GB_myShow = function(caption, url, /* optional */ height, width, callback_fn) {
    var options =
    {
      caption: caption,
      height: height || 500,
      width: width || 500,
      fullscreen: false,
      show_loading: false,
      callback_fn: callback_fn
    }
    var win = new GB_Window(options);
    return win.show(url);
  }