code: def _upgrade_frame(self):
          
  
          # turn 2.2 into 2.3/2.4 tags
          if len(type(self).__name__) == 3:
              base = type(self).__base__
              if base is Frame:
                  return
              return base(self)
          else:
              return self
docs: Returns either this instance or a new instance if this is a v2.2
          frame and an upgrade to a v2.3/4 equivalent is viable.
  
          If this is a v2.2 instance and there is no upgrade path, returns None.