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Make computation of directionality account for shadow trees
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This specifies (with some additional detail) the proposal in #3699 (comment). This changes three things:

* the inheritance of directionality,
* the inheritance of language, and
* the computation of dir=auto to account for shadow trees.

This builds on the work in #9452 and #9554 to refactor this section, and builds on work by Brian Kardell, Eric Meyer, and others in #7424 and in #9166 and work by fantasai, rniwa, smaug, MyIdShin, Brian Kardell, and others in #3699.

Fixes #3699.
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@dbaron
dbaron authored Oct 6, 2023
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Expand Up @@ -13283,7 +13283,8 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
<ref>XML</ref></p>

<p>If these attributes are omitted from an element, then the language of this element is the same
as the language of its parent element, if any.</p>
as the language of its parent element, if any (except for <code>slot</code> elements in a
<span>shadow tree</span>).</p>

<p>The <code data-x="attr-lang">lang</code> attribute in no namespace may be used on any <span
data-x="HTML elements">HTML element</span>.</p>
Expand Down Expand Up @@ -13314,28 +13315,36 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP

<hr>

<p>To determine the <dfn export for="Node">language</dfn> of a node, user agents must look at the
nearest ancestor element (including the element itself if the node is an element) that has a <span
data-x="attr-xml-lang"><code data-x="">lang</code> attribute in the <span>XML
namespace</span></span> set or is an <span data-x="HTML elements">HTML element</span> and has a
<code data-x="attr-lang">lang</code> in no namespace attribute set. That attribute specifies the
language of the node (regardless of its value).</p>

<p>If both the <code data-x="attr-lang">lang</code> attribute in no namespace and the <span
data-x="attr-xml-lang"><code data-x="">lang</code> attribute in the <span>XML
namespace</span></span> are set on an element, user agents must use the <span
data-x="attr-xml-lang"><code data-x="">lang</code> attribute in the <span>XML
namespace</span></span>, and the <code data-x="attr-lang">lang</code> attribute in no namespace
must be <span data-x="ignore">ignored</span> for the purposes of determining the element's
language.</p>
<p>To determine the <dfn export for="Node">language</dfn> of a node, user agents must use the
first appropriate step in the following list:</p>

<dl class="switch">
<dt>If the node is an element that has a <span data-x="attr-xml-lang"><code data-x="">lang</code>
attribute in the <span>XML namespace</span></span> set</dt>
<dd><p>Use the value of that attribute.</p></dd>

<dt>If the node is an <span data-x="HTML elements">HTML element</span> and has a <code
data-x="attr-lang">lang</code> in no namespace attribute set.</dt>
<dd><p>Use the value of that attribute.</p></dd>

<p>If node's <span data-x="inclusive ancestor">inclusive ancestors</span> do not have either
attribute set, but there is a <span>pragma-set default language</span> set, then that is the
language of the node. If there is no <span>pragma-set default language</span> set, then language
information from a higher-level protocol (such as HTTP), if any, must be used as the final
fallback language instead. In the absence of any such language information, and in cases where the
higher-level protocol reports multiple languages, the language of the node is unknown, and the
corresponding language tag is the empty string.</p>
<dt>If the node's parent is a <span>shadow root</span></dt>
<dt>If the node is a <code>slot</code> element whose <span>root</span> is a <span>shadow
root</span></dt>
<dd><p>Use the <span>language</span> of that <span>shadow root</span>'s <span
data-x="concept-DocumentFragment-host">host</span>.</p></dd>

<!-- this assumes that if there's an ancestor element, the parent must be an element -->
<dt>If the node's <span>parent element</span> is not null</dt>
<dd><p>Use the <span>language</span> of that <span>parent element</span>.</p></dd>

<dt>Otherwise</dt>
<dd><p>If there is a <span>pragma-set default language</span> set, then that is the language of
the node. If there is no <span>pragma-set default language</span> set, then language information
from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language
instead. In the absence of any such language information, and in cases where the higher-level
protocol reports multiple languages, the language of the node is unknown, and the corresponding
language tag is the empty string.</p></dd>
</dl>

<p>If the resulting value is not a recognized language tag, then it must be treated as an unknown
language having the given language tag, distinct from all other languages. For the purposes of
Expand Down Expand Up @@ -13551,7 +13560,17 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
<dd><p>Return '<span data-x="concept-rtl">rtl</span>'.</p></dd>

<dt><span data-x="attr-dir-auto-state">auto</span></dt>
<dd><p>Return the <span>auto directionality</span> of <var>element</var>.</p></dd>
<dd>
<ol>
<li><p>Let <var>result</var> be the <span>auto directionality</span> of
<var>element</var>.</p></li>

<li><p>If <var>result</var> is null, then return the <span>parent directionality</span> of
<var>element</var>.</p></li>

<li><p>Return <var>result</var>.</p></li>
</ol>
</dd>

<dt><span data-x="attr-dir-undefined-state">undefined</span></dt>
<dd>
Expand Down Expand Up @@ -13594,47 +13613,106 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
<li><p>If <var>element</var>'s <span data-x="concept-fe-value">value</span> is not the empty
string, then return '<span data-x="concept-ltr">ltr</span>'.</p></li>

<li><p>Return the <span>parent directionality</span> of <var>element</var>.</p></li>
<li><p>Return null.</p></li>
</ol>
</li>

<li><p>Let <var>codePoint</var> be null.</p></li>
<li>
<p>If <var>element</var> is a <code>slot</code> element whose <span>root</span> is a
<span>shadow root</span> and <var>element</var>'s <span>assigned nodes</span> are not empty:</p>

<ol>
<li>
<p><span data-x="list iterate">For each</span> node <var>child</var> of <var>element</var>'s
<span>assigned nodes</span>:</p>

<ol>
<li><p>Let <var>childDirection</var> be null.</p></li>

<li><p>If <var>child</var> is a <code>Text</code> node, then set <var>childDirection</var> to
the <span>text node directionality</span> of <var>child</var>.</p></li>

<li>
<p>Otherwise:</p>

<ol>
<li><p><span>Assert</span>: <var>child</var> is an <code>Element</code> node.</p></li>

<li><p>Set <var>childDirection</var> to the <span>auto directionality</span> of
<var>child</var>.</p></li>
</ol>
</li>

<li><p>If <var>childDirection</var> is not null, then return
<var>childDirection</var>.</p></li>
</ol>
</li>

<li><p>Return null.</p></li>
</ol>
</li>

<li>
<p>For each <code>Text</code> node <var>text</var> that is a descendant of <var>element</var>,
in <span>tree order</span>:</p>
<p><span data-x="list iterate">For each</span> node <var>descendant</var> of
<var>element</var>'s <span data-x="descendant">descendants</span>, in <span>tree
order</span>:</p>

<ol>
<li>
<p>If <var>text</var> has an ancestor element that is a descendant of <var>element</var> and
is also one of</p>
<p>If <var>descendant</var> has an ancestor element that is a descendant of <var>element</var>
and is also one of</p>

<ul class="brief">
<li>a <code>bdi</code> element</li>
<li>a <code>script</code> element</li>
<li>a <code>style</code> element</li>
<li>a <code>textarea</code> element</li>
<li>a <code>slot</code> element whose <span>root</span> is a <span>shadow
root</span></li>
<li>an element whose <code data-x="attr-dir">dir</code> attribute is not in the <span
data-x="attr-dir-undefined-state">undefined</span> state</li>
</ul>

<p>then <span>continue</span>.</p>
</li>

<li><p>If <var>text</var>'s <span data-x="concept-cd-data">data</span> does not contain a code
point whose bidirectional character type is L, AL, or R, then <span>continue</span>.
<ref>BIDI</ref></p></li>
<li>
<p>If <var>descendant</var> is a <code>slot</code> element whose <span>root</span> is a
<span>shadow root</span>, then:</p>

<li><p>Set <var>codePoint</var> to the first code point in <var>text</var>'s <span
data-x="concept-cd-data">data</span> whose bidirectional character type is L, AL, or
R.</p></li>
<ol>
<li><p>Let <var>result</var> be the <span>auto directionality</span> of
<var>descendant</var>.</p></li>.

<li><p>If <var>result</var> is not null, then return <var>result</var>.</p></li>

<li><p><span>Break</span>.</p></li>
<li><p>Return '<span data-x="concept-ltr">ltr</span>'.</p></li>
</ol>
</li>

<li><p>If <var>descendant</var> is not a <code>Text</code> node, then
<span>continue</span>.</p></li>

<li><p>Let <var>result</var> be the <span>text node directionality</span> of
<var>descendant</var>.</li>

<li><p>If <var>result</var> is not null, then return <var>result</var>.</p></li>
</ol>
</li>

<li><p>If <var>codePoint</var> is null, then return the <span>parent directionality</span> of
<var>element</var>.</p></li>
<li><p>Return null.</p></li>
</ol>

<p>To compute the <dfn>text node directionality</dfn> given a <code>Text</code> node
<var>text</var>:</p>

<ol>
<li><p>If <var>text</var>'s <span data-x="concept-cd-data">data</span> does not contain a code
point whose bidirectional character type is L, AL, or R, then return null.
<ref>BIDI</ref></p></li>

<li><p>Let <var>codePoint</var> be the first code point in <var>text</var>'s <span
data-x="concept-cd-data">data</span> whose bidirectional character type is L, AL, or R.</p></li>

<li><p>If <var>codePoint</var> is of bidirectional character type AL or R, then return '<span
data-x="concept-rtl">rtl</span>'.</p></li>
Expand All @@ -13646,11 +13724,21 @@ Transport Protocol">HTTP&lt;/abbr> today.&lt;/p></code></pre> <!-- DO NOT REWRAP
<p>To compute the <dfn>parent directionality</dfn> given an element <var>element</var>:</p>

<ol>
<li><p>If <var>element</var> has no <span>parent element</span>, then return '<span
data-x="concept-ltr">ltr</span>'.</p></li>
<li><p>If <var>element</var> is a <code>slot</code> element whose <span>root</span> is a
<span>shadow root</span>, then return the <span data-x="the directionality">directionality</span>
of <var>element</var>'s <span>root</span>'s <span
data-x="concept-DocumentFragment-host">host</span>.</p></li>

<li><p>Let <var>parentNode</var> be <var>element</var>'s parent node.</p></li>

<li><p>If <var>parentNode</var> is a <span>shadow root</span>, then return the <span data-x="the
directionality">directionality</span> of <var>parentNode</var>'s <span
data-x="concept-DocumentFragment-host">host</span>.</p></li>

<li><p>If <var>parentNode</var> is an element, then return the <span data-x="the
directionality">directionality</span> of <var>parentNode</var>.</p></li>

<li><p>Return <span data-x="the directionality">directionality</span> of <var>element</var>'s
<span data-x="parent element">parent</span>.</p></li>
<li><p>Return '<span data-x="concept-ltr">ltr</span>'.</p></li>
</ol>

<div w-nodev>
Expand Down Expand Up @@ -129391,15 +129479,16 @@ br[clear=all i], br[clear=both i] { clear: both; }</code></pre>

<pre><code class="css">@namespace "http://www.w3.org/1999/xhtml";

[dir]:dir(ltr), bdi:dir(ltr), input[type=tel i]:dir(ltr) { direction: ltr; }
[dir]:dir(rtl), bdi:dir(rtl) { direction: rtl; }
[dir]:dir(ltr), slot:dir(ltr), bdi:dir(ltr), input[type=tel i]:dir(ltr) { direction: ltr; }
[dir]:dir(rtl), slot:dir(rtl), bdi:dir(rtl) { direction: rtl; }

address, blockquote, center, div, figure, figcaption, footer, form, header, hr,
legend, listing, main, p, plaintext, pre, summary, xmp, article, aside, h1, h2,
h3, h4, h5, h6, hgroup, nav, section, search, table, caption, colgroup, col,
thead, tbody, tfoot, tr, td, th, dir, dd, dl, dt, menu, ol, ul, li, bdi, output,
[dir=ltr i], [dir=rtl i], [dir=auto i] {
unicode-bidi: isolate; <!-- anything that's similar to display:block, plus <bdi>, <output>, and dir="" -->
slot, [dir=ltr i], [dir=rtl i], [dir=auto i] {
unicode-bidi: isolate; <!-- anything that's similar to display:block, plus
<bdi>, <output>, <slot>, and dir="" -->
}

bdo, bdo[dir] { unicode-bidi: isolate-override; } <!-- bdo[dir] rule is to override the otherwise higher-specificity attribute selectors in the previous rule -->
Expand Down

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