This is the ValueSet that contains all the codes in Source Material Type (http://hl7.org/fhir/ValueSet/substance-source-material-type) and Source Type Terminology (http://hl7.org/fhir/us/pq-cmc-fda/ValueSet/pqcmc-source-type-terminology). E.g. what you have to deal with if you get resources containing codes in either of them