docs: def available(self, src, dst, model):
          """
          Iterate over all registered plugins or plugin points and prepare to add
          them to database.
          """
          for name, point in six.iteritems(src):
              inst = dst.pop(name, None)
              if inst is None:
                  self.print_(1, "Registering %s for %s" % (model.__name__,
                                                            name))
                  inst = model(pythonpath=name)
              if inst.status == REMOVED:
                  self.print_(1, "Updating %s for %s" % (model.__name__, name))
                  # re-enable a previously removed plugin point and its plugins
                  inst.status = ENABLED
              yield point, inst