Re: ligature exceptions

[Hans Hagen <pragma@wxs.nl>]

On 9/27/2017 5:53 PM, Ulrike Fischer wrote:
> Am Wed, 27 Sep 2017 15:10:33 +0200 schrieb Tomas Hala:
> 
>>  From this point of view, Auf{}lage seems better.
> 
> This doesn't prevent the ligature:
> 
> \starttext
> 
> Auflage Auf{}lage Auf\/lage
> 
> \stoptext
> 
> This also documented: "The most important change is that adding a
> brace group in the middle of a word (like in of{}fice) does not
> prevent ligature creation."
> 
> With pdftex it does avoid ligatures, but not reliably. There are
> cases where the brace group disappear when pdftex tries out
> hyphenation points.
in traditional tex hyphenation is integrated in the par builder which 
comes after ligaturing and kerning and tex only hyphenated where it 
'makes sense' and in the process (multi-pass, going into disc nodes) it 
will consult (deconstruct / reconstruct) ligatures and at that point 
it's not known that the input had a {}. Tricks like inserting something 
in between is also unreliable when done at the wrong time and it can 
also prevent for instance kerns of hyphenation.

Anyway, in addition to Thomas answer ... we already have this

\blockligatures[fi,ff] \blockligatures[fl]
\blockligatures[u:fl:age]

\definefontfeature[default:nolig][default][blockligatures=yes]

\startTEXpage[offset=1em]
     \definedfont[Serif*default:nolig]
     fi ff fl auflage
     \definedfont[Serif*default]
     fi ff fl auflage
\stopTEXpage

The \blockligatures[u:fl:age] is new and something of a joke experiment 
... I can probably come up with a real advanced and robust mechanism if 
motivated enough

Hans


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                                           Hans Hagen | PRAGMA ADE
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