当一个被采集的网页是开启压缩了的话，如果使用HtmlAgilityPack 的HtmlWeb默认配置去下载，下载回来的HTML代码是乱码，应该进行如下操作
HtmlWeb web = new HtmlWeb();
HtmlAgilityPack.HtmlWeb.PreRequestHandler handler = delegate(HttpWebRequest request)
{
request.Headers[HttpRequestHeader.AcceptEncoding] = "gzip, deflate";
request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
request.CookieContainer = new System.Net.CookieContainer();
return true;
};
web.PreRequest += handler;
web.OverrideEncoding = Encoding.Default;
而如果仅仅只是网页的编码问题，则只需要配置这个参数：
web.OverrideEncoding = Encoding.Default;