+.It Fl m
+If this flag is specified,
+.Nm
+will optimise the output for inodes having been changed but not
+modified since the last dump ('changed' and 'modified' have the
+meaning defined in stat(2)). For those inodes,
+.Nm
+will save only the metadata, instead of saving the entire inode
+contents. Inodes which are either directories or have been modified
+since the last dump are saved in a regular way.
+Uses of this flag must be consistent, meaning that either every dump
+in an incremental dump set have the flag, or no one has it.
+.Pp
+Tapes written using such 'metadata only' inodes will not be compatible
+with the BSD tape format or older versions of
+.Nm restore.