public function validateInteger(array $values)
    {
        if (count($values) != 1) {
            $vars = array('@field' => $this->translation->text('Condition'));
            return $this->translation->text('@field has invalid value', $vars);
        }

        $value = reset($values);

        if (strlen($value) > 10) {
            $vars = array('@max' => 10, '@field' => $this->translation->text('Value'));
            return $this->translation->text('@field must not be longer than @max characters', $vars);
        }

        if (ctype_digit($value)) {
            return true;
        }

        $vars = array('@field' => $this->translation->text('Condition'));
        return $this->translation->text('@field has invalid value', $vars);
    }