%D \module
%D   [       file=spac-ver,
%D        version=2009.10.16, % 1997.03.31, was core-spa.tex
%D          title=\CONTEXT\ Spacing Macros,
%D       subtitle=Vertical,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%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 Spacing Macros / Vertical}

\unprotect

\registerctxluafile{spac-ver}{1.001}

\newskip\blankskip          \blankskip=\bigskipamount

\def\skipfactor    {.75}
\def\skipgluefactor{.25}

\def\normalskipamount
  {\openlineheight
     \ifgridsnapping \else \ifblankflexible
       \!!plus \skipgluefactor\openlineheight
       \!!minus\skipgluefactor\openlineheight
     \fi \fi
   \relax}

\def\linedistance    {\normalskipamount}
\def\appliedblankskip{\skipfactor\linedistance}
\def\lastblankskip   {\blankskip}
\def\currentblank    {\v!big}
\def\oldprevdepth    {\prevdepth}
\def\newprevdepth    {-1001pt}
\def\mindimen        {1sp} % was: 0.00002pt

%D There are two ways to influence the interline spacing. The
%D most general and often most consistent way is using
%D
%D \showsetup{setupinterlinespace}
%D
%D For instance
%D
%D \starttyping
%D \setupinterlinespace[line=2.8ex]
%D \stoptyping
%D
%D This setting adapts itself to the bodyfontsize, while for
%D instance saying
%D
%D \starttyping
%D \setupinterlinespace[line=12pt]
%D \stoptyping
%D
%D sets things fixed for all sizes, which is definitely not
%D what we want. Therefore one can also say:
%D
%D \starttyping
%D \definebodyfontenvironment[9pt][interlinespace=11pt]
%D \stoptyping
%D
%D One can still use \type{\setupinterlinespace} (without
%D arguments) to set the interline space according to the
%D current font, e.g. a \type{\bfa}.

\newif\iflocalinterlinespace

% font-ini

\ifx\bodyfontinterlinespecs\undefined

  \let\bodyfontinterlinespecs\empty
  \let\bodyfontinterlinespace\empty

\fi

% \def\presetnormallineheight
%   {\edef\normallineheight{\@@itline}%
%   %done elsewhere : \spacing\!!plusone % new per 10/08/2004, else problems in otr / !! needed
%    \iflocalinterlinespace \else
%      \doifdefined\bodyfontinterlinespecs
%        {\doifsomething\bodyfontinterlinespace
%           {\edef\normallineheight{\bodyfontinterlinespace}}}%
%    \fi}

% \unexpanded\def\setupspecifiedinterlinespace[#1]%
%   {\getparameters[\??it][#1]%
%    \scratchdimen0\@@itheight\points
%    \advance\scratchdimen 0\@@itdepth\points
%    \ifdim\scratchdimen>\onepoint
%      \showmessage\m!layouts{10}{\@@itheight,\@@itdepth}%
%      \let\@@itheight\strutheightfactor
%      \let\@@itdepth \strutdepthfactor
%    \else
%      \let\strutheightfactor\@@itheight
%      \let\strutdepthfactor \@@itdepth
%    \fi
%    \let\minimumstrutheight \@@itminheight
%    \let\minimumstrutdepth  \@@itmindepth
%    \let\minimumlinedistance\@@itdistance
%    \let\normallineheight   \@@itline % let ! ! ! ! ! ivm ex
%    \doifelse\@@ittop\v!height % new, topskip does more bad than good
%      {\let\topskipfactor   \@@itheight}
%      {\let\topskipfactor   \@@ittop   }%
%    \let\maxdepthfactor     \@@itbottom
%    \let\baselinegluefactor \@@itstretch
%    \setfontparameters % redundant, can be \setstrut, test first
%    \updateraggedskips} % yes indeed

\def\presetnormallineheight
  {\edef\normallineheight{\interlinespaceparameter\c!line}%
  %done elsewhere : \spacing\!!plusone % new per 10/08/2004, else problems in otr / !! needed
   \iflocalinterlinespace \else
     \doifdefined\bodyfontinterlinespecs
       {\doifsomething\bodyfontinterlinespace
          {\edef\normallineheight{\bodyfontinterlinespace}}}%
   \fi}

\unexpanded\def\setupspecifiedinterlinespace[#1]%
  {\getparameters[\??it\currentinterlinespace][#1]%
   \dosetupspecifiedinterlinespaceindeed}

\def\dosetupspecifiedinterlinespaceindeed
  {\edef\strutheightfactor  {\interlinespaceparameter\c!height}%
   \edef\strutdepthfactor   {\interlinespaceparameter\c!depth}%
   \edef\minimumstrutheight {\interlinespaceparameter\c!minheight}%
   \edef\minimumstrutdepth  {\interlinespaceparameter\c!mindepth}%
   \edef\minimumlinedistance{\interlinespaceparameter\c!distance}%
   \edef\normallineheight   {\interlinespaceparameter\c!line}%
   \edef\topskipfactor      {\interlinespaceparameter\c!top}%
   \edef\maxdepthfactor     {\interlinespaceparameter\c!bottom}%
   \edef\baselinegluefactor {\interlinespaceparameter\c!stretch}%
   % often topskip does more bad than good, so:
   \ifx\topskipfactor\v!height
     \let\topskipfactor\strutheightfactor
   \fi
   \setfontparameters % redundant, can be \setstrut, test first
   \updateraggedskips} % yes indeed

\let\currentrelativeinterlinespace\empty

\setvalue{\??it::\v!on   }{\oninterlineskip}
\setvalue{\??it::\v!off  }{\offinterlineskip}
\setvalue{\??it::\v!reset}{\let\currentrelativeinterlinespace\empty
                           \let\setrelativeinterlinespace\relax
                           \setfontparameters}
\setvalue{\??it::\v!auto }{\let\setrelativeinterlinespace\dosetrelativeinterlinespace}

% \def\dosetspecifiedrelativeinterlinespace#1%
%   {\assignvalue{#1}\currentrelativeinterlinespace{1.00}{1.25}{1.50}%
%    \spacing\currentrelativeinterlinespace}

% \def\dosetspecifiedrelativeinterlinespace#1% fragile?
%   {\doifdimensionelse{#1}
%      {\setupspecifiedinterlinespace[\c!line=#1]}
%      {\assignvalue{#1}\currentrelativeinterlinespace{1.00}{1.25}{1.50}%
%       \spacing\currentrelativeinterlinespace}}

\def\dosetspecifiedrelativeinterlinespace#1% fragile?
  {\doifdimenstringelse{#1}
     {\setupspecifiedinterlinespace[\c!line=#1]}
     {\assignvalue{#1}\currentrelativeinterlinespace{1.00}{1.25}{1.50}%
      \spacing\currentrelativeinterlinespace}}

\unexpanded\def\setuprelativeinterlinespace[#1]%
  {\processcommalist[#1]\dosetuprelativeinterlinespace}

\def\dosetuprelativeinterlinespace#1%
  {\ifcsname\??it::#1\endcsname
     \csname\??it::#1\endcsname
   \else
     \dosetspecifiedrelativeinterlinespace{#1}%
   \fi}

\def\dosetrelativeinterlinespace
  {\ifx\currentrelativeinterlinespace\empty\else
     \spacing\currentrelativeinterlinespace
   \fi}

\let\setrelativeinterlinespace\relax

% \appendtoks \setrelativeinterlinespace \to \everybodyfont

\newtoks \everysetupglobalinterlinespace
\newtoks \everysetuplocalinterlinespace

% \def\complexsetupinterlinespace[#1]% \commalistelement ipv #1
%   {\doifassignmentelse{#1}\setupspecifiedinterlinespace\setuprelativeinterlinespace[#1]%
%    \the\iflocalinterlinespace\everysetuplocalinterlinespace\else\everysetupglobalinterlinespace\fi}

\def\interlinespaceparameter          #1{\csname\dointerlinespaceparameter{\??it\currentinterlinespace}#1\endcsname}
\def\dointerlinespaceparameter      #1#2{\ifcsname#1#2\endcsname#1#2\else\expandafter\dointerlinespaceparentparameter\csname#1\s!parent\endcsname#2\fi}
\def\dointerlinespaceparentparameter#1#2{\ifx#1\relax\s!empty\else\dointerlinespaceparameter#1#2\fi}

\newconditional\interlinespaceisset

\let\currentinterlinespace\empty

\unexpanded\def\defineinterlinespace
  {\dodoubleempty\dodefineinterlinespace}

\def\dodefineinterlinespace[#1][#2]%
  {\getparameters[\??it#1][\s!parent=\??it,#2]}

\unexpanded\def\setupinterlinespace
  {\dodoubleempty\dosetupinterlinespace}

\def\dosetupinterlinespace[#1][#2]%
  {\settrue\interlinespaceisset % reset has to be done when needed
   \ifsecondargument
     \getparameters[\??it#1][#2]%
   \else\iffirstargument
     \edef\currentinterlinespace{\ifcsname\??it#1\s!parent\endcsname#1\fi}%
     \ifx\currentinterlinespace\empty
       \complexsetupinterlinespace[#1]%
     \else
       \dosetupspecifiedinterlinespaceindeed
     \fi
   \else
     \let\currentinterlinespace\empty
     \simplesetupinterlinespace
   \fi\fi}

\def\complexsetupinterlinespace[#1]% \commalistelement ipv #1
  {\doifassignmentelse{#1}\setupspecifiedinterlinespace\setuprelativeinterlinespace[#1]%
   \the\iflocalinterlinespace\everysetuplocalinterlinespace\else\everysetupglobalinterlinespace\fi}

\def\simplesetupinterlinespace % adapts to the font
  {\localinterlinespacetrue
   \setfontparameters
   \updateraggedskips % funny one here
   \the\everysetuplocalinterlinespace
   \localinterlinespacefalse}

% \def\dosetupcheckedinterlinespace#1% often a chain
%   {\edef\askedinterlinespace{#1}%
%    \ifx\askedinterlinespace\empty
%      \simplesetupinterlinespace
%    \else
%      \normalexpanded{\noexpand\doifassignmentelse{\askedinterlinespace}%
%        \noexpand\setupspecifiedinterlinespace
%        \noexpand\setuprelativeinterlinespace[\askedinterlinespace]}%
%      \iflocalinterlinespace
%        \the\everysetuplocalinterlinespace
%      \else
%        \localinterlinespacetrue
%        \the\everysetuplocalinterlinespace
%        \localinterlinespacefalse
%      \fi
%    \fi}

\def\dosetupcheckedinterlinespace#1% often a chain
  {\edef\askedinterlinespace{#1}%
   \ifx\askedinterlinespace\empty
     \simplesetupinterlinespace
   \else\ifcsname\??it\askedinterlinespace\s!parent\endcsname
     \pushmacro\currentinterlinespace
     \let\currentinterlinespace\askedinterlinespace
     \dosetupspecifiedinterlinespaceindeed
     \iflocalinterlinespace
       \the\everysetuplocalinterlinespace
     \else
       \localinterlinespacetrue
       \the\everysetuplocalinterlinespace
       \localinterlinespacefalse
     \fi
     \popmacro\currentinterlinespace
   \else
     \normalexpanded{\noexpand\doifassignmentelse{\askedinterlinespace}%
       \noexpand\setupspecifiedinterlinespace
       \noexpand\setuprelativeinterlinespace[\askedinterlinespace]}%
     \iflocalinterlinespace
       \the\everysetuplocalinterlinespace
     \else
       \localinterlinespacetrue
       \the\everysetuplocalinterlinespace
       \localinterlinespacefalse
     \fi
   \fi\fi}

% \unexpanded\def\setuplocalinterlinespace[#1]%
%   {\localinterlinespacetrue
%    \let\@@saveditheight   \@@itheight
%    \let\@@saveditdepth    \@@itdepth
%    \let\@@saveditline     \@@itline
%    \let\@@saveditminheight\@@itminheight
%    \let\@@saveditmindepth \@@itmindepth
%    \let\@@saveditdistance \@@itdistance
%    \let\@@savedittop      \@@ittop
%    \let\@@saveditbottom   \@@itbottom
%    \let\@@saveditstretch  \@@itstretch
%    \setupinterlinespace[#1]%
%    \let\@@itheight   \@@saveditheight
%    \let\@@itdepth    \@@saveditdepth
%    \let\@@itline     \@@saveditline
%    \let\@@itminheight\@@saveditminheight
%    \let\@@itmindepth \@@saveditmindepth
%    \let\@@itdistance \@@saveditdistance
%    \let\@@ittop      \@@savedittop
%    \let\@@itbottom   \@@saveditbottom
%    \let\@@itstretch  \@@saveditstretch
%    \localinterlinespacefalse}

\unexpanded\def\setuplocalinterlinespace[#1]%
  {\localinterlinespacetrue
   \pushmacro\currentinterlinespace
   \setupinterlinespace[#1]%
   \popmacro\currentinterlinespace
   \localinterlinespacefalse}

\let\switchtointerlinespace\setuplocalinterlinespace

\definecomplexorsimple\setupinterlinespace

\def\removelastskip % a redefinition of plain
  {\ifvmode\ifdim\lastskip=\zeropoint\else\vskip-\lastskip\fi\fi}

\def\doifoutervmode#1%
  {\ifvmode\ifinner\else#1\fi\fi}

\def\dosomebreak#1%
  {\doifoutervmode
     {\scratchskip\lastskip
      \removelastskip
      %\leavevmode\type{#1}%
      #1\relax
      \ifdim\scratchskip=\zeropoint % else interference with footnotes
      \else
        \vskip\scratchskip
      \fi}}

\def\packed
  {\nointerlineskip}

\def\godown[#1]%
  {\relax
   \ifhmode\endgraf\fi
   \ifvmode\nointerlineskip\vskip#1\relax\fi}

\ifx\smallskip\undefined

  \def\smallskip{\vskip\smallskipamount}
  \def\medskip  {\vskip\medskipamount}
  \def\bigskip  {\vskip\bigskipamount}

\fi

\ifx\allowbreak\undefined

  \def\break     {\penalty\ifhmode-\plustenthousand\else\ejectpenalty\fi}
  \def\nobreak   {\penalty \plustenthousand}
  \def\allowbreak{\penalty \zeropoint}
  \def\filbreak  {\par\vfil\penalty-200\vfilneg}
  \def\goodbreak {\par\penalty-500 }

\fi

%D Made slightly more readable:

\ifx\vglue\undefined

  \def\vglue  {\afterassignment\dovglue\scratchskip=}
  \def\hglue  {\afterassignment\dohglue\scratchskip=}
  \def\topglue{\nointerlineskip\vglue-\topskip\vglue}

  \def\dovglue
    {\par
     \scratchdimen\prevdepth
     \hrule\!!height\zeropoint
     \nobreak
     \vskip\scratchskip
     \prevdepth\scratchdimen}

  \def\dohglue
    {\dontleavehmode % \leavevmode
     \scratchcounter\spacefactor
     \vrule\!!width\zeropoint
     \nobreak
     \hskip\scratchskip
     \spacefactor\scratchcounter}

\fi

\ifx\eject\undefined

  \def\eject{\par\break}

\fi

\ifx\supereject\undefined

  \def\supereject{\par\penalty\superpenalty}

\fi

\ifx\dosupereject\undefined

  \def\dosupereject
    {\ifnum\insertpenalties>\zerocount % something is being held over
       \line{}
       \kern-\topskip
       \nobreak
       \vfill\supereject
     \fi}

\fi

%D We adapt plain's \type {\removelastskip} a bit:

\ifx\removelastskip\undefined

  \def\removelastskip
    {\ifvmode \ifdim\lastskip=\zeropoint \else
       \vskip-\lastskip
     \fi \fi}

\fi

\ifx\smallbreak\undefined

\def\smallbreak
  {\par
   \ifdim\lastskip<\smallskipamount
     \removelastskip
     \penalty-50
     \smallskip
   \fi}

\def\medbreak
  {\par
   \ifdim\lastskip<\medskipamount
     \removelastskip
     \penalty-100
     \medskip
   \fi}

\def\bigbreak
  {\par
   \ifdim\lastskip<\bigskipamount
     \removelastskip
     \penalty-200
     \bigskip
   \fi}

\fi

\newskip\ctxparskip \ctxparskip\zeropoint

\newconditional \flexiblewhitespace \settrue\flexiblewhitespace

\def\currentwhitespace {\zeropoint}

\definecomplexorsimple\setupwhitespace

\def\simplesetupwhitespace
  {\doifnot\currentwhitespace\v!none\dosetupwhitespace}

\def\complexsetupwhitespace[#1]%
  {\edef\nextcurrentwhitespace{#1}%
   \ifx\nextcurrentwhitespace\empty
     \simplesetupwhitespace
   \else
     \let\currentwhitespace\nextcurrentwhitespace
     \dosetupwhitespace
   \fi}

\def\dosetupwhitespace % quick test for no list
  {\ifcsname\??ws\??ws\currentwhitespace\endcsname
     \csname\??ws\??ws\currentwhitespace\endcsname
   \else
     \expandafter\processcommalist\expandafter[\currentwhitespace]\dowhitespacemethod % can be raw
   \fi\relax
   \ifgridsnapping
     \setfalse\flexiblewhitespace
     \ifdim\ctxparskip>\zeropoint
       \ctxparskip
       \ifcase\baselinegridmode
         \baselineskip % normal ! ! ! ! !!
       \or
         \ifdim\scratchdimen=\baselineskip % maybe range
           \baselineskip % normal ! ! ! ! !!
         \else
           \numexpr\ctxparskip/\dimexpr.5\lineheight\relax\relax\dimexpr.5\lineheight\relax
         \fi
       \else
         \baselineskip % normal ! ! ! ! !!
       \fi
     \fi
   \else
     \ifconditional\flexiblewhitespace \else \ctxparskip1\ctxparskip \fi
   \fi
   \parskip\ctxparskip}

\chardef\baselinegridmode=0 % option in layout / 1=permit_half_lines

\def\dodosetupwhitespace
  {\ifgridsnapping
     \setfalse\flexiblewhitespace
     \ctxparskip1\ctxparskip
     \ifdim\ctxparskip>\zeropoint
       \ifcase\baselinegridmode
         \ctxparskip\baselineskip % normal ! ! ! ! !!
       \or
         \ifdim\scratchdimen=\baselineskip % maybe range
           \ctxparskip\baselineskip % normal ! ! ! ! !!
         \else
           \ctxparskip\numexpr\ctxparskip/\dimexpr.5\lineheight\relax\relax\dimexpr.5\lineheight\relax
         \fi
       \else
         \ctxparskip\baselineskip % normal ! ! ! ! !!
       \fi
     \fi
   \else
     \ifconditional\flexiblewhitespace \else \ctxparskip1\ctxparskip \fi
   \fi
   \parskip\ctxparskip}

\definesystemvariable {ws} % whitespace

\unexpanded\def\definewhitespacemethod[#1]#2{\setvalue{\??ws\??ws#1}{#2}}

\definewhitespacemethod [\v!fix]      {}
\definewhitespacemethod [\v!fixed]    {\setfalse\flexiblewhitespace}
\definewhitespacemethod [\v!flexible] {\settrue\flexiblewhitespace}
\definewhitespacemethod [\v!line]     {\ctxparskip  \baselineskip}
\definewhitespacemethod [\v!halfline] {\ctxparskip.5\baselineskip}
\definewhitespacemethod [\v!none]     {\ctxparskip  \zeropoint}
\definewhitespacemethod [\v!big]      {\ctxparskip  \bigskipamount}
\definewhitespacemethod [\v!medium]   {\ctxparskip  \medskipamount}
\definewhitespacemethod [\v!small]    {\ctxparskip  \smallskipamount}

\definewhitespacemethod [\s!default]  {\simplesetupwhitespace} % {\stelwitruimteopnieuwin}

\def\dowhitespacemethod#1%
  {\ifcsname\??ws\??ws#1\endcsname\csname\??ws\??ws#1\endcsname\else\ctxparskip#1\fi\relax}

% \def\nowhitespace
%   {\ifdim\parskip>\zeropoint\relax
%      \ifdim\lastskip=-\parskip
%      \else
%        \vskip-\parskip
%      \fi
%    \fi}
%
% \def\nowhitespaceunlessskip
%   {\ifdim\lastskip>\zeropoint \else
%      \nowhitespace
%    \fi}
%
% \def\whitespace
%   {\par
%    \ifdim\parskip>\zeropoint\relax
%     %\ifdim\lastskip>\parskip \else
%      % \removelastskip interferes with blanko blokkeer en klein
%        \vskip\parskip
%     %\fi
%    \fi}

\def\nowhitespace{\vspacing[\v!nowhite]}
\def\whitespace  {\vspacing[\v!white]}

% obsolete:
%
% \def\savedcurrentwhitespace{\currentwhitespace}
% \def\savecurrentwhitespace   {\edef\savedcurrentwhitespace{\currentwhitespace}}
% \def\restorecurrentwhitespace{\edef\currentwhitespace{\savedcurrentwhitespace}}

% De onderstaande macro handelt ook de situatie dat er geen
% tekst tussen \start ... \stop is geplaatst. Daartoe wordt de
% laatste skip over de lege tekst heen gehaald. Dit komt goed
% van pas bij het plaatsen van (mogelijk lege) lijsten.

\newsignal \noparskipsignal % \def\noparskipsignal {0.00001pt}
\def\lastdoneparskip {0pt}

\newconditional\noblankinpacked
\newcount\packeddepth

\unexpanded\def\startpacked
  {\dosingleempty\dostartpacked}

\def\dostartpacked[#1]% nesting afvangen
  {\global\advance\packeddepth\plusone
   \par
   \ifnum\packeddepth=\plusone \ifvmode
     \bgroup
     \whitespace % not combined
     \blank[\v!disable]%
     \doifelse{#1}\v!blank\setfalse\settrue\noblankinpacked
     \setupwhitespace[\v!none]%
   \fi \fi}

\unexpanded\def\stoppacked
  {\par
   \ifnum\packeddepth=\plusone \ifvmode
     \egroup
   \fi \fi
   \global\advance\packeddepth\minusone}

\unexpanded\def\startunpacked
  {\blank
   \bgroup}

\unexpanded\def\stopunpacked
  {\egroup
   \blank}

% De onderstaande macro's moeten nog eens nader worden uitgewerkt.
% Ze spelen een rol bij de spatiering rond omkaderde teksten
% en/of boxen zonder diepte.

% \prevdepth crosses pageboundaries!
%
% todo: a version that works ok inside a box

\let\doaroundlinecorrection\relax

\unexpanded\def\startlinecorrection
  {\dodoubleempty\dostartlinecorrection}

\def\dostartlinecorrection[#1][#2]% #2 gobbles spaces
  {\bgroup
   \processaction
     [#1]
     [  \v!blank=>\let\doaroundlinecorrection\blank,
      \s!default=>\let\doaroundlinecorrection\relax,
      \s!unknown=>{\def\doaroundlinecorrection{\blank[#1]}}]%
   \doaroundlinecorrection
   \startbaselinecorrection
   \offbaselinecorrection
   \ignorespaces}

\unexpanded\def\stoplinecorrection
  {\stopbaselinecorrection
   \doaroundlinecorrection
   \egroup}

\def\correctwhitespace
  {\dowithnextbox
     {\startbaselinecorrection
      \flushnextbox
      \stopbaselinecorrection}%
   \vbox}

\def\verticalstrut  {\normalvbox{\hsize\zeropoint\forgetall\strut}}
\def\horizontalstrut{\normalhbox                          {\strut}}

% Hieronder volgen enkele instellingen en macro's ten behoeve
% van de interlinie en \strut. De waarden 2.8, 0.07, 0.72 en
% 0.28 zijn ooit eens ontleend aan INRS-TEX en moeten wellicht
% nog eens instelbaar worden.
%
%   \lineheight        : de hoogte van een regel
%   \spacing{getal}    : instellen interlinie
%   \normalbaselines   : instellen regelafstend
%
%   \setstrut          : instellen \strut
%   \setnostrut        : resetten \strut, \endstrut, \begstrut
%
%   \setteststrut      : instellen zichtbare struts
%   \resetteststrut    : instellen onzichtbare struts
%
%   \setfontparameters : instellen na fontset
%
% De hoogte van een regel (\lineheight) is gelijk aan de
% som van de hoogte (\ht) en diepte (\dp) van \strutbox.
%
%   \strut            : denkbeeldig blokje met hoogte en diepte
%
% Een \hbox kan als deze aan het begin van een regel staat
% een breedte \hsize krijgen. Dit is soms te voorkomen met het
% commando \leavevmode. Binnen een \vbox geeft dit echter
% niet altijd het gewenste resultaat, vandaar het commando
%
%   \dontleavehmode

% Pas op: niet zomaar \topskip en \baselineskip aanpassen
% en zeker niet \widowpenalty. Dit kan ernstige gevolgen
% hebben voor kolommen.
%
% Enige glue kan op zich geen kwaad, echter als blanko=vast,
% dan moet ook de rek 0 zijn. Binnen kolommen is rek ook
% niet bepaald mooi. Een hele kleine waarde (0.025) voldoet,
% omdat een positieve glue eindeloos rekbaar is.

\newdimen\strutdimen
\newdimen\lineheight
\newdimen\openlineheight
\newdimen\openstrutheight
\newdimen\openstrutdepth
\newdimen\topskipgap
\newdimen\struttotal

\def\strutheightfactor      {.72}
\def\strutdepthfactor       {.28}

\def\baselinefactor         {2.8}
\def\baselinegluefactor     {0}

\def\minimumstrutheight     {0pt}
\def\minimumstrutdepth      {0pt}

\def\normallineheight       {\baselinefactor ex}
\def\minimumlinedistance    {\lineskip}

\def\strutheight            {0pt}
\def\strutdepth             {0pt}
\def\strutwidth             {0pt}

\let\spacingfactor          \plusone

\def\topskipfactor          {1.0}
\def\maxdepthfactor         {0.5}

\def\systemtopskipfactor    {\topskipfactor}
\def\systemmaxdepthfactor   {\maxdepthfactor}

\ifdefined\globalbodyfontsize\else
  \newdimen\globalbodyfontsize
  \globalbodyfontsize=12pt
\fi

\ifdefined\normalizedbodyfontsize\else
  \def\normalizedbodyfontsize{12pt}
\fi

% door een \dimen. Dit is geen probleem omdat (1) de default
% korpsgrootte 12pt is en (2) de fonts nog niet geladen zijn
% en de instellingen bij het laden nogmaals plaatsvinden.

\def\topskipcorrection
  {\simpletopskipcorrection
   \vskip-\struttotal
   \verticalstrut}

\def\simpletopskipcorrection
  {\ifdim\topskip>\openstrutheight
     % == \vskip\topskipgap
     \vskip\topskip
     \vskip-\openstrutheight
   \fi}

\def\settopskip % the extra test is needed for the lbr family
  {\topskip\systemtopskipfactor\globalbodyfontsize
   \ifgridsnapping \else
     \ifr@ggedbottom\!!plus5\globalbodyfontsize\fi
   \fi
\ifgridsnapping
    \topskip\zeropoint
\fi
   \relax % the skip
   \topskipgap\topskip
   \advance\topskipgap -\openstrutheight\relax
   \ifdim\minimumstrutheight>\zeropoint
     \ifdim\topskip<\minimumstrutheight
       \topskip\minimumstrutheight\relax
     \fi
  \else
     \ifdim\topskip<\strutheightfactor\openlineheight
       \topskip\strutheightfactor\openlineheight\relax
     \fi
  \fi}

\def\setmaxdepth
  {\maxdepth\systemmaxdepthfactor\globalbodyfontsize}

\def\normalbaselines
  {\baselineskip \normalbaselineskip
   \lineskip     \normallineskip
   \lineskiplimit\normallineskiplimit}

\def\setnormalbaselines
  {\ifdim\normallineheight>\zeropoint
     \lineheight\normallineheight
   \fi
   \openlineheight\spacingfactor\lineheight
   \openstrutheight \ifdim\minimumstrutheight>\zeropoint
     \minimumstrutheight % new
   \else
     \strutheightfactor\openlineheight
   \fi
   \openstrutdepth \ifdim\minimumstrutdepth>\zeropoint
     \minimumstrutdepth % new
   \else
     \strutdepthfactor \openlineheight
   \fi
   \ifdim\dimexpr\minimumstrutdepth+\minimumstrutheight\relax>\zeropoint
     \openlineheight\dimexpr\openstrutheight+\openstrutdepth\relax % new
   \fi
   \normalbaselineskip\openlineheight
     \ifgridsnapping\else
       \!!plus \baselinegluefactor\openlineheight
       \!!minus\baselinegluefactor\openlineheight
     \fi
   \normallineskip\minimumlinedistance\relax % \onepoint\relax
   \normallineskiplimit\zeropoint\relax
   \normalbaselines
  %\dosetupgridsnapping
  }

\def\spacing#1%
  {\ifgridsnapping
    %\ifdim#1\points=\onepoint\else\showmessage\m!layouts{11}{\withoutpt\the\dimexpr#1\points\relax}\fi
     \let\spacingfactor\plusone
   \else
     \edef\spacingfactor{#1}%
   \fi
   \edef\systemtopskipfactor {\withoutpt\the\dimexpr#1\dimexpr\topskipfactor \points}%
   \edef\systemmaxdepthfactor{\withoutpt\the\dimexpr#1\dimexpr\maxdepthfactor\points}%
   \setnormalbaselines
   \setstrut}

%D Sometimes one needs to freeze the interlinespacing
%D
%D \starttyping
%D \rm \saveinterlinespace .... {\ss \restoreinterlinespace .... \endgraf}
%D \stoptyping

\let\restoreinterlinespace\relax

\def\saveinterlinespace
  {\edef\restoreinterlinespace
     {\lineheight         \the\lineheight
      \openstrutheight    \the\openstrutheight
      \openstrutdepth     \the\openstrutdepth
      \openlineheight     \the\openlineheight
      \normalbaselineskip \the\normalbaselineskip
      \normallineskip     \the\normallineskip
      \normallineskiplimit\the\normallineskiplimit
      \noexpand\def\noexpand\normallineheight{\the\dimexpr\normallineheight}%
      \noexpand\normalbaselines}}

% plain definition:
%
% \def\strut{\relax\ifmmode\copy\strutbox\else\unhcopy\strutbox\fi}
%
% could be:
%
% \def\strut{\relax\ifmmode\copy\else\unhcopy\fi\strutbox}

\ifx\strutbox\undefined

  \newbox\strutbox

  \setbox\strutbox\normalhbox{\vrule height8.5pt depth3.5pt width\zeropoint}

  \def\strut{\relax\ifmmode\copy\else\unhcopy\fi\strutbox}

\fi

\let\normalstrut\strut

% The double \hbox construction enables us to \backtrack
% boxes.

\let\strutht\undefined \newdimen\strutht
\let\strutdp\undefined \newdimen\strutdp

\unexpanded\def\setstrut
  {\ifgridsnapping
     \setstrutgridyes
   \else
     \setstrutgridnop
   \fi}

\unexpanded\def\setstrutgridyes
  {\strutht\spacingfactor\dimexpr
     \ifdim\minimumstrutheight>\zeropoint
       \minimumstrutheight
     \else
       \strutheightfactor\dimexpr\normallineheight
     \fi
   \strutdp\dimexpr
     \ifdim\minimumstrutdepth>\zeropoint
       \minimumstrutdepth
     \else
       \normallineheight-\strutht
     \fi
   \dosetstrut}

\unexpanded\def\setstrutgridnop
  {\strutht\spacingfactor\dimexpr
     \ifdim\minimumstrutheight>\zeropoint
       \minimumstrutheight
     \else
       \strutheightfactor\dimexpr\normallineheight
     \fi
   \strutdp\spacingfactor\dimexpr
       \ifdim\minimumstrutdepth>\zeropoint
         \minimumstrutdepth
       \else
         \strutdepthfactor\dimexpr\normallineheight
       \fi
   \dosetstrut}

\unexpanded\def\setcharstrut#1%
  {\setbox\strutbox\normalhbox{#1}%
   \strutht\ht\strutbox
   \strutdp\dp\strutbox
   \dosetstrut}

\unexpanded\def\setfontstrut
  {\setcharstrut{(gplQT}}

\unexpanded\def\setcapstrut% could be M, but Q has descender
  {\setcharstrut{Q}}

%D Handy for math (used in mathml):

\def\charhtstrut
  {\begingroup
   \setcharstrut{GJY}%
   \vrule\!!width\zeropoint\!!depth\zeropoint\!!height\strutht
   \endgroup}

\def\chardpstrut
  {\begingroup
   \setcharstrut{gjy}%
   \vrule\!!width\zeropoint\!!depth\strutdp\!!height\zeropoint
   \endgroup}

% because of all the callbacks in mkiv, we avoid unnecessary boxes ...
% maybe use an attribute so that we can tag boxes that don't need a
% treatment; tests with using an attribute so far have shown that
% it's slower because testing the attribute takes time too

\newdimen\tempstrutdimen

\def\dosetstrut
  {\let\strut\normalstrut
   \tempstrutdimen\dimexpr\strutht+\strutdp-\lineheight\relax
   \ifabsnum\tempstrutdimen<\plustwo
      % compensate rounding error /- 1sp to avoid too many
      % 1sp baselineskips in for instance verbatim
      \strutht\dimexpr\strutht-\tempstrutdimen\relax
   \fi
   \edef\strutheight{\the\strutht}% maybe better \number\strutht sp
   \edef\strutdepth {\the\strutdp}%
   \ifdim\strutwidth=\zeropoint
      \dosetstruthide
   \else
      \dosetstrutvide
   \fi
   \struttotal\dimexpr\strutht+\strutdp\relax}

\def\dosetstruthide
  {\setbox\strutbox\normalhbox
     {\vrule
        \!!width \zeropoint
        \!!height\strutht
        \!!depth \strutdp}}

\def\dosetstrutvide
  {\setbox\strutbox\normalhbox
     {\normalhbox to \zeropoint
        {% \hss % new, will be option
         \vrule
           \!!width \strutwidth
           \!!height\strutht
           \!!depth \strutdp
         \hss}}}

%D The dimen \type {\struttotal} holds the exact size of the
%D strut; occasionally a one scaled point difference can show
%D up with the lineheight.

% experiment

\newbox\emptystrutbox \setbox\emptystrutbox\hbox{}

\def\dosetstruthide
  {\setbox\strutbox\copy\emptystrutbox
   \ht\strutbox\strutht
   \dp\strutbox\strutdp}

\def\strut{\relax\dontleavehmode\copy\strutbox} % still callbacks for \hbox{\strut}


\let\normalstrut\strut

%D Sometimes a capstrut comes in handy
%D
%D \starttabulate[|Tl|l|l|]
%D \NC yes          \NC normal strut               \NC {\showstruts\setupstrut[yes]\strut}  \NC \NR
%D \NC no           \NC no strut                   \NC {\showstruts\setupstrut[no]\strut}  \NC \NR
%D \NC kap          \NC a capital strut (i.e. Q)   \NC {\showstruts\setupstrut[cap]\strut} \NC \NR
%D \NC A B \unknown \NC a character strut (e.g. A) \NC {\showstruts\setupstrut[A]\strut}   \NC \NR
%D \NC              \NC a normal strut             \NC {\showstruts\setupstrut\strut}      \NC \NR
%D \stoptabulate

\unexpanded\def\setupstrut
  {\dosingleempty\dosetupstrut}

\def\dosetupstrut[#1]% yet undocumented, todo: fontstrut
  {\processaction
     [#1]
     [    \v!yes=>\setstrut,
         \v!auto=>\setautostrut,
           \v!no=>\setnostrut,
          \v!cap=>\setcapstrut,
          \v!fit=>\setfontstrut,
         \v!line=>\setstrut,
      \s!default=>\setstrut,
      \s!unknown=>\setcharstrut\commalistelement]}

\def\showstruts
  {\setteststrut
   \settestcrlf}

\def\setteststrut
  {\def\strutwidth{.8pt}%
   \setstrut}

\def\autostrutfactor{1.1}

\def\setautostrut
  {\begingroup
   \setbox\scratchbox\copy\strutbox
   \setstrut
   \ifdim\strutht>\autostrutfactor\ht\scratchbox
     \endgroup \setstrut
   \else\ifdim\strutdp>\autostrutfactor\dp\scratchbox
     \endgroup \setstrut
   \else
     \endgroup
   \fi\fi}

% when enabled, sigstruts will remove themselves if nothing
% goes inbetween

\newsignal\strutsignal \setfalse\sigstruts

\def\begstrut
  {\relax\ifcase\strutht\else
     \ifconditional\sigstruts
       \noindent\horizontalstrut
       \normalpenalty\plustenthousand
       \normalhskip-\strutsignal
       \normalhskip\strutsignal
     \else
       \strut
       \normalpenalty\plustenthousand
       \normalhskip\zeropoint
     \fi
     \expandafter \ignorespaces
   \fi}

\def\endstrut
  {\relax\ifhmode\ifcase\strutht\else
     \ifconditional\sigstruts
       \ifdim\lastskip=\strutsignal
         \unskip\unskip\unpenalty\setbox\scratchbox\lastbox
       \else
         \normalpenalty\plustenthousand
         \normalhskip\zeropoint
         \strut
       \fi
     \else
       \removeunwantedspaces
       \normalpenalty\plustenthousand
       \normalhskip\zeropoint
       \strut
     \fi
   \fi\fi}

\newbox\nostrutbox \setbox\nostrutbox\normalhbox{} % {\normalhbox{}}

\def\setnostrut
  {\setbox\strutbox\copy\nostrutbox
   \let\strut\empty
   \let\endstrut\empty
   \let\begstrut\empty
   \let\crlfplaceholder\empty}

% unsave:
%
% \def\pseudostrut
%   {\bgroup
%    \setnostrut
%    \normalstrut
%    \egroup}
%
% try:
%
% \startchemie
%   \chemie[ONE,Z0,SB15,MOV1,SB15,Z0][C,C]
% \stopchemie
%
% so:

\def\pseudostrut
  {\noindent} % better: \dontleavehmode

\let\pseudobegstrut\pseudostrut

\let\pseudoendstrut\removeunwantedspaces

\def\resetteststrut
  {\def\strutwidth{\zeropoint}% no let
   \setstrut}

\ifdefined\setfontparameters\else
  % problems ! ! ! !
  \def\setfontparameters{\the\everybodyfont}
\fi

%D Handy:

\def\baselinedistance{\the\lineheight}

%D We need \type{\normaloffinterlineskip} because the new
%D definition contains an assignment, and |<|don't ask me
%D why|>| this assignment gives troubles in for instance the
%D visual debugger.

%D The plain ones:

% \def\offinterlineskip
%   {\baselineskip-\thousandpoint
%    \lineskip\zeropoint
%    \lineskiplimit\maxdimen}

\def\offinterlineskip
  {\baselineskip-\thousandpoint
   \lineskip\zeropoint
   \lineskiplimit\maxdimen
   % We also need this here now; thanks to taco for figuring that out!
   \def\minimumlinedistance{\zeropoint}}

\def\nointerlineskip
  {\prevdepth-\thousandpoint}

\let\normaloffinterlineskip=\offinterlineskip % knuth's original

%D My own one:

\def\dopushinterlineskip
  {\edef\oninterlineskip
     {\baselineskip\the\baselineskip
      \lineskip\the\lineskip
      \lineskiplimit\the\lineskiplimit
      \noexpand\edef\noexpand\minimumlinedistance{\the\dimexpr\minimumlinedistance}%
      \let\noexpand\offinterlineskip\noexpand\normaloffinterlineskip}}

\def\nopushinterlineskip
  {\let\oninterlineskip\setnormalbaselines}

\def\offinterlineskip
  {\ifdim\baselineskip>\zeropoint
     \dopushinterlineskip
   \else
     \nopushinterlineskip
   \fi
   \normaloffinterlineskip}

\let\oninterlineskip=\relax

\def\leaveoutervmode
  {\ifvmode\ifinner\else
     \leavevmode
   \fi\fi}

% We stellen enkele penalties anders in dan Plain TEX:
%
% \widowpenalty=\defaultwidowpenalty\relax
% \clubpenalty =\defaultclubpenalty \relax

\def\resetpenalties#1%
  {\ifdefined#1%
     #1\minusone
   \fi}

\def\setpenalties#1#2#3%
  {\ifdefined#1% space before #3 prevents lookahead problems, needed when #3=text
     #1\numexpr#2+\plusone\relax\space\doexpandedrecurse{\the\numexpr#2\relax}{ #3}\zerocount\relax
   \fi}

\def\doexpandedrecurse#1#2%
  {\ifnum#1>\zerocount#2\@EA\doexpandedrecurse\@EA{\the\numexpr#1-1\relax}{#2}\fi}

%D \macros
%D   {keeplinestogether}
%D
%D Dirty hack, needed in margin content that can run of a page.

% just before margintexts ... will eventually be done differently in mkiv using
% attributes

\newcount\nofkeeplinestogether
\let\restoreinterlinepenalty\relax

\def\dorestoreinterlinepenalty
  {\global\let\restoreinterlinepenalty\relax
   \global\resetpenalties\interlinepenalties
   \global\nofkeeplinestogether\zerocount}

\def\keeplinestogether#1%
  {\ifnum#1>\nofkeeplinestogether
     \global\nofkeeplinestogether#1%
     \global\setpenalties\interlinepenalties\nofkeeplinestogether\plustenthousand
     \global\let\restoreinterlinepenalty\dorestoreinterlinepenalty
   \fi}

\newif\ifgridsnapping % to be sure

\def\defaultwidowpenalty         {2000} % was: 1000
\def\defaultclubpenalty          {2000} % was:  800
\def\defaultdisplaywidowpenalty    {50}
\def\defaultbrokenpenalty         {100}

\def\defaultgridwidowpenalty        {0}
\def\defaultgridclubpenalty         {0}
\def\defaultgriddisplaywidowpenalty {0}
\def\defaultgridbrokenpenalty       {0}

\def\nopenalties
  {\widowpenalty        \zerocount
   \clubpenalty         \zerocount
   \brokenpenalty       \zerocount
   \doublehyphendemerits\zerocount
   \finalhyphendemerits \zerocount
   \adjdemerits         \zerocount}

\def\setdefaultpenalties
  {\directsetup{\systemsetupsprefix\s!default}}

\startsetups [\systemsetupsprefix\s!reset]
  \resetpenalties\widowpenalties
  \resetpenalties\clubpenalties
  \resetpenalties\interlinepenalties
\stopsetups

% we use \directsetup because it's faster and we know there is no csl

\startsetups [\systemsetupsprefix\s!default]

  \directsetup{\systemsetupsprefix\s!reset}

  \widowpenalty       \defaultwidowpenalty
  \clubpenalty        \defaultclubpenalty
  \displaywidowpenalty\defaultdisplaywidowpenalty
  \brokenpenalty      \defaultbrokenpenalty

\stopsetups

\startsetups [\v!grid] [\systemsetupsprefix\s!default]

  \directsetup{\systemsetupsprefix\s!reset}

  \widowpenalty       \defaultgridwidowpenalty
  \clubpenalty        \defaultgridclubpenalty
  \displaywidowpenalty\defaultgriddisplaywidowpenalty
  \brokenpenalty      \defaultgridbrokenpenalty

\stopsetups

% as an illustration:

\startsetups [\systemsetupsprefix\v!strict]

   \directsetup{\systemsetupsprefix\s!reset}

   \setpenalties\widowpenalties2\maxdimen
   \setpenalties\clubpenalties 2\maxdimen
                \brokenpenalty  \maxdimen

\stopsetups

\setdefaultpenalties % will happen later in \setuplayout

%D To be checked:

\ifx\savedstrutbox\undefined \newbox\savedstrutbox \fi

\def\savestrut {\setbox\savedstrutbox\copy\strutbox}
\def\savedstrut{\copy  \savedstrutbox}

%D Page spacing

\chardef\bottomraggedness=0 % 0=ragged 1=normal/align 2=baseline

\def\bottomalignlimit{3\lineheight}

\newif\ifn@rmalbottom
\newif\ifr@ggedbottom
\newif\ifb@selinebottom

\def\normalbottom
  {% \topskip 10pt
   \r@ggedbottomfalse}

\def\raggedbottom
  {\chardef\bottomraggedness\zerocount
   \n@rmalbottomfalse
   \r@ggedbottomtrue
   \b@selinebottomfalse
   \settopskip}

\def\alignbottom
  {\chardef\bottomraggedness\plusone
   \n@rmalbottomtrue
   \r@ggedbottomfalse
   \b@selinebottomfalse
   \settopskip}

\def\baselinebottom
  {\chardef\bottomraggedness\plustwo
   \n@rmalbottomfalse
   \r@ggedbottomfalse
   \b@selinebottomtrue
   \settopskip}

\let\normalbottom=\alignbottom % downward compatible

% so, the new one will be
%
% \chardef\bottomraggedness=0 % 0=ragged 1=normal/align 2=baseline
%
% \def\bottomalignlimit{3\lineheight} % will be settable
%
% \def\raggedbottom  {\chardef\bottomraggedness=0 \settopskip}
% \def\alignbottom   {\chardef\bottomraggedness=1 \settopskip}
% \def\baselinebottom{\chardef\bottomraggedness=2 \settopskip}
%
% \let\normalbottom  =\alignbottom

%D Good old blank redone:

\definesystemattribute[kern-chars]
\definesystemattribute[skip-category]  \chardef\skipcategoryattribute  \dogetattributeid{skip-category}
\definesystemattribute[skip-penalty]   \chardef\skippenaltyattribute   \dogetattributeid{skip-penalty}
\definesystemattribute[skip-order]     \chardef\skiporderattribute     \dogetattributeid{skip-order}
\definesystemattribute[display-math]   \chardef\displaymathattribute   \dogetattributeid{display-math}
\definesystemattribute[snap-method]    \chardef\snapmethodattribute    \dogetattributeid{snap-method}
\definesystemattribute[snap-done]      \chardef\snapdoneattribute      \dogetattributeid{snap-done}

%definesystemattribute[snap-category]  \chardef\snapcategoryattribute  \dogetattributeid{snap-category}

% TODO: NAMED SNAPPERS

\newskip  \bodyfontlineheight
\newdimen \bodyfontstrutheight
\newdimen \bodyfontstrutdepth

\newskip  \globalbodyfontlineheight
\newdimen \globalbodyfontstrutheight
\newdimen \globalbodyfontstrutdepth

% \appendtoks
%     \dosetupgridsnapping
% \to \everysetupbodyfont

\def\installsnapvalues#1#2% todo: a proper define
  {\edef\currentsnapper{#1:#2}%
   \ifcsname\currentsnapper\endcsname \else
     \setevalue\currentsnapper{\ctxlua{vspacing.define_snap_method("#1","#2")}}%
   \fi
   \setevalue{\??gr:#1}{\attribute\snapmethodattribute\csname\currentsnapper\endcsname\space}}

\unexpanded\def\definegridsnapping
  {\dodoubleargument\dodefinegridsnapping}

\def\dodefinegridsnapping[#1][#2]%
  {\installsnapvalues{#1}{#2}}

\edef\resetsnapvalue
  {%\gridsnappingfalse
   \attribute\snapmethodattribute\attributeunsetvalue}

\def\setsnapvalue#1%
  {%\gridsnappingtrue
   \ifcsname\??gr:#1\endcsname\csname\??gr:#1\endcsname\fi}

\def\autosetsnapvalue#1%
  {\ifcsname\??gr:#1\endcsname
     \csname\??gr:#1\endcsname
   \else
     \installsnapvalues\s!dummy{#1}%
     \csname\??gr:\s!dummy\endcsname
   \fi}

% \installsnapvalues{loose} {\v!maxdepth:0.8,\v!maxheight:0.8,\v!strut}
% \installsnapvalues{normal}{\v!maxdepth:1.0,\v!maxheight:1.0,\v!strut}
% \installsnapvalues{tight} {\v!maxdepth:1.2,\v!maxheight:1.2,\v!strut}

% none             don't enlarge
% halfline         enlarge by halfline/halfline
% line             enlarge by line/line
% strut            enlarge by ht/dp (default)
% first            align to top line
% last             align to bottom line
% mindepth         round depth down
% maxdepth         round depth up
% minheight        round height down
% maxheight        round height up
% local            use local interline space
% shift:-3tp       vertical shift within box

%D We're not downward compatible with \MKII !

\definegridsnapping[\v!normal]   [\v!maxheight,\v!maxdepth,\v!strut]
\definegridsnapping[\v!standard] [\v!maxheight,\v!maxdepth,\v!strut]
\definegridsnapping[\v!yes]      [\v!maxheight,\v!maxdepth,\v!strut]

\definegridsnapping[\v!strict]   [\v!maxdepth:0.8,\v!maxheight:0.8,\v!strut]
\definegridsnapping[\v!tolerant] [\v!maxdepth:1.2,\v!maxheight:1.2,\v!strut]

\definegridsnapping[\v!top]      [\v!minheight,\v!maxdepth,\v!strut]
\definegridsnapping[\v!bottom]   [\v!maxheight,\v!mindepth,\v!strut]
\definegridsnapping[\v!both]     [\v!minheight,\v!mindepth,\v!strut]

\definegridsnapping[\v!broad]    [\v!maxheight,\v!maxdepth,\v!strut,0.8] % maybe 0.85
\definegridsnapping[\v!fit]      [\v!maxheight,\v!maxdepth,\v!strut,1.2] % tight 0.15

\definegridsnapping[\v!first]    [\v!first]
\definegridsnapping[\v!last]     [\v!last]
\definegridsnapping[\v!high]     [\v!minheight,\v!maxdepth,\v!none]
\definegridsnapping[\v!low]      [\v!maxheight,\v!mindepth,\v!none]
\definegridsnapping[\v!line]     [\v!line]
\definegridsnapping[\v!strut]    [\v!strut]

\definegridsnapping[\v!max]      [\v!maxdepth,\v!maxheight,\v!strut]
\definegridsnapping[\v!min]      [\v!mindepth,\v!minheight,\v!strut]

\newtoks\everysetupgridsnapping % this only happens at the setuplayout level

\def\dosetupgridsnapping{\the\everysetupgridsnapping} % not used !

\def\synchronizelocallinespecs
  {\bodyfontlineheight \normallineheight
   \bodyfontstrutheight\strutheight
   \bodyfontstrutdepth \strutdepth}

\def\synchronizegloballinespecs
  {\global\globalbodyfontlineheight \normallineheight
   \global\globalbodyfontstrutheight\strutheight
   \global\globalbodyfontstrutdepth \strutdepth}

% \appendtoks
%     \synchronizegloballinespecs
%     \synchronizelocallinespecs
% \to \everysetupgridsnapping

\appendtoks
    \synchronizegloballinespecs
    \synchronizelocallinespecs
\to \everysetupglobalinterlinespace

\appendtoks
    \synchronizelocallinespecs
\to \everysetuplocalinterlinespace

% \appendtoks
%     \resetsnapvalues
% \to \everyforgetall

%D Snapping.

\newif\ifgridsnapping

\let\showgridsnapping\relax

\def\snaptogrid {\dosingleempty\dosnaptogrid}
\def\moveongrid {\dosingleempty\domoveongrid}
\unexpanded\def\placeongrid{\dosingleempty\doplaceongrid}

\def\dodomoveongrid[#1]%
  {} % gone, unless we set an attribute

\def\doplaceongrid[#1]%
  {\snaptogrid[#1]\vbox}

\def\dosnaptogrid[#1]% list or predefined
  {\ifgridsnapping
     \expandafter\dodosnaptogrid
   \else
     \expandafter\gobbleoneargument
   \fi{#1}}

\def\dodosnaptogrid#1%
  {\bgroup
   \resetsnapvalue
   \dowithnextbox{\dododosnaptogrid{#1}}}

% eventually there will always be a line snap

\def\dododosnaptogrid#1%
  {\ifvbox\nextbox
     \ctxlua{nodes.collapse_vbox(\number\nextbox)}%
   \fi
   \doifelsenothing{#1}{\setsnapvalue\v!normal}{\autosetsnapvalue{#1}}%
   \ctxlua{vspacing.snap_box(\number\nextbox,\number\attribute\snapmethodattribute)}%
%    \ifzeropt\ht\nextbox
%      \ifzeropt\dp\nextbox
%        \box\nextbox % here, else empty and zero
%        \kern-\bodyfontlineheight
%      \else
%        \box\nextbox
%      \fi
%    \else
     \box\nextbox
%    \fi
   \egroup}

\def\docheckgridsnapping
  {\edef\askedgridmode{\layoutparameter\c!grid}% needs checking by WS
   \doifelse\askedgridmode\v!no
     {\gridsnappingfalse
      \resetsystemmode\v!grid
      \resetsnapvalue}
     {\gridsnappingtrue
      \setsystemmode\v!grid
      \autosetsnapvalue\askedgridmode}}

%D Visualization:

\definepalet
  [grid]
  [  one=red,
     two=green,
   three=blue,
    four=gray]

\def\setgridtracebox#1[#2]% % maybe reverse the order
  {\setbox\nextbox#1%
     {\hbox
        {\hbox to \zeropoint
           {\setlayoutcomponentattribute\v!grid\v!test
            \color[grid:#2]{\ruledhbox \layoutcomponentboxattribute {\fakebox\nextbox}}%
            \hss}%
         \flushnextbox}}}

\chardef\gridboxlinenomode\plusone % 0:nothing 1:all 2:lines 3:frame 4:l/r
\chardef\gridboxlinemode  \plusone

\def\gridboxvbox {\ifcase\gridboxlinemode\vbox\or\ruledvbox\or\vbox\or\ruledvbox\else\ruledvbox\fi}
\def\gridboxwidth{\ifcase\gridboxlinemode0\or.5\or.5\or0\else.5\fi\testrulewidth}

\def\setgridbox#1#2#3% maybe ifgridsnapping at outer level
  {\setbox#1\gridboxvbox to #3 % given size
     {\forgetall
      \resetteststrut
      \offinterlineskip
      \hsize#2%
      \baselinerulefalse
      \ifnum\gridboxlinenomode=\plusthree
        \chardef\gridboxlinenomode\ifodd\realpageno\plusone\else\plustwo\fi
      \fi
      \gridboxvbox % calculated size
        {\getrawnoflines{#3}% \getnoflines{#3}%
%          \ifgridsnapping \else
%            \vskip\topskip
%            \vskip-\strutht
%          \fi
         \scratchdimen#2\advance\scratchdimen \lineheight
         \dorecurse\noflines
           {\strut
            \hskip-.5\lineheight
            \ifcase\gridboxlinenomode\or
              \rlap
                {\hskip.2\bodyfontsize\hskip\scratchdimen
                 \infofont\hbox to 1em{\hss\recurselevel}}%
            \or
              \llap
                {\infofont\hbox to 1em{\hss\recurselevel}%
                 \hskip.2\bodyfontsize}%
            \fi
            \vrule
              \!!height \gridboxwidth
              \!!depth  \gridboxwidth
              \!!width  \scratchdimen
            \par}}
      \vfill}}

%D This has become obsolete:

\def\fuzzysnappedbox#1#2% \box<n> \unvbox<n>
  {#1#2}

% \def\moveboxontogrid#1#2#3% will become obsolete
%   {\doif{#2}\v!top   {\setbox#1\hbox{\snaptogrid[\v!first]\box#1}}%
%    \doif{#2}\v!bottom{\setbox#1\hbox{\snaptogrid[\v!last ]\box#1}}}

\def\moveboxontogrid#1#2#3% will become obsolete
  {}

%D Helper:

\def\doassignsomeskip#1\to#2% ook nog \v!halfline+fuzzysnap
  {\doifelse{#1}\v!line
     {#2\ifgridsnapping
        \bodyfontlineheight
      \else
        \openlineheight
      \fi}
     {\ifgridsnapping
        \assigndimension{#1}{#2}{.25\bodyfontlineheight}{.5\bodyfontlineheight}\bodyfontlineheight
      \else
        \assigndimension{#1}{#2}\smallskipamount\medskipamount\bigskipamount
      \fi}%
   \relax}

% \start \dosetstretch{.25em} \setuptolerance[tolerant,stretch] \input tufte \endgraf \stop
% \start \dosetstretch{.5em} effe flink doorfietsen \stop

% \def\dosetupgridsnapping % calls too often, only needed in gridsnapping
%   {\ctxlua{nodes.setsnapvalue(1,\number\openstrutheight,\number\openstrutdepth)}}
%
% \def\doenablegridsnapping
%   {\attribute\snapcategoryattribute\plusone
%    \topskip\strutht
%    \offinterlineskip}
%
% \def\dodisablegridsnapping
%   {\attribute\snapcategoryattribute\attributeunsetvalue
%    % reset topskip
%    \oninterlineskip}

% experimental code, not yet interfaced:

% category:
% 0 == discard                             discard
% 1 == only if larger                      largest
% 2 == force even if smaller               force
% 3 == only take penalty component         penalty
% 4 == add to existing skip                add
% 5 == disable (ignore following)          disable
% 6 == kill whitespace                     nowhite
% 7 == discard previous                    back
%
% penalty: larger wins
% order: larger wins
% category:2,order:5,penalty:10000,skip:value|kw
%
% \defineblankmethod  [\v!joinedup] {\ifvmode\nointerlineskip\fi}

% todo, in grid mode: vspacing.fixed = false

\let\saveouterspacing   \relax % for old times sake
\let\restoreouterspacing\relax % for old times sake

\newtoks\everybeforeblankhandling
\newtoks\everyafterblankhandling

\newconditional\someblankdone

\appendtoks
    \blankskip\zeropoint
    \attribute\skipcategoryattribute\plusone
    \attribute\skippenaltyattribute \attributeunsetvalue
    \attribute\skiporderattribute   \attributeunsetvalue
    \ifgridsnapping % \ifblankflexible
        \setfalse\blankisfixed
    \else
        \settrue\blankisfixed
    \fi
\to \everybeforeblankhandling

\appendtoks
    \ifconditional\blankisfixed
        \blankskip1\blankskip
    \else
        \blankskip1\blankskip\!!plus\skipgluefactor\blankskip\!!minus\skipgluefactor\blankskip
    \fi
\to \everyafterblankhandling

% \ifgridsnapping will go

\appendtoks
    \ifgridsnapping
        \settrue\blankisfixed
    \else
        \setfalse\blankisfixed
    \fi
\to \everybeforeblankhandling

\def\setblankcategory#1%
  {\settrue\someblankdone
   \attribute\skipcategoryattribute#1\relax}

\def\setblankorder#1%
  {\attribute\skiporderattribute#1\relax}

\def\fixedblankskip
  {\settrue\blankisfixed}

\def\flexibleblankskip
  {\setfalse\blankisfixed}

\def\addblankskip#1#2#3%
  {\settrue\someblankdone
   \advance\blankskip#1\dimexpr\ifgridsnapping#3\else#2\fi\relax\relax}

\def\setblankpenalty #1%
  {\flushblankhandling
   \settrue\someblankdone
   \attribute\skipcategoryattribute \plusthree
   \attribute\skippenaltyattribute #1\relax
   \flushblankhandling}

\unexpanded\def\startblankhandling
  {\par
   \ifvmode
     \expandafter\dostartblankhandling
   \else
     \expandafter\nostartblankhandling
   \fi}

\def\nostartblankhandling#1\stopblankhandling
  {}

\def\dostartblankhandling
  {\begingroup
   \setfalse\someblankdone
   \the\everybeforeblankhandling}

\unexpanded\def\stopblankhandling
  {\the\everyafterblankhandling
   \ifconditional\someblankdone
     \vskip\blankskip
   \fi
   \endgroup}

\def\flushblankhandling
  {\the\everyafterblankhandling
   \ifconditional\someblankdone
     \vskip\blankskip
   \fi
   \setfalse\someblankdone
   \the\everybeforeblankhandling}

% % % % we can move much to lua once we can expand there % % % %

\unexpanded\def\definevspacingamount
  {\dotripleempty\dodefinevspacingamount}

% \def\dodefinevspacingamount[#1][#2][#3]%
%   {\ctxlua{vspacing.setskip("#1",\!!bs\detokenize{#2}\!!es,\!!bs\detokenize{#3}\!!es)}}

\def\dodefinevspacingamount[#1][#2][#3]% can be combined
  {\setvalue{\??vs:#1}{\ifgridsnapping#3\else#2\fi}%
   \ctxlua{vspacing.setskip("#1")}}

\def\addpredefinedblankskip#1#2%
  {\settrue\someblankdone
   \advance\blankskip#1\dimexpr\csname\??vs:#2\endcsname\relax}

\def\addaskedblankskip#1#2%
  {\settrue\someblankdone
   \advance\blankskip#1\dimexpr#2\relax}

\unexpanded\def\definevspacing
  {\dodoubleempty\dodefinevspacing}

\def\dodefinevspacing[#1][#2]%
  {\ctxlua{vspacing.setmap("#1","#2")}}

\unexpanded\def\vspacing
  {\dosingleempty\dovspacing}

% todo: when packed blocks blank, we need to enable forced

\def\dovspacing % blank also has a \flushnotes
  {\ifinpagebody
     \expandafter\dovspacingyes
   \else\ifconditional\noblankinpacked % todo: better reset this conditional in pagebody
     \expandafter\expandafter\expandafter\dovspacingnop
   \else
     \expandafter\expandafter\expandafter\dovspacingyes
   \fi\fi}

\def\dovspacingyes[#1]%
  {\ifmmode\else\ctxlua{vspacing.analyse("\iffirstargument#1\else\s!default\fi")}\fi}

\def\dovspacingnop[#1]%
  {\ifmmode\else\par\fi}

% todo: check them and make them faster:

\definecomplexorsimple\setupvspacing

\let\currentvspacing\empty

\def\complexsetupvspacing[#1]%
  {\edef\currentvspacing{#1}}

\def\simplesetupvspacing
  {\ifx\empty\currentvspacing\else
     \let\currentvspacing\s!default
   \fi
   \simplesetupwhitespace}

\def\restorestandardblank
  {\let\currentvspacing\v!standard}

% used both

\def\doinhibitblank{\vspacing[\v!disable]} % can be made faster
\def\inhibitblank  {\vspacing[\v!disable]} % can be made faster

\let\setupblank      \setupvspacing
\let\simplesetupblank\simplesetupvspacing
\let\blank           \vspacing

% category:4 is default

% \definevspacingamount[\v!big]     [\bigskipamount]     [\openlineheight]
% \definevspacingamount[\v!medium]  [\medskipamount]     [0.50\openlineheight]
% \definevspacingamount[\v!small]   [\smallskipamount]   [0.25\openlineheight]
% \definevspacingamount[\v!line]    [\openlineheight]    [\openlineheight]
% \definevspacingamount[\v!halfline][0.50\openlineheight][0.50\openlineheight]
% \definevspacingamount[\v!formula] [\medskipamount]     [0.50\openlineheight]
% \definevspacingamount[\v!white]   [\parskip]           [\openlineheight]
% \definevspacingamount[\v!height]  [\strutheight]       [\strutheight]
% \definevspacingamount[\v!depth]   [\strutdepth]        [\strutdepth]

\definevspacingamount[\v!none]    [\zeropoint]         [\zeropoint]
\definevspacingamount[\v!big]     [\bigskipamount]     [\bodyfontlineheight]
\definevspacingamount[\v!medium]  [\medskipamount]     [0.50\bodyfontlineheight]
\definevspacingamount[\v!small]   [\smallskipamount]   [0.25\bodyfontlineheight]
\definevspacingamount[\v!line]    [\openlineheight]    [\bodyfontlineheight]
\definevspacingamount[\v!halfline][0.50\openlineheight][0.50\bodyfontlineheight]
\definevspacingamount[\v!formula] [\medskipamount]     [0.50\bodyfontlineheight]
\definevspacingamount[\v!white]   [\parskip]           [\bodyfontwhitespace]
\definevspacingamount[\v!height]  [\strutheight]       [\bodyfontstrutheight]
\definevspacingamount[\v!depth]   [\strutdepth]        [\bodyfontstrutdepth]

\def\bodyfontwhitespace
  {\dimexpr
     \ifdim\parskip=\zeropoint
       \zeropoint
     \else\ifgridsnapping
       \bodyfontlineheight
     \else
       \parskip
     \fi\fi
   \relax}

\definevspacing[\v!preference][penalty:-500]  % goodbreak
\definevspacing[\v!samepage]  [penalty:10000] % real strong
\definevspacing[\v!max]       [category:1]
\definevspacing[\v!force]     [category:2]
\definevspacing[\v!disable]   [category:5]
\definevspacing[\v!nowhite]   [category:6]
\definevspacing[\v!back]      [category:7]
\definevspacing[\v!always]    [category:0]
\definevspacing[\v!weak]      [order:0]
\definevspacing[\v!strong]    [order:100]

\definevspacing[\s!default] [\v!white] % was big for a while

\dorecurse{10} % todo: other values < 4000
  {\expanded{\definevspacing[\v!samepage-\recurselevel][penalty:\the\numexpr4000+250*\recurselevel\relax]}}

% \setfalse\vspacingenabled
%
% \newtoks\everyenablevspacing
% \newtoks\everydisablevspacing
%
% \def\enablevspacing {\the\everyenablevspacing}
% \def\disablevspacing{\the\everydisablevspacing}
%
% \appendtoks
%     \writestatus\m!systems{! ! enabling vspacing ! !}%
%     \settrue\vspacingenabled
%     \ctxlua{vspacing.enable()}%
% \to \everyenablevspacing
%
% \appendtoks
%     \writestatus\m!systems{! ! disabling vspacing ! !}%
%     \setfalse\vspacingenabled
%     \ctxlua{vspacing.disable()}%
% \to \everydisablevspacing

\let\blank            \vspacing
\let\defineblank      \definevspacing
\let\defineblankmethod\definevspacingamount

%D The following command is for Wolfgang. It has to be used with
%D care as it does {\em not} work in tandem with the other spacing
%D commands.

\unexpanded\def\definevspace
  {\dotripleempty\dodefinevspace}

\def\dodefinevspace[#1][#2][#3]%
  {\ifthirdargument
     \setvalue{\??va#1:#2}{#3}%
   \else
     \setvalue{\??va:#1}{#2}%
   \fi}

\unexpanded\def\vspace
  {\dodoubleempty\dovspace}

\def\dovspace[#1][#2]%
  {\ifsecondargument
     \dodovspace[#1][#2]%
   \else\iffirstargument
     \vspace[][#1]%
   \else
     \vspace[][\s!default]%
   \fi\fi}

\def\dodovspace[#1][#2]%
  {\par
   \ifvmode
     \removelastskip
     \vskip\vspaceamount{#1}{#2}\relax
   \fi}

\def\vspaceamount#1#2%
  {\executeifdefined{\??va#1:#2}{\executeifdefined{\??va:#2}\zeropoint}}

%D When spacing is active we need to handle commands in
%D a special way:
%D
%D \starttyping
%D \setuplines[space=on]
%D
%D \startlines
%D Let's talk about this{\ttsl\gobbleoneargument or}that.
%D \stoplines
%D
%D \startlines
%D Let's talk about this{\getvalue{ttsl}or}that.
%D \stoplines
%D \stoptyping
%D
%D One can indent in several ways:
%D
%D \starttyping
%D \setupindenting[medium] \setuplines[indenting=odd] % no yes odd even
%D
%D \startlines
%D first
%D second
%D third
%D fourth
%D \stoplines
%D \stoptyping

% \unexpanded\def\setuplines
%   {\dodoubleargument\getparameters[\??rg]}
%
% \unexpanded\def\startlines
%   {\@@rgbefore
%    \pushmacro\checkindentation
%    \whitespace
%   %\page[\v!preference]} gaat mis na koppen, nieuw: later \nobreak
%    \begingroup
%    \setupindenting[\@@rgindenting]%
%    \typesettinglinestrue
%    \setupwhitespace[\v!none]%
%    \obeylines
%    \ignorespaces
%    \gdef\afterfirstobeyedline % tzt two pass, net als opsomming
%      {\gdef\afterfirstobeyedline
%         {\nobreak
%          \doifnot\@@rgoption\v!packed{\global\let\afterfirstobeyedline\relax}}}%
%    \def\obeyedline
%      {\par
%       \futurelet\next\dobetweenthelines}%
%    \activatespacehandler\@@rgspace
%    \GotoPar}
%
% \unexpanded\def\stoplines
%   {\endgroup
%    \popmacro\checkindentation
%    \@@rgafter}
%
% \def\dobetweenthelines
%   {\doifmeaningelse\next\obeyedline
%     {\@@rginbetween}
%     {\afterfirstobeyedline}}
%
% \setuplines
%   [\c!option=,
%    \c!before=\blank,
%    \c!after=\blank,
%    \c!inbetween=\blank,
%    \c!indenting=\v!no,
%    \c!space=\v!default]

%D Contrary to \MKII\ we can now define classes of lines (generalized by
%D Wolfgang). I will probably rewrite bits in \LUA.

\let\currentlines\empty

\def\linesparameter    #1{\csname\dolinesparameter{\??rg\currentlines}#1\endcsname}
\def\linesparameterhash#1{\dolinesparameterhash   {\??rg\currentlines}#1}

\def\dolinesparameter    #1#2{\ifcsname#1#2\endcsname#1#2\else\expandafter\dolinesparentparameter    \csname#1\s!parent\endcsname#2\fi}
\def\dolinesparameterhash#1#2{\ifcsname#1#2\endcsname  #1\else\expandafter\dolinesparentparameterhash\csname#1\s!parent\endcsname#2\fi}

\def\dolinesparentparameter    #1#2{\ifx#1\relax\s!empty\else\dolinesparameter    #1#2\fi}
\def\dolinesparentparameterhash#1#2{\ifx#1\relax        \else\dolinesparameterhash#1#2\fi}

\def\dosetlinesattributes#1#2% style color
  {\edef\fontattributehash {\linesparameterhash#1}%
   \edef\colorattributehash{\linesparameterhash#2}%
   \ifx\fontattributehash \empty\else\dosetfontattribute \fontattributehash #1\fi
   \ifx\colorattributehash\empty\else\dosetcolorattribute\colorattributehash#2\fi}

\getparameters
  [\??rg]
  [\c!option=,
   \c!before=\blank,
   \c!after=\blank,
   \c!inbetween=\blank,
   \c!indenting=\v!no,
   \c!space=\v!default]

\unexpanded\def\definelines
  {\dodoubleempty\dodefinelines}

\def\dodefinelines[#1][#2]%
  {\getparameters[\??rg#1][\s!parent=\??rg,#2]%
   \setvalue{\e!start#1}{\dostartlines[#1]}%
   \setvalue{\e!stop #1}{\dostoplines}}

\unexpanded\def\setuplines
  {\dodoubleempty\dosetuplines}

\def\dosetuplines[#1][#2]%
  {\doifelsenothing{#2}
     {\getparameters[\??rg][#1]}
     {\def\docommand##1{\getparameters[\??rg##1][#2]}%
      \processcommacommand[#1]\docommand}}

\def\dostartlines[#1]%
  {\bgroup
   \edef\currentlines{#1}%
   \linesparameter\c!before
   \pushmacro\checkindentation
   \whitespace
   \begingroup
   \dosetlinesattributes\c!style\c!color
   \setupindenting[\linesparameter\c!indenting]%
   \setupalign[\linesparameter\c!align]%
   \typesettinglinestrue
   \setupwhitespace[\v!none]%
   \obeylines
   \ignorespaces
   \gdef\afterfirstobeyedline % tzt two pass, net als opsomming
     {\gdef\afterfirstobeyedline
        {\nobreak
         \doifnot{\linesparameter\c!option}\v!packed{\global\let\afterfirstobeyedline\relax}}}%
   \def\obeyedline
     {\par
      \futurelet\next\dobetweenthelines}%
   \activatespacehandler{\linesparameter\c!space}%
   \GotoPar}

\def\dostoplines
  {\endgroup
   \popmacro\checkindentation
   \linesparameter\c!after
   \egroup}

\def\dobetweenthelines
  {\doifmeaningelse\next\obeyedline
     {\linesparameter\c!inbetween}
     {\afterfirstobeyedline}}

\definelines[\v!lines]

\def\emptylines
  {\dosingleempty\doemptylines}

\def\doemptylines[#1]%
  {\endgraf\dorecurse{\iffirstargument#1\else3\fi}\crlf}

\protect \endinput