public function ElementsByRelation(string $relationName)
    {
        $filter = [ 'RelationName' => $relationName ];
        if (
            $this->owner->hasExtension(ElementBase::FLUENT_CLASS)
            && !is_a(Controller::curr(), LeftAndMain::class)
        ) {
            $filter['Visible'] = true;
        }

        return $this->owner
            ->Elements()
            ->filter($filter)
        ;
    }