This is the ValueSet that contains all the codes in MDC Device Identifier Types (http://hl7.org/fhir/uv/phd/ValueSet/MDCDeviceIdentifierTypes) and MDC Device Identifier Types (http://hl7.org/fhir/uv/phd/ValueSet/MDCDeviceIdentifierTypes). E.g. what you have to deal with if you get resources containing codes in either of them