git/Documentation/ref-reachability-filters.txt

When combining multiple `--contains` and `--no-contains` filters, only
references that contain at least one of the `--contains` commits and
contain none of the `--no-contains` commits are shown.

When combining multiple `--merged` and `--no-merged` filters, only
references that are reachable from at least one of the `--merged`
commits and from none of the `--no-merged` commits are shown.