code: def viewbox_key_event(self, event):
          
          PerspectiveCamera.viewbox_key_event(self, event)
  
          if event.handled or not self.interactive:
              return
  
          # Ensure the timer runs
          if not self._timer.running:
              self._timer.start()
  
          if event.key in self._keymap:
              val_dims = self._keymap[event.key]
              val = val_dims[0]
              # Brake or accelarate?
              if val == 0:
                  vec = self._brake
                  val = 1
              else:
                  vec = self._acc
              # Set
              if event.type == 'key_release':
                  val = 0
              for dim in val_dims[1:]:
                  factor = 1.0
                  vec[dim-1] = val * factor
docs: ViewBox key event handler
  
          Parameters
          ----------
          event : instance of Event
              The event.