A class must have a valid class name, or else it is not a class, or is it?
And if it is a valid class, then the FQCN will be exactly as described here.
So, why have this stuff in the spec at all?
The only real restriction is that the class must be namespaced, that is, it cannot be directly in the top-level namespace. So, why not just say that, and be done with it.