Fatal error: Uncaught Error: Class "HTMLPurifier_AttrTransform" not found in /srv/www/htdocs/moodle/lib/htmlpurifier/HTMLPurifier/AttrTransform/Background.php:6 Stack trace: #0 {main} thrown in /srv/www/htdocs/moodle/lib/htmlpurifier/HTMLPurifier/AttrTransform/Background.php on line 6