How are underlines positioned in Japanese text?

[r12a]

CSS and browser implementers are looking for information about how to position underlines for various scripts, including Japanese scripts. Can we provide them with the information they need (and add it to the layout requirements doc)? See w3c/csswg-drafts#459 (comment)

[macnmm]

I think this is a broader question about different lining styles that are in use -- we have the issue of font info being biased to Latin underlining conventions, with no set CJK locations specified; we have mixed Roman and CJK text and where the underline/strikethru/overline should go across mixed scripts; we have mixed sized text and whether the lines should break or not; we have special lining cases like for obituary use in vertical text in Japanese.

All these either require more data in fonts, or more options as to which heuristic to choose when drawing the lines, or decide on a 1 size fits all approach.