code: private String parseParse(VTDNav vn) throws NavException,
              PilotException {
          require (vn.matchElement(AgigaConstants.SENTENCE));
  
          // Move to the <parse> tag
          require (vn.toElement(VTDNav.FC, AgigaConstants.PARSE));
          String parseText = vn.toString(vn.getText());
          
          return parseText;
      }
docs: Assumes the position of vn is at a AgigaConstants.SENTENCE tag
  @return