private void warnIfMissingLang() throws SAXException {
        if (!htmlElementHasLang) {
            String message = "Consider adding a \u201Clang\u201D"
                    + " attribute to the \u201Chtml\u201D"
                    + " start tag to declare the language"
                    + " of this document.";
            warn(message, htmlStartTagLocator);
        }
    }
@see nu.validator.checker.Checker#endDocument()
src/nu/validator/checker/LanguageDetectingChecker.java