At this point, tweaking the shader is the least of my worries. Battling with syntax is.

What have I "learned"?... lights have gone on for a few things:

1. Naming a node function (like say an Add or Blend or ImageMap) in another node function will create that node and form a connection at the point the function was named. For example, in this statement,

s.Bump = Sub(ImageMap(Image_Source = "HeaFaceB.jpg", Background = Turbulence(.05,.05,.05,8,0,.5,.15)),.5) *.03

several nodes are created... a Math_Functions(Subtract) node, a imageMap node and a Turbulence node. There's a connection between the subtract node and the imageMap node because I named it in the Value_1 argument. I wanted a Turbulence node connecting to the Background channel on the imageMap node... the

Background = Turbulence(.05,.05,.05,8,0,.5,.15)),.5)

bit created the node, inserted the values into the channels of the Turbulence node, and formed the connection to the Background channel of the ImageMap node. All of these nodes are connected to the Bump channel on the PoserSurface node. Another thing I noticed was that whilst I was committed to naming each channel I was putting values into when I did start naming, I didn't have to name any I wasn't changing. In other words, in,

ImageMap(Image_Source = "HeaFaceB.jpg", Background = Turbulence(.05,.05,.05,8,0,.5,.15))

all I was changing was the Image_Source and Background channels... didn't have to do anything with any of the others.

Oh, and that .5?
Value_2 in the Subtract node.

And the * .03?
Assigns the desired value in the Bump channel of PoserSurface.

2. When Bill says once you name parameters, you need to keep naming them, he meant it. Not only for the rest of that node function, but for any embedded node functions as well! Found that out through a gazzillion error-compiles.

3. Oh, and I really like the .labelled("MyCoolNode") thingie you can tack on at the end of node definitions.

I do have some questions, but I think I'll have a re-read of the manual before asking them. This is starting to be fun again...

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