's most substantial feature for some time 
(ROOT (NP (NP (NP (POS 's)) (ADJP (RBS most) (JJ substantial)) (NN feature)) (PP (IN for) (NP (DT some) (NN time)))))
(ROOT (NP (NP (NP (POS )) (ADJP (RBS ) (JJ )) (NN )) (PP (IN ) (NP (DT ) (NN )))))