JavaScript请教高手

function UserLogout()
{
    var strTempHTML="";
    var dtime = 0;
    var outurl = siteroot + "User/User_Logout.asp?action=xml";
    var userhttp = getHTTPObject();
    userhttp.open("POST",outurl,false);
    userhttp.onreadystatechange = function () 
    {
        if (userhttp.readyState == 4) {
            if (userhttp.status==200){
                var xml; 
                xml = new ActiveXObject("Microsoft.XMLDOM");
                xml.async=false;
                xml.load(userhttp.responseXml);                var root = xml.getElementsByTagName("body");
                if(root.length == 1){
                    var syskey = root.item(0).getElementsByTagName("syskey");
                    if (syskey.length == 1) {
                        var iUrls = root.item(0).getElementsByTagName("apiurl");
                        for (var i=0; i<iUrls.length; i++){
                            dtime = dtime + 2000;
                            strTempHTML += "<iframe frameborder=\"0\" width=\"1\" height=\"1\" src=\"" + iUrls.item(i).text + "?syskey=" + syskey.item(0).text + "&username=" + username + "\" \/>";
                        }
                        if (iUrls.length > 0) $('UserLogin').innerHTML = "logouting..." + strTempHTML;
                    }
                }
                var dd = setTimeout("ShowUserLogin()",dtime);
            }else{
                reportError();
            }
        }
    }
    userhttp.send();
}那位高手能帮我标示每行是什么意思？