c matches the non-metacharacter c.
\c matches the literal character c.
. matches any character including newline.
^ matches the beginning of a string.
$ matches the end of a string.
[abc...] character class, matches any of the characters abc....
[^abc...] negated character class, matches any character except abc....
r1|r2 alternation: matches either r1 or r2.
r1r2 concatenation: matches r1, and then r2.
r+ matches one or more r's.
r* matches zero or more r's.
r? matches zero or one r's.
(r) grouping: matches r.
r{n}
r{n,}
r{n,m} One or two numbers inside braces denote an interval expres-
sion. If there is one number in the braces, the preceding
regular expression r is repeated n times. If there are two
numbers separated by a comma, r is repeated n to m times.
If there is one number followed by a comma, then r is
repeated at least n times.
Interval expressions are only available if either --posix or
--re-interval is specified on the command line.
\y matches the empty string at either the beginning or the end
of a word.
\B matches the empty string within a word.
\< matches the empty string at the beginning of a word.
\> matches the empty string at the end of a word.
\w matches any word-constituent character (letter, digit, or underscore).
\W matches any character that is not word-constituent.
\' matches the empty string at the end of a buffer.
