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34.3.1.2 Character Classes

Here is a table of the classes you can use in a character alternative, and what they mean:

[:ascii:]
This matches any ASCII character (codes 0–127).
[:alnum:]
This matches any letter or digit. (At present, for multibyte characters, it matches anything that has word syntax.)
[:alpha:]
This matches any letter. (At present, for multibyte characters, it matches anything that has word syntax.)
[:blank:]
This matches space and tab only.
[:cntrl:]
This matches any ASCII control character.
[:digit:]
This matches ‘0’ through ‘9’. Thus, ‘[-+[:digit:]]’ matches any digit, as well as ‘+’ and ‘-’.
[:graph:]
This matches graphic characters—everything except ASCII control characters, space, and the delete character.
[:lower:]
This matches any lower-case letter, as determined by the current case table (see Case Tables). If case-fold-search is non-nil, this also matches any upper-case letter.
[:multibyte:]
This matches any multibyte character (see Text Representations).
[:nonascii:]
This matches any non-ASCII character.
[:print:]
This matches printing characters—everything except ASCII control characters and the delete character.
[:punct:]
This matches any punctuation character. (At present, for multibyte characters, it matches anything that has non-word syntax.)
[:space:]
This matches any character that has whitespace syntax (see Syntax Class Table).
[:unibyte:]
This matches any unibyte character (see Text Representations).
[:upper:]
This matches any upper-case letter, as determined by the current case table (see Case Tables). If case-fold-search is non-nil, this also matches any lower-case letter.
[:word:]
This matches any character that has word syntax (see Syntax Class Table).
[:xdigit:]
This matches the hexadecimal digits: ‘0’ through ‘9’, ‘a’ through ‘f’ and ‘A’ through ‘F’.