[XeTeX] Discretionary hyphens don't work in paragraphed footnotes

[Bruno Le Floch]

On 10/8/15, David Carlisle <d.p.carlisle at gmail.com> wrote:
> On 8 October 2015 at 17:53, Dominik Wujastyk <wujastyk at gmail.com> wrote:
>> The original questioner said he was doing a critical edition.  If he's
>> using
>> EDMAC or LEDMAC then perhaps I can note that EDMAC does some work to
>> avoid
>> setting footnote text in "restricted horizontal mode".  Restricted
>> horizontal mode does a number of annoying things to text, including (I
>> think) things affecting hyphenation; Plain TeX goes to some lengths to
>> set
>> footnotes in unrestricted mode.  But LaTeX doesn't bother with these
>> niceties.  However, EDMAC does.
>>
>> Best,
>> Dominik
>>
>> The attached fnfix.sty file fixes LaTeX footnotes so that they're set in
>> unrestricted horizontal mode.
>>
>>
>
> ??? both standard latex footnotes and the paragraphed footnotes used
> from footmisc in the original question use unrestricted horizontal
> mode, if you set them in an hbox (restricted hmode) they wouldn't work
> at all if longer than a line.

This seems to be true of LaTeX footnotes but not of footmisc footnotes
with the option "para".  I added \tracingall\showlists at the end of
the footnote's argument in the OP's code:

\documentclass[a4paper]{article}
\usepackage{fontspec}
\usepackage[para]{footmisc}
\begin{document}
\footnote{XXXXXXXXXXXXXX just a few normal words to fill up the line
  up to my word hy\-phe\-na\-te\-me\tracingall\showlists}
\end{document}

and got (among other things) "### restricted horizontal mode", rather
than "### horizontal mode" as the innermost mode when the footnote's
argument is typeset.  Removing fontspec does not change that of
course.  Removing the "para" option to footmisc, or removing the
package entirely, makes the footnote text be typeset in unrestricted
hmode.

All in all, the original problem is due to the combination of (1)
footmisc's "para" option making footnotes be typeset in a restricted
horizontal box, (2) fontspec's default selecting some fancy font, (3)
XeTeX discarding discretionaries when not immediately used if such
fancy font is selected.

> The code posted allows catcode changes
>
> %   LaTeX style to redefine the \footnote command such that it allows the
> %   altering of catcodes.
> %   From: Joerg-Martin Schwarz <@MVS.GSI.DE:UPH508 at DDOHRZ11.BITNET>
> %   August 1992
>
>
> but that's unrelated (and by design not included in standard latex
> footnotes)
>
> David

David seems right about default LaTeX footnotes.

Bruno