RE: C-x a C-x C-h

[Drew Adams]

> >> When I hit `C-x a C-x' in the latest Emacs, it awaits 
> further input,
> >> as if it was a prefix key sequence. However, `C-x a C-x 
> C-h' reveals
> >> that there are no commands bound to anything beginning with that
> >> prefix. Why?
> >
> > Good question. I wonder too. Same thing in Emacs 22, 21, and 20.
> > And C-x C-x C-x C-x C-x ... just keeps on keepin on.
> 
> That doesn't happen here, it only gets to `C-x a C-x C-x', after which
> any further keypresses will say the sequence undefined.

I wasn't quite right.

On Emacs 20 and 21, you can just keep repeating C-x forever, with no apparent
effect.

On Emac 22 and 23, it seems that C-x a C-x C-x C-x calls
`exchange-point-and-mark', and every other `C-x' after that calls it again. So
here too I can keep repeating C-x C-x..., but each such pair invokes
`exchange-point-and-mark'.