This is the ValueSet that contains all the codes in BeCausativeAgent (https://www.ehealth.fgov.be/standards/fhir/allergy/ValueSet/be-causativeagent) and BeCausativeAgent (https://www.ehealth.fgov.be/standards/fhir/allergy/ValueSet/be-causativeagent). E.g. what you have to deal with if you get resources containing codes in either of them