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<pre class='metadata'>
Title: CSS Object Model (CSSOM)
ED: https://drafts.csswg.org/cssom/
TR: https://www.w3.org/TR/cssom-1/
Previous Version: https://www.w3.org/TR/2016/WD-cssom-1-20160317/
Previous Version: https://www.w3.org/TR/2013/WD-cssom-20131205/
Previous Version: https://www.w3.org/TR/2011/WD-cssom-20110712/
Previous Version: https://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/
Group: CSSWG
Status: ED
Work Status: Exploring
Shortname: cssom
Level: 1
Editor: Daniel Glazman, Disruptive Innovations http://disruptive-innovations.com/, daniel.glazman@disruptive-innovations.com, w3cid 13329
Editor: Emilio Cobos Álvarez 106537, Mozilla, emilio@mozilla.com
Former Editor: Simon Pieters, Opera Software AS http://www.opera.com, simonp@opera.com
Former Editor: Glenn Adams, Cox Communications, Inc. http://www.cox.com, glenn.adams@cos.com, http://www.w3.org/wiki/User:Gadams
Former Editor: Anne van Kesteren, Opera Software ASA http://www.opera.com, annevk@annevk.nl, https://annevankesteren.nl/
!Legacy issues list: <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=CSS&component=CSSOM&resolution=---">Bugzilla</a>
Abstract: CSSOM defines APIs (including generic parsing and serialization rules) for Media Queries, Selectors, and of course CSS itself.
Ignored Terms: EmptyString, group of selectors, list of css page selectors, -webkit-transform
Ignored Vars: m1, m2, camel_cased_attribute, webkit_cased_attribute, dashed_attribute
Include Can I Use Panels: true
Can I Use URL: https://drafts.csswg.org/cssom/
Can I Use URL: https://www.w3.org/TR/cssom-1/
Ignore Can I Use URL Failure: https://drafts.csswg.org/cssom/
Ignore Can I Use URL Failure: https://www.w3.org/TR/cssom-1/
</pre>
<pre class='anchors'>
urlPrefix: https://html.spec.whatwg.org/multipage/
urlPrefix: infrastructure.html
type: dfn
text: html elements
text: tree order
text: document base url
text: content-type metadata; url: #content-type
urlPrefix: rendering.html
type: dfn
text: being rendered
urlPrefix: browsers.html
type: interface; text: WindowProxy
type: dfn
text: browsing context
text: auxiliary browsing context
text: familiar with
text: same origin
urlPrefix: webappapis.html
type: dfn
text: responsible browsing context
text: incumbent settings object
text: event loop
text: event handlers
text: event handler event type
text: event handler IDL attributes
urlPrefix: infrastructure.html
type: dfn
text: split a string on commas
text: skip whitespace
text: collect a sequence of characters
text: space character
text: rules for parsing integers
urlPrefix: xhtml.html
type: dfn
text: xml parser
urlPrefix: semantics.html
type: dfn
text: a style sheet that is blocking scripts
text: style sheet ready
urlPrefix: https://dom.spec.whatwg.org/#concept-
type: dfn
text: dispatch; url: event-dispatch
text: event
text: event listener
text: quirks mode; url: document-quirks
text: fire an event; url: event-fire
text: node document
text: document url
urlPrefix: https://www.w3.org/TR/CSS21/visuren.html
type: dfn; text: anonymous block box; url: #anonymous-block-level
urlPrefix: http://heycam.github.io/webidl/#
type: interface; urlPrefix: idl-
text: double
text: long
type: dfn; urlPrefix: dfn-
text: converted to an IDL value
text: throw
text: supported property indices
urlPrefix: https://encoding.spec.whatwg.org/#; spec: ENCODING
type: dfn; text: get an encoding; url: concept-encoding-get
urlPrefix: https://url.spec.whatwg.org/#concept-
type: dfn
text: URL
text: URL parser
text: URL serializer
urlPrefix: https://www.w3.org/TR/xml-stylesheet/#dt-
type: dfn; text: xml-stylesheet processing instruction
type: dfn; text: pseudo-attribute
urlPrefix: https://fetch.spec.whatwg.org/#concept-
type: dfn;
text: fetch
text: request
for: request
text: url; url: request-url
text: origin; url: request-origin
text: referrer; url: request-referrer
text: network error
</pre>
<pre class='link-defaults'>
spec:css-display-3; type:value; for:display; text:table
spec:css-color-4; type:property; text:color
spec:css-position-3; type:property; text:left
spec:html; type:element; text:style
spec:css-namespaces-3; type:dfn; text:namespace prefix
spec:dom; type:interface; text:Document
spec:html; type:dfn; text:ascii case-insensitive
spec:html; type:dfn; text:case-sensitive
spec:infra; type:dfn; text:list
spec:css-logical; type:property; text:inline-size
spec:css-variables-1; type:dfn; text:custom property
spec:selectors-3; type:selector; text:::before
spec:selectors-3; type:selector; text:::after
spec:css-fonts-4; type:descriptor; text:unicode-range
spec:css-fonts-4; type:descriptor; text:font-variant
spec:css-fonts-4; type:descriptor; text:font-feature-settings
spec:css-fonts-4; type:descriptor; text:font-stretch
spec:css-fonts-4; type:descriptor; text:font-weight
spec:css-fonts-4; type:descriptor; text:font-style
</pre>
<script src=https://resources.whatwg.org/file-issue.js async data-file-issue-url="https://github.com/w3c/csswg-drafts/issues/new?title=%5Bcssom%5D%20"></script>
Introduction {#introduction}
============================
This document formally specifies the core features of the CSS Object Model (CSSOM). Other documents in the CSSOM family of specifications
as well as other CSS related specifications define extensions to these core features.
The core features of the CSSOM are oriented towards providing basic capabilities to author-defined scripts to permit access to
and manipulation of style related state information and processes.
The features defined below are fundamentally based on prior specifications of the W3C DOM Working Group, primarily
[[DOM-LEVEL-2-STYLE]]. The purposes of the present document are (1) to improve on that prior work by providing
more technical specificity (so as to improve testability and interoperability), (2) to deprecate or remove certain less-widely implemented
features no longer considered to be essential in this context, and (3) to newly specify certain extensions that have been
or expected to be widely implemented.
Terminology {#terminology}
==========================
This specification employs certain terminology from the following documents:
<cite>DOM</cite>,
<cite>HTML</cite>,
<cite>CSS Syntax</cite>,
<cite>Encoding</cite>,
<cite>URL</cite>,
<cite>Fetch</cite>,
<cite>Associating Style Sheets with XML documents</cite>
and
<cite>XML</cite>.
[[!DOM]]
[[!HTML]]
[[!CSS3SYN]]
[[!ENCODING]]
[[!URL]]
[[!FETCH]]
[[!XML-STYLESHEET]]
[[!XML]]
When this specification talks about object
<code><var>A</var></code> where <code><var>A</var></code> is actually an interface, it generally means an object implementing interface
<code><var>A</var></code>.
The terms <dfn>set</dfn> and <dfn>unset</dfn> to refer to the true and
false values of binary flags or variables, respectively. These terms are also used as verbs in which case they refer to
mutating some value to make it true or false, respectively.
The term <dfn export>supported styling language</dfn> refers to CSS.
Note: If another styling language becomes supported in user agents, this specification is expected to be updated as necessary.
The term <dfn export>supported CSS property</dfn> refers to a CSS property that the user agent
implements, including any vendor-prefixed properties, but excluding <a>custom properties</a>. A
<a>supported CSS property</a> must be in its lowercase form for the purpose of comparisons in this
specification.
In this specification the ''::before'' and ''::after'' pseudo-elements
are assumed to exist for all elements even if no box is generated for them.
When a method or an attribute is said to call another method or attribute, the user agent must invoke its internal API for that attribute or method so that
e.g. the author can't change the behavior by overriding attributes or methods with custom properties or functions in ECMAScript.
Unless otherwise stated, string comparisons are done in a <a>case-sensitive</a> manner.
Common Serializing Idioms {#common-serializing-idioms}
------------------------------------------------------
To <dfn>escape a character</dfn> means to create a string of
"<code>\</code>" (U+005C), followed by the character.
To <dfn lt="escape a character as code point|escaped as code point">escape a character as code point</dfn> means to create a
string of "<code>\</code>" (U+005C), followed by the Unicode code point as
the smallest possible number of hexadecimal digits in the range 0-9 a-f
(U+0030 to U+0039 and U+0061 to U+0066) to represent the code point in
base 16, followed by a single SPACE (U+0020).
To <dfn export>serialize an identifier</dfn> means to create a string represented
by the concatenation of, for each character of the identifier:
<ul>
<li>If the character is NULL (U+0000), then the REPLACEMENT CHARACTER (U+FFFD).
<li>If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F, then the character
<a>escaped as code point</a>.
<li>If the character is the first character and is in the range \[0-9]
(U+0030 to U+0039), then the character
<a>escaped as code point</a>.
<li>If the character is the second character and is in the range \[0-9]
(U+0030 to U+0039) and the first character is a "<code>-</code>"
(U+002D), then the character
<a>escaped as code point</a>.
<li>If the character is the first character and is a "<code>-</code>" (U+002D),
and there is no second character,
then the <a lt="escape a character">escaped</a> character.
<li>If the character is not handled by one of the above rules and is
greater than or equal to U+0080, is "<code>-</code>" (U+002D) or
"<code>_</code>" (U+005F), or is in one of the ranges \[0-9] (U+0030 to
U+0039), \[A-Z] (U+0041 to U+005A), or \[a-z] (U+0061 to U+007A), then the character
itself.
<li>Otherwise, the <a lt="escape a character">escaped</a>
character.
</ul>
To <dfn export>serialize a string</dfn> means to create a string represented
by '"' (U+0022), followed by the result of applying the rules
below to each character of the given string, followed by
'"' (U+0022):
<ul>
<li>If the character is NULL (U+0000), then the REPLACEMENT CHARACTER (U+FFFD).
<li>If the character is in the range [\1-\1f] (U+0001 to U+001F) or is U+007F, the character
<a>escaped as code point</a>.
<li>If the character is '"' (U+0022) or "<code>\</code>"
(U+005C), the <a lt="escape a character">escaped</a> character.
<li>Otherwise, the character itself.
</ul>
Note: "<code>'</code>" (U+0027) is not escaped because strings
are always serialized with '"' (U+0022).
To <dfn export>serialize a URL</dfn> means to create a string represented by
"<code>url(</code>", followed by the
<a lt="serialize a string">serialization</a> of the URL as a
string, followed by "<code>)</code>".
To <dfn export>serialize a LOCAL</dfn> means to create a string represented by
"<code>local(</code>", followed by the
<a lt="serialize a string">serialization</a> of the URL as a
string, followed by "<code>)</code>".
To <dfn export>serialize a comma-separated list</dfn> concatenate all items of
the list in list order while separating them by "<code>, </code>", i.e.,
COMMA (U+002C) followed by a single SPACE (U+0020).
To <dfn export>serialize a whitespace-separated list</dfn> concatenate all
items of the list in list order while separating them by "<code> </code>", i.e.,
a single SPACE (U+0020).
Note: When serializing a list according to the above rules,
extraneous whitespace is not inserted prior to the first item or subsequent to
the last item. Unless otherwise specified, an empty list is serialized as the
empty string.
CSSOMString {#cssomstring-type}
===============================
Most strings in CSSOM interfaces use the <dfn>CSSOMString</dfn> type.
Each implementation chooses to define it as either {{USVString}} or {{DOMString}}:
<pre class=idl>
typedef USVString CSSOMString;
</pre>
Or, alternatively:
<pre class="def lang-webidl">
typedef DOMString CSSOMString;
</pre>
<div class=note>
The difference is only observable from web content
when <a>surrogate</a> code units are involved.
{{DOMString}} would preserve them,
whereas {{USVString}} would replace them with U+FFFD REPLACEMENT CHARACTER.
This choice effectively allows implementations to do this replacement,
but does not require it.
Using {{USVString}} enables an implementation
to use UTF-8 internally to represent strings in memory.
Since well-formed UTF-8 specifically disallows <a>surrogate</a> code points,
it effectively requires this replacement.
On the other hand,
implementations that internally represent strings as 16-bit <a>code units</a>
might prefer to avoid the cost of doing this replacement.
</div>
Media Queries {#media-queries}
==============================
[=Media queries=] are defined by [[!MEDIAQUERIES]]. This
section defines various concepts around [=media queries=], including their API
and serialization form.
Parsing Media Queries {#parsing-media-queries}
----------------------------------------------
To <dfn export>parse a media query list</dfn> for a
given string <var>s</var> into a [=media query list=] is defined in
the Media Queries specification. Return the list of media
queries that the algorithm defined there gives. <!-- XXX ref -->
Note: A media query that ends up being "ignored" will turn
into "<code>not all</code>".
To <dfn export>parse a media query</dfn> for a given string
<var>s</var> means to follow the<
2A0
/div>
<a>parse a media query list</a> steps and return null if more
than one media query is returned or a media query if a
single media query is returned.
Note: Again, a media query that ends up being "ignored" will
turn into "<code>not all</code>".
Serializing Media Queries {#serializing-media-queries}
------------------------------------------------------
To
<dfn export>serialize a media query list</dfn>
run these steps:
<ol>
<li>If the [=media query list=] is empty, then return the empty string.
<li><a lt="serialize a media query">Serialize</a> each media query in the list of media queries, in the same order as they appear in the [=media query list=], and then <a lt="serialize a comma-separated list">serialize</a> the list.
</ol>
To
<dfn export>serialize a media query</dfn> let
<var>s</var> be the empty string, run the steps below:
<ol>
<li>If the [=media query=] is negated append "<code>not</code>", followed
by a single SPACE (U+0020), to <var>s</var>.
<li>Let <var>type</var> be the <a lt="serialize an identifier">serialization
as an identifier</a> of the [=media type=] of the [=media query=],
<a lt="ASCII lowercase">converted to ASCII lowercase</a>.
<li>If the [=media query=] does not contain [=media features=] append
<var>type</var>, to <var>s</var>,
then return <var>s</var>.
<li>If <var>type</var> is not "<code>all</code>" or if the
media query is negated append <var>type</var>, followed by a
single SPACE (U+0020), followed by "<code>and</code>", followed by a single SPACE
(U+0020), to <var>s</var>.
<li>Sort the [=media features=] in lexicographical order.
<li>
Then, for each [=media feature=]:
<ol>
<li>Append a "<code>(</code>" (U+0028), followed by the [=media feature=]
name, <a lt="ASCII lowercase">converted to ASCII lowercase</a>,
to <var>s</var>.
<li>If a value is given append a "<code>:</code>" (U+003A), followed
by a single SPACE (U+0020), followed by the
<a lt="serialize a media feature value">serialized media feature value</a>,
to <var>s</var>.
<li>Append a "<code>)</code>" (U+0029) to
<var>s</var>.
<li>If this is not the last [=media feature=] append a single SPACE (U+0020),
followed by "<code>and</code>", followed by a single SPACE (U+0020), to
<var>s</var>.
</ol>
<li>Return <var>s</var>.
</ol>
<div class="example">
Here are some examples of input (first column) and output (second
column):
<table class="complex data">
<thead>
<tr><th>Input<th>Output
<tbody>
<tr>
<td><pre>not screen and (min-WIDTH:5px) AND (max-width:40px)</pre>
<td><pre>not screen and (max-width: 40px) and (min-width: 5px)</pre>
<tr>
<td><pre>all and (color) and (color)</pre>
<td><pre>(color)</pre>
</table>
</div>
### Serializing Media Feature Values ### {#serializing-media-feature-values}
Issue: This should probably be done in terms of mapping it to
serializing CSS values as media features are defined in terms of CSS
values after all.
To <dfn export>serialize a media feature value</dfn>
named <var>v</var> locate <var>v</var> in the first
column of the table below and use the serialization format described in
the second column:
<table class="complex data" spec=mediaqueries-4>
<thead>
<tr>
<th>Media Feature
<th>Serialization
<tbody>
<tr>
<td>'@media/width'
<td>...
<tr>
<td>'@media/height'
<td>...
<tr>
<td>'device-width'
<td>...
<tr>
<td>'device-height'
<td>...
<tr>
<td>'orientation'
<td>
If the value is ''portrait'': "<code>portrait</code>".
If the value is ''landscape'': "<code>landscape</code>".
<tr>
<td>'aspect-ratio'
<td>...
<tr>
<td>'device-aspect-ratio'
<td>...
<tr>
<td>'@media/color'
<td>...
<tr>
<td>'color-index'
<td>...
<tr>
<td>'monochrome'
<td>...
<tr>
<td>'resolution'
<td>...
<tr>
<td>'scan'
<td>
If the value is ''progressive'': "<code>progressive</code>".
If the value is ''interlace'': "<code>interlace</code>".
<tr>
<td>'grid'
<td>...
</table>
Other specifications can extend this table and vendor-prefixed media
features can have custom serialization formats as well.
Comparing Media Queries {#comparing-media-queries}
--------------------------------------------------
To
<dfn export>compare media queries</dfn>
<var>m1</var> and <var>m2</var> means to
<a lt="serialize a media query">serialize</a> them both and
return true if they are a
<a>case-sensitive</a> match and false if they
are not.
The {{MediaList}} Interface {#the-medialist-interface}
------------------------------------------------------
An object that implements the <code>MediaList</code> interface has an associated <dfn export for=MediaList>collection of media queries</dfn>.
<pre class=idl>
[Exposed=Window]
interface MediaList {
stringifier attribute [TreatNullAs=EmptyString] CSSOMString mediaText;
readonly attribute unsigned long length;
getter CSSOMString? item(unsigned long index);
void appendMedium(CSSOMString medium);
void deleteMedium(CSSOMString medium);
};
</pre>
The object's <a>supported property indices</a> are the numbers in the range zero to one less than the number of media queries
in the <a>collection of media queries</a> represented by the collection. If there are no such media queries, then there are no
<a>supported property indices</a>.
To <dfn export>create a <code>MediaList</code> object</dfn> with a string <var>text</var>, run the following steps:
<ol>
<li>Create a new <code>MediaList</code> object.
<li>Set its {{MediaList/mediaText}} attribute to <var>text</var>.
<li>Return the newly created <code>MediaList</code> object.
</ol>
The <dfn attribute for=MediaList>mediaText</dfn> attribute, on getting, must return a
<a lt="serialize a media query list">serialization</a> of the <a>collection of media queries</a>.
Setting the {{MediaList/mediaText}} attribute must run these steps:
<ol>
<li>Empty the <a>collection of media queries</a>.
<li>If the given value is the empty string, then return.
<li>Append all the media queries as a result of <a lt="parse a media query list">parsing</a> the given
value to the <a>collection of media queries</a>.
</ol>
The <dfn method for=MediaList>item(<var>index</var>)</dfn> method must return a
<a lt="serialize a media query">serialization</a> of the media query in the <a>collection of media queries</a>
given by <var>index</var>, or null, if <var>index</var> is greater than or equal to the number of media queries
in the <a>collection of media queries</a>.
The <dfn attribute for=MediaList>length</dfn> attribute must return the number of media queries in the <a>collection of media
queries</a>.
The <dfn method for=MediaList>appendMedium(<var>medium</var>)</dfn> method must run these steps:
<ol>
<li>Let <var>m</var> be the result of <a lt="parse a media query">parsing</a> the given value.
<li>If <var>m</var> is null, then return.
<li>If <a lt="compare media queries">comparing</a> <var>m</var> with any of the media queries in the
<a>collection of media queries</a> returns true, then return.
<li>Append <var>m</var> to the <a>collection of media queries</a>.
</ol>
The <dfn method for=MediaList>deleteMedium(<var>medium</var>)</dfn> method must run these steps:
<ol>
<li>Let <var>m</var> be the result of <a lt="parse a media query">parsing</a> the given value.
<li>If <var>m</var> is null, then return.
<li>Remove any media query from the <a>collection of media queries</a> for which
<a lt="compare media queries">comparing</a> the media query with <var>m</var> returns true.
If nothing was removed, then <a>throw</a> a {{NotFoundError}} exception.
</ol>
Selectors {#selectors}
======================
Selectors are defined in the Selectors specification. This section
mainly defines how to serialize them. <!-- XXX ref -->
<!-- XXX ref universal selector etc? some are in A some not -->
Parsing Selectors {#parsing-selectors}
--------------------------------------
To
<dfn export>parse a group of selectors</dfn>
means to parse the value using the <code>selectors_group</code>
production defined in the Selectors specification and return either a
group of selectors if parsing did not fail or null if parsing did
fail. <!-- XXX ref -->
Serializing Selectors {#serializing-selectors}
----------------------------------------------
<!-- http://dump.testsuite.org/2009/cssom/serializing-selectors.htm -->
To
<dfn export>serialize a group of selectors</dfn>
<a lt="serialize a selector">serialize</a> each selector in the
group of selectors and then
<a lt="serialize a comma-separated list">serialize</a> a
comma-separated list of these serializations.
To <dfn export>serialize a selector</dfn> let
<var>s</var> be the empty string, run the steps below for each
part of the chain of the selector, and finally return
<var>s</var>:
<ol>
<li>If there is only one <a>simple selector</a> in the
<a>compound selectors</a> which is a
<a>universal selector</a>, append the result of
<a lt="serialize a simple selector">serializing</a> the
<a>universal selector</a> to <var>s</var>.
<li>Otherwise, for each <a>simple selector</a> in the
<a>compound selectors</a> that is not a
universal selector of which the
<a>namespace prefix</a> maps to a namespace that is not the
<a>default namespace</a>
<a lt="serialize a simple selector">serialize</a> the
<a>simple selector</a> and append the result to
<var>s</var>.
<li>If this is not the last part of the chain of the selector append a
single SPACE (U+0020), followed by the combinator
"<code>></code>",
"<code>+</code>",
"<code>~</code>",
"<code>>></code>",
"<code>||</code>",
as appropriate, followed by another single SPACE (U+0020) if the combinator was
not whitespace, to <var>s</var>.
<li>If this is the last part of the chain of the selector and there is
a pseudo-element, append "<code>::</code>" followed by the name of the
pseudo-element, to <var>s</var>.
</ol>
To
<dfn export>serialize a simple selector</dfn>
let <var>s</var> be the empty string, run the steps below, and
finally return <var>s</var>:
<dl class="switch">
<dt>type selector
<dt>universal selector
<dd>
<ol>
<li>If the <a>namespace prefix</a> maps to a namespace that is
not the <a>default namespace</a> and is not the
null namespace (not in a namespace) append the
<a lt="serialize an identifier">serialization</a> of the
<a>namespace prefix</a> as an identifier, followed by a
"<code>|</code>" (U+007C) to <var>s</var>.
<li>If the <a>namespace prefix</a> maps to a namespace that is
the null namespace (not in a namespace) append
"<code>|</code>" (U+007C) to <var>s</var>.
<!-- This includes |* -->
<li>If this is a type selector append the
<a lt="serialize an identifier">serialization</a> of the element name
as an identifier to <var>s</var>.
<li>If this is a universal selector append "<code>*</code>" (U+002A)
to <var>s</var>.
</ol>
<dt>attribute selector
<dd>
<ol>
<li>Append "<code>[</code>" (U+005B) to
<var>s</var>.
<li>If the <a>namespace prefix</a> maps to a namespace that is
not the null namespace (not in a namespace) append the
<a lt="serialize an identifier">serialization</a> of the
<a>namespace prefix</a> as an identifier, followed by a
"<code>|</code>" (U+007C) to <var>s</var>.
<li>Append the <a lt="serialize an identifier">serialization</a>
of the attribute name as an identifier to <var>s</var>.
<li>If there is an attribute value specified, append
"<code>=</code>",
"<code>~=</code>",
"<code>|=</code>",
"<code>^=</code>",
"<code>$=</code>", or
"<code>*=</code>"
as appropriate (depending on the type of attribute selector), followed
by the <a lt="serialize a string">serialization</a> of the
attribute value as a string, to <var>s</var>.
<li>If the attribute selector has the case-sensitivity flag present,
append "<code> i</code>" (U+0020 U+0069) to <var>s</var>.
<li>Append "<code>]</code>" (U+005D) to
<var>s</var>.
</ol>
<dt>class selector
<dd>Append a "<code>.</code>" (U+002E), followed by the
<a lt="serialize an identifier">serialization</a> of the class name
as an identifier to <var>s</var>.
<dt>ID selector
<dd>Append a "<code>#</code>" (U+0023), followed by the
<a lt="serialize an identifier">serialization</a> of the ID
as an identifier to <var>s</var>.
<dt>pseudo-class
<dd>
If the pseudo-class does not accept arguments append
"<code>:</code>" (U+003A), followed by the name of the pseudo-class, to
<var>s</var>.
Otherwise, append "<code>:</code>" (U+003A), followed by the name of
the pseudo-class, followed by "<code>(</code>" (U+0028), followed by the
value of the pseudo-class argument(s) determined as per below, followed by
"<code>)</code>" (U+0029), to <var>s</var>.
<dl class="switch">
<dt><code>:lang()</code>
<dd>The <a lt="serialize a comma-separated list">serialization of a
comma-separated list</a> of each argument's
<a lt="serialize a string">serialization as a string</a>, preserving
relative order.
<dt><code>:nth-child()</code>
<dt><code>:nth-last-child()</code>
<dt><code>:nth-of-type()</code>
<dt><code>:nth-last-of-type()</code>
<dd>The result of serializing the value using the rules to <a>serialize an <an+b> value</a>.
<dt><code>:not()</code>
<dd>The result of serializing the value using the rules for
<a lt="serialize a group of selectors">serializing a group of selectors</a>.
</dl>
</dl>
CSS {#css-object-model}
=======================
CSS Style Sheets {#css-style-sheets}
------------------------------------
A <dfn export>CSS style sheet</dfn> is an abstract concept that
represents a style sheet as defined by the CSS specification. In the CSSOM a
<a>CSS style sheet</a> is represented as a {{CSSStyleSheet}} object. A
<a>CSS style sheet</a> has a number of associated state items:
<dl dfn-for="CSSStyleSheet">
<dt><dfn id=concept-css-style-sheet-type>type</dfn>
<dd>The literal string "<code>text/css</code>".
<dt><dfn id=concept-css-style-sheet-location>location</dfn>
<dd>Specified when created. The <a>absolute-URL string</a> of the first request of the
<a>CSS style sheet</a> or null if the <a>CSS style sheet</a> was
embedded. Does not change during the lifetime of the <a>CSS style sheet</a>.
<dt><dfn id=concept-css-style-sheet-parent-css-style-sheet>parent CSS style sheet</dfn>
<dd>Specified when created. The <a>CSS style sheet</a> that is the parent of the
<a>CSS style sheet</a> or null if there is no associated parent.
<dt><dfn id=concept-css-style-sheet-owner-node>owner node</dfn>
<dd>Specified when created. The DOM node associated with the <a>CSS style sheet</a> or
null if there is no associated DOM node.
<dt><dfn id=concept-css-style-sheet-owner-css-rule>owner CSS rule</dfn>
<dd>Specified when created. The <a for=/>CSS rule</a>
in the <a for=CSSStyleSheet>parent CSS style sheet</a>
that caused the inclusion of the <a>CSS style sheet</a> or null if
there is no associated rule.
<dt><dfn id=concept-css-style-sheet-media>media</dfn>
<dd>
Specified when created. The {{MediaList}} object associated with the
<a>CSS style sheet</a>.
If this property is specified to a string, the <a>media</a> must be set to the return value of invoking
<a>create a <code>MediaList</code> object</a> steps for that string.
If this property is specified to an attribute of the <a for=CSSStyleSheet>owner node</a>, the
<a>media</a> must be set to the return value of invoking <a>create a <code>MediaList</code> object</a> steps
for the value of that attribute. Whenever the attribute is set, changed or removed, the <a>media</a>'s
{{MediaList/mediaText}} attribute must be set to the new value of the attribute, or to null if the attribute is absent.
Note: Changing the <a>media</a>'s {{MediaList/mediaText}} attribute does not
change the corresponding attribute on the <a for=CSSStyleSheet>owner node</a>.
<dt><dfn id=concept-css-style-sheet-title>title</dfn>
<dd>
Specified when created. The title of the <a>CSS style sheet</a>, which can be the empty string.
<div class="example">
In the following, the <a>title</a> is non-empty
for the first style sheet, but is empty for the second and third style sheets.
<pre>
<style title="papaya whip">
body { background: #ffefd5; }
</style>
</pre>
<pre>
<style title="">
body { background: orange; }
</style>
</pre>
<pre>
<style>
body { background: brown; }
</style>
</pre>
</div>
If this property is specified to an attribute of the <a for=CSSStyleSheet>owner node</a>, the
<a>title</a> must be set to the value of that attribute. Whenever the attribute is set, changed or removed, the
<a>title</a> must be set to the new value of the attribute, or to the empty string if the attribute is absent.
<dt><dfn id=concept-css-style-sheet-alternate-flag>alternate flag</dfn>
<dd>
Specified when created. Either set or unset. Unset by default.
<div class="example">
The following <a>CSS style sheets</a> have
their <a>alternate flag</a> set:
<pre><?xml-stylesheet alternate="yes" title="x" href="data:text/css,…"?></pre>
<pre><link rel="alternate stylesheet" title="x" href="data:text/css,…"></pre>
</div>
<dt><dfn id=concept-css-style-sheet-disabled-flag>disabled flag</dfn>
<dd>
Either set or unset. Unset by default.
Note: Even when unset it does not necessarily mean that the
<a>CSS style sheet</a> is actually used for rendering.
<dt><dfn id=concept-css-style-sheet-css-rules>CSS rules</dfn>
<dd>The CSS
1821
rules associated with the
<a>CSS style sheet</a>.
<dt><dfn id=concept-css-style-sheet-origin-clean-flag>origin-clean flag</dfn>
<dd>Specified when created. Either set or unset. If it is set, the API allows reading and modifying of the <a for=CSSStyleSheet>CSS rules</a>.
</dl>
### The {{StyleSheet}} Interface ### {#the-stylesheet-interface}
The {{StyleSheet}} interface represents an abstract, base style sheet.
<pre class=idl>
[Exposed=Window]
interface StyleSheet {
readonly attribute CSSOMString type;
readonly attribute USVString? href;
readonly attribute (Element or ProcessingInstruction)? ownerNode;
readonly attribute StyleSheet? parentStyleSheet;
readonly attribute DOMString? title;
[SameObject, PutForwards=mediaText] readonly attribute MediaList media;
attribute boolean disabled;
};
</pre>
The <dfn attribute for=StyleSheet>type</dfn> attribute must return the <a for=CSSStyleSheet>type</a>.
The <dfn attribute for=StyleSheet>href</dfn> attribute must return the <a>location</a>.
The <dfn attribute for=StyleSheet>ownerNode</dfn> attribute must return the <a for=CSSStyleSheet>owner node</a>.
The <dfn attribute for=StyleSheet>parentStyleSheet</dfn> attribute must return the
<a for=CSSStyleSheet>parent CSS style sheet</a>.
The <dfn attribute for=StyleSheet>title</dfn> attribute must return the <a>title</a> or null if
<a>title</a> is the empty string.
The <dfn attribute for=StyleSheet>media</dfn> attribute must return the <a>media</a>.
The <dfn attribute for=StyleSheet>disabled</dfn> attribute, on getting, must return true if the
<a>disabled flag</a>
is set, or false otherwise. On setting, the {{StyleSheet/disabled}} attribute must set the
<a>disabled flag</a> if the new value is true, or unset the
<a>disabled flag</a> otherwise.
### The {{CSSStyleSheet}} Interface ### {#the-cssstylesheet-interface}
The {{CSSStyleSheet}} interface represents a <a>CSS style sheet</a>.
<pre class=idl>
[Exposed=Window]
interface CSSStyleSheet : StyleSheet {
readonly attribute CSSRule? ownerRule;
[SameObject] readonly attribute CSSRuleList cssRules;
unsigned long insertRule(CSSOMString rule, optional unsigned long index = 0);
void deleteRule(unsigned long index);
};
</pre>
The <dfn attribute for=CSSStyleSheet>ownerRule</dfn> attribute must return the <a for=CSSStyleSheet>owner CSS rule</a>.
If a value other than null is ever returned, then that same value must always be returned on each get access.
The <dfn attribute for=CSSStyleSheet>cssRules</dfn> attribute must follow these steps:
<ol>
<li>If the <a>origin-clean flag</a> is unset,
<a>throw</a> a {{SecurityError}} exception.
<li>Return a read-only, live {{CSSRuleList}} object representing
the <a for=CSSStyleSheet>CSS rules</a>.
Note: Even though the returned {{CSSRuleList}} object is read-only (from the perspective of
client-authored script), it can nevertheless change over time due to its liveness status. For example, invoking
the {{CSSStyleSheet/insertRule()}} or {{CSSStyleSheet/deleteRule()}} methods can result in
mutations reflected in the returned object.
</ol>
The <dfn method for=CSSStyleSheet>insertRule(<var>rule</var>, <var>index</var>)</dfn> method must run the following steps:
<ol>
<li>If the <a>origin-clean flag</a> is unset,
<a>throw</a> a {{SecurityError}} exception.
<li>Return the result of invoking <a>insert a CSS rule</a> <var>rule</var> in the <a for=CSSStyleSheet>CSS rules</a>
at <var>index</var>.
</ol>
The <dfn method for=CSSStyleSheet>deleteRule(<var>index</var>)</dfn> method must run the following steps:
<ol>
<li>If the <a>origin-clean flag</a> is unset,
<a>throw</a> a {{SecurityError}} exception.
<li><a>Remove a CSS rule</a> in the <a for=CSSStyleSheet>CSS rules</a> at <var>index</var>.
</ol>
CSS Style Sheet Collections {#css-style-sheet-collections}
----------------------------------------------------------
Below various new concepts are defined that are associated with each
{{Document}} object.
Each {{Document}} has an associated list of zero or more
<a>CSS style sheets</a>, named the
<dfn>document CSS style sheets</dfn>. This is
an ordered list that contains all
<a>CSS style sheets</a> associated with the
{{Document}}, in
<a>tree order</a>, with
<a>CSS style sheets</a> created from HTTP
<code>Link</code> headers first, if any, in header
order.
To <dfn>create a CSS style sheet</dfn>, run these
steps:
<ol>
<li>Create a new <a>CSS style sheet</a> object and set its
properties as specified.
<li>
Then run the <a>add a CSS style sheet</a> steps for the newly created <a>CSS style sheet</a>.
<p class=warning>If the <a>origin-clean flag</a> is unset, this can expose information from the user's
intranet.
</ol>
To <dfn>add a CSS style sheet</dfn>, run these
steps:
<ol>
<li>Add the <a>CSS style sheet</a> to the list of
<a>document CSS style sheets</a> at the appropriate location. The
remainder of these steps deal with the
<a>disabled flag</a>.
<li>If the <a>disabled flag</a> is set, then return.
<li>If the <a>title</a> is not the empty string, the
<a>alternate flag</a> is unset, and
<a>preferred CSS style sheet set name</a> is the empty string
<a>change the preferred CSS style sheet set name</a> to the
<a>title</a>.
<li>
If any of the following is true, then unset the
<a>disabled flag</a> and return:
<ul>
<li>The <a>title</a> is the empty string.
<li>The <a>last CSS style sheet set name</a> is null and the
<a>title</a> is a
<a>case-sensitive</a> match
for the <a>preferred CSS style sheet set name</a>.