docs: public String getContentBetween( Position starting,
                                       Position end ) {
          CheckArg.isNotNull(starting, "starting");
  
          int startIndex = starting.getIndexInContent();
          int endIndex = inputString.length();
          if (end != null) {
              endIndex = end.getIndexInContent();
          }
  
          if (startIndex >= endIndex) {
              throw new IllegalArgumentException(CommonI18n.endPositionMustBeGreaterThanStartingPosition.text(startIndex, endIndex));
          }
  
          return inputString.substring(startIndex, endIndex);
      }