Cocoa seems to be using the triangle technique + a delay, FWIW: a submenu will close instantly when navigating vertically or to the opposite direction, but there is a lot of leeway when navigating in the triangle towards the submenu (eyeballing it, seems to take more than half a second for the submenu to close). And interestingly, you can also "overshoot" the submenu, it will delay its closing quite a bit when moving around/outside of it.

> - Tk 8.6 does what bootstrap does

Which is?