Reserved code elements are codes which have become obsolete, or are required in order to enable a particular user application of the standard but do not qualify for inclusion in ISO 3166-1. To avoid transitional application problems and to aid users who require specific additional code elements for the functioning of their coding systems, the ISO 3166/MA, when justified, reserves these codes which it undertakes not to use for other than specified purposes during a limited or indeterminate period of time. The reserved alpha-2 codes can be divided into the following four categories: exceptional reservations, transitional reservations, indeterminate reservations, and codes currently agreed not to use.