HTMLPurifier filter

Hi. I want to allow Iframe to be added in one table and dosnt want to uncheck “remove Xss” in advanced options.
Where do add this?
Tested to add this code:

$PurifierConfig = HTMLPurifier_Config::createDefault();
$PurifierConfig->set('Filter', 'HTML.SafeIframe', true);

in Global, All pages, Page_loading, result an error: “HTMLPurifier_Config’ not found”

You may try \HTMLPurifier_Config.

Thanks, helped me to solve the problem. This works:

    $PurifierConfig = \HTMLPurifier_Config::createDefault();
    $PurifierConfig->set('HTML.SafeIframe', true);
    $PurifierConfig->set('URI.SafeIframeRegexp', '%^https://(www.youtube.com/embed/|player.vimeo.com/video/)%');

Needed to add SafeIframeRegexp urls aswell and have the code in All pages, Global Code.