Flex’s Button component was the first to be implemented in the new Spark architecture, and is a good example of component and skin separation. The skin definition first references the component to which this skin can be applied. This optional metadata element allows the skin to hold a reference to the component class, if necessary. Next, the various component states are referenced, followed by visual definitions of the component:

The architecture of the new Spark components in Flex 4 supercedes the Halo components of Flex 3. Upon learning how to leverage the architecture of Spark components, you will find the improvements to be quite substantial.

The Flex 4 (codename: Gumbo) beta release is a major change from Flex 3. The Flex 4 beta introduces a new component and skinning architecture. As a Flex 3 developer, however, you will likely not encounter too many challenges when compiling Flex 3 applications with the Flex 4 beta, since a goal of the new release is to maintain backwards compatibility with Flex 3.