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Add a further explanation of ltr and rtl (based on ePub). #109

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merged 10 commits into from
Oct 31, 2024
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Add a further explanation of ltr and rtl (based on ePub). #109

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ef0c93f
Add a further explaination on `ltr` and `rtl` (based on ePub).
gkellogg Oct 24, 2024
d9980e0
Change description for `ltr` and `rtl`.
gkellogg Oct 25, 2024
93e44b5
Add example of displaying right-to-left text in its natural order vs …
gkellogg Oct 25, 2024
0bd3b8b
Fix markup errors.
gkellogg Oct 25, 2024
ecf192f
Apply suggestions from code review
gkellogg Oct 25, 2024
69102f3
Update I18N description of implicit initial text direction
gkellogg Oct 28, 2024
42eff58
Tweak language on left-to-right/right-to-left.
gkellogg Oct 28, 2024
e4a51e7
Use I18N-Glossary instead of UAX9 and UAX15 references.
gkellogg Oct 28, 2024
4a2d2af
Update Arabic exammple to Hebrew.
gkellogg Oct 28, 2024
038ffc5
bidi isolation
gkellogg Oct 29, 2024
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43 changes: 31 additions & 12 deletions spec/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -707,8 +707,7 @@ <h3>IRIs</h3>
“<code>%3f</code>”)</li>
<li>Punycode-encoding of Internationalized Domain Names
in IRIs [[RFC3492]]</li>
<li>IRIs that are not in Unicode
<a class="lint-ignore">Normalization Form C</a> [[UAX15]]</li>
<li>IRIs that are not in Unicode [=Normalization Form C=] [[I18N-Glossary]]</li>
</ul>
</div>
</section>
Expand Down Expand Up @@ -759,6 +758,12 @@ <h2>Literals</h2>
The third element, the language tag, is treated identically as in a <a>language-tagged string</a>,
and the fourth element, <a>base direction</a>, MUST be either `ltr` or `rtl`, which MUST be in lower case.</p>

<p>The meanings of the <a>base direction</a> values are:</p>
<ul>
<li>`ltr`: indicates that the initial text direction is set to left-to-right.</li>
<li>`rtl`: indicates that the initial text direction is set to right-to-left.</li>
</ul>

<p>Please note that concrete syntaxes MAY support
<dfn data-lt="simple literal" class="export">simple literals</dfn> consisting of only a
<a>lexical form</a> without any <a>datatype IRI</a>, <a>language tag</a>, or <a>base direction</a>.
Expand Down Expand Up @@ -806,14 +811,15 @@ <h2>Literals</h2>

<p><dfn data-local-lt="term-equal">Literal term equality</dfn>:
Two literals are term-equal (the same <a>RDF literal</a>)
if and only if:
<ul>
<li>the two <a>lexical forms</a> compare equal</li>
<li>the two <a>datatype IRIs</a> compare equal</li>
<li>the two <a>language tags</a> (if any) compare equal</li>
<li>the two <a>base directions</a> (if any) compare equal</li>
</ul>
Comparison is performed using
if and only if:</p>

<ul>
<li>the two <a>lexical forms</a> compare equal</li>
<li>the two <a>datatype IRIs</a> compare equal</li>
<li>the two <a>language tags</a> (if any) compare equal</li>
<li>the two <a>base directions</a> (if any) compare equal</li>
</ul>
<p>Comparison is performed using
<a data-cite="I18N-GLOSSARY#dfn-case-sensitive">case sensitive matching</a>
(see description of string comparison in
<a href="#rdf-strings" class="sectionRef"></a>)
Expand All @@ -839,7 +845,7 @@ <h3>Initial Text Direction</h3>
<p>The <a>base direction</a> of a <a>directional language-tagged string</a>
provides a means of establishing the initial direction of text,
including text which is a mixture of right-to-left and left-to-right scripts.
The [[[?UAX9]]] [[?UAX9]] provides support for automatically rendering
The [=Unicode Bidirectional Algorithm=] [[?I18N-Glossary]] provides support for automatically rendering
a sequence of characters in logical order,
so that they are visually ordered as expected,
but this is not sufficient to correctly render bidirectional text.</p>
Expand All @@ -851,6 +857,19 @@ <h3>Initial Text Direction</h3>
HTML's `dir` attribute) it can then be correctly presented as:
</p>
<div lang="he" dir="rtl">פעילות הבינאום, W3C</div>

<p>In the absence of an explicit initial text direction,
the [=Unicode Bidirectional Algorithm=] detects the text direction from the content.
This depends on the first strongly directional character in the text
or on the context.
To avoid [=spillover effects=], users need to employ [=bidi isolation=]
whenever text is inserted into a larger document.
For example,
&quot;<code>&lt;bdi lang="he"&gt;ספרים בינלאומיים!&lt;/bdi&gt;</code>&quot;
displays the Hebrew characters in a right-to-left fashion
— i.e., as &quot;<bdi lang="he">ספרים בינלאומיים!</bdi>&quot;
— while they would be stored in memory as
&quot;<bdo dir="ltr" lang="he">ספרים בינלאומיים!</bdo>&quot;</p>
</section>
</section>

Expand Down Expand Up @@ -1687,7 +1706,7 @@ <h2>Security Considerations</h2>
<section id="internationalization" class="appendix informative">
<h2>Internationalization Considerations</h2>
<p>Unicode [[UNICODE]] provides a mechanism for signaling direction within a string
(see [[[UAX9]]] [[UAX9]]).
(see [=Unicode Bidirectional Algorithm=] [[I18N-Glossary]]).
RDF provides a mechanism for specifying the <a>base direction</a>
of a <a>directional language-tagged string</a>
to signal the initial text direction of a string.
Expand Down
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