Re: 'M-o' ('facemap-keymap') has now been removed until March 10th 2021

["Paul W. Rankin" via "Emacs development discussions." <emacs-devel@gnu.org>]

> On 24 Mar 2021, at 10:12 pm, Gregory Heytings <gregory@heytings.org> wrote:
> 
> 
>>> Does it?  AFAICS, font-lock-unfontify-region does not "remove _all_ text properties", it uses remove-list-of-text-properties, which "removes _some_ properties from text", namely those of font-lock-mode.
>> 
>> Sure, you're right that it does not remove *all* text properties per se. It removes, let's say, "all that it can" which is more than "all that is intended".
>> 
> 
> Please provide a recipe to demonstrate when this actually matters.

Programs should do what they're intended to.

>>> It allows you to toggle font-lock-mode correctly, which M-x font-lock-mode can't do.  Try the following: emacs -Q, unless, M-., M-h, M-w, C-x b RET, M-x text-mode, C-y, M-x font-lock-mode.
>> 
>> This is again correct behaviour.  When you yank the defun from an emacs-lisp-mode buffer into a text-mode buffer, you're inserting text with (most of) its text properties, except for the property `(fontified . t)' because within the context of *this* buffer, the text properties have not been applied with font-lock-mode and so this would be false and prevent font-lock from doing its work.
>> 
> 
> This is not the problem here.  The problem is that M-x font-lock-mode (last part of the recipe) is supposed to turn font-lock-mode off, yet the font-lock-mode fontification remains.

I have quite fully explained how that is not the case as per your examples. The "font-lock-mode fontification" does not remain, only text properties that are not added by font-lock remain, and as such why should turning off font-lock remove these? As previously noted, you are confusing text properties and font-lock. Font-lock is only one method to manipulate text properties.

Please read the Elisp Info manual chapters on Font Lock and Text Properties.