boundary char and implicit kerns

[Han The Thanh]

> Perhaps I misunderstand something here: isn't it exactly the other way
> round that hanging characters (mid-line and/or begin/end-line) work in
> Tex only with the above described configuration?
> I.e. industry-standard fonts have kerns with respect to space (if at
> all) to allow for optical kerning with resepct to word-boundaries. Using
> space as a placeholder and translating into kerns with the Tex
> boundarychar is an obviuos way to make use of this concept in Tex
> despite it doesn't have a space character.
> 
> This works fine as far as I could see. Possibly you should consider how
> you achieve this effect in another way. In any case are the kerns with
> respect to the boundary character the first/last things which Tex sees
> at both ends of a line. It is essential for hanging characters that
> these kerns are not discarded.
> 
> Perhaps it is necessary to take those corrections in the AFM into
> account when defining hanging in an alternative approach to see the
> correct spacing at the end?

I think that kerns with respect to the space in some font are not intended
for hanging certain characters, but simply to make the interword space not
to look so large when the adjacent char is a period or a comma. I am not
sure about the real intention of the boundary char mechanism, but I think
it's similar, ie for optical adjustment of interword spaces.

Regards,
Thanh