code: public function supportsNormalization($data, $format = null)
      {
          return is_object($data) && ($data instanceof \DateTime) && (self::FORMAT === $format);
      }
docs: Checks whether the given class is supported for normalization by this normalizer
  
  @param mixed  $data   Data to normalize.
  @param string $format The format being (de-)serialized from or into.
  
  @return Boolean