class Textarea

class Textarea extends FormElementBase {
  
  /**
   * {@inheritdoc}
   */
  public function getInfo() {
    return [
      '#input' => TRUE,
      '#cols' => 60,
      '#rows' => 5,
      '#resizable' => 'vertical',
      '#process' => [
        [
          static::class,
          'processAjaxForm',
        ],
        [
          static::class,
          'processGroup',
        ],
      ],
      '#pre_render' => [
        [
          static::class,
          'preRenderGroup',
        ],
        [
          static::class,
          'preRenderAttachments',
        ],
      ],
      '#theme' => 'textarea',
      '#theme_wrappers' => [
        'form_element',
      ],
    ];
  }
  
  /**
   * Adds the textarea resize library.
   */
  public static function preRenderAttachments($element) : array {
    $element['#attached']['library'][] = 'core/drupal.textarea-resize';
    return $element;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
    if ($input !== FALSE && $input !== NULL) {
      // This should be a string, but allow other scalars since they might be
      // valid input in programmatic form submissions.
      return is_scalar($input) ? (string) $input : '';
    }
    return NULL;
  }

}