CONTEXTJ Rules (was: Re: draft-ietf-idnabis-tables-06a.txt)

[Alireza Saleh]

Mark Davis ⌛ wrote:
> I strongly agree.
>
> Mark
>
>     .......
>
>     ZWJ is *NOT* needed in the Arabic script (for the purposes we
>     are concerned with).
>
I think it would be true provided that labels are only meaning-full 
names  instead of series of characters  however without ZWJ it is not 
possible to correctly write some expressions and abbreviations, although 
I agree to prohibit ZWJ for Arabic script because of the security risk.
>
>     ....
>     =============================================================
>
>     Appendix A.2  ZERO WIDTH NON-JOINER
>       Code point:
>          U+200C
>       Overview:
>          This may occur in a formally cursive script (such
>          as Arabic) in a context where it breaks a cursive
>          connection as required for orthographic rules, as
>          in the Persian language, for example. It also may
>          occur in Indic scripts in a consonant conjunct
>          context (immediately following a virama), to
>          control required display of such conjuncts.
>       Lookup:
>          True
>       Rule Set:
>          False;
>          If Canonical_Combining_Class(Before(cp)) .eq. Virama Then True;
>          If RegExpMatch((Joining_Type:{L,D})(Joining_Type:T)*\u200C
>                         (Joining_Type:T)*(Joining_Type:{R,D})) Then True;
>
>     =============================================================
>
>     Appendix A.3  ZERO WIDTH JOINER
>       Code point:
>          U+200C
>       Overview:
>          This may occur in Indic scripts in a consonant conjunct
>          context (immediately following a virama), to
>          control required display of such conjuncts.
>       Lookup:
>          True
>       Rule Set:
>          False;
>          If Canonical_Combining_Class(Before(cp)) .eq. Virama Then True;
>
>     =============================================================
>
>     Note that I have also turned the default values around for
>     these rule sets. With the more cleanly defined contexts,
>     it is much better to default these to False, and then
>     only return True for the precisely defined exceptional contexts
>     where they may occur.
>
>     I think if the rule sets are stated this way, there is a vastly
>     greater chance that implementers will implement these context
>     rules in compatible and interoperable ways. The code will
>     also be immensely simpler (and less prone to irrelevant
>     bugs) than as the rules sets are stated in the current draft.
>
>     --Ken
>
>
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