Individual subdivisions are represented by instances of the Iso3166Part2Subdivision type. You don’t create instances of Iso3166Part2Subdivision yourself, but rather use predefined instances for each of the defined subdivision codes.
As the ISO 3166-2 standard defines an individual set of subdivision codes for most countries, the predefined subdivision codes are implemented in a hierarchical structure in which the subdivision codes are delineated by the country code of the country the subdivisions belong to. This takes the form of nested classes in the Iso3166Part2Subdivision type that are named after the ISO 3166-1 alpha-2 country code. In these nested classes are members for each of the subdivision codes defined by ISO 3166-2 for that country. For example,
// Australian Capital Territory
var act = Iso3166Part2Subdivision.AU._ACT;
You may notice that all subdivision codes start with an underscore. This was motivated by a technical limitation on the naming of identifiers in .Net: as it is not possible to start an identifier with a digit, and some subdivision codes defined by ISO 3166-2 do start with digits, it was decided to make all subdivision codes start with the underscore for consistency.