Repository: vega/altair

Issue:
Documentation bug: expr.format's second, not first argument, is the format specifier
https://github.com/altair-viz/altair/blob/7da67b09383f3c79a8a57fa1dfd428270cc25b31/altair/expr/funcs.py#L63

This matches the documetation but does not work, runs quite a while, and provides loads of NaN

```python
).transform_calculate(
    notweets_humans='format(".2s", datum.notweets)'
)
```

This works fine

```python
).transform_calculate(
    notweets_humans='format(datum.notweets, ".2s")'
)
```

I assume that "first" is not zero-indexed in the documentation, with a "zeroth" argument preceding it ;)

PS. Thanks for bringing _grammar of graphics_ to Python.


Discussion:
Wait, am I misunderstanding what is an "argument" in `expr` functions because the idea is that the first argument does not count, and by "first argument must be" means that an argument must be given? This could use some clarification in the docs, I think 🤔 
I think you're right, the documentation should be updated. It was copied from [this page](https://vega.github.io/vega/docs/expressions/) when the ``funcs.py`` module was created, and the source has already been updated to fix this issue.

Resolving patch:
diff --git a/altair/expr/funcs.py b/altair/expr/funcs.py
--- a/altair/expr/funcs.py
+++ b/altair/expr/funcs.py
@@ -2,73 +2,141 @@
 
 
 FUNCTION_LISTING = {
-  "utcyear": "returns the year for a given date input, in UTC time",
-  "indexof": "returns the first index of an element (for array inputs) or substring (for string inputs) e.g., `indexof(\"visualization\", \"i\") == 1",
-  "upper": "transforms a string to upper-case",
-  "asin": "trigonometric arcsine (alias to `Math.asin`)",
-  "length": "returns the length of an array or string",
-  "isFinite": "checks if a value is a finite number (same as JavaScript `isFinite`)",
-  "open": "opens a hyperlink (alias to `window.open`). This function is only valid when running in the browser. It should not be invoked within a server-side (e.g., node.js) environment.",
-  "cos": "trigonometric cosine (alias to `Math.cos`)",
-  "lastindexof": "returns the last index of an element (for array inputs) or substring (for string inputs)  e.g., `lastindexof(\"visualization\", \"i\") == 10",
-  "if": "if the first argument evaluates true then the second argument is returned, otherwise the third argument is returned (`if(a, b, c)` is equivalent to `a ? b : c`)",
-  "timeFormat": "formats a string as a local datetime; the first argument must be a valid [d3-time-format specifier](https://github.com/d3/d3-time-format/) (e.g., `timeFormat(\"%A\", datum.timestamp)`)",
-  "timezoneoffset": "returns the timezone offset from the local timezone to UTC for a given date input",
-  "utcmilliseconds": "returns the hours component for a given date input, in UTC time",
-  "test": "evaluates a regular expression against a string, returning true if the string matches the pattern, false otherwise. _Example_: `test(/\\d{3}/, \"32-21-9483\") -> true",
-  "utcmonth": "returns the (zero-based) month for a given date input, in UTC time",
-  "eventGroup": "returns the scenegraph group mark item within which the current event has occurred. If no arguments are provided, the immediate parent group is returned. If a group name is provided, the matching ancestor group item is returned.",
-  "minutes": "returns the minutes component for a given date input, in local time",
-  "tan": "trigonometric tangent (alias to `Math.tan`)",
-  "milliseconds": "returns the milliseconds component for a given date input, in local time",
-  "atan": "trigonometric arctangent (alias to `Math.atan`)",
-  "parseInt": "parses a string to an integer value (same as JavaScript `parseInt`)",
-  "year": "returns the year for a given date input, in local time",
-  "utcseconds": "returns the hours component for a given date input, in UTC time",
-  "seconds": "returns the seconds component for a given date input, in local time",
-  "pow": "exponentiates the first argument by the second argument (alias to `Math.pow`)",
-  "abs": "absolute value (alias to `Math.abs`)",
-  "utc": "returns a timestamp for a UTC date _(year, month[, day, hour, min, sec])",
-  "date": "returns the day of the month for a given date input, in local time",
-  "day": "return the day of the week for a given date input, in local time",
-  "acos": "trigonometric arccosine (alias to `Math.acos`)",
-  "time": "returns the epoch-based timestamp for a given date input",
-  "indata": "tests if a specified datasource contains a tuple with a given value for a specific field (i.e., `indata(\"table\", val, \"price\")`)",
-  "clamp": "restricts a value between a specified min and max (e.g. `clamp(value, min, max)`)",
-  "lower": "transforms a string to lower-case",
-  "log": "natural logarithm function (alias to `Math.log`)",
-  "atan2": "returns the arctangent of the quotient of its arguments (alias to `Math.atan2`)",
-  "eventX": "returns the x-coordinate for the current event. If no arguments are provided, the top-level coordinate space of the visualization is used. If a group name is provided, the coordinate-space of the matching ancestor group item is used.",
-  "month": "returns the (zero-based) month for a given date input, in local time",
-  "sin": "trigonometric sine (alias to `Math.sin`)",
-  "datetime": "returns a new `Date` instance _(year, month[, day, hour, min, sec, millisec])_  Note that, just like Javascript, `month` is 0-based. For example, `1` represents February.",
-  "scale": "applies a named scale transform to a specified value; by default, looks for the scale at the top-level of the specification, but an optional signal can also be supplied corresponding to the group which contains the scale (i.e., `scale(\"x\", val, group)`). *Note:* This function is only legal within signal stream handlers and mark [production rules](https://github.com/vega/vega/wiki/Marks#production-rules). Invoking this function elsewhere (e.g., with filter or formula transforms) will result in an error.",
-  "random": "generates a pseudo-random number in the range [0,1) (alias to `Math.random`)",
-  "sqrt": "square root function (alias to `Math.sqrt`)",
-  "round": "rounds to the nearest integer (alias to `Math.round`)",
-  "min": "returns the minimum argument value (alias to `Math.min`)",
-  "utcday": "returns the day of the week for a given date input, in UTC time",
-  "max": "return the maximum argument (alias to `Math.max`)",
-  "replace": "replace a pattern with a given string (alias to `String.replace`)",
-  "utcminutes": "returns the hours component for a given date input, in UTC time",
-  "regexp": "creates a regular expression instance from input strings (same as JavaScript `RegExp`)",
-  "utchours": "returns the hours component for a given date input, in UTC time",
-  "isNaN": "checks if a value is not-a-number (same as JavaScript `isNaN`)",
-  "eventItem": "a zero-argument function that returns the current scenegraph item that is the subject of the event.",
-  "utcdate": "returns the day of the month for a given date input, in UTC time",
-  "ceil": "rounds to the nearest integer of greater value (alias to `Math.ceil`)",
-  "utcFormat": "formats a string as a [UTC](https://en.wikipedia.org/wiki/Coordinated_Universal_Time) datetime; the first argument must be a valid [d3-time-format specifier](https://github.com/mbostock/d3/wiki/Time-Formatting) (e.g., `utcFormat(\"%\", datum.timestamp)`).",
-  "substring": "extracts a substring from a string (alias to `String.substring`)",
-  "hours": "returns the hours component for a given date input, in local time",
-  "format": "formats a string as a numeric value; the first argument must be a valid [d3-format specifier](https://github.com/d3/d3-format/) (e.g., `format(\",.2f\", datum.value)`)",
-  "exp": "raises _e_ to the provided exponent (alias to `Math.exp`)",
-  "parseFloat": "parses a string to a floating-point value (same as JavaScript `parseFloat`)",
-  "iscale": "applies an inverse scale transform to a specified value; by default, looks for the scale at the top-level of the specification, but an optional signal can also be supplied corresponding to the group which contains the scale (i.e., `iscale(\"x\", val, group)`). *Note:* This function is only legal within signal stream handlers and mark [production rules](https://github.com/vega/vega/wiki/Marks#production-rules). Invoking this function elsewhere (e.g., with filter or formula transforms) will result in an error.",
-  "now": "returns the timestamp for the current time",
-  "slice": "slices a string into a substring (alias to `String.slice`)",
-  "floor": "rounds to the nearest integer of lower value (alias to `Math.floor`)",
-  "inrange": "tests whether a value falls within a specified inclusive extent; an optional flag uses an exclusive extent instead (i.e., `inrange(value, a, b, exclusive?) `).",
-  "eventY": "returns the y-coordinate for the current event. If no arguments are provided, the top-level coordinate space of the visualization is used. If a group name is provided, the coordinate-space of the matching ancestor group item is used."
+    "isArray": r"Returns true if _value_ is an array, false otherwise.",
+    "isBoolean": r"Returns true if _value_ is a boolean (`true` or `false`), false otherwise.",
+    "isDate": r"Returns true if _value_ is a Date object, false otherwise. This method will return false for timestamp numbers or date-formatted strings; it recognizes Date objects only.",
+    "isNumber": r"Returns true if _value_ is a number, false otherwise. `NaN` and `Infinity` are considered numbers.",
+    "isObject": r"Returns true if _value_ is an object (including arrays and Dates), false otherwise.",
+    "isRegExp": r"Returns true if _value_ is a RegExp (regular expression) object, false otherwise.",
+    "isString": r"Returns true if _value_ is a string, false otherwise.",
+    "toBoolean": r"Coerces the input _value_ to a string. Null values and empty strings are mapped to `null`.",
+    "toDate": r"Coerces the input _value_ to a Date instance. Null values and empty strings are mapped to `null`. If an optional _parser_ function is provided, it is used to perform date parsing, otherwise `Date.parse` is used. Be aware that `Date.parse` has different implementations across browsers!",
+    "toNumber": r"Coerces the input _value_ to a number. Null values and empty strings are mapped to `null`.",
+    "toString": r"Coerces the input _value_ to a string. Null values and empty strings are mapped to `null`.",
+    "if": r"If _test_ is truthy, returns _thenValue_. Otherwise, returns _elseValue_. The _if_ function is equivalent to the ternary operator `a ? b : c`.",
+    "isNaN": r"Returns true if _value_ is not a number. Same as JavaScript's `isNaN`.",
+    "isFinite": r"Returns true if _value_ is a finite number. Same as JavaScript's `isFinite`.",
+    "abs": r"Returns the absolute value of _value_. Same as JavaScript's `Math.abs`.",
+    "acos": r"Trigonometric arccosine. Same as JavaScript's `Math.acos`.",
+    "asin": r"Trigonometric arcsine. Same as JavaScript's `Math.asin`.",
+    "atan": r"Trigonometric arctangent. Same as JavaScript's `Math.atan`.",
+    "atan2": r"Returns the arctangent of _dy / dx_. Same as JavaScript's `Math.atan2`.",
+    "ceil": r"Rounds _value_ to the nearest integer of equal or greater value. Same as JavaScript's `Math.ceil`.",
+    "clamp": r"Restricts _value_ to be between the specified _min_ and _max_.",
+    "cos": r"Trigonometric cosine. Same as JavaScript's `Math.cos`.",
+    "exp": r"Returns the value of _e_ raised to the provided _exponent_. Same as JavaScript's `Math.exp`.",
+    "floor": r"Rounds _value_ to the nearest integer of equal or lower value. Same as JavaScript's `Math.floor`.",
+    "log": r"Returns the natural logarithm of _value_. Same as JavaScript's `Math.log`.",
+    "max": r"Returns the maximum argument value. Same as JavaScript's `Math.max`.",
+    "min": r"Returns the minimum argument value. Same as JavaScript's `Math.min`.",
+    "pow": r"Returns _value_ raised to the given _exponent_. Same as JavaScript's `Math.pow`.",
+    "random": r"Returns a pseudo-random number in the range [0,1). Same as JavaScript's `Math.random`.",
+    "round": r"Rounds _value_ to the nearest integer. Same as JavaScript's `Math.round`.",
+    "sin": r"Trigonometric sine. Same as JavaScript's `Math.sin`.",
+    "sqrt": r"Square root function. Same as JavaScript's `Math.sqrt`.",
+    "tan": r"Trigonometric tangent. Same as JavaScript's `Math.tan`.",
+    "now": r"Returns the timestamp for the current time.",
+    "datetime": r"Returns a new `Date` instance. The _month_ is 0-based, such that `1` represents February.",
+    "date": r"Returns the day of the month for the given _datetime_ value, in local time.",
+    "day": r"Returns the day of the week for the given _datetime_ value, in local time.",
+    "year": r"Returns the year for the given _datetime_ value, in local time.",
+    "quarter": r"Returns the quarter of the year (0-3) for the given _datetime_ value, in local time.",
+    "month": r"Returns the (zero-based) month for the given _datetime_ value, in local time.",
+    "hours": r"Returns the hours component for the given _datetime_ value, in local time.",
+    "minutes": r"Returns the minutes component for the given _datetime_ value, in local time.",
+    "seconds": r"Returns the seconds component for the given _datetime_ value, in local time.",
+    "milliseconds": r"Returns the milliseconds component for the given _datetime_ value, in local time.",
+    "time": r"Returns the epoch-based timestamp for the given _datetime_ value.",
+    "timezoneoffset": r"Returns the timezone offset from the local timezone to UTC for the given _datetime_ value.",
+    "utc": r"Returns a timestamp for the given UTC date. The _month_ is 0-based, such that `1` represents February.",
+    "utcdate": r"Returns the day of the month for the given _datetime_ value, in UTC time.",
+    "utcday": r"Returns the day of the week for the given _datetime_ value, in UTC time.",
+    "utcyear": r"Returns the year for the given _datetime_ value, in UTC time.",
+    "utcquarter": r"Returns the quarter of the year (0-3) for the given _datetime_ value, in UTC time.",
+    "utcmonth": r"Returns the (zero-based) month for the given _datetime_ value, in UTC time.",
+    "utchours": r"Returns the hours component for the given _datetime_ value, in UTC time.",
+    "utcminutes": r"Returns the minutes component for the given _datetime_ value, in UTC time.",
+    "utcseconds": r"Returns the seconds component for the given _datetime_ value, in UTC time.",
+    "utcmilliseconds": r"Returns the milliseconds component for the given _datetime_ value, in UTC time.",
+    "extent": r"Returns a new _[min, max]_ array with the minimum and maximum values of the input array, ignoring `null`, `undefined`, and `NaN` values.",
+    "clampRange": r"Clamps a two-element _range_ array in a span-preserving manner. If the span of the input _range_ is less than _(max - min)_ and an endpoint exceeds either the _min_ or _max_ value, the range is translated such that the span is preserved and one endpoint touches the boundary of the _[min, max]_ range. If the span exceeds _(max - min)_, the range _[min, max]_ is returned.",
+    "indexof": r"Returns the first index of _value_ in the input _array_, or the first index of _substring_ in the input _string_..",
+    "inrange": r"Tests whether _value_ lies within (or is equal to either) the first and last values of the _range_ array.",
+    "join": r"Returns a new string by concatenating all of the elements of the input _array_, separated by commas or a specified _separator_ string.",
+    "lastindexof": r"Returns the last index of _value_ in the input _array_, or the last index of _substring_ in the input _string_..",
+    "length": r"Returns the length of the input _array_, or the length of the input _string_.",
+    "lerp": r"Returns the linearly interpolated value between the first and last entries in the _array_ for the provided interpolation _fraction_ (typically between 0 and 1). For example, `lerp([0, 50], 0.5)` returns 25.",
+    "peek": r"Returns the last element in the input _array_. Similar to the built-in `Array.pop` method, except that it does not remove the last element. This method is a convenient shorthand for `array[array.length - 1]`.",
+    "reverse": r"Returns a new array with elements in a reverse order of the input _array_. The first array element becomes the last, and the last array element becomes the first.",
+    "sequence": r"Returns an array containing an arithmetic sequence of numbers. If _step_ is omitted, it defaults to 1. If _start_ is omitted, it defaults to 0. The _stop_ value is exclusive; it is not included in the result. If _step_ is positive, the last element is the largest _start + i * step_ less than _stop_; if _step_ is negative, the last element is the smallest _start + i * step_ greater than _stop_. If the returned array would contain an infinite number of values, an empty range is returned. The arguments are not required to be integers.",
+    "slice": r"Returns a section of _array_ between the _start_ and _end_ indices. If the _end_ argument is negative, it is treated as an offset from the end of the array (_length(array) + end_).",
+    "span": r"Returns the span of _array_: the difference between the last and first elements, or _array[array.length-1] - array[0]_. Or if input is a string: a section of _string_ between the _start_ and _end_ indices. If the _end_ argument is negative, it is treated as an offset from the end of the string (_length(string) + end_)..",
+    "lower": r"Transforms _string_ to lower-case letters.",
+    "pad": r"Pads a _string_ value with repeated instances of a _character_ up to a specified _length_. If _character_ is not specified, a space (' ') is used. By default, padding is added to the end of a string. An optional _align_ parameter specifies if padding should be added to the `'left'` (beginning), `'center'`, or `'right'` (end) of the input string.",
+    "parseFloat": r"Parses the input _string_ to a floating-point value. Same as JavaScript's `parseFloat`.",
+    "parseInt": r"Parses the input _string_ to an integer value. Same as JavaScript's `parseInt`.",
+    "replace": r"Returns a new string with some or all matches of _pattern_ replaced by a _replacement_ string. The _pattern_ can be a string or a regular expression. If _pattern_ is a string, only the first instance will be replaced. Same as [JavaScript's String.replace](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace).",
+    "split": r"Returns an array of tokens created by splitting the input _string_ according to a provided _separator_ pattern. The result can optionally be constrained to return at most _limit_ tokens.",
+    "substring": r"Returns a section of _string_ between the _start_ and _end_ indices.",
+    "trim": r"Returns a trimmed string with preceding and trailing whitespace removed.",
+    "truncate": r"Truncates an input _string_ to a target _length_. The optional _align_ argument indicates what part of the string should be truncated: `'left'` (the beginning), `'center'`, or `'right'` (the end). By default, the `'right'` end of the string is truncated. The optional _ellipsis_ argument indicates the string to use to indicate truncated content; by default the ellipsis character `...` (`\\u2026`) is used.",
+    "upper": r"Transforms _string_ to upper-case letters.",
+    "merge": r"Merges the input objects _object1_, _object2_, etc into a new output object. Inputs are visited in sequential order, such that key values from later arguments can overwrite those from earlier arguments. Example: `merge({a:1, b:2}, {a:3}) -> {a:3, b:2}`.",
+    "dayFormat": r"Formats a (0-6) _weekday_ number as a full week day name, according to the current locale. For example: `dayFormat(0) -> \"Sunday\"`.",
+    "dayAbbrevFormat": r"Formats a (0-6) _weekday_ number as an abbreviated week day name, according to the current locale. For example: `dayAbbrevFormat(0) -> \"Sun\"`.",
+    "format": r"Formats a numeric _value_ as a string. The _specifier_ must be a valid [d3-format specifier](https://github.com/d3/d3-format/) (e.g., `format(value, ',.2f')`.",
+    "monthFormat": r"Formats a (zero-based) _month_ number as a full month name, according to the current locale. For example: `monthFormat(0) -> \"January\"`.",
+    "monthAbbrevFormat": r"Formats a (zero-based) _month_ number as an abbreviated month name, according to the current locale. For example: `monthAbbrevFormat(0) -> \"Jan\"`.",
+    "timeFormat": r"Formats a datetime _value_ (either a `Date` object or timestamp) as a string, according to the local time. The _specifier_ must be a valid [d3-time-format specifier](https://github.com/d3/d3-time-format/). For example: `timeFormat(timestamp, '%A')`.",
+    "timeParse": r"Parses a _string_ value to a Date object, according to the local time. The _specifier_ must be a valid [d3-time-format specifier](https://github.com/d3/d3-time-format/). For example: `timeParse('June 30, 2015', '%B %d, %Y')`.",
+    "utcFormat": r"Formats a datetime _value_ (either a `Date` object or timestamp) as a string, according to [UTC](https://en.wikipedia.org/wiki/Coordinated_Universal_Time) time. The _specifier_ must be a valid [d3-time-format specifier](https://github.com/d3/d3-time-format/). For example: `utcFormat(timestamp, '%A')`.",
+    "utcParse": r"Parses a _string_ value to a Date object, according to [UTC](https://en.wikipedia.org/wiki/Coordinated_Universal_Time) time. The _specifier_ must be a valid [d3-time-format specifier](https://github.com/d3/d3-time-format/). For example: `utcParse('June 30, 2015', '%B %d, %Y')`.",
+    "regexp": r"Creates a regular expression instance from an input _pattern_ string and optional _flags_. Same as [JavaScript's `RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp).",
+    "test": r"Evaluates a regular expression _regexp_ against the input _string_, returning `true` if the string matches the pattern, `false` otherwise. For example: `test(/\\d{3}/, \"32-21-9483\") -> true`.",
+    "rgb": r"Constructs a new [RGB](https://en.wikipedia.org/wiki/RGB_color_model) color. If _r_, _g_ and _b_ are specified, these represent the channel values of the returned color; an _opacity_ may also be specified. If a CSS Color Module Level 3 _specifier_ string is specified, it is parsed and then converted to the RGB color space. Uses [d3-color's rgb function](https://github.com/d3/d3-color#rgb).",
+    "hsl": r"Constructs a new [HSL](https://en.wikipedia.org/wiki/HSL_and_HSV) color. If _h_, _s_ and _l_ are specified, these represent the channel values of the returned color; an _opacity_ may also be specified. If a CSS Color Module Level 3 _specifier_ string is specified, it is parsed and then converted to the HSL color space. Uses [d3-color's hsl function](https://github.com/d3/d3-color#hsl).",
+    "lab": r"Constructs a new [CIE LAB](https://en.wikipedia.org/wiki/Lab_color_space#CIELAB) color. If _l_, _a_ and _b_ are specified, these represent the channel values of the returned color; an _opacity_ may also be specified. If a CSS Color Module Level 3 _specifier_ string is specified, it is parsed and then converted to the LAB color space. Uses [d3-color's lab function](https://github.com/d3/d3-color#lab).",
+    "hcl": r"Constructs a new [HCL](https://en.wikipedia.org/wiki/Lab_color_space#CIELAB) (hue, chroma, luminance) color. If _h_, _c_ and _l_ are specified, these represent the channel values of the returned color; an _opacity_ may also be specified. If a CSS Color Module Level 3 _specifier_ string is specified, it is parsed and then converted to the HCL color space. Uses [d3-color's hcl function](https://github.com/d3/d3-color#hcl).",
+    "item": r"Returns the current scenegraph item that is the target of the event.",
+    "group": r"Returns the scenegraph group mark item in which the current event has occurred. If no arguments are provided, the immediate parent group is returned. If a group name is provided, the matching ancestor group item is returned.",
+    "xy": r"Returns the x- and y-coordinates for the current event as a two-element array. If no arguments are provided, the top-level coordinate space of the view is used. If a scenegraph _item_ (or string group name) is provided, the coordinate space of the group item is used.",
+    "x": r"Returns the x coordinate for the current event. If no arguments are provided, the top-level coordinate space of the view is used. If a scenegraph _item_ (or string group name) is provided, the coordinate space of the group item is used.",
+    "y": r"Returns the y coordinate for the current event. If no arguments are provided, the top-level coordinate space of the view is used. If a scenegraph _item_ (or string group name) is provided, the coordinate space of the group item is used.",
+    "pinchDistance": r"Returns the pixel distance between the first two touch points of a multi-touch event.",
+    "pinchAngle": r"Returns the angle of the line connecting the first two touch points of a multi-touch event.",
+    "inScope": r"Returns true if the given scenegraph _item_ is a descendant of the group mark in which the event handler was defined, false otherwise.",
+    "data": r"Returns the array of data objects for the Vega data set with the given _name_. If the data set is not found, returns an empty array.",
+    "indata": r"Tests if the data set with a given _name_ contains a datum with a _field_ value that matches the input _value_. For example: `indata('table', 'category', value)`.",
+    "scale": r"Applies the named scale transform (or projection) to the specified _value_. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale or projection.",
+    "invert": r"Inverts the named scale transform (or projection) for the specified _value_. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale or projection.",
+    "copy": r"Returns a copy (a new cloned instance) of the named scale transform of projection, or `undefined` if no scale or projection is found. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale or projection.",
+    "domain": r"Returns the scale domain array for the named scale transform, or an empty array if the scale is not found. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale.",
+    "range": r"Returns the scale range array for the named scale transform, or an empty array if the scale is not found. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale.",
+    "bandwidth": r"Returns the current band width for the named band scale transform, or zero if the scale is not found or is not a band scale. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the scale.",
+    "bandspace": r"Returns the number of steps needed within a band scale, based on the _count_ of domain elements and the inner and outer padding values. While normally calculated within the scale itself, this function can be helpful for determining the size of a chart's layout.",
+    "gradient": r"Returns a linear color gradient for the _scale_ (whose range must be a [continuous color scheme](../schemes)) and starting and ending points _p0_ and _p1_, each an _[x, y]_ array. The points _p0_ and _p1_ should be expressed in normalized coordinates in the domain [0, 1], relative to the bounds of the item being colored. If unspecified, _p0_ defaults to `[0, 0]` and _p1_ defaults to `[1, 0]`, for a horizontal gradient that spans the full bounds of an item. The optional _count_ argument indicates a desired target number of sample points to take from the color scale.",
+    "panLinear": r"Given a linear scale _domain_ array with numeric or datetime values, returns a new two-element domain array that is the result of panning the domain by a fractional _delta_. The _delta_ value represents fractional units of the scale range; for example, `0.5` indicates panning the scale domain to the right by half the scale range.",
+    "panLog": r"Given a log scale _domain_ array with numeric or datetime values, returns a new two-element domain array that is the result of panning the domain by a fractional _delta_. The _delta_ value represents fractional units of the scale range; for example, `0.5` indicates panning the scale domain to the right by half the scale range.",
+    "panPow": r"Given a power scale _domain_ array with numeric or datetime values and the given _exponent_, returns a new two-element domain array that is the result of panning the domain by a fractional _delta_. The _delta_ value represents fractional units of the scale range; for example, `0.5` indicates panning the scale domain to the right by half the scale range.",
+    "panSymlog": r"Given a symmetric log scale _domain_ array with numeric or datetime values parameterized by the given _constant_, returns a new two-element domain array that is the result of panning the domain by a fractional _delta_. The _delta_ value represents fractional units of the scale range; for example, `0.5` indicates panning the scale domain to the right by half the scale range.",
+    "zoomLinear": r"Given a linear scale _domain_ array with numeric or datetime values, returns a new two-element domain array that is the result of zooming the domain by a _scaleFactor_, centered at the provided fractional _anchor_. The _anchor_ value represents the zoom position in terms of fractional units of the scale range; for example, `0.5` indicates a zoom centered on the mid-point of the scale range.",
+    "zoomLog": r"Given a log scale _domain_ array with numeric or datetime values, returns a new two-element domain array that is the result of zooming the domain by a _scaleFactor_, centered at the provided fractional _anchor_. The _anchor_ value represents the zoom position in terms of fractional units of the scale range; for example, `0.5` indicates a zoom centered on the mid-point of the scale range.",
+    "zoomPow": r"Given a power scale _domain_ array with numeric or datetime values and the given _exponent_, returns a new two-element domain array that is the result of zooming the domain by a _scaleFactor_, centered at the provided fractional _anchor_. The _anchor_ value represents the zoom position in terms of fractional units of the scale range; for example, `0.5` indicates a zoom centered on the mid-point of the scale range.",
+    "zoomSymlog": r"Given a symmetric log scale _domain_ array with numeric or datetime values parameterized by the given _constant_, returns a new two-element domain array that is the result of zooming the domain by a _scaleFactor_, centered at the provided fractional _anchor_. The _anchor_ value represents the zoom position in terms of fractional units of the scale range; for example, `0.5` indicates a zoom centered on the mid-point of the scale range.",
+    "geoArea": r"Returns the projected planar area (typically in square pixels) of a GeoJSON _feature_ according to the named _projection_. If the _projection_ argument is `null`, computes the spherical area in steradians using unprojected longitude, latitude coordinates. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the projection. Uses d3-geo's [geoArea](https://github.com/d3/d3-geo#geoArea) and [path.area](https://github.com/d3/d3-geo#path_area) methods.",
+    "geoBounds": r"Returns the projected planar bounding box (typically in pixels) for the specified GeoJSON _feature_, according to the named _projection_. The bounding box is represented by a two-dimensional array: [[_x0_, _y0_], [_x1_, _y1_]], where _x0_ is the minimum x-coordinate, _y0_ is the minimum y-coordinate, _x1_ is the maximum x-coordinate, and _y1_ is the maximum y-coordinate. If the _projection_ argument is `null`, computes the spherical bounding box using unprojected longitude, latitude coordinates. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the projection. Uses d3-geo's [geoBounds](https://github.com/d3/d3-geo#geoBounds) and [path.bounds](https://github.com/d3/d3-geo#path_bounds) methods.",
+    "geoCentroid": r"Returns the projected planar centroid (typically in pixels) for the specified GeoJSON _feature_, according to the named _projection_. If the _projection_ argument is `null`, computes the spherical centroid using unprojected longitude, latitude coordinates. The optional _group_ argument takes a scenegraph group mark item to indicate the specific scope in which to look up the projection. Uses d3-geo's [geoCentroid](https://github.com/d3/d3-geo#geoCentroid) and [path.centroid](https://github.com/d3/d3-geo#path_centroid) methods.",
+    "treePath": r"For the hierarchy data set with the given _name_, returns the shortest path through from the _source_ node id to the _target_ node id. The path starts at the _source_ node, ascends to the least common ancestor of the _source_ node and the _target_ node, and then descends to the _target_ node.",
+    "treeAncestors": r"For the hierarchy data set with the given _name_, returns the array of ancestors nodes, starting with the input _node_, then followed by each parent up to the root.",
+    "warn": r"Logs a warning message and returns the last argument. For the message to appear in the console, the visualization view must have the appropriate logging level set.",
+    "info": r"Logs an informative message and returns the last argument. For the message to appear in the console, the visualization view must have the appropriate logging level set.",
+    "debug": r"Logs a debugging message and returns the last argument. For the message to appear in the console, the visualization view must have the appropriate logging level set.",
+    "eventGroup": "returns the scenegraph group mark item within which the current event has occurred. If no arguments are provided, the immediate parent group is returned. If a group name is provided, the matching ancestor group item is returned.",
+    "eventItem": "a zero-argument function that returns the current scenegraph item that is the subject of the event.",
+    "eventX": "returns the x-coordinate for the current event. If no arguments are provided, the top-level coordinate space of the visualization is used. If a group name is provided, the coordinate-space of the matching ancestor group item is used.",
+    "eventY": "returns the y-coordinate for the current event. If no arguments are provided, the top-level coordinate space of the visualization is used. If a group name is provided, the coordinate-space of the matching ancestor group item is used.",
+    "iscale": "applies an inverse scale transform to a specified value; by default, looks for the scale at the top-level of the specification, but an optional signal can also be supplied corresponding to the group which contains the scale (i.e., `iscale(\"x\", val, group)`). *Note:* This function is only legal within signal stream handlers and mark [production rules](https://github.com/vega/vega/wiki/Marks#production-rules). Invoking this function elsewhere (e.g., with filter or formula transforms) will result in an error.",
+    "open": "opens a hyperlink (alias to `window.open`). This function is only valid when running in the browser. It should not be invoked within a server-side (e.g., node.js) environment.",
 }
 
 


Test patch: