[mrsmrtss]

Well the point of using abstractions is that you don't need to know the things that it is abstracting. I think the abstraction here is self explaining what it does and you can certainly understand and use it without needing to understand all the specifics behind it.

[CharlieDigital]

More importantly: it prevents "usr:alice_123" instead of "user:alice_123" by using the type constraint to generate the prefix for the identifier.