function toggleLayer( whichLayer )
	{
	  var elem, vis;
	  if( document.getElementById ) // standard method
		elem = document.getElementById( whichLayer );
	  else if( document.all ) // old Exploder
		  elem = document.all[whichLayer];
	  else if( document.layers ) // Netscape 4
		elem = document.layers[whichLayer];
	  vis = elem.style;
	  // resolve blank style.display value
	  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';
	}