code: @Override
      public StateIdsBuilder append(final String stateToken, final int start, final int end) {
          return doAppend(Collections.singletonList(new StateId(stateToken, start, end)));
      }
docs: Appends the specified state token and a zero-based document index range to this instance, returning {@code this}.
  
  @param stateToken The state token to append
  @param start The start index of the range
  @param end The end index of the range
  @return {@code this}