"Uncaught ReflectionException: Class DOMDocument does not exist" error On Ubuntu 16.04, I installed Drush using Composer: composer global require drush/drush:~8. Installation succeeded, but running drush --version, I got this error:


  PHP Fatal error:  Uncaught ReflectionException: Class DOMDocument does
  not exist in
  /.../composer/vendor/consolidation/output-formatters/src/Transformations/DomToArraySimplifier.php:24


What do I do now?
DOMDocument is included in the extension php-xml.  To install it on ubuntu, run:

sudo apt-get install php-xml