Yeah, that is the syntax for a type alias. You can use NewType to create an actual subclass of the type instead. https://docs.python.org/3/library/typing.html#newtype

In that case, you need a subclass of string that does nothing but has its type as FirstNameType. Wherever you create or return strings that are first names, you'll need to instantiate FirstNameType instead.

And in the future, they could be anything. Finland expanded the allowed characters in person identification numbers to support people born after 2000. Usually bad idea to be too strict in checking fields where people manually enter text.