depends_on='55af2cb1c267'
Currently, ``depends_on`` needs to be a real revision number, not a partial
-number or branch name.
+number or branch name. It can of course refer to a tuple of any number
+of dependent revisions::
+
+ # revision identifiers, used by Alembic.
+ revision = '2a95102259be'
+ down_revision = '29f859a13ea'
+ branch_labels = None
+ depends_on = ('55af2cb1c267', 'd747a8a8879', 'fa4456a9201')
+
We can see the effect this directive has when we view the history
of the ``networking`` branch in terms of "heads", e.g., all the revisions that