Serving the Correct MIME Type for XHTML using ASP.NET 2.0

String strContentType = null;

// Determine if the user agent returns any AcceptTypes (HTTP_ACCEPT) response
if (Request.AcceptTypes != null)
{
  // Determine if the user agent can handle XHTML served as "application/xhtml+xml" (e.g. FireFox, Opera)
  if (Array.IndexOf(Request.AcceptTypes, "application/xhtml+xml") > -1)
  {
    strContentType = "application/xhtml+xml";
  }
  else
  {
    // If the user agent does not specifiy acceptence of "application/xhtml+xml", then serve as "text/html" (e.g. Internet Explorer)
    strContentType = "text/html";
  }
}
else
{
  // If AcceptTypes is null, then serve as "application/xhtml+xml" (e.g. W3C Validator)
  strContentType = "application/xhtml+xml";
}

// Set the Response Content Type
Response.ContentType = strContentType.ToString();

if (strContentType == "text/html")
{
  // Generate a "content-type" meta tag in the page head
  HtmlMeta hmtContentType = new HtmlMeta();
  hmtContentType.HttpEquiv = "content-type";
  hmtContentType.Content = strContentType.ToString() + "; charset=UTF-8";
  Page.Header.Controls.Add(hmtContentType);
}
else
{
  // Generate xml declaration
  Response.Write("<?xml version="1.0" encoding="UTF-8" ?>
");
}

// Set the page encoding
Response.ContentEncoding = System.Text.Encoding.UTF8;

// Send a Vary header to inform proxy servers that content negotiation is taking place
Response.AddHeader("Vary", "Accept");