% \iffalse
% This is versonotes.dtx, which supports adding notes on verso pages,
% opposite annotation on the recto pages.  Still sketchy
%%
%% Release version 0.5, 2023 December 31.
%%
%% Copyright 2014, 2015, 2019, 2023 Norman Gray <https://nxg.me.uk>
%%
%% This work may be distributed and/or modified under the
%% conditions of the LaTeX Project Public License, either version 1.3
%% of this license or (at your option) any later version.
%% The latest version of this license is in
%%     http://www.latex-project.org/lppl.txt
%% and version 1.3 or later is part of all distributions of LaTeX
%% version 2005/12/01 or later.
%%
%% This work has the LPPL maintenance status `maintained'.
%%
%% The Current Maintainer of this work is Norman Gray
%%
%% This work consists of the files versonotes.dtx and versonotes.ins
%% and the derived file versonotes.sty.
%%
%%%% File: versonotes.dtx

%<+package|driver|example>%%%% Source: b86314fff92e, 2023-12-31T14:55:52+00:00
%%
%<+package>\NeedsTeXFormat{LaTeX2e}
%<+package>\ProvidesPackage{versonotes}[2023/12/31 v0.5]
%
%<*driver>
\documentclass{ltxdoc}
\title{versonotes: Notes on verso pages}
\author{Norman Gray\\\url{https://nxg.me.uk}}
\date{Release 0.5, 2023 December 31}
\usepackage{url}
\newcommand\Lopt[1]{\textsf {#1}} % options
\newcommand\file[1]{\texttt {#1}}
\newcommand\Lcount[1]{\textsl {\small#1}}
\newcommand\Lenv[1]{\texttt{\{#1\}}} %environments
\newcommand\Lpackage[1]{\{\textsf{#1}\}} %packages
%Make command strings easier to write
%{\catcode`\<=\active \gdef<#1>{\meta{#1}}}
{\catcode`\<=\active
  \gdef<#1>{{\ensuremath\langle\normalfont\textsl{#1}\ensuremath\rangle}}}
\def\cmd{\begingroup
 \catcode`\\=12 \catcode`\{=12 \catcode`\}=12
 \catcode`\<=\active \catcode`\|=12
 \docmd}
\def\docmd|#1|{\texttt{#1}\endgroup}
%%% \url macro (url.sty does this better)
%\def\setpathdots{\discretionary{.}{}{.}}
%\def\setpathslash{\discretionary{/}{}{/}}
%{\catcode`\.=\active
% \catcode`\/=\active
%  \gdef\pathcats{%
%    \catcode`\%=12      \catcode`\~=12
%    \catcode`\.=\active  \let.\setpathdots
%    \catcode`\/=\active \let/\setpathslash
%    \catcode`\#=12      \catcode`\_=12}%
%    }
%\def\setpath#1{\ttfamily <\nobreak #1\nobreak>\endgroup}
%\def\url{\begingroup\pathcats\setpath}

\def\bs{$\backslash$}

\begin{document}
\maketitle
%\tableofcontents
%\bigskip
\DocInput{versonotes.dtx}
\end{document}
%</driver>
%
% \fi
%
% \noindent This package allows you to place notes on the verso pages
% of an otherwise single-sided document.  If, in the run
% of text, you include a call to the macro
% |\versonote{This is a remark}|,
% then that text will be placed on the opposite (ie, `verso') page,
% lined up with the macro call.
% The notes may contain more than one paragraph.
%
% All the pages in the document appear as recto pages
% (ie, right-hand pages),
% and are numbered as such;
% the document should be formatted with that in mind.
%
% Since there is no page opposite the first page, any notes which are
% positioned to appear opposite page 1 are silently discarded.
%
% To invoke the package, use the command |\usepackage{versonotes}|.
%
% It is possible to start the document other than on page one.  To do
% this, you can call |\setcounter{page}{|\emph{n}|}| as usual, but it
% must be done \emph{before} the line |\usepackage{versonotes}|.  The
% package may get confused if the page number is changed at other times.
%
% If two notes come too close after one another, the second would
% overprint the first if we did not take steps to avoid this.  By
% default, they are separated from each other by a short horizontal
% line, but if the \Lopt{mergecollisions} option is provided when
% loading the package, then such notes are instead merged into a
% single block of text.  If a sequence of notes needs to be merged,
% then they will be added to the merged block one at a time in
% successive \LaTeX\ runs, since merging one note may make it
% unnecessary to merge the next.  If a large block of such notes need
% to be merged, it will therefore take several runs before the package
% finds a stable state.  If you find yourself inconvenienced by this,
% it sounds as if you are preparing a critical edition, and you might
% want to venture into a closer relationship with the
% \Lpackage{reledmac}
% package.\footnote{\texttt{https://www.ctan.org/pkg/reledmac} -- this
% is the current incarnation, as of 2023, of the eledmac, ledmac and
% edmac packages for scholarly editions.}.
%
% \emph{Note}:
% If we have a long versonote at the bottom of a page, then we
% don't try to spill over onto the next (that would be possible to
% implement, but would be a significant jump in complication).  We
% regard this situation as one for the user to work out for themself,
% perhaps with some strategic page-breaks.
%
% The dimensions |\versoleftmargin| and |\versotextwidth| specify the
% position of the text block on the verso page.  The defaults for
% these are based on the |\textwidth| and |\evensidemargin| of the
% document \emph{at the time the package is loaded}.
% By default, verso paragraphs are set ragged-left; with the
% declarations in |\versolayout| setting the paragraph parameters.
% You may reset the first two dimensions with for example
% |\versoleftmargin=4cm|, and use |\renewcommand\versolayout{...}| to
% override the paragraph formatting (this will typically require
% changing |\rightskip|, |\leftskip| and |\parfillskip|).  For more
% elaborate effects (for example changing the note font size and
% spacing), you will need to redefine |\versolayout|.
%
% \subsection*{Recto notes}
%
% If the package is invoked with the \Lopt{rectonotes} option, then it
% runs in a complementary mode in which the notes are placed on the
% recto page (the right-hand one) instead of the verso.  The default
% |\versolayout| in this case (which of course is really a recto
% layout) is slightly different, and is based on the preexisting
% document |\oddsidemargin|.  All the pages in the document (apart
% from the front page) are then formatted as verso pages, though still
% only the non-note pages are numbered.
%
% In this mode, the `add a note' command is still called
% |\versonote|.  You may find it convenient to rename that with
% |\let\rectonote = \versonote| or |\let\sidenote = \versonote|.
%
% \subsection*{Notes}
% \begin{itemize}
% \item The package uses the |\pdfsavepos| primitive (or the
% Lua\TeX\ equivalent), and so requires \texttt{pdflatex},
% \texttt{xelatex}, or \texttt{lualatex}.  In practice, this should
% mean that it will work with any reasonably current \LaTeX\ engine.
%
% \item The notes are handled using the |.aux| file, and so (i) they will
% only appear on the second and subsequent runs; and (ii) they will be
% located opposite the position where the |\versonote| macro was
% called on the \emph{previous} run.
%
% \item If notes collide, you may well have to re-run \LaTeX\ several
% times.  There is quite a lot of state in the |.aux| file.
%
% \item The package is available on CTAN at
% \texttt{macros/latex/contrib/versonotes/}.  The source is hosted at
% \url{https://heptapod.host/nxg/versonotes/}.
%
% \end{itemize}
%
% \subsection*{Acknowledgements, and release notes}
%
% \iffalse @RELEASENOTES@ \fi
% 
% 
% Thanks to Thomas H. Luxon for permission to include the
% Dartmouth Milton text\footnote{\url{https://milton.host.dartmouth.edu/}} of
% ‘Paradise Lost’ notes in the sample text.
% 
% \begin{description}
% \item[Version 0.5, 2023 December 31]\relax 
% \leavevmode\begin{itemize}
%   \item Now compatible with LuaTeX.
%   \item Now uses L3-style hooks, but retains compatibility with pre-2020 engines.
%   \item Updated the links to the repository, and to the Dartmouth Milton text.
% \end{itemize}
% \item[Version 0.4, 2019 July 6]\relax 
% Support changing the initial page number
% (thanks to P J Couch for the suggestion).
% \item[Version 0.3, 2015 December 8]\relax 
% \leavevmode\begin{itemize}
% \item Minor documentation adjustments.
% \item Added the [rectonotes] option
% (thanks to Axel Berger for this suggestion).
% \end{itemize}
% \item[Version 0.2, 2015 February 16]\relax 
% Initial public release.
% \end{description}
% 
%
% \StopEventually{}

% \newpage
% \section{Implementation}
%
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
% The package contains a single user-visible command, and three
% configuration parameters.
%
% The normal behaviour of this package is to place notes on the verso
% page (ahem, hence the name).  But we can swap that around.
%    \begin{macrocode}
\newif\if@verso@notesonleft
\@verso@notesonlefttrue
%    \end{macrocode}
%
% Define configuration options for the user:
%    \begin{macrocode}
\def\verso@resetmergestate{\verso@mergestate=2}
\DeclareOption{mergecollisions}{\def\verso@resetmergestate{\verso@mergestate=0}}
\DeclareOption{rectonotes}{\@verso@notesonleftfalse}
\ProcessOptions
%    \end{macrocode}
%
% The single user-visible command is |\versonote|.
% Use |\unexpanded| (from e-\TeX) so that macros in the argument are
% not expanded into the aux file.
%    \begin{macrocode}
\long\def\versonote#1{\@bsphack
  \pdfsavepos
  \write\@auxout{\string\verso@note{\the\c@page}{\the\pdflastypos sp}\unexpanded{{#1}}}%
  \@esphack}
%    \end{macrocode}
%
% \subsection{Housekeeping: sizes and sentinels}
%
% Now the layout parameters, and defaults.
% The dimensions |\versoleftmargin| and |\versotextwidth| specify the
% position of the text block on the verso page, and the declarations
% in |\versolayout| set the paragraph parameters.
%    \begin{macrocode}
\newdimen\versotextwidth
  \versotextwidth=\textwidth
\newdimen\versoleftmargin
  \versoleftmargin=\paperwidth
  \advance\versoleftmargin -\textwidth
  \advance\versoleftmargin -\hoffset
  \advance\versoleftmargin -1in
\if@verso@notesonleft
  \advance\versoleftmargin -\evensidemargin
  \def\versolayout{
    \leftskip=0pt plus 1fil
    \rightskip=0pt
    \parfillskip=0pt
    \parindent=0pt
    \parskip=\medskipamount
  }
\else
  \advance\versoleftmargin -\oddsidemargin
  \def\versolayout{
    \leftskip=0pt
    \rightskip=0pt plus 4em
    \parindent=0pt
    \parskip=\medskipamount
  }
\fi
%    \end{macrocode}
%
% Add a sentinel at the end of the document
%    \begin{macrocode}
\def\end@versonote{%
  \write\@auxout{\string\verso@note{\the\c@page}{-1pt}{}}}
\AtEndDocument{\end@versonote}
%    \end{macrocode}
%
% Define various bits of working storage.
%
% The |\verso@pages| token list needs to have an extra leading `page'
% since the logic in |\verso@processonepage@| can skip it.
%    \begin{macrocode}
\newtoks\verso@pages
  \if@verso@notesonleft
    \verso@pages={}
  \else
    \verso@pages={{}}
  \fi
%    \end{macrocode}
% Notes on a single page (which is kept track of by
% |\verso@currentpagenum| are assembled into |\verso@currentpage|
% before being transferred as a unit into |\verso@pages|.
%    \begin{macrocode}
\newtoks\verso@currentpage
%    \end{macrocode}
% We keep track of page numbers when invoking |\verso@note| below.  We
% initialise this to be the current page number (typically~1).  Doing
% this this way means that if the document sets the current page
% number using |\setcounter{page}{n}| \emph{before} loading the
% package, then we will respect that.  We will get confused if the
% page number is changed at other points.
%    \begin{macrocode}
\newcount\verso@currentpagenum
  \verso@currentpagenum=\c@page
\newcount\verso@currentnotenum
  \verso@currentnotenum=0
\newdimen\verso@spacerskip
  \verso@spacerskip=10pt
%    \end{macrocode}
% Flag |\if@verso@processversonotes| is set true if there are any
% |\verso@note|s found in the aux file.  If there are none -- so that
% this is still false at the first |\shipout| -- then the package
% carefully does nothing.
%    \begin{macrocode}
\newif\if@verso@processversonotes
  \@verso@processversonotesfalse
%    \end{macrocode}
%
% We need to be able to calculate our position on the page.
% The |\verso@pagebottom| is the position of the bottom of the page,
% in the same coordinates as |\verso@currentposition|, and is
% (textheight + top margin + \dots).
%    \begin{macrocode}
\newdimen\verso@pagebottom
  \verso@pagebottom=1in
  \advance\verso@pagebottom \topskip
  \advance\verso@pagebottom \topmargin
  \advance\verso@pagebottom \headheight
  \advance\verso@pagebottom \headsep
  \advance\verso@pagebottom \textheight
\newdimen\verso@currentposition
%    \end{macrocode}
% The paper size options to class files set |\paperheight| but not (or
% not necessarily) |\pdfpageheight|.  If we don't set this, then
% output vertical positions will come out incorrectly if the latter
% parameter doesn't default to the right value.  Lua\TeX\ and pdf\TeX\
% (which includes Xe\TeX\ for this purpose) have slightly different
% ways of organising page sizes, so we do have to conditionalise.
% Here, we assume that everything that isn't Lua\TeX\ is pdf\TeX-like
% enough that it has |\pdfpageheight|.
%    \begin{macrocode}
\RequirePackage{iftex}
\ifluatex
  \typeout{Detected LuaTeX}
  \pageheight=\paperheight
  \let\pdfsavepos=\savepos
  \let\pdflastypos=\lastypos
\else
  \pdfpageheight=\paperheight
\fi
%    \end{macrocode}
%
% \subsection{Core logic}
%
% Macro |\verso@note| is what's written to the aux file, and so is
% what we process on the next run, to discover the set of verso-notes
% we need to produce.
%    \begin{macrocode}
\long\def\verso@note#1#2#3{%
  \global\@verso@processversonotestrue
%    \end{macrocode}
% Store the target page number.  It would be nice to issue a warning if this is
% indicated to appear on the (ignored) first page; such notes are
% silently discarded below.  However detecting this here requires that
% |\@tempcnta| is equal to~1 on the call of this, and we can't
% guarantee this if we support calling |\setcounter{page}{x}| before
% loading the package.
%    \begin{macrocode}
  \@tempcnta=#1
%    \end{macrocode}
% Gather pages from the .aux file, assembling them into a single list
% in |\verso@pages| with one group per page, each containing a
% sequence of |\\{...}| note specifications.  This inserts empty
% groups for pages which have no verso-notes.
%    \begin{macrocode}
  \@tempdima=#2 % #2 < 0pt is the end-of-document flag
  \loop
    \@tempswafalse
    \ifnum\@tempcnta > \verso@currentpagenum
      \@tempswatrue
    \fi
    \ifdim\@tempdima < 0pt
      \@tempswatrue
      \@tempdima=0pt
    \fi
    \if@tempswa
      \edef\@tempa{\the\verso@pages {\the\verso@currentpage}}
      \global\verso@pages=\expandafter{\@tempa}
      \advance\verso@currentpagenum 1
      \verso@currentpage={}
  \repeat
  \verso@currentpage=\expandafter{\the\verso@currentpage \\{{#1}{#2}{#3}}}
%    \end{macrocode}
% The last time around, add an extra pair of tokens at the end of the
% |\verso@pages| list.  These provide the arguments to
% |\verso@processonepage@| on the last time it's called.
%    \begin{macrocode}
  \ifdim\@tempdima=0pt
    \global\verso@pages=\expandafter{\the\verso@pages {}{}}
  \fi
}
%    \end{macrocode}
%
% Disable |\verso@note| in time for the end-document aux reading.
% This isn't quite necessary, but it's tidy.
%    \begin{macrocode}
\AtEndDocument{\long\def\verso@note#1#2#3{}}
%    \end{macrocode}
%
% Test whether we want to merge the current note with the following
% one.  The arguments to this macro are the contents of
% |\verso@mergenotelist|, which is assembled from the
% |\verso@mergenote| commands read from the aux file.
%    \begin{macrocode}
\def\verso@testmergenote#1,#2\@nil{
  \def\@tempa{#1}
  \ifx\@tempa\@empty
    \@tempcnta=-1
  \else
    \@tempcnta=#1
  \fi
  \advance\@tempcnta -1
  \ifnum\@tempcnta=\verso@currentnotenum
%    \end{macrocode}
% Set |\if@tempswa| true, set |\verso@mergenotelist| to the tail of
% the list, and ensure that this note is merged next time round.
%    \begin{macrocode}
    \@tempswatrue
    \xdef\verso@mergenotelist{#2}
    \immediate\write\@auxout{\string\verso@mergenote{#1}}
  \else
    \@tempswafalse
  \fi
}
%    \end{macrocode}
%
% The macro |\verso@setnote| is the one which does the work of
% positioning a single note on the (verso) page.  We potentially work
% quite hard to avoid notes overwriting each other here.  If
% |\verso@mergestate| is greater than one (by default, it's
% initialised to~2, but any number greater than~1 would be equivalent)
% then when two notes collide, we simply put a horizontal bar between
% them, and hope for the best.  Each time we have a collision we
% increment this number, and if we find it has a value~1 (ie, the
% first collision) we we record in the aux file that this note should
% be merged with its predecessor, by writing a |\verso@mergenote|
% command.  Next time round, when we are about to set the note
% \emph{before} that one, we avoid setting it, and instead start
% accumulating the text of such merged notes, in the token register
% |\verso@accumulatenote|.  We only add a single note to the list of
% merged notes on each \LaTeX\ run, since merging one note may make it
% unnecessary to merge any more.  The only way to delete the
% collections of merged notes is to delete the aux file.
%    \begin{macrocode}
\newcount\verso@mergestate
  \verso@resetmergestate
\newtoks\verso@accumulatenote
  \verso@accumulatenote={}
%    \end{macrocode}
%
% Set the note.  The arguments are (1) the page number, (2) the
% position on the page, and (3) the text of the note.
%    \begin{macrocode}
\long\def\verso@setnote#1#2#3{
  \@tempdima=\paperheight \advance\@tempdima -#2
  % target position; will become skip to add
  \@tempdimb=\verso@currentposition
  \global\advance\verso@currentnotenum 1
%    \end{macrocode}
% Check whether we're to merge the following note into this one.
%    \begin{macrocode}
  \expandafter\verso@testmergenote\verso@mergenotelist,\@nil
  \if@tempswa
    \verso@accumulatenote=\expandafter{%
      \the\verso@accumulatenote
      #3%
      \quad\P~\nobreak}
    %\PackageInfo{versonotes}{\typeout{Merging notes on p#1}}
  \else
%    \end{macrocode}
% No merging: set the current note, possibly along with any
% accumulated notes, in a box, and then start to work out where to put it.
%    \begin{macrocode}
    \setbox0=\vtop{
      \versolayout
      \the\verso@accumulatenote
      #3\par}
    \verso@accumulatenote={}
%    \end{macrocode}
% We now know how big this box is (|\ht0|), how far down the page the
% accumulated boxes are (|\verso@currentposition|), and where the box
% is to appear, as an offset from the top of the paper (|\@tempdima|).
% Work how how much of a skip we have to add to get there.
%    \begin{macrocode}
    \ifdim\@tempdima>\verso@currentposition
%    \end{macrocode}
% The target position is below the current position; add a skip.  This
% is the straightforward case, and leaves the skip in |\@tempdima| and
% the new current position in |\@tempdimb|.
%    \begin{macrocode}
      \advance\@tempdima -\verso@currentposition
      \advance\@tempdima -\ht0
      \advance\@tempdimb \@tempdima
      \verso@resetmergestate
    \else
%    \end{macrocode}
% Or the target position is above the current position;
% thus the new material will have to be moved down
% (I'm not sure how best to handle the case where this skip results
% in the note hitting the bottom of the page.  Should it be merged
% with that case below, somehow?).
%    \begin{macrocode}
      % note: \PackageWarning seems to produce odd effects here
      \message{^^Jversonotes warning: Moved versonote text on p.#1.}
      \advance\verso@mergestate 1
      \ifnum\verso@mergestate=1
        \immediate\write\@auxout{\string\verso@mergenote{\the\verso@currentnotenum}}
      \fi
      \nointerlineskip
      \vbox to \verso@spacerskip{\vfil
        \hbox to \hsize{\hfil\vrule height 0.4pt width 10em}
        \vfil}
      \advance\@tempdimb \verso@spacerskip
      \@tempdima=0pt % ...so don't add any more skip
    \fi
    \advance\@tempdimb \ht0
    \advance\@tempdimb \dp0
%    \end{macrocode}
% Parameter |\@tempdimb| now holds the expected new value of
% |\verso@currentposition|.  Check to see if this would be beyond the bottom
% of the page, and move the text upwards in that case.
%    \begin{macrocode}
    \ifdim\@tempdimb>\verso@pagebottom
      \message{^^Jversonotes warning: versonote text on p.#1 hit bottom of page.}
      \advance\@tempdima -\@tempdimb
      \advance\@tempdima \verso@pagebottom
      \@tempdimb=\verso@pagebottom
    \fi
%    \end{macrocode}
% Finally, do the skip and add the box.
%    \begin{macrocode}
    \vskip\@tempdima
    \verso@currentposition=\@tempdimb
    \nointerlineskip
    \box0
  \fi
}
%    \end{macrocode}
%
% Log notes where a previous run has discovered they collide.
%    \begin{macrocode}
\def\verso@mergenotelist{}
\def\verso@mergenote#1{\xdef\verso@mergenotelist{\verso@mergenotelist #1,}}
%    \end{macrocode}
%
% \subsection{Overall processing logic, and shipout}
%
% We want to use the current shipout mechanism, but also to remain
% compatible with pre-2020 \LaTeX, so conditionalise appropriately.
% Note that we can't use the (apparently preferable)
% |\IfFormatAtLeastTF| command to do this test: we want to continue to
% work even when we're using a \LaTeX\ which is too old for this
% command to be defined.
%    \begin{macrocode}
\newif\ifverso@Liii
\@ifl@t@r\fmtversion{2020/10/01}\verso@Liiitrue\verso@Liiifalse
\PackageInfo{versonotes}
            {choosing support for \ifverso@Liii L3\else pre-L3\fi}
%    \end{macrocode}
%
% For the L3 case, we will use the |shipout/before| hook, and use
% |\RawShipout| to output the separate versonotes pages.
% See the \texttt{ltshipout-doc} documentation for details.
% But in the pre-L3 case, save the original definition of |\shipout|
% (using the L3 |\RawShipout| name for clarity),
% prior to our redefining it below.
% We could do this perfectly well using the \Lpackage{everyshi} package,
% but we do it by hand in order to avoid the extra dependency.
%    \begin{macrocode}
\ifverso@Liii\else
  \let\RawShipout\shipout
\fi
%    \end{macrocode}
%
% We process the versonotes a page at a time.  We don't have to do
% anything clever, because the page that a versonote lands on is
% governed by the page that the |\versonote| call appears on.  If we
% have a long versonote at the bottom of a page, then we don't try to
% spill over onto the next (that would presumably be possible, using
% the inserts mechanism, but would be a significant jump in
% complication).  We regard this situation as one for the user to work
% out for themself.
%
% Macro |\verso@processonepage@| consumes the next group in the
% |\verso@pages| list.
%
% Macro |\verso@processonepage| is called just before each shipout of
% a `real' page, as the content of the \texttt{shipout/before} hook
% (or as part of the redefined |\shipout| in the pre-L3 case).
% If we are putting notes on verso pages
% (ie, the usual case, as opposed to recto notes),
% then \emph{before} we ship out page~2, we must construct and
% ship out the notes for page~2; we will have a set of notes for
% page~1 (which we expect will be empty), which we must discard; we
% achieve this by simply doing nothing if the current page is page~1.
% If, on the other hand, we are putting notes on recto pages, then we
% must instead ship out the notes for page~2 just before shipping out page~3, and
% must similarly do nothing on pages~1 and~2.  This works because
% in the latter case we have initialised |\verso@pages| with an extra
% leading |{{}}|.
%
% We manage the page skipping by decrementing a `pages to skip'
% counter.  The more obvious way of doing that it to test the value of
% |\@tempcnta|, which at this point holds the current page number, but
% this produces the wrong answer if the document starts at other than
% page~1 (perhaps because the document includes |\setcounter{page}{99}|).
%    \begin{macrocode}
\newcount\verso@pagestoskip
\if@verso@notesonleft
  \verso@pagestoskip=1
\else
  \verso@pagestoskip=2
\fi
%    \end{macrocode}
%
% Define |\verso@processonepage@|.
%    \begin{macrocode}
\long\def\verso@processonepage@#1#2\@nil{
  \def\@tempa{#1}
%    \end{macrocode}
% Do nothing on page~1 (in the verso case), or pages~1 and~2 (in the
% recto case).  Any notes which would appear in such a position are
% silently discarded.
%    \begin{macrocode}
  \ifnum\verso@pagestoskip=0
%    \end{macrocode}
% If there are no verso-notes on this page, then ship out an empty box.
%    \begin{macrocode}
    \ifx\@tempa\@empty
      \RawShipout\vbox{}
%    \end{macrocode}
% This is the normal case:
% create a box containing the |\\{...}| contents of the
% current page's verso-notes
%    \begin{macrocode}
    \else
      \begingroup
%    \end{macrocode}
% Within the box we're about to create, we have to `un-protect' things.
% Robust commands (including for example |\emph| and other font-changing commands) are
% defined using |\protect|, which in the present context, inside
% |\@outputpage|, is |\let| equal to |\noexpand|.
% We must set this to be simply |\relax|,
% as it is in the normal run of text elsewhere
% (see \url{http://tex.stackexchange.com/questions/206673/}).
%    \begin{macrocode}
        \let\protect\relax
%    \end{macrocode}
% Set everything up for setting the verso page.
%    \begin{macrocode}
        \hoffset=-1in \advance\hoffset \versoleftmargin
        \voffset=-1in
        \hsize=\versotextwidth
        \topskip=0pt
        \topmargin=0pt
        \headheight=0pt
        \headsep=0pt
        \vsize=1000mm % larger than any actual note
        \normalfont\normalsize
%    \end{macrocode}
% Construct and ship out the page contents.
%    \begin{macrocode}
        \long\def\\##1{\verso@setnote ##1}
        \RawShipout\vbox{
          \verso@currentposition=0pt
          #1}
      \endgroup
    \fi
%    \end{macrocode}
% Otherwise, the |\verso@pagestoskip| counter is still positive,
% indicating that we are skipping pages.
% Decrement the counter and do nothing else.
%    \begin{macrocode}
  \else
    \global\advance\verso@pagestoskip -1
  \fi
%    \end{macrocode}
% Finally, set |\verso@pages| to the tail of the list.
%    \begin{macrocode}
  \global\verso@pages={#2}}
%    \end{macrocode}
%
% The command |\verso@processonepage| is invoked once on every |\shipout|.
%    \begin{macrocode}
\def\verso@processonepage{
  \if@verso@processversonotes
    \expandafter\verso@processonepage@\the\verso@pages\@nil
%    \end{macrocode}
% If this test is false, then we don't seem to have any versonotes in this file,
% so don't come here again.
%    \begin{macrocode}
  \else
    \global\let\verso@processonepage\relax
  \fi
}
%    \end{macrocode}
%
% And finally, do the |\shipout| gymnastics.
%    \begin{macrocode}
\ifverso@Liii
  \AddToHook{shipout/before}{\verso@processonepage}
\else
  \def\shipout{\verso@processonepage \RawShipout}
\fi
%    \end{macrocode}
%
% All done!
%    \begin{macrocode}
%</package>
%    \end{macrocode}
% \Finale
%
\endinput