A region code from the `ISO 3166` standard.
Some examples are `CAON` (`CA` for Canada, `ON` for Ontario), `USCA` (`US` for United States, `CA` for
California) or `IEL` (`IE` for Ireland, `L` for Leinster). The first part of the full `ISO 3166-2` code
is a 2 letter code for the country that contains the territory, the other 1 to 3 characters determine the
subdivision (province, region, parish, emirate or other variously named subdivisions).