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

{description: 'Base StructureDefinition for date Type: A date or partial date (e.g. just year or year + month). There is no time zone. The format is a union of the schema types gYear, gYearMonth and date.  Dates SHALL be valid dates.', derivation: specialization, name: date, type: date, class: primitive-type, kind: primitive-type, url: 'http://hl7.org/fhir/StructureDefinition/date', base: 'http://hl7.org/fhir/StructureDefinition/Element', version: 4.0.1}