~v message is part of a collapsed thread.
~V cryptographically verified messages
~x \fIEXPR\fP messages which contain \fIEXPR\fP in the \(lqReferences\(rq field
-~X \fIMIN\fP-\fIMAX\fP messages with MIN - MAX attachments
+~X \fIMIN\fP-\fIMAX\fP messages with MIN - MAX attachments
~y \fIEXPR\fP messages which contain \fIEXPR\fP in the \(lqX-Label\(rq field
~z \fIMIN\fP-\fIMAX\fP messages with a size in the range \fIMIN\fP to \fIMAX\fP
~= duplicated messages (see $duplicate_threads)