XmDropTransferStart(3) on Linux
The text ba98c3f7e421, 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 initiates a drop transfer "XmDropTransferStart" "Drag and Drop functions" "XmDropTransferStart"