var dropDownMenu = Class.create();
dropDownMenu.prototype = {
	initialize:function(cls){
		this.cls = cls;
		this.init();
	},
	
	init:function(){
		D$$(this.cls).each(function(o){
			o.observe("mouseover",function(){o.down(1).show()});
			o.observe("mouseout",function(){o.down(1).hide()});
		});
	}
};

document.observe("dom:loaded",function(){
	var newMenu = new dropDownMenu(".nav_li");
});