[tex-hyphen] String preparation

[Élie Roux]

> the problem with that is that we get a more and more complex routine 
> which degrades performance, makes it hard to configure and explain,
> even not intuitive

I don't agree but ok

> anyway, because in a glyph the left/right fields store the current 
> values of left and right hyphenmin it's not too hard to run over the 
> list using a callback and adapt that value (the first one in a word)
> 
> - identify start of word

That looks like a huge overhead and a fragile algorithm... But in a
first step it can be done quickly indeed.

> - look at left value of the first glyph - see if there is a char in
> the #left glyphs that you want to count more or less times - and
> adapt the left value accordingly

Well, if it's easy to configure and explain, and intuitive (which is not
obvious to me), that looks like a good solution indeed. But if changing
the left value of the glyph node works, I think the manual should be
changed, as it states "the frozen \lefthyphenmnin value" (section
7.1.2.12)... According to what you say, the value is not frozen, is it?

Thank you,
-- 
Elie