Re: :alnum: broken?

[Paul Eggert]

On 2/28/20 12:09 AM, Eli Zaretskii wrote:
> I don't believe it is right for us to reject questionable but
> valid code.

That begs the question. The code is valid only if we continue to insist that it 
be valid, despite the clear drawbacks of doing so. Instead, we can easily change 
the definition of Emacs regular expressions so that the code is invalid. Since 
such code is invariably a mistake, it's a win to make such a change. That's what 
GNU grep has done for many years, and it works.

> I can even agree to reject this at
> run time under a non-default value of some special variable

That would be better than nothing, but it's not very good since most people 
won't know about the variable and thus will continue to suffer from these 
errors. Better would be to make the default reject these buggy regexps, which is 
what GNU grep does (it accepts the buggy regexps only if POSIXLY_CORRECT is set).