ISO 4217 "ruble". In addition to codes for most active national currencies ISO 4217 provides codes for "supranational" currencies, procedural purposes, and several things which are "similar to" currencies: The use of an initial letter "X" for these purposes is facilitated by the ISO 3166 rule that no official country code beginning with X will ever be assigned. Because of this rule ISO 4217 can use X codes without risk of clashing with a future country code. ISO 3166 country codes beginning with "X" are used for private custom use (reserved), never for official codes. For instance, the ISO 3166-based NATO country
International Organization for Standardization ""ISO[/IEC] Guide N:yyyy: Title"".For example: ISO documents are copyrighted and ISO charges for most copies. It does not, however, charge for most draft copies of documents in electronic format. Although they are useful, care must be taken using these drafts as there is the possibility of substantial change before they become finalized as standards. Some standards by ISO and its official U.S. representative (and, via the U.S. National Committee, the International Electrotechnical Commission) are made freely available. A standard published by ISO/IEC is the last stage of a long process that commonly starts with the proposal of new work within