In VIM, I want to split a window in two parts where first one is the regular editor, and the second one is just read-only window for some auxiliary information.
The user should not be allowed to access (focus) the read-only window. Can I set that somehow?
set nomodifiable is helpful but it is not what I meant - I still can access the window.
Edit
Usually the preview window is used for auxiliary information, e.g. insert-mode completion can show additional information there. You can :pedit a scratch buffer, and show your information there.
I don't follow your requirement of not allowing to move into that window. That's not very Vim-like. You can disallow (accidental) editing with :setlocal nomodifiable, but why not allow the user to interact with the window?! (Some operations like resizing are way easier or only possible when you're inside the window.)
If the amount of information is small and only needs to be displayed for a short time, and you're in GVIM, you can also use tooltip popups via 'balloonexpr'.
