+\fBf <regexp>\fR (from) selects mails whose leading line From, or
+fields From:, Sender:, Reply-To:, or Return-Path: matches the regexp.
+.TP
+\fBt <regexp>\fR (to) selects mails whose field To:, Cc:, or Bcc: matches the regexp.
+.TP
+\fBp <regexp>\fR (participant) selects mails that would be selected by \fBf\fR or \fBt\fR.
+.TP
+\fBs <regexp>\fR (subject) selects mails whose field Subject: matches the regexp.