Handle-boxes would be very powerfull if the widget could be splitted into two
parts."docking child" and "docking area", and that the user could move the
"docking childs" inside the docking area after their own wish. Say for instance
that the program defines a docking area at the top and the bottom, and have 5
different tool-child's containing different tools. One user would like them
under-each other, another would like them compact.

These docking area's and childs would need to have a group identifier to tell
them which area's they can dock to and not.

Another needed API then, would be a method to retrieve the current layout (and
to set it).