bug#51733: 27.1; Detect impossible email addresses better

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 51733@debbugs.gnu.org
> Date: Mon, 17 Jan 2022 16:53:49 +0100
> 
> I'm now looking at 5.3 Mixed-Number Detection:
> 
> d U+09EA ( ৪ ) BENGALI DIGIT FOUR can be confused with U+0038 ( 8 )
> DIGIT EIGHT.
> 
> Right, but they recommend implementing this by looking at the digit
> version of the character first...  but...  Does Emacs have a function to
> get the number value of ৪?

Yes, we do have that:

  (get-char-code-property ?৪ 'numeric-value) => 4

> They then recommend comparing the value with the zero value of that
> system, and I'm pretty sure we don't have that.

Why not? what do you need, exactly?