The use case is the need to identify the admission source for an Emergency Department visit as an Emergency Medical Services (ambulance). The current Encounter.hospitalization.admissionSource includes a value set of options (http://hl7.org/fhir/valueset-encounter-admit-source.html) but the value set does not include EMS as an option. While the value set may be exemplary and not constrained, the option should be included. It will be helpful to provide clear guidance how to address the method of arrival for any encounter, not just hospitalization. So, perhaps, Encounter at a higher level needs an arrivalMethod metadata element. Please provide guidance or add appropriate metadata to accommodate the need.