public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $formats = explode(':', $this->getSetting('format'));
    $element += [
      '#type' => 'fieldset',
      '#attributes' => array('class' => ['container-inline', 'hms-field']),
    ];

    foreach ($formats as $format) {
      $element[$format] = [
        '#default_value' => isset($items[$delta]->value) ? $items[$delta]->value : NULL,
        '#format' => $format,
        '#type' => 'hms',
      ];
    }

    return array('value' => $element);
  }