public function book(array $attributes = []) : self
    {
        $tag = $this->lastTag('type');
        if (! $tag or $tag->value != 'book') {
            throw new Exception("Open Graph: Type has to be 'book' to add book attributes");
        }

        $valid = [
            'author',
            'isbn',
            'release_date',
            'tag',
        ];

        $this->unprefixedAttributes('book', $attributes);

        return $this;
    }