"Drew Adams" <drew.adams@oracle.com> writes:

> 1. Describe the parameter, INC.
>  
> 2. Describe the use of a prefix argument.
>  
> In general, describe this as a user command, from a user point of view,
> and not just as a function to be called from code.

See attached patch.

I enhanced the docstring and rewrote the command so that it does
not use a temporary keymap.  When I tried `C-x C-+' I was left with 
the `+' and `-' keys not usable anymore.

The patch also removes the redundant keybinding `C-x C-='.

And C-x C-0 does not allow adjusting further.  My feeling is that
it is not useful.

I'll apply this patch within a week if nobody is against it.