PHP Class 'DOMDocument' not found
Sample error
1[Wed Jan 10 14:56:38.031846 2018] [:error] [pid 9378] [client 115.85.11.98:23443] PHP Fatal error: Class 'DOMDocument' not found in /var/www/sites/site.example.com/docroot/core/lib/Drupal/Component/Utility/Html.php on line 286
Solution:
See details in https://stackoverflow.com/questions/14395239/class-domdocument-not-found