About boundary characters

Karl Berry karl at freefriends.org
Thu Sep 19 00:42:24 CEST 2019

Hi Didier,

    I have several questions about boundary characters in the TFM format.

I surmise experimentation is necessary. The "specifications", such as
they are, are insufficient, so far as I can tell. (Since they were added
in the 1989 update, Don had only a tiny amount of space in which to
describe them.)

It's never been clear to me what TeX actually does with boundary
characters (so maybe their metrics do not matter?). I believe that they
are only relevant in the ligkern table, but that's about all I know.
I read the descriptions in the {mf,tex}{book,.web}, as I suppose you
have also, but clarity is not forthcoming. As far as I know there is no
other significant source of information.

Doug, I surmise you may have more knowledge than anyone? But maybe your
re-implementation was too long ago now :).

It would be nice to have a thorough article for TUGboat on boundary

As for what existing fonts may or may not do with them, (1) it's hard to
say anything without knowing what fonts you are talking about, and (2) I
wouldn't take it too seriously. Maybe the font creators did lots of
experiments and created boundary chars the way they did for specific
reason, but IMHO it's equally likely that they simply followed some
examples, tried to do what they thought made sense, and whatever
happened, happened. --best, karl.

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