used (see Section“Recognize Coding” in GNU Emacs Manual).

md5 object &optional start end coding-system noerror[Function]
This function returns an MD5 hash. It is semi-obsolete, since for most purposes it isequivalent to calling secure-hash with md5 as the algorithm argument. The object,
start and end arguments have the same meanings as in secure-hash. The function
returns a 32-character string.
If coding-system is non-nil, it specifies a coding system to use to encode the text; ifomitted or nil, the default coding system is used, like in secure-hash.
Normally, md5 signals an error if the text can’t be encoded using the specified orchosen coding system. However, if noerror is non-nil, it silently uses raw-text coding
instead.

buffer-hash &optional buffer-or-name[Function]
Return a hash of buffer-or-name. If nil, this defaults to the current buffer. As
opposed to secure-hash, this function computes the hash based on the internal
representation of the buffer, disregarding any coding systems. It’s therefore only usefulwhen comparing two buffers running in the same Emacs, and is not guaranteed toreturn the same hash between different Emacs versions. It should be somewhat more
efficient on larger buffers than secure-hash is, and should not allocate more memory.

sha1 object &optional start end binary[Function]

This function is equivalent to calling secure-hash like this:(secure-hash 'sha1 object start end binary)
It returns a 40-character string if binary is nil, or a 40-byte unibyte string otherwise.

33.27 Suspicious Text
Emacs can display text from many external sources, like email and Web sites. Attackers may
attempt to confuse the user reading this text by using obfuscated URLs or email addresses,
and tricking the user into visiting a web page they didn’t intend to visit, or sending an email
to the wrong address.
This usually involves using characters from scripts that visually look like ASCII characters(i.e., are homoglyphs), but there are also other techniques used, like using bidirectional
overrides, or having an HTML link text that says one thing, while the underlying URL points
somewhere else.
To help identify these suspicious text strings, Emacs provides a library to do a numberof checks on text. (See UTS #39: Unicode Security Mechanisms (https://www.unicode.
org/reports/tr39/) for the rationale behind the checks that are available and more details

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about them.) Packages that present data that might be suspicious should use this library to
flag suspicious text on display.

textsec-suspicious-p object type

[Function]
This function is the high-level interface function that packages should use. It respects
the textsec-check user option, which allows the user to disable the checks.
This function checks object (whose data type depends on type) to see if it looks suspicious when interpreted as a thing of type. The available types and the corresponding
object data types are:domainCheck whether a domain (e.g., ‘www.gnu.org’ looks suspicious. object
should be a string, the domain name.

url

Check whether an URL (e.g., ‘http://gnu.org/foo/bar’) looks suspicious. object should be a string, the URL to check.

link

Check whether an HTML link (e.g., ‘<a href='http://gnu.org'>fsf.org</a>’looks suspicious. In this case, object should be a cons cell where thecar is the URL string, and the cdr is the link text. The link is deemedsuspicious if the link text contains a domain name, and that domainname points to something other than the URL.

email-address
Check whether an email address (e.g., ‘foo@example.org’) looks suspicious. object should be a string.
local-address
Check whether the local part of an email address (the bit before the ‘@’sign) looks suspicious. object should be a string.
name

Check whether a name (used in an email address header) looks suspicious.
object should be a string.

email-address-header
Check whether a full RFC2822 email address header (e.g.,‘=?utf-8?Q?=C3=81?= <foo@example.com>’) looks suspicious. object
should be a string.
If object is suspicious, this function returns a string that explains why it is suspicious.
If object is not suspicious, the function returns nil.
If the text is suspicious, the application should mark the suspicious text with thetextsec-suspicious face, and make the explanation returned by textsec-suspicious-p
available to the user in some way (for example, in a tooltip). The application might also
prompt the user for confirmation before taking any action on a suspicious string (like sending
an email to a suspicious email address).

33.28 GnuTLS Cryptography
If compiled with GnuTLS, Emacs offers built-in cryptographic support. Following the
GnuTLS API terminology, the available tools are digests, MACs, symmetric ciphers, and
AEAD ciphers.

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The terms used herein, such as IV (Initialization Vector), require some familiarity withcryptography and will not be defined in detail. Please consult https://www.gnutls.org/
for specific documentation which may help you understand the terminology and structure of
the GnuTLS library.

33.28.1 Format of GnuTLS Cryptography Inputs
The inputs to GnuTLS cryptographic functions can be specified in several ways, both asprimitive Emacs Lisp types or as lists.
The list form is currently similar to how md5 and secure-hash operate.
buffer

Simply passing a buffer as input means the whole buffer should be used.

stringA string as input will be used directly. It may be modified by the function(unlike most other Emacs Lisp functions) to reduce the chance of exposing
sensitive data after the function does its work.

(buffer-or-string start end coding-system noerror)
This specifies a buffer or a string as described above, but an optional range canbe specified with start and end.
In addition an optional coding-system can be specified if needed.
The last optional item, noerror, overrides the normal error when the text can’t be
encoded using the specified or chosen coding system. When noerror is non-nil,this function silently uses raw-text coding instead.
(iv-auto length)
This generates a random IV (Initialization Vector) of the specified length andpasses it to the function. This ensures that the IV is unpredictable and unlikely
to be reused in the same session.

33.28.2 GnuTLS Cryptographic Functions[Function]
This function returns the alist of the GnuTLS digest algorithms.
Each entry has a key which represents the algorithm, followed by a plist with internal
details about the algorithm. The plist will have :type gnutls-digest-algorithm
and also will have the key :digest-algorithm-length 64 to indicate the size, in
bytes, of the resulting digest.
There is a name parallel between GnuTLS MAC and digest algorithms but they areseparate things internally and should not be mixed.

gnutls-digests

gnutls-hash-digest digest-method input[Function]
The digest-method can be the whole plist from gnutls-digests, or just the symbol
key, or a string with the name of that symbol.
The input can be specified as a buffer or string or in other ways (see Section 33.28.1[Format of GnuTLS Cryptography Inputs], page 947).
This function returns nil on error, and signals a Lisp error if the digest-method or
input are invalid. On success, it returns a list of a binary string (the output) and the
IV used.

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948[Function]

This function returns the alist of the GnuTLS MAC algorithms.
Each entry has a key which represents the algorithm, followed by a plist with internal
details about the algorithm. The plist will have :type gnutls-mac-algorithm
and also will have the keys :mac-algorithm-length :mac-algorithm-keysize:mac-algorithm-noncesize to indicate the size, in bytes, of the resulting hash, thekey, and the nonce respectively.
The nonce is currently unused and only some MACs support it.
There is a name parallel between GnuTLS MAC and digest algorithms but they areseparate things internally and should not be mixed.

gnutls-hash-mac hash-method key input[Function]
The hash-method can be the whole plist from gnutls-macs, or just the symbol key,or a string with the name of that symbol.
The key can be specified as a buffer or string or in other ways (see Section 33.28.1[Format of GnuTLS Cryptography Inputs], page 947). The key will be wiped after
use if it’s a string.
The input can be specified as a buffer or string or in other ways (see Section 33.28.1[Format of GnuTLS Cryptography Inputs], page 947).
This function returns nil on error, and signals a Lisp error if the hash-method or key
or input are invalid.
On success, it returns a list of a binary string (the output) and the IV used.

gnutls-ciphers[Function]

This function returns the alist of the GnuTLS ciphers.
Each entry has a key which represents the cipher, followed by a plist with internal details
about the algorithm. The plist will have :type gnutls-symmetric-cipher and also
will have the keys :cipher-aead-capable set to nil or t to indicate AEAD capability;and :cipher-tagsize :cipher-blocksize :cipher-keysize :cipher-ivsize toindicate the size, in bytes, of the tag, block size of the resulting data, the key, and the
IV respectively.

gnutls-symmetric-encrypt cipher key iv input &optional aead auth[Function]
The cipher can be the whole plist from gnutls-ciphers, or just the symbol key, or astring with the name of that symbol.
The key can be specified as a buffer or string or in other ways (see Section 33.28.1[Format of GnuTLS Cryptography Inputs], page 947). The key will be wiped after
use if it’s a string.
The iv and input and the optional aead auth can be specified as a buffer or string or inother ways (see Section 33.28.1 [Format of GnuTLS Cryptography Inputs], page 947).
aead auth is only checked with AEAD ciphers, that is, ciphers whose plist has:cipher-aead-capable t. Otherwise it’s ignored.
This function returns nil on error, and signals a Lisp error if the cipher or key, iv, or
input are invalid, or if aead auth was specified with an AEAD cipher and was invalid.
On success, it returns a list of a binary string (the output) and the IV used.

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gnutls-symmetric-decrypt cipher key iv input &optional aead auth[Function]
The cipher can be the whole plist from gnutls-ciphers, or just the symbol key, or astring with the name of that symbol.
The key can be specified as a buffer or string or in other ways (see Section 33.28.1[Format of GnuTLS Cryptography Inputs], page 947). The key will be wiped after
use if it’s a string.
The iv and input and the optional aead auth can be specified as a buffer or string or inother ways (see Section 33.28.1 [Format of GnuTLS Cryptography Inputs], page 947).
aead auth is only checked with AEAD ciphers, that is, ciphers whose plist has:cipher-aead-capable t. Otherwise it’s ignored.
This function returns nil on decryption error, and signals a Lisp error if the cipher or
key, iv, or input are invalid, or if aead auth was specified with an AEAD cipher andwas invalid.
On success, it returns a list of a binary string (the output) and the IV used.

33.29 Database
Emacs can be compiled with built-in support for accessing SQLite databases. This section
describes the facilities available for accessing SQLite databases from Lisp programs.
[Function]
The function returns non-nil if built-in SQLite support is available in this Emacs
session.

sqlite-available-p

When SQLite support is available, the following functions can be used.

sqlite-open &optional file

[Function]
This function opens file as an SQLite database file. If file doesn’t exist, a new database
will be created and stored in that file. If file is omitted or nil, a new in-memory
database is created instead.
The return value is a database object that can be used as the argument to most of
the subsequent functions described below.

sqlitep object[Function]
This predicate returns non-nil if object is an SQLite database object. The databaseobject returned by the sqlite-open function satisfies this predicate.

sqlite-close db[Function]
Close the database db. It’s usually not necessary to call this function explicitly—the
database will automatically be closed if Emacs shuts down or the database object isgarbage collected.

sqlite-execute db statement &optional values[Function]

Execute the SQL statement. For instance:(sqlite-execute db "insert into foo values ('bar', 2)")
If the optional values parameter is present, it should be either a list or a vector ofvalues to bind while executing the statement. For instance:(sqlite-execute db "insert into foo values (?, ?)" '("bar" 2))Chapter 33: Text

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This has exactly the same effect as the previous example, but is more efficient andsafer (because it doesn’t involve any string parsing or interpolation).
sqlite-execute usually returns the number of affected rows. For instance,
an ‘insert’ statement will typically return ‘1’, whereas an ‘update’ statement
may return zero or a higher number. However, when using SQL statements
like ‘insert into ... returning ...’ and the like, the values specified by‘returning ...’ will be returned instead.
Strings in SQLite are, by default, stored as utf-8, and selecting a text column will
decode the string using that charset. Selecting a blob column will return the raw
data without any decoding (i.e., it will return a unibyte string containing the bytes as
stored in the database). Inserting binary data into blob columns, however, requires
some care, as sqlite-execute will, by default, interpret all strings as utf-8.
So if you have, for instance, GIF data in a unibyte string called gif, you have to markit specially to let sqlite-execute know this:(put-text-property 0 1 'coding-system 'binary gif)(sqlite-execute db "insert into foo values (?, ?)" (list gif 2))

sqlite-select db query &optional values return-type[Function]

Select some data from db and return them. For instance:(sqlite-select db "select * from foo where key = 2")⇒ (("bar" 2))As with the sqlite-execute, you can optionally pass in a list or a vector of values
that will be bound before executing the select:(sqlite-select db "select * from foo where key = ?" [2])⇒ (("bar" 2))This is usually more efficient and safer than the method used by the previous example.
By default, this function returns a list of matching rows, where each row is a list ofcolumn values. If return-type is full, the names of the columns (as a list of strings)
will be returned as the first element in the return value.
If return-type is set, this function will return a statement object instead. This object
can be examined by using the sqlite-next, sqlite-columns and sqlite-more-pfunctions. If the result set is small, it’s often more convenient to just return the data
directly, but if the result set is large (or if you won’t be using all the data from theset), using the set method will allocate a lot less memory, and is therefore morememory-efficient.

sqlite-next statement[Function]
This function returns the next row in the result set statement, typically an object
returned by sqlite-select.
(sqlite-next stmt)⇒ ("bar" 2)

sqlite-columns statement[Function]
This function returns the column names of the result set statement, typically an object
returned by sqlite-select.
(sqlite-columns stmt)

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⇒ ("name" "issue")sqlite-more-p statement[Function]
This predicate says whether there is more data to be fetched from the result set
statement, typically an object returned by sqlite-select.

sqlite-finalize statement[Function]
If statement is not going to be used any more, calling this function will free theresources used by statement. This is usually not necessary—when the statement
object is garbage-collected, Emacs will automatically free its resources.

sqlite-transaction db[Function]
Start a transaction in db. When in a transaction, other readers of the database won’t
access the results until the transaction has been committed by sqlite-commit.

sqlite-commit db[Function]

End a transaction in db and write the data out to its file.

sqlite-rollback db[Function]
End a transaction in db and discard any changes that have been made by thetransaction.

with-sqlite-transaction db body. . .

[Macro]Like progn (see Section 11.1 [Sequencing], page 158), but executes body with atransaction held, and commits the transaction at the end if body completes normally.
If body signals an error, or committing the transaction fails, the changes in db
performed by body are rolled back. The macro returns the value of body if itcompletes normally and commit succeeds.

sqlite-pragma db pragma[Function]
Execute pragma in db. A pragma is usually a command that affects the databaseoverall, instead of any particular table. For instance, to make SQLite automaticallygarbage collect data that’s no longer needed, you can say:(sqlite-pragma db "auto_vacuum = FULL")

This function returns non-nil on success and nil if the pragma failed. Many pragmas
can only be issued when the database is brand new and empty.

sqlite-load-extension db module[Function]
Load the named extension module into the database db. Extensions are usuallyshared-library files; on GNU and Unix systems, they have the .so file-name extension.

sqlite-version[Function]

Return a string denoting the version of the SQLite library in use.
If you wish to list the contents of an SQLite file, you can use the sqlite-mode-open-filecommand. This will pop to a buffer using sqlite-mode, which allows you to examine (andalter) the contents of an SQLite database.

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33.30 Parsing HTML and XML
Emacs can be compiled with built-in libxml2 support.
[Function]
This function returns non-nil if built-in libxml2 support is available in this Emacs
session.

libxml-available-p

When libxml2 support is available, the following functions can be used to parse HTMLor XML text into Lisp object trees.

libxml-parse-html-region &optional start end base-url
discard-comments[Function]

This function parses the text between start and end as HTML, and returns a list
representing the HTML parse tree. It attempts to handle real-world HTML by robustly
coping with syntax mistakes.
If start or end are nil, they default to the values from point-min and point-max,
respectively.
The optional argument base-url, if non-nil, should be used for warnings and errors
reported by the libxml2 library, but Emacs currently calls the library with errors andwarnings disabled, so this argument is not used.
If the optional argument discard-comments is non-nil, any top-level comment isdiscarded. (This argument is obsolete and will be removed in future Emacs versions.
To remove comments, use the xml-remove-comments utility function on the data
before you call the parsing function.)In the parse tree, each HTML node is represented by a list in which the first element isa symbol representing the node name, the second element is an alist of node attributes,
and the remaining elements are the subnodes.
The following example demonstrates this. Given this (malformed) HTML document:<html><head></head><body width=101><div class=thing>Foo<div>Yes
A call to libxml-parse-html-region returns this DOM (document object model):(html nil(head nil)(body ((width . "101"))(div ((class . "thing"))"Foo"(div nil"Yes"))))

shr-insert-document dom[Function]
This function renders the parsed HTML in dom into the current buffer. The argument
dom should be a list as generated by libxml-parse-html-region. This function is,e.g., used by The Emacs Web Wowser Manual.

libxml-parse-xml-region &optional start end base-url
discard-comments[Function]

This function is the same as libxml-parse-html-region, except that it parses the
text as XML rather than HTML (so it is stricter about syntax).

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33.30.1 Document Object Model
The DOM returned by libxml-parse-html-region (and the other XML parsing functions)is a tree structure where each node has a node name (called a tag), and optional key/value
attribute list, and then a list of child nodes. The child nodes are either strings or DOM
objects.
(body ((width . "101"))(div ((class . "thing"))"Foo"(div nil"Yes")))

dom-node tag &optional attributes &rest children[Function]
This function creates a DOM node of type tag. If given, attributes should be a
key/value pair list. If given, children should be DOM nodes.

The following functions can be used to work with this structure. Each function takes a
DOM node, or a list of nodes. In the latter case, only the first node in the list is used.

Simple accessors:
dom-tag node
Return the tag (also called “node name”) of the node.
dom-attr node attribute
Return the value of attribute in the node. A common usage would be:(dom-attr img 'href)=> "https://fsf.org/logo.png"
dom-children node
Return all the children of the node.
dom-non-text-children node
Return all the non-string children of the node.
dom-attributes node
Return the key/value pair list of attributes of the node.
dom-text node
Return all the textual elements of the node as a concatenated string.
dom-texts node
Return all the textual elements of the node, as well as the textual elements ofall the children of the node, recursively, as a concatenated string. This function
also takes an optional separator to be inserted between the textual elements.
dom-parent dom node
Return the parent of node in dom.
dom-remove dom node
Remove node from dom.
The following are functions for altering the DOM.
dom-set-attribute node attribute value
Set the attribute of the node to value.

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dom-remove-attribute node attribute
Remove attribute from node.
dom-append-child node child
Append child as the last child of node.
dom-add-child-before node child before
Add child to node’s child list before the before node. If before is nil, makechild the first child.
dom-set-attributes node attributes
Replace all the attributes of the node with a new key/value list.
The following are functions for searching for elements in the DOM. They all return listsof matching nodes.
dom-by-tag dom tag
Return all nodes in dom that are of type tag. A typical use would be:(dom-by-tag dom 'td)=> '((td ...) (td ...) (td ...))
dom-by-class dom match
Return all nodes in dom that have class names that match match, which is aregular expression.
dom-by-style dom style
Return all nodes in dom that have styles that match match, which is a regularexpression.
dom-by-id dom style
Return all nodes in dom that have IDs that match match, which is a regularexpression.
dom-search dom predicate
Return all nodes in dom where predicate returns a non-nil value. predicate iscalled with the node to be tested as its parameter.
dom-strings dom
Return all strings in dom.
Utility functions:dom-pp dom &optional remove-empty
Pretty-print dom at point. If remove-empty, don’t print textual nodes that justcontain white-space.
dom-print dom &optional pretty xml
Print dom at point. If xml is non-nil, print as XML; otherwise, print as HTML.
If pretty is non-nil, indent the HTML/XML logically.

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33.31 Parsing and generating JSON values
When Emacs is compiled with JSON (JavaScript Object Notation) support, it provides
several functions to convert between Lisp objects and JSON values. Any JSON value canbe converted to a Lisp object, but not vice versa. Specifically:• JSON uses three keywords: true, null, false. true is represented by the symbol t.
By default, the remaining two are represented, respectively, by the symbols :null and:false.
• JSON only has floating-point numbers. They can represent both Lisp integers and Lisp
floating-point numbers.
• JSON strings are always Unicode strings encoded in UTF-8. Lisp strings can containnon-Unicode characters.
• JSON has only one sequence type, the array. JSON arrays are represented using Lisp
vectors.
• JSON has only one map type, the object. JSON objects are represented using Lisp
hashtables, alists or plists. When an alist or plist contains several elements with thesame key, Emacs uses only the first element for serialization, in accordance with the
behavior of assq.
Note that nil, being both a valid alist and a valid plist, represents {}, the empty JSON
object; not null, false, or an empty array, all of which are different JSON values.
[Function]
This predicate returns non-nil if Emacs has been built with JSON support, and thelibrary is available on the current system.

json-available-p

If some Lisp object can’t be represented in JSON, the serialization functions will signal
an error of type wrong-type-argument. The parsing functions can also signal the following
errors:json-unavailable
Signaled when the parsing library isn’t available.
json-end-of-file
Signaled when encountering a premature end of the input text.
json-trailing-content
Signaled when encountering unexpected input after the first JSON object parsed.
json-parse-error
Signaled when encountering invalid JSON syntax.
Top-level values and the subobjects within these top-level values can be serialized to
JSON. Likewise, the parsing functions will return any of the possible types described above.

json-serialize object &rest args

[Function]
This function returns a new Lisp string which contains the JSON representationof object. The argument args is a list of keyword/argument pairs. The following
keywords are accepted::null-object
The value decides which Lisp object to use to represent the JSON keyword
null. It defaults to the symbol :null.

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:false-object
The value decides which Lisp object to use to represent the JSON keyword
false. It defaults to the symbol :false.

json-insert object &rest args

[Function]
This function inserts the JSON representation of object into the current buffer before
point. The argument args are interpreted as in json-parse-string.

json-parse-string string &rest args

[Function]
This function parses the JSON value in string, which must be a Lisp string. If string
doesn’t contain a valid JSON object, this function signals the json-parse-error
error.
The argument args is a list of keyword/argument pairs. The following keywords are
accepted::object-type
The value decides which Lisp object to use for representing the key-value
mappings of a JSON object. It can be either hash-table, the default, tomake hashtables with strings as keys; alist to use alists with symbols as
keys; or plist to use plists with keyword symbols as keys.
:array-type
The value decides which Lisp object to use for representing a JSON array.
It can be either array, the default, to use Lisp arrays; or list to use lists.
:null-object
The value decides which Lisp object to use to represent the JSON keyword
null. It defaults to the symbol :null.
:false-object
The value decides which Lisp object to use to represent the JSON keyword
false. It defaults to the symbol :false.

json-parse-buffer &rest args

[Function]
This function reads the next JSON value from the current buffer, starting at point.
It moves point to the position immediately after the value if contains a valid JSON
object; otherwise it signals the json-parse-error error and doesn’t move point. The
arguments args are interpreted as in json-parse-string.

33.32 JSONRPC communication
The jsonrpc library implements the JSONRPC specification, version 2.0, as it is describedin https://www.jsonrpc.org/. As the name suggests, JSONRPC is a generic Remote
Procedure Call protocol designed around JSON objects, which you can convert to and from
Lisp objects (see Section 33.31 [Parsing JSON], page 955).

33.32.1 Overview
Quoting from the spec (https://www.jsonrpc.org/), JSONRPC "is transport agnostic inthat the concepts can be used within the same process, over sockets, over http, or in manyvarious message passing environments."

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To model this agnosticism, the jsonrpc library uses objects of a jsonrpc-connection
class, which represent a connection to a remote JSON endpoint (for details on Emacs’s
object system, see EIEIO). In modern object-oriented parlance, this class is “abstract”, i.e.
the actual class of a useful connection object is always a subclass of jsonrpc-connection.
Nevertheless, we can define two distinct APIs around the jsonrpc-connection class:
1. A user interface for building JSONRPC applications
In this scenario, the JSONRPC application selects a concrete subclass ofjsonrpc-connection, and proceeds to create objects of that subclass using
make-instance. To initiate a contact to the remote endpoint, the JSONRPC application passes this object to the functions jsonrpc-notify, jsonrpc-request, and/or
jsonrpc-async-request. For handling remotely initiated contacts, which generally
come in asynchronously, the instantiation should include :request-dispatcher and:notification-dispatcher initargs, which are both functions of 3 arguments: theconnection object; a symbol naming the JSONRPC method invoked remotely; and a
JSONRPC params object.
The function passed as :request-dispatcher is responsible for handling the remote
endpoint’s requests, which expect a reply from the local endpoint (in this case, theprogram you’re building). Inside that function, you may either return locally (a normal
return) or non-locally (an error return). A local return value must be a Lisp object thatcan be serialized as JSON (see Section 33.31 [Parsing JSON], page 955). This determines
a success response, and the object is forwarded to the server as the JSONRPC result
object. A non-local return, achieved by calling the function jsonrpc-error, causes anerror response to be sent to the server. The details of the accompanying JSONRPC
error are filled out with whatever was passed to jsonrpc-error. A non-local return
triggered by an unexpected error of any other type also causes an error response to besent (unless you have set debug-on-error, in which case this calls the Lisp debugger,
see Section 19.1.1 [Error Debugging], page 333).
2. A inheritance interface for building JSONRPC transport implementations
In this scenario, jsonrpc-connection is subclassed to implement a different underlying
transport strategy (for details on how to subclass, see Section “Inheritance” in eieio.).
Users of the application-building interface can then instantiate objects of this concreteclass (using the make-instance function) and connect to JSONRPC endpoints usingthat strategy.
This API has mandatory and optional parts.
To allow its users to initiate JSONRPC contacts (notifications or requests) or reply to endpoint requests, the subclass must have an implementation of the jsonrpc-connectionsend method.
Likewise, for handling the three types of remote contacts (requests, notifications, andresponses to local requests), the transport implementation must arrange for the function
jsonrpc-connection-receive to be called after noticing a new JSONRPC message
on the wire (whatever that "wire" may be).
Finally, and optionally, the jsonrpc-connection subclass should implement thejsonrpc-shutdown and jsonrpc-running-p methods if these concepts apply to thetransport. If they do, then any system resources (e.g. processes, timers, etc.) used

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to listen for messages on the wire should be released in jsonrpc-shutdown, i.e. theyshould only be needed while jsonrpc-running-p is non-nil.

33.32.2 Process-based JSONRPC connections
For convenience, the jsonrpc library comes with a built-in jsonrpc-process-connection
transport implementation that can talk to local subprocesses (using the standard input andstandard output); or TCP hosts (using sockets); or any other remote endpoint that Emacs’s
process object can represent (see Chapter 40 [Processes], page 1078).
Using this transport, the JSONRPC messages are encoded on the wire as plain text andprefaced by some basic HTTP-style enveloping headers, such as “Content-Length”.
For an example of an application using this transport scheme on top of JSONRPC, see theLanguage Server Protocol (https://microsoft.github.io/language-server-protocol/
specification).
Along with the mandatory :request-dispatcher and :notification-dispatcher initargs, users of the jsonrpc-process-connection class should pass the following initargs
as keyword-value pairs to make-instance::process

Value must be a live process object or a function of no arguments producing
one such object. If passed a process object, the object is expected to contain a
pre-established connection; otherwise, the function is called immediately after
the object is made.

:on-shutdown
Value must be a function of a single argument, the jsonrpc-processconnection object. The function is called after the underlying process object
has been deleted (either deliberately by jsonrpc-shutdown, or unexpectedly,
because of some external cause).

33.32.3 JSONRPC JSON object format
JSONRPC JSON objects are exchanged as Lisp plists (see Section 5.9 [Property Lists],
page 99): JSON-compatible plists are handed to the dispatcher functions and, likewise,
JSON-compatible plists should be given to jsonrpc-notify, jsonrpc-request, andjsonrpc-async-request.
To facilitate handling plists, this library makes liberal use of cl-lib library (see Common
Lisp Extensions for GNU Emacs Lisp) and suggests (but doesn’t force) its clients to do
the same. A macro jsonrpc-lambda can be used to create a lambda for destructuring a
JSON-object like in this example:(jsonrpc-async-request
myproc :frobnicate `(:foo "trix"):success-fn (jsonrpc-lambda (&key bar baz &allow-other-keys)(message "Server replied back with %s and %s!"bar baz)):error-fn (jsonrpc-lambda (&key code message _data)(message "Sadly, server reports %s: %s"code message)))Chapter 33: Text

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33.32.4 Deferred JSONRPC requests
In many RPC situations, synchronization between the two communicating endpoints is amatter of correctly designing the RPC application: when synchronization is needed, requests(which are blocking) should be used; when it isn’t, notifications should suffice. However,when Emacs acts as one of these endpoints, asynchronous events (e.g. timer- or processrelated) may be triggered while there is still uncertainty about the state of the remote
endpoint. Furthermore, acting on these events may only sometimes demand synchronization,
depending on the event’s specific nature.
The :deferred keyword argument to jsonrpc-request and jsonrpc-async-request
is designed to let the caller indicate that the specific request needs synchronization and its
actual issuance may be delayed to the future, until some condition is satisfied. Specifying:deferred for a request doesn’t mean it will be delayed, only that it can be. If the request
isn’t sent immediately, jsonrpc will make renewed efforts to send it at certain key times
during communication, such as when receiving or sending other messages to the endpoint.
Before any attempt to send the request, the application-specific conditions are checked.
Since the jsonrpc library can’t know what these conditions are, the program can use
the jsonrpc-connection-ready-p generic function (see Section 13.8 [Generic Functions],
page 245) to specify them. The default method for this function returns t, but you can add
overriding methods that return nil in some situations, based on the arguments passed toit, which are the jsonrpc-connection object (see Section 33.32.1 [JSONRPC Overview],
page 956) and whichever value you passed as the :deferred keyword argument.

33.33 Atomic Change Groups
In database terminology, an atomic change is an indivisible change—it can succeed entirelyor it can fail entirely, but it cannot partly succeed. A Lisp program can make a series ofchanges to one or several buffers as an atomic change group, meaning that either the entire
series of changes will be installed in their buffers or, in case of an error, none of them will be.
To do this for one buffer, the one already current, simply write a call to atomic-changegroup around the code that makes the changes, like this:(atomic-change-group(insert foo)(delete-region x y))
If an error (or other nonlocal exit) occurs inside the body of atomic-change-group, it
unmakes all the changes in that buffer that were during the execution of the body. Thiskind of change group has no effect on any other buffers—any such changes remain.
If you need something more sophisticated, such as to make changes in various buffers constitute one atomic group, you must directly call lower-level functions that atomic-changegroup uses.

prepare-change-group &optional buffer[Function]
This function sets up a change group for buffer buffer, which defaults to the current
buffer. It returns a handle that represents the change group. You must use this handle
to activate the change group and subsequently to finish it.

To use the change group, you must activate it. You must do this before making any
changes in the text of buffer.

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activate-change-group handle

960[Function]

This function activates the change group that handle designates.
After you activate the change group, any changes you make in that buffer become partof it. Once you have made all the desired changes in the buffer, you must finish the changegroup. There are two ways to do this: you can either accept (and finalize) all the changes,
or cancel them all.

accept-change-group handle[Function]
This function accepts all the changes in the change group specified by handle, making
them final.

cancel-change-group handle[Function]
This function cancels and undoes all the changes in the change group specified byhandle.

You can cause some or all of the changes in a change group to be considered as a single
unit for the purposes of the undo commands (see Section 33.9 [Undo], page 895) by using
undo-amalgamate-change-group.
[Function]
Amalgamate all the changes made in the change-group since the state identified
by handle. This function removes all undo boundaries between undo records ofchanges since the state described by handle. Usually, handle is the handle returnedby prepare-change-group, in which case all the changes since the beginning of thechange-group are amalgamated into a single undo unit.

undo-amalgamate-change-group

Your code should use unwind-protect to make sure the group is always finished. The callto activate-change-group should be inside the unwind-protect, in case the user types C-g
just after it runs. (This is one reason why prepare-change-group and activate-changegroup are separate functions, because normally you would call prepare-change-group
before the start of that unwind-protect.) Once you finish the group, don’t use the handle
again—in particular, don’t try to finish the same group twice.
To make a multibuffer change group, call prepare-change-group once for each buffer
you want to cover, then use nconc to combine the returned values, like this:(nconc (prepare-change-group buffer-1)(prepare-change-group buffer-2))
You can then activate the multibuffer change group with a single call toactivate-change-group, and finish it with a single call to accept-change-group orcancel-change-group.
Nested use of several change groups for the same buffer works as you would expect.
Non-nested use of change groups for the same buffer will get Emacs confused, so don’t let it
happen; the first change group you start for any given buffer should be the last one finished.

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33.34 Change Hooks
These hook variables let you arrange to take notice of changes in buffers (or in a particularbuffer, if you make them buffer-local). See also Section 33.19.4 [Special Properties], page 924,
for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they doanything that uses regular expressions; otherwise, they will interfere in bizarre ways withthe editing operations that call them.
[Variable]
This variable holds a list of functions to call when Emacs is about to modify a buffer.
Each function gets two arguments, the beginning and end of the region that is about
to change, represented as integers. The buffer that is about to change is always thecurrent buffer when the function is called.

before-change-functions[Variable]
This variable holds a list of functions to call after Emacs modifies a buffer. Eachfunction receives three arguments: the beginning and end of the region just changed,
and the length of the text that existed before the change. All three arguments areintegers. The buffer that has been changed is always the current buffer when thefunction is called.
The length of the old text is the difference between the buffer positions before andafter that text as it was before the change. As for the changed text, its length issimply the difference between the first two arguments.

after-change-functions

Output of messages into the *Messages* buffer does not call these functions, and neither
do certain internal buffer changes, such as changes in buffers created by Emacs internallyfor certain jobs, that should not be visible to Lisp programs.
The vast majority of buffer changing primitives will call before-change-functions andafter-change-functions in balanced pairs, once for each change, where the arguments tothese hooks exactly delimit the change being made. Yet, hook functions should not rely on
this always being the case, because some complex primitives call before-change-functions
once before making changes, and then call after-change-functions zero or more times,
depending on how many individual changes the primitive is making. When that happens,
the arguments to before-change-functions will enclose a region in which the individualchanges are made, but won’t necessarily be the minimal such region, and the arguments
to each successive call of after-change-functions will then delimit the part of text beingchanged exactly. In general, we advise using either the before- or the after-change hook, but
not both.

combine-after-change-calls body. . .

[Macro]The macro executes body normally, but arranges to call the after-change functions
just once for a series of several changes—if that seems safe.
If a program makes several text changes in the same area of the buffer, using themacro combine-after-change-calls around that part of the program can make it
run considerably faster when after-change hooks are in use. When the after-change
hooks are ultimately called, the arguments specify a portion of the buffer including allof the changes made within the combine-after-change-calls body.

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Warning: You must not alter the values of after-change-functions within the bodyof a combine-after-change-calls form.
Warning: If the changes you combine occur in widely scattered parts of the buffer,
this will still work, but it is not advisable, because it may lead to inefficient behavior
for some change hook functions.

combine-change-calls beg end body. . .

[Macro]This executes body normally, except any buffer changes it makes do not trigger thecalls to before-change-functions and after-change-functions. Instead there
is a single call of each of these hooks for the region enclosed by beg and end, theparameters supplied to after-change-functions reflecting the changes made to thesize of the region by body.
The result of this macro is the result returned by body.
This macro is useful when a function makes a possibly large number of repetitivechanges to the buffer, and the change hooks would otherwise take a long time to run,were they to be run for each individual buffer modification. Emacs itself uses thismacro, for example, in the commands comment-region and uncomment-region.
Warning: You must not alter the values of before-change-functions orafter-change-function within body.
Warning: You must not make any buffer changes outside of the region specified by
beg and end.
[Variable]
This variable is a normal hook that is run whenever a buffer is changed that waspreviously in the unmodified state.

first-change-hook[Variable]
If this variable is non-nil, all of the change hooks are disabled; none of them run.
This affects all the hook variables described above in this section, as well as the hooks
attached to certain special text properties (see Section 33.19.4 [Special Properties],
page 924) and overlay properties (see Section 41.9.2 [Overlay Properties], page 1153).
Also, this variable is bound to non-nil while running those same hook variables, sothat by default modifying the buffer from a modification hook does not cause othermodification hooks to be run. If you do want modification hooks to be run in aparticular piece of code that is itself run from a modification hook, then rebind locallyinhibit-modification-hooks to nil. However, doing this may cause recursive calls
to the modification hooks, so be sure to prepare for that (for example, by binding
some variable which tells your hook to do nothing).
We recommend that you only bind this variable for modifications that do not result
in lasting changes to buffer text contents (for example face changes or temporary
modifications). If you need to delay change hooks during a series of changes (typicallyfor performance reasons), use combine-change-calls or combine-after-changecalls instead.

inhibit-modification-hooks

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34 Non-ASCII Characters
This chapter covers the special issues relating to characters and how they are stored instrings and buffers.

34.1 Text Representations
Emacs buffers and strings support a large repertoire of characters from many different scripts,
allowing users to type and display text in almost any known written language.
To support this multitude of characters and scripts, Emacs closely follows the UnicodeStandard. The Unicode Standard assigns a unique number, called a codepoint, to each andevery character. The range of codepoints defined by Unicode, or the Unicode codespace, is0..#x10FFFF (in hexadecimal notation), inclusive. Emacs extends this range with codepoints
in the range #x110000..#x3FFFFF, which it uses for representing characters that are notunified with Unicode and raw 8-bit bytes that cannot be interpreted as characters. Thus, acharacter codepoint in Emacs is a 22-bit integer.
To conserve memory, Emacs does not hold fixed-length 22-bit numbers that are codepointsof text characters within buffers and strings. Rather, Emacs uses a variable-length internal
representation of characters, that stores each character as a sequence of 1 to 5 8-bit bytes,
depending on the magnitude of its codepoint1 . For example, any ASCII character takes up
only 1 byte, a Latin-1 character takes up 2 bytes, etc. We call this representation of text
multibyte.
Outside Emacs, characters can be represented in many different encodings, such as
ISO-8859-1, GB-2312, Big-5, etc. Emacs converts between these external encodings and its
internal representation, as appropriate, when it reads text into a buffer or a string, or when
it writes text to a disk file or passes it to some other process.
Occasionally, Emacs needs to hold and manipulate encoded text or binary non-text data
in its buffers or strings. For example, when Emacs visits a file, it first reads the file’s text
verbatim into a buffer, and only then converts it to the internal representation. Before theconversion, the buffer holds encoded text.
Encoded text is not really text, as far as Emacs is concerned, but rather a sequence of raw
8-bit bytes. We call buffers and strings that hold encoded text unibyte buffers and strings,
because Emacs treats them as a sequence of individual bytes. Usually, Emacs displays
unibyte buffers and strings as octal codes such as \237. We recommend that you never use
unibyte buffers and strings except for manipulating encoded text or binary non-text data.
In a buffer, the buffer-local value of the variable enable-multibyte-characters specifies
the representation used. The representation for a string is determined and recorded in thestring when the string is constructed.
[Variable]
This variable specifies the current buffer’s text representation. If it is non-nil, thebuffer contains multibyte text; otherwise, it contains unibyte encoded text or binary
non-text data.

enable-multibyte-characters

1This internal representation is based on one of the encodings defined by the Unicode Standard, called
UTF-8, for representing any Unicode codepoint, but Emacs extends UTF-8 to represent the additional
codepoints it uses for raw 8-bit bytes and characters not unified with Unicode.

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You cannot set this variable directly; instead, use the function set-buffer-multibyte
to change a buffer’s representation.

position-bytes position[Function]
Buffer positions are measured in character units. This function returns the byteposition corresponding to buffer position position in the current buffer. This is 1 at
the start of the buffer, and counts upward in bytes. If position is out of range, thevalue is nil.

byte-to-position byte-position[Function]
Return the buffer position, in character units, corresponding to given byte-position in
the current buffer. If byte-position is out of range, the value is nil. In a multibyte
buffer, an arbitrary value of byte-position can be not at character boundary, but insidea multibyte sequence representing a single character; in this case, this function returns
the buffer position of the character whose multibyte sequence includes byte-position.
In other words, the value does not change for all byte positions that belong to thesame character.

The following two functions are useful when a Lisp program needs to map buffer positions
to byte offsets in a file visited by the buffer.

bufferpos-to-filepos position &optional quality coding-system[Function]
This function is similar to position-bytes, but instead of byte position in the current
buffer it returns the offset from the beginning of the current buffer’s file of the bytethat corresponds to the given character position in the buffer. The conversion requires
to know how the text is encoded in the buffer’s file; this is what the coding-system
argument is for, defaulting to the value of buffer-file-coding-system. The optional
argument quality specifies how accurate the result should be; it should be one of thefollowing:exact

The result must be accurate. The function may need to encode and decodea large part of the buffer, which is expensive and can be slow.

approximate
The value can be an approximation. The function may avoid expensive
processing and return an inexact result.
nil

If the exact result needs expensive processing, the function will return
nil rather than an approximation. This is the default if the argument isomitted.

filepos-to-bufferpos byte &optional quality coding-system[Function]
This function returns the buffer position corresponding to a file position specified bybyte, a zero-base byte offset from the file’s beginning. The function performs theconversion opposite to what bufferpos-to-filepos does. Optional arguments quality
and coding-system have the same meaning and values as for bufferpos-to-filepos.

multibyte-string-p string[Function]
Return t if string is a multibyte string, nil otherwise. This function also returns nil
if string is some object other than a string.

Chapter 34: Non-ASCII Characters965

string-bytes string[Function]
This function returns the number of bytes in string. If string is a multibyte string,
this can be greater than (length string).

unibyte-string &rest bytes[Function]
This function concatenates all its argument bytes and makes the result a unibyte
string.

34.2 Disabling Multibyte Characters
By default, Emacs starts in multibyte mode: it stores the contents of buffers and strings
using an internal encoding that represents non-ASCII characters using multi-byte sequences.
Multibyte mode allows you to use all the supported languages and scripts without limitations.
Under very special circumstances, you may want to disable multibyte character support,
for a specific buffer. When multibyte characters are disabled in a buffer, we call that unibyte
mode. In unibyte mode, each character in the buffer has a character code ranging from 0
through 255 (0377 octal); 0 through 127 (0177 octal) represent ASCII characters, and 128(0200 octal) through 255 (0377 octal) represent non-ASCII characters.
To edit a particular file in unibyte representation, visit it using find-file-literally.
See Section 26.1.1 [Visiting Functions], page 608. You can convert a multibyte buffer tounibyte by saving it to a file, killing the buffer, and visiting the file again with find-fileliterally. Alternatively, you can use C-x RET c (universal-coding-system-argument)
and specify ‘raw-text’ as the coding system with which to visit or save a file. See Section“Specifying a Coding System for File Text” in GNU Emacs Manual. Unlike find-fileliterally, finding a file as ‘raw-text’ doesn’t disable format conversion, uncompression,or auto mode selection.
The buffer-local variable enable-multibyte-characters is non-nil in multibyte buffers,
and nil in unibyte ones. The mode line also indicates whether a buffer is multibyte or not.
With a graphical display, in a multibyte buffer, the portion of the mode line that indicatesthe character set has a tooltip that (amongst other things) says that the buffer is multibyte.
In a unibyte buffer, the character set indicator is absent. Thus, in a unibyte buffer (whenusing a graphical display) there is normally nothing before the indication of the visited file’s
end-of-line convention (colon, backslash, etc.), unless you are using an input method.
You can turn off multibyte support in a specific buffer by invoking the command
toggle-enable-multibyte-characters in that buffer.

34.3 Converting Text Representations
Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte,
provided that the multibyte text contains only ASCII and 8-bit raw bytes. In general, theseconversions happen when inserting text into a buffer, or when putting text from several
strings together in one string. You can also explicitly convert a string’s contents to either
representation.
Emacs chooses the representation for a string based on the text from which it is constructed.
The general rule is to convert unibyte text to multibyte text when combining it with othermultibyte text, because the multibyte representation is more general and can hold whatever
characters the unibyte text has.

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When inserting text into a buffer, Emacs converts the text to the buffer’s representation,as specified by enable-multibyte-characters in that buffer. In particular, when you
insert multibyte text into a unibyte buffer, Emacs converts the text to unibyte, even though
this conversion cannot in general preserve all the characters that might be in the multibyte
text. The other natural alternative, to convert the buffer contents to multibyte, is not
acceptable because the buffer’s representation is a choice made by the user that cannot be
overridden automatically.
Converting unibyte text to multibyte text leaves ASCII characters unchanged, and converts
bytes with codes 128 through 255 to the multibyte representation of raw eight-bit bytes.
Converting multibyte text to unibyte converts all ASCII and eight-bit characters to theirsingle-byte form, but loses information for non-ASCII characters by discarding all but thelow 8 bits of each character’s codepoint. Converting unibyte text to multibyte and back tounibyte reproduces the original unibyte text.
The next two functions either return the argument string, or a newly created string withno text properties.

string-to-multibyte string[Function]
This function returns a multibyte string containing the same sequence of characters as
string. If string is a multibyte string, it is returned unchanged. The function assumes
that string includes only ASCII characters and raw 8-bit bytes; the latter are converted
to their multibyte representation corresponding to the codepoints #x3FFF80 through#x3FFFFF, inclusive (see Section 34.1 [Text Representations], page 963).

string-to-unibyte string[Function]
This function returns a unibyte string containing the same sequence of charactersas string. If string is a unibyte string, it is returned unchanged. Otherwise, ASCII
characters and characters in the eight-bit charset are converted to their corresponding
byte values. Use this function for string arguments that contain only ASCII and eightbit characters; the function signals an error if any other characters are encountered.

byte-to-string byte

[Function]
This function returns a unibyte string containing a single byte of character data, byte.
It signals an error if byte is not an integer between 0 and 255.

multibyte-char-to-unibyte char

[Function]
This converts the multibyte character char to a unibyte character, and returns thatcharacter. If char is neither ASCII nor eight-bit, the function returns −1.

unibyte-char-to-multibyte char

[Function]
This converts the unibyte character char to a multibyte character, assuming char iseither ASCII or raw 8-bit byte.

34.4 Selecting a Representation
Sometimes it is useful to examine an existing buffer or string as multibyte when it was
unibyte, or vice versa.

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set-buffer-multibyte multibyte[Function]
Set the representation type of the current buffer. If multibyte is non-nil, the buffer
becomes multibyte. If multibyte is nil, the buffer becomes unibyte.

This function leaves the buffer contents unchanged when viewed as a sequence of bytes.
As a consequence, it can change the contents viewed as characters; for instance, asequence of three bytes which is treated as one character in multibyte representation willcount as three characters in unibyte representation. Eight-bit characters representing
raw bytes are an exception. They are represented by one byte in a unibyte buffer, butwhen the buffer is set to multibyte, they are converted to two-byte sequences, andvice versa.
This function sets enable-multibyte-characters to record which representation isin use. It also adjusts various data in the buffer (including overlays, text properties
and markers) so that they cover the same text as they did before.
This function signals an error if the buffer is narrowed, since the narrowing might haveoccurred in the middle of multibyte character sequences.
This function also signals an error if the buffer is an indirect buffer. An indirect buffer
always inherits the representation of its base buffer.

string-as-unibyte string[Function]
If string is already a unibyte string, this function returns string itself. Otherwise,
it returns a new string with the same bytes as string, but treating each byte as aseparate character (so that the value may have more characters than string); as an
exception, each eight-bit character representing a raw byte is converted into a single
byte. The newly-created string contains no text properties.

string-as-multibyte string[Function]
If string is a multibyte string, this function returns string itself. Otherwise, it returns
a new string with the same bytes as string, but treating each multibyte sequence
as one character. This means that the value may have fewer characters than stringhas. If a byte sequence in string is invalid as a multibyte representation of a single
character, each byte in the sequence is treated as a raw 8-bit byte. The newly-createdstring contains no text properties.

34.5 Character Codes
The unibyte and multibyte text representations use different character codes. The validcharacter codes for unibyte representation range from 0 to #xFF (255)—the values that can
fit in one byte. The valid character codes for multibyte representation range from 0 to
#x3FFFFF. In this code space, values 0 through #x7F (127) are for ASCII characters, andvalues #x80 (128) through #x3FFF7F (4194175) are for non-ASCII characters.
Emacs character codes are a superset of the Unicode standard. Values 0 through#x10FFFF (1114111) correspond to Unicode characters of the same codepoint; values#x110000 (1114112) through #x3FFF7F (4194175) represent characters that are not unified with Unicode; and values #x3FFF80 (4194176) through #x3FFFFF (4194303) represent
eight-bit raw bytes.

Chapter 34: Non-ASCII Characterscharacterp charcode

968[Function]

This returns t if charcode is a valid character, and nil otherwise.
(characterp 65)⇒ t(characterp 4194303)⇒ t(characterp 4194304)⇒ nil

max-char &optional unicode[Function]
This function returns the largest value that a valid character codepoint can have inEmacs. If the optional argument unicode is non-nil, it returns the largest character
codepoint defined by the Unicode Standard (which is smaller than the maximum
codepoint supported by Emacs).
(characterp (max-char))⇒ t(characterp (1+ (max-char)))⇒ nilchar-from-name string &optional ignore-case[Function]
This function returns the character whose Unicode name is string. If ignore-case isnon-nil, case is ignored in string. This function returns nil if string does not name acharacter.
;; U+03A3(= (char-from-name "GREEK CAPITAL LETTER SIGMA") #x03A3)⇒ t

get-byte &optional pos string[Function]
This function returns the byte at character position pos in the current buffer. If
the current buffer is unibyte, this is literally the byte at that position. If the buffer
is multibyte, byte values of ASCII characters are the same as character codepoints,
whereas eight-bit raw bytes are converted to their 8-bit codes. The function signals
an error if the character at pos is non-ASCII.
The optional argument string means to get a byte value from that string instead of
the current buffer.

34.6 Character Properties
A character property is a named attribute of a character that specifies how the character
behaves and how it should be handled during text processing and display. Thus, character
properties are an important part of specifying the character’s semantics.
On the whole, Emacs follows the Unicode Standard in its implementation of character
properties. In particular, Emacs supports the Unicode Character Property Model (https://www.unicode.org/reports/tr23/), and the Emacs character property database is derived
from the Unicode Character Database (UCD). See the Character Properties chapter of
the Unicode Standard (https://www.unicode.org/versions/Unicode15.0.0/ch04.pdf),
for a detailed description of Unicode character properties and their meaning. This section

Chapter 34: Non-ASCII Characters969

assumes you are already familiar with that chapter of the Unicode Standard, and want toapply that knowledge to Emacs Lisp programs.
In Emacs, each property has a name, which is a symbol, and a set of possible values,
whose types depend on the property; if a character does not have a certain property, the value
is nil. As a general rule, the names of character properties in Emacs are produced from thecorresponding Unicode properties by downcasing them and replacing each ‘_’ character witha dash ‘-’. For example, Canonical_Combining_Class becomes canonical-combiningclass. However, sometimes we shorten the names to make their use easier.
Some codepoints are left unassigned by the UCD—they don’t correspond to any character.
The Unicode Standard defines default values of properties for such codepoints; they are
mentioned below for each property.
Here is the full list of value types for all the character properties that Emacs knows
about:
Corresponds to the Name Unicode property. The value is a string consisting ofupper-case Latin letters A to Z, digits, spaces, and hyphen ‘-’ characters. For
unassigned codepoints, the value is nil.

namegeneral-category
Corresponds to the General_Category Unicode property. The value is a symbol
whose name is a 2-letter abbreviation of the character’s classification. For
unassigned codepoints, the value is Cn.
canonical-combining-class
Corresponds to the Canonical_Combining_Class Unicode property. The value
is an integer. For unassigned codepoints, the value is zero.
bidi-class
Corresponds to the Unicode Bidi_Class property. The value is a symbol whosename is the Unicode directional type of the character. Emacs uses this property
when it reorders bidirectional text for display (see Section 41.27 [Bidirectional
Display], page 1250). For unassigned codepoints, the value depends on the code
blocks to which the codepoint belongs: most unassigned codepoints get thevalue of L (strong L), but some get values of AL (Arabic letter) or R (strong R).
decomposition
Corresponds to the Unicode properties Decomposition_Type andDecomposition_Value. The value is a list, whose first element may be asymbol representing a compatibility formatting tag, such as small2 ; the otherelements are characters that give the compatibility decomposition sequence of
this character. For characters that don’t have decomposition sequences, and forunassigned codepoints, the value is a list with a single member, the character
itself.
decimal-digit-value
Corresponds to the Unicode Numeric_Value property for characters whose
Numeric_Type is ‘Decimal’. The value is an integer, or nil if the character
2

The Unicode specification writes these tag names inside ‘<..>’ brackets, but the tag names in Emacs do
not include the brackets; e.g., Unicode specifies ‘<small>’ where Emacs uses ‘small’.

Chapter 34: Non-ASCII Characters970

has no decimal digit value. For unassigned codepoints, the value is nil, whichmeans NaN, or “not a number”.
digit-value
Corresponds to the Unicode Numeric_Value property for characters whose
Numeric_Type is ‘Digit’. The value is an integer. Examples of such characters
include compatibility subscript and superscript digits, for which the value is thecorresponding number. For characters that don’t have any numeric value, andfor unassigned codepoints, the value is nil, which means NaN.
numeric-value
Corresponds to the Unicode Numeric_Value property for characters whose
Numeric_Type is ‘Numeric’. The value of this property is a number. Examplesof characters that have this property include fractions, subscripts, superscripts,
Roman numerals, currency numerators, and encircled numbers. For example, thevalue of this property for the character U+2155 vulgar fraction one fifth
is 0.2. For characters that don’t have any numeric value, and for unassigned
codepoints, the value is nil, which means NaN.
mirroredCorresponds to the Unicode Bidi_Mirrored property. The value of this property
is a symbol, either Y or N. For unassigned codepoints, the value is N.

mirroring
Corresponds to the Unicode Bidi_Mirroring_Glyph property. The value of
this property is a character whose glyph represents the mirror image of thecharacter’s glyph, or nil if there’s no defined mirroring glyph. All the characters
whose mirrored property is N have nil as their mirroring property; however,some characters whose mirrored property is Y also have nil for mirroring,
because no appropriate characters exist with mirrored glyphs. Emacs uses
this property to display mirror images of characters when appropriate (seeSection 41.27 [Bidirectional Display], page 1250). For unassigned codepoints,
the value is nil.
paired-bracket
Corresponds to the Unicode Bidi_Paired_Bracket property. The value of thisproperty is the codepoint of a character’s paired bracket, or nil if the characteris not a bracket character. This establishes a mapping between characters thatare treated as bracket pairs by the Unicode Bidirectional Algorithm; Emacs uses
this property when it decides how to reorder for display parentheses, braces, andother similar characters (see Section 41.27 [Bidirectional Display], page 1250).
bracket-type
Corresponds to the Unicode Bidi_Paired_Bracket_Type property. For characters whose paired-bracket property is non-nil, the value of this property is asymbol, either o (for opening bracket characters) or c (for closing bracket characters). For characters whose paired-bracket property is nil, the value is the
symbol n (None). Like paired-bracket, this property is used for bidirectional
display.

Chapter 34: Non-ASCII Charactersold-name

971

Corresponds to the Unicode Unicode_1_Name property. The value is a string.
For unassigned codepoints, and characters that have no value for this property,
the value is nil.

iso-10646-comment
Corresponds to the Unicode ISO_Comment property. The value is either a stringor nil. For unassigned codepoints, the value is nil.
uppercase
Corresponds to the Unicode Simple_Uppercase_Mapping property. The valueof this property is a single character. For unassigned codepoints, the value isnil, which means the character itself.
lowercase
Corresponds to the Unicode Simple_Lowercase_Mapping property. The valueof this property is a single character. For unassigned codepoints, the value isnil, which means the character itself.
titlecase
Corresponds to the Unicode Simple_Titlecase_Mapping property. Title caseis a special form of a character used when the first character of a word needs tobe capitalized. The value of this property is a single character. For unassigned
codepoints, the value is nil, which means the character itself.
special-uppercase
Corresponds to Unicode language- and context-independent special upper-casing
rules. The value of this property is a string (which may be empty). For example
mapping for U+00DF latin small letter sharp s is "SS". For characterswith no special mapping, the value is nil which means uppercase property
needs to be consulted instead.
special-lowercase
Corresponds to Unicode language- and context-independent special lower-casing
rules. The value of this property is a string (which may be empty). For example
mapping for U+0130 latin capital letter i with dot above the value is"i\u0307" (i.e. 2-character string consisting of latin small letter i followedby U+0307 combining dot above). For characters with no special mapping,the value is nil which means lowercase property needs to be consulted instead.
special-titlecase
Corresponds to Unicode unconditional special title-casing rules. The value of
this property is a string (which may be empty). For example mapping for
U+FB01 latin small ligature fi the value is "Fi". For characters with nospecial mapping, the value is nil which means titlecase property needs to be
consulted instead.

get-char-code-property char propname
This function returns the value of char’s propname property.
(get-char-code-property ?\s 'general-category)⇒ Zs(get-char-code-property ?1 'general-category)⇒ Nd[Function]

Chapter 34: Non-ASCII Characters972;; U+2084(get-char-code-property ?\N{SUBSCRIPT FOUR}'digit-value)⇒ 4;; U+2155(get-char-code-property ?\N{VULGAR FRACTION ONE FIFTH}'numeric-value)⇒ 0.2;; U+2163(get-char-code-property ?\N{ROMAN NUMERAL FOUR}'numeric-value)⇒ 4(get-char-code-property ?\( 'paired-bracket)⇒ 41 ; closing parenthesis(get-char-code-property ?\) 'bracket-type)⇒ cchar-code-property-description prop value[Function]
This function returns the description string of property prop’s value, or nil if value
has no description.
(char-code-property-description 'general-category 'Zs)
⇒ "Separator, Space"(char-code-property-description 'general-category 'Nd)⇒ "Number, Decimal Digit"(char-code-property-description 'numeric-value '1/5)⇒ nil

put-char-code-property char propname value[Function]
This function stores value as the value of the property propname for the character
char.
[Variable]
The value of this variable is a char-table (see Section 6.6 [Char-Tables], page 119) thatspecifies, for each character, its Unicode General_Category property as a symbol.

unicode-category-table[Variable]
The value of this variable is a char-table that specifies, for each character, a symbol
whose name is the script to which the character belongs, according to the UnicodeStandard classification of the Unicode code space into script-specific blocks. Thischar-table has a single extra slot whose value is the list of all script symbols. Notethat Emacs’ classification of characters into scripts is not a 1-for-1 reflection of theUnicode standard, e.g. there is no ‘symbol’ script in Unicode.

char-script-table[Variable]
The value of this variable is a char-table that specifies the width of each character incolumns that it will occupy on the screen.

char-width-table

Chapter 34: Non-ASCII Characters

973[Variable]
The value of this variable is a char-table that specifies, for each character, whether itis printable or not. That is, if evaluating (aref printable-chars char) results in t,
the character is printable, and if it results in nil, it is not.

printable-chars

34.7 Character Sets
An Emacs character set, or charset, is a set of characters in which each character is assigned
a numeric code point. (The Unicode Standard calls this a coded character set.) Each Emacs
charset has a name which is a symbol. A single character can belong to any number of different
character sets, but it will generally have a different code point in each charset. Examplesof character sets include ascii, iso-8859-1, greek-iso8859-7, and windows-1255. The
code point assigned to a character in a charset is usually different from its code point usedin Emacs buffers and strings.
Emacs defines several special character sets. The character set unicode includes all thecharacters whose Emacs code points are in the range 0..#x10FFFF. The character set emacs
includes all ASCII and non-ASCII characters. Finally, the eight-bit charset includes the
8-bit raw bytes; Emacs uses it to represent raw bytes encountered in text.

charsetp object[Function]

Returns t if object is a symbol that names a character set, nil otherwise.

charset-list[Variable]

The value is a list of all defined character set names.

charset-priority-list &optional highestp[Function]
This function returns a list of all defined character sets ordered by their priority. Ifhighestp is non-nil, the function returns a single character set of the highest priority.

set-charset-priority &rest charsets[Function]

This function makes charsets the highest priority character sets.

char-charset character &optional restriction[Function]
This function returns the name of the character set of highest priority that character
belongs to. ASCII characters are an exception: for them, this function always returns
ascii.
If restriction is non-nil, it should be a list of charsets to search. Alternatively, it canbe a coding system, in which case the returned charset must be supported by thatcoding system (see Section 34.10 [Coding Systems], page 976).

charset-plist charset[Function]
This function returns the property list of the character set charset. Although charset isa symbol, this is not the same as the property list of that symbol. Charset properties
include important information about the charset, such as its documentation string,
short name, etc.

put-charset-property charset propname value
This function sets the propname property of charset to the given value.

[Function]

Chapter 34: Non-ASCII Characters

get-charset-property charset propname

974[Function]

This function returns the value of charsets property propname.

list-charset-chars charset[Command]This command displays a list of characters in the character set charset.
Emacs can convert between its internal representation of a character and the character’s
codepoint in a specific charset. The following two functions support these conversions.

decode-char charset code-point[Function]
This function decodes a character that is assigned a code-point in charset, to thecorresponding Emacs character, and returns it. If charset doesn’t contain a characterof that code point, the value is nil.
For backward compatibility, if code-point doesn’t fit in a Lisp fixnum (see Section 3.1[Integer Basics], page 38), it can be specified as a cons cell (high . low), where low are
the lower 16 bits of the value and high are the high 16 bits. This usage is obsolescent.

encode-char char charset[Function]
This function returns the code point assigned to the character char in charset. If
charset doesn’t have a codepoint for char, the value is nil.

The following function comes in handy for applying a certain function to all or part ofthe characters in a charset:

map-charset-chars function charset &optional arg from-code
to-code[Function]

Call function for characters in charset. function is called with two arguments. The
first one is a cons cell (from . to), where from and to indicate a range of characters
contained in charset. The second argument passed to function is arg, or nil if arg isomitted.
By default, the range of codepoints passed to function includes all the characters incharset, but optional arguments from-code and to-code limit that to the range ofcharacters between these two codepoints of charset. If either of them is nil, it defaults
to the first or last codepoint of charset, respectively. Note that from-code and to-code
are charset’s codepoints, not the Emacs codes of characters; by contrast, the values
from and to in the cons cell passed to function are Emacs character codes. Those
Emacs character codes are either Unicode code points, or Emacs internal code points
that extend Unicode and are beyond the Unicode range of characters 0..#x10FFFF(see Section 34.1 [Text Representations], page 963). The latter happens rarely, withlegacy CJK charsets for codepoints of charset which specify characters not yet unified
with Unicode.

34.8 Scanning for Character Sets
Sometimes it is useful to find out which character set a particular character belongs to. One
use for this is in determining which coding systems (see Section 34.10 [Coding Systems],
page 976) are capable of representing all of the text in question; another is to determine thefont(s) for displaying that text.

Chapter 34: Non-ASCII Characters975

charset-after &optional pos[Function]
This function returns the charset of highest priority containing the character at position
pos in the current buffer. If pos is omitted or nil, it defaults to the current value ofpoint. If pos is out of range, the value is nil.

find-charset-region beg end &optional translation[Function]
This function returns a list of the character sets of highest priority that containcharacters in the current buffer between positions beg and end.
The optional argument translation specifies a translation table to use for scanning thetext (see Section 34.9 [Translation of Characters], page 975). If it is non-nil, theneach character in the region is translated through this table, and the value returned
describes the translated characters instead of the characters actually in the buffer.

find-charset-string string &optional translation[Function]
This function returns a list of character sets of highest priority that contain charactersin string. It is just like find-charset-region, except that it applies to the contentsof string instead of part of the current buffer.

34.9 Translation of Characters
A translation table is a char-table (see Section 6.6 [Char-Tables], page 119) that specifies
a mapping of characters into characters. These tables are used in encoding and decoding,and for other purposes. Some coding systems specify their own particular translation tables;
there are also default translation tables which apply to all other coding systems.
A translation table has two extra slots. The first is either nil or a translation tablethat performs the reverse translation; the second is the maximum number of characters tolook up for translating sequences of characters (see the description of make-translationtable-from-alist below).

make-translation-table &rest translations[Function]
This function returns a translation table based on the argument translations. Eachelement of translations should be a list of elements of the form (from . to); this says
to translate the character from into to.
The arguments and the forms in each argument are processed in order, and if aprevious form already translates to to some other character, say to-alt, from is alsotranslated to to-alt.

During decoding, the translation table’s translations are applied to the characters that
result from ordinary decoding. If a coding system has the property :decode-translationtable, that specifies the translation table to use, or a list of translation tables to apply insequence. (This is a property of the coding system, as returned by coding-system-get, not a
property of the symbol that is the coding system’s name. See Section 34.10.1 [Basic Conceptsof Coding Systems], page 977.) Finally, if standard-translation-table-for-decode is
non-nil, the resulting characters are translated by that table.
During encoding, the translation table’s translations are applied to the characters inthe buffer, and the result of translation is actually encoded. If a coding system hasproperty :encode-translation-table, that specifies the translation table to use, or a list ofChapter 34: Non-ASCII Characters

976translation tables to apply in sequence. In addition, if the variable standard-translationtable-for-encode is non-nil, it specifies the translation table to use for translating theresult.
[Variable]
This is the default translation table for decoding. If a coding system specifies its own
translation tables, the table that is the value of this variable, if non-nil, is applied
after them.

standard-translation-table-for-decode[Variable]
This is the default translation table for encoding. If a coding system specifies its own
translation tables, the table that is the value of this variable, if non-nil, is applied
after them.

standard-translation-table-for-encode[Variable]
Self-inserting characters are translated through this translation table before they are
inserted. Search commands also translate their input through this table, so they cancompare more reliably with what’s in the buffer.

translation-table-for-inputThis variable automatically becomes buffer-local when set.

make-translation-table-from-vector vec[Function]
This function returns a translation table made from vec that is an array of 256
elements to map bytes (values 0 through #xFF) to characters. Elements may be nil
for untranslated bytes. The returned table has a translation table for reverse mappingin the first extra slot, and the value 1 in the second extra slot.
This function provides an easy way to make a private coding system that maps each byte
to a specific character. You can specify the returned table and the reverse translationtable using the properties :decode-translation-table and :encode-translationtable respectively in the props argument to define-coding-system.

make-translation-table-from-alist alist[Function]
This function is similar to make-translation-table but returns a complex translationtable rather than a simple one-to-one mapping. Each element of alist is of the form
(from . to), where from and to are either characters or vectors specifying a sequenceof characters. If from is a character, that character is translated to to (i.e., to acharacter or a character sequence). If from is a vector of characters, that sequence istranslated to to. The returned table has a translation table for reverse mapping in
the first extra slot, and the maximum length of all the from character sequences inthe second extra slot.

34.10 Coding Systems
When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives
text from a subprocess, it normally performs character code conversion and end-of-line
conversion as specified by a particular coding system.
How to define a coding system is an arcane matter, and is not documented here.

Chapter 34: Non-ASCII Characters977

34.10.1 Basic Concepts of Coding Systems
Character code conversion involves conversion between the internal representation of characters used inside Emacs and some other encoding. Emacs supports many different encodings,
in that it can convert to and from them. For example, it can convert text to or from encodingssuch as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In somecases, Emacs supports several alternative encodings for the same characters; for example,
there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and
KOI8.
Every coding system specifies a particular set of character code conversions, but thecoding system undecided is special: it leaves the choice unspecified, to be chosen heuristicallyfor each file or string, based on the file’s or string’s data, when they are decoded or encoded.
The coding system prefer-utf-8 is like undecided, but it prefers to choose utf-8 whenpossible.
In general, a coding system doesn’t guarantee roundtrip identity: decoding a byte
sequence using a coding system, then encoding the resulting text in the same coding system,
can produce a different byte sequence. But some coding systems do guarantee that the byte
sequence will be the same as what you originally decoded. Here are a few examples:
iso-8859-1, utf-8, big5, shift jis, euc-jp
Encoding buffer text and then decoding the result can also fail to reproduce the original
text. For instance, if you encode a character with a coding system which does not support
that character, the result is unpredictable, and thus decoding it using the same coding
system may produce a different text. Currently, Emacs can’t report errors that result fromencoding unsupported characters.
End of line conversion handles three different conventions used on various systems forrepresenting end of line in files. The Unix convention, used on GNU and Unix systems, is to
use the linefeed character (also called newline). The DOS convention, used on MS-Windows
and MS-DOS systems, is to use a carriage return and a linefeed at the end of a line. The
Mac convention is to use just carriage return. (This was the convention used in Classic Mac
OS.)
Base coding systems such as latin-1 leave the end-of-line conversion unspecified, to bechosen based on the data. Variant coding systems such as latin-1-unix, latin-1-dos andlatin-1-mac specify the end-of-line conversion explicitly as well. Most base coding systems
have three corresponding variants whose names are formed by adding ‘-unix’, ‘-dos’ and‘-mac’.
The coding system raw-text is special in that it prevents character code conversion,and causes the buffer visited with this coding system to be a unibyte buffer. For historicalreasons, you can save both unibyte and multibyte text with this coding system. When you
use raw-text to encode multibyte text, it does perform one character code conversion: it
converts eight-bit characters to their single-byte external representation. raw-text does not
specify the end-of-line conversion, allowing that to be determined as usual by the data, andhas the usual three variants which specify the end-of-line conversion.
no-conversion (and its alias binary) is equivalent to raw-text-unix: it specifies noconversion of either character codes or end-of-line.
The coding system utf-8-emacs specifies that the data is represented in the internal
Emacs encoding (see Section 34.1 [Text Representations], page 963). This is like raw-text inChapter 34: Non-ASCII Characters

978that no code conversion happens, but different in that the result is multibyte data. The nameemacs-internal is an alias for utf-8-emacs-unix (so it forces no conversion of end-of-line,
unlike utf-8-emacs, which can decode all 3 kinds of end-of-line conventions).

coding-system-get coding-system property[Function]
This function returns the specified property of the coding system coding-system. Most
coding system properties exist for internal purposes, but one that you might finduseful is :mime-charset. That property’s value is the name used in MIME for thecharacter coding which this coding system can read and write. Examples:(coding-system-get 'iso-latin-1 :mime-charset)⇒ iso-8859-1(coding-system-get 'iso-2022-cn :mime-charset)⇒ iso-2022-cn(coding-system-get 'cyrillic-koi8 :mime-charset)⇒ koi8-r
The value of the :mime-charset property is also defined as an alias for the coding
system.

coding-system-aliases coding-system[Function]

This function returns the list of aliases of coding-system.

34.10.2 Encoding and I/O
The principal purpose of coding systems is for use in reading and writing files. The function
insert-file-contents uses a coding system to decode the file data, and write-region
uses one to encode the buffer contents.
You can specify the coding system to use either explicitly (see Section 34.10.6 [Specifying
Coding Systems], page 986), or implicitly using a default mechanism (see Section 34.10.5[Default Coding Systems], page 983). But these methods may not completely specify what
to do. For example, they may choose a coding system such as undecided which leaves thecharacter code conversion to be determined from the data. In these cases, the I/O operation
finishes the job of choosing a coding system. Very often you will want to find out afterwards
which coding system was chosen.
[Variable]
This buffer-local variable records the coding system used for saving the buffer andfor writing part of the buffer with write-region. If the text to be written cannot besafely encoded using the coding system specified by this variable, these operations
select an alternative encoding by calling the function select-safe-coding-system(see Section 34.10.4 [User-Chosen Coding Systems], page 982). If selecting a different
encoding requires to ask the user to specify a coding system, buffer-file-codingsystem is updated to the newly selected coding system.

buffer-file-coding-systembuffer-file-coding-system does not affect sending text to a subprocess.
[Variable]
This variable specifies the coding system for saving the buffer (by overriding
buffer-file-coding-system). Note that it is not used for write-region.

save-buffer-coding-system

Chapter 34: Non-ASCII Characters

979

When a command to save the buffer starts out to use buffer-file-coding-system(or save-buffer-coding-system), and that coding system cannot handle the actual
text in the buffer, the command asks the user to choose another coding system(by calling select-safe-coding-system). After that happens, the command also
updates buffer-file-coding-system to represent the coding system that the user
specified.
[Variable]
I/O operations for files and subprocesses set this variable to the coding system namethat was used. The explicit encoding and decoding functions (see Section 34.10.7[Explicit Encoding], page 988) set it too.

last-coding-system-used

Warning: Since receiving subprocess output sets this variable, it can change wheneverEmacs waits; therefore, you should copy the value shortly after the function call that
stores the value you are interested in.
The variable selection-coding-system specifies how to encode selections for the window
system. See Section 30.20 [Window System Selections], page 840.
[Variable]
The variable file-name-coding-system specifies the coding system to use for encoding file names. Emacs encodes file names using that coding system for all file
operations. If file-name-coding-system is nil, Emacs uses a default coding systemdetermined by the selected language environment. In the default language environment,
any non-ASCII characters in file names are not encoded specially; they appear in thefile system using the internal Emacs representation.

file-name-coding-system

Warning: if you change file-name-coding-system (or the language environment) inthe middle of an Emacs session, problems can result if you have already visited files whosenames were encoded using the earlier coding system and are handled differently under the
new coding system. If you try to save one of these buffers under the visited file name, saving
may use the wrong file name, or it may get an error. If such a problem happens, use C-x
C-w to specify a new file name for that buffer.
On Windows 2000 and later, Emacs by default uses Unicode APIs to pass file names to
the OS, so the value of file-name-coding-system is largely ignored. Lisp applications thatneed to encode or decode file names on the Lisp level should use utf-8 coding-system whensystem-type is windows-nt; the conversion of UTF-8 encoded file names to the encoding
appropriate for communicating with the OS is performed internally by Emacs.

34.10.3 Coding Systems in Lisp
Here are the Lisp facilities for working with coding systems:

coding-system-list &optional base-only[Function]
This function returns a list of all coding system names (symbols). If base-only is
non-nil, the value includes only the base coding systems. Otherwise, it includes alias
and variant coding systems as well.

coding-system-p object
This function returns t if object is a coding system name or nil.

[Function]

Chapter 34: Non-ASCII Characters980

check-coding-system coding-system[Function]
This function checks the validity of coding-system. If that is valid, it returns codingsystem. If coding-system is nil, the function returns nil. For any other values, it
signals an error whose error-symbol is coding-system-error (see Section 11.7.3.1[Signaling Errors], page 180).

coding-system-eol-type coding-system[Function]
This function returns the type of end-of-line (a.k.a. eol) conversion used by codingsystem. If coding-system specifies a certain eol conversion, the return value is an
integer 0, 1, or 2, standing for unix, dos, and mac, respectively. If coding-systemdoesn’t specify eol conversion explicitly, the return value is a vector of coding systems,
each one with one of the possible eol conversion types, like this:(coding-system-eol-type 'latin-1)⇒ [latin-1-unix latin-1-dos latin-1-mac]
If this function returns a vector, Emacs will decide, as part of the text encoding or
decoding process, what eol conversion to use. For decoding, the end-of-line format of
the text is auto-detected, and the eol conversion is set to match it (e.g., DOS-style
CRLF format will imply dos eol conversion). For encoding, the eol conversion istaken from the appropriate default coding system (e.g., default value of buffer-filecoding-system for buffer-file-coding-system), or from the default eol conversion
appropriate for the underlying platform.

coding-system-change-eol-conversion coding-system eol-type[Function]
This function returns a coding system which is like coding-system except for its eol
conversion, which is specified by eol-type. eol-type should be unix, dos, mac, or nil.
If it is nil, the returned coding system determines the end-of-line conversion from thedata.
eol-type may also be 0, 1 or 2, standing for unix, dos and mac, respectively.

coding-system-change-text-conversion eol-coding text-coding[Function]
This function returns a coding system which uses the end-of-line conversion of eolcoding, and the text conversion of text-coding. If text-coding is nil, it returns
undecided, or one of its variants according to eol-coding.

find-coding-systems-region from to[Function]
This function returns a list of coding systems that could be used to encode a text
between from and to. All coding systems in the list can safely encode any multibyte
characters in that portion of the text.
If the text contains no multibyte characters, the function returns the list (undecided).

find-coding-systems-string string[Function]
This function returns a list of coding systems that could be used to encode the text ofstring. All coding systems in the list can safely encode any multibyte characters instring. If the text contains no multibyte characters, this returns the list (undecided).

find-coding-systems-for-charsets charsets[Function]
This function returns a list of coding systems that could be used to encode all thecharacter sets in the list charsets.

Chapter 34: Non-ASCII Characters981

check-coding-systems-region start end coding-system-list[Function]
This function checks whether coding systems in the list coding-system-list can
encode all the characters in the region between start and end. If all of the coding systems in the list can encode the specified text, the function returns nil. If some coding
systems cannot encode some of the characters, the value is an alist, each element of
which has the form (coding-system1 pos1 pos2 ...), meaning that coding-system1
cannot encode characters at buffer positions pos1, pos2, . . . .
start may be a string, in which case end is ignored and the returned value references
string indices instead of buffer positions.

detect-coding-region start end &optional highest[Function]
This function chooses a plausible coding system for decoding the text from start toend. This text should be a byte sequence, i.e., unibyte text or multibyte text with only
ASCII and eight-bit characters (see Section 34.10.7 [Explicit Encoding], page 988).
Normally this function returns a list of coding systems that could handle decoding thetext that was scanned. They are listed in order of decreasing priority. But if highest
is non-nil, then the return value is just one coding system, the one that is highest inpriority.
If the region contains only ASCII characters except for such ISO-2022 control charactersISO-2022 as ESC, the value is undecided or (undecided), or a variant specifying endof-line conversion, if that can be deduced from the text.
If the region contains null bytes, the value is no-conversion, even if the region
contains text encoded in some coding system.

detect-coding-string string &optional highest[Function]
This function is like detect-coding-region except that it operates on the contentsof string instead of bytes in the buffer.
[Variable]
If this variable has a non-nil value, null bytes are ignored when detecting the encodingof a region or a string. This allows the encoding of text that contains null bytes to becorrectly detected, such as Info files with Index nodes.

inhibit-null-byte-detection[Variable]
If this variable has a non-nil value, ISO-2022 escape sequences are ignored when
detecting the encoding of a region or a string. The result is that no text is everdetected as encoded in some ISO-2022 encoding, and all escape sequences become
visible in a buffer. Warning: Use this variable with extreme caution, because many
files in the Emacs distribution use ISO-2022 encoding.

inhibit-iso-escape-detection

coding-system-charset-list coding-system[Function]
This function returns the list of character sets (see Section 34.7 [Character Sets],page 973) supported by coding-system. Some coding systems that support too many
character sets to list them all yield special values:• If coding-system supports all Emacs characters, the value is (emacs).
• If coding-system supports all Unicode characters, the value is (unicode).
• If coding-system supports all ISO-2022 charsets, the value is iso-2022.

Chapter 34: Non-ASCII Characters982• If coding-system supports all the characters in the internal coding system usedby Emacs version 21 (prior to the implementation of internal Unicode support),
the value is emacs-mule.
See [Process Information], page 1095, in particular the description of the functions
process-coding-system and set-process-coding-system, for how to examine or set thecoding systems used for I/O to a subprocess.

34.10.4 User-Chosen Coding Systems
select-safe-coding-system from to &optional
default-coding-system accept-default-p file

[Function]

This function selects a coding system for encoding specified text, asking the user
to choose if necessary. Normally the specified text is the text in the current buffer
between from and to. If from is a string, the string specifies the text to encode, andto is ignored.
If the specified text includes raw bytes (see Section 34.1 [Text Representations],
page 963), select-safe-coding-system suggests raw-text for its encoding.
If default-coding-system is non-nil, that is the first coding system to try; if that canhandle the text, select-safe-coding-system returns that coding system. It can also
be a list of coding systems; then the function tries each of them one by one. After trying
all of them, it next tries the current buffer’s value of buffer-file-coding-system(if it is not undecided), then the default value of buffer-file-coding-system andfinally the user’s most preferred coding system, which the user can set using thecommand prefer-coding-system (see Section “Recognizing Coding Systems” in The
GNU Emacs Manual).
If one of those coding systems can safely encode all the specified text, select-safecoding-system chooses it and returns it. Otherwise, it asks the user to choose froma list of coding systems which can encode all the text, and returns the user’s choice.
default-coding-system can also be a list whose first element is t and whose otherelements are coding systems. Then, if no coding system in the list can handle thetext, select-safe-coding-system queries the user immediately, without trying anyof the three alternatives described above. This is handy for checking only the coding
systems in the list.
The optional argument accept-default-p determines whether a coding system selectedwithout user interaction is acceptable. If it’s omitted or nil, such a silent selectionis always acceptable. If it is non-nil, it should be a function; select-safe-codingsystem calls this function with one argument, the base coding system of the selected
coding system. If the function returns nil, select-safe-coding-system rejects thesilently selected coding system, and asks the user to select a coding system from a listof possible candidates.
If the variable select-safe-coding-system-accept-default-p is non-nil, it should
be a function taking a single argument. It is used in place of accept-default-p, overriding
any value supplied for this argument.
As a final step, before returning the chosen coding system, select-safe-codingsystem checks whether that coding system is consistent with what would be selected

Chapter 34: Non-ASCII Characters983

if the contents of the region were read from a file. (If not, this could lead to data
corruption in a file subsequently re-visited and edited.) Normally, select-safecoding-system uses buffer-file-name as the file for this purpose, but if file isnon-nil, it uses that file instead (this can be relevant for write-region and similarfunctions). If it detects an apparent inconsistency, select-safe-coding-system
queries the user before selecting the coding system.
[Variable]
This variable names the function to be called to request the user to select a proper
coding system for encoding text when the default coding system for an output operation
cannot safely encode that text. The default value of this variable is select-safecoding-system. Emacs primitives that write text to files, such as write-region, orsend text to other processes, such as process-send-region, normally call the valueof this variable, unless coding-system-for-write is bound to a non-nil value (seeSection 34.10.6 [Specifying Coding Systems], page 986).

select-safe-coding-system-function

Here are two functions you can use to let the user specify a coding system, with completion.
See Section 21.6 [Completion], page 395.

read-coding-system prompt &optional default[Function]
This function reads a coding system using the minibuffer, prompting with string
prompt, and returns the coding system name as a symbol. If the user enters null input,
default specifies which coding system to return. It should be a symbol or a string.

read-non-nil-coding-system prompt[Function]
This function reads a coding system using the minibuffer, prompting with string
prompt, and returns the coding system name as a symbol. If the user tries to enter
null input, it asks the user to try again. See Section 34.10 [Coding Systems], page 976.

34.10.5 Default Coding Systems
This section describes variables that specify the default coding system for certain files orwhen running certain subprograms, and the function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to the defaults you want,
and then do not change them again. To specify a particular coding system for a particular
operation in a Lisp program, don’t change these variables; instead, override them using
coding-system-for-read and coding-system-for-write (see Section 34.10.6 [Specifying
Coding Systems], page 986).
[User Option]
This variable is an alist of text patterns and corresponding coding systems. Eachelement has the form (regexp . coding-system); a file whose first few kilobytes
match regexp is decoded with coding-system when its contents are read into a buffer.
The settings in this alist take priority over coding: tags in the files and the contents
of file-coding-system-alist (see below). The default value is set so that Emacs
automatically recognizes mail files in Babyl format and reads them with no code
conversions.

auto-coding-regexp-alist

Chapter 34: Non-ASCII Characters

984[User Option]
This variable is an alist that specifies the coding systems to use for reading and writing
particular files. Each element has the form (pattern . coding), where pattern is aregular expression that matches certain file names. The element applies to file namesthat match pattern.

file-coding-system-alist

The cdr of the element, coding, should be either a coding system, a cons cell containing
two coding systems, or a function name (a symbol with a function definition). If
coding is a coding system, that coding system is used for both reading the file andwriting it. If coding is a cons cell containing two coding systems, its car specifies thecoding system for decoding, and its cdr specifies the coding system for encoding.
If coding is a function name, the function should take one argument, a list of allarguments passed to find-operation-coding-system. It must return a coding
system or a cons cell containing two coding systems. This value has the same meaning
as described above.
If coding (or what returned by the above function) is undecided, the normal codedetection is performed.
[User Option]
This variable is an alist that specifies the coding systems to use for reading and writing
particular files. Its form is like that of file-coding-system-alist, but, unlike thelatter, this variable takes priority over any coding: tags in the file.

auto-coding-alist[Variable]
This variable is an alist specifying which coding systems to use for a subprocess,depending on which program is running in the subprocess. It works like file-codingsystem-alist, except that pattern is matched against the program name used tostart the subprocess. The coding system or systems specified in this alist are used toinitialize the coding systems used for I/O to the subprocess, but you can specify othercoding systems later using set-process-coding-system.

process-coding-system-alist

Warning: Coding systems such as undecided, which determine the coding system fromthe data, do not work entirely reliably with asynchronous subprocess output. This is because
Emacs handles asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the end-of-line conversion
unspecified, Emacs must try to detect the proper conversion from one batch at a time, andthis does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a coding system which
determines both the character code conversion and the end of line conversion—that is, one
like latin-1-unix, rather than undecided or latin-1.
[Variable]
This variable is an alist that specifies the coding system to use for network streams.
It works much like file-coding-system-alist, with the difference that the patternin an element may be either a port number or a regular expression. If it is a regularexpression, it is matched against the network service name used to open the network
stream.

network-coding-system-alist

Chapter 34: Non-ASCII Characters

985[Variable]
This variable specifies the coding systems to use for subprocess (and network stream)
input and output, when nothing else specifies what to do.
The value should be a cons cell of the form (input-coding . output-coding). Hereinput-coding applies to input from the subprocess, and output-coding applies to
output to it.

default-process-coding-system[User Option]
This variable holds a list of functions that try to determine a coding system for a file
based on its undecoded contents.
Each function in this list should be written to look at text in the current buffer, butshould not modify it in any way. The buffer will contain the text of parts of the file.
Each function should take one argument, size, which tells it how many characters tolook at, starting from point. If the function succeeds in determining a coding system
for the file, it should return that coding system. Otherwise, it should return nil.
The functions in this list could be called either when the file is visited and Emacs
wants to decode its contents, and/or when the file’s buffer is about to be saved andEmacs wants to determine how to encode its contents.
If a file has a ‘coding:’ tag, that takes precedence, so these functions won’t be called.

auto-coding-functions

find-auto-coding filename size

[Function]
This function tries to determine a suitable coding system for filename. It examines
the buffer visiting the named file, using the variables documented above in sequence,
until it finds a match for one of the rules specified by these variables. It then returns
a cons cell of the form (coding . source), where coding is the coding system touse and source is a symbol, one of auto-coding-alist, auto-coding-regexp-alist,:coding, or auto-coding-functions, indicating which one supplied the matchingrule. The value :coding means the coding system was specified by the coding: tag inthe file (see Section “coding tag” in The GNU Emacs Manual). The order of looking
for a matching rule is auto-coding-alist first, then auto-coding-regexp-alist,
then the coding: tag, and lastly auto-coding-functions. If no matching rule wasfound, the function returns nil.
The second argument size is the size of text, in characters, following point. The
function examines text only within size characters after point. Normally, the buffer
should be positioned at the beginning when this function is called, because one of theplaces for the coding: tag is the first one or two lines of the file; in that case, size
should be the size of the buffer.

set-auto-coding filename size

[Function]
This function returns a suitable coding system for file filename. It uses find-autocoding to find the coding system. If no coding system could be determined, thefunction returns nil. The meaning of the argument size is like in find-auto-coding.

find-operation-coding-system operation &rest arguments[Function]
This function returns the coding system to use (by default) for performing operation
with arguments. The value has this form:(decoding-system . encoding-system)

Chapter 34: Non-ASCII Characters

986

The first element, decoding-system, is the coding system to use for decoding (in case
operation does decoding), and encoding-system is the coding system for encoding (incase operation does encoding).
The argument operation is a symbol; it should be one of write-region,
start-process, call-process, call-process-region, insert-file-contents, or
open-network-stream. These are the names of the Emacs I/O primitives that can
do character code and eol conversion.
The remaining arguments should be the same arguments that might be given to thecorresponding I/O primitive. Depending on the primitive, one of those arguments isselected as the target. For example, if operation does file I/O, whichever argument
specifies the file name is the target. For subprocess primitives, the process name is thetarget. For open-network-stream, the target is the service name or port number.
Depending on operation, this function looks up the target in file-coding-systemalist, process-coding-system-alist, or network-coding-system-alist. If thetarget is found in the alist, find-operation-coding-system returns its associationin the alist; otherwise it returns nil.
If operation is insert-file-contents, the argument corresponding to the target may
be a cons cell of the form (filename . buffer). In that case, filename is a file nameto look up in file-coding-system-alist, and buffer is a buffer that contains thefile’s contents (not yet decoded). If file-coding-system-alist specifies a function
to call for this file, and that function needs to examine the file’s contents (as it usuallydoes), it should examine the contents of buffer instead of reading the file.

34.10.6 Specifying a Coding System for One Operation
You can specify the coding system for a specific operation by binding the variables
coding-system-for-read and/or coding-system-for-write.
[Variable]
If this variable is non-nil, it specifies the coding system to use for reading a file, orfor input from a synchronous subprocess.

coding-system-for-read

It also applies to any asynchronous subprocess or network stream, but in a different
way: the value of coding-system-for-read when you start the subprocess or open
the network stream specifies the input decoding method for that subprocess or network
stream. It remains in use for that subprocess or network stream unless and until
overridden.
The right way to use this variable is to bind it with let for a specific I/O operation.
Its global value is normally nil, and you should not globally set it to any other value.
Here is an example of the right way to use the variable:;; Read the file with no character code conversion.
(let ((coding-system-for-read 'no-conversion))(insert-file-contents filename))
When its value is non-nil, this variable takes precedence over all other methods ofspecifying a coding system to use for input, including file-coding-system-alist,
process-coding-system-alist and network-coding-system-alist.

Chapter 34: Non-ASCII Characters

987[Variable]
This works much like coding-system-for-read, except that it applies to output
rather than input. It affects writing to files, as well as sending output to subprocesses
and net connections. It also applies to encoding command-line arguments with which
Emacs invokes subprocesses.

coding-system-for-write

When a single operation does both input and output, as do call-process-region andstart-process, both coding-system-for-read and coding-system-for-write affect it.
[Variable]
Binding coding-system-for-write to a non-nil value prevents output primitives
from calling the function specified by select-safe-coding-system-function (seeSection 34.10.4 [User-Chosen Coding Systems], page 982). This is because C-x RETc (universal-coding-system-argument) works by binding coding-system-forwrite, and Emacs should obey user selection. If a Lisp program binds coding-systemfor-write to a value that might not be safe for encoding the text to be written, it canalso bind coding-system-require-warning to a non-nil value, which will force theoutput primitives to check the encoding by calling the value of select-safe-codingsystem-function even though coding-system-for-write is non-nil. Alternatively,
call select-safe-coding-system explicitly before using the specified encoding.

coding-system-require-warning[User Option]
When this variable is non-nil, no end-of-line conversion is done, no matter whichcoding system is specified. This applies to all the Emacs I/O and subprocess primitives,
and to the explicit encoding and decoding functions (see Section 34.10.7 [Explicit
Encoding], page 988).

inhibit-eol-conversion

Sometimes, you need to prefer several coding systems for some operation, rather than fix
a single one. Emacs lets you specify a priority order for using coding systems. This ordering
affects the sorting of lists of coding systems returned by functions such as find-codingsystems-region (see Section 34.10.3 [Lisp and Coding Systems], page 979).

coding-system-priority-list &optional highestp[Function]
This function returns the list of coding systems in the order of their current priorities.
Optional argument highestp, if non-nil, means return only the highest priority coding
system.

set-coding-system-priority &rest coding-systems[Function]
This function puts coding-systems at the beginning of the priority list for coding
systems, thus making their priority higher than all the rest.

with-coding-priority coding-systems &rest body

[Macro]This macro executes body, like progn does (see Section 11.1 [Sequencing], page 158),
with coding-systems at the front of the priority list for coding systems. coding-systems
should be a list of coding systems to prefer during execution of body.

Chapter 34: Non-ASCII Characters988

34.10.7 Explicit Encoding and Decoding
All the operations that transfer text in and out of Emacs have the ability to use a coding
system to encode or decode the text. You can also explicitly encode and decode text using
the functions in this section.
The result of encoding, and the input to decoding, are not ordinary text. They logicallyconsist of a series of byte values; that is, a series of ASCII and eight-bit characters. In
unibyte buffers and strings, these characters have codes in the range 0 through #xFF (255).
In a multibyte buffer or string, eight-bit characters have character codes higher than #xFF
(see Section 34.1 [Text Representations], page 963), but Emacs transparently converts themto their single-byte values when you encode or decode such text.
The usual way to read a file into a buffer as a sequence of bytes, so you can decode thecontents explicitly, is with insert-file-contents-literally (see Section 26.3 [Readingfrom Files], page 614); alternatively, specify a non-nil rawfile argument when visiting a filewith find-file-noselect. These methods result in a unibyte buffer.
The usual way to use the byte sequence that results from explicitly encoding text is tocopy it to a file or process—for example, to write it with write-region (see Section 26.4
[Writing to Files], page 616), and suppress encoding by binding coding-system-for-write
to no-conversion.
Here are the functions to perform explicit encoding or decoding. The encoding functions
produce sequences of bytes; the decoding functions are meant to operate on sequences of bytes.
All of these functions discard text properties. They also set last-coding-system-used tothe precise coding system they used.

encode-coding-region start end coding-system &optional
destination[Command]This command encodes the text from start to end according to coding system codingsystem. Normally, the encoded text replaces the original text in the buffer, but theoptional argument destination can change that. If destination is a buffer, the encoded
text is inserted in that buffer after point (point does not move); if it is t, the command
returns the encoded text as a unibyte string without inserting it.
If encoded text is inserted in some buffer, this command returns the length of theencoded text.
The result of encoding is logically a sequence of bytes, but the buffer remains multibyte
if it was multibyte before, and any 8-bit bytes are converted to their multibyte
representation (see Section 34.1 [Text Representations], page 963).
Do not use undecided for coding-system when encoding text, since that may lead to
unexpected results. Instead, use select-safe-coding-system (see Section 34.10.4[User-Chosen Coding Systems], page 982) to suggest a suitable encoding, if there’s no
obvious pertinent value for coding-system.

encode-coding-string string coding-system &optional nocopy
buffer[Function]

This function encodes the text in string according to coding system coding-system. It
returns a new string containing the encoded text, except when nocopy is non-nil, in
which case the function may return string itself if the encoding operation is trivial.
The result of encoding is a unibyte string.

Chapter 34: Non-ASCII Charactersdecode-coding-region start end coding-system &optional
destination

989[Command]This command decodes the text from start to end according to coding system codingsystem. To make explicit decoding useful, the text before decoding ought to be asequence of byte values, but both multibyte and unibyte buffers are acceptable (inthe multibyte case, the raw byte values should be represented as eight-bit characters).
Normally, the decoded text replaces the original text in the buffer, but the optional
argument destination can change that. If destination is a buffer, the decoded text
is inserted in that buffer after point (point does not move); if it is t, the command
returns the decoded text as a multibyte string without inserting it.
If decoded text is inserted in some buffer, this command returns the length of thedecoded text. If that buffer is a unibyte buffer (see Section 34.4 [Selecting a Representation], page 966), the internal representation of the decoded text (see Section 34.1
[Text Representations], page 963) is inserted into the buffer as individual bytes.
This command puts a charset text property on the decoded text. The value of theproperty states the character set used to decode the original text.
This command detects the encoding of the text if necessary. If coding-system isundecided, the command detects the encoding of the text based on the byte sequences
it finds in the text, and also detects the type of end-of-line convention used by the
text (see Section 34.10.3 [Lisp and Coding Systems], page 979). If coding-system isundecided-eol-type, where eol-type is unix, dos, or mac, then the command detects
only the encoding of the text. Any coding-system that doesn’t specify eol-type, as in
utf-8, causes the command to detect the end-of-line convention; specify the encoding
completely, as in utf-8-unix, if the EOL convention used by the text is known inadvance, to prevent any automatic detection.

decode-coding-string string coding-system &optional nocopy
buffer[Function]

This function decodes the text in string according to coding-system. It returns a new
string containing the decoded text, except when nocopy is non-nil, in which case thefunction may return string itself if the decoding operation is trivial. To make explicit
decoding useful, the contents of string ought to be a unibyte string with a sequence ofbyte values, but a multibyte string is also acceptable (assuming it contains 8-bit bytes
in their multibyte form).
This function detects the encoding of the string if needed, like decode-coding-region
does.
If optional argument buffer specifies a buffer, the decoded text is inserted in thatbuffer after point (point does not move). In this case, the return value is the length ofthe decoded text. If that buffer is a unibyte buffer, the internal representation of thedecoded text is inserted into it as individual bytes.
This function puts a charset text property on the decoded text. The value of theproperty states the character set used to decode the original text:(decode-coding-string "Gr\374ss Gott" 'latin-1)⇒ #("Grüss Gott" 0 9 (charset iso-8859-1))

Chapter 34: Non-ASCII Charactersdecode-coding-inserted-region from to filename &optional visit
beg end replace

990[Function]

This function decodes the text from from to to as if it were being read from file
filename using insert-file-contents using the rest of the arguments provided.
The normal way to use this function is after reading text from a file without decoding,if you decide you would rather have decoded it. Instead of deleting the text andreading it again, this time with decoding, you can call this function.

34.10.8 Terminal I/O Encoding
Emacs can use coding systems to decode keyboard input and encode terminal output. This isuseful for terminals that transmit or display text using a particular encoding, such as Latin-1.
Emacs does not set last-coding-system-used when encoding or decoding terminal I/O.

keyboard-coding-system &optional terminal[Function]
This function returns the coding system used for decoding keyboard input fromterminal. A value of no-conversion means no decoding is done. If terminal isomitted or nil, it means the selected frame’s terminal. See Section 30.2 [Multiple
Terminals], page 787.

set-keyboard-coding-system coding-system &optional terminal[Command]This command specifies coding-system as the coding system to use for decoding
keyboard input from terminal. If coding-system is nil, that means not to decode
keyboard input. If terminal is a frame, it means that frame’s terminal; if it is nil, thatmeans the currently selected frame’s terminal. See Section 30.2 [Multiple Terminals],
page 787. Note that on modern MS-Windows systems Emacs always uses Unicode
input when decoding keyboard input, so the encoding set by this command has noeffect on Windows.

terminal-coding-system &optional terminal[Function]
This function returns the coding system that is in use for encoding terminal output
from terminal. A value of no-conversion means no encoding is done. If terminal is aframe, it means that frame’s terminal; if it is nil, that means the currently selected
frame’s terminal.

set-terminal-coding-system coding-system &optional terminal[Command]This command specifies coding-system as the coding system to use for encoding
terminal output from terminal. If coding-system is nil, that means not to encode
terminal output. If terminal is a frame, it means that frame’s terminal; if it is nil,that means the currently selected frame’s terminal.

34.11 Input Methods
Input methods provide convenient ways of entering non-ASCII characters from the keyboard.
Unlike coding systems, which translate non-ASCII characters to and from encodings meant tobe read by programs, input methods provide human-friendly commands. (See Section “Input
Methods” in The GNU Emacs Manual, for information on how users use input methods toenter text.) How to define input methods is not yet documented in this manual, but here
we describe how to use them.

Chapter 34: Non-ASCII Characters

991

Each input method has a name, which is currently a string; in the future, symbols may
also be usable as input method names.
[Variable]
This variable holds the name of the input method now active in the current buffer. (Itautomatically becomes local in each buffer when set in any fashion.) It is nil if no
input method is active in the buffer now.

current-input-method[User Option]
This variable holds the default input method for commands that choose an input
method. Unlike current-input-method, this variable is normally global.

default-input-method

set-input-method input-method[Command]This command activates input method input-method for the current buffer. It also
sets default-input-method to input-method. If input-method is nil, this command
deactivates any input method for the current buffer.

read-input-method-name prompt &optional default inhibit-null[Function]
This function reads an input method name with the minibuffer, prompting withprompt. If default is non-nil, that is returned by default, if the user enters empty
input. However, if inhibit-null is non-nil, empty input signals an error.
The returned value is a string.
[Variable]
This variable defines all the supported input methods. Each element defines one input
method, and should have the form:(input-method language-env activate-func
title description args...)Here input-method is the input method name, a string; language-env is another string,
the name of the language environment this input method is recommended for. (Thatserves only for documentation purposes.)
activate-func is a function to call to activate this method. The args, if any, arepassed as arguments to activate-func. All told, the arguments to activate-func are
input-method and the args.
title is a string to display in the mode line while this method is active. description isa string describing this method and what it is good for.

input-method-alist

The fundamental interface to input methods is through the variable input-methodfunction. See Section 22.8.2 [Reading One Event], page 462, and Section 22.8.4 [Invoking
the Input Method], page 467.

34.12 Locales
In POSIX, locales control which language to use in language-related features. These Emacs
variables control how Emacs interacts with these features.
[Variable]
This variable specifies the coding system to use for decoding system error messages
and—on X Window system only—keyboard input, for sending batch output to the

locale-coding-system

Chapter 34: Non-ASCII Characters992

standard output and error streams, for encoding the format argument to format-timestring, and for decoding the return value of format-time-string.
[Variable]
This variable specifies the locale to use for generating system error messages. Changing
the locale can cause messages to come out in a different language or in a different
orthography. If the variable is nil, the locale is specified by environment variables in
the usual POSIX fashion.

system-messages-locale[Variable]
This variable specifies the locale to use for formatting time values. Changing the locale
can cause messages to appear according to the conventions of a different language.
If the variable is nil, the locale is specified by environment variables in the usual
POSIX fashion.

system-time-locale

locale-info item

[Function]
This function returns locale data item for the current POSIX locale, if available. item
should be one of these symbols:
codesetReturn the character set as a string (locale item CODESET).

days

Return a 7-element vector of day names (locale items DAY_1 throughDAY_7);

monthsReturn a 12-element vector of month names (locale items MON_1 throughMON_12).

paper

Return a list (width height) of 2 integers, for the default paper size
measured in millimeters (locale items _NL_PAPER_WIDTH and _NL_PAPER_
HEIGHT).

If the system can’t provide the requested information, or if item is not one of those symbols, the value is nil. All strings in the return value are decoded using locale-codingsystem. See Section “Locales” in The GNU Libc Manual, for more information about
locales and locale items.

993

35 Searching and Matching
GNU Emacs provides two ways to search through a buffer for specified text: exact string
searches and regular expression searches. After a regular expression search, you can examine
the match data to determine which text matched the whole regular expression or various
portions of it.
The ‘skip-chars...’ functions also perform a kind of searching. See Section 31.2.7 [Skipping Characters], page 863. To search for changes in character properties, see Section 33.19.3[Property Search], page 921.

35.1 Searching for Strings
These are the primitive functions for searching through the text in a buffer. They are meant
for use in programs, but you may call them interactively. If you do so, they prompt for the
search string; the arguments limit and noerror are nil, and repeat is 1. For more details oninteractive searching, see Section “Searching and Replacement” in The GNU Emacs Manual.
These search functions convert the search string to multibyte if the buffer is multibyte;
they convert the search string to unibyte if the buffer is unibyte. See Section 34.1 [Text
Representations], page 963.

search-forward string &optional limit noerror count[Command]This function searches forward from point for an exact match for string. If successful,it sets point to the end of the occurrence found, and returns the new value of point. If
no match is found, the value and side effects depend on noerror (see below).
In the following example, point is initially at the beginning of the line. Then
(search-forward "fox") moves point after the last letter of ‘fox’:---------- Buffer: foo ---------?The quick brown fox jumped over the lazy dog.
---------- Buffer: foo ---------(search-forward "fox")⇒ 20---------- Buffer: foo ---------The quick brown fox? jumped over the lazy dog.
---------- Buffer: foo ---------The argument limit specifies the bound to the search, and should be a position in thecurrent buffer. No match extending after that position is accepted. If limit is omitted
or nil, it defaults to the end of the accessible portion of the buffer.

What happens when the search fails depends on the value of noerror. If noerror isnil, a search-failed error is signaled. If noerror is t, search-forward returns nil
and does nothing. If noerror is neither nil nor t, then search-forward moves point
to the upper bound and returns nil.
The argument noerror only affects valid searches which fail to find a match. Invalid
arguments cause errors regardless of noerror.

Chapter 35: Searching and Matching994

If count is a positive number n, the search is done n times; each successive search starts
at the end of the previous match. If all these successive searches succeed, the function
call succeeds, moving point and returning its new value. Otherwise the function call
fails, with results depending on the value of noerror, as described above. If count is anegative number −n, the search is done n times in the opposite (backward) direction.

search-backward string &optional limit noerror count[Command]This function searches backward from point for string. It is like search-forward,
except that it searches backwards rather than forwards. Backward searches leave pointat the beginning of the match.

word-search-forward string &optional limit noerror count[Command]This function searches forward from point for a word match for string. If it finds amatch, it sets point to the end of the match found, and returns the new value of point.

Word matching regards string as a sequence of words, disregarding punctuation that
separates them. It searches the buffer for the same sequence of words. Each word
must be distinct in the buffer (searching for the word ‘ball’ does not match the word‘balls’), but the details of punctuation and spacing are ignored (searching for ‘ballboy’ does match ‘ball. Boy!’).
In this example, point is initially at the beginning of the buffer; the search leaves it
between the ‘y’ and the ‘!’.
---------- Buffer: foo ---------?He said "Please! Find
the ball boy!"---------- Buffer: foo ---------(word-search-forward "Please find the ball, boy.")⇒ 39---------- Buffer: foo ---------He said "Please! Find
the ball boy?!"---------- Buffer: foo ---------If limit is non-nil, it must be a position in the current buffer; it specifies the upperbound to the search. The match found must not extend after that position.
If noerror is nil, then word-search-forward signals an error if the search fails. If
noerror is t, then it returns nil instead of signaling an error. If noerror is neither
nil nor t, it moves point to limit (or the end of the accessible portion of the buffer)and returns nil.
If count is a positive number, it specifies how many successive occurrences to searchfor. Point is positioned at the end of the last match. If count is a negative number,the search is backward and point is positioned at the beginning of the last match.
Internally, word-search-forward and related functions use the function
word-search-regexp to convert string to a regular expression that ignorespunctuation.

Chapter 35: Searching and Matching995

word-search-forward-lax string &optional limit noerror count[Command]This command is identical to word-search-forward, except that the beginning or
the end of string need not match a word boundary, unless string begins or ends inwhitespace. For instance, searching for ‘ball boy’ matches ‘ball boyee’, but does
not match ‘balls boy’.

word-search-backward string &optional limit noerror count[Command]This function searches backward from point for a word match to string. This function
is just like word-search-forward except that it searches backward and normallyleaves point at the beginning of the match.

word-search-backward-lax string &optional limit noerror count[Command]This command is identical to word-search-backward, except that the beginning or
the end of string need not match a word boundary, unless string begins or ends inwhitespace.

35.2 Searching and Case
By default, searches in Emacs ignore the case of the text they are searching through; if you
specify searching for ‘FOO’, then ‘Foo’ or ‘foo’ is also considered a match. This applies toregular expressions, too; thus, ‘[aB]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’.
If you do not want this feature, set the variable case-fold-search to nil. Then
all letters must match exactly, including case. This is a buffer-local variable; altering thevariable affects only the current buffer. (See Section 12.11.1 [Intro to Buffer-Local], page 207.)
Alternatively, you may change the default value. In Lisp code, you will more typically use
let to bind case-fold-search to the desired value.
Note that the user-level incremental search feature handles case distinctions differently.
When the search string contains only lower case letters, the search ignores case, but when
the search string contains one or more upper case letters, the search becomes case-sensitive.
But this has nothing to do with the searching functions used in Lisp code. See Section“Incremental Search” in The GNU Emacs Manual.
[User Option]
This buffer-local variable determines whether searches should ignore case. If thevariable is nil they do not ignore case; otherwise (and by default) they do ignore case.

case-fold-search[User Option]
This variable determines whether the higher-level replacement functions should preservecase. If the variable is nil, that means to use the replacement text verbatim. A
non-nil value means to convert the case of the replacement text according to the text
being replaced.
This variable is used by passing it as an argument to the function replace-match.
See Section 35.6.1 [Replacing Match], page 1012.

case-replace

35.3 Regular Expressions
A regular expression, or regexp for short, is a pattern that denotes a (possibly infinite) set
of strings. Searching for matches for a regexp is a very powerful operation. This section
explains how to write regexps; the following section says how to search for them.

Chapter 35: Searching and Matching996

For interactive development of regular expressions, you can use the M-x re-builder
command. It provides a convenient interface for creating regular expressions, by giving
immediate visual feedback in a separate buffer. As you edit the regexp, all its matches inthe target buffer are highlighted. Each parenthesized sub-expression of the regexp is shownin a distinct face, which makes it easier to verify even very complex regexps.
Note that by default Emacs search ignores case (see Section 35.2 [Searching and Case],
page 995). To enable case-sensitive regexp search and match, bind case-fold-search tonil around the code you want to be case-sensitive.

35.3.1 Syntax of Regular Expressions
Regular expressions have a syntax in which a few characters are special constructs and therest are ordinary. An ordinary character is a simple regular expression that matches thatcharacter and nothing else. The special characters are ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘^’, ‘$’, and ‘\’;no new special characters will be defined in the future. The character ‘]’ is special if it ends
a character alternative (see later). The character ‘-’ is special inside a character alternative.
A ‘[:’ and balancing ‘:]’ enclose a character class inside a character alternative. Any othercharacter appearing in a regular expression is ordinary, unless a ‘\’ precedes it.
For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regularexpression that matches the string ‘f’ and no other string. (It does not match the string ‘fg’,
but it does match a part of that string.) Likewise, ‘o’ is a regular expression that matches
only ‘o’.
Any two regular expressions a and b can be concatenated. The result is a regularexpression that matches a string if a matches some amount of the beginning of that string
and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get theregular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something
more powerful, you need to use one of the special regular expression constructs.

35.3.1.1 Special Characters in Regular Expressions
Here is a list of the characters that are special in a regular expression.
‘.’ (Period)
is a special character that matches any single character except a newline. Using
concatenation, we can make regular expressions like ‘a.b’, which matches any
three-character string that begins with ‘a’ and ends with ‘b’.
‘*’is not a construct by itself; it is a postfix operator that means to match thepreceding regular expression repetitively as many times as possible. Thus, ‘o*’matches any number of ‘o’s (including no ‘o’s).
‘*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ hasa repeating ‘o’, not a repeating ‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.
The matcher processes a ‘*’ construct by matching, immediately, as many
repetitions as can be found. Then it continues with the rest of the pattern. If
that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified
construct in the hope that this will make it possible to match the rest of thepattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’

Chapter 35: Searching and Matching997

first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is
only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match
only two ‘a’s. With this choice, the rest of the regexp matches successfully.
‘+’

is a postfix operator, similar to ‘*’ except that it must match the preceding
expression at least once. So, for example, ‘ca+r’ matches the strings ‘car’ and‘caaaar’ but not the string ‘cr’, whereas ‘ca*r’ matches all three strings.

‘?’

is a postfix operator, similar to ‘*’ except that it must match the preceding
expression either once or not at all. For example, ‘ca?r’ matches ‘car’ or ‘cr’;nothing else.

‘*?’, ‘+?’, ‘??’are non-greedy variants of the operators ‘*’, ‘+’ and ‘?’. Where those operators match the largest possible substring (consistent with matching the entire
containing expression), the non-greedy variants match the smallest possible
substring (consistent with matching the entire containing expression).
For example, the regular expression ‘c[ad]*a’ when applied to the string‘cdaaada’ matches the whole string; but the regular expression ‘c[ad]*?a’,applied to that same string, matches just ‘cda’. (The smallest possible matchhere for ‘[ad]*?’ that permits the whole expression to match is ‘d’.)‘[ ... ]’is a character alternative, which begins with ‘[’ and is terminated by ‘]’. In thesimplest case, the characters between the two brackets are what this character
alternative can match.
Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string
composed of just ‘a’s and ‘d’s (including the empty string). It follows that‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.
You can also include character ranges in a character alternative, by writing thestarting and ending characters with a ‘-’ between them. Thus, ‘[a-z]’ matches
any lower-case ASCII letter. Ranges may be intermixed freely with individual
characters, as in ‘[a-z$%.]’, which matches any lower case ASCII letter or ‘$’,‘%’ or period. However, the ending character of one range should not be thestarting point of another one; for example, ‘[a-m-z]’ should be avoided.
A character alternative can also specify named character classes (seeSection 35.3.1.2 [Char Classes], page 1000). For example, ‘[[:ascii:]]’matches any ASCII character. Using a character class is equivalent tomentioning each of the characters in that class; but the latter is not feasible
in practice, since some classes include thousands of different characters. A
character class should not appear as the lower or upper bound of a range.
The usual regexp special characters are not special inside a character alternative.
A completely different set of characters is special: ‘]’, ‘-’ and ‘^’. To include‘]’ in a character alternative, put it at the beginning. To include ‘^’, put it
anywhere but at the beginning. To include ‘-’, put it at the end. Thus, ‘[]^-]’
matches all three of these special characters. You cannot use ‘\’ to escape thesethree characters, since ‘\’ is not special here.

Chapter 35: Searching and Matching998

The following aspects of ranges are specific to Emacs, in that POSIX allows
but does not require this behavior and programs other than Emacs may behave
differently:
1. If case-fold-search is non-nil, ‘[a-z]’ also matches upper-case letters.
2. A range is not affected by the locale’s collation sequence: it always represents
the set of characters with codepoints ranging between those of its bounds,
so that ‘[a-z]’ matches only ASCII letters, even outside the C or POSIX
locale.
3. If the lower bound of a range is greater than its upper bound, the range isempty and represents no characters. Thus, ‘[z-a]’ always fails to match,and ‘[^z-a]’ matches any character, including newline. However, a reversed
range should always be from the letter ‘z’ to the letter ‘a’ to make it clearthat it is not a typo; for example, ‘[+-*/]’ should be avoided, because itmatches only ‘/’ rather than the likely-intended four characters.
4. If the end points of a range are raw 8-bit bytes (see Section 34.1 [Text
Representations], page 963), or if the range start is ASCII and the end is a
raw byte (as in ‘[a-\377]’), the range will match only ASCII charactersand raw 8-bit bytes, but not non-ASCII characters. This feature is intended
for searching text in unibyte buffers and strings.
Some kinds of character alternatives are not the best style even though they
have a well-defined meaning in Emacs. They include:
1. Although a range’s bound can be almost any character, it is better style
to stay within natural sequences of ASCII letters and digits because mostpeople have not memorized character code tables. For example, ‘[.-9]’
is less clear than ‘[./0-9]’, and ‘[`-~]’ is less clear than ‘[`a-z{|}~]’.
Unicode character escapes can help here; for example, for most programmers‘[--]’ is less clear than ‘[\u0E01-\u0E3A\u0E3F-\u0E5B]’.
2. Although a character alternative can include duplicates, it is better style to
avoid them. For example, ‘[XYa-yYb-zX]’ is less clear than ‘[XYa-z]’.
3. Although a range can denote just one, two, or three characters, it is simpler
to list the characters. For example, ‘[a-a0]’ is less clear than ‘[a0]’, ‘[i-j]’
is less clear than ‘[ij]’, and ‘[i-k]’ is less clear than ‘[ijk]’.
4. Although a ‘-’ can appear at the beginning of a character alternative or as
the upper bound of a range, it is better style to put ‘-’ by itself at the endof a character alternative. For example, although ‘[-a-z]’ is valid, ‘[a-z-]’is better style; and although ‘[*--]’ is valid, ‘[*+,-]’ is clearer.
‘[^ ... ]’ ‘[^’ begins a complemented character alternative. This matches any character
except the ones specified. Thus, ‘[^a-z0-9A-Z]’ matches all characters except
ASCII letters and digits.
‘^’ is not special in a character alternative unless it is the first character. The
character following the ‘^’ is treated as if it were first (in other words, ‘-’ and‘]’ are not special there).

Chapter 35: Searching and Matching999

A complemented character alternative can match a newline, unless newline ismentioned as one of the characters not to match. This is in contrast to thehandling of regexps in programs such as grep.
You can specify named character classes, just like in character alternatives. For
instance, ‘[^[:ascii:]]’ matches any non-ASCII character. See Section 35.3.1.2[Char Classes], page 1000.
‘^’

When matching a buffer, ‘^’ matches the empty string, but only at the beginningof a line in the text being matched (or the beginning of the accessible portion of
the buffer). Otherwise it fails to match anything. Thus, ‘^foo’ matches a ‘foo’
that occurs at the beginning of a line.
When matching a string instead of a buffer, ‘^’ matches at the beginning of thestring or after a newline character.
For historical compatibility reasons, ‘^’ can be used only at the beginning of
the regular expression, or after ‘\(’, ‘\(?:’ or ‘\|’.

‘$’is similar to ‘^’ but matches only at the end of a line (or the end of the accessible
portion of the buffer). Thus, ‘x+$’ matches a string of one ‘x’ or more at theend of a line.
When matching a string instead of a buffer, ‘$’ matches at the end of the string
or before a newline character.
For historical compatibility reasons, ‘$’ can be used only at the end of theregular expression, or before ‘\)’ or ‘\|’.

‘\’has two functions: it quotes the special characters (including ‘\’), and it introduces additional special constructs.
Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches
only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.
Note that ‘\’ also has special meaning in the read syntax of Lisp strings (seeSection 2.4.8 [String Type], page 20), and must be quoted with ‘\’. For example,
the regular expression that matches the ‘\’ character is ‘\\’. To write a Lisp
string that contains the characters ‘\\’, Lisp syntax requires you to quote each‘\’ with another ‘\’. Therefore, the read syntax for a regular expression matching‘\’ is "\\\\".

Please note: For historical compatibility, special characters are treated as ordinary ones
if they are in contexts where their special meanings make no sense. For example, ‘*foo’
treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It ispoor practice to depend on this behavior; quote the special character anyway, regardless of
where it appears.
As a ‘\’ is not special inside a character alternative, it can never remove the special
meaning of ‘-’, ‘^’ or ‘]’. You should not quote these characters when they have no special
meaning. This would not clarify anything, since backslashes can legitimately precede thesecharacters where they have special meaning, as in ‘[^\]’ ("[^\\]" for Lisp string syntax),
which matches any single character except a backslash.
In practice, most ‘]’ that occur in regular expressions close a character alternative andhence are special. However, occasionally a regular expression may try to match a complex

Chapter 35: Searching and Matching

1000

pattern of literal ‘[’ and ‘]’. In such situations, it sometimes may be necessary to carefullyparse the regexp from the start to determine which square brackets enclose a character
alternative. For example, ‘[^][]]’ consists of the complemented character alternative ‘[^][]’(which matches any single character that is not a square bracket), followed by a literal ‘]’.
The exact rules are that at the beginning of a regexp, ‘[’ is special and ‘]’ not. This lasts
until the first unquoted ‘[’, after which we are in a character alternative; ‘[’ is no longer
special (except when it starts a character class) but ‘]’ is special, unless it immediately
follows the special ‘[’ or that ‘[’ followed by a ‘^’. This lasts until the next special ‘]’ that
does not end a character class. This ends the character alternative and restores the ordinarysyntax of regular expressions; an unquoted ‘[’ is special again and a ‘]’ not.

35.3.1.2 Character Classes
Below is a table of the classes you can use in a character alternative, and what they mean.
Note that the ‘[’ and ‘]’ characters that enclose the class name are part of the name, so a
regular expression using these classes needs one more pair of brackets. For example, a regularexpression matching a sequence of one or more letters and digits would be ‘[[:alnum:]]+’,not ‘[:alnum:]+’.
‘[:ascii:]’
This matches any ASCII character (codes 0–127).
‘[:alnum:]’
This matches any letter or digit. For multibyte characters, it matches characters
whose Unicode ‘general-category’ property (see Section 34.6 [Character Properties], page 968) indicates they are alphabetic or decimal number characters.
‘[:alpha:]’This matches any letter. For multibyte characters, it matches characters whose
Unicode ‘general-category’ property (see Section 34.6 [Character Properties],
page 968) indicates they are alphabetic characters.
‘[:blank:]’
This matches horizontal whitespace, as defined by Annex C of the Unicode
Technical Standard #18. In particular, it matches spaces, tabs, and other characters whose Unicode ‘general-category’ property (see Section 34.6 [Character
Properties], page 968) indicates they are spacing separators.
‘[:cntrl:]’
This matches any character whose code is in the range 0–31.
‘[:digit:]’This matches ‘0’ through ‘9’. Thus, ‘[-+[:digit:]]’ matches any digit, as wellas ‘+’ and ‘-’.
‘[:graph:]’This matches graphic characters—everything except spaces, ASCII and nonASCII control characters, surrogates, and codepoints unassigned by Unicode,
as indicated by the Unicode ‘general-category’ property (see Section 34.6
[Character Properties], page 968).

Chapter 35: Searching and Matching

1001‘[:lower:]’This matches any lower-case letter, as determined by the current case table (seeSection 4.10 [Case Tables], page 74). If case-fold-search is non-nil, this also
matches any upper-case letter. Note that a buffer can have its own local casetable different from the default one.
‘[:multibyte:]’This matches any multibyte character (see Section 34.1 [Text Representations],
page 963).
‘[:nonascii:]’
This matches any non-ASCII character.
‘[:print:]’
This matches any printing character—either spaces or graphic charactersmatched by ‘[:graph:]’.
‘[:punct:]’
This matches any punctuation character. (At present, for multibyte characters,
it matches anything that has non-word syntax, and thus its exact definition canvary from one major mode to another, since the syntax of a character depends
on the major mode.)‘[:space:]’This matches any character that has whitespace syntax (see Section 36.2.1[Syntax Class Table], page 1023). Note that the syntax of a character, and thus
which characters are considered “whitespace”, depends on the major mode.
‘[:unibyte:]’This matches any unibyte character (see Section 34.1 [Text Representations],
page 963).
‘[:upper:]’This matches any upper-case letter, as determined by the current case table (seeSection 4.10 [Case Tables], page 74). If case-fold-search is non-nil, this also
matches any lower-case letter. Note that a buffer can have its own local casetable different from the default one.
‘[:word:]’This matches any character that has word syntax (see Section 36.2.1 [Syntax
Class Table], page 1023). Note that the syntax of a character, and thus whichcharacters are considered “word-constituent”, depends on the major mode.
‘[:xdigit:]’This matches the hexadecimal digits: ‘0’ through ‘9’, ‘a’ through ‘f’ and ‘A’through ‘F’.

35.3.1.3 Backslash Constructs in Regular Expressions
For the most part, ‘\’ followed by any character matches only that character. However,there are several exceptions: certain sequences starting with ‘\’ that have special meanings.
Here is a table of the special ‘\’ constructs.

Chapter 35: Searching and Matching

‘\|’

1002

specifies an alternative. Two regular expressions a and b with ‘\|’ in between
form an expression that matches anything that either a or b matches.
Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string.
‘\|’ applies to the largest possible surrounding expressions. Only a surrounding‘\( ... \)’ grouping can limit the grouping power of ‘\|’.
If you need full backtracking capability to handle multiple uses of ‘\|’, use
the POSIX regular expression functions (see Section 35.5 [POSIX Regexps],
page 1011).

‘\{m\}’

is a postfix operator that repeats the previous pattern exactly m times. Thus,‘x\{5\}’ matches the string ‘xxxxx’ and nothing else. ‘c[ad]\{3\}r’ matches
string such as ‘caaar’, ‘cdddr’, ‘cadar’, and so on.

‘\{m,n\}’is a more general postfix operator that specifies repetition with a minimum of mrepeats and a maximum of n repeats. If m is omitted, the minimum is 0; if n isomitted, there is no maximum. For both forms, m and n, if specified, may be
no larger than 216 − 1 .
For example, ‘c[ad]\{1,2\}r’ matches the strings ‘car’, ‘cdr’, ‘caar’, ‘cadr’,‘cdar’, and ‘cddr’, and nothing else.
‘\{0,1\}’ or ‘\{,1\}’ is equivalent to ‘?’.
‘\{0,\}’ or ‘\{,\}’ is equivalent to ‘*’.
‘\{1,\}’ is equivalent to ‘+’.

‘\( ... \)’is a grouping construct that serves three purposes:
1. To enclose a set of ‘\|’ alternatives for other operations. Thus, the regularexpression ‘\(foo\|bar\)x’ matches either ‘foox’ or ‘barx’.
2. To enclose a complicated expression for the postfix operators ‘*’, ‘+’and ‘?’ to operate on. Thus, ‘ba\(na\)*’ matches ‘ba’, ‘bana’, ‘banana’,‘bananana’, etc., with any number (zero or more) of ‘na’ strings.
3. To record a matched substring for future reference with ‘\digit’ (seebelow).
This last application is not a consequence of the idea of a parenthetical grouping;
it is a separate feature that was assigned as a second meaning to the same ‘\(... \)’ construct because, in practice, there was usually no conflict between
the two meanings. But occasionally there is a conflict, and that led to theintroduction of shy groups.
‘\(?: ... \)’is the shy group construct. A shy group serves the first two purposes of an
ordinary group (controlling the nesting of other operators), but it does not get
a number, so you cannot refer back to its value with ‘\digit’. Shy groups are
particularly useful for mechanically-constructed regular expressions, because
they can be added automatically without altering the numbering of ordinary,
non-shy groups.
Shy groups are also called non-capturing or unnumbered groups.

Chapter 35: Searching and Matching1003‘\(?num: ... \)’is the explicitly numbered group construct. Normal groups get their number
implicitly, based on their position, which can be inconvenient. This construct
allows you to force a particular group number. There is no particular restriction
on the numbering, e.g., you can have several groups with the same number inwhich case the last one to match (i.e., the rightmost match) will win. Implicitly
numbered groups always get the smallest integer larger than the one of any
previous group.
‘\digit’matches the same text that matched the digitth occurrence of a grouping (‘\(... \)’) construct.
In other words, after the end of a group, the matcher remembers the beginningand end of the text matched by that group. Later on in the regular expression
you can use ‘\’ followed by digit to match that same text, whatever it may havebeen.
The strings matching the first nine grouping constructs appearing in the entire
regular expression passed to a search or matching function are assigned numbers
1 through 9 in the order that the open parentheses appear in the regularexpression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by thecorresponding grouping constructs.
For example, ‘\(.*\)\1’ matches any newline-free string that is composed of
two identical halves. The ‘\(.*\)’ matches the first half, which may be anything,but the ‘\1’ that follows must match the same exact text.
If a ‘\( ... \)’ construct matches more than once (which can happen, forinstance, if it is followed by ‘*’), only the last match is recorded.
If a particular grouping construct in the regular expression was never matched—for instance, if it appears inside of an alternative that wasn’t used, or inside of arepetition that repeated zero times—then the corresponding ‘\digit’ constructnever matches anything. To use an artificial example, ‘\(foo\(b*\)\|lose\)\2’
cannot match ‘lose’: the second alternative inside the larger group matches it,
but then ‘\2’ is undefined and can’t match anything. But it can match ‘foobb’,
because the first alternative matches ‘foob’ and ‘\2’ matches ‘b’.

‘\w’

matches any word-constituent character. The editor syntax table determines
which characters these are. See Chapter 36 [Syntax Tables], page 1022.

‘\W’

matches any character that is not a word constituent.

‘\scode’matches any character whose syntax is code. Here code is a character that
represents a syntax code: thus, ‘w’ for word constituent, ‘-’ for whitespace, ‘(’for open parenthesis, etc. To represent whitespace syntax, use either ‘-’ or aspace character. See Section 36.2.1 [Syntax Class Table], page 1023, for a list ofsyntax codes and the characters that stand for them.

‘\Scode’matches any character whose syntax is not code.

‘\ccode’matches any character whose category is code. Here code is a character that
represents a category: for example, in the standard category table, ‘c’ stands for
Chinese characters and ‘g’ stands for Greek characters. You can see the list ofChapter 35: Searching and Matching1004

all the currently defined categories with M-x describe-categories RET. You
can also define your own categories in addition to the standard ones using thedefine-category function (see Section 36.8 [Categories], page 1036).
‘\Ccode’matches any character whose category is not code.

The following regular expression constructs match the empty string—that is, they don’t
consume any characters—but whether they match depends on the context. For all, thebeginning and end of the accessible portion of the buffer are treated as if they were theactual beginning and end of the buffer.
‘\`’

matches the empty string, but only at the beginning of the buffer or string being
matched against.

‘\'’

matches the empty string, but only at the end of the buffer or string being
matched against.

‘\=’

matches the empty string, but only at point. (This construct is not defined whenmatching against a string.)‘\b’matches the empty string, but only at the beginning or end of a word. Thus,‘\bfoo\b’ matches any occurrence of ‘foo’ as a separate word. ‘\bballs?\b’matches ‘ball’ or ‘balls’ as a separate word.
‘\b’ matches at the beginning or end of the buffer (or string) regardless of what
text appears next to it.

‘\B’matches the empty string, but not at the beginning or end of a word, nor at the
beginning or end of the buffer (or string).

‘\<’

matches the empty string, but only at the beginning of a word. ‘\<’ matchesat the beginning of the buffer (or string) only if a word-constituent character
follows.

‘\>’

matches the empty string, but only at the end of a word. ‘\>’ matches at theend of the buffer (or string) only if the contents end with a word-constituent
character.

‘\_<’matches the empty string, but only at the beginning of a symbol. A symbol is asequence of one or more word or symbol constituent characters. ‘\_<’ matchesat the beginning of the buffer (or string) only if a symbol-constituent character
follows.

‘\_>’

matches the empty string, but only at the end of a symbol. ‘\_>’ matches at theend of the buffer (or string) only if the contents end with a symbol-constituent
character.

Not every string is a valid regular expression. For example, a string that ends inside acharacter alternative without a terminating ‘]’ is invalid, and so is a string that ends witha single ‘\’. If an invalid regular expression is passed to any of the search functions, aninvalid-regexp error is signaled.

Chapter 35: Searching and Matching1005

35.3.2 Complex Regexp Example
Here is a complicated regexp which was formerly used by Emacs to recognize the end of asentence together with any whitespace that follows. (Nowadays Emacs uses a similar but
more complex default regexp constructed by the function sentence-end. See Section 35.8
[Standard Regexps], page 1020.)
Below, we show first the regexp as a string in Lisp syntax (to distinguish spaces from tabcharacters), and then the result of evaluating it. The string constant begins and ends with adouble-quote. ‘\"’ stands for a double-quote as part of the string, ‘\\’ for a backslash aspart of the string, ‘\t’ for a tab and ‘\n’ for a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"⇒ "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[]*"In the output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be deciphered as follows:[.?!]

The first part of the pattern is a character alternative that matches any oneof three characters: period, question mark, and exclamation mark. The match
must begin with one of these three characters. (This is one point where thenew default regexp used by Emacs differs from the old. The new value also
allows some non-ASCII characters that end a sentence without any following
whitespace.)[]\"')}]*The second part of the pattern matches any closing braces and quotation marks,
zero or more of them, that may follow the period, question mark or exclamation
mark. The \" is Lisp syntax for a double-quote in a string. The ‘*’ at theend indicates that the immediately preceding regular expression (a character
alternative, in this case) may be repeated zero or more times.
\\($\\| $\\|\t\\| \\)The third part of the pattern matches the whitespace that follows the endof a sentence: the end of a line (optionally with a space), or a tab, or two
spaces. The double backslashes mark the parentheses and vertical bars as
regular expression syntax; the parentheses delimit a group and the vertical bars
separate alternatives. The dollar sign is used to match the end of a line.
[ \t\n]*Finally, the last part of the pattern matches any additional whitespace beyond
the minimum needed to end a sentence.

35.3.3 Regular Expression Functions
These functions operate on regular expressions.

regexp-quote string[Function]
This function returns a regular expression whose only exact match is string. Using
this regular expression in looking-at will succeed only if the next characters in thebuffer are string; using it in a search function will succeed if the text being searchedcontains string. See Section 35.4 [Regexp Search], page 1008.

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This allows you to request an exact string match or search when calling a functionthat wants a regular expression.
(regexp-quote "^The cat$")⇒ "\\^The cat\\$"One use of regexp-quote is to combine an exact string match with context described
as a regular expression. For example, this searches for the string that is the value ofstring, surrounded by whitespace:(re-search-forward(concat "\\s-" (regexp-quote string) "\\s-"))
The returned string may be string itself if it does not contain any special characters.

regexp-opt strings &optional paren[Function]
This function returns an efficient regular expression that will match any of the stringsin the list strings. This is useful when you need to make matching or searching as fast
as possible—for example, for Font Lock mode1 .
If strings is the empty list, the return value is a regexp that never matches anything.
The optional argument paren can be any of the following:a string

The resulting regexp is preceded by paren and followed by ‘\)’, e.g. use‘"\\(?1:"’ to produce an explicitly numbered group.

words

The resulting regexp is surrounded by ‘\<\(’ and ‘\)\>’.

symbols

The resulting regexp is surrounded by ‘\_<\(’ and ‘\)\_>’ (this is often
appropriate when matching programming-language keywords and thelike).

non-nil

The resulting regexp is surrounded by ‘\(’ and ‘\)’.

nil

The resulting regexp is surrounded by ‘\(?:’ and ‘\)’, if it is necessary
to ensure that a postfix operator appended to it will apply to the wholeexpression.

The returned regexp is ordered in such a way that it will always match the longest
string possible.
Up to reordering, the resulting regexp of regexp-opt is equivalent to but usually more
efficient than that of a simplified version:(defun simplified-regexp-opt (strings &optional paren)(let ((parens(cond((stringp paren)(cons paren "\\)"))((eq paren 'words)'("\\<\\(" . "\\)\\>"))((eq paren 'symbols) '("\\_<\\(" . "\\)\\_>"))((null paren)'("\\(?:" . "\\)"))(t'("\\(" . "\\)")))))
1

Note that regexp-opt does not guarantee that its result is absolutely the most efficient form possible.
A hand-tuned regular expression can sometimes be slightly more efficient, but is almost never worth theeffort.

Chapter 35: Searching and Matching1007(concat (car parens)(mapconcat 'regexp-quote strings "\\|")(cdr parens))))regexp-opt-depth regexp[Function]
This function returns the total number of grouping constructs (parenthesized expressions) in regexp. This does not include shy groups (see Section 35.3.1.3 [Regexp
Backslash], page 1001).

regexp-opt-charset chars[Function]
This function returns a regular expression matching a character in the list of characterschars.
(regexp-opt-charset '(?a ?b ?c ?d ?e))⇒ "[a-e]"[Variable]
This variable contains a regexp that is guaranteed not to match any string at all. It
is particularly useful as default value for variables that may be set to a pattern that
actually matches something.

regexp-unmatchable

35.3.4 Problems with Regular Expressions
The Emacs regexp implementation, like many of its kind, is generally robust but occasionallycauses trouble in either of two ways: matching may run out of internal stack space andsignal an error, and it can take a long time to complete. The advice below will make these
symptoms less likely and help alleviate problems that do arise.
• Anchor regexps at the beginning of a line, string or buffer using zero-width assertions (‘^’and \`). This takes advantage of fast paths in the implementation and can avoid futile
matching attempts. Other zero-width assertions may also bring benefits by causing amatch to fail early.
• Avoid or-patterns in favor of character alternatives: write ‘[ab]’ instead of ‘a\|b’. Recall
that ‘\s-’ and ‘\sw’ are equivalent to ‘[[:space:]]’ and ‘[[:word:]]’, respectively.
• Since the last branch of an or-pattern does not add a backtrack point on the stack,consider putting the most likely matched pattern last. For example, ‘^\(?:a\|.b\)*c’
will run out of stack if trying to match a very long string of ‘a’s, but the equivalent‘^\(?:.b\|a\)*c’ will not.
(It is a trade-off: successfully matched or-patterns run faster with the most frequently
matched pattern first.)• Try to ensure that any part of the text can only match in a single way. For example,‘a*a*’ will match the same set of strings as ‘a*’, but the former can do so in many ways
and will therefore cause slow backtracking if the match fails later on. Make or-patternbranches mutually exclusive if possible, so that matching will not go far into more than
one branch before failing.
Be especially careful with nested repetitions: they can easily result in very slow matchingin the presence of ambiguities. For example, ‘\(?:a*b*\)+c’ will take a long time
attempting to match even a moderately long string of ‘a’s before failing. The equivalent‘\(?:a\|b\)*c’ is much faster, and ‘[ab]*c’ better still.

Chapter 35: Searching and Matching1008• Don’t use capturing groups unless they are really needed; that is, use ‘\(?:...\)’
instead of ‘\(...\)’ for bracketing purposes.
If you run into regexp stack overflow despite following the above advice, don’t be afraidof performing the matching in multiple function calls, each using a simpler regexp where
backtracking can more easily be contained.

35.4 Regular Expression Searching
In GNU Emacs, you can search for the next match for a regular expression (see Section 35.3.1[Syntax of Regexps], page 996) either incrementally or not. For incremental search commands,
see Section “Regular Expression Search” in The GNU Emacs Manual. Here we describe
only the search functions useful in programs. The principal one is re-search-forward.
These search functions convert the regular expression to multibyte if the buffer is multibyte;
they convert the regular expression to unibyte if the buffer is unibyte. See Section 34.1 [Text
Representations], page 963.

re-search-forward regexp &optional limit noerror count[Command]This function searches forward in the current buffer for a string of text that is matchedby the regular expression regexp. The function skips over any amount of text thatis not matched by regexp, and leaves point at the end of the first match found. It
returns the new value of point.
If limit is non-nil, it must be a position in the current buffer. It specifies the upperbound to the search. No match extending after that position is accepted. If limit isomitted or nil, it defaults to the end of the accessible portion of the buffer.
What re-search-forward does when the search fails depends on the value of noerror:nil

Signal a search-failed error.

t

Do nothing and return nil.

anything else
Move point to limit (or the end of the accessible portion of the buffer)and return nil.
The argument noerror only affects valid searches which fail to find a match. Invalid
arguments cause errors regardless of noerror.
If count is a positive number n, the search is done n times; each successive search starts
at the end of the previous match. If all these successive searches succeed, the function
call succeeds, moving point and returning its new value. Otherwise the function call
fails, with results depending on the value of noerror, as described above. If count is anegative number −n, the search is done n times in the opposite (backward) direction.
In the following example, point is initially before the ‘T’. Evaluating the search callmoves point to the end of that line (between the ‘t’ of ‘hat’ and the newline).
---------- Buffer: foo ---------I read "?The cat in the hatcomes back" twice.
---------- Buffer: foo ----------

Chapter 35: Searching and Matching1009(re-search-forward "[a-z]+" nil t 5)
⇒ 27---------- Buffer: foo ---------I read "The cat in the hat?
comes back" twice.
---------- Buffer: foo ----------

re-search-backward regexp &optional limit noerror count[Command]This function searches backward in the current buffer for a string of text that ismatched by the regular expression regexp, leaving point at the beginning of the firsttext found.
This function is analogous to re-search-forward, but they are not simple mirror
images. re-search-forward finds the match whose beginning is as close as possible
to the starting point. If re-search-backward were a perfect mirror image, it wouldfind the match whose end is as close as possible. However, in fact it finds the match
whose beginning is as close as possible (and yet ends before the starting point). The
reason for this is that matching a regular expression at a given spot always works
from beginning to end, and starts at a specified beginning position.

A true mirror-image of re-search-forward would require a special feature for matching regular expressions from end to beginning. It’s not worth the trouble of implementing that.

string-match regexp string &optional start inhibit-modify[Function]
This function returns the index of the start of the first match for the regular expression
regexp in string, or nil if there is no match. If start is non-nil, the search starts atthat index in string.
For example,(string-match"quick" "The quick brown fox jumped quickly.")⇒ 4(string-match"quick" "The quick brown fox jumped quickly." 8)⇒ 27
The index of the first character of the string is 0, the index of the second character is
1, and so on.
By default, if this function finds a match, the index of the first character beyond thematch is available as (match-end 0). See Section 35.6 [Match Data], page 1011. If
inhibit-modify is non-nil, the match data isn’t modified.
(string-match"quick" "The quick brown fox jumped quickly." 8)⇒ 27(match-end 0)⇒ 32

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string-match-p regexp string &optional start[Function]
This predicate function does what string-match does, but it avoids modifying thematch data.

looking-at regexp &optional inhibit-modify[Function]
This function determines whether the text in the current buffer directly following
point matches the regular expression regexp. “Directly following” means precisely
that: the search is “anchored” and it can succeed only starting with the first character
following point. The result is t if so, nil otherwise.
This function does not move point, but it does update the match data (if inhibit-modify
is nil or missing, which is the default). See Section 35.6 [Match Data], page 1011. As aconvenience, instead of using the inhibit-modify argument, you can use looking-at-p,
described below.
In this example, point is located directly before the ‘T’. If it were anywhere else, theresult would be nil.
---------- Buffer: foo ---------I read "?The cat in the hatcomes back" twice.
---------- Buffer: foo ---------(looking-at "The cat in the hat$")⇒ tlooking-back regexp limit &optional greedy[Function]
This function returns t if regexp matches the text immediately before point (i.e.,
ending at point), and nil otherwise.
Because regular expression matching works only going forward, this is implemented
by searching backwards from point for a match that ends at point. That can be quite
slow if it has to search a long distance. You can bound the time required by specifying
a non-nil value for limit, which says not to search before limit. In this case, thematch that is found must begin at or after limit. Here’s an example:---------- Buffer: foo ---------I read "?The cat in the hatcomes back" twice.
---------- Buffer: foo ----------(looking-back "read \"" 3)⇒ t(looking-back "read \"" 4)⇒ nil
If greedy is non-nil, this function extends the match backwards as far as possible,
stopping when a single additional previous character cannot be part of a match forregexp. When the match is extended, its starting position is allowed to occur before
limit.
As a general recommendation, try to avoid using looking-back wherever possible,
since it is slow. For this reason, there are no plans to add a looking-back-p function.

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looking-at-p regexp[Function]
This predicate function works like looking-at, but without updating the match data.
[Variable]
If this variable is non-nil, it should be a regular expression that says how to search forwhitespace. In that case, any group of spaces in a regular expression being searched
for stands for use of this regular expression. However, spaces inside of constructs suchas ‘[...]’ and ‘*’, ‘+’, ‘?’ are not affected by search-spaces-regexp.

search-spaces-regexp

Since this variable affects all regular expression search and match constructs, you
should bind it temporarily for as small as possible a part of the code, and only where
the Lisp code affected by the binding performs searches whose regexp was produced
from interactive user input. In other words, this variable should only be used to tellregexp search primitives how to interpret whitespace typed by the user.

35.5 POSIX Regular Expression Searching
The usual regular expression functions do backtracking when necessary to handle the ‘\|’and repetition constructs, but they continue this only until they find some match. Thenthey succeed and report the first match found.
This section describes alternative search functions which perform the full backtracking
specified by the POSIX standard for regular expression matching. They continue backtracking
until they have tried all possibilities and found all matches, so they can report the longest
match, as required by POSIX. This is much slower, so use these functions only when you
really need the longest match.
The POSIX search and match functions do not properly support the non-greedy repetition operators (see Section 35.3.1.1 [Regexp Special], page 996). This is because POSIX
backtracking conflicts with the semantics of non-greedy repetition.

posix-search-forward regexp &optional limit noerror count[Command]This is like re-search-forward except that it performs the full backtracking specified
by the POSIX standard for regular expression matching.

posix-search-backward regexp &optional limit noerror count[Command]This is like re-search-backward except that it performs the full backtracking specified
by the POSIX standard for regular expression matching.

posix-looking-at regexp &optional inhibit-modify[Function]
This is like looking-at except that it performs the full backtracking specified by the
POSIX standard for regular expression matching.

posix-string-match regexp string &optional start inhibit-modify[Function]
This is like string-match except that it performs the full backtracking specified by
the POSIX standard for regular expression matching.

35.6 The Match Data
Emacs keeps track of the start and end positions of the segments of text found during asearch; this is called the match data. Thanks to the match data, you can search for aChapter 35: Searching and Matching

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complex pattern, such as a date in a mail message, and then extract parts of the matchunder control of the pattern.
Because the match data normally describe the most recent search only, you must be
careful not to do another search inadvertently between the search you wish to refer back toand the use of the match data. If you can’t avoid another intervening search, you must saveand restore the match data around it, to prevent it from being overwritten.
Notice that all functions are allowed to overwrite the match data unless they’re explicitly
documented not to do so. A consequence is that functions that are run implicitly inthe background (see Section 42.11 [Timers], page 1281, and Section 42.12 [Idle Timers],
page 1284) should likely save and restore the match data explicitly.

35.6.1 Replacing the Text that MatchedThis function replaces all or part of the text matched by the last search. It works by meansof the match data.

replace-match replacement &optional fixedcase literal string subexp[Function]

This function performs a replacement operation on a buffer or string.
If you did the last search in a buffer, you should omit the string argument or specify
nil for it, and make sure that the current buffer is the one in which you performed
the last search. Then this function edits the buffer, replacing the matched text withreplacement. It leaves point at the end of the replacement text.
If you performed the last search on a string, pass the same string as string. Then thisfunction returns a new string, in which the matched text is replaced by replacement.
If fixedcase is non-nil, then replace-match uses the replacement text without caseconversion; otherwise, it converts the replacement text depending upon the capitalization of the text to be replaced. If the original text is all upper case, this converts thereplacement text to upper case. If all words of the original text are capitalized, thiscapitalizes all the words of the replacement text. If all the words are one-letter andthey are all upper case, they are treated as capitalized words rather than all-upper-casewords.
If literal is non-nil, then replacement is inserted exactly as it is, the only alterations
being case changes as needed. If it is nil (the default), then the character ‘\’ is treatedspecially. If a ‘\’ appears in replacement, then it must be part of one of the following
sequences:‘\&’

This stands for the entire text being replaced.

‘\n’, where n is a digit
This stands for the text that matched the nth subexpression in the original
regexp. Subexpressions are those expressions grouped inside ‘\(...\)’. If
the nth subexpression never matched, an empty string is substituted.
‘\\’

This stands for a single ‘\’ in the replacement text.

‘\?’

This stands for itself (for compatibility with replace-regexp and relatedcommands; see Section “Regexp Replace” in The GNU Emacs Manual).

Any other character following ‘\’ signals an error.

Chapter 35: Searching and Matching1013

The substitutions performed by ‘\&’ and ‘\n’ occur after case conversion, if any.
Therefore, the strings they substitute are never case-converted.
If subexp is non-nil, that says to replace just subexpression number subexp of theregexp that was matched, not the entire match. For example, after matching ‘foo\(ba*r\)’, calling replace-match with 1 as subexp means to replace just the textthat matched ‘\(ba*r\)’.

match-substitute-replacement replacement &optional fixedcase
literal string subexp[Function]

This function returns the text that would be inserted into the buffer by replace-match,
but without modifying the buffer. It is useful if you want to present the user withactual replacement result, with constructs like ‘\n’ or ‘\&’ substituted with matchedgroups. Arguments replacement and optional fixedcase, literal, string and subexp
have the same meaning as for replace-match.

35.6.2 Simple Match Data AccessThis section explains how to use the match data to find out what was matched by the lastsearch or match operation, if it succeeded.
You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which.
If count is zero, you are asking about the entire match. If count is positive, it specifies which
subexpression you want.
Recall that the subexpressions of a regular expression are those expressions grouped withescaped parentheses, ‘\(...\)’. The countth subexpression is found by counting occurrencesof ‘\(’ from the beginning of the whole regular expression. The first subexpression is
numbered 1, the second 2, and so on. Only regular expressions can have subexpressions—after a simple string search, the only information available is about the entire match.
Every successful search sets the match data. Therefore, you should query the match data
immediately after searching, before calling any other function that might perform anothersearch. Alternatively, you may save and restore the match data (see Section 35.6.4 [Saving
Match Data], page 1016) around the call to functions that could perform another search. Or
use the functions that explicitly do not modify the match data; e.g., string-match-p.
A search which fails may or may not alter the match data. In the current implementation,
it does not, but we may change it in the future. Don’t try to rely on the value of the matchdata after a failing search.

match-string count &optional in-string[Function]
This function returns, as a string, the text matched in the last search or match
operation. It returns the entire text if count is zero, or just the portion corresponding
to the countth parenthetical subexpression, if count is positive.
If the last such operation was done against a string with string-match, then you
should pass the same string as the argument in-string. After a buffer search or match,
you should omit in-string or pass nil for it; but you should make sure that thecurrent buffer when you call match-string is the one in which you did the searchingor matching. Failure to follow this advice will lead to incorrect results.
The value is nil if count is out of range, or for a subexpression inside a ‘\|’ alternativethat wasn’t used or a repetition that repeated zero times.

Chapter 35: Searching and Matching1014

match-string-no-properties count &optional in-string[Function]
This function is like match-string except that the result has no text properties.

match-beginning count[Function]
If the last regular expression search found a match, this function returns the positionof the start of the matching text or of a subexpression of it.
If count is zero, then the value is the position of the start of the entire match. Otherwise,
count specifies a subexpression in the regular expression, and the value of the functionis the starting position of the match for that subexpression.

The value is nil for a subexpression inside a ‘\|’ alternative that wasn’t used or arepetition that repeated zero times.

match-end count[Function]
This function is like match-beginning except that it returns the position of the endof the match, rather than the position of the beginning.

Here is an example of using the match data, with a comment showing the positions
within the text:(string-match "\\(qu\\)\\(ick\\)""The quick fox jumped quickly.");0123456789⇒ 4(match-string 0 "The quick fox jumped quickly.")⇒ "quick"(match-string 1 "The quick fox jumped quickly.")⇒ "qu"(match-string 2 "The quick fox jumped quickly.")⇒ "ick"(match-beginning 1)⇒ 4; The beginning of the match;with ‘qu’ is at index 4.

(match-beginning 2)⇒ 6; The beginning of the match;with ‘ick’ is at index 6.

(match-end 1)⇒ 6; The end of the match;with ‘qu’ is at index 6.

(match-end 2)⇒ 9; The end of the match;with ‘ick’ is at index 9.

Here is another example. Point is initially located at the beginning of the line. Searchingmoves point to between the space and the word ‘in’. The beginning of the entire matchis at the 9th character of the buffer (‘T’), and the beginning of the match for the firstsubexpression is at the 13th character (‘c’).

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(list
(re-search-forward "The \\(cat \\)")(match-beginning 0)(match-beginning 1))⇒ (17 9 13)---------- Buffer: foo ---------I read "The cat ?in the hat comes back" twice.
^^
9 13---------- Buffer: foo ---------(In this case, the index returned is a buffer position; the first character of the buffer counts
as 1.)

35.6.3 Accessing the Entire Match Data
The functions match-data and set-match-data read or write the entire match data, all at
once.

match-data &optional integers reuse reseat[Function]
This function returns a list of positions (markers or integers) that record all theinformation on the text that the last search matched. Element zero is the position of
the beginning of the match for the whole expression; element one is the position of
the end of the match for the expression. The next two elements are the positions of
the beginning and end of the match for the first subexpression, and so on. In general,
element number 2n corresponds to (match-beginning n); and element number 2n + 1
corresponds to (match-end n).
Normally all the elements are markers or nil, but if integers is non-nil, that means
to use integers instead of markers. (In that case, the buffer itself is appended as anadditional element at the end of the list, to facilitate complete restoration of the matchdata.) If the last match was done on a string with string-match, then integers arealways used, since markers can’t point into a string.
If reuse is non-nil, it should be a list. In that case, match-data stores the matchdata in reuse. That is, reuse is destructively modified. reuse does not need to have theright length. If it is not long enough to contain the match data, it is extended. If it is
too long, the length of reuse stays the same, but the elements that were not used are
set to nil. The purpose of this feature is to reduce the need for garbage collection.
If reseat is non-nil, all markers on the reuse list are reseated to point to nowhere.

As always, there must be no possibility of intervening searches between the call to asearch function and the call to match-data that is intended to access the match data
for that search.
(match-data)⇒ (#<marker at 9 in foo>#<marker at 17 in foo>#<marker at 13 in foo>#<marker at 17 in foo>)Chapter 35: Searching and Matching1016

set-match-data match-list &optional reseat[Function]
This function sets the match data from the elements of match-list, which should be alist that was the value of a previous call to match-data. (More precisely, anythingthat has the same format will work.)
If match-list refers to a buffer that doesn’t exist, you don’t get an error; that sets thematch data in a meaningless but harmless way.
If reseat is non-nil, all markers on the match-list list are reseated to point to nowhere.
store-match-data is a semi-obsolete alias for set-match-data.

35.6.4 Saving and Restoring the Match Data
When you call a function that may search, you may need to save and restore the match dataaround that call, if you want to preserve the match data from an earlier search for later use.
Here is an example that shows the problem that arises if you fail to save the match data:(re-search-forward "The \\(cat \\)")
⇒ 48
(foo)
; foo does more searching.
(match-end 0)⇒ 61; Unexpected result—not 48!
You can save and restore the match data with save-match-data:save-match-data body. . .

[Macro]This macro executes body, saving and restoring the match data around it. The return
value is the value of the last form in body.

You could use set-match-data together with match-data to imitate the effect of thespecial form save-match-data. Here is how:(let ((data (match-data)))(unwind-protect...
; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs process filter functions(see Section 40.9.2 [Filter Functions], page 1101) and process sentinels (see Section 40.10[Sentinels], page 1105).

35.7 Search and Replace
If you want to find all matches for a regexp in part of the buffer and replace them, the mostflexible way is to write an explicit loop using re-search-forward and replace-match, likethis:(while (re-search-forward "foo[ \t]+bar" nil t)(replace-match "foobar"))See Section 35.6.1 [Replacing the Text that Matched], page 1012, for a description of
replace-match.
It may be more convenient to limit the replacements to a specific region. The function
replace-regexp-in-region does that.

Chapter 35: Searching and Matching1017

replace-regexp-in-region regexp replacement &optional start end[Function]
This function replaces all the occurrences of regexp with replacement in the region of
buffer text between start and end; start defaults to position of point, and end defaults
to the last accessible position of the buffer. The search for regexp is case-sensitive,
and replacement is inserted without changing its letter-case. The replacement string
can use the same special elements starting with ‘\’ as replace-match does. The
function returns the number of replaced occurrences, or nil if regexp is not found.
The function preserves the position of point.
(replace-regexp-in-region "foo[ \t]+bar" "foobar")

replace-string-in-region string replacement &optional start end[Function]
This function works similarly to replace-regexp-in-region, but searches for, andreplaces, literal strings instead of regular expressions.

Emacs also has special functions for replacing matches in a string.

replace-regexp-in-string regexp rep string &optional fixedcase
literal subexp start[Function]

This function copies string and searches it for matches for regexp, and replaces themwith rep. It returns the modified copy. If start is non-nil, the search for matches
starts at that index in string, and the returned value does not include the first start
characters of string. To get the whole transformed string, concatenate the first start
characters of string with the return value.
This function uses replace-match to do the replacement, and it passes the optional
arguments fixedcase, literal and subexp along to replace-match.
Instead of a string, rep can be a function. In that case, replace-regexp-in-string
calls rep for each match, passing the text of the match as its sole argument. It collects
the value rep returns and passes that to replace-match as the replacement string.
The match data at this point are the result of matching regexp against a substring ofstring.

string-replace from-string to-string in-string[Function]
This function replaces all occurrences of from-string with to-string in in-string andreturns the result. It may return one of its arguments unchanged, a constant string or
a new string. Case is significant, and text properties are ignored.

If you want to write a command along the lines of query-replace, you can use
perform-replace to do the work.

perform-replace from-string replacements query-flag regexp-flag[Function]delimited-flag &optional repeat-count map start end backward
region-noncontiguous-pThis function is the guts of query-replace and related commands. It searches foroccurrences of from-string in the text between positions start and end and replaces
some or all of them. If start is nil (or omitted), point is used instead, and the end of
the buffer’s accessible portion is used for end. (If the optional argument backward is
non-nil, the search starts at end and goes backward.)

Chapter 35: Searching and Matching1018

If query-flag is nil, it replaces all occurrences; otherwise, it asks the user what to doabout each one.
If regexp-flag is non-nil, then from-string is considered a regular expression; otherwise,
it must match literally. If delimited-flag is non-nil, then only replacements surrounded
by word boundaries are considered.
The argument replacements specifies what to replace occurrences with. If it is a string,that string is used. It can also be a list of strings, to be used in cyclic order.
If replacements is a cons cell, (function . data), this means to call function after
each match to get the replacement text. This function is called with two arguments:
data, and the number of replacements already made.
If repeat-count is non-nil, it should be an integer. Then it specifies how many times
to use each of the strings in the replacements list before advancing cyclically to thenext one.
If from-string contains upper-case letters, then perform-replace binds case-foldsearch to nil, and it uses the replacements without altering their case.
Normally, the keymap query-replace-map defines the possible user responses forqueries. The argument map, if non-nil, specifies a keymap to use instead ofquery-replace-map.
Non-nil region-noncontiguous-p means that the region between start and end iscomposed of noncontiguous pieces. The most common example of this is a rectangularregion, where the pieces are separated by newline characters.
This function uses one of two functions to search for the next occurrence of from-string.
These functions are specified by the values of two variables: replace-re-searchfunction and replace-search-function. The former is called when the argument
regexp-flag is non-nil, the latter when it is nil.
[Variable]
This variable holds a special keymap that defines the valid user responses for
perform-replace and the commands that use it, as well as y-or-n-p andmap-y-or-n-p. This map is unusual in two ways:

query-replace-map• The key bindings are not commands, just symbols that are meaningful to thefunctions that use this map.
• Prefix keys are not supported; each key binding must be for a single-event key
sequence. This is because the functions don’t use read-key-sequence to get the
input; instead, they read a single event and look it up “by hand”.
Here are the meaningful bindings for query-replace-map. Several of them are meaningful
only for query-replace and friends.
act

Do take the action being considered—in other words, “yes”.

skip

Do not take action for this question—in other words, “no”.

exit

Answer this question “no”, and give up on the entire series of questions, assumingthat the answers will be “no”.

Chapter 35: Searching and Matching1019

exit-prefix
Like exit, but add the key that was pressed to unread-command-events (seeSection 22.8.6 [Event Input Misc], page 468).
act-and-exit
Answer this question “yes”, and give up on the entire series of questions, assumingthat subsequent answers will be “no”.
act-and-show
Answer this question “yes”, but show the results—don’t advance yet to the nextquestion.
automatic
Answer this question and all subsequent questions in the series with “yes”,
without further user interaction.
backupMove back to the previous place that a question was asked about.

undo

Undo last replacement and move back to the place where that replacement was
performed.

undo-all

Undo all replacements and move back to the place where the first replacement
was performed.

editEnter a recursive edit to deal with this question—instead of any other actionthat would normally be taken.

edit-replacement
Edit the replacement for this question in the minibuffer.
delete-and-edit
Delete the text being considered, then enter a recursive edit to replace it.
recenter
scroll-up
scroll-down
scroll-other-window
scroll-other-window-down
Perform the specified window scroll operation, then ask the same question again.
Only y-or-n-p and related functions use this answer.
quit

Perform a quit right away. Only y-or-n-p and related functions use this answer.

help

Display some help, then ask again.
[Variable]
This variable holds a keymap that extends query-replace-map by providing additional
key bindings that are useful in multi-buffer replacements. The additional bindings are:multi-query-replace-map

automatic-all
Answer this question and all subsequent questions in the series with “yes”,
without further user interaction, for all remaining buffers.
exit-current
Answer this question “no”, and give up on the entire series of questions
for the current buffer. Continue to the next buffer in the sequence.

Chapter 35: Searching and Matching

1020[Variable]
This variable specifies a function that perform-replace calls to search for the next
string to replace. Its default value is search-forward. Any other value should namea function of 3 arguments: the first 3 arguments of search-forward (see Section 35.1
[String Search], page 993).

replace-search-function[Variable]
This variable specifies a function that perform-replace calls to search for the next
regexp to replace. Its default value is re-search-forward. Any other value should
name a function of 3 arguments: the first 3 arguments of re-search-forward (seeSection 35.4 [Regexp Search], page 1008).

replace-re-search-function

35.8 Standard Regular Expressions Used in Editing
This section describes some variables that hold regular expressions used for certain purposesin editing:[User Option]
This is the regular expression describing line-beginnings that separate pages. The
default value is "^\014" (i.e., "^^L" or "^\C-l"); this matches a line that starts witha formfeed character.

page-delimiter

The following two regular expressions should not assume the match always starts at the
beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraphcommands do check for a match only at the beginning of a line, which means that ‘^’ would
be superfluous. When there is a nonzero left margin, they accept matches that start after
the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes
where a left margin is never used.
[User Option]
This is the regular expression for recognizing the beginning of a line that separates
paragraphs. (If you change this, you may have to change paragraph-start also.) The
default value is "[ \t\f]*$", which matches a line that consists entirely of spaces,tabs, and form feeds (after its left margin).

paragraph-separate[User Option]
This is the regular expression for recognizing the beginning of a line that starts or
separates paragraphs. The default value is "\f\\|[ \t]*$", which matches a line
containing only whitespace or starting with a form feed (after its left margin).

paragraph-start[User Option]
If non-nil, the value should be a regular expression describing the end of a sentence,
including the whitespace following the sentence. (All paragraph boundaries also end
sentences, regardless.)

sentence-end

If the value is nil, as it is by default, then the function sentence-end constructs theregexp. That is why you should always call the function sentence-end to obtain theregexp to be used to recognize the end of a sentence.

Chapter 35: Searching and Matching

1021[Function]
This function returns the value of the variable sentence-end, if non-nil. Otherwise
it returns a default value based on the values of the variables sentence-end-doublespace (see [Definition of sentence-end-double-space], page 901), sentence-endwithout-period, and sentence-end-without-space.

sentence-end

1022

36 Syntax Tables
A syntax table specifies the syntactic role of each character in a buffer. It can be used
to determine where words, symbols, and other syntactic constructs begin and end. This
information is used by many Emacs facilities, including Font Lock mode (see Section 24.6
[Font Lock Mode], page 563) and the various complex movement commands (see Section 31.2
[Motion], page 854).

36.1 Syntax Table Concepts
A syntax table is a data structure which can be used to look up the syntax class and othersyntactic properties of each character. Syntax tables are used by Lisp programs for scanningand moving across text.
Internally, a syntax table is a char-table (see Section 6.6 [Char-Tables], page 119). The element at index c describes the character with code c; its value is a cons cell which specifies thesyntax of the character in question. See Section 36.7 [Syntax Table Internals], page 1034, fordetails. However, instead of using aset and aref to modify and inspect syntax table contents,
you should usually use the higher-level functions char-syntax and modify-syntax-entry,
which are described in Section 36.3 [Syntax Table Functions], page 1027.

syntax-table-p object[Function]

This function returns t if object is a syntax table.
Each buffer has its own major mode, and each major mode has its own idea of the syntax
class of various characters. For example, in Lisp mode, the character ‘;’ begins a comment,
but in C mode, it terminates a statement. To support these variations, the syntax table islocal to each buffer. Typically, each major mode has its own syntax table, which it installs inall buffers that use that mode. For example, the variable emacs-lisp-mode-syntax-tableholds the syntax table used by Emacs Lisp mode, and c-mode-syntax-table holds thesyntax table used by C mode. Changing a major mode’s syntax table alters the syntax in allof that mode’s buffers, as well as in any buffers subsequently put in that mode. Occasionally,
several similar modes share one syntax table. See Section 24.2.9 [Example Major Modes],page 542, for an example of how to set up a syntax table.
A syntax table can inherit from another syntax table, which is called its parent syntax
table. A syntax table can leave the syntax class of some characters unspecified, by giving
them the “inherit” syntax class; such a character then acquires the syntax class specified by
the parent syntax table (see Section 36.2.1 [Syntax Class Table], page 1023). Emacs defines
a standard syntax table, which is the default parent syntax table, and is also the syntax
table used by Fundamental mode.
[Function]
This function returns the standard syntax table, which is the syntax table used in
Fundamental mode.

standard-syntax-table

Syntax tables are not used by the Emacs Lisp reader, which has its own built-in syntactic
rules which cannot be changed. (Some Lisp systems provide ways to redefine the read syntax,
but we decided to leave this feature out of Emacs Lisp for simplicity.)Chapter 36: Syntax Tables

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36.2 Syntax Descriptors
The syntax class of a character describes its syntactic role. Each syntax table specifies thesyntax class of each character. There is no necessary relationship between the class of acharacter in one syntax table and its class in any other table.
Each syntax class is designated by a mnemonic character, which serves as the name of
the class when you need to specify a class. Usually, this designator character is one that isoften assigned that class; however, its meaning as a designator is unvarying and independentof what syntax that character currently has. Thus, ‘\’ as a designator character always
stands for escape character syntax, regardless of whether the ‘\’ character actually has thatsyntax in the current syntax table.
A syntax descriptor is a Lisp string that describes the syntax class and other syntactic
properties of a character. When you want to modify the syntax of a character, that is doneby calling the function modify-syntax-entry and passing a syntax descriptor as one of its
arguments (see Section 36.3 [Syntax Table Functions], page 1027).
The first character in a syntax descriptor must be a syntax class designator character.
The second character, if present, specifies a matching character (e.g., in Lisp, the matching
character for ‘(’ is ‘)’); a space specifies that there is no matching character. Then
come characters specifying additional syntax properties (see Section 36.2.2 [Syntax Flags],
page 1026).
If no matching character or flags are needed, only one character (specifying the syntax
class) is sufficient.
For example, the syntax descriptor for the character ‘*’ in C mode is ". 23" (i.e.,punctuation, matching character slot unused, second character of a comment-starter, firstcharacter of a comment-ender), and the entry for ‘/’ is ‘. 14’ (i.e., punctuation, matching
character slot unused, first character of a comment-starter, second character of a commentender).
Emacs also defines raw syntax descriptors, which are used to describe syntax classes at alower level. See Section 36.7 [Syntax Table Internals], page 1034.

36.2.1 Table of Syntax Classes
Here is a table of syntax classes, the characters that designate them, their meanings, andexamples of their use.
Whitespace characters: ‘ ’ or ‘-’
Characters that separate symbols and words from each other. Typically, whitespace characters have no other syntactic significance, and multiple whitespacecharacters are syntactically equivalent to a single one. Space, tab, and formfeed
are classified as whitespace in almost all major modes.
This syntax class can be designated by either ‘ ’ or ‘-’. Both designators areequivalent.
Word constituents: ‘w’Parts of words in human languages. These are typically used in variable andcommand names in programs. All upper- and lower-case letters, and the digits,
are typically word constituents.

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Symbol constituents: ‘_’Extra characters used in variable and command names along with word constituents. Examples include the characters ‘$&*+-_<>’ in Lisp mode, which may
be part of a symbol name even though they are not part of English words. In
standard C, the only non-word-constituent character that is valid in symbols isunderscore (‘_’).
Punctuation characters: ‘.’Characters used as punctuation in a human language, or used in a programming
language to separate symbols from one another. Some programming language
modes, such as Emacs Lisp mode, have no characters in this class since thefew characters that are not symbol or word constituents all have other uses.
Other programming language modes, such as C mode, use punctuation syntax
for operators.
Open parenthesis characters: ‘(’
Close parenthesis characters: ‘)’Characters used in dissimilar pairs to surround sentences or expressions. Such agrouping is begun with an open parenthesis character and terminated with aclose. Each open parenthesis character matches a particular close parenthesis
character, and vice versa. Normally, Emacs indicates momentarily the matching
open parenthesis when you insert a close parenthesis. See Section 41.22 [Blinking],
page 1241.
In human languages, and in C code, the parenthesis pairs are ‘()’, ‘[]’, and ‘{}’.
In Emacs Lisp, the delimiters for lists and vectors (‘()’ and ‘[]’) are classified
as parenthesis characters.
String quotes: ‘"’Characters used to delimit string constants. The same string quote character
appears at the beginning and the end of a string. Such quoted strings do notnest.
The parsing facilities of Emacs consider a string as a single token. The usual
syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (‘"’) and verticalbar (‘|’). ‘|’ is not used in Emacs Lisp, but it is used in Common Lisp. C also
has two string quote characters: double-quote for strings, and apostrophe (‘'’)
for character constants.
Human text has no string quote characters. We do not want quotation marks
to turn off the usual syntactic properties of other characters in the quotation.
Escape-syntax characters: ‘\’Characters that start an escape sequence, such as is used in string and character
constants. The character ‘\’ belongs to this class in both C and Lisp. (In C, it
is used thus only inside strings, but it turns out to cause no trouble to treat it
this way throughout C code.)
Characters in this class count as part of words if words-include-escapes is
non-nil. See Section 31.2.2 [Word Motion], page 855.

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Character quotes: ‘/’Characters used to quote the following character so that it loses its normal
syntactic meaning. This differs from an escape character in that only thecharacter immediately following is ever affected.
Characters in this class count as part of words if words-include-escapes is
non-nil. See Section 31.2.2 [Word Motion], page 855.
This class is used for backslash in TEX mode.
Paired delimiters: ‘$’
Similar to string quote characters, except that the syntactic properties of thecharacters between the delimiters are not suppressed. Only TEX mode uses apaired delimiter presently—the ‘$’ that both enters and leaves math mode.
Expression prefixes: ‘'’Characters used for syntactic operators that are considered as part of an expression if they appear next to one. In Lisp modes, these characters include
the apostrophe, ‘'’ (used for quoting), the comma, ‘,’ (used in macros), and ‘#’(used in the read syntax for certain data types).
Comment starters: ‘<’Comment enders: ‘>’Characters used in various languages to delimit comments. Human text has
no comment characters. In Lisp, the semicolon (‘;’) starts a comment and a
newline or formfeed ends one.
Inherit standard syntax: ‘@’This syntax class does not specify a particular syntax. It says to look in theparent syntax table to find the syntax of this character.
Generic comment delimiters: ‘!’(This syntax class is also known as “comment-fence”.) Characters that startor end a special kind of comment. Any generic comment delimiter matches
any generic comment delimiter, but they cannot match a comment starter orcomment ender; generic comment delimiters can only match each other.
This syntax class is primarily meant for use with the syntax-table text property(see Section 36.4 [Syntax Properties], page 1029). You can mark any range ofcharacters as forming a comment, by giving the first and last characters of therange syntax-table properties identifying them as generic comment delimiters.
Generic string delimiters: ‘|’(This syntax class is also known as “string-fence”.) Characters that start or end
a string. This class differs from the string quote class in that any generic string
delimiter can match any other generic string delimiter; but they do not match
ordinary string quote characters.
This syntax class is primarily meant for use with the syntax-table text property(see Section 36.4 [Syntax Properties], page 1029). You can mark any range ofcharacters as forming a string constant, by giving the first and last characters of
the range syntax-table properties identifying them as generic string delimiters.

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36.2.2 Syntax Flags
In addition to the classes, entries for characters in a syntax table can specify flags. Thereare eight possible flags, represented by the characters ‘1’, ‘2’, ‘3’, ‘4’, ‘b’, ‘c’, ‘n’, and ‘p’.
All the flags except ‘p’ are used to describe comment delimiters. The digit flags areused for comment delimiters made up of 2 characters. They indicate that a character canalso be part of a comment sequence, in addition to the syntactic properties associated with
its character class. The flags are independent of the class and each other for the sake ofcharacters such as ‘*’ in C mode, which is a punctuation character, and the second characterof a start-of-comment sequence (‘/*’), and the first character of an end-of-comment sequence(‘*/’). The flags ‘b’, ‘c’, and ‘n’ are used to qualify the corresponding comment delimiter.
Here is a table of the possible flags for a character c, and what they mean:• ‘1’ means c is the start of a two-character comment-start sequence.
• ‘2’ means c is the second character of such a sequence.
• ‘3’ means c is the start of a two-character comment-end sequence.
• ‘4’ means c is the second character of such a sequence.
• ‘b’ means that c as a comment delimiter belongs to the alternative “b” comment style.
For a two-character comment starter, this flag is only significant on the second char,and for a 2-character comment ender it is only significant on the first char.
• ‘c’ means that c as a comment delimiter belongs to the alternative “c” comment style.
For a two-character comment delimiter, ‘c’ on either character makes it of style “c”.
• ‘n’ on a comment delimiter character specifies that this kind of comment can be nested.
Inside such a comment, only comments of the same style will be recognized. For a
two-character comment delimiter, ‘n’ on either character makes it nestable.
Emacs supports several comment styles simultaneously in any one syntax table. A
comment style is a set of flags ‘b’, ‘c’, and ‘n’, so there can be up to 8 different comment
styles, each one named by the set of its flags. Each comment delimiter has a styleand only matches comment delimiters of the same style. Thus if a comment starts
with the comment-start sequence of style “bn”, it will extend until the next matchingcomment-end sequence of style “bn”. When the set of flags has neither flag ‘b’ nor flag‘c’ set, the resulting style is called the “a” style.
The appropriate comment syntax settings for C++ can be as follows:
‘/’

‘124’

‘*’

‘23b’

newline‘>’This defines four comment-delimiting sequences:‘/*’

This is a comment-start sequence for “b” style because the second character,‘*’, has the ‘b’ flag.

‘//’

This is a comment-start sequence for “a” style because the second character,‘/’, does not have the ‘b’ flag.

‘*/’

This is a comment-end sequence for “b” style because the first character,‘*’, has the ‘b’ flag.

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newlineThis is a comment-end sequence for “a” style, because the newline character
does not have the ‘b’ flag.
• ‘p’ identifies an additional prefix character for Lisp syntax. These characters are treatedas whitespace when they appear between expressions. When they appear within an
expression, they are handled according to their usual syntax classes.
The function backward-prefix-chars moves back over these characters, as well asover characters whose primary syntax class is prefix (‘'’). See Section 36.5 [Motion and
Syntax], page 1030.

36.3 Syntax Table Functions
In this section we describe functions for creating, accessing and altering syntax tables.

make-syntax-table &optional table[Function]
This function creates a new syntax table. If table is non-nil, the parent of the new
syntax table is table; otherwise, the parent is the standard syntax table.
In the new syntax table, all characters are initially given the “inherit” (‘@’) syntax
class, i.e., their syntax is inherited from the parent table (see Section 36.2.1 [Syntax
Class Table], page 1023).

copy-syntax-table &optional table[Function]
This function constructs a copy of table and returns it. If table is omitted or nil, it
returns a copy of the standard syntax table. Otherwise, an error is signaled if table is
not a syntax table.

modify-syntax-entry char syntax-descriptor &optional table[Command]This function sets the syntax entry for char according to syntax-descriptor. char must
be a character, or a cons cell of the form (min . max); in the latter case, the function
sets the syntax entries for all characters in the range between min and max, inclusive.
The syntax is changed only for table, which defaults to the current buffer’s syntax
table, and not in any other syntax table.
The argument syntax-descriptor is a syntax descriptor, i.e., a string whose firstcharacter is a syntax class designator and whose second and subsequent characters
optionally specify a matching character and syntax flags. See Section 36.2 [Syntax
Descriptors], page 1023. An error is signaled if syntax-descriptor is not a valid syntax
descriptor.
This function always returns nil. The old syntax information in the table for thischaracter is discarded.
Examples:;; Put the space character in class whitespace.
(modify-syntax-entry ?\s " ")⇒ nil;; Make ‘$’ an open parenthesis character,;;with ‘^’ as its matching close.
(modify-syntax-entry ?$ "(^")⇒ nil

Chapter 36: Syntax Tables

1028;; Make ‘^’ a close parenthesis character,;;with ‘$’ as its matching open.
(modify-syntax-entry ?^ ")$")⇒ nil;; Make ‘/’ a punctuation character,;;the first character of a start-comment sequence,;;and the second character of an end-comment sequence.
;;
This is used in C mode.
(modify-syntax-entry ?/ ". 14")⇒ nilchar-syntax character[Function]
This function returns the syntax class of character, represented by its designator
character (see Section 36.2.1 [Syntax Class Table], page 1023). This returns only theclass, not its matching character or syntax flags.
The following examples apply to C mode. (We use string to make it easier to see thecharacter returned by char-syntax.);; Space characters have whitespace syntax class.
(string (char-syntax ?\s))⇒ " ";; Forward slash characters have punctuation syntax.
;; Note that this char-syntax call does not reveal;; that it is also part of comment-start and -end sequences.
(string (char-syntax ?/))
⇒ ".";; Open parenthesis characters have open parenthesis syntax.
;; Note that this char-syntax call does not reveal that;; it has a matching character, ‘)’.
(string (char-syntax ?\())⇒ "("set-syntax-table table[Function]
This function makes table the syntax table for the current buffer. It returns table.

[Function]
This function returns the current syntax table, which is the table for the current buffer.

syntax-table

describe-syntax &optional buffer[Command]This command displays the contents of the syntax table of buffer (by default, thecurrent buffer) in a help buffer.

with-syntax-table table body. . .

[Macro]This macro executes body using table as the current syntax table. It returns the valueof the last form in body, after restoring the old current syntax table.

Chapter 36: Syntax Tables

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Since each buffer has its own current syntax table, we should make that more precise:
with-syntax-table temporarily alters the current syntax table of whichever buffer iscurrent at the time the macro execution starts. Other buffers are not affected.

36.4 Syntax Properties
When the syntax table is not flexible enough to specify the syntax of a language, you canoverride the syntax table for specific character occurrences in the buffer, by applying a
syntax-table text property. See Section 33.19 [Text Properties], page 917, for how to apply
text properties.
The valid values of syntax-table text property are:syntax-table
If the property value is a syntax table, that table is used instead of the current
buffer’s syntax table to determine the syntax for the underlying text character.
(syntax-code . matching-char)
A cons cell of this format is a raw syntax descriptor (see Section 36.7 [Syntax
Table Internals], page 1034), which directly specifies a syntax class for theunderlying text character.
nil

If the property is nil, the character’s syntax is determined from the current
syntax table in the usual way.
[Variable]
If this is non-nil, the syntax scanning functions, like forward-sexp, pay attention tosyntax-table text properties. Otherwise they use only the current syntax table.

parse-sexp-lookup-properties[Variable]
This variable, if non-nil, should store a function for applying syntax-table properties
to a specified stretch of text. It is intended to be used by major modes to install afunction which applies syntax-table properties in some mode-appropriate way.

syntax-propertize-function

The function is called by syntax-ppss (see Section 36.6.2 [Position Parse], page 1032),
and by Font Lock mode during syntactic fontification (see Section 24.6.8 [Syntactic
Font Lock], page 575). It is called with two arguments, start and end, which are
the starting and ending positions of the text on which it should act. It is allowed toarbitrarily move point within the region delimited by start and end; such motions
don’t need to use save-excursion (see Section 31.3 [Excursions], page 864). It is also
allowed to call syntax-ppss on any position before end, but if a Lisp program calls
syntax-ppss on some position and later modifies the buffer at some earlier position,then it is that program’s responsibility to call syntax-ppss-flush-cache to flush the
now obsolete info from the cache.
Caution: When this variable is non-nil, Emacs removes syntax-table text properties
arbitrarily and relies on syntax-propertize-function to reapply them. Thus if thisfacility is used at all, the function must apply all syntax-table text properties usedby the major mode. In particular, Modes derived from a CC Mode mode must not
use this variable, since CC Mode uses other means to apply and remove these text
properties.

Chapter 36: Syntax Tables

1030[Variable]
This abnormal hook is run by the syntax parsing code prior to callingsyntax-propertize-function. Its role is to help locate safe starting and ending
buffer positions for passing to syntax-propertize-function. For example, a major
mode can add a function to this hook to identify multi-line syntactic constructs, andensure that the boundaries do not fall in the middle of one.

syntax-propertize-extend-region-functions

Each function in this hook should accept two arguments, start and end. It should
return either a cons cell of two adjusted buffer positions, (new-start . new-end), or
nil if no adjustment is necessary. The hook functions are run in turn, repeatedly,
until they all return nil.

36.5 Motion and Syntax
This section describes functions for moving across characters that have certain syntax classes.

skip-syntax-forward syntaxes &optional limit[Function]
This function moves point forward across characters having syntax classes mentioned
in syntaxes (a string of syntax class characters). It stops when it encounters the endof the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not insyntaxes.
The return value is the distance traveled, which is a nonnegative integer.

skip-syntax-backward syntaxes &optional limit[Function]
This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position
limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not insyntaxes.
The return value indicates the distance traveled. It is an integer that is zero or less.
[Function]
This function moves point backward over any number of characters with expression
prefix syntax. This includes both characters in the expression prefix syntax class, andcharacters with the ‘p’ flag.

backward-prefix-chars

36.6 Parsing Expressions
This section describes functions for parsing and scanning balanced expressions. We will referto such expressions as sexps, following the terminology of Lisp, even though these functions
can act on languages other than Lisp. Basically, a sexp is either a balanced parentheticalgrouping, a string, or a symbol (i.e., a sequence of characters whose syntax is either word
constituent or symbol constituent). However, characters in the expression prefix syntax class(see Section 36.2.1 [Syntax Class Table], page 1023) are treated as part of the sexp if they
appear next to it.
The syntax table controls the interpretation of characters, so these functions can beused for Lisp expressions when in Lisp mode and for C expressions when in C mode. See

Chapter 36: Syntax Tables

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Section 31.2.6 [List Motion], page 861, for convenient higher-level functions for moving overbalanced expressions.
A character’s syntax controls how it changes the state of the parser, rather than describing
the state itself. For example, a string delimiter character toggles the parser state between
in-string and in-code, but the syntax of characters does not directly say whether they are
inside a string. For example (note that 15 is the syntax code for generic string delimiters),(put-text-property 1 9 'syntax-table '(15 . nil))does not tell Emacs that the first eight chars of the current buffer are a string, but rather
that they are all string delimiters. As a result, Emacs treats them as four consecutive empty
string constants.

36.6.1 Motion Commands Based on Parsing
This section describes simple point-motion functions that operate based on parsing expressions.

scan-lists from count depth[Function]
This function scans forward count balanced parenthetical groupings from position
from. It returns the position where the scan stops. If count is negative, the scanmoves backwards.
If depth is nonzero, treat the starting position as being depth parentheses deep. The
scanner moves forward or backward through the buffer until the depth changes tozero count times. Hence, a positive value for depth has the effect of moving out depth
levels of parenthesis from the starting position, while a negative depth has the effectof moving deeper by -depth levels of parenthesis.
Scanning ignores comments if parse-sexp-ignore-comments is non-nil.
If the scan reaches the beginning or end of the accessible part of the buffer before it
has scanned over count parenthetical groupings, the return value is nil if the depth
at that point is zero; if the depth is non-zero, a scan-error error is signaled.

scan-sexps from count[Function]
This function scans forward count sexps from position from. It returns the position
where the scan stops. If count is negative, the scan moves backwards.
Scanning ignores comments if parse-sexp-ignore-comments is non-nil.
If the scan reaches the beginning or end of (the accessible part of) the buffer while inthe middle of a parenthetical grouping, an error is signaled. If it reaches the beginningor end between groupings but before count is used up, nil is returned.

forward-comment count[Function]
This function moves point forward across count complete comments (that is, including
the starting delimiter and the terminating delimiter if any), plus any whitespaceencountered on the way. It moves backward if count is negative. If it encounters
anything other than a comment or whitespace, it stops, leaving point at the place where
it stopped. This includes (for instance) finding the end of a comment when moving
forward and expecting the beginning of one. The function also stops immediately
after moving over the specified number of complete comments. If count comments

Chapter 36: Syntax Tables1032

are found as expected, with nothing except whitespace between them, it returns t;otherwise it returns nil.
This function cannot tell whether the comments it traverses are embedded within astring. If they look like comments, it treats them as comments.
To move forward over all comments and whitespace following point, use(forward-comment (buffer-size)). (buffer-size) is a good argument to use,
because the number of comments in the buffer cannot exceed that many.

36.6.2 Finding the Parse State for a Position
For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic
state corresponding to a given buffer position. This function does that conveniently.

syntax-ppss &optional pos[Function]
This function returns the parser state that the parser would reach at position pos
starting from the beginning of the visible portion of the buffer. See the next section
for a description of the parser state.
The return value is the same as if you call the low-level parsing functionparse-partial-sexp to parse from the beginning of the visible portion of the buffer
to pos (see Section 36.6.4 [Low-Level Parsing], page 1033). However, syntax-ppss
uses caches to speed up the computation. Due to this optimization, the second value(previous complete subexpression) and sixth value (minimum parenthesis depth) in
the returned parser state are not meaningful.
This function has a side effect: it adds a buffer-local entry to before-changefunctions (see Section 33.34 [Change Hooks], page 961) for syntax-ppss-flushcache (see below). This entry keeps the cache consistent as the buffer is modified. However, the cache might not be updated if syntax-ppss is called while before-changefunctions is temporarily let-bound, or if the buffer is modified without runningthe hook, such as when using inhibit-modification-hooks. In those cases, it isnecessary to call syntax-ppss-flush-cache explicitly.

syntax-ppss-flush-cache beg &rest ignored-args[Function]
This function flushes the cache used by syntax-ppss, starting at position beg. The
remaining arguments, ignored-args, are ignored; this function accepts them so that it
can be directly used on hooks such as before-change-functions (see Section 33.34[Change Hooks], page 961).

36.6.3 Parser StateA parser state is a list of (currently) eleven elements describing the state of the syntactic
parser, after it parses the text between a specified starting point and a specified end
point in the buffer using parse-partial-sexp (see Section 36.6.4 [Low-Level Parsing],
page 1033). Parsing functions such as syntax-ppss also return a parser state as the value.
parse-partial-sexp can accept a parser state as an argument, for resuming parsing.
Here are the meanings of the elements of the parser state:
0. The depth in parentheses, counting from 0. Warning: this can be negative if there are
more close parens than open parens between the parser’s starting point and end point.

Chapter 36: Syntax Tables1033

1. The character position of the start of the innermost parenthetical grouping containing
the stopping point; nil if none.
2. The character position of the start of the last complete subexpression terminated; nil
if none.
3. Non-nil if inside a string. More precisely, this is the character that will terminate thestring, or t if a generic string delimiter character should terminate it.
4. t if inside a non-nestable comment (of any comment style; see Section 36.2.2 [Syntax
Flags], page 1026); or the comment nesting level if inside a comment that can be nested.
5. t if the end point is just after a quote character.
6. The minimum parenthesis depth encountered during this scan.
7. What kind of comment is active: nil if not in a comment or in a comment of style‘a’; 1 for a comment of style ‘b’; 2 for a comment of style ‘c’; and syntax-table for acomment that should be ended by a generic comment delimiter character.
8. The string or comment start position. While inside a comment, this is the position
where the comment began; while inside a string, this is the position where the string
began. When outside of strings and comments, this element is nil.
9. The list of the positions of the currently open parentheses, starting with the outermost.
10. When the last buffer position scanned was the (potential) first character of a two
character construct (comment delimiter or escaped/char-quoted character pair), thesyntax-code (see Section 36.7 [Syntax Table Internals], page 1034) of that position.
Otherwise nil.
Elements 1, 2, and 6 are ignored in a state which you pass as an argument toparse-partial-sexp to continue parsing. Elements 9 and 10 are mainly used internally by
the parser code.
Some additional useful information is available from a parser state using these functions:syntax-ppss-toplevel-pos state[Function]
This function extracts, from parser state state, the last position scanned in the parse
which was at top level in grammatical structure. “At top level” means outside of any
parentheses, comments, or strings.

The value is nil if state represents a parse which has arrived at a top level position.

syntax-ppss-context state[Function]
Return string if the end position of the scan returning state is in a string, andcomment if it’s in a comment. Otherwise return nil.

36.6.4 Low-Level Parsing
The most basic way to use the expression parser is to tell it to start at a given position witha certain state, and parse up to a specified end position.

parse-partial-sexp start limit &optional target-depth stop-before
state stop-comment[Function]

This function parses a sexp in the current buffer starting at start, not scanning past
limit. It stops at position limit or when certain criteria described below are met, andChapter 36: Syntax Tables

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sets point to the location where parsing stops. It returns a parser state describing thestatus of the parse at the point where it stops.
If the third argument target-depth is non-nil, parsing stops if the depth in parentheses
becomes equal to target-depth. The depth starts at 0, or at whatever is given in state.
If the fourth argument stop-before is non-nil, parsing stops when it comes to any
character that starts a sexp. If stop-comment is non-nil, parsing stops after the startof an unnested comment. If stop-comment is the symbol syntax-table, parsing stops
after the start of an unnested comment or a string, or after the end of an unnested
comment or a string, whichever comes first.
If state is nil, start is assumed to be at the top level of parenthesis structure, suchas the beginning of a function definition. Alternatively, you might wish to resume
parsing in the middle of the structure. To do this, you must provide a state argumentthat describes the initial status of parsing. The value returned by a previous call toparse-partial-sexp will do nicely.

36.6.5 Parameters to Control Parsing[Variable]
If this variable is non-nil, scan-sexps treats all non-ASCII characters as symbol constituents regardless of what the syntax table says about them. (However,syntax-table text properties can still override the syntax.)

multibyte-syntax-as-symbol[User Option]
If the value is non-nil, then comments are treated as whitespace by the functions inthis section and by forward-sexp, scan-lists and scan-sexps.

parse-sexp-ignore-comments

The behavior of parse-partial-sexp is also affected by parse-sexp-lookupproperties (see Section 36.4 [Syntax Properties], page 1029).
[Variable]
If this buffer local variable is non-nil, a single character which usually terminates acomment doesn’t do so when that character is escaped. This is used in C and C++
Modes, where line comments starting with ‘//’ can be continued onto the next line byescaping the newline with ‘\’.

comment-end-can-be-escaped

You can use forward-comment to move forward or backward over one comment or several
comments.

36.7 Syntax Table Internals
Syntax tables are implemented as char-tables (see Section 6.6 [Char-Tables], page 119), but
most Lisp programs don’t work directly with their elements. Syntax tables do not store
syntax data as syntax descriptors (see Section 36.2 [Syntax Descriptors], page 1023); they
use an internal format, which is documented in this section. This internal format can also
be assigned as syntax properties (see Section 36.4 [Syntax Properties], page 1029).
Each entry in a syntax table is a raw syntax descriptor: a cons cell of the form (syntaxcode . matching-char). syntax-code is an integer which encodes the syntax class andChapter 36: Syntax Tables

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syntax flags, according to the table below. matching-char, if non-nil, specifies a matching
character (similar to the second character in a syntax descriptor).
Use aref (see Section 6.3 [Array Functions], page 116) to get the raw syntax descriptorof a character, e.g. (aref (syntax-table) ch).
Here are the syntax codes corresponding to the various syntax classes:
Code
Class
Code
Class
0
whitespace8
paired delimiter
1
punctuation
9
escape2
word
10character quote
3
symbol11comment-start
4
open parenthesis
12comment-end
5close parenthesis
13
inherit6expression prefix
14
generic comment
7
string quote
15
generic string
For example, in the standard syntax table, the entry for ‘(’ is (4 . 41). 41 is the charactercode for ‘)’.
Syntax flags are encoded in higher order bits, starting 16 bits from the least significant
bit. This table gives the power of two which corresponds to each syntax flag.
PrefixFlag
PrefixFlag‘1’(ash 1 16)‘p’(ash 1 20)‘2’(ash 1 17)‘b’(ash 1 21)‘3’(ash 1 18)‘n’(ash 1 22)‘4’(ash 1 19)‘c’(ash 1 23)

string-to-syntax desc

[Function]
Given a syntax descriptor desc (a string), this function returns the corresponding raw
syntax descriptor.

syntax-class-to-char syntax[Function]
Given a raw syntax descriptor syntax (an integer), this function returns the corresponding syntax descriptor (a character).

syntax-after pos[Function]
This function returns the raw syntax descriptor for the character in the buffer after
position pos, taking account of syntax properties as well as the syntax table. If pos is
outside the buffer’s accessible portion (see Section 31.4 [Narrowing], page 865), thereturn value is nil.

syntax-class syntax[Function]
This function returns the syntax code for the raw syntax descriptor syntax. Moreprecisely, it takes the raw syntax descriptor’s syntax-code component, masks off thehigh 16 bits which record the syntax flags, and returns the resulting integer.
If syntax is nil, the return value is nil. This is so that the expression(syntax-class (syntax-after pos))evaluates to nil if pos is outside the buffer’s accessible portion, without throwing
errors or returning an incorrect code.

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36.8 Categories
Categories provide an alternate way of classifying characters syntactically. You can define
several categories as needed, then independently assign each character to one or morecategories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one
character to belong to several categories.
Each buffer has a category table which records which categories are defined and also
which characters belong to each category. Each category table defines its own categories,
but normally these are initialized by copying from the standard categories table, so that thestandard categories are available in all modes.
Each category has a name, which is an ASCII printing character in the range ‘ ’ to ‘~’.
You specify the name of a category when you define it with define-category.
The category table is actually a char-table (see Section 6.6 [Char-Tables], page 119). The
element of the category table at index c is a category set—a bool-vector—that indicates
which categories character c belongs to. In this category set, if the element at index cat is t,that means category cat is a member of the set, and that character c belongs to categorycat.
For the next three functions, the optional argument table defaults to the current buffer’s
category table.

define-category char docstring &optional table[Function]
This function defines a new category, with name char and documentation docstring,for the category table table.
Here’s an example of defining a new category for characters that have strong rightto-left directionality (see Section 41.27 [Bidirectional Display], page 1250) and using
it in a special category table. To obtain the information about the directionality ofcharacters, the example code uses the ‘bidi-class’ Unicode property (see Section 34.6
[Character Properties], page 968).
(defvar special-category-table-for-bidi;;
Make an empty category-table.
(let ((category-table (make-category-table));; Create a char-table which gives the 'bidi-class' Unicode;; property for each character.
(uniprop-table(unicode-property-table-internal 'bidi-class)))(define-category ?R "Characters of bidi-class R, AL, or RLO"
category-table);; Modify the category entry of each character whose;; 'bidi-class' Unicode property is R, AL, or RLO -;; these have a right-to-left directionality.
(map-char-table(lambda (key val)(if (memq val '(R AL RLO))(modify-category-entry key ?R category-table)))uniprop-table)
category-table))Chapter 36: Syntax Tables1037

category-docstring category &optional table[Function]
This function returns the documentation string of category category in category table
table.
(category-docstring ?a)⇒ "ASCII"(category-docstring ?l)⇒ "Latin"

get-unused-category &optional table[Function]
This function returns a category name (a character) which is not currently defined intable. If all possible categories are in use in table, it returns nil.

category-table[Function]

This function returns the current buffer’s category table.

category-table-p object[Function]

This function returns t if object is a category table, otherwise nil.

standard-category-table[Function]

This function returns the standard category table.

copy-category-table &optional table[Function]
This function constructs a copy of table and returns it. If table is not supplied (or isnil), it returns a copy of the standard category table. Otherwise, an error is signaled
if table is not a category table.

set-category-table table[Function]
This function makes table the category table for the current buffer. It returns table.
[Function]
This creates and returns an empty category table. In an empty category table, nocategories have been allocated, and no characters belong to any categories.

make-category-tablemake-category-set categories[Function]
This function returns a new category set—a bool-vector—whose initial contents are
the categories listed in the string categories. The elements of categories should be
category names; the new category set has t for each of those categories, and nil forall other categories.
(make-category-set "al")⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"char-category-set char

[Function]
This function returns the category set for character char in the current buffer’s category
table. This is the bool-vector which records which categories the character char belongs
to. The function char-category-set does not allocate storage, because it returns
the same bool-vector that exists in the category table.
(char-category-set ?a)⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"Chapter 36: Syntax Tables

1038

category-set-mnemonics category-set[Function]
This function converts the category set category-set into a string containing thecharacters that designate the categories that are members of the set.
(category-set-mnemonics (char-category-set ?a))⇒ "al"

modify-category-entry char category &optional table reset[Function]
This function modifies the category set of char in category table table (which defaults
to the current buffer’s category table). char can be a character, or a cons cell of theform (min . max); in the latter case, the function modifies the category sets of all
characters in the range between min and max, inclusive.
Normally, it modifies a category set by adding category to it. But if reset is non-nil,then it deletes category instead.

describe-categories &optional buffer-or-name[Command]This function describes the category specifications in the current category table. It
inserts the descriptions in a buffer, and then displays that buffer. If buffer-or-name isnon-nil, it describes the category table of that buffer instead.

1039

37 Parsing Program Source
Emacs provides various ways to parse program source text and produce a syntax tree. In
a syntax tree, text is no longer considered a one-dimensional stream of characters, but astructured tree of nodes, where each node represents a piece of text. Thus, a syntax tree
can enable interesting features like precise fontification, indentation, navigation, structured
editing, etc.
Emacs has a simple facility for parsing balanced expressions (see Section 36.6 [Parsing
Expressions], page 1030). There is also the SMIE library for generic navigation andindentation (see Section 24.7.1 [SMIE], page 581).
In addition to those, Emacs also provides integration with the tree-sitter library (https://tree-sitter.github.io/tree-sitter) if support for it was compiled in. The tree-sitter
library implements an incremental parser and has support for a wide range of programming
languages.
[Function]
This function returns non-nil if tree-sitter features are available for the current Emacs
session.

treesit-available-p

To be able to parse the program source using the tree-sitter library and access the syntax
tree of the program, a Lisp program needs to load a language grammar library, and create aparser for that language and the current buffer. After that, the Lisp program can querythe parser about specific nodes of the syntax tree. Then, it can access various kinds ofinformation about each node, and search for nodes using a powerful pattern-matching syntax.
This chapter explains how to do all this, and also how a Lisp program can work with source
files that mix multiple programming languages.

37.1 Tree-sitter Language Grammar
Loading a language grammar
Tree-sitter relies on language grammar to parse text in that language. In Emacs, a language
grammar is represented by a symbol. For example, the C language grammar is represented
as the symbol c, and c can be passed to tree-sitter functions as the language argument.
Tree-sitter language grammars are distributed as dynamic libraries. In order to use alanguage grammar in Emacs, you need to make sure that the dynamic library is installed on
the system. Emacs looks for language grammars in several places, in the following order:• first, in the list of directories specified by the variable treesit-extra-load-path;• then, in the tree-sitter subdirectory of the directory specified by user-emacsdirectory (see Section 42.1.2 [Init File], page 1258);• and finally, in the system’s default locations for dynamic libraries.
In each of these directories, Emacs looks for a file with file-name extensions specified by
the variable dynamic-library-suffixes.
If Emacs cannot find the library or has problems loading it, Emacs signals thetreesit-load-language-error error. The data of that signal could be one of thefollowing:Chapter 37: Parsing Program Source

1040(not-found error-msg ...)
This means that Emacs could not find the language grammar library.
(symbol-error error-msg)
This means that Emacs could not find in the library the expected function thatevery language grammar library should export.
(version-mismatch error-msg)
This means that the version of the language grammar library is incompatible
with that of the tree-sitter library.
In all of these cases, error-msg might provide additional details about the failure.

treesit-language-available-p language &optional detail[Function]
This function returns non-nil if the language grammar for language exists and canbe loaded.
If detail is non-nil, return (t . nil) when language is available, and (nil . data)when it’s unavailable. data is the signal data of treesit-load-language-error.

By convention, the file name of the dynamic library for language is libtree-sitterlanguage.ext, where ext is the system-specific extension for dynamic libraries. Also by
convention, the function provided by that library is named tree_sitter_language. If alanguage grammar library doesn’t follow this convention, you should add an entry(language library-base-name function-name)to the list in the variable treesit-load-name-override-list, where library-base-nameis the basename of the dynamic library’s file name (usually, libtree-sitter-language),and function-name is the function provided by the library (usually, tree_sitter_language).
For example,(cool-lang "libtree-sitter-coool" "tree_sitter_cooool")for a language that considers itself too “cool” to abide by conventions.

treesit-library-abi-version &optional min-compatible[Function]
This function returns the version of the language grammar Application Binary Interface(ABI) supported by the tree-sitter library. By default, it returns the latest ABI version
supported by the library, but if min-compatible is non-nil, it returns the oldest ABI
version which the library still can support. Language grammar libraries must be built
for ABI versions between the oldest and the latest versions supported by the tree-sitter
library, otherwise the library will be unable to load them.

treesit-language-abi-version language[Function]
This function returns the ABI version of the language grammar library loaded byEmacs for language. If language is unavailable, this function returns nil.

Concrete syntax tree
A syntax tree is what a parser generates. In a syntax tree, each node represents a pieceof text, and is connected to each other by a parent-child relationship. For example, if thesource text is
1 + 2

Chapter 37: Parsing Program Source1041

its syntax tree could be+--------------+| root "1 + 2" |+--------------+|+--------------------------------+|
expression "1 + 2"|+--------------------------------+|||+------------++--------------++------------+| number "1" || operator "+" || number "2" |+------------++--------------++------------+
We can also represent it as an s-expression:(root (expression (number) (operator) (number)))

Node types
Names like root, expression, number, and operator specify the type of the nodes. However,
not all nodes in a syntax tree have a type. Nodes that don’t have a type are known asanonymous nodes, and nodes with a type are named nodes. Anonymous nodes are tokens
with fixed spellings, including punctuation characters like bracket ‘]’, and keywords likereturn.

Field names
To make the syntax tree easier to analyze, many language grammar assign field names tochild nodes. For example, a function_definition node could have a declarator and abody:(function_definition
declarator: (declaration)
body: (compound_statement))

Exploring the syntax tree
To aid in understanding the syntax of a language and in debugging Lisp programs that use
the syntax tree, Emacs provides an “explore” mode, which displays the syntax tree of thesource in the current buffer in real time. Emacs also comes with an “inspect mode”, whichdisplays information of the nodes at point in the mode-line.
[Command]This mode pops up a window displaying the syntax tree of the source in the current
buffer. Selecting text in the source buffer highlights the corresponding nodes in thesyntax tree display. Clicking on nodes in the syntax tree highlights the corresponding
text in the source buffer.

treesit-explore-mode[Command]This minor mode displays on the mode-line the node that starts at point. For example,
the mode-line can display
parent field: (node (child (...)))

treesit-inspect-mode

Chapter 37: Parsing Program Source

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where node, child, etc., are nodes which begin at point. parent is the parent of node.
node is displayed in a bold typeface. field-names are field names of node and of child,etc.
If no node starts at point, i.e., point is in the middle of a node, then the mode line
displays the earliest node that spans point, and its immediate parent.
This minor mode doesn’t create parsers on its own. It uses the first parser in(treesit-parser-list) (see Section 37.2 [Using Parser], page 1043).

Reading the grammar definition
Authors of language grammars define the grammar of a programming language, which
determines how a parser constructs a concrete syntax tree out of the program text. In order
to use the syntax tree effectively, you need to consult the grammar file.
The grammar file is usually grammar.js in a language grammar’s project repository. The
link to a language grammar’s home page can be found on tree-sitter’s homepage (https://tree-sitter.github.io/tree-sitter).
The grammar definition is written in JavaScript. For example, the rule matching afunction_definition node may look likefunction_definition: $ => seq($.declaration_specifiers,
field('declarator', $.declaration),field('body', $.compound_statement))
The rules are represented by functions that take a single argument $, representing the wholegrammar. The function itself is constructed by other functions: the seq function puts
together a sequence of children; the field function annotates a child with a field name. If
we write the above definition in the so-called Backus-Naur Form (BNF) syntax, it would
look likefunction_definition :=<declaration_specifiers> <declaration> <compound_statement>
and the node returned by the parser would look like(function_definition(declaration_specifier)declarator: (declaration)
body: (compound_statement))
Below is a list of functions that one can see in a grammar definition. Each function takesother rules as arguments and returns a new rule.
seq(rule1, rule2, ...)
matches each rule one after another.
choice(rule1, rule2, ...)
matches one of the rules in its arguments.
repeat(rule)matches rule zero or more times. This is like the ‘*’ operator in regularexpressions.

Chapter 37: Parsing Program Source1043

repeat1(rule)matches rule one or more times. This is like the ‘+’ operator in regular expressions.
optional(rule)matches rule zero or one times. This is like the ‘?’ operator in regular expressions.
field(name, rule)assigns field name name to the child node matched by rule.
alias(rule, alias)
makes nodes matched by rule appear as alias in the syntax tree generated by
the parser. For example,
alias(preprocessor_call_exp, call_expression)
makes any node matched by preprocessor_call_exp appear as
call_expression.
Below are grammar functions of lesser importance for reading a language grammar.
token(rule)marks rule to produce a single leaf node. That is, instead of generating a parent
node with individual child nodes under it, everything is combined into a single
leaf node. See Section 37.3 [Retrieving Nodes], page 1045.
token.immediate(rule)
Normally, grammar rules ignore preceding whitespace; this changes rule tomatch only when there is no preceding whitespace.
prec(n, rule)
gives rule the level-n precedence.
prec.left([n,] rule)marks rule as left-associative, optionally with level n.
prec.right([n,] rule)marks rule as right-associative, optionally with level n.
prec.dynamic(n, rule)
this is like prec, but the precedence is applied at runtime instead.
The documentation of the tree-sitter project has more about writing a grammar (https://tree-sitter.github.io/tree-sitter/creating-parsers). Read especially “The Grammar DSL” section.

37.2 Using Tree-sitter Parser
This section describes how to create and configure a tree-sitter parser. In Emacs, eachtree-sitter parser is associated with a buffer. As the user edits the buffer, the associatedparser and syntax tree are automatically kept up-to-date.
[Variable]
This variable contains the maximum size of buffers in which tree-sitter can be activated.
Major modes should check this value when deciding whether to enable tree-sitterfeatures.

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treesit-parser-create language &optional buffer no-reuse[Function]
Create a parser for the specified buffer and language (see Section 37.1 [Language
Grammar], page 1039). If buffer is omitted or nil, it stands for the current buffer.
By default, this function reuses a parser if one already exists for language in buffer,
but if no-reuse is non-nil, this function always creates a new parser.
If that buffer is an indirect buffer, its base buffer is used instead. That is, indirect
buffers use their base buffer’s parsers. If the base buffer is narrowed, an indirect buffer
might not be able to retrieve information of the portion of the buffer text that is
invisible in the base buffer. Lisp programs should widen as necessary should they want
to use a parser in an indirect buffer.

Given a parser, we can query information about it.

treesit-parser-buffer parser[Function]

This function returns the buffer associated with parser.

treesit-parser-language parser[Function]

This function returns the language used by parser.

treesit-parser-p object[Function]
This function checks if object is a tree-sitter parser, and returns non-nil if it is, andnil otherwise.

There is no need to explicitly parse a buffer, because parsing is done automatically andlazily. A parser only parses when a Lisp program queries for a node in its syntax tree.
Therefore, when a parser is first created, it doesn’t parse the buffer; it waits until the Lisp
program queries for a node for the first time. Similarly, when some change is made in thebuffer, a parser doesn’t re-parse immediately.
When a parser does parse, it checks for the size of the buffer. Tree-sitter can only
handle buffers no larger than about 4GB. If the size exceeds that, Emacs signals thetreesit-buffer-too-large error with signal data being the buffer size.
Once a parser is created, Emacs automatically adds it to the internal parser list. Everytime a change is made to the buffer, Emacs updates parsers in this list so they can update
their syntax tree incrementally.

treesit-parser-list &optional buffer[Function]
This function returns the parser list of buffer. If buffer is nil or omitted, it defaults
to the current buffer. If that buffer is an indirect buffer, its base buffer is used instead.
That is, indirect buffers use their base buffer’s parsers.

treesit-parser-delete parser[Function]

This function deletes parser.
Normally, a parser “sees” the whole buffer, but when the buffer is narrowed (seeSection 31.4 [Narrowing], page 865), the parser will only see the accessible portion of
the buffer. As far as the parser can tell, the hidden region was deleted. When the buffer islater widened, the parser thinks text is inserted at the beginning and at the end. AlthoughChapter 37: Parsing Program Source

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parsers respect narrowing, modes should not use narrowing as a means to handle a multilanguage buffer; instead, set the ranges in which the parser should operate. See Section 37.6
[Multiple Languages], page 1057.
Because a parser parses lazily, when the user or a Lisp program narrows the buffer, theparser is not affected immediately; as long as the mode doesn’t query for a node while thebuffer is narrowed, the parser is oblivious of the narrowing.
Besides creating a parser for a buffer, a Lisp program can also parse a string. Unlike abuffer, parsing a string is a one-off operation, and there is no way to update the result.

treesit-parse-string string language[Function]
This function parses string using language, and returns the root node of the generated
syntax tree.

Be notified by changes to the parse tree
A Lisp program might want to be notified of text affected by incremental parsing. For
example, inserting a comment-closing token converts text before that token into a comment.
Even though the text is not directly edited, it is deemed to be “changed” nevertheless.
Emacs lets a Lisp program register callback functions (a.k.a. notifiers) for these kinds ofchanges. A notifier function takes two arguments: ranges and parser. ranges is a list of cons
cells of the form (start . end), where start and end mark the start and the end positionsof a range. parser is the parser issuing the notification.
Every time a parser reparses a buffer, it compares the old and new parse-tree, computes
the ranges in which nodes have changed, and passes the ranges to notifier functions. Notethat the initial parse is also considered a “change”, so notifier functions are called on theinitial parse, with range being the whole buffer.

treesit-parser-add-notifier parser function[Function]
This function adds function to parser’s list of after-change notifier functions. function
must be a function symbol, not a lambda function (see Section 13.7 [Anonymous
Functions], page 243).

treesit-parser-remove-notifier parser function[Function]
This function removes function from the list of parser’s after-change notifier functions.
function must be a function symbol, rather than a lambda function.

treesit-parser-notifiers parser[Function]

This function returns the list of parser’s notifier functions.

37.3 Retrieving Nodes
Here are some terms and conventions we use when documenting tree-sitter functions.
A node in a syntax tree spans some portion of the program text in the buffer. We saythat a node is “smaller” or “larger” than another if it spans, respectively, a smaller or larger
portion of buffer text than the other node. Since nodes that are deeper (“lower”) in thetree are children of the nodes that are “higher” in the tree, it follows that a lower node will
always be smaller than a node that is higher in the node hierarchy. A node that is higher

Chapter 37: Parsing Program Source

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up in the syntax tree contains one or more smaller nodes as its children, and therefore spansa larger portion of buffer text.
When a function cannot find a node, it returns nil. For convenience, all functions thattake a node as argument and return a node, also accept the node argument of nil and inthat case just return nil.
Nodes are not automatically updated when the associated buffer is modified, and there
is no way to update a node once it is retrieved. Using an outdated node signals thetreesit-node-outdated error.

Retrieving nodes from syntax tree
treesit-node-at pos &optional parser-or-lang named[Function]
This function returns a leaf node at buffer position pos. A leaf node is a node that
doesn’t have any child nodes.
This function tries to return a node whose span covers pos: the node’s beginning
position is less than or equal to pos, and the node’s end position is greater than orequal to pos.
If no leaf node’s span covers pos (e.g., pos is in the whitespace between two leaf nodes),this function returns the first leaf node after pos.
Finally, if there is no leaf node after pos, return the first leaf node before pos.
If parser-or-lang is a parser object, this function uses that parser; if parser-or-lang
is a language, this function uses the first parser for that language in the current
buffer, or creates one if none exists; if parser-or-lang is nil, this function tries toguess the language at pos by calling treesit-language-at (see Section 37.6 [Multiple
Languages], page 1057).
If this function cannot find a suitable node to return, it returns nil.
If named is non-nil, this function looks only for named nodes (see [tree-sitter namednode], page 1041).
Example:;; Find the node at point in a C parser's syntax tree.
(treesit-node-at (point) 'c)⇒ #<treesit-node (primitive_type) in 23-27>

treesit-node-on beg end &optional parser-or-lang named[Function]
This function returns the smallest node that covers the region of buffer text between
beg and end. In other words, the start of the node is before or at beg, and the end of
the node is at or after end.
Beware: calling this function on an empty line that is not inside any top-level construct(function definition, etc.) most probably will give you the root node, because the root
node is the smallest node that covers that empty line. Most of the time, you want to
use treesit-node-at instead.
If parser-or-lang is a parser object, this function uses that parser; if parser-or-lang isa language, this function uses the first parser for that language in the current buffer,or creates one if none exists; if parser-or-lang is nil, this function tries to guess thelanguage at beg by calling treesit-language-at.

Chapter 37: Parsing Program Source

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If named is non-nil, this function looks for a named node only (see [tree-sitter namednode], page 1041).

treesit-parser-root-node parser[Function]
This function returns the root node of the syntax tree generated by parser.

treesit-buffer-root-node &optional language[Function]
This function finds the first parser for language in the current buffer, or creates one
if none exists, and returns the root node generated by that parser. If language isomitted, it uses the first parser in the parser list. If it cannot find an appropriate
parser, it returns nil.

Given a node, a Lisp program can retrieve other nodes starting from it, or query for
information about this node.

Retrieving nodes from other nodes
By kinshiptreesit-node-parent node

[Function]

This function returns the immediate parent of node.
If node is more than 1000 levels deep in a parse tree, the return value is undefined.
Currently it returns nil, but that could change in the future.

treesit-node-child node n &optional named[Function]
This function returns the n’th child of node. If named is non-nil, it counts only
named nodes (see [tree-sitter named node], page 1041).
For example, in a node that represents a string "text", there are three children nodes:
the opening quote ", the string text text, and the closing quote ". Among thesenodes, the first child is the opening quote ", and the first named child is the string
text.
This function returns nil if there is no n’th child. n could be negative, e.g., −1
represents the last child.

treesit-node-children node &optional named[Function]
This function returns all of node’s children as a list. If named is non-nil, it retrieves
only named nodes.

treesit-node-next-sibling node &optional named[Function]
This function finds the next sibling of node. If named is non-nil, it finds the next
named sibling.

treesit-node-prev-sibling node &optional named[Function]
This function finds the previous sibling of node. If named is non-nil, it finds theprevious named sibling.

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By field nameTo make the syntax tree easier to analyze, many language grammars assign field names
to child nodes (see [tree-sitter node field name], page 1041). For example, a function_
definition node could have a declarator node and a body node.

treesit-node-child-by-field-name node field-name[Function]
This function finds the child of node whose field name is field-name, a string.
;; Get the child that has "body" as its field name.
(treesit-node-child-by-field-name node "body")⇒ #<treesit-node (compound_statement) in 45-89>

By position
treesit-node-first-child-for-pos node pos &optional named[Function]
This function finds the first child of node that extends beyond buffer position pos.
“Extends beyond” means the end of the child node is greater or equal to pos. Thisfunction only looks for immediate children of node, and doesn’t look in its grandchildren.
If named is non-nil, it looks for the first named child (see [tree-sitter named node],
page 1041).

treesit-node-descendant-for-range node beg end &optional
named[Function]

This function finds the smallest descendant node of node that spans the region of
text between positions beg and end. It is similar to treesit-node-at. If named is
non-nil, it looks for the smallest named child.

Searching for node
treesit-search-subtree node predicate &optional backward all
depth[Function]

This function traverses the subtree of node (including node itself), looking for a node
for which predicate returns non-nil. predicate is a regexp that is matched against
each node’s type, or a predicate function that takes a node and returns non-nil if thenode matches. The function returns the first node that matches, or nil if none does.
By default, this function only traverses named nodes, but if all is non-nil, it traverses
all the nodes. If backward is non-nil, it traverses backwards (i.e., it visits the lastchild first when traversing down the tree). If depth is non-nil, it must be a numberthat limits the tree traversal to that many levels down the tree. If depth is nil, it
defaults to 1000.

treesit-search-forward start predicate &optional backward all[Function]
Like treesit-search-subtree, this function also traverses the parse tree and matches
each node with predicate (except for start), where predicate can be a regexp or afunction. For a tree like the one below where start is marked ‘S’, this function traverses
as numbered from 1 to 12:

Chapter 37: Parsing Program Source

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12
|
S--------3----------11|||
o--o-+--o 1--+--2
6--+-----10
| |
|
|
o o
+-+-+
+--+--+
|
|
| | |
4
5
7 8 9
Note that this function doesn’t traverse the subtree of start, and it always traverses
leaf nodes first, before moving upwards.
Like treesit-search-subtree, this function only searches for named nodes by default,
but if all is non-nil, it searches for all nodes. If backward is non-nil, it searches
backwards.
While treesit-search-subtree traverses the subtree of a node, this function starts
with node start and traverses every node that comes after it in the buffer position
order, i.e., nodes with start positions greater than the end position of start.
In the tree shown above, treesit-search-subtree traverses node ‘S’ (start) andnodes marked with o, whereas this function traverses the nodes marked with numbers.
This function is useful for answering questions like “what is the first node after startin the buffer that satisfies some condition?”treesit-search-forward-goto node predicate &optional start
backward all[Function]

This function moves point to the start or end of the next node after node in the bufferthat matches predicate. If start is non-nil, stop at the beginning rather than the endof a node.
This function guarantees that the matched node it returns makes progress in terms of
buffer position: the start/end position of the returned node is always greater thanthat of node.
Arguments predicate, backward, and all are the same as in treesit-search-forward.

treesit-induce-sparse-tree root predicate &optional process-fn
depth[Function]

This function creates a sparse tree from root’s subtree.
It takes the subtree under root, and combs it so only the nodes that match predicate
are left. Like previous functions, the predicate can be a regexp string that matches
against each node’s type, or a function that takes a node and returns non-nil if itmatches.
For example, given the subtree on the left that consists of both numbers and letters,
if predicate is “letter only”, the returned tree is the one on the right.

Chapter 37: Parsing Program Sourcea|+---+---+
|
|
|
b
1
2
|
|
c
+--+
|
| |
+--+
d 4
| |
e 5

=>

a
|
+---+---+
|
|
|
b
|
|
|
|
c
+
|
|
+--+
d
|
e

1050

=>

a
|
+---+---+
|
|
|
b
c
d
|
e

If process-fn is non-nil, instead of returning the matched nodes, this function passes
each node to process-fn and uses the returned value instead. If non-nil, depth limits
the number of levels to go down from root. If depth is nil, it defaults to 1000.
Each node in the returned tree looks like (tree-sitter-node . (child ...)). The
tree-sitter-node of the root of this tree will be nil if root doesn’t match predicate. If
no node matches predicate, the function returns nil.

More convenience functions
treesit-filter-child node predicate &optional named[Function]

This function finds immediate children of node that satisfy predicate.
The predicate function takes a node as argument and should return non-nil to indicatethat the node should be kept. If named is non-nil, this function only examines named
nodes.

treesit-parent-until node predicate &optional include-node[Function]
This function repeatedly finds the parents of node, and returns the parent that satisfies
predicate, a function that takes a node as argument and returns a boolean thatindicates a match. If no parent satisfies predicate, this function returns nil.
Normally this function only looks at the parents of node but not node itself. But if
include-node is non-nil, this function returns node if node satisfies predicate.

treesit-parent-while node predicate[Function]
This function goes up the tree starting from node, and keeps doing so as long as
the nodes satisfy predicate, a function that takes a node as argument. That is, thisfunction returns the highest parent of node that still satisfies predicate. Note that if
node satisfies predicate but its immediate parent doesn’t, node itself is returned.

treesit-node-top-level node &optional predicate include-node[Function]
This function returns the highest parent of node that has the same type as node. If
no such parent exists, it returns nil. Therefore this function is also useful for testingwhether node is top-level.
If predicate is nil, this function uses node’s type to find the parent. If predicate is
non-nil, this function searches the parent that satisfies predicate. If include-node is
non-nil, this function returns node if node satisfies predicate.

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37.4 Accessing Node Information
Basic information of NodeEvery node is associated with a parser, and that parser is associated with a buffer. The
following functions retrieve them.

treesit-node-parser node

[Function]

This function returns node’s associated parser.

treesit-node-buffer node

[Function]

This function returns node’s parser’s associated buffer.

treesit-node-language node

[Function]

This function returns node’s parser’s associated language.
Each node represents a portion of text in the buffer. Functions below find relevant
information about that text.

treesit-node-start node

[Function]

Return the start position of node.

treesit-node-end node

[Function]

Return the end position of node.

treesit-node-text node &optional object[Function]
Return the buffer text that node represents, as a string. (If node is retrieved fromparsing a string, it will be the text from that string.)

Here are some predicates on tree-sitter nodes:

treesit-node-p object[Function]

Checks if object is a tree-sitter syntax node.

treesit-node-eq node1 node2[Function]
Checks if node1 and node2 refer to the same node in a tree-sitter syntax tree. Thisfunction uses the same equivalence metric as equal. You can also compare nodes
using equal (see Section 2.8 [Equality Predicates], page 34).

Property information
In general, nodes in a concrete syntax tree fall into two categories: named nodes andanonymous nodes. Whether a node is named or anonymous is determined by the language
grammar (see [tree-sitter named node], page 1041).
Apart from being named or anonymous, a node can have other properties. A node canbe “missing”: such nodes are inserted by the parser in order to recover from certain kinds ofsyntax errors, i.e., something should probably be there according to the grammar, but is notthere. This can happen during editing of the program source, when the source is not yet inits final form.
A node can be “extra”: such nodes represent things like comments, which can appear
anywhere in the text.

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A node can be “outdated”, if its parser has reparsed at least once after the node wascreated.
A node “has error” if the text it spans contains a syntax error. It can be that the node
itself has an error, or one of its descendants has an error.
A node is considered live if its parser is not deleted, and the buffer to which it belongs isa live buffer (see Section 28.10 [Killing Buffers], page 685).

treesit-node-check node property[Function]
This function returns non-nil if node has the specified property. property can be
named, missing, extra, outdated, has-error, or live.

treesit-node-type node

[Function]
Named nodes have “types” (see [tree-sitter node type], page 1041). For example, a
named node can be a string_literal node, where string_literal is its type. The
type of an anonymous node is just the text that the node represents; e.g., the type ofa ‘,’ node is just ‘,’.

This function returns node’s type as a string.

Information as a child or parent
treesit-node-index node &optional named[Function]
This function returns the index of node as a child node of its parent. If named is
non-nil, it only counts named nodes (see [tree-sitter named node], page 1041).

treesit-node-field-name node

[Function]
A child of a parent node could have a field name (see [tree-sitter node field name],
page 1041). This function returns the field name of node as a child of its parent.

treesit-node-field-name-for-child node n[Function]
This function returns the field name of the n’th child of node. It returns nil if there
is no n’th child, or the n’th child doesn’t have a field name.
Note that n counts both named and anonymous children, and n can be negative, e.g.,−1 represents the last child.

treesit-node-child-count node &optional named[Function]
This function returns the number of children of node. If named is non-nil, it only
counts named children (see [tree-sitter named node], page 1041).

37.5 Pattern Matching Tree-sitter Nodes
Tree-sitter lets Lisp programs match patterns using a small declarative language. Thispattern matching consists of two steps: first tree-sitter matches a pattern against nodes inthe syntax tree, then it captures specific nodes that matched the pattern and returns thecaptured nodes.
We describe first how to write the most basic query pattern and how to capture nodes
in a pattern, then the pattern-matching function, and finally the more advanced patternsyntax.

Chapter 37: Parsing Program Source

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Basic query syntax
A query consists of multiple patterns. Each pattern is an s-expression that matches a certain
node in the syntax node. A pattern has the form (type (child...)).
For example, a pattern that matches a binary_expression node that contains number_
literal child nodes would look like(binary_expression (number_literal))
To capture a node using the query pattern above, append @capture-name after the node
pattern you want to capture. For example,(binary_expression (number_literal) @number-in-exp)
captures number_literal nodes that are inside a binary_expression node with the capture
name number-in-exp.
We can capture the binary_expression node as well, with, for example, the capture
name biexp:(binary_expression(number_literal) @number-in-exp) @biexp

Query function
Now we can introduce the query functions.

treesit-query-capture node query &optional beg end node-only[Function]
This function matches patterns in query within node. The argument query can beeither an s-expression, a string, or a compiled query object. For now, we focus on thes-expression syntax; string syntax and compiled queries are described at the end of
the section.
The argument node can also be a parser or a language symbol. A parser means use
its root node, a language symbol means find or create a parser for that language inthe current buffer, and use the root node.
The function returns all the captured nodes in an alist with elements of the form
(capture_name . node). If node-only is non-nil, it returns the list of nodes instead.
By default the entire text of node is searched, but if beg and end are both non-nil,they specify the region of buffer text where this function should match nodes. Anymatching node whose span overlaps with the region between beg and end is captured;it doesn’t have to be completely contained in the region.
This function raises the treesit-query-error error if query is malformed. The
signal data contains a description of the specific error. You can use treesit-queryvalidate to validate and debug the query.

For example, suppose node’s text is 1 + 2, and query is(setq query'((binary_expression(number_literal) @number-in-exp) @biexp)
Matching that query would return

Chapter 37: Parsing Program Source

1054(treesit-query-capture node query)⇒ ((biexp . <node for "1 + 2">)
(number-in-exp . <node for "1">)(number-in-exp . <node for "2">))
As mentioned earlier, query could contain multiple patterns. For example, it could have
two top-level patterns:(setq query'((binary_expression) @biexp(number_literal) @number @biexp)

treesit-query-string string query language[Function]
This function parses string as language, matches its root node with query, and returns
the result.

More query syntax
Besides node type and capture name, tree-sitter’s pattern syntax can express anonymous
node, field name, wildcard, quantification, grouping, alternation, anchor, and predicate.

Anonymous node
An anonymous node is written verbatim, surrounded by quotes. A pattern matching (andcapturing) keyword return would be"return" @keyword

Wild card
In a pattern, ‘(_)’ matches any named node, and ‘_’ matches any named or anonymous
node. For example, to capture any named child of a binary_expression node, the pattern
would be(binary_expression (_) @in-biexp)

Field name
It is possible to capture child nodes that have specific field names. In the pattern below,
declarator and body are field names, indicated by the colon following them.
(function_definition
declarator: (_) @func-declarator
body: (_) @func-body)
It is also possible to capture a node that doesn’t have a certain field, say, a function_
definition without a body field:(function_definition !body) @func-no-body

Quantify nodeTree-sitter recognizes quantification operators ‘:*’, ‘:+’, and ‘:?’. Their meanings are thesame as in regular expressions: ‘:*’ matches the preceding pattern zero or more times, ‘:+’matches one or more times, and ‘:?’ matches zero or one times.

Chapter 37: Parsing Program Source

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For example, the following pattern matches type_declaration nodes that have zero or
more long keywords.
(type_declaration "long" :*) @long-type
The following pattern matches a type declaration that may or may not have a long
keyword:(type_declaration "long" :?) @long-type

Grouping
Similar to groups in regular expressions, we can bundle patterns into groups and apply
quantification operators to them. For example, to express a comma-separated list ofidentifiers, one could write(identifier) ("," (identifier)) :*Alternation
Again, similar to regular expressions, we can express “match any one of these patterns” in apattern. The syntax is a vector of patterns. For example, to capture some keywords in C,
the pattern would be["return""break""if""else"] @keyword

Anchor
The anchor operator :anchor can be used to enforce juxtaposition, i.e., to enforce two things
to be directly next to each other. The two “things” can be two nodes, or a child and the endof its parent. For example, to capture the first child, the last child, or two adjacent children:;; Anchor the child with the end of its parent.
(compound_expression (_) @last-child :anchor);; Anchor the child with the beginning of its parent.
(compound_expression :anchor (_) @first-child);; Anchor two adjacent children.
(compound_expression(_) @prev-child:anchor(_) @next-child)
Note that the enforcement of juxtaposition ignores any anonymous nodes.

Predicate
It is possible to add predicate constraints to a pattern. For example, with the following
pattern:Chapter 37: Parsing Program Source

1056((array :anchor (_) @first (_) @last :anchor)(:equal @first @last))tree-sitter only matches arrays where the first element is equal to the last element. To
attach a predicate to a pattern, we need to group them together. Currently there are three
predicates: :equal, :match, and :pred.

:equal arg1 arg2

[Predicate]
Matches if arg1 is equal to arg2. Arguments can be either strings or capture names.
Capture names represent the text that the captured node spans in the buffer.

:match regexp capture-name[Predicate]
Matches if the text that capture-name’s node spans in the buffer matches regularexpression regexp, given as a string literal. Matching is case-sensitive.

:pred fn &rest nodes[Predicate]
Matches if function fn returns non-nil when passed each node in nodes as arguments.

Note that a predicate can only refer to capture names that appear in the same pattern.
Indeed, it makes little sense to refer to capture names in other patterns.

String patterns
Besides s-expressions, Emacs allows the tree-sitter’s native query syntax to be used bywriting them as strings. It largely resembles the s-expression syntax. For example, thefollowing query(treesit-query-capture
node '((addition_expression
left: (_) @left"+" @plus-sign
right: (_) @right) @addition["return" "break"] @keyword))
is equivalent to(treesit-query-capture
node "(addition_expression
left: (_) @left\"+\" @plus-sign
right: (_) @right) @addition[\"return\" \"break\"] @keyword")
Most patterns can be written directly as s-expressions inside a string. Only a few of themneed modification:• Anchor :anchor is written as ‘.’.
• ‘:?’ is written as ‘?’.
• ‘:*’ is written as ‘*’.

Chapter 37: Parsing Program Source1057• ‘:+’ is written as ‘+’.
• :equal, :match and :pred are written as #equal, #match and #pred, respectively. In
general, predicates change their ‘:’ to ‘#’.
For example,'(((compound_expression :anchor (_) @first (_) :* @rest)(:match "love" @first)))
is written in string form as"((compound_expression . (_) @first (_)* @rest)(#match \"love\" @first))"

Compiling queries
If a query is intended to be used repeatedly, especially in tight loops, it is important tocompile that query, because a compiled query is much faster than an uncompiled one. A
compiled query can be used anywhere a query is accepted.

treesit-query-compile language query[Function]
This function compiles query for language into a compiled query object and returns it.
This function raises the treesit-query-error error if query is malformed. The
signal data contains a description of the specific error. You can use treesit-queryvalidate to validate and debug the query.

treesit-query-language query[Function]

This function returns the language of query.

treesit-query-expand query[Function]

This function converts the s-expression query into the string format.

treesit-pattern-expand pattern[Function]

This function converts the s-expression pattern into the string format.
For more details, read the tree-sitter project’s documentation about pattern-matching,which can be found at https://tree-sitter.github.io/tree-sitter/using-parsers#
pattern-matching-with-queries.

37.6 Parsing Text in Multiple Languages
Sometimes, the source of a programming language could contain snippets of other languages;
HTML + CSS + JavaScript is one example. In that case, text segments written in different
languages need to be assigned different parsers. Traditionally, this is achieved by using
narrowing. While tree-sitter works with narrowing (see [tree-sitter narrowing], page 1044),
the recommended way is instead to specify regions of buffer text (i.e., ranges) in which aparser will operate. This section describes functions for setting and getting ranges for aparser.

Chapter 37: Parsing Program Source

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Lisp programs should call treesit-update-ranges to make sure the ranges for eachparser are correct before using parsers in a buffer, and call treesit-language-at tofigure out the language responsible for the text at some position. These two functions
don’t work by themselves, they need major modes to set treesit-range-settings andtreesit-language-at-point-function, which do the actual work. These functions andvariables are explained in more detail towards the end of the section.

Getting and setting ranges
treesit-parser-set-included-ranges parser ranges[Function]
This function sets up parser to operate on ranges. The parser will only read the textof the specified ranges. Each range in ranges is a pair of the form (beg . end).
The ranges in ranges must come in order and must not overlap. That is, in pseudocode:(cl-loop for idx from 1 to (1- (length ranges))for prev = (nth (1- idx) ranges)
for next = (nth idx ranges)
should (<= (car prev) (cdr prev)(car next) (cdr next)))
If ranges violates this constraint, or something else went wrong, this function signals
the treesit-range-invalid error. The signal data contains a specific error message
and the ranges we are trying to set.
This function can also be used for disabling ranges. If ranges is nil, the parser is set
to parse the whole buffer.
Example:(treesit-parser-set-included-ranges
parser '((1 . 9) (16 . 24) (24 . 25)))

treesit-parser-included-ranges parser[Function]
This function returns the ranges set for parser. The return value is the same as theranges argument of treesit-parser-included-ranges: a list of cons cells of theform (beg . end). If parser doesn’t have any ranges, the return value is nil.
(treesit-parser-included-ranges parser)⇒ ((1 . 9) (16 . 24) (24 . 25))

treesit-query-range source query &optional beg end[Function]
This function matches source with query and returns the ranges of captured nodes.
The return value is a list of cons cells of the form (beg . end), where beg and end
specify the beginning and the end of a region of text.
For convenience, source can be a language symbol, a parser, or a node. If it’s alanguage symbol, this function matches in the root node of the first parser using that
language; if a parser, this function matches in the root node of that parser; if a node,
this function matches in that node.
The argument query is the query used to capture nodes (see Section 37.5 [Pattern
Matching], page 1052). The capture names don’t matter. The arguments beg andend, if both non-nil, limit the range in which this function queries.

Chapter 37: Parsing Program Source

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Like other query functions, this function raises the treesit-query-error error if
query is malformed.

Supporting multiple languages in Lisp programs
It should suffice for general Lisp programs to call the following two functions in order tosupport program sources that mix multiple languages.

treesit-update-ranges &optional beg end[Function]
This function updates ranges for parsers in the buffer. It makes sure the parsers’
ranges are set correctly between beg and end, according to treesit-range-settings.
If omitted, beg defaults to the beginning of the buffer, and end defaults to the end of
the buffer.
For example, fontification functions use this function before querying for nodes in aregion.

treesit-language-at pos[Function]
This function returns the language of the text at buffer position pos. Under thehood it calls treesit-language-at-point-function and returns its return value. If
treesit-language-at-point-function is nil, this function returns the language ofthe first parser in the returned value of treesit-parser-list. If there is no parser
in the buffer, it returns nil.

Supporting multiple languages in major modes
Normally, in a set of languages that can be mixed together, there is a host language andone or more embedded languages. A Lisp program usually first parses the whole documentwith the host language’s parser, retrieves some information, sets ranges for the embedded
languages with that information, and then parses the embedded languages.
Take a buffer containing HTML, CSS, and JavaScript as an example. A Lisp program will
first parse the whole buffer with an HTML parser, then query the parser for style_element
and script_element nodes, which correspond to CSS and JavaScript text, respectively. Thenit sets the range of the CSS and JavaScript parsers to the range which their corresponding
nodes span.
Given a simple HTML document:<html><script>1 + 2</script><style>body { color: "blue"; }</style></html>a Lisp program will first parse with a HTML parser, then set ranges for CSS and JavaScript
parsers:;; Create parsers.
(setq html (treesit-parser-create 'html))(setq css (treesit-parser-create 'css))(setq js (treesit-parser-create 'javascript))Chapter 37: Parsing Program Source

1060;; Set CSS ranges.
(setq css-range(treesit-query-range'html'((style_element (raw_text) @capture))))(treesit-parser-set-included-ranges css css-range);; Set JavaScript ranges.
(setq js-range(treesit-query-range'html'((script_element (raw_text) @capture))))(treesit-parser-set-included-ranges js js-range)
Emacs automates this process in treesit-update-ranges. A multi-language major mode should set treesit-range-settings so that treesit-update-ranges knows
how to perform this process automatically. Major modes should use the helper function treesit-range-rules to generate a value that can be assigned to treesit-rangesettings. The settings in the following example directly translate into operations shown
above.
(setq treesit-range-settings(treesit-range-rules:embed 'javascript:host 'html'((script_element (raw_text) @capture)):embed 'css
:host 'html'((style_element (raw_text) @capture))))treesit-range-rules &rest query-specs[Function]
This function is used to set treesit-range-settings. It takes care of compiling
queries and other post-processing, and outputs a value that treesit-range-settings
can have.
It takes a series of query-specs, where each query-spec is a query preceded by zeroor more keyword/value pairs. Each query is a tree-sitter query in either the string,s-expression, or compiled form, or a function.
If query is a tree-sitter query, it should be preceded by two keyword/value pairs,
where the :embed keyword specifies the embedded language, and the :host keyword
specifies the host language.
treesit-update-ranges uses query to figure out how to set the ranges for parsers
for the embedded language. It queries query in a host language parser, computes theranges which the captured nodes span, and applies these ranges to embedded language
parsers.
If query is a function, it doesn’t need any keyword and value pair. It should be afunction that takes 2 arguments, start and end, and sets the ranges for parsers in theChapter 37: Parsing Program Source

1061

current buffer in the region between start and end. It is fine for this function to set
ranges in a larger region that encompasses the region between start and end.
[Variable]
This variable helps treesit-update-ranges in updating the ranges for parsers in thebuffer. It is a list of settings where the exact format of a setting is considered internal.
You should use treesit-range-rules to generate a value that this variable can have.

treesit-range-settings[Variable]
This variable’s value should be a function that takes a single argument, pos, which isa buffer position, and returns the language of the buffer text at pos. This variable isused by treesit-language-at.

treesit-language-at-point-function

37.7 Developing major modes with tree-sitterThis section covers some general guidelines on developing tree-sitter integration for a major
mode.
A major mode supporting tree-sitter features should roughly follow this pattern:(define-derived-mode woomy-mode prog-mode "Woomy""A mode for Woomy programming language."(when (treesit-ready-p 'woomy)(setq-local treesit-variables ...)...
(treesit-major-mode-setup)))treesit-ready-p automatically emits a warning if conditions for enabling tree-sitter
aren’t met.
If a tree-sitter major mode shares setup with its “native” counterpart, one can create a“base mode” that contains the common setup, like this:(define-derived-mode woomy--base-mode prog-mode "Woomy""An internal mode for Woomy programming language."(common-setup)...)(define-derived-mode woomy-mode woomy--base-mode "Woomy""A mode for Woomy programming language."(native-setup)...)(define-derived-mode woomy-ts-mode woomy--base-mode "Woomy""A mode for Woomy programming language."(when (treesit-ready-p 'woomy)(setq-local treesit-variables ...)...
(treesit-major-mode-setup)))treesit-ready-p language &optional quiet[Function]
This function checks for conditions for activating tree-sitter. It checks whether Emacs
was built with tree-sitter, whether the buffer’s size is not too large for tree-sitterChapter 37: Parsing Program Source1062

to handle, and whether the grammar for language is available on the system (seeSection 37.1 [Language Grammar], page 1039).
This function emits a warning if tree-sitter cannot be activated. If quiet is message,
the warning is turned into a message; if quiet is t, no warning or message is displayed.
If all the necessary conditions are met, this function returns non-nil; otherwise it
returns nil.

treesit-major-mode-setup[Function]

This function activates some tree-sitter features for a major mode.
Currently, it sets up the following features:• If treesit-font-lock-settings (see Section 24.6.10 [Parser-based Font Lock],
page 578) is non-nil, it sets up fontification.
• If treesit-simple-indent-rules (see Section 24.7.2 [Parser-based Indentation],
page 590) is non-nil, it sets up indentation.
• If treesit-defun-type-regexp is non-nil, it sets up navigation functions forbeginning-of-defun and end-of-defun.
• If treesit-defun-name-function is non-nil, it sets up add-log functions usedby add-log-current-defun.
• If treesit-simple-imenu-settings (see Section 24.5 [Imenu], page 561) is nonnil, it sets up Imenu.
For more information on these built-in tree-sitter features, see Section 24.6.10 [Parserbased Font Lock], page 578, see Section 24.7.2 [Parser-based Indentation], page 590, and see
Section 31.2.6 [List Motion], page 861.
For supporting mixing of multiple languages in a major mode, see Section 37.6 [Multiple
Languages], page 1057.
Besides beginning-of-defun and end-of-defun, Emacs provides some additional functions for working with defuns: treesit-defun-at-point returns the defun node at point,
and treesit-defun-name returns the name of a defun node.
[Function]
This function returns the defun node at point, or nil if none is found. It respects
treesit-defun-tactic: if its value is top-level, this function returns the top-level
defun, and if its value is nested, it returns the immediate enclosing defun.

treesit-defun-at-point

This function requires treesit-defun-type-regexp to work. If it is nil, this function
simply returns nil.

treesit-defun-name node

[Function]
This function returns the defun name of node. It returns nil if there is no defun namefor node, or if node is not a defun node, or if node is nil.
Depending on the language and major mode, the defun names are names like function
name, class name, struct name, etc.
If treesit-defun-name-function is nil, this function always returns nil.

Chapter 37: Parsing Program Source

1063[Variable]
If non-nil, this variable’s value should be a function that is called with a node as its
argument, and returns the defun name of the node. The function should have thesame semantics as treesit-defun-name: if the node is not a defun node, or the node
is a defun node but doesn’t have a name, or the node is nil, it should return nil.

treesit-defun-name-function

37.8 Tree-sitter C API Correspondence
Emacs’ tree-sitter integration doesn’t expose every feature provided by tree-sitter’s C API.
Missing features include:• Creating a tree cursor and navigating the syntax tree with it.
• Setting timeout and cancellation flag for a parser.
• Setting the logger for a parser.
• Printing a DOT graph of the syntax tree to a file.
• Copying and modifying a syntax tree. (Emacs doesn’t expose a tree object.)• Using (row, column) coordinates as position.
• Updating a node with changes. (In Emacs, retrieve a new node instead of updating theexisting one.)• Querying statics of a language grammar.
In addition, Emacs makes some changes to the C API to make the API more convenientand idiomatic:• Instead of using byte positions, the Emacs Lisp API uses character positions.
• Null nodes are converted to nil.
Below is the correspondence between all C API functions and their ELisp counterparts.
Sometimes one ELisp function corresponds to multiple C functions, and many C functions
don’t have an ELisp counterpart.
ts_parser_new
treesit-parser-create
ts_parser_delete
ts_parser_set_language
ts_parser_language
treesit-parser-language
ts_parser_set_included_ranges
treesit-parser-set-included-ranges
ts_parser_included_ranges
treesit-parser-included-ranges
ts_parser_parsets_parser_parse_string
treesit-parse-string
ts_parser_parse_string_encoding
ts_parser_resetts_parser_set_timeout_micros
ts_parser_timeout_micros
ts_parser_set_cancellation_flag
ts_parser_cancellation_flag
ts_parser_set_logger
ts_parser_logger
ts_parser_print_dot_graphs
ts_tree_copyChapter 37: Parsing Program Source1064

ts_tree_delete
ts_tree_root_node
ts_tree_language
ts_tree_edit
ts_tree_get_changed_ranges
ts_tree_print_dot_graphts_node_type
treesit-node-type
ts_node_symbol
ts_node_start_byte
treesit-node-start
ts_node_start_point
ts_node_end_byte
treesit-node-end
ts_node_end_point
ts_node_string
treesit-node-string
ts_node_is_null
ts_node_is_named
treesit-node-checkts_node_is_missing
treesit-node-checkts_node_is_extra
treesit-node-checkts_node_has_changes
ts_node_has_error
treesit-node-checkts_node_parent
treesit-node-parent
ts_node_childtreesit-node-childts_node_field_name_for_childtreesit-node-field-name-for-childts_node_child_counttreesit-node-child-countts_node_named_childtreesit-node-childts_node_named_child_counttreesit-node-child-countts_node_child_by_field_nametreesit-node-child-by-field-namets_node_child_by_field_id
ts_node_next_siblingtreesit-node-next-sibling
ts_node_prev_siblingtreesit-node-prev-sibling
ts_node_next_named_siblingtreesit-node-next-sibling
ts_node_prev_named_siblingtreesit-node-prev-sibling
ts_node_first_child_for_byte
treesit-node-first-child-for-pos
ts_node_first_named_child_for_byte
treesit-node-first-child-for-pos
ts_node_descendant_for_byte_range
treesit-node-descendant-for-range
ts_node_descendant_for_point_range
ts_node_named_descendant_for_byte_range treesit-node-descendant-for-range
ts_node_named_descendant_for_point_range
ts_node_edit
ts_node_eq
treesit-node-eq
ts_tree_cursor_new
ts_tree_cursor_delete
ts_tree_cursor_reset
ts_tree_cursor_current_node
ts_tree_cursor_current_field_namets_tree_cursor_current_field_id
ts_tree_cursor_goto_parent
ts_tree_cursor_goto_next_sibling

Chapter 37: Parsing Program Source

ts_tree_cursor_goto_first_child
ts_tree_cursor_goto_first_child_for_byte
ts_tree_cursor_goto_first_child_for_point
ts_tree_cursor_copy
ts_query_new
ts_query_delete
ts_query_pattern_countts_query_capture_countts_query_string_countts_query_start_byte_for_pattern
ts_query_predicates_for_pattern
ts_query_step_is_definite
ts_query_capture_name_for_id
ts_query_string_value_for_id
ts_query_disable_capture
ts_query_disable_pattern
ts_query_cursor_new
ts_query_cursor_delete
ts_query_cursor_exec
treesit-query-capture
ts_query_cursor_did_exceed_match_limit
ts_query_cursor_match_limit
ts_query_cursor_set_match_limit
ts_query_cursor_set_byte_range
ts_query_cursor_set_point_range
ts_query_cursor_next_match
ts_query_cursor_remove_match
ts_query_cursor_next_capture
ts_language_symbol_countts_language_symbol_namets_language_symbol_for_namets_language_field_countts_language_field_name_for_id
ts_language_field_id_for_namets_language_symbol_type
ts_language_version

1065

1066

38 Abbrevs and Abbrev Expansion
An abbreviation or abbrev is a string of characters that may be expanded to a longer string.
The user can insert the abbrev string and find it replaced automatically with the expansionof the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has alocal abbrev table, but normally all buffers in the same major mode share one abbrev table.
There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray. See Section 9.3 [Creating Symbols], page 135,
for information about obarrays. Each abbreviation is represented by a symbol in the obarray.
The symbol’s name is the abbreviation; its value is the expansion; its function definitionis the hook function for performing the expansion (see Section 38.2 [Defining Abbrevs],
page 1067); and its property list cell contains various additional properties, including theuse count and the number of times the abbreviation has been expanded (see Section 38.6
[Abbrev Properties], page 1071).
Certain abbrevs, called system abbrevs, are defined by a major mode instead of the user.
A system abbrev is identified by its non-nil :system property (see Section 38.6 [Abbrev
Properties], page 1071). When abbrevs are saved to an abbrev file, system abbrevs areomitted. See Section 38.3 [Abbrev Files], page 1068.
Because the symbols used for abbrevs are not interned in the usual obarray, they will
never appear as the result of reading a Lisp expression; in fact, normally they are never used
except by the code that handles abbrevs. Therefore, it is safe to use them in a nonstandard
way.
If the minor mode Abbrev mode is enabled, the buffer-local variable abbrev-mode is
non-nil, and abbrevs are automatically expanded in the buffer. For the user-level commands
for abbrevs, see Section “Abbrev Mode” in The GNU Emacs Manual.

38.1 Abbrev Tables
This section describes how to create and manipulate abbrev tables.

make-abbrev-table &optional props[Function]
This function creates and returns a new, empty abbrev table—an obarray containing
no symbols. It is a vector filled with zeros. props is a property list that is applied to
the new table (see Section 38.7 [Abbrev Table Properties], page 1072).

abbrev-table-p object[Function]

This function returns a non-nil value if object is an abbrev table.

clear-abbrev-table abbrev-table[Function]

This function undefines all the abbrevs in abbrev-table, leaving it empty.

copy-abbrev-table abbrev-table[Function]
This function returns a copy of abbrev-table—a new abbrev table containing the same
abbrev definitions. It does not copy any property lists; only the names, values, andfunctions.

Chapter 38: Abbrevs and Abbrev Expansion

define-abbrev-table tabname definitions &optional docstring&rest props

1067[Function]

This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable
whose value is an abbrev table. It defines abbrevs in the table according to definitions,a list of elements of the form (abbrevname expansion [hook] [props...]). Theseelements are passed as arguments to define-abbrev.
The optional string docstring is the documentation string of the variable tabname.
The property list props is applied to the abbrev table (see Section 38.7 [Abbrev Table
Properties], page 1072).
If this function is called more than once for the same tabname, subsequent calls add
the definitions in definitions to tabname, rather than overwriting the entire originalcontents. (A subsequent call only overrides abbrevs explicitly redefined or undefinedin definitions.)[Variable]
This is a list of symbols whose values are abbrev tables. define-abbrev-table adds
the new abbrev table name to this list.

abbrev-table-name-list

insert-abbrev-table-description name &optional human[Function]
This function inserts before point a description of the abbrev table named name. The
argument name is a symbol whose value is an abbrev table.
If human is non-nil, the description is human-oriented. System abbrevs are listed
and identified as such. Otherwise the description is a Lisp expression—a call todefine-abbrev-table that would define name as it is currently defined, but without
the system abbrevs. (The mode or package using name is supposed to add these toname separately.)38.2 Defining Abbrevs
define-abbrev is the low-level basic function for defining an abbrev in an abbrev table.
When a major mode defines a system abbrev, it should call define-abbrev and specify
t for the :system property. Be aware that any saved non-system abbrevs are restored atstartup, i.e., before some major modes are loaded. Therefore, major modes should notassume that their abbrev tables are empty when they are first loaded.

define-abbrev abbrev-table name expansion &optional hook &rest
props[Function]

This function defines an abbrev named name, in abbrev-table, to expand to expansion
and call hook, with properties props (see Section 38.6 [Abbrev Properties], page 1071).
The return value is name. The :system property in props is treated specially here: if it
has the value force, then it will overwrite an existing definition even for a non-systemabbrev of the same name.
name should be a string. The argument expansion is normally the desired expansion(a string), or nil to undefine the abbrev. If it is anything but a string or nil, thenthe abbreviation expands solely by running hook.
The argument hook is a function or nil. If hook is non-nil, then it is called with noarguments after the abbrev is replaced with expansion; point is located at the end of
expansion when hook is called.

Chapter 38: Abbrevs and Abbrev Expansion

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If hook is a non-nil symbol whose no-self-insert property is non-nil, hook can
explicitly control whether to insert the self-inserting input character that triggered
the expansion. If hook returns non-nil in this case, that inhibits insertion of thecharacter. By contrast, if hook returns nil, expand-abbrev (or abbrev-insert) also
returns nil, as if expansion had not really occurred.
Normally, define-abbrev sets the variable abbrevs-changed to t, if it actuallychanges the abbrev. This is so that some commands will offer to save the abbrevs. It
does not do this for a system abbrev, since those aren’t saved anyway.
[User Option]
If this variable is non-nil, it means that the user plans to use global abbrevs only. This
tells the commands that define mode-specific abbrevs to define global ones instead.
This variable does not alter the behavior of the functions in this section; it is examinedby their callers.

only-global-abbrevs

38.3 Saving Abbrevs in Files
A file of saved abbrev definitions is actually a file of Lisp code. The abbrevs are savedin the form of a Lisp program to define the same abbrev tables with the same contents.
Therefore, you can load the file with load (see Section 16.1 [How Programs Do Loading],
page 298). However, the function quietly-read-abbrev-file is provided as a moreconvenient interface. Emacs automatically calls this function at startup.
User-level facilities such as save-some-buffers can save abbrevs in a file automatically,
under the control of variables described here.
[User Option]
This is the default file name for reading and saving abbrevs. By default, Emacs will
look for ~/.emacs.d/abbrev_defs, and, if not found, for ~/.abbrev_defs; if neither
file exists, Emacs will create ~/.emacs.d/abbrev_defs.

abbrev-file-namequietly-read-abbrev-file &optional filename[Function]
This function reads abbrev definitions from a file named filename, previously written with write-abbrev-file. If filename is omitted or nil, the file specified inabbrev-file-name is used.
As the name implies, this function does not display any messages.

[User Option]
A non-nil value for save-abbrevs means that Emacs should offer to save abbrevs(if any have changed) when files are saved. If the value is silently, Emacs saves
the abbrevs without asking the user. abbrev-file-name specifies the file to save theabbrevs in. The default value is t.

save-abbrevs[Variable]
This variable is set non-nil by defining or altering any abbrevs (except system abbrevs).
This serves as a flag for various Emacs commands to offer to save your abbrevs.

abbrevs-changed

write-abbrev-file &optional filename[Command]
Save all abbrev definitions (except system abbrevs), for all abbrev tables listed inabbrev-table-name-list, in the file filename, in the form of a Lisp program that

Chapter 38: Abbrevs and Abbrev Expansion

1069

when loaded will define the same abbrevs. Tables that do not have any abbrevs to save
are omitted. If filename is nil or omitted, abbrev-file-name is used. This function
returns nil.

38.4 Looking Up and Expanding Abbreviations
Abbrevs are usually expanded by certain interactive commands, including self-insertcommand. This section describes the subroutines used in writing such commands, as well as
the variables they use for communication.

abbrev-symbol abbrev &optional table[Function]
This function returns the symbol representing the abbrev named abbrev. It returns
nil if that abbrev is not defined. The optional second argument table is the abbrev
table in which to look it up. If table is nil, this function tries first the current buffer’s
local abbrev table, and second the global abbrev table.

abbrev-expansion abbrev &optional table[Function]
This function returns the string that abbrev would expand into (as defined by theabbrev tables used for the current buffer). It returns nil if abbrev is not a valid abbrev.
The optional argument table specifies the abbrev table to use, as in abbrev-symbol.

[Command]This command expands the abbrev before point, if any. If point does not follow anabbrev, this command does nothing. To do the expansion, it calls the function that isthe value of the abbrev-expand-function variable, with no arguments, and returns
whatever that function does.

expand-abbrev

The default expansion function returns the abbrev symbol if it did expansion, andnil otherwise. If the abbrev symbol has a hook function that is a symbol whose
no-self-insert property is non-nil, and if the hook function returns nil as its value,then the default expansion function returns nil, even though expansion did occur.

abbrev-insert abbrev &optional name start end[Function]
This function inserts the abbrev expansion of abbrev, replacing the text between
start and end. If start is omitted, it defaults to point. name, if non-nil, should be
the name by which this abbrev was found (a string); it is used to figure out whether toadjust the capitalization of the expansion. The function returns abbrev if the abbrev
was successfully inserted, otherwise it returns nil.

abbrev-prefix-mark &optional arg[Command]This command marks the current location of point as the beginning of an abbrev. The
next call to expand-abbrev will use the text from here to point (where it is then) as
the abbrev to expand, rather than using the previous word as usual.
First, this command expands any abbrev before point, unless arg is non-nil. (Interactively, arg is the prefix argument.) Then it inserts a hyphen before point, toindicate the start of the next abbrev to be expanded. The actual expansion removes
the hyphen.

Chapter 38: Abbrevs and Abbrev Expansion

1070[User Option]
When this is set non-nil, an abbrev entered entirely in upper case is expanded using
all upper case. Otherwise, an abbrev entered entirely in upper case is expanded bycapitalizing each word of the expansion.

abbrev-all-caps[Variable]
The value of this variable is a buffer position (an integer or a marker) for
expand-abbrev to use as the start of the next abbrev to be expanded. The
value can also be nil, which means to use the word before point instead.
abbrev-start-location is set to nil each time expand-abbrev is called. Thisvariable is also set by abbrev-prefix-mark.

abbrev-start-location[Variable]
The value of this variable is the buffer for which abbrev-start-location has been
set. Trying to expand an abbrev in any other buffer clears abbrev-start-location.
This variable is set by abbrev-prefix-mark.

abbrev-start-location-buffer[Variable]
This is the abbrev-symbol of the most recent abbrev expanded. This information isleft by expand-abbrev for the sake of the unexpand-abbrev command (see Section“Expanding Abbrevs” in The GNU Emacs Manual).

last-abbrev[Variable]
This is the location of the most recent abbrev expanded. This contains information
left by expand-abbrev for the sake of the unexpand-abbrev command.

last-abbrev-location[Variable]
This is the exact expansion text of the most recent abbrev expanded, after caseconversion (if any). Its value is nil if the abbrev has already been unexpanded. This
contains information left by expand-abbrev for the sake of the unexpand-abbrev
command.

last-abbrev-text[Variable]
The value of this variable is a function that expand-abbrev will call with no arguments
to do the expansion. The function can do anything it wants before and after performing
the expansion. It should return the abbrev symbol if expansion took place.

abbrev-expand-function

The following sample code shows a simple use of abbrev-expand-function. It assumes
that foo-mode is a mode for editing certain files in which lines that start with ‘#’ are comments.
You want to use Text mode abbrevs for those lines. The regular local abbrev table, foo-modeabbrev-table is appropriate for all other lines. See Section 38.5 [Standard Abbrev Tables],page 1071, for the definitions of local-abbrev-table and text-mode-abbrev-table. See
Section 13.12 [Advising Functions], page 252, for details of add-function.
(defun foo-mode-abbrev-expand-function (expand)(if (not (save-excursion (forward-line 0) (eq (char-after) ?#)));; Performs normal expansion.
(funcall expand);; We're inside a comment: use the text-mode abbrevs.
(let ((local-abbrev-table text-mode-abbrev-table))(funcall expand))))Chapter 38: Abbrevs and Abbrev Expansion1071(add-hook 'foo-mode-hook(lambda ()(add-function :around (local 'abbrev-expand-function)#'foo-mode-abbrev-expand-function)))38.5 Standard Abbrev Tables
Here we list the variables that hold the abbrev tables for the preloaded major modes ofEmacs.
[Variable]
This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it
apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev
definitions take precedence over those in the global table.

global-abbrev-table[Variable]
The value of this buffer-local variable is the (mode-specific) abbreviation table of thecurrent buffer. It can also be a list of such tables.

local-abbrev-table[Variable]
The value of this variable is a list of elements of the form (mode . abbrev-table)
where mode is the name of a variable: if the variable is bound to a non-nil value,then the abbrev-table is active, otherwise it is ignored. abbrev-table can also be a listof abbrev tables.

abbrev-minor-mode-table-alist[Variable]
This is the local abbrev table used in Fundamental mode; in other words, it is the
local abbrev table in all buffers in Fundamental mode.

fundamental-mode-abbrev-tabletext-mode-abbrev-table[Variable]

This is the local abbrev table used in Text mode.
[Variable]
This is the local abbrev table used in Lisp mode. It is the parent of the local abbrev
table used in Emacs Lisp mode. See Section 38.7 [Abbrev Table Properties], page 1072.

lisp-mode-abbrev-table

38.6 Abbrev Properties
Abbrevs have properties, some of which influence the way they work. You can provide themas arguments to define-abbrev, and manipulate them with the following functions:abbrev-put abbrev prop val[Function]

Set the property prop of abbrev to value val.

abbrev-get abbrev prop

[Function]
Return the property prop of abbrev, or nil if the abbrev has no such property.

The following properties have special meanings::countThis property counts the number of times the abbrev has been expanded. If not
explicitly set, it is initialized to 0 by define-abbrev.

Chapter 38: Abbrevs and Abbrev Expansion:system1072

If non-nil, this property marks the abbrev as a system abbrev. Such abbrevs
are not saved (see Section 38.3 [Abbrev Files], page 1068).

:enable-function
If non-nil, this property should be a function of no arguments which returns
nil if the abbrev should not be used and t otherwise.
:case-fixed
If non-nil, this property indicates that the case of the abbrev’s name is significant
and should only match a text with the same pattern of capitalization. It also
disables the code that modifies the capitalization of the expansion.

38.7 Abbrev Table Properties
Like abbrevs, abbrev tables have properties, some of which influence the way they work.
You can provide them as arguments to define-abbrev-table, and manipulate them withthe functions:abbrev-table-put table prop val[Function]

Set the property prop of abbrev table table to value val.

abbrev-table-get table prop

[Function]
Return the property prop of abbrev table table, or nil if table has no such property.

The following properties have special meaning::enable-function
This is like the :enable-function abbrev property except that it applies toall abbrevs in the table. It is used before even trying to find the abbrev before
point, so it can dynamically modify the abbrev table.
:case-fixedThis is like the :case-fixed abbrev property except that it applies to all abbrevs
in the table.
:regexp

If non-nil, this property is a regular expression that indicates how to extract
the name of the abbrev before point, before looking it up in the table. Whenthe regular expression matches before point, the abbrev name is expected to bein submatch 1. If this property is nil, the default is to use backward-word andforward-word to find the name. This property allows the use of abbrevs whosename contains characters of non-word syntax.

:parents

This property holds a list of tables from which to inherit other abbrevs.

:abbrev-table-modiff
This property holds a counter incremented each time a new abbrev is added tothe table.

1073

39 Threads
Emacs Lisp provides a limited form of concurrency, called threads. All the threads in agiven instance of Emacs share the same memory. Concurrency in Emacs Lisp is “mostly
cooperative”, meaning that Emacs will only switch execution between threads at well-definedtimes. However, the Emacs thread support has been designed in a way to later allow morefine-grained concurrency, and correct programs should not rely on cooperative threading.
Currently, thread switching will occur upon explicit request via thread-yield, when
waiting for keyboard input or for process output from asynchronous processes (e.g., during
accept-process-output), or during blocking operations relating to threads, such as mutex
locking or thread-join.
Emacs Lisp provides primitives to create and control threads, and also to create andcontrol mutexes and condition variables, useful for thread synchronization.
While global variables are shared among all Emacs Lisp threads, local variables are
not—a dynamic let binding is local. Each thread also has its own current buffer (seeSection 28.2 [Current Buffer], page 671) and its own match data (see Section 35.6 [Match
Data], page 1011).
Note that let bindings are treated specially by the Emacs Lisp implementation. Thereis no way to duplicate this unwinding and rewinding behavior other than by using let. For
example, a manual implementation of let written using unwind-protect cannot arrange
for variable values to be thread-specific.
In the case of lexical bindings (see Section 12.10 [Variable Scoping], page 201), a closure isan object like any other in Emacs Lisp, and bindings in a closure are shared by any threads
invoking the closure.

39.1 Basic Thread Functions
Threads can be created and waited for. A thread cannot be exited directly, but the current
thread can be exited implicitly, and other threads can be signaled.

make-thread function &optional name

[Function]
Create a new thread of execution which invokes function. When function returns, thethread exits.

The new thread is created with no local variable bindings in effect. The new thread’s
current buffer is inherited from the current thread.
name can be supplied to give a name to the thread. The name is used for debugging
and informational purposes only; it has no meaning to Emacs. If name is provided, it
must be a string.
This function returns the new thread.

threadp object[Function]
This function returns t if object represents an Emacs thread, nil otherwise.

thread-join thread[Function]
Block until thread exits, or until the current thread is signaled. It returns the resultof the thread function. If thread has already exited, this returns immediately.

Chapter 39: Threads

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thread-signal thread error-symbol data

[Function]
Like signal (see Section 11.7.3.1 [Signaling Errors], page 180), but the signal is delivered in the thread thread. If thread is the current thread, then this just calls signal
immediately. Otherwise, thread will receive the signal as soon as it becomes current.
If thread was blocked by a call to mutex-lock, condition-wait, or thread-join;thread-signal will unblock it.
If thread is the main thread, the signal is not propagated there. Instead, it is shownas message in the main thread.

thread-yield[Function]

Yield execution to the next runnable thread.

thread-name thread[Function]

Return the name of thread, as specified to make-thread.

thread-live-p thread[Function]
Return t if thread is alive, or nil if it is not. A thread is alive as long as its function
is still executing.

thread--blocker thread[Function]
Return the object that thread is waiting on. This function is primarily intended fordebugging, and is given a “double hyphen” name to indicate that.
If thread is blocked in thread-join, this returns the thread for which it is waiting.
If thread is blocked in mutex-lock, this returns the mutex.
If thread is blocked in condition-wait, this returns the condition variable.

Otherwise, this returns nil.

current-thread[Function]

Return the current thread.
[Function]
Return a list of all the live thread objects. A new list is returned by each invocation.

all-threads[Variable]
This variable keeps the main thread Emacs is running, or nil if Emacs is compiled
without thread support.

main-thread

When code run by a thread signals an error that is unhandled, the thread exits. Other
threads can access the error form which caused the thread to exit using the following function.

thread-last-error &optional cleanup[Function]
This function returns the last error form recorded when a thread exited due to anerror. Each thread that exits abnormally overwrites the form stored by the previous
thread’s error with a new value, so only the last one can be accessed. If cleanup is
non-nil, the stored form is reset to nil.

Chapter 39: Threads

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39.2 Mutexes
A mutex is an exclusive lock. At any moment, zero or one threads may own a mutex. If a
thread attempts to acquire a mutex, and the mutex is already owned by some other thread,then the acquiring thread will block until the mutex becomes available.
Emacs Lisp mutexes are of a type called recursive, which means that a thread canre-acquire a mutex it owns any number of times. A mutex keeps a count of how many times
it has been acquired, and each acquisition of a mutex must be paired with a release. The
last release by a thread of a mutex reverts it to the unowned state, potentially allowing
another thread to acquire the mutex.

mutexp object[Function]
This function returns t if object represents an Emacs mutex, nil otherwise.

make-mutex &optional name

[Function]
Create a new mutex and return it. If name is specified, it is a name given to the mutex.
It must be a string. The name is for debugging purposes only; it has no meaning to
Emacs.

mutex-name mutex[Function]

Return the name of mutex, as specified to make-mutex.

mutex-lock mutex[Function]
This will block until this thread acquires mutex, or until this thread is signaled using
thread-signal. If mutex is already owned by this thread, this simply returns.

mutex-unlock mutex[Function]
Release mutex. If mutex is not owned by this thread, this will signal an error.

with-mutex mutex body. . .

[Macro]This macro is the simplest and safest way to evaluate forms while holding a mutex. It
acquires mutex, invokes body, and then releases mutex. It returns the result of body.

39.3 Condition Variables
A condition variable is a way for a thread to block until some event occurs. A thread can
wait on a condition variable, to be woken up when some other thread notifies the condition.
A condition variable is associated with a mutex and, conceptually, with some condition.
For proper operation, the mutex must be acquired, and then a waiting thread must loop,
testing the condition and waiting on the condition variable. For example:(with-mutex mutex(while (not global-variable)(condition-wait cond-var)))
The mutex ensures atomicity, and the loop is for robustness—there may be spurious
notifications.
Similarly, the mutex must be held before notifying the condition. The typical, and best,
approach is to acquire the mutex, make the changes associated with this condition, and thennotify it:(with-mutex mutex

Chapter 39: Threads

1076(setq global-variable (some-computation))(condition-notify cond-var))

make-condition-variable mutex &optional name

[Function]
Make a new condition variable associated with mutex. If name is specified, it is aname given to the condition variable. It must be a string. The name is for debugging
purposes only; it has no meaning to Emacs.

condition-variable-p object[Function]
This function returns t if object represents a condition variable, nil otherwise.

condition-wait cond[Function]
Wait for another thread to notify cond, a condition variable. This function will
block until the condition is notified, or until a signal is delivered to this thread using
thread-signal.
It is an error to call condition-wait without holding the condition’s associatedmutex.
condition-wait releases the associated mutex while waiting. This allows otherthreads to acquire the mutex in order to notify the condition.

condition-notify cond &optional all[Function]
Notify cond. The mutex with cond must be held before calling this. Ordinarily asingle waiting thread is woken by condition-notify; but if all is not nil, then all
threads waiting on cond are notified.
condition-notify releases the associated mutex while waiting. This allows otherthreads to acquire the mutex in order to wait on the condition.

condition-name cond[Function]

Return the name of cond, as passed to make-condition-variable.

condition-mutex cond[Function]
Return the mutex associated with cond. Note that the associated mutex cannot bechanged.

39.4 The Thread List
The list-threads command lists all the currently alive threads. In the resulting buffer,each thread is identified either by the name passed to make-thread (see Section 39.1 [BasicThread Functions], page 1073), or by its unique internal identifier if it was not created witha name. The status of each thread at the time of the creation or last update of the buffer isshown, in addition to the object the thread was blocked on at the time, if it was blocked.
[Variable]
The *Threads* buffer will automatically update twice per second. You can make therefresh rate faster or slower by customizing this variable.

thread-list-refresh-seconds

Here are the commands available in the thread list buffer:bShow a backtrace of the thread at point. This will show where in its code thethread had yielded or was blocked at the moment you pressed b. Be aware that

Chapter 39: Threads

1077

the backtrace is a snapshot; the thread could have meanwhile resumed execution,and be in a different state, or could have exited.
You may use g in the thread’s backtrace buffer to get an updated backtrace, as
backtrace buffers do not automatically update. See Section 19.1.8 [Backtraces],
page 338, for a description of backtraces and the other commands which workon them.
s

Signal the thread at point. After s, type q to send a quit signal or e to send
an error signal. Threads may implement handling of signals, but the default
behavior is to exit on any signal. Therefore you should only use this command
if you understand how to restart the target thread, because your Emacs session
may behave incorrectly if necessary threads are killed.

gUpdate the list of threads and their statuses.

1078

40 Processes
In the terminology of operating systems, a process is a space in which a program can execute.
Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of
their own. These are called subprocesses or child processes of the Emacs process, which istheir parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it
is created. When you create a synchronous subprocess, the Lisp program waits for the
subprocess to terminate before continuing execution. When you create an asynchronous
subprocess, it can run in parallel with the Lisp program. This kind of subprocess isrepresented within Emacs by a Lisp object which is also called a “process”. Lisp programs
can use this object to communicate with the subprocess or to control it. For example, you
can send signals, obtain status information, receive output from the process, or send input
to it.
In addition to processes that run programs, Lisp programs can open connections ofseveral types to devices or processes running on the same machine or on other machines. The
supported connection types are: TCP and UDP network connections, serial port connections,and pipe connections. Each such connection is also represented by a process object.

processp object[Function]
This function returns t if object represents an Emacs process object, nil otherwise.
The process object can represent a subprocess running a program or a connection of
any supported type.

In addition to subprocesses of the current Emacs session, you can also access otherprocesses running on your machine. See Section 40.12 [System Processes], page 1108.

40.1 Functions that Create Subprocesses
There are three primitives that create a new subprocess in which to run a program. Oneof them, make-process, creates an asynchronous process and returns a process object (seeSection 40.4 [Asynchronous Processes], page 1086). The other two, call-process andcall-process-region, create a synchronous process and do not return a process object (seeSection 40.3 [Synchronous Processes], page 1081). There are various higher-level functions
that make use of these primitives to run particular types of process.
Synchronous and asynchronous processes are explained in the following sections. Since
the three functions are all called in a similar fashion, their common arguments are describedhere.
In all cases, the functions specify the program to be run. An error is signaled if the file is
not found or cannot be executed. If the file name is relative, the variable exec-path contains
a list of directories to search. Emacs initializes exec-path when it starts up, based on thevalue of the environment variable PATH. The standard file name constructs, ‘~’, ‘.’, and ‘..’,are interpreted as usual in exec-path, but environment variable substitutions (‘$HOME’, etc.)
are not recognized; use substitute-in-file-name to perform them (see Section 26.9.4[File Name Expansion], page 639). nil in this list refers to default-directory.
Executing a program can also try adding suffixes to the specified name:Chapter 40: Processes

1079[User Option]
This variable is a list of suffixes (strings) to try adding to the specified program file
name. The list should include "" if you want the name to be tried exactly as specified.
The default value is system-dependent.

exec-suffixes

Please note: The argument program contains only the name of the program file; it may
not contain any command-line arguments. You must use a separate argument, args, toprovide those, as described below.
Each of the subprocess-creating functions has a buffer-or-name argument that specifies
where the output from the program will go. It should be a buffer or a buffer name; if it is abuffer name, that will create the buffer if it does not already exist. It can also be nil, whichsays to discard the output, unless a custom filter function handles it. (See Section 40.9.2[Filter Functions], page 1101, and Chapter 20 [Read and Print], page 371.) Normally, you
should avoid having multiple processes send output to the same buffer because their output
would be intermixed randomly. For synchronous processes, you can send the output to a fileinstead of a buffer (and the corresponding argument is therefore more appropriately called
destination). By default, both standard output and standard error streams go to the same
destination, but all the 3 primitives allow optionally to direct the standard error stream toa different destination.
All three of the subprocess-creating functions allow to specify command-line arguments
for the process to run. For call-process and call-process-region, these come in theform of a &rest argument, args. For make-process, both the program to run and its
command-line arguments are specified as a list of strings. The command-line arguments
must all be strings, and they are supplied to the program as separate argument strings.
Wildcard characters and other shell constructs have no special meanings in these strings,
since the strings are passed directly to the specified program.
The subprocess inherits its environment from Emacs, but you can specify overrides forit with process-environment. See Section 42.3 [System Environment], page 1265. The
subprocess gets its current directory from the value of default-directory.
[Variable]
The value of this variable is a string, the name of a directory that contains programs
that come with GNU Emacs and are intended for Emacs to invoke. The program
movemail is an example of such a program; Rmail uses it to fetch new mail from aninbox.

exec-directory[User Option]
The value of this variable is a list of directories to search for programs to run insubprocesses. Each element is either the name of a directory (i.e., a string), or nil,which stands for the default directory (which is the value of default-directory).
See Section 26.6.6 [Locating Files], page 628, for the details of this search.

exec-path

The value of exec-path is used by call-process and start-process when the
program argument is not an absolute file name.
Generally, you should not modify exec-path directly. Instead, ensure that your PATH
environment variable is set appropriately before starting Emacs. Trying to modify
exec-path independently of PATH can lead to confusing results.

Chapter 40: Processes

1080[Function]
This function is an extension of the variable exec-path. If default-directoryindicates a remote directory, this function returns a list of directories used for searching
programs on the respective remote host. In case of a local default-directory, thefunction returns just the value of the variable exec-path.

exec-path40.2 Shell Arguments
Lisp programs sometimes need to run a shell and give it a command that contains file namesthat were specified by the user. These programs ought to be able to support any valid file
name. But the shell gives special treatment to certain characters, and if these charactersoccur in the file name, they will confuse the shell. To handle these characters, use thefunction shell-quote-argument:shell-quote-argument argument &optional posix[Function]
This function returns a string that represents, in shell syntax, an argument whose
actual contents are argument. It should work reliably to concatenate the return value
into a shell command and then pass it to a shell for execution.
Precisely what this function does depends on your operating system. The function
is designed to work with the syntax of your system’s standard shell; if you use an
unusual shell, you will need to redefine this function. See Section 42.22 [Security
Considerations], page 1300.
;; This example shows the behavior on GNU and Unix systems.
(shell-quote-argument "foo > bar")⇒ "foo\\ \\>\\ bar";; This example shows the behavior on MS-DOS and MS-Windows.
(shell-quote-argument "foo > bar")⇒ "\"foo > bar\""Here’s an example of using shell-quote-argument to construct a shell command:(concat "diff -u "(shell-quote-argument oldfile)" "(shell-quote-argument newfile))
If the optional posix argument is non-nil, argument is quoted according to POSIX
shell quoting rules, regardless of the system’s shell. This is useful when your shell
could run on a remote host, which requires a POSIX shell in general.
(shell-quote-argument "foo > bar" (file-remote-p default-directory))

The following two functions are useful for combining a list of individual command-line
argument strings into a single string, and taking a string apart into a list of individualcommand-line arguments. These functions are mainly intended for converting user input inthe minibuffer, a Lisp string, into a list of string arguments to be passed to make-process,call-process or start-process, or for converting such lists of arguments into a single Lisp
string to be presented in the minibuffer or echo area. Note that if a shell is involved (e.g., if

Chapter 40: Processes

1081

using call-process-shell-command), arguments should still be protected by shell-quoteargument; combine-and-quote-strings is not intended to protect special characters fromshell evaluation.

split-string-shell-command string[Function]
This function splits string into substrings, respecting double and single quotes, as wellas backslash quoting.
(split-string-shell-command "ls /tmp/'foo bar'")⇒ ("ls" "/tmp/foo bar")

split-string-and-unquote string &optional separators[Function]
This function splits string into substrings at matches for the regular expression
separators, like split-string does (see Section 4.3 [Creating Strings], page 55); in
addition, it removes quoting from the substrings. It then makes a list of the substrings
and returns it.
If separators is omitted or nil, it defaults to "\\s-+", which is a regular expressionthat matches one or more characters with whitespace syntax (see Section 36.2.1 [Syntax
Class Table], page 1023).
This function supports two types of quoting: enclosing a whole string in double quotes"...", and quoting individual characters with a backslash escape ‘\’. The latter isalso used in Lisp strings, so this function can handle those as well.

combine-and-quote-strings list-of-strings &optional separator[Function]
This function concatenates list-of-strings into a single string, quoting each string asnecessary. It also sticks the separator string between each pair of strings; if separator
is omitted or nil, it defaults to " ". The return value is the resulting string.
The strings in list-of-strings that need quoting are those that include separator as
their substring. Quoting a string encloses it in double quotes "...". In the simplest
case, if you are consing a command from the individual command-line arguments,
every argument that includes embedded blanks will be quoted.

40.3 Creating a Synchronous Process
After a synchronous process is created, Emacs waits for the process to terminate before
continuing. Starting Dired on GNU or Unix1 is an example of this: it runs ls in a synchronous
process, then modifies the output slightly. Because the process is synchronous, the entire
directory listing arrives in the buffer before Emacs tries to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the user can quit bytyping C-g. The first C-g tries to kill the subprocess with a SIGINT signal; but it waits
until the subprocess actually terminates before quitting. If during that time the user types
another C-g, that kills the subprocess instantly with SIGKILL and quits immediately (except
on MS-DOS, where killing other processes doesn’t work). See Section 22.11 [Quitting],
page 471.
The synchronous subprocess functions return an indication of how the process terminated.
1

On other systems, Emacs uses a Lisp emulation of ls; see Section 26.10 [Contents of Directories],
page 645.

Chapter 40: Processes

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The output from a synchronous subprocess is generally decoded using a coding system,
much like text read from a file. The input sent to a subprocess by call-process-region is
encoded using a coding system, much like text written into a file. See Section 34.10 [Coding
Systems], page 976.

call-process program &optional infile destination display &rest
args[Function]

This function calls program and waits for it to finish.
The current working directory of the subprocess is set to the current buffer’s valueof default-directory if that is local (as determined by unhandled-file-namedirectory), or "~" otherwise. If you want to run a process in a remote directory use
process-file.
The standard input for the new process comes from file infile if infile is not nil, andfrom the null device otherwise. The argument destination says where to put theprocess output. Here are the possibilities:
a buffer

Insert the output in that buffer, before point. This includes both thestandard output stream and the standard error stream of the process.

a buffer name (a string)
Insert the output in a buffer with that name, before point.
t

Insert the output in the current buffer, before point.

nil

Discard the output.

0

Discard the output, and return nil immediately without waiting for the
subprocess to finish.
In this case, the process is not truly synchronous, since it can run inparallel with Emacs; but you can think of it as synchronous in that Emacs
is essentially finished with the subprocess as soon as this function returns.
MS-DOS doesn’t support asynchronous subprocesses, so this option doesn’t
work there.

(:file file-name)Send the output to the file name specified, overwriting it if it alreadyexists.
(real-destination error-destination)
Keep the standard output stream separate from the standard error stream;
deal with the ordinary output as specified by real-destination, and disposeof the error output according to error-destination. If error-destination
is nil, that means to discard the error output, t means mix it with theordinary output, and a string specifies a file name to redirect error output
into.
You can’t directly specify a buffer to put the error output in; that is too
difficult to implement. But you can achieve this result by sending theerror output to a temporary file and then inserting the file into a bufferwhen the subprocess finishes.

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If display is non-nil, then call-process redisplays the buffer as output is inserted.
(However, if the coding system chosen for decoding output is undecided, meaning
deduce the encoding from the actual data, then redisplay sometimes cannot continue
once non-ASCII characters are encountered. There are fundamental reasons why it ishard to fix this; see Section 40.9 [Output from Processes], page 1099.)
Otherwise the function call-process does no redisplay, and the results become visibleon the screen only when Emacs redisplays that buffer in the normal course of events.
The remaining arguments, args, are strings that specify command line arguments forthe program. Each string is passed to program as a separate argument.
The value returned by call-process (unless you told it not to wait) indicates thereason for process termination. A number gives the exit status of the subprocess; 0means success, and any other value means failure. If the process terminated with asignal, call-process returns a string describing the signal. If you told call-process
not to wait, it returns nil.
In the examples below, the buffer ‘foo’ is current.
(call-process "pwd" nil t)⇒ 0---------- Buffer: foo ---------/home/lewis/manual---------- Buffer: foo ---------(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")⇒ 0---------- Buffer: bar ---------lewis:x:1001:1001:Bil Lewis,,,,:/home/lewis:/bin/bash---------- Buffer: bar ----------

Here is an example of the use of call-process, as used to be found in the definitionof the insert-directory function:(call-process insert-directory-program nil t nil switches(if full-directory-p(concat (file-name-as-directory file) ".")file))

process-file program &optional infile buffer display &rest args

[Function]
This function processes files synchronously in a separate process. It is similar tocall-process, but may invoke a file name handler based on the value of the variable
default-directory, which specifies the current working directory of the subprocess.
The arguments are handled in almost the same way as for call-process, with thefollowing differences:
Some file name handlers may not support all combinations and forms of the arguments
infile, buffer, and display. For example, some file name handlers might behave as if
display were nil, regardless of the value actually passed. As another example, somefile name handlers might not support separating standard output and error output by
way of the buffer argument.
If a file name handler is invoked, it determines the program to run based on the firstargument program. For instance, suppose that a handler for remote files is invoked.

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Then the path that is used for searching for the program might be different fromexec-path.
The second argument infile may invoke a file name handler. The file name handler
could be different from the handler chosen for the process-file function itself. (Forexample, default-directory could be on one remote host, and infile on a different
remote host. Or default-directory could be non-special, whereas infile is on aremote host.)
If buffer is a list of the form (real-destination error-destination), and errordestination names a file, then the same remarks as for infile apply.
The remaining arguments (args) will be passed to the process verbatim. Emacs is
not involved in processing file names that are present in args. To avoid confusion, it
may be best to avoid absolute file names in args, but rather to specify all file names
as relative to default-directory. The function file-relative-name is useful for
constructing such relative file names. Alternatively, you can use file-local-name(see Section 26.12 [Magic File Names], page 649) to obtain an absolute file name as
seen from the remote host’s perspective.
[Variable]
This variable indicates whether a call of process-file changes remote files.

process-file-side-effects

By default, this variable is always set to t, meaning that a call of process-file could
potentially change any file on a remote host. When set to nil, a file name handler
could optimize its behavior with respect to remote file attribute caching.
You should only ever change this variable with a let-binding; never with setq.
[User Option]
This user option indicates whether a call of process-file returns a string describing
the signal interrupting a remote process.

process-file-return-signal-string

When a process returns an exit code greater than 128, it is interpreted as a signal.
process-file requires to return a string describing this signal.
Since there are processes violating this rule, returning exit codes greater than 128
which are not bound to a signal, process-file returns always the exit code as natural
number for remote processes. Setting this user option to non-nil forces process-file
to interpret such exit codes as signals, and to return a corresponding string.

call-process-region start end program &optional delete
destination display &rest args

[Function]

This function sends the text from start to end as standard input to a process running
program. It deletes the text sent if delete is non-nil; this is useful when destination
is t, to insert the output in the current buffer in place of the input.
The arguments destination and display control what to do with the output from thesubprocess, and whether to update the display as it comes in. For details, see thedescription of call-process, above. If destination is the integer 0, call-processregion discards the output and returns nil immediately, without waiting for the
subprocess to finish (this only works if asynchronous subprocesses are supported; i.e.,
not on MS-DOS).

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The remaining arguments, args, are strings that specify command line arguments forthe program.
The return value of call-process-region is just like that of call-process: nil if
you told it to return without waiting; otherwise, a number or string which indicates
how the subprocess terminated.
In the following example, we use call-process-region to run the cat utility, withstandard input being the first five characters in buffer ‘foo’ (the word ‘input’). cat
copies its standard input into its standard output. Since the argument destination ist, this output is inserted in the current buffer.
---------- Buffer: foo ---------input?
---------- Buffer: foo ---------(call-process-region 1 6 "cat" nil t)⇒ 0---------- Buffer: foo ---------inputinput?
---------- Buffer: foo ----------For example, the shell-command-on-region command uses call-shell-region ina manner similar to this:(call-shell-region
start endcommandnilbuffer); shell command; do not delete region; send output to buffer

call-process-shell-command command &optional infile destination
display[Function]

This function executes the shell command command synchronously. The other arguments are handled as in call-process. An old calling convention allowed passing any
number of additional arguments after display, which were concatenated to command;
this is still supported, but strongly discouraged.

process-file-shell-command command &optional infile destination
display[Function]

This function is like call-process-shell-command, but uses process-file internally.
Depending on default-directory, command can be executed also on remote hosts.
An old calling convention allowed passing any number of additional arguments after
display, which were concatenated to command; this is still supported, but strongly
discouraged.

call-shell-region start end command &optional delete destination[Function]
This function sends the text from start to end as standard input to an inferior shellrunning command. This function is similar than call-process-region, with process
being a shell. The arguments delete, destination and the return value are like incall-process-region. Note that this function doesn’t accept additional arguments.

shell-command-to-string command[Function]
This function executes command (a string) as a shell command, then returns thecommand’s output as a string.

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process-lines program &rest args

[Function]
This function runs program, waits for it to finish, and returns its output as a list of
strings. Each string in the list holds a single line of text output by the program; theend-of-line characters are stripped from each line. The arguments beyond program,args, are strings that specify command-line arguments with which to run the program.
If program exits with a non-zero exit status, this function signals an error.
This function works by calling call-process, so program output is decoded in thesame way as for call-process.

process-lines-ignore-status program &rest args

[Function]
This function is just like process-lines, but does not signal an error if program exits
with a non-zero exit status.

40.4 Creating an Asynchronous Process
In this section, we describe how to create an asynchronous process. After an asynchronous
process is created, it runs in parallel with Emacs, and Emacs can communicate with itusing the functions described in the following sections (see Section 40.7 [Input to Processes],
page 1096, and see Section 40.9 [Output from Processes], page 1099). Note that process
communication is only partially asynchronous: Emacs sends and receives data to and froma process only when those functions are called.
An asynchronous process is controlled either via a pty (pseudo-terminal) or a pipe. The
choice of pty or pipe is made when creating the process, by default based on the value of thevariable process-connection-type (see below). If available, ptys are usually preferable forprocesses visible to the user, as in Shell mode, because they allow for job control (C-c, C-z,etc.) between the process and its children, and because interactive programs treat ptys as
terminal devices, whereas pipes don’t support these features. However, for subprocesses
used by Lisp programs for internal purposes (i.e., no user interaction with the subprocess isrequired), where significant amounts of data need to be exchanged between the subprocess
and the Lisp program, it is often better to use a pipe, because pipes are more efficient. Also,
the total number of ptys is limited on many systems, and it is good not to waste them
unnecessarily.

make-process &rest args

[Function]
This function is the basic low-level primitive for starting asynchronous subprocesses. It
returns a process object representing the subprocess. Compared to the more high-level
start-process, described below, it takes keyword arguments, is more flexible, andallows to specify process filters and sentinels in a single call.
The arguments args are a list of keyword/argument pairs. Omitting a keyword isalways equivalent to specifying it with value nil. Here are the meaningful keywords::name name
Use the string name as the process name; if a process with this namealready exists, then name is modified (by appending ‘<1>’, etc.) to be
unique.
:buffer buffer
Use buffer as the process buffer. If the value is nil, the subprocess is not
associated with any buffer.

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Use command as the command line of the process. The value should be alist starting with the program’s executable file name, followed by strings
to give to the program as its arguments. If the first element of the list isnil, Emacs opens a new pseudoterminal (pty) and associates its input
and output with buffer, without actually running any program; the restof the list elements are ignored in that case.
:coding coding
If coding is a symbol, it specifies the coding system to be used for both
reading and writing of data from and to the connection. If coding is acons cell (decoding . encoding), then decoding will be used for readingand encoding for writing. The coding system used for encoding thedata written to the program is also used for encoding the command-line
arguments (but not the program itself, whose file name is encoded as anyother file name; see Section 34.10.2 [Encoding and I/O], page 978).
If coding is nil, the default rules for finding the coding system will apply.
See Section 34.10.5 [Default Coding Systems], page 983.
:connection-type type
Initialize the type of device used to communicate with the subprocess.
Possible values are pty to use a pty, pipe to use a pipe, or nil to use
the default derived from the value of the process-connection-type
variable. If type is a cons cell (input . output), then input will be used
for standard input and output for standard output (and standard error if:stderr is nil).
On systems where ptys are not available (MS-Windows), this parameteris ignored, and pipes are used unconditionally.
:noquery query-flag
Initialize the process query flag to query-flag. See Section 40.11 [Query
Before Exit], page 1107.
:stop stopped
If provided, stopped must be nil; it is an error to use any non-nil value.
The :stop key is ignored otherwise and is retained for compatibility withother process types such as pipe processes. Asynchronous subprocesses
never start in the stopped state.
:filter filter
Initialize the process filter to filter. If not specified, a default filter will
be provided, which can be overridden later. See Section 40.9.2 [Filter
Functions], page 1101.
:sentinel sentinel
Initialize the process sentinel to sentinel. If not specified, a default sentinel
will be used, which can be overridden later. See Section 40.10 [Sentinels],
page 1105.

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Associate stderr with the standard error of the process. A non-nil value
should be either a buffer or a pipe process created with make-pipeprocess, described below. If stderr is nil, standard error is mixed withstandard output, and both are sent to buffer or filter.
If stderr is a buffer, Emacs will create a pipe process, the standard
error process. This process will have the default filter (see Section 40.9.2[Filter Functions], page 1101), sentinel (see Section 40.10 [Sentinels],
page 1105), and coding systems (see Section 34.10.5 [Default Coding
Systems], page 983). On the other hand, it will use query-flag as its
query-on-exit flag (see Section 40.11 [Query Before Exit], page 1107).
It will be associated with the stderr buffer (see Section 40.9.1 [Process
Buffers], page 1099) and send its output (which is the standard error of
the main process) there. To get the process object for the standard error
process, pass the stderr buffer to get-buffer-process.
If stderr is a pipe process, Emacs will use it as standard error process forthe new process.
:file-handler file-handler
If file-handler is non-nil, then look for a file name handler for the current
buffer’s default-directory, and invoke that file name handler to makethe process. If there is no such handler, proceed as if file-handler werenil.
The original argument list, modified with the actual connection information, is available
via the process-contact function.
The current working directory of the subprocess is set to the current buffer’s valueof default-directory if that is local (as determined by unhandled-file-namedirectory), or ~ otherwise. If you want to run a process in a remote directory, pass:file-handler t to make-process. In that case, the current working directory is the
local name component of default-directory (as determined by file-local-name).
Depending on the implementation of the file name handler, it might not be possible
to apply filter or sentinel to the resulting process object. The :stderr argument
cannot be a pipe process, file name handlers do not support pipe processes for this. A
buffer as :stderr argument is accepted, its contents is shown without the use of pipe
processes. See Section 40.9.2 [Filter Functions], page 1101, Section 40.10 [Sentinels],
page 1105, and Section 40.9.4 [Accepting Output], page 1104.
Some file name handlers may not support make-process. In such cases, this function
does nothing and returns nil.

make-pipe-process &rest args

[Function]
This function creates a bidirectional pipe which can be attached to a child process.
This is useful with the :stderr keyword of make-process. The function returns aprocess object.
The arguments args are a list of keyword/argument pairs. Omitting a keyword isalways equivalent to specifying it with value nil.

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Here are the meaningful keywords::name name
Use the string name as the process name. As with make-process, it ismodified if necessary to make it unique.
:buffer buffer
Use buffer as the process buffer.
:coding coding
If coding is a symbol, it specifies the coding system to be used for both
reading and writing of data from and to the connection. If coding is acons cell (decoding . encoding), then decoding will be used for readingand encoding for writing.
If coding is nil, the default rules for finding the coding system will apply.
See Section 34.10.5 [Default Coding Systems], page 983.
:noquery query-flag
Initialize the process query flag to query-flag. See Section 40.11 [Query
Before Exit], page 1107.
:stop stopped
If stopped is non-nil, start the process in the stopped state. In the
stopped state, a pipe process does not accept incoming data, but you
can send outgoing data. The stopped state is set by stop-process andcleared by continue-process (see Section 40.8 [Signals to Processes],
page 1097).
:filter filter
Initialize the process filter to filter. If not specified, a default filter will be
provided, which can be changed later. See Section 40.9.2 [Filter Functions],
page 1101.
:sentinel sentinel
Initialize the process sentinel to sentinel. If not specified, a default sentinel
will be used, which can be changed later. See Section 40.10 [Sentinels],
page 1105.
The original argument list, modified with the actual connection information, is available
via the process-contact function.

start-process name buffer-or-name program &rest args

[Function]
This function is a higher-level wrapper around make-process, exposing an interface
that is similar to call-process. It creates a new asynchronous subprocess and starts
the specified program running in it. It returns a process object that stands for the
new subprocess in Lisp. The argument name specifies the name for the process object;
as with make-process, it is modified if necessary to make it unique. The buffer
buffer-or-name is the buffer to associate with the process.
If program is nil, Emacs opens a new pseudoterminal (pty) and associates its input
and output with buffer-or-name, without creating a subprocess. In that case, theremaining arguments args are ignored.

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The rest of args are strings that specify command line arguments for the subprocess.
In the example below, the first process is started and runs (rather, sleeps) for 100
seconds (the output buffer ‘foo’ is created immediately). Meanwhile, the second
process is started, and given the name ‘my-process<1>’ for the sake of uniqueness.
It inserts the directory listing at the end of the buffer ‘foo’, before the first process
finishes. Then it finishes, and a message to that effect is inserted in the buffer. Muchlater, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100")⇒ #<process my-process>(start-process "my-process" "foo" "ls" "-l" "/bin")⇒ #<process my-process<1>>---------- Buffer: foo ---------total 8336
-rwxr-xr-x 1 root root 971384 Mar 30 10:14 bash
-rwxr-xr-x 1 root root 146920 Jul 5 2011 bsd-csh...
-rwxr-xr-x 1 root root 696880 Feb 28 15:55 zsh4
Process my-process<1> finished
Process my-process finished---------- Buffer: foo ----------

start-file-process name buffer-or-name program &rest args

[Function]
Like start-process, this function starts a new asynchronous subprocess running
program in it, and returns its process object.

The difference from start-process is that this function may invoke a file namehandler based on the value of default-directory. This handler ought to run
program, perhaps on the local host, perhaps on a remote host that corresponds
to default-directory. In the latter case, the local part of default-directory
becomes the working directory of the process.
This function does not try to invoke file name handlers for program or for the restof args. For that reason, if program or any of args use the remote-file syntax (seeSection 26.12 [Magic File Names], page 649), they must be converted either to filenames relative to default-directory, or to names that identify the files locally on
the remote host, by running them through file-local-name.
Depending on the implementation of the file name handler, it might not be possible
to apply process-filter or process-sentinel to the resulting process object. See
Section 40.9.2 [Filter Functions], page 1101, and Section 40.10 [Sentinels], page 1105.
Some file name handlers may not support start-file-process (for example thefunction ange-ftp-hook-function). In such cases, this function does nothing andreturns nil.

start-process-shell-command name buffer-or-name command[Function]
This function is like start-process, except that it uses a shell to execute the specified command. The argument command is a shell command string. The variable
shell-file-name specifies which shell to use.

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The point of running a program through the shell, rather than directly withmake-process or start-process, is so that you can employ shell features such as
wildcards in the arguments. It follows that if you include any arbitrary user-specified
arguments in the command, you should quote them with shell-quote-argument
first, so that any special shell characters do not have their special shell meanings. See
Section 40.2 [Shell Arguments], page 1080. Of course, when executing commands
based on user input you should also consider the security implications.

start-file-process-shell-command name buffer-or-namecommand[Function]

This function is like start-process-shell-command, but uses start-file-processinternally. Because of this, command can also be executed on remote hosts, depending
on default-directory.
[Variable]
This variable controls the type of device used to communicate with asynchronous
subprocesses. If it is non-nil, then ptys are used, when available. Otherwise, pipes
are used.

process-connection-type

The value of process-connection-type takes effect when make-process or
start-process is called. So you can specify how to communicate with one subprocessby binding the variable around the call to these functions.
Note that the value of this variable is ignored when make-process is called with a
non-nil value of the :stderr parameter; in that case, Emacs will communicate withthe process using pipes. It is also ignored if ptys are unavailable (MS-Windows).
(let ((process-connection-type nil))(start-process ...)); use a pipe

To determine whether a given subprocess actually got a pipe or a pty, use the function
process-tty-name (see Section 40.6 [Process Information], page 1092).
[Variable]
If a process sentinel/filter function has an error, Emacs will (by default) pause Emacs
for process-error-pause-time seconds after displaying this error, so that users will
see the error in question. However, this can lead to situations where Emacs becomes
unresponsive (if there’s a lot of these errors happening), so this can be disabled by
setting process-error-pause-time to 0.

process-error-pause-time

40.5 Deleting Processes
Deleting a process disconnects Emacs immediately from the subprocess. Processes aredeleted automatically after they terminate, but not necessarily right away. You can deletea process explicitly at any time. If you explicitly delete a terminated process before it
is deleted automatically, no harm results. Deleting a running process sends a signal toterminate it (and its child processes, if any), and calls the process sentinel. See Section 40.10[Sentinels], page 1105.
When a process is deleted, the process object itself continues to exist as long as other
Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted
processes, but those that do I/O or send signals will report an error. The process mark

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continues to point to the same place as before, usually into a buffer where output from theprocess was being inserted.
[User Option]
This variable controls automatic deletion of processes that have terminated (due tocalling exit or to a signal). If it is nil, then they continue to exist until the user runs
list-processes. Otherwise, they are deleted immediately after they exit.

delete-exited-processes

delete-process &optional process[Function]
This function deletes a process, killing it with a SIGKILL signal if the process was
running a program. The argument may be a process, the name of a process, abuffer, or the name of a buffer. (A buffer or buffer-name stands for the process thatget-buffer-process returns, and a missing or nil process means that the current
buffer’s process should be killed.) Calling delete-process on a running process
terminates it, updates the process status, and runs the sentinel immediately. If theprocess has already terminated, calling delete-process has no effect on its status,
or on the running of its sentinel (which will happen sooner or later).
If the process object represents a network, serial, or pipe connection, its status changes
to closed; otherwise, it changes to signal, unless the process already exited. See
Section 40.6 [Process Information], page 1092.
(delete-process "*shell*")⇒ nil

40.6 Process Information
Several functions return information about processes.

list-processes &optional query-only buffer[Command]This command displays a listing of all living processes. In addition, it finally deletes
any process whose status was ‘Exited’ or ‘Signaled’. It returns nil.
The processes are shown in a buffer named *Process List* (unless you specify
otherwise using the optional argument buffer), whose major mode is Process Menu
mode.
If query-only is non-nil, it only lists processes whose query flag is non-nil. See
Section 40.11 [Query Before Exit], page 1107.

process-list[Function]

This function returns a list of all processes that have not been deleted.
(process-list)⇒ (#<process display-time> #<process shell>)

num-processors &optional query[Function]
This function returns the number of processors, a positive integer. Each usable thread
execution unit counts as a processor. By default, the count includes the number of available processors, which you can override by setting the OMP_NUM_THREADS environment
variable of OpenMP (https://www.openmp.org/spec-html/5.1/openmpse59.html).
If the optional argument query is current, this function ignores OMP_NUM_THREADS; ifquery is all, this function also counts processors that are on the system but are notavailable to the current process.

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get-process name

[Function]
This function returns the process named name (a string), or nil if there is none. The
argument name can also be a process object, in which case it is returned.
(get-process "shell")⇒ #<process shell>

process-command process[Function]
This function returns the command that was executed to start process. This is alist of strings, the first string being the program executed and the rest of the strings
being the arguments that were given to the program. For a network, serial, or pipe
connection, this is either nil, which means the process is running or t (process is
stopped).
(process-command (get-process "shell"))⇒ ("bash" "-i")process-contact process &optional key no-block[Function]
This function returns information about how a network, a serial, or a pipe connection
was set up. When key is nil, it returns (hostname service) for a network connection,(port speed) for a serial connection, and t for a pipe connection. For an ordinary
child process, this function always returns t when called with a nil key.
If key is t, the value is the complete status information for the connection, server,
serial port, or pipe; that is, the list of keywords and values specified in make-networkprocess, make-serial-process, or make-pipe-process, except that some of thevalues represent the current status instead of what you specified.
For a network process, the values include (see make-network-process for a completelist)::buffer

The associated value is the process buffer.

:filter

The associated value is the process filter function. See Section 40.9.2[Filter Functions], page 1101.

:sentinel
The associated value is the process sentinel function. See Section 40.10[Sentinels], page 1105.
:remoteIn a connection, the address in internal format of the remote peer.

:local

The local address, in internal format.

:service

In a server, if you specified t for service, this value is the actual port
number.

:local and :remote are included even if they were not specified explicitly in
make-network-process.
For a serial connection, see make-serial-process and serial-process-configure
for the list of keys. For a pipe connection, see make-pipe-process for the list of keys.
If key is a keyword, the function returns the value corresponding to that keyword.
If process is a non-blocking network stream that hasn’t been fully set up yet, then thisfunction will block until that has happened. If given the optional no-block parameter,
this function will return nil instead of blocking.

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process-id process[Function]
This function returns the PID of process. This is an integral number that distinguishes
the process process from all other processes running on the same computer at thecurrent time. The PID of a process is chosen by the operating system kernel when theprocess is started and remains constant as long as the process exists. For network,
serial, and pipe connections, this function returns nil.

process-name process[Function]

This function returns the name of process, as a string.

process-status process-name[Function]
This function returns the status of process-name as a symbol. The argument processname must be a process, a buffer, or a process name (a string).

The possible values for an actual subprocess are:runfor a process that is running.

stop

for a process that is stopped but continuable.

exit

for a process that has exited.

signalfor a process that has received a fatal signal.

open

for a network, serial, or pipe connection that is open.

closedfor a network, serial, or pipe connection that is closed. Once a connection
is closed, you cannot reopen it, though you might be able to open a newconnection to the same place.

connect

for a non-blocking connection that is waiting to complete.

failedfor a non-blocking connection that has failed to complete.

listenfor a network server that is listening.

nil

if process-name is not the name of an existing process.
(process-status (get-buffer "*shell*"))⇒ run

For a network, serial, or pipe connection, process-status returns one of the symbols
open, stop, or closed. The latter means that the other side closed the connection, orEmacs did delete-process. The value stop means that stop-process was calledon the connection.

process-live-p process[Function]
This function returns non-nil if process is alive. A process is considered alive if its
status is run, open, listen, connect or stop.

process-type process[Function]
This function returns the symbol network for a network connection or server, serial
for a serial port connection, pipe for a pipe connection, or real for a subprocesscreated for running a program.

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process-exit-status process[Function]
This function returns the exit status of process or the signal number that killed it.
(Use the result of process-status to determine which of those it is.) If process has
not yet terminated, the value is 0. For network, serial, and pipe connections that are
already closed, the value is either 0 or 256, depending on whether the connection wasclosed normally or abnormally.

process-tty-name process &optional stream[Function]
This function returns the terminal name that process is using for its communication
with Emacs—or nil if it is using pipes instead of a pty (see process-connectiontype in Section 40.4 [Asynchronous Processes], page 1086). By default, this function
returns the terminal name if any of process’s standard streams use a terminal. If
stream is one of stdin, stdout, or stderr, this function returns the terminal name(or nil, as above) that process uses for that stream specifically. You can use this todetermine whether a particular stream uses a pipe or a pty.
If process represents a program running on a remote host, this function returns the
local terminal name that communicates with process; you can get the terminal nameused by that program on the remote host with the process property remote-tty. If
process represents a network, serial, or pipe connection, this function always returns
nil.

process-coding-system process[Function]
This function returns a cons cell (decode . encode), describing the coding systems
in use for decoding output from, and encoding input to, process (see Section 34.10[Coding Systems], page 976).

set-process-coding-system process &optional decoding-system
encoding-system[Function]

This function specifies the coding systems to use for subsequent output from andinput to process. It will use decoding-system to decode subprocess output, andencoding-system to encode subprocess input.
Every process also has a property list that you can use to store miscellaneous values
associated with the process.

process-get process propname[Function]

This function returns the value of the propname property of process.

process-put process propname value[Function]

This function sets the value of the propname property of process to value.

process-plist process[Function]

This function returns the process plist of process.

set-process-plist process plist
This function sets the process plist of process to plist.

[Function]

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40.7 Sending Input to Processes
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is donewith the functions in this section. You must specify the process to send input to, and the
input data to send. If the subprocess runs a program, the data appears on the standard
input of that program; for connections, the data is sent to the connected device or program.
Some operating systems have limited space for buffered input in a pty. On these systems,
Emacs sends an EOF periodically amidst the other characters, to force them through. For
most programs, these EOFs do no harm.
Subprocess input is normally encoded using a coding system before the subprocess receives
it, much like text written into a file. You can use set-process-coding-system to specify
which coding system to use (see Section 40.6 [Process Information], page 1092). Otherwise,
the coding system comes from coding-system-for-write, if that is non-nil; or else fromthe defaulting mechanism (see Section 34.10.5 [Default Coding Systems], page 983).
Sometimes the system is unable to accept input for that process, because the input buffer
is full. When this happens, the send functions wait a short while, accepting output fromsubprocesses, and then try again. This gives the subprocess a chance to read more of its
pending input and make space in the buffer. It also allows filters (including the one currently
running), sentinels and timers to run—so take account of that in writing your code.
In these functions, the process argument can be a process or the name of a process, ora buffer or buffer name (which stands for a process via get-buffer-process). nil means
the current buffer’s process.

process-send-string process string[Function]
This function sends process the contents of string as standard input. It returns nil.
For example, to make a Shell buffer list files:(process-send-string "shell<1>" "ls\n")⇒ nilprocess-send-region process start end[Function]
This function sends the text in the region defined by start and end as standard input
to process.
An error is signaled unless both start and end are integers or markers that indicate
positions in the current buffer. (It is unimportant which number is larger.)process-send-eof &optional process[Function]
This function makes process see an end-of-file in its input. The EOF comes after any
text already sent to it. The function returns process.
(process-send-eof "shell")⇒ "shell"process-running-child-p &optional process[Function]
This function will tell you whether a process, which must not be a connection but
a real subprocess, has given control of its terminal to a child process of its own. If
this is true, the function returns the numeric ID of the foreground process group ofprocess; it returns nil if Emacs can be certain that this is not so. The value is t if
Emacs cannot tell whether this is true. This function signals an error if process is a
network, serial, or pipe connection, or if the subprocess is not active.

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40.8 Sending Signals to Processes
Sending a signal to a subprocess is a way of interrupting its activities. There are several
different signals, each with its own meaning. The set of signals and their names is definedby the operating system. For example, the signal SIGINT means that the user has typed
C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess,but some stop (or resume) execution instead. Most signals can optionally be handled byprograms; if the program handles the signal, then we can say nothing in general about its
effects.
You can send signals explicitly by calling the functions in this section. Emacs also
sends signals automatically at certain times: killing a buffer sends a SIGHUP signal to all its
associated processes; killing Emacs sends a SIGHUP signal to all remaining processes. (SIGHUP
is a signal that usually indicates that the user “hung up the phone”, i.e., disconnected.)
Each of the signal-sending functions takes two optional arguments: process and currentgroup.
The argument process must be either a process, a process name, a buffer, a buffer name,or nil. A buffer or buffer name stands for a process through get-buffer-process. nil
stands for the process associated with the current buffer. Except with stop-process andcontinue-process, an error is signaled if process does not identify an active process, or if
it represents a network, serial, or pipe connection.
The argument current-group is a flag that makes a difference when you are running a
job-control shell as an Emacs subprocess. If it is non-nil, then the signal is sent to thecurrent process-group of the terminal that Emacs uses to communicate with the subprocess.
If the process is a job-control shell, this means the shell’s current subjob. If current-group isnil, the signal is sent to the process group of the immediate subprocess of Emacs. If thesubprocess is a job-control shell, this is the shell itself. If current-group is lambda, the signal
is sent to the process-group that owns the terminal, but only if it is not the shell itself.
The flag current-group has no effect when a pipe is used to communicate with thesubprocess, because the operating system does not support the distinction in the caseof pipes. For the same reason, job-control shells won’t work when a pipe is used. See
process-connection-type in Section 40.4 [Asynchronous Processes], page 1086.

interrupt-process &optional process current-group[Function]
This function interrupts the process process by sending the signal SIGINT. Outside ofEmacs, typing the interrupt character (normally C-c on some systems, and DEL onothers) sends this signal. When the argument current-group is non-nil, you can thinkof this function as typing C-c on the terminal by which Emacs talks to the subprocess.

kill-process &optional process current-group[Command]This command kills the process process by sending the signal SIGKILL. This signal kills
the subprocess immediately, and cannot be handled by the subprocess. Interactively,
it’ll prompt the user for a process name, defaulting to the process (if any) in thecurrent buffer.

quit-process &optional process current-group[Function]
This function sends the signal SIGQUIT to the process process. This signal is the one
sent by the quit character (usually C-\) when you are not inside Emacs.

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stop-process &optional process current-group[Function]
This function stops the specified process. If it is a real subprocess running a program,it sends the signal SIGTSTP to that subprocess. If process represents a network, serial,or pipe connection, this function inhibits handling of the incoming data from theconnection; for a network server, this means not accepting new connections. Usecontinue-process to resume normal execution.
Outside of Emacs, on systems with job control, the stop character (usually C-z)
normally sends the SIGTSTP signal to a subprocess. When current-group is non-nil,
you can think of this function as typing C-z on the terminal Emacs uses to communicate
with the subprocess.

continue-process &optional process current-group[Function]
This function resumes execution of the process process. If it is a real subprocess
running a program, it sends the signal SIGCONT to that subprocess; this presumes
that process was stopped previously. If process represents a network, serial, or pipe
connection, this function resumes handling of the incoming data from the connection.
For serial connections, data that arrived during the time the process was stopped
might be lost.

signal-process process signal &optional remote[Command]This function sends a signal to process process. The argument signal specifies which
signal to send; it should be an integer, or a symbol whose name is a signal.
The process argument can be a system process ID (an integer); that allows you tosend signals to processes that are not children of Emacs. See Section 40.12 [System
Processes], page 1108.
If process is a process object which contains the property remote-pid, or process isa number and remote is a remote file name, process is interpreted as process on therespective remote host, which will be the process to signal.
If process is a string, it is interpreted as process object with the respective process
name, or as a number.

Sometimes, it is necessary to send a signal to a non-local asynchronous process. Thisis possible by writing an own interrupt-process or signal-process implementation.
This function must be added then to interrupt-process-functions or signal-processfunctions, respectively.
[Variable]
This variable is a list of functions to be called for interrupt-process. The argumentsof the functions are the same as for interrupt-process. These functions are calledin the order of the list, until one of them returns non-nil. The default function, whichshall always be the last in this list, is internal-default-interrupt-process.
This is the mechanism, how Tramp implements interrupt-process.

interrupt-process-functions[Variable]
This variable is a list of functions to be called for signal-process. The arguments ofthe functions are the same as for signal-process. These functions are called in theorder of the list, until one of them returns non-nil. The default function, which shallalways be the last in this list, is internal-default-signal-process.

signal-process-functions

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This is the mechanism, how Tramp implements signal-process.

40.9 Receiving Output from Processes
The output that an asynchronous subprocess writes to its standard output stream is passed
to a function called the filter function. The default filter function simply inserts the output
into a buffer, which is called the associated buffer of the process (see Section 40.9.1 [Process
Buffers], page 1099). If the process has no buffer then the default filter discards the output.
If the subprocess writes to its standard error stream, by default the error output is also
passed to the process filter function. Alternatively, you could use the :stderr parameterwith a non-nil value in a call to make-process (see Section 40.4 [Asynchronous Processes],
page 1086) to make the destination of the error output separate from the standard output.
When a subprocess terminates, Emacs reads any pending output, then stops reading
output from that subprocess. Therefore, if the subprocess has children that are still live andstill producing output, Emacs won’t receive that output.
Output from a subprocess can arrive only while Emacs is waiting: when reading terminal input (see the function waiting-for-user-input-p), in sit-for and sleep-for (seeSection 22.10 [Waiting], page 470), in accept-process-output (see Section 40.9.4 [Accepting Output], page 1104), and in functions which send data to processes (see Section 40.7
[Input to Processes], page 1096). This minimizes the problem of timing errors that usuallyplague parallel programming. For example, you can safely create a process and only thenspecify its buffer or filter function; no output can arrive before you finish, if the code in
between does not call any primitive that waits.
[Variable]
On some systems, when Emacs reads the output from a subprocess, the output data isread in very small blocks, potentially resulting in very poor performance. This behavior
can be remedied to some extent by setting the variable process-adaptive-readbuffering to a non-nil value (the default), as it will automatically delay readingfrom such processes, thus allowing them to produce more output before Emacs tries
to read it.

process-adaptive-read-buffering

40.9.1 Process Buffers
A process can (and usually does) have an associated buffer, which is an ordinary Emacs
buffer that is used for two purposes: storing the output from the process, and deciding whento kill the process. You can also use the buffer to identify a process to operate on, since innormal practice only one process is associated with any given buffer. Many applications ofprocesses also use the buffer for editing input to be sent to the process, but this is not built
into Emacs Lisp.
By default, process output is inserted in the associated buffer. (You can change thisby defining a custom filter function, see Section 40.9.2 [Filter Functions], page 1101.) The
position to insert the output is determined by the process-mark, which is then updated topoint to the end of the text just inserted. Usually, but not always, the process-mark is at
the end of the buffer.
Killing the associated buffer of a process also kills the process. Emacs asks for confirmation
first, if the process’s process-query-on-exit-flag is non-nil (see Section 40.11 [QueryChapter 40: Processes

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Before Exit], page 1107). This confirmation is done by the function process-kill-bufferquery-function, which is run from kill-buffer-query-functions (see Section 28.10[Killing Buffers], page 685).

process-buffer process[Function]

This function returns the associated buffer of the specified process.
(process-buffer (get-process "shell"))⇒ #<buffer *shell*>process-mark process[Function]
This function returns the process marker for process, which is the marker that says
where to insert output from the process.
If process does not have a buffer, process-mark returns a marker that points nowhere.
The default filter function uses this marker to decide where to insert process output,
and updates it to point after the inserted text. That is why successive batches of
output are inserted consecutively.
Custom filter functions normally should use this marker in the same fashion. For an
example of a filter function that uses process-mark, see [Process Filter Example],
page 1102.

When the user is expected to enter input in the process buffer for transmission to theprocess, the process marker separates the new input from previous output.

set-process-buffer process buffer[Function]
This function sets the buffer associated with process to buffer. If buffer is nil, theprocess becomes associated with no buffer; if non-nil and different from the buffer
associated with the process, the process mark will be set to point to the end of buffer(unless the process mark is already associated with buffer).

get-buffer-process buffer-or-name[Function]
This function returns a nondeleted process associated with the buffer specified bybuffer-or-name. If there are several processes associated with it, this function chooses
one (currently, the one most recently created, but don’t count on that). Deletion of aprocess (see delete-process) makes it ineligible for this function to return.
It is usually a bad idea to have more than one process associated with the same buffer.
(get-buffer-process "*shell*")⇒ #<process shell>

Killing the process’s buffer deletes the process, which kills the subprocess with a
SIGHUP signal (see Section 40.8 [Signals to Processes], page 1097).
If the process’s buffer is displayed in a window, your Lisp program may wish to tell
the process the dimensions of that window, so that the process could adapt its output tothose dimensions, much as it adapts to the screen dimensions. The following functions allow
communicating this kind of information to processes; however, not all systems support theunderlying functionality, so it is best to provide fallbacks, e.g., via command-line arguments
or environment variables.

Chapter 40: Processes1101

set-process-window-size process height width[Function]
Tell process that its logical window size has dimensions width by height, in character
units. If this function succeeds in communicating this information to the process, it
returns t; otherwise it returns nil.

When windows that display buffers associated with process change their dimensions,the affected processes should be told about these changes. By default, when the window
configuration changes, Emacs will automatically call set-process-window-size on behalfof every process whose buffer is displayed in a window, passing it the smallest dimensions of
all the windows displaying the process’s buffer. This works via window-configurationchange-hook (see Section 29.28 [Window Hooks], page 779), which is told to invoke thefunction that is the value of the variable window-adjust-process-window-size-function
for each process whose buffer is displayed in at least one window. You can customize thisbehavior by setting the value of that variable.
[User Option]
The value of this variable should be a function of two arguments: a process and the listof windows displaying the process’s buffer. When the function is called, the process’s
buffer is the current buffer. The function should return a cons cell (width . height)that describes the dimensions of the logical process window to be passed via a call to
set-process-window-size. The function can also return nil, in which case Emacs
will not call set-process-window-size for this process.
Emacs supplies two predefined values for this variable: window-adjust-processwindow-size-smallest, which returns the smallest of all the dimensions of thewindows that display a process’s buffer; and window-adjust-process-window-sizelargest, which returns the largest dimensions. For more complex strategies, write
your own function.
This variable can be buffer-local.

window-adjust-process-window-size-function

If the process has the adjust-window-size-function property (see Section 40.6 [Process Information], page 1092), its value overrides the global and buffer-local values ofwindow-adjust-process-window-size-function.

40.9.2 Process Filter Functions
A process filter function is a function that receives the standard output from the associatedprocess. All output from that process is passed to the filter. The default filter simply
outputs directly to the process buffer.
By default, the error output from the process, if any, is also passed to the filter function,
unless the destination for the standard error stream of the process was separated from thestandard output when the process was created. Emacs will only call the filter function
during certain function calls. See Section 40.9 [Output from Processes], page 1099. Notethat if any of those functions are called by the filter, the filter may be called recursively.
A filter function must accept two arguments: the associated process and a string, which
is output just received from it. The function is then free to do whatever it chooses with theoutput.
Quitting is normally inhibited within a filter function—otherwise, the effect of typing
C-g at command level or to quit a user command would be unpredictable. If you want toChapter 40: Processes

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permit quitting inside a filter function, bind inhibit-quit to nil. In most cases, the right
way to do this is with the macro with-local-quit. See Section 22.11 [Quitting], page 471.
If an error happens during execution of a filter function, it is caught automatically, sothat it doesn’t stop the execution of whatever program was running when the filter function
was started. However, if debug-on-error is non-nil, errors are not caught. This makes it
possible to use the Lisp debugger to debug filter functions. See Section 19.1 [Debugger],
page 333. If an error is caught, Emacs pauses for process-error-pause-time seconds sothat the user sees the error. See Section 40.4 [Asynchronous Processes], page 1086.
Many filter functions sometimes (or always) insert the output in the process’s buffer,
mimicking the actions of the default filter. Such filter functions need to make sure thatthey save the current buffer, select the correct buffer (if different) before inserting output,
and then restore the original buffer. They should also check whether the buffer is still alive,
update the process marker, and in some cases update the value of point. Here is how to dothese things:(defun ordinary-insertion-filter (proc string)(when (buffer-live-p (process-buffer proc))(with-current-buffer (process-buffer proc)(let ((moving (= (point) (process-mark proc))))(save-excursion;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))(insert string)(set-marker (process-mark proc) (point)))(if moving (goto-char (process-mark proc)))))))

To make the filter force the process buffer to be visible whenever new text arrives, you
could insert a line like the following just before the with-current-buffer construct:(display-buffer (process-buffer proc))

To force point to the end of the new output, no matter where it was previously, eliminate
the variable moving from the example and call goto-char unconditionally. Note that thisdoesn’t necessarily move the window point. The default filter actually uses insert-beforemarkers which moves all markers, including the window point. This may move unrelated
markers, so it’s generally better to move the window point explicitly, or set its insertion type
to t (see Section 29.19 [Window Point], page 758).
Note that Emacs automatically saves and restores the match data while executing filter
functions. See Section 35.6 [Match Data], page 1011.
The output to the filter may come in chunks of any size. A program that produces thesame output twice in a row may send it as one batch of 200 characters one time, and fivebatches of 40 characters the next. If the filter looks for certain text strings in the subprocess
output, make sure to handle the case where one of these strings is split across two or morebatches of output; one way to do this is to insert the received text into a temporary buffer,
which can then be searched.

set-process-filter process filter[Function]
This function gives process the filter function filter. If filter is nil, it gives the process
the default filter, which inserts the process output into the process buffer. If filter is t,
Emacs stops accepting output from the process, unless it’s a network server processthat listens for incoming connections.

Chapter 40: Processes

process-filter process

1103[Function]

This function returns the filter function of process.
In case the process’s output needs to be passed to several filters, you can use add-function
to combine an existing filter with a new one. See Section 13.12 [Advising Functions], page 252.
Here is an example of the use of a filter function:(defun keep-output (process output)(setq kept (cons output kept)))⇒ keep-output(setq kept nil)
⇒ nil(set-process-filter (get-process "shell") 'keep-output)⇒ keep-output(process-send-string "shell" "ls ~/other\n")
⇒ nil
kept
⇒ ("lewis@slug:$ ""FINAL-W87-SHORT.MSS
backup.otl
kolstad.mss~
address.txt
backup.psf
kolstad.psf
backup.bib~
david.mss
resume-Dec-86.mss~
backup.err
david.psf
resume-Dec.psf
backup.mssdlandsyllabus.mss""#backups.mss#
backup.mss~
kolstad.mss")

40.9.3 Decoding Process Output
When Emacs writes process output directly into a multibyte buffer, it decodes the output according to the process output coding system. If the coding system is raw-text
or no-conversion, Emacs converts the unibyte output to multibyte using string-tomultibyte, and inserts the resulting multibyte text.
You can use set-process-coding-system to specify which coding system to use (seeSection 40.6 [Process Information], page 1092). Otherwise, the coding system comes fromcoding-system-for-read, if that is non-nil; or else from the defaulting mechanism (seeSection 34.10.5 [Default Coding Systems], page 983). If the text output by a process contains
null bytes, Emacs by default uses no-conversion for it; see Section 34.10.3 [Lisp and Coding
Systems], page 979, for how to control this behavior.
Warning: Coding systems such as undecided, which determine the coding system fromthe data, do not work entirely reliably with asynchronous subprocess output. This is because
Emacs has to process asynchronous subprocess output in batches, as it arrives. Emacs
must try to detect the proper coding system from one batch at a time, and this does notalways work. Therefore, if at all possible, specify a coding system that determines both thecharacter code conversion and the end of line conversion—that is, one like latin-1-unix,
rather than undecided or latin-1.
When Emacs calls a process filter function, it provides the process output as a multibyte
string or as a unibyte string according to the process’s filter coding system. Emacs decodes
the output according to the process output coding system, which usually produces a multibyte
string, except for coding systems such as binary and raw-text.

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40.9.4 Accepting Output from Processes
Output from asynchronous subprocesses normally arrives only while Emacs is waiting forsome sort of external event, such as elapsed time or terminal input. Occasionally it is usefulin a Lisp program to explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.

accept-process-output &optional process seconds millisec
just-this-one[Function]

This function allows Emacs to read pending output from processes. The output isgiven to their filter functions. If process is non-nil then this function does not return
until some output has been received from process or process has closed the connection.
The arguments seconds and millisec let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds.
The two time periods thus specified are added together, and accept-process-output
returns after that much time, even if there is no subprocess output.
The argument millisec is obsolete (and should not be used), because seconds can befloating point to specify waiting a fractional number of seconds. If seconds is 0, thefunction accepts whatever output is pending but does not wait.
If process is a process, and the argument just-this-one is non-nil, only output fromthat process is handled, suspending output from other processes until some output has
been received from that process or the timeout expires. If just-this-one is an integer,
also inhibit running timers. This feature is generally not recommended, but may benecessary for specific applications, such as speech synthesis.
The function accept-process-output returns non-nil if it got output from process,or from any process if process is nil; this can occur even after a process has exited if
the corresponding connection contains buffered data. The function returns nil if thetimeout expired or the connection was closed before output arrived.
If a connection from a process contains buffered data, accept-process-output canreturn non-nil even after the process has exited. Therefore, although the following loop:;; This loop contains a bug.
(while (process-live-p process)(accept-process-output process))will often read all output from process, it has a race condition and can miss some output if
process-live-p returns nil while the connection still contains data. Better is to write theloop like this:(while (accept-process-output process))
If you have passed a non-nil stderr to make-process, it will have a standard error
process. See Section 40.4 [Asynchronous Processes], page 1086. In that case, waiting forprocess output from the main process doesn’t wait for output from the standard error
process. To make sure you have received both all of standard output and all of standard
error from a process, use the following code:(while (accept-process-output process))(while (accept-process-output stderr-process))Chapter 40: Processes

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If you passed a buffer to the stderr argument of make-process, you still have to wait forthe standard error process, like so:(let* ((stdout (generate-new-buffer "stdout"))(stderr (generate-new-buffer "stderr"))(process (make-process :name "test":command '("my-program"):buffer stdout:stderr stderr))(stderr-process (get-buffer-process stderr)))(unless (and process stderr-process)(error "Process unexpectedly nil"))(while (accept-process-output process))(while (accept-process-output stderr-process)))
Only when both accept-process-output forms return nil, you can be sure that the process
has exited and Emacs has read all its output.
Reading pending standard error from a process running on a remote host is not possible
this way.

40.9.5 Processes and Threads
Because threads were a relatively late addition to Emacs Lisp, and due to the way dynamic
binding was sometimes used in conjunction with accept-process-output, by default aprocess is locked to the thread that created it. When a process is locked to a thread, output
from the process can only be accepted by that thread.
A Lisp program can specify to which thread a process is to be locked, or instruct Emacs
to unlock a process, in which case its output can be processed by any thread. Only a single
thread will wait for output from a given process at one time—once one thread begins waitingfor output, the process is temporarily locked until accept-process-output or sit-for
returns.
If the thread exits, all the processes locked to it are unlocked.

process-thread process[Function]
Return the thread to which process is locked. If process is unlocked, return nil.

set-process-thread process thread[Function]
Set the locking thread of process to thread. thread may be nil, in which case theprocess is unlocked.

40.10 Sentinels: Detecting Process Status Changes
A process sentinel is a function that is called whenever the associated process changes status
for any reason, including signals (whether sent by Emacs or caused by the process’s own
actions) that terminate, stop, or continue the process. The process sentinel is also called
if the process exits. The sentinel receives two arguments: the process for which the event
occurred, and a string describing the type of event.
If no sentinel function was specified for a process, it will use the default sentinel function,
which inserts a message in the process’s buffer with the process name and the string describing
the event.

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The string describing the event looks like one of the following (but this is not an exhaustive
list of event strings):• "finished\n".
• "deleted\n".
• "exited abnormally with code exitcode (core dumped)\n".
part is optional, and only appears if the process dumped core.

The “core dumped”• "failed with code fail-code\n".
• "signal-description (core dumped)\n".
The signal-description is a systemdependent textual description of a signal, e.g., "killed" for SIGKILL. The “coredumped” part is optional, and only appears if the process dumped core.
• "open from host-name\n".
• "open\n".
• "run\n".
• "connection broken by remote peer\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal input, or for time toelapse, or for process output). This avoids the timing errors that could result from runningsentinels at random places in the middle of other Lisp programs. A program can wait, so that
sentinels will run, by calling sit-for or sleep-for (see Section 22.10 [Waiting], page 470),
or accept-process-output (see Section 40.9.4 [Accepting Output], page 1104). Emacs also
allows sentinels to run when the command loop is reading input. delete-process calls thesentinel when it terminates a running process.
Emacs does not keep a queue of multiple reasons to call the sentinel of one process; itrecords just the current status and the fact that there has been a change. Therefore twochanges in status, coming in quick succession, can call the sentinel just once. However,process termination will always run the sentinel exactly once. This is because the process
status can’t change again after termination.
Emacs explicitly checks for output from the process before running the process sentinel.
Once the sentinel runs due to process termination, no further output can arrive from theprocess.
A sentinel that writes the output into the buffer of the process should check whether the
buffer is still alive. If it tries to insert into a dead buffer, it will get an error. If the buffer isdead, (buffer-name (process-buffer process)) returns nil.
Quitting is normally inhibited within a sentinel—otherwise, the effect of typing C-g at
command level or to quit a user command would be unpredictable. If you want to permit
quitting inside a sentinel, bind inhibit-quit to nil. In most cases, the right way to do
this is with the macro with-local-quit. See Section 22.11 [Quitting], page 471.
If an error happens during execution of a sentinel, it is caught automatically, so that it
doesn’t stop the execution of whatever programs was running when the sentinel was started.
However, if debug-on-error is non-nil, errors are not caught. This makes it possible touse the Lisp debugger to debug the sentinel. See Section 19.1 [Debugger], page 333. If anerror is caught, Emacs pauses for process-error-pause-time seconds so that the user sees
the error. See Section 40.4 [Asynchronous Processes], page 1086.

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While a sentinel is running, the process sentinel is temporarily set to nil so that thesentinel won’t run recursively. For this reason it is not possible for a sentinel to specify a
new sentinel.
Note that Emacs automatically saves and restores the match data while executing
sentinels. See Section 35.6 [Match Data], page 1011.

set-process-sentinel process sentinel[Function]
This function associates sentinel with process. If sentinel is nil, then the process will
have the default sentinel, which inserts a message in the process’s buffer when theprocess status changes.
Changes in process sentinels take effect immediately—if the sentinel is slated to be
run but has not been called yet, and you specify a new sentinel, the eventual call tothe sentinel will use the new one.
(defun msg-me (process event)(princ(format "Process: %s had the event '%s'" process event)))(set-process-sentinel (get-process "shell") 'msg-me)⇒ msg-me(kill-process (get-process "shell"))a Process: #<process shell> had the event 'killed'⇒ #<process shell>

process-sentinel process[Function]

This function returns the sentinel of process.
In case a process status changes need to be passed to several sentinels, you can use
add-function to combine an existing sentinel with a new one. See Section 13.12 [Advising
Functions], page 252.
[Function]
While a sentinel or filter function is running, this function returns non-nil if Emacs
was waiting for keyboard input from the user at the time the sentinel or filter function
was called, or nil if it was not.

waiting-for-user-input-p40.11 Querying Before Exit
When Emacs exits, it terminates all its subprocesses. For subprocesses that run a program,it sends them the SIGHUP signal; connections are simply closed. Because subprocesses may
be doing valuable work, Emacs normally asks the user to confirm that it is ok to terminate
them. Each process has a query flag, which, if non-nil, says that Emacs should ask for
confirmation before exiting and thus killing that process. The default for the query flag is t,meaning do query.

process-query-on-exit-flag process[Function]

This returns the query flag of process.

set-process-query-on-exit-flag process flag

[Function]
This function sets the query flag of process to flag. It returns flag.
Here is an example of using set-process-query-on-exit-flag on a shell process to
avoid querying:(set-process-query-on-exit-flag (get-process "shell") nil)
⇒ nilChapter 40: Processes

1108[User Option]
If this user option is set to t (the default), then Emacs asks for confirmation before
killing processes on exit. If it is nil, Emacs kills processes without confirmation, i.e.,the query flag of all processes is ignored.

confirm-kill-processes

40.12 Accessing Other Processes
In addition to accessing and manipulating processes that are subprocesses of the current
Emacs session, Emacs Lisp programs can also access other processes. We call these systemprocesses, to distinguish them from Emacs subprocesses.
Emacs provides several primitives for accessing system processes. Not all platforms
support these primitives; on those which don’t, these primitives return nil.
[Function]
This function returns a list of all the processes running on the system. Each process
is identified by its PID, a numerical process ID that is assigned by the OS anddistinguishes the process from all the other processes running on the same machine at
the same time.
If default-directory points to a remote host, processes of that host are returned.

list-system-processes

process-attributes pid[Function]
This function returns an alist of attributes for the process specified by its process ID
pid. Each association in the alist is of the form (key . value), where key designates
the attribute and value is the value of that attribute. The various attribute keys
that this function can return are listed below. Not all platforms support all of these
attributes; if an attribute is not supported, its association will not appear in the
returned alist.
If default-directory points to a remote host, pid is regarded as process of that host.
euid

The effective user ID of the user who invoked the process. The corresponding value is a number. If the process was invoked by the same user who
runs the current Emacs session, the value is identical to what user-uid
returns (see Section 42.4 [User Identification], page 1269).

user

User name corresponding to the process’s effective user ID, a string.

egid

The group ID of the effective user ID, a number.

group

Group name corresponding to the effective user’s group ID, a string.

comm

The name of the command that runs in the process. This is a string thatusually specifies the name of the executable file of the process, without
the leading directories. However, some special system processes can reportstrings that do not correspond to an executable file of a program.

state

The state code of the process. This is a short string that encodes thescheduling state of the process. Here’s a list of the most frequently seencodes:"D"

uninterruptible sleep (usually I/O)

"R"

running

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"S"

interruptible sleep (waiting for some event)"T"

stopped, e.g., by a job control signal"Z"

zombie: a process that terminated, but was not reaped by its
parent

For the full list of the possible states, see the manual page of the pscommand.
ppid

The process ID of the parent process, a number.

pgrp

The process group ID of the process, a number.

sess

The session ID of the process. This is a number that is the process ID of
the process’s session leader.

ttnameA string that is the name of the process’s controlling terminal. On Unix
and GNU systems, this is normally the file name of the corresponding
terminal device, such as /dev/pts65.

tpgid

The numerical process group ID of the foreground process group that uses
the process’s terminal.

minflt

The number of minor page faults caused by the process since its beginning.
(Minor page faults are those that don’t involve reading from disk.)majflt

The number of major page faults caused by the process since its beginning.
(Major page faults require a disk to be read, and are thus more expensive
than minor page faults.)

cminflt
cmajflt

Like minflt and majflt, but include the number of page faults for all
the child processes of the given process.

utimeTime spent by the process in the user context, for running the application’scode. The corresponding value is a Lisp timestamp (see Section 42.5 [Timeof Day], page 1270).

stime

Time spent by the process in the system (kernel) context, for processing
system calls. The corresponding value is a Lisp timestamp.

time

The sum of utime and stime. The corresponding value is a Lisp timestamp.

cutimecstimectime

Like utime, stime, and time, but include the times of all the childprocesses of the given process.

pri

The numerical priority of the process.

nice

The nice value of the process, a number. (Processes with smaller nicevalues get scheduled more favorably.)

thcount

The number of threads in the process.

start

The time when the process was started, as a Lisp timestamp.

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etime

The time elapsed since the process started, as a Lisp timestamp.

vsize

The virtual memory size of the process, measured in kilobytes.

rss

The size of the process’s resident set, the number of kilobytes occupied by
the process in the machine’s physical memory.

pcpu

The percentage of the CPU time used by the process since it started. The
corresponding value is a nonnegative floating-point number. Although intheory the number can exceed 100 on a multicore platform, it is usuallyless than 100 because Emacs is typically single-threaded.

pmem

The percentage of the total physical memory installed on the machineused by the process’s resident set. The value is a floating-point number
between 0 and 100.

args

The command-line with which the process was invoked. This is a stringin which individual command-line arguments are separated by blanks;
whitespace characters that are embedded in the arguments are quoted as
appropriate for the system’s shell: escaped by backslash characters on
GNU and Unix, and enclosed in double quote characters on Windows.
Thus, this command-line string can be directly used in primitives such asshell-command.

40.13 Transaction Queues
You can use a transaction queue to communicate with a subprocess using transactions. First
use tq-create to create a transaction queue communicating with a specified process. Then
you can call tq-enqueue to send a transaction.

tq-create process[Function]
This function creates and returns a transaction queue communicating with process.
The argument process should be a subprocess capable of sending and receiving streams
of bytes. It may be a child process, or it may be a TCP connection to a server, possibly
on another machine.

tq-enqueue queue question regexp closure fn &optional
delay-question[Function]

This function sends a transaction to queue queue. Specifying the queue has the effectof specifying the subprocess to talk to.
The argument question is the outgoing message that starts the transaction. The
argument fn is the function to call when the corresponding answer comes back; it iscalled with two arguments: closure, and the answer received.
The argument regexp is a regular expression that should match text at the end of
the entire answer, but nothing before; that’s how tq-enqueue determines where theanswer ends.
If the argument delay-question is non-nil, delay sending this question until the process
has finished replying to any previous questions. This produces more reliable resultswith some processes.

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tq-close queue[Function]
Shut down transaction queue queue, waiting for all pending transactions to complete,
and then terminate the connection or child process.

Transaction queues are implemented by means of a filter function. See Section 40.9.2[Filter Functions], page 1101.

40.14 Network Connections
Emacs Lisp programs can open stream (TCP) and datagram (UDP) network connections(see Section 40.16 [Datagrams], page 1114) to other processes on the same machine orother machines. A network connection is handled by Lisp much like a subprocess, and isrepresented by a process object. However, the process you are communicating with is not achild of the Emacs process, has no process ID, and you can’t kill it or send it signals. All
you can do is send and receive data. delete-process closes the connection, but does notkill the program at the other end; that program must decide what to do about closure of
the connection.
Lisp programs can listen for connections by creating network servers. A network server isalso represented by a kind of process object, but unlike a network connection, the network
server never transfers data itself. When it receives a connection request, it creates a new
network connection to represent the connection just made. (The network connection inherits
certain information, including the process plist, from the server.) The network server thengoes back to listening for more connection requests.
Network connections and servers are created by calling make-network-process withan argument list consisting of keyword/argument pairs, for example :server t to createa server process, or :type 'datagram to create a datagram connection. See Section 40.17[Low-Level Network], page 1115, for details. You can also use the open-network-stream
function described below.
To distinguish the different types of processes, the process-type function returns the
symbol network for a network connection or server, serial for a serial port connection,pipe for a pipe connection, or real for a real subprocess.
The process-status function returns open, closed, connect, stop, or failed for
network connections. For a network server, the status is always listen. Except for stop,none of those values is possible for a real subprocess. See Section 40.6 [Process Information],
page 1092.
You can stop and resume operation of a network process by calling stop-process
and continue-process. For a server process, being stopped means not accepting newconnections. (Up to 5 connection requests will be queued for when you resume the server;
you can increase this limit, unless it is imposed by the operating system—see the :server
keyword of make-network-process, Section 40.17.1 [Network Processes], page 1115.) For a
network stream connection, being stopped means not processing input (any arriving input
waits until you resume the connection). For a datagram connection, some number of packets
may be queued but input may be lost. You can use the function process-command to
determine whether a network connection or server is stopped; a non-nil value means yes.
Emacs can create encrypted network connections, using the built-in support for the
GnuTLS Transport Layer Security Library; see the GnuTLS project page (https://www.

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gnu.org/software/gnutls/). If your Emacs was compiled with GnuTLS support, thefunction gnutls-available-p is defined and returns non-nil. For more details, see Section“Overview” in The Emacs-GnuTLS manual. The open-network-stream function can transparently handle the details of creating encrypted connections for you, using whatever support
is available.

open-network-stream name buffer host service &rest parameters[Function]
This function opens a TCP connection, with optional encryption, and returns a process
object that represents the connection.
The name argument specifies the name for the process object. It is modified asnecessary to make it unique.
The buffer argument is the buffer to associate with the connection. Output from theconnection is inserted in the buffer, unless you specify your own filter function tohandle the output. If buffer is nil, it means that the connection is not associatedwith any buffer.
The arguments host and service specify where to connect to; host is the host name(a string), and service is the name of a defined network service (a string) or a port
number (an integer like 80 or an integer string like "80").
The remaining arguments parameters are keyword/argument pairs that are mainly
relevant to encrypted connections::nowait boolean
If non-nil, try to make an asynchronous connection.
:noquery query-flag
Initialize the process query flag to query-flag. See Section 40.11 [Query
Before Exit], page 1107.
:coding coding
Use this to set the coding systems used by the network process, in preference to binding coding-system-for-read or coding-system-for-write.
See Section 40.17.1 [Network Processes], page 1115, for details.
:type type
The type of connection. Options are:plain

An ordinary, unencrypted connection.

tls
ssl

A TLS (Transport Layer Security) connection.

nil
network

Start with a plain connection, and if parameters ‘:success’and ‘:capability-command’ are supplied, try to upgrade to
an encrypted connection via STARTTLS. If that fails, retain
the unencrypted connection.

starttls

As for nil, but if STARTTLS fails, drop the connection.

shell

A shell connection.

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1113:always-query-capabilities boolean
If non-nil, always ask for the server’s capabilities, even when doing a‘plain’ connection.
:capability-command capability-command
Command to query the host capabilities. This can either be a string(which will then be sent verbatim to the server) or a function (called witha single parameter: the “greeting” from the server when connecting) thatshould return a string.
:end-of-command regexp:end-of-capability regexp
Regular expression matching the end of a command, or the end of thecommand capability-command. The latter defaults to the former.
:starttls-function function
Function of one argument (the response to capability-command), which
returns either nil or the command to activate STARTTLS, if supported.
:success regexp
Regular expression matching a successful STARTTLS negotiation.
:use-starttls-if-possible boolean
If non-nil, do opportunistic STARTTLS upgrades even if Emacs doesn’t
have built-in TLS support.
:warn-unless-encrypted boolean
If non-nil, and :return-value is also non-nil, Emacs will warn if theconnection isn’t encrypted. This is useful for protocols like IMAP and thelike, where most users would expect the network traffic to be encrypted.
:client-certificate list-or-t
Either a list of the form (key-file cert-file), naming the certificate
key file and certificate file itself, or t, meaning to query auth-source
for this information (see Section “auth-source” in Emacs auth-source
Library). Only used for TLS or STARTTLS. To enable automatic queriesof auth-source when :client-certificate is not specified customize
network-stream-use-client-certificates to t.
:return-list cons-or-nil
The return value of this function. If omitted or nil, return a process
object. Otherwise, a cons of the form (process-object . plist), whereplist can include the following keywords::greeting string-or-nil
If non-nil, the greeting string returned by the host.
:capabilities string-or-nil
If non-nil, the host’s capability string.
:type symbol
The connection type: ‘plain’ or ‘tls’.

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1114:shell-command string-or-nil
If the connection type is shell, this parameter will be interpreted as aformat-spec string (see Section 4.8 [Custom Format Strings], page 70)
that will be executed to make the connection. The specs available are‘%s’ for the host name and ‘%p’ for the port number. For instance, if you
want to first ssh to ‘gateway’ before making a plain connection, then thisparameter’s value could be something like ‘ssh gateway nc %s %p’.

40.15 Network Servers
You create a server by calling make-network-process (see Section 40.17.1 [Network Processes], page 1115) with :server t. The server will listen for connection requests fromclients. When it accepts a client connection request, that creates a new network connection,itself a process object, with the following parameters:• The connection’s process name is constructed by concatenating the server process’s
name with a client identification string. The client identification string for an IPv4
connection looks like ‘<a.b.c.d:p>’, which represents an address and port number.
Otherwise, it is a unique number in brackets, as in ‘<nnn>’. The number is unique foreach connection in the Emacs session.
• If the server has a non-default filter, the connection process does not get a separate
process buffer; otherwise, Emacs creates a new buffer for the purpose. The buffer nameis the server’s buffer name or process name, concatenated with the client identification
string.
The server’s process buffer value is never used directly, but the log function can retrieve
it and use it to log connections by inserting text there.
• The communication type and the process filter and sentinel are inherited from those of
the server. The server never directly uses its filter and sentinel; their sole purpose is toinitialize connections made to the server.
• The connection’s process contact information is set according to the client’s addressing
information (typically an IP address and a port number). This information is associatedwith the process-contact keywords :host, :service, :remote.
• The connection’s local address is set up according to the port number used for theconnection.
• The client process’s plist is initialized from the server’s plist.

40.16 Datagrams
A datagram connection communicates with individual packets rather than streams of data.
Each call to process-send sends one datagram packet (see Section 40.7 [Input to Processes],
page 1096), and each datagram received results in one call to the filter function.
The datagram connection doesn’t have to talk with the same remote peer all the time. It
has a remote peer address which specifies where to send datagrams to. Each time an incoming
datagram is passed to the filter function, the peer address is set to the address that datagram
came from; that way, if the filter function sends a datagram, it will go back to that place.
You can specify the remote peer address when you create the datagram connection using the:remote keyword. You can change it later on by calling set-process-datagram-address.

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process-datagram-address process[Function]
If process is a datagram connection or server, this function returns its remote peer
address.

set-process-datagram-address process address[Function]
If process is a datagram connection or server, this function sets its remote peer address
to address.

40.17 Low-Level Network Access
You can also create network connections by operating at a lower level than that ofopen-network-stream, using make-network-process.

40.17.1 make-network-process
The basic function for creating network connections and network servers is make-networkprocess. It can do either of those jobs, depending on the arguments you give it.

make-network-process &rest args

[Function]
This function creates a network connection or server and returns the process object
that represents it. The arguments args are a list of keyword/argument pairs. Omitting
a keyword is always equivalent to specifying it with value nil, except for :coding,:filter-multibyte, and :reuseaddr. Here are the meaningful keywords (thosecorresponding to network options are listed in the following section)::name name
Use the string name as the process name. It is modified if necessary to
make it unique.
:type type Specify the communication type. A value of nil specifies a stream connection (the default); datagram specifies a datagram connection; seqpacket
specifies a sequenced packet stream connection. Both connections andservers can be of these types.
:server server-flag
If server-flag is non-nil, create a server. Otherwise, create a connection.
For a stream type server, server-flag may be an integer, which thenspecifies the length of the queue of pending connections to the server. The
default queue length is 5.
:host host Specify the host to connect to. host should be a host name or Internet
address, as a string, or the symbol local to specify the local host. If you
specify host for a server, it must specify a valid address for the local host,and only clients connecting to that address will be accepted. When using
local, by default IPv4 will be used, specify a family of ipv6 to override
this. To listen on all interfaces, specify an address of ‘"0.0.0.0"’ for IPv4or ‘"::"’ for IPv6. Note that on some operating systems, listening on‘"::"’ will also listen on IPv4, so attempting to then listen separately on
IPv4 will result in EADDRINUSE errors (‘"Address already in use"’).
:service service
service specifies a port number to connect to; or, for a server, the port
number to listen on. It should be a service name like ‘"https"’ that

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translates to a port number, or an integer like ‘443’ or an integer string
like ‘"443"’ that specifies the port number directly. For a server, it canalso be t, which means to let the system select an unused port number.
:family familyfamily specifies the address (and protocol) family for communication. nil
means determine the proper address family automatically for the given
host and service. local specifies a Unix socket, in which case host isignored. ipv4 and ipv6 specify to use IPv4 and IPv6, respectively.
:use-external-socket use-external-socket
If use-external-socket is non-nil use any sockets passed to Emacs on
invocation instead of allocating one. This is used by the Emacs servercode to allow on-demand socket activation. If Emacs wasn’t passed asocket, this option is silently ignored.
:local local-address
For a server process, local-address is the address to listen on. It overrides
family, host and service, so you might as well not specify them.
:remote remote-address
For a connection, remote-address is the address to connect to. It overrides
family, host and service, so you might as well not specify them.
For a datagram server, remote-address specifies the initial setting of theremote datagram address.
The format of local-address or remote-address depends on the addressfamily:- An IPv4 address is represented as a five-element vector of four 8-bit
integers and one 16-bit integer [a b c d p] corresponding to numeric
IPv4 address a.b.c.d and port number p.
- An IPv6 address is represented as a nine-element vector of 16-bit
integers [a b c d e f g h p] corresponding to numeric IPv6 address
a:b:c:d:e:f :g:h and port number p.
- A local address is represented as a string, which specifies the addressin the local address space.
- An unsupported-family address is represented by a cons (f . av),
where f is the family number and av is a vector specifying the socket
address using one element per address data byte. Do not rely on thisformat in portable code, as it may depend on implementation definedconstants, data sizes, and data structure alignment.
:nowait bool
If bool is non-nil for a stream connection, return without waiting for theconnection to complete. When the connection succeeds or fails, Emacs willcall the sentinel function, with a second argument matching "open" (ifsuccessful) or "failed". The default is to block, so that make-networkprocess does not return until the connection has succeeded or failed.
If you’re setting up an asynchronous TLS connection, you have to also
provide the :tls-parameters parameter (see below).

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Depending on the capabilities of Emacs, how asynchronous :nowait is mayvary. The three elements that may (or may not) be done asynchronously
are domain name resolution, socket setup, and (for TLS connections) TLS
negotiation.
Many functions that interact with process objects, (for instance,
process-datagram-address) rely on them at least having a socket
before they can return a useful value. These functions will block until
the socket has achieved the desired status. The recommended way ofinteracting with asynchronous sockets is to place a sentinel on the process,and not try to interact with it before it has changed status to ‘"run"’.
That way, none of these functions will block.
:tls-parameters
When opening a TLS connection, this should be where the first element is
the TLS type (which should either be gnutls-x509pki or gnutls-anon,
and the remaining elements should form a keyword list acceptable forgnutls-boot. (This keyword list can be obtained from the gnutls-bootparameters function.) The TLS connection will then be negotiated after
completing the connection to the host.
:stop stopped
If stopped is non-nil, start the network connection or server in the stopped
state.
:buffer buffer
Use buffer as the process buffer.
:coding coding
Use coding as the coding system for this process. To specify different
coding systems for decoding data from the connection and for encoding
data sent to it, specify (decoding . encoding) for coding.
If you don’t specify this keyword at all, the default is to determine thecoding systems from the data.
:noquery query-flag
Initialize the process query flag to query-flag. See Section 40.11 [Query
Before Exit], page 1107.
:filter filter
Initialize the process filter to filter.
:filter-multibyte multibyte
If multibyte is non-nil, strings given to the process filter are multibyte,
otherwise they are unibyte. The default is t.
:sentinel sentinel
Initialize the process sentinel to sentinel.
:log log

Initialize the log function of a server process to log. The log function iscalled each time the server accepts a network connection from a client.
The arguments passed to the log function are server, connection, andChapter 40: Processes

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message; where server is the server process, connection is the new process
for the connection, and message is a string describing what has happened.
:plist plist Initialize the process plist to plist.
The original argument list, modified with the actual connection information, is available
via the process-contact function.

40.17.2 Network Options
The following network options can be specified when you create a network process. Except for:reuseaddr, you can also set or modify these options later, using set-network-processoption.
For a server process, the options specified with make-network-process are not inheritedby the client connections, so you will need to set the necessary options for each childconnection as it is created.
:bindtodevice device-name
If device-name is a non-empty string identifying a network interface name (seenetwork-interface-list), only handle packets received on that interface. If
device-name is nil (the default), handle packets received on any interface.
Using this option may require special privileges on some systems.
:broadcast broadcast-flag
If broadcast-flag is non-nil for a datagram process, the process will receive
datagram packet sent to a broadcast address, and be able to send packets to abroadcast address. This is ignored for a stream connection.
:dontroute dontroute-flag
If dontroute-flag is non-nil, the process can only send to hosts on the same
network as the local host.
:keepalive keepalive-flag
If keepalive-flag is non-nil for a stream connection, enable exchange of low-levelkeep-alive messages.
:linger linger-arg
If linger-arg is non-nil, wait for successful transmission of all queued packets
on the connection before it is deleted (see delete-process). If linger-arg is an
integer, it specifies the maximum time in seconds to wait for queued packets
to be sent before closing the connection. The default is nil, which means todiscard unsent queued packets when the process is deleted.
:oobinline oobinline-flag
If oobinline-flag is non-nil for a stream connection, receive out-of-band data in
the normal data stream. Otherwise, ignore out-of-band data.
:priority priority
Set the priority for packets sent on this connection to the integer priority. Theinterpretation of this number is protocol specific; such as setting the TOS (typeof service) field on IP packets sent on this connection. It may also have systemdependent effects, such as selecting a specific output queue on the network
interface.

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1119:reuseaddr reuseaddr-flag
If reuseaddr-flag is non-nil (the default) for a stream server process, allow thisserver to reuse a specific port number (see :service), unless another process
on this host is already listening on that port. If reuseaddr-flag is nil, there
may be a period of time after the last use of that port (by any process on thehost) where it is not possible to make a new server on that port.

set-network-process-option process option value &optional
no-error[Function]

This function sets or modifies a network option for network process process. The
accepted options and values are as for make-network-process. If no-error is non-nil,this function returns nil instead of signaling an error if option is not a supported
option. If the function successfully completes, it returns t.
The current setting of an option is available via the process-contact function.

40.17.3 Testing Availability of Network Features
To test for the availability of a given network feature, use featurep like this:(featurep 'make-network-process '(keyword value))
The result of this form is t if it works to specify keyword with value value in make-networkprocess. Here are some of the keyword—value pairs you can test in this way.
(:nowait t)
Non-nil if non-blocking connect is supported.
(:type datagram)
Non-nil if datagrams are supported.
(:family local)
Non-nil if local (a.k.a. “UNIX domain”) sockets are supported.
(:family ipv6)
Non-nil if IPv6 is supported.
(:service t)
Non-nil if the system can select the port for a server.
To test for the availability of a given network option, use featurep like this:(featurep 'make-network-process 'keyword)
The accepted keyword values are :bindtodevice, etc.
For the complete list,
see Section 40.17.2 [Network Options], page 1118.
This form returns non-nil
if that particular network option is supported by make-network-process (orset-network-process-option).

40.18 Misc Network Facilities
These additional functions are useful for creating and operating on network connections.
Note that they are supported only on some systems.

network-interface-list &optional full family[Function]
This function returns a list describing the network interfaces of the machine you
are using. The value is an alist whose elements have the form (ifname . address).

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ifname is a string naming the interface, address has the same form as the local-address
and remote-address arguments to make-network-process, i.e. a vector of integers.
By default both IPv4 and IPv6 addresses are returned if possible.
Optional argument full non-nil means to instead return a list of one or more elementsof the form (ifname addr bcast netmask). ifname is a non-unique string naming theinterface. addr, bcast, and netmask are vectors of integers detailing the IP address,
broadcast address, and network mask.
Optional argument family specified as symbol ipv4 or ipv6 restricts the returned
information to IPv4 and IPv6 addresses respectively, independently of the value offull. Specifying ipv6 when IPv6 support is not available will result in an error being
signaled.
Some examples:(network-interface-list) ⇒(("vmnet8" .
[172 16 76 1 0])("vmnet1" .
[172 16 206 1 0])("lo0" .
[65152 0 0 0 0 0 0 1 0])("lo0" .
[0 0 0 0 0 0 0 1 0])("lo0" .
[127 0 0 1 0]))
(network-interface-list t) ⇒(("vmnet8"[172 16 76 1 0][172 16 76 255 0][255 255 255 0 0])("vmnet1"[172 16 206 1 0][172 16 206 255 0][255 255 255 0 0])("lo0"[65152 0 0 0 0 0 0 1 0][65152 0 0 0 65535 65535 65535 65535 0][65535 65535 65535 65535 0 0 0 0 0])("lo0"[0 0 0 0 0 0 0 1 0]
[0 0 0 0 0 0 0 1 0][65535 65535 65535 65535 65535 65535 65535 65535 0])("lo0"[127 0 0 1 0][127 255 255 255 0][255 0 0 0 0]))

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network-interface-info ifname[Function]
This function returns information about the network interface named ifname. The
value is a list of the form (addr bcast netmask hwaddr flags).
addr

The Internet protocol address.

bcast

The broadcast address.

netmask

The network mask.

hwaddr

The layer 2 address (Ethernet MAC address, for instance).

flags

The current flags of the interface.

Note that this function returns only IPv4 information.

format-network-address address &optional omit-port[Function]
This function converts the Lisp representation of a network address to a string.
A five-element vector [a b c d p] represents an IPv4 address a.b.c.d and port number
p. format-network-address converts that to the string "a.b.c.d:p".
A nine-element vector [a b c d e f g h p] represents an IPv6 address alongwith a port number. format-network-address converts that to the string"[a:b:c:d:e:f:g:h]:p".
If the vector does not include the port number, p, or if omit-port is non-nil, the result
does not include the :p suffix.

network-lookup-address-info name &optional family hints[Function]
This function perform hostname lookups on name, which is expected to be an ASCIIonly string, otherwise it signals an error. Call puny-encode-domain on name first if
you wish to lookup internationalized hostnames.
If successful, this function returns a list of Lisp representations of network addresses(see Section 40.17.1 [Network Processes], page 1115, for a description of the format),otherwise return nil. In the latter case, it also logs an error message hopefully
explaining what went wrong.
By default, this function attempts both IPv4 and IPv6 lookups. The optional argument
family controls this behavior, specifying the symbol ipv4 or ipv6 restricts lookups toIPv4 and IPv6 respectively.
If optional argument hints is numeric, the function treats the name as a numerical IP
address (and does not perform DNS lookups). This can be used to check whether astring is a valid numerical representation of an IP address, or to convert a numericalstring to its canonical representation. e.g.
(network-lookup-address-info "127.1" 'ipv4 'numeric)⇒ ([127 0 0 1 0])(network-lookup-address-info "::1" nil 'numeric)⇒ ([0 0 0 0 0 0 0 1 0])
Be warned that there are some surprising valid forms, especially for IPv4, e.g‘0xe3010203’ and ‘0343.1.2.3’ are both valid, as are ‘0’ and ‘1’ (but they are invalid
for IPv6).

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40.19 Communicating with Serial Ports
Emacs can communicate with serial ports. For interactive use, M-x serial-term opens aterminal window. In a Lisp program, make-serial-process creates a process object.
The serial port can be configured at run-time, without having to close and re-open it.
The function serial-process-configure lets you change the speed, bytesize, and otherparameters. In a terminal window created by serial-term, you can click on the mode line
for configuration.
A serial connection is represented by a process object, which can be used in a similar
way to a subprocess or network process. You can send and receive data, and configure theserial port. A serial process object has no process ID, however, and you can’t send signals
to it, and the status codes are different from other types of processes. delete-process on
the process object or kill-buffer on the process buffer close the connection, but this does
not affect the device connected to the serial port.
The function process-type returns the symbol serial for a process object representing
a serial port connection.
Serial ports are available on GNU/Linux, Unix, and MS Windows systems.

serial-term port speed &optional line-mode[Command]Start a terminal-emulator for a serial port in a new buffer. port is the name of theserial port to connect to. For example, this could be /dev/ttyS0 on Unix. On MS
Windows, this could be COM1, or \\.\COM10 (double the backslashes in Lisp strings).
speed is the speed of the serial port in bits per second. 9600 is a common value. The
buffer is in Term mode; see Section “Term Mode” in The GNU Emacs Manual, forthe commands to use in that buffer. You can change the speed and the configurationin the mode line menu. If line-mode is non-nil, term-line-mode is used; otherwise
term-raw-mode is used.

make-serial-process &rest args

[Function]
This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here’s the list of the meaningful keywords, with the firsttwo (port and speed) being mandatory::port port
This is the name of the serial port. On Unix and GNU systems, this isa file name such as /dev/ttyS0. On Windows, this could be COM1, or\\.\COM10 for ports higher than COM9 (double the backslashes in Lisp
strings).
:speed speed
The speed of the serial port in bits per second. This function calls
serial-process-configure to handle the speed; see the following documentation of that function for more details.
:name name
The name of the process. If name is not given, port will serve as theprocess name as well.

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The buffer to associate with the process. The value can be either a buffer
or a string that names a buffer. Process output goes at the end of thatbuffer, unless you specify an output stream or filter function to handle
the output. If buffer is not given, the process buffer’s name is taken fromthe value of the :name keyword.
:coding coding
If coding is a symbol, it specifies the coding system used for both reading
and writing for this process. If coding is a cons (decoding . encoding),
decoding is used for reading, and encoding is used for writing. If not
specified, the default is to determine the coding systems from the data
itself.
:noquery query-flag
Initialize the process query flag to query-flag. See Section 40.11 [Query
Before Exit], page 1107. The flags defaults to nil if unspecified.
:stop bool
Start process in the stopped state if bool is non-nil. In the stopped
state, a serial process does not accept incoming data, but you can sendoutgoing data. The stopped state is cleared by continue-process andset by stop-process.
:filter filter
Install filter as the process filter.
:sentinel sentinel
Install sentinel as the process sentinel.
:plist plist
Install plist as the initial plist of the process.
:bytesize:parity:stopbits:flowcontrol
These are handled by serial-process-configure, which is called by
make-serial-process.
The original argument list, possibly modified by later configuration, is available via
the function process-contact.
Here is an example:(make-serial-process :port "/dev/ttyS0" :speed 9600)

serial-process-configure &rest args

[Function]
This function configures a serial port connection. Arguments are specified as keyword/argument pairs. Attributes that are not given are re-initialized from the process’s
current configuration (available via the function process-contact), or set to reasonable default values. The following arguments are defined:Chapter 40: Processes

1124:process process:name name:buffer buffer:port port
Any of these arguments can be given to identify the process that is tobe configured. If none of these arguments is given, the current buffer’s
process is used.
:speed speed
The speed of the serial port in bits per second, a.k.a. baud rate. The
value can be any number, but most serial ports work only at a few definedvalues between 1200 and 115200, with 9600 being the most common value.
If speed is nil, the function ignores all other arguments and does notconfigure the port. This may be useful for special serial ports such as
Bluetooth-to-serial converters, which can only be configured through ‘AT’commands sent through the connection. The value of nil for speed isvalid only for connections that were already opened by a previous call to
make-serial-process or serial-term.
:bytesize bytesize
The number of bits per byte, which can be 7 or 8. If bytesize is not given
or nil, it defaults to 8.
:parity parity
The value can be nil (don’t use parity), the symbol odd (use odd parity),or the symbol even (use even parity). If parity is not given, it defaults to
no parity.
:stopbits stopbits
The number of stopbits used to terminate a transmission of each byte.
stopbits can be 1 or 2. If stopbits is not given or nil, it defaults to 1.
:flowcontrol flowcontrol
The type of flow control to use for this connection, which is either nil(don’t use flow control), the symbol hw (use RTS/CTS hardware flow
control), or the symbol sw (use XON/XOFF software flow control). If
flowcontrol is not given, it defaults to no flow control.
Internally, make-serial-process calls serial-process-configure for the initialconfiguration of the serial port.

40.20 Packing and Unpacking Byte Arrays
This section describes how to pack and unpack arrays of bytes, usually for binary network
protocols. These functions convert byte arrays to alists, and vice versa. The byte arraycan be represented as a unibyte string or as a vector of integers, while the alist associates
symbols either with fixed-size objects or with recursive sub-alists. To use the functions
referred to in this section, load the bindat library.
Conversion from byte arrays to nested alists is also known as deserializing or unpacking,while going in the opposite direction is also known as serializing or packing.

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40.20.1 Describing Data Layout
To control unpacking and packing, you write a data layout specification, also called a Bindat
type expression. This can be a base type or a composite type made of several fields, where
the specification controls the length of each field to be processed, and how to pack or unpack
it. We normally keep bindat type values in variables whose names end in -bindat-spec; thatkind of name is automatically recognized as risky (see Section 12.12 [File Local Variables],page 213).

bindat-type &rest type

[Macro]Creates a Bindat type value object according to the Bindat type expression type.

A field’s type describes the size (in bytes) of the object that the field represents and, inthe case of multibyte fields, how the bytes are ordered within the field. The two possibleorderings are big endian (also known as “network byte ordering”) and little endian. For
instance, the number #x23cd (decimal 9165) in big endian would be the two bytes #x23
#xcd; and in little endian, #xcd #x23. Here are the possible type values:u8
byte

Unsigned byte, with length 1.

uint bitlen &optional leUnsigned integer in network byte order (big-endian), with bitlen bits. bitlen
has to be a multiple of 8. If le is non-nil, then use little-endian byte order.
sint bitlen leSigned integer in network byte order (big-endian), with bitlen bits. bitlen has
to be a multiple of 8. If le is non-nil, then use little-endian byte order.
str len

Unibyte string (see Section 34.1 [Text Representations], page 963) of length
len bytes. When packing, the first len bytes of the input string are copied tothe packed output. If the input string is shorter than len, the remaining bytes
will be null (zero) unless a pre-allocated string was provided to bindat-pack,in which case the remaining bytes are left unmodified. If the input string ismultibyte with only ASCII and eight-bit characters, it is converted to unibyte
before it is packed; other multibyte strings signal an error. When unpacking,
any null bytes in the packed input string will appear in the unpacked output.

strz &optional len
If len is not provided, this is a variable-length null-terminated unibyte string (seeSection 34.1 [Text Representations], page 963). When packing into strz, theentire input string is copied to the packed output followed by a null (zero) byte.
(If pre-allocated string is provided for packing into strz, that pre-allocatedstring should have enough space for the additional null byte appended to the
output string contents, see Section 40.20.2 [Bindat Functions], page 1127). The
length of the packed output is the length of the input string plus one (for thenull terminator). The input string must not contain any null bytes. If the input
string is multibyte with only ASCII and eight-bit characters, it is converted
to unibyte before it is packed; other multibyte strings signal an error. Whenunpacking a strz, the resulting output string will contain all bytes up to (butexcluding) the null byte that terminated the input string.

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If len is provided, strz behaves the same as str, but with a couple of differences:• When packing, a null terminator is written after the packed input string if
the number of characters in the input string is less than len.
• When unpacking, the first null byte encountered in the packed string isinterpreted as the terminating byte, and it and all subsequent bytes are
excluded from the result of the unpacking.
Caution: The packed output will not be null-terminated unless the
input string is shorter than len bytes or it contains a null byte within
the first len bytes.
vec len [type]
Vector of len elements. The type of the elements is given by type, defaulting tobytes. The type can be any Bindat type expression.
repeat len [type]
Like vec, but it unpacks to and packs from lists, whereas vec unpacks to vectors.
bits len

List of bits that are set to 1 in len bytes. The bytes are taken in big-endianorder, and the bits are numbered starting with 8 * len − 1 and ending withzero. For example: bits 2 unpacks #x28 #x1c to (2 3 4 11 13) and #x1c #x28
to (3 5 10 11 12).

fill lenlen bytes used as a mere filler. In packing, these bytes are left unchanged, which
normally means they remain zero. When unpacking, this just returns nil.

align len Same as fill except the number of bytes is that needed to skip to the next
multiple of len bytes.
type exp

This lets you refer to a type indirectly: exp is a Lisp expression which should
return a Bindat type value.

unit exp

This is a trivial type which uses up 0 bits of space. exp describes the value
returned when we try to “unpack” such a field.

struct fields...
Composite type made of several fields. Every field is of the form (name type)where type can be any Bindat type expression. name can be _ when the field’svalue does not deserve to be named, as is often the case for align and fill
fields. When the context makes it clear that this is a Bindat type expression,
the symbol struct can be omitted.
In the types above, len and bitlen are given as an integer specifying the number of bytes(or bits) in the field. When the length of a field is not fixed, it typically depends on thevalue of preceding fields. For this reason, the length len does not have to be a constant but
can be any Lisp expression and it can refer to the value of previous fields via their name.
For example, the specification of a data layout where a leading byte gives the size of asubsequent vector of 16 bit integers could be:(bindat-type(len
u8)(payload vec (1+ len) uint 16))

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40.20.2 Functions to Unpack and Pack Bytes
In the following documentation, type refers to a Bindat type value as returned frombindat-type, raw to a byte array, and struct to an alist representing unpacked field data.

bindat-unpack type raw &optional idx[Function]
This function unpacks data from the unibyte string or byte array raw according totype. Normally, this starts unpacking at the beginning of the byte array, but if idx is
non-nil, it specifies a zero-based starting position to use instead.
The value is an alist or nested alist in which each element describes one unpacked
field.

bindat-get-field struct &rest name

[Function]
This function selects a field’s data from the nested alist struct. Usually struct was
returned by bindat-unpack. If name corresponds to just one argument, that means
to extract a top-level field value. Multiple name arguments specify repeated lookup of
sub-structures. An integer name acts as an array index.
For example, (bindat-get-field struct a b 2 c) means to find field c in the third
element of subfield b of field a. (This corresponds to struct.a.b[2].c in the C
programming language syntax.)

Although packing and unpacking operations change the organization of data (in memory),
they preserve the data’s total length, which is the sum of all the fields’ lengths, in bytes.
This value is not generally inherent in either the specification or alist alone; instead, bothpieces of information contribute to its calculation. Likewise, the length of a string or array
being unpacked may be longer than the data’s total length as described by the specification.

bindat-length type struct[Function]
This function returns the total length of the data in struct, according to type.

bindat-pack type struct &optional raw idx[Function]
This function returns a byte array packed according to type from the data in thealist struct. It normally creates and fills a new byte array starting at the beginning.
However, if raw is non-nil, it specifies a pre-allocated unibyte string or vector to packinto. If idx is non-nil, it specifies the starting offset for packing into raw.
When pre-allocating, you should make sure (length raw) meets or exceeds the total
length to avoid an out-of-range error.

bindat-ip-to-string ip[Function]
Convert the Internet address vector ip to a string in the usual dotted notation.
(bindat-ip-to-string [127 0 0 1])⇒ "127.0.0.1"

40.20.3 Advanced data layout specifications
Bindat type expressions are not limited to the types described earlier. They can also
be arbitrary Lisp forms returning Bindat type expressions. For example, the type below
describes data which can either contain a 24-bit error code or a vector of bytes:(bindat-type

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(len
u8)
(payload . (if (zerop len) (uint 24) (vec (1- len)))))
Furthermore, while composite types are normally unpacked to (and packed from) association lists, this can be changed via the use of the following special keyword arguments::unpack-val exp
When the list of fields ends with this keyword argument, then the value returned
when unpacking is the value of exp instead of the standard alist. exp can refer
to all the previous fields by their name.
:pack-val exp
If a field’s type is followed by this keyword argument, then the value packed
into this field is returned by exp instead of being extracted from the alist.
:pack-var name
If the list of fields is preceded by this keyword argument, then all the subsequent:pack-val arguments can refer to the overall value to pack into this composite
type via the variable named name.
For example, one could describe a 16-bit signed integer as follows:(defconst sint16-bindat-spec(let* ((max (ash 1 15))
(wrap (+ max max)))(bindat-type :pack-var v(n uint 16 :pack-val (if (< v 0) (+ v wrap) v)):unpack-val (if (>= n max) (- n wrap) n))))Which would then behave as follows:(bindat-pack sint16-bindat-spec -8)⇒ "\377\370"(bindat-unpack sint16-bindat-spec "\300\100")⇒ -16320
Finally, you can define new Bindat type forms to use in Bindat type expressions withbindat-defmacro:bindat-defmacro name args &rest body

[Macro]Define a new Bindat type expression named name and taking arguments args. Itsbehavior follows that of defmacro, which the important difference that the new forms
can only be used within Bindat type expressions.

1129

41 Emacs Display
This chapter describes a number of features related to the display that Emacs presents tothe user.

41.1 Refreshing the Screen
The function redraw-frame clears and redisplays the entire contents of a given frame (seeChapter 30 [Frames], page 785). This is useful if the screen is corrupted.

redraw-frame &optional frame[Function]
This function clears and redisplays frame frame. If frame is omitted or nil, it redraws
the selected frame.

Even more powerful is redraw-display:

redraw-display[Command]This function clears and redisplays all visible frames.
In Emacs, processing user input takes priority over redisplay. If you call these functions
when input is available, they don’t redisplay immediately, but the requested redisplay does
happen eventually—after all the input has been processed.
On text terminals, suspending and resuming Emacs normally also refreshes the screen.
Some terminal emulators record separate contents for display-oriented programs such as
Emacs and for ordinary sequential display. If you are using such a terminal, you might want
to inhibit the redisplay on resumption.
[User Option]
This variable controls whether Emacs redraws the entire screen after it has beensuspended and resumed. Non-nil means there is no need to redraw, nil means
redrawing is needed. The default is nil.

no-redraw-on-reenter

41.2 Forcing Redisplay
Emacs normally tries to redisplay the screen whenever it waits for input. With the following
function, you can request an immediate attempt to redisplay, in the middle of Lisp code,
without actually waiting for input.

redisplay &optional force[Function]
This function tries immediately to redisplay. The optional argument force, if non-nil,forces the redisplay to be performed, instead of being preempted if input is pending.
The function returns t if it actually tried to redisplay, and nil otherwise. A value of t
does not mean that redisplay proceeded to completion; it could have been preemptedby newly arriving input.

Although redisplay tries immediately to redisplay, it does not change how Emacs decides
which parts of its frame(s) to redisplay. By contrast, the following function adds certain
windows to the pending redisplay work (as if their contents had completely changed), butdoes not immediately try to perform redisplay.

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force-window-update &optional object[Function]
This function forces some or all windows to be updated the next time Emacs does aredisplay. If object is a window, that window is to be updated. If object is a buffer orbuffer name, all windows displaying that buffer are to be updated. If object is nil (oromitted), all windows are to be updated.
This function does not do a redisplay immediately; Emacs does that as it waits for
input, or when the function redisplay is called.

[Variable]
A function run just before redisplay. It is called with one argument, the set of windows
to be redisplayed. The set can be nil, meaning only the selected window, or t,meaning all the windows.

pre-redisplay-function[Variable]
This hook is run just before redisplay. It is called once in each window that is about
to be redisplayed, with current-buffer set to the buffer displayed in that window.

pre-redisplay-functions

41.3 Truncation
When a line of text extends beyond the right edge of a window, Emacs can continue theline (make it wrap to the next screen line), or truncate the line (limit it to one screen line).
The additional screen lines used to display a long text line are called continuation lines.
Continuation is not the same as filling; continuation happens on the screen only, not in thebuffer contents, and it breaks a line precisely at the right margin, not at a word boundary.
See Section 33.11 [Filling], page 899.
On a graphical display, tiny arrow images in the window fringes indicate truncated andcontinued lines (see Section 41.13 [Fringes], page 1189). On a text terminal, and on agraphical display when fringe-mode was turned off, a ‘$’ in the rightmost column of thewindow indicates truncation; a ‘\’ on the rightmost column indicates a line that wraps. (Thedisplay table can specify alternate characters to use for this; see Section 41.23.2 [Display
Tables], page 1243).
Since wrapping and truncation of text contradict each other, Emacs turns off line
truncation when wrapping is requested, and vice versa.
[User Option]
If this buffer-local variable is non-nil, lines that extend beyond the right edge of
the window are truncated; otherwise, they are continued. As a special exception,
the variable truncate-partial-width-windows takes precedence in partial-width
windows (i.e., windows that do not occupy the entire frame width).

truncate-lines[User Option]
This variable controls line truncation in partial-width windows. A partial-width
window is one that does not occupy the entire frame width (see Section 29.7 [Splitting
Windows], page 708). If the value is nil, line truncation is determined by thevariable truncate-lines (see above). If the value is an integer n, lines are truncated
if the partial-width window has fewer than n columns, regardless of the value oftruncate-lines; if the partial-width window has n or more columns, line truncation
is determined by truncate-lines. For any other non-nil value, lines are truncatedin every partial-width window, regardless of the value of truncate-lines.

truncate-partial-width-windows

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When horizontal scrolling (see Section 29.23 [Horizontal Scrolling], page 767) is in use ina window, that forces truncation.
[Variable]
If this buffer-local variable is non-nil, it defines a wrap prefix which Emacs displays
at the start of every continuation line. (If lines are truncated, wrap-prefix is neverused.) Its value may be a string or an image (see Section 41.16.4 [Other Display Specs],
page 1203), or a stretch of whitespace such as specified by the :width or :align-to
display properties (see Section 41.16.2 [Specified Space], page 1200). The value isinterpreted in the same way as a display text property. See Section 41.16 [Display
Property], page 1198.

wrap-prefix

A wrap prefix may also be specified for regions of text, using the wrap-prefix text
or overlay property. This takes precedence over the wrap-prefix variable. See
Section 33.19.4 [Special Properties], page 924.
[Variable]
If this buffer-local variable is non-nil, it defines a line prefix which Emacs displays
at the start of every non-continuation line. Its value may be a string or an image(see Section 41.16.4 [Other Display Specs], page 1203), or a stretch of whitespacesuch as specified by the :width or :align-to display properties (see Section 41.16.2[Specified Space], page 1200). The value is interpreted in the same way as a display
text property. See Section 41.16 [Display Property], page 1198.

line-prefix

A line prefix may also be specified for regions of text using the line-prefix text
or overlay property. This takes precedence over the line-prefix variable. See
Section 33.19.4 [Special Properties], page 924.

41.4 The Echo Area
The echo area is used for displaying error messages (see Section 11.7.3 [Errors], page 179),
for messages made with the message primitive, and for echoing keystrokes. It is not thesame as the minibuffer, despite the fact that the minibuffer appears (when active) in thesame place on the screen as the echo area. See Section “The Minibuffer” in The GNU Emacs
Manual.
Apart from the functions documented in this section, you can print Lisp objects to theecho area by specifying t as the output stream. See Section 20.4 [Output Streams], page 375.

41.4.1 Displaying Messages in the Echo Area
This section describes the standard functions for displaying messages in the echo area.

message format-string &rest arguments[Function]
This function displays a message in the echo area. format-string is a format string, andarguments are the objects for its format specifications, like in the format-message
function (see Section 4.7 [Formatting Strings], page 66). The resulting formatted
string is displayed in the echo area; if it contains face text properties, it is displayedwith the specified faces (see Section 41.12 [Faces], page 1164). The string is also added
to the *Messages* buffer, but without text properties (see Section 41.4.3 [Logging
Messages], page 1137).

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Typically grave accent and apostrophe in the format translate to matching curved
quotes, e.g., "Missing ‘%s’" might result in "Missing ‘foo’". See Section 25.4
[Text Quoting Style], page 600, for how to influence or inhibit this translation.
In batch mode, the message is printed to the standard error stream, followed by anewline.
When inhibit-message is non-nil, no message will be displayed in the echo area, itwill only be logged to ‘*Messages*’.
If format-string is nil or the empty string, message clears the echo area; if theecho area has been expanded automatically, this brings it back to its normal size.
If the minibuffer is active, this brings the minibuffer contents back onto the screen
immediately.
(message "Reverting `%s'..." (buffer-name))a Reverting ‘subr.el’...
⇒ "Reverting ‘subr.el’..."---------- Echo Area ---------Reverting ‘subr.el’...
---------- Echo Area ---------To automatically display a message in the echo area or in a pop-buffer, depending on
its size, use display-message-or-buffer (see below).
Warning: If you want to use your own string as a message verbatim, don’t just write(message string). If string contains ‘%’, ‘`’, or ‘'’ it may be reformatted, with
undesirable results. Instead, use (message "%s" string).
The following facilities allow users and Lisp programs to control how echo-area messages
are displayed.
[Variable]
If this variable is non-nil, it should be a function of one argument, the text of amessage to display in the echo area. That function will be called by message andrelated functions. If the function returns nil, the message is displayed in the echoarea as usual. If the function returns a string, that string is displayed in the echo area
instead of the original message. If the function returns any other non-nil value, thatmeans the message was already handled, so message will not display anything in theecho area.
The default value calls set-minibuffer-message, described below.

set-message-function[Variable]
If this variable is non-nil, it should be a function of no arguments; message andrelated functions call it when their argument message is nil or the empty string, toclear the echo area.
Usually this function is called when the next input event arrives after displaying anecho-area message. The function is expected to clear the message displayed by its
counterpart function specified by set-message-function, but doesn’t have to. If
the function wants the echo area to remain uncleared, it should return the symbol
dont-clear-message; any other value will result in the echo area being cleared.

clear-message-function

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The default value is the function that clears the message displayed in an active
minibuffer.
[User Option]
The value of this user option is a list of functions to be called for handling displayof echo-area messages. Each function is called with one argument, the text of themessage to display. If the function returns a string, that string replaces the original
message, and the next function in the list is called with the new message text. If thefunction returns nil, the next function in the list is called with the same text; if thelast function in the list returns nil, the message text is displayed in the echo area. If
the function returns a non-nil value that is not a string, the message is considered tobe handled, and no further functions in the list are called.

set-message-functions

The three useful functions to be put in the list that is the value of this option are
described below.

set-minibuffer-message message[Function]
This function displays message in the echo-area when the minibuffer is not active,
and at the end of the minibuffer when the minibuffer is active. However, if thetext shown in the active minibuffer has the minibuffer-message text property (seeSection 33.19.4 [Special Properties], page 924) on some character, the message will be
displayed before the first character having that property.

This function is by default the only member of the list in set-message-functions.

inhibit-message message[Function]
If an echo-area message matches any regexp in the list that is the value of theuser option inhibit-message-regexps, this function suppresses the display of thatmessage and returns a non-nil value that is not a string. Thus, if this function isin the list set-message-functions, the rest of the functions in the list will not becalled when message matches the regexps in inhibit-message-regexps. To ensurea matching message will never be displayed, make this function be the first element of
the list in set-message-functions.

set-multi-message message[Function]
This function accumulates several echo-area messages emitted one after another, andreturns them as a single string in which individual messages are separated by newlines.
Up to multi-message-max recent messages can be accumulated. The accumulated
messages are discarded when more than multi-message-timeout seconds have elapsed
since the time the first message was emitted.

[Variable]
When this variable is non-nil, message and related functions will not display any
messages in the Echo Area. Echo-area messages are still logged in the *Messages*
buffer, though.

inhibit-message

with-temp-message message &rest body

[Macro]This construct displays a message in the echo area temporarily, during the executionof body. It displays message, executes body, then returns the value of the last bodyform while restoring the previous echo area contents.

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message-or-box format-string &rest arguments[Function]
This function displays a message like message, but may display it in a dialog box
instead of the echo area. If this function is called in a command that was invokedusing the mouse—more precisely, if last-nonmenu-event (see Section 22.5 [Command
Loop Info], page 436) is either nil or a list—then it uses a dialog box or pop-up menu
to display the message. Otherwise, it uses the echo area. (This is the same criterion
that y-or-n-p uses to make a similar decision; see Section 21.7 [Yes-or-No Queries],
page 413.)
You can force use of the mouse or of the echo area by binding last-nonmenu-eventto a suitable value around the call.

message-box format-string &rest arguments[Function]
This function displays a message like message, but uses a dialog box (or a pop-upmenu) whenever that is possible. If it is impossible to use a dialog box or pop-up
menu, because the terminal does not support them, then message-box uses the echo
area, like message.

display-message-or-buffer message &optional buffer-name action
frame[Function]

This function displays the message message, which may be either a string or abuffer. If it is shorter than the maximum height of the echo area, as defined by
max-mini-window-height, it is displayed in the echo area, using message. Otherwise,
display-buffer is used to show it in a pop-up buffer.
Returns either the string shown in the echo area, or when a pop-up buffer is used, thewindow used to display it.
If message is a string, then the optional argument buffer-name is the name of thebuffer used to display it when a pop-up buffer is used, defaulting to *Message*. In
the case where message is a string and displayed in the echo area, it is not specified
whether the contents are inserted into the buffer anyway.
The optional arguments action and frame are as for display-buffer, and only used
if a buffer is displayed.
[Function]
This function returns the message currently being displayed in the echo area, or nil if
there is none.

current-message

41.4.2 Reporting Operation Progress
When an operation can take a while to finish, you should inform the user about the progress
it makes. This way the user can estimate remaining time and clearly see that Emacs is busy
working, not hung. A convenient way to do this is to use a progress reporter.
Here is a working example that does nothing useful:(let ((progress-reporter(make-progress-reporter "Collecting mana for Emacs..."0 500)))(dotimes (k 500)
(sit-for 0.01)(progress-reporter-update progress-reporter k))(progress-reporter-done progress-reporter))Chapter 41: Emacs Display

make-progress-reporter message &optional min-value max-value
current-value min-change min-time

1135[Function]

This function creates and returns a progress reporter object, which you will use as anargument for the other functions listed below. The idea is to precompute as muchdata as possible to make progress reporting very fast.
When this progress reporter is subsequently used, it will display message in the echo
area, followed by progress percentage. message is treated as a simple string. If you
need it to depend on a filename, for instance, use format-message before calling thisfunction.
The arguments min-value and max-value should be numbers standing for the startingand final states of the operation. For instance, an operation that scans a buffer should
set these to the results of point-min and point-max correspondingly. max-value
should be greater than min-value.
Alternatively, you can set min-value and max-value to nil. In that case, the progress
reporter does not report process percentages; it instead displays a “spinner” thatrotates a notch each time you update the progress reporter.
If min-value and max-value are numbers, you can give the argument current-value anumerical value specifying the initial progress; if omitted, this defaults to min-value.
The remaining arguments control the rate of echo area updates. The progress reporter
will wait for at least min-change more percents of the operation to be completed before
printing next message; the default is one percent. min-time specifies the minimum
time in seconds to pass between successive prints; the default is 0.2 seconds. (On some
operating systems, the progress reporter may handle fractions of seconds with varying
precision).
This function calls progress-reporter-update, so the first message is printed immediately.

progress-reporter-update reporter &optional value suffix[Function]
This function does the main work of reporting progress of your operation. It displays themessage of reporter, followed by progress percentage determined by value. If percentage
is zero, or close enough according to the min-change and min-time arguments, then it
is omitted from the output.
reporter must be the result of a call to make-progress-reporter. value specifies
the current state of your operation and must be between min-value and max-value(inclusive) as passed to make-progress-reporter. For instance, if you scan a buffer,then value should be the result of a call to point.
Optional argument suffix is a string to be displayed after reporter’s main message andprogress text. If reporter is a non-numerical reporter, then value should be nil, or astring to use instead of suffix.
This function respects min-change and min-time as passed to make-progressreporter and so does not output new messages on every invocation. It is thus
very fast and normally you should not try to reduce the number of calls to it: resulting
overhead will most likely negate your effort.

Chapter 41: Emacs Display

progress-reporter-force-update reporter &optional value
new-message suffix

1136[Function]

This function is similar to progress-reporter-update except that it prints a message
in the echo area unconditionally.
reporter, value, and suffix have the same meaning as for progress-reporter-update.
Optional new-message allows you to change the message of the reporter. Since thisfunction always updates the echo area, such a change will be immediately presented
to the user.

progress-reporter-done reporter[Function]
This function should be called when the operation is finished. It prints the message ofreporter followed by word ‘done’ in the echo area.

You should always call this function and not hope for progress-reporter-update toprint ‘100%’. Firstly, it may never print it, there are many good reasons for this not
to happen. Secondly, ‘done’ is more explicit.

dotimes-with-progress-reporter (var count [result])
reporter-or-message body. . .

[Macro]This is a convenience macro that works the same way as dotimes does, but also reports
loop progress using the functions described above. It allows you to save some typing.
The argument reporter-or-message can be either a string or a progress reporter object.
You can rewrite the example in the beginning of this subsection using this macro as
follows:(dotimes-with-progress-reporter(k 500)"Collecting some mana for Emacs..."(sit-for 0.01))
Using a reporter object as the reporter-or-message argument is useful if you want tospecify the optional arguments in make-progress-reporter. For instance, you can write
the previous example as follows:(dotimes-with-progress-reporter(k 500)(make-progress-reporter "Collecting some mana for Emacs..." 0 500 0 1 1.5)
(sit-for 0.01))

dolist-with-progress-reporter (var list [result])
reporter-or-message body. . .

[Macro]This is another convenience macro that works the same way as dolist does, butalso reports loop progress using the functions described above. As in dotimes-withprogress-reporter, reporter-or-message can be a progress reporter or a string.
You can rewrite the previous example with this macro as follows:(dolist-with-progress-reporter(k (number-sequence 0 500))"Collecting some mana for Emacs..."(sit-for 0.01))

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with-delayed-message (timeout message) body. . .

[Macro]Sometimes it’s unclear whether an operation will take a long time to execute or not,or it can be inconvenient to implement a progress reporter. This macro can be usedin those situations.
(with-delayed-message (2 (format "Gathering data for %s" entry))(setq data (gather-data entry)))
In this example, if the body takes more than two seconds to execute, the message will
be displayed. If it takes a shorter time than that, the message won’t be displayed.
In either case, the body is evaluated as normally, and the return value of the final
element in the body is the return value of the macro.

The message element is evaluated before body, and is always evaluated, whether themessage is displayed or not.

41.4.3 Logging Messages in *Messages*
Almost all the messages displayed in the echo area are also recorded in the *Messages* buffer
so that the user can refer back to them. This includes all the messages that are output withmessage. By default, this buffer is read-only and uses the major mode messages-buffermode. Nothing prevents the user from killing the *Messages* buffer, but the next display ofa message recreates it. Any Lisp code that needs to access the *Messages* buffer directly
and wants to ensure that it exists should use the function messages-buffer.
[Function]
This function returns the *Messages* buffer. If it does not exist, it creates it, andswitches it to messages-buffer-mode.

messages-buffer[User Option]
This variable specifies how many lines to keep in the *Messages* buffer. The value tmeans there is no limit on how many lines to keep. The value nil disables message
logging entirely. Here’s how to display a message and prevent it from being logged:

message-log-max(let (message-log-max)(message ...))[Variable]
This variable has the name of the buffer where messages should be logged to, anddefaults to *Messages*. Some packages may find it useful to temporarily redirect theoutput to a different buffer (perhaps to write the buffer out to a log file later), andthey can bind this variable to a different buffer name. (Note that this buffer (if it
doesn’t exist already), will be created and put into messages-buffer-mode.)

messages-buffer-nameTo make *Messages* more convenient for the user, the logging facility combines successive
identical messages. It also combines successive related messages for the sake of two cases:
question followed by answer, and a series of progress messages.
A question followed by an answer has two messages like the ones produced by y-or-n-p:
the first is ‘question’, and the second is ‘question...answer’. The first message conveys
no additional information beyond what’s in the second, so logging the second message
discards the first from the log.

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A series of progress messages has successive messages like those produced by
make-progress-reporter. They have the form ‘base...how-far’, where base is the sameeach time, while how-far varies. Logging each message in the series discards the previous
one, provided they are consecutive.
The functions make-progress-reporter and y-or-n-p don’t have to do anything special
to activate the message log combination feature. It operates whenever two consecutive
messages are logged that share a common prefix ending in ‘...’.

41.4.4 Echo Area Customization
These variables control details of how the echo area works.
[Variable]
This variable controls where the cursor appears when a message is displayed in the echoarea. If it is non-nil, then the cursor appears at the end of the message. Otherwise,
the cursor appears at point—not in the echo area at all.
The value is normally nil; Lisp programs bind it to t for brief periods of time.

cursor-in-echo-area[Variable]
This normal hook is run whenever the echo area is cleared—either by (message nil)or for any other reason.

echo-area-clear-hook[User Option]
This variable determines how much time should elapse before command characters
echo. Its value must be a number, and specifies the number of seconds to wait before
echoing. If the user types a prefix key (such as C-x) and then delays this many seconds
before continuing, the prefix key is echoed in the echo area. (Once echoing begins
in a key sequence, all subsequent characters in the same key sequence are echoed
immediately.)If the value is zero, then command input is not echoed.

echo-keystrokes[Variable]
Normally, displaying a long message resizes the echo area to display the entire message,
wrapping long line as needed. But if the variable message-truncate-lines is non-nil,long lines of echo-area message are instead truncated to fit the mini-window width.

message-truncate-lines

The variable max-mini-window-height, which specifies the maximum height for resizing
minibuffer windows, also applies to the echo area (which is really a special use of theminibuffer window; see Section 21.11 [Minibuffer Windows], page 418).

41.5 Reporting Warnings
Warnings are a facility for a program to inform the user of a possible problem, but continue
running (as opposed to signaling an error, see Section 11.7.3 [Errors], page 179).

41.5.1 Warning Basics
Every warning is a textual message, which explains the problem for the user, with theassociated severity level which is a symbol. Here are the supported severity levels, in orderof decreasing severity, and their meanings:

Chapter 41: Emacs Display

1139:emergency
A problem that will seriously impair Emacs operation soon if the user does notattend to it promptly.
:error

A report about data or circumstances that are inherently wrong.

:warning

A report about data or circumstances that are not inherently wrong, but raisesuspicion of a possible problem.

:debugA report of information that may be useful if the user is currently debugging
the Lisp program which issues the warning.

When your program encounters invalid input data, it can either signal a Lisp error
by calling error or signal (see Section 11.7.3.1 [Signaling Errors], page 180) or reporta warning with severity :error. Signaling a Lisp error is the easiest thing to do, but itmeans the signaling program cannot continue execution. If you want to take the trouble of
implementing a way to continue processing despite the invalid data, then reporting a warningof severity :error is the right way of informing the user of the problem. For instance,
the Emacs Lisp byte compiler can report an error that way and continue compiling otherfunctions. (If the program signals a Lisp error and then handles it with condition-case, theuser won’t see the error message; reporting that as a warning instead avoids that problem.)
In addition to severity level, each warning has a warning type to classify it. The warning
type is either a symbol or a list of symbols. If it is a symbol, it should be the custom
group that you use for the program’s user options; if it is a list, the first element of the list
should be that custom group. For example, byte compiler warnings use the warning type(bytecomp). If the warning type is a list, the elements of the list after the first one, whichshould be arbitrary symbols, represent subcategories of the warning: they will be displayed
to the user to better explain the nature of the warning.

display-warning type message &optional level buffer-name[Function]
This function reports a warning, using the string message as the warning text andtype as the warning type. level should be the severity level, and defaults to :warning
if omitted or nil.
buffer-name, if non-nil, specifies the name of the buffer for logging the warning
message. By default, it is *Warnings*.

lwarn type level message &rest args

[Function]
This function reports a warning using the value returned by (format-message message args...)as the message text in the *Warnings* buffer. In other respects it is equivalent todisplay-warning.

warn message &rest args

[Function]
This function reports a warning using the value returned by (format-message message args...)as the message text, emacs as the warning type, and :warning as the severity level.
It exists for compatibility only; we recommend not using it, because you should
specify a specific warning type.

41.5.2 Warning Variables
Programs can customize how their warnings appear by binding the variables described inthis section.

Chapter 41: Emacs Display

1140[Variable]
This list defines the meaning and severity order of the warning severity levels. Eachelement defines one severity level, and they are arranged in order of decreasing severity.

warning-levels

Each element has the form (level string [function]), where level is the severity
level it defines. string specifies the textual description of this level. string should use‘%s’ to specify where to put the warning type information, or it can omit the ‘%s’ so as
not to include that information.
The optional function, if non-nil, is a function to call with no arguments, to get theuser’s attention. A notable example is ding (see Section 41.24 [Beeping], page 1247).
Normally you should not change the value of this variable.
[Variable]
If non-nil, the value is a function to generate prefix text for warnings. Programs canbind the variable to a suitable function. display-warning calls this function withthe warnings buffer the current buffer, and the function can insert text into it. Thattext becomes the beginning of the warning message.

warning-prefix-function

The function is called with two arguments, the severity level and its entry inwarning-levels. It should return a list to use instead of that entry (the value neednot be an actual member of warning-levels, but it must have the same structure).
By constructing this value, the function can change the severity of the warning, or
specify different handling for a given severity level.
If the variable’s value is nil, there’s no prefix text, before the warning is displayed,
starting with the string part of the entry in warning-levels corresponding to thewarning’s level.
[Variable]
Programs can bind this variable to t to say that the next warning should begin aseries. When several warnings form a series, that means to leave point on the firstwarning of the series, rather than keep moving it for each warning so that it appearson the last one. The series ends when the local binding of this variable is unboundand warning-series becomes nil again.

warning-series

The value can also be a symbol with a function definition. That is equivalent to t,
except that the next warning will also call the function with no arguments with thewarnings buffer the current buffer. The function can, for example, insert text which
will serve as a header for the series of warnings.
Once a series has begun, the value of this variable is a marker which points to thebuffer position in the warnings buffer of the start of the series.
The variable’s normal value is nil, which means to handle each warning separately.
[Variable]
When this variable is non-nil, it specifies a fill prefix to use for filling the text of eachwarning.

warning-fill-prefix

warning-fill-column
The column at which to fill warnings.

[Variable]

Chapter 41: Emacs Display

1141[Variable]
This variable specifies the format for displaying the warning type in the warning text.
The result of formatting the type this way gets included in the message under thecontrol of the string in the entry in warning-levels. The default value is " (%s)".
If you bind it to the empty string "" then the warning type won’t appear at all.

warning-type-format

41.5.3 Warning Options
These variables are used by users to control what happens when a Lisp program reports awarning.
[User Option]
This user option specifies the minimum severity level that should be shown immediately
to the user, by popping the warnings buffer in some window. The default is :warning,which means to show the warning buffer for any warning severity except :debug. The
warnings of lower severity levels will still be written into the warnings buffer, but thebuffer will not be forced onto display.

warning-minimum-level[User Option]
This user option specifies the minimum severity level that should be logged in thewarnings buffer. Warnings of lower severity will be completely ignored: not written to
the warnings buffer and not displayed. The default is :warning, which means to log
warnings of any severity except :debug.

warning-minimum-log-level[User Option]
This list specifies which warning types should not be displayed immediately when
they occur. Each element of the list should be a list of symbols. If an element of thislist has the same elements as the first elements in a warning type, then the warningof that type will not be shown on display by popping the warnings buffer in some
window (the warning will still be logged in the warnings buffer).

warning-suppress-types

For example, if the value of this variable is a list like this:((foo) (bar subtype))then warnings whose types are foo or (foo)(bar subtype other) will not be shown to the user.

or(foo something)or[User Option]
This list specifies which warning types should be ignored: not logged in the warnings
buffer and not shown to the user. The structure and the matching of warning types
are the same as for warning-suppress-types above.

warning-suppress-log-types

During startup, Emacs delays showing any warnings until after it loads and processes thesite-wide and user’s init files (see Section 42.1.1 [Startup Summary], page 1255). Let-binding(see Section 12.3 [Local Variables], page 190) the values of these options around some codein your init files which might emit a warning will therefore not work, because it will not
be in effect by the time the warning is actually processed. Thus, if you want to suppress
some warnings during startup, change the values of the above options in your init file earlyenough, or put those let-binding forms in your after-init-hook or emacs-startup-hook
functions. See Section 42.1.2 [Init File], page 1258.

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41.5.4 Delayed Warnings
Sometimes, you may wish to avoid showing a warning while a command is running, and only
show it only after the end of the command. You can use the function delay-warning forthis. Emacs automatically delays any warnings emitted during the early stages of startup,and shows them only after the init files are processed.

delay-warning type message &optional level buffer-name[Function]
This function is the delayed counterpart to display-warning (see Section 41.5.1[Warning Basics], page 1138), and it is called with the same arguments. The warning
message is queued into delayed-warnings-list.
[Variable]
The value of this variable is a list of warnings to be displayed after the current
command has finished. Each element must be a list

delayed-warnings-list(type message [level [buffer-name]])with the same form, and the same meanings, as the argument list of display-warning.
Immediately after running post-command-hook (see Section 22.1 [Command Overview],
page 423), the Emacs command loop displays all the warnings specified by this variable,
then resets the variable to nil.
Programs which need to further customize the delayed warnings mechanism can change
the variable delayed-warnings-hook:[Variable]
This is a normal hook which is run by the Emacs command loop, after post-commandhook, in order to process and display delayed warnings. Emacs also runs this hookduring startup, after loading the site-start and user init files (see Section 42.1.1 [Startup
Summary], page 1255), because warnings emitted before that are automatically delayed.
Its default value is a list of two functions:delayed-warnings-hook(collapse-delayed-warnings display-delayed-warnings)

The function collapse-delayed-warnings removes repeated entries fromdelayed-warnings-list.
The function display-delayed-warnings calls
display-warning on each of the entries in delayed-warnings-list, in turn, andthen sets delayed-warnings-list to nil.

41.6 Invisible Text
You can make characters invisible, so that they do not appear on the screen, with theinvisible property. This can be either a text property (see Section 33.19 [Text Properties],
page 917) or an overlay property (see Section 41.9 [Overlays], page 1150). Cursor motion
also partly ignores these characters; if the command loop finds that point is inside a range
of invisible text after a command, it relocates point to the other side of the text.
In the simplest case, any non-nil invisible property makes a character invisible. Thisis the default case—if you don’t alter the default value of buffer-invisibility-spec,
this is how the invisible property works. You should normally use t as the value of theinvisible property if you don’t plan to set buffer-invisibility-spec yourself.
More generally, you can use the variable buffer-invisibility-spec to control which
values of the invisible property make text invisible. This permits you to classify the text

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into different subsets in advance, by giving them different invisible values, and subsequently
make various subsets visible or invisible by changing the value of buffer-invisibilityspec.
Controlling visibility with buffer-invisibility-spec is especially useful in a program
to display the list of entries in a database. It permits the implementation of convenientfiltering commands to view just a part of the entries in the database. Setting this variable
is very fast, much faster than scanning all the text in the buffer looking for properties tochange.
[Variable]
This variable specifies which kinds of invisible properties actually make a character
invisible. Setting this variable makes it buffer-local.

buffer-invisibility-spect

A character is invisible if its invisible property is non-nil. This is thedefault.

a listEach element of the list specifies a criterion for invisibility; if a character’s
invisible property fits any one of these criteria, the character is invisible.
The list can have two kinds of elements:
atom

A character is invisible if its invisible property value isatom or if it is a list with atom as a member; comparison isdone with eq.

(atom . t)
A character is invisible if its invisible property value is atom
or if it is a list with atom as a member; comparison is donewith eq. Moreover, a sequence of such characters displays as
an ellipsis.
Two functions are specifically provided for adding elements to buffer-invisibilityspec and removing elements from it.

add-to-invisibility-spec element[Function]
This function adds the element element to buffer-invisibility-spec.
If
buffer-invisibility-spec was t, it changes to a list, (t), so that text whose
invisible property is t remains invisible.

remove-from-invisibility-spec element[Function]
This removes the element element from buffer-invisibility-spec. This doesnothing if element is not in the list.

A convention for use of buffer-invisibility-spec is that a major mode should use
the mode’s own name as an element of buffer-invisibility-spec and as the value of theinvisible property:;; If you want to display an ellipsis:(add-to-invisibility-spec '(my-symbol . t));; If you don’t want ellipsis:(add-to-invisibility-spec 'my-symbol)

Chapter 41: Emacs Display

1144(overlay-put (make-overlay beginning end)
'invisible 'my-symbol);; When done with the invisibility:(remove-from-invisibility-spec '(my-symbol . t));; Or respectively:(remove-from-invisibility-spec 'my-symbol)
You can check for invisibility using the following function:

invisible-p pos-or-prop[Function]
If pos-or-prop is a marker or number, this function returns a non-nil value if the text
at that position is currently invisible.
If pos-or-prop is any other kind of Lisp object, that is taken to mean a possible value ofthe invisible text or overlay property. In that case, this function returns a non-nil
value if that value would cause text to become invisible, based on the current value of
buffer-invisibility-spec.
The return value of this function is t if the text would be completely hidden on display,
or a non-nil, non-t value if the text would be replaced by an ellipsis.

Ordinarily, functions that operate on text or move point do not care whether the text
is invisible, they process invisible characters and visible characters alike. The user-levelline motion commands, such as next-line, previous-line, ignore invisible newlines ifline-move-ignore-invisible is non-nil (the default), i.e., behave like these invisible
newlines didn’t exist in the buffer, but only because they are explicitly programmed to doso.
If a command ends with point inside or at the boundary of invisible text, the main
editing loop relocates point to one of the two ends of the invisible text. Emacs chooses
the direction of relocation so that it is the same as the overall movement direction of thecommand; if in doubt, it prefers a position where an inserted char would not inherit theinvisible property. Additionally, if the text is not replaced by an ellipsis and the command
only moved within the invisible text, then point is moved one extra character so as to try
and reflect the command’s movement by a visible movement of the cursor.
Thus, if the command moved point back to an invisible range (with the usual stickiness),
Emacs moves point back to the beginning of that range. If the command moved point
forward into an invisible range, Emacs moves point forward to the first visible character
that follows the invisible text and then forward one more character.
These adjustments of point that ended up in the middle of invisible text can be disabled
by setting disable-point-adjustment to a non-nil value. See Section 22.6 [Adjusting
Point], page 439.
Incremental search can make invisible overlays visible temporarily and/or permanently
when a match includes invisible text. To enable this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a function to be calledwith the overlay as an argument. This function should make the overlay visible permanently;
it is used when the match overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by temporarily modifying
their invisible and intangible properties. If you want this to be done differently for a certain

Chapter 41: Emacs Display

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overlay, give it an isearch-open-invisible-temporary property which is a function. The
function is called with two arguments: the first is the overlay, and the second is nil to makethe overlay visible, or t to make it invisible again.

41.7 Selective Display
Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, was designed for use in a Lisp program: it
controls which lines are hidden by altering the text. This kind of hiding is now obsoleteand deprecated; instead you should use the invisible property (see Section 41.6 [Invisible
Text], page 1142) to get the same effect.
In the second variant, the choice of lines to hide is made automatically based on indentation.
This variant is designed to be a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with acarriage return (control-m). The text that was formerly a line following that newline is now
hidden. Strictly speaking, it is temporarily no longer a line at all, since only newlines canseparate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For example, C-f(forward-char) moves point unhesitatingly into hidden text. However, the replacement of
newline characters with carriage return characters affects some editing commands. For
example, next-line skips hidden lines, since it searches only for newlines. Modes thatuse selective display can also define commands that take account of the newlines, or that
control which parts of the text are hidden.
When you write a selectively displayed buffer into a file, all the control-m’s are output as
newlines. This means that when you next read in the file, it looks OK, with nothing hidden.
The selective display effect is seen only within Emacs.
[Variable]
This buffer-local variable enables selective display. This means that lines, or portionsof lines, may be made hidden.

selective-display• If the value of selective-display is t, then the character control-m marks thestart of hidden text; the control-m, and the rest of the line following it, are notdisplayed. This is explicit selective display.
• If the value of selective-display is a positive integer, then lines that start withmore than that many columns of indentation are not displayed.
When some portion of a buffer is hidden, the vertical movement commands operate asif that portion did not exist, allowing a single next-line command to skip any numberof hidden lines. However, character movement commands (such as forward-char) do
not skip the hidden portion, and it is possible (if tricky) to insert or delete text in ahidden portion.
In the examples below, we show the display appearance of the buffer foo, whichchanges with the value of selective-display. The contents of the buffer do notchange.

Chapter 41: Emacs Display

1146(setq selective-display nil)
⇒ nil---------- Buffer: foo ---------1 on this column
2on this column
3n this column
3n this column
2on this column
1 on this column---------- Buffer: foo ---------(setq selective-display 2)⇒ 2---------- Buffer: foo ---------1 on this column
2on this column
2on this column
1 on this column---------- Buffer: foo ---------[User Option]
If this buffer-local variable is non-nil, then Emacs displays ‘...’ at the end of a linethat is followed by hidden text. This example is a continuation of the previous one.

selective-display-ellipses(setq selective-display-ellipses t)⇒ t---------- Buffer: foo ---------1 on this column
2on this column ...
2on this column
1 on this column---------- Buffer: foo ---------You can use a display table to substitute other text for the ellipsis (‘...’). See
Section 41.23.2 [Display Tables], page 1243.

41.8 Temporary Displays
Temporary displays are used by Lisp programs to put output into a buffer and then present
it to the user for perusal rather than for editing. Many help commands use this feature.

with-output-to-temp-buffer buffer-name body. . .

[Macro]This function executes the forms in body while arranging to insert any output they
print into the buffer named buffer-name, which is first created if necessary, and put
into Help mode. (See the similar form with-temp-buffer-window below.) Finally,
the buffer is displayed in some window, but that window is not selected.

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If the forms in body do not change the major mode in the output buffer, so that itis still Help mode at the end of their execution, then with-output-to-temp-buffer
makes this buffer read-only at the end, and also scans it for function and variablenames to make them into clickable cross-references. See [Tips for Documentation
Strings], page 1339, in particular the item on hyperlinks in documentation strings, formore details.
The string buffer-name specifies the temporary buffer, which need not already exist.
The argument must be a string, not a buffer. The buffer is erased initially (with noquestions asked), and it is marked as unmodified after with-output-to-temp-buffer
exits.
with-output-to-temp-buffer binds standard-output to the temporary buffer, thenit evaluates the forms in body. Output using the Lisp output functions within bodygoes by default to that buffer (but screen display and messages in the echo area,
although they are “output” in the general sense of the word, are not affected). See
Section 20.5 [Output Functions], page 377.
Several hooks are available for customizing the behavior of this construct; they arelisted below.
The value of the last form in body is returned.
---------- Buffer: foo ---------This is the contents of foo.
---------- Buffer: foo ---------(with-output-to-temp-buffer "foo"(print 20)(print standard-output))⇒ #<buffer foo>---------- Buffer: foo ---------20#<buffer foo>---------- Buffer: foo ---------[User Option]
If this variable is non-nil, with-output-to-temp-buffer calls it as a function to do
the job of displaying a help buffer. The function gets one argument, which is thebuffer it should display.
It is a good idea for this function to run temp-buffer-show-hook just as
with-output-to-temp-buffer normally would, inside of save-selected-window
and with the chosen window and buffer selected.

temp-buffer-show-function[Variable]
This normal hook is run by with-output-to-temp-buffer before evaluating body.
When the hook runs, the temporary buffer is current. This hook is normally set up
with a function to put the buffer in Help mode.

temp-buffer-setup-hook

Chapter 41: Emacs Display

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This normal hook is run by with-output-to-temp-buffer after displaying the temporary buffer. When the hook runs, the temporary buffer is current, and the window
it was displayed in is selected.

temp-buffer-show-hookwith-temp-buffer-window buffer-or-name action quit-function
body. . .

[Macro]This macro is similar to with-output-to-temp-buffer. Like that construct, it
executes body while arranging to insert any output it prints into the buffer named
buffer-or-name and displays that buffer in some window. Unlike with-output-totemp-buffer, however, it does not automatically switch that buffer to Help mode.
The argument buffer-or-name specifies the temporary buffer. It can be either abuffer, which must already exist, or a string, in which case a buffer of that nameis created, if necessary. The buffer is marked as unmodified and read-only when
with-temp-buffer-window exits.
This macro does not call temp-buffer-show-function. Rather, it passes the action
argument to display-buffer (see Section 29.13.1 [Choosing Window], page 724) inorder to display the buffer.
The value of the last form in body is returned, unless the argument quit-function is
specified. In that case, it is called with two arguments: the window showing the buffer
and the result of body. The final return value is then whatever quit-function returns.
This macro uses the normal hooks temp-buffer-window-setup-hook andtemp-buffer-window-show-hook in place of the analogous hooks run by
with-output-to-temp-buffer.
The two constructs described next are mostly identical to with-temp-buffer-window
but differ from it as specified:

with-current-buffer-window buffer-or-name action quit-function&rest body

[Macro]This macro is like with-temp-buffer-window but unlike that makes the buffer specified by buffer-or-name current for running body.
A window showing a temporary buffer can be fitted to the size of that buffer using thefollowing mode:[User Option]
When this minor mode is enabled, windows showing a temporary buffer are automatically resized to fit their buffer’s contents.
A window is resized if and only if it has been specially created for the buffer. In
particular, windows that have shown another buffer before are not resized. By
default, this mode uses fit-window-to-buffer (see Section 29.5 [Resizing Windows],
page 703) for resizing. You can specify a different function by customizing the options
temp-buffer-max-height and temp-buffer-max-width below.
The effect of this option can be overridden by providing a suitable window-height,
window-width or window-size action alist entry for display-buffer (seeSection 29.13.3 [Buffer Display Action Alists], page 730).

temp-buffer-resize-mode

Chapter 41: Emacs Display

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This option specifies the maximum height (in lines) of a window displaying a temporary
buffer when temp-buffer-resize-mode is enabled. It can also be a function to becalled to choose the height for such a buffer. It gets one argument, the buffer, andshould return a positive integer. At the time the function is called, the window to be
resized is selected.

temp-buffer-max-height[User Option]
This option specifies the maximum width of a window (in columns) displaying atemporary buffer when temp-buffer-resize-mode is enabled. It can also be afunction to be called to choose the width for such a buffer. It gets one argument, thebuffer, and should return a positive integer. At the time the function is called, thewindow to be resized is selected.

temp-buffer-max-width

The following function uses the current buffer for temporary display:

momentary-string-display string position &optional char message[Function]
This function momentarily displays string in the current buffer at position. It has noeffect on the undo list or on the buffer’s modification status.
The momentary display remains until the next input event. If the next input event
is char, momentary-string-display ignores it and returns. Otherwise, that event
remains buffered for subsequent use as input. Thus, typing char will simply remove
the string from the display, while typing (say) C-f will remove the string from thedisplay and later (presumably) move point forward. The argument char is a space by
default.

The return value of momentary-string-display is not meaningful.
If the string string does not contain control characters, you can do the same job ina more general way by creating (and then subsequently deleting) an overlay with abefore-string property. See Section 41.9.2 [Overlay Properties], page 1153.
If message is non-nil, it is displayed in the echo area while string is displayed in thebuffer. If it is nil, a default message says to type char to continue.
In this example, point is initially located at the beginning of the second line:---------- Buffer: foo ---------This is the contents of foo.
?Second line.
---------- Buffer: foo ---------(momentary-string-display"**** Important Message! ****"(point) ?\r"Type RET when done reading")⇒ tChapter 41: Emacs Display

1150---------- Buffer: foo ---------This is the contents of foo.
**** Important Message! ****Second line.
---------- Buffer: foo ------------------- Echo Area ---------Type RET when done reading---------- Echo Area ----------

41.9 Overlays
You can use overlays to alter the appearance of a buffer’s text on the screen, for the sake ofpresentation features. An overlay is an object that belongs to a particular buffer, and has
a specified beginning and end. It also has properties that you can examine and set; these
affect the display of the text within the overlaid portion of the buffer.
Editing the text of the buffer adjusts the beginning and end of each overlay so that it
stays with the text. When you create the overlay, you can specify whether text inserted at
the beginning should be inside the overlay or outside, and likewise for the end of the overlay.

41.9.1 Managing Overlays
This section describes the functions to create, delete and move overlays, and to examine
their contents. Overlay changes are not recorded in the buffer’s undo list, since the overlays
are not considered part of the buffer’s contents.

overlayp object[Function]

This function returns t if object is an overlay.

make-overlay start end &optional buffer front-advance rear-advance[Function]
This function creates and returns an overlay that belongs to buffer and ranges fromstart to end. Both start and end must specify buffer positions; they may be integers
or markers. If buffer is omitted, the overlay is created in the current buffer.
An overlay whose start and end specify the same buffer position is known as empty. A
non-empty overlay can become empty if the text between its start and end is deleted.
When that happens, the overlay is by default not deleted, but you can cause it to bedeleted by giving it the ‘evaporate’ property (see Section 41.9.2 [Overlay Properties],
page 1153).
The arguments front-advance and rear-advance specify what happens when text isinserted at the beginning (i.e., before start) and at the end. If they are both nil,the default, then the overlay extends to include any text inserted at the beginning,
but not text inserted at the end. If front-advance is non-nil, text inserted at the
beginning of the overlay is excluded from the overlay. If rear-advance is non-nil, text
inserted at the end of the overlay is included in the overlay.

overlay-start overlay[Function]

This function returns the position at which overlay starts, as an integer.

overlay-end overlay
This function returns the position at which overlay ends, as an integer.

[Function]

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overlay-buffer overlay[Function]
This function returns the buffer that overlay belongs to. It returns nil if overlay has
been deleted.

delete-overlay overlay[Function]
This function deletes the specified overlay. The overlay continues to exist as a Lisp
object, and its property list is unchanged, but it ceases to be attached to the buffer it
belonged to, and ceases to have any effect on display.

A deleted overlay is not permanently disconnected. You can give it a position in abuffer again by calling move-overlay.

move-overlay overlay start end &optional buffer[Function]
This function moves overlay to buffer, and places its bounds at start and end in thatbuffer. Both arguments start and end must specify buffer positions; they may be
integers or markers.
If buffer is omitted, overlay stays in the same buffer it was already associated with; ifoverlay was previously deleted (and thus isn’t associated with any buffer), it goes into
the current buffer.

The return value is overlay.
This function is the only valid way to change the endpoints of an overlay.

remove-overlays &optional start end name value[Function]
This function removes all the overlays between start and end whose property namehas the specified value. It can move the endpoints of the overlays in the region, or
split them.
If name is omitted or nil, it means to delete all overlays in the specified region. If
start and/or end are omitted or nil, that means the beginning and end of the buffer
respectively. Therefore, (remove-overlays) removes all the overlays in the current
buffer.

copy-overlay overlay[Function]
This function returns a copy of overlay. The copy has the same endpoints andproperties as overlay. However, the text insertion type for the start of the overlay andfor the end of the overlay are set to their default values.

Here are some examples:;; Create an overlay.
(setq foo (make-overlay 1 10))⇒ #<overlay from 1 to 10 in display.texi>(overlay-start foo)
⇒ 1

Chapter 41: Emacs Display(overlay-end foo)
⇒ 10
(overlay-buffer foo)⇒ #<buffer display.texi>;; Give it a property we can check later.
(overlay-put foo 'happy t)⇒ t;; Verify the property is present.
(overlay-get foo 'happy)⇒ t;; Move the overlay.
(move-overlay foo 5 20)⇒ #<overlay from 5 to 20 in display.texi>(overlay-start foo)
⇒ 5(overlay-end foo)
⇒ 20;; Delete the overlay.
(delete-overlay foo)
⇒ nil;; Verify it is deleted.
foo⇒ #<overlay in no buffer>;; A deleted overlay has no position.
(overlay-start foo)
⇒ nil(overlay-end foo)
⇒ nil(overlay-buffer foo)
⇒ nil;; Undelete the overlay.
(move-overlay foo 1 20)⇒ #<overlay from 1 to 20 in display.texi>;; Verify the results.
(overlay-start foo)
⇒ 1
(overlay-end foo)
⇒ 20
(overlay-buffer foo)⇒ #<buffer display.texi>;; Moving and deleting the overlay does not change its properties.
(overlay-get foo 'happy)
⇒ t

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41.9.2 Overlay Properties
Overlay properties are like text properties in that the properties that alter how a characteris displayed can come from either source. But in most respects they are different. See
Section 33.19 [Text Properties], page 917, for comparison.
Text properties are considered a part of the text; overlays and their properties are
specifically considered not to be part of the text. Thus, copying text between various buffers
and strings preserves text properties, but does not try to preserve overlays. Changing abuffer’s text properties marks the buffer as modified, while moving an overlay or changing
its properties does not. Unlike text property changes, overlay property changes are notrecorded in the buffer’s undo list.
Since more than one overlay can specify a property value for the same character, Emacs
lets you specify a priority value of each overlay. The priority value is used to decide whichof the overlapping overlays will “win”.
These functions read and set the properties of an overlay:

overlay-get overlay prop

[Function]
This function returns the value of property prop recorded in overlay, if any. If overlay
does not record any value for that property, but it does have a category property
which is a symbol, that symbol’s prop property is used. Otherwise, the value is nil.

overlay-put overlay prop value[Function]
This function sets the value of property prop recorded in overlay to value. It returns
value.

overlay-properties overlay[Function]

This returns a copy of the property list of overlay.
See also the function get-char-property which checks both overlay properties and text
properties for a given character. See Section 33.19.1 [Examining Properties], page 917.
Many overlay properties have special meanings; here is a table of them:priorityThis property’s value determines the priority of the overlay. If you want tospecify a priority value, use either nil (or zero), or a positive integer, or a consof two values. Any other value triggers undefined behavior.
The priority matters when two or more overlays cover the same character andboth specify the same property with different values; the one whose priority
value is higher overrides the other. (For the face property, the higher priority
overlay’s value does not completely override the other value; instead, its individual face attributes override the corresponding face attributes of the faceproperty whose priority is lower.) If two overlays have the same priority value,
and one is “nested” in the other (i.e., covers fewer buffer or string positions),
then the inner one will prevail over the outer one. If neither is nested in theother then you should not make assumptions about which overlay will prevail.
When a Lisp program puts overlays with defined priorities on text that might
have overlays without priorities, this could cause undesirable results, because
any overlay with a positive priority value will override all the overlays without apriority. Since most Emacs features that use overlays don’t specify priorities

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for their overlays, integer priorities should be used with care. Instead of using
integer priorities and risk overriding other overlays, you can use priority values ofthe form (primary . secondary), where the primary value is used as describedabove, and secondary is the fallback value used when primary and the nesting
considerations fail to resolve the precedence between overlays. In particular,
priority value (nil . n), with n a positive integer, allows to have the overlays
ordered by priority when necessary without completely overriding other overlays.
Currently, all overlays take priority over text properties.
If you need to put overlays in priority order, use the sorted argument ofoverlays-at. See Section 41.9.3 [Finding Overlays], page 1157.
window

If the window property is non-nil, then the overlay applies only on that window.

category

If an overlay has a category property, we call it the category of the overlay.
It should be a symbol. The properties of the symbol serve as defaults for theproperties of the overlay.

faceThis property controls the appearance of the text (see Section 41.12 [Faces],
page 1164). The value of the property can be the following:• A face name (a symbol or string).
• An anonymous face: a property list of the form (keyword value ...),
where each keyword is a face attribute name and value is a value for that
attribute.
• A list of faces. Each list element should be either a face name or an
anonymous face. This specifies a face which is an aggregate of the attributesof each of the listed faces. Faces occurring earlier in the list have higher
priority.
• A cons cell of the form (foreground-color . color-name) or(background-color . color-name). This specifies the foreground or
background color, similar to (:foreground color-name) or (:backgroundcolor-name). This form is supported for backward compatibility only, andshould be avoided.

mouse-faceThis property is used instead of face when the mouse is within the range ofthe overlay. However, Emacs ignores all face attributes from this property thatalter the text size (e.g., :height, :weight, and :slant); those attributes arealways the same as in the unhighlighted text.
displayThis property activates various features that change the way text is displayed.
For example, it can make text appear taller or shorter, higher or lower, wider
or narrower, or replaced with an image. See Section 41.16 [Display Property],
page 1198.

help-echo
If an overlay has a help-echo property, then when you move the mouse onto
the text in the overlay, Emacs displays a help string in the echo area, or as atooltip. For details see [Text help-echo], page 926.

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Consecutive characters with the same field property constitute a field. Somemotion functions including forward-word and beginning-of-line stop moving
at a field boundary. See Section 33.19.9 [Fields], page 936.

modification-hooks
This property’s value is a list of functions to be called if any character within
the overlay is changed or if text is inserted strictly within the overlay.
The hook functions are called both before and after each change. If the functions
save the information they receive, and compare notes between calls, they candetermine exactly what change has been made in the buffer text.
When called before a change, each function receives four arguments: the overlay,
nil, and the beginning and end of the text range to be modified.
When called after a change, each function receives five arguments: the overlay,t, the beginning and end of the text range just modified, and the length of the
pre-change text replaced by that range. (For an insertion, the pre-change lengthis zero; for a deletion, that length is the number of characters deleted, and thepost-change beginning and end are equal.)
When these functions are called, inhibit-modification-hooks is boundto non-nil. If the functions modify the buffer, you might want to bindinhibit-modification-hooks to nil, so as to cause the change hooks to run
for these modifications. However, doing this may call your own change hookrecursively, so be sure to prepare for that. See Section 33.34 [Change Hooks],
page 961.
Text properties also support the modification-hooks property, but the details
are somewhat different (see Section 33.19.4 [Special Properties], page 924).
insert-in-front-hooks
This property’s value is a list of functions to be called before and after inserting
text right at the beginning of the overlay. The calling conventions are the same
as for the modification-hooks functions.
insert-behind-hooks
This property’s value is a list of functions to be called before and after inserting
text right at the end of the overlay. The calling conventions are the same as forthe modification-hooks functions.
invisible
The invisible property can make the text in the overlay invisible, which meansthat it does not appear on the screen. See Section 41.6 [Invisible Text], page 1142,
for details.
intangible
The intangible property on an overlay works just like the intangible text
property. It is obsolete. See Section 33.19.4 [Special Properties], page 924, fordetails.
isearch-open-invisible
This property tells incremental search (see Section “Incremental Search” in The
GNU Emacs Manual) how to make an invisible overlay visible, permanently, if
the final match overlaps it. See Section 41.6 [Invisible Text], page 1142.

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isearch-open-invisible-temporary
This property tells incremental search how to make an invisible overlay visible,
temporarily, during the search. See Section 41.6 [Invisible Text], page 1142.
before-string
This property’s value is a string to add to the display at the beginning of theoverlay. The string does not appear in the buffer in any sense—only on thescreen. Note that if the text at the beginning of the overlay is made invisible,
the string will not be displayed.
after-string
This property’s value is a string to add to the display at the end of the overlay.
The string does not appear in the buffer in any sense—only on the screen. Notethat if the text at the end of the overlay is made invisible, the string will not be
displayed.
line-prefix
This property specifies a display spec to prepend to each non-continuation line
at display-time. See Section 41.3 [Truncation], page 1130.
wrap-prefix
This property specifies a display spec to prepend to each continuation line at
display-time. See Section 41.3 [Truncation], page 1130.
evaporate
If this property is non-nil, the overlay is deleted automatically if it becomes
empty (i.e., if its length becomes zero). If you give an empty overlay (seeSection 41.9.1 [Managing Overlays], page 1150) a non-nil evaporate property,
that deletes it immediately. Note that, unless an overlay has this property, it
will not be deleted when the text between its starting and ending positions isdeleted from the buffer.
keymapIf this property is non-nil, it specifies a keymap for a portion of the text. This
keymap takes precedence over most other keymaps (see Section 23.7 [Active
Keymaps], page 489), and it is used when point is within the overlay, where thefront- and rear-advance properties define whether the boundaries are considered
as being within or not.

local-map
The local-map property is similar to keymap but replaces the buffer’s local
map rather than augmenting existing keymaps. This also means it has lower
precedence than minor mode keymaps.
The keymap and local-map properties do not affect a string displayed by the
before-string, after-string, or display properties. This is only relevant for mouseclicks and other mouse events that fall on the string, since point is never on the string. Tobind special mouse events for the string, assign it a keymap or local-map text property.
See Section 33.19.4 [Special Properties], page 924.

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41.9.3 Searching for Overlays
overlays-at pos &optional sorted[Function]
This function returns a list of all the overlays that cover the character at position pos
in the current buffer. If sorted is non-nil, the list is in decreasing order of priority,
otherwise it is in no particular order. An overlay contains position pos if it begins ator before pos, and ends after pos.
To illustrate usage, here is a Lisp function that returns a list of the overlays thatspecify property prop for the character at point:(defun find-overlays-specifying (prop)(let ((overlays (overlays-at (point)))
found)(while overlays(let ((overlay (car overlays)))(if (overlay-get overlay prop)(setq found (cons overlay found))))(setq overlays (cdr overlays)))found))

overlays-in beg end[Function]
This function returns a list of the overlays that overlap the region beg through end.
An overlay overlaps with a region if it contains one or more characters in the region;
empty overlays (see Section 41.9.1 [Managing Overlays], page 1150) overlap if they
are at beg, strictly between beg and end, or at end when end denotes the position at
the end of the accessible part of the buffer.

next-overlay-change pos[Function]
This function returns the buffer position of the next beginning or end of an overlay,
after pos. If there is none, it returns (point-max).

previous-overlay-change pos[Function]
This function returns the buffer position of the previous beginning or end of an overlay,
before pos. If there is none, it returns (point-min).

As an example, here’s a simplified (and inefficient) version of the primitive function
next-single-char-property-change (see Section 33.19.3 [Property Search], page 921). It
searches forward from position pos for the next position where the value of a given property
prop, as obtained from either overlays or text properties, changes.
(defun next-single-char-property-change (position prop)(save-excursion(goto-char position)(let ((propval (get-char-property (point) prop)))(while (and (not (eobp))(eq (get-char-property (point) prop) propval))(goto-char (min (next-overlay-change (point))(next-single-property-change (point) prop)))))(point)))41.10 Size of Displayed Text
Since not all characters have the same width, these functions let you check the width ofa character. See Section 33.17.1 [Primitive Indent], page 910, and Section 31.2.5 [ScreenLines], page 858, for related functions.

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char-width char

[Function]
This function returns the width in columns of the character char, if it were displayedin the current buffer (i.e., taking into account the buffer’s display table, if any; see
Section 41.23.2 [Display Tables], page 1243). The width of a tab character is usually
tab-width (see Section 41.23.1 [Usual Display], page 1242).

char-uppercase-p char

[Function]

Return non-nil if char is an uppercase character according to Unicode.

string-width string &optional from to[Function]
This function returns the width in columns of the string string, if it were displayedin the current buffer and the selected window. Optional arguments from and to
specify the substring of string to consider, and are interpreted as in substring (seeSection 4.3 [Creating Strings], page 55).
The return value is an approximation: it only considers the values returned bychar-width for the constituent characters, always takes a tab character as taking
tab-width columns, ignores display properties and fonts, etc. For these reasons,
we recommend using window-text-pixel-size or string-pixel-width, described
below, instead.

truncate-string-to-width string width &optional start-column
padding ellipsis ellipsis-text-property[Function]

This function returns a new string that is a truncation of string which fits within
width columns on display.
If string is narrower than width, the result is equal to string; otherwise excess characters
are omitted from the result. If a multi-column character in string exceeds the goal
width, that character is omitted from the result. Thus, the result can sometimes fallshort of width, but cannot go beyond it.
The optional argument start-column specifies the starting column; it defaults to zero.
If this is non-nil, then the first start-column columns of the string are omitted from theresult. If one multi-column character in string extends across the column start-column,that character is omitted.
The optional argument padding, if non-nil, is a padding character added at the
beginning and end of the result string, to extend it to exactly width columns. The
padding character is appended at the end of the result if it falls short of width, asmany times as needed to reach width. It is also prepended at the beginning of theresult if a multi-column character in string extends across the column start-column.
If ellipsis is non-nil, it should be a string which will replace the end of string when it
is truncated. In this case, more characters will be removed from string to free enoughspace for ellipsis to fit within width columns. However, if the display width of stringis less than the display width of ellipsis, ellipsis will not be appended to the result. If
ellipsis is non-nil and not a string, it stands for the value returned by the function
truncate-string-ellipsis, described below.
The optional argument ellipsis-text-property, if non-nil, means hide the excess parts ofstring with a display text property (see Section 41.16 [Display Property], page 1198)
showing the ellipsis, instead of actually truncating the string.

Chapter 41: Emacs Display

1159(truncate-string-to-width "\tab\t" 12 4)⇒ "ab"(truncate-string-to-width "\tab\t" 12 4 ?\s)⇒ "ab "This function uses string-width and char-width to find the suitable truncation
point when string is too wide, so it suffers from the same basic issues as string-width
does. In particular, when character composition happens within string, the display
width of a string could be smaller than the sum of widths of the constituent characters,
and this function might return inaccurate results.
[Function]
This function returns the string to be used as an ellipses in truncate-string-towidth and other similar contexts. The value is that of the variable truncate-stringellipsis, if it’s non-nil, the string with the single character U+2026 HORIZONTAL ELLIPSIS if that character can be displayed on the selected frame, and thestring ‘...’ otherwise.

truncate-string-ellipsis

The following function returns the size in pixels of text as if it were displayed in a given
window. This function is used by fit-window-to-buffer and fit-frame-to-buffer (seeSection 29.5 [Resizing Windows], page 703) to make a window exactly as large as the text it
contains.

window-text-pixel-size &optional window from to x-limit y-limit
mode-lines ignore-line-at-end[Function]

This function returns the size of the text of window’s buffer in pixels. window must
be a live window and defaults to the selected one. The return value is a cons of the
maximum pixel-width of any text line and the maximum pixel-height of all text lines.
This function exists to allow Lisp programs to adjust the dimensions of window tothe buffer text it needs to display, and for other similar situations.
The return value can also optionally (see below) include the buffer position of the firstline whose dimensions were measured.
The optional argument from, if non-nil, specifies the first text position to consider,and defaults to the minimum accessible position of the buffer. If from is t, it stands
for the minimum accessible position that is not a newline character. If from is a cons,
its car specifies a buffer position, and its cdr specifies the vertical offset in pixels fromthat position to the first screen line whose text is to be measured. (The measurement
will start from the visual beginning of that screen line.) In that case, the return value
will instead be a list of the pixel-width, pixel-height, and the buffer position of the firstline that was measured. The optional argument to, if non-nil, specifies the last text
position to consider, and defaults to the maximum accessible position of the buffer. If
to is t, it stands for the maximum accessible position that is not a newline character.
The optional argument x-limit, if non-nil, specifies the maximum X coordinate beyond
which text should be ignored; it is therefore also the largest value of pixel-width thatthe function can return. If x-limit nil or omitted, it means to use the pixel-width ofwindow’s body (see Section 29.4 [Window Sizes], page 699); this default means thattext of truncated lines wider than the window will be ignored. This default is usefulwhen the caller does not intend to change the width of window. Otherwise, the callerChapter 41: Emacs Display

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should specify here the maximum width window’s body may assume; in particular, if
truncated lines are expected and their text needs to be accounted for, x-limit should
be set to a large value. Since calculating the width of long lines can take some time,it’s always a good idea to make this argument as small as needed; in particular, if thebuffer might contain long lines that will be truncated anyway.
The optional argument y-limit, if non-nil, specifies the maximum Y coordinate beyond
which text is to be ignored; it is therefore also the maximum pixel-height that thefunction can return. If y-limit is nil or omitted, it means to consider all the lines oftext till the buffer position specified by to. Since calculating the pixel-height of a large
buffer can take some time, it makes sense to specify this argument; in particular, if
the caller does not know the size of the buffer.
The optional argument mode-lines nil or omitted means to not include the height ofthe mode-, tab- or header-line of window in the return value. If it is either the symbol
mode-line, tab-line or header-line, include only the height of that line, if present,in the return value. If it is t, include the height of all of these lines, if present, in the
return value.
The optional argument ignore-line-at-end controls whether or not to count the heightof text in to’s screen line as part of the returned pixel-height. This is useful if your Lisp
program is only interested in the dimensions of text up to and excluding the visual beginningof to’s screen line.
window-text-pixel-size treats the text displayed in a window as a whole and does
not care about the size of individual lines. The following function does.

window-lines-pixel-dimensions &optional window first last bodyinverse left

[Function]

This function calculates the pixel dimensions of each line displayed in the specified
window. It does so by walking window’s current glyph matrix—a matrix storing theglyph (see Section 41.23.4 [Glyphs], page 1245) of each buffer character currently
displayed in window. If successful, it returns a list of cons pairs representing the x- andy-coordinates of the lower right corner of the last character of each line. Coordinates
are measured in pixels from an origin (0, 0) at the top-left corner of window. window
must be a live window and defaults to the selected one.
If the optional argument first is an integer, it denotes the index (starting with 0) of
the first line of window’s glyph matrix to be returned. Note that if window has aheader line, the line with index 0 is that header line. If first is nil, the first line tobe considered is determined by the value of the optional argument body: If body is
non-nil, this means to start with the first line of window’s body, skipping any headerline, if present. Otherwise, this function will start with the first line of window’s glyph
matrix, possibly the header line.
If the optional argument last is an integer, it denotes the index of the last line ofwindow’s glyph matrix that shall be returned. If last is nil, the last line to beconsidered is determined by the value of body: If body is non-nil, this means to use
the last line of window’s body, omitting window’s mode line, if present. Otherwise,
this means to use the last line of window which may be the mode line.
The optional argument inverse, if nil, means that the y-pixel value returned for any
line specifies the distance in pixels from the left edge (body edge if body is non-nil)Chapter 41: Emacs Display1161

of window to the right edge of the last glyph of that line. inverse non-nil means thatthe y-pixel value returned for any line specifies the distance in pixels from the rightedge of the last glyph of that line to the right edge (body edge if body is non-nil) of
window. This is useful for determining the amount of slack space at the end of eachline.
The optional argument left, if non-nil means to return the x- and y-coordinates ofthe lower left corner of the leftmost character on each line. This is the value thatshould be used for windows that mostly display text from right to left.
If left is non-nil and inverse is nil, this means that the y-pixel value returned forany line specifies the distance in pixels from the left edge of the last (leftmost) glyphof that line to the right edge (body edge if body is non-nil) of window. If left andinverse are both non-nil, the y-pixel value returned for any line specifies the distancein pixels from the left edge (body edge if body is non-nil) of window to the left edgeof the last (leftmost) glyph of that line.
This function returns nil if the current glyph matrix of window is not up-to-date
which usually happens when Emacs is busy, for example, when processing a command.
The value should be retrievable though when this function is run from an idle timer
with a delay of zero seconds.

buffer-text-pixel-size &optional buffer-or-name window from to
x-limit y-limit[Function]

This is much like window-text-pixel-size, but can be used when the buffer isn’t
shown in a window. (window-text-pixel-size is faster when it is, so this function
shouldn’t be used in that case.)
buffer-or-name must specify a live buffer or the name of a live buffer and defaults tothe current buffer. window must be a live window and defaults to the selected one;the function will compute the text dimensions as if buffer is displayed in window. The
return value is a cons of the maximum pixel-width of any text line and the pixel-heightof all the text lines of the buffer specified by buffer-or-name.
The optional arguments x-limit and y-limit have the same meaning as withwindow-text-pixel-size.

string-pixel-width string[Function]
This is a convenience function that uses window-text-pixel-size to compute thewidth of string (in pixels).
[Function]
This function returns the height in pixels of the line at point in the selected window. The
value includes the line spacing of the line (see Section 41.11 [Line Height], page 1162).

line-pixel-height

string-glyph-split string[Function]
When character compositions are in effect, sequence of characters can be composedfor display to form grapheme clusters, for example to display accented characters,
or ligatures, or Emoji, or when complex text shaping requires that for some scripts.
When that happens, characters no longer map in a simple way to display columns, anddisplay layout decisions with such strings, such as truncating too wide strings, can be
a complex job. This function helps in performing such jobs: it splits up its argument

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string into a list of substrings, where each substring produces a single grapheme clusterthat should be displayed as a unit. Lisp programs can then use this list to constructvisually-valid substrings of string which will look correctly on display, or computethe width of any substring of string by adding the width of its constituents in the
returned list, etc.
For instance, if you want to display a string without the first glyph, you can say:(apply #'insert (cdr (string-glyph-split string))))When a buffer is displayed with line numbers (see Section “Display Custom” in The
GNU Emacs Manual), it is sometimes useful to know the width taken for displaying the line
numbers. The following function is for Lisp programs which need this information for layout
calculations.

line-number-display-width &optional pixelwise[Function]
This function returns the width used for displaying the line numbers in the selected
window. If the optional argument pixelwise is the symbol columns, the return value isa float number of the frame’s canonical columns; if pixelwise is t or any other non-nil
value, the value is an integer and is measured in pixels. If pixelwise is omitted or nil,the value is the integer number of columns of the font defined for the line-number
face, and doesn’t include the 2 columns used to pad the numbers on display. If line
numbers are not displayed in the selected window, the value is zero regardless of thevalue of pixelwise. Use with-selected-window (see Section 29.3 [Selecting Windows],
page 696) if you need this information about another window.

41.11 Line Height
The total height of each display line consists of the height of the contents of the line, plus
optional additional vertical line spacing above or below the display line.
The height of the line contents is the maximum height of any character or image on that
display line, including the final newline if there is one. (A display line that is continued
doesn’t include a final newline.) That is the default line height, if you do nothing to specify
a greater height. (In the most common case, this equals the height of the corresponding
frame’s default font, see Section 30.3.2 [Frame Font], page 797.)
There are several ways to explicitly specify a larger line height, either by specifying an
absolute height for the display line, or by specifying vertical space. However, no matter
what you specify, the actual line height can never be less than the default.
A newline can have a line-height text or overlay property that controls the total heightof the display line ending in that newline. The property value can be one of several forms:t

If the property value is t, the newline character has no effect on the displayed height of the line—the visible contents alone determine the height. The
line-spacing property of the newline, described below, is also ignored in thiscase. This is useful for tiling small images (or image slices) without adding
blank areas between the images.

(height total)
If the property value is a list of the form shown, that adds extra space below
the display line. First Emacs uses height as a height spec to control extra spaceChapter 41: Emacs Display

1163

above the line; then it adds enough space below the line to bring the total line
height up to total. In this case, any value of line-spacing property for the
newline is ignored.
Any other kind of property value is a height spec, which translates into a number—the
specified line height. There are several ways to write a height spec; here’s how each of themtranslates into a number:
integerIf the height spec is a positive integer, the height value is that integer.

float

If the height spec is a float, float, the numeric height value is float times theframe’s default line height.

(face . ratio)
If the height spec is a cons of the format shown, the numeric height is ratio
times the height of face face. ratio can be any type of number, or nil whichmeans a ratio of 1. If face is t, it refers to the current face.
(nil . ratio)
If the height spec is a cons of the format shown, the numeric height is ratio
times the height of the contents of the line.
Thus, any valid height spec determines the height in pixels, one way or another. If theline contents’ height is less than that, Emacs adds extra vertical space above the line toachieve the specified total height.
If you don’t specify the line-height property, the line’s height consists of the contents’height plus the line spacing. There are several ways to specify the line spacing for different
parts of Emacs text.
On graphical terminals, you can specify the line spacing for all lines in a frame, using theline-spacing frame parameter (see Section 30.4.3.4 [Layout Parameters], page 810). However, if the default value of line-spacing is non-nil, it overrides the frame’s line-spacing
parameter. An integer specifies the number of pixels put below lines. A floating-point
number specifies the spacing relative to the frame’s default line height.
You can specify the line spacing for all lines in a buffer via the buffer-local line-spacing
variable. An integer specifies the number of pixels put below lines. A floating-point number
specifies the spacing relative to the default frame line height. This overrides line spacings
specified for the frame.
Finally, a newline can have a line-spacing text or overlay property that can enlarge
the default frame line spacing and the buffer local line-spacing variable: if its value islarger than the buffer or frame defaults, that larger value is used instead, for the display
line ending in that newline (unless the newline also has the line-height property whose
value is one of the special values which cause line-spacing to be ignored, see above).
One way or another, these mechanisms specify a Lisp value for the spacing of each line.
The value is a height spec, and it translates into a Lisp value as described above. However,in this case the numeric height value specifies the line spacing, rather than the line height.
On text terminals, the line spacing cannot be altered.

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41.12 Faces
A face is a collection of graphical attributes for displaying text: font, foreground color,background color, optional underlining, etc. Faces control how Emacs displays text in buffers,
as well as other parts of the frame such as the mode line.
One way to represent a face is as a property list of attributes, like (:foreground "red":weight bold). Such a list is called an anonymous face. For example, you can assign ananonymous face as the value of the face text property, and Emacs will display the underlying
text with the specified attributes. See Section 33.19.4 [Special Properties], page 924.
More commonly, a face is referred to via a face name: a Lisp symbol associated with a set offace attributes1 . Named faces are defined using the defface macro (see Section 41.12.2 [Defining Faces], page 1168). Emacs comes with several standard named faces (see Section 41.12.8[Basic Faces], page 1178).
Some parts of Emacs require named faces (e.g., the functions documented in
Section 41.12.3 [Attribute Functions], page 1171). Unless otherwise stated, we will use theterm face to refer only to named faces.

facep object[Function]
This function returns a non-nil value if object is a named face: a Lisp symbol or
string which serves as a face name. Otherwise, it returns nil.

41.12.1 Face Attributes
Face attributes determine the visual appearance of a face. The following table lists all theface attributes, their possible values, and their effects.
Apart from the values given below, each face attribute can have the value unspecified.
This special value means that the face doesn’t specify that attribute directly. An
unspecified attribute tells Emacs to refer instead to a parent face (see the description:inherit attribute below); or, failing that, to an underlying face (see Section 41.12.4[Displaying Faces], page 1174). (However, unspecified is not a valid value in defface.)
A face attribute can also have the value reset. This special value stands for the value ofthe corresponding attribute of the default face.
The default face must explicitly specify all attributes, and cannot use the special value
reset.
Some of these attributes are meaningful only on certain kinds of displays. If your display
cannot handle a certain attribute, the attribute is ignored.
:family

Font family name (a string). See Section “Fonts” in The GNU Emacs Manual,
for more information about font families. The function font-family-list (seebelow) returns a list of available family names.

:foundryThe name of the font foundry for the font family specified by the :family
attribute (a string). See Section “Fonts” in The GNU Emacs Manual.

:widthRelative character width. This should be one of the symbols ultra-condensed,
extra-condensed, condensed, semi-condensed, normal, regular, medium,semi-expanded, expanded, extra-expanded, or ultra-expanded.

1

For backward compatibility, you can also use a string to specify a face name; that is equivalent to a Lisp
symbol with the same name.

Chapter 41: Emacs Display

1165:height

The height of the font. In the simplest case, this is an integer in units of 1/10
point.
The value can also be floating point or a function, which specifies the height
relative to an underlying face (see Section 41.12.4 [Displaying Faces], page 1174).
A floating-point value specifies the amount by which to scale the height of theunderlying face. A function value is called with one argument, the height of theunderlying face, and returns the height of the new face. If the function is passed
an integer argument, it must return an integer.
The height of the default face must be specified using an integer; floating pointand function values are not allowed.

:weight

Font weight—one of the symbols (from densest to faintest) ultra-bold,
extra-bold, bold, semi-bold, normal, semi-light, light, extra-light, or
ultra-light. On text terminals which support variable-brightness text, any
weight greater than normal is displayed as extra bright, and any weight lessthan normal is displayed as half-bright.

:slantFont slant—one of the symbols italic, oblique, normal, reverse-italic, orreverse-oblique. On text terminals that support variable-brightness text,
slanted text is displayed as half-bright.

:foreground
Foreground color, a string. The value can be a system-defined color name, ora hexadecimal color specification. See Section 30.23 [Color Names], page 846.
On black-and-white displays, certain shades of gray are implemented by stipple
patterns.
:distant-foreground
Alternative foreground color, a string. This is like :foreground but the color isonly used as a foreground when the background color is near to the foregroundthat would have been used. This is useful for example when marking text (i.e.,
the region face). If the text has a foreground that is visible with the region face,that foreground is used. If the foreground is near the region face background,:distant-foreground is used instead so the text is readable.
:background
Background color, a string. The value can be a system-defined color name, or ahexadecimal color specification. See Section 30.23 [Color Names], page 846.
:underline
Whether or not characters should be underlined, and in what way. The possible
values of the :underline attribute are:nil

Don’t underline.

t

Underline with the foreground color of the face.

color

Underline in color color, a string specifying a color.

(:color color :style style :position position)color is either a string, or the symbol foreground-color, meaning
the foreground color of the face. Omitting the attribute :color

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means to use the foreground color of the face. style should bea symbol line or wave, meaning to use a straight or wavy line.
Omitting the attribute :style means to use a straight line. position,
if non-nil, means to display the underline at the descent of the text,
instead of at the baseline level. If it is a number, then it specifies
the amount of pixels above the descent to display the underline.
:overline
Whether or not characters should be overlined, and in what color. If the value
is t, overlining uses the foreground color of the face. If the value is a string,overlining uses that color. The value nil means do not overline.
:strike-through
Whether or not characters should be strike-through, and in what color. The
value is used like that of :overline.
:box

Whether or not a box should be drawn around characters, its color, the widthof the box lines, and 3D appearance. Here are the possible values of the :box
attribute, and what they mean:
nil

Don’t draw a box.

t

Draw a box with lines of width 1, in the foreground color.

color

Draw a box with lines of width 1, in color color.

(:line-width (vwidth . hwidth) :color color :style style)
You can explicitly specify all aspects of the box with a plist on thisform. Any element in this plist can be omitted.
The values of vwidth and hwidth specify respectively the width ofthe vertical and horizontal lines to draw; they default to (1 . 1). A
negative horizontal or vertical width −n means to draw a line ofwidth n that occupies the space of the underlying text, thus avoiding
any increase in the character height or width. For simplification thewidth could be specified with only a single number n instead of alist, such case is equivalent to ((abs n) . n).
The value of color specifies the color to draw with. The default isthe background color of the face for 3D boxes and flat-button,
and the foreground color of the face for other boxes.
The value of style specifies whether to draw a 3D box. If it isreleased-button, the box looks like a 3D button that is not beingpressed. If it is pressed-button, the box looks like a 3D button
that is being pressed. If it is nil, flat-button or omitted, a plain
2D box is used.
If you use the :box face attribute on strings displayed instead of buffer text via
the display text property, special considerations might apply if the surrounding
buffer text also has the :box face attribute. See Section 41.16.1 [Replacing
Specs], page 1199.

Chapter 41: Emacs Display

1167:inverse-video
Whether or not characters should be displayed in inverse video. The value
should be t (yes) or nil (no).
:stipple

The background stipple, a bitmap.
The value can be a string; that should be the name of a file containing externalformat X bitmap data. The file is found in the directories listed in the variable
x-bitmap-file-path.
Alternatively, the value can specify the bitmap directly, with a list of the form
(width height data). Here, width and height specify the size in pixels, anddata is a string containing the raw bits of the bitmap, row by row. Each row
occupies (width+7)/8 consecutive bytes in the string (which should be a unibyte
string for best results). This means that each row always occupies at least one
whole byte.
If the value is nil, that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it is usedautomatically to handle certain shades of gray.

:font

The font used to display the face. Its value should be a font object or a fontset. If
it is a font object, it specifies the font to be used by the face for displaying ASCII
characters. See Section 41.12.12 [Low-Level Font], page 1184, for information
about font objects, font specs, and font entities. See Section 41.12.11 [Fontsets],page 1182, for information about fontsets.
When specifying this attribute using set-face-attribute or set-face-font(see Section 41.12.3 [Attribute Functions], page 1171), you may also supply afont spec, a font entity, or a string. Emacs converts such values to an appropriate
font object, and stores that font object as the actual attribute value. If you
specify a string, the contents of the string should be a font name (see Section“Fonts” in The GNU Emacs Manual); if the font name is an XLFD containing
wildcards, Emacs chooses the first font matching those wildcards. Specifying this
attribute also changes the values of the :family, :foundry, :width, :height,:weight, and :slant attributes.

:inherit

The name of a face from which to inherit attributes, or a list of face names.
Attributes from inherited faces are merged into the face like an underlying
face would be, with higher priority than underlying faces (see Section 41.12.4[Displaying Faces], page 1174). If the face to inherit from is unspecified, it istreated the same as nil, since Emacs never merges :inherit attributes. If alist of faces is used, attributes from faces earlier in the list override those fromlater faces.

:extend

Whether or not this face will be extended beyond end of line and will affect thedisplay of the empty space between the end of line and the edge of the window.
The value should be t to display the empty space between end of line and edgeof the window using this face, or nil to not use this face for the space between
the end of the line and the edge of the window. When Emacs merges several
faces for displaying the empty space beyond end of line, only those faces with:extend non-nil will be merged. By default, only a small number of faces,

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notably, region, have this attribute set. This attribute is different from theothers in that when a theme doesn’t specify an explicit value for a face, the value
from the original face definition by defface is inherited (see Section 41.12.2[Defining Faces], page 1168).
Some modes, like hl-line-mode, use a face with an :extend property to markthe entire current line. Note, however, that Emacs will always allow you tomove point after the final character in a buffer, and if the buffer ends with anewline character, point can be placed on what is seemingly a line at the endof the buffer—but Emacs can’t highlight that “line”, because it doesn’t reallyexist.

font-family-list &optional frame[Function]
This function returns a list of available font family names. The optional argument
frame specifies the frame on which the text is to be displayed; if it is nil, the selected
frame is used.
[User Option]
This variable specifies the minimum distance between the baseline and the underline,
in pixels, when displaying underlined text.

underline-minimum-offset[User Option]
This variable specifies a list of directories for searching for bitmap files, for the:stipple attribute.

x-bitmap-file-pathbitmap-spec-p object[Function]
This returns t if object is a valid bitmap specification, suitable for use with :stipple(see above). It returns nil otherwise.

41.12.2 Defining Faces
The usual way to define a face is through the defface macro. This macro associates a facename (a symbol) with a default face spec. A face spec is a construct which specifies what
attributes a face should have on any given terminal; for example, a face spec might specify
one foreground color on high-color terminals, and a different foreground color on low-color
terminals.
People are sometimes tempted to create a variable whose value is a face name. In thevast majority of cases, this is not necessary; the usual procedure is to define a face withdefface, and then use its name directly.
Note that once you have defined a face (usually with defface), you cannot later undefine
this face safely, except by restarting Emacs.

defface face spec doc [keyword value]. . .

[Macro]This macro declares face as a named face whose default face spec is given by spec.
You should not quote the symbol face, and it should not end in ‘-face’ (that would be
redundant). The argument doc is a documentation string for the face. The additional
keyword arguments have the same meanings as in defgroup and defcustom (seeSection 15.1 [Common Keywords], page 277).
If face already has a default face spec, this macro does nothing.

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The default face spec determines face’s appearance when no customizations are ineffect (see Chapter 15 [Customization], page 277). If face has already been customized(via Custom themes or via customizations read from the init file), its appearance
is determined by the custom face spec(s), which override the default face spec spec.
However, if the customizations are subsequently removed, the appearance of face willagain be determined by its default face spec.
As an exception, if you evaluate a defface form with C-M-x (eval-defun) or with
C-x C-e (eval-last-sexp) in Emacs Lisp mode, a special feature of these commands
overrides any custom face specs on the face, causing the face to reflect exactly what
the defface says.
The spec argument is a face spec, which states how the face should appear on different
kinds of terminals. It should be an alist whose elements each have the form
(display . plist)
display specifies a class of terminals (see below). plist is a property list of face
attributes and their values, specifying how the face appears on such terminals. For
backward compatibility, you can also write an element as (display plist).
The display part of an element of spec determines which terminals the element matches.
If more than one element of spec matches a given terminal, the first element thatmatches is the one used for that terminal. There are three possibilities for display:default

This element of spec doesn’t match any terminal; instead, it specifies
defaults that apply to all terminals. This element, if used, must be thefirst element of spec. Each of the following elements can override any or
all of these defaults.

tThis element of spec matches all terminals. Therefore, any subsequentelements of spec are never used. Normally t is used in the last (or only)
element of spec.

a listIf display is a list, each element should have the form (characteristic
value...). Here characteristic specifies a way of classifying terminals,
and the values are possible classifications which display should apply to.
Here are the possible values of characteristic:type

The kind of window system the terminal uses—either graphic(any graphics-capable display), x, pc (for the MS-DOS console), w32 (for MS Windows 9X/NT/2K/XP), haiku (forHaiku), pgtk (for pure GTK), or tty (a non-graphics-capable
display). See Section 41.25 [Window Systems], page 1248.

class

What kinds of colors the terminal supports—either color,grayscale, or mono.

backgroundThe kind of background—either light or dark.
min-colors
An integer that represents the minimum number of colors
the terminal should support. This matches a terminal if its
display-color-cells value is at least the specified integer.

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supports

Whether or not the terminal can display the face attributes
given in value . . . (see Section 41.12.1 [Face Attributes],
page 1164). See [Display Face Attribute Testing], page 850,
for more information on exactly how this testing is done.

If an element of display specifies more than one value for a given
characteristic, any of those values is acceptable. If display has more than
one element, each element should specify a different characteristic; theneach characteristic of the terminal must match one of the values specified
for it in display.
For example, here’s the definition of the standard face highlight:(defface highlight'((((class color) (min-colors 88) (background light)):background "darkseagreen2")(((class color) (min-colors 88) (background dark)):background "darkolivegreen")(((class color) (min-colors 16) (background light)):background "darkseagreen2")(((class color) (min-colors 16) (background dark)):background "darkolivegreen")(((class color) (min-colors 8)):background "green" :foreground "black")(t :inverse-video t))"Basic face for highlighting.":group 'basic-faces)
Internally, Emacs stores each face’s default spec in its face-defface-spec symbol
property (see Section 9.4 [Symbol Properties], page 138). The saved-face property stores
any face spec saved by the user using the customization buffer; the customized-faceproperty stores the face spec customized for the current session, but not saved; and thetheme-face property stores an alist associating the active customization settings and Custom
themes with the face specs for that face. The face’s documentation string is stored in theface-documentation property.
Normally, a face is declared just once, using defface, and any further changes to
its appearance are applied using the Customize framework (e.g., via the Customize userinterface or via the custom-set-faces function; see Section 15.5 [Applying Customizations],
page 294), or by face remapping (see Section 41.12.5 [Face Remapping], page 1175). In
the rare event that you need to change a face spec directly from Lisp, you can use theface-spec-set function.

face-spec-set face spec &optional spec-type[Function]
This function applies spec as a face spec for face. spec should be a face spec, as
described in the above documentation for defface.
This function also defines face as a valid face name if it is not already one, and(re)calculates its attributes on existing frames.
The optional argument spec-type determines which spec to set. If it is omitted or
nil or face-override-spec, this function sets the override spec, which overrides faceChapter 41: Emacs Display

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specs on face of all the other types mentioned below. This is useful when calling thisfunction outside of Custom code. If spec-type is customized-face or saved-face,
this function sets the customized spec or the saved custom spec, respectively. If it
is face-defface-spec, this function sets the default face spec (the same one set bydefface). If it is reset, this function clears out all customization specs and override
specs from face (in this case, the value of spec is ignored). The effect of any othervalue of spec-type on the face specs is reserved for internal use, but the function will
still define face itself and recalculate its attributes, as described above.

41.12.3 Face Attribute Functions
This section describes functions for directly accessing and modifying the attributes of a
named face.

face-attribute face attribute &optional frame inherit[Function]
This function returns the value of the attribute attribute for face on frame. See
Section 41.12.1 [Face Attributes], page 1164, for the supported attributes.
If frame is omitted or nil, that means the selected frame (see Section 30.10 [Input
Focus], page 824). If frame is t, this function returns the value of the specified attributefor newly-created frames, i.e. the value of the attribute before applying the face spec inthe face’s defface definition (see Section 41.12.2 [Defining Faces], page 1168) or the
spec set by face-spec-set. This default value of attribute is normally unspecified,unless you have specified some other value using set-face-attribute; see below.
If inherit is nil, only attributes directly defined by face are considered, so the return
value may be unspecified, or a relative value. If inherit is non-nil, face’s definitionof attribute is merged with the faces specified by its :inherit attribute; however the
return value may still be unspecified or relative. If inherit is a face or a list of faces,
then the result is further merged with that face (or faces), until it becomes specified
and absolute.
To ensure that the return value is always specified and absolute, use a value of default
for inherit; this will resolve any unspecified or relative values by merging with thedefault face (which is always completely specified).
For example,(face-attribute 'bold :weight)⇒ boldface-attribute-relative-p attribute value[Function]
This function returns non-nil if value, when used as the value of the face attributeattribute, is relative. This means it would modify, rather than completely override,any value that comes from a subsequent face in the face list or that is inherited fromanother face.
unspecified is a relative value for all attributes. For :height, floating point andfunction values are also relative.
For example:(face-attribute-relative-p :height 2.0)
⇒ tChapter 41: Emacs Display

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face-all-attributes face &optional frame[Function]
This function returns an alist of attributes of face. The elements of the result are
name-value pairs of the form (attr-name . attr-value). Optional argument frame
specifies the frame whose definition of face to return; if omitted or nil, the returned
value describes the default attributes of face for newly created frames, i.e. the values
these attributes have before applying the face spec in the face’s defface definition or
the spec set by face-spec-set. These default values of the attributes are normallyunspecified, unless you have specified some other value using set-face-attribute;see below.

merge-face-attribute attribute value1 value2[Function]
If value1 is a relative value for the face attribute attribute, returns it merged with theunderlying value value2; otherwise, if value1 is an absolute value for the face attributeattribute, returns value1 unchanged.

Normally, Emacs uses the face specs of each face to automatically calculate its attributeson each frame (see Section 41.12.2 [Defining Faces], page 1168). The function set-faceattribute can override this calculation by directly assigning attributes to a face, either ona specific frame or for all frames. This function is mostly intended for internal usage.

set-face-attribute face frame &rest arguments[Function]
This function sets one or more attributes of face for frame. The attributes specified
in this way override the face spec(s) belonging to face. See Section 41.12.1 [FaceAttributes], page 1164, for the supported attributes.
The extra arguments arguments specify the attributes to set, and the values for them.
They should consist of alternating attribute names (such as :family or :underline)
and values. Thus,(set-face-attribute 'foo nil :weight 'bold :slant 'italic)
sets the attribute :weight to bold and the attribute :slant to italic.
If frame is t, this function sets the default attributes for newly created frames; they
will effectively override the attribute values specified by defface. If frame is nil, thisfunction sets the attributes for all existing frames, as well as for newly created frames.
To reset the value of an attribute, that is, to indicate that the face doesn’t by itself
specify a value for the attribute, use the special value unspecified (not nil!) for theattribute, and set the frame argument to t, in addition to the call with frame set tonil. This is because the default attributes for newly created frames are merged withthe face’s spec in defface when a new frame is created, and so having unspecified
in the default attributes for new frames will be unable to override defface; the special
call to this function as described above will arrange for defface to be overridden.
Note that the attribute-value pairs are evaluated in the order they are specified, withthe exception of the :family and :foundry attributes, which are evaluated first. Thismeans that if a certain attribute is specified more than once, only the last value will
be used. It also means that in some cases a different order of attributes will produce
different results. For example, when :weight is placed before :font, the weight value
is applied to the current font of the face, and might be rounded to the closest available
weight of that font, whereas when :font is placed before :weight the weight value isapplied to the specified font.

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The following commands and functions mostly provide compatibility with old versionsof Emacs. They work by calling set-face-attribute. Values of t and nil (or omitted)
for their frame argument are handled just like set-face-attribute and face-attribute.
The commands read their arguments using the minibuffer, if called interactively.

set-face-foreground face color &optional frame
set-face-background face color &optional frame[Command][Command]
These set the :foreground attribute (or :background attribute, respectively) of faceto color.

set-face-stipple face pattern &optional frame[Command]This sets the :stipple attribute of face to pattern.

set-face-font face font &optional frame[Command]
Change the font-related attributes of face to those of font (a string or a font object).
See [face-font-attribute], page 1167, for the supported formats of the font argument.
This function sets the attribute :font of the face, and indirectly also the :family,:foundry, :width, :height, :weight, and :slant attributes, as defined by the font.
If frame is non-nil, only change the attributes on the specified frame.

set-face-bold face bold-p &optional frame[Function]
This sets the :weight attribute of face to normal if bold-p is nil, and to boldotherwise.

set-face-italic face italic-p &optional frame[Function]
This sets the :slant attribute of face to normal if italic-p is nil, and to italicotherwise.

set-face-underline face underline &optional frame[Command]This sets the :underline attribute of face to underline.

set-face-inverse-video face inverse-video-p &optional frame[Command]This sets the :inverse-video attribute of face to inverse-video-p.

invert-face face &optional frame[Command]This swaps the foreground and background colors of face face.

set-face-extend face extend &optional frame[Command]This sets the :extend attribute of face to extend.
The following functions examine the attributes of a face. They mostly provide compatibility with old versions of Emacs. If you don’t specify frame, they refer to the selected frame;t refers to the default data for new frames. They return unspecified if the face doesn’t
define any value for that attribute. If inherit is nil, only an attribute directly defined by
the face is returned. If inherit is non-nil, any faces specified by its :inherit attribute areconsidered as well, and if inherit is a face or a list of faces, then they are also considered,
until a specified attribute is found. To ensure that the return value is always specified, use avalue of default for inherit.

Chapter 41: Emacs Display

face-font face &optional frame character

1174[Function]

This function returns the name of the font used by the specified face.
If the optional argument frame is specified, it returns the name of the font of face forthat frame; frame defaults to the selected frame if it is nil or omitted. If frame is t,
the function reports on the font defaults for face to be used for new frames.
By default, the returned font is for displaying ASCII characters, but if frame isanything but t, and the optional third argument character is supplied, the function
returns the font name used by face for that character.

face-foreground face &optional frame inherit
face-background face &optional frame inherit[Function][Function]
These functions return the foreground color (or background color, respectively) of face
face, as a string. If the color is unspecified, they return nil.

face-stipple face &optional frame inherit[Function]
This function returns the name of the background stipple pattern of face face, or nil
if it doesn’t have one.

face-bold-p face &optional frame inherit[Function]
This function returns a non-nil value if the :weight attribute of face is bolder thannormal (i.e., one of semi-bold, bold, extra-bold, or ultra-bold). Otherwise, it
returns nil.

face-italic-p face &optional frame inherit[Function]
This function returns a non-nil value if the :slant attribute of face is italic or
oblique, and nil otherwise.

face-underline-p face &optional frame inherit[Function]
This function returns non-nil if face face specifies a non-nil :underline attribute.

face-inverse-video-p face &optional frame inherit[Function]
This function returns non-nil if face face specifies a non-nil :inverse-video attribute.

face-extend-p face &optional frame inherit[Function]
This function returns non-nil if face face specifies a non-nil :extend attribute. The
inherit argument is passed to face-attribute.

41.12.4 Displaying Faces
When Emacs displays a given piece of text, the visual appearance of the text may be
determined by faces drawn from different sources. If these various sources together specify
more than one face for a particular character, Emacs merges the attributes of the various
faces. Here is the order in which Emacs merges the faces, from highest to lowest priority:• If the text consists of a special glyph, the glyph can specify a particular face. See
Section 41.23.4 [Glyphs], page 1245.
• If the text lies within an active region, Emacs highlights it using the region face. See
Section “Standard Faces” in The GNU Emacs Manual.

Chapter 41: Emacs Display

1175• If the text lies within an overlay with a non-nil face property, Emacs applies theface(s) specified by that property. If the overlay has a mouse-face property and themouse is near enough to the overlay, Emacs applies the face or face attributes specified
by the mouse-face property instead. See Section 41.9.2 [Overlay Properties], page 1153.
When multiple overlays cover the same character, an overlay with higher priority
overrides those with lower priority. See Section 41.9 [Overlays], page 1150.
• If the text contains a face or mouse-face property, Emacs applies the specified faces
and face attributes. See Section 33.19.4 [Special Properties], page 924. (This is how
Font Lock mode faces are applied. See Section 24.6 [Font Lock Mode], page 563.)• If the text lies within the mode line of the selected window, Emacs applies the mode-line
face. For the mode line of a non-selected window, Emacs applies the mode-lineinactive face. For a header line, Emacs applies the header-line face. For a tab line,
Emacs applies the tab-line face.
• If the text comes from an overlay string via before-string or after-string properties(see Section 41.9.2 [Overlay Properties], page 1153), or from a display string (seeSection 41.16.4 [Other Display Specs], page 1203), and the string doesn’t contain aface or mouse-face property, or these properties leave some face attributes undefined,
but the buffer text affected by the overlay/display property does define a face or those
attributes, Emacs applies the face attributes of the “underlying” buffer text. Note that
this is so even if the overlay or display string is displayed in the display margins (seeSection 41.16.5 [Display Margins], page 1205).
• If any given attribute has not been specified during the preceding steps, Emacs applies
the attribute of the default face.
At each stage, if a face has a valid :inherit attribute, Emacs treats any attribute withan unspecified value as having the corresponding value drawn from the parent face(s). see
Section 41.12.1 [Face Attributes], page 1164. Note that the parent face(s) may also leave
the attribute unspecified; in that case, the attribute remains unspecified at the next level offace merging.

41.12.5 Face Remapping
The variable face-remapping-alist is used for buffer-local or global changes in the appearance of a face. For instance, it is used to implement the text-scale-adjust command(see Section “Text Scale” in The GNU Emacs Manual).
[Variable]
The value of this variable is an alist whose elements have the form (face . remapping).
This causes Emacs to display any text having the face face with remapping, rather
than the ordinary definition of face.
remapping may be any face spec suitable for a face text property: either a face (i.e.,a face name or a property list of attribute/value pairs), or a list of faces. For details,
see the description of the face text property in Section 33.19.4 [Special Properties],
page 924. remapping serves as the complete specification for the remapped face—it
replaces the normal definition of face, instead of modifying it.
If face-remapping-alist is buffer-local, its local value takes effect only within thatbuffer. If face-remapping-alist includes faces applicable only to certain windows,

face-remapping-alist

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by using the (:filtered (:window param val) spec), that face takes effect only inwindows that match the filter conditions (see Section 33.19.4 [Special Properties],
page 924). To turn off face filtering temporarily, bind face-filters-always-match
to a non-nil value, then all face filters will match any window.
Note: face remapping is non-recursive. If remapping references the same face nameface, either directly or via the :inherit attribute of some other face in remapping,that reference uses the normal definition of face. For instance, if the mode-line faceis remapped using this entry in face-remapping-alist:(mode-line italic mode-line)
then the new definition of the mode-line face inherits from the italic face, and thenormal (non-remapped) definition of mode-line face.
The following functions implement a higher-level interface to face-remapping-alist.
Most Lisp code should use these functions instead of setting face-remapping-alist directly,
to avoid trampling on remappings applied elsewhere. These functions are intended for bufferlocal remappings, so they all make face-remapping-alist buffer-local as a side-effect. They
manage face-remapping-alist entries of the form
(face relative-spec-1 relative-spec-2 ... base-spec)
where, as explained above, each of the relative-spec-N and base-spec is either a face name,or a property list of attribute/value pairs. Each of the relative remapping entries, relativespec-N, is managed by the face-remap-add-relative and face-remap-remove-relative
functions; these are intended for simple modifications like changing the text size. The baseremapping entry, base-spec, has the lowest priority and is managed by the face-remapset-base and face-remap-reset-base functions; it is intended for major modes to remap
faces in the buffers they control.

face-remap-add-relative face &rest specs[Function]
This function adds specs as relative remappings for face face in the current buffer.
specs should be a list where each element is either a face name, or a property list of
attribute/value pairs.

The return value is a Lisp object that serves as a cookie; you can pass this object as
an argument to face-remap-remove-relative if you need to remove the remapping
later.
;; Remap the 'escape-glyph' face into a combination;; of the 'highlight' and 'italic' faces:(face-remap-add-relative 'escape-glyph 'highlight 'italic);; Increase the size of the 'default' face by 50%:
(face-remap-add-relative 'default :height 1.5)
Note that buffer-local face remapping does not work reliably for parent faces of basic
faces (see Section 41.12.8 [Basic Faces], page 1178). (These are the faces that are usedin mode lines, header lines, and other basic decorations of windows and frames.) For
instance, mode-line-inactive inherits from mode-line, but remapping mode-line
won’t normally have the desired effect on mode-line-inactive, especially if done
locally for some buffers. Instead you have to remap mode-line-inactive directly.

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face-remap-remove-relative cookie[Function]
This function removes a relative remapping previously added by face-remap-addrelative. cookie should be the Lisp object returned by face-remap-add-relative
when the remapping was added.

face-remap-set-base face &rest specs[Function]
This function sets the base remapping of face in the current buffer to specs. If specs isempty, the default base remapping is restored, similar to calling face-remap-resetbase (see below); note that this is different from specs containing a single value nil,which has the opposite result (the global definition of face is ignored).
This overwrites the default base-spec, which inherits the global face definition, so it is
up to the caller to add such inheritance if so desired.

face-remap-reset-base face

[Function]
This function sets the base remapping of face to its default value, which inherits fromface’s global definition.

41.12.6 Functions for Working with Faces
Here are additional functions for creating and working with faces.

face-list[Function]

This function returns a list of all defined face names.

face-id face

[Function]
This function returns the face number of face face. This is a number that uniquely
identifies a face at low levels within Emacs. It is seldom necessary to refer to a face by
its face number. However, functions that manipulate glyphs, such as make-glyph-codeand glyph-face (see Section 41.23.4 [Glyphs], page 1245) access the face numbers
internally. Note that the face number is stored as the value of the face property of
the face symbol, so we recommend not to set that property of a face to any value of
your own.

face-documentation face

[Function]
This function returns the documentation string of face face, or nil if none was specified
for it.

face-equal face1 face2 &optional frame[Function]
This returns t if the faces face1 and face2 have the same attributes for display.

face-differs-from-default-p face &optional frame[Function]
This returns non-nil if the face face displays differently from the default face.

A face alias provides an equivalent name for a face. You can define a face alias bygiving the alias symbol the face-alias property, with a value of the target face name. The
following example makes modeline an alias for the mode-line face.
(put 'modeline 'face-alias 'mode-line)

define-obsolete-face-alias obsolete-face current-face when[Macro]This macro defines obsolete-face as an alias for current-face, and also marks it
as obsolete, indicating that it may be removed in future. when should be a string
indicating when obsolete-face was made obsolete (usually a version number string).

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41.12.7 Automatic Face Assignment
This hook is used for automatically assigning faces to text in the buffer. It is part of theimplementation of Jit-Lock mode, used by Font-Lock.
[Variable]
This variable holds a list of functions that are called by Emacs redisplay as needed,just before doing redisplay. They are called even when Font Lock Mode isn’t enabled.
When Font Lock Mode is enabled, this variable usually holds just one function,
jit-lock-function.

fontification-functions

The functions are called in the order listed, with one argument, a buffer position
pos. Collectively they should attempt to assign faces to the text in the current buffer
starting at pos.
The functions should record the faces they assign by setting the face property. They
should also add a non-nil fontified property to all the text they have assigned faces
to. That property tells redisplay that faces have been assigned to that text already.
It is probably a good idea for the functions to do nothing if the character after pos
already has a non-nil fontified property, but this is not required. If one function
overrides the assignments made by a previous one, the properties after the last function
finishes are the ones that really matter.
For efficiency, we recommend writing these functions so that they usually assign faces
to around 400 to 600 characters at each call.
Note that, when the buffer text includes very long lines, these functions are called asif they were in a with-restriction form (see Section 31.4 [Narrowing], page 865),with a long-line-optimizations-in-fontification-functions label and with thebuffer narrowed to a portion around pos.

41.12.8 Basic Faces
If your Emacs Lisp program needs to assign some faces to text, it is often a good idea to use
certain existing faces or inherit from them, rather than defining entirely new faces. Thisway, if other users have customized those existing faces to give Emacs a certain look, yourprogram will fit in without additional customization.
Some of the basic faces defined in Emacs are listed below. In addition to these, you
might want to make use of the Font Lock faces for syntactic highlighting, if highlighting
is not already handled by Font Lock mode, or if some Font Lock faces are not in use. See
Section 24.6.7 [Faces for Font Lock], page 573.
default

The default face, whose attributes are all specified. All other faces implicitly
inherit from it: any unspecified attribute defaults to the attribute on this face(see Section 41.12.1 [Face Attributes], page 1164).

mode-line-activemode-line-inactive
header-line
tab-line Basic faces used for the mode line, header line, and tab line.

Chapter 41: Emacs Display

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tool-bartab-barfringescroll-bar
window-divider
borderchild-frame-border
Basic faces used for the corresponding decorations of GUI frames.
cursor

The basic face used for the text cursor.

mouse

The basic face used for displaying mouse-sensitive text when the mouse pointeris on that text.

bold
italicbold-italic
underline
fixed-pitch
fixed-pitch-serif
variable-pitch
These have the attributes indicated by their names (e.g., bold has a bold :weight
attribute), with all other attributes unspecified (and so given by default).
shadow

For dimmed-out text. For example, it is used for the ignored part of a filenamein the minibuffer (see Section “Minibuffers for File Names” in The GNU Emacs
Manual).

link
link-visited
For clickable text buttons that send the user to a different buffer or location.
highlight
For stretches of text that should temporarily stand out. For example, it iscommonly assigned to the mouse-face property for cursor highlighting (seeSection 33.19.4 [Special Properties], page 924).
match
isearchlazy-highlight
For text matching (respectively) permanent search matches, interactive search
matches, and lazy highlighting other matches than the current interactive one.
error
warning
success

For text concerning errors, warnings, or successes. For example, these are used
for messages in *Compilation* buffers.

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41.12.9 Font Selection
Before Emacs can draw a character on a graphical display, it must select a font for thatcharacter2 . See Section “Fonts” in The GNU Emacs Manual. Normally, Emacs automaticallychooses a font based on the faces assigned to that character—specifically, the face attributes:family, :weight, :slant, and :width (see Section 41.12.1 [Face Attributes], page 1164).
The choice of font also depends on the character to be displayed; some fonts can only display
a limited set of characters. If no available font exactly fits the requirements, Emacs looks
for the closest matching font. The variables in this section control how Emacs makes thisselection.
[User Option]
If a given family is specified but does not exist, this variable specifies alternative fontfamilies to try. Each element should have this form:

face-font-family-alternatives(family alternate-families...)If family is specified but not available, Emacs will try the other families given inalternate-families, one by one, until it finds a family that does exist.
[User Option]
If there is no font that exactly matches all desired face attributes (:width, :height,:weight, and :slant), this variable specifies the order in which these attributes
should be considered when selecting the closest matching font. The value should be alist containing those four attribute symbols, in order of decreasing importance. The
default is (:width :height :weight :slant).

face-font-selection-order

Font selection first finds the best available matches for the first attribute in the list;
then, among the fonts which are best in that way, it searches for the best matches inthe second attribute, and so on.
The attributes :weight and :width have symbolic values in a range centered aroundnormal. Matches that are more extreme (farther from normal) are somewhat preferred
to matches that are less extreme (closer to normal); this is designed to ensure that
non-normal faces contrast with normal ones, whenever possible.
One example of a case where this variable makes a difference is when the default
font has no italic equivalent. With the default ordering, the italic face will use
a non-italic font that is similar to the default one. But if you put :slant before:height, the italic face will use an italic font, even if its height is not quite right.
[User Option]
This variable lets you specify alternative font registries to try, if a given registry is
specified and doesn’t exist. Each element should have this form:

face-font-registry-alternatives(registry alternate-registries...)If registry is specified but not available, Emacs will try the other registries given inalternate-registries, one by one, until it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use them.
2

In this context, the term font has nothing to do with Font Lock (see Section 24.6 [Font Lock Mode],
page 563).

Chapter 41: Emacs Display

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This variable controls which scalable fonts to use. A value of nil, the default, means
do not use scalable fonts. t means to use any scalable font that seems appropriate forthe text.
Otherwise, the value must be a list of regular expressions. Then a scalable font isenabled for use if its name matches any regular expression in the list. For example,(setq scalable-fonts-allowed '("iso10646-1$"))
allows the use of scalable fonts with registry iso10646-1.

scalable-fonts-allowed[Variable]
This variable specifies scaling for certain faces. Its value should be a list of elementsof the form
(fontname-regexp . scale-factor)
If fontname-regexp matches the font name that is about to be used, this says to choosea larger similar font according to the factor scale-factor. You would use this feature tonormalize the font size if certain fonts are bigger or smaller than their nominal heights
and widths would suggest.

face-font-rescale-alist

41.12.10 Looking Up Fonts
x-list-fonts name &optional reference-face frame maximum width[Function]
This function returns a list of available font names that match name. name should
be a string containing a font name in either the Fontconfig, GTK+, or XLFD format(see Section “Fonts” in The GNU Emacs Manual). Within an XLFD string, wildcard
characters may be used: the ‘*’ character matches any substring, and the ‘?’ character
matches any single character. Case is ignored when matching font names.
If the optional arguments reference-face and frame are specified, the returned list
includes only fonts that are the same size as reference-face (a face name) currently ison the frame frame.
The optional argument maximum sets a limit on how many fonts to return. If it isnon-nil, then the return value is truncated after the first maximum matching fonts.
Specifying a small value for maximum can make this function much faster, in cases
where many fonts match the pattern.
The optional argument width specifies a desired font width. If it is non-nil, thefunction only returns those fonts whose characters are (on average) width times aswide as reference-face.

x-family-fonts &optional family frame[Function]
This function returns a list describing the available fonts for family family on frame.
If family is omitted or nil, this list applies to all families, and therefore, it contains
all available fonts. Otherwise, family must be a string; it may contain the wildcards‘?’ and ‘*’.
The list describes the display that frame is on; if frame is omitted or nil, it applies
to the selected frame’s display (see Section 30.10 [Input Focus], page 824).
Each element in the list is a vector of the following form:[family width point-size weight slant

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fixed-p full registry-and-encoding]
The first five elements correspond to face attributes; if you specify these attributes fora face, it will use this font.
The last three elements give additional information about the font. fixed-p is non-nil
if the font is fixed-pitch. full is the full name of the font, and registry-and-encoding is
a string giving the registry and encoding of the font.

41.12.11 Fontsets
A fontset is a list of fonts, each assigned to a range of character codes. An individual
font cannot display the whole range of characters that Emacs supports, but a fontset can.
Fontsets have names, just as fonts do, and you can use a fontset name in place of a fontname when you specify the font for a frame or a face. Here is information about defining a
fontset under Lisp program control.

create-fontset-from-fontset-spec fontset-spec &optional
style-variant-p noerror[Function]

This function defines a new fontset according to the specification string fontset-spec.
The string should have this format:
fontpattern, [charset:font]. . .

Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font
name, except that the last two fields should be ‘fontset-alias’.
The new fontset has two names, one long and one short. The long name is fontpatternin its entirety. The short name is ‘fontset-alias’. You can refer to the fontset byeither name. If a fontset with the same name already exists, an error is signaled,
unless noerror is non-nil, in which case this function does nothing.
If optional argument style-variant-p is non-nil, that says to create bold, italic andbold-italic variants of the fontset as well. These variant fontsets do not have a short
name, only a long one, which is made by altering fontpattern to indicate the bold
and/or italic status.
The specification string also says which fonts to use in the fontset. See below for thedetails.
The construct ‘charset:font’ specifies which font to use (in this fontset) for one particularcharacter set. Here, charset is the name of a character set, and font is the font to use for thatcharacter set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don’t specify explicitly, Emacs chooses
a font based on fontpattern: it replaces ‘fontset-alias’ with a value that names one
character set. For the ASCII character set, ‘fontset-alias’ is replaced with ‘ISO8859-1’.
In addition, when several consecutive fields are wildcards, Emacs collapses them into asingle wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger
fonts are not usable for editing, and scaling a smaller font is not useful because it is better
to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24

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the font specification for ASCII characters would be this:-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:-*-fixed-medium-r-normal-*-24-*-gb2312*-*You may not have any Chinese font matching the above font specification. Most X
distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in the family
field. In such a case, ‘Fontset-n’ can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*

Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in thefamily field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ inthe family field.

set-fontset-font fontset characters font-spec &optional frame add[Function]
This function modifies the existing fontset to use the font specified by font-spec fordisplaying the specified characters.
If fontset is nil, this function modifies the fontset of the selected frame or that offrame if frame is not nil.
If fontset is t, this function modifies the default fontset, whose short name as a stringis ‘fontset-default’.
The characters argument can be a single character which should be displayed using
font-spec. It can also be a cons cell (from . to), where from and to are characters.
In that case, use font-spec for all the characters in the range from and to (inclusive).
characters may be a charset symbol (see Section 34.7 [Character Sets], page 973). In
that case, use font-spec for all the characters in the charset.
characters may be a script symbol (see Section 34.6 [Character Properties], page 968).
In that case, use font-spec for all the characters belonging to the script.
characters may be nil, which means to use font-spec for any character in fontset for
which no font-spec is specified.
font-spec may be a font-spec object created by the function font-spec (seeSection 41.12.12 [Low-Level Font], page 1184).
font-spec may be a cons cell (family . registry), where family is a family nameof a font (possibly including a foundry name at the head), and registry is a registryname of a font (possibly including an encoding name at the tail).
font-spec may be a font name, a string.
font-spec may be nil, which explicitly specifies that there’s no font for the specified
characters. This is useful, for example, to avoid expensive system-wide search for
fonts for characters that have no glyphs, like those from the Unicode Private Use Area
(PUA).
The optional argument add, if non-nil, specifies how to add font-spec to the fontspecifications previously set for characters. If it is prepend, font-spec is prepended
to the existing specs. If it is append, font-spec is appended. By default, font-spec
overwrites the previously set font specs.

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For instance, this changes the default fontset to use a font whose family name is‘Kochi Gothic’ for all characters belonging to the charset japanese-jisx0208:(set-fontset-font t 'japanese-jisx0208(font-spec :family "Kochi Gothic"))

Note that this function should generally be called from the user’s init files, and moregenerally before any of characters were displayed in the current Emacs session. That’s
because for some scripts, Emacs caches the way they are displayed, and the cachedinformation includes the font used for them – once these characters are displayed once,the cached font will continue to be used regardless of changes in the fontsets.

char-displayable-p char

[Function]
This function returns non-nil if Emacs ought to be able to display char. Or more
precisely, if the selected frame’s fontset has a font to display the character set thatchar belongs to.
Fontsets can specify a font on a per-character basis; when the fontset does that, thisfunction’s value may not be accurate.
This function may return non-nil even when there is no font available, since it also
checks whether the coding system for the text terminal can encode the character (seeSection 34.10.8 [Terminal I/O Encoding], page 990).

41.12.12 Low-Level Font Representation
Normally, it is not necessary to manipulate fonts directly. In case you need to do so, thissection explains how.
In Emacs Lisp, fonts are represented using three different Lisp object types: font objects,
font specs, and font entities.

fontp object &optional type

[Function]
Return t if object is a font object, font spec, or font entity. Otherwise, return nil.
The optional argument type, if non-nil, determines the exact type of Lisp object
to check for. In that case, type should be one of font-object, font-spec, or
font-entity.

A font object is a Lisp object that represents a font that Emacs has opened. Font objects
cannot be modified in Lisp, but they can be inspected.

font-at position &optional window string[Function]
Return the font object that is being used to display the character at position positionin the window window. If window is nil, it defaults to the selected window. If stringis nil, position specifies a position in the current buffer; otherwise, string should be astring, and position specifies a position in that string.

A font spec is a Lisp object that contains a set of specifications that can be used to finda font. More than one font may match the specifications in a font spec.

font-spec &rest arguments[Function]
Return a new font spec using the specifications in arguments, which should come inproperty-value pairs. The possible specifications are as follows::name

The font name (a string), in either XLFD, Fontconfig, or GTK+ format.
See Section “Fonts” in The GNU Emacs Manual.

Chapter 41: Emacs Display:family:foundry:weight:slant:width1185

These have the same meanings as the face attributes of the same name.
See Section 41.12.1 [Face Attributes], page 1164. :family and :foundry
are strings, while the other three are symbols. As example values, :slant
may be italic, :weight may be bold and :width may be normal.

:size

The font size—either a non-negative integer that specifies the pixel size,or a floating-point number that specifies the point size.

:adstyle

Additional typographic style information for the font, such as ‘sans’. The
value should be a string or a symbol.

:registry
The charset registry and encoding of the font, such as ‘iso8859-1’. The
value should be a string or a symbol.
:dpi

The resolution in dots per inch for which the font is designed. The value
must be a non-negative number.

:spacing

The spacing of the font: proportional, dual, mono, or charcell. The value
should be either an integer (0 for proportional, 90 for dual, 100 for mono,
110 for charcell) or a one-letter symbol (one of P, D, M, or C).

:avgwidth
The average width of the font in 1/10 pixel units. The value should be a
non-negative number.
:script

The script that the font must support (a symbol).

:lang

The language that the font should support. The value should be a symbol
whose name is a two-letter ISO-639 language name. On X, the value ismatched against the “Additional Style” field of the XLFD name of a font,
if it is non-empty. On MS-Windows, fonts matching the spec are required
to support codepages needed for the language. Currently, only a small set
of CJK languages is supported with this property: ‘ja’, ‘ko’, and ‘zh’.

:otf

The font must be an OpenType font that supports these OpenType
features, provided Emacs is compiled with a library, such as ‘libotf’ on
GNU/Linux, that supports complex text layout for scripts which need
that. The value must be a list of the form
(script-tag langsys-tag gsub gpos)

where script-tag is the OpenType script tag symbol; langsys-tag is the
OpenType language system tag symbol, or nil to use the default language
system; gsub is a list of OpenType GSUB feature tag symbols, or nil ifnone is required; and gpos is a list of OpenType GPOS feature tag symbols, or nil if none is required. If gsub or gpos is a list, a nil element inthat list means that the font must not match any of the remaining tag symbols. The gpos element may be omitted. For the list of OpenType script,

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language, and feature tags, see the list of registered OTF tags (https://
docs.microsoft.com/en-us/typography/opentype/spec/ttoreg).
:type

The symbol that specifies the font backend used to draw the characters.
The possible values depend on the platform and on how Emacs was
configured at build time. Typical values include ftcrhb and xfthb on X,
harfbuzz on MS-Windows, ns on GNUstep, etc. It can also be nil if left
unspecified, typically in a font-spec.

font-put font-spec property value[Function]
Set the font property property in the font-spec font-spec to value. The property can
any of the ones described above.

A font entity is a reference to a font that need not be open. Its properties are intermediate
between a font object and a font spec: like a font object, and unlike a font spec, it refers toa single, specific font. Unlike a font object, creating a font entity does not load the contentsof that font into computer memory. Emacs may open multiple font objects of different sizes
from a single font entity referring to a scalable font.

find-font font-spec &optional frame[Function]
This function returns a font entity that best matches the font spec font-spec on frame
frame. If frame is nil, it defaults to the selected frame.

list-fonts font-spec &optional frame num prefer[Function]
This function returns a list of all font entities that match the font spec font-spec.

The optional argument frame, if non-nil, specifies the frame on which the fonts areto be displayed. The optional argument num, if non-nil, should be an integer thatspecifies the maximum length of the returned list. The optional argument prefer,
if non-nil, should be another font spec, which is used to control the order of the
returned list; the returned font entities are sorted in order of decreasing closeness tothat font spec.
If you call set-face-attribute and pass a font spec, font entity, or font name string
as the value of the :font attribute, Emacs opens the best matching font that is available
for display. It then stores the corresponding font object as the actual value of the :fontattribute for that face.
The following functions can be used to obtain information about a font. For thesefunctions, the font argument can be a font object, a font entity, or a font spec.

font-get font property[Function]
This function returns the value of the font property property for font. The property
can any of the ones that font-spec supports.
If font is a font spec and the font spec does not specify property, the return value isnil. If font is a font object or font entity, the value for the :script property may be
a list of scripts supported by the font, and the value of the :otf property is a consof the form (gsub . gpos), where gsub and gpos are lists representing OpenType
features supported by the font, of the form((script-tag (langsys-tag feature...) ...) ...)

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where script-tag, langsys-tag, and feature are symbols representing OpenType layouttags.
If font is a font object, the special property :combining-capability is non-nil if the
font backend of font supports rendering of combining characters for non-OpenType
fonts.

font-face-attributes font &optional frame[Function]
This function returns a list of face attributes corresponding to font. The optional
argument frame specifies the frame on which the font is to be displayed. If it is nil,
the selected frame is used. The return value has the form(:family family :height height :weight weight:slant slant :width width)

where the values of family, height, weight, slant, and width are face attribute values.
Some of these key-attribute pairs may be omitted from the list if they are not specified
by font.

font-xlfd-name font &optional fold-wildcards[Function]
This function returns the XLFD (X Logical Font Descriptor), a string, matching font.
See Section “Fonts” in The GNU Emacs Manual, for information about XLFDs. If
the name is too long for an XLFD (which can contain at most 255 characters), thefunction returns nil.
If the optional argument fold-wildcards is non-nil, consecutive wildcards in the XLFD
are folded into one.

The following two functions return important information about a font.

font-info name &optional frame[Function]
This function returns information about a font specified by its name, a string, as it isused on frame. If frame is omitted or nil, it defaults to the selected frame.
The value returned by the function is a vector of the form [opened-name full-namesize height baseline-offset relative-compose default-ascent max-width
ascent descent space-width average-width filename capability]. Here’s thedescription of each components of this vector:
opened-name
The name used to open the font, a string.
full-name

The full name of the font, a string.

size

The pixel size of the font.

height

The height of the font in pixels.

baseline-offset
The offset in pixels from the ASCII baseline, positive upward.
relative-compose
default-ascent
Numbers controlling how to compose characters.
max-width
The maximum advance width of the font.

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The ascent and descent of this font. The sum of these two numbers shouldbe equal to the value of height above.

space-width
The width, in pixels, of the font’s space character.
average-width
The average width of the font characters. If this is zero, Emacs uses thevalue of space-width instead, when it calculates text layout on display.
filename

The file name of the font as a string. This can be nil if the font back-end
does not provide a way to find out the font’s file name.

capability

A list whose first element is a symbol representing the font type, oneof x, opentype, truetype, type1, pcf, or bdf. For OpenType fonts,
the list includes 2 additional elements describing the gsub and gpos
features supported by the font. Each of these elements is a list of the form((script (langsys feature ...) ...) ...), where script is a symbol
representing an OpenType script tag, langsys is a symbol representing an
OpenType langsys tag (or nil, which stands for the default langsys), andeach feature is a symbol representing an OpenType feature tag.

query-font font-object[Function]
This function returns information about a font-object. (This is in contrast to
font-info, which takes the font name, a string, as its argument.)
The value returned by the function is a vector of the form [name filename pixel-size
max-width ascent descent space-width average-width capability]. Here’s thedescription of each components of this vector:
name

The font name, a string.

filename

The file name of the font as a string. This can be nil if the font back-end
does not provide a way to find out the font’s file name.

pixel-size

The pixel size of the font used to open the font.

max-width
The maximum advance width of the font.
ascentdescent

The ascent and descent of this font. The sum of these two numbers gives
the font height.

space-width
The width, in pixels, of the font’s space character.
average-width
The average width of the font characters. If this is zero, Emacs uses thevalue of space-width instead, when it calculates text layout on display.
capability

A list whose first element is a symbol representing the font type, oneof x, opentype, truetype, type1, pcf, or bdf. For OpenType fonts,
the list includes 2 additional elements describing the gsub and gpos

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features supported by the font. Each of these elements is a list of the form((script (langsys feature ...) ...) ...), where script is a symbol
representing an OpenType script tag, langsys is a symbol representing an
OpenType langsys tag (or nil, which stands for the default langsys), andeach feature is a symbol representing an OpenType feature tag.
The following four functions return size information about fonts used by various faces,
allowing various layout considerations in Lisp programs. These functions take face remapping
into consideration, returning information about the remapped face, if the face in question
was remapped. See Section 41.12.5 [Face Remapping], page 1175.
[Function]
This function returns the average width in pixels of the font used by the current
buffer’s default face, as that face is defined for the selected frame.

default-font-width[Function]
This function returns the height in pixels of the font used by the current buffer’s
default face, as that face is defined for the selected frame.

default-font-heightwindow-font-width &optional window face

[Function]
This function returns the average width in pixels for the font used by face in window.
The specified window must be a live window. If nil or omitted, window defaults tothe selected window, and face defaults to the default face in window.

window-font-height &optional window face

[Function]
This function returns the height in pixels for the font used by face in window. The
specified window must be a live window. If nil or omitted, window defaults to theselected window, and face defaults to the default face in window.

41.13 Fringes
On graphical displays, Emacs draws fringes next to each window: thin vertical strips down
the sides which can display bitmaps indicating truncation, continuation, horizontal scrolling,and so on.

41.13.1 Fringe Size and Position
The following buffer-local variables control the position and width of fringes in windows
showing that buffer.
[Variable]
The fringes normally appear between the display margins and the window text. If
the value is non-nil, they appear outside the display margins. See Section 41.16.5[Display Margins], page 1205.

fringes-outside-margins[Variable]
This variable, if non-nil, specifies the width of the left fringe in pixels. A value ofnil means to use the left fringe width from the window’s frame.

left-fringe-width[Variable]
This variable, if non-nil, specifies the width of the right fringe in pixels. A value ofnil means to use the right fringe width from the window’s frame.

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Any buffer which does not specify values for these variables uses the values specified
by the left-fringe and right-fringe frame parameters (see Section 30.4.3.4 [Layout
Parameters], page 810).
The above variables actually take effect via the function set-window-buffer (seeSection 29.11 [Buffers and Windows], page 720), which calls set-window-fringes as a
subroutine. If you change one of these variables, the fringe display is not updated in existing
windows showing the buffer, unless you call set-window-buffer again in each affected
window. You can also use set-window-fringes to control the fringe display in individual
windows.

set-window-fringes window left &optional right outside-margins
persistent[Function]

This function sets the fringe widths of window window. If window is nil, the selected
window is used.
The argument left specifies the width in pixels of the left fringe, and likewise rightfor the right fringe. A value of nil for either one stands for the default width. If
outside-margins is non-nil, that specifies that fringes should appear outside of thedisplay margins.
If window is not large enough to accommodate fringes of the desired width, this leaves
the fringes of window unchanged.
The values specified here may be later overridden by invoking set-window-buffer(see Section 29.11 [Buffers and Windows], page 720) on window with its keep-margins
argument nil or omitted. However, if the optional fifth argument persistent is nonnil and the other arguments are processed successfully, the values specified here
unconditionally survive subsequent invocations of set-window-buffer. This can beused to permanently turn off fringes in the minibuffer window, consult the description of
set-window-scroll-bars for an example (see Section 41.14 [Scroll Bars], page 1195).

window-fringes &optional window[Function]
This function returns information about the fringes of a window window. If window isomitted or nil, the selected window is used. The value has the form (left-width
right-width outside-margins persistent).

41.13.2 Fringe Indicators
Fringe indicators are tiny icons displayed in the window fringe to indicate truncated orcontinued lines, buffer boundaries, etc.
[User Option]
When this is non-nil, Emacs displays a special glyph in the fringe of each empty line
at the end of the buffer, on graphical displays. See Section 41.13 [Fringes], page 1189.
This variable is automatically buffer-local in every buffer.

indicate-empty-lines[User Option]
This buffer-local variable controls how the buffer boundaries and window scrolling areindicated in the window fringes.
Emacs can indicate the buffer boundaries—that is, the first and last line in the buffer—with angle icons when they appear on the screen. In addition, Emacs can display anindicate-buffer-boundaries

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up-arrow in the fringe to show that there is text above the screen, and a down-arrow
to show there is text below the screen.
There are three kinds of basic values:
nil

Don’t display any of these fringe icons.

left

Display the angle icons and arrows in the left fringe.

right

Display the angle icons and arrows in the right fringe.

any non-alist
Display the angle icons in the left fringe and don’t display the arrows.
Otherwise the value should be an alist that specifies which fringe indicators to display
and where. Each element of the alist should have the form (indicator . position).
Here, indicator is one of top, bottom, up, down, and t (which covers all the icons not
yet specified), while position is one of left, right and nil.
For example, ((top . left) (t . right)) places the top angle bitmap in left fringe,
and the bottom angle bitmap as well as both arrow bitmaps in right fringe. To
show the angle bitmaps in the left fringe, and no arrow bitmaps, use ((top . left)(bottom . left)).
[Variable]
This buffer-local variable specifies the mapping from logical fringe indicators to theactual bitmaps displayed in the window fringes. The value is an alist of elements(indicator . bitmaps), where indicator specifies a logical indicator type and bitmaps
specifies the fringe bitmaps to use for that indicator.

fringe-indicator-alist

Each indicator should be one of the following symbols:
truncation, continuation.
Used for truncation and continuation lines.
up, down, top, bottom, top-bottom
Used when indicate-buffer-boundaries is non-nil: up and down indicate a buffer boundary lying above or below the window edge; topand bottom indicate the topmost and bottommost buffer text line; andtop-bottom indicates where there is just one line of text in the buffer.
empty-line
Used to indicate empty lines after the buffer end when indicate-emptylines is non-nil.
overlay-arrow
Used for overlay arrows (see Section 41.13.6 [Overlay Arrow], page 1194).
Each bitmaps value may be a list of symbols (left right [left1 right1]). The
left and right symbols specify the bitmaps shown in the left and/or right fringe, forthe specific indicator. left1 and right1 are specific to the bottom and top-bottom
indicators, and are used to indicate that the last text line has no final newline.
Alternatively, bitmaps may be a single symbol which is used in both left and rightfringes.

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See Section 41.13.4 [Fringe Bitmaps], page 1192, for a list of standard bitmap symbols
and how to define your own. In addition, nil represents the empty bitmap (i.e., anindicator that is not shown).
When fringe-indicator-alist has a buffer-local value, and there is no bitmap
defined for a logical indicator, or the bitmap is t, the corresponding value from thedefault value of fringe-indicator-alist is used.

41.13.3 Fringe Cursors
When a line is exactly as wide as the window, Emacs displays the cursor in the right fringe
instead of using two lines. Different bitmaps are used to represent the cursor in the fringe
depending on the current buffer’s cursor type.
[User Option]
If this is non-nil, lines exactly as wide as the window (not counting the final newline
character) are not continued. Instead, when point is at the end of the line, the cursor
appears in the right fringe.

overflow-newline-into-fringe[Variable]
This variable specifies the mapping from logical cursor type to the actual fringe bitmaps
displayed in the right fringe. The value is an alist where each element has the form
(cursor-type . bitmap), which means to use the fringe bitmap bitmap to display
cursors of type cursor-type.
Each cursor-type should be one of box, hollow, bar, hbar, or hollow-small. The
first four have the same meanings as in the cursor-type frame parameter (seeSection 30.4.3.9 [Cursor Parameters], page 817). The hollow-small type is usedinstead of hollow when the normal hollow-rectangle bitmap is too tall to fit on a
specific display line.
Each bitmap should be a symbol specifying the fringe bitmap to be displayed for that
logical cursor type. See the next subsection for details.
When fringe-cursor-alist has a buffer-local value, and there is no bitmap
defined for a cursor type, the corresponding value from the default value offringes-indicator-alist is used.

fringe-cursor-alist

41.13.4 Fringe Bitmaps
The fringe bitmaps are the actual bitmaps which represent the logical fringe indicators
for truncated or continued lines, buffer boundaries, overlay arrows, etc. Each bitmap isrepresented by a symbol. These symbols are referred to by the variables fringe-indicatoralist and fringe-cursor-alist, described in the previous subsections.
Lisp programs can also directly display a bitmap in the left or right fringe, by using adisplay property for one of the characters appearing in the line (see Section 41.16.4 [Other
Display Specs], page 1203). Such a display specification has the form
(fringe bitmap [face])
fringe is either the symbol left-fringe or right-fringe. bitmap is a symbol identifying
the bitmap to display. The optional face names a face whose foreground and backgroundcolors are to be used to display the bitmap, using the attributes of the fringe face for colors
that face didn’t specify. If face is omitted, that means to use the attributes of the default

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face for the colors which the fringe face didn’t specify. For predictable results that don’t
depend on the attributes of the default and fringe faces, we recommend you never omit
face, but always provide a specific face. In particular, if you want the bitmap to be always
displayed in the fringe face, use fringe as face.
For instance, to display an arrow in the left fringe, using the warning face, you could say
something like:(overlay-put(make-overlay (point) (point))'before-string (propertize"x" 'display`(left-fringe right-arrow warning)))
Here is a list of the standard fringe bitmaps defined in Emacs, and how they are currently
used in Emacs (via fringe-indicator-alist and fringe-cursor-alist):
left-arrow, right-arrow
Used to indicate truncated lines.
left-curly-arrow, right-curly-arrow
Used to indicate continued lines.
right-triangle, left-triangle
The former is used by overlay arrows. The latter is unused.
up-arrow, down-arrowbottom-left-angle, bottom-right-angle
top-left-angle, top-right-angle
left-bracket, right-bracket
empty-line
Used to indicate buffer boundaries.
filled-rectangle, hollow-rectangle
filled-square, hollow-squarevertical-bar, horizontal-bar
Used for different types of fringe cursors.
exclamation-mark, question-marklarge-circle
Not used by core Emacs features.
The next subsection describes how to define your own fringe bitmaps.

fringe-bitmaps-at-pos &optional pos window[Function]
This function returns the fringe bitmaps of the display line containing position pos inwindow window. The return value has the form (left right ov), where left is the
symbol for the fringe bitmap in the left fringe (or nil if no bitmap), right is similar
for the right fringe, and ov is non-nil if there is an overlay arrow in the left fringe.
The value is nil if pos is not visible in window. If window is nil, that stands for theselected window. If pos is nil, that stands for the value of point in window.

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41.13.5 Customizing Fringe Bitmaps
define-fringe-bitmap bitmap bits &optional height width align[Function]
This function defines the symbol bitmap as a new fringe bitmap, or replaces an existing
bitmap with that name.
The argument bits specifies the image to use. It should be either a string or a vector of
integers, where each element (an integer) corresponds to one row of the bitmap. Each
bit of an integer corresponds to one pixel of the bitmap, where the low bit corresponds
to the rightmost pixel of the bitmap. (Note that this order of bits is opposite of theorder in XBM images; see Section 41.17.3 [XBM Images], page 1211.)
The height is normally the length of bits. However, you can specify a different heightwith non-nil height. The width is normally 8, but you can specify a different widthwith non-nil width. The width must be an integer between 1 and 16.
The argument align specifies the positioning of the bitmap relative to the range ofrows where it is used; the default is to center the bitmap. The allowed values are top,
center, or bottom.
The align argument may also be a list (align periodic) where align is interpreted
as described above. If periodic is non-nil, it specifies that the rows in bits should be
repeated enough times to reach the specified height.

destroy-fringe-bitmap bitmap[Function]
This function destroys the fringe bitmap identified by bitmap. If bitmap identifies astandard fringe bitmap, it actually restores the standard definition of that bitmap,
instead of eliminating it entirely.

set-fringe-bitmap-face bitmap &optional face

[Function]
This sets the face for the fringe bitmap bitmap to face. If face is nil, it selects thefringe face. The bitmap’s face controls the color to draw it in.
face is merged with the fringe face, so normally face should specify only the foregroundcolor.

41.13.6 The Overlay Arrow
The overlay arrow is useful for directing the user’s attention to a particular line in a buffer.
For example, in the modes used for interface to debuggers, the overlay arrow indicatesthe line of code about to be executed. This feature has nothing to do with overlays (seeSection 41.9 [Overlays], page 1150).
[Variable]
This variable holds the string to display to call attention to a particular line, or nil if
the arrow feature is not in use. On a graphical display the contents of the string are
ignored if the left fringe is shown; instead a glyph is displayed in the fringe area tothe left of the display area.

overlay-arrow-string[Variable]
This variable holds a marker that indicates where to display the overlay arrow. It
should point at the beginning of a line. On a non-graphical display, or when the left
fringe is not shown, the arrow text appears at the beginning of that line, overlaying

overlay-arrow-position

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any text that would otherwise appear. Since the arrow is usually short, and the line
usually begins with indentation, normally nothing significant is overwritten.
The overlay-arrow string is displayed in any given buffer if the value of overlay-arrowposition in that buffer points into that buffer. Thus, it is possible to display multiple
overlay arrow strings by creating buffer-local bindings of overlay-arrow-position.
However, it is usually cleaner to use overlay-arrow-variable-list to achieve thisresult.
You can do a similar job by creating an overlay with a before-string property. See
Section 41.9.2 [Overlay Properties], page 1153.
You can define multiple overlay arrows via the variable overlay-arrow-variable-list.
[Variable]
This variable’s value is a list of variables, each of which specifies the position ofan overlay arrow. The variable overlay-arrow-position has its normal meaning
because it is on this list.

overlay-arrow-variable-list

Each variable on this list can have properties overlay-arrow-string andoverlay-arrow-bitmap that specify an overlay arrow string (for text terminals or graphicalterminals without the left fringe shown) or fringe bitmap (for graphical terminals with a left
fringe) to display at the corresponding overlay arrow position. If either property is not set,
the default overlay-arrow-string or overlay-arrow fringe indicator is used.

41.14 Scroll Bars
Normally the frame parameter vertical-scroll-bars controls whether the windows in
the frame have vertical scroll bars, and whether they are on the left or right. The frame
parameter scroll-bar-width specifies how wide they are (nil meaning the default).
The frame parameter horizontal-scroll-bars controls whether the windows in theframe have horizontal scroll bars. The frame parameter scroll-bar-height specifies howhigh they are (nil meaning the default). See Section 30.4.3.4 [Layout Parameters], page 810.
Horizontal scroll bars are not available on all platforms.
The function
horizontal-scroll-bars-available-p which takes no argument returns non-nil if they
are available on your system.
The following three functions take as argument a live frame which defaults to the selectedone.

frame-current-scroll-bars &optional frame[Function]
This function reports the scroll bar types for frame frame. The value is a cons cell
(vertical-type . horizontal-type), where vertical-type is either left, right, ornil (which means no vertical scroll bar.) horizontal-type is either bottom or nil(which means no horizontal scroll bar).

frame-scroll-bar-width &optional frame[Function]

This function returns the width of vertical scroll bars of frame in pixels.

frame-scroll-bar-height &optional frame[Function]
This function returns the height of horizontal scroll bars of frame in pixels.

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You can override the frame specific settings for individual windows by using the following
function:

set-window-scroll-bars window &optional width vertical-type
height horizontal-type persistent[Function]

This function sets the width and/or height and the types of scroll bars for window
window. If window is nil, the selected window is used.
width specifies the width of the vertical scroll bar in pixels (nil means use the width
specified for the frame). vertical-type specifies whether to have a vertical scroll bar
and, if so, where. The possible values are left, right, t, which means to use theframe’s default, and nil for no vertical scroll bar.
height specifies the height of the horizontal scroll bar in pixels (nil means use theheight specified for the frame). horizontal-type specifies whether to have a horizontal
scroll bar. The possible values are bottom, t, which means to use the frame’s default,
and nil for no horizontal scroll bar. Note that for a mini window the value t has
the same meaning as nil, namely to not show a horizontal scroll bar. You have to
explicitly specify bottom in order to show a horizontal scroll bar in a mini window.
If window is not large enough to accommodate a scroll bar of the desired dimension,
this leaves the corresponding scroll bar unchanged.
The values specified here may be later overridden by invoking set-window-buffer(see Section 29.11 [Buffers and Windows], page 720) on window with its keep-margins
argument nil or omitted. However, if the optional fifth argument persistent is nonnil and the other arguments are processed successfully, the values specified here
unconditionally survive subsequent invocations of set-window-buffer.
Using the persistent argument of set-window-scroll-bars and set-window-fringes(see Section 41.13.1 [Fringe Size/Pos], page 1189) you can reliably and permanently turn off
scroll bars and/or fringes in any minibuffer window by adding the following snippet to yourearly init file (see Section 42.1.2 [Init File], page 1258).
(add-hook 'after-make-frame-functions(lambda (frame)(set-window-scroll-bars(minibuffer-window frame) 0 nil 0 nil t)(set-window-fringes(minibuffer-window frame) 0 0 nil t)))

The following four functions take as argument a live window which defaults to the selectedone.

window-scroll-bars &optional window[Function]
This function returns a list of the form (width columns vertical-type height lines
horizontal-type persistent).
The value width is the value that was specified for the width of the vertical scroll bar(which may be nil); columns is the (possibly rounded) number of columns that thevertical scroll bar actually occupies.
The value height is the value that was specified for the height of the horizontal scrollbar (which may be nil); lines is the (possibly rounded) number of lines that thehorizontally scroll bar actually occupies.

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The value of persistent is the value specified for window with the last successful
invocation of set-window-scroll-bars, nil if there never was one.

window-current-scroll-bars &optional window[Function]
This function reports the scroll bar type for window window. The value is a cons cell
(vertical-type . horizontal-type). Unlike window-scroll-bars, this reports
the scroll bar type actually used, once frame defaults and scroll-bar-mode are taken
into account.

window-scroll-bar-width &optional window[Function]

This function returns the width in pixels of window’s vertical scrollbar.

window-scroll-bar-height &optional window[Function]
This function returns the height in pixels of window’s horizontal scrollbar.

If you do not specify a window’s scroll bar settings via set-window-scroll-bars, thebuffer-local variables vertical-scroll-bar, horizontal-scroll-bar, scroll-bar-widthand scroll-bar-height in the buffer being displayed control the window’s scroll bars. The
function set-window-buffer examines these variables. If you change them in a buffer thatis already visible in a window, you can make the window take note of the new values bycalling set-window-buffer specifying the same buffer that is already displayed.
You can control the appearance of scroll bars for a particular buffer by setting thefollowing variables which automatically become buffer-local when set.
[Variable]
This variable specifies the location of the vertical scroll bar. The possible values areleft, right, t, which means to use the frame’s default, and nil for no scroll bar.

vertical-scroll-bar[Variable]
This variable specifies the location of the horizontal scroll bar. The possible values
are bottom, t, which means to use the frame’s default, and nil for no scroll bar.

horizontal-scroll-bar[Variable]
This variable specifies the width of the buffer’s vertical scroll bars, measured in pixels.
A value of nil means to use the value specified by the frame.

scroll-bar-width[Variable]
This variable specifies the height of the buffer’s horizontal scroll bar, measured inpixels. A value of nil means to use the value specified by the frame.

scroll-bar-height

Finally you can toggle the display of scroll bars on all frames by customizing the variables
scroll-bar-mode and horizontal-scroll-bar-mode.
[User Option]
This variable controls whether and where to put vertical scroll bars in all frames. The
possible values are nil for no scroll bars, left to put scroll bars on the left and rightto put scroll bars on the right.

scroll-bar-mode[User Option]
This variable controls whether to display horizontal scroll bars on all frames.

horizontal-scroll-bar-mode

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41.15 Window Dividers
Window dividers are bars drawn between a frame’s windows. A right divider is drawn
between a window and any adjacent windows on the right. Its width (thickness) is specified
by the frame parameter right-divider-width. A bottom divider is drawn between awindow and adjacent windows on the bottom or the echo area. Its width is specified by theframe parameter bottom-divider-width. In either case, specifying a width of zero means
to not draw such dividers. See Section 30.4.3.4 [Layout Parameters], page 810.
Technically, a right divider belongs to the window on its left, which means that its width
contributes to the total width of that window. A bottom divider belongs to the window
above it, which means that its width contributes to the total height of that window. See
Section 29.4 [Window Sizes], page 699. When a window has both, a right and a bottom
divider, the bottom divider prevails. This means that a bottom divider is drawn over thefull total width of its window while the right divider ends above the bottom divider.
Dividers can be dragged with the mouse and are therefore useful for adjusting thesizes of adjacent windows with the mouse. They also serve to visually set apart adjacentwindows when no scroll bars or mode lines are present. The following three faces allow thecustomization of the appearance of dividers:window-divider
When a divider is less than three pixels wide, it is drawn solidly with theforeground of this face. For larger dividers this face is used for the inner part
only, excluding the first and last pixel.
window-divider-first-pixelThis is the face used for drawing the first pixel of a divider that is at least threepixels wide. To obtain a solid appearance, set this to the same value used forthe window-divider face.
window-divider-last-pixelThis is the face used for drawing the last pixel of a divider that is at least threepixels wide. To obtain a solid appearance, set this to the same value used forthe window-divider face.
You can get the sizes of the dividers of a specific window with the following two functions.

window-right-divider-width &optional window[Function]
Return the width (thickness) in pixels of window’s right divider. window must be alive window and defaults to the selected one. The return value is always zero for arightmost window.

window-bottom-divider-width &optional window[Function]
Return the width (thickness) in pixels of window’s bottom divider. window must
be a live window and defaults to the selected one. The return value is zero for theminibuffer window or a bottommost window on a minibuffer-less frame.

41.16 The display Property
The display text property (or overlay property) is used to insert images into text, andto control other aspects of how text displays. Display specifications in the same display
property value generally apply in parallel to the text they cover.

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If several sources (overlays and/or a text property) specify values for the display
property, only one of the values takes effect, following the rules of get-char-property. See
Section 33.19.1 [Examining Properties], page 917.
The value of the display property should be a display specification, or a list or vector
containing several display specifications.

get-display-property position prop &optional object properties[Function]
This convenience function can be used to get a specific display property, no matter
whether the display property is a vector, a list or a simple property. This is likeget-text-property (see Section 33.19.1 [Examining Properties], page 917), but works
on the display property only.
position is the position in the buffer or string to examine, and prop is the display
property to return. The optional object argument should be either a string or a buffer,and defaults to the current buffer. If the optional properties argument is non-nil, it
should be a display property, and in that case, position and object are ignored. (Thiscan be useful if you’ve already gotten the display property with get-char-property,
for instance (see Section 33.19.1 [Examining Properties], page 917).

add-display-text-property start end prop value &optional object[Function]

Add display property prop of value to the text from start to end.
If any text in the region has a non-nil display property, those properties are retained.
For instance:(add-display-text-property 4 8 'height 2.0)
(add-display-text-property 2 12 'raise 0.5)
After doing this, the region from 2 to 4 will have the raise display property, theregion from 4 to 8 will have both the raise and height display properties, andfinally the region from 8 to 12 will only have the raise display property.
If object is non-nil, it should be a string or a buffer. If nil, this defaults to thecurrent buffer.
Some of the display specifications allow inclusion of Lisp forms, which are evaluated at
display time. This could be unsafe in certain situations, e.g., when the display specification
was generated by some external program/agent. Wrapping a display specification in a listthat begins with the special symbol disable-eval, as in (disable-eval spec), will disable
evaluation of any Lisp in spec, while still supporting all the other display property features.
The rest of this section describes several kinds of display specifications and what theymean.

41.16.1 Display Specs That Replace The Text
Some kinds of display specifications specify something to display instead of the text that has
the property. These are called replacing display specifications. Emacs does not allow theuser to interactively move point into the middle of buffer text that is replaced in this way.
If a list of display specifications includes more than one replacing display specification, thefirst overrides the rest. Replacing display specifications make most other display specifications
irrelevant, since those don’t apply to the replacement.

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For replacing display specifications, the text that has the property means all the consecutive characters that have the same Lisp object as their display property; these characters
are replaced as a single unit. If two characters have different Lisp objects as their display
properties (i.e., objects which are not eq), they are handled separately.
Here is an example which illustrates this point. A string serves as a replacing display
specification, which replaces the text that has the property with the specified string (seeSection 41.16.4 [Other Display Specs], page 1203). Consider the following function:(defun foo ()(dotimes (i 5)(let ((string (concat "A"))(start (+ i i (point-min))))(put-text-property start (1+ start) 'display string)(put-text-property start (+ 2 start) 'display string))))This function gives each of the first ten characters in the buffer a display property which isa string "A", but they don’t all get the same string object. The first two characters get thesame string object, so they are replaced with one ‘A’; the fact that the display property was
assigned in two separate calls to put-text-property is irrelevant. Similarly, the next two
characters get a second string (concat creates a new string object), so they are replacedwith one ‘A’; and so on. Thus, the ten characters appear as five A’s.
Note: Using :box face attribute (see Section 41.12.1 [Face Attributes], page 1164) on a
replacing display string that is adjacent to normal text with the same :box style can leadto display artifacts when moving the cursor across the text with this face attribute. Thesecan be avoided by applying the :box attribute directly to the text being replaced, rather
than (or in addition to) the display string itself. Here’s an example:;; Causes display artifacts when moving the cursor across text
(progn(put-text-property 1 2 'display (propertize " [" 'face '(:box t)))(put-text-property 2 3 'face '(:box t))(put-text-property 3 4 'display (propertize "] " 'face '(:box t))));; No display artifacts due to `:box'(progn(add-text-properties 1 2 '(face (:box t) display " ["))
(put-text-property 2 3 'face '(:box t))(add-text-properties 3 4 '(face (:box t) display "] ")))

41.16.2 Specified Spaces
To display a space of specified width and/or height, use a display specification of the form
(space . props), where props is a property list (a list of alternating properties and values).
You can put this property on one or more consecutive characters; a space of the specified
height and width is displayed in place of all of those characters. These are the properties
you can use in props to specify the weight of the space::width width
If width is a number, it specifies that the space width should be width times
the normal character width. width can also be a pixel width specification (seeSection 41.16.3 [Pixel Specification], page 1201).
:relative-width factor
Specifies that the width of the stretch should be computed from the first characterin the group of consecutive characters that have the same display property.

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The space width is the pixel width of that character, multiplied by factor. (Ontext-mode terminals, the “pixel width” of a character is usually 1, but it could
be more for TABs and double-width CJK characters.):align-to hpos
Specifies that the space should be wide enough to reach the column hpos. If hpos
is a number, it is a column number, and is measured in units of the canonicalcharacter width (see Section 30.3.2 [Frame Font], page 797). hpos can also be a
pixel width specification (see Section 41.16.3 [Pixel Specification], page 1201).
When the current line is wider than the window, and is either displayed by one
or more continuation lines, or is truncated and possibly scrolled horizontally(see Section 29.23 [Horizontal Scrolling], page 767), hpos is measured from the
beginning of the logical line, not from the visual beginning of the screen line.
This way, alignment produced by :align-to is consistent with functions thatcount columns, such as current-column and move-to-column (see Section 33.16[Columns], page 909).
You should use one and only one of the above properties. You can also specify the heightof the space, with these properties::height height
Specifies the height of the space. If height is a number, it specifies that the
space height should be height times the normal character height. The height
may also be a pixel height specification (see Section 41.16.3 [Pixel Specification],
page 1201).
:relative-height factor
Specifies the height of the space, multiplying the ordinary height of the text
having this display specification by factor.
:ascent ascent
If the value of ascent is a non-negative number no greater than 100, it specifies
that ascent percent of the height of the space should be considered as the ascentof the space—that is, the part above the baseline. The ascent may also be
specified in pixel units with a pixel ascent specification (see Section 41.16.3[Pixel Specification], page 1201).
Don’t use both :height and :relative-height together.
The :width and :align-to properties are supported on non-graphic terminals, but theother space properties in this section are not.
Note that space properties are treated as paragraph separators for the purposes ofreordering bidirectional text for display. See Section 41.27 [Bidirectional Display], page 1250,
for the details.

41.16.3 Pixel Specification for Spaces
The value of the :width, :align-to, :height, and :ascent properties can be a special
kind of expression that is evaluated during redisplay. The result of the evaluation is used as
an absolute number of pixels.
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expr ::= num | (num) | unit | elem | pos | image | xwidget | form
num ::= integer | float | symbol
unit ::= in | mm | cm | width | heightelem ::= left-fringe | right-fringe | left-margin | right-margin| scroll-bar | text
pos ::= left | center | rightform ::= (num . expr) | (op expr ...)
op::= + | -The form num specifies a fraction of the default frame font height or width. The form(num) specifies an absolute number of pixels. If num is a symbol, symbol, its buffer-local
variable binding is used; that binding can be either a number or a cons cell of the forms
shown above (including yet another cons cell whose car is a symbol that has a buffer-local
binding).
The in, mm, and cm units specify the number of pixels per inch, millimeter, and centimeter,
respectively. The width and height units correspond to the default width and height ofthe current face. An image specification of the form (image . props) (see Section 41.17.2[Image Descriptors], page 1207) corresponds to the width or height of the specified image.
Similarly, an xwidget specification of the form (xwidget . props) stands for the width orheight of the specified xwidget. See Section 41.19 [Xwidgets], page 1228.
The elements left-fringe, right-fringe, left-margin, right-margin, scroll-bar,
and text specify the width of the corresponding area of the window. When the window
displays line numbers (see Section 41.10 [Size of Displayed Text], page 1157), the width of
the text area is decreased by the screen space taken by the line-number display.
The left, center, and right positions can be used with :align-to to specify a position
relative to the left edge, center, or right edge of the text area. When the window displays
line numbers, and :align-to is used in display properties of buffer text (as opposed toheader line, see below), the left and the center positions are offset to account for thescreen space taken by the line-number display.
Any of the above window elements (except text) can also be used with :align-to to
specify that the position is relative to the left edge of the given area. Once the base offset
for a relative position has been set (by the first occurrence of one of these symbols), further
occurrences of these symbols are interpreted as the width of the specified area. For example,
to align to the center of the left-margin, use:align-to (+ left-margin (0.5 . left-margin))If no specific base offset is set for alignment, it is always relative to the left edge of thetext area. For example, ‘:align-to 0’ aligns with the first text column in the text area.
When the window displays line numbers, the text is considered to start where the spaceused for line-number display ends.
A value of the form (num . expr) stands for the product of the values of num and expr.
For example, (2 . in) specifies a width of 2 inches, while (0.5 . image) specifies half thewidth (or height) of the specified image (which should be given by its image spec).
The form (+ expr ...) adds up the value of the expressions. The form (- expr ...)
negates or subtracts the value of the expressions.
Text shown in the header line that uses :align-to display specifications is not automatically realigned when display-line-numbers-mode is turned on and off, or when thewidth of line numbers on display changes. To arrange for the header-line text alignmentChapter 41: Emacs Display

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to be updated, thus keeping the header-line text aligned with the buffer text, turn on theheader-line-indent-mode in the buffer and use its two variables, header-line-indentand header-line-indent-width, in the display specification. See Section 24.4.7 [Header
Lines], page 559. Here’s a simple example:(setq header-line-format(concat (propertize " "'display'(space :align-to(+ header-line-indent-width 10)))"Column"))
This will keep the text ‘Column’ on the header line aligned with column 10 of buffer text,
regardless of whether display-line-numbers-mode is on or off, and also when line-number
display changes its width.

41.16.4 Other Display Specifications
Here are the other sorts of display specifications that you can use in the display text
property.
string

Display string instead of the text that has this property.
Recursive display specifications are not supported—string’s display properties,
if any, are not used.

(image . image-props)
This kind of display specification is an image descriptor (see Section 41.17.2[Image Descriptors], page 1207). When used as a display specification, it means
to display the image instead of the text that has the display specification.
(slice x y width height)
This specification together with image specifies a slice (a partial area) of theimage to display. The elements y and x specify the top left corner of the slice,
within the image; width and height specify the width and height of the slice.
Integers are numbers of pixels. A floating-point number in the range 0.0–1.0
stands for that fraction of the width or height of the entire image.
((margin nil) string)
A display specification of this form means to display string instead of the textthat has the display specification, at the same position as that text. It isequivalent to using just string, but it is done as a special case of marginal display(see Section 41.16.5 [Display Margins], page 1205).
(left-fringe bitmap [face])(right-fringe bitmap [face])
This display specification on any character of a line of text causes the specified
bitmap be displayed in the left or right fringes for that line, instead of thecharacters that have the display specification. The optional face specifies theface whose colors are to be used for the bitmap display. See Section 41.13.4[Fringe Bitmaps], page 1192, for the details.

Chapter 41: Emacs Display

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This display specification affects all the space characters within the text that has
the specification. It displays all of these spaces factor times as wide as normal.
The element factor should be an integer or float. Characters other than spaces
are not affected at all; in particular, this has no effect on tab characters.
(min-width (width))
This display specification ensures the text that has it takes at least width spaceon display, by adding a stretch of white space to the end of the text if the text isshorter than width. The text is partitioned using the identity of the parameter,
which is why the parameter is a list with one element. For instance:(insert (propertize "foo" 'display '(min-width (6.0))))This will add padding after ‘foo’ bringing the total width up to the width of six
normal characters. Note that the affected characters are identified by the (6.0)
list in the display property, compared with eq. The element width can be either
an integer or a float specifying the required minimum width of the text (seeSection 41.16.3 [Pixel Specification], page 1201).
(height height)
This display specification makes the text taller or shorter. Here are the possibilities for height:(+ n)This means to use a font that is n steps larger. A step is definedby the set of available fonts—specifically, those that match what
was otherwise specified for this text, in all attributes except height.
Each size for which a suitable font is available counts as anotherstep. n should be an integer.

(- n)This means to use a font that is n steps smaller.

a number, factor
A number, factor, means to use a font that is factor times as tall as
the default font.
a symbol, function
A symbol is a function to compute the height. It is called with thecurrent height as argument, and should return the new height touse.
anything else, form
If the height value doesn’t fit the previous possibilities, it is a form.
Emacs evaluates it to get the new height, with the symbol heightbound to the current specified font height.
(raise factor)
This kind of display specification raises or lowers the text it applies to, relative
to the baseline of the line. It is mainly meant to support display of subscripts
and superscripts.
The factor must be a number, which is interpreted as a multiple of the heightof the affected text. If it is positive, that means to display the characters raised.
If it is negative, that means to display them lower down.

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Note that if the text also has a height display specification, which was specified
before (i.e. to the left of) raise, the latter will affect the amount of raising or
lowering in pixels, because that is based on the height of the text being raised.
Therefore, if you want to display a sub- or superscript that is smaller than thenormal text height, consider specifying raise before height.
You can make any display specification conditional. To do that, package it in anotherlist of the form (when condition . spec). Then the specification spec applies only whencondition evaluates to a non-nil value. During the evaluation, object is bound to the stringor buffer having the conditional display property. position and buffer-position arebound to the position within object and the buffer position where the display property
was found, respectively. Both positions can be different when object is a string.
Note that condition will only be evaluated when redisplay examines the text where thisdisplay spec is located, so this feature is best suited for conditions that are relatively stable,
i.e. yield, for each particular buffer position, the same results on every evaluation. If theresults change for the same text location, e.g., if the result depends on the position of point,then the conditional specification might not do what you want, because redisplay examines
only those parts of buffer text where it has reasons to assume that something changed since
the last display cycle.

41.16.5 Displaying in the Margins
A buffer can have blank areas called display margins on the left and on the right. Ordinary
text never appears in these areas, but you can put things into the display margins using
the display property. There is currently no way to make text or images in the margin
mouse-sensitive.
The way to display something in the margins is to specify it in a margin display
specification in the display property of some text. This is a replacing display specification,
meaning that the text you put it on does not get displayed; the margin display appears, butthat text does not.
A margin display specification looks like ((margin right-margin) spec) or ((marginleft-margin) spec). Here, spec is another display specification that says what to display
in the margin. Typically it is a string of text to display, or an image descriptor.
To display something in the margin in association with certain buffer text, without alteringor preventing the display of that text, put on that text an overlay with a before-string
property, and put the margin display specification on the contents of the before-string.
Note that if the string to be displayed in the margin doesn’t specify a face, its face isdetermined using the same rules and priorities as it is for strings displayed in the text area(see Section 41.12.4 [Displaying Faces], page 1174). If this results in undesirable “leaking”
of faces into the margin, make sure the string has an explicit face specified for it.
Before the display margins can display anything, you must give them a nonzero width.
The usual way to do that is to set these variables:[Variable]
This variable specifies the width of the left margin, in character cell (a.k.a. “column”)
units. It is buffer-local in all buffers. A value of nil means no left marginal area.

left-margin-widthChapter 41: Emacs Display

1206[Variable]
This variable specifies the width of the right margin, in character cell units. It isbuffer-local in all buffers. A value of nil means no right marginal area.

right-margin-width

Setting these variables does not immediately affect the window. These variables arechecked when a new buffer is displayed in the window. Thus, you can make changes takeeffect by calling set-window-buffer. Do not use these variables to try to determine thecurrent width of the left or right margin. Instead, use the function window-margins.
You can also set the margin widths immediately.

set-window-margins window left &optional right[Function]
This function specifies the margin widths for window window, in character cell units.
The argument left controls the left margin, and right controls the right margin (default0).
If window is not large enough to accommodate margins of the desired width, thisleaves the margins of window unchanged.
The values specified here may be later overridden by invoking set-window-buffer(see Section 29.11 [Buffers and Windows], page 720) on window with its keep-margins
argument nil or omitted.

window-margins &optional window[Function]
This function returns the width of the left and right margins of window as a cons cellof the form (left . right). If one of the two marginal areas does not exist, its widthis returned as nil; if neither of the two margins exist, the function returns (nil). If
window is nil, the selected window is used.

41.17 Images
To display an image in an Emacs buffer, you must first create an image descriptor, then use
it as a display specifier in the display property of text that is displayed (see Section 41.16[Display Property], page 1198).
Emacs is usually able to display images when it is run on a graphical terminal. Images
cannot be displayed in a text terminal, on certain graphical terminals that lack the support for this, or if Emacs is compiled without image support. You can use the function
display-images-p to determine if images can in principle be displayed (see Section 30.26[Display Feature Testing], page 849).

41.17.1 Image Formats
Emacs can display a number of different image formats. Some of these image formats aresupported only if particular support libraries are installed. On some platforms, Emacs canload support libraries on demand; if so, the variable dynamic-library-alist can be used
to modify the set of known names for these dynamic libraries. See Section 42.21 [Dynamic
Libraries], page 1299.
Supported image formats (and the required support libraries) include PBM and XBM(which do not depend on support libraries and are always available), XPM (libXpm), GIF(libgif or libungif), JPEG (libjpeg), TIFF (libtiff), PNG (libpng), SVG (librsvg),
and WebP (libwebp).

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Each of these image formats is associated with an image type symbol. The symbols forthe above formats are, respectively, pbm, xbm, xpm, gif, jpeg, tiff, png, svg, and webp.
On some platforms, the built-in image support that doesn’t require any optional libraries
includes BMP images.3
Furthermore, if you build Emacs with ImageMagick (libMagickWand) support, Emacs
can display any image format that ImageMagick can. See Section 41.17.5 [ImageMagick
Images], page 1212. All images displayed via ImageMagick have type symbol imagemagick.
[Variable]
This variable contains a list of type symbols for image formats which are potentially
supported in the current configuration.
“Potentially” means that Emacs knows about the image types, not necessarily thatthey can be used (for example, they could depend on unavailable dynamic libraries).
To know which image types are really available, use image-type-available-p.

image-types

image-type-available-p type

[Function]
This function returns non-nil if images of type type can be loaded and displayed.
type must be an image type symbol.
For image types whose support libraries are statically linked, this function always
returns t. For image types whose support libraries are dynamically loaded, it returns
t if the library could be loaded and nil otherwise.

41.17.2 Image Descriptors
An image descriptor is a list which specifies the underlying data for an image, and how
to display it. It is typically used as the value of a display overlay or text property (seeSection 41.16.4 [Other Display Specs], page 1203); but See Section 41.17.9 [Showing Images],
page 1222, for convenient helper functions to insert images into buffers.
Each image descriptor has the form (image . props), where props is a property list ofalternating keyword symbols and values, including at least the pair :type type that specifies
the image type.
Image descriptors which define image dimensions, :width, :height, :max-width and:max-height, may take either an integer, which represents the dimension in pixels, or a pair(value . em), where value is the dimension’s length in ems 4 . One em is equivalent to theheight of the font and value may be an integer or a float.
The following is a list of properties that are meaningful for all image types (there arealso properties which are meaningful only for certain image types, as documented in thefollowing subsections)::type typeThe image type. Every image descriptor must include this property.
:file file
This says to load the image from file file. If file is not an absolute file name, it
is expanded relative to each of the directories mentioned by image-load-path(see Section 41.17.8 [Defining Images], page 1220).
3
4

On MS-Windows, this requires w32-use-native-image-API to be set non-nil.
In typography an em is a distance equivalent to the height of the type. For example when using 12 pointtype 1 em is equal to 12 points. Its use ensures distances and type remain proportional.

Chapter 41: Emacs Display

1208:data data
This specifies the raw image data. Each image descriptor must have either:data or :file, but not both.
For most image types, the value of a :data property should be a string containing
the image data. Some image types do not support :data; for some others, :dataalone is not enough, so you need to use other image properties along with :data.
See the following subsections for details.
:margin margin
This specifies how many pixels to add as an extra margin around the image.
The value, margin, must be a non-negative number, or a pair (x . y) of such
numbers. If it is a pair, x specifies how many pixels to add horizontally, andy specifies how many pixels to add vertically. If :margin is not specified, thedefault is zero.
:ascent ascentThis specifies the amount of the image’s height to use for its ascent—that is,
the part above the baseline. The value, ascent, must be a number in the range
0 to 100, or the symbol center.
If ascent is a number, that percentage of the image’s height is used for its ascent.
If ascent is center, the image is vertically centered around a centerline which
would be the vertical centerline of text drawn at the position of the image, in themanner specified by the text properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
:relief relief
This adds a shadow rectangle around the image. The value, relief, specifies thewidth of the shadow lines, in pixels. If relief is negative, shadows are drawn
so that the image appears as a pressed button; otherwise, it appears as anunpressed button.
:width width, :height height
The :width and :height keywords are used for scaling the image. If only oneof them is specified, the other one will be calculated so as to preserve the aspectratio. If both are specified, aspect ratio may not be preserved.
:max-width max-width, :max-height max-height
The :max-width and :max-height keywords are used for scaling if the size ofthe image exceeds these values. If :width is set, it will have precedence overmax-width, and if :height is set, it will have precedence over max-height, but
you can otherwise mix these keywords as you wish.
If both :max-width and :height are specified, but :width is not, preserving
the aspect ratio might require that width exceeds :max-width. If this happens,
scaling will use a smaller value for the height so as to preserve the aspect ratio
while not exceeding :max-width. Similarly when both :max-height and :width
are specified, but :height is not. For example, if you have a 200x100 image
and specify that :width should be 400 and :max-height should be 150, you’ll
end up with an image that is 300x150: Preserving the aspect ratio and notexceeding the “max” setting. This combination of parameters is a useful way ofChapter 41: Emacs Display

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saying “display this image as large as possible, but no larger than the available
display area”.
:scale scaleThis should be a number, where values higher than 1 means to increase thesize, and lower means to decrease the size, by multiplying both the width andheight. For instance, a value of 0.25 will make the image a quarter size ofwhat it originally was. If the scaling makes the image larger than specified by:max-width or :max-height, the resulting size will not exceed those two values.
If both :scale and :height/:width are specified, the height/width will be
adjusted by the specified scaling factor.
:rotation angle
Specifies a rotation angle in degrees. Only multiples of 90 degrees are supported,
unless the image type is imagemagick. Positive values rotate clockwise, negativevalues counter-clockwise. Rotation is performed after scaling and cropping.
:flip flip
If this is t, the image will be horizontally flipped. Currently it has no effect if
the image type is imagemagick. Vertical flipping can be achieved by rotating
the image 180 degrees and toggling this value.
:transform-smoothing smooth
If this is t, any image transform will have smoothing applied; if nil, no smoothing
will be applied. The exact algorithm used is platform dependent, but shouldbe equivalent to bilinear filtering. Disabling smoothing will use the nearest
neighbor algorithm.
If this property is not specified, create-image will use the image-transformsmoothing user option to say whether scaling should be done or not. This
option can be nil (no smoothing), t (use smoothing) or a predicate function
that’s called with the image object as the only parameter, and should return
either nil or t. The default is for down-scaling to apply smoothing, and forlarge up-scaling to not apply smoothing.
:index frame
See Section 41.17.10 [Multi-Frame Images], page 1224.
:conversion algorithm
This specifies a conversion algorithm that should be applied to the image before
it is displayed; the value, algorithm, specifies which algorithm.
laplaceembossSpecifies the Laplace edge detection algorithm, which blurs out
small differences in color while highlighting larger differences. People
sometimes consider this useful for displaying the image for a disabled
button.

(edge-detection :matrix matrix :color-adjust adjust)Specifies a general edge-detection algorithm. matrix must be either
a nine-element list or a nine-element vector of numbers. A pixel atposition x/y in the transformed image is computed from original

Chapter 41: Emacs Display

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pixels around that position. matrix specifies, for each pixel in theneighborhood of x/y, a factor with which that pixel will influence
the transformed pixel; element 0 specifies the factor for the pixel at
x − 1/y − 1, element 1 the factor for the pixel at x/y − 1 etc., asshown below:x − 1/y − 1 x/y − 1
 x − 1/yx/yx − 1/y + 1 x/y + 1


x + 1/y − 1
x + 1/y 
x + 1/y + 1
The resulting pixel is computed from the color intensity of the color
resulting from summing up the RGB values of surrounding pixels,
multiplied by the specified factors, and dividing that sum by thesum of the factors’ absolute values.
Laplace edge-detection currently uses a matrix of
1
0
0


0 0
0 0 
0 −1


Emboss edge-detection uses a matrix of
2 −1
 −1
0
0
1


disabled

0
1 
−2


Specifies transforming the image so that it looks disabled.

:mask mask
If mask is heuristic or (heuristic bg), build a clipping mask for the image,so that the background of a frame is visible behind the image. If bg is not
specified, or if bg is t, determine the background color of the image by looking
at the four corners of the image, assuming the most frequently occurring color
from the corners is the background color of the image. Otherwise, bg must be alist (red green blue) specifying the color to assume for the background of theimage.
If mask is nil, remove a mask from the image, if it has one. Images in someformats include a mask which can be removed by specifying :mask nil.
:pointer shape
This specifies the pointer shape when the mouse pointer is over this image. See
Section 30.19 [Pointer Shape], page 839, for available pointer shapes.
:map map

This associates an image map of hot spots with this image.
An image map is an alist where each element has the format (area id plist).
An area is specified as either a rectangle, a circle, or a polygon.
A rectangle is a cons (rect . ((x0 . y0) . (x1 . y1))) which specifies the
pixel coordinates of the upper left and bottom right corners of the rectangle
area.

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A circle is a cons (circle . ((x0 . y0) . r)) which specifies the center andthe radius of the circle; r may be a float or integer.
A polygon is a cons (poly . [x0 y0 x1 y1 ...]) where each pair in the vector
describes one corner in the polygon.
When the mouse pointer lies on a hot-spot area of an image, the plist of that
hot-spot is consulted; if it contains a help-echo property, that defines a tool-tip
for the hot-spot, and if it contains a pointer property, that defines the shape ofthe mouse cursor when it is on the hot-spot. See Section 30.19 [Pointer Shape],
page 839, for available pointer shapes.
When you click the mouse when the mouse pointer is over a hot-spot, an event
is composed by combining the id of the hot-spot with the mouse event; forinstance, [area4 mouse-1] if the hot-spot’s id is area4.
Note that the map’s coordinates should reflect the displayed image after alltransforms have been done (rotation, scaling and so on), and also note that
Emacs (by default) performs auto-scaling of images, so to make things match up,
you should either specify :scale 1.0 when creating the image, or use the resultof image-compute-scaling-factor to compute the elements of the map.

image-mask-p spec &optional frame[Function]
This function returns t if image spec has a mask bitmap. frame is the frame on which
the image will be displayed. frame nil or omitted means to use the selected frame(see Section 30.10 [Input Focus], page 824).

image-transforms-p &optional frame[Function]
This function returns non-nil if frame supports image scaling and rotation. frame nilor omitted means to use the selected frame (see Section 30.10 [Input Focus], page 824).
The returned list includes symbols that indicate which image transform operations
are supported:
scale

Image scaling is supported by frame via the :scale, :width, :height,:max-width, and :max-height properties.

rotate90

Image rotation is supported by frame if the rotation angle is an integral
multiple of 90 degrees.

If image transforms are not supported, :rotation, :crop, :width, :height, :scale,:max-width and :max-height will only be usable through ImageMagick, if available(see Section 41.17.5 [ImageMagick Images], page 1212).

41.17.3 XBM Images
To use XBM format, specify xbm as the image type. This image format doesn’t require an
external library, so images of this type are always supported.
Additional image properties supported for the xbm image type are::foreground foreground
The value, foreground, should be a string specifying the image foreground color,or nil for the default color. This color is used for each pixel in the XBM thatis 1. The default is the frame’s foreground color.

Chapter 41: Emacs Display

1212:background background
The value, background, should be a string specifying the image backgroundcolor, or nil for the default color. This color is used for each pixel in the XBM
that is 0. The default is the frame’s background color.
If you specify an XBM image using data within Emacs instead of an external file, use
the following three properties::data data
The value, data, specifies the contents of the image. There are three formats
you can use for data:• A vector of strings or bool-vectors, each specifying one line of the image.
Do specify :data-height and :data-width.
• A string containing the same byte sequence as an XBM file would contain.
• A string or a bool-vector containing the bits of the image (plus perhaps
some extra bits at the end that will not be used). It should contain at least
stride * height bits, where stride is the smallest multiple of 8 greaterthan or equal to the width of the image. In this case, you should specify:data-height, :data-width and :stride, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the sizeof the image.
:stride stride
The number of bool vector entries stored for each row; the smallest multiple of
8 greater than or equal to width.

41.17.4 XPM Images
To use XPM format, specify xpm as the image type. The additional image property:color-symbols is also meaningful with the xpm image type::color-symbols symbols
The value, symbols, should be an alist whose elements have the form (name .
color). In each element, name is the name of a color as it appears in the image
file, and color specifies the actual color to use for displaying that name.

41.17.5 ImageMagick Images
If your Emacs build has ImageMagick support, you can use the ImageMagick library to load
many image formats (see Section “File Conveniences” in The GNU Emacs Manual). The
image type symbol for images loaded via ImageMagick is imagemagick, regardless of theactual underlying image format.
To check for ImageMagick support, use the following:(image-type-available-p 'imagemagick)[Function]
This function returns a list of image file extensions supported by the current ImageMagick installation. Each list element is a symbol representing an internal ImageMagick
name for an image type, such as BMP for .bmp images.

imagemagick-types

Chapter 41: Emacs Display

1213[User Option]
The value of this variable is a list of ImageMagick image types which Emacs may
attempt to render using ImageMagick. Each list element should be one of the symbols
in the list returned by imagemagick-types, or an equivalent string. Alternatively, avalue of t enables ImageMagick for all possible image types. Regardless of the valueof this variable, imagemagick-types-inhibit (see below) takes precedence.

imagemagick-enabled-types[User Option]
The value of this variable lists the ImageMagick image types which should never berendered using ImageMagick, regardless of the value of imagemagick-enabled-types.
A value of t disables ImageMagick entirely.

imagemagick-types-inhibit[Variable]
This variable is an alist mapping image types to file name extensions. Emacs uses
this in conjunction with the :format image property (see below) to give a hint to the
ImageMagick library as to the type of an image. Each element has the form (typeextension), where type is a symbol specifying an image content-type, and extension
is a string that specifies the associated file name extension.

image-format-suffixes

Images loaded with ImageMagick support the following additional image descriptor
properties::background backgroundbackground, if non-nil, should be a string specifying a color, which is used as
the image’s background color if the image supports transparency. If the value isnil, it defaults to the frame’s background color.
:format typeThe value, type, should be a symbol specifying the type of the image data, as
found in image-format-suffixes. This is used when the image does not havean associated file name, to provide a hint to ImageMagick to help it detect theimage type.
:crop geometry
The value of geometry should be a list of the form (width height x y). widthand height specify the width and height of the cropped image. If x is a positive
number it specifies the offset of the cropped area from the left of the original
image, and if negative the offset from the right. If y is a positive number it
specifies the offset from the top of the original image, and if negative from thebottom. If x or y are nil or unspecified the crop area will be centered on theoriginal image.
If the crop area is outside or overlaps the edge of the image it will be reduced
to exclude any areas outside of the image. This means it is not possible to use:crop to increase the size of the image by entering large width or height values.
Cropping is performed after scaling but before rotation.

41.17.6 SVG Images
SVG (Scalable Vector Graphics) is an XML format for specifying images. SVG images
support the following additional image descriptor properties:

Chapter 41: Emacs Display

1214:foreground foregroundforeground, if non-nil, should be a string specifying a color, which is used as
the image’s foreground color. If the value is nil, it defaults to the current face’s
foreground color.
:background backgroundbackground, if non-nil, should be a string specifying a color, which is used as
the image’s background color if the image supports transparency. If the value isnil, it defaults to the current face’s background color.
:css css

css, if non-nil, should be a string specifying the CSS to override the default
CSS used when generating the image.

SVG library
If your Emacs build has SVG support, you can create and manipulate these images with thefollowing functions from the svg.el library.

svg-create width height &rest args

[Function]
Create a new, empty SVG image with the specified dimensions. args is an argument
plist with you can specify following::stroke-width
The default width (in pixels) of any lines created.
:stroke

The default stroke color on any lines created.

This function returns an SVG object, a Lisp data structure that specifies an SVG
image, and all the following functions work on that structure. The argument svg inthe following functions specifies such an SVG object.

svg-gradient svg id type stops[Function]
Create a gradient in svg with identifier id. type specifies the gradient type, and canbe either linear or radial. stops is a list of percentage/color pairs.

The following will create a linear gradient that goes from red at the start, to green
25% of the way, to blue at the end:
(svg-gradient svg "gradient1" 'linear'((0 . "red") (25 . "green") (100 . "blue")))
The gradient created (and inserted into the SVG object) can later be used by all
functions that create shapes.
All the following functions take an optional list of keyword parameters that alter thevarious attributes from their default values. Valid attributes include::stroke-width
The width (in pixels) of lines drawn, and outlines around solid shapes.
:stroke-color
The color of lines drawn, and outlines around solid shapes.
:fill-color
The color used for solid shapes.

Chapter 41: Emacs Display

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The identified of the shape.

:id:gradient

If given, this should be the identifier of a previously defined gradient object.
:clip-path
Identifier of a clip path.

svg-rectangle svg x y width height &rest args

[Function]
Add to svg a rectangle whose upper left corner is at position x/y and whose size iswidth/height.
(svg-rectangle svg 100 100 500 500 :gradient "gradient1")

svg-circle svg x y radius &rest args

[Function]

Add to svg a circle whose center is at x/y and whose radius is radius.

svg-ellipse svg x y x-radius y-radius &rest args

[Function]
Add to svg an ellipse whose center is at x/y, and whose horizontal radius is x-radius
and the vertical radius is y-radius.

svg-line svg x1 y1 x2 y2 &rest args

[Function]

Add to svg a line that starts at x1/y1 and extends to x2/y2.

svg-polyline svg points &rest args

[Function]
Add to svg a multiple-segment line (a.k.a. “polyline”) that goes through points, which
is a list of X/Y position pairs.
(svg-polyline svg '((200 . 100) (500 . 450) (80 . 100)):stroke-color "green")

svg-polygon svg points &rest args

[Function]
Add a polygon to svg where points is a list of X/Y pairs that describe the outercircumference of the polygon.
(svg-polygon svg '((100 . 100) (200 . 150) (150 . 90))
:stroke-color "blue" :fill-color "red")

svg-path svg commands &rest args

[Function]
Add the outline of a shape to svg according to commands, see [SVG Path Commands],
page 1217.
Coordinates by default are absolute. To use coordinates relative to the last position,or – initially – to the origin, set the attribute :relative to t. This attribute can be
specified for the function or for individual commands. If specified for the function, thenall commands use relative coordinates by default. To make an individual commanduse absolute coordinates, set :relative to nil.
(svg-path svg'((moveto ((100 . 100)))(lineto ((200 . 0) (0 . 200) (-200 . 0)))(lineto ((100 . 100)) :relative nil)):stroke-color "blue":fill-color "lightblue":relative t)

Chapter 41: Emacs Display

svg-text svg text &rest args

1216

[Function]

Add the specified text to svg.
(svg-text
svg "This is a text":font-size "40"
:font-weight "bold":stroke "black":fill "white":font-family "impact":letter-spacing "4pt":x 300:y 400:stroke-width 1)

svg-embed svg image image-type datap &rest args

[Function]
Add an embedded (raster) image to svg. If datap is nil, image should be a file name;otherwise it should be a string containing the image data as raw bytes. image-typeshould be a MIME image type, for instance "image/jpeg".
(svg-embed svg "~/rms.jpg" "image/jpeg" nil:width "100px" :height "100px":x "50px" :y "75px")

svg-embed-base-uri-image svg relative-filename &rest args

[Function]
To svg add an embedded (raster) image placed at relative-filename. relative-filename
is searched inside file-name-directory of the :base-uri svg image property.
:base-uri specifies a (possibly non-existing) file name of the svg image to be created,thus all the embedded files are searched relatively to the :base-uri filename’s
directory. If :base-uri is omitted, then filename from where svg image is loaded
is used. Using :base-uri improves the performance of embedding large images,
comparing to svg-embed, because all the work is done directly by librsvg.
;; Embedding /tmp/subdir/rms.jpg and /tmp/another/rms.jpg(svg-embed-base-uri-image svg "subdir/rms.jpg":width "100px" :height "100px":x "50px" :y "75px")(svg-embed-base-uri-image svg "another/rms.jpg":width "100px" :height "100px":x "75px" :y "50px")(svg-image svg :scale 1.0:base-uri "/tmp/dummy":width 175 :height 175)svg-clip-path svg &rest args

[Function]
Add a clipping path to svg. If applied to a shape via the :clip-path property, parts ofthat shape which lie outside of the clipping path are not drawn.
(let ((clip-path (svg-clip-path svg :id "foo")))(svg-circle clip-path 200 200 175))(svg-rectangle svg 50 50 300 300

Chapter 41: Emacs Display

1217:fill-color "red":clip-path "url(#foo)")svg-node svg tag &rest args

[Function]
Add the custom node tag to svg.
(svg-node svg'rect:width 300 :height 200 :x 50 :y 100 :fill-color "green")

svg-remove svg id[Function]

Remove the element with identifier id from the svg.

svg-image svg[Function]
Finally, the svg-image takes an SVG object as its argument and returns an image
object suitable for use in functions like insert-image.

Here’s a complete example that creates and inserts an image with a circle:(let ((svg (svg-create 400 400 :stroke-width 10)))(svg-gradient svg "gradient1" 'linear '((0 . "red") (100 . "blue")))(svg-circle svg 200 200 100 :gradient "gradient1":stroke-color "green")(insert-image (svg-image svg)))

SVG Path Commands
SVG paths allow creation of complex images by combining lines, curves, arcs, and otherbasic shapes. The functions described below allow invoking SVG path commands from a
Lisp program.

moveto points[Command]Move the pen to the first point in points. Additional points are connected with lines.
points is a list of X/Y coordinate pairs. Subsequent moveto commands represent thestart of a new subpath.
(svg-path svg '((moveto ((200 . 100) (100 . 200) (0 . 100)))):fill "white" :stroke "black")[Command]End the current subpath by connecting it back to its initial point. A line is drawn
along the connection.
(svg-path svg '((moveto ((200 . 100) (100 . 200) (0 . 100)))(closepath)(moveto ((75 . 125) (100 . 150) (125 . 125)))(closepath)):fill "red" :stroke "black")

closepath

lineto points[Command]Draw a line from the current point to the first element in points, a list of X/Y position
pairs. If more than one point is specified, draw a polyline.
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horizontal-lineto x-coordinates[Command]Draw a horizontal line from the current point to the first element in x-coordinates.
Specifying multiple coordinates is possible, although this usually doesn’t make sense.
(svg-path svg '((moveto ((100 . 200)))(horizontal-lineto (300))):stroke "green")

vertical-lineto y-coordinates[Command]Draw vertical lines.
(svg-path svg '((moveto ((200 . 100)))(vertical-lineto (300))):stroke "green")

curveto coordinate-sets[Command]Using the first element in coordinate-sets, draw a cubic Bézier curve from the current
point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is
a list of the form (x1 y1 x2 y2 x y), where (x, y) is the curve’s end point. (x1, y1)and (x2, y2) are control points at the beginning and at the end, respectively.
(svg-path svg '((moveto ((100 . 100)))(curveto ((200 100 100 200 200 200)
(300 200 0 100 100 100)))):fill "transparent" :stroke "red")smooth-curveto coordinate-sets[Command]Using the first element in coordinate-sets, draw a cubic Bézier curve from the current
point. If there are multiple coordinate sets, draw a polybezier. Each coordinate set is
a list of the form (x2 y2 x y), where (x, y) is the curve’s end point and (x2, y2) isthe corresponding control point. The first control point is the reflection of the second
control point of the previous command relative to the current point, if that command
was curveto or smooth-curveto. Otherwise the first control point coincides with thecurrent point.
(svg-path svg '((moveto ((100 . 100)))(curveto ((200 100 100 200 200 200)))(smooth-curveto ((0 100 100 100)))):fill "transparent" :stroke "blue")quadratic-bezier-curveto coordinate-sets[Command]Using the first element in coordinate-sets, draw a quadratic Bézier curve from thecurrent point. If there are multiple coordinate sets, draw a polybezier. Each coordinate
set is a list of the form (x1 y1 x y), where (x, y) is the curve’s end point and (x1, y1)
is the control point.
(svg-path svg '((moveto ((200 . 100)))(quadratic-bezier-curveto ((300 100 300 200)))(quadratic-bezier-curveto ((300 300 200 300)))(quadratic-bezier-curveto ((100 300 100 200)))(quadratic-bezier-curveto ((100 100 200 100)))):fill "transparent" :stroke "pink")

Chapter 41: Emacs Display1219

smooth-quadratic-bezier-curveto coordinate-sets[Command]Using the first element in coordinate-sets, draw a quadratic Bézier curve from thecurrent point. If there are multiple coordinate sets, draw a polybezier. Each coordinate
set is a list of the form (x y), where (x, y) is the curve’s end point. The control point is
the reflection of the control point of the previous command relative to the current point,
if that command was quadratic-bezier-curveto or smooth-quadratic-beziercurveto. Otherwise the control point coincides with the current point.
(svg-path svg '((moveto ((200 . 100)))(quadratic-bezier-curveto ((300 100 300 200)))(smooth-quadratic-bezier-curveto ((200 300)))(smooth-quadratic-bezier-curveto ((100 200)))(smooth-quadratic-bezier-curveto ((200 100)))):fill "transparent" :stroke "lightblue")elliptical-arc coordinate-sets[Command]Using the first element in coordinate-sets, draw an elliptical arc from the current
point. If there are multiple coordinate sets, draw a sequence of elliptical arcs. Eachcoordinate set is a list of the form (rx ry x y), where (x, y) is the end point of theellipse, and (rx, ry) are its radii. Attributes may be appended to the list::x-axis-rotation
The angle in degrees by which the x-axis of the ellipse is rotated relative
to the x-axis of the current coordinate system.
:large-arc
If set to t, draw an arc sweep greater than or equal to 180 degrees.
Otherwise, draw an arc sweep smaller than or equal to 180 degrees.
:sweepIf set to t, draw an arc in positive angle direction. Otherwise, draw it innegative angle direction.

(svg-path svg '((moveto ((200 . 250)))(elliptical-arc ((75 75 200 350)))):fill "transparent" :stroke "red")(svg-path svg '((moveto ((200 . 250)))(elliptical-arc ((75 75 200 350 :large-arc t)))):fill "transparent" :stroke "green")(svg-path svg '((moveto ((200 . 250)))(elliptical-arc ((75 75 200 350 :sweep t)))):fill "transparent" :stroke "blue")(svg-path svg '((moveto ((200 . 250)))(elliptical-arc ((75 75 200 350 :large-arc t:sweep t)))):fill "transparent" :stroke "gray")(svg-path svg '((moveto ((160 . 100)))(elliptical-arc ((40 100 80 0)))(elliptical-arc ((40 100 -40 -70:x-axis-rotation -120)))(elliptical-arc ((40 100 -40 70

Chapter 41: Emacs Display

1220:x-axis-rotation -240)))):stroke "pink" :fill "lightblue":relative t)

41.17.7 Other Image Types
For PBM images, specify image type pbm. Color, gray-scale and monochromatic images aresupported. For mono PBM images, two additional image properties are supported.
:foreground foreground
The value, foreground, should be a string specifying the image foreground color,or nil for the default color. This color is used for each pixel in the PBM that is
1. The default is the frame’s foreground color.
:background background
The value, background, should be a string specifying the image backgroundcolor, or nil for the default color. This color is used for each pixel in the PBM
that is 0. The default is the frame’s background color.
The remaining image types that Emacs can support are:
GIF

Image type gif. Supports the :index property. See Section 41.17.10 [MultiFrame Images], page 1224.

JPEG

Image type jpeg.

PNG

Image type png.

TIFF

Image type tiff. Supports the :index property. See Section 41.17.10 [MultiFrame Images], page 1224.

WebP

Image type webp.

41.17.8 Defining Images
The functions create-image, defimage and find-image provide convenient ways to create
image descriptors.

create-image file-or-data &optional type data-p &rest props[Function]
This function creates and returns an image descriptor which uses the data in file-or-data.
file-or-data can be a file name or a string containing the image data; data-p should
be nil for the former case, non-nil for the latter case. If file-or-data is a relative file
name, the function will search for it in directories mentioned in image-load-path.
The optional argument type is a symbol specifying the image type. If type is omitted
or nil, create-image tries to determine the image type from the file’s first few bytes,
or else from the file’s name.
The remaining arguments, props, specify additional image properties—for example,(create-image "foo.xpm" 'xpm nil :mask 'heuristic)
See Section 41.17.2 [Image Descriptors], page 1207, for the list of supported properties.
Some properties are specific to certain image types, and are described in subsections
specific to those types.
The function returns nil if images of this type are not supported. Otherwise it returns
an image descriptor.

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defimage symbol specs &optional doc[Macro]This macro defines symbol as an image name. The arguments specs is a list which specifies how to display the image. The third argument, doc, is an optional documentation
string.
Each argument in specs has the form of a property list, and each one should specify
at least the :type property and either the :file or the :data property. The value of:type should be a symbol specifying the image type, the value of :file is the file toload the image from, and the value of :data is a string containing the actual image
data. Here is an example:(defimage test-image((:type xpm :file "~/test1.xpm")(:type xbm :file "~/test1.xbm")))defimage tests each argument, one by one, to see if it is usable—that is, if the typeis supported and the file exists. The first usable argument is used to make an image
descriptor which is stored in symbol.
If none of the alternatives will work, then symbol is defined as nil.

image-property image property[Function]
Return the value of property in image. Properties can be set by using setf. Setting aproperty to nil will remove the property from the image.

find-image specs[Function]
This function provides a convenient way to find an image satisfying one of a list ofimage specifications specs.
Each specification in specs is a property list with contents depending on image type. All
specifications must at least contain the properties :type type and either :file fileor :data data, where type is a symbol specifying the image type, e.g., xbm, file is thefile to load the image from, and data is a string containing the actual image data.
The first specification in the list whose type is supported, and file exists, is used toconstruct the image specification to be returned. If no specification is satisfied, nil isreturned.

The image is looked for in image-load-path.
[User Option]
This variable’s value is a list of locations in which to search for image files. If anelement is a string or a variable symbol whose value is a string, the string is taken to
be the name of a directory to search. If an element is a variable symbol whose value
is a list, that is taken to be a list of directories to search.

image-load-path

The default is to search in the images subdirectory of the directory specified bydata-directory, then the directory specified by data-directory, and finally in the
directories in load-path. Subdirectories are not automatically included in the search,so if you put an image file in a subdirectory, you have to supply the subdirectory explicitly. For example, to find the image images/foo/bar.xpm within data-directory,
you should specify the image as follows:(defimage foo-image '((:type xpm :file "foo/bar.xpm")))Chapter 41: Emacs Display

image-load-path-for-library library image &optional pathno-error

1222[Function]

This function returns a suitable search path for images used by the Lisp package
library.
The function searches for image first using image-load-path, excluding
data-directory/images, and then in load-path, followed by a path suitable forlibrary, which includes ../../etc/images and ../etc/images relative to the library
file itself, and finally in data-directory/images.
Then this function returns a list of directories which contains first the directory inwhich image was found, followed by the value of load-path. If path is given, it isused instead of load-path.
If no-error is non-nil and a suitable path can’t be found, don’t signal an error. Instead,
return a list of directories as before, except that nil appears in place of the image
directory.
Here is an example of using image-load-path-for-library:(defvar image-load-path) ; shush compiler(let* ((load-path (image-load-path-for-library"mh-e" "mh-logo.xpm"))(image-load-path (cons (car load-path)
image-load-path)))(mh-tool-bar-folder-buttons-init))
Images are automatically scaled when created based on the image-scaling-factor
variable. The value is either a floating point number (where numbers higher than 1 means
to increase the size and lower means to shrink the size), or the symbol auto, which willcompute a scaling factor based on the font pixel size.

41.17.9 Showing Images
You can use an image descriptor by setting up the display property yourself, but it is easier
to use the functions in this section.

insert-image image &optional string area slice inhibit-isearch[Function]
This function inserts image in the current buffer at point. The value image should be
an image descriptor; it could be a value returned by create-image, or the value of asymbol defined with defimage. The argument string specifies the text to put in thebuffer to hold the image. If it is omitted or nil, insert-image uses " " by default.
The argument area specifies whether to put the image in a margin. If it is left-margin,
the image appears in the left margin; right-margin specifies the right margin. If area
is nil or omitted, the image is displayed at point within the buffer’s text.
The argument slice specifies a slice of the image to insert. If slice is nil or omitted
the whole image is inserted. (However, note that images are chopped on display at thewindow’s right edge, because wrapping images is not supported.) Otherwise, slice is alist (x y width height) which specifies the x and y positions and width and height of
the image area to insert. Integer values are in units of pixels. A floating-point numberin the range 0.0–1.0 stands for that fraction of the width or height of the entire image.

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Internally, this function inserts string in the buffer, and gives it a display property
which specifies image. See Section 41.16 [Display Property], page 1198. By default,
doing interactive searches in the buffer will consider string when searching. If inhibitisearch is non-nil, this is inhibited.

insert-sliced-image image &optional string area rows cols

[Function]
This function inserts image in the current buffer at point, like insert-image, but
splits the image into rowsxcols equally sized slices.
Emacs displays each slice as a separate image, and allows more intuitive scrollingup/down, instead of jumping up/down the entire image when paging through a bufferthat displays (large) images.

put-image image pos &optional string area

[Function]
This function puts image image in front of pos in the current buffer. The argument
pos should be an integer or a marker. It specifies the buffer position where the image
should appear. The argument string specifies the text that should hold the image as
an alternative to the default ‘x’.
The argument image must be an image descriptor, perhaps returned by create-image
or stored by defimage.
The argument area specifies whether to put the image in a margin. If it is left-margin,
the image appears in the left margin; right-margin specifies the right margin. If area
is nil or omitted, the image is displayed at point within the buffer’s text.
Internally, this function creates an overlay, and gives it a before-string property
containing text that has a display property whose value is the image. (Whew! that
was a mouthful. . . )remove-images start end &optional buffer[Function]
This function removes images in buffer between positions start and end. If buffer isomitted or nil, images are removed from the current buffer.
This removes only images that were put into buffer the way put-image does it, notimages that were inserted with insert-image or in other ways.

image-size spec &optional pixels frame[Function]
This function returns the size of an image as a pair (width . height). spec is animage specification. pixels non-nil means return sizes measured in pixels, otherwise
return sizes measured in the default character size of frame (see Section 30.3.2 [FrameFont], page 797). frame is the frame on which the image will be displayed. frame nilor omitted means use the selected frame (see Section 30.10 [Input Focus], page 824).
[Variable]
This variable is used to define the maximum size of image that Emacs will load. Emacs
will refuse to load (and display) any image that is larger than this limit.

max-image-size

If the value is an integer, it directly specifies the maximum image height and width,
measured in pixels. If it is floating point, it specifies the maximum image height andwidth as a ratio to the frame height and width. If the value is non-numeric, there is
no explicit limit on the size of images.

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The purpose of this variable is to prevent unreasonably large images from accidentally
being loaded into Emacs. It only takes effect the first time an image is loaded. Once
an image is placed in the image cache, it can always be displayed, even if the valueof max-image-size is subsequently changed (see Section 41.17.11 [Image Cache],page 1225).

image-at-point-p[Function]

This function returns t if point is on an image, and nil otherwise.
Images inserted with the insertion functions above also get a local keymap installed in
the text properties (or overlays) that span the displayed image. This keymap defines thefollowing commands:i+

Increase the image size (image-increase-size)i-Decrease the image size (image-decrease-size).

ir

Rotate the image (image-rotate).

ih

Flip the image horizontally (image-flip-horizontally).

iv

Flip the image vertically (image-flip-vertically).

io

Save the image to a file (image-save).

ic

Interactively crop the image (image-crop).

ix

Interactively cut a rectangle from the image (image-cut).

See Section “Image Mode” in The GNU Emacs Manual, for more details about theseimage-specific key bindings.

41.17.10 Multi-Frame Images
Some image files can contain more than one image. We say that there are multiple “frames”
in the image. At present, Emacs supports multiple frames for GIF, TIFF, and certain
ImageMagick formats such as DJVM.
The frames can be used either to represent multiple pages (this is usually the casewith multi-frame TIFF files, for example), or to create animation (usually the case withmulti-frame GIF files).
A multi-frame image has a property :index, whose value is an integer (counting from 0)that specifies which frame is being displayed.

image-multi-frame-p image[Function]
This function returns non-nil if image contains more than one frame. The actual
return value is a cons (nimages . delay), where nimages is the number of frames
and delay is the delay in seconds between them, or nil if the image does not specify adelay. Images that are intended to be animated usually specify a frame delay, whereas
ones that are intended to be treated as multiple pages do not.

image-current-frame image[Function]
This function returns the index of the current frame number for image, counting from0.

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image-show-frame image n &optional nocheck[Function]
This function switches image to frame number n. It replaces a frame number outside
the valid range with that of the end of the range, unless nocheck is non-nil. If image
does not contain a frame with the specified number, the image displays as a hollow
box.

image-animate image &optional index limit[Function]
This function animates image. The optional integer index specifies the frame fromwhich to start (default 0). The optional argument limit controls the length of theanimation. If omitted or nil, the image animates once only; if t it loops forever; if anumber animation stops after that many seconds.

Animation operates by means of a timer. Note that Emacs imposes a minimum frame delayof 0.01 (image-minimum-frame-delay) seconds. If the image itself does not specify a delay,
Emacs uses image-default-frame-delay.

image-animate-timer image[Function]
This function returns the timer responsible for animating image, if there is one.

41.17.11 Image Cache
Emacs caches images so that it can display them again more efficiently. When Emacs
displays an image, it searches the image cache for an existing image specification equal
to the desired specification. If a match is found, the image is displayed from the cache.
Otherwise, Emacs loads the image normally.

image-flush spec &optional frame[Function]
This function removes the image with specification spec from the image cache of frame
frame. Image specifications are compared using equal. If frame is nil, it defaults tothe selected frame. If frame is t, the image is flushed on all existing frames.
In Emacs’s current implementation, each graphical terminal possesses an image cache,which is shared by all the frames on that terminal (see Section 30.2 [Multiple Terminals],
page 787). Thus, refreshing an image in one frame also refreshes it in all other frameson the same terminal.

One use for image-flush is to tell Emacs about a change in an image file. If an image
specification contains a :file property, the image is cached based on the file’s contents
when the image is first displayed. Even if the file subsequently changes, Emacs continues
displaying the old version of the image. Calling image-flush flushes the image from thecache, forcing Emacs to re-read the file the next time it needs to display that image.
Another use for image-flush is for memory conservation. If your Lisp program creates alarge number of temporary images over a period much shorter than image-cache-evictiondelay (see below), you can opt to flush unused images yourself, instead of waiting for Emacs
to do it automatically.

clear-image-cache &optional filter[Function]
This function clears an image cache, removing all the images stored in it. If filter isomitted or nil, it clears the cache for the selected frame. If filter is a frame, it clears
the cache for that frame. If filter is t, all image caches are cleared. Otherwise, filter

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is taken to be a file name, and all images associated with that file name are removed
from all image caches.
If an image in the image cache has not been displayed for a specified period of time,
Emacs removes it from the cache and frees the associated memory.
[Variable]
This variable specifies the number of seconds an image can remain in the cache without
being displayed. When an image is not displayed for this length of time, Emacs
removes it from the image cache.
Under some circumstances, if the number of images in the cache grows too large, theactual eviction delay may be shorter than this.
If the value is nil, Emacs does not remove images from the cache except when you
explicitly clear it. This mode can be useful for debugging.

image-cache-eviction-delay[Function]
This function returns the total size of the current image cache, in bytes. An image ofsize 200x100 with 24 bits per color will have a cache size of 60000 bytes, for instance.

image-cache-size

41.18 Icons
Emacs sometimes uses buttons (for clicking on) or small graphics (to illustrate something).
Since Emacs is available on a wide variety of systems with different capabilities, and users
have different preferences, Emacs provides a facility to handle this in a convenient way,
allowing customization, graceful degradation, accessibility, as well as themability: Icons.
The central macro here is define-icon, and here’s a simple example:(define-icon outline-open button'((image "right.svg" "open.xpm" "open.pbm" :height line)(emoji "")(symbol "" "")(text "open" :face icon-button))"Icon used for buttons for opening a section in outline buffers.":version "29.1":help-echo "Open this section")
Which alternative will actually be displayed depends on the value of the user option
icon-preference (see Section “Icons” in The GNU Emacs Manual) and on the results ofrun-time checks for what the current frame’s terminal can actually display.
The macro in the example above defines outline-open as an icon, and inherits properties
from the icon called button (so this is meant as a clickable button to be inserted in a buffer).
It is followed by a list of icon types along with the actual icon shapes themselves. In addition,
there’s a doc string and various keywords that contain additional information and properties.
To instantiate an icon, you use icon-string, which will consult the current Customize
theming, and the icon-preference user option, and finally what the Emacs is able toactually display. If icon-preference is (image emoji symbol text) (i.e., allowing all ofthese forms of icons), in this case, icon-string will first check that Emacs is able to display
images at all, and then whether it has support for each of those different image formats. If
that fails, Emacs will check whether Emacs can display emojis (in the current frame). If

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that fails, it’ll check whether it can display the symbol in question. If that fails, it’ll use theplain text version.
For instance, if icon-preference doesn’t contain image or emoji, it’ll skip those entries.
Code can confidently call icon-string in all circumstances and be sure that somethingreadable will appear on the screen, no matter whether the user is on a graphical terminal ora text terminal, and no matter which features Emacs was built with.

define-icon name parent specs doc &rest keywords[Macro]Define an icon name, a symbol, with the display alternatives in spec, that can be later
instantiated using icon-string. The name is the name of the resulting keyword.
The resulting icon will inherit specs from parent, and from their parent’s parents, andso on, and the lowest descendent element wins.
specs is a list of icon specifications. The first element of each specification is the type,
and the rest is something that can be used as an icon of that type, and then optionallyfollowed by a keyword list. The following icon types are available:
image

In this case, there may be many images listed as candidates. Emacs will
choose the first one that the current Emacs instance can show. If an image
is listed is an absolute file name, it’s used as is, but it’s otherwise looked
up in the list image-load-path (see Section 41.17.8 [Defining Images],
page 1220).

emojiThis should be a (possibly colorful) emoji.

symbolThis should be a (monochrome) symbol character.

text

Icons should also have a textual fallback. This can also be used for thevisually impaired: if icon-preference is just (text), all icons will be
replaced by text.

Various keywords may follow the list of icon specifications. For instance:(symbol "" "" :face icon-button)
Unknown keywords are ignored. The following keywords are allowed::face

The face to be used for the icon.

:height

This is only valid for image icons, and can be either a number (which
specifies the height in pixels), or the symbol line, which will use thedefault line height in the currently selected window.

:widthThis is only valid for image icons, and can be either a number (which
specifies the width in pixels), or the symbol font, which will use the widthin pixels of the current buffer’s default face font.

doc should be a doc string.
keywords is a list of keyword/value pairs. The following keywords are allowed::version

The (approximate) Emacs version this button first appeared. (Thiskeyword is mandatory.):group

The customization group this icon belongs in. If not present, it is inferred.

:help-echo
The help string shown when hovering over the icon with the mouse pointer.

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icon-string icon

[Function]
This function returns a string suitable for display in the current buffer for icon.

icon-elements icon

[Function]
Alternatively, you can get a “deconstructed” version of icon with this function. It
returns a plist (see Section 5.9 [Property Lists], page 99) where the keys are string,
face and image. (The latter is only present if the icon is represented by an image.)This can be useful if the icon isn’t to be inserted directly in the buffer, but needs some
sort of pre-processing first.

Icons can be customized with M-x customize-icon. Themes can specify changes to icons
with, for instance:(custom-theme-set-icons'my-theme'(outline-open ((image :height 100)
(text " OPEN ")))'(outline-close ((image :height 100)
(text " CLOSE " :face warning))))41.19 Embedded Native Widgets
Emacs is able to display native widgets, such as GTK+ WebKit widgets, in Emacs buffers
when it was built with the necessary support libraries and is running on a graphicalterminal. To test whether Emacs supports display of embedded widgets, check that thexwidget-internal feature is available (see Section 16.7 [Named Features], page 309).
To display an embedded widget in a buffer, you must first create an xwidget object,
and then use that object as the display specifier in a display text or overlay property (seeSection 41.16 [Display Property], page 1198).
Embedded widgets can send events notifying Lisp code about changes occurring withinthem. (see Section 22.7.11 [Xwidget Events], page 449).

make-xwidget type title width height arguments &optional buffer
related[Function]

This creates and returns an xwidget object. If buffer is omitted or nil, it defaults tothe current buffer. If buffer names a buffer that doesn’t exist, it will be created. The
type identifies the type of the xwidget component, it can be one of the following:
webkit

The WebKit component.

The width and height arguments specify the widget size in pixels, and title, a string,
specifies its title. related is used internally by the WebKit widget, and specifies another
WebKit widget that the newly created widget should share settings and subprocesses
with.
The xwidget that is returned will be killed alongside its buffer (see Section 28.10[Killing Buffers], page 685). You can also kill it using kill-xwidget. Once it is killed,
the xwidget may continue to exist as a Lisp object and act as a display property
until all references to it are gone, but most actions that can be performed on live
xwidgets will no longer be available.

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1229[Function]

This function returns t if object is an xwidget, nil otherwise.

xwidget-live-p object[Function]
This function returns t if object is an xwidget that hasn’t been killed, and nil
otherwise.

kill-xwidget xwidget[Function]
This function kills xwidget, by removing it from its buffer and releasing window system
resources it holds.

xwidget-plist xwidget[Function]

This function returns the property list of xwidget.

set-xwidget-plist xwidget plist[Function]
This function replaces the property list of xwidget with a new property list given byplist.

xwidget-buffer xwidget[Function]
This function returns the buffer of xwidget. If xwidget has been killed, it returns nil.

set-xwidget-buffer xwidget buffer[Function]

This function sets the buffer of xwidget to buffer.

get-buffer-xwidgets buffer[Function]
This function returns a list of xwidget objects associated with the buffer, which canbe specified as a buffer object or a name of an existing buffer, a string. The value isnil if buffer contains no xwidgets.

xwidget-webkit-goto-uri xwidget uri[Function]
This function browses the specified uri in the given xwidget. The uri is a string thatspecifies the name of a file or a URL.

xwidget-webkit-execute-script xwidget script[Function]
This function causes the browser widget specified by xwidget to execute the specified
JavaScript script.

xwidget-webkit-execute-script-rv xwidget script &optional
default[Function]

This function executes the specified script like xwidget-webkit-execute-script
does, but it also returns the script’s return value as a string. If script doesn’t return avalue, this function returns default, or nil if default was omitted.

xwidget-webkit-get-title xwidget[Function]

This function returns the title of xwidget as a string.

xwidget-resize xwidget width height[Function]

This function resizes the specified xwidget to the size widthxheight pixels.

xwidget-size-request xwidget[Function]
This function returns the desired size of xwidget as a list of the form (width height).
The dimensions are in pixels.

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xwidget-info xwidget[Function]
This function returns the attributes of xwidget as a vector of the form [type title
width height]. The attributes are usually determined by make-xwidget when thexwidget is created.

set-xwidget-query-on-exit-flag xwidget flag

[Function]
This function allows you to arrange that Emacs will ask the user for confirmation
before exiting or before killing a buffer that has xwidget associated with it. If flag is
non-nil, Emacs will query the user, otherwise it will not.

xwidget-query-on-exit-flag xwidget[Function]
This function returns the current setting of xwidgets query-on-exit flag, either t ornil.

xwidget-perform-lispy-event xwidget event frame[Function]
Send an input event event to xwidget. The precise action performed is platform-specific.
See Section 22.7 [Input Events], page 440.

You can optionally pass the frame on which the event was generated via frame. On
X11, modifier keys in key events will not be considered if frame is nil, and the selected
frame is not an X-Windows frame.
On GTK, only keyboard and function key events are supported. Mouse, motion, andclick events are dispatched to the xwidget without going through Lisp code, and assuch shouldn’t require this function to be called.

xwidget-webkit-search query xwidget &optional case-insensitive
backwards wrap-around[Function]

Start an incremental search on the WebKit widget xwidget with the string queryas the query. case-insensitive denotes whether or not the search is case-insensitive,
backwards determines if the search is performed backwards towards the start of the
document, and wrap-around determines whether or not the search terminates at theend of the document.
If the function is called while a search query is already present, then the query specified
here will replace the existing query.
To stop a search query, use xwidget-webkit-finish-search.

xwidget-webkit-next-result xwidget[Function]
Display the next search result in xwidget. This function will signal an error if a search
query has not been already started in xwidget through xwidget-webkit-search.
If wrap-around was non-nil when xwidget-webkit-search was called, then the
search will restart from the beginning of the document when its end is reached.

xwidget-webkit-previous-result xwidget[Function]
Display the previous search result in xwidget. This function signals an error if a search
query has not been already started in xwidget through xwidget-webkit-search.
If wrap-around was non-nil when xwidget-webkit-search was called, then the
search will restart from the end of the document when its beginning is reached.

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xwidget-webkit-finish-search xwidget[Function]
Finish a search operation started with xwidget-webkit-search in xwidget. If there
is no query currently ongoing, this function signals an error.

xwidget-webkit-load-html xwidget text &optional base-uri[Function]
Load text, a string, into xwidget, which should be a WebKit xwidget. Any HTML
markup in text will be processed by xwidget while rendering the text.
Optional argument base-uri, which should be a string, specifies the absolute locationof the web resources referenced by text, to be used for resolving relative links in text.

xwidget-webkit-goto-history xwidget rel-pos[Function]
Make xwidget, a WebKit widget, load the rel-posth element in its navigation history.
If rel-pos is zero, the current page will be reloaded instead.

xwidget-webkit-back-forward-list xwidget &optional limit[Function]
Return the navigation history of xwidget, up to limit items in each direction. If not
specified, limit defaults to 50.

The returned value is a list of the form (back here forward), where here is thecurrent navigation item, while back is a list of items containing the items recorded by
WebKit before the current navigation item, and forward is a list of items recorded
after the current navigation item. back, here and forward can all be nil.
When here is nil, it means that no items have been recorded yet; if back or forward
are nil, it means that there is no history recorded before or after the current item
respectively.
Navigation items are themselves lists of the form (idx title uri). In these lists,
idx is an index that can be passed to xwidget-webkit-goto-history, title is thehuman-readable title of the item, and uri is the URI of the item. The user should
normally have no reason to load uri manually to reach a specific history item. Instead,idx should be passed as an index to xwidget-webkit-goto-history.

xwidget-webkit-estimated-load-progress xwidget[Function]
Return an estimate of how much data is remaining to be transferred before the page
displayed by the WebKit widget xwidget is fully loaded.

The value returned is a float ranging between 0.0 and 1.0.

xwidget-webkit-set-cookie-storage-file xwidget file

[Function]

Make the WebKit widget xwidget store cookies in file.
file must be an absolute file name. The new setting will also affect any xwidget thatwas created with xwidget as the related argument to make-xwidget, and widgets
related to those as well.
If this function is not called at least once on xwidget or a related widget, xwidget will
not store cookies on disk at all.

xwidget-webkit-stop-loading xwidget[Function]
Terminate any data transfer still in progress in the WebKit widget xwidget as part ofa page-loading operation. If a page is not being loaded, this function does nothing.

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41.20 Buttons
The Button package defines functions for inserting and manipulating buttons that can be
activated with the mouse or via keyboard commands. These buttons are typically used forvarious kinds of hyperlinks.
A button is essentially a set of text or overlay properties, attached to a stretch of text ina buffer. These properties are called button properties. One of these properties, the action
property, specifies a function which is called when the user invokes the button using the
keyboard or the mouse. The action function may examine the button and use its otherproperties as desired.
In some ways, the Button package duplicates the functionality in the Widget package.
See Section “Introduction” in The Emacs Widget Library. The advantage of the Button
package is that it is faster, smaller, and simpler to program. From the point of view of theuser, the interfaces produced by the two packages are very similar.

41.20.1 Button Properties
Each button has an associated list of properties defining its appearance and behavior, andother arbitrary properties may be used for application specific purposes. The following
properties have special meaning to the Button package:actionThe function to call when the user invokes the button, which is passed the single
argument button. By default this is ignore, which does nothing.

mouse-action
This is similar to action, and when present, will be used instead of action for
button invocations resulting from mouse-clicks (instead of the user hitting RET).
If not present, mouse-clicks use action instead.
faceThis is an Emacs face controlling how buttons of this type are displayed; bydefault this is the button face.

mouse-faceThis is an additional face which controls appearance during mouse-overs (mergedwith the usual button face); by default this is the usual Emacs highlight face.
keymapThe button’s keymap, defining bindings active within the button region. Bydefault this is the usual button region keymap, stored in the variable button-map,
which defines RET and mouse-2 to invoke the button.

type

The button type. See Section 41.20.2 [Button Types], page 1233.

help-echo
A string displayed by the Emacs tooltip help system; by default, "mouse-2,
RET: Push this button". Alternatively, a function that returns, or a form that
evaluates to, a string to be displayed or nil. For details see [Text help-echo],page 926.
The function is called with three arguments, window, object, and pos. The second
argument, object, is either the overlay that had the property (for overlay buttons),or the buffer containing the button (for text property buttons). The otherarguments have the same meaning as for the special text property help-echo.

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follow-link
The follow-link property, defining how a mouse-1 click behaves on this button,
See Section 33.19.8 [Clickable Text], page 934.
buttonAll buttons have a non-nil button property, which may be useful in finding
regions of text that comprise buttons (which is what the standard button
functions do).

There are other properties defined for the regions of text in a button, but these are notgenerally interesting for typical uses.

41.20.2 Button Types
Every button has a button type, which defines default values for the button’s properties.
Button types are arranged in a hierarchy, with specialized types inheriting from more general
types, so that it’s easy to define special-purpose types of buttons for specific tasks.

define-button-type name &rest properties[Function]
Define a button type called name (a symbol). The remaining arguments form asequence of property value pairs, specifying default property values for buttons withthis type (a button’s type may be set by giving it a type property when creating the
button, using the :type keyword argument).
In addition, the keyword argument :supertype may be used to specify a button-typefrom which name inherits its default property values. Note that this inheritance
happens only when name is defined; subsequent changes to a supertype are notreflected in its subtypes.

Using define-button-type to define default properties for buttons is not necessary—
buttons without any specified type use the built-in button-type button—but it is encouraged,
since doing so usually makes the resulting code clearer and more efficient.

41.20.3 Making Buttons
Buttons are associated with a region of text, using an overlay or text properties to holdbutton-specific information, all of which are initialized from the button’s type (which defaults
to the built-in button type button). Like all Emacs text, the appearance of the button isgoverned by the face property; by default (via the face property inherited from the button
button-type) this is a simple underline, like a typical web-page link.
For convenience, there are two sorts of button-creation functions, those that add button
properties to an existing region of a buffer, called make-...button, and those that also
insert the button text, called insert-...button.
The button-creation functions all take the &rest argument properties, which should
be a sequence of property value pairs, specifying properties to add to the button; see
Section 41.20.1 [Button Properties], page 1232. In addition, the keyword argument :type may
be used to specify a button-type from which to inherit other properties; see Section 41.20.2[Button Types], page 1233. Any properties not explicitly specified during creation will beinherited from the button’s type (if the type defines such a property).
The following functions add a button using an overlay (see Section 41.9 [Overlays],
page 1150) to hold the button properties:

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make-button beg end &rest properties[Function]
This makes a button from beg to end in the current buffer, and returns it.

insert-button label &rest properties[Function]

This inserts a button with the label label at point, and returns it.
The following functions are similar, but using text properties (see Section 33.19 [Text
Properties], page 917) to hold the button properties. Such buttons do not add markers
to the buffer, so editing in the buffer does not slow down if there is an extremely large
numbers of buttons. However, if there is an existing face text property on the text (e.g.,a face assigned by Font Lock mode), the button face may not be visible. Both of thesefunctions return the starting position of the new button.

make-text-button beg end &rest properties[Function]
This makes a button from beg to end in the current buffer, using text properties.

insert-text-button label &rest properties[Function]

This inserts a button with the label label at point, using text properties.

buttonize string callback &optional data

[Function]
Sometimes it’s more convenient to make a string into a button without inserting it intoa buffer immediately, for instance when creating data structures that may then, later,
be inserted into a buffer. This function makes string into such a string, and callback
will be called when the user clicks on the button. The optional data parameter will
be used as the parameter when callback is called. If nil, the button is used as theparameter instead.

41.20.4 Manipulating Buttons
These are functions for getting and setting properties of buttons. Often these are used by abutton’s invocation function to determine what to do.
Where a button parameter is specified, it means an object referring to a specific button,either an overlay (for overlay buttons), or a buffer-position or marker (for text property
buttons). Such an object is passed as the first argument to a button’s invocation function
when it is invoked.

button-start button[Function]

Return the position at which button starts.

button-end button[Function]

Return the position at which button ends.

button-get button prop

[Function]

Get the property of button button named prop.

button-put button prop val[Function]

Set button’s prop property to val.

button-activate button &optional use-mouse-action[Function]
Call button’s action property (i.e., invoke the function that is the value of thatproperty, passing it the single argument button). If use-mouse-action is non-nil, try

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to invoke the button’s mouse-action property instead of action; if the button has
no mouse-action property, use action as normal. If the button-data property ispresent in button, use that as the argument for the action function instead of button.

button-label button[Function]

Return button’s text label.

button-type button[Function]

Return button’s button-type.

button-has-type-p button type

[Function]

Return t if button has button-type type, or one of type’s subtypes.

button-at pos[Function]
Return the button at position pos in the current buffer, or nil. If the button at pos
is a text property button, the return value is a marker pointing to pos.

button-type-put type prop val[Function]

Set the button-type type’s prop property to val.

button-type-get type prop

[Function]

Get the property of button-type type named prop.

button-type-subtype-p type supertype[Function]

Return t if button-type type is a subtype of supertype.

41.20.5 Button Buffer Commands
These are commands and functions for locating and operating on buttons in an Emacs
buffer.
push-button is the command that a user uses to actually push a button, and is boundby default in the button itself to RET and to mouse-2 using a local keymap in the button’soverlay or text properties. Commands that are useful outside the buttons itself, such as
forward-button and backward-button are additionally available in the keymap stored in
button-buffer-map; a mode which uses buttons may want to use button-buffer-map as aparent keymap for its keymap. Alternatively, the button-mode can be switched on for muchthe same effect: It’s a minor mode that does nothing else than install button-buffer-map
as a minor mode keymap.
If the button has a non-nil follow-link property, and mouse-1-click-follows-link
is set, a quick mouse-1 click will also activate the push-button command. See Section 33.19.8[Clickable Text], page 934.

push-button &optional pos use-mouse-action[Command]
Perform the action specified by a button at location pos. pos may be either a buffer
position or a mouse-event. If use-mouse-action is non-nil, or pos is a mouse-event (seeSection 22.7.3 [Mouse Events], page 442), try to invoke the button’s mouse-action
property instead of action; if the button has no mouse-action property, use action
as normal. pos defaults to point, except when push-button is invoked interactively
as the result of a mouse-event, in which case, the mouse event’s position is used. If
there’s no button at pos, do nothing and return nil, otherwise return t.

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forward-button n &optional wrap display-message no-error[Command]Move to the nth next button, or nth previous button if n is negative. If n is zero,
move to the start of any button at point. If wrap is non-nil, moving past either endof the buffer continues from the other end. If display-message is non-nil, the button’s
help-echo string is displayed. Any button with a non-nil skip property is skipped
over. Returns the button found, and signals an error if no buttons can be found. If
no-error is non-nil, return nil instead of signaling the error.

backward-button n &optional wrap display-message no-error[Command]Move to the nth previous button, or nth next button if n is negative. If n is zero,
move to the start of any button at point. If wrap is non-nil, moving past either endof the buffer continues from the other end. If display-message is non-nil, the button’s
help-echo string is displayed. Any button with a non-nil skip property is skipped
over. Returns the button found, and signals an error if no buttons can be found. If
no-error is non-nil, return nil instead of signaling the error.

next-button pos &optional count-current
previous-button pos &optional count-current[Function][Function]
Return the next button after (for next-button) or before (for previous-button)
position pos in the current buffer. If count-current is non-nil, count any button at
pos in the search, instead of starting at the next button.

41.21 Abstract Display
The Ewoc package constructs buffer text that represents a structure of Lisp objects, andupdates the text to follow changes in that structure. This is like the “view” component in
the “model–view–controller” design paradigm. Ewoc means “Emacs’s Widget for Object
Collections”.
An ewoc is a structure that organizes information required to construct buffer text that
represents certain Lisp data. The buffer text of the ewoc has three parts, in order: first,
fixed header text; next, textual descriptions of a series of data elements (Lisp objects thatyou specify); and last, fixed footer text. Specifically, an ewoc contains information on:• The buffer which its text is generated in.
• The text’s start position in the buffer.
• The header and footer strings.
• A doubly-linked chain of nodes, each of which contains:• A data element, a single Lisp object.
• Links to the preceding and following nodes in the chain.
• A pretty-printer function which is responsible for inserting the textual representationof a data element value into the current buffer.
Typically, you define an ewoc with ewoc-create, and then pass the resulting ewoc
structure to other functions in the Ewoc package to build nodes within it, and display it in
the buffer. Once it is displayed in the buffer, other functions determine the correspondence
between buffer positions and nodes, move point from one node’s textual representation toanother, and so forth. See Section 41.21.1 [Abstract Display Functions], page 1237.

Chapter 41: Emacs Display

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A node encapsulates a data element much the way a variable holds a value. Normally,
encapsulation occurs as a part of adding a node to the ewoc. You can retrieve the data
element value and place a new value in its place, like so:(ewoc-data node)⇒ value(ewoc-set-data node new-value)⇒ new-value
You can also use, as the data element value, a Lisp object (list or vector) that is a container
for the real value, or an index into some other structure. The example (see Section 41.21.2[Abstract Display Example], page 1239) uses the latter approach.
When the data changes, you will want to update the text in the buffer. You can update
all nodes by calling ewoc-refresh, or just specific nodes using ewoc-invalidate, or all
nodes satisfying a predicate using ewoc-map. Alternatively, you can delete invalid nodes
using ewoc-delete or ewoc-filter, and add new nodes in their place. Deleting a nodefrom an ewoc deletes its associated textual description from buffer, as well.

41.21.1 Abstract Display Functions
In this subsection, ewoc and node stand for the structures described above (see Section 41.21[Abstract Display], page 1236), while data stands for an arbitrary Lisp object used as a data
element.

ewoc-create pretty-printer &optional header footer nosep[Function]
This constructs and returns a new ewoc, with no nodes (and thus no data elements).
pretty-printer should be a function that takes one argument, a data element of thesort you plan to use in this ewoc, and inserts its textual description at point using
insert (and never insert-before-markers, because that would interfere with the
Ewoc package’s internal mechanisms).
Normally, a newline is automatically inserted after the header, the footer and every
node’s textual description. If nosep is non-nil, no newline is inserted. This may be
useful for displaying an entire ewoc on a single line, for example, or for making nodes
invisible by arranging for pretty-printer to do nothing for those nodes.
An ewoc maintains its text in the buffer that is current when you create it, so switch
to the intended buffer before calling ewoc-create.

ewoc-buffer ewoc

[Function]

This returns the buffer where ewoc maintains its text.

ewoc-get-hf ewoc

[Function]
This returns a cons cell (header . footer) made from ewoc’s header and footer.

ewoc-set-hf ewoc header footer[Function]
This sets the header and footer of ewoc to the strings header and footer, respectively.

ewoc-enter-first ewoc data
ewoc-enter-last ewoc data

[Function][Function]
These add a new node encapsulating data, putting it, respectively, at the beginning or
end of ewoc’s chain of nodes.

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ewoc-enter-before ewoc node data
ewoc-enter-after ewoc node data

[Function][Function]
These add a new node encapsulating data, adding it to ewoc before or after node,
respectively.

ewoc-prev ewoc nodeewoc-next ewoc node

[Function][Function]
These return, respectively, the previous node and the next node of node in ewoc.

ewoc-nth ewoc n[Function]
This returns the node in ewoc found at zero-based index n. A negative n means countfrom the end. ewoc-nth returns nil if n is out of range.

ewoc-data node

[Function]

This extracts the data encapsulated by node and returns it.

ewoc-set-data node data

[Function]

This sets the data encapsulated by node to data.

ewoc-locate ewoc &optional pos guess[Function]
This determines the node in ewoc which contains point (or pos if specified), andreturns that node. If ewoc has no nodes, it returns nil. If pos is before the first node,
it returns the first node; if pos is after the last node, it returns the last node. The
optional third arg guess should be a node that is likely to be near pos; this doesn’talter the result, but makes the function run faster.

ewoc-location node

[Function]

This returns the start position of node.

ewoc-goto-prev ewoc arg
ewoc-goto-next ewoc arg[Function][Function]
These move point to the previous or next, respectively, argth node in ewoc. ewoc-gotoprev does not move if it is already at the first node or if ewoc is empty, whereas
ewoc-goto-next moves past the last node, returning nil. Excepting this special case,these functions return the node moved to.

ewoc-goto-node ewoc node

[Function]

This moves point to the start of node in ewoc.

ewoc-refresh ewoc

[Function]
This function regenerates the text of ewoc. It works by deleting the text between theheader and the footer, i.e., all the data elements’ representations, and then calling thepretty-printer function for each node, one by one, in order.

ewoc-invalidate ewoc &rest nodes[Function]
This is similar to ewoc-refresh, except that only nodes in ewoc are updated insteadof the entire set.

ewoc-delete ewoc &rest nodesThis deletes each node in nodes from ewoc.

[Function]

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ewoc-filter ewoc predicate &rest args

[Function]
This calls predicate for each data element in ewoc and deletes those nodes for which
predicate returns nil. Any args are passed to predicate.

ewoc-collect ewoc predicate &rest args

[Function]
This calls predicate for each data element in ewoc and returns a list of those elements
for which predicate returns non-nil. The elements in the list are ordered as in thebuffer. Any args are passed to predicate.

ewoc-map map-function ewoc &rest args

[Function]
This calls map-function for each data element in ewoc and updates those nodes forwhich map-function returns non-nil. Any args are passed to map-function.

41.21.2 Abstract Display Example
Here is a simple example using functions of the ewoc package to implement a color components
display, an area in a buffer that represents a vector of three integers (itself representing a
24-bit RGB value) in various ways.
(setq colorcomp-ewoc nil
colorcomp-data nil
colorcomp-mode-map nil
colorcomp-labels ["Red" "Green" "Blue"])(defun colorcomp-pp (data)(if data(let ((comp (aref colorcomp-data data)))(insert (aref colorcomp-labels data) "\t: #x"(format "%02X" comp) " "(make-string (ash comp -2) ?#) "\n"))(let ((cstr (format "#%02X%02X%02X"(aref colorcomp-data 0)(aref colorcomp-data 1)(aref colorcomp-data 2)))
(samp " (sample text) "))(insert "Color\t: "(propertize samp 'face`(foreground-color . ,cstr))(propertize samp 'face`(background-color . ,cstr))"\n"))))(defun colorcomp (color)"Allow fiddling with COLOR in a new buffer.
The buffer is in Color Components mode."(interactive "sColor (name or #RGB or #RRGGBB): ")(when (string= "" color)(setq color "green"))(unless (color-values color)Chapter 41: Emacs Display

1240(error "No such color: %S" color))(switch-to-buffer(generate-new-buffer (format "originally: %s" color)))(kill-all-local-variables)(setq major-mode 'colorcomp-mode
mode-name "Color Components")(use-local-map colorcomp-mode-map)(erase-buffer)(buffer-disable-undo)(let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))(color-values color))))(ewoc (ewoc-create 'colorcomp-pp"\nColor Components\n\n"(substitute-command-keys"\n\\{colorcomp-mode-map}"))))(set (make-local-variable 'colorcomp-data) data)(set (make-local-variable 'colorcomp-ewoc) ewoc)(ewoc-enter-last ewoc 0)(ewoc-enter-last ewoc 1)(ewoc-enter-last ewoc 2)(ewoc-enter-last ewoc nil)))This example can be extended to be a color selection widget (in other words, the“controller” part of the “model–view–controller” design paradigm) by defining commands
to modify colorcomp-data and to finish the selection process, and a keymap to tie it all
together conveniently.
(defun colorcomp-mod (index limit delta)(let ((cur (aref colorcomp-data index)))(unless (= limit cur)(aset colorcomp-data index (+ cur delta)))(ewoc-invalidate
colorcomp-ewoc(ewoc-nth colorcomp-ewoc index)(ewoc-nth colorcomp-ewoc -1))))(defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))(defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))(defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))(defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
(defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
(defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
(defun colorcomp-copy-as-kill-and-exit ()"Copy the color components into the kill ring and kill the buffer.
The string is formatted #RRGGBB (hash followed by six hex digits)."(interactive)(kill-new (format "#%02X%02X%02X"(aref colorcomp-data 0)(aref colorcomp-data 1)(aref colorcomp-data 2)))(kill-buffer nil))(setq colorcomp-mode-map

Chapter 41: Emacs Display

1241(define-keymap :suppress t"i" 'colorcomp-R-less"o" 'colorcomp-R-more"k" 'colorcomp-G-less"l" 'colorcomp-G-more"," 'colorcomp-B-less"." 'colorcomp-B-more"SPC" 'colorcomp-copy-as-kill-and-exit))

Note that we never modify the data in each node, which is fixed when the ewoc is created
to be either nil or an index into the vector colorcomp-data, the actual color components.

41.22 Blinking Parentheses
This section describes the mechanism by which Emacs shows a matching open parenthesis
when the user inserts a close parenthesis.
[Variable]
The value of this variable should be a function (of no arguments) to be called whenevera character with close parenthesis syntax is inserted. The value of blink-parenfunction may be nil, in which case nothing is done.

blink-paren-function

blink-matching-paren[User Option]

If this variable is nil, then blink-matching-open does nothing.
[User Option]
This variable specifies the maximum distance to scan for a matching parenthesis before
giving up.

blink-matching-paren-distance[User Option]
This variable specifies the number of seconds to keep indicating the matching parenthesis. A fraction of a second often gives good results, but the default is 1, whichworks on all systems.

blink-matching-delay[Command]This function is the default value of blink-paren-function. It assumes that point
follows a character with close parenthesis syntax and applies the appropriate effectmomentarily to the matching opening character. If that character is not already on thescreen, it displays the character’s context in the echo area. To avoid long delays, thisfunction does not search farther than blink-matching-paren-distance characters.

blink-matching-openHere is an example of calling this function explicitly.
(defun interactive-blink-matching-open ()"Indicate momentarily the start of parenthesized sexp before point."(interactive)(let ((blink-matching-paren-distance(buffer-size))(blink-matching-paren t))(blink-matching-open)))Chapter 41: Emacs Display

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41.23 Character Display
This section describes how characters are actually displayed by Emacs. Typically, a characteris displayed as a glyph (a graphical symbol which occupies one character position on thescreen), whose appearance corresponds to the character itself. For example, the character ‘a’(character code 97) is displayed as ‘a’. Some characters, however, are displayed specially.
For example, the formfeed character (character code 12) is usually displayed as a sequenceof two glyphs, ‘^L’, while the newline character (character code 10) starts a new screen line.
You can modify how each character is displayed by defining a display table, whichmaps each character code into a sequence of glyphs. See Section 41.23.2 [Display Tables],page 1243.

41.23.1 Usual Display Conventions
Here are the conventions for displaying each character code (in the absence of a display
table, which can override these conventions).
• The printable ASCII characters, character codes 32 through 126 (consisting of numerals,
English letters, and symbols like ‘#’) are displayed literally.
• The tab character (character code 9) displays as whitespace stretching up to the next
tab stop column. See Section “Text Display” in The GNU Emacs Manual. The variabletab-width controls the number of spaces per tab stop (see below).
• The newline character (character code 10) has a special effect: it ends the preceding
line and starts a new line.
• The non-printable ASCII control characters—character codes 0 through 31, as wellas the DEL character (character code 127)—display in one of two ways according to
the variable ctl-arrow. If this variable is non-nil (the default), these characters are
displayed as sequences of two glyphs, where the first glyph is ‘^’ (a display table canspecify a glyph to use instead of ‘^’); e.g., the DEL character is displayed as ‘^?’.
If ctl-arrow is nil, these characters are displayed as octal escapes (see below).
This rule also applies to carriage return (character code 13), if that character appears inthe buffer. But carriage returns usually do not appear in buffer text; they are eliminatedas part of end-of-line conversion (see Section 34.10.1 [Coding System Basics], page 977).
• Raw bytes are non-ASCII characters with codes 128 through 255 (see Section 34.1 [Text
Representations], page 963). These characters display as octal escapes: sequences offour glyphs, where the first glyph is the ASCII code for ‘\’, and the others are digit
characters representing the character code in octal. (A display table can specify a glyph
to use instead of ‘\’.)• Each non-ASCII character with code above 255 is displayed literally, if the terminal
supports it. If the terminal does not support it, the character is said to be glyphless, and
it is usually displayed using a placeholder glyph. For example, if a graphical terminal
has no font for a character, Emacs usually displays a box containing the character codein hexadecimal. See Section 41.23.5 [Glyphless Chars], page 1245.
The above display conventions apply even when there is a display table, for any character
whose entry in the active display table is nil. Thus, when you set up a display table, youneed only specify the characters for which you want special display behavior.

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The following variables affect how certain characters are displayed on the screen. Since
they change the number of columns the characters occupy, they also affect the indentation
functions. They also affect how the mode line is displayed; if you want to force redisplayof the mode line using the new values, call the function force-mode-line-update (seeSection 24.4 [Mode Line Format], page 550).
[User Option]
This buffer-local variable controls how control characters are displayed. If it is non-nil,they are displayed as a caret followed by the character: ‘^A’. If it is nil, they aredisplayed as octal escapes: a backslash followed by three octal digits, as in ‘\001’.

ctl-arrow[User Option]
The value of this buffer-local variable is the spacing between tab stops used for
displaying tab characters in Emacs buffers. The value is in units of columns, and thedefault is 8. Note that this feature is completely independent of the user-settabletab stops used by the command tab-to-tab-stop. See Section 33.17.5 [Indent Tabs],
page 915.

tab-width41.23.2 Display Tables
A display table is a special-purpose char-table (see Section 6.6 [Char-Tables], page 119),with display-table as its subtype, which is used to override the usual character display
conventions. This section describes how to make, inspect, and assign elements to a display
table object. The next section (see Section 41.23.3 [Active Display Table], page 1244)
describes the various standard display tables and their precedence.
[Function]
This creates and returns a display table. The table initially has nil in all elements.

make-display-table

The ordinary elements of the display table are indexed by character codes; the element at
index c says how to display the character code c. The value should be nil (which means todisplay the character c according to the usual display conventions; see Section 41.23.1 [Usual
Display], page 1242), or a vector of glyph codes (which means to display the character c as
those glyphs; see Section 41.23.4 [Glyphs], page 1245).
Warning: if you use the display table to change the display of newline characters, thewhole buffer will be displayed as one long line.
The display table also has six extra slots which serve special purposes. Here is a table oftheir meanings; nil in any slot means to use the default for that slot, as stated below.
0

The glyph for the end of a truncated screen line (the default for this is ‘$’). See
Section 41.23.4 [Glyphs], page 1245. On graphical terminals, Emacs by default
uses arrows in the fringes to indicate truncation, so the display table has noeffect, unless you disable the fringes (see Section “Window Fringes” in the GNU
Emacs Manual).

1

The glyph for the end of a continued line (the default is ‘\’). On graphicalterminals, Emacs by default uses curved arrows in the fringes to indicate
continuation, so the display table has no effect, unless you disable the fringes.

2

The glyph for indicating a character displayed as an octal character code (thedefault is ‘\’).

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3

The glyph for indicating a control character (the default is ‘^’).

4

A vector of glyphs for indicating the presence of invisible lines (the default is‘...’). See Section 41.7 [Selective Display], page 1145.

5

The glyph used to draw the border between side-by-side windows (the default
is ‘|’). See Section 29.7 [Splitting Windows], page 708. This currently has
effect only on text terminals; on graphical terminals, if vertical scroll bars aresupported and in use, a scroll bar separates the two windows, and if there areno vertical scroll bars and no dividers (see Section 41.15 [Window Dividers],
page 1198), Emacs uses a thin line to indicate the border.

For example, here is how to construct a display table that mimics the effect of setting
ctl-arrow to a non-nil value (see Section 41.23.4 [Glyphs], page 1245, for the function
make-glyph-code):(setq disptab (make-display-table))(dotimes (i 32)(or (= i ?\t)(= i ?\n)(aset disptab i(vector (make-glyph-code ?^ 'escape-glyph)(make-glyph-code (+ i 64) 'escape-glyph)))))(aset disptab 127(vector (make-glyph-code ?^ 'escape-glyph)(make-glyph-code ?? 'escape-glyph)))display-table-slot display-table slot

[Function]
This function returns the value of the extra slot slot of display-table. The argument
slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols aretruncation, wrap, escape, control, selective-display, and vertical-border.

set-display-table-slot display-table slot value[Function]
This function stores value in the extra slot slot of display-table. The argument slot
may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols aretruncation, wrap, escape, control, selective-display, and vertical-border.

describe-display-table display-table[Function]
This function displays a description of the display table display-table in a help buffer.

[Command]This command displays a description of the current display table in a help buffer.

describe-current-display-table

41.23.3 Active Display Table
Each window can specify a display table, and so can each buffer. The window’s display table,
if there is one, takes precedence over the buffer’s display table. If neither exists, Emacs tries
to use the standard display table; if that is nil, Emacs uses the usual character display
conventions (see Section 41.23.1 [Usual Display], page 1242). (Emacs does not “merge”
display tables: For instance, if the window has a display table, the buffer’s display table andthe standard display table are completely ignored.)Chapter 41: Emacs Display

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Note that display tables affect how the mode line is displayed, so if you want to force
redisplay of the mode line using a new display table, call force-mode-line-update (seeSection 24.4 [Mode Line Format], page 550).

window-display-table &optional window[Function]
This function returns window’s display table, or nil if there is none. The default forwindow is the selected window.

set-window-display-table window table[Function]
This function sets the display table of window to table. The argument table shouldbe either a display table or nil.
[Variable]
This variable is automatically buffer-local in all buffers; its value specifies the buffer’s
display table. If it is nil, there is no buffer display table.

buffer-display-table[Variable]
The value of this variable is the standard display table, which is used when Emacs
is displaying a buffer in a window with neither a window display table nor a buffer
display table defined, or when Emacs is outputting text to the standard output or error
streams. Although its default is typically nil, in an interactive session if the terminal
cannot display curved quotes, its default maps curved quotes to ASCII approximations.
See Section 25.4 [Text Quoting Style], page 600.

standard-display-table

The disp-table library defines several functions for changing the standard display table.

41.23.4 Glyphs
A glyph is a graphical symbol which occupies a single character position on the screen. Eachglyph is represented in Lisp as a glyph code, which specifies a character and optionally aface to display it in (see Section 41.12 [Faces], page 1164). The main use of glyph codes is as
the entries of display tables (see Section 41.23.2 [Display Tables], page 1243). The following
functions are used to manipulate glyph codes:

make-glyph-code char &optional face

[Function]
This function returns a glyph code representing char char with face face. If face isomitted or nil, the glyph uses the default face; in that case, the glyph code is an
integer. If face is non-nil, the glyph code is not necessarily an integer object.

glyph-char glyph[Function]

This function returns the character of glyph code glyph.

glyph-face glyph[Function]
This function returns face of glyph code glyph, or nil if glyph uses the default face.

41.23.5 Glyphless Character Display
Glyphless characters are characters which are displayed in a special way, e.g., as a box
containing a hexadecimal code, instead of being displayed literally. These include characterswhich are explicitly defined to be glyphless, as well as characters for which there is noavailable font (on a graphical display), and characters which cannot be encoded by theterminal’s coding system (on a text terminal).

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The glyphless-display-mode minor mode can be used to toggle displaying glyphlesscharacters in a convenient manner in the current buffer. If this mode is enabled, all theglyphless characters are displayed as boxes that display acronyms of their character names.
[Variable]
For more fine-grained (and global) control, this variable can be used. The value of thisvariable is a char-table which defines glyphless characters and how they are displayed.
Each entry must be one of the following display methods:

glyphless-char-display

Display the character in the usual way.

nil
zero-width

Don’t display the character.
thin-space
Display a thin space, 1-pixel wide on graphical displays, or 1-characterwide on text terminals.
empty-box
Display an empty box.
hex-code

Display a box containing the Unicode codepoint of the character, in
hexadecimal notation.

an ASCII string
Display a box containing that string. The string should contain at most 6
ASCII characters. As an exception, if the string includes just one character,on text-mode terminals that character will be displayed without a box;
this allows to handle such “acronyms” as a replacement character forcharacters that cannot be displayed by the terminal.
a cons cell (graphical . text)
Display with graphical on graphical displays, and with text on text
terminals. Both graphical and text must be one of the display methods
described above.
The thin-space, empty-box, hex-code, and ASCII string display methods are drawn
with the glyphless-char face. On text terminals, a box is emulated by square
brackets, ‘[]’.
The char-table has one extra slot, which determines how to display any character
that cannot be displayed with any available font, or cannot be encoded by theterminal’s coding system. Its value should be one of the above display methods, except
zero-width.
If a character has a non-nil entry in an active display table, the display table takes
effect; in this case, Emacs does not consult glyphless-char-display at all.
[User Option]
This user option provides a convenient way to set glyphless-char-display for groupsof similar characters. Do not set its value directly from Lisp code; the value takes effectonly via a custom :set function (see Section 15.3 [Variable Definitions], page 280),
which updates glyphless-char-display.

glyphless-char-display-control

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Its value should be an alist of elements (group . method), where group is a symbol
specifying a group of characters, and method is a symbol specifying how to display
them.
group should be one of the following:c0-control
ASCII control characters U+0000 to U+001F, excluding the newline and tabcharacters (normally displayed as escape sequences like ‘^A’; see Section“How Text Is Displayed” in The GNU Emacs Manual).
c1-control
Non-ASCII, non-printing characters U+0080 to U+009F (normally displayed
as octal escape sequences like ‘\230’).
format-control
Characters of Unicode General Category [Cf], such as U+200E left-toright mark, but excluding characters that have graphic images, such as
U+00AD soft hyphen.
bidi-control
This is a subset of format-control, but only includes characters that are
related to bidirectional formatting control, like U+2069 pop directional
isolate and U+202A left-to-right embedding. See Section 41.27[Bidirectional Display], page 1250.
Characters of Unicode General Category [Cf], such as U+200E left-toright mark, but excluding characters that have graphic images, such as
U+00AD soft hyphen.
variation-selectors
Unicode VS-1 through VS-256 (U+FE00 through U+FE0F and U+E0100
through U+E01EF), which are used to select between different glyphs forthe same codepoints (typically emojis).
no-font

Characters for which there is no suitable font, or which cannot be encodedby the terminal’s coding system, or those for which the text-mode terminal
has no glyphs.

The method symbol should be one of zero-width, thin-space, empty-box, or
hex-code. These have the same meanings as in glyphless-char-display, above.

41.24 Beeping
This section describes how to make Emacs ring the bell (or blink the screen) to attract theuser’s attention. Be conservative about how often you do this; frequent bells can become
irritating. Also be careful not to use just beeping when signaling an error is more appropriate(see Section 11.7.3 [Errors], page 179).

ding &optional do-not-terminate[Function]
This function beeps, or flashes the screen (see visible-bell below). It also terminates
any keyboard macro currently executing unless do-not-terminate is non-nil.

Chapter 41: Emacs Display

beep &optional do-not-terminate

1248[Function]

This is a synonym for ding.
[User Option]
This variable determines whether Emacs should flash the screen to represent a bell.
Non-nil means yes, nil means no. This is effective on graphical displays, and on text
terminals provided the terminal’s Termcap entry defines the visible bell capability(‘vb’).

visible-bell[User Option]
If this is non-nil, it specifies how Emacs should ring the bell. Its value should be afunction of no arguments. If this is non-nil, it takes precedence over the visible-bellvariable.

ring-bell-function

41.25 Window Systems
Emacs works with several window systems, most notably the X Window System. Both
Emacs and X use the term “window”, but use it differently. An Emacs frame is a single
window as far as X is concerned; the individual Emacs windows are not known to X at all.
[Variable]
This terminal-local variable tells Lisp programs what window system Emacs is using
for displaying the frame. The possible values arewindow-systemx

Emacs is displaying the frame using X.

w32

Emacs is displaying the frame using native MS-Windows GUI.

ns

Emacs is displaying the frame using the Nextstep interface (used on
GNUstep and macOS).

pc

Emacs is displaying the frame using MS-DOS direct screen writes.

haiku

Emacs is displaying the frame using the Application Kit on Haiku.

pgtk

Emacs is displaying the frame using pure GTK facilities.

nil

Emacs is displaying the frame on a character-based terminal.

[Variable]
This variable holds the value of window-system used for the first frame created byEmacs during startup. (When Emacs is invoked as a daemon, it does not create any
initial frames, so initial-window-system is nil, except on MS-Windows, where it
is still w32. See Section “Initial Options” in The GNU Emacs Manual.)

initial-window-systemwindow-system &optional frame[Function]
This function returns a symbol whose name tells what window system is used for
displaying frame (which defaults to the currently selected frame). The list of possible
symbols it returns is the same one documented for the variable window-system above.

Do not use window-system and initial-window-system as predicates or boolean flag
variables, if you want to write code that works differently on text terminals and graphic
displays. That is because window-system is not a good indicator of Emacs capabilities on
a given display type. Instead, use display-graphic-p or any of the other display-*-p
predicates described in Section 30.26 [Display Feature Testing], page 849.

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41.26 Tooltips
Tooltips are special frames (see Chapter 30 [Frames], page 785) that are used to display
helpful hints (a.k.a. “tips”) related to the current position of the mouse pointer. Emacs
uses tooltips to display help strings about active portions of text (see Section 33.19.4[Special Properties], page 924) and about various UI elements, such as menu items (seeSection 23.18.1.2 [Extended Menu Items], page 511) and tool-bar buttons (see Section 23.18.6[Tool Bar], page 517).
[Function]
Tooltip Mode is a minor mode that enables display of tooltips. Turning off this modecauses the tooltips be displayed in the echo area. On text-mode (a.k.a. “TTY”) frames,
tooltips are always displayed in the echo area.

tooltip-mode

When Emacs is built with the GTK+ toolkit or Haiku windowing support, it by default
displays tooltips using toolkit functions, and the appearance of the tooltips is then controlled
by the toolkit’s settings. Toolkit-provided tooltips can be disabled by changing the valueof the variable use-system-tooltips to nil. The rest of this subsection describes how tocontrol non-toolkit tooltips, which are presented by Emacs itself.
Tooltips are displayed in special frames called tooltip frames, which have their own frame
parameters (see Section 30.4 [Frame Parameters], page 802). Unlike other frames, the default
parameters for tooltip frames are stored in a special variable.
[User Option]
This customizable option holds the default frame parameters used for displaying
tooltips. Any font and color parameters are ignored, and the corresponding attributesof the tooltip face are used instead. If left or top parameters are included, they
are used as absolute frame-relative coordinates where the tooltip should be shown.
(Mouse-relative position of the tooltip can be customized using the variables describedin Section “Tooltips” in The GNU Emacs Manual.) Note that the left and top
parameters, if present, override the values of mouse-relative offsets.

tooltip-frame-parameters

The tooltip face determines the appearance of text shown in tooltips. It should generally
use a variable-pitch font of size that is preferably smaller than the default frame font.
[Variable]
This abnormal hook is a list of functions to call when Emacs needs to display a tooltip.
Each function is called with a single argument event which is a copy of the last mouse
movement event. If a function on this list actually displays the tooltip, it should
return non-nil, and then the rest of the functions will not be called. The default
value of this variable is a single function tooltip-help-tips.

tooltip-functions

If you write your own function to be put on the tooltip-functions list, you may needto know the buffer of the mouse event that triggered the tooltip display. The following
function provides that information.

tooltip-event-buffer event[Function]
This function returns the buffer over which event occurred. Call it with the argumentof the function from tooltip-functions to obtain the buffer whose text triggered
the tooltip. Note that the event might occur not over a buffer (e.g., over the tool bar),in which case this function will return nil.

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Other aspects of tooltip display are controlled by several customizable settings; see
Section “Tooltips” in The GNU Emacs Manual.

41.27 Bidirectional Display
Emacs can display text written in scripts, such as Arabic, Farsi, and Hebrew, whose naturalordering for horizontal text display runs from right to left. Furthermore, segments of Latin
script and digits embedded in right-to-left text are displayed left-to-right, while segments ofright-to-left script embedded in left-to-right text (e.g., Arabic or Hebrew text in comments
or strings in a program source file) are appropriately displayed right-to-left. We call such
mixtures of left-to-right and right-to-left text bidirectional text. This section describes thefacilities and options for editing and displaying bidirectional text.
Text is stored in Emacs buffers and strings in logical (or reading) order, i.e., the orderin which a human would read each character. In right-to-left and bidirectional text, theorder in which characters are displayed on the screen (called visual order) is not the same
as logical order; the characters’ screen positions do not increase monotonically with stringor buffer position. In performing this bidirectional reordering, Emacs follows the Unicode
Bidirectional Algorithm (a.k.a. UBA), which is described in Annex #9 of the Unicode standard (https://www.unicode.org/reports/tr9/). Emacs provides a “Full Bidirectionality”
class implementation of the UBA, consistent with the requirements of the Unicode Standard
v9.0. Note, however, that the way Emacs displays continuation lines when text direction is
opposite to the base paragraph direction deviates from the UBA, which requires to perform
line wrapping before reordering text for display.
[Variable]
If the value of this buffer-local variable is non-nil (the default), Emacs performs
bidirectional reordering for display. The reordering affects buffer text, as well as
display strings and overlay strings from text and overlay properties in the buffer(see Section 41.9.2 [Overlay Properties], page 1153, and see Section 41.16 [Display
Property], page 1198). If the value is nil, Emacs does not perform bidirectional
reordering in the buffer.
The default value of bidi-display-reordering controls the reordering of strings
which are not directly supplied by a buffer, including the text displayed in mode lines(see Section 24.4 [Mode Line Format], page 550) and header lines (see Section 24.4.7[Header Lines], page 559).

bidi-display-reordering

Emacs never reorders the text of a unibyte buffer, even if bidi-display-reordering
is non-nil in the buffer. This is because unibyte buffers contain raw bytes, not characters,
and thus lack the directionality properties required for reordering. Therefore, to test
whether text in a buffer will be reordered for display, it is not enough to test the value ofbidi-display-reordering alone. The correct test is this:(if (and enable-multibyte-charactersbidi-display-reordering);; Buffer is being reordered for display)
However, unibyte display and overlay strings are reordered if their parent buffer isreordered. This is because plain-ascii strings are stored by Emacs as unibyte strings. If aChapter 41: Emacs Display

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unibyte display or overlay string includes non-ascii characters, these characters are assumed
to have left-to-right direction.
Text covered by display text properties, by overlays with display properties whose
value is a string, and by any other properties that replace buffer text, is treated as a single
unit when it is reordered for display. That is, the entire chunk of text covered by theseproperties is reordered together. Moreover, the bidirectional properties of the characters insuch a chunk of text are ignored, and Emacs reorders them as if they were replaced witha single character U+FFFC, known as the Object Replacement Character. This means that
placing a display property over a portion of text may change the way that the surrounding
text is reordered for display. To prevent this unexpected effect, always place such properties
on text whose directionality is identical with text that surrounds it.
Each paragraph of bidirectional text has a base direction, either right-to-left or left-toright. Left-to-right paragraphs are displayed beginning at the left margin of the window, andare truncated or continued when the text reaches the right margin. Right-to-left paragraphs
are displayed beginning at the right margin, and are continued or truncated at the left
margin.
Where exactly paragraphs start and end, for the purpose of the Emacs UBA implementation, is determined by the following two buffer-local variables (note that paragraph-startand paragraph-separate have no influence on this). By default both of these variables arenil, and paragraphs are bounded by empty lines, i.e., lines that consist entirely of zero or
more whitespace characters followed by a newline.
[Variable]
If non-nil, this variable’s value should be a regular expression matching a line thatstarts or separates two paragraphs. The regular expression is always matched after a
newline, so it is best to anchor it, i.e., begin it with a "^".

bidi-paragraph-start-re[Variable]
If non-nil, this variable’s value should be a regular expression matching a line separates
two paragraphs. The regular expression is always matched after a newline, so it isbest to anchor it, i.e., begin it with a "^".

bidi-paragraph-separate-re

If you modify any of these two variables, you should normally modify both, to makesure they describe paragraphs consistently. For example, to have each new line start a newparagraph for bidi-reordering purposes, set both variables to "^".
By default, Emacs determines the base direction of each paragraph by looking at the
text at its beginning. The precise method of determining the base direction is specified by
the UBA; in a nutshell, the first character in a paragraph that has an explicit directionality
determines the base direction of the paragraph. However, sometimes a buffer may need toforce a certain base direction for its paragraphs. For example, buffers containing programsource code should force all paragraphs to be displayed left-to-right. You can use following
variable to do this:[User Option]
If the value of this buffer-local variable is the symbol right-to-left or left-toright, all paragraphs in the buffer are assumed to have that specified direction. Anyother value is equivalent to nil (the default), which means to determine the basedirection of each paragraph from its contents.

bidi-paragraph-direction

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Modes for program source code should set this to left-to-right. Prog mode does
this by default, so modes derived from Prog mode do not need to set this explicitly(see Section 24.2.5 [Basic Major Modes], page 536).

current-bidi-paragraph-direction &optional buffer[Function]
This function returns the paragraph direction at point in the named buffer. The
returned value is a symbol, either left-to-right or right-to-left. If buffer isomitted or nil, it defaults to the current buffer. If the buffer-local value of thevariable bidi-paragraph-direction is non-nil, the returned value will be identicalto that value; otherwise, the returned value reflects the paragraph direction determined
dynamically by Emacs. For buffers whose value of bidi-display-reordering is nil
as well as unibyte buffers, this function always returns left-to-right.

Sometimes there’s a need to move point in strict visual order, either to the left or to theright of its current screen position. Emacs provides a primitive to do that.

move-point-visually direction[Function]
This function moves point of the currently selected window to the buffer position thatappears immediately to the right or to the left of point on the screen. If direction
is positive, point will move one screen position to the right, otherwise it will move
one screen position to the left. Note that, depending on the surrounding bidirectional
context, this could potentially move point many buffer positions away. If invoked at
the end of a screen line, the function moves point to the rightmost or leftmost screen
position of the next or previous screen line, as appropriate for the value of direction.

The function returns the new buffer position as its value.
Bidirectional reordering can have surprising and unpleasant effects when two strings withbidirectional content are juxtaposed in a buffer, or otherwise programmatically concatenatedinto a string of text. A typical problematic case is when a buffer consists of sequences oftext fields separated by whitespace or punctuation characters, like Buffer Menu mode or
Rmail Summary Mode. Because the punctuation characters used as separators have weak
directionality, they take on the directionality of surrounding text. As result, a numeric fieldthat follows a field with bidirectional content can be displayed to the left of the preceding
field, messing up the expected layout. There are several ways to avoid this problem:− Append the special character U+200E left-to-right mark, or LRM, to the endof each field that may have bidirectional content, or prepend it to the beginning of
the following field. The function bidi-string-mark-left-to-right, described below,
comes in handy for this purpose. (In a right-to-left paragraph, use U+200F rightto-left mark, or RLM, instead.) This is one of the solutions recommended by the
UBA.
− Include the tab character in the field separator. The tab character plays the role ofsegment separator in bidirectional reordering, causing the text on either side to bereordered separately.
− Separate fields with a display property or overlay with a property value of the form
(space . PROPS) (see Section 41.16.2 [Specified Space], page 1200). Emacs treats thisdisplay specification as a paragraph separator, and reorders the text on either side
separately.

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bidi-string-mark-left-to-right string[Function]
This function returns its argument string, possibly modified, such that the result canbe safely concatenated with another string, or juxtaposed with another string in abuffer, without disrupting the relative layout of this string and the next one on display.
If the string returned by this function is displayed as part of a left-to-right paragraph,it will always appear on display to the left of the text that follows it. The function
works by examining the characters of its argument, and if any of those characters
could cause reordering on display, the function appends the LRM character to thestring. The appended LRM character is made invisible by giving it an invisible text
property of t (see Section 41.6 [Invisible Text], page 1142).

The reordering algorithm uses the bidirectional properties of the characters stored as theirbidi-class property (see Section 34.6 [Character Properties], page 968). Lisp programs
can change these properties by calling the put-char-code-property function. However,doing this requires a thorough understanding of the UBA, and is therefore not recommended.
Any changes to the bidirectional properties of a character have global effect: they affect all
Emacs frames and windows.
Similarly, the mirroring property is used to display the appropriate mirrored character inthe reordered text. Lisp programs can affect the mirrored display by changing this property.
Again, any such changes affect all of Emacs display.
The bidirectional properties of characters can be overridden by inserting into the text
special directional control characters, LEFT-TO-RIGHT OVERRIDE (LRO) and RIGHTTO-LEFT OVERRIDE (RLO). Any characters between a RLO and the following newline
or POP DIRECTIONAL FORMATTING (PDF) control character, whichever comes first,
will be displayed as if they were strong right-to-left characters, i.e. they will be reversedon display. Similarly, any characters between LRO and PDF or newline will display as if
they were strong left-to-right, and will not be reversed even if they are strong right-to-leftcharacters.
These overrides are useful when you want to make some text unaffected by the reordering
algorithm, and instead directly control the display order. But they can also be used formalicious purposes, known as phishing. Specifically, a URL on a Web page or a link in an
email message can be manipulated to make its visual appearance unrecognizable, or similar
to some popular benign location, while the real location, interpreted by a browser in the
logical order, is very different.
Emacs provides a primitive that applications can use to detect instances of text whosebidirectional properties were overridden so as to make a left-to-right character display as if
it were a right-to-left character, or vice versa.

bidi-find-overridden-directionality from to &optional object[Function]
This function looks at the text of the specified object between positions from (inclusive)
and to (exclusive), and returns the first position where it finds a strong left-to-rightcharacter whose directional properties were forced to display the character as right-toleft, or for a strong right-to-left character that was forced to display as left-to-right. If
it finds no such characters in the specified region of text, it returns nil.
The optional argument object specifies which text to search, and defaults to thecurrent buffer. If object is non-nil, it can be some other buffer, or it can be a stringChapter 41: Emacs Display

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or a window. If it is a string, the function searches that string. If it is a window, thefunction searches the buffer displayed in that window. If a buffer whose text you want
to examine is displayed in some window, we recommend to specify it by that window,
rather than pass the buffer to the function. This is because telling the function about
the window allows it to correctly account for window-specific overlays, which mightchange the result of the function if some text in the buffer is covered by overlays.
When text that includes mixed right-to-left and left-to-right characters and bidirectional
controls is copied into a different location, it can change its visual appearance, and also
can affect the visual appearance of the surrounding text at destination. This is because
reordering of bidirectional text specified by the UBA has non-trivial context-dependent
effects both on the copied text and on the text at copy destination that will surround it.
Sometimes, a Lisp program may need to preserve the exact visual appearance of thecopied text at destination, and of the text that surrounds the copy. Lisp programs can use
the following function to achieve that effect.

buffer-substring-with-bidi-context start end &optional
no-properties[Function]

This function works similar to buffer-substring (see Section 33.2 [Buffer Contents],
page 879), but it prepends and appends to the copied text bidi directional control
characters necessary to preserve the visual appearance of the text when it is inserted
at another place. Optional argument no-properties, if non-nil, means remove the text
properties from the copy of the text.

1255

42 Operating System Interface
This chapter is about starting and getting out of Emacs, access to values in the operating
system environment, and terminal input, output.
See Section E.1 [Building Emacs], page 1346, for related information. See Chapter 41[Display], page 1129, for additional operating system status information pertaining to theterminal and the screen.

42.1 Starting Up Emacs
This section describes what Emacs does when it is started, and how you can customize theseactions.

42.1.1 Summary: Sequence of Actions at Startup
When Emacs is started up, it performs the following operations (see normal-top-level instartup.el):
1. It adds subdirectories to load-path, by running the file named subdirs.el in eachdirectory in the list. Normally, this file adds the directory’s subdirectories to the list,
and those are scanned in their turn. The files subdirs.el are normally generated
automatically when Emacs is installed.
2. It loads any leim-list.el that it finds in the load-path directories. This file is intended
for registering input methods. The search is only for any personal leim-list.el files
that you may have created; it skips the directories containing the standard Emacs
libraries (these should contain only a single leim-list.el file, which is compiled into
the Emacs executable).
3. It sets the variable before-init-time to the value of current-time (see Section 42.5
[Time of Day], page 1270). It also sets after-init-time to nil, which signals to Lisp
programs that Emacs is being initialized.
4. It sets the language environment and the terminal coding system, if requested byenvironment variables such as LANG.
5. It does some basic parsing of the command-line arguments.
6. It loads your early init file (see Section “Early Init File” in The GNU Emacs Manual).
This is not done if the options ‘-q’, ‘-Q’, or ‘--batch’ were specified. If the ‘-u’ option
was specified, Emacs looks for the init file in that user’s home directory instead.
7. It calls the function package-activate-all to activate any optional Emacs Lisp packagethat has been installed. See Section 43.1 [Packaging Basics], page 1303. However, Emacs
doesn’t activate the packages when package-enable-at-startup is nil or when it’s
started with one of the options ‘-q’, ‘-Q’, or ‘--batch’. To activate the packages in thelatter case, package-activate-all should be called explicitly (e.g., via the ‘--funcall’
option).
8. If not running in batch mode, it initializes the window system that the variable
initial-window-system specifies (see Section 41.25 [Window Systems], page 1248).
The initialization function, window-system-initialization, is a generic function (seeSection 13.8 [Generic Functions], page 245) whose actual implementation is different for each supported window system. If the value of initial-window-system isChapter 42: Operating System Interface

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windowsystem, then the appropriate implementation of the initialization function isdefined in the file term/windowsystem-win.el. This file should have been compiled
into the Emacs executable when it was built.
9. It runs the normal hook before-init-hook.
10. If appropriate, it creates a graphical frame. As part of creating the graphical frame, it
initializes the window system specified by initial-frame-alist and default-framealist (see Section 30.4.2 [Initial Parameters], page 804) for the graphical frame, by
calling the window-system-initialization function for that window system. This is
not done in batch (noninteractive) or daemon mode.
11. It initializes the initial frame’s faces, and sets up the menu bar and tool bar if needed.
If graphical frames are supported, it sets up the tool bar even if the current frame is
not a graphical one, since a graphical frame may be created later on.
12. It use custom-reevaluate-setting to re-initialize the members of the list
custom-delayed-init-variables. These are any pre-loaded user options whose
default value depends on the run-time, rather than build-time, context. See Section E.1[Building Emacs], page 1346.
13. It loads the library site-start, if it exists. This is not done if the options ‘-Q’ or‘--no-site-file’ were specified.
14. It loads your init file (see Section 42.1.2 [Init File], page 1258). This is not done if theoptions ‘-q’, ‘-Q’, or ‘--batch’ were specified. If the ‘-u’ option was specified, Emacs
looks for the init file in that user’s home directory instead.
15. It loads the library default, if it exists. This is not done if inhibit-default-init isnon-nil, nor if the options ‘-q’, ‘-Q’, or ‘--batch’ were specified.
16. It loads your abbrevs from the file specified by abbrev-file-name, if that file exists
and can be read (see Section 38.3 [Abbrev Files], page 1068). This is not done if theoption ‘--batch’ was specified.
17. It sets the variable after-init-time to the value of current-time. This variable was
set to nil earlier; setting it to the current time signals that the initialization phase isover, and, together with before-init-time, provides the measurement of how long it
took.
18. It runs the normal hooks after-init-hook and delayed-warnings-hook. The lattershows any warnings emitted during previous stages of startup, which are automaticallydelayed.
19. If the buffer *scratch* exists and is still in Fundamental mode (as it should be by
default), it sets its major mode according to initial-major-mode.
20. If started on a text terminal, it loads the terminal-specific Lisp library (see Section 42.1.3[Terminal-Specific], page 1260), and runs the hook tty-setup-hook. This is not donein --batch mode, nor if term-file-prefix is nil.
21. It displays the initial echo area message, unless you have suppressed that with
inhibit-startup-echo-area-message.
22. It processes any command-line options that were not handled earlier.
23. It now exits if the option --batch was specified.
24. If the *scratch* buffer exists and is empty, it inserts (substitute-command-keys
initial-scratch-message) into that buffer.

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25. If initial-buffer-choice is a string, it visits the file (or directory) with that name.
If it is a function, it calls the function with no arguments and selects the bufferthat it returns. If one file is given as a command line argument, that file is visitedand its buffer displayed alongside initial-buffer-choice. If more than one file isgiven, all of the files are visited and the *Buffer List* buffer is displayed alongside
initial-buffer-choice.
26. It runs emacs-startup-hook.
27. It calls frame-notice-user-settings, which modifies the parameters of the selected
frame according to whatever the init files specify.
28. It runs window-setup-hook.
The only difference between this hook andemacs-startup-hook is that this one runs after the previously mentioned modifications
to the frame parameters.
29. It displays the startup screen, which is a special buffer that contains information about
copyleft and basic Emacs usage. This is not done if inhibit-startup-screen or
initial-buffer-choice are non-nil, or if the ‘--no-splash’ or ‘-Q’ command-line
options were specified.
30. If a daemon was requested, it calls server-start. (On POSIX systems, if a background
daemon was requested, it then detaches from the controlling terminal.) See Section“Emacs Server” in The GNU Emacs Manual.
31. If started by the X session manager, it calls emacs-session-restore passing it asargument the ID of the previous session. See Section 42.18 [Session Management],
page 1290.
The following options affect some aspects of the startup sequence.
[User Option]
This variable, if non-nil, inhibits the startup screen. In that case, Emacs typicallydisplays the *scratch* buffer; but see initial-buffer-choice, below.
Do not set this variable in the init file of a new user, or in a way that affects more than
one user, as that would prevent new users from receiving information about copyleft
and basic Emacs usage.
inhibit-startup-message and inhibit-splash-screen are aliases for this variable.

inhibit-startup-screen[User Option]
If non-nil, this variable is a string that specifies a file or directory for Emacs to display
after starting up, instead of the startup screen. If its value is a function, Emacs callsthat function which must return a buffer which is then displayed. If its value is t,
Emacs displays the *scratch* buffer.

initial-buffer-choice[User Option]
This variable controls the display of the startup echo area message. You can suppress
the startup echo area message by adding text with this form to your init file:(setq inhibit-startup-echo-area-message"your-login-name")
Emacs explicitly checks for an expression as shown above in your init file; your loginname must appear in the expression as a Lisp string constant. You can also use

inhibit-startup-echo-area-message

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the Customize interface. Other methods of setting inhibit-startup-echo-areamessage to the same value do not inhibit the startup message. This way, you caneasily inhibit the message for yourself if you wish, but thoughtless copying of your init
file will not inhibit the message for someone else.
[User Option]
This variable, if non-nil, should be a string, which is treated as documentation to
be inserted into the *scratch* buffer when Emacs starts up or when that buffer isrecreated. If it is nil, the *scratch* buffer is empty.

initial-scratch-message

The following command-line options affect some aspects of the startup sequence. See Section“Initial Options” in The GNU Emacs Manual.
--no-splash
Do not display a splash screen.
--batchRun without an interactive terminal. See Section 42.17 [Batch Mode], page 1289.

--daemon--bg-daemon--fg-daemon
Do not initialize any display; just start a server. (A “background” daemon
automatically runs in the background.)--no-init-file-q
Do not load either the init file, or the default library.
--no-site-file
Do not load the site-start library.
--quick-Q

Equivalent to ‘-q --no-site-file --no-splash’.

--init-directorySpecify the directory to use when finding the Emacs init files.

42.1.2 The Init File
When you start Emacs, it normally attempts to load your init file. This is either a file named.emacs or .emacs.el in your home directory, or a file named init.el in a subdirectory
named .emacs.d in your home directory.
The command-line switches ‘-q’, ‘-Q’, and ‘-u’ control whether and where to find theinit file; ‘-q’ (and the stronger ‘-Q’) says not to load an init file, while ‘-u user’ says toload user’s init file instead of yours. See Section “Entering Emacs” in The GNU Emacs
Manual. If neither option is specified, Emacs uses the LOGNAME environment variable, or the
USER (most systems) or USERNAME (MS systems) variable, to find your home directory andthus your init file; this way, even if you have su’d, Emacs still loads your own init file. If
those environment variables are absent, though, Emacs uses your user-id to find your home
directory.
Emacs also attempts to load a second init file, called the early init file, if it exists. Thisis a file named early-init.el in your ~/.emacs.d directory. The difference between theearly init file and the regular init file is that the early init file is loaded much earlier duringChapter 42: Operating System Interface1259

the startup process, so you can use it to customize some things that are initialized before
loading the regular init file. For example, you can customize the process of initializing the
package system, by setting variables such as package-load-list or package-enable-at-startup.
See Section “Package Installation” in The GNU Emacs Manual.
An Emacs installation may have a default init file, which is a Lisp library named
default.el. Emacs finds this file through the standard search path for libraries (seeSection 16.1 [How Programs Do Loading], page 298). The Emacs distribution does not comewith this file; it is intended for local customizations. If the default init file exists, it is loaded
whenever you start Emacs. But your own personal init file, if any, is loaded first; if it sets
inhibit-default-init to a non-nil value, then Emacs does not subsequently load thedefault.el file. In batch mode, or if you specify ‘-q’ (or ‘-Q’), Emacs loads neither yourpersonal init file nor the default init file.
Another file for site-customization is site-start.el. Emacs loads this before the user’s
init file. You can inhibit the loading of this file with the option ‘--no-site-file’.
[User Option]
This variable specifies the site-customization file to load before the user’s init file. Its
normal value is "site-start". The only way you can change it with real effect is to
do so before dumping Emacs.

site-run-file

See Section “Init File Examples” in The GNU Emacs Manual, for examples of how tomake various commonly desired customizations in your .emacs file.
[User Option]
If this variable is non-nil, it prevents Emacs from loading the default initialization
library file. The default value is nil.

inhibit-default-init[Variable]
This normal hook is run, once, just before loading all the init files (site-start.el,
your init file, and default.el). (The only way to change it with real effect is before
dumping Emacs.)

before-init-hook[Variable]
This normal hook is run, once, just after loading all the init files (site-start.el,
your init file, and default.el), before loading the terminal-specific library (if started
on a text terminal) and processing the command-line action arguments.

after-init-hook[Variable]
This normal hook is run, once, just after handling the command line arguments. In
batch mode, Emacs does not run this hook.

emacs-startup-hook[Variable]
This normal hook is very similar to emacs-startup-hook. The only difference is that
it runs slightly later, after setting of the frame parameters. See Section 42.1.1 [Startup
Summary], page 1255.

window-setup-hook[Variable]
This variable holds the absolute file name of the user’s init file. If the actual init fileloaded is a compiled file, such as .emacs.elc, the value refers to the corresponding
source file.

user-init-fileChapter 42: Operating System Interface

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This variable holds the name of the Emacs default directory. It defaults to ${XDG_
CONFIG_HOME-'~/.config'}/emacs/ if that directory exists and ~/.emacs.d/ and~/.emacs do not exist, otherwise to ~/.emacs.d/ on all platforms but MS-DOS. Here,${XDG_CONFIG_HOME-'~/.config'} stands for the value of the environment variable
XDG_CONFIG_HOME if that variable is set, and for ~/.config otherwise. See Section“How Emacs Finds Your Init File” in The GNU Emacs Manual.

user-emacs-directory

42.1.3 Terminal-Specific Initialization
Each terminal type can have its own Lisp library that Emacs loads when run on that typeof terminal. The library’s name is constructed by concatenating the value of the variable
term-file-prefix and the terminal type (specified by the environment variable TERM).
Normally, term-file-prefix has the value "term/"; changing this is not recommended. If
there is an entry matching TERM in the term-file-aliases association list, Emacs uses theassociated value in place of TERM. Emacs finds the file in the normal manner, by searching
the load-path directories, and trying the ‘.elc’ and ‘.el’ suffixes.
The usual role of a terminal-specific library is to enable special keys to send sequences that
Emacs can recognize. It may also need to set or add to input-decode-map if the Termcap or
Terminfo entry does not specify all the terminal’s function keys. See Section 42.13 [Terminal
Input], page 1285.
When the name of the terminal type contains a hyphen or underscore, and no libraryis found whose name is identical to the terminal’s name, Emacs strips from the terminal’sname the last hyphen or underscore and everything that follows it, and tries again. This
process is repeated until Emacs finds a matching library, or until there are no more hyphens
or underscores in the name (i.e., there is no terminal-specific library). For example, if
the terminal name is ‘xterm-256color’ and there is no term/xterm-256color.el library,
Emacs tries to load term/xterm.el. If necessary, the terminal library can evaluate (getenv"TERM") to find the full name of the terminal type.
Your init file can prevent the loading of the terminal-specific library by setting the variable
term-file-prefix to nil.
You can also arrange to override some of the actions of the terminal-specific library byusing tty-setup-hook. This is a normal hook that Emacs runs after initializing a new text
terminal. You could use this hook to define initializations for terminals that do not havetheir own libraries. See Section 24.1 [Hooks], page 524.
[User Option]
If the value of this variable is non-nil, Emacs loads a terminal-specific initialization
file as follows:(load (concat term-file-prefix (getenv "TERM")))
You may set the term-file-prefix variable to nil in your init file if you do not wish
to load the terminal-initialization file.
On MS-DOS, Emacs sets the TERM environment variable to ‘internal’.

term-file-prefix[User Option]
This variable is an association list mapping terminal types to their aliases. For example,
an element of the form ("vt102" . "vt100") means to treat a terminal of type ‘vt102’
like one of type ‘vt100’.

term-file-aliases

Chapter 42: Operating System Interface

1261[Variable]
This variable is a normal hook that Emacs runs after initializing a new text terminal.
(This applies when Emacs starts up in non-windowed mode, and when making a tty
emacsclient connection.) The hook runs after loading your init file (if applicable)
and the terminal-specific Lisp file, so you can use it to adjust the definitions made bythat file.

tty-setup-hook

For a related feature, see Section 42.1.2 [Init File], page 1258.

42.1.4 Command-Line Arguments
You can use command-line arguments to request various actions when you start Emacs.
Note that the recommended way of using Emacs is to start it just once, after logging in, andthen do all editing in the same Emacs session (see Section “Entering Emacs” in The GNU
Emacs Manual). For this reason, you might not use command-line arguments very often;
nonetheless, they can be useful when invoking Emacs from session scripts or debugging
Emacs. This section describes how Emacs processes command-line arguments.
[Function]
This function parses the command line that Emacs was called with, processes it, and(amongst other things) loads the user’s init file and displays the startup messages.

command-line

command-line-processed[Variable]

The value of this variable is t once the command line has been processed.
If you redump Emacs by calling dump-emacs (see Section E.1 [Building Emacs],
page 1346), you may wish to set this variable to nil first in order to cause the newdumped Emacs to process its new command-line arguments.
[Variable]
This variable is an alist of user-defined command-line options and associated handler
functions. By default it is empty, but you can add elements if you wish.

command-switch-alist

A command-line option is an argument on the command line, which has the form:-optionThe elements of the command-switch-alist look like this:(option . handler-function)
The car, option, is a string, the name of a command-line option (including the initial
hyphen). The handler-function is called to handle option, and receives the option
name as its sole argument.
In some cases, the option is followed in the command line by an argument. In thesecases, the handler-function can find all the remaining command-line arguments inthe variable command-line-args-left (see below). (The entire list of command-line
arguments is in command-line-args.)
Note that the handling of command-switch-alist doesn’t treat equals signs in option
specially. That is, if there’s an option like --name=value on the command line,
then only a command-switch-alist member whose car is literally --name=value will
match this option. If you want to parse such options, you need to use command-linefunctions instead (see below).

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The command-line arguments are parsed by the command-line-1 function in thestartup.el file. See also Section “Command Line Arguments for Emacs Invocation”
in The GNU Emacs Manual.
[Variable]
The value of this variable is the list of command-line arguments passed to Emacs.

command-line-args[Variable]
The value of this variable is the list of command-line arguments that have not yet
been processed.

command-line-args-left[Variable]
This variable’s value is a list of functions for handling an unrecognized command-line
argument. Each time the next argument to be processed has no special meaning, thefunctions in this list are called, in order of appearance, until one of them returns a
non-nil value.
These functions are called with no arguments. They can access the command-line
argument under consideration through the variable argi, which is bound temporarily
at this point. The remaining arguments (not including the current one) are in thevariable command-line-args-left.
When a function recognizes and processes the argument in argi, it should return a
non-nil value to say it has dealt with that argument. If it has also dealt with some of
the following arguments, it can indicate that by deleting them from command-lineargs-left.
If all of these functions return nil, then the argument is treated as a file name tovisit.

command-line-functions

42.2 Getting Out of Emacs
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently,
or you can suspend it, which permits you to reenter the Emacs process later. (In a graphicalenvironment, you can of course simply switch to another application without doing anything
special to Emacs, then switch back to Emacs when you want.)

42.2.1 Killing Emacs
Killing Emacs means ending the execution of the Emacs process. If you started Emacs froma terminal, the parent process normally resumes control. The low-level primitive for killing
Emacs is kill-emacs.

kill-emacs &optional exit-data restart[Command]This command calls the hook kill-emacs-hook, then exits the Emacs process andkills it.
If exit-data is an integer, that is used as the exit status of the Emacs process. (This isuseful primarily in batch operation; see Section 42.17 [Batch Mode], page 1289.)
If exit-data is a string, its contents are stuffed into the terminal input buffer so thatthe shell (or whatever program next reads input) can read them.
If exit-data is neither an integer nor a string, or is omitted, that means to use the(system-specific) exit status which indicates successful program termination.

Chapter 42: Operating System Interface1263

If restart is non-nil, instead of just exiting at the end, start a new Emacs process,using the same command line arguments as the currently running Emacs process.
The kill-emacs function is normally called via the higher-level command C-x C-c(save-buffers-kill-terminal). See Section “Exiting” in The GNU Emacs Manual. It isalso called automatically if Emacs receives a SIGTERM or SIGHUP operating system signal(e.g., when the controlling terminal is disconnected), or if it receives a SIGINT signal whilerunning in batch mode (see Section 42.17 [Batch Mode], page 1289).
[Variable]
This normal hook is run by kill-emacs, before it kills Emacs.
Because kill-emacs can be called in situations where user interaction is impossible(e.g., when the terminal is disconnected), functions on this hook should not attempt
to interact with the user. If you want to interact with the user when Emacs is shutting
down, use kill-emacs-query-functions, described below.

kill-emacs-hook

When Emacs is killed, all the information in the Emacs process, aside from files thathave been saved, is lost. Because killing Emacs inadvertently can lose a lot of work, thesave-buffers-kill-terminal command queries for confirmation if you have buffers thatneed saving or subprocesses that are running. It also runs the abnormal hook kill-emacsquery-functions:[User Option]
When save-buffers-kill-terminal is killing Emacs, it calls the functions in thishook, after asking the standard questions and before calling kill-emacs. The functions
are called in order of appearance, with no arguments. Each function can ask for
additional confirmation from the user. If any of them returns nil, save-bufferskill-emacs does not kill Emacs, and does not run the remaining functions in thishook. Calling kill-emacs directly does not run this hook.

kill-emacs-query-functions[Command]This command does the same as save-buffers-kill-emacs, but instead of just killingthe current Emacs process at the end, it’ll restart a new Emacs process, using thesame command line arguments as the currently running Emacs process.

restart-emacs

42.2.2 Suspending Emacs
On text terminals, it is possible to suspend Emacs, which means stopping Emacs temporarily
and returning control to its superior process, which is usually the shell. This allows you toresume editing later in the same Emacs process, with the same buffers, the same kill ring,
the same undo history, and so on. To resume Emacs, use the appropriate command in theparent shell—most likely fg.
Suspending works only on a terminal device from which the Emacs session was started.
We call that device the controlling terminal of the session. Suspending is not allowed if thecontrolling terminal is a graphical terminal. Suspending is usually not relevant in graphicalenvironments, since you can simply switch to another application without doing anything
special to Emacs.
Some operating systems (those without SIGTSTP, or MS-DOS) do not support suspensionof jobs; on these systems, suspension actually creates a new shell temporarily as a subprocessof Emacs. Then you would exit the shell to return to Emacs.

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suspend-emacs &optional string[Command]This function stops Emacs and returns control to the superior process. If and when
the superior process resumes Emacs, suspend-emacs returns nil to its caller in Lisp.
This function works only on the controlling terminal of the Emacs session; to relinquish
control of other tty devices, use suspend-tty (see below). If the Emacs session uses
more than one terminal, you must delete the frames on all the other terminals before
suspending Emacs, or this function signals an error. See Section 30.2 [Multiple
Terminals], page 787.
If string is non-nil, its characters are sent to Emacs’s superior shell, to be read as
terminal input. The characters in string are not echoed by the superior shell; only the
results appear.
Before suspending, suspend-emacs runs the normal hook suspend-hook. After theuser resumes Emacs, suspend-emacs runs the normal hook suspend-resume-hook.
See Section 24.1 [Hooks], page 524.
The next redisplay after resumption will redraw the entire screen, unless the variable
no-redraw-on-reenter is non-nil. See Section 41.1 [Refresh Screen], page 1129.
Here is an example of how you could use these hooks:(add-hook 'suspend-hook(lambda () (or (y-or-n-p "Really suspend?")(error "Suspend canceled"))))(add-hook 'suspend-resume-hook (lambda () (message "Resumed!")(sit-for 2)))

Here is what you would see upon evaluating (suspend-emacs "pwd"):---------- Buffer: Minibuffer ---------Really suspend? y---------- Buffer: Minibuffer ------------------- Parent Shell ---------bash$ /home/username
bash$ fg---------- Echo Area ---------Resumed!

Note that ‘pwd’ is not echoed after Emacs is suspended. But it is read and executedby the shell.

suspend-hook[Variable]

This variable is a normal hook that Emacs runs before suspending.
[Variable]
This variable is a normal hook that Emacs runs on resuming after a suspension.

suspend-resume-hooksuspend-tty &optional tty[Function]
If tty specifies a terminal device used by Emacs, this function relinquishes the device
and restores it to its prior state. Frames that used the device continue to exist, but
are not updated and Emacs doesn’t read input from them. tty can be a terminal
object, a frame (meaning the terminal for that frame), or nil (meaning the terminal
for the selected frame). See Section 30.2 [Multiple Terminals], page 787.
If tty is already suspended, this function does nothing.

Chapter 42: Operating System Interface

1265This function runs the hook suspend-tty-functions, passing the terminal object as
an argument to each function.

resume-tty &optional tty[Function]
This function resumes the previously suspended terminal device tty; where tty has
the same possible values as it does for suspend-tty.
This function reopens the terminal device, re-initializes it, and redraws it with thatterminal’s selected frame. It then runs the hook resume-tty-functions, passing theterminal object as an argument to each function.
If the same device is already used by another Emacs terminal, this function signals anerror. If tty is not suspended, this function does nothing.

controlling-tty-p &optional tty[Function]
This function returns non-nil if tty is the controlling terminal of the Emacs session;
tty can be a terminal object, a frame (meaning the terminal for that frame), or nil(meaning the terminal for the selected frame).
[Command]This command suspends a frame. For GUI frames, it calls iconify-frame (seeSection 30.11 [Visibility of Frames], page 828); for frames on text terminals, it calls
either suspend-emacs or suspend-tty, depending on whether the frame is displayedon the controlling terminal device or not.

suspend-frame

42.3 Operating System Environment
Emacs provides access to variables in the operating system environment through various
functions. These variables include the name of the system, the user’s UID, and so on.
[Variable]
This variable holds the standard GNU configuration name for the hardware/software
configuration of your system, as a string. For example, a typical value for a 64-bit
GNU/Linux system is ‘"x86_64-unknown-linux-gnu"’.

system-configuration[Variable]
The value of this variable is a symbol indicating the type of operating system Emacs
is running on. The possible values are:system-type

aix

IBM’s AIX.

berkeley-unix
Berkeley BSD and its variants.
cygwinCygwin, a POSIX layer on top of MS-Windows.

darwinDarwin (macOS).

gnu

The GNU system (using the GNU kernel, which consists of the HURD
and Mach).

gnu/linux
A GNU/Linux system—that is, a variant GNU system, using the Linuxkernel. (These systems are the ones people often call “Linux”, but actuallyLinux is just the kernel, not the whole system.)Chapter 42: Operating System Interface

1266

gnu/kfreebsd
A GNU (glibc-based) system with a FreeBSD kernel.
haiku

The Haiku operating system, a derivative of the Be Operating System.

hpux

Hewlett-Packard HPUX operating system.

nacl

Google Native Client (NaCl) sandboxing system.

ms-dosMicrosoft’s DOS. Emacs compiled with DJGPP for MS-DOS binds
system-type to ms-dos even when you run it on MS-Windows.

usg-unix-v
AT&T Unix System V.
windows-nt
Microsoft Windows NT, 9X and later. The value of system-type is always
windows-nt, e.g., even on Windows 10.
We do not wish to add new symbols to make finer distinctions unless it is absolutely
necessary! In fact, we hope to eliminate some of these alternatives in the future.
If you need to make a finer distinction than system-type allows for, you can test
system-configuration, e.g., against a regexp.
[Function]
This function returns the name of the machine you are running on, as a string.

system-name[User Option]
If this variable is non-nil, it is used instead of system-name for purposes of generating
email addresses. For example, it is used when constructing the default value ofuser-mail-address. See Section 42.4 [User Identification], page 1269.

mail-host-address

getenv var &optional frame[Command]This function returns the value of the environment variable var, as a string. var should
be a string. If var is undefined in the environment, getenv returns nil. It returns ‘""’if var is set but null. Within Emacs, a list of environment variables and their values is
kept in the variable process-environment.
(getenv "USER")⇒ "lewis"
The shell command printenv prints all or part of the environment:
bash$ printenv
PATH=/usr/local/bin:/usr/bin:/bin
USER=lewis
TERM=xterm
SHELL=/bin/bash
HOME=/home/lewis...

setenv variable &optional value substitute[Command]This command sets the value of the environment variable named variable to value.
variable should be a string. Internally, Emacs Lisp can handle any string. However,Chapter 42: Operating System Interface

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normally variable should be a valid shell identifier, that is, a sequence of letters, digits
and underscores, starting with a letter or underscore. Otherwise, errors may occur
if subprocesses of Emacs try to access the value of variable. If value is omitted ornil (or, interactively, with a prefix argument), setenv removes variable from theenvironment. Otherwise, value should be a string.
If the optional argument substitute is non-nil, Emacs calls the function
substitute-env-vars to expand any environment variables in value.
setenv works by modifying process-environment; binding that variable with let isalso reasonable practice.
setenv returns the new value of variable, or nil if it removed variable from theenvironment.

with-environment-variables variables body. . .

[Macro]This macro sets the environment variables according to variables temporarily when
executing body. The previous values are restored when the form finishes. The
argument variables should be a list of pairs of strings of the form (var value), wherevar is the name of the environment variable and value is that variable’s value.
(with-environment-variables (("LANG" "C")("LANGUAGE" "en_US:en"))(call-process "ls" nil t))[Variable]
This variable is a list of strings, each describing one environment variable. The
functions getenv and setenv work by means of this variable.

process-environment

process-environment⇒ ("PATH=/usr/local/bin:/usr/bin:/bin""USER=lewis""TERM=xterm""SHELL=/bin/bash""HOME=/home/lewis"...)

If process-environment contains multiple elements that specify the same environment
variable, the first of these elements specifies the variable, and the others are ignored.
[Variable]
This variable holds the list of environment variables Emacs inherited from its parent
process when Emacs started.

initial-environment[Variable]
This variable holds a string that says which character separates directories in a search
path (as found in an environment variable). Its value is ":" for Unix and GNU systems,and ";" for MS systems.

path-separator[Function]
This function returns the connection-local value of variable path-separator. Thatis ";" for MS systems and a local default-directory, and ":" for Unix and GNU
systems, or a remote default-directory.

path-separator

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parse-colon-path path

[Function]
This function takes a search path string such as the value of the PATH environment
variable, and splits it at the separators, returning a list of directories. nil in this list
means the current directory. Although the function’s name says “colon”, it actuallyuses the value of variable path-separator.
(parse-colon-path ":/foo:/bar")⇒ (nil "/foo/" "/bar/")[Variable]
This variable holds the program name under which Emacs was invoked. The value isa string, and does not include a directory name.

invocation-name[Variable]
This variable holds the directory in which the Emacs executable was located when it
was run, or nil if that directory cannot be determined.

invocation-directory[Variable]
If non-nil, this is a directory within which to look for the lib-src and etc subdirectories. In an installed Emacs, it is normally nil. It is non-nil when Emacs
can’t find those directories in their standard installed locations, but can find themin a directory related somehow to the one containing the Emacs executable (i.e.,
invocation-directory).

installation-directoryload-average &optional use-float[Function]
This function returns the current 1-minute, 5-minute, and 15-minute system load
averages, in a list. The load average indicates the number of processes trying to run
on the system.
By default, the values are integers that are 100 times the system load averages, but
if use-float is non-nil, then they are returned as floating-point numbers without
multiplying by 100.
If it is impossible to obtain the load average, this function signals an error. On some
platforms, access to load averages requires installing Emacs as setuid or setgid so thatit can read kernel information, and that usually isn’t advisable.
If the 1-minute load average is available, but the 5- or 15-minute averages are not,this function returns a shortened list containing the available averages.
(load-average)⇒ (169 48 36)(load-average t)⇒ (1.69 0.48 0.36)

The shell command uptime returns similar information.

emacs-pid[Function]

This function returns the process ID of the Emacs process, as an integer.
[Variable]
This variable holds the erase character that was selected in the system’s terminal
driver, before Emacs was started.

tty-erase-charChapter 42: Operating System Interface

1269[Variable]
This variable holds the system null device. Its value is "/dev/null" for Unix andGNU systems, and "NUL" for MS systems.

null-device[Function]
This function returns the connection-local value of variable null-device. That is"NUL" for MS systems and a local default-directory, and "/dev/null" for Unix
and GNU systems, or a remote default-directory.

null-device

42.4 User Identification[Variable]
This variable says which user’s init files should be used by Emacs—or nil if none. ""stands for the user who originally logged in. The value reflects command-line options
such as ‘-q’ or ‘-u user’.
Lisp packages that load files of customizations, or any other sort of user profile, shouldobey this variable in deciding where to find it. They should load the profile of the username found in this variable. If init-file-user is nil, meaning that the ‘-q’, ‘-Q’,or ‘-batch’ option was used, then Lisp packages should not load any customization
files or user profile.

init-file-user

user-mail-address[User Option]

This holds the email address of the user who is using Emacs.

user-login-name &optional uid[Function]
This function returns the name under which the user is logged in. It uses theenvironment variables LOGNAME or USER if either is set. Otherwise, the value is basedon the effective UID, not the real UID.
If you specify uid (a number), the result is the user name that corresponds to uid, or
nil if there is no such user.
[Function]
This function returns the user name corresponding to Emacs’s real UID. This ignores
the effective UID, and the environment variables LOGNAME and USER.

user-real-login-nameuser-full-name &optional uid[Function]
This function returns the full name of the logged-in user—or the value of the environment variable NAME, if that is set.
If the Emacs process’s user-id does not correspond to any known user (and provided
NAME is not set), the result is "unknown".
If uid is non-nil, then it should be a number (a user-id) or a string (a login name).
Then user-full-name returns the full name corresponding to that user-id or loginname. If you specify a user-id or login name that isn’t defined, it returns nil.

The symbols user-login-name, user-real-login-name and user-full-name are variables as well as functions. The functions return the same values that the variables hold. Thesevariables allow you to fake out Emacs by telling the functions what to return. The variables
are also useful for constructing frame titles (see Section 30.6 [Frame Titles], page 821).

Chapter 42: Operating System Interface

user-real-uid

1270[Function]

This function returns the real UID of the user.

user-uid[Function]

This function returns the effective UID of the user.

group-gid[Function]

This function returns the effective GID of the Emacs process.

group-real-gid[Function]

This function returns the real GID of the Emacs process.
[Function]
This function returns a list of strings, listing the user names on the system. If Emacs
cannot retrieve this information, the return value is a list containing just the value ofuser-real-login-name.

system-users[Function]
This function returns a list of strings, listing the names of user groups on the system.
If Emacs cannot retrieve this information, the return value is nil.

system-groups

group-name gid[Function]
This function returns the group name that corresponds to the numeric group ID gid,or nil if there is no such group.

42.5 Time of Day
This section explains how to determine the current time and time zone.
Many functions like current-time and file-attributes return Lisp timestamp values
that count seconds, and that can represent absolute time by counting seconds since theepoch of 1970-01-01 00:00:00 UTC (Coordinated Universal Time). Typically these counts
ignore leap seconds; however, GNU and some other operating systems can be configured tocount leap seconds.
Although traditionally Lisp timestamps were integer pairs, their form has evolved andprograms ordinarily should not depend on the current default form. If your program needsa particular timestamp form, you can use the time-convert function to convert it to theneeded form. See Section 42.7 [Time Conversion], page 1273.
There are currently three forms of Lisp timestamps, each of which represents a numberof seconds:• An integer. Although this is the simplest form, it cannot represent subsecond timestamps.
• A pair of integers (ticks . hz), where hz is positive. This represents ticks/hz seconds,
which is the same time as plain ticks if hz is 1. A common value for hz is 1000000000,
for a nanosecond-resolution clock.
• A list of four integers (high low micro pico), where 0≤low<65536, 0≤micro<1000000,
and 0≤pico<1000000. This represents the number of seconds using the formula: high ×
216 + low + micro × 10−6 + pico × 10−12 . If current-time-list is t, some functions
may default to returning two- or three-element lists, with omitted micro and pico

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components defaulting to zero. On all current machines pico is a multiple of 1000, but
this may change as higher-resolution clocks become available.
Function arguments, e.g., the time argument to format-time-string, accept a moregeneral time value format, which can be a Lisp timestamp, nil for the current time, afinite floating-point number for seconds, or a list (high low micro) or (high low) that is atruncated list timestamp with missing elements taken to be zero.
Time values can be converted to and from calendrical and other forms. Some of theseconversions rely on operating system functions that limit the range of possible time values,
and signal an error such as ‘"Specified time is not representable"’ if the limits are
exceeded. For instance, a system might not support timestamps before the epoch, or
years far in the future. You can convert a time value into a human-readable string using
format-time-string, into a Lisp timestamp using time-convert, and into other forms
using decode-time and float-time. These functions are described in the following sections.

current-time-string &optional time zone

[Function]
This function returns the current time and date as a human-readable string. The
format does not vary for the initial part of the string, which contains the day of week,
month, day of month, and time of day in that order: the number of characters used
for these fields is always the same, although (unless you require English weekday
or month abbreviations regardless of locale) it is typically more convenient to use
format-time-string than to extract fields from the output of current-time-string,as the year might not have exactly four digits, and additional information may someday be added at the end.
The argument time, if given, specifies a time to format, instead of the current time.
The optional argument zone defaults to the current time zone rule. See Section 42.6
[Time Zone Rules], page 1272. The operating system limits the range of time andzone values.
(current-time-string)⇒ "Fri Nov 1 15:59:49 2019"[Variable]
This boolean variable is a transition aid. If t, current-time and related functions
return timestamps in list form, typically (high low micro pico); otherwise, they use(ticks . hz) form. Currently this variable defaults to t, for behavior compatible
with previous Emacs versions. Developers are encouraged to test timestamp-related
code with this variable set to nil, as it will default to nil in a future Emacs version,
and will be removed in some version after that.

current-time-list[Function]
This function returns the current time as a Lisp timestamp. If current-time-list isnil, the timestamp has the form (ticks . hz) where ticks counts clock ticks and hz isthe clock ticks per second. Otherwise, the timestamp has the list form (high low usecpsec). You can use (time-convert nil t) or (time-convert nil 'list) to obtaina particular form regardless of the value of current-time-list. See Section 42.7
[Time Conversion], page 1273.

current-timeChapter 42: Operating System Interface

1272

float-time &optional time

[Function]
This function returns the current time as a floating-point number of seconds since theepoch. The optional argument time, if given, specifies a time to convert instead of thecurrent time.
Warning: Since the result is floating point, it may not be exact. Do not use this function if precise time stamps are required. For example, on typical systems (float-time'(1 . 10)) displays as ‘0.1’ but is slightly greater than 1/10.
time-to-seconds is an alias for this function.
[Function]
Return the current CPU time along with its resolution. The return value is a pair(CPU-TICKS . TICKS-PER-SEC). The CPU-TICKS counter can wrap around, so values
cannot be meaningfully compared if too much time has passed between them.

current-cpu-time

42.6 Time Zone Rules
The default time zone is determined by the TZ environment variable. See Section 42.3
[System Environment], page 1265. For example, you can tell Emacs to default to Universal
Time with (setenv "TZ" "UTC0"). If TZ is not in the environment, Emacs uses system wall
clock time, which is a platform-dependent default time zone.
The set of supported TZ strings is system-dependent. GNU and many other systems
support TZDB timezones, e.g., ‘"America/New_York"’ specifies the time zone and daylightsaving time history for locations near New York City. GNU and most other systems support
POSIX-style TZ strings, e.g., ‘"EST5EDT,M4.1.0,M10.5.0"’ specifies the rules used in New
York from 1987 through 2006. All systems support the string ‘"UTC0"’ meaning Universal
Time.
Functions that convert to and from local time accept an optional time zone rule argument,
which specifies the conversion’s time zone and daylight saving time history. If the timezone rule is omitted or nil, the conversion uses Emacs’s default time zone. If it is t, theconversion uses Universal Time. If it is wall, the conversion uses the system wall clock time.
If it is a string, the conversion uses the time zone rule equivalent to setting TZ to that string.
If it is a list (offset abbr), where offset is an integer number of seconds east of Universal
Time and abbr is a string, the conversion uses a fixed time zone with the given offset andabbreviation. An integer offset is treated as if it were (offset abbr), where abbr is a numericabbreviation on POSIX-compatible platforms and is unspecified on MS-Windows.

current-time-zone &optional time zone

[Function]
This function returns a list describing the time zone that the user is in.
The value has the form (offset abbr). Here offset is an integer giving the number of
seconds ahead of Universal Time (east of Greenwich). A negative value means westof Greenwich. The second element, abbr, is a string giving an abbreviation for thetime zone, e.g., ‘"CST"’ for China Standard Time or for U.S. Central Standard Time.
Both elements can change when daylight saving time begins or ends; if the user has
specified a time zone that does not use a seasonal time adjustment, then the value isconstant through time.
If the operating system doesn’t supply all the information necessary to compute thevalue, the unknown elements of the list are nil.

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The argument time, if given, specifies a time value to analyze instead of the current
time. The optional argument zone defaults to the current time zone rule. The
operating system limits the range of time and zone values.

42.7 Time Conversion
These functions convert time values (see Section 42.5 [Time of Day], page 1270) to Lisp
timestamps, or into calendrical information and vice versa.
Many operating systems use 64-bit signed integers to count seconds, and can represent
times far in the past or future. However, some are more limited. For example, old-fashioned
operating systems that use 32-bit signed integers typically handle only times from 1901-12-13
20:45:52 through 2038-01-19 03:14:07 Universal Time.
Calendrical conversion functions use the Gregorian calendar even for dates before theGregorian calendar was introduced, and for dates in the far distant past or future for which
the Gregorian calendar is wildly inaccurate and disagrees with common practice in scientificfields like astronomy and paleontology, which use Julian-calendar year lengths. Year numbers
count since the year 1 BCE, and do not skip zero as traditional Gregorian years do; forexample, the year number −37 represents the Gregorian year 38 BCE.

time-convert time form

[Function]

This function converts a time value into a Lisp timestamp.
The form argument specifies the timestamp form to be returned. If form is the symbol
integer, this function returns an integer count of seconds. If form is a positive integer,
it specifies a clock frequency and this function returns an integer-pair timestamp(ticks . form). If form is t, this function treats it as a positive integer suitable forrepresenting the timestamp; for example, it is treated as 1000000000 if time is nil
and the platform timestamp has nanosecond resolution. If form is list, this function
returns an integer list (high low micro pico). Although a nil form currently acts
like list, this is planned to change in a future Emacs version, so callers requiring list
timestamps should pass list explicitly.
If time is not a time value, this function signals an error. Otherwise, if time cannot
be represented exactly, conversion truncates it toward minus infinity. When form is t,conversion is always exact so no truncation occurs, and the returned clock resolution
is no less than that of time. By way of contrast, although float-time can also
convert any time value without signaling an error, the result might not be exact. See
Section 42.5 [Time of Day], page 1270.
For efficiency this function might return a value that is eq to time, or that otherwise
shares structure with time.
Although (time-convert nil nil) is equivalent to (current-time), the latter may
be a bit faster.
(setq a (time-convert nil t))⇒ (1564826753904873156 . 1000000000)(time-convert a 100000)⇒ (156482675390487 . 100000)(time-convert a 'integer)⇒ 1564826753

Chapter 42: Operating System Interface

1274(time-convert a 'list)⇒ (23877 23681 904873 156000)

decode-time &optional time zone form

[Function]
This function converts a time value into calendrical information. If you don’t specify
time, it decodes the current time, and similarly zone defaults to the current time zone
rule. See Section 42.6 [Time Zone Rules], page 1272. The operating system limits therange of time and zone values.
The form argument controls the form of the returned seconds element, as described
below. The return value is a list of nine elements, as follows:(seconds minutes hour day month year dow dst utcoff)
Here is what the elements mean:
seconds

The number of seconds past the minute, with form described below.

minutes

The number of minutes past the hour, as an integer between 0 and 59.

hour

The hour of the day, as an integer between 0 and 23.

day

The day of the month, as an integer between 1 and 31.

month

The month of the year, as an integer between 1 and 12.

year

The year, an integer typically greater than 1900.

dow

The day of week, as an integer between 0 and 6, where 0 stands for Sunday.

dst

t if daylight saving time is effect, nil if it is not in effect, and −1 if thisinformation is not available.

utcoffAn integer indicating the Universal Time offset in seconds, i.e., the numberof seconds east of Greenwich.

The seconds element is a Lisp timestamp that is nonnegative and less than 61; itis less than 60 except during positive leap seconds (assuming the operating system
supports leap seconds). If the optional form argument is t, seconds uses the same
precision as time; if form is integer, seconds is truncated to an integer. For example, if time is the timestamp (1566009571321 . 1000), which represents 2019-08-17
02:39:31.321 UTC on typical systems that lack leap seconds, then (decode-time timet t) returns ((31321 . 1000) 39 2 17 8 2019 6 nil 0), whereas (decode-time time
t 'integer) returns (31 39 2 17 8 2019 6 nil 0). If form is omitted or nil, it currently defaults to integer but this default may change in future Emacs releases, so
callers requiring a particular form should specify form.
Common Lisp Note: Common Lisp has different meanings for dow, dst and utcoff,and its second is an integer between 0 and 59 inclusive.
To access (or alter) the elements in the calendrical information, the decoded-timesecond,
decoded-time-minute,decoded-time-hour,decoded-timeday,
decoded-time-month,decoded-time-year,
decoded-time-weekday,
decoded-time-dst and decoded-time-zone accessors can be used.

Chapter 42: Operating System Interface

encode-time time &rest obsolescent-arguments

1275[Function]
This function converts time to a Lisp timestamp. It can act as the inverse of
decode-time.
Ordinarily the first argument is a list (second minute hour day month year ignored
dst zone) that specifies a decoded time in the style of decode-time. For the meaningsof these list elements, see the table under decode-time. In particular, dst says how tointerpret timestamps during a daylight saving fallback when timestamps are repeated.
If dst is −1, the DST value is guessed; if it is t or nil the timestamp with that DST
value is returned, with an error signaled if no such timestamp exists. Unfortunately adst value of t or nil does not disambiguate timestamps duplicated when a TZDB-based
timezone moves further west of Greenwich, such as disambiguating the two standardtime timestamps 2020-12-27 01:30 when zone is ‘"Europe/Volgograd"’, which at
02:00 that day changed standard time from 4 to 3 hours east of Greenwich; if you needto handle situations like this you can use a numeric zone to disambiguate instead.
The first argument can also be a list (second minute hour day month year), which
is treated like the list (second minute hour day month year nil -1 nil).
As an obsolescent calling convention, this function can be given six or more arguments.
The first six arguments second, minute, hour, day, month, and year specify most of
the components of a decoded time. If there are more than six arguments the lastargument is used as zone and any other extra arguments are ignored, so that (apply#'encode-time (decode-time ...)) works. In this obsolescent convention, dst is −1
and zone defaults to the current time zone rule (see Section 42.6 [Time Zone Rules],page 1272). When modernizing an obsolescent caller, ensure that the more-modern
list equivalent contains 9 elements with a dst element that is −1, not nil.
Year numbers less than 100 are not treated specially. If you want them to standfor years above 1900, or years above 2000, you must alter them yourself before you
call encode-time. The operating system limits the range of time and zone values.
However, timestamps ranging from the epoch to the near future are always supported.
The encode-time function acts as a rough inverse to decode-time. For example, you
can pass the output of the latter to the former as follows:(encode-time (decode-time ...))
You can perform simple date arithmetic by using out-of-range values for seconds,
minutes, hour, day, and month; for example, day 0 means the day preceding the given
month. Take care when doing so, as it is common for this to fail in some cases. For
example:;; Try to compute the time one month from now.
;; Watch out; this might not work as expected.
(let ((time (decode-time)))(setf (decoded-time-month time)(+ (decoded-time-month time) 1))
time)
Unfortunately, this code might not work as expected if the resulting time is invalid due
to month length differences, daylight saving transitions, time zone changes, or missing
leap days or leap seconds. For example, if executed on January 30 this code yields
a nonexistent date February 30, which encode-time would adjust to early March.

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Similarly, adding four years to February 29, 2096 would yield the nonexistent dateFebruary 29, 2100; and adding one hour to 01:30 on March 13, 2022 in New York
would yield a timestamp 02:30 that does not exist because clocks sprang forwardfrom 02:00 to 03:00 that day. To avoid some (though not all) of the problem, you
can base calculations on the middle of the affected unit, e.g., start at the 15th of themonth when adding months. Alternatively, you can use the calendar and time-datelibraries.

42.8 Parsing and Formatting Times
These functions convert time values to text in a string, and vice versa. Time values areeither represented as a Lisp timestamp (see Section 42.5 [Time of Day], page 1270) or adecoded time structure (see Section 42.7 [Time Conversion], page 1273).

date-to-time string[Function]
This function parses the time-string string and returns the corresponding Lisp timestamp. The argument string should represent a date-time, and should be in oneof the forms recognized by parse-time-string (see below). This function assumes
Universal Time if string lacks explicit time zone information, and assumes earliest
values if string lacks month, day, or time. The operating system limits the range oftime and zone values.

parse-time-string string[Function]
This function parses the time-string string into a decoded time structure (seeSection 42.7 [Time Conversion], page 1273). The argument string should resemble an
RFC 822 (or later) or ISO 8601 string, like “Fri, 25 Mar 2016 16:24:56 +0100” or“1998-09-12T12:21:54-0200”, but this function will attempt to parse less well-formed
time strings as well.

iso8601-parse string[Function]
For a more strict function (that will error out upon invalid input), this function
can be used instead. It can parse all variants of the ISO 8601 standard, so in
addition to the formats mentioned above, it also parses things like “1998W45-3”(week number) and “1998-245” (ordinal day number). To parse durations, there’s
iso8601-parse-duration, and to parse intervals, there’s iso8601-parse-interval.
All these functions return decoded time structures, except the final one, which returns
three of them (the start, the end, and the duration).

format-time-string format-string &optional time zone

[Function]
This function converts time (which should be a Lisp timestamp, and defaults to thecurrent time if time is omitted or nil) to a string according to format-string. The
conversion uses the time zone rule zone, which defaults to the current time zone rule.
See Section 42.6 [Time Zone Rules], page 1272. The argument format-string may
contain ‘%’-sequences which say to substitute parts of the time. Here is a table of whatthe ‘%’-sequences mean:‘%a’This stands for the abbreviated name of the day of week.

‘%A’

This stands for the full name of the day of week.

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‘%b’

This stands for the abbreviated name of the month.

‘%B’

This stands for the full name of the month.

‘%c’This is a synonym for ‘%x %X’.

‘%C’

This stands for the century, that is, the year divided by 100, truncatedtoward zero. The default field width is 2.

‘%d’This stands for the day of month, zero-padded.

‘%D’This is a synonym for ‘%m/%d/%y’.

‘%e’This stands for the day of month, blank-padded.

‘%F’This stands for the ISO 8601 date format, which is like ‘%+4Y-%m-%d’
except that any flags or field width override the ‘+’ and (after subtracting6) the ‘4’.

‘%g’

This stands for the year without century (00–99) corresponding to thecurrent ISO week number. ISO weeks start on Monday and end on Sunday.
If an ISO week begins in one year and ends in another, the rules regarding
which year ‘%g’ will produce are complex and will not be described here;
however, in general, if most of the week’s days are in the ending year, ‘%g’
will produce that year.

‘%G’

This stands for the year with century corresponding to the current ISO
week number.

‘%h’This is a synonym for ‘%b’.

‘%H’

This stands for the hour (00–23).

‘%I’

This stands for the hour (01–12).

‘%j’This stands for the day of the year (001–366).

‘%k’This stands for the hour (0–23), blank padded.

‘%l’This stands for the hour (1–12), blank padded.

‘%m’This stands for the month (01–12).

‘%M’

This stands for the minute (00–59).

‘%n’This stands for a newline.

‘%N’This stands for the nanoseconds (000000000–999999999). To ask for fewer
digits, use ‘%3N’ for milliseconds, ‘%6N’ for microseconds, etc. Any excess
digits are discarded, without rounding.

‘%p’This stands for ‘AM’ or ‘PM’, as appropriate.

‘%q’

This stands for the calendar quarter (1–4).

‘%r’This is a synonym for ‘%I:%M:%S %p’.

‘%R’

This is a synonym for ‘%H:%M’.

‘%s’This stands for the integer number of seconds since the epoch.

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‘%S’

This stands for the second (00–59, or 00–60 on platforms that support
leap seconds).

‘%t’

This stands for a tab character.

‘%T’

This is a synonym for ‘%H:%M:%S’.

‘%u’

This stands for the numeric day of week (1–7). Monday is day 1.

‘%U’This stands for the week of the year (01–52), assuming that weeks starton Sunday.

‘%V’

This stands for the week of the year according to ISO 8601.

‘%w’

This stands for the numeric day of week (0–6). Sunday is day 0.

‘%W’This stands for the week of the year (01–52), assuming that weeks starton Monday.

‘%x’

This has a locale-specific meaning. In the default locale (named ‘C’), it isequivalent to ‘%D’.

‘%X’

This has a locale-specific meaning. In the default locale (named ‘C’), it isequivalent to ‘%T’.

‘%y’

This stands for the year without century (00–99).

‘%Y’

This stands for the year with century.

‘%Z’

This stands for the time zone abbreviation (e.g., ‘EST’).

‘%z’

This stands for the time zone numerical offset. The ‘z’ can be precededby one, two, or three colons; if plain ‘%z’ stands for ‘-0500’, then ‘%:z’stands for ‘-05:00’, ‘%::z’ stands for ‘-05:00:00’, and ‘%:::z’ is like‘%::z’ except it suppresses trailing instances of ‘:00’ so it stands for ‘-05’
in the same example.

‘%%’

This stands for a single ‘%’.

One or more flag characters can appear immediately after the ‘%’. ‘0’ pads with zeros,‘+’ pads with zeros and also puts ‘+’ before nonnegative year numbers with more thanfour digits, ‘_’ pads with blanks, ‘-’ suppresses padding, ‘^’ upper-cases letters, and‘#’ reverses the case of letters.
You can also specify the field width and type of padding for any of these ‘%’-sequences.
This works as in printf: you write the field width as digits in a ‘%’-sequence, after
any flags. For example, ‘%S’ specifies the number of seconds since the minute; ‘%03S’means to pad this with zeros to 3 positions, ‘%_3S’ to pad with spaces to 3 positions.
Plain ‘%3S’ pads with zeros, because that is how ‘%S’ normally pads to two positions.
The characters ‘E’ and ‘O’ act as modifiers when used after any flags and field widths
in a ‘%’-sequence. ‘E’ specifies using the current locale’s alternative version of the date
and time. In a Japanese locale, for example, %Ex might yield a date format based on
the Japanese Emperors’ reigns. ‘E’ is allowed in ‘%Ec’, ‘%EC’, ‘%Ex’, ‘%EX’, ‘%Ey’, and‘%EY’.
‘O’ means to use the current locale’s alternative representation of numbers, instead of
the ordinary decimal digits. This is allowed with most letters, all the ones that output
numbers.

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To help debug programs, unrecognized ‘%’-sequences stand for themselves and are
output as-is. Programs should not rely on this behavior, as future versions of Emacs
may recognize new ‘%’-sequences as extensions.
This function uses the C library function strftime (see Section “Formatting Calendar
Time” in The GNU C Library Reference Manual) to do most of the work. In order
to communicate with that function, it first converts time and zone to internal form;
the operating system limits the range of time and zone values. This function also
encodes format-string using the coding system specified by locale-coding-system(see Section 34.12 [Locales], page 991); after strftime returns the resulting string,
this function decodes the string using that same coding system.

format-seconds format-string seconds[Function]
This function converts its argument seconds into a string of years, days, hours, etc.,
according to format-string. The argument format-string may contain ‘%’-sequences
which control the conversion. Here is a table of what the ‘%’-sequences mean:
‘%y’
‘%Y’

The integer number of 365-day years.

‘%d’
‘%D’

The integer number of days.

‘%h’
‘%H’

The integer number of hours.

‘%m’
‘%M’

The integer number of minutes.

‘%s’
‘%S’

The number of seconds. If the optional ‘,’ parameter is used, it’s a floating
point number, and the number after the ‘,’ specifies how many decimals
to be used. ‘%,2s’ means “use two decimals”.

‘%z’

Non-printing control flag. When it is used, other specifiers must be givenin the order of decreasing size, i.e., years before days, hours before minutes,
etc. Nothing will be produced in the result string to the left of ‘%z’ until
the first non-zero conversion is encountered. For example, the default
format used by emacs-uptime (see Section 42.9 [Processor Run Time],
page 1280) "%Y, %D, %H, %M, %z%S" means that the number of seconds
will always be produced, but years, days, hours, and minutes will only beshown if they are non-zero.

‘%x’

Non-printing control flag that works along the same lines as ‘%z’, butinstead suppresses printing of trailing zero-value time elements.

‘%%’

Produces a literal ‘%’.

Upper-case format sequences produce the units in addition to the numbers, lower-caseformats produce only the numbers.
You can also specify the field width by following the ‘%’ with a number; shorter
numbers will be padded with blanks. An optional period before the width requests
zero-padding instead. For example, "%.3Y" might produce "004 years".

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42.9 Processor Run time
Emacs provides several functions and primitives that return time, both elapsed and processor
time, used by the Emacs process.

emacs-uptime &optional format[Command]This function returns a string representing the Emacs uptime—the elapsed wall-clock
time this instance of Emacs is running. The string is formatted by format-seconds
according to the optional argument format. For the available format descriptors, see
Section 42.8 [Time Parsing], page 1276. If format is nil or omitted, it defaults to"%Y, %D, %H, %M, %z%S".
When called interactively, it prints the uptime in the echo area.
[Function]
This function returns the processor run time used by Emacs, as a Lisp timestamp (seeSection 42.5 [Time of Day], page 1270).
Note that the time returned by this function excludes the time Emacs was not using
the processor, and if the Emacs process has several threads, the returned value is thesum of the processor times used up by all Emacs threads.
If the system doesn’t provide a way to determine the processor run time,
get-internal-run-time returns the same time as current-time.

get-internal-run-time[Command]This function returns the duration of the Emacs initialization (see Section 42.1.1[Startup Summary], page 1255) in seconds, as a string. When called interactively, it
prints the duration in the echo area.

emacs-init-time

42.10 Time Calculations
These functions perform calendrical computations using time values (see Section 42.5 [Timeof Day], page 1270). As with any time value, a value of nil for any of their time-value
arguments stands for the current system time, and a finite number stands for the number of
seconds since the epoch.

time-less-p t1 t2[Function]

This returns t if the time value t1 is less than the time value t2.

time-equal-p t1 t2[Function]
This returns t if the two time values t1 and t2 are equal. The result is nil if either
argument is a NaN. For the purpose of comparison, a nil argument represents thecurrent time with infinite resolution, so this function returns nil if one argument is
nil and the other is not, and callers can therefore use nil to represent an unknown
time value that does not equal any timestamp.

time-subtract t1 t2[Function]
This returns the time difference t1 − t2 between two time values, as a Lisp timestamp.
The result is exact and its clock resolution is no worse than the worse of its twoarguments’ resolutions. If you need the difference in units of elapsed seconds, you canconvert it with time-convert or float-time. See Section 42.7 [Time Conversion],
page 1273.

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time-add t1 t2[Function]
This returns the sum of two time values, using the same conversion rules astime-subtract. One argument should represent a time difference rather than a point
in time, as a time value that is often just a single number of elapsed seconds. Here is
how to add a number of seconds to a time value:(time-add time seconds)

time-to-days time-value[Function]
This function returns the number of days between the beginning of year 1 and timevalue, assuming the default time zone. The operating system limits the range of timeand zone values.

days-to-time days

[Function]
This is not quite the inverse of the time-to-days function, as it uses the Emacs
epoch (instead of the year 1) for historical reasons. To get the inverse, subtract(time-to-days 0) from days, in which case days-to-time may return nil if days is
negative.

time-to-day-in-year time-value[Function]
This returns the day number within the year corresponding to time-value, assuming
the default time zone. The operating system limits the range of time and zone values.

date-leap-year-p year

[Function]

This function returns t if year is a leap year.

date-days-in-month year month[Function]
Return the number of days in month in year. For instance, February 2020 has 29 days.

date-ordinal-to-time year ordinal[Function]
Return the date of ordinal in year as a decoded time structure. For instance, the120th day in 2004 is April 29th.

42.11 Timers for Delayed Execution
You can set up a timer to call a function at a specified future time or after a certain lengthof idleness. A timer is a special object that stores the information about the next invocation
times and the function to invoke.

timerp object[Function]

This predicate function returns non-nil if object is a timer.
Emacs cannot run timers at any arbitrary point in a Lisp program; it can run them only
when Emacs could accept output from a subprocess: namely, while waiting or inside certain
primitive functions such as sit-for or read-event which can wait. Therefore, a timer’s
execution may be delayed if Emacs is busy. However, the time of execution is very precise if
Emacs is idle.
Emacs binds inhibit-quit to t before calling the timer function, because quittingout of many timer functions can leave things in an inconsistent state. This is normallyunproblematical because most timer functions don’t do a lot of work. Indeed, for a timer

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to call a function that takes substantial time to run is likely to be annoying. If a timer
function needs to allow quitting, it should use with-local-quit (see Section 22.11 [Quitting],
page 471). For example, if a timer function calls accept-process-output to receive output
from an external process, that call should be wrapped inside with-local-quit, to ensurethat C-g works if the external process hangs.
It is usually a bad idea for timer functions to alter buffer contents. When they do, theyusually should call undo-boundary both before and after changing the buffer, to separate
the timer’s changes from user commands’ changes and prevent a single undo entry fromgrowing to be quite large.
Timer functions should also avoid calling functions that cause Emacs to wait, such as
sit-for (see Section 22.10 [Waiting], page 470). This can lead to unpredictable effects,
since other timers (or even the same timer) can run while waiting. If a timer function needs
to perform an action after a certain time has elapsed, it can do this by scheduling a newtimer.
If a timer function performs a remote file operation, it can be in conflict with an alreadyrunning remote file operation of the same connection. Such conflicts are detected, and they
result in a remote-file-error error (see Appendix F [Standard Errors], page 1390). Thisshould be protected by wrapping the timer function body with
(ignore-error 'remote-file-error...)
If a timer function calls functions that can change the match data, it should save andrestore the match data. See Section 35.6.4 [Saving Match Data], page 1016.

run-at-time time repeat function &rest args

[Command]This sets up a timer that calls the function function with arguments args at time time.
If repeat is a number (integer or floating point), the timer is scheduled to run again
every repeat seconds after time. If repeat is nil, the timer runs only once.
time may specify an absolute or a relative time.
Absolute times may be specified using a string with a limited variety of formats, andare taken to be times today, even if already in the past. The recognized forms are‘xxxx’, ‘x:xx’, or ‘xx:xx’ (military time), and ‘xxam’, ‘xxAM’, ‘xxpm’, ‘xxPM’, ‘xx:xxam’,‘xx:xxAM’, ‘xx:xxpm’, or ‘xx:xxPM’. A period can be used instead of a colon to separate
the hour and minute parts.
To specify a relative time as a string, use numbers followed by units. For example:‘1 min’denotes 1 minute from now.

‘1 min 5 sec’denotes 65 seconds from now.
‘1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year’
denotes exactly 103 months, 123 days, and 10862 seconds from now.
For relative time values, Emacs considers a month to be exactly thirty days, and ayear to be exactly 365.25 days.
Not all convenient formats are strings. If time is a number (integer or floating point),that specifies a relative time measured in seconds. The result of encode-time canalso be used to specify an absolute value for time.

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In most cases, repeat has no effect on when first call takes place—time alone specifies
that. There is one exception: if time is t, then the timer runs whenever the time
is a multiple of repeat seconds after the epoch. This is useful for functions like
display-time. For instance, the following will make function run at every “whole”
minute (e.g., ‘11:03:00’, ‘11:04:00’, etc):(run-at-time t 60 function)
If Emacs didn’t get any CPU time when the timer would have run (for example if
the system was busy running another process or if the computer was sleeping or in asuspended state), the timer will run as soon as Emacs resumes and is idle.
The function run-at-time returns a timer value that identifies the particular scheduled
future action. You can use this value to call cancel-timer (see below).

run-with-timer secs repeat function &rest args

[Command]This is exactly the same as run-at-time (so see that definition for an explanationof the parameters; secs is passed as time to that function), but is meant to be used
when the delay is specified in seconds.

A repeating timer nominally ought to run every repeat seconds, but remember that any
invocation of a timer can be late. Lateness of one repetition has no effect on the scheduled
time of the next repetition. For instance, if Emacs is busy computing for long enough tocover three scheduled repetitions of the timer, and then starts to wait, it will immediately
call the timer function three times in immediate succession (presuming no other timers
trigger before or between them). If you want a timer to run again no less than n seconds
after the last invocation, don’t use the repeat argument. Instead, the timer function should
explicitly reschedule the timer.
[User Option]
This variable’s value specifies the maximum number of times to repeat calling a timer
function in a row, when many previously scheduled calls were unavoidably delayed.

timer-max-repeats

with-timeout (seconds timeout-forms. . . ) body. . .

[Macro]Execute body, but give up after seconds seconds. If body finishes before the time is up,
with-timeout returns the value of the last form in body. If, however, the execution ofbody is cut short by the timeout, then with-timeout executes all the timeout-forms
and returns the value of the last of them.

This macro works by setting a timer to run after seconds seconds. If body finishes
before that time, it cancels the timer. If the timer actually runs, it terminates executionof body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a primitivethat can wait, with-timeout cannot stop executing body while it is in the midst of acomputation—only when it calls one of those primitives. So use with-timeout onlywith a body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use a timer to avoid
waiting too long for an answer. See Section 21.7 [Yes-or-No Queries], page 413.

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cancel-timer timer[Function]
This cancels the requested action for timer, which should be a timer—usually, one
previously returned by run-at-time or run-with-idle-timer. This cancels the effectof that call to one of these functions; the arrival of the specified time will not cause
anything special to happen.

The list-timers command lists all the currently active timers. The command c(timer-list-cancel) will cancel the timer on the line under point. You can sort the listby column using the command S (tabulated-list-sort).

42.12 Idle Timers
Here is how to set up a timer that runs when Emacs is idle for a certain length of time.
Aside from how to set them up, idle timers work just like ordinary timers.

run-with-idle-timer secs repeat function &rest args

[Command]Set up a timer which runs the next time Emacs is idle for secs seconds. The value ofsecs may be a number or a value of the type returned by current-idle-time.
If repeat is nil, the timer runs just once, the first time Emacs remains idle for a longenough time. More often repeat is non-nil, which means to run the timer each time
Emacs remains idle for secs seconds.
The function run-with-idle-timer returns a timer value which you can use in calling
cancel-timer (see Section 42.11 [Timers], page 1281).

Emacs becomes idle when it starts waiting for user input (unless it waits for input witha timeout, see Section 22.8.2 [Reading One Event], page 462), and it remains idle until theuser provides some input. If a timer is set for five seconds of idleness, it runs approximately
five seconds after Emacs first becomes idle. Even if repeat is non-nil, this timer will not
run again as long as Emacs remains idle, because the duration of idleness will continue toincrease and will not go down to five seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from asubprocess. But these interludes during idleness do not interfere with idle timers, because
they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run
when ten minutes have elapsed since the last user command was finished, even if subprocess
output has been accepted thousands of times within those ten minutes, and even if there
have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Thenit becomes idle again, and all the idle timers that are set up to repeat will subsequently run
another time, one by one.
Do not write an idle timer function containing a loop which does a certain amount ofprocessing each time around, and exits when (input-pending-p) is non-nil. This approachseems very natural but has two problems:• It blocks out all process output (since Emacs accepts process output only while waiting).
• It blocks out any idle timers that ought to run during that time.
Similarly, do not write an idle timer function that sets up another idle timer (including
the same idle timer) with secs argument less than or equal to the current idleness time.

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Such a timer will run almost immediately, and continue running again and again, instead of
waiting for the next time Emacs becomes idle. The correct approach is to reschedule with
an appropriate increment of the current value of the idleness time, as described below.
[Function]
If Emacs is idle, this function returns the length of time Emacs has been idle, using
the same format as current-time (see Section 42.5 [Time of Day], page 1270).
When Emacs is not idle, current-idle-time returns nil. This is a convenient way
to test whether Emacs is idle.

current-idle-time

The main use of current-idle-time is when an idle timer function wants to “take abreak” for a while. It can set up another idle timer to call the same function again, after a
few seconds more idleness. Here’s an example:(defvar my-resume-timer nil"Timer for `my-timer-function' to reschedule itself, or nil.")(defun my-timer-function ();; If the user types a command while my-resume-timer;; is active, the next time this function is called from;; its main idle timer, deactivate my-resume-timer.
(when my-resume-timer(cancel-timer my-resume-timer))...do the work for a while...
(when taking-a-break(setq my-resume-timer(run-with-idle-timer;; Compute an idle time break-length;; more than the current value.
(time-add (current-idle-time) break-length)nil'my-timer-function))))42.13 Terminal Input
This section describes functions and variables for recording or manipulating terminal input.
See Chapter 41 [Display], page 1129, for related functions.

42.13.1 Input Modes
set-input-mode interrupt flow meta &optional quit-char[Function]
This function sets the mode for reading keyboard input. If interrupt is non-nil, thenEmacs uses input interrupts. If it is nil, then it uses cbreak mode. The default
setting is system-dependent. Some systems always use cbreak mode regardless ofwhat is specified.
When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-nil, then Emacs uses xon/xoff (C-q, C-s) flow control for output tothe terminal. This has no effect except in cbreak mode.

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The argument meta controls support for input character codes above 127. If meta
is t, Emacs converts characters with the 8th bit set into Meta characters, before it
decodes them as needed (see Section 34.10.8 [Terminal I/O Encoding], page 990). If
meta is nil, Emacs disregards the 8th bit; this is necessary when the terminal uses it
as a parity bit. If meta is the symbol encoded, Emacs first decodes the charactersusing all the 8 bits of each byte, and then converts the decoded single-byte characters
into Meta characters if they have their eighth bit set. Finally, if meta is neither t
nor nil nor encoded, Emacs uses all 8 bits of input unchanged, both before and after
decoding them. This is good for terminals that use 8-bit character sets and don’t
encode the Meta modifier as the eighth bit.
If quit-char is non-nil, it specifies the character to use for quitting. Normally thischaracter is C-g. See Section 22.11 [Quitting], page 471.
The current-input-mode function returns the input mode settings Emacs is currently
using.
[Function]
This function returns the current mode for reading keyboard input. It returns a list,
corresponding to the arguments of set-input-mode, of the form (interrupt flowmeta quit) in which:current-input-mode

interrupt

is non-nil when Emacs is using interrupt-driven input. If nil, Emacs isusing cbreak mode.

flow

is non-nil if Emacs uses xon/xoff (C-q, C-s) flow control for output tothe terminal. This value is meaningful only when interrupt is nil.

meta

is t if Emacs treats the eighth bit of input characters as the Meta bit
before decoding input; encoded if Emacs treats the eighth bit of thedecoded single-byte characters as the Meta bit; nil if Emacs clears theeighth bit of every input character; any other value means Emacs uses alleight bits as the basic character code.

quit

is the character Emacs currently uses for quitting, usually C-g.

42.13.2 Recording Input
recent-keys &optional include-cmds[Function]
This function returns a vector containing the last 300 input events from the keyboard
or mouse. All input events are included, whether or not they were used as parts ofkey sequences. Thus, you always get the last 300 input events, not counting events
generated by keyboard macros. (These are excluded because they are less interestingfor debugging; it should be enough to see the events that invoked the macros.)
If include-cmds is non-nil, complete key sequences in the result vector are interleavedwith pseudo-events of the form (nil . COMMAND), where COMMAND is the bindingof the key sequence (see Section 22.1 [Command Overview], page 423).

A call to clear-this-command-keys (see Section 22.5 [Command Loop Info], page 436)
causes this function to return an empty vector immediately afterward.

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open-dribble-file filename[Command]This function opens a dribble file named filename. When a dribble file is open, each
input event from the keyboard or mouse (but not those from keyboard macros) is
written in that file. A non-character event is expressed using its printed representation
surrounded by ‘<...>’. Be aware that sensitive information (such as passwords) may
end up recorded in the dribble file.
You close the dribble file by calling this function with an argument of nil.

See also the open-termscript function (see Section 42.14 [Terminal Output], page 1287).

42.14 Terminal Output
The terminal output functions send output to a text terminal, or keep track of output sent
to the terminal. The variable baud-rate tells you what Emacs thinks is the output speedof the terminal.
[User Option]
This variable’s value is the output speed of the terminal, as far as Emacs knows.
Setting this variable does not change the speed of actual data transmission, but thevalue is used for calculations such as padding.
It also affects decisions about whether to scroll part of the screen or repaint on text
terminals. See Section 41.2 [Forcing Redisplay], page 1129, for the corresponding
functionality on graphical terminals.
The value is measured in baud.

baud-rate

If you are running across a network, and different parts of the network work at different
baud rates, the value returned by Emacs may be different from the value used by your local
terminal. Some network protocols communicate the local terminal speed to the remotemachine, so that Emacs and other programs can get the proper value, but others do not.
If Emacs has the wrong value, it makes decisions that are less than optimal. To fix the
problem, set baud-rate.

send-string-to-terminal string &optional terminal[Function]
This function sends string to terminal without alteration. Control characters instring have terminal-dependent effects. (If you need to display non-ASCII text on theterminal, encode it using one of the functions described in Section 34.10.7 [Explicit
Encoding], page 988.) This function operates only on text terminals. terminal may be
a terminal object, a frame, or nil for the selected frame’s terminal. In batch mode,
string is sent to stdout when terminal is nil.
One use of this function is to define function keys on terminals that have downloadable
function key definitions. For example, this is how (on certain terminals) to definefunction key 4 to move forward four characters (by transmitting the characters C-u
C-f to the computer):(send-string-to-terminal "\eF4\^U\^F")⇒ nilopen-termscript filename[Command]This function is used to open a termscript file that will record all the characters sentby Emacs to the terminal. It returns nil. Termscript files are useful for investigating

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problems where Emacs garbles the screen, problems that are due to incorrect Termcap
entries or to undesirable settings of terminal options more often than to actual Emacs
bugs. Once you are certain which characters were actually output, you can determine
reliably whether they correspond to the Termcap specifications in use.
(open-termscript "../junk/termscript")⇒ nil
You close the termscript file by calling this function with an argument of nil.
See also open-dribble-file in Section 42.13.2 [Recording Input], page 1286.

42.15 Sound Output
To play sound using Emacs, use the function play-sound. Only certain systems aresupported; if you call play-sound on a system which cannot really do the job, it gives anerror.
The sound must be stored as a file in RIFF-WAVE format (‘.wav’) or Sun Audio format(‘.au’).

play-sound sound[Function]
This function plays a specified sound. The argument, sound, has the form (soundproperties...), where the properties consist of alternating keywords (particularsymbols recognized specially) and values corresponding to them.
Here is a table of the keywords that are currently meaningful in sound, and their
meanings::file file
This specifies the file containing the sound to play. If the file name is not
absolute, it is expanded against the directory data-directory.
:data data
This specifies the sound to play without need to refer to a file. The value,
data, should be a string containing the same bytes as a sound file. We
recommend using a unibyte string.
:volume volume
This specifies how loud to play the sound. It should be a number in therange of 0 to 1. The default is to use whatever volume has been specified
before.
:device device
This specifies the system device on which to play the sound, as a string.
The default device is system-dependent.
Before actually playing the sound, play-sound calls the functions in the list
play-sound-functions. Each function is called with one argument, sound.

play-sound-file file &optional volume device[Command]This function is an alternative interface to playing a sound file specifying an optional
volume and device.

Chapter 42: Operating System Interface

1289[Variable]
A list of functions to be called before playing a sound. Each function is called with
one argument, a property list that describes the sound.

play-sound-functions

42.16 Operating on X11 Keysyms
To define system-specific X11 keysyms, set the variable system-key-alist.
[Variable]
This variable’s value should be an alist with one element for each system-specifickeysym. Each element has the form (code . symbol), where code is the numerickeysym code (not including the vendor-specific bit, −228 ), and symbol is the name forthe function key.
For example (168 . mute-acute) defines a system-specific key (used by HP X servers)
whose numeric code is −228 + 168.
It is not crucial to exclude from the alist the keysyms of other X servers; those do noharm, as long as they don’t conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See
Section 30.2 [Multiple Terminals], page 787.

system-key-alist

You can specify which keysyms Emacs should use for the Control, Meta, Alt, Hyper, andSuper modifiers by setting these variables:[Variable][Variable][Variable][Variable][Variable]
The name of the keysym that should stand for the Control modifier (respectively, forAlt, Meta, Hyper, and Super). For example, here is how to swap the Meta and Alt
modifiers within Emacs:(setq x-alt-keysym 'meta)(setq x-meta-keysym 'alt)

x-ctrl-keysym
x-alt-keysym
x-meta-keysym
x-hyper-keysym
x-super-keysym

42.17 Batch Mode
The command-line option ‘-batch’ causes Emacs to run noninteractively. In this mode,
Emacs does not read commands from the terminal, it does not alter the terminal modes,
and it does not expect to be outputting to an erasable screen. The idea is that you specify
Lisp programs to run; when they are finished, Emacs should exit. The way to specify the
programs to run is with ‘-l file’, which loads the library named file, or ‘-f function’,
which calls function with no arguments, or ‘--eval=form’.

noninteractive[Variable]

This variable is non-nil when Emacs is running in batch mode.
If the specified Lisp program signals an unhandled error in batch mode, Emacs exits witha non-zero exit status after invoking the Lisp debugger which shows the Lisp backtrace (seeSection 19.1.10 [Invoking the Debugger], page 340) on the standard error stream:Chapter 42: Operating System Interface

1290$ emacs -Q --batch --eval '(error "foo")'; echo $?
Error: error ("foo")
mapbacktrace(#f(compiled-function (evald func args flags) #<bytecode -0x4f85c5
7c45e2f81>))
debug-early-backtrace()debug-early(error (error "foo"))signal(error ("foo"))error("foo")eval((error "foo") t)
command-line-1(("--eval" "(error \"foo\")"))
command-line()
normal-top-level()foo
255
Any Lisp program output that would normally go to the echo area, either using message,or using prin1, etc., with t as the stream (see Section 20.4 [Output Streams], page 375),
goes instead to Emacs’s standard descriptors when in batch mode: message writes to thestandard error descriptor, while prin1 and other print functions write to the standard
output. Similarly, input that would normally come from the minibuffer is read from thestandard input descriptor. Thus, Emacs behaves much like a noninteractive application
program. (The echo area output that Emacs itself normally generates, such as command
echoing, is suppressed entirely.)
Non-ASCII text written to the standard output or error descriptors is by default encodedusing locale-coding-system (see Section 34.12 [Locales], page 991) if it is non-nil; thiscan be overridden by binding coding-system-for-write to a coding system of you choice(see Section 34.10.7 [Explicit Encoding], page 988).
In batch mode, Emacs will enlarge the value of the gc-cons-percentage variable fromthe default of ‘0.1’ up to ‘1.0’. Batch jobs that are supposed to run for a long time should
adjust the limit back down again, because this means that less garbage collection will be
performed by default (and more memory consumed).

42.18 Session Management
Emacs supports the X Session Management Protocol, which is used to suspend and restart
applications. In the X Window System, a program called the session manager is responsible
for keeping track of the applications that are running. When the X server shuts down, thesession manager asks applications to save their state, and delays the actual shutdown until
they respond. An application can also cancel the shutdown.
When the session manager restarts a suspended session, it directs these applications
to individually reload their saved state. It does this by specifying a special command-line
argument that says what saved session to restore. For Emacs, this argument is ‘--smid
session’.
[Variable]
Emacs supports saving state via a hook called emacs-save-session-functions.
Emacs runs this hook when the session manager tells it that the window system is

emacs-save-session-functions

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shutting down. The functions are called with no arguments, and with the current
buffer set to a temporary buffer. Each function can use insert to add Lisp code tothis buffer. At the end, Emacs saves the buffer in a file, called the session file.
Subsequently, when the session manager restarts Emacs, it loads the session fileautomatically (see Chapter 16 [Loading], page 298). This is performed by a function
named emacs-session-restore, which is called during startup. See Section 42.1.1[Startup Summary], page 1255.
If a function in emacs-save-session-functions returns non-nil, Emacs tells thesession manager to cancel the shutdown.
Here is an example that just inserts some text into *scratch* when Emacs is restarted
by the session manager.
(add-hook 'emacs-save-session-functions 'save-yourself-test)(defun save-yourself-test ()(insert(format "%S" '(with-current-buffer "*scratch*"(insert "I am restored"))))
nil)

42.19 Desktop Notifications
Emacs is able to send notifications on systems that support the freedesktop.org Desktop
Notifications Specification and on MS-Windows. In order to use this functionality on POSIX
hosts, Emacs must have been compiled with D-Bus support, and the notifications librarymust be loaded. See Section “D-Bus” in D-Bus integration in Emacs. The following function
is supported when D-Bus support is available:

notifications-notify &rest params[Function]
This function sends a notification to the desktop via D-Bus, consisting of the parametersspecified by the params arguments. These arguments should consist of alternating
keyword and value pairs. The supported keywords and values are as follows::bus bus

The D-Bus bus. This argument is needed only if a bus other than :session
shall be used.

:title title
The notification title.
:body text
The notification body text. Depending on the implementation of thenotification server, the text could contain HTML markups, like ‘"<b>boldtext</b>"’, hyperlinks, or images. Special HTML characters must be
encoded, as ‘"Contact &lt;postmaster@localhost&gt;!"’.
:app-name name
The name of the application sending the notification. The default is
notifications-application-name.

Chapter 42: Operating System Interface

1292:replaces-id id
The notification id that this notification replaces. id must be the result ofa previous notifications-notify call.
:app-icon icon-file
The file name of the notification icon. If set to nil, no icon is displayed.
The default is notifications-application-icon.
:actions (key title key title ...)
A list of actions to be applied. key and title are both strings. The default
action (usually invoked by clicking the notification) should have a key
named ‘"default"’. The title can be anything, though implementations
are free not to display it.
:timeout timeout
The timeout time in milliseconds since the display of the notification atwhich the notification should automatically close. If −1, the notification’s
expiration time is dependent on the notification server’s settings, andmay vary for the type of notification. If 0, the notification never expires.
Default value is −1.
:urgency urgency
The urgency level. It can be low, normal, or critical.
:action-items
When this keyword is given, the title string of the actions is interpreted
as icon name.
:category category
The type of notification this is, a string. See the Desktop Notifications
Specification(https://specifications.freedesktop.org/
notification-spec/notification-spec-latest.html#categories)
for a list of standard categories.
:desktop-entry filename
This specifies the name of the desktop filename representing the calling
program, like ‘"emacs"’.
:image-data (width height rowstride has-alpha bits channels data)
This is a raw data image format that describes the width, height, rowstride,
whether there is an alpha channel, bits per sample, channels and image
data, respectively.
:image-path path
This is represented either as a URI (‘file://’ is the only URI schema
supported right now) or a name in a freedesktop.org-compliant icon themefrom ‘$XDG_DATA_DIRS/icons’.
:sound-file filename
The path to a sound file to play when the notification pops up.
:sound-name name
A themable named sound from the freedesktop.org sound naming specification from ‘$XDG_DATA_DIRS/sounds’, to play when the notification

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pops up. Similar to the icon name, only for sounds. An example wouldbe ‘"message-new-instant"’.
:suppress-soundCauses the server to suppress playing any sounds, if it has that ability.
:resident
When set the server will not automatically remove the notification whenan action has been invoked. The notification will remain resident in theserver until it is explicitly removed by the user or by the sender. This hint
is likely only useful when the server has the :persistence capability.
:transient
When set the server will treat the notification as transient and by-pass
the server’s persistence capability, if it should exist.
:x position:y position
Specifies the X, Y location on the screen that the notification should point
to. Both arguments must be used together.
:on-action function
Function to call when an action is invoked. The notification id and the
key of the action are passed as arguments to the function.
:on-close function
Function to call when the notification has been closed by timeout or by
the user. The function receive the notification id and the closing reason
as arguments:• expired if the notification has expired• dismissed if the notification was dismissed by the user
• close-notification if the notification was closed by a call to
notifications-close-notification• undefined if the notification server hasn’t provided a reason
Which parameters are accepted by the notification server can be checked via
notifications-get-capabilities.
This function returns a notification id, an integer, which can be used to manipulate thenotification item with notifications-close-notification or the :replaces-id
argument of another notifications-notify call. For example:(defun my-on-action-function (id key)
(message "Message %d, key \"%s\" pressed" id key))⇒ my-on-action-function(defun my-on-close-function (id reason)(message "Message %d, closed due to \"%s\"" id reason))⇒ my-on-close-function

Chapter 42: Operating System Interface

1294(notifications-notify:title "Title":body "This is <b>important</b>.":actions '("Confirm" "I agree" "Refuse" "I disagree"):on-action 'my-on-action-function:on-close 'my-on-close-function)⇒ 22
A message window opens on the desktop. Press ``I agree''.
⇒ Message 22, key "Confirm" pressed
Message 22, closed due to "dismissed"

notifications-close-notification id &optional bus[Function]
This function closes a notification with identifier id. bus can be a string denoting a
D-Bus connection, the default is :session.

notifications-get-capabilities &optional bus[Function]
Returns the capabilities of the notification server, a list of symbols. bus can be a string
denoting a D-Bus connection, the default is :session. The following capabilities canbe expected::actions

The server will provide the specified actions to the user.

:body

Supports body text.

:body-hyperlinks
The server supports hyperlinks in the notifications.
:body-images
The server supports images in the notifications.
:body-markup
Supports markup in the body text.
:icon-multi
The server will render an animation of all the frames in a given image
array.
:icon-static
Supports display of exactly 1 frame of any given image array. This value
is mutually exclusive with :icon-multi.
:persistence
The server supports persistence of notifications.
:soundThe server supports sounds on notifications.

Further vendor-specific caps start with :x-vendor, like :x-gnome-foo-cap.

notifications-get-server-information &optional bus[Function]
Return information on the notification server, a list of strings. bus can be a string
denoting a D-Bus connection, the default is :session. The returned list is (namevendor version spec-version).
name

The product name of the server.

Chapter 42: Operating System Interface

vendor

The vendor name. For example, ‘"KDE"’, ‘"GNOME"’.

versionThe server’s version number.

1295

spec-version
The specification version the server is compliant with.
If spec version is nil, the server supports a specification prior to ‘"1.0"’.
When Emacs runs on MS-Windows as a GUI session, it supports a small subset of the
D-Bus notifications functionality via a native primitive:

w32-notification-notify &rest params[Function]
This function displays an MS-Windows tray notification as specified by params. MSWindows tray notifications are displayed in a balloon from an icon in the notification
area of the taskbar.
Value is the integer unique ID of the notification that can be used to remove thenotification using w32-notification-close, described below. If the function fails,
the return value is nil.
The arguments params are specified as keyword/value pairs. All the parameters are
optional, but if no parameters are specified, the function will do nothing and returnnil.
The following parameters are supported::icon icon
Display icon in the system tray. If icon is a string, it should specify afile name from which to load the icon; the specified file should be a .ico
Windows icon file. If icon is not a string, or if this parameter is not
specified, the standard Emacs icon will be used.
:tip tip

Use tip as the tooltip for the notification. If tip is a string, this is the textof a tooltip that will be shown when the mouse pointer hovers over the tray
icon added by the notification. If tip is not a string, or if this parameter
is not specified, the default tooltip text is ‘Emacs notification’. The
tooltip text can be up to 127 characters long (63 on Windows versions
before W2K). Longer strings will be truncated.

:level level
Notification severity level, one of info, warning, or error. If given, thevalue determines the icon displayed to the left of the notification title, but
only if the :title parameter (see below) is also specified and is a string.
:title title
The title of the notification. If title is a string, it is displayed in a larger
font immediately above the body text. The title text can be up to 63
characters long; longer text will be truncated.
:body body
The body of the notification. If body is a string, it specifies the text ofthe notification message. Use embedded newlines to control how the text
is broken into lines. The body text can be up to 255 characters long, andChapter 42: Operating System Interface

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will be truncated if it’s longer. Unlike with D-Bus, the body text shouldbe plain text, with no markup.
Note that versions of Windows before W2K support only :icon and :tip. The otherparameters can be passed, but they will be ignored on those old systems.
There can be at most one active notification at any given time. An active notificationmust be removed by calling w32-notification-close before a new one can be shown.
To remove the notification and its icon from the taskbar, use the following function:

w32-notification-close id[Function]

This function removes the tray notification given by its unique id.

42.20 Notifications on File Changes
Several operating systems support watching of filesystems for changes to files or their
attributes. If configured properly, Emacs links a respective library like inotify, kqueue,
gfilenotify, or w32notify statically. These libraries enable watching of filesystems on thelocal machine.
It is also possible to watch filesystems on remote machines, see Section “Remote Files”
in The GNU Emacs Manual. This does not depend on one of the libraries linked to Emacs.
Since all these libraries emit different events upon notified file changes, Emacs provides a
special library filenotify which presents a unified interface to applications. Lisp programs
that want to receive file notifications should always use this library in preference to thenative ones. This section documents the filenotify library functions and variables.

file-notify-add-watch file flags callback[Function]
Add a watch for filesystem events pertaining to file. This arranges for filesystem events
pertaining to file to be reported to Emacs.
The returned value is a descriptor for the added watch. Its type depends on theunderlying library, and in general cannot be assumed to be an integer as in the example
below. It should be used for comparison by equal only.
If the file cannot be watched for some reason, this function signals a file-notifyerror error.
Sometimes, mounted filesystems cannot be watched for file changes. This is notdetected by this function, and so a non-nil return value does not guarantee thatchanges on file will be actually notified.
If file is a symlink, it doesn’t follow that link. Just file itself will be watched.
flags is a list of conditions to set what will be watched for. It can include the following
symbols:changewatch for changes in file’s contents

attribute-change
watch for changes in file attributes, like permissions or modification time
If file is a directory, change watches for file creation and deletion in that directory.
Some of the native file notification libraries also report file changes in that case. This
does not work recursively.

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When any event happens, Emacs will call the callback function passing it a single
argument event, which is of the form
(descriptor action file [file1])
descriptor is the same object as the one returned by this function. action is thedescription of the event. It could be any one of the following symbols:
createdfile was createddeletedfile was deletedchangedfile’s contents has changed; with w32notify library, reports attributechanges as well

renamedfile has been renamed to file1

attribute-changed
a file attribute was changed
stoppedwatching file has stopped

Note that the w32notify library does not report attribute-changed events. Whensome file’s attribute, like permissions or modification time, has changed, this library
reports a changed event. Likewise, the kqueue library does not reliably report fileattribute changes when watching a directory.
The stopped event means that watching the file has been discontinued. This could
be because file-notify-rm-watch was called (see below), or because the file being
watched was deleted, or due to another error reported from the underlying librarywhich makes further watching impossible.
file and file1 are the name of the file(s) whose event is being reported. For example:(require 'filenotify)⇒ filenotify(defun my-notify-callback (event)(message "Event %S" event))⇒ my-notify-callback(file-notify-add-watch"/tmp" '(change attribute-change) 'my-notify-callback)⇒ 35025468(write-region "foo" nil "/tmp/foo")⇒ Event (35025468 created "/tmp/.#foo")
Event (35025468 created "/tmp/foo")
Event (35025468 changed "/tmp/foo")
Event (35025468 deleted "/tmp/.#foo")(write-region "bla" nil "/tmp/foo")⇒ Event (35025468 created "/tmp/.#foo")
Event (35025468 changed "/tmp/foo")
Event (35025468 deleted "/tmp/.#foo")Chapter 42: Operating System Interface

1298(set-file-modes "/tmp/foo" (default-file-modes) 'nofollow)⇒ Event (35025468 attribute-changed "/tmp/foo")
Whether the action renamed is returned depends on the used watch library. Otherwise,
the actions deleted and created could be returned in a random order.
(rename-file "/tmp/foo" "/tmp/bla")⇒ Event (35025468 renamed "/tmp/foo" "/tmp/bla")(delete-file "/tmp/bla")⇒ Event (35025468 deleted "/tmp/bla")

file-notify-rm-watch descriptor[Function]
Removes an existing file watch specified by its descriptor. descriptor should be an
object returned by file-notify-add-watch.

[Command]Removes all existing file notification watches from Emacs.
Use this command with caution, because it could have unexpected side effects on
packages relying on file watches. It is intended mainly for debugging purposes, orwhen Emacs has been stalled.

file-notify-rm-all-watches

file-notify-valid-p descriptor[Function]
Checks a watch specified by its descriptor for validity. descriptor should be an object
returned by file-notify-add-watch.
A watch can become invalid if the file or directory it watches is deleted, or if thewatcher thread exits abnormally for any other reason. Removing the watch by callingfile-notify-rm-watch also makes it invalid.
(make-directory "/tmp/foo")⇒ Event (35025468 created "/tmp/foo")(setq desc
(file-notify-add-watch"/tmp/foo" '(change) 'my-notify-callback))⇒ 11359632(file-notify-valid-p desc)⇒ t(write-region "bla" nil "/tmp/foo/bla")⇒ Event (11359632 created "/tmp/foo/.#bla")
Event (11359632 created "/tmp/foo/bla")
Event (11359632 changed "/tmp/foo/bla")
Event (11359632 deleted "/tmp/foo/.#bla");; Deleting a file in the directory doesn't invalidate the watch.
(delete-file "/tmp/foo/bla")⇒ Event (11359632 deleted "/tmp/foo/bla")

Chapter 42: Operating System Interface

1299(write-region "bla" nil "/tmp/foo/bla")⇒ Event (11359632 created "/tmp/foo/.#bla")
Event (11359632 created "/tmp/foo/bla")
Event (11359632 changed "/tmp/foo/bla")
Event (11359632 deleted "/tmp/foo/.#bla");; Deleting the directory invalidates the watch.
;; Events arrive for different watch descriptors.
(delete-directory "/tmp/foo" 'recursive)⇒ Event (35025468 deleted "/tmp/foo")
Event (11359632 deleted "/tmp/foo/bla")
Event (11359632 deleted "/tmp/foo")
Event (11359632 stopped "/tmp/foo")(file-notify-valid-p desc)⇒ nil

42.21 Dynamically Loaded Libraries
A dynamically loaded library is a library that is loaded on demand, when its facilities are
first needed. Emacs supports such on-demand loading of support libraries for some of its
features.
[Variable]
This is an alist of dynamic libraries and external library files implementing them.

dynamic-library-alist

Each element is a list of the form (library files...), where the car is a symbol
representing a supported external library, and the rest are strings giving alternate
filenames for that library.
Emacs tries to load the library from the files in the order they appear in the list; ifnone is found, the Emacs session won’t have access to that library, and the features it
provides will be unavailable.
Image support on some platforms uses this facility. Here’s an example of setting thisvariable for supporting images on MS-Windows:(setq dynamic-library-alist'((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll")(png "libpng12d.dll" "libpng12.dll" "libpng.dll""libpng13d.dll" "libpng13.dll")(jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll""jpeg.dll")(tiff "libtiff3.dll" "libtiff.dll")(gif "giflib4.dll" "libungif4.dll" "libungif.dll")(svg "librsvg-2-2.dll")(gdk-pixbuf "libgdk_pixbuf-2.0-0.dll")(glib "libglib-2.0-0.dll")(gobject "libgobject-2.0-0.dll")))Chapter 42: Operating System Interface

1300

Note that image types pbm and xbm do not need entries in this variable because they
do not depend on external libraries and are always available in Emacs.
Also note that this variable is not meant to be a generic facility for accessing external
libraries; only those already known by Emacs can be loaded through it.
This variable is ignored if the given library is statically linked into Emacs.

42.22 Security Considerations
Like any application, Emacs can be run in a secure environment, where the operating system
enforces rules about access and the like. With some care, Emacs-based applications canalso be part of a security perimeter that checks such rules. Although the default settings
for Emacs work well for a typical software development environment, they may require
adjustment in environments containing untrusted users that may include attackers. Here is
a compendium of security issues that may be helpful if you are developing such applications.
It is by no means complete; it is intended to give you an idea of the security issues involved,
rather than to be a security checklist.
File local variables
A file that Emacs visits can contain variable settings that affect the buffer
visiting that file; See Section 12.12 [File Local Variables], page 213. Similarly, a
directory can specify local variable values common to all files in that directory;see Section 12.13 [Directory Local Variables], page 217. Although Emacs takessome effort to protect against misuse of these variables, a security hole can becreated merely by a package setting safe-local-variable too optimistically,a problem that is all too common. To disable this feature for both files anddirectories, set enable-local-variables to nil.
Access control
Although Emacs normally respects access permissions of the underlying operating
system, in some cases it handles accesses specially. For example, file names
can have handlers that treat the files specially, with their own access checking.
See Section 26.12 [Magic File Names], page 649. Also, a buffer can be readonly even if the corresponding file is writable, and vice versa, which can result
in messages such as ‘File passwd is write-protected; try to save anyway?
(yes or no)’. See Section 28.7 [Read Only Buffers], page 680.
Authentication
Emacs has several functions that deal with passwords, e.g., read-passwd. See
Section 21.9 [Reading a Password], page 417. Although these functions do not
attempt to broadcast passwords to the world, their implementations are not
proof against determined attackers with access to Emacs internals. For example,
even if Elisp code uses clear-string to scrub a password from its memory
after using it, remnants of the password may still reside in the garbage-collected
free list. See Section 4.4 [Modifying Strings], page 59.
Code injection
Emacs can send commands to many other applications, and applications shouldtake care that strings sent as operands of these commands are not misinterpreted
as directives. For example, when using a shell command to rename a file a to

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b, do not simply use the string mv a b, because either file name might startwith ‘-’, or might contain shell metacharacters like ‘;’. Although functions
like shell-quote-argument can help avoid this sort of problem, they are notpanaceas; for example, on a POSIX platform shell-quote-argument quotes
shell metacharacters but not leading ‘-’. On MS-Windows, quoting for ‘%’ assumes none of the environment variables have ‘^’ in their name. See Section 40.2
[Shell Arguments], page 1080. Typically it is safer to use call-process than asubshell. See Section 40.3 [Synchronous Processes], page 1081. And it is safer
yet to use builtin Emacs functions; for example, use (rename-file "a" "b" t)instead of invoking mv. See Section 26.7 [Changing Files], page 629.
Coding systems
Emacs attempts to infer the coding systems of the files and network connections
it accesses. See Section 34.10 [Coding Systems], page 976. If Emacs infers
incorrectly, or if the other parties to the network connection disagree with
Emacs’s inferences, the resulting system could be unreliable. Also, even when
it infers correctly, Emacs often can use bytes that other programs cannot. For
example, although to Emacs the null byte is just a character like any other,many other applications treat it as a string terminator and mishandle strings orfiles containing null bytes.
Environment and configuration variables
POSIX specifies several environment variables that can affect how Emacs behaves.
Any environment variable whose name consists entirely of uppercase ASCII
letters, digits, and the underscore may affect the internal behavior of Emacs.
Emacs uses several such variables, e.g., EMACSLOADPATH. See Section 16.3
[Library Search], page 301. On some platforms some environment variables(e.g., PATH, POSIXLY_CORRECT, SHELL, TMPDIR) need to have properly-configured
values in order to get standard behavior for any utility Emacs might invoke.
Even seemingly-benign variables like TZ may have security implications. See
Section 42.3 [System Environment], page 1265.
Emacs has customization and other variables with similar considerations. For
example, if the variable shell-file-name specifies a shell with nonstandard
behavior, an Emacs-based application may misbehave.
Installation
When Emacs is installed, if the installation directory hierarchy can be modified
by untrusted users, the application cannot be trusted. This applies also to thedirectory hierarchies of the programs that Emacs uses, and of the files that
Emacs reads and writes.
Network access
Emacs often accesses the network, and you may want to configure it to avoid
network accesses that it would normally do. For example, unless you set
tramp-mode to nil, file names using a certain syntax are interpreted as being
network files, and are retrieved across the network. See The Tramp Manual.
Race conditions
Emacs applications have the same sort of race-condition issues that other applications do. For example, even when (file-readable-p "foo.txt") returns t,

Chapter 42: Operating System Interface1302

it could be that foo.txt is unreadable because some other program changed
the file’s permissions between the call to file-readable-p and now. See
Section 26.6.1 [Testing Accessibility], page 619.
Resource limits
When Emacs exhausts memory or other operating system resources, its behavior
can be less reliable, in that computations that ordinarily run to completion may
abort back to the top level. This may cause Emacs to neglect operations that it
normally would have done.

1303

43 Preparing Lisp code for distribution
Emacs provides a standard way to distribute Emacs Lisp code to users. A package is acollection of one or more files, formatted and bundled in such a way that users can easily
download, install, uninstall, and upgrade it.
The following sections describe how to create a package, and how to put it in a packagearchive for others to download. See Section “Packages” in The GNU Emacs Manual, for a
description of user-level features of the packaging system.
These sections are mostly directed towards package archive maintainers—much of thisinformation is not relevant for package authors (i.e., people who write code that will be
distributed via these archives).

43.1 Packaging Basics
A package is either a simple package or a multi-file package. A simple package is stored in a
package archive as a single Emacs Lisp file, while a multi-file package is stored as a tar file(containing multiple Lisp files, and possibly non-Lisp files such as a manual).
In ordinary usage, the difference between simple packages and multi-file packages isrelatively unimportant; the Package Menu interface makes no distinction between them.
However, the procedure for creating them differs, as explained in the following sections.
Each package (whether simple or multi-file) has certain attributes:
Name

A short word (e.g., ‘auctex’). This is usually also the symbol prefix used in the
program (see Section D.1 [Coding Conventions], page 1331).

VersionA version number, in a form that the function version-to-list understands(e.g., ‘11.86’). Each release of a package should be accompanied by an increasein the version number so that it will be recognized as an upgrade by users
querying the package archive.

Brief description
This is shown when the package is listed in the Package Menu. It should occupy
a single line, ideally in 36 characters or less.
Long description
This is shown in the buffer created by C-h P (describe-package), following the
package’s brief description and installation status. It normally spans multiplelines, and should fully describe the package’s capabilities and how to begin using
it once it is installed.
Dependencies
A list of other packages (possibly including minimal acceptable version numbers)
on which this package depends. The list may be empty, meaning this package has
no dependencies. Otherwise, installing this package also automatically installs
its dependencies, recursively; if any dependency cannot be found, the package
cannot be installed.
Installing a package, either via the command package-install-file, or via the Package
Menu, creates a subdirectory of package-user-dir named name-version, where name isthe package’s name and version its version (e.g., ~/.emacs.d/elpa/auctex-11.86/). We

Chapter 43: Preparing Lisp code for distribution

1304

call this the package’s content directory. It is where Emacs puts the package’s contents (thesingle Lisp file for a simple package, or the files extracted from a multi-file package).
Emacs then searches every Lisp file in the content directory for autoload magic comments(see Section 16.5 [Autoload], page 304). These autoload definitions are saved to a file
named name-autoloads.el in the content directory. They are typically used to autoload
the principal user commands defined in the package, but they can also perform other tasks,
such as adding an element to auto-mode-alist (see Section 24.2.2 [Auto Major Mode],
page 531). Note that a package typically does not autoload every function and variable
defined within it—only the handful of commands typically called to begin using the package.
Emacs then byte-compiles every Lisp file in the package.
After installation, the installed package is loaded: Emacs adds the package’s content
directory to load-path, and evaluates the autoload definitions in name-autoloads.el.
Whenever Emacs starts up, it automatically calls the function package-activate-all
to make installed packages available to the current session. This is done after loading
the early init file, but before loading the regular init file (see Section 42.1.1 [Startup
Summary], page 1255). Packages are not automatically made available if the user option
package-enable-at-startup is set to nil in the early init file.
[Function]
This function makes the packages available to the current session. The user option
package-load-list specifies which packages to make available; by default, all installed
packages are made available. See Section “Package Installation” in The GNU Emacs
Manual.

package-activate-all

In most cases, you should not need to call package-activate-all, as this is done
automatically during startup. Simply make sure to put any code that should run
before package-activate-all in the early init file, and any code that should run
after it in the primary init file (see Section “Init File” in The GNU Emacs Manual).

package-initialize &optional no-activate[Command]This function initializes Emacs’ internal record of which packages are installed, andthen calls package-activate-all.
The optional argument no-activate, if non-nil, causes Emacs to update its record of
installed packages without actually making them available.

43.2 Simple Packages
A simple package consists of a single Emacs Lisp source file. The file must conform to
the Emacs Lisp library header conventions (see Section D.8 [Library Headers], page 1343).
The package’s attributes are taken from the various headers, as illustrated by the following
example:;;; superfrobnicator.el --- Frobnicate and bifurcate flanges;; Copyright (C) 2022 Free Software Foundation, Inc.
;; Author: J. R. Hacker <jrh@example.com>;; Version: 1.3-*- lexical-binding:t -*-Chapter 43: Preparing Lisp code for distribution

1305;; Package-Requires: ((flange "1.0"));; Keywords: multimedia, hypermedia;; URL: https://example.com/jrhacker/superfrobnicate...
;;; Commentary:;; This package provides a minor mode to frobnicate and/or;; bifurcate any flanges you desire. To activate it, just type...
;;;###autoload(define-minor-mode superfrobnicator-mode...
The name of the package is the same as the base name of the file, as written on the firstline. Here, it is ‘superfrobnicator’.
The brief description is also taken from the first line. Here, it is ‘Frobnicate andbifurcate flanges’.
The version number comes from the ‘Package-Version’ header, if it exists, or from the‘Version’ header otherwise. One or the other must be present. Here, the version number is
1.3.
If the file has a ‘;;; Commentary:’ section, this section is used as the long description.
(When displaying the description, Emacs omits the ‘;;; Commentary:’ line, as well as theleading comment characters in the commentary itself.)
If the file has a ‘Package-Requires’ header, that is used as the package dependencies.
In the above example, the package depends on the ‘flange’ package, version 1.0 or higher.
See Section D.8 [Library Headers], page 1343, for a description of the ‘Package-Requires’
header. If the header is omitted, the package has no dependencies.
The ‘Keywords’ and ‘URL’ headers are optional, but recommended. The commanddescribe-package uses these to add links to its output. The ‘Keywords’ header should
contain at least one standard keyword from the finder-known-keywords list.
The file ought to also contain one or more autoload magic comments, as explainedin Section 43.1 [Packaging Basics], page 1303. In the above example, a magic comment
autoloads superfrobnicator-mode.
See Section 43.4 [Package Archives], page 1307, for an explanation of how to add asingle-file package to a package archive.

43.3 Multi-file Packages
A multi-file package is less convenient to create than a single-file package, but it offers morefeatures: it can include multiple Emacs Lisp files, an Info manual, and other file types (suchas images).
Prior to installation, a multi-file package is stored in a package archive as a tar file. The
tar file must be named name-version.tar, where name is the package name and version

Chapter 43: Preparing Lisp code for distribution

1306

is the version number. Its contents, once extracted, must all appear in a directory named
name-version, the content directory (see Section 43.1 [Packaging Basics], page 1303). Files
may also extract into subdirectories of the content directory.
One of the files in the content directory must be named name-pkg.el. It must containa single Lisp form, consisting of a call to the function define-package, described below.
This defines the package’s attributes: version, brief description, and requirements.
For example, if we distribute version 1.3 of the superfrobnicator as a multi-file package, thetar file would be superfrobnicator-1.3.tar. Its contents would extract into the directory
superfrobnicator-1.3, and one of these would be the file superfrobnicator-pkg.el.

define-package name version &optional docstring requirements[Function]
This function defines a package. name is the package name, a string. version is theversion, as a string of a form that can be understood by the function version-to-list.
docstring is the brief description.
requirements is a list of required packages and their versions. Each element in this list
should have the form (dep-name dep-version), where dep-name is a symbol whosename is the dependency’s package name, and dep-version is the dependency’s version(a string).

If the content directory contains a file named README, this file is used as the longdescription (overriding any ‘;;; Commentary:’ section).
If the content directory contains a file named dir, this is assumed to be an Info directory
file made with install-info. See Section “Invoking install-info” in Texinfo. The relevant
Info files should also be present in the content directory. In this case, Emacs will automatically
add the content directory to Info-directory-list when the package is activated.
Do not include any .elc files in the package. Those are created when the package isinstalled. Note that there is no way to control the order in which files are byte-compiled.
Do not include any file named name-autoloads.el. This file is reserved for the package’s autoload definitions (see Section 43.1 [Packaging Basics], page 1303). It is createdautomatically when the package is installed, by searching all the Lisp files in the package forautoload magic comments.
If the multi-file package contains auxiliary data files (such as images), the package’s Lisp
code can refer to these files via the variable load-file-name (see Chapter 16 [Loading],
page 298). Here is an example:(defconst superfrobnicator-base (file-name-directory load-file-name))(defun superfrobnicator-fetch-image (file)(expand-file-name file superfrobnicator-base))

If your package contains files that you don’t wish to distribute to users (e.g. regression
tests), you can add them to an .elpaignore file. In this file, each line lists a file or a
wildcard matching files; those files should be ignored when producing your package’s tarballon ELPA (see Section 43.4 [Package Archives], page 1307). (ELPA will pass this file to thetar command via the -X command-line option, when it prepares the package for download.)Chapter 43: Preparing Lisp code for distribution

1307

43.4 Creating and Maintaining Package Archives
Via the Package Menu, users may download packages from package archives. Such archives
are specified by the variable package-archives, whose default value lists the archives hosted
on GNU ELPA (https://elpa.gnu.org) and non-GNU ELPA (https://elpa.nongnu.
org). This section describes how to set up and maintain a package archive.
[User Option]
The value of this variable is an alist of package archives recognized by the Emacs
package manager.
Each alist element corresponds to one archive, and should have the form (id .
location), where id is the name of the archive (a string) and location is its baselocation (a string).
If the base location starts with ‘http:’ or ‘https:’, it is treated as an HTTP(S) URL,
and packages are downloaded from this archive via HTTP(S) (as is the case for thedefault GNU archive).
Otherwise, the base location should be a directory name. In this case, Emacs retrieves
packages from this archive via ordinary file access. Such local archives are mainly
useful for testing.

package-archives

A package archive is simply a directory in which the package files, and associated files, arestored. If you want the archive to be reachable via HTTP, this directory must be accessible
to a web server; See Section 43.5 [Archive Web Server], page 1308.
A convenient way to set up and update a package archive is via the package-x library. This
is included with Emacs, but not loaded by default; type M-x load-library RET package-x
RET to load it, or add (require 'package-x) to your init file. See Section “Lisp Libraries”
in The GNU Emacs Manual.
After you create an archive, remember that it is not accessible in the Package Menu interface
unless it is in package-archives.
Maintaining a public package archive entails a degree of responsibility. When Emacs
users install packages from your archive, those packages can cause Emacs to run arbitrarycode with the permissions of the installing user. (This is true for Emacs code in general, notjust for packages.) So you should ensure that your archive is well-maintained and keep the
hosting system secure.
One way to increase the security of your packages is to sign them using a cryptographic
key. If you have generated a private/public gpg key pair, you can use gpg to sign the package
like this:gpg -ba -o file.sig file
For a single-file package, file is the package Lisp file; for a multi-file package, it is the package
tar file. You can also sign the archive’s contents file in the same way. Make the .sig
files available in the same location as the packages. You should also make your public key
available for people to download; e.g., by uploading it to a key server such as https://pgp.
mit.edu/. When people install packages from your archive, they can use your public key toverify the signatures.
A full explanation of these matters is outside the scope of this manual. For more
information on cryptographic keys and signing, see Section “GnuPG” in The GNU Privacy

Chapter 43: Preparing Lisp code for distribution

1308

Guard Manual. Emacs comes with an interface to GNU Privacy Guard, see Section “EasyPG”
in Emacs EasyPG Assistant Manual.

43.5 Interfacing to an archive web server
A web server providing access to a package archive must support the following queries:
archive-contents
Return a lisp form describing the archive contents. The form is a list of ’packagedesc’ structures (see package.el), except the first element of the list is thearchive version.
<package name>-readme.txt
Return the long description of the package.
<file name>.sig
Return the signature for the file.
<file name>Return the file. This will be the tarball for a multi-file package, or the single
file for a simple package.

1309

Appendix A Emacs 28 Antinews
For those users who live backwards in time, here is information about downgrading to Emacs
version 28.2. We hope you will enjoy the greater simplicity that results from the absence ofmany Emacs 29.1.90 features.
• The implementation of overlays is back to its simple, time-proven storage in a pair oflinear linked lists centered around some buffer position. No more fancy interval trees
and suchlikes. Lisp programs that use overlays once again need to recenter overlays
around the buffer position of interest, and display-related features should again makesure they don’t use too many overlays in a buffer, lest redisplay will be too slow.
• Several functions stopped the annoying conversion of quotes and key sequences by nolonger calling substitute-command-keys. One prominent example is format-prompt
and all its many callers. This makes the strings they produce much more predictable,
returning to you, the Lisp programmer, control on which punctuation characters willappear in the text presented to the users. For similar reasons, the substitute-quotes
function was deleted.
• The venerable buffer-modified-p function again reliably returns either nil or t, notany other confusing values.
• The support for ‘medium’ weight of fonts was dropped. Emacs now considers ‘medium’and ‘regular’ weights to be the same. We believe this will simplify your font setup,since there’s no longer a need to worry about fonts that support ‘regular’ weight, but
not the ‘medium’ one, or vice versa: either one will do!
• To reduce the amount of code in Emacs related to unimportant features, we’ve removed
the function compiled-function-p. Lisp programs are expected to test explicitly forthe relevant types of function objects: built-in, byte-compiled, and natively-compiled.
For the same reasons we deleted the functions pos-bol, pos-eol, file-attributefile-identifier, and quite a few others. We don’t expect anyone to miss those fancy
functions.
• The timeout used by x-show-tip can no longer be specified by Lisp programs; it ishard-coded in the function. This will lead to a simpler, easier maintained code, and noone should want to control the timeout after which the tip pops down.
• The macro setopt was deleted; use customize-variable instead, or invoke the :setfunction from Lisp.
• We removed the lisp-directory variable, as the value can be easily deduced fromother similar variables, like installation-directory and source-directory, each
one when it’s relevant.
• To simplify code and reduce complexity, we deleted the functions get-displayproperty and add-display-text-property; use the generic get-text-property andput-text-property instead.
• Support for pinch input events and for modern drag-and-drop functionality on X was
dropped. As you move back in time, these facilities will become less and less important,
and will soon enough disappear, so there’s no reason to keep them in Emacs.
• To keep Emacs clean and elegant, we’ve removed the textsec.el library, with its
facilities for checking whether some text is “suspicious”. We consider our users smart

Appendix A: Emacs 28 Antinews

1310

enough to detect maliciously modified text by just looking at it or by moving the cursor
across it, and the whole idea that someone would wish to deliberately deceive Emacs
users ridiculous and unworthy of complicating our elegant text-processing and display
capabilities.
• The
functionskeymap-set,
keymap-global-set,
keymap-local-set,
keymap-substitute, keymap-lookup, and some others were deleted.
We
have found the traditional define-key, global-set-key, local-set-key,
substitute-key-definition, and key-binding more than enough, and their minor
inconsistencies in the syntax of keys they accept a source of endless fun in Emacs Lisp
programming. Why make Emacs programming a dull place? For the same reasons wedeleted key-valid-p, since we consider the permissive nature of kbd more in the spiritof Emacs Lisp.
• Yanking of anything but plain text from other applications becomes more and more
an unnecessary feature as you move back in time, so we dropped support for pasting
media like HTML and images via the clipboard. If you really need to yank those into
an Emacs buffer, you can go via a disk file.
• We removed unnecessary functions string-pixel-width and string-glyph-split, as
we consider it inappropriate for Lisp programs to do display layout calculations, wherethese functions come in handy. Display is for the display engine, written in C, andshould stay there!
• Various new Xwidget functions, such as xwidget-perform-lispy-event,xwidget-webkit-load-html, and xwidget-webkit-back-forward-list, weredeleted as part of our continuing effort to gradually delete the entire Xwidgetfunctionality in some previous release of Emacs.
• Setting the :stderr property of a process in a make-process call once again forces theprocess’s connection to use pipes, not ptys, for all the standard streams — a considerable
simplification of this complex interface.
• To keep the amount of Lisp functions from growing out of control, we deleted
string-equal-ignore-case. Use compare-strings instead.
Several features that complicated the byte compiler have been removed:− The warnings about quoting mistakes in documentation strings. You are expected
to find such mistakes yourself, by eyeballing the resulting *Help* buffer display.
− The warnings about malformed defcustom types, like double-quoting symbols inchoice lists.
• The macro with-buffer-unmodified-if-unchanged was deleted. Lisp programs thatneed to leave the buffer unmodified in these cases can always compare the text before
and after the modifications.
• The functions string-edit and read-string-from-buffer were removed, as we consider the fun of programming them anew every time an important part of the educationof each Emacs Lisp developer.
• We deleted the function readablep and the related variable print-unreadablefunction, since no one is supposed to want to print unreadable Lisp objects.
• The facility for storing multisession variables was deleted as an unnecessary complication. With it are gone multisession-value, define-multisession-variable, andlist-multisession-values.

Appendix A: Emacs 28 Antinews

1311• The support for the cursor-face text property was dropped. We consider the rest of
the faces adequate for supporting this functionality.
• The function tooltip-show dropped support for optional face arguments text-faceand default-face that allow fancy control of the face of the tip text and top frame
colors. We decided that tooltips should all look the same, to prevent user confusion.
• As part of the ongoing quest for simplicity, many other functions and variables havebeen eliminated. Other functions and variables, that were declared obsolete since Emacs
24, have been added back, in preparation for releasing Emacs 24 in some distant past.

1312

Appendix B GNU Free Documentation License
Version 1.3, 3 November 2008c
Copyright
2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
https://fsf.org/
Everyone is permitted to copy and distribute verbatim copiesof this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional anduseful document free in the sense of freedom: to assure everyone the effective freedom
to copy and redistribute it, with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible for modifications
made by others.
This License is a kind of “copyleft”, which means that derivative works of the document
must themselves be free in the same sense. It complements the GNU General Public
License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because
free software needs free documentation: a free program should come with manuals
providing the same freedoms that the software does. But this License is not limited tosoftware manuals; it can be used for any textual work, regardless of subject matter orwhether it is published as a printed book. We recommend this License principally forworks whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONSThis License applies to any manual or other work, in any medium, that contains a noticeplaced by the copyright holder saying it can be distributed under the terms of thisLicense. Such a notice grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The “Document”, below, refers
to any such manual or work. Any member of the public is a licensee, and is addressed
as “you”. You accept the license if you copy, modify or distribute the work in a way
requiring permission under copyright law.
A “Modified Version” of the Document means any work containing the Document or
a portion of it, either copied verbatim, or with modifications and/or translated intoanother language.
A “Secondary Section” is a named appendix or a front-matter section of the Documentthat deals exclusively with the relationship of the publishers or authors of the Document
to the Document’s overall subject (or to related matters) and contains nothing that
could fall directly within that overall subject. (Thus, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any mathematics.) The
relationship could be a matter of historical connection with the subject or with related
matters, or of legal, commercial, philosophical, ethical or political position regardingthem.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as
being those of Invariant Sections, in the notice that says that the Document is released

Appendix B: GNU Free Documentation License1313

under this License. If a section does not fit the above definition of Secondary then it is
not allowed to be designated as Invariant. The Document may contain zero Invariant
Sections. If the Document does not identify any Invariant Sections then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-CoverTexts or Back-Cover Texts, in the notice that says that the Document is released under
this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented in aformat whose specification is available to the general public, that is suitable for revising
the document straightforwardly with generic text editors or (for images composed ofpixels) generic paint programs or (for drawings) some widely available drawing editor,
and that is suitable for input to text formatters or for automatic translation to avariety of formats suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup, or absence of markup, has been arranged tothwart or discourage subsequent modification by readers is not Transparent. An image
format is not Transparent if used for any substantial amount of text. A copy that is
not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain ASCII without
markup, Texinfo input format, LaTEX input format, SGML or XML using a publicly
available DTD, and standard-conforming simple HTML, PostScript or PDF designed
for human modification. Examples of transparent image formats include PNG, XCF
and JPG. Opaque formats include proprietary formats that can be read and edited only
by proprietary word processors, SGML or XML for which the DTD and/or processing
tools are not generally available, and the machine-generated HTML, PostScript or PDF
produced by some word processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following
pages as are needed to hold, legibly, the material this License requires to appear in thetitle page. For works in formats which do not have any title page as such, “Title Page”
means the text near the most prominent appearance of the work’s title, preceding the
beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document to
the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either
is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in
another language. (Here XYZ stands for a specific section name mentioned below, suchas “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve
the Title” of such a section when you modify the Document means that it remains asection “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that
this License applies to the Document. These Warranty Disclaimers are considered to be
included by reference in this License, but only as regards disclaiming warranties: anyother implication that these Warranty Disclaimers may have is void and has no effecton the meaning of this License.
2. VERBATIM COPYING

Appendix B: GNU Free Documentation License1314

You may copy and distribute the Document in any medium, either commercially or
noncommercially, provided that this License, the copyright notices, and the license
notice saying this License applies to the Document are reproduced in all copies, andthat you add no other conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further copying of the copies
you make or distribute. However, you may accept compensation in exchange for copies.
If you distribute a large enough number of copies you must also follow the conditions in
section 3.
You may also lend copies, under the same conditions stated above, and you may publicly
display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of
the Document, numbering more than 100, and the Document’s license notice requires
Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, allthese Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify you as the publisherof these copies. The front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the title of theDocument and satisfy these conditions, can be treated as verbatim copying in otherrespects.
If the required texts for either cover are too voluminous to fit legibly, you should put
the first ones listed (as many as fit reasonably) on the actual cover, and continue therest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100,
you must either include a machine-readable Transparent copy along with each Opaquecopy, or state in or with each Opaque copy a computer-network location from which
the general network-using public has access to download using public-standard network
protocols a complete Transparent copy of the Document, free of added material. If
you use the latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent copy willremain thus accessible at the stated location until at least one year after the last time
you distribute an Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the Document wellbefore redistributing any large number of copies, to give them a chance to provide youwith an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditionsof sections 2 and 3 above, provided that you release the Modified Version under precisely
this License, with the Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever possesses a copy of it.
In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from that of theDocument, and from those of previous versions (which should, if there were any,Appendix B: GNU Free Documentation License1315

be listed in the History section of the Document). You may use the same title as aprevious version if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible forauthorship of the modifications in the Modified Version, together with at least fiveof the principal authors of the Document (all of its principal authors, if it has fewer
than five), unless they release you from this requirement.
C. State on the Title page the name of the publisher of the Modified Version, as the
publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the othercopyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public
permission to use the Modified Version under the terms of this License, in the formshown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections and required CoverTexts given in the Document’s license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item
stating at least the title, year, new authors, and publisher of the Modified Version as
given on the Title Page. If there is no section Entitled “History” in the Document,
create one stating the title, year, authors, and publisher of the Document as given
on its Title Page, then add an item describing the Modified Version as stated in
the previous sentence.
J. Preserve the network location, if any, given in the Document for public access toa Transparent copy of the Document, and likewise the network locations given in
the Document for previous versions it was based on. These may be placed in the“History” section. You may omit a network location for a work that was publishedat least four years before the Document itself, or if the original publisher of theversion it refers to gives permission.
K. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Titleof the section, and preserve in the section all the substance and tone of each of thecontributor acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their text andin their titles. Section numbers or the equivalent are not considered part of thesection titles.
M. Delete any section Entitled “Endorsements”. Such a section may not be includedin the Modified Version.
N. Do not retitle any existing section to be Entitled “Endorsements” or to conflict intitle with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as
Secondary Sections and contain no material copied from the Document, you may atyour option designate some or all of these sections as invariant. To do this, add theirAppendix B: GNU Free Documentation License

1316

titles to the list of Invariant Sections in the Modified Version’s license notice. These
titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but
endorsements of your Modified Version by various parties—for example, statements ofpeer review or that the text has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up
to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified
Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the Document alreadyincludes a cover text for the same cover, previously added by you or by arrangement
made by the same entity you are acting on behalf of, you may not add another; but
you may replace the old one, on explicit permission from the previous publisher that
added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission
to use their names for publicity for or to assert or imply endorsement of any Modified
Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License,
under the terms defined in section 4 above for modified versions, provided that you
include in the combination all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your combined work in its license
notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identicalInvariant Sections may be replaced with a single copy. If there are multiple Invariant
Sections with the same name but different contents, make the title of each such section
unique by adding at the end of it, in parentheses, the name of the original author or
publisher of that section if known, or else a unique number. Make the same adjustment
to the section titles in the list of Invariant Sections in the license notice of the combinedwork.
In the combination, you must combine any sections Entitled “History” in the various
original documents, forming one section Entitled “History”; likewise combine any
sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You
must delete all sections Entitled “Endorsements.”
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released
under this License, and replace the individual copies of this License in the various
documents with a single copy that is included in the collection, provided that you follow
the rules of this License for verbatim copying of each of the documents in all otherrespects.
You may extract a single document from such a collection, and distribute it individually
under this License, provided you insert a copy of this License into the extracted
document, and follow this License in all other respects regarding verbatim copying ofthat document.

Appendix B: GNU Free Documentation License1317

7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent
documents or works, in or on a volume of a storage or distribution medium, is called an“aggregate” if the copyright resulting from the compilation is not used to limit the legal
rights of the compilation’s users beyond what the individual works permit. When theDocument is included in an aggregate, this License does not apply to the other works
in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document,
then if the Document is less than one half of the entire aggregate, the Document’s CoverTexts may be placed on covers that bracket the Document within the aggregate, or theelectronic equivalent of covers if the Document is in electronic form. Otherwise theymust appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translationsof the Document under the terms of section 4. Replacing Invariant Sections withtranslations requires special permission from their copyright holders, but you may
include translations of some or all Invariant Sections in addition to the original versionsof these Invariant Sections. You may include a translation of this License, and all thelicense notices in the Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the original versions of those
notices and disclaimers. In case of a disagreement between the translation and theoriginal version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically requirechanging the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly
provided under this License. Any attempt otherwise to copy, modify, sublicense, or
distribute it is void, and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyrightholder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is thefirst time you have received notice of violation of this License (for any work) from thatcopyright holder, and you cure the violation prior to 30 days after your receipt of thenotice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights have been
terminated and not permanently reinstated, receipt of a copy of some or all of the samematerial does not give you any rights to use it.

Appendix B: GNU Free Documentation License1318

10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free
Documentation License from time to time. Such new versions will be similar in spirit
to the present version, but may differ in detail to address new problems or concerns.
See https://www.gnu.org/licenses/.
Each version of the License is given a distinguishing version number. If the Document
specifies that a particular numbered version of this License “or any later version” applies
to it, you have the option of following the terms and conditions either of that specified
version or of any later version that has been published (not as a draft) by the Free
Software Foundation. If the Document does not specify a version number of this License,
you may choose any version ever published (not as a draft) by the Free Software
Foundation. If the Document specifies that a proxy can decide which future versionsof this License can be used, that proxy’s public statement of acceptance of a version
permanently authorizes you to choose that version for the Document.
11. RELICENSING“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide
Web server that publishes copyrightable works and also provides prominent facilities foranybody to edit those works. A public wiki that anybody can edit is an example ofsuch a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in thesite means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license publishedby Creative Commons Corporation, a not-for-profit corporation with a principal placeof business in San Francisco, California, as well as future copyleft versions of that license
published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part ofanother Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works
that were first published under this License somewhere other than this MMC, andsubsequently incorporated in whole or in part into the MMC, (1) had no cover texts orinvariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under
CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is
eligible for relicensing.

Appendix B: GNU Free Documentation License

1319

ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the
document and put the following copyright and license notices just after the title page:
Copyright (C) year your name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;with no Invariant Sections, no Front-Cover Texts, and no Back-CoverTexts. A copy of the license is included in the section entitled ``GNUFree Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the“with. . . Texts.” line with this:with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.

If you have Invariant Sections without Cover Texts, or some other combination of thethree, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasingthese examples in parallel under your choice of free software license, such as the GNU
General Public License, to permit their use in free software.

1320

Appendix C GNU General Public License
Version 3, 29 June 2007
Copyright c 2007 Free Software Foundation, Inc. https://fsf.org/
Everyone is permitted to copy and distribute verbatim copies of thislicense document, but changing it is not allowed.

Preamble
The GNU General Public License is a free, copyleft license for software and other kinds ofworks.
The licenses for most software and other practical works are designed to take away yourfreedom to share and change the works. By contrast, the GNU General Public License isintended to guarantee your freedom to share and change all versions of a program—to makesure it remains free software for all its users. We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to any other work
released this way by its authors. You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General
Public Licenses are designed to make sure that you have the freedom to distribute copies offree software (and charge for them if you wish), that you receive source code or can get it if
you want it, that you can change the software or use pieces of it in new free programs, andthat you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking
you to surrender the rights. Therefore, you have certain responsibilities if you distributecopies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, youmust pass on to the recipients the same freedoms that you received. You must make surethat they, too, receive or can get the source code. And you must show them these terms sothey know their rights.
Developers that use the GNU GPL protect your rights with two steps: (1) assert copyrighton the software, and (2) offer you this License giving you legal permission to copy, distribute
and/or modify it.
For the developers’ and authors’ protection, the GPL clearly explains that there is no
warranty for this free software. For both users’ and authors’ sake, the GPL requires thatmodified versions be marked as changed, so that their problems will not be attributed
erroneously to authors of previous versions.
Some devices are designed to deny users access to install or run modified versions of
the software inside them, although the manufacturer can do so. This is fundamentally
incompatible with the aim of protecting users’ freedom to change the software. The
systematic pattern of such abuse occurs in the area of products for individuals to use, which
is precisely where it is most unacceptable. Therefore, we have designed this version of the
GPL to prohibit the practice for those products. If such problems arise substantially inother domains, we stand ready to extend this provision to those domains in future versionsof the GPL, as needed to protect the freedom of users.

Appendix C: GNU General Public License

1321

Finally, every program is threatened constantly by software patents. States should notallow patents to restrict development and use of software on general-purpose computers, but
in those that do, we wish to avoid the special danger that patents applied to a free program
could make it effectively proprietary. To prevent this, the GPL assures that patents cannot
be used to render the program non-free.
The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS
0. Definitions.
“This License” refers to version 3 of the GNU General Public License.
“Copyright” also means copyright-like laws that apply to other kinds of works, such as
semiconductor masks.
“The Program” refers to any copyrightable work licensed under this License. Eachlicensee is addressed as “you”. “Licensees” and “recipients” may be individuals ororganizations.
To “modify” a work means to copy from or adapt all or part of the work in a fashionrequiring copyright permission, other than the making of an exact copy. The resulting
work is called a “modified version” of the earlier work or a work “based on” the earlier
work.
A “covered work” means either the unmodified Program or a work based on the Program.
To “propagate” a work means to do anything with it that, without permission, would
make you directly or secondarily liable for infringement under applicable copyright law,
except executing it on a computer or modifying a private copy. Propagation includes
copying, distribution (with or without modification), making available to the public,
and in some countries other activities as well.
To “convey” a work means any kind of propagation that enables other parties to makeor receive copies. Mere interaction with a user through a computer network, with notransfer of a copy, is not conveying.
An interactive user interface displays “Appropriate Legal Notices” to the extent that it
includes a convenient and prominently visible feature that (1) displays an appropriate
copyright notice, and (2) tells the user that there is no warranty for the work (except tothe extent that warranties are provided), that licensees may convey the work under thisLicense, and how to view a copy of this License. If the interface presents a list of usercommands or options, such as a menu, a prominent item in the list meets this criterion.
1. Source Code.
The “source code” for a work means the preferred form of the work for making modifications to it. “Object code” means any non-source form of a work.
A “Standard Interface” means an interface that either is an official standard definedby a recognized standards body, or, in the case of interfaces specified for a particular
programming language, one that is widely used among developers working in that
language.
The “System Libraries” of an executable work include anything, other than the work as
a whole, that (a) is included in the normal form of packaging a Major Component, but

Appendix C: GNU General Public License

1322

which is not part of that Major Component, and (b) serves only to enable use of thework with that Major Component, or to implement a Standard Interface for which an
implementation is available to the public in source code form. A “Major Component”,
in this context, means a major essential component (kernel, window system, and soon) of the specific operating system (if any) on which the executable work runs, or acompiler used to produce the work, or an object code interpreter used to run it.
The “Corresponding Source” for a work in object code form means all the source codeneeded to generate, install, and (for an executable work) run the object code and to
modify the work, including scripts to control those activities. However, it does notinclude the work’s System Libraries, or general-purpose tools or generally available freeprograms which are used unmodified in performing those activities but which are notpart of the work. For example, Corresponding Source includes interface definition files
associated with source files for the work, and the source code for shared libraries anddynamically linked subprograms that the work is specifically designed to require, suchas by intimate data communication or control flow between those subprograms andother parts of the work.
The Corresponding Source need not include anything that users can regenerate automatically from other parts of the Corresponding Source.
The Corresponding Source for a work in source code form is that same work.
2. Basic Permissions.
All rights granted under this License are granted for the term of copyright on the
Program, and are irrevocable provided the stated conditions are met. This License
explicitly affirms your unlimited permission to run the unmodified Program. The output
from running a covered work is covered by this License only if the output, given its
content, constitutes a covered work. This License acknowledges your rights of fair use
or other equivalent, as provided by copyright law.
You may make, run and propagate covered works that you do not convey, without
conditions so long as your license otherwise remains in force. You may convey covered
works to others for the sole purpose of having them make modifications exclusively
for you, or provide you with facilities for running those works, provided that youcomply with the terms of this License in conveying all material for which you do notcontrol copyright. Those thus making or running the covered works for you must do so
exclusively on your behalf, under your direction and control, on terms that prohibit
them from making any copies of your copyrighted material outside their relationshipwith you.
Conveying under any other circumstances is permitted solely under the conditions
stated below. Sublicensing is not allowed; section 10 makes it unnecessary.
3. Protecting Users’ Legal Rights From Anti-Circumvention Law.
No covered work shall be deemed part of an effective technological measure under
any applicable law fulfilling obligations under article 11 of the WIPO copyright treaty
adopted on 20 December 1996, or similar laws prohibiting or restricting circumventionof such measures.
When you convey a covered work, you waive any legal power to forbid circumvention oftechnological measures to the extent such circumvention is effected by exercising rights
under this License with respect to the covered work, and you disclaim any intention

Appendix C: GNU General Public License1323

to limit operation or modification of the work as a means of enforcing, against thework’s users, your or third parties’ legal rights to forbid circumvention of technologicalmeasures.
4. Conveying Verbatim Copies.
You may convey verbatim copies of the Program’s source code as you receive it, in any
medium, provided that you conspicuously and appropriately publish on each copy anappropriate copyright notice; keep intact all notices stating that this License and any
non-permissive terms added in accord with section 7 apply to the code; keep intact all
notices of the absence of any warranty; and give all recipients a copy of this Licensealong with the Program.
You may charge any price or no price for each copy that you convey, and you may offer
support or warranty protection for a fee.
5. Conveying Modified Source Versions.
You may convey a work based on the Program, or the modifications to produce it fromthe Program, in the form of source code under the terms of section 4, provided thatyou also meet all of these conditions:a. The work must carry prominent notices stating that you modified it, and giving a
relevant date.
b. The work must carry prominent notices stating that it is released under thisLicense and any conditions added under section 7. This requirement modifies therequirement in section 4 to “keep intact all notices”.
c. You must license the entire work, as a whole, under this License to anyone whocomes into possession of a copy. This License will therefore apply, along with any
applicable section 7 additional terms, to the whole of the work, and all its parts,
regardless of how they are packaged. This License gives no permission to license
the work in any other way, but it does not invalidate such permission if you haveseparately received it.
d. If the work has interactive user interfaces, each must display Appropriate Legal
Notices; however, if the Program has interactive interfaces that do not display
Appropriate Legal Notices, your work need not make them do so.
A compilation of a covered work with other separate and independent works, which are
not by their nature extensions of the covered work, and which are not combined with itsuch as to form a larger program, in or on a volume of a storage or distribution medium,is called an “aggregate” if the compilation and its resulting copyright are not used tolimit the access or legal rights of the compilation’s users beyond what the individual
works permit. Inclusion of a covered work in an aggregate does not cause this License
to apply to the other parts of the aggregate.
6. Conveying Non-Source Forms.
You may convey a covered work in object code form under the terms of sections 4 and5, provided that you also convey the machine-readable Corresponding Source under theterms of this License, in one of these ways:
a. Convey the object code in, or embodied in, a physical product (including a physicaldistribution medium), accompanied by the Corresponding Source fixed on a durable
physical medium customarily used for software interchange.

Appendix C: GNU General Public License1324

b. Convey the object code in, or embodied in, a physical product (including a physicaldistribution medium), accompanied by a written offer, valid for at least three
years and valid for as long as you offer spare parts or customer support for that
product model, to give anyone who possesses the object code either (1) a copy of
the Corresponding Source for all the software in the product that is covered by thisLicense, on a durable physical medium customarily used for software interchange,
for a price no more than your reasonable cost of physically performing this conveyingof source, or (2) access to copy the Corresponding Source from a network server at
no charge.
c. Convey individual copies of the object code with a copy of the written offer toprovide the Corresponding Source. This alternative is allowed only occasionallyand noncommercially, and only if you received the object code with such an offer,in accord with subsection 6b.
d. Convey the object code by offering access from a designated place (gratis or for acharge), and offer equivalent access to the Corresponding Source in the same way
through the same place at no further charge. You need not require recipients tocopy the Corresponding Source along with the object code. If the place to copy theobject code is a network server, the Corresponding Source may be on a different
server (operated by you or a third party) that supports equivalent copying facilities,
provided you maintain clear directions next to the object code saying where tofind the Corresponding Source. Regardless of what server hosts the Corresponding
Source, you remain obligated to ensure that it is available for as long as needed tosatisfy these requirements.
e. Convey the object code using peer-to-peer transmission, provided you inform otherpeers where the object code and Corresponding Source of the work are being offeredto the general public at no charge under subsection 6d.
A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object
code work.
A “User Product” is either (1) a “consumer product”, which means any tangible personal
property which is normally used for personal, family, or household purposes, or (2)anything designed or sold for incorporation into a dwelling. In determining whether aproduct is a consumer product, doubtful cases shall be resolved in favor of coverage. For
a particular product received by a particular user, “normally used” refers to a typicalor common use of that class of product, regardless of the status of the particular user
or of the way in which the particular user actually uses, or expects or is expected touse, the product. A product is a consumer product regardless of whether the producthas substantial commercial, industrial or non-consumer uses, unless such uses represent
the only significant mode of use of the product.
“Installation Information” for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of acovered work in that User Product from a modified version of its Corresponding Source.
The information must suffice to ensure that the continued functioning of the modified
object code is in no case prevented or interfered with solely because modification has
been made.

Appendix C: GNU General Public License

1325

If you convey an object code work under this section in, or with, or specifically for use
in, a User Product, and the conveying occurs as part of a transaction in which the rightof possession and use of the User Product is transferred to the recipient in perpetuity or
for a fixed term (regardless of how the transaction is characterized), the Corresponding
Source conveyed under this section must be accompanied by the Installation Information.
But this requirement does not apply if neither you nor any third party retains theability to install modified object code on the User Product (for example, the work has
been installed in ROM).
The requirement to provide Installation Information does not include a requirement
to continue to provide support service, warranty, or updates for a work that has been
modified or installed by the recipient, or for the User Product in which it has been
modified or installed. Access to a network may be denied when the modification itself
materially and adversely affects the operation of the network or violates the rules andprotocols for communication across the network.
Corresponding Source conveyed, and Installation Information provided, in accord withthis section must be in a format that is publicly documented (and with an implementation
available to the public in source code form), and must require no special password or
key for unpacking, reading or copying.
7. Additional Terms.
“Additional permissions” are terms that supplement the terms of this License by making
exceptions from one or more of its conditions. Additional permissions that are applicableto the entire Program shall be treated as though they were included in this License, tothe extent that they are valid under applicable law. If additional permissions apply only
to part of the Program, that part may be used separately under those permissions, but
the entire Program remains governed by this License without regard to the additional
permissions.
When you convey a copy of a covered work, you may at your option remove any
additional permissions from that copy, or from any part of it. (Additional permissions
may be written to require their own removal in certain cases when you modify thework.) You may place additional permissions on material, added by you to a covered
work, for which you have or can give appropriate copyright permission.
Notwithstanding any other provision of this License, for material you add to a covered
work, you may (if authorized by the copyright holders of that material) supplement theterms of this License with terms:
a. Disclaiming warranty or limiting liability differently from the terms of sections 15
and 16 of this License; orb. Requiring preservation of specified reasonable legal notices or author attributionsin that material or in the Appropriate Legal Notices displayed by works containing
it; orc. Prohibiting misrepresentation of the origin of that material, or requiring thatmodified versions of such material be marked in reasonable ways as different fromthe original version; or
d. Limiting the use for publicity purposes of names of licensors or authors of thematerial; orAppendix C: GNU General Public License

1326

e. Declining to grant rights under trademark law for use of some trade names, trademarks, or service marks; or
f. Requiring indemnification of licensors and authors of that material by anyone who
conveys the material (or modified versions of it) with contractual assumptionsof liability to the recipient, for any liability that these contractual assumptions
directly impose on those licensors and authors.
All other non-permissive additional terms are considered “further restrictions” within
the meaning of section 10. If the Program as you received it, or any part of it, contains
a notice stating that it is governed by this License along with a term that is a further
restriction, you may remove that term. If a license document contains a further
restriction but permits relicensing or conveying under this License, you may add to acovered work material governed by the terms of that license document, provided thatthe further restriction does not survive such relicensing or conveying.
If you add terms to a covered work in accord with this section, you must place, in therelevant source files, a statement of the additional terms that apply to those files, or a
notice indicating where to find the applicable terms.
Additional terms, permissive or non-permissive, may be stated in the form of a separately
written license, or stated as exceptions; the above requirements apply either way.
8. Termination.
You may not propagate or modify a covered work except as expressly provided under thisLicense. Any attempt otherwise to propagate or modify it is void, and will automaticallyterminate your rights under this License (including any patent licenses granted under
the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyrightholder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is thefirst time you have received notice of violation of this License (for any work) from thatcopyright holder, and you cure the violation prior to 30 days after your receipt of thenotice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights have been
terminated and not permanently reinstated, you do not qualify to receive new licenses
for the same material under section 10.
9. Acceptance Not Required for Having Copies.
You are not required to accept this License in order to receive or run a copy of theProgram. Ancillary propagation of a covered work occurring solely as a consequence ofusing peer-to-peer transmission to receive a copy likewise does not require acceptance.
However, nothing other than this License grants you permission to propagate or modify
any covered work. These actions infringe copyright if you do not accept this License.
Therefore, by modifying or propagating a covered work, you indicate your acceptanceof this License to do so.

Appendix C: GNU General Public License

1327

10. Automatic Licensing of Downstream Recipients.
Each time you convey a covered work, the recipient automatically receives a licensefrom the original licensors, to run, modify and propagate that work, subject to thisLicense. You are not responsible for enforcing compliance by third parties with thisLicense.
An “entity transaction” is a transaction transferring control of an organization, or
substantially all assets of one, or subdividing an organization, or merging organizations.
If propagation of a covered work results from an entity transaction, each party to thattransaction who receives a copy of the work also receives whatever licenses to the work
the party’s predecessor in interest had or could give under the previous paragraph, plus
a right to possession of the Corresponding Source of the work from the predecessor ininterest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted oraffirmed under this License. For example, you may not impose a license fee, royalty, orother charge for exercise of rights granted under this License, and you may not initiate
litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patentclaim is infringed by making, using, selling, offering for sale, or importing the Programor any portion of it.
11. Patents.
A “contributor” is a copyright holder who authorizes use under this License of theProgram or a work on which the Program is based. The work thus licensed is called thecontributor’s “contributor version”.
A contributor’s “essential patent claims” are all patent claims owned or controlled
by the contributor, whether already acquired or hereafter acquired, that would be
infringed by some manner, permitted by this License, of making, using, or sellingits contributor version, but do not include claims that would be infringed only as aconsequence of further modification of the contributor version. For purposes of thisdefinition, “control” includes the right to grant patent sublicenses in a manner consistent
with the requirements of this License.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent licenseunder the contributor’s essential patent claims, to make, use, sell, offer for sale, importand otherwise run, modify and propagate the contents of its contributor version.
In the following three paragraphs, a “patent license” is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission
to practice a patent or covenant not to sue for patent infringement). To “grant” sucha patent license to a party means to make such an agreement or commitment not toenforce a patent against the party.
If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under
the terms of this License, through a publicly available network server or other readily
accessible means, then you must either (1) cause the Corresponding Source to be soavailable, or (2) arrange to deprive yourself of the benefit of the patent license for thisparticular work, or (3) arrange, in a manner consistent with the requirements of thisLicense, to extend the patent license to downstream recipients. “Knowingly relying”
means you have actual knowledge that, but for the patent license, your conveying theAppendix C: GNU General Public License

1328

covered work in a country, or your recipient’s use of the covered work in a country,
would infringe one or more identifiable patents in that country that you have reason tobelieve are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey,
or propagate by procuring conveyance of, a covered work, and grant a patent license
to some of the parties receiving the covered work authorizing them to use, propagate,
modify or convey a specific copy of the covered work, then the patent license you grantis automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage,
prohibits the exercise of, or is conditioned on the non-exercise of one or more of therights that are specifically granted under this License. You may not convey a covered
work if you are a party to an arrangement with a third party that is in the business of
distributing software, under which you make payment to the third party based on theextent of your activity of conveying the work, and under which the third party grants,
to any of the parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work conveyed by you (orcopies made from those copies), or (b) primarily for and in connection with specificproducts or compilations that contain the covered work, unless you entered into that
arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license orother defenses to infringement that may otherwise be available to you under applicablepatent law.
12. No Surrender of Others’ Freedom.
If conditions are imposed on you (whether by court order, agreement or otherwise) that
contradict the conditions of this License, they do not excuse you from the conditionsof this License. If you cannot convey a covered work so as to satisfy simultaneously
your obligations under this License and any other pertinent obligations, then as aconsequence you may not convey it at all. For example, if you agree to terms thatobligate you to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this License would
be to refrain entirely from conveying the Program.
13. Use with the GNU Affero General Public License.
Notwithstanding any other provision of this License, you have permission to link or
combine any covered work with a work licensed under version 3 of the GNU Affero
General Public License into a single combined work, and to convey the resulting work.
The terms of this License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License, section 13,
concerning interaction through a network will apply to the combination as such.
14. Revised Versions of this License.
The Free Software Foundation may publish revised and/or new versions of the GNU
General Public License from time to time. Such new versions will be similar in spirit to
the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies thata certain numbered version of the GNU General Public License “or any later version”
applies to it, you have the option of following the terms and conditions either of that

Appendix C: GNU General Public License

1329

numbered version or of any later version published by the Free Software Foundation. If
the Program does not specify a version number of the GNU General Public License,
you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU
General Public License can be used, that proxy’s public statement of acceptance of aversion permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no
additional obligations are imposed on any author or copyright holder as a result of yourchoosing to follow a later version.
15. Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN
WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDETHE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIEDWARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCEOF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.
16. Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO
IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY
WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE,
BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSSOF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINEDBY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATEWITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY
HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
17. Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided above cannot be given
local legal effect according to their terms, reviewing courts shall apply local law thatmost closely approximates an absolute waiver of all civil liability in connection with
the Program, unless a warranty or assumption of liability accompanies a copy of theProgram in return for a fee.

END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest possible use to the public,
the best way to achieve this is to make it free software which everyone can redistribute andchange under these terms.

Appendix C: GNU General Public License

1330

To do so, attach the following notices to the program. It is safest to attach them to thestart of each source file to most effectively state the exclusion of warranty; and each fileshould have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (atyour option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public Licensealong with this program. If not, see https://www.gnu.org/licenses/.

Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it
starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
This is free software, and you are welcome to redistribute it
under certain conditions; type ‘show c’ for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of
the General Public License. Of course, your program’s commands might be different; for a
GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, tosign a “copyright disclaimer” for the program, if necessary. For more information on this,and how to apply and follow the GNU GPL, see https://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may consider it more
useful to permit linking proprietary applications with the library. If this is what you want
to do, use the GNU Lesser General Public License instead of this License. But first, please
read https://www.gnu.org/licenses/why-not-lgpl.html.

1331

Appendix D Tips and Conventions
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making
effective use of the features described in the previous chapters, and describes conventions
Emacs Lisp programmers should follow.
You can automatically check some of the conventions described below by running thecommand M-x checkdoc RET when visiting a Lisp file. It cannot check all of the conventions,and not all the warnings it gives necessarily correspond to problems, but it is worth examining
them all. Alternatively, use the command M-x checkdoc-current-buffer RET to check theconventions in the current buffer, or checkdoc-file when you want to check a file in batch
mode, e.g., with a command run by M-x compile RET.

D.1 Emacs Lisp Coding Conventions
Here are conventions that you should follow when writing Emacs Lisp code intended forwidespread use:
• Simply loading a package should not change Emacs’s editing behavior. Include acommand or commands to enable and disable the feature, or to invoke it.
This convention is mandatory for any file that includes custom definitions. If fixing sucha file to follow this convention requires an incompatible change, go ahead and make theincompatible change; don’t postpone it.
• You should choose a short word to distinguish your program from other Lisp programs.
The names of all global symbols in your program, that is the names of variables,
constants, and functions, should begin with that chosen prefix. Separate the prefix fromthe rest of the name with a hyphen, ‘-’. This practice helps avoid name conflicts, since
all global variables in Emacs Lisp share the same name space, and all functions shareanother name space1 . Use two hyphens to separate prefix and name if the symbol is
not meant to be used by other packages.
Occasionally, for a command name intended for users to use, it is more convenient if
some words come before the package’s name prefix. For example, it is our convention
to have commands that list objects named as ‘list-something’, e.g., a package called‘frob’ could have a command ‘list-frobs’, when its other global symbols begin with‘frob-’. Also, constructs that define functions, variables, etc., work better if they startwith ‘define-’, so put the name prefix later on in the name.
This recommendation applies even to names for traditional Lisp primitives that are notprimitives in Emacs Lisp—such as copy-list. Believe it or not, there is more than one
plausible way to define copy-list. Play it safe; append your name prefix to produce a
name like foo-copy-list or mylib-copy-list instead.
If you write a function that you think ought to be added to Emacs under a certain
name, such as twiddle-files, don’t call it by that name in your program. Call it
mylib-twiddle-files in your program, and send mail to ‘bug-gnu-emacs@gnu.org’suggesting we add it to Emacs. If and when we do, we can change the name easily
enough.
1

The benefits of a Common Lisp-style package system are considered not to outweigh the costs.

Appendix D: Tips and Conventions

1332

If one prefix is insufficient, your package can use two or three alternative common
prefixes, so long as they make sense.
• We recommend enabling lexical-binding in new code, and converting existing Emacs
Lisp code to enable lexical-binding if it doesn’t already. See Section 12.10.4 [Using
Lexical Binding], page 204.
• Put a call to provide at the end of each separate Lisp file. See Section 16.7 [Named
Features], page 309.
• If a file requires certain other Lisp programs to be loaded beforehand, then the comments
at the beginning of the file should say so. Also, use require to make sure they areloaded. See Section 16.7 [Named Features], page 309.
• If a file foo uses a macro defined in another file bar, but does not use any functions orvariables defined in bar, then foo should contain the following expression:(eval-when-compile (require 'bar))
This tells Emacs to load bar just before byte-compiling foo, so that the macro definition
is available during compilation. Using eval-when-compile avoids loading bar when
the compiled version of foo is used. It should be called before the first use of the macroin the file. See Section 14.3 [Compiling Macros], page 270.
• Avoid loading additional libraries at run time unless they are really needed. If your file
simply cannot work without some other library, then just require that library at the
top-level and be done with it. But if your file contains several independent features, andonly one or two require the extra library, then consider putting require statements
inside the relevant functions rather than at the top-level. Or use autoload statements
to load the extra library when needed. This way people who don’t use those aspects ofyour file do not need to load the extra library.
• If you need Common Lisp extensions, use the cl-lib library rather than the old cl
library. The latter library is deprecated and will be removed in a future version of
Emacs.
• When defining a major mode, please follow the major mode conventions. See
Section 24.2.1 [Major Mode Conventions], page 528.
• When defining a minor mode, please follow the minor mode conventions. See
Section 24.3.1 [Minor Mode Conventions], page 544.
• If the purpose of a function is to tell you whether a certain condition is true or false,
give the function a name that ends in ‘p’ (which stands for “predicate”). If the name is
one word, add just ‘p’; if the name is multiple words, add ‘-p’. Examples are framep
and frame-live-p. We recommend to avoid using this -p suffix in boolean variablenames, unless the variable is bound to a predicate function; instead, use a -flag suffix
or names like is-foo.
• If the purpose of a variable is to store a single function, give it a name that ends in‘-function’. If the purpose of a variable is to store a list of functions (i.e., the variable
is a hook), please follow the naming conventions for hooks. See Section 24.1 [Hooks],
page 524.
• Using unload-feature will undo the changes usually done by loading a feature (likeadding functions to hooks). However, if loading feature does something unusual andmore complex, you can define a function named feature-unload-function, and make

Appendix D: Tips and Conventions

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it undo any such special changes. unload-feature will then automatically run thisfunction if it exists. See Section 16.9 [Unloading], page 313.
• It is a bad idea to define aliases for the Emacs primitives. Normally you should use thestandard names instead. The case where an alias may be useful is where it facilitates
backwards compatibility or portability.
• If a package needs to define an alias or a new function for compatibility with some otherversion of Emacs, name it with the package prefix, not with the raw name with which
it occurs in the other version. Here is an example from Gnus, which provides many
examples of such compatibility issues.
(defalias 'gnus-point-at-bol(if (fboundp 'point-at-bol)'point-at-bol'line-beginning-position))• Redefining or advising an Emacs primitive is a bad idea. It may do the right thing for aparticular program, but there is no telling what other programs might break as a result.
• It is likewise a bad idea for one Lisp package to advise a function in another Lisp
package (see Section 13.12 [Advising Functions], page 252).
• Avoid using eval-after-load and with-eval-after-load in libraries and packages(see Section 16.10 [Hooks for Loading], page 313). This feature is meant for personalcustomizations; using it in a Lisp program is unclean, because it modifies the behaviorof another Lisp file in a way that’s not visible in that file. This is an obstacle fordebugging, much like advising a function in the other package.
• If a file does replace any of the standard functions or library programs of Emacs,
prominent comments at the beginning of the file should say which functions are replaced,and how the behavior of the replacements differs from that of the originals.
• Constructs that define a function or variable should be macros, not functions, and theirnames should start with ‘define-’. The macro should receive the name to be definedas the first argument. That will help various tools find the definition automatically.
Avoid constructing the names in the macro itself, since that would confuse these tools.
• In some other systems there is a convention of choosing variable names that begin andend with ‘*’. We don’t use that convention in Emacs Lisp, so please don’t use it in yourprograms. (Emacs uses such names only for special-purpose buffers.) People will findEmacs more coherent if all libraries use the same conventions.
• The default file coding system for Emacs Lisp source files is UTF-8 (see Section 34.1 [Text
Representations], page 963). In the rare event that your program contains characterswhich are not in UTF-8, you should specify an appropriate coding system in the source
file’s ‘-*-’ line or local variables list. See Section “Local Variables in Files” in The
GNU Emacs Manual.
• Indent the file using the default indentation parameters.
• Don’t make a habit of putting close-parentheses on lines by themselves; Lisp programmers
find this disconcerting.
• Please put a copyright notice and copying permission notice on the file if you distributecopies. See Section D.8 [Library Headers], page 1343.

Appendix D: Tips and Conventions

1334• For variables holding (or functions returning) a file or directory name, avoid using pathin its name, preferring file, file-name, or directory instead, since Emacs follows the
GNU convention to use the term path only for search paths, which are lists of directory
names.

D.2 Key Binding Conventions• Many special major modes, like Dired, Info, Compilation, and Occur, are designed tohandle read-only text that contains hyper-links. Such a major mode should redefinemouse-2 and RET to follow the links. It should also set up a follow-link condition, sothat the link obeys mouse-1-click-follows-link. See Section 33.19.8 [Clickable Text],
page 934. See Section 41.20 [Buttons], page 1232, for an easy method of implementing
such clickable links.
• Don’t define C-c letter as a key in Lisp programs. Sequences consisting of C-c and a
letter (either upper or lower case; ASCII or non-ASCII) are reserved for users; they are
the only sequences reserved for users, so do not block them.
Changing all the Emacs major modes to respect this convention was a lot of work;abandoning this convention would make that work go to waste, and inconvenience users.
Please comply with it.
• Function keys F5 through F9 without modifier keys are also reserved for users to define.
• Sequences consisting of C-c followed by a control character or a digit are reserved for
major modes.
• Sequences consisting of C-c followed by {, }, <, >, : or ; are also reserved for major
modes.
• Sequences consisting of C-c followed by any other ASCII punctuation or symbol characterare allocated for minor modes. Using them in a major mode is not absolutely prohibited,
but if you do that, the major mode binding may be shadowed from time to time byminor modes.
• Don’t bind C-h following any prefix character (including C-c). If you don’t bind C-h, it
is automatically available as a help character for listing the subcommands of the prefix
character.
• Don’t bind a key sequence ending in ESC except following another ESC. (That is, it is
OK to bind a sequence ending in ESC ESC.)The reason for this rule is that a non-prefix binding for ESC in any context prevents
recognition of escape sequences as function keys in that context.
• Similarly, don’t bind a key sequence ending in C-g, since that is commonly used tocancel a key sequence.
• Anything that acts like a temporary mode or state that the user can enter and leaveshould define ESC ESC or ESC ESC ESC as a way to escape.
For a state that accepts ordinary Emacs commands, or more generally any kind of statein which ESC followed by a function key or arrow key is potentially meaningful, then you
must not define ESC ESC, since that would preclude recognizing an escape sequence after
ESC. In these states, you should define ESC ESC ESC as the way to escape. Otherwise,
define ESC ESC instead.

Appendix D: Tips and Conventions

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D.3 Emacs Programming Tips
Following these conventions will make your program fit better into Emacs when it runs.
• Don’t use next-line or previous-line in programs; nearly always, forward-line ismore convenient as well as more predictable and robust. See Section 31.2.4 [Text Lines],
page 856.
• Don’t call functions that set the mark, unless setting the mark is one of the intendedfeatures of your program. The mark is a user-level feature, so it is incorrect to change
the mark except to supply a value for the user’s benefit. See Section 32.7 [The Mark],
page 873.
In particular, don’t use any of these functions:• beginning-of-buffer, end-of-buffer• replace-string, replace-regexp• insert-file, insert-buffer
If you just want to move point, or replace a certain string, or insert a file or buffer’s
contents, without any of the other features intended for interactive users, you canreplace these functions with one or two lines of simple Lisp code.
• Use lists rather than vectors, except when there is a particular reason to use a vector.
Lisp has more facilities for manipulating lists than for vectors, and working with lists is
usually more convenient.
Vectors are advantageous for tables that are substantial in size and are accessed in
random order (not searched front to back), provided there is no need to insert or delete
elements (only lists allow that).
• The recommended way to show a message in the echo area is with the message function,
not princ. See Section 41.4 [The Echo Area], page 1131.
• When you encounter an error condition, call the function error (or signal). The
function error does not return. See Section 11.7.3.1 [Signaling Errors], page 180.
Don’t use message, throw, sleep-for, or beep to report errors.
• An error message should start with a capital letter but should not end with a period orother punctuation.
It is occasionally useful to tell the user where an error originated, even if debug-onerror is nil. In such cases, a lower-case Lisp symbol can be prepended to the error
message. For example, the error message “Invalid input” could be extended to say“some-function: Invalid input”.
• A question asked in the minibuffer with yes-or-no-p or y-or-n-p should start with acapital letter and end with ‘?’.
• When you mention a default value in a minibuffer prompt, put it and the word ‘default’inside parentheses. It should look like this:Enter the answer (default 42):
• In interactive, if you use a Lisp expression to produce a list of arguments, don’t try
to provide the correct default values for region or position arguments. Instead, provide
nil for those arguments if they were not specified, and have the function body computethe default value when the argument is nil. For instance, write this:(defun foo (pos)Appendix D: Tips and Conventions

1336(interactive(list (if specified specified-pos)))(unless pos (setq pos default-pos))...)rather than this:(defun foo (pos)(interactive(list (if specified specified-pos
default-pos)))...)
This is so that repetition of the command will recompute these defaults based on thecurrent circumstances.
You do not need to take such precautions when you use interactive specs ‘d’, ‘m’ and ‘r’,
because they make special arrangements to recompute the argument values on repetitionof the command.
• Many commands that take a long time to execute display a message that says something
like ‘Operating...’ when they start, and change it to ‘Operating...done’ when theyfinish. Please keep the style of these messages uniform: no space around the ellipsis,and no period after ‘done’. See Section 41.4.2 [Progress], page 1134, for an easy way togenerate such messages.
• Try to avoid using recursive edits. Instead, do what the Rmail e command does: usea new local keymap that contains a command defined to switch back to the old local
keymap. Or simply switch to another buffer and let the user switch back at will. See
Section 22.13 [Recursive Editing], page 475.

D.4 Tips for Making Compiled Code Fast
Here are ways of improving the execution speed of byte-compiled Lisp programs.
• Profile your program, to find out where the time is being spent. See Section 19.5
[Profiling], page 369.
• Use iteration rather than recursion whenever possible. Function calls are slow in Emacs
Lisp even when a compiled function is calling another compiled function.
• Using the primitive list-searching functions memq, member, assq, or assoc is even fasterthan explicit iteration. It can be worth rearranging a data structure so that one ofthese primitive search functions can be used.
• Certain built-in functions are handled specially in byte-compiled code, avoiding theneed for an ordinary function call. It is a good idea to use these functions rather thanalternatives. To see whether a function is handled specially by the compiler, examine
its byte-compile property. If the property is non-nil, then the function is handled
specially.
For example, the following input will show you that aref is compiled specially (seeSection 6.3 [Array Functions], page 116):(get 'aref 'byte-compile)⇒ byte-compile-two-args

Appendix D: Tips and Conventions

1337

Note that in this case (and many others), you must first load the bytecomp library,which defines the byte-compile property.
• If calling a small function accounts for a substantial part of your program’s runningtime, make the function inline. This eliminates the function call overhead. Since making
a function inline reduces the flexibility of changing the program, don’t do it unless it
gives a noticeable speedup in something slow enough that users care about the speed.
See Section 13.14 [Inline Functions], page 261.

D.5 Tips for Avoiding Compiler Warnings• Try to avoid compiler warnings about undefined free variables, by adding dummy
defvar definitions for these variables, like this:(defvar foo)
Such a definition has no effect except to tell the compiler not to warn about uses of thevariable foo in this file.
• Similarly, to avoid a compiler warning about an undefined function that you know will
be defined, use a declare-function statement (see Section 13.16 [Declaring Functions],
page 265).
• If you use many functions, macros, and variables from a certain file, you can add
a require (see Section 16.7 [Named Features], page 309) for that package to avoid
compilation warnings for them, like this:(require 'foo)
If you need only macros from some file, you can require it only at compile time (seeSection 17.5 [Eval During Compile], page 320). For instance,(eval-when-compile(require 'foo))• If you bind a variable in one function, and use it or set it in another function, thecompiler warns about the latter function unless the variable has a definition. But adding
a definition would be unclean if the variable has a short name, since Lisp packages
should not define short variable names. The right thing to do is to rename this variable
to start with the name prefix used for the other functions and variables in your package.
• The last resort for avoiding a warning, when you want to do something that is usuallya mistake but you know is not a mistake in your usage, is to put it inside with-nowarnings. See Section 17.6 [Compiler Errors], page 321.

D.6 Tips for Documentation Strings
Here are some tips and conventions for the writing of documentation strings. You can checkmany of these conventions by running the command M-x checkdoc-minor-mode.
• Every command, function, or variable intended for users to know about should have a
documentation string.
• An internal variable or subroutine of a Lisp program might as well have a documentation
string. Documentation strings take up very little space in a running Emacs.
• Format the documentation string so that it fits in an Emacs window on an 80-column
screen. It is a good idea for most lines to be no wider than 60 characters. The first line
should not be wider than 67 characters or it will look bad in the output of apropos.

Appendix D: Tips and Conventions

1338

You can fill the text if that looks good. Emacs Lisp mode fills documentation strings
to the width specified by emacs-lisp-docstring-fill-column. However, you cansometimes make a documentation string much more readable by adjusting its line
breaks with care. Use blank lines between sections if the documentation string is long.
• The first line of the documentation string should consist of one or two complete sentencesthat stand on their own as a summary. M-x apropos displays just the first line, and ifthat line’s contents don’t stand on their own, the result looks bad. In particular, start
the first line with a capital letter and end it with a period.
For a function, the first line should briefly answer the question, “What does this function
do?” For a variable, the first line should briefly answer the question, “What does thisvalue mean?” Prefer to answer these questions in a way that will make sense to users
and callers of the function or the variable. In particular, do not tell what the function
does by enumerating the actions of its code; instead, describe the role of these actions
and the function’s contract.
Don’t limit the documentation string to one line; use as many lines as you need to
explain the details of how to use the function or variable. Please use complete sentences
for the rest of the text too.
• When the user tries to use a disabled command, Emacs displays just the first paragraphof its documentation string—everything through the first blank line. If you wish, you
can choose which information to include before the first blank line so as to make thisdisplay useful.
• The first line should mention all the important arguments of the function (in particular,
the mandatory arguments), and should mention them in the order that they are written
in a function call. If the function has many arguments, then it is not feasible tomention them all in the first line; in that case, the first line should mention the first few
arguments, including the most important arguments.
• When a function’s documentation string mentions the value of an argument of thefunction, use the argument name in capital letters as if it were a name for that value.
Thus, the documentation string of the function eval refers to its first argument as‘FORM’, because the actual argument name is form:
Evaluate FORM and return its value.
Also write metasyntactic variables in capital letters, such as when you show thedecomposition of a list or vector into subunits, some of which may vary. ‘KEY’ and‘VALUE’ in the following example illustrate this practice:
The argument TABLE should be an alist whose elements
have the form (KEY . VALUE). Here, KEY is ...
• Never change the case of a Lisp symbol when you mention it in a doc string. If thesymbol’s name is foo, write “foo”, not “Foo” (which is a different symbol).
This might appear to contradict the policy of writing function argument values, butthere is no real contradiction; the argument value is not the same thing as the symbolthat the function uses to hold the value.
If this puts a lower-case letter at the beginning of a sentence and that annoys you,rewrite the sentence so that the symbol is not at the start of it.
• Do not start or end a documentation string with whitespace.

Appendix D: Tips and Conventions

1339• Do not indent subsequent lines of a documentation string so that the text is lined up
in the source code with the text of the first line. This looks nice in the source code,
but looks bizarre when users view the documentation. Remember that the indentation
before the starting double-quote is not part of the string!
• When documentation should display an ASCII apostrophe or grave accent, use ‘\\='’or ‘\\=`’ in the documentation string literal so that the character is displayed as-is.
• In documentation strings, do not quote expressions that are not Lisp symbols, as these
expressions can stand for themselves. For example, write ‘Return the list (NAME TYPERANGE) ...’ instead of ‘Return the list `(NAME TYPE RANGE)' ...’ or ‘Return thelist \\='(NAME TYPE RANGE) ...’.
• When a documentation string refers to a Lisp symbol, write it as it would be printed(which usually means in lower case), with a grave accent ‘`’ before and apostrophe ‘'’after it. There are two exceptions: write t and nil without surrounding punctuation.
For example:
CODE can be `lambda', nil, or t.
Note that when Emacs displays these doc strings, Emacs will usually display ‘`’ (grave
accent) as ‘‘’ (left single quotation mark) and ‘'’ (apostrophe) as ‘’’ (right single
quotation mark), if the display supports displaying these characters. See Section 25.3
[Keys in Documentation], page 598. (Some previous versions of this section recommended
using the non-ASCII single quotation marks directly in doc strings, but this is now
discouraged, since that leads to broken help string displays on terminals that don’t
support displaying those characters.)
Help mode automatically creates a hyperlink when a documentation string uses asingle-quoted symbol name, if the symbol has either a function or a variable definition.
You do not need to do anything special to make use of this feature. However, when asymbol has both a function definition and a variable definition, and you want to referto just one of them, you can specify which one by writing one of the words ‘variable’,‘option’, ‘function’, or ‘command’, immediately before the symbol name. (Case makes
no difference in recognizing these indicator words.) For example, if you write
This function sets the variable `buffer-file-name'.
then the hyperlink will refer only to the variable documentation of buffer-file-name,and not to its function documentation.
If a symbol has a function definition and/or a variable definition, but those are irrelevantto the use of the symbol that you are documenting, you can write the words ‘symbol’or ‘program’ before the symbol name to prevent making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list',
this function returns a list of all the objects
that satisfy the criterion.
does not make a hyperlink to the documentation, irrelevant here, of the function list.
Normally, no hyperlink is made for a variable without variable documentation. You canforce a hyperlink for such variables by preceding them with one of the words ‘variable’or ‘option’.
Hyperlinks for faces are only made if the face name is preceded or followed by the word
‘face’. In that case, only the face documentation will be shown, even if the symbol isalso defined as a variable or as a function.

Appendix D: Tips and Conventions

1340

To make a hyperlink to Info documentation, write the single-quoted name of theInfo node (or anchor), preceded by ‘info node’, ‘Info node’, ‘info anchor’ or ‘Info
anchor’. The Info file name defaults to ‘emacs’. For example,
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.

To make a hyperlink to a man page, write the single-quoted name of the man page,
preceded by ‘Man page’, ‘man page’, or ‘man page for’. For example,
See the man page `chmod(1)' for details.

The Info documentation is always preferable to man pages, so be sure to link to an
Info manual where available. For example, chmod is documented in the GNU Coreutils
manual, so it is better to link to that instead of the man page.
To link to a customization group, write the single-quoted name of the group, precededby ‘customization group’ (the first character in each word is case-insensitive). For
example,See the customization group `whitespace' for details.

Finally, to create a hyperlink to URLs, write the single-quoted URL, preceded by ‘URL’.
For example,
The GNU project website has more information (see URL`https://www.gnu.org/').

• Don’t write key sequences directly in documentation strings. Instead, use the ‘\\[...]’
construct to stand for them. For example, instead of writing ‘C-f’, write the construct‘\\[forward-char]’. When Emacs displays the documentation string, it substitutes
whatever key is currently bound to forward-char. (This is normally ‘C-f’, but it may
be some other character if the user has moved key bindings.) See Section 25.3 [Keys inDocumentation], page 598.
• In documentation strings for a major mode, you will want to refer to the key bindings ofthat mode’s local map, rather than global ones. Therefore, use the construct ‘\\<...>’
once in the documentation string to specify which key map to use. Do this before
the first use of ‘\\[...]’, and not in the middle of a sentence (since if the map is notloaded, the reference to the map will be replaced with a sentence saying the map is not
currently defined). The text inside the ‘\\<...>’ should be the name of the variable
containing the local keymap for the major mode.
Each use of ‘\\[...]’ slows the display of the documentation string by a tiny amount.
If you use a lot of them, these tiny slowdowns will add up, and might become tangible,
especially on slow systems. So our recommendation is not to over-use them; e.g., try to
avoid using more than one reference to the same command in the same doc string.
• For consistency, phrase the verb in the first sentence of a function’s documentation
string as an imperative—for instance, use “Return the cons of A and B.” in preference
to “Returns the cons of A and B.” Usually it looks good to do likewise for the restof the first paragraph. Subsequent paragraphs usually look better if each sentence isindicative and has a proper subject.
• The documentation string for a function that is a yes-or-no predicate should start withwords such as “Return t if”, to indicate explicitly what constitutes truth. The word
“return” avoids starting the sentence with lower-case “t”, which could be somewhat
distracting.

Appendix D: Tips and Conventions

1341• Write documentation strings in the active voice, not the passive, and in the present
tense, not the future. For instance, use “Return a list containing A and B.” instead of“A list containing A and B will be returned.”• Avoid using the word “cause” (or its equivalents) unnecessarily. Instead of, “Cause
Emacs to display text in boldface”, write just “Display text in boldface”.
• Avoid using “iff” (a mathematics term meaning “if and only if”), since many people areunfamiliar with it and mistake it for a typo. In most cases, the meaning is clear withjust “if”. Otherwise, try to find an alternate phrasing that conveys the meaning.
• Try to avoid using abbreviations such as “e.g.” (for “for example”), “i.e.” (for “thatis”), “no.” (for “number”), “cf.” (for “compare”/“see also”) and “w.r.t.” (for “withrespect to”) as much as possible. It is almost always clearer and easier to read the
expanded version.2• When a command is meaningful only in a certain mode or situation, do mention thatin the documentation string. For example, the documentation of dired-find-file is:
In Dired, visit the file or directory named on this line.
• When you define a variable that represents an option users might want to set, use
defcustom. See Section 12.5 [Defining Variables], page 194.
• The documentation string for a variable that is a yes-or-no flag should start with words
such as “Non-nil means”, to make it clear that all non-nil values are equivalent andindicate explicitly what nil and non-nil mean.
• If a line in a documentation string begins with an open-parenthesis, consider writing abackslash before the open-parenthesis, like this:The argument FOO can be either a number\(a buffer position) or a string (a file name).
This avoids a bug in Emacs versions older than 27.1, where the ‘(’ was treated as thestart of a defun (see Section “Defuns” in The GNU Emacs Manual). If you do not
anticipate anyone editing your code with older Emacs versions, there is no need for thiswork-around.

D.7 Tips on Writing Comments
We recommend these conventions for comments:‘;’

Comments that start with a single semicolon, ‘;’, should all be aligned to thesame column on the right of the source code. Such comments usually explain
how the code on that line does its job. For example:(setq base-version-list(assoc (substring fn 0 start-vn)
file-version-assoc-list))

‘;;’

2

; There was a base; version to which; this looks like; a subversion.

Comments that start with two semicolons, ‘;;’, should be aligned to the samelevel of indentation as the code. Such comments usually describe the purpose of
the following lines or the state of the program at that point. For example:

We do use these occasionally, but try not to overdo it.

Appendix D: Tips and Conventions

1342(prog1 (setq auto-fill-function...
...
;; Update mode line.
(force-mode-line-update)))We also normally use two semicolons for comments outside functions.
;; This Lisp code is run in Emacs when it is to operate as;; a server for other processes.

If a function has no documentation string, it should instead have a two-semicoloncomment right before the function, explaining what the function does and how
to call it properly. Explain precisely what each argument means and how
the function interprets its possible values. It is much better to convert suchcomments to documentation strings, though.
‘;;;’Comments that start with three (or more) semicolons, ‘;;;’, should start at theleft margin. We use them for comments that should be considered a heading
by Outline minor mode. By default, comments starting with at least threesemicolons (followed by a single space and a non-whitespace character) areconsidered section headings, comments starting with two or fewer are not.
(Historically, triple-semicolon comments have also been used for commenting
out lines within a function, but this use is discouraged in favor of using justtwo semicolons. This also applies when commenting out entire functions; when
doing that use two semicolons as well.)Three semicolons are used for top-level sections, four for sub-sections, five forsub-sub-sections and so on.
Typically libraries have at least four top-level sections. For example when thebodies of all of these sections are hidden:;;; backquote.el --- implement the ` Lisp construct...
;;; Commentary:...
;;; Code:...
;;; backquote.el ends here

(In a sense the last line is not a section heading as it must never be followed byany text; after all it marks the end of the file.)
For longer libraries it is advisable to split the code into multiple sections. Thiscan be done by splitting the ‘Code:’ section into multiple sub-sections. Even
though that was the only recommended approach for a long time, many people
have chosen to use multiple top-level code sections instead. You may choseeither style.
Using multiple top-level code sections has the advantage that it avoids introducing an additional nesting level but it also means that the section named ‘Code’
does not contain all the code, which is awkward. To avoid that, you should put
no code at all inside that section; that way it can be considered a separator
instead of a section heading.
Finally, we recommend that you don’t end headings with a colon or any otherpunctuation for that matter. For historic reasons the ‘Code:’ and ‘Commentary:’

Appendix D: Tips and Conventions

1343

headings end with a colon, but we recommend that you don’t do the same forother headings anyway.
Generally speaking, the M-; (comment-dwim) command automatically starts a comment of
the appropriate type; or indents an existing comment to the right place, depending on thenumber of semicolons. See Section “Manipulating Comments” in The GNU Emacs Manual.

D.8 Conventional Headers for Emacs Libraries
Emacs has conventions for using special comments in Lisp libraries to divide them into
sections and give information such as who wrote them. Using a standard format for these
items makes it easier for tools (and people) to extract the relevant information. This section
explains these conventions, starting with an example:;;; foo.el --- Support for the Foo programming language-*- lexical-binding: t; -*-;; Copyright (C) 2010-2021 Your Name;; Author: Your Name <yourname@example.com>;; Maintainer: Someone Else <someone@example.com>;; Created: 14 Jul 2010;; Keywords: languages;; URL: https://example.com/foo;; This file is not part of GNU Emacs.
;; This file is free software...
...
;; along with this file. If not, see <https://www.gnu.org/licenses/>.

The very first line should have this format:;;; filename --- description-*- lexical-binding: t; -*-The description should be contained in one line. If the file needs to set more variables in the‘-*-’ specification, add it after lexical-binding. If this would make the first line too long,
use a Local Variables section at the end of the file.
The copyright notice usually lists your name (if you wrote the file). If you have an
employer who claims copyright on your work, you might need to list them instead. Do not
say that the copyright holder is the Free Software Foundation (or that the file is part of
GNU Emacs) unless your file has been accepted into the Emacs distribution. For more
information on the form of copyright and license notices, see the guide on the GNU website(https://www.gnu.org/licenses/gpl-howto.html).
After the copyright notice come several header comment lines, each beginning with ‘;;
header-name:’. Here is a table of the conventional possibilities for header-name:‘Author’This header states the name and email address of at least the principal author of
the library. If there are multiple authors, list them on continuation lines led by;; and a tab or at least two spaces. We recommend including a contact email
address, of the form ‘<...>’. For example:;; Author: Your Name <yourname@example.com>;;
Someone Else <someone@example.com>;;
Another Person <another@example.com>

Appendix D: Tips and Conventions

1344‘Maintainer’This header has the same format as the Author header. It lists the person(s)who currently maintain(s) the file (respond to bug reports, etc.).
If there is no Maintainer header, the person(s) in the Author header is/are presumed to be the maintainer(s). Some files in Emacs use ‘emacs-devel@gnu.org’
for the maintainer, which means the author is no longer responsible for the file,and that it is maintained as part of Emacs.
‘Created’This optional line gives the original creation date of the file, and is for historicalinterest only.

‘Version’If you wish to record version numbers for the individual Lisp program, put themin this line. Lisp files distributed with Emacs generally do not have a ‘Version’
header, since the version number of Emacs itself serves the same purpose. If
you are distributing a collection of multiple files, we recommend not writing theversion in every file, but only the main one.

‘Keywords’
This line lists keywords for the finder-by-keyword help command. Please usethat command to see a list of the meaningful keywords. The command M-x
checkdoc-package-keywords RET will find and display any keywords that are
not in finder-known-keywords. If you set the variable checkdoc-packagekeywords-flag non-nil, checkdoc commands will include the keyword verification in its checks.
This field is how people will find your package when they’re looking for things
by topic. To separate the keywords, you can use spaces, commas, or both.
The name of this field is unfortunate, since people often assume it is the place
to write arbitrary keywords that describe their package, rather than just therelevant Finder keywords.
‘URL’‘Homepage’
These lines state the website of the library.
‘Package-Version’
If ‘Version’ is not suitable for use by the package manager, then a package candefine ‘Package-Version’; it will be used instead. This is handy if ‘Version’ isan RCS id or something else that cannot be parsed by version-to-list. See
Section 43.1 [Packaging Basics], page 1303.
‘Package-Requires’If this exists, it names packages on which the current package depends for proper
operation. See Section 43.1 [Packaging Basics], page 1303. This is used by
the package manager both at download time (to ensure that a complete set ofpackages is downloaded) and at activation time (to ensure that a package is only
activated if all its dependencies have been).
Its format is a list of lists on a single line. The car of each sub-list is the nameof a package, as a symbol. The cadr of each sub-list is the minimum acceptableversion number, as a string that can be parsed by version-to-list. An entry

Appendix D: Tips and Conventions

1345

that lacks a version (i.e., an entry which is just a symbol, or a sub-list of one
element) is equivalent to entry with version "0". For instance:;; Package-Requires: ((gnus "1.0") (bubbles "2.7.2") cl-lib (seq))

Packages that don’t need to support Emacs versions older than Emacs 27 canhave the ‘Package-Requires’ header split across multiple lines, like this:;; Package-Requires: ((emacs "27.1");;(compat "29.1.4.1"))

Note that with this format, you still need to start the list on the same line as‘Package-Requires’.
The package code automatically defines a package named ‘emacs’ with theversion number of the currently running Emacs. This can be used to require aminimal version of Emacs for a package.
Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment
lines. Use the others if they are appropriate. You can also put in header lines with otherheader names—they have no standard meanings, so they can’t do any harm.
We use additional stylized comments to subdivide the contents of the library file. Theseshould be separated from anything else by blank lines. Here is a table of them:‘;;; Commentary:’
This begins introductory comments that explain how the library works. It
should come right after the copying permissions, terminated by a ‘Change Log’,‘History’ or ‘Code’ comment line. This text is used by the Finder package, so it
should make sense in that context.
‘;;; Change Log:’
This begins an optional log of changes to the file over time. Don’t put too muchinformation in this section—it is better to keep the detailed logs in a version
control system (as Emacs does) or in a separate ChangeLog file. ‘History’ is analternative to ‘Change Log’.
‘;;; Code:’This begins the actual code of the program.
‘;;; filename ends here’
This is the footer line; it appears at the very end of the file. Its purpose is toenable people to detect truncated versions of the file from the lack of a footer
line.

1346

Appendix E GNU Emacs Internals
This chapter describes how the runnable Emacs executable is dumped with the preloaded
Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that
may be of interest to C programmers.

E.1 Building Emacs
This section explains the steps involved in building the Emacs executable. You don’t haveto know this material to build and install Emacs, since the makefiles do all these things
automatically. This information is pertinent to Emacs developers.
Building Emacs requires GNU Make version 3.81 or later.
Compilation of the C source files in the src directory produces an executable file calledtemacs, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/Oroutines, but not the editing commands.
The command temacs -l loadup would run temacs and direct it to load loadup.el.
The loadup library loads additional Lisp libraries, which set up the normal Emacs editing
environment. After this step, the Emacs executable is no longer bare.
Because it takes some time to load the standard Lisp files, the temacs executable usually
isn’t run directly by users. Instead, one of the last steps of building Emacs runs the command ‘temacs -batch -l loadup --temacs=dump-method’. The special option --temacs
tells temacs how to record all the standard preloaded Lisp functions and variables, so thatwhen you subsequently run Emacs, it will start much faster. The --temacs option requires
an argument dump-method, which can be one of the following:‘pdump’

Record the preloaded Lisp data in a dump file. This method produces anadditional data file which Emacs will load at startup. The produced dump file isusually called emacs.pdmp, and is installed in the Emacs exec-directory (seeSection 25.6 [Help Functions], page 602). This method is the most preferred
one, as it does not require Emacs to employ any special techniques of memory
allocation, which might get in the way of various memory-layout techniques
used by modern systems to enhance security and privacy.

‘pbootstrap’
Like ‘pdump’, but used while bootstrapping Emacs, when no previous Emacs
binary and no *.elc byte-compiled Lisp files are available. The produced dump
file is usually named bootstrap-emacs.pdmp in this case.
‘dump’

This method causes temacs to dump out an executable program, called emacs,
which has all the standard Lisp files already preloaded into it. (The ‘-batch’argument prevents temacs from trying to initialize any of its data on the terminal,
so that the tables of terminal information are empty in the dumped Emacs.)
This method is also known as unexec, because it produces a program file from arunning process, and thus is in some sense the opposite of executing a program
to start a process. Although this method was the way that Emacs traditionally
saved its state, it is now deprecated.

‘bootstrap’
Like ‘dump’, but used when bootstrapping Emacs with the unexec method.

Appendix E: GNU Emacs Internals

1347

The dumped emacs executable (also called a pure Emacs) is the one which is installed.
If the portable dumper was used to build Emacs, the emacs executable is actually an exact
copy of temacs, and the corresponding emacs.pdmp file is installed as well. The variable
preloaded-file-list stores a list of the preloaded Lisp files recorded in the dump file orin the dumped Emacs executable. If you port Emacs to a new operating system, and are
not able to implement dumping of any kind, then Emacs must load loadup.el each time it
starts.
By default the dumped emacs executable records details such as the build time and hostname. Use the --disable-build-details option of configure to suppress these details,
so that building and installing Emacs twice from the same sources is more likely to result in
identical copies of Emacs.
You can specify additional files to preload by writing a library named site-load.el
that loads them. You may need to rebuild Emacs with an added definition#define SITELOAD_PURESIZE_EXTRA n
to make n added bytes of pure space to hold the additional files; see src/puresize.h. (Tryadding increments of 20000 until it is big enough.) However, the advantage of preloading
additional files decreases as machines get faster. On modern machines, it is usually notadvisable.
After loadup.el reads site-load.el, it finds the documentation strings for primitiveand preloaded functions (and variables) in the file etc/DOC where they are stored, by calling
Snarf-documentation (see [Accessing Documentation], page 598).
You can specify other Lisp expressions to execute just before dumping by putting themin a library named site-init.el. This file is executed after the documentation strings arefound.
If you want to preload function or variable definitions, there are three ways you can dothis and make their documentation strings accessible when you subsequently run Emacs:• Arrange to scan these files when producing the etc/DOC file, and load them withsite-load.el.
• Load the files with site-init.el, then copy the files into the installation directory for
Lisp files when you install Emacs.
• Specify a nil value for byte-compile-dynamic-docstrings as a local variable in eachof these files, and load them with either site-load.el or site-init.el. (This method
has the drawback that the documentation strings take up space in Emacs all the time.)
It is not advisable to put anything in site-load.el or site-init.el that would alter
any of the features that users expect in an ordinary unmodified Emacs. If you feel you mustoverride normal features for your site, do it with default.el, so that users can override
your changes if they wish. See Section 42.1.1 [Startup Summary], page 1255. Note that ifeither site-load.el or site-init.el changes load-path, the changes will be lost after
dumping. See Section 16.3 [Library Search], page 301. To make a permanent change toload-path, use the --enable-locallisppath option of configure.
In a package that can be preloaded, it is sometimes necessary (or useful) to delay certain
evaluations until Emacs subsequently starts up. The vast majority of such cases relate to thevalues of customizable variables. For example, tutorial-directory is a variable defined instartup.el, which is preloaded. The default value is set based on data-directory. The

Appendix E: GNU Emacs Internals

1348

variable needs to access the value of data-directory when Emacs starts, not when it isdumped, because the Emacs executable has probably been installed in a different location
since it was dumped.

custom-initialize-delay symbol value[Function]
This function delays the initialization of symbol to the next Emacs start. You normallyuse this function by specifying it as the :initialize property of a customizablevariable. (The argument value is unused, and is provided only for compatibility withthe form Custom expects.)

In the unlikely event that you need a more general functionality thancustom-initialize-delay provides, you can use before-init-hook (see Section 42.1.1[Startup Summary], page 1255).

dump-emacs-portable to-file &optional track-referrers[Function]
This function dumps the current state of Emacs into a dump file to-file, using the
pdump method. Normally, the dump file is called emacs-name.dmp, where emacs-nameis the name of the Emacs executable file. The optional argument track-referrers, if
non-nil, causes the portable dumper to keep additional information to help trackdown the provenance of object types that are not yet supported by the pdump method.

Although the portable dumper code can run on many platforms, the dump files thatit produces are not portable—they can be loaded only by the Emacs executable that
dumped them.
If you want to use this function in an Emacs that was already dumped, you must run
Emacs with the ‘-batch’ option.
If you’re including ‘.el’ files in the dumped Emacs and that ‘.el’ file has code that isnormally run at load time, that code won’t be run when Emacs starts after dumping.
To help work around that problem, you can put functions on the after-pdump-loadhook hook. This hook is run when starting Emacs.

dump-emacs to-file from-file[Function]
This function dumps the current state of Emacs into an executable file to-file, using
the unexec method. It takes symbols from from-file (this is normally the executable
file temacs).
This function cannot be used in an Emacs that was already dumped. This function isdeprecated, and by default Emacs is built without unexec support so this function is
not available.
[Function]
If the current Emacs session restored its state from a dump file,
this function returns information about the dump file and thetime it took to restore the Emacs state.
The value is an alist((dumped-with-pdumper . t) (load-time . time) (dump-file-name . file)),where file is the name of the dump file, and time is the time in seconds it took to
restore the state from the dump file. If the current session was not restored from adump file, the value is nil.

pdumper-stats

Appendix E: GNU Emacs Internals

1349

E.2 Pure Storage
Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and purestorage. Normal storage is where all the new data created during an Emacs session are kept
(see Section E.3 [Garbage Collection], page 1350). Pure storage is used for certain datain the preloaded standard Lisp files—data that should never change during actual use ofEmacs.
Pure storage is allocated only while temacs is loading the standard preloaded Lisp
libraries. In the file emacs, it is marked as read-only (on operating systems that permit this),so that the memory space can be shared by all the Emacs jobs running on the machine atonce. Pure storage is not expandable; a fixed amount is allocated when Emacs is compiled,
and if that is not sufficient for the preloaded libraries, temacs allocates dynamic memory forthe part that didn’t fit. If Emacs will be dumped using the pdump method (see Section E.1[Building Emacs], page 1346), the pure-space overflow is of no special importance (it justmeans some of the preloaded stuff cannot be shared with other Emacs jobs). However, if
Emacs will be dumped using the now obsolete unexec method, the resulting image will
work, but garbage collection (see Section E.3 [Garbage Collection], page 1350) is disabledin this situation, causing a memory leak. Such an overflow normally won’t happen unless
you try to preload additional libraries or add features to the standard ones. Emacs will
display a warning about the overflow when it starts, if it was dumped using unexec. If thishappens, you should increase the compilation parameter SYSTEM_PURESIZE_EXTRA in thefile src/puresize.h and rebuild Emacs.

purecopy object[Function]
This function makes a copy in pure storage of object, and returns it. It copies a stringby simply making a new string with the same characters, but without text properties,
in pure storage. It recursively copies the contents of vectors and cons cells. It does
not make copies of other objects such as symbols, but just returns them unchanged.
It signals an error if asked to copy markers.

This function is a no-op except while Emacs is being built and dumped; it is usuallycalled only in preloaded Lisp files.
[Variable]
The value of this variable is the number of bytes of pure storage allocated so far.
Typically, in a dumped Emacs, this number is very close to the total amount of purestorage available—if it were not, we would preallocate less.

pure-bytes-used[Variable]
This variable determines whether defun should make a copy of the function definitionin pure storage. If it is non-nil, then the function definition is copied into purestorage.

purify-flag

This flag is t while loading all of the basic functions for building Emacs initially(allowing those functions to be shareable and non-collectible). Dumping Emacs as an
executable always writes nil in this variable, regardless of the value it actually has
before and after dumping.
You should not change this flag in a running Emacs.

Appendix E: GNU Emacs Internals

1350

E.3 Garbage Collection
When a program creates a list or the user defines a new function (such as by loading alibrary), that data is placed in normal storage. If normal storage runs low, then Emacs
asks the operating system to allocate more memory. Different types of Lisp objects, such as
symbols, cons cells, small vectors, markers, etc., are segregated in distinct blocks in memory.
(Large vectors, long strings, buffers and certain other editing types, which are fairly large,
are allocated in individual blocks, one per object; small strings are packed into blocks of 8k
bytes, and small vectors are packed into blocks of 4k bytes).
Beyond the basic vector, a lot of objects like markers, overlays and buffers are managed asif they were vectors. The corresponding C data structures include the union vectorlike_header field whose size member contains the subtype enumerated by enum pvec_type andan information about how many Lisp_Object fields this structure contains and what thesize of the rest data is. This information is needed to calculate the memory footprint of an
object, and used by the vector allocation code while iterating over the vector blocks.
It is quite common to use some storage for a while, then release it by (for example) killinga buffer or deleting the last pointer to an object. Emacs provides a garbage collector toreclaim this abandoned storage. The garbage collector operates, in essence, by finding andmarking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes
all the symbols, their values and associated function definitions, and any data presently on
the stack, are accessible. Any objects that can be reached indirectly through other accessible
objects are also accessible, but this calculation is done “conservatively”, so it may slightly
overestimate how many objects that are accessible.
When marking is finished, all objects still unmarked are garbage. No matter what the
Lisp program or the user does, it is impossible to refer to them, since there is no longer a way
to reach them. Their space might as well be reused, since no one will miss them. The second(sweep) phase of the garbage collector arranges to reuse them. (But since the marking wasdone “conservatively”, not all unused objects are guaranteed to be garbage-collected by any
one sweep.)
The sweep phase puts unused cons cells onto a free list for future allocation; likewise forsymbols and markers. It compacts the accessible strings so they occupy fewer 8k blocks;
then it frees the other 8k blocks. Unreachable vectors from vector blocks are coalesced tocreate largest possible free areas; if a free area spans a complete 4k block, that block is
freed. Otherwise, the free area is recorded in a free list array, where each entry corresponds
to a free list of areas of the same size. Large vectors, buffers, and other large objects areallocated and freed individually.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call thegarbage collector when the free list is empty. Instead, it simply requests
the operating system to allocate more storage, and processing continues until
gc-cons-threshold bytes have been used.
This means that you can make sure that the garbage collector will not run
during a certain portion of a Lisp program by calling the garbage collector
explicitly just before it (provided that portion of the program does not use somuch space as to force a second garbage collection).

Appendix E: GNU Emacs Internals

1351[Command]This command runs a garbage collection, and returns information on the amount of
space in use. (Garbage collection can also occur spontaneously if you use more thangc-cons-threshold bytes of Lisp data since the previous garbage collection.)
garbage-collect returns a list with information on amount of space in use, where
each entry has the form ‘(name size used)’ or ‘(name size used free)’. In the entry,
name is a symbol describing the kind of objects this entry represents, size is the numberof bytes used by each one, used is the number of those objects that were found live inthe heap, and optional free is the number of those objects that are not live but that
Emacs keeps around for future allocations. So an overall result is:((conses cons-size used-conses free-conses)(symbols symbol-size used-symbols free-symbols)(strings string-size used-strings free-strings)(string-bytes byte-size used-bytes)(vectors vector-size used-vectors)(vector-slots slot-size used-slots free-slots)(floats float-size used-floats free-floats)(intervals interval-size used-intervals free-intervals)(buffers buffer-size used-buffers)(heap unit-size total-size free-size))
Here is an example:(garbage-collect)⇒ ((conses 16 49126 8058) (symbols 48 14607 0)(strings 32 2942 2607)(string-bytes 1 78607) (vectors 16 7247)(vector-slots 8 341609 29474) (floats 8 71 102)
(intervals 56 27 26) (buffers 944 8)(heap 1024 11715 2678))
Below is a table explaining each element. Note that last heap entry is optional andpresent only if an underlying malloc implementation provides mallinfo function.

garbage-collectcons-size

Internal size of a cons cell, i.e., sizeof (struct Lisp_Cons).

used-conses
The number of cons cells in use.
free-conses
The number of cons cells for which space has been obtained from theoperating system, but that are not currently being used.
symbol-sizeInternal size of a symbol, i.e., sizeof (struct Lisp_Symbol).
used-symbols
The number of symbols in use.
free-symbols
The number of symbols for which space has been obtained from theoperating system, but that are not currently being used.

Appendix E: GNU Emacs Internals

1352

string-size Internal size of a string header, i.e., sizeof (struct Lisp_String).
used-strings
The number of string headers in use.
free-strings
The number of string headers for which space has been obtained from theoperating system, but that are not currently being used.
byte-size

This is used for convenience and equals to sizeof (char).

used-bytes The total size of all string data in bytes.
vector-size Size in bytes of a vector of length 1, including its header.
used-vectors
The number of vector headers allocated from the vector blocks.
slot-size

Internal size of a vector slot, always equal to sizeof (Lisp_Object).

used-slots

The number of slots in all used vectors. Slot counts might include someor all overhead from vector headers, depending on the platform.

free-slots

The number of free slots in all vector blocks.

float-sizeInternal size of a float object, i.e., sizeof (struct Lisp_Float). (Donot confuse it with the native platform float or double.)used-floats
The number of floats in use.
free-floats

The number of floats for which space has been obtained from the operating
system, but that are not currently being used.

interval-sizeInternal size of an interval object, i.e., sizeof (struct interval).
used-intervals
The number of intervals in use.
free-intervals
The number of intervals for which space has been obtained from theoperating system, but that are not currently being used.
buffer-size Internal size of a buffer, i.e., sizeof (struct buffer). (Do not confuse
with the value returned by buffer-size function.)used-buffers
The number of buffer objects in use. This includes killed buffers invisible
to users, i.e., all buffers in all_buffers list.
unit-size

The unit of heap space measurement, always equal to 1024 bytes.

total-size

Total heap size, in unit-size units.

free-size

Heap space which is not currently used, in unit-size units.

If there was overflow in pure space (see Section E.2 [Pure Storage], page 1349),
and Emacs was dumped using the (now obsolete) unexec method (see Section E.1[Building Emacs], page 1346), then garbage-collect returns nil, because a real
garbage collection cannot be done in that case.

Appendix E: GNU Emacs Internals

1353[User Option]
If this variable is non-nil, Emacs displays a message at the beginning and end of
garbage collection. The default value is nil.

garbage-collection-messages[Variable]
This is a normal hook that is run at the end of garbage collection. Garbage collection
is inhibited while the hook functions run, so be careful writing them.

post-gc-hook[User Option]
The value of this variable is the number of bytes of storage that must be allocated for
Lisp objects after one garbage collection in order to trigger another garbage collection.
You can use the result returned by garbage-collect to get an information about sizeof the particular object type; space allocated to the contents of buffers does not count.
The initial threshold value is GC_DEFAULT_THRESHOLD, defined in alloc.c. Since it’s
defined in word_size units, the value is 400,000 for the default 32-bit configuration
and 800,000 for the 64-bit one. If you specify a larger value, garbage collection will
happen less often. This reduces the amount of time spent garbage collecting (so Lisp
programs will run faster between cycles of garbage collection that happen more rarely),
but increases total memory use. You may want to do this when running a programthat creates lots of Lisp data, especially if you need it to run faster. However, werecommend against increasing the threshold for prolonged periods of time, and advisethat you never set it higher than needed for the program to run in reasonable time.
Using thresholds higher than necessary could potentially cause higher system-wide
memory pressure, and also make each garbage-collection cycle take much more time,and should therefore be avoided.
You can make collections more frequent by specifying a smaller value, down to 1/10thof GC_DEFAULT_THRESHOLD. A value less than this minimum will remain in effect only
until the subsequent garbage collection, at which time garbage-collect will set thethreshold back to the minimum.

gc-cons-threshold[User Option]
The value of this variable specifies the amount of consing before a garbage collection
occurs, as a fraction of the current heap size. This criterion and gc-cons-threshold
apply in parallel, and garbage collection occurs only when both criteria are satisfied.
As the heap size increases, the time to perform a garbage collection increases. Thus,
it can be desirable to do them less frequently in proportion.
As with gc-cons-threshold, do not enlarge this more than necessary, and never for
prolonged periods of time.

gc-cons-percentage

Control over the garbage collector via gc-cons-threshold and gc-cons-percentage isonly approximate. Although Emacs checks for threshold exhaustion regularly, for efficiency
reasons it does not do so immediately after every change to the heap or to gc-consthreshold or gc-cons-percentage, so exhausting the threshold does not immediately
trigger garbage collection. Also, for efficiency in threshold calculations Emacs approximates
the heap size, which counts the bytes used by currently-accessible objects in the heap.
The value returned by garbage-collect describes the amount of memory used by
Lisp data, broken down by data type. By contrast, the function memory-limit provides
information on the total amount of memory Emacs is currently using.

Appendix E: GNU Emacs Internals

1354[Function]
This function returns an estimate of the total amount of bytes of virtual memory that
Emacs is currently using, divided by 1024. You can use this to get a general idea of
how your actions affect the memory usage.

memory-limit[Variable]
This variable is t if Emacs is nearly out of memory for Lisp objects, and nil otherwise.

memory-full[Function]
This returns a list of numbers that count the number of objects created in this Emacs
session. Each of these counters increments for a certain kind of object. See thedocumentation string for details.

memory-use-counts[Function]
This functions returns an amount of total system memory and how much of it is free.
On an unsupported system, the value may be nil.
If default-directory points to a remote host, memory information of that host isreturned.

memory-info[Variable]
This variable contains the total number of garbage collections done so far in thisEmacs session.

gcs-done[Variable]
This variable contains the total number of seconds of elapsed time during garbage
collection so far in this Emacs session, as a floating-point number.

gc-elapsed[Function]
It can sometimes be useful to see where Emacs is using memory (in various variables, buffers, and caches). This command will open a new buffer (called ‘"*Memory
Report*"’) that will give an overview, in addition to listing the “largest” buffers andvariables.
All the data here is approximate, because there’s really no consistent way to computethe size of a variable. For instance, two variables may share parts of a data structure,and this will be counted twice, but this command may still give a useful high-level
overview of which parts of Emacs are using memory.

memory-report

E.4 Stack-allocated Objects
The garbage collector described above is used to manage data visible from Lisp programs,
as well as most of the data internally used by the Lisp interpreter. Sometimes it may be
useful to allocate temporary internal objects using the C stack of the interpreter. Thiscan help performance, as stack allocation is typically faster than using heap memory toallocate and the garbage collector to free. The downside is that using such objects after they
are freed results in undefined behavior, so uses should be well thought out and carefully
debugged by using the GC_CHECK_MARKED_OBJECTS feature (see src/alloc.c). In particular,
stack-allocated objects should never be made visible to user Lisp code.
Currently, cons cells and strings can be allocated this way. This is implemented by
C macros like AUTO_CONS and AUTO_STRING that define a named Lisp_Object with blockAppendix E: GNU Emacs Internals

1355

lifetime. These objects are not freed by the garbage collector; instead, they have automaticstorage duration, i.e., they are allocated like local variables and are automatically freed at
the end of execution of the C block that defined the object.
For performance reasons, stack-allocated strings are limited to ASCII characters, andmany of these strings are immutable, i.e., calling ASET on them produces undefined behavior.

E.5 Memory Usage
These functions and variables give information about the total amount of memory allocationthat Emacs has done, broken down by data type. Note the difference between these and thevalues returned by garbage-collect; those count objects that currently exist, but thesecount the number or size of all allocations, including those for objects that have since been
freed.
[Variable]
The total number of cons cells that have been allocated so far in this Emacs session.

cons-cells-consed[Variable]
The total number of floats that have been allocated so far in this Emacs session.

floats-consed[Variable]
The total number of vector cells that have been allocated so far in this Emacs session.
This includes vector-like objects such as markers and overlays, plus certain objects
not visible to users.

vector-cells-consed[Variable]
The total number of symbols that have been allocated so far in this Emacs session.

symbols-consed[Variable]
The total number of string characters that have been allocated so far in this session.

string-chars-consed[Variable]
The total number of intervals that have been allocated so far in this Emacs session.

intervals-consed[Variable]
The total number of strings that have been allocated so far in this Emacs session.

strings-consed

E.6 C Dialect
The C part of Emacs is portable to C99 or later: C11-specific features such as ‘<stdalign.h>’and ‘_Noreturn’ are not used without a check, typically at configuration time, and theEmacs build procedure provides a substitute implementation if necessary. Some C11 features,such as anonymous structures and unions, are too difficult to emulate, so they are avoided
entirely.
At some point in the future the base C dialect will no doubt change to C11.

Appendix E: GNU Emacs Internals

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E.7 Writing Emacs Primitives
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function
so that Lisp can call it are handled by a few C macros. The only way to really understandhow to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from eval.c. (An ordinary function
would have the same general appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
doc: /* Eval args until one of them yields non-nil,then return that value.
The remaining args are not evalled at all.
If all args return nil, return nil.
usage: (or CONDITIONS...) */)(Lisp_Object args){
Lisp_Object val = Qnil;
while (CONSP (args)){
val = eval_sub (XCAR (args));if (!NILP (val))
break;
args = XCDR (args);
maybe_quit ();}return val;}

Let’s start with a precise explanation of the arguments to the DEFUN macro. Here is atemplate for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
lnameThis is the name of the Lisp symbol to define as the function name; in theexample above, it is or.

fnameThis is the C function name for this function. This is the name that is used in
C code for calling the function. The name is, by convention, ‘F’ prepended to
the Lisp name, with all dashes (‘-’) in the Lisp name changed to underscores.
Thus, to call this function from C code, call For.

sname

This is a C variable name to use for a structure that holds the data for the subr
object that represents the function in Lisp. This structure conveys the Lisp
symbol name to the initialization routine that will create the symbol and store
the subr object as its definition. By convention, this name is always fname with‘F’ replaced with ‘S’.

min

This is the minimum number of arguments that the function requires. The
function or allows a minimum of zero arguments.

max

This is the maximum number of arguments that the function accepts, if there isa fixed maximum. Alternatively, it can be UNEVALLED, indicating a special form
that receives unevaluated arguments, or MANY, indicating an unlimited numberof evaluated arguments (the equivalent of &rest). Both UNEVALLED and MANY
are macros. If max is a number, it must be more than min but less than 8.

Appendix E: GNU Emacs Internals

1357

interactive
This is an interactive specification, a string such as might be used as the argument of interactive in a Lisp function (see Section 22.2.1 [Using Interactive],
page 424). In the case of or, it is 0 (a null pointer), indicating that or cannot
be called interactively. A value of "" indicates a function that should receive noarguments when called interactively. If the value begins with a ‘"(’, the stringis evaluated as a Lisp form. For example:
DEFUN ("foo", Ffoo, Sfoo, 0, 3,"(list (read-char-by-name \"Insert character: \")\
(prefix-numeric-value current-prefix-arg)\t)",
doc: /* ... */)doc

This is the documentation string. It uses C comment syntax rather than C string
syntax because comment syntax requires nothing special to include multiplelines. The ‘doc:’ identifies the comment that follows as the documentation
string. The ‘/*’ and ‘*/’ delimiters that begin and end the comment are notpart of the documentation string.
If the last line of the documentation string begins with the keyword ‘usage:’,the rest of the line is treated as the argument list for documentation purposes.
This way, you can use different argument names in the documentation stringfrom the ones used in the C code. ‘usage:’ is required if the function has anunlimited number of arguments.
Some primitives have multiple definitions, one per platform (e.g., x-createframe). In such cases, rather than writing the same documentation string ineach definition, only one definition has the actual documentation. The others
have placeholders beginning with ‘SKIP’, which are ignored by the function thatparses the DOC file.
All the usual rules for documentation strings in Lisp code (see Section D.6[Documentation Tips], page 1337) apply to C code documentation strings too.
The documentation string can be followed by a list of C function attributes for
the C function that implements the primitive, like this:
DEFUN ("bar", Fbar, Sbar, 0, UNEVALLED, 0
doc: /* ... */attributes: attr1 attr2 ...)
You can specify more than a single attribute, one after the other. Currently,
only the following attributes are recognized:
noreturn

Declares the C function as one that never returns.
This
corresponds to the C11 keyword _Noreturn and to__attribute__ ((__noreturn__)) attribute of GCC (see Section“Function Attributes” in Using the GNU Compiler Collection).

const

Declares that the function does not examine any values except
its arguments, and has no effects except the return value. This
corresponds to __attribute__ ((__const__)) attribute of GCC.

Appendix E: GNU Emacs Internals

noinline

1358

This corresponds to __attribute__ ((__noinline__)) attributeof GCC, which prevents the function from being considered for
inlining. This might be needed, e.g., to countermand effects oflink-time optimizations on stack-based variables.

After the call to the DEFUN macro, you must write the argument list for the C function,
including the types for the arguments. If the primitive accepts a fixed maximum number ofLisp arguments, there must be one C argument for each Lisp argument, and each argument
must be of type Lisp_Object. (Various macros and functions for creating values of type
Lisp_Object are declared in the file lisp.h.) If the primitive is a special form, it must
accept a Lisp list containing its unevaluated Lisp arguments as a single argument of type
Lisp_Object. If the primitive has no upper limit on the number of evaluated Lisp arguments,
it must have exactly two C arguments: the first is the number of Lisp arguments, and thesecond is the address of a block containing their values. These have types ptrdiff_t and
Lisp_Object *, respectively. Since Lisp_Object can hold any Lisp object of any data type,
you can determine the actual data type only at run time; so if you want a primitive toaccept only a certain type of argument, you must check the type explicitly using a suitablepredicate (see Section 2.7 [Type Predicates], page 30).
Within the function For itself, the local variable args refers to objects controlled byEmacs’s stack-marking garbage collector. Although the garbage collector does not reclaim
objects reachable from C Lisp_Object stack variables, it may move some of the components
of an object, such as the contents of a string or the text of a buffer. Therefore, functions
that access these components must take care to refetch their addresses after performing Lisp
evaluation. This means that instead of keeping C pointers to string contents or buffer text,
the code should keep the buffer or string position, and recompute the C pointer from theposition after performing Lisp evaluation. Lisp evaluation can occur via calls to eval_sub
or Feval, either directly or indirectly.
Note the call to maybe_quit inside the loop: this function checks whether the user pressed
C-g, and if so, aborts the processing. You should do that in any loop that can potentiallyrequire a large number of iterations; in this case, the list of arguments could be very long.
This increases Emacs responsiveness and improves user experience.
You must not use C initializers for static or global variables unless the variables are neverwritten once Emacs is dumped. These variables with initializers are allocated in an areaof memory that becomes read-only (on certain operating systems) as a result of dumping
Emacs. See Section E.2 [Pure Storage], page 1349.
Defining the C function is not enough to make a Lisp primitive available; you must also
create the Lisp symbol for the primitive and store a suitable subr object in its function cell.
The code looks like this:defsubr (&sname);
Here sname is the name you used as the third argument to DEFUN.
If you add a new primitive to a file that already has Lisp primitives defined in it, findthe function (near the end of the file) named syms_of_something, and add the call to
defsubr there. If the file doesn’t have this function, or if you create a new file, add to ita syms_of_filename (e.g., syms_of_myfile). Then find the spot in emacs.c where all ofthese functions are called, and add a call to syms_of_filename there.

Appendix E: GNU Emacs Internals

1359

The function syms_of_filename is also the place to define any C variables that are to
be visible as Lisp variables. DEFVAR_LISP makes a C variable of type Lisp_Object visible
in Lisp. DEFVAR_INT makes a C variable of type int visible in Lisp with a value that isalways an integer. DEFVAR_BOOL makes a C variable of type int visible in Lisp with a valuethat is either t or nil. Note that variables defined with DEFVAR_BOOL are automatically
added to the list byte-boolean-vars used by the byte compiler.
These macros all expect three arguments:
lname

The name of the variable to be used by Lisp programs.

vname

The name of the variable in the C sources.

doc

The documentation for the variable, as a C comment. See Section 25.1 [Documentation Basics], page 595, for more details.

By convention, when defining variables of a “native” type (int and bool), the name of
the C variable is the name of the Lisp variable with - replaced by _. When the variable has
type Lisp_Object, the convention is to also prefix the C variable name with V. i.e.
DEFVAR_INT ("my-int-variable", my_int_variable,
doc: /* An integer variable. */);
DEFVAR_LISP ("my-lisp-variable", Vmy_lisp_variable,
doc: /* A Lisp variable. */);

There are situations in Lisp where you need to refer to the symbol itself rather than thevalue of that symbol. One such case is when temporarily overriding the value of a variable,
which in Lisp is done with let. In C sources, this is done by defining a corresponding,constant symbol, and using specbind. By convention, Qmy_lisp_variable corresponds toVmy_lisp_variable; to define it, use the DEFSYM macro. i.e.
DEFSYM (Qmy_lisp_variable, "my-lisp-variable");To perform the actual binding:
specbind (Qmy_lisp_variable, Qt);

In Lisp symbols sometimes need to be quoted, to achieve the same effect in C you again
use the corresponding constant symbol Qmy_lisp_variable. For example, when creating abuffer-local variable (see Section 12.11 [Buffer-Local Variables], page 207) in Lisp you would
write:(make-variable-buffer-local 'my-lisp-variable)

In C the corresponding code uses Fmake_variable_buffer_local in combination with
DEFSYM, i.e.
DEFSYM (Qmy_lisp_variable, "my-lisp-variable");Fmake_variable_buffer_local (Qmy_lisp_variable);

If you want to make a Lisp variable that is defined in C behave like one declaredwith defcustom, add an appropriate entry to cus-start.el. See Section 15.3 [Variable
Definitions], page 280, for a description of the format to use.
If you directly define a file-scope C variable of type Lisp_Object, you must protect itfrom garbage-collection by calling staticpro in syms_of_filename, like this:staticpro (&variable);

Appendix E: GNU Emacs Internals

1360

Here is another example function, with more complicated arguments. This comes fromthe code in window.c, and it demonstrates the use of macros and functions to manipulate
Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2, 0,
doc: /* Return non-nil if COORDINATES are in WINDOW.
...
or `right-margin' is returned. */)(register Lisp_Object coordinates, Lisp_Object window){
struct window *w;
struct frame *f;
int x, y;
Lisp_Object lx, ly;
w = decode_live_window (window);
f = XFRAME (w->frame);
CHECK_CONS (coordinates);lx = Fcar (coordinates);ly = Fcdr (coordinates);
CHECK_NUMBER (lx);
CHECK_NUMBER (ly);x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH (f);y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH (f);switch (coordinates_in_window (w, x, y)){case ON_NOTHING:/* NOT in window at all.
return Qnil;*/...
case ON_MODE_LINE:
return Qmode_line;/* In mode line of window.

*/...
case ON_SCROLL_BAR:/* On scroll-bar of window. *//* Historically we are supposed to return nil in this case.
return Qnil;*/

default:
emacs_abort ();}}Note that C code cannot call functions by name unless they are defined in C. The way
to call a function written in Lisp is to use Ffuncall, which embodies the Lisp function
funcall. Since the Lisp function funcall accepts an unlimited number of arguments, in C
it takes two: the number of Lisp-level arguments, and a one-dimensional array containing
their values. The first Lisp-level argument is the Lisp function to call, and the rest are thearguments to pass to it.
The C functions call0, call1, call2, and so on, provide handy ways to call a Lisp
function conveniently with a fixed number of arguments. They work by calling Ffuncall.

Appendix E: GNU Emacs Internals

1361

eval.c is a very good file to look through for examples; lisp.h contains the definitions
for some important macros and functions.
If you define a function which is side-effect free or pure, give it a non-nil side-effectfree or pure property, respectively (see Section 9.4.2 [Standard Properties], page 139).

E.8 Writing Dynamically-Loaded Modules
This section describes the Emacs module API and how to use it as part of writing extension
modules for Emacs. The module API is defined in the C programming language, therefore
the description and the examples in this section assume the module is written in C. For
other programming languages, you will need to use the appropriate bindings, interfaces andfacilities for calling C code. Emacs C code requires a C99 or later compiler (see Section E.6[C Dialect], page 1355), and so the code examples in this section also follow that standard.
Writing a module and integrating it into Emacs comprises the following tasks:• Writing initialization code for the module.
• Writing one or more module functions.
• Communicating values and objects between Emacs and your module functions.
• Handling of error conditions and nonlocal exits.
The following subsections describe these tasks and the API itself in more detail.
Once your module is written, compile it to produce a shared library, according to
the conventions of the underlying platform. Then place the shared library in a directory
mentioned in load-path (see Section 16.3 [Library Search], page 301), where Emacs willfind it.
If you wish to verify the conformance of a module to the Emacs dynamic module API,
invoke Emacs with the --module-assertions option. See Section “Initial Options” in The
GNU Emacs Manual.

E.8.1 Module Initialization CodeBegin your module by including the header file emacs-module.h and defining the GPL
compatibility symbol:#include <emacs-module.h>int plugin_is_GPL_compatible;
The emacs-module.h file is installed into your system’s include tree as part of the Emacs
installation. Alternatively, you can find it in the Emacs source tree.
Next, write an initialization function for the module.

int emacs_module_init (struct emacs_runtime *runtime)[Function]
Emacs calls this function when it loads a module. If a module does not export afunction named emacs_module_init, trying to load the module will signal an error.
The initialization function should return zero if the initialization succeeds, non-zerootherwise. In the latter case, Emacs will signal an error, and the loading of the module
will fail. If the user presses C-g during the initialization, Emacs ignores the return
value of the initialization function and quits (see Section 22.11 [Quitting], page 471). (IfAppendix E: GNU Emacs Internals

1362

needed, you can catch user quitting inside the initialization function, see [should quit],
page 1374.)
The argument runtime is a pointer to a C struct that includes 2 public fields: size,
which provides the size of the structure in bytes; and get_environment, which provides
a pointer to a function that allows the module initialization function access to theEmacs environment object and its interfaces.
The initialization function should perform whatever initialization is required for themodule. In addition, it can perform the following tasks:
Compatibility verification
A module can verify that the Emacs executable which loads the module
is compatible with the module, by comparing the size member of theruntime structure with the value compiled into the module:int
emacs_module_init (struct emacs_runtime *runtime){
if (runtime->size < sizeof (*runtime))
return 1;}
If the size of the runtime object passed to the module is smaller than what
it expects, it means the module was compiled for an Emacs version newer(later) than the one which attempts to load it, i.e. the module might beincompatible with the Emacs binary.
In addition, a module can verify the compatibility of the module API withwhat the module expects. The following sample code assumes it is part ofthe emacs_module_init function shown above:
emacs_env *env = runtime->get_environment (runtime);
if (env->size < sizeof (*env))
return 2;
This calls the get_environment function using the pointer provided in
the runtime structure to retrieve a pointer to the API’s environment, aC struct which also has a size field holding the size of the structure inbytes.
Finally, you can write a module that will work with older versions ofEmacs, by comparing the size of the environment passed by Emacs withknown sizes, like this:emacs_env *env = runtime->get_environment (runtime);
if (env->size >= sizeof (struct emacs_env_26))
emacs_version = 26; /* Emacs 26 or later. */else if (env->size >= sizeof (struct emacs_env_25))
emacs_version = 25;
else
return 2; /* Unknown or unsupported version. */This works because later Emacs versions always add members to theenvironment, never remove any members, so the size can only grow with

Appendix E: GNU Emacs Internals

1363

new Emacs releases. Given the version of Emacs, the module can use only
the parts of the module API that existed in that version, since those parts
are identical in later versions.
emacs-module.h defines a preprocessor macro EMACS_MAJOR_VERSION. It
expands to an integer literal which is the latest major version of Emacs
supported by the header. See Section 1.4 [Version Info], page 6. Notethat the value of EMACS_MAJOR_VERSION is a compile-time constant anddoes not represent the version of Emacs that is currently running andhas loaded your module. If you want your module to be compatible withvarious versions of emacs-module.h as well as various versions of Emacs,
you can use conditional compilation based on EMACS_MAJOR_VERSION.
We recommend that modules always perform the compatibility verification,
unless they do their job entirely in the initialization function, and don’t
access any Lisp objects or use any Emacs functions accessible through theenvironment structure.
Binding module functions to Lisp symbols
This gives the module functions names so that Lisp code could call itby that name. We describe how to do this in Section E.8.2 [Module
Functions], page 1363, below.

E.8.2 Writing Module Functions
The main reason for writing an Emacs module is to make additional functions available toLisp programs that load the module. This subsection describes how to write such module
functions.
A module function has the following general form and signature:emacs_value emacs_function (emacs_env *env, ptrdiff_t
nargs, emacs_value *args, void *data)[Function]

The env argument provides a pointer to the API environment, needed to access Emacs
objects and functions. The nargs argument is the required number of arguments,
which can be zero (see make_function below for more flexible specification of theargument number), and args is a pointer to the array of the function arguments.
The argument data points to additional data required by the function, which wasarranged when make_function (see below) was called to create an Emacs function
from emacs_function.
Module functions use the type emacs_value to communicate Lisp objects between
Emacs and the module (see Section E.8.3 [Module Values], page 1366). The API,
described below and in the following subsections, provides facilities for conversion
between basic C data types and the corresponding emacs_value objects.
In the module function’s body, do not attempt to access elements of the args array
beyond the index nargs-1: memory for the args array is allocated exactly to accommodate nargs values, and accessing beyond that will most probably crash your module.
In particular, if the value of nargs passed to the function at run time is zero, it must
not access args at all, as no memory will have been allocated for it in that case.
A module function always returns a value. If the function returns normally, the Lisp
code which called it will see the Lisp object corresponding to the emacs_value value

Appendix E: GNU Emacs Internals

1364

the function returned. However, if the user typed C-g, or if the module function orits callees signaled an error or exited nonlocally (see Section E.8.5 [Module Nonlocal],page 1375), Emacs will ignore the returned value and quit or throw as it does when
Lisp code encounters the same situations.
The header emacs-module.h provides the type emacs_function as an alias type fora function pointer to a module function.
After writing your C code for a module function, you should make a Lisp function object
from it using the make_function function, whose pointer is provided in the environment(recall that the pointer to the environment is returned by get_environment). This isnormally done in the module initialization function (see [module initialization function],
page 1361), after verifying the API compatibility.

emacs_value make_function (emacs_env *env, ptrdiff_t[Function]
min_arity, ptrdiff_t max_arity, emacs_function func, const
char *docstring, void *data)
This returns an Emacs function created from the C function func, whose signature
is as described for emacs_function above. The arguments min arity and max arity
specify the minimum and maximum number of arguments that func can accept. The
max arity argument can have the special value emacs_variadic_function, whichmakes the function accept an unlimited number of arguments, like the &rest keyword
in Lisp (see Section 13.2.3 [Argument List], page 234).
The argument data is a way to arrange for arbitrary additional data to be passed to
func when it is called. Whatever pointer is passed to make_function will be passed
unaltered to func.
The argument docstring specifies the documentation string for the function. It shouldbe either an ASCII string, or a UTF-8 encoded non-ASCII string, or a NULL pointer;in the latter case the function will have no documentation. The documentation stringcan end with a line that specifies the advertised calling convention, see Section 13.2.4[Function Documentation], page 235.
Since every module function must accept the pointer to the environment as its firstargument, the call to make_function could be made from any module function, but
you will normally want to do that from the module initialization function, so that all
the module functions are known to Emacs once the module is loaded.
Finally, you should bind the Lisp function to a symbol, so that Lisp code could call yourfunction by name. For that, use the module API function intern (see [intern], page 1374)
whose pointer is also provided in the environment that module functions can access.
Combining the above steps, code that arranges for a C function module_func to becallable as module-func from Lisp will look like this, as part of the module initialization
function:
emacs_env *env = runtime->get_environment (runtime);
emacs_value func = env->make_function (env, min_arity, max_arity,
module_func, docstring, data);
emacs_value symbol = env->intern (env, "module-func");emacs_value args[] = {symbol, func};

Appendix E: GNU Emacs Internals

1365

env->funcall (env, env->intern (env, "defalias"), 2, args);
This makes the symbol module-func known to Emacs by calling env->intern, then invokes
defalias from Emacs to bind the function to that symbol. Note that it is possible to use
fset instead of defalias; the differences are described in Section 13.4 [Defining Functions],
page 237.
Module functions including the emacs_module_init function (see [module initialization
function], page 1361) may only interact with Emacs by calling environment functions fromsome live emacs_env pointer while being called directly or indirectly from Emacs. In otherwords, if a module function wants to call Lisp functions or Emacs primitives, convert emacs_
value objects to and from C datatypes (see Section E.8.3 [Module Values], page 1366), orinteract with Emacs in any other way, some call from Emacs to emacs_module_init or
to a module function must be in the call stack. Module functions may not interact with
Emacs while garbage collection is running; see Section E.3 [Garbage Collection], page 1350.
They may only interact with Emacs from Lisp interpreter threads (including the mainthread) created by Emacs; see Chapter 39 [Threads], page 1073. The --module-assertionscommand-line option can detect some violations of the above requirements. See Section“Initial Options” in The GNU Emacs Manual.
Using the module API, it is possible to define more complex function and data types:
inline functions, macros, etc. However, the resulting C code will be cumbersome and hard to
read. Therefore, we recommend that you limit the module code which creates functions anddata structures to the absolute minimum, and leave the rest for a Lisp package that willaccompany your module, because doing these additional tasks in Lisp is much easier, and willproduce a much more readable code. For example, given a module function module-func
defined as above, one way of making a macro module-macro based on it is with the following
simple Lisp wrapper:(defmacro module-macro (&rest args)"Documentation string for the macro."(module-func args))
The Lisp package which goes with your module could then load the module using theload primitive (see Section 16.11 [Dynamic Modules], page 314) when the package is loaded
into Emacs.
By default, module functions created by make_function are not interactive. To makethem interactive, you can use the following function.

void make_interactive (emacs_env *env, emacs_valuefunction, emacs_value spec)[Function]

This function, which is available since Emacs 28, makes the function function interactive
using the interactive specification spec. Emacs interprets spec like the argument to theinteractive form. Section 22.2.1 [Using Interactive], page 424, and see Section 22.2.2[Interactive Codes], page 427. function must be an Emacs module function returned
by make_function.
Note that there is no native module support for retrieving the interactive specificationof a module function. Use the function interactive-form for that. Section 22.2.1 [Using
Interactive], page 424. It is not possible to make a module function non-interactive once you
have made it interactive using make_interactive.

Appendix E: GNU Emacs Internals

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If you want to run some code when a module function object (i.e., an object returned by
make_function) is garbage-collected, you can install a function finalizer. Function finalizers
are available since Emacs 28. For example, if you have passed some heap-allocated structure
to the data argument of make_function, you can use the finalizer to deallocate the structure.
See Section “Basic Allocation” in libc, and see Section “Freeing after Malloc” in libc. The
finalizer function has the following signature:void finalizer (void *data)
Here, data receives the value passed to data when calling make_function. Note that the
finalizer can’t interact with Emacs in any way.
Directly after calling make_function, the newly-created function doesn’t have a finalizer.
Use set_function_finalizer to add one, if desired.

void emacs_finalizer (void *ptr)[Function]
The header emacs-module.h provides the type emacs_finalizer as a type alias for
an Emacs finalizer function.

emacs_finalizer get_function_finalizer (emacs_env *env,
emacs_value arg)

[Function]

This function, which is available since Emacs 28, returns the function finalizer associated with the module function represented by arg. arg must refer to a module
function, that is, an object returned by make_function. If no finalizer is associatedwith the function, NULL is returned.

void set_function_finalizer (emacs_env *env, emacs_valuearg, emacs_finalizer fin)[Function]

This function, which is available since Emacs 28, sets the function finalizer associatedwith the module function represented by arg to fin. arg must refer to a module
function, that is, an object returned by make_function. fin can either be NULL toclear arg’s function finalizer, or a pointer to a function to be called when the object
represented by arg is garbage-collected. At most one function finalizer can be set perfunction; if arg already has a finalizer, it is replaced by fin.

E.8.3 Conversion Between Lisp and Module Values
With very few exceptions, most modules need to exchange data with Lisp programs thatcall them: accept arguments to module functions and return values from module functions.
For this purpose, the module API provides the emacs_value type, which represents Emacs
Lisp objects communicated via the API; it is the functional equivalent of the Lisp_Object
type used in Emacs C primitives (see Section E.7 [Writing Emacs Primitives], page 1356).
This section describes the parts of the module API that allow to create emacs_value objects
corresponding to basic Lisp data types, and how to access from C data in emacs_value
objects that correspond to Lisp objects.
All of the functions described below are actually function pointers provided via thepointer to the environment which every module function accepts. Therefore, module codeshould call these functions through the environment pointer, like this:emacs_env *env; /* the environment pointer */env->some_function (arguments...);

Appendix E: GNU Emacs Internals

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The emacs_env pointer will usually come from the first argument to the module function, orfrom the call to get_environment if you need the environment in the module initialization
function.
Most of the functions described below became available in Emacs 25, the first Emacs
release that supported dynamic modules. For the few functions that became available inlater Emacs releases, we mention the first Emacs version that supported them.
The following API functions extract values of various C data types from emacs_value
objects. They all raise the wrong-type-argument error condition (see Section 2.7 [TypePredicates], page 30) if the argument emacs_value object is not of the type expected by
the function. See Section E.8.5 [Module Nonlocal], page 1375, for details of how signaling
errors works in Emacs modules, and how to catch error conditions inside the module before
they are reported to Emacs. The API function type_of (see Section E.8.4 [Module Misc],
page 1373) can be used to obtain the type of a emacs_value object.

intmax_t extract_integer (emacs_env *env, emacs_value arg)

[Function]
This function returns the value of a Lisp integer specified by arg. The C data typeof the return value, intmax_t, is the widest integer data type supported by the Ccompiler, typically long long. If the value of arg doesn’t fit into an intmax_t, thefunction signals an error using the error symbol overflow-error.

bool extract_big_integer (emacs_env *env, emacs_value arg,
[Function]
int *sign, ptrdiff_t *count, emacs_limb_t *magnitude)
This function, which is available since Emacs 27, extracts the integer value of arg.
The value of arg must be an integer (fixnum or bignum). If sign is not NULL, it storesthe sign of arg (-1, 0, or +1) into *sign. The magnitude is stored into magnitude as
follows. If count and magnitude are both non-NULL, then magnitude must point toan array of at least *count unsigned long elements. If magnitude is large enough tohold the magnitude of arg, then this function writes the magnitude into the magnitude
array in little-endian form, stores the number of array elements written into *count,and returns true. If magnitude is not large enough, it stores the required array size
into *count, signals an error, and returns false. If count is not NULL and magnitude
is NULL, then the function stores the required array size into *count and returns true.
Emacs guarantees that the maximum required value of *count never exceedsmin (PTRDIFF_MAX, SIZE_MAX) / sizeof (emacs_limb_t), so you can use malloc(*count * sizeof *magnitude) to allocate the magnitude array without worrying
about integer overflow in the size calculation.
[Type alias]
This is an unsigned integer type, used as the element type for the magnitude arraysfor the big integer conversion functions. The type is guaranteed to have unique object
representations, i.e., no padding bits.

emacs_limb_t[Macro]This macro expands to a constant expression specifying the maximum possible value
for an emacs_limb_t object. The expression is suitable for use in #if.

EMACS_LIMB_MAX

double extract_float (emacs_env *env, emacs_value arg)

[Function]
This function returns the value of a Lisp float specified by arg, as a C double value.

Appendix E: GNU Emacs Internals

struct timespec extract_time (emacs_env *env, emacs_value
arg)

1368

[Function]

This function, which is available since Emacs 27, interprets arg as an Emacs Lisp
time value and returns the corresponding struct timespec. See Section 42.5 [Time ofDay], page 1270. struct timespec represents a timestamp with nanosecond precision.
It has the following members:
time_t tv_sec
Whole number of seconds.
long tv_nsec
Fractional seconds as a number of nanoseconds. For timestamps returnedby extract_time, this is always nonnegative and less than one billion.
(Although POSIX requires the type of tv_nsec to be long, the type islong long on some nonstandard platforms.)
See Section “Elapsed Time” in libc.
If time has higher precision than nanoseconds, then this function truncates it tonanosecond precision towards negative infinity. This function signals an error if time(truncated to nanoseconds) cannot be represented by struct timespec. For example,
if time_t is a 32-bit integer type, then a time value of ten billion seconds would signal
an error, but a time value of 600 picoseconds would get truncated to zero.
If you need to deal with time values that are not representable by struct timespec,
or if you want higher precision, call the Lisp function encode-time and work with its
return value. See Section 42.7 [Time Conversion], page 1273.

bool copy_string_contents (emacs_env *env, emacs_valuearg, char *buf, ptrdiff_t *len)[Function]

This function stores the UTF-8 encoded text of a Lisp string specified by arg in thearray of char pointed by buf, which should have enough space to hold at least *lenbytes, including the terminating null byte. The argument len must not be a NULL
pointer, and, when the function is called, it should point to a value that specifies thesize of buf in bytes.
If the buffer size specified by *len is large enough to hold the string’s text, the function
stores in *len the actual number of bytes copied to buf, including the terminating nullbyte, and returns true. If the buffer is too small, the function raises the args-outof-range error condition, stores the required number of bytes in *len, and returns
false. See Section E.8.5 [Module Nonlocal], page 1375, for how to handle pending
error conditions.
The argument buf can be a NULL pointer, in which case the function stores in *lenthe number of bytes required for storing the contents of arg, and returns true. Thisis how you can determine the size of buf needed to store a particular string: firstcall copy_string_contents with NULL as buf, then allocate enough memory to holdthe number of bytes stored by the function in *len, and call the function again with
non-NULL buf to actually perform the text copying.

Appendix E: GNU Emacs Internals

emacs_value vec_get (emacs_env *env, emacs_value vector,
ptrdiff_t index)

1369[Function]

This function returns the element of vector at index. The index of the first vector
element is zero. The function raises the args-out-of-range error condition if thevalue of index is invalid. To extract C data from the value the function returns, use
the other extraction functions described here, as appropriate for the Lisp data typestored in that element of the vector.

ptrdiff_t vec_size (emacs_env *env, emacs_value vector)[Function]

This function returns the number of elements in vector.

void vec_set (emacs_env *env, emacs_value vector,
ptrdiff_t index, emacs_value value)[Function]

This function stores value in the element of vector whose index is index. It raises theargs-out-of-range error condition if the value of index is invalid.
The following API functions create emacs_value objects from basic C data types. They
all return the created emacs_value object.

emacs_value make_integer (emacs_env *env, intmax_t n)[Function]
This function takes an integer argument n and returns the corresponding emacs_value
object. It returns either a fixnum or a bignum depending on whether the value of n
is inside the limits set by most-negative-fixnum and most-positive-fixnum (seeSection 3.1 [Integer Basics], page 38).

emacs_value make_big_integer (emacs_env *env, int sign,
ptrdiff_t count, const emacs_limb_t *magnitude)[Function]

This function, which is available since Emacs 27, takes an arbitrary-sized integer
argument and returns a corresponding emacs_value object. The sign argument gives
the sign of the return value. If sign is nonzero, then magnitude must point to an arrayof at least count elements specifying the little-endian magnitude of the return value.
The following example uses the GNU Multiprecision Library (GMP) to calculate thenext probable prime after a given integer. See gmp, for a general overview of GMP, and see
Section “Integer Import and Export” in gmp for how to convert the magnitude array to andfrom GMP mpz_t values.
#include <emacs-module.h>int plugin_is_GPL_compatible;#include <assert.h>#include <limits.h>#include <stdint.h>#include <stdlib.h>#include <string.h>#include <gmp.h>
static void
memory_full (emacs_env *env)

Appendix E: GNU Emacs Internals

1370{
static const char message[] = "Memory exhausted";
emacs_value data = env->make_string (env, message,
strlen (message));env->non_local_exit_signal(env, env->intern (env, "error"),env->funcall (env, env->intern (env, "list"), 1, &data));}enum{
order = -1, endian = 0, nails = 0,
limb_size = sizeof (emacs_limb_t),
max_nlimbs = ((SIZE_MAX < PTRDIFF_MAX ? SIZE_MAX : PTRDIFF_MAX)/ limb_size)};
static bool
extract_big_integer (emacs_env *env, emacs_value arg, mpz_t result){ptrdiff_t nlimbs;
bool ok = env->extract_big_integer (env, arg, NULL, &nlimbs, NULL);
if (!ok)return false;
assert (0 < nlimbs && nlimbs <= max_nlimbs);
emacs_limb_t *magnitude = malloc (nlimbs * limb_size);if (magnitude == NULL){
memory_full (env);
return false;}
int sign;
ok = env->extract_big_integer (env, arg, &sign, &nlimbs, magnitude);assert (ok);mpz_import (result, nlimbs, order, limb_size, endian, nails, magnitude);free (magnitude);if (sign < 0)
mpz_neg (result, result);
return true;}
static emacs_value
make_big_integer (emacs_env *env, const mpz_t value){
size_t nbits = mpz_sizeinbase (value, 2);
int bitsperlimb = CHAR_BIT * limb_size - nails;
size_t nlimbs = nbits / bitsperlimb + (nbits % bitsperlimb != 0);Appendix E: GNU Emacs Internals

1371

emacs_limb_t *magnitude= nlimbs <= max_nlimbs ? malloc (nlimbs * limb_size) : NULL;
if (magnitude == NULL){
memory_full (env);
return NULL;}
size_t written;
mpz_export (magnitude, &written, order, limb_size, endian, nails, value);assert (written == nlimbs);
assert (nlimbs <= PTRDIFF_MAX);
emacs_value result = env->make_big_integer (env, mpz_sgn (value),nlimbs, magnitude);free (magnitude);return result;}static emacs_value
next_prime (emacs_env *env, ptrdiff_t nargs, emacs_value *args,
void *data){assert (nargs == 1);
mpz_t p;mpz_init (p);extract_big_integer (env, args[0], p);
mpz_nextprime (p, p);emacs_value result = make_big_integer (env, p);
mpz_clear (p);return result;}int
emacs_module_init (struct emacs_runtime *runtime){
emacs_env *env = runtime->get_environment (runtime);
emacs_value symbol = env->intern (env, "next-prime");emacs_value func
= env->make_function (env, 1, 1, next_prime, NULL, NULL);
emacs_value args[] = {symbol, func};
env->funcall (env, env->intern (env, "defalias"), 2, args);
return 0;}

emacs_value make_float (emacs_env *env, double d)[Function]
This function takes a double argument d and returns the corresponding Emacs
floating-point value.

Appendix E: GNU Emacs Internals

emacs_value make_time (emacs_env *env, struct timespec
time)

1372

[Function]

This function, which is available since Emacs 27, takes a struct timespec argument
time and returns the corresponding Emacs timestamp as a pair (ticks . hz). See
Section 42.5 [Time of Day], page 1270. The return value represents exactly the sametimestamp as time: all input values are representable, and there is never a loss of
precision. time.tv_sec and time.tv_nsec can be arbitrary values. In particular,
there’s no requirement that time be normalized. This means that time.tv_nsec canbe negative or larger than 999,999,999.

emacs_value make_string (emacs_env *env, const char *str,
ptrdiff_t len)

[Function]

This function creates an Emacs string from C text string pointed by str whose length
in bytes, not including the terminating null byte, is len. The original string in str
can be either an ASCII string or a UTF-8 encoded non-ASCII string; it can include
embedded null bytes, and doesn’t have to end in a terminating null byte at str[len].
The function raises the overflow-error error condition if len is negative or exceeds
the maximum length of an Emacs string. If len is zero, then str can be NULL, otherwise
it must point to valid memory. For nonzero len, make_string returns unique mutablestring objects.

emacs_value make_unibyte_string (emacs_env *env, const
char *str, ptrdiff_t len)

[Function]

This function is like make_string, but has no restrictions on the values of the bytes in
the C string, and can be used to pass binary data to Emacs in the form of a unibyte
string.
The API does not provide functions to manipulate Lisp data structures, for example,
create lists with cons and list (see Section 5.4 [Building Lists], page 82), extract list
members with car and cdr (see Section 5.3 [List Elements], page 79), create vectors with
vector (see Section 6.5 [Vector Functions], page 118), etc. For these, use intern andfuncall, described in the next subsection, to call the corresponding Lisp functions.
Normally, emacs_value objects have a rather short lifetime: it ends when the emacs_env
pointer used for their creation goes out of scope. Occasionally, you may need to create
global references: emacs_value objects that live as long as you wish. Use the following two
functions to manage such objects.

emacs_value make_global_ref (emacs_env *env, emacs_value
value)[Function]

This function returns a global reference for value.

void free_global_ref (emacs_env *env, emacs_value
global_value)[Function]

This function frees the global value previously created by make_global_ref. The
global value is no longer valid after the call. Your module code should pair each callto make_global_ref with the corresponding free_global_ref.
An alternative to keeping around C data structures that need to be passed to module
functions later is to create user pointer objects. A user pointer, or user-ptr, object is a Lisp

Appendix E: GNU Emacs Internals

1373

object that encapsulates a C pointer and can have an associated finalizer function, which iscalled when the object is garbage-collected (see Section E.3 [Garbage Collection], page 1350).
The module API provides functions to create and access user-ptr objects. These functions
raise the wrong-type-argument error condition if they are called on emacs_value that
doesn’t represent a user-ptr object.

emacs_value make_user_ptr (emacs_env *env, emacs_finalizer
fin, void *ptr)[Function]

This function creates and returns a user-ptr object which wraps the C pointer ptr.
The finalizer function fin can be a NULL pointer (meaning no finalizer), or it can be afunction of the following signature:
typedef void (*emacs_finalizer) (void *ptr);
If fin is not a NULL pointer, it will be called with the ptr as the argument when theuser-ptr object is garbage-collected. Don’t run any expensive code in a finalizer,
because GC must finish quickly to keep Emacs responsive.

void *get_user_ptr (emacs_env *env, emacs_value arg)

[Function]
This function extracts the C pointer from the Lisp object represented by arg.

void set_user_ptr (emacs_env *env, emacs_value arg, void
*ptr)

[Function]

This function sets the C pointer embedded in the user-ptr object represented by arg
to ptr.

emacs_finalizer get_user_finalizer (emacs_env *env,
emacs_value arg)

[Function]

This function returns the finalizer of the user-ptr object represented by arg, or NULL
if it doesn’t have a finalizer.

void set_user_finalizer (emacs_env *env, emacs_value arg,
emacs_finalizer fin)[Function]

This function changes the finalizer of the user-ptr object represented by arg to be
fin. If fin is a NULL pointer, the user-ptr object will have no finalizer.
Note that the emacs_finalizer type works for both user pointer an module function
finalizers. See [Module Function Finalizers], page 1365.

E.8.4 Miscellaneous Convenience Functions for Modules
This subsection describes a few convenience functions provided by the module API. Like thefunctions described in previous subsections, all of them are actually function pointers, andneed to be called via the emacs_env pointer. Description of functions that were introduced
after Emacs 25 calls out the first version where they became available.

bool eq (emacs_env *env, emacs_value a, emacs_value b)[Function]
This function returns true if the Lisp objects represented by a and b are identical,
false otherwise. This is the same as the Lisp function eq (see Section 2.8 [Equality
Predicates], page 34), but avoids the need to intern the objects represented by thearguments.
There are no API functions for other equality predicates, so you will need to useintern and funcall, described below, to perform more complex equality tests.

Appendix E: GNU Emacs Internals

1374

bool is_not_nil (emacs_env *env, emacs_value arg)

[Function]
This function tests whether the Lisp object represented by arg is non-nil; it returns
true or false accordingly.
Note that you could implement an equivalent test by using intern to get an emacs_
value representing nil, then use eq, described above, to test for equality. But using
this function is more convenient.

emacs_value type_of (emacs_env *env, emacs_value arg)

[Function]
This function returns the type of arg as a value that represents a symbol: string fora string, integer for an integer, process for a process, etc. See Section 2.7 [TypePredicates], page 30. You can use intern and eq to compare against known typesymbols, if your code needs to depend on the object type.

emacs_value intern (emacs_env *env, const char *name)[Function]
This function returns an interned Emacs symbol whose name is name, which should
be an ASCII null-terminated string. It creates a new symbol if one does not alreadyexist.
Together with funcall, described below, this function provides a means for invoking
any Lisp-callable Emacs function, provided that its name is a pure ASCII string.
For example, here’s how to intern a symbol whose name name_str is non-ASCII, by
calling the more powerful Emacs intern function (see Section 9.3 [Creating Symbols],
page 135):
emacs_value fintern = env->intern (env, "intern");
emacs_value sym_name =env->make_string (env, name_str, strlen (name_str));emacs_value symbol = env->funcall (env, fintern, 1, &sym_name);

emacs_value funcall (emacs_env *env, emacs_value func,
ptrdiff_t nargs, emacs_value *args)[Function]

This function calls the specified func passing it nargs arguments from the array pointed
to by args. The argument func can be a function symbol (e.g., returned by interndescribed above), a module function returned by make_function (see Section E.8.2[Module Functions], page 1363), a subroutine written in C, etc. If nargs is zero, args
can be a NULL pointer.
The function returns the value that func returned.
If your module includes potentially long-running code, it is a good idea to check from time
to time in that code whether the user wants to quit, e.g., by typing C-g (see Section 22.11[Quitting], page 471). The following function, which is available since Emacs 26.1, is provided
for that purpose.

bool should_quit (emacs_env *env)[Function]
This function returns true if the user wants to quit. In that case, we recommend thatyour module function aborts any on-going processing and returns as soon as possible.
In most cases, use process_input instead.

To process input events in addition to checking whether the user wants to quit, use thefollowing function, which is available since Emacs 27.1.

Appendix E: GNU Emacs Internals

enum emacs_process_input_result process_input (emacs_env
*env)

1375

[Function]

This function processes pending input events. It returns emacs_process_input_quit
if the user wants to quit or an error occurred while processing signals. In that case,
we recommend that your module function aborts any on-going processing and returns
as soon as possible. If the module code may continue running, process_input returns emacs_process_input_continue. The return value is emacs_process_input_
continue if and only if there is no pending nonlocal exit in env. If the module
continues after calling process_input, global state such as variable values and buffer
content may have been modified in arbitrary ways.

int open_channel (emacs_env *env, emacs_value pipe_process)[Function]
This function, which is available since Emacs 28, opens a channel to an existing pipe
process. pipe process must refer to an existing pipe process created by make-pipeprocess. [Pipe Processes], page 1088. If successful, the return value will be a new filedescriptor that you can use to write to the pipe. Unlike all other module functions,
you can use the returned file descriptor from arbitrary threads, even if no module
environment is active. You can use the write function to write to the file descriptor.
Once done, close the file descriptor using close. Section “Low-Level I/O” in libc.

E.8.5 Nonlocal Exits in Modules
Emacs Lisp supports nonlocal exits, whereby program control is transferred from one point
in a program to another remote point. See Section 11.7 [Nonlocal Exits], page 177. Thus,
Lisp functions called by your module might exit nonlocally by calling signal or throw, andyour module functions must handle such nonlocal exits properly. Such handling is needed
because C programs will not automatically release resources and perform other cleanups inthese cases; your module code must itself do it. The module API provides facilities for that,
described in this subsection. They are generally available since Emacs 25; those of themthat became available in later releases explicitly call out the first Emacs version where they
became part of the API.
When some Lisp code called by a module function signals an error or throws, the nonlocal
exit is trapped, and the pending exit and its associated data are stored in the environment.
Whenever a nonlocal exit is pending in the environment, any module API function calledwith a pointer to that environment will return immediately without any processing (thefunctions non_local_exit_check, non_local_exit_get, and non_local_exit_clear are
exceptions from this rule). If your module function then does nothing and returns to Emacs,a pending nonlocal exit will cause Emacs to act on it: signal an error or throw to thecorresponding catch.
So the simplest “handling” of nonlocal exits in module functions is to do nothing special
and let the rest of your code to run as if nothing happened. However, this can cause twoclasses of problems:− Your module function might use uninitialized or undefined values, since API functions
return immediately without producing the expected results.
− Your module might leak resources, because it might not have the opportunity to releasethem.

Appendix E: GNU Emacs Internals

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Therefore, we recommend that your module functions check for nonlocal exit conditions
and recover from them, using the functions described below.

enum emacs_funcall_exit non_local_exit_check (emacs_env*env)[Function]

This function returns the kind of nonlocal exit condition stored in env. The possible
values are:emacs_funcall_exit_return
The last API function exited normally.
emacs_funcall_exit_signal
The last API function signaled an error.
emacs_funcall_exit_throw
The last API function exited via throw.

enum emacs_funcall_exit non_local_exit_get (emacs_env*env, emacs_value *symbol, emacs_value *data)[Function]

This function returns the kind of nonlocal exit condition stored in env, like non_local_
exit_check does, but it also returns the full information about the nonlocal exit,
if any. If the return value is emacs_funcall_exit_signal, the function stores theerror symbol in *symbol and the error data in *data (see Section 11.7.3.1 [Signaling
Errors], page 180). If the return value is emacs_funcall_exit_throw, the function
stores the catch tag symbol in *symbol and the throw value in *data. The function
doesn’t store anything in memory pointed by these arguments when the return value
is emacs_funcall_exit_return.
You should check nonlocal exit conditions where it matters: before you allocated someresource or after you allocated a resource that might need freeing, or where a failure means
further processing is impossible or infeasible.
Once your module function detected that a nonlocal exit is pending, it can either returnto Emacs (after performing the necessary local cleanup), or it can attempt to recover fromthe nonlocal exit. The following API functions will help with these tasks.

void non_local_exit_clear (emacs_env *env)[Function]
This function clears the pending nonlocal exit conditions and data from env. Aftercalling it, the module API functions will work normally. Use this function if yourmodule function can recover from nonlocal exits of the Lisp functions it calls andcontinue, and also before calling any of the following two functions (or any other API
functions, if you want them to perform their intended processing when a nonlocal exit
is pending).

void non_local_exit_throw (emacs_env *env, emacs_valuetag, emacs_value value)[Function]

This function throws to the Lisp catch symbol represented by tag, passing it value as
the value to return. Your module function should in general return soon after calling
this function. One use of this function is when you want to re-throw a non-local exitfrom one of the called API or Lisp functions.

Appendix E: GNU Emacs Internals

void non_local_exit_signal (emacs_env *env, emacs_value
symbol, emacs_value data)

1377[Function]

This function signals the error represented by the error symbol symbol with thespecified error data data. The module function should return soon after calling thisfunction. This function could be useful, e.g., for signaling errors from module functions
to Emacs.

E.9 Object Internals
Emacs Lisp provides a rich set of the data types. Some of them, like cons cells, integers andstrings, are common to nearly all Lisp dialects. Some others, like markers and buffers, arequite special and needed to provide the basic support to write editor commands in Lisp.
To implement such a variety of object types and provide an efficient way to pass objects
between the subsystems of an interpreter, there is a set of C data structures and a special
type to represent the pointers to all of them, which is known as tagged pointer.
In C, the tagged pointer is an object of type Lisp_Object. Any initialized variable ofsuch a type always holds the value of one of the following basic data types: integer, symbol,
string, cons cell, float, or vectorlike object. Each of these data types has the corresponding
tag value. All tags are enumerated by enum Lisp_Type and placed into a 3-bit bitfield of the
Lisp_Object. The rest of the bits is the value itself. Integers are immediate, i.e., directly
represented by those value bits, and all other objects are represented by the C pointers to acorresponding object allocated from the heap. Width of the Lisp_Object is platform- andconfiguration-dependent: usually it’s equal to the width of an underlying platform pointer(i.e., 32-bit on a 32-bit machine and 64-bit on a 64-bit one), but also there is a special
configuration where Lisp_Object is 64-bit but all pointers are 32-bit. The latter trick was
designed to overcome the limited range of values for Lisp integers on a 32-bit system byusing 64-bit long long type for Lisp_Object.
The following C data structures are defined in lisp.h to represent the basic data types
beyond integers:
struct Lisp_Cons
Cons cell, an object used to construct lists.
struct Lisp_String
String, the basic object to represent a sequence of characters.
struct Lisp_Vector
Array, a fixed-size set of Lisp objects which may be accessed by an index.
struct Lisp_Symbol
Symbol, the unique-named entity commonly used as an identifier.
struct Lisp_Float
Floating-point value.
These types are the first-class citizens of an internal type system. Since the tag spaceis limited, all other types are the subtypes of Lisp_Vectorlike. Vector subtypes are
enumerated by enum pvec_type, and nearly all complex objects like windows, buffers,
frames, and processes fall into this category.

Appendix E: GNU Emacs Internals

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Below there is a description of a few subtypes of Lisp_Vectorlike. Buffer object
represents the text to display and edit. Window is the part of display structure which shows
the buffer or is used as a container to recursively place other windows on the same frame.
(Do not confuse Emacs Lisp window object with the window as an entity managed by theuser interface system like X; in Emacs terminology, the latter is called frame.) Finally,
process object is used to manage the subprocesses.

E.9.1 Buffer Internals
Two structures (see buffer.h) are used to represent buffers in C. The buffer_text structure
contains fields describing the text of a buffer; the buffer structure holds other fields. In
the case of indirect buffers, two or more buffer structures reference the same buffer_text
structure.
Here are some of the fields in struct buffer_text:beg
gpt
gpt_byte

The address of the buffer contents. The buffer contents is a linear C array ofchar, with the gap somewhere in its midst.
The character and byte positions of the buffer gap. See Section 28.13 [Buffer
Gap], page 688.

zz_byte

The character and byte positions of the end of the buffer text.

gap_size

The size of buffer’s gap. See Section 28.13 [Buffer Gap], page 688.

modiffsave_modiff
chars_modiff
overlay_modiff
These fields count the number of buffer-modification events performed in thisbuffer. modiff is incremented after each buffer-modification event, and is neverotherwise changed; save_modiff contains the value of modiff the last time
the buffer was visited or saved; chars_modiff counts only modifications tothe characters in the buffer, ignoring all other kinds of changes (such as text
properties); and overlay_modiff counts only modifications to the buffer’s
overlays.
beg_unchanged
end_unchanged
The number of characters at the start and end of the text that are known to beunchanged since the last complete redisplay.
unchanged_modified
overlay_unchanged_modified
The values of modiff and overlay_modiff, respectively, after the last complete
redisplay. If their current values match modiff or overlay_modiff, that means
beg_unchanged and end_unchanged contain no useful information.
markers

The markers that refer to this buffer. This is actually a single marker, andsuccessive elements in its marker chain (a linked list) are the other markers
referring to this buffer text.

Appendix E: GNU Emacs Internals

1379

intervals
The interval tree which records the text properties of this buffer.
Some of the fields of struct buffer are:header

A header of type union vectorlike_header is common to all vectorlike objects.

own_text

A struct buffer_text structure that ordinarily holds the buffer contents. In
indirect buffers, this field is not used.

text

A pointer to the buffer_text structure for this buffer. In an ordinary buffer,
this is the own_text field above. In an indirect buffer, this is the own_text fieldof the base buffer.

next

A pointer to the next buffer, in the chain of all buffers, including killed buffers.
This chain is used only for allocation and garbage collection, in order to collect
killed buffers properly.

pt
pt_byte

The character and byte positions of point in a buffer.

begv
begv_byte
The character and byte positions of the beginning of the accessible range of text
in the buffer.
zv
zv_byte

The character and byte positions of the end of the accessible range of text inthe buffer.

base_buffer
In an indirect buffer, this points to the base buffer. In an ordinary buffer, it isnull.
local_flags
This field contains flags indicating that certain variables are local in this buffer.
Such variables are declared in the C code using DEFVAR_PER_BUFFER, and theirbuffer-local bindings are stored in fields in the buffer structure itself. (Some ofthese fields are described in this table.)
modtime

The modification time of the visited file. It is set when the file is written or read.
Before writing the buffer into a file, this field is compared to the modification
time of the file to see if the file has changed on disk. See Section 28.5 [Buffer
Modification], page 677.

auto_save_modified
The time when the buffer was last auto-saved.
last_window_start
The window-start position in the buffer as of the last time the buffer was
displayed in a window.
clip_changed
This flag indicates that narrowing has changed in the buffer. See Section 31.4
[Narrowing], page 865.

Appendix E: GNU Emacs Internals

1380

prevent_redisplay_optimizations_p
This flag indicates that redisplay optimizations should not be used to display
this buffer.
inhibit_buffer_hooks
This flag indicates that the buffer should not run the hooks kill-buffer-hook,kill-buffer-query-functions (see Section 28.10 [Killing Buffers], page 685),
and buffer-list-update-hook (see Section 28.8 [Buffer List], page 681). It
is set at buffer creation (see Section 28.9 [Creating Buffers], page 684), andavoids slowing down internal or temporary buffers, such as those created bywith-temp-buffer (see [Current Buffer], page 673).
name

A Lisp string that names the buffer. It is guaranteed to be unique. See
Section 28.3 [Buffer Names], page 674. This and the following fields have theirnames in the C struct definition end in a _ to indicate that they should not be
accessed directly, but via the BVAR macro, like this:Lisp_Object buf_name = BVAR (buffer, name);

save_length
The length of the file this buffer is visiting, when last read or saved. It can have
2 special values: −1 means auto-saving was turned off in this buffer, and −2means don’t turn off auto-saving if buffer text shrinks a lot. This and otherfields concerned with saving are not kept in the buffer_text structure because
indirect buffers are never saved.
directory
The directory for expanding relative file names. This is the value of the bufferlocal variable default-directory (see Section 26.9.4 [File Name Expansion],
page 639).
filename

The name of the file visited in this buffer, or nil. This is the value of thebuffer-local variable buffer-file-name (see Section 28.4 [Buffer File Name],
page 675).

undo_list
backed_up
auto_save_file_nameauto_save_file_format
read_only
file_format
file_truename
invisibility_spec
display_countdisplay_time
These fields store the values of Lisp variables that are automatically bufferlocal (see Section 12.11 [Buffer-Local Variables], page 207), whose corresponding
variable names have the additional prefix buffer- and have underscores replacedwith dashes. For instance, undo_list stores the value of buffer-undo-list.
mark

The mark for the buffer. The mark is a marker, hence it is also included on thelist markers. See Section 32.7 [The Mark], page 873.

Appendix E: GNU Emacs Internals

1381

local_var_alist
The association list describing the buffer-local variable bindings of this buffer,
not including the built-in buffer-local bindings that have special slots in thebuffer object. (Those slots are omitted from this table.) See Section 12.11[Buffer-Local Variables], page 207.

major_mode
Symbol naming the major mode of this buffer, e.g., lisp-mode.

mode_name
Pretty name of the major mode, e.g., "Lisp".

keymapabbrev_tablesyntax_table
category_tabledisplay_table
These fields store the buffer’s local keymap (see Chapter 23 [Keymaps], page 480),
abbrev table (see Section 38.1 [Abbrev Tables], page 1066), syntax table (seeChapter 36 [Syntax Tables], page 1022), category table (see Section 36.8 [Categories], page 1036), and display table (see Section 41.23.2 [Display Tables],page 1243).

downcase_tableupcase_table
case_canon_table
These fields store the conversion tables for converting text to lower case, upper
case, and for canonicalizing text for case-fold search. See Section 4.10 [CaseTables], page 74.

minor_modes
An alist of the minor modes of this buffer.

pt_marker
begv_marker
zv_marker
These fields are only used in an indirect buffer, or in a buffer that is the base of an
indirect buffer. Each holds a marker that records pt, begv, and zv respectively,
for this buffer when the buffer is not current.

Appendix E: GNU Emacs Internals

1382

mode_line_format
header_line_format
case_fold_search
tab_widthfill_column
left_margin
auto_fill_function
truncate_lines
word_wrap
ctl_arrowbidi_display_reorderingbidi_paragraph_direction
selective_display
selective_display_ellipses
overwrite_mode
abbrev_mode
mark_active
enable_multibyte_charactersbuffer_file_coding_systemcache_long_line_scanspoint_before_scroll
left_fringe_width
right_fringe_width
fringes_outside_margins
scroll_bar_width
indicate_empty_lines
indicate_buffer_boundaries
fringe_indicator_alist
fringe_cursor_alist
scroll_up_aggressively
scroll_down_aggressively
cursor_type
cursor_in_non_selected_windows
These fields store the values of Lisp variables that are automatically buffer-local(see Section 12.11 [Buffer-Local Variables], page 207), whose corresponding
variable names have underscores replaced with dashes. For instance, mode_
line_format stores the value of mode-line-format.
overlays

The interval tree containing this buffer’s overlays.

last_selected_window
This is the last window that was selected with this buffer in it, or nil if thatwindow no longer displays this buffer.

E.9.2 Window Internals
The fields of a window (for a complete list, see the definition of struct window in window.h)include:frame

The frame that this window is on, as a Lisp object.

Appendix E: GNU Emacs Internals

mini

1383

Non-zero if this window is a minibuffer window, a window showing the minibuffer
or the echo area.

pseudo_window_p
Non-zero if this window is a pseudo window. A pseudo window is either a windowused to display the menu bar or the tool bar (when Emacs uses toolkits that don’t
display their own menu bar and tool bar) or the tab bar or a window showing atooltip on a tooltip frame. Pseudo windows are in general not accessible from
Lisp code.
parentInternally, Emacs arranges windows in a tree; each group of siblings has a parent
window whose area includes all the siblings. This field points to the window’s
parent in that tree, as a Lisp object. For the root window of the tree and aminibuffer window this is always nil.
Parent windows do not display buffers, and play little role in display except toshape their child windows. Emacs Lisp programs cannot directly manipulate
parent windows; they operate on the windows at the leaves of the tree, which
actually display buffers.

contents

For a leaf window and windows showing a tooltip, this is the buffer, as a Lisp
object, that the window is displaying. For an internal (“parent”) window, thisis its first child window. For a pseudo window showing a menu or tool bar thisis nil. It is also nil for a window that has been deleted.

next
prev

The next and previous sibling of this window as Lisp objects. next is nil if thewindow is the right-most or bottom-most in its group; prev is nil if it is theleft-most or top-most in its group. Whether the sibling is left/right or up/down
is determined by the horizontal field of the sibling’s parent: if it’s non-zero,
the siblings are arranged horizontally.
As a special case, next of a frame’s root window points to the frame’s minibuffer
window, provided this is not a minibuffer-only or minibuffer-less frame. On suchframes prev of the minibuffer window points to that frame’s root window. In
any other case, the root window’s next and the minibuffer window’s (if present)
prev fields are nil.

left_colThe left-hand edge of the window, measured in columns, relative to the leftmost
column (column 0) of the window’s native frame.

top_line

The top edge of the window, measured in lines, relative to the topmost line (line0) of the window’s native frame.

pixel_left
pixel_top
The left-hand and top edges of this window, measured in pixels, relative to the
top-left corner (0, 0) of the window’s native frame.
total_cols
total_lines
The total width and height of the window, measured in columns and lines
respectively. The values include scroll bars and fringes, dividers and/or the
separator line on the right of the window (if any).

Appendix E: GNU Emacs Internals

1384

pixel_width;
pixel_height;
The total width and height of the window measured in pixels.
start

A marker pointing to the position in the buffer that is the first character (in the
logical order, see Section 41.27 [Bidirectional Display], page 1250) displayed in
the window.

pointmThis is the value of point in the current buffer when this window is selected;
when it is not selected, it retains its previous value.

old_pointm
The value of pointm at the last redisplay time.
force_start
If this flag is non-nil, it says that the window has been scrolled explicitly by
the Lisp program, and the value of the window’s start was set for redisplay
to honor. This affects what the next redisplay does if point is off the screen:
instead of scrolling the window to show the text around point, it moves point toa location that is on the screen.
optional_new_startThis is similar to force_start, but the next redisplay will only obey it if pointstays visible.
start_at_line_beg
Non-nil means current value of start was the beginning of a line when it waschosen.
use_time

This is the last time that the window was selected. The function get-lruwindow uses this field.

sequence_number
A unique number assigned to this window when it was created.
last_modified
The modiff field of the window’s buffer, as of the last time a redisplay completed
in this window.
last_overlay_modified
The overlay_modiff field of the window’s buffer, as of the last time a redisplay
completed in this window.
last_point
The buffer’s value of point, as of the last time a redisplay completed in thiswindow.
last_had_star
A non-zero value means the window’s buffer was modified when the window waslast updated.
vertical_scroll_bar_type
horizontal_scroll_bar_type
The types of this window’s vertical and horizontal scroll bars.

Appendix E: GNU Emacs Internals

1385

scroll_bar_width
scroll_bar_height
The width of this window’s vertical scroll bar and the height of this window’s
horizontal scroll bar, in pixels.
left_margin_cols
right_margin_cols
The widths of the left and right margins in this window. A value of zero meansno margin.
left_fringe_width
right_fringe_width
The pixel widths of the left and right fringes in this window. A value of −1means use the values of the frame.
fringes_outside_margins
A non-zero value means the fringes outside the display margins; othersize they
are between the margin and the text.
window_end_pos
This is computed as z minus the buffer position of the last glyph in the current
matrix of the window. The value is only valid if window_end_valid is non-zero.
window_end_bytepos
The byte position corresponding to window_end_pos.
window_end_vpos
The window-relative vertical position of the line containing window_end_pos.
window_end_valid
This field is set to a non-zero value if window_end_pos and window_end_vpos
are truly valid. This is zero if nontrivial redisplay is pre-empted, since in thatcase the display that window_end_pos was computed for did not get onto thescreen.
cursor

A structure describing where the cursor is in this window.

last_cursor_vpos
The window-relative vertical position of the line showing the cursor as of thelast redisplay that finished.
phys_cursor
A structure describing where the cursor of this window physically is.
phys_cursor_type
phys_cursor_heightphys_cursor_width
The type, height, and width of the cursor that was last displayed on this window.
phys_cursor_on_pThis field is non-zero if the cursor is physically on.
cursor_off_p
Non-zero means the cursor in this window is logically off. This is used forblinking the cursor.

Appendix E: GNU Emacs Internals

1386

last_cursor_off_p
This field contains the value of cursor_off_p as of the time of the last redisplay.
must_be_updated_pThis is set to 1 during redisplay when this window must be updated.
hscroll

This is the number of columns that the display in the window is scrolled
horizontally to the left. Normally, this is 0. When only the current line ishscrolled, this describes how much the current line is scrolled.

min_hscroll
Minimum value of hscroll, set by the user via set-window-hscroll (seeSection 29.23 [Horizontal Scrolling], page 767). When only the current line ishscrolled, this describes the horizontal scrolling of lines other than the currentone.
vscroll

Vertical scroll amount, in pixels. Normally, this is 0.

dedicated
Non-nil if this window is dedicated to its buffer.
combination_limit
This window’s combination limit, meaningful only for a parent window. If this ist, then it is not allowed to delete this window and recombine its child windows
with other siblings of this window.
window_parameters
The alist of this window’s parameters.
display_table
The window’s display table, or nil if none is specified for it.
update_mode_line
Non-zero means this window’s mode line needs to be updated.
mode_line_height
header_line_height
The height in pixels of the mode line and the header line, or −1 if not known.
base_line_number
The line number of a certain position in the buffer, or zero. This is used for
displaying the line number of point in the mode line.
base_line_pos
The position in the buffer for which the line number is known, or zero meaning
none is known. If it is −1, don’t display the line number as long as the windowshows that buffer.
column_number_displayed
The column number currently displayed in this window’s mode line, or −1 ifcolumn numbers are not being displayed.
current_matrix
desired_matrix
Glyph matrices describing the current and desired display of this window.

Appendix E: GNU Emacs Internals

1387

E.9.3 Process Internals
The fields of a process (for a complete list, see the definition of struct Lisp_Process inprocess.h) include:
name

A Lisp string, the name of the process.

command

A list containing the command arguments that were used to start this process.
For a network or serial process, it is nil if the process is running or t if theprocess is stopped.

filterA Lisp function used to accept output from the process.

sentinel

A Lisp function called whenever the state of the process changes.

buffer

The associated buffer of the process.

pid

An integer, the operating system’s process ID. Pseudo-processes such as networkor serial connections use a value of 0.

childpA flag, t if this is really a child process. For a network or serial connection, it
is a plist based on the arguments to make-network-process or make-serialprocess.

mark

A marker indicating the position of the end of the last output from this processinserted into the buffer. This is often but not always the end of the buffer.

kill_without_query
If this is non-zero, killing Emacs while this process is still running does not ask
for confirmation about killing the process.
raw_status
The raw process status, as returned by the wait system call.
statusThe process status, as process-status should return it. This is a Lisp symbol,
a cons cell, or a list.

tick
update_tick
If these two fields are not equal, a change in the status of the process needs
to be reported, either by running the sentinel or by inserting a message in theprocess buffer.
pty_flagNon-zero if communication with the subprocess uses a pty; zero if it uses a pipe.

infd

The file descriptor for input from the process.

outfd

The file descriptor for output to the process.

tty_name

The name of the terminal that the subprocess is using, or nil if it is using pipes.

decode_coding_system
Coding-system for decoding the input from this process.
decoding_buf
A working buffer for decoding.
decoding_carryover
Size of carryover in decoding.

Appendix E: GNU Emacs Internals

1388

encode_coding_system
Coding-system for encoding the output to this process.
encoding_buf
A working buffer for encoding.
inherit_coding_system_flag
Flag to set coding-system of the process buffer from the coding system used
to decode process output.
type

Symbol indicating the type of process: real, network, serial.

E.10 C Integer Types
Here are some guidelines for use of integer types in the Emacs C source code. These
guidelines sometimes give competing advice; common sense is advised.
• Avoid arbitrary limits. For example, avoid int len = strlen (s); unless the length ofs is required for other reasons to fit in int range.
• Do not assume that signed integer arithmetic wraps around on overflow. This is nolonger true of Emacs porting targets: signed integer overflow has undefined behavior inpractice, and can dump core or even cause earlier or later code to behave illogically.
Unsigned overflow does wrap around reliably, modulo a power of two.
• Prefer signed types to unsigned, as code gets confusing when signed and unsigned types
are combined. Many other guidelines assume that types are signed; in the rarer cases
where unsigned types are needed, similar advice may apply to the unsigned counterparts(e.g., size_t instead of ptrdiff_t, or uintptr_t instead of intptr_t).
• Prefer int for Emacs character codes, in the range 0 .. 0x3FFFFF. More generally,
prefer int for integers known to be in int range, e.g., screen column counts.
• Prefer ptrdiff_t for sizes, i.e., for integers bounded by the maximum size of any
individual C object or by the maximum number of elements in any C array. This ispart of Emacs’s general preference for signed types. Using ptrdiff_t limits objects to
PTRDIFF_MAX bytes, but larger objects would cause trouble anyway since they would
break pointer subtraction, so this does not impose an arbitrary limit.
• Avoid ssize_t except when communicating to low-level APIs that have ssize_t-related
limitations. Although it’s equivalent to ptrdiff_t on typical platforms, ssize_t is
occasionally narrower, so using it for size-related calculations could overflow. Also,
ptrdiff_t is more ubiquitous and better-standardized, has standard printf formats,and is the basis for Emacs’s internal size-overflow checking. When using ssize_t, please
note that POSIX requires support only for values in the range −1 .. SSIZE_MAX.
• Normally, prefer intptr_t for internal representations of pointers, or for integers
bounded only by the number of objects that can exist at any given time or by the total
number of bytes that can be allocated. However, prefer uintptr_t to represent pointerarithmetic that could cross page boundaries. For example, on a machine with a 32-bit
address space an array could cross the 0x7fffffff/0x80000000 boundary, which would
cause an integer overflow when adding 1 to (intptr_t) 0x7fffffff.
• Prefer the Emacs-defined type EMACS_INT for representing values converted to or from
Emacs Lisp fixnums, as fixnum arithmetic is based on EMACS_INT.

Appendix E: GNU Emacs Internals

1389• When representing a system value (such as a file size or a count of seconds since the
Epoch), prefer the corresponding system type (e.g., off_t, time_t). Do not assume
that a system type is signed, unless this assumption is known to be safe. For example,
although off_t is always signed, time_t need not be.
• Prefer intmax_t for representing values that might be any signed integer value. A
printf-family function can print such a value via a format like "%"PRIdMAX.
• Prefer bool, false and true for booleans. Using bool can make programs easier toread and a bit faster than using int. Although it is also OK to use int, 0 and 1, thisolder style is gradually being phased out. When using bool, respect the limitations of
the replacement implementation of bool. In particular, boolean bitfields should be oftype bool_bf, not bool, so that they work correctly even when compiling Objective Cwith standard GCC.
• In bitfields, prefer unsigned int or signed int to int, as int is less portable: it might
be signed, and might not be. Single-bit bit fields should be unsigned int or bool_bf
so that their values are 0 or 1.

1390

Appendix F Standard Errors
Here is a list of the more important error symbols in standard Emacs, grouped by concept.
The list includes each symbol’s message and a cross reference to a description of how theerror can occur.
Each error symbol has a set of parent error conditions that is a list of symbols. Normallythis list includes the error symbol itself and the symbol error. Occasionally it includes
additional symbols, which are intermediate classifications, narrower than error but broader
than a single error symbol. For example, all the errors in accessing files have the condition
file-error. If we do not say here that a certain error symbol has additional error conditions,that means it has none.
As a special exception, the error symbols quit and minibuffer-quit don’t have thecondition error, because quitting is not considered an error.
Most of these error symbols are defined in C (mainly data.c), but some are defined in
Lisp. For example, the file userlock.el defines the file-locked and file-supersession
errors. Several of the specialized Lisp libraries distributed with Emacs define their own error
symbols. We do not attempt to list of all those here.
See Section 11.7.3 [Errors], page 179, for an explanation of how errors are generated andhandled.
error

The message is ‘error’. See Section 11.7.3 [Errors], page 179.

quit

The message is ‘Quit’. See Section 22.11 [Quitting], page 471.

minibuffer-quit
The message is ‘Quit’. This is a subcategory of quit. See Section 22.11[Quitting], page 471.
args-out-of-range
The message is ‘Args out of range’. This happens when trying to access anelement beyond the range of a sequence, buffer, or other container-like object.
See Chapter 6 [Sequences Arrays Vectors], page 102, and see Chapter 33 [Text],
page 878.
arith-error
The message is ‘Arithmetic error’. This occurs when trying to perform integer
division by zero. See Section 3.5 [Numeric Conversions], page 43, and see
Section 3.6 [Arithmetic Operations], page 45.
beginning-of-buffer
The message is ‘Beginning of buffer’. See Section 31.2.1 [Character Motion],
page 854.
buffer-read-only
The message is ‘Buffer is read-only’. See Section 28.7 [Read Only Buffers],
page 680.
circular-list
The message is ‘List contains a loop’. This happens when a circular structureis encountered. See Section 2.6 [Circular Objects], page 30.

Appendix F: Standard Errors

1391

cl-assertion-failed
The message is ‘Assertion failed’. This happens when the cl-assert macrofails a test. See Section “Assertions” in Common Lisp Extensions.
coding-system-error
The message is ‘Invalid coding system’. See Section 34.10.3 [Lisp and Coding
Systems], page 979.
cyclic-function-indirection
The message is ‘Symbol's chain of function indirections contains aloop’. See Section 10.1.4 [Function Indirection], page 147.
cyclic-variable-indirection
The message is ‘Symbol's chain of variable indirections contains aloop’. See Section 12.15 [Variable Aliases], page 222.
dbus-error
The message is ‘D-Bus error’. See Section “Errors and Events” in D-Bus
integration in Emacs.
end-of-buffer
The message is ‘End of buffer’. See Section 31.2.1 [Character Motion], page 854.
end-of-file
The message is ‘End of file during parsing’. Note that this is not a subcategory of file-error, because it pertains to the Lisp reader, not to file I/O. See
Section 20.3 [Input Functions], page 374.
file-already-exists
This is a subcategory of file-error. See Section 26.4 [Writing to Files],page 616.
permission-denied
This is a subcategory of file-error, which occurs when the OS doesn’t allow
Emacs to access a file or a directory for some reason.
file-date-error
This is a subcategory of file-error. It occurs when copy-file tries and fails
to set the last-modification time of the output file. See Section 26.7 [Changing
Files], page 629.
file-error
We do not list the error-strings of this error and its subcategories, because theerror message is normally constructed from the data items alone when the error
condition file-error is present. Thus, the error-strings are not very relevant.
However, these error symbols do have error-message properties, and if nodata is provided, the error-message property is used. See Chapter 26 [Files],page 608.
file-missing
This is a subcategory of file-error. It occurs when an operation attempts to
act on a file that is missing. See Section 26.7 [Changing Files], page 629.

Appendix F: Standard Errors

1392

compression-error
This is a subcategory of file-error, which results from problems handling acompressed file. See Section 16.1 [How Programs Do Loading], page 298.
file-lockedThis is a subcategory of file-error. See Section 26.5 [File Locks], page 617.
file-supersession
This is a subcategory of file-error. See Section 28.6 [Modification Time],
page 678.
file-notify-error
This is a subcategory of file-error. It happens, when a file could not bewatched for changes. See Section 42.20 [File Notifications], page 1296.
remote-file-error
This is a subcategory of file-error, which results from problems in accessing a
remote file. See Section “Remote Files” in The GNU Emacs Manual. Often, thiserror appears when timers, process filters, process sentinels or special events ingeneral try to access a remote file, and collide with another remote file operation.
In general it is a good idea to write a bug report. See Section “Bugs” in The
GNU Emacs Manual.
ftp-error
This is a subcategory of remote-file-error, which results from problems inaccessing a remote file using ftp. See Section “Remote Files” in The GNU
Emacs Manual.
invalid-function
The message is ‘Invalid function’. See Section 10.1.4 [Function Indirection],
page 147.
invalid-read-syntax
The message is usually ‘Invalid read syntax’. See Section 2.1 [Printed
Representation], page 8. This error can also be raised by commands likeeval-expression when there’s text following an expression. In that case, themessage is ‘Trailing garbage following expression’.
invalid-regexp
The message is ‘Invalid regexp’. See Section 35.3 [Regular Expressions],
page 995.
mark-inactive
The message is ‘The mark is not active now’. See Section 32.7 [The Mark],
page 873.
no-catch

The message is ‘No catch for tag’. See Section 11.7.1 [Catch and Throw],
page 177.

range-error
The message is Arithmetic range error.

Appendix F: Standard Errors

1393

overflow-error
The message is ‘Arithmetic overflow error’. This is a subcategory ofrange-error. This can happen with integers exceeding the integer-width
limit. See Section 3.1 [Integer Basics], page 38.
scan-error
The message is ‘Scan error’. This happens when certain syntax-parsing functions find invalid syntax or mismatched parentheses. Conventionally raised withthree argument: a human-readable error message, the start of the obstacle thatcannot be moved over, and the end of the obstacle. See Section 31.2.6 [List
Motion], page 861, and see Section 36.6 [Parsing Expressions], page 1030.
search-failed
The message is ‘Search failed’. See Chapter 35 [Searching and Matching],
page 993.
setting-constant
The message is ‘Attempt to set a constant symbol’. This happens when attempting to assign values to nil, t, most-positive-fixnum, most-negativefixnum, and keyword symbols. It also happens when attempting to assign
values to enable-multibyte-characters and some other symbols whose direct
assignment is not allowed for some reason. See Section 12.2 [Constant Variables],page 189.
text-read-only
The message is ‘Text is read-only’. This is a subcategory of buffer-readonly. See Section 33.19.4 [Special Properties], page 924.
undefined-color
The message is ‘Undefined color’. See Section 30.23 [Color Names], page 846.
user-error
The message is the empty string. See Section 11.7.3.1 [Signaling Errors], page 180.
user-search-failed
This is like ‘search-failed’, but doesn’t trigger the debugger, like ‘user-error’.
See Section 11.7.3.1 [Signaling Errors], page 180, and see Chapter 35 [Searchingand Matching], page 993. This is used for searching in Info files, see Section“Search Text” in Info.
void-function
The message is ‘Symbol's function definition is void’. See Section 13.9
[Function Cells], page 248.
void-variable
The message is ‘Symbol's value as variable is void’. See Section 12.7 [Accessing Variables], page 197.
wrong-number-of-arguments
The message is ‘Wrong number of arguments’. See Section 13.2.3 [Argument
List], page 234.

Appendix F: Standard Errors

1394

wrong-type-argument
The message is ‘Wrong type argument’. See Section 2.7 [Type Predicates],
page 30.
unknown-image-type
The message is ‘Cannot determine image type’. See Section 41.17 [Images],
page 1206.
inhibited-interaction
The message is ‘User interaction while inhibited’. This error is signaled
when inhibit-interaction is non-nil and a user interaction function (likeread-from-minibuffer) is called.

1395

Appendix G Standard Keymaps
In this section we list some of the more general keymaps. Many of these exist when Emacs
is first started, but some are loaded only when the respective feature is accessed.
There are many other, more specialized, maps than these; in particular those associatedwith major and minor modes. The minibuffer uses several keymaps (see Section 21.6.3[Completion Commands], page 400). For more details on keymaps, see Chapter 23 [Keymaps],
page 480.
2C-mode-map
A sparse keymap for subcommands of the prefix C-x 6.
See Section “Two-Column Editing” in The GNU Emacs Manual.
abbrev-map
A sparse keymap for subcommands of the prefix C-x a.
See Section “Defining Abbrevs” in The GNU Emacs Manual.
button-buffer-map
A sparse keymap useful for buffers containing buffers.
You may want to use this as a parent keymap. See Section 41.20 [Buttons],
page 1232.
button-map
A sparse keymap used by buttons.
ctl-x-4-map
A sparse keymap for subcommands of the prefix C-x 4.
ctl-x-5-map
A sparse keymap for subcommands of the prefix C-x 5.
ctl-x-map
A full keymap for C-x commands.
ctl-x-r-map
A sparse keymap for subcommands of the prefix C-x r.
See Section “Registers” in The GNU Emacs Manual.
esc-map

A full keymap for ESC (or Meta) commands.

function-key-map
The parent keymap of all local-function-key-map (q.v.) instances.
global-map
The full keymap containing default global key bindings.
Modes should not modify the Global map.
goto-map

A sparse keymap used for the M-g prefix key.

help-map

A sparse keymap for the keys following the help character C-h.
See Section 25.6 [Help Functions], page 602.

Helper-help-map
A full keymap used by the help utility package.
It has the same keymap in its value cell and in its function cell.

Appendix G: Standard Keymaps

1396

input-decode-map
The keymap for translating keypad and function keys.
If there are none, then it contains an empty sparse keymap. See Section 23.15[Translation Keymaps], page 504.
key-translation-map
A keymap for translating keys. This one overrides ordinary key bindings, unlike
local-function-key-map. See Section 23.15 [Translation Keymaps], page 504.
kmacro-keymap
A sparse keymap for keys that follows the C-x C-k prefix search.
See Section “Keyboard Macros” in The GNU Emacs Manual.
local-function-key-map
The keymap for translating key sequences to preferred alternatives.
If there are none, then it contains an empty sparse keymap. See Section 23.15[Translation Keymaps], page 504.
menu-bar-file-menu
menu-bar-edit-menu
menu-bar-options-menu
global-buffers-menu-map
menu-bar-tools-menu
menu-bar-help-menu
These keymaps display the main, top-level menus in the menu bar.
Some of them contain sub-menus. For example, the Edit menu contains
menu-bar-search-menu, etc. See Section 23.18.5 [Menu Bar], page 516.
minibuffer-inactive-mode-map
A full keymap used in the minibuffer when it is not active.
See Section “Editing in the Minibuffer” in The GNU Emacs Manual.
mode-line-coding-system-map
mode-line-input-method-map
mode-line-column-line-number-mode-map
These keymaps control various areas of the mode line.
See Section 24.4 [Mode Line Format], page 550.
mode-specific-map
The keymap for characters following C-c. Note, this is in the global map. Thismap is not actually mode-specific: its name was chosen to be informative in C-hb (display-bindings), where it describes the main use of the C-c prefix key.
mouse-appearance-menu-map
A sparse keymap used for the S-mouse-1 key.
mule-keymap
The global keymap used for the C-x RET prefix key.
narrow-map
A sparse keymap for subcommands of the prefix C-x n.

Appendix G: Standard Keymaps

1397

prog-mode-map
The keymap used by Prog mode.
See Section 24.2.5 [Basic Major Modes], page 536.
query-replace-map
multi-query-replace-map
A sparse keymap used for responses in query-replace and related commands;
also for y-or-n-p and map-y-or-n-p. The functions that use this map do notsupport prefix keys; they look up one event at a time. multi-query-replacemap extends query-replace-map for multi-buffer replacements. See Section 35.7
[Search and Replace], page 1016.
search-map
A sparse keymap that provides global bindings for search-related commands.
special-mode-map
The keymap used by Special mode.
See Section 24.2.5 [Basic Major Modes], page 536.
tab-prefix-map
The global keymap used for the C-x t prefix key for tab-bar related commands.
See Section “Tab Bars” in The GNU Emacs Manual.
tab-bar-map
The keymap defining the contents of the tab bar.
See Section “Tab Bars” in The GNU Emacs Manual.
tool-bar-map
The keymap defining the contents of the tool bar.
See Section 23.18.6 [Tool Bar], page 517.
universal-argument-map
A sparse keymap used while processing C-u.
See Section 22.12 [Prefix Command Arguments], page 473.
vc-prefix-map
The global keymap used for the C-x v prefix key.
x-alternatives-map
A sparse keymap used to map certain keys under graphical frames.
The function x-setup-function-keys uses this.

1398

Appendix H Standard Hooks
The following is a list of some hook variables that let you provide functions to be calledfrom within Emacs on suitable occasions.
Most of these variables have names ending with ‘-hook’. They are normal hooks, run bymeans of run-hooks. The value of such a hook is a list of functions; the functions are calledwith no arguments and their values are completely ignored. The recommended way to put a
new function on such a hook is to call add-hook. See Section 24.1 [Hooks], page 524, formore information about using hooks.
The variables whose names end in ‘-functions’ are usually abnormal hooks (some oldcode may also use the deprecated ‘-hooks’ suffix). Their values are lists of functions, butthese functions are called in a special way: they are either passed arguments, or their return
values are used in some way. The variables whose names end in ‘-function’ have single
functions as their values.
This is not an exhaustive list, it only covers the more general hooks. For example, every
major mode defines a hook named ‘modename-mode-hook’. The major mode command runs
this normal hook with run-mode-hooks as the very last thing it does. See Section 24.2.6[Mode Hooks], page 537. Most minor modes have mode hooks too.
A special feature allows you to specify expressions to evaluate if and when a file is loaded(see Section 16.10 [Hooks for Loading], page 313). That feature is not exactly a hook, butdoes a similar job.
activate-mark-hookdeactivate-mark-hook
See Section 32.7 [The Mark], page 873.
after-change-functions
before-change-functions
first-change-hook
See Section 33.34 [Change Hooks], page 961.
after-change-major-mode-hookchange-major-mode-after-body-hook
See Section 24.2.6 [Mode Hooks], page 537.
after-init-hook
before-init-hookemacs-startup-hookwindow-setup-hook
See Section 42.1.2 [Init File], page 1258.
after-insert-file-functions
write-region-annotate-functions
write-region-post-annotation-function
See Section 26.13 [Format Conversion], page 654.
after-make-frame-functions
before-make-frame-hookserver-after-make-frame-hook
See Section 30.1 [Creating Frames], page 786.

Appendix H: Standard Hooks

1399

after-save-hook
before-save-hookwrite-contents-functions
write-file-functions
See Section 26.2 [Saving Buffers], page 612.
after-setting-font-hook
Hook run after a frame’s font changes.
auto-save-hook
See Section 27.2 [Auto-Saving], page 664.
before-hack-local-variables-hookhack-local-variables-hook
See Section 12.12 [File Local Variables], page 213.
buffer-access-fontify-functions
See Section 33.19.7 [Lazy Properties], page 933.
buffer-list-update-hook
Hook run when the buffer list changes (see Section 28.8 [Buffer List], page 681).
buffer-quit-function
Function to call to quit the current buffer.
change-major-mode-hook
See Section 12.11.2 [Creating Buffer-Local], page 208.
comint-password-function
This abnormal hook permits a derived mode to supply a password for theunderlying command interpreter without prompting the user.
command-line-functions
See Section 42.1.4 [Command-Line Arguments], page 1261.
delayed-warnings-hook
The command loop runs this soon after post-command-hook (q.v.).
focus-in-hookfocus-out-hook
See Section 30.10 [Input Focus], page 824.
delete-frame-functions
after-delete-frame-functions
See Section 30.7 [Deleting Frames], page 822.
delete-terminal-functions
See Section 30.2 [Multiple Terminals], page 787.
pop-up-frame-function
split-window-preferred-function
See Section 29.13.4 [Choosing Window Options], page 736.
echo-area-clear-hook
See Section 41.4.4 [Echo Area Customization], page 1138.

Appendix H: Standard Hooks

1400

find-file-hookfind-file-not-found-functions
See Section 26.1.1 [Visiting Functions], page 608.
font-lock-extend-after-change-region-function
See Section 24.6.9.2 [Region to Refontify], page 578.
font-lock-extend-region-functions
See Section 24.6.9 [Multiline Font Lock], page 576.
font-lock-fontify-buffer-function
font-lock-fontify-region-function
font-lock-mark-block-function
font-lock-unfontify-buffer-function
font-lock-unfontify-region-function
See Section 24.6.4 [Other Font Lock Variables], page 571.
fontification-functions
See Section 41.12.7 [Automatic Face Assignment], page 1178.
frame-auto-hide-function
See Section 29.16 [Quitting Windows], page 749.
quit-window-hook
See Section 29.16 [Quitting Windows], page 749.
kill-buffer-hookkill-buffer-query-functions
See Section 28.10 [Killing Buffers], page 685.
kill-emacs-hookkill-emacs-query-functions
See Section 42.2.1 [Killing Emacs], page 1262.
menu-bar-update-hook
See Section 23.18.5 [Menu Bar], page 516.
minibuffer-setup-hookminibuffer-exit-hook
See Section 21.15 [Minibuffer Misc], page 421.
mouse-leave-buffer-hook
Hook run when the user mouse-clicks in a window.
mouse-position-function
See Section 30.16 [Mouse Position], page 835.
prefix-command-echo-keystrokes-functions
An abnormal hook run by prefix commands (such as C-u) which should returna string describing the current prefix state. For example, C-u produces ‘C-u-’and ‘C-u 1 2 3-’. Each hook function is called with no arguments and should
return a string describing the current prefix state, or nil if there’s no prefix
state. See Section 22.12 [Prefix Command Arguments], page 473.

Appendix H: Standard Hooks

1401

prefix-command-preserve-state-hook
Hook run when a prefix command needs to preserve the prefix by passing thecurrent prefix command state to the next command. For example, C-u needs topass the state to the next command when the user types C-u - or follows C-u
with a digit.
pre-redisplay-functions
Hook run in each window just before redisplaying it. See Section 41.2 [Forcing
Redisplay], page 1129.
post-command-hookpre-command-hook
See Section 22.1 [Command Overview], page 423.
post-gc-hook
See Section E.3 [Garbage Collection], page 1350.
post-self-insert-hook
See Section 24.3.2 [Keymaps and Minor Modes], page 546.
suspend-hooksuspend-resume-hooksuspend-tty-functions
resume-tty-functions
See Section 42.2.2 [Suspending Emacs], page 1263.
syntax-begin-function
syntax-propertize-extend-region-functions
syntax-propertize-function
font-lock-syntactic-face-function
See Section 24.6.8 [Syntactic Font Lock], page 575. See Section 36.4 [Syntax
Properties], page 1029.
temp-buffer-setup-hook
temp-buffer-show-function
temp-buffer-show-hook
See Section 41.8 [Temporary Displays], page 1146.
tty-setup-hook
See Section 42.1.3 [Terminal-Specific], page 1260.
window-configuration-change-hookwindow-scroll-functions
window-size-change-functions
See Section 29.28 [Window Hooks], page 779.

1402

Index
"

+

‘"’ in printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377‘"’ in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45‘+’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 997#,‘##’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15‘#$’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319‘#'’ syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244‘#(’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22‘#:’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15‘#^’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22‘#@count’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319‘#n#’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30‘#n=’ read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

, (with backquote). . . . . . . . . . . . . . . . . . . . . . . . . . . . 152,@ (with backquote) . . . . . . . . . . . . . . . . . . . . . . . . . . 152$‘$’ in display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130‘$’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 999%% . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47‘%’ in format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67&‘&’ in replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1012
&optional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234&rest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234’‘'’ for quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151(‘(’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002‘(...)’ in lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16‘(?:’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002
(emacs_env . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1373)‘)’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002*
* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46‘*’ in interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425‘*’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996*scratch* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532–- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46--disable-build-details
option to configure . . . . . . . . . . . . . . . . . . . . . . . 1347--enable-locallisppath option
to configure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347--temacs option, and dumping method . . . . . . 1346.
‘.’ in lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18‘.’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996.#, lock file names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617.elpaignore file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1306
.emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258/
/ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46/= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
/dev/tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122:
:deferred, JSONRPC keyword . . . . . . . . . . . . . . . 959:documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236:equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056
:match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056
:notification-dispatcher . . . . . . . . . . . . . . . . . . . 957:pred . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056
:repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485:request-dispatcher . . . . . . . . . . . . . . . . . . . . . . . . 957;‘;’ for commenting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10<
< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43<= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Index== . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42>
> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43>= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43?
‘?’ in character constant . . . . . . . . . . . . . . . . . . . . . . . 11
? in minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390‘?’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 997

[

1403

‘\b’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\B’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\e’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\f’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\n’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\n’ in print. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380‘\n’ in replacement . . . . . . . . . . . . . . . . . . . . . . . . . . 1012‘\r’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\s’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\s’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003‘\S’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003‘\t’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\v’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\w’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003‘\W’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003‘[’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 997[. . . ] (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361]|‘]’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 997‘|’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002^‘^’ in interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425‘^’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 998

1‘

1+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
1- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
1value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369` . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151‘ (list substitution) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151@‘@’ in interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425\‘\’ in character constant . . . . . . . . . . . . . . . . . . . . . . . 12‘\’ in display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130‘\’ in printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377‘\’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 999‘\’ in replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1012‘\’ in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20‘\’ in symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14‘\'’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004\( in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862‘\<’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\=’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\>’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\_<’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\_>’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\`’ in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004‘\a’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12‘\b’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
2C-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
2D box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1166

3
3D box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1166

IndexAabbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
abbrev properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
abbrev table properties . . . . . . . . . . . . . . . . . . . . . . 1072
abbrev tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
abbrev tables in modes . . . . . . . . . . . . . . . . . . . . . . . 529
abbrev-all-caps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
abbrev-expand-function . . . . . . . . . . . . . . . . . . . . 1070
abbrev-expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
abbrev-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
abbrev-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
abbrev-insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
abbrev-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395
abbrev-minor-mode-table-alist . . . . . . . . . . . . 1071
abbrev-prefix-mark . . . . . . . . . . . . . . . . . . . . . . . . 1069
abbrev-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1071
abbrev-start-location . . . . . . . . . . . . . . . . . . . . . 1070
abbrev-start-location-buffer . . . . . . . . . . . . . 1070
abbrev-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
abbrev-table-get . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072
abbrev-table-name-list . . . . . . . . . . . . . . . . . . . . 1067
abbrev-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
abbrev-table-put . . . . . . . . . . . . . . . . . . . . . . . . . . . 1072
abbreviate-file-name . . . . . . . . . . . . . . . . . . . . . . . 639
abbreviated file names . . . . . . . . . . . . . . . . . . . . . . . . 638
abbrevs, looking up and expanding . . . . . . . . . . . 1069
abbrevs-changed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
abnormal hook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
abort-recursive-edit . . . . . . . . . . . . . . . . . . . . . . . 476
aborting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
abs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
absolute edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
absolute file name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
absolute frame edges . . . . . . . . . . . . . . . . . . . . . . . . . . 795
absolute frame position . . . . . . . . . . . . . . . . . . . . . . . 795
absolute position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
accept input from processes . . . . . . . . . . . . . . . . . . 1104
accept-change-group . . . . . . . . . . . . . . . . . . . . . . . . 960
accept-process-output . . . . . . . . . . . . . . . . . . . . . 1104
access control list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
access minibuffer contents . . . . . . . . . . . . . . . . . . . . . 419
access-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620
accessibility of a file. . . . . . . . . . . . . . . . . . . . . . . . . . . 619
accessible portion (of a buffer) . . . . . . . . . . . . . . . . 865
accessible-keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . 507
accessing documentation strings . . . . . . . . . . . . . . . 596
accessing hash tables . . . . . . . . . . . . . . . . . . . . . . . . . . 129
accessing plist properties . . . . . . . . . . . . . . . . . . . . . . 100
ACL entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
acos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
action (button property) . . . . . . . . . . . . . . . . . . . . 1232
action alist for buffer display . . . . . . . . . . . . . . . . . . 730
action function, for buffer display . . . . . . . . . . . . . 726
action, customization keyword . . . . . . . . . . . . . . . 292
activate-change-group . . . . . . . . . . . . . . . . . . . . . . 960
activate-mark-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 876
active display table . . . . . . . . . . . . . . . . . . . . . . . . . . 1244
active keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

1404

active keymap, controlling . . . . . . . . . . . . . . . . . . . . 491
active minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
active-minibuffer-window . . . . . . . . . . . . . . . . . . . 418
ad-activate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
adaptive-fill-first-line-regexp . . . . . . . . . . . 905
adaptive-fill-function . . . . . . . . . . . . . . . . . . . . . 905
adaptive-fill-mode . . . . . . . . . . . . . . . . . . . . . . . . . . 904
adaptive-fill-regexp . . . . . . . . . . . . . . . . . . . . . . . 905
add-display-text-property . . . . . . . . . . . . . . . . 1199
add-face-text-property . . . . . . . . . . . . . . . . . . . . . 920
add-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
add-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
add-name-to-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
add-text-properties . . . . . . . . . . . . . . . . . . . . . . . . 919
add-to-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
add-to-invisibility-spec . . . . . . . . . . . . . . . . . . 1143
add-to-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
add-to-ordered-list. . . . . . . . . . . . . . . . . . . . . . . . . . 87
add-variable-watcher . . . . . . . . . . . . . . . . . . . . . . . 200
address field of register . . . . . . . . . . . . . . . . . . . . . . . . . 16
adjust-window-trailing-edge . . . . . . . . . . . . . . . 704
adjusting point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
advertised binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599
advertised-calling-convention(declare spec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
advice, add and remove . . . . . . . . . . . . . . . . . . . . . . . 253
advice-add . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
advice-eval-interactive-spec . . . . . . . . . . . . . . 255
advice-function-mapc . . . . . . . . . . . . . . . . . . . . . . . 255
advice-function-member-p . . . . . . . . . . . . . . . . . . . 255
advice-mapc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
advice-member-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
advice-remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
advices, porting from defadvice . . . . . . . . . . . . . . 258
advising functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
advising named functions . . . . . . . . . . . . . . . . . . . . . 255
AEAD cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
affixation-function, in completion . . . . . . . . . . 410
after-change notifier, fortree-sitter parse-tree . . . . . . . . . . . . . . . . . . . . . . . 1045
after-change-functions . . . . . . . . . . . . . . . . . . . . . 961
after-change-major-mode-hook . . . . . . . . . . . . . . 538
after-delete-frame-functions . . . . . . . . . . . . . . 822
after-find-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
after-focus-change-function . . . . . . . . . . . . . . . 827
after-init-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
after-init-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256
after-insert-file-functions . . . . . . . . . . . . . . . 658
after-load-functions . . . . . . . . . . . . . . . . . . . . . . . 314
after-make-frame-functions . . . . . . . . . . . . . . . . 786
after-pdump-load-hook . . . . . . . . . . . . . . . . . . . . . 1348
after-revert-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
after-save-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614
after-setting-font-hook . . . . . . . . . . . . . . . . . . . 1399
after-string (overlay property) . . . . . . . . . . . . . 1156
alias, for coding systems . . . . . . . . . . . . . . . . . . . . . . 978alias, for faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
alias, for functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Indexalias, for variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
aligning header line, when line
numbers are displayed . . . . . . . . . . . . . . . . . . . . . 1202
alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
alist vs. plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
alist-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
all-completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
all-threads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
allow-no-window, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
alnum character class, regexp . . . . . . . . . . . . . . . . 1000
alpha character class, regexp . . . . . . . . . . . . . . . . . 1000
alpha, a frame parameter . . . . . . . . . . . . . . . . . . . . . 819
alpha-background, a frame parameter . . . . . . . . 819
alt characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
alternative commands, defining. . . . . . . . . . . . . . . . 431
always . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
amalgamating commands, and undo . . . . . . . . . . . 897
amalgamating-undo-limit . . . . . . . . . . . . . . . . . . . . 897
ancestor directory of file . . . . . . . . . . . . . . . . . . . . . . 647
and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
annotation-function, in completion . . . . . . . . . . 410
anonymous face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
anonymous function . . . . . . . . . . . . . . . . . . . . . . . . . . 243
anonymous node, tree-sitter . . . . . . . . . . . . . . . . . . 1041
apostrophe for quoting . . . . . . . . . . . . . . . . . . . . . . . . 151
apostrophe, quoting in
documentation strings . . . . . . . . . . . . . . . . . . . . . 1339
append. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
append-to-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616
apply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
apply, and debugging . . . . . . . . . . . . . . . . . . . . . . . . . 343
apply-partially . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
applying customizations. . . . . . . . . . . . . . . . . . . . . . . 294
apropos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602
archive web server . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308
aref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
args, customization keyword . . . . . . . . . . . . . . . . . . 290
argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
argument binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
argument lists, features . . . . . . . . . . . . . . . . . . . . . . . 234
arguments for shell commands . . . . . . . . . . . . . . . 1080
arguments, interactive entry . . . . . . . . . . . . . . . . . . 424
arguments, reading . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
argv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
arith-error example . . . . . . . . . . . . . . . . . . . . . . . . . 184
arith-error in division . . . . . . . . . . . . . . . . . . . . . . . . 46
arithmetic operations . . . . . . . . . . . . . . . . . . . . . . . . . . 45
arithmetic shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
array elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
arrayp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
ascii character class, regexp . . . . . . . . . . . . . . . . . . 1000
ascii-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
ASCII character codes . . . . . . . . . . . . . . . . . . . . . . . . . . 11
ASCII control characters . . . . . . . . . . . . . . . . . . . . . 1242
aset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

1405

ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
asin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
ask-user-about-lock . . . . . . . . . . . . . . . . . . . . . . . . 618
ask-user-about-supersession-threat . . . . . . . 679
asking the user questions . . . . . . . . . . . . . . . . . . . . . . 413
assoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
assoc-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
assoc-delete-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
assoc-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
association list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
assq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
assq-delete-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
asynchronous native compilation, disable . . . . . . 331
asynchronous subprocess . . . . . . . . . . . . . . . . . . . . . 1086
atan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
atomic changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 959
atomic windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
atoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
attributes of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
Auto Fill mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905
auto-coding-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . 984
auto-coding-functions . . . . . . . . . . . . . . . . . . . . . . 985
auto-coding-regexp-alist . . . . . . . . . . . . . . . . . . . 983
auto-fill-chars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905
auto-fill-function . . . . . . . . . . . . . . . . . . . . . . . . . . 905
auto-hide-function, a frame parameter . . . . . . 813
auto-hscroll-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 768
auto-lower, a frame parameter . . . . . . . . . . . . . . . 815
auto-mode-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
auto-raise, a frame parameter . . . . . . . . . . . . . . . 814
auto-raise-tool-bar-buttons . . . . . . . . . . . . . . . 520
auto-resize-tool-bars . . . . . . . . . . . . . . . . . . . . . . 520
auto-save-default . . . . . . . . . . . . . . . . . . . . . . . . . . . 666
auto-save-file-name-p . . . . . . . . . . . . . . . . . . . . . . 665
auto-save-file-name-transforms . . . . . . . . . . . . 664
auto-save-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666
auto-save-interval . . . . . . . . . . . . . . . . . . . . . . . . . . 666
auto-save-list-file-name . . . . . . . . . . . . . . . . . . . 667
auto-save-list-file-prefix . . . . . . . . . . . . . . . . 667
auto-save-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
auto-save-timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . 666
auto-save-visited-file-name . . . . . . . . . . . . . . . 665
auto-selection of window . . . . . . . . . . . . . . . . . . . . . . 773
auto-window-vscroll . . . . . . . . . . . . . . . . . . . . . . . . 767
autoload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
autoload by prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
autoload cookie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
autoload cookie, and safe values of variable . . . . 215
autoload errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
autoload object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
autoload, when to use . . . . . . . . . . . . . . . . . . . . . . . . . 307
autoload-compute-prefixes. . . . . . . . . . . . . . . . . . 307
autoload-do-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
autoloadp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
automatic face assignment . . . . . . . . . . . . . . . . . . . 1178
automatically buffer-local . . . . . . . . . . . . . . . . . . . . . 207

IndexB
back-to-indentation . . . . . . . . . . . . . . . . . . . . . . . . 915
background-color, a frame parameter . . . . . . . . 819
background-mode, a frame parameter . . . . . . . . . 818
backing store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
backquote (list substitution) . . . . . . . . . . . . . . . . . . 151
backquote-style patterns . . . . . . . . . . . . . . . . . . . . . . 171
backslash in character constants . . . . . . . . . . . . . . . . 12
backslash in regular expressions . . . . . . . . . . . . . . 1001
backslash in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
backslash in symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
backspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
backtrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
backtrace buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
backtrace from emacsclient’s --eval . . . . . . . . . . 334
backtrace of thread . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
backtrace-debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
backtrace-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
backtrace-on-error-noninteractive . . . . . . . . 342
backtrace-on-redisplay-error . . . . . . . . . . . . . . 336
backtracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
backtracking and POSIX
regular expressions . . . . . . . . . . . . . . . . . . . . . . . . 1011
backtracking and regular expressions . . . . . . . . . . 996
backup file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
backup files, rename or copy . . . . . . . . . . . . . . . . . . 661
backup-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
backup-by-copying . . . . . . . . . . . . . . . . . . . . . . . . . . . 661
backup-by-copying-when-linked . . . . . . . . . . . . . 661
backup-by-copying-when-mismatch . . . . . . . . . . . 661
backup-by-copying-whenprivileged-mismatch . . . . . . . . . . . . . . . . . . . . . . 661
backup-directory-alist . . . . . . . . . . . . . . . . . . . . . 660
backup-enable-predicate . . . . . . . . . . . . . . . . . . . . 660
backup-file-name-p . . . . . . . . . . . . . . . . . . . . . . . . . . 663
backup-inhibited . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660
backups and auto-saving . . . . . . . . . . . . . . . . . . . . . . 659
backward-button . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
backward-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
backward-delete-char-untabify . . . . . . . . . . . . . 887
backward-delete-char-untabify-method . . . . . 887
backward-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
backward-prefix-chars . . . . . . . . . . . . . . . . . . . . . 1030
backward-sexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862
backward-to-indentation . . . . . . . . . . . . . . . . . . . . 915
backward-up-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
backward-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
backward-word-strictly . . . . . . . . . . . . . . . . . . . . . 856
balance-windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
balance-windows-area . . . . . . . . . . . . . . . . . . . . . . . 706
balanced parenthesis motion . . . . . . . . . . . . . . . . . . 861
balancing parentheses . . . . . . . . . . . . . . . . . . . . . . . . 1241
balancing window sizes. . . . . . . . . . . . . . . . . . . . . . . . 706
bare symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
bare-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
barf-if-buffer-read-only . . . . . . . . . . . . . . . . . . . 681
base 64 encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943
base buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

1406

base coding system . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
base direction of a paragraph . . . . . . . . . . . . . . . . 1251
base for reading an integer . . . . . . . . . . . . . . . . . . . . . 38
base location, package archive . . . . . . . . . . . . . . . . 1307
base remapping, faces . . . . . . . . . . . . . . . . . . . . . . . . 1176
base type, in bindat specification . . . . . . . . . . . . . 1125
base64-decode-region . . . . . . . . . . . . . . . . . . . . . . . 943
base64-decode-string . . . . . . . . . . . . . . . . . . . . . . . 944
base64-encode-region . . . . . . . . . . . . . . . . . . . . . . . 943
base64-encode-string . . . . . . . . . . . . . . . . . . . . . . . 943
base64url-encode-region . . . . . . . . . . . . . . . . . . . . 943
base64url-encode-string . . . . . . . . . . . . . . . . . . . . 943
basic code (of input character) . . . . . . . . . . . . . . . . 440
basic faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1178
batch mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
batch-byte-compile . . . . . . . . . . . . . . . . . . . . . . . . . . 318
batch-native-compile . . . . . . . . . . . . . . . . . . . . . . . 328
baud, in serial connections . . . . . . . . . . . . . . . . . . . 1123
baud-rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
beep. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
before point, insertion . . . . . . . . . . . . . . . . . . . . . . . . 882
before-change-functions . . . . . . . . . . . . . . . . . . . . 961
before-hack-local-variables-hook . . . . . . . . . 215
before-init-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
before-init-time . . . . . . . . . . . . . . . . . . . . . . . . . . . 1255
before-make-frame-hook . . . . . . . . . . . . . . . . . . . . . 786
before-revert-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 668
before-save-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614
before-string (overlay property) . . . . . . . . . . . . 1156
beginning of line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
beginning of line in regexp . . . . . . . . . . . . . . . . . . . . 999
beginning-of-buffer . . . . . . . . . . . . . . . . . . . . . . . . 856
beginning-of-defun . . . . . . . . . . . . . . . . . . . . . . . . . . 862
beginning-of-defun-function . . . . . . . . . . . . . . . 862
beginning-of-line . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1247
bell character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
benchmark.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
best practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331
bidi-display-reordering . . . . . . . . . . . . . . . . . . . 1250
bidi-find-overridden-directionality . . . . . 1253
bidi-paragraph-direction . . . . . . . . . . . . . . . . . . 1251
bidi-paragraph-separate-re . . . . . . . . . . . . . . . 1251
bidi-paragraph-start-re . . . . . . . . . . . . . . . . . . . 1251
bidi-string-mark-left-to-right . . . . . . . . . . . 1253
bidirectional class of characters . . . . . . . . . . . . . . . 969
bidirectional display . . . . . . . . . . . . . . . . . . . . . . . . . 1250
bidirectional reordering . . . . . . . . . . . . . . . . . . . . . . 1250
big endian, in bindat specification . . . . . . . . . . . . 1125
bignum range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
bignump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
binary coding system . . . . . . . . . . . . . . . . . . . . . . . . . 977
binary I/O in batch mode . . . . . . . . . . . . . . . . . . . . . 375
bindat computed types . . . . . . . . . . . . . . . . . . . . . . 1127
bindat functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1127
bindat packing and unpacking into
arbitrary types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1128

Indexbindat type expression . . . . . . . . . . . . . . . . . . . . . . . 1125
bindat types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1125
bindat, define new type forms . . . . . . . . . . . . . . . . 1128
bindat-defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1128
bindat-get-field . . . . . . . . . . . . . . . . . . . . . . . . . . . 1127
bindat-ip-to-string . . . . . . . . . . . . . . . . . . . . . . . 1127
bindat-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1127
bindat-pack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1127
bindat-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1125
bindat-unpack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1127
binding arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
binding local variables . . . . . . . . . . . . . . . . . . . . . . . . 190
binding of a key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
bitmap-spec-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
bitmaps, fringe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
bitwise arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
blink-cursor-alist . . . . . . . . . . . . . . . . . . . . . . . . . . 818
blink-matching-delay . . . . . . . . . . . . . . . . . . . . . . 1241
blink-matching-open . . . . . . . . . . . . . . . . . . . . . . . 1241
blink-matching-paren . . . . . . . . . . . . . . . . . . . . . . 1241
blink-matching-paren-distance . . . . . . . . . . . . 1241
blink-paren-function . . . . . . . . . . . . . . . . . . . . . . 1241
blinking parentheses . . . . . . . . . . . . . . . . . . . . . . . . . 1241
bobp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
body height of a window . . . . . . . . . . . . . . . . . . . . . . 700
body of a window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691
body of function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
body size of a window . . . . . . . . . . . . . . . . . . . . . . . . 701
body width of a window . . . . . . . . . . . . . . . . . . . . . . 701
body-function, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
bolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
bool-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
bool-vector length . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
bool-vector-count-consecutive . . . . . . . . . . . . . 122
bool-vector-count-population . . . . . . . . . . . . . . 122
bool-vector-exclusive-or . . . . . . . . . . . . . . . . . . . 122
bool-vector-intersection . . . . . . . . . . . . . . . . . . . 122
bool-vector-not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
bool-vector-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
bool-vector-set-difference . . . . . . . . . . . . . . . . 122
bool-vector-subsetp . . . . . . . . . . . . . . . . . . . . . . . . 122
bool-vector-union . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Bool-vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
boolean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
booleanp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
bootstrapping Emacs . . . . . . . . . . . . . . . . . . . . . . . . 1346
border-color, a frame parameter . . . . . . . . . . . . . 820
border-width, a frame parameter . . . . . . . . . . . . . 810
bottom dividers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
bottom-divider, prefix key . . . . . . . . . . . . . . . . . . . 462
bottom-divider-width, a frame parameter . . . . 811
bottom-visible, a frame parameter . . . . . . . . . . . 814
boundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
box diagrams, for lists . . . . . . . . . . . . . . . . . . . . . . . . . 16
box face attribute, and display properties . . . 1200
break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
breakpoints (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 350

1407

bucket (in obarray) . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
buffer boundaries, indicating . . . . . . . . . . . . . . . . . 1190
buffer contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
buffer display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
buffer display action alist . . . . . . . . . . . . . . . . . . . . . 730
buffer display action function . . . . . . . . . . . . . . . . . 726
buffer display action functions, precedence . . . . 738
buffer display conventions . . . . . . . . . . . . . . . . . . . . . 743
buffer display display action. . . . . . . . . . . . . . . . . . . 724
buffer file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
buffer gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688
buffer input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
buffer internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1378
buffer list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681
buffer modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677
buffer names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
buffer output stream . . . . . . . . . . . . . . . . . . . . . . . . . . 375
buffer point changed by Edebug . . . . . . . . . . . . . . . 357
buffer portion as string . . . . . . . . . . . . . . . . . . . . . . . 879
buffer position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
buffer text notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
buffer, read-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
buffer-access-fontified-property . . . . . . . . . 934
buffer-access-fontify-functions . . . . . . . . . . . 933
buffer-auto-save-file-format . . . . . . . . . . . . . . 657
buffer-auto-save-file-name . . . . . . . . . . . . . . . . 664
buffer-backed-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
buffer-base-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 688
buffer-button-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
buffer-chars-modified-tick . . . . . . . . . . . . . . . . 678
buffer-disable-undo . . . . . . . . . . . . . . . . . . . . . . . . 898
buffer-display-count . . . . . . . . . . . . . . . . . . . . . . . 720
buffer-display-table . . . . . . . . . . . . . . . . . . . . . . 1245
buffer-display-time . . . . . . . . . . . . . . . . . . . . . . . . 720
buffer-enable-undo . . . . . . . . . . . . . . . . . . . . . . . . . . 898
buffer-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
buffer-file-coding-system. . . . . . . . . . . . . . . . . . 978buffer-file-format . . . . . . . . . . . . . . . . . . . . . . . . . . 656
buffer-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
buffer-file-number . . . . . . . . . . . . . . . . . . . . . . . . . . 676
buffer-file-truename . . . . . . . . . . . . . . . . . . . . . . . 676
buffer-hash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
buffer-invisibility-spec . . . . . . . . . . . . . . . . . . 1143
buffer-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681
buffer-list, a frame parameter . . . . . . . . . . . . . . 812
buffer-list-update-hook . . . . . . . . . . . . . . 683, 1399
buffer-list-update-hook in
temporary buffers . . . . . . . . . . . . . . . . . . . . . . . . . . 673
buffer-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687
buffer-local variables . . . . . . . . . . . . . . . . . . . . . . . . . . 207
buffer-local variables in modes . . . . . . . . . . . . . . . . 530
buffer-local-boundp . . . . . . . . . . . . . . . . . . . . . . . . 210
buffer-local-restore-state . . . . . . . . . . . . . . . . 550
buffer-local-set-state . . . . . . . . . . . . . . . . . . . . . 550
buffer-local-value . . . . . . . . . . . . . . . . . . . . . . . . . . 210
buffer-local-variables . . . . . . . . . . . . . . . . . . . . . 210
buffer-match-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683

Indexbuffer-modified-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 677
buffer-modified-tick . . . . . . . . . . . . . . . . . . . . . . . 678
buffer-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
buffer-name-history . . . . . . . . . . . . . . . . . . . . . . . . 394
buffer-narrowed-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
buffer-offer-save . . . . . . . . . . . . . . . . . . . . . . . . . . . 686
buffer-predicate, a frame parameter . . . . . . . . 812
buffer-quit-function . . . . . . . . . . . . . . . . . . . . . . 1399
buffer-read-only . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
buffer-save-without-query. . . . . . . . . . . . . . . . . . 687
buffer-saved-size . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
buffer-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
buffer-stale-function . . . . . . . . . . . . . . . . . . . . . . 669
buffer-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880
buffer-substring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
buffer-substring-no-properties . . . . . . . . . . . . 880
buffer-substring-with-bidi-context . . . . . . 1254
buffer-swap-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688
buffer-text-pixel-size . . . . . . . . . . . . . . . . . . . . 1161
buffer-undo-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896
bufferp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
bufferpos-to-filepos . . . . . . . . . . . . . . . . . . . . . . . 964
buffers to display on frame . . . . . . . . . . . . . . . . . . . . 812
buffers without undo information . . . . . . . . . . . . . 674
buffers, controlled in windows . . . . . . . . . . . . . . . . . 720
buffers, creating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
buffers, killing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
bugs in this manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
build details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
building Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
building lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
built-in function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
bump-use-time, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
bury-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
butlast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
button (button property) . . . . . . . . . . . . . . . . . . . . 1233
button buffer commands . . . . . . . . . . . . . . . . . . . . . 1235
button properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232
button types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233
button-activate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
button-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-down event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
button-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
button-face, customization keyword . . . . . . . . . . 292
button-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
button-has-type-p . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232
button-prefix, customization keyword . . . . . . . 292
button-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
button-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
button-suffix, customization keyword . . . . . . . 292
button-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-type-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-type-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
button-type-subtype-p . . . . . . . . . . . . . . . . . . . . . 1235

1408

buttonize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
buttons in buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232
byte compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
byte compiler warnings, how to avoid . . . . . . . . 1337
byte packing and unpacking. . . . . . . . . . . . . . . . . . 1124
byte to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
byte-boolean-vars . . . . . . . . . . . . . . . . . . . . . 223, 1358
byte-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
byte-code function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
byte-code object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
byte-code-function-p . . . . . . . . . . . . . . . . . . . . . . . 232
byte-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
byte-compile and byte-optimize, advising . . . 259
byte-compile-debug . . . . . . . . . . . . . . . . . . . . . . . . . . 316
byte-compile-dynamic . . . . . . . . . . . . . . . . . . . . . . . 320
byte-compile-dynamic-docstrings . . . . . . . . . . . 319
byte-compile-error-on-warn . . . . . . . . . . . . . . . . 322
byte-compile-file . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
byte-compiler errors . . . . . . . . . . . . . . . . . . . . . . . . . . 321
byte-compiler warnings . . . . . . . . . . . . . . . . . . . . . . . 321
byte-compiling macros . . . . . . . . . . . . . . . . . . . . . . . . 270
byte-compiling require . . . . . . . . . . . . . . . . . . . . . . . 309
byte-recompile-directory . . . . . . . . . . . . . . . . . . . 318
byte-to-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964
byte-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
bytesize, in serial connections . . . . . . . . . . . . . . . . 1123

C
C programming language . . . . . . . . . . . . . . . . . . . . 1355
C-c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
C-h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-M-x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
C-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x C-a C-m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
C-x RET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
C-x X = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
caaaar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caaadr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caaar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caadar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caaddr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caadr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cadaar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cadadr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cadar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caddar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cadddr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
caddr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cadr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Indexcalendrical computations . . . . . . . . . . . . . . . . . . . . . 1280
calendrical information . . . . . . . . . . . . . . . . . . . . . . 1273
call stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
call-interactively . . . . . . . . . . . . . . . . . . . . . . . . . . 433
call-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082
call-process, command-line
arguments from minibuffer. . . . . . . . . . . . . . . . . 1080
call-process-region . . . . . . . . . . . . . . . . . . . . . . . 1084
call-process-shell-command . . . . . . . . . . . . . . . 1085
call-shell-region . . . . . . . . . . . . . . . . . . . . . . . . . . 1085
called-interactively-p . . . . . . . . . . . . . . . . . . . . . 435
calling a function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
cancel-change-group . . . . . . . . . . . . . . . . . . . . . . . . 960
cancel-debug-on-entry . . . . . . . . . . . . . . . . . . . . . . 337
cancel-debug-on-variable-change . . . . . . . . . . . 337
cancel-timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284
canonical character height. . . . . . . . . . . . . . . . . . . . . 797
canonical character width . . . . . . . . . . . . . . . . . . . . . 797
capitalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
capitalize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
capitalize-region . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
capitalize-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
caption bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
capturing, tree-sitter node . . . . . . . . . . . . . . . . . . . 1052
car . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
car-safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
case conversion in buffers . . . . . . . . . . . . . . . . . . . . . 916
case conversion in Lisp . . . . . . . . . . . . . . . . . . . . . . . . . 72
case in replacements . . . . . . . . . . . . . . . . . . . . . . . . . 1012
case-fold, text property . . . . . . . . . . . . . . . . . . . . . 389
case-fold-search . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
case-replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
case-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
catch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
catch-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
categories of characters . . . . . . . . . . . . . . . . . . . . . . 1036
category (overlay property) . . . . . . . . . . . . . . . . . 1154
category (text property) . . . . . . . . . . . . . . . . . . . . . 924
category set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1036
category table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1036
category, in completion . . . . . . . . . . . . . . . . . . . . . . 410
category, regexp search for . . . . . . . . . . . . . . . . . . . 1003
category-docstring . . . . . . . . . . . . . . . . . . . . . . . . 1037
category-set-mnemonics . . . . . . . . . . . . . . . . . . . . 1038
category-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1037
category-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1037
cdaaar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdaadr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdaar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdadar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdaddr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdadr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cddaar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cddadr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cddar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdddar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cddddr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811409

cdddr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cddr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
cdr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
cdr-safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
ceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
centering point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
change hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961
change hooks for a character . . . . . . . . . . . . . . . . . . 930
change load-path at configure time . . . . . . . . . . 1347
change-major-mode-after-body-hook . . . . . . . . 538
change-major-mode-hook . . . . . . . . . . . . . . . . . . . . . 211
changing key bindings. . . . . . . . . . . . . . . . . . . . . . . . . 497
changing text properties . . . . . . . . . . . . . . . . . . . . . . 919
changing to another buffer . . . . . . . . . . . . . . . . . . . . 671
changing window size . . . . . . . . . . . . . . . . . . . . . . . . . 703
char-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
char-before . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
char-category-set . . . . . . . . . . . . . . . . . . . . . . . . . . 1037
char-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
char-code-property-description . . . . . . . . . . . . 972
char-displayable-p . . . . . . . . . . . . . . . . . . . . . . . . 1184
char-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
char-from-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
char-or-string-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
char-property-alias-alist. . . . . . . . . . . . . . . . . . 918
char-script-table . . . . . . . . . . . . . . . . . . . . . . . . . . . 972
char-syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028
char-table length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
char-table-extra-slot . . . . . . . . . . . . . . . . . . . . . . 120
char-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
char-table-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
char-table-range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
char-table-subtype . . . . . . . . . . . . . . . . . . . . . . . . . . 120
char-tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
char-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
char-uppercase-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158
char-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158
char-width-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972
character alternative (in regexp) . . . . . . . . . . . . . . 997
character arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
character case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
character categories . . . . . . . . . . . . . . . . . . . . . . . . . . 1036
character classes in regexp . . . . . . . . . . . . . . . . . . . 1000
character code conversion . . . . . . . . . . . . . . . . . . . . . 977
character codepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
character codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967
character event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
character insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884
character printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
character properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
character set, searching . . . . . . . . . . . . . . . . . . . . . . . 974
character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
character to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
character translation tables . . . . . . . . . . . . . . . . . . . 975
character width on display . . . . . . . . . . . . . . . . . . . 1157
characterp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
characters for interactive codes . . . . . . . . . . . . . . . . 427

Indexcharacters, multi-byte . . . . . . . . . . . . . . . . . . . . . . . . . 963
characters, representation in
buffers and strings . . . . . . . . . . . . . . . . . . . . . . . . . . 963
charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
charset, coding systems to encode . . . . . . . . . . . . . 980
charset, text property on buffer text . . . . . . . . . 989
charset, text property on strings . . . . . . . . . . . . . 989
charset-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975
charset-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
charset-plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
charset-priority-list . . . . . . . . . . . . . . . . . . . . . . 973
charsetp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
charsets supported by a coding system . . . . . . . . 981
check-coding-system . . . . . . . . . . . . . . . . . . . . . . . . 980
check-coding-systems-region . . . . . . . . . . . . . . . 981
check-declare-directory . . . . . . . . . . . . . . . . . . . . 266
check-declare-file . . . . . . . . . . . . . . . . . . . . . . . . . . 266
checkdoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331
checkdoc-current-buffer . . . . . . . . . . . . . . . . . . . 1331
checkdoc-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331
checkdoc-minor-mode . . . . . . . . . . . . . . . . . . . . . . . 1337
checkdoc-package-keywords . . . . . . . . . . . . . . . . 1344
checkdoc-package-keywords-flag . . . . . . . . . . . 1344
child frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
child process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
child window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
child-frame-border-width, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
child-frame-parameters, a buffer
display action alist entry . . . . . . . . . . . . . . . . . . . . 735
choice, customization types . . . . . . . . . . . . . . . . . . . 291
cipher, AEAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
cipher, symmetric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
circular list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
circular structure, read syntax. . . . . . . . . . . . . . . . . . 30
cl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
cl-call-next-method . . . . . . . . . . . . . . . . . . . . . . . . 248
cl-defgeneric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
cl-defmethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
cl-next-method-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
cl-old-struct-compat-mode. . . . . . . . . . . . . . . . . . 126
CL note—allocate more storage . . . . . . . . . . . . . . 1350
CL note—case of letters . . . . . . . . . . . . . . . . . . . . . . . . 14
CL note—default optional arg. . . . . . . . . . . . . . . . . 234
CL note—interning existing symbol . . . . . . . . . . . 137
CL note—lack union, intersection . . . . . . . . . . . . 91
CL note—no continuable errors . . . . . . . . . . . . . . . 181
CL note—no setf functions . . . . . . . . . . . . . . . . . . . 227
CL note—only throw in Emacs. . . . . . . . . . . . . . . . 178
CL note—rplaca vs setcar . . . . . . . . . . . . . . . . . . . . 88
CL note—special forms compared . . . . . . . . . . . . . 150
CL note—symbol in obarrays . . . . . . . . . . . . . . . . . 136
classification of file types . . . . . . . . . . . . . . . . . . . . . . 621
classifying events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
clean-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
cleanup forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
clear-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . 1066
clear-image-cache . . . . . . . . . . . . . . . . . . . . . . . . . . 1225

1410

clear-message-function . . . . . . . . . . . . . . . . . . . . 1132
clear-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
clear-this-command-keys . . . . . . . . . . . . . . . . . . . . 437
clear-visited-file-modtime . . . . . . . . . . . . . . . . 679
click event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
clickable buttons in buffers . . . . . . . . . . . . . . . . . . . 1232
clickable text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934
clipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
clipboard support (for MS-Windows) . . . . . . . . . . 840
clone-indirect-buffer . . . . . . . . . . . . . . . . . . . . . . 687
clone-of, a window parameter . . . . . . . . . . . . . . . . 778
closepath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
closure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
closures, example of using . . . . . . . . . . . . . . . . . . . . . 204
CLOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
clrhash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
coded character set . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
codepoint, largest value . . . . . . . . . . . . . . . . . . . . . . . 968
codes, interactive, description of. . . . . . . . . . . . . . . 427
codespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
coding conventions in Emacs Lisp . . . . . . . . . . . . 1331
coding standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1331
coding system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976
coding system for operation . . . . . . . . . . . . . . . . . . . 986
coding system, automatically determined . . . . . . 983
coding system, validity check . . . . . . . . . . . . . . . . . . 980
coding systems for encoding a string . . . . . . . . . . 980
coding systems for encoding region . . . . . . . . . . . . 980
coding systems, priority . . . . . . . . . . . . . . . . . . . . . . . 987
coding-system-aliases . . . . . . . . . . . . . . . . . . . . . . 978coding-system-change-eol-conversion . . . . . . 980
coding-system-change-text-conversion . . . . . 980
coding-system-charset-list . . . . . . . . . . . . . . . . 981
coding-system-eol-type . . . . . . . . . . . . . . . . . . . . . 980
coding-system-for-read . . . . . . . . . . . . . . . . . . . . . 986
coding-system-for-write . . . . . . . . . . . . . . . . . . . . 987
coding-system-get . . . . . . . . . . . . . . . . . . . . . . . . . . . 978coding-system-list . . . . . . . . . . . . . . . . . . . . . . . . . . 979
coding-system-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 979
coding-system-priority-list . . . . . . . . . . . . . . . 987
coding-system-require-warning . . . . . . . . . . . . . 987
collapse-delayed-warnings . . . . . . . . . . . . . . . . 1142
color names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
color-dark-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
color-defined-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
color-gray-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
color-name-to-rgb . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
color-supported-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
color-values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
colors on text terminals . . . . . . . . . . . . . . . . . . . . . . . 847
column width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
column-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
COM1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122
combine-after-change-calls . . . . . . . . . . . . . . . . 961
combine-and-quote-strings . . . . . . . . . . . . . . . . 1081
combine-change-calls . . . . . . . . . . . . . . . . . . . . . . . 962
combining conditions . . . . . . . . . . . . . . . . . . . . . . . . . 162

Indexcommand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
command descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
command history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
command in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . 494
command loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
command loop variables. . . . . . . . . . . . . . . . . . . . . . . 436
command loop, recursive . . . . . . . . . . . . . . . . . . . . . . 475
command-completion-default-include-p . . . . . 434
command-debug-status . . . . . . . . . . . . . . . . . . . . . . . 343
command-error-function . . . . . . . . . . . . . . . . . . . . . 182
command-execute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
command-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
command-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261
command-line arguments . . . . . . . . . . . . . . . . . . . . 1261
command-line options. . . . . . . . . . . . . . . . . . . . . . . . 1261
command-line-args . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
command-line-args-left . . . . . . . . . . . . . . . . . . . . 1262
command-line-functions . . . . . . . . . . . . . . . . . . . . 1262
command-line-processed . . . . . . . . . . . . . . . . . . . . 1261
command-query . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
command-remapping . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
command-switch-alist . . . . . . . . . . . . . . . . . . . . . . 1261
commandp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
commandp example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
commands, defining . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
commands, mode-specific . . . . . . . . . . . . . . . . . . . . . 430
commands, specify as mode-specific . . . . . . . . . . . 430
comment style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026
comment syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1025
comment-auto-fill-only-comments . . . . . . . . . . . 906
comment-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
comment-end-can-be-escaped . . . . . . . . . . . . . . . 1034
comment-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
commentary, in a Lisp library . . . . . . . . . . . . . . . . 1345
comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10comments, Lisp convention for . . . . . . . . . . . . . . . 1341
Common Lisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
comp-native-version-dir . . . . . . . . . . . . . . . . . . . . 303
compare tree-sitter syntax nodes . . . . . . . . . . . . . 1051
compare-buffer-substrings. . . . . . . . . . . . . . . . . . 882
compare-strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
comparing buffer text . . . . . . . . . . . . . . . . . . . . . . . . . 882
comparing file modification time . . . . . . . . . . . . . . 678
comparing numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
comparing time values . . . . . . . . . . . . . . . . . . . . . . . 1280
compatibility, between modules and Emacs . . . 1362
compilation (Emacs Lisp) . . . . . . . . . . . . . . . . . . . . . 316
compilation functions . . . . . . . . . . . . . . . . . . . . . . . . . 316
compilation to native code (Emacs Lisp) . . . . . . 327
compile-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
compile-time constant . . . . . . . . . . . . . . . . . . . . . . . . . 321
compiled function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
compiled-function-p . . . . . . . . . . . . . . . . . . . . . . . . 232
compiler errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
compiler macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
compiler macros, advising . . . . . . . . . . . . . . . . . . . . . 259
compiling tree-sitter queries . . . . . . . . . . . . . . . . . . 1057
complete key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481

1411

completing-read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
completing-read-function . . . . . . . . . . . . . . . . . . . 400
completion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
completion category . . . . . . . . . . . . . . . . . . . . . . . . . . 410
completion metadata. . . . . . . . . . . . . . . . . . . . . . . . . . 410
completion styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
completion table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
completion table, modifying . . . . . . . . . . . . . . . . . . . 398
completion tables, combining . . . . . . . . . . . . . . . . . . 398
completion, file name . . . . . . . . . . . . . . . . . . . . . . . . . 643
completion-at-point . . . . . . . . . . . . . . . . . . . . . . . . 411
completion-at-point-functions . . . . . . . . . . . . . 411
completion-auto-help . . . . . . . . . . . . . . . . . . . . . . . 401
completion-boundaries . . . . . . . . . . . . . . . . . . . . . . 397
completion-category-overrides . . . . . . . . . . . . . 408
completion-extra-properties . . . . . . . . . . . . . . . 408
completion-ignore-case . . . . . . . . . . . . . . . . . . . . . 398
completion-ignored-extensions . . . . . . . . . . . . . 644
completion-in-region . . . . . . . . . . . . . . . . . . . . . . . 413
completion-regexp-list . . . . . . . . . . . . . . . . . . . . . 398
completion-styles . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
completion-styles-alist . . . . . . . . . . . . . . . . . . . . 407
completion-table-case-fold . . . . . . . . . . . . . . . . 398
completion-table-dynamic . . . . . . . . . . . . . . . . . . . 411
completion-table-in-turn . . . . . . . . . . . . . . . . . . . 398
completion-table-merge . . . . . . . . . . . . . . . . . . . . . 398
completion-table-subvert . . . . . . . . . . . . . . . . . . . 398
completion-table-with-cache . . . . . . . . . . . . . . . 411
completion-table-with-predicate . . . . . . . . . . . 398
completion-table-with-quoting . . . . . . . . . . . . . 398
completion-table-with-terminator . . . . . . . . . 398
complex arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
complex command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
composite type, in bindat specification . . . . . . . 1125
composite types (customization) . . . . . . . . . . . . . . 286
composition (text property) . . . . . . . . . . . . . . . . . . 931
composition property, and point display . . . . . . 439
compute-motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
computed documentation string . . . . . . . . . . . . . . . 236
concat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
concatenating bidirectional strings . . . . . . . . . . . 1252
concatenating lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
concatenating strings . . . . . . . . . . . . . . . . . . . . . . . . . . 57
concurrency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
cond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
condition name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
condition-case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
condition-case-unless-debug . . . . . . . . . . . . . . . 183
condition-mutex . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
condition-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
condition-notify . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
condition-variable-p . . . . . . . . . . . . . . . . . . . . . . 1076
condition-wait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
conditional evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 159
conditional selection of windows . . . . . . . . . . . . . . . 719
confirm-kill-processes . . . . . . . . . . . . . . . . . . . . 1108
connection local profiles . . . . . . . . . . . . . . . . . . . . . . . 218
connection local variables . . . . . . . . . . . . . . . . . . . . . 218

Indexconnection local variables, applying . . . . . . . . . . . 220
connection-local-criteria-alist . . . . . . . . . . . 220
connection-local-default-application . . . . . 221
connection-local-get-profile-variables . . . 219
connection-local-profile-alist . . . . . . . . . . . . 219
connection-local-profile-name-for-setq . . . 221
connection-local-set-profile-variables . . . 218
connection-local-set-profiles . . . . . . . . . . . . . 219
cons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
cons cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
cons-cells-consed . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
consing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
consp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
constant variables . . . . . . . . . . . . . . . . . . . . . . . . 189, 195
constrain-to-field . . . . . . . . . . . . . . . . . . . . . . . . . . 937
content directory, package. . . . . . . . . . . . . . . . . . . . 1303
context menus, for a major mode . . . . . . . . . . . . . 530
context-menu-functions . . . . . . . . . . . . . . . . . . . . . 530
continuation lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130
continue-process . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098
control character key constants . . . . . . . . . . . . . . . . 501
control character printing . . . . . . . . . . . . . . . . . . . . . 601
control characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
control characters in display . . . . . . . . . . . . . . . . . 1243
control characters, reading . . . . . . . . . . . . . . . . . . . . 467
control structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Control-X-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
controller part, model/view/controller . . . . . . . . 1240
controlling terminal . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
controlling-tty-p . . . . . . . . . . . . . . . . . . . . . . . . . . 1265
conventions for documentation strings . . . . . . . . 1337
conventions for Emacs Lisp programs . . . . . . . . 1331
conventions for Emacs programming . . . . . . . . . 1335
conventions for key bindings . . . . . . . . . . . . . . . . . 1334
conventions for library header comments . . . . . 1343
conventions for Lisp comments . . . . . . . . . . . . . . . 1341
conventions for writing major modes . . . . . . . . . . 528
conventions for writing minor modes . . . . . . . . . . 544
conversion of strings . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
convert buffer position to file byte . . . . . . . . . . . . . 964
convert file byte to buffer position . . . . . . . . . . . . . 964
convert sequence to another type . . . . . . . . . . . . . . 113
convert-standard-filename. . . . . . . . . . . . . . . . . . 645
converting file names from/toMS-Windows syntax . . . . . . . . . . . . . . . . . . . . . . . . 634
converting numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
coordinate, relative to frame . . . . . . . . . . . . . . . . . . 769
Coordinated Universal Time . . . . . . . . . . . . . . . . . 1270
coordinates-in-window-p . . . . . . . . . . . . . . . . . . . . 770
copy-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
copy-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
copy-category-table . . . . . . . . . . . . . . . . . . . . . . . 1037
copy-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
copy-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630
copy-hash-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
copy-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
copy-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
copy-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151

1412

copy-region-as-kill . . . . . . . . . . . . . . . . . . . . . . . . 890
copy-sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
copy-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . 1027
copy-tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
copy_string_contents . . . . . . . . . . . . . . . . . . . . . . 1368
copying alists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
copying bidirectional text,
preserve visual order. . . . . . . . . . . . . . . . . . . . . . . 1254
copying files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
copying lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
copying sequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
copying strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
copying vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
copysign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
cos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
count-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
count-loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
count-screen-lines . . . . . . . . . . . . . . . . . . . . . . . . . . 859
count-words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
counting columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
counting set bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
coverage testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
coverage testing (Edebug) . . . . . . . . . . . . . . . . . . . . . 356
create subprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
create-file-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 611
create-fontset-from-fontset-spec . . . . . . . . 1182
create-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220
create-lockfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
creating buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
creating hash tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
creating keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
creating markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
creating strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
creating tree-sitter parsers . . . . . . . . . . . . . . . . . . . 1044
creating, copying and deleting directories . . . . . . 648
cryptographic hash . . . . . . . . . . . . . . . . . . . . . . . 944, 946
ctl-arrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1243
ctl-x-4-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
ctl-x-5-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
ctl-x-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
ctl-x-r-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395
curly quotes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600, 1339
curly quotes, in formatted messages . . . . . . . . . . . . 66
current binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
current buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
current buffer mark . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
current buffer point and mark (Edebug) . . . . . . . 357
current buffer position . . . . . . . . . . . . . . . . . . . . . . . . 853
current command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
current stack frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
current-active-maps . . . . . . . . . . . . . . . . . . . . . . . . 490
current-bidi-paragraph-direction . . . . . . . . 1252
current-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
current-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
current-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
current-cpu-time . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
current-fill-column . . . . . . . . . . . . . . . . . . . . . . . . 903
current-frame-configuration . . . . . . . . . . . . . . . 831

Indexcurrent-global-map . . . . . . . . . . . . . . . . . . . . . . . . . . 491
current-idle-time . . . . . . . . . . . . . . . . . . . . . . . . . . 1285
current-indentation . . . . . . . . . . . . . . . . . . . . . . . . 910
current-input-method . . . . . . . . . . . . . . . . . . . . . . . 991
current-input-mode . . . . . . . . . . . . . . . . . . . . . . . . 1286
current-justification . . . . . . . . . . . . . . . . . . . . . . 901
current-kill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893
current-left-margin . . . . . . . . . . . . . . . . . . . . . . . . 903
current-local-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
current-message . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134
current-minibuffer-command . . . . . . . . . . . . . . . . 437
current-minor-mode-maps . . . . . . . . . . . . . . . . . . . . 492
current-prefix-arg . . . . . . . . . . . . . . . . . . . . . . . . . . 474
current-thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
current-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1271
current-time-list . . . . . . . . . . . . . . . . . . . . . . . . . . 1271
current-time-string . . . . . . . . . . . . . . . . . . . . . . . 1271
current-time-zone . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
current-window-configuration . . . . . . . . . . . . . . 774
current-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 881
currying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
cursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
cursor (text property) . . . . . . . . . . . . . . . . . . . . . . . . 928
cursor position for display
properties and overlays . . . . . . . . . . . . . . . . . . . . . 929
cursor, and frame parameters . . . . . . . . . . . . . . . . . 817
cursor, fringe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
cursor-color, a frame parameter . . . . . . . . . . . . . 820
cursor-face (text property) . . . . . . . . . . . . . . . . . . 925
cursor-face-highlight-mode . . . . . . . . . . . . . . . . 925
cursor-face-highlightnonselected-window . . . . . . . . . . . . . . . . . . . . . . . 925
cursor-in-echo-area . . . . . . . . . . . . . . . . . . . . . . . 1138
cursor-in-non-selected-windows . . . . . . . . . . . . 817
cursor-intangible (text property) . . . . . . . . . . . 928
cursor-intangible-mode . . . . . . . . . . . . . . . . . . . . . 928
cursor-sensor-functions (text property) . . . . 931
cursor-sensor-inhibit . . . . . . . . . . . . . . . . . . . . . . 928
cursor-sensor-mode . . . . . . . . . . . . . . . . . . . . . . . . . . 931
cursor-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
cursor-type, a frame parameter . . . . . . . . . . . . . . 817
curved quotes . . . . . . . . . . . . . . . . . . . . . . . . . . . 600, 1339
curved quotes, in formatted messages . . . . . . . . . . . 66
curveto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1218
custom ‘%’-sequence in format . . . . . . . . . . . . . . . . . . 70
custom format string . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
custom themes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
custom-add-frequent-value. . . . . . . . . . . . . . . . . . 283
custom-group property . . . . . . . . . . . . . . . . . . . . . . . 280
custom-initialize-delay . . . . . . . . . . . . . . . . . . . 1348
custom-known-themes . . . . . . . . . . . . . . . . . . . . . . . . 296
custom-reevaluate-setting. . . . . . . . . . . . . . . . . . 284
custom-set-faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
custom-set-variables . . . . . . . . . . . . . . . . . . . . . . . 294
custom-theme-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
custom-theme-set-faces . . . . . . . . . . . . . . . . . . . . . 296
custom-theme-set-variables . . . . . . . . . . . . . . . . 295
custom-unlispify-remove-prefixes . . . . . . . . . 280

1413

custom-variable-history . . . . . . . . . . . . . . . . . . . . 394
custom-variable-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
customizable variables, how to define . . . . . . . . . . 280
customization groups, defining . . . . . . . . . . . . . . . . 279
customization item. . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
customization keywords . . . . . . . . . . . . . . . . . . . . . . . 277
customization types . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
customization types, define new . . . . . . . . . . . . . . . 293
customize-package-emacs-version-alist . . . . 279
customized-face (face symbol property) . . . . . 1170
cycle-sort-function, in completion . . . . . . . . . . 410
cyclic ordering of windows . . . . . . . . . . . . . . . . . . . . 717
cygwin-convert-file-name-from-windows . . . . 634
cygwin-convert-file-name-to-windows . . . . . . 634

Ddangling symlinks, testing for existence . . . . . . . . 619
data layout specification . . . . . . . . . . . . . . . . . . . . . 1125
data type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
data-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
database access, SQLite . . . . . . . . . . . . . . . . . . . . . . . 949
database object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114
date-days-in-month . . . . . . . . . . . . . . . . . . . . . . . . 1281
date-leap-year-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
date-ordinal-to-time . . . . . . . . . . . . . . . . . . . . . . 1281
date-to-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
days-to-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
deactivate-mark . . . . . . . . . . . . . . . . . . . . . . . . 875, 876
deactivate-mark-hook . . . . . . . . . . . . . . . . . . . . . . . 876
debug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
debug-allow-recursive-debug . . . . . . . . . . 335, 340
debug-ignored-errors . . . . . . . . . . . . . . . . . . . . . . . 334
debug-on-entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
debug-on-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
debug-on-error use . . . . . . . . . . . . . . . . . . . . . . . . . . 182
debug-on-event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
debug-on-message . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
debug-on-next-call . . . . . . . . . . . . . . . . . . . . . . . . . . 343
debug-on-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
debug-on-signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
debug-on-variable-change . . . . . . . . . . . . . . . . . . . 337
debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
debugger command list . . . . . . . . . . . . . . . . . . . . . . . 339
debugger for Emacs Lisp . . . . . . . . . . . . . . . . . . . . . . 333
debugger, explicit entry . . . . . . . . . . . . . . . . . . . . . . . 337
debugger-bury-or-kill . . . . . . . . . . . . . . . . . . . . . . 338
debugger-stack-frame-as-list . . . . . . . . . . . . . . 343
debugging changes to variables . . . . . . . . . . . . . . . . 337
debugging errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
debugging font-lock . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
debugging invalid Lisp syntax . . . . . . . . . . . . . . . . . 367
debugging lisp programs . . . . . . . . . . . . . . . . . . . . . . 333
debugging redisplay errors . . . . . . . . . . . . . . . . . . . . 335
debugging specific functions . . . . . . . . . . . . . . . . . . . 336
declare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
declare-function . . . . . . . . . . . . . . . . . . . . . . . 265, 266

Indexdeclaring functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
decode process output . . . . . . . . . . . . . . . . . . . . . . . 1103
decode-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974
decode-coding-inserted-region . . . . . . . . . . . . . 990
decode-coding-region . . . . . . . . . . . . . . . . . . . . . . . 989
decode-coding-string . . . . . . . . . . . . . . . . . . . . . . . 989
decode-time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1274
decoding file formats . . . . . . . . . . . . . . . . . . . . . . . . . . 654
decoding in coding systems . . . . . . . . . . . . . . . . . . . 988
decrement field of register . . . . . . . . . . . . . . . . . . . . . . 16
dedicated window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749
dedicated, a buffer display action alist entry . . 734
def-edebug-elem-spec . . . . . . . . . . . . . . . . . . . . . . . 361
def-edebug-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
defadvice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
defalias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
defalias-fset-function property . . . . . . . . . . . . . . . . . 238
default argument string . . . . . . . . . . . . . . . . . . . . . . . 427
default character height . . . . . . . . . . . . . . . . . . . . . . . 797
default character size . . . . . . . . . . . . . . . . . . . . . . . . . 797
default character width . . . . . . . . . . . . . . . . . . . . . . . 797
default coding system . . . . . . . . . . . . . . . . . . . . . . . . . 983
default coding system,functions to determine . . . . . . . . . . . . . . . . . . . . . . 985
default filter function of a process . . . . . . . . . . . . 1101
default font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
default height of character . . . . . . . . . . . . . . . . . . . . 797
default init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
default key binding . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
default sentinel function of a process . . . . . . . . . 1105
default value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
default value of char-table. . . . . . . . . . . . . . . . . . . . . 119
default width of character . . . . . . . . . . . . . . . . . . . . . 797
default-boundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
default-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . 640
default-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . 632
default-font-height . . . . . . . . . . . . . . . . . . . . . . . 1189
default-font-width . . . . . . . . . . . . . . . . . . . . . . . . 1189
default-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . 804
default-input-method . . . . . . . . . . . . . . . . . . . . . . . 991
default-justification . . . . . . . . . . . . . . . . . . . . . . 901
default-minibuffer-frame . . . . . . . . . . . . . . . . . . . 824
default-process-coding-system . . . . . . . . . . . . . 985
default-text-properties . . . . . . . . . . . . . . . . . . . . 918
default-toplevel-value . . . . . . . . . . . . . . . . . . . . . 213
default-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
default.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256
defconst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
defcustom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
deferred evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
defface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
defgroup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
defimage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
define customization group . . . . . . . . . . . . . . . . . . . . 279
define customization options . . . . . . . . . . . . . . . . . . 280
define hash comparisons . . . . . . . . . . . . . . . . . . . . . . 130
define image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220
define new bindat type forms . . . . . . . . . . . . . . . . 1128

1414

define new customization types. . . . . . . . . . . . . . . . 293
define-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067
define-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . 1067
define-advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
define-alternatives . . . . . . . . . . . . . . . . . . . . . . . . 432
define-button-type . . . . . . . . . . . . . . . . . . . . . . . . 1233
define-category . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1036
define-derived-mode . . . . . . . . . . . . . . . . . . . . . . . . 534
define-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
define-fringe-bitmap . . . . . . . . . . . . . . . . . . . . . . 1194
define-generic-mode . . . . . . . . . . . . . . . . . . . . . . . . 541
define-globalized-minor-mode . . . . . . . . . . . . . . 549
define-hash-table-test . . . . . . . . . . . . . . . . . . . . . 130
define-icon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227
define-inline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
define-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
define-key-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
define-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
define-minor-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
define-multisession-variable . . . . . . . . . . . . . . 228
define-obsolete-face-alias . . . . . . . . . . . . . . . 1177
define-obsolete-function-alias . . . . . . . . . . . . 260
define-obsolete-variable-alias . . . . . . . . . . . . 222
define-package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1306
define-prefix-command . . . . . . . . . . . . . . . . . . . . . . 489
define-short-documentation-group . . . . . . . . . 605
defined-colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
defining a function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
defining abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1067
defining commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
defining customization variables in C . . . . . . . . . 1359
defining faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
defining functions dynamically . . . . . . . . . . . . . . . . 238
defining Lisp variables in C . . . . . . . . . . . . . . . . . . 1358
defining macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
defining menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
defining tokens, SMIE . . . . . . . . . . . . . . . . . . . . . . . . 585
defining-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . 478
definition-prefixes . . . . . . . . . . . . . . . . . . . . . . . . 307
definitions of symbols . . . . . . . . . . . . . . . . . . . . . . . . . 134
defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
defsubr, Lisp symbol for a primitive . . . . . . . . . 1358
defsubst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
deftheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
defun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
defun-prompt-regexp . . . . . . . . . . . . . . . . . . . . . . . . 862
DEFUN, C macro to define Lisp primitives . . . . . 1356
defvar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
defvar-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
defvar-local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
DEFVAR_INT, DEFVAR_LISP,DEFVAR_BOOL, DEFSYM . . . . . . . . . . . . . . . . . . . . . . 1358
defvaralias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
delay-mode-hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
delay-warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
delayed warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
delayed-warnings-hook . . . . . . . . . . . . . . . 1142, 1399
delayed-warnings-list . . . . . . . . . . . . . . . . . . . . . 1142

Indexdelete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
delete-and-extract-region. . . . . . . . . . . . . . . . . . 886
delete-auto-save-file-if-necessary . . . . . . . 666
delete-auto-save-files . . . . . . . . . . . . . . . . . . . . . 666
delete-backward-char . . . . . . . . . . . . . . . . . . . . . . . 886
delete-before, a frame parameter . . . . . . . . . . . . 812
delete-blank-lines . . . . . . . . . . . . . . . . . . . . . . . . . . 889
delete-by-moving-to-trash . . . . . . . . . . . . . 631, 649
delete-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
delete-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
delete-dups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
delete-exited-processes . . . . . . . . . . . . . . . . . . . 1092
delete-field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937
delete-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631
delete-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
delete-frame event. . . . . . . . . . . . . . . . . . . . . . . . . . . 450
delete-frame-functions . . . . . . . . . . . . . . . . . . . . . 822
delete-horizontal-space . . . . . . . . . . . . . . . . . . . . 887
delete-indentation . . . . . . . . . . . . . . . . . . . . . . . . . . 888
delete-minibuffer-contents . . . . . . . . . . . . . . . . 420
delete-old-versions . . . . . . . . . . . . . . . . . . . . . . . . 662
delete-other-frames . . . . . . . . . . . . . . . . . . . . . . . . 823
delete-other-windows . . . . . . . . . . . . . . . . . . . . . . . 711
delete-other-windows, a window parameter . . 777
delete-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151
delete-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
delete-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
delete-selection, symbol property . . . . . . . . . . 877
delete-selection-helper . . . . . . . . . . . . . . . . . . . . 877
delete-selection-pre-hook. . . . . . . . . . . . . . . . . . 877
delete-terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
delete-terminal-functions. . . . . . . . . . . . . . . . . . 788
delete-to-left-margin . . . . . . . . . . . . . . . . . . . . . . 903
delete-trailing-whitespace . . . . . . . . . . . . . . . . 889
delete-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
delete-window, a window parameter . . . . . . . . . . 777
delete-window-choose-selected . . . . . . . . . . . . . 711
delete-windows-on . . . . . . . . . . . . . . . . . . . . . . . . . . . 712
deleting files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
deleting frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
deleting list elements . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
deleting previous char . . . . . . . . . . . . . . . . . . . . . . . . . 886
deleting processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1091
deleting text vs killing . . . . . . . . . . . . . . . . . . . . . . . . 886
deleting whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . 887
deleting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
delq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
dependencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
derived mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
derived-mode-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
describe characters and events . . . . . . . . . . . . . . . . 601
describe-bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
describe-buffer-case-table. . . . . . . . . . . . . . . . . . 76
describe-categories . . . . . . . . . . . . . . . . . . . . . . . 1038
describe-current-display-table . . . . . . . . . . . 1244
describe-display-table . . . . . . . . . . . . . . . . . . . . 1244
describe-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
describe-prefix-bindings . . . . . . . . . . . . . . . . . . . 603

1415

describe-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028
description for interactive codes . . . . . . . . . . . . . . . 427
description format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
deserializing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
desktop notifications . . . . . . . . . . . . . . . . . . . . . . . . . 1291
desktop save mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594
desktop-buffer-mode-handlers . . . . . . . . . . . . . . 594
desktop-save-buffer . . . . . . . . . . . . . . . . . . . . . . . . 594
destroy-fringe-bitmap . . . . . . . . . . . . . . . . . . . . . 1194
destructive list operations . . . . . . . . . . . . . . . . . . . . . . 87
destructuring with pcase patterns . . . . . . . . . . . . . 172
detect-coding-region . . . . . . . . . . . . . . . . . . . . . . . 981
detect-coding-string . . . . . . . . . . . . . . . . . . . . . . . 981
deterministic build . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
device names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
device-class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
diagrams, boxed, for lists . . . . . . . . . . . . . . . . . . . . . . . 16
dialog boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
digit-argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
ding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1247
dir-locals-class-alist . . . . . . . . . . . . . . . . . . . . . 218
dir-locals-directory-cache . . . . . . . . . . . . . . . . 218
dir-locals-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
dir-locals-set-class-variables . . . . . . . . . . . . 217
dir-locals-set-directory-class . . . . . . . . . . . . 218
direct save protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
direction, a buffer display action alist entry . . 735
directional overrides . . . . . . . . . . . . . . . . . . . . . . . . . 1253
directory file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
directory local variables . . . . . . . . . . . . . . . . . . . . . . . 217
directory name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
directory part (of file name) . . . . . . . . . . . . . . . . . . . 634
directory-abbrev-alist . . . . . . . . . . . . . . . . . . . . . 638
directory-empty-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 646
directory-file-name . . . . . . . . . . . . . . . . . . . . . . . . 638
directory-files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646
directory-files-and-attributes . . . . . . . . . . . . 647
directory-files-no-dot-files-regexp . . . . . . 647
directory-files-recursively . . . . . . . . . . . . . . . 646
directory-name-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638
directory-oriented functions . . . . . . . . . . . . . . . . . . . 645
dired-kept-versions . . . . . . . . . . . . . . . . . . . . . . . . 662
disable asynchronous native compilation . . . . . . . 331
disable-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
disable-point-adjustment . . . . . . . . . . . . . . . . . . . 440
disable-theme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
disabled command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
disabled-command-function. . . . . . . . . . . . . . . . . . 477
disabling multibyte . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
disabling undo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898
disassemble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
disassembled byte-code . . . . . . . . . . . . . . . . . . . . . . . 324
discard-input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
discarding input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
dispatch of methods for generic function. . . . . . . 248
display (overlay property) . . . . . . . . . . . . . . . . . . 1154
display (text property) . . . . . . . . . . . . . . . . . . . . . 1198

Indexdisplay action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
display area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
display feature testing . . . . . . . . . . . . . . . . . . . . . . . . 849
display margins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1205
display message in echo area . . . . . . . . . . . . . . . . . 1131
display name on X . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
display origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
display properties, and bidi
reordering of text . . . . . . . . . . . . . . . . . . . . . . . . . . 1251
display property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
display property, and point display . . . . . . . . . . . 439
display property, unsafe evaluation . . . . . . . . . . . 1199
display specification . . . . . . . . . . . . . . . . . . . . . . . . . 1198
display table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1243
display, a frame parameter . . . . . . . . . . . . . . . . . . . 805
display, abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
display, arbitrary objects. . . . . . . . . . . . . . . . . . . . . 1236
display-backing-store . . . . . . . . . . . . . . . . . . . . . . 851
display-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
display-buffer-alist . . . . . . . . . . . . . . . . . . . . . . . 726
display-buffer-at-bottom . . . . . . . . . . . . . . . . . . . 729
display-buffer-base-action . . . . . . . . . . . . . . . . 726
display-buffer-below-selected . . . . . . . . . . . . . 729
display-buffer-fallback-action . . . . . . . . . . . . 726
display-buffer-full-frame. . . . . . . . . . . . . . . . . . 729
display-buffer-in-atom-window . . . . . . . . . . . . . 757
display-buffer-in-child-frame . . . . . . . . . . . . . 730
display-buffer-in-direction . . . . . . . . . . . . . . . 728
display-buffer-in-previous-window . . . . . . . . 727
display-buffer-in-side-window . . . . . . . . . . . . . 752
display-buffer-no-window . . . . . . . . . . . . . . . . . . . 730
display-buffer-overriding-action . . . . . . . . . 726
display-buffer-pop-up-frame . . . . . . . . . . . . . . . 729
display-buffer-pop-up-window . . . . . . . . . . . . . . 727
display-buffer-reuse-mode-window . . . . . . . . . 726
display-buffer-reuse-window . . . . . . . . . . . . . . . 726
display-buffer-same-window . . . . . . . . . . . . . . . . 726
display-buffer-use-least-recent-window . . . 728
display-buffer-use-some-frame . . . . . . . . . . . . . 730
display-buffer-use-some-window . . . . . . . . . . . . 727
display-color-cells . . . . . . . . . . . . . . . . . . . . . . . . 851
display-color-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
display-completion-list . . . . . . . . . . . . . . . . . . . . 401
display-delayed-warnings . . . . . . . . . . . . . . . . . . 1142
display-graphic-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
display-grayscale-p . . . . . . . . . . . . . . . . . . . . . . . . 850
display-images-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
display-message-or-buffer . . . . . . . . . . . . . . . . 1134
display-mm-dimensions-alist . . . . . . . . . . . . . . . 851
display-mm-height . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
display-mm-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
display-monitor-attributes-list . . . . . . . . . . . 789
display-monitors-changed-functions . . . . . . . 791
display-mouse-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
display-pixel-height . . . . . . . . . . . . . . . . . . . . . . . 850
display-pixel-width . . . . . . . . . . . . . . . . . . . . . . . . 850
display-planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
display-popup-menus-p . . . . . . . . . . . . . . . . . . . . . . 849

1416

display-save-under . . . . . . . . . . . . . . . . . . . . . . . . . . 851
display-screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
display-selections-p . . . . . . . . . . . . . . . . . . . . . . . 850
display-sort-function, in completion . . . . . . . 410
display-start position . . . . . . . . . . . . . . . . . . . . . . . . . 759
display-supports-face-attributes-p . . . . . . . 850
display-table-slot . . . . . . . . . . . . . . . . . . . . . . . . 1244
display-type, a frame parameter . . . . . . . . . . . . . 805
display-visual-class . . . . . . . . . . . . . . . . . . . . . . . 851
display-warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139
displaying a buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
displaying faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
displays, multiple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
distance between strings . . . . . . . . . . . . . . . . . . . . . . . 64
distinguish interactive calls. . . . . . . . . . . . . . . . . . . . 435
dlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
dnd-begin-drag-files . . . . . . . . . . . . . . . . . . . . . . . 844
dnd-begin-file-drag . . . . . . . . . . . . . . . . . . . . . . . . 843
dnd-begin-text-drag . . . . . . . . . . . . . . . . . . . . . . . . 843
dnd-direct-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
dnd-protocol-alist . . . . . . . . . . . . . . . . . . . . . . . . . . 841
do-auto-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666
doc, customization keyword . . . . . . . . . . . . . . . . . . . 292
doc-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598
DOC (documentation) file . . . . . . . . . . . . . . . . . . . . . . 595
Document Object Model . . . . . . . . . . . . . . . . . . . . . . 953
documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
documentation conventions. . . . . . . . . . . . . . . . . . . . 595
documentation for major mode . . . . . . . . . . . . . . . . 534
documentation groups . . . . . . . . . . . . . . . . . . . . . . . . 605
documentation notation . . . . . . . . . . . . . . . . . . . . . . . . . 3
documentation string of function . . . . . . . . . . . . . . 235
documentation strings . . . . . . . . . . . . . . . . . . . . . . . . 595
documentation strings,
conventions and tips . . . . . . . . . . . . . . . . . . . . . . . 1337
documentation, keys in . . . . . . . . . . . . . . . . . . . . . . . 598
documentation-property . . . . . . . . . . . . . . . . . . . . . 596
dolist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
dolist-with-progress-reporter . . . . . . . . . . . . 1136
dom-node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
DOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
dotimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
dotimes-with-progress-reporter . . . . . . . . . . . 1136
dotted list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
dotted lists (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 362
dotted pair notation . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
double-click events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
double-click-fuzz . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
double-click-time . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
double-quote in strings . . . . . . . . . . . . . . . . . . . . . . . . . 20
down-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
downcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
downcase-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
downcase-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
downcasing in lookup-key . . . . . . . . . . . . . . . . . . . . 462
download-callback xwidget events . . . . . . . . . . . 450
download-started xwidget events . . . . . . . . . . . . . 450
drag and drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841

Indexdrag and drop protocols, X . . . . . . . . . . . . . . . . . . . 845
drag and drop, other formats. . . . . . . . . . . . . . . . . . 842
drag and drop, X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
drag event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
drag-internal-border, a frame parameter . . . . 814
drag-n-drop event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
drag-with-header-line, a frame parameter. . . 814
drag-with-mode-line, a frame parameter . . . . . 814
drag-with-tab-line, a frame parameter . . . . . . 814
dribble file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
drop target, in drag-and-drop operations . . . . . . 843
dump file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
dump-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1348
dump-emacs-portable . . . . . . . . . . . . . . . . . . . . . . . 1348
dumping Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
dynamic binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
dynamic binding, temporarily . . . . . . . . . . . . . . . . . 192
dynamic extent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
dynamic let-binding . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
dynamic libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1299
dynamic loading of documentation . . . . . . . . . . . . 319
dynamic loading of functions . . . . . . . . . . . . . . . . . . 319
dynamic modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
dynamic modules, writing . . . . . . . . . . . . . . . . . . . . 1361
dynamic scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
dynamic-library-alist . . . . . . . . . . . . . . . . . . . . . 1299

Eeager macro expansion . . . . . . . . . . . . . . . . . . . . . . . . 299
early init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258
early-init.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258
easy-menu-define . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
easy-mmode-define-minor-mode . . . . . . . . . . . . . . 548
echo area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
echo area customization . . . . . . . . . . . . . . . . . . . . . . 1138
echo-area-clear-hook . . . . . . . . . . . . . . . . . . . . . . 1138
echo-keystrokes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
edebug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
Edebug debugging facility . . . . . . . . . . . . . . . . . . . . . 344
Edebug execution modes . . . . . . . . . . . . . . . . . . . . . . 347
edebug overwrites buffer point position . . . . . . . . 357
Edebug specification list . . . . . . . . . . . . . . . . . . . . . . 359
edebug, failure to instrument . . . . . . . . . . . . . . . . . . 346
edebug-after-instrumentation-function . . . . 367
edebug-all-defs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
edebug-all-forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
edebug-backtrace-hide-instrumentation . . . . 349
edebug-backtrace-show-instrumentation . . . . 349
edebug-behavior-alist . . . . . . . . . . . . . . . . . . . . . . 367
edebug-continue-kbd-macro. . . . . . . . . . . . . . . . . . 366
edebug-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
edebug-display-freq-count. . . . . . . . . . . . . . . . . . 356
edebug-eval-macro-args . . . . . . . . . . . . . . . . 359, 365
edebug-eval-top-level-form . . . . . . . . . . . . . . . . 346
edebug-global-break-condition . . . . . . . . . . . . . 366
edebug-initial-mode . . . . . . . . . . . . . . . . . . . . . . . . 365
edebug-max-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

1417

edebug-new-definition-function . . . . . . . . . . . . 367
edebug-on-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
edebug-on-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
edebug-print-circle . . . . . . . . . . . . . . . . . . . . 355, 366
edebug-print-length . . . . . . . . . . . . . . . . . . . . 354, 366
edebug-print-level . . . . . . . . . . . . . . . . . . . . . 355, 366
edebug-print-trace-after . . . . . . . . . . . . . . . . . . . 355
edebug-print-trace-before. . . . . . . . . . . . . . . . . . 355
edebug-remove-instrumentation . . . . . . . . . . . . . 346
edebug-save-displayed-buffer-points . . . . . . 365
edebug-save-windows . . . . . . . . . . . . . . . . . . . . . . . . 365
edebug-set-global-break-condition . . . . . . . . 351
edebug-set-initial-mode . . . . . . . . . . . . . . . . . . . . 347
edebug-setup-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
edebug-sit-for-seconds . . . . . . . . . . . . . . . . 348, 366
edebug-sit-on-break . . . . . . . . . . . . . . . . . . . . . . . . 367
edebug-temp-display-freq-count . . . . . . . . . . . . 356
edebug-test-coverage . . . . . . . . . . . . . . . . . . . . . . . 365
edebug-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355, 365
edebug-tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
edebug-unwrap-results . . . . . . . . . . . . . . . . . . . . . . 366
edge detection, images . . . . . . . . . . . . . . . . . . . . . . . 1209
edit distance between strings . . . . . . . . . . . . . . . . . . . 64
edit-and-eval-command . . . . . . . . . . . . . . . . . . . . . . 392
editing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
editor command loop . . . . . . . . . . . . . . . . . . . . . . . . . 423
eight-bit, a charset . . . . . . . . . . . . . . . . . . . . . . . . . . 973
electric-future-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 6element (of list) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
elements of sequences . . . . . . . . . . . . . . . . . . . . . . . . . 103
elliptical-arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1219
elp.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
elt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Emacs event standard notation. . . . . . . . . . . . . . . . 601
Emacs process run time . . . . . . . . . . . . . . . . . . . . . . 1280
emacs, a charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
emacs-build-number . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
emacs-build-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
emacs-init-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
emacs-internal coding system. . . . . . . . . . . . . . . . 977
emacs-lisp-docstring-fill-column . . . . . . . . 1337
emacs-lisp-native-compile. . . . . . . . . . . . . . . . . . 329
emacs-lisp-native-compile-and-load . . . . . . . 329
emacs-major-version . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
emacs-minor-version . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
emacs-pid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
emacs-repository-branch . . . . . . . . . . . . . . . . . . . . . . 7
emacs-repository-version . . . . . . . . . . . . . . . . . . . . . 7
emacs-save-session-functions . . . . . . . . . . . . . 1290
emacs-session-restore . . . . . . . . . . . . . . . . . . . . . 1291
emacs-startup-hook . . . . . . . . . . . . . . . . . . . . . . . . 1259
emacs-uptime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
emacs-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
emacs_finalizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366
emacs_funcall_exit, enumeration . . . . . . . . . . . 1376
emacs_funcall_exit_return . . . . . . . . . . . . . . . . 1376
emacs_funcall_exit_signal . . . . . . . . . . . . . . . . 1376
emacs_funcall_exit_throw . . . . . . . . . . . . . . . . . . 1376

Index

emacs_function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1363
emacs_module_init . . . . . . . . . . . . . . . . . . . . . 314, 1361
emacs_value data type . . . . . . . . . . . . . . . . . . . . . . 1366
emacs_variadic_function . . . . . . . . . . . . . . . . . . . 1364
EMACS_LIMB_MAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367
emacsclient, getting a backtrace . . . . . . . . . . . . . . . 334
EMACSLOADPATH environment variable . . . . . . . . . . 302
embedded language, tree-sitter . . . . . . . . . . . . . . . 1059
embedded widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
empty file name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
empty file name, and file-exists-p . . . . . . . . . . 619
empty file names, and expand-file-name . . . . . 640
empty lines, indicating . . . . . . . . . . . . . . . . . . . . . . . 1190
empty list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
empty overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
empty region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
emulation-mode-map-alists. . . . . . . . . . . . . . . . . . 493
enable-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
enable-connection-local-variables . . . . . . . . 222
enable-dir-local-variables . . . . . . . . . . . . . . . . 218
enable-local-eval . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
enable-local-variables . . . . . . . . . . . . . . . . . . . . . 214
enable-multibyte-characters . . . . . . . . . . 963, 965
enable-recursive-minibuffers . . . . . . . . . . . . . . 420
enable-theme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
encapsulation, ewoc . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
encode-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974
encode-coding-region . . . . . . . . . . . . . . . . . . . . . . . 988
encode-coding-string . . . . . . . . . . . . . . . . . . . . . . . 988
encode-time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1275
encoding file formats . . . . . . . . . . . . . . . . . . . . . . . . . . 654
encoding in coding systems . . . . . . . . . . . . . . . . . . . 988
encrypted network connections . . . . . . . . . . . . . . . 1111
end of line in regexp . . . . . . . . . . . . . . . . . . . . . . . . . . 999
end-of-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856
end-of-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862
end-of-defun-function . . . . . . . . . . . . . . . . . . . . . . 862
end-of-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
end-of-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
end-of-line conversion . . . . . . . . . . . . . . . . . . . . . . . . . 977
end-session event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
endianness, in bindat specification . . . . . . . . . . . 1125
ensure-empty-lines . . . . . . . . . . . . . . . . . . . . . . . . . . 885
ensure-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
environment variable access . . . . . . . . . . . . . . . . . . 1266
environment variables, subprocesses . . . . . . . . . . 1079
eobp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
eol conversion of coding system . . . . . . . . . . . . . . . 980
eol type of coding system . . . . . . . . . . . . . . . . . . . . . 980
EOL conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
eolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
epoch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34, 1373
eql . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
equal-including-properties. . . . . . . . . . . . . . . . . . 36
equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

1418

erase-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
error cleanup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
error debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
error description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
error display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
error handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
error in debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
error message notation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
error name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
error symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
error-conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
error-message-string . . . . . . . . . . . . . . . . . . . . . . . 184
errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
esc-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
ESC-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
escape (ASCII character) . . . . . . . . . . . . . . . . . . . . . . 12
escape characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
escape characters in printing . . . . . . . . . . . . . . . . . . 377
escape sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
escaping apostrophe and grave
accent in doc strings . . . . . . . . . . . . . . . . . . . . . . . 1339
ESC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
eval during compilation . . . . . . . . . . . . . . . . . . . . . . . 320
eval, and debugging . . . . . . . . . . . . . . . . . . . . . . . . . . 343
eval-and-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
eval-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
eval-buffer (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . 346
eval-defun (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 346
eval-defun, and defcustom forms . . . . . . . . . . . . 281
eval-defun, and defface forms . . . . . . . . . . . . . . 1169
eval-defun, and defvar forms . . . . . . . . . . . . . . . . 195
eval-defun, and explicit entry to debugger . . . . 337
eval-expression (Edebug) . . . . . . . . . . . . . . . . . . . 346
eval-expression, and lexical-binding . . . . . . 205
eval-expression-debug-on-error . . . . . . . . . . . . 334
eval-expression-print-length . . . . . . . . . . . . . . 381
eval-expression-print-level . . . . . . . . . . . . . . . 381
eval-last-sexp, and defface forms . . . . . . . . . 1169
eval-last-sexp, and defvar forms . . . . . . . . . . . 195
eval-minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
eval-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
eval-region (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . 346
eval-when-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
evaluated expression argument . . . . . . . . . . . . . . . . 429
evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
evaluation list group . . . . . . . . . . . . . . . . . . . . . . . . . . 353
evaluation notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
evaluation of buffer contents . . . . . . . . . . . . . . . . . . 154
evaluation of special forms . . . . . . . . . . . . . . . . . . . . 149
evaporate (overlay property) . . . . . . . . . . . . . . . . 1156
even-window-sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
event printing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
event translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
event type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
event, reading only one . . . . . . . . . . . . . . . . . . . . . . . 462
event-basic-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456

Index

event-click-count . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
event-convert-list . . . . . . . . . . . . . . . . . . . . . . . . . . 503
event-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
event-modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
event-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
eventp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
ewoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
ewoc-buffer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
ewoc-collect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239
ewoc-create. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
ewoc-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-delete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-enter-after . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-enter-before . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-enter-first . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
ewoc-enter-last . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
ewoc-filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239
ewoc-get-hf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
ewoc-goto-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-goto-node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-goto-prev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-invalidate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-locate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1239
ewoc-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-nth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-prev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-set-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1238
ewoc-set-hf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237
examining text properties . . . . . . . . . . . . . . . . . . . . . 917
examining the interactive form . . . . . . . . . . . . . . 426
examining windows . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
examples of using interactive . . . . . . . . . . . . . . . 430
excess close parentheses . . . . . . . . . . . . . . . . . . . . . . . 368
excess open parentheses . . . . . . . . . . . . . . . . . . . . . . . 367
excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
exec-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
exec-path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079, 1080
exec-suffixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
executable-find . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
execute program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
execute with prefix argument . . . . . . . . . . . . . . . . . 434
execute-extended-command . . . . . . . . . . . . . . . . . . . 434
execute-extended-command-for-buffer . . . . . . 434
execute-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
executing-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . 478
execution order of buffer display
action functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
execution speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1336
exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
exit recursive editing . . . . . . . . . . . . . . . . . . . . . . . . . . 475
exit-minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
exit-recursive-edit . . . . . . . . . . . . . . . . . . . . . . . . 476
exiting Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

1419

expand-abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
expand-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639
expanding abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
expansion of file names . . . . . . . . . . . . . . . . . . . . . . . 639
expansion of macros . . . . . . . . . . . . . . . . . . . . . . . . . . 268
explicit selective display . . . . . . . . . . . . . . . . . . . . . 1145
explicit-name, a frame parameter . . . . . . . . . . . . 805
explore tree-sitter syntax tree . . . . . . . . . . . . . . . . 1041
expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
expt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
extended file attributes . . . . . . . . . . . . . . . . . . . . . . . 627
extended menu item . . . . . . . . . . . . . . . . . . . . . . . . . . 511
extended-command-history . . . . . . . . . . . . . . . . . . . 394
extent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
external border . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
external menu bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
external tool bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
external-debugging-output. . . . . . . . . . . . . . . . . . 377
extra node, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . 1051
extra slots of char-table . . . . . . . . . . . . . . . . . . . . . . . 119
extra-keyboard-modifiers . . . . . . . . . . . . . . . . . . . 466
extract_big_integer . . . . . . . . . . . . . . . . . . . . . . . 1367
extract_float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367
extract_integer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367
extract_time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1368

F
face (button property) . . . . . . . . . . . . . . . . . . . . . . 1232
face (non-removability of) . . . . . . . . . . . . . . . . . . . . 1168
face (overlay property) . . . . . . . . . . . . . . . . . . . . . . 1154
face (text property) . . . . . . . . . . . . . . . . . . . . . . . . . . 925
face alias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
face attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
face attributes, access and modification . . . . . . 1171
face codes of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925
face merging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
face number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
face property of face symbols . . . . . . . . . . . . . . . . 1177
face remapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1175
face spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
face-all-attributes . . . . . . . . . . . . . . . . . . . . . . . 1172
face-attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1171
face-attribute-relative-p . . . . . . . . . . . . . . . . 1171
face-background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-bold-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-defface-spec (face symbol property) . . 1170
face-differs-from-default-p . . . . . . . . . . . . . . 1177
face-documentation . . . . . . . . . . . . . . . . . . . . 596, 1177
face-documentation (facesymbol property) . . . . . . . . . . . . . . . . . . . . . . . . . . 1170
face-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
face-extend-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-filters-always-match. . . . . . . . . . . . . . . . . . 932
face-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-font-family-alternatives . . . . . . . . . . . . 1180
face-font-registry-alternatives. . . . . . . . . . 1180

Indexface-font-rescale-alist . . . . . . . . . . . . . . . . . . . 1181
face-font-selection-order . . . . . . . . . . . . . . . . 1180
face-foreground . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
face-inverse-video-p . . . . . . . . . . . . . . . . . . . . . . 1174
face-italic-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1177
face-name-history . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
face-remap-add-relative . . . . . . . . . . . . . . . . . . . 1176
face-remap-remove-relative . . . . . . . . . . . . . . . 1177
face-remap-reset-base . . . . . . . . . . . . . . . . . . . . . 1177
face-remap-set-base . . . . . . . . . . . . . . . . . . . . . . . 1177
face-remapping-alist . . . . . . . . . . . . . . . . . . . . . . 1175
face-spec-set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1170
face-stipple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
face-underline-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1174
facep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1164
faces for font lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
faces, automatic choice. . . . . . . . . . . . . . . . . . . . . . . 1178
false . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
fboundp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
fceiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
feature-unload-function . . . . . . . . . . . . . . . . . . . . 313
featurep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309, 311
fetch-bytecode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
ffloor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
field (overlay property) . . . . . . . . . . . . . . . . . . . . . 1155
field (text property) . . . . . . . . . . . . . . . . . . . . . . . . . 928
field name, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . 1041
field numbers in format spec . . . . . . . . . . . . . . . . . . . 68
field width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
field-beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937
field-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937
field-is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
field-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937
field-string-no-properties . . . . . . . . . . . . . . . . 937
fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 936
fifo data structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
file accessibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
file age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
file attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
file classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
file contents, and default coding system . . . . . . . 983
file format conversion . . . . . . . . . . . . . . . . . . . . . . . . . 654
file hard link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
file local variables . . . . . . . . . . . . . . . . . . . . . . . 213, 1300
file locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
file mode specification error . . . . . . . . . . . . . . . . . . . 532
file modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
file modes and MS-DOS. . . . . . . . . . . . . . . . . . . . . . . 621
file modes, setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
file modification time . . . . . . . . . . . . . . . . . . . . . . . . . 624
file name abbreviations . . . . . . . . . . . . . . . . . . . . . . . 638
file name completion subroutines . . . . . . . . . . . . . . 643
file name handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
file name of buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675

1420

file name of directory . . . . . . . . . . . . . . . . . . . . . . . . . 637
file name, and default coding system . . . . . . . . . . 984
file names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
file names in directory . . . . . . . . . . . . . . . . . . . . . . . . 645
file names, trailing whitespace . . . . . . . . . . . . . . . . . 619
file notifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1296
file open error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
file permissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
file permissions, setting . . . . . . . . . . . . . . . . . . . . . . . 632
file with multiple names . . . . . . . . . . . . . . . . . . . . . . . 629
file, ancestor directory of . . . . . . . . . . . . . . . . . . . . . . 647
file, information about . . . . . . . . . . . . . . . . . . . . . . . . 619
file-accessible-directory-p . . . . . . . . . . . . . . . 620
file-acl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
file-already-exists . . . . . . . . . . . . . . . . . . . . . . . . 631
file-attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
file-backup-file-names . . . . . . . . . . . . . . . . . . . . . 664
file-chase-links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
file-coding-system-alist . . . . . . . . . . . . . . . . . . . 984
file-directory-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622
file-equal-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
file-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
file-executable-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 620
file-exists-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
file-expand-wildcards . . . . . . . . . . . . . . . . . . . . . . 647
file-extended-attributes . . . . . . . . . . . . . . . . . . . 628
file-has-changed-p . . . . . . . . . . . . . . . . . . . . . . . . . . 625
file-in-directory-p . . . . . . . . . . . . . . . . . . . . . . . . 647
file-local-copy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
file-local-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
file-local-variables-alist . . . . . . . . . . . . . . . . 215
file-locked . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
file-locked-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
file-modes-number-to-symbolic . . . . . . . . . . . . . 633
file-modes-symbolic-to-number . . . . . . . . . . . . . 633
file-name encoding, MS-Windows. . . . . . . . . . . . . . 979
file-name-absolute-p . . . . . . . . . . . . . . . . . . . . . . . 637
file-name-all-completions. . . . . . . . . . . . . . . . . . 643
file-name-as-directory . . . . . . . . . . . . . . . . . . . . . 638
file-name-base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636
file-name-case-insensitive-p . . . . . . . . . . . . . . 624
file-name-coding-system . . . . . . . . . . . . . . . . . . . . 979
file-name-completion . . . . . . . . . . . . . . . . . . . . . . . 644
file-name-concat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638
file-name-directory . . . . . . . . . . . . . . . . . . . . . . . . 635
file-name-extension . . . . . . . . . . . . . . . . . . . . . . . . 635
file-name-handler-alist . . . . . . . . . . . . . . . . . . . . 649
file-name-history . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
file-name-nondirectory . . . . . . . . . . . . . . . . . . . . . 635
file-name-parent-directory . . . . . . . . . . . . . . . . 639
file-name-quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
file-name-quoted-p . . . . . . . . . . . . . . . . . . . . . . . . . . 641
file-name-sans-extension . . . . . . . . . . . . . . . . . . . 636
file-name-sans-versions . . . . . . . . . . . . . . . . . . . . 635
file-name-split . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636
file-name-unquote . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
file-name-with-extension . . . . . . . . . . . . . . . . . . . 636

Indexfile-newer-than-file-p . . . . . . . . . . . . . . . . . . . . . 624
file-newest-backup . . . . . . . . . . . . . . . . . . . . . . . . . . 664
file-nlinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
file-notify-add-watch . . . . . . . . . . . . . . . . . . . . . 1296
file-notify-rm-all-watches . . . . . . . . . . . . . . . 1298
file-notify-rm-watch . . . . . . . . . . . . . . . . . . . . . . 1298
file-notify-valid-p . . . . . . . . . . . . . . . . . . . . . . . 1298
file-ownership-preserved-p . . . . . . . . . . . . . . . . 620
file-precious-flag . . . . . . . . . . . . . . . . . . . . . . . . . . 614
file-readable-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620
file-regular-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
file-relative-name . . . . . . . . . . . . . . . . . . . . . . . . . . 637
file-remote-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
file-selinux-context . . . . . . . . . . . . . . . . . . . . . . . 627
file-supersession . . . . . . . . . . . . . . . . . . . . . . . . . . . 679
file-symlink-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
file-truename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
file-writable-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620
filepos-to-bufferpos . . . . . . . . . . . . . . . . . . . . . . . 964
fill-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903
fill-context-prefix . . . . . . . . . . . . . . . . . . . . . . . . 904
fill-forward-paragraph-function . . . . . . . . . . . 902
fill-individual-paragraphs . . . . . . . . . . . . . . . . 900
fill-individual-varying-indent . . . . . . . . . . . . 901
fill-nobreak-predicate . . . . . . . . . . . . . . . . . . . . . 904
fill-paragraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
fill-paragraph-function . . . . . . . . . . . . . . . . . . . . 902
fill-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902
fill-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900
fill-region-as-paragraph . . . . . . . . . . . . . . . . . . . 901
fill-separate-heterogeneouswords-with-space . . . . . . . . . . . . . . . . . . . . . . . . . . 902
fillarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
filling text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
filling, automatic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 905
filter function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1101
filter multibyte flag, of process . . . . . . . . . . . . . . . 1103
filter-buffer-substring . . . . . . . . . . . . . . . . . . . . 880
filter-buffer-substring-function . . . . . . . . . 880
filter-buffer-substring-functions . . . . . . . . 881
filtered-frame-list . . . . . . . . . . . . . . . . . . . . . . . . 824
filtering killed text . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890
filtering sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
find file in path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628
find library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
find-auto-coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985
find-backup-file-name . . . . . . . . . . . . . . . . . . . . . . 663
find-buffer-visiting . . . . . . . . . . . . . . . . . . . . . . . 676
find-charset-region . . . . . . . . . . . . . . . . . . . . . . . . 975
find-charset-string . . . . . . . . . . . . . . . . . . . . . . . . 975
find-coding-systems-for-charsets . . . . . . . . . 980
find-coding-systems-region . . . . . . . . . . . . . . . . 980
find-coding-systems-string . . . . . . . . . . . . . . . . 980
find-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609
find-file-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610
find-file-literally . . . . . . . . . . . . . . . . . . . . 609, 611
find-file-name-handler . . . . . . . . . . . . . . . . . . . . . 652
find-file-noselect . . . . . . . . . . . . . . . . . . . . . . . . . . 609

1421

find-file-not-found-functions . . . . . . . . . . . . . 610
find-file-other-window . . . . . . . . . . . . . . . . . . . . . 610
find-file-read-only . . . . . . . . . . . . . . . . . . . . . . . . 610
find-file-wildcards . . . . . . . . . . . . . . . . . . . . . . . . 610
find-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186
find-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
find-operation-coding-system . . . . . . . . . . . . . . 985
find-word-boundary-function-table . . . . . . . . 855
finding files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
finding windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
first-change-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 962
first-sibling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
fit-frame-to-buffer . . . . . . . . . . . . . . . . . . . . . . . . 705
fit-frame-to-buffer-margins . . . . . . . . . . . . . . . 706
fit-frame-to-buffer-margins, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
fit-frame-to-buffer-sizes. . . . . . . . . . . . . . . . . . 706
fit-frame-to-buffer-sizes, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
fit-window-to-buffer . . . . . . . . . . . . . . . . . . . . . . . 704
fit-window-to-buffer-horizontally . . . . . . . . 705
fixed-size window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
fixnump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
fixup-whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 888
flags in format specifications . . . . . . . . . . . . . . . . . . . 68
flatten-tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
float-e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
float-output-format . . . . . . . . . . . . . . . . . . . . . . . . 382
float-pi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
float-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
floating-point functions . . . . . . . . . . . . . . . . . . . . . . . . 51
floatp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
floats-consed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
flowcontrol, in serial connections . . . . . . . . . . . . . 1123
flush-standard-output . . . . . . . . . . . . . . . . . . . . . . 379
flushing input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
fmakunbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
fn in function’s documentation string . . . . . . . . . 306
focus event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
focus-follows-mouse . . . . . . . . . . . . . . . . . . . . . . . . 828
focus-in-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1399
focus-out-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1399
follow links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934
follow-link (button property) . . . . . . . . . . . . . . 1233
follow-link (text or overlay property). . . . . . . . 935
following-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
font and color, frame parameters . . . . . . . . . . . . . . 818
font backend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186
font entity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186
font information for layout . . . . . . . . . . . . . . . . . . . 1189
font lock faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
Font Lock mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
font lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1181
font object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
font property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
font registry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185

Index

font selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180
font spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
font, a frame parameter . . . . . . . . . . . . . . . . . . . . . . 819
font-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
font-backend, a frame parameter . . . . . . . . . . . . . 818
font-face-attributes . . . . . . . . . . . . . . . . . . . . . . 1187
font-family-list . . . . . . . . . . . . . . . . . . . . . . . . . . . 1168
font-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186
font-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187
font-lock-add-keywords . . . . . . . . . . . . . . . . . . . . . 569
font-lock-bracket-face . . . . . . . . . . . . . . . . . . . . . 575
font-lock-builtin-face . . . . . . . . . . . . . . . . . . . . . 574
font-lock-comment-delimiter-face . . . . . . . . . 574
font-lock-comment-face . . . . . . . . . . . . . . . . . . . . . 574
font-lock-constant-face . . . . . . . . . . . . . . . . . . . . 574
font-lock-debug-fontify . . . . . . . . . . . . . . . . . . . . 564
font-lock-defaults . . . . . . . . . . . . . . . . . . . . . . . . . . 565
font-lock-delimiter-face . . . . . . . . . . . . . . . . . . . 575
font-lock-doc-face . . . . . . . . . . . . . . . . . . . . . . . . . . 574
font-lock-doc-markup-face. . . . . . . . . . . . . . . . . . 574
font-lock-ensure &optional beg end . . . . . . . . 564
font-lock-ensure-function. . . . . . . . . . . . . . . . . . 572
font-lock-escape-face . . . . . . . . . . . . . . . . . . . . . . 574
font-lock-extend-after-changeregion-function . . . . . . . . . . . . . . . . . . . . . . . . . . . 578
font-lock-extra-managed-props . . . . . . . . . . . . . 571
font-lock-face (text property). . . . . . . . . . . . . . . 925
font-lock-flush &optional beg end. . . . . . . . . . 564
font-lock-flush-function . . . . . . . . . . . . . . . . . . . 572
font-lock-fontify-buffer . . . . . . . . . . . . . . . . . . . 564
font-lock-fontify-buffer-function . . . . . . . . 571
font-lock-fontify-region beg end&optional loudly . . . . . . . . . . . . . . . . . . . . . . . . . . 564
font-lock-fontify-region-function . . . . . . . . 571
font-lock-function-call-face . . . . . . . . . . . . . . 574
font-lock-function-name-face . . . . . . . . . . . . . . 573
font-lock-ignore . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
font-lock-keyword-face . . . . . . . . . . . . . . . . . . . . . 574
font-lock-keywords . . . . . . . . . . . . . . . . . . . . . . . . . . 565
font-lock-keywords-case-fold-search . . . . . . 568
font-lock-keywords-only . . . . . . . . . . . . . . . . . . . . 576
font-lock-mark-block-function . . . . . . . . . . . . . 571
font-lock-misc-punctuation-face . . . . . . . . . . . 575
font-lock-multiline . . . . . . . . . . . . . . . . . . . . . . . . 577
font-lock-negation-char-face . . . . . . . . . . . . . . 574
font-lock-number-face . . . . . . . . . . . . . . . . . . . . . . 575
font-lock-operator-face . . . . . . . . . . . . . . . . . . . . 575
font-lock-preprocessor-face . . . . . . . . . . . . . . . 574
font-lock-property-name-face . . . . . . . . . . . . . . 575
font-lock-property-use-face . . . . . . . . . . . . . . . 575
font-lock-punctuation-face . . . . . . . . . . . . . . . . 575
font-lock-remove-keywords. . . . . . . . . . . . . . . . . . 569
font-lock-string-face . . . . . . . . . . . . . . . . . . . . . . 574
font-lock-syntactic-face-function . . . . . . . . 576
font-lock-syntax-table . . . . . . . . . . . . . . . . . . . . . 576
font-lock-type-face . . . . . . . . . . . . . . . . . . . . . . . . 574
font-lock-unfontify-buffer . . . . . . . . . . . . . . . . 564
font-lock-unfontify-buffer-function . . . . . . 571

1422

font-lock-unfontify-region beg end . . . . . . . . 564
font-lock-unfontify-region-function . . . . . . 571
font-lock-variable-name-face . . . . . . . . . . . . . . 574
font-lock-variable-use-face . . . . . . . . . . . . . . . 574
font-lock-warning-face . . . . . . . . . . . . . . . . . . . . . 573
font-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186
font-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
font-xlfd-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187
fontification-functions . . . . . . . . . . . . . . . . . . . 1178
fontifications with tree-sitter, overview . . . . . . . . 578
fontified (text property) . . . . . . . . . . . . . . . . . . . . 926
fontp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
fontset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1182
foo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
force coding system for operation . . . . . . . . . . . . . 986
force entry to debugger . . . . . . . . . . . . . . . . . . . . . . . 337
force-mode-line-update . . . . . . . . . . . . . . . . . . . . . 550
force-window-update . . . . . . . . . . . . . . . . . . . . . . . 1130
forcing redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
foreground-color, a frame parameter . . . . . . . . 819
form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
form, self-evaluating . . . . . . . . . . . . . . . . . . . . . . . . . . 146
format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
format definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655
format of gnutls cryptography inputs . . . . . . . . . . 947
format of keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
format specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
format, customization keyword . . . . . . . . . . . . . . . 291
format-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655
format-find-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656
format-insert-file . . . . . . . . . . . . . . . . . . . . . . . . . . 656
format-message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
format-mode-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
format-network-address . . . . . . . . . . . . . . . . . . . . 1121
format-prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
format-seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1279
format-spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
format-time-string . . . . . . . . . . . . . . . . . . . . . . . . 1276
format-write-file . . . . . . . . . . . . . . . . . . . . . . . . . . . 656
formatting numbers for rereading later . . . . . . . . . 69
formatting strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
formatting time values . . . . . . . . . . . . . . . . . . . . . . . 1276
formfeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
forms for cleanup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
forms for control structures . . . . . . . . . . . . . . . . . . . 158
forms for handling errors . . . . . . . . . . . . . . . . . . . . . . 182
forms for nonlocal exits . . . . . . . . . . . . . . . . . . . . . . . 177
forms for sequential execution . . . . . . . . . . . . . . . . . 158
forms, backquote. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
forms, conditional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
forms, function call . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
forms, iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
forms, list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
forms, macro call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
forms, quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
forms, special . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
forms, symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Indexforward-button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
forward-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
forward-comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1031
forward-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
forward-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
forward-sexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862
forward-to-indentation . . . . . . . . . . . . . . . . . . . . . 915
forward-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
forward-word-strictly . . . . . . . . . . . . . . . . . . . . . . 856
frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
frame configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
frame creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786
frame geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
frame height ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808
frame interaction parameters . . . . . . . . . . . . . . . . . . 812
frame layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
frame layout parameters . . . . . . . . . . . . . . . . . . . . . . 810
frame parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802
frame parameters for windowed displays . . . . . . . 805
frame position . . . . . . . . . . . . . . . . . . . . . . . 791, 798, 805
frame position changes, a hook . . . . . . . . . . . . . . . . 798
frame size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791, 799
frame stacking order . . . . . . . . . . . . . . . . . . . . . . . . . . 829
frame title . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821
frame visibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
frame width ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808
frame without a minibuffer . . . . . . . . . . . . . . . . . . . . 824
frame Z-order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
frame, which buffers to display . . . . . . . . . . . . . . . . 812
frame-alpha-lower-limit . . . . . . . . . . . . . . . . . . . . 819
frame-ancestor-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
frame-auto-hide-function . . . . . . . . . . . . . . . . . . . 751
frame-char-height . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
frame-char-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
frame-current-scroll-bars . . . . . . . . . . . . . . . . 1195
frame-edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
frame-first-window . . . . . . . . . . . . . . . . . . . . . . . . . . 694
frame-focus-state . . . . . . . . . . . . . . . . . . . . . . . . . . . 827
frame-geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
frame-height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-inherited-parameters . . . . . . . . . . . . . . . . 787
frame-inhibit-implied-resize . . . . . . . . . . . . . . 802
frame-inner-height . . . . . . . . . . . . . . . . . . . . . . . . . . 800
frame-inner-width . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
frame-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
frame-list-z-order . . . . . . . . . . . . . . . . . . . . . . . . . . 823
frame-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
frame-monitor-attributes . . . . . . . . . . . . . . . . . . . 790
frame-native-height . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-native-width . . . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-old-selected-window. . . . . . . . . . . . . . . . . . 783
frame-outer-height . . . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-outer-width . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803
frame-parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803
frame-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
frame-pointer-visible-p . . . . . . . . . . . . . . . . . . . . 836
frame-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798

1423

frame-predicate, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
frame-relative coordinate . . . . . . . . . . . . . . . . . . . . . . 769
frame-resize-pixelwise . . . . . . . . . . . . . . . . . . . . . 800
frame-restack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
frame-root-window . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
frame-scroll-bar-height . . . . . . . . . . . . . . . . . . . 1195
frame-scroll-bar-width . . . . . . . . . . . . . . . . . . . . 1195
frame-selected-window . . . . . . . . . . . . . . . . . . . . . . 697
frame-size-changed-p . . . . . . . . . . . . . . . . . . . . . . . 801
frame-terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
frame-text-height . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
frame-text-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
frame-title-format . . . . . . . . . . . . . . . . . . . . . . . . . . 821
frame-visible-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
frame-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
frame-window-state-change. . . . . . . . . . . . . . . . . . 782
framep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
frames, scanning all . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
frameset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
free list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1350
free variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
free variable, byte-compiler warning . . . . . . . . . . . 321
free_global_ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1372
frequency counts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
frexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
fringe bitmaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
fringe bitmaps, customizing . . . . . . . . . . . . . . . . . . 1194
fringe cursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1192
fringe indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1190
fringe-bitmaps-at-pos . . . . . . . . . . . . . . . . . . . . . 1193
fringe-cursor-alist . . . . . . . . . . . . . . . . . . . . . . . 1192
fringe-indicator-alist . . . . . . . . . . . . . . . . . . . . 1191
fringes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1189
fringes, and empty line indication . . . . . . . . . . . . 1190
fringes-outside-margins . . . . . . . . . . . . . . . . . . . 1189
front-sticky text property . . . . . . . . . . . . . . . . . . . . . 932
fround. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
fset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
ftp-login . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
ftruncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
full keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
full-height window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
full-width window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
fullboth frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
fullheight frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
fullscreen, a frame parameter . . . . . . . . . . . . . . . 809
fullscreen-restore, a frame parameter . . . . . . 809
fullwidth frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
func-arity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
funcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239, 1374
funcall, and debugging . . . . . . . . . . . . . . . . . . . . . . 343
funcall-interactively . . . . . . . . . . . . . . . . . . . . . . 433
function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
function aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
function call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
function call debugging . . . . . . . . . . . . . . . . . . . . . . . 336
function cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

Indexfunction cell in autoload . . . . . . . . . . . . . . . . . . . . . . 305
function declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
function definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
function descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
function form evaluation . . . . . . . . . . . . . . . . . . . . . . 148
function groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
function input stream . . . . . . . . . . . . . . . . . . . . . . . . . 372
function invocation . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
function keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
function name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
function not known to be defined,
compilation warning . . . . . . . . . . . . . . . . . . . . . . . . 321
function output stream . . . . . . . . . . . . . . . . . . . . . . . 375
function quoting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
function safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
function’s documentation string . . . . . . . . . . . . . . . 235
function-alias-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
function-documentation . . . . . . . . . . . . . . . . . . . . . 596
function-documentation property . . . . . . . . . . . . 595
function-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
function-history (function
symbol property) . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
function-key-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
function-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
functionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
functionp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
functions in modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
functions, making them interactive . . . . . . . . . . . . 424
fundamental-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
fundamental-mode-abbrev-table . . . . . . . . . . . . 1071
future history in minibuffer input . . . . . . . . . . . . . 386

Ggamma correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818
gap-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689
gap-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689
garbage collection. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1350
garbage collection protection . . . . . . . . . . . . . . . . . 1358
garbage-collect . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1351
garbage-collection-messages . . . . . . . . . . . . . . 1353
gc-cons-percentage . . . . . . . . . . . . . . . . . . . . . . . . 1353
gc-cons-percentage, in batch mode . . . . . . . . . 1290
gc-cons-threshold . . . . . . . . . . . . . . . . . . . . . . . . . . 1353
gc-elapsed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
gcs-done . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
generalized variable . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
generate-new-buffer . . . . . . . . . . . . . . . . . . . . . . . . 685
generate-new-buffer-name . . . . . . . . . . . . . . . . . . . 675
generated-autoload-file . . . . . . . . . . . . . . . . . . . . 307
generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
generic commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
generic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
generic mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
gensym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
geometry specification . . . . . . . . . . . . . . . . . . . . . . . . 820
get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
get node, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . . . 1045

1424

get, defcustom keyword . . . . . . . . . . . . . . . . . . . . . . 282
get-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
get-buffer-create . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
get-buffer-process . . . . . . . . . . . . . . . . . . . . . . . . 1100
get-buffer-window . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
get-buffer-window-list . . . . . . . . . . . . . . . . . . . . . 721
get-buffer-xwidgets . . . . . . . . . . . . . . . . . . . . . . . 1229
get-byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
get-char-code-property . . . . . . . . . . . . . . . . . . . . . 971
get-char-property . . . . . . . . . . . . . . . . . . . . . . . . . . . 918
get-char-property-and-overlay . . . . . . . . . . . . . 918
get-charset-property . . . . . . . . . . . . . . . . . . . . . . . 974
get-device-terminal . . . . . . . . . . . . . . . . . . . . . . . . 787
get-display-property . . . . . . . . . . . . . . . . . . . . . . 1199
get-file-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676
get-internal-run-time . . . . . . . . . . . . . . . . . . . . . 1280
get-largest-window . . . . . . . . . . . . . . . . . . . . . . . . . . 719
get-load-suffixes . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
get-lru-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
get-mru-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
get-pos-property . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918
get-process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093
get-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
get-text-property . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
get-unused-category . . . . . . . . . . . . . . . . . . . . . . . 1037
get-variable-watchers . . . . . . . . . . . . . . . . . . . . . . 200
get-window-with-predicate. . . . . . . . . . . . . . . . . . 719
get_function_finalizer . . . . . . . . . . . . . . . . . . . . 1366
get_user_finalizer . . . . . . . . . . . . . . . . . . . . . . . . 1373
getenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1266
gethash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
GID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
global binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
global break condition . . . . . . . . . . . . . . . . . . . . . . . . 351
global keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
global variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
global-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . 1071
global-buffers-menu-map . . . . . . . . . . . . . . . . . . . 1396
global-disable-point-adjustment . . . . . . . . . . . 440
global-key-binding . . . . . . . . . . . . . . . . . . . . . . . . . . 503
global-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
global-minor-modes . . . . . . . . . . . . . . . . . . . . . . . . . . 544
global-mode-string . . . . . . . . . . . . . . . . . . . . . . . . . . 556
global-set-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
global-unset-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
glyph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
glyph code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
glyph-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
glyph-face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
glyphless characters . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
glyphless-char face . . . . . . . . . . . . . . . . . . . . . . . . 1246
glyphless-char-display . . . . . . . . . . . . . . . . . . . . 1246
glyphless-char-display-control . . . . . . . . . . . 1246
glyphless-display-mode . . . . . . . . . . . . . . . . . . . . 1245
GNU ELPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
gnutls cryptographic functions . . . . . . . . . . . . . . . . 947
gnutls cryptography inputs format . . . . . . . . . . . . 947
gnutls-ciphers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948

Indexgnutls-digests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 947
gnutls-hash-digest . . . . . . . . . . . . . . . . . . . . . . . . . . 947
gnutls-hash-mac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948
gnutls-macs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948
gnutls-symmetric-decrypt . . . . . . . . . . . . . . . . . . . 949
gnutls-symmetric-encrypt . . . . . . . . . . . . . . . . . . . 948
goto-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
goto-history-element . . . . . . . . . . . . . . . . . . . . . . . 418
goto-line-history . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
goto-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
grammar, SMIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
grand-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
grapheme cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1161
graphical display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
graphical terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
grave accent, quoting in
documentation strings . . . . . . . . . . . . . . . . . . . . . 1339
great-grand-parent . . . . . . . . . . . . . . . . . . . . . . . . . . 593
group, customization keyword . . . . . . . . . . . . . . . . . 277
group-function, in completion . . . . . . . . . . . . . . . 410
group-gid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
group-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
group-real-gid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
groups of functions . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
gui-get-selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
gui-set-selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
guidelines for buffer display . . . . . . . . . . . . . . . . . . . 743
gv-define-expander . . . . . . . . . . . . . . . . . . . . . . . . . . 226
gv-define-setter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
gv-define-simple-setter . . . . . . . . . . . . . . . . . . . . 225
gv-letplace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

H
hack-connection-local-variables . . . . . . . . . . . 220
hack-connection-local-variables-apply . . . . 220
hack-dir-local-variables . . . . . . . . . . . . . . . . . . . 217
hack-dir-local-variablesnon-file-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
hack-local-variables . . . . . . . . . . . . . . . . . . . . . . . 214
hack-local-variables-hook. . . . . . . . . . . . . . . . . . 215
Hamming weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
handle Lisp errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
handle-focus-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
handle-shift-selection . . . . . . . . . . . . . . . . . . . . . 876
handle-switch-frame . . . . . . . . . . . . . . . . . . . . . . . . 826
handling errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1300
has error, tree-sitter node . . . . . . . . . . . . . . . . . . . . 1052
hash code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
hash notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
hash table access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
hash tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
hash, cryptographic . . . . . . . . . . . . . . . . . . . . . . 944, 946
hash-table-count . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
hash-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
hash-table-rehash-size . . . . . . . . . . . . . . . . . . . . . 132
hash-table-rehash-threshold . . . . . . . . . . . . . . . 132

1425

hash-table-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
hash-table-test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
hash-table-weakness . . . . . . . . . . . . . . . . . . . . . . . . 132
hashing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
header comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1343
header line (of a window) . . . . . . . . . . . . . . . . . . . . . 559
header line alignment when line
numbers are displayed . . . . . . . . . . . . . . . . . . . . . 1202
header-line, prefix key . . . . . . . . . . . . . . . . . . . . . . . 462
header-line-format . . . . . . . . . . . . . . . . . . . . . . . . . . 559
header-line-format, a window parameter . . . . 779
header-line-format, and :align-to . . . . . . . . 1202
header-line-indent . . . . . . . . . . . . . . . . . . . . . . . . . . 559
header-line-indent-mode . . . . . . . . . . . . . . . . . . . . 559
header-line-indent-width . . . . . . . . . . . . . . . . . . . 560
height of a line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162
height of a window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
height spec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1163
height, a frame parameter . . . . . . . . . . . . . . . . . . . . 808
help for major mode . . . . . . . . . . . . . . . . . . . . . . . . . . 534
help functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602
help-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
help-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
help-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
help-echo (button property) . . . . . . . . . . . . . . . . 1232
help-echo (overlay property) . . . . . . . . . . . . . . . . 1154
help-echo (text property) . . . . . . . . . . . . . . . . . . . . 926
help-echo event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
help-echo text, avoid
command-key substitution . . . . . . . . . . . . . . . . . . 926
help-echo, customization keyword . . . . . . . . . . . . 292
help-echo-inhibit-substitution(text property) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926
help-event-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
help-form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
help-key-binding (face) . . . . . . . . . . . . . . . . . . . . . . 599
help-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 603
help-setup-xref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
help-window-select . . . . . . . . . . . . . . . . . . . . . . . . . . 604
Helper-describe-bindings . . . . . . . . . . . . . . . . . . . 604
Helper-help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
Helper-help-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
hex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
hidden buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
history list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
history of commands . . . . . . . . . . . . . . . . . . . . . . . . . . 477
history-add-new-input . . . . . . . . . . . . . . . . . . . . . . 393
history-delete-duplicates. . . . . . . . . . . . . . . . . . 393
history-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
HOME environment variable . . . . . . . . . . . . . . . . . . . 1078
hook variables, list of . . . . . . . . . . . . . . . . . . . . . . . . 1398
hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
hooks for changing a character . . . . . . . . . . . . . . . . 930
hooks for loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
hooks for motion of point . . . . . . . . . . . . . . . . . . . . . 930
hooks for text changes . . . . . . . . . . . . . . . . . . . . . . . . 961
hooks for window operations . . . . . . . . . . . . . . . . . . 779
horizontal combination . . . . . . . . . . . . . . . . . . . . . . . . 693

Indexhorizontal position . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
horizontal scrolling. . . . . . . . . . . . . . . . . . . . . . . . . . . . 767
horizontal-lineto . . . . . . . . . . . . . . . . . . . . . . . . . . 1218
horizontal-scroll-bar . . . . . . . . . . . . . . . . . . . . . 1197
horizontal-scroll-bar, prefix key . . . . . . . . . . . 462
horizontal-scroll-bar-mode . . . . . . . . . . . . . . . 1197
horizontal-scroll-bars, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810
horizontal-scroll-bars-available-p . . . . . . 1195
host language, tree-sitter . . . . . . . . . . . . . . . . . . . . . 1059
how to visit files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
HTML DOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
hyper characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
hyperlinks in documentation strings . . . . . . . . . . 1339

I
icon keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227
icon types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227
icon-elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
icon-left, a frame parameter . . . . . . . . . . . . . . . . 807
icon-name, a frame parameter . . . . . . . . . . . . . . . . 815
icon-string. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
icon-title-format . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
icon-top, a frame parameter . . . . . . . . . . . . . . . . . 807
icon-type, a frame parameter . . . . . . . . . . . . . . . . 815
iconified frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
iconify-child-frame . . . . . . . . . . . . . . . . . . . . . . . . 834
iconify-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
iconify-frame event . . . . . . . . . . . . . . . . . . . . . . . . . 450
identical-contents objects, and byte-compiler . . . 35
identity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
idle timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284
idleness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284
IEEE floating point . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
if-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
ignore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
ignore-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
ignore-errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
ignore-window-parameters . . . . . . . . . . . . . . . . . . . 777
ignored-local-variable-values . . . . . . . . . . . . . 215
ignored-local-variables . . . . . . . . . . . . . . . . . . . . 216
image animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225
image descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207
image formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
image frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image maps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1210
image slice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
image types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
image-animate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225
image-animate-timer . . . . . . . . . . . . . . . . . . . . . . . 1225
image-at-point-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image-cache-eviction-delay . . . . . . . . . . . . . . . 1226
image-cache-size . . . . . . . . . . . . . . . . . . . . . . . . . . . 1226
image-compute-scaling-factor . . . . . . . . . . . . . 1211
image-crop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224

1426

image-current-frame . . . . . . . . . . . . . . . . . . . . . . . 1224
image-cut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image-decrease-size . . . . . . . . . . . . . . . . . . . . . . . 1224
image-default-frame-delay . . . . . . . . . . . . . . . . 1225
image-flip-horizontally . . . . . . . . . . . . . . . . . . . 1224
image-flip-vertically . . . . . . . . . . . . . . . . . . . . . 1224
image-flush. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225
image-format-suffixes . . . . . . . . . . . . . . . . . . . . . 1213
image-increase-size . . . . . . . . . . . . . . . . . . . . . . . 1224
image-load-path . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
image-load-path-for-library . . . . . . . . . . . . . . 1222
image-mask-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
image-minimum-frame-delay . . . . . . . . . . . . . . . . 1225
image-multi-frame-p . . . . . . . . . . . . . . . . . . . . . . . 1224
image-property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
image-rotate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
image-scaling-factor . . . . . . . . . . . . . . . . . . . . . . 1222
image-show-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 1225
image-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
image-transforms-p . . . . . . . . . . . . . . . . . . . . . . . . 1211
image-type-available-p . . . . . . . . . . . . . . . . . . . . 1207
image-types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207
ImageMagick images . . . . . . . . . . . . . . . . . . . . . . . . . 1212
imagemagick-enabled-types . . . . . . . . . . . . . . . . 1213
imagemagick-types . . . . . . . . . . . . . . . . . . . . . . . . . . 1212
imagemagick-types-inhibit . . . . . . . . . . . . . . . . 1213
images in buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
images, support for more formats . . . . . . . . . . . . 1212
Imenu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
imenu-add-to-menubar . . . . . . . . . . . . . . . . . . . . . . . 561
imenu-case-fold-search . . . . . . . . . . . . . . . . . . . . . 561
imenu-create-index-function . . . . . . . . . . . . . . . 562
imenu-extract-index-name-function . . . . . . . . 562
imenu-generic-expression . . . . . . . . . . . . . . . . . . . 561
imenu-prev-index-position-function . . . . . . . 562
imenu-syntax-alist . . . . . . . . . . . . . . . . . . . . . . . . . . 562
implicit progn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
implied frame resizing. . . . . . . . . . . . . . . . . . . . . . . . . 801
implied resizing of frame . . . . . . . . . . . . . . . . . . . . . . 801
inactive minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
inc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
indefinite extent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
indent-according-to-mode . . . . . . . . . . . . . . . . . . . 912
indent-code-rigidly . . . . . . . . . . . . . . . . . . . . . . . . 914
indent-for-tab-command . . . . . . . . . . . . . . . . . . . . . 911
indent-line-function . . . . . . . . . . . . . . . . . . . . . . . 911
indent-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913
indent-region-function . . . . . . . . . . . . . . . . . . . . . 913
indent-relative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
indent-relative-first-indent-point . . . . . . . 915
indent-rigidly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
indent-tabs-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911
indent-to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911
indent-to-left-margin . . . . . . . . . . . . . . . . . . . . . . 903
indentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
indentation rules, forparser-based indentation . . . . . . . . . . . . . . . . . . . . 591

Indexindentation rules, SMIE . . . . . . . . . . . . . . . . . . . . . . . 587
indicate-buffer-boundaries . . . . . . . . . . . . . . . 1190
indicate-empty-lines . . . . . . . . . . . . . . . . . . . . . . 1190
indicators, fringe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1190
indirect buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687
indirect specifications . . . . . . . . . . . . . . . . . . . . . . . . . 361
indirect-function . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
indirect-variable . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
indirection for functions . . . . . . . . . . . . . . . . . . . . . . . 147
infinite loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
infinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
information of node, syntax trees . . . . . . . . . . . . 1051
inheritance, for faces . . . . . . . . . . . . . . . . . . . . . . . . . 1167
inheritance, keymap . . . . . . . . . . . . . . . . . . . . . . . . . . 487
inheritance, syntax table . . . . . . . . . . . . . . . . . . . . . 1022
inheritance, text property . . . . . . . . . . . . . . . . . . . . . 932
inhibit asynchronous native compilation . . . . . . . 331
inhibit-default-init . . . . . . . . . . . . . . . . . . . . . . 1259
inhibit-double-buffering, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
inhibit-eol-conversion . . . . . . . . . . . . . . . . . . . . . 987
inhibit-field-text-motion. . . . . . . . . . . . . . . . . . 855
inhibit-file-name-handlers . . . . . . . . . . . . . . . . 652
inhibit-file-name-operation . . . . . . . . . . . . . . . 652
inhibit-interaction . . . . . . . . . . . . . . . . . . . . . . . . 420
inhibit-isearch (text property) . . . . . . . . . . . . . 927
inhibit-iso-escape-detection . . . . . . . . . . . . . . 981
inhibit-local-variables-regexps . . . . . . 214, 532
inhibit-message . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1133
inhibit-message-regexps . . . . . . . . . . . . . . . . . . . 1133
inhibit-modification-hooks . . . . . . . . . . . . . . . . 962
inhibit-null-byte-detection . . . . . . . . . . . . . . . 981
inhibit-point-motion-hooks . . . . . . . . . . . . . . . . 931
inhibit-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
inhibit-read-only . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
inhibit-read-only (text property) . . . . . . . . . . . 927
inhibit-same-window, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
inhibit-splash-screen . . . . . . . . . . . . . . . . . . . . . 1257
inhibit-startup-echo-area-message . . . . . . . 1257
inhibit-startup-message . . . . . . . . . . . . . . . . . . . 1257
inhibit-startup-screen . . . . . . . . . . . . . . . . . . . . 1257
inhibit-switch-frame, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
inhibit-x-resources . . . . . . . . . . . . . . . . . . . . . . . . 849
init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258
init-file-user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
init.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1258
initial-buffer-choice . . . . . . . . . . . . . . . . . . . . . 1257
initial-environment . . . . . . . . . . . . . . . . . . . . . . . 1267
initial-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . 804
initial-major-mode . . . . . . . . . . . . . . . . . . . . . . . . . . 532
initial-scratch-message . . . . . . . . . . . . . . . . . . . 1258
initial-window-system . . . . . . . . . . . . . . . . . . . . . 1248
initial-window-system, and startup . . . . . . . . 1255
initialization of Emacs . . . . . . . . . . . . . . . . . . . . . . . 1255
initialize, defcustom keyword . . . . . . . . . . . . . . 282
initiating drag-and-drop. . . . . . . . . . . . . . . . . . . . . . . 843

1427

initiating drag-and-drop, low-level . . . . . . . . . . . . . 844
inline completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
inline functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
inline-const-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
inline-const-val . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
inline-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
inline-letevals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
inline-quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
inner edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
inner frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
inner height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
inner size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
inner width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
innermost containing parentheses . . . . . . . . . . . . 1033
input devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
input events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
input events, prevent recording . . . . . . . . . . . . . . . . 468
input focus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824
input methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 990
input modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1285
input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
input-decode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
input-method-alist . . . . . . . . . . . . . . . . . . . . . . . . . . 991
input-method-function . . . . . . . . . . . . . . . . . . . . . . 467
input-pending-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
insecure text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883
insert-abbrev-table-description. . . . . . . . . . 1067
insert-and-inherit . . . . . . . . . . . . . . . . . . . . . . . . . . 933
insert-before-markers . . . . . . . . . . . . . . . . . . . . . . 883
insert-before-markers-and-inherit . . . . . . . . 933
insert-behind-hooks (overlay property) . . . . . 1155
insert-behind-hooks (text property) . . . . . . . . . 930
insert-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884
insert-buffer-substring . . . . . . . . . . . . . . . . . . . . 883
insert-buffer-substring-as-yank . . . . . . . . . . . 891
insert-buffer-substring-no-properties . . . . 884
insert-button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
insert-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883
insert-default-directory . . . . . . . . . . . . . . . . . . . 406
insert-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
insert-directory-program . . . . . . . . . . . . . . . . . . . 648
insert-file-contents . . . . . . . . . . . . . . . . . . . . . . . 614
insert-file-contents-literally . . . . . . . . . . . . 615
insert-for-yank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 891
insert-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222
insert-in-front-hooks (overlay property) . . 1155
insert-in-front-hooks (text property). . . . . . . 930
insert-into-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 884
insert-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
insert-sliced-image . . . . . . . . . . . . . . . . . . . . . . . 1223
insert-text-button . . . . . . . . . . . . . . . . . . . . . . . . 1234
inserting killed text . . . . . . . . . . . . . . . . . . . . . . . . . . . 892
insertion before point . . . . . . . . . . . . . . . . . . . . . . . . . 882
insertion of text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882
insertion type of a marker . . . . . . . . . . . . . . . . . . . . . 872
inside comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033
inside string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033

Indexinspection of tree-sitter parse tree nodes. . . . . . 1041
installation-directory . . . . . . . . . . . . . . . . . . . . 1268
instrumenting for Edebug . . . . . . . . . . . . . . . . . . . . . 346
int-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
intangible (overlay property) . . . . . . . . . . . . . . . 1155
intangible (text property) . . . . . . . . . . . . . . . . . . . 927
integer range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
integer to decimal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
integer to hexadecimal . . . . . . . . . . . . . . . . . . . . . . . . . 67
integer to octal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
integer to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
integer types (C programming language) . . . . . 1388
integer-or-marker-p . . . . . . . . . . . . . . . . . . . . . . . . 870
integer-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
integerp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
integers in specific radix. . . . . . . . . . . . . . . . . . . . . . . . 38
interaction parameters between frames . . . . . . . . 812
interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
interactive call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
interactive code description . . . . . . . . . . . . . . . . . . . 427
interactive completion . . . . . . . . . . . . . . . . . . . . . . . . 427
interactive function . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
interactive spec, using . . . . . . . . . . . . . . . . . . . . . . . . 424
interactive specification in primitives . . . . . . . . . 1356
interactive, examples of using . . . . . . . . . . . . . . . 430
interactive-form . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
interactive-form property . . . . . . . . . . . . . . . . . . . 424
interactive-form, symbol property . . . . . . . . . . 424
interactive-only property . . . . . . . . . . . . . . . . . . . 424
intern. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137, 1374
intern-soft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
internal menu bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
internal representation of characters . . . . . . . . . . . 963
internal tool bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
internal windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
internal-border-width, a frame parameter. . . 810
internals, of buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 1378
internals, of process . . . . . . . . . . . . . . . . . . . . . . . . . . 1387
internals, of window . . . . . . . . . . . . . . . . . . . . . . . . . 1382
interning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
interpreter-mode-alist . . . . . . . . . . . . . . . . . . . . . 533
interprogram-cut-function. . . . . . . . . . . . . . . . . . 894
interprogram-paste-function . . . . . . . . . . . . . . . 894
interrupt Lisp functions . . . . . . . . . . . . . . . . . . . . . . . 471
interrupt-process . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
interrupt-process-functions . . . . . . . . . . . . . . 1098
intersection of sequences . . . . . . . . . . . . . . . . . . . . . . 113
intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 938
intervals-consed . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
invalid prefix key error . . . . . . . . . . . . . . . . . . . . . . . . 498
invalid-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
invalid-read-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
invalid-regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1004
invert-face. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
invisible (overlay property) . . . . . . . . . . . . . . . . 1155
invisible (text property) . . . . . . . . . . . . . . . . . . . . 927

1428

invisible frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
invisible text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
invisible-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1144
invisible/intangible text, and point . . . . . . . . . . . . 439
invocation-directory . . . . . . . . . . . . . . . . . . . . . . 1268
invocation-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
invoking input method . . . . . . . . . . . . . . . . . . . . . . . . 467
invoking lisp debugger . . . . . . . . . . . . . . . . . . . . . . . . 340
is this call interactive . . . . . . . . . . . . . . . . . . . . . . . . . 435
is_not_nil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374
isnan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
iso8601-parse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
ISO 8601 date/time strings . . . . . . . . . . . . . . . . 1276
ISO week, in time formatting . . . . . . . . . . . . . . . . 1277
italic text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165
iter-close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
iter-defun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
iter-do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
iter-lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
iter-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
iter-yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
iter-yield-from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
iteration over vector or string . . . . . . . . . . . . . . . . . 114

J
JavaScript Object Notation . . . . . . . . . . . . . . . . . . . 955
javascript-callback xwidget events . . . . . . . . . 450
jit-lock functions, debugging . . . . . . . . . . . . . . . . . . 572
jit-lock-debug-mode . . . . . . . . . . . . . . . . . . . . . . . . 572
jit-lock-register . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
jit-lock-unregister . . . . . . . . . . . . . . . . . . . . . . . . 572
joining lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
json-available-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955
json-insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
json-parse-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
json-parse-string . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
json-serialize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955
JSON remote procedure call protocol. . . . . . . . . . 956
jsonrpc-async-request . . . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-connection . . . . . . . . . . . . . . . . . . . . . . . . . . 956
jsonrpc-connection-ready-p . . . . . . . . . . . . . . . . 959
jsonrpc-connection-receive . . . . . . . . . . . . . . . . 957
jsonrpc-connection-send . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958
jsonrpc-notify . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-process-connection . . . . . . . . . . . . . . . . 958
jsonrpc-request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-running-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 957
jsonrpc-shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957
JSON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955
JSONRPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956
JSONRPC application interfaces . . . . . . . . . . . . . . 957
JSONRPC connection initargs . . . . . . . . . . . . . . . . 958
JSONRPC deferred requests . . . . . . . . . . . . . . . . . . 959
JSONRPC object format . . . . . . . . . . . . . . . . . . . . . 958

IndexJSONRPC process-based connections . . . . . . . . . 958
jumbled display of bidirectional text . . . . . . . . . 1252
just-one-space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
justify-current-line . . . . . . . . . . . . . . . . . . . . . . . 901

K
kbd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
kbd-macro-termination-hook . . . . . . . . . . . . . . . . 479
keep-ratio, a frame parameter . . . . . . . . . . . . . . . 813
kept-new-versions . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
kept-old-versions . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
key binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
key binding, conventions for. . . . . . . . . . . . . . . . . . 1334
key lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
key sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
key sequence error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
key sequence input . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
key substitution sequence . . . . . . . . . . . . . . . . . . . . . 598
key translation function . . . . . . . . . . . . . . . . . . . . . . . 505
key-binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
key-description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
key-translate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
key-translation-map . . . . . . . . . . . . . . . . . . . . . . . . 505
key-valid-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
keyboard events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
keyboard events in strings. . . . . . . . . . . . . . . . . . . . . 459
keyboard events, data in . . . . . . . . . . . . . . . . . . . . . . 456
keyboard input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
keyboard input decoding on X . . . . . . . . . . . . . . . . 991
keyboard macro execution . . . . . . . . . . . . . . . . . . . . 434
keyboard macro termination . . . . . . . . . . . . . . . . . 1247
keyboard macro, terminating . . . . . . . . . . . . . . . . . . 469
keyboard macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
keyboard macros (Edebug) . . . . . . . . . . . . . . . . . . . . 348
keyboard-coding-system . . . . . . . . . . . . . . . . . . . . . 990
keyboard-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
keyboard-translate . . . . . . . . . . . . . . . . . . . . . . . . . . 502
keyboard-translate-table . . . . . . . . . . . . . . . . . . . 466
keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
keymap (button property) . . . . . . . . . . . . . . . . . . . . 1232
keymap (overlay property) . . . . . . . . . . . . . . . . . . . . 1156
keymap (text property) . . . . . . . . . . . . . . . . . . . . . . . . 926
keymap entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
keymap format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
keymap in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
keymap inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
keymap inheritance from multiple maps . . . . . . . 487
keymap of character . . . . . . . . . . . . . . . . . . . . . . . . . . 926
keymap of character (and overlays) . . . . . . . . . . 1156
keymap prompt string . . . . . . . . . . . . . . . . . . . . . . . . 482
keymap-global-lookup . . . . . . . . . . . . . . . . . . . . . . . 496
keymap-global-set . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
keymap-global-unset . . . . . . . . . . . . . . . . . . . . . . . . 507
keymap-local-lookup . . . . . . . . . . . . . . . . . . . . . . . . 496
keymap-local-set . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
keymap-local-unset . . . . . . . . . . . . . . . . . . . . . . . . . . 507

1429

keymap-lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
keymap-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
keymap-prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
keymap-set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
keymap-set-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
keymap-unset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
keymapp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
keymaps for translating events . . . . . . . . . . . . . . . . 504
keymaps in modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
keymaps, scanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
keymaps, standard . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395
keys in documentation strings . . . . . . . . . . . . . . . . . 598
keys, reserved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334
keystroke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
keyword symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
keywordp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
kill command repetition . . . . . . . . . . . . . . . . . . . . . . . 436
kill ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
kill-all-local-variables . . . . . . . . . . . . . . . . . . . 211
kill-append . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
kill-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686
kill-buffer-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686
kill-buffer-hook in temporary buffers . . . . . . . 673
kill-buffer-query-functions . . . . . . . . . . . . . . . 686
kill-buffer-query-functions in
temporary buffers . . . . . . . . . . . . . . . . . . . . . . . . . . 673
kill-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
kill-emacs-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
kill-emacs-query-functions . . . . . . . . . . . . . . . 1263
kill-local-variable . . . . . . . . . . . . . . . . . . . . . . . . 210
kill-new . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
kill-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
kill-read-only-ok . . . . . . . . . . . . . . . . . . . . . . . . . . . 890
kill-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890
kill-ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
kill-ring-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
kill-ring-yank-pointer . . . . . . . . . . . . . . . . . . . . . 895
kill-xwidget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
killing buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
killing Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1262
kinship, syntax tree nodes . . . . . . . . . . . . . . . . . . . 1047
kmacro-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1396

Llabeled narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
labeled restriction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
lambda expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
lambda in debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
lambda in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
lambda list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
lambda-list (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . . 362
language argument, for tree-sitter . . . . . . . . . . . . 1039
language grammar version, compatibility . . . . . 1040
language grammar, for tree-sitter . . . . . . . . . . . . 1039
language-change event . . . . . . . . . . . . . . . . . . . . . . . 453
largest fixnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Indexlargest window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
last . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
last visible position in a window. . . . . . . . . . . . . . . 760
last-abbrev. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
last-abbrev-location . . . . . . . . . . . . . . . . . . . . . . 1070
last-abbrev-text . . . . . . . . . . . . . . . . . . . . . . . . . . . 1070
last-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
last-coding-system-used . . . . . . . . . . . . . . . . . . . . 979
last-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
last-command-event . . . . . . . . . . . . . . . . . . . . . . . . . . 438
last-event-device . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
last-event-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
last-input-event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
last-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479
last-nonmenu-event . . . . . . . . . . . . . . . . . . . . . . . . . . 438
last-prefix-arg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
last-repeatable-command . . . . . . . . . . . . . . . . . . . . 436
lax-plist-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
lax-plist-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
layout of frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
layout on display, and bidirectional text . . . . . . 1252
layout parameters of frames . . . . . . . . . . . . . . . . . . . 810
lazy evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
lazy loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
lazy-completion-table . . . . . . . . . . . . . . . . . . . . . . 398
ldexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
leaf node, of tree-sitter parse tree . . . . . . . . . . . . 1046
leap seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
least recently used window . . . . . . . . . . . . . . . . . . . . 719
left and right window decorations . . . . . . . . . . . . . 691
left position ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
left, a frame parameter . . . . . . . . . . . . . . . . . . . . . . 806
left-fringe, a frame parameter . . . . . . . . . . . . . . 810
left-fringe, prefix key . . . . . . . . . . . . . . . . . . . . . . . 462
left-fringe-width . . . . . . . . . . . . . . . . . . . . . . . . . . 1189
left-margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904
left-margin, prefix key . . . . . . . . . . . . . . . . . . . . . . . 462
left-margin-width . . . . . . . . . . . . . . . . . . . . . . . . . . 1205
length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
length< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
length= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
length> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
let* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
let-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
letrec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Levenshtein distance . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
lexical binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
lexical binding (Edebug) . . . . . . . . . . . . . . . . . . . . . . 353
lexical comparison of strings . . . . . . . . . . . . . . . . . . . 61
lexical environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
lexical scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
lexical-binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
library compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
library header comments . . . . . . . . . . . . . . . . . . . . . 1343
library search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
libxml-available-p . . . . . . . . . . . . . . . . . . . . . . . . . . 952

1430

libxml-parse-html-region . . . . . . . . . . . . . . . . . . . 952
libxml-parse-xml-region . . . . . . . . . . . . . . . . . . . . 952
line end conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
line height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797, 1162
line number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
line truncation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130
line wrapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130
line-beginning-position . . . . . . . . . . . . . . . . . . . . 857
line-end-position . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
line-height (text property) . . . . . . . . . . . . 929, 1162
line-move-ignore-invisible . . . . . . . . . . . . . . . 1144
line-number-at-pos . . . . . . . . . . . . . . . . . . . . . . . . . . 858
line-number-display-width . . . . . . . . . . . . . . . . 1162
line-pixel-height . . . . . . . . . . . . . . . . . . . . . . . . . . 1161
line-prefix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
line-spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1163
line-spacing (text property) . . . . . . . . . . . 929, 1163
line-spacing, a frame parameter . . . . . . . . . . . . . 811
lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 856
lines in region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
lineto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
link, customization keyword . . . . . . . . . . . . . . . . . . 277
linked list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
linking files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
Lisp debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
Lisp expression motion . . . . . . . . . . . . . . . . . . . . . . . . 861
Lisp history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Lisp library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
Lisp nesting error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Lisp object. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Lisp objects, stack-allocated . . . . . . . . . . . . . . . . . 1354
Lisp package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
Lisp printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
Lisp reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
Lisp timestamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
lisp variables defined in C, restrictions. . . . . . . . . 223
lisp-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
lisp-indent-function property . . . . . . . . . . . . . . 275
lisp-mode-abbrev-table . . . . . . . . . . . . . . . . . . . . 1071
lisp-mode-autoload-regexp. . . . . . . . . . . . . . . . . . 307
lisp-mode.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
list all coding systems . . . . . . . . . . . . . . . . . . . . . . . . . 979
list elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
list form evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
list in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
list length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
list modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
list motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
list of threads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
list predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
list reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
list structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16, 77
list to vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
list, replace element . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
list-buffers-directory . . . . . . . . . . . . . . . . . . . . . 677
list-charset-chars . . . . . . . . . . . . . . . . . . . . . . . . . . 974
list-fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1186

Indexlist-load-path-shadows . . . . . . . . . . . . . . . . . . . . . 303
list-multisession-values . . . . . . . . . . . . . . . . . . . 229
list-processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
list-system-processes . . . . . . . . . . . . . . . . . . . . . 1108
list-threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
list-timers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1284
listify-key-sequence . . . . . . . . . . . . . . . . . . . . . . . 469
listing all buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681
listp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
lists and cons cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
lists as sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
literal evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
literate programming . . . . . . . . . . . . . . . . . . . . . . . . . 912
little endian, in bindat specification . . . . . . . . . . 1125
live buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
live node, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . . 1052
live windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
ln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631
load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
load error with require . . . . . . . . . . . . . . . . . . . . . . . . 309
load errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
load, customization keyword . . . . . . . . . . . . . . . . . . 278
load-average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
load-changed xwidget event . . . . . . . . . . . . . . . . . . 449‘load-committed’ in xwidgets . . . . . . . . . . . . . . . . . 450
load-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
load-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
load-file-rep-suffixes . . . . . . . . . . . . . . . . . . . . . 301‘load-finished’ in xwidgets . . . . . . . . . . . . . . . . . . 449
load-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
load-in-progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
load-library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
load-path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
load-prefer-newer . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
load-read-function . . . . . . . . . . . . . . . . . . . . . . . . . . 300‘load-redirected’ in xwidgets . . . . . . . . . . . . . . . . 449‘load-started’ in xwidgets . . . . . . . . . . . . . . . . . . . 449
load-suffixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
load-theme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
loaddefs-generate . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
loading and configuring features . . . . . . . . . . . . . . . 311
loading hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
loading language grammar for tree-sitter . . . . . 1039
loading, and non-ASCII characters . . . . . . . . . . . . 304
loadup.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
local binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
local keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
local part of remote file name . . . . . . . . . . . . . . . . . 653
local variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
local variables, killed by major mode . . . . . . . . . . 211
local, defcustom keyword . . . . . . . . . . . . . . . . . . . . 283
local-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . 1071
local-function-key-map . . . . . . . . . . . . . . . . . . . . . 505
local-key-binding . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
local-map (overlay property) . . . . . . . . . . . . . . . . 1156
local-map (text property) . . . . . . . . . . . . . . . . . . . . 927

1431

local-minor-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
local-set-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
local-unset-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
local-variable-if-set-p . . . . . . . . . . . . . . . . . . . . 210
local-variable-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
locale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991
locale-coding-system . . . . . . . . . . . . . . . . . . . . . . . 991
locale-dependent string comparison . . . . . . . . . . . . . 62
locale-dependent string equivalence . . . . . . . . . . . . . 61
locale-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992
locate file in path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628
locate-dominating-file . . . . . . . . . . . . . . . . . . . . . 647
locate-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628
locate-library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
locate-user-emacs-file . . . . . . . . . . . . . . . . . . . . . 645
lock file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
lock-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
lock-file-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
lock-file-name-transforms. . . . . . . . . . . . . . . . . . 618
log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
logand. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
logb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
logcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
logging echo-area messages . . . . . . . . . . . . . . . . . . . 1137
logical arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
logical lines, moving by . . . . . . . . . . . . . . . . . . . . . . . 856
logical order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250
logical shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
logior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
lognot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
logxor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
looking up abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . 1069
looking up fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1181
looking-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1010
looking-at-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1011
looking-back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1010
lookup tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
lookup-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
loops, infinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
low-level key bindings . . . . . . . . . . . . . . . . . . . . . . . . . 501
lower case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
lower-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
lowering a frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
LRO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1253
lru-frames, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
lru-time, a buffer display action alist entry . . . 734
lsh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
lwarn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139

IndexM
M-g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
M-s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
M-S-x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
M-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
M-X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
Maclisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
macro argument evaluation . . . . . . . . . . . . . . . . . . . 272
macro call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
macro call evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 149
macro caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
macro compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
macro descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
macro expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
macro, how to define . . . . . . . . . . . . . . . . . . . . . . . . . . 270
macroexpand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
macroexpand-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
macroexpand-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
macrop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
macros, at compile time . . . . . . . . . . . . . . . . . . . . . . . 321
magic autoload comment . . . . . . . . . . . . . . . . . . . . . . 305
magic file names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
magic-fallback-mode-alist. . . . . . . . . . . . . . . . . . 533
magic-mode-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
mail-host-address . . . . . . . . . . . . . . . . . . . . . . . . . . 1266
main window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
main window of a frame . . . . . . . . . . . . . . . . . . . . . . 752
main-thread. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
major mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
major mode command . . . . . . . . . . . . . . . . . . . . . . . . 526
major mode conventions . . . . . . . . . . . . . . . . . . . . . . 528
major mode hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
major mode keymap . . . . . . . . . . . . . . . . . . . . . . . . . . 489
major mode, automatic selection . . . . . . . . . . . . . . 531
major mode, developing with tree-sitter . . . . . . 1061
major-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
major-mode-restore . . . . . . . . . . . . . . . . . . . . . . . . . . 527
major-mode-suspend . . . . . . . . . . . . . . . . . . . . . . . . . . 527
make-abbrev-table . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
make-auto-save-file-name . . . . . . . . . . . . . . . . . . . 665
make-backup-file-name . . . . . . . . . . . . . . . . . . . . . . 663
make-backup-file-name-function . . . . . . . . . . . . 660
make-backup-files . . . . . . . . . . . . . . . . . . . . . . . . . . . 660
make-bool-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
make-button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
make-byte-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
make-category-set . . . . . . . . . . . . . . . . . . . . . . . . . . 1037
make-category-table . . . . . . . . . . . . . . . . . . . . . . . 1037
make-char-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
make-composed-keymap . . . . . . . . . . . . . . . . . . . . . . . 487
make-condition-variable . . . . . . . . . . . . . . . . . . . 1076
make-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
make-display-table . . . . . . . . . . . . . . . . . . . . . . . . 1243
make-empty-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
make-finalizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
make-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786

1432

make-frame-invisible . . . . . . . . . . . . . . . . . . . . . . . 829
make-frame-on-display . . . . . . . . . . . . . . . . . . . . . . 789
make-frame-on-monitor . . . . . . . . . . . . . . . . . . . . . . 790
make-frame-visible . . . . . . . . . . . . . . . . . . . . . . . . . . 829
make-frame-visible event . . . . . . . . . . . . . . . . . . . . 451
make-glyph-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
make-hash-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
make-help-screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
make-indirect-buffer . . . . . . . . . . . . . . . . . . . . . . . 687
make-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
make-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
make-local-variable . . . . . . . . . . . . . . . . . . . . . . . . 208
make-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
make-multisession . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
make-mutex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
make-nearby-temp-file . . . . . . . . . . . . . . . . . . . . . . 643
make-network-process . . . . . . . . . . . . . . . . . . . . . . 1115
make-obsolete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
make-obsolete-generalized-variable . . . . . . . 227
make-obsolete-variable . . . . . . . . . . . . . . . . . . . . . 222
make-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
make-pipe-process . . . . . . . . . . . . . . . . . . . . . . . . . . 1088
make-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086
make-progress-reporter . . . . . . . . . . . . . . . . . . . . 1135
make-record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
make-ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
make-serial-process . . . . . . . . . . . . . . . . . . . . . . . 1122
make-sparse-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . 483
make-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
make-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
make-symbolic-link . . . . . . . . . . . . . . . . . . . . . . . . . . 631
make-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . 1027
make-temp-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
make-temp-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
make-text-button . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234
make-thread. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
make-translation-table . . . . . . . . . . . . . . . . . . . . . 975
make-translation-table-from-alist . . . . . . . . 976
make-translation-table-from-vector . . . . . . . 976
make-variable-buffer-local . . . . . . . . . . . . . . . . 209
make-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
make-vtable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
make-xwidget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
make_big_integer . . . . . . . . . . . . . . . . . . . . . . . . . . . 1369
make_float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1371
make_function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364
make_global_ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1372
make_integer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1369
make_interactive . . . . . . . . . . . . . . . . . . . . . . . . . . . 1365
make_string. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1372
make_time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1372
make_unibyte_string . . . . . . . . . . . . . . . . . . . . . . . 1372
make_user_ptr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1373
making backup files . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
making buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1233
makunbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
malicious use of directional overrides . . . . . . . . . 1253
managing overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150

Indexmanipulating buttons . . . . . . . . . . . . . . . . . . . . . . . . 1234
map-char-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
map-charset-chars . . . . . . . . . . . . . . . . . . . . . . . . . . . 974
map-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
map-y-or-n-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
mapatoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
mapbacktrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
mapc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
mapcan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
mapcar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
mapconcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
maphash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
mapped frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
mapping functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
margins, display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1205
margins, filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902
mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
mark excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
mark ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
mark, the . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
mark-active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876
mark-even-if-inactive . . . . . . . . . . . . . . . . . . . . . . 875
mark-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
mark-ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876
mark-ring-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
marker argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
marker creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
marker garbage collection . . . . . . . . . . . . . . . . . . . . . 869
marker information . . . . . . . . . . . . . . . . . . . . . . . . . . . 872
marker input stream . . . . . . . . . . . . . . . . . . . . . . . . . . 371
marker output stream . . . . . . . . . . . . . . . . . . . . . . . . . 375
marker relocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
marker, how to move position . . . . . . . . . . . . . . . . . 873
marker-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872
marker-insertion-type . . . . . . . . . . . . . . . . . . . . . . 873
marker-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872
markerp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
markers as numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
markers, predicates for . . . . . . . . . . . . . . . . . . . . . . . . 870
match. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
match data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1011
match, customization keyword . . . . . . . . . . . . . . . . . 292
match-alternatives,
customization keyword. . . . . . . . . . . . . . . . . . . . . . 290
match-beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1014
match-buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1015
match-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1014
match-inline, customization keyword . . . . . . . . . 292
match-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1013
match-string-no-properties . . . . . . . . . . . . . . . 1014
match-substitute-replacement . . . . . . . . . . . . . 1013
matching, structural . . . . . . . . . . . . . . . . . . . . . . . . . . 171
mathematical functions . . . . . . . . . . . . . . . . . . . . . . . . 51
max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
max-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968
max-image-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223

1433

max-lisp-eval-depth . . . . . . . . . . . . . . . . . . . . . . . . 154
max-mini-window-height . . . . . . . . . . . . . . . . . . . . . 419
maximize-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
maximized frames. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 809
maximizing windows . . . . . . . . . . . . . . . . . . . . . . . . . . 706
maximum fixnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
maximum value of character codepoint . . . . . . . . 968
maximum value of sequence . . . . . . . . . . . . . . . . . . . 114
maximum-scroll-margin . . . . . . . . . . . . . . . . . . . . . . 764
maybe_quit, use in Lisp primitives . . . . . . . . . . . 1358
md5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
MD5 checksum. . . . . . . . . . . . . . . . . . . . . . . . . . . 944, 946
measuring resource usage . . . . . . . . . . . . . . . . . . . . . 369
member. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
member-ignore-case . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
membership in a list . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
memory allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1350
memory usage . . . . . . . . . . . . . . . . . . . . . . . . . . 369, 1355
memory-full. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
memory-info. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
memory-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
memory-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
memory-use-counts . . . . . . . . . . . . . . . . . . . . . . . . . . 1354
memq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
memql . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
menu bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
menu bar keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . 1396
menu definition example . . . . . . . . . . . . . . . . . . . . . . 515
menu item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
menu keymaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
menu modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
menu prompt string . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
menu separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
menu-bar, prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . 462
menu-bar-file-menu . . . . . . . . . . . . . . . . . . . . . . . . 1396
menu-bar-final-items . . . . . . . . . . . . . . . . . . . . . . . 517
menu-bar-help-menu . . . . . . . . . . . . . . . . . . . . . . . . 1396
menu-bar-lines, a frame parameter . . . . . . . . . . . 811
menu-bar-options-menu . . . . . . . . . . . . . . . . . . . . . 1396
menu-bar-tools-menu . . . . . . . . . . . . . . . . . . . . . . . 1396
menu-bar-update-hook . . . . . . . . . . . . . . . . . . . . . . . 517
menu-item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
menu-prompt-more-char . . . . . . . . . . . . . . . . . . . . . . 515
menus, popup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
merge-face-attribute . . . . . . . . . . . . . . . . . . . . . . 1172
message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
message digest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944
message, finding what causes aparticular message . . . . . . . . . . . . . . . . . . . . . . . . . . 335
message-box. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134
message-log-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1137
message-or-box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134
message-truncate-lines . . . . . . . . . . . . . . . . . . . . 1138
messages-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1137
messages-buffer-name . . . . . . . . . . . . . . . . . . . . . . 1137
meta character key constants. . . . . . . . . . . . . . . . . . 501
meta character printing . . . . . . . . . . . . . . . . . . . . . . . 601
meta characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Indexmeta characters lookup . . . . . . . . . . . . . . . . . . . . . . . 482
meta-prefix-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
min-height, a frame parameter . . . . . . . . . . . . . . . 809
min-margins, a window parameter . . . . . . . . . . . . 779
min-width, a frame parameter . . . . . . . . . . . . . . . . 808
minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
minibuffer completion . . . . . . . . . . . . . . . . . . . . . . . . . 398
minibuffer contents, accessing . . . . . . . . . . . . . . . . . 419
minibuffer history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
minibuffer input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
minibuffer input, andcommand-line arguments . . . . . . . . . . . . . . . . . . 1080
minibuffer input, reading lisp objects . . . . . . . . . . 391
minibuffer input, reading text strings . . . . . . . . . . 386
minibuffer window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
minibuffer window, and next-window . . . . . . . . . . 717
minibuffer windows . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
minibuffer, a frame parameter . . . . . . . . . . . . . . . 812
minibuffer-allow-text-properties . . . . . . . . . 389
minibuffer-auto-raise . . . . . . . . . . . . . . . . . . . . . . 830
minibuffer-beginning-ofbuffer-movement . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
minibuffer-complete . . . . . . . . . . . . . . . . . . . . . . . . 401
minibuffer-complete-and-exit . . . . . . . . . . . . . . 401
minibuffer-complete-word . . . . . . . . . . . . . . . . . . . 401
minibuffer-completion-confirm . . . . . . . . . . . . . 400
minibuffer-completion-help . . . . . . . . . . . . . . . . 401
minibuffer-completion-predicate . . . . . . . . . . . 400
minibuffer-completion-table . . . . . . . . . . . . . . . 400
minibuffer-confirm-exit-commands . . . . . . . . . 401
minibuffer-contents . . . . . . . . . . . . . . . . . . . . . . . . 420
minibuffer-contents-no-properties . . . . . . . . 420
minibuffer-default-add-function . . . . . . . . . . . 393
minibuffer-default-prompt-format . . . . . . . . . 390
minibuffer-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
minibuffer-exit, a frame parameter . . . . . . . . . 813
minibuffer-exit-hook . . . . . . . . . . . . . . . . . . . . . . . 421
minibuffer-frame-alist . . . . . . . . . . . . . . . . . . . . . 804
minibuffer-help-form . . . . . . . . . . . . . . . . . . . . . . . 421
minibuffer-history . . . . . . . . . . . . . . . . . . . . . . . . . . 394
minibuffer-inactive-mode . . . . . . . . . . . . . . . . . . . 422
minibuffer-inactive-mode-map . . . . . . . . . . . . . . . . 1396
minibuffer-less frame . . . . . . . . . . . . . . . . . . . . . . . . . . 795
minibuffer-local-completion-map . . . . . . . . . . . 402
minibuffer-local-filenamecompletion-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
minibuffer-local-map . . . . . . . . . . . . . . . . . . . . . . . 389
minibuffer-local-must-match-map . . . . . . . . . . . 402
minibuffer-local-ns-map . . . . . . . . . . . . . . . . . . . . 390
minibuffer-local-shell-command-map . . . . . . . 407
minibuffer-message . . . . . . . . . . . . . . . . . . . . . . . . . . 422
minibuffer-message (text property) . . . . . . . . . . 931
minibuffer-message-timeout . . . . . . . . . . . . . . . . 422
minibuffer-mode-map . . . . . . . . . . . . . . . . . . . . . . . . 389
minibuffer-only frame . . . . . . . . . . . . . . . . . . . . 795, 804
minibuffer-prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
minibuffer-prompt-end . . . . . . . . . . . . . . . . . . . . . . 419

1434

minibuffer-prompt-properties . . . . . . . . . . . . . . 387
minibuffer-prompt-width . . . . . . . . . . . . . . . . . . . . 420
minibuffer-scroll-window . . . . . . . . . . . . . . . . . . . 421
minibuffer-selected-window . . . . . . . . . . . . . . . . 421
minibuffer-setup-hook . . . . . . . . . . . . . . . . . . . . . . 421
minibuffer-window . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
minibuffer-window-active-p . . . . . . . . . . . . . . . . 418
minibuffer-with-setup-hook . . . . . . . . . . . . . . . . 421
minibufferp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
minimize-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
minimized frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
minimizing windows . . . . . . . . . . . . . . . . . . . . . . . . . . 706
minimum fixnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
minimum value of sequence . . . . . . . . . . . . . . . . . . . 114
minor mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
minor mode conventions . . . . . . . . . . . . . . . . . . . . . . 544
minor-mode-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556
minor-mode-key-binding . . . . . . . . . . . . . . . . . . . . . 497
minor-mode-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
minor-mode-map-alist . . . . . . . . . . . . . . . . . . . . . . . 492
minor-mode-overriding-map-alist . . . . . . . . . . . 492
mirroring of characters . . . . . . . . . . . . . . . . . . . . . . . . 970
missing node, tree-sitter . . . . . . . . . . . . . . . . . . . . . 1051
mkdir. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
mod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
mode bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
mode help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
mode hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
mode line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
mode line construct . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
mode loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
mode variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
mode, a buffer display action alist entry . . . . . . . . 731
mode-class (property) . . . . . . . . . . . . . . . . . . . . . . . . 531
mode-line, prefix key . . . . . . . . . . . . . . . . . . . . . . . . . 462
mode-line-buffer-identification . . . . . . . . . . . 554
mode-line-client . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
mode-line-coding-system-map . . . . . . . . . . . . . . 1396
mode-line-column-line-number-mode-map . . . 1396
mode-line-compact . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
mode-line-end-spaces . . . . . . . . . . . . . . . . . . . . . . . 555
mode-line-format . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
mode-line-format, a window parameter . . . . . . 778
mode-line-frame-identification . . . . . . . . . . . . 554
mode-line-front-space . . . . . . . . . . . . . . . . . . . . . . 555
mode-line-input-method-map . . . . . . . . . . . . . . . 1396
mode-line-misc-info . . . . . . . . . . . . . . . . . . . . . . . . 555
mode-line-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
mode-line-modified . . . . . . . . . . . . . . . . . . . . . . . . . . 554
mode-line-mule-info . . . . . . . . . . . . . . . . . . . . . . . . 554
mode-line-percent-position . . . . . . . . . . . . . . . . 554
mode-line-position . . . . . . . . . . . . . . . . . . . . . . . . . . 554
mode-line-position-column-format . . . . . . . . . 555
mode-line-position-column-line-format . . . . 555
mode-line-position-line-format . . . . . . . . . . . . 555
mode-line-process . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
mode-line-remote . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555

Indexmode-line-window-selected-p . . . . . . . . . . . . . . . 551
mode-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
mode-specific commands . . . . . . . . . . . . . . . . . . . . . . 430
mode-specific-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
model/view/controller . . . . . . . . . . . . . . . . . . . . . . . 1236
modification flag (of buffer) . . . . . . . . . . . . . . . . . . . 677
modification of lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
modification time of buffer . . . . . . . . . . . . . . . . . . . . 678
modification time of file . . . . . . . . . . . . . . . . . . . . . . . 625
modification-hooks (overlay property) . . . . . . 1155
modification-hooks (text property) . . . . . . . . . . 930
modifier bits (of input character) . . . . . . . . . . . . . . 440
modifiers of events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
modify a list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
modify-all-frames-parameters . . . . . . . . . . . . . . 803
modify-category-entry . . . . . . . . . . . . . . . . . . . . . 1038
modify-frame-parameters . . . . . . . . . . . . . . . . . . . . 803
modify-syntax-entry . . . . . . . . . . . . . . . . . . . . . . . 1027
modifying strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
module API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1361
module functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1363
module initialization . . . . . . . . . . . . . . . . . . . . . . . . . 1361
module runtime environment . . . . . . . . . . . . . . . . . 1362
module values, conversion . . . . . . . . . . . . . . . . . . . . 1366
module-file-suffix . . . . . . . . . . . . . . . . . . . . . . . . . . 314
module-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
momentary-string-display . . . . . . . . . . . . . . . . . . 1149
monitor change functions . . . . . . . . . . . . . . . . . . . . . 791
most recently selected windows. . . . . . . . . . . . . . . . 697
most recently used window . . . . . . . . . . . . . . . . . . . . 719
most-negative-fixnum . . . . . . . . . . . . . . . . . . . . . . . . 39
most-positive-fixnum . . . . . . . . . . . . . . . . . . . . . . . . 39
motion based on parsing . . . . . . . . . . . . . . . . . . . . . 1031
motion by chars, words, lines, lists . . . . . . . . . . . . 854
motion event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
mouse click event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
mouse drag event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
mouse dragging parameters . . . . . . . . . . . . . . . . . . . 813
mouse events, data in . . . . . . . . . . . . . . . . . . . . . . . . . 456
mouse events, in special parts ofwindow or frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
mouse events, repeated . . . . . . . . . . . . . . . . . . . . . . . 446
mouse motion events . . . . . . . . . . . . . . . . . . . . . . . . . . 447
mouse pointer shape . . . . . . . . . . . . . . . . . . . . . . . . . . 839
mouse position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
mouse position list . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
mouse position list, accessing. . . . . . . . . . . . . . . . . . 457
mouse tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
mouse wheel event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
mouse, a face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819
mouse, availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
mouse-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934
mouse-1-click-follows-link . . . . . . . . . . . . . . . . 935
mouse-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334
mouse-absolute-pixel-position . . . . . . . . . . . . . 836
mouse-action (button property) . . . . . . . . . . . . . 1232
mouse-appearance-menu-map . . . . . . . . . . . . . . . . 1396

1435

mouse-autoselect-window . . . . . . . . . . . . . . . . . . . . 773
mouse-color, a frame parameter . . . . . . . . . . . . . . 819
mouse-face (button property) . . . . . . . . . . . . . . . 1232
mouse-face (overlay property) . . . . . . . . . . . . . . . 1154
mouse-face (text property) . . . . . . . . . . . . . . . . . . . 925
mouse-fine-grained-tracking . . . . . . . . . . . . . . . 448
mouse-leave-buffer-hook . . . . . . . . . . . . . . . . . . . 1400
mouse-movement-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
mouse-on-link-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 936
mouse-pixel-position . . . . . . . . . . . . . . . . . . . . . . . 836
mouse-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
mouse-position-function . . . . . . . . . . . . . . . . . . . . 836
mouse-wheel-down-event . . . . . . . . . . . . . . . . . . . . . 451
mouse-wheel-frame, a frame parameter . . . . . . . 813
mouse-wheel-left-event . . . . . . . . . . . . . . . . . . . . . 451
mouse-wheel-right-event . . . . . . . . . . . . . . . . . . . . 451
mouse-wheel-up-event . . . . . . . . . . . . . . . . . . . . . . . 451
move to beginning or end of buffer . . . . . . . . . . . . 856
move-frame-functions . . . . . . . . . . . . . . . . . . . . . . . 798
move-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
move-overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151
move-point-visually . . . . . . . . . . . . . . . . . . . . . . . 1252
move-to-column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
move-to-left-margin . . . . . . . . . . . . . . . . . . . . . . . . 903
move-to-window-group-line. . . . . . . . . . . . . . . . . . 860
move-to-window-group-line-function . . . . . . . 860
move-to-window-line . . . . . . . . . . . . . . . . . . . . . . . . 859
movemail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
moveto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
moving across syntax classes . . . . . . . . . . . . . . . . . 1030
moving markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
MS-DOS and file modes. . . . . . . . . . . . . . . . . . . . . . . 621
MS-Windows file-name syntax . . . . . . . . . . . . . . . . 634
mule-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
multi-file package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1305
multi-frame images . . . . . . . . . . . . . . . . . . . . . . . . . . 1224
multi-message-max . . . . . . . . . . . . . . . . . . . . . . . . . . 1133
multi-message-timeout . . . . . . . . . . . . . . . . . . . . . 1133
multi-mode indentation . . . . . . . . . . . . . . . . . . . . . . . 912
multi-monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
multi-query-replace-map . . . . . . . . . . . . . . . . . . . 1019
multi-tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
multibyte characters . . . . . . . . . . . . . . . . . . . . . . . . . . 963
multibyte text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
multibyte-char-to-unibyte. . . . . . . . . . . . . . . . . . 966
multibyte-string-p . . . . . . . . . . . . . . . . . . . . . . . . . . 964
multibyte-syntax-as-symbol . . . . . . . . . . . . . . . 1034
multiline font lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576
multiple languages, parsing with tree-sitter . . . 1057
multiple terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
multiple windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
multiple X displays . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
multiple yes-or-no questions . . . . . . . . . . . . . . . . . . . 414
multiple-dispatch methods . . . . . . . . . . . . . . . . . . . . 248
multiple-frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
multisession variable . . . . . . . . . . . . . . . . . . . . . . . . . . 227
multisession-delete . . . . . . . . . . . . . . . . . . . . . . . . 229
multisession-directory . . . . . . . . . . . . . . . . . . . . . 229

Indexmultisession-edit-mode . . . . . . . . . . . . . . . . . . . . . 229
multisession-storage . . . . . . . . . . . . . . . . . . . . . . . 229
multisession-value . . . . . . . . . . . . . . . . . . . . . . . . . . 228
mutable lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
mutable objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
mutex-lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
mutex-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
mutex-unlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
mutexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
mwheel-coalesce-scroll-events . . . . . . . . . . . . . 451

Nn-p-gp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
name, a frame parameter . . . . . . . . . . . . . . . . . . . . . . 805
named function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
named node, tree-sitter . . . . . . . . . . . . . . . . . . . . . . 1041
named-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
namespace etiquette . . . . . . . . . . . . . . . . . . . . . . . . . . 142
namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
namespacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
naming backup files . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
NaN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
narrow-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1396
narrow-to-page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
narrow-to-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
native code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
native compilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
native compilation, prevent
writing *.eln files . . . . . . . . . . . . . . . . . . . . . . . . . . 327
native edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
native-comp-async-jobs-number . . . . . . . . . . . . . 330
native-comp-async-query-on-exit . . . . . . . . . . . 331
native-comp-async-reportwarnings-errors . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
native-comp-available-p . . . . . . . . . . . . . . . . . . . . 329
native-comp-debug . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
native-comp-eln-load-path. . . . . . . . . . . . . . . . . . 303
native-comp-enable-subr-trampolines . . . . . . 331
native-comp-jit-compilation . . . . . . . . . . . . . . . 331
native-comp-limple-mode . . . . . . . . . . . . . . . . . . . . 328
native-comp-speed . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
native-comp-verbose . . . . . . . . . . . . . . . . . . . . 328, 330
native-compilation functions . . . . . . . . . . . . . . . . . . 328
native-compilation variables . . . . . . . . . . . . . . . . . . . 330
native-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
native-compile, a Lisp feature . . . . . . . . . . . . . . . 327
native-compile-async . . . . . . . . . . . . . . . . . . . . . . . 329
natnump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
natural numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
nbutlast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
nconc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

1436

negative infinity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
negative-argument . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
nest frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
network byte ordering, in
Bindat specification . . . . . . . . . . . . . . . . . . . . . . . 1125
network connection . . . . . . . . . . . . . . . . . . . . . . . . . . 1111
network connection, encrypted . . . . . . . . . . . . . . . 1111
network servers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114
network service name, and default
coding system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984
network-coding-system-alist . . . . . . . . . . . . . . . 984
network-interface-info . . . . . . . . . . . . . . . . . . . . 1121
network-interface-list . . . . . . . . . . . . . . . . . . . . 1119
network-lookup-address-info . . . . . . . . . . . . . . 1121
network-stream-use-clientcertificates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1113
new file message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
newline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12, 885
newline and Auto Fill mode . . . . . . . . . . . . . . . . . . . 885
newline in print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
newline in strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
newline-and-indent . . . . . . . . . . . . . . . . . . . . . . . . . . 912
next input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
next-button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
next-char-property-change. . . . . . . . . . . . . . . . . . 922
next-complete-history-element . . . . . . . . . . . . . 418
next-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
next-history-element . . . . . . . . . . . . . . . . . . . . . . . 417
next-matching-history-element . . . . . . . . . . . . . 417
next-overlay-change . . . . . . . . . . . . . . . . . . . . . . . 1157
next-property-change . . . . . . . . . . . . . . . . . . . . . . . 921
next-screen-context-lines. . . . . . . . . . . . . . . . . . 765
next-single-char-property-change . . . . . . . . . 923
next-single-property-change . . . . . . . . . . . . . . . 922
next-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
nil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
nil as a list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
nil in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
nil input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
nil output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
nlistp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
no-accept-focus, a frame parameter . . . . . . . . . 816
no-byte-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
no-catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
no-conversion coding system . . . . . . . . . . . . . . . . . 977
no-delete-other-windows, awindow parameter . . . . . . . . . . . . . . . . . . . . . . . . . . 778
no-focus-on-map, a frame parameter . . . . . . . . . 816
no-indent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
no-native-compile . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
no-node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
no-other-frame, a frame parameter . . . . . . . . . . . 813
no-other-window, a window parameter . . . . . . . . 778
no-redraw-on-reenter . . . . . . . . . . . . . . . . . . . . . . 1129
no-self-insert property . . . . . . . . . . . . . . . . . . . . 1067
no-special-glyphs, a frame parameter . . . . . . . 811
node types, in a syntax tree . . . . . . . . . . . . . . . . . . 1041
node, ewoc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236

Indexnode-is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
nodes, by field name . . . . . . . . . . . . . . . . . . . . . . . . . 1048
nodes, by kinship . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
nodes, by position . . . . . . . . . . . . . . . . . . . . . . . . . . . 1048
non-ASCII characters . . . . . . . . . . . . . . . . . . . . . . . . . 963
non-ASCII characters in loaded files . . . . . . . . . . . 304
non-ASCII text in key bindings . . . . . . . . . . . . . . . . 507
non-capturing group . . . . . . . . . . . . . . . . . . . . . . . . . 1002
non-GNU ELPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
non-greedy repetition characters in regexp . . . . . 997
non_local_exit_check . . . . . . . . . . . . . . . . . . . . . . 1376
non_local_exit_clear . . . . . . . . . . . . . . . . . . . . . . 1376
non_local_exit_get . . . . . . . . . . . . . . . . . . . . . . . . 1376
non_local_exit_signal . . . . . . . . . . . . . . . . . . . . . 1377
non_local_exit_throw . . . . . . . . . . . . . . . . . . . . . . 1376
nondirectory part (of file name) . . . . . . . . . . . . . . . 634
noninteractive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
nonlocal exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
nonlocal exits, cleaning up . . . . . . . . . . . . . . . . . . . . 187
nonlocal exits, in modules. . . . . . . . . . . . . . . . . . . . 1375
nonprinting characters, reading . . . . . . . . . . . . . . . 467
noreturn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
normal hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
normal-auto-fill-function. . . . . . . . . . . . . . . . . . 905
normal-backup-enable-predicate . . . . . . . . . . . . 660
normal-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
not recording input events . . . . . . . . . . . . . . . . . . . . 468
not-modified . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678
notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
notifications, on desktop . . . . . . . . . . . . . . . . . . . . . 1291
notifications-close-notification . . . . . . . . 1294
notifications-get-capabilities . . . . . . . . . . . 1294
notifications-get-server-information . . . . 1294
notifications-notify . . . . . . . . . . . . . . . . . . . . . . 1291
notifiers, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . . . 1045
nreverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
ns-appearance, a frame parameter . . . . . . . . . . . . 816
ns-transparent-titlebar, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
ntake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
nth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
nth-sibling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
nthcdr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
null . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
null bytes, and decoding text . . . . . . . . . . . . . . . . . . 981
null-device. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
num-input-keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
num-nonmacro-input-events. . . . . . . . . . . . . . . . . . 464
num-processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
number comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
number conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
number of bignum bits, limit on . . . . . . . . . . . . . . . . 39
number-or-marker-p . . . . . . . . . . . . . . . . . . . . . . . . . . 870
number-sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
number-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
numbered backups . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
numberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

1437

numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
numeric prefix argument . . . . . . . . . . . . . . . . . . . . . . 473
numeric prefix argument usage . . . . . . . . . . . . . . . . 429
numerical RGB color specification . . . . . . . . . . . . . 846

O
obarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135, 137
obarray in completion . . . . . . . . . . . . . . . . . . . . . . . . . 396
object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
object internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1377
object to string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
object-intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
objects with identical contents,
and byte-compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
obsolete (declare spec) . . . . . . . . . . . . . . . . . . . . . . 263
obsolete functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
oclosure-define . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
oclosure-interactive-form. . . . . . . . . . . . . . . . . . 426
oclosure-lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
oclosure-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
oclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
octal character code . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
octal character input . . . . . . . . . . . . . . . . . . . . . . . . . . 467
octal escapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1242
octal numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
old advices, porting . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
old-selected-frame . . . . . . . . . . . . . . . . . . . . . . . . . . 783
old-selected-window . . . . . . . . . . . . . . . . . . . . . . . . 783
one-window-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
only-global-abbrevs . . . . . . . . . . . . . . . . . . . . . . . 1068
opacity, frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819
open closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
open-dribble-file . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
open-network-stream . . . . . . . . . . . . . . . . . . . . . . . 1112
open-paren-in-column-0-is-defun-start . . . . 862
open-termscript . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
open_channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375
OpenType font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1185
operating system environment . . . . . . . . . . . . . . . 1265
operating system signal . . . . . . . . . . . . . . . . . . . . . . 1263
operations (property) . . . . . . . . . . . . . . . . . . . . . . . . 652
operations on images . . . . . . . . . . . . . . . . . . . . . . . . 1224
optimize regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006
option descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
optional arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
options on command line . . . . . . . . . . . . . . . . . . . . 1261
options, defcustom keyword . . . . . . . . . . . . . . . . . . 281
or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
ordering of windows, cyclic . . . . . . . . . . . . . . . . . . . . 717
origin of display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
other-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
other-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
other-window, a window parameter . . . . . . . . . . . 778
other-window-scroll-buffer . . . . . . . . . . . . . . . . 764
outdated node, tree-sitter . . . . . . . . . . . . . . . . . . . . 1051
outer border . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792

Indexouter frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
outer-window-id, a frame parameter . . . . . . . . . 815
output from processes . . . . . . . . . . . . . . . . . . . . . . . 1099
output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
output variables, overriding . . . . . . . . . . . . . . . . . . . 383
output-controlling variables . . . . . . . . . . . . . . . . . . . 380
overall prompt string . . . . . . . . . . . . . . . . . . . . . . . . . 482
overflow-newline-into-fringe . . . . . . . . . . . . . 1192
overlay properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
overlay, empty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlay-arrow-position . . . . . . . . . . . . . . . . . . . . 1194
overlay-arrow-string . . . . . . . . . . . . . . . . . . . . . . 1194
overlay-arrow-variable-list . . . . . . . . . . . . . . 1195
overlay-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151
overlay-end. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlay-get. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
overlay-properties . . . . . . . . . . . . . . . . . . . . . . . . 1153
overlay-put. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
overlay-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlayp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlays, managing . . . . . . . . . . . . . . . . . . . . . . . . . . 1150
overlays, searching for . . . . . . . . . . . . . . . . . . . . . . . 1157
overlays-at. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1157
overlays-in. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1157
overlined text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1166
override existing functions . . . . . . . . . . . . . . . . . . . . 238
override redirect frames . . . . . . . . . . . . . . . . . . . . . . . 816
override spec (for a face) . . . . . . . . . . . . . . . . . . . . . 1170
override-redirect, a frame parameter . . . . . . . 816
overrides, in output functions . . . . . . . . . . . . . . . . . 383
overriding bidirectional properties . . . . . . . . . . . . 1253
overriding-local-map . . . . . . . . . . . . . . . . . . . . . . . 492
overriding-local-map-menu-flag . . . . . . . . . . . . 493
overriding-terminal-local-map . . . . . . . . . . . . . 493
overwrite-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885

P
package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
package archive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
package archive security . . . . . . . . . . . . . . . . . . . . . 1307
package attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
package autoloads . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
package dependencies . . . . . . . . . . . . . . . . . . . . . . . . 1303
package name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
package signing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
package version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1303
package-activate-all . . . . . . . . . . . . . . . . . . . . . . 1304
package-archives . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
package-initialize . . . . . . . . . . . . . . . . . . . . . . . . 1304
package-version, customization keyword . . . . . 279
packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
padding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

1438

page-delimiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1020
paragraph-separate . . . . . . . . . . . . . . . . . . . . . . . . 1020
paragraph-separate, andbidirectional display . . . . . . . . . . . . . . . . . . . . . . . 1251
paragraph-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1020
paragraph-start, and bidirectional display . . . . 1251
parameters for moving frameswith the mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813
parameters for resizing frameswith the mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813
parameters of initial frame . . . . . . . . . . . . . . . . . . . . 804
parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
parent directory of file . . . . . . . . . . . . . . . . . . . . . . . . 647
parent frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
parent of char-table . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
parent process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
parent window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
parent-bol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
parent-frame, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
parent-frame, a frame parameter . . . . . . . . . . . . . 812
parent-is . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
parenthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
parenthesis depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1034
parenthesis matching . . . . . . . . . . . . . . . . . . . . . . . . 1241
parenthesis mismatch, debugging . . . . . . . . . . . . . . 367
parity, in serial connections . . . . . . . . . . . . . . . . . . 1123
parse state for a position . . . . . . . . . . . . . . . . . . . . . 1032
parse string, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . 1045
parse-colon-path . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
parse-partial-sexp . . . . . . . . . . . . . . . . . . . . . . . . 1033
parse-sexp-ignore-comments . . . . . . . . . . . . . . . 1034
parse-sexp-lookup-properties . . . . . . . . . . . . . 1029
parse-time-string . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
parser state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1032
parser-based font-lock . . . . . . . . . . . . . . . . . . . . . . . . . 578
parser-based indentation . . . . . . . . . . . . . . . . . . . . . . 590
parsing buffer text . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
parsing expressions . . . . . . . . . . . . . . . . . . . . . . . . . . 1030
parsing html . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
parsing multiple languages with tree-sitter . . . 1057
parsing program source . . . . . . . . . . . . . . . . . . . . . . 1039
parsing xml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
parsing, control parameters . . . . . . . . . . . . . . . . . . 1034
partial application of functions . . . . . . . . . . . . . . . . 240
partial-width windows . . . . . . . . . . . . . . . . . . . . . . . 1130
passwords, reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
path-separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267
PATH environment variable . . . . . . . . . . . . . . . . . . . 1078
pattern matching with tree-sitter nodes . . . . . . 1052
pattern matching, programming style . . . . . . . . . 163
pattern syntax, tree-sitter query . . . . . . . . . . . . . 1053
patterns, tree-sitter, in string form . . . . . . . . . . . 1056
PBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1220
pcase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163, 164pcase pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
pcase, defining new kinds of patterns . . . . . . . . . . 170
pcase-defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

Indexpcase-dolist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
pcase-lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
pcase-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
pcase-let* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
pcase-setq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
pdumper-stats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1348
peculiar error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
peeking at input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
percent symbol in mode line . . . . . . . . . . . . . . . . . . 551
perform-replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017
performance analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 369
performance analysis (Edebug) . . . . . . . . . . . . . . . . 356
permanent local variable . . . . . . . . . . . . . . . . . . . . . . 211
permanently-enabled-local-variables . . . . . . 214
permissions, file . . . . . . . . . . . . . . . . . . . . . . . . . . 621, 632
persistent window parameters . . . . . . . . . . . . . . . . . 777
phishing using directional overrides . . . . . . . . . . 1253
physical lines, moving by . . . . . . . . . . . . . . . . . . . . . . 856
piece of advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
pinch event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
pipe, when to use for subprocess
communications . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086
pixel height of a window . . . . . . . . . . . . . . . . . . . . . . 700
pixel width of a window . . . . . . . . . . . . . . . . . . . . . . . 700
pixel-fill-region . . . . . . . . . . . . . . . . . . . . . . . . . . . 900
pixel-fill-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900
pixel-resolution wheel events . . . . . . . . . . . . . . . . . . 451
pixelwise, resizing windows . . . . . . . . . . . . . . . . . . . . 704
place form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
play-sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
play-sound-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
play-sound-functions . . . . . . . . . . . . . . . . . . . . . . 1289
plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
plist access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
plist vs. alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
plist-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
plist-member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
plist-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
plistp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
plugin_is_GPL_compatible . . . . . . . . . . . . . . . . . . . 314
point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
point excursion . . . . . . . . . . . . . . . . . . . . . . . . . . 864, 865
point in window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
point with narrowing . . . . . . . . . . . . . . . . . . . . . . . . . 853
point-entered (text property) . . . . . . . . . . . . . . . . 930
point-left (text property) . . . . . . . . . . . . . . . . . . . 930
point-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
point-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
point-max-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
point-min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
point-min-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
pointer (text property) . . . . . . . . . . . . . . . . . . . . . . . 929
pointer shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
pointers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
pop-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
pop-to-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723

1439

pop-up-frame-alist . . . . . . . . . . . . . . . . . . . . . . . . . . 737
pop-up-frame-function . . . . . . . . . . . . . . . . . . . . . . 737
pop-up-frame-parameters, a buffer
display action alist entry . . . . . . . . . . . . . . . . . . . . 734
pop-up-frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
pop-up-frames, replacement for . . . . . . . . . . . . . . . 738
pop-up-windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736
pop-up-windows, replacement for. . . . . . . . . . . . . . 738
popcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
port number, and default coding system . . . . . . . 984
pos-bol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
pos-eol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857
pos-visible-in-window-group-p . . . . . . . . . . . . . 762
pos-visible-in-window-group-p-function . . . 762
pos-visible-in-window-p . . . . . . . . . . . . . . . . . . . . 761
position (in buffer) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
position argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
position in window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
position of frame . . . . . . . . . . . . . . . . . . . . . . . . . 791, 798
position of mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
position-bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964
position-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
positive infinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
posix-looking-at . . . . . . . . . . . . . . . . . . . . . . . . . . . 1011
posix-search-backward . . . . . . . . . . . . . . . . . . . . . 1011
posix-search-forward . . . . . . . . . . . . . . . . . . . . . . 1011
posix-string-match . . . . . . . . . . . . . . . . . . . . . . . . 1011
posn-actual-col-row . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
posn-at-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
posn-at-x-y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
posn-col-row . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
posn-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-object-width-height . . . . . . . . . . . . . . . . . . . 458
posn-object-x-y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
posn-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-timestamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
posn-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
posn-x-y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
posnp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
post-command-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
post-gc-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1353
post-self-insert-hook . . . . . . . . . . . . . . . . . . . . . . 884
pp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
pre-command-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
pre-redisplay-function . . . . . . . . . . . . . . . . . . . . 1130
pre-redisplay-functions . . . . . . . . . . . . . . . . . . . 1130
precedence of buffer display action functions. . . 738
preceding-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
precision in format specifications . . . . . . . . . . . . . . . 69
predicates for lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
predicates for markers . . . . . . . . . . . . . . . . . . . . . . . . 870
predicates for numbers . . . . . . . . . . . . . . . . . . . . . . . . . 41
predicates for strings . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
predicates for syntax tree nodes . . . . . . . . . . . . . . 1051
preedit-text event. . . . . . . . . . . . . . . . . . . . . . . . . . . 452

Indexprefer-utf-8 coding system . . . . . . . . . . . . . . . . . . 977
prefix argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
prefix argument unreading . . . . . . . . . . . . . . . . . . . . 468
prefix command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
prefix, defgroup keyword . . . . . . . . . . . . . . . . . . . . 280
prefix-arg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
prefix-command-echokeystrokes-functions . . . . . . . . . . . . . . . . . . . . 1400
prefix-command-preserve-state-hook . . . . . . 1401
prefix-help-command . . . . . . . . . . . . . . . . . . . . . . . . 603
prefix-numeric-value . . . . . . . . . . . . . . . . . . . . . . . 474
preloaded Lisp files . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
preloaded-file-list . . . . . . . . . . . . . . . . . . . . . . . 1347
preloading additional functionsand variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
prepare-change-group . . . . . . . . . . . . . . . . . . . . . . . 959
preserve-size, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
preserving window sizes . . . . . . . . . . . . . . . . . . . . . . . 707
pretty-printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
prev-adaptive-prefix . . . . . . . . . . . . . . . . . . . . . . . 593
prev-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
prev-sibling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
prevent warnings in init files . . . . . . . . . . . . . . . . . 1141
preventing backtracking . . . . . . . . . . . . . . . . . . . . . . . 361
preventing prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . 495
preventing quitting . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
previous complete subexpression . . . . . . . . . . . . . 1033
previous-button . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236
previous-char-property-change . . . . . . . . . . . . . 922
previous-complete-history-element . . . . . . . . 417
previous-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824
previous-history-element . . . . . . . . . . . . . . . . . . . 417
previous-matching-history-element . . . . . . . . 417
previous-overlay-change . . . . . . . . . . . . . . . . . . . 1157
previous-property-change . . . . . . . . . . . . . . . . . . . 922
previous-single-char-property-change . . . . . 923
previous-single-property-change . . . . . . . . . . . 922
previous-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
previous-window, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
primary selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
primitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
primitive function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
primitive function internals . . . . . . . . . . . . . . . . . . 1356
primitive type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
primitive-undo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897
prin1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
prin1-to-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
princ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
print. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
print example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
print name cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
print-charset-text-property . . . . . . . . . . . . . . . 381
print-circle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
print-continuous-numbering . . . . . . . . . . . . . . . . 382
print-escape-control-characters . . . . . . . . . . . 380

1440

print-escape-multibyte . . . . . . . . . . . . . . . . . . . . . 381
print-escape-newlines . . . . . . . . . . . . . . . . . . . . . . 380
print-escape-nonascii . . . . . . . . . . . . . . . . . . . . . . 381
print-gensym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
print-integers-as-characters . . . . . . . . . . . . . . 382
print-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
print-level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
print-number-table . . . . . . . . . . . . . . . . . . . . . . . . . . 382
print-quoted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
print-symbols-bare . . . . . . . . . . . . . . . . . . . . . . . . . . 144
print-unreadable-function. . . . . . . . . . . . . . . . . . 382
printable ASCII characters . . . . . . . . . . . . . . . . . . . 1242
printable-chars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
printed representation . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
printed representation for characters . . . . . . . . . . . 11
printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
printing (Edebug). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
printing circular structures . . . . . . . . . . . . . . . . . . . . 354
printing limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
printing notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3priority (overlay property) . . . . . . . . . . . . . . . . . 1153
priority order of coding systems . . . . . . . . . . . . . . . 987
process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
process creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
process filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1101
process filter multibyte flag . . . . . . . . . . . . . . . . . . 1103
process information . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
process input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096
process internals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1387
process output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099
process sentinel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105
process signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
process-adaptive-read-buffering. . . . . . . . . . 1099
process-attributes . . . . . . . . . . . . . . . . . . . . . . . . 1108
process-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1100
process-coding-system . . . . . . . . . . . . . . . . . . . . . 1095
process-coding-system-alist . . . . . . . . . . . . . . . 984
process-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093
process-connection-type . . . . . . . . . . . . . . . . . . . 1091
process-contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1093
process-datagram-address . . . . . . . . . . . . . . . . . . 1115
process-environment . . . . . . . . . . . . . . . . . . . . . . . 1267
process-error-pause-time . . . . . . . . . . . . . . . . . . 1091
process-exit-status . . . . . . . . . . . . . . . . . . . . . . . 1095
process-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083
process-file-return-signal-string . . . . . . . 1084
process-file-shell-command . . . . . . . . . . . . . . . 1085
process-file-side-effects . . . . . . . . . . . . . . . . 1084
process-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103
process-get. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
process-id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094
process-kill-buffer-query-function . . . . . . 1099
process-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086
process-lines-ignore-status . . . . . . . . . . . . . . 1086
process-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1092
process-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094
process-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1100
process-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094

Index

process-plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
process-put. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
process-query-on-exit-flag . . . . . . . . . . . . . . . 1107
process-running-child-p . . . . . . . . . . . . . . . . . . . 1096
process-send-eof . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096
process-send-region . . . . . . . . . . . . . . . . . . . . . . . 1096
process-send-string . . . . . . . . . . . . . . . . . . . . . . . 1096
process-sentinel . . . . . . . . . . . . . . . . . . . . . . . . . . . 1107
process-status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094
process-thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105
process-tty-name . . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
process-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1094
process_input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375
processes, threads. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105
processing of errors . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
processor run time . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
processp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
profiler-find-profile . . . . . . . . . . . . . . . . . . . . . . 369
profiler-find-profile-other-window . . . . . . . 369
profiler-report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
profiler-report-compare-profile . . . . . . . . . . . 369
profiler-report-describe-entry . . . . . . . . . . . . 369
profiler-report-find-entry . . . . . . . . . . . . . . . . 369
profiler-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
profiler-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
prog-first-column . . . . . . . . . . . . . . . . . . . . . . . . . . . 913
prog-indentation-context . . . . . . . . . . . . . . . . . . . 913
prog-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
prog-mode, andbidi-paragraph-direction . . . . . . . . . . . . . . . 1251
prog-mode-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
prog-mode-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1396
prog1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
prog2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
progn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
program arguments . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
program directories . . . . . . . . . . . . . . . . . . . . . . . . . . 1079
program name, and default coding system . . . . . 984
programmed completion . . . . . . . . . . . . . . . . . . . . . . 409
programming conventions . . . . . . . . . . . . . . . . . . . . 1335
programming types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
progress reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . 1134
progress-reporter-done . . . . . . . . . . . . . . . . . . . . 1136
progress-reporter-force-update . . . . . . . . . . . 1136
progress-reporter-update . . . . . . . . . . . . . . . . . . 1135
prompt for file name . . . . . . . . . . . . . . . . . . . . . . . . . . 404
prompt string (of menu) . . . . . . . . . . . . . . . . . . . . . . 510
prompt string of keymap . . . . . . . . . . . . . . . . . . . . . . 482
proper list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
proper-list-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
properties of text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
propertize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921
property category of text character . . . . . . . . . . . . 924
property list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
property list cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
property lists vs association lists . . . . . . . . . . . . . . 100

1441

protect C variables from garbage collection . . . 1358
protected forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
provide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
provide-theme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
providing features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
pseudo window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1383
pty, when to use for subprocess
communications . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086
pure function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
pure property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
pure storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349
pure-bytes-used . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349
purecopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349
purify-flag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349
push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
push-button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
push-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
put-char-code-property . . . . . . . . . . . . . . . . . . . . . 972
put-charset-property . . . . . . . . . . . . . . . . . . . . . . . 973
put-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
put-text-property . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
puthash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Q
quadratic-bezier-curveto . . . . . . . . . . . . . . . . . . 1218
quantify node, tree-sitter. . . . . . . . . . . . . . . . . . . . . 1054
queries, compiling . . . . . . . . . . . . . . . . . . . . . . . . . . . 1057
query. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
query functions, tree-sitter . . . . . . . . . . . . . . . . . . . 1053
query, tree-sitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1053
query-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1188
query-replace-history . . . . . . . . . . . . . . . . . . . . . . 394
query-replace-map . . . . . . . . . . . . . . . . . . . . . . . . . . 1018
querying the user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
question mark in character constant . . . . . . . . . . . . 11
quietly-read-abbrev-file . . . . . . . . . . . . . . . . . . 1068
quit-flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
quit-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
quit-restore, a window parameter . . . . . . . . . . . 778
quit-restore-window . . . . . . . . . . . . . . . . . . . . . . . . 750
quit-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750
quit-window-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750
quitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
quitting from infinite loop . . . . . . . . . . . . . . . . . . . . . 336
quitting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749
quote. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
quote character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1033
quote special characters in regexp . . . . . . . . . . . . 1005
quoted character input . . . . . . . . . . . . . . . . . . . . . . . . 467
quoted-insert suppression . . . . . . . . . . . . . . . . . . . 500
quoting and unquoting
command-line arguments . . . . . . . . . . . . . . . . . . 1080
quoting apostrophe and grave
accent in doc strings . . . . . . . . . . . . . . . . . . . . . . . 1339
quoting characters in printing . . . . . . . . . . . . . . . . . 377
quoting using apostrophe . . . . . . . . . . . . . . . . . . . . . 151

IndexRradio, customization types . . . . . . . . . . . . . . . . . . . . 288
radix for reading an integer . . . . . . . . . . . . . . . . . . . . 38
raise-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
raising a frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
random. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
random numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
rassoc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
rassq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
rassq-delete-all . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
raw prefix argument . . . . . . . . . . . . . . . . . . . . . . . . . . 473
raw prefix argument usage . . . . . . . . . . . . . . . . . . . . 429
raw syntax descriptor . . . . . . . . . . . . . . . . . . . . . . . . 1034
raw-text coding system . . . . . . . . . . . . . . . . . . . . . . 977
re-builder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
re-search-backward . . . . . . . . . . . . . . . . . . . . . . . . 1009
re-search-forward . . . . . . . . . . . . . . . . . . . . . . . . . . 1008
read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
read command name . . . . . . . . . . . . . . . . . . . . . . . . . . 434
read file names. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
read input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
read syntax for characters . . . . . . . . . . . . . . . . . . . . . . 11
read-answer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416
read-answer-short . . . . . . . . . . . . . . . . . . . . . . . . . . . 416
read-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
read-buffer-completion-ignore-case . . . . . . . 403
read-buffer-function . . . . . . . . . . . . . . . . . . . . . . . 403
read-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
read-char-choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
read-char-choice-use-read-key . . . . . . . . . . . . . 465
read-char-exclusive . . . . . . . . . . . . . . . . . . . . . . . . 464
read-char-from-minibuffer. . . . . . . . . . . . . . . . . . 416
read-circle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
read-coding-system . . . . . . . . . . . . . . . . . . . . . . . . . . 983
read-color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
read-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
read-directory-name . . . . . . . . . . . . . . . . . . . . . . . . 406
read-event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
read-expression-history . . . . . . . . . . . . . . . . . . . . 394
read-extended-command-predicate . . . . . . 431, 434
read-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
read-file-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
read-file-name-completion-ignore-case . . . . 406
read-file-name-function . . . . . . . . . . . . . . . . . . . . 406
read-from-minibuffer . . . . . . . . . . . . . . . . . . . . . . . 386
read-from-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
read-hide-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
read-input-method-name . . . . . . . . . . . . . . . . . . . . . 991
read-kbd-macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602
read-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
read-key-sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
read-key-sequence-vector . . . . . . . . . . . . . . . . . . . 462
read-minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
read-minibuffer-restore-windows . . . . . . . . . . . 391
read-multiple-choice . . . . . . . . . . . . . . . . . . . . . . . 465
read-no-blanks-input . . . . . . . . . . . . . . . . . . . . . . . 390
read-non-nil-coding-system . . . . . . . . . . . . . . . . 983

1442

read-number-history . . . . . . . . . . . . . . . . . . . . . . . . 394
read-only (text property) . . . . . . . . . . . . . . . . . . . . 927
read-only buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
read-only buffers in interactive . . . . . . . . . . . . . . . . 425
read-only character . . . . . . . . . . . . . . . . . . . . . . . . . . . 927
read-only variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
read-only-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680
read-passwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
read-positioning-symbols . . . . . . . . . . . . . . . . . . . 374
read-quoted-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
read-quoted-char quitting . . . . . . . . . . . . . . . . . . . 472
read-regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
read-regexp-case-fold-search . . . . . . . . . . . . . . 389
read-regexp-defaults-function . . . . . . . . . . . . . 389
read-shell-command . . . . . . . . . . . . . . . . . . . . . . . . . . 407
read-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
read-string-from-buffer . . . . . . . . . . . . . . . . . . . . 388
read-symbol-shorthands . . . . . . . . . . . . . . . . . . . . . 142
read-variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
read-variable, history list . . . . . . . . . . . . . . . . . . . 394
readable syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
readablep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
reading a single event . . . . . . . . . . . . . . . . . . . . . . . . . 462
reading from files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614
reading from minibuffer with completion . . . . . . 398
reading grammar definition, tree-sitter . . . . . . . 1042
reading interactive arguments . . . . . . . . . . . . . . . . . 427
reading numbers in hex, octal, and binary . . . . . . 38
reading order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250
reading symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
real-last-command . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
rear-nonsticky text property . . . . . . . . . . . . . . . . . . 932
rear-nonsticky, andcursor-intangible property . . . . . . . . . . . . . . . . . . 928
rearrangement of lists . . . . . . . . . . . . . . . . . . . . . . . . . . 90
rebinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
recent-auto-save-p . . . . . . . . . . . . . . . . . . . . . . . . . . 666
recent-keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1286
recenter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
recenter-positions . . . . . . . . . . . . . . . . . . . . . . . . . . 766
recenter-redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . 766
recenter-top-bottom . . . . . . . . . . . . . . . . . . . . . . . . 766
recenter-window-group . . . . . . . . . . . . . . . . . . . . . . 766
recenter-window-group-function . . . . . . . . . . . . 766
recombining windows . . . . . . . . . . . . . . . . . . . . . . . . . 712
record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
record command history . . . . . . . . . . . . . . . . . . . . . . 433
recording input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1286
recordp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
rectangle, as contents of a register . . . . . . . . . . . . . 940
recursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
recursion-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
recursive command loop . . . . . . . . . . . . . . . . . . . . . . 475
recursive editing level . . . . . . . . . . . . . . . . . . . . . . . . . 475
recursive evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
recursive minibuffers . . . . . . . . . . . . . . . . . . . . . . . . . . 420

Indexrecursive traverse of directory tree. . . . . . . . . . . . . 646
recursive-edit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
redefine existing functions . . . . . . . . . . . . . . . . . . . . . 238
redirect-frame-focus . . . . . . . . . . . . . . . . . . . . . . . 826
redisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
redisplay errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
redo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
redraw-display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
redraw-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
reducing sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
reference to free variable,
compilation warning . . . . . . . . . . . . . . . . . . . . . . . . 321
references, following . . . . . . . . . . . . . . . . . . . . . . . . . 1334
refresh the screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
regexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
regexp alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002
regexp grouping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002
regexp searching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1008
regexp stack overflow . . . . . . . . . . . . . . . . . . . . . . . . 1007
regexp syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 996
regexp, special characters in. . . . . . . . . . . . . . . . . . . 996
regexp-history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
regexp-opt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006
regexp-opt-charset . . . . . . . . . . . . . . . . . . . . . . . . 1007
regexp-opt-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007
regexp-quote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005
regexp-unmatchable . . . . . . . . . . . . . . . . . . . . . . . . 1007
regexps used standardly in editing . . . . . . . . . . . 1020
region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
region argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
region-beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
region-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
register preview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
register-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
register-definition-prefixes . . . . . . . . . . . . . . 307
register-read-with-preview . . . . . . . . . . . . . . . . 941
registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
regular expression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
regular expression problems . . . . . . . . . . . . . . . . . . 1007
regular expression searching . . . . . . . . . . . . . . . . . . 1008
regular expressions, developing . . . . . . . . . . . . . . . . 995
reindent-then-newline-and-indent . . . . . . . . . 912
relative file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
relative remapping, faces . . . . . . . . . . . . . . . . . . . . . 1176
remainder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
remapping commands . . . . . . . . . . . . . . . . . . . . . . . . . 503
remhash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
remote-file-name-inhibit-cache . . . . . . . . . . . . 653
remote-file-name-inhibit-locks . . . . . . . . . . . . 619
remove. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
remove-from-invisibility-spec . . . . . . . . . . . . 1143
remove-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
remove-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
remove-images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
remove-list-of-text-properties . . . . . . . . . . . . 920
remove-overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151
remove-text-properties . . . . . . . . . . . . . . . . . . . . . 920
remove-variable-watcher . . . . . . . . . . . . . . . . . . . . 200

1443

removing from sequences . . . . . . . . . . . . . . . . . . . . . . 109
remq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
rename-auto-save-file . . . . . . . . . . . . . . . . . . . . . . 667
rename-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
rename-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630
rendering html . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
reordering, of bidirectional text . . . . . . . . . . . . . . 1250
reordering, of elements in lists . . . . . . . . . . . . . . . . . . 90
reparent frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
repeat events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
repeat-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
repeatable key bindings . . . . . . . . . . . . . . . . . . . . . . . 485
repeated loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
replace bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
replace characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 939
replace characters in region . . . . . . . . . . . . . . . . . . . 939
replace characters in string . . . . . . . . . . . . . . . . . . . . 939
replace list element . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
replace matched text. . . . . . . . . . . . . . . . . . . . . . . . . 1012
replace part of list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
replace-buffer-contents . . . . . . . . . . . . . . . . . . . . 941
replace-buffer-in-windows. . . . . . . . . . . . . . . . . . 721
replace-match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1012
replace-re-search-function . . . . . . . . . . . . . . . 1020
replace-regexp-in-region . . . . . . . . . . . . . . . . . . 1017
replace-regexp-in-string . . . . . . . . . . . . . . . . . . 1017
replace-region-contents . . . . . . . . . . . . . . . . . . . . 942
replace-search-function . . . . . . . . . . . . . . . . . . . 1020
replace-string-in-region . . . . . . . . . . . . . . . . . . 1017
replacement after search . . . . . . . . . . . . . . . . . . . . . 1016
replacing display specs . . . . . . . . . . . . . . . . . . . . . . . 1199
require . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
require, customization keyword . . . . . . . . . . . . . . 278
require-final-newline . . . . . . . . . . . . . . . . . . . . . . 614
require-theme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
requiring features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
reserved keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334
reset, face attribute value . . . . . . . . . . . . . . . . . . . . 1164
resize window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
resize-mini-frames . . . . . . . . . . . . . . . . . . . . . . . . . . 419
resize-mini-windows . . . . . . . . . . . . . . . . . . . . . . . . 419
rest arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
restacking a frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
restart-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
restore-buffer-modified-p. . . . . . . . . . . . . . . . . . 678
restricted-sexp, customization types . . . . . . . . . . . 290
restriction (in a buffer). . . . . . . . . . . . . . . . . . . . . . . . 865
resume (cf. no-redraw-on-reenter) . . . . . . . . . . 1129
resume-tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1265
resume-tty-functions . . . . . . . . . . . . . . . . . . . . . . 1265
rethrow a signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
retrieve node, tree-sitter . . . . . . . . . . . . . . . . . . . . . 1045
retrieving tree-sitter nodes . . . . . . . . . . . . . . . . . . . 1046
return (ASCII character) . . . . . . . . . . . . . . . . . . . . . . . 12
return value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
reusable-frames, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Indexreversing a list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
reversing a string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
reversing a vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
revert-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
revert-buffer-function . . . . . . . . . . . . . . . . . . . . . 668
revert-buffer-in-progress-p . . . . . . . . . . . . . . . 668
revert-buffer-insert-filecontents-function . . . . . . . . . . . . . . . . . . . . . . . . 668
revert-without-query . . . . . . . . . . . . . . . . . . . . . . . 668
reverting buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
rgb value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
right dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
right-divider, prefix key . . . . . . . . . . . . . . . . . . . . 462
right-divider-width, a frame parameter . . . . . 811
right-fringe, a frame parameter . . . . . . . . . . . . . 810
right-fringe, prefix key . . . . . . . . . . . . . . . . . . . . . 462
right-fringe-width . . . . . . . . . . . . . . . . . . . . . . . . 1189
right-margin, prefix key . . . . . . . . . . . . . . . . . . . . . 462
right-margin-width . . . . . . . . . . . . . . . . . . . . . . . . 1206
right-to-left text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250
ring data structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-bell-function . . . . . . . . . . . . . . . . . . . . . . . . 1248
ring-copy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-empty-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
ring-insert-at-beginning . . . . . . . . . . . . . . . . . . . 124
ring-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
ring-remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
ring-resize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
ring-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
risky, defcustom keyword . . . . . . . . . . . . . . . . . . . . 283
risky-local-variable-p . . . . . . . . . . . . . . . . . . . . . 216
RLO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1253
rm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631
root window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
root window of atomic window . . . . . . . . . . . . . . . . 757
round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
rounding in conversions . . . . . . . . . . . . . . . . . . . . . . . . 43
rounding without conversion . . . . . . . . . . . . . . . . . . . 48
rplaca. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
rplacd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
run time stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
run-at-time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1282
run-hook-with-args . . . . . . . . . . . . . . . . . . . . . . . . . . 525
run-hook-with-args-until-failure . . . . . . . . . 525
run-hook-with-args-until-success . . . . . . . . . 525
run-hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
run-mode-hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
run-with-idle-timer . . . . . . . . . . . . . . . . . . . . . . . 1284
run-with-timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1283
running a hook when a window gets selected . . 696

1444

S
S-expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
safe local variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
safe, defcustom keyword . . . . . . . . . . . . . . . . . . . . . 283
safe-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
safe-local-eval-forms . . . . . . . . . . . . . . . . . . . . . . 216
safe-local-variable, property of variable . . . . 215
safe-local-variable-p . . . . . . . . . . . . . . . . . . . . . . 216
safe-local-variable-values . . . . . . . . . . . . . . . . 215
safe-magic (property) . . . . . . . . . . . . . . . . . . . . . . . . 652
safely encode a string . . . . . . . . . . . . . . . . . . . . . . . . . 980
safely encode characters in a charset . . . . . . . . . . 980
safely encode region. . . . . . . . . . . . . . . . . . . . . . . . . . . 980
safety of functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
same-window-buffer-names, replacement for . . 738
same-window-regexps, replacement for . . . . . . . . 738
save abbrevs in files . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
save-abbrevs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
save-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612
save-buffer-coding-system. . . . . . . . . . . . . . . . . . 978save-current-buffer . . . . . . . . . . . . . . . . . . . . . . . . 673
save-excursion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
save-mark-and-excursion . . . . . . . . . . . . . . . . . . . . 865
save-match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016
save-restriction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
save-selected-window . . . . . . . . . . . . . . . . . . . . . . . 697
save-some-buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . 612
save-some-buffers-default-predicate . . . . . . 612
save-window-excursion . . . . . . . . . . . . . . . . . . . . . . 775
saved-face (face symbol property) . . . . . . . . . . 1170
SaveUnder feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
saving buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612
saving text properties . . . . . . . . . . . . . . . . . . . . . . . . . 654
saving window information . . . . . . . . . . . . . . . . . . . . 774
scalable fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180
scalable-fonts-allowed . . . . . . . . . . . . . . . . . . . . 1181
scan-lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1031
scan-sexps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1031
scanning expressions . . . . . . . . . . . . . . . . . . . . . . . . . 1030
scanning for character sets . . . . . . . . . . . . . . . . . . . . 974
scanning keymaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
scoping rule. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
screen layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
screen lines, moving by . . . . . . . . . . . . . . . . . . . . . . . 858
screen of terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
screen refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129
screen-gamma, a frame parameter . . . . . . . . . . . . . 818
script symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972
scroll bar events, data in . . . . . . . . . . . . . . . . . . . . . . 459
scroll bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1195
scroll-bar-background, a frame parameter. . . 820
scroll-bar-event-ratio . . . . . . . . . . . . . . . . . . . . . 459
scroll-bar-foreground, a frame parameter. . . 820
scroll-bar-height . . . . . . . . . . . . . . . . . . . . . . . . . . 1197
scroll-bar-height, a frame parameter . . . . . . . 810
scroll-bar-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197
scroll-bar-scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

Indexscroll-bar-width . . . . . . . . . . . . . . . . . . . . . . . . . . . 1197
scroll-bar-width, a frame parameter . . . . . . . . 810
scroll-command property . . . . . . . . . . . . . . . . . . . . . 765
scroll-conservatively . . . . . . . . . . . . . . . . . . . . . . 764
scroll-down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
scroll-down-aggressively . . . . . . . . . . . . . . . . . . . 765
scroll-down-command . . . . . . . . . . . . . . . . . . . . . . . . 763
scroll-error-top-bottom . . . . . . . . . . . . . . . . . . . . 765
scroll-left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 768
scroll-margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
scroll-other-window . . . . . . . . . . . . . . . . . . . . . . . . 764
scroll-other-window-down . . . . . . . . . . . . . . . . . . . 764
scroll-preserve-screen-position . . . . . . . . . . . 765
scroll-right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 768
scroll-step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
scroll-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
scroll-up-aggressively . . . . . . . . . . . . . . . . . . . . . 765
scroll-up-command . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
scrolling textually . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
search-backward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 994
search-failed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
search-forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
search-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
search-spaces-regexp . . . . . . . . . . . . . . . . . . . . . . 1011
searching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
searching active keymaps for keys . . . . . . . . . . . . . 490
searching and case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995
searching and replacing . . . . . . . . . . . . . . . . . . . . . . 1016
searching for overlays . . . . . . . . . . . . . . . . . . . . . . . . 1157
searching for regexp . . . . . . . . . . . . . . . . . . . . . . . . . 1008
searching text properties . . . . . . . . . . . . . . . . . . . . . . 921
secondary selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
secondary storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
secure-hash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944
secure-hash-algorithms . . . . . . . . . . . . . . . . . . . . . 944
security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1300
security vulnerabilities in text . . . . . . . . . . . . . . . . . 945
security, and display specifications . . . . . . . . . . . 1199
seed, for random number generation . . . . . . . . . . . . 52
select safe coding system . . . . . . . . . . . . . . . . . . . . . . 982
select window hooks . . . . . . . . . . . . . . . . . . . . . . . . . . 696
select-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
select-frame-set-input-focus . . . . . . . . . . . . . . 825
select-safe-coding-system. . . . . . . . . . . . . . . . . . 982
select-safe-coding-systemaccept-default-p . . . . . . . . . . . . . . . . . . . . . . . . . . 982
select-safe-coding-system-function . . . . . . . 983
select-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
selected frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 824
selected window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
selected-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
selected-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
selected-window-group . . . . . . . . . . . . . . . . . . . . . . 698
selected-window-group-function . . . . . . . . . . . . 698
selecting a buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
selecting a font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1180
selecting a window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
selection (for window systems) . . . . . . . . . . . . . . . . 840

1445

selection-coding-system . . . . . . . . . . . . . . . . . . . . 840
selective-display . . . . . . . . . . . . . . . . . . . . . . . . . . 1145
selective-display-ellipses . . . . . . . . . . . . . . . 1146
selectively disabling font-lock fontifications . . . . 570
self-evaluating form . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
self-insert-and-exit . . . . . . . . . . . . . . . . . . . . . . . 417
self-insert-command . . . . . . . . . . . . . . . . . . . . . . . . 884
self-insert-command override . . . . . . . . . . . . . . . . 500
self-insert-command, minor modes . . . . . . . . . . 546
self-insert-uses-region-functions . . . . . . . . 884
self-insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884
SELinux context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
send-string-to-terminal . . . . . . . . . . . . . . . . . . . 1287
sending signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
sentence-end . . . . . . . . . . . . . . . . . . . . . . . . . 1020, 1021
sentence-end-double-space. . . . . . . . . . . . . . . . . . 901
sentence-end-without-period . . . . . . . . . . . . . . . 902
sentence-end-without-space . . . . . . . . . . . . . . . . 902
sentinel (of process). . . . . . . . . . . . . . . . . . . . . . . . . . 1105
seq library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
seq-concatenate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
seq-contains-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-difference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
seq-doseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
seq-drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
seq-drop-while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
seq-elt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
seq-empty-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-every-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
seq-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
seq-find . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
seq-group-by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-intersection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-into . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-keep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
seq-length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
seq-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
seq-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
seq-map-indexed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
seq-mapcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-mapn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
seq-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
seq-min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
seq-partition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
seq-positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
seq-random-elt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
seq-reduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
seq-remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
seq-remove-at-position . . . . . . . . . . . . . . . . . . . . . 109
seq-set-equal-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-setq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
seq-some . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
seq-sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-sort-by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
seq-split . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Indexseq-subseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
seq-take . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
seq-take-while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
seq-union . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
seq-uniq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
seqp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
sequence destructuring . . . . . . . . . . . . . . . . . . . 114, 115
sequence functions in seq. . . . . . . . . . . . . . . . . . . . . . 107
sequence iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
sequence length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
sequence maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
sequence minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
sequence reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
sequencep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
sequences, generalized. . . . . . . . . . . . . . . . . . . . . . . . . 107
sequences, intersection of. . . . . . . . . . . . . . . . . . . . . . 113
sequences, union of . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
sequencing pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
sequential execution . . . . . . . . . . . . . . . . . . . . . . . . . . 158
serial connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122
serial-process-configure . . . . . . . . . . . . . . . . . . 1123
serial-term. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122
serializing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
server-after-make-frame-hook . . . . . . . . . . . . . . 787
session file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1290
session manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1290
set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
set, defcustom keyword . . . . . . . . . . . . . . . . . . . . . . 281
set-advertised-calling-convention . . . . . . . . 260
set-after, defcustom keyword . . . . . . . . . . . . . . . 283
set-auto-coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985
set-auto-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
set-binary-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
set-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672
set-buffer-auto-saved . . . . . . . . . . . . . . . . . . . . . . 666
set-buffer-major-mode . . . . . . . . . . . . . . . . . . . . . . 532
set-buffer-modified-p . . . . . . . . . . . . . . . . . . . . . . 677
set-buffer-multibyte . . . . . . . . . . . . . . . . . . . . . . . 967
set-case-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
set-case-syntax-delims . . . . . . . . . . . . . . . . . . . . . . 76
set-case-syntax-pair . . . . . . . . . . . . . . . . . . . . . . . . 76
set-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
set-category-table . . . . . . . . . . . . . . . . . . . . . . . . 1037
set-char-table-extra-slot. . . . . . . . . . . . . . . . . . 120
set-char-table-parent . . . . . . . . . . . . . . . . . . . . . . 120
set-char-table-range . . . . . . . . . . . . . . . . . . . . . . . 120
set-charset-priority . . . . . . . . . . . . . . . . . . . . . . . 973
set-coding-system-priority . . . . . . . . . . . . . . . . 987
set-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
set-default-file-modes . . . . . . . . . . . . . . . . . . . . . 632
set-default-toplevel-value . . . . . . . . . . . . . . . . 213
set-display-table-slot . . . . . . . . . . . . . . . . . . . . 1244
set-face-attribute . . . . . . . . . . . . . . . . . . . . . . . . 1172
set-face-background . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-bold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-extend . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173

1446

set-face-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-foreground . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-inverse-video . . . . . . . . . . . . . . . . . . . . 1173
set-face-italic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-stipple . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
set-face-underline . . . . . . . . . . . . . . . . . . . . . . . . 1173
set-file-acl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
set-file-extended-attributes . . . . . . . . . . . . . . 633
set-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
set-file-selinux-context . . . . . . . . . . . . . . . . . . . 633
set-file-times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 633
set-fontset-font . . . . . . . . . . . . . . . . . . . . . . . . . . . 1183
set-frame-configuration . . . . . . . . . . . . . . . . . . . . 831
set-frame-font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797
set-frame-height . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
set-frame-parameter . . . . . . . . . . . . . . . . . . . . . . . . 803
set-frame-position . . . . . . . . . . . . . . . . . . . . . . . . . . 798
set-frame-selected-window. . . . . . . . . . . . . . . . . . 697
set-frame-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
set-frame-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
set-frame-window-state-change . . . . . . . . . . . . . 782
set-fringe-bitmap-face . . . . . . . . . . . . . . . . . . . . 1194
set-input-method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 991
set-input-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1285
set-keyboard-coding-system . . . . . . . . . . . . . . . . 990
set-keymap-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
set-left-margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903
set-mark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
set-marker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
set-marker-insertion-type. . . . . . . . . . . . . . . . . . 872
set-match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016
set-message-function . . . . . . . . . . . . . . . . . . . . . . 1132
set-message-functions . . . . . . . . . . . . . . . . . . . . . 1133
set-minibuffer-message . . . . . . . . . . . . . . . . . . . . 1133
set-minibuffer-window . . . . . . . . . . . . . . . . . . . . . . 418
set-mouse-absolute-pixel-position . . . . . . . . 836
set-mouse-pixel-position . . . . . . . . . . . . . . . . . . . 836
set-mouse-position . . . . . . . . . . . . . . . . . . . . . . . . . . 836
set-multi-message . . . . . . . . . . . . . . . . . . . . . . . . . . 1133
set-network-process-option . . . . . . . . . . . . . . . 1119
set-process-buffer . . . . . . . . . . . . . . . . . . . . . . . . 1100
set-process-coding-system . . . . . . . . . . . . . . . . 1095
set-process-datagram-address . . . . . . . . . . . . . 1115
set-process-filter . . . . . . . . . . . . . . . . . . . . . . . . 1102
set-process-plist . . . . . . . . . . . . . . . . . . . . . . . . . . 1095
set-process-query-on-exit-flag . . . . . . . . . . . 1107
set-process-sentinel . . . . . . . . . . . . . . . . . . . . . . 1107
set-process-thread . . . . . . . . . . . . . . . . . . . . . . . . 1105
set-process-window-size . . . . . . . . . . . . . . . . . . . 1101
set-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 940
set-right-margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903
set-standard-case-table . . . . . . . . . . . . . . . . . . . . . 75
set-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028
set-terminal-coding-system . . . . . . . . . . . . . . . . 990
set-terminal-parameter . . . . . . . . . . . . . . . . . . . . . 821
set-text-properties . . . . . . . . . . . . . . . . . . . . . . . . 920
set-transient-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
set-transient-map-timeout. . . . . . . . . . . . . . . . . . 494

Index

set-visited-file-modtime . . . . . . . . . . . . . . . . . . . 679
set-visited-file-name . . . . . . . . . . . . . . . . . . . . . . 676
set-window-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
set-window-combination-limit . . . . . . . . . . . . . . 716
set-window-configuration . . . . . . . . . . . . . . . . . . . 774
set-window-dedicated-p . . . . . . . . . . . . . . . . . . . . . 749
set-window-display-table . . . . . . . . . . . . . . . . . . 1245
set-window-fringes . . . . . . . . . . . . . . . . . . . . . . . . 1190
set-window-group-start . . . . . . . . . . . . . . . . . . . . . 761
set-window-group-start-function . . . . . . . . . . . 761
set-window-hscroll . . . . . . . . . . . . . . . . . . . . . . . . . . 769
set-window-margins . . . . . . . . . . . . . . . . . . . . . . . . 1206
set-window-next-buffers . . . . . . . . . . . . . . . . . . . . 747
set-window-parameter . . . . . . . . . . . . . . . . . . . . . . . 776
set-window-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
set-window-prev-buffers . . . . . . . . . . . . . . . . . . . . 747
set-window-scroll-bars . . . . . . . . . . . . . . . . . . . . 1196
set-window-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
set-window-vscroll . . . . . . . . . . . . . . . . . . . . . . . . . . 767
set-xwidget-buffer . . . . . . . . . . . . . . . . . . . . . . . . 1229
set-xwidget-plist . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
set-xwidget-query-on-exit-flag . . . . . . . . . . . 1230
set_function_finalizer . . . . . . . . . . . . . . . . . . . . 1366
set_user_finalizer . . . . . . . . . . . . . . . . . . . . . . . . 1373
set_user_ptr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1373
setcar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
setcdr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
setenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1266
setf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
setopt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
setplist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
setq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
setq-connection-local . . . . . . . . . . . . . . . . . . . . . . 221
setq-default . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
setq-local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
setting modes of files . . . . . . . . . . . . . . . . . . . . . . . . . . 629
setting-constant error . . . . . . . . . . . . . . . . . . . . . . 189
severity level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
sexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
sexp motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
sha1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
SHA hash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944, 946
shaded, a frame parameter . . . . . . . . . . . . . . . . . . . . 815
shadowed Lisp files . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
shadowing of variables . . . . . . . . . . . . . . . . . . . . . . . . 190
shared structure, read syntax. . . . . . . . . . . . . . . . . . . 30
shell command arguments. . . . . . . . . . . . . . . . . . . . 1080
shell-command-history . . . . . . . . . . . . . . . . . . . . . . 394
shell-command-to-string . . . . . . . . . . . . . . . . . . . 1085
shell-quote-argument . . . . . . . . . . . . . . . . . . . . . . 1080
shift-selection, and interactive spec . . . . . . . . . 425
shift-translation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
shortdoc-add-function . . . . . . . . . . . . . . . . . . . . . . 607
shorthands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
should_quit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374
show image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1222
show-help-function . . . . . . . . . . . . . . . . . . . . . . . . . . 931

1447

shr-insert-document . . . . . . . . . . . . . . . . . . . . . . . . 952
shrink-window-if-larger-than-buffer . . . . . . 706
shy groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002
sibling window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
side effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
side windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
side, a buffer display action alist entry . . . . . . . . 735
side-effect-free property . . . . . . . . . . . . . . . . . . . 141
SIGHUP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
SIGINT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
signal-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098
signal-process-functions . . . . . . . . . . . . . . . . . . 1098
signaling errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097
SIGTERM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
SIGTSTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
sigusr1 event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
sigusr2 event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
simple package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
sin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
single file package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
single-function hook . . . . . . . . . . . . . . . . . . . . . . . . . . 524
single-key-description . . . . . . . . . . . . . . . . . . . . . 601
sit-for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
site-init.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
site-lisp directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
site-load.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347
site-run-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
site-start.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256
size of frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
size of image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
size of text on display . . . . . . . . . . . . . . . . . . . . . . . . 1157
size of window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
skip-chars-backward . . . . . . . . . . . . . . . . . . . . . . . . 864
skip-chars-forward . . . . . . . . . . . . . . . . . . . . . . . . . . 863
skip-syntax-backward . . . . . . . . . . . . . . . . . . . . . . 1030
skip-syntax-forward . . . . . . . . . . . . . . . . . . . . . . . 1030
skip-taskbar, a frame parameter . . . . . . . . . . . . . 815
skipping characters . . . . . . . . . . . . . . . . . . . . . . . . . . . 863
skipping characters of certain syntax . . . . . . . . . 1030
skipping comments . . . . . . . . . . . . . . . . . . . . . . . . . . 1034
sleep-for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
slice, image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1223
slot, a buffer display action alist entry . . . . . . . . 735
small-temporary-file-directory . . . . . . . . . . . . 642
smallest fixnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
smie-bnf->prec2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
smie-close-block . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
smie-config . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
smie-config-guess . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
smie-config-local . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
smie-config-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
smie-config-set-indent . . . . . . . . . . . . . . . . . . . . . 590
smie-config-show-indent . . . . . . . . . . . . . . . . . . . . 590
smie-down-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
smie-merge-prec2s . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
smie-prec2->grammar . . . . . . . . . . . . . . . . . . . . . . . . 583

Indexsmie-precs->prec2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
smie-rule-bolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-hanging-p . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-next-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-parent-p . . . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-prev-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-separator . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-rule-sibling-p . . . . . . . . . . . . . . . . . . . . . . . . 588
smie-setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
SMIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
SMIE grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
SMIE lexer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
smooth-curveto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1218smooth-quadratic-bezier-curveto. . . . . . . . . . 1219
snap-width, a frame parameter . . . . . . . . . . . . . . . 814
Snarf-documentation . . . . . . . . . . . . . . . . . . . . . . . . 598
sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
sort-columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
sort-fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
sort-fold-case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 907
sort-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 908
sort-numeric-base . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
sort-numeric-fields . . . . . . . . . . . . . . . . . . . . . . . . 909
sort-pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 909
sort-paragraphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 908
sort-regexp-fields . . . . . . . . . . . . . . . . . . . . . . . . . . 907
sort-subr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906
sorting lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
sorting sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
sorting text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906
sorting vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
source breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
space (ASCII character). . . . . . . . . . . . . . . . . . . . . . . . 12
space display spec, and bidirectional text . . . . 1252
spaces, pixel specification . . . . . . . . . . . . . . . . . . . . 1201
spaces, specified height or width . . . . . . . . . . . . . 1200
sparse keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
SPC in minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
special events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
special form descriptions . . . . . . . . . . . . . . . . . . . . . . . . 4
special forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
special forms for control structures . . . . . . . . . . . . 158
special modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
special read syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
special variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
special-event-map . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
special-form-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
special-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
special-mode-map. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1397
special-variable-p . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Specified time is not representable . . . . . . . . . . . 1271
specify coding system . . . . . . . . . . . . . . . . . . . . . . . . . 986
specify color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
speedups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1336
splicing (with backquote) . . . . . . . . . . . . . . . . . . . . . 152
split-height-threshold . . . . . . . . . . . . . . . . . . . . . 737

1448

split-root-window-below . . . . . . . . . . . . . . . . . . . . 710
split-root-window-right . . . . . . . . . . . . . . . . . . . . 710
split-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
split-string-and-unquote . . . . . . . . . . . . . . . . . . 1081
split-string-default-separators . . . . . . . . . . . . 58
split-string-shell-command . . . . . . . . . . . . . . . 1081
split-width-threshold . . . . . . . . . . . . . . . . . . . . . . 737
split-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
split-window, a window parameter . . . . . . . . . . . 778
split-window-below . . . . . . . . . . . . . . . . . . . . . . . . . . 710
split-window-keep-point . . . . . . . . . . . . . . . . . . . . 710
split-window-preferred-function . . . . . . . . . . . 736
split-window-right . . . . . . . . . . . . . . . . . . . . . . . . . . 710
split-window-sensibly . . . . . . . . . . . . . . . . . . . . . . 736
splitting windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
sqlite-available-p . . . . . . . . . . . . . . . . . . . . . . . . . . 949
sqlite-close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
sqlite-columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950
sqlite-commit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-execute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
sqlite-finalize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-load-extension . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-mode-open-file . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-more-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950
sqlite-open . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
sqlite-pragma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-rollback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950
sqlite-transaction . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlite-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
sqlitep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
stable sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
stack allocated Lisp objects . . . . . . . . . . . . . . . . . . 1354
stack frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
stack overflow in regexp. . . . . . . . . . . . . . . . . . . . . . 1007
standalone-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
standard abbrev tables. . . . . . . . . . . . . . . . . . . . . . . 1071
standard colors for character terminals . . . . . . . . 818
standard error process . . . . . . . . . . . . . . . . . . . . . . . 1088
standard errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1390
standard hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1398
standard regexps used in editing . . . . . . . . . . . . . 1020
standard syntax table . . . . . . . . . . . . . . . . . . . . . . . . 1022
standard-case-table. . . . . . . . . . . . . . . . . . . . . . . . . . 75
standard-category-table . . . . . . . . . . . . . . . . . . . 1037
standard-display-table . . . . . . . . . . . . . . . . . . . . 1245
standard-input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
standard-output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
standard-syntax-table . . . . . . . . . . . . . . . . . . . . . 1022
standard-translation-table-for-decode . . . . 976
standard-translation-table-for-encode . . . . 976
standards of coding style . . . . . . . . . . . . . . . . . . . . . 1331
start-file-process . . . . . . . . . . . . . . . . . . . . . . . . 1090
start-file-process-shell-command . . . . . . . . 1091
start-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1089

Indexstart-process, command-line
arguments from minibuffer. . . . . . . . . . . . . . . . . 1080
start-process-shell-command . . . . . . . . . . . . . . 1090
STARTTLS network connections . . . . . . . . . . . . . . 1111
startup of Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1255
startup screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1257
startup-redirect-eln-cache . . . . . . . . . . . . . . . . 330
startup.el . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1255
statement object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 950
staticpro, protection from GC . . . . . . . . . . . . . . 1359
stderr stream, use for debugging . . . . . . . . . . . . . 377
sticky text properties . . . . . . . . . . . . . . . . . . . . . . . . . 932
sticky, a frame parameter . . . . . . . . . . . . . . . . . . . . 815
stop points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
stop-process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1098
stopbits, in serial connections . . . . . . . . . . . . . . . . 1123
stopping an infinite loop . . . . . . . . . . . . . . . . . . . . . . 336
stopping on events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
storage of vector-like Lisp objects . . . . . . . . . . . . 1350
store-match-data . . . . . . . . . . . . . . . . . . . . . . . . . . . 1016
store-substring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
stream (for printing) . . . . . . . . . . . . . . . . . . . . . . . . . . 375
stream (for reading) . . . . . . . . . . . . . . . . . . . . . . . . . . 371
strike-through text. . . . . . . . . . . . . . . . . . . . . . . . . . . 1166
string. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
string creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
string equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
string in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
string input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
string length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
string modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
string reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
string search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 993
string to number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
string to object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
string to vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
string, number of bytes . . . . . . . . . . . . . . . . . . . . . . . 965
string, writing a doc string . . . . . . . . . . . . . . . . . . . . 595
string-as-multibyte . . . . . . . . . . . . . . . . . . . . . . . . 967
string-as-unibyte . . . . . . . . . . . . . . . . . . . . . . . . . . . 967
string-bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
string-chars-consed . . . . . . . . . . . . . . . . . . . . . . . 1355
string-chop-newline. . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-clean-whitespace . . . . . . . . . . . . . . . . . . . . . 58
string-collate-equalp . . . . . . . . . . . . . . . . . . . . . . . 61
string-collate-lessp . . . . . . . . . . . . . . . . . . . . . . . . 62
string-distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
string-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
string-equal-ignore-case . . . . . . . . . . . . . . . . . . . . 61
string-fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-glyph-split . . . . . . . . . . . . . . . . . . . . . . . . 1161
string-greaterp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
string-lessp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
string-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1009
string-match-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1010

1449

string-or-null-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
string-pad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-pixel-width . . . . . . . . . . . . . . . . . . . . . . . . 1161
string-prefix-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
string-replace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017
string-search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
string-suffix-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
string-to-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
string-to-int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
string-to-multibyte . . . . . . . . . . . . . . . . . . . . . . . . 966
string-to-number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
string-to-syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035
string-to-unibyte . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
string-trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-trim-left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-trim-right . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
string-version-lessp . . . . . . . . . . . . . . . . . . . . . . . . 63
string-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158
string< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
string= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
stringp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
strings with keyboard events . . . . . . . . . . . . . . . . . . 459
strings, formatting them . . . . . . . . . . . . . . . . . . . . . . . 66
strings-consed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
structural matching . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
sub-sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
submenu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
subprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1078
subr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
subr-arity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
subrp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
subst-char-in-region . . . . . . . . . . . . . . . . . . . . . . . 939
subst-char-in-string . . . . . . . . . . . . . . . . . . . . . . . 939
substitute characters . . . . . . . . . . . . . . . . . . . . . . . . . . 939
substitute-command-keys . . . . . . . . . . . . . . . . . . . . 599
substitute-in-file-name . . . . . . . . . . . . . . . . . . . . 640
substitute-key-definition . . . . . . . . . . . . . 499, 502
substitute-quotes . . . . . . . . . . . . . . . . . . . . . . . . . . . 600
substituting keys in documentation. . . . . . . . . . . . 598
substring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
substring-no-properties . . . . . . . . . . . . . . . . . . . . . 56
subtype of char-table . . . . . . . . . . . . . . . . . . . . . . . . . 119
success handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
super characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
support for touchscreens . . . . . . . . . . . . . . . . . . . . . . 448
suppress-keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
surrogate minibuffer frame . . . . . . . . . . . . . . . . . . . . 824
suspend (cf. no-redraw-on-reenter) . . . . . . . . . 1129
suspend evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
suspend major mode temporarily. . . . . . . . . . . . . . 526
suspend-emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264
suspend-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1265
suspend-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264
suspend-resume-hook . . . . . . . . . . . . . . . . . . . . . . . 1264
suspend-tty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264
suspend-tty-functions . . . . . . . . . . . . . . . . . . . . . 1264

Indexsuspending Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263
suspicious text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945
suspicious text strings. . . . . . . . . . . . . . . . . . . . . . . . . 945
svg path commands. . . . . . . . . . . . . . . . . . . . . . . . . . 1217
svg-circle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-clip-path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1216
svg-create . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1214
svg-ellipse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-embed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1216
svg-embed-base-uri-image . . . . . . . . . . . . . . . . . . 1216
svg-gradient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1214
svg-image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
svg-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
svg-path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-polygon. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-polyline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-rectangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215
svg-remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217
svg-text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1216
SVG images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1213
SVG object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1214
swap text between buffers . . . . . . . . . . . . . . . . . . . . . 688
switch-to-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722
switch-to-buffer-in-dedicated-window . . . . . 722
switch-to-buffer-obey-display-actions . . . . 723
switch-to-buffer-other-frame . . . . . . . . . . . . . . 723
switch-to-buffer-other-window . . . . . . . . . . . . . 723
switch-to-buffer-preserve-window-point . . . 722
switch-to-next-buffer . . . . . . . . . . . . . . . . . . . . . . 747
switch-to-prev-buffer . . . . . . . . . . . . . . . . . . . . . . 747
switch-to-prev-buffer-skip . . . . . . . . . . . . . . . . 748
switch-to-prev-buffer-skip-regexp . . . . . . . . 748
switches on command line . . . . . . . . . . . . . . . . . . . 1261
switching to a buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 721
sxhash-eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
sxhash-eql . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
sxhash-equal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
symbol components . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
symbol equality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
symbol evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
symbol forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
symbol function indirection . . . . . . . . . . . . . . . . . . . 147
symbol in keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
symbol name hashing . . . . . . . . . . . . . . . . . . . . . . . . . 135
symbol property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
symbol that evaluates to itself. . . . . . . . . . . . . . . . . 189
symbol with constant value . . . . . . . . . . . . . . . . . . . 189
symbol with position . . . . . . . . . . . . . . . . . . . . . . . . . . 143
symbol, where defined . . . . . . . . . . . . . . . . . . . . . . . . 311
symbol-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
symbol-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
symbol-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
symbol-plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
symbol-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
symbol-with-pos-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
symbol-with-pos-pos . . . . . . . . . . . . . . . . . . . . . . . . 144

1450

symbolic links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
symbolic shorthands . . . . . . . . . . . . . . . . . . . . . . . . . . 142
symbolp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
symbols-consed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
symbols-with-pos-enabled . . . . . . . . . . . . . . . . . . . 144
symmetric cipher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
synchronized multisession variables . . . . . . . . . . . . 228
synchronous subprocess . . . . . . . . . . . . . . . . . . . . . . 1081
syntactic font lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575
syntax class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023
syntax class table . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023
syntax code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1034
syntax descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1023
syntax entry, setting . . . . . . . . . . . . . . . . . . . . . . . . . 1027
syntax error (Edebug) . . . . . . . . . . . . . . . . . . . . . . . . 363
syntax flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026
syntax for characters . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
syntax highlighting and coloring. . . . . . . . . . . . . . . 563
syntax of regular expressions . . . . . . . . . . . . . . . . . . 996
syntax table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
syntax table example . . . . . . . . . . . . . . . . . . . . . . . . . 542
syntax table internals . . . . . . . . . . . . . . . . . . . . . . . . 1034
syntax tables (accessing elements of) . . . . . . . . . 1035
syntax tables in modes . . . . . . . . . . . . . . . . . . . . . . . . 529
syntax tree nodes, by field name . . . . . . . . . . . . . 1048
syntax tree nodes, by kinship . . . . . . . . . . . . . . . . 1047
syntax tree nodes, by position. . . . . . . . . . . . . . . . 1048
syntax tree nodes, retrievingfrom other nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
syntax tree, concrete . . . . . . . . . . . . . . . . . . . . . . . . . 1040
syntax tree, from parsing program source . . . . 1039
syntax tree, retrieving nodes . . . . . . . . . . . . . . . . . 1046
syntax trees, node information . . . . . . . . . . . . . . . 1051
syntax-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035
syntax-class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1035
syntax-class-to-char . . . . . . . . . . . . . . . . . . . . . . 1035
syntax-ppss. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1032
syntax-ppss-context . . . . . . . . . . . . . . . . . . . . . . . 1033
syntax-ppss-flush-cache . . . . . . . . . . . . . . . . . . . 1032
syntax-ppss-toplevel-pos . . . . . . . . . . . . . . . . . . 1033
syntax-propertize-extendregion-functions. . . . . . . . . . . . . . . . . . . . . . . . . 1030
syntax-propertize-function . . . . . . . . . . . . . . . 1029
syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028
syntax-table (text property) . . . . . . . . . . . . . . . . 1029
syntax-table-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
system abbrev . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066
system processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108
system tooltips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
system type and name . . . . . . . . . . . . . . . . . . . . . . . 1265
system-configuration . . . . . . . . . . . . . . . . . . . . . . 1265
system-groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
system-key-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
system-messages-locale . . . . . . . . . . . . . . . . . . . . . 992
system-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1266
system-time-locale . . . . . . . . . . . . . . . . . . . . . . . . . . 992
system-type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1265
system-users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270

IndexTt ............................................... 2t input stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
t output stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
tab (ASCII character) . . . . . . . . . . . . . . . . . . . . . . . . . . 12
tab bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
tab deletion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887
tab-always-indent . . . . . . . . . . . . . . . . . . . . . . . . . . . 912
tab-bar mouse events . . . . . . . . . . . . . . . . . . . . . . . . . 445
tab-bar, prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
tab-bar-lines, a frame parameter . . . . . . . . . . . . 811
tab-bar-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1397
tab-first-completion . . . . . . . . . . . . . . . . . . . . . . . 912
tab-line, prefix key . . . . . . . . . . . . . . . . . . . . . . . . . . 462
tab-line-format, a window parameter . . . . . . . . 779
tab-prefix-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
tab-stop-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915
tab-to-tab-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915
tab-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1243
TAB in minibuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
tabs stops for indentation . . . . . . . . . . . . . . . . . . . . . 915
Tabulated List mode . . . . . . . . . . . . . . . . . . . . . . . . . . 538
tabulated-list-clear-all-tags . . . . . . . . . . . . . 541
tabulated-list-delete-entry . . . . . . . . . . . . . . . 540
tabulated-list-entries . . . . . . . . . . . . . . . . . . . . . 539
tabulated-list-format . . . . . . . . . . . . . . . . . . . . . . 539
tabulated-list-get-entry . . . . . . . . . . . . . . . . . . . 541
tabulated-list-get-id . . . . . . . . . . . . . . . . . . . . . . 541
tabulated-list-gui-sort-indicator-asc . . . . 538
tabulated-list-gui-sort-indicator-desc . . . 539
tabulated-list-header-overlay-p . . . . . . . . . . . 541
tabulated-list-init-header . . . . . . . . . . . . . . . . 540
tabulated-list-mode . . . . . . . . . . . . . . . . . . . . . . . . 538
tabulated-list-padding . . . . . . . . . . . . . . . . . . . . . 541
tabulated-list-print . . . . . . . . . . . . . . . . . . . . . . . 540
tabulated-list-printer . . . . . . . . . . . . . . . . . . . . . 540
tabulated-list-put-tag . . . . . . . . . . . . . . . . . . . . . 541
tabulated-list-revert-hook . . . . . . . . . . . . . . . . 540
tabulated-list-set-col . . . . . . . . . . . . . . . . . . . . . 541
tabulated-list-sort-key . . . . . . . . . . . . . . . . . . . . 540
tabulated-list-tty-sort-indicator-asc . . . . 539
tabulated-list-tty-sort-indicator-desc . . . 539
tabulated-list-use-header-line . . . . . . . . . . . . 541
tag on run time stack . . . . . . . . . . . . . . . . . . . . . . . . . 178
tag, customization keyword . . . . . . . . . . . . . . . . . . . 277
take . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
tan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1111
temacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346
temp-buffer-max-height . . . . . . . . . . . . . . . . . . . . 1149
temp-buffer-max-width . . . . . . . . . . . . . . . . . . . . . 1149
temp-buffer-resize-mode . . . . . . . . . . . . . . . . . . . 1148
temp-buffer-setup-hook . . . . . . . . . . . . . . . . . . . . 1147
temp-buffer-show-function . . . . . . . . . . . . . . . . 1147
temp-buffer-show-hook . . . . . . . . . . . . . . . . . . . . . 1148
temp-buffer-window-setup-hook . . . . . . . . . . . . 1148
temp-buffer-window-show-hook . . . . . . . . . . . . . 1148
TEMP environment variable . . . . . . . . . . . . . . . . . . . . 642

1451

temporary buffer display . . . . . . . . . . . . . . . . . . . . . 1146
temporary display . . . . . . . . . . . . . . . . . . . . . . . . . . . 1146
temporary file on a remote host . . . . . . . . . . . . . . . 643
temporary files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
temporary-file-directory . . . . . . . . . . . . . . 642, 643
term-file-aliases . . . . . . . . . . . . . . . . . . . . . . . . . . 1260
term-file-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . 1260
TERM environment variable . . . . . . . . . . . . . . . . . . . 1260
Termcap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1260
terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
terminal input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1285
terminal input modes . . . . . . . . . . . . . . . . . . . . . . . . 1285
terminal output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
terminal parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 820
terminal screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
terminal type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
terminal-coding-system . . . . . . . . . . . . . . . . . . . . . 990
terminal-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
terminal-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
terminal-local variables . . . . . . . . . . . . . . . . . . . . . . . 788
terminal-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
terminal-parameter . . . . . . . . . . . . . . . . . . . . . . . . . . 821
terminal-parameters . . . . . . . . . . . . . . . . . . . . . . . . 820
terminal-specific initialization . . . . . . . . . . . . . . . . 1260
terminology, for tree-sitter functions . . . . . . . . . 1045
termscript file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1287
terpri . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
test-completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
testcover-mark-all . . . . . . . . . . . . . . . . . . . . . . . . . . 368
testcover-next-mark . . . . . . . . . . . . . . . . . . . . . . . . 368
testcover-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
testing types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
text area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795
text area of a window . . . . . . . . . . . . . . . . . . . . . . . . . 691
text comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
text conversion of coding system . . . . . . . . . . . . . . 980
text deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
text height of a frame . . . . . . . . . . . . . . . . . . . . . . . . . 799
text insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882
text near point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
text parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1022
text properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
text properties in files . . . . . . . . . . . . . . . . . . . . . . . . . 654
text properties in the mode line . . . . . . . . . . . . . . . 558
text properties, changing . . . . . . . . . . . . . . . . . . . . . . 919
text properties, examining . . . . . . . . . . . . . . . . . . . . 917
text properties, read syntax . . . . . . . . . . . . . . . . . . . . 22
text properties, searching . . . . . . . . . . . . . . . . . . . . . 921
text representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
text size of a frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
text terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
text width of a frame . . . . . . . . . . . . . . . . . . . . . . . . . 799
text-char-description . . . . . . . . . . . . . . . . . . . . . . 602
text-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
text-mode-abbrev-table . . . . . . . . . . . . . . . . . . . . 1071
text-properties-at . . . . . . . . . . . . . . . . . . . . . . . . . . 918
text-property-any . . . . . . . . . . . . . . . . . . . . . . . . . . . 923

Indextext-property-default-nonsticky . . . . . . . . . . . 933
text-property-not-all . . . . . . . . . . . . . . . . . . . . . . 923
text-property-search-backward . . . . . . . . . . . . . 924
text-property-search-forward . . . . . . . . . . . . . . 923
text-quoting-style . . . . . . . . . . . . . . . . . . . . . 600, 601
text-terminal focus notification . . . . . . . . . . . . . . . . 826
textsec-check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 946
textsec-suspicious (face) . . . . . . . . . . . . . . . . . . . 946
textsec-suspicious-p . . . . . . . . . . . . . . . . . . . . . . . 946
textual order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
textual scrolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
theme-face (face symbol property) . . . . . . . . . . 1170
thing-at-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 881
thing-at-point-provider-alist . . . . . . . . . . . . . 881
this-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
this-command-keys . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
this-command-keys-shift-translated . . . . . . . 462
this-command-keys-vector . . . . . . . . . . . . . . . . . . . 437
this-original-command . . . . . . . . . . . . . . . . . . . . . . 437
thread backtrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
thread list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076
thread--blocker . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
thread-join. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
thread-last-error . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
thread-list-refresh-seconds . . . . . . . . . . . . . . 1076
thread-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
thread-name. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
thread-signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
thread-yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1074
threadp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1073
three-step-help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
throw. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
throw example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
thunk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
thunk-delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
thunk-force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
thunk-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
thunk-let* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
tiled windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
time calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
time conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273
time formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
time of day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
time parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276
time value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1271
time zone rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
time zone rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
time zone, current . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272
time-add . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
time-convert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273
time-equal-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
time-less-p. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
time-subtract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
time-to-day-in-year . . . . . . . . . . . . . . . . . . . . . . . 1281
time-to-days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
timer-max-repeats . . . . . . . . . . . . . . . . . . . . . . . . . . 1283
timerp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281

1452

timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1281
timestamp of a mouse event . . . . . . . . . . . . . . . . . . . 458
timestamp, Lisp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
timing programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
tips for documentation strings . . . . . . . . . . . . . . . 1337
tips for faster Lisp code . . . . . . . . . . . . . . . . . . . . . . 1336
tips for writing Lisp . . . . . . . . . . . . . . . . . . . . . . . . . 1331
title bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
title, a frame parameter . . . . . . . . . . . . . . . . . . . . . 805
TLS network connections. . . . . . . . . . . . . . . . . . . . . 1111
TMP environment variable . . . . . . . . . . . . . . . . . . . . . 642
TMPDIR environment variable . . . . . . . . . . . . . . . . . . 642
toggle-enable-multibyte-characters . . . . . . . 965
tool bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
tool-bar mouse events . . . . . . . . . . . . . . . . . . . . . . . . . 445
tool-bar-add-item . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
tool-bar-add-item-from-menu . . . . . . . . . . . . . . . 519
tool-bar-border . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
tool-bar-button-margin . . . . . . . . . . . . . . . . . . . . . 520
tool-bar-button-relief . . . . . . . . . . . . . . . . . . . . . 520
tool-bar-lines, a frame parameter . . . . . . . . . . . 811
tool-bar-local-item-from-menu . . . . . . . . . . . . . 520
tool-bar-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
tool-bar-position, a frame parameter . . . . . . . 811
tooltip face. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
tooltip for help strings . . . . . . . . . . . . . . . . . . . . . . . . 926
tooltip frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
tooltip window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
tooltip-event-buffer . . . . . . . . . . . . . . . . . . . . . . 1249
tooltip-frame-parameters . . . . . . . . . . . . . . . . . . 1249
tooltip-functions . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
tooltip-help-tips . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
tooltip-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
tooltips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1249
top and bottom window decorations . . . . . . . . . . . 691
top frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
top position ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
top, a frame parameter . . . . . . . . . . . . . . . . . . . . . . . 807
top-level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
top-level default value. . . . . . . . . . . . . . . . . . . . . . . . . 213
top-level form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
top-level frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786
top-visible, a frame parameter . . . . . . . . . . . . . . 814
total height of a window . . . . . . . . . . . . . . . . . . . . . . 699
total pixel height of a window . . . . . . . . . . . . . . . . . 700
total pixel width of a window . . . . . . . . . . . . . . . . . 700
total width of a window . . . . . . . . . . . . . . . . . . . . . . . 699
touch point, in touchscreen events . . . . . . . . . . . . . 448
touch-end event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
touchscreen events . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
touchscreen-begin event . . . . . . . . . . . . . . . . . . . . . 448
touchscreen-end event . . . . . . . . . . . . . . . . . . . . . . . 448
touchscreen-update event . . . . . . . . . . . . . . . . . . . . 448
tq-close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1111
tq-create . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110
tq-enqueue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110
trace buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
tracing Lisp programs . . . . . . . . . . . . . . . . . . . . . . . . . 333

Indextrack-mouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
tracking frame size changes . . . . . . . . . . . . . . . . . . . 801
trailing blanks in file names . . . . . . . . . . . . . . . . . . . 619
trampolines, in native compilation . . . . . . . . . . . . 331
transaction queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1110
transcendental functions . . . . . . . . . . . . . . . . . . . . . . . 51
transient keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
transient-mark-mode . . . . . . . . . . . . . . . . . . . . . . . . 875
translate-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . 939
translate-upper-case-key-bindings . . . . . . . . 462
translating input events . . . . . . . . . . . . . . . . . . . . . . . 466
translation keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
translation tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975
translation-table-for-input . . . . . . . . . . . . . . . 976
transparency, frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 819
transpose-regions . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
trash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631, 649
tray notifications, MS-Windows . . . . . . . . . . . . . . 1295
tree-sitter extra node . . . . . . . . . . . . . . . . . . . . . . . . 1051
tree-sitter fontifications, overview . . . . . . . . . . . . . 578
tree-sitter host and embedded languages . . . . . 1059
tree-sitter missing node . . . . . . . . . . . . . . . . . . . . . . 1051
tree-sitter narrowing . . . . . . . . . . . . . . . . . . . . . . . . . 1044
tree-sitter node field name . . . . . . . . . . . . . . . . . . . 1041
tree-sitter node that has error . . . . . . . . . . . . . . . . 1052
tree-sitter nodes, comparing. . . . . . . . . . . . . . . . . . 1051
tree-sitter outdated node. . . . . . . . . . . . . . . . . . . . . 1051
tree-sitter parse string . . . . . . . . . . . . . . . . . . . . . . . 1045
tree-sitter parse tree, leaf node . . . . . . . . . . . . . . . 1046
tree-sitter parse-tree, update andafter-change callback . . . . . . . . . . . . . . . . . . . . . . 1045
tree-sitter parser, creating . . . . . . . . . . . . . . . . . . . 1044
tree-sitter parser, using . . . . . . . . . . . . . . . . . . . . . . 1043
tree-sitter patterns as strings . . . . . . . . . . . . . . . . . 1056
tree-sitter query pattern syntax . . . . . . . . . . . . . . 1053
tree-sitter, find node . . . . . . . . . . . . . . . . . . . . . . . . . 1045
tree-sitter, live parsing node . . . . . . . . . . . . . . . . . 1052
treesit-available-p . . . . . . . . . . . . . . . . . . . . . . . 1039
treesit-beginning-of-defun . . . . . . . . . . . . . . . . 863
treesit-buffer-root-node . . . . . . . . . . . . . . . . . . 1047
treesit-buffer-too-large . . . . . . . . . . . . . . . . . . 1044
treesit-check-indent . . . . . . . . . . . . . . . . . . . . . . . 594
treesit-defun-at-point . . . . . . . . . . . . . . . . . . . . 1062
treesit-defun-name . . . . . . . . . . . . . . . . . . . . . . . . 1062
treesit-defun-name-function . . . . . . . . . . . . . . 1063
treesit-defun-tactic . . . . . . . . . . . . . . . . . . . . . . . 863
treesit-defun-type-regexp. . . . . . . . . . . . . . . . . . 863
treesit-end-of-defun . . . . . . . . . . . . . . . . . . . . . . . 863
treesit-explore-mode . . . . . . . . . . . . . . . . . . . . . . 1041
treesit-extra-load-path . . . . . . . . . . . . . . . . . . . 1039
treesit-filter-child . . . . . . . . . . . . . . . . . . . . . . 1050
treesit-font-lock-feature-list . . . . . . . . . . . . 580
treesit-font-lock-recompute-features . . . . . 580
treesit-font-lock-rules . . . . . . . . . . . . . . . . . . . . 579
treesit-font-lock-settings . . . . . . . . . . . . . . . . 580
treesit-fontify-with-override . . . . . . . . . . . . . 580
treesit-indent-function . . . . . . . . . . . . . . . . . . . . 591
treesit-induce-sparse-tree . . . . . . . . . . . . . . . 1049

1453

treesit-inspect-mode . . . . . . . . . . . . . . . . . . . . . . 1041
treesit-language-abi-version . . . . . . . . . . . . . 1040
treesit-language-at . . . . . . . . . . . . . . . . . . . . . . . 1059
treesit-language-at-point-function . . . . . . 1061
treesit-language-available-p . . . . . . . . . . . . . 1040
treesit-library-abi-version . . . . . . . . . . . . . . 1040
treesit-load-language-error . . . . . . . . . . . . . . 1039
treesit-load-name-override-list. . . . . . . . . . 1040
treesit-major-mode-setup . . . . . . . . . . . . . . . . . . 1062
treesit-max-buffer-size . . . . . . . . . . . . . . . . . . . 1043
treesit-node-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046
treesit-node-buffer . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-check . . . . . . . . . . . . . . . . . . . . . . . . 1052
treesit-node-child . . . . . . . . . . . . . . . . . . . . . . . . 1047
treesit-node-child-by-field-name . . . . . . . . 1048
treesit-node-child-count . . . . . . . . . . . . . . . . . . 1052
treesit-node-children . . . . . . . . . . . . . . . . . . . . . 1047
treesit-node-descendant-for-range . . . . . . . 1048
treesit-node-end . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-field-name . . . . . . . . . . . . . . . . . . . 1052
treesit-node-field-name-for-child . . . . . . . 1052
treesit-node-first-child-for-pos . . . . . . . . 1048
treesit-node-index . . . . . . . . . . . . . . . . . . . . . . . . 1052
treesit-node-language . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-next-sibling . . . . . . . . . . . . . . . . 1047
treesit-node-on . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046
treesit-node-outdated . . . . . . . . . . . . . . . . . . . . . 1046
treesit-node-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-parent . . . . . . . . . . . . . . . . . . . . . . . 1047
treesit-node-parser . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-prev-sibling . . . . . . . . . . . . . . . . 1047
treesit-node-start . . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-text . . . . . . . . . . . . . . . . . . . . . . . . . . 1051
treesit-node-top-level . . . . . . . . . . . . . . . . . . . . 1050
treesit-node-type . . . . . . . . . . . . . . . . . . . . . . . . . . 1052
treesit-parent-until . . . . . . . . . . . . . . . . . . . . . . 1050
treesit-parent-while . . . . . . . . . . . . . . . . . . . . . . 1050
treesit-parse-string . . . . . . . . . . . . . . . . . . . . . . 1045
treesit-parser-add-notifier . . . . . . . . . . . . . . 1045
treesit-parser-buffer . . . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-create . . . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-delete . . . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-included-ranges . . . . . . . . . . . 1058
treesit-parser-language . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-list . . . . . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-notifiers . . . . . . . . . . . . . . . . . . 1045
treesit-parser-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044
treesit-parser-remove-notifier . . . . . . . . . . . 1045
treesit-parser-root-node . . . . . . . . . . . . . . . . . . 1047
treesit-parser-set-included-ranges . . . . . . 1058
treesit-pattern-expand . . . . . . . . . . . . . . . . . . . . 1057
treesit-query-capture . . . . . . . . . . . . . . . . . . . . . 1053
treesit-query-compile . . . . . . . . . . . . . . . . . . . . . 1057
treesit-query-error . . . . . . . . . . . . . . . . . . . . . . . 1053
treesit-query-expand . . . . . . . . . . . . . . . . . . . . . . 1057
treesit-query-language . . . . . . . . . . . . . . . . . . . . 1057
treesit-query-range . . . . . . . . . . . . . . . . . . . . . . . 1058

Indextreesit-query-string . . . . . . . . . . . . . . . . . . . . . . 1054
treesit-query-validate . . . . . . . . . . . . . . . . . . . . 1053
treesit-range-invalid . . . . . . . . . . . . . . . . . . . . . 1058
treesit-range-rules . . . . . . . . . . . . . . . . . . . . . . . 1060
treesit-range-settings . . . . . . . . . . . . . . . . . . . . 1061
treesit-ready-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1061
treesit-search-forward . . . . . . . . . . . . . . . . . . . . 1048
treesit-search-forward-goto . . . . . . . . . . . . . . 1049
treesit-search-subtree . . . . . . . . . . . . . . . . . . . . 1048
treesit-simple-imenu-settings . . . . . . . . . . . . . 563
treesit-simple-indent-presets . . . . . . . . . . . . . 591
treesit-simple-indent-rules . . . . . . . . . . . . . . . 591
treesit-update-ranges . . . . . . . . . . . . . . . . . . . . . 1059
triple-click events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
true. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
true list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
truename (of file) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
truncate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
truncate-lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130
truncate-partial-width-windows . . . . . . . . . . . 1130
truncate-string-ellipsis . . . . . . . . . . . . . . . . . . 1159
truncate-string-to-width . . . . . . . . . . . . . . . . . . 1158
truth value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
try-completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
tty-color-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
tty-color-approximate . . . . . . . . . . . . . . . . . . . . . . 848
tty-color-clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
tty-color-define . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
tty-color-mode, a frame parameter . . . . . . . . . . . 818
tty-color-translate . . . . . . . . . . . . . . . . . . . . . . . . 848
tty-erase-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
tty-menu-calls-mouse-position-function . . . 836
tty-setup-hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261
tty-top-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
turn multibyte support on or off . . . . . . . . . . . . . . 965
two’s complement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
type (button property) . . . . . . . . . . . . . . . . . . . . . . 1232
type checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
type checking internals . . . . . . . . . . . . . . . . . . . . . . . 1358
type of node, tree-sitter . . . . . . . . . . . . . . . . . . . . . . 1041
type predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
type, defcustom keyword . . . . . . . . . . . . . . . . . . . . . 284
type-error, customization keyword . . . . . . . . . . . 293
type-of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
type_of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374
typographic conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
TZ, environment variable . . . . . . . . . . . . . . . . . . . . . 1272

U
UBA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250
UDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1111
UID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
unassigned character codepoints . . . . . . . . . . . . . . . 969
unbalanced parentheses . . . . . . . . . . . . . . . . . . . . . . . 367
unbinding keys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507

1454

unbury-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683
undecided coding system . . . . . . . . . . . . . . . . . . . . . 977
undecided coding-system, when decoding . . . . . . 989
undecided coding-system, when encoding . . . . . 988
undecorated, a frame parameter . . . . . . . . . . . . . . 816
undefined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496
undefined in keymap . . . . . . . . . . . . . . . . . . . . . . . . . 495
undefined key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
underline-minimum-offset . . . . . . . . . . . . . . . . . . 1168
underlined text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1165
undo avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 939
undo in temporary buffers . . . . . . . . . . . . . . . . . . . . 673
undo-amalgamate-change-group . . . . . . . . . . . . . . 960
undo-ask-before-discard . . . . . . . . . . . . . . . . . . . . 899
undo-auto-amalgamate . . . . . . . . . . . . . . . . . . . . . . . 897
undo-auto-current-boundary-timer . . . . . . . . . 897
undo-boundary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897
undo-in-progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897
undo-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
undo-outer-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
undo-strong-limit . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
unexec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1346, 1348
unhandled-file-name-directory . . . . . . . . . . . . . 653
unibyte buffers, and bidi reordering . . . . . . . . . . 1250
unibyte text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
unibyte-char-to-multibyte. . . . . . . . . . . . . . . . . . 966
unibyte-string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
Unicode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
unicode bidirectional algorithm . . . . . . . . . . . . . . 1250
unicode character escape . . . . . . . . . . . . . . . . . . . . . . . 12
unicode general category . . . . . . . . . . . . . . . . . . . . . . 969
unicode, a charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973
unicode-category-table . . . . . . . . . . . . . . . . . . . . . 972
unintern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
uninterned symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
uninterned symbol, and generating Lisp code . . 136
union of sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
unique file names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
Universal Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
universal-argument . . . . . . . . . . . . . . . . . . . . . . . . . . 474
universal-argument-map . . . . . . . . . . . . . . . . . . . . 1397
unless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
unload-feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
unload-feature-special-hooks . . . . . . . . . . . . . . 313
unloading packages . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
unloading packages, preparing for . . . . . . . . . . . . 1332
unlock-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
unmapped frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
unnumbered group . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002
unpacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124
unread-command-events . . . . . . . . . . . . . . . . . . . . . . 468
unsafep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
unspecified, face attribute value . . . . . . . . . . . . . . 1164
unsplittable, a frame parameter . . . . . . . . . . . . . 812
unused lexical variable . . . . . . . . . . . . . . . . . . . . . . . . 206
unwind-protect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
unwinding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
up-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861

Indexupcase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
upcase-initials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
upcase-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
upcase-word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
update callback, for tree-sitter parse-tree . . . . . 1045
upper case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
upper case key sequence . . . . . . . . . . . . . . . . . . . . . . 462
uptime of Emacs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1280
use time of window . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
use-empty-active-region . . . . . . . . . . . . . . . . . . . . 877
use-frame-synchronization, aframe parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
use-global-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
use-hard-newlines . . . . . . . . . . . . . . . . . . . . . . . . . . . 902
use-local-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
use-package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
use-region-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
use-system-tooltips . . . . . . . . . . . . . . . . . . . . . . . 1249
user errors, signaling . . . . . . . . . . . . . . . . . . . . . . . . . . 181
user groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
user identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
user options, how to define . . . . . . . . . . . . . . . . . . . . 280
user pointer object . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
user pointer, using in module functions . . . . . . . 1372
user signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
user-defined error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
user-emacs-directory . . . . . . . . . . . . . . . . . . . . . . 1260
user-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
user-full-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
user-init-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
user-login-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
user-mail-address . . . . . . . . . . . . . . . . . . . . . . . . . . 1269
user-position, a frame parameter . . . . . . . . . . . . 807
user-ptr object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
user-ptrp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
user-real-login-name . . . . . . . . . . . . . . . . . . . . . . 1269
user-real-uid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
user-size, a frame parameter . . . . . . . . . . . . . . . . 808
user-uid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
UTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270
utf-8-emacs coding system . . . . . . . . . . . . . . . . . . . 977
utility functions for parser-based indentation . . 594

Vvalid windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
validity of coding system . . . . . . . . . . . . . . . . . . . . . . 980
value cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
value of expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
value of function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
variable aliases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
variable definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
variable descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
variable pitch tables . . . . . . . . . . . . . . . . . . . . . . . . . . 538
variable watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . 200
variable with constant value . . . . . . . . . . . . . . . . . . . 189

1455

variable write debugging . . . . . . . . . . . . . . . . . . . . . . 337
variable, buffer-local . . . . . . . . . . . . . . . . . . . . . . . . . . 207
variable-documentation property . . . . . . . . . . . . 595
variable-width spaces . . . . . . . . . . . . . . . . . . . . . . . . 1200
variant coding system . . . . . . . . . . . . . . . . . . . . . . . . . 977
vc-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
vc-prefix-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
vc-responsible-backend . . . . . . . . . . . . . . . . . . . . . 624
vconcat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
vec_get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1369
vec_set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1369
vec_size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1369
vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
vector (type) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
vector evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
vector length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
vector reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
vector to list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
vector-cells-consed . . . . . . . . . . . . . . . . . . . . . . . 1355
vector-like objects, storage . . . . . . . . . . . . . . . . . . . 1350
vectorp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
verify-visited-file-modtime . . . . . . . . . . . . . . . 679
version number (in file name) . . . . . . . . . . . . . . . . . 634
version, customization keyword . . . . . . . . . . . . . . 279
version-control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
vertical combination . . . . . . . . . . . . . . . . . . . . . . . . . . 693
vertical fractional scrolling . . . . . . . . . . . . . . . . . . . . 766
vertical scroll position. . . . . . . . . . . . . . . . . . . . . . . . . 766
vertical tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
vertical-line, prefix key . . . . . . . . . . . . . . . . . . . . 462
vertical-lineto . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1218
vertical-motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
vertical-scroll-bar . . . . . . . . . . . . . . . . . . . . . . . 1197
vertical-scroll-bar, prefix key . . . . . . . . . . . . . 462
vertical-scroll-bars, a frame parameter . . . . 810
view part, model/view/controller. . . . . . . . . . . . . 1236
view-register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 941
virtual buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688
visibility, a frame parameter . . . . . . . . . . . . . . . 814
visible frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
visible-bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
visible-frame-list . . . . . . . . . . . . . . . . . . . . . . . . . . 823
visited file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
visited file mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
visited-file-modtime . . . . . . . . . . . . . . . . . . . . . . . 679
visiting files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608
visiting files, functions for . . . . . . . . . . . . . . . . . . . . . 608
visual lines, moving by . . . . . . . . . . . . . . . . . . . . . . . . 858
visual order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1250
visual order, preserve when copying
bidirectional text . . . . . . . . . . . . . . . . . . . . . . . . . . 1254
visual-order cursor motion . . . . . . . . . . . . . . . . . . . 1252
void function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
void function cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
void variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
void-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
void-text-area-pointer . . . . . . . . . . . . . . . . . . . . . 839
void-variable error . . . . . . . . . . . . . . . . . . . . . . . . . . 193

IndexW
w32-collate-ignore-punctuation . . . . . . . . . . . . . 61
w32-notification-close . . . . . . . . . . . . . . . . . . . . 1296
w32-notification-notify . . . . . . . . . . . . . . . . . . . 1295
wait-for-wm, a frame parameter . . . . . . . . . . . . . . 815
waiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
waiting for command key input . . . . . . . . . . . . . . . 469
waiting-for-user-input-p . . . . . . . . . . . . . . . . . . 1107
walk-windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
warn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139
warning options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1141
warning type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139
warning variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1139
warning-fill-column . . . . . . . . . . . . . . . . . . . . . . . 1140
warning-fill-prefix . . . . . . . . . . . . . . . . . . . . . . . 1140
warning-levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1140
warning-minimum-level . . . . . . . . . . . . . . . . . . . . . 1141
warning-minimum-log-level . . . . . . . . . . . . . . . . 1141
warning-prefix-function . . . . . . . . . . . . . . . . . . . 1140
warning-series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1140
warning-suppress-log-types . . . . . . . . . . . . . . . 1141
warning-suppress-types . . . . . . . . . . . . . . . . . . . . 1141
warning-type-format . . . . . . . . . . . . . . . . . . . . . . . 1141
warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1138
warnings from byte compiler . . . . . . . . . . . . . . . . . 1337
warnings, delayed . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
warnings, suppressing during startup . . . . . . . . . 1141
watch, for filesystem events . . . . . . . . . . . . . . . . . . 1296
watchpoints for Lisp variables . . . . . . . . . . . . . . . . . 200
webkit browser widget . . . . . . . . . . . . . . . . . . . . . . . 1228
wheel-down event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
wheel-up event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
when . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
when-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
where was a symbol defined . . . . . . . . . . . . . . . . . . . 311
where-is-internal . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
while. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
while-let . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
while-no-input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
while-no-input-ignore-events . . . . . . . . . . . . . . 469
whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
wholenump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
widen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
widening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
width of a window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
width, a frame parameter . . . . . . . . . . . . . . . . . . . . . 808
window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
window (overlay property) . . . . . . . . . . . . . . . . . . . . 1154
window auto-selection . . . . . . . . . . . . . . . . . . . . . . . . . 773
window body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691
window body height . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window body size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
window body width . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
window buffer change . . . . . . . . . . . . . . . . . . . . . . . . . 780
window change functions . . . . . . . . . . . . . . . . . . . . . . 780
window combination . . . . . . . . . . . . . . . . . . . . . . . . . . 693
window combination limit . . . . . . . . . . . . . . . . . . . . . 715
window configuration (Edebug) . . . . . . . . . . . . . . . 357

1456

window configuration change . . . . . . . . . . . . . . . . . . 781
window configurations . . . . . . . . . . . . . . . . . . . . . . . . 774
window decorations . . . . . . . . . . . . . . . . . . . . . . . . . . . 691
window dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1198
window end position . . . . . . . . . . . . . . . . . . . . . . . . . . 760
window excursions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
window header line . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
window height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
window history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746
window in direction . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
window internals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1382
window layout in a frame . . . . . . . . . . . . . . . . . . . . . . 27
window layout, all frames . . . . . . . . . . . . . . . . . . . . . . 28
window manager interaction, andframe parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 814
window order by time of last use . . . . . . . . . . . . . . 698
window ordering, cyclic . . . . . . . . . . . . . . . . . . . . . . . 717
window parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
window pixel height . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window pixel width . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
window point internals . . . . . . . . . . . . . . . . . . . . . . . 1384
window position. . . . . . . . . . . . . . . . . . . . . . . . . . 758, 769
window position on display . . . . . . . . . . . . . . . . . . . 805
window positions and window managers . . . . . . . 807
window resizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
window selected within a frame . . . . . . . . . . . . . . . 696
window selection change . . . . . . . . . . . . . . . . . . . . . . 780
window size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
window size change . . . . . . . . . . . . . . . . . . . . . . . . . . . 780
window size on display . . . . . . . . . . . . . . . . . . . . . . . . 808
window size, changing. . . . . . . . . . . . . . . . . . . . . . . . . 703
window splitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
window start position . . . . . . . . . . . . . . . . . . . . . . . . . 759
window state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
window state change . . . . . . . . . . . . . . . . . . . . . . . . . . 781
window state change flag . . . . . . . . . . . . . . . . . . . . . . 782
window that satisfies a predicate . . . . . . . . . . . . . . 719
window top line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
window tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
window use time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
window width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
window, a buffer display action alist entry . . . . . 735
window-absolute-body-pixel-edges . . . . . . . . . 772
window-absolute-pixel-edges . . . . . . . . . . . . . . . 772
window-absolute-pixel-position . . . . . . . . . . . . 772
window-adjust-process-windowsize-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1101
window-at . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 770
window-at-side-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
window-atom, a window parameter . . . . . . . . . . . . 778
window-atom-root . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757
window-body-edges . . . . . . . . . . . . . . . . . . . . . . . . . . . 770
window-body-height . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window-body-pixel-edges . . . . . . . . . . . . . . . . . . . . 771
window-body-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
window-body-width . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
window-bottom-divider-width . . . . . . . . . . . . . . 1198

Indexwindow-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
window-buffer-change-functions . . . . . . . . . . . . 780
window-bump-use-time . . . . . . . . . . . . . . . . . . . . . . . 698
window-child . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
window-combination-limit . . . . . . . . . . . . . . 714, 716
window-combination-resize. . . . . . . . . . . . . . . . . . 716
window-combined-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
window-configuration-change-hook . . . . . . . . . 781
window-configuration-equal-p . . . . . . . . . . . . . . 775
window-configuration-frame . . . . . . . . . . . . . . . . 775
window-configuration-p . . . . . . . . . . . . . . . . . . . . . 775
window-current-scroll-bars . . . . . . . . . . . . . . . 1197
window-dedicated-p . . . . . . . . . . . . . . . . . . . . . . . . . . 749
window-display-table . . . . . . . . . . . . . . . . . . . . . . 1245
window-edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 770
window-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
window-font-height . . . . . . . . . . . . . . . . . . . . . . . . 1189
window-font-width . . . . . . . . . . . . . . . . . . . . . . . . . . 1189
window-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
window-fringes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1190
window-full-height-p . . . . . . . . . . . . . . . . . . . . . . . 700
window-full-width-p . . . . . . . . . . . . . . . . . . . . . . . . 700
window-group-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
window-group-end-function. . . . . . . . . . . . . . . . . . 760
window-group-start . . . . . . . . . . . . . . . . . . . . . . . . . . 759
window-group-start-function . . . . . . . . . . . . . . . 759
window-header-line-height . . . . . . . . . . . . . 560, 702
window-height, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
window-hscroll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 768
window-id, a frame parameter . . . . . . . . . . . . . . . . 815
window-in-direction . . . . . . . . . . . . . . . . . . . . . . . . 695
window-largest-empty-rectangle . . . . . . . . . . . . 772
window-left-child . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
window-line-height . . . . . . . . . . . . . . . . . . . . . . . . . . 762
window-lines-pixel-dimensions . . . . . . . . . . . . 1160
window-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
window-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
window-main-window . . . . . . . . . . . . . . . . . . . . . . . . . . 754
window-make-atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757
window-margins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206
window-max-chars-per-line. . . . . . . . . . . . . . . . . . 702
window-min-height . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
window-min-height, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
window-min-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
window-min-width . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
window-min-width, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
window-minibuffer-p . . . . . . . . . . . . . . . . . . . . . . . . 418
window-mode-line-height . . . . . . . . . . . . . . . . . . . . 701
window-next-buffers . . . . . . . . . . . . . . . . . . . . . . . . 747
window-next-sibling . . . . . . . . . . . . . . . . . . . . . . . . 694
window-old-body-pixel-height . . . . . . . . . . . . . . 783
window-old-body-pixel-width . . . . . . . . . . . . . . . 783
window-old-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 782
window-old-pixel-height . . . . . . . . . . . . . . . . . . . . 783
window-old-pixel-width . . . . . . . . . . . . . . . . . . . . . 783

1457

window-parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
window-parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
window-parameters, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
window-parent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
window-persistent-parameters . . . . . . . . . . . . . . 777
window-pixel-edges . . . . . . . . . . . . . . . . . . . . . . . . . . 771
window-pixel-height . . . . . . . . . . . . . . . . . . . . . . . . 700
window-pixel-width . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window-point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
window-point-insertion-type . . . . . . . . . . . . . . . 759
window-preserve-size . . . . . . . . . . . . . . . . . . . . . . . 707
window-preserved-size . . . . . . . . . . . . . . . . . . . . . . 708
window-preserved-size, awindow parameter . . . . . . . . . . . . . . . . . . . . . . . . . . 778
window-prev-buffers . . . . . . . . . . . . . . . . . . . . . . . . 746
window-prev-sibling . . . . . . . . . . . . . . . . . . . . . . . . 694
window-resizable . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
window-resize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
window-resize-pixelwise . . . . . . . . . . . . . . . . . . . . 704
window-right-divider-width . . . . . . . . . . . . . . . 1198
window-scroll-bar-height . . . . . . . . . . . . . . . . . . 1197
window-scroll-bar-width . . . . . . . . . . . . . . . . . . . 1197
window-scroll-bars . . . . . . . . . . . . . . . . . . . . . . . . 1196
window-scroll-functions . . . . . . . . . . . . . . . . . . . . 779
window-selection-change-functions . . . . . . . . 780
window-setup-hook . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
window-side, a window parameter . . . . . . . . . . . . 778
window-sides-reversed . . . . . . . . . . . . . . . . . . . . . . 754
window-sides-slots . . . . . . . . . . . . . . . . . . . . . . . . . . 753
window-sides-vertical . . . . . . . . . . . . . . . . . . . . . . 753
window-size, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 733
window-size-change-functions . . . . . . . . . . . . . . 780
window-size-fixed . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
window-slot, a window parameter . . . . . . . . . . . . 778
window-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
window-state-change-functions . . . . . . . . . . . . . 781
window-state-change-hook . . . . . . . . . . . . . . . . . . . 782
window-state-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
window-state-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
window-swap-states . . . . . . . . . . . . . . . . . . . . . . . . . . 776
window-system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
window-system window . . . . . . . . . . . . . . . . . . . . . . . 690
window-system-initialization . . . . . . . . . . . . . 1255
window-tab-line-height . . . . . . . . . . . . . . . . . . . . . 701
window-text-pixel-size . . . . . . . . . . . . . . . . . . . . 1159
window-toggle-side-windows . . . . . . . . . . . . . . . . 754
window-top-child . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694
window-total-height . . . . . . . . . . . . . . . . . . . . . . . . 699
window-total-size . . . . . . . . . . . . . . . . . . . . . . . . . . . 700
window-total-width . . . . . . . . . . . . . . . . . . . . . . . . . . 699
window-tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
window-use-time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
window-valid-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691
window-vscroll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 767
window-width, a buffer display
action alist entry . . . . . . . . . . . . . . . . . . . . . . . . . . . 733

Indexwindowp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
windows, controlling precisely . . . . . . . . . . . . . . . . . 720
windows, recombining . . . . . . . . . . . . . . . . . . . . . . . . . 712
with-case-table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
with-coding-priority . . . . . . . . . . . . . . . . . . . . . . . 987
with-connection-localapplication-variables . . . . . . . . . . . . . . . . . . . . 220
with-connection-local-variables . . . . . . . . . . . 221
with-current-buffer . . . . . . . . . . . . . . . . . . . . . . . . 673
with-current-buffer-window . . . . . . . . . . . . . . . 1148
with-delayed-message . . . . . . . . . . . . . . . . . . . . . . 1137
with-demoted-errors . . . . . . . . . . . . . . . . . . . . . . . . 185
with-environment-variables . . . . . . . . . . . . . . . 1267
with-eval-after-load . . . . . . . . . . . . . . . . . . . . . . . 314
with-existing-directory . . . . . . . . . . . . . . . . . . . . 620
with-file-modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
with-help-window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
with-local-quit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
with-mutex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1075
with-no-warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
with-output-to-string . . . . . . . . . . . . . . . . . . . . . . 379
with-output-to-temp-buffer . . . . . . . . . . . . . . . 1146
with-restriction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
with-selected-frame . . . . . . . . . . . . . . . . . . . . . . . . 698
with-selected-window . . . . . . . . . . . . . . . . . . . . . . . 698
with-silent-modifications. . . . . . . . . . . . . . . . . . 678
with-silent-modifications, and changes
in text properties . . . . . . . . . . . . . . . . . . . . . . . . 921
with-sqlite-transaction . . . . . . . . . . . . . . . . . . . . 951
with-suppressed-warnings . . . . . . . . . . . . . . . . . . . 322
with-syntax-table . . . . . . . . . . . . . . . . . . . . . . . . . . 1028
with-temp-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673
with-temp-buffer-window . . . . . . . . . . . . . . . . . . . 1148
with-temp-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
with-temp-message . . . . . . . . . . . . . . . . . . . . . . . . . . 1133
with-timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1283
with-undo-amalgamate . . . . . . . . . . . . . . . . . . . . . . . 898
without-restriction . . . . . . . . . . . . . . . . . . . . . . . . 867
word-search-backward . . . . . . . . . . . . . . . . . . . . . . . 995
word-search-backward-lax . . . . . . . . . . . . . . . . . . . 995
word-search-forward . . . . . . . . . . . . . . . . . . . . . . . . 994
word-search-forward-lax . . . . . . . . . . . . . . . . . . . . 995
word-search-regexp . . . . . . . . . . . . . . . . . . . . . . . . . . 994
words in region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
words-include-escapes . . . . . . . . . . . . . . . . . . . . . . 855
wrap-prefix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131
write-abbrev-file . . . . . . . . . . . . . . . . . . . . . . . . . . 1068
write-char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
write-contents-functions . . . . . . . . . . . . . . . . . . . 613
write-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612
write-file-functions . . . . . . . . . . . . . . . . . . . . . . . 613
write-region . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616, 634
write-region-annotate-functions . . . . . . . . . . . 657
write-region-inhibit-fsync . . . . . . . . . . . . . . . . 617
write-region-post-annotation-function . . . . 658
writing a documentation string . . . . . . . . . . . . . . . . 595
writing buffer display actions. . . . . . . . . . . . . . . . . . 743
writing emacs modules . . . . . . . . . . . . . . . . . . . . . . . 1361

1458

writing Emacs primitives . . . . . . . . . . . . . . . . . . . . 1356
writing module functions. . . . . . . . . . . . . . . . . . . . . 1363
writing to files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 616
wrong-number-of-arguments. . . . . . . . . . . . . . . . . . 234
wrong-type-argument. . . . . . . . . . . . . . . . . . . . . . . . . . 30

X
x-alt-keysym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
x-alternatives-map . . . . . . . . . . . . . . . . . . . . . . . . 1397
x-begin-drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
x-bitmap-file-path . . . . . . . . . . . . . . . . . . . . . . . . 1168
x-close-connection . . . . . . . . . . . . . . . . . . . . . . . . . . 789
x-color-defined-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
x-color-values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
x-ctrl-keysym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
x-defined-colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
x-display-color-p . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
x-display-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
x-dnd-direct-save-function . . . . . . . . . . . . . . . . 842
x-dnd-disable-motif-protocol . . . . . . . . . . . . . . 845
x-dnd-known-types . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
x-dnd-save-direct . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
x-dnd-save-direct-immediately . . . . . . . . . . . . . 843
x-dnd-test-function . . . . . . . . . . . . . . . . . . . . . . . . 842
x-dnd-types-alist . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
x-dnd-use-offix-drop . . . . . . . . . . . . . . . . . . . . . . . 845
x-dnd-use-unsupported-drop . . . . . . . . . . . . . . . . 845
x-double-buffered-p . . . . . . . . . . . . . . . . . . . . . . . . 829
x-family-fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1181
x-focus-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
x-get-resource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
x-hyper-keysym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
x-list-fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1181
x-meta-keysym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
x-open-connection . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
x-parse-geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
x-pointer-shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
x-popup-dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
x-popup-menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
x-pre-popup-menu-hook . . . . . . . . . . . . . . . . . . . . . . 838
x-resource-class . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
x-resource-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
x-sensitive-text-pointer-shape . . . . . . . . . . . . 839
x-server-vendor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852
x-server-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852
x-setup-function-keys . . . . . . . . . . . . . . . . . . . . . 1397
x-stretch-cursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
x-super-keysym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
X display names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
X Window System . . . . . . . . . . . . . . . . . . . . . . . . . . . 1248
X11 keysyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1289
XBM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
xdigit character class, regexp. . . . . . . . . . . . . . . . . 1000
XDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
XML DOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953
xor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
XPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1212

Indexxwidget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1228
xwidget callbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
xwidget property list . . . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
xwidget-buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget-display-event event . . . . . . . . . . . . . . . . 450
xwidget-event event . . . . . . . . . . . . . . . . . . . . . . . . . 449
xwidget-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1230
xwidget-live-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget-perform-lispy-event . . . . . . . . . . . . . . 1230
xwidget-plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget-query-on-exit-flag . . . . . . . . . . . . . . . 1230
xwidget-resize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget-size-request . . . . . . . . . . . . . . . . . . . . . . 1229
xwidget-view type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
xwidget-webkit-back-forward-list . . . . . . . . 1231
xwidget-webkit-estimatedload-progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1231
xwidget-webkit-execute-script . . . . . . . . . . . . 1229
xwidget-webkit-execute-script-rv . . . . . . . . 1229
xwidget-webkit-finish-search . . . . . . . . . . . . . 1231
xwidget-webkit-get-title . . . . . . . . . . . . . . . . . . 1229
xwidget-webkit-goto-history . . . . . . . . . . . . . . 1231
xwidget-webkit-goto-uri . . . . . . . . . . . . . . . . . . . 1229
xwidget-webkit-load-html . . . . . . . . . . . . . . . . . . 1231
xwidget-webkit-next-result . . . . . . . . . . . . . . . 1230
xwidget-webkit-previous-result . . . . . . . . . . . 1230
xwidget-webkit-search . . . . . . . . . . . . . . . . . . . . . 1230

1459

xwidget-webkit-set-cookiestorage-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1231
xwidget-webkit-stop-loading . . . . . . . . . . . . . . 1231
xwidgetp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1229

Yy-or-n-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
y-or-n-p-with-timeout . . . . . . . . . . . . . . . . . . . . . . 414
yank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892
yank suppression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
yank-excluded-properties . . . . . . . . . . . . . . . . . . . 892
yank-handled-properties . . . . . . . . . . . . . . . . . . . . 891
yank-media-handler . . . . . . . . . . . . . . . . . . . . . . . . . . 841
yank-pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892
yank-transform-functions . . . . . . . . . . . . . . . . . . . 892
yank-undo-function . . . . . . . . . . . . . . . . . . . . . . . . . . 893
yanking and text properties . . . . . . . . . . . . . . . . . . . 891
yes-or-no questions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
yes-or-no-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

Zz-group, a frame parameter . . . . . . . . . . . . . . . . . . . 807
Z-order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
zerop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
zlib-available-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942
zlib-decompress-region . . . . . . . . . . . . . . . . . . . . . 942