JGo for Swing version 5.2 includes a new sample application, BoxApp.
This simple application makes use of the new JGoSubGraphBase class to construct a simple BoxArea class that acts like a "box", allowing the user to add or remove objects by drag-and-drop. Boxes can be added to boxes, to support nesting. A custom JGoView highlights a BoxArea if it could be the target of a drop, and actually implements the calls to JGoArea.addCollection to add dragged objects to a BoxArea, or to JGoLayer.addCollection to make the dragged objects top-level objects.
The following screen shot was taken during the drag of a blue node into the nested Box 2: