csswg-drafts/cssom-view/Overview.html at d9779908a63fa8baae6add0431e0b3f3f0c7c2df · w3c/csswg-drafts · GitHub

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">

<html lang=en-US>
 <head>
  <title>CSSOM View Module</title>

  <style type="text/css">
   pre.idl { border:solid thin; background:#eee; color:#000; padding:0.5em }
   pre.idl :link, pre.idl :visited { color:inherit; background:transparent }
   dfn { font-weight:bold; font-style:normal }
   div.example { margin-left:1em; padding-left:1em; border-left:double; color:#222; background:#fcfcfc }
   div.example code { color:inherit }
   p.note {  margin-left:2em; color:green; font-style:italic; font-weight:bold }
   p.note::before { content:"Note: " }
   .XXX { padding:.5em; border:solid red }
   .XXX::before { content:"Issue: " }
   em.ct { font-weight:bold; font-style:normal }
   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> <!--begin-logo-->
   <p><a href="http://www.w3.org/"><img alt=W3C height=48
    src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->

   <h1 id=cssom-view-module>CSSOM View Module</h1>

   <h2 class="no-num no-toc" id=w3c-doctype>Editor's Draft 13 August 2010</h2>

   <dl>
    <dt>This Version:

    <dd><a
     href="http://www.w3.org/TR/2010/ED-cssom-view-20100813/">http://www.w3.org/TR/2010/ED-cssom-view-20100813/</a>

    <dt>Latest Version:

    <dd><a
     href="http://www.w3.org/TR/cssom-view/">http://www.w3.org/TR/cssom-view/</a>

    <dt>Latest Editor Version:

    <dd><a
     href="http://dev.w3.org/csswg/cssom-view/">http://dev.w3.org/csswg/cssom-view/</a>

    <dt>Previous Versions:

    <dd><a
     href="http://www.w3.org/TR/2009/WD-cssom-view-20090804/">http://www.w3.org/TR/2009/WD-cssom-view-20090804/</a>

    <dd><a
     href="http://www.w3.org/TR/2008/WD-cssom-view-20080222/">http://www.w3.org/TR/2008/WD-cssom-view-20080222/</a>

    <dt>Editor:

    <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;
   </dl>
   <!--begin-copyright-->
   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
    rel=license>Copyright</a> &copy; 2010 <a
    href="http://www.w3.org/"><acronym title="World Wide Web
    Consortium">W3C</acronym></a><sup>&reg;</sup> (<a
    href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
    of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
    title="European Research Consortium for Informatics and
    Mathematics">ERCIM</acronym></a>, <a
    href="http://www.keio.ac.jp/">Keio</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>

  <h2 class="no-num no-toc" id=abstract>Abstract</h2>

  <p>The APIs introduced by this specification provide authors with a way to
   inspect and manipulate the visual view of a document. This includes
   getting the position of element layout boxes, obtaining the width of the
   viewport through script, and also scrolling an element.

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

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

  <p>The (<a
   href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
   mailing list <a
   href="mailto:www-style@w3.org?Subject=%5Bcssom-view%5D%20PUT%20SUBJECT%20HERE">
   www-style@w3.org</a> (see <a
   href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
   discussion of this specification. When sending e-mail, please put the text
   &#8220;cssom-view&#8221; in the subject, preferably like this:
   &#8220;[<!---->cssom-view<!---->] <em>&hellip;summary of
   comment&hellip;</em>&#8221;

  <p>This document was produced by the <a href="/Style/CSS/members">CSS
   Working Group</a> (part of the <a href="/Style/">Style Activity</a>).

  <p>This document was produced by a group operating under the <a
   href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
   Policy</a>. W3C maintains a <a href="/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="/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
   W3C Patent Policy</a>.</p>
  <!--end-status-->

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

  <ul class=toc>
   <li><a href="#background"><span class=secno>1. </span>Background</a>

   <li><a href="#conformance"><span class=secno>2. </span>Conformance
    Criteria</a>
    <ul class=toc>
     <li><a href="#webidl"><span class=secno>2.1. </span>Web IDL</a>

     <li><a href="#terminology"><span class=secno>2.2. </span>Terminology</a>


     <li><a href="#css-pixels"><span class=secno>2.3. </span>CSS pixels</a>
    </ul>

   <li><a href="#extensions-to-the-window-interface"><span class=secno>3.
    </span>Extensions to the <code title="">Window</code> Interface</a>
    <ul class=toc>
     <li><a href="#the-stylemedia-interface"><span class=secno>3.1.
      </span>The <code title="">StyleMedia</code> Interface</a>

     <li><a href="#the-screen-interface"><span class=secno>3.2. </span>The
      <code title="">Screen</code> Interface</a>
    </ul>

   <li><a href="#extensions-to-the-document-interface"><span class=secno>4.
    </span>Extensions to the <code title="">Document</code> Interface</a>
    <ul class=toc>
     <li><a href="#the-caretposition-interface"><span class=secno>4.1.
      </span>The <code title="">CaretPosition</code> Interface</a>
    </ul>

   <li><a href="#extensions-to-the-element-interface"><span class=secno>5.
    </span>Extensions to the <code title="">Element</code> Interface</a>
    <ul class=toc>
     <li><a href="#the-getclientrects-and-getboundingclient"><span
      class=secno>5.1. </span>The <code title="">getClientRects()</code> and
      <code title="">getBoundingClientRect()</code> methods</a>

     <li><a href="#scroll-attributes"><span class=secno>5.2. </span>The <code
      title="">scrollTop</code>, <code title="">scrollLeft</code>, <code
      title="">scrollWidth</code>, and <code title="">scrollHeight</code>
      attributes</a>

     <li><a href="#client-attributes"><span class=secno>5.3. </span>The <code
      title="">clientTop</code>, <code title="">clientLeft</code>, <code
      title="">clientWidth</code>, and <code title="">clientHeight</code>
      attributes</a>
    </ul>

   <li><a href="#extensions-to-the-htmlelement-interface"><span
    class=secno>6. </span>Extensions to the <code title="">HTMLElement</code>
    Interface</a>
    <ul class=toc>
     <li><a href="#offset-attributes"><span class=secno>6.1. </span>The <code
      title="">offsetParent</code>, <code title="">offsetTop</code>, <code
      title="">offsetLeft</code>, <code title="">offsetWidth</code>, and
      <code title="">offsetHeight</code> attributes</a>
    </ul>

   <li><a href="#extensions-to-the-range-interface"><span class=secno>7.
    </span>Extensions to the <code title="">Range</code> Interface</a>

   <li><a href="#extensions-to-the-mouseevent-interface"><span class=secno>8.
    </span>Extensions to the <code title="">MouseEvent</code> Interface</a>

   <li><a href="#rectangles"><span class=secno>9. </span>Rectangles</a>
    <ul class=toc>
     <li><a href="#the-clientrectlist-interface"><span class=secno>9.1.
      </span>The <code title="">ClientRectList</code> Interface</a>

     <li><a href="#the-clientrect-interface"><span class=secno>9.2.
      </span>The <code title="">ClientRect</code> Interface</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=background><span class=secno>1. </span>Background</h2>

  <p>Many of the features defined in this specification have been supported
   by browsers for a long period of time. The goal of this specification is
   to define these features in such a way that they can be implemented by all
   browsers in an interoperable manner. The specification also defines a
   couple of new features that will hopefully be useful to authors. (If they
   are not you can bug us!)

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

  <p>Everything in this specification is normative except for diagrams,
   examples, notes and sections marked non-normative.</p>
  <!--<p>The key word <em class="ct">must</em>, <em class=&qu
8096
ot;ct">must not</em>,
  <em class="ct">should</em> and <em class="ct">may</em> in this document
  are to be interpreted as described in RFC 2119.-->

  <p>The key word <em class=ct>must</em> in this document is to be
   interpreted as described in RFC 2119. [<cite><a
   href="#ref-rfc2119">RFC2119</a></cite>]

  <p>A conforming user agent implements all the requirements made by this
   specification.

  <h3 id=webidl><span class=secno>2.1. </span>Web IDL</h3>

  <p>The IDL fragments in this specification <em class=ct>must</em> be
   interpreted as required for conforming IDL fragments, as described in the
   Web IDL specification. [<cite><a href="#ref-webidl">WebIDL</a></cite>]

  <h3 id=terminology><span class=secno>2.2. </span>Terminology</h3>

  <p><dfn id=document><code>Document</code></dfn> and <dfn
   id=element><code>Element</code></dfn> are defined by DOM Level 3 Core.
   [<cite><a href="#ref-dom3core">DOM3Core</a></cite>]

  <p><dfn id=range><code>Range</code></dfn> is defined in DOM Level 2
   Traversal and Range. [<cite><a href="#ref-dom2tr">DOM2TR</a></cite>]

  <p><dfn id=mouseevent><code>MouseEvent</code></dfn> is defined in DOM Level
   2 Events. [<cite><a href="#ref-dom2events">DOM2Events</a></cite>]

  <p> <dfn id=compare-lists-of-media-queries>Compare lists of media
   queries</dfn> and <dfn id=parse-a-list-of-media-queries>parse a list of
   media queries</dfn> are defined by the CSSOM. [<cite><a
   href="#ref-cssom">CSSOM</a></cite>]

  <p> <dfn id=fire-a-simple-event title="Fire a simple event">Firing a simple
   event named <var title="">e</var></dfn>, <dfn id=html-element>HTML
   element</dfn>, <dfn id=htmlelement><code>HTMLElement</code></dfn>, <dfn
   id=queue-a-task>queue a task</dfn>, <dfn id=quirks-mode>quirks mode</dfn>,
   <dfn id=task>task</dfn>, and <dfn id=window><code>Window</code></dfn> are
   defined by HTML5. [<cite><a href="#ref-html5">HTML5</a></cite>]

  <p><dfn id=the-html-body-element>The HTML <code>body</code> element</dfn>
   is the first <code>body</code> <a href="#html-element">HTML element</a>
   child of the root <a href="#html-element">HTML element</a>
   <code>html</code>.

  <p><dfn id=content-edge>Content edge</dfn>, <dfn id=padding-edge>padding
   edge</dfn>, <dfn id=border-edge>border edge</dfn>, and <dfn
   id=canvas>canvas</dfn> are defined by CSS 2.1. [<cite><a
   href="#ref-css21">CSS21</a></cite>]

  <p><dfn id=viewport>Viewport</dfn> and <dfn
   id=initial-containing-block>initial containing block</dfn> are defined by
   CSS 2.1 unless there is an ancestor <code>foreignObject</code> element in
   the <code>http://www.w3.org/2000/svg</code> namespace in which case that
   element acts as viewport and initial containing block. [<cite><a
   href="#ref-css21">CSS21</a></cite>] [<cite><a
   href="#ref-svg">SVG</a></cite>]

  <p>The term <dfn id=content>content</dfn> refers to the dimensions of the
   element's content area, including overflown content. [<cite><a
   href="#ref-css21">CSS21</a></cite>]

  <p>The term <dfn id=document-content>document content</dfn> refers to the
   area on the <a href="#canvas">canvas</a> that is rendered upon, excluding
   content on negative axis.

  <h3 id=css-pixels><span class=secno>2.3. </span>CSS pixels</h3>

  <p>All coordinates and dimensions for the APIs defined in this
   specification are in CSS pixels. [<cite><a
   href="#ref-css21">CSS21</a></cite>]

  <p class=note>This does not apply to e.g. <a
   href="#dom-stylemedia-matchmedia"><code
   title=dom-StyleMedia-matchMedia>matchMedia()</code></a> as the units are
   explicitly given there.

  <h2 id=extensions-to-the-window-interface><span class=secno>3.
   </span>Extensions to the <code title="">Window</code> Interface</h2>

  <pre class=idl>[Supplemental] interface <a href="#window">Window</a> {
  readonly attribute <a href="#stylemedia">StyleMedia</a> <a href="#dom-window-stylemedia" title=dom-Window-styleMedia>styleMedia</a>;
  readonly attribute <a href="#screen">Screen</a> <a href="#dom-window-screen" title=dom-Window-screen>screen</a>;

  // viewport
  readonly attribute long <a href="#dom-window-innerwidth">innerWidth</a>;
  readonly attribute long <a href="#dom-window-innerheight">innerHeight</a>;
  readonly attribute long <a href="#dom-window-pagexoffset">pageXOffset</a>;
  readonly attribute long <a href="#dom-window-pageyoffset">pageYOffset</a>;
  void <a href="#dom-window-scroll" title=dom-Window-scroll>scroll</a>(long <var title="">x</var>, long <var title="">y</var>);
  void <a href="#dom-window-scrollto" title=dom-Window-scrollto>scrollTo</a>(long <var title="">x</var>, long <var title="">y</var>);
  void <a href="#dom-window-scrollby" title=dom-Window-scrollby>scrollBy</a>(long <var title="">x</var>, long <var title="">y</var>);

  // client
  readonly attribute long <a href="#dom-window-screenx">screenX</a>;
  readonly attribute long <a href="#dom-window-screeny">screenY</a>;
  readonly attribute long <a href="#dom-window-outerwidth">outerWidth</a>;
  readonly attribute long <a href="#dom-window-outerheight">outerHeight</a>;
};</pre>

  <p>The <dfn id=dom-window-stylemedia
   title=dom-Window-styleMedia><code>styleMedia</code></dfn> attribute <em
   class=ct>must</em> return the <a
   href="#stylemedia"><code>StyleMedia</code></a> object associated with the
   <a href="#window"><code>Window</code></a> object. It always returns the
   same object.

  <p>The <dfn id=dom-window-screen
   title=dom-Window-screen><code>screen</code></dfn> attribute <em
   class=ct>must</em> return the <a href="#screen"><code>Screen</code></a>
   object associated with the <a href="#window"><code>Window</code></a>
   object. It always returns the same object.

  <p class=note>Accessing <a href="#dom-window-stylemedia"><code
   title=dom-Window-styleMedia>styleMedia</code></a> or <a
   href="#dom-window-screen"><code title=dom-Window-screen>screen</code></a>
   through a <code>WindowProxy</code> object might yield different results
   when the document is navigated.

  <p>The <dfn id=dom-window-innerwidth><code>innerWidth</code></dfn>
   attribute <em class=ct>must</em> return the <a
   href="#viewport">viewport</a> width including the size of a rendered
   scroll bar (if any).

  <div class=example>
   <p>The following snippet shows how to obtain the width of the viewport:</p>

   <pre><code>var viewportWidth = innerWidth</code></pre>
  </div>

  <p>The <dfn id=dom-window-innerheight><code>innerHeight</code></dfn>
   attribute <em class=ct>must</em> return the <a
   href="#viewport">viewport</a> height including the size of a rendered
   scroll bar (if any).

  <p>The <dfn id=dom-window-pagexoffset><code>pageXOffset</code></dfn>
   attribute <em class=ct>must</em> return the x-coordinate, relative to the
   <a href="#initial-containing-block">initial containing block</a> origin,
   of the left of the <a href="#viewport">viewport</a>.

  <p>The <dfn id=dom-window-pageyoffset><code>pageYOffset</code></dfn>
   attribute <em class=ct>must</em> return the y-coordinate, relative to the
   <a href="#initial-containing-block">initial containing block</a> origin,
   of the top of the <a href="#viewport">viewport</a>.

  <p>When the <dfn id=dom-window-scroll
   title=dom-Window-scroll><code>scroll(<var title="">x</var>,<var
   title="">y</var>)</code></dfn> method is invoked these steps <em
   class=ct>must</em> be run:

  <ol>
   <li>
    <p>If either <var title="">x</var> or <var title="">y</var> is infinite
     or NaN stop this algorithm.

   <li>
    <dl>
     <dt>If <a href="#document-content">document content</a> can have
      overflow to the right

     <dd>
      <ol>
       <li>
        <p>Let <var title="">x</var> be min(<var title="">x</var>, <a
         href="#content">content</a> width - <a href="#content-edge">content
         edge</a> width).

       <li>
        <p>If <var title="">x</var> is negative let it be zero.
      </ol>

     <dt>If <a href="#document-content">document content</a> can have
      overflow to the left (under right-to-left conditions)

     <dd>
      <ol>
       <li>
        <p>Let <var title="">x</var> be max(<var title="">x</var>, <a
         href="#content-edge">content edge</a> width - <a
         href="#content">content</a> width).

       <li>
        <p>If <var title="">x</var> is non-negative let it be zero.
      </ol>
    </dl>

   <li>
    <p>Let <var title="">y</var> be min(<var title="">y</var>, <a
     href="#document-content">document content</a> height - <a
     href="#viewport">viewport</a> height excluding the size of a rendered
     scroll bar (if any)).

   <li>
    <p>If <var title="">y</var> is negative let it be zero.

   <li>
    <p>Align the x-coordinate <var title="">x</var> of the <a
     href="#document-content">document content</a> with the left of the <a
     href="#viewport">viewport</a> and align the y-coordinate <var
     title="">y</var> of the <a href="#document-content">document content</a>
     with the top of the <a href="#viewport">viewport</a>.

   <li>
    <p>If the aligning caused content to move <a href="#queue-a-task">queue a
     task</a> to <a href="#fire-a-simple-event">fire a simple event</a> named
     <code title=event-scroll>scroll</code> that bubbles at the <a
     href="#document"><code>Document</code></a> object, unless a <a
     href="#task">task</a> to fire that event at the <a
     href="#document"><code>Document</code></a> object was already <a
     href="#queue-a-task" title="queue a task">queued</a>.
  </ol>

  <p>When the <dfn id=dom-window-scrollto
   title=dom-Window-scrollto><code>scrollTo(<var title="">x</var>,<var
   title="">y</var>)</code></dfn> method is invoked, the user agent <em
   class=ct>must</em> act as if the <a href="#dom-window-scroll"><code
   title=dom-Window-scroll>scroll()</code></a> method was invoked with the
   same arguments.

  <p>When the <dfn id=dom-window-scrollby
   title=dom-Window-scrollby><code>scrollBy(<var title="">x</var>,<var
   title="">y</var>)</code></dfn> method is invoked, the user agent <em
   class=ct>must</em> act as if the <a href="#dom-window-scroll"><code
   title=dom-Window-scroll>scroll()</code></a> method was invoked with <var
   title="">x</var> plus <a
   href="#dom-window-pagexoffset"><code>pageXOffset</code></a> as first
   argument and <var title="">y</var> plus <a
   href="#dom-window-pageyoffset"><code>pageYOffset</code></a> as second
   argument.

  <p>The <dfn id=dom-window-screenx><code>screenX</code></dfn> attribute <em
   class=ct>must</em> return the x-coordinate, relative to the origin of the
   screen of the output device, of the top of the client window as number of
   pixels, or zero if there is no such thing.

  <p>The <dfn id=dom-window-screeny><code>screenY</code></dfn> attribute <em
   class=ct>must</em> return the y-coordinate, relative to the origin of the
   screen of the output device, of the left of the client window as number of
   pixels, or zero if there is no such thing.

  <p>The <dfn id=dom-window-outerwidth><code>outerWidth</code></dfn>
   attribute <em class=ct>must</em> return the width of the client window. If
   there is no client window this attribute <em class=ct>must</em> return
   zero.

  <p>The <dfn id=dom-window-outerheight><code>outerHeight</code></dfn>
   attribute <em class=ct>must</em> return the height of the client window.
   If there is no client window this attribute <em class=ct>must</em> return
   zero.

  <h3 id=the-stylemedia-interface><span class=secno>3.1. </span>The <code
   title="">StyleMedia</code> Interface</h3>

  <pre class=idl>interface <dfn id=stylemedia>StyleMedia</dfn> {
  readonly attribute DOMString <a href="#dom-stylemedia-type" title=dom-StyleMedia-type>type</a>;
  boolean <a href="#dom-stylemedia-matchmedia" title=dom-StyleMedia-matchMedia>matchMedia</a>(DOMString <var title="">mq_list</var>);

  void <a href="#dom-stylemedia-addmedialistener" title=dom-StyleMedia-addMediaListener>addMediaListener</a>(DOMString <var title="">mq_list</var>, <a href="#booleancallback">BooleanCallback</a> <var title="">mq_callback</var>);
  void <a href="#dom-stylemedia-removemedialistener" title=dom-StyleMedia-removeMediaListener>removeMediaListener</a>(DOMString <var title="">mq_list</var>, <a href="#booleancallback">BooleanCallback</a> <var title="">mq_callback</var>);
};

[Callback=FunctionOnly, NoInterfaceObject]
interface <dfn id=booleancallback>BooleanCallback</dfn> {
  void <span>handleEvent</span>(boolean <var title="">arg</var>);
};</pre>

  <p>The <dfn id=dom-stylemedia-type
   title=dom-StyleMedia-type><code>type</code></dfn> attribute <em
   class=ct>must</em> return the string that represents the media type used
   for rendering the <a href="#document"><code>Document</code></a>. The media
   types are defined by CSS 2.1 (<code title="">screen</code>,
   <code>print</code>, et cetera). [<cite><a
   href="#ref-css21">CSS21</a></cite>]

  <div class=example>
   <p>The following snippet determines whether the page is rendered using the
    projection media type:</p>

   <pre><code>var isProjection = media.type == "projection"</code></pre>
  </div>

  <p>The <dfn id=dom-stylemedia-matchmedia
   title=dom-StyleMedia-matchMedia><code>matchMedia(<var
   title="">mq_list</var>)</code></dfn> method <em class=ct>must</em> run
   these steps:

  <ol>
   <li>
    <p>Let <var title="">parsed_mq_list</var> be the result of <a
     href="#parse-a-list-of-media-queries" title="parse a list of media
     queries">parsing</a> <var title="">mq_list</var>.

   <li>
    <p>Return true if <var title="">parsed_mq_list</var> matches the state of
     the rendered <a href="#document"><code>Document</code></a> and false if
     it does not.
  </ol>

  <div class=example>
   <p>The following snippet determines whether the device is a color device:</p>

   <pre><code>var isColorDevice = styleMedia.matchMedia("(color)")</code></pre>
  </div>

  <p>Each <a href="#window"><code>Window</code></a> has an associated ordered
   <dfn id=list-of-media-listeners>list of media listeners</dfn>. Each
   listener consists of a list of media queries and a callback.

  <p class=note>Due to the rules for <a
   href="#dom-stylemedia-addmedialistener"><code
   title=dom-StyleMedia-addMediaListener>addMediaListener()</code></a> below
   each listener is unique. Lists of media queries and callbacks are not
   necessarily unique.

  <p>The <dfn id=dom-stylemedia-addmedialistener
   title=dom-StyleMedia-addMediaListener><code>addMediaListener(<var
   title="">mq_list</var>, <var title="">mq_callback</var>)</code></dfn>
   method <em class=ct>must</em> run these steps:</p>
  <!-- based on dom-MediaList-appendMedium -->

  <ol>
   <li>
    <p>Let <var title="">parsed_mq_list</var> be the result of <a
     href="#parse-a-list-of-media-queries" title="parse a list of media
     queries">parsing</a> <var title="">mq_list</var>.

   <li>
    <p>If <a href="#compare-lists-of-media-queries" title="compare lists of
     media queries">comparing</a> <var title="">parsed_mq_list</var> with any
     of the list of media queries in the <a
     href="#list-of-media-listeners">list of media listeners</a> returns true
     <em>and</em> the associated callback of that media query is the same as
     <var title="">mq_callback</var>, terminate these steps.

   <li>
    <p>Append the tuple of <var title="">parsed_mq_list</var> and <var
     title="">mq_callback</var> to the <a
     href="#list-of-media-listeners">list of media listeners</a>.
  </ol>

  <p>The <dfn id=dom-stylemedia-removemedialistener
   title=dom-StyleMedia-removeMediaListener><code>removeMediaListener(<var
   title="">mq_list</var>, <var title="">mq_callback</var>)</code></dfn>
   method <em class=ct>must</em> run these steps:

  <ol>
   <li>
    <p>Let <var title="">parsed_mq_list</var> be the result of <a
     href="#parse-a-list-of-media-queries" title="parse a list of media
     queries">parsing</a> <var title="">mq_list</var>.

   <li>
    <p>If <a href="#compare-lists-of-media-queries" title="compare lists of
     media queries">comparing</a> <var title="">parsed_mq_list</var> with any
     of the media queries in the <a href="#list-of-media-listeners">list of
     media listeners</a> returns true <em>and</em> the associated callback of
     that media query is the same as <var title="">mq_callback</var>, remove
     the tuple of <var title="">parsed_mq_list</var> and <var
     title="">mq_callback</var> from the <a
     href="#list-of-media-listeners">list of media listeners</a>.
  </ol>

  <p>If one or more lists of media queries in the <a
   href="#list-of-media-listeners">list of media listeners</a> changes in
   evaluation then for each list of media queries of which the evaluation
   changes, in the order of the <a href="#list-of-media-listeners">list of
   media listeners</a>, <a href="#queue-a-task">queue a task</a> that invokes
   the associated callback, passing as argument whether the list of media
   queries matches the state of the rendered <a
   href="#document"><code>Document</code></a> at the time the <a
   href="#task">task</a> was <a href="#queue-a-task" title="queue a
   task">queued</a>.

  <div class=example>
   <p>A simple pie
6D5F
ce of code that detects changes in the orientation of the
    viewport can be written as follows:</p>

   <pre><code>function handleOrientationChange(landscape) {
  if(landscape)
    &hellip;
  else
    &hellip;
}
styleMedia.addMediaListener("(orientation:landscape)", handleOrientationChange)</code></pre>

   <p>A more generic handler for media query changes could be written as
    follows:</p>

   <pre><code>function handleMediaQueryChange(query, matches) {
  &hellip;
}
function addMediaListener(query) {
  styleMedia.addMediaListener(
    query,
    function(matches) { handleMediaQueryChange(query, matches) }
  )
}</code></pre>
  </div>

  <h3 id=the-screen-interface><span class=secno>3.2. </span>The <code
   title="">Screen</code> Interface</h3>

  <p>As its name suggests, the <a href="#screen"><code>Screen</code></a>
   interface represents information about the screen of the output device.

  <pre class=idl>interface <dfn id=screen>Screen</dfn> {
  readonly attribute unsigned long <a href="#dom-screen-availwidth">availWidth</a>;
  readonly attribute unsigned long <a href="#dom-screen-availheight">availHeight</a>;
  readonly attribute unsigned long <a href="#dom-screen-width">width</a>;
  readonly attribute unsigned long <a href="#dom-screen-height">height</a>;
  readonly attribute unsigned long <a href="#dom-screen-colordepth">colorDepth</a>;
  readonly attribute unsigned long <a href="#dom-screen-pixeldepth">pixelDepth</a>;
};</pre>

  <p>The <dfn id=dom-screen-availwidth><code>availWidth</code></dfn>
   attribute <em class=ct>must</em> return the available width of the
   rendering surface of the output device.

  <p>The <dfn id=dom-screen-availheight><code>availHeight</code></dfn>
   attribute <em class=ct>must</em> return the available height of the
   rendering surface of the output device.

  <p>The <dfn id=dom-screen-width><code>width</code></dfn> attribute <em
   class=ct>must</em> return the width of the output device.

  <p>The <dfn id=dom-screen-height><code>height</code></dfn> attribute <em
   class=ct>must</em> return the height of the output device.

  <p>The <dfn id=dom-screen-colordepth><code>colorDepth</code></dfn> and <dfn
   id=dom-screen-pixeldepth><code>pixelDepth</code></dfn> attributes <em
   class=ct>must</em> both return the number of bits allocated to colors
   (i.e. excluding the alpha channel) in the output device. If the output
   device does not support colors these attributes <em class=ct>must</em>
   return zero.</p>
  <!-- pixelDepth is not supported by Internet Explorer 7 -->

  <h2 id=extensions-to-the-document-interface><span class=secno>4.
   </span>Extensions to the <code title="">Document</code> Interface</h2>

  <pre class=idl>[Supplemental] interface <a href="#document">Document</a> {
  Element <a href="#dom-document-elementfrompoint">elementFromPoint</a>(float <var title="">x</var>, float <var title="">y</var>);
  <a href="#caretposition">CaretPosition</a> <a href="#dom-document-caretpositionfrompoint">caretPositionFromPoint</a>(float <var title="">x</var>, float <var title="">y</var>);
};</pre>

  <p>The <dfn id=dom-document-elementfrompoint
   title=elementfrompoint><code>elementFromPoint(<var title="">x</var>, <var
   title="">y</var>)</code></dfn> method, when invoked, <em
   class=ct>must</em> return the element at coordinates
   <var>x</var>,<var>y</var> in the <a href="#viewport">viewport</a>. The
   element to be returned is determined through hit testing. If either
   argument is negative, <var title="">x</var> is greater than the <a
   href="#viewport">viewport</a> width excluding the size of a rendered
   scroll bar (if any), or <var title="">y</var> is greather than the <a
   href="#viewport">viewport</a> height excluding the size of a rendered
   scroll bar (if any), the method <em class=ct>must</em> return
   <code>null</code>. If there is no element at the given position the method
   <em class=ct>must</em> return the root element, if any, or
   <code>null</code> otherwise.

  <p>The <dfn id=dom-document-caretpositionfrompoint
   title=caretpositionfrompoint><code>caretPositionFromPoint(<var
   title="">x</var>, <var title="">y</var>)</code></dfn> method, when
   invoked, <em class=ct>must</em> return the result of running these steps:

  <ol>
   <li>
    <p>If either argument is negative, <var title="">x</var> is greater than
     the <a href="#viewport">viewport</a> width excluding the size of a
     rendered scroll bar (if any), <var title="">y</var> is greather than the
     <a href="#viewport">viewport</a> height excluding the size of a rendered
     scroll bar (if any) return null.

   <li>
    <p>If at the coordinates <var title="">x&
9E61
lt;/var>,<var title="">y</var> in
     the <a href="#viewport">viewport</a> no text insertion point indicator
     would have been inserted return null.

   <li>
    <p>If at the coordinates <var title="">x</var>,<var title="">y</var> in
     the <a href="#viewport">viewport</a> a text insertion point indicator
     would have been inserted in a text entry widget which is also a replaced
     element return a <a href="#caret-position">caret position</a> with its
     properties set as follows:</p>

    <dl>
     <dt><a href="#caret-node">caret node</a>

     <dd>
      <p>The node corresponding to the text entry widget.

     <dt><a href="#caret-offset">caret offset</a>

     <dd>
      <p>The amount of 16-bit units to the left of where the text insertion
       point indicator would have inserted.

     <dt><a href="#caret-range">caret range</a>

     <dd>
      <p>null
    </dl>

   <li>
    <p>Otherwise, return a <a href="#caret-position">caret position</a> where
     the <a href="#caret-range">caret range</a> is a collapsed <a
     href="#range"><code>Range</code></a> object for the position where the
     text insertion point indicator would have been inserted and the other
     properties are set as follows:</p>

    <dl>
     <dt><a href="#caret-node">caret node</a>

     <dd>
      <p>The <code title=dom-Range-startContainer>startContainer</code> of
       the <a href="#caret-range">caret range</a>.

     <dt><a href="#caret-offset">caret offset</a>

     <dd>
      <p>The <code title=dom-Range-startOffset>startOffset</code> of the <a
       href="#caret-range">caret range</a>.</p>
    </dl>
  </ol>

  <p class=note>The specifics of hit testing are out of scope of this
   specification and therefore the exact details of <a
   href="#dom-document-elementfrompoint"><code>elementFromPoint()</code></a>
   and <a
   href="#dom-document-caretpositionfrompoint"><code>caretPositionFromPoint()</code></a>
   are therefore too. Hit testing will hopefully be defined in a future
   revision of CSS or HTML.

  <h3 id=the-caretposition-interface><span class=secno>4.1. </span>The <code
   title="">CaretPosition</code> Interface</h3>

  <p>A <dfn id=caret-position>caret position</dfn> gives the position of a
   text insertion point indicator. It always has an associated <dfn
   id=caret-node>caret node</dfn>, <dfn id=caret-offset>caret offset</dfn>,
   and <dfn id=caret-range>caret range</dfn>. It is represented by a <a
   href="#caretposition"><code>CaretPosition</code></a> object.

  <pre class=idl>interface <dfn id=caretposition>CaretPosition</dfn> {
  readonly attribute <span>Node</span> <a href="#dom-caretposition-offsetnode" title=dom-CaretPosition-offsetNode>offsetNode</a>;
  readonly attribute unsigned long <a href="#dom-caretposition-offset" title=dom-CaretPosition-offset>offset</a>;
  readonly attribute <a href="#range">Range</a> <a href="#dom-caretposition-range" title=dom-CaretPosition-range>range</a>;
};</pre>

  <p>The <dfn id=dom-caretposition-offsetnode
   title=dom-CaretPosition-offsetNode><code>offsetNode</code></dfn> attribute
   <em class=ct>must</em> return the <a href="#caret-node">caret node</a>.

  <p>The <dfn id=dom-caretposition-offset
   title=dom-CaretPosition-offset><code>offset</code></dfn> attribute <em
   class=ct>must</em> return the <a href="#caret-offset">caret offset</a>.

  <p>The <dfn id=dom-caretposition-range
   title=dom-CaretPosition-range><code>range</code></dfn> attribute <em
   class=ct>must</em> return the <a href="#caret-range">caret range</a>.</p>
  <!-- https://bugs.webkit.org/show_bug.cgi?id=27046 -->

  <h2 id=extensions-to-the-element-interface><span class=secno>5.
   </span>Extensions to the <code title="">Element</code> Interface</h2>

  <pre class=idl>[Supplemental] interface <a href="#element">Element</a> {
  <a href="#clientrectlist">ClientRectList</a> <a href="#dom-element-getclientrects">getClientRects</a>();
  <a href="#clientrect">ClientRect</a> <a href="#dom-element-getboundingclientrect">getBoundingClientRect</a>();

           attribute long <a href="#dom-element-scrolltop">scrollTop</a>;   // scroll on setting
           attribute long <a href="#dom-element-scrollleft">scrollLeft</a>;  // scroll on setting
  readonly attribute long <a href="#dom-element-scrollwidth">scrollWidth</a>;
  readonly attribute long <a href="#dom-element-scrollheight">scrollHeight</a>;

  readonly attribute long <a href="#dom-element-clienttop">clientTop</a>;
  readonly attribute long <a href="#dom-element-clientleft">clientLeft</a>;
  readonly attribute long <a href="#dom-element-clientwidth">clientWidth</a>;
  readonly attribute long <a href="#dom-element-clientheight">clientHeight</a>;
};</pre>

  <h3 id=the-getclientrects-and-getboundingclient><span class=secno>5.1.
   </span>The <code title="">getClientRects()</code> and <code
   title="">getBoundingClientRect()</code> methods</h3>

  <p>The <a
   href="#dom-element-getclientrects"><code>getClientRects()</code></a> and
   <a
   href="#dom-element-getboundingclientrect"><code>getBoundingClientRect()</code></a>
   methods provide information about the position of the border box edges of
   an element relative to the viewport. The objects these methods return <em
   class=ct>must</em> be static. That is, changes to the underlying document
   are not reflected in the objects.

  <p>The <dfn
   id=dom-element-getclientrects><code>getClientRects()</code></dfn> method,
   when invoked, <em class=ct>must</em> return the result of the following
   algorithm:

  <ol>
   <li>
    <p>If the element on which it was invoked does not have an associated CSS
     layout box and is not in the <code>http://www.w3.org/2000/svg</code>
     namespace return an empty <a
     href="#clientrectlist"><code>ClientRectList</code></a> object and stop
     this algorithm.

   <li>
    <p>If the element does not have an associated CSS layout box and is in
     the <code>http://www.w3.org/2000/svg</code> namespace return a <a
     href="#clientrectlist"><code>ClientRectList</code></a> object containing
     a single <a href="#clientrect"><code>ClientRect</code></a> object that
     describes the bounding box of the element as defined by the SVG
     specification. [<cite><a href="#ref-svg">SVG</a></cite>]

   <li>
    <p>Return a <a href="#clientrectlist"><code>ClientRectList</code></a>
     object containing a list of <a
     href="#clientrect"><code>ClientRect</code></a> objects in content order
     describing the border boxes (including those with a height or width of
     zero) with the following constraints:</p>

    <ul>
     <li>
      <p>If the element on which the method was invoked has a computed value
       for <code>display</code> property of <code>table</code> or
       <code>inline-table</code> include both the table box and the caption
       box, if any, but not the anonymous container box. [<cite><a
       href="#ref-css21">CSS21</a></cite>]

     <li>
      <p>Replace each <a
       href="http://www.w3.org/TR/CSS21/visuren.html#anonymous-block-level">anonymous
       block box</a> with its child box(es) and repeat this until no
       anonymous block boxes are left in the final list. [<cite><a
       href="#ref-css21">CSS21</a></cite>]
    </ul>
  </ol>

  <p>The <dfn
   id=dom-element-getboundingclientrect><code>getBoundingClientRect()</code></dfn>
   method, when invoked, <em class=ct>must</em> return the result of the
   following algorithm:

  <ol>
   <li>
    <p>Let <var>list</var> be the result of invoking <a
     href="#dom-element-getclientrects"><code>getClientRects()</code></a> on
     the same element this method was invoked on.

   <li>
    <p>If the <var>list</var> is empty return a <a
     href="#clientrect"><code>ClientRect</code></a> object whose <a
     href="#dom-clientrect-top"><code
     title=dom-clientrect-top>top</code></a>, <a
     href="#dom-clientrect-right"><code
     title=dom-clientrect-right>right</code></a>, <a
     href="#dom-clientrect-bottom"><code
     title=dom-clientrect-bottom>bottom</code></a> and <a
     href="#dom-clientrect-left"><code
     title=dom-clientrect-left>left</code></a> members are zero.

   <li>
    <p>Otherwise, return a <a href="#clientrect"><code>ClientRect</code></a>
     object describing the smallest rectangle that includes the first
     rectangle in <var>list</var> and all of the remaining rectangles of
     which the height or width is not zero.
  </ol>

  <div class=example>
   <p>The following snippet gets the dimensions of the first <code>div</code>
    element in a document:</p>

   <pre><code>var example = document.getElementsByTagName("div")[0].getBoundingClientRect();
var exampleWidth = example.width;
var exampleHeight = example.height;</code></pre>
  </div>

  <h3 id=scroll-attributes><span class=secno>5.2. </span>The <code
   title="">scrollTop</code>, <code title="">scrollLeft</code>, <code
   title="">scrollWidth</code>, and <code title="">scrollHeight</code>
   attributes</h3>

  <p>The <dfn id=dom-element-scrolltop><code>scrollTop</code></dfn> attribute
   <em class=ct>must</em> return the result of running these steps:

  <ol>
   <li>
    <p>If the element does not have any associated CSS layout box or the
     element is the root element and the <a
     href="#document"><code>Document</code></a> is in <a
     href="#quirks-mode">quirks mode</a> return zero and terminate these
     steps.

   <li>
    <p>If the element is the root element return the value of <a
     href="#dom-window-pageyoffset"><code>pageYOffset</code></a>.

   <li>
    <p>If the element is <a href="#the-html-body-element">the HTML
     <code>body</code> element</a>, the <a
     href="#document"><code>Document</code></a> is in <a
     href="#quirks-mode">quirks mode</a>, and the element does not have any
     overflow, return the value of <a
     href="#dom-window-pageyoffset"><code>pageYOffset</code></a>.

   <li>
    <p>Return the y-coordinate of the <a href="#content">content</a> at the
     alignment point with the top of the <a href="#content-edge">content
     edge</a> of the element.
  </ol>

  <p>When setting the <a
   href="#dom-element-scrolltop"><code>scrollTop</code></a> attribute these
   steps <em class=ct>must</em> be run:

  <ol>
   <li>
    <p>Let <var title="">y</var> be the given value.

   <li>
    <p>If the element does not have any associated CSS layout box, the
     element is the root element and the <a
     href="#document"><code>Document</code></a> is in <a
     terminate these steps.

   <li>
    <p>If the element is the root element invoke <a
     href="#dom-window-scroll"><code
     title=dom-Window-scroll>scroll()</code></a> with zero as first argument
     and <var title="">y</var> as second.

   <li>
    <p>If the element is <a href="#the-html-body-element">the HTML
     <code>body</code> element</a>, the <a
     href="#document"><code>Document</code></a> is in <a
     href="#quirks-mode">quirks mode</a>, and the element does not have any
     vertical overflow, invoke <a href="#dom-window-scroll"><code
     title=dom-Window-scroll>scroll()</code></a> with zero as first argument
     and <var title="">y</var> as second.

   <li>
    <p>If <var title="">y</var> is infinite or NaN stop this algorithm.</p>

   <li>
    <p>Let <var title="">y</var> be max(0, min(<var title="">y</var>, <a
     href="#content">content</a> height - <a href="#content-edge">content
     edge</a> height)).

   <li>
    <p>Align <a href="#content">content</a> y-coordinate <var
     title="">y</var> with the top of the <a href="#content-edge">content
     edge</a> of the element.

   <li>
    <p>If the aligning caused content to move <a href="#queue-a-task">queue a
     task</a> to <a href="#fire-a-simple-event">fire a simple event</a> named
     <code title=event-scroll>scroll</code> at the element, unless a <a
     href="#task">task</a> to fire that event at the element was already <a
     href="#queue-a-task" title="queue a task">queued</a>.
  </ol>

  <p>The <dfn id=dom-element-scrollleft><code>scrollLeft</code></dfn>
   attribute <em class=ct>must</em> return the result of running these steps:

  <ol>
   <li>
    <p>If the element does not have any associated CSS layout box or the
     element is the root element and the <a
     href="#document"><code>Document</code></a> is in <a
     href="#quirks-mode">quirks mode</a> return zero and terminate these
     steps.

   <li>
    <p>If the element is the root element return the value of <a
     href="#dom-window-pagexoffset"><code>pageXOffset</code></a>.

   <li>
    <p>If the element is <a href="#the-html-body-element">the HTML
     <code>body</code> element</a>, the <a
     href="#document"><code>Document</code></a> is in <a