I prefer letting people use arbitrary keys, with a _caveat emptor_. It's much cleaner and easier to use. And it the vast majority of cases there will never be

I prefer letting people use arbitrary keys, with a _caveat emptor_. It's much cleaner and easier to use. And it the vast majority of cases there will never be a collision. You can also pin your schema version with `$schema`, so breaking changes should be opt-in only.