_Response.AddHeader("Accept-Ranges", "bytes");_Response.Buffer = false;這個(gè)是什么意思?if (_Request.Headers["Range"] != null)                {                    _Response.StatusCode = 206;                    string[] range = _Request.Headers["Range"].Split(new char[] { '=', '-' });                    startBytes = Convert.ToInt64(range[1]);                }這又是什么意思啊_Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());_Response.AddHeader("Connection", "Keep-Alive");                _Response.ContentType = "application/octet-stream";                _Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(_fileName, System.Text.Encoding.UTF8));這些東西都不懂，有誰可以幫我解釋下這些代碼嘛？