public static function isVariableRef($string)
    {
        $firstBrace = substr($string, 0, 1);
        $secondBrace = substr($string, -1);

        if ($firstBrace == '{' && $secondBrace == '}') {
            return self::isIdentifier(substr($string, 1, -1));
        } else {
            return self::isIdentifier($string);
        }
    }