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So we're rendering the same cube but this time the light path has to exclusively include all the light bouncing off of and through the rightWall object. So our result is a very green object since we captured just the green wall's bounce light. You can see now how to separate light paths to get what you need to adjust for later compositing. I'm rendering the tall rectangle and all the light that lands on it after leaving the green wall.

Of course I can also exclude just the green wall. Maybe the green wall is generating noise, I can avoid those light paths by using the caret and a simple tweak of my LPE

lpe:C<[RT][DS]'scatterCube'>+<[RT][DS][^'rightWall']>[<L.>O]


Shorthand
lpe:C<..'scatterCube'>+<..[^'rightWall']>[<L.>O]

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The Importance of Naming

Naming your channels is important not just for pipeline reasons and readability, but because the Denoiser utility requires that you follow a naming convention in order to be denoised. Since the tool isn't psychic, it needs a hint as to what is inside the framebuffer/AOV and it uses the name to decide this. There are two main ways the Denoiser filters results, and the way triggered by a "diffuse" keyword is that the albedo is divided out before denoising happens, this is done to prevent texture smearing. So when naming your AOVs, keep that in mind knowing that you'll most likely want your results to be denoised. Below are the acceptable prefixes given again.

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