/lib/udev/rules.d/69-wacom.rules is in xserver-xorg-input-wacom 0.34.0-1.
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 8 9 10 11 12 13 14 15 16 | ACTION!="add|change", GOTO="wacom_end"
# Match all serial wacom tablets with a serial ID starting with WACf
# Notes: We assign NAME though we shouldn't, but currently the server requires it
# We assign the lot to subsystem pnp too because server reads NAME from
# the parent device. Once all that's fixed, as simple SUBSYSTEM="tty"
# will do and the ENV{NAME} can be removed.
SUBSYSTEM=="tty|pnp", SUBSYSTEMS=="pnp", ATTRS{id}=="WACf*", ENV{ID_MODEL}="Serial Wacom Tablet $attr{id}", ENV{ID_INPUT}="1", ENV{ID_INPUT_TABLET}="1", ENV{NAME}="Serial Wacom Tablet $attr{id}"
SUBSYSTEM=="tty|pnp", SUBSYSTEMS=="pnp", ATTRS{id}=="FUJ*", ENV{ID_MODEL}="Serial Wacom Tablet $attr{id}", ENV{ID_INPUT}="1", ENV{ID_INPUT_TABLET}="1", ENV{NAME}="Serial Wacom Tablet $attr{id}"
# comment out the next line if your distribution does not provide systemd
# If a /dev/ttySx device with the WACf name is detected, start the
# wacom-inputattach service with the kernel name as parameter
SUBSYSTEM=="tty|pnp", KERNEL=="ttyS[0-9]*", ATTRS{id}=="WACf*", TAG+="systemd", ENV{SYSTEMD_WANTS}+="wacom-inputattach@%k.service"
LABEL="wacom_end"
|