CL_KHR_gl_sharing documentation

In section B1 (page 279, 5/16/09 revision) of the OpenCL specification there is a CL_KHR_gl_sharing extension mentioned.

Is documentation available for this extension? I didn’t see anything about CL_KHR_gl_sharing at the url given in the specification (http://www.khronos.org/registry/cl/)