This is the CodeSystem that contains all the codes in BeCdFedCountry (https://www.ehealth.fgov.be/standards/fhir/core/CodeSystem/cd-fed-country) and BeCdFedCountry (https://www.ehealth.fgov.be/standards/fhir/core/CodeSystem/cd-fed-country). E.g. what you have to deal with if you get resources containing codes in either of them