Source

File: wp-admin/includes/template.php

function iframe_footer() {
	/*
	 * We're going to hide any footer output on iFrame pages,
	 * but run the hooks anyway since they output JavaScript
	 * or other needed content.
	 */

	/**
	 * @global string $hook_suffix
	 */
	global $hook_suffix;
	?>
	<div class="hidden">
	<?php
	/** This action is documented in wp-admin/admin-footer.php */
	do_action( 'admin_footer', $hook_suffix );

	/** This action is documented in wp-admin/admin-footer.php */
	do_action( "admin_print_footer_scripts-{$hook_suffix}" ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores

	/** This action is documented in wp-admin/admin-footer.php */
	do_action( 'admin_print_footer_scripts' );
	?>
	</div>
<script type="text/javascript">if(typeof wpOnload=="function")wpOnload();</script>
</body>
</html>
	<?php
}