And then we got to "you have to run a profiler to know it matters." I contend it’s possible to use your eyes and brain to see that a div is on the critical path

And then we got to "you have to run a profiler to know it matters." I contend it’s possible to use your eyes and brain to see that a div is on the critical path in an inner loop without fancy tools. You just have to have a rough sense of operation cost and how out-of-order CPUs work I'd be convinced only if you showed a benchmark with and without the trick. I still suspect it doesn't matter in the end. But the only we'd know is if the author ran a benchmark. Which he refuses to do, because he is so sure of himself.