setting of interword glue

[Lars Hellström]

At 17.40 +0200 0-07-27, Han The Thanh wrote:
>Hi all,
>
>can someone please explain to me the reason for setting of interword
>stretching/shrinking as follow
>
>   ...
>   \setint{fontdimen(3)}{\scale{\int{interword}}{600}}% interword stretch
>
>   \setint{fontdimen(4)}{\scale{\int{interword}}{240}}% interword shrink
>
>   ...
>
>
>Another question is that why it is given in ext file? Shouldn't it be
>rather in a mtx file?

The reason fontdimens are set by ETX files is that the meaning of a
fontdimen depends on the encoding, e.g. in T1 fontdimen 8 is the cap
height, but in OMS it is the amount by which the numerator in displaystyle
fractions should be raised when forming the fractions (not sure this latter
description is 100% correct, but that's irrelevant). Recall that it is not
uncommon to compile one set of metrics and then generate several VPLs from
it by using different ETXs. As fontdimens 3 and 4 have the same meaning in
all TeX fonts there probably aren't any side effects with setting them in
an MTX file, but there's a point in working by a rule that works for all
fontdimens.

It's another matter that the above code probably isn't the _right_ way to
set these fontdimens. That would instead be to use the values in the two
integers interwordstretch and interwordshrink which the above code would
provide the default values for, but whose values could be set already in
some MTX file. I guess this is another of the "things to fix in the MTX/ETX
files", but it seems I never get around to doing them. Any volunteers?

Lars Hellström