docs: def post(method, hmc, uri, uri_parms, body, logon_required,
               wait_for_completion):
          """Operation: Modify Storage Group Properties."""
          assert wait_for_completion is True  # async not supported yet
          # The URI is a POST operation, so we need to construct the SG URI
          storage_group_oid = uri_parms[0]
          storage_group_uri = '/api/storage-groups/' + storage_group_oid
          try:
              storage_group = hmc.lookup_by_uri(storage_group_uri)
          except KeyError:
              raise InvalidResourceError(method, uri)
  
          # Reflect the result of modifying the storage group
  
          body2 = body.copy()
          sv_requests = body2.pop('storage-volumes', None)
          storage_group.update(body2)
  
          sv_uris = []
          if sv_requests:
              for sv_req in sv_requests:
                  check_required_fields(method, uri, sv_req, ['operation'])
                  operation = sv_req['operation']
                  if operation == 'create':
                      sv_props = sv_req.copy()
                      del sv_props['operation']
                      if 'element-uri' in sv_props:
                          raise BadRequestError(
                              method, uri, 7,
                              "The 'element-uri' field in storage-volumes is "
                              "invalid for the create operation")
                      sv_uri = storage_group.storage_volumes.add(sv_props)
                      sv_uris.append(sv_uri)
                  elif operation == 'modify':
                      check_required_fields(method, uri, sv_req, ['element-uri'])
                      sv_uri = sv_req['element-uri']
                      storage_volume = hmc.lookup_by_uri(sv_uri)
                      storage_volume.update_properties(sv_props)
                  elif operation == 'delete':
                      check_required_fields(method, uri, sv_req, ['element-uri'])
                      sv_uri = sv_req['element-uri']
                      storage_volume = hmc.lookup_by_uri(sv_uri)
                      storage_volume.delete()
                  else:
                      raise BadRequestError(
                          method, uri, 5,
                          "Invalid value for storage-volumes 'operation' "
                          "field: %s" % operation)
  
          return {
              'element-uris': sv_uris,  # SVs created, maintaining the order
          }