ISO 639-3:2007 provides a code, published by the Registration Authority of ISO 639-3, consisting of language code elements comprising three-letter language identifiers for the representation of languages. The language identifiers according to this ISO 639-3:2007 were devised for use in a wide range of applications, especially in computer systems, where there is potential need to support a large number of the languages that are known to have ever existed. Whereas ISO 639-1 and ISO 639-2 are intended to focus on the major languages of the world that are most frequently represented in the total body of the world's literature, ISO 639-3:2007 attempts to provide as complete an enumeration of languages as possible, including living, extinct, ancient and constructed languages, whether major or minor, written or unwritten. As a result, ISO 639-3:2007 deals with a very large number of lesser-known languages. Languages designed exclusively for machine use, such as computer-programming languages and reconstructed languages, are not included in this code.