WordPress at a glance
function is not described

rest_output_link_header() WP 4.4.0

Sends a Link header for the REST API.

No Hooks.

Return

Nothing (null).

Usage

rest_output_link_header();

Code of rest output link header: wp-includes/rest-api.php WP 5.2.1

<?php
function rest_output_link_header() {
	if ( headers_sent() ) {
		return;
	}

	$api_root = get_rest_url();

	if ( empty( $api_root ) ) {
		return;
	}

	header( 'Link: <' . esc_url_raw( $api_root ) . '>; rel="https://api.w.org/"', false );
}