DOC: add behavior change note

tacaswell · tacaswell · commit 08236e7c83ec · 2020-10-30T18:33:18.000-04:00
diff --git a/doc/api/next_api_changes/behavior/16220-AL.rst b/doc/api/next_api_changes/behavior/16220-AL.rst
@@ -0,0 +1,8 @@
+Canvas's callback registry now stored on Figure
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The canonical location of the `~.cbook.CallbackRegistry` used to
+handle Figure/Canvas events has been moved from the Canvas to the
+Figure.  This change should be transparent to almost all users,
+however if you are swapping switching the Figure out from on top of a
+Canvas or visa versa you may see a change in behavior.
