needed for field "modifier_device" in the following requests:
* GrabDeviceKey
* UngrabDeviceKey
* GrabDeviceButton
* UngrabDeviceButton
spec:
http://cgit.freedesktop.org/xorg/lib/libXi/tree/specs/encoding.xml#n1147
http://cgit.freedesktop.org/xorg/proto/inputproto/tree/XI.h#n187
<!-- GrabDeviceKey -->
+ <enum name="ModifierDevice">
+ <item name="UseXKeyboard"><value>255</value></item> <!-- 0xff -->
+ </enum>
+
<request name="GrabDeviceKey" opcode="15">
<field type="WINDOW" name="grab_window" />
<field type="CARD16" name="num_classes" />