function toggleLayer(whichLayer) {
  var elem, vis;
  if(document.getElementById) // this is the way the standards work
    elem = document.getElementById(whichLayer);
  else if(document.all) // this is the way old msie versions work
      elem = document.all[whichLayer];
  else if(document.layers) // this is the way nn4 works
    elem = document.layers[whichLayer];
  vis = elem.style;
  // if the style.display value is blank we try to figure it out here
  if(vis.display==''&&elem.offsetWidth!=undefined&&elem.offsetHeight!=undefined)
    vis.display = (elem.offsetWidth!=0&&elem.offsetHeight!=0)?'block':'none';
  vis.display = (vis.display==''||vis.display=='block')?'none':'block';
}