sub validate($$){
    my($self,$name) = @_;

    if(! defined($self->{params}->{$name}) ){
        return $self->setError("'$name' was not given.");
    }

    my $value = $self->{params}->{$name} || 
            $self->{params}->{retvals}->{$name};
            

    my $field = $self->getField($name);
    my $allowed = $field->{allowed};
    my $comment = $field->{comment};
    my $escape  = $field->{escape} || "yes"; 

    if($value =~ /^$allowed$/){
       return (($escape eq "no") ? $value : quotemeta($value));
    }elsif(! $allowed){
       return $self->setError("No constraints defined for '$name'");
    }else{
       return $self->setError("Forbidden characters in $name: '".
         quotemeta($value)."' ". ($comment ? "($comment)" : ""));
    }
}