Pros:
- it is convenient to type and read numbers this way;
- Ada, Perl, C++, Go and Rust already support that;
- can support thousands as well as lakhs and crores;

Cons:
- standard SQL does not have this support;
- PostgreSQL treat `SELECT 1_000_000` as number one with `_000_000` alias: http://sqlfiddle.com/#!17/0a28f/400
- C++ has `1'000'000` instead of `1_000_000`;

What do you think?

{
    uint8_t uc = c;
    return uc >= 32 && uc <= 126;   
}
inline bool isPunctuationASCII(char c)
{
    uint8_t uc = c;
    return (uc >= 33 && uc <= 47)
        || (uc >= 58 && uc <= 64)
        || (uc >= 91 && uc <= 96)
        || (uc >= 123 && uc <= 125);
}
inline bool isValidIdentifier(std::string_view str)
{
    return !str.empty()
        && isValidIdentifierBegin(str[0])
        && std::all_of(str.begin() + 1, str.end(), isWordCharASCII)
        
        && !(str.size() == strlen("null") && 0 == strncasecmp(str.data(), "null", strlen("null")));
}
inline char toLowerIfAlphaASCII(char c)
{
    return c | 0x20;
}
inline char toUpperIfAlphaASCII(char c)
{
    return c & (~0x20);
}
inline char alternateCaseIfAlphaASCII(char c)