docs: def process_models(attrs, base_model_class):
          """
          Attach default fields and meta options to models
          """
          attrs.update(base_model_class._DEFAULT_BASE_FIELDS)
          attrs['_instance_registry'] = set()
          attrs['_is_unpermitted_fields_set'] = False
          attrs['save_meta_data'] = None
          attrs['_pre_save_hook_called'] = False
          attrs['_post_save_hook_called'] = False
          DEFAULT_META = {'bucket_type': settings.DEFAULT_BUCKET_TYPE,
                          'field_permissions': {},
                          'app': 'main',
                          'list_fields': [],
                          'list_filters': [],
                          'search_fields': [],
                          'fake_model': False,
                          }
          if 'Meta' not in attrs:
              attrs['Meta'] = type('Meta', (object,), DEFAULT_META)
          else:
              for k, v in DEFAULT_META.items():
                  if k not in attrs['Meta'].__dict__:
                      setattr(attrs['Meta'], k, v)