XmGetDestination(3) on Linux
The text c91da3bbe99d, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A function that returns the widget ID of the widget to be used as the current destination for quick paste and certain clipboard operations "XmGetDestination"