This is the ValueSet that contains all the codes in LOINC Codes (http://hl7.org/fhir/ValueSet/observation-codes) and Screening and Assessment Survey Codes (http://cts.nlm.nih.gov/fhir/ValueSet/2.16.840.1.113762.1.4.1267.13). E.g. what you have to deal with if you get resources containing codes in either of them