It's true that ActionScript 3.0 is a complete rewrite of Flash's internal scripting language, and it's also true that ActionScript 3.0 doesn't share the same runtime code base as prior versions of ActionScript. But that's all behind the scenes. The truth is, all versions of ActionScript to date share quite a bit in common.
That is not to say that the language isn't growing. Certainly, each new version of ActionScript introduces a batch of newly supported features, as is true with the evolution of most programming languages. And, since the decision was made to write ActionScript 3.0 from the ground up, the opportunity presented itself to tidy up a few messy things that lingered from previous versions—namely, tightening up and requiring best practices that had been optional, and restructuring the event and display systems.
All of this progress, however, did not steamroll over the standard upon which ActionScript is based, and most of the language fundamentals remain intact. With the intention to focus on new ActionScript 3.0 options later on, we want to cover some of the more important fundamentals up-front. We do not intend to ignore these ideas throughout the rest of the book. However, because they are ...