Explanation: Debian <%= codename %>
Package: *
Pin: release o=Debian,n=<%= codename %>
Pin-Priority: 990

Explanation: Debian backports
Package: *
Pin: origin backports.debian.org
Pin-Priority: 200

Explanation: Debian wheezy
Package: *
Pin: release o=Debian,n=wheezy
Pin-Priority: 2

Explanation: Debian sid
Package: *
Pin: release o=Debian,n=sid
Pin-Priority: 1

Explanation: Debian fallback
Package: *
Pin: release o=Debian
Pin-Priority: -10