MathML Core output for HTML export #7436
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Jan 10, 2026
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| if let Some((tag, other_children)) = match (tl, tr, bl, br) { | ||
| (None, None, None, None) => None, | ||
| (None, None, None, Some(br)) => Some((tag::msub, eco_vec![br])), | ||
| (None, Some(tr), None, None) => Some((tag::msup, eco_vec![tr])), | ||
| (None, Some(tr), None, Some(br)) => Some((tag::msubsup, eco_vec![br, tr])), | ||
| (tl, tr, bl, br) => { | ||
| let unwrap = |node: Option<HtmlNode>| { | ||
| node.unwrap_or(HtmlElement::new(tag::mrow).into()) | ||
| }; | ||
| Some(( | ||
| tag::mmultiscripts, | ||
| eco_vec![ | ||
| unwrap(br), | ||
| unwrap(tr), | ||
| HtmlElement::new(tag::mprescripts).into(), | ||
| unwrap(bl), | ||
| unwrap(tl), | ||
| ], | ||
| )) | ||
| } | ||
| } { | ||
| let mut children = eco_vec![base]; | ||
| children.extend(other_children); | ||
| base = HtmlElement::new(tag).with_children(children).into(); | ||
| } | ||
|
|
||
| if let Some((tag, other_children)) = match (t, b) { | ||
| (None, None) => None, | ||
| (Some(t), None) => Some((tag::mover, eco_vec![t])), | ||
| (None, Some(b)) => Some((tag::munder, eco_vec![b])), | ||
| (Some(t), Some(b)) => Some((tag::munderover, eco_vec![b, t])), | ||
| } { | ||
| let mut children = eco_vec![base]; | ||
| children.extend(other_children); | ||
| base = HtmlElement::new(tag).with_children(children).into(); | ||
| } |
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I got curious about this from my other work on scripts with primes, and when both under/over and sub/super scripts are present, Firefox and Chrome seem to render better when doing under/over inside sub/super. In particular if you have attach(sum, tr: 2, t: n), placing the mover outside the msup causes the n to be centered around sum^2, which looks quite bad.
<math display="block">
<mover><msup><mo>∑</mo><mn>2</mn></msup><mi>n</mi></mover>
<mo>≠</mo>
<msup><mover><mo>∑</mo><mi>n</mi></mover><mn>2</mn></msup>
</math>However, this makes me worried about how users would typeset annotations on something with a normal attachment, e.g. attach(limits(x^2), b: "squared"). So I think we should consider updating the attachment model to improve this generally, although maybe after this PR or after my other fix for scripts lands.
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Supersedes #7206, depends on typst/typst-assets#13.
Note that it is not quite as complete as the old PR just yet.
Notes
Stylesheet
To have the output in a browser match Typst's paged output exactly, we'd ideally override parts of the user agent stylesheet instead of having to supply things to each instance of an element. Since doing the former isn't possible yet and the latter isn't great (we are initially focusing on semantics after all), I'm ignoring all of this stuff. There is one exception, though: I need to disable the
text-transform: math-autoproperty formi(by using themathvariant="normal"attribute) to stop the browser from auto italicizing things.Questions
What Should the Width of a Space Be?
We occasionally need to emit a single space, but we cannot obtain the font's space width! So we may need to choose something. Some choices I've found elsewhere:
4/18emin https://github.com/jgm/texmath/blob/aee6b494595a58dbbf769264061876778f7aa269/src/Text/TeXMath/Shared.hs#L251C1-L251C37Resources
Specifications
Other Implementations
Fonts
Browser Problems
Below I collect issues in the main 3 browser engine's MathML implementations that cause the MathML generated by this PR to display incorrectly. Whilst I do think we should work around these where possible, for my initial implementation I have not done so.
Gecko
Blink
WebKit