The elements of a pop-up menu must be visually searched repeatedly.
Therefore: Make them short, fixed and single-level.
It's interesting that this pattern was easily met because of the conditions set up by Window Per Task and Nouns And Verbs.
See original on c2.com 
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Ward via matrix got to reminiscing with Robert about patterns in context.
> Smalltalk-80 had an excellent UI framework so long as you approached your application in the one way that worked. I had been teaching the framework to computer science researchers when I had need to explain it to technologists of a different bent. So I wrote the patterns that established the context for this one: https://wiki.c2.com/?ShortMenus
> Folks who were very proud of their multi-level menu systems took offense. I would point out to others (but not the offended) that popular systems at the time were operated in the "clerical" position with feet on the floor and both hands on the keyboard. We wrote smalltalk in the "executive" position sitting back, making judgements, with one hand on the mouse. Regretfully this excellence has been lost. Mostly what we were doing is finding code and moving it around. Occasionally we had to type some new code. Federated wiki remembers those days and offers drag-and-drop refactoring in its place.
In 1987, Ward and Kent were consulting with Tektronix's Semiconductor Test Systems Group that was having troubles finishing a design. They decided to try out the pattern stuff they'd been studying. Like Alexander who said the occupiers of a building should design it, Ward and Kent let representatives of the users (a trainer and a field engineer) finish the design.