This parameter is a 'user_data', for callbacks; many bindings can pass NULL here.
This symbol is a constructor, not a static method.
This parameter is a 'destroy_data', for callbacks.
Parameter for input and for returning results. Default is transfer full.
NULL may be passed as the value in, out, in-out; or as a return value.
NULL may be passed instead of a pointer to a location.
Parameter for returning results. Default is transfer full.
The callback is valid only during the call to the method.
The callback is valid until the GDestroyNotify argument is called.
The caller owns the data, and is responsible for free it.
The data is owned by the callee, which is responsible of freeing it.