[XeTeX] Line-breaking algorithms in XeTeX

[Pander]

John Was wrote:
> Dear All
>  
> Since starting to use (plain) XeTeX I've noticed something strange with
> the paragraphing/line-breaking mechanism which has never happened during
> the ten years or so during which I have used traditional TeX.  It is
> cropping up in the fourth issue of a periodical that I have set with
> XeTeX, so I'm pretty sure that it's not a random fluke.
>  
> (1) I sometimes get an overfull rule (i.e. rectangular box) at the
> right-hand side which will disappear when I either (a) attach the word
> causing the problem to the next word with ~, forcing it over (I
> sometimes have to put the word in an \hbox{} as well); or (b) when I
> increase the line-count by giving \looseness1 for the paragraph.  In the
> past, plain TeX would always make such decisions for itself and never
> generate an overfull rule when it could find a way to justify the
> paragraph without doing so.  This happens most frequently in the reviews
> section of the periodical, where  \looseness is set to -1 by default to
> save as much space as possible:  but until I started to use XeTeX, it
> was always the case that if the paragraph could not lose a line, then
> the negative looseness was ignored and the paragraph was set
> successfully with normal looseness  (i.e. \looseness = 0).  It was never
> (I think) the case that a tight looseness which generated an overfull
> box would get through and need manual intervention from me.  So has
> something altered in the way XeTeX is handling the line-breaks, giving
> priority to the looseness command even at the expense of generating an
> overfull rule, and even when zero looseness would cause that error to
> disappear?
>  
> (2) This is even more puzzling (and more of an nuisance).  For the
> purpose of sending contributors proofs of their reviews I start each
> review on a new page so that they don't also receive the tops and tails
> of adjacent reviews, but while initially typesetting I have the reviews
> running on consecutively, as they will do in the final published
> version.  There is a switch at the end of each review which generates a
> \vfill \eject when \ifseparatereviews is true, otherwise it just
> produces a \vskip: there is no other difference.  Yet I sometimes get
> overfull rules showing up (at random points) when the reviews are
> separated out, even though the same paragraph typeset without error
> while the reviews were set to run on continuously.  The problem almost
> (but not entirely) disappears if I double the \hfuzz when the
> \ifseparatereviews switch is true, but that is no more than a quick fix
> to prevent authors receiving proofs with worrying blobs at the
> right-hand side.  This seems incomprehensible, but as it has happened
> with four out of four periodical issues I can't be imagining it - and
> the commands are precisely the same as the ones I used when the
> periodical was typeset using traditional plain TeX, with no new
> parameters such as alteration to \spaceskip or anything else that might
> cause this to happen.
>  
> (1) and (2) seem likely to be part of the same problem (though not
> necessarily so).  Any ideas, or at least insight into what XeTeX is
> doing that old plain TeX didn't?
>  
> Thanks
>  
>  
> John

Hi all,

Slightly related is something I have made. Sometimes you have some
freedom of choice in font and in the dimensions of the margins of the
work you are about to make. Each selection will have a different amount of:
- Overfull
- Underfull
- hyphenation exceptions

I have made a python script that, via exhaustive enumeration, will find
the optimum settings for a minimum amount of occurrences of the list
above. Using those optimal settings could be a smarter starting point
for fixing widows, orphans and hyphenation exceptions.

If someone is interested in this script. please contact me.

Regards,

Pander

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