My understanding of NIP-01 is that filter tags are meant to relate directly to event tags - that’s why there is confusion.
Discussion
ok, that makes sense but ultimately filters are just a query API and nothing says they cannot extend beyond simple matching if the database can do that
this will simplify your code a lot if it's just a small extension of tags instead of the whole REQ, simpler to adopt or reject, or ignore... it won't match, obviously, for relays that don't understand it, i'm not sure what that behaviour is though
that is an issue that needs to be figured out then i guess
the naive, intuitive sense of it is that filters are queries and thus they need to be more flexible than the data they relate to