When I first installed foobar2000 years ago, there was a feature I really liked - one of the playlist tabs reflected live whatever is selected in the Album List panel. For example, if you clicked on "Radiohead" in the album list, this playlist would automatically contain all Radiohead songs. If you clicked one of the album sub-trees of Radiohead, the playlist would update to show just the songs from that album.
Also, if you type a phrase in the Filter box below the Album List, you can make the playlist automatically contain all the tracks that match.
I'm not sure when this playlist feature disappeared, but I have since reinstalled foobar2000 a few times and I can't get the feature back. I've tried Googling but I'm not sure what the feature was called.
Update: I found the setting, thanks to searching terms provided by afrazier. It is called Library viewer selection playlist (which is in Preferences: Media Library).