The trick is to allocate a node for each object.

技巧是为每一个对象分配一个节点。

youdao

So long as the operands are both already sorted into document order, this avoids the need to allocate memory for the intermediate node sets.

只要已经按文档顺序排序了这两个操作数，就不必为中间节点集分配内存。

youdao