I'm working on an application where tags are structures hierarchically - so while the list of tags is organized as a tree (just like categories), the items can appear under several such tags.
The users should be able to search using the tags - what's the best way to do that? One of the challenges I could think of is that since an item can have several tags, users may want to use and/or search to locate items which have both tags or items which have either one. I also don't want this to look like a query builder or a tag cloud (tag popularity is irrelevant).
Do you know of any good examples?