1.   But we hope that both sides in the presidential contest realize they are pushing the outside of the acceptability envelope.

2.   He will continue to fly World War II vintage aircraft and an ultralight he owns, but will no longer push the outside of that envelope in jets.

3.   There is a world of metaphoric difference between shoving a piece of stationery around and pushing the outside of a container from the inside.

4.   When a test pilot presses against those outer limits, he pushes the outside of the envelope.