[abc] Any one of a, b, or c. (Enumeration.) [a-c] Any one of a, b, or c. (Range.) [^abc] Any character except a, b, or c. (Negation.) [[a-f][0-9]] Any character in either range. (Union.) [[a-z]&&[jkl]] Any character in both ranges. (Intersection.) Most of the time, the built-in character classes are more useful: