https://www.hl7.org/fhir/codesystem-definitions.html#CodeSystem.compositional Add text to the Comment: Note that the code system resource does not define what the compositional grammar is, only whether or not there is one.  To result in this: Note that the code system resource does not define what the compositional grammar is, only whether or not there is one. Review the Using Code System X with HL7 Standards (where Code System X is a specific code system) pages at [terminology.hl7.org| https://terminology.hl7.org/external_terminologies.html ] to learn about a code system's post coordination support. Coding.code has some more information about how a post coordinated expression may be exchanged in a code element.