Updated documentation for abstract reference changes

Author: AWhetter

AUTHORS

@@ -230,3 +230,4 @@ that much better:
  * Amit Lichtenberg (https://github.com/amitlicht)
  * Lars Butler (https://github.com/larsbutler)
  * George Macon (https://github.com/gmacon)
+ * Ashley Whetter (https://github.com/AWhetter)

docs/changelog.rst

@@ -6,6 +6,7 @@ Changes in 0.10.2
 =================
 - Allow shard key to point to a field in an embedded document. #551
 - Allow arbirary metadata in fields. #1129
+- ReferenceFields now support abstract document types. #837
 
 Changes in 0.10.1
 =======================

mongoengine/fields.py

@@ -896,6 +896,10 @@ def __init__(self, document_type, dbref=False,
           or as the :class:`~pymongo.objectid.ObjectId`.id .
         :param reverse_delete_rule: Determines what to do when the referring
           object is deleted
+
+        .. note ::
+            A reference to an abstract document type is always stored as a
+            :class:`~pymongo.dbref.DBRef`, regardless of the value of `dbref`.
         """
         if not isinstance(document_type, basestring):
             if not issubclass(document_type, (Document, basestring)):