LPE documentation - it is for Iray 3ds Max but should work in DS as well.

cgidesign

I found a good LPE documentation. It is for Iray in 3ds Max but the expressions should work in DS as well. If it has been posted already take this as a backup post ;-)

https://www.lightworkdesign.com/images/support/3dsMaxDocumentation/features/light-path-expressions.html

Richard Haseltine

There is documentation on nVidia's own site https://raytracing-docs.nvidia.com/iray/manual/index.html#reference#light-path-expressions

vectorinus

And there is an example of using this technology in Daz Studio       https://www.deviantart.com/linvanoak/journal/Iray-Light-Path-Expressions-in-DAZ-Studio-735776339

And some interesting historical discussion of this topic on the Daz forum in 2015   https://www.daz3d.com/forums/discussion/58695/anyone-using-lpe/p1

However, what a pity that there is no time to try all these wonderful tricks and effects. As Joe Cotter said: "...While I do have a programming background, I don't like to strain my brain more then I have to as I find it interferes with my creative side, only so many brain cells to go around at any one time. I know that's just me, but I'm guessing there are some out there who share this..."

I share this, Joe Cotter!