docs: def attributes_dict(self):
          """Returns the mapping of the model attributes and their
          values.
          """
          h = {}
          for k in self.attributes.keys():
              h[k] = getattr(self, k)
          for k in self.lists.keys():
              h[k] = getattr(self, k)
          for k in self.references.keys():
              h[k] = getattr(self, k)
          return h