From: Peter Constable (petercon@microsoft.com)
Date: Wed Nov 21 2007 - 14:46:41 CST
> From: unicode-bounce@unicode.org [mailto:unicode-bounce@unicode.org] On
> Behalf Of James Kass
> (Another scan from this site shows both Arabic and Latin
> embedded in vertical Chinese -- and the Arabic is running
> from bottom to top!)
So, obviously if there was Mongolian embedded in the Arabic that's embedded in the Chinese, the Mongolian would also go bottom to top, right?
We need to separate two issues:
1) How are fonts and rendering implemented to draw a single line of text?
2) What higher-level layout control is provided for how runs of text in a given script get orientented when embedded in matrix text perhaps of another script and perhaps with a different orientation?
The first should be driven by the most common scenarios and will determine how text will get handled in mixed-script scenarios by default -- which will mean, in many application contexts.
The second is necessitated by realities that mixing horizontal and vertical scripts is awkward with no single obvious and right solution, and so authors may need flexibility for some content creation. But since this kind of flexibility takes considerably more engineering, it's not going to be as widely available.
In the case of Mongolian, the correct answer for 1 entails that, when set horizontally, it will display LTR, and that's going to be the default whether it's embedded in Chinese, Latin, Arabic or Hebrew. If an app vendor has enough user need for other options, they may support different layout options. From evidence I've seen, the need for short vertical runs of Mongolian embedding in horizontal text is much greater than the need for RTL Mongolian when embedded in Arabic, but there certainly may be other evidence that has yet to come to light.
Peter
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