Object ╰── PopupMenu.PopupMenuBase ╰── PopupMenu.PopupSubMenu
A submenu to be included in
PopupMenuSections. You usually don't want to create these manually. Instead you want to create a
PopupSubMenuMenuItem, which creates a
PopupSubMenu, and shows/hides the menu when clicked.
Since submenus are usually used to hide long lists of things, they are automatically put into a
St.ScrollView such that their height will be limited by the css max-height property.
Opens the submenu