% ----------------------------------------------------------------------------
% the EXSHEETS package
% 
%   Yet another package for the creation of exercise sheets
% 
% ----------------------------------------------------------------------------
% Clemens Niederberger
% Web:    https://bitbucket.org/cgnieder/exsheets/
% E-Mail: contact@mychemistry.eu
% ----------------------------------------------------------------------------
% Copyright 2011-2013 Clemens Niederberger
% 
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3
% of this license or (at your option) any later version.
% The latest version of this license is in
%   http://www.latex-project.org/lppl.txt
% and version 1.3 or later is part of all distributions of LaTeX
% version 2005/12/01 or later.
% 
% This work has the LPPL maintenance status `maintained'.
% 
% The Current Maintainer of this work is Clemens Niederberger.
% ----------------------------------------------------------------------------
% If you have any ideas, questions, suggestions or bugs to report, please
% feel free to contact me.
% ----------------------------------------------------------------------------
\def\exsheets@date{2013/12/27}
\def\exsheets@version{0.12b}

\RequirePackage { expl3 , xparse }
\ProvidesExplPackage
  {exsheets}
  {\exsheets@date}
  {\exsheets@version}
  {Yet another package for the creation of exercise sheets and exams.}

% --------------------------------------------------------------------------
% check expl3 version:
\@ifpackagelater { expl3 } { 2012/11/21 }
  { }
  {
    \PackageError { exsheets } { Support~package~expl3~too~old }
      {
        You~need~to~update~your~installation~of~the~bundles~'l3kernel'~and~
        'l3packages'.\MessageBreak
        Loading~exsheets~will~abort!
      }
    \tex_endinput:D
  }

% ----------------------------------------------------------------------------
% variants of kernel functions:
\cs_generate_variant:Nn \prop_get:NnN    { Nx }
\cs_generate_variant:Nn \prop_get:NnN    { cf }
\cs_generate_variant:Nn \prop_get:NnNTF  { Nx }
\cs_generate_variant:Nn \prop_gput:Nnn   { Nf , Nff , Nfx }
\cs_generate_variant:Nn \prop_gput:Nnn   { Nx , Nxx }
\cs_generate_variant:Nn \prop_gput:Nnn   { cf , cff }
\cs_generate_variant:Nn \tl_if_blank:nTF { x }

% ----------------------------------------------------------------------------
% temporary variables
\tl_new:N    \l__exsheets_tmpa_tl
\tl_new:N    \l__exsheets_tmpb_tl
\tl_new:N    \l__exsheets_tmpc_tl
\int_new:N   \l__exsheets_tmpa_int
\int_new:N   \l__exsheets_tmpb_int
\int_new:N   \l__exsheets_tmpc_int
\int_new:N   \l__exsheets_tmpd_int
\int_new:N   \l__exsheets_tmpe_int
\dim_new:N   \l__exsheets_tmpa_dim
\dim_new:N   \l__exsheets_tmpb_dim
\seq_new:N   \l__exsheets_tmpa_seq
\fp_new:N    \l__exsheets_tmpa_fp
\clist_new:N \l__exsheets_tmpa_clist
\bool_new:N  \l__exsheets_tmpa_bool

% ----------------------------------------------------------------------------
% messages
\msg_new:nnn { exsheets} { totalpoints }
  {
    You~need~to~activate~`points/parse'~if~you~want~to~use~
    \token_to_str:N \totalpoints .~I~will~do~nothing~instead.
  }

\msg_new:nnn { exsheets} { parse-points }
  {
    You~need~to~activate~`points/parse'~if~you~want~to~use~
    \token_to_str:N #1 .~I~will~do~nothing~instead.
  }

\msg_new:nnn { exsheets} { headings }
  {
    You~requested~the~headings~instance~`#1'~\msg_line_context: \c_space_tl
    which~is~not~defined.~Did~you~forget~to~use~the~package~option~
    `load-headings'?~Anyway,~I~will~use~the~instance~`block'~instead~and~
    pretend~nothing~happened.
  }

\msg_new:nnn { exsheets } { random-file }
  {
    You~asked~me~to~select~#1~questions~from~file~#2~which~contains~#3~questions.~
    I'll~select~all~of~them.
  }

\msg_new:nnn { exsheets } { random-selectable }
  {
    You~asked~me~to~select~#1~questions~from~file~#2~which~contains~#3~questions.~
    #4~of~these~are~selectable,~so~I'll~select~all~of~them.
  }

\msg_new:nnn { exsheets } { only-inside-question }
  {
    The~command~`~\token_to_str:N #1 \c_space_tl'~can~only~be~used~inside~
    the~question~environment.
  }

\msg_new:nnn { exsheets } { loading-configurations }
  { Loading~custom~configurations~file~`exsheets_configurations.cgf'. }

\msg_new:nnn { exsheets } { deprecated-command }
  {
    The~command~`~\token_to_str:N #1 \c_space_tl'~is~deprecated.~
    Use~`~\token_to_str:N #2 \c_space_tl'~instead.
  }

\msg_new:nnn { exsheets } { dropped-option }
  { The~option~`#1'~has~been~dropped. }

\msg_new:nnn { exsheets } { grade-missing }
  { The~grade~`#1'~has~never~been~declared. }

\msg_new:nnn { exsheets } { grade-parse }
  {
    I~cannot~calculate~the~points~for~grade~`#1'~since~you're~using~the~option~
    `points/parse=false'.
  }

\msg_new:nnn { exsheets } { variations }
  {
    The~number~of~variations~must~at~least~be~`2'.~You~chose~`#1'~hence~I'm~
    doing~nothing.
  }

\msg_new:nnn { exsheets } { variant }
  {
    You~must~choose~an~integer~between~`1'~and~`#1'.~You~chose~`#2'~hence~
    I'm~doing~nothing.
  }

\cs_new_protected:Npn \exsheets_depr_cmd:nn #1#2
  {
    \cs_new:Npn #1
      { \msg_warning:nnnn { exsheets } { deprecated-command } { #1 } { #2 } #2 }
  }

\cs_new_protected:Npn \exsheets_option_dropped:n #1
  { \msg_warning:nnn { exsheets } { dropped-option } { #1 } }

% ----------------------------------------------------------------------------
\RequirePackage
  { xtemplate , l3sort , l3keys2e , xcolor , etoolbox , environ , pgfcore }

% ----------------------------------------------------------------------------
% color:
\xdefinecolor { exsheetsblue } { rgb } { 0.02 , 0.04 , 0.48 }
\xdefinecolor { exsheetsred  } { rgb } { 0.65 , 0.04 , 0.07 }
% \tl_new:N   \g__exsheets_color_tl
\tl_const:Nn \c__exsheets_color_tl { exsheetsblue }

% ----------------------------------------------------------------------------
% write to aux file:
\cs_new_protected:Npn \exsheets_write_to_aux_x:n #1
  { \if@filesw \iow_now:Nx \@auxout { #1 } \fi }

% prevent compilatin errors when exsheets is removed from a document:
\AtBeginDocument{
  \exsheets_write_to_aux_x:n
    {
      \exp_not:N \providecommand \exp_not:N \exsheets@question@property[3]{} ^^J
      \exp_not:N \providecommand \exp_not:N \exsheets@save@number[2]{} ^^J
      \exp_not:N \providecommand \exp_not:N \exsheets@sum@of@points[1]{} ^^J
      \exp_not:N \providecommand \exp_not:N \exsheets@sum@of@bonus[1]{}
    }
}

% ----------------------------------------------------------------------------
% how are questions/solutions/... counted?
\bool_new:N      \l__exsheets_print_number_bool
\bool_set_true:N \l__exsheets_print_number_bool

\tl_new:N  \l__exsheets_qu_counter_pattern_tl
\tl_set:Nn \l__exsheets_qu_counter_pattern_tl { qu. }
\tl_new:N  \l__exsheets_qu_counter_interpretation_tl
\tl_new:N  \l__exsheets_counter_patterns_tl
\tl_new:N  \l__exsheets_current_pattern_interpretation_tl
\tl_new:N  \l__exsheets_current_pattern_tl

\RequirePackage { cntformats }

\cs_if_exist:NT \thechapter
  {
    \AddCounterPattern* [ exsheets ] { chapter } { ch }
    \ReadCounterFrom [ exsheets ] { chapter } \l__exsheets_counter_ch_int
  }

\AddCounterPattern* [ exsheets ] { section } { se }
\ReadCounterFrom [ exsheets ] { section } \l__exsheets_counter_sec_int

\NewCounterPattern* [ exsheets ] { question } { qu }
\ReadCounterFrom [ exsheets ] { question } \l__exsheets_counter_qu_int

% ----------------------------------------------------------------------------
% (also) package options:
\bool_new:N \l__exsheets_load_headings_bool
\bool_new:N \l__exsheets_load_tasks_bool
\bool_new:N \l__exsheets_solutions_by_ref_bool
\bool_new:N \l__exsheets_questions_totoc_bool
\bool_new:N \l__exsheets_solutions_totoc_bool
\bool_new:N \l__exsheets_auto_label_bool

\tl_new:N   \l__exsheets_heading_instance_tl
\tl_set:Nn  \l__exsheets_heading_instance_tl { block }
\tl_new:N   \l__exsheets_question_heading_instance_tl
\tl_new:N   \l__exsheets_solution_heading_instance_tl
\tl_new:N   \l_exsheets_heading_title_user_format_tl
\tl_set:Nn  \l_exsheets_heading_title_user_format_tl { \normalsize\bfseries }
\tl_new:N   \l_exsheets_heading_subtitle_user_format_tl
\tl_set:Nn  \l_exsheets_heading_subtitle_user_format_tl { \normalsize\itshape }
\tl_new:N   \l__exsheets_questions_toclevel_tl
\tl_set:Nn  \l__exsheets_questions_toclevel_tl { subsection }
\tl_new:N   \l__exsheets_solutions_toclevel_tl
\tl_set:Nn  \l__exsheets_solutions_toclevel_tl { subsection }

\AtBeginDocument{
  \cs_if_exist:NF \phantomsection
    { \cs_new:Npn \phantomsection {} }
}

\keys_define:nn { exsheets }
  {
    color                     .code:n     =
      \exsheets_option_dropped:n { color } ,
    counter-format            .code:n     =
      \SaveCounterPattern [ exsheets ]
        \l__exsheets_qu_counter_pattern_tl
        \l__exsheets_qu_counter_interpretation_tl
        { #1 } ,
    counter-within            .code:n     = \@addtoreset{question}{#1} ,
    headings                  .tl_set:N   = \l__exsheets_heading_instance_tl ,
    load-headings             .bool_set:N = \l__exsheets_load_headings_bool ,
    headings-format           .tl_set:N   =
      \l_exsheets_heading_title_user_format_tl ,
    subtitle-format           .tl_set:N   =
      \l_heading_exsheets_subtitle_user_format_tl ,
    load-tasks                .bool_set:N = \l__exsheets_load_tasks_bool ,
    use-ref                   .bool_set:N = \l__exsheets_solutions_by_ref_bool ,
    totoc                     .choice: ,
    totoc / true              .code:n     =
      \bool_set_true:N \l__exsheets_questions_totoc_bool
      \bool_set_true:N \l__exsheets_solutions_totoc_bool ,
    totoc / false             .code:n     =
      \bool_set_false:N \l__exsheets_questions_totoc_bool
      \bool_set_false:N \l__exsheets_solutions_totoc_bool ,
    totoc                     .default:n  = true ,
    questions-totoc           .bool_set:N = \l__exsheets_questions_totoc_bool ,
    solutions-totoc           .bool_set:N = \l__exsheets_solutions_totoc_bool ,
    toc-level                 .code:n     =
      \tl_set:Nn \l__exsheets_questions_toclevel_tl { #1 }
      \tl_set:Nn \l__exsheets_solutions_toclevel_tl { #1 } ,
    questions-toc-level       .tl_set:N   = \l__exsheets_questions_toclevel_tl ,
    solutions-toc-level       .tl_set:N   = \l__exsheets_solutions_toclevel_tl ,
    auto-label                .bool_set:N = \l__exsheets_auto_label_bool
  }
\keys_set:nn { exsheets} { counter-format = qu. }

% process package options:
\ProcessKeysOptions { exsheets }

% ----------------------------------------------------------------------------
% points for exercises
\bool_new:N       \l__exsheets_points_questions_default_bool
\bool_set_false:N \l__exsheets_points_questions_default_bool
\bool_new:N       \l__exsheets_parse_points_bool
\bool_set_true:N  \l__exsheets_parse_points_bool
\bool_new:N       \l__exsheets_points_name_bool
\bool_set_true:N  \l__exsheets_points_name_bool
\bool_new:N       \l__exsheets_points_separate_bonus_bool

\fp_new:N         \g__exsheets_points_sum_fp
\fp_new:N         \l__exsheets_points_default_fp
\fp_set:Nn        \l__exsheets_points_default_fp { 1 }
\fp_new:N         \l__exsheets_question_points_fp
% this one should be public:
\fp_new:N         \g_exsheets_total_points_fp
\fp_new:N         \g__exsheets_bonus_sum_fp
\fp_new:N         \l__exsheets_question_bonus_fp
% this one should be public
\fp_new:N         \g_exsheets_total_bonus_fp

\tl_new:N         \l__exsheets_points_name_tl
\tl_set:Nn        \l__exsheets_points_name_tl { P. }
\tl_new:N         \l__exsheets_points_name_plural_tl
\tl_set:Nn        \l__exsheets_points_name_plural_tl { P. }
\tl_new:N         \l__exsheets_bonus_name_tl
\tl_set:Nn        \l__exsheets_bonus_name_tl { P. }
\tl_new:N         \l__exsheets_bonus_name_plural_tl
\tl_set:Nn        \l__exsheets_bonus_name_plural_tl { P. }
\tl_new:N         \l__exsheets_points_number_format_tl
\tl_new:N         \l__exsheets_bonus_number_format_tl
\tl_new:N         \l__exsheets_points_pre_bonus_marker_tl
\tl_set:Nn        \l__exsheets_points_pre_bonus_marker_tl { \space(+ }
\tl_new:N         \l__exsheets_points_post_bonus_marker_tl
\tl_set:Nn        \l__exsheets_points_post_bonus_marker_tl { ) }
\tl_new:N         \l__exsheets_points_format_tl
\tl_set:Nn        \l__exsheets_points_format_tl { \use:n }

\cs_new_protected_nopar:Npn \exsheets_set_points_name:n #1
  {
    \tl_if_in:nnTF { #1 } { / }
      { \__exsheets_set_points_name_aux:nn #1 \q_stop }
      { \__exsheets_set_points_name_aux:nn #1 / \q_stop }
  }

\cs_new_protected_nopar:Npn \__exsheets_set_points_name_aux:nn #1/#2 \q_stop
  {
    \tl_set:Nn \l__exsheets_points_name_tl { #1 }
    \tl_set:Nn \l__exsheets_points_name_plural_tl { #1#2 }
  }

\cs_new_protected_nopar:Npn \exsheets_set_bonus_name:n #1
  {
    \tl_if_in:nnTF { #1 } { / }
      { \__exsheets_set_bonus_name_aux:nn #1 \q_stop }
      { \__exsheets_set_bonus_name_aux:nn #1 / \q_stop }
  }

\cs_new_protected_nopar:Npn \__exsheets_set_bonus_name_aux:nn #1/#2 \q_stop
  {
    \tl_set:Nn \l__exsheets_bonus_name_tl { #1 }
    \tl_set:Nn \l__exsheets_bonus_name_plural_tl { #1#2 }
  }

% FIXME: \fp_add will deprecate!
\cs_new_protected_nopar:Npn \exsheets_add_points:n #1
  { 
    \fp_gadd:Nn \g__exsheets_points_sum_fp { #1 }
    \fp_gadd:Nn \g__exsheets_this_question_points_fp { #1 }
  }
\cs_generate_variant:Nn \exsheets_add_points:n { V }

\cs_new_protected_nopar:Npn \exsheets_add_bonus:n #1
  {
    \fp_gadd:Nn \g__exsheets_bonus_sum_fp { #1 }
    \fp_gadd:Nn \g__exsheets_this_question_bonus_fp { #1 }
  }
\cs_generate_variant:Nn \exsheets_add_bonus:n { V }

\cs_new_protected_nopar:Npn \exsheets@sum@of@points #1
  { \fp_gset:Nn \g_exsheets_total_points_fp { #1 } }

\cs_new_protected_nopar:Npn \exsheets@sum@of@bonus #1
  { \fp_gset:Nn \g_exsheets_total_bonus_fp { #1 } }

\cs_new_nopar:Npn \exsheets_parse_points:n #1
  {
    \group_begin:
      \tl_use:N \l__exsheets_points_number_format_tl
        {
          \bool_if:NTF \l__exsheets_parse_points_bool
            { \exsheets_num:n { \fp_to_decimal:n { #1 } } }
            { \use:n { #1 } }
        }
    \group_end:
  }
\cs_generate_variant:Nn \exsheets_parse_points:n { V }

\cs_new_nopar:Npn \exsheets_parse_bonus:n #1
  {
    \group_begin:
      \tl_use:N \l__exsheets_bonus_number_format_tl
        {
          \bool_if:NTF \l__exsheets_parse_points_bool
            { \exsheets_num:n { \fp_to_decimal:n { #1 } } }
            { \use:n { #1 } }
        }
    \group_end:
  }
\cs_generate_variant:Nn \exsheets_parse_bonus:n { V }

\cs_new_protected_nopar:Npn \exsheets_num:n #1
  {
    \group_begin:
      \fp_set:Nn \l__exsheets_tmpa_tl { #1 }
      \fp_to_tl:N \l__exsheets_tmpa_tl
    \group_end:
  }
\cs_generate_variant:Nn \exsheets_num:n { V,x }

\cs_new_nopar:Npn \exsheets_points_name:n #1
  {
    \bool_if:NT \l__exsheets_points_name_bool
      {
        \,
        \hbox:n
          {
            \bool_if:NTF \l__exsheets_parse_points_bool
              {
                \tl_if_eq:nnTF { #1 } { ?? }
                  { \tl_use:N \l__exsheets_points_name_plural_tl }
                  {
                    \fp_compare:nTF { #1 <=  1 }
                      { \tl_use:N \l__exsheets_points_name_tl }
                      { \tl_use:N \l__exsheets_points_name_plural_tl }
                  }
              }
              { \tl_use:N \l__exsheets_points_name_plural_tl }
          }
      }
  }
\cs_generate_variant:Nn \exsheets_points_name:n { V }

\cs_new_nopar:Npn \exsheets_bonus_name:n #1
  {
    \bool_if:NT \l__exsheets_points_name_bool
      {
        \,
        \hbox:n
          {
            \bool_if:NTF \l__exsheets_parse_points_bool
              {
                \tl_if_eq:nnTF { #1 } { ?? }
                  { \tl_use:N \l__exsheets_bonus_name_plural_tl }
                  {
                    \fp_compare:nTF { #1 <=  1 }
                      { \tl_use:N \l__exsheets_bonus_name_tl }
                      { \tl_use:N \l__exsheets_bonus_name_plural_tl }
                  }
              }
              { \tl_use:N \l__exsheets_bonus_name_plural_tl }
          }
      }
  }
\cs_generate_variant:Nn \exsheets_bonus_name:n { V }

\NewDocumentCommand \addpoints { sm }
  {
    \bool_if:NTF \l__exsheets_inside_question_bool
      {
        \exsheets_add_points:n { #2 }
        \IfBooleanF { #1 } { \exsheets_print_points:n { #2 } }
      }
      { \msg_error:nnn { exsheets } { only-inside-question } { \addpoints } }
  }

\NewDocumentCommand \addbonus { sm }
  {
    \bool_if:NTF \l__exsheets_inside_question_bool
      {
        \exsheets_add_bonus:n { #2 }
        \IfBooleanF { #1 } { \exsheets_print_bonus:n { #2 } }
      }
      { \msg_error:nnn { exsheets } { only-inside-question } { \addbonus } }
  }

\NewDocumentCommand \points { sm }
  {
    \IfBooleanTF { #1 }
      { \exsheets_parse_points:n { #2 } }
      { \exsheets_print_points:n { #2 } }
  }

\NewDocumentCommand \bonus { sm }
  {
    \IfBooleanTF { #1 }
      { \exsheets_parse_bonus:n { #2 } }
      { \exsheets_print_bonus:n { #2 } }
  }

\cs_new_protected_nopar:Npn \exsheets_print_points:n #1
  {
    \group_begin:
      \tl_use:N \l__exsheets_points_format_tl
        {
          \exsheets_parse_points:n { #1 }
          \exsheets_points_name:n { #1 }
        }
    \group_end:
  }
\cs_generate_variant:Nn \exsheets_print_points:n { V }

\cs_new_protected_nopar:Npn \exsheets_print_bonus:n #1
  {
    \exsheets_parse_bonus:n { #1 }
    \exsheets_bonus_name:n { #1 }
  }
\cs_generate_variant:Nn \exsheets_print_bonus:n { V }

\NewDocumentCommand \pointssum { s }
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      {
        \IfBooleanTF { #1 }
          { \exsheets_parse_points:n { \g_exsheets_total_points_fp } }
          { \exsheets_print_points:n { \g_exsheets_total_points_fp } }
      }
      { \msg_warning:nnn { exsheets } { parse-points } { \pointssum } }
  }

\NewDocumentCommand \bonussum { s }
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      {
        \IfBooleanTF { #1 }
          { \exsheets_parse_bonus:n { \g_exsheets_total_bonus_fp } }
          { \exsheets_print_bonus:n { \g_exsheets_total_bonus_fp } }
      }
      { \msg_warning:nnn { exsheets } { parse-points } { \bonussum } }
  }

\NewDocumentCommand \currentpointssum { s }
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      {
        \IfBooleanTF { #1 }
          { \exsheets_parse_points:n { \g__exsheets_points_sum_fp } }
          { \exsheets_print_points:n { \g__exsheets_points_sum_fp } }
      }
      { \msg_warning:nnn { exsheets } { parse-points } { \currentpointssum } }
  }

\NewDocumentCommand \currentbonussum { s }
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      {
        \IfBooleanTF { #1 }
          { \exsheets_parse_bonus:n { \g__exsheets_bonus_sum_fp } }
          { \exsheets_print_bonus:n { \g__exsheets_bonus_sum_fp } }
      }
      { \msg_warning:nnn { exsheets } { parse-points } { \currentbonussum } }
  }

\NewDocumentCommand \totalpoints { s }
  {
    \group_begin:
      \tl_use:N \l__exsheets_points_format_tl
      {
        \exsheets_totalpoints:
        \IfBooleanF { #1 }
          {
            \bool_if:nT
              {
                \l__exsheets_points_separate_bonus_bool ||
                \fp_compare_p:n { \g_exsheets_total_bonus_fp = 0 }
              }
              { \exsheets_points_name:n { \g_exsheets_total_points_fp } }
          }
        \exsheets_totalbonus:
        \IfBooleanF { #1 }
          {
            \fp_compare:nF { \g_exsheets_total_bonus_fp = 0 }
              {
                \bool_if:NTF \l__exsheets_points_separate_bonus_bool
                  { \exsheets_bonus_name:n { \g_exsheets_total_bonus_fp } }
                  {
                    \exsheets_points_name:n
                      { \g_exsheets_total_points_fp + \g_exsheets_total_bonus_fp }
                  }
              }
          }
      }
    \group_end:
  }

\exsheets_depr_cmd:nn { \sumpoints } { \totalpoints* }

\cs_new_nopar:Npn \exsheets_totalpoints:
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      {
        \fp_compare:nTF { \g_exsheets_total_points_fp = 0 }
          { ?? \, \exsheets_points_name:n { ?? } }
          {
            \exsheets_parse_points:n
              { \g_exsheets_total_points_fp }
          }
      }
      { \msg_warning:nn { exsheets } { totalpoints } }
  }

\cs_new_nopar:Npn \exsheets_totalbonus:
  {
    \bool_if:NT \l__exsheets_parse_points_bool
      {
        \fp_compare:nF { \g_exsheets_total_bonus_fp = 0 }
          {
            \tl_use:N \l__exsheets_points_pre_bonus_marker_tl
            \exsheets_parse_bonus:n
              { \g_exsheets_total_bonus_fp }
            \tl_use:N \l__exsheets_points_post_bonus_marker_tl
          }
      }
  }

\keys_define:nn { exsheets / points }
  {
    name                 .code:n     =
      \exsheets_set_points_name:n { #1 }
      \exsheets_set_bonus_name:n { #1 } ,
    name-plural          .code:n     =
      \tl_set:Nn \l__exsheets_points_name_plural_tl { #1 }
      \tl_set:Nn \l__exsheets_bonus_name_plural_tl { #1 } ,
    bonus-name           .code:n     = \exsheets_set_bonus_name:n { #1 } ,
    bonus-plural         .tl_set:N   = \l__exsheets_bonus_name_plural_tl ,
    pre-bonus            .tl_set:N   = \l__exsheets_points_pre_bonus_marker_tl ,
    post-bonus           .tl_set:N   = \l__exsheets_points_post_bonus_marker_tl ,
    use-name             .bool_set:N = \l__exsheets_points_name_bool ,
    format               .tl_set:N   = \l__exsheets_points_format_tl ,
    number-format        .tl_set:N   = \l__exsheets_points_number_format_tl ,
    bonus-format         .tl_set:N   = \l__exsheets_bonus_number_format_tl ,
    parse                .bool_set:N = \l__exsheets_parse_points_bool ,
    separate-bonus       .bool_set:N = \l__exsheets_points_separate_bonus_bool
  }

% ----------------------------------------------------------------------------
% variations of an exam, see http://tex.stackexchange.com/q/57012/5049 for
% inspiration of the following features
\int_zero_new:N \l__exsheets_variations_int

\cs_new_protected:Npn \exsheets_set_variations:n #1
  {
    \int_compare:nNnTF { #1 } < { 2 }
      { \msg_warning:nnn { exsheets } { variations } { #1 } }
      {
        \int_set:Nn \l__exsheets_variations_int { #1 }
        \int_zero:N \l__exsheets_tmpa_int
        \int_do_while:nNnn
          { \l__exsheets_tmpa_int } < { \l__exsheets_variations_int }
          {
            \int_incr:N \l__exsheets_tmpa_int
            \__exsheets_generate_variation_auxiliary:n
              { \l__exsheets_tmpa_int }
            \__exsheets_reset_variation_auxiliary:x
              { \int_use:N \l__exsheets_tmpa_int }
          }
        \__exsheets_generate_variation_auxiliary:n
          { \l__exsheets_variations_int + 1 }
        \exsheets_variant:n { 1 }
      }
  }

\cs_new_protected:Npn \exsheets_variant:n #1
  {
    \bool_if:nTF
      {
        \int_compare_p:nNn { #1 } > { 0 } &&
        \int_compare_p:nNn { #1 } < { \l__exsheets_variations_int + 1 }
      }
      {
        \int_zero:N \l__exsheets_tmpa_int
        \int_do_while:nNnn
          { \l__exsheets_tmpa_int } < { \l__exsheets_variations_int }
          {
            \int_incr:N \l__exsheets_tmpa_int
            \__exsheets_reset_variation_auxiliary:x
              { \int_use:N \l__exsheets_tmpa_int }
          }
        \cs_set:cpn { __exsheets_variation_ \int_to_roman:n { #1 } :n } ##1
          {
            ##1
            \cs_set:Npn \exsheets_last_variant: { ##1 }
            \use:c { __exsheets_variation_ \int_to_roman:n { #1 + 1 } :n }
          }
      }
      {
        \msg_warning:nnxx { exsheets } { variant }
          { \int_use:N \l__exsheets_variations_int } { #1 }
      }
  }

\cs_new:Npn \exsheets_vary:w
  { \__exsheets_variation_i:n }
  
\cs_new:Npn \exsheets_last_variant: { }

\cs_new_protected:Npn \__exsheets_generate_variation_auxiliary:n #1
  {
    \cs_if_exist:cTF { __exsheets_variation_ \int_to_roman:n { #1 } :n }
      { \cs_set:cpn { __exsheets_variation_ \int_to_roman:n { #1 } :n } { } }
      { \cs_new:cpn { __exsheets_variation_ \int_to_roman:n { #1 } :n } { } }
  }

\cs_new_protected:Npn \__exsheets_reset_variation_auxiliary:n #1
  {
    \cs_set:cpn { __exsheets_variation_ \int_to_roman:n { #1 } :n } ##1
      { \use:c { __exsheets_variation_ \int_to_roman:n { #1 + 1 } :n } }
  }
\cs_generate_variant:Nn \__exsheets_reset_variation_auxiliary:n { x }

\NewDocumentCommand \SetVariations { m }
  { \exsheets_set_variations:n { #1 } }

\NewDocumentCommand \variant { m }
  { \exsheets_variant:n { #1 } }

\NewDocumentCommand \vary { }
  { \exsheets_vary:w }

\NewDocumentCommand \lastvariant { }
  { \exsheets_last_variant: }

% initiate: two variations, first is default
\SetVariations { 2 }
\variant    { 1 }

% ----------------------------------------------------------------------------
% grades distribution
\prop_new:N \l__exsheets_relgrades_prop
\fp_new:N   \l__exsheets_grade_round_fp
\fp_zero:N  \l__exsheets_grade_round_fp
\bool_new:N \l__exsheets_grades_half_bool

\cs_new:Npn \__exsheets_fp_round_to_half:n #1
  { round( 2*(#1),0)/2 }

\cs_new:Npn \__exsheets_grades_round:n #1
  { round ( #1 , \l__exsheets_grade_round_fp ) }

\cs_new:Npn \__exsheets_grade_rounded:
  {
    \bool_if:NTF { \l__exsheets_grades_half_bool }
      { \__exsheets_fp_round_to_half:n }
      { \__exsheets_grades_round:n }
    { \g_exsheets_total_points_fp * \l__exsheets_tmpa_fp }
  }

\cs_new:Npn \exsheets_strip_braces:N #1
  { \exp_after:wN \__exsheets_strip_braces:w \exp_after:wN #1#1 \q_stop }
\cs_new_protected:Npn \__exsheets_strip_braces:w #1#2 \q_stop
  { \tl_set:Nn #1 { #2 } }

\cs_new_protected:Npn \__exsheets_declare_relgrades:n #1
  {
    \clist_set:Nn \l__exsheets_tmpa_clist { #1 }
    \clist_map_inline:Nn \l__exsheets_tmpa_clist
      { \__exsheets_declare_relgrade:w ##1 \q_stop }
  }

\cs_new_protected:Npn \__exsheets_declare_relgrade:w #1 = #2 \q_stop
  {
    \tl_set:Nn \l__exsheets_tmpa_tl { #1 }
    \tl_set:Nn \l__exsheets_tmpb_tl { #2 }
    \tl_trim_spaces:N \l__exsheets_tmpa_tl
    \exsheets_strip_braces:N \l__exsheets_tmpa_tl
    \tl_trim_spaces:N \l__exsheets_tmpb_tl
    \exsheets_strip_braces:N \l__exsheets_tmpb_tl
    \prop_put:NVV \l__exsheets_relgrades_prop
      \l__exsheets_tmpa_tl
      \l__exsheets_tmpb_tl
  }

\NewDocumentCommand \DeclareRelGrades { m }
  { \__exsheets_declare_relgrades:n { #1 } }
\@onlypreamble \DeclareRelGrades

\cs_new_protected:Npn \__exsheets_grade:nn #1#2
  {
    \prop_get:NnNTF \l__exsheets_relgrades_prop { #2 } \l__exsheets_tmpa_fp
      {
        \bool_if:NTF \l__exsheets_parse_points_bool
          {
            \exsheets_parse_points:n
              { min( \__exsheets_grade_rounded: , \g_exsheets_total_points_fp ) }
            \int_compare:nT { #1 = 1 }
              {
                \exsheets_points_name:n
                  { min( \__exsheets_grade_rounded: , \g_exsheets_total_points_fp ) }
              }
          }
          { \msg_warning:nnn { exsheets } { grade-parse } { #1 } \textbf{??} }
      }
      { \msg_warning:nnn { exsheets } { grade-missing } { #1 } \textbf{??} }
  }

\NewDocumentCommand \grade { sm }
  {
    \IfBooleanTF { #1 }
      { \__exsheets_grade:nn { 0 } { #2 } }
      { \__exsheets_grade:nn { 1 } { #2 } }
  }

\keys_define:nn { exsheets / grades }
  {
    round .fp_set:N   = \l__exsheets_grade_round_fp ,
    half  .bool_set:N = \l__exsheets_grades_half_bool
  }

% ----------------------------------------------------------------------------
% Aufgaben und Lösungen
\bool_new:N        \g__exsheets_questions_use_bool
\bool_gset_true:N  \g__exsheets_questions_use_bool
\bool_new:N        \l__exsheets_questions_use_bool
\bool_set_true:N   \l__exsheets_questions_use_bool
\bool_new:N        \l__exsheets_questions_deactivate_bool

\bool_new:N        \l__exsheets_solutions_use_bool
\bool_set_true:N   \l__exsheets_solutions_use_bool

\dim_new:N         \l__exsheets_questions_skip_below_dim
\dim_set:Nn        \l__exsheets_questions_skip_below_dim { .5\baselineskip }
\dim_new:N         \l__exsheets_solutions_skip_below_dim
\dim_set:Nn        \l__exsheets_solutions_skip_below_dim { .5\baselineskip }

\cs_new_nopar:Npn \exsheets_glue:N #1
  { \cleaders \vbox:n {} \skip_vertical:N #1 }

\keys_define:nn { exsheets }
  {
    skip-below .code:n =
      \dim_set:Nn \l__exsheets_questions_skip_below_dim { #1 }
      \dim_set:Nn \l__exsheets_solutions_skip_below_dim { #1 }
  }

% Einteilung in Klassen, Themen und andere Gruppierungen:
\prop_new:N \l__exsheets_class_prop
\tl_new:N   \l__exsheets_step_counter_tl
\bool_new:N \l__exsheets_use_this_question_bool

\cs_new_protected:Npn \exsheets_new_question_class:nn #1#2
  {
    \prop_put:Nnn \l__exsheets_class_prop { #2 } { #1 }
    \prop_new:c { g__exsheets_questions_#1_prop }
    \prop_new:c { g__exsheets_#2_prop }
    \prop_new:c { g__exsheets_#2_active_prop }
    \bool_new:c { l__exsheets_questions_#1_bool }
    \bool_new:c { g__exsheets_use_#2_bool }
    \bool_new:c { l__exsheets_#1_active_bool }
    \tl_new:c   { l__exsheets_questions_#1_tl }
    \keys_define:nn { exsheets }
      {
        use-#2 .code:n =
          {
            \bool_gset_true:c { g__exsheets_use_#2_bool }
            \use:c { __exsheets_activate_#2:n } { ##1 }
          } ,
        question / #1 .code:n =
          \bool_set_true:c { l__exsheets_questions_#1_bool }
          \tl_set:cn { l__exsheets_questions_#1_tl } { ##1 }
%           \exsheets_set_question_properties:n { #1 = ##1 }
      }
    \cs_new_protected:cpn { __exsheets_activate_#2:n } ##1
      {
        \prop_gclear:c { g__exsheets_#2_active_prop }
        \seq_set_split:Nnn \l__exsheets_tmpa_seq { , } { ##1 }
        \seq_map_inline:Nn \l__exsheets_tmpa_seq
          {
            \prop_gput:cnn { g__exsheets_#2_active_prop }
              { ####1 } { \__exsheets_dummy: }
          }
      }
    \cs_new_protected:cpn { __exsheets_questions_use_#2: }
      {
        % is there a #1 provided?
        \bool_if:cT { l__exsheets_questions_#1_bool }
          {
            % add #1 to questions property
            \prop_gput:cff { g__exsheets_questions_#1_prop }
              { \int_to_arabic:n { \g__exsheets_questions_id_int } }
              { \tl_use:c { l__exsheets_questions_#1_tl } }
            % add to #2 list, if it's a new one
            \prop_get:cfN { g__exsheets_#2_prop }
              { \tl_use:c { l__exsheets_questions_#1_tl } }
              \l__exsheets_tmpa_tl
            \tl_if_eq:NNT \l__exsheets_tmpa_tl \q_no_value
              {
                \prop_gput:cfn { g__exsheets_#2_prop }
                  { \tl_use:c { l__exsheets_questions_#1_tl } }
                  { \__exsheets_dummy: }
              }
          }
        % are we using #2?
        \bool_if:cT { g__exsheets_use_#2_bool }
          {
            % is this question an active one?
            \prop_get:cfN { g__exsheets_#2_active_prop }
              { \tl_use:c { l__exsheets_questions_#1_tl } }
              \l__exsheets_tmpa_tl
            \tl_if_eq:NNTF \l__exsheets_tmpa_tl \q_no_value
              {
                \bool_set_false:c { l__exsheets_#1_active_bool }
                \bool_set_false:N \l__exsheets_questions_print_bool
              }
              {
                \bool_set_true:c { l__exsheets_#1_active_bool }
                \bool_set_true:N \l__exsheets_use_this_question_bool
              }
          }
      }
    \cs_new_protected:cpn { __exsheets_solutions_use_#2: }
      {
        % are we using #2?
        \bool_if:cT { g__exsheets_use_#2_bool }
          {
            % is the question to this solution an active one?
            % get question number from ID
            \prop_get:NoN \g__exsheets_questions_id_prop
              { \g__exsheets_questions_current_id_tl } \l__exsheets_tmpa_tl
            % get question #1 from number
            \prop_get:coN { g__exsheets_questions_#1_prop }
              { \l__exsheets_tmpa_tl } \l__exsheets_tmpb_tl
            % test if #1 is active
            \prop_get:coN { g__exsheets_#2_active_prop }
              { \l__exsheets_tmpb_tl } \l__exsheets_tmpc_tl
            \tl_if_eq:NNT \l__exsheets_tmpc_tl \q_no_value
              { \bool_set_false:N \l__exsheets_solutions_use_bool }
          }
      }
  }

\cs_new_protected:Npn \exsheets_declare_question_class:nn #1#2
  {
    \prop_if_in:NnTF \l__exsheets_class_prop { #2 }
      {}
      { \exsheets_new_question_class:nn { #1 } { #2 } }
  }

\NewDocumentCommand \DeclareQuestionClass { mm }
  { \exsheets_declare_question_class:nn { #1 } { #2 } }
\@onlypreamble \DeclareQuestionClass

\cs_new:Npn \exsheets_get_question_class:n #1
  {
    \cs_if_exist:cT { l__exsheets_questions_#1_tl }
      { \tl_use:c { l__exsheets_questions_#1_tl } }
  }

\DeclareExpandableDocumentCommand \GetQuestionClass { m }
  { \exsheets_get_question_class:n { #1 } }

\cs_new_protected:Npn \exsheets_print_question_class:nTF #1#2#3
  {
    \group_begin:
      \tl_set:Nx \l__exsheets_tmpa_tl
        { \exsheets_get_question_class:n { #1 } }
      \tl_if_blank:VTF \l__exsheets_tmpa_tl
        { #3 }
        {
          \cs_set_protected:Npn \__exsheets_print_question_class:n ##1 { #2 }
          \__exsheets_print_question_class:n
            { \exsheets_get_question_class:n { #1 } }
        }
    \group_end:
  }
\NewDocumentCommand \PrintQuestionClassTF { mmm }
  { \exsheets_print_question_class:nTF { #1 } { #2 } { #3 } }
\NewDocumentCommand \PrintQuestionClassT { mm }
  { \exsheets_print_question_class:nTF { #1 } { #2 } {    } }
\NewDocumentCommand \PrintQuestionClassF { mm }
  { \exsheets_print_question_class:nTF { #1 } {    } { #2 } }

% ----------------------------------------------------------------------------
% die 'question' Umgebung
\tl_new:N         \l__exsheets_questions_name_tl
\tl_set:Nn        \l__exsheets_questions_name_tl { Question }
\tl_new:N         \l__exsheets_exercise_name_tl
\tl_set:Nn        \l__exsheets_exercise_name_tl { Exercise }

\tl_new:N \CurrentQuestionID

\bool_new:N       \l__exsheets_questions_print_bool
\bool_set_true:N  \l__exsheets_questions_print_bool
\bool_new:N       \l__exsheets_inside_question_bool

\int_new:N        \g__exsheets_questions_id_int
\int_gzero:N      \g__exsheets_questions_id_int

\cs_new:Npn \IfInsideQuestionTF
  { \bool_if:NTF \l__exsheets_inside_question_bool }
\cs_new:Npn \IfInsideQuestionT
  { \bool_if:NT \l__exsheets_inside_question_bool }
\cs_new:Npn \IfInsideQuestionF
  { \bool_if:NF \l__exsheets_inside_question_bool }

\cs_new_eq:NN \exsheets_par: \par

\NewEnviron { __exsheets_questions_internal: }
  {
    \csappto { BODY }
      {
        \cs_if_eq:NNTF \exsheets_par: \scan_stop:
          { \c_space_tl }
          {
            \exsheets_par:
            \dim_compare:nNnT { \parskip } = { 0pt }
              { \exsheets_glue:N \l__exsheets_questions_skip_below_dim }
          }
      }
    \bool_if:nT
      {
        \l__exsheets_questions_print_bool &&
        \g__exsheets_questions_use_bool &&
        !\l__exsheets_questions_deactivate_bool
      }
      {
        \__exsheets_save_number_in:N \g__exsheets_question_number_prop
        \BODY
      }
  }

\prop_new:N \g__exsheets_questions_id_prop
\prop_new:N \g__exsheets_questions_subtitle_prop
\prop_new:N \g__exsheets_questions_used_prop
\int_new:N  \g__exsheets_questions_used_int

\tl_new:N   \l__exsheets_questions_id_tl
\tl_new:N   \l__exsheets_questions_subtitle_tl
\tl_new:N   \g__exsheets_questions_current_id_tl
\tl_new:N   \l__exsheets_questions_title_tl
\tl_new:N   \l__exsheets_questions_label_tl
\tl_new:N   \l__exsheets_questions_points_tl

\prg_new_conditional:Npnn \exsheets_if_question_subtitle: { p,T,F,TF }
  {
    \tl_if_blank:VTF \l__exsheets_questions_subtitle_tl
      { \prg_return_false: }
      { \prg_return_true: }
  }

\cs_new:Npn \IfQuestionSubtitleTF { \exsheets_if_question_subtitle:TF }
\cs_new:Npn \IfQuestionSubtitleT  { \exsheets_if_question_subtitle:T }
\cs_new:Npn \IfQuestionSubtitleF  { \exsheets_if_question_subtitle:F }

\bool_new:N \l__exsheets_only_print_points_bool

\fp_new:N \g__exsheets_this_question_points_fp
\fp_new:N \g__exsheets_this_question_bonus_fp

\cs_new:Npn \__exsheets_read_points:w #1 ! #2 ! #3 \q_stop
  {
    \tl_if_blank:nTF { #1 }
      {
        \bool_set_true:N \l__exsheets_only_print_points_bool
        \tl_set:Nn \l__exsheets_questions_points_tl { #2 }
      }
      {
        \bool_set_false:N \l__exsheets_only_print_points_bool
        \__exsheets_read_points_aux:w #1++ \q_stop
      }
  }

\cs_new_protected:Npn \__exsheets_read_points_aux:w #1+#2+#3 \q_stop
  {
    \tl_if_blank:nTF { #1 }
      { \fp_zero:N \l__exsheets_question_points_fp }
      { \fp_set:Nn \l__exsheets_question_points_fp { #1 } }
    \tl_if_blank:nTF { #2 }
      { \fp_zero:N \l__exsheets_question_bonus_fp }
      {
        \tl_if_blank:nTF { #3 }
          { \fp_zero:N \l__exsheets_question_bonus_fp }
          { \fp_set:Nn \l__exsheets_question_bonus_fp { #2 } }
      }
  }
\cs_new_protected:Npn \__exsheets_read_points:n #1
  {
    \bool_if:NTF \l__exsheets_parse_points_bool
      { \__exsheets_read_points:w #1!! \q_stop }
      { \tl_set:Nn \l__exsheets_questions_points_tl { #1 } }
  }

\cs_new:Npn \exsheets_label_format:n #1 { qu:#1 }
\cs_new:Npn \__exsheets_label:n { \label }
\cs_new:Npn \exsheets_label:n { }
\cs_generate_variant:Nn \exsheets_label:n { V }
\cs_new:Npn \__exsheets_ref:n { \ref }
\cs_new:Npn \exsheets_ref:n { }
\cs_new:Npn \__exsheets_pageref:n { \pageref }
\cs_new:Npn \exsheets_pageref:n { }

\cs_new_protected:Npn \exsheets_update_referencing_command:NN #1#2
  {
    \cs_set:Npx #1 ##1
      { \exp_not:o { #2 } { \exsheets_label_format:n { ##1 } } }
  }

\cs_new_protected:Npn \exsheets_update_referencing_commands:
  {
    \exsheets_update_referencing_command:NN \exsheets_label:n \__exsheets_label:n
    \exsheets_update_referencing_command:NN \exsheets_ref:n \__exsheets_ref:n
    \exsheets_update_referencing_command:NN \exsheets_pageref:n \__exsheets_pageref:n
  }

\cs_new_protected:Npn \exsheets_set_ref_properties:n #1
  {
    \exsheets_set_question_properties:x
      {
        ref = \exp_not:o { \exsheets_ref:n { #1 } } ,
        pageref = \exp_not:o { \exsheets_pageref:n { #1 } }
      }
  }
\cs_generate_variant:Nn \exsheets_set_ref_properties:n { V }

\keys_define:nn { exsheets }
  {
    label-format .code:n =
      \cs_set:Npn \exsheets_label_format:n ##1 { #1 }
      \exsheets_update_referencing_commands: ,
    label-cmd    .code:n =
      \cs_set:Npn \__exsheets_label:n { #1 }
      \exsheets_update_referencing_commands: ,
    ref-cmd      .code:n =
      \cs_set:Npn \__exsheets_ref:n { #1 }
      \exsheets_update_referencing_commands: ,
    page-ref-cmd .code:n =
      \cs_set:Npn \__exsheets_pageref:n { #1 }
      \exsheets_update_referencing_commands:
  }

\exsheets_update_referencing_commands:

\newenvironment { __exsheets_question: } [2]
  {
    \bool_set_true:N \l__exsheets_inside_question_bool
    \bool_if:NT \l__exsheets_questions_use_bool
      { \bool_gset_true:N \g__exsheets_questions_use_bool }
    % Optionen:
    \IfNoValueF { #1 } { \keys_set:nn { exsheets / question } { #1 } }
    % ID:
    \bool_if:nT
      { 
        (\l__exsheets_questions_deactivate_bool && \l__exsheets_select_questions_bool)
          ||
        !\l__exsheets_select_questions_bool
      }
      {
        \int_gincr:N \g__exsheets_questions_id_int
        \tl_if_blank:VTF \l__exsheets_questions_id_tl
          {
            \tl_gset:Nx \g__exsheets_questions_current_id_tl
              { \int_use:N \g__exsheets_questions_id_int }
          }
          {
            \tl_gset:Nx \g__exsheets_questions_current_id_tl
              { \tl_use:N \l__exsheets_questions_id_tl }
          }   
        \tl_if_blank:VF \l__exsheets_questions_subtitle_tl
          {
            \exsheets_set_question_properties:x
              { subtitle = { \exp_not:V \l__exsheets_questions_subtitle_tl } }
            % this is used in the headings instance; could maybe be replaced
            % by retrieving the property...
            % \prop_gput:NVV \g__exsheets_questions_subtitle_prop
            %   \g__exsheets_questions_current_id_tl
            %   \l__exsheets_questions_subtitle_tl
          }
      }
    \bool_if:nT
      { 
        !\l__exsheets_questions_deactivate_bool &&
        !\l__exsheets_select_questions_bool
      }
      {
        \bool_if:NT \l__exsheets_questions_use_bool
          {
            \prop_gput:NVV \g__exsheets_questions_used_prop
              \g__exsheets_questions_current_id_tl
              \g__exsheets_questions_id_int
            \int_gincr:N \g__exsheets_questions_used_int
          }
        \prop_gput:NVV \g__exsheets_questions_id_prop
          \g__exsheets_questions_current_id_tl
          \g__exsheets_questions_id_int
      }
    % Punktevergabe:
    \fp_gzero:N \g__exsheets_this_question_points_fp
    \fp_gzero:N \g__exsheets_this_question_bonus_fp
    \IfNoValueTF { #2 }
      {
        \__exsheets_read_points:n { 0 }
        \bool_if:NT \l__exsheets_points_questions_default_bool
          {
            \fp_set_eq:NN
              \l__exsheets_question_points_fp
              \l__exsheets_points_default_fp
            % check if moving this to a later point has negative effects...
            % \exsheets_set_question_properties:x
            %   { points = \fp_to_tl:N \l__exsheets_points_default_fp }
          }
      }
      {
        \fp_gset_eq:NN
          \g__exsheets_this_question_points_fp
          \l__exsheets_question_points_fp
        \__exsheets_read_points:n { #2 }
        % check if moving this to a later point has negative effects...
        % \exsheets_set_question_properties:n { points = #2 }
      }
    \tl_if_blank:VT \l__exsheets_question_heading_instance_tl
      {
        \tl_set_eq:NN
          \l__exsheets_question_heading_instance_tl
          \l__exsheets_heading_instance_tl
      }
    % Auswahl der Frage:
    \__exsheets_select_question:V \g__exsheets_questions_current_id_tl
    \prop_map_inline:Nn \l__exsheets_class_prop
      { \use:c { __exsheets_questions_use_##1: } }
    \bool_if:nT
      {
        \g__exsheets_questions_use_bool &&
        !\l__exsheets_questions_deactivate_bool
      }
      {
        \tl_clear:N \l__exsheets_step_counter_tl
        % das ist etwas mühsam: abhängig von der Nutzung der verschiedenen
        % Gruppierungsmöglichkeiten muss der Counter erhöht werden:
        \prop_map_inline:Nn \l__exsheets_class_prop
          {
            \use:c { __exsheets_questions_use_##1: }
            \bool_if:nTF
              {
                (
                  \l__exsheets_use_this_question_bool
                    &&
                  \bool_if_p:c { l__exsheets_##2_active_bool }
                )
                  ||
                ! \bool_if_p:c { g__exsheets_use_##1_bool }
              }
              { \tl_put_right:Nn \l__exsheets_step_counter_tl { y } }
              { \tl_put_right:Nn \l__exsheets_step_counter_tl { n } }
          }
        % erhöhe jetzt, wenn kein Nein dabei war:
        \tl_if_in:NnF \l__exsheets_step_counter_tl { n }
          { \refstepcounter{question} }
        % label:
        \tl_if_blank:VTF \l__exsheets_questions_label_tl
          {
            \bool_if:NT \l__exsheets_auto_label_bool
              {
                \exsheets_label:V \g__exsheets_questions_current_id_tl
                \exsheets_set_ref_properties:V \g__exsheets_questions_current_id_tl
              }
          }
          {
            \exsheets_label:V \l__exsheets_questions_label_tl
            \exsheets_set_ref_properties:V \l__exsheets_questions_label_tl
          }
        \__exsheets_get_sectioning_numbers:
        \bool_if:nT
          {
            (
              \l__exsheets_points_questions_default_bool &&
              \l__exsheets_parse_points_bool
            ) ||
            (
              \l__exsheets_parse_points_bool &&
              \l__exsheets_questions_print_bool
            )
          }
          {
            \exsheets_add_points:V \l__exsheets_question_points_fp
            \exsheets_add_bonus:V  \l__exsheets_question_bonus_fp
          }
        \bool_if:NT \l__exsheets_questions_print_bool
          {
            \bool_if:NTF \l__exsheets_exam_bool
              {
                \tl_set_eq:NN
                  \l__exsheets_questions_title_tl
                  \l__exsheets_questions_name_tl
              }
              {
                \tl_set_eq:NN
                  \l__exsheets_questions_title_tl
                  \l__exsheets_exercise_name_tl
              }
            \tl_if_blank:VTF \l__exsheets_questions_id_tl
              {
                \tl_set:Nx \l__exsheets_tmpa_tl
                  { \int_use:N \g__exsheets_questions_id_int }
              }
              {
                \tl_set_eq:NN
                  \l__exsheets_tmpa_tl
                  \l__exsheets_questions_id_tl
              }
            \tl_set_eq:NN \CurrentQuestionID \l__exsheets_tmpa_tl
            \bool_if:nTF
              { \l__exsheets_parse_points_bool && !\l__exsheets_only_print_points_bool }
              {
                \__exsheets_use_heading:VVVnnV
                  \l__exsheets_question_heading_instance_tl
                  \l__exsheets_questions_title_tl
                  \l__exsheets_qu_counter_interpretation_tl
                  { \l__exsheets_question_points_fp }
                  { \l__exsheets_question_bonus_fp }
                  \l__exsheets_tmpa_tl
              }
              {
                \bool_if:NT \l__exsheets_only_print_points_bool
                  { \bool_set_false:N \l__exsheets_parse_points_bool }
                % might be dangerous to expand here...
                \tl_if_blank:xTF { \l__exsheets_questions_points_tl }
                  {
                    \__exsheets_use_heading:VVVnnV
                      \l__exsheets_question_heading_instance_tl
                      \l__exsheets_questions_title_tl
                      \l__exsheets_qu_counter_interpretation_tl
                      { 0 }
                      { 0 }
                      \l__exsheets_tmpa_tl
                  }
                  {
                    \__exsheets_use_heading:VVVnnV
                      \l__exsheets_question_heading_instance_tl
                      \l__exsheets_questions_title_tl
                      \l__exsheets_qu_counter_interpretation_tl
                      { \l__exsheets_questions_points_tl }
                      { 0 }
                      \l__exsheets_tmpa_tl
                  }
              }
          }
      }
    \__exsheets_questions_internal:
  }
  {
    \end__exsheets_questions_internal:
    \bool_if:NF \l__exsheets_points_questions_default_bool
      {
        \fp_compare:nT { \g__exsheets_this_question_points_fp > 0 }
          {
            \exsheets_set_question_properties:x
              { points = \fp_to_tl:N \g__exsheets_this_question_points_fp }
          }
      }
  }

% current question number:
\prop_new:N \g__exsheets_question_number_prop

\cs_new_protected:Npn \exsheets@save@number #1#2
  { \expandafter\global\expandafter\edef\csname exsheets@question@#1\endcsname{#2} }

\cs_new_protected:Npn \__exsheets_save_number_in_aux_x:Nnn #1#2#3
  {
    \prop_gput:Nfx #1 { #2 } { #3 }
    \exsheets_write_to_aux_x:n { \exsheets@save@number { #2 } { #3 } }
  }

\cs_new_protected:Npn \__exsheets_save_number_in:N #1
  {
    \bool_if:NTF \l__exsheets_print_number_bool
      {
        \cs_if_exist:NTF \thechapter
          {
            \__exsheets_save_number_in_aux_x:Nnn #1
              { \int_use:N \g__exsheets_questions_id_int }
              { \arabic{chapter}-\arabic{section}-\arabic{question} }
          }
          {
            \__exsheets_save_number_in_aux_x:Nnn #1
              { \int_use:N \g__exsheets_questions_id_int }
              { -\arabic{section}-\arabic{question} }
          }
      }
      {
        \cs_if_exist:NTF \thechapter
          {
            \__exsheets_save_number_in_aux_x:Nnn #1
              { \int_use:N \g__exsheets_questions_id_int }
              { @@@\arabic{chapter}-\arabic{section}-\arabic{question} }
          }
          {
            \__exsheets_save_number_in_aux_x:Nnn #1
              { \int_use:N \g__exsheets_questions_id_int }
              { @@@-\arabic{section}-\arabic{question} }
          }
      }
  }

\cs_new_protected:Npn \__exsheets_restore_number_from_and_do:Nnn #1#2#3
  {
    \prop_get:NnN #1 { #2 } \l__exsheets_tmpc_tl
    \tl_if_eq:NNF \l__exsheets_tmpc_tl \q_no_value
      {
        \exp_after:wN
        \__exsheets_read_number:w \l__exsheets_tmpc_tl \q_stop
        #3
      }
    % use \exsheets_read_counter_settings:V \l__exsheets_qu_counter_format_tl
    % afterwards to print the number
  }
\cs_generate_variant:Nn \__exsheets_restore_number_from_and_do:Nnn { NV }

\NewDocumentCommand \QuestionNumber { m }
  { \exsheets_question_number:n { #1 } }

\cs_new_protected:Npn \exsheets_question_number:n #1
  {
    \prop_get:NnNTF \g__exsheets_questions_id_prop { #1 } \l__exsheets_tmpa_tl
      { \__exsheets_question_number:c { exsheets@question@\l__exsheets_tmpa_tl } }
      { \textbf{??} }
  }
 
\cs_new:Npn \__exsheets_question_number:N #1
  {
    \cs_if_exist:NTF #1
      {
        \exp_after:wN \__exsheets_get_question_number:w #1 \q_stop
        \ReadCounterPatternFrom [ exsheets ] \l__exsheets_qu_counter_pattern_tl
      }
      { \textbf{??} }
  }
\cs_generate_variant:Nn \__exsheets_question_number:N { c }

\cs_new_protected:Npn \__exsheets_get_question_number:w #1-#2-#3 \q_stop
  {
    \cs_if_exist:NT \thechapter
      { \int_set:Nn \l__exsheets_counter_ch_int { #1 } }
    \int_set:Nn \l__exsheets_counter_sec_int { #2 }
    \int_set:Nn \l__exsheets_counter_qu_int { #3 }
  }

% ----------------------------------------------------------------------------
% title of a question:
\input { exsheets_headings.def }
\bool_if:NT \l__exsheets_load_headings_bool
  { \input { exsheets_headings.cfg } }
% #1: instance
% #2: title
% #3: number
% #4: points
% #5: bonus
% #6: id
\cs_new_nopar:Npn \__exsheets_use_heading:nnnnnn #1#2#3#4#5#6
  {
    \IfInstanceExistTF { exsheets-heading } { #1 }
      { \UseInstance { exsheets-heading } { #1 } }
      {
        \msg_warning:nnx { exsheets} { headings } { #1 }
        \UseInstance { exsheets-heading } { block }
      }
    { #2 } { #3 } { #4 } { #5 } { #6 }
  }
\cs_generate_variant:Nn \__exsheets_use_heading:nnnnnn { V , VVVnnV }

\bool_new:N       \l__exsheets_exam_bool
\bool_set_false:N \l__exsheets_exam_bool
\bool_new:N       \l__exsheets_questions_runin_bool
\bool_set_false:N \l__exsheets_questions_runin_bool

% options for the questions:
\keys_define:nn { exsheets / question }
  {
    type            .choice: ,
    type / exam     .code:n      =
      \bool_set_true:N \l__exsheets_exam_bool ,
    type / exercise .code:n      =
      \bool_set_false:N \l__exsheets_exam_bool ,
    name            .code:n      =
      \tl_set:Nn \l__exsheets_exercise_name_tl { #1 }
      \tl_set:Nn \l__exsheets_questions_name_tl { #1 } ,
    headings        .tl_set:N    = \l__exsheets_question_heading_instance_tl ,
    subtitle        .tl_set:N    = \l__exsheets_questions_subtitle_tl ,
    print           .bool_set:N  = \l__exsheets_questions_print_bool ,
    print           .default:n   = true ,
    ID              .tl_set:N    = \l__exsheets_questions_id_tl ,
    label           .tl_set:N    = \l__exsheets_questions_label_tl ,
    use             .choice: ,
    use / true      .code:n      =
      \bool_gset_true:N \g__exsheets_questions_use_bool
      \bool_set_true:N  \l__exsheets_questions_use_bool ,
    use / false     .code:n      =
      \bool_gset_false:N \g__exsheets_questions_use_bool
      \bool_set_false:N  \l__exsheets_questions_use_bool ,
    use             .default:n   = true ,
    skip-below      .dim_set:N   = \l__exsheets_questions_skip_below_dim
  }

% ----------------------------------------------------------------------------
% using ``metadata'':
\cs_new_protected:Npn \exsheets_declare_question_property:n #1
  {
    \prop_new:c { g__exsheets_question_property_#1_prop }
    \keys_define:nn { question / meta }
      { #1 .code:n = \__exsheets_question_set_property:nn { #1 } { ##1 } }
  }

\NewDocumentCommand \DeclareQuestionProperty { m }
  { \exsheets_declare_question_property:n { #1 } }
\@onlypreamble \DeclareQuestionProperty

\cs_new_protected:Npn \exsheets_set_question_properties:n #1
  {
    \@bsphack
      \bool_if:NTF \l__exsheets_inside_question_bool
        { \keys_set:nn { question / meta } { #1 } }
        {
          \msg_error:nnn { exsheets } { only-inside-question }
            { \SetQuestionProperties }
        }
    \@esphack
  }
\cs_generate_variant:Nn \exsheets_set_question_properties:n { x }

\NewDocumentCommand \SetQuestionProperties { m }
  { \exsheets_set_question_properties:n { #1 } }

% #1: ID
% #2: property
% #3: value
\cs_new:Npn \exsheets@question@property #1#2#3
  {
    \prop_gput:cnn { g__exsheets_question_property_#2_prop }
      { #1 } { #3 }
  }

% #1: property
% #2: value
\cs_new_protected:Npn \__exsheets_question_set_property:nn #1#2
  {
    \prop_gput:cVn { g__exsheets_question_property_#1_prop }
      \g__exsheets_questions_current_id_tl { #2 }
    % watch if this has negativ effects:
    \exsheets_write_to_aux_x:n
      {
        \exp_not:N \exsheets@question@property
          { \g__exsheets_questions_current_id_tl }
          { \exp_not:n {#1} }
          { \exp_not:n {#2} }
      }
  }

% #1: property
% #2: ID
\DeclareExpandableDocumentCommand \GetQuestionProperty { mm }
  { \exsheets_get_question_property:no { #1 } { #2 } }

\cs_new:Npn \exsheets_get_question_property:nn #1#2
  {
    \prop_if_in:cnT { g__exsheets_question_property_#1_prop } { #2 }
      { \prop_get:cn { g__exsheets_question_property_#1_prop } { #2 } }
  }
\cs_generate_variant:Nn \exsheets_get_question_property:nn { no }

\int_new:N \g__exsheets_tmpa_int
\cs_new_protected:Npn \ForEachQuestion #1
  {
    \int_gzero:N \g__exsheets_tmpa_int
    \prop_map_inline:Nn \g__exsheets_questions_used_prop
      { \int_gincr:N \g__exsheets_tmpa_int #1 }
  }

\cs_new:Npn \iflastquestion
  {
    \int_compare:nTF
      { \g__exsheets_questions_used_int = \g__exsheets_tmpa_int }
  }
  
\cs_new:Npn \numberofquestions
  { \int_use:N \g__exsheets_questions_used_int }

% ----------------------------------------------------------------------------
% debug-Info:
\bool_new:N       \l__exsheets_questions_debug_bool
\bool_set_false:N \l__exsheets_questions_debug_bool

\colorlet { exsheetsdebugcolor } { yellow }

\cs_new_protected:Npn \exsheets_debug_box:nn #1#2
  {
    \exsheets_par:
    \noindent
    \group_begin:
      \normalfont\normalsize\normalcolor
      \colorbox { exsheetsdebugcolor }
        { \parbox { \dim_eval:n { #1  - 2 \fboxsep } } { #2 } }
    \group_end:
    \exsheets_par:
  }

\cs_new:Npn \__exsheets_list_comma: {}

\cs_new_protected:Npn \exsheets_questions_debug:
  {
    \bool_if:nT
      { \l__exsheets_questions_debug_bool && \l__exsheets_inside_question_bool }
      {
        \exsheets_debug_box:nn { \linewidth }
          {
            \fbox
              {
                ID:~
                \textit
                  {
                    \tl_if_blank:VTF \l__exsheets_questions_id_tl
                      { \int_use:N \g__exsheets_questions_id_int }
                      { \tl_use:N \l__exsheets_questions_id_tl }
                  }
              }
            \cs_set_protected:Npn \__exsheets_list_comma:
              { ~ \cs_set:Npn \__exsheets_list_comma: { ,~ } }
            \prop_map_inline:Nn \l__exsheets_class_prop
              {
                \bool_if:cT { l__exsheets_questions_##2_bool }
                  {
                    \__exsheets_list_comma: ##2:~
                    \textit { \tl_use:c { l__exsheets_questions_##2_tl } }
                  }
              }
          }
      }
  }

\NewDocumentCommand \DebugExSheets { G{true} }
  { \use:c { bool_set_#1:N } \l__exsheets_questions_debug_bool }

% ----------------------------------------------------------------------------
% include random/selected questions from a file:
\bool_new:N      \l__exsheets_select_questions_bool
\bool_new:N      \l__exsheets_include_all_bool
\bool_new:N      \l__exsheets_include_random_bool
\bool_new:N      \l__exsheets_include_by_id_bool
\bool_set_true:N \l__exsheets_include_all_bool

\prop_new:N      \g__exsheets_included_questions_prop
\clist_new:N     \l__exsheets_include_id_clist
\clist_new:N     \l__exsheets_exclude_id_clist
\clist_new:N     \questionsincludedlast

\int_new:N       \l__exsheets_include_random_int
\int_zero:N      \l__exsheets_include_random_int

\cs_new:Npn \exsheets_file_input_if_exist:n #1
  { \file_if_exist:nT { #1 } { \file_input:n { #1 } } }

\cs_new_protected:Npn \exsheets_prop_count:N #1
  {
    \__exsheets_prop_count:NN #1 \l__exsheets_tmpa_int
    \int_use:N \l__exsheets_tmpa_int
  }

\cs_new_protected:Npn \__exsheets_prop_count:NN #1#2
  {
    \int_zero:N #2
    \prop_map_inline:Nn #1
      { \int_incr:N #2 }
  }

\NewDocumentCommand \includequestions { om }
  {
    \group_begin:
      \IfNoValueF { #1 }
        { \keys_set:nn { exsheets / include } { #1 } }
      \exsheets_include_questions:n { #2 }
    \group_end:
  }

\int_new:N \l__exsheets_questions_set_int
\int_new:N \g__exsheets_select_random_int

\cs_new_protected:Npn \exsheets_include_questions:n #1
  {
    \bool_set_true:N \l__exsheets_select_questions_bool
    \clist_gclear:N \questionsincludedlast
    \seq_set_split:Nnn \l__exsheets_tmpa_seq { , } { #1 }
    \seq_map_inline:Nn \l__exsheets_tmpa_seq
      {
        \bool_set_true:N \l__exsheets_questions_deactivate_bool
        \int_set_eq:NN
          \l__exsheets_questions_set_int
          \g__exsheets_questions_used_int
        \int_set_eq:NN
          \l__exsheets_tmpc_int
          \g__exsheets_questions_id_int
        \int_gzero:N \g__exsheets_select_random_int
        \exsheets_file_input_if_exist:n { ##1 }
        \__exsheets_prop_count:NN
          \g__exsheets_included_questions_prop
          \l__exsheets_tmpa_int
        \bool_if:NT \l__exsheets_questions_debug_bool
          {
            \exsheets_debug_box:nn
              { \linewidth }
              {
                The~file~ ` \texttt { \tl_to_str:n { ##1 } } ' ~contains~
                \exsheets_prop_count:N \g__exsheets_included_questions_prop
                \c_space_tl questions~with~the~following~IDs:\par
                \cs_set_protected:Npn \__exsheets_list_comma:
                  { \cs_set:Npn \__exsheets_list_comma: { ,~ } }
                \prop_map_inline:Nn \g__exsheets_included_questions_prop
                  { \__exsheets_list_comma: ####2 }
              }
          }
        \bool_set_false:N \l__exsheets_questions_deactivate_bool
        \int_set_eq:NN    \l__exsheets_tmpd_int \g__exsheets_questions_id_int
        \int_gset_eq:NN   \g__exsheets_questions_id_int \l__exsheets_tmpc_int
        \__exsheets_select_question_random:n { ##1 }
        \exsheets_file_input_if_exist:n { ##1 }
        \int_gset_eq:NN   \g__exsheets_questions_id_int \l__exsheets_tmpd_int
        \prop_gclear:N    \g__exsheets_included_questions_prop
        \clist_clear:N    \l__exsheets_include_id_clist
        \clist_clear:N    \l__exsheets_exclude_id_clist
        \int_gzero:N      \g__exsheets_selection_number_int
      }
    \bool_set_false:N \l__exsheets_select_questions_bool
  }

% options:
%  - IDs=<list of IDs>
%  - all=true|false    % default when no option is given
%  - random=<num>
%  - exclude=<list of IDs>
\keys_define:nn { exsheets / include }
  {
    all     .bool_set:N  = \l__exsheets_include_all_bool ,
    IDs     .code:n      =
      \bool_set_false:N \l__exsheets_include_all_bool
      \bool_set_false:N \l__exsheets_include_random_bool
      \bool_set_true:N  \l__exsheets_include_by_id_bool
      \clist_set:Nn \l__exsheets_include_id_clist { #1 } ,
    % the `exclude' option does _not_ set \l__exsheets_include_random_bool ,
    % \l__exsheets_include_by_id_bool or \l__exsheets_include_all_bool so
    % it can be combined with the other options:
    exclude .clist_set:N = \l__exsheets_exclude_id_clist ,
    random  .code:n      =
      \bool_set_false:N \l__exsheets_include_all_bool
      \bool_set_true:N  \l__exsheets_include_random_bool
      \bool_set_false:N \l__exsheets_include_by_id_bool
      \int_set:Nn \l__exsheets_include_random_int { #1 }
  }

\int_new:N \g__exsheets_selection_number_int

\cs_new_protected:Npn \__exsheets_select_question:n #1
  {
    \bool_if:NT \l__exsheets_select_questions_bool
      {
        \bool_if:NTF \l__exsheets_questions_deactivate_bool
          {
            \bool_if:NT \l__exsheets_questions_use_bool
              {
                \int_gincr:N \g__exsheets_selection_number_int
                \bool_if:NTF \l__exsheets_include_random_bool
                  {
                    \prop_gput:Nxn \g__exsheets_included_questions_prop
                      { \int_use:N \g__exsheets_selection_number_int } { #1 }
                  }
                  {
                    \prop_gput:Nxn \g__exsheets_included_questions_prop
                      { \int_use:N \g__exsheets_questions_id_int } { #1 }
                  }
              }
          }
          {
            \int_gincr:N \g__exsheets_questions_id_int
            \bool_if:NTF \l__exsheets_include_random_bool
              {
                \int_gincr:N \g__exsheets_select_random_int
                \int_set_eq:NN \l__exsheets_tmpa_int \g__exsheets_select_random_int
%                 ID: \int_use:N \g__exsheets_questions_id_int ,~
%                 set: \int_use:N \l__exsheets_questions_set_int ,~
%                 selection: \int_use:N \g__exsheets_selection_number_int ,~
%                 tmpa: \int_use:N \l__exsheets_tmpa_int \par
              }
              {
                \int_set_eq:NN
                  \l__exsheets_tmpa_int
                  \g__exsheets_questions_id_int
              }
            \prop_get:NxN \g__exsheets_included_questions_prop
              {  \int_use:N \l__exsheets_tmpa_int }
              \l__exsheets_tmpa_tl
            \__exsheets_select_question_by_id:V \l__exsheets_tmpa_tl
          }
      }
  }
\cs_generate_variant:Nn \__exsheets_select_question:n { V }

\cs_new_protected:Npn \__exsheets_select_question_by_id:n #1
  {
    \bool_if:NTF \l__exsheets_include_all_bool
      {% parsing list of excluded IDs
        \clist_if_in:NnTF
          \l__exsheets_exclude_id_clist
          { #1 }
          { \bool_gset_false:N  \g__exsheets_questions_use_bool }
          {
            \bool_gset_true:N \g__exsheets_questions_use_bool
            \clist_gput_right:Nn \questionsincludedlast { #1 }
            \prop_gput:NnV \g__exsheets_questions_used_prop
              { #1 }
              \g__exsheets_questions_id_int
            \int_gincr:N \g__exsheets_questions_used_int
            \prop_gput:NnV \g__exsheets_questions_id_prop
              { #1 }
              \g__exsheets_questions_id_int
          }
      }
      {% parsing list of included IDs
        \clist_if_in:NnTF
          \l__exsheets_include_id_clist
          { #1 }
          {
            \clist_if_in:NnTF
              \l__exsheets_exclude_id_clist
              { #1 }
              { \bool_gset_false:N \g__exsheets_questions_use_bool }
              {
                \bool_gset_true:N  \g__exsheets_questions_use_bool
                \clist_gput_right:Nn \questionsincludedlast { #1 }
                \prop_gput:NnV \g__exsheets_questions_used_prop
                  { #1 }
                  \g__exsheets_questions_id_int
                \int_gincr:N \g__exsheets_questions_used_int
                \prop_gput:NnV \g__exsheets_questions_id_prop
                  { #1 }
                  \g__exsheets_questions_id_int
              }
          }
          { \bool_gset_false:N \g__exsheets_questions_use_bool }
      }
  }
\cs_generate_variant:Nn \__exsheets_select_question_by_id:n { V }

\tl_new:N \l__exsheets_include_id_tl
\bool_new:N \l__exsheets_use_selection_bool
% TODO: poor efficiency -- there should be no need to map through
% \l__exsheets_class_prop *two* times
\cs_new_protected:Npn \__exsheets_select_question_random:n #1
  {
    \bool_if:NT \l__exsheets_include_random_bool
      {
        % number of question in file:
        \__exsheets_prop_count:NN
          \g__exsheets_included_questions_prop
          \l__exsheets_tmpa_int
        % number of selectable questions in file:
        \int_zero:N \l__exsheets_tmpb_int
        \prop_map_inline:Nn \g__exsheets_included_questions_prop
          {
            \prop_map_inline:Nn \l__exsheets_class_prop
              {
                \bool_if:cT { g__exsheets_use_####1_bool }
                  {
                    \bool_set_true:N \l__exsheets_use_selection_bool
                    \prop_get:cnNT { g__exsheets_questions_####2_prop } { ##1 }
                      \l__exsheets_tmpa_tl
                      {
                        \prop_if_in:cVT { g__exsheets_####1_active_prop }
                          \l__exsheets_tmpa_tl
                          { \int_incr:N \l__exsheets_tmpb_int }
                      }
                  }
              }
          }
        \int_compare:nTF { \l__exsheets_include_random_int >= \l__exsheets_tmpa_int }
          {
            % not enough questions available:
            \msg_warning:nnxxx { exsheets } { random-file }
              { \int_use:N \l__exsheets_include_random_int }
              { #1 }
              { \int_use:N \l__exsheets_tmpa_int }
            \bool_set_true:N \l__exsheets_include_all_bool
          }
          {
            \bool_if:nTF
              {
                \int_compare_p:n
                  { \l__exsheets_include_random_int >= \l__exsheets_tmpb_int }
                  &&
                \l__exsheets_use_selection_bool
              }
              {
                % not enough questions selectable:
                \msg_warning:nnxxxx { exsheets } { random-selectable }
                  { \int_use:N \l__exsheets_include_random_int }
                  { #1 }
                  { \int_use:N \l__exsheets_tmpa_int }
                  { \int_use:N \l__exsheets_tmpb_int }
                \bool_set_true:N \l__exsheets_include_all_bool
              }
              {
                \int_zero:N \l__exsheets_tmpb_int
                \int_do_while:nn
                  { \l__exsheets_tmpb_int < \l__exsheets_include_random_int }
                  {
                    \pgfmathparse { random(\int_use:N \l__exsheets_tmpa_int) }
                    \tl_set_eq:NN \l__exsheets_tmpa_tl \pgfmathresult
                    \prop_get:NVN \g__exsheets_included_questions_prop
                      \l__exsheets_tmpa_tl
                      \l__exsheets_tmpb_tl
                    \clist_if_in:NVF \l__exsheets_include_id_clist \l__exsheets_tmpb_tl
                      {
                        \tl_clear:N \l__exsheets_include_id_tl
                        \prop_map_inline:Nn \l__exsheets_class_prop
                          {
                            \prop_get:cVNT { g__exsheets_questions_##2_prop }
                              \l__exsheets_tmpa_tl \l__exsheets_tmpc_tl
                              {
                                \bool_if:cT { g__exsheets_use_##1_bool }
                                  {
                                    \prop_if_in:cVTF { g__exsheets_##1_active_prop }
                                      \l__exsheets_tmpc_tl
                                      { \tl_put_right:Nn \l__exsheets_include_id_tl { y } }
                                      { \tl_put_right:Nn \l__exsheets_include_id_tl { n } }
                                  }
                              }
                          }
                        \tl_if_in:NnF \l__exsheets_include_id_tl { n }
                          {
                            \clist_if_in:NVF \l__exsheets_exclude_id_clist \l__exsheets_tmpb_tl
                              {
                                \clist_put_right:NV
                                  \l__exsheets_include_id_clist
                                  \l__exsheets_tmpb_tl
                                \int_incr:N \l__exsheets_tmpb_int
                              }
                          }
                      }
                  }
              }
          }
      }
  }

\NewDocumentCommand \PrintIfIncludeActiveTF { mm }
  { \bool_if:NTF \l__exsheets_questions_deactivate_bool { #2 } { #1 } }

\NewDocumentCommand \PrintIfIncludeActiveT { }
  { \bool_if:NF \l__exsheets_questions_deactivate_bool }

\NewDocumentCommand \PrintIfIncludeActiveF { }
  { \bool_if:NT \l__exsheets_questions_deactivate_bool }

% ----------------------------------------------------------------------------
% die 'solution' Umgebung:
\bool_new:N       \l__exsheets_solutions_print_bool
\bool_set_false:N \l__exsheets_solutions_print_bool
\bool_new:N       \l__exsheets_solutions_print_here_bool
\bool_set_false:N \l__exsheets_solutions_print_here_bool
\bool_new:N       \l__exsheets_solutions_print_section_bool
\bool_set_false:N \l__exsheets_solutions_print_section_bool
\bool_new:N       \l__exsheets_solutions_print_chapter_bool
\bool_set_false:N \l__exsheets_solutions_print_chapter_bool
\bool_new:N       \l__exsheets_solutions_print_all_bool
\bool_set_false:N \l__exsheets_solutions_print_all_bool

% \prop_new:N       \g__exsheets_question_number_prop
\prop_new:N       \g__exsheets_solutions_content_prop
\prop_new:N       \g__exsheets_solutions_questions_id_prop
\prop_new:N       \g__exsheets_solutions_names_prop

\tl_new:N         \l__exsheets_solutions_name_tl
\tl_set:Nn        \l__exsheets_solutions_name_tl { Solution }

\cs_new_protected:Npn \__exsheets_save_solution:n #1
  {
    % save for later use
    \bool_if:NTF \l__exsheets_include_all_bool
      { \int_set:Nn \l__exsheets_tmpe_int { \g__exsheets_questions_id_int -1 } }
      { \int_set_eq:NN \l__exsheets_tmpe_int \g__exsheets_questions_id_int }
    \prop_gput:Nff \g__exsheets_solutions_content_prop
      { \int_use:N \g__exsheets_questions_id_int }
      { #1 }
    \prop_gput:Nff \g__exsheets_solutions_questions_id_prop
      { \int_use:N \g__exsheets_questions_id_int }
      { \tl_use:N \g__exsheets_questions_current_id_tl }
    \prop_gput:Nff \g__exsheets_solutions_names_prop
      { \int_use:N \g__exsheets_questions_id_int }
      { \tl_use:N \l__exsheets_solutions_name_tl }
    % print here
    \bool_if:NT \l__exsheets_solutions_print_here_bool
      {
        \int_set:Nn \l__exsheets_counter_qu_int { \arabic{question} }
        \__exsheets_get_sectioning_numbers:
        \__exsheets_solutions_name:VVV
          \l__exsheets_qu_counter_interpretation_tl
          \l__exsheets_solutions_name_tl
          \g__exsheets_questions_current_id_tl
        \use:n { #1 }
        \cs_if_eq:NNTF \exsheets_par: \scan_stop:
          { \c_space_tl }
          {
            \exsheets_par:
            \dim_compare:nNnT { \parskip } = { 0pt }
              { \exsheets_glue:N \l__exsheets_solutions_skip_below_dim }
          }
      }
  }
\cs_generate_variant:Nn \__exsheets_save_solution:n { V }

\NewEnviron { __exsheets_solution_internal: }
  {
    \bool_if:nT
      { \g__exsheets_questions_use_bool && \l__exsheets_solutions_use_bool }
      { \__exsheets_save_solution:V \BODY }
  }

\bool_new:N       \l__exsheets_inside_solution_bool
\bool_set_false:N \l__exsheets_inside_solution_bool

\tl_new:N \l__exsheets_use_solution_tl

\newenvironment { __exsheets_solution: } [1]
  {
    \tl_clear:N \l__exsheets_use_solution_tl
    \prop_map_inline:Nn \l__exsheets_class_prop
      {
        \use:c { __exsheets_solutions_use_##1: }
        \bool_if:nTF
          {
            (
              \l__exsheets_solutions_use_bool
                &&
              \bool_if_p:c { l__exsheets_##2_active_bool }
            )
             ||
            ! \bool_if_p:c { g__exsheets_use_##1_bool }
          }
          { \tl_put_right:Nn \l__exsheets_use_solution_tl { y } }
          { \tl_put_right:Nn \l__exsheets_use_solution_tl { n } }
      }
    % verwende, wenn ein Ja dabei war:
    \tl_if_in:NnT \l__exsheets_use_solution_tl { y }
      { \bool_set_true:N \l__exsheets_solutions_use_bool }
    \bool_if:NT \l__exsheets_questions_deactivate_bool
      { \bool_set_false:N \l__exsheets_solutions_use_bool }
    \bool_if:NT \l__exsheets_solutions_use_bool
      {
        \bool_set_true:N \l__exsheets_inside_solution_bool
        \IfNoValueF { #1 } { \keys_set:nn { exsheets / solution } { #1 } }
      }
    \tl_if_blank:VT \l__exsheets_solution_heading_instance_tl
      {
        \tl_set_eq:NN
          \l__exsheets_solution_heading_instance_tl
          \l__exsheets_heading_instance_tl
      }
    \__exsheets_solution_internal:
  }
  { \end__exsheets_solution_internal: }

\bool_new:N       \l__exsheets_solutions_runin_bool
\bool_set_false:N \l__exsheets_solutions_runin_bool

\cs_new_protected_nopar:Npn \__exsheets_solutions_name:nnn #1#2#3
  {
    \tl_if_blank:VT \l__exsheets_solution_heading_instance_tl
      {
        \tl_set_eq:NN
          \l__exsheets_solution_heading_instance_tl
          \l__exsheets_heading_instance_tl
      }
    \__exsheets_use_heading:Vnnnnn
      \l__exsheets_solution_heading_instance_tl
      { #2 } { #1 } { 0 } { 0 } { #3 }
  }
\cs_generate_variant:Nn \__exsheets_solutions_name:nnn { VV , VVV }

\tl_new:N  \l_exsheets_solutions_name_style_tl
\tl_set:Nn \l_exsheets_solutions_name_style_tl { \normalsize \bfseries }

\cs_new:Npn \exsheets_solutions_name_style:n #1
  { \l_exsheets_solutions_name_style_tl #1 }

% ----------------------------------------------------------------------------
% print solutions:
% save section / chapter counter:
\cs_new_protected:Npn \__exsheets_exlabel:n #1
  {
    \@bsphack
      \exsheets_write_to_aux_x:n
        {
          \token_to_str:N \newlabel { exse:#1 }
            { { \arabic { section } } { \thepage } }
        }
      \cs_if_exist:NT \thechapter
        {
          \exsheets_write_to_aux_x:n
            {
              \token_to_str:N \newlabel { exch:#1 }
                { { \arabic { chapter } } { \thepage } }
            }
        }
    \@esphack
  }

% user command:
\cs_new_eq:NN \exlabel \__exsheets_exlabel:n

% adapt \label, maybe do this _after_ BeginDocument:
\bool_if:NT \l__exsheets_solutions_by_ref_bool
  {
    \cs_new_eq:NN \__exsheets_saved_label:n \label
    \cs_set:Npn \label #1
      { \__exsheets_saved_label:n { #1 } \__exsheets_exlabel:n { #1 } }
  }

% this is like \ref from latex.ltx
\cs_new:Npn \__exsheets_exref:n #1
  {
    \cs_if_exist:cTF { r@#1 }
     { \__exsheets_exref_aux:n { #1 } }
     {
       1\relax
       \protect\G@refundefinedtrue
       \@latex@warning{exlabel `#1' on page \thepage \space undefined}%
     }
  }

\cs_new:Npn \__exsheets_exref_aux:n #1
  { \exp_after:wN \exp_after:wN \exp_after:wN \use_i:nn \cs:w r@#1 \cs_end: }

\cs_new_eq:NN \exref \__exsheets_exref:n

% user command:
\NewDocumentCommand \printsolutions { O{all} }
  { \exsheets_print_solutions:n { #1 } }

% internal command:
\cs_new_protected:Npn \exsheets_print_solutions:n #1
  {
    \group_begin:
      \bool_set_true:N \l__exsheets_solutions_print_bool
      \bool_set_true:N \l__exsheets_inside_solution_bool
      \cs_set:Npn \S ##1 { \exref { exse:##1 } }
      \cs_set:Npn \C ##1 { \exref { exch:##1 } }
      \keys_set:nn { exsheets / exsheets_print_solutions } { #1 }
    \group_end:
  }

\keys_define:nn { exsheets }
  {
    exsheets_print_solutions           .choice: ,
    exsheets_print_solutions / section .code:n    =
      { \exsheets_print_solutions_section:n { #1 } } ,
    exsheets_print_solutions / chapter .code:n    =
      { \exsheets_print_solutions_chapter:n { #1 } } ,
    exsheets_print_solutions / all     .code:n    =
      { \exsheets_print_solutions_all: } ,
    exsheets_print_solutions / byID    .code:n    =
      { \exsheets_print_solutions_byID:n { #1 } }
  }

\int_new:N \l__exsheets_counter_ch_int
\int_new:N \l__exsheets_counter_sec_int
\int_new:N \l__exsheets_counter_qu_int

\cs_new_protected:Npn \__exsheets_get_sectioning_numbers:
  {
    \cs_if_exist:NT \chapter
      { \int_set:Nn \l__exsheets_counter_ch_int { \arabic{chapter} } }
    \int_set:Nn \l__exsheets_counter_sec_int { \arabic{section} }
    \int_set:Nn \l__exsheets_counter_qu_int { \arabic{question} }
  }

\cs_new_protected:Npn \__exsheets_print_solution_if:nn #1#2
  {
    \bool_if:nT { #2 }
      {
        \prop_get:NnN \g__exsheets_solutions_names_prop
          { #1 } \l__exsheets_tmpa_tl
        \prop_get:NnN \g__exsheets_solutions_content_prop
          { #1 } \l__exsheets_tmpb_tl
        \prop_get:NnN \g__exsheets_solutions_questions_id_prop
          { #1 } \l__exsheets_tmpc_tl
        \eSaveCounterPatternFrom [ exsheets ]
          \l__exsheets_current_pattern_interpretation_tl
          \l__exsheets_current_pattern_tl
          \l__exsheets_qu_counter_pattern_tl
        \exsheets_solutions_print_name:VVV
          \l__exsheets_current_pattern_tl
          \l__exsheets_tmpa_tl
          \l__exsheets_tmpc_tl
        \tl_use:N \l__exsheets_tmpb_tl
        \cs_if_eq:NNTF \exsheets_par: \scan_stop:
          { \c_space_tl }
          {
            \exsheets_par:
            \dim_compare:nNnT { \parskip } = { 0pt }
              { \exsheets_glue:N \l__exsheets_solutions_skip_below_dim }
          }
      }
  }

% print by section:
\cs_new:Npn \exsheets_print_solutions_section:n #1
  {
    \tl_if_blank:nTF { #1 }
      {
        \prop_map_inline:Nn \g__exsheets_question_number_prop
          {
            \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
              {
                \__exsheets_print_solutions_section:nnn { ##1 } { ##2 }
                  { \arabic{section} }
              }
          }
      }
      {
        \clist_map_inline:nn { #1 }
          { \__exsheets_print_solutions_by_section:w ##1-- \q_stop }
      }
  }

\cs_new_protected:Npn \__exsheets_print_solutions_by_section:w #1-#2-#3 \q_stop
  {
    % wenn #3=-, dann range-Input
    \tl_if_eq:nnTF { #3 } { - }
      {
        \int_zero:N \l__exsheets_tmpa_int
        \int_set_eq:NN \l__exsheets_tmpb_int \c_ten_thousand
        \tl_if_blank:nF { #1 } { \int_set:Nn \l__exsheets_tmpa_int { #1 } }
        \tl_if_blank:nF { #2 } { \int_set:Nn \l__exsheets_tmpb_int { #2 } }
        \int_do_while:nn { \l__exsheets_tmpa_int <= \l__exsheets_tmpb_int }
          {
            \prop_map_inline:Nn \g__exsheets_question_number_prop
              {
                \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
                  {
                    \__exsheets_print_solutions_section:nnn
                      { ##1 } { ##2 } { \l__exsheets_tmpa_int }
                  }
              }
            \int_incr:N \l__exsheets_tmpa_int
          }
      }
      {
        \prop_map_inline:Nn \g__exsheets_question_number_prop
          {
            \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
              { \__exsheets_print_solutions_section:nnn { ##1 } { ##2 } { #1 } }
          }
      }
  }

\cs_new:Npn \__exsheets_print_solutions_section:nnn #1#2#3
  {
    \__exsheets_read_number:w #2 \q_stop
    \__exsheets_print_solution_if:nn { #1 }
      { \int_compare_p:n { \l__exsheets_counter_sec_int = #3 } }
  }

% print by chapter:
\cs_new:Npn \exsheets_print_solutions_chapter:n #1
  {
    \tl_if_blank:nTF { #1 }
      {
        \prop_map_inline:Nn \g__exsheets_question_number_prop
          {
            \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
              {
                \__exsheets_print_solutions_chapter:nnn { ##1 } { ##2 }
                  { \arabic{chapter} }
              }
          }
      }
      {
        \clist_map_inline:nn { #1 }
          { \__exsheets_print_solutions_by_chapter:w ##1-- \q_stop }
      }
  }

\cs_new_protected:Npn \__exsheets_print_solutions_by_chapter:w #1-#2-#3 \q_stop
  {
    % wenn #3=-, dann range-Input
    \tl_if_eq:nnTF { #3 } { - }
      {
        \int_zero:N \l__exsheets_tmpa_int
        \int_set_eq:NN \l__exsheets_tmpb_int \c_ten_thousand
        \tl_if_blank:nF { #1 } { \int_set:Nn \l__exsheets_tmpa_int { #1 } }
        \tl_if_blank:nF { #2 } { \int_set:Nn \l__exsheets_tmpb_int { #2 } }
        \int_do_while:nn { \l__exsheets_tmpa_int <= \l__exsheets_tmpb_int }
          {
            \prop_map_inline:Nn \g__exsheets_question_number_prop
              {
                \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
                  {
                    \__exsheets_print_solutions_chapter:nnn
                      { ##1 } { ##2 } { \l__exsheets_tmpa_int }
                  }
              }
            \int_incr:N \l__exsheets_tmpa_int
          }
      }
      {
        \prop_map_inline:Nn \g__exsheets_question_number_prop
          {
            \prop_if_in:NnT \g__exsheets_solutions_names_prop { ##1 }
              { \__exsheets_print_solutions_chapter:nnn { ##1 } { ##2 } { #1 } }
          }
      }
  }

\cs_new:Npn \__exsheets_print_solutions_chapter:nnn #1#2#3
  {
    \__exsheets_read_number:w #2 \q_stop
    \__exsheets_print_solution_if:nn { #1 }
      { \int_compare_p:n { \l__exsheets_counter_ch_int = #3 } }
  }

% print all:
\cs_new:Npn \exsheets_print_solutions_all:
  {
    \prop_map_function:NN \g__exsheets_question_number_prop
      \__exsheets_print_solutions_all:nn
  }

\cs_new_protected:Npn \__exsheets_print_solutions_all:nn #1#2
  {
    \__exsheets_read_number:w #2 \q_stop
    \prop_get:NnNT \g__exsheets_solutions_names_prop
      { #1 } \l__exsheets_tmpa_tl
      {
        \tl_set_eq:NN \l__exsheets_solutions_name_tl \l__exsheets_tmpa_tl
        \prop_get:NnN \g__exsheets_solutions_content_prop
          { #1 } \l__exsheets_tmpb_tl
        \prop_get:NnN \g__exsheets_solutions_questions_id_prop
          { #1 } \l__exsheets_tmpc_tl
        \eSaveCounterPatternFrom [ exsheets ]
          \l__exsheets_current_pattern_interpretation_tl
          \l__exsheets_current_pattern_tl
          \l__exsheets_qu_counter_pattern_tl
        \exsheets_solutions_print_name:VVV
          \l__exsheets_current_pattern_tl
          \l__exsheets_tmpa_tl
          \l__exsheets_tmpc_tl
        \tl_use:N \l__exsheets_tmpb_tl
        \cs_if_eq:NNTF \exsheets_par: \scan_stop:
          { \c_space_tl }
          {
            \exsheets_par:
            \dim_compare:nNnT { \parskip } = { 0pt }
              { \exsheets_glue:N \l__exsheets_solutions_skip_below_dim }
          }
      }
  }

% print by ID:
\seq_new:N \l__exsheets_solutions_byID_seq
\cs_new_protected:Npn \exsheets_print_solutions_byID:n #1
  {
    \seq_set_split:Nnn \l__exsheets_solutions_byID_seq { , } { #1 }
    \seq_clear:N \l__exsheets_tmpa_seq
    \seq_map_inline:Nn \l__exsheets_solutions_byID_seq
      {
        \prop_get:NnN \g__exsheets_questions_id_prop
          { ##1 } \l__exsheets_tmpa_tl
        \seq_put_right:NV \l__exsheets_tmpa_seq \l__exsheets_tmpa_tl
      }
    \bool_if:NT \l__exsheets_print_byID_sorted_bool
      {
        \seq_sort:Nn \l__exsheets_tmpa_seq
          {
            \int_compare:nNnTF { ##1 } > { ##2 }
              { \sort_reversed: }
              { \sort_ordered: }
          }
      }
    \seq_map_inline:Nn \l__exsheets_tmpa_seq
      {
        \group_begin:
          \tl_if_eq:nnF { ##1 } { \q_no_value }
            {
              \prop_get:NnNT \g__exsheets_solutions_names_prop
                { ##1 } \l__exsheets_tmpa_tl
                {
                  \prop_get:NnN \g__exsheets_solutions_content_prop
                    { ##1 } \l__exsheets_tmpb_tl
                  \prop_get:NnN \g__exsheets_solutions_questions_id_prop
                    { ##1 } \l__exsheets_tmpc_tl
                  \__exsheets_restore_number_from_and_do:Nnn
                    \g__exsheets_question_number_prop
                    { ##1 }
                    {
                      \eSaveCounterPatternFrom [ exsheets ]
                        \l__exsheets_current_pattern_interpretation_tl
                        \l__exsheets_current_pattern_tl
                        \l__exsheets_qu_counter_pattern_tl
                      \exsheets_solutions_print_name:VVV
                        \l__exsheets_current_pattern_tl
                        \l__exsheets_tmpa_tl
                        \l__exsheets_tmpc_tl
                      \tl_use:N \l__exsheets_tmpb_tl
                      \cs_if_eq:NNTF \exsheets_par: \scan_stop:
                        { \c_space_tl }
                        {
                          \exsheets_par:
                          \dim_compare:nNnT { \parskip } = { 0pt }
                            { \exsheets_glue:N \l__exsheets_solutions_skip_below_dim }
                        }
                    }
                }
            }
        \group_end:
      }
  }

\cs_new_protected_nopar:Npn \__exsheets_read_number:w #1-#2-#3 \q_stop
  {
    \int_zero:N \l__exsheets_counter_ch_int
    \int_zero:N \l__exsheets_counter_sec_int
    \int_zero:N \l__exsheets_counter_qu_int
    \tl_if_in:nnF { #1 } { @@@ }
      {
        \tl_if_blank:nF { #1 }
          { \int_set:Nn \l__exsheets_counter_ch_int { #1 } }
      }
    \int_set:Nn \l__exsheets_counter_sec_int { #2 }
    \int_set:Nn \l__exsheets_counter_qu_int { #3 }
  }

\cs_new_protected_nopar:Npn \exsheets_solutions_print_name:nnn #1#2#3
  {
    \tl_set_rescan:Nnn \l__exsheets_tmpa_tl
      { \char_set_catcode_letter:N \@ } { #1 }
    \tl_if_in:nnTF { #1 } { @@@ }
      { \__exsheets_solutions_name:nnn { } { #2 } { #3 } }
      { \__exsheets_solutions_name:nnn { #1 } { #2  } { #3 } }
    \tex_penalty:D \c_ten_thousand
  }
\cs_generate_variant:Nn \exsheets_solutions_print_name:nnn { VVV }

\cs_new:Npn \PrintSolutionsTF
  { \bool_if:NTF \l__exsheets_solutions_print_bool }
\cs_new:Npn \PrintSolutionsT
  { \bool_if:NT \l__exsheets_solutions_print_bool }
\cs_new:Npn \PrintSolutionsF
  { \bool_if:NF \l__exsheets_solutions_print_bool }

\bool_new:N      \l__exsheets_print_byID_sorted_bool
\bool_set_true:N \l__exsheets_print_byID_sorted_bool

\keys_define:nn { exsheets / solution }
  {
    headings        .tl_set:N   = \l__exsheets_solution_heading_instance_tl ,
    print           .choice: ,
    print / true    .code:n     =
      {
        \bool_set_true:N  \l__exsheets_solutions_print_bool
        \bool_set_true:N  \l__exsheets_solutions_print_here_bool
        \bool_set_false:N \l__exsheets_solutions_print_section_bool
        \bool_set_false:N \l__exsheets_solutions_print_chapter_bool
        \bool_set_false:N \l__exsheets_solutions_print_all_bool
      } ,
    print / false   .code:n     =
      {
        \bool_set_false:N \l__exsheets_solutions_print_bool
      } ,
    print           .default:n  = true ,
    name            .tl_set:N   = \l__exsheets_solutions_name_tl ,
    sorted          .bool_set:N = \l__exsheets_print_byID_sorted_bool ,
    skip-below      .dim_set:N  = \l__exsheets_solutions_skip_below_dim
  }

% ----------------------------------------------------------------------------
% create question/solution pairs
\cs_new_protected:Npn \__exsheets_new_qu_sol_pair:nnnnnn #1#2#3#4#5#6
  {
    \NewDocumentEnvironment { #1 } { O{}G{} }
      { \keys_set:nn { exsheets } { #3 } \__exsheets_question: {#2,##1} {##2} }
      { \end__exsheets_question: }
    \NewDocumentEnvironment { #4 } { O{} }
      { \keys_set:nn { exsheets } { #6 } \__exsheets_solution: {#5,##1} }
      { \end__exsheets_solution: }
  }

\cs_new_protected:Npn \__exsheets_renew_qu_sol_pair:nnnnnn #1#2#3#4#5#6
  {
    \RenewDocumentEnvironment { #1 } { O{}G{} }
      { \keys_set:nn { exsheets } { #3 } \__exsheets_question: {#2,##1} {##2} }
      { \end__exsheets_question: }
    \RenewDocumentEnvironment { #4 } { O{} }
      { \keys_set:nn { exsheets } { #6 } \__exsheets_solution: {#5,##1} }
      { \end__exsheets_solution: }
  }

\NewDocumentCommand \NewQuSolPair { mO{}O{}mO{}O{} }
  { \__exsheets_new_qu_sol_pair:nnnnnn { #1 } { #2 } { #3 } { #4 } { #5 } { #6 } }
\@onlypreamble \NewQuSolPair

\NewDocumentCommand \RenewQuSolPair { mO{}O{}mO{}O{} }
  { \__exsheets_renew_qu_sol_pair:nnnnnn { #1 } { #2 } { #3 } { #4 } { #5 } { #6 } }
\@onlypreamble \RenewQuSolPair

% ----------------------------------------------------------------------------
% the `tasks' list
\bool_if:NTF \l__exsheets_load_tasks_bool
  { \RequirePackage [ more ] { tasks } }
  { \RequirePackage { tasks } }
\AddCounterPattern* [ tasks ] { question } { qu }
\ReadCounterFrom [ tasks ] { question } \l__exsheets_counter_qu_int

% ----------------------------------------------------------------------------
% the \blank{<words>} command
\RequirePackage { ulem } \normalem
\dim_new:N  \l__exsheets_blank_dim
\tl_new:N   \l__exsheets_blank_linespread_tl
\tl_set:Nn  \l__exsheets_blank_linespread_tl { 1 }
\tl_new:N   \l__exsheets_blank_scale_tl
\tl_set:Nn  \l__exsheets_blank_scale_tl { 1 }
\box_new:N  \l__exsheets_blank_box
\bool_new:N \l__exsheets_blank_width_bool
\bool_new:N \l__exsheets_blank_linespread_bool

\cs_new:Npn \exsheets_write_blank:n #1 { #1 }
\cs_set_eq:NN \exsheets_write_blank:n \uline

\keys_define:nn { exsheets / blank }
  {
    style          .choice: ,
    style / line   .code:n =
      \cs_set_eq:NN \exsheets_write_blank:n \uline ,
    style / wave   .code:n =
      \cs_set_eq:NN \exsheets_write_blank:n \uwave ,
    style / dline  .code:n =
      \cs_set_eq:NN \exsheets_write_blank:n \uuline ,
    style / dotted .code:n =
      \cs_set_eq:NN \exsheets_write_blank:n \dotuline ,
    style / dashed .code:n =
      \cs_set_eq:NN \exsheets_write_blank:n \dashuline ,
    scale          .tl_set:N = \l__exsheets_blank_scale_tl ,
    width          .code:n =
      {
        \bool_set_true:N \l__exsheets_blank_width_bool
        \dim_set:Nn \l__exsheets_blank_dim { #1 }
      } ,
    linespread     .code:n =
      \bool_set_true:N \l__exsheets_blank_linespread_bool
      \tl_set:Nn \l__exsheets_blank_linespread_tl { #1 }
  }

\NewDocumentCommand \blank { som }
  {
    \group_begin:
      \IfNoValueF { #2 } { \keys_set:nn { exsheets / blank } { #2 } }
      \mode_if_vertical:TF
        {
          \IfBooleanF { #1 } { \noindent }
          \exsheets_blank:n { #3 }
          \IfBooleanF { #1 }
            {
              \bool_if:NT \l__exsheets_blank_linespread_bool
                { \linespread { \l__exsheets_blank_linespread_tl } \selectfont }
              \par
            }
        }
        { \exsheets_blank:n { #3 } }
    \group_end:
  }

\cs_new_protected:Npn \exsheets_blank:n #1
  {
    \box_clear:N \l__exsheets_blank_box
    \mode_if_math:TF
      { \hbox_set:Nn \l__exsheets_blank_box { $ \m@th \mathpalette{}{#1} $ } }
      { \hbox_set:Nn \l__exsheets_blank_box { #1 } }
    \bool_if:NTF \l__exsheets_inside_solution_bool
      { \exsheets_write_blank:n { #1 } }
      {
        \bool_if:NTF \l__exsheets_blank_width_bool
          { \__exsheets_blank_skip:N \l__exsheets_blank_dim }
          {
            \__exsheets_blank_skip:n
              { \box_wd:N \l__exsheets_blank_box }
          }
      }
  }

\cs_new_protected:Npn \__exsheets_blank_skip:N #1
  {
    \bool_if:NTF \l__exsheets_blank_width_bool
      { \dim_set:Nn \l__exsheets_tmpa_dim { #1 } }
      {
        \fp_set:Nn \l__exsheets_tmpa_fp
          { \dim_to_fp:n { #1 } * \l__exsheets_blank_scale_tl }
        \dim_set:Nn \l__exsheets_tmpa_dim { \fp_to_dim:N \l__exsheets_tmpa_fp }
      }
    \dim_compare:nTF { \l__exsheets_tmpa_dim > 2em }
      {
        \mode_if_math:TF
          { \exsheets_write_blank:n { \skip_horizontal:N \l__exsheets_tmpa_dim } }
          {
            \exsheets_write_blank:n { \skip_horizontal:n { 1em } }
            \dim_sub:Nn \l__exsheets_tmpa_dim { 2em }
            \dim_do_while:nn { \l__exsheets_tmpa_dim > \c_zero_dim }
              {
                \tex_penalty:D \hyphenpenalty
                \dim_compare:nTF { \l__exsheets_tmpa_dim < 1pt }
                  { \exsheets_write_blank:n { \skip_horizontal:N \l__exsheets_tmpa_dim } }
                  { \exsheets_write_blank:n { \skip_horizontal:n { 1pt } } }
                \dim_sub:Nn \l__exsheets_tmpa_dim { 1pt }
              }
            \exsheets_write_blank:n { \skip_horizontal:n { 1em } }
          }
      }
      { \exsheets_write_blank:n { \skip_horizontal:N \l__exsheets_tmpa_dim } }
  }
\cs_generate_variant:Nn \__exsheets_blank_skip:N { n }

% the following code from Heiko Oberdieck in d.c.t.t served as inspiration
% and basis for the \blank command:
% 
% \makeatletter
% \newcommand*{\luecke}{%
%   \begingroup
%     \setlength{\dimen@}{6cm}%
%     \ifdim\dimen@>2em %
%       \underline{\hspace{1em}}%
%       \advance\dimen@ by -2em\relax
%       \@whiledim\dimen@>0pt\do{%
%         \penalty\hyphenpenalty
%         \ifdim\dimen@<1pt %
%           \underline{\hspace{\dimen@}}%
%         \else
%           \underline{\hspace{1pt}}%
%         \fi
%         \advance\dimen@ by -1pt %
%       }%
%       \underline{\hspace{1em}}%
%     \else
%       \underline{\hspace{\dimen@}}%
%     \fi
%   \endgroup
%   \xspace
% }
% \makeatother

% ----------------------------------------------------------------------------
% \examspace
% insert space for a student to answer a question
\cs_new_protected:Npn \__exsheets_examspace:nn #1#2
  {
    \par
    \tex_penalty:D -100 \scan_stop:
    \dim_set:Nn \l__exsheets_tmpa_dim { #2 }
    \dim_set:Nn \l__exsheets_tmpb_dim { \pagegoal - \pagetotal - \baselineskip }
    \dim_compare:nTF { \l__exsheets_tmpa_dim > \l__exsheets_tmpb_dim }
      {
        \dim_compare:nT { \l__exsheets_tmpb_dim > 0pt } { \vfil }
        \break
        \IfBooleanF { #1 }
          {
            \dim_sub:Nn \l__exsheets_tmpa_dim { \l__exsheets_tmpb_dim }
            \vspace* { \l__exsheets_tmpa_dim }
          }
      }
      { \skip_vertical:N \l__exsheets_tmpa_dim }
  }
\NewDocumentCommand \examspace { sm }
  { \__exsheets_examspace:nn { #1 } { #2 } }

% ----------------------------------------------------------------------------
% SETUP
\NewDocumentCommand \SetupExSheets { o m }
  {
    \IfNoValueTF { #1 }
      { \keys_set:nn { exsheets } { #2 } }
      { \keys_set:nn { exsheets / #1 } { #2 } }
  }

% ----------------------------------------------------------------------------
% default definitions:
% question / solution pair:
\NewQuSolPair{question}{solution}

% properties:
\DeclareQuestionProperty{points}
\DeclareQuestionProperty{subtitle}
\bool_if:NT \l__exsheets_auto_label_bool
  {
    \DeclareQuestionProperty{ref}
    \DeclareQuestionProperty{pageref}
  }

% classes:
\DeclareQuestionClass{class}{classes}
\DeclareQuestionClass{topic}{topics}

% ----------------------------------------------------------------------------
% Sprachanpassungen
\RequirePackage { translations }
% translation for the exercises
\DeclareTranslationFallback       { exsheets-exercise-name } { Exercise     }
\DeclareTranslation { English   } { exsheets-exercise-name } { Exercise     }
\DeclareTranslation { British   } { exsheets-exercise-name } { Exercise     }
\DeclareTranslation { American  } { exsheets-exercise-name } { Exercise     }
\DeclareTranslation { French    } { exsheets-exercise-name } { Exercise     }
\DeclareTranslation { German    } { exsheets-exercise-name } { \"Ubung      }
\DeclareTranslation { Italian   } { exsheets-exercise-name } { Esercizio    }
\DeclareTranslation { Spanish   } { exsheets-exercise-name } { Ejercicio    }
\DeclareTranslation { Catalan   } { exsheets-exercise-name } { Exercici     }
\DeclareTranslation { Turkish   } { exsheets-exercise-name } { Egzersiz     }
\DeclareTranslation { Croatian  } { exsheets-exercise-name } { Primjer      }
\DeclareTranslation { Hungarian } { exsheets-exercise-name } { Gyakorol     }
\DeclareTranslation { Danish    } { exsheets-exercise-name } { \O{}velse    }
\DeclareTranslation { Norsk     } { exsheets-exercise-name } { Oppgave      }
\DeclareTranslation { Portuges  } { exsheets-exercise-name } { Exerc\'\i cio }
% translation for the question
\DeclareTranslationFallback       { exsheets-question-name } { Question     }
\DeclareTranslation { English   } { exsheets-question-name } { Question     }
\DeclareTranslation { British   } { exsheets-question-name } { Question     }
\DeclareTranslation { American  } { exsheets-question-name } { Question     }
\DeclareTranslation { French    } { exsheets-question-name } { Question     }
\DeclareTranslation { German    } { exsheets-question-name } { Aufgabe      }
\DeclareTranslation { Italian   } { exsheets-question-name } { Questione    }
\DeclareTranslation { Spanish   } { exsheets-question-name } { Pregunta     }
\DeclareTranslation { Catalan   } { exsheets-question-name } { Q\"uesti\'o  }
\DeclareTranslation { Turkish   } { exsheets-question-name } { Soru         }
\DeclareTranslation { Croatian  } { exsheets-question-name } { Zadatak      }
\DeclareTranslation { Hungarian } { exsheets-question-name } { Feladat      }
\DeclareTranslation { Danish    } { exsheets-question-name } { Opgave       }
\DeclareTranslation { Norsk     } { exsheets-question-name } { Oppgave      }
\DeclareTranslation { Portuges  } { exsheets-question-name } { Quest\~ao    }
% translation for the solutions
\DeclareTranslationFallback       { exsheets-solution-name } { Solution     }
\DeclareTranslation { English   } { exsheets-solution-name } { Solution     }
\DeclareTranslation { British   } { exsheets-solution-name } { Solution     }
\DeclareTranslation { American  } { exsheets-solution-name } { Solution     }
\DeclareTranslation { French    } { exsheets-solution-name } { Solution     }
\DeclareTranslation { German    } { exsheets-solution-name } { L\"osung     }
\DeclareTranslation { Italian   } { exsheets-solution-name } { Soluzione    }
\DeclareTranslation { Spanish   } { exsheets-solution-name } { Soluci\'on   }
\DeclareTranslation { Catalan   } { exsheets-solution-name } { Soluci\'o    }
\DeclareTranslation { Turkish   } { exsheets-solution-name } { \c C\"oz\"um }
\DeclareTranslation { Croatian  } { exsheets-solution-name } { Rje\v{s}enje }
\DeclareTranslation { Hungarian } { exsheets-solution-name } { Megold\'{a}s }
\DeclareTranslation { Danish    } { exsheets-solution-name } { Opl\o{}sning }
\DeclareTranslation { Norsk     } { exsheets-solution-name } { L\o{}sning   }
\DeclareTranslation { Portuges  } { exsheets-solution-name } { Solu\c c\~ao }
% the actual translating
\tl_set:Nn \l__exsheets_exercise_name_tl
  { \GetTranslation { exsheets-exercise-name } }
\tl_set:Nn \l__exsheets_questions_name_tl
  { \GetTranslation { exsheets-question-name } }
\tl_set:Nn \l__exsheets_solutions_name_tl
  { \GetTranslation { exsheets-solution-name } }


% ----------------------------------------------------------------------------
% save total points in .aux file to make it available for \allpoints anywhere
\AtEndDocument
  {
    \exsheets_write_to_aux_x:n
      {
        \exp_not:N \exsheets@sum@of@points
          { \fp_eval:n { \g__exsheets_points_sum_fp } }^^J
        \exp_not:N \exsheets@sum@of@bonus
          { \fp_eval:n { \g__exsheets_bonus_sum_fp } }
      }
  }

% ----------------------------------------------------------------------------
% load custom configuration
\file_if_exist:nT { exsheets_configurations.cfg }
  {
    \AtBeginDocument
      {
        \msg_info:nn { exsheets } { loading-configurations }
        \file_input:n { exsheets_configurations.cfg }
      }
  }

\tex_endinput:D

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
HISTORY:
2011/11/23 v0.1pre     - first upload to bitbucket and all changes until
                         considered stable enough/ready to be called
                         0.1alpha. There'll be no further descriptions until
                         then.
2012/06/08 v0.1alpha   - first hopefully stable version
2012/06/11 v0.1alpha-a - added headings instances, slightly rewritten
                         `exercises-tasks' object and `tasks' environment
2012/06/11 v0.1alpha-b - added `multiplechoice' instance and `load-tasks'
                         option 
2012/06/12 v0.1alpha-c - renamed from `exercises' into `ExSheets'
2012/06/15 v0.1alpha-d - added more flexible solution printing method
2012/06/15 v0.1beta    - filled in some blanks in the documentation, now we
                         need some testing!
2012/09/07 v0.1beta-a  - adjustments to the updated l3kernel
2012/09/08 v0.1beta-b  - sort solutions printed with the `byID' key
2012/09/16 v0.1beta-c  - renamed option `questions-counter-format' into
                         `counter-format'
2012/09/19 v0.1beta-d  - added `topic' key, provide \includequestions with
                         options `all' and `IDs'
2012/09/24 v0.1beta-e  - added question properties and improved random
                         question selection
2012/09/27 v0.1        - added two headings instances, new option
                         `headings-format' 
                       - small changes in the definition of the
                         `exsheets-headings' object
                       - preliminary version of totoc options. Unfortunatly
                         \exsheets@recover@number is not expandable => no
                         hyperref support
2012/09/30 v0.2beta    - version numbering gone crazy! this will now stay
                         0.2beta until upload to CTAN (v0.2)
                       - integrated packages `translations' and `cntformats':
                         trnslt: provide expandable version of `translator's
                           \translate
                         cntfmts: outsourced previous counter formatting
                           commands; should now be usable in other packages,
                           too, and simplified definitions in `ExSheets'
                       - thanks to `translations' and `cntformats' the `totoc'
                         option now works with `hyperref'
2012/10/05 v0.2        - removed \sumpoints and moved the functionality to
                         \totalpoints*
                       - changed meaning of \addpoints* and moved former
                         functionality to \points
                       - added bonus point functionality including \addbonus,
                         \bonus, \bonussum, \pointssum, \currentpointssum,
                         \currentbonussum
                       - added grades distribution
2012/10/05 v0.2a       - resolved bug in saving and recovering question number
                         using \exsheets@save@number and \QuestionNumber
2012/10/08 v0.2b       - improved the reference to chapter/solution numbers
                         in \printsolutions
                       - resolved bug in \printsolutions introduced in the
                         last update
                       - upload to CTAN

2012/10/23 v0.3        - bugfix in \exref
                       - new: \NewQuSolPair, \RenewQuSolPair, \examspace
2012/10/24 v0.3a       - fix of headings when followed by a list
                       - changed syntax of {tasks} list to resemble the real
                         lists like enumerate
2012/10/26 v0.3b       - small fix to the {tasks} environment, \NewTasks,
                         \RenewTasks, resolve stupid bug:
                         \ckeckedchoicebox => \checkedchoicebox
2012/11/08 v0.4        - compatibility with KOMA-Script's `parskip' option:
                         now no unwanted skip and no overfull hbox is produced
                       - env {task} now supports inner environments
2012/12/02 v0.5        - added \CurrentQuestionID
2012/12/06 v0.5a       - bug fix: solutions had wrong numbers with
                         counter-format=se.qu and [print] option
2012/12/18 v0.6        - variations, Hungarian translations, corrected
                         Catalanian translations
2012/12/23 v0.6a       - bug fix: labels and items of {tasks} weren't joined
                         at their baselines
2013/01/06 v0.6b       - bug fix: ID counting fixed in \includequestions
2013/01/19 v0.7        - extracted `tasks' environment into standalone
                         package; this also lead to a slightly new syntax and
                         a few new options for it
                       - changed internals for random selection of questions:
                         uses `pgf' instead of `lcg' and seems to be more
                         reliable than before
2013/01/21 v0.7a       - added option `auto-label' and questions key `label',
                         also added question properties `ref' and `pageref'
2013/02/17 v0.7b       - bug fix: question selection by ID now works again
2013/03/10 v0.8        - \prop_length => \exsheets_prop_count
                       - define unexpandable internal commands protected
                       - translations basic dictionaries for English, German,
                         French and Spanish
                       - new \includequestions option `exclude'
                       - new way of handling the `class' of questions:
                         instead of hard-coded `classes' and `topics'
                         individual groups like e.g. `difficulties' can be
                         chosen; `classes' and `topics' are still provided for
                         backwards compatibility; this introduces the new
                         command \DeclareQuestionClass
                       - minor changes to the debugging information layout
                       - bug fix in number saving mechanism
                       - \includequestions[random=<num>] now obeys class
                         as done with \SetupExSheets{use-topics={foo,bar}}
                       - new macro \questionsincludedlast
2013/04/04 v0.8a       - added Portuguese translations
2013/04/07 v0.9        - protected internal commands where appropriate
                       - added possibility to set general options with
                         \NewQuSolPair and \RenewQuSolPair
2013/04/08 v0.9a       - added headings instance `empty'
2013/04/18 v0.9b       - fixed erroneous behaviour of \includequestions when
                         used more than once
                       - added hook \l__exsheets_heading_points_post_hook_tl
2013/04/21 v0.9c       - bug fix: \ForEachQuestion seems to work correctly
                         again
2013/04/25 v0.9d       - bug fix: \includequestions works correctly when used
                         multiple times together with ordinary instances of
                         the {question} environment
                       - bug fix: points/parse=false correctly disables
                         parsing points again
                       - bug fix: \addpoints didn't add to the question
                         property
                       - new option `points/format'
                       - \blank now works in math mode, it doesn't do
                         linebreaks there if `ulem' doesn't allow them (which
                         it doesn't)
2013/05/01 v0.9e       - corrected erroneous behaviour of \examspace
2013/05/26 v0.9f       - fixed incorrectly placed links when the `totoc'
                         option is enabled and questions/solutions are at the
                         top of a new page because there wasn't enough place
                         left at the page before
2013/05/30 v0.9g       - obey \if@filesw
2013/06/28 v0.9h       - cleaner internal use of
                         \exsheets_set_question_properties:n
2013/07/17 v0.9i       - made \g__exsheets_total_bonus_fp and
                         \g__exsheets_total_points_fp public
                       - removed `translations' from the bundle
2013/10/11 v0.10       - require `translations' like any other package
                       - added `exsheets-listings' package
                       - added Norwegian translations
                       - changed horizontal spaces declared as `1ex' into
                         `.3333em' in the declarations of the headings
                         instances
                       - added subtitles
2013/11/07 v0.10a      - fix bug in loading headings of questions;  when
                         included from an external file sometimes the wrong ID
                         has been passed to the headings
2013/11/20 v0.11       - \GetQuestionClass{}
                       - \PrintQuestionClass(TF)
2013/12/02 v0.12       - fix issue with \CurrentQuestionID
                       - new options `label-format', `label-cmd', `ref-cmd'
                         and `pageref-cmd' for `auto-label' options that
                         allow specification of labelling command and thus
                         compatibility with packages like `cleveref'
                       - write question properties to aux file so they can be
                         retrieved before the corresponding question is
                         printed
                       - make \GetQuestionProperty expandable
                       - new syntax feature in points argument: a leading
                         bang prevents the points from being added to the sum
                         of points
                       - added possibility for
                         https://bitbucket.org/cgnieder/exsheets/issue/15
                       - added \IfQuestionSubtitle(TF)
                       - added `subtitle' property
                       - dropped `color' option
2013/12/08 v0.12a      - changed details in the printing mechanism of the
                         points which seems to be more consistent
                       - fix bug introduced in the last update: subtitles work
                         again
2013/12/27 v0.12b      - ensure that points are not parsed if a leading bang
                         is inserted
                       - fix bug in parsing the points

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% TODO:
- points/decimal-marker, points/frac (?), points/format (?,im interface)
- points: swedish style
- \examspace inside {tasks} => possible? (\pagegoal-\pagetotal) gives wrong
  values here
- remove doubled points name if total points are unknown