@evan whatever the mechanism i do think isActivity() needs to be specified within mainline AP. i know we have a primer page but having it in-spec would be really useful too.

something similar for allowing Actor to be declared on objects with ldp:inbox and as:outbox could also be useful if we *really* wanna avoid duck-typing. although i am not as opposed to duck-typing as you are…

the definition of as:Actor would specifically be “my ldp:inbox dereferences to a Collection of Activity or subtype”