http://hl7.org/fhir/StructureDefinition/humanname-fathers-family|5.2.0

The portion of the family name that is derived from the person's father.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/string