% ^module name=''cssyntax'' container=''(standalone)'':
%
%   ^purpose:Core syntax layer providing readable, structured internal
%     command names via extended catcodes, plus a small set of
%     readable aliases for common TeX primitives._purpose:
%
%   ^desc:
%     This package activates "_", ":" and "/" as letter-category
%     characters for the scope in which structured command names
%     (container_module_type_subtype/description) are written or
%     invoked. It has no domain of its own and can be used by any
%     package author, inside or outside the lingwrit bundle.
%   _desc:
%
% _module:

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{cssyntax}[2026/07/20 v0.1.0 Control-sequence syntax]

% ^section title=''Bootstrap'':
%   ^rem:These commands must never contain "_", ":" or "/" in their own
%     name: they must remain usable BEFORE the extended syntax is
%     active._rem:
% _section:

% ^cs name=''\csSyntaxOn'':
%   ^desc:Activates "_", ":" and "/" as letter-category characters,
%     opening the scope in which structured command names can be
%     typed literally._desc:
%   ^syn:\csSyntaxOn_syn:
%   ^code language=''latex'':
\providecommand\csSyntaxOn{%
	\makeatletter
	\catcode`\_=11
	\catcode`\:=11
	\catcode`\/=11
}
%   _code:
%   ^synonym:\csSyntaxEnabled_synonym:
% _cs:
\NewCommandCopy{\csSyntaxEnabled}{\csSyntaxOn}

% ^cs name=''\csSyntaxOff'':
%   ^desc:Restores the original catcodes of "_", ":" and "/",
%     closing the scope opened by \csSyntaxOn._desc:
%   ^syn:\csSyntaxOff_syn:
%   ^code language=''latex'':
\providecommand\csSyntaxOff{%
	\makeatother
	\catcode`\_=8
	\catcode`\:=12
	\catcode`\/=12
}
%   _code:
%   ^synonym:\csSyntaxDisabled_synonym:
% _cs:
\NewCommandCopy{\csSyntaxDisabled}{\csSyntaxOff}

\RequirePackage{xifthen}
\RequirePackage{xparse}
\RequirePackage{expl3}
\RequirePackage{l3keys2e}

\csSyntaxOn

% ^section title=''Copy and definition primitives'':
%   ^rem:The bodies of _fun_copy/cs, _fun_save/cs, _fun_use/cs,
%     _fun_reset/cs and _fun_swap/cs keep a raw \let internally --
%     these implement idempotent, repeatable operations (a scratch
%     variable reused on every call, a save/reset that must be
%     callable more than once on the same name), which
%     \NewCommandCopy's collision protection would break. Every
%     ":"-alias declaration of these commands, by contrast, is a
%     one-time definition and uses \NewCommandCopy._rem:
% _section:

% ^cs name=''\_fun_copy/cs'':
%   ^desc:Copies the meaning of one control sequence into another
%     (wraps \let). Kept on \let internally: this command's whole
%     purpose is to expose \let's overwrite-friendly semantics, not
%     to add collision protection on top of it._desc:
%   ^syn:\_fun_copy/cs{<target>}{<source>}_syn:
%   ^code language=''latex'':
\def\_fun_copy/cs#1#2{\let#1#2}
%   _code:
%   ^synonym:\_fun_copy:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_copy:cs}{\_fun_copy/cs}

% ^cs name=''\_fun_define/cs'':
%   ^desc:Defines a command with no argument-expansion (wraps \def)._desc:
%   ^syn:\_fun_define/cs <cs> {<replacement text>}_syn:
%   ^code language=''latex'':
\def\_fun_define/cs#1#2{\def#1{#2}}
%   _code:
%   ^synonym:\_fun_define:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_define:cs}{\_fun_define/cs}

% ^cs name=''\_fun_define/exp'':
%   ^desc:Defines a command with local expansion of the replacement
%     text (wraps \edef)._desc:
%   ^syn:\_fun_define/exp <cs> {<replacement text>}_syn:
%   ^code language=''latex'':
\def\_fun_define/exp#1#2{\edef#1{#2}}
%   _code:
%   ^synonym:\_fun_define:exp_synonym:
% _cs:
\NewCommandCopy{\_fun_define:exp}{\_fun_define/exp}

% ^cs name=''\_fun_define/global'':
%   ^desc:Defines a command globally, without expansion
%     (wraps \gdef)._desc:
%   ^syn:\_fun_define/global <cs> {<replacement text>}_syn:
%   ^code language=''latex'':
\def\_fun_define/global#1#2{\gdef#1{#2}}
%   _code:
%   ^synonym:\_fun_define:global_synonym:
% _cs:
\NewCommandCopy{\_fun_define:global}{\_fun_define/global}

% ^cs name=''\_fun_define/global_exp'':
%   ^desc:Defines a command globally, with expansion of the
%     replacement text (wraps \xdef)._desc:
%   ^syn:\_fun_define/global_exp <cs> {<replacement text>}_syn:
%   ^code language=''latex'':
\def\_fun_define/global_exp#1#2{\xdef#1{#2}}
%   _code:
%   ^synonym:\_fun_define:global_exp_synonym:
% _cs:
\NewCommandCopy{\_fun_define:global_exp}{\_fun_define/global_exp}

% ^cs name=''\_fun_define/protected_exp'':
%   ^desc:Defines a command with protected expansion
%     (wraps \protected@edef)._desc:
%   ^syn:\_fun_define/protected_exp <cs> {<replacement text>}_syn:
%   ^code language=''latex'':
\def\_fun_define/protected_exp#1#2{\protected@edef#1{#2}}
%   _code:
%   ^synonym:\_fun_define:protected_exp_synonym:
% _cs:
\NewCommandCopy{\_fun_define:protected_exp}{\_fun_define/protected_exp}

% ^section title=''Expansion and introspection'':

% ^cs name=''\_fun_expand/after'':
%   ^desc:Reorders expansion of the following tokens
%     (alias of \expandafter)._desc:
%   ^syn:\_fun_expand/after <token1> <token2>_syn:
%   ^synonym:\_fun_expand:after_synonym:
% _cs:
\NewCommandCopy{\_fun_expand/after}{\expandafter}
\NewCommandCopy{\_fun_expand:after}{\expandafter}

% ^cs name=''\_fun_expand/prevent'':
%   ^desc:Protects the following token from expansion
%     (alias of \noexpand)._desc:
%   ^syn:\_fun_expand/prevent <token>_syn:
%   ^synonym:\_fun_expand:prevent_synonym:
% _cs:
\NewCommandCopy{\_fun_expand/prevent}{\noexpand}
\NewCommandCopy{\_fun_expand:prevent}{\noexpand}

% ^cs name=''\_fun_build/cs'':
%   ^desc:Builds and invokes a control sequence from a character
%     string, regardless of the current catcode of its characters
%     (wraps \csname...\endcsname)._desc:
%   ^syn:\_fun_build/cs{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_build/cs#1{\csname#1\endcsname}
%   _code:
%   ^synonym:\_fun_build:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_build:cs}{\_fun_build/cs}

% ^rem:\csname...\endcsname has a subtle side effect worth stating
%   explicitly: if <name> was never defined, \csname implicitly
%   creates it as \relax rather than raising an error. A typo in a
%   dynamically-built name therefore fails silently (nothing visible
%   happens) instead of producing "Undefined control sequence"._rem:

% ^cs name=''\_fun_build/def'':
%   ^desc:Defines a NEW command whose name is built from a character
%     string, with a TeX-style parameter text and a body -- the
%     "definitional" counterpart of \_fun_build/cs, which only
%     invokes an EXISTING command. Wraps expl3's \cs_new:cpn, so it
%     refuses to (re)define a name that already exists. The
%     parameter-text argument must be passed exactly as it would be
%     typed directly after a bare \cs_new:cpn{<name>} call -- do not
%     add an extra pair of braces around it in the body of a wrapper
%     built on top of this command; expl3's "p"-type argument does
%     not accept a braced group there._desc:
%   ^syn:\_fun_build/def{<name>}<parameter text>{<body>}_syn:
%   ^code language=''latex'':
\def\_fun_build/def#1#2#3{\cs_new:cpn{#1}#2{#3}}
%   _code:
%   ^synonym:\_fun_build:def_synonym:
% _cs:
\NewCommandCopy{\_fun_build:def}{\_fun_build/def}

% ^cs name=''\_fun_build/redef'':
%   ^desc:Same as \_fun_build/def, but silently overwrites an
%     existing command of the same name instead of refusing to
%     (wraps expl3's \cs_set:cpn)._desc:
%   ^syn:\_fun_build/redef{<name>}<parameter text>{<body>}_syn:
%   ^code language=''latex'':
\def\_fun_build/redef#1#2#3{\cs_set:cpn{#1}#2{#3}}
%   _code:
%   ^synonym:\_fun_build:redef_synonym:
% _cs:
\NewCommandCopy{\_fun_build:redef}{\_fun_build/redef}

% ^cs name=''\_fun_get/cs_string'':
%   ^desc:Returns the printable string form of a control sequence
%     (alias of \string)._desc:
%   ^syn:\_fun_get/cs_string <cs>_syn:
%   ^synonym:\_fun_get:cs_string_synonym:
% _cs:
\NewCommandCopy{\_fun_get/cs_string}{\string}
\NewCommandCopy{\_fun_get:cs_string}{\string}

% ^cs name=''\_fun_get/cs_meaning'':
%   ^desc:Returns the current definition of a control sequence
%     (alias of \meaning)._desc:
%   ^syn:\_fun_get/cs_meaning <cs>_syn:
%   ^synonym:\_fun_get:cs_meaning_synonym:
% _cs:
\NewCommandCopy{\_fun_get/cs_meaning}{\meaning}
\NewCommandCopy{\_fun_get:cs_meaning}{\meaning}

% ^rem:Both commands above must only ever be invoked while the
%   csSyntaxOn scope is still active -- "/" is not a letter once
%   csSyntaxOff has run, so a call written after that point would
%   be misparsed as two separate tokens._rem:

% ^section title=''Groups'':
%   ^rem:"group" (no qualifier) is the general-purpose scoping
%     mechanism for local assignments -- counters, lengths, patched
%     commands -- and is the pair to reach for by default (alias of
%     \begingroup/\endgroup). "token_group" is the more specialised
%     pair: \bgroup/\egroup are literal begin-group/end-group
%     CHARACTER TOKENS wearing a command name, usable anywhere TeX
%     expects an actual brace-catcode token -- e.g. as the
%     delimiters of \hbox\_fun_enter/token_group ... \_fun_exit/
%     token_group, which \begingroup/\endgroup cannot substitute
%     for._rem:
% _section:

% ^cs name=''\_fun_enter/group'':
%   ^desc:Opens a general-purpose local-values scope, e.g. for
%     temporary counters, lengths, or patched commands (alias of
%     \begingroup)._desc:
%   ^synonym:\_fun_enter:group_synonym:
% _cs:
\NewCommandCopy{\_fun_enter/group}{\begingroup}
\NewCommandCopy{\_fun_enter:group}{\begingroup}

% ^cs name=''\_fun_exit/group'':
%   ^desc:Closes a general-purpose local-values scope (alias of
%     \endgroup)._desc:
%   ^synonym:\_fun_exit:group_synonym:
% _cs:
\NewCommandCopy{\_fun_exit/group}{\endgroup}
\NewCommandCopy{\_fun_exit:group}{\endgroup}

% ^cs name=''\_fun_enter/token_group'':
%   ^desc:Opens a scope using a literal begin-group character token
%     wearing a command name -- usable anywhere TeX expects an
%     actual brace-catcode token, e.g. as a box-construction
%     delimiter (alias of \bgroup)._desc:
%   ^synonym:\_fun_enter:token_group_synonym:
% _cs:
\NewCommandCopy{\_fun_enter/token_group}{\bgroup}
\NewCommandCopy{\_fun_enter:token_group}{\bgroup}

% ^cs name=''\_fun_exit/token_group'':
%   ^desc:Closes a scope opened with \_fun_enter/token_group (alias
%     of \egroup)._desc:
%   ^synonym:\_fun_exit:token_group_synonym:
% _cs:
\NewCommandCopy{\_fun_exit/token_group}{\egroup}
\NewCommandCopy{\_fun_exit:token_group}{\egroup}

% ^section title=''Generic helpers'':

% ^cs name=''\_fun_save/cs'':
%   ^desc:Stores the current definition of a control sequence for
%     later retrieval via \_fun_use/cs. Kept on \let internally:
%     must remain callable more than once on the same name (e.g.
%     to refresh a snapshot)._desc:
%   ^syn:\_fun_save/cs{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_save/cs#1{%
	\expandafter\let\csname _cssyntax_saved/#1\expandafter\endcsname\csname#1\endcsname
}
%   _code:
%   ^synonym:\_fun_save:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_save:cs}{\_fun_save/cs}

% ^cs name=''\_fun_use/cs'':
%   ^desc:Recalls a definition previously stored by
%     \_fun_save/cs._desc:
%   ^syn:\_fun_use/cs{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_use/cs#1{\csname _cssyntax_saved/#1\endcsname}
%   _code:
%   ^synonym:\_fun_use:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_use:cs}{\_fun_use/cs}

% ^cs name=''\_fun_reset/cs'':
%   ^desc:Resets a control sequence to \relax. Kept on \let
%     internally: must remain idempotent (callable again on an
%     already-reset name)._desc:
%   ^syn:\_fun_reset/cs{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_reset/cs#1{\expandafter\let\csname#1\endcsname\relax}
%   _code:
%   ^synonym:\_fun_reset:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_reset:cs}{\_fun_reset/cs}

% ^cs name=''\_fun_swap/cs'':
%   ^desc:Exchanges the definitions of two control sequences. Kept
%     on \let internally: reuses a single scratch control sequence
%     across every call, which \NewCommandCopy's collision
%     protection would break after the first use._desc:
%   ^syn:\_fun_swap/cs{<cs1>}{<cs2>}_syn:
%   ^code language=''latex'':
\def\_fun_swap/cs#1#2{%
	\let\_cssyntax_tmp_cs#1%
	\let#1#2%
	\let#2\_cssyntax_tmp_cs%
}
%   _code:
%   ^synonym:\_fun_swap:cs_synonym:
% _cs:
\NewCommandCopy{\_fun_swap:cs}{\_fun_swap/cs}

% ^cs name=''\_fun_pick/first'':
%   ^desc:Discards the second of two arguments, keeps the first
%     (alias of \@firstoftwo)._desc:
%   ^synonym:\_fun_pick:first_synonym:
% _cs:
\NewCommandCopy{\_fun_pick/first}{\@firstoftwo}
\NewCommandCopy{\_fun_pick:first}{\@firstoftwo}

% ^cs name=''\_fun_pick/second'':
%   ^desc:Discards the first of two arguments, keeps the second
%     (alias of \@secondoftwo)._desc:
%   ^synonym:\_fun_pick:second_synonym:
% _cs:
\NewCommandCopy{\_fun_pick/second}{\@secondoftwo}
\NewCommandCopy{\_fun_pick:second}{\@secondoftwo}

% ^cs name=''\_fun_gobble/one'':
%   ^desc:Discards one argument (alias of \@gobble)._desc:
%   ^synonym:\_fun_gobble:one_synonym:
% _cs:
\NewCommandCopy{\_fun_gobble/one}{\@gobble}
\NewCommandCopy{\_fun_gobble:one}{\@gobble}

% ^cs name=''\_fun_gobble/two'':
%   ^desc:Discards two arguments (alias of \@gobbletwo)._desc:
%   ^synonym:\_fun_gobble:two_synonym:
% _cs:
\NewCommandCopy{\_fun_gobble/two}{\@gobbletwo}
\NewCommandCopy{\_fun_gobble:two}{\@gobbletwo}

% ^section title=''Files'':

% ^cs name=''\_fun_load/'':
%   ^desc:Unconditionally loads a file (alias of \input). The base
%     case of the load family takes no qualifier._desc:
%   ^syn:\_fun_load/{<filename>}_syn:
%   ^synonym:\_fun_load:_synonym:
% _cs:
\NewCommandCopy{\_fun_load/}{\input}
\NewCommandCopy{\_fun_load:}{\input}

% ^cs name=''\_fun_load/if_exists'':
%   ^desc:Loads a file if it exists, with distinct branches for the
%     found/not-found cases. Built on \IfFileExists (which takes a
%     true/false branch pair) combined with \input, NOT on
%     \InputIfFileExists -- the latter is a 2-argument kernel
%     command (filename, code-to-run-after-input) with no built-in
%     "not found" branch at all; passing it a third argument, as an
%     earlier version of this file mistakenly did, leaves that third
%     argument dangling in the input stream rather than raising an
%     error, producing confusing downstream failures._desc:
%   ^syn:\_fun_load/if_exists{<filename>}{<if found>}{<if not found>}_syn:
%   ^code language=''latex'':
\NewDocumentCommand\_fun_load/if_exists{m m m}{\IfFileExists{#1}{\input{#1}#2}{#3}}
%   _code:
%   ^synonym:\_fun_load:if_exists_synonym:
% _cs:
\NewCommandCopy{\_fun_load:if_exists}{\_fun_load/if_exists}

% ^cs name=''\_fun_enter/source'':
%   ^desc:No-op marker, kept purely for visual symmetry, meant to be
%     placed at the top of a file loaded via \_fun_load/if_exists._desc:
%   ^synonym:\_fun_enter:source, \_fun_enter/input, \_fun_enter:input_synonym:
% _cs:
\NewCommandCopy{\_fun_enter/source}{\relax}
\NewCommandCopy{\_fun_enter:source}{\relax}
\NewCommandCopy{\_fun_enter/input}{\_fun_enter/source}
\NewCommandCopy{\_fun_enter:input}{\_fun_enter/source}

% ^cs name=''\_fun_exit/source'':
%   ^desc:A real \endinput: stops reading the current file at this
%     exact point. Scope is strictly local to the file it appears
%     in -- if that file was itself loaded from another file, only
%     the inner file's reading stops._desc:
%   ^synonym:\_fun_exit:source, \_fun_exit/input, \_fun_exit:input_synonym:
% _cs:
\NewCommandCopy{\_fun_exit/source}{\endinput}
\NewCommandCopy{\_fun_exit:source}{\endinput}
\NewCommandCopy{\_fun_exit/input}{\endinput}
\NewCommandCopy{\_fun_exit:input}{\endinput}

% ^section title=''Low-level environment declaration'':
%   ^rem:These commands let a package author emulate
%     \begin{env}...\end{env} at a low level, anywhere -- including
%     the preamble, where \newenvironment does not always work.
%     They remain low-level building blocks, not a replacement for
%     \newenvironment's argument-parsing features._rem:
%   ^rem:Each declaration also generates a matching
%     \_fun_use/<name>{<content>} command, which opens the
%     environment, typesets its argument, and closes it again --
%     the same way a command copied with \_fun_copy/cs is used
%     identically regardless of whether it was originally \def'ed
%     or \edef'ed: the declaration style is a choice made once, at
%     declaration time, and is invisible at the point of use._rem:
%   ^rem:The ":"-alias generated for each declared <name> uses a
%     plain \let, not \NewCommandCopy: unlike cssyntax's own fixed,
%     one-time alias declarations above, a module may legitimately
%     redeclare the same environment name while iterating on its
%     own code._rem:
% _section:

% ^cs name=''\_fun_declare/env'':
%   ^desc:Declares a low-level environment with no automatic
%     grouping: the author is responsible for placing their own
%     \begingroup/\bgroup (or none at all) inside the enter/exit
%     code. Generates \_fun_enter/<name>, \_fun_exit/<name>, and
%     \_fun_use/<name>, plus their ":" synonyms._desc:
%   ^syn:\_fun_declare/env{<name>}{<enter code>}{<exit code>}_syn:
%   ^code language=''latex'':
\def\_fun_declare/env#1#2#3{%
	\expandafter\def\csname _fun_enter/#1\endcsname{#2}%
	\expandafter\let\csname _fun_enter:#1\expandafter\endcsname\csname _fun_enter/#1\endcsname
	\expandafter\def\csname _fun_exit/#1\endcsname{#3}%
	\expandafter\let\csname _fun_exit:#1\expandafter\endcsname\csname _fun_exit/#1\endcsname
	\expandafter\def\csname _fun_use/#1\endcsname##1{%
		\csname _fun_enter/#1\endcsname
		##1%
		\csname _fun_exit/#1\endcsname
	}%
	\expandafter\let\csname _fun_use:#1\expandafter\endcsname\csname _fun_use/#1\endcsname
}
%   _code:
%   ^synonym:\_fun_declare:env_synonym:
% _cs:
\NewCommandCopy{\_fun_declare:env}{\_fun_declare/env}

% ^cs name=''\_fun_declare/auto_group'':
%   ^desc:Same as \_fun_declare/env, but automatically wraps the
%     enter code in \begingroup and the exit code in \endgroup._desc:
%   ^syn:\_fun_declare/auto_group{<name>}{<enter code>}{<exit code>}_syn:
%   ^code language=''latex'':
\def\_fun_declare/auto_group#1#2#3{%
	\expandafter\def\csname _fun_enter/#1\endcsname{\begingroup#2}%
	\expandafter\let\csname _fun_enter:#1\expandafter\endcsname\csname _fun_enter/#1\endcsname
	\expandafter\def\csname _fun_exit/#1\endcsname{#3\endgroup}%
	\expandafter\let\csname _fun_exit:#1\expandafter\endcsname\csname _fun_exit/#1\endcsname
	\expandafter\def\csname _fun_use/#1\endcsname##1{%
		\csname _fun_enter/#1\endcsname
		##1%
		\csname _fun_exit/#1\endcsname
	}%
	\expandafter\let\csname _fun_use:#1\expandafter\endcsname\csname _fun_use/#1\endcsname
}
%   _code:
%   ^synonym:\_fun_declare:auto_group_synonym:
% _cs:
\NewCommandCopy{\_fun_declare:auto_group}{\_fun_declare/auto_group}

% ^section title=''Booleans'':
%   ^rem:Built on xifthen's \newboolean/\setboolean/\boolean rather
%     than a hand-rolled \newif wrapper. Two consequences follow:
%     declaring a boolean under a name already taken raises an
%     explicit error instead of silently overwriting the previous
%     one, and \boolean{...} returns the raw conditional token
%     itself, so it plugs directly into \_fun_enter/test_bool
%     below. The "_user_bool/" prefix protects against collisions
%     with the rest of the document (user macros, other packages)
%     but not against two bundle modules picking the same short
%     name -- callers should still prefix their own module name in
%     <name>, e.g. \_fun_declare/bool{nx_note_forced_margin}._rem:
% _section:

% ^cs name=''\_fun_declare/bool'':
%   ^desc:Creates a new boolean, initialised to false, under the
%     internal "_user_bool/" prefix (wraps \newboolean)._desc:
%   ^syn:\_fun_declare/bool{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_declare/bool#1{\newboolean{_user_bool/#1}}
%   _code:
%   ^synonym:\_fun_declare:bool_synonym:
% _cs:
\NewCommandCopy{\_fun_declare:bool}{\_fun_declare/bool}

% ^cs name=''\_fun_set/bool_true'':
%   ^desc:Sets a previously declared boolean to true
%     (wraps \setboolean)._desc:
%   ^syn:\_fun_set/bool_true{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_set/bool_true#1{\setboolean{_user_bool/#1}{true}}
%   _code:
%   ^synonym:\_fun_set:bool_true_synonym:
% _cs:
\NewCommandCopy{\_fun_set:bool_true}{\_fun_set/bool_true}

% ^cs name=''\_fun_set/bool_false'':
%   ^desc:Sets a previously declared boolean to false
%     (wraps \setboolean)._desc:
%   ^syn:\_fun_set/bool_false{<name>}_syn:
%   ^code language=''latex'':
\def\_fun_set/bool_false#1{\setboolean{_user_bool/#1}{false}}
%   _code:
%   ^synonym:\_fun_set:bool_false_synonym:
% _cs:
\NewCommandCopy{\_fun_set:bool_false}{\_fun_set/bool_false}

% ^section title=''The _fun_test/ family -- native TeX conditionals'':
%   ^rem:One command opens a given test, a single common command
%     closes it, whatever kind of test was opened._rem:
%   ^rem:_fun_doif/false, _fun_doif/else, _fun_doif/case and
%     _fun_exit/test MUST remain genuine aliases of the real
%     primitives (\else, \or, \fi), never \def-based macros
%     standing in for them. TeX recognises \else/\or/\fi during
%     conditional-skipping by comparing MEANING, without ever
%     expanding the tokens it scans past -- a \def-based stand-in
%     is invisible to that scan and produces "Incomplete
%     \ifdim/\ifnum/..." errors. \NewCommandCopy preserves this
%     property exactly as \let did, since both produce a true
%     meaning-equal alias. _fun_doif/true is unaffected: it is only
%     ever executed when its branch is the one actually taken,
%     never required to be recognised during a skip._rem:
% _section:

% ^cs name=''\_fun_enter/test_bool'':
%   ^desc:Opens a test on a previously declared boolean. Reads the
%     conditional created by \newboolean directly via \csname...
%     \endcsname -- NOT through ifthen's \boolean macro, which is a
%     two-argument helper meant to be assembled inside \ifthenelse
%     and is not usable standalone as a conditional-opener._desc:
%   ^syn:\_fun_enter/test_bool{<name>} ... \_fun_exit/test_syn:
%   ^code language=''latex'':
\def\_fun_enter/test_bool#1{\csname if_user_bool/#1\endcsname}
%   _code:
%   ^synonym:\_fun_enter:test_bool_synonym:
% _cs:
\NewCommandCopy{\_fun_enter:test_bool}{\_fun_enter/test_bool}

% ^cs name=''\_fun_enter/test_dim'':
%   ^desc:Opens a dimension comparison (wraps \ifdim)._desc:
%   ^syn:\_fun_enter/test_dim{<a>}{<rel>}{<b>} ... \_fun_exit/test_syn:
%   ^code language=''latex'':
\def\_fun_enter/test_dim#1#2#3{\ifdim#1#2#3}
%   _code:
%   ^synonym:\_fun_enter:test_dim_synonym:
% _cs:
\NewCommandCopy{\_fun_enter:test_dim}{\_fun_enter/test_dim}

% ^cs name=''\_fun_enter/test_num'':
%   ^desc:Opens an integer comparison (wraps \ifnum)._desc:
%   ^syn:\_fun_enter/test_num{<a>}{<rel>}{<b>} ... \_fun_exit/test_syn:
%   ^code language=''latex'':
\def\_fun_enter/test_num#1#2#3{\ifnum#1#2#3}
%   _code:
%   ^synonym:\_fun_enter:test_num_synonym:
% _cs:
\NewCommandCopy{\_fun_enter:test_num}{\_fun_enter/test_num}

% ^cs name=''\_fun_enter/test_cs'':
%   ^desc:Opens a comparison of two control sequences (wraps \ifx)._desc:
%   ^syn:\_fun_enter/test_cs{<cs1>}{<cs2>} ... \_fun_exit/test_syn:
%   ^code language=''latex'':
\def\_fun_enter/test_cs#1#2{\ifx#1#2}
%   _code:
%   ^synonym:\_fun_enter:test_cs_synonym:
% _cs:
\NewCommandCopy{\_fun_enter:test_cs}{\_fun_enter/test_cs}

% ^cs name=''\_fun_enter/test_case'':
%   ^desc:Opens a multi-way branch (wraps \ifcase)._desc:
%   ^syn:\_fun_enter/test_case{<n>} ... \_fun_exit/test_syn:
%   ^code language=''latex'':
\def\_fun_enter/test_case#1{\ifcase#1\relax}
%   _code:
%   ^synonym:\_fun_enter:test_case_synonym:
% _cs:
\NewCommandCopy{\_fun_enter:test_case}{\_fun_enter/test_case}

% ^cs name=''\_fun_doif/true'':
%   ^desc:Branch executed when the currently open test is true.
%     Expands to its argument as-is; the only branch in this
%     family that remains a plain \def macro, since it is never
%     required to be recognised during a conditional skip._desc:
%   ^syn:\_fun_doif/true{<code>}_syn:
%   ^code language=''latex'':
\def\_fun_doif/true#1{#1}
%   _code:
%   ^synonym:\_fun_doif:true_synonym:
% _cs:
\NewCommandCopy{\_fun_doif:true}{\_fun_doif/true}

% ^cs name=''\_fun_doif/false'':
%   ^desc:Branch executed when the currently open test is false.
%     A genuine alias of \else, not a macro expanding to it._desc:
%   ^syn:\_fun_doif/false{<code>}_syn:
%   ^synonym:\_fun_doif:false, \_fun_doif/else, \_fun_doif:else_synonym:
% _cs:
\NewCommandCopy{\_fun_doif/false}{\else}
\NewCommandCopy{\_fun_doif:false}{\else}
\NewCommandCopy{\_fun_doif/else}{\else}
\NewCommandCopy{\_fun_doif:else}{\else}

% ^cs name=''\_fun_doif/case'':
%   ^desc:One branch of a multi-way test opened with
%     \_fun_enter/test_case. A genuine alias of \or. Cannot take a
%     documentary branch-index argument: write
%     "\_fun_doif/case <code>" directly, exactly as one would
%     write \or in a native \ifcase._desc:
%   ^syn:\_fun_doif/case <code>_syn:
%   ^synonym:\_fun_doif:case_synonym:
% _cs:
\NewCommandCopy{\_fun_doif/case}{\or}
\NewCommandCopy{\_fun_doif:case}{\or}

% ^cs name=''\_fun_exit/test'':
%   ^desc:Closes any test opened by the \_fun_enter/test_* family,
%     whatever its nature. A genuine alias of \fi._desc:
%   ^syn:\_fun_exit/test_syn:
%   ^synonym:\_fun_exit:test_synonym:
% _cs:
\NewCommandCopy{\_fun_exit/test}{\fi}
\NewCommandCopy{\_fun_exit:test}{\fi}

% ^section title=''The _fun_check/ family -- declarative macro-based tests'':
%   ^rem:These are not native TeX conditionals but macros taking a
%     subject plus named branches (true/else). They neither open
%     nor close: there is no matching \_fun_exit/check._rem:
%   ^rem:\ExplSyntaxOff resets "_" and ":" to their hard-coded LaTeX2e
%     defaults rather than to whatever was active before entering,
%     so a bare \csSyntaxOn is called again immediately afterwards
%     to restore cssyntax's own extended state. A \begingroup/
%     \endgroup wrapper was tried first and rejected: catcode
%     assignments are inherently global, but \keys_define:nn's own
%     key registration is NOT global by default, and closing such a
%     group silently wiped the "true"/"else" keys, producing
%     "unknown key" errors at first real use._rem:
% _section:

\ExplSyntaxOn
\tl_new:N \l__cssyntax_true_code_tl
\tl_new:N \l__cssyntax_else_code_tl

\keys_define:nn { lwcheck } {
	true  .tl_set:N = \l__cssyntax_true_code_tl ,
	else  .tl_set:N = \l__cssyntax_else_code_tl ,
	false .tl_set:N = \l__cssyntax_else_code_tl ,
	true  .initial:n = { } ,
	else  .initial:n = { } ,
}
\ExplSyntaxOff
\csSyntaxOn

% ^cs name=''\_fun_check/defined'':
%   ^desc:Tests whether a control sequence is currently defined._desc:
%   ^syn:\_fun_check/defined{<cs>}{true={<code>}, else={<code>}}_syn:
%   ^code language=''latex'':
\NewDocumentCommand\_fun_check/defined{m m}{%
	\tl_clear:N \l__cssyntax_true_code_tl
	\tl_clear:N \l__cssyntax_else_code_tl
	\keys_set:nn { lwcheck } { #2 }
	\@ifundefined{#1}
		{ \l__cssyntax_else_code_tl }
		{ \l__cssyntax_true_code_tl }
}
%   _code:
%   ^synonym:\_fun_check:defined_synonym:
% _cs:
\NewCommandCopy{\_fun_check:defined}{\_fun_check/defined}

% ^cs name=''\_fun_check/pkg_loaded'':
%   ^desc:Tests whether a package is currently loaded._desc:
%   ^syn:\_fun_check/pkg_loaded{<package>}{true={<code>}, else={<code>}}_syn:
%   ^code language=''latex'':
\NewDocumentCommand\_fun_check/pkg_loaded{m m}{%
	\tl_clear:N \l__cssyntax_true_code_tl
	\tl_clear:N \l__cssyntax_else_code_tl
	\keys_set:nn { lwcheck } { #2 }
	\@ifpackageloaded{#1}
		{ \l__cssyntax_true_code_tl }
		{ \l__cssyntax_else_code_tl }
}
%   _code:
%   ^synonym:\_fun_check:pkg_loaded_synonym:
% _cs:
\NewCommandCopy{\_fun_check:pkg_loaded}{\_fun_check/pkg_loaded}

% ^cs name=''\_fun_check/streq'':
%   ^desc:Tests whether two strings are equal._desc:
%   ^syn:\_fun_check/streq{<a>}{<b>}{true={<code>}, else={<code>}}_syn:
%   ^code language=''latex'':
\NewDocumentCommand\_fun_check/streq{m m m}{%
	\tl_clear:N \l__cssyntax_true_code_tl
	\tl_clear:N \l__cssyntax_else_code_tl
	\keys_set:nn { lwcheck } { #3 }
	\ifthenelse{\equal{#1}{#2}}
		{ \l__cssyntax_true_code_tl }
		{ \l__cssyntax_else_code_tl }
}
%   _code:
%   ^synonym:\_fun_check:streq_synonym:
% _cs:
\NewCommandCopy{\_fun_check:streq}{\_fun_check/streq}

% ^rem:if_next_char and if_next_group are position-sensitive: unlike
%   the rest of the _fun_check/ family, they inspect whatever token
%   comes right after their own call in the input stream, rather
%   than testing a value already in hand. Two consequences follow.
%   First, they close cssyntax's own syntax scope (\csSyntaxOff)
%   as the very FIRST action of their body, so the caller must NOT
%   also write \csSyntaxOff between the call and the content being
%   tested -- doing so would insert \csSyntaxOff itself as the
%   token being peeked at, hiding the real one. Second, both are
%   defined here with \cs_new:cpn while \ExplSyntaxOn is active at
%   AUTHORING time, not merely called at run time inside a plain
%   \def written under \csSyntaxOn alone: a literal space typed in
%   an ordinary \def's body is stored as a real catcode-10 token
%   forever, regardless of any \ExplSyntaxOn invoked later at run
%   time, and such a token sitting inside \peek_catcode:NTF's own
%   branch was found experimentally to make it misreport its
%   result. Definining under \ExplSyntaxOn instead makes space
%   catcode-9 (ignored) at the point the definition is scanned, so
%   no such token is ever stored. A second, independent finding:
%   \keys_set:nn must never be called BEFORE a \peek_catcode:NTF in
%   the same expansion -- even a call to a completely unrelated key
%   group placed earlier was enough to make the peek misreport its
%   result. It is safe only when placed textually inside peek's own
%   true/false branches, after the branch has already been chosen._rem:

% ^cs name=''\_fun_check/if_next_char'':
%   ^desc:Tests whether a specific character follows, without
%     consuming it (wraps \@ifnextchar). Position-sensitive -- see
%     the remark above._desc:
%   ^syn:\_fun_check/if_next_char{<char>}{true={<code>}, else={<code>}}_syn:
%   ^code language=''latex'':
\ExplSyntaxOn
\cs_new:cpn { _fun_check/if_next_char } #1#2 {
	\csSyntaxOff
	\@ifnextchar #1
		{
			\tl_clear:N \l__cssyntax_true_code_tl
			\tl_clear:N \l__cssyntax_else_code_tl
			\keys_set:nn { lwcheck } { #2 }
			\l__cssyntax_true_code_tl
		}
		{
			\tl_clear:N \l__cssyntax_true_code_tl
			\tl_clear:N \l__cssyntax_else_code_tl
			\keys_set:nn { lwcheck } { #2 }
			\l__cssyntax_else_code_tl
		}
}
\ExplSyntaxOff
%   _code:
%   ^synonym:\_fun_check:if_next_char_synonym:
% _cs:
\NewCommandCopy{\_fun_check:if_next_char}{\_fun_check/if_next_char}

% ^cs name=''\_fun_check/if_next_group'':
%   ^desc:Tests whether a brace-delimited group follows, without
%     consuming it (wraps expl3's \peek_catcode:NTF against
%     \c_group_begin_token). The building block for macros that
%     accept a flexible, unbounded number of {<group>}{<group>}...
%     arguments: each processing step tests whether another group
%     follows and loops if so. Position-sensitive -- see the remark
%     above._desc:
%   ^syn:\_fun_check/if_next_group{true={<code>}, else={<code>}}_syn:
%   ^code language=''latex'':
\ExplSyntaxOn
\cs_new:cpn { _fun_check/if_next_group } #1 {
	\csSyntaxOff
	\peek_catcode:NTF \c_group_begin_token
		{
			\tl_clear:N \l__cssyntax_true_code_tl
			\tl_clear:N \l__cssyntax_else_code_tl
			\keys_set:nn { lwcheck } { #1 }
			\l__cssyntax_true_code_tl
		}
		{
			\tl_clear:N \l__cssyntax_true_code_tl
			\tl_clear:N \l__cssyntax_else_code_tl
			\keys_set:nn { lwcheck } { #1 }
			\l__cssyntax_else_code_tl
		}
}
\ExplSyntaxOff
%   _code:
%   ^synonym:\_fun_check:if_next_group_synonym:
% _cs:
\NewCommandCopy{\_fun_check:if_next_group}{\_fun_check/if_next_group}

\csSyntaxOff

\endinput