so you can have classes within classes (inner classes).
how about modules within modules (inner modules)?
why? as a means to enforce private 'within' a module.
// -----
module test;
inner module myClasses
{
     class Foo
     {
         // private to the inner module
         private int _num;
     }
}
void main()
{
     Foo f = new test.myClasses.Foo();
     f._num++; // nope!
}
// ---