A spec the team can build from without asking what was meant
Turning a prioritized item into a written spec a team can build from — the problem and the one story that proves it, goals with honest baselines, scope and non-goals, and the intended behavior down to the edge cases. The work runs from framing the problem and the appetite, through scenarios and numbered behavior rules written as what the user does and sees, to a versioned spec that the engineers and designer walk through and the assembler re-issues with every change logged.
Its purpose is to make the spec unambiguous without taking the solution away from the people who build it. A spec that prescribes screens gets argued with; one that leaves the edge cases out gets built twice.