code: public final void addNeutralElement(AnalyzedTokenReadings analyzedTokenReadings) {
      tokSequence.add(analyzedTokenReadings);
      List<Map<String, Set<String>>> tokEquivs = new ArrayList<>(analyzedTokenReadings.getReadingsLength());
      Map<String, Set<String>> map = new ConcurrentHashMap<>();
      map.put(UNIFY_IGNORE, new HashSet<>());
      for (int i = 0; i < analyzedTokenReadings.getReadingsLength(); i++) {
        tokEquivs.add(map);
      }
      tokSequenceEquivalences.add(tokEquivs);
      readingsCounter++;
    }
docs: Used to add neutral elements ({@link AnalyzedTokenReadings} to the
  unified sequence. Useful if the sequence contains punctuation or connectives, for example.
  @param analyzedTokenReadings A neutral element to be added.
  @since 2.5