Do these check that all uses of the param hash use the right keys? What you describe sounds to me like a sub that's called when populating the hash from @_ -- that's a good idea, but it's still not strict enough. I've come across code that uses 'style' in one place and 'stytle' in others.

Clamped, read-only, psuedo-, or tied-hashes can fix this, but they're probably rare in production code.

I wouldn't mind this convenience occasionally...