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dap commit: Add WD.

From: Mercurial notifier <cvsmail@w3.org>
Date: Fri, 23 Nov 2012 17:03:43 +0000
Message-Id: <E1TbwfH-000648-VT@mcbain.w3.org>
To: public-dap-commits@w3.org
changeset:   286:92a648fdcd25
tag:         tip
user:        Mounir Lamouri <mounir.lamouri@gmail.com>
date:        Fri Nov 23 17:01:32 2012 +0000
files:       network-api/published/20121123.html
description:
Add WD.


diff -r aafd460349e1 -r 92a648fdcd25 network-api/published/20121123.html
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/network-api/published/20121123.html	Fri Nov 23 17:01:32 2012 +0000
@@ -0,0 +1,851 @@
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+</style><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet"><!--[if lt IE 9]><script src='http://www.w3.org/2008/site/js/html5shiv.js'></script><![endif]--></head>
+
+  <body><div class="head">
+  <p>
+    
+      <a href="http://www.w3.org/"><img src="http://www.w3.org/Icons/w3c_home" alt="W3C" height="48" width="72"></a>
+    
+  </p>
+  <h1 class="title" id="title">The Network Information API</h1>
+  
+  <h2 id="w3c-working-draft-23-november-2012"><abbr title="World Wide Web Consortium">W3C</abbr> Working Draft 23 November 2012</h2>
+  <dl>
+    
+      <dt>This version:</dt>
+      <dd><a href="http://www.w3.org/TR/2012/WD-netinfo-api-20121123/">http://www.w3.org/TR/2012/WD-netinfo-api-20121123/</a></dd>
+      <dt>Latest published version:</dt>
+      <dd><a href="http://www.w3.org/TR/netinfo-api/">http://www.w3.org/TR/netinfo-api/</a></dd>
+    
+    
+      <dt>Latest editor's draft:</dt>
+      <dd><a href="http://dvcs.w3.org/hg/dap/raw-file/tip/network-api/Overview.html">http://dvcs.w3.org/hg/dap/raw-file/tip/network-api/Overview.html</a></dd>
+    
+    
+    
+    
+    
+      <dt>Previous version:</dt>
+      <dd><a href="http://www.w3.org/TR/2011/WD-netinfo-api-20110607/">http://www.w3.org/TR/2011/WD-netinfo-api-20110607/</a></dd>
+    
+    
+    <dt>Editor:</dt>
+    <dd><span>Mounir Lamouri</span>, <a href="http://mozilla.org/">Mozilla</a></dd>
+
+    
+  </dl>
+  
+  
+  
+  
+    
+      <p class="copyright">
+        <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 
+        2012
+        
+        <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>), All Rights Reserved.
+        <abbr title="World Wide Web Consortium">W3C</abbr> <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>
+    <section class="introductory" id="abstract"><h2>Abstract</h2><p>
+      The Network Information API provides an interface for web applications to
+      access the underlying connection information of the device.
+    </p></section><section id="sotd" class="introductory"><h2>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 <abbr title="World Wide Web Consortium">W3C</abbr> publications and the latest revision
+          of this technical report can be found in the <a href="http://www.w3.org/TR/"><abbr title="World Wide Web Consortium">W3C</abbr> technical reports
+          index</a> at http://www.w3.org/TR/.</em>
+        </p>
+        
+      <p>
+        The functionality described in this specification was initially specified as part of the
+        <a href="http://www.w3.org/TR/system-info-api/">System Information API</a> but has been
+        extracted in order to be more readily available, more straightforward to implement, and
+        in order to produce a specification that could be implemented on its own merits without
+        interference with other, often unrelated, features.
+      </p>
+    
+        <p>
+          This document was published by the <a href="http://www.w3.org/2009/dap/">Device APIs and Policy Working Group</a> as a Working Draft.
+          
+            This document is intended to become a <abbr title="World Wide Web Consortium">W3C</abbr> Recommendation.
+          
+          If you wish to make comments regarding this document, please send them to 
+          <a href="mailto:public-device-apis@w3.org">public-device-apis@w3.org</a> 
+          (<a href="mailto:public-device-apis-request@w3.org?subject=subscribe">subscribe</a>,
+          <a href="http://lists.w3.org/Archives/Public/public-device-apis/">archives</a>).
+          
+          
+          All feedback is welcome.
+        </p>
+        
+          <p>
+            Publication as a Working Draft does not imply endorsement by the <abbr title="World Wide Web Consortium">W3C</abbr> 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 <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
+          
+          
+          
+            
+              <abbr title="World Wide Web Consortium">W3C</abbr> maintains a <a href="http://www.w3.org/2004/01/pp-impl/43696/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 <abbr title="World Wide Web Consortium">W3C</abbr> Patent Policy</a>.
+          
+          
+        </p>
+        
+      
+    
+  
+</section><section id="toc"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a class="tocxref" href="#introduction"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#use-cases"><span class="secno">1.1 </span>Use Cases</a></li><li class="tocline"><a class="tocxref" href="#outstanding-issues"><span class="secno">1.2 </span>Outstanding issues</a></li></ul></li><li class="tocline"><a class="tocxref" href="#conformance"><span class="secno">2. </span>Conformance</a></li><li class="tocline"><a class="tocxref" href="#terminology"><span class="secno">3. </span>Terminology</a></li><li class="tocline"><a class="tocxref" href="#security-and-privacy-considerations"><span class="secno">4. </span>Security and privacy considerations</a></li><li class="tocline"><a class="tocxref" href="#the-networkinformation-interface"><span class="secno">5. </span>The <span class="formerLink"><code>NetworkInformation</code></span> interface</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#attributes"><span class="secno">5.1 </span>Attributes</a></li></ul></li><li class="tocline"><a class="tocxref" href="#the-connection-interface"><span class="secno">6. </span>The <span class="formerLink"><code>Connection</code></span> interface</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#attributes-1"><span class="secno">6.1 </span>Attributes</a></li><li class="tocline"><a class="tocxref" href="#event-handlers"><span class="secno">6.2 </span>Event handlers</a></li></ul></li><li class="tocline"><a class="tocxref" href="#examples"><span class="secno">7. </span>Examples</a></li><li class="tocline"><a class="tocxref" href="#acknowledgments"><span class="secno">A. </span>Acknowledgments</a></li><li class="tocline"><a class="tocxref" href="#references"><span class="secno">B. </span>References</a><ul class="toc"><li class="tocline"><a class="tocxref" href="#normative-references"><span class="secno">B.1 </span>Normative references</a></li></ul></li></ul></section>
+
+    
+
+    <section id="introduction" class="informative">
+      <!--OddPage--><h2><span class="secno">1. </span>Introduction</h2><p><em>This section is non-normative.</em></p>
+      <p>
+        The Network Information API provides an interface enabling web applications to access the underlying
+        connection information of the device.
+      </p>
+
+      <section id="use-cases">
+        <h3><span class="secno">1.1 </span>Use Cases</h3><p><em>This section is non-normative.</em></p>
+        <p>
+          The main use case of the Network Information API is to allow
+          applications to be gentle with the user's bandwidth when they know it
+          is rare or expensive. Even if there are not many applications that do
+          this currently, this specification offers the the tools needed to
+          enable this, allowing it to become more common.
+        </p>
+        <p>
+          A few hypothetical examples would be:
+          </p><ul>
+            <li>An image viewer showing very low resolution thumbnails when the
+              user has a low bandwidth or a metered connection. 
+            </li><li>A video game loading low textures when the user has a low
+              bandwidth or a metered connection.</li>
+            <li>An email client downloading only headers or even asking the user
+              to download headers when he/she has a low bandwidth or a metered
+              connection.</li>
+            <li>Any app trying to aggressively cache any downloaded asset when
+              the user has a low bandwidth or a metered connection.</li>
+          </ul>
+        <p></p>
+      </section>
+
+      <section id="outstanding-issues">
+        <h3><span class="secno">1.2 </span>Outstanding issues</h3>
+        <p>
+          The specification currently requests the <a class="internalDFN" href="#dfn-user-agent">user agent</a> to expose
+          two properties: <code>bandwidth</code> and <code>metered</code>. The
+          working group currently does not have consensus on these.
+        </p>
+        <p>
+          One concern is that <code>bandwidth</code> may be hard to implement,
+          can be quite power-consuming to keep up-to-date and its value might be
+          unrelated to the actual connection quality that could be affected by
+          the server.<br>
+          A solution to fix this would be to return non absolute values that
+          couldn't be easily abused and would be more simple to produce for the
+          <a class="internalDFN" href="#dfn-user-agent">user agent</a>. For example, having a set of values like
+          <code>very-slow</code>, <code>slow</code>, <code>fast</code> and
+          <code>very-fast</code>. Another solution would be to have only values
+          like <code>very-slow</code>, <code>slow</code> and the empty string."
+        </p>
+        <p>
+          <code>metered</code> may also be hard to implement as there is
+          currently no standard way for the OS to know if the current connection
+          is metered.  The approach of the specification is to leave the
+          implementation details to the <a class="internalDFN" href="#dfn-user-agent">user agent</a>. That way, the
+          attribute could return a value based on a heuristic, on knowledge of
+          the current connection status or even by directly asking the user for
+          the information.<br>
+          It is interesting to point that Android 4.1 and Windows 8 both have a
+          way to check if the current connection is metered. Android is using a
+          boolean (isActiveNetworkMetered()) while Windows 8 allow the developer
+          to ask for different information (NetworkCostType,
+          ApproachingDataLimit, OverDataLimit, Roaming).
+          <!--
+            Android: https://developer.android.com/reference/android/net/ConnectivityManager.html#isActiveNetworkMetered%28%29
+            Windows: http://msdn.microsoft.com/en-us/library/windows/apps/hh465399.aspx#adapt
+          -->
+        </p>
+      </section>
+    </section>
+
+    <section id="conformance"><!--OddPage--><h2><span class="secno">2. </span>Conformance</h2>
+<p>
+  As well as sections marked as non-normative, all authoring guidelines, diagrams, examples,
+  and notes in this specification are non-normative. Everything else in this specification is
+  normative.
+</p>
+<p>
+  The key words <em title="must" class="rfc2119">must</em>, <em title="must not" class="rfc2119">must not</em>, <em title="required" class="rfc2119">required</em>, <em title="should" class="rfc2119">should</em>, <em title="should not" class="rfc2119">should not</em>, <em title="recommended" class="rfc2119">recommended</em>, <em title="may" class="rfc2119">may</em>,
+  and <em title="optional" class="rfc2119">optional</em> in this specification are to be interpreted as described in [<cite><a href="#bib-RFC2119" class="bibref">RFC2119</a></cite>].
+</p>
+
+      <p>
+        This specification defines conformance criteria that apply to a single
+        product: the <dfn id="dfn-user-agent">user agent</dfn> that implements the interfaces that
+        it contains.
+      </p>
+      <p>
+        Implementations that use ECMAScript to expose the APIs defined in this specification must implement them in a manner
+        consistent with the ECMAScript Bindings defined in the Web IDL specification [<cite><a href="#bib-WEBIDL" class="bibref">WEBIDL</a></cite>].
+      </p>
+    </section>
+
+    <section id="terminology">
+      <!--OddPage--><h2><span class="secno">3. </span>Terminology</h2>
+      <p>
+        The <code><a href="http://dev.w3.org/html5/spec/webappapis.html#function">
+        Function</a></code> interface represents a function in the scripting
+        language being used as defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+      <p>
+        The concepts <dfn id="dfn-queue-a-task"><a href="http://dev.w3.org/html5/spec/webappapis.html#queue-a-task">
+        queue a task</a></dfn> and
+        <dfn id="dfn-fire-a-simple-event"><a href="http://dev.w3.org/html5/spec/webappapis.html#fire-a-simple-event">
+        fire a simple event</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+
+      <p>
+        The terms <dfn id="dfn-event-handlers"> <a href="http://dev.w3.org/html5/spec/webappapis.html#event-handlers">
+        event handlers</a></dfn> and
+        <dfn id="dfn-event-handler-event-types"><a href="http://dev.w3.org/html5/spec/webappapis.html#event-handler-event-type">
+        event handler event types</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+
+      <p>
+        The concepts of <dfn id="dfn-browsing-context"><a href="http://dev.w3.org/html5/spec/browsers.html#browsing-context">
+        browsing context</a></dfn> and
+        <dfn id="dfn-active-document"><a href="http://dev.w3.org/html5/spec/browsers.html#active-document">
+        active document</a></dfn> are defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+
+      <p>
+        The concept of document <dfn id="dfn-domain"><a href="http://dev.w3.org/html5/spec/origin-0.html#the-document-s-domain">
+        domain</a></dfn> is defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+    </section>
+
+    <section id="security-and-privacy-considerations">
+      <!--OddPage--><h2><span class="secno">4. </span>Security and privacy considerations</h2>
+      <p>
+        The API defined in this specification is used to determine the connection information
+        of the hosting device. The information disclosed has minimal
+        impact on privacy or fingerprinting, and therefore is exposed without
+        permission grants. For example, authors cannot directly know what kind of connection
+        is currently in use by the hosting device.
+      </p>
+    </section>
+
+    <section id="the-networkinformation-interface">
+      <!--OddPage--><h2><span class="secno">5. </span>The <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface</h2>
+      <p>
+        The <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface is exposed on the 
+        <code>Navigator</code> object.
+      </p>
+      <pre class="idl"><span class="idlImplements"><a>Navigator</a> implements <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a>;</span></pre><div class="idlImplementsDesc"><p>All instances of the <code><a>Navigator</a></code> type are defined to also implement the <a class="idlType" href="#idl-def-NetworkInformation"><code>NetworkInformation</code></a> interface.</p></div>
+      <pre class="idl"><span class="idlInterface" id="idl-def-NetworkInformation">[<span class="extAttr">NoInterfaceObject</span>]
+interface <span class="idlInterfaceID">NetworkInformation</span> {
+<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a class="idlType" href="#idl-def-Connection"><code>Connection</code></a></span> <span class="idlAttrName"><a href="#widl-NetworkInformation-connection">connection</a></span>;</span>
+};</span></pre><section id="attributes"><h3><span class="secno">5.1 </span>Attributes</h3><dl class="attributes"><dt id="widl-NetworkInformation-connection"><code>connection</code> of type <span class="idlAttrType"><a class="idlType" href="#idl-def-Connection"><code>Connection</code></a></span>, readonly</dt><dd>
+          The object from which connection information is accessed.
+        </dd></dl></section>
+    </section>
+
+    <section id="the-connection-interface">
+      <!--OddPage--><h2><span class="secno">6. </span>The <a class="idlType" href="#idl-def-Connection"><code>Connection</code></a> interface</h2>
+      <p>
+        The <a class="idlType" href="#idl-def-Connection"><code>Connection</code></a> interface provides a handle to the device's connection information.
+      </p>
+      <pre class="idl"><span class="idlInterface" id="idl-def-Connection">[<span class="extAttr">NoInterfaceObject</span>]
+interface <span class="idlInterfaceID">Connection</span> : <span class="idlSuperclass"><a>EventTarget</a></span> {
+<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>double</a></span>    <span class="idlAttrName"><a href="#widl-Connection-bandwidth">bandwidth</a></span>;</span>
+<span class="idlAttribute">    readonly attribute <span class="idlAttrType"><a>boolean</a></span>   <span class="idlAttrName"><a href="#widl-Connection-metered">metered</a></span>;</span>
+<span class="idlAttribute">    [<span class="extAttr">TreatNonCallableAsNull</span>]
+             attribute <span class="idlAttrType"><a>Function</a>?</span> <span class="idlAttrName"><a href="#widl-Connection-onchange">onchange</a></span>;</span>
+};</span></pre><section id="attributes-1"><h3><span class="secno">6.1 </span>Attributes</h3><dl class="attributes"><dt id="widl-Connection-bandwidth"><code>bandwidth</code> of type <span class="idlAttrType"><a>double</a></span>, readonly</dt><dd>
+          The <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> set the value of the <code>bandwidth</code> attribute to:
+          <ul>
+            <li>0 if the user is currently offline;</li>
+            <li>Infinity if the bandwidth is unknown;</li>
+            <li>an estimation of the current bandwidth in MB/s (Megabytes per seconds) available for communication with the
+                <a class="internalDFN" href="#dfn-browsing-context">browsing context</a> <a class="internalDFN" href="#dfn-active-document">active document</a>'s <a class="internalDFN" href="#dfn-domain">domain</a>.
+            </li>
+          </ul>
+        </dd><dt id="widl-Connection-metered"><code>metered</code> of type <span class="idlAttrType"><a>boolean</a></span>, readonly</dt><dd>
+          <p>
+            A connection is <dfn id="dfn-metered">metered</dfn> when the user's connection is subject to a limitation from his Internet Service Provider
+            strong enough to request web applications to be careful with the bandwidth usage.
+          </p>
+          <div class="note"><div class="note-title"><span>Note</span></div><div class="">
+            What is a metered connection is voluntarily left to the <a class="internalDFN" href="#dfn-user-agent">user agent</a> to judge. It would not be possible to give an exhaustive
+            list of limitations considered strong enough to flag the connection as metered and even if doable, some limitations can be
+            considered strong or weak depending on the context.<br>
+            Examples of metered connections are mobile connections with a small bandwidth quota or connections with a pay-per use plan.
+          </div></div>
+          <p>
+            The <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> set the value of the <code>metered</code> attribute to true if the connection with the
+            <a class="internalDFN" href="#dfn-browsing-context">browsing context</a> <a class="internalDFN" href="#dfn-active-document">active document</a>'s <a class="internalDFN" href="#dfn-domain">domain</a> is <a class="internalDFN" href="#dfn-metered" title="metered">metered</a> and false otherwise.
+            If the implementation is not able to know the status of the connection or if the user is offline, the value <em title="must" class="rfc2119">must</em> be set to false.
+          </p>
+          <div class="note"><div class="note-title"><span>Note</span></div><div class="">
+            If unable to know if a connection is metered, a <a class="internalDFN" href="#dfn-user-agent">user agent</a> could ask the user about the status of his current connection.
+            For example, a preference could let the user define if the mobile connection used on the device is metered.
+          </div></div>
+        </dd><dt id="widl-Connection-onchange"><code>onchange</code> of type <span class="idlAttrType"><a>Function</a></span>, nullable</dt><dd></dd></dl></section>
+
+      <p>
+        When the <code>Connection</code> changes, the <a class="internalDFN" href="#dfn-user-agent">user agent</a> <em title="must" class="rfc2119">must</em> <a class="internalDFN" href="#dfn-queue-a-task">queue a task</a> which updates
+        the <code>Connection</code> properties and <a class="internalDFN" href="#dfn-fire-a-simple-event">fire a simple event</a> named <code>change</code> at the
+        <code>Connection</code> object.
+      </p>
+
+      <p>
+        When the user goes online or offline, in addition to the <code>change</code> event fired on the <code>Connection</code>
+        object, the <a class="internalDFN" href="#dfn-user-agent">user agent</a> has to <a class="internalDFN" href="#dfn-fire-a-simple-event">fire a simple event</a> named either <code>online</code> or <code>offline</code>
+        depending on the applicable value, as defined in [<cite><a href="#bib-HTML5" class="bibref">HTML5</a></cite>].
+      </p>
+
+      <section id="event-handlers">
+        <h3><span class="secno">6.2 </span>Event handlers</h3>
+        <p>
+          The following are the <a class="internalDFN" href="#dfn-event-handlers">event handlers</a> (and their corresponding
+          <a class="internalDFN" href="#dfn-event-handler-event-types">event handler event types</a>) that <em title="must" class="rfc2119">must</em> be supported as
+          attributes by the <code>Connection</code> object:
+        </p>
+
+        <table class="simple">
+          <thead>
+            <tr>
+              <th>event handler</th>
+              <th>event handler event type</th>
+            </tr>
+          </thead>
+          <tbody>
+
+            <tr>
+              <td><strong><code>onchange</code></strong></td>
+              <td><code>change</code></td>
+            </tr>
+          </tbody>
+        </table>
+      </section>
+    </section>
+
+    <section id="examples" class="informative">
+      <!--OddPage--><h2><span class="secno">7. </span>Examples</h2><p><em>This section is non-normative.</em></p>
+      <p>
+        This trivial example writes the connection bandwidth to the console and shows it again each time it is changing:
+      </p>
+      <div class="example"><div class="example-title"><span>Example 1</span></div><pre class="example highlight prettyprint"><span class="kwd">function</span><span class="pln"> show</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+  console</span><span class="pun">.</span><span class="pln">log</span><span class="pun">(</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">bandwidth</span><span class="pun">);</span><span class="pln">
+</span><span class="pun">}</span><span class="pln">
+
+navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">addEventListener</span><span class="pun">(</span><span class="str">'change'</span><span class="pun">,</span><span class="pln"> show</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">false</span><span class="pun">);</span><span class="pln">
+
+show</span><span class="pun">();</span></pre></div>
+
+      <p>
+        This example shows how an image viewer can select a low definition or a high definition image based on the
+        current connection bandwidth:
+      </p>
+      <div class="example"><div class="example-title"><span>Example 2</span></div><pre class="example highlight prettyprint"><span class="dec">&lt;!DOCTYPE&gt;</span><span class="pln">
+</span><span class="tag">&lt;html&gt;</span><span class="pln">
+  </span><span class="tag">&lt;head&gt;</span><span class="pln">
+    </span><span class="tag">&lt;title&gt;</span><span class="pln">Pony viewer</span><span class="tag">&lt;/title&gt;</span><span class="pln">
+  </span><span class="tag">&lt;/head&gt;</span><span class="pln">
+  </span><span class="tag">&lt;body&gt;</span><span class="pln">
+    </span><span class="tag">&lt;img</span><span class="pln"> </span><span class="atn">id</span><span class="pun">=</span><span class="atv">'pony'</span><span class="pln"> </span><span class="atn">alt</span><span class="pun">=</span><span class="atv">"An image showing a pony"</span><span class="pln"> </span><span class="atn">title</span><span class="pun">=</span><span class="atv">"My precious!"</span><span class="tag">&gt;</span><span class="pln">
+    </span><span class="tag">&lt;script&gt;</span><span class="pln">
+      </span><span class="kwd">var</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> document</span><span class="pun">.</span><span class="pln">getElementById</span><span class="pun">(</span><span class="str">'pony'</span><span class="pun">);</span><span class="pln">
+
+      </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">bandwidth </span><span class="pun">&gt;</span><span class="pln"> </span><span class="lit">2</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+        i</span><span class="pun">.</span><span class="pln">src </span><span class="pun">=</span><span class="pln"> </span><span class="str">"http://example.com/pony_hd.png"</span><span class="pun">;</span><span class="pln">
+      </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+        i</span><span class="pun">.</span><span class="pln">src </span><span class="pun">=</span><span class="pln"> </span><span class="str">"http://example.com/pony_ld.png"</span><span class="pun">;</span><span class="pln">
+      </span><span class="pun">}</span><span class="pln">
+    </span><span class="tag">&lt;/script&gt;</span><span class="pln">
+  </span><span class="tag">&lt;/body&gt;</span><span class="pln">
+</span><span class="tag">&lt;/html&gt;</span></pre></div>
+
+      <p>
+        This example shows how an application can prevent automatic polling using the metered attribute:
+      </p>
+      <div class="example"><div class="example-title"><span>Example 3</span></div><pre class="example highlight prettyprint"><span class="dec">&lt;!DOCTYPE html&gt;</span><span class="pln">
+</span><span class="tag">&lt;html&gt;</span><span class="pln">
+  </span><span class="tag">&lt;head&gt;</span><span class="pln">
+    </span><span class="tag">&lt;title&gt;</span><span class="pln">Conditional polling</span><span class="tag">&lt;/title&gt;</span><span class="pln">
+    </span><span class="tag">&lt;script&gt;</span><span class="pln">
+      </span><span class="kwd">var</span><span class="pln"> gPreviousMetered </span><span class="pun">=</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">;</span><span class="pln">
+      </span><span class="kwd">var</span><span class="pln"> gIntervalId</span><span class="pun">;</span><span class="pln">
+
+      </span><span class="kwd">function</span><span class="pln"> poll</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+        </span><span class="com">// poll stuff</span><span class="pln">
+      </span><span class="pun">}</span><span class="pln">
+
+      navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">addEventListener</span><span class="pun">(</span><span class="str">'change'</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">function</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+        </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">gPreviousMetered </span><span class="pun">==</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+          </span><span class="kwd">return</span><span class="pun">;</span><span class="pln">
+        </span><span class="pun">}</span><span class="pln">
+
+        gPreviousMetered </span><span class="pun">=</span><span class="pln"> navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">;</span><span class="pln">
+        </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(!</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+          gIntervalId </span><span class="pun">=</span><span class="pln"> setInterval</span><span class="pun">(</span><span class="pln">poll</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1000</span><span class="pun">);</span><span class="pln">
+        </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+          clearInterval</span><span class="pun">(</span><span class="pln">gIntervalId</span><span class="pun">);</span><span class="pln">
+        </span><span class="pun">}</span><span class="pln">
+      </span><span class="pun">},</span><span class="pln"> </span><span class="kwd">false</span><span class="pun">);</span><span class="pln">
+
+      </span><span class="com">// At load time.</span><span class="pln">
+      </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(!</span><span class="pln">navigator</span><span class="pun">.</span><span class="pln">connection</span><span class="pun">.</span><span class="pln">metered</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
+        gIntervalId </span><span class="pun">=</span><span class="pln"> setInterval</span><span class="pun">(</span><span class="pln">poll</span><span class="pun">,</span><span class="pln"> </span><span class="lit">1000</span><span class="pun">);</span><span class="pln">
+      </span><span class="pun">}</span><span class="pln">
+    </span><span class="tag">&lt;/script&gt;</span><span class="pln">
+  </span><span class="tag">&lt;/head&gt;</span><span class="pln">
+  </span><span class="tag">&lt;body&gt;</span><span class="pln">
+    </span><span class="tag">&lt;button</span><span class="pln"> </span><span class="atn">onclick</span><span class="pun">=</span><span class="atv">"</span><span class="pln">poll</span><span class="pun">();</span><span class="atv">"</span><span class="tag">&gt;</span><span class="pln">Poll</span><span class="tag">&lt;/button&gt;</span><span class="pln">
+  </span><span class="tag">&lt;/body&gt;</span><span class="pln">
+</span><span class="tag">&lt;/html&gt;</span></pre></div>
+    </section>
+
+    <section id="acknowledgments" class="appendix">
+      <!--OddPage--><h2><span class="secno">A. </span>Acknowledgments</h2>
+      <p>
+        Thanks to Robin Berjon, Frederick Hirsch and Jonas Sicking for their help.
+      </p>
+    </section>
+  
+<section class="appendix" id="references"><!--OddPage--><h2><span class="secno">B. </span>References</h2><section id="normative-references"><h3><span class="secno">B.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-HTML5">[HTML5]</dt><dd>Ian Hickson; David Hyatt. <a href="http://www.w3.org/TR/html5"><cite>HTML5.</cite></a> 29 March 2012. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/html5">http://www.w3.org/TR/html5</a> 
+</dd><dt id="bib-RFC2119">[RFC2119]</dt><dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key words for use in RFCs to Indicate Requirement Levels.</cite></a> March 1997. Internet RFC 2119.  URL: <a href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a> 
+</dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2011/WD-WebIDL-20110927/"><cite>Web IDL.</cite></a> 27 September 2011. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/WD-WebIDL-20110927/">http://www.w3.org/TR/2011/WD-WebIDL-20110927/</a> 
+</dd></dl></section></section></body></html>
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