function findHighestZIndex(elem) {
	var elems = document.getElementsByTagName(elem);
	var highest = 0;
 
	for (var i = 0; i < elems.length; i++) {
		var zindex=document.defaultView.getComputedStyle(elems[i],null).getPropertyValue("z-index");
		if ((zindex > highest) && (zindex != 'auto')) {
			highest = zindex;
		}
	}
 
	return highest;
}