Someone on the Mate forums advocated a way to treat a modal popup as a state of a view, where the presentation model has a "modalShown" property, and the view observes it using bindSetter.
This has the nice effect of avoiding the need to pass in Application.application to createPopUp, but it's obviously quite a bit more work to create the bubbling events and injections. And in the end you typically want to center the popup over the whole application, rather than some intermediate container. So I find myself wondering if there is a cleaner way than Application.application to refer to the root context. Follow the DisplayObject.parent chain until it's null?