code: public function serialize($data, $format, array $context = array())
      {
          if ('jsonld' !== $format) {
              throw new UnexpectedValueException('Serialization for the format ' . $format . ' is not supported');
          }
  
          if (false === is_object($data)) {
              throw new \Exception('Only objects can be serialized');
          }
  
          return JsonLD::toString($this->doSerialize($data, true), true);
      }
docs: Serializes data in the appropriate format
  
  @param mixed  $data    any data
  @param string $format  format name
  @param array  $context options normalizers/encoders have access to
  
  @return string