Regular expressions are composed of the following operators:

.		Match any single character
XY		Match X immediately followed by Y
X*		Match zero-or-more of X
X+		Match one-or-more of X
X?		Match zero-or-one of X
X%|Y		Match either X or Y
[charset]	Match any single character in `charset'
[^charset]	Match any single character not in `charset'
%(X%)		Match X, but also remember the match as a subexpression
%digit		Match the numbered previous subexpression
^X		Match X anchored at the beginning of a line
X$		Match X anchored at the end of a line
%b		Match the empty string at the beginning or end of a word
%B		Match the empty string only within the middle of a word
%<		Match the beginning of a word
%>		Match the end of a word
%w		Match any word-constituent character
%W		Match any character that is not word-constituent

Any other character in a regular expression is matched literally with itself.
To match any of the special operator characters .*+?%[^$ literally, precede
the character with `%'.

A `charset' is formed by listing all desired characters with brackets. To
include a literal `^' in a charset, do not list it in the first position. To
include a literal `]', list it immediately after the opening `[' or `[^'. All
characters are non-special (and should not be escaped) within a charset,
except `-', which denotes a character range. To include a literal `-', list it
either first or last.