Fixed #19352 - Added an example in the QuerySet docs.

    Blog.objects.filter(entry__headline__contains='Lennon').filter(

            entry__pub_date__year=2008)

In this second example, the first filter restricted the queryset to all those

blogs linked to that particular type of entry. The second filter restricted

the set of blogs *further* to those that are also linked to the second type of

entry. The entries select by the second filter may or may not be the same as

the entries in the first filter. We are filtering the ``Blog`` items with each

filter statement, not the ``Entry`` items.

Suppose there is only one blog that had both entries containing *"Lennon"* and

entries from 2008, but that none of the entries from 2008 contained *"Lennon"*.

The first query would not return any blogs, but the second query would return

that one blog.

In the second example, the first filter restricts the queryset to all those

blogs linked to entries with *"Lennon"* in the headline. The second filter

restricts the set of blogs *further* to those that are also linked to entries

that were published in 2008. The entries selected by the second filter may or

may not be the same as the entries in the first filter. We are filtering the

``Blog`` items with each filter statement, not the ``Entry`` items.

All of this behavior also applies to

:meth:`~django.db.models.query.QuerySet.exclude`: all the conditions in a