Regular expressions (regexes) may be one of the most powerful but least used technologies available to authors. Most authoring tools provide a regex option in the search dialog, but when did you use it last? A regex is a special syntax that matches on a pattern of characters. Regexes can be quite complex, but a simple regex can do amazing things. What's nice is that you can learn this language slowly on an as-needed basis, and it's [mostly] not tool-specific. Learn how to use real regexes in your daily work to potentially save considerable time from tedious search and replace operations. You'll see how to use regexes in various authoring tools as well as in scripting such as Perl or ExtendScript (JavaScript), when some really heavy lifting is required.
