> > Whatever implementation will be , it must define the events as elisp
> > functions ; even after the creation of a tab, there must be an event that
> > calls a lisp function.
>
> In http://bzr.sv.gnu.org/lh/emacs/x-tabs I added a new frame parameter
> `tab_bar_lines' that holds a keymap with items bound to Lisp functions.
>
>
I did the same.



> But now I tend to try side windows and atomic windows because
> frame-level features (like a frame parameter or native GTK tabs)
> are of no help for implementing per-window tabs.
>

That is also a possibility, but they must respond to events, too.