Hello, Currently MathML attributes mathvariant, displaystyle and scriptlevel [1] [2] are implemented in WebKit using custom "style resolution" and "one-glyph rendering" inside the MathML layout code [3] [4] [5]. These features involve text rendering and interaction with CSS font-size, so it is difficult to implement them properly and completely that way. There are known bugs and missing features right now (e.g. mathvariant transform only applies to one-character strings, automatic displaystyle/scriptlevel does not work with fractions, etc)
Several years ago, Gecko used to do something similar but that was causing a lot of problems (dynamic update, assertion failures...). At the end, this is now implemented in Gecko more reliably by mapping the attributes to internal CSS properties ; [6] is based on that. When I tried to do something like this in WebKit three years ago, I was only able to rely on proprietary -webkit-* extensions exposed to users [7]. So my questions are: (1) What is WebKit's mechanism to implement such stylistic attributes? (2) Is it possible to implement internal (i.e. not web-exposed to users) CSS properties/values in WebKit? (3) Is it ok to add more -webkit-* properties/values or should these properties be standardized at the CSS WG instead? I understand answers to these general questions from other browser project is either use internal properties or standardize them. Thanks, Frédéric PS: For a concrete example, see [8]. Automatic mathvariant is used for italic variables while font-size in fractions is calculated according to displaystyle / scriptlevel rules. The latter is incorrect (check the attached screenshot) while selection highlight is broken for the former. [1] https://mathml-refresh.github.io/mathml-core/#the-mathvariant-attribute [2] https://mathml-refresh.github.io/mathml-core/#the-displaystyle-and-scriptlevel-attributes [3] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/css/mathml.css [4] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/rendering/mathml/MathMLStyle.cpp [5] https://trac.webkit.org/browser/webkit/trunk/Source/WebCore/rendering/mathml/RenderMathMLToken.cpp#L593 [6] https://mathml-refresh.github.io/mathml-core/#css-extensions-for-math-layout [7] https://bugs.webkit.org/show_bug.cgi?id=133845#c5 [8] https://bug-201242-attachments.webkit.org/attachment.cgi?id=377730 -- Frédéric Wang
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