code: public function handle(GetPropertyOptionsEvent $event)
      {
          if (('tl_metamodel_dca' !== $event->getEnvironment()->getDataDefinition()->getName())
              || ('backendsection' !== $event->getPropertyName())) {
              return;
          }
  
          $event->setOptions(array_keys($GLOBALS['BE_MOD']));
      }
docs: Retrieve a list of all backend sections, like "content", "system" etc.
  
  @param GetPropertyOptionsEvent $event The event.
  
  @return void
  
  @SuppressWarnings(PHPMD.Superglobals)
  @SuppressWarnings(PHPMD.CamelCaseVariableName)