0, but the old VM is still there for backward compatibility in order
to run applications using ActionScript 1 and 2. Don??™t worry if you??™re not sure what a VM is??”it sounds
complicated but it??™s very simple. Essentially, a VM is like an interpreter, and it means that you just need
to write your applications in one language, ActionScript, and the Flash Player??™s VM will translate that
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into code that the computer it??™s running on understands. You don??™t need to know if the user is running
Windows, Mac OS X, Linux, or whatever??”the VM will make sure your code runs on that system
without a hitch.
Explaining the differences between versions of ActionScript is beyond the scope of this book, but the
differences are mostly evolutionary in nature, and for someone new to it, is a good idea to learn
ActionScript in its current incarnation as 3.0.
To understand ActionScript, you must familiarize yourself with a number of concepts; it will be nearly
impossible to explain it all in one chapter. The goal here is not to convert you into a developer but to
demystify some of the key concepts, allowing you to better understand Flex and communicate more
efficiently with a developer.
What is MXML?
Flex in addition to ActionScript also includes a markup language named MXML that is based on XML.
Its purpose is to simplify the process of creating interfaces and layouts in Flex. There is no canvas onto
which you can draw something directly in Flex as you would in Flash, and it would be tedious to have
to create a graphical user interface (GUI) programmatically entirely in ActionScript.
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