Correctly document the format of tabulated-list-groups

* lisp/emacs-lisp/tabulated-list.el (tabulated-list-groups):
Correct format in doc string (bug#79220).

* doc/lispref/modes.texi (Tabulated List Mode):
Correct format in manual.

doc/lispref/modes.texi

@@ -1289,10 +1289,11 @@ the Tabulated List buffer.  Its value should be either a list or a
 function.
 
 If the value is a list, each list element corresponds to one group, and
-should have the form @w{@code{(@var{group-name} @var{entries})}}, where
+should have the form
+@w{@code{(@var{group-name} @var{entry1} @var{entry2} @dots{})}}, where
 @var{group-name} is a string inserted before all group entries, and
-@var{entries} have the same format as @code{tabulated-list-entries}
-(see above).
+@var{entry1}, @var{entry2} and so on each have the same format as an
+element of @code{tabulated-list-entries} (see above).
 
 Otherwise, the value should be a function which returns a list of the
 above form when called with no arguments.

lisp/emacs-lisp/tabulated-list.el

@@ -142,13 +142,14 @@ arguments and must return a list of the above form.")
 (defvar-local tabulated-list-groups nil
   "Groups displayed in the current Tabulated List buffer.
 This should be either a function, or a list.
-If a list, each element has the form (GROUP-NAME ENTRIES),
+If a list, each element has the form (GROUP-NAME ENTRY1 ENTRY2 ...),
 where:
 
  - GROUP-NAME is a group name as a string, which is displayed
    at the top line of each group.
 
- - ENTRIES is a list described in `tabulated-list-entries'.
+ - ENTRY1, ENTRY2 and so on each have the same format as an element
+   of `tabulated-list-entries'.
 
 If `tabulated-list-groups' is a function, it is called with no
 arguments and must return a list of the above form.")