HeaderController widget
http://resources.arcgis.com/en/help/flex-viewer/concepts/
This widget defines the upper section of the Viewer application UI. It displays the application title, subtitle, and logo. It also contains the widget tray and an About button. The widget tray contains shortcuts to widgets that are stored in widget container tags. The About button provides information on the Viewer application when clicked. Its contents is typicaly very similar to the contents of the application splash screen. The HeaderController widget is the default Viewer UI display.
Screen capture of the About display screen.
Since the HeaderController is intended to be part of the Viewer UI, its <widget> tag is always referenced as an independent widget in the Viewer application configuration file, and not within a widget container.
Test drive the HeaderController widget or see its tag reference.