private void warnAboutAttributeOnElement(String attributeName, String elementName) throws SAXException {
      warn("The \u201C" + attributeName + "\u201D attribute on the"
          + " \u201C" + elementName + "\u201D element is not supported"
          + " in all browsers. Please be sure to test, and consider"
          + " using a polyfill.");
    }
@see nu.validator.checker.Checker#startElement(java.lang.String,
     java.lang.String, java.lang.String, org.xml.sax.Attributes)
src/nu/validator/checker/UnsupportedFeatureChecker.java