XmDropSiteRegistered(3) on Linux
The text c13004500f6b, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Drag and Drop function that determines if a drop site has been registered "XmDropSiteRegistered" "Drag and Drop functions" "XmDropSiteRegistered" "register functions" "XmDropSiteRegistered"