I find all of the explanations really fuzzy. Does it distinguish between edges and structure, or is it merely some midfrequency/highfrequency tilt parameter of the "gaussian"?
It's fuzzy, a bit of a blur, indeed. Since it's proprietary, we'll never know exactly, but at 0 it's supposedly a form of USM sharpening, and at 100 it's a form of deconvolution sharpening (I'm not sure if it's based on a Gaussian PSF shape, or something more disc shaped). In between 0 and 100 it's a sort of mix between USM and Deconvolution.