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 was created in 2009 for the purpose of "[s]tandardization in the field of energy efficiency and renewable energy sources". ISO has 162 national members. ISO has three membership categories: Participating members are called "P" members, as opposed to observing members, who are called "O" members. ISO is funded by a combination of: ISO's main products are international standards. ISO also publishes technical reports, technical specifications, publicly available specifications, technical corrigenda, and guides. International standards Technical reports Technical and publicly available specifications Technical corrigenda ISO guides These are meta-standards covering "matters related to international standardization". They are named using the format