Converting Affix Files:  Understanding the Affix File Format
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An affix is either a  prefix or a suffix attached to root words to make 
other words.  For example supply -> supplied by dropping the "y" and
adding an "ied" (the suffix). 

Here is an example of how to define one specific suffix borrowed 
from the en_US.aff file used by the OpenOffice org spellchecker

SFX D Y 4
SFX D   0     d          e
SFX D   y     ied        [^aeiou]y
SFX D   0     ed         [^ey]
SFX D   0     ed         [aeiou]y

This file is space delimited and case sensitive.
So this information can be interpreted as follows:

The first line has 4 fields:

Field
-----
1     SFX - indicates this is a suffix
2     D   - is the name of the character which represents this suffix
3     Y   - indicates it can be combined with prefixes (cross product)
4     4   - indicates that sequence of 4 affix entries are needed to
               properly store the affix information

The remaining lines describe the unique information for the 4 affix
entries that make up this affix.  Each line can be interpreted
as follows: (note fields 1 and 2 are used as a check against line 1 info)

Field
-----
1     SFX         - indicates this is a suffix
2     D           - is the name of the character which represents this affix
3     y           - the string of chars to strip off before adding affix
                         (a 0 here indicates the NULL string)
4     ied         - the string of affix characters to add
                         (a 0 here indicates the NULL string)
5     [^aeiou]y   - the conditions which must be met before the affix
                    can be applied

Field 5 is interesting.  Since this is a suffix, field 5 tells us that
there are 2 conditions that must be met.  The first condition is that 
the next to the last character in the word must *NOT* be any of the 
following "a", "e", "i", "o" or "u".  The second condition is that
the last character of the word must end in "y".

Now for comparison purposes, here is the same information from the 
Ispell english.aff compression file which was used as the basis
for the OOo one.

flag *D:
    E		>	D		# As in create > created
    [^AEIOU]Y	>	-Y,IED		# As in imply > implied
    [^EY]	>	ED		# As in cross > crossed
    [AEIOU]Y	>	ED		# As in convey > conveyed

The Ispell information has exactly the same information but in a 
slightly different (case-insensitive) format:

Here are the ways to see the mapping from Ispell .aff format to our
OOo format.

1. The ispell english.aff has flag D under the "suffix" section so 
you know it is a suffix.

2.  The D is the character assigned to this suffix

3. * indicates that it can be combined with prefixes

4. Each line following the : describes the affix entries needed
   to define this suffix

   - The first field is the conditions that must be met.

   - The second field is after the > if a "-" occurs is the
         string to strip off (can be blank).

   - The third field is the string to add (the affix)

In addition all chars in ispell aff files are in UPPERCASE.

So the easiest way to create an OOo .aff file is to start with
an Ispell .aff file (make sure you get the wordlist author's 
permission first).  Then literally one by one, use a text editor
to convert the information for each prefix and suffix into the 
OOo format (or write a perl script if need be).

Note:  MySpell does *NOT* support multi-byte characters. It needs both
the affix file and the wordlist to use just one 8-bit character set which
is then specified in the affix file.

If the Ispell affix file and wordlist uses multiple bytes to 
indicate one character, a script or editor must be used to convert
them to the proper single byte character encoding.  For example,
the Ispell german affix file uses the byte sequence u" to actually
indicate the a u-umlaut character. All occurences of these
multi-byte characters must be converted to their single byte encoding
using the ISO-8859-1 character set in the affix file and the
wordlist. 

FYI, the changes made to the format of the .aff file are necessary 
to support on-the-fly parsing of both the affix .aff file and the
munched wordlists so that all dictionaries are literally stored
as ISO text files with associated .aff files and not endian 
dependent binary hash tables dumped in some compile specific 
format.  The code is then smart enough to build a hashtable on 
the fly just from the munched wordlist and the .aff file as long
as the text files end in either \r\n or simply \n.


There are two other things you need to add to the MySpell affix file.

The first line specifies the character set used for both the 
wordlist and the affix file (should be all uppercase). 

For example:

SET ISO8859-1

And the second line specifies the characters to be used in building
suggestions for misspelled words.  The should be listed in order or
character frequency (highest to lowest).  A good way to develop this
string is to sort a simple character count of the wordlist.

For example:

TRY esianrtolcdugmphbyfvkw


Converting an Ispell "munched" Wordlists
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To convert an Ispell "munched" wordlist to the format needed
by MySpell simply count the number of "root" words in the file and
add that count to the first line of the file (this speeds loading
the file since two passes are not needed).