Gtk.Dialog.prototype.add_action_widget

function add_action_widget(child:Gtk.Widget, response_id:Number):void {
    // Gjs wrapper for gtk_dialog_add_action_widget()
}

Adds an activatable widget to the action area of a Gtk.Dialog, connecting a signal handler that will emit the Gtk.response signal on the dialog when the widget is activated. The widget is appended to the end of the dialog's action area. If you want to add a non-activatable widget, simply pack it into the @action_area field of the Gtk.Dialog struct.