[css-text-decor] text-underline-position auto in vertical text

[r12a]

2.6. Text Underline Position: the text-underline-position property > Auto
https://drafts.csswg.org/css-text-decor-3/#underline-auto

If you apply text-underline-position: auto, should the underline appear on the right of Japanese (and Mongolian) text, as is recommended for the default text-decoration(-line):underline values?

If so, it would be good to make that clear (and btw how 'alphabetic baseline' relates to cjk positioning of an underline in vertical text).

[fantasai]

No, auto does not switch sides. It only allows the position to be automatically adjusted on that side

[r12a]

Could we add a note or some text to clarify that?

[hober]

Both Chrome and Firefox put the underline on the right by default in vertical Japanese when text-underline-position is auto. We should probably update the spec to allow that.

[fantasai]

See testcase.

This is currently not allowed per spec; instead the spec has UA rules that set the behavior per language.

Do we want to

• Update the definition of auto to match Firefox?
• Or update implementations to match the spec?