Re: [csswg-drafts] [css-fonts] `system-ui` behavior is undesired for some users (#3658)

> A quick check with my friend found that MacOS and iOS do support language-specific tagging in system-ui, albeit only tested in English OS. This is a true OS-level text shaping support as SC, TC and JP uses different fonts (PingFang SC, PingFang TC [different 示] and Hiragino Kaku), so I suspect it'll work on Chinese/Japanese OS too. Screenshot of Safari on Mac, Chrome on Mac and Safari on iPad:

Thank you for your quick investigation. I am glad to hear that. Indeed, UAs in Apple OSes can recognize `lang` attributes even in `system-ui` and make it behave like a virtual Pan-CJK font. I was able to confirm this behavior in my antique iPhone.

https://codepen.io/tats-u/pen/JoGPgxN


c.f. Windows for Japanese + Firefox (1st) / Chrome (2nd):

<img width="691" height="672" alt="Image" src="https://github.com/user-attachments/assets/c0d00a87-7ba9-42b6-bd22-23f435a9e7dc" />

<img width="659" height="709" alt="Image" src="https://github.com/user-attachments/assets/d6178c05-3d02-4065-a470-c2378dcae1d1" />

> thus do break down if I use another font. Shown is my POCO phone that uses MiSans by default on first row (no pan-CJK support, but P/S: demonstrate that system-ui does correctly use what my system is using),

What I had feared happened there.

- Windows: 100% fail
- macOS/iOS: 100% pass
- Linux/Android: depends on whether it adopts Noto CJK as UI font (I want to believe that most of major ones do but some definitely do not)

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Received on Thursday, 18 September 2025 13:44:08 UTC