OIC. Scalar context giving the next index. Hadn't seen this before, but it's interesting.
I don't think I would use this myself, as I don't know who would be maintaining my code. I'd prefer the alternative you gave for transparency. Doubly preferred, given the OP's apparent sophistication level.
Quantum Mechanics: The dreams stuff is made of
I agree with you. I probably should have used the less esoteric version given the OP's demonstrated level of expertise. However, you now know a new technique, so maybe pushing the edge of the envelope a little was the right thing after all. ;)