In the main Cache article, you can see this example at the beginning:

# config/packages/cache.yaml
framework:
    cache:
        app: cache.adapter.filesystem
        system: cache.adapter.system

However, the cache.adapter.system is not documented anywhere (we document all the other adapters). So, is this something to be documented for end users or not? Is this something "special" or "internal" and should not be documented? Ping @nicolas-grekas Thanks!