The common language of Flex 2 applications is ActionScript 3.0. You can't use any older versions of ActionScript, nor is it possible to create a functional application without at least some ActionScript 3.0. Additionally, we will soon see that MXML and AS3 are fundamentally related.
ActionScript's third incarnation is a mature language, as well as being substantially different from ActionScript 2. This chapter will rapidly cover all the fundamental aspects of ActionScript 3.0, but is by no means a full course. For more instruction, there is a list of useful further reading at the bottom of this Short Cut.
Readers who understand ActionScript 2 should be comfortable transitioning to ActionScript 3.0. The following chapter specifically addresses new concepts since AS2, so read on!
Readers versed in C# or Java should find themselves at home with AS3 in short time, but should note a few differences in syntax and features. In any case, this chapter assumes, at minimum, basic knowledge of object-oriented programming.