In the documentation it shows series.1.line.open.y:[series.2.name] and the opposite for series.2 so the lines are open toward each other. I'm guess that's what creates the shaded area.
In the documentation it shows series.1.line.open.y:[series.2.name] and the opposite for series.2 so the lines are open toward each other. I'm guess that's what creates the shaded area.