function loadXMLDoc(dname, _callback) 
{
    try //Internet Explorer
    {
        xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
    }
    catch(e)
    {
        try //Firefox, Mozilla, Opera, etc.
        {
            xmlDoc=document.implementation.createDocument("","",null);
        }
        catch(e) {alert(e.message)}
    }
    try 
    {
        //默认异步模式载入,如下设置同步载入
        xmlDoc.async=false;
        xmlDoc.onreadystatechange = function ()
        {   
            if (xmlDoc.readyState == 4)
            {   
                   if(_callback) _callback();   
            }   
        };   
        
        xmlDoc.load(dname);
        return(xmlDoc);
    }
    catch(e) {alert(e.message)}
    return(null);
}