- `@supports selector( <complex-selector> )` - From CSS Conditionals Module Level 4 (https://drafts.csswg.org/css-conditional-4/) As browsers start to roll out selectors from level 4 – :focus-within, :focus-visible, :is, :where, ::marker, extended :not and :nth-child, etc – authors are excited to start using these new tools, but we don't have the @supports control to manage fallbacks. That problem is exacerbated by the new selectors landing *before* our ability to check for them. It's frustrating to have a feature-query that has less support than the feature being queried. The longer this feature is delayed, the less useful it becomes for a new round of selectors already appearing in browsers. Firefox has already shipped, and chromium is planning to implement this month (https://bugs.chromium.org/p/chromium/issues/detail?id=979041#c8).
<rdar://problem/57257368>
*** This bug has been marked as a duplicate of bug 199237 ***