my $profile = {
       required => [qw( cc_type
                        cc_name
                        cc_number
                        cc_expiry
                        cc_3digit_code )],

       constraints => {
                        # field must match one of visa amex or mc
                        cc_type => qr/^(visa|amex|mc)$/,

                        # match to a name
                        cc_name => qr/^([\w ]+)$/,

                        # use built in cc_number function to validate
                        # credit card numbers.  the validation
                        # routine needs both the cc_number and the
                        # cc_type to do the validation

                        cc_number => { constraint => 'cc_number', 
                                       params => [qw(cc_number
                                                     cc_type)]
                                     },

                        # use the builting cc_exp routine to validate
                        # the expiry date
                        cc_expiry => 'cc_exp',

                        # field must be a 3 or 4 word or
                        # digit characters

                        cc_3digit_code => qr/^([\w\d]{3,4})$/,
       },
};

# Check the profile to make sure everything was filled in correctly
my $query = CGI->new();
my $results = Data::FormValidator->check($query, $profile);

if ($results->has_invalid or $results->has_missing) {
  # There were some problems with the form values
  # so redisplay the form
  ...
} else {
  # The form was properly filled out
  my $valid = $results->valid();

  # now $valid contains a hashref of all the validated data
  # so do something with the values
  ...
}