Symfony\Component\Form\CollectionField::configure PHP Method

    protected function configure()
    {
        $this->addOption('modifiable', false);

        if ($this->getOption('modifiable')) {
            $field = $this->newField('$$key$$', null);
            // TESTME
            $field->setRequired(false);
            $this->add($field);
        }

        parent::configure();
    }