The best documentation about this is Greedy Plugs. As you said yourself, this is not the most clear documentation because it includes some information for the people creating declarations (snap store staff) and some info for developers creating snaps.
I’m wondering what the best place is to put this information. The only place I can find information about auto-connections is the interface management page, but that page is aimed towards users, not developers/publishers. Maybe we should just create a page about auto-connections specifically tailored towards publishers? Which contains info about the regular behavior + greedy plugs.
Edit: Another possibility is to include an “auto-connections” section to the Adding interfaces page meant for developers. What do you think would work best, @bmw?