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

    public function toDOMElement($document = null)
    {
        if (!$document) {
            $document = new \DOMDocument();
        }
        // Builds and appends head to the HTML document
        $html = $document->createElement('html');
        if ($this->isRTLEnabled) {
            $html->setAttribute('dir', 'rtl');
        }
        $head = $document->createElement('head');
        $html->appendChild($head);
        $link = $document->createElement('link');
        $link->setAttribute('rel', 'canonical');
        $link->setAttribute('href', $this->canonicalURL);
        $head->appendChild($link);
        $charset = $document->createElement('meta');
        $charset->setAttribute('charset', $this->charset);
        $head->appendChild($charset);
        $this->addMetaProperty('op:markup_version', $this->markupVersion);
        if ($this->header && count($this->header->getAds()) > 0) {
            $this->addMetaProperty('fb:use_automatic_ad_placement', $this->isAutomaticAdPlaced ? 'true' : 'false');
        }
        if ($this->style) {
            $this->addMetaProperty('fb:article_style', $this->style);
        }
        // Adds all meta properties
        foreach ($this->metaProperties as $property_name => $property_content) {
            $head->appendChild($this->createMetaElement($document, $property_name, $property_content));
        }
        // Build and append body and article tags to the HTML document
        $body = $document->createElement('body');
        $article = $document->createElement('article');
        $body->appendChild($article);
        $html->appendChild($body);
        if ($this->header && $this->header->isValid()) {
            $article->appendChild($this->header->toDOMElement($document));
        }
        if ($this->children) {
            foreach ($this->children as $child) {
                if (Type::is($child, TextContainer::getClassName())) {
                    if (count($child->getTextChildren()) === 0) {
                        continue;
                    } elseif (count($child->getTextChildren()) === 1) {
                        if (Type::is($child->getTextChildren()[0], Type::STRING) && trim($child->getTextChildren()[0]) === '') {
                            continue;
                        }
                    }
                }
                $article->appendChild($child->toDOMElement($document));
            }
            if ($this->footer && $this->footer->isValid()) {
                $article->appendChild($this->footer->toDOMElement($document));
            }
        } else {
            $article->appendChild($document->createTextNode(''));
        }
        return $html;
    }