Currently, FHIR CodeSystem instances may use any code value in CodeSystem.property.code when declaring a property. However, given that the codes in the http://hl7.org/fhir/concept-properties code system are provided for use with all code systems in the FHIR ecosystem, it is desirable that these codes not be used for other properties. It is also desirable that when a property is not explicitly declared (in CodeSystem.property) it should be safe to assume that the properties using these codes (in CodeSystem.concept.property.code) are referring to the properties defined in the http://hl7.org/fhir/concept-properties code system.

Noting that the CodeSystem resource type is normative and that many implementers (including HL7) may have authored and deployed production CodeSystem instances which do not align to these desires, it is not possible to add rules which mandate the desired behaviours in new versions of FHIR. However, it is possible to provide recommendations which encourage best practice going forward.

Accordingly, this tracker requests that the following text is added in the Defined Concept Properties subsection of the FHIR CodeSystem resource type page after "Code System representations SHOULD use these properties where possible":

.. and these codes for these properties. Code System representations SHOULD regard the codes for these properties (e.g. status, inactive, notSelectable, etc.) as reserved values in CodeSystem.property.code values and that when used they SHOULD refer to the properties defined in the concept properties code system.

In the absence of CodeSystem.property data elements being provided, when properties with these code values are added to a concept (in CodeSystem.concept.property.code) the intended property SHOULD be assumed to refer to the defined concept properties in the http://hl7.org/fhir/concept-properties code system.