This is a point I keep coming back to again and again.
AS2 and AP are focused around the question of "how do I describe the world." This is also what RDF and by extension JSON-LD are focused on. You see this assumption further embedded in how people talk about the "open world assumption" and needing essentially unlimited flexibility, because they are trying to _describe_ things.
But that's not how protocols work. That's not how _any_ protocols work outside of AP.
https://hachyderm.io/@jenniferplusplus/113415270719967178