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+% \iffalse meta-comment
+%
+%% File: l3kernel-functions.dtx
+%
+% Copyright (C) 2018-2024 The LaTeX Project
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version. The latest version
+% of this license is in the file
+%
+% https://www.latex-project.org/lppl.txt
+%
+% This file is part of the "l3kernel bundle" (The Work in LPPL)
+% and all files in that bundle must be distributed together.
+%
+% -----------------------------------------------------------------------
+%
+% The development version of the bundle can be found at
+%
+% https://github.com/latex3/latex3
+%
+% for those people who are interested.
+%
+%<*driver>
+\documentclass[full,kernel]{l3doc}
+\begin{document}
+ \DocInput{\jobname.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \title{^^A
+% The \pkg{l3kernel-functions} module\\ Kernel-reserved functions^^A
+% }
+%
+% \author{^^A
+% The \LaTeX{} Project\thanks
+% {^^A
+% E-mail:
+% \href{mailto:latex-team@latex-project.org}
+% {latex-team@latex-project.org}^^A
+% }^^A
+% }
+%
+% \date{Released 2024-05-08}
+%
+% \maketitle
+%
+% \begin{documentation}
+%
+% \end{documentation}
+%
+% \begin{implementation}
+%
+% \section{\pkg{l3kernel-functions}: kernel-reserved functions}
+%
+% \subsection{Internal \pkg{l3debug} kernel functions}
+% \label{sec:l3kernel-functions:l3debug-internals}
+%
+% These function are only created if debugging is enabled, hence they are
+% actually defined in \pkg{l3debug}.
+%
+% \begin{function}{\__kernel_chk_var_local:N, \__kernel_chk_var_global:N}
+% \begin{syntax}
+% \cs{__kernel_chk_var_local:N} \meta{var}
+% \cs{__kernel_chk_var_global:N} \meta{var}
+% \end{syntax}
+% Applies \cs{__kernel_chk_var_exist:N} \meta{var} as well as
+% \cs{__kernel_chk_var_scope:NN} \meta{scope} \meta{var}, where
+% \meta{scope} is |l| or~|g|.
+% \end{function}
+%
+% \begin{function}{\__kernel_chk_var_scope:NN}
+% \begin{syntax}
+% \cs{__kernel_chk_var_scope:NN} \meta{scope} \meta{var}
+% \end{syntax}
+% Checks the \meta{var} has the correct \meta{scope}, and if not
+% raises a kernel-level error.
+% The \meta{scope} is a single letter |l|, |g|,
+% |c| denoting local variables, global variables, or constants. More
+% precisely, if the variable name starts with a letter and an
+% underscore (normal \pkg{expl3} convention) the function checks that
+% this single letter matches the \meta{scope}. Otherwise the function
+% cannot know the scope \meta{var} the first time: instead, it defines
+% |\__debug_chk_/|\meta{var name} to store that information for the
+% next call. Thus, if a given \meta{var} is subject to assignments of
+% different scopes a kernel error will result.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_chk_cs_exist:N,
+% \__kernel_chk_cs_exist:c,
+% \__kernel_chk_var_exist:N
+% }
+% \begin{syntax}
+% \cs{__kernel_chk_cs_exist:N} \meta{cs}
+% \cs{__kernel_chk_var_exist:N} \meta{var}
+% \end{syntax}
+% Checks that their argument is defined according to the criteria for
+% \cs{cs_if_exist_p:N},
+% and if not raises a kernel-level error. Error messages are
+% different.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_chk_flag_exist:NN}
+% \begin{syntax}
+% \cs{__kernel_chk_flag_exist:NN}
+% \meta{function} \meta{flag}
+% \end{syntax}
+% Checks that the \meta{flag} is defined according to the criterion for
+% \cs{flag_if_exist_p:N}, and if not raises a kernel-level error and
+% calls the function with the argument \cs{l_tmpa_flag} to proceed
+% somehow without producing too many errors.
+% \end{function}
+%
+% \begin{function}{\__kernel_debug_log:e}
+% \begin{syntax}
+% \cs{__kernel_debug_log:e} \Arg{message text}
+% \end{syntax}
+% If the \texttt{log-functions} option is active, this function writes
+% the \meta{message text} to the log file using \cs{iow_log:e}.
+% Otherwise, the \meta{message text} is ignored using \cs{use_none:n}.
+% \end{function}
+%
+% \subsection{Internal kernel functions}
+%
+% \begin{function}{\__kernel_chk_defined:NT}
+% \begin{syntax}
+% \cs{__kernel_chk_defined:NT} \meta{variable} \Arg{true code}
+% \end{syntax}
+% If \meta{variable} is not defined (according to
+% \cs{cs_if_exist:NTF}), this triggers an error, otherwise the
+% \meta{true code} is run.
+% \end{function}
+%
+% \begin{function}{\__kernel_chk_expr:nNnN}
+% \begin{syntax}
+% \cs{__kernel_chk_expr:nNnN} \Arg{expr} \meta{eval} \Arg{convert} \meta{caller}
+% \end{syntax}
+% This function is only created if debugging is enabled. By default
+% it is equivalent to \cs{use_i:nnnn}. When expression checking is
+% enabled, it leaves in the input stream the result of \cs{tex_the:D}
+% \meta{eval} \meta{expr} \cs{tex_relax:D} after checking that no
+% token was left over. If any token was not taken as part of the
+% expression, there is an error message displaying the result of the
+% evaluation as well as the \meta{caller}. For instance \meta{eval}
+% can be \cs{__int_eval:w} and \meta{caller} can be \cs{int_eval:n} or
+% \cs{int_set:Nn}. The argument \meta{convert} is empty except for mu
+% expressions where it is \cs{tex_mutoglue:D}, used for internal
+% purposes.
+% \end{function}
+%
+% \begin{function}{\__kernel_chk_tl_type:NnnT}
+% \begin{syntax}\parskip=0pt\obeylines
+% \cs{__kernel_chk_tl_type:NnnT} \meta{control sequence} \Arg{specific type} \\
+% | |\Arg{reconstruction} \Arg{true code}
+% \end{syntax}
+% Helper to test that the \meta{control sequence} is a variable of the
+% given \meta{specific type} of token list. Produces suitable error
+% messages if the \meta{control sequence} does not exist, or if it is
+% not a token list variable at all, or if the \meta{control sequence}
+% differs from the result of |e|-expanding \meta{reconstruction}. If
+% all of these tests succeed then the \meta{true code} is run.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_codepoint_to_bytes:n}
+% \begin{syntax}
+% \cs{__kernel_codepoint_to_bytes:n} \Arg{codepoint}
+% \end{syntax}
+% Converts the \meta{codepoint} to UTF-8 bytes. The expansion
+% of this function comprises four brace groups, each of which will contain
+% a hexadecimal value: the appropriate byte. As UTF-8 is a variable-length,
+% one or more of the groups may be empty: the bytes read in the logical order,
+% such that a two-byte codepoint will have groups |#1| and |#2| filled
+% and |#3| and |#4| empty.
+% \end{function}
+%
+% \begin{function}{\__kernel_cs_parm_from_arg_count:nnF}
+% \begin{syntax}
+% \cs{__kernel_cs_parm_from_arg_count:nnF} \Arg{follow-on} \Arg{args} \Arg{false code}
+% \end{syntax}
+% Evaluates the number of \meta{args} and leaves the \meta{follow-on} code
+% followed by a brace group containing the required number of primitive
+% parameter markers (|#1|, \emph{etc}.). If the number of \meta{args} is outside
+% the range $[0,9]$, the \meta{false code} is inserted \emph{instead} of
+% the \meta{follow-on}.
+% \end{function}
+%
+% \begin{function}{
+% \__kernel_dependency_version_check:Nn,
+% \__kernel_dependency_version_check:nn,
+% }
+% \begin{syntax}
+% \cs{__kernel_dependency_version_check:Nn} \Arg{\cs{date}} \Arg{file}
+% \cs{__kernel_dependency_version_check:nn} \Arg{date} \Arg{file}
+% \end{syntax}
+% Checks if the loaded version of the \pkg{expl3} kernel is at least \meta{date},
+% required by \meta{file}. If the kernel date is older than \meta{date}, the
+% loading of \meta{file} is aborted and an error is raised.
+% \end{function}
+%
+% \begin{function}{\__kernel_deprecation_code:nn}
+% \begin{syntax}
+% \cs{__kernel_deprecation_code:nn} \Arg{error code} \Arg{working code}
+% \end{syntax}
+% Stores both an \meta{error} and \meta{working} definition for given material
+% such that they can be exchanged by \cs{debug_on:n} and \cs{debug_off:n}.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_exp_not:w}
+% \begin{syntax}
+% \cs{__kernel_exp_not:w} \meta{expandable tokens} \Arg{content}
+% \end{syntax}
+% Carries out expansion on the \meta{expandable tokens} before preventing
+% further expansion of the \meta{content} as for \cs{exp_not:n}. Typically,
+% the \meta{expandable tokens} will alter the nature of the \meta{content},
+% \emph{i.e.}~allow it to be generated in some way.
+% \end{function}
+%
+% \begin{variable}{\l__kernel_expl_bool}
+% A boolean which records the current code syntax status: \texttt{true} if
+% currently inside a code environment. This variable should only be
+% set by \cs{ExplSyntaxOn}/\cs{ExplSyntaxOff}.
+% \end{variable}
+%
+% \begin{variable}{\c__kernel_expl_date_tl}
+% A token list containing the release date of the \pkg{l3kernel} preloaded
+% in \LaTeXe{} used to check if dependencies match.
+% \end{variable}
+%
+% \begin{function}{\__kernel_file_missing:n}
+% \begin{syntax}
+% \cs{__kernel_file_missing:n} \Arg{name}
+% \end{syntax}
+% Expands the \meta{name} as per \cs{__kernel_file_name_sanitize:n} then
+% produces an error message indicating that this file was not found.
+% \end{function}
+%
+% \begin{function}[EXP,updated = 2021-04-17]{\__kernel_file_name_sanitize:n}
+% \begin{syntax}
+% \cs{__kernel_file_name_sanitize:n} \Arg{name}
+% \end{syntax}
+% Expands the file name using a \tn{csname}-based approach, and
+% relies on active characters (for example from UTF-8 characters)
+% being properly set up to expand to a expansion-safe version using
+% \cs{ifcsname}. This is less conservative than the token-by-token
+% approach used before, but it is much faster.
+% \end{function}
+%
+% \begin{function}{\__kernel_file_input_push:n, \__kernel_file_input_pop:}
+% \begin{syntax}
+% \cs{__kernel_file_input_push:n} \Arg{name}
+% \cs{__kernel_file_input_pop:}
+% \end{syntax}
+% Used to push and pop data from the internal file stack: needed only
+% in package mode, where interfacing with the \LaTeXe{} kernel is necessary.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_int_add:nnn}
+% \begin{syntax}
+% \cs{__kernel_int_add:nnn} \Arg{integer_1} \Arg{integer_2} \Arg{integer_3}
+% \end{syntax}
+% Expands to the result of adding the three \meta{integers} (which
+% must be suitable input for \cs{int_eval:w}), avoiding intermediate
+% overflow. Overflow occurs only if the overall result is outside
+% $[-2^{31}+1,2^{31}-1]$. The \meta{integers} may be of the form
+% \cs{int_eval:w} \dots{} \cs{scan_stop:} but may be evaluated more
+% than once.
+% \end{function}
+%
+% \begin{function}[added = 2018-03-31]{\__kernel_intarray_gset:Nnn}
+% \begin{syntax}
+% \cs{__kernel_intarray_gset:Nnn} \meta{intarray~var} \Arg{index} \Arg{value}
+% \end{syntax}
+% Faster version of \cs{intarray_gset:Nnn}. Stores the \meta{value}
+% into the \meta{integer array variable} at the \meta{position}. The
+% \meta{index} and \meta{value} must be suitable for a direct
+% assignment to a \TeX{} count register, for instance expanding to an
+% integer denotation or obtained through the primitive \tn{numexpr}
+% (which may be un-terminated). No bound checking is performed: the
+% caller is responsible for ensuring that the \meta{position} is
+% between $1$ and the \cs{intarray_count:N}, and the \meta{value}'s
+% absolute value is at most $2^{30}-1$. Assignments are always
+% global.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2018-03-31]{\__kernel_intarray_item:Nn}
+% \begin{syntax}
+% \cs{__kernel_intarray_item:Nn} \meta{intarray~var} \Arg{index}
+% \end{syntax}
+% Faster version of \cs{intarray_item:Nn}. Expands to the integer
+% entry stored at the \meta{index} in the \meta{integer array
+% variable}. The \meta{index} must be suitable for a direct
+% assignment to a \TeX{} count register and must be between $1$ and
+% the \cs{intarray_count:N}, lest a low-level \TeX{} error occur.
+% \end{function}
+%
+% \begin{function}[rEXP, added = 2020-07-12]{\__kernel_intarray_range_to_clist:Nnn}
+% \begin{syntax}
+% \cs{__kernel_intarray_range_to_clist:Nnn} \meta{intarray~var} \Arg{start index} \Arg{end index}
+% \end{syntax}
+% Converts to integer denotations separated by commas the entries of
+% the \meta{intarray} from positions \meta{start index} to \meta{end
+% index} included. The \meta{start index} and \meta{end index} must
+% be suitable for a direct assignment to a \TeX{} count register, must
+% be between $1$ and the \cs{intarray_count:N}, and be suitably
+% ordered. All tokens have category code other.
+% \end{function}
+%
+% \begin{function}[added = 2020-07-12]{\__kernel_intarray_gset_range_from_clist:Nnn}
+% \begin{syntax}
+% \cs{__kernel_intarray_gset_range_from_clist:Nnn} \meta{intarray~var} \Arg{start index} \Arg{integer clist}
+% \end{syntax}
+% Stores the entries of the \meta{clist} as entries of the
+% \meta{intarray~var} starting from the \meta{start index}, upwards.
+% This is done without any bound checking. The \meta{start index} and
+% all entries of the \meta{integer comma list} (which do not undergo
+% space trimming and brace stripping as in normal clist mappings) must
+% be suitable for a direct assignment to a \TeX{} count register. An
+% empty entry may stop the loop.
+% \end{function}
+%
+% \begin{function}{\__kernel_ior_open:Nn, \__kernel_ior_open:No}
+% \begin{syntax}
+% \cs{__kernel_ior_open:Nn} \meta{stream} \Arg{file name}
+% \end{syntax}
+% This function has identical syntax to the public version. However,
+% is does not take precautions against active characters in the
+% \meta{file name}, and it does not attempt to add a \meta{path} to
+% the \meta{file name}: it is therefore intended to be used by
+% higher-level
+% functions which have already fully expanded the \meta{file name} and which
+% need to perform multiple open or close operations. See for example the
+% implementation of \cs{ior_shell_open:Nn}.
+% \end{function}
+%
+% \begin{function}{\__kernel_iow_open:Nn, \__kernel_iow_open:No}
+% \begin{syntax}
+% \cs{__kernel_iow_open:Nn} \meta{stream} \Arg{file name}
+% \end{syntax}
+% This function has identical syntax to the public version. However,
+% is does not take precautions against active characters in the
+% \meta{file name}, and it does not attempt to add a \meta{path} to
+% the \meta{file name}: it is therefore intended to be used by
+% higher-level
+% functions which have already fully expanded the \meta{file name} and which
+% need to perform multiple open or close operations. See for example the
+% implementation of \cs{iow_shell_open:Nn}.
+% \end{function}
+%
+% \begin{function}{\__kernel_iow_with:Nnn}
+% \begin{syntax}
+% \cs{__kernel_iow_with:Nnn} \meta{integer} \Arg{value} \Arg{code}
+% \end{syntax}
+% If the \meta{integer} is equal to the \meta{value} then this
+% function simply runs the \meta{code}. Otherwise it saves the
+% current value of the \meta{integer}, sets it to the \meta{value},
+% runs the \meta{code}, and restores the \meta{integer} to its former
+% value. This is used to ensure that the \tn{newlinechar} is~$10$
+% when writing to a stream, which lets \cs{iow_newline:} work, and
+% that \tn{errorcontextlines} is $-1$ when displaying a message.
+% \end{function}
+%
+% \begin{variable}{\__kernel_kern:n}
+% \begin{syntax}
+% \cs{__kernel_kern:n} \Arg{length}
+% \end{syntax}
+% Inserts a kern of the specified \meta{length}, a dimension expression.
+% \end{variable}
+%
+% \begin{function}{\__kernel_msg_show_eval:Nn, \__kernel_msg_log_eval:Nn}
+% \begin{syntax}
+% \cs{__kernel_msg_show_eval:Nn} \meta{function} \Arg{expression}
+% \end{syntax}
+% Shows or logs the \meta{expression} (turned into a string), an equal
+% sign, and the result of applying the \meta{function} to the
+% \Arg{expression} (with \texttt{f}-expansion). For instance, if the
+% \meta{function} is \cs{int_eval:n} and the \meta{expression} is
+% |1+2| then this logs |> 1+2=3.|
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_pdf_object_id:n, \__kernel_pdf_object_id_indexed:nn}
+% \begin{syntax}
+% \cs{__kernel_pdf_object_id:n} \Arg{object}
+% \cs{__kernel_pdf_object_id_indexed:nn} \Arg{class} \Arg{number}
+% \end{syntax}
+% Expands to the ID of \meta{object} (or object of \meta{number} within
+% the \meta{class}), in for example page resource allocation. Depending on
+% the backend, the result may be the same as
+% \cs{pdf_object_id:n}/\cs{pdf_object_id_indexed:nn}.
+% \end{function}
+%
+% \begin{variable}{\g__kernel_prg_map_int}
+% This integer is used by non-expandable mapping functions to track
+% the level of nesting in force. The functions
+% \cs[no-index]{\meta{type}_map_1:w},
+% \cs[no-index]{\meta{type}_map_2:w}, \emph{etc.}, labelled by
+% \cs{g__kernel_prg_map_int}
+% hold functions to be mapped over various list datatypes in inline
+% and variable mappings.
+% \end{variable}
+%
+% \begin{function}{\__kernel_quark_new_test:N}
+% \begin{syntax}
+% \cs{__kernel_quark_new_test:N} \cs[no-index]{\meta{name}:\meta{arg spec}}
+% \end{syntax}
+% Defines a quark-test function \cs[no-index]{\meta{name}:\meta{arg spec}}
+% which tests if its argument is \cs[no-index]{q__\meta{namespace}_recursion_tail},
+% then acts accordingly, as described below for each possible
+% \meta{arg spec}.
+%
+% The \meta{namespace} is determined as the first (nonempty)
+% |_|-delimited word in \meta{name} and is used internally
+% in the definition of auxiliaries. The function
+% \cs{__kernel_quark_new_test:N} does \emph{not} define
+% the \cs[no-index]{q__\meta{namespace}_recursion_tail} and
+% \cs[no-index]{q__\meta{namespace}_recursion_stop} quarks.
+% They should be manually defined with \cs{quark_new:N}.
+%
+% There are $6$ different types of quark-test functions. Which one is
+% defined depends on the \meta{arg spec}, which \emph{must} be one of
+% the options listed now. Four of them are modeled after
+% \cs[no-index]{quark_if_recursion_tail:(N|n)} and
+% \cs[no-index]{quark_if_recursion_tail_do:(N|n)n}.
+% \begin{description}
+% \def\makelabel#1{\texttt{#1}}
+% \item[n] defines \cs[no-index]{\meta{name}:n} such that it
+% checks if |#1| contains only \cs[no-index]{q__\meta{namespace}_recursion_tail}, and
+% if so consumes all tokens up to \cs[no-index]{q__\meta{namespace}_recursion_stop}
+% (\emph{c.f.}~\cs{quark_if_recursion_tail_stop:n}).
+% \item[nn] defines \cs[no-index]{\meta{name}:nn} such that it
+% checks if |#1| contains only \cs[no-index]{q__\meta{namespace}_recursion_tail}, and
+% if so consumes all tokens up to \cs[no-index]{q__\meta{namespace}_recursion_stop},
+% then executes the code |#2| after that
+% (\emph{c.f.}~\cs{quark_if_recursion_tail_stop_do:nn}).
+% \item[N] defines \cs[no-index]{\meta{name}:N} such that it
+% checks if |#1| is \cs[no-index]{q__\meta{namespace}_recursion_tail}, and if so consumes
+% all tokens up to \cs[no-index]{q__\meta{namespace}_recursion_stop}
+% (\emph{c.f.}~\cs{quark_if_recursion_tail_stop:N}).
+% \item[Nn] defines \cs[no-index]{\meta{name}:Nn} such that it
+% checks if |#1| is \cs[no-index]{q__\meta{namespace}_recursion_tail}, and if so consumes
+% all tokens up to \cs[no-index]{q__\meta{namespace}_recursion_stop}, then executes
+% the code |#2| after that
+% (\emph{c.f.}~\cs{quark_if_recursion_tail_stop_do:Nn}).
+% \end{description}
+% The last two are modeled after
+% \cs[no-index]{quark_if_recursion_tail_break:(n|N)N}, and in those
+% cases the quark \cs[no-index]{q__\meta{namespace}_recursion_stop} is
+% not used (and thus needs not be defined).
+% \begin{description}
+% \def\makelabel#1{\texttt{#1}}
+% \item[nN] defines \cs[no-index]{\meta{name}:nN} such that it
+% checks if |#1| contains only \cs[no-index]{q__\meta{namespace}_recursion_tail}, and
+% if so uses the \cs[no-index]{\meta{type}_map_break:} function |#2|.
+% \item[NN] defines \cs[no-index]{\meta{name}:NN} such that it
+% checks if |#1| is \cs[no-index]{q__\meta{namespace}_recursion_tail}, and if so uses
+% the \cs[no-index]{\meta{type}_map_break:} function |#2|.
+% \end{description}
+% Any other signature, as well as a function without signature
+% are errors, and in such case the definition is aborted.
+% \end{function}
+%
+% \begin{function}{\__kernel_quark_new_conditional:Nn}
+% \begin{syntax}
+% \cs{__kernel_quark_new_conditional:Nn} \cs[no-index]{__\meta{namespace}_quark_if_\meta{name}:\meta{arg spec}} \Arg{conditions}
+% \end{syntax}
+% Defines a collection of quark conditionals that test if their
+% argument is the quark \cs[no-index]{q__\meta{namespace}_\meta{name}}
+% and perform suitable actions. The \meta{conditions} are a
+% comma-separated list of one or more of |p|, |T|, |F|, and |TF|, and
+% one conditional is defined for each \meta{condition} in the list, as
+% described for \cs{prg_new_conditional:Npnn}. The conditionals are
+% defined using \cs{prg_new_conditional:Npnn}, so that their name is
+% obtained by adding |p|, |T|, |F|, or |TF| to the base name
+% \cs[no-index]{__\meta{namespace}_quark_if_\meta{name}:\meta{arg spec}}.
+%
+% The first argument of \cs{__kernel_quark_new_conditional:Nn} must
+% contain |_quark_if_| and |:|, as these markers are used to determine
+% the \meta{name} of the quark
+% \cs[no-index]{q__\meta{namespace}_\meta{name}} to be tested. This
+% quark should be manually defined with \cs{quark_new:N}, as
+% \cs{__kernel_quark_new_conditional:Nn} does \emph{not} define it.
+%
+% The function \cs{__kernel_quark_new_conditional:Nn} can define $2$
+% different types of quark conditionals. Which one is defined depends
+% on the \meta{arg spec}, which \emph{must} be one of the following
+% options, modeled after \cs[index=quark_if_nil:NTF]{quark_if_nil:(N|n)(TF)}.
+% \begin{description}
+% \def\makelabel#1{\texttt{#1}}
+% \item[n] defines \cs[no-index]{__\meta{namespace}_quark_if_\meta{name}:n(TF)} such that it
+% checks if |#1| contains only \cs[no-index]{q__\meta{namespace}_\meta{name}}, and
+% executes the proper conditional branch.
+% \item[N] defines \cs[no-index]{__\meta{namespace}_quark_if_\meta{name}:N(TF)} such that it
+% checks if |#1| is \cs[no-index]{q__\meta{namespace}_\meta{name}}, and
+% executes the proper conditional branch.
+% \end{description}
+% Any other signature, as well as a function without signature
+% are errors, and in such case the definition is aborted.
+% \end{function}
+%
+% \begin{function}{\__kernel_sys_everyjob:}
+% \begin{syntax}
+% \cs{__kernel_sys_everyjob:}
+% \end{syntax}
+% Inserts the internal token list required at the start of every run (job).
+% \end{function}
+%
+% \begin{variable}{\c__kernel_randint_max_int}
+% Maximal allowed argument to \cs{__kernel_randint:n}. Equal to
+% $2^{17}-1$.
+% \end{variable}
+%
+% \begin{function}{\__kernel_randint:n}
+% \begin{syntax}
+% \cs{__kernel_randint:n} \Arg{max}
+% \end{syntax}
+% Used in an integer expression this gives a pseudo-random number
+% between $1$ and $\meta{max}$ included. One must have
+% $\meta{max}\leq 2^{17}-1$. The \meta{max} must be suitable for
+% \cs{int_value:w} (and any \cs{int_eval:w} must be terminated by
+% \cs{scan_stop:} or equivalent).
+% \end{function}
+%
+% \begin{function}{\__kernel_randint:nn}
+% \begin{syntax}
+% \cs{__kernel_randint:nn} \Arg{min} \Arg{max}
+% \end{syntax}
+% Used in an integer expression this gives a pseudo-random number
+% between $\meta{min}$ and $\meta{max}$ included. The \meta{min} and
+% \meta{max} must be suitable for \cs{int_value:w} (and any
+% \cs{int_eval:w} must be terminated by \cs{scan_stop:} or
+% equivalent). For small ranges
+% $R=\meta{max}-\meta{min}+1\leq 2^{17}-1$,
+% $\meta{min} - 1 + \cs{__kernel_randint:n} |{|R|}|$ is faster.
+% \end{function}
+%
+% \begin{function}{\__kernel_register_show:N, \__kernel_register_show:c}
+% \begin{syntax}
+% \cs{__kernel_register_show:N} \meta{register}
+% \end{syntax}
+% Used to show the contents of a \TeX{} register at the terminal, formatted
+% such that internal parts of the mechanism are not visible.
+% \end{function}
+%
+% \begin{function}
+% {\__kernel_register_log:N, \__kernel_register_log:c}
+% \begin{syntax}
+% \cs{__kernel_register_log:N} \meta{register}
+% \end{syntax}
+% Used to write the contents of a \TeX{} register to the log file in a
+% form similar to \cs{__kernel_register_show:N}.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_str_to_other:n}
+% \begin{syntax}
+% \cs{__kernel_str_to_other:n} \Arg{token list}
+% \end{syntax}
+% Converts the \meta{token list} to a \meta{other string}, where
+% spaces have category code \enquote{other}. This function can be
+% \texttt{f}-expanded without fear of losing a leading space, since
+% spaces do not have category code $10$ in its result. It takes a
+% time quadratic in the character count of the string.
+% \end{function}
+%
+% \begin{function}[rEXP]{\__kernel_str_to_other_fast:n}
+% \begin{syntax}
+% \cs{__kernel_str_to_other_fast:n} \Arg{token list}
+% \end{syntax}
+% Same behaviour \cs{__kernel_str_to_other:n} but only restricted-expandable.
+% It takes a time linear in the character count of the string.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_tl_to_str:w}
+% \begin{syntax}
+% \cs{__kernel_tl_to_str:w} \meta{expandable tokens} \Arg{tokens}
+% \end{syntax}
+% Carries out expansion on the \meta{expandable tokens} before conversion of
+% the \meta{tokens} to a string as describe for \cs{tl_to_str:n}. Typically,
+% the \meta{expandable tokens} will alter the nature of the \meta{tokens},
+% \emph{i.e.}~allow it to be generated in some way. This function requires
+% only a single expansion.
+% \end{function}
+%
+% \begin{function}{\__kernel_tl_set:Nx, \__kernel_tl_gset:Nx}
+% \begin{syntax}
+% \cs{__kernel_tl_set:Nx} \meta{tl~var} \Arg{tokens}
+% \end{syntax}
+% Fully expands \meta{tokens} and assigns the result to \meta{tl~var}.
+% \meta{tokens} must be given in braces and there must be no token between
+% \meta{tl~var} and \meta{tokens}.
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_codepoint_data:nn}
+% \begin{syntax}
+% \cs{__kernel_codepoint_data:nn} \Arg{type} \Arg{codepoint}
+% \end{syntax}
+% Expands to the appropriate value for the \meta{type} of data
+% requested for a \meta{codepoint}. The current list of \meta{types} and
+% results are
+% \begin{description}
+% \item[\texttt{lowercase}] The \emph{single} codepoint specified by
+% \texttt{UnicodeData.txt} for lowercase mapping of the codepoint:
+% will be equal to the input \meta{codepoint} if there is no mapping
+% specified in \texttt{UnicodeData.txt}
+% \item[\texttt{uppercase}] The \emph{single} codepoint specified by
+% \texttt{UnicodeData.txt} for uppercase mapping of the codepoint:
+% will be equal to the input \meta{codepoint} if there is no mapping
+% specified in \texttt{UnicodeData.txt}
+% \end{description}
+% \end{function}
+%
+% \begin{function}[EXP]{\__kernel_codepoint_case:nn}
+% \begin{syntax}
+% \cs{__kernel_codepoint_case:nn} \Arg{mapping} \Arg{codepoint}
+% \end{syntax}
+% Expands to a list of three balanced text, of which at least the first
+% will contain a codepoint. This list of up to three codepoints specifies
+% the full case mapping for the input \meta{codepoint}. The \meta{mapping}
+% should be one of
+% \begin{itemize}
+% \item \texttt{casefold}
+% \item \texttt{lowercase}
+% \item \texttt{titlecase}
+% \item \texttt{uppercase}
+% \end{itemize}
+% \end{function}
+%
+% \subsection{Kernel backend functions}
+%
+% These functions are required to pass information to the backend. The nature
+% of these means that they are defined only when the relevant backend is in
+% use.
+%
+% \begin{function}
+% {
+% \__kernel_backend_literal:n,
+% \__kernel_backend_literal:e,
+% \__kernel_backend_literal:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_literal:n} \Arg{content}
+% \end{syntax}
+% Adds the \meta{content} literally to the current vertical list as a
+% whatsit. The nature of the \meta{content} will depend on the backend in
+% use.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_backend_literal_postscript:n,
+% \__kernel_backend_literal_postscript:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_literal_postscript:n} \Arg{PostScript}
+% \end{syntax}
+% Adds the \meta{PostScript} literally to the current vertical list as a
+% whatsit. No positioning is applied.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_backend_literal_pdf:n,
+% \__kernel_backend_literal_pdf:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_literal_pdf:n} \Arg{PDF instructions}
+% \end{syntax}
+% Adds the \meta{PDF instructions} literally to the current vertical list as
+% a whatsit. No positioning is applied.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_backend_literal_svg:n,
+% \__kernel_backend_literal_svg:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_literal_svg:n} \Arg{SVG instructions}
+% \end{syntax}
+% Adds the \meta{SVG instructions} literally to the current vertical list as
+% a whatsit. No positioning is applied.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_backend_postscript:n,
+% \__kernel_backend_postscript:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_postscript:n} \Arg{PostScript}
+% \end{syntax}
+% Adds the \meta{PostScript} to the current vertical list as a
+% whatsit. The PostScript reference point is adjusted to match the
+% current position. The PostScript is inserted inside a |SDict begin|/|end|
+% pair.
+% \end{function}
+%
+% \begin{function}{\__kernel_backend_align_begin:, \__kernel_backend_align_end:}
+% \begin{syntax}
+% \cs{__kernel_backend_align_begin:}
+% \meta{PostScript literals}
+% \cs{__kernel_backend_align_end:}
+% \end{syntax}
+% Arranges to align the PostScript and DVI current positions and scales.
+% \end{function}
+%
+% \begin{function}{\__kernel_backend_scope_begin:, \__kernel_backend_scope_end:}
+% \begin{syntax}
+% \cs{__kernel_backend_scope_begin:}
+% \meta{content}
+% \cs{__kernel_backend_scope_end:}
+% \end{syntax}
+% Creates a scope for instructions at the backend level.
+% \end{function}
+%
+% \begin{function}
+% {
+% \__kernel_backend_matrix:n,
+% \__kernel_backend_matrix:e
+% }
+% \begin{syntax}
+% \cs{__kernel_backend_matrix:n} \Arg{matrix}
+% \end{syntax}
+% Applies the \meta{matrix} to the current transformation matrix.
+% \end{function}
+%
+% \begin{function}{\g__kernel_backend_header_bool}
+% Specifies whether to write headers for the backend.
+% \end{function}
+%
+% \begin{function}{\l__kernel_color_stack_int}
+% The color stack used in \pdfTeX{} and \LuaTeX{} for the main color.
+% \end{function}
+%
+% \end{implementation}
+%
+% \PrintIndex