code: @Nonnull
      protected Word<I> subWordInternal(int fromIndex, int toIndex) {
          int len = toIndex - fromIndex;
          Object[] array = new Object[len];
          writeToArray(fromIndex, array, 0, len);
          return new SharedWord<>(array);
      }
docs: Internal subword operation implementation. In contrast to {@link #subWord(int, int)}, no range checks need to be
  performed. As this method is flagged as {@code protected}, implementations may rely on the specified indices
  being valid.
  
  @param fromIndex
  the first index, inclusive (guaranteed to be valid)
  @param toIndex
  the last index, exclusive (guaranteed to be valid)
  
  @return the word representing the specified subrange