Added a note about queryset.query being opaque.

reduced to a list of individual values using the ``values()`` method,

and then converted into a query using the ``query`` attribute::

    Entry.objects.filter(blog__in=Blog.objects.filter(name__contains='Cheddar').values('pk').query)

    q = Blog.objects.filter(name__contains='Cheddar').values('pk').query

    e = Entry.objects.filter(blog__in=q)

.. warning::

    This ``query`` attribute should be considered an opaque internal attribute.

    It's fine to use it like above, but its API may change between Django

    versions.

This queryset will be evaluated as subselect statement::

Less than or equal to.

in

~~

In a given list.

Example::

    Entry.objects.filter(id__in=[1, 3, 4])

SQL equivalent::

    SELECT ... WHERE id IN (1, 3, 4);

startswith

~~~~~~~~~~