The Empty node is basically a placeholder that does nothing.
Empty节点其实是一个占位符，它什么都不做。
A query node is a placeholder for a candidate object, a constraint decides whether to add or exclude candidates from the result.
每个查询节点都是一个存放候选对象的地方，每个约束则标识了是否从结果集中添加还是排除候选者。
A query node is a placeholder for a candidate object, a constraint decides whether to add or exclude candidates from the result.
每个查询节点都是一个存放候选对象的地方，每个约束则标识了是否从结果集中添加还是排除候选者。
应用推荐