docs: def _subj_dict_from_pyxb(self, access_pyxb):
          """Return a dict representation of ``access_pyxb``, which is an AccessPolicy
          PyXB object.
  
          This also remove any duplicate subjects and permissions in the PyXB object.
  
          """
          subj_dict = {}
          for allow_pyxb in access_pyxb.allow:
              perm_set = set()
              for perm_pyxb in allow_pyxb.permission:
                  perm_set.add(perm_pyxb)
              for subj_pyxb in allow_pyxb.subject:
                  subj_dict.setdefault(subj_pyxb.value(), set()).update(perm_set)
          return subj_dict