Document folders?

[Xiaopangzi]

I am looking for folders other than /mnt/us/documents where books would be found by the framework. The fact that the pre-installed dictionaries are not in /mnt/us/documents suggests this is possible. Is there a search path for all books? Can new folders be added to it? I would like to add a folder to the search path, then be able to mount/unmount (compressed,encrypted,...) volumes containing books using that folder as a mount point. I checked that mounting this way to /mnt/us/pictures works fine but it is limited to picture collections.