Fixed -- Clarifed pk_set difference in m2m_changed signal receivers for add() and remove().
Thank you to Mariusz Felisiak for review.
@@ -270,9 +270,16 @@ Arguments sent with this signal:
from the relation.
``pk_set``
- For the ``pre_add``, ``post_add``, ``pre_remove`` and ``post_remove``
- actions, this is a set of primary key values that have been added to
- or removed from the relation.
+ For the ``pre_add`` and ``post_add`` actions, this is a set of primary key
+ values that will be, or have been, added to the relation. This may be a
+ subset of the values submitted to be added, since inserts must filter
+ existing values in order to avoid a database ``IntegrityError``.
+
+ For the ``pre_remove`` and ``post_remove`` actions, this is a set of
+ primary key values that was submitted to be removed from the relation. This
+ is not dependent on whether the values actually will be, or have been,
+ removed. In particular, non-existent values may be submitted, and will
+ appear in ``pk_set``, even though they have no effect on the database.
For the ``pre_clear`` and ``post_clear`` actions, this is ``None``.
