The Concept Hierarchy documentation states that "Code systems may be presented hierarchically, using nested concept elements, where the hierarchy has a defined meaning specified in hierarchyMeaning" and in cases when a concept has multiple parents in the hierarchy "the relationships between concepts should be defined using properties".  But hierarchyMeaning is an optional element and this requirement is currently not enforced.  Some (likely many) of the code systems in the spec that contain a hierarchy do not currently have a hierarchyMeaning element (e.g. condition-ver-status).

Suggest adding invariant(s) to the CodeSystem resource for:

• concept.concept.exists() implies hierarchyMeaning.exists()
• concept.where(property.code = 'parent' or property.code = 'child').exists() implies hierarchyMeaning.exists()

See Zulip discussion here.

And add hierarchyMeaning to the code systems instances in the spec where it currently is missing.