> Pseudo-elements cannot be represented by the matches-any pseudo-class; they are not valid within :is().
That seems to me like :is(foo::before) should be invalid at parse-time. Instead webkit parses it, but never matches it.
Created attachment 396899 [details]
Created attachment 396903 [details]
Committed r260338: <https://trac.webkit.org/changeset/260338>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 396903 [details].