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Merge pull request #2832 from w3c/chore/revert-html-syntax
Remove references to html syntax
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‎epub34/authoring/index.html‎

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@@ -226,25 +226,15 @@ <h4>Relationship to HTML</h4>
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<p>The [[html]] standard defines a single content model with rules for expressing a tag set using
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either the <a data-cite="html#syntax">HTML syntax</a> or the <a
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data-cite="html#the-xhtml-syntax">XML syntax</a>. EPUB 3 allows authoring of content
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documents using either of these syntaxes even though the [[html]] standard <a
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data-cite="html/xhtml.html#the-xhtml-syntax">no longer recommends the use of the XML
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syntax</a>. The Working Group recognizes that XML remains an integral technology in the
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publishing ecosystem and will not remove support for the XML syntax from EPUB 3. Regardless,
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publishers that prefer to keep using the XML syntax will need to monitor future support for it,
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and might have to adapt to the HTML syntax to gain access to some features of [[html]].</p>
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<div class="issue" data-number="2715" title="Adoption of the HTML syntax">
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<p>The change to allow both syntaxes of HTML is an open issue in EPUB 3.4. The above paragraph
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was added to help explain the change, but would be amended if the HTML syntax is not
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adopted.</p>
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</div>
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data-cite="html#the-xhtml-syntax">XML syntax</a>. EPUB 3, however, only allows authoring of
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content documents using the XML syntax, in what are referred to as [=XHTML content
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documents=].</p>
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<p>The <a href="#sec-xhtml">HTML profile defined by this specification</a> inherits all definitions
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<p>The <a href="#sec-xhtml">XHTML profile defined by this specification</a> inherits all definitions
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of semantics, structure and processing behaviors from [[html]] unless otherwise specified.</p>
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<p>In addition, this specification <a href="#sec-xhtml-extensions">defines a set of extensions</a>
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to the [[html]] document model that can be included in [=HTML content documents=].</p>
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to the [[html]] document model that can be included in XHTML content documents.</p>
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</section>
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<section id="sec-overview-relations-svg">
@@ -498,35 +488,6 @@ <h3>Terminology</h3>
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</div>
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</dd>
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<dt>
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<dfn class="export">HTML content document</dfn>
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</dt>
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<dt>
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<small>(formerly <dfn class="export">XHTML content document</dfn>)</small>
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</dt>
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<dd>
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<p>An [=EPUB content document=] that conforms to the profile of [[html]] defined in <a
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href="#sec-xhtml"></a>.</p>
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<p>HTML content documents can be expressed in either the <a data-cite="html#syntax">HTML
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syntax</a> or the <a data-cite="html#the-xhtml-syntax">XML syntax</a> [[html]].</p>
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<div class="note">
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<p>EPUB 3 previously supported only the XML syntax of [[html]] via what were called XHTML
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content documents. The change of name to HTML content documents is not to give priority
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to the HTML syntax but to better reflect that [[html]] is the common standard for both
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syntaxes. The term "XHTML" used to refer to [[xhtml11]], but that was replaced by the
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XML syntax of [[html]] in 2011, which also officially superseded [[xhtml11]] in
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2018.</p>
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</div>
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<div class="issue" data-number="2715" title="Adoption of the HTML syntax">
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<p>The change to allow both syntaxes of HTML is an open issue in EPUB 3.4. It is important
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to note that EPUB 3 is already based on [[html]] and this change only makes the HTML
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syntax valid to use. Because EPUB 2's XHTML content documents were implemented using
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[[xhtml11]], some authors mistakenly assume EPUB 3's XHTML content documents use the
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same technology and that this change represents a move to a new standard.</p>
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<p>This new definition will be amended if the HTML syntax is not adopted.</p>
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</div>
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</dd>
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<dt>
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<dfn class="export">linked resource</dfn>
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</dt>
@@ -648,6 +609,23 @@ <h3>Terminology</h3>
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chain</a>.</p>
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</dd>
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<dt>
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<dfn class="export">XHTML content document</dfn>
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</dt>
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<dd>
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<p>An [=EPUB content document=] that conforms to the profile of [[html]] defined in <a
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href="#sec-xhtml"></a>.</p>
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<p>XHTML content documents are expressed using the <a data-cite="html#the-xhtml-syntax">XML
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syntax</a> [[html]].</p>
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<div class="note">
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<p>Although the [[html]] standard no longer refers to the XML syntax as "XHTML", the name
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XHTML was still current at the time EPUB 3.0 was developed. The name "XHTML content
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document" was also used in EPUB 2, so keeping it unchanged was intended to help ease
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transition to the new format. Unlike in EPUB 2, XHTML in this document does not refer to
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[[xhtml11]], which was officially superseded in 2018.</p>
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</div>
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</dd>
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<dt>
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<dfn class="export">unique identifier</dfn>
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</dt>
@@ -987,21 +965,12 @@ <h3>Core media types</h3>
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<tr>
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<th colspan="3" id="cmt-grp-html" class="tbl-group">HTML</th>
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</tr>
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<tr>
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<td id="cmt-html">
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<code>text/html</code>
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</td>
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<td>
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<a href="#sec-xhtml">HTML content documents</a>
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</td>
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<td>HTML documents that use the <a data-cite="html#syntax">HTML syntax</a> [[html]]</td>
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</tr>
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<tr>
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<td id="cmt-xhtml">
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<code>application/xhtml+xml</code>
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</td>
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<td>
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<a href="#sec-xhtml">HTML content documents</a>
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<a href="#sec-xhtml">XHTML content documents</a>
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</td>
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<td>HTML documents that use the <a data-cite="html#the-xhtml-syntax">XML syntax</a>
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[[html]]</td>
@@ -3061,10 +3030,10 @@ <h2>Package document</h2>
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<section id="sec-package-intro" class="informative">
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<h3>Introduction</h3>
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<p>The [=package document=] is an XML document that consists of a set of elements that each encapsulate
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information about a particular aspect of an [=EPUB publication=]. These elements serve to centralize
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metadata, detail the individual resources, and provide the reading order and other information
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necessary for its rendering.</p>
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<p>The [=package document=] is an <a href="#sec-xml-constraints">XML document</a> that consists of a set
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of elements that each encapsulate information about a particular aspect of an [=EPUB publication=].
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These elements serve to centralize metadata, detail the individual resources, and provide the
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reading order and other information necessary for its rendering.</p>
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<p>The following list summarizes the information found in the package document:</p>
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@@ -5864,40 +5833,51 @@ <h4>The <code>itemref</code> element</h4>
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<h2>EPUB content documents</h2>
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<section id="sec-xhtml">
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<h3>HTML content documents</h3>
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<div class="ednote">
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<p>Support for the HTML syntax is still an <a href="https://github.com/w3c/epub-specs/issues/2715"
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>open issue</a> in the EPUB 3.4 revision. It is <b><i>at risk</i></b>, depending on authors'
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and implementers' feedback. This specification introduces it as a core media type and also
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minimally adds requirements for its authoring in this section to begin making readers aware of
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the proposed change.</p>
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<p>Much of this specification, and the Reading Systems specification [[epub-rs-34]], continues to
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refer only to XHTML content documents and their authoring requirements, a number of which need
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resolving (e.g., providing an <a href="#sec-epub-type-attribute">alternative to the
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<code>epub:type</code> attribute</a>). These references and requirements will be updated
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once it is clearer that support will definitely be added in this revision. Until then, the
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specification should be read as also supporting HTML wherever it currently refers to XHTML,
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despite the support inconsistencies.</p>
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<p>To provide feedback on this change, please add comments to <a
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href="https://github.com/w3c/epub-specs/issues/2715">issue 2715</a> in the GitHub
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tracker.</p>
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</div>
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<h3>XHTML content documents</h3>
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<section id="sec-xhtml-intro" class="informative">
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<h4>Introduction</h4>
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<p>This section defines a profile of [[html]] for creating HTML content documents. An instance of an
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HTML document that conforms to this profile is a [=core media type resource=].</p>
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<p>An [=XHTML content document=] is an instance of an <a href="#sec-xml-constraints">XML
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document</a> expressed using the <a data-cite="html#the-xml-syntax">XML syntax</a> of the
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[[[html]]] [[html]].</p>
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<p>XHTML content documents that conform to this profile are [=core media type resources=] and one of
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the two formats that constitute [=EPUB content documents=] &#8212; that can be used without
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fallbacks in the [^spine^].</p>
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<div class="note">
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<p>EPUB 3 does not support the <a data-cite="html#the-html-syntax">HTML syntax</a> of [[html]]
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as a core media type. Although both serializations allow the same elements to be expressed,
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not all JavaScript libraries and APIs are designed to handle the XML syntax, in particular
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the shadow DOM. This means, for example, that although the [^template^] element [[html]] can
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be authored in the XML syntax it may not be usable in the same way as in the HTML
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syntax.</p>
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<p>The Publishing Maintenance Working Group is aware that the HTML Standard no longer recommends
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the use of the XML syntax. XML, however, is integral to many publishing workflows and
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expected in many vendor ingestion systems and reading systems. It is also not expected that
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support for XHTML will be dropped from browsers, even if there are additional support
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differences between the syntax in the future. Support for the HTML syntax may be addressed
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in a successor format to EPUB 3.</p>
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</div>
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<div class="note">
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<p>Earlier versions of EPUB 3 referred to W3C's HTML5 standard to define EPUB content documents,
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but that standard was largely a snapshot of the HTML Standard maintained by the WHATWG.
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After reaching an <a href="https://www.w3.org/2019/04/WHATWG-W3C-MOU.html">agreement</a> on the development of HTML in 2019, the W3C standard was retired
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and EPUB 3 now exclusively refers to the HTML Standard. It does not mean that EPUB 3 does
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not support HTML5 anymore in XHTML content documents, only that HTML5 is now a marketing
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term that refers to the HTML Standard as the successor to HTML 4.01 and XHTML 1.1.</p>
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</div>
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</section>
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<section id="sec-xhtml-req" data-epubcheck="true"
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data-tests="https://w3c.github.io/epub-structural-tests/#06-content-document_content-document-xhtml.feature_L21,https://w3c.github.io/epub-structural-tests/#06-content-document_content-document-xhtml.feature_L26,https://w3c.github.io/epub-structural-tests/#06-content-document_content-document-xhtml.feature_L32,https://w3c.github.io/epub-structural-tests/#06-content-document_content-document-xhtml.feature_L529,https://w3c.github.io/epub-structural-tests/#06-content-document_content-document-xhtml.feature_L534">
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<h4>HTML requirements</h4>
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<h4>XHTML requirements</h4>
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<p>An HTML content document:</p>
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<p>An XHTML content document:</p>
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<ul class="conformance-list">
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<li>
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conformance constraints defined therein.</p>
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</li>
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<li>
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<p id="confreq-cd-html-docprops-syntax">MUST either:</p>
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<ul class="conformance-list">
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<li id="confreq-cd-html-docprops-syntax-html">conform to the <a data-cite="html#writing"
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>HTML syntax</a> [[html]] when defined in the [=epub manifest|manifest=] as
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having the media type <code>text/html</code>; or</li>
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<li id="confreq-cd-html-docprops-syntax-xml">conform to the <a
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data-cite="html#writing-xhtml-documents">XML syntax</a> [[html]] when defined in
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the [=epub manifest|manifest=] as having the media type
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<code>application/xhtml+xml</code>.</li>
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</ul>
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<p id="confreq-cd-html-docprops-syntax-xml">MUST be an [[html]] document that conforms to
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the <a data-cite="html#writing-xhtml-documents">XML syntax</a>.</p>
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</li>
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</ul>
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<p>Unless specified otherwise, HTML content documents inherit all definitions of semantics,
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<p>Unless specified otherwise, XHTML content documents inherit all definitions of semantics,
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structure, and processing behaviors from the [[html]] specification.</p>
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<div class="note">
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<p>The recommendation that [=EPUB publications=] follow the accessibility requirements in
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[[epub-a11y-12]] applies to HTML content documents. See <a href="#confreq-a11y"
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[[epub-a11y-12]] applies to XHTML content documents. See <a href="#confreq-a11y"
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>Accessibility</a>.</p>
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</div>
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</section>
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</section>
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<section id="sec-epub-type-attribute">
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<h3>The <code>type</code> attribute</h3>
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<h3>The <code>epub:type</code> attribute</h3>
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<section id="sec-structural-semantics">
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<h4>Structural semantics</h4>
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<section id="type-attr-syntax">
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<h4>Syntax</h4>
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<dl>
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<dt>XHTML serialization</dt>
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<dd>
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<dl class="elemdef" id="attrdef-epub-type-xhtml">
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<dt>Attribute Name:</dt>
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<dd>
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<p>
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<dfn class="export" data-lt-no-plural="" data-dfn-type="element-attr">
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<code>epub:type</code>
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</dfn>
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</p>
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</dd>
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<dt>Namespace:</dt>
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<dd>
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<p>
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<code>http://www.idpf.org/2007/ops</code>
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</p>
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</dd>
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<dt>Usage:</dt>
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<dd>
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<p>Refer to the requirements for <a href="#sec-xhtml-structural-semantics"
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>XHTML</a>, <a href="#confreq-svg-structural-semantics">SVG</a>, and <a
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href="#sec-overlays-def">media overlays</a>.</p>
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</dd>
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<dt>Value:</dt>
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<dd>
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<p>A <a data-cite="xml#NT-S">whitespace-separated</a> [[xml]] list of [=compact
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URLs=], with restrictions as defined in <a href="#sec-vocab-assoc"></a>.</p>
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</dd>
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</dl>
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<dl class="elemdef" id="attrdef-epub-type-xhtml">
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<dt>Attribute Name:</dt>
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<dd>
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<p>
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<dfn class="export" data-lt-no-plural="" data-dfn-type="element-attr">
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<code>epub:type</code>
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</dfn>
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</p>
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</dd>
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<dt>HTML serialization</dt>
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<dt>Namespace:</dt>
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<dd>
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<dl class="elemdef" id="attrdef-epub-type-html">
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<dt>Attribute Name:</dt>
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<dd>
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<p>
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<dfn class="export" data-lt-no-plural="" data-dfn-type="element-attr">
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<code>epub-type</code>
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</dfn>
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</p>
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</dd>
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<p>
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<code>http://www.idpf.org/2007/ops</code>
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</p>
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</dd>
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<dt>Usage:</dt>
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<dd>
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<p>Refer to the requirements for <a href="#sec-xhtml-structural-semantics"
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>HTML</a>.</p>
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</dd>
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<dt>Usage:</dt>
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<dd>
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<p>Refer to the requirements for <a href="#sec-xhtml-structural-semantics">XHTML</a>, <a
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href="#confreq-svg-structural-semantics">SVG</a>, and <a
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href="#sec-overlays-def">media overlays</a>.</p>
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</dd>
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<dt>Value:</dt>
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<dd>
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<p>A [=ASCII whitespace|whitespace-separated=] [[infra]] list of values that
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SHOULD be taken from the EPUB 3 Structural Semantics Vocabulary
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[[epub-ssv-11]].</p>
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</dd>
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</dl>
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<dt>Value:</dt>
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<dd>
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<p>A <a data-cite="xml#NT-S">whitespace-separated</a> [[xml]] list of [=compact URLs=],
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with restrictions as defined in <a href="#sec-vocab-assoc"></a>.</p>
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</dd>
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</dl>
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<div class="ednote">
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<p>Support for an HTML serialization of the <code>epub:type</code> attribute depends on the
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addition of support for the <a href="#sec-xhtml">HTML syntax</a> in the EPUB 3.4
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revision. It is <b><i>at risk</i></b>, depending on authors' and implementers'
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feedback.</p>
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<p>The proposed <code>epub-type</code> will provide similar functionality for HTML content
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documents but with some restrictions (namely, no extensibility through the
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<code>epub:prefix</code> attribute). The attribute should be read as a replacement
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for <code>epub:type</code> where this specification and the Reading Systems
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specification [[epub-rs-34]] refer to that attribute for XHTML content documents. These
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references will be updated once it is clearer that support will definitely be added in
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this revision.</p>
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<p>The <code>epub:type</code> attribute will remain the sole means of including semantics in
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XML grammars in EPUB (i.e., XHTML content documents, SVG content documents, and media
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overlay documents).</p>
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<p>To provide feedback on this change, please open issues in the <a
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href="https://github.com/w3c/epub-specs/issues">GitHub tracker for the EPUB
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specifications</a>.</p>
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</div>
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<div class="caution">
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<p>Although the <code>epub:type</code> attribute is similar in nature to the [^/role^]
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attribute&#160;[[html]], the attributes serve different purposes. The values of the
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<details id="changes-epub-33" open="open">
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<summary>Substantive changes since <a href="https://www.w3.org/TR/epub-33/">EPUB 3.3</a></summary>
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<ul>
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<li>11-Nov-2025: Removed support for the HTML syntax.</li>
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<li>10-Oct-2025: Added caution that SHA-1 is being phased out so other methods of protecting fonts
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than the font obfuscation are advised. See <a
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href="https://github.com/w3c/epub-specs/issues/2807">issue 2807</a>.</li>

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