[css-text-decor] Proposal for the 'text-emphasis-position' property syntax values #1207

3.4. Emphasis Mark Position: the text-emphasis-position property
https://drafts.csswg.org/css-text-decor-3/#text-emphasis-position-property

This picks up from a comment sent in email by Momdo Nakamura. See
https://lists.w3.org/Archives/Public/www-style/2015Dec/0199.html

Basically Nakamura-san thought that having to always specify two values for text-emphasis-position was painful for the author and unnecessary. I have to agree that i was also surprised by that. It seems it's not only a pain to have to enter double values, but potentially also problematic, since it's unusual to require two values in this way, and i think content authors may forget that they have to do it.

The text in the ED (which i think was changed as a result) says that the values are expressed by:

[ over | under ] && [ right | left ]?

1. i'm not sure that this is grammatically correct – the && means that both must occur, but the ? means that one doesn't have to occur. Doesn't the && symbol need to become || ?
2. i have a nagging worry about relying on the browser default stylesheet to produce something sensible, since i think it should be possible to use a similar model for other formats that may not interact with a browser default stylesheet. (For example, TTML2)
3. over and under mean all sorts of things in CSS at the moment, and i found myself wishing there was a little more standardisation recently, when trying to explain things that cut across text-decoration, ruby, and writing-modes.
4. a propos (3), writing-modes defines over to mean on the 'ascender side' of vertical text, rather than block-before. This seems a useful approach wrt naming values that could be used also for line-decoration surely? That way there would only need to be two values over and under. (Of course there's a clash with the existing under value name, but that could be fixed by using line-over or line-under (which are less ambiguous anyway), or changing current under to something like clear.

There may well be things i'm missing here. Please let me know if so.