Source

File: wp-includes/rest-api.php

function rest_output_rsd() {
	$api_root = get_rest_url();

	if ( empty( $api_root ) ) {
		return;
	}
	?>
	<api name="WP-API" blogID="1" preferred="false" apiLink="<?php echo esc_url( $api_root ); ?>" />
	<?php
}