//用于bbs的nav.asp的导航的折叠和显示
function nav(child)
{
var display = document.getElementById(child).style.display;

if(display == "none")
{
document.getElementById(child).style.display="";
document.getElementById(child+"_switch").style.background="background: url(../img/common/menu_bg1.gif) #fff no-repeat left top;";
}else if(display==""){
document.getElementById(child).style.display="none";
document.getElementById(child+"_switch").style.background="background: url(../img/common/menu_bg2.gif) #fff no-repeat left top;";
}


}