Issue #9343: Document that argparse parent parsers must be configured before their children. (Merge from 3.2.)
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 459647b..b34be8a 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -347,6 +347,11 @@
 :class:`ArgumentParser` will see two ``-h/--help`` options (one in the parent
 and one in the child) and raise an error.
 
+.. note::
+   You must fully initialize the parsers before passing them via ``parents=``.
+   If you change the parent parsers after the child parser, those changes will
+   not be reflected in the child.
+
 
 formatter_class
 ^^^^^^^^^^^^^^^