Not sure if this it the correct place to put my suggestions, so adding them here.

I have not had time to fully review all aspects of the specification or what they would mean for our implementations, so these comments should be considered with that in mind.

First, an executive summary with the key functional requirements and entailed  that are addressed should be included.  This can include implications for FHIR implementations. This would help those who don't have as much time as well as those who are less familiar with terminological engineering. 
 
Second, our community wants to ensure that local terminological content as well as OBO style OWL ontologies are easily integratable. This would require the ability to define rules for determination of equivalencies of mappings or other logical entailments. Provenance of the mapping should be part of the required documentation. We have been developing the SSSOM standard for terms and enums, attirbution, versioning, and both human readable URIs and numeric ones. I prefer too that the URIs are resolvable. I would like to be able to use DL queries or other rules to define codests/enums for the mapping, and have this be in the provenance of the mappings.
 
I hope that these ideas are helpful, I am very excited to see this work and the idea that we can bring better semantics and utility to FHIR and better support translational use cases such as in Vulcan and local use cases.