public class Customer {
    public static class EmailSpecification extends AbstractSpecification<String> {
        public String satisfiesSafely(String proposed) {
            return EmailUtil.ensureValidEmail(proposed);    (1)
        }
    }
    @Action(semantics=SemanticsOf.IDEMPOTENT)
    public Customer updateEmail(
        @Parameter(
            maxLength=30,
            mustSatisfy=EmailSpecification.class,
            optionality=Optionality.OPTIONAL,
            regexPattern = "(\\w+\\.)*\\w+@(\\w+\\.)+[A-Za-z]+",
            regexPatternFlags=Pattern.CASE_INSENSITIVE
        )
        @ParameterLayout(named="New Email Address")
        final String newEmailAddress
        ...
    }
}