I'm adding some tests in https://bugzilla.mozilla.org/show_bug.cgi?id=1632647. But TLDR, these shouldn't probably parse, or if you disagree they probably shouldn't match: ::part(foo):is([attr='value']) :host(:is(div .foo))
Following WPT test was pushed as part of Mozilla bug: https://github.com/web-platform-tests/wpt/pull/23711/files and we are only failing single test: https://wpt.fyi/results/css/selectors/is-where-parsing.html?label=master&label=experimental&aligned&q=is-where-parsing.html >>> Nested inside :host, with combinators Don't know whether we have it as separate tracking or not but still adding 'BrowserCompat' and "WPTImpact' tags for future tracking.
<rdar://problem/122574812>