Gtk standard package
A box is a container that can have multiple children, organized either horizontally or vertically. Two subtypes are provided, Gtk_Hbox and Gtk_Vbox, to conform to the C API. In Ada, you do not need to distinguish between the two, but note that the Gtk_Box type is conceptually an abstract type: there is no way to create a "Gtk_Box", only ways to create either an horizontal box, or a vertical box.