Expanded class hierarchy of UserMailUnique in Drupal 9
- class \Drupal\Core\Validation\Plugin\Validation\Constraint\UniqueFieldConstraint extends \Symfony\Component\Validator\Constraint
- class \Drupal\aggregator\Plugin\Validation\Constraint\FeedTitleConstraint
- class \Drupal\aggregator\Plugin\Validation\Constraint\FeedUrlConstraint
- class \Drupal\user\Plugin\Validation\Constraint\UserMailUnique
- class \Drupal\user\Plugin\Validation\Constraint\UserNameUnique