Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / themes / classy / templates / views / views-view-mapping-test.html.twig

{#
/**
 * @file
 * Theme override for testing the mapping row style.
 *
 * Available variables:
 * - element: The view content.
 *
 * @see template_preprocess_views_view_mapping_test()
 */
#}
{{ element }}