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So there you have some useful practical applications for expressions in visual effects work. Maybe you still want morea more thorough understanding of the basics, if you're a beginner, or more advice on developing your own expressions, if you're an expert.

Unfortunately, expressions is one area where the official After Effects documentation falls short. Plenty of information is there, but it's organized in such a way that you already need to know quite a bit about expressions before you can understand it.

Happily, a couple of Web sites take up the slack. They are excellent, and at this writing they are still very much up to date:

• www.motionscript.com: This site is the work of Dan Ebberts, a prolific contributor of expressions information in various online forums. One section of the site, Mastering Expressions, thoroughly explains how JavaScript works as is implemented in After Effects. The Expressions Lab contains more hands-on examples for you to dissect.

• www.aenhancers.com: This is a forum-based site filled with sample expressions and scripts created for specific purposes, as well as areas for discussion about how they work.

Both sites also include information on scripting, an automation feature set in After Effects that, alas, makes creating expressions look like child's play (and I should know, having documented this feature for version 6.0 and 6.5). Someday, perhaps the development team will be able to add recordable Actions as are found in Photoshop, and scripting will be unlocked for the masses. For now, how-ever, the scripting controls are double blackdiamond expert features, for the most part requiring full-fledged programming capabilities to accomplish anything truly significant.

And hold onto your hats, because the complicated stuff isn't over with yet. The next chapter deals with issues specific to film, most of which have never been handled in any book on After Effects.