code: private function formatTimestamp($timestamp, $format)
      {
          if (strncmp($format, 'php:', 4) === 0) {
              $format = substr($format, 4);
          } else {
              $format = FormatConverter::convertDateIcuToPhp($format, 'date');
          }
  
          $date = new DateTime();
          $date->setTimestamp($timestamp);
          $date->setTimezone(new \DateTimeZone($this->timestampAttributeTimeZone));
          return $date->format($format);
      }
docs: Formats a timestamp using the specified format.
  @param int $timestamp
  @param string $format
  @return string