This dialog will show the whole project starting with top most widgets, down the line. Right clicking on any in the list will bring the widget's popup menu to top. The display is in a "colapsable tree" format, you will see them in a parent/child heirarchy list. The list will also contain a small square beside elements that have children, double clicking on this will toggle the display of said element's children.
The viewer will also aid in window management as you can close a window that you're not currently operating on and gain access to it's source or attributes from this dialog, while hidden. As said above this means you can right click to access the widget's settings, double clicking on the widget name itself will bring this widget back to display.