http://hl7.org/fhir/StructureDefinition/patient-relatedPerson|5.2.0

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.
NameFlagsCardTypeDescription & Constraints
Extension
0..*This contact may have further details in this RelatedPerson
 
extension
?..0
 
url
?..?
 
value[x] *
1..?
 
 
valueReference *
1..?Reference