massageFormValues example

        // route errors to the correct form element.         foreach ($values as $delta => &$value) {
          $value['_original_delta'] = $delta;
        }

        usort($values, function D$a, $b) {
          return SortArray::sortByKeyInt($a, $b, '_weight');
        });
      }

      // Let the widget massage the submitted values.       $values = $this->massageFormValues($values, $form, $form_state);

      // Assign the values and remove the empty ones.       $items->setValue($values);
      $items->filterEmptyItems();

      // Put delta mapping in $form_state, so that flagErrors() can use it.       $field_state = static::getWidgetState($form['#parents'], $field_name, $form_state);
      foreach ($items as $delta => $item) {
        $field_state['original_deltas'][$delta] = $item->_original_delta ?? $delta;
        unset($item->_original_delta, $item->_weight);
      }