How to use multiple simultaneous depth units?

I want do depth peeling as Interactive Order-Independent Transparency says.But it says “imagine that OpenGL supported multiple simultaneous depth units”.Does OpenGL offer the function like multiple simultaneous depth units?If not,how to do depth peeling in a simple way by OpenGL?
Thanks!

You have already posted this question in the openGL basic forum.

Please do not cross-post!

First, you asked this question in another thread.

Second, I don’t understand what confuses you about the statement “imagine that OpenGL supported multiple simultaneous depth units.” If the paper has to ask you to imagine it, then odds are good that it isn’t true, right? If it were true, wouldn’t it make more sense to just say, “OpenGL supports multiple simultaneous depth units,” as well as explain how to use that feature? But the paper doesn’t; it talks about using depth comparisons and alpha tests.

If not,how to do depth peeling in a simple way by OpenGL?

Why don’t you read past page 4 of the paper (that has the quote you mentioned)? I downloaded the paper, and it seems quite thorough in explaining how to do depth peeling. Now granted, it sets things up in terms of the horrible “texture shaders” of the GeForce 3 days, but the technique would be easily adaptable to modern shaders today.