Re: TAB for non-editing modes

[Richard Stallman]

    If no truly useful Dired binding for `TAB' can be found now, then let's
    leave it alone - something will come up eventually.

I think that is wise.

    Similarly for other bindings that invoke commands that modify the buffer -
    why not bind them to `undefined'? I do that in read-only buffers such as
    *Buffer List*. Besides preventing the read-only error message, it prevents
    users from thinking that a key sequence might be unavailable for their own
    use.

suppress-keymap already does this with self-inserting commands.  Your
idea is to do this with the other normal commands that alter the text.

Doing this with kill commands would take away a feature: you can use
them in read-only buffers to copy text to the kill ring.  That feature
may not be very useful in read-only buffers, but I am not convinced it
is an improvement to make it entirely unavailable there.

Aside from that, I think it is more coherent for global
buffer-modifying commands to give errors "buffer read-only" in
read-only buffers, rather than acting as if they did not exist.

For TAB, which varies between modes anyway, making it undefined
might be good.