[tex-hyphen] Hyphenation of Uyghur

[Jonathan Kew]

On 26/02/2021 22:44, Yannis Haralambous wrote:
> 
> 
>> Le 26 févr. 2021 à 23:37, Jonathan Kew <jfkthame at gmail.com 
>> <mailto:jfkthame at gmail.com>> a écrit :
>>
>> On 26/02/2021 22:00, Yannis Haralambous wrote:
>>> dear TeX-hyphen members,
>>> I'm new to this list (although not necessarily new to TeX hyphenation :-)
>>> Here is the problem: we are preparing hyphenation patterns for 
>>> Uyghur, written in Arabic script.
>>> As letters must be in initial/medial form before the hyphen and 
>>> medial/final form on the next line begin,
>>> I was wondering if we could change TeX internals so that instead of 
>>> one, three hyphenchars are used:
>>> ^^^^200d and `-' on the upper line and ^^^^200d on the lower line, in 
>>> order to obtain the equivalent
>>> of \discretionary{^^^^200d-}{^^^^200d}{}
> 
> Hi Jonathan,
> 
>> The problem with this is that it wouldn't be the appropriate 
>> \discretionary in the case where the letter before the hyphenation 
>> position is a right- (rather than dual-) joining character.
> 
> Sorry I don't understand what you mean. You mean when it is a biform 
> character like the waw or the ra? In that case the ZWJ will do no harm. 
> It is an invisible character that does not affect glyphs of biform 
> characters.
> 

Yes, the ZWJ before the hyphen on the first line would be harmless. But 
the ZWJ after the break (at the beginning of the second line) will cause 
the following character to take on a medial or final form, whereas it 
should remain initial or medial when it's after alef/dal/re/waw.

JK