In the search categories selection you can show all categories. Then you select one category and it produces a list of all stories in that category. It would be great if you could specify more than one category and find a list of all stories with the categories you specified.
You are not limited to a single category selection, you can select multiple categories within a group and across groups. The stories returned will have all the category tags you've selected.
This is true for free members (which I am). Premier members have the option to exclude tags from the search.