Agreed, provide a definition of Must Support for the profiles in this IG: Certain elements in the profiles defined in this implementation guide are marked as Must Support. This flag is used to indicate that the element plays a critical role in defining and sharing artifacts, and implementations SHALL understand and process the element. In addition, because artifact specifications typically make use of data implementation guides (e.g. IPS, US Core, QI-Core), the implications of the Must Support flag for profiles used from those implementation guides must be considered. For more information, see the definition of Must Support in the base FHIR specification. Conformance Requirement 3.18 (Must Support Elements): For resource instances claiming to conform to CRMI IG profiles, Must Support on any profile data element SHALL be interpreted as follows: Authoring systems and knowledge repositories SHALL be capable of populating all Must Support data elements. Evaluating systems SHALL be capable of processing resource instances containing Must Support data elements without generating an error or causing the evaluation to fail. In situations where information on a particular data element is not present and the reason for absence is unknown, authoring and repository systems SHALL NOT include the data elements in the resource instance. For example, for systems using ‘9999’ to indicate unknown data values, do not include ‘9999’ in the resource instance. When consuming resource instances, evaluating systems SHALL interpret missing data elements within resource instances as data not present for the artifact. Submitting and receiving systems using knowledge artifacts to perform data exchange or artifact evaluation operations SHALL respect the must support requirements of the profiles used by the artifact to describe the data involved in the operation.