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<div class="head">
<p>
<a href="http://www.w3.org/"><img alt="W3C" src="http://www.w3.org/Icons/w3c_home" height="48" width="72"></a>
</p>

<h1>Resource Timing</h1>

<h2 class="no-num no-toc" id="working-draft-august-11-2011">W3C Working Draft 11 August 2011</h2>
<dl>
  <dt>This version:</dt>
    <dd><a href="http://www.w3.org/TR/2011/WD-resource-timing-20110811/">http://www.w3.org/TR/2011/WD-resource-timing-20110811/</a></dd>
  <dt>Latest version:</dt>
      <dd><a href="http://www.w3.org/TR/resource-timing/">http://www.w3.org/TR/resource-timing/</a></dd>
  <dt>Latest Editor's Draft:</dt>
  <dd><a href='http://www.w3c-test.org/webperf/specs/ResourceTiming/'>http://www.w3c-test.org/webperf/specs/ResourceTiming/</a></dd>
  <dt>Previous versions:</dt>
    <dd><a href="http://www.w3.org/TR/2011/WD-resource-timing-20110524/">http://www.w3.org/TR/2011/WD-resource-timing-20110524/</a></dd>
  <dt>Editors:</dt>
    <dd class="vcard"><span class="fn">Jatinder Mann</span>, <span
      class="org">Microsoft Inc.</span>, <span
      class="email">jmann@microsoft.com</span> </dd>
    <dd class="vcard"><span class="fn">Zhiheng Wang</span>, <span
      class="org">Google Inc.</span>, <span
      class="email">zhihengw@google.com</span> </dd>
    <dd class="vcard"><span class="fn">Anderson Quach</span>, <span
      class="org">Microsoft Inc. <i>(Until March 2011)</i></span></dd>
</dl>

   <p class=copyright><a
    href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
    &copy; 2011 <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>
<hr>

</div>

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

<p>This specification defines an interface for web applications to access
timing information related to HTML elements. </p>

<h2 class="no-num no-toc" id="status-of-this-document">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</a> at http://www.w3.org/TR/.</em></p>

<p>This is a <strong>work in progress</strong> and may change without any
notices. </p>

<p>This is the <strong>Last Call</strong> Working Draft of the Resource Timing specification. Please send comments
   to <a href="mailto:public-web-perf@w3.org?subject=[ResourceTiming]%20">public-web-perf@w3.org</a>
   (<a href="http://lists.w3.org/Archives/Public/public-web-perf/">archived</a>)
   with <samp>[ResourceTiming]</samp> at the start of the subject line <strong>by 15 September 2011</strong>.</p>

<p>
A <a href='diff.html'>diff document</a> with the previous draft is available.
</p>

<p>This document is produced by
   the <a href="http://www.w3.org/2010/webperf/">Web Performance</a>
   Working Group. The Web Performance Working Group is part of
   the <a href="http://www.w3.org/2006/rwc/Activity">Rich Web Clients
   Activity</a> in the
   W3C <a href="http://www.w3.org/Interaction/">Interaction
   Domain</a>.

<p>
<strong>You can find the latest <a href="http://www.w3c-test.org/webperf/specs/ResourceTiming/">Editor's Draft</a> of this document in the <a href="https://dvcs.w3.org/hg/webperf/">W3C's Mercurial repository</a>, which is updated on a regular basis.</strong>
</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. </p>

<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/45211/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 id="unstable"><strong class="redNote">Implementers should be aware that this document is not
        stable.</strong> Implementers who are not taking part in the discussions
        are likely to find the specification changing out from under them in
        incompatible ways. Vendors interested in implementing this document
        before it eventually reaches the Candidate Recommendation stage should
        join the aforementioned mailing lists and take part in the discussions.</p>

<h2 class="no-num no-toc" id="table-of-contents">Table of Contents</h2>
<!--begin-toc-->
<ol class="toc">
  <li><a href="#introduction"><span class="secno">1
  </span>Introduction</a></li>
  <li><a href="#conformance-requirements"><span class="secno">2
    </span>Conformance requirements</a></li>
  <li><a href="#terminology"><span class="secno">3 </span>Terminology</a></li>
  <li><a href="#resource-timing"><span class="secno">4 </span>Resource
    Timing</a>
    <ol class="toc">
      <li><a href="#introduction-1"><span class="secno">4.1</span> Introduction</a></li>
      <li><a href="#resources-included"><span class="secno">4.2</span> Resources Included in the <code>PerformanceResourceTiming</code> Interface</a></li>
	  <li><a href="#sec-window.performance-attribute"><span class="secno">4.3</span> The <code>window.performance</code> Attribute</a></li>
      <li><a href="#performance-resource-timing"><span class="secno">4.4</span> The <code>PerformanceResourceTiming</code> Interface</a></li>
      <li><a href="#performance-resource-timing-methods"><span class="secno">4.5 </span> The Resource Timing Methods</a></li>
      <li><a href="#cross-origin-resources"><span class="secno">4.6 </span> Cross-origin Resources</a></li>
      <li><a href="#vendor-prefixes"><span class="secno">4.7 </span> Vendor Prefixes</a></li>
    </ol>
  </li>
  <li><a href="#process"><span class="secno">5 </span>Process</a>
    <ol class="toc">
        <li><a href="#processing-model"><span class="secno">5.1</span> Processing Model</a></li>
        <li><a href="#monotonic-clock"><span class="secno">5.2</span> Monotonic Clock</a></li>
    </ol>
  </li>
  <li><a href="#privacy"><span class="secno">6 </span>Privacy</a></li>
  <li><a href="#security"><span class="secno">7 </span>Security</a></li>
  <li><a class="no-num" href="#acknowledgements">Acknowledgements</a></li>
</ol>
<!--end-toc-->

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

<p>This section is non-normative.</p>
<p>
User latency is an important quality benchmark for Web Applications. While
JavaScript-based mechanisms can provide comprehensive instrumentation for
user latency measurements within an application, in many cases, they are
unable to provide a complete end-to-end latency picture. While Navigation Timing <a href="#NavigationTiming">[NavigationTiming]</a> addresses
part of the problem by providing timing information associated with a
navigation, this document introduces the <a href="#resource-timing">ResourceTiming</a>
interface to allow Javascript mechanisms to collect complete timing
information related to resources on a document.
</p>


<div class="example">
<p>For example, the following Javascript shows a simple attempt to
measure the time it takes to fetch a resource:</p>

<pre>
&lt;!doctype html&gt;
&lt;html&gt;
  &lt;head&gt;
  &lt;/head&gt;
  &lt;body onload="loadResources()"&gt;
    &lt;script&gt;
        function loadResources()
        {
           var start = new Date().getTime();
           var image1 = new Image();
           image1.src = 'http://w3c-test.org/webperf/image1.png';
           image1.onload = resourceTiming;

           var resourceTiming = function() {
               var now = new Date().getTime();
               var latency = now - start;
               alert("End to end resource fetch: " + latency);
           };
        }
    &lt;/script&gt;
    &lt;img src="http://w3c-test.org/webperf/image0.png"&gt;
  &lt;/body&gt;
&lt;/html&gt;
</pre>
</div>

<p>Though this script can measure the time it takes to fetch a resource,
it cannot break down the time spent in various phases. Further, the script
cannot easily measure the time it takes to fetch resources described in markup.</p>

<p>To address the need for complete information on user experience, this document
introduces the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface.
This interface allows JavaScript mechanisms to provide complete client-side latency measurements within applications.
With this interface, the previous example can be modified to measure a user's
perceived load time of a resource.
</p>

<div class="example">
<p>The following script calculates the amount of time it takes to fetch every resource in the
page, even those defined in markup. This example assumes
that this page is hosted on http://w3c-test.org.
One could further measure the amount of time it takes in every phase of fetching a resource
with the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface.
</p>
<pre>
&lt;!doctype html&gt;
&lt;html&gt;
  &lt;head&gt;
  &lt;/head&gt;
  &lt;body onload="loadResources()"&gt;
    &lt;script&gt;
       function loadResources()
       {
          var image1 = new Image();
          image1.src = 'http://w3c-test.org/webperf/image1.png';
          image1.onload = resourceTiming;
       }

       function resourceTiming()
       {
           var resourceList = window.performance.getEntriesByType(window.performance.PERF_RESOURCE);
           for (i = 0; i < resourceList.length; i++)
           {
              if (resourceList[i].initiatorType == window.performance.INITIATOR_IMAGE)
              {
                 alert("End to end resource fetch: "+ resourceList[i].responseEnd - resourceList[i].startTime);
              }
           }
       }
    &lt;/script&gt;
    &lt;img id="image0" src="http://w3c-test.org/webperf/image0.png"&gt;
  &lt;/body&gt;
&lt;/html&gt;
</pre>
</div>

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

<p>The key words "MUST", "MUST NOT", "REQUIRED", "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="#rfc2119">[RFC2119]</a>
</p>

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

<p>Some conformance requirements are phrased as requirements on attributes,
methods or objects. Such requirements are to be interpreted as requirements
on user agents. </p>

<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>

    <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="#WebIDL">[Web IDL]</a></p>

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

<p>The construction "a <code title="">Foo</code> object", where <code
title="">Foo</code> is actually an interface, is sometimes used instead of
the more accurate "an object implementing the interface <code
title="">Foo</code>". </p>

<p>The term DOM is used to refer to the API set made available to scripts in
Web applications, and does not necessarily imply the existence of an actual
<code>Document</code> object or of any other <code>Node</code> objects as
defined in the DOM Core specifications. <a href="#DOM3Core">[DOM3CORE]</a>
</p>

<p>A DOM attribute is said to be <em>getting</em> when its value is being
retrieved (such as by author script), and is said to be <em>setting</em> when
a new value is assigned to it. </p>

<p>The term "JavaScript" is used to refer to ECMA262, rather than the
official term ECMAScript, since the term JavaScript is more widely known. <a href="#ECMA262">[ECMA262]</a>
</p>

<p>Throughout this work, time is measured in milliseconds since midnight of January 1, 1970 (UTC).</p>

<h2 id="resource-timing"><span class="secno">4 </span>Resource Timing</h2>

<h3 id="introduction-1"><span class="secno">4.1 </span>Introduction</h3>

<p>This section is non-normative.</p>

<p>
    The <a href="#performance-resource-timing">PerformanceResourceTiming</a>
    interface facilitates timing measurement of downloadable resources on the
    root page. It represents the timing information related to resources that
    initiate network downloads. For example, this interface is available for
    <a href="http://www.w3.org/TR/XMLHttpRequest/#the-xmlhttprequest-interface">XMLHttpRequest</a> objects <a href='#XHR'>[XMLHttpRequest]</a>, HTML
    elements <a href='#HTML5'>[HTML5]</a> such as
    <a href="http://www.w3.org/TR/html5/the-iframe-element.html#the-iframe-element">iframe</a>,
    <a href="http://www.w3.org/TR/html5/embedded-content-1.html#the-img-element">img</a>,
    <a href="http://www.w3.org/TR/html5/scripting-1.html#script">script</a>,
    <a href="http://www.w3.org/TR/html5/the-iframe-element.html#the-object-element">object</a>,
    <a href="http://www.w3.org/TR/html5/video.html#audio">audio</a>,
    <a href="http://www.w3.org/TR/html5/video.html#video">video</a>,
    <a href="http://www.w3.org/TR/html5/the-iframe-element.html#the-embed-element">embed</a>,
    and <a href="http://www.w3.org/TR/html5/semantics.html#the-link-element">link</a>
    with the link type of
    <a href="http://www.w3.org/TR/html5/links.html#link-type-stylesheet">stylesheet</a>,
    and SVG elements <a href='#SVG'>[SVG]</a> such
    as <a href="http://www.w3.org/TR/SVG11/struct.html#SVGElement">svg</a>.

</p>

<p>The term "resource" is also used to refer to these elements in this work. </p>

<div class="head">
<h3 id="resources-included"><span class="secno">4.2 Resources Included
in the</span>
<code><a href="#performance-resource-timing">PerformanceResourceTiming</a></code> Interface</h3>
<p>
    The <a href="#performance-resource-timing">PerformanceResourceTiming</a>
    interface must include all resources fetched from the networking layer by the current browsing context. Resources that are
    retrieved from the user agent's networking layer cache must be included in the
    <a href="#performance-resource-timing">PerformanceResourceTiming</a>
    interface.
</p>
<p>The rest of this section is non-normative.</p>
<p>
    Examples:
    <ul>
        <li>If the same canonical URL is used as the <code>src</code> attribute of two <code>IMG</code> elements,
            the fetch of the resource initiated by the first <code>IMG</code> element should be included in the
            <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface.  The user agent might not re-request the
            URL from the networking layer for the second <code>IMG</code> element, instead using an in-memory browser cache.
            In this case, there is only a single request sent to the networking layer for retrieval, so the fetch of the resource by the first
            <code>IMG</code> element would be the only occurrence in the <a href="#performance-resource-timing">PerformanceResourceTiming</a>
            interface.
        </li>
        <li>If the <code>src</code> attribute of an <code>IMG</code> element is changed via script, both the fetch of the original resource as well
            as the fetch of the new URL would be included in the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface.
        </li>
        <li>
            If a <code>XMLHttpRequest</code> is generated twice for the same canonical URL, both fetches of the resource would be
            included in the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface. This is because the user agent must validate
            both requests from the networking layer, even if the resource is in a disk cache from the first request.
        </li>
        <li>
            If an <code>IFRAME</code> element is included on the page, then only the resource requested by <code>IFRAME</code> <code>src</code> attribute is included
            in the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface. Sub-resources requested by the <code>IFRAME</code> document
            will be included in the <code>IFRAME</code> document's <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface and not the parent
            document's <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface.
        </li>
        <li>
            If an <code>IMG</code> element has a <code><a href="http://tools.ietf.org/html/rfc2397">data: URI</a></code> as its source, then this resource will not
            be included in the <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface. By definition <code><a href="http://tools.ietf.org/html/rfc2397">data: URI</a></code>
            contains embedded data and does not require access to the networking layer.
        </li>
    </ul>
<p>
    The user agent may choose to limit how many resources are included in the
    <a href="#performance-resource-timing">PerformanceResourceTiming</a>
    interface.  The recommended maximum number of resources is 150, though this may be changed by the user agent.
    <a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a>
    can be called to request a change to this limit.
</p>

<h3 id="sec-window.performance-attribute"><span class="secno">4.3 </span> The <code>window.performance</code>
Attribute</h3>
<pre class="idl">
  partial interface <dfn id="nt-performance-interface">Performance</dfn> {
  const unsigned short <a href="#perf-resource">PERF_RESOURCE</a> = 1;

  const unsigned short <a href="#type-other">INITIATOR_OTHER</a> = 0;
  const unsigned short <a href="#type-link">INITIATOR_LINK</a> = 1;
  const unsigned short <a href="#type-css">INITIATOR_CSS</a> = 2;
  const unsigned short <a href="#type-script">INITIATOR_SCRIPT</a> = 3;
  const unsigned short <a href="#type-image">INITIATOR_IMAGE</a> = 4;
  const unsigned short <a href="#type-object">INITIATOR_OBJECT</a> = 5;
  const unsigned short <a href="#type-subdocument">INITIATOR_SUBDOCUMENT</a> = 6;
  const unsigned short <a href="#type-xhr">INITIATOR_XMLHTTPREQUEST</a> = 7;
  const unsigned short <a href="#type-embed">INITIATOR_EMBED</a> = 8;
  const unsigned short <a href="#type-audio">INITIATOR_AUDIO</a> = 9;
  const unsigned short <a href="#type-video">INITIATOR_VIDEO</a> = 10;
  const unsigned short <a href="#type-svg">INITIATOR_SVG</a> = 11;
};
</pre>

<h3><span class="secno">4.4 </span>The
<code><a id="performance-resource-timing">PerformanceResourceTiming</a></code> Interface</h3>

<pre class="idl">interface <a href="#performance-resource-timing">PerformanceResourceTiming</a> : <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntry-interface">PerformanceEntry</a> {
  readonly attribute unsigned short <a href="#initiatorType" title="initiatorType">initiatorType</a>;

  readonly attribute unsigned long long <a href="#redirect-start" title="redirectstart">redirectStart</a>;
  readonly attribute unsigned long long <a href="#redirect-end" title="redirectend">redirectEnd</a>;
  readonly attribute unsigned long long <a href="#fetch-start" title="fetchstart">fetchStart</a>;
  readonly attribute unsigned long long <a href="#domainlookup-start" title="domainlookupstart">domainLookupStart</a>;
  readonly attribute unsigned long long <a href="#domainlookup-end" title="domainlookupend">domainLookupEnd</a>;
  readonly attribute unsigned long long <a href="#connect-start" title="connectstart">connectStart</a>;
  readonly attribute unsigned long long <a href="#connect-end" title="connectend">connectEnd</a>;
  readonly attribute unsigned long long <a href="#secureconnection-start" title="secureconnectionstart">secureConnectionStart</a>;
  readonly attribute unsigned long long <a href="#request-start" title="requeststart">requestStart</a>;
  readonly attribute unsigned long long <a href="#response-start" title="responsestart">responseStart</a>;
  readonly attribute unsigned long long <a href="#response-end" title="responseend">responseEnd</a>;
};</pre>

<p>
The <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface participates in the
	<a href="http://www.w3.org/TR/performance-timeline/#sec-performance-timeline">Performance Timeline</a> and extends the following attributes of the
<a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntry-interface">PerformanceEntry</a> interface:</p>

<div class="parameters">
    <p>
    	The <code id="name-attribute">name</code> attribute must return the resolved <a href="http://www.w3.org/TR/html5/urls.html#resolve-a-url">URL</a> of the
    	requested resource. This attribute must not change even if the fetch redirected to a different URL.
   	</p>
    <p>The <code id="entryType-attribute">entryType</code> attribute must return <code id="perf-resource">PERF_RESOURCE</code>.</p>
    <p>The <code id="startTime-attribute">startTime</code> attribute must return the time immediately before the user agent starts to queue the resource for fetching.
       If there are HTTP redirects <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes"> or equivalent</a>
       when fetching the resource and if all the redirects or equivalent are from the <a href="#origin"> same origin</a> as the current
       document, this attribute must return the same value as <a href="#redirect-start">redirectStart</a>. Otherwise, this attribute must
       return the same value as <a href="#fetch-start">fetchStart</a>.
    </p>
    <p>The <code id="duration-attribute">duration</code> attribute must return a timestamp equal to the difference between <a href="#response-end">responseEnd</a> and <a href="#startTime-attribute">startTime</a>, respectively.</p>
</div>

<h4 id="initiatorType-attribute"><code><dfn id="initiatorType">initiatorType</dfn></code> attribute</h4>

<p>This attribute must return the type of object that initiated the request for the resource: </p>
<dl>
  <dt><dfn id="type-other">INITIATOR_OTHER</dfn>: The initiator is not of any type listed below.</dt>
  <dt><dfn id="type-link">INITIATOR_LINK</dfn>: The initiator is the <code>href</code> attribute of the <code>&lt;link&gt;</code> element.</dt>
  <dt><dfn id="type-css">INITIATOR_CSS</dfn>: The initiator is any CSS resource downloaded via the <a href="http://www.w3.org/TR/CSS21/syndata.html#uri">url()</a> syntax, such as <code>@import url()</code>, <code>background: url()</code>, etc.</dt>
  <dt><dfn id="type-script">INITIATOR_SCRIPT</dfn>: The initiator is the <code>src</code> attribute of the <code>&lt;script&gt;</code> element.</dt>
  <dt><dfn id="type-image">INITIATOR_IMAGE</dfn>: The initiator is the <code>src</code> attribute of the <code>&lt;img&gt;</code> element.</dt>
  <dt><dfn id="type-object">INITIATOR_OBJECT</dfn>: The initiator is the <code>data</code> attribute of the <code>&lt;object&gt;</code> element.</dt>
  <dt><dfn id="type-subdocument">INITIATOR_SUBDOCUMENT</dfn>: The initiator is the <code>src</code> attribute of the <code>&lt;frame&gt;</code> or <code>&lt;iframe&gt;</code> elements.</dt>
  <dt><dfn id="type-xhr">INITIATOR_XMLHTTPREQUEST</dfn>: The initiator is a XMLHttpRequest object.</dt>
  <dt><dfn id="type-embed">INITIATOR_EMBED</dfn>: The initiator is the <code>src</code> attribute of the <code>&lt;embed&gt;</code> element.</dt>
  <dt><dfn id="type-audio">INITIATOR_AUDIO</dfn>: The initiator is the <code>src</code> attribute of the <code>&lt;audio&gt;</code> element
  or the <code>src</code> attribute of the <code>&lt;source&gt;</code> element associated with an <code>&lt;audio&gt;</code> element. </dt>
  <dt><dfn id="type-video">INITIATOR_VIDEO</dfn>: The initiator is the <code>src</code> or <code>poster</code> attribute of the <code>&lt;video&gt;</code> element
  or the <code>src</code> attribute of the <code>&lt;source&gt;</code> element associated with a <code>&lt;video&gt;</code> element. </dt>
  <dt><dfn id="type-svg">INITIATOR_SVG</dfn>: The initiator is the <code>&lt;svg&gt;</code> element .</dt>
</dl>

<h4 id="redirect-start-attribute"><code><dfn id="redirect-start">redirectStart</dfn></code> attribute</h4>

<p>If there are HTTP redirects <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes">or equivalent</a>
when fetching the resource and if all the redirects or equivalent are from the <a href="#origin">same origin</a> as the current document,
this attribute must return the <a href="#fetch-start">starting time of the fetch</a> that initiates the redirect.</p>

<p>If there are HTTP redirects <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes">or equivalent</a>
when fetching the resource and if any of the redirects are not from the <a href="#origin">same origin</a> as the current document,
and the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules are met, this attribute must
return the <a href="#fetch-start">starting time of the fetch</a> that initiates the redirect.
Otherwise, this attribute must return zero. </p>

<h4 id="redirect-end-attribute"><code><dfn id="redirect-end">redirectEnd</dfn></code> attribute</h4>

<p>If there are HTTP redirects <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes">or equivalent</a>
when fetching the resource and if all the redirects or equivalent are from the <a href="#origin">same origin</a> as the current document,
this attribute must return the time immediately after receiving the last byte of the response of the last redirect.</p>

<p>If there are HTTP redirects <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes">or equivalent</a>
when fetching the resource and if any of the redirects are not from the <a href="#origin">same origin</a> as the current document,
and the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules are met, this attribute must return the
time immediately after receiving the last byte of the response of the last redirect.
Otherwise, this attribute must return zero. </p>

<h4 id="fetch-start-attribute"><code><dfn id="fetch-start">fetchStart</dfn></code> attribute</h4>

<p>This attribute must return the time immediately before the user agent starts to <a
href="http://www.w3.org/TR/html5/fetching-resources.html#fetching-resources">fetch</a> the
    resource.</p>

<h4 id="domainlookup-start-attribute"><code><dfn
id="domainlookup-start">domainLookupStart</dfn></code> attribute</h4>

<p>This attribute must return the time immediately before the user agent starts
the domain name lookup for the resource.
If a <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1">persistent
connection</a> [<a href='#rfc2616'>RFC 2616</a>] is used or the resource
is retrieved from <a href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">relevant
application caches</a> or local resources, this attribute must return the same
value as <a href="#fetch-start">fetchStart</a>. </p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#domainlookup-start">domainLookupStart</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="domainlookup-end-attribute"><code><dfn id="domainlookup-end">domainLookupEnd</dfn></code> attribute</h4>

<p>This attribute must return the time immediately after the user agent finishes
the domain name lookup for the resource.
If a <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1">persistent
connection</a> [<a href='#rfc2616'>RFC 2616</a>] is used or the resource
is retrieved from <a href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">relevant
application caches</a> or local resources, this attribute must return the same
value as <a href="#fetch-start">fetchStart</a>. </p>

<p>If the user agent has the domain information in cache,
domainLookupStart and domainLookupEnd represent the times when the user agent
starts and ends the domain data retrieval from the cache. </p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#domainlookup-end">domainLookupEnd</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="connect-start-attribute"><code><dfn id="connect-start">connectStart</dfn></code> attribute</h4>

<p>This attribute must return the time immediately before the user agent start
establishing the connection to the server to retrieve the resource.
If a <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1">persistent
connection</a> [<a href='#rfc2616'>RFC 2616</a>] is used or the resource is retrieved from <a
href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">relevant
application caches</a> or local resources, this attribute must return value of
<a href="#domainlookup-end">domainLookupEnd</a>.</p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#connect-start">connectStart</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="connect-end-attribute"><code><dfn
id="connect-end">connectEnd</dfn></code> attribute </h4>

<p>This attribute must return the time immediately after the user agent finishes
establishing the connection to the server to retrieve the resource.
If a <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1">persistent
connection</a> [<a href='#rfc2616'>RFC 2616</a>] is used or the resource is retrieved from <a
href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">relevant
application caches</a> or local resources, this attribute must return the value of
<a href="#domainlookup-end">domainLookupEnd</a>.</p>

<p>If the transport connection fails and the user agent reopens a connection,
<a href="#connect-start">connectStart</a> and <a
href="#connect-end">connectEnd</a> should return the corresponding
values of the new connection. </p>

<p><a href="#connect-end">connectEnd</a> must include the time interval to
establish the transport connection. It must not include other time interval
such as SSL handshake and SOCKS authentication. </p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#connect-end">connectEnd</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="secureconnection-start-attribute"><code><dfn
id="secureconnection-start">secureConnectionStart</dfn></code> attribute </h4>


<p>This attribute is optional. User agents that don't have this attribute available must set it as undefined.
When this attribute is available, if the <a href="http://www.w3.org/TR/html5/urls.html#url-scheme">scheme</a>
of the current page is <a href="http://tools.ietf.org/html/rfc2817">HTTPS</a>, this attribute must return the
time immediately before the user agent starts the handshake process to secure the current connection. If the
secureConnectionStart attribute is available but HTTPS is not used, this attribute must return zero.</p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#secureconnection-start">secureConnectionStart</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="request-start-attribute"><code><dfn id="request-start">requestStart</dfn></code> attribute</h4>

<p>This attribute must return the time immediately before the user agent
starts requesting the resource from the server, or from
<a href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">
relevant application caches</a> or from local resources.</p>

<p>If the transport connection fails after a request is sent and the user
agent reopens a connection and resend the request, <a
href="#request-start">requestStart</a> must return the corresponding values
of the new request.</p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#request-start">requestStart</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="response-start-attribute"><code><dfn id="response-start">responseStart</dfn></code> attribute </h4>

<p>This attribute must return the time immediately after the user agent receives
the first byte of the response from the server, or from <a
href="http://www.whatwg.org/specs/web-apps/current-work/#relevant-application-cache">relevant
application caches</a> or from local resources.</p>

<p>
If the last non-redirected fetch of the resource is not the same origin as the current document,
<a href="#response-start">responseStart</a> must return
zero unless the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header rules apply.</p>

<h4 id="response-end-attribute"><code><dfn id="response-end">responseEnd</dfn></code> attribute </h4>

<p>This attribute must return the time immediately after the user agent finishes
receiving the last byte of the resource from from <a
href="http://www.whatwg.org/specs/web-apps/current-work/#relevant-application-cache">relevant
application caches</a> or from local resources.</p>

<h3 id="performance-resource-timing-methods"><span class="secno">4.5 </span>The Resource Timing Methods</h3>

<pre class="idl">
partial interface Performance {
  void clearResourceTimings();
  void setResourceTimingBufferSize (in unsigned long maxSize);

  attribute Function onresourcetimingbufferfull;
};</pre>

<div class="methods">
    <h4 id="rt-clearResourceTimings"><code>clearResourceTimings</code> method</h4>
	<p>The method <code>clearResourceTimings</code> clears the buffer used to store the current
    list of <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources.
    </p>
		<div class="parameters">
			<p><b>No parameters</b></p>
			<p><b>No return value</b></p>
			<p><b>No exceptions</b></p>
		</div>
</div>

<div class="methods">
	<h4 id="rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code> method</h4>
	<p>The <code>setResourceTimingBufferSize</code> method, when invoked, must set the maximum number of <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources that may be stored in
	the buffer to the value of the maxSize parameter.</p>
	<p>If this method is not called, the default maximum number of <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources stored must be 150, unless otherwise specified by the user agent.</p>
		<div class="parameters">
			<p><b>Parameters</b></p>
			in <code>maxSize</code> type of unsigned long
			<p>The maxSize parameter sets the maximum number of <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources that will be stored in the buffer.</p>
			<p><b>No return value</b></p>
			<p><b>No exceptions</b></p>
		</div>
</div>

<div class="methods">
	<h4 id="rt-onresourcetimingbufferfull"><code>onresourcetimingbufferfull</code> attribute</h4>
	<p>The callback onresourcetimingbufferfull is triggered when the buffer used to store the list of <a href="#performance-resource-timing">PerformanceResourceTiming</a> is full.
    The callback can be used to package existing <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources and
    clear the buffered <a href="#performance-resource-timing">PerformanceResourceTiming</a> list.
    While executing the onresourcetimingbufferfull callback, <a href="#performance-resource-timing">PerformanceResourceTiming</a> will continue to be collected beyond the maximum limit of the resources allowed in the
    <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface until one of the following occurs:
    <ol>
		<li>
            <a href="#rt-clearResourceTimings"><code>clearResourceTimings</code></a> is called - The <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntryList-interface">PerformanceEntryList</a>
            will begin with the n+1th item if it exists and the first n elements are released, where n is the maximum number of resources allowed in the <a href="#performance-resource-timing">PerformanceResourceTiming</a>
            interface. If the n+1th item does not exist, the buffer is cleared. The max length of the <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntryList-interface">PerformanceEntryList</a>
            does not change unless otherwise specified by <a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a>.
        </li>
		<li><a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a> is called - The <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntryList-interface">PerformanceEntryList</a> will extend and / or truncate to the buffer size specified.</li>
		<li>
            Neither <a href="#rt-clearResourceTimings"><code>clearResourceTimings</code></a> or
            <a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a> is called during the execution of the onresourcetimingbufferfull callback
            - no updates are made to the <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntryList-interface">PerformanceEntryList</a>.</li>
    </ol>
</div>

<h3 id="cross-origin-resources">4.6 Cross-origin Resources</h3>
    <p>
        Information from cross-origin resources must be included in the
        <a href="#performance-resource-timing">PerformanceResourceTiming</a> interface. In the absence of the
        <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header,
        these attributes must be set to zero: <a href="#redirect-start">redirectStart</a>, <a href="#redirect-end">redirectEnd</a>,
        <a href="#domainlookup-start">domainLookupStart</a>, <a href="#domainlookup-end">domainLookupEnd</a>, <a href="#connect-start">connectStart</a>,
        <a href="#connect-end">connectEnd</a>, <a href="#request-start">requestStart</a>, <a href="#response-start">responseStart</a>,
        and <a href="#response-end">responseEnd</a>.
    </p>
    <p>
        The terms <dfn id="origin">origin</dfn> and <dfn id="same-origin">same origin</dfn>
        are defined by The HTTP Origin Header. <a href="#ref-origin">[ORIGIN]</a>
    </p>
    <p>
        The term <dfn id="cross-origin">cross-origin</dfn> is used to mean non
        <a href="#same-origin">same origin</a>.
    </p>
    <p>
        Server-side applications may return the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header
        to allow the User Agent to fully expose, to the document origin(s) specified, the
        values of attributes that would have been zero due to the cross-origin
        restrictions previously specified in this section. </p>
    <h4 id="timing-allow-origin"><code>Timing-Allow-Origin</code> Response Header</h4>
    <div class="parameters">
        <p>The <dfn id="http-access-control-allow-origin"><code>Timing-Allow-Origin</code></dfn> header indicates whether a resource's timing can be
            shared based by returning the value of the Origin request header in the
            response. ABNF:</p>
        <pre>Timing-Allow-Origin = &quot;Timing-Allow-Origin&quot; &quot;:&quot; origin-list-or-null | &quot;*&quot;</pre>
        <p>
            <code>origin-list-or-null</code> is defined by The HTTP Origin Header. <a href="#ref-origin">
            [ORIGIN]</a>
        </p>
    </div>

<h3 id="vendor-prefixes">4.7 Vendor Prefixes</h3>

<p>Vendor-specific proprietary user agent extensions to this specification are strongly discouraged.
If such extensions are needed, e.g. for experimental purposes, vendors must use the following extension mechanisms:</p>

<p>If the extension to be added is an INITIATOR <a href="#initiatorType-attribute">initiatorType</a>, the INITIATOR <a href="#initiatorType-attribute">initiatorType</a> must:</p>
<ul>
    <li>Follow this naming convention: INITIATOR_[VENDORPREFIX]_[TYPE], where [VENDORPREFIX] is a name that identifies the vendor.</li>
    <li>Have a value in the range of 100 to 200.</li>
</ul>

<p>If the extension is a new timing attribute, it must:</p>
<ul>
    <li>Follow this naming convention: [vendorPrefix]TimeName, where [vendorPrefix] is a
        name that identifies the vendor and TimeName identifies the name given to the
        timing attribute. </li>
    <li>Use a monotonically increasing clock, as defined in Section 5.2 <a href="#monotonic-clock">Monotonic Clock</a>.</li>
    <li>Be measured in milliseconds since midnight of January 1, 1970 (UTC), as defined in Section 3 <a href="#terminology">Terminology</a>.
</ul>

<h2 id="process"><span class="secno">5 </span>Process</h2>
<h3 id="processing-model"><span class="secno">5.1 </span>Processing Model</h3>

<p>Illustration</p>

<p>This section is non-normative.</p>

<p>The following graph illustrates the timing attributes defined by the PerformanceResourceTiming interface. Attributes underlined may not be available when fetching resources from different <a href="#same-origin">origins</a>. User agents may perform internal processing in between timings, which allow for non-normative intervals between timings.</p>

<p><img width="85%" src="resource-timing-overview.png" alt='Resource Timing attributes'></p>

<ol>
  <li>Once <a href="http://www.w3.org/TR/html5/history.html#create-a-document-object">Window object of
  the current document is created</a>, the user agent must create a <a href="http://www.w3.org/TR/performance-timeline/#pt-performanceEntryList-interface">PerformanceEntryList</a>
  <i>primary buffer</i> object to store the list
  of <a href="#performance-resource-timing">PerformanceResourceTiming</a> resources.</li>
  <li>Set the <i>primary buffer</i> to a size of 150, unless otherwise specified
  by the user agent or set by the <a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a> method.
  </li>
  <li>For each resource fetched by the current browsing context, perform the following steps:
  <ol>
      <li id="step-create-object">Create a new <a href="#performance-resource-timing">PerformanceResourceTiming</a> object and
      set <a href="#entryType-attribute">entryType</a> to <a href="#perf-resource"><code>PERF_RESOURCE</code></a>.
      </li>
      <li>Immediately before the user agent starts to queue the resource for retrieval,
       record the current time in <a href="#startTime-attribute">startTime</a>.
      </li>
      <li>Record the initiator of the resource in <a href="#initiatorType-attribute">initiatorType</a>.
      </li>
      <li>Record the resolved <a href="http://www.w3.org/TR/html5/urls.html#resolve-a-url">URL</a> of the requested resource in <a href="#name-attribute">name</a>.
      </li>
      <li id="step-fetch-start">If the new resource is to be fetched using HTTP GET
       <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes"> or equivalent</a>,
       immediately before a user agent checks with the <a href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">
       relevant application caches</a>, record the current time as <a href="#fetch-start">fetchStart</a>. Otherwise, immediately
       before a user agent starts the <a href="http://www.w3.org/TR/html5/fetching-resources.html#fetching-resources">
       fetching process</a>, record the current time as <a href="#fetch-start">
       fetchStart</a>. Let
     <a href="#domainlookup-start">domainLookupStart</a>,
     <a href="#domainlookup-end">domainLookupEnd</a>,
     <a href="#connect-start">connectStart</a> and
     <a href="#connect-end">connectEnd</a> be the same value as
     <a href="#fetch-start">fetchStart</a>.
      </li>
      <li id="step-collection-start">If the resource is not to be fetched from the
          networking layer, such as being fetched from an in-memory cache, abort the
          following steps.
      </li>
      <li>If fetching the resource is aborted for any reason, abort the following steps.       </li>
      <li>If the last non-redirected fetch of the resource is not the same origin as the current document
      and the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header does not apply, the user agent
      must set
      <a href="#redirect-start">redirectStart</a>,
      <a href="#redirect-end">redirectEnd</a>,
      <a href="#domainlookup-start">domainLookupStart</a>,
      <a href="#domainlookup-end">domainLookupEnd</a>,
      <a href="#connect-start">connectStart</a>,
      <a href="#connect-end">connectEnd</a>,
      <a href="#request-start">requestStart</a>,
      <a href="#response-start">responseStart</a>,
      <a href="#response-end">responseEnd</a>,
      and <a href="#duration-attribute">duration</a> to zero and abort the following steps.
      </li>
        <li>Let <a href="#domainlookup-start">domainLookupStart</a>,
       <a href="#domainlookup-end">domainLookupEnd</a>,
       <a href="#connect-start">connectStart</a> and
       <a href="#connect-end">connectEnd</a> be the same value as
       <a href="#fetch-start">fetchStart</a>.</li>
      <li>If the resource is fetched from the <a href="http://www.w3.org/TR/html5/offline.html#relevant-application-cache">
       relevant application cache</a> or local resources, including the <a
       href="http://www.ietf.org/rfc/rfc2616.txt">HTTP</a> cache,
     go to step <a href="#step-request-start">3.15</a>.
      </li>
      <li>If no domain lookup is required, go to step <a href="#step-connect-start">3.13</a>. Otherwise, immediately before a user agent
       starts the domain name lookup, record the time as <a href="#domainlookup-start">domainLookupStart</a>.</li>
      <li>Record the time as <a href="#domainlookup-end">domainLookupEnd</a> immediately after the
       domain name lookup is successfully done. A user agent may need multiple retries before that. If
       the domain lookup fails, abort the following steps. </li>
      <li id="step-connect-start">If a persistent transport connection is used to fetch the resource,
       let <a href="#connect-start">connectStart</a> and <a href="#connect-end">connectEnd</a>
       be the same value of <a href="#domainlookup-end">domainLookupEnd</a>. Otherwise, record the time as
       <a href="#connect-start">connectStart</a> immediately before initiating the connection to the server
       and record the time as <a href="#connect-end">connectEnd</a> immediately after the connection to the
       server or the proxy is established. A user agent may need multiple retries
       before this time. If a connection can not be established, abort the following steps.
      </li>
      <li>If the user agent supports the <a href="#secureconnection-start">secureConnectionStart</a> attribute,
      in step <a href="#step-connect-start">3.13</a>, a user agent should also carry out these additional steps:
        <ol>
        <li>If the scheme of the current resource is HTTPS, the user agent must record the
         time as <a href="#secureconnection-start">secureConnectionStart</a>
         immediately before the handshake process to secure the connection.
        </li>
        <li>If the scheme of the current resource is not HTTPS, the user agent must set the
        value of <a href="#secureconnection-start">secureConnectionStart</a> to 0.
        </li>
        </ol>
      </li>
      <li id="step-request-start">Immediately before a user agent starts sending the request
      for the resource, record the current time as <a href="#request-start">requestStart</a>.
      </li>
      <li id="step-response-start">Record the time as <a href="#response-start">
      responseStart</a> immediately after the user agent receives the first byte of the response.
      </li>
      <li id="step-response-end">Record the time as <a href="#response-end">responseEnd</a>
      immediately after receiving the last byte of the response.
        <p>Return to step <a href="#step-connect-start">3.13</a> if the user agent fails to send the request
        or receive the entire response, and needs to reopen the connection.</p>

        <div class="example">
        <div class="exampleHeader">Example</div>
        <p>When <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1"> persistent connection</a>
        [<a href='#rfc2616'>RFC 2616</a>] is enabled, a user agent may first try to re-use an open connect to
        send the request while the connection can be <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html#sec8.1.4">asynchronously
        closed</a>. In such case, <a href="#connect-start">connectStart</a>, <a href="#connect-end">connectEnd</a> and
        <a href="#request-start">requestStart</a> should represent timing information collected over the re-open connection. </p>
        </div>
      </li>
      <li>Record the difference between <a href="#response-end">responseEnd</a> and <a href="#startTime-attribute">startTime</a> in <a href="#duration-attribute">duration</a>.</li>
      <li>If the fetched resource results in an HTTP redirect
      <a href="http://www.w3.org/TR/html5/fetching-resources.html#concept-http-equivalent-codes"> or equivalent</a>, then
      <ol style="list-style-type:lower-alpha;">
            <li>If the current resource and the resource that is redirected to are not from the
             <a href="http://www.w3.org/TR/html5/origin-0.html#origin">same origin</a>, set <a href="#redirect-start">
             redirectStart</a> and <a href="#redirect-end">redirectEnd</a> to 0. Then, return to step <a href="#step-fetch-start">
             3.5</a> with the new resource.
	        </li>
            <li>If the value of redirectStart is not set, let it be the value of fetchStart.
            </li>
            <li>Let redirectEnd be the value of responseEnd.
            </li>
            <li>Set all the attributes in the <a href="#performance-resource-timing">
             PerformanceResourceTiming</a> object to 0 except
             <a href="#startTime-attribute">startTime</a>,
             <a href="#redirect-start">redirectStart</a>, <a href="#redirect-end"> and
             redirectEnd</a>, <a href="#initiatorType-attribute">initiatorType</a>.
            </li>
            <li>Return to step <a href="#step-fetch-start">3.5</a> with the new resource.
            </li>
        </ol>
      </li>
      <li>If the <i>primary buffer</i> is full, the callback <a href="#rt-onresourcetimingbufferfull"><code>onresourcetimingbufferfull</code></a>
          must be triggered.<ol>
            <li>Create a <i>temporary buffer</i> of <a href="#performance-resource-timing">PerformanceResourceTiming</a> objects.
            </li>
            <li>Add the current resource to the <i>temporary buffer</i>.
            </li>
            <li>If there are additional resources that are collected during the <a href="#rt-onresourcetimingbufferfull"><code>onresourcetimingbufferfull</code></a>
            callback, add them to the <i>temporary buffer</i>.
            </li>
            <li>
            If the <a href="#rt-clearResourceTimings"><code>clearResourceTimings</code></a> method is called in the <a href="#rt-onresourcetimingbufferfull"><code>onresourcetimingbufferfull</code></a> callback,
            clear all <a href="#performance-resource-timing">PerformanceResourceTiming</a> objects in the <i>primary buffer</i>.
            Copy all <a href="#performance-resource-timing">PerformanceResourceTiming</a> objects in the <i>temporary buffer</i> to the
            <i>primary buffer</i>.
            </li>
            <li>
            If the <a href="#rt-setResourceTimingBufferSize"><code>setResourceTimingBufferSize</code></a> method is called in the <a href="#rt-onresourcetimingbufferfull"><code>onresourcetimingbufferfull</code></a> callback,
            set the maximum size of the <i>primary buffer</i> to the maxSize parameter. If the maxSize parameter is larger than the previous size of the <i>primary buffer</i>,
            append <a href="#performance-resource-timing">PerformanceResourceTiming</a> objects in the <i>temporary buffer</i> to the <i>primary buffer</i> up to the maxSize parameter.
            </li>
		    <li>Discard the <i>temporary buffer</i>.
		    </li>
        </ol>
      </li>
      <li>If the <i>primary buffer</i> is not full, add the <a href="#performance-resource-timing">PerformanceResourceTiming</a> object,
      created in step <a href="#step-create-object">3.1</a>, to the <i>primary buffer</i>.
      </li>
      <li id="step-collection-end">If there are additional resources, return to step <a href="#step-collection-start">3.1</a>.
      </li>
  </ol>
  </li>
</ol>

<h3 id="monotonic-clock"><span class="secno">5.2 </span>Monotonic Clock</h3>
<p>The value of the timing attributes must monotonically increase to ensure timing attributes are not
skewed by adjustments to the system clock during the navigation. The difference between any two chronologically
recorded timing attributes must never be negative. The user agent must record the system clock at the beginning
of the navigation and define subsequent timing attributes in terms of a monotonic clock measuring time elapsed
from the beginning of the navigation.
</p>

<h2 id="privacy"><span class="secno">6 </span>Privacy</h2>

<p>This section is non-normative.</p>

<p>When giving various timing information of how a resource is requested and
process, the <a href="#performance-resource-timing">ResourceTiming</a> interface potentially
exposes such information to any page that has this resource included. To
limit the access to the ResourceTiming interface, the <a
href="http://www.w3.org/TR/html5/origin-0.html#origin">same origin</a>
policy is enforced by default. Additionally, resource providers can
explicitely allow timing information to be collected over a resource by
adding the <a href="#timing-allow-origin">Timing-Allow-Origin</a> HTTP response header, which specifies the
domains that are allowed to access the timing information. </p>

<h2 id="security"><span class="secno">7 </span>Security</h2>

<p>This section is non-normative.</p>

<p>Similar to the discussion in the Privacy section. </p>

<h2 class="no-num" id="acknowledgements">Acknowledgements</h2>

<p>We would like to sincerely thank Karen Anderson, Darin Fisher, Tony Gentilcore,
Nic Jansma, Arvind Jain, Kyle Scholz, Jonas Sicking, James Simonsen, Steve Souders,
Annie Sullivan, Sigbjørn Vik, Jason Weber to acknowledge their contributions to this work.</p>

<h2 class="no-num" id=references>References</h2>

<dl>
   <dt><a name="rfc2119" id="rfc2119">[IETF RFC 2119]</a></dt>
   <dd>
    <cite><a href="http://www.ietf.org/rfc/rfc2119.txt">Key words for use in RFCs to Indicate Requirement Levels</a></cite>,
    Scott Bradner, Author. Internet Engineering Task Force, March 1997. Available at
    http://www.ietf.org/rfc/rfc2119.txt.
   </dd>

   <dt id="ref-origin">[ORIGIN]</dt>
   <dd><cite><a href="http://tools.ietf.org/html/draft-abarth-origin">The
   Web Origin Concept</a></cite>, A. Barth, Author. Internet
   Engineering Task Force, November 2010. Available at
    http://tools.ietf.org/html/draft-abarth-origin.
   </dd>

   <dt><a name="rfc2616" id="rfc2616">[IETF RFC 2616]</a></dt>
   <dd><cite><a href="http://www.ietf.org/rfc/rfc2616.txt">Hypertext Transfer Protocol -- HTTP/1.1</a></cite>,
    R. Fielding et al., Authors. Internet Engineering Task Force, June 1999. Available at
    http://www.ietf.org/rfc/rfc2616.txt.
   </dd>

    <dt>[<a name="DOM3Core" id='DOM3Core'>DOM Level 3 Core</a>]</dt>
    <dd>
     <cite><a href="http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/">Document Object Model Level 3 Core
     Specification</a></cite>, A. Le Hors, et al., Editors. World
     Wide Web Consortium, 7 April 2004. This version of the Document
     Object Model Level 3 Core Recommendation is
     http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407. The <a class="normative" href="http://www.w3.org/TR/domcore/">latest version of
     DOM Core</a> is available at
     http://www.w3.org/TR/domcore/.
    </dd>

    <dt>[<a name="ECMA262" id="ECMA262">ECMA-262</a>]</dt>
    <dd>
     <cite><a href='http://www.ecma-international.org/publications/standards/Ecma-262.htm'>ECMAScript Language Specification</a></cite>, 5<sup>th</sup>
     Edition. ECMA International, Standard
     ECMA-262, December 2009. This version of the ECMAScript
     Language is available from http://www.ecma-international.org/publications/standards/Ecma-262.htm.
    </dd>

    <dt>[<a name="XHR" id="XHR">XMLHttpRequest</a>]</dt>
    <dd>
     <cite><a href='http://www.w3.org/TR/2010/CR-XMLHttpRequest-20100803/'>XMLHttpRequest</a></cite>,
     Anne van Kesteren, Editor. World Wide Web Consortium, August
     2010. This version of the XMLHttpRequest Candidate Recommendation
     is
     http://www.w3.org/TR/2010/CR-XMLHttpRequest-20100803/. The <a class="normative"
     href="http://www.w3.org/TR/XMLHttpRequest/">latest version of
     XMLHttpRequest</a> is available at
     http://www.w3.org/TR/XMLHttpRequest/.
    </dd>
   <dt>[<a name="HTML5" id="HTML5">HTML5</a>]</dt>
   <dd><cite><a href='http://www.w3.org/TR/html5/'>HTML5</a></cite>, Ian Hickson, Editor. World Wide Web Consortium, May 2011. This version of the HTML5 is available from <a href='http://www.w3.org/TR/html5/'>http://www.w3.org/TR/html5/</a>. The <a href='http://dev.w3.org/html5/spec/'>latest editor's draft</a> is available at http://dev.w3.org/html5/spec/.</dd>
   <dt>[<a name="SVG" id="SVG">SVG</a>]</dt>
   <dd><cite><a href='http://www.w3.org/TR/2011/WD-SVG11-20110512/'>Scalable Vector Graphics (SVG) 1.1</a></cite>, Erik Dahlstr&#246;m, et al, Editors. World Wide Web Consortium, May 2011. This version of the SVG specification is available from <a href='http://www.w3.org/TR/2011/WD-SVG11-20110512/'>http://www.w3.org/TR/2011/WD-SVG11-20110512/</a>. The <a href='http://www.w3.org/TR/SVG/'>latest version of SVG</a> is available at http://www.w3.org/TR/SVG/.</dd>

   <dt>[<a name="NavigationTiming" id="NavigationTiming">Navigation Timing</a>]</dt>
   <dd><cite><a href='http://www.w3.org/TR/2011/CR-navigation-timing-20110602/'>Navigation Timing</a></cite>, Zhiheng Wang, Editor. World Wide Web Consortium, June 2011. This version of the Navigation Timing specification is available from http://www.w3.org/TR/2011/CR-navigation-timing-20110602/. The <a href='http://www.w3.org/TR/navigation-timing/'>latest version of Navigation Timing</a> is available at http://www.w3.org/TR/navigation-timing/.</dd>

   <dt>[<a name="PerformanceTimeline" id="PerformanceTimeline">Performance Timeline</a>]</dt>
   <dd><cite><a href='http://www.w3.org/TR/2011/WD-performance-timeline-20110811/'>Performance Timeline</a></cite>, Jatinder Mann, et al, Editors. World Wide Web Consortium, July 2011. This version of the Performance Timline specification is available from <a href='http://www.w3.org/TR/2011/WD-performance-timeline-20110811/'>http://www.w3.org/TR/2011/WD-performance-timeline-20110811/</a>. The <a href='http://www.w3.org/TR/performance-timeline/'>latest version of Performance Timeline</a> is available at http://www.w3.org/TR/performance-timeline/.</dd>

   <dt>[<a name="WebIDL" id="WebIDL">Web IDL</a>]</dt>
   <dd><cite><a href='http://www.w3.org/TR/2011/WD-WebIDL-20110712/'>Web IDL</a></cite>, Cameron McCormack, Editor. World Wide Web Consortium, July 2011. This version of the Web IDL specification is available from http://www.w3.org/TR/2011/WD-WebIDL-20110712/. The <a href='http://www.w3.org/TR/WebIDL/'>latest version of Web IDL</a> is available at http://www.w3.org/TR/WebIDL/.</dd>
</dl>

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