Macromedia Flex is an alternative means of creating Flash applications. It is a presentation server that is installed on a web server. At the time of writing, Flex was only available for Suns Java 2 Enterprise Edition (J2EE) application servers.
Flex includes a library of components and uses Macromedias Maximum Experience Markup Language (MXML), an XML-based language to describe the interface for an application with ActionScript. MXML lays out the visual components and defines aspects like data sources and data bindings. You can also extend MXML with custom components .
You write the MXML in XML files using a text or XML editor. You can also use Macromedias Flex Builder. Each MXML file must end with the file extension .mxml . Learning about XML will help you to use Flex to create applications.
I havent covered Flex in this book as it could be an entire book in its own right. You can find out more about it at www.macromedia.com/software/flex/.