Is it correct to assume that placing an object in a file zones.d/<zone>/<file>.conf is equivalent to placing the same object elsewhere (in conf.d/<file>.conf say) and giving it an attribute zone = "<zone>"? And if this is true, which way has priority over the other? Thanks.
An empirical check suggests that placing an object inside zones.d/<zone> implicitly sets its zone attribute, and that if this is set explicitly to another zone that will have precedence (according to icinga2 object list).