Common Identifier
http://fhir.patientsknowbest.com/id/common-identifier
https://www.hl7.org/fhir/R4/namingsystem.html
kind
identifier
description
An extension to represent [[Appointment.Common ID]].
uniqueId
uniqueId[0]
type = uri
value = “http://fhir.patientsknowbest.com/id/common-identifier”
preferred = true