Install an accelerator.
Pick the type of the UI element according to context.
Create a menu.
Create a menubar.
Create a menuitem.
Insert a placeholder.
Create a popup menu.
Same as %GTK_UI_MANAGER_POPUP, but the actions’ accelerators are shown.
Create a separator.
Create a toolbar.
Create a toolitem.
These enumeration values are used by gtk_ui_manager_add_ui() to determine what UI element to create.