Press-drag-release

Put the pointer on a menu title, press, and the menu appears while the button is still down. Keep holding and slide down the list: the highlight follows the pointer from item to item, not because anything was clicked but because the press never ended. Let go over the item you want and it runs. That is one gesture, a single press with a single release, and for the first decade of graphical interfaces it was the only way a menu could be operated at all. The pointer was assumed to be a mouse in a hand that was already down.

The two-click habit came later. Mac OS 8 added what Apple called sticky menus: press and release on the title without travelling anywhere, and the menu stays up on its own, so a second click picks from it at leisure. That mode is now the one most people know, and it is why the gesture reads as an easter egg rather than as the design. The interesting claim is that a menu should answer both. The same surface serves the reader who lets go by reflex and the reader who never lets go, and neither has to be taught which mode they are in, because the difference is only whether the button came up before or after the travel.

Two details carry the weight. Releasing away from every item commits nothing, which is the escape hatch pointer cancellation asks for by name: a press that landed on the wrong title can be slid off and abandoned. And the pointer has to be held. A drag that starts on the trigger will leave the trigger immediately, so the implementation takes pointer capture on the press and resolves the item under the pointer by coordinate rather than by event target. Skip that and the gesture dies the instant the pointer crosses the trigger’s edge, which is a bug no click-driven test will ever find.

Set against its neighbours: a marking menu is also answered by a stroke, but there the direction is the choice and a confident stroke skips drawing the menu entirely, so the gesture replaces the reading. Press-drag-release still asks you to look. A long press is a trigger, the hold that opens something, and it says nothing about what the same press does afterwards. Which is also why this gesture belongs to pointers: a finger cannot see the highlight it is covering, so touch menus open on tap and are picked on a second tap, and the one-gesture path quietly goes away.