This is the ValueSet that contains all the codes in TransferDocumentType (http://hl7.org/fhir/us/ccda/ValueSet/2.16.840.1.113883.1.11.20.2.4) and TransferDocumentType (http://hl7.org/fhir/us/ccda/ValueSet/2.16.840.1.113883.1.11.20.2.4). E.g. what you have to deal with if you get resources containing codes in either of them