add: struct icalproperty_impl *impl = (struct icalproperty_impl*)prop;
context: void icalproperty_add_parameters(struct icalproperty_impl *impl,va_list args){    void* vp;        while((vp = va_arg(args, void*)) != 0) {	if (icalvalue_isa_value(vp) != 0 ){	} else if (icalparameter_isa_parameter(vp) != 0 ){	    icalproperty_add_parameter((icalproperty*)impl,				       (icalparameter*)vp);	} else {	    assert(0);	}    }        }