Things change. All things change. And software often changes faster than the ability of printed books to keep up with it. It will therefore be useful for the reader to know what versions of software I was looking at when I wrote this edition of the book. The first draft was written using Mac OS X 10.4.2 ("Tiger") and AppleScript 1.10; the book was finished under Mac OS X 10.4.3 and AppleScript 1.10.3. Apple's Script Editor was at version 2.1 (later 2.1.1). Late Night Software's Script Debugger 4 was still in beta. (This means that screen shots of Script Debugger 4 don't quite match the finished product.) There may be further changes in Tiger, and possibly even in AppleScript, by the time the book goes to print, but if so, it seems unlikely that these will affect the book's content; still, the reader should be alert to the possibility of slight discrepancies between what I describe and the now-current state of things.
The book is written entirely from the perspective of Mac OS X. This is a deliberate design decision. There is an important sense in which Mac OS 9 really is frozen, if not downright moribund; very few new applications of any importance are being written for it, it is not likely to evolve further to any significant extent, and Apple has begun to produce computers that won't even boot in it (and will soon move to a system where Classic will not run at all). If you are not using Mac OS X, this book might still be useful to you, but please keep in mind that it isn't geared primarily to your situation.
This second edition is written entirely from the perspective of Tiger. Not much attention has been paid to differences between the Tiger version of AppleScript and earlier versions. Where a feature is new in Tiger, I say so. But if you are still using Panther (or Jaguar), you should stick with the first edition of this book.