http://hl7.org/fhir/StructureDefinition/questionnaire-referenceResource|5.2.0

Where the type for a question is \"Reference\", indicates a type of resource that is permitted.
NameFlagsCardTypeDescription & Constraints
Extension
0..*Allowed resource for reference
 
extension
?..0
 
url
?..?
 
value[x] *
1..? ResourceType (required)
 
 
valueCode *
1..?code ResourceType (required)