Rationale US Core promotes interoperability and adoption through common implementation. Although we recognize the value of Goal.expressedBy element, it is not a minimum expectation for the US Core Goal resource. However, other profiles and implementers, such as the PACIO Advance Directive Interoperability Implementation Guide, can introduce it and describe the best practices for their use cases. When there is sufficient adoption by the implementation community, we can reconsider adding it to the US Core Profiles.   At this time, the expressedBy won't be added as Must Support to US Core. Further investigation and discussion with Patient Care is needed.