function toggleLayer( whichLayer )
{
  var elem, vis;
  if( document.getElementById ) 
    elem = document.getElementById( whichLayer );
  else if( document.all ) 
      elem = document.all[whichLayer];
  else if( document.layers ) 
    elem = document.layers[whichLayer];
if (document.getElementById(whichLayer)) {
  vis = elem.style;
  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';
}
}