private static String stringLiteral(CharSequence cs) {
        if (cs == null) {
            return "null";
        }
        StringBuilder sb = new StringBuilder();
        sb.append('\"');
        int len = cs.length();
        for (int i = 0; i < len; i++) {
            sb.append(unquotedCharLiteral(cs.charAt(i)));
        }
        sb.append('\"');
        return sb.toString();
    }
@see org.xml.sax.ContentHandler#skippedEntity(java.lang.String)
src/nu/validator/xml/SaxCompiler.java