docs: protected void makeLayerElement() {
      plotwidth = StyleLibrary.SCALE;
      plotheight = StyleLibrary.SCALE / optics.getOPTICSPlot(context).getRatio();
      final double margin = context.getStyleLibrary().getSize(StyleLibrary.MARGIN);
      layer = SVGUtil.svgElement(svgp.getDocument(), SVGConstants.SVG_G_TAG);
      final String transform = SVGUtil.makeMarginTransform(getWidth(), getHeight(), plotwidth, plotheight, margin * .5, margin * .5, margin * 1.5, margin * .5);
      SVGUtil.setAtt(layer, SVGConstants.SVG_TRANSFORM_ATTRIBUTE, transform);
    }