MedicationAdministration, MedicationDispense and the equivalent of MedicaitonStatement (MedicationUsage) repeat in R5 but don't in R4. We'll update the mapping to indicate that a standard extension will need to be used if multiple categories are specified. The intention is that there can be a wide variety of categories covering different axes of categorization. As well, the binding in the HL7 specification is 'example', which means that there are no constraints on what can be used.