[HarfBuzz] The canonical ordering of hamza marks

[Jonathan Kew]

On 2/9/12 05:07, Khaled Hosny wrote:
> On Sat, Sep 01, 2012 at 06:40:40PM -0400, Behdad Esfahbod wrote:
>> On 08/26/2012 07:15 PM, Khaled Hosny wrote:
>>> Hi Behdad,
>>>
>>> I just noticed that hamza above and below marks (U+0654, U+0655), are
>>> reordered after Arabic vowel marks because they have much higher
>>> combining classes, 230 and 222 (the "generic" combining class above and
>>> below, respectively), which breaks mkmk positioning.
>>>
>>> I tried to make a patch to handle them like the shadda, but I'm not sure
>>> how safe it is with such generic combining classes.
>>
>> Khaled,
>>
>> Given that there's a few handfuls of Arabic marks with 220/230 ccc, can you
>> help me figure out what the expected behavior is, in respect to the main marks
>> and shadda?  I can try to implement that after.
>
> Ideally, I think hamza and madda should come first, then shadda, then
> the vowel marks then everything else:
>
> * hamzat and maddat: U+0653-U+0655, U+065F, U+0674, U+06E4
> * shadda: U+0651
> * vowel marks: U+064B-U+0650, U+0652, U+0656-U+065E, U+08F0-U+08F2
>

The ordering of madda and vowel marks was raised on the Unicode list in 
July 2011, and at that point the responses indicated that madda should 
*follow* vowel marks; see 
http://www.unicode.org/mail-arch/unicode-ml/y2011-m07/0143.html and its 
replies.

JK