Fixed #13015 -- Clarified language about model instances attached to forms.

You can override the ``clean()`` method on a model form to provide additional

validation in the same way you can on a normal form.

A model form instance bound to a model object will contain an ``instance``

A model form instance attached to a model object will contain an ``instance``

attribute that gives its methods access to that specific model instance.

.. warning::

  a default field. To opt-out from default fields, see

  :ref:`modelforms-selecting-fields`.

Providing initial values

------------------------

As with regular forms, it's possible to specify initial data for forms by

specifying an ``initial`` parameter when instantiating the form. Initial

values provided this way will override both initial values from the form field

and values from an attached model instance. For example::

    >>> article = Article.objects.get(pk1=)

    >>> article.headline

    'My headline'

    >>> form = ArticleForm(initial={'headline': 'Initial headline'), instance=article)

    >>> form['pub_date'].value()

    'Initial headline'

.. _modelforms-factory:

ModelForm factory function

<formsets-initial-data>` for forms in the formset by specifying an ``initial``

parameter when instantiating the model formset class returned by

:func:`~django.forms.models.modelformset_factory`. However, with model

formsets, the initial values only apply to extra forms, those that aren't bound

to an existing object instance.

formsets, the initial values only apply to extra forms, those that aren't

attached to an existing model instance.

.. _saving-objects-in-the-formset: