public function validateLength($min_length, $max_length)
    {
        $this->validator_attributes[] = 'data-parsley-length="[' . (int)$min_length . ', ' . (int)$max_length . ']"';

        $this->validator_checks['min_length'] = (int)$min_length;
        $this->validator_checks['max_length'] = (int)$max_length;

        return $this;
    }