Rendering everything BEHIND a z-mask layer

Hi, Blender Artists–

In the render layers panel, mask layers are useful for hiding parts of a render layer that are behind the objects in the mask layer, but I have an effect that requires the reverse effect. I want to hide everything that is in front of the mask layer, and render everything behind it.

How can I make that happen?

You could look at the ‘Negate’ option in the Render / Layers

Hey, that works! Thanks, Richard!

I should have mentioned I was using cycles, though. How do I do that in Cycles?