Pin, Pin-Priority, and Tracking

["Paul E Condon,,," <pecondon@quiknet.com>]

I recently dist-upgraded to Woody, using a script by Osamu Aoki. It took 
many hours over ppp,
but it worked. Thanks, Osamu!

And he is right in saying the install of Woody is too easy. Beyond 
stumbling onto his post telling about his script very little was 
required of me. But now a question:

Part of the upgrade was, of course, upgrading apt-get and dpkg. The 
script installed a file
/etc/apt/preferences which had not been there before and gave some brief 
instructions about
something called "tracking". I'm guessing this new stuff has something 
to do with keeping
track of stable, testing, and unstable all at once. What does this stuff 
really do? How does it
work? Where do I look to find out?

Thanks,

Paul