WP Dynamically Replace H Tags

/*--------------------------------------------*/
/* Replace H Tags
/*--------------------------------------------*/

function get_inner_html( $node ) { 
	$innerHTML= ''; 
	$children = $node->childNodes; 
	foreach ($children as $child) { 
		$innerHTML .= $child->ownerDocument->saveXML( $child ); 
	} 
	return $innerHTML; 
}

function my_added_page_content ( $content ) {
	if ( is_page() ) {
		
		$dom = new DOMDocument();
    	// $dom->loadHTML($content);
		$dom->loadHTML('<?xml encoding="utf-8" ?>' . $content);

		$xpath = new DOMXPath($dom);

		$items = array('h1','h2','h3','h4','h5');

		foreach ($items as $item) {

    		// $tags = $dom->getElementsByTagName($item);
			$tags = $xpath->evaluate("//".$item);

			foreach ($tags as $tag) {

				$style = $tag->getAttribute('style');
				$class = $tag->getAttribute('class');
    			// $newtag = $dom->createElement('div', htmlspecialchars($tag->nodeValue));
				$newtag = $dom->createElement('div', get_inner_html($tag));

				$newtag->setAttribute('class', $item.' '.$class);
				if($style) $newtag->setAttribute('style', $style);
				$tag->parentNode->replaceChild($newtag, $tag);
			}
		}

		$dom = $dom->saveHTML();
    	// return $dom;
		return htmlspecialchars_decode($dom);

	} else {
		return $content;
	}
}
add_filter( 'the_content', 'my_added_page_content');