GtkObject is the base
of GTK+'s object hierarchy. It is not a graphical
component; it implements interfaces for reference
counting, attaching key-value pairs to objects and
object destruction ("virtual destructors" in C++
itself makes heavy use of the GTK+ type system. The
signal/callback infrastructure of GTK+ works in terms
of GtkObject---that is,
signals are emitted from a particular GtkObject, and callbacks are
connected to a particular object and signal.
the chapter called The
GTK+ Object and Type System covers GtkObject in detail.