code: public function isValid($value)
      {
          try {
              $this->validator->check($value);
              $this->errorMessage = '';
              return true;
          } catch (ValidationException $e) {
              $this->errorMessage = (empty($this->label) ? '' : "{$this->label}: ") . $e->getMessage();
              return false;
          }
      }
docs: {@inheritdoc}