reason

Why this decision is being taken — the label its caller gave to decide or requestDecision (S§C.11.3, D6).

A rule serving an element that is called from several places behaves differently depending on which one is asking: ordering up to S on a stockout is not the same act as topping up at a scheduled review, even though the surface is identical. Before this, nothing distinguished them.

Epoch-scoped, so it is subject to the staleness discipline like every other member that means something different at the next epoch. Defaulted so that no existing implementation of this interface breaks.