Define the "right level" of interoperability

From https://matrix.to/#/!uHqAjmOtrLtidOiczC:matrix.org/$D31omcSRjOOXYtSpivZesVtE_P5fV4tDJS84lgjjKCc?via=matrix.org&via=mozilla.org&via=one.ems.host

Helge says:

I think the stuff is with interoperability is also problematic because statements are either "trivial" or "overreach" with probably no middle ground in between. I'm talking here in the context of defining a protocol. This protocol is called hypothetical Fediverse core protocol (HFCP)

"Trivial interoperability": If Alice and Bob both implement HFCP and Alice sends a HFCP message to Bob, then Bob correctly receives the message.

"Overreach interoperability": If Alice and Bob both implement HFCP and Alice sends a HFCP message to Bob, then Bob's app correctly displays the message.