The purpose is the following. I have a package course management with two object types (at the moment): Course and Courseinstance (similar to dotlrn). For editing the course instance I want to have one tree, for editing the course I want to use two other trees.
In the custom package this can be easily solved by adding the category_tree_id to the ad_form, but if you want to generalize this you are stuck. because there is no way to do this kind of mapping.
I think I will use a mapping within categories, but for the time being it is a custom package so I dont have to worry about it too much. And adding the mapping in categories would mean a lot of code writing, so I will stay away from it until needed (as you should provide an UI for it as well ...).
