Fix the documentation for reverse_delete_rule.

docs/guide/signals.rst

@@ -145,7 +145,7 @@ cleaner looking while still allowing manual execution of the callback::
 ReferenceFields and Signals
 ---------------------------
 
-Currently `reverse_delete_rules` do not trigger signals on the other part of
+Currently `reverse_delete_rule` does not trigger signals on the other part of
 the relationship.  If this is required you must manually handle the
 reverse deletion.
 

mongoengine/fields.py

@@ -859,7 +859,7 @@ class ReferenceField(BaseField):
 
     Use the `reverse_delete_rule` to handle what should happen if the document
     the field is referencing is deleted.  EmbeddedDocuments, DictFields and
-    MapFields do not support reverse_delete_rules and an `InvalidDocumentError`
+    MapFields does not support reverse_delete_rule and an `InvalidDocumentError`
     will be raised if trying to set on one of these Document / Field types.
 
     The options are:
@@ -883,7 +883,7 @@ class ReferenceField(BaseField):
         Bar.register_delete_rule(Foo, 'bar', NULLIFY)
 
     .. note ::
-        `reverse_delete_rules` do not trigger pre / post delete signals to be
+        `reverse_delete_rule` does not trigger pre / post delete signals to be
         triggered.
 
     .. versionchanged:: 0.5 added `reverse_delete_rule`

tests/document/instance.py

@@ -1795,7 +1795,7 @@ class InstanceTest(unittest.TestCase):
         self.assertEqual(Bar.objects.count(), 1)  # No effect on the BlogPost
         self.assertEqual(Bar.objects.get().foo, None)
 
-    def test_invalid_reverse_delete_rules_raise_errors(self):
+    def test_invalid_reverse_delete_rule_raise_errors(self):
 
         def throw_invalid_document_error():
             class Blog(Document):