pub fn region_chart(
regions: Vec<ChartRegion>,
ticks: Vec<ChartTick>,
x_max: f32,
y_max: f32,
ref_lines: Vec<ChartRefLine>,
legend: Vec<ChartLegendItem>,
) -> WidgetExpand description
A variable-width stacked-region (“coverage-gap” / Marimekko) chart. regions are rectangles in
the [0, x_max] × [0, y_max] plane (build with ChartRegion::new); ticks label the
irregular x-axis; ref_lines are horizontal target/max lines (ChartRefLine::target/::max);
legend names the colors. Add a right-side bracket annotation with with_bracket.