This is the ValueSet that contains all the codes in US Core DocumentReference Category (http://hl7.org/fhir/us/core/ValueSet/us-core-documentreference-category) and US Core DocumentReference Category (http://hl7.org/fhir/us/core/ValueSet/us-core-documentreference-category). E.g. what you have to deal with if you get resources containing codes in either of them