Catching invisible edits: problem understanding doc

[Alain.Cochard@unistra.fr]

Hello.  The documentation (version 9.6) says:

   2.2.3 Catching invisible edits
   ------------------------------

   Sometimes you may inadvertently edit an invisible part of the
   buffer and be confused on what has been edited and how to undo the
   mistake.  Setting ‘org-fold-catch-invisible-edits’ to non-‘nil’
   helps preventing this.


I visit a new file.  I type

   * foo

then
   
   <RET>

then

   bar

Then I move the cursor one line up and press

   <TAB>

So now the headline is folded and I see

   * foo...

In my understanding, 'bar' is now in an invisible part of the buffer.
But whether org-fold-catch-invisible-edits is set to 'nil, 'error',
'show', 'show-and-error' or nothing (i.e., 'smart' by default in 9.6),
if then I do

   M-x undo

I visually see no change, but I can observe by unfolding the headline
that 'bar' has disappeared.  In my understanding of the documentation
above and of the docstring for org-fold-catch-invisible-edits, this
should only happen with 'nil'.

What am I understanding incorrectly?  Thank you.

Tests performed with 'emacs -Q -l .emacs.git' with '.emacs.git' being 

   (add-to-list 'load-path "~/Org/Coch-git/org-mode/lisp")
   (custom-set-variables
    '(org-fold-catch-invisible-edits 'nil)
    ;; or 'error or 'show or 'show-and-error (or nothing)
    )

giving:

   Org mode version 9.6.1 (release_9.6.1-239-g739ccf @
   /home/cochard/Org/Coch-git/org-mode/lisp/)

PS: a very minor incidental point: after 'bar' has disappeared, the
headline is then void, so I tend to say that the ellipsis should
immediately disappear as well.


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