This differs from example Ruby on Rails where validators instead have the option.
It is unit tested with 100% code coverage and can be considered fit for production.
Unless otherwise specified you can always specify the message option to customize the message returned if the validator doesn't pass.
Just remember to not include the attribute name since it's automatically prepended to the error message.
If an is thrown from an async validator the argument passed to the rejection handler will be that error.
This allows you to differentiate from coding errors and validation errors.
The project can be found on Git Hub where you can also find our issue tracker.