code: @Override
      public int wordFrequency(@NonNull String word) {
          // TODO: proper wordFrequency impl should return long, instead of int
          T element = extendedVocabulary.get(word);
          if (element != null)
              return (int) element.getElementFrequency();
          return 0;
      }
docs: Returns the SequenceElement's frequency over training corpus
  
  @param word the word to retrieve the occurrence frequency for
  @return