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

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

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

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