It is more than 'paper prototypes' -- you actually need to know how the system s...

It is more than 'paper prototypes' -- you actually need to know how the system should work, from the users' point of view.

Ben Cchneiderman (http://www.cs.umd.edu/~ben/) took this a step further in 1987: design the documentation first:

Shneiderman, B. (1987), Designing the User Interface: Strategies for Effective Human-Computer Interaction. Reading, Mass.: Addison-Wesley.

I referenced the technique in my thesis, and proposed it for aircraft autoflight systems!