$compare_two_mode = is_numeric( $from );
  if ( ! $compare_two_mode ) {
    $found = array_search( $selected_revision_id, array_keys( $revisions ), true );
    if ( $found ) {
      $from = array_keys( array_slice( $revisions, $found - 1, 1, true ) );
      $from = reset( $from );
    } else {
      $from = 0;
    }
  }

  $from = absint( $from );

  $diffs = array(
    array(
      'id'     => $from . ':' . $selected_revision_id,
      'fields' => wp_get_revision_ui_diff( $post->ID, $from, $selected_revision_id ),
    ),
  );

  return array(
    'postId'         => $post->ID,
    'nonce'          => wp_create_nonce( 'revisions-ajax-nonce' ),
    'revisionData'   => array_values( $revisions ),
    'to'             => $selected_revision_id,
    'from'           => $from,
    'diffData'       => $diffs,
    'baseUrl'        => parse_url( admin_url( 'revision.php' ), PHP_URL_PATH ),
    'compareTwoMode' => absint( $compare_two_mode ), // Apparently booleans are not allowed.
    'revisionIds'    => array_keys( $revisions ),
  );
}