readme: Input a noun phrase (NP) and the model will tag its syntactic head as HEAD.
  Non-head tokens will be tagged as NA.
  
  The model is intended to tag multiple heads in compound NPs. It is not 
  intended to tag all heads in complex NPs.
  
  The training data is derived from a dataset in which NPs are identified 
  using the Berkeley neural parser which does not identify the heads of 
  syntactic constituents. The training data includes erroneous NPs in 
  which each token is tagged as ERROR.
  
  Examples you might try include:
  
  The bottle of ginger beer
  
  John, Peter, and Mary, who lives in Sri Lanka
  
  The man who won the race