HARD-SPLICE

Hard-splice is destructive version of splice-unquote form expects one argument. Like splice-unquote or unquote, it is ignored if it appears outside of backquoted list. Under backquoted list it works just like splice-unquote, with the difference when the unquoted item evaluates to proper list. In that case the list is destructively spliced into the containing backquoted list. The splice-unqoute has the special character ,. (comma-dot).

>(setq b (list 'c 'd))   ; setting variable b to be list
(C D)                    ; this is it
 
>`(a ,.b e f) 
(A C D E F)              ;  list (C D) spliced-in
 
>b
(C D E F)                ; B now shares the E F tail