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ISO 3166-2:JP is the ISO 3166-2's part for Japan. It is part of the ISO 3166 standard published by the International Organization for Standardization (ISO). It says the codes for the names of the main subdivisions (e.g.provinces or states) of all countries in ISO 3166-1.
Subdivision names are listed as in the ISO 3166-2 standard published by the ISO 3166 Maintenance Agency (ISO 3166/MA).