[selectors] [cssom] How should invalid selectors inside :is(), :where(), and :not() be treated for serialization?

[emilio]

Split from #3264. It's not clear what happens if you add an invalid selector inside :is or :not or :where in terms of serialization.

• Should we just skip them?
• Should we serialize it as :not(*|*) (like invalid media queries which serialize as not all)?
• Something else?

/cc @ericwilligers

[ewilligers]

I propose skipping them. When none of the selectors are vallid, we end up with :is(), :where(), :has(), :nth-child(even of), :nth-last-child(2n+1 of).

[emilio]

Would those parse? We'd need them to roundtrip, you should be able to do ruleA.selectorText = ruleB.selectorText. We'd probably have to change the grammar of the property to allow 0 or more selectors.

[ewilligers]

Would those parse?

Yes, they parse and roundtrip due to error recovery.

:not is excluded - empty and invalid selectors inside :not() do not parse (see resolution).

[emilio]

So :not(<invalid>, <invalid>) would become :not(), and that would not parse?

Edit: NVM

[ewilligers]

:not would be just like any other traditional selector with no error recovery. :not(<invalid>, <invalid>) and :nth-col(random .nonsense) do not parse, they never become :not() or :nth-col().