let [_a-zA-Z] /* Letter */
alnum [_a-zA-Z0-9] /* Alphanumeric character */
h [0-9a-fA-F] /* Hexadecimal digit */
o [0-7] /* Octal digit */
d [0-9] /* Decimal digit */
suffix [UuLl] /* Suffix in integral numeric constant */
white [\x00-\x09\x0b\s] /* White space: all control chars but \n */