Each area code is a 3-digit number which can refer to a wide variety of geographical and political regions, like a continent and a country.
[a] Some of these codes, those representing countries and territories, were first included as part of the ISO 3166-1 standard in its second edition in 1981, but they have been released by the United Nations Statistics Division since 1970.
[4] Another part of these numeric codes, those representing geographical (continental and sub-continental) supranational regions, was also included in the IANA registry for region subtags (first described in September 2006 in the now obsoleted RFC 4646, but confirmed in its successor RFC 5646, published in September 2009) for use within language tags, as specified in IETF's BCP 47 (where the ISO 3166-1 alpha-2 codes are used as region subtags, instead of UN M.49 codes, for countries and territories).
Some of these private-use codes may be found in some UN statistics reports and databases, for their own specific purpose.
[6] Early editions of M.49 used one- or two-digit prefixes to designate economic regions rather than assigning 3-digit codes.