drupal/core/modules/big_pipe/templates/big-pipe-interface-preview.html.twig

{#
/**
 * @file
 * Default theme implementation for a BigPipe JS placeholder interface preview.
 *
 * @see \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy::createBigPipeJsPlaceholder()
 */
#}
{{ preview }}