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.