"1 Preliminary Note
I'm using a Debian Lenny (stable) system here. I will explain
apt-pinning on the basis of the package phpmyadmin which is
available in three different versions in the stable, testing, and
unstable repositories (at the time of this writing) - see
lenny (stable): version 4:18.104.22.168-5
squeeze (testing): version 4:3.1.2-2
sid (unstable): version 4:3.1.3-1"