%D \module
%D   [     file=supp-vis,
%D      version=1996.6.25,
%D        title=\CONTEXT\ Support Macros,
%D     subtitle=Visualization,
%D       author=J. Hagen,
%D         date=\huidigedatum,
%D    copyright=J. Hagen / \PRAGMA]
%D
%
% This module is part of \CONTEXT, a general purpose,
% parameter driven, macro package programmed in \TEX. This
% module may only be distributed as part of \CONTEXT. 

%D \gdef\ShowBufferedExample% private typeseting macro
%D   {\startregelcorrectie
%D    \bgroup
%D    \steltypenin[marge=0pt,optie=kleur]
%D    \showmakeup
%D    \centeredvcuetrue
%D    \dontinterfere
%D    \baselinerulefalse
%D    \normalvbox
%D      {\normalhbox to \hsize
%D         {$\hsize=.5\hsize
%D          \advance\hsize by -.5em
%D          \vcenter{\vbox{\haalbuffer}}\normalhss
%D          \vcenter{\vbox{\dontshowcomposition\typebuffer}}$}}
%D    \egroup
%D    \stopregelcorrectie}
%D
%D \gdef\ShowBufferedExampleBox% private typeseting macro
%D   {\startregelcorrectie
%D    \bgroup
%D    \steltypenin[marge=0pt,optie=kleur]
%D    \showmakeup
%D    \centeredvcuetrue
%D    \dontinterfere
%D    \baselinerulefalse
%D    \normalvbox
%D      {\normalhbox to \hsize
%D         {$\hsize=.5\hsize
%D          \advance\hsize by -.5em
%D          \vcenter{\baselineruletrue\vbox{\haalbuffer}}\normalhss
%D          \vcenter{\vbox{\dontshowcomposition\typebuffer}}$}}
%D    \egroup
%D    \stopregelcorrectie}

%D Although an integral part of \CONTEXT, this module is one
%D of the support modules. Its stand alone character permits
%D use in \PLAIN\ \TEX\ or \TEX\ based macropackages.
%D \ifCONTEXT \else If in some examples the verbatim listings
%D don't show up nice, this is due to processing by a system
%D that does not support buffering. In \CONTEXT\ we show the
%D commands in the margin, use bit more advanced way of
%D numbering, and typeset the source in \TEX nicolored
%D verbatim. Sorry for this inconvenience.\fi 

%D This module is still in development. Depending on my 
%D personal need and those of whoever uses it, the macros will
%D be improved in terms of visualization, efficiency and 
%D compatibility.  

\ifx \undefined \writestatus \input supp-mis.tex \fi

%D One of the strong points of \TEX\ is abstraction of textual
%D input. When macros are defined well and do what we
%D want them to do, we will seldom need the tools present in
%D What You See Is What You Get systems. For instance, when
%D entering text we don't need rulers, because no manual
%D shifting and/or alignment of text is needed. On the other
%D hand, when we are designing macros or specifying layout
%D elements, some insight in \TEX's advanced spacing, kerning,
%D filling, boxing and punishment abilities will be handy.
%D That's why we've implemented a mechanism that shows some of
%D the inner secrets of \TEX.

\writestatus{loading}{Context Support Macros / Visualization}

%D In this module we are going to redefine some \TEX\
%D primitives and \PLAIN\ macro's. Their original meaning is
%D saved in macros with corresponding names, preceded by
%D \type{normal}. These original macros are (1)~used to
%D temporary restore the old values when needed and
%D (2)~used to prevent recursive calls in the macros that
%D replace them.

\unprotect

%D \macros
%D   {normalhbox,
%D    normalvbox,normalvtop}
%D   {}
%D
%D There are three types of boxes, one horizontal and two
%D vertical in nature. As we will see later on, all three types
%D are to be handled according to their orientation and
%D baseline behavior. Especially \type{\vtop}'s need our
%D special attention.

\let\normalhbox     = \hbox
\let\normalvbox     = \vbox
\let\normalvtop     = \vtop

%D \macros
%D   {normalhskip,
%D    normalvskip}
%D   {}
%D
%D Next come the flexible skips, which come in two flavors
%D too. Like boxes these are handled with \TEX\ primitives.

\let\normalhskip    = \hskip
\let\normalvskip    = \vskip

%D \macros
%D   {normalpenalty,
%D    normalkern}
%D   {}
%D
%D Both penalties and kerns are taken care of by mode sensitive
%D primitives. This means that when making them visible, we
%D have to take the current mode into account.

\let\normalpenalty  = \penalty
\let\normalkern     = \kern

%D \macros
%D   {normalhglue,
%D    normalvglue}
%D   {}
%D
%D Glues on the other hand are macro's defined in \PLAIN\ \TEX.
%D As we will see, their definitions make the implementation of
%D their visible counterparts a bit more \TeX{}nical.

\let\normalhglue    = \hglue
\let\normalvglue    = \vglue

%D \macros
%D   {normalmkern,
%D    normalmskip}
%D   {}
%D
%D Math mode has its own spacing primitives, preceded by
%D \type{m}. Due to the relation with the current font and the
%D way math is typeset, their unit \type{mu} is not compatible
%D with other dimensions. As a result, the visual appearance
%D of these primitives is kept primitive too.

\let\normalmkern    = \mkern
\let\normalmskip    = \mskip

%D \macros
%D   {hfilneg,
%D    vfilneg}
%D   {}
%D
%D Fills can be made visible quite easy. We only need some
%D additional negation macros. Because \PLAIN\ \TEX\ only
%D offers \type{\hfilneg} and \type{\vfilneg}, we define our
%D own alternative double \type{ll}'ed ones.

\def\hfillneg%
  {\normalhskip\!!zeropoint \!!plus-1fill\relax}

\def\vfillneg%
  {\normalvskip\!!zeropoint \!!plus-1fill\relax}

%D \macros
%D   {normalhss,normalhfil,normalhfill,
%D    normalvss,normalvfil,normalvfill}
%D   {}
%D
%D The positive stretch primitives are used independant and in
%D combination with \type{\leaders}.

\let\normalhss      = \hss
\let\normalhfil     = \hfil
\let\normalhfill    = \hfill
\let\normalvss      = \vss
\let\normalvfil     = \vfil
\let\normalvfill    = \vfill

%D \macros
%D   {normalhfilneg,normalhfillneg,
%D    normalvfilneg,normalvfillneg}
%D   {}
%D
%D Keep in mind that both \type{\hfillneg} and \type{\vfillneg}
%D are not part of \PLAIN\ \TEX\ and therefore not documented
%D in standard \TEX\ documentation. They can nevertheless be
%D used at will.

\let\normalhfilneg  = \hfilneg
\let\normalhfillneg = \hfillneg
\let\normalvfilneg  = \vfilneg
\let\normalvfillneg = \vfillneg

%D Visualization is not always wanted. Instead of turning this
%D option off in those (unpredictable) situations, we just
%D redefine a few \PLAIN\ macros.

\def\rlap#1{\normalhbox to \!!zeropoint{#1\normalhss}}
\def\llap#1{\normalhbox to \!!zeropoint{\normalhss#1}}

\def~{\normalpenalty\!!tenthousand\ }

%D \macros
%D   {makeruledbox}
%D   {}
%D
%D Ruled boxes can be typeset is many ways. Here we present
%D just one alternative. This implementation may be a little 
%D complicated, but it supports all three kind of boxes. The 
%D next command expects a \BOX\ specification, like: 
%D
%D \starttypen
%D \makeruledbox0
%D \stoptypen

%D \macros
%D   {baselinerule,baselinefill,baselinesmash}
%D   {}
%D
%D We can make the baseline of a box visible, both dashed and
%D as a rule. Normally the line is drawn on top of the baseline,
%D but a smashed alternative is offered too. If we want them
%D all, we just say:
%D
%D \starttypen
%D \baselineruletrue
%D \baselinefilltrue
%D \baselinesmashtrue
%D \stoptypen
%D
%D At the cost of some overhead these alternatives are
%D implemented using \type{\if}'s:

\newif\ifbaselinerule  \baselineruletrue
\newif\ifbaselinefill  \baselinefillfalse
\newif\ifbaselinesmash \baselinesmashfalse

%D \macros
%D   {toprule,bottomrule,leftrule,rightrule}
%D   {}
%D
%D Rules can be turned on and off, but by default we have:
%D
%D \starttypen
%D \topruletrue
%D \bottomruletrue
%D \leftruletrue
%D \rightruletrue
%D \stoptypen
%D
%D As we see below:

\newif\iftoprule       \topruletrue
\newif\ifbottomrule    \bottomruletrue
\newif\ifleftrule      \leftruletrue
\newif\ifrightrule     \rightruletrue

%D \macros
%D   {boxrulewidth}
%D   {}
%D
%D The width in the surrounding rules can be specified by
%D assigning an apropriate value to the dimension used. This
%D module defaults the width to:
%D
%D \starttypen
%D \boxrulewidth=.2pt
%D \stoptypen
%D
%D Although we are already low on \DIMENSIONS\ it's best to
%D spend one here, mainly because it enables easy manipulation,
%D like multiplication by a given factor.

\newdimen\boxrulewidth \boxrulewidth=.2pt

%D The core macro \type{\makeruledbox} looks a bit hefty. The
%D manipulation at the end is needed because we want to
%D preserve both the mode and the baseline. This means that
%D \type{\vtop}'s and \type{\vbox}'es behave the way we expect
%D them to do.
%D
%D \startregelcorrectie
%D \hbox
%D   {\ruledhbox to 5em{\strut test\normalhss}\hskip1em
%D    \ruledvbox{\hsize 5em\strut test \par test\strut}\hskip1em
%D    \ruledvtop{\hsize 5em\strut test \par test\strut}}
%D \stopregelcorrectie
%D
%D The \type{\cleaders} part of the macro is responsible for
%D the visual baseline. The \type{\normalhfill} belongs to this
%D primitive too. By storing and restoring the height and depth
%D of box \type{#1}, we preserve the mode.

\def\makeruledbox#1%
  {\edef\ruledheight {\the\ht#1}%
   \edef\ruleddepth  {\the\dp#1}%
   \edef\ruledwidth  {\the\wd#1}%
   \setbox\scratchbox=\normalvbox
     {\dontcomplain
      \offinterlineskip
      \hrule
        \!!height\boxrulewidth
        \iftoprule\else\!!width\!!zeropoint\fi
      \normalvskip-\boxrulewidth
      \normalhbox to \ruledwidth
         {\vrule
            \!!height\ruledheight
            \!!depth\ruleddepth
            \!!width\ifleftrule\else0\fi\boxrulewidth
          \ifdim\ruledheight>\!!zeropoint \else \baselinerulefalse \fi
          \ifdim\ruleddepth>\!!zeropoint \else \baselinerulefalse \fi
          \ifbaselinerule
            \ifdim\ruledwidth<20\boxrulewidth
              \baselinefilltrue
            \fi
            \cleaders
              \ifbaselinefill
                \hrule
                  \ifbaselinesmash
                    \!!height\boxrulewidth
                  \else
                    \!!height.5\boxrulewidth
                    \!!depth.5\boxrulewidth
                  \fi
              \else
                \normalhbox
                  {\normalhskip2.5\boxrulewidth
                   \vrule
                   \ifbaselinesmash
                     \!!height\boxrulewidth
                   \else
                     \!!height.5\boxrulewidth
                     \!!depth.5\boxrulewidth
                   \fi
                   \!!width5\boxrulewidth
                   \normalhskip2.5\boxrulewidth}%
              \fi
          \fi
          \normalhfill
          \vrule
            \!!width\ifrightrule\else0\fi\boxrulewidth}%
        \normalvskip-\boxrulewidth
        \hrule
          \!!height\boxrulewidth
          \ifbottomrule\else\!!width\!!zeropoint\fi}%
   \wd#1=\!!zeropoint
   \setbox#1=\ifhbox#1\normalhbox\else\normalvbox\fi
     {\normalhbox{\box#1\lower\ruleddepth\box\scratchbox}}%
   \ht#1=\ruledheight
   \wd#1=\ruledwidth
   \dp#1=\ruleddepth}

%D Just in case one didn't notice: the rules are in fact layed
%D over the box. This way the contents of a box cannot
%D visually interfere with the rules around (upon) it. A more
%D advanced version of ruled boxes can be found in one of the 
%D core modules of \CONTEXT. There we take offsets, color, 
%D rounded corners, backgrounds and alignment into account too.

%D \macros
%D   {ruledhbox,
%D    ruledvbox,ruledvtop}
%D   {}
%D
%D These macro's can be used instead of \type{\hbox},
%D \type{\vbox} and \type{\vtop}. They just do what their names
%D state. Using an auxiliary macro would save us a few words
%D of memory, but it would make their appearance even more
%D obscure.
%D
%D \startbuffer
%D \hbox
%D   {\strut
%D    one
%D    two
%D    \hbox{three}
%D    four
%D    five}
%D \stopbuffer
%D
%D \ShowBufferedExampleBox

\def\ruledhbox%
  {\normalhbox\bgroup
   \dowithnextbox{\makeruledbox\nextbox\box\nextbox\egroup}%
   \normalhbox}

%D \startbuffer
%D \vbox
%D   {\strut
%D    first line  \par
%D    second line \par
%D    third line  \par
%D    fourth line \par
%D    fifth line
%D    \strut }
%D \stopbuffer
%D
%D \ShowBufferedExampleBox

\def\ruledvbox%
  {\normalvbox\bgroup
   \dowithnextbox{\makeruledbox\nextbox\box\nextbox\egroup}%
   \normalvbox}

%D \startbuffer
%D \vtop
%D   {\strut
%D    first line  \par
%D    second line \par
%D    third line  \par
%D    fourth line \par
%D    fifth line
%D    \strut }
%D \stopbuffer
%D
%D \ShowBufferedExampleBox

\def\ruledvtop%
  {\normalvtop\bgroup
   \dowithnextbox{\makeruledbox\nextbox\box\nextbox\egroup}%
   \normalvtop}

%D \macros
%D   {ruledbox,
%D    setruledbox}
%D   {}
%D
%D Of the next two macros the first can be used to precede a
%D box of ones own choice. One can for instance prefix boxes
%D with \type{\ruledbox} and afterwards --- when the macro
%D satisfy the needs --- let it to \type{\relax}.
%D
%D \starttypen
%D \ruledbox\hbox{What rules do you mean?}
%D \stoptypen
%D
%D The macro \type{\setruledbox} can be used to directly
%D rule a box.
%D
%D \starttypen
%D \setruledbox12=\hbox{Who's talking about rules here?}
%D \stoptypen
%D
%D At the cost of some extra macros we can implement a
%D variant that does not need the~\type{=}, but we stick to:

\def\ruledbox%
  {\dowithnextbox{\makeruledbox\nextbox\box\nextbox}}

\def\setruledbox#1=%
  {\dowithnextbox{\makeruledbox\nextbox\setbox#1=\nextbox}}

%D \macros
%D   {investigateskip,
%D    investigatecount,
%D    investigatemuskip}
%D   {}
%D
%D Before we meet the visualizing macro's, we first implement
%D ourselves some handy utility ones. Just for the sake of
%D efficiency and readability, we introduce some status
%D variables, that tell us a bit more about the registers we
%D use:
%D
%D \starttypen
%D \ifflexible
%D \ifzero
%D \ifnegative
%D \ifpositive
%D \stoptypen
%D
%D These status variables are set when we call for one of the
%D investigation macros, e.g.
%D
%D \starttypen
%D \investigateskip\scratchskip
%D \stoptypen
%D
%D We use some dirty trick to check stretchability of \SKIPS.
%D Users of these macros are invited to study their exact
%D behavior first. The positive and negative states both
%D include zero and are in fact non-negative ($\geq0$) and
%D non-positive ($\leq0$) .

\newif\ifflexible
\newif\ifzero
\newif\ifnegative
\newif\ifpositive

\def\investigateskip#1%
  {\relax
   \scratchdimen=#1\relax
   \edef\!!stringa{\the\scratchdimen}%
   \edef\!!stringb{\the#1}%
   \ifx\!!stringa\!!stringb \flexiblefalse \else \flexibletrue \fi
   \ifdim#1=\!!zeropoint\relax
     \zerotrue      \else
     \zerofalse     \fi
   \ifdim#1<\!!zeropoint\relax
     \positivefalse \else
     \positivetrue  \fi
   \ifdim#1>\!!zeropoint\relax
     \negativefalse \else
     \negativetrue  \fi}

\def\investigatecount#1%
  {\relax
   \flexiblefalse
   \ifnum#1=0
     \zerotrue      \else
     \zerofalse     \fi
   \ifnum#1<0
     \positivefalse \else
     \positivetrue  \fi
   \ifnum#1>0
     \negativefalse \else
     \negativetrue  \fi}

\def\investigatemuskip#1%
  {\relax
   \edef\!!stringa{\the\scratchmuskip}%
   \edef\!!stringb{0mu}%
   \def\!!stringc##1##2\\{##1}%
   \expandafter\edef\expandafter\!!stringc\expandafter
     {\expandafter\!!stringc\!!stringa\\}%
   \edef\!!stringd{-}%
   \flexiblefalse
   \ifx\!!stringa\!!stringb
     \zerotrue
     \negativefalse
     \positivefalse
   \else
     \zerofalse
     \ifx\!!stringc\!!stringd
       \positivefalse
       \negativetrue
     \else
       \positivetrue
       \negativefalse
     \fi
   \fi}

%D \macros
%D   {dontinterfere}
%D   {}
%D
%D Indentation, left and/or right skips, redefinition of
%D \type{\par} and assignments to \type{\everypar} can lead to
%D  unwanted results. We can therefore turn all those things
%D off with \type{\dontinterfere}.

\def\dontinterfere%
  {\everypar  = {}%
   \let\par   = \endgraf
   \parindent = \!!zeropoint
   \parskip   = \!!zeropoint
   \leftskip  = \!!zeropoint
   \rightskip = \!!zeropoint
   \relax}

%D \macros
%D   {dontcomplain}
%D   {}
%D
%D In this module we do a lot of box manipulations. Because we
%D don't want to be confronted with to many over- and underfull
%D messages we introduce \type{\dontcomplain}.

\def\dontcomplain%
  {\hbadness  = \!!tenthousand
   \hfuzz     = \maxdimen
   \vbadness  = \!!tenthousand
   \vfuzz     = \maxdimen}

%D Now the neccessary utility macros are defined, we can make a
%D start with the visualizing ones. The implementation of these
%D macros is a compromise between readability, efficiency of
%D coding and processing speed. Sometimes we do in steps what
%D could have been done in combination, sometimes we use a few
%D boxes more or less then actually needed, and more than once
%D one can find the same piece of rule drawing code twice.

%D \macros
%D   {ifcenteredvcue,normalvcue}
%D   {}
%D
%D Depending on the context, one can force visual vertical cues 
%D being centered along \type{\hsize} or being put at the 
%D current position. Although centering often looks better, 
%D we've chosen the second alternative as default. The main 
%D reason for doing so is that often when we don't set the 
%D \type{\hsize} ourselves, \TEX\ takes the value of the 
%D surrounding box. As a result the visual cues can migrate 
%D outside the current context. 
%D 
%D This behavior is accomplished by a small but effective 
%D auxiliary macro, which behavior can be influenced by the 
%D boolean \type{\centeredvcue}. By saying 
%D
%D \starttypen 
%D \centeredvcuetrue
%D \stoptypen
%D 
%D one turns centering on. As said, we turn it off. 

\newif\ifcenteredvcue  \centeredvcuefalse

\def\normalvcue#1%
  {\normalhbox \ifcenteredvcue to \hsize \fi {\normalhss#1\normalhss}}

%D We could have used the more robust version 
%D 
%D \starttypen
%D \def\normalvcue%
%D   {\normalhbox \ifcenteredvcue to \hsize \fi
%D    \bgroup\bgroup\normalhss
%D    \aftergroup\normalhss\aftergroup\egroup
%D    \let\next=}
%D \stoptypen
%D 
%D or the probably best one: 
%D 
%D \starttypen
%D \def\normalvcue%
%D   {\hbox \ifcenteredvcue to \hsize
%D      \bgroup\bgroup\normalhss
%D      \aftergroup\normalhss\aftergroup\egroup
%D    \else
%D      \bgroup
%D    \fi
%D    \let\next=}
%D \stoptypen
%D 
%D Because we don't have to preserve \CATCODES\ and only use 
%D small arguments, we stick to the first alternative. 

%D \macros
%D   {testrulewidth}
%D   {}
%D
%D We build our visual cues out of rules. At the cost of a much
%D bigger \DVI\ file, this is to be prefered over using
%D characters (1)~because we cannot be sure of their
%D availability and (2)~because their dimensions are fixed.
%D
%D As with ruled boxes, we use a \DIMENSION\ to specify the
%D width of the ruled elements. This dimension defaults to:
%D
%D \starttypen
%D \testrulewidth=\boxrulewidth
%D \stoptypen
%D
%D Because we prefer whole numbers for specifying the
%D dimensions, we often use even multiples of
%D \type{\testrulewidth}.

%D \macros
%D   {visiblestretch}
%D   {}
%D 
%D A second variable is introduced because of the stretch
%D components of \SKIPS. At the cost of some accuracy we can
%D make this stretch visible. 
%D 
%D \starttypen
%D \visiblestretchtrue
%D \stoptypen

\newdimen\testrulewidth  \testrulewidth=\boxrulewidth
\newif\ifvisiblestretch  \visiblestretchfalse

%D \macros
%D   {ruledhss,
%D    ruledhfil,ruledhfilneg,
%D    ruledhfill,ruledhfillneg}
%D   {}
%D
%D We start with the easiest part, the fills. The scheme we
%D follow is {\em visual filling -- going back -- normal
%D filling}. Visualizing is implemented using \type{\cleaders}.
%D Because the \BOX\ that follows this command is constructed
%D only once, the \type{\copy} is not really a prerequisite. We
%D prefer using a \type{\normalhbox} here instead of a
%D \type{\hbox}.

\def\setvisiblehfilbox#1\to#2#3#4%
  {\setbox#1=\normalhbox
     {\vrule
        \!!width#2\testrulewidth
        \!!height#3\testrulewidth
        \!!depth#4\testrulewidth}%
   \smashbox#1}

\def\doruledhfiller#1#2#3#4%
  {#1#2%
   \bgroup
     \dontinterfere
     \dontcomplain
     \setvisiblehfilbox0\to{4}{#3}{#4}%
     \setvisiblehfilbox2\to422%
     \copy0\copy2
     \bgroup
       \setvisiblehfilbox0\to422%
       \cleaders
         \normalhbox to 12\testrulewidth
           {\normalhss\copy0\normalhss}%
         #1%
     \egroup
     \setbox0=\normalhbox
       {\normalhskip-4\testrulewidth\copy0\copy2}%
     \smashbox0
     \box0
   \egroup}

%D The horizontal fillers differ in their boundary
%D visualization. Watch the small dots. Fillers can be 
%D combined within reasonable margins.   
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\type{\hss}\ruledhss test}
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\type{\hfil}\ruledhfil test}
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\type{\hfill}\ruledhfill test}
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut
%D    \type{\hfil}\type{\hfil}\ruledhfil\ruledhfil 
%D    test%
%D    \ruledhfil\type{\hfil}}
%D \stopregelcorrectie
%D
%D The negative counterparts are visualizes, but seldom
%D become visible, apart from their boundaries.
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\type{\hfilneg}\ruledhfilneg test}
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\type{\hfillneg}\ruledhfillneg test}
%D \stopregelcorrectie
%D
%D Although leaders are used for visualizing, they are
%D visualized themselves correctly as the next example shows.
%D
%D \startregelcorrectie
%D \baselinerulefalse
%D \ruledhbox to \hsize
%D   {\strut\cleaders\normalhbox to 2em{\normalhss$\circ$\normalhss}\ruledhfill}
%D \stopregelcorrectie
%D
%D All five substitutions use the same auxiliary macro. Watch
%D the positive first -- negative next approach.

\def\ruledhss%
  {\doruledhfiller\normalhss\normalhfilneg{0}{0}}

\def\ruledhfil%
  {\doruledhfiller\normalhfil\normalhfilneg{10}{-6}}

\def\ruledhfill%
  {\doruledhfiller\normalhfill\normalhfillneg{18}{-14}}

\def\ruledhfilneg%
  {\doruledhfiller\normalhfilneg\normalhfil{-6}{10}}

\def\ruledhfillneg%
  {\doruledhfiller\normalhfillneg\normalhfill{-14}{18}}

%D \macros
%D   {ruledvss,
%D    ruledvfil,ruledvfilneg,
%D    ruledvfill,ruledvfillneg}
%D   {}
%D
%D The vertical mode commands adopt the same visualization
%D scheme, but are implemented in a slightly different way.

\def\setvisiblevfilbox#1\to#2#3#4%
  {\setbox#1=\normalvcue 
     {\vrule
        \!!width#2\testrulewidth
        \!!height#3\testrulewidth
        \!!depth#4\testrulewidth}%
   \smashbox#1}%

\def\doruledvfiller#1#2#3%
  {#1#2%
   \bgroup
     \dontinterfere
     \dontcomplain
     \offinterlineskip
     \setvisiblevfilbox0\to422%
     \setbox2=\normalhbox
       {\normalhskip -#3\testrulewidth\copy0}%
     \smashbox2
     \copy2
     \bgroup
       \setbox2=\normalhbox
         {\normalhskip -2\testrulewidth\copy0}%
       \smashbox2
       \copy2
       \cleaders
         \normalvbox to 12\testrulewidth
           {\normalvss\copy2\normalvss}%
         #1%
       \setbox2=\normalvbox
         {\vskip-2\testrulewidth\copy2}%
       \smashbox2
       \box2
     \egroup
     \setbox2=\normalvbox
       {\vskip-2\testrulewidth\copy2}%
     \smashbox2
     \box2
   \egroup}

%D Because they act the same as their horizontal counterparts
%D we only show a few examples.
%D
%D \startregelcorrectie
%D \hbox to \hsize
%D   {\dontinterfere
%D    \baselinerulefalse
%D    \centeredvcuetrue
%D    \ruledvbox to 10ex
%D      {\hsize.18\hsize
%D       \type{\vss}\ruledvss last line}\normalhss
%D    \ruledvbox to 10ex
%D      {\hsize.18\hsize
%D       \type{\vfil}\ruledvfil last line}\normalhss
%D    \ruledvbox to 10ex
%D      {\hsize.18\hsize
%D       \type{\vfill}\ruledvfill last line}\normalhss
%D    \ruledvbox to 10ex
%D      {\hsize.18\hsize
%D       \type{\vfilneg}\ruledvfilneg last line}\normalhss
%D    \ruledvbox to 10ex
%D      {\hsize.18\hsize
%D       \type{\vfillneg}\ruledvfillneg last line}}
%D \stopregelcorrectie
%D 
%D Keep in mind that \type{\vfillneg} is not part of \PLAIN\
%D \TEX, but are mimmicked by a macro. 

\def\ruledvss%
  {\doruledvfiller\normalvss\normalvfilneg{2}}

\def\ruledvfil%
  {\doruledvfiller\normalvfil\normalvfilneg{-4}}

\def\ruledvfill%
  {\doruledvfiller\normalvfill\normalvfillneg{-12}}

\def\ruledvfilneg%
  {\doruledvfiller\normalvfilneg\normalvfil{8}}

\def\ruledvfillneg%
  {\doruledvfiller\normalvfillneg\normalvfill{16}}

%D \macros
%D   {ruledhskip}
%D   {}
%D
%D Skips differ from kerns in two important aspects:
%D
%D \startopsomming[opelkaar]
%D \som  line and pagebreaks are allowed at a skip
%D \som  skips can have a positive and/or negative
%D       stretchcomponent
%D \stopopsomming
%D
%D Stated a bit different: kerns are fixed skips at which no
%D line or pagebreak can occur. Because skips have a more open
%D character, they are visualized in a open way.
%D
%D \startbuffer
%D one
%D \hskip +30pt plus 5pt
%D two
%D \hskip +30pt
%D \hskip -10pt plus 5pt
%D three
%D \hskip   0pt
%D four
%D \hskip +30pt
%D five
%D \stopbuffer
%D
%D \ShowBufferedExample
%D
%D When skips have a stretch component, this is visualized by
%D means of a dashed line. Positive skips are on top of the
%D baseline, negative ones are below it. This way we can show
%D the combined results. An alternative visualization of
%D stretch could be drawing the mid line over a length of the
%D stretch, in positive or negative direction.

\def\doruledhskip%
  {\relax
   \dontinterfere
   \dontcomplain
   \investigateskip\scratchskip
   \ifzero
     \setbox0=\normalhbox
       {\normalhskip-\testrulewidth
        \vrule
          \!!width4\testrulewidth
          \!!height16\testrulewidth
          \!!depth16\testrulewidth}%
   \else
     \setbox0=\normalhbox to \ifnegative-\fi\scratchskip
       {\vrule
          \!!width2\testrulewidth
          \ifnegative\!!depth\else\!!height\fi16\testrulewidth
        \cleaders
          \hrule
            \ifnegative
              \!!depth2\testrulewidth
              \!!height\!!zeropoint
            \else
              \!!height2\testrulewidth
              \!!depth\!!zeropoint
            \fi
          \normalhfill
        \ifflexible
          \normalhskip\ifnegative\else-\fi\scratchskip 
          \normalhskip2\testrulewidth
          \cleaders
            \normalhbox
              {\normalhskip 2\testrulewidth
               \vrule
                 \!!width2\testrulewidth
                 \!!height\ifnegative-7\else9\fi\testrulewidth
                 \!!depth\ifnegative9\else-7\fi\testrulewidth
               \normalhskip 2\testrulewidth}%
            \normalhfill
        \fi
        \vrule
          \!!width2\testrulewidth
          \ifnegative\!!depth\else\!!height\fi16\testrulewidth}%
     \setbox0=\normalhbox
       {\ifnegative\else\normalhskip-\scratchskip\fi
        \box0}%
   \fi
   \smashbox0%
   \ifvisiblestretch \else
     \flexiblefalse
   \fi
   \ifflexible
     % breaks ok but small displacements can occur
     \skip2=\scratchskip
     \advance\skip2 by -1\scratchskip
     \divide\skip2 by 2
     \advance\scratchskip by -\skip2
     \normalhskip\scratchskip
     \normalpenalty\!!tenthousand
     \box0
     \normalhskip\skip2
   \else
     \normalhskip\scratchskip
     \box0
   \fi
   \egroup}

\def\ruledhskip%
  {\bgroup
   \afterassignment\doruledhskip
   \scratchskip=}

%D The visual skip is located at a feasible point. Normally
%D this does not interfere with the normaltypesetting process.
%D The next examples show (1)~the default behavior, (2)~the
%D (not entirely correct) distributed stretch and (3)~the way
%D the text is typeset without cues.
%D
%D \startbuffer
%D \dorecurse
%D   {15}
%D   {test\hskip1em plus .5em minus .5em
%D    test\hskip2em
%D    test}
%D \stopbuffer
%D
%D \startregelcorrectie
%D \showmakeup
%D \haalbuffer
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \showmakeup
%D \visiblestretchtrue
%D \haalbuffer
%D \stopregelcorrectie
%D
%D \startregelcorrectie
%D \haalbuffer
%D \stopregelcorrectie

%D \macros
%D   {ruledvskip}
%D   {}
%D
%D We are less fortunate when implementing the vertical skips.
%D This is a direct result of interference between the boxes that
%D visualize the skip and skip removal at a pagebreak. Normally
%D skips disappear at the top of a page, but not of course when
%D visualized in a \type{\vbox}. A quite perfect simulation
%D could have been built if we would have had available two
%D more primitives: \type{\hnop} and \type{\vnop}. These new
%D primitives could stand for boxes that are visible but are
%D not taken into account in any way. They are there for us,
%D but not for \TEX.
%D
%D \startbuffer
%D first line
%D \vskip +30pt plus 5pt
%D second line
%D \vskip +30pt
%D \vskip -10pt plus 5pt
%D third line
%D \par
%D fourth line
%D \vskip +30pt
%D fifth line
%D \vskip   0pt
%D sixth line
%D \stopbuffer
%D
%D \ShowBufferedExample
%D
%D We have to postpone \type{\prevdepth}. Although this 
%D precaution probably is not completely waterproof, it works 
%D quite well. 

\def\dodoruledvskip%
  {\nextdepth=\prevdepth
   \dontinterfere
   \dontcomplain
   \offinterlineskip
   \investigateskip\scratchskip
   \ifzero
     \setbox0=\normalvcue
       {\vrule
          \!!width32\testrulewidth
          \!!height2\testrulewidth
          \!!depth2\testrulewidth}%
   \else
     \setbox0=\normalvbox to \ifnegative-\fi\scratchskip
       {\hrule
          \!!width16\testrulewidth
          \!!height2\testrulewidth
        \ifflexible
          \cleaders
            \normalhbox to 16\testrulewidth
              {\normalhss
               \normalvbox
                 {\normalvskip 2\testrulewidth
                  \hrule
                  \!!width2\testrulewidth
                  \!!height2\testrulewidth
                  \normalvskip 2\testrulewidth}%
               \normalhss}%
            \normalvfill
        \else
          \normalvfill
        \fi
        \hrule
          \!!width16\testrulewidth
          \!!height2\testrulewidth}%
     \setbox2=\normalvbox to \ht0
       {\hrule
          \!!width2\testrulewidth
          \!!height\ht0}%
     \ifnegative
       \ht0=\!!zeropoint
       \setbox0=\normalhbox
         {\normalhskip2\testrulewidth % will be improved
          \normalhskip-\wd0\box0}%
     \fi
     \smashbox0%
     \smashbox2%
     \setbox0=\normalvcue
       {\box2\box0}%
     \setbox0=\normalvbox
       {\ifnegative\normalvskip\scratchskip\fi\box0}%
     \smashbox0%
   \fi
   \ifvisiblestretch
     \ifflexible                      
       \skip2=\scratchskip            
       \advance\skip2 by -1\scratchskip
       \divide\skip2 by 2              
       \advance\scratchskip by -\skip2 
       \normalvskip\skip2              
     \fi
   \fi
   \normalpenalty\!!tenthousand
   \box0
   \prevdepth=\nextdepth % not \dp0=\nextdepth
   \normalvskip\scratchskip}

%D We try to avoid interfering at the top of a page. Of course
%D we only do so when we are in the main vertical list.

\def\doruledvskip%
  {\par
   \ifdim\pagegoal=\maxdimen
     \ifinner
       \dodoruledvskip
     \fi
   \else
     \dodoruledvskip
   \fi
   \egroup}

\def\ruledvskip%
  {\bgroup
   \afterassignment\doruledvskip
   \scratchskip=}

%D \macros
%D   {ruledkern}
%D   {}
%D
%D The macros that implement the kerns are a bit more
%D complicated than needed, because they also serve the
%D visualization of glue, our \PLAIN\ defined kerns with
%D stretch or shrink. We've implemented both horizontal and
%D vertical kerns as ruled boxes.
%D
%D \startbuffer
%D one
%D \kern +30pt
%D two
%D \kern +30pt
%D \kern -10pt
%D three
%D \kern   0pt
%D four
%D \kern +30pt
%D five
%D \stopbuffer
%D
%D \ShowBufferedExample
%D
%D Positive and negative kerns are placed on top or below the
%D baseline, so we are able to track their added result. We
%D didn't mention spacings of 0~pt yet. Zero values are 
%D visualized a bit different, because we want to see them 
%D anyhow.

\def\doruledhkern%
  {\dontinterfere
   \dontcomplain
   \baselinerulefalse
   \investigateskip\scratchskip
   \boxrulewidth=2\testrulewidth
   \ifzero
     \setbox0=\ruledhbox to 8\testrulewidth
       {\vrule
          \!!width\!!zeropoint
          \!!height16\testrulewidth
          \!!depth16\testrulewidth}%
     \setbox0=\normalhbox
       {\normalhskip-4\testrulewidth\box0}%
   \else
     \setbox0=\ruledhbox to \ifnegative-\fi\scratchskip
       {\vrule
          \!!width\!!zeropoint
          \ifnegative\!!depth\else\!!height\fi16\testrulewidth
        \ifflexible
          \normalhskip2\testrulewidth
          \cleaders
            \normalhbox
              {\normalhskip 2\testrulewidth
               \vrule
                 \!!width2\testrulewidth
                 \!!height\ifnegative-7\else9\fi\testrulewidth
                 \!!depth\ifnegative9\else-7\fi\testrulewidth
               \normalhskip 2\testrulewidth}%
            \normalhfill
        \else
          \normalhfill
        \fi}%
     \testrulewidth=2\testrulewidth
     \setbox0=\ruledhbox{\box0}%  \make...
   \fi
   \smashbox0%
   \normalpenalty\!!tenthousand
   \normalhbox to \!!zeropoint
     {\ifnegative\normalhskip1\scratchskip\fi
      \box0}%
   \afterwards\scratchskip
   \egroup}

\def\ruledhkern#1%
  {\bgroup
   \let\afterwards=#1\relax
   \afterassignment\doruledhkern
   \scratchskip=}

%D After having seen the horizontal ones, the vertical kerns
%D will not surprise us. In this example we use \type{\par} to
%D switch to vertical mode.
%D
%D \startbuffer
%D first line
%D \par \kern +30pt
%D second line
%D \par \kern +30pt
%D \par \kern -10pt
%D third line
%D \par
%D fourth line
%D \par \kern +30pt
%D fifth line
%D \par \kern   0pt
%D sixth line
%D \stopbuffer
%D
%D \ShowBufferedExample
%D
%D Like before, we have to postpone \type{\prevdepth}. If we 
%D leave out this trick, we got ourselves some wrong spacing. 

\def\dodoruledvkern%
  {\nextdepth=\prevdepth
   \dontinterfere
   \dontcomplain
   \baselinerulefalse
   \offinterlineskip
   \investigateskip\scratchskip
   \boxrulewidth=2\testrulewidth
   \ifzero
     \setbox0=\ruledhbox to 32\testrulewidth
       {\vrule
          \!!width\!!zeropoint
          \!!height4\testrulewidth
          \!!depth4\testrulewidth}%
   \else
     \setbox0=\ruledvbox to \ifnegative-\fi\scratchskip
       {\hsize16\testrulewidth
        \ifflexible
          \cleaders
            \normalhbox to 16\testrulewidth
              {\normalhss
               \normalvbox
                 {\normalvskip 2\testrulewidth
                  \hrule
                    \!!width2\testrulewidth
                    \!!height2\testrulewidth
                  \normalvskip 2\testrulewidth}%
               \normalhss}%
            \normalvfill
        \else
          \vrule
            \!!width\!!zeropoint
            \!!height\ifnegative-\fi\scratchskip
          \normalhfill
        \fi}
   \fi
   \testrulewidth=2\testrulewidth
   \setbox0=\ruledvbox{\box0}%  \make...
   \smashbox0%
   \setbox0=\normalvbox
     {\ifnegative\normalvskip\scratchskip\fi
      \normalvcue 
       {\ifnegative\normalhskip-16\testrulewidth\fi\box0}}%
   \smashbox0%
   \normalpenalty\!!tenthousand
   \box0
   \prevdepth=\nextdepth} % not \dp0=\nextdepth

\def\doruledvkern%
  {\ifdim\pagegoal=\maxdimen
     \ifinner
       \dodoruledvkern
     \fi
   \else
     \dodoruledvkern
   \fi
   \afterwards\scratchskip
   \egroup}

\def\ruledvkern#1%
  {\bgroup
   \let\afterwards=#1\relax
   \afterassignment\doruledvkern
   \scratchskip=}

\def\ruledkern%
  {\ifvmode
     \let\next=\ruledvkern
   \else
     \let\next=\ruledhkern
   \fi
   \next\normalkern}

%D \macros
%D   {ruledhglue,ruledvglue}
%D   {}
%D
%D The non-primitive glue commands are treated as kerns with
%D stretch. This stretch is presented as a dashed line. I
%D have to admit that until now, I've never used these glue
%D commands.
%D
%D \startbuffer
%D one
%D \hglue +30pt plus 5pt
%D two
%D \hglue +30pt
%D \hglue -10pt plus 5pt
%D three
%D \hglue   0pt
%D four
%D \hglue +30pt
%D five
%D \stopbuffer
%D
%D \ShowBufferedExample

\def\doruledhglue%
  {\leavevmode
   \scratchcounter=\spacefactor
   \vrule\!!width\!!zeropoint
   \normalpenalty\!!tenthousand
   \ruledhkern\normalhskip\scratchskip
   \spacefactor=\scratchcounter
   \egroup}

\def\ruledhglue%
  {\bgroup
   \afterassignment\doruledhglue\scratchskip=}

%D \startbuffer
%D first line
%D \vglue +30pt plus 5pt
%D second line
%D \vglue +30pt
%D \vglue -10pt plus 5pt
%D third line
%D \par
%D fourth line
%D \vglue +30pt
%D fifth line
%D \vglue   0pt
%D sixth line
%D \stopbuffer
%D
%D \ShowBufferedExample

\def\doruledvglue%
  {\par
   \nextdepth=\prevdepth 
   \hrule\!!height\!!zeropoint
   \normalpenalty\!!tenthousand
   \ruledvkern\normalvskip\scratchskip
   \prevdepth=\nextdepth
   \egroup}

\def\ruledvglue%
  {\bgroup
   \afterassignment\doruledvglue\scratchskip=}

%D \macros
%D   {ruledmkern,ruledmskip}
%D   {}
%D
%D Mathematical kerns and skips are specified in mu. This
%D font related unit is incompatible with those of \DIMENSIONS\
%D and \SKIPS. Because in math mode spacing is often a very
%D subtle matter, we've used a very simple, not overloaded way
%D to show them.

\def\dodoruledmkern#1%
  {\dontinterfere
   \dontcomplain
   \setbox0=\normalhbox
     {$\normalmkern\ifnegative-\fi\scratchmuskip$}%
   \setbox0=\normalhbox to \wd0
     {\vrule
        \!!height16\testrulewidth
        \!!depth16\testrulewidth
        \!!width\testrulewidth
      \leaders
        \hrule
          \!!height\ifpositive16\else-14\fi\testrulewidth
          \!!depth\ifpositive-14\else16\fi\testrulewidth
        \normalhfill
      \ifflexible
        \normalhskip-\wd0
        \leaders
          \hrule
            \!!height\testrulewidth
            \!!depth\testrulewidth
          \normalhfill
      \fi
      \vrule
        \!!height16\testrulewidth
        \!!depth16\testrulewidth
        \!!width\testrulewidth}%
   \smashbox0%
   \ifnegative
      #1\scratchmuskip
     \box0
   \else
     \box0
      #1\scratchmuskip
   \fi
   \egroup}

%D \startbuffer
%D $a \mkern3mu = \mkern3mu
%D  b \quad
%D  \mkern-2mu + \mkern-2mu
%D  \quad c$
%D \stopbuffer
%D
%D \ShowBufferedExample

\def\doruledmkern%
  {\investigatemuskip\scratchmuskip
   \flexiblefalse
   \dodoruledmkern\normalmkern}

\def\ruledmkern%
  {\bgroup
   \afterassignment\doruledmkern\scratchmuskip=}

%D \startbuffer
%D $a \mskip3mu = \mskip3mu
%D  b \quad
%D  \mskip-2mu + \mskip-2mu
%D  \quad c$
%D \stopbuffer
%D
%D \ShowBufferedExample

\def\doruledmskip%
  {\investigatemuskip\scratchmuskip
   \flexibletrue
   \dodoruledmkern\normalmskip}

\def\ruledmskip%
  {\bgroup
   \afterassignment\doruledmskip\scratchmuskip=}

%D \macros
%D   {penalty}
%D   {}
%D
%D After presenting fills, skip, kerns and glue we've come to
%D see penalties. In the first implementation --- most of the
%D time needed to develop this set of macros went into testing
%D different types of visualization --- penalties were mere
%D small blocks with one black half, depending on the sign.
%D This most recent version also gives an indication of the
%D amount of penalty. Penalties can go from less than $-10000$
%D to over $+10000$, and their behavior is somewhat
%D non-lineair, with some values having special meanings. We
%D therefore decided not to use its value for a lineair
%D indicator.
%D
%D \startbuffer
%D one
%D \penalty +100
%D two
%D \penalty +100
%D \penalty -100
%D three
%D \penalty    0
%D four
%D \penalty +100
%D five
%D \stopbuffer
%D
%D \ShowBufferedExample
%D
%D The small sticks at the side of the penalty indicate it
%D size. The next example shows the positive and negative
%D penalties of 0, 1, 10, 100, 1000 and 10000.
%D
%D \startregelcorrectie
%D \hbox
%D   {test \ruledhpenalty0
%D    test \ruledhpenalty1
%D    test \ruledhpenalty10
%D    test \ruledhpenalty100
%D    test \ruledhpenalty1000
%D    test \ruledhpenalty10000
%D    test}
%D \stopregelcorrectie
%D
%D \blanko
%D
%D \startregelcorrectie
%D \hbox
%D   {test \ruledhpenalty0
%D    test \ruledhpenalty-1
%D    test \ruledhpenalty-10
%D    test \ruledhpenalty-100
%D    test \ruledhpenalty-1000
%D    test \ruledhpenalty-10000
%D    test}
%D \stopregelcorrectie
%D
%D \blanko
%D
%D This way stacked penalties of different severance can be
%D shown in combination.
%D
%D test \ruledhpenalty10 \ruledhpenalty100
%D test
%D test \ruledhpenalty1000 \ruledhpenalty-1000
%D test

\def\setruledpenaltybox#1#2#3#4#5#6%
  {\setbox#1=\normalhbox
     {\ifnum#2=0 \else
        \ifnum#2>0
          \def\sign{+}%
        \else
          \def\sign{-}%
        \fi
        \dimen0=\ifnum\sign#2>9999
                  28\else
                \ifnum\sign#2>999
                  22\else
                \ifnum\sign#2>99
                  16\else
                \ifnum\sign#2>9
                  10\else
                  4
                \fi\fi\fi\fi \testrulewidth
        \ifnum#2<0
          \normalhskip-\dimen0
          \normalhskip-2\testrulewidth
          \vrule
            \!!width2\testrulewidth
            \!!height#3\testrulewidth
            \!!depth#4\testrulewidth
        \fi
        \vrule
          \!!width\dimen0
          \!!height#5\testrulewidth
          \!!depth#6\testrulewidth
        \ifnum#2>0
          \vrule
            \!!width2\testrulewidth
            \!!height#3\testrulewidth
            \!!depth#4\testrulewidth
         \fi
      \fi}%
   \smashbox#1}

\def\doruledhpenalty%
  {\dontinterfere
   \dontcomplain
   \investigatecount\scratchcounter
   \testrulewidth=2\testrulewidth
   \boxrulewidth=\testrulewidth
   \setbox0=\ruledhbox to 8\testrulewidth
     {\ifnegative\else\normalhss\fi
      \vrule
        \!!depth8\testrulewidth
        \!!width\ifzero0\else4\fi\testrulewidth
      \ifpositive\else\normalhss\fi}%
   \setruledpenaltybox{2}{\scratchcounter}{0}{8}{-3.5}{4.5}%
   \normalpenalty\!!tenthousand
   \setbox0=\normalhbox
     {\normalhskip-4\testrulewidth
      \ifnegative
        \box2\box0
      \else
        \box0\box2
      \fi}%
   \smashbox0%
   \box0
   \normalpenalty\scratchcounter
   \egroup}

\def\ruledhpenalty%
  {\bgroup
   \afterassignment\doruledhpenalty
   \scratchcounter=}

%D The size of a vertical penalty is also shown on the
%D horizontal axis. This way there is less interference with
%D the often preceding or following skips and kerns.
%D
%D \startbuffer
%D first line
%D \par \penalty +100
%D second line
%D \par \penalty +100
%D \par \penalty -100
%D third line
%D \par \penalty    0
%D fourth line
%D \par \penalty +100
%D fifth line
%D \stopbuffer
%D
%D \ShowBufferedExample

\def\doruledvpenalty%
  {\ifdim\pagegoal=\maxdimen
   \else
     \nextdepth=\prevdepth  
     \dontinterfere
     \dontcomplain
     \investigatecount\scratchcounter
     \testrulewidth=2\testrulewidth
     \boxrulewidth=\testrulewidth
     \setbox0=\ruledhbox
       {\vrule
          \!!height4\testrulewidth
          \!!depth4\testrulewidth
          \!!width\!!zeropoint
        \vrule
          \!!height\ifnegative.5\else4\fi\testrulewidth
          \!!depth\ifpositive.5\else4\fi\testrulewidth
          \!!width8\testrulewidth}%
     \setruledpenaltybox{2}{\scratchcounter}{4}{4}{.5}{.5}%
     \setbox0=\normalhbox
       {\normalhskip-4\testrulewidth
        \ifnegative
          \box2\box0
        \else
          \box0\box2
        \fi
        \normalhss}%
     \smashbox0%
     \normalpenalty\!!tenthousand
     \nointerlineskip
     \dp0=\nextdepth  % not \prevdepth=\nextdepth 
     \normalvbox
       {\normalvcue{\box0}}%
   \fi
   \normalpenalty\scratchcounter
   \egroup}

\def\ruledvpenalty%
  {\bgroup
   \afterassignment\doruledvpenalty
   \scratchcounter=}

\def\ruledpenalty%
  {\ifvmode
     \let\next=\ruledvpenalty
   \else
     \let\next=\ruledhpenalty
   \fi
   \next}

%D \macros
%D   {showfils,dontshowfils,
%D    showboxes,dontshowboxes,
%D    showskips,dontshowskips,
%D    showpenalties,dontshowpenalties}
%D   {}
%D
%D For those who want to manipulate the visual cues in detail,
%D we have grouped them.

\def\showfils%
  {\let\hss      = \ruledhss
   \let\hfil     = \ruledhfil
   \let\hfill    = \ruledhfill
   \let\hfilneg  = \ruledhfilneg
   \let\hfillneg = \ruledhfillneg
   \let\vss      = \ruledvss
   \let\vfil     = \ruledvfil
   \let\vfill    = \ruledvfill
   \let\vfilneg  = \ruledvfilneg
   \let\vfillneg = \ruledvfillneg}

\def\dontshowfils%
  {\let\hss      = \normalhss
   \let\hfil     = \normalhfil
   \let\hfill    = \normalhfill
   \let\hfilneg  = \normalhfilneg
   \let\hfillneg = \normalhfillneg
   \let\vss      = \normalvss
   \let\vfil     = \normalvfil
   \let\vfill    = \normalvfill
   \let\vfilneg  = \normalvfilneg
   \let\vfillneg = \normalvfillneg}

\def\showboxes%
  {\baselineruletrue
   \let\hbox     = \ruledhbox
   \let\vbox     = \ruledvbox
   \let\vtop     = \ruledvtop}

\def\dontshowboxes%
  {\let\hbox     = \normalhbox
   \let\vbox     = \normalvbox
   \let\vtop     = \normalvtop}

\def\showskips%
  {\let\hskip    = \ruledhskip
   \let\vskip    = \ruledvskip
   \let\kern     = \ruledkern
   \let\mskip    = \ruledmskip
   \let\mkern    = \ruledmkern
   \let\hglue    = \ruledhglue
   \let\vglue    = \ruledvglue}

\def\dontshowskips%
  {\let\hskip    = \normalhskip
   \let\vskip    = \normalvskip
   \let\kern     = \normalkern
   \let\mskip    = \normalmskip
   \let\mkern    = \normalmkern
   \let\hglue    = \normalhglue
   \let\vglue    = \normalvglue}

\def\showpenalties%
  {\let\penalty  = \ruledpenalty}

\def\dontshowpenalties%
  {\let\penalty  = \normalpenalty}

%D \macros
%D   {showingcomposition,
%D    showcomposition,dontshowcomposition,}
%D   {}
%D
%D All these nice options come together in two macros. The
%D first one turns the options on, the second turnes them off.
%D Both macros only do their job when we are actually showing
%D the composition.
%D
%D \starttypen
%D \showingcompositiontrue
%D \showcomposition
%D \stoptypen
%D 
%D Because the output routine can do tricky things, like
%D multiple column typesetting and manipulation of the
%D pagebody, shifting things around and so on, the macro
%D \type{\dontshowcomposition} best can be called when we enter
%D this routine. Too much visual cues just don't make sense. In
%D \CONTEXT\ this has been taken care of. 

\newif\ifshowingcomposition

\def\showcomposition%
  {\ifshowingcomposition
     \showfils
     \showboxes
     \showskips
     \showpenalties
   \fi}

\def\dontshowcomposition%
  {\ifshowingcomposition
     \dontshowfils
     \dontshowboxes
     \dontshowskips
     \dontshowpenalties
   \fi}

%D \macros
%D   {showmakeup,
%D    defaulttestrulewidth}
%D   {}
%D
%D Just to make things even more easy, we have defined:
%D
%D \starttypen
%D \showmakeup
%D \stoptypen
%D
%D For the sake of those who don't (yet) use \CONTEXT\ we 
%D preset \type{\defaulttestrulewidth} to the already set 
%D value. Otherwise we default to a corps related value.
%D
%D \starttypen
%D \def\defaulttestrulewidth{.2pt}
%D \stoptypen
%D
%D Beware, it's a macro not a \DIMENSION.

\ifx\korpsgrootte\undefined
  \edef\defaulttestrulewidth{\the\testrulewidth}
\else
  \def\defaulttestrulewidth{.02\korpsgrootte}  % still dutch
\fi

\def\showmakeup%
  {\testrulewidth=\defaulttestrulewidth
   \showingcompositiontrue
   \showcomposition}

\protect

%D \ifCONTEXT \let\next=\relax \else \let\next=\endinput 
%D The documented source you have been reading was processed
%D using some surrogate makeup. When this file is processed
%D in \CONTEXT, a few more examples show up here, like a local
%D table of contents and a local register. 
%D \fi \next

%D Lets end with some more advanced examples. When visualized,
%D the table of contents of the outer level is typeset as:
%D
%D {\showmakeup\plaatsinhoud[criterium=vorige]}
%D
%D Definitions and enumerations come in many flavors. The 
%D next one for instance is defined as: 
%D
%D \starttypen
%D \definedescription[test][place=left,hang=3,width=6em]
%D \stoptypen
%D
%D When applied to some text, this would look like: 
%D
%D \bgroup
%D \showmakeup
%D \doordefinieren[test][plaats=links,hang=3,breedte=6em]
%D
%D \test{visual\\debugger} I would be very pleased if \TEX\
%D had two more primitives: \type{\vnop} and \type{\hnop}. Both
%D should act and show up as normal boxes, but stay invisible
%D for \TEX\ when it's doing calculations. The \type{\vnop} 
%D for instance should not interact with the internal mechanism 
%D responsible for the disappearing skips, kerns and penalties
%D at a pagebreak. As long as we don't have these two boxtypes, 
%D visual debugging will never be perfect. 
%D
%D \egroup
%D
%D The index to this section looks like:
%D
%D {\showmakeup\plaatsindex[criterium=lokaal]}
%D
%D Although not impressive examples or typesetting, both
%D show us how and where things happen. When somehow the last
%D lines in this two column index don't allign, then this is
%D due to some still unknown interference.