XmDropTransferAdd(3) on Linux
The text d74020a6a3e9, 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 enables additional drop transfer entries to be processed after initiating a drop transfer "XmDropTransferAdd" "Drag and Drop functions" "XmDropTransferAdd"