If a given practitioner has >1 related role in the required valueset (e.g., one individual might be admitter, attender, referred, and ordered), this is awkward to express, since it requires supplying multiple PractitionerRole resources each with a single code. Is this intentional? It would better leverage existing semantics (PractitionerRole.code is 0..*) to allow multiple codes, rather than constraining each instance to a single code.