get_header( string $name = null )

function get_header( $name = null ) {
	/**
	 * Fires before the header template file is loaded.
	 *
	 * @since WP-2.1.0
	 * @since WP-2.8.0 $name parameter added.
	 *
	 * @param string|null $name Name of the specific header file to use. null for the default header.
	 */
	do_action( 'get_header', $name );

	$templates = array();
	$name = (string) $name;
	if ( '' !== $name ) {
		$templates[] = "header-{$name}.php";
	}

	$templates[] = 'header.php';

	locate_template( $templates, true );
}