Agreed create a cpg-unknownBehavior extension code 0..1 on Expression | DataRequirement | ParameterDefinition ignore - The default evaluation path is followed (e.g. assume false in a population or eligibility criteria) warning - The default evaluation path is followed but a warning is surfaced prompt - User interaction is required to provide the data require - An error is raised, the default evaluation path is interrupted   Provide guidance around the "require" option to indicate that workflows surfacing these behaviors need to take context into account and ensure that users have the ability to proceed and take appropriate action, exercising clinical judgement.