Charniak (2000) shows the value his parser gains from parentannotation of nodes, suggesting that this information is at least partly complementary to information derivable from lexicalization, and <cite>Collins (1999)</cite> uses a range of linguistically motivated and carefully hand-engineered subcategorizations to break down wrong context-freedom assumptions of the naive Penn treebank covering PCFG, such as differentiating "base NPs" from noun phrases with phrasal modifiers, and distinguishing sentences with empty subjects from those where there is an overt subject NP.