%D \module
%D   [       file=page-mvl,
%D        version=2024.10.15, % variant on page-cst etc
%D          title=\CONTEXT\ Page Macros,
%D       subtitle=Columnsets,
%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
% todo : linenumbers per slot
% todo : \ignoremvl
% todo : intercept in mvl
% todo : inserts like top
% todo : flush pages when flush
% todo : color now mess up grid color
% todo : wipe all mvls

%D This is the new columnset module. For sure it will evolve a bit over time.
%D We don't really need an output routine but it just fits in.

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

\unprotect

\ifdefined\v!columnset             \else \cdef\v!columnset            {columnset}             \fi
\ifdefined\v!columnsetsheet        \else \cdef\v!columnsetsheet       {columnsetsheet}        \fi
\ifdefined\v!columnsetsheetdelayed \else \cdef\v!columnsetsheetdelayed{columnsetsheetdelayed} \fi
\ifdefined\v!columnsetspreadsheets \else \cdef\v!columnsetspreadsheets{columnsetspreadsheets} \fi
\ifdefined\v!setcolumnsetsheet     \else \cdef\v!setcolumnsetsheet    {setcolumnsetsheet}     \fi
\ifdefined\v!slot                  \else \cdef\v!slot                 {slot}                  \fi

\newdimension\d_page_mvl_column_width
\newdimension\d_page_mvl_max_height
\newdimension\d_page_mvl_max_width
\newdimension\d_page_mvl_distance

\newdimension\d_page_mvl_reserved_height
\newdimension\d_page_mvl_reserved_width
\newinteger  \c_page_mvl_reserved_state

\newdimension\d_page_mvl_last_ht
\newdimension\d_page_mvl_last_dp

\newinteger\c_page_mvl_n_of_left
\newinteger\c_page_mvl_n_of_right
\newinteger\c_page_mvl_n_of_rows
\newinteger\c_page_mvl_first_column
\newinteger\c_page_mvl_last_column
\newinteger\c_page_mvl_last_overflow
\newinteger\c_page_mvl_current_sheet
\newinteger\c_page_mvl_current_spreadsheet
\newinteger\c_page_mvl_level
\newinteger\c_page_mvl_main_level
\newinteger\c_page_mvl_max_used_cells

\newconditional\c_page_mvl_active

\newbox\b_page_mvl_collected
\newbox\b_page_mvl_column

\permanent\protected\untraced\def\currentsheet{\the\c_page_mvl_current_sheet}

\registerctxluafile{page-mvl}{autosuffix}

% 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.

%D Many years later: subcolumnsets, nested columnsets, split notes, etc. much was
%D done with Frost* on the headphone(s); new double cd plus all stuff I hadn't yet
%D on cd gotten from bandcamp, so a 2024 crossing into 2025 timestamp, waiting for
%D the DVD.

\installcorenamespace{columnset}

\installframedcommandhandler \??columnset {columnset} \??columnset

\setupcolumnset
  [\c!distance=1.5\bodyfontsize,
   \c!n=\plustwo,
   \c!nleft=\columnsetparameter\c!n,
   \c!nright=\columnsetparameter\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, % gone
   \c!width=\v!auto,
   \c!limit=\plusone,
   \c!page=,
   \c!state=\v!start,
   \c!direction=\v!normal, % todo
   \c!maxheight=\textheight,
   \c!maxwidth=\makeupwidth]

%         lineheight \strutht
%         linedepth  \strutdp
%       \ifchkdimension\p_width\or
%         width      \p_width
%       \fi
%         distance   \d_page_mvl_distance
%         maxwidth   \d_page_mvl_max_width

\appendtoks % could become an option
    \ifempty\currentcolumnset\else
      \protected\frozen\instance\edefcsname\e!start\currentcolumnset\endcsname{\startcolumnset[\currentcolumnset]}%
      \protected\frozen\instance\edefcsname\e!stop \currentcolumnset\endcsname{\stopcolumnset}%
      \clf_definecolumnset {
        name     {\currentcolumnset}%
        nofrows  {\columnsetparameter\c!lines}%
        nofleft  {\columnsetparameter\c!nleft}%
        nofright {\columnsetparameter\c!nright}%
      }%
    \fi
\to \everydefinecolumnset

\appendtoks
    \ifcstok{\columnsetparameter\c!state}\v!start
       \expandafter\setmode
    \else
       \expandafter\resetmode
    \fi{\v!columnset:\currentcolumnset}%
\to \everysetupcolumnset

\newtoks\t_every_columnset_yes
\newtoks\t_every_columnset_nop

%D All the parameters are mandate!

\permanent\tolerant\protected\def\setupcolumnsetlines[#1]#*[#2]#*[#3]#*[#4]% id page col value
  {\ifcstok{\namedcolumnsetparameter{#1}\c!state}\v!start
     % todo : check validity of arguments
     \clf_setcolumnsetlines{name {#1} sheet #2 column #3 value #4}%
   \fi}

\permanent\tolerant\protected\def\setupcolumnsetstart[#1]#*[#2]#*[#3]#*[#4]% id page col value
  {\ifcstok{\namedcolumnsetparameter{#1}\c!state}\v!start
     % todo : check validity of arguments
     % todo : check validity of arguments
     \clf_setcolumnsetstart{name {#1} sheet #2 column #3 value #4}%
   \fi}

\protected\def\page_mvl_check
  {\dorecurse{(\columnsetparameter\c!nleft)+(\columnsetparameter\c!nright)}%
     {\page_mvl_check_column{##1}}}

\protected\def\page_mvl_check_column#1%
  {\chaintocurrentcolumnset{\currentcolumnset:#1}%
   \begingroup
   % We group because we cannot inherit as unset signal auto. This is realy
   % ugly coding.
   \let\tempstring\currentcolumnset
   \cdef\currentcolumnset{\currentcolumnset:#1}%
   \clf_setcolumnsetproperties {%
      name {\tempstring}%
      column {#1}%
      \ifchkdimexpr\directcolumnsetparameter\c!distance\or
        distance \lastchkdimension
      \fi
      \ifchkdimexpr\directcolumnsetparameter\c!width\or
        width \lastchkdimension
      \fi
   }%
   \endgroup}

\appendtoks
   \dorecurse{(\columnsetparameter\c!nleft)+(\columnsetparameter\c!nright)}%
     {\chaintocurrentcolumnset{\currentcolumnset:#1}}%
\to \everydefinecolumnset

% \nooutputboxerror\plusthree % bitset as we have two cases where it's checked

\mutable\let\maincolumnset\empty

\def\page_mvl_unknown
  {\writestatus\m!columns{unknown columnset '\currentcolumnset'}%
   \page_mvl_start_dummy}

\permanent\tolerant\protected\def\startcolumnset[#S#1]#*[#S#2]%
  {\bgroup
   \let\maincolumnset\currentcolumnset
   \cdef\currentcolumnset{#1}%
   \advanceby\c_page_mvl_main_level\plusone
   \ifcase\c_page_mvl_main_level
     % can't happen
   \or
   \else
     \enforced\let\startcolumnset\page_mvl_start_dummy
   \fi
   \ifempty\currentcolumnset
     \expandafter\page_mvl_unknown
   \orelse\ifhastok={#1}%
     \expandafter\page_mvl_unknown
   \orunless\ifcstok{\columnsetparameter\c!state}\v!start
     \page_mvl_start_dummy
   \else
     \doifelsecommandhandler\??columnset\currentcolumnset
       {\setupcurrentcolumnset[#2]%
        \expandafter\page_mvl_start}
       {\expandafter\page_mvl_unknown}%
   \fi}
 % \orelse\ifcommandhandler{\??columnset\currentcolumnset}%
 %   \setupcurrentcolumnset[#2]%
 %   \expandafter\page_mvl_start
 % \else
 %   \expandafter\page_mvl_unknown
 % \fi}

\def\page_mvl_start
  {\c_page_mvl_active\conditionaltrue
   \expand\t_every_columnset_nop\relax
   %
   \nooutputboxerror\plusthree % bitset as we have two cases where it's checked
   %
   \usepageparameter\columnsetparameter
   \c_page_mvl_n_of_left {\columnsetparameter\c!nleft}%
   \c_page_mvl_n_of_right{\columnsetparameter\c!nright}%
   \c_page_mvl_n_of_rows {\columnsetparameter\c!lines}%
   \d_page_mvl_max_width {\columnsetparameter\c!maxwidth}%
   \d_page_mvl_max_height{\columnsetparameter\c!maxheight}%
   \d_page_mvl_distance  {\columnsetparameter\c!distance}%
   %
   \usealignparameter\columnsetparameter
   %
   \ifcase\c_page_mvl_n_of_rows
     \getrawnoflines{\dimexpr\d_page_mvl_max_height-\strutheight+\topskip\relax}%
     \c_page_mvl_n_of_rows\noflines
   \fi
   %
   \insidecolumnstrue % will be different flag in addition
   %
   \page_mvl_check
   %
   \clf_resetcolumnset {%
        name        {\currentcolumnset}
        nofrows     \c_page_mvl_n_of_rows
        nofleft     \c_page_mvl_n_of_left
        nofright    \c_page_mvl_n_of_right
       %topskip
        lineheight  \strutht
        linedepth   \strutdp
      \ifchkdimexpr\columnsetparameter\c!width\or
        width       \lastchkdimension
      \fi
        distance    \d_page_mvl_distance
        maxwidth    \d_page_mvl_max_width
        limit       {\columnsetparameter\c!limit}%
        doublesided \ifconditional\layoutisdoublesided tru\else fals\fi e
   }%
   %
   \clf_flushcolumnsetareas{\currentcolumnset}\relax
   \setupoutputroutine[\s!columnset]%
   \page_mvl_command_set_hsize
   \page_mvl_command_set_vsize
   %
   \columnwidth   \d_page_mvl_column_width
   \columndistance\d_page_mvl_distance
   \nofcolumns    \c_page_mvl_n_of_left    % not always ok
   \textwidth     \d_page_mvl_column_width % kind of redundant but we had it so ...
   %
 % \let\topskipcorrection\relax % maybe here too, see below
   \letinterlinespaceparameter\c!top\v!height % we have to check this
   %
   \page_mvl_command_set_vsize
   \nointerlineskip
   \page_mvl_main_mvl_begin}

\tolerant\def\page_mvl_start_dummy[#S#1]#*[#S#2]%
  {\c_page_mvl_active\conditionalfalse
   \expand\t_every_columnset_nop\relax
   \let\page_mvl_stop\egroup}

\def\page_mvl_stop
  {\scratchcounter\mvlcurrentlyactive
   \page_mvl_main_mvl_end
   \page_mvl_command_set_vsize
   \clf_presetcolumnsetspreadsheets\currentcolumnset
   \clf_presetcolumnsetsheets\currentcolumnset
   \clf_columnsetlimit\currentcolumnset
   \page_mvl_command_set_vsize
   \begingroup
   \dontcomplain
   %
   \enforced\let\topskipcorrection\relax % otherwise we get a displaced \showgrid
   %
   \automigrationmode\zerocount
   %
   \ifnum\scratchcounter=\plusone
     \scratchcounterone\plusone
     \scratchcountertwo\plusone
   \else % \ifcsname\??subcolumnset\currentcolumnset\endcsname
     \scratchcounterone\plustwo
     \scratchcountertwo\columnsetlastmvl{\currentcolumnset}\relax % lookahead
   \fi
   \ifconditional\c_page_mvl_trace_n
     \writestatus\m!columnset{flushing mlv: \the\scratchcounterone ..\the\scratchcountertwo}%
   \fi
   \localcontrolledloop \scratchcounterone \scratchcountertwo \plusone {%
     \clf_setcolumnsetmvl{\currentcolumnset}\currentloopiterator\relax
     \clf_gotocolumnsetslot{\currentcolumnset}\relax
     \setbox\scratchboxone\flushmvl\currentloopiterator\relax
     \page_mvl_process_mvl
   }%
   %
   \scratchcounter\columnsetlastfuture\currentcolumnset\relax % lookahead
   \clf_columnsetresetdirect\maincolumnset\relax
   \localcontrolledrepeat \scratchcounter {%
     \clf_setcolumnsetpresent\currentcolumnset\currentloopiterator
     \scratchcounterone\columnsethascontent\currentcolumnset\currentloopiterator\relax
     \ifcase\scratchcounterone
       % nothing
     \or
       % 1 = left
       \page_mvl_command_flush_page
     \or
       % 2 = right
       \page_mvl_command_flush_page
     \or
       % 3 = both
       \page_mvl_command_flush_page
       \page_mvl_command_flush_page
     \fi
   }%
   \endgroup
   \clf_cleancolumnset{\currentcolumnset}%
   \egroup
   \page_otr_command_set_vsize
   \page_otr_command_set_hsize}

\permanent\protected\def\stopcolumnset
  {\page_mvl_stop}

% maybe use a dedicated setter:

\def\page_mvl_common_dummy_preset % [#1]
  {\c_page_floats_ignore_method\conditionaltrue
   \letdummyparameter\c!c      \zerocount
   \letdummyparameter\c!r      \zerocount
   \letdummyparameter\c!nc     \plusone
   \letdummyparameter\c!nr     \zerocount
   \letdummyparameter\c!method \v!here
   \letdummyparameter\c!option \v!none
   \letdummyparameter\c!height \lineheight % convenient
   \letdummyparameter\c!width  \emwidth    % the last one
   \letdummyparameter\c!ntop   \zerocount
   \letdummyparameter\c!nbottom\zerocount
   \getdummyparameters} % [#1]

\permanent\protected\def\reservecolumnset
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \expandafter\page_mvl_reserve_columnset
   \else
     \expandafter\gobbleoneoptional
   \fi}

\tolerant\def\page_mvl_reserve_columnset[#S#1]%
  {\begingroup
   \letdummyparameter\c!c\plusone
   \letdummyparameter\c!r\plusone
   \letdummyparameter\c!nc\plusone
   \letdummyparameter\c!nr\plusone
   \getdummyparameters[#1]%
   \clf_blockcolumnset {%
     name {\currentcolumnset}%
     c    {\dummyparameter\c!c}%
     r    {\dummyparameter\c!r}%
     nc   {\dummyparameter\c!nc}%
     nr   {\dummyparameter\c!nr}%
   }%
   \endgroup}

\permanent\protected\def\setcolumnset
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \expandafter\page_mvl_set_column_set_yes
   \else
     \expandafter\gobbleoneoptional
   \fi}

\tolerant\def\page_mvl_set_column_set_yes[#S#1]%
  {\begingroup
   \page_mvl_common_dummy_preset[#1]%
  %\dowithnextboxcs\page_mvl_set_indeed\hbox}
   \afterassigned{%
     \aftergroup\page_mvl_set_indeed
     \atendofgroup\removeunwantedspaces
     \ignorespaces
   }\setbox\nextbox\hbox}

\permanent\protected\def\startsetcolumnset % todo: interface
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \expandafter\page_mvl_start_set_column_set_yes
   \else
     \expandafter\page_mvl_start_set_column_set_nop
   \fi}

\tolerant\protected\def\page_mvl_start_set_column_set_yes[#S#1]%
  {\begingroup
   \page_mvl_common_dummy_preset[#1]%
   \setbox\nextbox\hbox\bgroup\ignorespaces}

\def\page_mvl_start_set_column_set_nop
  {\ignorenestedupto\startsetcolumnset\stopsetcolumnset} % todo: interface

\permanent\protected\def\stopsetcolumnset % todo: interface
  {\removeunwantedspaces
   \egroup
   \page_mvl_set_indeed}

\def\page_mvl_set_indeed
  {\clf_checkcolumnset {
     name    {\currentcolumnset}
     c       \dummyparameter\c!c
     r       \dummyparameter\c!r
     box     \nextbox
     method  {\dummyparameter\c!method}
     option  {\dummyparameter\c!option}
   \ifempty{\dummyparameter\c!ntop}\else
     ntop    \lastnamedcs
   \fi
   \ifempty{\dummyparameter\c!nbottom}\else
     nbottom \lastnamedcs
   \fi
   }%
   \ifcase\c_page_mvl_reserved_state
     \setbox\nextbox\vpack to \d_page_mvl_reserved_height \bgroup
       \vss
       \hpack to \d_page_mvl_reserved_width \bgroup
         \box\nextbox
         \hss
       \egroup
       \vss
     \egroup
     \wd\nextbox\d_page_mvl_reserved_width
     \clf_putincolumnset {
       name {\currentcolumnset}
       box \nextbox
     }%
   \fi
   \endgroup}

\permanent\protected\def\emptycolumnset
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \expandafter\page_mvl_empty_columnset
   \else
     \expandafter\gobbleoneoptional
   \fi}

\tolerant\protected\def\page_mvl_empty_columnset[#S#1]%
  {\begingroup
   \page_mvl_common_dummy_preset[#1]%
   \setbox\nextbox\hpack\bgroup
     \page_mvl_show_ruled
       \s!width  {\dummyparameter\c!width}%
       \s!height {\dummyparameter\c!height}%
   \egroup
   \page_mvl_set_indeed}

% \protected\def\page_mvl_command_set_vsize % todo: just intercept
%   {\vsize\textheight}

\protected\def\page_mvl_command_set_vsize % todo: just intercept
  {\vsize\snappedtextheight}

\protected\def\page_mvl_command_set_hsize
  {\ifempty\currentsubcolumnset
     \clf_sethsizecolumnset{\currentcolumnset}%
     \hsize\d_page_mvl_column_width
     \textwidth\d_page_mvl_column_width
   \else
     % hack
   \fi}

\protected\def\page_mvl_command_synchronize_hsize
  {\page_mvl_command_set_hsize}

\protected\def\page_mvl_command_flush_page_column#1#2%
  {\privatescratchcounter#1\relax % or just currentcolumn as in page-col.mkiv
   \clf_flushcolumnsetcolumn{\currentcolumnset}\privatescratchcounter
   \anch_mark_column_box\b_page_mvl_column\privatescratchcounter
% \page_marks_synchronize_column\c_page_mvl_first_column\c_page_mvl_last_column\privatescratchcounter\b_page_mvl_column
   \ifnum\privatescratchcounter>\c_page_mvl_n_of_left
     \advanceby\privatescratchcounter-\c_page_mvl_n_of_left
     \page_lines_add_numbers_to_box\b_page_mvl_column\privatescratchcounter\c_page_mvl_n_of_right\plustwo
   \else
     \page_lines_add_numbers_to_box\b_page_mvl_column\privatescratchcounter\c_page_mvl_n_of_left\plustwo
   \fi
   \begingroup
   \cdef\currentcolumnset{\currentcolumnset:#1}%
   \setbox\scratchbox\hpack\bgroup
     \novrule
       \s!width \wd\b_page_mvl_column
       \s!height\ht\b_page_mvl_column
       \s!depth \dp\b_page_mvl_column
     \relax
   \egroup
   \global\setbox\globalscratchbox\hpack\bgroup
      \box\globalscratchbox
      \inheritedcolumnsetframedbox\currentcolumnset\scratchbox
      \ifzeropt#2\else\kern#2\fi
   \egroup
   \relax
   \box\b_page_mvl_column
   \ifzeropt#2\else\kern#2\fi
   \endgroup}

\installtextracker{columnsets.state}
  {\let\page_mvl_show_state\page_mvl_show_state_indeed
   \let\page_mvl_show_ruled\vrule
   \let\page_mvl_show_slot \ruledhpack}
  {\let\page_mvl_show_state\relax
   \let\page_mvl_show_ruled\novrule
   \let\page_mvl_show_slot \hpack}

\installtextracker{columnsets.noisy}
  {\c_page_mvl_trace\conditionaltrue}
  {\c_page_mvl_trace\conditionalfalse}

\let\page_mvl_show_state\relax
\let\page_mvl_show_ruled\novrule
\let\page_mvl_show_slot \hpack

\def\page_mvl_show_state_indeed
  {\setbox\scratchbox\hpack \s!yoffset -1.5\globalbodyfontsize\bgroup
     \infofont\clf_columnsetstatus{\currentcolumnset}%
   \egroup
   \smashboxed\scratchbox}

\protected\def\page_mvl_command_next_page_and_inserts
  {\page_mvl_command_flush_all_floats
   \page_mvl_command_next_page}

\let\page_mvl_command_flush_all_floats  \page_one_command_flush_all_floats
\let\page_mvl_command_package_contents  \page_one_command_package_contents
\let\page_mvl_command_flush_all_floats  \page_one_command_flush_all_floats
\let\page_mvl_command_flush_saved_floats\relax

% needs checking

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

\def\page_mvl_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_mvl_command_flush_floats_indeed
   \fi}

% so far

\protected\def\page_mvl_command_check_if_float_fits
  {\clf_checkcolumnset {
     name   {\currentcolumnset}
     method {\floatmethod}
   % c      \zerocount
   % r      \zerocount
     box    \floatbox
   }%
   \ifcase\c_page_mvl_reserved_state
     \global\c_page_floats_room\conditionaltrue
   \else
     \global\c_page_floats_room\conditionalfalse
   \fi}

\protected\def\page_mvl_place_float_here_indeed
  {\setbox\floatbox\vpack to \d_page_mvl_reserved_height \bgroup
     \vss
     \hpack to \d_page_mvl_reserved_width \bgroup
     % \hss % no
       \box\floatbox
       \hss
     \egroup
     \vss
   \egroup
   \clf_putincolumnset {
     name {\currentcolumnset}
     box  \floatbox
   }}

\def\page_mvl_place_float_slot
  {\ifempty\floatmethod
     \let\floatmethod\v!here
   \fi
   \ifconditional\c_page_mvl_inside_specification
     % synchronize
    %\penalty\c_page_otr_eject_penalty % really ?
     % push
     \setbox\savedfloatbox\box\floatbox
     \page_mvl_command_flush_saved_floats
     \setbox\floatbox\box\savedfloatbox
     % pop
     \ifconditional\c_page_floats_some_waiting
       \page_floats_save\s!text % check this
       \nonoindentation
     \else
       \clf_checkcolumnset {
         name   {\currentcolumnset}
         method {\floatmethod}
       \ifempty\floatcolumn \else
         c      \floatcolumn
       \fi
       \ifempty\floatrow \else
         r      \floatrow
       \fi
         box    \floatbox
       }%
       \ifcase\c_page_mvl_reserved_state
         \page_mvl_place_float_here_indeed
       \else
         \page_floats_save\s!text
         \nonoindentation
       \fi
     \fi
   \else
     \page_mvl_place_float_force
   \fi}

\def\page_mvl_place_float_fixed % todo: fallback on here
  {\page_mvl_place_float_force}

\def\page_mvl_place_float_here
  {\ifconditional\c_page_mvl_inside_specification
     \let\floatmethod\v!here
     \page_mvl_place_float_slot
   \else
     \page_mvl_place_float_force
   \fi}

\def\page_mvl_place_float_page
  {\ifdim\wd\floatbox>\columnwidth
     \page_floats_save\s!text % check this
   \else
     \page_mvl_place_float_force
   \fi}

%D Kind of neat:

\ifdefined\s!columnsettop    \else \cdef\s!columnsettop   {columnsettop}    \fi
\ifdefined\s!columnsetbottom \else \cdef\s!columnsetbottom{columnsetbottom} \fi

\defineinsertion[\s!columnsettop]
\defineinsertion[\s!columnsetbottom]

\newdimension\d_page_mvl_top_insertions_height
\newdimension\d_page_mvl_bottom_insertions_height

\definesystemattribute[balancescaled][public]

\newbox\b_page_inserts_uinsert

\def\c_page_mvl_traced_float_indeed
  {\framed
     [\c!offset=\v!overlay,
      \c!framecolor=darkgray,
      \c!rulethickness=5\linewidth]}

\let\c_page_mvl_traced_float\relax

\installtextracker{columnsets.floats}
  {\let\c_page_mvl_traced_float\c_page_mvl_traced_float_indeed}
  {\let\c_page_mvl_traced_float\relax}

\permanent\protected\def\page_inserts_handle_uinsert#1%
  {\setbox\b_page_inserts_uinsert\hpack\bgroup
     \c_page_mvl_traced_float{\scale[\c!sx=1,\c!sy=#1]{\box\b_page_inserts_uinsert}}%
   \egroup}

\def\page_mvl_top_insertions
  {\setcurrentinsertion\s!columnsettop
   \setbox\scratchbox\hpack\bgroup\vbalancedinsert\b_page_mvl_current_content
     \s!index \currentinsertionnumber
     \s!descend
   \relax\egroup
   \global\d_page_mvl_top_insertions_height\htdp\scratchbox
   \ifvoid\scratchbox\else
     \box\scratchbox
   \fi}

\def\page_mvl_bottom_insertions
  {\setcurrentinsertion\s!columnsetbottom
   \setbox\scratchbox\hpack\bgroup\vbalancedinsert\b_page_mvl_current_content
     \s!index \currentinsertionnumber
     \s!descend
   \relax\egroup
   \global\d_page_mvl_bottom_insertions_height\htdp\scratchbox
   \ifvoid\scratchbox\else
     \box\scratchbox
   \fi}

\def\page_mvl_place_float_top
  {\begingroup
   \setcurrentinsertion\s!columnsettop
   \insertstretch\currentinsertionnumber.5\lineheight
 % \insertshrink \currentinsertionnumber.5\lineheight
   \insert
     \s!callback \plusone
     \s!index    \currentinsertionnumber
   \bgroup
     \boxattribute\floatbox\balancescaledattribute\plusone
     \box\floatbox
     \vkern\lineheight % for the moment hard coded
   \egroup
   \endgroup}

\def\page_mvl_place_float_bottom
  {\begingroup
   \setcurrentinsertion\s!columnsetbottom
   \insertstretch\currentinsertionnumber.5\lineheight
 % \insertshrink \currentinsertionnumber.5\lineheight
   \insert
     \s!callback \plustwo
     \s!index    \currentinsertionnumber
   \bgroup
     \vkern\lineheight % for the moment hard coded
     \boxattribute\floatbox\balancescaledattribute\plusone
     \box\floatbox
   \egroup
   \endgroup}

%permanent\untraced\protected\def\columnsetgridlines#1{\dimexpr#1lh-1sd\relax}
\permanent\untraced\protected\def\columnsetgridlines#1{\dimexpr#1\lineheight-\strutdp\relax}

%D Till here. The nbext one is used when inside a sheet or spread setting environment:

\def\page_mvl_place_float_box{\box\floatbox} % none was taklen for aligned

\installfloatmethod \s!columnset \s!box         \page_mvl_place_float_box
\installfloatmethod \s!columnset \v!here        \page_mvl_place_float_here
\installfloatmethod \s!columnset \v!force       \page_mvl_place_float_force % todo
%installfloatmethod \s!columnset \v!left
%installfloatmethod \s!columnset \v!right
%installfloatmethod \s!columnset \v!text
\installfloatmethod \s!columnset \v!top         \page_mvl_place_float_top
\installfloatmethod \s!columnset \v!bottom      \page_mvl_place_float_bottom
%installfloatmethod \s!columnset \v!auto
%installfloatmethod \s!columnset \v!margin
%installfloatmethod \s!columnset \v!opposite
\installfloatmethod \s!columnset \v!page        \page_mvl_place_float_page
%installfloatmethod \s!columnset \v!leftpage
%installfloatmethod \s!columnset \v!rightpage
%installfloatmethod \s!columnset \v!inmargin
%installfloatmethod \s!columnset \v!inleft
%installfloatmethod \s!columnset \v!inright
%installfloatmethod \s!columnset \v!leftmargin
%installfloatmethod \s!columnset \v!rightmargin
%installfloatmethod \s!columnset \v!leftedge
%installfloatmethod \s!columnset \v!rightedge
%installfloatmethod \s!columnset \v!somewhere
%installfloatmethod \s!columnset \v!backspace
%installfloatmethod \s!columnset \v!cutspace
\installfloatmethod \s!columnset \s!tblr        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!lrtb        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!tbrl        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!rltb        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!fxtb        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!btlr        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!lrbt        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!btrl        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!rlbt        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!fxbt        \page_mvl_place_float_slot
\installfloatmethod \s!columnset \s!fixd        \page_mvl_place_float_fixed

\protected\def\page_mvl_command_side_float_output      {} % nothing, reset anyway
\protected\def\page_mvl_command_flush_side_floats      {\page_sides_forget_floats}
\protected\def\page_mvl_command_synchronize_side_floats{\page_sides_forget_floats}

% spans

\installcorenamespace{columnsetspan}

\installframedcommandhandler \??columnsetspan {columnsetspan} \??columnsetspan

\setupcolumnsetspan
  [\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_mvl_span_width,
   \c!indenting=,
   \c!indentnext=\v!yes,
   \c!method=\s!tblr,
  %\c!alternative=\v!a, % gone
   \c!default=\v!here]

\newdimension\d_page_mvl_span_width

\let\page_mvl_span_stop\relax

\permanent\protected\def\startcolumnsetspan
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \expandafter\page_mvl_start_columnset_span_yes
   \else
   \fi}

\permanent\tolerant\protected\def\page_mvl_start_columnset_span_yes[#1]#*[#2]#*[#3]% [#3] gobbles space
  {\endgraf % else rubish output if forgotten
  %\synchronizecolumnset
  %\balancesubcolumnsets\relax % [#1]%
   \bgroup
   \forgetall
   \cdef\currentcolumnsetspan{#1}%
   \clf_sethsizecolumnspan{\currentcolumnset}\columnsetspanparameter\c!n\relax
   \setbox\scratchbox\hbox\bgroup\inheritedcolumnsetspanframed\bgroup
     \def\page_mvl_span_stop{\page_mvl_span_stop_indeed{#2}}%
     \usecolumnsetspanstyleandcolor\c!style\c!color
     \columnsetspanparameter\c!before
     \ignorespaces}

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

\permanent\tolerant\protected\def\page_mvl_start_columnset_span_nop
  {\ignorenestedupto\startcolumnsetspan\stopcolumnsetspan} % todo: interface

\permanent\protected\def\stopcolumnsetspan % indirectness permits aliasing
  {\page_mvl_span_stop}

\permanent\protected\def\columnsethspan#1#2%
  {\ifconditional\c_page_mvl_active
     \clf_columnsethspan\currentcolumnset{#1}{#2}%
   \else
     \textwidth
   \fi}

\permanent\def\columnsetspanwidth#1% assumes equal distances, expanded
  {\todimension{%
    \ifconditional\c_page_mvl_active
       #1\d_page_mvl_column_width
      +#1\d_page_mvl_distance
      -  \d_page_mvl_distance
     \else
       \textwidth
     \fi
   }}

% areas

\installcorenamespace{columnsetarea}

\installframedcommandhandler \??columnsetarea {columnsetarea} \??columnsetarea

\setupcolumnsetarea
  [\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=,
   \c!sheet=\plusone,
   \c!state=\v!stop]

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

\appendtoks
     \clf_registercolumnsetarea {%
        name  {\currentcolumnsetarea}%
        kind  {\columnsetareaparameter\c!type}%
        sheet {\columnsetareaparameter\c!sheet}%
        state {\columnsetareaparameter\c!state}%
        c     {\columnsetareaparameter\c!x}%
        r     {\columnsetareaparameter\c!y}%
        nc    {\columnsetareaparameter\c!nx}%
        nr    {\columnsetareaparameter\c!ny}%
     }%
\to \everydefinecolumnsetarea

\permanent\tolerant\protected\def\setupcolumnsetareatext[#1]#*[#S#2]% a it like headers and footers, use setups
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \cdef\currentcolumnsetarea{#1}%
     \setcolumnsetareaparameter\c!text{#2}%
   \fi}

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

% used at the lua end: name,area.name,column,row,width,height,start,left

\permanent\protected\def\page_mvl_set_area#1#2#3#4#5#6#7#8% can be optimized
  {\begingroup
   \cdef\currentcolumnsetarea{#2}%
   \setcolumnsetareaparameter\c!width {#5\scaledpoint}%
   \setcolumnsetareaparameter\c!height{#6\scaledpoint}%
   \setbox\nextbox\hpack\bgroup\inheritedcolumnsetareaframed\bgroup
     \usecolumnsetareastyleandcolor\c!style\c!color
     \ignorespaces
     \columnsetareaparameter\c!text
   \egroup\egroup
   %
   \scratchdimen#8\scaledpoint
   \ifdim\scratchdimen>\zeropoint
     \setbox\scratchbox\vbox\bgroup
       \clip
         [     \c!offset=\columnsetareaparameter\c!clipoffset,%
          \c!rightoffset=\columnsetareaparameter\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=\columnsetareaparameter\c!clipoffset,%
          \c!leftoffset=\columnsetareaparameter\c!leftoffset,%
             \c!hoffset=\scratchdimen,%
               \c!width=\wd\nextbox-\scratchdimen,%
            % \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}

% sheets

\mutable\lettonothing\askedsheet
\mutable\lettonothing\askedsheetoption
\mutable\lettonothing\askedspreadsheets

\permanent\protected\defcsname\e!start\v!columnsetsheet\endcsname
  {\begingroup
   \obeylines
  %\lettonothing\currentcolumnset
   \cdef\askedsheet{1}%
   \page_mvl_sheet_start}

\permanent\protected\defcsname\e!stop\v!columnsetsheet\endcsname
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \clf_registercolumnsetsheet{\currentcolumnset}{\askedsheet}{\askedsheetoption}\relax
   \else
     \rawbuffer{page:mvl:temp}% no real need for using a buffer in this case
   \fi
   \endgroup}

\permanent\protected\defcsname\e!start\v!columnsetsheetdelayed\endcsname
  {\begingroup
   \obeylines
  %\lettonothing\currentcolumnset
   \cdef\askedsheet{1}%
   \page_mvl_sheet_start_delayed}

\permanent\protected\defcsname\e!stop\v!columnsetsheetdelayed\endcsname
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \clf_registercolumnsetsheet{\currentcolumnset}{\askedsheet}{\v!page}\relax
   \else
     \rawbuffer{page:mvl:temp}% no real need for usung a buffer in this case
   \fi
   \endgroup}

\tolerant\def\page_mvl_sheet_start_delayed[#1]#*[#2]%  columnset sheetnumber
  {\ifparameter#2\or
     \ifchknum#2\or
       \cdef\currentcolumnset{#1}%
       \cdef\askedsheet{#2}%
     \orelse\ifchknum#1\or
       \cdef\askedsheet{#1}%
     \fi
   \orelse\ifparameter#1\or
     \ifchknum#1\or
       \cdef\askedsheet{#1}%
     \fi
   \fi
   \grabbufferdatadirect{page:mvl:temp}{\e!start\v!columnsetsheetdelayed}{\e!stop\v!columnsetsheetdelayed}}

\tolerant\def\page_mvl_sheet_start[#1]#*[#2]#*[#3]%  columnset sheetnumber [page]
  {\ifparameter#2\or
     \ifchknum#2\or
       \cdef\currentcolumnset{#1}%
       \cdef\askedsheet{#2}%
       \cdef\askedsheetoption{#3}%
     \orelse\ifchknum#1\or
       \cdef\askedsheet{#1}%
       \cdef\askedsheetoption{#2}%
     \fi
   \orelse\ifparameter#1\or
     \ifchknum#1\or
       \cdef\askedsheet{#1}%
       \cdef\askedsheetoption{#2}%
     \fi
   \fi
   \grabbufferdatadirect{page:mvl:temp}{\e!start\v!columnsetsheet}{\e!stop\v!columnsetsheet}}

\permanent\protected\defcsname\e!start\v!columnsetspreadsheets\endcsname
  {\begingroup
   \obeylines
  %\lettonothing\currentcolumnset
   \cdef\askedspreadsheets{1}%
   \page_mvl_spreadsheets_start}

\permanent\protected\defcsname\e!stop\v!columnsetspreadsheets\endcsname
  {\ifcstok{\columnsetparameter\c!state}\v!start
     \clf_registercolumnsetspreadsheets{\currentcolumnset}{\askedspreadsheets}\relax
   \else
     \rawbuffer{page:mvl:temp}% no real need for usung a buffer in this case
   \fi
   \endgroup}

\tolerant\def\page_mvl_spreadsheets_start[#1]#*[#2]%  columnset spreadnumber
  {\ifparameter#2\or
     \ifchknum#2\or
       \cdef\currentcolumnset{#1}%
       \cdef\askedspreadsheets{#2}%
     \orelse\ifchknum#1\or
       \cdef\askedspreadsheets{#1}%
     \fi
   \orelse\ifparameter#1\or
     \ifchknum#1\or
       \cdef\askedspreadsheets{#1}%
     \fi
   \fi
   \grabbufferdatadirect{page:mvl:temp}{\e!start\v!columnsetspreadsheets}{\e!stop\v!columnsetspreadsheets}}

% we need a discard otr .. beware: these buffers are grouped

\newconditional\c_page_mvl_inside_specification

\cdef\m_page_mvl_buffer{page:mvl:temp} % todo low level buffer call

\def\page_mvl_process_sheet
  {\begingroup
   \c_page_mvl_inside_specification\conditionaltrue
   \setbox\scratchbox\vpack{\rawbuffer{\m_page_mvl_buffer}}%
   \endgroup}

\def\page_mvl_process_delayed
  {\begingroup
   \c_page_mvl_inside_specification\conditionaltrue
   \setbox\scratchbox\vpack{\rawbuffer{\m_page_mvl_buffer}}%
   \endgroup}

\def\page_mvl_process_spread
  {\begingroup
   \setbox\scratchbox\vpack{\rawbuffer{\m_page_mvl_buffer}}%
   \endgroup}

%D Experimental:

\installcorenamespace {subcolumnset}

\installcommandhandler \??subcolumnset {subcolumnset} \??subcolumnset

\pushoverloadmode

% \permanent\tolerant\protected\def\definesubcolumnset[#1]#*[#2]#*[#3]%
%   {\ifcsname\??subcolumnset#1\endcsname\else
%      \xdefcsname\??subcolumnset#1\endcsname{#2}%
%    \fi
%    \scratchcounter\clf_definesubcolumnset
%        name    {#1}%
%        subname {#2}%
%        columns {#3}%
%    \relax
%    \expandafter\integerdef\csname\??subcolumnset:#1:#2\endcsname\scratchcounter}

\permanent\tolerant\protected\def\definesubcolumnset[#1]#*[#2]#*[#3]%
  {\ifcsname\??subcolumnset#1\endcsname\else
     \xdefcsname\??subcolumnset#1\endcsname{#2}%
     \ifcsname\namedsubcolumnsethash#1:#2\s!parent\endcsname\else
       \edefcsname\??subcolumnset#1:#2:\s!parent\endcsname{\??subcolumnset#1}%
     \fi
   \fi
   \scratchcounter\clf_definesubcolumnset
       name    {#1}%
       subname {#2}%
       columns {#3}%
   \relax
   \expandafter\integerdef\csname\??subcolumnset:#1:#2\endcsname\scratchcounter}

\popoverloadmode

\newconditional\c_page_mvl_trace_n

\installtextracker{columnsets.mvl}
  {\c_page_mvl_trace_n\conditionaltrue}
  {\c_page_mvl_trace_n\conditionalfalse}

\def\page_mvl_sub_columnset_start#1%
   {\beginmvl
      \s!options {\ignoreprevdepthmvloptioncode+\discardtopmvloptioncode}%
      \s!index   {#1}%
    \relax
    \ifconditional\c_page_mvl_trace_n
      \writestatus\m!columnset{start sub mvl \number\mvlcurrentlyactive}%
    \fi}

\def\page_mvl_sub_columnset_stop
  {\ifconditional\c_page_mvl_trace_n
     \writestatus\m!columnset{stop sub mvl \number\mvlcurrentlyactive}%
   \fi
   \endmvl}

\def\page_mvl_main_mvl_begin
  {\beginmvl
     \s!options {\ignoreprevdepthmvloptioncode+\discardtopmvloptioncode}%
     \s!index   \plusone
   \relax
   \ifconditional\c_page_mvl_trace_n
     \writestatus\m!columnset{start main mvl \number\mvlcurrentlyactive}%
   \fi
   \ifcsname\??subcolumnset\currentcolumnset\endcsname
     \hsize\clf_columnsetcolumnwidth\currentcolumnset{\lastnamedcs}\relax
   \fi}

\def\page_mvl_main_mvl_end
  {\ifconditional\c_page_mvl_trace_n
     \writestatus\m!columnset{stop main mvl \number\mvlcurrentlyactive}%
   \fi
   \endmvl}

% beware: width settings ... has changed

% \permanent\tolerant\protected\def\startsubcolumnset[#1]#*[#2]% #,[#1]#,#*[#2]
%   {\unless\ifconditional\c_page_mvl_active
%      \par
%    \orelse\ifcase\c_page_mvl_level
%      \page_mvl_main_mvl_end
%      \let\page_mvl_main_mvl_end\relax
%    \fi
%    \begingroup
%    \advanceby\c_page_mvl_level\plusone
%    \ifnum\c_page_mvl_level=\plusone
%      \ifhastok={#1}%
%        \cdef\currentsubcolumnset{\currentcolumnset:}%
%        \setupcurrentsubcolumnset[#1]%
%      \else
%        \cdef\currentsubcolumnset{\currentcolumnset:#1}%
%        \ifparameter#2\or
%          \setupcurrentsubcolumnset[#2]%
%        \fi
%      \fi
%      \uselanguageparameter\subcolumnsetparameter
%      \usesubcolumnsetstyleandcolor\c!style\c!color
%      \usealignparameter\subcolumnsetparameter
%      \hsize\clf_columnsetcolumnwidth\currentcolumnset{#1}%
%      \scratchcounter\ifcsname\??subcolumnset:\currentsubcolumnset\endcsname\lastnamedcs\else\plusone\fi
%      \ifconditional\c_page_mvl_active
%        \page_mvl_sub_columnset_start\scratchcounter
%      \else
%        \subcolumnsetparameter\c!before
%      \fi
%    \fi}

\lettonothing\currentsubcolumnsetname

\permanent\tolerant\protected\def\startsubcolumnsetgroup[#1]#*[#2]% #,[#1]#,#*[#2]
  {\begingroup
   \advanceby\c_page_mvl_level\plusone
   \ifnum\c_page_mvl_level=\plusone
     \ifhastok={#1}%
       \cdef\currentsubcolumnset{\currentcolumnset:}%
       \lettonothing\currentsubcolumnsetname
       \setupcurrentsubcolumnset[#1]%
     \else
       \cdef\currentsubcolumnset{\currentcolumnset:#1}%
       \cdef\currentsubcolumnsetname{#1}%
       \ifparameter#2\or
         \setupcurrentsubcolumnset[#2]%
       \fi
     \fi
     \uselanguageparameter\subcolumnsetparameter
     \usesubcolumnsetstyleandcolor\c!style\c!color
     \usealignparameter\subcolumnsetparameter
    %\hsize\clf_columnsetcolumnwidth\currentcolumnset{#1}%
     \hsize\clf_columnsetcolumnwidth\currentcolumnset\currentsubcolumnsetname % adapted
   \fi}

\permanent\protected\def\stopsubcolumnsetgroup
  {\endgroup}

\permanent\tolerant\protected\def\startsubcolumnset[#1]#*[#2]% #,[#1]#,#*[#2]
  {\unless\ifconditional\c_page_mvl_active
     \par
   \orelse\ifcase\c_page_mvl_level
     \page_mvl_main_mvl_end
     \let\page_mvl_main_mvl_end\relax
   \fi
   \begingroup
   \advanceby\c_page_mvl_level\plusone
   \ifnum\c_page_mvl_level=\plusone
     \ifhastok={#1}%
       \cdef\currentsubcolumnset{\currentcolumnset:}%
       \lettonothing\currentsubcolumnsetname
       \setupcurrentsubcolumnset[#1]%
     \else
       \cdef\currentsubcolumnset{\currentcolumnset:#1}%
       \cdef\currentsubcolumnsetname{#1}%
       \ifparameter#2\or
         \setupcurrentsubcolumnset[#2]%
       \fi
     \fi
     \uselanguageparameter\subcolumnsetparameter
     \usesubcolumnsetstyleandcolor\c!style\c!color
     \usealignparameter\subcolumnsetparameter
    %\hsize\clf_columnsetcolumnwidth\currentcolumnset{#1}%
     \hsize\clf_columnsetcolumnwidth\currentcolumnset\currentsubcolumnsetname % adapted
     \scratchcounter\ifcsname\??subcolumnset:\currentsubcolumnset\endcsname\lastnamedcs\else\plusone\fi
     \ifconditional\c_page_mvl_active
       \page_mvl_sub_columnset_start\scratchcounter
     \else
       \subcolumnsetparameter\c!before
     \fi
   \fi}

\permanent\protected\def\stopsubcolumnset
  {\unless\ifconditional\c_page_mvl_active
     \par
     \subcolumnsetparameter\c!after
   \orelse\ifnum\c_page_mvl_level=\plusone
     \page_mvl_sub_columnset_stop
   \fi
   \endgroup}

% \startsetups example:balance
%     \balancevsize            \vsize
%     \balancetopskip          \strutht
%     \balancebottomskip       \strutdp
%     \balanceadjdemerits      10000
%     \balancetolerance        10 % or 0
%   % \balanceemergencystretch 1\lineheight
% \stopsetups

%D The balancing code is kind of complex with call outs to \LUA\ because we store
%D specification and states there. Much of what is below can therefore as well be
%D done at the \LUA\ end but it is also a demonstration of some recent (2024)
%D \LUAMETATEX\ primitives. Eventually I might decide to do more in \LUA\ and
%D comment code here. Performance is no argument, clearity is, although the \LUA\
%D end also needs a cleanup (some old code in there).

\newconditional\c_page_mvl_balancing
\newconditional\c_page_mvl_trace
\newconditional\c_page_mvl_preroll_quit

\newconditional\c_page_mvl_inserts       \c_page_mvl_inserts      \conditionaltrue
\newconditional\c_page_mvl_split_inserts \c_page_mvl_split_inserts\conditionaltrue
\newconditional\c_page_mvl_discard       \c_page_mvl_discard      \conditionaltrue

\newbox        \b_page_mvl_collected_content
\newbox        \b_page_mvl_split_content
\newbox        \b_page_mvl_current_content

\newinteger    \c_page_mvl_global_dead_cycles
\newinteger    \c_page_mvl_local_dead_cycles
\newinteger    \c_page_mvl_current_n_of_slots
\newinteger    \c_page_mvl_previous_n_of_slots

\newinteger    \c_page_mvl_balance_dead_cycles
\newinteger    \c_page_mvl_balance_boundary
\newinteger    \c_page_mvl_balance_n_of_slots
\newinteger    \c_page_mvl_balance_n_of_sheets
\newinteger    \c_page_mvl_balance_n_of_columns
\newinteger    \c_page_mvl_balance_first_htdp   % gone

\lettonothing  \d_d_page_mvl_htdp % \mutable

\def\c_page_mvl_balance_sheet{\columnsetshapepage\currentcolumnset\c_page_mvl_current_n_of_slots}

\newinteger\c_page_mvl_htdp_options \c_page_mvl_htdp_options\numexpr
    \defaultspecificationoptioncode
  + \doublespecificationoptioncode
  + \rotatespecificationoptioncode
\relax

\newinteger\c_page_mvl_balance_extra
\newinteger\c_page_mvl_balance_first
\newinteger\c_page_mvl_balance_last
\newinteger\c_page_mvl_balance_page  % redundant, used for tracing

\newinteger\globaldeadcycles \globaldeadcycles\plusonethousand
\newinteger\localdeadcycles  \localdeadcycles \plushundred

\def\page_mvl_process_mvl_preroll_step
  {\ifconditional\c_page_mvl_inserts
     \ifconditional\c_page_mvl_split_inserts
       \vbalanceddeinsert\scratchboxone
         \s!descend \relaxedspace
         \s!forcedepth
       \relax
     \fi
   \fi
   \setbox\b_page_mvl_split_content\vbalance\scratchboxone\s!trial\relax
   \c_page_mvl_current_n_of_slots \zerocount
   \c_page_mvl_local_dead_cycles  \localdeadcycles
   \c_page_mvl_previous_n_of_slots\zerocount
   \c_page_mvl_global_dead_cycles \globaldeadcycles
   %
   \d_page_mvl_last_ht \zeropoint
   \d_page_mvl_last_dp \zeropoint
   %
   \relax
   \localcontrolledendless {%
     \ifcase\c_page_mvl_local_dead_cycles
       \writestatus\m!columnset\empty
       \writestatus\m!columnset{quitting '\currentcolumnset' due to local deadcyling}%
       \writestatus\m!columnset\empty
       \quitloop
     \orelse\ifcase\c_page_mvl_global_dead_cycles
       \writestatus\m!columnset\empty
       \writestatus\m!columnset{quitting '\currentcolumnset' due to global deadcyling}%
       \writestatus\m!columnset\empty
       \quitloop
     \orelse\ifvoid\b_page_mvl_split_content
       \quitloop
     \else
       \advanceby\c_page_mvl_current_n_of_slots\plusone
       \setbox\b_page_mvl_current_content\vbalancedbox\b_page_mvl_split_content
       \scratchheight\balanceshapevsize\c_page_mvl_current_n_of_slots\relax
       \scratchdimen{\ht\b_page_mvl_current_content-\scratchheight}%
       \d_page_mvl_last_ht\ht\b_page_mvl_current_content
       \d_page_mvl_last_dp\dp\b_page_mvl_current_content
       \ifconditional\c_page_mvl_balancing
         \d_d_page_mvl_htdp\currentloopiterator\d_page_mvl_last_ht\d_page_mvl_last_dp
       \fi
       \ifdim\scratchdimen>\zeropoint
         \ifnum\clf_columnsetsetshapeextra\currentcolumnset\c_page_mvl_current_n_of_slots=\plusone
          %\writestatus\m!columnset\empty
          %\writestatus\m!columnset{set '\currentcolumnset', slot \the\c_page_mvl_current_n_of_slots, target \the\scratchheight, height \the\ht\b_page_mvl_current_content, delta \the\scratchdimen}%
          %\writestatus\m!columnset\empty
           \clf_columnsetreshape\currentcolumnset
           \setbox\b_page_mvl_split_content\vbalance\scratchboxone\s!trial\relax
           \advance\c_page_mvl_global_dead_cycles\minusone
           \ifnum\c_page_mvl_current_n_of_slots>\c_page_mvl_previous_n_of_slots
             \c_page_mvl_local_dead_cycles\plushundred
           \else
             \advance\c_page_mvl_local_dead_cycles\minusone
           \fi
           \c_page_mvl_current_n_of_slots\zerocount
         \else
           \c_page_mvl_previous_n_of_slots\c_page_mvl_current_n_of_slots
         \fi
       \else
         \c_page_mvl_previous_n_of_slots\c_page_mvl_current_n_of_slots
       \fi
     \fi}%
     }

\def\page_mvl_process_mvl_preroll_balance_more
  {\localcontrolledloop \c_page_mvl_balance_first\c_page_mvl_balance_last \plusone {%
     \ifcase\clf_columnsetsetshapeextra\currentcolumnset\currentloopiterator\relax
       \c_page_mvl_balance_dead_cycles\plustwohundred
     \fi}%
   \ifconditional\c_page_mvl_trace
     \writestatus\m!columnset{more: \the\c_page_mvl_balance_first..\the\c_page_mvl_balance_last}%
     \columnsetshowshape\currentcolumnset
   \fi
   \clf_columnsetreshape\currentcolumnset\relax
   \page_mvl_process_mvl_preroll_step\relax}

\def\page_mvl_process_mvl_preroll_balance_less
  {\localcontrolledloop \c_page_mvl_balance_first\c_page_mvl_balance_last \plusone {%
     \ifcase\clf_columnsetresetshapeextra\currentcolumnset\currentloopiterator\relax
       \c_page_mvl_balance_dead_cycles\plustwohundred
     \fi}%
    \ifconditional\c_page_mvl_trace
     \writestatus\m!columnset{less: \the\c_page_mvl_balance_first..\the\c_page_mvl_balance_last}%
     \columnsetshowshape\currentcolumnset
   \fi
   \clf_columnsetreshape\currentcolumnset\relax
   \page_mvl_process_mvl_preroll_step\relax}

\def\page_mvl_process_mvl_preroll_balance
  {\relax
   \ifcase\c_page_mvl_current_n_of_slots
   \orelse\ifcase\c_page_mvl_local_dead_cycles
   \orelse\ifcase\c_page_mvl_global_dead_cycles
   \orelse\ifconditional\c_page_mvl_balancing
     \ifconditional\c_page_mvl_trace
       \writestatus\m!columnset{balancing \the\c_page_mvl_current_n_of_slots\space slots}%
       \columnsetshowshape\currentcolumnset
     \fi
     % we need to make sure we add shapes for the rest of the spread / sheet
     \clf_columnsetshapebalanceextend\currentcolumnset{\c_page_mvl_current_n_of_slots+\nofcolumns}% can be automatic
     \clf_columnsetshapesetbalancerange\currentcolumnset\c_page_mvl_current_n_of_slots
     \c_page_mvl_balance_n_of_slots\columnsetshapeslots\currentcolumnset
     \c_page_mvl_balance_first\clf_columnsetbalancefirst\currentcolumnset
     \c_page_mvl_balance_last\clf_columnsetbalancelast\currentcolumnset
     \c_page_mvl_balance_page\clf_columnsetbalancepage\currentcolumnset
     \ifnum\c_page_mvl_balance_last !>\c_page_mvl_balance_first
       \writestatus\m!columnset\empty
       \writestatus\m!columnset{quit balancing, no valid slot in sheet \the\c_page_mvl_balance_page}%
       \writestatus\m!columnset\empty
       \c_page_mvl_preroll_quit\conditionaltrue
     \orelse\ifcase\clf_columnsetshapebalancecheck\currentcolumnset\c_page_mvl_balance_first\relax
% not yet ok on right sheet while actually we are on the next
       \writestatus\m!columnset\empty
       \writestatus\m!columnset{quit balancing, multiple slots in sheet \the\c_page_mvl_balance_page}%
       \writestatus\m!columnset\empty
       \c_page_mvl_preroll_quit\conditionaltrue
     \or
       \ifconditional\c_page_mvl_trace
         \writestatus\m!columnset{analyzed,
           \the\c_page_mvl_balance_n_of_slots\space slots,
           sheet \the\c_page_mvl_balance_page,
           first \the\c_page_mvl_balance_first,
           last  \the\c_page_mvl_balance_last,
           index \the\c_page_mvl_current_n_of_slots
         }%
         \columnsetshowshape\currentcolumnset
       \fi
       % we are one ahead as we have the generic shape slot too
       \advanceby\c_page_mvl_balance_n_of_slots\minusone
       \c_page_mvl_balance_extra{\c_page_mvl_balance_n_of_slots-\c_page_mvl_current_n_of_slots}%
       \c_page_mvl_balance_n_of_sheets\columnsetshapepage\currentcolumnset\c_page_mvl_current_n_of_slots
       \ifconditional\c_page_mvl_trace
         \writestatus\m!columnset{\the\c_page_mvl_balance_extra\space extra slots}%
         \writestatus\m!columnset{balancing sheet \the\c_page_mvl_balance_n_of_sheets}%
       \fi
       %
       \c_page_mvl_balance_n_of_columns\nofcolumns % \c_page_mvl_balance_n_of_slots
       \c_page_mvl_balance_boundary{\c_page_mvl_balance_first+\minusone}%
       %
       \c_page_mvl_balance_dead_cycles\zerocount
       \localcontrolledendless {%
         \advanceby\c_page_mvl_balance_dead_cycles\plusone
         \page_mvl_process_mvl_preroll_balance_more
         \ifnum\c_page_mvl_balance_dead_cycles !<\localdeadcycles\relax % todo: its own one
           \ifconditional\c_page_mvl_trace
             \writestatus\m!columnset{quit balancing, dead cycles}%
           \fi
           \page_mvl_process_mvl_preroll_balance_less
           \quitloop
         \orelse\ifcase\c_page_mvl_current_n_of_slots\relax
           \ifconditional\c_page_mvl_trace
             \writestatus\m!columnset{quit balancing, no slots}%
           \fi
           \page_mvl_process_mvl_preroll_balance_less
           \quitloop
         \orelse\ifnum\c_page_mvl_balance_sheet>\c_page_mvl_balance_n_of_sheets\relax
           \page_mvl_process_mvl_preroll_balance_less
           \ifconditional\c_page_mvl_trace
             \writestatus\m!columnset{quit balancing, reached}%
             \columnsetshowshape\currentcolumnset
           \fi
           \quitloop
         \fi}%
     \fi
  \fi}

\protected\def\page_mvl_process_mvl_preroll
  {\relax
  %\balancetolerance        \plustwohundred
   \balancevsize            \vsize
   \balancetopskip          \strutht    % set otherwise
   \balancebottomskip       \strutdp
   \balanceemergencystretch \lineheight
   %balanceemergencyshrink  \lineheight
   \usesetupsparameter\columnsetparameter
   \clf_columnsetshape\currentcolumnset
   \forgetall
   \dontcomplain
   \resetgridsnapping
   \resetgridlinesnapping
   \specificationdef\d_d_page_mvl_htdp\dimen
      {\nofcolumns}%
      \s!options \c_page_mvl_htdp_options
      \zeropoint \zeropoint
   \relax
   \c_page_mvl_preroll_quit\conditionalfalse
   \ifconditional\c_page_mvl_trace
     \writestatus\m!columnset{before preroll, shapes \the\columnsetshapecount\currentcolumnset}%
     \columnsetshowshape\currentcolumnset
     \page_mvl_process_mvl_preroll_step
     \writestatus\m!columnset{after  preroll, shapes \the\columnsetshapecount\currentcolumnset, slots \the\c_page_mvl_current_n_of_slots}%
     \columnsetshowshape\currentcolumnset
   \else
     \page_mvl_process_mvl_preroll_step
   \fi
   \page_mvl_process_mvl_preroll_balance}

% TODO: no need for notes that are not used, we can have some flag per
% note

\def\page_mvl_place_note_inserts
  {\c_strc_notes_first_placed\conditionalfalse
   \strc_notes_process\page_mvl_place_note_inserts_indeed}

\def\page_mvl_place_note_inserts_indeed % similar to page
  {\setbox\b_strc_notes_inserts\vbalancedinsert\b_page_mvl_current_content
     \s!index \currentnoteinsertionnumber
     \s!descend
   \relax
   \ifvoid\b_strc_notes_inserts\else
     \ifcase\insertmultiplier\currentnoteinsertionnumber\else
       \strc_notes_place_inserts_very_indeed\relax
       \c_strc_notes_first_placed\conditionaltrue
     \fi
   \fi}

\def\page_mvl_process_mvl_final
  {\clf_columnsetreshape\currentcolumnset
   \setbox\scratchboxtwo\vbalance\scratchboxone\relax % otherwise loop expands
   \ifconditional\c_page_mvl_discard
     \vbalanceddiscard\scratchboxtwo
       \s!descend
     \relax
   \fi
   \localcontrolledendless {%
     \ifvoid\scratchboxtwo
       \expandafter\quitloop
     \else
       \setbox\b_page_mvl_current_content\page_mvl_show_slot\bgroup\vbalancedbox\scratchboxtwo\egroup
       \ifconditional\c_page_mvl_inserts
         \ifconditional\c_page_mvl_split_inserts
           \vbalancedreinsert\b_page_mvl_current_content
              \s!descend
           \relax
         \fi
         \ifnum\boxinserts\b_page_mvl_current_content>\plusthree
           \setbox\scratchboxfour\vpack to \ht\b_page_mvl_current_content\bgroup
             \page_mvl_top_insertions
             \vfill
             \page_mvl_bottom_insertions
             \page_mvl_place_note_inserts
           \egroup
           \ifvoid\scratchboxfour\else
             \setbox\b_page_mvl_current_content\hpack to \wd\b_page_mvl_current_content\bgroup
               \wd\b_page_mvl_current_content\zeropoint
               \getnoflines\d_page_mvl_top_insertions_height
               \boxyoffset\b_page_mvl_current_content-\noflines\lineheight
             % \boxyoffset\b_page_mvl_c urrent_content-\d_page_mvl_top_insertions_height % only when testing overlap
               \box\b_page_mvl_current_content
               \box\scratchboxfour
             \egroup
           \fi
         \fi
       \fi
       \boxyoffset\b_page_mvl_current_content-\strutdp
       \clf_addtocolumnsetmvl\currentcolumnset\b_page_mvl_current_content\currentloopiterator
   \fi}}

\installtextracker{columnsets.keepdiscard}
  {\c_page_mvl_discard\conditionalfalse}
  {\c_page_mvl_discard\conditionaltrue}

\def\page_mvl_process_mvl_flush
  {\clf_columnsetreshape\currentcolumnset
   \setbox\b_page_mvl_split_content\vbalance\scratchboxone\relax % otherwise loop expands
   \ifconditional\c_page_mvl_discard
     \vbalanceddiscard\b_page_mvl_split_content
       \s!descend
     \relax
   \fi
   \localcontrolledendless {%
     \ifvoid\b_page_mvl_split_content
       \expandafter\quitloop
     \else
       \setbox\b_page_mvl_current_content\page_mvl_show_slot\bgroup\vbalancedbox\b_page_mvl_split_content\egroup
       \ifconditional\c_page_mvl_inserts
         \ifconditional\c_page_mvl_split_inserts
           \vbalancedreinsert\b_page_mvl_current_content
             \s!descend
           \relax
         \fi
         \ifnum\boxinserts\b_page_mvl_current_content>\plusthree
           \donetrue
         \else
           \donefalse
         \fi
       \else
         \donefalse
       \fi
       \ifdone
         \setbox\scratchboxfour\vpack to \ht\b_page_mvl_current_content\bgroup
           \page_mvl_top_insertions
           \vfill
           \page_mvl_bottom_insertions
           \page_mvl_place_note_inserts
         \egroup
         \ifvoid\scratchboxfour\else
           \setbox\b_page_mvl_current_content\hpack to \wd\b_page_mvl_current_content\bgroup
             \wd\b_page_mvl_current_content\zeropoint
             \box\b_page_mvl_current_content
             \box\scratchboxfour
           \egroup
         \fi
         \boxyoffset\b_page_mvl_current_content-\strutdp
         \clf_addtocolumnsetmvl\currentcolumnset\b_page_mvl_current_content\currentloopiterator
       \else
         \boxyoffset\b_page_mvl_current_content-\strutdp
         \ifvoid\b_page_mvl_split_content
           \boxyoffset\b_page_mvl_current_content-\dimexpr\ht\b_page_mvl_current_content-\d_page_mvl_last_ht\relax
           \ht\b_page_mvl_current_content\d_page_mvl_last_ht
           \dp\b_page_mvl_current_content\d_page_mvl_last_dp
           \clf_subtocolumnsetmvl\currentcolumnset\b_page_mvl_current_content\currentloopiterator
         \else\ifconditional\c_page_mvl_balancing
           \ifnum\currentloopiterator>\c_page_mvl_balance_boundary
             \scratchheight\d_d_page_mvl_htdp\numexpr\currentloopiterator\relax\plusone
             \scratchdepth \d_d_page_mvl_htdp\numexpr\currentloopiterator\relax\plustwo
             \boxyoffset\b_page_mvl_current_content{\scratchheight-\ht\b_page_mvl_current_content}%
             \ht\b_page_mvl_current_content\scratchheight
             \dp\b_page_mvl_current_content\scratchdepth
             \clf_subtocolumnsetmvlbalance\currentcolumnset\b_page_mvl_current_content\currentloopiterator
           \else
             \clf_addtocolumnsetmvl\currentcolumnset\b_page_mvl_current_content\currentloopiterator
           \fi
         \else
           \clf_addtocolumnsetmvl\currentcolumnset\b_page_mvl_current_content\currentloopiterator
         \fi
        \fi
       \fi
   \fi}}

\def\page_mvl_process_mvl
  {\page_mvl_process_mvl_preroll
   \page_mvl_process_mvl_final}

\def\page_mvl_flush_mvl
  {\page_mvl_process_mvl_preroll
   \ifconditional\c_page_mvl_preroll_quit
     \page_mvl_process_mvl_final
   \else
     \page_mvl_process_mvl_flush
   \fi}

\def\page_mvl_intermediate#1%
  {\clf_presetcolumnsetspreadsheets\currentcolumnset
   \clf_presetcolumnsetsheets\currentcolumnset
   \clf_columnsetlimit\currentcolumnset
   \begingroup
   \dontcomplain
   \scratchcounterone\plustwo
   \scratchcountertwo\columnsetlastmvl{\currentcolumnset}\relax % lookahead
   \ifnum\scratchcounterone>\scratchcountertwo
     \scratchcounterone\plusone
     \scratchcountertwo\plusone
   \fi
   \ifconditional\c_page_mvl_trace_n
     \writestatus\m!columnset{intermediate mlv: \the\scratchcounterone ..\the\scratchcountertwo}%
   \fi
   \localcontrolledloop \scratchcounterone \scratchcountertwo \plusone {%
     \clf_setcolumnsetmvl{\currentcolumnset}\currentloopiterator\relax
     \clf_gotocolumnsetslot{\currentcolumnset}\relax
     \setbox\scratchboxone\flushmvl\currentloopiterator\relax
     #1%
   }%
   \endgroup}

\permanent\protected\def\flushcolumnset
  {\ifconditional\c_page_mvl_active
     \page_mvl_intermediate\page_mvl_flush_mvl
   \fi}

\permanent\protected\def\processcolumnset
  {\ifconditional\c_page_mvl_active
     \page_mvl_intermediate\page_mvl_process_mvl
   \fi}

\permanent\tolerant\protected\def\balancesubcolumnsets[#1]%
  {\unless\ifconditional\c_page_mvl_active
     % do nothing
%    \orelse\ifcase\columnsetlastmvl{\currentcolumnset}\or
   \else%\ifcase\columnsetlastmvl{\currentcolumnset}\or
    % messy, we're counting mvls from 2 if we have subs
    %\writestatus{>>>>}{\the\columnsetlastmvl{\currentcolumnset}}%
     \c_page_mvl_balancing\conditionaltrue
     \flushsubcolumnsets[#1]%
     \c_page_mvl_balancing\conditionalfalse
%    \else
%      \flushsubcolumnsets[#1]%
   \fi
   \relax}

\protected\def\page_mvl_command_flush_page
  {\ifnum\c_page_mvl_main_level>\plusone
     \page_mvl_flush_nested_page
   \else % e.g. specific backgrounds
     \clf_delayedcolumnsetsheet\currentcolumnset
   \fi
   \setbox\b_page_mvl_collected\hpack\bgroup
     \clf_preparecolumnsetflush{\currentcolumnset}%
     \global\setbox\globalscratchbox\emptybox
     \page_mvl_show_state
     \letcolumnsetparameter\c!region\currentcolumnset
     \ifcstok{\columnsetparameter\c!direction}\v!reverse
       \dostepwiserecurse\c_page_mvl_last_column\c_page_mvl_first_column\minusone
         {\scratchdistance
            \ifnum##1>\plusone
              {\namedcolumnsetparameter{\currentcolumnset:##1}\c!distance}%
            \else
              \zeropoint
            \fi
          \page_mvl_command_flush_page_column{##1}\scratchdistance}%
     \else
       \dostepwiserecurse\c_page_mvl_first_column\c_page_mvl_last_column\plusone
         {\scratchdistance
            \ifnum##1<\c_page_mvl_last_column
              {\namedcolumnsetparameter{\currentcolumnset:##1}\c!distance}%
            \else
              \zeropoint
            \fi
          \page_mvl_command_flush_page_column{##1}\scratchdistance}%
     \fi
     \clf_finishcolumnsetflush{\currentcolumnset}%
   \egroup
   \setbox\b_page_mvl_collected\hpack\bgroup
     \wd\globalscratchbox\zeropoint
     \box\globalscratchbox
     \box\b_page_mvl_collected
   \egroup
   \ifnum\c_page_mvl_main_level>\plusone
     \page_mvl_flush_nested_page
   \else
     \page_boxes_shipout{\page_boxes_constructed_page\box\b_page_mvl_collected}% \hbox removed
     \strc_pagenumbers_increment_counters % should hook into an every
   \fi}

\def\page_mvl_flush_nested_page
  {\begingroup
   \scratchtotal \ht\b_page_mvl_collected
   \boxyoffset\b_page_mvl_collected{-\scratchtotal+\strutht}%
   \clf_putincolumnsetdirect {
     name     {\maincolumnset}%
     box       \b_page_mvl_collected
     location {\columnsetparameter\c!location}%
     lines    {\columnsetparameter\c!lines}%
   }%
  %\columnsetshowgrid\maincolumnset
   \endgroup}

\permanent\tolerant\protected\def\flushsubcolumnsets[#1]%
  {\begingroup
   \dontcomplain
   \automigrationmode\zerocount
   \flushcolumnset
   % todo: numbers
   \clf_columnsetsblockrows\currentcolumnset{#1}\columnsetlastfuture\currentcolumnset\relax
   \endgroup}

\permanent\protected\def\blockcolumnsetrows
  {\ifconditional\c_page_mvl_active
     % maybe left and right keys, currently spread
     \clf_columnsetsblockrows\currentcolumnset{\v!spread}\columnsetlastfuture\currentcolumnset\relax
   \fi}

% We start an mvl so whatever is there wil be flushed afterwards. Actually we don't
% end up in the output routine because we intercept and directly shipout. So we can
% just assume the main single column one to work.

\protected\def\page_mvl_command_routine
  {\page_mvl_command_set_vsize}

% \setupfloats
%   [spacebefore=halflinebefore,
%    spaceafter=halflineafter]

% \setupfloats
%   [spacebefore=halfline, % maybe spacearound
%    spaceafter=halfline]

\def\page_mvl_place_float_force
  {\let\floatmethod\v!force
   \ifdim\wd\floatbox>\columnwidth
     \page_floats_save\s!text % check this
   \else
     \begingroup
     \edef\p_spacebefore{\floatparameter\c!spacebefore}%
     \edef\p_spaceafter {\floatparameter\c!spaceafter}%
     \ifx\p_spacebefore\v!halfline
       \blank[\v!keep,\v!halfline]% \direct...
     \else
       \blank[\p_spacebefore]%
     \fi
    %\snaptogrid\vpack\bgroup
     \vpack\bgroup
       \getnoflines{\ht\floatbox}%
       \scratchheight{\noflines\lineheight-\strutdp}%
       \boxyoffset\floatbox{\ht\floatbox-\scratchheight}%
       \ht\floatbox\scratchheight
       \dp\floatbox\zeropoint
       \box\floatbox
     \egroup
     \ifx\p_spacebefore\v!halfline % we check before here
       \blank[\v!halfline]%
     \else
       \blank[\p_spaceafter]%
     \fi
     \endgroup
   \fi}

\def\page_mvl_break#1%
  {\directcheckedvspacing\v!back
   \ifconditional\c_page_mvl_active
     \begingroup
     \forgetall
     \par
     \balanceboundary#1\plusone\relax
     \scratchcounter{\columnsetshapeworst\currentcolumnset+\plusone}%
     \multiplyby\scratchcounter\plustwo
     \localcontrolledrepeat \scratchcounter
       {\vskip\zeropoint
        \balanceboundary#1\zerocount}%
     \par
     \balanceboundary\zerocount\zerocount\relax
     \endgroup
     % good enough but it should be a property of \balanceboundary or
     % we could actually intercept it in spac-ver
  % \inhibitblank
  % \nowhitespace
    \inhibitallspacing
   \fi}

\protected\def\page_mvl_command_next_spread{\page_mvl_break\plusone}
\protected\def\page_mvl_command_next_page  {\page_mvl_break\plustwo}
\protected\def\page_mvl_command_next_column{\page_mvl_break\plusthree}

\protected\def\page_mvl_command_next_slot
  {\ifconditional\c_page_mvl_active
     \begingroup
     \forgetall
     \par
     \balanceboundary\plusfour\plusone\relax
     \endgroup
   \fi}

\protected\def\page_mvl_command_test_column[#1][#2]% we ignore the second argument
  {\ifconditional\c_page_mvl_active
     \ifchknumber#1\or
       \balanceboundary\plusfive\lastchknumber
     \orelse\ifchkdimension#1\or
       \balanceboundary\plussix\lastchkdimension
     \else
       % error
     \fi
   \fi}

% todo: also make this installable

%installpagebreakmethod              \v!unknown{\page_mvl_command_next_page}
%installpagebreakmethod              \v!yes    {\page_mvl_command_next_page}
\installpagebreakmethod              \v!spread {\page_mvl_command_next_spread}

\installcolumnbreakmethod\s!columnset\s!unknown{\page_mvl_command_next_column}
\installcolumnbreakmethod\s!columnset\v!yes    {\page_mvl_command_next_column}
\installcolumnbreakmethod\s!columnset\v!slot   {\page_mvl_command_next_slot}

\installcolumnbreakmethod\s!columnset\v!here   {\flushcolumnset}
\installcolumnbreakmethod\s!columnset\v!force  {\processcolumnset}

%D Spanning all columns (single column mode):

% \setuplayout[grid=yes]
%
% \definecolumnset[example][n=2]
%
% \definesubcolumnset[example][1][1,3]
% \definesubcolumnset[example][2][2,4]
%
% \startcolumnsetsheet[example][2]
%   \startsetcolumnset[c=3,r=1]
%     \framed
%       [width=\columnsetspanwidth{1},
%        height=6\lineheight,
%        background=color,
%        backgroudncolor=darkyellow]{TEST}
%   \stopsetcolumnset
% \stopcolumnsetsheet
%
% \starttext
%     \null\page
%     \startcolumnset[example]
%         \startsubcolumnset[1]
%             \dorecurse{2}{\samplefile{ward}\par}
%         \stopsubcolumnset
%         \startsubcolumnset[2]
%             \dorecurse{1}{\samplefile{knuth}\par}
%         \stopsubcolumnset
%        % \startsubcolumnset[1] % automatic
%          \startwidecolumnset
%              \red \dorecurse{2}{
%                 \begstrut\samplefile{tufte}\endstrut\par
%             }
%          \stopwidecolumnset
%        % \stopsubcolumnset
%         \startsubcolumnset[1]
%             \dorecurse{10}{\samplefile{ward}\par}
%         \stopsubcolumnset
%     \stopcolumnset
% \stoptext

% \enabletrackers[columnsets.keepdiscard]

\def\page_mvl_wide_before
  {\begingroup
   \unless\ifempty{\subcolumnsetparameter\c!top}%
     \forgetall \par \vskip\zeropoint % skip not really needed
     \ruledvbox
       \s!discardable
       {\hpack{\strut\lastnamedcs}}%
     \par
   \orelse\ifcstok{\subcolumnsetparameter\c!spacebefore}\v!line
     \forgetall \par \vskip\zeropoint
     \hrule
       \s!discardable
       \s!width  \emwidth
       \s!height \strutht
       \s!depth  \strutdp
     \relax
     \par
   \fi
   \endgroup
   \hsize\makeupwidth\relax}

\def\page_mvl_wide_after
  {\begingroup
   \unless\ifempty{\subcolumnsetparameter\c!bottom}%
     \forgetall \par \vskip\zeropoint
     \ruledvbox
       \s!discardable
       {\hpack{\strut\lastnamedcs}}%
     \penalty\minusone % really needed to trigger a flush
     \par
   \orelse\ifcstok{\subcolumnsetparameter\c!spaceafter}\v!line
     \forgetall \par \vskip\zeropoint % skip not really needed
     \hrule
       \s!discardable
       \s!width  \emwidth
       \s!height \strutht
       \s!depth  \strutdp
     \relax
     \par
   \fi
   \endgroup}

\permanent\tolerant\protected\def\page_mvl_start_wide_yes[#1]%
  {\flushsubcolumnsets\relax
   \begingroup
  %\ifnum\columnsetlastmvl{\currentcolumnset}=\plusone
   \ifnum\columnsetlastmvl{\currentcolumnset}=\plusthree % changeD
     \startsubcolumnset[1][\c!width=\makeupwidth,#1]\relax
     \page_mvl_wide_before\relax
     \enforced\let\stopwidecolumnset\page_mvl_stop_wide_yes
   \else
     \enforced\let\stopwidecolumnset\page_mvl_stop_wide_nop
   \fi
   \enforced\let\startwidecolumnset\page_mvl_start_wide_nop}

\permanent\tolerant\protected\def\page_mvl_start_wide_nop[#1]%
  {\flushsubcolumnsets
   \begingroup}

\aliased\let\startwidecolumnset\page_mvl_start_wide_yes
\aliased\let\stopwidecolumnset \relax

\permanent\protected\def\page_mvl_stop_wide_yes
  {\par
   \page_mvl_wide_after\relax
   \stopsubcolumnset
   % hm:
   \startsubcolumnset\relax
   \stopsubcolumnset
   \endgroup
   \clf_columnsetenablewide\currentcolumnset\relax
   \flushsubcolumnsets\relax
   \clf_columnsetdisablewide\currentcolumnset\relax}

\permanent\protected\def\page_mvl_stop_wide_nop
  {\par
   \endgroup
   \flushsubcolumnsets}

%D

\defineoutputroutine
  [\s!columnset]
  [\s!page_otr_command_routine                =\page_mvl_command_routine,
   \s!page_otr_command_package_contents       =\page_mvl_command_package_contents,
   \s!page_otr_command_set_vsize              =\page_mvl_command_set_vsize,
   \s!page_otr_command_set_hsize              =\page_mvl_command_set_hsize, % tricky, goes wrong
   \s!page_otr_command_synchronize_hsize      =\page_mvl_command_synchronize_hsize,
   \s!page_otr_command_next_page              =\page_mvl_command_next_page,
   \s!page_otr_command_next_page_and_inserts  =\page_mvl_command_next_page_and_inserts,
 % \s!page_otr_command_set_top_insertions     =\page_mvl_command_set_top_insertions,
 % \s!page_otr_command_set_bottom_insertions  =\page_mvl_command_set_bottom_insertions,
 % \s!page_otr_command_flush_top_insertions   =\page_mvl_command_flush_top_insertions,
 % \s!page_otr_command_flush_bottom_insertions=\page_mvl_command_flush_bottom_insertions,
   \s!page_otr_command_check_if_float_fits    =\page_mvl_command_check_if_float_fits,
 % \s!page_otr_command_set_float_hsize        =\page_mvl_command_set_float_hsize,
 % \s!page_otr_command_flush_float_box        =\page_mvl_command_flush_float_box,
   \s!page_otr_command_synchronize_side_floats=\page_mvl_command_synchronize_side_floats,
   \s!page_otr_command_side_float_output      =\page_mvl_command_side_float_output,
   \s!page_otr_command_flush_floats           =\page_mvl_command_flush_floats,
   \s!page_otr_command_flush_side_floats      =\page_mvl_command_flush_side_floats,
   \s!page_otr_command_flush_saved_floats     =\page_mvl_command_flush_saved_floats,
   \s!page_otr_command_flush_all_floats       =\page_mvl_command_flush_all_floats,
 % \s!page_otr_command_flush_margin_blocks    =\page_mvl_command_flush_margin_blocks, % not used
   \s!page_otr_command_test_column            =\page_mvl_command_test_column,
  ]

%D Additional wrappers:

\permanent\tolerant\protected\defcsname\e!start\v!setcolumnsetsheet\endcsname[#1]#*%
  {\begingroup
   \obeylines
   \cdef\askedsheet{#1}%
   \grabbufferdatadirect{page:mvl:temp}{\e!start\v!setcolumnsetsheet}{\e!stop\v!setcolumnsetsheet}}

\permanent\protected\defcsname\e!stop\v!setcolumnsetsheet\endcsname
  {\clf_registercolumnsetsheet{\currentcolumnset}{\askedsheet}{_sht_}\relax
   \endgroup}

\tolerant\protected\def\startsetcolumnsetsht[#S#1]%
  {\begingroup
   \page_mvl_common_dummy_preset[#1]%
   \setbox\nextbox\hbox\bgroup
   \hsize{\columnsethspan{1}{\dummyparameter\c!nc}}%
   \ifnum{\dummyparameter\c!nc}>\zerocount
     \vsize{(\dummyparameter\c!nr)*\lineheight}%
   \fi
   \ignorespaces}

\permanent\protected\def\stopsetcolumnsetsht
  {\removeunwantedspaces
   \egroup
   \page_mvl_set_indeed}

\protect \endinput