I’m trying to learn a little bit of Flex 4 development. I’ve done a lot of Flash/AS3 since more than a year now but I haven’t really gotten into Flex yet. From what I learned in a day, they did a lot of improvements in separating the logic from the presentation (design). Most of this is done through skins (i.e. separate mxml files defining how a control will look). Skins act just like a container; it can contain shapes and additional controls. If applied to a control, that control will inherit all the shapes and controls from that skin.