function menu() {

   var navItems = document.getElementById("nav").getElementsByTagName("li");
    
   for (var i=0; i< navItems.length; i++) {
      if(navItems[i].className == "submenu") {
         navItems[i].onmouseover=function() 
		 {this.getElementsByTagName('ul')[0].style.display="block";}
         navItems[i].onmouseout=function()
		  {this.getElementsByTagName('ul')[0].style.display="none";}
      }
   }

}