2016-01-12 16:26:00

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+%D \module
+%D   [       file=trac-vis, % was core-vis,
+%D        version=1996.06.01,
+%D          title=\CONTEXT\ Tracking Macros,
+%D       subtitle=Visualization,
+%D         author=Hans Hagen,
+%D           date=\currentdate,
+%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
+%C
+%C This module is part of the \CONTEXT\ macro||package and is
+%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
+%C details.
+
+%D This module adds some more visualization cues to the ones
+%D supplied in the support module.
+%D
+%D %\everypar   dual character, \the\everypar and \everypar=
+%D %\hrule      cannot be grabbed in advance, switches mode
+%D %\vrule      cannot be grabbed in advance, switches mode
+%D %
+%D %\indent     only explicit ones
+%D %\noindent   only explicit ones
+%D %\par        only explicit ones
+%D
+%D %\leftskip   only if explicit one
+%D %\rightskip  only if explicit one
+
+\writestatus{loading}{ConTeXt Tracking Macros / Visualization}
+
+\unprotect
+
+%D \macros
+%D   {indent, noindent, par}
+%D
+%D \TeX\ acts upon paragraphs. In mosts documents paragraphs
+%D are separated by empty lines, which internally are handled as
+%D \type{\par}. Paragraphs can be indented or not, depending on
+%D the setting of \type{\parindent}, the first token of a
+%D paragraph and/or user suppressed or forced indentation.
+%D
+%D Because the actual typesetting is based on both explicit
+%D user and implicit system actions, visualization is only
+%D possible for the user supplied \type{\indent},
+%D \type{\noindent}, and \type{\par}. Other
+%D 'clever' tricks will quite certainly lead to more failures
+%D than successes, so we only support these three explicit
+%D primitives and one macro:
+
+\def\showparagraphcue#1#2#3#4#5%
+  {\bgroup
+   \scratchdimen#1\relax
+   \dontinterfere
+   \dontcomplain
+   \boxrulewidth5\testrulewidth
+   #3#4\relax
+   \setbox\scratchbox\normalhbox to \scratchdimen
+     {#2{\ruledhbox to \scratchdimen
+           {\vrule #5 20\testrulewidth \!!width \zeropoint
+            \normalhss}}}%
+   \smashbox\scratchbox
+   \normalpenalty\!!tenthousand
+   \box\scratchbox
+   \egroup}
+
+\def\ruledhanging
+  {\ifdim\hangindent>\zeropoint
+     \ifnum\hangafter<\zerocount
+       \normalhbox
+         {\boxrulewidth5\testrulewidth
+          \setbox\scratchbox\ruledhbox to \hangindent
+            {\scratchdimen\strutht
+             \advance\scratchdimen \strutdp
+             \vrule
+               \!!width  \zeropoint
+               \!!height \zeropoint
+               \!!depth -\hangafter\scratchdimen}%
+          \normalhskip-\hangindent
+          \smashbox\scratchbox
+          \raise\strutht\box\scratchbox}%
+     \fi
+   \fi}
+
+\def\ruledparagraphcues
+  {\bgroup
+   \dontcomplain
+   \normalhbox to \zeropoint
+     {\ifdim\leftskip>\zeropoint\relax
+        \showparagraphcue\leftskip\llap\relax\relax\!!depth
+        \normalhskip-\leftskip
+      \fi
+      \ruledhanging
+      \normalhskip\hsize
+      \ifdim\rightskip>\zeropoint\relax
+        \normalhskip-\rightskip
+        \showparagraphcue\rightskip\relax\relax\relax\!!depth
+      \fi}%
+   \egroup}
+
+\def\ruledpar
+  {\relax
+   \ifhmode
+     \showparagraphcue{40\testrulewidth}\relax\rightrulefalse\relax\!!height
+   \fi
+   \normalpar}
+
+\def\rulednoindent
+  {\relax
+   \normalnoindent
+   \ruledparagraphcues
+   \showparagraphcue{40\testrulewidth}\llap\leftrulefalse\relax\!!height}
+
+\def\ruledindent
+  {\relax
+   \normalnoindent
+   \ruledparagraphcues
+   \ifdim\parindent>\zeropoint
+     \showparagraphcue\parindent\relax\relax\relax\!!height
+   \else
+     \showparagraphcue{40\testrulewidth}\llap\relax\relax\!!height
+   \fi
+   \normalhskip\parindent}
+
+\def\dontshowimplicits
+  {\let\noindent   \normalnoindent
+   \let\indent     \normalindent
+   \let\par        \normalpar}
+
+\def\showimplicits
+  {\testrulewidth  \defaulttestrulewidth
+   \let\noindent   \rulednoindent
+   \let\indent     \ruledindent
+   \let\par        \ruledpar}
+
+%D The next few||line examples show the four cues. Keep in
+%D mind that we only see them when we explicitly open or close
+%D a paragraph.
+%D
+%D \bgroup
+%D \def\voorbeeld#1%
+%D   {#1Visualizing some \TeX\ primitives and Plain \TeX\
+%D    macros can be very instructive, at least it is to me.
+%D    Here we see {\tt\string#1} and {\tt\string\ruledpar} in
+%D    action, while {\tt\string\parindent} equals
+%D    {\tt\the\parindent}.\ruledpar}
+%D
+%D \showimplicits
+%D
+%D \voorbeeld \indent
+%D \voorbeeld \noindent
+%D
+%D \parindent=60pt
+%D
+%D \voorbeeld \indent
+%D \voorbeeld \noindent
+%D
+%D \startnarrower
+%D \voorbeeld \indent
+%D \voorbeeld \noindent
+%D \stopnarrower
+%D \egroup
+%D
+%D These examples also demonstrate the visualization of
+%D \type {\leftskip} and \type {\rightskip}. The macro
+%D \type {\nofruledbaselines} determines the number of lines
+%D shown.
+
+\newcounter\ruledbaselines
+
+\def\nofruledbaselines{3}
+
+\def\debuggertext#1%
+  {\ifx\ttxx\undefined
+     $\scriptscriptstyle#1$%
+   \else
+     {\ttxx#1}%
+   \fi}
+
+\def\ruledbaseline
+  {\vrule \!!width \zeropoint
+   \bgroup
+   \dontinterfere
+   \doglobal\increment\ruledbaselines
+   \scratchdimen\nofruledbaselines\baselineskip
+   \setbox\scratchbox\normalvbox to 2\scratchdimen
+     {\leaders
+        \normalhbox
+          {\strut
+           \vrule
+             \!!height \testrulewidth
+             \!!depth \testrulewidth
+             \!!width 120\points}
+      \normalvfill}%
+   \smashbox\scratchbox
+   \advance\scratchdimen \strutheightfactor\baselineskip
+   \setbox\scratchbox\normalhbox
+     {\normalhskip -48\points
+      \normalhbox to 24\points
+        {\normalhss\debuggertext\ruledbaselines\normalhskip6\points}%
+      \raise\scratchdimen\box\scratchbox}%
+   \smashbox\scratchbox
+   \box\scratchbox
+   \egroup}
+
+\def\showbaselines
+  {\testrulewidth\defaulttestrulewidth
+   \EveryPar{\ruledbaseline}}
+
+%D \macros
+%D   {showpagebuilder}
+%D
+%D The next tracing option probaly is only of use to me and a
+%D few \CONTEXT\ hackers.
+
+\def\showpagebuilder
+  {\EveryPar{\doshowpagebuilder}}
+
+\def\doshowpagebuilder
+  {\strut\llap
+     {\startcolor[blue]\vl
+      \high{\infofont v:\the\vsize    }\vl
+      \high{\infofont g:\the\pagegoal }\vl
+      \high{\infofont t:\the\pagetotal}\vl
+      \stopcolor}}
+
+%D \macros
+%D   {makecutbox, cuthbox, cutvbox, cutvtop}
+%D
+%D Although mainly used for marking the page, these macros can
+%D also serve local use.
+%D
+%D \startbuffer
+%D \setbox0=\vbox{a real \crlf vertical box} \makecutbox0
+%D \stopbuffer
+%D
+%D \typebuffer
+%D
+%D This marked \type{\vbox} shows up as:
+%D
+%D \startlinecorrection
+%D \getbuffer
+%D \stoplinecorrection
+%D
+%D The alternative macros are used as:
+%D
+%D \startbuffer
+%D \cuthbox{a made cut box}
+%D \stopbuffer
+%D
+%D \typebuffer
+%D
+%D This is typeset as:
+%D
+%D \startlinecorrection
+%D \getbuffer
+%D \stoplinecorrection
+%D
+%D By setting the next macros one can influence the length of
+%D the marks as well as the horizontal and vertical divisions.
+
+\def\cutmarklength           {2\bodyfontsize}
+\chardef\horizontalcutmarks = 2
+\chardef\verticalcutmarks   = 2
+\chardef\cutmarkoffset      = 1
+\let\cutmarksymbol          = \relax
+\let\cutmarktoptext         = \empty
+\let\cutmarkbottomtext      = \empty
+
+\def\horizontalcuts
+  {\normalhbox to \ruledwidth
+     {\dorecurse\horizontalcutmarks
+        {\vrule\!!width\boxrulewidth\!!height\cutmarklength\normalhfill}%
+      \unskip}}
+
+\def\verticalcuts
+  {\scratchdimen\ruledheight
+   \advance\scratchdimen \ruleddepth
+   \normalvbox to \scratchdimen
+     {\hsize\cutmarklength
+      \dorecurse\verticalcutmarks
+        {\vrule\!!height\boxrulewidth\!!width\hsize\normalvfill}%
+      \unskip}}
+
+\def\baselinecuts
+  {\ifdim\ruleddepth>\zeropoint
+     \scratchdimen\ruledheight
+     \advance\scratchdimen \ruleddepth
+     \normalvbox to \scratchdimen
+       {\scratchdimen\cutmarklength
+        \divide\scratchdimen 2
+        \hsize\scratchdimen
+        \normalvskip\zeropoint\!!plus\ruledheight
+        \vrule\!!height\boxrulewidth\!!width\hsize
+        \normalvskip\zeropoint\!!plus\ruleddepth}%
+   \fi}
+
+\def\cutmarksymbols#1%
+  {\normalhbox to \ruledwidth
+     {\setbox\scratchbox\normalhbox to \cutmarklength
+        {\normalhss\infofont\cutmarksymbol\normalhss}%
+      \normalhss
+      \normalvbox to \cutmarklength
+        {\scratchdimen\cutmarklength
+         \divide\scratchdimen \plustwo
+         \normalvss
+         \hbox to \ruledwidth
+           {\llap{\copy\scratchbox\normalhskip\cutmarkoffset\scratchdimen}%
+            \normalhskip\scratchdimen\hss\infofont#1\hss\normalhskip\scratchdimen
+            \rlap{\normalhskip\cutmarkoffset\scratchdimen\copy\scratchbox}}%
+         \normalvss}%
+      \normalhss}}
+
+\def\makecutbox#1% simplier with layers, todo
+  {\edef\ruledheight{\the\ht#1}%
+   \edef\ruleddepth {\the\dp#1}%
+   \edef\ruledwidth {\the\wd#1}%
+   \setbox#1\normalhbox
+     {\dontcomplain
+      \forgetall
+      \boxmaxdepth\maxdimen
+      \offinterlineskip
+      \scratchdimen\cutmarklength
+      \divide\scratchdimen \plustwo
+      \hsize\ruledwidth
+      \setbox\scratchbox\normalvbox
+        {\setbox\scratchbox\normalhbox{\horizontalcuts}%
+         \normalvskip-\cutmarkoffset\scratchdimen
+         \normalvskip-2\scratchdimen
+         \copy\scratchbox
+         \normalvskip\cutmarkoffset\scratchdimen
+         \hbox to \ruledwidth
+           {\setbox\scratchbox\normalhbox{\verticalcuts}%
+            \llap{\copy\scratchbox\normalhskip\cutmarkoffset\scratchdimen}%
+            \bgroup
+            \setbox\scratchbox\normalhbox{\baselinecuts}%
+            \llap{\copy\scratchbox\normalhskip\cutmarkoffset\scratchdimen}%
+            \normalhfill
+            \rlap{\normalhskip\cutmarkoffset\scratchdimen\copy\scratchbox}%
+            \egroup
+            \rlap{\normalhskip\cutmarkoffset\scratchdimen\copy\scratchbox}}%
+         \normalvskip\cutmarkoffset\scratchdimen
+         \copy\scratchbox}%
+      \ht\scratchbox\ruledheight
+      \dp\scratchbox\ruleddepth
+      \wd\scratchbox\zeropoint
+      \resetcolorseparation
+      \localstartcolor[\defaulttextcolor]%
+      \box\scratchbox
+      \ifx\cutmarksymbol\relax \else
+        \setbox\scratchbox\normalvbox
+          {\vskip-\cutmarkoffset\scratchdimen
+           \vskip-\cutmarklength
+           \normalhbox{\cutmarksymbols\cutmarktoptext}%
+           \vskip\cutmarkoffset\scratchdimen
+           \vskip\ruledheight
+           \vskip\ruleddepth
+           \vskip\cutmarkoffset\scratchdimen
+           \normalhbox{\cutmarksymbols\cutmarkbottomtext}}%
+        \ht\scratchbox\ruledheight
+        \dp\scratchbox\ruleddepth
+        \wd\scratchbox\zeropoint
+        \box\scratchbox
+      \fi
+      \localstopcolor
+      \box#1}%
+   \wd#1=\ruledwidth
+   \ht#1=\ruledheight
+   \dp#1=\ruleddepth}
+
+\def\cuthbox
+  {\normalhbox\bgroup
+   \dowithnextbox{\makecutbox\nextbox\flushnextbox\egroup}\normalhbox}
+
+\def\cutvbox
+  {\normalvbox\bgroup
+   \dowithnextbox{\makecutbox\nextbox\flushnextbox\egroup}\normalvbox}
+
+\def\cutvtop
+  {\normalvtop\bgroup
+   \dowithnextbox{\makecutbox\nextbox\flushnextbox\egroup}\normalvtop}
+
+%D \macros
+%D   {colormarkbox,rastermarkbox}
+%D
+%D This macro is used in the pagebody routine. No other use
+%D is advocated here.
+%D
+%D \starttyping
+%D \colormarkbox0
+%D \stoptyping
+
+\def\colormarkoffset{\cutmarkoffset}
+\def\colormarklength{\cutmarklength}
+
+\def\colorrangeA#1#2#3#4%
+  {\vbox
+     {\scratchdimen-\colormarklength
+      \multiply\scratchdimen 4
+      \advance\scratchdimen \ruledheight
+      \advance\scratchdimen \ruleddepth
+      \divide\scratchdimen 21
+      \def\docommand##1%
+        {\vbox
+           {\hsize3em % \scratchdimen
+            \definecolor
+              [\s!dummy]
+              [\c!c=#2##1\else0\fi,
+               \c!m=#3##1\else0\fi,
+               \c!y=#4##1\else0\fi,
+               \c!k=0]%
+            \localstartcolor[\s!dummy]%
+            \hrule
+              \!!width 3em
+              \!!height \scratchdimen
+              \!!depth  \zeropoint
+            \localstopcolor
+            \ifdim\scratchdimen>1ex
+              \vskip-\scratchdimen
+              \vbox to \scratchdimen
+                {\vss
+                 \hbox to 3em
+                   {\hss
+                    \localstartcolor[\s!white]%
+                    \ifdim##1\points=\zeropoint#1\else##1\fi
+                    \localstopcolor
+                    \hss}%
+                 \vss}%
+            \fi}}%
+      \offinterlineskip
+      \processcommalist[1.00,0.95,0.75,0.50,0.25,0.05,0.00]\docommand}}
+
+\def\colorrangeB
+  {\hbox
+     {\scratchdimen-\colormarklength
+      \multiply\scratchdimen \plustwo
+      \advance\scratchdimen \ruledwidth
+      \divide\scratchdimen 11
+      \def\docommand ##1 ##2 ##3##4##5##6%
+        {\definecolor
+           [\s!dummy]
+           [\c!c=##3##2\else0\fi,
+            \c!m=##4##2\else0\fi,
+            \c!y=##5##2\else0\fi,
+            \c!k=##6##2\else0\fi]%
+         \localstartcolor[\s!dummy]%
+         \vrule
+           \!!width  \scratchdimen
+           \!!height \colormarklength
+           \!!depth  \zeropoint
+         \localstopcolor
+         \ifdim\scratchdimen>2em
+           \hskip-\scratchdimen
+           \vbox to \colormarklength
+             {\vss
+              \hbox to \scratchdimen
+                {\hss
+                 \localstartcolor[\s!white]%
+                 \ifdim##2\points=.5\points##2~\fi##1%
+                 \localstopcolor
+                 \hss}
+              \vss}%
+         \fi}%
+      \docommand C .5 \iftrue \iffalse\iffalse\iffalse
+      \docommand M .5 \iffalse\iftrue \iffalse\iffalse
+      \docommand Y .5 \iffalse\iffalse\iftrue \iffalse
+      \docommand K .5 \iffalse\iffalse\iffalse\iftrue
+      \docommand C 1  \iftrue \iffalse\iffalse\iffalse
+      \docommand G 1  \iftrue \iffalse\iftrue \iffalse
+      \docommand Y 1  \iffalse\iffalse\iftrue \iffalse
+      \docommand R 1  \iffalse\iftrue \iftrue \iffalse
+      \docommand M 1  \iffalse\iftrue \iffalse\iffalse
+      \docommand B 1  \iftrue \iftrue \iffalse\iffalse
+      \docommand K 1  \iffalse\iffalse\iffalse\iftrue}}
+
+\def\colorrangeC
+  {\hbox
+     {\resetcolorseparation
+      \scratchdimen-\colormarklength
+      \multiply\scratchdimen 2
+      \advance\scratchdimen \ruledwidth
+      \divide\scratchdimen 14
+      \def\docommand##1%
+        {\definecolor[\s!dummy][\c!s=##1]%
+         \localstartcolor[\s!dummy]%
+         \vrule
+           \!!width  \scratchdimen
+           \!!height \colormarklength
+           \!!depth  \zeropoint
+         \localstopcolor
+         \ifdim\scratchdimen>2em
+           \hskip-\scratchdimen
+           \vbox to \colormarklength
+             {\vss
+              \localstartcolor[\s!white]%
+              \hbox to \scratchdimen{\hss##1\hss}
+              \localstopcolor
+             \vss}%
+         \fi}%
+      \processcommalist[1,.95,.9,.85,.8,.75,.7,.6,.5,.4,.3,.2,.1,0]\docommand}}
+
+\def\docolormarkbox#1#2%
+  {\edef\ruledheight{\the\ht#2}%
+   \edef\ruleddepth {\the\dp#2}%
+   \edef\ruledwidth {\the\wd#2}%
+   \setbox#2\hbox
+     {\scratchdimen\colormarklength
+      \divide\scratchdimen \plustwo
+      \forgetall
+      \ssxx
+      \setbox\scratchbox\vbox
+        {\offinterlineskip
+         \vskip-\colormarkoffset\scratchdimen
+         \vskip-2\scratchdimen\relax % relax needed
+         % beware: no \ifcase, due to nested \iftrue/\iffalse
+         % and lacking \fi's
+         \doifelse{#1}{0}%
+           {\vskip\colormarklength
+            \vskip\colormarkoffset\scratchdimen
+            \vskip\ruledheight}
+           {\hbox to \ruledwidth{\hss\hbox{\colorrangeB}\hss}%
+            \vskip\colormarkoffset\scratchdimen
+            \vbox to \ruledheight
+              {\vss
+               \hbox to \ruledwidth
+                 {\llap{\colorrangeA C\iftrue\iffalse\iffalse\hskip\colormarkoffset\scratchdimen}%
+                  \hfill
+                  \rlap{\hskip\colormarkoffset\scratchdimen\colorrangeA R\iffalse\iftrue\iftrue}}%
+               \vss
+               \hbox to \ruledwidth
+                 {\llap{\colorrangeA M\iffalse\iftrue\iffalse\hskip\colormarkoffset\scratchdimen}%
+                  \hfill
+                  \rlap{\hskip\colormarkoffset\scratchdimen\colorrangeA G\iftrue\iffalse\iftrue}}%
+               \vss
+               \hbox to \ruledwidth
+                 {\llap{\colorrangeA Y\iffalse\iffalse\iftrue\hskip\colormarkoffset\scratchdimen}%
+                  \hfill
+                  \rlap{\hskip\colormarkoffset\scratchdimen\colorrangeA B\iftrue\iftrue\iffalse}}%
+               \vss}}%
+         \vskip\colormarkoffset\scratchdimen
+         \hbox to \ruledwidth
+           {\hss\lower\ruleddepth\hbox{\colorrangeC}\hss}}%
+      \ht\scratchbox\ruledheight
+      \dp\scratchbox\ruleddepth
+      \wd\scratchbox\zeropoint
+      \box\scratchbox
+      \box#2}%
+   \wd#2=\ruledwidth
+   \ht#2=\ruledheight
+   \dp#2=\ruleddepth}
+
+\def\colormarkbox % #1
+  {\ifincolor\@EA\docolormarkbox\else\@EA\gobbletwoarguments\fi1}
+
+\def\rastermarkbox % #1
+  {\ifincolor\@EA\docolormarkbox\else\@EA\gobbletwoarguments\fi0}
+
+%D \macros
+%D   {showwhatsits, dontshowwhatsits}
+%D
+%D \TEX\ has three so called whatsits: \type {\mark}, \type
+%D {\write} and \type {\special}. The first one keeps track of
+%D the current state at page boundaries, the last two are used
+%D to communicate to the outside world. Due to fact that
+%D especially \type {\write} is often used in conjunction with
+%D \type {\edef}, we can only savely support that one in \ETEX.
+%D
+%D \bgroup \showwhatsits \setupcolors[state=start]
+%D
+%D Whatsits show up \color[blue]{in color} and are
+%D characterized bij their first character.\footnote [some note]
+%D {So we may encounter \type {w}, \type {m} and \type{s}.}
+%D They are \writestatus{dummy}{demo}\color[yellow]{stacked}.
+%D
+%D \egroup
+
+\newif\ifimmediatewrite
+
+\ifx\eTeXversion\undefined
+
+  \let\showwhatsits    \relax
+  \let\dontshowwhatsits\relax
+
+\else
+
+  \let\supernormalmark  \normalmark  % mark may already been superseded
+  \let\supernormalmarks \normalmarks % mark may already been superseded
+
+  \def\showwhatsits
+    {\protected\def\normalmark {\visualwhatsit100+m\supernormalmark }%
+     \protected\def\normalmarks{\visualwhatsit100+m\supernormalmarks}%
+     \protected\def\special    {\visualwhatsit0100s\normalspecial   }%
+     \protected\def\write      {\visualwhatsit001-w\normalwrite     }%
+     \let\immediate\immediatewhatsit
+     \appendtoks\dontshowwhatsits\to\everystoptext}
+
+  \def\immediatewhatsit
+    {\bgroup\futurelet\next\doimmediatewhatsit}
+
+  \def\doimmediatewhatsit
+    {\ifx\next\write
+       \egroup\immediatewritetrue
+     \else
+       \egroup\expandafter\normalimmediate
+     \fi}
+
+  \def\dontshowwhatsits
+    {\let\immediate \normalimmediate
+     \let\normalmark\supernormalmark
+     \let\special   \normalspecial
+     \let\write     \normalwrite}
+
+  \def\visualwhatsit#1#2#3#4#5%
+    {\bgroup
+     \pushwhatsit
+     \dontinterfere
+     \dontcomplain
+     \dontshowcomposition
+     \dontshowwhatsits
+     \ttx
+     \ifvmode\donetrue\else\donefalse\fi
+     \setbox\scratchbox\hbox
+       {\ifdone\dostartgraycolormode0\else\dostartrgbcolormode#1#2#3\fi
+        #5\dostopcolormode}%
+     \setbox\scratchbox\hbox
+       {\ifdone\dostartrgbcolormode#1#2#3\else\dostartgraycolormode0\fi
+        \vrule\!!width\wd\scratchbox\dostopcolormode
+        \hskip-\wd\scratchbox\box\scratchbox}%
+     \scratchdimen1ex
+     \setbox\scratchbox\hbox
+       {\ifdone\hskip\else\raise#4\fi\scratchdimen\box\scratchbox}%
+     \smashbox\scratchbox
+     \ifdone\nointerlineskip\fi
+     \box\scratchbox
+     \ifvmode\nointerlineskip\fi
+     \popwhatsit
+     \egroup
+     \ifimmediatewrite
+       \immediatewritefalse
+       \expandafter\normalimmediate
+     \fi}
+
+  \def\pushwhatsit
+    {\ifzeropt\lastskip
+       \ifcase\lastpenalty
+         \ifzeropt\lastkern
+           \ifhmode
+             \let\popwhatsit\relax
+           \else
+             \edef\popwhatsit{\prevdepth\the\prevdepth}%
+           \fi
+         \else
+           \ifhmode
+             \edef\popwhatsit{\kern\the\lastkern}\unkern
+           \else
+             \edef\popwhatsit{\kern\the\lastkern\prevdepth\the\prevdepth}%
+             \kern-\lastkern
+           \fi
+         \fi
+       \else
+         \ifhmode
+           \edef\popwhatsit{\the\lastpenalty}%
+           \unpenalty
+         \else
+           \edef\popwhatsit{\penalty\the\lastpenalty\prevdepth\the\prevdepth}%
+          %\nobreak
+         \fi
+       \fi
+     \else
+       \ifhmode
+         \edef\popwhatsit{\hskip\the\lastskip}\unskip
+       \else
+         \edef\popwhatsit{\vskip\the\lastskip\prevdepth\the\prevdepth}%
+         \vskip-\lastskip
+       \fi
+     \fi}
+
+\fi
+
+%D The next macro can be used to keep track of classes of
+%D boxes (handy for development cq.\ tracing).
+
+\def\dodotagbox#1#2#3% can be reimplemented
+  {\def\next##1##2##3##4%
+     {\vbox to \ht#2{##3\hbox to \wd#2{##1#3##2}##4}}%
+   \processaction
+     [#1]
+     [        l=>\next\relax\hfill\vfill\vfill,
+              r=>\next\hfill\relax\vfill\vfill,
+              t=>\next\hfill\hfill\relax\vfill,
+              b=>\next\hfill\hfill\vfill\relax,
+             lt=>\next\relax\hfill\relax\vfill,
+             lb=>\next\relax\hfill\vfill\relax,
+             rt=>\next\hfill\relax\relax\vfill,
+             rb=>\next\hfill\relax\vfill\relax,
+             tl=>\next\relax\hfill\relax\vfill,
+             bl=>\next\relax\hfill\vfill\relax,
+             tr=>\next\hfill\relax\relax\vfill,
+             br=>\next\hfill\relax\vfill\relax,
+     \s!default=>\next\hfill\hfill\vfill\vfill,
+     \s!unknown=>\next\hfill\hfill\vfill\vfill]}
+
+\def\dotagbox[#1]#2%
+  {\bgroup
+   \dowithnextbox
+     {\setbox\scratchbox\flushnextbox
+      \setbox\nextbox\ifhbox\nextbox\hbox\else\vbox\fi
+        \bgroup
+          \startoverlay
+            {\copy\scratchbox}
+            {\dodotagbox{#1}\scratchbox{\framed
+               [\c!background=\v!screen,\c!backgroundscreen=1]{#2}}}
+          \stopoverlay
+        \egroup
+      \nextboxwd\the\wd\scratchbox
+      \nextboxht\the\ht\scratchbox
+      \nextboxdp\the\dp\scratchbox
+      \flushnextbox
+      \egroup}}
+
+\def\tagbox
+  {\dosingleempty\dotagbox}
+
+%D \macros
+%D   {coloredhbox,coloredvbox,coloredvtop,
+%D    coloredstrut}
+%D
+%D The following visualizations are used in some of the manuals:
+
+\definecolor[boxcolor:ht][r=.5,g=.75,b=.5]
+\definecolor[boxcolor:dp][r=.5,g=.5,b=.75]
+\definecolor[boxcolor:wd][r=.75,g=.5,b=.5]
+\definecolor[strutcolor] [r=.5,g=.25,b=.25]
+
+\def\coloredbox#1%
+  {\dowithnextbox{#1{\hbox
+     {\blackrule[\c!width=\nextboxwd,\c!height=\nextboxht,\c!depth=\zeropoint,\c!color=boxcolor:ht]%
+      \hskip-\nextboxwd
+      \blackrule[\c!width=\nextboxwd,\c!height=\zeropoint,\c!depth=\nextboxdp,\c!color=boxcolor:dp]%
+      \hskip-\nextboxwd
+      \box\nextbox}}}#1}
+
+\def\coloredhbox{\coloredbox\hbox}
+\def\coloredvbox{\coloredbox\vbox}
+\def\coloredvtop{\coloredbox\vtop}
+
+\def\coloredstrut
+  {\color[strutcolor]{\def\strutwidth{2\points}\setstrut\strut}}
+
+\protect \endinput