This is a special class object that holds all the information returned by a particular GSG to indicate the geom’s internal context identifier.
Geoms typically have an immediate-mode and a retained-mode operation. When using geoms in retained-mode (in response to
Geom::prepare()), the GSG will create some internal handle for the geom and store it here. The geom stores all of these handles internally.
In the case of OpenGL, for example, a GeomContext corresponds to a display list identifier.