13.2.3 Some frequently used character classes

Some standard character classes can be conveniently represented as metasequences instead of as explicit bracketed expressions. \d matches a digit ([0-9]); \s matches a whitespace character; and \w matches a character that could be part of a “word”.(6)

The upper-case versions of these metasequences stand for the inversions of the corresponding character classes. Thus \D matches a non-digit, \S a non-whitespace character, and \W a non-“word” character.

Remember to include a double backslash when putting these metasequences in a Scheme string:

(pregexp-match "\\d\\d" "0 dear, 1 have 2 read catch 22 before 9") ⇒ ("22")

These character classes can be used inside a bracketed expression. Eg, "[a-z\\d]" matches a lower-case letter or a digit.

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