The CSSContainerRule interface says about its containerQuery that it "must return the <container-query> that was specified".
The grammar allows a rule with only a container name and no container query, so I'm wondering: What should this return in such a case?
Empty string seems to make sense, given that's what containerName does.

Currently, neither Firefox nor Chrome seem to support this so unless Safari does, I don't think there's any precedent here.