code: def _extend(self, newsub):
          '''
          Append a subclass (extension) after the base class. For parser internal use.
          '''
          current = self
          while hasattr(current, '_sub'):
              current = current._sub
          _set(current, '_sub', newsub)
          try:
              object.__delattr__(self, '_extra')
          except:
              pasf _extend(self, newsub):
          '''
          Append a subclass (extension) after the base class. For parser internal use.
          '''
          current = self
          while hasattr(current, '_sub'):
              current = current._sub
          _set(current, '_sub', newsub)
          try:
              object.__delattr__(self, '_extra')
          except:
              pass
docs: Append a subclass (extension) after the base class. For parser internal use.