, b , or B , while [A-Z-[IO]] matches any upper- or lower-case ASCII alphabetic character except i , I , o , or O .
When a character range is used, the expression matches the characters in the range together with their case variants. For example, [P-U] has the same effect as [PQRSTU] : it matches all characters that are case variants of any of these six letters. As it happens, this includes the six letters pqrstu together with f (x017F, long S , an archaic form of the letter s ).