Activity Type connections documentation?

Is there any documentation on what the ActivityItemID and ActivityItemDetailID refer to for each of the built-in Activity types?

I believe for Forms it used to be ActivityItemID -> Form's FormID, and ActivityItemDetailID is the form row's ID (though it's possible that's no longer true), but I'm hoping there's a full list somewhere.

I'm putting together reporting on a user's activities (to expose to an external marketing system via API) - I'm currently working on the reporting for Email clicks and Page visits, but I suspect they'll eventually want reporting on all the built-in types (plus the custom types, but I set the ids on those myself :) ).