[1.9.x] Fixed #26256 -- Added note about primary key serialization

    data = serializers.serialize('xml', SomeModel.objects.all(), fields=('name','size'))

In this example, only the ``name`` and ``size`` attributes of each model will

be serialized.

be serialized. The primary key is always serialized as the ``pk`` element in the

resulting output; it never appears in the ``fields`` part.

.. note::