Function paint 

pub fn paint(
    paint: &mut PaintCtx<'_>,
    band: Rect,
    leading: f64,
    trailing: f64,
    label: &str,
    ink: Ink,
)

Paint label centred in band, its rules running from leading to the words and from them to trailing (the message column’s edges, not the window’s), each stopping an s3 gap short of the label.