> To be clear, HL7 is a not-for-profit organization which has created several sets of standards over its history (HL7-V1, V2, V3, etc)--those standards are probably what you are referring to. HL7, as an organization, is very much a leader in this space.

I'm being sarcastic when I say HL7 isn't a leader. Obviously their psuedo-standards are widespread; they're just terrible.

I haven't dug much into FHIR because, when I last needed to implement any of this, literally nobody was actually using it. That said, based on everything else I've seen, I'm skeptical that it's actually a proper standard in the strict sense. Even the other message types that HL7 has produced are not properly specified, with ambiguous language that allows for multiple interpretations and "valid" (but incompatible) implementations.