Different Bidirectional Character Types

[Andreas Prilop]

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?