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%D \module
%D   [       file=spac-fil,
%D        version=2013.01.13,
%D          title=\CONTEXT\ Spacing Macros,
%D       subtitle=Fillers,
%D         author={Hans Hagen and Wolfgang Schuster},
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{ConTeXt Spacing Macros / Fillers}

\unprotect

%D A bit more extensive variant of a prototype posted by Wolfgang to the
%D development list. Instead of dealing with a few leader types it makes
%D sense to support them all as well as simple rule fillers. Eventually we
%D can also use in for the mathfillers. We distinguish between alternatives
%D and with them methods, and a checker is provided for use in applying
%D e.g.\ fillers in lists.

\installcorenamespace{filler}
\installcorenamespace{filleralternative}
\installcorenamespace{fillerleadermethod}

\installcommandhandler \??filler {filler} \??filler

\let\setupfillers\setupfiller

\unexpanded\def\filler
  {\dosingleempty\spac_fillers_indeed}

\unexpanded\def\checkedfiller#1%
  {\ifcsname\namedfillerhash{#1}\s!parent\endcsname
     \spac_fillers_indeed[#1]%
     \expandafter\gobbleoneargument
   \else
     \expandafter\firstofoneargument
   \fi{#1}}

\def\spac_fillers_indeed[#1]%
  {\removeunwantedspaces
   \begingroup
   \edef\currentfiller{#1}%
   \usefillerstyleandcolor\c!style\c!color
   \scratchdimen\fillerparameter\c!leftmargin\relax
   \ifzeropt\scratchdimen\else
     \hskip\scratchdimen
   \fi
   \fillerparameter\c!left\relax
   \expandnamespaceparameter\??filleralternative\fillerparameter\c!alternative\s!unknown\relax
   \fillerparameter\c!right\relax
   \scratchdimen\fillerparameter\c!rightmargin\relax
   \ifzeropt\scratchdimen\else
     \hskip\scratchdimen
   \fi
   \endgroup
   \ignorespaces}

% \definefiller
%   [MyFiller]
%   [offset=.25\emwidth,
%    rightmargindistance=-\rightskip,
%    method=middle]
%
% \startitemize[packed,joinedup][rightmargin=5em]
%     \startitem
%         \input sapolsky \fillupto[MyFiller]{RS}
%     \stopitem
% \stopitemize

\unexpanded\def\fillupto
  {\dosingleempty\spac_fillers_upto}

\def\spac_fillers_upto[#1]#2%
  {\removeunwantedspaces
   \begingroup
   \edef\currentfiller{#1}%
   \scratchdimen\dimexpr\fillerparameter\c!rightmargindistance\relax
   \ifzeropt\scratchdimen\else
     \parfillskip \scratchdimen\s!plus \plusone\s!fil\relax
   \fi
   \spac_fillers_indeed[#1]%
   \doifsomething{#2}{\hbox{#2}}%
   \par
   \endgroup
   \ignorespaces}

\setvalue{\??filleralternative\s!unknown}%
  {}

\setvalue{\??filleralternative\v!symbol}%
  {\expandnamespaceparameter\??fillerleadermethod\fillerparameter\c!method\v!local
     \ifdim\fillerparameter\c!offset>\zeropoint
        \simplealignedspreadbox
          {2\dimexpr\fillerparameter\c!offset\relax}%
          {\fillerparameter\c!align}%
          {\fillerparameter\c!symbol}%
     \else
        \simplealignedbox
          {\fillerparameter\c!width}%
          {\fillerparameter\c!align}%
          {\fillerparameter\c!symbol}%
     \fi
   \hfill}

\setvalue{\??filleralternative\v!stretch}%
  {\hfill}

\setvalue{\??filleralternative\v!space}%
  {\hskip\fillerparameter\c!distance\relax}

\setvalue{\??filleralternative\v!rule}%
  {\expandnamespaceparameter\??fillerleadermethod\fillerparameter\c!method\v!local
     \hrule
       \s!height\fillerparameter\c!height
       \s!depth \fillerparameter\c!depth
   \hfill}

\letvalue{\??fillerleadermethod\s!local }\normalleaders  % overflow ends up inbetween (current box)
\letvalue{\??fillerleadermethod\v!global}\normalgleaders % overflow ends up inbetween (outermost box)
\letvalue{\??fillerleadermethod\v!middle}\normalcleaders % overflow ends up before, after (current box)
\letvalue{\??fillerleadermethod\v!broad }\normalxleaders % overflow ends up before, inbetween, after (current box)

\setupfillers
  [\c!width=\emwidth,
   \c!symbol=.,
   \c!distance=\emwidth,
   \c!offset=\zeropoint,
   \c!align=\v!middle,
   \c!height=.1\exheight,
   \c!depth=\zeropoint,
   \c!leftmargin=\zeropoint,
   \c!rightmargin=\zeropoint,
   \c!rightmargindistance=\zeropoint,
   \c!alternative=\v!symbol,
   \c!method=\s!local]

\definefiller
  [\v!sym]
  [\c!method=\v!global,
   \c!width=.5\emwidth,
   \c!leftmargin=.5\emwidth,
   \c!rightmargin=.5\emwidth]

\definefiller
  [\v!symbol]
  [\c!method=\v!global,
   \c!offset=.125\emwidth,
   \c!leftmargin=.5\emwidth,
   \c!rightmargin=.5\emwidth]

\definefiller
  [\v!rule]
  [\c!alternative=\v!rule,
   \c!leftmargin=.5\emwidth,
   \c!rightmargin=.5\emwidth]

\definefiller
  [\v!width]
  [\c!alternative=\v!stretch]

\definefiller
  [\v!space]
  [\c!alternative=\v!space,
   \c!distance=3\emwidth]

% maybe box -> symbol

\protect \endinput

% \definefiller[test-a][alternative=stretch]
% \definefiller[test-b][alternative=symbol,symbol=!]
% \definefiller[test-c][alternative=rule,height=.1ex,leftmargin=.5em,rightmargin=.25em]

% \starttext
%     text\filler[test-a]text \par
%     text\filler[test-b]text \par
%     text\filler[test-c]text \par
%     text\checkedfiller{<nothing>}text \par
% \stoptext