csswg-drafts/cssom/Overview.html at 1993905ca291cdfdbf878f567be7f6370ea543b7 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html><html lang="en-US"><head>
  <meta charset="utf-8">
  <title>CSS Object Model (CSSOM)</title>
  <link href="cssom.css" rel="stylesheet">
  <link href="https://www.w3.org/StyleSheets/TR/W3C-ED" rel="stylesheet">
 </head>
 <body class="draft">
  <div class="head">

<!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="https://www.w3.org/Icons/w3c_home" width="72"></a></p>
<!--end-logo-->

   <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
   <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

   <h1 id="cssom">CSS Object Model (CSSOM)</h1>

   <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

   <h2 class="no-num no-toc" id="w3c-doctype">Editor's Draft 18 March 2013</h2>

   <dl>

    <dt>This Version:</dt>
    <dd class="dontpublish"><a href="https://dvcs.w3.org/hg/csswg/raw-file/tip/cssom/Overview.html">https://dvcs.w3.org/hg/csswg/raw-file/tip/cssom/Overview.html</a></dd>
    <dt class="dontpublish">Participate:</dt>
    <dd class="dontpublish"><a href="mailto:www-style@w3.org?subject==%5Bcssom%5D%20">www-style@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)</dd>
    <dd class="dontpublish"><a href="https://www.w3.org/Bugs/Public/enter_bug.cgi?product=CSS&amp;component=CSSOM">File a bug</a> (<a href="https://www.w3.org/Bugs/Public/buglist.cgi?component=CSSOM&amp;product=CSS&amp;resolution=---">open bugs</a>) <script async="" src="https://w3c-test.org/resources.whatwg.org/file-bug.js"></script></dd>
    <dd class="dontpublish"><a href="irc://irc.w3.org:6665/css">IRC: #css on W3C</a></dd>

    <dt class="dontpublish">Previous Version:</dt>
    <dd class="dontpublish"><a href="http://www.w3.org/TR/2011/WD-cssom-20110712/">http://www.w3.org/TR/2011/WD-cssom-20110712/</a></dd>
    <dd class="dontpublish"><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></dd>

    <dt>Editors:</dt>
    <dd><a href="http://www.w3.org/wiki/User:Gadams">Glenn Adams</a>
    (<a href="http://www.cox.com/">Cox Communications, Inc.</a>)
    &lt;<a href="mailto:glenn.adams@cox.com">glenn.adams@cox.com</a>&gt;</dd>
    <dd><a>Simon Pieters</a>
    (<a href="http://www.opera.com/">Opera Software ASA</a>)
    &lt;<a href="mailto:simponp@opera.com">simonp@opera.com</a>&gt;</dd>
    <dd><a>Shane Stephens</a>
    (<a href="http://www.google.com/">Google, Inc.</a>)
    &lt;<a href="mailto:shans@google.com">shans@google.com</a>&gt;</dd>
    <dt>Previous Editor:</dt>
    <dd><a href="http://annevankesteren.nl/">Anne van Kesteren</a>
    (<a href="http://www.opera.com/">Opera Software ASA</a>)
    &lt;<a href="mailto:annevk@opera.com">annevk@opera.com</a>&gt;</dd>
   </dl>


<!--begin-copyright-->
<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2013 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.</p>
<!--end-copyright-->

  </div>

  <hr class="top">

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <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.</p>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 class="no-num no-toc" id="sotd">Status of this Document</h2>

  <p>This is a public copy of the editors' draft. It is provided for discussion only and may change at any moment.
  Its publication here does not imply endorsement of its contents by W3C or by the CSS Working Group. Don't cite
  this document other than as work in progress.</p>

  <p class="note">Implementers should note well that this specification is an ongoing effort to sort out
  what has been widely implemented and deployed from <a href="#refsDOM2STYLE">[DOM2STYLE]</a> as well as common extensions thereto, some details
  of which are currently interoperable and others which are not currently interoperable. As this specification moves
  forward, it is hoped that these differences will be resolved and an unambiguous and adequate consensus-based
  specification will emerge.</p>

  <p><em>This section describes the status of this document at the time of
  its publication. Other documents may supersede this document. A list of
  current W3C publications and the latest revision of this technical report
  can be found in the
  <a href="http://www.w3.org/TR/">W3C technical reports index at http://www.w3.org/TR/.</a></em>

  <p class="dontpublish">This is the 18 March 2013 Editor's Draft of CSSOM. Please send comments to
  <a href="mailto:www-style@w3.org?subject=%5Bcssom%5D%20">www-style@w3.org</a>
  (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>)
  with <samp>[cssom]</samp> at the start of the subject line.

  <p>This document was produced by a group operating under the
  <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
  W3C maintains a
  <a href="http://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a>
  made in connection with the deliverables of the group; that page also
  includes instructions for disclosing a patent. An individual who has
  actual knowledge of a patent which the individual believes contains
  <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a>
  must disclose the information in accordance with
  <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.</p>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 class="no-num no-toc" id="toc">Table of Contents</h2>


<!--begin-toc-->
<ol class="toc">
 <li><a href="#introduction"><span class="secno">1 </span>Introduction</a></li>
 <li><a href="#conformance"><span class="secno">2 </span>Conformance</a></li>
 <li><a href="#terminology"><span class="secno">3 </span>Terminology</a>
  <ol class="toc">
   <li><a href="#common-serializing-idioms"><span class="secno">3.1 </span>Common Serializing Idioms</a></ol></li>
 <li><a href="#media-queries"><span class="secno">4 </span>Media Queries</a>
  <ol class="toc">
   <li><a href="#parsing-media-queries"><span class="secno">4.1 </span>Parsing Media Queries</a></li>
   <li><a href="#serializing-media-queries"><span class="secno">4.2 </span>Serializing Media Queries</a>
    <ol class="toc">
     <li><a href="#serializing-media-feature-values"><span class="secno">4.2.1 </span>Serializing Media Feature Values</a></ol></li>
   <li><a href="#comparing-media-queries"><span class="secno">4.3 </span>Comparing Media Queries</a></li>
   <li><a href="#the-medialist-interface"><span class="secno">4.4 </span>The <code>MediaList</code> Interface</a></ol></li>
 <li><a href="#selectors"><span class="secno">5 </span>Selectors</a>
  <ol class="toc">
   <li><a href="#parsing-selectors"><span class="secno">5.1 </span>Parsing Selectors</a></li>
   <li><a href="#serializing-selectors"><span class="secno">5.2 </span>Serializing Selectors</a></ol></li>
 <li><a href="#css"><span class="secno">6 </span>CSS</a>
  <ol class="toc">
   <li><a href="#css-style-sheets"><span class="secno">6.1 </span>CSS Style Sheets</a>
    <ol class="toc">
     <li><a href="#the-stylesheet-interface"><span class="secno">6.1.1 </span>The <code>StyleSheet</code> Interface</a></li>
     <li><a href="#the-cssstylesheet-interface"><span class="secno">6.1.2 </span>The <code>CSSStyleSheet</code> Interface</a></ol></li>
   <li><a href="#style-sheet-collections"><span class="secno">6.2 </span>Style Sheet Collections</a>
    <ol class="toc">
     <li><a href="#the-http-default-style-header"><span class="secno">6.2.1 </span>The HTTP <code>Default-Style</code> Header</a></li>
     <li><a href="#the-stylesheetlist-sequence"><span class="secno">6.2.2 </span>The <code>StyleSheetList</code> Sequence</a></li>
     <li><a href="#extensions-to-the-document-interface"><span class="secno">6.2.3 </span>Extensions to the <code>Document</code> Interface</a></li>
     <li><a href="#interaction-with-the-user-interface"><span class="secno">6.2.4 </span>Interaction with the User Interface</a>
      <ol class="toc">
       <li><a href="#persisting-the-selected-style-sheet-set"><span class="secno">6.2.4.1 </span>Persisting the selected style sheet set</a></ol></li>
     <li><a href="#examples"><span class="secno">6.2.5 </span>Examples</a></ol></li>
   <li><a href="#style-sheet-association"><span class="secno">6.3 </span>Style Sheet Association</a>
    <ol class="toc">
     <li><a href="#the-linkstyle-interface"><span class="secno">6.3.1 </span>The <code>LinkStyle</code> Interface</a></li>
     <li><a href="#requirements-on-specifications"><span class="secno">6.3.2 </span>Requirements on specifications</a></li>
     <li><a href="#requirements-on-user-agents-implementing-the-xml-stylesheet-processing-instruction"><span class="secno">6.3.3 </span>Requirements on User Agents Implementing the
  <span><code>xml-stylesheet</code> processing instruction</span></a></li>
     <li><a href="#requirements-on-user-agents-implementing-the-http-link-header"><span class="secno">6.3.4 </span>Requirements on User Agents Implementing the HTTP
  <code>Link</code> Header</a></ol></li>
   <li><a href="#css-rules"><span class="secno">6.4 </span>CSS Rules</a>
    <ol class="toc">
     <li><a href="#the-cssrulelist-sequence"><span class="secno">6.4.1 </span>The <code>CSSRuleList</code> Sequence</a></li>
     <li><a href="#the-cssrule-interface"><span class="secno">6.4.2 </span>The <code>CSSRule</code> Interface</a></li>
     <li><a href="#the-cssstylerule-interface"><span class="secno">6.4.3 </span>The <code>CSSStyleRule</code> Interface</a></li>
     <li><a href="#the-csscharsetrule-interface"><span class="secno">6.4.4 </span>The <code>CSSCharsetRule</code> Interface</a></li>
     <li><a href="#the-cssimportrule-interface"><span class="secno">6.4.5 </span>The <code>CSSImportRule</code> Interface</a></li>
     <li><a href="#the-cssmediarule-interface"><span class="secno">6.4.6 </span>The <code>CSSMediaRule</code> Interface</a></li>
     <li><a href="#the-cssfontfacerule-interface"><span class="secno">6.4.7 </span>The <code>CSSFontFaceRule</code> Interface</a></li>
     <li><a href="#the-csspagerule-interface"><span class="secno">6.4.8 </span>The <code>CSSPageRule</code> Interface</a></li>
     <li><a href="#the-cssnamespacerule-interface"><span class="secno">6.4.9 </span>The <code>CSSNamespaceRule</code> Interface</a></ol></li>
   <li><a href="#css-declaration-blocks"><span class="secno">6.5 </span>CSS Declaration Blocks</a>
    <ol class="toc">
     <li><a href="#the-cssstyledeclaration-interface"><span class="secno">6.5.1 </span>The <code>CSSStyleDeclaration</code> Interface</a></ol></li>
   <li><a href="#css-values"><span class="secno">6.6 </span>CSS Values</a>
    <ol class="toc">
     <li><a href="#parsing-css-values"><span class="secno">6.6.1 </span>Parsing CSS Values</a></li>
     <li><a href="#serializing-css-values"><span class="secno">6.6.2 </span>Serializing CSS Values</a>
      <ol class="toc">
       <li><a href="#examples-0"><span class="secno">6.6.2.1 </span>Examples</a></ol></ol></ol></li>
 <li><a href="#dom-access-to-css-declaration-blocks"><span class="secno">7 </span>DOM Access to CSS Declaration Blocks</a>
  <ol class="toc">
   <li><a href="#the-elementcssinlinestyle-interface"><span class="secno">7.1 </span>The <code>ElementCSSInlineStyle</code> Interface</a></li>
   <li><a href="#extensions-to-the-window-interface"><span class="secno">7.2 </span>Extensions to the <code>Window</code> Interface</a></ol></li>
 <li><a href="#resolved-values"><span class="secno">8 </span>Resolved Values</a></li>
 <li><a href="#iana-considerations"><span class="secno">9 </span>IANA Considerations</a>
  <ol class="toc">
   <li><a href="#default-style"><span class="secno">9.1 </span><code>Default-Style</code></a></ol></li>
 <li><a class="no-num" href="#references">References</a>
  <ol class="toc">
   <li><a class="no-num" href="#normative-references">Normative references</a></li>
   <li><a class="no-num" href="#informative-references">Informative references</a></ol></li>
 <li><a class="no-num" href="#changes">Change History</a>
  <ol class="toc">
   <li><a class="no-num" href="#changes-from-dom2">Changes From DOM-2 Style</a></ol></li>
 <li><a class="no-num" href="#acknowledgments">Acknowledgments</a></ol>
<!--end-toc-->

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="introduction"><span class="secno">1 </span>Introduction</h2>

  <p>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.</p>

  <p>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.</p>

  <p>The features defined below are fundamentally based on prior specifications of the W3C DOM Working Group, primarily
  <a href="#refsDOM2STYLE">[DOM2STYLE]</a>. 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.</p>

  <p>A full list of the changes to API signatures can be found in <a href="#changes-from-dom2"><cite>Changes from DOM-2 Style</cite></a>.</p>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="conformance"><span class="secno">2 </span>Conformance</h2>

  <p>All diagrams, examples, and notes in this specification are
  non-normative, as are all sections explicitly marked non-normative.
  Everything else in this specification is normative.

  <p>The key words "MUST", "MUST NOT", "REQUIRED", <!--"SHALL", "SHALL
  NOT",--> "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
  "OPTIONAL" in the normative parts of this document are to be
  interpreted as described in RFC2119. For readability, these words do
  not appear in all uppercase letters in this specification.
  <a href="#refsRFC2119">[RFC2119]</a>

  <p>Requirements phrased in the imperative as part of algorithms
  (such as "strip any leading space characters" or "return false and
  terminate these steps") are to be interpreted with the meaning of the
  key word ("must", "should", "may", etc) used in introducing the
  algorithm.

  <p>Conformance requirements phrased as algorithms or specific steps
  may be implemented in any manner, so long as the end result is
  equivalent. (In particular, the algorithms defined in this
  specification are intended to be easy to follow, and not intended to
  be performant.)

  <p id="hardwareLimitations">User agents may impose
  implementation-specific limits on otherwise unconstrained inputs,
  e.g. to prevent denial of service attacks, to guard against running
  out of memory, or to work around platform-specific limitations.

  <p>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.

  <p>Unless otherwise stated, string comparisons are done in a
  <a class="external" href="http://dom.spec.whatwg.org/#case-sensitive">case-sensitive</a> manner.

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="terminology"><span class="secno">3 </span>Terminology</h2>

  <p>This specification employs certain terminology from the following documents:
  <cite>DOM4</cite>,
  <cite>HTML</cite>,
  <cite>Associating Style Sheets with XML documents</cite>
  and
  <cite>XML</cite>
  <a href="#refsDOM">[DOM]</a>
  <a href="#refsHTML">[HTML]</a>
  <a href="#refsXMLSS">[XMLSS]</a>
  <a href="#refsXML">[XML]</a>.

  <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> is used as defined in <a href="#refsCSS">[CSS]</a>.

  <p>The terms <dfn id="set">set</dfn> and <dfn id="clear">clear</dfn> to refer to the <code>true</code> and
  <code>false</code> 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 <code>true</code> or <code>false</code>, respectively.</p>

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="common-serializing-idioms"><span class="secno">3.1 </span>Common Serializing Idioms</h3>

  <p>To <dfn id="escape-a-character">escape a character</dfn> means to create a string of
  "<code>\</code>" (U+005C), followed by the character.</p>

  <p>To <dfn id="escape-a-character-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).</p>

  <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:</p>

  <ul>
   <li>If the character is NULL (U+0000), then <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throw</a> an
   <code class="external"><a href="http://dom.spec.whatwg.org/#invalidcharactererror">InvalidCharacterError</a></code> exception and terminate these steps.</li>
   <li>If the character is in the range [\1-\1f] (U+0001 to U+001F) or
   [\7f-\9f] (U+007F to U+009F), then the character
   <a href="#escape-a-character-as-code-point" title="escape a character as code point">escaped as code point</a>.</li>
   <li>If the character is the first character and is in the range [0-9]
   (U+0030 to U+0039), then the character
   <a href="#escape-a-character-as-code-point" title="escape a character as code point">escaped as code point</a>.</li>
   <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 href="#escape-a-character-as-code-point" title="escape a character as code point">escaped as code point</a>.</li>
   <li>If the character is the second character and is "<code>-</code>"
   (U+002D) and the first character is "<code>-</code>" as well, then the
   <a href="#escape-a-character" title="escape a character">escaped</a> character.</li>
   <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>
   <li>Otherwise, the <a href="#escape-a-character" title="escape a character">escaped</a>
   character.</li>
  </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):</p>

  <ul>
   <li>If the character is NULL (U+0000), then <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throw</a> an
   <code class="external"><a href="http://dom.spec.whatwg.org/#invalidcharactererror">InvalidCharacterError</a></code> exception and terminate these steps.</li>
   <li>If the character is in the range [\1-\1f] (U+0001 to U+001F) or [\7f-\9f] (U+007F to
   U+009F), the character <a href="#escape-a-character-as-code-point" title="escape a character as code point">escaped as code point</a>.</li>
   <li>If the character is '<code>"</code>' (U+0022) or '<code>\</code>'
   (U+005C), the <a href="#escape-a-character" title="escape a character">escaped</a> character.</li>
   <li>Otherwise, the character itself.</li>
  </ul>

  <p class="note">"<code>'</code>" (U+0027) is not escaped because strings
  are always serialized with '<code>"</code>' (U+0022).</p>

  <p>To <dfn id="serialize-a-url">serialize a URL</dfn> means to create a string represented by
  "<code>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>

  <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>", i.e.,
  COMMA (U+002C) followed by a single SPACE (U+0020).</p>

  <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 by "<code> </code>", i.e.,
  a single SPACE (U+0020).</p>

  <p class="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.</p>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="media-queries"><span class="secno">4 </span>Media Queries</h2>

  <p>Media queries are defined by the Media Queries specification. This
  section defines various concepts around media queries, including their API
  and serialization form.</p>

  <!-- XXX ref -->

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="parsing-media-queries"><span class="secno">4.1 </span>Parsing Media Queries</h3>

  <p>To
  <dfn id="parse-a-media-query-list">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 one or more media
  queries that the algorithm defined there gives.</p> <!-- XXX ref -->

  <p class="note">A media query that ends up being "ignored" will turn
  into "<code>not all</code>".</p>

  <p>To
  <dfn id="parse-a-media-query">parse a media query</dfn> for a g
8026
iven string
  <var>s</var> means to follow the
  <a href="#parse-a-media-query-list">parse a media query list</a> steps and return <code>null</code> if more
  than one media query is returned or a media query if a
  single media query is returned.</p>

  <p class="note">Again, a media query that ends up being "ignored" will
  turn into "<code>not all</code>".</p>

  <!-- ........................................................................................................................ -->

  <h3 id="serializing-media-queries"><span class="secno">4.2 </span>Serializing Media Queries</h3>

  <p>To
  <dfn id="serialize-a-media-query-list">serialize a media query list</dfn>
  run these steps:</p>

  <ol>
   <li><p>If the media query list is empty return the empty string and
   terminate these steps.</li>

   <li><p><a href="#serialize-a-media-query" title="serialize a media query">Serialize</a> each
   media query in the list of media queries, sort them in lexicographical
   order, and then
   <a href="#serialize-a-comma-separated-list" title="serialize a comma-separated list">serialize</a> the
   list.</li>
  </ol>

  <p>To
  <dfn id="serialize-a-media-query">serialize a media query</dfn> let
  <var>s</var> be the empty string, run the steps below, and
  finally return <var>s</var>:</p>

  <ol>
   <li><p>If the media query is negated append "<code>not</code>", followed
   by a single SPACE (U+0020), to <var>s</var>.</li>

   <li><p>Let <var>type</var> be the media type of the media query,
   <a href="#serialize-an-identifier" title="serialize an identifier">escaped</a> and
   <a class="external" href="http://dom.spec.whatwg.org/#converted-to-ascii-lowercase">converted to ASCII lowercase</a>.</li>

   <li><p>If the media query does not contain media features append
   <var>type</var>, to <var>s</var>,
   then return <var>s</var> and terminate this algorithm.</li>

   <li><p>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>

   <li><p>Sort the media features in lexicographical order.</li>

   <li>
    <p>Then, for each media feature:</p>

    <ol>
     <li>Append a "<code>(</code>" (U+0028), followed by the media feature
     name, <a class="external" href="http://dom.spec.whatwg.org/#converted-to-ascii-lowercase">converted to ASCII lowercase</a>,
     to <var>s</var>.<p></li>

     <li><p>If a value is given append a "<code>:</code>" (U+003A), followed
     by a single 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>s</var>.</li>

     <li><p>Append a "<code>)</code>" (U+0029) to
     <var>s</var>.</li>

     <li><p>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>.</li>
    </ol>
   </li>
  </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><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>


  <!-- ........................................................................................................................ -->

  <h4 id="serializing-media-feature-values"><span class="secno">4.2.1 </span>Serializing Media Feature Values</h4>

  <p class="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.</p>

  <p>To <dfn id="serialize-a-media-feature-value">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:</p>

  <table>
   <tr>
    <th>Media Feature
    <th>Serialization
   <tr>
    <td><code>width</code>
    <td>...
   <tr>
    <td><code>height</code>
    <td>...
   <tr>
    <td><code>device-width</code>
    <td>...
   <tr>
    <td><code>device-height</code>
    <td>...
   <tr>
    <td><code>orientation</code>
    <td>
     <p>If the value is `<code>portrait</code>`: "<code>portrait</code>".</p>
     <p>If the value is `<code>landscape</code>`: "<code>landscape</code>".</p>
   <tr>
    <td><code>aspect-ratio</code>
    <td>...
   <tr>
    <td><code>device-aspect-ratio</code>
    <td>...
   <tr>
    <td><code>color</code>
    <td>...
   <tr>
    <td><code>color-index</code>
    <td>...
   <tr>
    <td><code>monochrome</code>
    <td>...
   <tr>
    <td><code>resolution</code>
    <td>...
   <tr>
    <td><code>scan</code>
    <td>
     <p>If the value is `<code>progressive</code>`: "<code>progressive</code>".</p>
     <p>If the value is `<code>interlace</code>`: "<code>interlace</code>".</p>
   <tr>
    <td><code>grid</code>
    <td>...
  </table>

  <p>Other specifications can extend this table and vendor-prefixed media
  features can have custom serialization formats as well.</p>

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="comparing-media-queries"><span class="secno">4.3 </span>Comparing Media Queries</h3>

  <p>To
  <dfn id="compare-media-queries">compare media queries</dfn>
  <var>m1</var> and <var>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 class="external" href="http://dom.spec.whatwg.org/#case-sensitive">case-sensitive</a> match and false if they
  are not.</p>

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="the-medialist-interface"><span class="secno">4.4 </span>The <code>MediaList</code> Interface</h3>

  <p>An object that implements the <a class="idlType" href="#widl-def-MediaList"><code>MediaList</code></a> interface has an associated <dfn id="collection-of-media-queries">collection of media queries</dfn>.</p>
<pre class="idl"><span class="idlInterface" id="widl-def-MediaList">[Constructor(DOMString text)]
interface <span class="idlInterfaceID">MediaList</span> {
<span class="idlAttribute">    stringifier attribute <span class="idlAttrType"><a>DOMString</a></span> <span class="idlAttrName"><a href="#widl-MediaList-mediaText">mediaText</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>unsigned long</a></span> <span class="idlAttrName"><a href="#widl-MediaList-length">length</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a>DOMString</a></span> <span class="idlMethName"><a href="#widl-MediaList-item-DOMString-unsigned-long-index">item</a></span> (<span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaList-appendMedium-void-DOMString-medium">appendMedium</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">medium</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-MediaList-deleteMedium-void-DOMString-medium">deleteMedium</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">medium</span></span>);</span>
};</span></pre>
<dl class="constructors">
<dt class="constructor" id="widl-MediaList-DOMString-text">
<code>MediaList</code> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">text</span></span>)</dt>
<dd>
<p>To <dfn id="create-a-medialist-object">create a <code>MediaList</code> object</dfn> from a string <var>text</var>, run these steps:</p>   <ol>    <li><p>Create a new <code>MediaList</code> object.</li>    <li><p>Set its <span title="dom-MediaList-mediaText">mediaText</span> attribute to <var>text</var>.</li>    <li><p>Return the newly created <code><code>MediaList</code></code> object.</li>   </ol></dd>
</dl>
<dl class="attributes">
<dt class="attribute" id="widl-MediaList-mediaText">
<code>mediaText</code> of type <span class="idlAttrType"><a>DOMString</a></span></dt>
<dd>
<p>The <code>mediaText</code> attribute must return a <a href="#serialize-a-media-query-list" title="serialize a media query list">serialization</a>   of the <a href="#collection-of-media-queries">collection of media queries</a>.</p>   <p>Setting the <code>mediaText</code> attribute must run these steps:   <ol>    <li><p>Empty the <a href="#collection-of-media-queries">collection of media queries</a>.</li>    <li><p>If the given value is the empty string terminate these steps.</li>    <li><p>Append all the media queries as a result of <a href="#parse-a-media-query-list" title="parse a media query list">parsing</a> the given    value to the <a href="#collection-of-media-queries">collection of media queries</a>.</li>   </ol></dd>
<dt class="attribute" id="widl-MediaList-length">
<code>length</code> of type <span class="idlAttrType"><a>unsigned long</a></span>, readonly</dt>
<dd>
<p>The <code>length</code> attribute must return the number of media queries in the <a href="#collection-of-media-queries">collection of media queries</a>.</dd>
</dl>
<dl class="methods">
<dt class="method" id="widl-MediaList-item-DOMString-unsigned-long-index">
<code>item</code> (<span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>), returns <span class="idlMethType"><a>DOMString</a></span></dt>
<dd>
<p>The <code>item</code> method must return the media query in the <a href="#collection-of-media-queries">collection of media queries</a> given by   <var>index</var>, or <code>null</code>, if <var>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>.</dd>
<dt class="method" id="widl-MediaList-appendMedium-void-DOMString-medium">
<code>appendMedium</code> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">medium</span></span>), returns <span class="idlMethType"><a>void</a></span></dt>
<dd>
<p>The <code>appendMedium</code> method must run these steps:</p>   <ol>    <li><p>Let <var>m</var> be the result of <a href="#parse-a-media-query" title="parse a media query">parsing</a> the given value.</li>    <li><p>If <var>m</var> is <code>null</code> terminate these steps.</li>    <li><p>If <a href="#compare-media-queries" title="compare media queries">comparing</a> <var>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>    <li><p>Append <var>m</var> to the <a href="#collection-of-media-queries">collection of media queries</a>.</li>   </ol></dd>
<dt class="method" id="widl-MediaList-deleteMedium-void-DOMString-medium">
<code>deleteMedium</code> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">medium</span></span>), returns <span class="idlMethType"><a>void</a></span></dt>
<dd>
<p>The <code>deleteMedium</code> method must run these steps:</p>   <ol>    <li><p>Let <var>m</var> be the result of <a href="#parse-a-media-query" title="parse a media query">parsing</a> the given value.</li>    <li><p>If <var>m</var> is <code>null</code> terminate these steps.</li>    <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>m</var> returns true.</li>   </ol></dd>
</dl>


  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="selectors"><span class="secno">5 </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">5.1 </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>selectors_group</code>
  production defined in the Selectors specification and return either a
  group of selectors if parsing did not fail or <code>null</code> if parsing did
  fail.</p> <!-- XXX ref -->

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="serializing-selectors"><span class="secno">5.2 </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>

  <p>To <dfn id="serialize-a-selector">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>:</p>

  <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>s</var>.</li>

   <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>s</var>.</li>

   <li><p>If this is not the last part of the chain of the selector append a
   single SPACE (U+0020), followed by the combinator
   "<code>&gt;</code>",
   "<code>+</code>", or
   "<code>~</code>"
   as appropriate, followed by another single SPACE (U+0020) if the combinator was
   not whitespace, to <var>s</var>.</li>

   <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>s</var>.</li>
  </ol>


  <p>To
  <dfn id="serialize-a-simple-selector">serialize a simple selector</dfn>
  let <var>s</var> be the empty string, run the steps below, and
  finally return <var>s</var>:</p>

  <dl class="switch">
   <dt>type selector</dt>
   <dt>universal selector</dt>
   <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>s</var>.</li>

     <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>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>s</var>.</li>

     <li><p>If this is a universal selector append "<code>*</code>" (U+002A)
     to <var>s</var>.</li>
    </ol>
   </dd>

   <dt>attribute selector</dt>
   <dd>
    <ol>
     <li><p>Append "<code>[</code>" (U+005B) to
     <var>s</var>.</li>

     <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>s</var>.</li>

     <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>s</var>.</li>
     <!-- This includes |* -->

     <li><p>Append the <a href="#serialize-an-identifier" title="serialize an identifier">escaped</a>
     attribute name to <var>s</var>.</li>

     <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>s</var>.</li>

     <li><p>Append "<code>]</code>" (U+005D) to
     <var>s</var>.</li>
    </ol>
   </dd>

   <dt>class selector</dt>
   <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>s</var>.</dd>

   <dt>ID selector</dt>
   <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>s</var>.</dd>

   <dt>pseudo-class</dt>
   <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>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>s</var>.</p>

    <dl class="switch">
     <dt><code>:lang()</code></dt>
     <dd><p>The <a href="#serialize-an-identifier" title="serialize an identifier">escaped</a>
     value.</dd>

     <dt><code>:nth-child()</code></dt>
     <dt><code>:nth-last-child()</code></dt>
     <dt><code>:nth-of-type()</code></dt>
     <dt><code>:nth-last-of-type()</code></dt>
     <dd>
      <ol>
       <li><p>If the value is odd let the value be
       "<code>2n+1</code>".</li>

       <li><p>If the value is even let the value be
       "<code>2n</code>".</li>

       <li><p>If <var>a</var> is zero let the value be
       <var>b</var>
       <a href="#serialize-a-css-value-component" title="serialize a CSS component value">serialized</a> as &lt;integer&gt;.</li>

       <li><p>If <var>a</var> is one or minus one and
       <var>b</var> is zero let the value be
       "<code>n</code>" (U+006E).</li>

       <li><p>If <var>a</var> is one or minus one let the value be
       "<code>n</code>" (U+006E), followed by
       "<code>+</code>" (U+002B) if <var>b</var> is positive,
       followed by <var>b</var>
       <a href="#serialize-a-css-value-component" title="serialize a CSS component value">serialized</a> as &lt;integer&gt;.</li>

       <li><p>If <var>b</var> is zero let the value be
       <var>a</var>
       <a href="#serialize-a-css-value-component" title="serialize a CSS component value">serialized</a> as &lt;integer&gt;,
       followed by "<code>n</code>" (U+006E).</li>

       <li><p>Otherwise let the value be
       <var>a</var>
       <a href="#serialize-a-css-value-component" title="serialize a CSS component value">serialized</a> as &lt;integer&gt;,
       followed by "<code>n</code>" (U+006E), followed by
       "<code>+</code>" (U+002B) if <var>b</var> is positive,
       followed by <var>b</var>
       <a href="#serialize-a-css-value-component" title="serialize a CSS component value">serialized</a> as &lt;integer&gt;.</li>
      </ol>
     </dd>

     <dt><code>:not()</code></dt>
     <dd><p>The result of serializing the value using the rules for
     <a href="#serialize-a-group-of-selectors" title="serialize a group of selectors">serializing a group of
6936
 selectors</a>.</dd>
    </dl>
   </dd>
  </dl>

  <!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->

  <h2 id="css"><span class="secno">6 </span>CSS</h2>

  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="css-style-sheets"><span class="secno">6.1 </span>CSS Style Sheets</h3>

  <!-- XXX
   element inserted into the DOM, style sheet created, element removed from
   the DOM, what happens to StyleSheet?
  -->

  <p>A <dfn id="css-style-sheet">CSS style sheet</dfn> is an abstract concept that
  represents a style sheet as defined by the CSS specification. In the CSSOM a
  <a href="#css-style-sheet">CSS style sheet</a> is represented as a <code>CSSStyleSheet</code> object. A
  <a href="#css-style-sheet">CSS style sheet</a> has a number of associated state items:</p>

  <dl>
   <dt><dfn id="style-sheet-type">style sheet type</dfn></dt>
   <dd><p>The literal string "<code>text/css</code>".</dd>

   <dt><dfn id="style-sheet-location">style sheet location</dfn></dt>
   <dd><p>The <a class="external" href="http://dev.w3.org/html5/spec/single-page.html#url">URL</a> of the
   <span>style sheet</span> or <code>null</code> if the <span>style sheet</span> was
   embedded.</dd>

   <dt><dfn id="style-sheet-parent">style sheet parent</dfn></dt>
   <dd><p>The <span>style sheet</span> that is the parent of the
   <span>style sheet</span> or <code>null</code> if there is no associated parent.</dd>

   <dt><dfn id="style-sheet-owner-node">style sheet owner node</dfn></dt>
   <dd><p>The DOM node associated with the <span>style sheet</span> or
   <code>null</code> if there is no associated DOM node.</dd>

   <dt><dfn id="style-sheet-owner-css-rule">style sheet owner CSS rule</dfn></dt>
   <dd><p>The <a href="#rule">CSS rule</a> in the <a href="#style-sheet-parent">style sheet parent</a>
   that caused the inclusion of the <span>style sheet</span> or <code>null</code> if
   there is no associated rule.</dd>

   <dt><dfn id="style-sheet-media">style sheet media</dfn></dt>
   <dd>
    <p>The <code>MediaList</code> object associated with the
    <span>style sheet</span>.</p>

    <p>If this property is set to a string run the
    <a href="#create-a-medialist-object">create a <code>MediaList</code> object</a> steps for that
    string and associate the returned object with the
    <span>style sheet</span>.</p>
   </dd>

   <dt><dfn id="style-sheet-title">style sheet title</dfn></dt>
   <dd>
    <p>The title of the <span>style sheet</span> or <code>null</code> if no title
    is specified or is the empty string, in which case the title is referred to
    as an empty title.</p>

    <div class="example">
     <p>In the following, the <a href="#style-sheet-title">style sheet title</a> is non-empty
     for the first style sheet, but is empty for the second and third style sheets.</p>
     <pre>&lt;style title="papaya whip"&gt;
  body { background: #ffefd5; }
&lt;/style&gt;</pre>
     <pre>&lt;style title=""&gt;
  body { background: orange; }
&lt;/style&gt;</pre>
     <pre>&lt;style&gt;
  body { background: brown; }
&lt;/style&gt;</pre>
    </div>
   </dd>

   <dt><dfn id="style-sheet-alternate-flag">style sheet alternate flag</dfn></dt>
   <dd>
    <p>Either set or clear. Clear by default.</p>

    <div class="example">
     <p>The following <span title="style sheet">style sheets</span> have
     their <a href="#style-sheet-alternate-flag">style sheet alternate flag</a> set:</p>

     <pre>&lt;?xml-stylesheet alternate="yes" title="x" href="data:text/css,…"?&gt;</pre>

     <pre>&lt;link rel="alternate stylesheet" title="x" href="data:text/css,…"&gt;</pre>
    </div>
   </dd>

   <dt><dfn id="style-sheet-disabled-flag">style sheet disabled flag</dfn></dt>
   <dd>
    <p>Either set or clear. Clear by default.</p>

    <p class="note">Even when clear it does not necessarily mean that the
   </dd>


   <dt><dfn id="style-sheet-css-rules">style sheet CSS rules</dfn></dt>
   <dd><p>The <a href="#rule" title="CSS rule">CSS rules</a> associated with the
   <span>style sheet</span>.</dd>
  </dl>

  <p>When you are to <a href="#create-a-style-sheet">create a style sheet</a> the above properties,
  with the exception of <a href="#style-sheet-type">style sheet type</a> and
  <a href="#style-sheet-css-rules">style sheet CSS rules</a>, are to be set to
  their proper values.</p>

  <!-- same-origin restrictions -->

  <!-- ........................................................................................................................ -->

  <h4 id="the-stylesheet-interface"><span class="secno">6.1.1 </span>The <code>StyleSheet</code> Interface</h4>

  <p>The <code>StyleSheet</code> interface represents an abstract, base style sheet.</p>
<pre class="idl"><span class="idlInterface" id="widl-def-StyleSheet">interface <span class="idlInterfaceID">StyleSheet</span> {
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a></span> <span class="idlAttrName"><a href="#widl-StyleSheet-type">type</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a>?</span> <span class="idlAttrName"><a href="#widl-StyleSheet-href">href</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>Node</a></span> <span class="idlAttrName"><a href="#widl-StyleSheet-ownerNode">ownerNode</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>StyleSheet</a>?</span> <span class="idlAttrName"><a href="#widl-StyleSheet-parentStyleSheet">parentStyleSheet</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>DOMString</a>?</span> <span class="idlAttrName"><a href="#widl-StyleSheet-title">title</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>MediaList</a></span> <span class="idlAttrName"><a href="#widl-StyleSheet-media">media</a></span>;</span>
<span class="idlAttribute">    attribute <span class="idlAttrType"><a>boolean</a></span> <span class="idlAttrName"><a href="#widl-StyleSheet-disabled">disabled</a></span>;</span>
};</span></pre>
<dl class="attributes">
<dt class="attribute" id="widl-StyleSheet-type">
<code>type</code> of type <span class="idlAttrType"><a>DOMString</a></span>, readonly</dt>
<dd>
<p>The <code>type</code> attribute must return the <a href="#style-sheet-type">style sheet type</a>.</dd>
<dt class="attribute" id="widl-StyleSheet-href">
<code>href</code> of type <span class="idlAttrType"><a>DOMString</a>?</span>, readonly</dt>
<dd>
<p>The <code>href</code> attribute must return the <a href="#style-sheet-location">style sheet location</a> or <code>null</code> if none.</p>    <p class="issue">What should the default value be if not known or specified upon creation? an empty string or <code>null</code>?</dd>
<dt class="attribute" id="widl-StyleSheet-ownerNode">
<code>ownerNode</code> of type <span class="idlAttrType"><a>Node</a></span>, readonly</dt>
<dd>
<p>The <code>ownerNode</code> attribute must return the <a href="#style-sheet-owner-node">style sheet owner node</a>.</p>    <p class="issue">Should <code>ownerNode</code> be nullable?</dd>
<dt class="attribute" id="widl-StyleSheet-parentStyleSheet">
<code>parentStyleSheet</code> of type <span class="idlAttrType"><a>StyleSheet</a>?</span>, readonly</dt>
<dd>
<p>The <code>parentStyleSheet</code> attribute must return the <a href="#style-sheet-parent">style sheet parent</a> or <code>null</code> if there is none.</dd>
<dt class="attribute" id="widl-StyleSheet-title">
<code>title</code> of type <span class="idlAttrType"><a>DOMString</a>?</span>, readonly</dt>
<dd>
<p>The <code>title</code> attribute must return the <a href="#style-sheet-title">style sheet title</a> or <code>null</code> if none.</p>    <p class="issue">What should the default value be if not known or specified upon creation? an empty string or <code>null</code>?</dd>
<dt class="attribute" id="widl-StyleSheet-media">
<code>media</code> of type <span class="idlAttrType"><a>MediaList</a></span>, readonly</dt>
<dd>
<p>The <code>media</code> attribute must return the <a href="#style-sheet-media">style sheet media</a>.</p>    <p class="issue">Should <code>media</code> be nullable?</p>    <p class="issue">Need to define a setter that implements the semantics of setting this attribute to a string representing a MediaList.</dd>
<dt class="attribute" id="widl-StyleSheet-disabled">
<code>disabled</code> of type <span class="idlAttrType"><a>boolean</a></span></dt>
<dd>
<p>The <code>disabled</code> attribute must return true if the <a href="#style-sheet-disabled-flag">style sheet disabled flag</a>    is set, or false otherwise.</p>    <p>Setting the <code>disabled</code> attribute must set the <a href="#style-sheet-disabled-flag">style sheet disabled flag</a>    if the new value is true, or unset the <a href="#style-sheet-disabled-flag">style sheet disabled flag</a> otherwise.</dd>
</dl>


  <!-- ........................................................................................................................ -->

  <h4 id="the-cssstylesheet-interface"><span class="secno">6.1.2 </span>The <code>CSSStyleSheet</code> Interface</h4>

  <p>The <code>CSSStyleSheet</code> interface represents a CSS <span>style sheet</span> rule.</p>
<pre class="idl"><span class="idlInterface" id="widl-def-CSSStyleSheet">interface <span class="idlInterfaceID">CSSStyleSheet</span> : <span class="idlSuperclass"><a class="idlType" href="#widl-def-StyleSheet"><code>StyleSheet</code></a></span> {
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>CSSRule</a>?</span> <span class="idlAttrName"><a href="#widl-CSSStyleSheet-ownerRule">ownerRule</a></span>;</span>
<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>CSSRuleList</a></span> <span class="idlAttrName"><a href="#widl-CSSStyleSheet-cssRules">cssRules</a></span>;</span>
<span class="idlMethod">    <span class="idlMethType"><a>unsigned long</a></span> <span class="idlMethName"><a href="#widl-CSSStyleSheet-insertRule-unsigned-long-DOMString-rule-unsigned-long-index">insertRule</a></span> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">rule</span></span>, <span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>);</span>
<span class="idlMethod">    <span class="idlMethType"><a>void</a></span> <span class="idlMethName"><a href="#widl-CSSStyleSheet-deleteRule-void-unsigned-long-index">deleteRule</a></span> (<span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>);</span>
};</span></pre>
<dl class="attributes">
<dt class="attribute" id="widl-CSSStyleSheet-ownerRule">
<code>ownerRule</code> of type <span class="idlAttrType"><a>CSSRule</a>?</span>, readonly</dt>
<dd>
<p>The <code>ownerRule</code> attribute must return the <a href="#style-sheet-owner-css-rule">style sheet owner CSS rule</a> or <code>null</code> if none.    If a value other than <code>null</code> is ever returned, than that same value must always be returned on each get access.</dd>
<dt class="attribute" id="widl-CSSStyleSheet-cssRules">
<code>cssRules</code> of type <span class="idlAttrType"><a>CSSRuleList</a></span>, readonly</dt>
<dd>
<p>The <code>cssRules</code> attribute must return a read-only, live <code>CSSRuleList</code> object representing the <a href="#style-sheet-css-rules">style    sheet CSS rules</a>. The same object must be returned on each get access.</p>    <p class="note">Even though the returned <code>CSSRuleList</code> object is read-only (from the perspective of    client-authored script), it may nevertheless change over time due to its liveness status. For example, invoking    the <code>insertRule</code> or <code>deleteRule</code> operation may result in mutations reflected in the returned object.</dd>
</dl>
<dl class="methods">
<dt class="method" id="widl-CSSStyleSheet-insertRule-unsigned-long-DOMString-rule-unsigned-long-index">
<code>insertRule</code> (<span class="idlParam"><span class="idlParamType"><a>DOMString</a></span> <span class="idlParamName">rule</span></span>, <span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>), returns <span class="idlMethType"><a>unsigned long</a></span></dt>
<dd>
<p>The <code>insertRule</code> operation performs <dfn id="insert-a-css-rule">insert a CSS rule</dfn> <var>rule</var> as follows:</p>    <ol>    <li><p>Set <var>newRule</var> to the results of performing <a href="#parse-a-css-rule">parse a CSS rule</a>    on argument <var>rule</var>, <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throwing</a>    a "<code class="external"><a href="http://dom.spec.whatwg.org/#syntaxerror">SyntaxError</a></code>" exception if a parse error occurs.</li>    <li><p>Set <var>N</var> to <code>cssLength.length</code>.</li>    <li><p>If argument <var>index</var> is greater than <var>N</var>, then <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throw</a>    an "<code class="external"><a href="http://dom.spec.whatwg.org/#indexsizeerror">IndexSizeError</a></code>" exception.</li>    <li><p>If the rule <var>newRule</var> cannot be inserted into the specified <var>index</var> due to constraints specified    by <a href="#refsCSS">[CSS]</a>, then <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throw</a>    a "<code class="external"><a href="http://dom.spec.whatwg.org/#hierarchyrequesterror">HierarchyRequestError</a></code>" exception.</p>    <p class="note">For example, a CSS style sheet cannot contain more than one <code>@charset</code> rule, which,    if present, must be the first rule.</li>    <li><p>Set <var>newRule</var><code>.parentStyleSheet</code> to <code>this</code> (i.e., this <code>CSSStyleSheet</code> instance object).</li>    <li><p>Insert rule <var>newRule</var> into <code>cssRules</code> at the zero-indexed position <var>index</var>.<p></li>    <li><p>Return <var>index</var>.</li>    </ol>    <p class="note">If a new rule is inserted, then any rule previously located at position <var>index</var> through    <var>N</var> minus 1 is shifted to position <var>index</var> plus 1 through <var>N</var>,    In addition, <code>cssRules.length</code> is (internally) incremented.</p>    <p class="issue">DOM-2 CSS specifies that a <code>NO_MODIFICATION_ALLOWED_ERR</code> exception is thrown    if the style sheet is read-only. Are there any read-only style sheets?</dd>
<dt class="method" id="widl-CSSStyleSheet-deleteRule-void-unsigned-long-index">
<code>deleteRule</code> (<span class="idlParam"><span class="idlParamType"><a>unsigned long</a></span> <span class="idlParamName">index</span></span>), returns <span class="idlMethType"><a>void</a></span></dt>
<dd>
<p>The <code>deleteRule</code> operation performs <dfn id="remove-a-css-rule">remove a CSS rule</dfn> as follows:</p>    <ol>    <li><p>Set <var>N</var> to <code>cssLength.length</code>.</li>    <li><p>If argument <var>index</var> is greater than or equal to <var>N</var>, then <a class="external" href="http://dom.spec.whatwg.org/#concept-throw" title="concept-throw">throw</a>    an "<code class="external"><a href="http://dom.spec.whatwg.org/#indexsizeerror">IndexSizeError</a></code>" exception.</li>    <li><p>Set <var>oldRule</var> to <code>cssRules.prototype.item(<var>index</var>)</code>.</li>    <li><p>Set <var>oldRule</var><code>.parentStyleSheet</code> to <code>null</code>.</li>    <li><p>Remove rule <var>oldRule</var> from <code>cssRules</code> at the zero-indexed position <var>index</var>.<p></li>    </ol>    <p class="note">If an existing rule is deleted, then any rule previously located at position <var>index</var> plus 1 through    <var>N</var> minus 1 is shifted to position <var>index</var> through <var>N</var> minus 2,    In addition, <code>cssRules.length</code> is (internally) decremented.</dd>
</dl>


  <!-- ........................................................................................................................ -->
  <!-- ........................................................................................................................ -->

  <h3 id="style-sheet-collections"><span class="secno">6.2 </span>Style Sheet Collections</h3>

  <p>Below various new concepts are defined that are associated with each
  <code class="external"><a href="http://dom.spec.whatwg.org/#document">Document</a></code> object.</p>

  <p>Each <code class="external"><a href="http://dom.spec.whatwg.org/#document">Document</a></code> has an associated list of zero or more
  <span title="style sheet">style sheets</span>, named the
  <dfn id="document-style-sheets">document style sheets</dfn>. This is
  an ordered list that contains all
  <span title="style sheet">style sheets</span> associated with the