DOCSP-43733 - Default JSON mode (#246)

Author: mongoKart

source/upgrade/v3.txt

@@ -115,4 +115,24 @@ Version 3.0 Breaking Changes
   apply the ``[BsonRepresentation(BsonType.String)]`` attribute to the field.
 
   To learn more about specifying BSON types during serialization, see the
-  :ref:`Custom Serialization <csharp-custom-serialization>` section of the POCOs page.
+  :ref:`Custom Serialization <csharp-custom-serialization>` section of the POCOs page.
+
+- The default JSON output mode is Relaxed Extended JSON, a string format based on the
+  JSON standard that describes BSON documents. Relaxed Extended JSON emphasizes
+  readability and interoperability at the expense of type preservation.
+
+  To use a different JSON output mode, create a new ``JsonWriterSettings`` object. Set
+  the ``OutputMode`` property of this object to a value from the ``JsonOutputMode`` enum,
+  then pass the object to the ``ToJson()`` method when you serialize your document.
+  The following code example shows how to serialize a BSON document to Strict JSON:
+
+  .. code-block:: csharp
+
+     // Configure JsonWriterSettings
+     var jsonWriterSettings = new JsonWriterSettings
+     {
+         OutputMode = JsonOutputMode.Strict
+     };
+
+     // Serialize the document to JSON using the configured settings
+     var json = document.ToJson(jsonWriterSettings);