The XGrabDeviceKey request establishes a passive grab. In the
future, the device is actively grabbed (as for XGrabDevice, the
last-device-grab time is set to the time at which the Key was
pressed (as transmitted in the DeviceKeyPress event), and the
DeviceKeyPress event is reported if all of the following
conditions are true:
  * The device is not grabbed, and the specified key is
    logically pressed when the specified modifier keys are
    logically down, and no other keys or modifier keys are
    logically down.
  * The grab_window is an ancestor (or is) the focus window OR
    the grab window is a descendant of the focus window and
    contains the device.
  * The confine_to window (if any) is viewable.
  * A passive grab on the same key/modifier combination does
    not exist on any ancestor of grab_window.

The interpretation of the remaining arguments is as for
XGrabDevice. The active grab is terminated automatically when
the logical state of the device has the specified key released.

Note that the logical state of a device (as seen by means of
the X protocol ) may lag the physical state if device event
processing is frozen.

If the key is not AnyKey, it must be in the range specified by
min_keycode and max_keycode as returned by the
XListInputDevices request. Otherwise, a BadValue error results.

This request overrides all previous grabs by the same client on
the same Key/modifier combinations on the same window. A
modifier of AnyModifier is equivalent to issuing the grab
request for all possible modifier combinations (including the
combination of no modifiers). It is not required that all
modifiers specified have currently assigned KeyCodes. A key of
AnyKey is equivalent to issuing the request for all possible
keys. Otherwise, it is not required that the specified key
currently be assigned to a physical Key.

If a modifier_device of NULL is specified, the X keyboard will
be used as the modifier_device.

If some other client has already issued a XGrabDeviceKey with
the same Key/modifier combination on the same window, a
BadAccess error results. When using AnyModifier or AnyKey, the
request fails completely, and a BadAccess error results (no
grabs are established) if there is a conflicting grab for any
combination. XGrabDeviceKey has no effect on an active grab.

XGrabDeviceKey can generate BadAccess, BadClass, BadDevice,
BadMatch, BadValue, and BadWindow errors. It returns Success on
successful completion of the request.

The XUngrabDeviceKey request releases the passive grab for a
key/modifier combination on the specified window if it was
grabbed by this client. A modifier of AnyModifier is equivalent
to issuing the ungrab request for all possible modifier
combinations, including the combination of no modifiers. A Key
of AnyKey is equivalent to issuing the request for all possible
Keys. XUngrabDeviceKey has no effect on an active grab.

If a modifier_device of NULL is specified, the X keyboard will
be used as the modifier_device.

XUngrabDeviceKey can generate BadDevice, BadMatch, BadValue and
BadWindow errors.

BadDevice
       An invalid device was specified. The specified device
       does not exist or has not been opened by this client via
       XOpenInputDevice. This error may also occur if the
       specified device is the X keyboard or X pointer device.

BadMatch
       This error may occur if an XGrabDeviceKey request was
       made specifying a device that has no keys, or a modifier
       device that has no keys.

BadValue
       Some numeric value falls outside the range of values
       accepted by the request. Unless a specific range is
       specified for an argument, the full range defined by the
       argument's type is accepted. Any argument defined as a
       set of alternatives can generate this error.

BadWindow
       A value for a Window argument does not name a defined
       Window.

XAllowDeviceEvents(3), XGrabDevice(3), XGrabDeviceButton(3)