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+% \iffalse meta-comment
+%
+%% File: l3prop.dtx
+%
+% Copyright (C) 1990-2024 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{l3prop} module\\ Property lists^^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 2024-04-11}
+%
+% \maketitle
+%
+% \begin{documentation}
+%
+% \pkg{expl3} implements a \enquote{property list} data type, which contain
+% an unordered list of entries each of which consists of a \meta{key} (string)
+% and an associated \meta{value} (token list). The \meta{key} and \meta{value}
+% may both be given as any balanced text, and the \meta{key} is processed using
+% \cs{tl_to_str:n}, meaning that category codes are ignored. Entries can be
+% manipulated individually, as well as collectively by applying a function to
+% every key--value pair within the list.
+%
+% Each entry in a property list must have a unique \meta{key}: if an entry is
+% added to a property list which already contains the \meta{key} then the new
+% entry overwrites the existing one. The \meta{keys} are compared on a
+% string basis, using the same method as \cs{str_if_eq:nnTF}.
+%
+% Property lists are intended for storing key-based information for use within
+% code. They can be converted from and to key--value lists, which are a form of
+% \emph{input} parsed by the \pkg{l3keys} module. If a key--value list contains
+% a \meta{key} multiple times, only the last \meta{value} associated to it will
+% be kept in the conversion to a property list.
+%
+% Internally, property lists can use two distinct implementations with different
+% data storage, which are decided when declaring the property list variable
+% using \cs{prop_new:N} (\enquote{flat} storage) or \cs{prop_new_linked:N}
+% (\enquote{linked} storage). After a property list is declared with
+% \cs{prop_new:N} or \cs{prop_new_linked:N}, the type of internal data storage
+% can be changed by \cs{prop_make_flat:N} or \cs{prop_make_linked:N}, but only
+% at the outermost group level. All other \pkg{l3prop} functions transparently
+% manipulate either storage method and convert as needed.
+% \begin{itemize}
+% \item
+% The (default) \enquote{flat} storage method is suited for a relatively
+% small number of entries, or when the property list is likely to be
+% manipulated (copied, mapped) as a whole rather than entry-wise. It is
+% significantly faster for \cs{prop_set_eq:NN}, and only slightly faster for
+% \cs{prop_clear:N}, \cs{prop_concat:NNN}, and mapping functions
+% \cs[no-index]{prop_map_\ldots{}}.
+%
+% \item
+% The \enquote{linked} storage method is meant for property lists with a
+% large numbers of entries. It takes up more of \TeX{}'s memory during a run, but is
+% significantly faster (for long lists) when accessing or modifying
+% individual entries using functions such as \cs{prop_if_in:Nn},
+% \cs{prop_item:Nn}, \cs{prop_put:Nnn}, \cs{prop_get:NnN},
+% \cs{prop_pop:NnN}, \cs{prop_remove:Nn}, as it takes a constant
+% time for these operations (rather than the number of items for a
+% \enquote{flat} property list). A technical drawback is that
+% memory is permanently used\footnote{Until the end of the run, that
+% is.} by \meta{keys} stored in a \enquote{linked} property list,
+% even after they are removed and the property list is deleted.
+% \end{itemize}
+%
+% \section{Creating and initialising property lists}
+%
+% \begin{function}{\prop_new:N, \prop_new:c}
+% \begin{syntax}
+% \cs{prop_new:N} \meta{property list}
+% \end{syntax}
+% Creates a new \enquote{flat} \meta{property list} or raises an error if the
+% name is already taken. The declaration is global. The \meta{property list}
+% initially contains no entries. See also \cs{prop_new_linked:N}.
+% \end{function}
+%
+% \begin{function}[added = 2024-02-12]{\prop_new_linked:N, \prop_new_linked:c}
+% \begin{syntax}
+% \cs{prop_new_linked:N} \meta{property list}
+% \end{syntax}
+% Creates a new \enquote{linked} \meta{property list} or raises an error if
+% the name is already taken. The declaration is global. The \meta{property
+% list} initially contains no entries. The internal data storage differs from
+% that produced by \cs{prop_new:N} and it is optimized for property lists with
+% a large number of entries.
+% \end{function}
+%
+% \begin{function}
+% {\prop_clear:N, \prop_clear:c, \prop_gclear:N, \prop_gclear:c}
+% \begin{syntax}
+% \cs{prop_clear:N} \meta{property list}
+% \end{syntax}
+% Clears all entries from the \meta{property list}.
+% \end{function}
+%
+% \begin{function}
+% {
+% \prop_clear_new:N, \prop_clear_new:c,
+% \prop_gclear_new:N, \prop_gclear_new:c
+% }
+% \begin{syntax}
+% \cs{prop_clear_new:N} \meta{property list}
+% \end{syntax}
+% Ensures that the \meta{property list} exists globally by applying
+% \cs{prop_new:N} if necessary, then applies
+% \cs[index=prop_clear:N]{prop_(g)clear:N} to leave the list empty.
+% \begin{texnote}
+% If the property list exists and is of \enquote{linked} type, it
+% is cleared but not made into a flat property list.
+% \end{texnote}
+% \end{function}
+%
+% \begin{function}[added = 2024-02-12]
+% {
+% \prop_clear_new_linked:N, \prop_clear_new_linked:c,
+% \prop_gclear_new_linked:N, \prop_gclear_new_linked:c
+% }
+% \begin{syntax}
+% \cs{prop_clear_new_linked:N} \meta{property list}
+% \end{syntax}
+% Ensures that the \meta{property list} exists globally by applying
+% \cs{prop_new_linked:N} if necessary, then applies
+% \cs[index=prop_clear:N]{prop_(g)clear:N} to leave the list empty.
+% \begin{texnote}
+% If the property list exists and is of \enquote{flat} type, it
+% is cleared but not made into a linked property list.
+% \end{texnote}
+% \end{function}
+%
+% \begin{function}
+% {
+% \prop_set_eq:NN, \prop_set_eq:cN, \prop_set_eq:Nc, \prop_set_eq:cc,
+% \prop_gset_eq:NN, \prop_gset_eq:cN, \prop_gset_eq:Nc, \prop_gset_eq:cc
+% }
+% \begin{syntax}
+% \cs{prop_set_eq:NN} \meta{property list_1} \meta{property list_2}
+% \end{syntax}
+% Sets the content of \meta{property list_1} equal to that of \meta{property
+% list_2}. This converts as needed between the two storage types.
+% \end{function}
+%
+% \begin{function}[added = 2017-11-28, updated = 2021-11-07]
+% {
+% \prop_set_from_keyval:Nn, \prop_set_from_keyval:cn,
+% \prop_gset_from_keyval:Nn, \prop_gset_from_keyval:cn,
+% }
+% \begin{syntax}
+% \cs{prop_set_from_keyval:Nn} \meta{property list}
+% \{
+% \meta{key1} |=| \meta{value1} |,|
+% \meta{key2} |=| \meta{value2} |,| \ldots{}
+% \}
+% \end{syntax}
+% Sets \meta{property list} to contain key--value pairs given in the second
+% argument. If duplicate keys appear only the last of the values is kept.
+% In contrast to most keyval lists (\emph{e.g.}~those in \pkg{l3keys}), each
+% key here \emph{must} be followed with an \texttt{=} sign even to specify an
+% empty \meta{value}.
+%
+% Spaces are trimmed around every \meta{key} and every \meta{value},
+% and if the result of trimming spaces consists of a single brace
+% group then a set of outer braces is removed. This enables both the
+% \meta{key} and the \meta{value} to contain spaces, commas or equal
+% signs. The \meta{key} is then processed by \cs{tl_to_str:n}.
+% This function correctly detects the |=| and |,| signs provided they
+% have the standard category code~$12$ or they are active.
+% \end{function}
+%
+% \begin{function}[added = 2017-11-28, updated = 2021-11-07]
+% {\prop_const_from_keyval:Nn, \prop_const_from_keyval:cn}
+% \begin{syntax}
+% \cs{prop_const_from_keyval:Nn} \meta{property list}
+% \{
+% \meta{key1} |=| \meta{value1} |,|
+% \meta{key2} |=| \meta{value2} |,| \ldots{}
+% \}
+% \end{syntax}
+% Creates a new constant \enquote{flat} \meta{property list} or raises
+% an error if the
+% name is already taken. The \meta{property list} is set globally to
+% contain key--value pairs given in the second argument, processed in
+% the way described for \cs{prop_set_from_keyval:Nn}. If duplicate
+% keys appear only the last of the values is kept.
+% This function correctly detects the |=| and |,| signs provided they
+% have the standard category code~$12$ or they are active.
+% \end{function}
+%
+% \begin{function}[added = 2024-02-12]
+% {\prop_const_linked_from_keyval:Nn, \prop_const_linked_from_keyval:cn}
+% \begin{syntax}
+% \cs{prop_const_linked_from_keyval:Nn} \meta{prop~var}
+% \{
+% \meta{key1} |=| \meta{value1} |,|
+% \meta{key2} |=| \meta{value2} |,| \ldots{}
+% \}
+% \end{syntax}
+% Creates a new constant \enquote{linked} \meta{prop~var} or raises an
+% error if the
+% name is already taken. The \meta{prop~var} is set globally to
+% contain key--value pairs given in the second argument, processed in
+% the way described for \cs{prop_set_from_keyval:Nn}. If duplicate
+% keys appear only the last of the values is kept.
+% This function correctly detects the |=| and |,| signs provided they
+% have the standard category code~$12$ or they are active.
+% \end{function}
+%
+% \begin{function}[added = 2024-02-12]{\prop_make_flat:N, \prop_make_flat:c}
+% \begin{syntax}
+% \cs{prop_make_flat:N} \meta{property list}
+% \end{syntax}
+% Changes the internal storage type of the \meta{property list} to be
+% the same \enquote{flat} storage as \cs{prop_new:N}. The key--value
+% pairs of the \meta{property list} are preserved by the change. If
+% the property list was already flat then nothing is done. This
+% function can only be used at the outermost group level.
+% \end{function}
+%
+% \begin{function}[added = 2024-02-12]{\prop_make_linked:N, \prop_make_linked:c}
+% \begin{syntax}
+% \cs{prop_make_linked:N} \meta{property list}
+% \end{syntax}
+% Changes the internal storage type of the \meta{property list} to be
+% the same \enquote{linked} storage as \cs{prop_new_linked:N}. The
+% key--value pairs of the \meta{property list} are preserved by the
+% change. If the property list was already linked then nothing is
+% done. This function can only be used at the outermost group level.
+% \end{function}
+%
+% \section{Adding and updating property list entries}
+%
+% \begin{function}[updated = 2012-07-09]
+% {
+% \prop_put:Nnn, \prop_put:NnV, \prop_put:Nnv, \prop_put:Nne,
+% \prop_put:NVn, \prop_put:NVV, \prop_put:NVv, \prop_put:NVe,
+% \prop_put:Nvn, \prop_put:NvV, \prop_put:Nvv, \prop_put:Nve,
+% \prop_put:Nen, \prop_put:NeV, \prop_put:Nev, \prop_put:Nee,
+% \prop_put:Nno, \prop_put:Non, \prop_put:Noo,
+% \prop_put:cnn, \prop_put:cnV, \prop_put:cnv, \prop_put:cne,
+% \prop_put:cVn, \prop_put:cVV, \prop_put:cVv, \prop_put:cVe,
+% \prop_put:cvn, \prop_put:cvV, \prop_put:cvv, \prop_put:cve,
+% \prop_put:cen, \prop_put:ceV, \prop_put:cev, \prop_put:cee,
+% \prop_put:cno, \prop_put:con, \prop_put:coo,
+% \prop_gput:Nnn, \prop_gput:NnV, \prop_gput:Nnv, \prop_gput:Nne,
+% \prop_gput:NVn, \prop_gput:NVV, \prop_gput:NVv, \prop_gput:NVe,
+% \prop_gput:Nvn, \prop_gput:NvV, \prop_gput:Nvv, \prop_gput:Nve,
+% \prop_gput:Nen, \prop_gput:NeV, \prop_gput:Nev, \prop_gput:Nee,
+% \prop_gput:Nno, \prop_gput:Non, \prop_gput:Noo,
+% \prop_gput:cnn, \prop_gput:cnV, \prop_gput:cnv, \prop_gput:cne,
+% \prop_gput:cVn, \prop_gput:cVV, \prop_gput:cVv, \prop_gput:cVe,
+% \prop_gput:cvn, \prop_gput:cvV, \prop_gput:cvv, \prop_gput:cve,
+% \prop_gput:cen, \prop_gput:ceV, \prop_gput:cev, \prop_gput:cee,
+% \prop_gput:cno, \prop_gput:con, \prop_gput:coo
+% }
+% \begin{syntax}
+% \cs{prop_put:Nnn} \meta{property list} \Arg{key} \Arg{value}
+% \end{syntax}
+% Adds an entry to the \meta{property list} which may be accessed
+% using the \meta{key} and which has \meta{value}. If the \meta{key}
+% is already present in the \meta{property list}, the existing entry
+% is overwritten by the new \meta{value}. Both the \meta{key} and
+% \meta{value} may contain any \meta{balanced text}. The \meta{key} is
+% stored after processing with \cs{tl_to_str:n}, meaning that category
+% codes are ignored.
+% \end{function}
+%
+% \begin{function}[added = 2024-03-30]
+% {
+% \prop_put_if_not_in:Nnn, \prop_put_if_not_in:NVn, \prop_put_if_not_in:NnV,
+% \prop_put_if_not_in:cnn, \prop_put_if_not_in:cVn, \prop_put_if_not_in:cnV,
+% \prop_gput_if_not_in:Nnn, \prop_gput_if_not_in:NVn, \prop_gput_if_not_in:NnV,
+% \prop_gput_if_not_in:cnn, \prop_gput_if_not_in:cVn, \prop_gput_if_not_in:cnV
+% }
+% \begin{syntax}
+% \cs{prop_put_if_not_in:Nnn} \meta{property list} \Arg{key} \Arg{value}
+% \end{syntax}
+% If the \meta{key} is present in the \meta{property list} then no
+% action is taken. Otherwise, a new entry is added as described for
+% \cs{prop_put:Nnn}.
+% \end{function}
+%
+% \begin{function}[added = 2021-05-16]
+% {
+% \prop_concat:NNN, \prop_concat:ccc,
+% \prop_gconcat:NNN, \prop_gconcat:ccc
+% }
+% \begin{syntax}
+% \cs{prop_concat:NNN} \meta{property list_1} \meta{property list_2} \meta{property list3}
+% \end{syntax}
+% Combines the key--value pairs of \meta{property list_2} and
+% \meta{property list_3}, and saves the result in \meta{property list_1}. If a
+% key appears in both \meta{property list_2} and \meta{property list_3} then the
+% last value, namely the value in \meta{property list_3} is kept.
+% This converts as needed between the two storage types.
+% \end{function}
+%
+% \begin{function}[added = 2021-05-16, updated = 2021-11-07]
+% {
+% \prop_put_from_keyval:Nn, \prop_put_from_keyval:cn,
+% \prop_gput_from_keyval:Nn, \prop_gput_from_keyval:cn,
+% }
+% \begin{syntax}
+% \cs{prop_put_from_keyval:Nn} \meta{property list}
+% \{
+% \meta{key1} |=| \meta{value1} |,|
+% \meta{key2} |=| \meta{value2} |,| \ldots{}
+% \}
+% \end{syntax}
+% Updates the \meta{property list} by adding entries for each key--value
+% pair given in the second argument. The addition is done through
+% \cs{prop_put:Nnn}, hence if the \meta{property list} already contains
+% some of the keys, the corresponding values are discarded and
+% replaced by those given in the key--value list. If duplicate keys
+% appear in the key--value list then only the last of the values is kept.
+%
+% The function is equivalent to storing the key--value pairs in a
+% temporary property list using \cs{prop_set_from_keyval:Nn}, then
+% combining \meta{property list} with the temporary variable using
+% \cs{prop_concat:NNN}. In particular, the \meta{keys} and
+% \meta{values} are space-trimmed and unbraced as described in
+% \cs{prop_set_from_keyval:Nn}.
+% This function correctly detects the |=| and |,| signs provided they
+% have the standard category code~$12$ or they are active.
+% \end{function}
+%
+% \section{Recovering values from property lists}
+%
+% \begin{function}[updated = 2011-08-28]
+% {
+% \prop_get:NnN, \prop_get:NVN, \prop_get:NvN, \prop_get:NeN,
+% \prop_get:NoN,
+% \prop_get:cnN, \prop_get:cVN, \prop_get:cvN, \prop_get:ceN,
+% \prop_get:coN,
+% \prop_get:cnc
+% }
+% \begin{syntax}
+% \cs{prop_get:NnN} \meta{property list} \Arg{key} \meta{tl var}
+% \end{syntax}
+% Recovers the \meta{value} stored with \meta{key} from the
+% \meta{property list}, and places this in the \meta{token list
+% variable}. If the \meta{key} is not found in the
+% \meta{property list} then the \meta{token list variable} is set
+% to the special marker \cs{q_no_value}. The \meta{token list
+% variable} is set within the current \TeX{} group. See also
+% \cs{prop_get:NnNTF}.
+% \end{function}
+%
+% \begin{function}[updated = 2011-08-18]
+% {
+% \prop_pop:NnN, \prop_pop:NVN,
+% \prop_pop:NoN,
+% \prop_pop:cnN, \prop_pop:cVN,
+% \prop_pop:coN
+% }
+% \begin{syntax}
+% \cs{prop_pop:NnN} \meta{property list} \Arg{key} \meta{tl var}
+% \end{syntax}
+% Recovers the \meta{value} stored with \meta{key} from the
+% \meta{property list}, and places this in the \meta{token list
+% variable}. If the \meta{key} is not found in the
+% \meta{property list} then the \meta{token list variable} is set
+% to the special marker \cs{q_no_value}. The \meta{key} and
+% \meta{value} are then deleted from the property list. Both
+% assignments are local. See also \cs{prop_pop:NnNTF}.
+% \end{function}
+%
+% \begin{function}[updated = 2011-08-18]
+% {
+% \prop_gpop:NnN, \prop_gpop:NVN,
+% \prop_gpop:NoN,
+% \prop_gpop:cnN, \prop_gpop:cVN,
+% \prop_gpop:coN
+% }
+% \begin{syntax}
+% \cs{prop_gpop:NnN} \meta{property list} \Arg{key} \meta{tl var}
+% \end{syntax}
+% Recovers the \meta{value} stored with \meta{key} from the
+% \meta{property list}, and places this in the \meta{token list
+% variable}. If the \meta{key} is not found in the
+% \meta{property list} then the \meta{token list variable} is set
+% to the special marker \cs{q_no_value}. The \meta{key} and
+% \meta{value} are then deleted from the property list.
+% The \meta{property list} is modified globally, while the assignment of
+% the \meta{token list variable} is local. See also \cs{prop_gpop:NnNTF}.
+% \end{function}
+%
+% \begin{function}[EXP, added = 2014-07-17]
+% {
+% \prop_item:Nn, \prop_item:NV, \prop_item:Ne, \prop_item:No,
+% \prop_item:cn, \prop_item:cV, \prop_item:ce, \prop_item:co
+% }
+% \begin{syntax}
+% \cs{prop_item:Nn} \meta{property list} \Arg{key}
+% \end{syntax}
+% Expands to the \meta{value} corresponding to the \meta{key} in
+% the \meta{property list}. If the \meta{key} is missing, this has
+% an empty expansion.
+% \begin{texnote}
+% For \enquote{flat} property lists, this expandable function iterates
+% through every key--value pair and is therefore slower than a
+% non-expandable approach based on \cs{prop_get:NnN}.
+% (For \enquote{linked} property lists both functions are fast.)
+%
+% The result is returned within the \tn{unexpanded}
+% primitive (\cs{exp_not:n}), which means that the \meta{value}
+% does not expand further when appearing in an \texttt{e}-type
+% or \texttt{x}-type argument expansion.
+% \end{texnote}
+% \end{function}
+%
+% \begin{function}[EXP]{\prop_count:N, \prop_count:c}
+% \begin{syntax}
+% \cs{prop_count:N} \meta{property list}
+% \end{syntax}
+% Leaves the number of key--value pairs in the \meta{property list} in
+% the input stream as an \meta{integer denotation}.
+% \end{function}
+%
+% \begin{function}[EXP]{\prop_to_keyval:N}
+% \begin{syntax}
+% \cs{prop_to_keyval:N} \meta{property list}
+% \end{syntax}
+% Expands to the \meta{property list} in a key--value notation. Keep in mind
+% that a \meta{property list} is \emph{unordered}, while key--value interfaces
+% are not necessarily, so this cannot be used for arbitrary interfaces.
+% \begin{texnote}
+% The result is returned within the \tn{unexpanded} primitive
+% (\cs{exp_not:n}), which means that the key--value list does not expand
+% further when appearing in an \texttt{e}-type or \texttt{x}-type argument expansion.
+% It also needs exactly two steps of expansion.
+% \end{texnote}
+% \end{function}
+%
+% \section{Modifying property lists}
+%
+% \begin{function}[added = 2012-05-12]
+% {
+% \prop_remove:Nn, \prop_remove:NV, \prop_remove:Ne,
+% \prop_remove:cn, \prop_remove:cV, \prop_remove:ce,
+% \prop_gremove:Nn, \prop_gremove:NV, \prop_gremove:Ne,
+% \prop_gremove:cn, \prop_gremove:cV, \prop_gremove:ce,
+% }
+% \begin{syntax}
+% \cs{prop_remove:Nn} \meta{property list} \Arg{key}
+% \end{syntax}
+% Removes the entry listed under \meta{key} from the
+% \meta{property list}. If the \meta{key} is
+% not found in the \meta{property list} no change occurs,
+% \emph{i.e}~there is no need to test for the existence of a key before
+% deleting it.
+% \end{function}
+%
+% \section{Property list conditionals}
+%
+% \begin{function}[EXP, pTF, added = 2012-03-03]
+% {\prop_if_exist:N, \prop_if_exist:c}
+% \begin{syntax}
+% \cs{prop_if_exist_p:N} \meta{property list}
+% \cs{prop_if_exist:NTF} \meta{property list} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Tests whether the \meta{property list} is currently defined. This does not
+% check that the \meta{property list} really is a property list variable.
+% \end{function}
+%
+% \begin{function}[EXP, pTF]{\prop_if_empty:N, \prop_if_empty:c}
+% \begin{syntax}
+% \cs{prop_if_empty_p:N} \meta{property list}
+% \cs{prop_if_empty:NTF} \meta{property list} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Tests if the \meta{property list} is empty (containing no entries).
+% \end{function}
+%
+% \begin{function}[EXP, pTF, updated = 2011-09-15]
+% {
+% \prop_if_in:Nn, \prop_if_in:NV, \prop_if_in:Ne, \prop_if_in:No,
+% \prop_if_in:cn, \prop_if_in:cV, \prop_if_in:ce, \prop_if_in:co
+% }
+% \begin{syntax}
+% \cs{prop_if_in_p:Nn} \meta{property list} \Arg{key}
+% \cs{prop_if_in:NnTF} \meta{property list} \Arg{key} \Arg{true code} \Arg{false code}
+% \end{syntax}
+% Tests if the \meta{key} is present in the \meta{property list},
+% making the comparison using the method described by \cs{str_if_eq:nnTF}.
+% \begin{texnote}
+% For \enquote{flat} property lists, this expandable function iterates
+% through every key--value pair and is therefore slower than a
+% non-expandable approach based on \cs{prop_get:NnNTF}.
+% (For \enquote{linked} property lists both functions are fast.)
+% \end{texnote}
+% \end{function}
+%
+% \section{Recovering values from property lists with branching}
+%
+% The functions in this section combine tests for the presence of a key
+% in a property list with recovery of the associated valued. This makes them
+% useful for cases where different code follows depending on the presence
+% or absence of a key in a property list. They offer increased readability
+% and performance over separate testing and recovery phases.
+%
+% \begin{function}[TF, updated = 2012-05-19]
+% {
+% \prop_get:NnN, \prop_get:NVN, \prop_get:NvN, \prop_get:NeN,
+% \prop_get:NoN,
+% \prop_get:cnN, \prop_get:cVN, \prop_get:cvN, \prop_get:ceN,
+% \prop_get:coN,
+% \prop_get:cnc
+% }
+% \begin{syntax}
+% \cs{prop_get:NnNTF} \meta{property list} \Arg{key} \meta{token list variable} \\
+% ~~\Arg{true code} \Arg{false code}
+% \end{syntax}
+% If the \meta{key} is not present in the \meta{property list}, leaves
+% the \meta{false code} in the input stream. The value of the
+% \meta{token list variable} is not defined in this case and should
+% not be relied upon. If the \meta{key} is present in the
+% \meta{property list}, stores the corresponding \meta{value} in the
+% \meta{token list variable} without removing it from the
+% \meta{property list}, then leaves the \meta{true code} in the input
+% stream. The \meta{token list variable} is assigned locally.
+% \end{function}
+%
+% \begin{function}[TF, added = 2011-08-18, updated = 2012-05-19]
+% {
+% \prop_pop:NnN, \prop_pop:NVN,
+% \prop_pop:NoN,
+% \prop_pop:cnN, \prop_pop:cVN,
+% \prop_pop:coN
+% }
+% \begin{syntax}
+% \cs{prop_pop:NnNTF} \meta{property list} \Arg{key} \meta{token list variable} \\
+% ~~\Arg{true code} \Arg{false code}
+% \end{syntax}
+% If the \meta{key} is not present in the \meta{property list}, leaves
+% the \meta{false code} in the input stream. The value of the
+% \meta{token list variable} is not defined in this case and should
+% not be relied upon. If the \meta{key} is present in
+% the \meta{property list}, pops the corresponding \meta{value}
+% in the \meta{token list variable}, \emph{i.e.}~removes the item from
+% the \meta{property list}.
+% Both the \meta{property list} and the \meta{token list variable}
+% are assigned locally.
+% \end{function}
+%
+% \begin{function}[TF, added = 2011-08-18, updated = 2012-05-19]
+% {
+% \prop_gpop:NnN, \prop_gpop:NVN,
+% \prop_gpop:NoN,
+% \prop_gpop:cnN, \prop_gpop:cVN,
+% \prop_gpop:coN
+% }
+% \begin{syntax}
+% \cs{prop_gpop:NnNTF} \meta{property list} \Arg{key} \meta{token list variable} \\
+% ~~\Arg{true code} \Arg{false code}
+% \end{syntax}
+% If the \meta{key} is not present in the \meta{property list}, leaves
+% the \meta{false code} in the input stream. The value of the
+% \meta{token list variable} is not defined in this case and should
+% not be relied upon. If the \meta{key} is present in
+% the \meta{property list}, pops the corresponding \meta{value}
+% in the \meta{token list variable}, \emph{i.e.}~removes the item from
+% the \meta{property list}.
+% The \meta{property list} is modified globally, while the
+% \meta{token list variable} is assigned locally.
+% \end{function}
+%
+% \section{Mapping over property lists}
+%
+% All mappings are done at the current group level, \emph{i.e.}~any
+% local assignments made by the \meta{function} or \meta{code} discussed
+% below remain in effect after the loop.
+%
+% \begin{function}[rEXP, updated = 2013-01-08]
+% {\prop_map_function:NN, \prop_map_function:cN}
+% \begin{syntax}
+% \cs{prop_map_function:NN} \meta{property list} \meta{function}
+% \end{syntax}
+% Applies \meta{function} to every \meta{entry} stored in the
+% \meta{property list}. The \meta{function} receives two arguments for
+% each iteration: the \meta{key} and associated \meta{value}.
+% The order in which \meta{entries} are returned is not defined and
+% should not be relied upon.
+% To pass further arguments to the \meta{function}, see
+% \cs{prop_map_inline:Nn} (non-expandable) or \cs{prop_map_tokens:Nn}.
+% \end{function}
+%
+% \begin{function}[updated = 2013-01-08]
+% {\prop_map_inline:Nn, \prop_map_inline:cn}
+% \begin{syntax}
+% \cs{prop_map_inline:Nn} \meta{property list} \Arg{inline function}
+% \end{syntax}
+% Applies \meta{inline function} to every \meta{entry} stored
+% within the \meta{property list}. The \meta{inline function} should
+% consist of code which receives the \meta{key} as |#1| and the
+% \meta{value} as |#2|.
+% The order in which \meta{entries} are returned is not defined and
+% should not be relied upon.
+% \end{function}
+%
+% \begin{function}[rEXP]
+% {\prop_map_tokens:Nn, \prop_map_tokens:cn}
+% \begin{syntax}
+% \cs{prop_map_tokens:Nn} \meta{property list} \Arg{code}
+% \end{syntax}
+% Analogue of \cs{prop_map_function:NN} which maps several tokens
+% instead of a single function. The \meta{code} receives each
+% key--value pair in the \meta{property list} as two trailing brace
+% groups. For instance,
+% \begin{verbatim}
+% \prop_map_tokens:Nn \l_my_prop { \str_if_eq:nnT { mykey } }
+% \end{verbatim}
+% expands to the value corresponding to \texttt{mykey}: for each
+% pair in |\l_my_prop| the function \cs{str_if_eq:nnT} receives
+% \texttt{mykey}, the \meta{key} and the \meta{value} as its three
+% arguments. For that specific task, \cs{prop_item:Nn} is faster.
+% \end{function}
+%
+% \begin{function}[rEXP, updated = 2012-06-29]{\prop_map_break:}
+% \begin{syntax}
+% \cs{prop_map_break:}
+% \end{syntax}
+% Used to terminate a \cs[no-index]{prop_map_\ldots} function before all
+% entries in the \meta{property list} have been processed. This
+% normally takes place within a conditional statement, for example
+% \begin{verbatim}
+% \prop_map_inline:Nn \l_my_prop
+% {
+% \str_if_eq:nnTF { #1 } { bingo }
+% { \prop_map_break: }
+% {
+% % Do something useful
+% }
+% }
+% \end{verbatim}
+% Use outside of a \cs[no-index]{prop_map_\ldots} scenario leads to low
+% level \TeX{} errors.
+% \begin{texnote}
+% When the mapping is broken, additional tokens may be inserted
+% before further items are taken
+% from the input stream. This depends on the design of the mapping
+% function.
+% \end{texnote}
+% \end{function}
+%
+% \begin{function}[rEXP, updated = 2012-06-29]{\prop_map_break:n}
+% \begin{syntax}
+% \cs{prop_map_break:n} \Arg{code}
+% \end{syntax}
+% Used to terminate a \cs[no-index]{prop_map_\ldots} function before all
+% entries in the \meta{property list} have been processed, inserting
+% the \meta{code} after the mapping has ended. This
+% normally takes place within a conditional statement, for example
+% \begin{verbatim}
+% \prop_map_inline:Nn \l_my_prop
+% {
+% \str_if_eq:nnTF { #1 } { bingo }
+% { \prop_map_break:n { <code> } }
+% {
+% % Do something useful
+% }
+% }
+% \end{verbatim}
+% Use outside of a \cs[no-index]{prop_map_\ldots} scenario leads to low
+% level \TeX{} errors.
+% \begin{texnote}
+% When the mapping is broken, additional tokens may be inserted
+% before the \meta{code} is
+% inserted into the input stream.
+% This depends on the design of the mapping function.
+% \end{texnote}
+% \end{function}
+%
+% \section{Viewing property lists}
+%
+% \begin{function}[updated = 2021-04-29]{\prop_show:N, \prop_show:c}
+% \begin{syntax}
+% \cs{prop_show:N} \meta{property list}
+% \end{syntax}
+% Displays the entries in the \meta{property list} in the terminal,
+% and specifies its storage type.
+% \end{function}
+%
+% \begin{function}[added = 2014-08-12, updated = 2021-04-29]{\prop_log:N, \prop_log:c}
+% \begin{syntax}
+% \cs{prop_log:N} \meta{property list}
+% \end{syntax}
+% Writes the entries in the \meta{property list} in the log file,
+% and specifies its storage type.
+% \end{function}
+%
+% \section{Scratch property lists}
+%
+% There is no need to include both flat and linked property lists as
+% scratch variables. We arbitrarily pick the older implementation.
+%
+% \begin{variable}[added = 2012-06-23]{\l_tmpa_prop, \l_tmpb_prop}
+% Scratch \enquote{flat} property lists for local assignment.
+% These are never used by
+% the kernel code, and so are safe for use with any \LaTeX3-defined
+% function. However, they may be overwritten by other non-kernel
+% code and so should only be used for short-term storage.
+% \end{variable}
+%
+% \begin{variable}[added = 2012-06-23]{\g_tmpa_prop, \g_tmpb_prop}
+% Scratch \enquote{flat} property lists for global assignment.
+% These are never used by
+% the kernel code, and so are safe for use with any \LaTeX3-defined
+% function. However, they may be overwritten by other non-kernel
+% code and so should only be used for short-term storage.
+% \end{variable}
+%
+% \section{Constants}
+%
+% \begin{variable}{\c_empty_prop}
+% A permanently-empty property list used for internal comparisons.
+% \end{variable}
+%
+% \end{documentation}
+%
+% \begin{implementation}
+%
+% \section{\pkg{l3prop} implementation}
+%
+% \TestFiles{m3prop001, m3prop002, m3prop003, m3prop004, m3show001}
+%
+% \begin{macrocode}
+%<*package>
+% \end{macrocode}
+%
+% \begin{macrocode}
+%<@@=prop>
+% \end{macrocode}
+%
+% With the (default) flat data storage, a property list is a macro whose
+% top-level expansion is of the form
+% \begin{quote}
+% \cs{s_@@} \cs{@@_chk:w}
+% \cs{@@_pair:wn} \meta{key_1} \cs{s_@@} \Arg{value_1} \\
+% \ldots{} \\
+% \cs{@@_pair:wn} \meta{key_n} \cs{s_@@} \Arg{value_n} \\
+% \end{quote}
+% where \cs{s_@@} is a scan mark (equal to \cs{scan_stop:}), \cs{@@_chk:w}
+% produces a suitable error if the property list is used directly in the input
+% stream, and \cs{@@_pair:wn} can be used to map through the property list.
+%
+% With the linked data storage, each property list entry
+% \meta{key_i}--\meta{value_i} is stored into a token list
+% \cs[no-index]{@@~\meta{prefix}~\meta{key_i}}. The \meta{prefix} is one or
+% more characters (no spaces), constructed automatically only once, when the
+% property list is initially declared. The control sequence name does not
+% conform to standard naming for variables because (1) this is an internal
+% control sequence, not really a \pkg{expl3} variable; (2) keeping track of the
+% scope |l| or~|g| throughout all functions would be a pretty big mess,
+% especially if users accidentally mix local and global use (we would have to
+% always check for such mistakes, rather than only checking when suitable debug
+% options are set); (3) shorter control sequence names use less memory and are
+% quicker in case of hash collisions, which may matter since we are using many
+% control sequences.
+%
+% We need to enable mapping through such a property list, but without storing a
+% list of all entries anywhere: this is achieved by making each of these token
+% lists also store a pointer to the next entry. To enable efficient deletion,
+% the token lists also store a pointer to the previous entry. This means we
+% have a doubly-linked list. To avoid having to special-case the two ends of
+% the doubly-linked list when deleting entries, we include as a zeroth entry in
+% the doubly-linked list the property list variable itself, and we include as an
+% $(n+1)$-th entry in the doubly-linked list an end-pointer
+% \cs{@@~\meta{prefix}} (no trailing space, so it differs from an empty key).
+% The space before \meta{prefix} ensures there is no collision with
+% other \pkg{l3prop} internal functions, even if we have very many
+% linked property lists being defined.
+%
+% The property list variable itself is a token list of the form
+% \begin{quote}
+% \cs{@@_flatten:w} \cs{@@~\meta{prefix}} \cs{s_@@} \Arg{prefix}
+% \cs[no-index]{@@~\meta{prefix}~\meta{key_1}}
+% \end{quote}
+% Here, \cs{@@_flatten:w} serves as an efficiently recognized marker, and when
+% \texttt{f}-expanded it is tasked with fully unpacking the property list into
+% the same form as the default data storage so as to ease conversion. The
+% \meta{prefix} is used when looking up an entry. The token list
+% \cs{@@~\meta{prefix}} (see below) contains a pointer to the last key to help
+% insert a new entry. The pointer to \meta{key_1} is needed to start a mapping.
+% The token list labeled by \meta{key_i} is of the form
+% \begin{quote}
+% \cs{use_none:n} \cs[no-index]{@@~\meta{prefix}~\meta{key$_{i-1}$}}
+% \cs{@@_pair:wn} \meta{key_i} \cs{s_@@} \Arg{value_i}
+% \cs[no-index]{@@~\meta{prefix}~\meta{key$_{i+1}$}}
+% \end{quote}
+% where the pointer to \meta{key$_{i-1}$} is needed when deleting the
+% \meta{key_i}. Expanding this will run \cs{@@_pair:wn} on the
+% \meta{key_i}--\meta{value_i} pair (for speed, \meta{key_i} is kept as explicit
+% tokens rather than slowly extracting it from a control sequence name), then
+% move on to the next key, thus mapping through the whole list. The mapping is
+% ended upon expanding \cs{@@~\meta{prefix}}, which is the token list
+% \begin{quote}
+% \cs{use_none:n} \cs[no-index]{@@~\meta{prefix}~\meta{key_n}}
+% \end{quote}
+% Let us think about deleting the \meta{key_i}. We need to update the
+% \meta{key$_{i-1}$} and \meta{key$_{i+1}$} to point to each other
+% instead of \meta{key_i}. To edit the corresponding token lists, it is
+% important that \cs[no-index]{@@~\meta{prefix}~\meta{key_i}} be at the
+% \enquote{same place} in the token lists also in the boundary cases
+% $i=1$ or $i=n$, namely as the second token, or as the second argument
+% after \cs{s_@@}.
+%
+% \subsection{Internal auxiliaries}
+%
+% \begin{macro}{\@@_tmp:w}
+% Scratch macro, defined as needed, for instance to save \cs{@@_pair:wn} when
+% concatenating.
+% \begin{macrocode}
+\cs_new_eq:NN \@@_tmp:w ?
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}{\l_@@_internal_tl}
+% Token list used in various places: for the prefix; when converting from flat
+% to linked props; and to store the new key--value pair inserted by
+% \cs{prop_put:Nnn}.
+% \begin{macrocode}
+\tl_new:N \l_@@_internal_tl
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{variable}{\s_@@_mark,\s_@@_stop}
+% Internal scan marks.
+% \begin{macrocode}
+\scan_new:N \s_@@_mark
+\scan_new:N \s_@@_stop
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{variable}{\q_@@_recursion_tail,\q_@@_recursion_stop}
+% Internal recursion quarks.
+% \begin{macrocode}
+\quark_new:N \q_@@_recursion_tail
+\quark_new:N \q_@@_recursion_stop
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}[EXP]{\@@_if_recursion_tail_stop:n}
+% \begin{macro}[EXP]{\@@_if_recursion_tail_stop:o}
+% Functions to query recursion quarks.
+% \begin{macrocode}
+\__kernel_quark_new_test:N \@@_if_recursion_tail_stop:n
+\cs_generate_variant:Nn \@@_if_recursion_tail_stop:n { o }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Structure of a property list}
+%
+% \begin{macro}{\s_@@}
+% A private scan mark is used as a marker after each key, and at the
+% very beginning of the property list.
+% \begin{macrocode}
+\scan_new:N \s_@@
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_chk:w, \@@_chk_loop:nw, \@@_chk_get:nw}
+% This removes the flat property list from the input stream and complains
+% about a bad use of a property list. Since property lists do not have an
+% end-marker, we slowly peek ahead in a loop. Speed does not matter since
+% this is for an error situation. While \cs{@@_pair:wn} does not keep a fixed
+% definition, it always includes the internal \cs{s_@@} in its argument
+% specification, so that there is no risk of accidentally picking up a public
+% token instead of \cs{@@_pair:wn} when doing a meaning test. We collect the
+% keys and values to produce a more useful error message.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_chk:w { \@@_chk_loop:nw { } }
+\cs_new_protected:Npn \@@_chk_loop:nw #1
+ {
+ \peek_meaning:NTF \@@_pair:wn
+ { \@@_chk_get:nw {#1} }
+ { \msg_error:nne { prop } { misused } {#1} }
+ }
+\cs_new_protected:Npn \@@_chk_get:nw #1 \@@_pair:wn #2 \s_@@ #3
+ { \@@_chk_loop:nw { #1 , ~ {#2} = { \tl_to_str:n {#3} } } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_pair:wn}
+% Used as \cs{@@_pair:wn} \meta{key} \cs{s_@@} \Arg{item} for both storage
+% types, this internal token starts each key--value pair in the property list.
+% This default definition is changed globally by any mapping function, so
+% there is not much point trying to make it an error. Instead, the error is
+% produced by \cs{@@_chk:w}.
+% \begin{macrocode}
+\cs_new:Npn \@@_pair:wn #1 \s_@@ #2 { }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_flatten:w}
+% We implement here the fact that \texttt{f}-expanding a linked property list
+% gives a flat property list.
+% Leaving a linked property list in the input stream will turn it into a flat
+% property list so that the error implemented by \cs{@@_chk:w} will correctly
+% be triggered.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_flatten:w #1 \s_@@ #2#3
+ { \use:e { \@@_flatten_aux:N #3 } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[rEXP]
+% {\@@_flatten:N, \@@_flatten_aux:w, \@@_flatten_aux:N, \@@_flatten_loop:w}
+% The main function \cs{@@_flatten:N} receives a linked property list and
+% flattens it. The auxiliary \cs{@@_flatten_aux:N} receives a pointer to the
+% first key and flattens the linked property list into a flat property list.
+% This is only restricted-expandable as it involves mapping through all of the
+% property list's entries starting from \meta{key_1}. The looping function
+% \cs{@@_flatten_loop:w} removes \cs{use_none:n} and a backwards pointer~|#2|,
+% leaves the key--value pair for \cs{use:e} to receive, and calls itself
+% again after expanding the next key's token list. Its argument |#3| is
+% empty, except at the end where it is the \cs{use_none:nnnn} appearing in the
+% definition of~\cs{@@_flatten_aux:N}, which ends the loop.
+% \begin{macrocode}
+\cs_new:Npn \@@_flatten:N #1
+ { \exp_after:wN \@@_flatten_aux:w #1 }
+\cs_new:Npn \@@_flatten_aux:w #1 \s_@@ #2 { \@@_flatten_aux:N }
+\cs_new:Npn \@@_flatten_aux:N #1
+ {
+ \s_@@ \@@_chk:w
+ \exp_after:wN \@@_flatten_loop:w #1
+ \use_none:nnnn \@@_pair:wn \s_@@ { }
+ }
+\cs_new:Npn \@@_flatten_loop:w #1#2#3 \@@_pair:wn #4 \s_@@ #5
+ {
+ #3
+ \exp_not:n { \@@_pair:wn #4 \s_@@ {#5} }
+ \exp_after:wN \@@_flatten_loop:w
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}{\g_@@_prefix_int, \c_@@_basis_int}
+% Used to assign prefixes for each linked property list. It is converted to
+% base \cs{c_@@_basis_int}, then each digit is converted to a character,
+% starting at |!| (the character after space).
+% \begin{macrocode}
+\int_new:N \g_@@_prefix_int
+\int_const:Nn \c_@@_basis_int { \c_max_char_int - `\! }
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}{\@@_next_prefix:, \@@_to_prefix:n}
+% Store in \cs{l_@@_internal_tl} the conversion of \cs{g_@@_prefix_int} to
+% characters, and increment this integer for use in the next linked property
+% list. No need to optimize since this is only used when declaring the
+% property list the first time.
+% The aim here is to make this string as short as we can, given the
+% range of distinct characters available. This speeds up the work of
+% \cs{cs:w} \ldots{} \cs{cs_end:} that looks up keys in the hash table.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_next_prefix:
+ {
+ \tl_set:Ne \l_@@_internal_tl
+ { \@@_to_prefix:n { \g_@@_prefix_int } }
+ \int_gincr:N \g_@@_prefix_int
+ }
+\cs_new:Npn \@@_to_prefix:n #1
+ {
+ \int_compare:nNnTF {#1} > \c_@@_basis_int
+ {
+ \exp_args:Nf \@@_to_prefix:n
+ { \int_div_truncate:nn {#1} \c_@@_basis_int }
+ \exp_args:Nf \@@_to_prefix:n
+ { \int_mod:nn {#1} \c_@@_basis_int }
+ }
+ { \char_generate:nn { `\! + #1 } { 12 } }
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_if_flat:NTF, \@@_if_flat_aux:w}
+% We could either test for the presence of \cs{@@_chk:w} (flat
+% property list) or of \cs{@@_flatten:w} (linked property list). We
+% make the second choice; this way props that are accidentally
+% \tn{relax} are treated as they were before. The auxiliary receives
+% \cs{use_i:nn} or \cs{use_ii:nn} as~|#3|.
+% As a transitional fix we avoid erroring in case the prop is undefined (the \cs{exp_after:wN} is omitted in that case, taking the flat branch).
+% \begin{macrocode}
+\cs_new:Npn \@@_if_flat:NTF #1
+ {
+ \prop_if_exist:NT #1
+ \exp_after:wN \@@_if_flat_aux:w #1
+ \s_@@_mark \use_ii:nn
+ \@@_flatten:w \s_@@_mark \use_i:nn \s_@@_stop
+ }
+\cs_new:Npn \@@_if_flat_aux:w
+ #1 \@@_flatten:w #2 \s_@@_mark #3 #4 \s_@@_stop {#3}
+% \end{macrocode}
+% \end{macro}
+%
+% \subsection{Allocation and initialisation}
+%
+% \begin{variable}[tested = m3prop004]{\c_empty_prop}
+% An empty flat prop.
+% \begin{macrocode}
+\tl_const:Nn \c_empty_prop { \s_@@ \@@_chk:w }
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}[tested = m3prop001]{\prop_new:N, \prop_new:c}
+% Flat property lists are initialized with the value \cs{c_empty_prop}.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_new:N #1
+ {
+ \__kernel_chk_if_free_cs:N #1
+ \cs_gset_eq:NN #1 \c_empty_prop
+ }
+\cs_generate_variant:Nn \prop_new:N { c }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop001]{\prop_new_linked:N, \prop_new_linked:c}
+% \begin{macro}{\@@_new_linked:N}
+% The auxiliary is used in \cs{prop_make_linked:N}.
+% For linked property lists, get a new prefix in \cs{l_@@_internal_tl}, then
+% use it to set up the internal structure: the last token in~|#1| is usually a
+% pointer to the first key, which is here the end-pointer. That end-pointer
+% has a pointer to the previous key (usually the last key), which is the
+% variable~|#1| itself that begins the doubly-linked list.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_new_linked:N #1
+ {
+ \__kernel_chk_if_free_cs:N #1
+ \@@_new_linked:N #1
+ }
+\cs_new_protected:Npn \@@_new_linked:N #1
+ {
+ \@@_next_prefix:
+ \cs_gset_nopar:Npe #1
+ {
+ \@@_flatten:w
+ \exp_not:c { @@ ~ \l_@@_internal_tl }
+ \s_@@ { \l_@@_internal_tl }
+ \exp_not:c { @@ ~ \l_@@_internal_tl }
+ }
+ \cs_gset_nopar:cpe { @@ ~ \l_@@_internal_tl }
+ {
+ \exp_not:N \use_none:n
+ \exp_not:N #1
+ }
+ }
+\cs_generate_variant:Nn \prop_new_linked:N { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop001]{\prop_clear:N, \prop_clear:c}
+% \begin{macro}[tested = m3prop001]{\prop_gclear:N, \prop_gclear:c}
+% \begin{macro}{\@@_clear:NNN, \@@_clear:wNNN, \@@_clear_loop:Nw}
+% Clearing a flat property list is like declaring it anew, simply setting it
+% equal to \cs{c_empty_prop}. For linked property lists we must clear all of
+% the variables storing individual keys, which requires a loop. At each step
+% of the loop, \cs{@@_clear_loop:Nw} receives
+% \cs[index=cs_set_eq:NN]{cs_(g)set_eq:NN}, \cs{use_none:n}, the backwards
+% pointer, an empty~|#4| (except at the end of the loop), and the key--value
+% pair |#5=#6| which we disregard. The looping auxiliary undefines the
+% previous key's token list (this includes the main token list, but that is
+% fine because it is restored at the end) and calls itself after expanding the
+% next key's token list. The loop ends when |#4| is \cs{use_none:nnnn}.
+% After the loop, \cs{@@_clear:wNNN} correctly sets up the main variable~|#6|
+% and the end-pointer~|#1|. Importantly, this is done using
+% \cs[index=cs_set_nopar:Npe]{cs_(g)set_nopar:Npe} and \cs{exp_not:n} because
+% the almost-equivalent \cs{tl_set:Nn} would complain in debug mode about the
+% fact that the main variable is undefined at this stage. Importantly,
+% \cs{@@_clear_entries:NN} is used in the implementation of
+% \cs{prop_set_eq:NN}.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_clear:N
+ { \@@_clear:NNN \cs_set_eq:NN \cs_set_nopar:Npe }
+\cs_generate_variant:Nn \prop_clear:N { c }
+\cs_new_protected:Npn \prop_gclear:N
+ { \@@_clear:NNN \cs_gset_eq:NN \cs_gset_nopar:Npe }
+\cs_generate_variant:Nn \prop_gclear:N { c }
+\cs_new_protected:Npn \@@_clear:NNN #1#2#3
+ {
+ \@@_if_flat:NTF #3
+ { #1 #3 \c_empty_prop }
+ { \exp_after:wN \@@_clear:wNNN #3 #1 #2 #3 }
+ }
+\cs_new_protected:Npn \@@_clear:wNNN
+ \@@_flatten:w #1 \s_@@ #2#3#4#5#6
+ {
+ \@@_clear_entries:NN #4 #3
+ #5 #6 { \exp_not:n { \@@_flatten:w #1 \s_@@ {#2} #1 } }
+ #5 #1 { \exp_not:n { \use_none:n #6 } }
+ }
+\cs_new_protected:Npn \@@_clear_entries:NN #1#2
+ {
+ \exp_after:wN \@@_clear_loop:Nw \exp_after:wN #1 #2
+ \use_none:nnnn \@@_pair:wn \s_@@ { }
+ }
+\cs_new_protected:Npn \@@_clear_loop:Nw
+ #1#2#3#4 \@@_pair:wn #5 \s_@@ #6
+ {
+ #1 #3 \tex_undefined:D
+ #4
+ \exp_after:wN \@@_clear_loop:Nw
+ \exp_after:wN #1
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop001]
+% {
+% \prop_clear_new:N, \prop_clear_new:c,
+% \prop_gclear_new:N, \prop_gclear_new:c,
+% \prop_clear_new_linked:N, \prop_clear_new_linked:c,
+% \prop_gclear_new_linked:N, \prop_gclear_new_linked:c
+% }
+% A simple variation of the token list functions.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_clear_new:N #1
+ { \prop_if_exist:NTF #1 { \prop_clear:N #1 } { \prop_new:N #1 } }
+\cs_generate_variant:Nn \prop_clear_new:N { c }
+\cs_new_protected:Npn \prop_gclear_new:N #1
+ { \prop_if_exist:NTF #1 { \prop_gclear:N #1 } { \prop_new:N #1 } }
+\cs_generate_variant:Nn \prop_gclear_new:N { c }
+\cs_new_protected:Npn \prop_clear_new_linked:N #1
+ { \prop_if_exist:NTF #1 { \prop_clear:N #1 } { \prop_new_linked:N #1 } }
+\cs_generate_variant:Nn \prop_clear_new_linked:N { c }
+\cs_new_protected:Npn \prop_gclear_new_linked:N #1
+ { \prop_if_exist:NTF #1 { \prop_gclear:N #1 } { \prop_new_linked:N #1 } }
+\cs_generate_variant:Nn \prop_gclear_new_linked:N { c }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop001]
+% {\prop_set_eq:NN, \prop_set_eq:cN, \prop_set_eq:Nc, \prop_set_eq:cc}
+% \begin{macro}[tested = m3prop001]
+% {\prop_gset_eq:NN, \prop_gset_eq:cN, \prop_gset_eq:Nc, \prop_gset_eq:cc}
+% \begin{macro}
+% {
+% \@@_set_eq:NNNN, \@@_set_eq:wNNNN, \@@_set_eq:nNnNN,
+% \@@_set_eq_loop:NNnw, \@@_set_eq_end:w
+% }
+% If both variables are accidentally the same variable (or equal flat property
+% lists, as it turns out) we do nothing, otherwise the following code would
+% lose all entries. If the target variable~|#3| is a flat prop, either copy
+% directly or flatten before copying. If it is a linked prop, we must clear
+% it, then go through the entries in~|#4| to add them to~|#3|.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_set_eq:NN
+ { \@@_set_eq:NNNN \cs_set_eq:NN \cs_set_nopar:Npe }
+\cs_generate_variant:Nn \prop_set_eq:NN { Nc , cN , cc }
+\cs_new_protected:Npn \prop_gset_eq:NN
+ { \@@_set_eq:NNNN \cs_gset_eq:NN \cs_gset_nopar:Npe }
+\cs_generate_variant:Nn \prop_gset_eq:NN { Nc , cN , cc }
+\cs_new_protected:Npn \@@_set_eq:NNNN #1#2#3#4
+ {
+ \cs_if_eq:NNF #3#4
+ {
+ \@@_if_flat:NTF #3
+ {
+ \@@_if_flat:NTF #4
+ { #1 #3 #4 }
+ { #2 #3 { \@@_flatten:N #4 } }
+ }
+ { \exp_after:wN \@@_set_eq:wNNNN #3 #1#2#3#4 }
+ }
+ }
+\cs_new_protected:Npn \@@_set_eq:wNNNN
+ \@@_flatten:w #1 \s_@@ #2#3#4#5#6#7
+ {
+ \@@_clear_entries:NN #4 #3
+ \exp_args:Nf \@@_set_eq:nNnNN {#7} #1 {#2} #5 #6
+ }
+% \end{macrocode}
+% We have used that |f|-expanding either type of prop gives a flat prop. At
+% this stage \cs{@@_set_eq:nNnNN} receives the second variable as a flat prop,
+% the end-pointer, the prefix, the suitable
+% \cs[index=cs_set_nopar:Npe]{cs_(g)set_nopar:Npe} assignment, and the first
+% variable itself. Remove the leading \cs{s_@@} and \cs{@@_chk:w} with
+% \cs{use_i:nnn}, then start the loop.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_set_eq:nNnNN #1#2#3#4#5
+ {
+ \use_i:nnn
+ {
+ \@@_set_eq_loop:NNnw #5 #4 {#3}
+ \@@_flatten:w #2 \s_@@ {#3}
+ }
+ #1
+ \use_none:n \@@_pair:wn ? \s_@@
+ }
+% \end{macrocode}
+% The looping function receives the current pointer~|#1| (initially the
+% variable itself), the defining function~|#2| and the prefix~|#3|, then a
+% partial definition~|#4| (which in later stages includes the backwards
+% pointer), followed by the current value as \cs{s_@@} |{#5}|. It seeks the
+% next key~|#7| to construct in \cs{l_@@_internal_tl} the next pointer
+% \cs[no-index]{@@~\meta{prefix}~\meta{next key}} (the
+% argument~|#6| is empty, except at the end of the loop, where it is
+% \cs{use_none:n} in such a way as to delete the \meta{space} and \meta{next
+% key}). Then the token list (current pointer)~|#1| is set-up to contain the
+% partial definition and current value, as well as the newly constructed next
+% pointer. After a line responsible for correctly ending the loop with
+% \cs{@@_set_eq_end:w}, we loop, setting up the next definition, which starts
+% with \cs{use_none:n} and a backwards pointer to~|#1| followed by the
+% \meta{next key}~|#7| and so on.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_set_eq_loop:NNnw
+ #1#2#3#4 \s_@@ #5#6 \@@_pair:wn #7 \s_@@
+ {
+ \tl_set:Ne \l_@@_internal_tl { \exp_not:c { @@ ~ #3 #6 ~ #7 } }
+ #2 #1 { \exp_not:n { #4 \s_@@ {#5} } \exp_not:o \l_@@_internal_tl }
+ \use_none:n #6 \@@_set_eq_end:w
+ \exp_after:wN \@@_set_eq_loop:NNnw \l_@@_internal_tl #2 {#3}
+ \use_none:n #1 \@@_pair:wn #7 \s_@@
+ }
+% \end{macrocode}
+% The end-code picks up what is needed to correctly assign the last token
+% list (the end pointer), which is simply \cs{use_none:n}
+% \cs[no-index]{@@_\meta{prefix}\meta{space}\meta{key_n}}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_set_eq_end:w
+ \exp_after:wN \@@_set_eq_loop:NNnw #1#2#3
+ \use_none:n #4#5 \s_@@
+ {
+ \exp_after:wN #2 \l_@@_internal_tl { \exp_not:n { \use_none:n #4 } }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\prop_make_flat:N, \prop_make_flat:c \@@_make_flat:Nn}
+% The only interesting case is when given a linked prop. Clear the
+% linked property list using \cs{@@_clear:wNNN} with local assignments
+% (it does not matter since we are at the outermost group level, and
+% \cs{cs_set_eq:NN} is very slightly faster than its global version.
+% Then store the contents (expanded preventively by \cs{exp_args:NNf})
+% with an assignment \cs{cs_set_nopar:Npe} that does not perform
+% \pkg{l3debug} checks.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_make_flat:N #1
+ {
+ \int_compare:nNnTF { \tex_currentgrouplevel:D } = 0
+ {
+ \@@_if_flat:NTF #1 { }
+ { \exp_args:NNf \@@_make_flat:Nn #1 {#1} }
+ }
+ {
+ \msg_error:nnee { prop } { inner-make }
+ { \token_to_str:N \prop_make_flat:N } { \token_to_str:N #1 }
+ }
+ }
+\cs_generate_variant:Nn \prop_make_flat:N { c }
+\cs_new_protected:Npn \@@_make_flat:Nn #1#2
+ {
+ \exp_after:wN \@@_clear:wNNN #1 \cs_set_eq:NN \cs_set_nopar:Npe #1
+ \cs_set_nopar:Npe #1 { \exp_not:n {#2} }
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\prop_make_linked:N, \prop_make_linked:c, \@@_make_linked:Nn}
+% The only interesting case is when given a flat prop. We expand the
+% contents for later use. Then \cs{@@_new_linked:N} disregards that
+% previous value of~|#1| and initializes the linked prop. We can then
+% use an auxiliary \cs{@@_set_eq:wNNNN} underlying
+% \cs{prop_set_eq:NN}, with the prop contents saved as
+% \cs{l_@@_internal_tl}. That step is a bit unsafe, as
+% \cs{l_@@_internal_tl} (really, a flat prop here) is used within
+% \cs{@@_set_eq:wNNNN} itself, but it is in fact expanded early enough
+% to be ok.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_make_linked:N #1
+ {
+ \int_compare:nNnTF { \tex_currentgrouplevel:D } = 0
+ {
+ \@@_if_flat:NTF #1
+ { \exp_args:NNo \@@_make_linked:Nn #1 {#1} } { }
+ }
+ {
+ \msg_error:nnee { prop } { inner-make }
+ { \token_to_str:N \prop_make_linked:N } { \token_to_str:N #1 }
+ }
+ }
+\cs_generate_variant:Nn \prop_make_linked:N { c }
+\cs_new_protected:Npn \@@_make_linked:Nn #1#2
+ {
+ \@@_new_linked:N #1
+ \tl_set:Nn \l_@@_internal_tl {#2}
+ \exp_after:wN \@@_set_eq:wNNNN #1
+ \cs_set_eq:NN \cs_set_nopar:Npe #1 \l_@@_internal_tl
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}[tested = m3prop004]{\l_tmpa_prop, \l_tmpb_prop}
+% \begin{variable}[tested = m3prop004]{\g_tmpa_prop, \g_tmpb_prop}
+% We can now initialize the scratch variables.
+% \begin{macrocode}
+\prop_new:N \l_tmpa_prop
+\prop_new:N \l_tmpb_prop
+\prop_new:N \g_tmpa_prop
+\prop_new:N \g_tmpb_prop
+% \end{macrocode}
+% \end{variable}
+% \end{variable}
+%
+% \begin{macro}
+% {
+% \prop_concat:NNN, \prop_concat:ccc,
+% \prop_gconcat:NNN, \prop_gconcat:ccc,
+% \@@_concat:NNNNN, \@@_concat:nNNN
+% }
+% The basic strategy is to copy the first variable into the target,
+% then loop through the second variable, calling
+% \cs[index=prop_put:Nnn]{prop_(g)put:Nnn} on each item. To avoid
+% running the \pkg{l3debug} scope checks on each of these steps, we
+% use the auxiliaries that underly \cs{prop_set_eq:NN} and
+% \cs{prop_put:Nnn}, whose syntax is a bit unwieldy.
+% We work directly with the target prop |#3| as a scratch space,
+% because copying over from a temporary variable to |#3| would be slow
+% in the linked case. If |#5| is |#3| itself we have to be careful
+% not to lose the data, and we even take the opportunity to skip the
+% copying step completely. To keep the correct version of the
+% duplicate keys we use the code underlying \cs{prop_put_if_not_in:Nnn},
+% which involves passing \cs{use_none:nnn} to the auxiliary instead of
+% nothing.
+% There is no need to check for the case where |#3| is equal to~|#4|
+% because in that case \cs[index=prop_set_eq:NN]{prop_(g)set_eq:NN}
+% |#3| |#4| (or rather the underlying auxiliary) is correctly set up
+% to do no needless work.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_concat:NNN
+ { \@@_concat:NNNNN \cs_set_eq:NN \cs_set_nopar:Npe }
+\cs_generate_variant:Nn \prop_concat:NNN { ccc }
+\cs_new_protected:Npn \prop_gconcat:NNN
+ { \@@_concat:NNNNN \cs_gset_eq:NN \cs_gset_nopar:Npe }
+\cs_generate_variant:Nn \prop_gconcat:NNN { ccc }
+\cs_new_protected:Npn \@@_concat:NNNNN #1#2#3#4#5
+ {
+ \cs_if_eq:NNTF #3 #5
+ { \@@_concat:nNNN \use_none:nnn #2 #3 #4 }
+ {
+ \@@_set_eq:NNNN #1 #2 #3 #4
+ \@@_concat:nNNN { } #2 #3 #5
+ }
+ }
+\cs_new_protected:Npn \@@_concat:nNNN #1#2#3#4
+ {
+ \cs_gset_eq:NN \@@_tmp:w \@@_pair:wn
+ \cs_gset_protected:Npn \@@_pair:wn ##1 \s_@@
+ { \@@_put:nNNnn {#1} #2 #3 {##1} }
+ \exp_last_unbraced:Nf \use_none:nn #4
+ \cs_gset_eq:NN \@@_pair:wn \@@_tmp:w
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}
+% {
+% \prop_put_from_keyval:Nn, \prop_put_from_keyval:cn,
+% \prop_gput_from_keyval:Nn, \prop_gput_from_keyval:cn,
+% \@@_from_keyval:nn, \@@_from_keyval:Nnn,
+% \@@_missing_eq:n
+% }
+% The core is a call to \cs{keyval_parse:nnn}, with an error message
+% \cs{@@_missing_eq:n} for entries without~|=|, and a call to (essentially)
+% \cs[index=prop_put:Nnn]{prop_(g)put:Nnn} for valid key--value pairs.
+% To avoid repeated scope checks (and errors) when \pkg{l3debug} is
+% active, we instead use the auxiliary underlying \cs{prop_put:Nnn}.
+% Because blank keys are valid here, in contrast to \pkg{l3keys}, we set and
+% restore \cs{l__kernel_keyval_allow_blank_keys_bool}.
+% The key--value argument may be quite large so we avoid reading it until it
+% is really necessary.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_put_from_keyval:Nn #1
+ { \@@_from_keyval:nn { \@@_put:nNNnn { } \cs_set_nopar:Npe #1 } }
+\cs_generate_variant:Nn \prop_put_from_keyval:Nn { c }
+\cs_new_protected:Npn \prop_gput_from_keyval:Nn #1
+ { \@@_from_keyval:nn { \@@_put:nNNnn { } \cs_gset_nopar:Npe #1 } }
+\cs_generate_variant:Nn \prop_gput_from_keyval:Nn { c }
+\cs_new_protected:Npn \@@_from_keyval:nn
+ {
+ \bool_if:NTF \l__kernel_keyval_allow_blank_keys_bool
+ { \@@_from_keyval:Nnn \c_true_bool }
+ { \@@_from_keyval:Nnn \c_false_bool }
+ }
+\cs_new_protected:Npn \@@_from_keyval:Nnn #1#2#3
+ {
+ \bool_set_eq:NN \l__kernel_keyval_allow_blank_keys_bool \c_true_bool
+ \keyval_parse:nnn \@@_missing_eq:n {#2} {#3}
+ \bool_set_eq:NN \l__kernel_keyval_allow_blank_keys_bool #1
+ }
+\cs_new_protected:Npn \@@_missing_eq:n
+ { \msg_error:nnn { prop } { prop-keyval } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}
+% {
+% \prop_set_from_keyval:Nn, \prop_set_from_keyval:cn,
+% \prop_gset_from_keyval:Nn, \prop_gset_from_keyval:cn,
+% }
+% Just empty the prop (with the auxiliary underlying
+% \cs{prop_clear:N} to avoid \pkg{l3debug} problems) and push
+% key--value entries using
+% \cs[index=prop_put_from_keyval:Nn]{prop_(g)put_from_keyval:Nn}.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_set_from_keyval:Nn #1
+ {
+ \@@_clear:NNN \cs_set_eq:NN \cs_set_nopar:Npe #1
+ \prop_put_from_keyval:Nn #1
+ }
+\cs_generate_variant:Nn \prop_set_from_keyval:Nn { c }
+\cs_new_protected:Npn \prop_gset_from_keyval:Nn #1
+ {
+ \@@_clear:NNN \cs_gset_eq:NN \cs_gset_nopar:Npe #1
+ \prop_gput_from_keyval:Nn #1
+ }
+\cs_generate_variant:Nn \prop_gset_from_keyval:Nn { c }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}
+% {
+% \prop_const_from_keyval:Nn, \prop_const_from_keyval:cn,
+% \prop_const_linked_from_keyval:Nn, \prop_const_linked_from_keyval:cn
+% }
+% For both flat and linked constant props, we create |#1| then use the
+% same auxiliary as for \cs{prop_gput_from_keyval:Nn}. It is most
+% natural to use the already packaged \cs{prop_gput:Nnn}, but that
+% would mean doing an assignment on a supposedly constant property
+% list. To avoid errors when \pkg{l3debug} is activated, we use the
+% auxiliary underlying \cs{prop_gput:Nnn}.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_const_from_keyval:Nn #1
+ {
+ \prop_new:N #1
+ \@@_from_keyval:nn { \@@_put:nNNnn { } \cs_gset_nopar:Npe #1 }
+ }
+\cs_generate_variant:Nn \prop_const_from_keyval:Nn { c }
+\cs_new_protected:Npn \prop_const_linked_from_keyval:Nn #1
+ {
+ \prop_new_linked:N #1
+ \@@_from_keyval:nn { \@@_put:nNNnn { } \cs_gset_nopar:Npe #1 }
+ }
+\cs_generate_variant:Nn \prop_const_linked_from_keyval:Nn { c }
+% \end{macrocode}
+% \end{macro}
+%
+% \subsection{Accessing data in property lists}
+%
+% Accessing/deleting/adding entries is mostly done by \cs{@@_split:NnTFn}, which
+% must be fast because it is used in many \pkg{l3prop} functions. Its syntax is
+% as follows.
+% \begin{quote}
+% \cs{@@_split:NnTFn} \meta{property list} \Arg{key} \\
+% ~~\Arg{true code} \Arg{false code} \Arg{link code}
+% \end{quote}
+% If the \meta{property list} uses the linked data storage, then it runs
+% the \meta{link code}, otherwise it does as follows.
+%
+% It splits the \meta{property list} at the \meta{key}, giving three
+% token lists: the \meta{entries before} the \meta{key}, the
+% \meta{value} associated with the \meta{key} and the \meta{entries
+% after} the \meta{key}. Both the \meta{entries before} and the
+% \meta{entries after} can be empty or consist of some number of
+% consecutive entries \cs{@@_pair:wn} \meta{key_i} \cs{s_@@}
+% \Arg{value_i}. If the \meta{key} is present in the \meta{property
+% list} then the \meta{true code} is left in the input stream, with
+% |#1|, |#2|, and |#3| replaced by the \meta{entries before},
+% \meta{value}, and \meta{entries after}. If the \meta{key} is not
+% present in the \meta{property list} then the \meta{false code} is left
+% in the input stream. Only the \meta{true code} is used in the
+% replacement text of a macro defined internally, which requires
+% |##|~doubling.
+%
+% \begin{macro}
+% {
+% \@@_split:NnTFn, \@@_split_aux:nNTFn, \@@_split_test:wn,
+% \@@_split_flat:w, \@@_split_linked:w, \@@_split_wrong:Nw
+% }
+% The aim is to distinguish four cases: a flat prop that contains the
+% given \meta{key}, a flat prop that does not contain it, a linked
+% prop, and an invalid prop. The last case includes those that are
+% set to \tn{relax} by \texttt{c}-expansion, as well as unrelated
+% token list variables since these unfortunately used to
+% \enquote{work} in earlier implementations.
+% In the first three cases we run the \texttt{T}, \texttt{F}, and
+% \texttt{n} arguments, and in the last case we raise an error, set
+% the variable to a known state (empty prop), and run the \texttt{F}
+% code (some conditionals such as \cs{prop_pop:NnNTF} otherwise blow
+% up pretty badly).
+%
+% The first distinction between these cases is done by
+% \cs{@@_split_test:wn}, which looks for the argument after \cs{s_@@}.
+% For a flat prop it will be \cs{@@_chk:w}, which leads to running
+% \cs{@@_split_flat:w}, explained below. For a linked prop it is the
+% prefix, consisting of characters, so we end up running
+% \cs{@@_split_linked:w}, which cleans up and selects the
+% aforementioned \texttt{n} argument. For invalid props, or rather,
+% variables that do not contain \cs{s_@@}, the argument includes
+% \cs{fi:}, and we end up calling \cs{@@_split_wrong:Nw}, which calls
+% \cs{prop_show:N} to raise a detailed error stating how the variable
+% is wrong.
+%
+% Let us return to \cs{@@_split_flat:w}. This function is defined
+% dynamically as
+% \begin{quote}
+% \cs{cs_set:Npn} \cs{@@_split_flat:w} \cs{@@_split_linked:w} |#1| \\
+% \quad \cs{@@_pair:wn} \meta{key} \cs{s_@@} |#2| \\
+% \quad |#3| \cs{s_@@_mark} |#4| |#5| \cs{s_@@_stop} \\
+% \quad |{| |#4| \Arg{true code} |}|
+% \end{quote}
+% Its job is to seek the \meta{key} in the property list (known to be
+% flat at this stage) by using an argument |#1| delimited essentially
+% by that key. If indeed the variable contained the \meta{key}, then
+% |#1|~is the \meta{extract_1} before the key--value pair, |#2|~is the
+% \meta{value} associated with the \meta{key}, |#3|~is the
+% \meta{extract_2} after the key--value pair, |#4|~is \cs{use_i:nnn},
+% and we run \cs{use_i:nnn} \Arg{true code} \Arg{false code} \Arg{link
+% code}, selecting the \meta{true code}. Otherwise, the whole
+% property list together with \cs{s_@@_mark} \cs{use_i:nnn} is taken
+% in as |#1|, then |#2| is some tokens |?| \cs{fi:}
+% \cs{@@_split_wrong:Nw} \meta{variable} that were only useful in the
+% case of invalid props, |#3|~is empty, and most importantly |#4| is
+% \cs{use_ii:nnn}. This command selects the \meta{false code}.
+%
+% Note that we define \cs{@@_split_flat:w} in all cases even though it
+% is only used in the flat case. Indeed, to avoid taking in the whole
+% property list (which may be large) as an argument more than strictly
+% necessary, we would have to keep the \meta{true code} positioned
+% before the expansion of the prop variable in order to use it in the
+% definition. The only way to do that is to store it using an
+% assignment so we might as well just perform the assignment that we
+% can actually use in the flat case.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_split:NnTFn #1#2
+ {
+ \exp_after:wN \@@_split_aux:nNTFn
+ \exp_after:wN { \tl_to_str:n {#2} } #1
+ }
+\cs_new_protected:Npn \@@_split_aux:nNTFn #1#2#3
+ {
+ \cs_set:Npn \@@_split_flat:w \@@_split_linked:w ##1
+ \@@_pair:wn #1 \s_@@ ##2 ##3 \s_@@_mark ##4 ##5 \s_@@_stop
+ { ##4 {#3} }
+ \exp_after:wN \@@_split_test:wn #2 \s_@@_mark \use_i:nnn
+ \@@_pair:wn #1 \s_@@ { ? \fi: \@@_split_wrong:Nw #2 }
+ \s_@@_mark \use_ii:nnn
+ \s_@@_stop
+ }
+\cs_new:Npn \@@_split_flat:w { }
+\cs_new_protected:Npn \@@_split_test:wn #1 \s_@@ #2
+ {
+ \if_meaning:w \@@_chk:w #2 \exp_after:wN \@@_split_flat:w \fi:
+ \@@_split_linked:w
+ }
+\cs_new_protected:Npn \@@_split_linked:w #1 \s_@@_stop #2#3 {#3}
+\cs_new_protected:Npn \@@_split_wrong:Nw #1#2 \s_@@_stop #3#4
+ {
+ \prop_show:N #1
+ \cs_gset_eq:NN #1 \c_empty_prop
+ #3
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_get:NnN, \prop_get:NVN, \prop_get:NvN, \prop_get:NeN,
+% \prop_get:NoN, \prop_get:NxN,
+% \prop_get:cnN, \prop_get:cVN, \prop_get:cvN, \prop_get:ceN,
+% \prop_get:coN, \prop_get:cxN,
+% \prop_get:cnc
+% }
+% \begin{macro}[TF, tested = m3prop004]
+% {
+% \prop_get:NnN, \prop_get:NVN, \prop_get:NvN, \prop_get:NeN,
+% \prop_get:NoN, \prop_get:NxN,
+% \prop_get:cnN, \prop_get:cVN, \prop_get:cvN, \prop_get:ceN,
+% \prop_get:coN, \prop_get:cxN,
+% \prop_get:cnc
+% }
+% \begin{macro}{\@@_get:NnnTF}
+% \begin{macro}[EXP]{\@@_get_linked:w, \@@_get_linked_aux:w}
+% Here we implement both \cs{prop_get:NnN} and its branching version through
+% \cs{@@_get:NnnTF}. It receives the prop and key, followed by an assignment
+% used when the value is found, \meta{true code} to run after the assignment,
+% and some fall-back \meta{false code} for absent values. It relies on
+% \cs{@@_split:NnTFn}. For a flat prop, the first four arguments of
+% \cs{@@_split:NnTFn} are used, and run either the assignment~|#3{##3}| and
+% \meta{true code}~|#4|, or the \meta{false code}~|#5|.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_get:NnN #1#2#3
+ {
+ \@@_get:NnnTF #1 {#2}
+ { \tl_set:Nn #3 } { } { \tl_set:Nn #3 { \q_no_value } }
+ }
+\cs_generate_variant:Nn \prop_get:NnN { NV , Nv , Ne , c , cV , cv , ce }
+\cs_generate_variant:Nn \prop_get:NnN { No , Nx , co , cx }
+\cs_generate_variant:Nn \prop_get:NnN { cnc }
+\prg_new_protected_conditional:Npnn \prop_get:NnN #1#2#3 { T , F , TF }
+ {
+ \@@_get:NnnTF #1 {#2}
+ { \tl_set:Nn #3 } \prg_return_true: \prg_return_false:
+ }
+\prg_generate_conditional_variant:Nnn \prop_get:NnN
+ { NV , Nv , Ne , c , cV , cv , ce } { T , F , TF }
+\prg_generate_conditional_variant:Nnn \prop_get:NnN
+ { No , Nx , co , cx } { T , F , TF }
+\prg_generate_conditional_variant:Nnn \prop_get:NnN
+ { cnc } { T , F , TF }
+\cs_new_protected:Npn \@@_get:NnnTF #1#2#3#4#5
+ {
+ \@@_split:NnTFn #1 {#2}
+ { #3 {##2} #4 }
+ {#5}
+ { \exp_after:wN \@@_get_linked:w #1 {#2} {#3} {#4} {#5} }
+ }
+% \end{macrocode}
+% For a linked prop we must work a bit: \cs{@@_get_linked:w} is followed by
+% the expansion of the prop, then by four brace groups: the key~|#4|, the
+% assignment code~|#5|, \meta{true code}~|#6|, and \meta{false code}~|#7|. If
+% the key is present, its value is stored in the token list
+% \cs[no-index]{@@_}|#2~#4|. If that token list exists,
+% \cs{@@_get_linked_aux:w} gets called followed by the expansion of that token
+% list and we grab as~|#2| the value associated to that key, which we feed to
+% the assignment code and follow-up code. If the key is absent the token list
+% can be \tn{undefined} or \tn{relax}. In both cases \cs{@@_get_linked_aux:w}
+% finds an empty brace group as~|#2|, \cs{use_none:n} as~|#4| and the
+% \meta{false code} as~|#5|.
+% Note that we made \cs{@@_get_linked:w} and subsequent auxiliaries
+% expandable, because they are also used in \cs{prop_item:Nn}.
+% \begin{macrocode}
+\cs_new:Npn \@@_get_linked:w
+ \@@_flatten:w #1 \s_@@ #2#3#4#5#6#7
+ {
+ \if_cs_exist:w @@ ~ #2 ~ \tl_to_str:n {#4} \cs_end:
+ \exp_after:wN \exp_after:wN \exp_after:wN \@@_get_linked_aux:w
+ \cs:w @@ ~ #2 ~ \tl_to_str:n {#4} \exp_after:wN \cs_end:
+ \else:
+ \exp_after:wN \@@_get_linked_aux:w
+ \fi:
+ \s_@@_mark {#5} {#6}
+ \s_@@ { } \s_@@_mark \use_none:n {#7}
+ \s_@@_stop
+ }
+\cs_new:Npn \@@_get_linked_aux:w
+ #1 \s_@@ #2 #3 \s_@@_mark #4 #5 #6 \s_@@_stop { #4 {#2} #5 }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]
+% {
+% \prop_item:Nn, \prop_item:NV, \prop_item:No, \prop_item:Ne,
+% \prop_item:cn, \prop_item:cV, \prop_item:co, \prop_item:ce
+% }
+% \begin{macro}[EXP]{\@@_item:nnn}
+% Getting the value corresponding to a key in a flat property list in an
+% expandable fashion simply uses \cs{prop_map_tokens:Nn} to go through
+% the property list. The auxiliary \cs{@@_item:nnn} receives the
+% search string~|#1|, the key~|#2| and the value~|#3| and returns as
+% appropriate.
+% \begin{macrocode}
+\cs_new:Npn \prop_item:Nn #1#2
+ {
+ \@@_if_flat:NTF #1
+ {
+ \exp_args:NNo \prop_map_tokens:Nn #1
+ {
+ \exp_after:wN \@@_item:nnn
+ \exp_after:wN { \tl_to_str:n {#2} }
+ }
+ }
+ { \exp_after:wN \@@_get_linked:w #1 {#2} \use:n { } { } }
+ }
+\cs_new:Npn \@@_item:nnn #1#2#3
+ {
+ \str_if_eq:eeT {#1} {#2}
+ { \prop_map_break:n { \exp_not:n {#3} } }
+ }
+\cs_generate_variant:Nn \prop_item:Nn { NV , No , Ne , c , cV , co , ce }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Removing data from property lists}
+%
+% \begin{macro}
+% {
+% \@@_pop:NnNNnTF,
+% \@@_pop_linked:wnNNnTF, \@@_pop_linked:NNNn,
+% \@@_pop_linked:w,
+% \@@_pop_linked_prev:w, \@@_pop_linked_next:w
+% }
+% This auxiliary is used by both the \cs[no-index]{prop_pop} family and
+% the \cs[no-index]{prop_remove} family of functions.
+% It receives a \meta{prop} and a \Arg{key}, three assignment functions
+% (\cs{tl_set:Nn} \cs{cs_set_eq:NN} \cs{cs_set_nopar:Npe} or their global
+% versions), then \Arg{code} \Arg{true code} \Arg{false code}.
+%
+% For a flat prop, split it. If the \meta{key} is there, reconstruct the rest
+% of the prop from the two extracts |##2| |##4| and assign using
+% \cs[index=tl_set:Nn]{tl_(g)set:Nn}, then run \meta{code} \Arg{value} with
+% the \meta{value} found, and run the \meta{true code}. If the \meta{key} is
+% absent, run the \meta{false code}.
+%
+% For a linked prop, the removal is done by \cs{@@_pop_linked:wnNNnTF}, which
+% removes the key--value pair from the doubly-linked list and runs its last
+% three arguments \Arg{code} \Arg{true code} \Arg{false code} depending on
+% whether the key--value is found, in the same way as for flat props.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_pop:NnNNnTF #1#2#3#4#5#6#7
+ {
+ \@@_split:NnTFn #1 {#2}
+ {
+ #4 #1 { \exp_not:n { \s_@@ \@@_chk:w ##1 ##3 } }
+ #5 {##2}
+ #6
+ }
+ {#7}
+ {
+ \exp_after:wN \@@_pop_linked:wnNNnTF #1 {#2}
+ #3 #4 {#5} {#6} {#7}
+ }
+ }
+% \end{macrocode}
+% The next auxiliary \cs{@@_pop_linked:wnNNnTF}, together with the |NNNn|
+% auxiliary, checks if the key is present in the \meta{linked prop}, then the
+% corresponding value (if present) is passed as a braced argument to the
+% \meta{code} and the \meta{true code} or \meta{false code} is run as
+% appropriate. Before that, there are also three assignments: the token lists
+% for the previous key and next key are made to point to each other, cf.\
+% \cs{@@_pop_linked:w}, and the token list for the given key is made
+% undefined.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_pop_linked:wnNNnTF
+ \@@_flatten:w #1 \s_@@ #2#3#4#5#6#7
+ {
+ \if_cs_exist:w @@ ~ #2 ~ \tl_to_str:n {#4} \cs_end:
+ \exp_after:wN \@@_pop_linked:NNNn
+ \cs:w @@ ~ #2 ~ \tl_to_str:n {#4} \cs_end:
+ #5 #6 {#7}
+ \else:
+ \exp_after:wN \use_iii:nnn
+ \fi:
+ \use_i:nn
+ }
+\cs_new_protected:Npn \@@_pop_linked:NNNn #1#2#3#4
+ {
+ \if_meaning:w \scan_stop: #1
+ \exp_after:wN \exp_after:wN \exp_after:wN \use_iii:nnn
+ \else:
+ \exp_after:wN \@@_pop_linked:w #1 #1 #2 #3 {#4}
+ \fi:
+ }
+\cs_new_protected:Npn \@@_pop_linked:w
+ \use_none:n #1#2 \s_@@ #3#4#5#6#7#8
+ {
+ #6 #5 \tex_undefined:D
+ #7 #1
+ {
+ \exp_after:wN \@@_pop_linked_prev:w #1
+ \exp_not:N #4
+ }
+ #7 #4
+ {
+ \exp_not:n { \use_none:n #1 }
+ \exp_not:f { \exp_after:wN \@@_pop_linked_next:w #4 }
+ }
+ #8 {#3}
+ }
+\cs_new:Npn \@@_pop_linked_prev:w #1 \s_@@ #2#3
+ { \exp_not:n { #1 \s_@@ {#2} } }
+\cs_new:Npn \@@_pop_linked_next:w \use_none:n #1 { \exp_stop_f: }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_remove:Nn, \prop_remove:NV, \prop_remove:Ne,
+% \prop_remove:cn, \prop_remove:cV, \prop_remove:ce
+% }
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_gremove:Nn, \prop_gremove:NV, \prop_gremove:Ne,
+% \prop_gremove:cn, \prop_gremove:cV, \prop_gremove:ce
+% }
+% Deleting from a property relies on \cs{@@_pop:NnNNnTF}. The three
+% assignment functions are suitably local or global. The last three arguments
+% are \cs{use_none:n} and two empty brace groups: if the key is found we get
+% \cs{use_none:n} \Arg{key} \meta{empty}, which expands to nothing, and
+% otherwise we just get \meta{empty}. The auxiliary takes care of actually
+% removing the entry from the prop.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_remove:Nn #1#2
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_set_eq:NN \cs_set_nopar:Npe
+ \use_none:n { } { }
+ }
+\cs_new_protected:Npn \prop_gremove:Nn #1#2
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_gset_eq:NN \cs_gset_nopar:Npe
+ \use_none:n { } { }
+ }
+\cs_generate_variant:Nn \prop_remove:Nn { NV , Ne , c , cV , ce }
+\cs_generate_variant:Nn \prop_gremove:Nn { NV , Ne , c , cV , ce }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_pop:NnN, \prop_pop:NVN, \prop_pop:NoN,
+% \prop_pop:cnN, \prop_pop:cVN, \prop_pop:coN,
+% \prop_gpop:NnN, \prop_gpop:NVN, \prop_gpop:NoN,
+% \prop_gpop:cnN, \prop_gpop:cVN, \prop_gpop:coN,
+% }
+% \begin{macro}[TF, tested = m3prop004]
+% {
+% \prop_pop:NnN, \prop_pop:NVN, \prop_pop:NoN,
+% \prop_pop:cnN, \prop_pop:cVN, \prop_pop:coN,
+% \prop_gpop:NnN, \prop_gpop:NVN, \prop_gpop:NoN,
+% \prop_gpop:cnN, \prop_gpop:cVN, \prop_gpop:coN,
+% }
+% Popping a value is almost the same, but the value found is kept.
+% For the non-branching version, we additionally set the target token list to
+% \cs{q_no_value}, while for the branching version we must produce
+% \cs{prg_return_true:} or \cs{prg_return_false:}.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_pop:NnN #1#2#3
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_set_eq:NN \cs_set_nopar:Npe
+ { \tl_set:Nn #3 } { } { \tl_set:Nn #3 { \q_no_value } }
+ }
+\cs_new_protected:Npn \prop_gpop:NnN #1#2#3
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_gset_eq:NN \cs_gset_nopar:Npe
+ { \tl_set:Nn #3 } { } { \tl_set:Nn #3 { \q_no_value } }
+ }
+\cs_generate_variant:Nn \prop_pop:NnN { NV , No }
+\cs_generate_variant:Nn \prop_pop:NnN { c , cV , co }
+\cs_generate_variant:Nn \prop_gpop:NnN { NV , No }
+\cs_generate_variant:Nn \prop_gpop:NnN { c , cV , co }
+\prg_new_protected_conditional:Npnn \prop_pop:NnN #1#2#3 { T , F , TF }
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_set_eq:NN \cs_set_nopar:Npe
+ { \tl_set:Nn #3 } \prg_return_true: \prg_return_false:
+ }
+\prg_new_protected_conditional:Npnn \prop_gpop:NnN #1#2#3 { T , F , TF }
+ {
+ \@@_pop:NnNNnTF #1 {#2}
+ \cs_gset_eq:NN \cs_gset_nopar:Npe
+ { \tl_set:Nn #3 } \prg_return_true: \prg_return_false:
+ }
+\prg_generate_conditional_variant:Nnn \prop_pop:NnN
+ { NV , No , c , cV , co } { T , F , TF }
+\prg_generate_conditional_variant:Nnn \prop_gpop:NnN
+ { NV , No , c , cV , co } { T , F , TF }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Adding data to property lists}
+%
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_put:Nnn, \prop_put:NnV, \prop_put:Nnv, \prop_put:Nne,
+% \prop_put:NVn, \prop_put:NVV, \prop_put:NVv, \prop_put:NVe,
+% \prop_put:Nvn, \prop_put:NvV, \prop_put:Nvv, \prop_put:Nve,
+% \prop_put:Nen, \prop_put:NeV, \prop_put:Nev, \prop_put:Nee,
+% \prop_put:Nno, \prop_put:Non, \prop_put:Noo,
+% \prop_put:Nnx, \prop_put:NVx, \prop_put:NxV, \prop_put:Nxx,
+% \prop_put:cnn, \prop_put:cnV, \prop_put:cnv, \prop_put:cne,
+% \prop_put:cVn, \prop_put:cVV, \prop_put:cVv, \prop_put:cVe,
+% \prop_put:cvn, \prop_put:cvV, \prop_put:cvv, \prop_put:cve,
+% \prop_put:cen, \prop_put:ceV, \prop_put:cev, \prop_put:cee,
+% \prop_put:cno, \prop_put:con, \prop_put:coo,
+% \prop_put:cnx, \prop_put:cVx, \prop_put:cxV, \prop_put:cxx
+% }
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_gput:Nnn, \prop_gput:NnV, \prop_gput:Nnv, \prop_gput:Nne,
+% \prop_gput:NVn, \prop_gput:NVV, \prop_gput:NVv, \prop_gput:NVe,
+% \prop_gput:Nvn, \prop_gput:NvV, \prop_gput:Nvv, \prop_gput:Nve,
+% \prop_gput:Nen, \prop_gput:NeV, \prop_gput:Nev, \prop_gput:Nee,
+% \prop_gput:Nno, \prop_gput:Non, \prop_gput:Noo,
+% \prop_gput:Nnx, \prop_gput:NVx, \prop_gput:NxV, \prop_gput:Nxx,
+% \prop_gput:cnn, \prop_gput:cnV, \prop_gput:cnv, \prop_gput:cne,
+% \prop_gput:cVn, \prop_gput:cVV, \prop_gput:cVv, \prop_gput:cVe,
+% \prop_gput:cvn, \prop_gput:cvV, \prop_gput:cvv, \prop_gput:cve,
+% \prop_gput:cen, \prop_gput:ceV, \prop_gput:cev, \prop_gput:cee,
+% \prop_gput:cno, \prop_gput:con, \prop_gput:coo,
+% \prop_gput:cnx, \prop_gput:cVx, \prop_gput:cxV, \prop_gput:cxx
+% }
+% \begin{macro}[tested = m3prop002]
+% {
+% \prop_put_if_not_in:Nnn, \prop_put_if_not_in:NVn, \prop_put_if_not_in:NnV,
+% \prop_put_if_not_in:cnn, \prop_put_if_not_in:cVn, \prop_put_if_not_in:cnV,
+% \prop_gput_if_not_in:Nnn, \prop_gput_if_not_in:NVn, \prop_gput_if_not_in:NnV,
+% \prop_gput_if_not_in:cnn, \prop_gput_if_not_in:cVn, \prop_gput_if_not_in:cnV
+% }
+% \begin{macro}[tested = m3prop002]
+% {
+% \@@_put:NNNnn, \@@_put_linked:wnNN,
+% \@@_put_linked:NNNN, \@@_put_linked_old:w,
+% \@@_put_linked_new:w
+% }
+% All of the \cs[no-index]{prop_(g)put(_if_new):Nnn} functions are
+% based on the same auxiliary, which receives \meta{code} and an
+% \enquote{assignment}, followed by \meta{prop} \Arg{key} \Arg{new
+% value}. The
+% assignment \cs[index=cs_set_nopar:Npe]{cs_(g)set_nopar:Npe} is the
+% primitive assignment without any checking: in the case of linked
+% props it is applied to individual
+% pieces of the linked prop, which are typically not yet defined.
+% Debugging the scope of the variable is done at a higher level by
+% letting \pkg{l3debug} change \cs{prop_put:Nnn} and friends. This
+% allows other \pkg{l3prop} commands to directly call the underlying
+% auxiliary to skip this checking step and avoid getting multiple
+% error messages for the same error.
+% The \meta{code} (empty for |put| and \cs{use_none:nnn} for
+% |put_if_not_in|) is placed before the assignment in cases where the key
+% is already present, in order to suppress the assignment in the
+% |put_if_not_in| case.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_put:Nnn
+ { \@@_put:nNNnn { } \cs_set_nopar:Npe }
+\cs_new_protected:Npn \prop_gput:Nnn
+ { \@@_put:nNNnn { } \cs_gset_nopar:Npe }
+\cs_new_protected:Npn \prop_put_if_not_in:Nnn
+ { \@@_put:nNNnn \use_none:nnn \cs_set_nopar:Npe }
+\cs_new_protected:Npn \prop_gput_if_not_in:Nnn
+ { \@@_put:nNNnn \use_none:nnn \cs_gset_nopar:Npe }
+\cs_generate_variant:Nn \prop_put:Nnn
+ {
+ NnV , Nnv , Nne , NV , NVV , NVv , NVe ,
+ Nv , NvV , Nvv , Nve , Ne , NeV , Nev , Nee
+ }
+\cs_generate_variant:Nn \prop_put:Nnn
+ { Nno , No , Noo , Nnx , NVx , NxV , Nxx }
+\cs_generate_variant:Nn \prop_put:Nnn
+ {
+ c , cnV , cnv , cne , cV , cVV , cVv , cVe ,
+ cv , cvV , cvv , cve , ce , ceV , cev , cee
+ }
+\cs_generate_variant:Nn \prop_put:Nnn
+ { cno , co , coo , cnx , cVx , cxV , cxx }
+\cs_generate_variant:Nn \prop_gput:Nnn
+ {
+ NnV , Nnv , Nne , NV , NVV , NVv , NVe ,
+ Nv , NvV , Nvv , Nve , Ne , NeV , Nev , Nee
+ }
+\cs_generate_variant:Nn \prop_gput:Nnn
+ { Nno , No , Noo , Nnx , NVx , NxV , Nxx }
+\cs_generate_variant:Nn \prop_gput:Nnn
+ {
+ c , cnV , cnv , cne , cV , cVV , cVv , cVe ,
+ cv , cvV , cvv , cve , ce , ceV , cev , cee
+ }
+\cs_generate_variant:Nn \prop_gput:Nnn
+ { cno , co , coo , cnx , cVx , cxV , cxx }
+\cs_generate_variant:Nn \prop_put_if_not_in:Nnn
+ { NnV , NV , c , cnV , cV }
+\cs_generate_variant:Nn \prop_gput_if_not_in:Nnn
+ { NnV , NV , c , cnV , cV }
+% \end{macrocode}
+% Since the true branch of \cs{@@_split:NnTFn} is used as the
+% replacement text of an internal macro, and since the \meta{key} and
+% new \meta{value} may contain arbitrary tokens, it is not safe to
+% include them in the argument of \cs{@@_split:NnTFn}. We thus start
+% by storing in \cs{l_@@_internal_tl} tokens which (after
+% \texttt{x}-expansion) encode the key--value pair. This variable can
+% safely be used in \cs{@@_split:NnTFn}. For a flat prop, if the
+% \meta{key} was absent, append the new key--value to the list;
+% otherwise concatenate the extracts |##2| and |##4| with the new
+% key--value pair \cs{l_@@_internal_tl}. The updated entry is placed
+% at the same spot as the original \meta{key} in the property list,
+% preserving the order of entries. For a linked prop, call
+% \cs{@@_put_linked:wnNN}, which constructs the control sequence in
+% which we will place the new value. If it matches \cs{scan_stop:}
+% then the key was not yet there and we add it using
+% \cs{@@_put_linked_new:w}, otherwise it was already there and we use
+% \cs{@@_put_linked_old:w}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_put:nNNnn #1#2#3#4#5
+ {
+ \tl_set:Nn \l_@@_internal_tl
+ {
+ \exp_not:N \@@_pair:wn \tl_to_str:n {#4}
+ \s_@@ { \exp_not:n {#5} }
+ }
+ \@@_split:NnTFn #3 {#4}
+ {
+ #1 #2 #3
+ {
+ \s_@@ \@@_chk:w \exp_not:n {##1}
+ \l_@@_internal_tl \exp_not:n {##3}
+ }
+ }
+ { #2 #3 { \exp_not:o {#3} \l_@@_internal_tl } }
+ { \exp_after:wN \@@_put_linked:wnnN #3 {#4} {#1} #2 }
+ }
+\cs_new_protected:Npn \@@_put_linked:wnnN
+ \@@_flatten:w #1 \s_@@ #2#3#4
+ {
+ \exp_after:wN \@@_put_linked:NNnN
+ \cs:w @@ ~ #2 ~ \tl_to_str:n {#4} \cs_end:
+ #1
+ }
+\cs_new_protected:Npn \@@_put_linked:NNnN #1#2#3#4
+ {
+ \if_meaning:w \scan_stop: #1
+ \exp_after:wN \@@_put_linked_new:w #2 #1 #2 #4
+ \else:
+ \exp_after:wN \@@_put_linked_old:w #1 { #3 #4 #1 }
+ \fi:
+ }
+% \end{macrocode}
+% To add a new entry, \cs{@@_put_linked_new:w} receives the expansion
+% of the end-pointer, namely \cs{use_none:n} \meta{last key pointer},
+% followed by the new key pointer~|#2|, the end pointer~|#3|, and an
+% assignment function~|#4|. Set up the doubly-linked list in the
+% order |#1|, |#2|, |#3|, placing the key--value pair
+% \cs{l_@@_internal_tl} in~|#2|. To replace an old entry,
+% \cs{@@_put_linked_old:w} receives the expansion of that entry, and
+% it reassigns it (|#5|) using the assignment~|#6|, by simply
+% replacing the payload |#2| \cs{s_@@} |#3| by \cs{l_@@_internal_tl}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_put_linked_new:w
+ \use_none:n #1#2#3#4
+ {
+ #4 #1
+ {
+ \exp_after:wN \@@_pop_linked_prev:w #1
+ \exp_not:N #2
+ }
+ #4 #2
+ {
+ \exp_not:n { \use_none:n #1 }
+ \l_@@_internal_tl
+ \exp_not:N #3
+ }
+ #4 #3 { \exp_not:n { \use_none:n #2 } }
+ }
+\cs_new_protected:Npn \@@_put_linked_old:w
+ \use_none:n #1#2 \s_@@ #3#4#5
+ {
+ #5
+ {
+ \exp_not:n { \use_none:n #1 }
+ \l_@@_internal_tl
+ \exp_not:N #4
+ }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Property list conditionals}
+%
+% \begin{macro}[pTF, tested = m3prop004]{\prop_if_exist:N, \prop_if_exist:c}
+% Copies of the \texttt{cs} functions defined in \pkg{l3basics}.
+% \begin{macrocode}
+\prg_new_eq_conditional:NNn \prop_if_exist:N \cs_if_exist:N
+ { TF , T , F , p }
+\prg_new_eq_conditional:NNn \prop_if_exist:c \cs_if_exist:c
+ { TF , T , F , p }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[pTF, tested = m3prop003]{\prop_if_empty:N, \prop_if_empty:c}
+% \begin{macro}{\@@_if_empty_return:w}
+% A flat property list is empty if it matches \cs{c_empty_prop}. A linked
+% property list is empty if its second token (the end pointer) and last token
+% (the first key pointer) are equal. There cannot be false positives because
+% the end pointer takes the form \cs{use_none:n} \meta{pointer} while the
+% other pointers have more elaborate structure. The subtle code branch here
+% is when a non-empty flat property list is given: then \cs{@@_if_empty:w}
+% reads the whole property list as~|#1| and |#2|, |#3|, |#4| are |2|, |3|,
+% |4|, respectively.
+% \begin{macrocode}
+\prg_new_conditional:Npnn \prop_if_empty:N #1 { p , T , F , TF }
+ {
+ \if_meaning:w #1 \c_empty_prop
+ \prg_return_true:
+ \else:
+ \exp_after:wN \@@_if_empty_return:w #1
+ \@@_flatten:w 2 \s_@@ 34 \s_@@_stop
+ \fi:
+ }
+\cs_new:Npn \@@_if_empty_return:w
+ #1 \@@_flatten:w #2 \s_@@ #3#4#5 \s_@@_stop
+ {
+ \if_meaning:w #2 #4
+ \prg_return_true:
+ \else:
+ \prg_return_false:
+ \fi:
+ }
+\prg_generate_conditional_variant:Nnn \prop_if_empty:N
+ { c } { p , T , F , TF }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[pTF, tested = m3prop003]
+% {
+% \prop_if_in:Nn, \prop_if_in:NV, \prop_if_in:Ne, \prop_if_in:No,
+% \prop_if_in:cn, \prop_if_in:cV, \prop_if_in:ce, \prop_if_in:co
+% }
+% \begin{macro}[EXP]{\@@_if_in_flat:nnn}
+% For a linked prop, use \cs{@@_get_linked:w} to look up whether the control
+% sequence constructed from the prefix and the sought-after key exists; this
+% auxiliary calls \cs{use_none:n} \Arg{value} \cs{prg_return_true:} if the key
+% is found, and otherwise \cs{prg_return_false:}. For a flat prop, testing
+% expandably if a key is there requires to go through the key--value pairs one
+% by one. This is rather slow, and a faster test would be
+% \begin{verbatim}
+% \prg_new_protected_conditional:Npnn \prop_if_in:Nn #1 #2
+% {
+% \@@_split:NnTFn #1 {#2}
+% { \prg_return_true: }
+% { \prg_return_false: }
+% { ... }
+% }
+% \end{verbatim}
+% but \cs{@@_split:NnTFn} is non-expandable.
+% Instead, we use \cs{prop_map_tokens:Nn} to compare the search key to
+% each key in turn using \cs{str_if_eq:ee}, which is expandable.
+% \begin{macrocode}
+\prg_new_conditional:Npnn \prop_if_in:Nn #1#2 { p , T , F , TF }
+ {
+ \@@_if_flat:NTF #1
+ {
+ \exp_after:wN \prop_map_tokens:Nn \exp_after:wN #1
+ {
+ \exp_after:wN \@@_if_in_flat:nnn
+ \exp_after:wN { \tl_to_str:n {#2} }
+ }
+ \prg_return_false:
+ }
+ {
+ \exp_after:wN \@@_get_linked:w #1 {#2}
+ \use_none:n \prg_return_true: \prg_return_false:
+ }
+ }
+\cs_new:Npn \@@_if_in_flat:nnn #1#2#3
+ {
+ \str_if_eq:eeT {#1} {#2}
+ { \prop_map_break:n { \use_i:nn \prg_return_true: } }
+ }
+\prg_generate_conditional_variant:Nnn \prop_if_in:Nn
+ { NV , Ne , No , c , cV , ce , co } { p , T , F , TF }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Mapping over property lists}
+%
+% \begin{macro}[tested = m3prop003]
+% {
+% \prop_map_function:NN, \prop_map_function:Nc,
+% \prop_map_function:cN, \prop_map_function:cc
+% }
+% \begin{macro}{\@@_map_function:Nw}
+% We first |f|-expand to flatten~|#1| in case it was a linked list.
+% The \cs{use_i:nnn} removes the leading \cs{s_@@} \cs{@@_chk:w} of
+% the flattened prop.
+% The even-numbered arguments of \cs{@@_map_function:Nw} are keys,
+% hence have string catcodes, except at the end where they are
+% \cs{fi:} \cs{prop_map_break:}. The \cs{fi:} ends the \cs{if_false:}
+% |#|\meta{even} \cs{fi:} construction and we jump out of the loop.
+% No need for any quark test.
+% \begin{macrocode}
+\cs_new:Npn \prop_map_function:NN #1#2
+ {
+ \exp_last_unbraced:Nnf
+ \use_i:nnn { \@@_map_function:Nw #2 } #1
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \prg_break_point:Nn \prop_map_break: { }
+ }
+\cs_new:Npn \@@_map_function:Nw #1
+ \@@_pair:wn #2 \s_@@ #3
+ \@@_pair:wn #4 \s_@@ #5
+ \@@_pair:wn #6 \s_@@ #7
+ \@@_pair:wn #8 \s_@@ #9
+ {
+ \if_false: #2 \fi: #1 {#2} {#3}
+ \if_false: #4 \fi: #1 {#4} {#5}
+ \if_false: #6 \fi: #1 {#6} {#7}
+ \if_false: #8 \fi: #1 {#8} {#9}
+ \@@_map_function:Nw #1
+ }
+\cs_generate_variant:Nn \prop_map_function:NN { Nc , c , cc }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[tested = m3prop003]{\prop_map_inline:Nn, \prop_map_inline:cn}
+% Mapping in line requires a nesting level counter. Store the current
+% definition of \cs{@@_pair:wn}, and define it anew. At the end of
+% the loop, revert to the earlier definition. Note that besides pairs
+% of the form \cs{@@_pair:wn} \meta{key} \cs{s_@@} \Arg{value}, there
+% are a leading and a trailing tokens, but both are equal to
+% \cs{scan_stop:}, hence have no effect in such inline mapping.
+% Such \cs{scan_stop:} could have affected ligatures if they appeared
+% during the mapping.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_map_inline:Nn #1#2
+ {
+ \cs_gset_eq:cN
+ { @@_map_ \int_use:N \g__kernel_prg_map_int :wn } \@@_pair:wn
+ \int_gincr:N \g__kernel_prg_map_int
+ \cs_gset_protected:Npn \@@_pair:wn ##1 \s_@@ ##2 {#2}
+ \exp_last_unbraced:Nf \use_none:nn #1
+ \prg_break_point:Nn \prop_map_break:
+ {
+ \int_gdecr:N \g__kernel_prg_map_int
+ \cs_gset_eq:Nc \@@_pair:wn
+ { @@_map_ \int_use:N \g__kernel_prg_map_int :wn }
+ }
+ }
+\cs_generate_variant:Nn \prop_map_inline:Nn { c }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}[rEXP]{\prop_map_tokens:Nn, \prop_map_tokens:cn}
+% \begin{macro}{\@@_map_tokens:nw}
+% The mapping is very similar to \cs{prop_map_function:NN}.
+% The odd construction
+% |\use:n {#1}| allows |#1| to contain any token without interfering
+% with \cs{prop_map_break:}. The loop stops when the \meta{key}
+% between \cs{@@_pair:wn} and \cs{s_@@} is \cs{fi:}
+% \cs{prop_map_break:} instead of being a string.
+% \begin{macrocode}
+\cs_new:Npn \prop_map_tokens:Nn #1#2
+ {
+ \exp_last_unbraced:Nnf
+ \use_i:nnn { \@@_map_tokens:nw {#2} } #1
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \@@_pair:wn \fi: \prop_map_break: \s_@@ { }
+ \prg_break_point:Nn \prop_map_break: { }
+ }
+\cs_new:Npn \@@_map_tokens:nw #1
+ \@@_pair:wn #2 \s_@@ #3
+ \@@_pair:wn #4 \s_@@ #5
+ \@@_pair:wn #6 \s_@@ #7
+ \@@_pair:wn #8 \s_@@ #9
+ {
+ \if_false: #2 \fi: \use:n {#1} {#2} {#3}
+ \if_false: #4 \fi: \use:n {#1} {#4} {#5}
+ \if_false: #6 \fi: \use:n {#1} {#6} {#7}
+ \if_false: #8 \fi: \use:n {#1} {#8} {#9}
+ \@@_map_tokens:nw {#1}
+ }
+\cs_generate_variant:Nn \prop_map_tokens:Nn { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+%
+% \begin{macro}[tested = m3prop003]{\prop_map_break:}
+% \begin{macro}[tested = m3prop003]{\prop_map_break:n}
+% The break statements are based on the general \cs{prg_map_break:Nn}.
+% \begin{macrocode}
+\cs_new:Npn \prop_map_break:
+ { \prg_map_break:Nn \prop_map_break: { } }
+\cs_new:Npn \prop_map_break:n
+ { \prg_map_break:Nn \prop_map_break: }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Uses of mapping over property lists}
+%
+% \begin{macro}[EXP]{\prop_count:N, \prop_count:c}
+% \begin{macro}[EXP]{\@@_count:nn}
+% Counting the key--value pairs in a property list is done using the
+% same approach as for other count functions: turn each entry into a
+% \texttt{+1} then use integer evaluation to actually do the
+% mathematics.
+% \begin{macrocode}
+\cs_new:Npn \prop_count:N #1
+ {
+ \int_eval:n
+ {
+ 0
+ \prop_map_function:NN #1 \@@_count:nn
+ }
+ }
+\cs_new:Npn \@@_count:nn #1#2 { + 1 }
+\cs_generate_variant:Nn \prop_count:N { c }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}[EXP]{\prop_to_keyval:N}
+% \begin{macro}[EXP]
+% {\@@_to_keyval_exp_after:wN, \@@_to_keyval:nn, \@@_to_keyval:nnw}
+% Each property name and value pair will be returned in the form
+% \verb*| |\marg{name}\verb*|= |\marg{value}. As one of the main use cases for
+% this macro is to pass the \meta{property list} on to a key--value parser, we
+% have to make sure that the behaviour is as good as possible. Using a space
+% before the opening brace we get the correct brace stripping behaviour for
+% most of the key--value parsers available in \LaTeX{}.
+% Iterate over the
+% \meta{property list} and remove the leading comma afterwards. Only the value
+% has to be protected in \cs{__kernel_exp_not:w} as the property name is
+% always a string. After the loop the leading comma is removed by
+% \cs{use_none:n} and afterwards \cs{__kernel_exp_not:w} eventually finds the
+% opening brace of its argument.
+% \begin{macrocode}
+\cs_new:Npn \prop_to_keyval:N #1
+ {
+ \__kernel_exp_not:w
+ \prop_if_empty:NTF #1
+ { {} }
+ {
+ \exp_after:wN \exp_after:wN \exp_after:wN
+ {
+ \tex_expanded:D
+ {
+ \exp_not:N \use_none:n
+ \prop_map_function:NN #1 \@@_to_keyval:nn
+ }
+ }
+ }
+ }
+\cs_new:Npn \@@_to_keyval:nn #1#2
+ { , ~ {#1} =~ { \__kernel_exp_not:w {#2} } }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \subsection{Viewing property lists}
+%
+% \begin{macro}[tested = m3show001]
+% {\prop_show:N, \prop_show:c, \prop_log:N, \prop_log:c}
+% \begin{macro}{\@@_show:NN, \@@_show_finally:NNn, \@@_show_prepare:w, \@@_show_loop:NNw, \@@_show_bad_name:NNN, \@@_show_end:NNN, \@@_show_loop_key:wNNN}
+% \begin{macro}[rEXP]{\@@_show_flat:w, \@@_show_linked:w}
+% Experience shows one source of problems is very hard to debug: when
+% a data structure such as a |seq| or~|prop| gets corrupted. In the
+% past, \cs{prop_show:N} would in some cases happily show items of
+% such a |prop|, even though other more demanding \pkg{l3prop}
+% functions would choke. It is thus best to make \cs{prop_show:N}
+% check very thoroughly the structure and flag issues, even though
+% that is very painful for linked props. Throughout the code below,
+% we strive to remain as safe as possible, but in the explanations we
+% only state what the arguments are when the prop is correctly formed,
+% rather than saying at every step that various arguments can be
+% arbitrary junk, made safe by using \cs{tl_to_str:n} generously.
+%
+% The general \cs{__kernel_chk_tl_type:NnnT} checks that its first
+% argument is a token list, and if it is, then it \texttt{e}-expands
+% its second argument and compares with the contents of its first
+% argument. Thus, within this \texttt{e}-expansion it is safe to use
+% \cs{@@_if_flat:NTF} to check if the prop is flat or linked. In the
+% flat case we simply reconstruct the expected structure using
+% \cs{@@_show_flat:w}, which loops through the prop and correctly
+% turns all keys to strings for instance. In the linked case, we use
+% \cs{@@_show_linked:w}, which ensures the form \cs{@@_flatten:w}
+% \cs[no-index]{@@~\meta{prefix}} \cs{s_@@} \Arg{prefix} \meta{rest},
+% where \meta{prefix} is made into a string and \meta{rest} cannot be
+% a brace group or multiple tokens since \cs{@@_show_linked:w} would
+% in such cases give a different result from the original token list.
+% \begin{macrocode}
+\cs_new_protected:Npn \prop_show:N { \@@_show:NN \msg_show:nneeee }
+\cs_generate_variant:Nn \prop_show:N { c }
+\cs_new_protected:Npn \prop_log:N { \@@_show:NN \msg_log:nneeee }
+\cs_generate_variant:Nn \prop_log:N { c }
+\cs_new_protected:Npn \@@_show:NN #1#2
+ {
+ \__kernel_chk_tl_type:NnnT #2 { prop }
+ {
+ \@@_if_flat:NTF #2
+ {
+ \s_@@ \@@_chk:w
+ \exp_after:wN \@@_show_flat:w #2
+ \s_@@ { }
+ \@@_pair:wn \q_@@_recursion_tail \s_@@ { }
+ \q_@@_recursion_stop
+ }
+ { \exp_after:wN \@@_show_linked:w #2 \s_@@ ! ? \s_@@_stop }
+ }
+ {
+ \@@_if_flat:NTF #2
+ { \@@_show_finally:NNn #1 #2 { flat } }
+ {
+ \tl_set:Nn \l_@@_internal_tl { #1 #2 }
+ \exp_after:wN \@@_show_prepare:w #2 #2
+ }
+ }
+ }
+\cs_new:Npn \@@_show_flat:w #1 \@@_pair:wn #2 \s_@@ #3
+ {
+ \@@_if_recursion_tail_stop:n {#2}
+ \exp_not:N \@@_pair:wn \tl_to_str:n {#2} \s_@@ \exp_not:n { {#3} }
+ \@@_show_flat:w
+ }
+\cs_new:Npn \@@_show_linked:w #1 \s_@@ #2#3#4 \s_@@_stop
+ {
+ \exp_not:N \@@_flatten:w
+ \exp_not:c { @@ ~ \tl_to_str:n {#2} }
+ \s_@@ { \tl_to_str:n {#2} }
+ \exp_not:n {#3}
+ }
+% \end{macrocode}
+% For flat props we are done by using \cs{msg_show:nneeee} or
+% \cs{msg_log:nneeee}. The auxiliary \cs{@@_show_finally:NNn} is
+% eventually also used in the linked case after some more tests. To
+% avoid having to bring along the message function and the property
+% list, we store them into \cs{l_@@_internal_tl}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_finally:NNn #1#2#3
+ {
+ #1 { prop } { show }
+ { \token_to_str:N #2 }
+ { \prop_map_function:NN #2 \msg_show_item:nn }
+ {#3} { }
+ }
+% \end{macrocode}
+% For linked props, we now know they have a reasonable form so that we
+% are calling \cs{@@_show_prepare:w} \cs{@@_flatten:w}
+% \cs[no-index]{@@~\meta{prefix}} \cs{s_@@} \Arg{prefix} \meta{token}
+% \meta{property list}, and the task is to loop through the linked
+% list and check integrity. We first set things up: the auxiliary
+% \cs{@@_tmp:w} will be in charge of checking that various tokens
+% start with \cs[no-index]{@@~\meta{prefix}} (in the sense of string
+% representations), and calling one of \cs{@@_show_loop_key:wNNN},
+% \cs{@@_show_end:NNN}, \cs{@@_show_bad_name:NNN}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_prepare:w
+ \@@_flatten:w #1 \s_@@ #2#3#4
+ {
+ \use:e
+ {
+ \cs_set_nopar:Npn \exp_not:N \@@_tmp:w
+ ##1 \token_to_str:N #1 ##2 \s_@@_mark ##3 \s_@@_stop
+ {
+ \exp_not:N \tl_if_empty:nTF {##1}
+ {
+ \exp_not:N \tl_if_head_is_space:nTF {##2}
+ { \exp_not:N \exp_args:Nf \@@_show_loop_key:wNNN }
+ { \exp_not:N \tl_if_empty:nTF }
+ {##2}
+ }
+ { \exp_not:N \use_ii:nn }
+ \@@_show_end:NNN
+ \@@_show_bad_name:NNN
+ }
+ }
+ \exp_last_unbraced:NNNo \@@_show_loop:NNw #1 #4 #4
+ }
+% \end{macrocode}
+% The loop will consist of calls to \cs{@@_show_loop:NNw}
+% \cs[no-index]{@@~\meta{prefix}} \meta{token} \meta{expansion}, where
+% \meta{token} is one of the items in the list, specifically the key
+% container for \meta{key$_{i-1}$} (starting at $i=1$ with the
+% property list variable itself), and \meta{expansion} stands for the
+% expansion of that token, which has already been checked, and takes
+% the form \meta{junk} \cs{s_@@} \Arg{value}
+% \cs[no-index]{@@~\meta{prefix}~\meta{key_i}}. Thus, the loop
+% auxiliary receives the prefix command as |#1|, and the $(i-1)$-th
+% and $i$-th key containers as |#2| and~|#5|. Then \cs{@@_tmp:w}
+% checks that the name of the $i$-th key container is valid.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_loop:NNw #1#2 #3 \s_@@ #4#5
+ {
+ \exp_last_two_unbraced:Noo \@@_tmp:w
+ { \token_to_str:N #5 \s_@@_mark }
+ { \token_to_str:N #1 \s_@@_mark \s_@@_stop }
+ #1 #2 #5
+ }
+% \end{macrocode}
+% If the $i$-th key container has the wrong name we get
+% \cs{@@_show_bad_name:NNN} \cs[no-index]{@@~\meta{prefix}}
+% \meta{previous container} \meta{current container with bad name}.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_bad_name:NNN #1#2#3
+ {
+ \msg_error:nneeee { prop } { bad-link }
+ { \tl_tail:N \l_@@_internal_tl }
+ { \token_to_str:N #2 }
+ { \token_to_str:N #3 }
+ { \token_to_str:N #1 }
+ }
+% \end{macrocode}
+% If the $i$-th key container has the name
+% \cs[no-index]{@@~\meta{prefix}} (without space), it is the trailing
+% one. We check that it is the right kind of macro to be a token
+% list, and that it has the right contents \cs{use_none:n}
+% \meta{previous container}. If so, we are done checking everything,
+% and we display the property list using the message function and
+% property list name stored in \cs{l_@@_internal_tl}. Note that we
+% also use this \cs{l_@@_internal_tl} in the type argument of
+% \cs{__kernel_chk_tl_type:NnnT}, to build up the name
+% \enquote{\meta{property list} prop entry} used in error messages.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_end:NNN #1#2#3
+ {
+ \__kernel_chk_tl_type:NnnT #3
+ { \tl_tail:N \l_@@_internal_tl prop~entry }
+ { \exp_not:n { \use_none:n #2 } }
+ {
+ \exp_after:wN \@@_show_finally:NNn
+ \l_@@_internal_tl { linked }
+ }
+ }
+% \end{macrocode}
+% If the $i$-th container has a name \cs[no-index]{@@~\meta{prefix}
+% \meta{key}} (with a space before the key), then we have a call to
+% \cs{@@_show_loop_key:wNNN} \Arg{key} \meta{junk_1} \meta{junk_2}
+% \cs[no-index]{@@~\meta{prefix}} \meta{previous container}
+% \meta{current container}. (with an \texttt{f}-expansion to eliminate
+% the space). The first argument is the \meta{key} without a leading
+% space, thanks to a judicious \texttt{f}-expansion earlier on. We
+% check that the \meta{current container} is a token list with the
+% expected structure \cs{use_none:n} \meta{previous container}
+% \cs{@@_pair:wn} \meta{string} \cs{s_@@} \Arg{anything} \meta{single
+% token}. The auxiliary \cs{@@_show_flat:w} is reused to produce the
+% \cs{@@_pair:wn} part, and the last token is produced by
+% \cs{tl_item:Nn} (we don't waste a specialized auxiliary to speed
+% that up). If the check succeed, move on to the next item.
+% \begin{macrocode}
+\cs_new_protected:Npn \@@_show_loop_key:wNNN #1#2#3#4#5#6
+ {
+ \__kernel_chk_tl_type:NnnT #6
+ { \tl_tail:N \l_@@_internal_tl prop~entry }
+ {
+ \exp_not:n { \use_none:n #5 }
+ \exp_after:wN \@@_show_flat:w #6 \s_@@ { }
+ \@@_pair:wn \q_@@_recursion_tail \s_@@ { }
+ \q_@@_recursion_stop
+ \tl_item:Nn #6 { -1 }
+ }
+ { \exp_last_unbraced:NNNo \@@_show_loop:NNw #4 #6 #6 }
+ }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macrocode}
+%</package>
+% \end{macrocode}
+%
+% \end{implementation}
+%
+% \PrintIndex