Bug 281232 – <mspace width="1ch"> doens't work

• Component: MathML
• Status: NEW

[Simon Fraser (smfr)]

Created attachment 472896 [details]
Test case

<mspace width="1ch"> doesn't work in Safari or Firefox. It works in Chrome.

[Radar WebKit Bug Importer]

<rdar://problem/137687694>

[Simon Fraser (smfr)]

Testcase is derived from a PR on the AVIF spec, so this has real-world impact.

[Frédéric Wang (:fredw)]

Thanks the issue is probably that Firefox and WebKit initially relied on the MathML definition of lengths from MathML3 which does not accept ch. They haven't completely migrated to MathML Core's definition, which is just CSS's <length-percentage>:

https://developer.mozilla.org/en-US/docs/Web/MathML/Values#legacy_mathml_lengths

Regarding tests,

web-platform-tests/mathml/relations/css-styling/lengths-1.html
web-platform-tests/mathml/relations/css-styling/lengths-2.html

don't seem to cover this case.

Ideally, we should just switch to the CSS parser for MathML lengths, but meanwhile we could just tweak MathMLElement::LengthType to handle this unit.

[Frédéric Wang (:fredw)]

Comparing https://drafts.csswg.org/css-values/#length-value Vs https://www.w3.org/TR/MathML3/chapter2.html#fund.units the following are missing:

ch 
cap
ic
vm
vh
vi
vmin
vmax
rem
lh
rlh

Maybe a first step would be to switch from MathMLElement::Length to CSSValue (see https://searchfox.org/wubkat/rev/cde6cf2e21001cb4055a5f891ce3d7abe5eee3e9/Source/WebCore/css/CSSUnits.h#57) similar to what Firefox does.

I guess ideally we should just map MathML attribute values to presentational hints similar to what we do for mathsize for example: https://searchfox.org/wubkat/search?q=addPropertyToPresentationalHintStyle&path=Source%2FWebCore%2Fmathml&case=false&regexp=false ; but using internal (non-webexposed) CSS properties instead. But probably this can be for follow-up bugs.

[Frédéric Wang (:fredw)]

Assigning to Harry, he is willing to give a try.