Very nice contribution!
Your system to manage postprocessing remembers me a lot at the one sylex3 uses which is alright but a bit uncomfortable because you need to know the already taken numbers.
Having used sylex3 for some time as well as having seen quite some big but unflexible contributions, I am know working on a postprocessingpack for some time trying to avoid those mistakes. Having some problems with getting the average screenbrightness for hdr I am awaiting your solution

For transparancysupport for the DoF, the easiest and as I think the only real solution ist to simply use alphatesting.

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