Refer to strftime(3) manpage for platform specific format codes.
Suggested by Skip Montanaro on docs@.
diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
index 4e922f0..0de7391 100644
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -1603,7 +1603,8 @@
The full set of format codes supported varies across platforms, because Python
calls the platform C library's :func:`strftime` function, and platform
-variations are common.
+variations are common. To see the full set of format codes supported on your
+platform, consult the :manpage:`strftime(3)` documentation.
The following is a list of all the format codes that the C standard (1989
version) requires, and these work on all platforms with a standard C