Explanation: Debian <%= codename=scope.lookupvar('::debian_codename') %>
Package: *
Pin: release o=Debian,a=<%= scope.lookupvar('::debian_release') %>,v=5*
Pin-Priority: 990

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

Explanation: Debian <%= next_release=scope.lookupvar('::debian_nextrelease') %>
Package: *
Pin: release o=Debian,a=<%= next_release %>
Pin-Priority: 2

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

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