CngxChartPlotArea

The rectangle the chart's scales map onto: the viewBox minus the space reserved for axis decoration, in viewBox user units. Without axes it equals the box.

x0/y0 are the top-left corner, x1/y1 the bottom-right one, and width/height the extents between them. Every chart child that needs to know where the plot starts reads this rather than subtracting an inset from the box itself - one derivation, so the scales and the axis lines cannot drift apart.

A collapsed plot (a box narrower than the room its axes need) reports width or height at or below 0. Readers guard on the extent; the chart hands out its NOOP scale in the same case.