http://hl7.org/fhir/StructureDefinition/structuredefinition-fhir-type|4.0.1

The formal FHIR type of a property - used for the value property of a primitive type (for which there is no type in the FHIR typing system), and Element.id and Extension.url.
NameFlagsCardTypeDescription & Constraints
Extension
0..1FHIR type for value property - when a simple system type
 
extension
?..0
 
url
?..?
 
value[x] *
1..?
 
 
valueUrl *
1..?url