Issue #3370179 by fago, Wim Leers, borisson_, smustgrave: Clarify why...

   * {@inheritdoc}

   */

  public function getDataType() {

    // This object serves as data definition for field item lists, thus

    // the correct data type is 'list'. This is not to be confused with

    // the config schema type, 'field_config_base', which is used to

    // describe the schema of the configuration backing this objects.

    // @see \Drupal\Core\Field\FieldItemList

    // @see \Drupal\Core\TypedData\DataDefinitionInterface

    return 'list';

  }