but they are really just analogs of Python object properties. The magic function
is basically a "setter" for a dictionary element.
effect, just like ``push()`` for an instance. The difference is, ``push()`` does
not allow new options (keys) to be defined; ``add()`` does. It is also possible to
assign the special null object ``Prohibited``, which will disallow instances of the
-subclass from setting those values.
+subclass from setting those values.
options = Superclass.options.add(