This permits implementation of window manager facilities that aid debugging. A client can set its close-down mode to RetainTemporary. If the client then crashes, its win dows would not be destroyed. The programmer can then inspect the application's window tree and use the window manager to destroy the zombie windows. XKillClient can generate a BadValue error.
Some numeric value falls outside the range of values accepted by the request.
Any argument defined as a set of alternatives can generate this error.