Follow-up to Monday's discussion of digits

[Eric Brunner-Williams]

Thanks Ken.

Kenneth Whistler wrote:
> Eric Brunner asked:
>
>   
>> Could you point out where the "slightly different *directional* 
>> behavior, with distinct bidi properties" is present? I'm reading TR9 but 
>> I don't yet see where this matters. Examples of the differences would be 
>> nice.
>>
>>     
>
> Well, I'm not a bidi expert myself, so I'd appreciate it
> if anyone who has actually implemented this stuff could
> chime in here...
>
> But my reading of the bidi algorithm would concur that for
> *most* contexts, bc=AN versus bc=EN isn't going to make any
> difference in the final layout order of lines.
>
> The exception would seem to be in the following contexts:
>
> L N EN --> L N L  --> L L L
> L N AN --> L N AN --> L e AN
>
> For L L L you are going to get resolved levels 0 0 0 in a L-to-R
> context and 2 2 2 in a R-to-L context. And everything in the
> stretch is going to display L-to-R in either.
>
> For L e AN you get resolved levels 0 0 2 in a L-to-R context
> and 2 1 2 in a R-to-L context. For that one, the neutrals
> in between the L and the AN make a significant difference then
> in the final layout result. You reverse both runs of 2's
> separately, and then the entire span including the neutrals.
> That gives you a very different outcome than if you had
> started with an L N EN sequence, instead.
>
> I could be wrong here, though -- so if somebody who knows better
> can correct me, that would be great. Also I'm not clear
> regarding what about the behavior of neutrals in the context
> of strong L strings and Perso-Arabic numbers versus Arabic
> numbers led the designers of the bidi algorithm in the first
> place to difurcate the properties to have this result.
>
> --Ken
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