You can add pop-up menus to shelf items to perform custom tasks. Pop-up menus appear when you right-click each shelf item.
To create a new pop-up menu
An entry called User Menu Item appears in the Menu Items list.
Now if you right-click the corresponding shelf item, your new menu item appears in the pop-up menu. If you select it, Maya performs the actions defined by the script.
You can modify a script at any time to adjust the functionality of your menu items. You can also adjust the order in which the items appear by reordering them with the Move Up () and Move Down () buttons. You can delete a menu item by highlighting it and clicking the Delete Menu Item () button.