code: def _appendGuideline(self, position, angle, name=None, color=None, identifier=None, **kwargs):
          
          self.raiseNotImplementedError()
docs: position will be a valid position (x, y).
          angle will be a valid angle.
          name will be a valid guideline name or None.
          color will be a valid color or None .
          identifier will be a valid, nonconflicting identifier.
  
          This must return the new guideline.
  
          Subclasses may override this method.