This is the CodeSystem that contains all the codes in FR Core CodeSystem Identifier Type (https://hl7.fr/ig/fhir/core/CodeSystem/fr-core-cs-identifier-type) and FR Core CodeSystem Identifier Type (https://hl7.fr/ig/fhir/core/CodeSystem/fr-core-cs-identifier-type). E.g. what you have to deal with if you get resources containing codes in either of them