>>>I wouldn't be surprised if you could do that with a horizontal one as well. You have a set of clickable labels, basically, with their surrounding rectangle, laid out in a line. Whether the line is horizontal or vertical affects only their layout, not the functionality. So the decision to have AT clause in activate popup but not in activate menu is actually quite arbitrary. The code inside is the same.
>>>
>>>Or, if it is not the same, then I consider it a serious consequence of the western inductive method of learning (specially sciences). Someone failed to notice the identical behavior and wrote code twice.
>>
>>Obviously the horizontal one is designed to stuck on a window (...), while to vertical one is designed to float and be visible only temporary. For the designers that time it was a huge enough difference?
>
>Or the difference is even older - menus existed even before windowses. They somehow become part of any graphical environment's window handler, so the code for the menu system doesn't come from the language you use, it comes from outside, as a system service (ditto in all flavors of linux I tried so far... and apart from that, I think very few apps I ever saw had their own menu handler, about 99% rely on system). IOW we aren't talking about Dr Dave here, we're talking about the guys who wrote for Mac back in the eighties, or even their predecessors. Who knows what happened then.
>
>I've always felt the menu system as a foreign body grafted on Fox.

One of the most popular programs I ever wrote was a menu app written in the Basic that used to come with MS-Dos.
All it did was execute a bat file that called programs like Lotus 123, etc.
Sounds primitive but it was a lot better than navigating to the .exe.
Windows made it obsolete.