/lib/udev/rules.d/70-touchpad.rules is in udev 232-25+deb9u8.
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 | # do not edit this file, it will be overwritten on update
ACTION=="remove", GOTO="touchpad_end"
ENV{ID_INPUT}=="", GOTO="touchpad_end"
ENV{ID_INPUT_TOUCHPAD}=="", GOTO="touchpad_end"
KERNEL!="event*", GOTO="touchpad_end"
# touchpad:<subsystem>:v<vid>p<pid>:name:<name>:*
KERNELS=="input*", ENV{ID_BUS}!="", \
IMPORT{builtin}="hwdb 'touchpad:$env{ID_BUS}:v$attr{id/vendor}p$attr{id/product}:name:$attr{name}:'", \
GOTO="touchpad_end"
LABEL="touchpad_end"
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