Interpretation of new display: math/inline-math and compatibility with block/inline

[fred-wang]

This is from the hackfest notes by @bkardell @fantasai ; originally #171 but it got off topic, so I'm opening a clean issue.

Need to also evaluate Web-compat of introducing display: math, in case authors are already setting display: block etc. and expecting no change to internal contents.

Also cc'ing @bfgeek who proposed adding inline-math in addition to math.

The idea is when "display: math" or "display: inline-math" is used, the math layout described in MathML Core is performed. In other cases, layout is described by other CSS specifications, allowing authors to override the default layout of MathML elements.

When people explicitly set "display: block" or "display: inline" then the spec says to use the corresponding CSS layout. Is there any compat risk that people are doing that? On all elements or only the <math> root? If so, should we make display computes to "math" and "inline-math" for these values?

Additionally, "display: inline-math" on all but the <math> root should probably compute to "display: math".

Maybe more?

[fred-wang]

From MathML Core Meeting of June 8, 2020:

Resolved: we discussed and felt that this shouldn’t be a problem because there is existing incompatibility now.

Regarding the separate issue:

Additionally, "display: inline-math" on all but the root should probably compute to "display: math".

I think the spec currently defines MathML layout for these two cases, so it looks fine as it. Let's see what the CSS people say when we propose it.