N. Freed; N. Borenstein. <a href="http://www.ietf.org/rfc/rfc2046.txt"><cite>Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types.</cite></a> November 1996. Internet RFC 2046. URL: <a href="http://www.ietf.org/rfc/rfc2046.txt">http://www.ietf.org/rfc/rfc2046.txt</a>