The GtkBin widget is a container with just one child.
It is not very useful itself, but it is useful for deriving subclasses,
since it provides common code needed for handling a single child widget.
Many GTK+ widgets are subclasses of GtkBin, including GtkWindow, GtkButton,
GtkFrame, GtkHandleBox, and GtkScrolledWindow.
The GtkBin struct contains the following fields.
(These fields should be considered read-only. They should never be set by