← ReferenceStandards
What is Must-Support?
mustSupport is a flag in a Profile that marks an element as significant for conformance. A system claiming to implement the profile must be able to meaningfully store and return the element if it is present.
mustSupport ≠ required
mustSupport does not change cardinality. An element can be 0..1 and mustSupport — it is still optional in the resource, but if present, the system must handle it. To make an element required, you must change the cardinality to 1..1.
What mustSupport requires
- Sender: Must populate the element when the information is available.
- Receiver: Must store the element and return it in subsequent reads. Must not discard it as unknown.
- Profile author defines: The exact meaning of "support" depends on the profile context. Each IG should document what mustSupport means in their context.
Example from FhirSkPatient
In our FhirSkPatient profile, Patient.address and Patient.communication are mustSupport but remain 0..*. A system implementing this profile must store and return addresses and language preferences when present — but is not required to collect them if unavailable.