I don't think what matters is whether someone could be expected to know a feature, but rather whether they could be expected to correctly guess what it does. T

I don't think what matters is whether someone could be expected to know a feature, but rather whether they could be expected to correctly guess what it does. That comma operator is pretty odd; someone could easily be surprised by that behavior. Labeled breaks and additional arguments to setTimeout, though, do exactly what they look like. You might be surprised that the code works, but you wouldn't be so surprised at what it does.