An RFC from the IETF, see also the MIME standard,

• Full text of RFC 3023 (http://www.ietf.org/rfc/rfc3023.txt) XML Media Types. M. Murata, S. St.Laurent, D. Kohn. January 2001. (Format: TXT=86011 bytes) (Obsoletes RFC 2376[?]) (Updates RFC 2048) (Status: PROPOSED STANDARD)