[Xquartz-dev] Xephyr +GLX?

I'm trying to start Xephyr with "+extension GLX" and I'm getting a statement indicating that GLX is unrecognized and is not among the extensions that can be enabled at run-time. Apple's X11.app does allow the "+extension GLX" argument but crashes on complaints that its missing some ".so" file. The GLX extension is available in XQuartz, but is unavailable through Xephyr? Will this support eventually become possible? I can't seem to find any recent information regarding Xephyr+GLX on Mac OS X. Thanks.