protected function addElementClasses(string $option, $classes): Breadcrumbs
    {
        if (is_string($classes)) {
            $classes = explode(' ', $classes);
        }
        $this->validateClasses($classes);

        $classes = array_merge(
            $this->getOption($option),
            $classes
        );
        $this->setOption($option, array_unique($classes));

        return $this;
    }