code: def cto(self):
          
          cto = -1
          try:
              if self.lnk.type == Lnk.CHARSPAN:
                  cto = self.lnk.data[1]
          except AttributeError:
              pass  # use default cto of -1
          return cto
docs: The final character position in the surface string.
  
          Defaults to -1 if there is no valid cto value.