## Special Extra key doesn't work(System, Audio control keys)
+You need to define `EXTRAKEY_ENABLE` in **makefile** to use them in TMK.
+```
+EXTRAKEY_ENABLE = yes # Audio control and System control
+```
http://deskthority.net/workshop-f7/tmk-keyboard-firmware-collection-t4478-60.html#p157919
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