bug#51733: 27.1; Detect impossible email addresses better

[Lars Ingebrigtsen]

I'm looking at the Confusable section now. 

https://www.unicode.org/reports/tr39/#Confusable_Detection

Looks easy enough to implement (and the ELPA package already does the
parsing, so I'll be reusing bits from that).

But...  I'm wondering what the higher level interface would be?  I mean,
quite a lot of strings are confusable with something else, but which
ones are interesting?  The only thing that seems immediately interesting
to check for is whether a string is confusable with ASCII?

That is,

(textsec-confusable-with-ascii-p "C𝗂𝗋𝖼𝗅𝖾")
=> t

Because the ASCII characters are the ones that people rely on when doing
... things, like email and browsing the web.

But I mean, "C𝗂𝗋𝖼𝗅𝖾" is confusable with "СігсӀе" (the latter is
Cyrillic), and if you're writing Russian, that might also be
interesting.  So perhaps a 

(textsec-confusable-with-script-p "C𝗂𝗋𝖼𝗅𝖾" 'cyrillic)
=> t

?  But...  I'm not sure in which contexts that would actually be vital
to know.  Hm.

Anybody have any thoughts here?  

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no