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Edit Book: Remove unused CSS: Fix an erro if an HTML file links to a missing stylesheet
Edit Book: Spell check dialog: Add an option to make filtering the word list case sensitive
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Partial fix for check book with epub files with non-ascii internal filenames on os x
Edit Book: Fix various problems when editing EPUB files with non-ascii filenames on OS X. Fixes #1317883 [calibre should care of 'decomposed UTF-8' filenames on Darwin platform](https://bugs.launchpad.net/calibre/+bug/1317883)
Edit Book: When editing HTML files that have charset encoding declarations, automatically change the declared encoding (if any) to UTF-8 on save, since the editor always saves files in the UTF-8 encoding.

This prevents a mismatch between the declared encoding and the actual
encoding if the HTML file was originally in an encoding other than
UTF-8.
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Edit Book: Check Book: Add a check for HTML files with non UTF-8 encoding declarations
Refactor html syntax highlighting and implement profiling
Edit Book: 2x speedup for inline spell checking. Useful if you are editing large HTML files (over 100KB in size).

Qt's text layout engine becomes very slow if we store arbitrary python
objects in QTextCharFormat classes. So refactor to not do that.
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A small speedup by using QTextCharFormat instead of SyntaxCharFormat when cloning formats
Another small speedup
Another small speedup
30% speed up on html syntax highlighting by using a C implementation for the Tag and State classes
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Edit Book: Fix non-BMP unicode characters causing matching tag highlighting to be slightly off on linux