227391 2021-06-25 02:29:43 -0700 MobileSafari cannot parse `@supports selector(…)` 2021-06-25 15:06:20 -0700 1 1 1 Unclassified WebKit CSS Other iPhone / iPad Unspecified RESOLVED INVALID P2 Normal --- 1 bramus webkit-unassigned ap oldest_to_newest 1772595 0 bramus 2021-06-25 02:29:43 -0700 Safari/MobileSafari currently are the only browsers that support the `:nth-child(An+B [of S]?)` selector. When checking for support for `:nth-child(An+B [of S]?)` using @supports, only Safari on Desktop claims it does; MobileSafari does not understand the rule. ``` @supports selector(:nth-child(1 of x)) { /* BUG: Only targets Desktop Safari, although MobileSafari also supports the selector … */ … } ``` See demo at https://codepen.io/bramus/pen/3c476384f0adadd65a0b53db15f86cf4 - Safari: The background is hotpink - MobileSafari: The background remains the default color Further findings: 1. MobileSafari's parsing breaks on `selector(:nth-child(1 of x))`. Extending the @supports rule with a check for `-webkit-touch-callout: none` (which MobileSafari does understand) does nothing. ``` @supports selector(:nth-child(1 of x)) or (-webkit-touch-callout: none) { … } ``` 2. When adding extra parens around the `selector()` MobileSafari does seem to be able to parse the expression: ``` @supports (selector(:nth-child(1 of x))) or (-webkit-touch-callout: none) { … } ``` 3. Singling out `selector()` with extra parens added also doesn't work on MobileSafari: ``` @supports (selector(:nth-child(1 of x))) { … } ``` It is expected that MobileSafari understands all code examples shown, whereas now it only understands the syntax used in the "Further Findings 2" example. 1772599 1 bramus 2021-06-25 02:40:19 -0700 By extension, after some further testing: MobileSafari simply does not understand `@supports selector(…)`. See https://codepen.io/bramus/pen/2abd4b7e1d411fa687295f0697e294d4 for a demo. 1772734 2 ap 2021-06-25 11:35:54 -0700 I cannot reproduce this on iOS 14.6 or iOS 15 beta. Not sure what could be different in your testing. Any chance that you were using an older iOS version? 1772769 3 bramus 2021-06-25 15:06:20 -0700 I see that my phone still was on iOS 14.4. Testing on 14.6 indeed confirms it works. Thanks!