APT 3.1.x introduces a new behavior versioning mechanism, providing primarily stable command-line interfaces for scripting.
The CLI version can be specified using --cli-version A[.B][.C].
If the B component is missing, the highest even B currently supported is selected. For example, --cli-version 3 will select 3.2 but not 3.3 in APT 3.3.x, as odd versions are development series.
If the C component is missing, all possible values are allowed.