From: Mark Davis (mark.davis@jtcsv.com)
Date: Fri Nov 26 2004 - 14:09:56 CST
The statements below are incorrect, but I don't have the time to correct
them all.
Mark
----- Original Message -----
From: "Philippe Verdy" <verdy_p@wanadoo.fr>
To: "Mark Davis" <mark.davis@jtcsv.com>
Cc: <unicode@unicode.org>
Sent: Friday, November 26, 2004 11:13
Subject: Re: CGJ , RLM
> From: "Mark Davis" <mark.davis@jtcsv.com>
> >I want to correct some misperceptions about CGJ; it should not be used
for
> > ligatures.
>
> True. CGJ is a combining character that extends the grapheme cluster
started
> before it, but it does not imply any linking with the next grapheme
cluster
> starting at a base character.
>
> So, even if one encodes, A+CGJ+E, there will still be two distinct
grapheme
> clusters A+CGJ and E, and the exact role of the trailing CGJ in the A+CGJ
is
> probably just a pollution, given that this CGJ has no influence on the
> collation order, so that the sequence A+CGJ+E will collate like A+E, and
it
> does not influence the rendering as well.
>
> A "correct" ligaturing would be A+ZWJ+E, with the effect of creating three
> default grapheme clusters, that can be rendered as a single ligature, or
as
> separate A and E glyphs if the ZWJ is ignored.
>
> For example, a ligaturing opportunity can be encoded explicitly in the
> French word "efficace":
> "ef"+ZWJ+"f"+ZWJ+"icace".
>
> Note however that the ZWJ prohibits breaking, despite in French there's a
> possible hyphenation at the first occurence, where it is also a syllable
> break, but not for the second occurence that occurs in the middle of the
> second syllable.
>
> I don't know how one can encode an explicit ligaturing opportunity, while
> also encoding the possibility of an hyphenation (where the sequence above
> would be rendered as if the first ZWJ had been replaced by an hyphen
> followed a newline.)
>
> To encode the hyphenation opportunity, normally I would use the SHY format
> control (soft hyphen):
> "ef"+SHY+"fi"+SHY+"ca"+SHY+"ce"
>
> If I want to encode explicit ligatures for the "ffi" cluster, if it is not
> hyphenated, I need to add ZWJ:
> "ef"+ZWJ+SHY+"f"+ZWJ+"i"+SHY+"ca"+SHY+"ce" (1)
>
> The problem is whever ZWJ will have the expected role of enabling a
ligature
> if it is inserted between a letter and a SHY, instead of the two ligated
> glyphs. In any case, the ligature should not be rendered if hyphenation
does
> occur, else the SHY should be ignored. So two rendering are to be
generated
> depending on the presence or absence of the conditional syllable break:
> - syllable break occurs, render as: "ef-"+NL+"f"+ZWJ+"icace", i.e. with a
> ligature only for the "fi" pair, but not for the "ff" pair and not even
for
> the generated "f"+hyphen...
> - syllable break does not occur, render as "ef"+ZWJ+"f"+ZWJ+"icace", i.e.
> with the 3-letter "ffi" ligature...
>
> I am not sure if the string coded as (1) above has the expected behavior,
> including for collation where it should still collate like the unmarked
word
> "efficace"...
>
>
>
>
This archive was generated by hypermail 2.1.5 : Fri Nov 26 2004 - 14:11:36 CST