CSS selector for the band's one <path>, drawn by d3.area() over the
band's rows, which are its bound datum.
The quantile the band's low edge is, as a fraction below 0.5.
The quantile the band's high edge is, as a fraction above 0.5.
Optionaly0Accessor for the low edge.
Optionaly1Accessor for the high edge.
One band of a D3PercentileBandConfig.