docs: public static Element setupCanvas(SVGPlot svgp, Projection2D proj, double margin, double width, double height) {
      final CanvasSize canvas = proj.estimateViewport();
      final double sizex = canvas.getDiffX();
      final double sizey = canvas.getDiffY();
      String transform = SVGUtil.makeMarginTransform(width, height, sizex, sizey, margin) + " translate(" + SVGUtil.fmt(sizex * .5) + " " + SVGUtil.fmt(sizey * .5) + ")";
  
      final Element layer = SVGUtil.svgElement(svgp.getDocument(), SVGConstants.SVG_G_TAG);
      SVGUtil.setAtt(layer, SVGConstants.SVG_TRANSFORM_ATTRIBUTE, transform);
      return layer;
    }