bug#34975: 26.1.92; In backquote, the comma marker does not work with variable name started with dot

[Drew Adams]

> Yes, thanks.  I also found that post:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__lists.gnu.org_archive_html_emacs-2Ddevel_2012-
> 2D02_msg00330.html&d=DwIFAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=k
> I3P6ljGv6CTHIKju0jqInF6AOwMCYRDQUmqX22rJ98&m=CxM0DPMvIA0IaOjx7pLPUAWhhKla65XR
> UOtlWoUp1pM&s=3ooHHbORUe59GfFU53KZE6gD6KNQLvxSeAKZuHs8TT8&e=
> 
> The state is the same as back then: ,. is a reader macro in Emacs Lisp,
> but the head of the expansion (the symbol named ",.") doesn't have any
> semantics, even not in backquote.

You're right; I was wrong.  I thought it did what
,@ does (which it should, whether or not it has the
extra difference of behavior specified for CL).

What it does in Emacs Lisp is _completely_ wrong, IMO.

(setq c 42)         ; c = 42
(setq a `(b ,. c))  ; a = (b (\,\. c))