docs: public WidgetBuilder selectorAttr(String name, String value) throws IOException {
          if (value != null) {
              ResponseWriter rw = context.getResponseWriter();
              rw.write(",");
              rw.write(name);
              rw.write(":\"");
              rw.write(ComponentUtils.escapeSelector(value));
              rw.write("\"");
          }
  
          return this;
      }