// the function toggleLayer is based on code from http://www.netlobo.com/div_hiding.html
function toggleLayer(whichLayer)
{
  var elem, sty;
  if(document.getElementById){
    elem = document.getElementById(whichLayer);
  }else if(document.all){
    elem = document.all[whichLayer];
  }else if(document.layers){
    elem = document.layers[whichLayer];
  }
  sty = elem.style;
  // if the style.display value is blank we try to figure it out here
  if(sty.display == '' && elem.offsetWidth != undefined && elem.offsetHeight != undefined){
    sty.display = (elem.offsetWidth != 0 && elem.offsetHeight != 0) ? 'block' : 'none';
  }
  sty.display = (sty.display == '' || sty.display == 'block') ? 'none' : 'block';
}