Existing Wording: extensible To be conformant, instances of this element must include a code from the specified value set if any of the codes within the value set can apply to the concept being communicated. If the value set does not cover the concept (based on human review), alternate coding (or, data type allowing, text) may be included instead.

Proposed Wording: extensible To be conformant, instances of this element must include a code from the specified value set if any of the codes within the value set can apply to the concept being communicated. If the value set does not cover an intended concept a change proposal to address the gap should be submitted to the organization administering the value set. In the interim a text value may be used for human review.

Comment:

This binding strengths would allow for gaps in value sets to persist. We need a way to address gaps in value sets over time (using versioning perhaps). If implementers are free to add ad-hoc extensions, these gaps are not addressed and a growing list of ad-hoc codes would be persist and prevent semantic interoperability. Furthermore, this type of binding cannot be used effectively for testing, validation, and certification.