HTML and CSS Reference
Any nonwhitespace character
Any word character (letters, digits, and the underscore)
Any nonword character
Any digit (0-9)
The characters a , b , and c in that order
\1, \2, ...
First matched pattern, second matched pattern, ...
For more information on regular expressions, including lots more examples, some advanced features I
haven't gone into here, and details about dialect variations, I recommend Mastering Regular Expressions ,
3rd Edition, by Jeffrey E. F. Friedl (O'Reilly, 2006).