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l3keys.dtx
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l3keys.dtx
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% \iffalse meta-comment
%
%% File: l3keys.dtx Copyright (C) 2006-2018 The LaTeX3 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{l3keys} package\\ Key--value interfaces^^A
% }
%
% \author{^^A
% The \LaTeX3 Project\thanks
% {^^A
% E-mail:
% \href{mailto:latex-team@latex-project.org}
% {latex-team@latex-project.org}^^A
% }^^A
% }
%
% \date{Released 2018/03/05}
%
% \maketitle
%
% \begin{documentation}
%
% The key--value method is a popular system for creating large numbers
% of settings for controlling function or package behaviour. The
% system normally results in input of the form
% \begin{verbatim}
% \MyModuleSetup{
% key-one = value one,
% key-two = value two
% }
% \end{verbatim}
% or
% \begin{verbatim}
% \MyModuleMacro[
% key-one = value one,
% key-two = value two
% ]{argument}
% \end{verbatim}
% for the user.
%
% The high level functions here are intended as a method to create
% key--value controls. Keys are themselves created using a key--value
% interface, minimising the number of functions and arguments
% required. Each key is created by setting one or more \emph{properties}
% of the key:
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key-one .code:n = code including parameter #1,
% key-two .tl_set:N = \l_mymodule_store_tl
% }
% \end{verbatim}
% These values can then be set as with other key--value approaches:
% \begin{verbatim}
% \keys_set:nn { mymodule }
% {
% key-one = value one,
% key-two = value two
% }
% \end{verbatim}
%
% At a document level, \cs{keys_set:nn} is used within a
% document function, for example
% \begin{verbatim}
% \DeclareDocumentCommand \MyModuleSetup { m }
% { \keys_set:nn { mymodule } { #1 } }
% \DeclareDocumentCommand \MyModuleMacro { o m }
% {
% \group_begin:
% \keys_set:nn { mymodule } { #1 }
% % Main code for \MyModuleMacro
% \group_end:
% }
% \end{verbatim}
%
% Key names may contain any tokens, as they are handled internally
% using \cs{tl_to_str:n}. As discussed in
% section~\ref{sec:l3keys:subdivision}, it is suggested that the character
% |/| is reserved for sub-division of keys into logical
% groups. Functions and variables are \emph{not} expanded when creating
% key names, and so
% \begin{verbatim}
% \tl_set:Nn \l_mymodule_tmp_tl { key }
% \keys_define:nn { mymodule }
% {
% \l_mymodule_tmp_tl .code:n = code
% }
% \end{verbatim}
% creates a key called |\l_mymodule_tmp_tl|, and not one called
% \texttt{key}.
%
% \section{Creating keys}
%
% \begin{function}[updated = 2015-11-07]{\keys_define:nn}
% \begin{syntax}
% \cs{keys_define:nn} \Arg{module} \Arg{keyval list}
% \end{syntax}
% Parses the \meta{keyval list} and defines the keys listed there for
% \meta{module}. The \meta{module} name should be a text value, but
% there are no restrictions on the nature of the text. In practice the
% \meta{module} should be chosen to be unique to the module in question
% (unless deliberately adding keys to an existing module).
%
% The \meta{keyval list} should consist of one or more key names along
% with an associated key \emph{property}. The properties of a key
% determine how it acts. The individual properties are described
% in the following text; a typical use of \cs{keys_define:nn} might
% read
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% keyname .code:n = Some~code~using~#1,
% keyname .value_required:n = true
% }
% \end{verbatim}
% where the properties of the key begin from the |.| after the key
% name.
% \end{function}
%
% The various properties available take either no arguments at
% all, or require one or more arguments. This is indicated in the
% name of the property using an argument specification. In the following
% discussion, each property is illustrated attached to an
% arbitrary \meta{key}, which when used may be supplied with a
% \meta{value}. All key \emph{definitions} are local.
%
% Key properties are applied in the reading order and so the ordering
% is significant. Key properties which define \enquote{actions}, such
% as |.code:n|, |.tl_set:N|, \emph{etc.}, override one another.
% Some other properties are mutually exclusive, notably |.value_required:n|
% and |.value_forbidden:n|, and so they replace one another. However,
% properties covering non-exclusive behaviours may be given in any order. Thus
% for example the following definitions are equivalent.
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% keyname .code:n = Some~code~using~#1,
% keyname .value_required:n = true
% }
% \keys_define:nn { mymodule }
% {
% keyname .value_required:n = true,
% keyname .code:n = Some~code~using~#1
% }
% \end{verbatim}
% Note that with the exception of the special |.undefine:| property, all
% key properties define the key within the current \TeX{} scope.
%
% \begin{function}[updated = 2013-07-08]
% {.bool_set:N, .bool_set:c, .bool_gset:N, .bool_gset:c}
% \begin{syntax}
% \meta{key} .bool_set:N = \meta{boolean}
% \end{syntax}
% Defines \meta{key} to set \meta{boolean} to \meta{value} (which
% must be either \texttt{true} or \texttt{false}). If the variable
% does not exist, it will be created globally at the point that
% the key is set up.
% \end{function}
%
% \begin{function}[added = 2011-08-28, updated = 2013-07-08]
% {
% .bool_set_inverse:N, .bool_set_inverse:c,
% .bool_gset_inverse:N, .bool_gset_inverse:c
% }
% \begin{syntax}
% \meta{key} .bool_set_inverse:N = \meta{boolean}
% \end{syntax}
% Defines \meta{key} to set \meta{boolean} to the logical
% inverse of \meta{value} (which must be either \texttt{true} or
% \texttt{false}).
% If the \meta{boolean} does not exist, it will be created globally
% at the point that the key is set up.
% \end{function}
%
% \begin{function}{.choice:}
% \begin{syntax}
% \meta{key} .choice:
% \end{syntax}
% Sets \meta{key} to act as a choice key. Each valid choice
% for \meta{key} must then be created, as discussed in
% section~\ref{sec:l3keys:choice}.
% \end{function}
%
% \begin{function}[added = 2011-08-21, updated = 2013-07-10]
% {.choices:nn, .choices:Vn, .choices:on, .choices:xn}
% \begin{syntax}
% \meta{key} .choices:nn = \Arg{choices} \Arg{code}
% \end{syntax}
% Sets \meta{key} to act as a choice key, and defines a series \meta{choices}
% which are implemented using the \meta{code}. Inside \meta{code},
% \cs{l_keys_choice_tl} will be the name of the choice made, and
% \cs{l_keys_choice_int} will be the position of the choice in the list
% of \meta{choices} (indexed from~$1$).
% Choices are discussed in detail in section~\ref{sec:l3keys:choice}.
% \end{function}
%
% \begin{function}[added = 2011-09-11]
% {.clist_set:N, .clist_set:c, .clist_gset:N, .clist_gset:c}
% \begin{syntax}
% \meta{key} .clist_set:N = \meta{comma list variable}
% \end{syntax}
% Defines \meta{key} to set \meta{comma list variable} to \meta{value}.
% Spaces around commas and empty items will be stripped.
% If the variable does not exist, it
% is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}[updated = 2013-07-10]{.code:n}
% \begin{syntax}
% \meta{key} .code:n = \Arg{code}
% \end{syntax}
% Stores the \meta{code} for execution when \meta{key} is used.
% The \meta{code} can include one parameter (|#1|), which will be the
% \meta{value} given for the \meta{key}. The \texttt{x}-type variant
% expands \meta{code} at the point where the \meta{key} is
% created.
% \end{function}
%
% \begin{function}[updated = 2013-07-09]
% {.default:n, .default:V, .default:o, .default:x}
% \begin{syntax}
% \meta{key} .default:n = \Arg{default}
% \end{syntax}
% Creates a \meta{default} value for \meta{key}, which is used if no
% value is given. This will be used if only the key name is given,
% but not if a blank \meta{value} is given:
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .code:n = Hello~#1,
% key .default:n = World
% }
% \keys_set:nn { mymodule }
% {
% key = Fred, % Prints 'Hello Fred'
% key, % Prints 'Hello World'
% key = , % Prints 'Hello '
% }
% \end{verbatim}
% The default does not affect keys where values are required or
% forbidden. Thus a required value cannot be supplied by a default
% value, and giving a default value for a key which cannot take a value
% does not trigger an error.
% \end{function}
%
% \begin{function}{.dim_set:N, .dim_set:c, .dim_gset:N, .dim_gset:c}
% \begin{syntax}
% \meta{key} .dim_set:N = \meta{dimension}
% \end{syntax}
% Defines \meta{key} to set \meta{dimension} to \meta{value} (which
% must a dimension expression). If the variable does not exist, it
% is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}{.fp_set:N, .fp_set:c, .fp_gset:N, .fp_gset:c}
% \begin{syntax}
% \meta{key} .fp_set:N = \meta{floating point}
% \end{syntax}
% Defines \meta{key} to set \meta{floating point} to \meta{value}
% (which must a floating point expression). If the variable does not exist,
% it is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}[added = 2013-07-14]
% {.groups:n}
% \begin{syntax}
% \meta{key} .groups:n = \Arg{groups}
% \end{syntax}
% Defines \meta{key} as belonging to the \meta{groups} declared. Groups
% provide a \enquote{secondary axis} for selectively setting keys, and are
% described in Section~\ref{sec:l3keys:selective}.
% \end{function}
%
% \begin{function}[added = 2016-11-22]{.inherit:n}
% \begin{syntax}
% \meta{key} .inherit:n = \Arg{parents}
% \end{syntax}
% Specifies that the \meta{key} path should inherit the keys listed
% as \meta{parents}. For example, after setting
% \begin{verbatim}
% \keys_define:n { foo } { test .code:n = \tl_show:n {#1} }
% \keys_define:n { } { bar .inherit:n = foo }
% \end{verbatim}
% setting
% \begin{verbatim}
% \keys_set:n { bar } { test = a }
% \end{verbatim}
% will be equivalent to
% \begin{verbatim}
% \keys_set:n { foo } { test = a }
% \end{verbatim}
% \end{function}
%
% \begin{function}[updated = 2013-07-09]
% {.initial:n, .initial:V, .initial:o, .initial:x}
% \begin{syntax}
% \meta{key} .initial:n = \Arg{value}
% \end{syntax}
% Initialises the \meta{key} with the \meta{value}, equivalent to
% \begin{quote}
% \cs{keys_set:nn} \Arg{module} \{ \meta{key} = \meta{value} \}
% \end{quote}
% \end{function}
%
% \begin{function}{.int_set:N, .int_set:c, .int_gset:N, .int_gset:c}
% \begin{syntax}
% \meta{key} .int_set:N = \meta{integer}
% \end{syntax}
% Defines \meta{key} to set \meta{integer} to \meta{value} (which
% must be an integer expression). If the variable does not exist, it
% is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}[updated = 2013-07-10]{.meta:n}
% \begin{syntax}
% \meta{key} .meta:n = \Arg{keyval list}
% \end{syntax}
% Makes \meta{key} a meta-key, which will set \meta{keyval list} in
% one go. If \meta{key} is given with a value at the time the key
% is used, then the value will be passed through to the subsidiary
% \meta{keys} for processing (as |#1|).
% \end{function}
%
% \begin{function}[added = 2013-07-10]{.meta:nn}
% \begin{syntax}
% \meta{key} .meta:nn = \Arg{path} \Arg{keyval list}
% \end{syntax}
% Makes \meta{key} a meta-key, which will set \meta{keyval list} in
% one go using the \meta{path} in place of the current one.
% If \meta{key} is given with a value at the time the key
% is used, then the value will be passed through to the subsidiary
% \meta{keys} for processing (as |#1|).
% \end{function}
%
% \begin{function}[added = 2011-08-21]{.multichoice:}
% \begin{syntax}
% \meta{key} .multichoice:
% \end{syntax}
% Sets \meta{key} to act as a multiple choice key. Each valid choice
% for \meta{key} must then be created, as discussed in
% section~\ref{sec:l3keys:choice}.
% \end{function}
%
% \begin{function}[added = 2011-08-21, updated = 2013-07-10]
% {.multichoices:nn, .multichoices:Vn, .multichoices:on, .multichoices:xn}
% \begin{syntax}
% \meta{key} .multichoices:nn \Arg{choices} \Arg{code}
% \end{syntax}
% Sets \meta{key} to act as a multiple choice key, and defines a series
% \meta{choices}
% which are implemented using the \meta{code}. Inside \meta{code},
% \cs{l_keys_choice_tl} will be the name of the choice made, and
% \cs{l_keys_choice_int} will be the position of the choice in the list
% of \meta{choices} (indexed from~$1$).
% Choices are discussed in detail in section~\ref{sec:l3keys:choice}.
% \end{function}
%
% \begin{function}{.skip_set:N, .skip_set:c, .skip_gset:N, .skip_gset:c}
% \begin{syntax}
% \meta{key} .skip_set:N = \meta{skip}
% \end{syntax}
% Defines \meta{key} to set \meta{skip} to \meta{value} (which
% must be a skip expression). If the variable does not exist, it
% is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}{.tl_set:N, .tl_set:c, .tl_gset:N, .tl_gset:c}
% \begin{syntax}
% \meta{key} .tl_set:N = \meta{token list variable}
% \end{syntax}
% Defines \meta{key} to set \meta{token list variable} to \meta{value}.
% If the variable does not exist, it is created globally
% at the point that the key is set up.
% \end{function}
%
% \begin{function}{.tl_set_x:N, .tl_set_x:c, .tl_gset_x:N, .tl_gset_x:c}
% \begin{syntax}
% \meta{key} .tl_set_x:N = \meta{token list variable}
% \end{syntax}
% Defines \meta{key} to set \meta{token list variable} to \meta{value},
% which will be subjected to an \texttt{x}-type expansion
% (\emph{i.e.}~using \cs{tl_set:Nx}). If the variable does not exist,
% it is created globally at the point that the key is set up.
% \end{function}
%
% \begin{function}[added = 2015-07-14]{.undefine:}
% \begin{syntax}
% \meta{key} .undefine:
% \end{syntax}
% Removes the definition of the \meta{key} within the current scope.
% \end{function}
%
% \begin{function}[added = 2015-07-14]{.value_forbidden:n}
% \begin{syntax}
% \meta{key} .value_forbidden:n = \texttt{true\string|false}
% \end{syntax}
% Specifies that \meta{key} cannot receive a \meta{value} when used.
% If a \meta{value} is given then an error will be issued. Setting
% the property \texttt{false} cancels the restriction.
% \end{function}
%
% \begin{function}[added = 2015-07-14]{.value_required:n}
% \begin{syntax}
% \meta{key} .value_required:n = \texttt{true\string|false}
% \end{syntax}
% Specifies that \meta{key} must receive a \meta{value} when used.
% If a \meta{value} is not given then an error will be issued. Setting
% the property \texttt{false} cancels the restriction.
% \end{function}
%
% \section{Sub-dividing keys}
% \label{sec:l3keys:subdivision}
%
% When creating large numbers of keys, it may be desirable to divide
% them into several sub-groups for a given module. This can be achieved
% either by adding a sub-division to the module name:
% \begin{verbatim}
% \keys_define:nn { module / subgroup }
% { key .code:n = code }
% \end{verbatim}
% or to the key name:
% \begin{verbatim}
% \keys_define:nn { mymodule }
% { subgroup / key .code:n = code }
% \end{verbatim}
% As illustrated, the best choice of token for sub-dividing keys in
% this way is |/|. This is because of the method that is
% used to represent keys internally. Both of the above code fragments
% set the same key, which has full name \texttt{module/subgroup/key}.
%
% As illustrated in the next section, this subdivision is
% particularly relevant to making multiple choices.
%
% \section{Choice and multiple choice keys}
% \label{sec:l3keys:choice}
%
% The \pkg{l3keys} system supports two types of choice key, in which a series
% of pre-defined input values are linked to varying implementations. Choice
% keys are usually created so that the various values are mutually-exclusive:
% only one can apply at any one time. \enquote{Multiple} choice keys are also
% supported: these allow a selection of values to be chosen at the same time.
%
% Mutually-exclusive choices are created by setting the \texttt{.choice:}
% property:
% \begin{verbatim}
% \keys_define:nn { mymodule }
% { key .choice: }
% \end{verbatim}
% For keys which are set up as choices, the valid choices are generated
% by creating sub-keys of the choice key. This can be carried out in
% two ways.
%
% In many cases, choices execute similar code which is dependant only
% on the name of the choice or the position of the choice in the
% list of all possibilities. Here, the keys can share the same code, and can
% be rapidly created using the \texttt{.choices:nn} property.
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .choices:nn =
% { choice-a, choice-b, choice-c }
% {
% You~gave~choice~'\tl_use:N \l_keys_choice_tl',~
% which~is~in~position~\int_use:N \l_keys_choice_int \c_space_tl
% in~the~list.
% }
% }
% \end{verbatim}
% The index \cs{l_keys_choice_int} in the list of choices starts at~$1$.
%
% \begin{variable}{\l_keys_choice_int, \l_keys_choice_tl}
% Inside the code block for a choice generated using \texttt{.choices:nn},
% the variables \cs{l_keys_choice_tl} and \cs{l_keys_choice_int} are
% available to indicate the name of the current choice, and its position in
% the comma list. The position is indexed from~$1$. Note that, as with
% standard key code generated using \texttt{.code:n}, the value passed to
% the key (i.e.~the choice name) is also available as |#1|.
% \end{variable}
%
% On the other hand, it is sometimes useful to create choices which
% use entirely different code from one another. This can be achieved
% by setting the \texttt{.choice:} property of a key, then manually
% defining sub-keys.
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .choice:,
% key / choice-a .code:n = code-a,
% key / choice-b .code:n = code-b,
% key / choice-c .code:n = code-c,
% }
% \end{verbatim}
%
% It is possible to mix the two methods, but manually-created choices
% should \emph{not} use \cs{l_keys_choice_tl} or \cs{l_keys_choice_int}.
% These variables do not have defined behaviour when used outside of
% code created using \texttt{.choices:nn}
% (\emph{i.e.}~anything might happen).
%
% It is possible to allow choice keys to take values which have not previously
% been defined by adding code for the special \texttt{unknown} choice. The
% general behavior of the \texttt{unknown} key is described in
% Section~\ref{sec:l3keys:unknown}. A typical example in the case of a choice
% would be to issue a custom error message:
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .choice:,
% key / choice-a .code:n = code-a,
% key / choice-b .code:n = code-b,
% key / choice-c .code:n = code-c,
% key / unknown .code:n =
% \msg_error:nnxxx { mymodule } { unknown-choice }
% { key } % Name of choice key
% { choice-a , choice-b , choice-c } % Valid choices
% { \exp_not:n {#1} } % Invalid choice given
% %
% %
% }
% \end{verbatim}
%
% Multiple choices are created in a very similar manner to mutually-exclusive
% choices, using the properties \texttt{.multichoice:} and
% \texttt{.multichoices:nn}. As with mutually exclusive choices, multiple
% choices are define as sub-keys. Thus both
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .multichoices:nn =
% { choice-a, choice-b, choice-c }
% {
% You~gave~choice~'\tl_use:N \l_keys_choice_tl',~
% which~is~in~position~
% \int_use:N \l_keys_choice_int \c_space_tl
% in~the~list.
% }
% }
% \end{verbatim}
% and
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% key .multichoice:,
% key / choice-a .code:n = code-a,
% key / choice-b .code:n = code-b,
% key / choice-c .code:n = code-c,
% }
% \end{verbatim}
% are valid.
%
% When a multiple choice key is set
% \begin{verbatim}
% \keys_set:nn { mymodule }
% {
% key = { a , b , c } % 'key' defined as a multiple choice
% }
% \end{verbatim}
% each choice is applied in turn, equivalent to a \texttt{clist} mapping or
% to applying each value individually:
% \begin{verbatim}
% \keys_set:nn { mymodule }
% {
% key = a ,
% key = b ,
% key = c ,
% }
% \end{verbatim}
% Thus each separate choice will have passed to it the
% \cs{l_keys_choice_tl} and \cs{l_keys_choice_int} in exactly
% the same way as described for \texttt{.choices:nn}.
%
% \section{Setting keys}
%
% \begin{function}[updated = 2015-11-07]
% {\keys_set:nn, \keys_set:nV, \keys_set:nv, \keys_set:no}
% \begin{syntax}
% \cs{keys_set:nn} \Arg{module} \Arg{keyval list}
% \end{syntax}
% Parses the \meta{keyval list}, and sets those keys which are defined
% for \meta{module}. The behaviour on finding an unknown key can be set
% by defining a special \texttt{unknown} key: this is illustrated
% later.
% \end{function}
%
% \begin{variable}[updated = 2015-07-14]
% {\l_keys_key_tl, \l_keys_path_tl, \l_keys_value_tl}
% For each key processed, information of the full \emph{path} of the
% key, the \emph{name} of the key and the \emph{value} of the key is
% available within three token list variables. These may be used within
% the code of the key.
%
% The \emph{value} is everything after the \texttt{=}, which may be
% empty if no value was given. This is stored in \cs{l_keys_value_tl}, and
% is not processed in any way by \cs{keys_set:nn}.
%
% The \emph{path} of the key is a \enquote{full} description of the key,
% and is unique for each key. It consists of the module and full key name,
% thus for example
% \begin{verbatim}
% \keys_set:nn { mymodule } { key-a = some-value }
% \end{verbatim}
% has path \texttt{mymodule/key-a} while
% \begin{verbatim}
% \keys_set:nn { mymodule } { subset / key-a = some-value }
% \end{verbatim}
% has path \texttt{mymodule/subset/key-a}. This information is stored in
% \cs{l_keys_path_tl}, and will have been processed by \cs{tl_to_str:n}.
%
% The \emph{name} of the key is the part of the path after the last
% \texttt{/}, and thus is not unique. In the preceding examples, both keys
% have name \texttt{key-a} despite having different paths. This information
% is stored in \cs{l_keys_key_tl}, and will have been processed by
% \cs{tl_to_str:n}.
% \end{variable}
%
% \section{Handling of unknown keys}
% \label{sec:l3keys:unknown}
%
% If a key has not previously been defined (is unknown), \cs{keys_set:nn}
% looks for a special \texttt{unknown} key for the same module, and if this is
% not defined raises an error indicating that the key name was unknown. This
% mechanism can be used for example to issue custom error texts.
% \begin{verbatim}
% \keys_define:nn { mymodule }
% {
% unknown .code:n =
% You~tried~to~set~key~'\l_keys_key_tl'~to~'#1'.
% }
% \end{verbatim}
%
% \begin{function}[added = 2011-08-23, updated = 2017-05-27]
% {
% \keys_set_known:nnN, \keys_set_known:nVN,
% \keys_set_known:nvN, \keys_set_known:noN,
% \keys_set_known:nn, \keys_set_known:nV,
% \keys_set_known:nv, \keys_set_known:no
% }
% \begin{syntax}
% \cs{keys_set_known:nnN} \Arg{module} \Arg{keyval list} \meta{tl}
% \end{syntax}
% In some cases, the desired behavior is to simply ignore unknown keys,
% collecting up information on these for later processing. The
% \cs{keys_set_known:nnN} function parses the \meta{keyval list}, and sets
% those keys which are defined for \meta{module}. Any keys which are unknown
% are not processed further by the parser.
% The key--value pairs for each \emph{unknown} key name are
% stored in the \meta{tl} in a comma-separated form (\emph{i.e.}~an edited
% version of the \meta{keyval list}). The \cs{keys_set_known:nn} version
% skips this stage.
%
% Use of \cs{keys_set_known:nnN} can be nested, with the correct residual
% \meta{keyval list} returned at each stage.
% \end{function}
%
% \section{Selective key setting}
% \label{sec:l3keys:selective}
%
% In some cases it may be useful to be able to select only some keys for
% setting, even though these keys have the same path. For example, with
% a set of keys defined using
% \begin{verbatim}
% \keys define:nn { mymodule }
% {
% key-one .code:n = { \my_func:n {#1} } ,
% key-two .tl_set:N = \l_my_a_tl ,
% key-three .tl_set:N = \l_my_b_tl ,
% key-four .fp_set:N = \l_my_a_fp ,
% }
% \end{verbatim}
% the use of \cs{keys_set:nn} attempts to set all four keys. However, in
% some contexts it may only be sensible to set some keys, or to control the
% order of setting. To do this, keys may be assigned to \emph{groups}:
% arbitrary sets which are independent of the key tree. Thus modifying the
% example to read
% \begin{verbatim}
% \keys define:nn { mymodule }
% {
% key-one .code:n = { \my_func:n {#1} } ,
% key-one .groups:n = { first } ,
% key-two .tl_set:N = \l_my_a_tl ,
% key-two .groups:n = { first } ,
% key-three .tl_set:N = \l_my_b_tl ,
% key-three .groups:n = { second } ,
% key-four .fp_set:N = \l_my_a_fp ,
% }
% \end{verbatim}
% assigns \texttt{key-one} and \texttt{key-two} to group \texttt{first},
% \texttt{key-three} to group \texttt{second}, while \texttt{key-four} is
% not assigned to a group.
%
% Selective key setting may be achieved either by selecting one or more
% groups to be made \enquote{active}, or by marking one or more groups to
% be ignored in key setting.
%
% \begin{function}[added = 2013-07-14, updated = 2017-05-27]
% {
% \keys_set_filter:nnnN, \keys_set_filter:nnVN,
% \keys_set_filter:nnvN, \keys_set_filter:nnoN,
% \keys_set_filter:nnn, \keys_set_filter:nnV,
% \keys_set_filter:nnv, \keys_set_filter:nno
% }
% \begin{syntax}
% \cs{keys_set_filter:nnnN} \Arg{module} \Arg{groups} \Arg{keyval list} \meta{tl}
% \end{syntax}
% Activates key filtering in an \enquote{opt-out} sense: keys assigned to any
% of the \meta{groups} specified are ignored. The \meta{groups} are
% given as a comma-separated list. Unknown keys are not assigned to any
% group and are thus always set. The key--value pairs for each
% key which is filtered out are stored in the \meta{tl} in a
% comma-separated form (\emph{i.e.}~an edited version of the \meta{keyval
% list}). The \cs{keys_set_filter:nnn} version skips this stage.
%
% Use of \cs{keys_set_filter:nnnN} can be nested, with the correct residual
% \meta{keyval list} returned at each stage.
% \end{function}
%
% \begin{function}[added = 2013-07-14, updated = 2017-05-27]
% {
% \keys_set_groups:nnn, \keys_set_groups:nnV,
% \keys_set_groups:nnv, \keys_set_groups:nno
% }
% \begin{syntax}
% \cs{keys_set_groups:nnn} \Arg{module} \Arg{groups} \Arg{keyval list}
% \end{syntax}
% Activates key filtering in an \enquote{opt-in} sense: only keys assigned to
% one or more of the \meta{groups} specified are set. The \meta{groups} are
% given as a comma-separated list. Unknown keys are not assigned to any
% group and are thus never set.
% \end{function}
%
% \section{Utility functions for keys}
%
% \begin{function}[EXP, pTF, updated = 2015-11-07]{\keys_if_exist:nn}
% \begin{syntax}
% \cs{keys_if_exist_p:nn} \Arg{module} \Arg{key} \\
% \cs{keys_if_exist:nnTF} \Arg{module} \Arg{key} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests if the \meta{key} exists for \meta{module}, \emph{i.e.}~if any code
% has been defined for \meta{key}.
% \end{function}
%
% \begin{function}[added = 2011-08-21,EXP,pTF, updated = 2015-11-07]
% {\keys_if_choice_exist:nnn}
% \begin{syntax}
% \cs{keys_if_choice_exist_p:nnn} \Arg{module} \Arg{key} \Arg{choice} \\
% \cs{keys_if_choice_exist:nnnTF} \Arg{module} \Arg{key} \Arg{choice} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests if the \meta{choice} is defined for the \meta{key} within the
% \meta{module}, \emph{i.e.}~if any code has been defined for
% \meta{key}/\meta{choice}. The test is \texttt{false} if the \meta{key}
% itself is not defined.
% \end{function}
%
% \begin{function}[updated = 2015-08-09]{\keys_show:nn}
% \begin{syntax}
% \cs{keys_show:nn} \Arg{module} \Arg{key}
% \end{syntax}
% Displays in the terminal
% the information associated to the \meta{key} for a \meta{module},
% including the function which is used to actually implement it.
% \end{function}
%
% \begin{function}[added = 2014-08-22, updated = 2015-08-09]{\keys_log:nn}
% \begin{syntax}
% \cs{keys_log:nn} \Arg{module} \Arg{key}
% \end{syntax}
% Writes in the log file the information associated to the \meta{key}
% for a \meta{module}. See also \cs{keys_show:nn} which displays the
% result in the terminal.
% \end{function}
%
% \section{Low-level interface for parsing key--val lists}
%
% To re-cap from earlier, a key--value list is input of the form
% \begin{verbatim}
% KeyOne = ValueOne ,
% KeyTwo = ValueTwo ,
% KeyThree
% \end{verbatim}
% where each key--value pair is separated by a comma from the rest of
% the list, and each key--value pair does not necessarily contain an
% equals sign or a value! Processing this type of input correctly
% requires a number of careful steps, to correctly account for
% braces, spaces and the category codes of separators.
%
% While the functions described earlier are used as a high-level interface
% for processing such input, in special circumstances you may wish to use
% a lower-level approach.
% The low-level parsing system converts a \meta{key--value list}
% into \meta{keys} and associated \meta{values}. After the parsing phase
% is completed, the resulting keys and values (or keys alone) are
% available for further processing. This processing is not carried out by the
% low-level parser itself, and so the parser requires the names of
% two functions along with the key--value list. One function is
% needed to process key--value pairs (it receives two arguments),
% and a second function is required for keys given without any value
% (it is called with a single argument).
%
% The parser does not double |#| tokens or expand any input. Active
% tokens |=| and |,| appearing at the outer level of braces are converted
% to category \enquote{other} (12) so that the parser does not \enquote{miss}
% any due to category code changes. Spaces are removed from the ends
% of the keys and values. Keys and values which are given in braces
% have exactly one set removed (after space trimming), thus
% \begin{verbatim}
% key = {value here},
% \end{verbatim}
% and
% \begin{verbatim}
% key = value here,
% \end{verbatim}
% are treated identically.
%
% \begin{function}[updated = 2011-09-08]{\keyval_parse:NNn}
% \begin{syntax}
% \cs{keyval_parse:NNn} \meta{function_1} \meta{function_2} \Arg{key--value list}
% \end{syntax}
% Parses the \meta{key--value list} into a series of \meta{keys} and
% associated \meta{values}, or keys alone (if no \meta{value} was
% given). \meta{function_1} should take one argument, while
% \meta{function_2} should absorb two arguments. After
% \cs{keyval_parse:NNn} has parsed the \meta{key--value list},
% \meta{function_1} is used to process keys given with no value
% and \meta{function_2} is used to process keys given with a
% value. The order of the \meta{keys} in the \meta{key--value list}
% is preserved. Thus
% \begin{verbatim}
% \keyval_parse:NNn \function:n \function:nn
% { key1 = value1 , key2 = value2, key3 = , key4 }
% \end{verbatim}
% is converted into an input stream
% \begin{verbatim}
% \function:nn { key1 } { value1 }
% \function:nn { key2 } { value2 }
% \function:nn { key3 } { }
% \function:n { key4 }
% \end{verbatim}
% Note that there is a difference between an empty value (an equals
% sign followed by nothing) and a missing value (no equals sign at
% all). Spaces are trimmed from the ends of the \meta{key} and \meta{value},
% then one \emph{outer} set of braces is removed from the \meta{key}
% and \meta{value} as part of the processing.
% \end{function}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{\pkg{l3keys} Implementation}
%
% \begin{macrocode}
%<*initex|package>
% \end{macrocode}
%
% \subsection{Low-level interface}
%
% The low-level key parser is based heavily on \pkg{keyval}, but with a number
% of additional \enquote{safety} requirements and with the idea that the
% parsed list of key--value pairs can be processed in a variety of ways.
% The net result is that this code needs around twice the amount of time
% as \pkg{keyval} to parse the same list of keys. To optimise speed as far
% as reasonably practical, a number of lower-level approaches are taken
% rather than using the higher-level \pkg{expl3} interfaces.
%
% \begin{macrocode}
%<@@=keyval>
% \end{macrocode}
%
% \begin{variable}{\l_@@_key_tl, \l_@@_value_tl}
% The current key name and value.
% \begin{macrocode}
\tl_new:N \l_@@_key_tl
\tl_new:N \l_@@_value_tl
% \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_sanitise_tl}
% A token list variable for dealing with awkward category codes in the
% input.
% \begin{macrocode}
\tl_new:N \l_@@_sanitise_tl
% \end{macrocode}
% \end{variable}
%
% \begin{macro}{\keyval_parse:NNn}
% The main function starts off by normalising category codes in package mode.
% That's relatively \enquote{expensive} so is skipped (hopefully) in format
% mode. We then hand off to the parser. The use of \cs{q_mark} here prevents
% loss of braces from the key argument. Notice that by passing the two
% processor commands along the input stack we avoid the need to track these
% at all.
% \begin{macrocode}
\cs_new_protected:Npn \keyval_parse:NNn #1#2#3
{
%<*initex>
\@@_loop:NNw #1#2 \q_mark #3 , \q_recursion_tail ,
%</initex>
%<*package>
\tl_set:Nn \l_@@_sanitise_tl {#3}
\@@_sanitise_equals:
\@@_sanitise_comma:
\exp_after:wN \@@_loop:NNw \exp_after:wN #1 \exp_after:wN #2
\exp_after:wN \q_mark \l_@@_sanitise_tl , \q_recursion_tail ,
%</package>
}
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_sanitise_equals:, \@@_sanitise_comma:}
% \begin{macro}
% {
% \@@_sanitise_equals_auxi:w, \@@_sanitise_equals_auxii:w,
% \@@_sanitise_comma_auxi:w, \@@_sanitise_comma_auxii:w,
% \@@_sanitise_aux:w
% }
% A reasonably fast search and replace set up specifically for the active
% tokens. The nature of the input is known so everything is hard-coded.
% With only two tokens to cover, the speed gain from using dedicated
% functions is worth it.
% \begin{macrocode}
%<*package>
\group_begin:
\char_set_catcode_active:n { `\= }
\char_set_catcode_active:n { `\, }
\cs_new_protected:Npn \@@_sanitise_equals:
{
\exp_after:wN \@@_sanitise_equals_auxi:w \l_@@_sanitise_tl
\q_mark = \q_nil =
\exp_after:wN \@@_sanitise_aux:w \l_@@_sanitise_tl
}
\cs_new_protected:Npn \@@_sanitise_equals_auxi:w #1 =
{
\tl_set:Nn \l_@@_sanitise_tl {#1}
\@@_sanitise_equals_auxii:w
}
\cs_new_protected:Npn \@@_sanitise_equals_auxii:w #1 =
{
\if_meaning:w \q_nil #1 \scan_stop:
\else:
\tl_set:Nx \l_@@_sanitise_tl
{
\exp_not:o \l_@@_sanitise_tl
\token_to_str:N =
\exp_not:n {#1}
}
\exp_after:wN \@@_sanitise_equals_auxii:w
\fi:
}
\cs_new_protected:Npn \@@_sanitise_comma:
{
\exp_after:wN \@@_sanitise_comma_auxi:w \l_@@_sanitise_tl
\q_mark , \q_nil ,
\exp_after:wN \@@_sanitise_aux:w \l_@@_sanitise_tl
}
\cs_new_protected:Npn \@@_sanitise_comma_auxi:w #1 ,
{
\tl_set:Nn \l_@@_sanitise_tl {#1}
\@@_sanitise_comma_auxii:w
}
\cs_new_protected:Npn \@@_sanitise_comma_auxii:w #1 ,
{
\if_meaning:w \q_nil #1 \scan_stop:
\else:
\tl_set:Nx \l_@@_sanitise_tl
{
\exp_not:o \l_@@_sanitise_tl
\token_to_str:N ,
\exp_not:n {#1}
}
\exp_after:wN \@@_sanitise_comma_auxii:w
\fi:
}
\group_end: