protected void doAppendTo(Appendable a) {
    if (isVisible) 
      try {
        for (CatNode cn:childNodes)
          cn.appendTo(a);
        if (copies!=null)
          for (CatNodeSection cns: copies)
            cns.appendTo(a);
      } catch (Exception e){
        throw new SectionRenderingException(this, e);
      }
  }