-When undefined:
-
-- `USR1` defaults to `KC_SPC`, otherwise use `CFQ_USER_KEY1`.
-- `USR2` defaults to `KC_ENT`, otherwise use `CFQ_USER_KEY2`.
-- `USR3` defaults to `KC_FN3`, otherwise use `CFQ_USER_KEY3`.
-- `USR4` defaults to `APP`, otherwise use `CFQ_USER_KEY4`.
-