Quote - def CSBSurface(item):

Here's the meat. And no, I haven't seen formulas like this anywhere. I spent ages trying to get my head around your reflectionValue Blender node.  Your accompanying explanation pretty much covered what was happening here but questions remain.

There's two levels of inquiry, here. One: Python(Poser) programming. Creating classes is a new wrinkle, so I'll have to play with that for a bit to make sure I get it. You've covered that bit really well.
The other, more elusive aspect are your formulas... and for now I'm just going to accept them as is, without any discussion. It's like in my first class in nursing and the instructor asked: "Any questions?" and we looked at each other in bewilderment... no one had a clue, no one understood enough to even pose any questions.

I can ask programming questions. Formulas? Not yet. They are obviously the product of years and thousands of hours of experimentation and a profound knowledge of mathematics as it applies to (poser) functions.

This doesn't mean I don't want to know. I just don't want to ask for information I'm not ready to process yet.

= Blend((1 - .18 * EdgeBlend(1, 0, 1)) ** 30.8, 1, .03)
is not
= Diffuse(color, .85 * (1 - specular))
in terms of degree of complexity. I can get my head around what thought process led to the .85 value for diffuse: trial and error? and the (1 - specular) is brilliant and yet the logic is quite easy to follow.
That Blend for reflectionValue, though... I would never have thought to plug in an EdgeBlend into the input_1 channel. And upping that whole value to the power of 30.8???

What's equally important to me was having a more macro look at this script in terms of anti-gamma -> process -> gamma. I'll admit, Bill, I look at all these formulas with an ulterior motive: to apply the information you've provided in this shader to gamma-correcting - heck, or just plain-ol' correcting - existing shaders.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks