Key operations in the control lifecycle are wrapped by a pair of events, one firing before the operation takes place and one firing immediately after the operation has completed.
控件生命周期中的关键操作被包装在一对事件中，一个在操作发生前触发，另一个在操作完成后立即触发。
2
We want the client to be able to just place the order and continue with other work, so the operation is one-way.
我们只要求客户端能提供订单，然后执行其他工作，因此该操作是单向的。
3
Most instructions have one or more operands, specifying the source values to references in performing an operation and the destination location into which to place result.