http://hl7.org/fhir/StructureDefinition/Period|4.0.1

Base StructureDefinition for Period Type: A time period defined by a start and end date and optionally time.

element_id	types
Period
Period.start	dateTime
Period.end	dateTime
Period
Period.id	http://hl7.org/fhirpath/System.String
Period.extension	Extension
Period.start	dateTime
Period.end	dateTime