Note that the tap rules are in the over current article. A 14ga tap on a 20a circuit would still need 15a Over current protection somewhere. As close as you get is fixture wires but that needs to be within the listed equipment.
For the Canadians who read this, we have a tap rule (30-412) that allows a 7.5m (24.5 foot) tap with a #14 from a 20 amp circuit, for one light or one row of lights provided #14 is large enough for the load. So, it is safe in the North but not in the South.
