Another way of saying: Allows the use of normal selection (ie. Tag Browser) within a restricted set of books.
I have a filter (saved Searches are also filters) to show only books I have not run past Flightcrew.
formats:"=EPUB" and not #ok_fc:true
Now I can use the Tag Browser.
In this case, lets set it to Show 'Sort By Popularity'
Now I Expand 'Series' and I see one of my favorite series is near the top of list, making it a priority candidate for Validation and touchup
You coud accomplish this with a hand generated, complex search... But Why