"thin", "thick", "medium" values mfrac@linethickness

[fred-wang]

From https://mathml-refresh.github.io/mathml/chapter3.html#presm.mfrac :

Specifies the thickness of the horizontal "fraction bar", or "rule" The default value is "medium", "thin" is thinner, but visible, "thick" is thicker; the exact thickness of these is left up to the rendering agent.

The MathML Core spec suggests 50%, 100%, 200%.

It's possible that we also want to remove/deprecate these values if they are not used in practice.

Math WG discussion: https://lists.w3.org/Archives/Public/www-math/2016Aug/0001.html

[physikerwelt]

I think we should remove the string constants "thin" (50%), "thick" (200%), "medium" (100%)

[fred-wang]

cc @rwlbuis, @emilio :

This was removed from MathML core in w3c/mathml-core@ce02fd1

I'm leaving this open because it still remains to:

• Remove WPT tests if any.
• Send intent-to-remove to mozilla/webkit-dev mailing lists (maybe old Math WG too?).
• Remove browser implementation.
• Decide what to do for the full MathML spec (remove values? deprecate them? specify explicit numbers?).
• Add polyfill to https://github.com/mathml-refresh/mathml-polyfills (e.g. convert to linethickness="50%", "100%", "200%" respectively).

[fred-wang]

Decision is to keep in MathML full but note in main spec that non core features will require polyfills so you may not want to use them. https://lists.w3.org/Archives/Public/public-mathml4/2019Mar/0026.html

[fred-wang]

Resolution:
#4 (comment)

Specification:
Add deprecation warning in Full?

Implementation:
WebKit: https://bugs.webkit.org/show_bug.cgi?id=196142
Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1548529
Not implemented in Chromium.

Polyfill:
Convert to length values
Maybe using CSS variables to make values configurable?

Tests:

• Remove WPT tests or check that these values are not supported.