I am really confused. I have read that the back button 

* [calls onDestroy()](https://stackoverflow.com/questions/6848260/android-does-not-destroy-data-on-back-button/6848302#6848302)
* [can close up your currently-running activity](https://stackoverflow.com/questions/2033914/quitting-an-application-is-that-frowned-upon/2034238#2034238)
* [calls onPause()](https://stackoverflow.com/q/5267250/194894)

I think onPause() should be right. But this is an side effect, because the Activity gets into the background. I found nothing [in the docs.](http://developer.android.com/reference/android/app/Activity.html) But maybe I have overlooked something.

Can someone please explain to me what the back button is supposed to do programmatically? Some references would also be nice. :-)