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?

{
    return static_cast<unsigned char>(c) < 0x80;
}
inline bool isLowerAlphaASCII(char c)
{
    return (c >= 'a' && c <= 'z');
}
inline bool isUpperAlphaASCII(char c)
{
    return (c >= 'A' && c <= 'Z');
}
inline bool isAlphaASCII(char c)
{
    return isLowerAlphaASCII(c) || isUpperAlphaASCII(c);
}
inline bool isNumericASCII(char c)
{
    
    
    
    return (c >= '0' && c <= '9');
}
inline bool isHexDigit(char c)
{
    return isNumericASCII(c)
        || (c >= 'a' && c <= 'f')
        || (c >= 'A' && c <= 'F');
}
inline bool isAlphaNumericASCII(char c)