The series drawing the band, as a native range construct: a Highcharts
arearange or areasplinerange, or an amCharts series bound to both
openValueYField and valueYField. Its low edge is read as the lower
quantile and its high edge as the upper one, matched to the median by x.
The quantile its low edge is, as a fraction below 0.5 — 0.05, not 5.
The quantile its high edge is, as a fraction above 0.5 — 0.95, not 95.
One band of a PercentileBandDeclaration: the companion series that draws it, and the two quantile levels its edges are.