apt-pinning

pinning:
Test 1:
Package: php5-ps
Pin: release n=jessie
Pin-Priority: 20
Pin: release n=wheezy
Pin-Priority: 10
Pin: release n=squeeze
Pin-Priority: 1905

Test 2:
Package: php5-ps
Pin: release a=jessie
Pin-Priority: 20
Pin: release a=wheezy
Pin-Priority: 10
Pin: release a=squeeze
Pin-Priority: 1905

Test 3:
Package: php5-ps
Pin: release a=jessie
Pin-Priority: 20

Package: php5-ps
Pin: release a=wheezy
Pin-Priority: 10

Package: php5-ps
Pin: release a=squeeze
Pin-Priority: 1905

APT-CACHE POLICY OUTPUT:
php5-ps:
  Installed: (none)
  Candidate: 1.3.6-3+b1
  Package pin: 1.3.6-3+b1
  Version table:
     1.3.7-1+b1 1905
        500 http://debian.sil.at/debian/ jessie/main amd64 Packages
     1.3.7-1 1905
        500 http://debian.sil.at/debian/ wheezy/main amd64 Packages
     1.3.6-3+b1 1905
        500 http://debian.sil.at/debian/ squeeze/main amd64 Packages