Regular expressions are case sensitive; lower case /s/ is distinct from upper case /S/ (/s/ matches a lower case s but not an upper case S). This means that the pattern /woodchucks/ will not match the string Woodchucks. We can solve this problem with the use of the square braces [ and ] . The string of characters inside the braces specifies a disjunction of characters to match. For example, Fig. 2.2 shows that the pattern /[wW]/ matches patterns containing either w or W.