[css-env-1] Add a text-scale env() (name to be bikeshedded). #10674

[tabatkins]

No description provided.

[JoshTumath]

Thanks for sharing the initial draft!

[JoshTumath]

That doesn't seem right to me. In #10674 (comment), I defined it as the computed value of font-size: medium × env(bikeshed-text-scale)

I don't think we discussed in the issue whether the unit could be relative to 1em unit - the computed value of the selected element's font-size. My understanding was the computed value of 1bsem would be the same regardless of what element it was used on.

[davidsgrogan]

I think my understanding matches Josh's -- computed value of 1bsem would be the same regardless of what element it was used on.

[tabatkins]

I was under the impression that the point of the unit was to allow authors to avoid having to manually type calc(... * env(preferred-text-scale)) all over the place; it was supposed to be syntax sugar for that expression, essentially. Thus, it should scale with the local definition of the em; otherwise, authors can just set a variable at the root and use that instead, and we don't care quite as much about the verbosity in that case.

That said, putting some thought into this revealed that the definition of the unit is going to be very problematically tied into the definition of text-size-adjust itself, which is currently both underspecified (it doesn't actually say enough about its effects) and wrongly specified (it claims to be a computed-time adjustment, which testing trivially shows it isn't).

Luckily, the unit isn't meant to be defined by this spec; it goes over into V&U. So I'll just leave the references here for now, and deal with the definition of pem elsewhere when we resolve the text-size-adjust issues more generally.

[tabatkins]

See #11636 for discussion on this.