Mixing of AN and EN (Re: Protocol-08 (and status of Defs-04 and Rationale-06))

Harald Tveit Alvestrand harald at alvestrand.no
Wed Dec 17 09:02:26 CET 2008


Alireza Saleh skrev:
> Harald,
>
> Would you please test the following examples :
>
> 1) <U+062C>a<U+U0664>-<U+0665>
> 2) <U+062C>a<U+U06F4>-<U+06F5>
Why?

This (if I interpret it rightly) is BIDI class AL L AN ES AN and AL L EN 
ES EN, and is forbidden as a label because of the mixing between AL and L.

In an LTR context, the string .<U+062C>a<U+U0664>-<U+0665>.<U+062D> 
(adding a following RTL character after a dot) would display in the 
order .<U+062C>a<U+U0664></U+062D>.<U+0665>-<U+0664> - which violates 
the grouping criterion.

In an RTL context, CS AL L EN ES EN CS L NSM (the second label followed 
by a LTR character with a combining mark) would display in the order L 
EN ES EN CS L NSM AL CS - also violating the grouping criterion.
>
> I'm a little bit confused about what -bidi is aiming at  ?  This is 
> the RFC that going to be used to display the labels, or the labels 
> should be tested against it during the registration ?
What Erik said: MUST test at registration, SHOULD test at lookup.
>
> Besides, Would you please tell me if it is correct for numbers to be 
> displayed in RTL order.As far as I know, the numbers should be 
> displayed in LTR order even in RTL languages. At least I'm sure about 
> Persian, Arabic and Urdu.
To be extremely precise:

In all cases I know of, the most significant digit goes on the left. I 
have heard verbal reports that some people actually write the least 
significant digit first, but I have also seen with my own eyes (in 
Egypt) people writing the most significant digit first while writing 
Arabic-Indic numerals; this would mean that they write the numbers 
left-to-right when writing a text that's otherwise right-to-left.

Whether the ones who write the least significant digit first consider 
the numbers to be displayed left-to-right or right-to-left .... I don't 
know.

                 Harald



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