Adding menu items
Menu items are the starting point for user interface navigation. They form a hierarchical structure, where the top-level items represent applications, and the level below is the application main menu. Further sub-menu levels can be added.
Menu items with no sub-menus are actionable and can trigger an action that tells the web client what to do, such as opening a view.
Menu items are stored in the ir.ui.menu model and can be browsed via the Settings | Technical | User Interface | Menu Items menu.
The library_app add-on module created a top-level menu for the library books, while the library_checkout add-on module added the menu items for the checkouts and checkout stages. These are both implemented in library_checkout/views/library_menu.xml.
This is the XML for the checkout menu item:
<menuitem id="menu_library_checkout" name="...
