[csswg-drafts] [css-inline-3] Ascent and Descent Metrics in vertical flow (#5381)

kojiishi has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-inline-3] Ascent and Descent Metrics in vertical flow ==
A follow up for #5312.

Currently IIUC [Ascent and Descent Metrics] is used only for Canvas [TextMetrics] and that vertical flow support is not needed, but raising this because we might need it to define in CSS and for [Font Metrics API].

When [text-orientation: mixed], glyphs may be rendered upright or rotated sideways. Should [Ascent and Descent Metrics] use horizontal metrics for rotated sideways glyphs, or vertical metrics for upright glyphs?

[Ascent and Descent Metrics]: https://drafts.csswg.org/css-inline-3/#ascent-descent
[Font Metrics API]: https://drafts.css-houdini.org/font-metrics-api/
[TextMetrics]: https://html.spec.whatwg.org/multipage/canvas.html#textmetrics
[text-orientation: mixed]: https://drafts.csswg.org/css-writing-modes-3/#valdef-text-orientation-mixed

/cc @fantasai @litherum @jfkthame @yiyix @macnmm

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5381 using your GitHub account


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