Attaching modified patch.  Patch is generated against revno: 109935.

>> Once patch goes through, I will submit a second part which updates
>> regs.texi.
>
> I think the change is OK.  I would prefer a single `cond' form with the
> `error' in the last branch (instead of unless+if) so as to avoid
> a redundant `numberp' check (not as a matter of efficiency, of course,
> but maintenance).
> If you send such an updated patch with the corresponding regs.texi
> change, we'll install it.

Done.

>> I usually to use M-x append-to-register (and with this patch `C-x r +')
>> to collect sexps.  I think it will be convenient to have the collected
>> snippets separated by a suitable separator. Is it OK if a default "\n"
>> be used? WDYT.
>
> I think I'd rather not add any separator by default.  

> In many cases adding such a separator would render the command
> inconvenient, and in many others the user can easily make sure the
> text he appends includes an appropriate separator.

> I can see cases where adding a separator could be handy, but I'm not
> sure hardcoding "\n" would solve enough of those cases.  

> Maybe you could prompt for a separator if the user provided a C-u
> prefix?

Prefix is used as a `delete-flag' already ...

I have introduced an extra indirection via a `separator-register' (which
is nil by default) Now what gets used as a separator - a newline, a
double newline, a comma or a tab - is under user control.

There is already one user - that is me - who will find this feature
useful.