%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 \& \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 Structure Macros / Registers}

\registerctxluafile{strc-reg}{1.001}

\unprotect

\startcontextdefinitioncode

% todo: tag:: becomes rendering
% todo: language, character, linked, location
% todo: fonts etc at sublevels (already defined)

% \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

%  \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}

% tzt variant with n entries, parameters and userdata (altnum)

\installcorenamespace{register}

\installcommandhandler\??register {register} \??register

\let\strc_registers_setup_saved\setupregister

\unexpanded\def\setupregister % maybe we should drop the plural form
  {\dotripleempty\strc_registers_setup}

\def\strc_registers_setup[#1][#2][#3]%
  {\ifthirdargument
     \def\strc_registers_setup_step##1{\strc_registers_setup_saved[#1:##1][#3]}%
     \processcommalist[#2]\strc_registers_setup_step
   \else\ifsecondargument
     \strc_registers_setup_saved[#1][#2]%
   \else
     \strc_registers_setup_saved[#1]%
   \fi\fi}

\unexpanded\def\setupregisters
  {\dosingleempty\strc_registers_setup_root}

\def\strc_registers_setup_root[#1]%
  {\strc_registers_setup_saved[#1]\relax}

\setupregister
  [\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=\emwidth,
   \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]%

% yes or no shared ?

\setupregister
  [\c!label=,
   \c!entries=,
   \c!alternative=]


\definemixedcolumns
  [\v!register]
  [\c!n=\registerparameter\c!n,
   \c!balance=\registerparameter\c!balance,
   \c!align=\registerparameter\c!align,
   \c!tolerance=\registerparameter\c!tolerance]

%D \starttyping
%D \setupregister[index][1][textcolor=darkred]
%D \setupregister[index][2][textcolor=darkgreen,textstyle=bold]
%D
%D \placeregister[index][n=1] \blank[3*big]
%D
%D test \index{test+one} test \index{test+two} more \index{more}
%D \stoptyping

\newconditional\c_strc_registers_defining
\setnewconstant\c_strc_registers_maxlevel \plusfive

\ifdefined\Word \else \unexpanded\def\Word#1{#1} \fi

\appendtoks
    \ifconditional\c_strc_registers_defining \else % todo: dosingle ...
      \settrue\c_strc_registers_defining
      \definemixedcolumns[\currentregister][\v!register]% first as otherwise it overloads start/stop
      \ctxcommand{defineregister("\currentregister","\registerparameter\c!referencemethod")}%
      \normalexpanded{\presetheadtext[\currentregister=\Word{\currentregister}]}%
      \setuevalue{\currentregister}{\dodoubleempty\strc_registers_insert_entry[\currentregister]}%
      \setuevalue{\e!see\currentregister}{\dodoubleempty\strc_registers_insert_see[\currentregister]}%
      %setuevalue{\e!coupled\currentregister}{\dolinkedregister{\currentregister}}%
      % historic ballast
      \setuevalue{\e!place\currentregister}{\placeregister[\currentregister]}%
      \setuevalue{\e!complete\currentregister}{\completeregister[\currentregister]}%
      \setuevalue{\e!setup\currentregister\e!endsetup}{\setupregister[\currentregister]}%
      \dorecurse\c_strc_registers_maxlevel{% weird, expanded should not be needed
        \normalexpanded{\defineregister[\currentregister:\recurselevel][\currentregister]}%
       %\defineregister[\currentregister:\recurselevel][\currentregister]%
        \letregisterparameter{\c!entries:\recurselevel}\empty % needed as we use detokenize (ok, we can
        \letregisterparameter{\c!keys   :\recurselevel}\empty % avoid it, but it's faster too)
      }%
      %
      \setfalse\c_strc_registers_defining
    \fi
\to \everydefineregister

\appendtoks
    \ctxcommand{setregistermethod("\currentregister","\registerparameter\c!referencemethod")}%
\to \everysetupregister

%D Registering:

\def\strc_registers_register_page_entry
  {\iftrialtypesetting
     \expandafter\gobblethreearguments
   \else
     \expandafter\strc_registers_register_page_entry_indeed
   \fi}

\def\strc_registers_register_page_expand_xml_entries
  {\xmlstartraw
     \xdef\currentregisterentriesa{\registerparameter{\c!entries:1}}%
     \xdef\currentregisterentriesb{\registerparameter{\c!entries:2}}%
     \xdef\currentregisterentriesc{\registerparameter{\c!entries:3}}%
   \xmlstopraw
   \globallet\currentregistercoding\s!xml}

\def\strc_registers_register_page_expand_yes_entries
  {\xdef\currentregisterentriesa{\registerparameter{\c!entries:1}}%
   \xdef\currentregisterentriesb{\registerparameter{\c!entries:2}}%
   \xdef\currentregisterentriesc{\registerparameter{\c!entries:3}}%
   \globallet\currentregistercoding\s!tex}

\def\strc_registers_register_page_expand_nop_entries
  {\xdef\currentregisterentriesa{\detokenizedregisterparameter{\c!entries:1}}%
   \xdef\currentregisterentriesb{\detokenizedregisterparameter{\c!entries:2}}%
   \xdef\currentregisterentriesc{\detokenizedregisterparameter{\c!entries:3}}%
   \globallet\currentregistercoding\s!tex}

\def\strc_registers_register_page_expand_xml
  {\xmlstartraw
     \xdef\currentregisterentries{\registerparameter\c!entries}%
   \xmlstopraw
   \globallet\currentregistercoding\s!xml}

\def\strc_registers_register_page_expand_yes
  {\xdef\currentregisterentries{\registerparameter\c!entries}%
   \globallet\currentregistercoding\s!tex}

\def\strc_registers_register_page_expand_nop
  {\xdef\currentregisterentries{\detokenizedregisterparameter\c!entries}%
   \globallet\currentregistercoding\s!tex}

\def\strc_registers_register_page_expand_xml_keys
  {\xmlstartraw
     \xdef\currentregisterkeysa{\registerparameter{\c!keys:1}}%
     \xdef\currentregisterkeysb{\registerparameter{\c!keys:2}}%
     \xdef\currentregisterkeysc{\registerparameter{\c!keys:3}}%
   \xmlstopraw}

\def\strc_registers_register_page_expand_yes_keys
  {\xdef\currentregisterkeysa{\registerparameter{\c!keys:1}}%
   \xdef\currentregisterkeysb{\registerparameter{\c!keys:2}}%
   \xdef\currentregisterkeysc{\registerparameter{\c!keys:3}}}

\def\strc_registers_register_page_entry_indeed#1#2#3% register data userdata
  {\begingroup
   \edef\currentregister{#1}%
   %\setupcurrentregister[\c!entries=,\c!label=,\c!keys=,\c!alternative=,#2]%
   \setupcurrentregister[#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
       \strc_registers_register_page_expand_xml_entries
     \else\ifx\currentregisterexpansion\v!yes
       \strc_registers_register_page_expand_yes_entries
     \else
       \strc_registers_register_page_expand_nop_entries
     \fi\fi
   \else
     \ifx\currentregisterexpansion\s!xml
       \strc_registers_register_page_expand_xml
     \else\ifx\currentregisterexpansion\v!yes
       \strc_registers_register_page_expand_yes
     \else
       \strc_registers_register_page_expand_nop
     \fi\fi
   \fi
   \ifx\currentregisterkeys\empty
     \ifx\currentregistercoding\s!xml
       \strc_registers_register_page_expand_xml_keys
     \else
       \strc_registers_register_page_expand_yes_keys
     \fi
   \fi
   \setnextinternalreference
   % we could consider storing register entries in a list which we
   % could then sort
   \xdef\currentregisternumber{\ctxcommand{storeregister{ % '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
        \ifx\currentreferencecoding\s!xml
            xmlroot  =  "\xmldocument", % only useful when text
        \fi
        \ifx\currentregisterxmlsetup\empty \else
            xmlsetup = "\currentregisterxmlsetup",
        \fi
        },
        references = {
          % internal = \nextinternalreference,
          % section  = structures.sections.currentid(), % hm, why then not also lastsection the same way
        \ifx\currentregisterlabel\empty \else
            label    = "\currentregisterlabel",
        \fi
        },
    % \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)
     }
   }}%
 % \ctxcommand{setinternalreference(nil,nil,\nextinternalreference)}% in previous
   \ifx\currentregisterownnumber\v!yes
     \glet\currentregistersynchronize\relax
   \else
     \xdef\currentregistersynchronize{\ctxlatecommand{enhanceregister("\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 \signalcharacter % no \strut as it will be removed during cleanup
   \endgroup}

\unexpanded\def\strc_registers_insert_entry[#1][#2]%
  {\def\currentregister{#1}%
   \doifelse{\registerparameter\c!ownnumber}\v!yes
     \strc_registers_insert_entry_yes
     \strc_registers_insert_entry_nop
     {#2}}

\def\strc_registers_insert_entry_nop#1#2%
  {\doflushatpar{\strc_registers_register_page_entry\currentregister{\c!keys={#1},\c!entries={#2}}{}}}

\def\strc_registers_insert_entry_yes#1#2#3%
  {\doflushatpar{\strc_registers_register_page_entry\currentregister{\c!keys={#1},\c!alternative=#2,\c!entries={#3}}{}}}

\unexpanded\def\startregister{\doquadrupleempty\strc_registers_start_entry}
\unexpanded\def\stopregister {\dodoubleargument\strc_registers_stop_entry}

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

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

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

\def\strc_registers_stop_entry[#1][#2]%
  {\normalexpanded{\ctxlatecommand{extendregister("#1","#2")}}}

\def\setregisterentry   {\dotripleempty\strc_registers_set_entry}
\def\finishregisterentry{\dotripleempty\strc_registers_finish_entry}

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

\def\strc_registers_set_entry   [#1][#2][#3]{\doflushatpar{\strc_registers_register_page_entry{#1}{#2}{#3}}}
\def\strc_registers_finish_entry[#1][#2][#3]{\strc_registers_finish_entry_indeed{#1}{#2}{#3}}

\def\strc_registers_finish_entry_indeed#1#2#3% register data userdata
  {\begingroup
   \edef\currentregister{#1}%
   \setupcurrentregister[\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{\ctxcommand{extendregister("\currentregister","\currentregisterlabel", {
            metadata = {
            \ifx\currentregisterownnumber\v!yes
                own = "\registerparameter\c!alternative", % can be used instead of pagenumber
            \fi
            },
            userdata = \!!bs\detokenize{#3}\!!es
         })%
       }}%
   \else
       \normalexpanded{\ctxcommand{extendregister("\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 = \!!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

% some overlap with previous

\unexpanded\def\setstructurepageregister
  {\dotripleempty\strc_registers_set}

\def\strc_registers_set[#1][#2][#3]% [register][settings][userdata]
  {\doflushatpar{\strc_registers_register_page_entry{#1}{#2}{#3}}}

\unexpanded\def\startstructurepageregister{\doquadrupleempty\strc_registers_start}
\unexpanded\def\stopstructurepageregister {\dodoubleargument\strc_registers_stop}

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

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

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

% So far.

\unexpanded\def\strc_registers_insert_see[#1][#2]#3#4%
  {\doflushatpar{\strc_registers_insert_see_indeed{#1}{#2}{#3}{#4}}}

\def\strc_registers_insert_see_indeed#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{\ctxcommand{storeregister{
        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
            \!!bs\currentregisterentries\!!es,
            \!!bs#2\!!es
        },
        seeword = {
            text = \!!bs\currentregisterseeword\!!es
        },
     }
   }}%
   \endgroup}

%D Rendering:

% todo: c!language ipv s!language

\let\utilityregisterlength\!!zerocount

\def\determineregistercharacteristics
  {\dodoubleempty\strc_registers_determine_characteristics}

\def\strc_registers_determine_characteristics[#1][#2]%
  {\begingroup
   \edef\currentregister{#1}%
   \setupregister[\currentregister][#2]%
   \normalexpanded{\endgroup\noexpand\xdef\noexpand\utilityregisterlength{\ctxcommand{analyzeregister('\currentregister',{
        language    = "\registerparameter\s!language",
        method      = "\registerparameter\c!method",
        numberorder = "\registerparameter\c!numberorder",
        compress    = "\registerparameter\c!compress",
        criterium   = "\registerparameter\c!criterium",
        pagenumber  = \ifx\registerpageseparatorsymbol\empty false\else true\fi,
   })}}}% brrr
   \ifcase\utilityregisterlength\relax
     \resetsystemmode\v!register
   \else
     \setsystemmode  \v!register
   \fi}

\newtoks\everyplaceregister

\appendtoks
    \dontcomplain
\to \everyplaceregister

\unexpanded\def\placeregister
  {\dodoubleempty\strc_registers_place}

% \def\strc_registers_place[#1][#2]%
%   {\iffirstargument
%      \begingroup
%     %\forgetall
%      \edef\currentregister{#1}%
%      \setupregister[\currentregister][#2]%
%      \the\everyplaceregister
%      \ifnum\registerparameter\c!n>\plusone
%        \startcolumns
%          [\c!n=\registerparameter\c!n,
%           \c!balance=\registerparameter\c!balance,
%           \c!align=\registerparameter\c!align,
%           \c!tolerance=\registerparameter\c!tolerance]%
%        \strc_registers_place_indeed
%        \stopcolumns
%      \else
%        \strc_registers_place_indeed
%      \fi
%      \endgroup
%    \fi}

\def\strc_registers_place[#1][#2]%
  {\iffirstargument
     \begingroup
    %\forgetall
     \edef\currentregister{#1}%
     \setupregister[\currentregister][#2]%
     \the\everyplaceregister
     \ifnum\namedmixedcolumnsparameter\currentregister\c!n>\plusone
       \startmixedcolumns[\currentregister]
         \strc_registers_place_indeed
       \stopmixedcolumns
     \else
       \strc_registers_place_indeed
     \fi
     \endgroup
   \fi}

% \def\strc_registers_place_columns
%   {\startmixedcolumns[\currentregister]
%      \startpacked[\v!blank]%
%        \strc_registers_place_indeed
%      \stoppacked
%    \stopmixedcolumns}
%
% \def\strc_registers_place_normal
%   {\startpacked[\v!blank]%
%      \strc_registers_place_indeed
%    \stoppacked}

\def\strc_registers_place_indeed
  {\ctxcommand{processregister('\currentregister',{
        language    = "\registerparameter\s!language",
        method      = "\registerparameter\c!method",
        numberorder = "\registerparameter\c!numberorder",
        compress    = "\registerparameter\c!compress",
        criterium   = "\registerparameter\c!criterium",
        pagenumber  = \ifx\registerpageseparatorsymbol\empty false\else true\fi,
   },{
        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",
   })}}

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

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

\unexpanded\def\completeregister
  {\dodoubleempty\strc_registers_complete}

\def\strc_registers_complete[#1][#2]%
  {\iffirstargument
     \begingroup
     \edef\currentregister{#1}%
     \normalexpanded{\startnamedsection[\v!chapter][\c!title={\headtext{\currentregister}},reference=\currentregister]}%
     \placeregister[\currentregister][#2]%
     \page[\v!yes]%
     \stopnamedsection
     \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):

\installcorenamespace{registerindicator}

\def\defaultregistercharacter#1%
  {\edef\currentregistercharacter{#1}%
   \ifx\currentregistercharacter\empty
     % skip
   \else\ifx\currentregistercharacter\s!unknown
     % skip
   \else
     \edef\p_indicator{\registerparameter\c!indicator}%
     \ifx\p_indicator\v!yes
       \strc_registers_place_character_yes
     \else
       \strc_registers_place_character_nop
     \fi
   \fi\fi}

\def\strc_registers_place_character_yes
  {\expandnamespaceparameter\??registerindicator\registerparameter\c!alternative\v!a{\currentregistercharacter}}

\def\strc_registers_place_character_nop
  {\registerparameter\c!before
   \goodbreak}

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

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

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

\setvalue{\??registerindicator b}#1% will be shared with a
  {\registerparameter\c!before
   \begingroup
   \useregisterstyleandcolor\c!style\c!color
   \dontleavehmode
   \strut
   \iflocation
     \dosetdirectpagereference{\currentregister:\v!section:#1}%
   \fi
   \registerparameter\c!command{#1}%
   \endgroup
   \registerparameter\c!after
   \nobreak}

\setvalue{\??registerindicator A}#1{\getvalue{\??registerindicator a}{\WORD{#1}}}
\setvalue{\??registerindicator B}#1{\getvalue{\??registerindicator 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.

\newconditional\c_strc_registers_page_done
\newdimen      \d_strc_registers_distance

\unexpanded\def\startregisteroutput
  {\endgraf
   \begingroup
   \d_strc_registers_distance\registerparameter\c!distance\relax
   \dostarttagged\t!register\currentregister
   \forgeteverypar
   \forgetparindent
   \forgetparskip}

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

% \unexpanded\def\startregisterentries#1% depth
%   {\endgraf
%    \begingroup
%    \dostarttagged\t!registerentries\empty
%    \let\savedcurrentregister\currentregister
%    \edef\currentregister{\currentregister:#1}%
%    \useregisterstyleandcolor\c!textstyle\c!textcolor
%    \advance\leftskip\numexpr#1-\plusone\relax\dimexpr\d_strc_registers_distance\relax
%    \hangindent\registerparameter\c!distance\relax
%    \hangafter\plusone
%    \let\currentregister\savedcurrentregister}

\newdimen\d_strc_registers_hangindent
\newcount\c_strc_registers_hangafter

\unexpanded\def\startregisterentries#1% depth
  {\endgraf
   \begingroup
   \scratchcounter\ifnum#1>\c_strc_registers_maxlevel\c_strc_registers_maxlevel\else#1\fi\relax
   \dostarttagged\t!registerentries\empty
   \let\savedcurrentregister\currentregister
   \edef\currentregister{\currentregister:\number\scratchcounter}%
   \useregisterstyleandcolor\c!textstyle\c!textcolor
   \ifnum\scratchcounter>\plusone
     \advance\leftskip\d_strc_registers_distance\relax
   \fi
   \d_strc_registers_hangindent\registerparameter\c!distance\relax
   \c_strc_registers_hangafter \plusone
\blank[\v!samepage]%
   \let\currentregister\savedcurrentregister}

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

\unexpanded\def\startregisterentry#1% todo: level
  {\begingroup
   \hangindent\d_strc_registers_hangindent
   \hangafter \c_strc_registers_hangafter}

\unexpanded\def\stopregisterentry
  {\endgraf
   \endgroup}

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

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

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

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

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

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

\unexpanded\def\registerpageseparator% todo: , configurable
  {\ifconditional\c_strc_registers_page_done
     \registerpageseparatorsymbol
   \else
     \hskip\d_strc_registers_distance\relax
     \settrue\c_strc_registers_page_done
   \fi}

\unexpanded\def\registeronepagerangeseparator
  {|\endash|} % todo use \prewordbreak

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

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

\unexpanded\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}

\let\strc_register_injector_process\relax
\let\strc_register_injector_show   \relax

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

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

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

\unexpanded\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\c_strc_registers_page_done
   \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{\ctxcommand{registeruserdata(#1,"#2")}}
\def\currentregisterpageuserdata    {\registerpageuserdata\currentregisterpageindex} % {#1}

% not yet ok : new internal handler names

\unexpanded\def\registerpagebuttonsymbol
  {\vrule\s!width\emwidth\s!height\exheight\s!depth\zeropoint\relax}

\installcorenamespace{registersymbol}

\setvalue{\??registersymbol n}%
  {\def\registerpageseparatorsymbol{,\space}}

\setvalue{\??registersymbol a}%
  {\def\registerpageseparatorsymbol{,\space}} % now done via conversion

\setvalue{\??registersymbol\v!none}%
  {\let\registerpageseparatorsymbol\empty
   \let\registeronepage            \gobblefourarguments
   \let\registerpagerange          \gobblesevenarguments}

\setvalue{\??registersymbol 1}%
  {\let\registerpageseparatorsymbol\space
   \def\registeronepage  {\symbol[1]\gobblefourarguments}%
   \def\registerpagerange{\symbol[1]\gobblesevenarguments}}

\setvalue{\??registersymbol 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\??registersymbol n\endcsname
   \else\ifcsname\??registersymbol\currentregisterpagesymbol\endcsname
     \csname\??registersymbol\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]

\stopcontextdefinitioncode

\protect \endinput