code: def _contribute_to_class(self, mcs_args: McsArgs):
          
          self._mcs_args = mcs_args
  
          Meta = mcs_args.clsdict.pop('Meta', None)  # type: Type[object]
          base_classes_meta = mcs_args.getattr('Meta', None)  # type: MetaOptionsFactory
  
          mcs_args.clsdict['Meta'] = self  # must come before _fill_from_meta, because
                                           # some meta options may depend upon having
                                           # access to the values of earlier meta options
          self._fill_from_meta(Meta, base_classes_meta, mcs_args)
  
          for option in self._get_meta_options():
              option_value = getattr(self, option.name, None)
              option.contribute_to_class(mcs_args, option_value)
docs: Where the magic happens. Takes one parameter, the :class:`McsArgs` of the
          class-under-construction, and processes the declared ``class Meta`` from
          it (if any). We fill ourself with the declared meta options' name/value pairs,
          give the declared meta options a chance to also contribute to the class-under-
          construction, and finally replace the class-under-construction's ``class Meta``
          with this populated factory instance (aka ``self``).