$options = [ 'choices' => ['en' => 'English', 'fr' => 'French'], 'choice_options' => [ 'wrapper' => ['class' => 'choice-wrapper'], 'label_attr' => ['class' => 'label-class'], ], 'expanded' => true, 'multiple' => true ]; $this->plainForm->add('test', 'choice', $options); echo $this->plainForm->test->getName(); // test var_dump($this->plainForm->test->getOption('tmp.multipleBracesSet')); // Null $this->plainForm->modify('test', 'choice', [ 'rules' => 'required', ]); echo $this->plainForm->test->getName(); // test[] var_dump($this->plainForm->test->getOption('tmp.multipleBracesSet')); // true $this->plainForm->modify('test', 'choice', [ 'rules' => 'required', ]); echo $this->plainForm->test->getName(); // test var_dump($this->plainForm->test->getOption('tmp.multipleBracesSet')); // true