XmListItemExists(3) on Linux
The text 38fc18032337, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A List function that checks if a specified item is in the list "XmListItemExists" "List functions" "XmListItemExists"