[Cache] Adding about marshallers

Author: Nyholm

components/cache.rst

@@ -192,6 +192,18 @@ Now you can create, retrieve, update and delete items using this cache pool::
 
 For a list of all of the supported adapters, see :doc:`/components/cache/cache_pools`.
 
+Serializing Data
+----------------
+
+When an item is stored in the cache, it is serialised to a string. It a class implementing
+:class:`Symfony\\Component\\Cache\\Marshaller\\MarshallerInterface` that is responsible
+for serializing and unserializing. Or to be technically correct: To ``marshall()``
+and to ``unmarshall()``.
+
+The :class:`Symfony\\Component\\Cache\\Marshaller\\DefaultMarshaller` is using PHP's
+``serialize()`` or ``igbinary_serialize()`` if the Igbinary extension is installed.
+There are other marshallers that will encrypt or compress the data before storing it.
+
 Advanced Usage
 --------------