//ͨõ˵Ч

function menu_action(sender) {
   var lis = sender.getElementsByTagName("li");
   for (var key in lis) {
    lis[key].onmouseover=onMouseOver;
    lis[key].onMouseDown=onMouseDown;
    lis[key].onMouseUp=onMouseUp;
    lis[key].onmouseout=onMouseOut;
   }
   sender.onmouseover = null;
}
function onMouseOver(){OnMouse(this,"block")}
function onMouseDown(){OnMouse(this,"block")}
function onMouseUp(){OnMouse(this,"none")}
function onMouseOut(){OnMouse(this,"none")}
function OnMouse(Obj,Display){
   var ul = Obj.getElementsByTagName("ul")[0];
   if(ul!=null){
    ul.style.display=Display;
   }
}