XmSeparator(3) on Linux
The text 9ca7e7ae546b, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
The Separator widget class "XmSeparator" "widget class" "Separator"