Michal Sojka <sojkam1@fel.cvut.cz> writes:

> +    (when return-action (nconc args '(return-action)))
> +    (apply 'message-setup-1
> +	   ;; The following sexp is copied from `message-mail'

> +	   (nconc
> +	    `((To . ,(or to "")) (Subject . ,(or subject "")))

I missed this the first time, but I a bit worried about this used of
nconc. It seems to fall under "A common pitfall is to use a quoted
constant list as a non-last argument to ‘nconc’"  (from the elisp
manual).  In any case it's not really performance critical code (I
guess?) so maybe we could just use append?

The other use of nconc is more understandable to me.