docs: def remove_perm(self, subj_str, perm_str):
          """Remove permission from a subject.
  
          Args:
            subj_str : str
              Subject for which to remove permission(s)
  
            perm_str : str
              Permission to remove. Implicitly removes all higher permissions. E.g., ``write``
              will also remove ``changePermission`` if previously granted.
  
          """
          self._assert_valid_permission(perm_str)
          for perm_str in self._equal_or_higher_perm(perm_str):
              self._perm_dict.setdefault(perm_str, set()).discard(subj_str)