A variance-band draw layer: fills the envelope between the lower and upper
columns of series (typically rollingByColumn percentiles), gap-aware, and
registers itself into the enclosing Layers. Renders nothing to the
DOM — the row draws it.
Compose two for a two-tone spread — author the wider band first so it sits behind (declaration order = z-order, back-to-front), then the line on top:
<Layers>
<BandChart series={s} lower="p5" upper="p95" as="outer" />
<BandChart series={s} lower="p25" upper="p75" as="inner" />
<LineChart series={s} column="p50" />
</Layers>