Country and issuing codes
ISO 3166-1 alpha-3 and the Doc 9303 extensions.
Issuing State and nationality use three-letter codes. The base list is ISO 3166-1 alpha-3; Doc 9303 Part 3 adds a small set of extensions and special values.
- UTO is the specimen country used in examples; it is test data only.
- Special codes cover stateless persons, refugees, the United Nations and unspecified nationality.
- Some issuing authorities use reserved codes that the toolkit reports as a warning rather than a hard error because the published list is incomplete.
Source: Doc 9303 Part 3 — codes — reference/9303-standands/Doc 9303 - Part 3 - Machine Readable Travel Documents (1).html