Smart Playlist criteria

Please can anyone advise me as to how to deploy the File Location criterion to help with sorting a smart playlist? Is it governed by limitations of how much the file is nested in folders for example? My library (which I wish could be two switchable libraries) is made from scans of two separate folders. I would like to be able to limit the smart playlist criteria to one folder or the other, by using File Location. I have not been able to get it to work. Entering the actual file location address can be open to errors, so I tried dragging and dropping the relevant folder into the location box in the criteria list and this seemed to enter the correct address. Of course being a music source folder means it is a bucket full of buckets full of buckets of tracks and I am wondering if that is the thing which is stopping it from working.

This is all to do with separating “popular” music from “classical” music. I have two sources for the library so defined and, at the moment, they are all lumped together in the library. I have been able to provide a level of separation by making sure the genre tags are unique to one folder or the other but I would like to be able to manipulate playlists based on one group or the other, i.e. having the separating criterion applied first. The problem would not exist if it were possible to have two libraries and the ability to switch between them :confused: