%D \module
%D   [       file=page-cst,
%D        version=2016.12.15,
%D          title=\CONTEXT\ Page Macros,
%D       subtitle=Page Grids (aka Column Sets),
%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.

% todo : markings per column

%D This module is work in progress and in due time it will replace
%D columnsets.

\writestatus{loading}{ConTeXt Page Macros / Page Grids}

\registerctxluafile{page-cst}{}

\unprotect

% maybe some protected def ([esc])

%D Columnsets are kind of special. They are mostly meant for special products with
%D magazine like properties. They are normally not mixed with single column layouts
%D and not all features of \CONTEXT\ might cooperate well with a mechanism like
%D this. We use the name page grid because (as with other reimplementations of
%D \MKII\ features in \MKIV, we need another namespace in order to migrate stepwise.
%D
%D This implementation is not neccessarily better than the previous one but it might
%D be easier to extend it. It should be a bit more efficient.
%D
%D When writing this code I occasionally needed a motivational musical time||out and
%D watching the latest Snarky Puppy DVD brought me the musically and visually videos
%D of Jacob Collier (Piano, voice, anything) on YouTube (and yes, music keeps amazing
%D me). It's definitely more fun to watch that than to write code like this.

\definesystemconstant{pagegrid}

\installcorenamespace{pagegrid}

\installframedcommandhandler \??pagegrid {pagegrid} \??pagegrid

\setuppagegrid
  [\c!distance=1.5\bodyfontsize,
   \c!n=\plustwo,
   \c!nleft=\pagegridparameter\c!n,
   \c!nright=\pagegridparameter\c!n,
  %\c!align=, % inherit
  %\c!separator=\v!none,
  %\c!setups=,
   \c!lines=\layoutparameter\c!lines,
   \c!frame=\v!off,
   \c!strut=\v!no,
   \c!offset=\v!overlay,
   \c!alternative=\v!local,
   \c!width=\v!auto,
   \c!page=,
   \c!direction=\v!normal, % todo
   \c!maxheight=\textheight,
   \c!maxwidth=\makeupwidth]

\appendtoks % could become an option
    \protected\frozen\instance\edefcsname\e!start\currentpagegrid\endcsname{\startpagegrid[\currentpagegrid]}%
    \protected\frozen\instance\edefcsname\e!stop \currentpagegrid\endcsname{\stoppagegrid}%
    \clf_definecolumnset {
        name {\currentpagegrid}%
    }%
\to \everydefinepagegrid

\newdimension\d_page_grd_column_width
\newdimension\d_page_grd_max_height
\newdimension\d_page_grd_max_width
\newdimension\d_page_grd_distance

\newdimension\d_page_grd_reserved_height
\newdimension\d_page_grd_reserved_width
\newinteger  \c_page_grd_reserved_state

\newdimension\d_page_grd_gap_height

\newinteger  \c_page_grd_n_of_left
\newinteger  \c_page_grd_n_of_right
\newinteger  \c_page_grd_n_of_rows
\newinteger  \c_page_grd_first_column
\newinteger  \c_page_grd_last_column

\newbox      \b_page_grd_collected
\newbox      \b_page_grd_column_rest
\newbox      \b_page_grd_column

%D All the parameters are mandate!

\permanent\tolerant\protected\def\setuppagegridlines[#1]#*[#2]#*[#3]#*[#4]% id page col value
  {\clf_setcolumnsetlines{name {#1} page {#2} column {#3} value {#4}}}

\permanent\tolerant\protected\def\setuppagegridstart[#1]#*[#2]#*[#3]#*[#4]% id page col value
  {\clf_setcolumnsetstart{name {#1} page {#2} column {#3} value {#4}}}

\protected\def\page_grd_check
  {\dorecurse{(\pagegridparameter\c!nleft)+(\pagegridparameter\c!nright)}
     {\page_grd_check_column{##1}}}

\protected\def\page_grd_check_column#1%
  {\chaintocurrentpagegrid{\currentpagegrid:#1}%
   \edef\p_distance{\namedpagegridparameter{\currentpagegrid:#1}\c!distance}%
   \edef\p_width   {\namedpagegridparameter{\currentpagegrid:#1}\c!width}%
   \clf_setcolumnsetproperties {%
      name {\currentpagegrid}%
      column {#1}%
      \ifchkdimension\p_distance\or
        distance \lastchkdimension
      \fi
      \ifx\p_width\v!auto\orelse\ifchkdimension\p_width\or
        width \lastchkdimension
      \fi
   }}

\appendtoks
   \dorecurse{(\pagegridparameter\c!nleft)+(\pagegridparameter\c!nright)}%
     {\chaintocurrentpagegrid{\currentpagegrid:#1}}%
\to \everydefinepagegrid

\permanent\tolerant\protected\def\startpagegrid[#S#1]#*[#S#2]%
  {\bgroup
   \enforced\let\startpagegrid\page_grd_start_dummy
   \ifarguments
     \lettonothing\currentpagegrid
   \or
     \ifhastok={#1}%
       \lettonothing\currentpagegrid
       \setupcurrentpagegrid[#1]%
     \else
       \cdef\currentpagegrid{#1}%
     \fi
   \or
     \cdef\currentpagegrid{#1}%
     \setupcurrentpagegrid[#2]%
   \fi
   \usepageparameter\pagegridparameter
   \c_page_grd_n_of_left {\pagegridparameter\c!nleft}%
   \c_page_grd_n_of_right{\pagegridparameter\c!nright}%
   \c_page_grd_n_of_rows {\pagegridparameter\c!lines}%
   \d_page_grd_max_width {\pagegridparameter\c!maxwidth}%
   \d_page_grd_max_height{\pagegridparameter\c!maxheight}%
   \d_page_grd_distance  {\pagegridparameter\c!distance}%
   %
   \automigrationmode\zerocount % for now
   %
   \ifcase\c_page_grd_n_of_rows
      \getrawnoflines{\d_page_grd_max_height-\strutheight+\topskip}%
      \c_page_grd_n_of_rows\noflines
   \fi
   \edef\p_width{\pagegridparameter\c!width}%
   \insidecolumnstrue % will be different flag in addition
   \clf_resetcolumnset {
        name       {\currentpagegrid}
        nofrows    \c_page_grd_n_of_rows
        nofleft    \c_page_grd_n_of_left
        nofright   \c_page_grd_n_of_right
        lineheight \strutht
        linedepth  \strutdp
      \ifx\p_width\v!auto
        % sets \d_page_grd_column_width
      \else
        width      \p_width
      \fi
        distance   \d_page_grd_distance
        maxwidth   \d_page_grd_max_width
   }%
   %
   \page_grd_check
   %
   \clf_flushcolumnsetareas{\currentpagegrid}\relax
   \setupoutputroutine[\s!pagegrid]%
   \page_grd_command_set_hsize
   \page_grd_command_set_vsize
   %
   \columnwidth   \d_page_grd_column_width
   \columndistance\d_page_grd_distance
   \nofcolumns    \c_page_grd_n_of_left    % not always ok
   \textwidth     \d_page_grd_column_width % kind of redundant but we had it so ...
   %
   }%\begingroup}

\tolerant\def\page_grd_start_dummy[#S#1]#*[#S#2]%
  {\let\page_grd_stop\egroup}

\permanent\protected\def\stoppagegrid
  {\page_grd_stop}

\def\page_grd_stop
  {\endgraf % needed, else wrong vsize in one par case
   \vfill % otherwise weird \placenotes[endnotes]
   \page_grd_command_set_vsize % needed
   \penalty\c_page_otr_eject_penalty
   \page_grd_command_flush_page
   \page_otr_fill_and_eject_page
   \page_grd_command_set_vsize % why here
   \egroup
   \page_otr_command_set_vsize
   \page_otr_command_set_hsize}

\permanent\protected\def\reservepagegrid[#S#1]%
  {\begingroup
   \letdummyparameter\c!c\plusone
   \letdummyparameter\c!r\plusone
   \letdummyparameter\c!nc\plusone
   \letdummyparameter\c!nr\plusone
   \getdummyparameters[#1]%
   \clf_blockcolumnset {
     name {\currentpagegrid}
     c  \dummyparameter\c!c
     r  \dummyparameter\c!r
     nc \dummyparameter\c!nc
     nr \dummyparameter\c!nr
   }%
   \endgroup}

\permanent\tolerant\protected\def\setpagegrid[#S#1]%
  {\begingroup
   \letdummyparameter\c!c\zerocount
   \letdummyparameter\c!r\zerocount
   \letdummyparameter\c!method\v!here
   \letdummyparameter\c!option\v!none
   \getdummyparameters[#1]%
   \dowithnextboxcs\page_grd_set_indeed\hbox}

\def\page_grd_set_indeed
  {\clf_checkcolumnset {%
     name   {\currentpagegrid}%
     c      {\dummyparameter\c!c}%
     r      {\dummyparameter\c!r}%
     box    \nextbox
     method {\dummyparameter\c!method}%
     option {\dummyparameter\c!option}%
   }%
   \ifcase\c_page_grd_reserved_state
     \setbox\nextbox\vpack to \d_page_grd_reserved_height \bgroup
       \vss
       \hpack to \d_page_grd_reserved_width \bgroup
         \box\nextbox
         \hss
       \egroup
       \vss
     \egroup
     \wd\nextbox\d_page_grd_reserved_width
     \clf_putincolumnset {
       name {\currentpagegrid}
       box \nextbox
     }%
   \fi
   \endgroup}

\protected\def\page_grd_command_set_vsize
  {\clf_setvsizecolumnset{\currentpagegrid}%
   \ifdim\d_page_grd_gap_height<\lineheight
     \page_grd_command_flush_page
     \page_otr_fill_and_eject_page
   \fi
   \global\vsize\d_page_grd_gap_height
   \pagegoal\vsize}

\protected\def\page_grd_command_set_hsize
  {\clf_sethsizecolumnset{\currentpagegrid}%
   \hsize\d_page_grd_column_width
   \textwidth\d_page_grd_column_width}

\protected\def\page_grd_command_routine
  {\ifvoid\normalpagebox \else
     \clf_addtocolumnset{\currentpagegrid}\normalpagebox
   \fi
   \page_grd_command_set_vsize
   \page_grd_command_flush_saved_floats
   \page_grd_command_set_vsize
   \ifdim\d_page_grd_gap_height<\lineheight
     \page_grd_command_flush_page
   \fi
   \page_grd_command_set_vsize
   \clf_flushcolumnsetrest {\currentpagegrid}\normalpagebox
   \ifvoid\normalpagebox \else
     \unvbox\normalpagebox
   \fi}

\installoutputroutine\synchronizepagegrid
  {\ifvoid\normalpagebox\else
     \clf_addtocolumnset{\currentpagegrid}\normalpagebox
     \page_grd_command_set_vsize
     \clf_flushcolumnsetrest{\currentpagegrid}\normalpagebox
     \ifvoid\normalpagebox \else
       \unvbox\normalpagebox
     \fi
   \fi}

% todo line numbers and marks

\protected\def\page_grd_command_flush_page_column#1%
  {\privatescratchcounter#1\relax % or just currentcolumn as in page-col.mkiv
   \clf_flushcolumnsetcolumn{\currentpagegrid}\privatescratchcounter
   \anch_mark_column_box\b_page_grd_column\privatescratchcounter
   \page_marks_synchronize_column\c_page_grd_first_column\c_page_grd_last_column\privatescratchcounter\b_page_grd_column
   \ifnum\privatescratchcounter>\c_page_grd_n_of_left
     \advanceby\privatescratchcounter-\c_page_grd_n_of_left
     \page_lines_add_numbers_to_box\b_page_grd_column\privatescratchcounter\c_page_grd_n_of_right\plustwo
   \else
     \page_lines_add_numbers_to_box\b_page_grd_column\privatescratchcounter\c_page_grd_n_of_left\plustwo
   \fi
   \begingroup
   \cdef\currentpagegrid{\currentpagegrid:#1}%
   \inheritedpagegridframedbox\currentpagegrid\b_page_grd_column
   \endgroup}

\protected\def\page_grd_command_flush_page
  {\deactivatecolor % puzzling, try ungrouped color \red or so
   \setbox\b_page_grd_collected\hpack\bgroup
     \clf_preparecolumnsetflush{\currentpagegrid}%
     \letpagegridparameter\c!region\currentpagegrid
     \ifcstok{\pagegridparameter\c!direction}\v!reverse
       \dostepwiserecurse\c_page_grd_last_column\c_page_grd_first_column\minusone
         {\page_grd_command_flush_page_column{##1}%
          \ifnum##1>\plusone
            \kern{\namedpagegridparameter{\currentpagegrid:##1}\c!distance}%
          \fi}%
     \else
       \dostepwiserecurse\c_page_grd_first_column\c_page_grd_last_column\plusone
         {\page_grd_command_flush_page_column{##1}%
          \ifnum##1<\c_page_grd_last_column
            \kern{\namedpagegridparameter{\currentpagegrid:##1}\c!distance}%
          \fi}%
     \fi
     \clf_finishcolumnsetflush{\currentpagegrid}%
   \egroup
   \page_otr_construct_and_shipout\box\b_page_grd_collected\zerocount % three arguments
   \clf_flushcolumnsetareas{\currentpagegrid}\relax
   \page_grd_command_flush_saved_floats}

% slow but robust

\protected\def\page_grd_command_next_progress
  {\strut
   \page_grd_command_flush_all_floats
   \page_otr_eject_page
   \ifcase\clf_columnsetnoto\else
     \expandafter\page_grd_command_next_progress
   \fi}

\protected\def\page_grd_command_handle_column
  {\ifcase\clf_columnsetgoto{\currentpagegrid}{\page_breaks_columns_current_option}\relax\else
     \expandafter\page_grd_command_next_progress
   \fi}

\installcolumnbreakmethod\s!pagegrid\s!unknown {\page_grd_command_handle_column}
\installcolumnbreakmethod\s!pagegrid\v!yes     {\page_grd_command_handle_column}

\protected\def\page_grd_command_next_page
  {\ifcase\clf_columnsetgoto{\currentpagegrid}{\v!page}\relax\else
     \page_grd_command_flush_page
   \fi}

\protected\def\page_grd_command_next_page_and_inserts
  {\page_grd_command_flush_all_floats
   \page_grd_command_next_page}

\let\page_grd_command_flush_all_floats\page_one_command_flush_all_floats
\let\page_grd_command_package_contents\page_one_command_package_contents

\protected\def\page_grd_command_flush_saved_floats
  {\ifconditional\c_page_floats_flushing \else
     \ifconditional\c_page_floats_some_waiting
       \page_grd_command_flush_saved_floats_indeed
     \fi
   \fi}

\protected\def\page_grd_command_flush_saved_floats_indeed
  {\page_floats_flush\s!text\plusone
   \clf_checkcolumnset {
     name   {\currentpagegrid}
     method {\floatmethod}
     width  \wd\floatbox
     height \ht\floatbox
   }%
   \ifcase\c_page_grd_reserved_state
     \page_grd_place_float_here_indeed
     \page_grd_command_set_vsize % needed
     \ifconditional\c_page_floats_some_waiting
       \doubleexpandafter\page_grd_command_flush_saved_floats_indeed
     \fi
   \else
     \page_floats_resave\s!text
   \fi}

% needs checking

\protected\def\page_grd_command_flush_floats
  {\wait\global\c_page_floats_flushing\conditionaltrue
   \ifconditional\c_page_floats_some_waiting
     \par
     \page_grd_command_flush_floats_indeed
   \fi
   \global\savednoffloats\zerocount
   \global\c_page_floats_some_waiting\conditionalfalse
   \global\c_page_floats_flushing\conditionalfalse}

\def\page_grd_command_flush_floats_indeed % much in common with OTRSET
  {\ifconditional\c_page_floats_some_waiting
     \ifconditional\c_page_floats_compress_flushed
       \page_floats_collect\s!text\hsize\d_page_floats_compress_distance
       \ifcase\nofcollectedfloats
         \page_floats_get
     % \or
     %   \page_floats_get
       \else
         \c_page_floats_center_box\conditionalfalse % not needed as we do call directly
         \global\setbox\floatbox\hbox to \hsize
           {\hfil
            \dorecurse\nofcollectedfloats
              {\ifcase\columndirection % nog document wide
                 \page_floats_flush\s!text\plusone
               \else
                 \page_floats_flush\s!text{\tointeger{\nofcollectedfloats-\recurselevel+1}}%
               \fi
               \ifdim\wd\floatbox>\makeupwidth % \hsize
                 \hbox to \makeupwidth{\hss\box\floatbox\hss}%
               \else
                 \box\floatbox
               \fi
               \ifnum\recurselevel<\nofcollectedfloats
                 \hfil
               \fi}%
            \hfil}%
         \fi
     \else
       \page_floats_get
     \fi
     \doplacefloatbox
     \expandafter\page_grd_command_flush_floats_indeed
   \fi}

% so far

\protected\def\page_grd_command_check_if_float_fits
  {\clf_checkcolumnset {
     name   {\currentpagegrid}
     method {\floatmethod}
   % c      \zerocount
   % r      \zerocount
     box    \floatbox
   }%
   \ifcase\c_page_grd_reserved_state
     \global\c_page_floats_room\conditionaltrue
   \else
     \global\c_page_floats_room\conditionalfalse
   \fi}

\protected\def\page_grd_place_float_here_indeed
  {\setbox\floatbox\vpack to \d_page_grd_reserved_height \bgroup
     \vss
     \hpack to \d_page_grd_reserved_width \bgroup
     % \hss % no
       \box\floatbox
       \hss
     \egroup
     \vss
   \egroup
   \clf_putincolumnset {
     name {\currentpagegrid}
     box  \floatbox
   }}

\def\page_grd_place_float_slot
  {% safeguard
   \ifempty\floatmethod
     \let\floatmethod\v!here
   \fi
   % synchronize
   \penalty\c_page_otr_eject_penalty
   % push
   \setbox\savedfloatbox\box\floatbox
   \page_grd_command_flush_saved_floats
   \setbox\floatbox\box\savedfloatbox
   % pop
   \ifconditional\c_page_floats_some_waiting
     \page_floats_save\s!text
     \nonoindentation
   \else
     \clf_checkcolumnset {
       name   {\currentpagegrid}
       method {\floatmethod}
     \ifempty\floatcolumn \else
       c      \floatcolumn
     \fi
     \ifempty\floatrow \else
       r      \floatrow
     \fi
       box    \floatbox
     }%
     \ifcase\c_page_grd_reserved_state
       \page_grd_place_float_here_indeed
     \else
       \page_floats_save\s!text
       \nonoindentation
     \fi
   \fi}

\def\page_grd_place_float_fixed % todo: fallback on here
  {\ifempty\floatcolumn
     \let\floatmethod\v!here
   \orelse\ifempty\floatrow
     \let\floatmethod\v!here
   \else
     \let\floatmethod\v!fixed
   \fi
   \page_grd_place_float_slot}

\def\page_grd_place_float_force
  {% synchronize
   \penalty\c_page_otr_eject_penalty
   \clf_checkcolumnset {
     name   {\currentpagegrid}
     method {\floatmethod}
     box    \floatbox
   }%
   \ifcase\c_page_grd_reserved_state
     \page_grd_place_float_here_indeed
   \else
     \page_floats_save\s!text
     \nonoindentation
   \fi}

\def\page_grd_place_float_page  {\page_grd_place_float_slot} % todo: fallback on here

\def\page_grd_place_float_here  {\let\floatmethod\v!here\page_grd_place_float_slot}
\def\page_grd_place_float_top   {\page_grd_place_float_slot}
\def\page_grd_place_float_bottom{\page_grd_place_float_slot}

\installfloatmethod \s!pagegrid \v!here        \page_grd_place_float_here
\installfloatmethod \s!pagegrid \v!force       \page_grd_place_float_force % todo
%installfloatmethod \s!pagegrid \v!left
%installfloatmethod \s!pagegrid \v!right
%installfloatmethod \s!pagegrid \v!text
\installfloatmethod \s!pagegrid \v!top         \page_grd_place_float_top
\installfloatmethod \s!pagegrid \v!bottom      \page_grd_place_float_bottom
%installfloatmethod \s!pagegrid \v!auto
%installfloatmethod \s!pagegrid \v!margin
%installfloatmethod \s!pagegrid \v!opposite
\installfloatmethod \s!pagegrid \v!page        \page_grd_place_float_page
%installfloatmethod \s!pagegrid \v!leftpage
%installfloatmethod \s!pagegrid \v!rightpage
%installfloatmethod \s!pagegrid \v!inmargin
%installfloatmethod \s!pagegrid \v!inleft
%installfloatmethod \s!pagegrid \v!inright
%installfloatmethod \s!pagegrid \v!leftmargin
%installfloatmethod \s!pagegrid \v!rightmargin
%installfloatmethod \s!pagegrid \v!leftedge
%installfloatmethod \s!pagegrid \v!rightedge
%installfloatmethod \s!pagegrid \v!somewhere
%installfloatmethod \s!pagegrid \v!backspace
%installfloatmethod \s!pagegrid \v!cutspace
\installfloatmethod \s!pagegrid \s!tblr        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!lrtb        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!tbrl        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!rltb        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!fxtb        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!btlr        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!lrbt        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!btrl        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!rlbt        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!fxbt        \page_grd_place_float_slot
\installfloatmethod \s!pagegrid \s!fixd        \page_grd_place_float_fixed

\protected\def\page_grd_command_side_float_output
  {} % nothing, reset anyway

\protected\def\page_grd_command_flush_side_floats
  {\page_sides_forget_floats}

\protected\def\page_grd_command_synchronize_side_floats
  {\page_sides_forget_floats}

\protected\def\page_grd_command_synchronize_hsize
  {\page_grd_command_set_hsize}

\protected\def\page_grd_command_flush_all_floats
  {\page_one_command_flush_all_floats}

\defineoutputroutine
  [\s!pagegrid]
  [\s!page_otr_command_routine                =\page_grd_command_routine,
   \s!page_otr_command_package_contents       =\page_grd_command_package_contents,
   \s!page_otr_command_set_vsize              =\page_grd_command_set_vsize,
   \s!page_otr_command_set_hsize              =\page_grd_command_set_hsize, % tricky, goes wrong
   \s!page_otr_command_synchronize_hsize      =\page_grd_command_synchronize_hsize,
   \s!page_otr_command_next_page              =\page_grd_command_next_page,
   \s!page_otr_command_next_page_and_inserts  =\page_grd_command_next_page_and_inserts,
 % \s!page_otr_command_set_top_insertions     =\page_grd_command_set_top_insertions,
 % \s!page_otr_command_set_bottom_insertions  =\page_grd_command_set_bottom_insertions,
 % \s!page_otr_command_flush_top_insertions   =\page_grd_command_flush_top_insertions,
 % \s!page_otr_command_flush_bottom_insertions=\page_grd_command_flush_bottom_insertions,
   \s!page_otr_command_check_if_float_fits    =\page_grd_command_check_if_float_fits,
 % \s!page_otr_command_set_float_hsize        =\page_grd_command_set_float_hsize,
 % \s!page_otr_command_flush_float_box        =\page_grd_command_flush_float_box,
   \s!page_otr_command_synchronize_side_floats=\page_grd_command_synchronize_side_floats,
   \s!page_otr_command_side_float_output      =\page_grd_command_side_float_output,
   \s!page_otr_command_flush_floats           =\page_grd_command_flush_floats,
   \s!page_otr_command_flush_side_floats      =\page_grd_command_flush_side_floats,
   \s!page_otr_command_flush_saved_floats     =\page_grd_command_flush_saved_floats,
   \s!page_otr_command_flush_all_floats       =\page_grd_command_flush_all_floats,
 % \s!page_otr_command_flush_margin_blocks    =\page_grd_command_flush_margin_blocks, % not used
  ]

% spans

\installcorenamespace{pagegridspan}

\installframedcommandhandler \??pagegridspan {pagegridspan} \??pagegridspan

\setuppagegridspan
  [\c!frame=\v!off,
   \c!before=,
   \c!after=,
   \c!offset=\v!overlay,
   \c!location=\v!left,
   \c!linecorrection=\v!off,
   \c!depthcorrection=\v!off,
   \c!n=\plustwo,
   \c!nlines=\zerocount,
   \c!align=\v!normal,
   \c!width=\d_page_grd_span_width,
   \c!indenting=,
   \c!indentnext=\v!yes,
   \c!default=\v!here,
   \c!alternative=\v!a]

\newdimension\d_page_grd_span_width

\let\page_grd_span_stop\relax

\permanent\tolerant\protected\def\startpagegridspan[#1]#*[#2]#*[#3]% [#3] gobbles space
  {\endgraf % else rubish output if forgotten
   \synchronizepagegrid
   \bgroup
   \forgetall
   \cdef\currentpagegridspan{#1}%
   \clf_sethsizecolumnspan{\currentpagegrid}\pagegridspanparameter\c!n\relax
   \setbox\scratchbox\hbox\bgroup\inheritedpagegridspanframed\bgroup
     \def\page_grd_span_stop{\page_grd_span_stop_indeed{#2}}%
     \usepagegridspanstyleandcolor\c!style\c!color
     \pagegridspanparameter\c!before
     \ignorespaces}

\protected\def\page_grd_span_stop_indeed#1%
  {\removeunwantedspaces
   \par
   \verticalstrut
   \kern-2\struttotal
   \verticalstrut
   \endgraf
   \pagegridspanparameter\c!after
   \egroup\egroup
   \setpagegrid[#1]{\box\scratchbox}%
   % todo: push into slot
   \egroup
   \endgraf}

\permanent\protected\def\stoppagegridspan % indirectness permits aliasing
  {\page_grd_span_stop}

\permanent\def\pagegridspanwidth#1% assumes equal distances
  {\todimension{#1\d_page_grd_column_width+#1\d_page_grd_distance-\d_page_grd_distance}}

% areas

\installcorenamespace{pagegridarea}

\installframedcommandhandler \??pagegridarea {pagegridarea} \??pagegridarea

\setuppagegridarea
  [\c!x=\plusone,
   \c!y=\plusone,
   \c!nx=\plusone,
   \c!ny=\plusone,
   \c!clipoffset=2\lineheight,
   \c!leftoffset=\zeropoint,
   \c!rightoffset=\zeropoint,
   \c!offset=\v!overlay,
   \c!strut=\v!no,
   \c!frame=\v!off,
  %\c!type=\v!next,
   \c!align=\v!normal,
   \c!page=\plusone,
   \c!state=\v!stop]

% type: both fixed left right next (not now), then better
% lefttext and righttext or so

\appendtoks
   % \edef\p_type{}%
   % \ifx\p_type\v!next
   %    \doifelseoddpage
   %        {\letpagegridareaparameter\c!type\v!right}%
   %        {\letpagegridareaparameter\c!type\v!left}%
   % \fi
     \clf_registercolumnsetarea {%
        name  {\currentpagegridarea}%
      % type  {\p_type}
      % page  \pagegridareaparameter\c!page
        state {\pagegridareaparameter\c!state}%
        c     {\pagegridareaparameter\c!x}%
        r     {\pagegridareaparameter\c!y}%
        nc    {\pagegridareaparameter\c!nx}%
        nr    {\pagegridareaparameter\c!ny}%
     }%
\to \everydefinepagegridarea

\permanent\tolerant\protected\def\setuppagegridareatext[#1]#*[#2]%
  {\cdef\currentpagegridarea{#1}%
   \setpagegridareaparameter\c!text{#2}}

% maybe move the left/right correction to the tex end or the offset to lua

\permanent\protected\def\page_grd_set_area#1#2#3#4#5#6#7#8% can be optimized
  {\begingroup
   \cdef\currentpagegridarea{#2}%
   \setpagegridareaparameter\c!width {#5\scaledpoint}%
   \setpagegridareaparameter\c!height{#6\scaledpoint}%
   \setbox\nextbox\hpack\bgroup\inheritedpagegridareaframed\bgroup
     \usepagegridareastyleandcolor\c!style\c!color
     \ignorespaces
     \pagegridareaparameter\c!text
   \egroup\egroup
   %
   \scratchdimen#8\scaledpoint
   \ifdim\scratchdimen>\zeropoint
     \setbox\scratchbox\vbox\bgroup
       \clip
         [     \c!offset=\pagegridareaparameter\c!clipoffset,%
          \c!rightoffset=\pagegridareaparameter\c!rightoffset,%
                \c!width=\scratchdimen,%
             % \c!height=
         ]%
         {\copy\nextbox}%
     \egroup
     \clf_setcolumnsetarea{name {#1} box \scratchbox c #3 r #4}%
     \setbox\scratchbox\vbox\bgroup
       \hskip-\layoutparameter\c!backspace % todo: #9
       \clip
         [    \c!offset=\pagegridareaparameter\c!clipoffset,%
          \c!leftoffset=\pagegridareaparameter\c!rightoffset,%
             \c!hoffset=\scratchdimen,%
               \c!width=\dimexpr\wd\nextbox-\scratchdimen\relax,%
            % \c!height=
         ]%
         {\box\nextbox}%
     \egroup
     \clf_setcolumnsetarea{name {#1} box \scratchbox c #7 r #4}%
   \else
     \setbox\scratchbox\vbox\bgroup
        \box\nextbox % wrapping needed
     \egroup
     \clf_setcolumnsetarea{name {#1} box \scratchbox c #3 r #4}%
   \fi
   \endgroup}

% state start | repeat

%D The old one, for now:

\aliased\let\definecolumnset       \definepagegrid
\aliased\let\setupcolumnset        \setuppagegrid
\aliased\let\setupcolumnsetlines   \setuppagegridlines
\aliased\let\setupcolumnsetstart   \setuppagegridstart
\aliased\let\startcolumnset        \startpagegrid
\aliased\let\stopcolumnset         \stoppagegrid
\aliased\let\definecolumnsetspan   \definepagegridspan
\aliased\let\setupcolumnsetspan    \setuppagegridspan
\aliased\let\startcolumnsetspan    \startpagegridspan
\aliased\let\stopcolumnsetspan     \stoppagegridspan
\aliased\let\columnsetspanwidth    \pagegridspanwidth
\aliased\let\definecolumnsetarea   \definepagegridarea
\aliased\let\setupcolumnsetarea    \setuppagegridarea
\aliased\let\setupcolumnsetareatext\setuppagegridareatext

%D It ends here.

\protect \endinput