Int returns a validator for integers.

NonEmptyString is a validator for non-empty strings.

Optional returns a validator that treats an argument as optional.

Rest returns a validator that validates each of the remaining arguments.

String is a validator for strings.

Validate can be used as a command's Before function to validate the arguments to the command.

ErrInvalidUsage is returned when there is a validation error.

Validator is an argument validator function.