+If it is prefaced by the character "!", a condition is negated and has
+to be false for a mail to be selected.
+
+.TP
+\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.