Different Bidirectional Character Types

[Eli Zaretskii]

> Date: Sat, 02 Jul 2022 11:22:09 +0000
> From: Andreas Prilop via Unicode <unicode at corp.unicode.org>
> 
> On 2 July 2022, Eli Zaretskii wrote:
> 
> > I think a simpler answer is that Arabic letters (bidi class AL) in
> > some cases make European Numbers (EN) behave like Arabic Numbers (AN);
> > see rule W2 of UAX#9. And Arabic Numbers then affect how other "weak"
> > characters are reordered, see W6.
> 
> My question was: Why?
> 
> http://google.com/search?q=555-2368+%22%D7%A8%D7%95%D7%A7%D7%A4%D7%95%D7%A8%D7%93%22&filter=0
> displays the number “555-2368”.
> 
> http://google.com/search?q=555-2368+%22%D8%B1%D9%88%D9%83%D9%81%D9%88%D8%B1%D8%AF%22&filter=0
> displays the number “2368-555”.
> 
> Why this difference?
> 
> And why are Arabic-Indic digits (U+0660 …) and Persian digits (U+06F0 …)
> treated differently?

Because the expected order on display is different.

The expected order differs because the way different script are
written differs, the reasons are largely historical and cultural,
AFAIK.

IOW, the reasons for these differences are instrumental, not
theoretical: we need the characters to behave differently when
reordered.