a rare window on an artistic collaboration 
(ROOT (NP (NP (DT a) (JJ rare) (NN window)) (PP (IN on) (NP (DT an) (JJ artistic) (NN collaboration)))))
(ROOT (NP (NP (DT ) (JJ ) (NN )) (PP (IN ) (NP (DT ) (JJ ) (NN )))))