Выбор первых картинок из контента

<?php
//OnDocFormSave
$TvValue = $modx->getOption('TV',$scriptProperties,'firstImage');
$def_img = 'assets/images/default.png';
$img = $resource->GetTVValue($TvValue);
$text = $resource->content;

if(empty($img)) {
  if (preg_match_all( '|<img.*?src=[\'"](.*?)[\'"].*?>|i',$text , $matches )!=0)
    {
        $img = $matches[1][0];
    }
    else{
    $img = $def_img;
    }
}

$resource->setTVValue($TvValue,$img);
$resource->save();

<?php
if ($modx->event->name == 'OnBeforeDocFormSave') {

    //get current content for resource
    $content = $resource->getContent();
    if (!empty($content)){
    //get first image in content
    $doc = new DOMDocument();
    $doc->loadHTML($content);
    $xml = simplexml_import_dom($doc);
    $images = $xml->xpath('//img');
    foreach ($images as $img) {
        //also avaliable in array  $img['alt'] и $img['title]
        $file_headers = @get_headers($img['src']);
        if ($file_headers[0] != 'HTTP/1.1 404 Not Found') {
            $first_img_src = $img['src'];
            break;
        }
    }

    //get properties
    $properties = $resource->get('properties');

    //here you can check for empty $first_img_src and set default noImage photo

    //save or override first_img_src
    $properties['first_img_src'] = $first_img_src;
    $resource->set('properties', $properties);

}
}