NULL is OK, both for passing and for returning.
Parameter points to an array of items.
This parameter is a 'user_data', for callbacks; many bindings can pass NULL here.
Generics and defining elements of containers and arrays.
The callback is valid until first called.
Exposed in C code, not necessarily available in other languages.
The caller owns the data container, but not the data inside it.
The caller owns the data, and is responsible for free it.
The data is owned by the callee, which is responsible of freeing it.
Override the parsed C type with given type.