csswg-drafts/cssom-view/Overview.html at 8c7d23c243a6ff5d116634f5e4ebc3b06c2dc616 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html><html lang="en-US"><head>
  <meta charset="utf-8">
  <title>CSSOM View Module</title>
  <style>
   .propdef { font:inherit; line-height:2.3 }
  </style>
  <link href="../default.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>CSSOM View Module</h1>

 <h2 class="no-num no-toc" id="w3c-doctype">Editor's Draft 9 January 2014</h2>

 <dl>

  <dt>This Version:</dt>
  <dd class="dontpublish"><a href="http://dev.w3.org/csswg/cssom-view/">http://dev.w3.org/csswg/cssom-view/</a></dd>


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


  <dt>Previous Versions:</dt>
  <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>
  <dd><a href="http://www.w3.org/TR/2008/WD-cssom-view-20080222/">http://www.w3.org/TR/2008/WD-cssom-view-20080222/</a></dd>
  <dd><a href="http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/">http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/</a></dd>

  <dt>Editors:</dt>
  <dd>Simon Pieters
  (<a href="http://www.opera.com/">Opera Software ASA</a>)
  &lt;<a href="mailto:simonp@opera.com">simonp@opera.com</a>&gt;</dd>
  <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>

  <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@annevk.nl">annevk@annevk.nl</a>&gt;</dd>
 </dl>


<!--begin-copyright-->
<p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2014 <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>

<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.</p>


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

<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>This is the 9 January 2014 Editor's Draft of CSSOM View. Please send
comments to
<a href="mailto:www-style@w3.org?subject=%5Bcssom-view%5D%20">www-style@w3.org</a>
(<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>)
with <samp>[cssom-view]</samp> at the start of the subject line.

<p>This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of
the <a href="http://www.w3.org/Style/">Style Activity</a>).

<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>

<p>Publication as a Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.


<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>
 <li><a href="#conformance"><span class="secno">2 </span>Conformance</a>
  <ul class="toc">
   <li><a href="#web-idl"><span class="secno">2.1 </span>Web IDL</a></ul></li>
 <li><a href="#terminology"><span class="secno">3 </span>Terminology</a>
  <ul class="toc">
   <li><a href="#css-pixels"><span class="secno">3.1 </span>CSS pixels</a></li>
   <li><a href="#zooming"><span class="secno">3.2 </span>Zooming</a></ul></li>
 <li><a href="#common-infrastructure"><span class="secno">4 </span>Common Infrastructure</a>
  <ul class="toc">
 <li><a href="#extensions-to-the-window-interface"><span class="secno">5 </span>Extensions to the <code title="">Window</code> Interface</a>
  <ul class="toc">
   <li><a href="#the-features-argument-to-the-open()-method"><span class="secno">5.1 </span>The <var>features</var> argument to the <code title="">open()</code> method</a></li>
   <li><a href="#the-mediaquerylist-interface"><span class="secno">5.2 </span>The <code title="">MediaQueryList</code> Interface</a></li>
   <li><a href="#the-screen-interface"><span class="secno">5.3 </span>The <code title="">Screen</code> Interface</a></ul></li>
 <li><a href="#extensions-to-the-document-interface"><span class="secno">6 </span>Extensions to the <code title="">Document</code> Interface</a>
  <ul class="toc">
   <li><a href="#the-caretposition-interface"><span class="secno">6.1 </span>The <code title="">CaretPosition</code> Interface</a></ul></li>
 <li><a href="#extensions-to-the-element-interface"><span class="secno">7 </span>Extensions to the <code title="">Element</code> Interface</a>
  <ul class="toc">
   <li><a href="#the-getclientrects()-and-getboundingclientrect()-methods"><span class="secno">7.1 </span>The <code title="">getClientRects()</code> and
<code title="">getBoundingClientRect()</code> methods</a></li>
   <li><a href="#element-scrolling-members"><span class="secno">7.2 </span><code title="">Element</code> Scrolling Members</a></ul></li>
 <li><a href="#extensions-to-the-htmlelement-interface"><span class="secno">8 </span>Extensions to the <code title="">HTMLElement</code> Interface</a></li>
 <li><a href="#excensions-to-the-htmlimageelement-interface"><span class="secno">9 </span>Excensions to the <code title="">HTMLImageElement</code> Interface</a></li>
 <li><a href="#extensions-to-the-range-interface"><span class="secno">10 </span>Extensions to the <code title="">Range</code> Interface</a></li>
 <li><a href="#extensions-to-the-mouseevent-interface"><span class="secno">11 </span>Extensions to the <code title="">MouseEvent</code> Interface</a></li>
 <li><a href="#geometry"><span class="secno">12 </span>Geometry</a>
  <ul class="toc">
   <li><a class="atrisk" href="#the-geometryutils-interface"><span class="secno">12.1 </span>The <code title="">GeometryUtils</code> Interface</a></ul></li>
 <li><a href="#events"><span class="secno">13 </span>Events</a>
  <ul class="toc">
   <li><a href="#resizing-viewports"><span class="secno">13.1 </span>Resizing viewports</a></li>
   <li><a href="#scrolling-0"><span class="secno">13.2 </span>Scrolling</a></ul></li>
 <li><a href="#css-properties"><span class="secno">14 </span>CSS properties</a>
  <ul class="toc">
   <li><a href="#smooth-scrolling:-the-'scroll-behavior'-property"><span class="secno">14.1 </span>Smooth Scrolling: The 'scroll-behavior' Property</a></ul></li>
 <li><a class="no-num" href="#references">References</a></li>
 <li><a class="no-num" href="#change-history">Change History</a>
  <ul class="toc">
   <li><a class="no-num" href="#changes-from-4-august-2011-to-17-december-2013">Changes From 4 August 2011 To 17 December 2013</a></ul></li>
 <li><a class="no-num" 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!)</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. <!--fingerprint-->

<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" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#case-sensitive">case-sensitive</a> manner.

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


<h3 id="web-idl"><span class="secno">2.1 </span>Web IDL</h3>

<p>The IDL fragments in this specification must be
interpreted as required for conforming IDL fragments, as described in the
Web IDL specification. <a href="#refsWEBIDL">[WEBIDL]</a>


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

<p>Terminology used in this specification is from
DOM,
CSSOM and
HTML.
<a href="#refsDOM">[DOM]</a>
<a href="#refsCSSOM">[CSSOM]</a>
<a href="#refsHTML">[HTML]</a>

<p class="issue"><dfn id="mouseevent"><code>MouseEvent</code></dfn> and <dfn id="mouseeventinit"><code>MouseEventInit</code></dfn> are defined in …

<p><dfn id="dompoint"><code>DOMPoint</code></dfn>,
<dfn id="dompointreadonly"><code>DOMPointReadOnly</code></dfn>,
<dfn id="dompointinit"><code>DOMPointInit</code></dfn>,
<dfn id="domrect"><code>DOMRect</code></dfn>,
<dfn id="domrectreadonly"><code>DOMRectReadOnly</code></dfn>,
<dfn id="domquad"><code>DOMQuad</code></dfn> are defined in Geometry Interfaces Module. <a href="#refsGEOMETRY">[GEOMETRY]</a>

<p><dfn id="the-html-body-element">The HTML <code title="">body</code> element</dfn> is the first
<code title="">body</code>
<a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#html-elements" title="HTML elements">HTML element</a> child of the root
<a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#html-elements" title="HTML elements">HTML element</a> <code title="">html</code>.</p>

<p><dfn id="content-edge">Content edge</dfn>,
<dfn id="padding-edge">padding edge</dfn>,
<dfn id="border-edge">border edge</dfn>,
<dfn id="margin-edge">margin edge</dfn> and
<dfn id="canvas">canvas</dfn> are defined by CSS.
<!--<span data-anolis-ref>CSS</span>-->

<p><dfn id="viewport">Viewport</dfn> and <dfn id="initial-containing-block">initial containing block</dfn> are defined by CSS 2.1. <!--<span data-anolis-ref>CSS</span>-->

<p><dfn id="block-flow-direction">Block flow direction</dfn> and <dfn id="inline-base-direction">inline base direction</dfn> are defined in CSS Writing Modes Module. <a href="#refsCSSWRITINGMODES">[CSSWRITINGMODES]</a>

<p>Elements and <a href="#viewport" title="viewport">viewports</a> have an associated <dfn id="scrolling-box">scrolling box</dfn> if has a scrolling mechanism<!--XXX xref--> or it overflows
its content area<!--XXX xref--> and the used value of the 'overflow-x' or 'overflow-y' property is 'hidden'. <a href="#refsCSSBOX">[CSSBOX]</a>

<p>A <a href="#scrolling-box">scrolling box</a> of a <a href="#viewport">viewport</a> or element has two <dfn id="overflow-directions">overflow directions</dfn>, depending on the <a href="#viewport">viewport</a>'s or
element's <a href="#block-flow-direction">block flow direction</a> and <a href="#inline-base-direction">inline base direction</a>, as follows:

<dl class="switch">
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is top-to-bottom and the <a href="#inline-base-direction">inline base direction</a> is left-to-right
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is left-to-right and the <a href="#inline-base-direction">inline base direction</a> is left-to-right
 <dd><p>Rightward and downward.
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is top-to-bottom and the <a href="#inline-base-direction">inline base direction</a> is right-to-left
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is right-to-left and the <a href="#inline-base-direction">inline base direction</a> is left-to-right
 <dd><p>Leftward and downward.
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is right-to-left and the <a href="#inline-base-direction">inline base direction</a> is right-to-left
 <dd><p>Leftward and upward.
 <dt>If the <a href="#block-flow-direction">block flow direction</a> is left-to-right and the <a href="#inline-base-direction">inline base direction</a> is right-to-left
 <dd><p>Righward and upward.
</dl>

<p>The term <dfn id="scrolling-area">scrolling area</dfn> refers to a box of a <a href="#viewport">viewport</a> or an element that has the following edges, depending on the
<a href="#viewport">viewport</a>'s or element's <a href="#scrolling-box">scrolling box</a>'s <a href="#overflow-directions">overflow directions</a>.

<table class="complex data">
 <thead>
  <tr>
   <th>If the <a href="#overflow-directions">overflow directions</a> are…
   <th>For a <a href="#viewport">viewport</a>
   <th>For an element
 <tbody>
  <tr>
   <td>rightward and downward
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top edge of the <a href="#initial-containing-block">initial containing block</a>.
     <dt>right edge
     <dd><p>The right-most edge of the right edge of the <a href="#initial-containing-block">initial containing block</a> and the right <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>bottom edge
     <dd><p>The bottom-most edge of the bottom edge of the <a href="#initial-containing-block">initial containing block</a> and the bottom <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>left edge
     <dd><p>The left edge of the <a href="#initial-containing-block">initial containing block</a>.
    </dl>
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The element's top <a href="#padding-edge">padding edge</a>.
     <dt>right edge
     <dd><p>The right-most edge of the element's right <a href="#padding-edge">padding edge</a> and the right <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
     <dt>bottom edge
     <dd><p>The bottom-most edge of the element's bottom <a href="#padding-edge">padding edge</a> and the bottom <a href="#margin-edge">margin edge</a> of the element's all descendant
     boxes, excluding boxes that have an ancestor of the element as their containing block.
     <dt>left edge
     <dd><p>The element's left <a href="#padding-edge">padding edge</a>.
    </dl>
  <tr>
   <td>leftward and downward
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top edge of the <a href="#initial-containing-block">initial containing block</a>.
     <dt>right edge
     <dd><p>The right edge of the <a href="#initial-containing-block">initial containing block</a>.
     <dt>bottom edge
     <dd><p>The bottom-most edge of the bottom edge of the <a href="#initial-containing-block">initial containing block</a> and the bottom <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>left edge
     <dd><p>The left-most edge of the left edge of the <a href="#initial-containing-block">initial containing block</a> and the left <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
    </dl>
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The element's top <a href="#padding-edge">padding edge</a>.
     <dt>right edge
     <dd><p>The element's right <a href="#padding-edge">padding edge</a>.
     <dt>bottom edge
     <dd><p>The bottom-most edge of the element's bottom <a href="#padding-edge">padding edge</a> and the bottom <a href="#margin-edge">margin edge</a> of the element's all descendant
     boxes, excluding boxes that have an ancestor of the element as their containing block.
     <dt>left edge
     <dd><p>The left-most edge of the element's left <a href="#padding-edge">padding edge</a> and the left <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
    </dl>
  <tr
8F9
>
   <td>leftward and upward
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top-most edge of the top edge of the <a href="#initial-containing-block">initial containing block</a> and the top <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>right edge
     <dd><p>The right edge of the <a href=&qu
102C7
ot;#initial-containing-block">initial containing block</a>.
     <dt>bottom edge
     <dd><p>The bottom edge of the <a href="#initial-containing-block">initial containing block</a>.
     <dt>left edge
     <dd><p>The left-most edge of the left edge of the <a href="#initial-containing-block">initial containing block</a> and the left <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
    </dl>
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top-most edge of the element's top <a href="#padding-edge">padding edge</a> and the top <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
     <dt>right edge
     <dd><p>The element's right <a href="#padding-edge">padding edge</a>.
     <dt>bottom edge
     <dd><p>The element's bottom <a href="#padding-edge">padding edge</a>.
     <dt>left edge
     <dd><p>The left-most edge of the element's left <a href="#padding-edge">padding edge</a> and the left <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
    </dl>
  <tr>
   <td>rightward and upward
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top-most edge of the top edge of the <a href="#initial-containing-block">initial containing block</a> and the top <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>right edge
     <dd><p>The right-most edge of the right edge of the <a href="#initial-containing-block">initial containing block</a> and the right <a href="#margin-edge">margin edge</a> of the
     <a href="#viewport">viewport</a>'s all descendant boxes.
     <dt>bottom edge
     <dd><p>The bottom edge of the <a href="#initial-containing-block">initial containing block</a>.
     <dt>left edge
     <dd><p>The left edge of the <a href="#initial-containing-block">initial containing block</a>.
    </dl>
   <td class="long">
    <dl>
     <dt>top edge
     <dd><p>The top-most edge of the element's top <a href="#padding-edge">padding edge</a> and the top <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
     <dt>right edge
     <dd><p>The right-most edge of the element's right <a href="#padding-edge">padding edge</a> and the right <a href="#margin-edge">margin edge</a> of the element's all descendant boxes,
     excluding boxes that have an ancestor of the element as their containing block.
     <dt>bottom edge
     <dd><p>The element's bottom <a href="#padding-edge">padding edge</a>.
     <dt>left edge
     <dd><p>The element's left <a href="#padding-edge">padding edge</a>.
    </dl>
</table>

<p>The <dfn id="beginning-edges">beginning edges</dfn> of a particular set of edges of a box or element are the following edges:

<dl class="switch">
 <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and downward
 <dd><p>The top and left edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and downward
 <dd><p>The top and right edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and upward
 <dd><p>The bottom and right edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and upward
 <dd><p>The bottom and left edges.
</dl>

<p>The <dfn id="ending-edges">ending edges</dfn> of a particular set of edges of a box or element are the following edges:

<dl class="switch">
 <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and downward
 <dd><p>The bottom and right edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and downward
 <dd><p>The bottom and left edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are leftward and upward
 <dd><p>The top and left edges.
 <dt>If the <a href="#overflow-directions">overflow directions</a> are rightward and upward
 <dd><p>The top and right edges.
</dl>

<p>The term <dfn id="css-layout-box">CSS layout box</dfn> refers to the same term in CSS. For the purpose
of the requirements in this specification, elements that have a computed value of the
'display' property that is 'table-column' or
'table-column-group' must be considered to have an associated <a href="#css-layout-box">CSS
layout box</a> (the column or column group, respectively).</p>

<p>The term <dfn id="svg-layout-box">SVG layout box</dfn> refers to the same term in SVG.

<p class="issue">The terms <a href="#css-layout-box">CSS layout box</a> and <a href="#svg-layout-box">SVG layout box</a> are not currently defined by CSS or SVG.

<p>The term <dfn id="layout-box">layout box</dfn> refers to either a <a href="#css-layout-box">CSS layout box</a> or an <a href="#svg-layout-box">SVG layout box</a>.

<p>The term <dfn id="transforms">transforms</dfn> refers to SVG transforms and CSS transforms. <a href="#refsSVG">[SVG]</a> <a href="#refsCSSTRANSFORMS">[CSSTRANSFORMS]</a>


<h3 id="css-pixels"><span class="secno">3.1 </span>CSS pixels</h3>

<p>All coordinates and dimensions for the APIs defined in this
specification are in CSS pixels, unless otherwise specified. <!--<span data-anolis-ref>CSS</span>-->

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


<h3 id="zooming"><span class="secno">3.2 </span>Zooming</h3>

<p>There are two kinds of zoom, <dfn id="page-zoom">page zoom</dfn> which affects the size of the initial viewport<!-- XXX ref -->, and <dfn id="pinch-zoom">pinch zoom</dfn> which acts like
a magnifying glass and does not affect the initial viewport<!-- XXX ref --> or actual viewport<!-- XXX ref -->. <a href="#refsCSSDEVICEADAPT">[CSSDEVICEADAPT]</a>


<h2 id="common-infrastructure"><span class="secno">4 </span>Common Infrastructure</h2>

<h3 id="scrolling"><span class="secno">4.1 </span>Scrolling</h3>

<p>When a user agent is to <dfn id="perform-a-scroll">perform a scroll</dfn> of a <a href="#scrolling-box">scrolling box</a> <var>box</var>, to a given position <var>position</var>, with a set of
steps <var>task</var>, an associated element <var>element</var> and optionally a scroll behavior <var>behavior</var> (which is
<code title="">auto</code> if omitted), the following steps must be run:

<ol>
 <li><p><a href="#concept-smooth-scroll-aborted" title="concept-smooth-scroll-aborted">Abort</a> any ongoing <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a> for <var>box</var>.
 <li><p>If the user agent honors the '<a href="#scroll-behavior">scroll-behavior</a>' property and one of the following are true:
  <ul>
   <li><p><var>behavior</var> is <code title="">auto</code> and <var>element</var> is not null and its computed value of the
   '<a href="#scroll-behavior">scroll-behavior</a>' property is '<a href="#scroll-behavior-smooth" title="scroll-behavior-smooth">smooth</a>'
   <li><p><var>behavior</var> is <code title="">smooth</code>
  </ul>
  <p>...then follow these substeps:
  <ol>
   <li><p>Perform a <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a> of <var>box</var> to <var>position</var>.
   <li><p><a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#queue-a-task">Queue a task</a> to run <var>task</var>, unless a <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#concept-task" title="concept-task">task</a> to
   run <var>task</var> is in the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#queue-a-task" title="queue a task">queue</a>.
   <li><p>Repeat the previous step in a user-agent-defined interval while the <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a> is ongoing, as well as when
   the <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a> is <a href="#concept-smooth-scroll-completed" title="concept-smooth-scroll-completed">completed</a> (but not if it is
   <a href="#concept-smooth-scroll-aborted" title="concept-smooth-scroll-aborted">aborted</a>). <!--fingerprint-->
  </ol>
 <li><p>Otherwise, follow these substeps:
  <ol>
   <li><p>Perform an <a href="#concept-instant-scroll" title="concept-instant-scroll">instant scroll</a> of <var>box</var> to <var>position</var>.
   <li><p><a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#queue-a-task">Queue a task</a> to run <var>task</var>, unless a <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#concept-task" title="concept-task">task</a> to
   run <var>task</var> is in the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#queue-a-task" title="queue a task">queue</a>.
  </ol>
</ol>

<p>When a user agent is to perform a <dfn id="concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</dfn> of a <a href="#scrolling-box">scrolling box</a> <var>box</var> to <var>position</var>,
it must update the scroll position of <var>box</var> in a user-agent-defined fashion over a user-agent-defined amount of time. When the scroll is
<dfn id="concept-smooth-scroll-completed" title="concept-smooth-scroll-completed">completed</dfn>, the scroll position of <var>box</var> must be <var>position</var>. The scroll can also
be <dfn id="concept-smooth-scroll-aborted" title="concept-smooth-scroll-aborted">aborted</dfn>, either by an algorithm or by the user. <!--fingerprint-->

<p>When a user agent is to perform an <dfn id="concept-instant-scroll" title="concept-instant-scroll">instant scroll</dfn> of a <a href="#scrolling-box">scrolling box</a> <var>box</var> to
<var>position</var>, it must update the scroll position of <var>box</var> to <var>position</var>.

<p>To <dfn id="scroll-to-the-beginning-of-the-document">scroll to the beginning of the document</dfn> for a document <var>document</var>, follow these steps:

<ol>
 <li><p>Let <var>viewport</var> be the <a href="#viewport">viewport</a> that is associated with <var>document</var>. <!-- This assumes that there is a viewport, since
 it is only invoked when navigating -->
 <li><p>Let <var>position</var> be the the scroll position <var>viewport</var> would have by aligning the <a href="#beginning-edges">beginning edges</a> of the
 <a href="#scrolling-area">scrolling area</a> with the <a href="#beginning-edges">beginning edges</a> of <var>viewport</var>.
 <li><p>If <var>position</var> is the same as <var>viewport</var>'s current scroll position, and <var>viewport</var> does not have an ongoing
 <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a>, abort these steps.
 <li><p>Let <var>task</var> be these steps:
  <ol>
   <li><p><a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#concept-event-fire" title="concept-event-fire">Fire an event</a> named <code title="">scroll</code> that bubbles at <var>document</var>.
  </ol>
 <li><p><a href="#perform-a-scroll">Perform a scroll</a> of <var>viewport</var> to <var>position</var>, with the set of steps <var>task</var>, and <var>document</var>'s root
 element as the associated element, if there is one, or null otherwise.
</ol>

<p class="note">This algorithm is used when navigating to the <code title="">#top</code> fragment identifier, as defined in HTML. <a href="#refsHTML">[HTML]</a>

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

<pre class="idl">enum <dfn id="scrollbehavior">ScrollBehavior</dfn> { "auto", "instant", "smooth" };

dictionary <dfn id="scrolloptions">ScrollOptions</dfn> {
  <a href="#scrollbehavior">ScrollBehavior</a> behavior = "auto";
};

partial interface <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#window">Window</a> {
  <a href="#mediaquerylist">MediaQueryList</a> <a href="#dom-window-matchmedia" title="dom-Window-matchMedia">matchMedia</a>(DOMString query);
  [SameObject] readonly attribute <a href="#screen">Screen</a> <a href="#dom-window-screen" title="dom-Window-screen">screen</a>;

  // browsing context
  void <a href="#dom-window-moveto" title="dom-Window-moveTo">moveTo</a>(double x, double y);
  void <a href="#dom-window-moveby" title="dom-Window-moveBy">moveBy</a>(double x, double y);
  void <a href="#dom-window-resizeto" title="dom-Window-resizeTo">resizeTo</a>(double x, double y);
  void <a href="#dom-window-resizeby" title="dom-Window-resizeBy">resizeBy</a>(double x, double y);

  // viewport
  readonly attribute double <a href="#dom-window-innerwidth" title="dom-Window-innerWidth">innerWidth</a>;
  readonly attribute double <a href="#dom-window-innerheight" title="dom-Window-innerHeight">innerHeight</a>;

  // viewport scrolling
  readonly attribute double <a href="#dom-window-scrollx" title="dom-Window-scrollX">scrollX</a>;
  readonly attribute double <a href="#dom-window-pagexoffset" title="dom-Window-pageXOffset">pageXOffset</a>;
  readonly attribute double <a href="#dom-window-scrolly" title="dom-Window-scrollY">scrollY</a>;
  readonly attribute double <a href="#dom-window-pageyoffset" title="dom-Window-pageYOffset">pageYOffset</a>;
  void <a href="#dom-window-scroll" title="dom-Window-scroll">scroll</a>(double x, double y, optional <a href="#scrolloptions">ScrollOptions</a> options);
  void <a href="#dom-window-scrollto" title="dom-Window-scrollTo">scrollTo</a>(double x, double y, optional <a href="#scrolloptions">ScrollOptions</a> options);
  void <a href="#dom-window-scrollby" title="dom-Window-scrollBy">scrollBy</a>(double x, double y, optional <a href="#scrolloptions">ScrollOptions</a> options);

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

<p>When the <dfn id="dom-window-matchmedia" title="dom-Window-matchMedia"><code>matchMedia(<var>query</var>)</code></dfn> method is invoked these steps must be run:</p>
<ol>
 <a class="external" data-anolis-spec="cssom" href="http://dev.w3.org/csswg/cssom/#parse-a-media-query-list" title="parse a media query list">parsing</a>
 <var>query</var>.</li>
 <li><p>Return a <em>new</em> <code><a href="#mediaquerylist">MediaQueryList</a></code> object,
 associated with the <code class="external" data-anolis-spec="html"><a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#window">Window</a></code> object, with
 <var>parsed media query list</var> as its associated
 media query list.</li>
</ol>

<p>The <dfn id="dom-window-screen" title="dom-Window-screen"><code>screen</code></dfn> attribute must return the <code><a href="#screen">Screen</a></code> object
associated with the <code class="external" data-anolis-spec="html"><a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#window">Window</a></code> object.</p>
<p class="note">Accessing <code title="dom-Window-screen"><a href="#dom-window-screen">screen</a></code> through a <code class="external" data-anolis-spec="html"><a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#windowproxy">WindowProxy</a></code> object might yield different
results when the <code class="external" data-anolis-spec="dom"><a href="http://dom.spec.whatwg.org/#document">Document</a></code> is navigated.</p>

<p>The <dfn id="dom-window-moveto" title="dom-Window-moveTo">moveTo(<var>x</var>, <var>y</var>)</dfn> method must follow these steps:

<ol>
 <li><p>Optionally, terminate these steps.
 <li><p>Let <var>target</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a> of the <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#context-object">context
 object</a>.
 <li><p>Let <var>source</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#responsible-browsing-context">responsible browsing context</a> of the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#incumbent-settings-object">incumbent settings
 object</a>.
 <li><p>If <var>source</var> is not <a href="#allowed-to-resize-and-move">allowed to resize and move</a> <var>target</var>, terminate these steps.
 <li><p>Optionally, clamp <var>x</var> and <var>y</var> in a user-agent-defined manner so that the window does not move outside the available space.
 <li><p>Move <var>target</var>'s window such that the window's top left corner is at coordinates (<var>x</var>, <var>y</var>) relative to the top left corner of
 the output device, measured in CSS pixels of <var>target</var>. The positive axes are rightward and downward.
</ol>

<p>The <dfn id="dom-window-moveby" title="dom-Window-moveBy">moveBy(<var>x</var>, <var>y</var>)</dfn> method must follow these steps:

<ol>
 <li><p>Optionally, terminate these steps.
 <li><p>Let <var>target</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a> of the <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#context-object">context
 object</a>.
 <li><p>Let <var>source</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#responsible-browsing-context">responsible browsing context</a> of the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#incumbent-settings-object">incumbent settings
 object</a>.
 <li><p>If <var>source</var> is not <a href="#allowed-to-resize-and-move">allowed to resize and move</a> <var>target</var>, terminate these steps.
 <li><p>Optionally, clamp <var>x</var> and <var>y</var> in a user-agent-defined manner so that the window does not move outside the available space.
 <li><p>Move <var>target</var>'s window <var>x</var> CSS pixels of <var>target</var> righward and <var>y</var> CSS pixels of <var>target</var> downward.
</ol>


<p>The <dfn id="dom-window-resizeto" title="dom-Window-resizeTo">resizeTo(<var>x</var>, <var>y</var>)</dfn> method must follow these steps:

<ol>
 <li><p>Optionally, terminate these steps.
 <li><p>Let <var>target</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a> of the <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#context-object">context
 object</a>.
 <li><p>Let <var>source</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#responsible-browsing-context">responsible browsing context</a> of the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#incumbent-settings-object">incumbent settings
 object</a>.
 <li><p>If <var>source</var> is not <a href="#allowed-to-resize-and-move">allowed to resize and move</a> <var>target</var>, terminate these steps.
 <li><p>Optionally, clamp <var>x</var> and <var>y</var> in a user-agent-defined manner so that the window does not get too small or bigger than the available
 space.
 <li><p>Resize <var>target</var>'s window by moving its right and bottom edges such that the distance between the left and right edges of the viewport are
 <var>x</var> CSS pixels of <var>target</var> and the distance between the top and bottom edges of the viewport are <var>y</var> CSS pixels of
 <var>target</var>.
 <li><p>Optionally, move <var>target</var>'s window in a user-agent-defined manner so that it does not grow outside the available space.
</ol>

<p>The <dfn id="dom-window-resizeby" title="dom-Window-resizeBy">resizeBy(<var>x</var>, <var>y</var>)</dfn> method must follow these steps:

<ol>
 <li><p>Optionally, terminate these steps.
 <li><p>Let <var>target</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a> of the <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#context-object">context
 object</a>.
 <li><p>Let <var>source</var> be the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#responsible-browsing-context">responsible browsing context</a> of the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#incumbent-settings-object">incumbent settings
 object</a>.
 <li><p>If <var>source</var> is not <a href="#allowed-to-resize-and-move">allowed to resize and move</a> <var>target</var>, terminate these steps.
 <li><p>Optionally, clamp <var>x</var> and <var>y</var> in a user-agent-defined manner so that the window does not get too small or bigger than the available
 space.
 <li><p>Resize <var>target</var>'s window by moving its right edge <var>x</var> CSS pixels of <var>target</var> righward and its bottom edge <var>y</var> CSS
 pixels of <var>target</var> downward.
 <li><p>Optionally, move <var>target</var>'s window in a user-agent-defined manner so that it does not grow outside the available space.
</ol>

<p>A <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing context</a> <var>A</var> is <dfn id="allowed-to-resize-and-move">allowed to resize and move</dfn> a <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#browsing-context">browsing
context</a> <var>B</var> if all the following conditions are met:

<ul>
 <li><p><var>B</var> is an <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#auxiliary-browsing-context">auxiliary browsing context</a> that was created by a script (as opposed to by an action of the user).
 <li><p><var>A</var> is <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#familiar-with">familiar with</a> <var>B</var>.
</ul>

<p>The <dfn id="dom-window-innerwidth" title="dom-Window-innerWidth"><code>innerWidth</code></dfn> attribute must return the <a href="#viewport">viewport</a> width including the size of a rendered
scroll bar (if any), or zero if there is no <a href="#viewport">viewport</a>. <!--fingerprint--></p>
<div class="example">
 <p>The following snippet shows how to obtain the width of the viewport:</p>
 <pre>var viewportWidth = innerWidth</pre>
</div>


<p>The  <dfn id="dom-window-innerheight" title="dom-Window-innerHeight"><code>innerHeight</code></dfn> attribute must return the <a href="#viewport">viewport</a> height including the size of a rendered
scroll bar (if any), or zero if there is no <a href="#viewport">viewport&
942B
lt;/a>. <!--fingerprint--></p>


<p>The <dfn id="dom-window-scrollx" title="dom-Window-scrollX"><code>scrollX</code></dfn> attribute attribute must 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>, or zero if there is no <a href="#viewport">viewport</a>. <!--fingerprint--></p>

<p>The <dfn id="dom-window-pagexoffset" title="dom-Window-pageXOffset"><code>pageXOffset</code></dfn> attribute must return the value returned by the
<code title="dom-Window-scrollX"><a href="#dom-window-scrollx">scrollX</a></code> attribute.</p>

<p>The <dfn id="dom-window-scrolly" title="dom-Window-scrollY"><code>scrollY</code></dfn> attribute attribute must 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>, or zero if there is no <a href="#viewport">viewport</a>. <!--fingerprint--></p>

<p>The <dfn id="dom-window-pageyoffset" title="dom-Window-pageYOffset"><code>pageYOffset</code></dfn> attribute must return the value returned by the
<code title="dom-Window-scrollY"><a href="#dom-window-scrolly">scrollY</a></code> attribute.</p>

<p>When the <dfn id="dom-window-scroll" title="dom-Window-scroll"><code>scroll(<var>x</var>, <var>y</var>, <var>options</var>)</code></dfn> method is invoked these
steps must be run:</p>
<ol>
 <li><p>If there is no <a href="#viewport">viewport</a>, abort these steps.
 <li><p>Let <var>viewport width</var> be the width of the <a href="#viewport">viewport</a> excluding the width of the scroll bar, if any.
 <li><p>Let <var>viewport height</var> be the height of the <a href="#viewport">viewport</a> excluding the height of the scroll bar, if any.
 <li>
  <dl class="switch">
   <dt>If the <a href="#viewport">viewport</a> has rightward <a href="#overflow-directions" title="overflow directions">overflow direction</a>
   <dd><p>Let <var>x</var> be max(0, min(<var>x</var>,
   <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a> width - <var>viewport width</var>)).</dd>
   <dt>If the <a href="#viewport">viewport</a> has leftward <a href="#overflow-directions" title="overflow directions">overflow direction</a>
   <dd><p>Let <var>x</var> be min(0, max(<var>x</var>,
   <var>viewport width</var> - <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a>
   width)).</dd>
  </dl>
 <li>
  <dl class="switch">
   <dt>If the <a href="#viewport">viewport</a> has downward <a href="#overflow-directions" title="overflow directions">overflow direction</a>
   <dd><p>Let <var>y</var> be max(0, min(<var>y</var>,
   <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a> height - <var>viewport height</var>)).</dd>
   <dt>If the <a href="#viewport">viewport</a> has upward <a href="#overflow-directions" title="overflow directions">overflow direction</a>
   <dd><p>Let <var>y</var> be min(0, max(<var>y</var>,
   <var>viewport height</var> - <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a>
   height)).</dd>
  </dl>
 <li><p>Let <var>position</var> be the scroll position the <a href="#viewport">viewport</a> would have by aligning the x-coordinate <var>x</var> of the
 <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a> with the left of the <a href="#viewport">viewport</a> and aligning the y-coordinate <var>y</var> of the
 <a href="#viewport">viewport</a> <a href="#scrolling-area">scrolling area</a> with the top of the <a href="#viewport">viewport</a>.
 <li><p>If <var>position</var> is the same as the <a href="#viewport">viewport</a>'s current scroll position, and the <a href="#viewport">viewport</a> does not have an ongoing
 <a href="#concept-smooth-scroll" title="concept-smooth-scroll">smooth scroll</a>, abort these steps.
 <li><p>Let <var>task</var> be these steps:
  <ol>
   <li><p><a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#concept-event-fire" title="concept-event-fire">Fire an event</a> named <code title="">scroll</code> that bubbles at the
   <code class="external" data-anolis-spec="dom"><a href="http://dom.spec.whatwg.org/#document">Document</a></code> object.
  </ol>
 <li><p><a href="#perform-a-scroll">Perform a scroll</a> of the <a href="#viewport">viewport</a> to <var>position</var>, with the set of steps <var>task</var>, and the
 <code class="external" data-anolis-spec="dom"><a href="http://dom.spec.whatwg.org/#document">Document</a></code>'s root element as the associated element, if there is one, or null otherwise, and the scroll behavior being the
 value of the <code title="">behavior</code> dictionary member of <var>options</var>.
</ol>

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

<p>When the <dfn id="dom-window-scrollby" title="dom-Window-scrollBy"><code>scrollBy(<var>x</var>, <var>y</var>, <var>options</var>)</code></dfn> method is invoked, the
user agent must act as if the <code title="dom-Window-scroll"><a href="#dom-window-scroll">scroll()</a></code> method was invoked with
<var>x</var> plus <code title="dom-Window-scrollX"><a href="#dom-window-scrollx">scrollX</a></code>
as first argument and <var>y</var> plus
<code title="dom-Window-scrollY"><a href="#dom-window-scrolly">scrollY</a></code> as second argument.</p>

<p>The <dfn id="dom-window-screenx" title="dom-Window-screenX"><code>screenX</code></dfn> attribute must return the x-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. <!--fingerprint--></p>

<p>The <dfn id="dom-window-screeny" title="dom-Window-screenY"><code>screenY</code></dfn> attribute must return the y-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. <!--fingerprint--></p>

<p>The <dfn id="dom-window-outerwidth" title="dom-Window-outerWidth"><code>outerWidth</code></dfn> attribute must return the width of the
client window. If there is no client window this
attribute must return zero. <!--fingerprint--></p>

<p>The <dfn id="dom-window-outerheight" title="dom-Window-outerHeight"><code>outerHeight</code></dfn> attribute must return the height of the
client window. If there is no client window this
attribute must return zero. <!--fingerprint--></p>

<p>The <dfn id="dom-window-devicepixelratio" title="dom-Window-devicePixelRatio"><code>devicePixelRatio</code></dfn> attribute must return the result of the following algorithm:

<ol>
 <li><p>If there is no output device, return 1 and abort these steps.
 <li><p>Let <var>CSS pixel size</var> be the size of a CSS pixel at the current <a href="#page-zoom">page zoom</a> scale factor and at a <a href="#pinch-zoom">pinch zoom</a> scale
 factor of 1.0.
 <li><p>Let <var>device pixel size</var> be the size of a device pixel of the output device, in one dimension (vertical or horizontal). If the device pixel is
 not square, then use the smaller of the vertical or horizontal size of the smallest bounding box of the device pixel.
 <li><p>Return the result of dividing <var>CSS pixel size</var> by <var>device pixel size</var>.
</ol>


<h4 id="the-features-argument-to-the-open()-method"><span class="secno">5.1 </span>The <var>features</var> argument to the <code title="">open()</code> method</h4>

<p>HTML defines the <code class="external" data-anolis-spec="html" title="dom-open"><a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#dom-open">open()</a></code> method but has no defined effect for the third argument, <var>features</var>.
<a href="#refsHTML">[HTML]</a>

<p>This specification defines the effect of the <var>features</var> argument for user agents that do not opt to ignore it, as follows:

<ol>
 <li><p>If the method does not result in a new <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#auxiliary-browsing-context">auxiliary browsing context</a> being created, terminate these steps.
 <li><p>Let <var>target</var> be the new <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/browsers.html#auxiliary-browsing-context">auxiliary browsing context</a>.
 <li><p>Let <var>tokens</var> be the result of <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#split-a-string-on-commas" title="split a string on commas">splitting <var>features</var> on commas</a>.
 <li><p>Let <var>parsed features</var> be a new empty dictionary.
 <li><p><i>Token loop</i>: For each token <var>token</var> in <var>tokens</var>, follow these substeps:
  <ol>
   <li><p>Let <var>input</var> be <var>token</var>.
   <li><p>Let <var>position</var> point at the first character of <var>input</var>.
   <li><p><a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#skip-whitespace">Skip whitespace</a>.
   <li><p><a class="external" data-anolis-spec="ht
7795
ml" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#collect-a-sequence-of-characters">Collect a sequence of characters</a> that are not <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#space-character" title="space character">space
   characters</a> nor "<code title="">=</code>" (U+003D). Let <var>name</var> be the collected characters, <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#converted-to-ascii-lowercase">converted to ASCII
   lowercase</a>.
   <li><p>If <var>name</var> is in <var>parsed features</var> or if <var>name</var> is not a <a href="#supported-open()-feature-name">supported <code title="">open()</code> feature name</a>,
   continue <i>token loop</i>.
   <li><p><a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#skip-whitespace">Skip whitespace</a>.
   <li><p>If the character at <var>position</var> is not "<code title="">=</code>" (U+003D), continue <i>token loop</i>.
   <li><p>Advance <var>position</var> by one.
   <li><p>If <var>position</var> is past the end of <var>input</var>, continue <i>token loop</i>.
   <li><p><a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#collect-a-sequence-of-characters">Collect a sequence of characters</a> that are any characters. Let <var>raw value</var> be the collected characters.
   <li><p>Let <var>value</var> be the result of invoking the <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#rules-for-parsing-integers">rules for parsing integers</a> on <var>raw value</var>.
   <li><p>If <var>value</var> is an error, continue <i>token loop</i>.
   <li><p>Set <var>name</var> in <var>parsed features</var> to <var>value</var>.
  </ol>
 <li><p>If <code title="dom-open-features-left"><a href="#dom-open-features-left">left</a></code> is present in <var>parsed features</var>, follow these substeps:
  <ol>
   <li><p>Let <var>x</var> be the value of <code title="dom-open-features-left"><a href="#dom-open-features-left">left</a></code>.
   <li><p>Optionally, clamp <var>x</var> in a user-agent-defined manner so that the window does not move outside the available space.
   <li><p>Optionally, move <var>target</var>'s window such that the window's left edge is at the horizontal coordinate <var>x</var> relative to the left edge of
   the output device, measured in CSS pixels of <var>target</var>. The positive axis is rightward.
  </ol>
 <li><p>If <code title="dom-open-features-top"><a href="#dom-open-features-top">top</a></code> is present in <var>parsed features</var>, follow these substeps:
  <ol>
   <li><p>Let <var>y</var> be the value of <code title="dom-open-features-top"><a href="#dom-open-features-top">top</a></code>.
   <li><p>Optionally, clamp <var>y</var> in a user-agent-defined manner so that the window does not move outside the available space.
   <li><p>Optionally, move <var>target</var>'s window such that the window's top edge is at the vertical coordinate <var>y</var> relative to the top edge of
   the output device, measured in CSS pixels of <var>target</var>. The positive axis is downward.
  </ol>
 <li><p>If <code title="dom-open-features-width"><a href="#dom-open-features-width">width</a></code> is present in <var>parsed features</var>, follow these substeps:
  <ol>
   <li><p>Let <var>x</var> be the value of <code title="dom-open-features-width"><a href="#dom-open-features-width">width</a></code>.
   <li><p>Optionally, clamp <var>x</var> in a user-agent-defined manner so that the window does not get too small or bigger than the available space.
   <li><p>Optionally, size <var>target</var>'s window by moving its right edge such that the distance between the left and right edges of the viewport are
   <var>x</var> CSS pixels of <var>target</var>.
   <li><p>Optionally, move <var>target</var>'s window in a user-agent-defined manner so that it does not grow outside the available space.
  </ol>
 <li><p>If <code title="dom-open-features-height"><a href="#dom-open-features-height">height</a></code> is present in <var>parsed features</var>, follow these substeps:
  <ol>
   <li><p>Let <var>y</var> be the value of <code title="dom-open-features-height"><a href="#dom-open-features-height">height</a></code>.
   <li><p>Optionally, clamp <var>y</var> in a user-agent-defined manner so that the window does not get too small or bigger than the available space.
   <li><p>Optionally, size <var>target</var>'s window by moving its bottom edge such that the distance between the top and bottom edges of the viewport are
   <var>y</var> CSS pixels of <var>target</var>.
   <li><p>Optionally, move <var>target</var>'s window in a user-agent-defined manner so that it does not grow outside the available space.
  </ol>
</ol>

<p>A <dfn id="supported-open()-feature-name">supported <code title="">open()</code> feature name</dfn> is one of the following:

<dl>
 <dt><dfn id="dom-open-features-width" title="dom-open-features-width">width</dfn>
 <dd><p>The width of the viewport.
 <dt><dfn id="dom-open-features-height" title="dom-open-features-height">height</dfn>
 <dd><p>The height of the viewport.
 <dt><dfn id="dom-open-features-left" title="dom-open-features-left">left</dfn>
 <dd><p>The left position of the window.
 <dt><dfn id="dom-open-features-top" title="dom-open-features-top">top</dfn>
 <dd><p>The top position of the window.
</dl>


<h3 id="the-mediaquerylist-interface"><span class="secno">5.2 </span>The <code title="">MediaQueryList</code> Interface</h3>

<p>A <code><a href="#mediaquerylist">MediaQueryList</a></code> object has an associated media query list set on creation and an associated
<dfn id="list-of-media-query-list-listeners">list of media query list listeners</dfn>, which is initially empty.</p>
<p>If the associated media query list changes in evaluation then, for each
listener in the <a href="#list-of-media-query-list-listeners">list of media query list listeners</a> — in
appending order, <a class="external" data-anolis-spec="html" href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#queue-a-task">queue a task</a> that invokes the listener,
passing as argument the <code><a href="#mediaquerylist">MediaQueryList</a></code> object.</p>
<div class="example">
<p>A simple piece of code that detects changes in the orientation of the viewport can be written as follows:</p>
<pre>function handleOrientationChange(mql) {
    if(mql.matches) // landscape
      …
    else
      …
  }
  var mql = matchMedia("(orientation:landscape)")
  mql.addListener(handleOrientationChange)</pre>
</div>

<pre class="idl">interface <dfn id="mediaquerylist">MediaQueryList</dfn> {
  readonly attribute DOMString <a href="#dom-mediaquerylist-media" title="dom-MediaQueryList-media">media</a>;
  readonly attribute boolean <a href="#dom-mediaquerylist-matches" title="dom-MediaQueryList-matches">matches</a>;
  void <a href="#dom-mediaquerylist-addlistener" title="dom-MediaQueryList-addListener">addListener</a>(<a href="#mediaquerylistlistener">MediaQueryListListener</a> listener);
  void <a href="#dom-mediaquerylist-removelistener" title="dom-MediaQueryList-removeListener">removeListener</a>(<a href="#mediaquerylistlistener">MediaQueryListListener</a> listener);
};

callback <dfn id="mediaquerylistlistener">MediaQueryListListener</dfn> = void (<a href="#mediaquerylist">MediaQueryList</a> list);</pre>

<p>The <dfn id="dom-mediaquerylist-media" title="dom-MediaQueryList-media"><code>media</code></dfn> attribute must return the

<p>The <dfn id="dom-mediaquerylist-matches" title="dom-MediaQueryList-matches"><code>matches</code></dfn> attribute must return true if the associated media query list
matches the state of the rendered <code class="external" data-anolis-spec="dom"><a href="http://dom.spec.whatwg.org/#document">Document</a></code> and false if it does not. <!--fingerprint--></p>

<p>When the <dfn id="dom-mediaquerylist-addlistener" title="dom-MediaQueryList-addListener"><code>addListener(<var>listener</var>)</code></dfn> method is invoked <var>listener</var> must
be appended to the <a href="#list-of-media-query-list-listeners">list of media query list listeners</a>, unless
it is already in the <a href="#list-of-media-query-list-listeners">list of media query list listeners</a>.</p>

<p>When the <dfn id="dom-mediaquerylist-removelistener" title="dom-MediaQueryList-removeListener"><code>removeListener(<var>listener</var>)</code></dfn> method is invoked
<var>listener</var> must be removed from the <a href="#list-of-media-query-list-listeners">list of media query list listeners</a>.</p>

<h3 id="the-screen-interface"><span class="secno">5.3 </span>The <code title="">Screen</code> Interface</h3>

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

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

<p>The <dfn id="dom-screen-availwidth" title="dom-Screen-availWidth"><code>availWidth</code></dfn> attribute must return the available width of the rendering surface of the output device,
in CSS pixels. <!--fingerprint--></p>

<p>The <dfn id="dom-screen-availheight" title="dom-Screen-availHeight"><code>availHeight</code></dfn> attribute must return the available height of the rendering surface of the output
device, in CSS pixels. <!--fingerprint--></p>

<p>The <dfn id="dom-screen-width" title="dom-Screen-width"><code>width</code></dfn> attribute must return the width of the output device, in CSS pixels. <!--fingerprint--></p>

<p>The <dfn id="dom-screen-height" title="dom-Screen-height"><code>height</code></dfn> attribute must return the height of the output device, in CSS pixels. <!--fingerprint--></p>

<p>The <dfn id="dom-screen-colordepth" title="dom-Screen-colorDepth"><code>colorDepth</code></dfn> attribute must return 24.</p>

<p>The <dfn id="dom-screen-pixeldepth" title="dom-Screen-pixelDepth"><code>pixelDepth</code></dfn> attribute must return 24.</p>

<p class="note">The <code title="dom-Screen-colorDepth"><a href="#dom-screen-colordepth">colorDepth</a></code> and <code title="dom-Screen-pixelDepth"><a href="#dom-screen-pixeldepth">pixelDepth</a></code> attributes are useless but are
included for compatibility.


<h2 id="extensions-to-the-document-interface"><span class="secno">6 </span>Extensions to the <code title="">Document</code> Interface</h2>

<pre class="idl">partial interface <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#document">Document</a> {
  <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#element">Element</a>? <a href="#dom-document-elementfrompoint" title="dom-Document-elementFromPoint">elementFromPoint</a>(double x, double y);
  sequence&lt;<a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#element">Element</a>&gt; <a href="#dom-document-elementsfrompoint" title="dom-Document-elementsFromPoint">elementsFromPoint</a>(double x, double y);
  <a href="#caretposition">CaretPosition</a>? <a href="#dom-document-caretpositionfrompoint" title="dom-Document-caretPositionFromPoint">caretPositionFromPoint</a>(double x, double y);
};</pre>

<p>The <dfn id="dom-document-elementfrompoint" title="dom-Document-elementFromPoint"><code>elementFromPoint(<var>x</var>, <var>y</var>)</code></dfn> method must follow these steps:

<ol>
 <li><p>If either argument is negative, <var>x</var> is greater than the <a href="#viewport">viewport</a> width excluding the size of a rendered scroll bar (if any), or
 <var>y</var> is greater than the <a href="#viewport">viewport</a> height excluding the size of a rendered scroll bar (if any), or there is no <a href="#viewport">viewport</a>
 associated with the document, return null and terminate these steps.
 <li><p>If there is a <a href="#layout-box">layout box</a> in the <a href="#viewport">viewport</a> that would be a target for hit testing at coordinates <var>x</var>,<var>y</var>,
 when applying the <a href="#transforms">transforms</a> that apply to the descendants of the <a href="#viewport">viewport</a>, return the associated element and terminate these steps.
 <li><p>If the document has a root element, return the root element and terminate these steps.
 <li><p>Return null.
</ol>

<p class="note">The <code title="dom-Document-elementFromPoint"><a href="#dom-document-elementfrompoint">elementFromPoint()</a></code> method does not necessarily return the top-most painted element. For
instance, an element can be excluded from being a target for hit testing by using the 'pointer-events' CSS property.

<p class="atrisk">The <dfn id="dom-document-elementsfrompoint" title="dom-Document-elementsFromPoint"><code>elementsFromPoint(<var>x</var>, <var>y</var>)</code></dfn> method must follow these steps:

<ol>
 <li><p>Let <var>sequence</var> be a new empty sequence.
 <li><p>If either argument is negative, <var>x</var> is greater than the <a href="#viewport">viewport</a> width excluding the size of a rendered scroll bar (if any), or
 <var>y</var> is greater than the <a href="#viewport">viewport</a> height excluding the size of a rendered scroll bar (if any), or there is no <a href="#viewport">viewport</a>
 associated with the document, return <var>sequence</var> and terminate these steps.
 <li><p>For each <a href="#layout-box">layout box</a> in the <a href="#viewport">viewport</a>, in paint order, starting with the topmost box, that would be a target for hit testing at
 coordinates <var>x</var>,<var>y</var> even if nothing would be overlapping it, when applying the <a href="#transforms">transforms</a> that apply to the descendants of the
 <a href="#viewport">viewport</a>, append the associated element to <var>sequence</var>.
 <li><p>If the document has a root element, and the last item in <var>sequence</var> is not the root element, append the root element to <var>sequence</var>.
 <li><p>Return <var>sequence</var>.
</ol>

<p>The <dfn id="dom-document-caretpositionfrompoint" title="dom-Document-caretPositionFromPoint"><code>caretPositionFromPoint(<var>x</var>, <var>y</var>)</code></dfn> method must return the
result of running these steps:</p>
<ol>
 <li><p>If there is no <a href="#viewport">viewport</a> associated with the document, return null.
 <li><p>If either argument is negative, <var>x</var> is greater
 than the <a href="#viewport">viewport</a> width excluding the size of a rendered
 scroll bar (if any), <var>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>
 <li><p>If at the coordinates <var>x</var>,<var>y</var>
 in the <a href="#viewport">viewport</a> no text insertion point indicator would have
 been inserted when applying the <a href="#transforms">transforms</a> that apply to the descendants of the <a href="#viewport">viewport</a>, return null.</li>
 <li>
  <p>If at the coordinates <var>x</var>,<var>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, when applying the <a href="#transforms">transforms</a> that apply to the descendants of the
  <a href="#viewport">viewport</a>, 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></dt>
   <dd><p>The node corresponding to the text entry widget.</dd>
   <dt><a href="#caret-offset">caret offset</a></dt>
   <dd><p>The amount of 16-bit units to the left of where the
   text insertion point indicator would have inserted.</dd>
   <dt><a href="#caret-range">caret range</a></dt>
   <dd><p>null</dd>
  </dl>
 </li>
 <li>
  <p>Otherwise, return a <a href="#caret-position">caret position</a> where the
  <a href="#caret-range">caret range</a> is a collapsed
  <code class="external" data-anolis-spec="dom"><a href="http://dom.spec.whatwg.org/#range">Range</a></code> object for the position
  where the text insertion point indicator would have been inserted when applying the <a href="#transforms">transforms</a> that apply to the descendants of the
  <a href="#viewport">viewport</a>, and the other properties are set as follows:</p>
  <dl>
   <dt><a href="#caret-node">caret node</a></dt>
   of the <a href="#caret-range">caret range</a>.</dd>
   <dt><a href="#caret-offset">caret offset</a></dt>
   <dd><p>The <code class="external" data-anolis-spec="dom" title="dom-Range-startOffset"><a href="http://dom.spec.whatwg.org/#dom-range-startoffset">startOffset</a></code> of
   the <a href="#caret-range">caret range</a>.</p>
  </dl>
 </li>
</ol>
<p class="note">The specifics of hit testing are out of scope of this
specification and therefore the exact details of
<code title="dom-Document-elementFromPoint"><a href="#dom-document-elementfrompoint">elementFromPoint()</a></code> and
<code title="dom-Document-caretPositionFromPoint"><a href="#dom-document-caretpositionfrompoint">caretPositionFromPoint()</a></code>
are therefore too. Hit testing will hopefully be defined in a future
revision of CSS or HTML.</p>

<h3 id="the-caretposition-interface"><span class="secno">6.1 </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 <code><a href="#caretposition">CaretPosition</a></code> object.</p>

<pre class="idl">interface <dfn id="caretposition">CaretPosition</dfn> {
  readonly attribute <a class="external" data-anolis-spec="dom" href="http://dom.spec.whatwg.org/#node">Node</a> <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>;
  <a href="#domrect">DOMRect</a>? <a href="#dom-caretposition-getclientrect" title="dom-CaretPosition-getClientRect">getClientRect</a>();
};</pre>

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

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

<p>The <dfn id="dom-caretposition-getclientrect" title="dom-CaretPosition-getClientRect"><code>getClientRect()</code></dfn> method must follow these steps, aborting on the first step that
returns a value:</p>
<ol>
 <li>
  <p>If <a href="#caret-range">caret range</a> is not null:
  <ol>
   <li><p>Let <var>list</var> be the result of invoking the
   <code title="dom-Range-getClientRects"><a href="#dom-range-getclientrects">getClientRects()</a></code> method on the
   range.
   <li><p>If <var>list</var> is empty, return null.