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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang=en-US>
<head>
<title>Cascading Style Sheets Object Model (CSSOM)</title>
<style type="text/css">
pre.idl { border:solid thin; background:#eee; color:#000; padding:0.5em }
pre.idl :link, pre.idl :visited { color:inherit; background:transparent }
dfn { font-weight:bold; font-style:normal }
div.example { margin-left:1em; padding-left:1em; border-left:double; color:#222; background:#fcfcfc }
div.example table code { color:inherit }
td, th { padding:.1em }
.proposal { padding:.5em; border:solid blue }
p.note { margin-left:2em; color:green; font-style:italic; font-weight:bold }
p.note::before { content:"Note: " }
.issue { padding:.5em; border:solid red }
.issue::before { content:"Issue: " }
em.ct { text-transform:lowercase; font-variant:small-caps; font-style:normal }
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code :link, code :visited { color:inherit }
.members dt { margin:.5em 0 }
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.members dd p:last-child { margin-bottom:0 }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel=stylesheet>
<body class=draft>
<div class=head>
<h1 id=cssom>Cascading Style Sheets Object Model (<abbr>CSSOM</abbr>)</h1>
<h2 class="no-num no-toc" id="">Editor's Draft 30 December 2007</h2>
<dl>
<dt>This version:
<dd><a
href="http://dev.w3.org/csswg/cssom/">http://dev.w3.org/csswg/cssom/</a></dd>
<!--<dd><a href="http://www.w3.org/TR/2007/ED-cssom-20071230/">http://www.w3.org/TR/2007/WD-cssom-20071230/</a></dd>-->
<dt>Latest version:
<dd><a href="http://www.w3.org/TR/cssom/">http://www.w3.org/TR/cssom/</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/">http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/</a>
<dt>Editor:
<dd><a href="http://annevankesteren.nl/">Anne van Kesteren</a> (<a
href="http://www.opera.com/">Opera Software ASA</a>) <<a
href="mailto:annevk@opera.com">annevk@opera.com</a>>
</dl>
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>The Cascading Style Sheets Object Model defines enables developers to
find style sheets associated with a <code>Document</code> and to query and
modify rules within a CSS style sheet (through an object model).
<h2 class="no-num no-toc" id=sotd>Status of this Document</h2>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. It probably contains errors.
Its publication here does not imply endorsement of its contents by W3C.
<!--end-status-->
<p class=issue>This document is in its very early stages. The intention is
that this specification will in due course supersede DOM Level 2 Style.
<h2 class="no-num no-toc" id=toc>Table of Contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<ul class=toc>
<li><a href="#history"><span class=secno>1.1. </span>History</a>
</ul>
<li><a href="#conformance"><span class=secno>2. </span>Conformance
Requirements</a>
<ul class=toc>
<li><a href="#terminology"><span class=secno>2.1. </span>Terminology</a>
</ul>
<li><a href="#style"><span class=secno>3. </span>Style Sheets and the
DOM</a>
<ul class=toc>
<li><a href="#style0"><span class=secno>3.1. </span>Style Sheet</a>
<ul class=toc>
<li><a href="#the-stylesheet"><span class=secno>3.1.1. </span>The
<code title="">StyleSheet</code> Interface</a>
<li><a href="#the-stylesheetlist"><span class=secno>3.1.2. </span>The
<code title="">StyleSheetList</code> Interface</a>
</ul>
<li><a href="#media"><span class=secno>3.2. </span>Media Queries</a>
<ul class=toc>
<li><a href="#the-medialist"><span class=secno>3.2.1. </span>The
<code>MediaList</code> Interface</a>
</ul>
<li><a href="#style1"><span class=secno>3.3. </span>Style Sheet
Types</a>
<li><a href="#accessing"><span class=secno>3.4. </span>Accessing Style
Sheets</a>
<ul class=toc>
<li><a href="#the-linkstyle"><span class=secno>3.4.1. </span>The <code
title="">LinkStyle</code> Interface</a>
<ul class=toc>
<li><a href="#requirements"><span class=secno>3.4.1.1.
</span>Requirements on specifications</a>
</ul>
<li><a href="#requirements0"><span class=secno>3.4.2.
</span>Requirements User Agents Implementing SVG</a>
<li><a href="#requirements1"><span class=secno>3.4.3.
</span>Requirements on User Agents Implementing
<code><?xml-stylesheet?></code></a>
<li><a href="#requirements2"><span class=secno>3.4.4.
</span>Requirements on User Agents Implementing the HTTP <code
title="">Link</code> Header</a>
<li><a href="#the-documentstyle"><span class=secno>3.4.5. </span>The
<code title="">DocumentStyle</code> Interface</a>
</ul>
<li><a href="#dynamically"><span class=secno>3.5. </span>Dynamically
adding new style sheets</a>
<ul class=toc>
<li><a href="#adding"><span class=secno>3.5.1. </span>Adding style
sheets</a>
<li><a href="#changing"><span class=secno>3.5.2. </span>Changing the
preferred style sheet set</a>
<li><a href="#examples"><span class=secno>3.5.3. </span>Examples</a>
</ul>
<li><a href="#interaction"><span class=secno>3.6. </span>Interaction
with the User Interface</a>
<ul class=toc>
<li><a href="#persisting"><span class=secno>3.6.1. </span>Persisting
the selected style sheet set</a>
</ul>
<li><a href="#forward"><span class=secno>3.7. </span>Forward
compatibility</a>
</ul>
<li><a href="#cascading"><span class=secno>4. </span>Cascading Style
Sheets APIs</a>
<ul class=toc>
<li><a href="#parsing"><span class=secno>4.1. </span>Parsing and
Serializing CSS Constructs</a>
<ul class=toc>
<li><a href="#css-value"><span class=secno>4.1.1. </span>CSS Value
Rules</a>
<ul class=toc>
<li><a href="#examples0"><span class=secno>4.1.1.1. </span>Examples
of the CSS Value Serializing Algorithm </a>
</ul>
<li><a href="#selectors"><span class=secno>4.1.2. </span>Selectors
Rules</a>
<li><a href="#css-page"><span class=secno>4.1.3. </span>CSS Page
Selectors Rules</a>
<li><a href="#processing"><span class=secno>4.1.4. </span>Processing
CSS Statements</a>
</ul>
<li><a href="#the-cssstylesheet"><span class=secno>4.2. </span>The <code
title="">CSSStyleSheet</code> Interface</a>
<li><a href="#the-cssrulelist"><span class=secno>4.3. </span>The <code
title="">CSSRuleList</code> Interface</a>
<li><a href="#interfaces"><span class=secno>4.4. </span>Interfaces for
CSS Statements</a>
<ul class=toc>
<li><a href="#the-cssrule"><span class=secno>4.4.1. </span>The <code
title="">CSSRule</code> Interface</a>
<ul class=toc>
<li><a href="#extensibility"><span class=secno>4.4.1.1.
</span>Extensibility</a>
</ul>
<li><a href="#the-cssstylerule"><span class=secno>4.4.2. </span>The
<code title="">CSSStyleRule</code> Interface</a>
<li><a href="#the-cssimportrule"><span class=secno>4.4.3. </span>The
<code title="">CSSImportRule</code> Interface</a>
<li><a href="#the-cssmediarule"><span class=secno>4.4.4. </span>The
<code title="">CSSMediaRule</code> Interface</a>
<li><a href="#the-cssfontfacerule"><span class=secno>4.4.5. </span>The
<code title="">CSSFontFaceRule</code> Interface</a>
<li><a href="#the-csspagerule"><span class=secno>4.4.6. </span>The
<code title="">CSSPageRule</code> Interface</a>
<li><a href="#the-cssnamespacerule"><span class=secno>4.4.7.
</span>The <code title="">CSSNamespaceRule</code> Interface</a>
</ul>
<li><a href="#accessing0"><span class=secno>4.5. </span>Accessing
declaration blocks</a>
<ul class=toc>
<li><a href="#the-elementcssinlinestyle"><span class=secno>4.5.1.
</span>The <code>ElementCSSInlineStyle</code> Interface</a>
<li><a href="#the-viewcss"><span class=secno>4.5.2. </span>The <code
title="">ViewCSS</code> Interface</a>
</ul>
<li><a href="#css-declaration-blocks"><span class=secno>4.6. </span>CSS
Declaration Blocks</a>
<ul class=toc>
<li><a href="#the-cssstyledeclaration"><span class=secno>4.6.1.
</span>The <code title="">CSSStyleDeclaration</code> Interface</a>
<li><a href="#the-css2properties"><span class=secno>4.6.2. </span>The
<code title="">CSS2Properties</code> Interface</a>
</ul>
</ul>
<li class=no-num><a href="#references">References</a>
<li class=no-num><a href="#acknowledgements">Acknowledgements</a>
</ul>
<!--end-toc-->
<h2 id=introduction><span class=secno>1. </span>Introduction</h2>
<p class=issue>...
<h3 id=history><span class=secno>1.1. </span>History</h3>
<p>Several interfaces from DOM Level 2 Style <a
href="http://www.w3.org/mid/Pine.LNX.4.05.10310302134070.1173-100000@lanalana.inria.fr"
title="[CSSOM] CSSValue and related interfaces (message from the CSS
WG)">have been obsoleted</a> because they where thought to be too awkward
for frequent use. This specification no longer contains those features.
<code>DOMImplementationCSS</code> and <code>CSSCharsetRule</code> have
been removed as well as they were not deemed necessary.
<h2 id=conformance><span class=secno>2. </span>Conformance Requirements</h2>
<p>Everything in this specification is normative except for diagrams,
examples, notes and sections marked non-normative.
<p>The key words <em class=ct>must</em>, <em class=ct>must not</em>, <em
class=ct>required</em>, <em class=ct>shall</em>, <em class=ct>shall
not</em>, <em class=ct>should</em>, <em class=ct>should not</em>, <em
class=ct>recommended</em>, <em class=ct>may</em>, and <em
class=ct>optional</em> in the normative parts of this document are to be
interpreted as described in [<cite><a
href="#ref-rfc2119">RFC2119</a></cite>].
<p>The following conformance classes are defined (and considered) by this
specification:
<dl>
<dt><dfn id=conforming-implementation>conforming implementation</dfn>
<dd>A user agent that implements all interfaces described in this
specification and follows all <em class=ct>must</em>-, <em
class=ct>required</em>- and <em class=ct>shall</em>-level of criteria in
this specification.
<dt><dfn id=conforming-document>conforming document</dfn>
<dd>A document that follows all <em class=ct>must</em>-, <em
class=ct>required</em>- and <em class=ct>shall</em>-level of criteria in
this specification that apply to document authors.
<dt><dfn id=conforming-authoring-tool>conforming authoring tool</dfn>
<dd>One that produces conforming documents.
</dl>
<h3 id=terminology><span class=secno>2.1. </span>Terminology</h3>
<p>A <dfn id=color>color component integer</dfn> is a base-ten integer in
the range 0-255 using digits 0-9, U+0030 to U+0039, in the shortest form
possible.
<p>A <dfn id=color0>color component separator</dfn> is a literal U+002C
COMMA followed by a U+0020 SPACE.
<p>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>.</p>
<!--
<p>The term <dfn id="whitespace">whitespace</dfn> when used in this
specification refers to the U+0020 SPACE, U+0009 <control>, U+000A
<control>, U+000D <control> and U+000C <control> (if
applicable).</p>
-->
<p>The terms <dfn id=whitespace>whitespace</dfn> and <dfn
id=style-sheet>style sheet</dfn> are used as defined in the <cite>CSS 2.1
Specification</cite> [CSS21].
<p>A <dfn id=css-style-sheet>CSS style sheet</dfn> is a <a
href="#style-sheet">style sheet</a> that conforms to the CSS syntax rules.</p>
<!-- XXX: "Cascading Style Sheet style sheet" is just a joke... -->
<h2 id=style><span class=secno>3. </span>Style Sheets and the DOM</h2>
<h3 id=style0><span class=secno>3.1. </span>Style Sheet</h3>
<p>Each document has a collection of zero or more associated style sheets.
A <dfn id=style-sheet>style sheet</dfn> is represented by an object that
implements the <code><a href="#stylesheet">StyleSheet</a></code> interface
(as described below) and has a number of properties that need to be set
when a style sheet is created. These properties can be modified over time.
<dl>
<dt><dfn id=style-sheet-type>style sheet type</dfn>
<dd>
<p>A string that is the MIME type of the style sheet. [RFC2046].
<dt><dfn id=style-sheet-location>style sheet location</dfn>
<dd>
<p>A string that is the URI of the style sheet's location or the
<code>null</code> value if the style sheet was embedded within a
document.
<dt><dfn id=style-sheet-media>style sheet media</dfn>
<dd>
<p>A string with the media queries applicable to the style sheet. When
the style sheet is created the <code>mediaText</code> attribute returned
by the <code>media</code> attribute on the style sheet <em
class=ct>must</em> be set to this string.
<dt><dfn id=style-sheet-title>style sheet title</dfn>
<dd>
<p>A string that is the title of the style sheet. A style sheet is said
to <dfn id=have-a>have a title</dfn> if this string is not the empty
string.</p>
<div class=example>
<p>The following CSS style sheets have a style sheet title that is the
empty string:</p>
<pre><style title=""> body { background:lime } </style></pre>
<pre><style> body { background:lime } </style></pre>
</div>
<dt><dfn id=style-sheet-alternate-flag>style sheet alternate flag</dfn>
<dd>
<p>...</p>
<div class=example>
<p>The following style sheets have their style sheet alternate flag set
to <i>true</i>:</p>
<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=style2>style sheet disabled flag</dfn>
<dd>
<p>...</p>
<p class=note>This flag is independent of whether the style sheet is
actually applied. That depends on the style sheet media as well, for
instance.</p>
</dl>
<p>Specifications <em class=ct>must not</em> allow the creation of <a
href="#style-sheet" title="style sheet">style sheets</a> with the <a
href="#style-sheet-alternate-flag">style sheet alternate flag</a> set to
<i>true</i> and the <a href="#style-sheet-title">style sheet title</a> set
to the empty string. In addition they <em class=ct>must not</em> allow the
creation of <a href="#style-sheet" title="style sheet">style sheets</a>
for which the user agent does not support the style sheet language.
<h4 id=the-stylesheet><span class=secno>3.1.1. </span>The <code
title="">StyleSheet</code> Interface</h4>
<pre class=idl>interface <dfn id=stylesheet>StyleSheet</dfn> {
readonly attribute DOMString <a href="#stylesheet-type" title=stylesheet-type>type</a>;
attribute boolean <a href="#stylesheet-disabled" title=stylesheet-disabled>disabled</a>;
readonly attribute Node <a href="#stylesheet-ownernode" title=stylesheet-ownernode>ownerNode</a>;
readonly attribute <a href="#stylesheet">StyleSheet</a> <a href="#stylesheet-parentstylesheet" title=stylesheet-parentstylesheet>parentStyleSheet</a>;
readonly attribute DOMString <a href="#stylesheet-href" title=stylesheet-href>href</a>;
readonly attribute DOMString <a href="#stylesheet-title" title=stylesheet-title>title</a>;
[PutForwards=mediaText] readonly attribute <a href="#medialist">MediaList</a> <a href="#stylesheet-media" title=stylesheet-media>media</a>;
};</pre>
<p class=note>CSS style sheets objects implement the <code><a
href="#cssstylesheet">CSSStyleSheet</a></code> interface which inherits
from the <code><a href="#stylesheet">StyleSheet</a></code> interface.
<p>The <dfn id=stylesheet-type
title=stylesheet-type><code>type</code></dfn> attribute, on getting, <em
class=ct>must</em> return the <a href="#style-sheet-type">style sheet
type</a>.
<p>The <dfn id=stylesheet-disabled
title=stylesheet-disabled><code>disabled</code></dfn> attribute, on
getting, <em class=ct>must</em> return <code>true</code> when the <a
href="#style2">style sheet disabled flag</a> is <i>true</i> and
<code>false</code> if that flag is <i>false</i>. On setting, it <em
class=ct>must</em> set the <a href="#style2">style sheet disabled flag</a>
to <i>true</i> if set to <code>true</code>, and set the flag to
<i>false</i> if set to <code>false</code>.
<p>The <dfn id=stylesheet-ownernode
title=stylesheet-ownernode><code>ownerNode</code></dfn> attribute, on
getting, <em class=ct>must</em> return the <code>Node</code> that
associates the style sheet with the document or it <em class=ct>must</em>
return <code>null</code> if there is no such <code>Node</code>.
<p class=note>The aformentioned <code>Node</code> has implemented the
<code><a href="#linkstyle">LinkStyle</a></code> interface.
<p>The <dfn id=stylesheet-parentstylesheet
title=stylesheet-parentstylesheet><code>parentStyleSheet</code></dfn>
attribute, on getting, <em class=ct>must</em> return the <code><a
href="#stylesheet">StyleSheet</a></code> object that caused the inclusion
of the current style sheet or <code>null</code> if there is no such
object.
<p>The <dfn id=stylesheet-href
title=stylesheet-href><code>href</code></dfn> attribute, on getting, <em
class=ct>must</em> return the <a href="#style-sheet-location">style sheet
location</a>.
<p>The <dfn id=stylesheet-title
title=stylesheet-title><code>title</code></dfn> attribute, on getting, <em
class=ct>must</em> return the <a href="#style-sheet-title">style sheet
title</a>.
<p>The <dfn id=stylesheet-media
title=stylesheet-media><code>media</code></dfn> attribute, on getting, <em
class=ct>must</em> return an object implementing the <code><a
href="#medialist">MediaList</a></code> interface that represents the <a
href="#style-sheet-media">style sheet media</a>.
title="">StyleSheetList</code> Interface</h4>
<p>The object implementing this interface represents an ordered collection
of objects implementing the <code><a
href="#stylesheet">StyleSheet</a></code> interface. Items in this
collection are accessible through an integral index, starting from zero.
<pre class=idl>interface <dfn id=stylesheetlist>StyleSheetList</dfn> {
readonly attribute unsigned long <a href="#stylesheetlist-length" title=stylesheetlist-length>length</a>;
[IndexGetter] <a href="#stylesheet">StyleSheet</a> <a href="#stylesheetlist-item" title=stylesheetlist-item>item</a>(in unsigned long <var title="">index</var>);
};</pre>
<p>The <dfn id=stylesheetlist-length
title=stylesheetlist-length><code>length</code></dfn> attribute, on
getting, <em class=ct>must</em> return the number of objects currently in
the list.
<p>The <dfn id=stylesheetlist-item
title=stylesheetlist-item><code>item(<var
title="">index</var>)</code></dfn> method, when invoked, <em
class=ct>must</em> return the <code><a
href="#stylesheet">StyleSheet</a></code> object in the list given by
<var>index</var>, or <code>null</code>, if <var>index</var> is greater
than or equal to the number of items in the list.
<h3 id=media><span class=secno>3.2. </span>Media Queries</h3>
<p>creating a MediaList object?
<p>The <dfn id=parsing-media-query title="parsing media query">rules for
parsing a media query</dfn> for a given string <var>s</var> are to follow
the <span>rules for parsing a list of media queries</span> and return the
first media query those rules return, or <i>null</i> if <i>null</i> is
returned.
<p>The <dfn id=parsing-media-queries title="parsing media queries">rules
for parsing a list of media queries</dfn> ...
<p>The <dfn id=serializing-media-query title="serializing media
query">rules for serializing a media query</dfn> are as follows:
<ol>
<li>
<p>Let <var>s</var> be the empty string.
<li>
<p>If the media query is negated append the literal string
"<code>not</code>", followed by a U+0020 character, to <var>s</var>.
<li>
<p>If the media query does not contain media features append the
canonical form of the media type (as specified in the syntax) to
<var>s</var>, then return <var>s</var> and terminate this algorithm.
<li>
<p>If the media type is not <code>all</code> append the canonical form of
the media type, followed by a U+0020 character, followed by the literal
string "<code>and</code>", followed by a U+0020 character, to
<var>s</var>.
<li>
<p>Remove all duplicate media features.
<li>
<p>Convert each media feature name and media feature value to its
canonical form (as specified in the syntax).
<li>
<p>Sort the media features in lexicographical order.
<li>
<p>Then, for each media feature:</p>
<ol>
<li>Append a U+0028 (<code>(</code>) character, followed by the media
feature name, to <var>s</var>.
<li>
<p>If a value is given append a U+003A (<code>:</code>) character,
followed by a U+0020 character, followed by the media feature value,
to <var>s</var>.</p>
<li>
<p>Append a U+0029 (<code>)</code>) character to <var>s</var>.
<li>
<p>If this is not the last media feature append a U+0020 character,
followed by the literal string "<code>and</code>", followed by a
U+0020 character, to <var>s</var>.</p>
</ol>
<li>
<p>Return <var>s</var>.
</ol>
<div class=example>
<p>Here are some examples of input and output:</p>
<table>
<thead>
<tr>
<th>Input
<th>Output
<tbody>
<tr>
<td><code>not screen and (min-WIDTH:5px) AND (max-width:40px )</code>
<td><code>not screen and (max-width: 40px) and (min-width: 5px)</code>
<tr>
<td><code>all and (color) and (color)</code>
<td><code>(color)</code>
</table>
</div>
<p>The <dfn id=serializing-media-queries title="serializing media
queries">rules for serializing a list of media queries</dfn> are as
follows:
<ol>
<li>
<p>Let <var>s</var> be the empty string.
<li>
<p>If the list is empty return <var>s</var> and terminate this algorithm.
<li>
<p>For each media query in the list:</p>
<ol>
<li>
<p>Append the result of <span title=serializing-media-query>serializing
the media query</span> to <var>s</var>.
<li>
<p>If this is not the last media query append a U+002C (<code>,</code>)
character, followed by a U+0020 character to <var>s</var>.
</ol>
<li>
<p>Return <var>s</var>.
</ol>
<p>The <dfn id=compare-media-queries title="compare media queries">rules
for comparing media queries</dfn> <var>m1</var> and <var>m2</var> are to
<a href="#serializing-media-query" title="serializing media
query">serialize</a> them both and if they are equal return <i>true</i>
and <i>false</i> otherwise.
<h4 id=the-medialist><span class=secno>3.2.1. </span>The <code><a
href="#medialist">MediaList</a></code> Interface</h4>
<div class=issue>
<p>There are several rules:</p>
<ul>
<li>No duplicates
<li>Canonicalized on getting
</ul>
</div>
<p>Objects implementing the <code><a href="#medialist">MediaList</a></code>
interface represent an ordered collection of media queries. Items in this
collection are accessible through an integral index, starting from zero.
<pre class=idl>interface <dfn id=medialist>MediaList</dfn> {
attribute DOMString <a href="#medialist-mediatext" title=medialist-mediatext>mediaText</a>;
readonly attribute unsigned long <a href="#medialist-length" title=medialist-length>length</a>;
[IndexGetter] DOMString <a href="#medialist-item" title=medialist-item>item</a>(in unsigned long <var title="">index</var>);
void <a href="#medialist-appendmedium" title=medialist-appendmedium>appendMedium</a>(in DOMString <var title="">medium</var>)
void <a href="#medialist-deletemedium" title=medialist-deletemedium>deleteMedium</a>(in DOMString <var title="">medium</var>)
};</pre>
<p>In bindings that allow it, such as ECMAScript, <code><a
href="#medialist">MediaList</a></code> objects <em class=ct>must</em>
stringify to their <code title=medialist-mediatext><a
href="#medialist-mediatext">mediaText</a></code> attribute's value.</p>
<!-- XXX Web IDL ^^ -->
<p>The <dfn id=medialist-mediatext
title=medialist-mediatext><code>mediaText</code></dfn> attribute, on
getting, <em class=ct>must</em> return a <a
href="#serializing-media-queries" title="serializing media
queries">serialization of the media qeuries</a>. On setting, setting <em
class=ct>must</em> be ignored if the return value of <a
href="#parsing-media-queries" title="parsing media queries">parsing</a>
the setted string is <i>null</i>. Otherwise the return values of parsing
<em class=ct>must</em> be used as the new media queries.</p>
<!-- XXX empty string -->
<p>The <dfn id=medialist-length
title=medialist-length><code>length</code></dfn> attribute, on getting,
<em class=ct>must</em> return the number of items in the collection.
<p>The <dfn id=medialist-item title=medialist-item><code>item(<var
title="">index</var>)</code></dfn> method, when invoked, <em
class=ct>must</em> return the item in the list given by <var>index</var>,
or <code>null</code>, if <var>index</var> is greater than or equal to the
number of items in the list.
<p>The <dfn id=medialist-appendmedium
title=medialist-appendmedium><code>appendMedium(<var
title="">medium</var>)</code></dfn> method, when invoked, <span
class=issue>...</span>.
<p>The <dfn id=medialist-deletemedium
title=medialist-deletemedium><code>deleteMedium(<var
title="">medium</var>)</code></dfn> method, when invoked, <em
class=ct>must</em> raise a <code>NOT_FOUND_ERR</code> exception when
<var>medium</var> is not in the collection. Otherwise, <var>medium</var>
<em class=ct>must</em> be removed from the collection.
<h3 id=style1><span class=secno>3.3. </span>Style Sheet Types</h3>
<p>A <dfn id=persistent-style-sheet>persistent style sheet</dfn> is a <a
href="#style-sheet">style sheet</a> whose <a
href="#style-sheet-title">style sheet title</a> is the empty string.
<p>A <dfn id=style-sheet-set>style sheet set</dfn> is a collection of one
or more <a href="#style-sheet" title="style sheet">style sheets</a> which
have an identical <a href="#style-sheet-title">style sheet title</a> that
is not the empty string.
<p>An <dfn id=alternative-style-sheet-set>alternative style sheet set</dfn>
is a <a href="#style-sheet-set">style sheet set</a> of which the <a
href="#style-sheet-alternate-flag">style sheet alternate flag</a> is
<i>true</i>.
<p class=issue><dfn id=preferred>preferred style sheet set</dfn>
<h3 id=accessing><span class=secno>3.4. </span>Accessing Style Sheets</h3>
<h4 id=the-linkstyle><span class=secno>3.4.1. </span>The <code
title="">LinkStyle</code> Interface</h4>
<p>The <code><a href="#linkstyle">LinkStyle</a></code> interface provides a
bridge between the node that takes care of the embedding or inclusion of a
<a href="#style-sheet">style sheet</a> and the <code><a
href="#stylesheet">StyleSheet</a></code> object representing the style
sheet.
<p class=note>The <code>style</code> content attribute found in various
markup languages does not embed, or represent, a style sheet.
<pre class=idl>interface <dfn id=linkstyle>LinkStyle</dfn> {
readonly attribute <a href="#stylesheet">StyleSheet</a> <a href="#linkstyle-sheet" title=linkstyle-sheet>sheet</a>;
};</pre>
<p>The <dfn id=linkstyle-sheet
title=linkstyle-sheet><code>sheet</code></dfn> attribute, on getting, <em
class=ct>must</em> return the associated <code><a
href="#stylesheet">StyleSheet</a></code> object, or <code>null</code>, if
there is no associated <code><a href="#stylesheet">StyleSheet</a></code>
object.
<div class=example>
<p>In the following HTML snippet the first HTML <code>style</code> element
has a <code>sheet</code> attribute that returns a <code><a
href="#stylesheet">StyleSheet</a></code> object representing the CSS
style sheet, but for the second <code>style</code> attribute it returns
<code>null</code>. (Assuming the user agent supports CSS
(<code>text/css</code>) and does not support ExampleSheets
(<code>text/example-sheets</code>).</p>
<pre><style type=text/css> body { background:lime } </style>
<style type=text/example-sheets> $(body).background := lime </style></pre>
</div>
<p class=note>Whether or not the node refers to a style sheet is defined
8812
by
the specification that defines the semantics of said node.
<h5 id=requirements><span class=secno>3.4.1.1. </span>Requirements on
specifications</h5>
<p>Specifications introducing new ways of associating style sheets through
the DOM <em class=ct>should</em> define which <code>Node</code>s implement
the <code><a href="#linkstyle">LinkStyle</a></code> interface. These
specifications <em class=ct>should</em> also define how the various
properties of a <a href="#style-sheet">style sheet</a> are set when <code
title=linkstyle-sheet><a href="#linkstyle-sheet">sheet</a></code> is not
<code>null</code>.
<p class=note>This specification defines it for SVG,
<code><?xml-stylesheet?></code>, and the HTTP <code>Link</code> header
for the time being.
<h4 id=requirements0><span class=secno>3.4.2. </span>Requirements User
Agents Implementing SVG</h4>
<p><em>This section applies to user agents implementing SVG.</em>
<p>SVG user agents <em class=ct>must</em> implement the <code><a
href="#linkstyle">LinkStyle</a></code> interfaces on objects implementing
the <code>SVGStyleElement</code> interface.
<p class=issue>...
<h4 id=requirements1><span class=secno>3.4.3. </span>Requirements on User
Agents Implementing <code><?xml-stylesheet?></code></h4>
<p><em>This section applies to user agents implementing
<code><?xml-stylesheet?></code>.</em>
<p>User agents supporting supporting <code><?xml-stylesheet?></code> <em
class=ct>must</em> implement the <code><a
href="#linkstyle">LinkStyle</a></code> on objects implementing
<code>ProcessingInstruction</code>.
<p>If the <code title="">target</code> DOM attribute of the
<code>ProcessingInstruction</code> is not <code>xml-stylesheet</code> then
the <code title=linkstyle-sheet><a
href="#linkstyle-sheet">sheet</a></code> attribute of the node's <code><a
href="#linkstyle">LinkStyle</a></code> interface <em class=ct>must</em>
return <code>null</code>.
<p>Else, if the <code title="">target</code> DOM attribute is
<code>xml-stylesheet</code> but the specified resource has not completed
downloading, or is not a supported style sheet language the <code
title=linkstyle-sheet><a href="#linkstyle-sheet">sheet</a></code>
attribute of the node's <code><a href="#linkstyle">LinkStyle</a></code>
interface <em class=ct>must</em> return <code>null</code>.
<p>Otherwise, a new <a href="#style-sheet">style sheet</a> <em
class=ct>must</em> be created with <a href="#style-sheet-type">style sheet
type</a> set to the canonical type, <a href="#style-sheet-location">style
sheet location</a> to the location of the style sheet, <a
href="#style-sheet-title">style sheet title</a> to the value of the <code
title="">title</code> pseudo-attribute, <a href="#style-sheet-media">style
sheet media</a> to the value of the <code title="">media</code>
pseudo-attribute, the <a href="#style-sheet-alternate-flag">style sheet
alternate flag</a> to <i>true</i> if the <code title="">alternate</code>
pseudo-attribute is "<code>yes</code>" and <i>false</i> otherwise, and the
<a href="#style2">style sheet disabled flag</a> to <i>false</i>.
<h4 id=requirements2><span class=secno>3.4.4. </span>Requirements on User
Agents Implementing the HTTP <code title="">Link</code> Header</h4>
<p class=issue>...
<h4 id=the-documentstyle><span class=secno>3.4.5. </span>The <code
title="">DocumentStyle</code> Interface</h4>
<p>Any object implementing the <code>Document</code> interface <em
class=ct>must</em> also implement the <code><a
href="#documentstyle">DocumentStyle</a></code> interface.</p>
<!-- https://bugzilla.mozilla.org/show_bug.cgi?id=200930 (FIXED) -->
<pre class=idl>interface <dfn id=documentstyle>DocumentStyle</dfn> {
readonly attribute <a href="#stylesheetlist">StyleSheetList</a> <a href="#documentstyle-stylesheets">styleSheets</a>;
attribute DOMString <a href="#documentstyle-selectedStyleSheetSet">selectedStyleSheetSet</a>;
readonly attribute DOMString <a href="#documentstyle-lastStyleSheetSet">lastStyleSheetSet</a>;
readonly attribute DOMString <a href="#documentstyle-preferredStyleSheetSet">preferredStyleSheetSet</a>;
readonly attribute DOMStringList <a href="#documentstyle-styleSheetSets">styleSheetSets</a>;
void <a href="#documentstyle-enablestylesheetsforset" title=documentstyle-enablestylesheetsforset>enableStylesheetsForSet</a>(in DOMString <var>name</var>);
};</pre>
<!-- XXX Web IDL \/ -->
<p>For this interface, the <code>DOMString</code> values <code>null</code>
and "the empty string" are distinct and <em class=ct>must</em> not be
considered equivalent.
<dl class=members>
<dt><dfn id=documentstyle-stylesheets><code>styleSheets</code></dfn> of
type <code><a href="#stylesheetlist">StyleSheetList</a></code>
<dd>
<p>This attribute <em class=ct>must</em> be a <code><a
href="#stylesheetlist">StyleSheetList</a></code> object containing a
collection of all <code><a href="#stylesheet">StyleSheet</a></code>
objects in document order (those returned by <code
title=linkstyle-sheet><a href="#linkstyle-sheet">sheet</a></code>
attribute on objects implementing the <code><a
href="#linkstyle">LinkStyle</a></code> interface) preceded by style
sheets introduced through the HTTP <code>Link</code> header.
<dt><dfn
id=documentstyle-selectedStyleSheetSet><code>selectedStyleSheetSet</code></dfn>
of type <code>DOMString</code>
<dd>
<p>This attribute indicates which <a href="#style-sheet-set">style sheet
set</a> is in use. This attribute is <span>live</span>; changing the
<code title=stylesheet-disabled><a
href="#stylesheet-disabled">disabled</a></code> attribute on style
sheets directly will change the value of this attribute.</p>
<p>If all the sheets that are enabled and <a href="#have-a">have a
title</a> have the <em>same</em> title (by <span>case-sensitive</span>
comparisons) then the value of this attribute <em class=ct>must</em> be
exactly equal to the title of the first enabled style sheet with a title
in the <code><a href="#documentstyle-stylesheets">styleSheets</a></code>
list. Otherwise, if style sheets from different sets are enabled, then
the return value <em class=ct>must</em> be <code>null</code> (there is
no way to determine what the currently selected style sheet set is in
those conditions). Otherwise, either all style sheets that <a
href="#have-a">have a title</a> are disabled, or there are no
alternative style sheets, and <code><a
href="#documentstyle-selectedStyleSheetSet">selectedStyleSheetSet</a></code>
<em class=ct>must</em> return the empty string.</p>
<p>Setting this attribute to the <code>null</code> value <em
class=ct>must</em> have no effect.</p>
<p>Setting this attribute to a non-<code>null</code> value <em
class=ct>must</em> call <code
title=documentstyle-enablestylesheetsforset><a
href="#documentstyle-enablestylesheetsforset">enableStylesheetsForSet()</a></code>
with that value as the method's argument, and set <code><a
href="#documentstyle-lastStyleSheetSet">lastStyleSheetSet</a></code> to
that value.</p>
<p>From the DOM's perspective, all views have the same <code><a
href="#documentstyle-selectedStyleSheetSet">selectedStyleSheetSet</a></code>.
If a user agent supports multiple views with different selected
alternative style sheets, then this attribute (and the <code><a
href="#stylesheet">StyleSheet</a></code> interface's
<code>disabled</code> attribute) <em class=ct>must</em> return and set
the value for the default view.</p>
<dt><dfn
id=documentstyle-lastStyleSheetSet><code>lastStyleSheetSet</code></dfn>
of type <code>DOMString</code>, readonly
<dd>
<p>This attribute <em class=ct>must</em> initially have the value
<code>null</code>. Its value changes when the <code><a
href="#documentstyle-selectedStyleSheetSet">selectedStyleSheetSet</a></code>
attribute is set.</p>
<dt><dfn
id=documentstyle-preferredStyleSheetSet><code>preferredStyleSheetSet</code></dfn>
of type <code>DOMString</code>, readonly
<dd>
<p>This attribute <em class=ct>must</em> be the preferred style sheet set
as set by the author. It is determined from the order of style sheet
declarations and the <code>Default-Style</code> HTTP headers. If there
is no preferred style sheet set, this attribute <em class=ct>must</em>
be the empty string. The case of this attribute <em class=ct>must</em>
exactly match the case given by the author where the preferred style
sheet is specified or implied. This attribute <em class=ct>must</em>
never be <code>null</code>.</p>
<dt><dfn id=documentstyle-styleSheetSets><code>styleSheetSets</code></dfn>
of type <code>DOMStringList</code>, readonly
<dd>
<p>This <em class=ct>must</em> be a <span>live</span> list of the
currently available <span>style sheet sets</span>. This list is
constructed by enumerating all the style sheets for this document
available to the implementation, in the order they are listed in the
<code><a href="#documentstyle-stylesheets">styleSheets</a></code>
attribute, adding the title of each style sheet <a href="#have-a"
title="have a title">with a title</a> to the list, avoiding duplicates
by dropping titles that match (<span>case-sensitively</span>) titles
that have already been added to the list.</p>
<dt><dfn id=documentstyle-enablestylesheetsforset
title=documentstyle-enablestylesheetsforset><code>enableStylesheetsForSet(<var
title="">name</var>)</code></dfn>, method
<dd>
<p>Invoking this method <em class=ct>must</em> change the <code
title=stylesheet-disabled><a
href="#stylesheet-disabled">disabled</a></code> attribute on each
<code><a href="#stylesheet">StyleSheet</a></code> object <a
href="#have-a" title="have a title">with a title</a> in the <code><a
href="#documentstyle-stylesheets">styleSheets</a></code> attribute, so
that all those whose title matches the <var title="">name</var> argument
are enabled, and all others are disabled. Title matches <em
class=ct>must</em> be <span>case-sensitive</span>.</p>
<p>Invoking this method with the empty string value <em
class=ct>must</em> disable all alternative and preferred style sheets
(but does not change the state of persistent style sheets).</p>
<p>Invoking this method with the <code>null</code> value <em
class=ct>must</em> have no effect.</p>
<!-- fact: -->
<p>Style sheets that do not <a href="#have-a">have a title</a> are never
affected by this method. This method does not change the values of the
<code><a
href="#documentstyle-lastStyleSheetSet">lastStyleSheetSet</a></code> or
<code><a
href="#documentstyle-preferredStyleSheetSet">preferredStyleSheetSet</a></code>
attributes.</p>
</dl>
<h3 id=dynamically><span class=secno>3.5. </span>Dynamically adding new
style sheets</h3>
<p>If new style sheets <a href="#have-a" title="have a title">with
titles</a> are added to the document, the user agent <em
class=ct>must</em> decide whether or not the style sheets should be
initially enabled or not. How this happens depends on the exact state of
the document at the time the style sheet is added, as follows.
<h4 id=adding><span class=secno>3.5.1. </span>Adding style sheets</h4>
<p>First, if the style sheet is a preferred style sheet (it <a
href="#have-a" title="have a title">has a title</a>, but is not marked as
alternative), and there is no current preferred style sheet (the <code><a
href="#documentstyle-preferredStyleSheetSet">preferredStyleSheetSet</a></code>
attribute is equal to the empty string) then the <code><a
href="#documentstyle-preferredStyleSheetSet">preferredStyleSheetSet</a></code>
attribute is set to the exact value of this style sheet's title. (This
changes the preferred style sheet set, which causes further changes
— see below.)
<p>Then, for all sheets, if any of the following is true, then the style
sheet <em class=ct>must</em> be enabled:
<ul>
<li>The style sheet has an empty title.
<li>The <code><a
href="#documentstyle-lastStyleSheetSet">lastStyleSheetSet</a></code> is
<code>null</code>, and the style sheet's title matches (by
<span>case-sensitive</span> match) the value of the <code><a
href="#documentstyle-preferredStyleSheetSet">preferredStyleSheetSet</a></code>
attribute.
<li>The style sheet's title matches (by <span>case-sensitive</span> match)
the value of the <code><a
href="#documentstyle-lastStyleSheetSet">lastStyleSheetSet</a></code>
attribute.
</ul>
<p>Otherwise, the style sheet <em class=ct>must</em> be disabled.
<h4 id=changing><span class=secno>3.5.2. </span>Changing the preferred
style sheet set</h4>