Discretionary hyphenation
-------------------------

Some languages use discretionary hyphenation; `discretionary'
character changes at hyphenation points. For example,
Catalan: paral·lel -> paral-lel,
Dutch: omaatje -> oma-tje,
German (before the new orthography): Schiffahrt -> Schiff-fahrt,
Hungarian: asszonnyal -> asz-szony-nyal,
Swedish: tillata -> till-lata.

Using this extended library, you can define 
discretionary hyphenation patterns. For example:

l·1l/l=l
a1atje./a=t,1,3
.schif1fahrt/ff=f,5,2
.as3szon/sz=sz,2,3
n1nyal./ny=ny,1,3
.til1lata./ll=l,3,2

Syntax of the discretionary hyphenation patterns
------------------------------------------------

pat1tern/change[,start,cut]

If this pattern matches the word, and this pattern win (see README.hyphen)
in the change region of the pattern, then pattern[start, start + cut - 1]
substring will be replaced with the "change".

For example, a German ff -> ff-f hyphenation:

f1f/ff=f 

or with expansion

f1f/ff=f,1,2

will change every "ff" with "ff=f" at hyphenation.

A more real example:

% simple ff -> f-f hyphenation
f1f
% Schiffahrt -> Schiff-fahrt hyphenation
% 
schif3fahrt/ff=f,5,2

Specification

- Pattern: matching patterns of the original Liang's algorithm
  - patterns must contain only one hyphenation point at change region
    signed with an one-digit odd number (1, 3, 5, 7 or 9).
  - only the greater value guarantees the win (don't mix discretionary and
    non-discretionary patterns with the same value, for example
    instead of f3f and schif3fahrt/ff=f,5,2 use f3f and schif5fahrt/ff=f,5,2)

- Change: new characters.
  Arbitrary character sequence. Equal sign (=) signs hyphenation points
  for OpenOffice.org (like in the example). (In a possible German LaTeX
  preprocessor, ff could be replaced with "ff, for a Hungarian one, ssz
  with `ssz, according to the German and Hungarian Babel settings.)

- Start: starting position of the change region.
  - begins with 1 (not 0): schif3fahrt/ff=f,5,2
  - start dot doesn't matter: .schif3fahrt/ff=f,5,2
  - numbers don't matter: .s2c2h2i2f3f2ahrt/ff=f,5,2
  - In UTF-8 encoding, use Unicode character positions: össze/sz=sz,2,3
    ("össze" looks "össze" in an ISO 8859-1 8-bit editor). 

- Cut: length of the removed character sequence in the original word.
  - In UTF-8 encoding, use Unicode character length: paral·1lel/l=l,5,3
    ("paral·lel" looks "paral·1lel" in an ISO 8859-1 8-bit editor).

Dictionary developing
---------------------

There hasn't been extended PatGen pattern generator for discretionary
hyphenation patterns, yet.

Fortunatelly, discretionary hyphenation points are forbidden in the PatGen
generated hyphenation patterns, so with a little patch can be develop
discretionary hyphenation patterns also in this case.

Warning: If you use UTF-8 Unicode encoding in your patterns, call
substrings.pl with UTF-8 parameter to calculate right
character positions for discretionary hyphenation:

./substrings.pl input output UTF-8

Programming
-----------

Use hyphenate2() for handling discretionary hyphenation.
See hyphen.h for the documentation of the hyphenate2() function.
See example.c for processing the output of the hyphenate2() function.
Check discretionary hyphenations with the -dd option of the example program.

Warning: change characters are lower cased in the source, so you may need
case conversion of the change characters based on input word case detection.
For example, see OpenOffice.org source
(lingucomponent/source/hyphenator/altlinuxhyph/hyphen/hyphenimp.cxx).

Németh László
<nemeth (at) openoffice.org>