http://hl7.org/fhir/StructureDefinition/additionalIdentifier|5.2.0

An additional identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.

Structure JSON Dependencies FHIRSchema Other Versions Dependant (0)Elements Summary

description: An additional identifier for the target resource. This is used when there is no way to reference the other resource directly, either because the entity it represents is not available through a FHIR server, or because there is no way for the author of the resource to convert a known identifier to an actual location. There is no requirement that a Reference.identifier point to something that is actually exposed as a FHIR instance, but it SHALL point to a business concept that would be expected to be exposed as a FHIR instance, and that instance would need to be of a FHIR resource type allowed by the reference.
derivation: constraint
name: AdditionalIdentifier
type: Extension
elements:
  extension: {index: 0}
  url:
    pattern: {type: Uri, value: 'http://hl7.org/fhir/StructureDefinition/additionalIdentifier'}
    index: 1
  value:
    choices: []
    index: 3
extensions: {}
class: extension
kind: complex-type
url: http://hl7.org/fhir/StructureDefinition/additionalIdentifier
base: http://hl7.org/fhir/StructureDefinition/Extension
version: 5.2.0
required: [value]