RE: C-x SPC : rectangle-mark-mode or gud-break?

[Drew Adams]

> I know I am opening up a can of worms here, but I am going to argue that
> `C-x SPC' be changed back to `gud-break'.

1. `gud-break' should never have been given a global binding on prefix
   `C-x'.  It is fine for it to have a binding on `gud-key-prefix', i.e.,
   `C-x C-a'.  Why does it need a global binding?  And if it really does,
   for some reason, why sacrifice such an important global prefix key as
   `C-x' for it?

2. `C-x SPC' should never have been given as a global key binding to
   `rectangle-mark-mode'.

`C-x SPC' should be left UNbound.  If and when a library or Emacs itself
binds `C-x SPC', there should be good reasons for that.  Other things
being equal, if bound, `C-x SPC' should be used as a prefix key, letting
users take advantage of `C-x SPC SPC SPC...' for a repeatable command.

There is no good reason (none) to bind `C-x SPC' to `rectangle-mark-mode'
in the global map.  That command should have been put on prefix key
`C-x r', like the other rectangle commands.  `C-x' is far too precious
to waste on this.

AFAICT, not one argument was ever given in favor of binding `C-x SPC'
to `rectangle-mark-mode'.  The only real support for it was this
non-argument from Eli: "`C-x SPC' is available", followed by "Why is
everybody ignoring the `C-x SPC' suggestion?"

And all objections to this binding, including the reasons given
against, were simply ignored.  The only replies to the objections were
messages in support of the objections - also ignored.

http://lists.gnu.org/archive/html/emacs-devel/2013-11/msg00046.html