backport adds a new include which, at this point, is only used in 1 file (#5775)

Author: MongoCaleb

source/core/document.txt

@@ -89,16 +89,7 @@ names:
 
 .. include:: /includes/fact-document-field-name-restrictions.rst
 
-BSON documents may have more than one field with the same name.
-Most :driver:`MongoDB interfaces </>`, however, represent MongoDB
-with a structure (e.g. a hash table) that does not support duplicate
-field names. If you need to manipulate documents that have more than one
-field with the same name, see the :driver:`driver documentation
-</>` for your driver.
-
-Some documents created by internal MongoDB processes may have duplicate
-fields, but *no* MongoDB process will *ever* add duplicate fields to an
-existing user document.
+.. include:: /includes/warning-document-duplicate-key-names-body.rst
 
 Field Value Limit
 ~~~~~~~~~~~~~~~~~

source/includes/warning-document-duplicate-key-names-body.rst

@@ -0,0 +1,7 @@
+The MongoDB Query Language does not support documents with duplicate
+field names. While some BSON builders may support creating a BSON document with
+duplicate field names, inserting these documents into MongoDB is not supported 
+*even if* the insert succeeds, or appears to succeed. For example, inserting a 
+BSON document with duplicate field names through a MongoDB driver may result in 
+the driver silently dropping the duplicate values prior to insertion, or may 
+result in an invalid document being inserted that contains duplicate fields. Querying against any such documents would lead to arbitrary and inconsistent results.