Reference

XGetWMHints(3x) on Linux

The text bf47524b9fba, as Debian 2.2 (Potato), Debian 2.1 (Slink), Debian 2.0 (Hamm), Debian 1.3 (Bo) shipped it.

allocate window manager hints structure and set or read a window's WM_HINTS property

XGetWMHints(3x) on Linux now