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Being able to tag games with whatever attribute I want is great, but it would be even better if I could use that tag system with the library search.
Can you be more specific? If you just want to see the games with a specific tag, hit "All Games" in the sidebar, then click "Filter" at the top and then "Tags" and your selected tag. That will show only the games with that tag. And if you want quick access to that in the future, hit the bookmark button in the top right and it will save that filter to the sidebar (this works with any filter or combination thereof, not just tags).