--- a/longdesc1/longdesc.html Wed Jun 19 10:32:41 2013 +0200
+++ b/longdesc1/longdesc.html Wed Jun 19 10:51:06 2013 +0200
@@ -1,12 +1,14 @@
-<html dir="ltr" lang="en">
<head>
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/*****************************************************************
* ReSpec 3 CSS
* Robin Berjon - http://berjon.com/
*****************************************************************/
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<!--[if lt IE 9]><script src='undefined://www.w3.org/2008/site/js/html5shiv.js'></script><![endif]-->
</head>
<body><br>
<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 class="title" id="title">HTML5 Image Description Extension</h1>
<h2 id="w3c-working-draft-20-september-2012"><abbr title="World Wide Web Consortium">W3C</abbr>
Editors' Draft 17 May 2013</h2>
<dl>
<dt>Latest published version:</dt>
<dd><a href="http://www.w3.org/TR/HTML-longdesc">http://www.w3.org/TR/HTML-longdesc</a></dd>
<dt>Latest editor's draft:</dt>
<dd> <a href="http://dvcs.w3.org/hg/html-proposals/raw-file/default/longdesc1/longdesc.html">http://dvcs.w3.org/hg/html-proposals/raw-file/default/longdesc1/longdesc.html</a></dd>
<dt>Editors:</dt>
<dd><a href="mailto:chaals@yandex-team.ru">Charles (McCathie) Nevile</a>,
<a href="http://www.yandex.ru">Яндекс</a>—<a href="http://yandex.com">Yandex</a></dd>
</dl>
<p class="copyright"> <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
© 2012-2013 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>),
+<html dir="ltr" lang="en">
<head>
<meta content="text/html; charset=UTF-8" http-equiv="content-type">
<style>
.issue {border: dashed red 2px; background-color: #ffd}
.example, .example code {color: #404; background-color:#eee}
.example::before {float:left;
margin-top: -.2em;
background-color: white;
display: block;
border: 1px solid black;
color: #404;
padding: 2px;
content: "Example: (non-normative)"}
.example:first-child {padding-top:1em}
/* Make these stand-out more... */
.externalDFN {
font-style: italic;
background-color: #fff9d6;
}
/* Switch statement */
dl.switch dt::before {
content: "↪ ";
margin-left: 1em;
}
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margin: 1em 0;
}
/* domintro styling */
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background-color: rgb(221, 255, 221);
padding: 1em 0.5em 1em 2em;
clear: both;
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dl.domintro dt {
color: black;
}
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color: green;
}
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float: right;
background-color: white;
display: block;
border: 2px solid black;
color: green;
margin-top: -20px;
padding: 2px;
content: "This box is non-normative.";
}
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table {
border-collapse: collapse;
}
thead tr {
border-bottom: 2px solid black;
}
tbody tr:not(:last-child) {
border-bottom: 1px solid black;
}
td {
border-left: 1px solid black;
padding: 4px;
}
/*****************************************************************
* ReSpec 3 CSS
* Robin Berjon - http://berjon.com/
*****************************************************************/
/* --- INLINES --- */
em.rfc2119 {
text-transform: lowercase;
font-variant: small-caps;
font-style: normal;
color: #900;
}
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font-style: normal;
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code {
color: #ff4500;
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text-decoration: none;
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color: #000;
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list-style: none outside none;
}
.caption {
margin-top: 0.5em;
font-style: italic;
}
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margin-top: 0;
}
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margin-bottom: 0;
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margin-bottom: 1em;
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}
</style> <link href="https://www.w3.org/StyleSheets/TR/W3C-ED" rel="stylesheet">
<!--[if lt IE 9]><script src='undefined://www.w3.org/2008/site/js/html5shiv.js'></script><![endif]-->
</head>
<body><br>
<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 class="title" id="title">HTML5 Image Description Extension</h1>
<h2 id="w3c-working-draft-20-september-2012"><abbr title="World Wide Web Consortium">W3C</abbr>
Editors' Draft 19 June 2013</h2>
<dl>
<dt>Latest published version:</dt>
<dd><a href="http://www.w3.org/TR/HTML-longdesc">http://www.w3.org/TR/HTML-longdesc</a></dd>
<dt>Latest editor's draft:</dt>
<dd> <a href="http://dvcs.w3.org/hg/html-proposals/raw-file/default/longdesc1/longdesc.html">http://dvcs.w3.org/hg/html-proposals/raw-file/default/longdesc1/longdesc.html</a></dd>
<dt>Editors:</dt>
<dd><a href="mailto:chaals@yandex-team.ru">Charles (McCathie) Nevile</a>,
<a href="http://www.yandex.ru">Яндекс</a>—<a href="http://yandex.com">Yandex</a></dd>
</dl>
<p class="copyright"> <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
© 2012-2013 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup>
(<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>,
<a href="http://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>,
<a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>),
All Rights Reserved. <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>This specification defines a <code>longdesc</code> attribute to link
descriptions to images in HTML5-based content.</p>
</section>
<section class="introductory" id="sotd">
<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> This document is an editors' draft proposed to the HTML Working Group
Accessibility Task Force for publication as a Last Call Working Draft.
Following feedback on the <a href="http://www.w3.org/TR/2013/WD-html-longdesc-20130312/">First
- Public Working Draft</a>, a number of <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=HTML%20WG&amp;component=HTML%20Image%20Description%20Extension">bugs</a>
were raised and resolved and a Second Public Working Draft was published
for review. Review of this draft did not produce any new substantive
issues. Significant changes between successive public drafts are tracked
in the Change History section.</p>
<p>If you wish to make comments regarding this document, please send them
to <a href="mailto:public-html-a11y@w3.org">public-html-a11y@w3.org</a>
(<a href="mailto:public-html-a11y-request@w3.org?subject=subscribe">subscribe</a>,
<a href="http://lists.w3.org/Archives/Public/public-html-a11y/">archives</a>).
+ use</a> rules apply. </p>
<hr> </div>
<section class="introductory" id="abstract">
<h2>Abstract</h2>
<p>This specification defines a <code>longdesc</code> attribute to link
descriptions to images in HTML5-based content. Note that by allowing a
hyperlink inside another one, this document explicitly redefines the
HTML concept of hyperlink in a limited set of circumstances.</p>
</section>
<section class="introductory" id="sotd">
<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> This document is an editors' draft proposed to the HTML Working Group
Accessibility Task Force for publication as a Last Call Working Draft.
Following feedback on the <a href="http://www.w3.org/TR/2013/WD-html-longdesc-20130312/">First
+ Public Working Draft</a>, a number of <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=HTML%20WG&amp;component=HTML%20Image%20Description%20Extension">bugs</a>
were raised and resolved and a <a href="http://www.w3.org/TR/2013/WD-html-longdesc-20130606/">Second
+ Public Working Draft</a> was published for review. Review of this
draft did not produce any new substantive issues. Significant changes
between successive public drafts are tracked in the Change History
section.</p>
<p>If you wish to make comments regarding this document, please send them
to <a href="mailto:public-html-a11y@w3.org">public-html-a11y@w3.org</a>
(<a href="mailto:public-html-a11y-request@w3.org?subject=subscribe">subscribe</a>,
<a href="http://lists.w3.org/Archives/Public/public-html-a11y/">archives</a>).
All
feedback is welcome. Bugs can also be filed directly into the <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=HTML%20WG&amp;component=HTML%20Image%20Description%20Extension">W3C
Bug tracker for this specification</a>.</p>
<section class="introductory" id="sotd">
<p>This document is intended to become a <abbr title="World Wide Web Consortium">W3C</abbr>
Recommendation, either on its own or merged into an HTML
Recommendation. </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/42538/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</a> of the <abbr title="World Wide Web Consortium">W3C</abbr>
Patent Policy. </p>
</section>
</section>
<section id="toc">
<h2 class="introductory">Table of Contents</h2>
<ul class="toc">
<li class="tocline"><a class="tocxref" href="#intro"><span class="secno">
</span>Introduction</a></li>
<li class="tocline"><a class="tocxref" href="#conformance"><span class="secno">1.
+ Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
+ 6</a> of the <abbr title="World Wide Web Consortium">W3C</abbr>
Patent Policy. </p>
</section>
</section>
<section id="toc">
<h2 class="introductory">Table of Contents</h2>
<ul class="toc">
<li class="tocline"><a class="tocxref" href="#intro"><span class="secno">
</span>Introduction</a></li>
<li class="tocline"><a class="tocxref" href="#conformance"><span class="secno">1.
</span>Conformance</a>
<ul class="toc">
<li class="tocline"><a class="tocxref" href="#dependencies"><span class="secno">1.1
</span>Dependencies</a></li>
</ul>
</li>
<li class="tocline"><a class="tocxref" href="#UCnR"><span class="secno">2.
</span>Use Cases and Requirements</a></li>
<li class="tocline"><a class="tocxref" href="#longdesc"><span class="secno">3.
@@ -20,10 +22,10 @@
</span>Change History</a></li>
</ul>
</section>
<section id="intro" class="introductory">
<h1>Introduction</h1>
<p>HTML 4 provided a <code>longdesc</code> attribute for the <code>img</code>
element. This enabled a machine-discoverable description of an image to
be linked to the image. This extension specification defines the same
functionality for HTML5-based content.</p>
<pre class="example"><code><br><br><!-- The description is somewhere on the same page as the image -->
<img src="http://example.com/graph1" alt="(Drinks are getting sweeter)" title="Figure One" <strong>longdesc="#graph1Explained"</strong>>
<!-- The description is a page on its own -->
<img src="figure1" alt="figure 1" <strong>longdesc="http://example.com/desc1"</strong>>
<!-- The description is one of several within an external page -->
<img src="ExampleImage" alt="example" <strong>longdesc="http://example.com/descs#item3"</strong>>
<!-- The description is included in a data: URI -->
<img src="logo" alt="W3C" <strong>longdesc="data:text/html;charset=utf-8;,%3C!DOCTYPE%20html%3E%3Chtml%3E%3Chead%3E
%3Ctitle%3EDescription%20of%20the%20W3C%20Logo%3C/title%3E%3C/head%3E%3Cbody%3E%3Cp%3EA%20blue%20capital%20letter<br>%20%22W%22%20with%20kerning%20so%20it%20touches%20a%20blue%203%2C%20followed%20by%20a%20black%20shadow%20<br>of%20a%20white%20capital%20letter%20C%20all%20on%20a%20white%20background%3C/body%3E%3C/html%3E"</strong>></code></pre>
</section>
<section id="conformance">
<h2><span class="secno">1. </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="should"
class="rfc2119">should</em>,
<em title="should not" class="rfc2119"></em><em title="recommended" class="rfc2119"></em>and
<em title="may" class="rfc2119">may</em><em title="optional" class="rfc2119"></em>
in this specification are to be interpreted as described in [<cite><a class="bibref"
href="#bib-RFC2119">RFC2119</a></cite>].</p>
<section id="dependencies">
<h3><span class="secno">1.1 </span>Dependencies and definitions</h3>
<p>The IDL fragments in this specification <em title="must" class="rfc2119">must</em>
be interpreted as required for conforming IDL fragments, as described
in the Web IDL specification. [<cite><a class="bibref" href="#bib-WEBIDL">WEBIDL</a></cite>]</p>
<p>The terms "<a href="http://www.w3.org/TR/html5/infrastructure.html#valid-url-potentially-surrounded-by-spaces">valid
non-empty URL potentially surrounded by spaces</a>", "<a href="http://www.w3.org/TR/html5/links.html#hyperlink">hyperlink"</a>,
and "<a href="http://www.w3.org/TR/html5/infrastructure.html#reflect">reflect</a>",
- used in this specification are defined in [<cite><a class="bibref" href="#bib-HTML5">HTML5</a></cite>].</p>
<p>This document does not define the term "accessible" nor
accessibility, but uses them with the sense they have in [<a href="#bib-WCAG2">WCAG</a>]</p>
</section>
</section>
<section id="UCnR">
<h2><span class="secno">2. </span>Use Cases and Requirements</h2>
<p>There are many ways users can successfully interact with content even
if they cannot see, or see well, images included in that content. The <code>alt</code>
attribute is designed to ensure that for everyday work, a user has
enough information to replace an image, and often this is more helpful
than a detailed description of every image. The <code>longdesc</code>
attribute is designed to complement this functionality, to meet the
following use cases. </p>
<h3 id="use-cases">Use Cases</h3>
<dl>
<dt>Identifying a well-known image</dt>
</dl>
<dl>
<dd>There are many well-known images which are widely reproduced and
well known. In some cases, such as "Mona Lisa", "Gerníka", Cubbin's
"Lost", Leunig's "ramming the shears", the most effective way to refer
identify an image to another person is by the creator, title, and
similar information that would be found in a catalog. But different
people know the images by different titles, and some images have no
widely known titles. Identifying an image is often an important part
of framing a discussion. Where the image itself cannot be seen, a
description can often be used to offer easier recognition than the
cataloging information, for example "Washington crossing some river,
standing heroically in the boat, while soldiers do the hard work", or
"the Da Vinci picture of the guy in a square and a circle".</dd>
<dd><em>Requires</em>: Discoverability</dd>
<dd><em>Helped by</em>: Inline, Reuse</dd>
<dt>Describing a complex diagram</dt>
<dd>In many environments diagrams are used to explain a concept or
transmit information efficiently. Where a user has a reduced ability
to see the image (poor contrast vision and other conditions are as
relevant here as a complete lack of vision), a description can enable
that user to understand the information being presented.</dd>
<dd><em>Requires</em>: Structured Markup, Inline, Reuse, Simple Return</dd>
<dt>Teaching Accessible Development</dt>
<dd>In many environments producing content that is accessible to users
regardless of disability is a legal and/or market requirement. </dd>
<dd><em>Requires</em>: Maintenance, Backwards compatibility</dd>
<dt>A self-describing artistic work</dt>
<dd>For many pages the visual design of the page is an important part of
the message it conveys to a fully-sighted user, but the author would
like to convey as much of that design as possible to a user with low
or no vision available. </dd>
<dd><em>Requires</em>: No visual encumbrance, Structured Markup</dd>
<dd><em>Helped by</em>: Reuse, Simple Return</dd>
<dt>Referring to an existing description</dt>
<dd>Many well-known images are already described by other sources. The
copyright on those sources may not be compatible with re-publishing
the description, but there is little value in making a new one. </dd>
<dd><em>Requires</em>: Reuse, Structured Markup, Simple Return, Optional
Consumption </dd>
<dd><em>Helped by</em>: No Visual Encumbrance</dd>
<dt>Linking to a description included within a page</dt>
<dd>In some cases an image already has a description included within a
page. Making the linkage explicit can provide further clarity for a
user navigating the page who is not able to interpret the default
layout, e.g. because they have forced a re-layout of the page
elements, or because they do not see the default visual relationship
between the element and its description.</dd>
<dd>This practice also enables description to be provided for all users.</dd>
<dd>By keeping the association clear the content maintainer can more
easily check that the description and link are actually correct.</dd>
<dd><em>Requires</em>: Inline, Simple Return, Structured Markup,
Optional Consumption </dd>
<dt>Localizing descriptions</dt>
<dd>When content is localized to multiple languages, it is important
that metadata intended for human consumption, such as image
descriptions, can be readily localized.</dd>
<dd><em>Helped by</em>: Structured Markup, Reuse, Maintenance.</dd>
</dl>
<h3 id="requirements">Requirements for an Image Description functionality</h3>
<dl>
<dt>No visual encumbrance</dt>
<dd>It <em class="rfc2119">must</em> be possible to provide a
description for an image without any visual encumbrance on the page.</dd>
<dt>Structured Markup</dt>
<dd>It <em class="rfc2119">must</em> be possible to include rich markup
(e.g. HTML5) in the description of the image.</dd>
<dt>Inline</dt>
<dd>It <em class="rfc2119">must</em> be possible to associate a
description in the body of a page with an image in that page. </dd>
<dt>Reuse</dt>
<dd>It <em class="rfc2119">must</em> be possible to re-use a single
description for multiple occurrences of an image.</dd>
<dt>Maintenance</dt>
<dd>It <em class="rfc2119">must</em> be simple to maintain a library of
images and descriptions for dynamic assembly, or dis-assembly and
re-assembly, of content. </dd>
<dt>Discoverability </dt>
<dd class="rfc2119">It <em class="rfc2119">must</em> be simple for a
user agent to automatically discover a description provided for a
given image.</dd>
<dd>A user <em class="rfc2119">should</em> be able to determine that
there is a description available for a given image. </dd>
<dt>Optional consumption</dt>
<dd>A user <em class="rfc2119">must</em> be able to choose not to read
the long description of a given image.</dd>
<dt>Simple return</dt>
<dd>A user <em class="rfc2119">must</em> be able to return from the
description to the image. </dd>
<dt>Backwards Compatibility </dt>
<dd>It <em class="rfc2119">should</em> be possible to use existing
tools and techniques to associate an image with its description. </dd>
</dl>
</section>
<section id="longdesc">
<h2><span class="secno"></span>3. The <code>longdesc</code> attribute</h2>
<h3 id="implementation">3.0 Implementation</h3>
<h4 id="authors-and-conformance-checkers">3.0.1 Authors and Conformance
checkers</h4>
<section id="parsing">
<p class="rfc2119">Zero or one <code>longdesc</code> attributes <em class="rfc2119">may</em>
be added to any <code>img</code> element.</p>
<p>The <code>longdesc</code> attribute <em class="rfc2119">must</em>
contain a <a href="http://www.w3.org/TR/html5/infrastructure.html#valid-url-potentially-surrounded-by-spaces">valid
- non-empty URL potentially surrounded by spaces</a>. The URL is a <a
href="http://dev.w3.org/html5/spec/links.html#hyperlink">hyperlink</a>
to a description of the image that its parent <code>img</code>
element represents. </p>
<p>The linked description <em class="rfc2119">should</em> be a broadly
accessible format. (For example, a link to another version of the
image is almost certainly not a useful description, and plain text is
an extremely limiting format).</p>
<div class="note">
<p><em>This section is informative</em></p>
<p>Best practices for checking descriptions of images are beyond the
scope of this document, but there are many resources available.
For further guidance tool developers can consult e.g. [<a href="#bib-ATAGB3">ATAGB3</a>].
+ used in this specification are defined in [<cite><a class="bibref" href="#bib-HTML5">HTML5</a></cite>].</p>
<p>This document does not define the term "accessible" nor
accessibility, but uses them with the sense they have in [<a href="#bib-WCAG2">WCAG</a>]</p>
</section>
</section>
<section id="UCnR">
<h2><span class="secno">2. </span>Use Cases and Requirements</h2>
<p>There are many ways users can successfully interact with content even
if they cannot see, or see well, images included in that content. The <code>alt</code>
attribute is designed to ensure that for everyday work, a user has
enough information to replace an image, and often this is more helpful
than a detailed description of every image. The <code>longdesc</code>
attribute is designed to complement this functionality, to meet the
following use cases. </p>
<h3 id="use-cases">Use Cases</h3>
<dl>
<dt>Identifying a well-known image</dt>
</dl>
<dl>
<dd>There are many well-known images which are widely reproduced and
well known. In some cases, such as "Mona Lisa", "Gerníka", Cubbin's
"Lost", Leunig's "ramming the shears", the most effective way to refer
identify an image to another person is by the creator, title, and
similar information that would be found in a catalog. But different
people know the images by different titles, and some images have no
widely known titles. Identifying an image is often an important part
of framing a discussion. Where the image itself cannot be seen, a
description can often be used to offer easier recognition than the
cataloging information, for example "Washington crossing some river,
standing heroically in the boat, while soldiers do the hard work", or
"the Da Vinci picture of the guy in a square and a circle".</dd>
<dd><em>Requires</em>: Discoverability</dd>
<dd><em>Helped by</em>: Inline, Reuse</dd>
<dt>Describing a complex diagram</dt>
<dd>In many environments diagrams are used to explain a concept or
transmit information efficiently. Where a user has a reduced ability
to see the image (poor contrast vision and other conditions are as
relevant here as a complete lack of vision), a description can enable
that user to understand the information being presented.</dd>
<dd><em>Requires</em>: Structured Markup, Inline, Reuse, Simple Return</dd>
<dt>Teaching Accessible Development</dt>
<dd>In many environments producing content that is accessible to users
regardless of disability is a legal and/or market requirement. </dd>
<dd><em>Requires</em>: Maintenance, Backwards compatibility</dd>
<dt>A self-describing artistic work</dt>
<dd>For many pages the visual design of the page is an important part of
the message it conveys to a fully-sighted user, but the author would
like to convey as much of that design as possible to a user with low
or no vision available. </dd>
<dd><em>Requires</em>: No visual encumbrance, Structured Markup</dd>
<dd><em>Helped by</em>: Reuse, Simple Return</dd>
<dt>Referring to an existing description</dt>
<dd>Many well-known images are already described by other sources. The
copyright on those sources may not be compatible with re-publishing
the description, but there is little value in making a new one. </dd>
<dd><em>Requires</em>: Reuse, Structured Markup, Simple Return, Optional
Consumption </dd>
<dd><em>Helped by</em>: No Visual Encumbrance</dd>
<dt>Linking to a description included within a page</dt>
<dd>In some cases an image already has a description included within a
page. Making the linkage explicit can provide further clarity for a
user navigating the page who is not able to interpret the default
layout, e.g. because they have forced a re-layout of the page
elements, or because they do not see the default visual relationship
between the element and its description.</dd>
<dd>This practice also enables description to be provided for all users.</dd>
<dd>By keeping the association clear the content maintainer can more
easily check that the description and link are actually correct.</dd>
<dd><em>Requires</em>: Inline, Simple Return, Structured Markup,
Optional Consumption </dd>
<dt>Localizing descriptions</dt>
<dd>When content is localized to multiple languages, it is important
that metadata intended for human consumption, such as image
descriptions, can be readily localized.</dd>
<dd><em>Helped by</em>: Structured Markup, Reuse, Maintenance.</dd>
</dl>
<h3 id="requirements">Requirements for an Image Description functionality</h3>
<dl>
<dt>No visual encumbrance</dt>
<dd>It <em class="rfc2119">must</em> be possible to provide a
description for an image without any visual encumbrance on the page.</dd>
<dt>Structured Markup</dt>
<dd>It <em class="rfc2119">must</em> be possible to include rich markup
(e.g. HTML5) in the description of the image.</dd>
<dt>Inline</dt>
<dd>It <em class="rfc2119">must</em> be possible to associate a
description in the body of a page with an image in that page. </dd>
<dt>Reuse</dt>
<dd>It <em class="rfc2119">must</em> be possible to re-use a single
description for multiple occurrences of an image.</dd>
<dt>Maintenance</dt>
<dd>It <em class="rfc2119">must</em> be simple to maintain a library of
images and descriptions for dynamic assembly, or dis-assembly and
re-assembly, of content. </dd>
<dt>Discoverability </dt>
<dd class="rfc2119">It <em class="rfc2119">must</em> be simple for a
user agent to automatically discover a description provided for a
given image.</dd>
<dd>A user <em class="rfc2119">should</em> be able to determine that
there is a description available for a given image. </dd>
<dt>Optional consumption</dt>
<dd>A user <em class="rfc2119">must</em> be able to choose not to read
the long description of a given image.</dd>
<dt>Simple return</dt>
<dd>A user <em class="rfc2119">must</em> be able to return from the
description to the image. </dd>
<dt>Backwards Compatibility </dt>
<dd>It <em class="rfc2119">should</em> be possible to use existing
tools and techniques to associate an image with its description. </dd>
</dl>
</section>
<section id="longdesc">
<h2><span class="secno"></span>3. The <code>longdesc</code> attribute</h2>
<p>This extension changes the definition of a hyperlink in HTML, by
allowing a <code>longdesc</code> attribute to occur inside a hyperlink.</p>
<h3 id="implementation">3.0 Implementation</h3>
<h4 id="authors-and-conformance-checkers">3.0.1 Authors and Conformance
checkers</h4>
<section id="parsing">
<p class="rfc2119">Zero or one <code>longdesc</code> attributes <em class="rfc2119">may</em>
be added to any <code>img</code> element.</p>
<p>The <code>longdesc</code> attribute <em class="rfc2119">must</em>
contain a <a href="http://www.w3.org/TR/html5/infrastructure.html#valid-url-potentially-surrounded-by-spaces">valid
+ non-empty URL potentially surrounded by spaces</a>. The URL is a <a
href="http://dev.w3.org/html5/spec/links.html#hyperlink">hyperlink</a>
to a description of the image that its parent <code>img</code>
element represents. </p>
<p>The linked description <em class="rfc2119">should</em> be a broadly
accessible format.</p>
<div class="note">
<p><em>This section is not normative</em></p>
<p>Best practices for checking descriptions of images are beyond the
scope of this document, but there are many resources available.
For further guidance tool developers can consult e.g. [<a href="#bib-ATAGB3">ATAGB3</a>].
<span class="issue">ISSUE: This doesn't seem a great reference - is
there anything better? This is tracked in <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=21501">bug
- 21501</a> and its dependent bugs. Unless a proposal for
improvement is made and accepted this bug will simply be closed
after Last Call.</span></p>
</div>
<h4 id="authors">3.0.2 Authors</h4>
<p>Authors <em class="rfc2119">should</em> put descriptions within an
element which is the target of a fragment link (e.g. <code>longdesc="example.html#description"</code>)
if a description is only part of the target document. </p>
<div class="note">
<p><em>This section is informative</em></p>
<p>Best practices for full descriptions of images are beyond the scope
of this document, but there are many resources available.</p>
<p>This document does not define the term "accessible" nor
accessibility. For further guidance on making an accessible
document, authors can consult e.g. [<a href="#bib-WCAG2">WCAG</a>].</p>
</div>
<h4 id="user-agents">3.0.3 User Agents</h4>
<p>If the <code>longdesc</code> value is valid, User agents <em class="rfc2119">must</em>
make the link available to all users through the regular user
interface(s). </p>
<p>If the <code>longdesc</code> value is valid, User agents <em class="rfc2119">must</em>
expose the link to relevant APIs, especially accessibility-oriented
APIs. </p>
<p>User agents <em class="rfc2119">should</em> enable users to discover
when images in a page contain a long description.</p>
<div class="note">
<p><em>This section is informative</em></p>
<p>Complete documentation of best practices for implementation is
beyond the scope of this document. These notes are offered to help
minimise the impact of common mistakes.</p>
<p>A common mistake in the past has been to use a description, instead
of a URL that links to a description. Converting such values to
data: URLs is a repair strategy for user agents that can help users
to recover in cases where authors have made this mistake. </p>
<p>It is usually helpful when the behaviour for finding, reading, and
returning from a long description to the image described is a
consistent experience.</p>
<p>Further information on making user agents accessible can be found
in [<a href="file:///Users/chaals/Documents/w3c/html-proposals/longdesc1/longdesc.html#bib-UAAG">UAAG</a>].</p>
</div>
</section>
<section id="extensions-to-the-element-interface">
<h3><span class="secno">3.1 </span>Extension to the <code><a title="element"
class="externalDFN"
data-spec="HTML5">HTMLImageElement</a></code>
interface</h3>
<pre class="idl"><span class="idlInterface" id="idl-def-Element">partial interface <span
class="idlInterfaceID">HTMLImageElement</span> {
<span class="idlAttribute"> attribute <span class="idlAttrType"><a>DOMString</a></span> <span
class="idlAttrName"><a
href="#widl-Element-longdesc">longdesc</a></span>;</span>
};</span></pre>
<section id="attributes">
<h4><span class="secno">3.1.1 </span>Attribute</h4>
<dl class="attributes">
<dt id="widl-Element-longdesc"><code>longdesc</code> of type <span
class="idlAttrType"><a>DOMString</a></span></dt>
<dd>
<p class="rfc2119">The <dfn id="dfn-dom-element-longdesc"><code>longdesc</code></dfn>
IDL attribute <em class="rfc2119">must</em> be a valid
non-empty URL potentially surrounded by spaces. It represents a
hyperlink to a detailed description of the image its parent <code><a
title="element"
class="externalDFN"
data-spec="DOM4">HTMLImageElement</a></code>
represents.</p>
</dd>
<dd>
<p>The <code>longdesc</code> IDL attribute <em class="rfc2119">must</em>
<a href="http://www.w3.org/TR/html5/infrastructure.html#reflect">reflect</a>
the HTML content attribute <code>longdesc</code>. </p>
</dd>
<dd>
<dl class="note">
<dt>
<p><em>This section is informative</em></p>
<p><var>image</var>.<code title="dom-Element-innerHTML">longdesc</code>
[ = <var>value</var> ]</p>
</dt>
<dd>
<p>Returns a DOMString that represents the attribute's
contents. </p>
<p>Can be set, to replace the contents of the attribute with
the given string.</p>
</dd>
</dl>
</dd>
</dl>
<pre class="example"><code>//Make the first internal longdesc reference absolute
var baseURL = document.location.origin + document.location.pathname
var someImage = document.querySelector('img[longdesc^=#]');
someImage.longdesc = baseURL + someImage.longdesc;</code></pre>
<pre class="example"><code>//Open new windows for each longdesc found
var describedImages = document.querySelectorAll('img[longdesc]');
for (i in describedImages) {
if (i.<strong>longdesc</strong>)
window.open(i.<strong>longdesc</strong>);
}</code></pre>
<pre class="example"><code>//Tries to repair errors where the longdesc isn't a URI
var describedImages = document.querySelectorAll('img[longdesc]');
for (i in describedImages) {
if (i.longdesc && !(validURL(i.longdesc)) { //assumes some URL validating function
var theData = encodeURIComponent(i.longdesc);
i.longdesc = "data:text/plain;charset=";
i.longdesc += document.charset;
i.longdesc += theData;
}
}</code></pre>
</section>
</section>
<section class="appendix" id="acknowledgements">
<h2><span class="secno">A. </span>Acknowledgements</h2>
<p>Thanks to the HTML Working Group of the late 1990s for the original
specification of longdesc, to those who have implemented it in various
kinds of software, and to many many people involved with the
development of HTML5 (including but not limited to those who discussed
"ISSUE-30" in the HTML Working Group, the Protocols and Formats
Working Group, the W3C Advisory Board, and around countless dinner
tables, coffee breaks, and elsewhere) for the ideas, discussions and
contributions that led to the initial draft of this specification.
With the exception of Laura Carlson, who did far more very valuable
work than it took me to produce this specification, I haven't named
them: the list might be larger than the content of the specification.</p>
<p>For specific comments and suggestions that led to improvements over
successive drafts of this specification, thanks to the W3C's HTML
Accessibility Task Force, the W3C Internationalization Working Group,
and to Jonathan Avila, Robin Berjon, James Craig, Steve Faulkner, John
Foliot, Geoff Freed, Richard Ishida, Anne van Kesteren, David
MacDonald, Chris Mills, Jay Munro, Devarshi Pant, Silvia Pfeiffer,
Leif Halvard Silli, Mathew Turvey and Boris Zbarsky. Any errors are
despite, not as a result of, their efforts.</p>
</section>
<section class="appendix" id="references">
<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>Robin Berjon et. al., eds. <a href="http://www.w3.org/TR/html5/"><cite>HTML5.</cite></a>
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
+ 21501</a> and its dependent bugs. Unless a proposal for
improvement is made and accepted this bug will simply be closed
after Last Call.</span></p>
<p>High quality implementation in authoring and content management
tools is likely to inclde checking for common errors, such as
including a description instead of a URL in the attribute, or
pointing to a resource that is an image or plain text, which are
often poor choices for a high-quality description.</p>
</div>
<h4 id="authors">3.0.2 Authors</h4>
<p>Authors <em class="rfc2119">should</em> put descriptions within an
element which is the target of a fragment link (e.g. <code>longdesc="example.html#description"</code>)
if a description is only part of the target document. </p>
<div class="note">
<p><em>This section is not normative</em></p>
<p>Best practices for full descriptions of images are beyond the scope
of this document, but there are many resources available.</p>
<p>This document does not define the term "accessible" nor
accessibility. For further guidance on making an accessible
document, authors can consult e.g. [<a href="#bib-WCAG2">WCAG</a>].</p>
</div>
<h4 id="user-agents">3.0.3 User Agents</h4>
<p>If the <code>longdesc</code> value is valid, User agents <em class="rfc2119">must</em>
make the link available to all users through the regular user
interface(s). </p>
<p>If the <code>longdesc</code> value is valid, User agents <em class="rfc2119">must</em>
expose the link to relevant APIs, especially accessibility-oriented
APIs. </p>
<p>User agents <em class="rfc2119">should</em> enable users to discover
when images in a page contain a long description.</p>
<div class="note">
<p><em>This section is not normative</em></p>
<p><code>longdesc</code> can be present on an image within a hyperlink.
This does not change the requirements on user agents, which must
still enable the hyperlink to be followed.</p>
<p>Complete documentation of best practices for implementation is
beyond the scope of this document. These notes are offered to help
minimise the impact of common mistakes.</p>
<p>A common mistake in the past has been to use a description, instead
of a URL that links to a description. Converting such values to
data: URLs is a repair strategy for user agents that can help users
to recover in cases where authors have made this mistake. </p>
<p>It is usually helpful when the behaviour for finding, reading, and
returning from a long description to the image described is a
consistent experience.</p>
<p>Further information on making user agents accessible can be found
in [<a href="file:///Users/chaals/Documents/w3c/html-proposals/longdesc1/longdesc.html#bib-UAAG">UAAG</a>].</p>
</div>
</section>
<section id="extensions-to-the-element-interface">
<h3><span class="secno">3.1 </span>Extension to the <code><a title="element"
class="externalDFN"
data-spec="HTML5">HTMLImageElement</a></code>
interface</h3>
<pre class="idl"><span class="idlInterface" id="idl-def-Element">partial interface <span
class="idlInterfaceID">HTMLImageElement</span> {
<span class="idlAttribute"> attribute <span class="idlAttrType"><a>DOMString</a></span> <span
class="idlAttrName"><a
href="#widl-Element-longdesc">longdesc</a></span>;</span>
};</span></pre>
<section id="attributes">
<h4><span class="secno">3.1.1 </span>Attribute</h4>
<dl class="attributes">
<dt id="widl-Element-longdesc"><code>longdesc</code> of type <span
class="idlAttrType"><a>DOMString</a></span></dt>
<dd>
<p class="rfc2119">The <dfn id="dfn-dom-element-longdesc"><code>longdesc</code></dfn>
IDL attribute <em class="rfc2119">must</em> be a valid
non-empty URL potentially surrounded by spaces. It represents a
hyperlink to a detailed description of the image its parent <code><a
title="element"
class="externalDFN"
data-spec="DOM4">HTMLImageElement</a></code>
represents.</p>
</dd>
<dd>
<p>The <code>longdesc</code> IDL attribute <em class="rfc2119">must</em>
<a href="http://www.w3.org/TR/html5/infrastructure.html#reflect">reflect</a>
the HTML content attribute <code>longdesc</code>. </p>
</dd>
<dd>
<dl class="note">
<dt>
<p><em>This section is not normative</em></p>
<p><var>image</var>.<code title="dom-Element-innerHTML">longdesc</code>
[ = <var>value</var> ]</p>
</dt>
<dd>
<p>Returns a DOMString that represents the attribute's
contents. </p>
<p>Can be set, to replace the contents of the attribute with
the given string.</p>
</dd>
</dl>
</dd>
</dl>
<pre class="example"><code>//Make the first internal longdesc reference absolute
var baseURL = document.location.origin + document.location.pathname
var someImage = document.querySelector('img[longdesc^=#]');
someImage.longdesc = baseURL + someImage.longdesc;</code></pre>
<pre class="example"><code>//Open new windows for each longdesc found
var describedImages = document.querySelectorAll('img[longdesc]');
for (i in describedImages) {
if (i.<strong>longdesc</strong>)
window.open(i.<strong>longdesc</strong>);
}</code></pre>
<pre class="example"><code>//Tries to repair errors where the longdesc isn't a URI
var describedImages = document.querySelectorAll('img[longdesc]');
for (i in describedImages) {
if (i.longdesc && !(validURL(i.longdesc)) { //assumes some URL validating function
var theData = encodeURIComponent(i.longdesc);
i.longdesc = "data:text/plain;charset=";
i.longdesc += document.charset;
i.longdesc += theData;
}
}</code></pre>
</section>
</section>
<section class="appendix" id="acknowledgements">
<h2><span class="secno">A. </span>Acknowledgements</h2>
<p><em>This section is not normative</em></p>
<p>Thanks to the HTML Working Group of the late 1990s for the original
specification of longdesc, to those who have implemented it in various
kinds of software, and to many many people involved with the
development of HTML5 (including but not limited to those who discussed
"ISSUE-30" in the HTML Working Group, the Protocols and Formats
Working Group, the W3C Advisory Board, and around countless dinner
tables, coffee breaks, and elsewhere) for the ideas, discussions and
contributions that led to the initial draft of this specification.
With the exception of Laura Carlson, who did far more very valuable
work than it took me to produce this specification, I haven't named
them: the list might be larger than the content of the specification.</p>
<p>For specific comments and suggestions that led to improvements over
successive drafts of this specification, thanks to the W3C's HTML
Accessibility Task Force, the W3C Internationalization Working Group,
and to Jonathan Avila, Robin Berjon, James Craig, Steve Faulkner, John
Foliot, Geoff Freed, Richard Ishida, Anne van Kesteren, David
MacDonald, Chris Mills, Jay Munro, Devarshi Pant, Silvia Pfeiffer,
Leif Halvard Silli, Mathew Turvey and Boris Zbarsky. Any errors are
despite, not as a result of, their efforts.</p>
</section>
<section class="appendix" id="references">
<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>Robin Berjon et. al., eds. <a href="http://www.w3.org/TR/html5/"><cite>HTML5.</cite></a>
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 id="informative-references">
<h3><span class="secno">B.2 </span>Informative references</h3>
<dl class="bibliography">
<dt id="bib-ATAGB3">[ATAGB3]</dt>
<dd>Jutta Treviranus et. al., eds. <a href="http://www.w3.org/TR/ATAG20-TECHS/#principle_b3"><cite>Implementing
ATAG 2.0</cite></a>, Principle B3 "Authors must be supported
in improving the accessibility of existing content" October 2011.
W3C Working Draft. URL: <a href="http://www.w3.org/TR/ATAG20-TECHS/#principle_b3">http://www.w3.org/TR/ATAG20-TECHS/#principle_b3</a></dd>
<dt id="bib-WCAG2">[WCAG]</dt>
<dd>Ben Caldwell et. al., eds. <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/"><cite>Web