code: def set_marktype_cb(self, w, index):
          
          self.marktype = self._mark_options[index]
  
          # Mark size is not used for point
          if self.marktype != 'point':
              self.w.mark_size.set_enabled(True)
          else:
              self.w.mark_size.set_enabled(False)
docs: Set type of marking.