Use this method to add container controls to a list of controls that the WindowSplitter will internally manage. Once you have told the WindowSplitter about controls that should be affected by the splitter movement then the WindowSplitter will take care of resizing and moving them when the WindowSplitter moves.
Using this method can in most cases eliminate the need to do size calculations in the SplitterMoved event.
The parameter takes a Window. ContainerControls inherit from a window. The method takes a window to make sure the WindowSplitter does not have dependency on container controls when they are not in use. Do not pass anything but container control instances to the container parameter.