The concepts in ConceptMapRelationship http://build.fhir.org/valueset-concept-map-relationship.html are exhaustive and mutually exclusive, and the value set is bound to ConceptMap.relationship with required binding strength.

Guidance text should be added to recommend how to add and manage extensions to cover any additional concepts to refine or extend ConceptMapRelationship such as categorized-by or grouped-by. 

Note: this is referenced in https://jira.hl7.org/browse/FHIR-22632 as the 7th item, and has not been done.