Added the explanation of the "version" argument

components/cache/cache_pools.rst

@@ -74,7 +74,10 @@ degrade performance significantly::
  $namespace = '',
  // in seconds; applied to cache items that don't define their own lifetime
  // 0 means to store the cache items indefinitely (i.e. until the APC memory is deleted)
- $defaultLifetime = 0
+ $defaultLifetime = 0,
+ // if present, this string is added to the namespace to simplify the
+ // invalidation of the entire cache (e.g. when deploying the application)
+ $version = null
  );
 
 Redis Cache Adapter