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<div class="head">
<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src=
"http://www.w3.org/Icons/w3c_home" width="72"></a></p>
<h1>HTML+RDFa</h1>
<h2 class="no-num no-toc" id="a-mechanism-for-embedding-rdf-in-html">A
mechanism for embedding RDF in HTML</h2>
<h2 class="no-num no-toc" id="editor-s-draft-date-04-March-2010">W3C
Working Draft 04 March 2010</h2><!--:ZZZ-->
<dl>
<dt>This Version</dt>
<dd><a href=
"http://www.w3.org/TR/2010/WD-rdfa-in-html-20100304/">http://www.w3.org/TR/2010/WD-rdfa-in-html-20100304/</a></dd>
<dt>Latest Version</dt>
<dd><a href=
"http://www.w3.org/TR/rdfa-in-html/">http://www.w3.org/TR/rdfa-in-html/</a></dd>
<dt>Previous Versions</dt>
<dd><a href=
"http://www.w3.org/TR/2009/WD-rdfa-in-html-20091015/">http://www.w3.org/TR/2009/WD-rdfa-in-html-20091015/</a></dd>
<dt>Authors (alphabetical order):</dt>
<dd>Ben Adida (Chair, RDFa Task Force, Creative Commons)</dd>
<dd>Mark Birbeck (Editor, XHTML+RDFa and inventor of RDFa concept, Web
Backplane Ltd.)</dd>
<dd>Shane McCarron (Editor, XHTML+RDFa, Applied Testing and Technology,
Inc.)</dd>
<dd>Steven Pemberton (Chair, XHTML2 and RDFa Task Force member,
CWI)</dd>
<dd><a href="mailto:msporny@digitalbazaar.com">Manu Sporny</a>,
(Editor, HTML+RDFa and RDFa Task Force member, Digital Bazaar,
Inc.)</dd>
</dl>
<p class="copyright"><a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
© 2010 <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. W3C
<a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a href=
"http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a href=
"http://www.w3.org/Consortium/Legal/copyright-documents">document use</a>
rules apply.</p>
</div>
<hr class="top">
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>This specification defines rules and guidelines for adapting the RDF in
XHTML: Syntax and Processing (RDFa) specification for use in the HTML5 and
XHTML5 members of the HTML family. The rules defined in this specification
not only apply to HTML5 documents in non-XML and XML mode, but also to
HTML4 and XHTML documents interpreted through the HTML5 parsing rules.</p>
<h2 class="no-num no-toc" id="status-of-this-document">Status of this
document</h2><!-- intro boilerplate (required) -->
<p><em>This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
index</a> at http://www.w3.org/TR/.</em></p>
<p>This is a Working Draft of the "HTML+RDFa: A mechanism for embedding RDF
in HTML" specification for review by W3C members and other interested
parties.</p>
<p>This Working Draft includes the following changes:</p>
<ul>
<li>Updating HTML5 coercion to Infoset rules (normative)</li>
<li>Clarifying how to extract RDFa attributes via Infoset
(informative)</li>
<li>Clarifying how to extract RDFa attributes via DOM2 (informative)</li>
</ul>
<p>If you wish to make comments regarding this document, please send them
to <a href=
"mailto:public-rdf-in-xhtml-tf@w3.org">public-rdf-in-xhtml-tf@w3.org</a>
(<a href=
"mailto:public-rdf-in-xhtml-tf-request@w3.org?subject=subscribe">subscribe</a>,
<a href=
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or submit them using the <a href=
"http://www.w3.org/Bugs/Public/enter_bug.cgi">W3C's public bug
database</a>.</p><!-- UNDER NO CIRCUMSTANCES IS THE FOLLOWING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST --><!-- UNDER NO CIRCUMSTANCES IS THE PRECEDING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST --><!-- stability (required) -->
<p>Implementors should be aware that this specification is not stable.
<strong>Implementors who are not taking part in the discussions are likely
to find the specification changing out from under them in incompatible
ways.</strong> Vendors interested in implementing this specification should
note the status, and are encouraged to join the RDFa Working Group.</p>
<!-- not everyone agrees with html5 (requested before fpwd) -->
<p>Publication as a Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or
obsoleted by other documents at any time. It is inappropriate to cite this
document as other than work in progress.</p>
<p>The publication of this document by the W3C as a W3C Working Draft does
not imply that all of the participants in the W3C HTML working group
endorse the contents of the specification. Indeed, for any section of the
specification, one can usually find many members of the working group or of
the W3C as a whole who object strongly to the current text, the existence
of the section at all, or the idea that the working group should even spend
time discussing the concept of that section.</p>
<p>The latest stable version of the editor's draft of this specification is
always available on <a href="http://dev.w3.org/html5/rdfa/">the W3C CVS
server</a>. The <a href=
"http://html5.digitalbazaar.com/specs/rdfa.html">latest editor's working
copy</a> (which may contain unfinished text in the process of being
prepared) is also available. A <a href=
"http://www.w3.org/TR/2010/WD-rdfa-in-html-20100304/diffs.html">Diff-marked version</a> is available.
</p>
<p>This specification has been jointly developed by the <a href=
"http://www.w3.org/2001/sw/BestPractices/HTML/">RDFa Task Force</a> and the
<a href="http://www.w3.org/html/wg/">HTML Working Group</a> and is
currently being published by the <a href="http://www.w3.org/html/wg/">HTML
Working Group</a> to further discussions there.</p>
<p>This specification is an extension to the HTML5 language. All normative
content in the HTML5 specification, unless specifically overridden by this
specification, is intended to be the basis for this specification.</p>
<p>This document was produced by a group operating under the <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C
Patent Policy</a>. W3C maintains a <a href=
"http://www.w3.org/2004/01/pp-impl/40318/status" rel="disclosure">public
list of any patent disclosures</a> made in connection with the deliverables
of the group; that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual
believes contains <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a href=
"http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
6 of the W3C Patent Policy</a>.</p>
<h2 class="no-num no-toc" id="contents">Table of contents</h2>
<!--begin-toc-->
<ol class="toc">
<li>
<a href="#introduction"><span class="secno">1</span> Introduction</a>
<ol>
<li><a href="#history"><span class="secno">1.1</span>
History</a></li>
</ol>
</li>
<li>
<a href="#parsing-model"><span class="secno">2</span> Parsing Model</a>
<ol>
<li><a href="#modifying-the-input-document"><span class=
"secno">2.1</span> Modifying the Input Document</a></li>
</ol>
</li>
<li>
<a href="#conformance-requirements"><span class="secno">3</span>
Conformance Requirements</a>
<ol>
<li><a href="#document-conformance"><span class="secno">3.1</span>
Document Conformance</a></li>
<li><a href="#user-agent-conformance"><span class="secno">3.2</span>
User Agent Conformance</a></li>
<li><a href="#rdfa-processor-conformance"><span class=
"secno">3.3</span> RDFa Processor Conformance</a></li>
</ol>
</li>
<li>
<a href="#modifications-to-xhtml-rdfa"><span class="secno">4</span>
Modifications to XHTML+RDFa</a>
<ol>
<li><a href="#specifying-the-language-for-a-literal"><span class=
"secno">4.1</span> Specifying the language for a literal</a></li>
<li><a href="#invalid-xmlliteral-values"><span class=
"secno">4.2</span> Invalid XMLLiteral values</a></li>
<li><a href="#xmlns:-prefixed-attributes"><span class=
"secno">4.3</span> <code>xmlns:</code>-Prefixed Attributes</a></li>
</ol>
</li>
<li>
<a href="#extensions-to-the-html5-syntax"><span class="secno">5</span>
Extensions to the HTML5 Syntax</a>
<ol>
<li><a href="#the-rdfa-attributes-and-valid-values"><span class=
"secno">5.1</span> The RDFa Attributes and Valid Values</a></li>
<li><a href=
"#conformance-criteria-for-xmlns:-prefixed-attributes"><span class=
"secno">5.2</span> Conformance Criteria for
<code>xmlns:</code>-Prefixed Attributes</a></li>
<li><a href=
"#preserving-namespaces-via-coercion-to-infoset"><span class=
"secno">5.3</span> Preserving Namespaces via Coercion to
Infoset</a></li>
</ol>
</li>
<li>
<a href="#infoset-based-processors"><span class="secno">6</span>
Infoset-based Processors</a>
<ol>
<li><a href="#processing-namespaced-rdfa-attributes"><span class=
"secno">6.1</span> Processing Namespaced RDFa Attributes</a></li>
<li><a href="#processing-rdfa-attributes"><span class=
"secno">6.2</span> Processing RDFa Attributes</a></li>
</ol>
</li>
<li>
<a href="#dom-level-2-based-processors"><span class="secno">7</span>
DOM Level 2-based Processors</a>
<ol>
<li><a href="#processing-namespaced-rdfa-attributes-0"><span class=
"secno">7.1</span> Processing Namespaced RDFa Attributes</a></li>
<li><a href="#processing-rdfa-attributes-0"><span class=
"secno">7.2</span> Processing RDFa Attributes</a></li>
</ol>
</li>
<li>
<a href="#references"><span class="secno">8</span> References</a>
<ol>
<li><a href="#normative-references"><span class="secno">8.1</span>
Normative References</a></li>
<li><a href="#non-normative-references"><span class=
"secno">8.2</span> Non-Normative References</a></li>
</ol>
</li>
</ol><!--end-toc-->
<h2 id="introduction"><span class="secno">1</span> Introduction</h2>
<p><em>This section is informative.</em></p>
<p>Today's web is built predominantly for human consumption. Even as
machine-readable data begins to permeate the web, it is typically
distributed in a separate file, with a separate format, and very limited
correspondence between the human and machine versions. As a result, web
browsers can provide only minimal assistance to humans in parsing and
processing web data: browsers only see presentation information. RDFa is
intended to solve the problem of machine-readable data in HTML documents.
RDFa provides a set of HTML attributes to augment visual data with
machine-readable hints. Using RDFa, authors may turn their existing
human-visible text and links into machine-readable data without repeating
content.</p>
<h3 id="history"><span class="secno">1.1</span> History</h3>
<p>In early 2004, Mark Birbeck published a document named [<a href=
"#refsXHTMLRDF">XHTMLRDF</a>] via the XHTML2 Working Group wherein he laid
the groundwork for what would eventually become RDFa (The Resource
Description Framework in Attributes).</p>
<p>In 2006, the work was co-sponsored by the Semantic Web Deployment Work
Group, which began to formalize a technology to express semantic data in
XHTML. This technology was successfully developed and reached consensus at
the W3C, later published as an official W3C Recommendation. While HTML
provides a mechanism to express the structure of a document (title,
paragraphs, links), RDFa provides a mechanism to express the meaning in a
document (people, places, events).</p>
<p>The document, titled "RDF in XHTML: Syntax and Processing" [<a href=
"#refsXHTMLRDFA">XHTML+RDFa</a>], defined a set of attributes and rules for
processing those attributes that resulted in the output of machine-readable
semantic data. While the document applied to XHTML, the attributes and
rules were always intended to operate across any tree-based structure
containing attributes on tree nodes (such as HTML4, SVG and ODF).</p>
<p>While RDFa was initially specified for use in XHTML, adoption by a
number of large organizations on the Web spurred RDFa's use in non-XHTML
languages. Its use in HTML4, before an official specification was developed
for those languages, caused concern regarding document conformance.</p>
<p>Over the years, the members of the RDFa Task Force [<a href=
"http://rdfa.info/">RDFaTF</a>] had discussed the possibility of applying
the same attributes and processing rules outlined in the XHTML+RDFa
specification to all HTML family documents. By design, the possibility of a
unified semantic data expression mechanism between all HTML and XHTML
family documents was squarely in the realm of possibility.</p>
<p>This section describes the modifications to the original XHTML+RDFa
specification that permit the use of RDFa in all HTML family documents. By
using the attributes and processing rules described in the XHTML+RDFa
specification and heeding the minor changes in this section, authors can
expect to generate markup that produces the same semantic data output in
HTML4, HTML5 and XHTML5.</p>
<h2 id="parsing-model"><span class="secno">2</span> Parsing Model</h2>
<p><em>This section is normative.</em></p>
<p><a href="http://www.w3.org/TR/rdfa-syntax/#sec_5.5.">Section 5.5:
Sequence</a>, of the [<a href=
"http://www.w3.org/TR/rdfa-syntax/">XHTML+RDFa</a>] specification defines a
generic processing model for extracting RDF from a tree-based model. The
method of transforming an input document into a model suited for the RDFa
processing rules is intentionally not defined in the XHTML+RDFa
specification. The method of transformation was intended to be defined in
the implementation language, in this case, this section of the HTML+RDFa
specification.</p>
<p>The HTML5 and XHTML5 DOMs are each a super-set of the tree-based model
on which the RDFa processing rules operate. Therefore, a mapping mechanism
to translate from a DOM to a tree-model is not necessary. The HTML5 and
XHTML5 DOM, or equivalent data structure, should be used as input to the
RDFa processing rules. The normative language for construction of the HTML5
DOM and XHTML5 DOM is contained in the HTML5 specification.</p>
<h3 id="modifying-the-input-document"><span class="secno">2.1</span>
Modifying the Input Document</h3>
<p><em>This section is informative.</em></p>
<p>RDFa's tree-based processing rules, outlined in <a href=
"http://www.w3.org/TR/rdfa-syntax/#sec_5.5.">Section 5.5: Sequence</a> of
the XHTML+RDFa specification, allow an input document to be automatically
corrected, cleaned-up, re-arranged, or modified in any way that is approved
by the host language prior to processing. For example, element nesting
issues in HTML documents may be corrected before the input document is
translated into the DOM, a valid tree-based model, on which the RDFa
processing rules will operate.</p>
<p>Any mechanism that generates a data structure equivalent to the HTML5 or
XHTML5 DOM, such as the html5lib library, may be used as the mechanism to
construct the tree-based model provided as input to the RDFa processing
rules.</p>
<h2 id="conformance-requirements"><span class="secno">3</span> Conformance
Requirements</h2>
<p><em>This section is normative.</em></p>
<p>The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in [<a class="nref" href=
"#refsRFC2119">RFC2119</a>].</p>
<h3 id="document-conformance"><span class="secno">3.1</span> Document
Conformance</h3>
<p>In order for a document to claim that it is a conforming HTML+RDFa
document, it must provide the facilities described as mandatory in this
section. The document conformance criteria are listed below, of which only
a subset are mandatory:</p>
<ol>
<li>All document conformance requirements stated as mandatory in the
HTML5 specification must be met.</li>
<li>There should be a <code>version</code> attribute on the
<code>html</code> element. The value of the <code>version</code>
attribute should be "HTML+RDFa 1.0" if the document is a non-XML mode
document, or "XHTML+RDFa 1.0" if the document is a XML mode
document.</li>
<li>There may be a <code>link</code> element contained in the
<code>head</code> element that contains <code>profile</code> for the the
<code>rel</code> attribute and
<code>http://www.w3.org/1999/xhtml/vocab</code> for the <code>href</code>
attribute.</li>
</ol>
<h3 id="user-agent-conformance"><span class="secno">3.2</span> User Agent
Conformance</h3>
<p>A conforming RDFa user agent must:</p>
<ul>
<li>Conform to all requirements listed in the <span>Conformance
requirements</span> section of the HTML5 specification.</li>
<li>Implement all of the features required by this specification.</li>
<li>Implement all of the features specified in the XHTML+RDFa
specification, excluding those features which are specifically overridden
by this specification as detailed in the <a href=
"#modifications-to-xhtml-rdfa">Modifications to XHTML+RDFa</a>.</li>
</ul>
<h3 id="rdfa-processor-conformance"><span class="secno">3.3</span> RDFa
Processor Conformance</h3>
<p>A conforming RDFa Processor must implement all of the mandatory features
specified in the XHTML+RDFa specification. It must also support any
mandatory features specified in this specification.</p>
<h2 id="modifications-to-xhtml-rdfa"><span class="secno">4</span>
Modifications to XHTML+RDFa</h2>
<p><em>This section is normative.</em></p>
<p>The [<a href="http://www.w3.org/TR/rdfa-syntax/">XHTML+RDFa</a>]
Recommendation is the base document on which this specification builds.
XHTML+RDFa specifies the attributes, in <a href=
"http://www.w3.org/TR/rdfa-syntax/#rdfa-attributes">Section 2.1: The RDFa
Attributes</a>, and processing model, in <a href=
"http://www.w3.org/TR/rdfa-syntax/#s_model">Section 5: Processing
Model</a>, for extracting RDF from an XHTML document. This section
specifies changes to the attributes and processing model defined in
XHTML+RDFa in order to support extracting RDF from HTML documents.</p>
<p>The requirements and rules, as specified in XHTML+RDFa and further
modified in this document, apply to all HTML5 documents. The RDFa Processor
operating on HTML and XHTML documents, specifically the resulting DOMs,
must apply the same processing rules for both types of serializations and
DOMs.</p>
<h3 id="specifying-the-language-for-a-literal"><span class=
"secno">4.1</span> Specifying the language for a literal</h3>
<p>The <code>lang</code> attribute must be processed in the same manner as
the <code>xml:lang</code> attribute is in the XHTML+RDFa specification,
<a href="http://www.w3.org/TR/rdfa-syntax/#sec_5.5.">Section 5.5:
Sequence</a>, step #3.</p>The rules for determining the language of a node
are specified in the section titled <a href=
"http://www.w3.org/TR/html5/Overview.html#the-lang-and-xml:lang-attributes">
The lang and xml:lang attributes</a> in the HTML5 specification.
<p>If an author is editing an HTML fragment and is unsure of the final
encapsulating MIME type for their markup, it is suggested that the author
specify both <code>lang</code> and <code>xml:lang</code> where the value in
both attributes is exactly the same.</p>
<h3 id="invalid-xmlliteral-values"><span class="secno">4.2</span> Invalid
XMLLiteral values</h3>
<p>When generating literals of type XMLLiteral, the processor must ensure
that the output XMLLiteral is a namespace well-formed XML fragment. A
namespace well-formed XML fragment has the following properties:</p>
<ul>
<li>The XML fragment, when placed inside of a single root element, must
validate as well-formed XML. The normative language that describes a
well-formed XML document is specified in <a href=
"http://www.w3.org/TR/REC-xml/#sec-well-formed">Section 2.1 "Well-Formed
XML Documents"</a> of the XML specification.</li>
<li>A case-insensitive match for the currently active <code>xmlns</code>
attribute as well as all currently active attributes starting with
<code>xmlns:</code> must be preserved in the generated XMLLiteral. This
preservation must be accomplished by placing all active namespaces in
each top-level element in the generated XMLLiteral, taking care to not
over-write pre-existing namespace values.</li>
</ul>If the input is not a namespace well-formed XML fragment, the
processor must transform the input text in a way that ensures the
well-formedness rules described in this section. If a sequence of
characters cannot be transformed into a namespace well-formed XML fragment,
the triple containing the XMLLiteral must not be generated.
<p>An RDFa Processor that transforms the XML fragment must use the <a href=
"http://www.w3.org/TR/html5/Overview.html#coercing-an-html-dom-into-an-infoset">
Coercing an HTML DOM into an Infoset</a> rules, as specified in the HTML5
specification, prior to generating the triple containing the XMLLiteral.
The serialization algorithm that must be used for generating the XMLLiteral
is normatively defined in the <a href=
"http://www.w3.org/TR/html5/Overview.html#serializing-xhtml-fragments">Serializing
XHTML Fragments</a> section of the HTML5 specification.</p>
<p>Transformation to a namespace well-formed XML fragment is required
because an application that consumes XMLLiteral data expects that data to
be a namespace well-formed XML fragment.</p>
<p>The transformation requirement does not apply to input data that are
text-only, such as literals that contain a <code>datatype</code> attribute
with an empty value (<code>""</code>), or input data that that contain only
text nodes.</p>
<p>An example transformation demonstrating the preservation of namespace
values is provided below. The → symbol is used to denote that the line
is a continuation of the previous line and is included purely for the
purposes of readability:</p>
<pre>
<p xmlns:ex="http://example.org/vocab#"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
Two rectangles (the example markup for them are stored in a triple):
<svg xmlns="http://www.w3.org/2000/svg" property="ex:markup" datatype="rdf:XMLLiteral">
→ <rect width="300" height="100"
→ style="fill:rgb(0,0,255);stroke-width:1; stroke:rgb(0,0,0)"/>
→ <rect width="50" height="50"
→ style="fill:rgb(255,0,0);stroke-width:2;
→ stroke:rgb(0,0,0)"/></svg>
</p>
</pre>The markup above should produce the following triple:
<pre>
<>
<http://example.org/vocab#markup>
"<rect xmlns=\"http://www.w3.org/2000/svg\" width=\"300\"
→ height=\"100\" style=\"fill:rgb(0,0,255);stroke-width:1; stroke:rgb(0,0,0)\"/>
→ <rect xmlns=\"http://www.w3.org/2000/svg\" width=\"50\"
→ height=\"50\" style=\"fill:rgb(255,0,0);stroke-width:2;
→ stroke:rgb(0,0,0)\"/>"^^http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral
</pre>Note the preservation of the SVG namespace by injecting a new
<code>xmlns</code> attribute. Since the <code>ex</code> and <code>rdf</code>
namespaces are not used in either <code>rect</code> element, they are not
preserved in the XMLLiteral.
<h3 id="xmlns:-prefixed-attributes"><span class="secno">4.3</span>
<code>xmlns:</code>-Prefixed Attributes</h3>
<p class="XXX">While this section outlines xmlns: processing in RDFa, the
support for distributed extensibility in non-XML mode HTML5 (using xmlns
and xmlns:) is still an open issue. This section may be further modified
before Last Call based on progress made on the distributed extensibility
issue.</p>
<p>CURIE prefix mappings specified using attributes prepended with
<code>xmlns:</code> must be processed using the rules specified in
<a
href="http://www.w3.org/TR/rdfa-syntax/#s_curieprocessing">Section
5.4, CURIE and URI Processing,</a> contained in the XHTML+RDFa
specification.</p>
<p>Since CURIE prefix mappings have been specified using
<code>xmlns:</code>, and since HTML attribute names are case-insensitive,
CURIE prefix names declared using the <code>xmlns:</code>attribute-name
pattern <code>xmlns:<PREFIX>="<URI>"</code> should be specified
using only lower-case characters. For example, the text
"<code>xmlns:</code>" and the text in <code>"<PREFIX>"</code> should
be lower-case only. This is to ensure that prefix mappings are interpreted
in the same way between HTML (case-insensitive attribute names) and XHTML
(case-sensitive attribute names) document types.</p>
<h2 id="extensions-to-the-html5-syntax"><span class="secno">5</span>
Extensions to the HTML5 Syntax</h2>
<p class="XXX annotation"><b>Status:</b> <a href="http://www.w3.org/html/wg/tracker/issues/41">ISSUE-41</a> (decentralized extensibility) blocks progress to Last Call</p>
<p><em>This section is normative.</em></p>
<p>There are a few changes that are required to the HTML5 specification in
order to fully support RDFa. The following sub-sections outline the
necessary modifications to the base HTML5 specification.</p>
<h3 id="the-rdfa-attributes-and-valid-values"><span class=
"secno">5.1</span> The RDFa Attributes and Valid Values</h3>
<p>All RDFa attributes and valid values (including CURIEs), as listed in
<a href="http://www.w3.org/TR/rdfa-syntax/#rdfa-attributes">Section 2.1:
The RDFa Attributes</a>, are conforming when used in an HTML5 or XHTML5
document.</p>
<h3 id="conformance-criteria-for-xmlns:-prefixed-attributes"><span class=
"secno">5.2</span> Conformance Criteria for <code>xmlns:</code>-Prefixed
Attributes</h3>
<p class="XXX">While this section outlines xmlns: conformance criteria for
HTML+RDFa, the support for distributed extensibility in non-XML mode HTML5
(using xmlns and xmlns:) is still an open issue. This section may be
further modified before Last Call based on progress made on the distributed
extensibility issue.</p>
<p>Since RDFa uses attributes starting with <code>xmlns:</code> to specify
CURIE prefixes, it is important that any attribute starting with a
case-insensitive match on the text string "<code>xmlns:</code>" be
preserved in the DOM or other tree-like model that is passed to the RDFa
Processor. While it is specified that HTML5 must preserve these attributes
in the DOM, it must also accept these attributes as conforming in non-XML
HTML5. For documents conforming to this specification, attributes with
names that have the case insensitive prefix "<code>xmlns:</code>" are
conforming in both HTML5 and XHTML5.</p>
<h3 id="preserving-namespaces-via-coercion-to-infoset"><span class=
"secno">5.3</span> Preserving Namespaces via Coercion to Infoset</h3>
<p class="XXX">This section needs feedback from the user agent vendors to
ensure that this feature does not conflict with user agent architecture and
has no technical reason that it cannot be implemented.</p>
<p>RDFa is currently dependent on the <code>xmlns:</code> pattern to
declare prefix mappings, it is imperative that namespace information that
is declared in non-XML mode HTML5 documents are mapped to an Infoset
correctly. In order to ensure this mapping is performed correctly, the
"Coercing an HTML DOM into an infoset" rules defined in [<a href=
"#refsHTML5">HTML5</a>] must be modified to include the following rule:</p>
<p>If the XML API is namespace-aware, the tool must ensure that proper
([<a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">namespace
name</a>], [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">local name</a>],
[<a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">normalized
value</a>]) namespace tuples are created when converting the non-XML mode
DOM into an Infoset.</p>
<p>For example, given the following input text:</p>
<pre>
<div xmlns:audio="http://purl.org/media/audio#">
</pre>The <code>div</code> element above, when coerced from an HTML DOM into
an Infoset, should contain an attribute in the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.element">namespace
attributes</a>] list with a [namespace name] set to
"<code>http://www.w3.org/2000/xmlns/</code>", a [local name] set to
<code>audio</code>, and a [normalized value] of
"<code>http://purl.org/media/audio#</code>".
<h2 id="infoset-based-processors"><span class="secno">6</span>
Infoset-based Processors</h2>
<p><em>This section is informative</em></p>
<p>While the intent of the RDFa processing instructions were to provide a
set of rules that are as language and toolchain agnostic as possible, for
the sake of clarity, detailed methods of extracting RDFa content from
processors operating on an XML Information Set are provided below.</p>
<h3 id="processing-namespaced-rdfa-attributes"><span class=
"secno">6.1</span> Processing Namespaced RDFa Attributes</h3>
<p>Extracting namespaced RDFa attributes while operating from within an
Infoset-based RDFa processor can be achieved using the following
algorithm:</p>
<p>While processing an element as described in [<a href=
"#refsXHTMLRDFA">XHTML+RDFA</a>], Section 5.5, <a href=
"http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">Step #2</a>:</p>
<ol>
<li>For each attribute in the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.element">namespace
attributes</a>] list that has a [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">prefix</a>] value,
create a [<a href="http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">URI
mapping</a>] by storing the [prefix] as the value to be mapped, and the
[<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">normalized
value</a>] as the value to map.</li>
<li>For each attribute in the in the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.element">attributes</a>] list
that has no value for [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">prefix</a>] and a
[<a href="http://www.w3.org/TR/xml-infoset/#infoitem.attribute">local
name</a>] that starts with <code>xmlns:</code>, create a [<a href=
"http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">URI mapping</a>] by
storing the [local name] part with the <code>xmlns:</code> characters
removed as the value to be mapped, and the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">normalized
value</a>] as the value to map.<br>
<br>
<span class="XXX">Note: This step is unnecessary if the Infoset coercion
rules preserve namespaces specified in non-XML mode.</span></li>
</ol>
<p>To demonstrate, assume that the following markup is processed by an
Infoset-based RDFa processor:</p>
<pre>
<div xmlns:audio="http://purl.org/media/audio#" ...
</pre>After the markup is processed, there should exist a [URI mapping] in
the [local list of URI mappings] that contains a mapping from
<code>audio</code> to <code>http://purl.org/media/audio#</code>.
<h3 id="processing-rdfa-attributes"><span class="secno">6.2</span>
Processing RDFa Attributes</h3>
<p>There are a number of non-prefixed attributes that are associated with
RDFa Processing in HTML5. If an XML Information Set based RDFa processor is
used to process these attributes, the following algorithm should be used to
detect and extract the values of the attributes.</p>
<p>While processing an element as described in [<a href=
"#refsXHTMLRDFA">XHTML+RDFA</a>], Section 5.5, <a href=
"http://www.w3.org/TR/rdfa-syntax/#T_current_element">Step #4 through Step
#9</a>:</p>
<ol>
<li>For each RDFa attribute in the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">attributes</a>]
list that has a [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">prefix</a>]] with
no value or a [prefix] with the value of
<code>http://www.w3.org/1999/xhtml</code>, extract and use the [<a href=
"http://www.w3.org/TR/xml-infoset/#infoitem.attribute">normalized
value</a>].</li>
</ol>
<h2 id="dom-level-2-based-processors"><span class="secno">7</span> DOM
Level 2-based Processors</h2>
<p><em>This section is informative</em></p>
<p class="XXX">This mechanism should be double-checked against all of the
RDFa Javascript implementations to ensure correctness.</p>
<p>While the intent of the RDFa processing instructions were to provide a
set of rules that are as language and toolchain agnostic as possible, for
the sake of clarity, detailed methods of extracting RDFa content from
processors operating in a DOM2 environment are provided below.</p>
<h3 id="processing-namespaced-rdfa-attributes-0"><span class=
"secno">7.1</span> Processing Namespaced RDFa Attributes</h3>
<p>Extracting namespaced RDFa attributes while operating from within a DOM
Level 2 based RDFa processor can be achieved using the following
algorithm:</p>
<p>While processing each [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-745549614">Element</a>]
as described in [<a href="#refsXHTMLRDFA">XHTML+RDFA</a>], Section 5.5,
<a href="http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">Step #2</a>:</p>
<ol>
<li>For each [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-745549614">Attr</a>]
in the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-1950641247">Node.attributes</a>]
list that has a [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-namespaceprefix">namespace
prefix</a>] value of <code>xmlns</code>, create a [<a href=
"http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">URI mapping</a>] by
storing the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-localname">local
name</a>] as the value to be mapped, and the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-F68D080">Node.nodeValue</a>]
as the value to map.</li>
<li>For each [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-745549614">Attr</a>]
in the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-1950641247">Node.attributes</a>]
list that has a [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-namespaceprefix">namespace
prefix</a>] value of null and a [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-localname">local
name</a>] that starts with <code>xmlns:</code>, create a [<a href=
"http://www.w3.org/TR/rdfa-syntax/#T_URI_mapping">URI mapping</a>] by
storing the [local name] part with the <code>xmlns:</code> characters
removed as the value to be mapped, and the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-F68D080">Node.nodeValue</a>]
as the value to map.<br>
<br>
<span class="XXX">Note: This step is unnecessary if the XML and non-XML
mode DOMs are namespace consistent.</span></li>
</ol>
<p>To demonstrate, assume that the following markup is processed by a
DOM2-based RDFa processor:</p>
<pre>
<div xmlns:audio="http://purl.org/media/audio#" ...
</pre>After the markup is processed, there should exist a [URI mapping] in
the [local list of URI mappings] that contains a mapping from
<code>audio</code> to <code>http://purl.org/media/audio#</code>.
<h3 id="processing-rdfa-attributes-0"><span class="secno">7.2</span>
Processing RDFa Attributes</h3>
<p>There are a number of non-prefixed attributes that are associated with
RDFa processing in HTML5. If an DOM2-based RDFa processor is used to
process these attributes, the following algorithm should be used to detect
and extract the values of the attributes.</p>
<p>While processing an element as described in [<a href=
"#refsXHTMLRDFA">XHTML+RDFA</a>], Section 5.5, <a href=
"http://www.w3.org/TR/rdfa-syntax/#T_current_element">Step #4 through Step
#9</a>:</p>
<ol>
<li>For each RDFa attribute in the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-84CF096">Node.attributes</a>] list that has a [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/glossary.html#dt-namespaceprefix">namespace
prefix</a>] that is null or a [namespace prefix] with the value of
<code>http://www.w3.org/1999/xhtml</code>, extract and use the [<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-F68D080">Node.nodeValue</a>]
as the value.</li>
</ol>
<h2 id="references"><span class="secno">8</span> References</h2>
<h3 id="normative-references"><span class="secno">8.1</span> Normative
References</h3>
<dl>
<dt id="refsHTML5">[<a href="http://www.w3.org/TR/html5/">HTML5</a>]
(currently not a REC)</dt>
<dd>The HTML5 Specification, Ian Hickson. W3C, Work in Progress</dd>
<dt id="refsRFC2119">[<a href=
"http://www.ietf.org/rfc/rfc2119.txt">RFC2119</a>]</dt>
<dd>RFC2119: Key words for use in RFCs to Indicate Requirement Levels, S.
Bradner. IETF, March 1997.</dd>
<dt id="refsXHTMLRDFA">[<a href=
"http://www.w3.org/TR/rdfa-syntax/">XHTML+RDFA</a>]</dt>
<dd>RDFa in XHTML: Syntax and Processing, Mark Birbeck, Shane McCarron,
Steven Pemberton. W3C, October 2008.</dd>
<dt id="refsDOM2">[<a href=
"http://www.w3.org/TR/DOM-Level-2-Core/">DOM2</a>]</dt>
<dd>Document Object Model (DOM) Level 2 Core Specification, Arnaud Le
Hors, Philippe Le Hégaret, Lauren Wood, Gavin Nicol, Jonathan
Robie, Mike Champion, Steve Byrne, W3C, November 2000</dd>
<dt id="refsInfoset">[<a href=
"http://www.w3.org/TR/xml-infoset/">INFOSET</a>]</dt>
<dd>XML Information Set (Second Edition), John Cowan, Richard Tobin, W3C,
February 2004</dd>
</dl>
<h3 id="non-normative-references"><span class="secno">8.2</span>
Non-Normative References</h3>
<dl>
<dt id="refsXHTMLRDF">[<a href=
"http://www.w3.org/MarkUp/2004/02/xhtml-rdf.html">XHTMLRDF</a>]</dt>
<dd>XHTML and RDF, Mark Birbeck. W3C, February 2004.</dd>
</dl>
</body>
</html>