http://hl7.org/fhir/StructureDefinition/patient-relatedPerson|4.0.1

In some cases a Patient.contact will also be populated as a RelatedPerson resource. This linkage permits the linkage between the 2 resources to be able to accurately indicate a representation of the same individual, and updating details between could be appropriate.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/Reference
Extension.value[x].targetProfilehttp://hl7.org/fhir/StructureDefinition/RelatedPerson