bug#44226: display-fill-column-indicator not ready for prime time

[積丹尼 Dan Jacobson]

emacs-version "27.1"
In 'GNU Emacs NEWS -- history of user-visible changes.'
I saw

;;  Customize the buffer-local user options 'display-fill-column-indicator'
;; and 'display-fill-column-indicator-character' to activate the
;; indicator.

Sounds great. I'm hyped!

Alas,
for my average file.txt
setting display-fill-column-indicator to t did nothing.

OK describe-variable display-fill-column-indicator leads to
(info "(emacs) Displaying Boundaries")
OK, starting over, maybe I need to change display-fill-column-indicator-
character
user-error: Value ‘|’ does not match type choice of 
display-fill-column-indicator-character
user-error: Value ‘x’ does not match type choice of 
display-fill-column-indicator-character

OK checking the docs it says

   display-fill-column-indicator-character is a variable defined in ‘C source 
code’.
   Its value is nil
   ^^^^^^^^^^^^^^^^
     Automatically becomes buffer-local when set.
     Calls these functions when changed: (#<subr set-buffer-redisplay>)
     This variable is safe as a file local variable if its value
     satisfies the predicate ‘(lambda (value) (or (characterp value) (null 
value)))’.
     You can customize this variable.


   This variable was introduced, or its default value was changed, in
   version 27.1 of Emacs.

   Documentation:
   Character to draw the indicator when ‘display-fill-column-indicator’ is 
non-nil.
   The default is U+2502 but a good alternative is (ascii 124)
   ^^^^^^^^^^^SO WHY IS IT STILL NIL?              ^^^^^^^^^^ ALSO SAY '|'
   if the font in fill-column-indicator face does not support Unicode 
characters.
   See Info node ‘Displaying Boundaries’ for details.

OK, let's try some more.
user-error: Value ‘U+2502’ does not match type choice of 
display-fill-column-indicator-character
user-error: Value ‘│’ does not match type choice of 
display-fill-column-indicator-character

Conclusion: why not, in the INFO manual, add a full example, of how to
get started with display-fill-column-indicator. In fact, say so, of what
to put in .emacs, to get it working globally.