=head1 MH
Not yet supported, locking semantics (or lack thereof) appear to
-make it unsuitable for parallel access.
+make it unsuitable for parallel access. It is widely-supported
+by a variety of MUAs and mailing list managers, however.
+
+=head1 MMDF
+
+Not yet supported, and it's unclear if current usage/support makes
+it worth supporting.
=head1 IMAP