## User manual and reference guide version 5.52.0

CodeMirror is a code-editor component that can be embedded in Web pages. The core library provides only the editor component, no accompanying buttons, auto-completion, or other IDE functionality. It does provide a rich API on top of which such functionality can be straightforwardly implemented. See the addons included in the distribution, and the list of externally hosted addons, for reusable implementations of extra features.

CodeMirror works with language-specific modes. Modes are JavaScript programs that help color (and optionally indent) text written in a given language. The distribution comes with a number of modes (see the `mode/` directory), and it isn't hard to write new ones for other languages.

## Basic Usage

The easiest way to use CodeMirror is to simply load the script and style sheet found under `lib/` in the distribution, plus a mode script from one of the `mode/` directories. For example:

    <script src="lib/codemirror.js"></script>
    <link rel="stylesheet" href="lib/codemirror.css">
    <script src="mode/javascript/javascript.js"></script>

(Alternatively, use a module loader. More about that later.)

Having done this, an editor instance can be created like this:

    var myCodeMirror = CodeMirror(document.body);

The editor will be appended to the document body, will start empty, and will use the mode that we loaded. To have more control over the new editor, a configuration object can be passed to `CodeMirror` as a second argument:

    var myCodeMirror = CodeMirror(document.body, {
      value: "function myScript(){return 100;}\n",
      mode:  "javascript"
    });

This will initialize the editor with a piece of code already in it, and explicitly tell it to use the JavaScript mode (which is useful when multiple modes are loaded). See below for a full discussion of the configuration options that CodeMirror accepts.

In cases where you don't want to append the editor to an element, and need more control over the way it is inserted, the first argument to the `CodeMirror` function can also be a function that, when given a DOM element, inserts it into the document somewhere. This could be used to, for example, replace a textarea with a real editor:

    var myCodeMirror = CodeMirror(function(elt) {
      myTextArea.parentNode.replaceChild(elt, myTextArea);
    }, {value: myTextArea.value});

However, for this use case, which is a common way to use CodeMirror, the library provides a much more powerful shortcut:

    var myCodeMirror = CodeMirror.fromTextArea(myTextArea);

This will, among other things, ensure that the textarea's value is updated with the editor's contents when the form (if it is part of a form) is submitted. See the API reference for a full description of this method.

### Module loaders

The files in the CodeMirror distribution contain shims for loading them (and their dependencies) in AMD or CommonJS environments. If the variables `exports` and `module` exist and have type object, CommonJS-style require will be used. If not, but there is a function `define` with an `amd` property present, AMD-style (RequireJS) will be used.

It is possible to use Browserify or similar tools to statically build modules using CodeMirror. Alternatively, use RequireJS to dynamically load dependencies at runtime. Both of these approaches have the advantage that they don't use the global namespace and can, thus, do things like load multiple versions of CodeMirror alongside each other.

Here's a simple example of using RequireJS to load CodeMirror:

    require([
      "cm/lib/codemirror", "cm/mode/htmlmixed/htmlmixed"
    ], function(CodeMirror) {
      CodeMirror.fromTextArea(document.getElementById("code"), {
        lineNumbers: true,
        mode: "htmlmixed"
      });
    });

It will automatically load the modes that the mixed HTML mode depends on (XML, JavaScript, and CSS). Do not use RequireJS' `paths` option to configure the path to CodeMirror, since it will break loading submodules through relative paths. Use the `packages` configuration option instead, as in:

    require.config({
      packages: [{
        name: "codemirror",
        location: "../path/to/codemirror",
        main: "lib/codemirror"
      }]
    });

## Configuration

Both the `CodeMirror` function and its `fromTextArea` method take as second (optional) argument an object containing configuration options. Any option not supplied like this will be taken from `CodeMirror.defaults`, an object containing the default options. You can update this object to change the defaults on your page.

Options are not checked in any way, so setting bogus option values is bound to lead to odd errors.

These are the supported options:

`value: string|CodeMirror.Doc`
  The starting value of the editor. Can be a string, or a document object.
`mode: string|object`
  The mode to use. When not given, this will default to the first mode that was loaded. It may be a string, which either simply names the mode or is a MIME type associated with the mode. The value `"null"` indicates no highlighting should be applied. Alternatively, it may be an object containing configuration options for the mode, with a `name` property that names the mode (for example `{name: "javascript", json: true}`). The demo pages for each mode contain information about what configuration parameters the mode supports. You can ask CodeMirror which modes and MIME types have been defined by inspecting the `CodeMirror.modes` and `CodeMirror.mimeModes` objects. The first maps mode names to their constructors, and the second maps MIME types to mode specs.
`lineSeparator: string|null`
  Explicitly set the line separator for the editor. By default (value `null`), the document will be split on CRLFs as well as lone CRs and LFs, and a single LF will be used as line separator in all output (such as `getValue`). When a specific string is given, lines will only be split on that string, and output will, by default, use that same separator.
`theme: string`
  The theme to style the editor with. You must make sure the CSS file defining the corresponding `.cm-s-[name]` styles is loaded (see the `theme` directory in the distribution). The default is `"default"`, for which colors are included in `codemirror.css`. It is possible to use multiple theming classes at once—for example `"foo bar"` will assign both the `cm-s-foo` and the `cm-s-bar` classes to the editor.
`indentUnit: integer`
  How many spaces a block (whatever that means in the edited language) should be indented. The default is 2.
`smartIndent: boolean`
  Whether to use the context-sensitive indentation that the mode provides (or just indent the same as the line before). Defaults to true.
`tabSize: integer`
  The width of a tab character. Defaults to 4.
`indentWithTabs: boolean`
  Whether, when indenting, the first N*`tabSize` spaces should be replaced by N tabs. Default is false.
`electricChars: boolean`
  Configures whether the editor should re-indent the current line when a character is typed that might change its proper indentation (only works if the mode supports indentation). Default is true.
`specialChars: RegExp`
  A regular expression used to determine which characters should be replaced by a special placeholder. Mostly useful for non-printing special characters. The default is `/[\u0000-\u001f\u007f-\u009f\u00ad\u061c\u200b-\u200f\u2028\u2029\ufeff\ufff9-\ufffc]/`.
`specialCharPlaceholder: function(char) → Element`
  A function that, given a special character identified by the `specialChars` option, produces a DOM node that is used to represent the character. By default, a red dot (•) is shown, with a title tooltip to indicate the character code.
`direction: "ltr" | "rtl"`
  Flips overall layout and selects base paragraph direction to be left-to-right or right-to-left. Default is "ltr". CodeMirror applies the Unicode Bidirectional Algorithm to each line, but does not autodetect base direction — it's set to the editor direction for all lines. The resulting order is sometimes wrong when base direction doesn't match user intent (for example, leading and trailing punctuation jumps to the wrong side of the line). Therefore, it's helpful for multilingual input to let users toggle this option.
`rtlMoveVisually: boolean`
  Determines whether horizontal cursor movement through right-to-left (Arabic, Hebrew) text is visual (pressing the left arrow moves the cursor left) or logical (pressing the left arrow moves to the next lower index in the string, which is visually right in right-to-left text). The default is `false` on Windows, and `true` on other platforms.
`keyMap: string`
  Configures the key map to use. The default is `"default"`, which is the only key map defined in `codemirror.js` itself. Extra key maps are found in the `key map` directory. See the section on key maps for more information.
`extraKeys: object`
  Can be used to specify extra key bindings for the editor, alongside the ones defined by `keyMap`. Should be either null, or a valid key map value.
`configureMouse: fn(cm: CodeMirror, repeat: "single" | "double" | "triple", event: Event) → Object`
  Allows you to configure the behavior of mouse selection and dragging. The function is called when the left mouse button is pressed. The returned object may have the following properties:
  `unit: "char" | "word" | "line" | "rectangle" | fn(CodeMirror, Pos) → {from: Pos, to: Pos}`
    The unit by which to select. May be one of the built-in units or a function that takes a position and returns a range around that, for a custom unit. The default is to return `"word"` for double clicks, `"line"` for triple clicks, `"rectangle"` for alt-clicks (or, on Chrome OS, meta-shift-clicks), and `"single"` otherwise.
  `extend: bool`
    Whether to extend the existing selection range or start a new one. By default, this is enabled when shift clicking.
  `addNew: bool`
    When enabled, this adds a new range to the existing selection, rather than replacing it. The default behavior is to enable this for command-click on Mac OS, and control-click on other platforms.
  `moveOnDrag: bool`
    When the mouse even drags content around inside the editor, this controls whether it is copied (false) or moved (true). By default, this is enabled by alt-clicking on Mac OS, and ctrl-clicking elsewhere.
`lineWrapping: boolean`
  Whether CodeMirror should scroll or wrap for long lines. Defaults to `false` (scroll).
`lineNumbers: boolean`
  Whether to show line numbers to the left of the editor.
`firstLineNumber: integer`
  At which number to start counting lines. Default is 1.
`lineNumberFormatter: function(line: integer) → string`
  A function used to format line numbers. The function is passed the line number, and should return a string that will be shown in the gutter.
`gutters: array<string | {className: string, style: ?string}>`
  Can be used to add extra gutters (beyond or instead of the line number gutter). Should be an array of CSS class names or class name / CSS string pairs, each of which defines a `width` (and optionally a background), and which will be used to draw the background of the gutters. May include the `CodeMirror-linenumbers` class, in order to explicitly set the position of the line number gutter (it will default to be to the right of all other gutters). These class names are the keys passed to `setGutterMarker`.
`fixedGutter: boolean`
  Determines whether the gutter scrolls along with the content horizontally (false) or whether it stays fixed during horizontal scrolling (true, the default).
`scrollbarStyle: string`
  Chooses a scrollbar implementation. The default is `"native"`, showing native scrollbars. The core library also provides the `"null"` style, which completely hides the scrollbars. Addons can implement additional scrollbar models.
`coverGutterNextToScrollbar: boolean`
  When `fixedGutter` is on, and there is a horizontal scrollbar, by default the gutter will be visible to the left of this scrollbar. If this option is set to true, it will be covered by an element with class `CodeMirror-gutter-filler`.
`inputStyle: string`
  Selects the way CodeMirror handles input and focus. The core library defines the `"textarea"` and `"contenteditable"` input models. On mobile browsers, the default is `"contenteditable"`. On desktop browsers, the default is `"textarea"`. Support for IME and screen readers is better in the `"contenteditable"` model. The intention is to make it the default on modern desktop browsers in the future.
`readOnly: boolean|string`
  This disables editing of the editor content by the user. If the special value `"nocursor"` is given (instead of simply `true`), focusing of the editor is also disallowed.
`showCursorWhenSelecting: boolean`
  Whether the cursor should be drawn when a selection is active. Defaults to false.
`lineWiseCopyCut: boolean`
  When enabled, which is the default, doing copy or cut when there is no selection will copy or cut the whole lines that have cursors on them.
`pasteLinesPerSelection: boolean`
  When pasting something from an external source (not from the editor itself), if the number of lines matches the number of selection, CodeMirror will by default insert one line per selection. You can set this to `false` to disable that behavior.
`selectionsMayTouch: boolean`
  Determines whether multiple selections are joined as soon as they touch (the default) or only when they overlap (true).
`undoDepth: integer`
  The maximum number of undo levels that the editor stores. Note that this includes selection change events. Defaults to 200.
`historyEventDelay: integer`
  The period of inactivity (in milliseconds) that will cause a new history event to be started when typing or deleting. Defaults to 1250.
`tabindex: integer`
  The tab index to assign to the editor. If not given, no tab index will be assigned.
`autofocus: boolean`
  Can be used to make CodeMirror focus itself on initialization. Defaults to off. When `fromTextArea` is used, and no explicit value is given for this option, it will be set to true when either the source textarea is focused, or it has an `autofocus` attribute and no other element is focused.
`phrases: ?object`
  Some addons run user-visible strings (such as labels in the interface) through the `phrase` method to allow for translation. This option determines the return value of that method. When it is null or an object that doesn't have a property named by the input string, that string is returned. Otherwise, the value of the property corresponding to that string is returned.

Below this a few more specialized, low-level options are listed. These are only useful in very specific situations, you might want to skip them the first time you read this manual.

`dragDrop: boolean`
  Controls whether drag-and-drop is enabled. On by default.
`allowDropFileTypes: array<string>`
  When set (default is `null`) only files whose type is in the array can be dropped into the editor. The strings should be MIME types, and will be checked against the `type` of the `File` object as reported by the browser.
`cursorBlinkRate: number`
  Half-period in milliseconds used for cursor blinking. The default blink rate is 530ms. By setting this to zero, blinking can be disabled. A negative value hides the cursor entirely.
`cursorScrollMargin: number`
  How much extra space to always keep above and below the cursor when approaching the top or bottom of the visible view in a scrollable document. Default is 0.
`cursorHeight: number`
  Determines the height of the cursor. Default is 1, meaning it spans the whole height of the line. For some fonts (and by some tastes) a smaller height (for example `0.85`), which causes the cursor to not reach all the way to the bottom of the line, looks better
`resetSelectionOnContextMenu: boolean`
  Controls whether, when the context menu is opened with a click outside of the current selection, the cursor is moved to the point of the click. Defaults to `true`.
`workTime, workDelay: number`
  Highlighting is done by a pseudo background-thread that will work for `workTime` milliseconds, and then use timeout to sleep for `workDelay` milliseconds. The defaults are 200 and 300, you can change these options to make the highlighting more or less aggressive.
`pollInterval: number`
  Indicates how quickly CodeMirror should poll its input textarea for changes (when focused). Most input is captured by events, but some things, like IME input on some browsers, don't generate events that allow CodeMirror to properly detect it. Thus, it polls. Default is 100 milliseconds.
`flattenSpans: boolean`
  By default, CodeMirror will combine adjacent tokens into a single span if they have the same class. This will result in a simpler DOM tree, and thus perform better. With some kinds of styling (such as rounded corners), this will change the way the document looks. You can set this option to false to disable this behavior.
`addModeClass: boolean`
  When enabled (off by default), an extra CSS class will be added to each token, indicating the (inner) mode that produced it, prefixed with `"cm-m-"`. For example, tokens from the XML mode will get the `cm-m-xml` class.
`maxHighlightLength: number`
  When highlighting long lines, in order to stay responsive, the editor will give up and simply style the rest of the line as plain text when it reaches a certain position. The default is 10 000. You can set this to `Infinity` to turn off this behavior.
`viewportMargin: integer`
  Specifies the amount of lines that are rendered above and below the part of the document that's currently scrolled into view. This affects the amount of updates needed when scrolling, and the amount of work that such an update does. You should usually leave it at its default, 10. Can be set to `Infinity` to make sure the whole document is always rendered, and thus the browser's text search works on it. This will have bad effects on performance of big documents.
`spellcheck: boolean`
  Specifies whether or not spellcheck will be enabled on the input.
`autocorrect: boolean`
  Specifies whether or not autocorrect will be enabled on the input.
`autocapitalize: boolean`
  Specifies whether or not autocapitalization will be enabled on the input.

## Events

Various CodeMirror-related objects emit events, which allow client code to react to various situations. Handlers for such events can be registered with the `on` and `off` methods on the objects that the event fires on. To fire your own events, use `CodeMirror.signal(target, name, args...)`, where `target` is a non-DOM-node object.

An editor instance fires the following events. The `instance` argument always refers to the editor itself.

`"change" (instance: CodeMirror, changeObj: object)`
  Fires every time the content of the editor is changed. The `changeObj` is a `{from, to, text, removed, origin}` object containing information about the changes that occurred as second argument. `from` and `to` are the positions (in the pre-change coordinate system) where the change started and ended (for example, it might be `{ch:0, line:18}` if the position is at the beginning of line #19). `text` is an array of strings representing the text that replaced the changed range (split by line). `removed` is the text that used to be between `from` and `to`, which is overwritten by this change. This event is fired before the end of an operation, before the DOM updates happen.
`"changes" (instance: CodeMirror, changes: array<object>)`
  Like the `"change"` event, but batched per operation, passing an array containing all the changes that happened in the operation. This event is fired after the operation finished, and display changes it makes will trigger a new operation.
`"beforeChange" (instance: CodeMirror, changeObj: object)`
  This event is fired before a change is applied, and its handler may choose to modify or cancel the change. The `changeObj` object has `from`, `to`, and `text` properties, as with the `"change"` event. It also has a `cancel()` method, which can be called to cancel the change, and, if the change isn't coming from an undo or redo event, an `update(from, to, text)` method, which may be used to modify the change. Undo or redo changes can't be modified, because they hold some metainformation for restoring old marked ranges that is only valid for that specific change. All three arguments to `update` are optional, and can be left off to leave the existing value for that field intact. Note: you may not do anything from a `"beforeChange"` handler that would cause changes to the document or its visualization. Doing so will, since this handler is called directly from the bowels of the CodeMirror implementation, probably cause the editor to become corrupted.
`"cursorActivity" (instance: CodeMirror)`
  Will be fired when the cursor or selection moves, or any change is made to the editor content.
`"keyHandled" (instance: CodeMirror, name: string, event: Event)`
  Fired after a key is handled through a key map. `name` is the name of the handled key (for example `"Ctrl-X"` or `"'q'"`), and `event` is the DOM `keydown` or `keypress` event.
`"inputRead" (instance: CodeMirror, changeObj: object)`
  Fired whenever new input is read from the hidden textarea (typed or pasted by the user).
`"electricInput" (instance: CodeMirror, line: integer)`
  Fired if text input matched the mode's electric patterns, and this caused the line's indentation to change.
`"beforeSelectionChange" (instance: CodeMirror, obj: {ranges, origin, update})`
  This event is fired before the selection is moved. Its handler may inspect the set of selection ranges, present as an array of `{anchor, head}` objects in the `ranges` property of the `obj` argument, and optionally change them by calling the `update` method on this object, passing an array of ranges in the same format. The object also contains an `origin` property holding the origin string passed to the selection-changing method, if any. Handlers for this event have the same restriction as `"beforeChange"` handlers — they should not do anything to directly update the state of the editor.
`"viewportChange" (instance: CodeMirror, from: number, to: number)`
  Fires whenever the view port of the editor changes (due to scrolling, editing, or any other factor). The `from` and `to` arguments give the new start and end of the viewport.
`"swapDoc" (instance: CodeMirror, oldDoc: Doc)`
  This is signalled when the editor's document is replaced using the `swapDoc` method.
`"gutterClick" (instance: CodeMirror, line: integer, gutter: string, clickEvent: Event)`
  Fires when the editor gutter (the line-number area) is clicked. Will pass the editor instance as first argument, the (zero-based) number of the line that was clicked as second argument, the CSS class of the gutter that was clicked as third argument, and the raw `mousedown` event object as fourth argument.
`"gutterContextMenu" (instance: CodeMirror, line: integer, gutter: string, contextMenu: Event: Event)`
  Fires when the editor gutter (the line-number area) receives a `contextmenu` event. Will pass the editor instance as first argument, the (zero-based) number of the line that was clicked as second argument, the CSS class of the gutter that was clicked as third argument, and the raw `contextmenu` mouse event object as fourth argument. You can `preventDefault` the event, to signal that CodeMirror should do no further handling.
`"focus" (instance: CodeMirror, event: Event)`
  Fires whenever the editor is focused.
`"blur" (instance: CodeMirror, event: Event)`
  Fires whenever the editor is unfocused.
`"scroll" (instance: CodeMirror)`
  Fires when the editor is scrolled.
`"refresh" (instance: CodeMirror)`
  Fires when the editor is refreshed or resized. Mostly useful to invalidate cached values that depend on the editor or character size.
`"optionChange" (instance: CodeMirror, option: string)`
  Dispatched every time an option is changed with `setOption`.
`"scrollCursorIntoView" (instance: CodeMirror, event: Event)`
  Fires when the editor tries to scroll its cursor into view. Can be hooked into to take care of additional scrollable containers around the editor. When the event object has its `preventDefault` method called, CodeMirror will not itself try to scroll the window.
`"update" (instance: CodeMirror)`
  Will be fired whenever CodeMirror updates its DOM display.
`"renderLine" (instance: CodeMirror, line: LineHandle, element: Element)`
  Fired whenever a line is (re-)rendered to the DOM. Fired right after the DOM element is built, before it is added to the document. The handler may mess with the style of the resulting element, or add event handlers, but should not try to change the state of the editor.
`"mousedown", "dblclick", "touchstart", "contextmenu", "keydown", "keypress", "keyup", "cut", "copy", "paste", "dragstart", "dragenter", "dragover", "dragleave", "drop" (instance: CodeMirror, event: Event)`
  Fired when CodeMirror is handling a DOM event of this type. You can `preventDefault` the event, or give it a truthy `codemirrorIgnore` property, to signal that CodeMirror should do no further handling.

Document objects (instances of `CodeMirror.Doc`) emit the following events:

`"change" (doc: CodeMirror.Doc, changeObj: object)`
  Fired whenever a change occurs to the document. `changeObj` has a similar type as the object passed to the editor's `"change"` event.
`"beforeChange" (doc: CodeMirror.Doc, change: object)`
  See the description of the same event on editor instances.
`"cursorActivity" (doc: CodeMirror.Doc)`
  Fired whenever the cursor or selection in this document changes.
`"beforeSelectionChange" (doc: CodeMirror.Doc, selection: {head, anchor})`
  Equivalent to the event by the same name as fired on editor instances.

Line handles (as returned by, for example, `getLineHandle`) support these events:

`"delete" ()`
  Will be fired when the line object is deleted. A line object is associated with the start of the line. Mostly useful when you need to find out when your gutter markers on a given line are removed.
`"change" (line: LineHandle, changeObj: object)`
  Fires when the line's text content is changed in any way (but the line is not deleted outright). The `change` object is similar to the one passed to change event on the editor object.

Marked range handles (`CodeMirror.TextMarker`), as returned by `markText` and `setBookmark`, emit the following events:

`"beforeCursorEnter" ()`
  Fired when the cursor enters the marked range. From this event handler, the editor state may be inspected but not modified, with the exception that the range on which the event fires may be cleared.
`"clear" (from: {line, ch}, to: {line, ch})`
  Fired when the range is cleared, either through cursor movement in combination with `clearOnEnter` or through a call to its `clear()` method. Will only be fired once per handle. Note that deleting the range through text editing does not fire this event, because an undo action might bring the range back into existence. `from` and `to` give the part of the document that the range spanned when it was cleared.
`"hide" ()`
  Fired when the last part of the marker is removed from the document by editing operations.
`"unhide" ()`
  Fired when, after the marker was removed by editing, a undo operation brought the marker back.

Line widgets (`CodeMirror.LineWidget`), returned by `addLineWidget`, fire these events:

`"redraw" ()`
  Fired whenever the editor re-adds the widget to the DOM. This will happen once right after the widget is added (if it is scrolled into view), and then again whenever it is scrolled out of view and back in again, or when changes to the editor options or the line the widget is on require the widget to be redrawn.

## Key Maps

Key maps are ways to associate keys and mouse buttons with functionality. A key map is an object mapping strings that identify the buttons to functions that implement their functionality.

The CodeMirror distributions comes with Emacs, Vim, and Sublime Text-style keymaps.

Keys are identified either by name or by character. The `CodeMirror.keyNames` object defines names for common keys and associates them with their key codes. Examples of names defined here are `Enter`, `F5`, and `Q`. These can be prefixed with `Shift-`, `Cmd-`, `Ctrl-`, and `Alt-` to specify a modifier. So for example, `Shift-Ctrl-Space` would be a valid key identifier.

Common example: map the Tab key to insert spaces instead of a tab character.

    editor.setOption("extraKeys", {
      Tab: function(cm) {
        var spaces = Array(cm.getOption("indentUnit") + 1).join(" ");
        cm.replaceSelection(spaces);
      }
    });

Alternatively, a character can be specified directly by surrounding it in single quotes, for example `'$'` or `'q'`. Due to limitations in the way browsers fire key events, these may not be prefixed with modifiers.

To bind mouse buttons, use the names `LeftClick`, `MiddleClick`, and `RightClick`. These can also be prefixed with modifiers, and in addition, the word `Double` or `Triple` can be put before `Click` (as in `LeftDoubleClick`) to bind a double- or triple-click. The function for such a binding is passed the position that was clicked as second argument.

Multi-stroke key bindings can be specified by separating the key names by spaces in the property name, for example `Ctrl-X Ctrl-V`. When a map contains multi-stoke bindings or keys with modifiers that are not specified in the default order (`Shift-Cmd-Ctrl-Alt`), you must call `CodeMirror.normalizeKeyMap` on it before it can be used. This function takes a keymap and modifies it to normalize modifier order and properly recognize multi-stroke bindings. It will return the keymap itself.

The `CodeMirror.keyMap` object associates key maps with names. User code and key map definitions can assign extra properties to this object. Anywhere where a key map is expected, a string can be given, which will be looked up in this object. It also contains the `"default"` key map holding the default bindings.

The values of properties in key maps can be either functions of a single argument (the CodeMirror instance), strings, or `false`. Strings refer to commands, which are described below. If the property is set to `false`, CodeMirror leaves handling of the key up to the browser. A key handler function may return `CodeMirror.Pass` to indicate that it has decided not to handle the key, and other handlers (or the default behavior) should be given a turn.

Keys mapped to command names that start with the characters `"go"` or to functions that have a truthy `motion` property (which should be used for cursor-movement actions) will be fired even when an extra `Shift` modifier is present (i.e. `"Up": "goLineUp"` matches both up and shift-up). This is used to easily implement shift-selection.

Key maps can defer to each other by defining a `fallthrough` property. This indicates that when a key is not found in the map itself, one or more other maps should be searched. It can hold either a single key map or an array of key maps.

When a key map needs to set something up when it becomes active, or tear something down when deactivated, it can contain `attach` and/or `detach` properties, which should hold functions that take the editor instance and the next or previous keymap. Note that this only works for the top-level keymap, not for fallthrough maps or maps added with `extraKeys` or `addKeyMap`.

## Commands

Commands are parameter-less actions that can be performed on an editor. Their main use is for key bindings. Commands are defined by adding properties to the `CodeMirror.commands` object. A number of common commands are defined by the library itself, most of them used by the default key bindings. The value of a command property must be a function of one argument (an editor instance).

Some of the commands below are referenced in the default key map, but not defined by the core library. These are intended to be defined by user code or addons.

Commands can also be run with the `execCommand` method.

`selectAll` Ctrl-A (PC), Cmd-A (Mac)
  Select the whole content of the editor.
`singleSelection` Esc
  When multiple selections are present, this deselects all but the primary selection.
`killLine` Ctrl-K (Mac)
  Emacs-style line killing. Deletes the part of the line after the cursor. If that consists only of whitespace, the newline at the end of the line is also deleted.
`deleteLine` Ctrl-D (PC), Cmd-D (Mac)
  Deletes the whole line under the cursor, including newline at the end.
`delLineLeft`
  Delete the part of the line before the cursor.
`delWrappedLineLeft` Cmd-Backspace (Mac)
  Delete the part of the line from the left side of the visual line the cursor is on to the cursor.
`delWrappedLineRight` Cmd-Delete (Mac)
  Delete the part of the line from the cursor to the right side of the visual line the cursor is on.
`undo` Ctrl-Z (PC), Cmd-Z (Mac)
  Undo the last change. Note that, because browsers still don't make it possible for scripts to react to or customize the context menu, selecting undo (or redo) from the context menu in a CodeMirror instance does not work.
`redo` Ctrl-Y (PC), Shift-Cmd-Z (Mac), Cmd-Y (Mac)
  Redo the last undone change.
`undoSelection` Ctrl-U (PC), Cmd-U (Mac)
  Undo the last change to the selection, or if there are no selection-only changes at the top of the history, undo the last change.
`redoSelection` Alt-U (PC), Shift-Cmd-U (Mac)
  Redo the last change to the selection, or the last text change if no selection changes remain.
`goDocStart` Ctrl-Home (PC), Cmd-Up (Mac), Cmd-Home (Mac)
  Move the cursor to the start of the document.
`goDocEnd` Ctrl-End (PC), Cmd-End (Mac), Cmd-Down (Mac)
  Move the cursor to the end of the document.
`goLineStart` Alt-Left (PC), Ctrl-A (Mac)
  Move the cursor to the start of the line.
`goLineStartSmart` Home
  Move to the start of the text on the line, or if we are already there, to the actual start of the line (including whitespace).
`goLineEnd` Alt-Right (PC), Ctrl-E (Mac)
  Move the cursor to the end of the line.
`goLineRight` Cmd-Right (Mac)
  Move the cursor to the right side of the visual line it is on.
`goLineLeft` Cmd-Left (Mac)
  Move the cursor to the left side of the visual line it is on. If this line is wrapped, that may not be the start of the line.
`goLineLeftSmart`
  Move the cursor to the left side of the visual line it is on. If that takes it to the start of the line, behave like `goLineStartSmart`.
`goLineUp` Up, Ctrl-P (Mac)
  Move the cursor up one line.
`goLineDown` Down, Ctrl-N (Mac)
  Move down one line.
`goPageUp` PageUp, Shift-Ctrl-V (Mac)
  Move the cursor up one screen, and scroll up by the same distance.
`goPageDown` PageDown, Ctrl-V (Mac)
  Move the cursor down one screen, and scroll down by the same distance.
`goCharLeft` Left, Ctrl-B (Mac)
  Move the cursor one character left, going to the previous line when hitting the start of line.
`goCharRight` Right, Ctrl-F (Mac)
  Move the cursor one character right, going to the next line when hitting the end of line.
`goColumnLeft`
  Move the cursor one character left, but don't cross line boundaries.
`goColumnRight`
  Move the cursor one character right, don't cross line boundaries.
`goWordLeft` Alt-B (Mac)
  Move the cursor to the start of the previous word.
`goWordRight` Alt-F (Mac)
  Move the cursor to the end of the next word.
`goGroupLeft` Ctrl-Left (PC), Alt-Left (Mac)
  Move to the left of the group before the cursor. A group is a stretch of word characters, a stretch of punctuation characters, a newline, or a stretch of more than one whitespace character.
`goGroupRight` Ctrl-Right (PC), Alt-Right (Mac)
  Move to the right of the group after the cursor (see above).
`delCharBefore` Shift-Backspace, Ctrl-H (Mac)
  Delete the character before the cursor.
`delCharAfter` Delete, Ctrl-D (Mac)
  Delete the character after the cursor.
`delWordBefore` Alt-Backspace (Mac)
  Delete up to the start of the word before the cursor.
`delWordAfter` Alt-D (Mac)
  Delete up to the end of the word after the cursor.
`delGroupBefore` Ctrl-Backspace (PC), Alt-Backspace (Mac)
  Delete to the left of the group before the cursor.
`delGroupAfter` Ctrl-Delete (PC), Ctrl-Alt-Backspace (Mac), Alt-Delete (Mac)
  Delete to the start of the group after the cursor.
`indentAuto` Shift-Tab
  Auto-indent the current line or selection.
`indentMore` Ctrl-] (PC), Cmd-] (Mac)
  Indent the current line or selection by one indent unit.
`indentLess` Ctrl-[ (PC), Cmd-[ (Mac)
  Dedent the current line or selection by one indent unit.
`insertTab`
  Insert a tab character at the cursor.
`insertSoftTab`
  Insert the amount of spaces that match the width a tab at the cursor position would have.
`defaultTab` Tab
  If something is selected, indent it by one indent unit. If nothing is selected, insert a tab character.
`transposeChars` Ctrl-T (Mac)
  Swap the characters before and after the cursor.
`newlineAndIndent` Enter
  Insert a newline and auto-indent the new line.
`toggleOverwrite` Insert
  Flip the overwrite flag.
`save` Ctrl-S (PC), Cmd-S (Mac)
  Not defined by the core library, only referred to in key maps. Intended to provide an easy way for user code to define a save command.
`find` Ctrl-F (PC), Cmd-F (Mac)
`findNext` Ctrl-G (PC), Cmd-G (Mac)
`findPrev` Shift-Ctrl-G (PC), Shift-Cmd-G (Mac)
`replace` Shift-Ctrl-F (PC), Cmd-Alt-F (Mac)
`replaceAll` Shift-Ctrl-R (PC), Shift-Cmd-Alt-F (Mac)
  Not defined by the core library, but defined in the search addon (or custom client addons).

## Customized Styling

Up to a certain extent, CodeMirror's look can be changed by modifying style sheet files. The style sheets supplied by modes simply provide the colors for that mode, and can be adapted in a very straightforward way. To style the editor itself, it is possible to alter or override the styles defined in `codemirror.css`.

Some care must be taken there, since a lot of the rules in this file are necessary to have CodeMirror function properly. Adjusting colors should be safe, of course, and with some care a lot of other things can be changed as well. The CSS classes defined in this file serve the following roles:

`CodeMirror`
  The outer element of the editor. This should be used for the editor width, height, borders and positioning. Can also be used to set styles that should hold for everything inside the editor (such as font and font size), or to set a background. Setting this class' `height` style to `auto` will make the editor resize to fit its content (it is recommended to also set the `viewportMargin` option to `Infinity` when doing this.
`CodeMirror-focused`
  Whenever the editor is focused, the top element gets this class. This is used to hide the cursor and give the selection a different color when the editor is not focused.
`CodeMirror-gutters`
  This is the backdrop for all gutters. Use it to set the default gutter background color, and optionally add a border on the right of the gutters.
`CodeMirror-linenumbers`
  Use this for giving a background or width to the line number gutter.
`CodeMirror-linenumber`
  Used to style the actual individual line numbers. These won't be children of the `CodeMirror-linenumbers` (plural) element, but rather will be absolutely positioned to overlay it. Use this to set alignment and text properties for the line numbers.
`CodeMirror-lines`
  The visible lines. This is where you specify vertical padding for the editor content.
`CodeMirror-cursor`
  The cursor is a block element that is absolutely positioned. You can make it look whichever way you want.
`CodeMirror-selected`
  The selection is represented by `span` elements with this class.
`CodeMirror-matchingbracket`, `CodeMirror-nonmatchingbracket`
  These are used to style matched (or unmatched) brackets.

If your page's style sheets do funky things to all `div` or `pre` elements (you probably shouldn't do that), you'll have to define rules to cancel these effects out again for elements under the `CodeMirror` class.

Themes are also simply CSS files, which define colors for various syntactic elements. See the files in the `theme` directory.

## Programming API

A lot of CodeMirror features are only available through its API. Thus, you need to write code (or use addons) if you want to expose them to your users.

Whenever points in the document are represented, the API uses objects with `line` and `ch` properties. Both are zero-based. CodeMirror makes sure to 'clip' any positions passed by client code so that they fit inside the document, so you shouldn't worry too much about sanitizing your coordinates. If you give `ch` a value of `null`, or don't specify it, it will be replaced with the length of the specified line. Such positions may also have a `sticky` property holding `"before"` or `"after"`, whether the position is associated with the character before or after it. This influences, for example, where the cursor is drawn on a line-break or bidi-direction boundary.

Methods prefixed with `doc.` can, unless otherwise specified, be called both on `CodeMirror` (editor) instances and `CodeMirror.Doc` instances. Methods prefixed with `cm.` are only available on `CodeMirror` instances.

### Constructor

Constructing an editor instance is done with the `CodeMirror(place: Element|fn(Element), ?option: object)` constructor. If the `place` argument is a DOM element, the editor will be appended to it. If it is a function, it will be called, and is expected to place the editor into the document. `options` may be an element mapping option names to values. The options that it doesn't explicitly specify (or all options, if it is not passed) will be taken from `CodeMirror.defaults`.

Note that the options object passed to the constructor will be mutated when the instance's options are changed, so you shouldn't share such objects between instances.

See `CodeMirror.fromTextArea` for another way to construct an editor instance.

### Content manipulation methods

`doc.getValue(?separator: string) → string`
  Get the current editor content. You can pass it an optional argument to specify the string to be used to separate lines (defaults to `"\n"`).
`doc.setValue(content: string)`
  Set the editor content.
`doc.getRange(from: {line, ch}, to: {line, ch}, ?separator: string) → string`
  Get the text between the given points in the editor, which should be `{line, ch}` objects. An optional third argument can be given to indicate the line separator string to use (defaults to `"\n"`).
`doc.replaceRange(replacement: string, from: {line, ch}, to: {line, ch}, ?origin: string)`
  Replace the part of the document between `from` and `to` with the given string. `from` and `to` must be `{line, ch}` objects. `to` can be left off to simply insert the string at position `from`. When `origin` is given, it will be passed on to `"change"` events, and its first letter will be used to determine whether this change can be merged with previous history events, in the way described for selection origins.
`doc.getLine(n: integer) → string`
  Get the content of line `n`.
`doc.lineCount() → integer`
  Get the number of lines in the editor.
`doc.firstLine() → integer`
  Get the number of first line in the editor. This will usually be zero but for linked sub-views, or documents instantiated with a non-zero first line, it might return other values.
`doc.lastLine() → integer`
  Get the number of last line in the editor. This will usually be `doc.lineCount() - 1`, but for linked sub-views, it might return other values.
`doc.getLineHandle(num: integer) → LineHandle`
  Fetches the line handle for the given line number.
`doc.getLineNumber(handle: LineHandle) → integer`
  Given a line handle, returns the current position of that line (or `null` when it is no longer in the document).
`doc.eachLine(f: (line: LineHandle))`
`doc.eachLine(start: integer, end: integer, f: (line: LineHandle))`
  Iterate over the whole document, or if `start` and `end` line numbers are given, the range from `start` up to (not including) `end`, and call `f` for each line, passing the line handle. This is a faster way to visit a range of line handlers than calling `getLineHandle` for each of them. Note that line handles have a `text` property containing the line's content (as a string).
`doc.markClean()`
  Set the editor content as 'clean', a flag that it will retain until it is edited, and which will be set again when such an edit is undone again. Useful to track whether the content needs to be saved. This function is deprecated in favor of `changeGeneration`, which allows multiple subsystems to track different notions of cleanness without interfering.
`doc.changeGeneration(?closeEvent: boolean) → integer`
  Returns a number that can later be passed to `isClean` to test whether any edits were made (and not undone) in the meantime. If `closeEvent` is true, the current history event will be ‘closed’, meaning it can't be combined with further changes (rapid typing or deleting events are typically combined).
`doc.isClean(?generation: integer) → boolean`
  Returns whether the document is currently clean — not modified since initialization or the last call to `markClean` if no argument is passed, or since the matching call to `changeGeneration` if a generation value is given.

### Cursor and selection methods

`doc.getSelection(?lineSep: string) → string`
  Get the currently selected code. Optionally pass a line separator to put between the lines in the output. When multiple selections are present, they are concatenated with instances of `lineSep` in between.
`doc.getSelections(?lineSep: string) → array<string>`
  Returns an array containing a string for each selection, representing the content of the selections.
`doc.replaceSelection(replacement: string, ?select: string)`
  Replace the selection(s) with the given string. By default, the new selection ends up after the inserted text. The optional `select` argument can be used to change this—passing `"around"` will cause the new text to be selected, passing `"start"` will collapse the selection to the start of the inserted text.
`doc.replaceSelections(replacements: array<string>, ?select: string)`
  The length of the given array should be the same as the number of active selections. Replaces the content of the selections with the strings in the array. The `select` argument works the same as in `replaceSelection`.
`doc.getCursor(?start: string) → {line, ch}`
  Retrieve one end of the primary selection. `start` is an optional string indicating which end of the selection to return. It may be `"from"`, `"to"`, `"head"` (the side of the selection that moves when you press shift+arrow), or `"anchor"` (the fixed side of the selection). Omitting the argument is the same as passing `"head"`. A `{line, ch}` object will be returned.
`doc.listSelections() → array<{anchor, head}>`
  Retrieves a list of all current selections. These will always be sorted, and never overlap (overlapping selections are merged). Each object in the array contains `anchor` and `head` properties referring to `{line, ch}` objects.
`doc.somethingSelected() → boolean`
  Return true if any text is selected.
`doc.setCursor(pos: {line, ch}|number, ?ch: number, ?options: object)`
  Set the cursor position. You can either pass a single `{line, ch}` object, or the line and the character as two separate parameters. Will replace all selections with a single, empty selection at the given position. The supported options are the same as for `setSelection`.
`doc.setSelection(anchor: {line, ch}, ?head: {line, ch}, ?options: object)`
  Set a single selection range. `anchor` and `head` should be `{line, ch}` objects. `head` defaults to `anchor` when not given. These options are supported:
  `scroll: boolean`
    Determines whether the selection head should be scrolled into view. Defaults to true.
  `origin: string`
    Determines whether the selection history event may be merged with the previous one. When an origin starts with the character `+`, and the last recorded selection had the same origin and was similar (close in time, both collapsed or both non-collapsed), the new one will replace the old one. When it starts with `*`, it will always replace the previous event (if that had the same origin). Built-in motion uses the `"+move"` origin. User input uses the `"+input"` origin.
  `bias: number`
    Determine the direction into which the selection endpoints should be adjusted when they fall inside an atomic range. Can be either -1 (backward) or 1 (forward). When not given, the bias will be based on the relative position of the old selection—the editor will try to move further away from that, to prevent getting stuck.
`doc.setSelections(ranges: array<{anchor, head}>, ?primary: integer, ?options: object)`
  Sets a new set of selections. There must be at least one selection in the given array. When `primary` is a number, it determines which selection is the primary one. When it is not given, the primary index is taken from the previous selection, or set to the last range if the previous selection had less ranges than the new one. Supports the same options as `setSelection`.
`doc.addSelection(anchor: {line, ch}, ?head: {line, ch})`
  Adds a new selection to the existing set of selections, and makes it the primary selection.
`doc.extendSelection(from: {line, ch}, ?to: {line, ch}, ?options: object)`
  Similar to `setSelection`, but will, if shift is held or the extending flag is set, move the head of the selection while leaving the anchor at its current place. `to` is optional, and can be passed to ensure a region (for example a word or paragraph) will end up selected (in addition to whatever lies between that region and the current anchor). When multiple selections are present, all but the primary selection will be dropped by this method. Supports the same options as `setSelection`.
`doc.extendSelections(heads: array<{line, ch}>, ?options: object)`
  An equivalent of `extendSelection` that acts on all selections at once.
`doc.extendSelectionsBy(f: function(range: {anchor, head}) → {line, ch}), ?options: object)`
  Applies the given function to all existing selections, and calls `extendSelections` on the result.
`doc.setExtending(value: boolean)`
  Sets or clears the 'extending' flag, which acts similar to the shift key, in that it will cause cursor movement and calls to `extendSelection` to leave the selection anchor in place.
`doc.getExtending() → boolean`
  Get the value of the 'extending' flag.
`cm.hasFocus() → boolean`
  Tells you whether the editor currently has focus.
`cm.findPosH(start: {line, ch}, amount: integer, unit: string, visually: boolean) → {line, ch, ?hitSide: boolean}`
  Used to find the target position for horizontal cursor motion. `start` is a `{line, ch}` object, `amount` an integer (may be negative), and `unit` one of the string `"char"`, `"column"`, or `"word"`. Will return a position that is produced by moving `amount` times the distance specified by `unit`. When `visually` is true, motion in right-to-left text will be visual rather than logical. When the motion was clipped by hitting the end or start of the document, the returned value will have a `hitSide` property set to true.
`cm.findPosV(start: {line, ch}, amount: integer, unit: string) → {line, ch, ?hitSide: boolean}`
  Similar to `findPosH`, but used for vertical motion. `unit` may be `"line"` or `"page"`. The other arguments and the returned value have the same interpretation as they have in `findPosH`.
`cm.findWordAt(pos: {line, ch}) → {anchor: {line, ch}, head: {line, ch}}`
  Returns the start and end of the 'word' (the stretch of letters, whitespace, or punctuation) at the given position.

### Configuration methods

`cm.setOption(option: string, value: any)`
  Change the configuration of the editor. `option` should the name of an option, and `value` should be a valid value for that option.
`cm.getOption(option: string) → any`
  Retrieves the current value of the given option for this editor instance.
`cm.addKeyMap(map: object, bottom: boolean)`
  Attach an additional key map to the editor. This is mostly useful for addons that need to register some key handlers without trampling on the `extraKeys` option. Maps added in this way have a higher precedence than the `extraKeys` and `keyMap` options, and between them, the maps added earlier have a lower precedence than those added later, unless the `bottom` argument was passed, in which case they end up below other key maps added with this method.
`cm.removeKeyMap(map: object)`
  Disable a keymap added with `addKeyMap`. Either pass in the key map object itself, or a string, which will be compared against the `name` property of the active key maps.
`cm.addOverlay(mode: string|object, ?options: object)`
  Enable a highlighting overlay. This is a stateless mini-mode that can be used to add extra highlighting. For example, the search addon uses it to highlight the term that's currently being searched. `mode` can be a mode spec or a mode object (an object with a `token` method). The `options` parameter is optional. If given, it should be an object, optionally containing the following options:
  `opaque: bool`
    Defaults to off, but can be given to allow the overlay styling, when not `null`, to override the styling of the base mode entirely, instead of the two being applied together.
  `priority: number`
    Determines the ordering in which the overlays are applied. Those with high priority are applied after those with lower priority, and able to override the opaqueness of the ones that come before. Defaults to 0.
`cm.removeOverlay(mode: string|object)`
  Pass this the exact value passed for the `mode` parameter to `addOverlay`, or a string that corresponds to the `name` property of that value, to remove an overlay again.
`cm.on(type: string, func: (...args))`
  Register an event handler for the given event type (a string) on the editor instance. There is also a `CodeMirror.on(object, type, func)` version that allows registering of events on any object.
`cm.off(type: string, func: (...args))`
  Remove an event handler on the editor instance. An equivalent `CodeMirror.off(object, type, func)` also exists.

### Document management methods

Each editor is associated with an instance of `CodeMirror.Doc`, its document. A document represents the editor content, plus a selection, an undo history, and a mode. A document can only be associated with a single editor at a time. You can create new documents by calling the `CodeMirror.Doc(text: string, mode: Object, firstLineNumber: ?number, lineSeparator: ?string)` constructor. The last three arguments are optional and can be used to set a mode for the document, make it start at a line number other than 0, and set a specific line separator respectively.

`cm.getDoc() → Doc`
  Retrieve the currently active document from an editor.
`doc.getEditor() → CodeMirror`
  Retrieve the editor associated with a document. May return `null`.
`cm.swapDoc(doc: CodeMirror.Doc) → Doc`
  Attach a new document to the editor. Returns the old document, which is now no longer associated with an editor.
`doc.copy(copyHistory: boolean) → Doc`
  Create an identical copy of the given doc. When `copyHistory` is true, the history will also be copied. Can not be called directly on an editor.
`doc.linkedDoc(options: object) → Doc`
  Create a new document that's linked to the target document. Linked documents will stay in sync (changes to one are also applied to the other) until unlinked. These are the options that are supported:
  `sharedHist: boolean`
    When turned on, the linked copy will share an undo history with the original. Thus, something done in one of the two can be undone in the other, and vice versa.
  `from: integer`
  `to: integer`
    Can be given to make the new document a subview of the original. Subviews only show a given range of lines. Note that line coordinates inside the subview will be consistent with those of the parent, so that for example a subview starting at line 10 will refer to its first line as line 10, not 0.
  `mode: string|object`
    By default, the new document inherits the mode of the parent. This option can be set to a mode spec to give it a different mode.
`doc.unlinkDoc(doc: CodeMirror.Doc)`
  Break the link between two documents. After calling this, changes will no longer propagate between the documents, and, if they had a shared history, the history will become separate.
`doc.iterLinkedDocs(function: (doc: CodeMirror.Doc, sharedHist: boolean))`
  Will call the given function for all documents linked to the target document. It will be passed two arguments, the linked document and a boolean indicating whether that document shares history with the target.

### History-related methods

`doc.undo()`
  Undo one edit (if any undo events are stored).
`doc.redo()`
  Redo one undone edit.
`doc.undoSelection()`
  Undo one edit or selection change.
`doc.redoSelection()`
  Redo one undone edit or selection change.
`doc.historySize() → {undo: integer, redo: integer}`
  Returns an object with `{undo, redo}` properties, both of which hold integers, indicating the amount of stored undo and redo operations.
`doc.clearHistory()`
  Clears the editor's undo history.
`doc.getHistory() → object`
  Get a (JSON-serializable) representation of the undo history.
`doc.setHistory(history: object)`
  Replace the editor's undo history with the one provided, which must be a value as returned by `getHistory`. Note that this will have entirely undefined results if the editor content isn't also the same as it was when `getHistory` was called.

### Text-marking methods

`doc.markText(from: {line, ch}, to: {line, ch}, ?options: object) → TextMarker`
  Can be used to mark a range of text with a specific CSS class name. `from` and `to` should be `{line, ch}` objects. The `options` parameter is optional. When given, it should be an object that may contain the following configuration options:
  `className: string`
    Assigns a CSS class to the marked stretch of text.
  `inclusiveLeft: boolean`
    Determines whether text inserted on the left of the marker will end up inside or outside of it.
  `inclusiveRight: boolean`
    Like `inclusiveLeft`, but for the right side.
  `selectLeft: boolean`
    For atomic ranges, determines whether the cursor is allowed to be placed directly to the left of the range. Has no effect on non-atomic ranges.
  `selectRight: boolean`
    Like `selectLeft`, but for the right side.
  `atomic: boolean`
    Atomic ranges act as a single unit when cursor movement is concerned—i.e. it is impossible to place the cursor inside of them. You can control whether the cursor is allowed to be placed directly before or after them using `selectLeft` or `selectRight`. If `selectLeft` (or right) is not provided, then `inclusiveLeft` (or right) will control this behavior.
  `collapsed: boolean`
    Collapsed ranges do not show up in the display. Setting a range to be collapsed will automatically make it atomic.
  `clearOnEnter: boolean`
    When enabled, will cause the mark to clear itself whenever the cursor enters its range. This is mostly useful for text-replacement widgets that need to 'snap open' when the user tries to edit them. The `"clear"` event fired on the range handle can be used to be notified when this happens.
  `clearWhenEmpty: boolean`
    Determines whether the mark is automatically cleared when it becomes empty. Default is true.
  `replacedWith: Element`
    Use a given node to display this range. Implies both collapsed and atomic. The given DOM node must be an inline element (as opposed to a block element).
  `handleMouseEvents: boolean`
    When `replacedWith` is given, this determines whether the editor will capture mouse and drag events occurring in this widget. Default is false—the events will be left alone for the default browser handler, or specific handlers on the widget, to capture.
  `readOnly: boolean`
    A read-only span can, as long as it is not cleared, not be modified except by calling `setValue` to reset the whole document. Note: adding a read-only span currently clears the undo history of the editor, because existing undo events being partially nullified by read-only spans would corrupt the history (in the current implementation).
  `addToHistory: boolean`
    When set to true (default is false), adding this marker will create an event in the undo history that can be individually undone (clearing the marker).
  `startStyle: string`
    Can be used to specify an extra CSS class to be applied to the leftmost span that is part of the marker.
  `endStyle: string`
    Equivalent to `startStyle`, but for the rightmost span.
  `css: string`
    A string of CSS to be applied to the covered text. For example `"color: #fe3"`.
  `attributes: object`
    When given, add the attributes in the given object to the elements created for the marked text. Adding `class` or `style` attributes this way is not supported.
  `shared: boolean`
    When the target document is linked to other documents, you can set `shared` to true to make the marker appear in all documents. By default, a marker appears only in its target document.
  The method will return an object that represents the marker (with constructor `CodeMirror.TextMarker`), which exposes three methods: `clear()`, to remove the mark, `find()`, which returns a `{from, to}` object (both holding document positions), indicating the current position of the marked range, or `undefined` if the marker is no longer in the document, and finally `changed()`, which you can call if you've done something that might change the size of the marker (for example changing the content of a `replacedWith` node), and want to cheaply update the display.
`doc.setBookmark(pos: {line, ch}, ?options: object) → TextMarker`
  Inserts a bookmark, a handle that follows the text around it as it is being edited, at the given position. A bookmark has two methods `find()` and `clear()`. The first returns the current position of the bookmark, if it is still in the document, and the second explicitly removes the bookmark. The options argument is optional. If given, the following properties are recognized:
  `widget: Element`
    Can be used to display a DOM node at the current location of the bookmark (analogous to the `replacedWith` option to `markText`).
  `insertLeft: boolean`
    By default, text typed when the cursor is on top of the bookmark will end up to the right of the bookmark. Set this option to true to make it go to the left instead.
  `shared: boolean`
    See the corresponding option to `markText`.
  `handleMouseEvents: boolean`
    As with `markText`, this determines whether mouse events on the widget inserted for this bookmark are handled by CodeMirror. The default is false.
`doc.findMarks(from: {line, ch}, to: {line, ch}) → array<TextMarker>`
  Returns an array of all the bookmarks and marked ranges found between the given positions (non-inclusive).
`doc.findMarksAt(pos: {line, ch}) → array<TextMarker>`
  Returns an array of all the bookmarks and marked ranges present at the given position.
`doc.getAllMarks() → array<TextMarker>`
  Returns an array containing all marked ranges in the document.

### Widget, gutter, and decoration methods

`doc.setGutterMarker(line: integer|LineHandle, gutterID: string, value: Element) → LineHandle`
  Sets the gutter marker for the given gutter (identified by its CSS class, see the `gutters` option) to the given value. Value can be either `null`, to clear the marker, or a DOM element, to set it. The DOM element will be shown in the specified gutter next to the specified line.
`doc.clearGutter(gutterID: string)`
  Remove all gutter markers in the gutter with the given ID.
`doc.addLineClass(line: integer|LineHandle, where: string, class: string) → LineHandle`
  Set a CSS class name for the given line. `line` can be a number or a line handle. `where` determines to which element this class should be applied, can can be one of `"text"` (the text element, which lies in front of the selection), `"background"` (a background element that will be behind the selection), `"gutter"` (the line's gutter space), or `"wrap"` (the wrapper node that wraps all of the line's elements, including gutter elements). `class` should be the name of the class to apply.
`doc.removeLineClass(line: integer|LineHandle, where: string, class: string) → LineHandle`
  Remove a CSS class from a line. `line` can be a line handle or number. `where` should be one of `"text"`, `"background"`, or `"wrap"` (see `addLineClass`). `class` can be left off to remove all classes for the specified node, or be a string to remove only a specific class.
`doc.lineInfo(line: integer|LineHandle) → object`
  Returns the line number, text content, and marker status of the given line, which can be either a number or a line handle. The returned object has the structure `{line, handle, text, gutterMarkers, textClass, bgClass, wrapClass, widgets}`, where `gutterMarkers` is an object mapping gutter IDs to marker elements, and `widgets` is an array of line widgets attached to this line, and the various class properties refer to classes added with `addLineClass`.
`cm.addWidget(pos: {line, ch}, node: Element, scrollIntoView: boolean)`
  Puts `node`, which should be an absolutely positioned DOM node, into the editor, positioned right below the given `{line, ch}` position. When `scrollIntoView` is true, the editor will ensure that the entire node is visible (if possible). To remove the widget again, simply use DOM methods (move it somewhere else, or call `removeChild` on its parent).
`doc.addLineWidget(line: integer|LineHandle, node: Element, ?options: object) → LineWidget`
  Adds a line widget, an element shown below a line, spanning the whole of the editor's width, and moving the lines below it downwards. `line` should be either an integer or a line handle, and `node` should be a DOM node, which will be displayed below the given line. `options`, when given, should be an object that configures the behavior of the widget. The following options are supported (all default to false):
  `coverGutter: boolean`
    Whether the widget should cover the gutter.
  `noHScroll: boolean`
    Whether the widget should stay fixed in the face of horizontal scrolling.
  `above: boolean`
    Causes the widget to be placed above instead of below the text of the line.
  `handleMouseEvents: boolean`
    Determines whether the editor will capture mouse and drag events occurring in this widget. Default is false—the events will be left alone for the default browser handler, or specific handlers on the widget, to capture.
  `insertAt: integer`
    By default, the widget is added below other widgets for the line. This option can be used to place it at a different position (zero for the top, N to put it after the Nth other widget). Note that this only has effect once, when the widget is created.
  `className: string`
    Add an extra CSS class name to the wrapper element created for the widget.
  Note that the widget node will become a descendant of nodes with CodeMirror-specific CSS classes, and those classes might in some cases affect it. This method returns an object that represents the widget placement. It'll have a `line` property pointing at the line handle that it is associated with, and the following methods:
  `clear()`
    Removes the widget.
  `changed()`
    Call this if you made some change to the widget's DOM node that might affect its height. It'll force CodeMirror to update the height of the line that contains the widget.

### Sizing, scrolling and positioning methods

`cm.setSize(width: number|string, height: number|string)`
  Programmatically set the size of the editor (overriding the applicable CSS rules). `width` and `height` can be either numbers (interpreted as pixels) or CSS units (`"100%"`, for example). You can pass `null` for either of them to indicate that that dimension should not be changed.
`cm.scrollTo(x: number, y: number)`
  Scroll the editor to a given (pixel) position. Both arguments may be left as `null` or `undefined` to have no effect.
`cm.getScrollInfo() → {left, top, width, height, clientWidth, clientHeight}`
  Get an `{left, top, width, height, clientWidth, clientHeight}` object that represents the current scroll position, the size of the scrollable area, and the size of the visible area (minus scrollbars).
`cm.scrollIntoView(what: {line, ch}|{left, top, right, bottom}|{from, to}|null, ?margin: number)`
  Scrolls the given position into view. `what` may be `null` to scroll the cursor into view, a `{line, ch}` position to scroll a character into view, a `{left, top, right, bottom}` pixel range (in editor-local coordinates), or a range `{from, to}` containing either two character positions or two pixel squares. The `margin` parameter is optional. When given, it indicates the amount of vertical pixels around the given area that should be made visible as well.
`cm.cursorCoords(where: boolean|{line, ch}, mode: string) → {left, top, bottom}`
  Returns an `{left, top, bottom}` object containing the coordinates of the cursor position. If `mode` is `"local"`, they will be relative to the top-left corner of the editable document. If it is `"page"` or not given, they are relative to the top-left corner of the page. If `mode` is `"window"`, the coordinates are relative to the top-left corner of the currently visible (scrolled) window. `where` can be a boolean indicating whether you want the start (`true`) or the end (`false`) of the selection, or, if a `{line, ch}` object is given, it specifies the precise position at which you want to measure.
`cm.charCoords(pos: {line, ch}, ?mode: string) → {left, right, top, bottom}`
  Returns the position and dimensions of an arbitrary character. `pos` should be a `{line, ch}` object. This differs from `cursorCoords` in that it'll give the size of the whole character, rather than just the position that the cursor would have when it would sit at that position.
`cm.coordsChar(object: {left, top}, ?mode: string) → {line, ch}`
  Given an `{left, top}` object (e.g. coordinates of a mouse event) returns the `{line, ch}` position that corresponds to it. The optional `mode` parameter determines relative to what the coordinates are interpreted. It may be `"window"`, `"page"` (the default), or `"local"`.
`cm.lineAtHeight(height: number, ?mode: string) → number`
  Computes the line at the given pixel height. `mode` can be one of the same strings that `coordsChar` accepts.
`cm.heightAtLine(line: integer|LineHandle, ?mode: string, ?includeWidgets: bool) → number`
  Computes the height of the top of a line, in the coordinate system specified by `mode` (see `coordsChar`), which defaults to `"page"`. When a line below the bottom of the document is specified, the returned value is the bottom of the last line in the document. By default, the position of the actual text is returned. If `includeWidgets` is true and the line has line widgets, the position above the first line widget is returned.
`cm.defaultTextHeight() → number`
  Returns the line height of the default font for the editor.
`cm.defaultCharWidth() → number`
  Returns the pixel width of an 'x' in the default font for the editor. (Note that for non-monospace fonts, this is mostly useless, and even for monospace fonts, non-ascii characters might have a different width).
`cm.getViewport() → {from: number, to: number}`
  Returns a `{from, to}` object indicating the start (inclusive) and end (exclusive) of the currently rendered part of the document. In big documents, when most content is scrolled out of view, CodeMirror will only render the visible part, and a margin around it. See also the `viewportChange` event.
`cm.refresh()`
  If your code does something to change the size of the editor element (window resizes are already listened for), or unhides it, you should probably follow up by calling this method to ensure CodeMirror is still looking as intended. See also the autorefresh addon.

### Mode, state, and token-related methods

When writing language-aware functionality, it can often be useful to hook into the knowledge that the CodeMirror language mode has. See the section on modes for a more detailed description of how these work.

`doc.getMode() → object`
  Gets the (outer) mode object for the editor. Note that this is distinct from `getOption("mode")`, which gives you the mode specification, rather than the resolved, instantiated mode object.
`cm.getModeAt(pos: {line, ch}) → object`
  Gets the inner mode at a given position. This will return the same as `getMode` for simple modes, but will return an inner mode for nesting modes (such as `htmlmixed`).
`cm.getTokenAt(pos: {line, ch}, ?precise: boolean) → object`
  Retrieves information about the token the current mode found before the given position (a `{line, ch}` object). The returned object has the following properties:
  `start`
    The character (on the given line) at which the token starts.
  `end`
    The character at which the token ends.
  `string`
    The token's string.
  `type`
    The token type the mode assigned to the token, such as `"keyword"` or `"comment"` (may also be null).
  `state`
    The mode's state at the end of this token.
  If `precise` is true, the token will be guaranteed to be accurate based on recent edits. If false or not specified, the token will use cached state information, which will be faster but might not be accurate if edits were recently made and highlighting has not yet completed.
`cm.getLineTokens(line: integer, ?precise: boolean) → array<{start, end, string, type, state}>`
  This is similar to `getTokenAt`, but collects all tokens for a given line into an array. It is much cheaper than repeatedly calling `getTokenAt`, which re-parses the part of the line before the token for every call.
`cm.getTokenTypeAt(pos: {line, ch}) → string`
  This is a (much) cheaper version of `getTokenAt` useful for when you just need the type of the token at a given position, and no other information. Will return `null` for unstyled tokens, and a string, potentially containing multiple space-separated style names, otherwise.
`cm.getHelpers(pos: {line, ch}, type: string) → array<helper>`
  Fetch the set of applicable helper values for the given position. Helpers provide a way to look up functionality appropriate for a mode. The `type` argument provides the helper namespace (see `registerHelper`), in which the values will be looked up. When the mode itself has a property that corresponds to the `type`, that directly determines the keys that are used to look up the helper values (it may be either a single string, or an array of strings). Failing that, the mode's `helperType` property and finally the mode's name are used.
  For example, the JavaScript mode has a property `fold` containing `"brace"`. When the `brace-fold` addon is loaded, that defines a helper named `brace` in the `fold` namespace. This is then used by the `foldcode` addon to figure out that it can use that folding function to fold JavaScript code.
  When any 'global' helpers are defined for the given namespace, their predicates are called on the current mode and editor, and all those that declare they are applicable will also be added to the array that is returned.
`cm.getHelper(pos: {line, ch}, type: string) → helper`
  Returns the first applicable helper value. See `getHelpers`.
`cm.getStateAfter(?line: integer, ?precise: boolean) → object`
  Returns the mode's parser state, if any, at the end of the given line number. If no line number is given, the state at the end of the document is returned. This can be useful for storing parsing errors in the state, or getting other kinds of contextual information for a line. `precise` is defined as in `getTokenAt()`.

### Miscellaneous methods

`cm.operation(func: () → any) → any`
  CodeMirror internally buffers changes and only updates its DOM structure after it has finished performing some operation. If you need to perform a lot of operations on a CodeMirror instance, you can call this method with a function argument. It will call the function, buffering up all changes, and only doing the expensive update after the function returns. This can be a lot faster. The return value from this method will be the return value of your function.
`cm.startOperation()`
`cm.endOperation()`
  In normal circumstances, use the above `operation` method. But if you want to buffer operations happening asynchronously, or that can't all be wrapped in a callback function, you can call `startOperation` to tell CodeMirror to start buffering changes, and `endOperation` to actually render all the updates. Be careful: if you use this API and forget to call `endOperation`, the editor will just never update.
`cm.indentLine(line: integer, ?dir: string|integer)`
  Adjust the indentation of the given line. The second argument (which defaults to `"smart"`) may be one of:
  `"prev"`
    Base indentation on the indentation of the previous line.
  `"smart"`
    Use the mode's smart indentation if available, behave like `"prev"` otherwise.
  `"add"`
    Increase the indentation of the line by one indent unit.
  `"subtract"`
    Reduce the indentation of the line.
  `<integer>`
    Add (positive number) or reduce (negative number) the indentation by the given amount of spaces.
`cm.toggleOverwrite(?value: boolean)`
  Switches between overwrite and normal insert mode (when not given an argument), or sets the overwrite mode to a specific state (when given an argument).
`cm.isReadOnly() → boolean`
  Tells you whether the editor's content can be edited by the user.
`doc.lineSeparator()`
  Returns the preferred line separator string for this document, as per the option by the same name. When that option is `null`, the string `"\n"` is returned.
`cm.execCommand(name: string)`
  Runs the command with the given name on the editor.
`doc.posFromIndex(index: integer) → {line, ch}`
  Calculates and returns a `{line, ch}` object for a zero-based `index` who's value is relative to the start of the editor's text. If the `index` is out of range of the text then the returned object is clipped to start or end of the text respectively.
`doc.indexFromPos(object: {line, ch}) → integer`
  The reverse of `posFromIndex`.
`cm.focus()`
  Give the editor focus.
`cm.phrase(text: string) → string`
  Allow the given string to be translated with the `phrases` option.
`cm.getInputField() → Element`
  Returns the input field for the editor. Will be a textarea or an editable div, depending on the value of the `inputStyle` option.
`cm.getWrapperElement() → Element`
  Returns the DOM node that represents the editor, and controls its size. Remove this from your tree to delete an editor instance.
`cm.getScrollerElement() → Element`
  Returns the DOM node that is responsible for the scrolling of the editor.
`cm.getGutterElement() → Element`
  Fetches the DOM node that contains the editor gutters.

### Static properties

The `CodeMirror` object itself provides several useful properties.

`CodeMirror.version: string`
  It contains a string that indicates the version of the library. This is a triple of integers `"major.minor.patch"`, where `patch` is zero for releases, and something else (usually one) for dev snapshots.
`CodeMirror.fromTextArea(textArea: TextAreaElement, ?config: object)`
  This method provides another way to initialize an editor. It takes a textarea DOM node as first argument and an optional configuration object as second. It will replace the textarea with a CodeMirror instance, and wire up the form of that textarea (if any) to make sure the editor contents are put into the textarea when the form is submitted. The text in the textarea will provide the content for the editor. A CodeMirror instance created this way has three additional methods:
  `cm.save()`
    Copy the content of the editor into the textarea.
  `cm.toTextArea()`
    Remove the editor, and restore the original textarea (with the editor's current content). If you dynamically create and destroy editors made with `fromTextArea`, without destroying the form they are part of, you should make sure to call `toTextArea` to remove the editor, or its `"submit"` handler on the form will cause a memory leak.
  `cm.getTextArea() → TextAreaElement`
    Returns the textarea that the instance was based on.
`CodeMirror.defaults: object`
  An object containing default values for all options. You can assign to its properties to modify defaults (though this won't affect editors that have already been created).
`CodeMirror.defineExtension(name: string, value: any)`
  If you want to define extra methods in terms of the CodeMirror API, it is possible to use `defineExtension`. This will cause the given value (usually a method) to be added to all CodeMirror instances created from then on.
`CodeMirror.defineDocExtension(name: string, value: any)`
  Like `defineExtension`, but the method will be added to the interface for `Doc` objects instead.
`CodeMirror.defineOption(name: string, default: any, updateFunc: function)`
  Similarly, `defineOption` can be used to define new options for CodeMirror. The `updateFunc` will be called with the editor instance and the new value when an editor is initialized, and whenever the option is modified through `setOption`.
`CodeMirror.defineInitHook(func: function)`
  If your extension just needs to run some code whenever a CodeMirror instance is initialized, use `CodeMirror.defineInitHook`. Give it a function as its only argument, and from then on, that function will be called (with the instance as argument) whenever a new CodeMirror instance is initialized.
`CodeMirror.registerHelper(type: string, name: string, value: helper)`
  Registers a helper value with the given `name` in the given namespace (`type`). This is used to define functionality that may be looked up by mode. Will create (if it doesn't already exist) a property on the `CodeMirror` object for the given `type`, pointing to an object that maps names to values. I.e. after doing `CodeMirror.registerHelper("hint", "foo", myFoo)`, the value `CodeMirror.hint.foo` will point to `myFoo`.
`CodeMirror.registerGlobalHelper(type: string, name: string, predicate: fn(mode, CodeMirror), value: helper)`
  Acts like `registerHelper`, but also registers this helper as 'global', meaning that it will be included by `getHelpers` whenever the given `predicate` returns true when called with the local mode and editor.
`CodeMirror.Pos(line: integer, ?ch: integer, ?sticky: string)`
  A constructor for the objects that are used to represent positions in editor documents. `sticky` defaults to null, but can be set to `"before"` or `"after"` to make the position explicitly associate with the character before or after it.
`CodeMirror.changeEnd(change: object) → {line, ch}`
  Utility function that computes an end position from a change (an object with `from`, `to`, and `text` properties, as passed to various event handlers). The returned position will be the end of the changed range, after the change is applied.
`CodeMirror.countColumn(line: string, index: number, tabSize: number) → number`
  Find the column position at a given string index using a given tabsize.

## Addons

The `addon` directory in the distribution contains a number of reusable components that implement extra editor functionality (on top of extension functions like `defineOption`, `defineExtension`, and `registerHelper`). In brief, they are:

`dialog/dialog.js`
  Provides a very simple way to query users for text input. Adds the `openDialog(template, callback, options) → closeFunction` method to CodeMirror instances, which can be called with an HTML fragment or a detached DOM node that provides the prompt (should include an `input` or `button` tag), and a callback function that is called when the user presses enter. It returns a function `closeFunction` which, if called, will close the dialog immediately. `openDialog` takes the following options:
  `closeOnEnter: bool`
    If true, the dialog will be closed when the user presses enter in the input. Defaults to `true`.
  `closeOnBlur: bool`
    Determines whether the dialog is closed when it loses focus. Defaults to `true`.
  `onKeyDown: fn(event: KeyboardEvent, value: string, close: fn()) → bool`
    An event handler that will be called whenever `keydown` fires in the dialog's input. If your callback returns `true`, the dialog will not do any further processing of the event.
  `onKeyUp: fn(event: KeyboardEvent, value: string, close: fn()) → bool`
    Same as `onKeyDown` but for the `keyup` event.
  `onInput: fn(event: InputEvent, value: string, close: fn()) → bool`
    Same as `onKeyDown` but for the `input` event.
  `onClose: fn(instance)`:
    A callback that will be called after the dialog has been closed and removed from the DOM. No return value.

  Also adds an `openNotification(template, options) → closeFunction` function that simply shows an HTML fragment as a notification at the top of the editor. It takes a single option: `duration`, the amount of time after which the notification will be automatically closed. If `duration` is zero, the dialog will not be closed automatically.

  Depends on `addon/dialog/dialog.css`.

`search/searchcursor.js`
  Adds the `getSearchCursor(query, start, options) → cursor` method to CodeMirror instances, which can be used to implement search/replace functionality. `query` can be a regular expression or a string. `start` provides the starting position of the search. It can be a `{line, ch}` object, or can be left off to default to the start of the document. `options` is an optional object, which can contain the property `caseFold: false` to disable case folding when matching a string, or the property `multiline: disable` to disable multi-line matching for regular expressions (which may help performance). A search cursor has the following methods:
  `findNext() → boolean`
  `findPrevious() → boolean`
    Search forward or backward from the current position. The return value indicates whether a match was found. If matching a regular expression, the return value will be the array returned by the `match` method, in case you want to extract matched groups.
  `from() → {line, ch}`
  `to() → {line, ch}`
    These are only valid when the last call to `findNext` or `findPrevious` did not return false. They will return `{line, ch}` objects pointing at the start and end of the match.
  `replace(text: string, ?origin: string)`
    Replaces the currently found match with the given text and adjusts the cursor position to reflect the replacement.
`search/search.js`
  Implements the search commands. CodeMirror has keys bound to these by default, but will not do anything with them unless an implementation is provided. Depends on `searchcursor.js`, and will make use of `openDialog` when available to make prompting for search queries less ugly.
`search/jump-to-line.js`
  Implements a `jumpToLine` command and binding `Alt-G` to it. Accepts `linenumber`, `+/-linenumber`, `line:char`, `scroll%` and `:linenumber` formats. This will make use of `openDialog` when available to make prompting for line number neater.
`search/matchesonscrollbar.js`
  Adds a `showMatchesOnScrollbar` method to editor instances, which should be given a query (string or regular expression), optionally a case-fold flag (only applicable for strings), and optionally a class name (defaults to `CodeMirror-search-match`) as arguments. When called, matches of the given query will be displayed on the editor's vertical scrollbar. The method returns an object with a `clear` method that can be called to remove the matches. Depends on the `annotatescrollbar` addon, and the `matchesonscrollbar.css` file provides a default (transparent yellowish) definition of the CSS class applied to the matches. Note that the matches are only perfectly aligned if your scrollbar does not have buttons at the top and bottom. You can use the `simplescrollbar` addon to make sure of this. If this addon is loaded, the `search` addon will automatically use it.
`edit/matchbrackets.js`
  Defines an option `matchBrackets` which, when set to true or an options object, causes matching brackets to be highlighted whenever the cursor is next to them. It also adds a method `matchBrackets` that forces this to happen once, and a method `findMatchingBracket` that can be used to run the bracket-finding algorithm that this uses internally. It takes a start position and an optional config object. By default, it will find the match to a matchable character either before or after the cursor (preferring the one before), but you can control its behavior with these options:
  `afterCursor`
    Only use the character after the start position, never the one before it.
  `strict`
    Causes only matches where both brackets are at the same side of the start position to be considered.
  `maxScanLines`
    Stop after scanning this amount of lines without a successful match. Defaults to 1000.
  `maxScanLineLength`
    Ignore lines longer than this. Defaults to 10000.
  `maxHighlightLineLength`
    Don't highlight a bracket in a line longer than this. Defaults to 1000.
`edit/closebrackets.js`
  Defines an option `autoCloseBrackets` that will auto-close brackets and quotes when typed. By default, it'll auto-close `()[]{}''""`, but you can pass it a string similar to that (containing pairs of matching characters), or an object with `pairs` and optionally `explode` properties to customize it. `explode` should be a similar string that gives the pairs of characters that, when enter is pressed between them, should have the second character also moved to its own line. By default, if the active mode has a `closeBrackets` property, that overrides the configuration given in the option. But you can add an `override` property with a truthy value to override mode-specific configuration. Demo here.
`edit/matchtags.js`
  Defines an option `matchTags` that, when enabled, will cause the tags around the cursor to be highlighted (using the `CodeMirror-matchingtag` class). Also defines a command `toMatchingTag`, which you can bind a key to in order to jump to the tag matching the one under the cursor. Depends on the `addon/fold/xml-fold.js` addon. Demo here.
`edit/trailingspace.js`
  Adds an option `showTrailingSpace` which, when enabled, adds the CSS class `cm-trailingspace` to stretches of whitespace at the end of lines. The demo has a nice squiggly underline style for this class.
`edit/closetag.js`
  Defines an `autoCloseTags` option that will auto-close XML tags when '`>`' or '`/`' is typed, and a `closeTag` command that closes the nearest open tag. Depends on the `fold/xml-fold.js` addon. See the demo.
`edit/continuelist.js`
  Markdown specific. Defines a `"newlineAndIndentContinueMarkdownList"` command that can be bound to `enter` to automatically insert the leading characters for continuing a list. See the Markdown mode demo.
`comment/comment.js`
  Addon for commenting and uncommenting code. Adds four methods to CodeMirror instances:
  `toggleComment(?options: object)`
    Tries to uncomment the current selection, and if that fails, line-comments it.
  `lineComment(from: {line, ch}, to: {line, ch}, ?options: object)`
    Set the lines in the given range to be line comments. Will fall back to `blockComment` when no line comment style is defined for the mode.
  `blockComment(from: {line, ch}, to: {line, ch}, ?options: object)`
    Wrap the code in the given range in a block comment. Will fall back to `lineComment` when no block comment style is defined for the mode.
  `uncomment(from: {line, ch}, to: {line, ch}, ?options: object) → boolean`
    Try to uncomment the given range. Returns `true` if a comment range was found and removed, `false` otherwise.
  The `options` object accepted by these methods may have the following properties:
  `blockCommentStart, blockCommentEnd, blockCommentLead, lineComment: string`
    Override the comment string properties of the mode with custom comment strings.
  `padding: string`
    A string that will be inserted after opening and leading markers, and before closing comment markers. Defaults to a single space.
  `commentBlankLines: boolean`
    Whether, when adding line comments, to also comment lines that contain only whitespace.
  `indent: boolean`
    When adding line comments and this is turned on, it will align the comment block to the current indentation of the first line of the block.
  `fullLines: boolean`
    When block commenting, this controls whether the whole lines are indented, or only the precise range that is given. Defaults to `true`.
  The addon also defines a `toggleComment` command, which is a shorthand command for calling `toggleComment` with no options.
`fold/foldcode.js`
  Helps with code folding. Adds a `foldCode` method to editor instances, which will try to do a code fold starting at the given line, or unfold the fold that is already present. The method takes as first argument the position that should be folded (may be a line number or a `Pos`), and as second optional argument either a range-finder function, or an options object, supporting the following properties:
  `rangeFinder: fn(CodeMirror, Pos)`
    The function that is used to find foldable ranges. If this is not directly passed, it will default to `CodeMirror.fold.auto`, which uses `getHelpers` with a `"fold"` type to find folding functions appropriate for the local mode. There are files in the `addon/fold/` directory providing `CodeMirror.fold.brace`, which finds blocks in brace languages (JavaScript, C, Java, etc), `CodeMirror.fold.indent`, for languages where indentation determines block structure (Python, Haskell), and `CodeMirror.fold.xml`, for XML-style languages, and `CodeMirror.fold.comment`, for folding comment blocks.
  `widget: string | Element | fn(from: Pos, to: Pos) → string|Element`
    The widget to show for folded ranges. Can be either a string, in which case it'll become a span with class `CodeMirror-foldmarker`, or a DOM node. To dynamically generate the widget, this can be a function that returns a string or DOM node, which will then render as described. The function will be invoked with parameters identifying the range to be folded.
  `scanUp: boolean`
    When true (default is false), the addon will try to find foldable ranges on the lines above the current one if there isn't an eligible one on the given line.
  `minFoldSize: integer`
    The minimum amount of lines that a fold should span to be accepted. Defaults to 0, which also allows single-line folds.
  See the demo for an example.
`fold/foldgutter.js`
  Provides an option `foldGutter`, which can be used to create a gutter with markers indicating the blocks that can be folded. Create a gutter using the `gutters` option, giving it the class `CodeMirror-foldgutter` or something else if you configure the addon to use a different class, and this addon will show markers next to folded and foldable blocks, and handle clicks in this gutter. Note that CSS styles should be applied to make the gutter, and the fold markers within it, visible. A default set of CSS styles are available in: `addon/fold/foldgutter.css` . The option can be either set to `true`, or an object containing the following optional option fields:
  `gutter: string`
    The CSS class of the gutter. Defaults to `"CodeMirror-foldgutter"`. You will have to style this yourself to give it a width (and possibly a background). See the default gutter style rules above.
  `indicatorOpen: string | Element`
    A CSS class or DOM element to be used as the marker for open, foldable blocks. Defaults to `"CodeMirror-foldgutter-open"`.
  `indicatorFolded: string | Element`
    A CSS class or DOM element to be used as the marker for folded blocks. Defaults to `"CodeMirror-foldgutter-folded"`.
  `rangeFinder: fn(CodeMirror, Pos)`
    The range-finder function to use when determining whether something can be folded. When not given, `CodeMirror.fold.auto` will be used as default.
  The `foldOptions` editor option can be set to an object to provide an editor-wide default configuration. Demo here.
`runmode/runmode.js`
  Can be used to run a CodeMirror mode over text without actually opening an editor instance. See the demo for an example. There are alternate versions of the file available for running stand-alone (without including all of CodeMirror) and for running under node.js (see `bin/source-highlight` for an example of using the latter).
`runmode/colorize.js`
  Provides a convenient way to syntax-highlight code snippets in a webpage. Depends on the `runmode` addon (or its standalone variant). Provides a `CodeMirror.colorize` function that can be called with an array (or other array-ish collection) of DOM nodes that represent the code snippets. By default, it'll get all `pre` tags. Will read the `data-lang` attribute of these nodes to figure out their language, and syntax-color their content using the relevant CodeMirror mode (you'll have to load the scripts for the relevant modes yourself). A second argument may be provided to give a default mode, used when no language attribute is found for a node. Used in this manual to highlight example code.
`mode/overlay.js`
  Mode combinator that can be used to extend a mode with an 'overlay' — a secondary mode is run over the stream, along with the base mode, and can color specific pieces of text without interfering with the base mode. Defines `CodeMirror.overlayMode`, which is used to create such a mode. See this demo for a detailed example.
`mode/multiplex.js`
  Mode combinator that can be used to easily 'multiplex' between several modes. Defines `CodeMirror.multiplexingMode` which, when given as first argument a mode object, and as other arguments any number of `{open, close, mode [, delimStyle, innerStyle, parseDelimiters]}` objects, will return a mode object that starts parsing using the mode passed as first argument, but will switch to another mode as soon as it encounters a string that occurs in one of the `open` fields of the passed objects. When in a sub-mode, it will go back to the top mode again when the `close` string is encountered. Pass `"\n"` for `open` or `close` if you want to switch on a blank line.
  - When `delimStyle` is specified, it will be the token style returned for the delimiter tokens (as well as `[delimStyle]-open` on the opening token and `[delimStyle]-close` on the closing token).
  - When `innerStyle` is specified, it will be the token style added for each inner mode token.
  - When `parseDelimiters` is true, the content of the delimiters will also be passed to the inner mode. (And `delimStyle` is ignored.)
  The outer mode will not see the content between the delimiters. See this demo for an example.
`hint/show-hint.js`
  Provides a framework for showing autocompletion hints. Defines `editor.showHint`, which takes an optional options object, and pops up a widget that allows the user to select a completion. Finding hints is done with a hinting functions (the `hint` option), which is a function that take an editor instance and options object, and return a `{list, from, to}` object, where `list` is an array of strings or objects (the completions), and `from` and `to` give the start and end of the token that is being completed as `{line, ch}` objects. An optional `selectedHint` property (an integer) can be added to the completion object to control the initially selected hint.
  If no hinting function is given, the addon will use `CodeMirror.hint.auto`, which calls `getHelpers` with the `"hint"` type to find applicable hinting functions, and tries them one by one. If that fails, it looks for a `"hintWords"` helper to fetch a list of completable words for the mode, and uses `CodeMirror.hint.fromList` to complete from those.
  When completions aren't simple strings, they should be objects with the following properties:
  `text: string`
    The completion text. This is the only required property.
  `displayText: string`
    The text that should be displayed in the menu.
  `className: string`
    A CSS class name to apply to the completion's line in the menu.
  `render: fn(Element, self, data)`
    A method used to create the DOM structure for showing the completion by appending it to its first argument.
  `hint: fn(CodeMirror, self, data)`
    A method used to actually apply the completion, instead of the default behavior.
  `from: {line, ch}`
    Optional `from` position that will be used by `pick()` instead of the global one passed with the full list of completions.
  `to: {line, ch}`
    Optional `to` position that will be used by `pick()` instead of the global one passed with the full list of completions.
  The plugin understands the following options, which may be either passed directly in the argument to `showHint`, or provided by setting an `hintOptions` editor option to an object (the former takes precedence). The options object will also be passed along to the hinting function, which may understand additional options.
  `hint: function`
    A hinting function, as specified above. It is possible to set the `async` property on a hinting function to true, in which case it will be called with arguments `(cm, callback, ?options)`, and the completion interface will only be popped up when the hinting function calls the callback, passing it the object holding the completions. The hinting function can also return a promise, and the completion interface will only be popped when the promise resolves. By default, hinting only works when there is no selection. You can give a hinting function a `supportsSelection` property with a truthy value to indicate that it supports selections.
  `completeSingle: boolean`
    Determines whether, when only a single completion is available, it is completed without showing the dialog. Defaults to true.
  `alignWithWord: boolean`
    Whether the pop-up should be horizontally aligned with the start of the word (true, default), or with the cursor (false).
  `closeOnUnfocus: boolean`
    When enabled (which is the default), the pop-up will close when the editor is unfocused.
  `customKeys: keymap`
    Allows you to provide a custom key map of keys to be active when the pop-up is active. The handlers will be called with an extra argument, a handle to the completion menu, which has `moveFocus(n)`, `setFocus(n)`, `pick()`, and `close()` methods (see the source for details), that can be used to change the focused element, pick the current element or close the menu. Additionally `menuSize()` can give you access to the size of the current dropdown menu, `length` give you the number of available completions, and `data` give you full access to the completion returned by the hinting function.
  `extraKeys: keymap`
    Like `customKeys` above, but the bindings will be added to the set of default bindings, instead of replacing them.
  The following events will be fired on the completions object during completion:
  `"shown" ()`
    Fired when the pop-up is shown.
  `"select" (completion, Element)`
    Fired when a completion is selected. Passed the completion value (string or object) and the DOM node that represents it in the menu.
  `"pick" (completion)`
    Fired when a completion is picked. Passed the completion value (string or object).
  `"close" ()`
    Fired when the completion is finished.
  This addon depends on styles from `addon/hint/show-hint.css`. Check out the demo for an example.
`hint/javascript-hint.js`
  Defines a simple hinting function for JavaScript (`CodeMirror.hint.javascript`) and CoffeeScript (`CodeMirror.hint.coffeescript`) code. This will simply use the JavaScript environment that the editor runs in as a source of information about objects and their properties.
`hint/xml-hint.js`
  Defines `CodeMirror.hint.xml`, which produces hints for XML tagnames, attribute names, and attribute values, guided by a `schemaInfo` option (a property of the second argument passed to the hinting function, or the third argument passed to `CodeMirror.showHint`).
  The schema info should be an object mapping tag names to information about these tags, with optionally a `"!top"` property containing a list of the names of valid top-level tags. The values of the properties should be objects with optional properties `children` (an array of valid child element names, omit to simply allow all tags to appear) and `attrs` (an object mapping attribute names to `null` for free-form attributes, and an array of valid values for restricted attributes).
  The hint options accept an additional property:
  `matchInMiddle: boolean`
    Determines whether typed characters are matched anywhere in completions, not just at the beginning. Defaults to false.
  Demo here.
`hint/html-hint.js`
  Provides schema info to the xml-hint addon for HTML documents. Defines a schema object `CodeMirror.htmlSchema` that you can pass to as a `schemaInfo` option, and a `CodeMirror.hint.html` hinting function that automatically calls `CodeMirror.hint.xml` with this schema data. See the demo.
`hint/css-hint.js`
  A hinting function for CSS, SCSS, or LESS code. Defines `CodeMirror.hint.css`.
`hint/anyword-hint.js`
  A very simple hinting function (`CodeMirror.hint.anyword`) that simply looks for words in the nearby code and completes to those. Takes two optional options, `word`, a regular expression that matches words (sequences of one or more character), and `range`, which defines how many lines the addon should scan when completing (defaults to 500).
`hint/sql-hint.js`
  A simple SQL hinter. Defines `CodeMirror.hint.sql`. Takes two optional options, `tables`, a object with table names as keys and array of respective column names as values, and `defaultTable`, a string corresponding to a table name in `tables` for autocompletion.
`search/match-highlighter.js`
  Adds a `highlightSelectionMatches` option that can be enabled to highlight all instances of a currently selected word. Can be set either to true or to an object containing the following options: `minChars`, for the minimum amount of selected characters that triggers a highlight (default 2), `style`, for the style to be used to highlight the matches (default `"matchhighlight"`, which will correspond to CSS class `cm-matchhighlight`), `trim`, which controls whether whitespace is trimmed from the selection, and `showToken` which can be set to `true` or to a regexp matching the characters that make up a word. When enabled, it causes the current word to be highlighted when nothing is selected (defaults to off). Demo here.
`lint/lint.js`
  Defines an interface component for showing linting warnings, with pluggable warning sources (see `html-lint.js`, `json-lint.js`, `javascript-lint.js`, `coffeescript-lint.js`, and `css-lint.js` in the same directory). Defines a `lint` option that can be set to an annotation source (for example `CodeMirror.lint.javascript`), to an options object (in which case the `getAnnotations` field is used as annotation source), or simply to `true`. When no annotation source is specified, `getHelper` with type `"lint"` is used to find an annotation function. An annotation source function should, when given a document string, an options object, and an editor instance, return an array of `{message, severity, from, to}` objects representing problems. When the function has an `async` property with a truthy value, it will be called with an additional second argument, which is a callback to pass the array to. The linting function can also return a promise, in that case the linter will only be executed when the promise resolves. By default, the linter will run (debounced) whenever the document is changed. You can pass a `lintOnChange: false` option to disable that. You can pass a `selfContain: true` option to render the tooltip inside the editor instance. Depends on `addon/lint/lint.css`. A demo can be found here.
`selection/mark-selection.js`
  Causes the selected text to be marked with the CSS class `CodeMirror-selectedtext` when the `styleSelectedText` option is enabled. Useful to change the colour of the selection (in addition to the background), like in this demo.
`selection/active-line.js`
  Defines a `styleActiveLine` option that, when enabled, gives the wrapper of the line that contains the cursor the class `CodeMirror-activeline`, adds a background with the class `CodeMirror-activeline-background`, and adds the class `CodeMirror-activeline-gutter` to the line's gutter space is enabled. The option's value may be a boolean or an object specifying the following options:
  `nonEmpty: bool`
    Controls whether single-line selections, or just cursor selections, are styled. Defaults to false (only cursor selections).
  See the demo.
`selection/selection-pointer.js`
  Defines a `selectionPointer` option which you can use to control the mouse cursor appearance when hovering over the selection. It can be set to a string, like `"pointer"`, or to true, in which case the `"default"` (arrow) cursor will be used. You can see a demo here.
`mode/loadmode.js`
  Defines a `CodeMirror.requireMode(modename, callback)` function that will try to load a given mode and call the callback when it succeeded. You'll have to set `CodeMirror.modeURL` to a string that mode paths can be constructed from, for example `"mode/%N/%N.js"`—the `%N`'s will be replaced with the mode name. Also defines `CodeMirror.autoLoadMode(instance, mode)`, which will ensure the given mode is loaded and cause the given editor instance to refresh its mode when the loading succeeded. See the demo.
`mode/meta.js`
  Provides meta-information about all the modes in the distribution in a single file. Defines `CodeMirror.modeInfo`, an array of objects with `{name, mime, mode}` properties, where `name` is the human-readable name, `mime` the MIME type, and `mode` the name of the mode file that defines this MIME. There are optional properties `mimes`, which holds an array of MIME types for modes with multiple MIMEs associated, and `ext`, which holds an array of file extensions associated with this mode. Four convenience functions, `CodeMirror.findModeByMIME`, `CodeMirror.findModeByExtension`, `CodeMirror.findModeByFileName` and `CodeMirror.findModeByName` are provided, which return such an object given a MIME, extension, file name or mode name string. Note that, for historical reasons, this file resides in the top-level `mode` directory, not under `addon`. Demo.
`comment/continuecomment.js`
  Adds a `continueComments` option, which sets whether the editor will make the next line continue a comment when you press Enter inside a comment block. Can be set to a boolean to enable/disable this functionality. Set to a string, it will continue comments using a custom shortcut. Set to an object, it will use the `key` property for a custom shortcut and the boolean `continueLineComment` property to determine whether single-line comments should be continued (defaulting to `true`).
`display/placeholder.js`
  Adds a `placeholder` option that can be used to make content appear in the editor when it is empty and not focused. It can hold either a string or a DOM node. Also gives the editor a `CodeMirror-empty` CSS class whenever it doesn't contain any text. See the demo.
`display/fullscreen.js`
  Defines an option `fullScreen` that, when set to `true`, will make the editor full-screen (as in, taking up the whole browser window). Depends on `fullscreen.css`. Demo here.
`display/autorefresh.js`
  This addon can be useful when initializing an editor in a hidden DOM node, in cases where it is difficult to call `refresh` when the editor becomes visible. It defines an option `autoRefresh` which you can set to true to ensure that, if the editor wasn't visible on initialization, it will be refreshed the first time it becomes visible. This is done by polling every 250 milliseconds (you can pass a value like `{delay: 500}` as the option value to configure this). Note that this addon will only refresh the editor once when it first becomes visible, and won't take care of further restyling and resizing.
`scroll/simplescrollbars.js`
  Defines two additional scrollbar models, `"simple"` and `"overlay"` (see demo) that can be selected with the `scrollbarStyle` option. Depends on `simplescrollbars.css`, which can be further overridden to style your own scrollbars.
`scroll/annotatescrollbar.js`
  Provides functionality for showing markers on the scrollbar to call out certain parts of the document. Adds a method `annotateScrollbar` to editor instances that can be called, with a CSS class name as argument, to create a set of annotations. The method returns an object whose `update` method can be called with a sorted array of `{from: Pos, to: Pos}` objects marking the ranges to be highlighted. To detach the annotations, call the object's `clear` method.
`display/rulers.js`
  Adds a `rulers` option, which can be used to show one or more vertical rulers in the editor. The option, if defined, should be given an array of `{column [, className, color, lineStyle, width]}` objects or numbers (which indicate a column). The ruler will be displayed at the column indicated by the number or the `column` property. The `className` property can be used to assign a custom style to a ruler. Demo here.
`display/panel.js`
  Defines an `addPanel` method for CodeMirror instances, which places a DOM node above or below an editor, and shrinks the editor to make room for the node. The method takes as first argument as DOM node, and as second an optional options object. The `Panel` object returned by this method has a `clear` method that is used to remove the panel, and a `changed` method that can be used to notify the addon when the size of the panel's DOM node has changed.
  The method accepts the following options:
  `position: string`
    Controls the position of the newly added panel. The following values are recognized:
    `top (default)`
      Adds the panel at the very top.
    `after-top`
      Adds the panel at the bottom of the top panels.
    `bottom`
      Adds the panel at the very bottom.
    `before-bottom`
      Adds the panel at the top of the bottom panels.
  `before: Panel`
    The new panel will be added before the given panel.
  `after: Panel`
    The new panel will be added after the given panel.
  `replace: Panel`
    The new panel will replace the given panel.
  `stable: bool`
    Whether to scroll the editor to keep the text's vertical position stable, when adding a panel above it. Defaults to false.
  When using the `after`, `before` or `replace` options, if the panel doesn't exists or has been removed, the value of the `position` option will be used as a fallback.
  A demo of the addon is available here.
`wrap/hardwrap.js`
  Addon to perform hard line wrapping/breaking for paragraphs of text. Adds these methods to editor instances:
  `wrapParagraph(?pos: {line, ch}, ?options: object)`
    Wraps the paragraph at the given position. If `pos` is not given, it defaults to the cursor position.
  `wrapRange(from: {line, ch}, to: {line, ch}, ?options: object)`
    Wraps the given range as one big paragraph.
  `wrapParagraphsInRange(from: {line, ch}, to: {line, ch}, ?options: object)`
    Wraps the paragraphs in (and overlapping with) the given range individually.
  The following options are recognized:
  `paragraphStart, paragraphEnd: RegExp`
    Blank lines are always considered paragraph boundaries. These options can be used to specify a pattern that causes lines to be considered the start or end of a paragraph.
  `column: number`
    The column to wrap at. Defaults to 80.
  `wrapOn: RegExp`
    A regular expression that matches only those two-character strings that allow wrapping. By default, the addon wraps on whitespace and after dash characters.
  `killTrailingSpace: boolean`
    Whether trailing space caused by wrapping should be preserved, or deleted. Defaults to true.
  A demo of the addon is available here.
`merge/merge.js`
  Implements an interface for merging changes, using either a 2-way or a 3-way view. The `CodeMirror.MergeView` constructor takes arguments similar to the `CodeMirror` constructor, first a node to append the interface to, and then an options object. Options are passed through to the editors inside the view. These extra options are recognized:
  `origLeft` and `origRight: string`
    If given these provide original versions of the document, which will be shown to the left and right of the editor in non-editable CodeMirror instances. The merge interface will highlight changes between the editable document and the original(s). To create a 2-way (as opposed to 3-way) merge view, provide only one of them.
  `revertButtons: boolean`
    Determines whether buttons that allow the user to revert changes are shown. Defaults to true.
  `revertChunk: fn(mv: MergeView, from: CodeMirror, fromStart: Pos, fromEnd: Pos, to: CodeMirror, toStart: Pos, toEnd: Pos)`
    Can be used to define custom behavior when the user reverts a changed chunk.
  `connect: string`
    Sets the style used to connect changed chunks of code. By default, connectors are drawn. When this is set to `"align"`, the smaller chunk is padded to align with the bigger chunk instead.
  `collapseIdentical: boolean|number`
    When true (default is false), stretches of unchanged text will be collapsed. When a number is given, this indicates the amount of lines to leave visible around such stretches (which defaults to 2).
  `allowEditingOriginals: boolean`
    Determines whether the original editor allows editing. Defaults to false.
  `showDifferences: boolean`
    When true (the default), changed pieces of text are highlighted.
  `chunkClassLocation: string|Array`
    By default the chunk highlights are added using `addLineClass` with "background". Override this to customize it to be any valid `where` parameter or an Array of valid `where` parameters.
  The addon also defines commands `"goNextDiff"` and `"goPrevDiff"` to quickly jump to the next changed chunk. Demo here.
`tern/tern.js`
  Provides integration with the Tern JavaScript analysis engine, for completion, definition finding, and minor refactoring help. See the demo for a very simple integration. For more involved scenarios, see the comments at the top of the addon and the implementation of the (multi-file) demonstration on the Tern website.

## Writing CodeMirror Modes

Modes typically consist of a single JavaScript file. This file defines, in the simplest case, a lexer (tokenizer) for your language—a function that takes a character stream as input, advances it past a token, and returns a style for that token. More advanced modes can also handle indentation for the language.

This section describes the low-level mode interface. Many modes are written directly against this, since it offers a lot of control, but for a quick mode definition, you might want to use the simple mode addon.

The mode script should call `CodeMirror.defineMode` to register itself with CodeMirror. This function takes two arguments. The first should be the name of the mode, for which you should use a lowercase string, preferably one that is also the name of the files that define the mode (i.e. `"xml"` is defined in `xml.js`). The second argument should be a function that, given a CodeMirror configuration object (the thing passed to the `CodeMirror` function) and an optional mode configuration object (as in the `mode` option), returns a mode object.

Typically, you should use this second argument to `defineMode` as your module scope function (modes should not leak anything into the global scope!), i.e. write your whole mode inside this function.

The main responsibility of a mode script is parsing the content of the editor. Depending on the language and the amount of functionality desired, this can be done in really easy or extremely complicated ways. Some parsers can be stateless, meaning that they look at one element (token) of the code at a time, with no memory of what came before. Most, however, will need to remember something. This is done by using a state object, which is an object that is always passed when reading a token, and which can be mutated by the tokenizer.

Modes that use a state must define a `startState` method on their mode object. This is a function of no arguments that produces a state object to be used at the start of a document.

The most important part of a mode object is its `token(stream, state)` method. All modes must define this method. It should read one token from the stream it is given as an argument, optionally update its state, and return a style string, or `null` for tokens that do not have to be styled. For your styles, you are encouraged to use the 'standard' names defined in the themes (without the `cm-` prefix). If that fails, it is also possible to come up with your own and write your own CSS theme file.

A typical token string would be `"variable"` or `"comment"`. Multiple styles can be returned (separated by spaces), for example `"string error"` for a thing that looks like a string but is invalid somehow (say, missing its closing quote). When a style is prefixed by `"line-"` or `"line-background-"`, the style will be applied to the whole line, analogous to what the `addLineClass` method does—styling the `"text"` in the simple case, and the `"background"` element when `"line-background-"` is prefixed.

The stream object that's passed to `token` encapsulates a line of code (tokens may never span lines) and our current position in that line. It has the following API:

`eol() → boolean`
  Returns true only if the stream is at the end of the line.
`sol() → boolean`
  Returns true only if the stream is at the start of the line.
`peek() → string`
  Returns the next character in the stream without advancing it. Will return a `null` at the end of the line.
`next() → string`
  Returns the next character in the stream and advances it. Also returns `null` when no more characters are available.
`eat(match: string|regexp|function(char: string) → boolean) → string`
  `match` can be a character, a regular expression, or a function that takes a character and returns a boolean. If the next character in the stream 'matches' the given argument, it is consumed and returned. Otherwise, `undefined` is returned.
`eatWhile(match: string|regexp|function(char: string) → boolean) → boolean`
  Repeatedly calls `eat` with the given argument, until it fails. Returns true if any characters were eaten.
`eatSpace() → boolean`
  Shortcut for `eatWhile` when matching white-space.
`skipToEnd()`
  Moves the position to the end of the line.
`skipTo(str: string) → boolean`
  Skips to the start of the next occurrence of the given string, if found on the current line (doesn't advance the stream if the string does not occur on the line). Returns true if the string was found.
`match(pattern: string, ?consume: boolean, ?caseFold: boolean) → boolean`
`match(pattern: regexp, ?consume: boolean) → array<string>`
  Act like a multi-character `eat`—if `consume` is true or not given—or a look-ahead that doesn't update the stream position—if it is false. `pattern` can be either a string or a regular expression starting with `^`. When it is a string, `caseFold` can be set to true to make the match case-insensitive. When successfully matching a regular expression, the returned value will be the array returned by `match`, in case you need to extract matched groups.
`backUp(n: integer)`
  Backs up the stream `n` characters. Backing it up further than the start of the current token will cause things to break, so be careful.
`column() → integer`
  Returns the column (taking into account tabs) at which the current token starts.
`indentation() → integer`
  Tells you how far the current line has been indented, in spaces. Corrects for tab characters.
`current() → string`
  Get the string between the start of the current token and the current stream position.
`lookAhead(n: number) → ?string`
  Get the line `n` (>0) lines after the current one, in order to scan ahead across line boundaries. Note that you want to do this carefully, since looking far ahead will make mode state caching much less effective.
`baseToken() → ?{type: ?string, size: number}`
  Modes added through `addOverlay` (and only such modes) can use this method to inspect the current token produced by the underlying mode.

By default, blank lines are simply skipped when tokenizing a document. For languages that have significant blank lines, you can define a `blankLine(state)` method on your mode that will get called whenever a blank line is passed over, so that it can update the parser state.

Because state object are mutated, and CodeMirror needs to keep valid versions of a state around so that it can restart a parse at any line, copies must be made of state objects. The default algorithm used is that a new state object is created, which gets all the properties of the old object. Any properties which hold arrays get a copy of these arrays (since arrays tend to be used as mutable stacks). When this is not correct, for example because a mode mutates non-array properties of its state object, a mode object should define a `copyState` method, which is given a state and should return a safe copy of that state.

If you want your mode to provide smart indentation (through the `indentLine` method and the `indentAuto` and `newlineAndIndent` commands, to which keys can be bound), you must define an `indent(state, textAfter)` method on your mode object.

The indentation method should inspect the given state object, and optionally the `textAfter` string, which contains the text on the line that is being indented, and return an integer, the amount of spaces to indent. It should usually take the `indentUnit` option into account. An indentation method may return `CodeMirror.Pass` to indicate that it could not come up with a precise indentation.

To work well with the commenting addon, a mode may define `lineComment` (string that starts a line comment), `blockCommentStart`, `blockCommentEnd` (strings that start and end block comments), and `blockCommentLead` (a string to put at the start of continued lines in a block comment). All of these are optional.

Finally, a mode may define either an `electricChars` or an `electricInput` property, which are used to automatically reindent the line when certain patterns are typed and the `electricChars` option is enabled. `electricChars` may be a string, and will trigger a reindent whenever one of the characters in that string are typed. Often, it is more appropriate to use `electricInput`, which should hold a regular expression, and will trigger indentation when the part of the line before the cursor matches the expression. It should usually end with a `$` character, so that it only matches when the indentation-changing pattern was just typed, not when something was typed after the pattern.

So, to summarize, a mode must provide a `token` method, and it may provide `startState`, `copyState`, and `indent` methods. For an example of a trivial mode, see the diff mode, for a more involved example, see the C-like mode.

Sometimes, it is useful for modes to nest—to have one mode delegate work to another mode. An example of this kind of mode is the mixed-mode HTML mode. To implement such nesting, it is usually necessary to create mode objects and copy states yourself. To create a mode object, there are `CodeMirror.getMode(options, parserConfig)`, where the first argument is a configuration object as passed to the mode constructor function, and the second argument is a mode specification as in the `mode` option. To copy a state object, call `CodeMirror.copyState(mode, state)`, where `mode` is the mode that created the given state.

In a nested mode, it is recommended to add an extra method, `innerMode` which, given a state object, returns a `{state, mode}` object with the inner mode and its state for the current position. These are used by utility scripts such as the tag closer to get context information. Use the `CodeMirror.innerMode` helper function to, starting from a mode and a state, recursively walk down to the innermost mode and state.

To make indentation work properly in a nested parser, it is advisable to give the `startState` method of modes that are intended to be nested an optional argument that provides the base indentation for the block of code. The JavaScript and CSS parser do this, for example, to allow JavaScript and CSS code inside the mixed-mode HTML mode to be properly indented.

It is possible, and encouraged, to associate your mode, or a certain configuration of your mode, with a MIME type. For example, the JavaScript mode associates itself with `text/javascript`, and its JSON variant with `application/json`. To do this, call `CodeMirror.defineMIME(mime, modeSpec)`, where `modeSpec` can be a string or object specifying a mode, as in the `mode` option.

If a mode specification wants to add some properties to the resulting mode object, typically for use with `getHelpers`, it may contain a `modeProps` property, which holds an object. This object's properties will be copied to the actual mode object.

Sometimes, it is useful to add or override mode object properties from external code. The `CodeMirror.extendMode` function can be used to add properties to mode objects produced for a specific mode. Its first argument is the name of the mode, its second an object that specifies the properties that should be added. This is mostly useful to add utilities that can later be looked up through `getMode`.

## VIM Mode API

CodeMirror has a robust VIM mode that attempts to faithfully emulate VIM's most useful features. It can be enabled by including `keymap/vim.js` and setting the `keyMap` option to `"vim"`.

### Configuration

VIM mode accepts configuration options for customizing behavior at run time. These methods can be called at any time and will affect all existing CodeMirror instances unless specified otherwise. The methods are exposed on the `CodeMirror.Vim` object.

`setOption(name: string, value: any, ?cm: CodeMirror, ?cfg: object)`
  Sets the value of a VIM option. `name` should be the name of an option. If `cfg.scope` is not set and `cm` is provided, then sets the global and instance values of the option. Otherwise, sets either the global or instance value of the option depending on whether `cfg.scope` is `global` or `local`.
`getOption(name: string, ?cm: CodeMirror: ?cfg: object)`
  Gets the current value of a VIM option. If `cfg.scope` is not set and `cm` is provided, then gets the instance value of the option, falling back to the global value if not set. If `cfg.scope` is provided, then gets the `global` or `local` value without checking the other.
`map(lhs: string, rhs: string, ?context: string)`
  Maps a key sequence to another key sequence. Implements VIM's `:map` command. To map ; to : in VIM would be `:map ; :`. That would translate to `CodeMirror.Vim.map(';', ':');`. The `context` can be `normal`, `visual`, or `insert`, which correspond to `:nmap`, `:vmap`, and `:imap` respectively.
`mapCommand(keys: string, type: string, name: string, ?args: object, ?extra: object)`
  Maps a key sequence to a `motion`, `operator`, or `action` type command. The args object is passed through to the command when it is invoked by the provided key sequence. `extras.context` can be `normal`, `visual`, or `insert`, to map the key sequence only in the corresponding mode. `extras.isEdit` is applicable only to actions, determining whether it is recorded for replay for the `.` single-repeat command.

### Extending VIM

CodeMirror's VIM mode implements a large subset of VIM's core editing functionality. But since there's always more to be desired, there is a set of APIs for extending VIM's functionality. As with the configuration API, the methods are exposed on `CodeMirror.Vim` and may be called at any time.

`defineOption(name: string, default: any, type: string, ?aliases: array<string>, ?callback: function (?value: any, ?cm: CodeMirror) → ?any)`
  Defines a VIM style option and makes it available to the `:set` command. Type can be `boolean` or `string`, used for validation and by `:set` to determine which syntax to accept. If a `callback` is passed in, VIM does not store the value of the option itself, but instead uses the callback as a setter/getter. If the first argument to the callback is `undefined`, then the callback should return the value of the option. Otherwise, it should set instead. Since VIM options have global and instance values, whether a `CodeMirror` instance is passed in denotes whether the global or local value should be used. Consequently, it's possible for the callback to be called twice for a single `setOption` or `getOption` call. Note that right now, VIM does not support defining buffer-local options that do not have global values. If an option should not have a global value, either always ignore the `cm` parameter in the callback, or always pass in a `cfg.scope` to `setOption` and `getOption`.
`defineMotion(name: string, fn: function(cm: CodeMirror, head: {line, ch}, ?motionArgs: object}) → {line, ch})`
  Defines a motion command for VIM. The motion should return the desired result position of the cursor. `head` is the current position of the cursor. It can differ from `cm.getCursor('head')` if VIM is in visual mode. `motionArgs` is the object passed into `mapCommand()`.
`defineOperator(name: string, fn: function(cm: CodeMirror, ?operatorArgs: object, ranges: array<{anchor, head}>) → ?{line, ch})`
  Defines an operator command, similar to `defineMotion`. `ranges` is the range of text the operator should operate on. If the cursor should be set to a certain position after the operation finishes, it can return a cursor object.
`defineAction(name: string, fn: function(cm: CodeMirror, ?actionArgs: object))`
  Defines an action command, similar to `defineMotion`. Action commands can have arbitrary behavior, making them more flexible than motions and operators, at the loss of orthogonality.
`defineEx(name: string, ?prefix: string, fn: function(cm: CodeMirror, ?params: object))`
  Defines an Ex command, and maps it to `:name`. If a prefix is provided, it, and any prefixed substring of the `name` beginning with the `prefix` can be used to invoke the command. If the `prefix` is falsy, then `name` is used as the prefix. `params.argString` contains the part of the prompted string after the command name. `params.args` is `params.argString` split by whitespace. If the command was prefixed with a `line range`, `params.line` and `params.lineEnd` will be set.