jonathanstrange parent
That's neat, I was about to ask which languages support that since the vast majority don't. I didn't know that you can do that in Typescript.
Any language with an type system really...
Even OOP : if you have a string class, you can have a String_Formated_For_API subtype.
Just extends String, and add some checking.
But now the type checker "knows" it can print() a String_Formated_For_API just fine but not call_API(string).