aspx页面导出成word文档

在网上 看见这段，可是，谁能帮我解释几个问题吗？这个 方法中的3个参数，第2个是导出的类型吧，第3个是导出的编码吧，第一个是什么呢？

在后置代码中添加

public void ExpertControl(Control source, string doctype, string docName)
{

Response.Clear();
Response.Buffer = true;
Response.Charset = "GB2312";
Response.ContentEncoding = Encoding.UTF8;
//设置Http的头信息,编码格式
if (doctype == "excel")
{
//Excel
Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(docName, System.Text.Encoding.UTF8) + ".xls");
Response.ContentType = "application/ms-excel";
}
if (doctype == "word")
{
//Word
Response.AppendHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(docName, System.Text.Encoding.UTF8) + ".doc");
Response.ContentType = "application/ms-word";
}
//关闭控件的视图状态
source.Page.EnableViewState = false;
//初始化HtmlWriter
StringWriter writer = new StringWriter();
HtmlTextWriter htmlWriter = new HtmlTextWriter(writer);
source.RenderControl(htmlWriter);
//输出
Response.Write(writer.ToString());
Response.End();
}