docs: public static void addCSSClass(Element e, String cssclass) {
      String oldval = e.getAttribute(SVGConstants.SVG_CLASS_ATTRIBUTE);
      if(oldval == null || oldval.length() == 0) {
        setAtt(e, SVGConstants.SVG_CLASS_ATTRIBUTE, cssclass);
        return;
      }
      String[] classes = oldval.split(" ");
      for(String c : classes) {
        if(c.equals(cssclass)) {
          return;
        }
      }
      setAtt(e, SVGConstants.SVG_CLASS_ATTRIBUTE, oldval + " " + cssclass);
    }