From: Peter Constable <>
Date: Thu, 25 Aug 2011 02:39:42 +0000

From: [] On Behalf Of Philippe Verdy

> 2011/8/22 Peter Constable <>:

>> Of course _OpenType_ cannot, but any rendering engine that uses OpenType
>> _must_ resolve the bidi level of _all_ characters in a sequence that it is given to
>> render. Given our current situation, a default rendering implementation would
>> resolve PUA characters to an even (LTR) level unless, of course, bidi control
>> characters -- particularly RLO -- are used to override the directionality of the
>> character, as you mention.


> So now I perceive your opinion :
> - you don't want the solution proposed by Michael Everson (simply adding a range
> of RTL PUA), that I also think is not necessary, but is clearly a possible solution.

You're putting words in my mouth: I don't think I've expressed any opinion in this thread for or against Michael's proposal. All I've commented on is that the OpenType spec has a model for glyph mirroring that can work for mirroring of PUA characters as well, that bidi category is one of several properties that can affect text processing, and that people shouldn’t expect PUA characters to behave as they desire in all software titles.

> - you propose to use BiDi overrrides.

Again, you're putting words in my mouth. All I said is that default behaviour can be expected to observe bidi categories unless bidi controls are used to override the assigned categories for characters in a run.

Received on Wed Aug 24 2011 - 21:42:37 CDT

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