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<!doctype html>
<html>
<head>
<title>CodeMirror: User Manual</title>
<link rel="stylesheet" type="text/css" href="css/docs.css"/>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<style>dl dl {margin: 0;}</style>
</head>
<body>
<h1><span class="logo-braces">{ }</span> <a href="http://codemirror.net/">CodeMirror</a></h1>
<pre class="grey">
<img src="css/baboon.png" class="logo" alt="logo"/>/* User manual and
reference guide */
</pre>
<div class="clear"><div class="leftbig blk">
<h2 id="overview">Overview</h2>
<p>CodeMirror is a code-editor component that can be embedded in
Web pages. It provides <em>only</em> the editor component, no
accompanying buttons
(see <a href="http://www.octolabs.com/javascripts/codemirror-ui/">CodeMirror
UI</a> for a drop-in button bar), auto-completion, or other IDE
functionality. It does provide a rich API on top of which such
functionality can be straightforwardly implemented.</p>
<p>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 few
modes (see the <code>mode/</code> directory), and it isn't hard
to <a href="#modeapi">write new ones</a> for other languages.</p>
<h2 id="usage">Basic Usage</h2>
<p>The easiest way to use CodeMirror is to simply load the script
and style sheet found under <code>lib/</code> in the distribution,
plus the script and style sheet for the mode(s) you want to use.
(See also <a href="compress.html">the compresion helper</a>.) For
example:</p>
<pre><script src="lib/codemirror.js"></script>
<link rel="stylesheet" href="lib/codemirror.css">
<script src="mode/javascript/javascript.js"></script>
<link rel="stylesheet" href="mode/javascript/javascript.css"></pre>
<p>Having done this, an editor instance can be created like
this:</p>
<pre>var myCodeMirror = CodeMirror(document.body);</pre>
<p>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 <code>CodeMirror</code> as a second argument:</p>
<pre>var myCodeMirror = CodeMirror(document.body, {
value: "function myScript(){return 100;}\n",
mode: "javascript"
});</pre>
<p>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 <a href="#config">below</a> for a full discussion of the
configuration options that CodeMirror accepts.</p>
<p>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 <code>CodeMirror</code> 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:</p>
<pre>var myCodeMirror = CodeMirror(function(elt) {
myTextArea.parentNode.replaceChild(myTextArea, elt);
}, {value: myTextArea.value});</pre>
<p>However, for this use case, which is a common way to use
CodeMirror, the library provides a much more powerful
shortcut:</p>
<pre>var myCodeMirror = CodeMirror.fromTextArea(myTextArea);</pre>
<p>This will, among other things, ensure that the textarea's value
is updated when the form (if it is part of a form) is submitted.
See the <a href="#fromTextArea">API reference</a> for a full
description of this method.</p>
<h2 id="config">Configuration</h2>
<p>Both the <code>CodeMirror</code> function and
its <code>fromTextArea</code> method take as second (optional)
argument an object containing configuration options. Any option
not supplied like this will be taken
from <code>CodeMirror.defaults</code>, an object containing the
default options. You can update this object to change the defaults
on your page.</p>
<p>Options are not checked in any way, so setting bogus option
values is bound to lead to odd errors.</p>
<p><em>Note:</em> CodeMirror
2 <a href="internals.html#summary">does not support</a>
line-wrapping. I would have very much liked to support it, but it
combines extremely poorly with the way the editor is
implemented.</p>
<p>These are the supported options:</p>
<dl>
<dt id="option_value"><code>value (string)</code></dt>
<dd>The starting value of the editor.</dd>
<dt id="option_mode"><code>mode (string or object)</code></dt>
<dd>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 <a href="http://en.wikipedia.org/wiki/MIME">MIME</a> type
associated with the mode. Alternatively, it may be an object
containing configuration options for the mode, with
a <code>name</code> property that names the mode (for
example <code>{name: "javascript", json: true}</code>). The demo
pages for each mode contain information about what configuration
parameters the mode supports. You can ask CodeMirror which modes
and MIME types are loaded with
the <code>CodeMirror.listModes</code>
and <code>CodeMirror.listMIMEs</code> functions.</dd>
<dt id="option_indentUnit"><code>indentUnit (integer)</code></dt>
<dd>How many spaces a block (whatever that means in the edited
language) should be indented. The default is 2.</dd>
<dt id="option_indentWithTabs"><code>indentWithTabs (boolean)</code></dt>
<dd>Whether, when indenting, the first N*8 spaces should be
replaced by N tabs. Default is false.</dd>
<dt id="option_tabMode"><code>tabMode (string)</code></dt>
<dd>Determines what happens when the user presses the tab key.
Must be one of the following:
<dl>
<dt><code>"classic" (the default)</code></dt>
<dd>When nothing is selected, insert a tab. Otherwise,
behave like the <code>"shift"</code> mode. (When shift is
held, this behaves like the <code>"indent"</code> mode.)</dd>
<dt><code>"shift"</code></dt>
<dd>Indent all selected lines by
one <a href="#option_indentUnit"><code>indentUnit</code></a>.
If shift was held while pressing tab, un-indent all selected
lines one unit.</dd>
<dt><code>"indent"</code></dt>
<dd>Indent the line the 'correctly', based on its syntactic
context. Only works if the
mode <a href="#indent">supports</a> it.</dd>
<dt><code>"default"</code></dt>
<dd>Do not capture tab presses, let the browser apply its
default behaviour (which usually means it skips to the next
control).</dd>
</dl></dd>
<dt id="option_enterMode"><code>enterMode (string)</code></dt>
<dd>Determines whether and how new lines are indented when the
enter key is pressed. The following modes are supported:
<dl>
<dt><code>"indent" (the default)</code></dt>
<dd>Use the mode's indentation rules to give the new line
the correct indentation.</dd>
<dt><code>"keep"</code></dt>
<dd>Indent the line the same as the previous line.</dd>
<dt><code>"flat"</code></dt>
<dd>Do not indent the new line.</dd>
</dl></dd>
<dt id="option_electricChars"><code>electricChars (boolean)</code></dt>
<dd>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.</dd>
<dt id="option_lineNumbers"><code>lineNumbers (boolean)</code></dt>
<dd>Whether to show line numbers to the left of the editor.</dd>
<dt id="option_firstLineNumber"><code>firstLineNumber (integer)</code></dt>
<dd>At which number to start counting lines. Default is 1.</dd>
<dt id="option_gutter"><code>gutter (boolean)</code></dt>
<dd>Can be used to force a 'gutter' (empty space on the left of
the editor) to be shown even when no line numbers are active.
This is useful for setting <a href="#setMarker">markers</a>.</dd>
<dt id="option_readOnly"><code>readOnly (boolean)</code></dt>
<dd>This disables editing of the editor content by the user.
(Changes through API functions will still be possible.)</dd>
<dt id="option_onChange"><code>onChange (function)</code></dt>
<dd>When given, this function will be called every time the
content of the editor is changed. It will be given the editor
instance as only argument.</dd>
<dt id="option_onCursorActivity"><code>onCursorActivity (function)</code></dt>
<dd>Like <code>onChange</code>, but will also be called when the
cursor moves without any changes being made.</dd>
<dt id="option_onGutterClick"><code>onGutterClick (function)</code></dt>
<dd>When given, will be called whenever the editor gutter (the
line-number area) is clicked. Will be given the editor instance
as first argument, and the (zero-based) number of the line that
was clicked as second argument.</dd>
<dt id="option_onFocus"><code>onFocus, onBlur (function)</code></dt>
<dd>The given functions will be called whenever the editor is
focused or unfocused.</dd>
<dt id="option_onScroll"><code>onScroll (function)</code></dt>
<dd>When given, will be called whenever the editor is
scrolled.</dd>
<dt id="option_matchBrackets"><code>matchBrackets (boolean)</code></dt>
<dd>Determines whether brackets are matched whenever the cursor
is moved next to a bracket.</dd>
<dt id="option_workTime"><code>workTime, workDelay (number)</code></dt>
<dd>Highlighting is done by a pseudo background-thread that will
work for <code>workTime</code> milliseconds, and then use
timeout to sleep for <code>workDelay</code> milliseconds. The
defaults are 200 and 300, you can change these options to make
the highlighting more or less aggressive.</dd>
<dt id="option_undoDepth"><code>undoDepth (integer)</code></dt>
<dd>The maximum number of undo levels that the editor stores.
Defaults to 40.</dd>
<dt id="option_tabindex"><code>tabindex (integer)</code></dt>
<dd>The <a href="http://www.w3.org/TR/html401/interact/forms.html#adef-tabindex">tab
index</a> to assign to the editor. If not given, no tab index
will be assigned.</dd>
<dt id="option_onKeyEvent"><code>onKeyEvent (function)</code></dt>
<dd>This provides a rather low-level hook into CodeMirror's key
handling. If provided, this function will be called on
every <code>keydown</code> and <code>keypress</code> event that
CodeMirror captures. It will be passed two arguments, the editor
instance and the key event. This key event is pretty much the
raw key event, except that a <code>stop()</code> method is
always added to it. You could feed it to, for
example, <code>jQuery.Event</code> to further normalize
it.<br>This function can inspect the key event, and handle it if
it wants to. It may return true to tell CodeMirror to ignore the
event. Be wary that, on some browsers, stopping
a <code>keydown</code> does not stop the <code>keypress</code>
from firing, whereas on others it does. If you respond to an
event, you should probably inspect its <code>type</code>
property and only do something when it is <code>keydown</code>
(or <code>keypress</code> for actions that need character
data).</dd>
</dl>
<h2 id="styling">Customized Styling</h2>
<p>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 <a href="lib/codemirror.css"><code>codemirror.css</code></a>.</p>
<p>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:</p>
<dl>
<dt id="class_CodeMirror"><code>CodeMirror</code></dt>
<dd>The outer element of the editor. This determines whether the
editor scrolls (<code>overflow: auto</code> + fixed height). Can
also be used to set styles that should hold for everything
inside the editor, or to set a background.</dd>
<dt id="class_CodeMirror_focused"><code>CodeMirror-focused</code></dt>
<dd>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.</dd>
<dt id="class_CodeMirror_gutter"><code>CodeMirror-gutter</code></dt>
<dd>Use this for giving a background or a border to the editor
gutter. Don't set any padding here,
use <code>CodeMirror-gutter-text</code> for that. By default,
the gutter is 'fluid', meaning it will adjust its width to the
maximum line number or line marker width. You can also set a
fixed width if you want.</dd>
<dt id="class_CodeMirror_gutter_text"><code>CodeMirror-gutter-text</code></dt>
<dd>Used to style the actual line numbers. For the numbers to
line up, you'll want this style to use exactly the same font and
vertical padding as normal edited text, as per
the <code>CodeMirror-lines</code> class.</dd>
<dt id="class_CodeMirror_lines"><code>CodeMirror-lines</code></dt>
<dd>The visible lines. If this has vertical
padding, <code>CodeMirror-gutter</code> should have the same
padding.</dd>
<dt id="class_CodeMirror_cursor"><code>CodeMirror-cursor</code></dt>
<dd>The cursor is a block element that is absolutely positioned.
You can make it look whichever way you want.</dd>
<dt id="class_CodeMirror_selected"><code>CodeMirror-selected</code></dt>
<dd>The selection is represented by <code>span</code> elements
with this class.</dd>
<dt id="class_CodeMirror_matchingbracket"><code>CodeMirror-matchingbracket</code>,
<code>CodeMirror-matchingbracket</code></dt>
<dd>These are used to style matched (or unmatched) brackets.</dd>
</dl>
<p>The actual lines, as well as the cursor, are represented
by <code>pre</code> elements. By default no text styling (such as
bold) that might change line height is applied. If you do want
such effects, you'll have to give <code>CodeMirror pre</code> a
fixed height. Also, you must still take care that character width
is constant.</p>
<p>If your page's style sheets do funky things to
all <code>div</code> or <code>pre</code> elements (you probably
shouldn't do that), you'll have to define rules to cancel these
effects out again for elements under the <code>CodeMirror</code>
class.</p>
<h2 id="api">Programming API</h2>
<p>A lot of CodeMirror features are only available through its API.
This has the disadvantage that you need to do work to enable them,
and the advantage that CodeMirror will fit seamlessly into your
application.</p>
<p>Whenever points in the document are represented, the API uses
objects with <code>line</code> and <code>ch</code> 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 <code>ch</code> a value of <code>null</code>, or don't
specify it, it will be replaced with the length of the specified
line.</p>
<dl>
<dt id="getValue"><code>getValue() → string</code></dt>
<dd>Get the current editor content.</dd>
<dt id="setValue"><code>setValue(string)</code></dt>
<dd>Set the editor content.</dd>
<dt id="getSelection"><code>getSelection() → string</code></dt>
<dd>Get the currently selected code.</dd>
<dt id="replaceSelection"><code>replaceSelection(string)</code></dt>
<dd>Replace the selection with the given string.</dd>
<dt id="focus"><code>focus()</code></dt>
<dd>Give the editor focus.</dd>
<dt id="setOption"><code>setOption(option, value)</code></dt>
<dd>Change the configuration of the editor. <code>option</code>
should the name of an <a href="#config">option</a>,
and <code>value</code> should be a valid value for that
option.</dd>
<dt id="getOption"><code>getOption(option) → value</code></dt>
<dd>Retrieves the current value of the given option for this
editor instance.</dd>
<dt id="cursorCoords"><code>cursorCoords(start) → object</code></dt>
<dd>Returns an <code>{x, y, yBot}</code> object containing the
coordinates of the cursor relative to the top-left corner of the
page. <code>yBot</code> is the coordinate of the bottom of the
cursor. <code>start</code> is a boolean indicating whether you
want the start or the end of the selection.</dd>
<dt id="charCoords"><code>charCoords(pos) → object</code></dt>
<dd>Like <code>cursorCoords</code>, but returns the position of
an arbitrary characters. <code>pos</code> should be
a <code>{line, ch}</code> object.</dd>
<dt id="coordsChar"><code>coordsChar(object) → pos</code></dt>
<dd>Given an <code>{x, y}</code> object (in page coordinates),
returns the <code>{line, ch}</code> position that corresponds to
it.</dd>
<dt id="undo"><code>undo()</code></dt>
<dd>Undo one edit (if any undo events are stored).</dd>
<dt id="redo"><code>redo()</code></dt>
<dd>Redo one undone edit.</dd>
<dt id="historySize"><code>historySize() → object</code></dt>
<dd>Returns an object with <code>{undo, redo}</code> properties,
both of which hold integers, indicating the amount of stored
undo and redo operations.</dd>
<dt id="indentLine"><code>indentLine(line)</code></dt>
<dd>Reset the given line's indentation to the indentation
prescribed by the mode.</dd>
<dt id="getSearchCursor"><code>getSearchCursor(query, start, caseFold) → cursor</code></dt>
<dd>Used to implement search/replace
functionality. <code>query</code> can be a regular expression or
a string (only strings will match across lines—if they contain
newlines). <code>start</code> provides the starting position of
the search. It can be a <code>{line, ch}</code> object, or can
be left off to default to the start of the
document. <code>caseFold</code> is only relevant when matching a
string. It will cause the search to be case-insensitive. A
search cursor has the following methods:
<dl>
<dt><code>findNext(), findPrevious() → boolean</code></dt>
<dd>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 <code>match</code> method, in case you
want to extract matched groups.</dd>
<dt><code>from(), to() → object</code></dt>
<dd>These are only valid when the last call
to <code>findNext</code> or <code>findPrevious</code> did
not return false. They will return <code>{line, ch}</code>
objects pointing at the start and end of the match.</dd>
</dl></dd>
<dt id="getTokenAt"><code>getTokenAt(pos) → object</code></dt>
<dd>Retrieves information about the token the current mode found
at the given position (a <code>{line, ch}</code> object). The
returned object has the following properties:
<dl>
<dt><code>start</code></dt><dd>The character (on the given line) at which the token starts.</dd>
<dt><code>end</code></dt><dd>The character at which the token ends.</dd>
<dt><code>string</code></dt><dd>The token's string.</dd>
<dt><code>className</code></dt><dd>The class the mode assigned
to the token. (Can be null when no class was assigned.)</dd>
</dl></dd>
<dt id="markText"><code>markText(from, to, className) → function</code></dt>
<dd>Can be used to mark a range of text with a specific CSS
class name. <code>from</code> and <code>to</code> should
be <code>{line, ch}</code> objects. The method will return a
function that can be called to remove the marking.</dd>
<dt id="setMarker"><code>setMarker(line, text, className) → lineHandle</code></dt>
<dd>Add a gutter marker for the given line. Gutter markers are
shown in the line-number area (instead of the number for this
line). Both <code>text</code> and <code>className</code> are
optional. Setting <code>text</code> to a Unicode character like
● tends to give a nice effect. To put a picture in the gutter,
set <code>text</code> to a space and <code>className</code> to
something that sets a background image. If you
specify <code>text</code>, the given text (which may contain
HTML) will, by default, replace the line number for that line.
If this is not what you want, you can include the
string <code>%N%</code> in the text, which will be replaced by
the line number.</dd>
<dt id="clearMarker"><code>clearMarker(line)</code></dt>
<dd>Clears a marker created
with <code>setMarker</code>. <code>line</code> can be either a
number or a handle returned by <code>setMarker</code> (since a
number may now refer to a different line if something was added
or deleted).</dd>
<dt id="setLineClass"><code>setLineClass(line, className) → lineHandle</code></dt>
<dd>Set a CSS class name for the given line. <code>line</code>
can be a number or a line handle (as returned
by <code>setMarker</code> or this function).
Pass <code>null</code> to clear the class for a line.</dd>
<dt id="lineInfo"><code>lineInfo(line) → object</code></dt>
<dd>Returns the line number, text content, and marker status of
the given line, which can be either a number or a handle
returned by <code>setMarker</code>. The returned object has the
structure <code>{line, text, markerText, markerClass}</code>.</dd>
<dt id="addWidget"><code>addWidget(pos, node, scrollIntoView)</code></dt>
<dd>Puts <code>node</code>, which should be an absolutely
positioned DOM node, into the editor, positioned right below the
given <code>{line, ch}</code> position.
When <code>scrollIntoView</code> 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 <code>removeChild</code> on its parent).</dd>
<dt id="matchBrackets"><code>matchBrackets()</code></dt>
<dd>Force matching-bracket-highlighting to happen.</dd>
<dt id="lineCount"><code>lineCount() → number</code></dt>
<dd>Get the number of lines in the editor.</dd>
<dt id="getCursor"><code>getCursor(start) → object</code></dt>
<dd><code>start</code> is a boolean indicating whether the start
or the end of the selection must be retrieved. If it is not
given, the current cursor pos, i.e. the side of the selection
that would move if you pressed an arrow key, is chosen.
A <code>{line, ch}</code> object will be returned.</dd>
<dt id="somethingSelected"><code>somethingSelected() → boolean</code></dt>
<dd>Return true if any text is selected.</dd>
<dt id="setCursor"><code>setCursor(pos)</code></dt>
<dd>Set the cursor position. You can either pass a
single <code>{line, ch}</code> object, or the line and the
character as two separate parameters.</dd>
<dt id="setSelection"><code>setSelection(start, end)</code></dt>
<dd>Set the selection range. <code>start</code>
and <code>end</code> should be <code>{line, ch}</code> objects.</dd>
<dt id="getLine"><code>getLine(n) → string</code></dt>
<dd>Get the content of line <code>n</code>.</dd>
<dt id="setLine"><code>setLine(n, text)</code></dt>
<dd>Set the content of line <code>n</code>.</dd>
<dt id="removeLine"><code>removeLine(n)</code></dt>
<dd>Remove the given line from the document.</dd>
<dt id="getRange"><code>getRange(from, to) → string</code></td>
<dd>Get the text between the given points in the editor, which
should be <code>{line, ch}</code> objects.</dd>
<dt id="replaceRange"><code>replaceRange(string, from, to)</code></dt>
<dd>Replace the part of the document between <code>from</code>
and <code>to</code> with the given string. <code>from</code>
and <code>to</code> must be <code>{line, ch}</code>
objects. <code>to</code> can be left off to simply insert the
string at position <code>from</code>.</dd>
</dl>
<p>The following are more low-level methods:</p>
<dl>
<dt id="operation"><code>operation(func) → result</code></dt>
<dd>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.</dd>
<dt id="refresh"><code>refresh()</code></dt>
<dd>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.</dd>
<dt id="getInputField"><code>getInputField() → textarea</code></dt>
<dd>Returns the hiden textarea used to read input.</dd>
<dt id="getWrapperElement"><code>getWrapperElement() → node</code></dt>
<dd>Returns the DOM node that represents the editor. Remove this
from your tree to delete an editor instance.</dd>
</dl>
<p id="fromTextArea">Finally, the <code>CodeMirror</code> object
itself has a method <code>fromTextArea</code>. This 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. A CodeMirror instance created this way has two
additional methods:</p>
<dl>
<dt id="save"><code>save()</code></dt>
<dd>Copy the content of the editor into the textarea.</dd>
<dt id="toTextArea"><code>toTextArea()</code></dt>
<dd>Remove the editor, and restore the original textarea (with
the editor's current content).</dd>
</dl>
<h2 id="modeapi">Writing CodeMirror Modes</h2>
<p>Modes typically consist of a JavaScript file and a CSS file.
The CSS file (see, for
example <a href="mode/javascript/javascript.css"><code>javascript.css</code></a>)
defines the classes that will be used to style the syntactic
elements of the code, and the script contains the logic to
actually assign these classes to the right pieces of text.</p>
<p>You'll usually want to use some kind of prefix for your CSS
classes, so that they are unlikely to clash with other classes,
both those used by other modes and those defined by the page in
which CodeMirror is embedded.</p>
<p id="defineMode">The mode script should
call <code>CodeMirror.defineMode</code> 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. <code>"xml"</code> is defined <code>xml.js</code>). The
second argument should be a function that, given a CodeMirror
configuration object (the thing passed to
the <code>CodeMirror</code> function) and a mode configuration
object (as in the <a href="#option_mode"><code>mode</code></a>
option), returns a mode object.</p>
<p>Typically, you should use this second argument
to <code>defineMode</code> as your module scope function (modes
should not leak anything into the global scope!), i.e. write your
whole mode inside this function.</p>
<p>The main responsibility of a mode script is <em>parsing</em>
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 (<em>token</em>) 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 <em>state
object</em>, which is an object that can be mutated every time a
new token is read.</p>
<p id="startState">Modes that use a state must define
a <code>startState</code> 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.</p>
<p id="token">The most important part of a mode object is
its <code>token(stream, state)</code> 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
CSS class string, or <code>null</code> for tokens that do not have
to be styled.<p>
<p id="StringStream">The stream object encapsulates a line of code
(tokens may never span lines) and our current position in that
line. It has the following API:</p>
<dl>
<dt><code>eol() → boolean</code></dt>
<dd>Returns true only if the stream is at the end of the
line.</dd>
<dt><code>sol() → boolean</code></dt>
<dd>Returns true only if the stream is at the start of the
line.</dd>
<dt><code>peek() → character</code></dt>
<dd>Returns the next character in the stream without advancing
it. Will return <code>undefined</code> at the end of the
line.</dd>
<dt><code>next() → character</code></dt>
<dd>Returns the next character in the stream and advances it.
Also returns <code>undefined</code> when no more characters are
available.</dd>
<dt><code>eat(match) → character</code></dt>
<dd><code>match</code> 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, <code>undefined</code>
is returned.</dd>
<dt><code>eatWhile(match) → boolean</code></dt>
<dd>Repeatedly calls <code>eat</code> with the given argument,
until it fails. Returns true if any characters were eaten.</dd>
<dt><code>eatSpace() → boolean</code></dt>
<dd>Shortcut for <code>eatWhile</code> when matching
white-space.</dd>
<dt><code>skipToEnd()</code></dt>
<dd>Moves the position to the end of the line.</dd>
<dt><code>skipTo(ch) → boolean</code></dt>
<dd>Skips to the next occurrence of the given character, if
found. Returns true if the character was found.</dd>
<dt><code>match(pattern, consume, caseFold) → boolean</code></dt>
<dd>Act like a
multi-character <code>eat</code>—if <code>consume</code> is true
or not given—or a look-ahead that doesn't update the stream
position—if it is false. <code>pattern</code> can be either a
string or a regular expression starting with <code>^</code>.
When it is a string, <code>caseFold</code> 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 <code>match</code>, in case you need to extract
matched groups.</dd>
<dt><code>backUp(n)</code></dt>
<dd>Backs up the stream <code>n</code> characters. Backing it up
further than the start of the current token will cause things to
break, so be careful.</dd>
<dt><code>column() → integer</code></dt>
<dd>Returns the column (taking into account tabs) at which the
current token starts. Can be used to find out whether a token
starts a new line.</dd>
<dt><code>indentation() → integer</code></dt>
<dd>Tells you how far the current line has been indented, in
spaces. Corrects for tab characters.</dd>
<dt><code>current() → string</code></dt>
<dd>Get the string between the start of the current token and
the current stream position.</dd>
</dl>
<p id="copyState">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 <code>copyState</code> method,
which is given a state and should return a safe copy of that
state.</p>
<p id="indent">If you want your mode to provide smart indentation
(see <a href="#option_enterMode"><code>entermode</code></a>
and <a href="#option_tabMode"><code>tabMode</code></a> when they
have a value of <code>"indent"</code>), you must define
an <code>indent(state, textAfter)</code> method on your mode
object.</p>
<p>The indentation method should inspect the given state object,
and optionally the <code>textAfter</code> 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 <a href="#option_indentUnit"><code>indentUnit</code></a>
option into account.</p>
<p id="electricChars">Finally, a mode may define
an <code>electricChars</code> property, which should hold a string
containing all the characters that should trigger the behaviour
described for
the <a href="#option_electricChars"><code>electricChars</code></a>
option.</p>
<p>So, to summarize, a mode <em>must</em> provide
a <code>token</code> method, and it <em>may</em>
provide <code>startState</code>, <code>copyState</code>,
and <code>indent</code> methods. For an example of a trivial mode,
see the <a href="mode/diff/diff.js">diff mode</a>, for a more
involved example, see
the <a href="mode/javascript/javascript.js">JavaScript
mode</a>.</p>
<p>Sometimes, it is useful for modes to <em>nest</em>—to have one
mode delegate work to another mode. An example of this kind of
mode is the <a href="mode/htmlmixed/htmlmixed.js">mixed-mode HTML
mode</a>. To implement such nesting, it is usually necessary to
create mode objects and copy states yourself. To create a mode
object, there are <code>CodeMirror.getMode(options,
parserConfig)</code>, 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 <a href="#option_mode"><code>mode</code></a> option. To copy a
state object, call <code>CodeMirror.copyState(mode, state)</code>,
where <code>mode</code> is the mode that created the given
state.</p>
<p>To make indentation work properly in a nested parser, it is
advisable to give the <code>startState</code> 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.</p>
<p>Finally, it is possible to associate your mode, or a certain
configuration of your mode, with
a <a href="http://en.wikipedia.org/wiki/MIME">MIME</a> type. For
example, the JavaScript mode associates itself
with <code>text/javascript</code>, and its JSON variant
with <code>application/json</code>. To do this,
call <code>CodeMirror.defineMIME(mime, modeSpec)</code>,
where <code>modeSpec</code> can be a string or object specifying a
mode, as in the <a href="#option_mode"><code>mode</code></a>
option.</p>
</div><div class="rightsmall blk">
<h2>Contents</h2>
<ul>
<li><a href="#overview">Overview</a></li>
<li><a href="#usage">Basic Usage</a></li>
<li><a href="#config">Configuration</a></li>
<li><a href="#styling">Customized Styling</a></li>
<li><a href="#api">Programming API</a></li>
<li><a href="#modeapi">Writing CodeMirror Modes</a></li>
</ul>
</div></div>
<div style="height: 2em"> </div>
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