your validation function would probably look more like ```ts const validateUserId = (x: number): x is UserId => {}; ``` for the `UserId` type declaration,

your validation function would probably look more like ```ts const validateUserId = (x: number): x is UserId => {}; ``` for the `UserId` type declaration, I'm actually a little unsure of the best way to go about it. But I feel like using enums, typed string literals, or classes might be better approach. Would be interested if anyone has any thoughts on this