- may be used to activate arbitrary units,
- when a specific device becomes
- available.</para></listitem>
+ may be used to activate arbitrary
+ units, when a specific device becomes
+ available. Note that this and the
+ other tags are not taken into account
+ unless the device is tagged with the
+ "<literal>systemd</literal>" string in
+ the udev database, because otherwise
+ the device is not exposed as systemd
+ unit.</para></listitem>