Paste gist.github.com URL in Gutenberg -> get the embed [WordPress]

gists_in_gutenberg.php

//Important: When adding a gist link in Editor you MUST choose - convert to link, not Embed!			
//Embed Gists to be displayed in Gutenberg without plugin, works on new and existing ones

add_filter( 'the_content', 'sz_embed_gists_in_gutenberg' );
function sz_embed_gists_in_gutenberg( $content ) {
	if(empty($content)) return;
	$dom = new DOMDocument;
	libxml_use_internal_errors(true);
    $content = mb_convert_encoding($content, 'HTML-ENTITIES', "UTF-8"); 
	$dom->loadHTML($content);
	$paragraphs = $dom->getElementsByTagName('p');
	$domElemsToTarget = array();
		foreach ( $paragraphs as $paragraph ) {
				$paragraph_content = $paragraph->nodeValue;
				if (strpos($paragraph_content, "gist.github.com") !== false) {
					$domElemsToTarget[] = $paragraph;
				}
		}
	foreach( $domElemsToTarget as $domElement ){
		//in case it's a link to a specific file inside the  gist:		
		$p_content = $domElement->nodeValue;
		$url_string = explode('#',$p_content);
		//create link
		$link = $dom->createElement('script');
		$specific_file_string = (!empty($url_string[1])) ? "?".preg_replace(['/^file-/','/-php$/'],['file=','.php'],$url_string[1]) : ''; 		
		$link->setAttribute('src', $url_string[0].".js".$specific_file_string);
		//wrap it in <p> (for some reason, <script> that goes just after the <h> tag without wrapper gets missed out)
		$p_new = $dom->createElement('p');
		$p_new->setAttribute("class", "gist-embed-php");
		$p_new->appendChild($link); //nest it		
		
		$domElement->replaceWith($p_new);
		/** For PHP < 8
		//remove initial contents of the paragraph		
		while ($domElement->hasChildNodes()) {
		   $domElement->removeChild($domElement->firstChild);
		 }
		//append the new one
		$domElement->appendChild($p_new);
		**/	
	}
	$content= $dom->saveHtml();
	return $content;
}