[css-contain] <container-name> in @container ambiguities #7203

Two thoughts:

• <container-name> kinda conflicts with <container-condition>, as not can be a valid <container-name>, how should @container not (width > 300px) be parsed? There's an obvious answer, but probably that means that not should not be a valid <container-name>?

• Per spec <container-name> includes none and multiple <custom-idents>, is @container foo bar (width > 300px) expected to be valid? I don't see any test for multiple container names in the rule, so just checking whether that's intentional or not.

cc @andruud @mirisuzanne @anttijk