debian pinning packages
Package: *
Pin: origin my.custom.repo.url
Pin-Priority: P
Package: *
Pin: origin packages.sury.org
Pin-Priority: 999
P > 1000
causes a version to be installed even if this constitutes a downgrade of the package
990 < P <=1000
causes a version to be installed even if it does not come from the target release, unless the installed version is more recent
500 < P <=990
causes a version to be installed unless there is a version available belonging to the target release or the installed version is more recent
100 < P <=500
causes a version to be installed unless there is a version available belonging to some other distribution or the installed version is more recent
0 < P <=100
causes a version to be installed only if there is no installed version of the package
P < 0
prevents the version from being installed