From: Peter Constable <>
Date: Sun, 21 Aug 2011 15:56:02 +0000

From: [] On Behalf Of Philippe Verdy

> Hmmm.... Given the current standard in OpenType, and the fact that
> OpenType fonts cannot reorder glyphs to support the BiDi algorithm
> and correctly handle featues like ligatures...

I agree that OpenType font tables cannot to glyph re-ordering. But totally incorrect in saying that it cannot handle ligatures.

> What this means is that, in practice, PUA are only usable in fonts for
> characters with strong LTR directionality, excluding all reordering and
> mirroring.

In the OpenType specification, the only data related to glyph mirroring that a rendering engine is assumed to have is the bidi mirroring data from TUS 5.1. (See All other glyph mirroring is to be handled using glyph substitution data in OpenType Layout tables in fonts.

Received on Sun Aug 21 2011 - 10:59:33 CDT

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