Volume rendering presets

I’m trying to understand the values in the preset file used in Volume Rendering.
The preset file is found by searching “preset” in …Program Files/slicer…

For instance, why is there 5 values in gradientOpacity, and what are the different values?
Is there a transferfunction or shader that explains these settings?

Thanks in advance!

See specification of .vp file here. The page also describes how to specify custom volume rendering presets.