A good rule of thumb for this could be: if you can define an “operator” overload for something, then it is an operator and should be fontified as such.

Some examples:

1. `&&` or `and`, can define `operator &&()` or `operator and()` -> operator face.
2. `and_eq` or `&=`, can operator &=()` or `operator and_eq()` -> operator face.
3. `for`, cannot define `operator for()` -> keyword face.
4. `while`, cannot define `operator while()` -> keyword face. 

Just my pair of pennies...

Best Regards,

Jacob Faibussowitsch
(Jacob Fai - booss - oh - vitch)

> On Jan 8, 2025, at 7:49 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Tue, 7 Jan 2025 19:09:40 -0800
>> Cc: Jacob Faibussowitsch <jacob.fai@gmail.com>,
>> 75226@debbugs.gnu.org
>> 
>> I found that both c++-mode and c++-ts-mode fontifies C++ alternative operators like and_eq, xor, etc as keywords. Maybe we should fontify them in operator face (added in Emacs 29) instead?
> 
> What do other editors do?
> 
> Alan, WDYT about this?