Flex enables enterprise-class Rich Internet Applications and is
designed to address a certain class of problems around multistep
processes, client-side validation, data manipulation, and data
visualization. This package allows you to build Flex documents
programmatically.

MXML is the XML language for writing Macromedia Flex applications that
you can use to lay out user-interface components.

You can also use MXML to declaratively define non-visual aspects of an
application, such as access to server-side data sources and data
bindings between user-interface components and server-side data
sources.

The API follows closely Stephan Schmidts XUL-Package.