Level missing in YAML for "Enable stale cache"

[xi-ao]

Issue in ./help/implementation-playbook/best-practices/planning/redis-service-configuration.md

Missign the frontend level in the given snippet.

INVALID (?):

stage:
  deploy:
    REDIS_BACKEND: '\Magento\Framework\Cache\Backend\RemoteSynchronizedCache'
    CACHE_CONFIGURATION:
      _merge: true
      default:
        backend_options:
          use_stale_cache: false
...

VALID:

stage:
  deploy:
    REDIS_BACKEND: '\Magento\Framework\Cache\Backend\RemoteSynchronizedCache'
    CACHE_CONFIGURATION:
      _merge: true
      frontend:                                   <-- here
        default:
          backend_options:
            use_stale_cache: false

Or maybe it means something else?