\|

This specifies an alternative.

For example, foo\|bar matches either foo or bar but no other string.

Full backtracking capability allows you to handle multiple uses of \|.

\( ... \)

This grouping construct serves three purposes:

1. To enclose a set of \| alternatives for other operations. Therefore, \(foo\|bar\)x matches either foox or barx.
2. To enclose a complicated expression for the postfix * to operate on. Therefore, ba\(na\)* matches ‘bananana’ with any (zero or more) number of na strings
3. To mark a matched substring for future reference. See \n below.

\n

After the end of a \( ... \) construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the expression, you can use \ followed by n to mean “match the same text matched the nth time by the
\( ...\) construct.”

\‘

This matches the empty string, provided it is at the beginning of the buffer.

\’

This matches the empty string, provided it is at the end of the buffer.

\B

This matches the empty string, provided it is not at the beginning or end of a word.

\<

This matches the empty string, provided it is at the beginning of a word.

\>

This matches the empty string, provided it is at the end of a word.

\w

This matches any word-constituent character determined by the editor syntax table.

\W

This matches any character that is not a word-constituent.

\scode

This matches any character whose syntax is code (a character that represents syntax code)

\Scode

This matches any character whose syntax is not code.