/lib/udev/rules.d/70-gspl-printers.rules is in gnuspool 1.7ubuntu1.
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 | # Low-level USB device add trigger
ACTION=="add", SUBSYSTEM=="usb", ATTR{bInterfaceClass}=="07", ATTR{bInterfaceSubClass}=="01", RUN+="udev-configure-gnuspool add %p"
# usblp device add trigger (needed when usblp is already loaded)
ACTION=="add", KERNEL=="lp*", RUN+="udev-configure-gnuspool add %p"
# Low-level USB device remove trigger
ACTION=="remove", SUBSYSTEM=="usb", ENV{ID_USB_INTERFACES}=="*:0701*:*", RUN+="udev-configure-gnuspool remove %p"
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