I remember looking at PLbindef and liking that more explicit “duality”. With Pdef.envir, there’s the issue that sometimes you’d want the “*def-object” to be notified when certain changes happen in/via the envir. But you don’t get that if Pdef.envir is geared to accept any “legacy” Environment/Event. But there are some issues with subclassing Environments as I mentioned in that thread too.