Here on Meta, if you search for a tag, then click on one of the 'related tags', it gets added to the search. I was looking for that on Stack Overflow and it's not there, I gather it's an earlier version of the engine?
I would like to expand on the 'click a tag to add to the search' functionality. Some things that would be nice to do with the mouse are:
- remove a tag from the search
- add a tag as an 'or' in the search
- add a tag as an 'and' to part of the search expression
With a simple click, it's hard to imagine more functionality than there is here on Meta (i.e., click to add as an 'and', click a searched tag to search for that tag only, though for me it would make more sense to 'click to remove from the search').
There are other interface options (though some might argue certain ones are too complex..)
- put add/remove/'add as or' links in the hover popup
- use double clicks and/or dwell clicks
The hover popup seems a better idea to me, and it could be added to the current functionality on Meta without confusion.