% Copyright (C) 2026 Yu Zhai <me@zhaiyusci.net>
% This work may be distributed and/or modified under the LaTeX Project
% Public License, version 1.3c or (at your option) any later version.
% https://www.latex-project.org/lppl.txt
% LPPL maintenance status: maintained.
% Current Maintainer: Yu Zhai <me@zhaiyusci.net>.
% The distributed Work is listed in MANIFEST.md.
%
\NeedsTeXFormat{LaTeX2e}[2020-10-01]
\IfFormatAtLeastTF{2020-10-01}{}{%
  \PackageError{matchedsplit}{LaTeX 2020-10-01 or newer is required}%
    {Update your LaTeX format and packages before loading matchedsplit.}%
  \endinput
}
\ProvidesExplPackage{matchedsplit}{2026-10-29}{0.8.1}{Nested matched delimiters across aligned rows}
\RequirePackage{amsmath}
\RequirePackage{xcolor}
\RequirePackage{l3keys2e}
\ExplSyntaxOn

\bool_new:N \g__ms_override_split_bool
\bool_new:N \g__ms_override_align_bool
\bool_new:N \g__ms_rainbow_bool
\bool_new:N \l__ms_rainbow_bool
\clist_new:N \g__ms_colors_clist
\clist_new:N \l__ms_colors_clist
\prop_new:N \l__ms_color_prop
\definecolor{msblue}{HTML}{0072B2}
\definecolor{msorange}{HTML}{D55E00}
\definecolor{msgreen}{HTML}{009E73}
\definecolor{mspurple}{HTML}{9B51A0}
\definecolor{msred}{HTML}{B33A3A}
\definecolor{mscyan}{HTML}{00838F}
\clist_gset:Nn \g__ms_colors_clist
 {msblue,msorange,msgreen,mspurple,msred,mscyan}
\msg_new:nnn {matchedsplit}{empty-colors}{The~colors~list~must~not~be~empty.}
\cs_new_protected:Npn \__ms_set_colors:Nn #1#2
 {\clist_set:Nn \l_tmpa_clist {#2}
  \clist_if_empty:NTF \l_tmpa_clist
   {\msg_error:nn {matchedsplit}{empty-colors}}
   {\clist_set_eq:NN #1\l_tmpa_clist}}
\keys_define:nn {matchedsplit/package}
 {
  overridesplit .bool_gset:N = \g__ms_override_split_bool,
  overridealign .bool_gset:N = \g__ms_override_align_bool,
  rainbow .bool_gset:N = \g__ms_rainbow_bool,
  colors .code:n =
   {\__ms_set_colors:Nn \l__ms_colors_clist {#1}
    \clist_gset_eq:NN \g__ms_colors_clist \l__ms_colors_clist}
 }
\clist_set_eq:NN \l__ms_colors_clist \g__ms_colors_clist
\ProcessKeysOptions{matchedsplit/package}
\keys_define:nn {matchedsplit/environment}
 {
  rainbow .bool_set:N = \l__ms_rainbow_bool,
  colors .code:n = {\__ms_set_colors:Nn \l__ms_colors_clist {#1}}
 }
\cs_new_protected:Npn \__ms_options:n #1
 {\bool_set_eq:NN \l__ms_rainbow_bool \g__ms_rainbow_bool
  \clist_set_eq:NN \l__ms_colors_clist \g__ms_colors_clist
  \keys_set:nn {matchedsplit/environment}{#1}}
\cs_generate_variant:Nn \tl_if_head_is_group:nTF {V}
\cs_generate_variant:Nn \tl_if_head_eq_charcode:nNT {VN}
\tl_new:N \l__ms_input_tl
\tl_new:N \l__ms_render_tl
\tl_new:N \l__ms_content_tl
\tl_new:N \l__ms_key_tl
\seq_new:N \l__ms_stack_seq
\int_new:N \l__ms_id_int
\int_new:N \l__ms_pending_int
\int_new:N \l__ms_env_depth_int
\int_new:N \l__ms_env_pending_int
\prop_new:N \l__ms_content_prop
\bool_new:N \l__ms_valid_bool
\msg_new:nnn {matchedsplit} {unmatched} {Unmatched~#1~in~matchedsplit.}
\msg_new:nnn {matchedsplit} {metadata} {Expected~a~braced~argument~after~label/tag/intertext.}
\msg_new:nnn {matchedsplit} {row-space} {Missing~closing~bracket~in~row~spacing.}
\msg_new:nnn {matchedsplit} {delimiter} {Missing~delimiter~after~left/middle/right.}
\cs_new_protected:Npn \__ms_fail:n #1
 {\bool_set_false:N \l__ms_valid_bool \msg_error:nnn {matchedsplit}{unmatched}{#1}}
\cs_new_protected:Npn \__ms_append_active:n #1
 {\seq_map_inline:Nn \l__ms_stack_seq
   {\prop_get:NnN \l__ms_content_prop {##1} \l__ms_content_tl
    \tl_put_right:Nn \l__ms_content_tl {#1}
    \prop_put:NnV \l__ms_content_prop {##1} \l__ms_content_tl}}
\cs_new_protected:Npn \__ms_close:n #1
 {
  \seq_pop_right:NN \l__ms_stack_seq \l__ms_key_tl
  \prop_get:NVN \l__ms_content_prop \l__ms_key_tl \l__ms_content_tl
  \box_if_exist:cF {l__ms_delim_\l__ms_key_tl _box}
   {\box_new:c {l__ms_delim_\l__ms_key_tl _box}}
  % Invisible delimiters support middle without inflating the measured height.
  \hbox_set:cn {l__ms_delim_\l__ms_key_tl _box}
   {$\displaystyle \left.\l__ms_content_tl\right.$}
  \tl_put_right:Nx \l__ms_render_tl
   {\exp_not:N \__ms_right:nn {\l__ms_key_tl}{\exp_not:n{#1}}}
  \__ms_append_active:n {\right#1}
 }
\cs_new_protected:Npn \__ms_token:n #1
 {
  \int_compare:nNnTF {\l__ms_pending_int} > {0}
   {
    \int_case:nn {\l__ms_pending_int}
     {
      {1}{\__ms_append_active:n {\left#1}
          \int_incr:N \l__ms_id_int
          \tl_set:Nx \l__ms_key_tl {\int_use:N \l__ms_id_int}
          \seq_put_right:NV \l__ms_stack_seq \l__ms_key_tl
          \prop_put:NVx \l__ms_color_prop \l__ms_key_tl
           {\int_eval:n {\int_mod:nn
             {\seq_count:N \l__ms_stack_seq - 1}
             {\clist_count:N \l__ms_colors_clist} + 1}}
          \prop_put:NVn \l__ms_content_prop \l__ms_key_tl {}
          \tl_put_right:Nx \l__ms_render_tl
            {\exp_not:N \__ms_left:nn {\l__ms_key_tl}{\exp_not:n{#1}}}}
      {2}{\seq_if_empty:NTF \l__ms_stack_seq
           {\__ms_fail:n {middle}}
           {\seq_get_right:NN \l__ms_stack_seq \l__ms_key_tl
            \tl_put_right:Nx \l__ms_render_tl
             {\exp_not:N \__ms_middle:nn {\l__ms_key_tl}{\exp_not:n{#1}}}
            \__ms_append_active:n {\middle#1}}}
      {3}{\seq_if_empty:NTF \l__ms_stack_seq
           {\__ms_fail:n {right}} {\__ms_close:n {#1}}}
     }
    \int_zero:N \l__ms_pending_int
   }
   {
    \token_if_eq_meaning:NNTF #1 \left
      {\int_set:Nn \l__ms_pending_int {1}}
      {\token_if_eq_meaning:NNTF #1 \middle
        {\int_set:Nn \l__ms_pending_int {2}}
        {\token_if_eq_meaning:NNTF #1 \right
          {\int_set:Nn \l__ms_pending_int {3}}
          {\tl_put_right:Nn \l__ms_render_tl {#1}
           \token_if_eq_meaning:NNTF #1 \\
             {\__ms_row_options:}
             {\token_if_eq_charcode:NNF #1 & {\__ms_append_active:n {#1}}}}}}
   }
 }
% Preserve row spacing in the output, but remove it from the measurement.
\cs_new_protected:Npn \__ms_row_options:
 {
  \tl_trim_spaces:N \l__ms_input_tl
  \tl_if_head_eq_charcode:VNT \l__ms_input_tl *
   {\tl_put_right:Nn \l__ms_render_tl {*}
    \tl_set:Nx \l__ms_input_tl {\exp_not:f {\tl_tail:V \l__ms_input_tl}}}
  \tl_trim_spaces:N \l__ms_input_tl
  \tl_if_head_eq_charcode:VNT \l__ms_input_tl [
   {\tl_if_in:NnTF \l__ms_input_tl {]}
     {\exp_after:wN \__ms_row_space:w \l__ms_input_tl \q_mark \q_stop}
     {\bool_set_false:N \l__ms_valid_bool
      \tl_clear:N \l__ms_input_tl \msg_error:nn {matchedsplit}{row-space}}}
 }
\cs_new_protected:Npn \__ms_row_space:w [#1]#2\q_stop
 {\tl_put_right:Nn \l__ms_render_tl {[#1]} \tl_set:Nn \l__ms_input_tl {#2}\tl_remove_once:Nn \l__ms_input_tl {\q_mark}}
% Groups are opaque: keep braces and native math environments intact.
\cs_new_protected:Npn \__ms_scan:
 {
  \tl_trim_spaces:N \l__ms_input_tl
  \tl_if_empty:NF \l__ms_input_tl
   {\tl_if_head_is_group:VTF \l__ms_input_tl
     {\exp_after:wN \__ms_group:w \l__ms_input_tl \q_mark \q_stop}
     {\exp_after:wN \__ms_single:w \l__ms_input_tl \q_mark \q_stop}
    \__ms_scan:}
 }
\cs_new_protected:Npn \__ms_group:w #1#2\q_stop
 {\tl_set:Nn \l__ms_input_tl {#2}\tl_remove_once:Nn \l__ms_input_tl {\q_mark}
  \int_compare:nNnTF {\l__ms_pending_int} = {0}
   {\int_add:Nn \l__ms_env_depth_int {\l__ms_env_pending_int}
    \int_zero:N \l__ms_env_pending_int
    \__ms_append_active:n {{#1}} \tl_put_right:Nn \l__ms_render_tl {{#1}}}
   {\bool_set_false:N \l__ms_valid_bool \msg_error:nn {matchedsplit}{delimiter}
    \int_zero:N \l__ms_pending_int}}
\cs_new_protected:Npn \__ms_single:w #1#2\q_stop
 {\tl_set:Nn \l__ms_input_tl {#2}\tl_remove_once:Nn \l__ms_input_tl {\q_mark} \__ms_dispatch:n {#1}}
% Keep nested environments opaque; their alignment tokens belong to them.
\cs_new_protected:Npn \__ms_copy:n #1
 {\__ms_append_active:n {#1}\tl_put_right:Nn \l__ms_render_tl {#1}}
\cs_new_protected:Npn \__ms_dispatch:n #1
 {
  \token_if_eq_meaning:NNTF #1 \begin
   {\int_set:Nn \l__ms_env_pending_int {1}\__ms_copy:n {#1}}
   {\token_if_eq_meaning:NNTF #1 \end
     {\int_set:Nn \l__ms_env_pending_int {-1}\__ms_copy:n {#1}}
     {\int_compare:nNnTF {\l__ms_env_depth_int} > {0}
       {\__ms_copy:n {#1}}
       {\token_if_eq_meaning:NNTF #1 \label
         {\__ms_metadata:n {#1}}
         {\token_if_eq_meaning:NNTF #1 \tag
           {\__ms_metadata:n {#1}}
           {\token_if_eq_meaning:NNTF #1 \notag
             {\tl_put_right:Nn \l__ms_render_tl {#1}}
             {\token_if_eq_meaning:NNTF #1 \nonumber
               {\tl_put_right:Nn \l__ms_render_tl {#1}}
               {\token_if_eq_meaning:NNTF #1 \intertext
                 {\__ms_metadata:n {#1}}
                 {\token_if_eq_meaning:NNTF #1 \displaybreak
                   {\tl_put_right:Nn \l__ms_render_tl {#1}\__ms_row_options:}
                   {\__ms_token:n {#1}}}}}}}}}}
 }
% Labels and tags must run only during amsmath's numbering pass, never
% while measuring delimiter content (which may span several numbered rows).
\cs_new_protected:Npn \__ms_metadata:n #1
 {
  \tl_put_right:Nn \l__ms_render_tl {#1}
  \tl_trim_spaces:N \l__ms_input_tl
  \token_if_eq_meaning:NNT #1 \tag
   {\tl_if_head_eq_charcode:VNT \l__ms_input_tl *
     {\tl_put_right:Nn \l__ms_render_tl {*}
      \tl_set:Nx \l__ms_input_tl {\exp_not:f {\tl_tail:V \l__ms_input_tl}}}}
  \tl_trim_spaces:N \l__ms_input_tl
  \tl_if_head_is_group:VTF \l__ms_input_tl
   {\exp_after:wN \__ms_metadata_arg:w \l__ms_input_tl \q_mark \q_stop}
   {\bool_set_false:N \l__ms_valid_bool
    \tl_clear:N \l__ms_input_tl \msg_error:nn {matchedsplit}{metadata}}
 }
\cs_new_protected:Npn \__ms_metadata_arg:w #1#2\q_stop
 {\tl_put_right:Nn \l__ms_render_tl {{#1}}
  \tl_set:Nn \l__ms_input_tl {#2}\tl_remove_once:Nn \l__ms_input_tl {\q_mark}}
\cs_new_protected:Npn \__ms_color:n #1
 {\bool_if:NT \l__ms_rainbow_bool
   {\exp_args:Nx \color
     {\clist_item:Nn \l__ms_colors_clist {\prop_item:Nn \l__ms_color_prop {#1}}}}}
\cs_new:Npn \__ms_phantom:n #1
 {\vphantom{\box_use:c {l__ms_delim_#1_box}}}
\cs_new:Npn \__ms_left:nn #1#2
 {\mathopen{\__ms_color:n {#1}\nulldelimiterspace=0pt \left#2\__ms_phantom:n{#1}\right.}}
\cs_new:Npn \__ms_middle:nn #1#2
 {\mathrel{\__ms_color:n {#1}\nulldelimiterspace=0pt \left.\__ms_phantom:n{#1}\middle#2\right.}}
\cs_new:Npn \__ms_right:nn #1#2
 {\mathclose{\__ms_color:n {#1}\nulldelimiterspace=0pt \left.\__ms_phantom:n{#1}\right#2}}
\cs_new_protected:Npn \__ms_prepare:n #1
 {
  \tl_set:Nn \l__ms_input_tl {#1}
  \tl_clear:N \l__ms_render_tl
  \seq_clear:N \l__ms_stack_seq
  \prop_clear:N \l__ms_content_prop
  \prop_clear:N \l__ms_color_prop
  \int_zero:N \l__ms_env_depth_int
  \int_zero:N \l__ms_env_pending_int
  \int_zero:N \l__ms_id_int
  \int_zero:N \l__ms_pending_int
  \bool_set_true:N \l__ms_valid_bool
  \__ms_scan:
  \int_compare:nNnF {\l__ms_pending_int} = {0}
   {\bool_set_false:N \l__ms_valid_bool \msg_error:nn {matchedsplit}{delimiter}}
  \seq_if_empty:NF \l__ms_stack_seq {\__ms_fail:n {left}}
 }
\cs_new_protected:Npn \__ms_typeset:nnn #1#2#3
 {\group_align_safe_begin:
  \group_begin:
  \__ms_options:n {#3}
  \__ms_prepare:n {#1}
  \bool_if:NT \l__ms_valid_bool
   {\begin{aligned}[#2]\tl_use:N \l__ms_render_tl\end{aligned}}
  \group_end:\group_align_safe_end:}
\NewDocumentEnvironment{matchedsplit}{O{} +b}
 {\__ms_typeset:nnn {#2}{c}{#1}}{}
\bool_if:NT \g__ms_override_split_bool
 {
  \RenewDocumentEnvironment{split}{O{} +b}
   {\ifctagsplit@
      \__ms_typeset:nnn {#2}{c}{#1}
    \else
      \iftagsleft@ \__ms_typeset:nnn {#2}{t}{#1}
      \else \__ms_typeset:nnn {#2}{b}{#1}\fi
    \fi}{}
  % amsmath locally restores split from insplit@ inside align and gather.
  \cs_set_eq:NN \insplit@ \split
 }
% Retain native amsmath numbering, measuring, tags and display layout.
\NewCommandCopy\msnativealign\align
\NewCommandCopy\endmsnativealign\endalign
\exp_args:Ncc \NewCommandCopy {msnativealign*}{align*}
\exp_args:Ncc \NewCommandCopy {endmsnativealign*}{endalign*}
\cs_new_protected:Npn \__ms_align:nnn #1#2#3
 {\group_begin:
  \group_align_safe_begin:
  \__ms_options:n {#3}
  \__ms_prepare:n {#1}
  \group_align_safe_end:
  \bool_if:NT \l__ms_valid_bool
   {\exp_args:NnV \__ms_align_render:nn {#2}\l__ms_render_tl}
  \group_end:}
\cs_new_protected:Npn \__ms_align_render:nn #1#2
 {\cs_set_eq:NN \endalign \endmsnativealign
  \begin{msnativealign#1}#2\end{msnativealign#1}}
\NewDocumentEnvironment{matchedalign}{O{} +b}{\__ms_align:nnn {#2}{}{#1}}{}
\NewDocumentEnvironment{matchedalign*}{O{} +b}{\__ms_align:nnn {#2}{*}{#1}}{}
\bool_if:NT \g__ms_override_align_bool
 {
  \RenewDocumentEnvironment{align}{O{} +b}{\__ms_align:nnn {#2}{}{#1}}{}
  \RenewDocumentEnvironment{align*}{O{} +b}{\__ms_align:nnn {#2}{*}{#1}}{}
  % These native environments also finish through endalign. Restore its
  % native meaning locally so the opt-in replacement cannot break them.
  \clist_map_inline:nn {alignat,alignat*,xalignat,xalignat*,xxalignat,flalign,flalign*}
   {\AddToHook{env/#1/begin}{\cs_set_eq:NN \endalign \endmsnativealign}}
 }
\ExplSyntaxOff