Please provide a Alert/Popup/Dialog main class...

And for RIA (applet mode at least) , we do need an "internal" popup/alert control such Flex or JS does.
Stages "window oriented" are useful for desktop apps, but in a Browser environment (multi tabs...) a flat Dialog control would make more sense. This control should not be draggable out of the parent's bounds, like JInternalFrame did.
Moreover, when prompting this control, the background of the parent stage could be blurred for example...

Thanks.