I've tried to use JSON Schema and the big gap I couldn't figure was how to handle polymorphism.

That is, if I have a case where object

    {
        "Foo": {
            "Type":"Fred"
            "Bar":1
            "Baz":2
            "Quux":2
        }
    }

and the object

    {
        "Foo": {
            "Type":"Waldo"
            "Bar":1
            "Corge":2
            "Xyzzy":7
        }
    }

are both valid, without just allowing any object members or allowing the union of their members.

I did a hack by multiplexing the types into a child-object, but that was ugly and clumsy.

In XSD or any statically-typed programming language I could handle this trivially using types and polymorphism, because "Fred" and "Waldo" would be different types.

But I can't figure out how to do that in Json Schema.