How come that the developer exhausts quicker in shadow areas

Hi
How come that the following regarding water bath development is right. You can read it in the Darkroom Cookbook , on page 87.

The developing agent in the shadow areas will quickly exhaust, while the developing agent in the thinly exposed highlight areas will continue to work

How come that the developer exhausts quicker in shadow areas?

That sounds like it is for prints.

Yes , I forgot to say that.

The available developer on the print carried over into the waterbath exhausts because of the excessive amount of exposed silver available in the shadow areas to be developed (by so little developer). Opposite in the highlights...the carried over developer is enough to develop all silver exposed in the highlights (since there is not much exposed silver to develop).

What Vaughn says - some printers use the last 15 - 20 seconds before (and the first 15 - 20 seconds after) completion time (for me 2 minutes) to anticipate highlight density. You have to get use to it and have decent safelight illumination. It's not really Kosher ( strict time and temp approach is considered the best in terms of the craft of printing) but you can save a print now and then by watching highlights and pulling a bit early or leaving in a bit longer, if you learn to anticipate with a plain water stop bath.
I've been told that with modern emulsions (thinner), water bath technique doesn't get you much, paper or film.