Format of callback arguments in YAML files

For instance, for the Filter module, in filter.permissions.yml, custom permissions are defined:

permission_callbacks:
  - Drupal\filter\FilterPermissions::permissions

That looks like a static function, but it isn't. How does that work? Is the format for this kind of callback argument documented or defined anywhere?

I believe that this is a Symfony format. I can't find it in the documentation, but this talks about it https://symfonycasts.com/screencast/deep-dive/controller-setup

I found the code (or some code) in https://api.drupal.org/api/drupal/vendor%21symfony%21http-kernel%21Controller%21ControllerResolver.php/9.1.x

The Symfony Controller code explodes the string around the '::' into $class and $method and figures out if it's $classobject->$method() or $class::$method().

Documentation is here: https://api.drupal.org/api/drupal/core%21modules%21user%21src%21PermissionHandler.php/class/PermissionHandler/9.1.x

If your module needs to define dynamic permissions you can use the permission_callbacks key to declare a callable that will return an array of permissions, keyed by machine name. Each item in the array can contain the same keys as an entry in $module.permissions.yml.