OpenType MathTopAccentAttachment

[fred-wang]

It it used during the layout of munderover

https://mathml-refresh.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover

but we need tests for that.

[fred-wang]

Consensus from 2020/06: keep the current text for now, let's see if we have time to implement this and write tests etc. add a warning label

[NSoiffer]

Current spec uses this for the layout of mtext: https://w3c.github.io/mathml-core/#layout-of-mtext

Note: link above for munderover is out of date. Use https://w3c.github.io/mathml-core/Overview.html#base-with-underscript-and-overscript. No mention of MathTopAccentAttachment in the layout algorithm there.

There is a mention that this is at risk in https://w3c.github.io/mathml-core/Overview.html#glyph-information-mathglyphinfo.

@fred-wang: should this get a "needs spec update" or a "level 2" label?

[fred-wang]

It's mentioned in the layout of mover https://w3c.github.io/mathml-core/#base-with-overscript which is itself used for the layout of munderover.

(I'm not sure whether we want this for level 1, I thought we had agreed to postpone many OpenType features for later. On the other hand this seems a small feature.)

Anyway, let's keep it open since it needs tests.