gdk:window-set-skip-taskbar-hint (window skips-taskbar)

window -- a toplevel gdk:window object
skips-taskbar -- true to skip the taskbar

Toggles whether a window should appear in a task list or window list. If a window's semantic type as specified with the gdk:window-type-hint function already fully describes the window, this function should not be called in addition, instead you should allow the window to be treated according to standard policy for its semantic type.