Hard to understand Exception for string type constraints

[s-heppner]

Currently, when string types (such as NameType, PathType, ContentType, ...) have their constraints violated, the exception mentions the name of the type that was violated.
This can be confusing, since the __init__-functions of the classes using these types in their attributes, only call for str in their type.
We should improve the error message in the exception to make it less confusing.

[jkhsjdhjs]

since the init-functions of the classes using these types in their attributes, only call for str in their type.

This isn't true, the __init__ functions also use types like NameType, PathType, etc.

[jkhsjdhjs]

Ah, maybe you're referring to the docs, where the str type aliases are indeed shown as just str. Maybe we can use typing.NewType instead of the current way of just aliasing the str type.