When I select the application to appear on the furthest left, all the running apps that offer Split View open up in the right-hand side in a Mission Control-type view. You can then mouse over a window, and it will tell you whether that app supports Split View.
TextWrangler doesn't, which is annoying. It would be nice to have TW and Terminal on the screen. It would be nice to have one on top of the other (so that there's a top half and a bottom half, not a left half and a right half).