a.Owner {"pet": {"kind": "cat"}}: Owner(pet=Pet(root=Cat(kind='cat', meow=None)))
a.Owner {"pet": {"kind": "kitty"}}: rejected
b.Owner {"pet": {"kind": "kitty"}}: Owner(pet=Pet(root=Cat(kind='kitty', meow=None)))
b.Owner {"pet": {"kind": "cat"}}: rejected
