Error - Class 'Grav\Plugin\DOMDocument' not found

I am new to custom plugin creation (per the Plugin Tutorial) and I have a problem. My custom GRAV plugin throws a fatal PHP error:

Class 'Grav\Plugin\DOMDocument' not found

when I attempt to create (and use) the following:

namespace Grav\Plugin;

use Composer\Autoload\ClassLoader;
use Grav\Common\Plugin;

/* SEE: */
use Grav\Common\Page\Collection;
use Grav\Common\Uri;
use Grav\Common\Taxonomy;
/* use Grav\Common\Event; */

use Grav\Common\Page\Page;
use RocketTheme\Toolbox\Event\Event;
use RocketTheme\Toolbox\File\File;
use Thunder\Shortcode\Shortcode\ShortcodeInterface;

use ReflectionProperty;

class MyCustomPlugin extends Plugin
    public function onFormProcessed(Event $event)
      $dom = new DOMDocument();

even though ‘dom’ and ‘mbstring’ appear to be loaded extensions (apache 2.4.51, php 7.4.26, win10) as shown below:

-- PHP Loaded Extensions
 With function get_loaded_extensions()

 bcmath        bz2           calendar      com_dotnet    Core          ctype        
 curl          date          **dom**           exif          fileinfo      filter       
 gd            gettext       gmp           hash          iconv         imap         
 intl          json          ldap          libxml        **mbstring**      mysqli       
 mysqlnd       openssl       pcre          PDO           pdo_mysql     pdo_sqlite   
 Phar          readline      Reflection    session       SimpleXML     soap         
 sockets       SPL           sqlite3       standard      tokenizer     xdebug       
 xml           xmlreader     xmlrpc        xmlwriter     xsl           Zend OPcache 
 zip           zlib         

Is there a use ... statement that would solve my (fatal) php problem/error?

What if you try this?

$dom = new \DOMDocument();

Thank for trying to help!

In Visual Studio Code I searched for the term “domDocument” in the GRAV plugins directory and found other plugins’ main php file with:

use domDocument;

above the class definition. Adding this to my main php page solved my problem.