XmArrowButton(3) on Linux
The text dec96f61b599, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
The ArrowButton widget class "XmArrowButton" "widget class" "ArrowButton"