Parameter for returning results. Default is transfer full.

NULL is ok, both for passing and for returning.

Don't free data after the code is done.

Parameter points to an array of items.

Generics and defining elements of containers and arrays.

Free data container after the code is done.

Parameter for input. Default is transfer none.

Free data after the code is done.

The callback is valid only during the call to the method.

Typed errors. Similar to throws in Java.