code: private function addEditMultipleCommand(Contao2BackendViewDefinitionInterface $view)
      {
          $definition = $this->container->getBasicDefinition();
          // No actions allowed. Don't add the select command button.
          if (!$definition->isEditable() && !$definition->isDeletable() && !$definition->isCreatable()) {
              return;
          }
  
          $commands = $view->getGlobalCommands();
          $command  = new SelectCommand();
          $command
              ->setName('all')
              ->setLabel('MSC.all.0')
              ->setDescription('MSC.all.1');
  
          $parameters        = $command->getParameters();
          $parameters['act'] = 'select';
          $extra             = $command->getExtra();
          $extra['class']    = 'header_edit_all';
  
          $commands->addCommand($command);
      }
docs: Add the select command to the backend view definition.
  
  @param Contao2BackendViewDefinitionInterface $view The backend view definition.
  
  @return void