code: public static List<String> process(List<String> tokens, Policy policy) {
  	if (policy == Policy.CONCATENATE) {
  	    return concatenate(tokens);
  	}
  	else {
  	    return expand(tokens);
  	}
      }
docs: Process a list of tokens to apply the stated policy to the tokens.
  @param tokens a list of tokens to process
  @param policy either to expand or concatenate tokens in the list
  @return a processed list of tokens