Simplification of munder/mover/munderover/msub/msup/msubsup/mmultiscripts

[fred-wang]

MathML Core has various scripted elements:

https://mathml-refresh.github.io/mathml-core/#scriptsandlimits

One may argue that there are duplicate features (for example msub/msup/msubsup are <mmultiscripts> with approprate <none> children or <munder> is an <munderover> with a zero-size <mspace> as overscript) and hence some elements could be removed.

That's not true strictly speaking: Even if a zero-size script is not visible it still affects the layout because of the various shift/gap conditions. Karl Tomlinson (Mozilla) suggested that adding a special treatment for empty boxes in would bring extra complexity ( https://bugzilla.mozilla.org/show_bug.cgi?id=827713#c36 ) so it's not clear whether there is a benefit to drop some elements, we would still need special cases.

Additionally, I believe all these scripted elements are quite popular in existing web pages (much more than elements like mphantom #65 or merror #70 that clearly duplicates mrow+CSS) and are implemented in Gecko/WebKit so it seems hard to remove them.

Proposal: Keep them in MathML Core and close this.

[fred-wang]

From https://lists.w3.org/Archives/Public/public-mathml4/2019Apr/0022.html
Agreed: keep all the munderover variants in core.

[fred-wang]

Resolution:
#73 (comment)

Specification: N/A

Implementation: N/A

Polyfill: N/A

Tests: N/A