http://hl7.org/fhir/StructureDefinition/observation-sequelTo|4.0.1

This observation follows the target observation (e.g. timed tests such as Glucose Tolerance Test).

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