GL_CLIP_VOLUME_CLIPPING_HINT_EXT

Does CLIP_VOLUME_CLIPPING_HINT_EXT implemented on Nvidia drivers?? if so how to use it?
glHint(GL_CLIP_VOLUME_CLIPPING_HINT_EXT,GL_DONT_CARE); //to disable??

what is it to enable clipping??

in fact does it really works???