Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Thu, 22 Dec 2022 02:51:32 +0100
>> From: Vincent Lefevre <vincent@vinc17.net>
>> 
>> 1. Open file.html with "emacs -Q file.html".
>> 2. Go to the end of the file.
>> 
>> In the paragraph starting with
>> 
>> <p>The first version of unums, formally known as Type I unum, was introduced in Gustafson's book <i>The End of Error</i> as a superset
>> 
>> everything from "'s book" is highlighted in a different color.
>
> HTML Mode evidently considers what follows the apostrophe to be a
> string.  Replacing the literal apostrophe with &#39; fixes the
> display.

I confirm Vincent observation:  HTML Mode behavior with quotes is
inconsistent.

Bug still present with 30.0.50 build from commit b9a910a701a.

I reproduced with emacs -Q and the files test.html and test_ko.html
attached to this message.

Note that removing random space charaters in the style element sometime
fix the problem.