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Add support for RTL mirroring of operators
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‎spec.html‎

Lines changed: 85 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -1738,13 +1738,21 @@ <h4>Layout of operators</h4>
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<a data-xref-type="css-property">color</a>
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of the <code>&lt;mo&gt;</code> element.
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</p>
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<p>
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Let <code>dir</code> be the element's computed
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<a data-xref-type="css-property">direction</a>.
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</p>
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<p>Operators are laid out as follows:</p>
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<ol class="algorithm">
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<li>
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If the content of the <code>&lt;mo&gt;</code> element is not
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made
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of a single character <code>c</code> then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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Otherwise, let <code>g</code> be the result of running
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<a>get a glyph</a> corresponding to <code>c</code>
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with directionality <code>dir</code>.
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</li>
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<li>
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If the operator has the [=embellished operator/stretchy=] property:
@@ -1754,11 +1762,10 @@ <h4>Layout of operators</h4>
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<ol>
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<li>
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If it is not possible to <a>shape a stretchy glyph</a>
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corresponding to <code>c</code> in the inline direction
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with the
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<a>first available font</a>
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then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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<code>g</code> in the inline direction with the
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<a>first available font</a> then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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</li>
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<li>
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The <a>min-content inline size</a> and
@@ -1772,18 +1779,19 @@ <h4>Layout of operators</h4>
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<code>T<sub>inline</sub></code>
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then
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fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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</li>
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<li>
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The <a>inline size</a> and (ink) block metrics of the math content
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are given by algorithm to
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<a>shape a stretchy glyph</a> to <a>inline dimension</a>
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<code>T<sub>inline</sub></code>.
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<a>shape a stretchy glyph</a> <code>g</code> to
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<a>inline dimension</a> <code>T<sub>inline</sub></code>.
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</li>
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<li>
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The painting of the operator is performed by the
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algorithm
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to <a>shape a stretchy glyph</a>
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to <a>shape a stretchy glyph</a> <code>g</code>
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stretched to <a>inline dimension</a>
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<code>T<sub>inline</sub></code> and
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at position determined by the previous box metrics.
@@ -1796,11 +1804,10 @@ <h4>Layout of operators</h4>
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<ol>
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<li>
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If it is not possible to <a>shape a stretchy glyph</a>
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corresponding to <code>c</code> in the block direction
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with the
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<a>first available font</a>
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then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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<code>g</code> in the block direction with the
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<a>first available font</a> then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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</li>
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<li>
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The <a>min-content inline size</a> and
@@ -1815,7 +1822,8 @@ <h4>Layout of operators</h4>
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<code>(U<sub>ascent</sub>, U<sub>descent</sub>)</code>
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then
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fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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</li>
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<li>If the operator has the [=embellished operator/symmetric=] property
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then set the target sizes
@@ -1920,7 +1928,7 @@ <h4>Layout of operators</h4>
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<a>line-descent</a>
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of the math content
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are obtained by the algorithm to
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<a>shape a stretchy glyph</a>
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<a>shape a stretchy glyph</a> <code>g</code>
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to <a>block dimension</a>
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<code>T<sub>ascent</sub></code> +
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<code>T<sub>descent</sub></code>.
@@ -1937,7 +1945,7 @@ <h4>Layout of operators</h4>
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</li>
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<li>
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The painting of the operator is performed by the
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algorithm to <a>shape a stretchy glyph</a>
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algorithm to <a>shape a stretchy glyph</a> <code>g</code>
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stretched to <a>block dimension</a>
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<code>T<sub>ascent</sub></code> +
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<code>T<sub>descent</sub></code>
@@ -1962,11 +1970,10 @@ <h4>Layout of operators</h4>
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<ol>
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<li>
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If it is not possible to <a>shape a stretchy glyph</a>
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corresponding to <code>c</code> in the block direction
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with the
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<a>first available font</a>
1968-
then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>.
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<code>g</code> in the block direction with the
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<a>first available font</a> then fall back to the
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layout algorithm of <a href="#layout-of-mtext"></a>
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and return.
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<div class="note">
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Here we treat a non-[=embellished operator/stretchy=] [=embellished operator/largeop=]
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glyph as stretchy with target dimension <a>DisplayOperatorMinHeight</a>.
@@ -1986,7 +1993,7 @@ <h4>Layout of operators</h4>
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<a>line-descent</a>
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of the math content
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are obtained by the algorithm to
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<a>shape a stretchy glyph</a>
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<a>shape a stretchy glyph</a> <code>g</code>
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to <a>block dimension</a>
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<a>DisplayOperatorMinHeight</a>.
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The <a>inline size</a> of the math content is the width of
@@ -2015,7 +2022,7 @@ <h4>Layout of operators</h4>
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</li>
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<li>
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The painting of the operator is performed by the
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algorithm to <a>shape a stretchy glyph</a>
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algorithm to <a>shape a stretchy glyph</a> <code>g</code>
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stretched to <a>block dimension</a>
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<a>DisplayOperatorMinHeight</a>
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and at position determined by the previous box metrics
@@ -2878,8 +2885,11 @@ <h5>Radical symbol</h5>
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of that element.
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</p>
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<p>
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The <dfn>radical glyph</dfn> is the glyph obtained for the
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character U+221A SQUARE ROOT.
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Let <code>dir</code> be the computed <a data-xref-type="css-property">direction</a>
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of the <code>&lt;msqrt&gt;</code> or <code>&lt;mroot&gt;</code> element.
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The <dfn>radical glyph</dfn> is the glyph obtained as a result of running
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<a>get a glyph</a> corresponding to the U+221A SQUARE ROOT character
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given <code>dir</code>.
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</p>
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<p>
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The <dfn>radical gap</dfn> is given by
@@ -2896,8 +2906,8 @@ <h5>Radical symbol</h5>
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<p>
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The <dfn>box metrics of the radical glyph</dfn>
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and <dfn>painting of the surd</dfn> are given by the algorithm to
2899-
<a>shape a stretchy glyph</a> to <a>block dimension</a> the
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target size for the radical glyph.
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<a>shape a stretchy glyph</a> to the
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target size for the radical glyph in the <a>block dimension</a>.
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</p>
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</section>
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<section>
@@ -5679,6 +5689,52 @@ <h4>Algorithms for glyph stretching</h4>
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such as
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the one suggested in <a href="#unicode-based-glyph-assemblies"></a>.
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</div>
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<p>
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The algorithm to <dfn>get a glyph</dfn> corresponding to a character <code>c</code> given a directionality <code>dir</code>
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is the following:
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</p>
5696+
<ul class="algorithm">
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<li>
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Let <code>g</code> be the glyph corresponding to <code>c</code>.
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</li>
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<li>
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If <code>dir</code> is <code>rtl</code>:
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<ul>
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<li>
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If there exists an OpenType rtlm variant of
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<code>g</code>, then return it. [[OPEN-FONT-FORMAT]]
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</li>
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<li>
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Otherwise, if <code>c</code> has the Bidi_Mirrored property [[BIDI]]:
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<ul>
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<li>
5711+
If <code>c</code> has a corresponding codepoint, <code>c'</code>,
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for which its glyph is typically the mirror image of <code>g</code>,
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then return the glyph corresponding to <code>c'</code>.
5714+
</li>
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<li>
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Otherwise, transform <code>g</code> by scaling it by a factor
5717+
of -1 horizontally and return the result.
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<div class="note">
5719+
This exists as a fallback for when a character should be mirrored
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according to its Bidi_Mirrored property, but no corresponding codepoint
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or glyph exists.
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</div>
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</li>
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</ul>
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</li>
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<li>
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Otherwise, return <code>g</code>.
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</li>
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</ul>
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</li>
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<li class="assert">
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Assert: <code>dir</code> is <code>ltr</code>.
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</li>
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<li>
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Return <code>g</code>.
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</li>
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</ul>
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</section>
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</section>
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</section>

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