出口门同理可知，因为它是一个返回消息，连接从一个生命线到图的框架，箭头连接框架。
The exit gate is known, because it's a return message that is connected from a lifeline to the diagram's frame with the arrowhead connected to the frame.
一个门只是一个消息，图形表示为一端连接序列图的框架边缘，另一端连接到生命线。
A gate is merely a message that is illustrated with one end connected to the sequence diagram's frame's edge and the other end connected to a lifeline.
Rails构建于一门优秀语言（Ruby）和坚实的相关配套设施之上，是一个强大的web框架。
Rails is a strong web framework, built on an excellent language (Ruby), and surrounded by a solid ecosystem.
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