On Tuesday, July 2, 2002, at 06:51 AM, Michael Everson wrote:
> That is absolutely true. I have never argued that the only way to turn
> ligatures on or off is in plain text. I saw that there were difficult
> edge cases and sought blessing for the ZWJ/ZWNJ mechanism to handle them,
> and won the day. But it would certainly be my view that those should
> only be used where predictable ligation does not occur. A Runic font
> which had an AAT/OpenType/Graphite ligatures-on mechanism would, in my
> view, be inappropriate, because ligation is unusual in Runic, never the
> norm, and should only be used on a case-by-case basis. Runic fonts should
> have the ZWJ pairs encoded in the glyph tables.
Alas, but that's technically impossible. Both OT and AAT (I'm not sure
about Graphite) require that single characters map to single glyphs, which
are then processed. (In OT, of course, you are also supposed to do some
preprocessing in character space, but that doesn't solve this problem.)
It would be nice to have a cmap format which maps multiple characters to
single glyphs initially.
The way we deal with this is to have the ligatures with the ZWJ inserted
as part of a ligature table which is on by default and which isn't
revealed to the UI so that the user can't turn them off.
John H. Jenkins
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