 IETF language tags were first defined in RFC 1766, edited by Harald Tveit Alvestrand, published in March 1995.The tags used ISO 639 two-letter language codes and ISO 3166 two-letter country codes, and allowed registration of whole tags that included variant or script subtags of three to eight letters.In January 2001 this was updated by RFC 3066, which added the use of ISO 639-2 three-letter codes, permitted subtags with digits, and adopted the concept of language ranges from HTTP/1.1 to help with matching of language tags.