:'''<nowiki>#</nowiki>''' - ''Information not available''.:'''u''' - ''Unknown''. Used when codes are being assigned, but the appropriate specific value cannot be determined.:'''x''' - ''Not applicable''. Used when a characteristic is not appropriate for the type of entity being described.:'''y''' - ''Not present''. Used when the characteristic being coded is not present for the entity being described.:'''z''' - ''Other''. Used when codes are being assigned and the characteristics of the entity are known, but none of the defined codes is appropriate.:'''|''' - ''Fill character''. Used when no attempt is being made to assign the codes.