[css-fonts] Add a ui-sans-serif keyword to go with ui-serif

[AmeliaBR]

A follow-up to #4107:

In that issue we agreed to add ui-serif, ui-monospaced, and ui-rounded to allow access to variants of system fonts other than the standard system-ui font. However, this set of names assumes that system-ui is a sans-serif style, which may not always be true.

There should be a ui-sans-serif keyword for authors who want to specifically request the system's sans serif style. The system-ui keyword would continue to be the primary font used by the system interface, regardless of style. These two keywords might map to the same font; the difference is in intent.

[Crissov]

The result of the discussion in #4397, which is about Nastaliq and styles or hands of other non-European scripts, should probably also inform the decision which UI fonts should be accessible through CSS, and perhaps voice versa (re rounded).

[css-meeting-bot]

The CSS Working Group just discussed [css-fonts] Add a ui-sans-serif keyword to go with ui-serif, and agreed to the following:

• RESOLVED: add ui-sans-serif

The full IRC log of that discussion

<myles> Topic: [css-fonts] Add a ui-sans-serif keyword to go with ui-serif
<myles> GitHub: https://github.com//issues/4468
<myles> AmeliaBR: With the new ui- font family keywords. Based on the resolution, we had ui-serif, ui-monospace, and ui-rounded keywords. ui-sans-serif wasn't initially added because the system ui fonts of current systems are all sans-serif, so we didn't need a new keyword
<chris> q+
<myles> AmeliaBR: Logically there's nothing in system-ui that says it must be sans-serif, and in the future, system-ui might be serif. A more logical system would have ui-sans-serif keyword, so if you care about it, you can specify it explicitly, vs system-ui gives you the default system font regardless of its styling. In most systems these would map to the same font
<myles> chris: I agree it's currently not like that, but it could change in the future
<myles> chris: I agree with this suggestion
<fantasai> +1 to proposal
<myles> chris: We've already clarified that these names can all point to the same thing
<fantasai> myles: Mildly against this just because it's building infrastructure for a computer that doesn't exist
<myles> astearns: I can see the future possibility, we coudl add the additional keyword when it becomes necessary.
<myles> chris: But people will use it in the interim to mean sans-serif will be surprised.
<myles> astearns: I'm not sure people aren't already going to make that assumption regardless of another keyword
<myles> fantasai: But this means they ahve to make that assumption
<myles> chris: It lets authors be more precise
<myles> fantasai: If we don't add this, then they have to make the assumption. If we add this keyword, they don't have to
<myles> astearns: I'm not strongly opposed to adding it
<myles> plinss: I have slippery slope concerns here. It sounds like we're re-inventing things we had in the 90s. <lists many system- prefixed font names like dingbats and swashes>
<myles> AmeliaBR: We've already made the agreement on adding a set of stylistic system fonts. Do we acknowledge that system-ui is by default a sans-serif, or do we include a sans-serif in a stylistic set of keywrods
<myles> chris: The people arguing against this are arguing against the keywords in the first place
<myles> plinss: I don't think it should be serif or sans-serif
<myles> chris: Yes, system-ui shouldn't include that. But we've already got ui-serif and ui-monospaced. Those are 2 of the generic font families. I don't think anyone is asking for more
<myles> plinss: People will ask for stylistic, semantic implications, one being used for body text or headings ... again, it seems like it's going to get out of hand. Not a strong objection, I'm just concerned
<myles> chris: I can understand that.
<fantasai> Note, it's ui-monospace not ui-monospaced now
<myles> astearns: I'm not a big fan of ui-serif and ui-monospace, but we have decided to add them, and I'm somewhat convinced by the argument that, since we have ui-serif, we should also have ui-sans-serif to future-proof
<myles> astearns: We shouldn't have ui-serif in the first place. The connotations of what it means will change over time. I don't see how that's getting you anything
<myles> plinss: ui-monospace has a functional difference.
<myles> s/astearns: We shouldn't have/plinss: We shouldn't have/
<myles> astearns: Does anyone want to really object? Or shall we put it in for now?
<myles> <silence>
<fantasai> I think given we have ui-serif/ui-rounded/ui-monospace, I think it's important to have ui-sans-serif
<myles> astearns: The proposal is to add ui-sans-serif (as a sibling to ui-serif)
<myles> astearns: Sounds like we're leaning toward it.
<myles> astearns: Objections?
<myles> plinss: I'd like to reconsider ui-serif
<myles> astearns: Oh, certainly, we can re-litigate adding the pair of them, but if we have one, the proposal is we should have the other.
<myles> plinss: I agree.
<myles> chris: Do these set size and style as well?
<myles> AmeliaBR and myles: no
<myles> RESOLVED: add ui-sans-serif