+memcached_fetch_execute() is a callback function for result sets. Instead
+of returning the results to you for processing, it passes each of the
+result sets to the list of functions you provide. It passes to the function
+a memcached_st that can be cloned for use in the called function (it can not
+be used directly). It also passes a result set which does not need to be freed.
+Finally it passes a "context". This is just a pointer to a memory reference
+you supply the calling function. Currently only one value is being passed
+to each function call. In the future there will be an option to allow this
+to be an array.
+
+memcached_get_by_key() and memcached_mget_by_key() behave in a similar nature
+as memcached_get() and memcached_mget(). The difference is that they take
+a master key that is used for determining which server an object was stored
+if key partitioning was used for storage.
+
+All of the above functions are not supported when the C<MEMCACHED_BEHAVIOR_USE_UDP>
+has been set. Executing any of these functions with this behavior on will result in
+C<MEMCACHED_NOT_SUPPORTED> being returned or, for those functions which do not return
+a C<memcached_return>, the error function parameter will be set to
+C<MEMCACHED_NOT_SUPPORTED>.
+