Clerk: Single or return?

职员：单程票还是来回票？

Single or return fare?

单程票还是往返票？

Single or return?

单程票还是来回票？

A single method on the facade interface can execute one or more command objects, so the facade input parameters and the method return value need to be well chosen.

在facade接口中一个单独的方法可以执行一个或多个command对象，因此facade输入参数和方法返回值需要进行很好的选择。

You use it when you know the XPath expression will only return a single node or you don't want more than one node.

只有知道XPath表达式只返回一个节点或者只需要一个节点时才使用它。