http://hl7.org/fhir/StructureDefinition/composition-section-subject|5.2.0

Specifies that the section has a different subject than the Composition, or its container section.

element_id	types
Extension
Extension.extension
Extension.url
Extension.value[x]	string
Extension
Extension.id	http://hl7.org/fhirpath/System.String
Extension.extension	Extension
Extension.url	http://hl7.org/fhirpath/System.String
Extension.value[x]	string