I didn't know that you could negate subsets the same way as you can for light categories, but it totally works. You need to assign the group via rib attributes, to the geometry.
e.g.
Attribute "grouping" "string membership" ["noRflOccl"]
Cool.
Maybe the most boring blog ever... but it's *my* most boring blog ever.
Attribute "grouping" "string membership" ["noRflOccl"]
string $ws = `workspace -q -rd`;