### Note: untested code

     # Require food_name and food_group
     # color is optional, but validate it if they pass it in
     my $fields_profile = {
        required => [ "food_name", "food_group" ],
        optional => [ "color" ],
        constraints => {
            food_name  => \&validate_word,
            food_group => \&validate_word,
            color      => \&validate_word,
        },
        # Untaint a field if and only if it passes a constraint
        untaint_all_constraints => 1,
    }; 

    # You can simply pass in your CGI object along with your fields profile
    my $results = Data::FormValidator->check($q, $fields_profile);

    # If data is missing or invalid, just print it out
    if ($results->has_missing or $results->has_invalid) {
        print "Missing: ", join ", ", $results->missing;
        print "Invalid: ", join ", ", $results->invalid;
    }
    else {
        print "Excellent food submission!";
    }

    # Called by Data::FormValidator when it needs to validate our parameters
    sub validate_word {
        my $val = shift;
        return $val =~ /^[\w ]+$/
    }