code: def process_event(self, event):
          
          # Convert into absolute coordinates if needed.
          new_event = event
          if self._absolute:
              new_event.y -= self._canvas.start_line
  
          # Process event if needed.
          if self.is_mouse_over(new_event) and event.buttons != 0:
              self._set_pos((new_event.y - self._y) / (self._height - 1))
              return True
          return False
docs: Handle input on the scroll bar.
  
          :param event: the event to be processed.
  
          :returns: True if the scroll bar handled the event.