function getLayerRef ( /* String */ id, 
                       /* optional HTML-Object */ document) {
  if (!document)
    document = window.document;

  if (document.layers) {
    for (var l = 0; l < document.layers.length; l++)
      if (document.layers[l].id == id)
        return document.layers[l];
    for (var l = 0; l < document.layers.length; l++) {
      var result = getLayerRef(id, document.layers[l].document);
      if (result)
        return result;
    }
    return null;
  } else if (document.all) {
    return document.all[id];
  } else if (document.getElementById) {
    return document.getElementById(id);
  }
}