Reference

XtPopupSpringLoaded(3x) on Linux

The text ff7ceef6f7c8, as Debian 2.2 (Potato), Debian 2.1 (Slink), Debian 2.0 (Hamm), Debian 1.3 (Bo) shipped it.

map a pop-up

XtPopupSpringLoaded(3x) on Linux now