docs: def _set_motion_handle(self, event):
          """Sets motion handle to currently grabbed handle
          """
          item = self.grabbed_item
          handle = self.grabbed_handle
          pos = event.x, event.y
          self.motion_handle = HandleInMotion(item, handle, self.view)
          self.motion_handle.GLUE_DISTANCE = self._parent_state_v.border_width
          self.motion_handle.start_move(pos)