Sets or unsets the "submenu" link of menu_item to submenu.
If submenu is non-null, it is linked to. If it is null then the link is unset.
The effect of having one menu appear as a submenu of another is exactly as it sounds.
a #GMenuModel, or null
Sets or unsets the "submenu" link of menu_item to submenu.
If submenu is non-null, it is linked to. If it is null then the link is unset.
The effect of having one menu appear as a submenu of another is exactly as it sounds.