IdentifierUse

This code system http://hl7.org/fhir/identifier-use defines the following codes:

Code	Display	Definition
usual	Usual	The identifier recommended for display and use in real-world interactions.
official	Official	The identifier considered to be most trusted for the identification of this item.
temp	Temp	A temporary identifier.
secondary	Secondary	An identifier that was assigned in secondary use - it serves to identify the object in a relative context, but cannot be consistently assigned to the same object again in a different context.