The following alpha-3 codes can be user-assigned: AAA to AAZ, QMA to QZZ, XAA to XZZ, and ZZA to ZZZ.
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.
[5] Exceptionally reserved code elements are codes reserved at the request of national ISO member bodies, governments and international organizations, which are required in order to support a particular application, as specified by the requesting body and limited to such use; any further use of such code elements is subject to approval by the ISO 3166/MA.
These codes may be reassigned by the ISO 3166/MA after the expiration of the transitional period.
For example, several codes are reserved because they are used for international intellectual property organizations in WIPO Standard ST.3.