Re: [csswg-drafts] [css-fonts-4] `system-ui` generic font keyword and lang attribute (#9518)

(Disclaimer: I don't work on web tech any more; I'm just commenting to provide background info.)

I think we're discussing a few different things here:
1. The purpose of system-ui is supposed to be "make this text look like it was drawn by the native ui text-drawing routines." On macOS/iOS, those native ui text-drawing routines behave as-if they expand the single font to become a whole cascade list - so that's what WebKit's implementation does too. Ideally, all browsers on those operating systems would behave accordingly; though I can't comment on their behavior.
2. That's a different thing than what the OP is describing - the OP is asking whether that expansion operation should be affected by locale or not. Following from the goal of "make this text look like it was drawn by the native ui text-drawing routines," that expansion operation is affected by locale on macOS/iOS, so system-ui should behave that way in browsers too on those OSes.
3. That locale should definitely be able to be specified by the web author via lang=. If they don't specify it, I'm not sure what the best behavior should be. I see an argument of "using the OS's locale is going to be the option that most likely produces text that's best for the user" but I also see an argument of "different users shouldn't see different fonts for the same content on the same OS." I think there is an analogous situation here with hyphenation, but the failure case is different: picking a different font makes the text look weird but still legible, whereas picking different hyphenation locations makes the text not really legible any more.
4. Anyway, back to the OP: I think it's good to have tests to make sure that the expansion is locale-dependent to match OS behavior: it's easy to make real bugs here, and this is a situation where if a browser doesn't do it, the browser is clearly and visibly wrong on those OSes. However, I don't know how to fit that into the WPT infrastructure - is it possible to make an OS-specific test?

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Received on Wednesday, 25 October 2023 17:08:12 UTC