+ "List of tag changes to apply to a message when it is marked as read.
+
+Tags starting with \"+\" (or not starting with either \"+\" or
+\"-\") in the list will be added, and tags starting with \"-\"
+will be removed from the message being marked as read.
+
+For example, if you wanted to remove an \"unread\" tag and add a
+\"read\" tag (which would make little sense), you would set:
+ (\"-unread\" \"+read\")"