Kirby3 feeds: location for collection

The CMS Questions
1

The readme says:

For the default (firehose) syndication feed, you need to ensure that you have a collection and have configured it.

<?php

return function ($site) {
    return $site->find('blog')->children()->listed()->flip();
};

Where do I have to put this code?

2

Into site/collections/name_of_collection.php

https://getkirby.com/docs/guide/templates/collections

3

My fault: I’ve misread collections for controllers – but now I learned something new. Great addition to Kirby 3 (I hope they weren’t in Kirby 2 already).

4

And thanks again – have some great eastern holidays.