-regexp. This requires reading the original mboxes completely, which
-can be slow. Header conditions have to be fulfilled before checking
-the body ones, which may speed things up.
+regexp. Evaluatin such a condition requires to read the original
+mboxes completely, which can be slow. However, header conditions are
+checked first to read the bodies only for mails which fulfill them
+entirely.
+.TP
+\fB8h\fR, \fBtoday\fR, \fB24h\fR, \fBweek\fR, and \fBmonth\fR selects
+mails received respectively during the last 8, 24, 24, 7 * 24 hours or
+31 * 24 hours.
+.TP
+\fByesterday\fR selects mails received between 48h and 24h ago.
+.TP
+\fBmonday\fR, \fBtuesday\fR, ..., \fBsunday\fR selects mails received
+the most recent such day