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add table of suggested chars for accents/lines #552

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9d33bd1
add table of suggested chars for accents/lines
NSoiffer Nov 13, 2025
2caf807
redid table of accent chars
NSoiffer Nov 16, 2025
7a88dc6
Merge branch 'w3c:main' into accents-clean
NSoiffer Nov 16, 2025
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220 changes: 220 additions & 0 deletions src/character-set.html
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Expand Up @@ -526,6 +526,226 @@ <h4 id="chars_comb-chars">Combining Characters</h4>

</section>

<section>
<h4 id="accent-characters">Accent Characters</h4>

<p> There are a large number of look-alike characters that might be used to for
accents or diacritical marks above or below a base element.
However, fonts have limitations as to which of these can stretch and which have
proper positioning when used as accents. This section has recommendations
for which characters to use as accents in MathML. It is important to note that
only a limited number of fonts support proper mathematical layout.
Browsers and likely other software currently require the use of fonts with an OpenType MATH table.

<table>
<thead>
<tr>
<th>Unicode</th>
<th>Description</th>
<th>Glyph</th>
<th>Example</th>
<th>Stretchy</th>
<th>Comments</th>
</tr>
</thead>
<tbody>
<tr>
<td>U+0060</td>
<td>grave</td>
<td>&#x0060;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x0060;</mo></mover></math></td>
<td></td>
<td>U+0300 looks poor in Chrome</td>
</tr>
<tr>
<td>U+00B4</td>
<td>acute</td>
<td>&#x00B4;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x00B4;</mo></mover></math></td>
<td></td>
<td>U+0301 looks poor in Chrome</td>
</tr>
<tr>
<td>U+0302</td>
<td>hat</td>
<td>◌̂</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x0302;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x0302;</mo></mover></math></td>
<td>U+005E doesn't stretch in Chrome</td>
</tr>
<tr>
<td>U+007E</td>
<td>tilde</td>
<td>&#x007E;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x007E;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x007E;</mo></mover></math></td>
<td>U+0303 doesn't stretch; U+007E doesn't stretch in Chrome</td>
</tr>
<tr>
<td>U+005F</td>
<td>lowline (mover)</td>
<td>&#x005F;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x005F;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x005F;</mo></mover></math></td>
<td>U+00AF (overline) doesn't stretch in Chrome and displays poorly in Safari. U+0304 and U+0305 don't stretch anywhere</td>
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@davidcarlisle davidcarlisle Jan 22, 2026

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I don't think we can be making comparative judgements of specific implementations in the spec, I think we should just have a paragraph describing the issue. We can link to appendix B.3 of mathml-core (assuming we land the PR to update that and also, we could link to MathFonts.github.io accents test to tell people to see which characters stretch in current implementations.

</tr>
<tr>
<td>U+005F</td>
<td>lowline (munder)</td>
<td>&#x005F;</td>
<td><math><munder accent="true"><mi>x</mi><mo>&#x005F;</mo></munder></math></td>
<td><math><munder accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x005F;</mo></munder></math></td>
<td>U+005F is a little better than U+0332, but Chrome doesn't stretch either for a few fonts and Safari doesn't stretch either for many fonts</td>
</tr>
<tr>
<td>U+02D8</td>
<td>breve</td>
<td>◌̆</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x02D8;</mo></mover></math></td>
<td></td>
<td>U+02D8 is a little better horizontally positioned than U+0306</td>
</tr>
<tr>
<td>U+02D9</td>
<td>dot above</td>
<td>&#x02D9;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x02D9;</mo></mover></math></td>
<td></td>
<td>U+002E is similar; U+0307 displays poorly in Chrome and Safari</td>
</tr>
<tr>
<td>U+00A8</td>
<td>double dot</td>
<td>◌̈</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x00A8;</mo></mover></math></td>
<td></td>
<td>U+0308 displays poorly in Chrome</td>
</tr>
<tr>
<td>U+20DB</td>
<td>triple dots</td>
<td>⃛</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x20DB;</mo></mover></math></td>
<td></td>
<td>displays poorly in Chrome</td>
</tr>
<tr>
<td>U+20DC</td>
<td>quadruple dots</td>
<td>⃜</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x20DC;</mo></mover></math></td>
<td></td>
<td>displays poorly in Chrome</td>
</tr>
<tr>
<td>U+0309</td>
<td>hook above</td>
<td>◌̉</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x0309;</mo></mover></math></td>
<td></td>
<td>displays poorly in Chrome</td>
</tr>
<tr>
<td>U+02DA</td>
<td>ring</td>
<td>&#x02DA;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x02DA;</mo></mover></math></td>
<td></td>
<td>U+030A displays poorly in Chrome</td>
</tr>
<tr>
<td>U+02C7</td>
<td>caron</td>
<td>&#x02C7;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x02C7;</mo></mover></math></td>
<td></td>
<td>U+030C displays poorly in Chrome</td>
</tr>
<tr>
<td>U+21BC</td>
<td>left harpoon</td>
<td>&#x21BC;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x21BC;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x21BC;</mo></mover></math></td>
<td>U+20D0 is poorly positioned in Chrome and doesn't stretch in most fonts in Safari. It is better in Firefox and Safari for single characters because U+21BC is a little long. </td>
</tr>
<tr>
<td>U+21C0</td>
<td>right harpoon</td>
<td>&#x21C0;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x21C0;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x21C0;</mo></mover></math></td>
<td>U+20D1 is poorly positioned in Chrome and doesn't stretch in most fonts in Safari. U+20D1 is better in Firefox and Safari for single characters because U+21C0 is a little long. </td>
</tr>
<tr>
<td>U+2192</td>
<td>right arrow</td>
<td>⃗</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x2192;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x2192;</mo></mover></math></td>
<td>U+20D7 is poorly positioned in Chrome and doesn't stretch in most fonts in Safari. U+20D7 is better in Firefox and Safari for single characters because U+2192 is a little long. U+27F6 doesn't stretch in Chrome and Safari, and is too long for single characters. </td>
</tr>
<tr>
<td>U+23B4</td>
<td>top square bracket</td>
<td>&#x23B4;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x23B4;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23B4;</mo></mover></math></td>
<td></td>
<td></td>
</tr>
<tr>
<td>U+23B5</td>
<td>bottom square bracket</td>
<td>&#x23B5;</td>
<td><math><munder><mi>x</mi><mo>&#x23B5;</mo></munder></math></td>
<td><math><munder><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23B5;</mo></munder></math></td>
<td></td>
<td></td>
</tr>
<tr>
<td>U+23DC</td>
<td>top parenthesis</td>
<td>&#x23DC;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x23DC;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23DC;</mo></mover></math></td>
<td></td>
<td></td>
</tr>
<tr>
<td>U+23DD</td>
<td>bottom parenthesis</td>
<td>&#x23DD;</td>
<td><math><munder><mi>x</mi><mo>&#x23DD;</mo></munder></math></td>
<td><math><munder><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23DD;</mo></munder></math></td>
<td></td>
<td></td>
</tr>
<tr>
<td>U+23DE</td>
<td>top curly bracket</td>
<td>&#x23DE;</td>
<td><math><mover accent="true"><mi>x</mi><mo>&#x23DE;</mo></mover></math></td>
<td><math><mover accent="true"><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23DE;</mo></mover></math></td>
<td></td>
<td></td>
</tr>
<tr>
<td>U+23DF</td>
<td>bottom curly bracket</td>
<td>&#x23DF;</td>
<td><math><munder><mi>x</mi><mo>&#x23DF;</mo></munder></math></td>
<td><math><munder><mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow><mo stretchy='true'>&#x23DF;</mo></munder></math></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>

</p>

</section>

</section>

</section>