          '''
            ASN.1 specification:

            CapitalOrSmall ::=
                IA5String (FROM ("A".."Z") | FROM ("a".."z"))
            '''
            subtypeSpec = ConstraintsUnion(
                PermittedAlphabetConstraint('A', 'Z'),
                PermittedAlphabetConstraint('a', 'z')
            )

        # this will succeed
        capital_or_small = CapitalAndSmall('Hello')

        # this will raise ValueConstraintError
        capital_or_small = CapitalOrSmall('hello!')
    c