This is an old trick concerning sorting in reports and templates.
Let’s say your report uses an object prompt containing a number of attributes and you want the results to be ordered by those attributes. If you simply go to the ‘Advanced Sorting’ menu you will see that the attributes are not there, obviously because they are not part of the report itself.

Here comes the trick. Just add the attributes to the report, define the sorting and then remove them. Go again into the ‘Advanced Sorting’ menu and you will see that they are still there. Neat!

So now, when you execute the report and select your attributes from the object prompt in any combination, the Analytical Engine will know how to deal with them. Even if you play with the position of the attributes (rows, columns or page-by) the sorting options will be maintained.