var DropdownMenu = Class.create();
DropdownMenu.prototype =
{
    initialize : function(menuNode)
    {
        var dropdowns = menuNode.getElementsByTagName('li');

        for(var i = 0; i < dropdowns.length; i++) {
            dropdowns[i].onmouseover = function() {
                Element.addClassName(this, 'over') }
            dropdowns[i].onmouseout  = function() {
                Element.removeClassName(this, 'over') }
        }
    }
}

Event.observe(window, 'load', function() {
        ClassObject.assign('top-nav', DropdownMenu);
    });

var ClassObject={assign:function(className,objectCopy)
{var elements=document.getElementsByClassName(className);if(typeof elements!='undefined'){for(var i=0;i<elements.length;i++){new objectCopy(elements[i]);}}}}