Apple Color 1.0 - Manual (Page 169)

Chapter 9 Primary In 169
 If Limit Shadow Adjustments is turned off: Contrast adjustments with the shadows
slider are performed as a simple lift operation. The resulting correction uniformly
lightens or darkens the entire image, altering the shadows, midtones, and highlights
by the same amount. This can be seen most clearly when adjusting the black point of
a linear black-to-white gradient, which appears in the Waveform Monitor as a straight
diagonal slope. Notice how the entire slope of the gradient in the Waveform Monitor
moves up.
 If Limit Shadow Adjustments is turned on: The black point is raised, but the white
point remains at 100 percent. This means that when you make any adjustments with
the Shadow contrast slider, all midtones in the image are scaled between the new
black point and 100 percent. Notice how the top of the slope in the waveform
monitor stays in place while the black point changes.