Bidi - BN - clarifying suggestion

Harald Alvestrand harald at
Tue Sep 8 21:11:15 CEST 2009

I think the smallest possible change that addresses the issue of BN is this:


   o  BN - Boundary Neutral - control characters


   o  BN - Boundary Neutral - control characters, including ZWNJ and ZWJ

Those two characters are, AFAIK, the only two BN characters that are 
allowed by -protocol, so indicating that these two are members of BN 
should be a sufficient indication of why the class is included in the 
BIDI algorithm.

(Similarly, the only allowed member of ON is, if I remember correctly, 

John C Klensin wrote:
> Hi.
> I've just taken a careful look at the bidi doc wrt the BN issue 
> and suggest that one of the two suggestions that follow might 
> help to clarify things without changing anything of importance.
> Either (rewrites at the discretion of the editors, obviously)...
>     (1) Add an additional sentence to the end of bullet (2) of
>     Section 2:
>     Note that many of these characters, especially most of those
>     in BN, are DISALLOWED by [Tables].
> or
>     (2) Add the following to the end of the introductory
>     paragraph of Section 2:
>     Passing the BIDI test is not sufficient for a label
>     containing applicable characters to be valid because many of
>     the labels that would pass this test would still be invalid
>     because they contain characters that are DISALLOWED
>     [Tables], or that must satisfy context-dependent rules that
>     are not met [Protocol].
> Now, I am convinced that the above clarifications don't change 
> anything -- the relevant rules are enforced by Protocol whether 
> Bidi is invoked or not.  But, if the inclusion of, e.g., BN, in 
> the Bidi-valid list has confused some of us, it is much more 
> likely to confuse others.
>      john
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