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];
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';
}