RangeAreaMark<T> class final

A filled band between paired low/high values at each x.

Gaps

low and high are FieldAccessor<T, num?>, not num, because RangeAreaDataPoint.gap is a real point with no interval and a TOTAL accessor cannot express one. Both null at a row lowers to RangeAreaDataPoint.gap; exactly one null is an authoring error and raises GrammarDiagnosticCode.incompleteRangeAreaInterval rather than guessing a bound. This mirrors PolarMark.intervalLow/intervalHigh.

No channels

Deliberate, not an omission. The range-area painter reads no per-point colour: it paints from the series colour, fillOpacity, the two boundary styles and the theme, and RangeAreaScreenPoint carries only the interval geometry. A colorBy or size channel would be accepted and then ignored, so none is offered.

What this mark does NOT carry

isXOrdered is absent because RangeAreaChartSeries hard-codes it true in its constructor — exactly as CandlestickChartSeries does — so a knob would be a lie.

fillGradient and pathAnimation WERE in this list. They were deliberately withheld when this mark shipped, because AreaMark and LineMark still refused the same two and carrying them here would have left an asymmetry a user hits immediately. Roadmap 1d closed that by giving all three families the path fields in one slice, which is why they are constructor parameters now rather than named refusals.

Every config field is nullable and null means "the RangeAreaChartSeries default". The defaults live on the series class alone and are resolved once at lowering, so the mark cannot carry a stale copy of one.