[d.r.l]

Originally Posted by chaley

Click the top level tag until you see the two plus signs. For a hierarchical item the order is

1. One plus sign: search for books with this tag
2. Two plus signs: search for this tag and all its children
3. One minus sign: search for everything except this tag
4. Two minus signs: search for everything except this tag and all its children

Thanks for clarifying that, I do feel silly not having found it myself!