code: protected void addExamplePair(IncorrectExample incorrectSentence, CorrectExample correctSentence) {
      String correctExample = correctSentence.getExample();
      int markerStart= correctExample.indexOf("<marker>");
      int markerEnd = correctExample.indexOf("</marker>");
      if (markerStart != -1 && markerEnd != -1) {
        List<String> correction = Collections.singletonList(correctExample.substring(markerStart + "<marker>".length(), markerEnd));
        incorrectExamples.add(new IncorrectExample(incorrectSentence.getExample(), correction));
      } else {
        incorrectExamples.add(incorrectSentence);
      }
      correctExamples.add(correctSentence);
    }
docs: Convenience method to add a pair of sentences: an incorrect sentence and the same sentence
  with the error corrected.
  @since 2.5