Render only a small region?

Hello, I can’t seem to remember how I render just a small region of the image instead of the whole frame. How do I do this?

It is a little confusing if you used to shift+p in 2.49.
Now it is shift+b but it only works in camera-view.

Also don’t forget shift+F can be used while in camera view to move around, so you can use that in conjunction with shift + b to get those test renders…

Cool Thanks! this is going to save me lots of time!