code: def get_builder_toplevel(self, builder):
          
          toplevel = builder.get_object(self.toplevel_name)
          if toplevel is None:
              toplevel = get_first_builder_window(builder).child
          if toplevel is not None:
              #XXX: what to do if a developer
              #     gave the name of a window instead of its child
              toplevel.get_parent().remove(toplevel)
          return toplevel
docs: Get the toplevel widget from a Gtk.Builder file.
  
          The slave view implementation first searches for the widget named as
          self.toplevel_name (which defaults to "main". If this is missing, the
          first toplevel widget is discovered in the Builder file, and it's
          immediate child is used as the toplevel widget for the delegate.