Test pilots try to push the envelope.

试飞员试图把飞机开到极速.

It is what you can do to push the envelope.

就是你挑战极限的方式。

The question quickly becomes not how little to put in but how far to push the envelope.

但问题很快发生了变化，不再是插入的代码有多么少，而是革新的路能走多远。

Lorenzo? Well, he certainly likes to push the envelope, but he's also a loose cannon.

洛伦索？当然他不会墨守陈规，但是也不好管理。

When it comes to population density (the number of people per square mile), some cities really push the envelope.

当涉及到人口密度（每平方英里上的人数） ，一些城市真的要被挤爆了。

While some of the tests seem outlandish in hindsight, the military continues to push the envelope in seeking new warfare techniques based on cutting-edge science and technology.

而事后观之，其中一些测试其实非常古怪，非比寻常。军方持续推进这一进程，致力于找寻基于前沿科学技术的新型战争技术。

Decide whom to invite. Choose guests who will get along, but don't be afraid to push the envelope. Mix Democrats with Republicans, book-lovers with TV junkies, artists with tycoons.

决定邀请谁。选择容易相处的人，但是不要害怕越界。可以邀请民主党人，也可以邀请共和党人，书籍爱好者和电视爱好者，艺术家和商业巨头。