From: John Hudson (tiro@tiro.com)
Date: Wed Dec 31 2003 - 02:49:17 EST
At 01:13 PM 12/30/2003, Peter Kirk wrote:
>But if it were, this ligature would be very interesting and problematic
>because it is a ligature between a base character and a diacritic. This is
>not a problem if it is always used, in a particular font, but it is
>problematic if the ligature is optional. This is because ZWNJ and ZWJ
>cannot be used between base characters and diacritics because they break
>the combining sequence. We came across this problem before with Hebrew
>script, but in a rather different (and less ambiguous) context, that of
>the need for a ligature between meteg and hataf vowels.
We should probably be careful to distinguish between ligation explicitly
requested in text using ZWJ -- which is very much a minority case -- and
ligation that occurs as either default rendering or as the result of a
higher level font feature request. There are lots of ligatures of bases and
marks in lots of fonts: ligation is one possible method of rendering any
sequence of base plus mark(s), and in some cases if preferable to dynamic
mark positioning.
>OpenType etc fonts are currently able to make these distinctions
>consistently, with the mechanisms John described above; but these
>mechanisms fail if there is a need for the ligature to be optional, as
>ZWNJ and ZWJ cannot be used.
Again, there is the question of whether an optional ligation needs to be
requested or inhibited in plain text, using these control characters, or
can be handled at a higher level using markup. In OT rendering, only
lookups in the Required Ligatures <rlig> feature cannot be turned off, so
one would put optional ligatures in the Standard Ligatures <liga> feature
if you wanted them on by default, or in the Discretionary Ligatures <dlig>
feature if you wanted them off by default.
John Hudson
Tiro Typeworks www.tiro.com
Vancouver, BC tiro@tiro.com
What was venerated as style was nothing more than
an imperfection or flaw that revealed the guilty hand.
- Orhan Pamuk, _My name is red_
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