code: public function buildForm(FormBuilderInterface $builder, CustomField $customField)
      {
          $options =  $customField->getOptions();
  
          $type = ($options[self::MAX_LENGTH] < 256) ? 'text' 
                : 'textarea';
  
          $attrArray = array();
  
          if(array_key_exists(self::MULTIPLE_CF_INLINE, $options) and
              $options[self::MULTIPLE_CF_INLINE]) {
              $attrArray['class'] = 'multiple-cf-inline';   
          }
           
          $builder->add($customField->getSlug(), $type, array(
              'label' => $this->translatableStringHelper->localize($customField->getName()),
              'required' => false,
              'attr' => $attrArray
          ));
      }
docs: Create a form according to the maxLength option
  
  if maxLength < 256 THEN the form type is 'text'
  if not, THEN the form type is textarea
  
  @param FormBuilderInterface $builder
  @param CustomField $customField