=item MEMCACHED_CALLBACK_PREFIX_KEY
You can set a value which will be used to create a domain for your keys.
-The value specified here will be appended to each of your keys. The value can not
-be greater then MEMCACHED_PREFIX_KEY_MAX_SIZE and will reduce MEMCACHED_MAX_KEY by
+The value specified here will be prefixed to each of your keys. The value can not
+be greater then MEMCACHED_PREFIX_KEY_MAX_SIZE - 1 and will reduce MEMCACHED_MAX_KEY by
the value of your key. The prefix key is only applied to the primary key,
-not the master key.
+not the master key. MEMCACHED_FAILURE will be returned if no key is set. In the case
+of a key which is too long MEMCACHED_BAD_KEY_PROVIDED will be returned.
=item MEMCACHED_CALLBACK_USER_DATA