--- a/longdesc1/longdesc.html Wed Apr 03 14:26:03 2013 +0200
+++ b/longdesc1/longdesc.html Wed Apr 03 14:26:39 2013 +0200
@@ -1,4 +1,4 @@
-<!DOCTYPE html>
<html dir="ltr" lang="en">
<head>
<meta content="text/html; charset=UTF-8" http-equiv="content-type">
<title>HTML Image Description Extension</title>
<style>
.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;
}
/* Better spacing around various lists (implied paragraph children) */
ol > li, section:not(#toc) ul > li, section dl > dt {
margin: 1em 0;
}
/* domintro styling */
dl.domintro {
background-color: rgb(221, 255, 221);
padding: 1em 0.5em 1em 2em;
clear: both;
}
dl.domintro dt {
color: black;
}
dl.domintro > dd {
color: green;
}
dl.domintro::before {
float: right;
background-color: white;
display: block;
border: 2px solid black;
color: green;
margin-top: -20px;
padding: 2px;
content: "This box is non-normative.";
}
/* Fancy table stuff */
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;
}
h1 acronym, h2 acronym, h3 acronym, h4 acronym, h5 acronym, h6 acronym, a acronym,
h1 abbr, h2 abbr, h3 abbr, h4 abbr, h5 abbr, h6 abbr, a abbr {
border: none;
}
dfn {
font-weight: bold;
}
a.internalDFN {
color: inherit;
border-bottom: 1px solid #99c;
text-decoration: none;
}
a.externalDFN {
color: inherit;
border-bottom: 1px dotted #ccc;
text-decoration: none;
}
a.bibref {
text-decoration: none;
}
cite .bibref {
font-style: normal;
}
code {
color: #ff4500;
}
/* --- TOC --- */
.toc a, .tof a {
text-decoration: none;
}
a .secno, a .figno {
color: #000;
}
ul.tof, ol.tof {
list-style: none outside none;
}
.caption {
margin-top: 0.5em;
font-style: italic;
}
/* --- DL --- */
.section dd > p:first-child {
margin-top: 0;
}
.section dd > p:last-child {
margin-bottom: 0;
}
.section dd {
margin-bottom: 1em;
}
.section dl.attrs dd, .section dl.eldef dd {
margin-bottom: 0;
}
/* --- ISSUES/NOTES --- */
div.note-title {
padding-right: 1em;
min-width: 7.5em;
color: #b9ab2d;
}
div.note-title { color: #52e052; }
div.note-title span {
text-transform: uppercase;
}
div.note {
margin-top: 1em;
margin-bottom: 1em;
}
.note > p:first-child { margin-top: 0 }
.note {
padding: .5em;
border-left-width: .5em;
border-left-style: solid;
}
div.note {
padding: 0.5em;
margin: 1em 0;
position: relative;
clear: both;
}
span.note { padding: .1em .5em .15em; }
.note {
border-color: #52e052;
background: #e9fbe9;
}
pre.idl {
border-top: 1px solid #90b8de;
border-bottom: 1px solid #90b8de;
padding: 1em;
line-height: 120%;
}
pre.idl::before {
content: "WebIDL";
display: block;
width: 8ex;
background: #90b8de;
color: #fff;
font-family: initial;
padding: 3px;
font-weight: bold;
margin: -1em 0 1em -1em;
}
.idlType {
color: #ff4500;
font-weight: bold;
text-decoration: none;
}
/*.idlInterface*/
.idlInterfaceID, .idlDictionaryID, .idlCallbackID, .idlEnumID {
font-weight: bold;
color: #005a9c;
}
.idlSuperclass {
font-style: italic;
color: #005a9c;
}
/*.idlAttribute*/
.idlAttrType, .idlFieldType, .idlMemberType {
color: #005a9c;
}
.idlAttrName, .idlFieldName, .idlMemberName {
color: #ff4500;
}
.idlAttrName a, .idlFieldName a, .idlMemberName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
.extAttr {
color: #666;
}
/*.idlConst*/
.idlConstType {
color: #005a9c;
}
.idlConstName {
color: #ff4500;
}
.idlConstName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
.idlImplements a {
font-weight: bold;
}
dl.attributes, dl.methods, dl.constants, dl.fields, dl.dictionary-members {
margin-left: 2em;
}
.attributes dt, .methods dt, .constants dt, .fields dt, .dictionary-members dt {
font-weight: normal;
}
.attributes dt code, .methods dt code, .constants dt code, .fields dt code, .dictionary-members dt code {
font-weight: bold;
color: #000;
font-family: monospace;
}
.attributes dt code, .fields dt code, .dictionary-members dt code {
background: #ffffd2;
}
.attributes dt .idlAttrType code, .fields dt .idlFieldType code, .dictionary-members dt .idlMemberType code {
color: #005a9c;
background: transparent;
font-family: inherit;
font-weight: normal;
font-style: italic;
}
.attributes dd, .methods dd, .constants dd, .fields dd, .dictionary-members dd {
margin-bottom: 1em;
}
</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>
<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 2 April 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>),
+<!DOCTYPE html>
<html dir="ltr" lang="en">
<head>
<meta content="text/html; charset=UTF-8" http-equiv="content-type">
<title>HTML Image Description Extension</title>
<style>
.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;
}
/* Better spacing around various lists (implied paragraph children) */
ol > li, section:not(#toc) ul > li, section dl > dt {
margin: 1em 0;
}
/* domintro styling */
dl.domintro {
background-color: rgb(221, 255, 221);
padding: 1em 0.5em 1em 2em;
clear: both;
}
dl.domintro dt {
color: black;
}
dl.domintro > dd {
color: green;
}
dl.domintro::before {
float: right;
background-color: white;
display: block;
border: 2px solid black;
color: green;
margin-top: -20px;
padding: 2px;
content: "This box is non-normative.";
}
/* Fancy table stuff */
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;
}
h1 acronym, h2 acronym, h3 acronym, h4 acronym, h5 acronym, h6 acronym, a acronym,
h1 abbr, h2 abbr, h3 abbr, h4 abbr, h5 abbr, h6 abbr, a abbr {
border: none;
}
dfn {
font-weight: bold;
}
a.internalDFN {
color: inherit;
border-bottom: 1px solid #99c;
text-decoration: none;
}
a.externalDFN {
color: inherit;
border-bottom: 1px dotted #ccc;
text-decoration: none;
}
a.bibref {
text-decoration: none;
}
cite .bibref {
font-style: normal;
}
code {
color: #ff4500;
}
/* --- TOC --- */
.toc a, .tof a {
text-decoration: none;
}
a .secno, a .figno {
color: #000;
}
ul.tof, ol.tof {
list-style: none outside none;
}
.caption {
margin-top: 0.5em;
font-style: italic;
}
/* --- DL --- */
.section dd > p:first-child {
margin-top: 0;
}
.section dd > p:last-child {
margin-bottom: 0;
}
.section dd {
margin-bottom: 1em;
}
.section dl.attrs dd, .section dl.eldef dd {
margin-bottom: 0;
}
/* --- ISSUES/NOTES --- */
div.note-title {
padding-right: 1em;
min-width: 7.5em;
color: #b9ab2d;
}
div.note-title { color: #52e052; }
div.note-title span {
text-transform: uppercase;
}
div.note {
margin-top: 1em;
margin-bottom: 1em;
}
.note > p:first-child { margin-top: 0 }
.note {
padding: .5em;
border-left-width: .5em;
border-left-style: solid;
}
div.note {
padding: 0.5em;
margin: 1em 0;
position: relative;
clear: both;
}
span.note { padding: .1em .5em .15em; }
.note {
border-color: #52e052;
background: #e9fbe9;
}
pre.idl {
border-top: 1px solid #90b8de;
border-bottom: 1px solid #90b8de;
padding: 1em;
line-height: 120%;
}
pre.idl::before {
content: "WebIDL";
display: block;
width: 8ex;
background: #90b8de;
color: #fff;
font-family: initial;
padding: 3px;
font-weight: bold;
margin: -1em 0 1em -1em;
}
.idlType {
color: #ff4500;
font-weight: bold;
text-decoration: none;
}
/*.idlInterface*/
.idlInterfaceID, .idlDictionaryID, .idlCallbackID, .idlEnumID {
font-weight: bold;
color: #005a9c;
}
.idlSuperclass {
font-style: italic;
color: #005a9c;
}
/*.idlAttribute*/
.idlAttrType, .idlFieldType, .idlMemberType {
color: #005a9c;
}
.idlAttrName, .idlFieldName, .idlMemberName {
color: #ff4500;
}
.idlAttrName a, .idlFieldName a, .idlMemberName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
.extAttr {
color: #666;
}
/*.idlConst*/
.idlConstType {
color: #005a9c;
}
.idlConstName {
color: #ff4500;
}
.idlConstName a {
color: #ff4500;
border-bottom: 1px dotted #ff4500;
text-decoration: none;
}
.idlImplements a {
font-weight: bold;
}
dl.attributes, dl.methods, dl.constants, dl.fields, dl.dictionary-members {
margin-left: 2em;
}
.attributes dt, .methods dt, .constants dt, .fields dt, .dictionary-members dt {
font-weight: normal;
}
.attributes dt code, .methods dt code, .constants dt code, .fields dt code, .dictionary-members dt code {
font-weight: bold;
color: #000;
font-family: monospace;
}
.attributes dt code, .fields dt code, .dictionary-members dt code {
background: #ffffd2;
}
.attributes dt .idlAttrType code, .fields dt .idlFieldType code, .dictionary-members dt .idlMemberType code {
color: #005a9c;
background: transparent;
font-family: inherit;
font-weight: normal;
font-style: italic;
}
.attributes dd, .methods dd, .constants dd, .fields dd, .dictionary-members dd {
margin-bottom: 1em;
}
</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>
<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 3 April 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
extended descriptions with 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 following the First Public Working Draft of an
HTML extension Proposal. 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.
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
@@ -19,6 +19,8 @@
<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</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://dev.w3.org/html5/spec/urls.html#valid-url-potentially-surrounded-by-spaces">valid
non-emptyURL potentially surrounded by spaces</a>", "<a href="http://dev.w3.org/html5/spec/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-DOM4"></a></cite>
[<cite><a class="bibref" href="#bib-HTML5">HTML5</a></cite>]<cite><a class="bibref"
href="#bib-XML10"></a></cite>.
</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.<br>
</p>
<h3>Use Cases</h3>
<dl>
<dt>Describing a well-known image</dt>
</dl>
<dl>
<dd>There are many well-known images which are widely reproduced - Mona
Lisa, Washington crossing some river, the Da Vinci picture of the guy
in a square and a circle, Gerníka, Cubbin's "Lost", Leunig's "ramming
the shears". While different people know the images by different
titles, and some images have no widely known titles, visually
recognising the 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 the same recognition.</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<br>
</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<br>
</dd>
</dl>
<h3>Requirements </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.<br>
</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>
<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://dev.w3.org/html5/spec/urls.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. The linked description should be a broadly
accessible format. (for example, a link to another version of the
image is not a useful description).</p>
<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 accessibility. For further guidance
on making the description an accessible document, authors should
consult [<a href="#bib-WCAG">WCAG</a>]</p>
</div>
<p>User agents <em class="rfc2119">should</em> make the link available
to all users through the regular user interface. <br>
</p>
<p>User agents <em class="rfc2119">should</em> expose the link to
relevant APIs, especially accessibility-oriented APIs.<br>
</p>
<p>User agents <em class="rfc2119">should</em> enable users to discover
when images in a page contain a long description.</p>
<p>If a <code>longdesc</code> attribute has invalid content, user
agents <em class="rfc2119">may</em> make that content available to
the user. This is because a common authoring error is to include the
text of a description, instead of the URL of a description, as the
value of the attribute.</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. However the following notes are
offered to help repair a common authoring mistake and avoid a common
user agent mistake.</p>
<p>One of the most common mistakes authors make that is easily
repaired by user agents is to use a description, instead of a URL
that links to a description. This means there is often plain text
description in the content of an invalid longdesc attribute.
Converting such attributes to data URLs is a simple repair strategy
that can help recover from cases where authors have made this
mistake. </p>
<p>Since some images with long description are also normal link
content, it is important for implementations to ensure that users
can activate both behaviours. Likewise, it is generally helpful when
the behaviour for finding, reading, and returning from a long
description to the image described is a consistent experience. </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>.<br>
</p>
</dd>
<dd>
<dl class="domintro">
<dt><var>image</var>.<code title="dom-Element-innerHTML">longdesc</code>
[ = <var>value</var> ] </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 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, and to Robin Berjon, James Craig, John
Foliot, Geoff Freed, Anne van Kesteren, David McDonald, Leif Halvard
Silli, Mathew Turvey. Any errors are despite, not because 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
+ 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. The linked description should be a broadly
accessible format. (for example, a link to another version of the
image is not a useful description).</p>
<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 accessibility. For further guidance
on making the description an accessible document, authors should
consult [<a href="#bib-WCAG">WCAG</a>].</p>
</div>
<p>User agents <em class="rfc2119">should</em> make the link available
to all users through the regular user interface. <br>
</p>
<p>User agents <em class="rfc2119">should</em> expose the link to
relevant APIs, especially accessibility-oriented APIs.<br>
</p>
<p>User agents <em class="rfc2119">should</em> enable users to discover
when images in a page contain a long description.</p>
<p>If a <code>longdesc</code> attribute has invalid content, user
agents <em class="rfc2119">may</em> make that content available to
the user. This is because a common authoring error is to include the
text of a description, instead of the URL of a description, as the
value of the attribute.</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. However the following notes are
offered to help repair a common authoring mistake and avoid a common
user agent mistake.</p>
<p>One of the most common mistakes authors make that is easily
repaired by user agents is to use a description, instead of a URL
that links to a description. This means there is often plain text
description in the content of an invalid longdesc attribute.
Converting such attributes to data URLs is a simple repair strategy
that can help recover from cases where authors have made this
mistake. </p>
<p>Since some images with long description are also normal link
content, it is important for implementations to ensure that users
can activate both behaviours. Likewise, it is generally helpful when
the behaviour for finding, reading, and returning from a long
description to the image described is a consistent experience.</p>
<p>Obviously, it is important that access to the long description is
accessible to users. Further information on how to do this can be
found in [<a href="#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>.<br>
</p>
</dd>
<dd>
<dl class="domintro">
<dt><var>image</var>.<code title="dom-Element-innerHTML">longdesc</code>
[ = <var>value</var> ] </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 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, and to Robin Berjon, James Craig, John
Foliot, Geoff Freed, Anne van Kesteren, David McDonald, Leif Halvard
Silli, Mathew Turvey. Any errors are despite, not because 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-WCAG2">[WCAG]</dt>
<dd>Ben Caldwell et. al., eds. <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/"><cite>Web
Content Accessibility Guidelines 2.0</cite></a>, December
2008. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/">http://www.w3.org/TR/2008/REC-WCAG20-20081211/</a></dd>
</dl>
<p></p>
<dl class="bibliography">
</dl>
</section>
</section>
</section>
</body>
</html>
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+ 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-WCAG2">[WCAG]</dt>
<dd>Ben Caldwell et. al., eds. <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/"><cite>Web
+ Content Accessibility Guidelines 2.0</cite></a>, December
2008. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2008/REC-WCAG20-20081211/">http://www.w3.org/TR/2008/REC-WCAG20-20081211/</a></dd>
<dt id="bib-UAAG">[UAAG]</dt>
<dd>Ian Jacobs et. al., eds. <a href="http://www.w3.org/TR/2002/REC-UAAG10-20021217/"><cite>User
+ Agent Accessibility Guidelines 2.0</cite></a>, December 2002.
W3C Recommendation. URL: <a href="http://www.w3.org/TR/2002/REC-UAAG10-20021217/">http://www.w3.org/TR/2002/REC-UAAG10-20021217/</a>.
A draft for a version 2.0 is available at <a href="http://www.w3.org/TR/UAAG20/">http://www.w3.org/TR/UAAG20/</a></dd>
</dl>
<p></p>
<dl class="bibliography">
</dl>
</section>
</section>
</section>
</body>
</html>
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