whatsnew-1.6: more detail in note on JSON charset

Addressing Pylons#236

docs/whatsnew-1.6.txt

@@ -65,8 +65,17 @@ Bugfixes
   https://github.com/Pylons/webob/pull/183 for more information.
 
 - The application/json media type does not allow for a charset as discovery of
-  the encoding is done at the JSON layer. Upon initialization of a Response
-  WebOb will no longer add a charset if the content-type is set to JSON. See
-  https://github.com/Pylons/webob/pull/197 and
+  the encoding is done at the JSON layer, and it must always be UTF-{8,16,32}.
+  See the IANA spec at
+  https://www.iana.org/assignments/media-types/application/json, which notes
+
+    No "charset" parameter is defined for this registration.
+    Adding one really has no effect on compliant recipients.
+
+  RFC4627 describes the method for encoding discovery using the JSON content
+  itself. Upon initialization of a Response WebOb will no longer add a charset
+  if the content-type is set to JSON. See
+  https://github.com/Pylons/webob/pull/197,
+  https://github.com/Pylons/webob/issues/237 and
   https://github.com/Pylons/pyramid/issues/1611