ACTION

Matches the name of the action that led to an event. For example, ACTION="add" or ACTION="remove".

ENV{key}

Matches a value for the device property key. For example, ENV{DEVTYPE}=="disk".

KERNEL

Matches the name of the device that is affected by an event. For example, KERNEL=="dm-*" for disk media.

NAME

Matches the name of a device file or network interface. For example, NAME="?*" for any name that consists of one or more characters.

SUBSYSTEM

Matches the subsystem of the device that is affected by an event. For example, SUBSYSTEM=="tty".

TEST

Tests wheter the specified file or path exists; for example, TEST=="/lib/udev/devices/$name", where $name is the name of the matched device file.