update    http://build.fhir.org/ig/HL7/US-Core/conformance-expectations.html#must-support---choice-of-profile-elements to:    There are several instances in this Guide where there is a choice of supporting one or another profile element to meet the must support requirement.  In such instances, the server SHALL support at least one such element, and the client application SHALL support all such elements. There is no way to define this in a computable way, but these instances are clearly documented in the Profile specific implementation guidance sections For example: US Core Medication Request Profile  - The MedicationRequest resource can represent that information is from a secondary source using either a boolean flag or reference in  MedicationRequest.reportedBoolean , or a reference using  MedicationRequest.reportedReference  to Practitioner or other resource. Although both are marked as must support, servers are not required to support both a boolean and a reference, but  SHALL  choose to support  at least one  of these elements.