How do you use attributes for cast credits if a cast member had more than one role?

If John Smith voiced the character of Bob in a film, you're supposed to use the (voice) attribute. However, if John also played Dave on-screen, the credit would need to be Dave/Bob or Bob/Dave, but using the (voice) attribute would imply that both roles are voices. The same problem applies to any attribute that doesn't apply to every role the actor plays in the film. How do you deal with that? Do you just not use the attributes? Would you write Dave/Voice of Bob? (The last one doesn't work for other attributes.)