- * backends for local hash array and SQL table included:
- * @code
- * $bag = new HashBagOStuff();
- * $bag = new SqlBagOStuff(); # connect to db first
- * @endcode
+ * This interface is intended to be more or less compatible with the PHP memcached client.
+ *
+ * Instances of this class should be created with an intended access scope, such as:
+ * - a) A single PHP thread on a server (e.g. stored in a PHP variable)
+ * - b) A single application server (e.g. stored in APC or sqlite)
+ * - c) All application servers in datacenter (e.g. stored in memcached or mysql)
+ * - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
+ *
+ * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
+ * should make sure the configuration for those factory methods matches their access scope.
+ * BagOStuff subclasses have widely varying levels of support for replication features.
+ *
+ * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
+ * should semantically operate over its entire access scope; any nodes/threads in that scope
+ * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
+ * from one node in its access scope should reflect the prior changes of any other node its access
+ * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.