WordPress at a glance
function is not described

wp_admin_bar_header() WP 3.1.0

Style and scripts for the admin bar.

No Hooks.

Return

Nothing (null).

Usage

wp_admin_bar_header();

Code of wp admin bar header: wp-includes/admin-bar.php WP 5.2.2

<?php
function wp_admin_bar_header() {
	?>
<style type="text/css" media="print">#wpadminbar { display:none; }</style>
	<?php
}