The statements below are incorrect, but I don't have the time to correct them all.
âMark ----- Original Message ----- From: "Philippe Verdy" <[EMAIL PROTECTED]> To: "Mark Davis" <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]> Sent: Friday, November 26, 2004 11:13 Subject: Re: CGJ , RLM > From: "Mark Davis" <[EMAIL PROTECTED]> > >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 would be rendered as if the first ZWJ had been replaced by an hyphen 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"... > > > >
