After discussion on Zulip: https://chat.fhir.org/#narrow/stream/terminology/subject/ConceptMap.20priority

Alexander Henket: Suppose I have a concept that maps to multiple other concepts e.g. in a SNOMED CT / ICD10 map. How do I give one mapping priority over the other? I could not find any text that hints at priority. I'm currently assuming that the order of ConceptMap.group and ConceptMap.group.element bears implicit relevance, but since that behavior is not defined it feels dangerous to rely on.

Rob Hausam: You shouldn't assume that there is any meaning implied by the ordering of ConceptMap.group and ConceptMap.group.element. I think if you really feel that being able to indicate the mapping priority is needed, then that needs to be added as an extension.

Alexander Henket: Well I'm told none of the SNOMED/ICD mappings work without priority. That means that without it you rule out a very important part of the mapping world. I.e.: the priority sounds like something in the 80% is missing and adding it as an extension doesn't do justice to its importance. At very least, guidance that makes explicit that order of the mappings doesn't imply priority is called for. Secondly should the committee decode that priority is not in the 80%, then I feel a core extension is in order.