This is the ValueSet that contains all the codes in x_MedicationOrImmunization (http://terminology.hl7.org/ValueSet/v3-xMedicationOrImmunization) and x_MedicationOrImmunization (http://terminology.hl7.org/ValueSet/v3-xMedicationOrImmunization). E.g. what you have to deal with if you get resources containing codes in either of them