N. Freed, K. Moore.  <a href="http://www.ietf.org/rfc/rfc2231.txt"><cite>MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations.</cite></a> November 1997.  IETF RFC 2231. URL: <a href="http://www.ietf.org/rfc/rfc2231.txt">http://www.ietf.org/rfc/rfc2231.txt</a>