whatsnew: ChainMap.new_child *m* argument.
And NEWS entry.
diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst
index f41a6ac..e7fd3a9 100644
--- a/Doc/whatsnew/3.4.rst
+++ b/Doc/whatsnew/3.4.rst
@@ -596,6 +596,15 @@
project, Serhiy Storchaka, and Antoine Pitrou in :issue:`17618`.)
+collections
+-----------
+
+The :meth:`.ChainMap.new_child` method now accepts an *m* argument specifying
+the child map to add to the chain. This allows an existing mapping and/or a
+custom mapping type to be used for the child. (Contributed by Vinay Sajip in
+:issue:`16613`.)
+
+
colorsys
--------
diff --git a/Misc/NEWS b/Misc/NEWS
index 68cb379..214e8fc 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -2376,6 +2376,9 @@
- Issue #14850: Now a charmap decoder treats U+FFFE as "undefined mapping"
in any mapping, not only in a string.
+- Issue #16613: Add *m* argument to ``collections.Chainmap.new_child`` to
+ allow the new child map to be specified explicitly.
+
- Issue #16730: importlib.machinery.FileFinder now no longers raises an
exception when trying to populate its cache and it finds out the directory is
unreadable or has turned into a file. Reported and diagnosed by