Opens a submenu of the @popover. The @name
must be one of the names given to the submenus
of @popover with #GtkPopoverMenu:submenu, or
"main" to switch back to the main menu.
#GtkModelButton will open submenus automatically
when the #GtkModelButton:menu-name property is set,
so this function is only needed when you are using
other kinds of widgets to initiate menu changes.
Opens a submenu of the @popover. The @name must be one of the names given to the submenus of @popover with #GtkPopoverMenu:submenu, or "main" to switch back to the main menu.
#GtkModelButton will open submenus automatically when the #GtkModelButton:menu-name property is set, so this function is only needed when you are using other kinds of widgets to initiate menu changes.