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Merged
merged 6 commits into from
Oct 17, 2022
Merged

Allow properties without values in viewport meta tags #2457

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8d350c5
make viewport meta property assignment character and value optional
mattgarrish Oct 15, 2022
d9bc550
typo
mattgarrish Oct 15, 2022
6442989
cleanup meta definition
mattgarrish Oct 15, 2022
a12814d
Merge branch 'main' into fix/viewport-properties
mattgarrish Oct 16, 2022
663aaf0
move restriction against duplicate height/width properties to fxl sec…
mattgarrish Oct 17, 2022
131a4c3
Merge branch 'main' into fix/viewport-properties
mattgarrish Oct 17, 2022
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56 changes: 29 additions & 27 deletions epub33/core/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -7575,6 +7575,9 @@ <h4>Content document dimensions</h4>
</ul>
<p>The <code>device-width</code> and <code>device-height</code> values refer to the 100%
of the width and height, respectively, of the reading system's [=viewport=].</p>
<p>EPUB creators MUST NOT specify duplicate <code>height</code> or <code>width</code>
definitions either within a single <code>viewport meta</code> tag or by specifying
multiple <code>viewport meta</code> tags.</p>
<aside class="example"
title="Specifying the initial containing block in a viewport meta tag">
<pre>&lt;html …>
Expand Down Expand Up @@ -10644,9 +10647,9 @@ <h3>Introduction</h3>
<section id="app-viewport-meta-syntax">
<h3>Syntax</h3>

<p>A <code>viewport</code>
<a data-cite="html#meta"><code>meta</code></a> tag [[html]] MUST have <code>name</code> and
<code>content</code> attributes that conform to the following definition:</p>
<p>For [=fixed-layout documents=], a <code>viewport</code> [^meta^] tag [[html]] MUST have
<code>name</code> and <code>content</code> attributes that conform to the following
definition:</p>

<dl>
<dt id="viewport-name-attr">name</dt>
Expand All @@ -10667,16 +10670,16 @@ <h3>Syntax</h3>
<a href="#viewport.ebnf.def">viewport</a>
</td>
<td>=</td>
<td><a href="#viewport.ebnf.property">property</a>, {<a href="#viewport.ebnf.sep"
>sep</a>, <a href="#viewport.ebnf.property">property</a>} ;</td>
<td><a href="#viewport.ebnf.property">property</a>, { <a href="#viewport.ebnf.sep"
>sep</a>, <a href="#viewport.ebnf.property">property</a> } ;</td>
</tr>
<tr>
<td id="viewport.ebnf.property">
<a href="#viewport.ebnf.property">property</a>
</td>
<td>=</td>
<td><a href="viewport.ebnf.name">name</a>, <a href="viewport.ebnf.assign">assign</a>, <a
href="viewport.ebnf.value">value</a> ;</td>
<td><a href="#viewport.ebnf.name">name</a>, [ <a href="#viewport.ebnf.assign"
>assign</a>, <a href="#viewport.ebnf.value">value</a> ] ;</td>
</tr>
<tr>
<td id="viewport.ebnf.name">
Expand Down Expand Up @@ -10713,8 +10716,8 @@ <h3>Syntax</h3>
<a href="#viewport.ebnf.assign">assign</a>
</td>
<td>=</td>
<td>[<a href="#viewport.ebnf.space">space</a>], "=", [<a href="#viewport.ebnf.space"
>space</a>] ;</td>
<td>[ <a href="#viewport.ebnf.space">space</a> ], "=", [ <a href="#viewport.ebnf.space"
>space</a> ] ;</td>
</tr>
<tr>
<td id="viewport.ebnf.space">
Expand All @@ -10727,31 +10730,28 @@ <h3>Syntax</h3>
</dd>
</dl>

<p>This specification only defines <a href="#viewport.ebnf.value">value</a> requirements for the
<code>height</code> and <code>width</code> properties (see <a href="#sec-fxl-content-dimensions"
></a>). It imposes no restrictions on other property names and values except that they MUST NOT
contain <a href="#viewport.ebnf.sep-char">separator characters</a> or the <a
href="#viewport.ebnf.assign">assignment character</a>.</p>
<p>The only restriction on property <a href="#viewport.ebnf.name">names</a> and <a
href="#viewport.ebnf.value">values</a> is that they MUST NOT contain <a
href="#viewport.ebnf.sep-char">separator characters</a> or the <a href="#viewport.ebnf.assign"
>assignment character</a>.</p>

<p> The [^meta/content^] attribute MUST NOT include several <code>height</code>, respectively
<code>width</code>, assignments. </p>
<p>The authoring requirements in this section apply <em>after</em>
<a data-cite="xml#AVNormalize">whitespace normalization</a> [[xml]] (i.e., after a reading system
strips leading and trailing whitespace and compacts all instances of multiple whitespace within the
attribute to single spaces). EPUB creators MAY include any valid [=ascii whitespace=] [[infra]] in
the authored tag so long as the result is valid to this definition.</p>

<p>There are no restrictions on any other attributes allowed on the [^meta^] element by the [[html]]
grammar.</p>

<div class="note">
<p>Although the <code>viewport meta</code> tag allows EPUB creators to use properties other than
<code>height</code> and <code>width</code>, such use is strongly discouraged. Setting other
properties may have unintended consequences on the rendering of [=fixed-layout documents=].</p>
</div>
<p>For more information about specifying the required <code>height</code> and <code>width</code>
properties, and their required values, refer to <a href="#sec-fxl-content-dimensions"></a>.</p>

<div class="note">
<p>The authoring requirements in this section apply <em>after</em>
<a data-cite="xml#AVNormalize">whitespace normalization</a> [[xml]] (i.e., after a reading
system strips leading and trailing whitespace and compacts all instances of multiple whitespace
within the attribute to single spaces). EPUB creators can include any valid HTML whitespace
characters (e.g., tabs, line feeds) in the authored tag so long as the result is valid to this
definition.</p>
<p>Although the <code>viewport meta</code> tag allows EPUB creators to use properties other than
<code>height</code> and <code>width</code>, and to not include values for these properties,
such use is strongly discouraged. Setting other properties may have unintended consequences on
the rendering of fixed-layout documents.</p>
</div>
</section>
</section>
Expand Down Expand Up @@ -11728,6 +11728,8 @@ <h3>Substantive changes since <a href="https://www.w3.org/TR/2022/CR-epub-33-202
Recommendation</a></h3>

<ul>
<li>15-Oct-2022: Allow properties without values in <code>viewport meta</code> tag definition. See
<a href="https://github.com/w3c/epub-specs/pull/2457">pull request 2457</a>.</li>
<li>11-Oct-2022: Added additional requirement that <code>viewport meta</code> height and width not
be declared multiple times. See <a href="https://github.com/w3c/epub-specs/issues/2442">issue
2442</a>.</li>
Expand Down