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]);
			}
		}
	}
}