[lltx] announcing lualatex-doc

[Stephan Hennig]

Am 08.11.2010 18:00, schrieb Manuel Pégourié-Gonnard:
> Le 08/11/2010 17:16, Stephan Hennig a écrit :
>> * Add a warning/note that different line (and page) breaks are to be
>>      expected in comparison to pdfLaTeX, because LuaTeX has some modified
>>      algorithms, different font formats might have different metrics,
>>      LuaTeX doesn't necessarily uses the same hyphenation patterns than
>>      pdfTeX, ...
>>
> It's not very clear to me to which extend one may expect differences. I'm under
> the impression the differences in the algorithm are mostly negligible except in
> edge case.

Oh, I didn't meant to say all line breaks will turn out different when 
switching from pdfTeX to LuaTeX.  But for LuaTeX, in contrast to other 
engines, identical typesetting results for legacy documents have not 
been a design goal.  LaTeX users switching to LuaTeX should keep that in 
mind.

Sources of incompatibility that I know:

* LuaTeX hyphenates the first word of a paragraph.
   use-case: long words in narrow table columns

* In LuaTeX font switching doesn't imply a word boundary (see
   luatexref-t.pdf, sec. 6.4, 'Applying hyphenation').  That is, words
   containing letters typeset in different fonts are hyphenated
   correctly.  As an example, compare the result of pdftex and luatex
   with this code:

\hsize2cm
An  intere{\it st\/}ing word.
\bye

   use-case: educational texts

* Ligature handling.  Unfortunately, I don't understand ligature
   handling of neither TeX nor LuaTeX well enough to explain the
   differences, but reading sec. 6.5, 'Applying ligatures and kerning,'
   of luatexref-t.pdf, my impression is they are not 100 % compatible.
   use-case: possibly any text?

Which of these items is an edge-case is hard to tell.  From an 
algorithmic point of view all of these are surely edge-cases.  But from 
a document designer's point of view, any of that might just affect you.

> The patterns are the same for XeTeX and LuaTeX.

Sure.  I was aiming at LaTeX users switching from traditional TeX or 
pdfTeX to LuaTeX.  I know of at least one language where there are 
different patterns used by traditional and modern engines (German, 
incidentally).


> So, the only important source of differences is the fonts that may not be
> selected the same way and are never used in exactly the same way (there is a
> fundamental difference between XeTeX and LuaTeX here indeed).

Are you actually focusing on differences between XeTeX and LaTeX?


> I'm not saying there are no differences, but for the moment I'm hesitating to
> mention them since the extent isn't very clear to me.

It isn't very clear to me too, but then again, mentioning possible 
incompatibilities in the document should put you (and the users) on the 
safe side.  Going into detail with examples isn't necessary, I think.

Best regards,
Stephan Hennig