I have setup a custom layout that is a copy of the Perform layout but with the "document split view" button added so that I can toggle showing the songlist and lyrics or just lyrics. Is there a way to make the lyrics box adjustable so that if I am viewing just the lyrics box, it extends full screen left to right, but if I press the "document split view" button and display the songlist, the lyrics box would resize to fit the screen? Does this make sense?
It makes sense, but there's currently no way to move or resize the layout elements automatically when you resize the columns. What I would do is resize the lyrics to fit the full screen without the song list, then when the song list appears it will push the right side of the lyrics off the screen, but this shouldn't be a problem assuming you only want to see the song list long enough to select the next song.
If you add the Open Song List button to the Document Only layout instead of the Perform layout, the lyrics will already be sized this way.