[luatex] Hyphenation on ligatures

[Hans Hagen]

On 2/13/2016 10:10 PM, Reinhard Kotucha wrote:
> On 2016-02-12 at 21:32:40 +0700, Igor Liferenko wrote:
>
>   > Can anybody explain why and how luatex hyphenates on ligatures? Is
>   > this incompatibility with TeX intentional, or is it just a bug
>   > which has not been fixed?
>
> I don't think that it's deprecated to hyphenate at ligatures in
> general.  This heavily depends on the language and maybe other
> constraints.

when luatex hyphenates it just looks at a sequence of characters .. 
ligatures don't relate to that as they are a property of turning 
character sequences into glyphs (and we have not only pattern driven 
hyphenation points but also explicit hyphens and such + pre/post hyphen 
characters to deal with)

so what happens after that is up to the font handler

> A problem is that TeX doesn't know when a ligature is appropriate
> or not.  At least in German, ligatures are deprecated at boundaries of
> composed words.

i sometimes wonder what would have happened if letterboxes had have 
10000 slots and we'd have thousands of combinations in lead ... that not 
having happened in turn makes me wonder if we could do without the 
(somewhat traditionally small set of f* ligatures) ... what if we'd 
never had a dot on the i ... so, this is why i don't worry too much 
about missing a few (after all fonts are not always having all the f* 
ones either)

> Consider the German word Auflage.  The fl-ligature is deprecated and
> LaTeX users write
>
>    \usepackage[german]{babel}
>    ....
>    Auf"|lage
>
> in order to avoid the ligature.  Nevertheless, Auf-lage is a good
> hyphenation point despite the ligature, even if it wasn't disabled
> manually.

within some constraints the discretionary mechanism can deal with it (it 
gets hairy when there are several ligatures in a row

> On the other hand I suppose that the Dutch ij-ligature shall never be
> hyphenated.  But with proper hyphenation patterns it won't happen
> anyway.

worse: ij is indeed not so much a ligature as a sound thingie but in 
fijn you definitely don't want a fi ligature and preferably some ij 
kerning at least ... latin modern actually has a f i j contextual lookup 
for nld for that reason

Hans

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