public function setClass($class = '')
    {
        if (is_string($class) && (empty($class) === true || Format::isClass($class) === true)) {
            $class = trim($class);
            $this->class = $class;
        } else {
            $msg = "The 'class' argument must be a valid class name, '" . $class . "' given";
            throw new InvalidArgumentException($msg);
        }
    }