The Top container

The top container is the panel containing the design grid. It is special in that you can select it only from the grid context menu or from the current layout's context menu.
Grid context menu Project view context menu
If your exported layout extends JPanel, the JPanel constructed by the RADi runtime library is the top container.
If your exported layout extends JFrame, JDialog or JApplet, the top container will be added to the ContentPane.

If you define a FocusTraversalPolicy you generally do this for the top container.
As with internal panels, you can display background images for the top container.