Area spline · Stacked area spline

Smooth layers with shared boundaries and original values.

Use a smooth filled trend for ordered values. The monotone curve adds no new observations; the fill ends at zero.

Category, numeric or UTC-time X and nullable Y. Null breaks outline and fill. Only original points appear in detail.

Markers, shared detail, legend, references and viewport are supported. Interpolation is fixed. Stacking and stack labels are rejected.