Add a comment on a caveat for future reference.

        // codesSize == 0 means we are trying to find bigram predictions.

        if (codesSize < 1 || checkFirstCharacter(bigramBuffer)) {

            const int bigramFreq = UnigramDictionary::MASK_ATTRIBUTE_FREQUENCY & bigramFlags;

            // Due to space constraints, the frequency for bigrams is approximate - the lower the

            // unigram frequency, the worse the precision. The theoritical maximum error in

            // resulting frequency is 8 - although in the practice it's never bigger than 3 or 4

            // in very bad cases. This means that sometimes, we'll see some bigrams interverted

            // here, but it can't get too bad.

            const int frequency =

                    BinaryFormat::computeFrequencyForBigram(unigramFreq, bigramFreq);

            if (addWordBigram(bigramBuffer, length, frequency)) {