I went to the local box store and bought a UL=-listed light for my front porch. Just a simple, basic fixture.
In preparation, I replaced the old-fashioned 'poke the cable through a hole and splice inside the fixture' arrangement with a proper box. Part of my reason for doing this was because the clapboard siding meant that there would be a substantial gap behind parts of the fixture.
Much to my surprise, I was not able to figure out a way to mount the fixture in an NEC-compliant manner. There was simply no way to keep the wires within the box.
I made a mock-up for this picture, to illustrate the problem:
The wires exit the fixture as sent from the factory. The fixture is mounted using factory KO's. Wires cannot be run within the fixture, due to bulb placement.