A common pattern in FHIR is the CodeableReference, which allows for representation of a concept through either a terminology or a reference to a resource which has a terminology. When retrieves are invoked against elements of this type, the current retrieve cannot push the terminology filter through the retrieve, forcing authors to separate the terminology filter outside the retrieve. The ModelInfo should be aware of and support this pattern so that authors do not have to deal with this complexity.

An example of this is the MedicationRequest resource medication element. When retrieving a MedicationRequest, the translator could expand the retrieve to:

define TestChoiceMedicationRequest:
[MedicationRequest: "Aspirin"]

// If the terminology target is a choice of a terminology-valued element and a reference

define TestChoiceMedicationRequestExpanded:
[MedicationRequest: medication in "Aspirin"]
union (
[MedicationRequest] MR
with [Medication] M
such that M.id = Last(Split(MR.medication.reference, '/'))
and M.code in "Aspirin"
)