I still do not understand the difference between a main package and a non-main package as far as Ultimate++ is concerned. Why divide your idea of a package into these two distinct categories ? In other words what does a main package consist of that a non-main package does not have and why is this important to either the IDE or to a person using Ultimate++ to create executables or libraries to be run cross-platform ?

Also I think I do understand assemblies/nests as merely grouping mechanisms in the IDE in order to specify a package or a particular build of a package in a particular category ( assembly ). If they exist as anything else please tell me.