Interface StacksFromBinsOptions

Use uniform unit slots ([i, i+1]) for the bins instead of their numeric [start, end] edges — an ordinal band axis (heart-rate zones, Coggan power zones) where every band reads the same width regardless of its numeric span. The caller labels the slots via <YAxis ticks> at i + 0.5. Omitted / false ⇒ real numeric edges (a true value axis — power W, risk %).