I think the *idea* was that yes, the constraintKey will be some weird string, but then maybe the user registered a constraint with that name. It should absolutely work. Weird, yes, but still work. We weren't necessarily trying to create a proper grammar here, and as such, any "unknown" syntax just means "custom string."

Of course, maybe we could revisit that and say that `(`, `)`, and `,` are all reserved characters for the grammar and can't appear in a constraint name.