text-underline-position:under will make an underline clear nastaliq Arabic descenders.

[r12a]

test

Tested with Noto Nastaliq Urdu, Farisi*.
* Asterisked fonts cannot be tested on Safari unless served as webfonts.

NOTE: The pass/fail criterion for this test relates specifically to the assertion. Failure to clear the lowest ink may not be innapropriate for use of this feature.

Results:

• Gecko: ✅❌ Works fine with Farisi, but Noto Nastaliq Urdu cuts through the low vowel diacritics. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:94.0) Gecko/20100101 Firefox/94.0
• Blink: ❌ Fails for both fonts. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36
• Webkit: ✅❌ Works fine with Farisi in terms of distance, but Noto Nastaliq Urdu cuts through the low vowel diacritics. With Farisi, there are gaps in the line where the meem descenders occur. Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.1 Safari/605.1.15