[1.6.x] Improved docs for ModelFormSet.clean().

                # your custom formset validation

                ...

Also note that by the time you reach this step, individual model instances

have already been created for each ``Form``. Modifying a value in

``form.cleaned_data`` is not sufficient to affect the saved value. If you wish

to modify a value in ``ModelFormSet.clean()`` you must modify

``form.instance``::

    from django.forms.models import BaseModelFormSet

    class MyModelFormSet(BaseModelFormSet):

        def clean(self):

            super(MyModelFormSet, self).clean()

            for form in self.forms:

                name = form.cleaned_data['name'].upper()

                form.cleaned_data['name'] = name

                # update the instance value.

                form.instance.name = name

Using a custom queryset

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