normalize_email should be called on the instance, not the class. This
has the same effect normally but is more helpful to subclassers. When
methods are called directly on the class, subclasses can't override
them.
The origin statement "which could be ... or whatever" **misguides** many newbies like me.
In fact, the ``login`` function in ``contrib.auth`` stores ``user.pk`` in session, then ``get_user`` function in ``contrib.auth`` gets ``user.pk`` in session and then passes it to your custom ``get_user`` as ``user_id``.
Which means, ``user_id`` prarameter in your custom ``get_user`` has to be the primary key of ``User`` object, too.
This also updates all dependent functionality, including modelform_factory
and modelformset_factory, and the generic views `ModelFormMixin`,
`CreateView` and `UpdateView` which gain a new `fields` attribute.
The auth doc was a single page which had grown unwieldy.
This refactor split and grouped the content into sub-topics.
Additional corrections and cleanups were made along the way.
