Add note advising that 'filter' be used as a keyword-argument.
diff --git a/Doc/library/tarfile.rst b/Doc/library/tarfile.rst
index 60b9cd4..a8e1d56 100644
--- a/Doc/library/tarfile.rst
+++ b/Doc/library/tarfile.rst
@@ -419,7 +419,9 @@
.. deprecated:: 2.7
The *exclude* parameter is deprecated, please use the *filter* parameter
- instead.
+ instead. For maximum portability, *filter* should be used as a keyword
+ argument rather than as a positional argument so that code won't be
+ affected when *exclude* is ultimately removed.
.. method:: TarFile.addfile(tarinfo, fileobj=None)