%D \module
%D   [       file=strc-reg,
%D        version=2008.10.20,
%D          title=\CONTEXT\ Structure Macros,
%D       subtitle=Registers,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright=PRAGMA-ADE / Hans Hagen]
%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 Structure Macros / Registers}

\registerctxluafile{strc-reg}{1.001}

\unprotect

% todo: tag:: becomes rendering
% todo: language, character, linked, location

%D Helper:

% \def\doflushatpar{\ifvmode\expandafter\dogotopar\else\expandafter\firstofoneargument\fi}

\def\doflushatpar{\ifvmode\expandafter\flushatnextpar\else\expandafter\firstofoneargument\fi}

% \starttext
% \placeregister[index]
% \chapter{a} \index{93} \index{456} \index{***} \index{*} \index{@}
% test \index{aa} test \startregister[index][x]{bb} test \page test \page test \page test \stopregister[index][x]
% test \index{aa} test \setregisterentry[index][label=x,entries=bb] test \page test \page test \page test \finishregisterentry[index][label=x]
% test \index{aa} test \setregisterentry[index][label=y] test \page test \page test \page test \finishregisterentry[index][label=y,entries=yy]
% \stoptext

%  In plaats van + kan een & worden gebruikt. Ook kan als
%  eerste karakter worden opgegeven wat de scheider is.
%
%  \index                {entry}
%  \index[key]           {entry}
%  \index[pageclass::]   {entry}
%  \index[pageclass::key]{entry}
%  \index                {textclass::entry}
%  \index[key]           {textclass::entry}
%  \index[pageclass::]   {textclass::entry}
%  \index[pageclass::key]{textclass::entry}

%D Parameters:

\let\currentregister\empty

% \def\registerparameter#1{\csname\??id\currentregister#1\endcsname}

\def\detokenizedregisterparameter#1{\detokenize\expandafter\expandafter\expandafter{\csname\??id#1\endcsname}} % always root

\def\registerparameter    #1{\csname\doregisterparameter{\??id\currentregister}{#1}\endcsname}
\def\registerparameterhash#1{\doregisterparameterhash   {\??id\currentregister}#1}

\def\doregisterparameter    #1#2{\ifcsname#1#2\endcsname#1#2\else\expandafter\doregisterparentparameter    \csname#1\s!parent\endcsname{#2}\fi}
\def\doregisterparameterhash#1#2{\ifcsname#1#2\endcsname  #1\else\expandafter\doregisterparentparameterhash\csname#1\s!parent\endcsname{#2}\fi}

\def\doregisterparentparameter    #1#2{\ifx#1\relax\s!empty\else\doregisterparameter    #1{#2}\fi}
\def\doregisterparentparameterhash#1#2{\ifx#1\relax        \else\doregisterparameterhash#1{#2}\fi}

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

%D Setup:

\newtoks\everysetupregister

\unexpanded\def\setupregisters
  {\dotripleempty\dosetupregisters}

\def\dosetupregisters[#1][#2][#3]%
  {\ifthirdargument
     \def\dodosetupregister##1{\getparameters[\??id##1#2][#3]}%
     \processcommalist[#1]\dodosetupregister
   \else\ifsecondargument
     \def\dodosetupregister##1{\edef\currentregister{##1}\getparameters[\??id##1][#2]\the\everysetupregister}%
     \processcommalist[#1]\dodosetupregister
   \else
     \getparameters[\??id][#1]%
   \fi\fi}

\let\setupregister\setupregisters

\setupregisters
  [\c!n=2,
   \c!balance=\v!yes,  % \v!no komt niet zo vaak voor
   \c!align=\v!flushleft,
   \c!tolerance=\v!stretch,
   \c!before=\blank,
  %\c!after=,
  %\c!symbol=,
   \c!compress=\v!no,
   \c!interaction=\v!pagenumber,
   \c!alternative=\v!a,
   \c!distance=1em,
   \c!style=\v!bold,
   \c!pagestyle=\v!slanted,
   \c!indicator=\v!yes,
   \c!criterium=\v!all,
  %\c!command=,
   \c!referencing=\v!on,
   \c!location=\v!middle,
  %\c!maxwidth=,
   \c!number=\v!no,
   \c!unknownreference=\v!empty,
   \c!prefix=\v!both,
  %\c!expansion=,
%\c!xmlsetup=,
   \c!pagenumber=\v!yes,
   \c!pageprefixconnector=\endash,
   \c!pagesegments=2:2,
   \c!file=\jobname,
  %\c!deeptextcommand=, % undefined by default !
   \c!method=, % no default as we have them in the module, maybe some day in lang-*
   \c!numberorder=\v!numbers, % \v!characters
   \s!language=\currentmainlanguage]%

%D Definition:

\unexpanded\def\defineregister
  {\dodoubleargument\dodefineregister}

\def\dodefineregister[#1][#2]% #2?
  {\setupregister[#1][\s!parent=\??id]%
   \ctxlua{structures.registers.define('#1')}%
   \presetheadtext[#1=\Word{#1}]%
   \setuvalue{#1}{\dodoubleempty\doregister[#1]}%
   \setuvalue{\e!see#1}{\dodoubleempty\doseeregister[#1]}%
%  \setuvalue{\e!coupled#1}{\dolinkedregister{#1}}%
   \setvalue{\e!place#1}{\placeregister[#1]}%
   \setvalue{\e!complete#1}{\completeregister[#1]}%
   \setvalue{\e!setup#1\e!endsetup}[##1]{\getparameters[\??id#1][##1]}}

%D Registering:

\newif\ifwritetoregister \writetoregistertrue

% tzt variant met n entries, parameters en userdata (altnum)

\getparameters
  [\??id]
  [\c!label=,
   \c!entries=,
   \c!entries:1=,\c!entries:2=,\c!entries:3=,
   \c!keys:1=,\c!keys:2=,\c!keys:3=,
   \c!alternative=]

\def\doregisterstructurepageregister
  {\iftrialtypesetting
     \expandafter\gobblethreearguments
   \else
     \expandafter\dodoregisterstructurepageregister
   \fi}

\def\dodoregisterstructurepageregister#1#2#3% register data userdata
  {\begingroup
   \edef\currentregister{#1}%
   %getparameters[\??id][\c!entries=,\c!label=,\c!keys=,\c!alternative=,#2]%
   \getparameters[\??id][#2]%
   \edef\currentregisterlabel    {\registerparameter\c!label}%
   \edef\currentregisterexpansion{\registerparameter\c!expansion}%
   \edef\currentregisterownnumber{\registerparameter\c!ownnumber}%
   \xdef\currentregisterkeys     {\registerparameter\c!keys}%
   \xdef\currentregisterentries  {\registerparameter\c!entries}%
   \xdef\currentregisterxmlsetup {\registerparameter\c!xmlsetup}%
   \ifx\currentregisterentries\empty
     \ifx\currentregisterexpansion\s!xml
       \xmlstartraw
         \xdef\currentregisterentriesa{\registerparameter{\c!entries:1}}%
         \xdef\currentregisterentriesb{\registerparameter{\c!entries:2}}%
         \xdef\currentregisterentriesc{\registerparameter{\c!entries:3}}%
       \xmlstopraw
       \globallet\currentregistercoding\s!xml
     \else
       \ifx\currentregisterexpansion\v!yes
         \xdef\currentregisterentriesa{\registerparameter{\c!entries:1}}%
         \xdef\currentregisterentriesb{\registerparameter{\c!entries:2}}%
         \xdef\currentregisterentriesc{\registerparameter{\c!entries:3}}%
       \else
         \xdef\currentregisterentriesa{\detokenizedregisterparameter{\c!entries:1}}%
         \xdef\currentregisterentriesb{\detokenizedregisterparameter{\c!entries:2}}%
         \xdef\currentregisterentriesc{\detokenizedregisterparameter{\c!entries:3}}%
       \fi
       \globallet\currentregistercoding\s!tex
     \fi
   \else
     \ifx\currentregisterexpansion\s!xml
       \xmlstartraw
         \xdef\currentregisterentries{\registerparameter\c!entries}%
       \xmlstopraw
       \globallet\currentregistercoding\s!xml
     \else
       \ifx\currentregisterexpansion\v!yes
         \xdef\currentregisterentries{\registerparameter\c!entries}%
       \else
         \xdef\currentregisterentries{\detokenizedregisterparameter\c!entries}%
       \fi
       \globallet\currentregistercoding\s!tex
     \fi
   \fi
   \ifx\currentregisterkeys\empty
     \ifx\currentregistercoding\s!xml
       \xmlstartraw
         \xdef\currentregisterkeysa{\registerparameter{\c!keys:1}}%
         \xdef\currentregisterkeysb{\registerparameter{\c!keys:2}}%
         \xdef\currentregisterkeysc{\registerparameter{\c!keys:3}}%
       \xmlstopraw
     \else
       \xdef\currentregisterkeysa{\registerparameter{\c!keys:1}}%
       \xdef\currentregisterkeysb{\registerparameter{\c!keys:2}}%
       \xdef\currentregisterkeysc{\registerparameter{\c!keys:3}}%
     \fi
   \fi
   \setnextinternalreference
   % we could consider storing register entries in a list which we
   % could then sort
   \xdef\currentregisternumber{\ctxlua{
    structures.registers.store { % 'own' should not be in metadata
        metadata = {
            kind     = "entry",
            name     = "\currentregister",
            level    = structures.sections.currentlevel(),
            coding   = "\currentregistercoding",
            catcodes = \the\catcodetable,
        \ifx\currentregisterownnumber\v!yes
            own      = "\registerparameter\c!alternative", % can be used instead of pagenumber
        \fi
            xmlroot  = \ifx\currentreferencecoding\s!xml "\xmldocument" \else nil \fi, % only useful when text
        \ifx\currentregisterxmlsetup\empty \else
            xmlsetup = "\currentregisterxmlsetup",
        \fi
        },
        references = {
            internal = \nextinternalreference,
            section  = structures.sections.currentid(), % hm, why then not also lastsection the same way
            label    = "\currentregisterlabel",
        },
%     \ifx\currentregisterentries\empty \else
        entries = {
            % we need a special one for xml, this is just a single one
            \ifx\currentregisterentries\empty
                { \!!bs\currentregisterentriesa\!!es, \!!bs\currentregisterentriesb\!!es, \!!bs\currentregisterentriesc\!!es },
            \else
                \!!bs\currentregisterentries\!!es,
            \fi
            \ifx\currentregisterkeys\empty
                { \!!bs\currentregisterkeysa\!!es, \!!bs\currentregisterkeysb\!!es, \!!bs\currentregisterkeysc\!!es },
            \else
                \!!bs\currentregisterkeys\!!es,
            \fi
        },
%     \fi
        userdata = structures.helpers.touserdata(\!!bs\detokenize{#3}\!!es)
     }
   } }%
   \ctxlua{structures.references.setinternalreference(nil,nil,\nextinternalreference)}%
   \ifx\currentregisterownnumber\v!yes
     \glet\currentregistersynchronize\relax
   \else
     \xdef\currentregistersynchronize{\ctxlatelua{structures.registers.enhance("\currentregister",\currentregisternumber)}}%
   \fi
   \currentregistersynchronize % here?
   % needs thinking ... bla\index{bla}. will break before the . but adding a
   % penalty is also no solution
   \attribute\destinationattribute\lastdestinationattribute \forcecolorhack % no \strut as it will be removed during cleanup
   \endgroup}

\def\doregister[#1][#2]%
  {\def\currentregister{#1}%
   \doifelse{\registerparameter\c!ownnumber}\v!yes\dodoregister\donoregister{#1}{#2}}

\def\donoregister  #1#2#3{\doflushatpar{\doregisterstructurepageregister{#1}{\c!keys={#2},\c!entries={#3}}{}}}
\def\dodoregister#1#2#3#4{\doflushatpar{\doregisterstructurepageregister{#1}{\c!keys={#2},\c!alternative=#3,\c!entries={#4}}{}}}

\unexpanded\def\startregister{\doquadrupleempty\dostartregister}
\unexpanded\def\stopregister {\dodoubleargument\dostopregister}

% a synonym, so that we can nest with overlap without syntax check problems

\let\openregisterrange \startregister
\let\closeregisterrange\stopregister

\def\dostartregister[#1][#2][#3][#4]#5%
  {\iffourthargument
     % #1=register #2=tag #3=own #4=sortkey #5=entry
     \doflushatpar{\doregisterstructurepageregister{#1}{\c!label=#2,\c!alternative=#3,\c!keys={#4},\c!entries={#5}}{}}%
   \else
     % #1=register #2=tag #3=sortkey #5=entry
     \doflushatpar{\doregisterstructurepageregister{#1}{\c!label=#2,\c!keys={#3},\c!entries={#5}}{}}%
   \fi}

\def\dostopregister[#1][#2]%
  {\normalexpanded{\ctxlatelua{structures.registers.extend("#1","#2")}}}

\def\setregisterentry   {\dotripleempty\dosetregisterentry}
\def\finishregisterentry{\dotripleempty\dofinishregisterentry}

% not yet document, not sure if this will stay:

\def\dosetregisterentry   [#1][#2][#3]{\doflushatpar{\doregisterstructurepageregister{#1}{#2}{#3}}}
\def\dofinishregisterentry[#1][#2][#3]{\dofinishregisterstructurepageregister{#1}{#2}{#3}}

\def\dofinishregisterstructurepageregister#1#2#3% register data userdata
  {\begingroup
   \edef\currentregister{#1}%
   \getparameters[\??id][\c!entries=,\c!label=,\c!keys=,\c!alternative=,#2]%
   \edef\currentregisterlabel    {\registerparameter\c!label}%
   \edef\currentregisterexpansion{\registerparameter\c!expansion}%
   \edef\currentregisterownnumber{\registerparameter\c!ownnumber}%
   \xdef\currentregisterkeys     {\registerparameter\c!keys}%
   \ifx\currentregisterexpansion\s!xml
     \xmlstartraw
       \xdef\currentregisterentries{\registerparameter\c!entries}%
     \xmlstopraw
     \globallet\currentregistercoding\s!xml
   \else
     \ifx\currentregisterexpansion\v!yes
       \xdef\currentregisterentries{\registerparameter\c!entries}%
     \else
       \xdef\currentregisterentries{\detokenizedregisterparameter\c!entries}%
     \fi
     \globallet\currentregistercoding\s!tex
   \fi
   % I hate this kind of mess ... but it's a user request.
   \ifx\currentregisterentries\empty
       \normalexpanded{\ctxlua{structures.registers.extend("\currentregister","\currentregisterlabel", {
            metadata = {
            \ifx\currentregisterownnumber\v!yes
                own      = "\registerparameter\c!alternative", % can be used instead of pagenumber
            \fi
            },
            userdata = structures.helpers.touserdata(\!!bs\detokenize{#3}\!!es)
         })%
       }}%
   \else
       \normalexpanded{\ctxlua{structures.registers.extend("\currentregister","\currentregisterlabel", {
            metadata = {
                catcodes = \the\catcodetable,
                coding   = "\currentregistercoding",
            \ifx\currentregisterownnumber\v!yes
                own      = "\registerparameter\c!alternative", % can be used instead of pagenumber
            \fi
            },
            entries = {
                % we need a special one for xml, this is just a single one
                \!!bs\currentregisterentries\!!es, \!!bs\currentregisterkeys\!!es
            },
            userdata = structures.helpers.touserdata(\!!bs\detokenize{#3}\!!es)
         })
       }}%
   \fi
   \endgroup}

% The following variants are meant for (for instance xml). There is some
% overlap with previously defined macros.
%
% \starttext
%     \setstructurepageregister[index][entries=alpha]a
%     \setstructurepageregister[index][entries=gamma]g
%     \setstructurepageregister[index][entries=beta]b
%     \setstructurepageregister[index][entries:1=alpha,keys:1=z]a
%     \setstructurepageregister[index][entries:1=gamma,keys:1=x]g
%     \setstructurepageregister[index][entries:1=beta, keys:1=y]b
%     \index{alpha}a
%     \index{gamma}g
%     \index{beta}b
%     \placeregister[index][n=1]
% \stoptext

\def\setstructurepageregister{\dotripleempty\dosetstructurepageregister}

\def\dosetstructurepageregister[#1][#2][#3]% [register][settings][userdata]
  {\doflushatpar{\doregisterstructurepageregister{#1}{#2}{#3}}}

\unexpanded\def\startstructurepageregister{\doquadrupleempty\dostartstructurepageregister}
\unexpanded\def\stopstructurepageregister {\dodoubleargument\dostopstructurepageregister}

\let\openstructurepageregisterrange \startstructurepageregister
\let\closestructurepageregisterrange\stopstructurepageregister

\def\dostartstructurepageregister[#1][#2][#3][#4]% [register][tag][settings][userdata]
  {\doflushatpar{\doregisterstructurepageregister{#1}{\c!label=#2,#3}{#4}}}

\def\dostopstructurepageregister[#1][#2]%
  {\normalexpanded{\ctxlatelua{structures.registers.extend("#1","#2")}}}

% So far.

\def\doseeregister[#1][#2]#3#4%
  {\doflushatpar{\doprocessseeregister{#1}{#2}{#3}{#4}}}

\def\doprocessseeregister#1#2#3#4% register key entry seeword
  {\begingroup
   \edef\currentregister{#1}%
   \edef\currentregisterexpansion{\registerparameter\c!expansion}%
   \ifx\currentregisterexpansion\s!xml
     \xmlstartraw
       \xdef\currentregisterentries{\detokenize{#3}}% not ok yet
       \xdef\currentregisterseeword{\detokenize{#4}}% not ok yet
     \xmlstopraw
     \globallet\currentregistercoding\s!xml
   \else
     \ifx\currentregisterexpansion\v!yes
       \xdef\currentregisterentries{#3}% not ok yet
       \xdef\currentregisterseeword{#4}% not ok yet
     \else
       \xdef\currentregisterentries{\detokenize{#3}}% not ok yet
       \xdef\currentregisterseeword{\detokenize{#4}}% not ok yet
     \fi
     \globallet\currentregistercoding\s!tex
   \fi
   \setnextinternalreference
   % we could consider storing register entries in list
   \edef\temp{\ctxlua{ structures.registers.store {
        metadata = {
            kind     = "see",
            name     = "\currentregister",
            level    = structures.sections.currentlevel(),
            catcodes = \the\catcodetable,
        },
        references = {
            internal = \nextinternalreference,
            section  = structures.sections.currentid(),
        },
        entries = {
            % we need a special one for xml, this is just a single one
            "\currentregisterentries", "#2"
        },
        seeword = {
            text = "\currentregisterseeword"
        },
     }
   }}%
   \endgroup}

%D Rendering:

% todo: c!language ipv s!language

\let\utilityregisterlength\!!zerocount

\def\determineregistercharacteristics
  {\dodoubleempty\dodetermineregistercharacteristics}

\def\dodetermineregistercharacteristics[#1][#2]%
  {\begingroup
   \edef\currentregister{#1}%
   \setupregister[\currentregister][#2]%
   \normalexpanded{\endgroup\noexpand\xdef\noexpand\utilityregisterlength{\ctxlua{structures.registers.analyze('\currentregister',{
        language    = "\registerparameter\s!language",
        method      = "\registerparameter\c!method",
        numberorder = "\registerparameter\c!numberorder",
        compress    = "\registerparameter\c!compress",
        criterium   = "\registerparameter\c!criterium",
   })}}}% brrr
   \ifcase\utilityregisterlength\relax
     \resetsystemmode\v!register
   \else
     \setsystemmode  \v!register
   \fi}

\newtoks\everyplaceregister

\appendtoks
    \dontcomplain
\to \everyplaceregister

\unexpanded\def\placeregister
  {\dodoubleempty\doplaceregister}

\def\doplaceregister[#1][#2]%
  {\iffirstargument
     \begingroup
%      \forgetall
     \edef\currentregister{#1}%
     \setupregister[\currentregister][#2]%
     \the\everyplaceregister
     \startcolumns
       [\c!n=\registerparameter\c!n,
        \c!balance=\registerparameter\c!balance,
        \c!align=\registerparameter\c!align,
        \c!tolerance=\registerparameter\c!tolerance]%
       \startpacked[\v!blank]%
         \ctxlua{structures.registers.process('\currentregister',{
            language    = "\registerparameter\s!language",
            method      = "\registerparameter\c!method",
            numberorder = "\registerparameter\c!numberorder",
            compress    = "\registerparameter\c!compress",
            criterium   = "\registerparameter\c!criterium",
         },
        {
%             prefix        = "\registerparameter\c!pageprefix",
            separatorset  = "\registerparameter\c!pageprefixseparatorset",
            conversionset = "\registerparameter\c!pageprefixconversionset",
            starter       = \!!bs\registerparameter\c!pageprefixstarter\!!es,
            stopper       = \!!bs\registerparameter\c!pageprefixstopper\!!es,
            set           = "\registerparameter\c!pageprefixset",
            segments      = "\registerparameter\c!pageprefixsegments",
            connector     = \!!bs\registerparameter\c!pageprefixconnector\!!es,
        },
        {
            prefix        = "\registerparameter\c!pageprefix",
            separatorset  = "\registerparameter\c!pageseparatorset",
            conversionset = "\registerparameter\c!pageconversionset",
            starter       = \!!bs\registerparameter\c!pagestarter\!!es,
            stopper       = \!!bs\registerparameter\c!pagestopper\!!es,
            segments      = "\registerparameter\c!pagesegments",
        }
         )}%
       \stoppacked
     \stopcolumns
     \endgroup
   \fi}

\def\dolimitedregisterentry#1{\limitatetext{#1}\currentregistermaxwidth\unknown}%

\appendtoks
    \edef\currentregistermaxwidth{\registerparameter\c!maxwidth}%
    \ifx\currentregistermaxwidth\empty
      \let\limitedregisterentry\firstofoneargument
    \else
      \let\limitedregisterentry\dolimitedregisterentry
    \fi
\to \everyplaceregister

\def\completeregister
  {\dodoubleempty\docompleteregister}

\def\docompleteregister[#1][#2]%
  {\iffirstargument
     \begingroup
     \edef\currentregister{#1}%
     % the expansion is needed because we don't want \v!'s in the tuo file (french)
     \normalexpanded{\systemsuppliedchapter[\currentregister]{\noexpand\headtext{\currentregister}}}%
     \placeregister[\currentregister][#2]%
     \page[\v!yes]%
     \endgroup
   \fi}

% test case for collapsing (experimental, for Steffen Wolfrum)
%
% \starttext
% \placeregister[index][compress=no]  \blank[2*big]
% \placeregister[index][compress=yes] \blank[2*big]
% \placeregister[index][compress=all] \page
% \dorecurse{10}{test 1:!\index{test} test \page}
% \dorecurse{5} {test 2:\recurselevel      \page}
% \dorecurse{10}{test 3:!\index{test} test \page}
% \dorecurse{5} {test 4:\recurselevel      \page}
% \dorecurse{1} {test 5:!\index{test} test \page}
% \dorecurse{5} {test 6:\recurselevel      \page}
% \dorecurse{10}{test 7:!\index{test} test \page}
% \dorecurse{5} {test 8:\recurselevel      \page}
% oeps \index{oeps}
% xxxx \index{xxxx}
% todo \index{todo}
% \stoptext

%D Character rendering (sections):

\def\defaultregistercharacter#1%
  {\doifsomething{#1}
     {\doifnot{#1}\s!unknown
        {\doifelse{\registerparameter\c!indicator}\v!yes
           {\doregistercharacter{#1}}
           {\noregistercharacter{#1}}}}}

% \def\doregistercharacter#1%
%   {\expandcheckedcsname % why no \executeifdefined
%      {\??id:\c!indicator:}%
%      {\registerparameter\c!alternative}%
%      {a}%
%      {#1}}

\def\doregistercharacter#1%
  {\expandcheckedcsname % why no \executeifdefined
     {\??id:\c!indicator:}%
     {\registerparameter\c!alternative}%
     {a}%
     {#1}}

\def\noregistercharacter#1%
  {\registerparameter\c!before
   \goodbreak}

% a = <before> <goodbreak> <character> <par> <after> <nobreak>

\setvalue{\??id:\c!indicator:a}#1%
  {\registerparameter\c!before
   % bugged, why does leftskip gets set: \vskip\lineheight\goodbreak\vskip-\lineheight
   \begingroup
   \dosetregisterattributes\c!style\c!color
   \dontleavehmode
   \strut
   \iflocation
     \pagereference[\currentregister:\v!section:#1]%
   \fi
   \registerparameter\c!command{#1}%
   \endgroup
   \registerparameter\c!after
   \par
   \nobreak}

% b = <goodbreak> <before> <character> <after> <nobreak>

\setvalue{\??id:\c!indicator:b}#1% will be shared with a
  {\registerparameter\c!before
   \begingroup
   \dosetregisterattributes\c!style\c!color
   \dontleavehmode
   \strut
   \iflocation
     \pagereference[\currentregister:\v!section:#1]%
   \fi
   \registerparameter\c!command{#1}%
   \endgroup
   \registerparameter\c!after
   \nobreak}

\setvalue{\??id:\c!indicator:A}#1{\getvalue{\??id:\c!indicator:a}{\WORD{#1}}}
\setvalue{\??id:\c!indicator:B}#1{\getvalue{\??id:\c!indicator:b}{\WORD{#1}}}

%D The following macros are the interface to the rendering. These are
%D generated by \LUA. This might change.

%D Beware, we get funny side effects when a dangling \index precedes an
%D placeindex as then flushing takes place inside the index. Took me hours
%D to notice that.

\unexpanded\def\startregisteroutput
  {\endgraf
   \begingroup
   \dostarttagged\t!register\currentregister
   \forgetparindent
   \forgetparskip}

\unexpanded\def\stopregisteroutput
  {\endgraf
   \dostoptagged
   \endgroup}

\unexpanded\def\startregisterentries#1% depth
  {\endgraf
   \begingroup
   \dostarttagged\t!registerentries\empty
   \dosetregisterattributes\c!textstyle\c!textcolor
   \advance\leftskip\numexpr#1-1\relax\dimexpr\registerparameter\c!distance\relax
   \hangindent\registerparameter\c!distance\hangafter\plusone}

\unexpanded\def\stopregisterentries
  {\endgraf
   \dostoptagged
   \endgroup}

\unexpanded\def\startregistersection#1% title
  {\dostarttagged\t!registersection\empty
   \dostarttagged\t!registertag\empty
   \registercharacter{#1}\endgraf
   \dostoptagged}

\unexpanded\def\stopregistersection
  {\dostoptagged
   \endgraf}

\newconditional\registerpagedone

\unexpanded\def\startregisterpages
  {\begingroup
   \dostarttagged\t!registerpages\empty
   \setfalse\registerpagedone
   \dosetregisterattributes\c!pagestyle\c!pagecolor}

\unexpanded\def\stopregisterpages
  {\dostoptagged
   \endgroup}

\unexpanded\def\startregisterseewords
  {\ifhmode\crlf\fi
   \begingroup
   \setfalse\registerpagedone
   \dostarttagged\t!registerpage\empty
   \dosetregisterattributes\c!pagestyle\c!pagecolor}

\unexpanded\def\stopregisterseewords
  {\dostoptagged
   \endgroup}

\def\registerpageseparator% todo: , configurable
  {\ifconditional\registerpagedone
     \registerpageseparatorsymbol
   \else
     \hskip\registerparameter\c!distance\relax
     \settrue\registerpagedone
   \fi}

\def\registeronepagerangeseparator{|\endash|}

\def\withregisterpagecommand#1#2#3#4%
  {\def\currentregisterpageindex{#2}%
   \iflocation
     \goto{\registerparameter\c!pagecommand{#4}}[internal(#2)]%
   \else
     \registerparameter\c!pagecommand{#4}%
   \fi}

\def\registeronepage#1#2#3#4% #1:processor content
  {\registerpageseparator
   \dostarttagged\t!registerpage\empty
   \withregisterpagecommand{#1}{#2}{#3}{#4}%
   \dostoptagged}

\def\registerpagerange#1#2#3#4#5#6#7% #1:processor  content, content todo: -- configurable
  {\registerpageseparator
   \dostarttagged\t!registerpagerange\empty
   \dostarttagged\t!registerfrompage\empty
   \withregisterpagecommand{#1}{#2}{#3}{#4}%
   \dostoptagged
   \registeronepagerangeseparator
   \dostarttagged\t!registertopage\empty
   \withregisterpagecommand{#1}{#5}{#6}{#7}%
   \dostoptagged
   \dostoptagged}

\def\doapplyregisterentrycommand#1#2% processor text
  {\dostarttagged\t!registerentry\empty
   \ifx\currentregisterseeindex\empty \else
     \dontleavehmode
     \pagereference[seeindex:\currentregisterseeindex]% maybe some day we will support an area
   \fi
   \applyprocessor{#1}{\registerparameter\c!textcommand{\limitedregisterentry{\registerparameter\c!deeptextcommand{#2}}}}%
   \dostoptagged}

\def\defaultregisterentry#1#2#3#4% #1:processor #2:internal #3:seeindex #4:word
  {\def\currentregisterpageindex{#2}%
   \iflocation
     \def\currentregisterseeindex{#3}%
     \doifelse{\registerparameter\c!interaction}\v!text
       {\directgoto{\setlocationcolor\??ia\doapplyregisterentrycommand{#1}{#4}}[internal(#2)]}
       {\doapplyregisterentrycommand{#1}{#4}}%
   \else
     \let\currentregisterseeindex\empty
     \doapplyregisterentrycommand{#1}{#4}%
   \fi}

\unexpanded\def\doapplyregisterseecommand#1#2%
  {\ifx\currentregisterseeindex\empty
   % \dontleavehmode
     \applyprocessor{#1}{#2}%
   \else
     \goto{\applyprocessor{#1}{#2}}[seeindex:\currentregisterseeindex]%
   \fi}

\def\defaultregisterseeword#1#2#3#4#5#6% i n #3:processor #4:internal #5:seeindex #6:word
  {%\registerpageseparator
   \def\currentregisterpageindex{#4}%
   \dostarttagged\t!registersee\empty
   \settrue\registerpagedone
   \iflocation
     \def\currentregisterseeindex{#5}%
   \else
     \let\currentregisterseeindex\empty
   \fi
   \ifnum#1=\plusone
     \labeltexts\v!see{\doapplyregisterseecommand{#3}{#6}}%
   \else\ifnum#1=#2\relax
     \labeltexts\v!and{\doapplyregisterseecommand{#3}{#6}}%
   \else
     ,\space\doapplyregisterseecommand{#3}{#6}%
   \fi\fi
   \dostoptagged}

\let\registerseeword  \defaultregisterseeword
\let\registerentry    \defaultregisterentry
\let\registercharacter\defaultregistercharacter

%D A few specific rendering variants:

% \def\doregisterpagelocation#1#2%
%   {\nextregisterpage
%    \hbox to 1em{\hss\doregisterpagehowto{#1}{#2}\hss}}

% todo: \installregisterpagehandler

% \def\MyRegisterPageCommand#1%
%   {#1\currentregisterpageuserdata{whatever}}
%
% \starttext
%     \setregisterentry[index][entries=aaa][whatever=f.] test \index{bbb} test
%     \placeregister[index][n=1,pagecommand=\MyRegisterPageCommand]
% \stoptext

\def\registerpageuserdata       #1#2{\ctxlua{structures.registers.userdata(#1,"#2")}}
\def\currentregisterpageuserdata    {\registerpageuserdata\currentregisterpageindex} % {#1}

% not yet ok : new internal handler names

\def\registerpagebuttonsymbol{\vrule\!!width1em\!!height1ex\!!depth\zeropoint\relax}

\setvalue{\??id:\c!symbol:\c!n}%
  {\def\registerpageseparatorsymbol{, }}

\setvalue{\??id:\c!symbol:\c!a}%
  {\def\registerpageseparatorsymbol{, }} % now done via conversion

\setvalue{\??id:\c!symbol:\v!none}%
  {\let\registerpageseparatorsymbol\empty
   \let\registeronepage            \gobblefourarguments
   \let\registerpagerange          \gobblesevenarguments}

\setvalue{\??id:\c!symbol:1}%
  {\let\registerpageseparatorsymbol\space
   \def\registeronepage           {\symbol[1]\gobblefourarguments}%
   \def\registerpagerange         {\symbol[1]\gobblesevenarguments}}

\setvalue{\??id:\c!symbol:2}%
  {\let\registerpageseparatorsymbol\space
   \def\registeronepage           {\registerpagebuttonsymbol\gobblefourarguments}%
   \def\registerpagerange         {\registerpagebuttonsymbol\gobblesevenarguments}}

\def\setregisterpagerendering
  {\doifelse{\registerparameter\c!pagenumber}\v!no
     {\let \currentregisterpagesymbol\v!none}
     {\edef\currentregisterpagesymbol{\registerparameter\c!symbol}}%
   \ifx\currentregisterpagesymbol\empty
     \csname\??id:\c!symbol:\c!n\endcsname
   \else\ifcsname\??id:\c!symbol:\currentregisterpagesymbol\endcsname
     \csname\??id:\c!symbol:\currentregisterpagesymbol\endcsname
   \else
     \let\registerpageseparatorsymbol\space
     \def\registeronepage           {\registerparameter\c!symbol\gobblefourarguments}%
     \def\registerpagerange         {\registerparameter\c!symbol\gobblesevenarguments}%
   \fi\fi}

\appendtoks
     \setregisterpagerendering
\to \everyplaceregister

%D The linked register code will be reimplemented (not that hard) when it's needed
%D again and/or when I'm bored.

%D Default index:

\defineregister
  [\v!index]
  [\v!indices]

\protect \endinput