This extension can be used to enable CSAA in an application window without rendering to a framebuffer object (without using NV_framebuffer_multisample_coverage). It should behave like WGL_ARB_mulsample.
I can’t find the specification here and on Nvidia website. There is a sample named “Multisample Coverage” here:
… but the download link is broken (file multisample.zip is not there). And the sample is not part of the SDK 10 package that can be downloaded.
If it is not supported anymore, then it should be removed from the extension list (still listed in latest 177.35).