code: def _handle_event(self, conv_event):
          
          if not self._is_scrolling:
              self.set_focus(conv_event.id_)
          else:
              self._modified()
docs: Handle updating and scrolling when a new event is added.
  
          Automatically scroll down to show the new text if the bottom is
          showing. This allows the user to scroll up to read previous messages
          while new messages are arriving.