bpo-30550: Clarify JSON ordering guarantees (GH-15397)
diff --git a/Doc/library/json.rst b/Doc/library/json.rst
index b476c37..56c16f5 100644
--- a/Doc/library/json.rst
+++ b/Doc/library/json.rst
@@ -120,6 +120,18 @@
value) is also a subset of YAML 1.0 and 1.1. This module can thus also be
used as a YAML serializer.
+.. note::
+
+ This module's encoders and decoders preserve input and output order by
+ default. Order is only lost if the underlying containers are unordered.
+
+ Prior to Python 3.7, :class:`dict` was not guaranteed to be ordered, so
+ inputs and outputs were typically scrambled unless
+ :class:`collections.OrderedDict` was specifically requested. Starting
+ with Python 3.7, the regular :class:`dict` became order preserving, so
+ it is no longer necessary specify :class:`collections.OrderedDict` for
+ JSON generation and parsing.
+
Basic Usage
-----------