Each time you have a search result you see a TAG's line at the bottom of the screen (some of these TAGs might be selected).  The GREY color means it is selected.

In general when we get a search result, we also show all TAGs attached to the search set at the bottom of the screen. We are selecting one Tag in case ALL records belong to one of the TAGs listed.

Let's give you an example. Imagine we are looking for 'London', so we enter it in a search window, then hit SEARCH. We got 5 results, all of those contain 'London' inside, two of them attached to 'MAP' tag and three to 'MAP' and 'SUBWAY' tags, so we will see both MAP and SUBWAY at the bottom.

If we click MAP, nothing will be changed since all results belong to MAP, but if we click SUBWAY, only last three resords will stay on the screen.

It sounds a little bit complex but once you understand the general idea you will like it, it is quite natural.