Issue #2820580 by anavarre, hardikpandya, Wim Leers, Berdir, cilefen: Drupal >=8.2.x doesn't allow to override all cache bins with $settings['cache']['default'] anymore, documentation says otherwise

core/core.api.php

@@ -584,9 +584,10 @@
  *
  * @section configuration Configuration
  *
- * By default cached data is stored in the database. This can be configured
- * though so that all cached data, or that of an individual cache bin, uses a
- * different cache backend, such as APCu or Memcache, for storage.
+ * By default, cached data is stored in the database. However, Drupal can be
+ * configured to use a different backend (specified in their service
+ * definition), e.g. APCu or Memcache. This configuration can nominate a
+ * different backend for all cached data or for specific cache bins.
  *
  * In a settings.php file, you can override the service used for a particular
  * cache bin. For example, if your service implementation of

core/lib/Drupal/Core/Cache/CacheFactory.php

@@ -23,11 +23,11 @@ class CacheFactory implements CacheFactoryInterface, ContainerAwareInterface {
   /**
    * A map of cache bin to default cache backend service name.
    *
-   * All mappings in $settings takes precedence over this, but this can be used
-   * to optimize cache storage for a Drupal installation without cache
-   * customizations in settings.php. For example, this can be used to map the
-   * 'bootstrap' bin to 'cache.backend.chainedfast', while allowing other bins
-   * to fall back to the global default of 'cache.backend.database'.
+   * All bin-specific mappings in $settings take precedence over this, but it
+   * can be used to optimize cache storage for a Drupal installation without
+   * cache customizations in settings.php. For example, this can be used to map
+   * the 'bootstrap' bin to 'cache.backend.chainedfast', while allowing other
+   * bins to fall back to the global default of 'cache.backend.database'.
    *
    * @var array
    */