Re: keymap inheritance for non-sparse keymaps

[Richard Stallman]

    Because that mode (debug-mode) uses buttons now, so I wanted to use
    `button-buffer-map' as a parent keymap, which adds some common bindings
    for buffers that use buttons (currently only TAB and backtab).

I see your point, and if parents for non-sparse keymaps worked
that MIGHT be a good way to handle this.  (But maybe not, because
some of those keymaps might want other parents.)

But I think it is clean enough just to bind TAB and BACKTAB directly
in these keymaps.  You could make a subroutine to do it.
That is easy; changing what non-sparse keymaps do is hard.

We can't afford to spend time on generalizing non-sparse keymaps
when there are so many *important* things to do.