var popupwnd = null;

function popup(url,xs,ys) {
  if (popupwnd != null && !popupwnd.closed) {
    popupwnd.focus();
  }
  x = window.screen.width;
  y = window.screen.height;
  if (x != 0 && y != 0) {
    x = (x - xs) / 2;
    y = (y - ys) / 2;
  }
  coords = ",screenx=" + x + ",screeny=" + y + ",left=" + x + ",top=" + y;
  popupwnd = window.open(url,"bfpopupwnd","toolbar=no,directories=no,menubar=no,width="+xs+",height="+ys+",scrollbars=yes,resizable=no"+coords);
}