efl/src/lib/elementary/efl_ui_box_stack.eo

class Efl.Ui.Box_Stack (Efl.Ui.Box, Efl.Pack.Layout)
{
   [[A custom layout engine for @Efl.Ui.Box that stacks items.

     Items will be stacked on top of each other (in the Z direction).
   ]]
   data: null;
   implements {
      Efl.Pack.Layout.layout_update;
   }
}