Quote Originally Posted by PAlexC View Post
Eh, MXML isn't really "markup" language. You're still just delivering instructions to a compiler, you're not validating for compliance issues, or using it to describe content, it's just an alternative method for getting those instructions TO the compiler.
The process of using MXML is somewhat different than HTML. But, MXML is still a markup language. Actionscript is used within MXML and is not a markup language. Similar to how Javascript is used within HTML and is not a markup language.

MXML, an XML-based markup language, offers a way to build and lay out graphic user interfaces. Interactivity is achieved through the use of ActionScript, the core language of Flash Player that is based on the ECMAScript standard.
http://en.wikipedia.org/wiki/Adobe_Flex