code: private void expandTo(int wordIndex)
    {
      int wordsRequired = wordIndex + 1;
      if (firstEmptyWord < wordsRequired) {
        ensureCapacity(wordsRequired);
        firstEmptyWord = wordsRequired;
      }
    }
docs: Ensures that the {@link FastSet} can accommodate a given word index
  
  @param wordIndex the index to be accommodated.