It is interpreted as an "aligned" expansion producing something like 00, 01, 02... 10 instead of 0, 1, 2... 10.

https://pastila.nl/?09014b44/8155336bcfbf55d813814753465a1adf
buf_for_escaping << letter;
    }
    std::string escaped_with_globs = buf_for_escaping.str();
    static const re2::RE2 enum_or_range(R"({([\d]+\.\.[\d]+|[^{}*,]+,[^{}*]*[^{}*,])})");    
    re2::StringPiece input(escaped_with_globs);
    re2::StringPiece matched;
    std::ostringstream oss_for_replacing;       
    oss_for_replacing.exceptions(std::ios::failbit);
    size_t current_index = 0;
    while (RE2::FindAndConsume(&input, enum_or_range, &matched))
    {
        std::string buffer = matched.ToString();
        oss_for_replacing << escaped_with_globs.substr(current_index, matched.data() - escaped_with_globs.data() - current_index - 1) << '(';
        if (buffer.find(',') == std::string::npos)
        {
            size_t range_begin = 0;
            size_t range_end = 0;
            char point;
            ReadBufferFromString buf_range(buffer);
            buf_range >> range_begin >> point >> point >> range_end;
            bool leading_zeros = buffer[0] == '0';
            size_t num_len = std::to_string(range_end).size();
            if (leading_zeros)
                oss_for_replacing << std::setfill('0') << std::setw(num_len);
            oss_for_replacing << range_begin;
            for (size_t i = range_begin + 1; i <= range_end; ++i)
            {
                oss_for_replacing << '|';
                if (leading_zeros)
                    oss_for_replacing << std::setfill('0') << std::setw(num_len);