%D \module
%D   [       file=page-ini,
%D        version=2000.10.20,
%D          title=\CONTEXT\ Page Macros,
%D       subtitle=Initializations,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{ConTeXt Page Macros / Initializations}

% still a dutch/english mess

%D This class of modules implements the output routines and
%D floating body support. Although the modules are relatively
%D new, the code herein is rather old. This reordering was
%D needed when column sets were implemented and sharing code
%D started to make sense.

%D The history shows from the code, since both column
%D mechanism use a different way of looping over columns.

\unprotect

\def\m!otr{otr}

\chardef\normalpagebox=255

\newbox\pagebox

\ifx\recalculatelayout\undefined

  \let \recalculatelayout \relax

\fi

\ifx\recalculatelogos\undefined

  \let \recalculatelogos  \relax
  \let \addlogobackground \gobbleoneargument % <box>

\fi

\ifx\recalculatebackgrounds\undefined

  \let \recalculatebackgrounds \relax
  \let \addmainbackground      \gobbleoneargument % <box>
  \let \addtextbackground      \gobbleoneargument % <box>
  \let \addpagebackground      \gobbleoneargument % <box>
  \let \addprintbackground     \gobbleoneargument % <box>
  \let \addstatusinfo          \gobbleoneargument % <box>

\fi

\ifx\realpageno\undefined

  \countdef\realpageno = 0   \realpageno = 1
  \countdef\userpageno = 1   \userpageno = 1
  \countdef\subpageno  = 2   \subpageno  = 0 % !!
  \countdef\arrangeno  = 3   \arrangeno  = 0 % !!

  \let\pageno\userpageno

\fi

\ifx\realfolio\undefined

  \def\realfolio{\the\realpageno}

\fi

\newcount\nofshipouts

\appendtoks
  \global\advance\nofshipouts\plusone
\to \everyaftershipout

% principle:
%
% multiple otr's
%
% (1) single column, simple routine (old one)
% (2) multi column, collect and split routine (old one)
% (3) multi column, page by page (new one, needed for taco)
% (4) single column, spread handling (for fun)
% (5) multi column, page by page, spread handling (as challenge)
%
% common components
%
% (1) float placement
% (2) float flushing
% (3) page body building
% (4) ...
%
% ort
%
% + balancing
% - mixed / one / multi / balancetofit
% + backgrounds
% + pre / post
% + distances / heights
% + ragged / baseline / normal
% - pos sync
% - last page
%
% - itemize / subtexts -> old mechanism
%
% floats
%
% - top / bottom / side / page / column / spead
% - flush / packed flush / current page / next page / area
%
% footnotes
%
% + carry over pre column / local to column
% + last column / pre last column / each column
% - multiple classes
% - area / page / end
%
% areas
%
% - top / bottom / mid in spread
%
% IMPORTANT
%
% switchtobodyfont in between ivm top

% floats:
%
% tricky in balancing mode, a la huidige multi columns

% messages moved

% messages moved

% messages moved

% messages moved

% messages moved

% messages moved

% messages moved

% messages moved

\ifx\dosetuplayout\undefined % overloaded in page-lay !

  \def\setuplayout{\dodoubleempty\getparameters[\??ly]}

\fi

\ifx\mkprocesscolumncontents\undefined\let\mkprocesscolumncontents\gobbleoneargument\fi
\ifx\mkprocesspagecontents  \undefined\let\mkprocesspagecontents  \gobbleoneargument\fi
\ifx\mkprocessboxcontents   \undefined\let\mkprocessboxcontents   \gobbleoneargument\fi

\def\normalejectpenalty{-\plustenthousand   }  \let\ejectpenalty\normalejectpenalty
\def\normalsuperpenalty{-\plustwentythousand}  \let\superpenalty\normalsuperpenalty

%D In case we're not running \ETEX, we need to bypass a
%D couple of primitives.

% ONE = single column
% MUL = multi column
% SET = columns sets

\def\@@OTR{OTR}

\let\OTRdefault\empty

\def\OTRcommand#1%
  {\csname\@@OTR
     \ifcsname\@@OTR\OTRidentifier\strippedcsname#1\endcsname
       \OTRidentifier
     \else\ifcsname\@@OTR\OTRdefault\strippedcsname#1\endcsname % fallback
       \OTRdefault
     \fi\fi
   \strippedcsname#1\endcsname}

% obsolete

\def\installotr#1% andere naam, beter \connectotr of zo
  {\def\OTRidentifier{#1}}

\def\activateotr#1#2%
  {\def\OTRidentifier{#1}%
   \def\OTRdefault   {#2}}

%D The initialization of the \type {\hsize} and \type {\vsize}
%D depends on the OTR used.

\def\setvsize             {\OTRcommand\setvsize}
\def\sethsize             {\OTRcommand\sethsize}
\def\finalsidefloatoutput {\OTRcommand\finalsidefloatoutput}
\def\dopagecontents       {\OTRcommand\dopagecontents}

\def\dosettopinserts      {\OTRcommand\dosettopinserts}
\def\dosetbotinserts      {\OTRcommand\dosetbotinserts}
\def\dotopinsertions      {\OTRcommand\dotopinsertions}
\def\dobotinsertions      {\OTRcommand\dobotinsertions}
\def\dosetbothinserts     {\OTRcommand\dosetbothinserts}

\def\doflushfloats        {\OTRcommand\doflushfloats}
\def\flushfloatbox        {\OTRcommand\flushfloatbox}
\def\docheckiffloatfits   {\OTRcommand\docheckiffloatfits}

\def\someherefloat        {\OTRcommand\someherefloat}
\def\somefixdfloat        {\OTRcommand\somefixdfloat}
\def\somepagefloat        {\OTRcommand\somepagefloat}
\def\sometopsfloat        {\OTRcommand\sometopsfloat}
\def\somebotsfloat        {\OTRcommand\somebotsfloat}
\def\somesidefloat        {\OTRcommand\somesidefloat}

\def\flushsavedfloats     {\OTRcommand\flushsavedfloats}

\def\synchronizehsize     {\OTRcommand\synchronizehsize}

\def\gotonextpage {\OTRcommand\gotonextpage }
\def\gotonextpageX{\OTRcommand\gotonextpageX} % will become obsolete

% beter een \installotr#1 met #1 = macro en auto test

\newif   \iftraceotr
\newif   \ifinotr
\newtoks \mainoutput
\newcount\otrlevel

% When issuing two \par\penalty-\plustenthousand's, only the first
% triggers the otr; obscure feature or optimization?

\def\outputcounter{-100010} % -10010

\def\doinvokeoutput
  {\iftraceotr
     \expandafter\dodotracedoutput
   \else
     \expandafter\dodoinvokeoutput
   \fi}

\def\outputmessage#1#2#3%
  {\iftraceotr\writestatus\m!otr{#1 #2 \number#3}\fi}

\def\dodoinvokeoutput#1%
  {\outputmessage+{special}{#1}%
   \bgroup\par\penalty#1\relax\egroup
   \outputmessage-{special}{#1}}

\def\dodotracedoutput#1%
  {\outputmessage+{traced}{#1/\the\outputpenalty}%
   \writestatus\m!otr{c:\number\mofcolumns,v:\the\vsize,g:\the\pagegoal,t:\the\pagetotal}%
   \dodoinvokeoutput{#1}%
   \writestatus\m!otr{c:\number\mofcolumns,v:\the\vsize,g:\the\pagegoal,t:\the\pagetotal}%
   \outputmessage-{traced}{#1/\the\outputpenalty}}

\def\installoutput#1#2% \invoke \action
  {\decrement\outputcounter
   \edef#1{\noexpand\doinvokeoutput{\outputcounter}}%
   \setvalue{\@@OTR\outputcounter}{#2}}

\def\invokeoutputroutine
  {\outputmessage+{trying}\outputpenalty
   \executeifdefined{\@@OTR\the\outputpenalty}\dodonormaloutput
   \outputmessage-{trying}\outputpenalty}

\def\dodonormaloutput
  {\outputmessage+{normal}\outputpenalty
   \the\OTRcommand\output
   \outputmessage-{normal}\outputpenalty}

\mainoutput{\invokeoutputroutine} \output{\inotrtrue\the\mainoutput}

%D Some hooks:

\output{\inotrtrue\the\everybeforeoutput\the\mainoutput\the\everyafteroutput}

\ifx\pagediscards\undefined \let\pagediscards\relax \fi

\installoutput\synchronizeoutput % maybe add pagediscards
  {\ifvoid\normalpagebox\else
     \unvbox\normalpagebox
     \pagediscards % maybe not needed ?
   \fi}

\installoutput\discardpage
  {\setbox\scratchbox\box\normalpagebox}

%D In order to force consistent use of variables, we
%D predefine a lot of them here.

%D The next two registers can be used to store pre column
%D material as well as footnotes or so.

\newbox\precolumnbox   \newdimen\precolumnboxheight
\newbox\postcolumnbox  \newdimen\postcolumnboxheight

%D We reserve a counter for the number of columns as well as
%D the current column. Both are not to be changed by users!

\newcount\nofcolumns \nofcolumns = 1
\newcount\mofcolumns \mofcolumns = 1

\chardef\maxnofcolumns       = 50
\chardef\allocatednofcolumns =  0

%D The next dimensions reports the final column height

\newdimen\finalcolumnheights
\newcount\finalcolumnlines

%D During initialization the temporary boxes are allocated.
%D This enables us to use as much columns as we want, without
%D exhausting the pool of boxes too fast. We could have packed
%D them in one box, but we've got enough boxes.
%D
%D Two sets of boxes are declared, the txtboxes are used for
%D the text, the topboxes are for moved column floats.

\def\@col@{@col@}

\def\initializecolumns#1%
  {\ifnum#1>\maxnofcolumns
     \showmessage\m!columns1\maxnofcolumns
     \nofcolumns\maxnofcolumns
   \else
     \nofcolumns#1\relax
   \fi
   \ifnum\nofcolumns>\allocatednofcolumns
     \dorecurse\nofcolumns
       {\ifnum\recurselevel>\allocatednofcolumns\relax
          % \newbox\next \letgvalue{\@col@-\recurselevel-t}=\next
          \@EA\newbox\csname\@col@-\recurselevel-t\endcsname % text
          \@EA\newbox\csname\@col@-\recurselevel-f\endcsname % foot
          \@EA\newbox\csname\@col@-\recurselevel-h\endcsname % top insert
          \@EA\newbox\csname\@col@-\recurselevel-l\endcsname % top insert
        \fi}%
     \global\chardef\allocatednofcolumns=\nofcolumns
   \fi}

\def\firstcolumnbox     {\columntextbox\plusone}
\def\currentcolumnbox   {\columntextbox\mofcolumns}
\def\lastcolumnbox      {\columntextbox\nofcolumns}

\def\firsttopcolumnbox  {\columntopbox \plusone}
\def\currenttopcolumnbox{\columntopbox \mofcolumns}
\def\lasttopcolumnbox   {\columntopbox \nofcolumns}

\def\columntextbox#1{\csname\@col@-\number#1-t\endcsname}
\def\columnfootbox#1{\csname\@col@-\number#1-f\endcsname}
\def\columntopbox #1{\csname\@col@-\number#1-h\endcsname}
\def\columnbotbox #1{\csname\@col@-\number#1-l\endcsname}

\def\columnsettextbox{\global\setbox\columntextbox}
\def\columnsetfootbox{\global\setbox\columnfootbox}
\def\columnsettopbox {\global\setbox\columntopbox}
\def\columnsetbotbox {\global\setbox\columnbotbox}

\def\columngettextbox{\copy\columntextbox}
\def\columngetfootbox{\copy\columnfootbox}
\def\columngettopbox {\copy\columntopbox}
\def\columngetbotbox {\copy\columnbotbox}

\def\columnerasetextboxes{\dorecurse\allocatednofcolumns{\columnsettextbox\recurselevel\emptybox}}
\def\columnerasefootboxes{\dorecurse\allocatednofcolumns{\columnsetfootbox\recurselevel\emptybox}}
\def\columnerasetopboxes {\dorecurse\allocatednofcolumns{\columnsettopbox \recurselevel\emptybox}}
\def\columnerasebotboxes {\dorecurse\allocatednofcolumns{\columnsetbotbox \recurselevel\emptybox}}

%D Without going in details we present two macro's which handle
%D the columns. The action which is transfered by the the first
%D and only parameter can do something with \type
%D {\currentcolumnbox}. In case of the mid columns, \type
%D {\firstcolumnbox} and \type {\lastcolumnbox} are handled
%D outside these macro's.

\def\dohandlecolumn#1%
  {\mofcolumns\recurselevel
   \let\currentcolumn\recurselevel
   #1\relax}

\def\dohandleallcolumns#1%
  {\dorecurse\nofcolumns{\dohandlecolumn{#1}}}

\def\dohandlerevcolumns#1%
  {\dostepwiserecurse\nofcolumns\plusone\minusone{\dohandlecolumn{#1}}}

\def\dohandlemidcolumns#1%
  {\dohandleallcolumns
     {\ifnum\recurselevel>\plusone
        \ifnum\recurselevel<\nofcolumns
          \dohandlecolumn{#1}%
        \fi
      \fi}}

%D This register can be used as a temporary storage for page
%D content.

\newbox\restofpage

%D Features.

\newif\ifintermediatefootnotes
\newif\ifcarryoverfootnotes  %\carryoverfootnotestrue
\newif\iflastcolumnfootnotes %\lastcolumnfootnotestrue
\newif\ifbalancecolumns      %\balancecolumnstrue
\newif\ifbalancetoheight     %\balancetoheighttrue
\newif\ifforcecolumngrid      \forcecolumngridtrue
\newif\ifstretchcolumns       \stretchcolumnsfalse
\newif\ifinheritcolumns       \inheritcolumnsfalse
\newif\ifheightencolumns      \heightencolumnsfalse

\newif\ifbalancingcolumns
\newif\ifcollectingcontent
\newif\ifcolumnoverflow
\newif\iffinalflushingfloats
\newif\ifpackflushedfloats   \packflushedfloatstrue % for the moment

\newdimen\intercolumnwidth
\newdimen\localcolumnwidth
\newdimen\savedpagetotal

\chardef\columndirection=0   % 0:lr 1:rl

\def\minbalancetoplines      {1}
\def\minfreecolumnlines      {2}

\newif\ifrecentercolumnbox    \recentercolumnboxtrue
\newif\ifrerecentercolumnbox  \rerecentercolumnboxtrue
\newif\ifpackcolumnfloats     \packcolumnfloatstrue

\newbox\collectedpagefloats
\newbox\collectedleftpagefloats
\newbox\collectedrightpagefloats

%D The \type {\ifdim} test is needed, because otherwise the
%D last line of a text end up on top of the baseline instead of
%D on the baseline, as is the case with preceding pages.
%D Also, a \type {\vfil} better than a \type {\vfill}.

% to be replaced by \page[now] \page[final] / merged

% \def\eject         {\par\penalty-\plustenthousand   } % == {\par\break} % plain
% \def\supereject    {\par\penalty-\plustwentythousand} % also plain

\def\eject         {\par\ifvmode\penalty\ejectpenalty\fi\resetpagebreak} % == {\par\break} % plain
\def\supereject    {\par\ifvmode\penalty\superpenalty\fi\resetpagebreak} % also plain

\def\doejectpage   {\par\ifvmode\ifdim\pagetotal>\pagegoal\else\normalvfil\fi\fi} % pg set to \textheight
\def\ejectpage     {\doejectpage\eject}
\def\superejectpage{\doejectpage\supereject}

\ifx\bye\undefined \def\bye{\par\vfill\supereject\end} \fi % plain tex command

% floats
%
% \def\ejectinsert
%   {\flushnotes
%    \bgroup
%    \noftopfloats\plusthousand
%    \nofbotfloats\zerocount
%    \doflushfloats
%    \egroup}

\def\ejectinsert
  {\flushnotes
   \bgroup
   \noftopfloats\plusthousand
   \nofbotfloats\zerocount
   % this is needed in case a float that has been stored
   % ends up at the current page; this border case occurs when
   % the calculated room is 'eps' smaller that the room available
   % when just flushing; so now we have (maybe optional):
   \pagebaselinecorrection
   % alas, this is tricky but needed (first surfaced in prikkels)
   \doflushfloats
   \egroup}

\def\ejectdummypage
  {\endgraf \ifvmode
     \ejectinsert
     \hardespatie % will be different
     \vfill
     \gotonextpage
   \fi}

\def\beforefinaloutput
  {}

\def\afterfinaloutput
  {\forgetall
   \vskip\zeropoint\relax
   \ifvoid\normalpagebox \else
     \unvbox\normalpagebox
     \penalty\outputpenalty
   \fi
   % not really needed, replaced by \flushsavedfloats
   \ifnum\outputpenalty>\superpenalty \else % better use a proper otr signal
     \dosupereject
   \fi
   % but does not hurt either (we're still in the otr!)
   \inpagebodytrue      % needed for enabling \blank !
   \flushsavedfloats    % was \dosetbothinserts; only otr one !
   \setvsize            % this is needed for interacting components, like floats and multicolumns
   \adaptfuzzypagegoal} % watch this hack!

\def\dofinaloutput#1#2% \vbox: prevents spurious spaces in every..pagebody
  {\beforefinaloutput
   \the\everybeforeshipout % brrr not in shipout
   \ifspecialbasedsettings
     \myshipout{\hbox{\hbox to \zeropoint{\the\pageboundsettings}%
                      \hbox{\vbox{\dopagebody#1#2\setpagecounters}}}}%
   \else
     \the\pageboundsettings
     \myshipout{\hbox{\vbox{\dopagebody#1#2\setpagecounters}}}%
   \fi
   \the\everyaftershipout
   \afterfinaloutput
   \popproperties}  % ... and here ...

\def\donofinaloutput#1#2%
  {\beforefinaloutput
   \the\everybeforeshipout
   \setpagecounters
   \message{[-\the\realpageno]}%
   \setbox\scratchbox\hbox
     {%\the\everyshipout % still needed here ?
      \dopagebody#1#2}%
   \deadcycles\zerocount
   \gotonextrealpage
   \the\everyaftershipout
   \afterfinaloutput
   \popproperties}  % ... and here

% beware: \ifprocessingpages is in use

\ifx\checkpageversion\undefined \let\checkpageversion\relax \fi % todo: hook into \everybeforeshipout
\ifx\doflushspread   \undefined \let\doflushspread   \relax \fi % todo

\def\finaloutput#1#2%
  {\checkpageversion
   \ifprocessingpages
     \ifpageselected
       \@EAEAEA\dofinaloutput
     \else
       \@EAEAEA\donofinaloutput
     \fi
   \else
     \ifpageselected
       \@EAEAEA\donofinaloutput
     \else
       \@EAEAEA\dofinaloutput
     \fi
   \fi#1#2%
   \resetselectiepagina
   \incrementpagenumber
   \checkpagedimensions
   \ifnum\outputpenalty>\superpenalty \else
     \dosupereject
   \fi
   \doflushspread
   \dopostponeblock}

\def\dooutput
  {\finaloutput\unvbox\normalpagebox}

\maxdeadcycles=1000

% will be installable tracer; better use chardef

% this needs a real cleanup

\def\doplaceversiontext#1#2%
  {\doifsomething{#2}
     {\defconvertedcommand\ascii{#2}%
      \space#1:\space\ascii\space
      \!!doneatrue}}

\def\placeversioninfo % nog engels maken
  {\ifcase\conceptmode
     % 0 : nothing
   \or
     % 1 : simple
     \vskip\!!sixpoint
     \hbox to \makeupwidth
       {\infofont
        \v!concept:\space\currentdate
        \hss\reportpagedimensions}%
   \else
     % 2/3 : extensive
     \vskip\!!sixpoint
     \hbox to \makeupwidth
       {\infofont
        \getmessage\m!systems{27}:\space\currentdate\space
        \doplaceversiontext\v!project  \currentproject
        \doplaceversiontext\v!product  \currentproduct
        \doplaceversiontext\v!component\currentcomponent
        \if!!donea\else\space\v!file:\space\jobname\fi
        \hss\reportpagedimensions}%
   \fi}

% tot hier

\def\doversion[#1]%
  {\chardef\conceptmode\zerocount
   \overfullrule\zeropoint
   \processaction % \v!final=>
     [#1]
     [  \v!concept=>\chardef\conceptmode\plusone,  % simple banner
           \v!file=>\chardef\conceptmode\plustwo,  % full banner
      \v!temporary=>\chardef\conceptmode\plusthree % full banner plus
                    \overfullrule5\points]}        % info in the margin

\def\version
  {\dosingleargument\doversion}

\def\addstatusinfo
  {\ifcase\conceptmode
     \@EA\gobbleoneargument
   \else
     \@EA\doaddstatusinfo
   \fi}

\def\doaddstatusinfo#1%
  {\setbox#1\vbox to \paperheight
     {\vsmashbox#1\box#1%
      \offinterlineskip
      \vskip\topspace
      \hsize\paperwidth
      \hfill\hbox{\placetestinfo\hskip.5cm}\vss
      \settexthoffset\hskip\texthoffset % brrrr
     %\tlap{\placeversioninfo}\vskip.5cm
      \vbox to 1cm{\vss\placeversioninfo\vss}}}

\def\dotestinfo#1#2#3%
  {\ifinpagebody\else\ifnum\conceptmode=\plusthree
     \begingroup
       \defconvertedcommand\ascii{#3}%
       \xdef\extratestinfo
         {#2\space\ascii}%
       \gdef\totaltestinfo
         {\global\setbox#1\vbox
            {\unvbox#1\relax
             \infofont \setupinterlinespace
             \hbox
               {\strut
                \expanded{\doboundtext{\extratestinfo}{12em}{..}}%
                \quad}}}%
     \endgroup
     \ifinner
       \aftergroup\totaltestinfo
     \else
       \totaltestinfo
     \fi
   \fi\fi}

% this will be inserts some day

% \installinsertion\referenceinfobox
% \installinsertion\registerinfobox
% \installinsertion\floatinfobox

\newbox\referenceinfobox
\newbox\registerinfobox
\newbox\floatinfobox

\def\referenceinfo{\dotestinfo\referenceinfobox}
\def\registerinfo  {\dotestinfo\registerinfobox}
\def\floatinfo     {\dotestinfo\floatinfobox}

\def\placetestinfo
  {\vbox to \makeupheight
     {\forgetall
      \infofont
      \hsize10em
      \ifvoid\floatinfobox\else
        \strut \getmessage\m!systems{24}%
        \vskip\!!sixpoint
        \unvbox\floatinfobox
        \vskip\!!twelvepoint
      \fi
      \ifvoid\referenceinfobox\else
        \strut \getmessage\m!systems{25}%
        \vskip\!!sixpoint
        \unvbox\referenceinfobox
        \vskip\!!twelvepoint
      \fi
      \ifvoid\registerinfobox\else
        \strut \getmessage\m!systems{26}%
        \vskip\!!sixpoint
        \unvbox\registerinfobox
      \fi
      \vss}}

\version[\v!final]

% bewaren tvb documentatie
%
% \hbox to \hsize
%   {\en
%    \switchnaarkorps[5pt]%
%    \emergencystretch2em
%    \dimen0=\baselineskip
%    \baselineskip=\dimen0 plus 1pt
%    \hsize=.2\hsize
%    \vsize=2\hsize
%    \ruledvbox to \vsize{\input tufte \par}\hss
%    \ruledvbox to \vsize{\input tufte \par\kern-\prevdepth}\hss
%    \ruledvbox to \vsize{\input tufte \par\kern0pt}\hss
%    \ruledvbox to \vsize{\input tufte \par\vfill}\hss
%    \ruledvbox to \vsize{\input tufte \par\kern-\prevdepth\vfill}}
%
% \hbox to \hsize
%   {\en
%    \switchnaarkorps[5pt]%
%    \emergencystretch2em
%    \dimen0=\baselineskip
%    \baselineskip=\dimen0 plus 1pt
%    \hsize=.18\hsize
%    \vsize=2.5\hsize
%    \setbox0=\vbox{\input tufte\relax}%
%    \ruledvbox to \vsize{\unvcopy0}\hss
%    \ruledvbox to \vsize{\unvcopy0\kern-\dp0}\hss
%    \ruledvbox to \vsize{\unvcopy0\kern0pt}\hss
%    \ruledvbox to \vsize{\unvcopy0\vfill}\hss
%    \ruledvbox to \vsize{\unvcopy0\kern-\dp0\vfill}}

\newtoks\afterpage     \newtoks\aftereverypage
\newtoks\beforepage    \newtoks\beforeeverypage

\chardef\showgridstate=0

\def\showgrid
  {\dosingleempty\doshowgrid}

\def\doshowgrid[#1]%
  {\chardef\showgridstate    \plusone % downward compatible default
   \chardef\gridboxlinemode  \plusone
   \chardef\gridboxlinenomode\plusone
   \processallactionsinset
     [#1]%
     [ \v!reset=>\chardef\showgridstate    \zerocount,
      \v!bottom=>\chardef\showgridstate    \plusone,
         \v!top=>\chardef\showgridstate    \plustwo,
        \v!none=>\chardef\gridboxlinemode  \zerocount,
         \v!all=>\chardef\gridboxlinemode  \plusone,
       \v!lines=>\chardef\gridboxlinemode  \plustwo,
       \v!frame=>\chardef\gridboxlinemode  \plusthree,
    \v!nonumber=>\chardef\gridboxlinenomode\zerocount,
       \v!right=>\chardef\gridboxlinenomode\plusone,
        \v!left=>\chardef\gridboxlinenomode\plustwo]}

\def\buildpagebox#1%
  {\setbox#1\vbox to \paperheight
     {\hsize\paperwidth
      \vskip\topspace
      \doifbothsides
        {\hskip\backspace}
        {\hskip\backspace}
        {\hskip\paperwidth \hskip-\backspace \hskip-\makeupwidth}%
      \box#1}%
   \dp#1\zeropoint}

% \newif\ifpagebodyornaments \pagebodyornamentstrue
%
% \appendtoks
%   \global\pagebodyornamentstrue
% \to \everyaftershipout

\newif\ifarrangingpages    \arrangingpagesfalse

\chardef\pageornamentstate\zerocount % 0=on 1=one-off 2=always-off

\def\pagebodyornamentstrue {\chardef\pageornamentstate\zerocount} % for a while
\def\pagebodyornamentsfalse{\chardef\pageornamentstate\plusone}   % for a while

\appendtoks
  \ifcase\pageornamentstate\or
    \chardef\pageornamentstate\zerocount
  \fi
\to \everyaftershipout

\let\poparrangedpages\relax
\let\pusharrangedpage\relax

\ifx\shiftprintpagebox\undefined
  \let\shiftprintpagebox\gobbleoneargument
  \let\shiftpaperpagebox\gobbleoneargument
\fi

\ifx\registerpageposition\undefined
  \let\registerpageposition\gobbleoneargument
\fi

\def\reportarrangedpage#1%
  {\showmessage\m!systems
     {23}{\the\realpageno.\the\pageno\ifnum\subpageno>0 .\the\subpageno\fi,#1}}

\newif\ifsavepagebody \newbox\savedpagebody

% beware, \??ly is used before defined, i.e. bad module design

\setuplayout[\c!method=\v!normal]

\def\buildpagebody#1#2%
  {\ifsavepagebody\global\setbox\savedpagebody\fi
   \vbox
     {\beginrestorecatcodes
      \forgetall  % igv problemen, check: \boxmaxdepth\maxdimen
      \boxmaxdepth\maxdimen % new
      \dontcomplain
      % the following plugin uses and sets pagebox; beware: this
      % will change and is for my (hh) personal experiments
      \executeifdefined{\??ly\c!method\@@lymethod}%
        {\getvalue{\??ly\c!method\v!normal}}#1#2%
      % the finishing touch
      \ifcase\pageornamentstate
        \addpagebackground \pagebox
      \fi
      \registerpageposition\pagebox
      \ifarrangingpages
        \shiftpaperpagebox \pagebox % \v!paper
      \else
        \clippagebox       \pagebox
        \doifelse\@@lymarking\v!page
          {\replicatepagebox  \pagebox
           \addpagecutmarks   \pagebox}
          {\addpagecutmarks   \pagebox
           \replicatepagebox  \pagebox}%
        \scalepagebox      \pagebox
        \mirrorpaperbox    \pagebox
        \orientpaperbox    \pagebox
        \addpagecolormarks \pagebox
        \centerpagebox     \pagebox
        \addprintbackground\pagebox
        \mirrorprintbox    \pagebox
        \orientprintbox    \pagebox
        \shiftprintpagebox \pagebox % \v!page
        \offsetprintbox    \pagebox
        \negateprintbox    \pagebox
      \fi
      \box\pagebox
      \endrestorecatcodes}%
   \ifsavepagebody\copy\savedpagebody\fi}

\setvalue{\??ly\c!method\v!normal}#1#2%
  {\setbox\pagebox\vbox
     {\offinterlineskip
      \ifcase\pageornamentstate
        \bgroup % else footnotes get inconsistent font/baseline
          \dostartattributes\??ly\c!style\c!color\empty
            \offinterlineskip
            \gettextboxes
          \dostopattributes
        \egroup
      \fi
      \getmainbox#1#2}% including footnotes
   \ifcase\pageornamentstate
     \addmainbackground \pagebox
     \addlogobackground \pagebox
   \fi
   \buildpagebox  \pagebox
   \addstatusinfo \pagebox}

\def\finishpagebox#1%
  {\ifarrangingpages
     \addpagecutmarks  #1%
     \addpagecolormarks#1%
     \centerpagebox    #1%
     \mirrorprintbox   #1%
     \orientprintbox   #1%
     \offsetprintbox   #1%
     \negateprintbox   #1%
   \fi}

\appendtoks \restoreglobalbodyfont \to \everybeforepagebody
\appendtoks \restorecolumnsettings \to \everybeforepagebody

\ifx\nestednewbox\undefined \newbox\nestednextbox \fi

\prependtoks \let\nextbox\nestednextbox \to \everybeforepagebody

\def\dopagebody#1#2%
  {%\getallmarks % now in following token register
   \the\everybeforepagebody
   \starttextproperties
   \gotonextsubpage  % nog eens: als in pagina (tbv standaard opmaak)
   \dontshowboxes    % dan hier blokkeren en verderop resetten
%    \shipoutfacingpage
   \checkreferences
   \checkmargeblokken
   \the\beforeeverypage
   \flushtoks\beforepage
   \inpagebodytrue\buildpagebody#1#2%
   \flushtoks\afterpage
   \the\aftereverypage
   \resetpagebreak
   %updatelistreferences % now in aftereverypage
   \resetlayouttextlines % will go to \aftereverypage
   \stoptextproperties
   \the\everyafterpagebody}

\newtoks\pageboundsettings

\prependtoks \initializepaper \to \pageboundsettings

% not here

\newif\ifpagebreakdisabled \pagebreakdisabledfalse

% \chardef\testpagemethod=0 % todo: \testnewpage[method=,lines=,voffset=]
%
% \def\testpage    {\dotripleempty\dotestpage[\plusone]}
% \def\testpageonly{\dotripleempty\dotestpage[\plustwo]}
%
% \def\dotestpage[#1][#2][#3]%
%   {%\relax % needed  before \if
%    \endgraf
%    \ifpagebreakdisabled
%      % do nothing
%    \else
%      %ifnum#1=\plusone\synchronizeoutput\fi
%      \ifdim\pagegoal<\maxdimen \relax
%        \ifdim\pagetotal<\pagegoal \relax
%          \scratchdimen\lineheight
%          \multiply\scratchdimen#2\relax
%          \advance\scratchdimen \pagetotal
%          \ifdim\lastskip<\parskip
%            \advance\scratchdimen \parskip
%          \fi
%          \ifthirdargument
%            \advance\scratchdimen#3\relax
%          \fi
%          \ifcase\testpagemethod
%            \ifdim\scratchdimen>.99\pagegoal
%              \vfill\eject % \penalty-\!!tenthousand\relax
%            \fi
%          \or
%            \advance\scratchdimen-\pagegoal
%            \ifdim\scratchdimen>-\lineheight
%              \vfill\eject % \penalty-\!!tenthousand\relax
%            \fi
%          \or
%            \getnoflines\pagegoal
%            \advance\scratchdimen-\noflines\lineheight \relax
%            \ifdim\scratchdimen>-\lineheight
%              \vfill\eject % \penalty-\!!tenthousand\relax
%            \fi
%          \or % same as 0 but more accurate
%            \advance\scratchdimen-10\s!sp\relax
%            \ifdim\scratchdimen>\pagegoal
%              \vfill\eject % \penalty-\!!tenthousand\relax
%            \fi
%          \fi
%        \else
%          % force page break / new
%          % \vfill\eject % \penalty-\!!tenthousand\relax
%        \fi
%      \else
%        \ifnum#1=\plusone\goodbreak\fi
%      \fi
%    \fi}

\chardef\testpagemethod \zerocount % todo: \testnewpage[method=,lines=,voffset=]
\chardef\testpagetrigger\zerocount

\def\testpage    {\dotripleempty\dotestpage[\plusone  ]} %
\def\testpageonly{\dotripleempty\dotestpage[\plustwo  ]} % no penalties added to the mvl
\def\testpagesync{\dotripleempty\dotestpage[\plusthree]} % force sync

\def\dotestpage[#1][#2][#3]% don't change, only add more methods
  {\relax % needed before \if
   \ifpagebreakdisabled
     \endgraf
   \else
     % new from here
     \ifcase\testpagetrigger
       \endgraf
     \or
       \ifvmode
         \dosomebreak\allowbreak
       \else % indeed?
         \vadjust{\allowbreak}%
         \endgraf
       \fi
     \fi
     % till here
     \ifdim\pagegoal<\maxdimen \relax
       \ifdim\pagetotal<\pagegoal \relax
         \scratchdimen\lineheight
         \multiply\scratchdimen#2\relax
         \advance\scratchdimen \pagetotal
         \ifdim\lastskip<\parskip
           \advance\scratchdimen \parskip
         \fi
         \ifthirdargument
           \advance\scratchdimen#3\relax
         \fi
         \ifcase\testpagemethod
           \ifdim\scratchdimen>.99\pagegoal
             \penalty-\!!tenthousand\relax
           \fi
         \or
           \advance\scratchdimen-\pagegoal
           \ifdim\scratchdimen>-\lineheight
             \penalty-\!!tenthousand\relax
           \fi
         \or
           \getnoflines\pagegoal
           \advance\scratchdimen-\noflines\lineheight \relax
           \ifdim\scratchdimen>-\lineheight
             \penalty-\!!tenthousand\relax
           \fi
         \or % same as 0 but more accurate
           \advance\scratchdimen-10\s!sp\relax
           \ifdim\scratchdimen>\pagegoal
             \penalty-\!!tenthousand\relax
           \fi
         \fi
       \else
         \ifnum#1=\plusthree
           \flushpagesofar
         \fi
       \fi
     \else
       \ifnum#1=\plusone\goodbreak\fi
     \fi
   \fi}

\def\flushpagesofar
  {\endgraf
   \ifdim\pagetotal>\pagegoal
     \ifdim\dimexpr\pagetotal-\pageshrink\relax>\pagegoal
       \goodbreak % \penalty0
     \else
       \page
     \fi
   \else
   \fi}

\def\testcolumn
  {\dodoubleempty\dotestcolumn}

\def\dotestcolumn[#1][#2]%
  {%\relax % needed before \if !
   \endgraf
   \ifdim\pagegoal<\maxdimen \ifdim\pagetotal<\pagegoal % \relax
     \scratchdimen\pagegoal
     \advance\scratchdimen-\pagetotal
     \ifdim\lastskip<\parskip
       \advance\scratchdimen \parskip
     \fi
     \ifsecondargument
       \advance\scratchdimen#2%
     \fi
     \getrawnoflines\scratchdimen % raw !
   % \message{[\number#1>\number\noflines ?}\wait
     \ifnum#1>\noflines
       \column
     \fi
   \else
     \penalty-\!!tenthousand % untested ! ! \column
   \fi \fi}

\let\resetcurrentsectionmarks\relax

% was: \resetsectionmarks\firstsection, zie \handlepagebreak

\def\page{\pagebreak} % the short form of \pagebreak (mult-com one)

\def\resetpagebreak
  {\global\pagebreakdisabledfalse}

\def\simplifypagebreak
  {\def\dopagebreak[##1]{\goodbreak}}

\def\disablepagebreaks
  {\def\dopagebreak[##1]{}}

\def\executepagebreakhandler#1%
  {\edef\@@pagespecification{#1}%
   \doifdefinedelse{\??pe:\@@pagespecification}
     {\getvalue{\??pe:\@@pagespecification}}
     {\doifdefinedelse{\??pe::\@@pagespecification}
        {\executepagebreakhandlers{\getvalue{\??pe::\@@pagespecification}}}
        {\getvalue{\??pe:\s!unknown}}}}

\long\def\installpagebreakhandler#1#2%
  {\long\setvalue{\??pe:#1}{#2}}

% \definecomplexorsimple\pagebreak

% \def\simplepagebreak
%   {\executepagebreakhandler\v!ja}

% \def\complexpagebreak[#1]% if empty, do nothing and avoid processing,
%   {\flushnotes           % see head's; watch how we group
%    \doifsomething{#1}{\bgroup\executepagebreakhandlers{#1}\egroup}}

\unexpanded\def\pagebreak
  {\dosingleempty\dopagebreak}

\def\dopagebreak[#1]% so, page ornaments are reset after a pagebreak command, unless set
  {\bgroup
   \edef\prevrealpageno{\the\realpageno}%
   \ifcase\pageornamentstate \or
     % disable reset after shipout
     \global\chardef\pageornamentstate\plustwo
   \fi
   \iffirstargument % or if empty i.e. []
     \flushnotes\executepagebreakhandlers{#1}%
   \else % so, no pagebreak when \pagebreak[] ! ! !
     \flushnotes\executepagebreakhandler\v!yes
   \fi
   \ifnum\prevrealpageno<\realpageno
     \global\chardef\pageornamentstate\zerocount
   \fi
   \egroup}

\def\executepagebreakhandlers#1%
  {\processcommacommand[#1]\executepagebreakhandler}

\installpagebreakhandler \s!dummy
  {\ejectinsert
   \gotonextpage
   \ejectdummypage}

\installpagebreakhandler \v!frame
  {\page\bgroup\showframe\page[\v!empty]\egroup}

\installpagebreakhandler \s!unknown
  {\doifinstringelse{+}\@@pagespecification
     {\ejectinsert
      \gotonextpage
      \dorecurse\@@pagespecification\ejectdummypage}
     {\doifnumberelse\@@pagespecification
        {\ejectinsert
         \gotonextpage
         \doloop
           {\ifnum\userpageno<\@@pagespecification\relax
              \ejectdummypage
            \else
              \exitloop
            \fi}}
        {}}}

\installpagebreakhandler \s!default
  {} % do nothing if empty

\installpagebreakhandler \v!reset
  {% better not: \global\chardef\pageornamentstate\zerocount
   \resetpagebreak}

\installpagebreakhandler \v!disable
  {\global\pagebreakdisabledtrue}

\installpagebreakhandler \v!yes
  {\ifpagebreakdisabled\else
     \ejectinsert
     \gotonextpage
     \ifinsidecolumns % this will move to MUL
       \ejectpage  % anders soms geen overgang
     \fi
   \fi}

\installpagebreakhandler \v!makeup % ??
  {\ifpagebreakdisabled\else
     \eject
   \fi}

\installpagebreakhandler \v!blank
  {\ifcase\pageornamentstate
     \global\chardef\pageornamentstate\plusone
   \fi}

\installpagebreakhandler \v!no
  {\ifpagebreakdisabled\else
     \dosomebreak\nobreak
   \fi}

\installpagebreakhandler \v!preference
  {\ifpagebreakdisabled\else
     \ifinsidecolumns % this will move to MUL
       \dosomebreak\goodbreak
     \else
       \testpage[3][\zeropoint]%
     \fi
    \fi}

\installpagebreakhandler \v!bigpreference
  {\ifpagebreakdisabled\else
     \ifinsidecolumns % this will move to MUL
       \dosomebreak\goodbreak
     \else
       \testpage[5][\zeropoint]%
     \fi
   \fi}

\installpagebreakhandler \v!empty
  {\ejectinsert
   \gotonextpage
   \doifnotvalue{\??tk\v!header\c!state}\v!stop{\setupheader[\c!state=\v!empty]}%
   \doifnotvalue{\??tk\v!footer\c!state}\v!stop{\setupfooter[\c!state=\v!empty]}%
   \ejectdummypage}

\installpagebreakhandler \v!left
  {\ejectinsert
   \gotonextpageX % will become \gotonextpage
   \doifbothsidesoverruled{}{\resetcurrentsectionmarks\ejectdummypage}{}}

\installpagebreakhandler \v!right
  {\ejectinsert
   \gotonextpageX % will become \gotonextpage
   \doifbothsidesoverruled{}{}{\resetcurrentsectionmarks\ejectdummypage}}

\installpagebreakhandler \v!even
  {\page
   \doifoddpageelse{\resetcurrentsectionmarks\ejectdummypage}\donothing}

\installpagebreakhandler \v!odd
  {\page
   \doifoddpageelse\donothing{\resetcurrentsectionmarks\ejectdummypage}}

\installpagebreakhandler \v!quadruple % not yet ok inside columnsets
  {\ifdoublesided
     \!!counta\realpageno
     \!!countb\realpageno
     \divide\!!counta 4
     \divide\!!countb 2
     \ifnum\!!counta=\!!countb
     \else
       \executepagebreakhandler\v!yes
       \executepagebreakhandler\v!empty
       \executepagebreakhandler\v!empty
     \fi
   \fi}

\installpagebreakhandler \v!last
  {\ejectinsert
   \gotonextpageX % will become \gotonextpage
   \relax
   \doifbothsidesoverruled
     {\shipoutfacingpage}
     {}
     {\noheaderandfooterlines \ejectdummypage}%
   \filluparrangedpages}

\installpagebreakhandler \v!lastpage % handy for backpage preceded by empty pages
  {\executepagebreakhandler\v!yes
   \ifdoublesided
     \executepagebreakhandler\v!left
     \executepagebreakhandler\v!empty
     \executepagebreakhandler\v!empty
   \fi}

\installpagebreakhandler \v!start
  {\globallet\shipout\normalshipout}

\installpagebreakhandler \v!stop
  {\globallet\shipout\noshipout}

% nb: \executepagebreakhandler\v!hoofd in other ones

\installpagebreakhandler \v!header
  {\doifnotvalue{\??tk\v!header\c!state}\v!stop{\setupheader[\c!state=\v!empty]}}

\installpagebreakhandler \v!footer
  {\doifnotvalue{\??tk\v!footer\c!state}\v!stop{\setupfooter[\c!state=\v!empty]}}

% \definepagebreak
%   [chapter]
%   [yes,header,right]
%
% \setuphead
%   [chapter]
%   [page=chapter,
%    header=empty,
%    footer=chapter]
%
% \definepagebreak % untested
%   [lastpage]
%   [left,{empty,right},{empty,left}]

% public page handler, beware: definepage already in use (core-ref)
%
% \definepagebreak[instance][forsure]
% \definepagebreak[forsure][yes,+4]

\def\definepagebreak
  {\dodoubleargument\dodefinepagebreak}

\def\dodefinepagebreak[#1][#2]% non recursive, meant for simple mappings
  {\setvalue{\??pe::#1}{#2}}

% hier nog uti blokkeren

% don't change this / test case:
%
% \setupbackgrounds[state=repeat]
% \setupbackgrounds[text][text][background=whatever]
% \couplepage[chapter][before={\defineoverlay[whatever][ON]}]
% \setuphead[chapter][before={\pagetype[chapter]}]
% \chapter{First} \page test \chapter{second} \page test

\long\def\installcolumnbreakhandler#1#2#3% #1=otr-id #2=tag
  {\long\setvalue{\??cn:#1:#2}{#3}}

\def\definecolumnbreak
  {\dodoubleargument\dodefinecolumnbreak}

\def\dodefinecolumnbreak[#1][#2]% non recursive, meant for simple mappings
  {\setvalue{\??cn::#1}{#2}}

%\def\columnbreak
%  {\dosingleempty\docolumnbreak}
%
%\def\docolumnbreak[#1]%
%  {\expanded{\nextcolumn[\executeifdefined{\??cn::#1}{#1}]}}

\definecomplexorsimple\columnbreak

\def\simplecolumnbreak
  {\executecolumnbreakhandler\v!yes}

\def\complexcolumnbreak[#1]% if empty, do nothing and avoid processing
  {\doifsomething{#1}{\executecolumnbreakhandlers{#1}}}

\def\executecolumnbreakhandlers#1%
  {\processcommacommand[#1]\executecolumnbreakhandler}

\def\executecolumnbreakhandler#1% here no commalist
  {\edef\@@columnspecification{#1}%
   \doifdefinedelse{\??cn:\OTRidentifier:\@@columnspecification}
     {\getvalue{\??cn:\OTRidentifier:\@@columnspecification}}
     {\doifdefinedelse{\??cn::\@@columnspecification}
        {\executecolumnbreakhandlers{\getvalue{\??cn::\@@columnspecification}}}
        {\getvalue{\??cn:\OTRidentifier:\s!unknown}}}}

%let\nextcolumn\columnbreak
\let\column    \columnbreak

% We don't want spurious last pages (due to left over marks):

\def\noshipout
  {\writestatus\m!systems{ignoring further shipouts}%
   \global\advance\realpageno\minusone % else no flush of resources
   \dowithnextbox{\deadcycles\zerocount}}

% \def\doignorerestoftext
%   {\ifarrangingpages \else \ifnum\textlevel>\zerocount \else
%      \globallet\shipout\noshipout
%    \fi \fi}
%
% better:

\def\doignorerestoftext
  {\ifarrangingpages \else \ifnum\textlevel=\plusone
     \globallet\shipout\noshipout
   \fi \fi}

\let\ignorerestoftext\donothing

\prependtoks % only ignore in a symmetrical doc
  \globallet\ignorerestoftext\doignorerestoftext
\to \everystarttext

% \appendtoks
%   \ignorerestoftext
% \to \everylastshipout

\newif\ifpageselected   \pageselectedtrue
\newif\ifselectingpages \selectingpagesfalse
\newif\ifprocessingpages\processingpagestrue

\let\pageselection       \empty
\let\currentpageselection\empty
\let\aftershipout        \relax
\let\beforeshipout       \relax

\def\dodobeforeshipout#1%
  {\global\let\beforeshipout\relax
   \getvalue{\??pg#1\c!before}}

\def\dobeforeshipout
  {\doifsomething\currentpageselection
     {\processcommacommand[\currentpageselection]\dodobeforeshipout}}

\def\dododoaftershipout#1%
  {\global\let\aftershipout\relax
   \global\let\currentpageselection\empty
   \getvalue{\??pg#1\c!after}}

\def\dodoaftershipout#1%
  {\doifelsevalue{\??pg#1\c!option}\v!doublesided
     {\doifbothsidesoverruled
        {\dododoaftershipout{#1}}
        {\dododoaftershipout{#1}}
        {}}
     {\dododoaftershipout{#1}}}

\def\doaftershipout
  {\doifsomething\currentpageselection
     {\processcommacommand[\currentpageselection]\dodoaftershipout}}

% Dit wordt eigenlijk nooit en moet worden vervangen door
% het meer algemene mechanisme.

\def\dopagetype[#1]%
  {\edef\desoortpagina{#1}%
   \ifx\desoortpagina\empty \else
     \@EA\doglobal\@EA\addtocommalist\@EA{\desoortpagina}\currentpageselection
     \ifselectingpages
       \fullexpandtwoargsafter\doifcommon\desoortpagina\pageselection
         {\global\pageselectedtrue}%
     \fi
     \gdef\beforeshipout{\dobeforeshipout}%
     \gdef\aftershipout {\doaftershipout}%
   \fi}

\def\pagetype
  {\dosingleargument\dopagetype}

\def\docouplepage[#1][#2]%
  {\getparameters
     [\??pg]
     [\c!before=,
      \c!after=,
      \c!option=,
      #2]%
   \def\docommand##1%
     {\getparameters
        [\??pg##1]
        [\c!before=\@@pgbefore,
         \c!after=\@@pgafter,
         \c!option=\@@pgoption]}%
   \processcommalist[#1]\docommand}%

\def\couplepage
  {\dodoubleargument\docouplepage}

\def\doprocesspage[#1][#2]%
  {\processaction
     [#2]
     [\v!yes=>\global\processingpagestrue,
       \v!no=>\global\processingpagesfalse]%
   \gdef\pageselection{#1}%
   \global\selectingpagestrue
   \global\pageselectedfalse}

\def\processpage
  {\dodoubleargument\doprocesspage}

\def\resetselectiepagina
  {\ifselectingpages
     \doifbothsidesoverruled{\global\pageselectedfalse}{}{\global\pageselectedfalse}%
   \fi}

\newif\ifregistertextareas
\newif\iftracetextareas

\newbox\registertextbox

% \def\registeredtextarea#1#2#3% #1=lower-dp #2=correct-ht #3=box
%   {\hbox{\box#3}}

\def\enabletextarearegistration{\global\registertextareastrue}

\def\registeredtextarea#1#2#3% #1=lower-dp #2=correct-ht #3=box
  {\hbox\bgroup
     \ifregistertextareas \ifx\registerMPtextarea\undefined \else
       \setbox\registertextbox\null
       \wd\registertextbox\wd#3%
       \ht\registertextbox\ht#3%
       \dp\registertextbox\dp#3%
       \ifcase#1\or % 1
         \setbox\registertextbox\hbox{\lower\strutdp\box\registertextbox}%
       \fi
       \ifcase#2\or % 1
         \setbox\registertextbox\hbox{\raise\topskip\hbox{\lower\strutht\box\registertextbox}}%
         \dp\registertextbox\strutdp
       \fi
       \dp\registertextbox\strutdp % needed
      %\setbox\registertextbox\hbox
      %  {\iftracetextareas\gray\boxrulewidth2pt\ruledhbox\fi
      %   {\registerMPtextarea{\box\registertextbox}}}%
       \setbox\registertextbox\hbox
         {\registerMPtextarea{\box\registertextbox}}%
       \smashbox\registertextbox
       \box\registertextbox
     \fi \fi
     \box#3%
   \egroup}

%D \macros
%D   {setupoppositeplacing,startopposite}
%D
%D \starttyping
%D \starttext
%D test \startopposite \blackrule[width=3cm,height=4cm] \stopopposite test
%D test \startopposite \blackrule[width=3cm,height=4cm] \stopopposite test
%D \stoptext
%D \stoptyping

% Moved from page-mar.tex, made english, cleaned up, but still to be
% redesigned

\newbox\facingpage

\def\setupoppositeplacing
  {\dodoubleargument\getparameters[\??np]}

\def\startopposite
  {\dowithnextboxcontent
     {\hsize\makeupwidth}%
     {\global\setbox\facingpage\vbox
        {\ifvoid\facingpage
           \@@npbefore
         \else
           \@@npinbetween
           \unvbox\facingpage
         \fi
         \box\nextbox}}%
     \vbox\bgroup}

\def\stopopposite
  {\egroup}

\def\finishfacingpage
  {\ifvoid\facingpage\else
     \global\setbox\facingpage\vbox to \makeupheight
       {\unvbox\facingpage
        \@@npafter
        \vss}%
   \fi}

\def\shipoutfacingpage
  {\doif\@@npstate\v!start
     {\ifvoid\facingpage\else
        \ifnum\realpageno>\plusone
          \bgroup
          \chardef\pageornamentstate\plusone
          \finishfacingpage
          \myshipout{\buildpagebody\box\facingpage}%
          \egroup
        \else
          \global\setbox\facingpage\emptybox
        \fi
      \fi}}

\setupoppositeplacing
  [\c!state=\v!start,
   \c!before=,
   \c!inbetween=\blank,
   \c!after=]

\protect \endinput