http://hl7.org/fhir/StructureDefinition/elementdefinition-allowedUnits|5.2.0

Identifies the units of measure in which the element should be captured or expressed.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/CodeableConcept
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/canonical
Extension.value[x].targetProfilehttp://hl7.org/fhir/StructureDefinition/ValueSet
Extension.value[x].binding.valueSethttp://hl7.org/fhir/ValueSet/ucum-units