This is the ValueSet that contains all the codes in Appointment Type and Reasons (http://hl7.org/fhir/uv/smart-scheduling-links/ValueSet/appointment-type-and-reasons-vs) and hl7VS-appointmentReasonCodes (http://terminology.hl7.org/ValueSet/v2-0276). E.g. what you have to deal with if you get resources containing codes in either of them