/etc/acpi/events/asus-keyboard-backlight-down is in acpi-support 0.142.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | # /etc/acpi/events/asus-keyboard-backlight-down
# This is called when the user presses the key brightness
# down button and calls /etc/acpi/asus-keyboard-backlight.sh for
# further processing.
event=hotkey ATKD 000000c5
action=/etc/acpi/asus-keyboard-backlight.sh down
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