code: public function classNamesBySeverity(Issue\IssueSeverity $severity)
      {
          $this->typeCheck->classNamesBySeverity(func_get_args());
  
          $classNames = array();
          foreach ($this->issuesBySeverity($severity) as $issue) {
              if (
                  $issue instanceof Issue\ClassRelatedIssueInterface &&
                  !in_array(
                      $issue->classDefinition()->className(),
                      $classNames
                  )
              ) {
                  $classNames[] = $issue->classDefinition()->className();
              }
          }
          sort($classNames, SORT_STRING);
  
          return $classNames;
      }
docs: @param Issue\IssueSeverity $severity
  
  @return array<ClassName>