+files or directories.
+Beginning with version 3.0.0, you may specify bf(--max-delete=0) to
+be warned about any extraneous files in the destination, but be very
+careful to never specify a 0 value to an older rsync client, or the
+option will be silently ignored. (A 3.0.0 client will die with an
+error if the remote rsync is not new enough to handle the situation.)