Doing this enables us to use a mediation to apply optional messaging processing, such as filtering the message content or routing to a different destination, just to name a few.

它可以使我们使用中介来应用可选的消息传递的处理，比如过滤消息内容或者路由到其它不同的目的地，仅仅是命名几个而已。

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The optional match section of the iptables command specifies the characteristics that a packet should have to match the rule, such as source and destination address, protocol, etc.

iptables 命令的可选 match 部分指定信息包与规则匹配所应具有的特征（如源和目的地地址、协议等）。

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Life is like a curve, starting point and the destination are not optional, but countless opportunities are between starting point and destination.

人生好似一条曲线，起点和终点是无可选择的，而起点和终点之间充满著无数个选择的机会。

youdao

On the road: Optional City Navigator mapping provides detailed street maps, millions of preloaded points of interest and onscreen turn-by-turn directions to your destination, and an optional Auto Nav kit adds a suction mount and car charger.

ENGADGET: Four new Oregon touchscreen GPS devices pop up on Garmin's website (updated)