Parameter for returning results. Default is transfer full.

The callback is valid until first called.

NULL is ok, both for passing and for returning.

This parameter is a 'user_data', for callbacks; many bindings can pass NULL here.

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 after the code is done.

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