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What is an applications submenu

The part of the MenuPart that is specific to the application
The application submenu is defined in the skin file named skinSubmenu.php in the application folder. The application developer has to create it manually. If it is missing, the default skinSubmenu.php file in the includes folder will be used.

The skin or the way it is used can be overridden by adding a class MenuPart. See how to change an applications submenu.