If you’re going to be doing any more than a little programming in nip2 you probably won’t want to use the built-in editor. I suggest you start your favorite editor in one window on the screen and then in the nip2 program window click File / Open Toolkit and check the Pin-up box in the file selector.
Now every time you want to try out your definition, save the file from your external editor and click OK in nip2’s file selector.
nip2’s editor automatically adds some semicolon characters to separate definitions in a file. If you’re using an external editor, you’ll need to put these in yourself. Also check the syntax for adding separators and column items to menus.