Facebook\InstantArticles\Elements\InstantArticle::isValid PHP Method

    public function isValid()
    {
        $header_valid = false;
        if ($this->getHeader()) {
            $header_valid = $this->getHeader()->isValid();
        }
        $items = $this->getChildren();
        $one_item_valid = false;
        if ($items) {
            foreach ($items as $item) {
                if ($item->isValid()) {
                    $one_item_valid = true;
                    break;
                }
            }
        }
        $footer_valid = true;
        if ($this->getFooter()) {
            $footer_valid = $this->getFooter()->isValid();
        }
        return $this->canonicalURL && !Type::isTextEmpty($this->canonicalURL) && $header_valid && $footer_valid && $one_item_valid;
    }