public function format(array $record)
    {
        if (isset($record["datetime"]) && ($record["datetime"] instanceof \DateTime)) {
            $record["timestamp"] = $record["datetime"]->format("Y-m-d\TH:i:s.uO");
            // TODO 2.0 unset the 'datetime' parameter, retained for BC
        }

        return parent::format($record);
    }