code: @Nullable
    protected List<Match> addLegacyMatches(List <Match> existingSugMatches, String messageStr,
        boolean inMessage) {
      List<Match> sugMatch = new ArrayList<>();
      int pos = 0;
      int ind = 0;
      int matchCounter = 0;
      while (pos != -1) {
        pos = messageStr.indexOf('\\', ind);
        if (pos != -1 && messageStr.length() > pos && Character.isDigit(messageStr.charAt(pos + 1))) {
          if (pos == 0 || messageStr.charAt(pos - 1) != '\u0001') {
            Match mWorker = new Match(null, null, false, null,
                null, Match.CaseConversion.NONE, false, false, Match.IncludeRange.NONE);
            mWorker.setInMessageOnly(true);
            sugMatch.add(mWorker);
          } else if (messageStr.charAt(pos - 1) == '\u0001') { // real suggestion marker
            sugMatch.add(existingSugMatches.get(matchCounter));
            if (inMessage) {
              message.deleteCharAt(pos - 1 - matchCounter);
            } else {
              suggestionsOutMsg.deleteCharAt(pos - 1 - matchCounter);
            }
            matchCounter++;
          }
        }
        ind = pos + 1;
      }
  
      if (sugMatch.isEmpty()) {
        return existingSugMatches;
      }
      return sugMatch;
    }
docs: Adds Match objects for all references to tokens
  (including '\1' and the like).