The chart element drawn under a point of the page (clientX, clientY), as the chart is
painted now; null outside the chart, or before it is painted.
The chart as an SVG document of the element's unzoomed size; null while the chart has no
layout or the element no size. It is drawn light, a chart area with no fill of its own white,
unless darkMode.
The chart drawn;
nulluntil aPromiseinput resolves.