code: @Override
    public String[] synthesize(AnalyzedToken token, String posTag,
        boolean posTagRegExp) throws IOException {
  
      if (posTag != null && posTagRegExp) {
        String myPosTag = posTag;
        String det = "";
        if (posTag.endsWith(ADD_IND_DETERMINER)) {
          myPosTag = myPosTag.substring(0, myPosTag.indexOf(ADD_IND_DETERMINER) - "\\".length());
          det = aVsAnRule.suggestAorAn(token.getLemma());
          det = det.substring(0, det.indexOf(' ') + " ".length());
        } else if (posTag.endsWith(ADD_DETERMINER)) {
          myPosTag = myPosTag.substring(0, myPosTag.indexOf(ADD_DETERMINER) - "\\".length());
          det = "the ";
        }
  
        initPossibleTags();
        Pattern p = Pattern.compile(myPosTag);
        List<String> results = new ArrayList<>();
  
        for (String tag : possibleTags) {
          Matcher m = p.matcher(tag);
          if (m.matches()) {
            lookup(token.getLemma(), tag, results, det);
          }
        }
        return results.toArray(new String[results.size()]);
      }
  
      return synthesize(token, posTag);
    }
docs: Special English regexp based synthesizer that allows adding articles
  when the regexp-based tag ends with a special signature {@code \\+INDT} or {@code \\+DT}.
  
  @since 2.5