[Dev-luatex] A few newbie questions

[Taco Hoekwater]

David Kastrup wrote:
> 
> I think that 0.25.x might have the big bad hyphenation bug.  

It had several of those, in fact.

>                                                             However, I
> suppose even when using a version where this has been sorted out, TeX's
> behavior for things like shelf{}ful will not be imitated (in this case,
> TeX separates the ligature unless it does a hyphenation pass on the
> paragraph (can be forced with \pretolerance=-10000) in which case the
> ligature will get recombined.  That's not something worth imitating.

Last time we checked the typeset output (two weeks ago), there were
some dozens of differences between pdftex and luatex when compiling
the texbook, and these differences were all in one of three categories:

* Missed hyphenations.
  This is a known bug caused by nested discretionaries that will be
  solved eventually (#9 in the tracker)

* Additional hyphenations (in typewriter text).
  These were added because luatex is willing to hyphenate words that
  start with a non-letter: luatex just starts the word at the first
  thing that is a letter. An argument can be made for maintaining
  compatibility, but currenty we do not intent to make that change
  as the new behaviour is desired much more often. (the same can be
  said for hyphenating the first word in a paragraph, but that case
  never arises in the texbook)

* Extra or slightly different ligatures.
  These are caused by stuff like the self{}ful example above, and this
  incompatibity will definately remain. TeX's exact behaviour was an
  implementation artifact that is pretty hard to mimic, and any attempt
  to do so would lead to extremely ugly code.

Best wishes,
Taco