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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang=en-US>
<head>
<title>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 }
.example { margin-left:1em; padding-left:1em; border-left:double; color:#222; background:#fcfcfc }
.example table code { color:inherit }
td, th { padding:.1em }
.note { margin-left:2em; color:green; font-style:italic; font-weight:bold }
p.note::before { content:"Note: " }
.XXX { padding:.5em; border:solid red }
p.XXX::before { content:"Issue: " }
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code { color:orangered }
code :link, code :visited { color:inherit }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED" rel=stylesheet>
<body class=draft>
<div class=head>
<h1 id=cssom>CSSOM</h1>
<h2 class="no-num no-toc" id="">Editor's Draft 31 March 2010</h2>
<dl>
<dt>This Version:
<dd><a
href="http://www.w3.org/TR/2010/ED-cssom-20100331/">http://www.w3.org/TR/2010/ED-cssom-20100331/</a>
<dt>Latest Version:
<dd><a href="http://www.w3.org/TR/cssom/">http://www.w3.org/TR/cssom/</a>
<dt>Latest Editor's draft:
<dd><a
href="http://dev.w3.org/csswg/cssom/">http://dev.w3.org/csswg/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>CSSOM defines APIs (including generic parsing and serialization rules)
for Media Queries, Selectors, and of course CSS itself.
<h2 class="no-num no-toc" id=sotd>Status of this Document</h2>
<p class=XXX>The plan is that this document provides the successor to DOM
Level 2 Style.</p>
<!--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-->
<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="#infrastructure"><span class=secno>2. </span>Common
Infrastructure</a>
<ul class=toc>
<li><a href="#terminology"><span class=secno>2.1. </span>Terminology</a>
<li><a href="#conformance"><span class=secno>2.2. </span>Conformance
Requirements</a>
<li><a href="#common-serializing-idioms"><span class=secno>2.3.
</span>Common Serializing Idioms</a>
</ul>
<li><a href="#media-queries"><span class=secno>3. </span>Media Queries</a>
<ul class=toc>
<li><a href="#parsing-media-queries"><span class=secno>3.1.
</span>Parsing Media Queries</a>
<li><a href="#serializing-media-queries"><span class=secno>3.2.
</span>Serializing Media Queries</a>
<ul class=toc>
<li><a href="#serializing-media-feature-values"><span
class=secno>3.2.1. </span>Serializing Media Feature Values</a>
</ul>
<li><a href="#comparing-media-queries"><span class=secno>3.3.
</span>Comparing Media Queries</a>
<li><a href="#the-medialist-interface"><span class=secno>3.4. </span>The
<code title="">MediaList</code> Interface</a>
<li><a href="#creating-a-medialist-object"><span class=secno>3.5.
</span>Creating a <code title="">MediaList</code> Object</a>
</ul>
<li><a href="#selectors"><span class=secno>4. </span>Selectors</a>
<ul class=toc>
<li><a href="#parsing-selectors"><span class=secno>4.1. </span>Parsing
Selectors</a>
<li><a href="#serializing-selectors"><span class=secno>4.2.
</span>Serializing Selectors</a>
</ul>
<li><a href="#css"><span class=secno>5. </span>CSS</a>
<ul class=toc>
<li><a href="#style-sheet0"><span class=secno>5.1. </span>Style
Sheet</a>
<ul class=toc>
<li><a href="#the-stylesheet-interface"><span class=secno>5.1.1.
</span>The <code title="">StyleSheet</code> Interface</a>
<li><a href="#the-cssstylesheet-interface"><span class=secno>5.1.2.
</span>The <code title="">CSSStyleSheet</code> Interface</a>
</ul>
<li><a href="#style-sheet-collections"><span class=secno>5.2.
</span>Style Sheet Collections</a>
<ul class=toc>
<li><a href="#the-http-default-style-header"><span class=secno>5.2.1.
</span>The HTTP <code title="">Default-Style</code> Header</a>
<li><a href="#the-stylesheetlist-sequence"><span class=secno>5.2.2.
</span>The <code title="">StyleSheetList</code> Sequence</a>
<li><a href="#extensions-to-the-document-interface"><span
class=secno>5.2.3. </span>Extensions to the <code
title="">Document</code> Interface</a>
<li><a href="#interaction-with-the-user-interface"><span
class=secno>5.2.4. </span>Interaction with the User Interface</a>
<ul class=toc>
<li><a href="#persisting-the-selected-style-sheet-set"><span
class=secno>5.2.4.1. </span>Persisting the selected style sheet
set</a>
</ul>
<li><a href="#examples"><span class=secno>5.2.5. </span>Examples</a>
</ul>
<li><a href="#style-sheet-association"><span class=secno>5.3.
</span>Style Sheet Association</a>
<ul class=toc>
<li><a href="#the-linkstyle-interface"><span class=secno>5.3.1.
</span>The <code title="">LinkStyle</code> Interface</a>
<li><a href="#requirements-on-specifications"><span class=secno>5.3.2.
</span>Requirements on specifications</a>
<li><a href="#requirements-on-user-agents-implementing"><span
class=secno>5.3.3. </span>Requirements on User Agents Implementing
the <span title=""><code>xml-stylesheet</code> processing
instruction</span></a>
<li><a href="#requirements-on-user-agents-implementing0"><span
class=secno>5.3.4. </span>Requirements on User Agents Implementing
the HTTP <code title="">Link</code> Header</a>
</ul>
<li><a href="#css-rules"><span class=secno>5.4. </span>CSS Rules</a>
<ul class=toc>
<li><a href="#the-cssrulelist-sequence"><span class=secno>5.4.1.
</span>The <code title="">CSSRuleList</code> Sequence</a>
<li><a href="#the-cssrule-interface"><span class=secno>5.4.2.
</span>The <code title="">CSSRule</code> Interface</a>
<ul class=toc>
<li><a href="#extensibility"><span class=secno>5.4.2.1.
</span>Extensibility</a>
</ul>
<li><a href="#css-style-rule-rule-set"><span class=secno>5.4.3.
</span>CSS Style Rule (Rule Set)</a>
<li><a href="#css-import-rule"><span class=secno>5.4.4. </span>CSS
<code title="">@import</code> Rule</a>
<li><a href="#css-media-rule"><span class=secno>5.4.5. </span>CSS
<code title="">@media</code> Rule</a>
<li><a href="#css-font-face-rule"><span class=secno>5.4.6. </span>CSS
<code title="">@font-face</code> Rule</a>
<li><a href="#css-page-rule"><span class=secno>5.4.7. </span>CSS <code
title="">@page</code> Rule</a>
<li><a href="#css-namespace-rule"><span class=secno>5.4.8. </span>CSS
<code title="">@namespace</code> Rule</a>
</ul>
<li><a href="#css-declaration-blocks"><span class=secno>5.5. </span>CSS
Declaration Blocks</a>
<ul class=toc>
<li><a href="#the-cssstyledeclaration-interface"><span
class=secno>5.5.1. </span>The <code
title="">CSSStyleDeclaration</code> Interface</a>
<li><a href="#the-cssstyledeclarationvalue-interface"><span
class=secno>5.5.2. </span>The <code
title="">CSSStyleDeclarationValue</code> Interface</a>
</ul>
<li><a href="#css-values"><span class=secno>5.6. </span>CSS Values</a>
<ul class=toc>
<li><a href="#parsing-css-values"><span class=secno>5.6.1.
</span>Parsing CSS Values</a>
<li><a href="#serializing-css-values"><span class=secno>5.6.2.
</span>Serializing CSS Values</a>
<ul class=toc>
<li><a href="#examples0"><span class=secno>5.6.2.1.
</span>Examples</a>
</ul>
<li><a href="#the-cssvalue-interface"><span class=secno>5.6.3.
</span>The <code title="">CSSValue</code> Interface</a>
<li><a href="#the-csscomponentvalue-interface"><span
class=secno>5.6.4. </span>The <code title="">CSSComponentValue</code>
Interface</a>
<li><a href="#the-csscolorcomponentvalue-interface"><span
class=secno>5.6.5. </span>The <code
title="">CSSColorComponentValue</code> Interface</a>
<li><a href="#the-csslengthcomponentvalue-interface"><span
class=secno>5.6.6. </span>The <code
title="">CSSLengthComponentValue</code> Interface</a>
<li><a href="#the-csspercentagecomponentvalue-interfac"><span
class=secno>5.6.7. </span>The <code
title="">CSSPercentageComponentValue</code> Interface</a>
<li><a href="#the-cssurlcomponentvalue-interface"><span
class=secno>5.6.8. </span>The <code
title="">CSSURLComponentValue</code> Interface</a>
</ul>
</ul>
<li><a href="#dom-access-to-css-declaration-blocks"><span class=secno>6.
</span>DOM Access to CSS Declaration Blocks</a>
<ul class=toc>
<li><a href="#the-elementcssinlinestyle-interface"><span
class=secno>6.1. </span>The <code>ElementCSSInlineStyle</code>
Interface</a>
<li><a href="#extensions-to-the-window-interface"><span class=secno>6.2.
</span>Extensions to the <code title="">Window</code> Interface</a>
</ul>
<li><a href="#resolved-values"><span class=secno>7. </span>Resolved
Values</a>
<li><a href="#iana-considerations"><span class=secno>8. </span>IANA
Considerations</a>
<ul class=toc>
<li><a href="#default-style-"><span class=secno>8.1.
</span><code>Default-Style</code> </a>
</ul>
<li class=no-num><a href="#references">References</a>
<li class=no-num><a href="#acknowledgments">Acknowledgments</a>
</ul>
<!--end-toc-->
<h2 id=introduction><span class=secno>1. </span>Introduction</h2>
<p class=XXX>...
<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=infrastructure><span class=secno>2. </span>Common Infrastructure</h2>
<h3 id=terminology><span class=secno>2.1. </span>Terminology</h3>
<p class=XXX> <dfn id=resolve-a-url>resolve a URL</dfn>, <dfn
id=case-sensitive>case-sensitive</dfn>, <dfn
id=converted-to-ascii-lowercase>converted to ASCII lowercase</dfn>, <dfn
id=ascii-case-insensitive>ASCII case-insensitive</dfn>, <dfn
id=url>URL</dfn>, <dfn id=content-type-metadata>Content-Type
metadata</dfn>, <dfn id=supported-styling-language>supported styling
language</dfn>, <dfn
id=xml-stylesheet-processing-instruction><code>xml-stylesheet</code>
processing instruction</dfn>, <dfn id=fetch>fetch</dfn>, ...
<p>When this specification talks about object <code><var
title="">A</var></code> where <code><var title="">A</var></code> is
actually an interface, it generally means an object implementing interface
<code><var title="">A</var></code>.
<p>The term <dfn id=whitespace>whitespace</dfn> is used as defined in CSS.
<!--XXX <a href="#ref-css">[CSS]</a>-->
<h3 id=conformance><span class=secno>2.2. </span>Conformance Requirements</h3>
<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 RFC 2119 <a href="#ref-rfc2119">[RFC2119]</a>.</p>
<!-- XXX
<p>The following conformance classes are defined (and considered) by this
specification:</p>
<dl>
<dt><dfn id="conforming-implementation">conforming implementation</dfn></dt>
<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.</dd>
<dt><dfn id="conforming-document">conforming document</dfn></dt>
<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.</dd>
<dt><dfn id="conforming-authoring-tool">conforming authoring tool</dfn></dt>
<dd>One that produces conforming documents.</dd>
</dl>
-->
<h3 id=common-serializing-idioms><span class=secno>2.3. </span>Common
Serializing Idioms</h3>
<p>To <dfn id=serialize-a-character>serialize a character</dfn> means to
create a string of "<code>\</code>" (U+005C), followed by the character.
<p>To <dfn id=serialize-a-character-as-code-point>serialize 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 space
(U+0020).
<p>To <dfn id=serialize-an-identifier>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 in the range U+0000 to U+001F, the character <a
href="#serialize-a-character-as-code-point" title="serialize a character
as code point">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), the character <a
href="#serialize-a-character-as-code-point" title="serialize a character
as code point">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), the character <a href="#serialize-a-character-as-code-point"
title="serialize a character as code point">escaped as code point</a>.
<li>If the character is the second character and is "<code>-</code>"
(U+002D) and the first character is "<code>-</code>" too, the <a
href="#serialize-a-character" title="serialize 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), the character
itself.
<li>Otherwise, the <a href="#serialize-a-character" title="serialize a
character">escaped</a> character.
</ul>
<p>To <dfn id=serialize-a-string>serialize a string</dfn> means to create a
string represented by '<code>"</code>' (U+0022), followed by the result of
applying the rules below to each character of the given string, followed
by '<code>"</code>' (U+0022):
<ul>
<li>If the character is in the range U+0000 to U+001F, the character <a
href="#serialize-a-character-as-code-point" title="serialize a character
as code point">escaped as code point</a>.
<li>If the character is '<code>"</code>' (U+0022) or '<code>\</code>'
(U+005C), the <a href="#serialize-a-character" title="serialize a
character">escaped</a> character.
<li>Otherwise, the character itself.
</ul>
<p class=note>"<code>'</code>" (U+0027) is not escaped because strings are
always serialized with '<code>"</code>' (U+0022).
<p>To <dfn id=serialize-a-url>serialize a URL</dfn> means to create a
string represented by "<code title="">url(</code>", followed by the <a
href="#serialize-a-string" title="serialize a string">string escaped</a>
value of the given string, followed by "<code>)</code>".
<p>To <dfn id=serialize-a-comma-separated-list>serialize a comma-separated
list</dfn> concatenate all items of the list in list order while
separating them by "<code>,</code>" (U+002C), followed by a space
(U+0020).
<p>To <dfn id=serialize-a-whitespace-separated-list>serialize a
whitespace-separated list</dfn> concatenate all items of the list in list
order while separating them a space (U+0020).
<h2 id=media-queries><span class=secno>3. </span>Media Queries</h2>
<p><dfn id="media queries">Media queries</dfn> are defined by the Media
Queries specification. This section defines various concepts around media
queries, including their API and serialization form.</p>
<!-- XXX maybe not a <dfn> -->
<!-- XXX ref -->
<h3 id=parsing-media-queries><span class=secno>3.1. </span>Parsing Media
Queries</h3>
<p>To <dfn id=parse-a-list-of-media-queries>parse a list of media
queries</dfn> for a given string <var title="">s</var> into a list of
media queries is defined in the Media Queries specification. Return the
list of one or more media queries that the algorithm defined there gives.</p>
<!-- XXX ref -->
<p class=note>If everything ends up being ignored the list will contain the
media query "<code title="">not all</code>".
<p>To <dfn id=parse-a-media-query>parse a media query</dfn> for a given
string <var title="">s</var> means to follow the <a
href="#parse-a-list-of-media-queries">parse a list of media queries</a>
steps and return null if more than one media query is returned or a media
query if a single media query is returned.
<h3 id=serializing-media-queries><span class=secno>3.2. </span>Serializing
Media Queries</h3>
<p>To <dfn id=serialize-a-list-of-media-queries>serialize a list of media
queries</dfn> <a href="#serialize-a-media-query" title="serialize a media
query">serialize</a> each media query in the list of media queries and
then <a href="#serialize-a-comma-separated-list" title="serialize a
comma-separated list">serialize</a> the list.
<p>To <dfn id=serialize-a-media-query>serialize a media query</dfn> let
<var title="">s</var> be the empty string, run the steps below, and
finally return <var title="">s</var>:
<ol>
<li>
<p>If the media query is negated append "<code>not</code>", followed by a
space (U+0020), to <var title="">s</var>.
<li>
<p>Let <var title="">type</var> be the media type of the media query, <a
href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> and <a
href="#converted-to-ascii-lowercase">converted to ASCII lowercase</a>.
<li>
<p>If the media query does not contain media features append <var
title="">type</var>, to <var title="">s</var>, then return <var
title="">s</var> and terminate this algorithm.
<li>
<p>If <var title="">type</var> is not "<code>all</code>" or if the media
query is negated append <var title="">type</var>, followed by a space
(U+0020), followed by "<code>and</code>", followed by a space (U+0020),
to <var title="">s</var>.
<li>
<p>Sort the media features in lexicographical order.
<li>
<p>Then, for each media feature:</p>
<ol>
<li>Append a "<code>(</code>" (U+0028), followed by the media feature
name, <a href="#converted-to-ascii-lowercase">converted to ASCII
lowercase</a>, to <var title="">s</var>.
<li>
<p>If a value is given append a "<code>:</code>" (U+003A), followed by
a space (U+0020), followed by the <a
href="#serialize-a-media-feature-value" title="serialize a media
feature value">serialized media feature value</a>, to <var
title="">s</var>.</p>
<li>
<p>Append a "<code>)</code>" (U+0029) to <var title="">s</var>.
<li>
<p>If this is not the last media feature append a space (U+0020),
followed by "<code>and</code>", followed by a space (U+0020), to <var
title="">s</var>.
</ol>
</ol>
<div class=example>
<p>Here are some examples of input (first column) and output (second
column):</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>
<h4 id=serializing-media-feature-values><span class=secno>3.2.1.
</span>Serializing Media Feature Values</h4>
<p class=XXX>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.
<p>To <dfn id=serialize-a-media-feature-value>serialize a media feature
value</dfn> named <var title="">v</var> locate <var title="">v</var> in
the first column of the table below and use the serialization format
described in the second column:
<table>
<tbody>
<tr>
<th>Media Feature
<th>Serialization
<tr>
<td><code title="">width</code>
<td>...
<tr>
<td><code title="">height</code>
<td>...
<tr>
<td><code title="">device-width</code>
<td>...
<tr>
<td><code title="">device-height</code>
<td>...
<tr>
<td><code title="">orientation</code>
<td>
<p>If the value is `<code title="">portrait</code>`: "<code
title="">portrait</code>".</p>
<p>If the value is `<code title="">landscape</code>`: "<code
title="">landscape</code>".</p>
<tr>
<td><code title="">aspect-ratio</code>
<td>...
<tr>
<td><code title="">device-aspect-ratio</code>
<td>...
<tr>
<td><code title="">color</code>
<td>...
<tr>
<td><code title="">color-index</code>
<td>...
<tr>
<td><code title="">monochrome</code>
<td>...
<tr>
<td><code title="">resolution</code>
<td>...
<tr>
<td><code title="">scan</code>
<td>
<p>If the value is `<code title="">progressive</code>`: "<code
title="">progressive</code>".</p>
<p>If the value is `<code title="">interlace</code>`: "<code
title="">interlace</code>".</p>
<tr>
<td><code title="">grid</code>
<td>...
</table>
<p>Other specifications can extend this table and vendor-prefixed media
features can have custom serialization formats as well.
<h3 id=comparing-media-queries><span class=secno>3.3. </span>Comparing
Media Queries</h3>
<p>To <dfn id=compare-media-queries>compare media queries</dfn> <var
title="">m1</var> and <var title="">m2</var> means to <a
href="#serialize-a-media-query" title="serialize a media
query">serialize</a> them both and return true if they are a <a
href="#case-sensitive">case-sensitive</a> match and false if they are not.
<h3 id=the-medialist-interface><span class=secno>3.4. </span>The <code
title="">MediaList</code> Interface</h3>
<p>An object that implements the <code><a
href="#medialist">MediaList</a></code> interface has an associated <dfn
id=collection-of-media-queries>collection of media queries</dfn>.</p>
<!-- http://dev.w3.org/2006/webapi/WebIDL/#idl-indexed-properties -->
<pre class=idl>interface <dfn id=medialist>MediaList</dfn> {
stringifier attribute DOMString <a href="#dom-medialist-mediatext" title=dom-MediaList-mediaText>mediaText</a>;
readonly attribute unsigned long <a href="#dom-medialist-length" title=dom-MediaList-length>length</a>;
getter DOMString <a href="#dom-medialist-item" title=dom-MediaList-item>item</a>(unsigned long <var title="">index</var>);
void <a href="#dom-medialist-appendmedium" title=dom-MediaList-appendMedium>appendMedium</a>(DOMString <var title="">medium</var>);
void <a href="#dom-medialist-deletemedium" title=dom-MediaList-deleteMedium>deleteMedium</a>(DOMString <var title="">medium</var>);
};</pre>
<p>The <dfn id=dom-medialist-mediatext
title=dom-MediaList-mediaText><code>mediaText</code></dfn> attribute, on
getting, <em class=ct>must</em> return a <a
href="#serialize-a-list-of-media-queries" title="serialize a list of media
queries">serialization</a> of the <span>list of media queries</span>.
<p>On setting the <code title=dom-MediaList-mediaText><a
href="#dom-medialist-mediatext">mediaText</a></code> attribute these steps
<em class=ct>must</em> be run:
<ol>
<li>
<p>Empty the <a href="#collection-of-media-queries">collection of media
queries</a>.
<li>
<p>If the given value is the empty string terminate these steps.
<li>
<p>Append all the media queries as a result of <a
href="#parse-a-list-of-media-queries" title="parse a list of media
queries">parsing</a> the given value to the <a
href="#collection-of-media-queries">collection of media queries</a>.
</ol>
<p>The <dfn id=dom-medialist-length
title=dom-MediaList-length><code>length</code></dfn> attribute <em
class=ct>must</em> return the number of media queries in the <a
href="#collection-of-media-queries">collection of media queries</a>.
<p>The <dfn id=dom-medialist-item title=dom-MediaList-item><code>item(<var
title="">index</var>)</code></dfn> method <em class=ct>must</em> return
the media query in the <a href="#collection-of-media-queries">collection
of media queries</a> given by <var title="">index</var>, or null, if <var
title="">index</var> is greater than or equal to the number of media
queries in the <a href="#collection-of-media-queries">collection of media
queries</a>.</p>
<!-- XXX need consistency here WebIDL? list of media queries? -->
<p>The <dfn id=dom-medialist-appendmedium
title=dom-MediaList-appendmedium><code>appendMedium(<var
title="">medium</var>)</code></dfn> method <em class=ct>must</em> run
these steps:
<ol>
<li>
<p>Let <var title="">m</var> be the result of <a
href="#parse-a-media-query" title="parse a media query">parsing</a> the
given value.
<li>
<p>If <var title="">m</var> is null terminate these steps.
<li>
<p>If <a href="#compare-media-queries" title="compare media
queries">comparing</a> <var title="">m</var> with any of the media
queries in the <a href="#collection-of-media-queries">collection of
media queries</a> returns true terminate these steps.
<li>
<p>Append <var title="">m</var> to the <a
href="#collection-of-media-queries">collection of media queries</a>.
</ol>
<p>The <dfn id=dom-medialist-deletemedium
title=dom-MediaList-deletemedium><code>deleteMedium(<var
title="">medium</var>)</code></dfn> method <em class=ct>must</em> run
these steps:
<ol>
<li>
<p>Let <var title="">m</var> be the result of <a
href="#parse-a-media-query" title="parse a media query">parsing</a> the
given value.
<li>
<p>If <var title="">m</var> is null terminate these steps.
<li>
<p>Remove any media query from the <a
href="#collection-of-media-queries">collection of media queries</a> for
which <a href="#compare-media-queries" title="compare media
queries">comparing</a> the media query with <var title="">m</var>
returns true.
</ol>
<h3 id=creating-a-medialist-object><span class=secno>3.5. </span>Creating a
<code title="">MediaList</code> Object</h3>
<p>To <dfn id=create-a-medialist-object>create a <code>MediaList</code>
object</dfn> from <var title="">s</var> run these steps:
<ol>
<li>
<p>Create a new <code><a href="#medialist">MediaList</a></code> object.
<li>
<p>Set its <a href="#dom-medialist-mediatext"
title=dom-MediaList-mediaText>mediaText</a> attribute to <var
title="">s</var>.
<li>
<p>Return the newly created <code><a
href="#medialist">MediaList</a></code> object.
</ol>
<h2 id=selectors><span class=secno>4. </span>Selectors</h2>
<p>Selectors are defined in the Selectors specification. This section
mainly defines how to serialize them.</p>
<!-- XXX ref -->
<!-- XXX ref universal selector etc? some are in <span> some not -->
<h3 id=parsing-selectors><span class=secno>4.1. </span>Parsing Selectors</h3>
<p>To <dfn id=parse-a-group-of-selectors>parse a group of selectors</dfn>
means to parse the value using the <code title="">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.</p>
<!-- XXX ref -->
<h3 id=serializing-selectors><span class=secno>4.2. </span>Serializing
Selectors</h3>
<!-- http://dump.testsuite.org/2009/cssom/serializing-selectors.htm -->
<p>To <dfn id=serialize-a-group-of-selectors>serialize a group of
selectors</dfn> <a href="#serialize-a-selector" title="serialize a
selector">serialize</a> each selector in the group of selectors and then
<a href="#serialize-a-comma-separated-list" title="serialize a
comma-separated list">serialize</a> the group.
<p>To <dfn id=serialize-a-selector>serialize a selector</dfn> let <var
title="">s</var> be the empty string, run the steps below for each part of
the chain of the selector, and finally return <var title="">s</var>:
<ol>
<li>
<p>If there is only one <span>simple selector</span> in the
<span>sequence of simple selectors</span> which is a <span>universal
selector</span>, append the result of <a
href="#serialize-a-simple-selector" title="serialize a simple
selector">serializing</a> the <span>universal selector</span> to <var
title="">s</var>.
<li>
<p>Otherwise, for each <span>simple selector</span> in the <span>sequence
of simple selectors</span> that is not a universal selector of which the
<span>namespace prefix</span> maps to the null namespace (not in a
namespace) or of which the <span>namespace prefix</span> maps to a
namespace that is not the <span>default namespace</span> <a
href="#serialize-a-simple-selector" title="serialize a simple
selector">serialize</a> the <span>simple selector</span> and append the
result to <var title="">s</var>.
<li>
<p>If this is not the last part of the chain of the selector append a
space (U+0020), followed by the combinator "<code>></code>",
"<code>+</code>", or "<code>~</code>" as appropriate, followed by
another space (U+0020) if the combinator was not whitespace, to <var
title="">s</var>.
<li>
<p>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-class, to <var title="">s</var>.
</ol>
<p>To <dfn id=serialize-a-simple-selector>serialize a simple selector</dfn>
let <var title="">s</var> be the empty string, run the steps below, and
finally return <var title="">s</var>:
<dl class=switch>
<dt>type selector
<dt>universal selector
<dd>
<ol>
<li>
<p>If the <span>namespace prefix</span> maps to a namespace that is not
the <span>default namespace</span> and is not the null namespace (not
in a namespace) append the <a href="#serialize-an-identifier"
title="serialize an identifier">escaped</a> <span>namespace
prefix</span>, followed by a "<code>|</code>" (U+007C) to <var
title="">s</var>.
<li>
<p>If the <span>namespace prefix</span> maps to a namespace that is the
null namespace (not in a namespace) append "<code>|</code>" (U+007C)
to <var title="">s</var>.
</li>
<!-- This includes |* -->
<li>
<p>If this is a type selector append the <a
href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> element name to <var title="">s</var>.</p>
<li>
<p>If this is a universal selector append "<code>*</code> (U+002A) to
<var title="">s</var>.
</ol>
<dt>attribute selector
<dd>
<ol>
<li>
<p>Append "<code>[</code>" (U+005B) to <var title="">s</var>.
<li>
<p>If the <span>namespace prefix</span> maps to a namespace that is not
the null namespace (not in a namespace) append the <a
href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> <span>namespace prefix</span>, followed by a
"<code>|</code>" (U+007C) to <var title="">s</var>.
<li>
<p>If the <span>namespace prefix</span> maps to a namespace that is the
null namespace (not in a namespace) append "<code>|</code>" (U+007C)
to <var title="">s</var>.
</li>
<!-- This includes |* -->
<li>
<p>Append the <a href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> attribute name to <var title="">s</var>.
<li>
<p>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
href="#serialize-a-string" title="serialize a string">string
escaped</a> attribute value, to <var title="">s</var>.
<li>
<p>Append "<code>]</code>" (U+005D) to <var title="">s</var>.
</ol>
<dt>class selector
<dd>
<p>Append a "<code>.</code>" (U+002E), followed by the <a
href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> class name to <var title="">s</var>.
<dt>ID selector
<dd>
<p>Append a "<code>#</code>" (U+0023), followed by the <a
href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> ID to <var title="">s</var>.
<dt>pseudo-class
<dd>
<p>If the pseudo-class does not accept arguments append "<code>:</code>"
(U+003A), followed by the name of the pseudo-class, to <var
title="">s</var>.</p>
<p>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 determined as per below, followed by
"<code>)</code>" (U+0029), to <var title="">s</var>.</p>
<dl class=switch>
<dt><code title="">:lang()</code>
<dd>
<p>The <a href="#serialize-an-identifier" title="serialize an
identifier">escaped</a> value.
<dt><code title="">:nth-child()</code>
<dt><code title="">:nth-last-child()</code>
<dt><code title="">:nth-of-type()</code>
<dt><code title="">:nth-last-of-type()</code>
<dd>
<ol>
<li>
<p>If the value is odd let the value be "<code title="">2n+1</code>".
<li>
<p>If the value is even let the value be "<code title="">2n</code>".
<li>
<p>If <var title="">a</var> is zero let the value be <var
title="">b</var> <a href="#serialize-a-css-value-component"
title="serialize a CSS component value">serialized</a> as
<integer>.
<li>
<p>If <var title="">a</var> is one or minus one and <var
title="">b</var> is zero let the value be "<code title="">n</code>"
(U+006E).
<li>
<p>If <var title="">a</var> is one or minus one let the value be
"<code title="">n</code>" (U+006E), followed by "<code>+</code>"
(U+002B) if <var title="">b</var> is positive, followed by <var
title="">b</var> <a href="#serialize-a-css-value-component"
title="serialize a CSS component value">serialized</a> as
<integer>.
<li>
<p>If <var title="">b</var> is zero let the value be <var
title="">a</var> <a href="#serialize-a-css-value-component"
title="serialize a CSS component value">serialized</a> as
<integer>, followed by "<code title="">n</code>" (U+006E).
<li>
<p>Otherwise let the value be <var title="">a</var> <a
href="#serialize-a-css-value-component" title="serialize a CSS
component value">serialized</a> as <integer>, followed by "<code
title="">n</code>" (U+006E), followed by "<code>+</code>" (U+002B)
if <var title="">b</var> is positive, followed by <var