/// <summary>
 /// 根据 xpath 选择 node 集合, node 非 root node
 /// </summary>
 /// <remarks>Hesinx 2016-05-26</remarks>
 /// <param name="navigator"></param>
 /// <param name="xpath"></param>
 /// <returns></returns>
 public static IEnumerable <HtmlNodeNavigator> SelectSet(this HtmlNodeNavigator navigator, string xpath)
 {
     return(navigator.ToElement().Select(xpath).Cast <HtmlNodeNavigator>());
     //return from HtmlNodeNavigator m in navigator.Select(xpath) select m;
 }
 /// <summary>
 /// 根据 xpath 选择单个 node, 非 root node
 /// </summary>
 /// <param name="navigator"></param>
 /// <param name="xpath"></param>
 /// <returns></returns>
 public static HtmlNodeNavigator SelectSingle(this HtmlNodeNavigator navigator, string xpath)
 {
     return(navigator.ToElement().SelectSingleNode(xpath) as HtmlNodeNavigator);
 }