bug

<!-- language-all: lang-none --> hint doesn't seem to work anymore

This post has a <!-- language-all: lang-none --> hint at the top of the post to prevent all the code blocks in it from being highlighted. I tried changing lang-none to none and it still didn't work. (As you say in your post, Prettify identifiers will still continue to work even after the change.)

We were told at the time of the CommonMark migration that <!-- language-all: [language] --> hints would continue to be supported, unlike the <!-- language: [language] --> syntax which was being deprecated.

This issue seems to be specific to the lang-none and none hints as part of this style of HTML comment; other ones seem to be working fine. As an example, this post contains such a comment to indicate C as the highlighting language, and the below snippet is highlighted in C:

#include <stdio.h>

(To test, I also changed the comment to indicate Python and it highlighted the above as Python.)

It seems to work for individual code blocks, using the code fence notation (i.e. ```none and ```lang-none):

#include <stdio.h>

In summary: <!-- language-all: lang-none --> and <!-- language-all: none --> don't seem to work to disable syntax highlighting for a particular post.