The spec requires that an invalid <media-query> be replaced with not all. (In #7595, it was resolved to apply this at serialization time only when it is syntactically invalid.)

I have concerns about the parsing model implied by this requirement.

How is a parser supposed to recognize an input as invalid for a production, but still accept it for that production? I feel like the not all-ification should only apply when <media-query> is produced by <media-query-list>, similarly as invalid selectors are ignored when produced by <forgiving-selector-list>.

If you ever want to parse <media-query> unforgivingly in another context, you can't.

<media-query> was only produced by <media-query-list> before if() was specified. But I think could use <media-query-list> instead.