private function appendProperForm(FormInterface $form, Definition $definition)
    {
        $identifier = $definition->getIdentifier();
        if ($form->has($identifier)) {
            return;
        }

        $type = sprintf('ekyna_%s_characteristic', $definition->getType());
        $options = array();
        if ($definition->getType() == 'choice') {
            $options['identifier'] = $identifier;
        }

        $parentData = null;
        if (null !== $this->parentDatas && null !== $characteristic = $this->parentDatas->findCharacteristicByIdentifier($identifier)) {
            $parentData = $characteristic->display($definition);
        }

        $form->add($identifier, $type, array_merge(array(
            'property_path' => '[' . $identifier . ']',
            'label' => $definition->getTitle(),
            'parent_data' => $parentData,
        ), $options));
    }