public static function mergeReferences(Translation $from, Translation $to, $options = self::DEFAULTS)
    {
        if ($options & self::REFERENCES_THEIRS) {
            $to->deleteReferences();
        }

        if (!($options & self::REFERENCES_OURS)) {
            foreach ($from->getReferences() as $reference) {
                $to->addReference($reference[0], $reference[1]);
            }
        }
    }