docs: public static void validateHTMLConfiguration () throws IllegalStateException
    {
      // This will throw an IllegalStateException for wrong files in html/js.xml
      // and html/css.xml
      PhotonCSS.readCSSIncludesForGlobal (new ClassPathResource (PhotonCSS.DEFAULT_FILENAME));
      PhotonJS.readJSIncludesForGlobal (new ClassPathResource (PhotonJS.DEFAULT_FILENAME));
    }