GtkButtonBox::set_child_secondary
This group appears after the other children if the style is Gtk::BUTTONBOX_START, Gtk::BUTTONBOX_SPREAD or GTK::BUTTONBOX_EDGE, and before the other children if the style is GTK::BUTTONBOX_END. For horizontal button boxes, the definition of before/after depends on direction of the widget (see set_direction() ). If the style is Gtk::BUTTONBOX_START or Gtk::BUTTONBOX_END, then the secondary children are aligned at the other end of the button box from the main children. For the other styles, they appear immediately next to the main children.