var cur_lyr;	// holds id of currently visible layer
	function swapLayers(id) {
	  if (cur_lyr) hideLayer(cur_lyr);
	  showLayer(id);
	  cur_lyr = id;
	}
	
	function showLayer(id) {
	  var lyr = getElemRefs(id);
	  if (lyr && lyr.css) lyr.css.visibility = "visible";
	}
	
	function hideLayer(id) {
	  var lyr = getElemRefs(id);
	  if (lyr && lyr.css) lyr.css.visibility = "hidden";
	}
	
	function getElemRefs(id) {
		var el = (document.getElementById)? document.getElementById(id): (document.all)? document.all[id]: (document.layers)? getLyrRef(id,document): null;
		if (el) el.css = (el.style)? el.style: el;
		return el;
	}
	
	// get reference to nested layer for ns4
	// from old dhtmllib.js by Mike Hall of www.brainjar.com
	function getLyrRef(lyr,doc) {
		if (document.layers) {
			var theLyr;
			for (var i=0; i<doc.layers.length; i++) {
			theLyr = doc.layers[i];
				if (theLyr.name == lyr) return theLyr;
				else if (theLyr.document.layers.length > 0) 
				if ((theLyr = getLyrRef(lyr,theLyr.document)) != null)
						return theLyr;
		  }
			return null;
	  }
	}