+ """
+ :class:`Attribute`\ s exist primarily to let arbitrary data be attached to arbitrary model instances without altering the database schema and without guaranteeing that the data will be available on every instance of that model.
+
+ Generally, :class:`Attribute`\ s will not be accessed as models; instead, they will be accessed through the :attr:`Entity.attributes` property, which allows direct dictionary getting and setting of the value of an :class:`Attribute` with its key.
+
+ """