>> Adding more invalid hyphenation points only happens if you use an
>> incorrect (i.e., a too small) value for lefthyphenmin and/or
>> righthyphenmin.
>
> I do not profess to know anything about the hyphenation algorithm,
> but this statement suggests to me that inconsistent ("incorrect")
> combinations of hyphenation settings should be diagnosed.
Well, it's quite easy and not inconsistent IMHO: Don't use smaller
values for \lefthyphenmin and \righthyphenmin (in TeX speak) than
specified for a given language's pattern, otherwise the pattern
themselves can introduce invalid hyphenation points, which in turn
might trigger more invalid hyphenation points due to groff's
implementation.
It is unfortunate that those values can't be extracted from the
pattern files themselves, but as mentioned in another e-mail, the TeX
hyphenation team is going to change this by adding YAML headers to all
patterns, which will contain this information also.
An improved version of groff might parse the pattern file headers to
get those values automatically (and in turn prohibit or warn incorrect
`.hy' settings) – some weeks ago something similar was already
suggested on the list.
> This kind of arcana should not have to be kept in mind, even if it's
> documented somewhere.
Honestly, I don't see an immediate reason to do anything (given my
limited time and, admittedly, my limited interest), except improving
the documentation – just now I've added a table to the info file that
shows the necessary left and right minimum values for hyphenation.
Werner
