function getAbsTop(obj){ //得到对象的绝对y坐标
    var myTop=0;
    do myTop+=obj.offsetTop; 
	while(obj=obj.offsetParent);
    return myTop;
}
function showclass(o,id)
{
	var showit =  document.getElementById(id);
	showit.style.left =12;
	showit.style.top =getAbsTop(o) + 17;
	showit.style.display = "block";
	
}
function hiddenclass(id)
{
	var showit =  document.getElementById(id);
	showit.style.display = "none";
}