On 02/09/2019 22:12, Ryosuke Niwa wrote: > > On Mon, Sep 2, 2019 at 7:11 AM Frédéric Wang <fw...@igalia.com > <mailto:fw...@igalia.com>> wrote: > > > Currently MathML attributes mathvariant, displaystyle and > scriptlevel   are implemented in WebKit using custom "style > resolution" and "one-glyph rendering" inside the MathML layout > code   . 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 ;  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 . > > So my questions are: > > (1) What is WebKit's mechanism to implement such stylistic attributes? > > > It looks like -internal-text-autosizing-status is such a property. > This is a property the author can never set and we set it internally > for implementation purposes. > ComputedStyleExtractor::valueForPropertyInStyle manually skips it so > it's never exposed anywhere. > > One subtle thing I didn't check is whether it would affect the CSS > parser or not (as in whether it would be considered as a valid CSS > property or not). There might be some subtle effect there. > > -webkit-text-decorations-in-effect is also a CSS property we use > internally to compute the effective set of text decorations applied to > text for editing purposes. The author can never set it but it's > unfortunately exposed via computed style. > > (2) Is it possible to implement internal (i.e. not web-exposed to > users) CSS properties/values in WebKit? > > > It appears possible today using the technique deployed by > CSSPropertyInternalTextAutosizingStatus. > > Thanks for the pointers! I think it is worth trying to (re-)implement these MathML attributes using internal properties.
-- Frédéric Wang
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