xbiff(1) on Linux
The text 530ad018b200, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye) shipped it.
mailbox flag for X
Flags it lists
-
-bd -
-bg -
-bw -
-display -
-fg -
-file -
-geometry -
-help -
-rv -
-shape -
-update -
-volume -
-xrm