returns the type(s) at compile-time. which is string or list of strings or a list of type expressions.
currently the string comes from the stash name, but in the future a type can also be an object (as in perl6), not a stash. the return value of typeof must be parsable as valid type declaration. so it should honor list context to listify | alternations.

similar to ref, which returns one run-time string, the current type. (but even if the value contains multiple types, only one is returned with ref).
but typeof gets the type from the OP*, not the attached SV*.