ZWJ/ZWNJ - Are they legal to use with combining marks?

[Peter Kirk]

On 15/08/2003 07:57, Paul Nelson (TYPOGRAPHY) wrote:

>>This brings us back to the earlier quesion of whether it is
>>legitimate to use ZWJ or ZWNJ between combining marks
>>
>>
>
>It sure better be. This is done in Khmer for controlling register shift
>combinations for exception words. I have seen nothing in Unicode that
>states that the ZWJ/ZWNJ can only be used with base type characters.
>
>Paul
>
>
>
>
Well, I understood that ZWJ/ZWNJ followed by a combining mark gives a
defective combining sequence, which is not illegal but whose rendering
is undefined - and which Uniscribe tends to render with a dotted circle.
Is that correct? But then I was advised that it was permissible to use
such a sequence for word initial holam male, as long as the font knows
to expect it.

I'm copying this to the main Unicode list as its relevance is wider than
Hebrew.

--
Peter Kirk
***@qaya.org (personal)
***@qaya.org (work)
http://www.qaya.org/




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[John Hudson]

At 08:08 AM 8/15/2003, Paul Nelson \(TYPOGRAPHY\) wrote:

> >I understood that ZWJ/ZWNJ followed by a combining mark gives a
>defective
> >combining sequence, which is not illegal but whose rendering is
>undefined
> >- and which Uniscribe tends to render with a dotted circle.

>This is not a correct understanding. Uniscribe does not insert dotted
>circles based on the presence of ZWJ/ZWNJ.

Indeed. However, perhaps you can explain why

alef hatafsegol ZWNJ meteg

produces

alef hatafsegol dotted-circle meteg

in Word 2002. Is this simply a Word bug/feature? The same sequence renders
correctly in Wordpad and Notepad, so I know that Uniscribe is not to blame.
I'd really like to understand why this happens.

John Hudson

Tiro Typeworks www.tiro.com
Vancouver, BC ***@tiro.com

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[Kent Karlsson]

I admit I haven't been able to catch up with the flood of messages on
the
Hebrew list...

> On 15/08/2003 07:57, Paul Nelson (TYPOGRAPHY) wrote:
>
> >>This brings us back to the earlier quesion of whether it is
> >>legitimate to use ZWJ or ZWNJ between combining marks
> >>
> >>
> >
> >It sure better be. This is done in Khmer for controlling register
shift

I noticed, somewhat to my surprise!

> >combinations for exception words. I have seen nothing in Unicode that
> >states that the ZWJ/ZWNJ can only be used with base type characters.
> >
> >Paul
> >
> >
> >
> >
> Well, I understood that ZWJ/ZWNJ followed by a combining mark gives a
> defective combining sequence,

Yes, it does. I would suggest reclassifying ZWJ and ZWNJ as combining
marks,
i.e. Mn instead of Cf as "general category". They would have to keep
their
combining class of 0, in order not to change any normal forms. As I've
mentioned, I think class 0, with its special treatment is problematic,
and
hence ZWJ and ZWNJ should not be "acknowledged" just anywhere in any
combining sequence. There is no problem to have them at the end of a
combining sequence, that is what has to all intents and purposes been
the case all the time, even as Cf *just after* a combining sequence.
"New"
cases, that are not "acknowledged" with ZWJ/ZWNJ as Cf, but should be
with ZWJ/ZWNJ as Mn: just after a base character (even when followed by
more combining characters) [this takes care of the Khmer cases], between
two combining marks in a combining sequence that would be in canonical
order *if* the ZWJ/ZWNJs were removed from the sequence (this may take
care of some Hebrew ligation cases, I'm not sure). Other placements of
ZWJ/ZWNJ should not be "acknowledged", but should be deprecated.
ZWJ/ZWNJ would remain "default ignorable".

/kent k



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