expkv.dtx

% \iffalse meta-comment
%
% File: expkv.dtx Copyright (C) 2020-2021 Jonathan P. Spratte
%
% This work  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:
%
%   http://www.latex-project.org/lppl.txt
%
% ------------------------------------------------------------------------------
%
%<*driver>^^A>>=
\def\nameofplainTeX{plain}
\ifx\fmtname\nameofplainTeX\else
  \expandafter\begingroup
\fi
\input l3docstrip.tex
\askforoverwritefalse
\preamble

--------------------------------------------------------------
expkv -- an expandable key=val implementation
E-mail: jspratte@yahoo.de
Released under the LaTeX Project Public License v1.3c or later
See http://www.latex-project.org/lppl.txt
--------------------------------------------------------------

Copyright (C) 2020-2021 Jonathan P. Spratte

This  work 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:

  http://www.latex-project.org/lppl.txt

This work is "maintained" (as per LPPL maintenance status) by
  Jonathan P. Spratte.

This work consists of the file  expkv.dtx
and the derived files           expkv.pdf
                                expkv.sty
                                expkv.tex
                                t-expkv.tex

\endpreamble
% stop docstrip adding \endinput
\postamble
\endpostamble
\generate{\file{expkv.sty}{\from{expkv.dtx}{pkg}}}
\generate{\file{expkv.tex}{\from{expkv.dtx}{tex}}}
\generate{\file{t-expkv.tex}{\from{expkv.dtx}{ctx}}}
\ifx\fmtname\nameofplainTeX
  \expandafter\endbatchfile
\else
  \expandafter\endgroup
\fi
%
\IfFileExists{expkv.tex}{\input{expkv.tex}}{}
\ProvidesFile{expkv.dtx}
  [\csname ekvDate\endcsname\ an expandable key=val implementation]
\PassOptionsToPackage{full}{textcomp}
\documentclass{l3doc}
\RequirePackage[oldstylenums,nott]{kpfonts}
\input{glyphtounicode}
\pdfgentounicode=1
\RequirePackage{xfp} ^^A required for an example
\RequirePackage{listings}
\RequirePackage{booktabs}
\RequirePackage{array}
\RequirePackage{collcell}
\RequirePackage{siunitx}
\DeclareSIUnit\ops{ops}
\RequirePackage{xcolor}
\RequirePackage{caption}
\RequirePackage{microtype}
\RequirePackage{accsupp}
\RequirePackage{enumitem}
\RequirePackage{tcolorbox}
\newtcolorbox{exresult}[2][]
  {colback=expkvgrey!10!white,colframe=expkvgrey,fontupper=\small,width={#2},#1}
\newtcbox\exres[1][]
  {
     colback=expkvgrey!10!white
    ,colframe=expkvgrey
    ,size=small
    ,nobeforeafter
    ,tcbox raise base
    ,fontupper=\small
    ,#1
  }
\def\mylstwd{.55em}
\lstdefinelanguage{expkv}[primitive]{TeX}
  {
    ,moretexcs=[4]^^A e-TeX
      {
        expanded,
        numexpr,
        protected,
        unexpanded,
      }
    ,moretexcs=[5]^^A plain/LaTeX/ConTeXt
      {
        approx,
        begin,
        empty,
        item,
        LaTeX,
        makeatletter,makeatother,
        newcommand,newdimen,
        RequirePackage,
        rule,
        TeX,
        textit,texttt,
        usepackage,
        usemodule,
        @gobble,@gobbletwo,
      }
    ,moretexcs=[6]^^A used packages
      {
        ^^A xfp
        fpeval,
        ^^A keyval
        setkeys,
        ^^A yax
        defactiveparameter,storevalue,setparameterlist
      }
    ,moretexcs=[2]^^A expkv macros
      {
        ekvdef,ekvdefNoVal,^^A
        ekvlet,ekvletNoVal,ekvletkv,ekvletkvNoVal,^^A
        ekvdefunknown,ekvdefunknownNoVal,^^A
        ekvletunknown,ekvletunknownNoVal,^^A
        ekvredirectunknown,ekvredirectunknownNoVal,^^A
        ekvset,ekvsetSneaked,^^A
        ekvsetdef,ekvsetSneakeddef,ekvsetdefSneaked,^^A
        ekvparse,^^A
        ekvVersion,ekvDate,^^A
        ekvifdefined,ekvifdefinedNoVal,ekvifdefinedset,^^A
        ekvbreak,ekvbreakPreSneak,ekvbreakPostSneak,^^A
        ekvsneak,ekvsneakPre,^^A
        ekvchangeset,^^A
        ekvoptarg,ekvoptargTF,^^A
        ekvcsvloop,^^A
        ekverr,^^A
        ekv@name,^^A
      }
    ,moretexcs=[3]^^A expkv-pkg macros
      {
        ^^A expkv-cs
        ekvcSecondaryKeys,ekvcSplitAndForward,
        ^^A expkv-def
        ekvdefinekeys
      }
  }
\colorlet{codeparam}{cyan!65!black}
\lstset
  {
    ,language=expkv
    ,flexiblecolumns=false
    ,basewidth=\mylstwd
    ,gobble=2
    ,basicstyle=\fontfamily{jkp}\itshape
    ,texcsstyle=*[1]{\bfseries\color{expkvgrey}} ^^A primitives
    ,texcsstyle=*[2]{\bfseries\color{expkvred}}  ^^A expkv
    ,texcsstyle=*[3]{\color{expkvred}}           ^^A expkv-pkg
    ,texcsstyle=*[4]{\bfseries\color{expkvgrey}} ^^A e-TeX
    ,texcsstyle=*[5]{\bfseries\color{expkvgrey}} ^^A plain/LaTeX macros
    ,texcsstyle=*[6]{}                           ^^A macros of other packages
    ,commentstyle=\color[gray]{0.4}
    ,literate=
              {\{} {{\CodeUpBf\{}}{1}
              {\}} {{\CodeUpBf\}}}{1}
              {$}  {{\CodeUpBf\$}}{1}
              {[}  {{\CodeUp[}}{1}
              {]}  {{\CodeUp]}}{1}
              {(}  {{\CodeUp(}}{1}
              {)}  {{\CodeUp)}}{1}
              {*}  {{$*$}}{1}
              {1}  {{\CodeUp{1}}}{1}
              {2}  {{\CodeUp{2}}}{1}
              {3}  {{\CodeUp{3}}}{1}
              {4}  {{\CodeUp{4}}}{1}
              {5}  {{\CodeUp{5}}}{1}
              {6}  {{\CodeUp{6}}}{1}
              {7}  {{\CodeUp{7}}}{1}
              {8}  {{\CodeUp{8}}}{1}
              {9}  {{\CodeUp{9}}}{1}
              {0}  {{\CodeUp{0}}}{1}
              {##} {{\CodeColored{codeparam}{1}{\#}}}{1}
              {##1}{{\CodeColored{codeparam}{2}{\#1}}}{2}
              {##2}{{\CodeColored{codeparam}{2}{\#2}}}{2}
              {##3}{{\CodeColored{codeparam}{2}{\#3}}}{2}
              {##4}{{\CodeColored{codeparam}{2}{\#4}}}{2}
              {##5}{{\CodeColored{codeparam}{2}{\#5}}}{2}
              {##6}{{\CodeColored{codeparam}{2}{\#6}}}{2}
              {##7}{{\CodeColored{codeparam}{2}{\#7}}}{2}
              {##8}{{\CodeColored{codeparam}{2}{\#8}}}{2}
              {##9}{{\CodeColored{codeparam}{2}{\#9}}}{2}
              {<key>}{{$\langle$}key{$\rangle$}}{5}
              {<set>}{{$\langle$}set{$\rangle$}}{5}
              {<set1>}{{$\langle$}set1{$\rangle$}}{6}
              {<set2>}{{$\langle$}set2{$\rangle$}}{6}
    ^^A,literate=*{<key>}{\key}{4}{<set>}{\set}{4}
  }
\newcommand*\CodeColored[3]{\textcolor{#1}{\makebox[\dimexpr\mylstwd*#2]{#3}}}
\newcommand*\CodeUpBf[1]{\makebox[\mylstwd]{\textup{\textbf{#1}}}}
\newcommand*\CodeUp[1]{\makebox[\mylstwd]{\textup{#1}}}
\RequirePackage{randtext}
\let\metaORIG\meta
\protected\def\meta #1{\texttt{\metaORIG{#1}}}
\renewcommand*\thefootnote{\fnsymbol{footnote}}
\definecolor{expkvred}{HTML}{9F393D}
\colorlet{expkvgrey}{black!75}
\makeatletter
\newcommand*\example{\par\smallskip\noindent\textit{Example:} \ignorespaces}
\newcommand*\expFormat
  {^^A
    {^^A
      \rmfamily
      \bfseries
      {\color{expkvgrey}e\kern-.05em x\kern-.05em}^^A
      \lower.493ex\hbox{{\color{expkvgrey}P}}^^A
    }^^A
  }
\newcommand*\kvstyle
  {^^A
    \normalfont\rmfamily\bfseries\color{expkvred}^^A
  }
\newcommand*\expkv
  {^^A
    \texorpdfstring
      {^^A
        \mbox
          {^^A
            \BeginAccSupp{ActualText=expkv}^^A
            \href{https://github.com/Skillmon/tex_expkv}
              {^^A
                \rmfamily
                \bfseries
                {\color{expkvgrey}e\kern-.05em x\kern-.05em}^^A
                \lower.493ex
                  \hbox{{\color{expkvgrey}P}\kern-.1em{\color{expkvred}k}}^^A
                \kern-.18em{\color{expkvred}v}^^A
              }^^A
            \EndAccSupp{}^^A
          }^^A
      }
      {expkv}^^A
  }
\newcommand*\expkvpkg[1]
  {^^A
    \texorpdfstring
      {^^A
        \mbox
          {^^A
            \BeginAccSupp{ActualText=expkv-#1}^^A
            \href{https://github.com/Skillmon/tex_expkv-#1}
              {^^A
                \rmfamily
                \bfseries
                {\color{expkvgrey}e\kern-.05em x\kern-.05em}^^A
                \lower.493ex
                  \hbox{{\color{expkvgrey}P}\kern-.1em{\color{expkvred}k}}^^A
                \kern-.18em{\color{expkvred}v}^^A
                {\color{expkvgrey}^^A
                  \kern.05em\rule[-.1ex]{.08em}{1.2ex}\kern.05em\textsc{#1}^^A
                }^^A
              }^^A
            \EndAccSupp{}^^A
          }^^A
      }
      {expkv-#1}^^A
  }
\newcommand*\expkvd{\expkvpkg{def}}
\newcommand*\expkvc{\expkvpkg{cs}}
\newcommand*\expkvo{\expkvpkg{opt}}
\ExplSyntaxOn
\newcommand*\pkglogo[1]
  {
    \texorpdfstring
      {
        \mbox
          {
            \BeginAccSupp{ActualText=#1}
            \rmfamily
            \str_case:nn {#1}
              {
                {yax}
                  {
                    Y\kern-.1em
                    \raise.15em\hbox{\scshape a}
                    \kern-.1em \lower.15em\hbox{X}%
                  }
              }
            \EndAccSupp{}
          }
      }
      {#1}
  }
\newcommand*\yax{\pkglogo{yax}}
\ExplSyntaxOff
\newcommand\kv{\meta{key}=\meta{value}}
\newcommand\key{\meta{key}}
\newcommand\val{\meta{value}}
\newcommand\set{\meta{set}}
\hypersetup{linkcolor=red!80!black,urlcolor=purple!80!black}
\DoNotIndex{\directlua}
\DoNotIndex{\def,\edef,\,,\=,\begingroup,\catcode,\chardef,\csname,\endcsname}
\DoNotIndex{\endgroup,\endinput,\errmessage,\expandafter,\input,\let,\long}
\DoNotIndex{\protected,\ProvidesFile,\ProvidesPackage,\relax,\space}
\DoNotIndex{\^,\@,\unexpanded,\string,\expanded,\detokenize,\meaning}
\DoNotIndex{\lastnamedcs,\romannumeral,\z@}
\DoNotIndex{\noexpand,\normalexpanded,\normalunexpanded}
\DoNotIndex{\par,\protect}
\DoNotIndex{\unprotect}
\DoNotIndex{\writestatus}
\DoNotIndex{\ifcsname}
\DoNotIndex{\ifx}
\DoNotIndex{\iffalse}
\DoNotIndex{\ifnum}
\DoNotIndex{\else}
\DoNotIndex{\fi}
\@gobble\fi ^^A ignoring \ifx etc., but only one \fi
\@gobble\fi ^^A ignoring \ifx etc., but only one \fi
\@gobble\fi ^^A ignoring \ifx etc., but only one \fi
\@ifdefinable\gobbledocstriptag{\def\gobbledocstriptag#1>{}}
\newcommand*\pmso[1] ^^A poor man's strike out
  {^^A
    \leavevmode
    \begingroup
      \sbox0{#1}^^A
      \rlap{\vrule height .6ex depth -.5ex width \wd0\relax}^^A
      \usebox0\relax
    \endgroup
  }
\makeatother
\begin{document}
  \title
    {^^A
      \texorpdfstring
        {^^A
          \huge\expkv
          \\[\medskipamount]
          \Large an {\expFormat}andable
          \meta{{\kvstyle k}\kern-.05em ey}=^^A
          \meta{{\kvstyle v}\kern-.05em alue}
          implementation^^A
        }{expkv - an expandable <key>=<value> implementation}^^A
    }
  \date{\ekvDate\space v\ekvVersion}
  \author{Jonathan P. Spratte\thanks{\protect\randomize{jspratte@yahoo.de}}}
  \DocInput{expkv.dtx}
\end{document}
%</driver>^^A=<<
% \fi
%
% \maketitle
% \renewcommand*\thefootnote{\arabic{footnote}}
%
% \begin{abstract}
% \noindent\parfillskip=0pt
% \expkv\ provides a small interface for \kv\ parsing. The parsing macro is
% \emph{fully expandable}, the \meta{code} of your keys might be not. \expkv\ is
% \emph{swift}, close to the fastest \kv\ implementation. However it is the
% fastest which copes with active commas and equal signs and doesn't strip
% braces accidentally.
% \end{abstract}
%
% \tableofcontents
%
% \begin{documentation}^^A>>=
%
% \section{Documentation}
%
% \expkv\ provides an expandable \kv\ parser. The \kv\ pairs should be given as
% a comma separated list and the separator between a \key\ and the associated
% \val\ should be an equal sign. Both, the commas and the equal signs, might be
% of category 12 (other) or 13 (active). To support this is necessary as for
% example \pkg{babel} turns characters active for some languages, for instance
% the equal sign is turned active for Turkish.
%
% \expkv\ is usable as generic code, as a \LaTeX\ package or as a \ConTeXt\
% module. To use it, just use one of:
% \begin{lstlisting}
% \input expkv       % plainTeX
% \usepackage{expkv} % LaTeX
% \usemodule[expkv]  % ConTeXt
% \end{lstlisting}
% Both the \LaTeX\ package and the \ConTeXt\ module don't do more than
% \file{expkv.tex}, except calling |\ProvidesPackage| and setting things up such
% that \file{expkv.tex} will use |\ProvidesFile|, or printing some status
% information. The \ConTeXt\ support is not thoroughly tested, though (since I
% don't use \ConTeXt\ myself I don't know if there are additional pitfalls I
% wasn't aware of).
%
% In the \expkv\ family are other packages contained which provide additional
% functionality. Those packages currently are:
% \begin{description}[format=\expkvpkg]
%   \item[def]
%     a key-defining frontend for \expkv\ using a \kv\ syntax
%   \item[cs]
%     define expandable \kv\ macros using \expkv
%   \item[opt]
%     parse package and class options with \expkv
% \end{description}
% Note that while the package names are stylised with a vertical rule, their
% names are all lower case with a hyphen (\emph{e.g.}, \file{expkv-def}).
%
% A list of concise comparisons to other \kv\ packages is contained in
% \autoref{sec:cmp}.
%
% \subsection{Setting up Keys}\label{sec:define}
% \expkv\ provides a rather simple approach to setting up keys, similar to
% \pkg{keyval}. However there is an auxiliary package named \expkvd\ which
% provides a more sophisticated interface, similar to well established packages
% like \pkg{pgfkeys} or \pkg{l3keys}.
%
% Keys in \expkv\ (as in almost all other \kv\ implementations) belong to a
% \emph{set} such that different sets can contain keys of the same name. Unlike
% many other implementations \expkv\ doesn't provide means to set a default
% value, instead we have keys that take values and keys that don't (the latter
% are called |NoVal| keys by \expkv), but both can have the same name (on the
% user level).
%
% The following macros are available to define new keys. Those macros containing
% ``|def|'' in their name can be prefixed by anything allowed to prefix |\def|
% (but \emph{don't} use |\outer|, keys defined with it won't ever be usable),
% prefixes allowed for |\let| can prefix those with ``|let|'' in their name,
% accordingly. Neither \set\ nor \key\ are allowed to be empty for new keys.
% \set\ will be used as is inside of |\csname ...\endcsname| and \key\ will get
% |\detokenize|d. Also \set\ should not contain an explicit |\par| token.
%
% \begin{function}{\ekvdef}
%   \begin{syntax}
%     \cs{ekvdef}\marg{set}\marg{key}\marg{code}
%   \end{syntax}
%   Defines a \key\ taking a value in a \set\ to expand to \meta{code}. In
%   \meta{code} you can use |#1| to refer to the given value.
% \end{function}
% \example Define |text| in |foo| to store the value inside |\foo@text|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \protected\long\ekvdef{foo}{text}{\def\foo@text{#1}}
% \end{lstlisting}
%
% \begin{function}{\ekvdefNoVal}
%   \begin{syntax}
%     \cs{ekvdefNoVal}\marg{set}\marg{key}\marg{code}
%   \end{syntax}
%   Defines a no value taking \key\ in a \set\ to expand to \meta{code}.
% \end{function}
% \example Define |bool| in |foo| to set |\iffoo@bool| to |true|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \protected\ekvdefNoVal{foo}{bool}{\foo@booltrue}
% \end{lstlisting}
%
% \begin{function}{\ekvlet}
%   \begin{syntax}
%     \cs{ekvlet}\marg{set}\marg{key}\meta{cs}
%   \end{syntax}
%   Let the value taking \key\ in \set\ to \meta{cs}, there are no checks on
%   \meta{cs} enforced, but the code should expect the value as a single braced
%   argument directly following it.
% \end{function}
% \example Let |cmd| in |foo| do the same as |\foo@cmd|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvlet{foo}{cmd}\foo@cmd
% \end{lstlisting}
%
% \begin{function}{\ekvletNoVal}
%   \begin{syntax}
%     \cs{ekvletNoVal}\marg{set}\marg{key}\meta{cs}
%   \end{syntax}
%   Let the no value taking \key\ in \set\ to \meta{cs}, it is not checked
%   whether \meta{cs} exists or that it takes no parameter.
% \end{function}
% \example See above.
%
% \begin{function}{\ekvletkv}
%   \begin{syntax}
%     \cs{ekvletkv}\marg{set}\marg{key}\marg{set2}\marg{key2}
%   \end{syntax}
%   Let the \key\ in \set\ to \meta{key2} in \meta{set2}, it is not checked
%   whether that second key exists (but take a look at
%   \cs[no-index]{ekvifdefined}).
% \end{function}
% \example Let |B| in |bar| be an alias for |A| in |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvletkv{bar}{B}{foo}{A}
% \end{lstlisting}
%
% \begin{function}{\ekvletkvNoVal}
%   \begin{syntax}
%     \cs{ekvletkvNoVal}\marg{set}\marg{key}\marg{set2}\marg{key2}
%   \end{syntax}
%   Let the \key\ in \set\ to \meta{key2} in \meta{set2}, it is not checked
%   whether that second key exists (but take a look at
%   \cs[no-index]{ekvifdefinedNoVal}).
% \end{function}
% \example See above.
%
% \begin{function}{\ekvdefunknown}
%   \begin{syntax}
%     \cs{ekvdefunknown}\marg{set}\marg{code}
%   \end{syntax}
%   By default an error will be thrown if an unknown \key\ is encountered. With
%   this macro you can define \meta{code} that will be executed for a given
%   \set\ when an unknown \key\ with a \val\ was encountered instead of throwing
%   an error. You can refer to the given \val\ with |#1| and to the unknown
%   \key's name with |#2| in \meta{code}.\footnotemark{}
%   |\ekvdefunknown| and |\ekvredirectunknown| are mutually exclusive,
%   you can't use both.
% \end{function}
% \footnotetext{That order is correct, this way the code is faster.}
% \example Also search |bar| for undefined keys of set |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \long\ekvdefunknown{foo}{\ekvset{bar}{#2={#1}}}
% \end{lstlisting}
% This example differs from using |\ekvredirectunknown{foo}{bar}| (see below) in
% that also the unknown-key handler of the |bar| set will be triggered, error
% messages for undefined keys will look different, and this is slower than using
% |\ekvredirectunknown|.
%
% \begin{function}{\ekvdefunknownNoVal}
%   \begin{syntax}
%     \cs{ekvdefunknownNoVal}\marg{set}\marg{code}
%   \end{syntax}
%   As already explained for \cs[no-index]{ekvdefunknown}, \expkv\ would throw
%   an error when encountering an unknown \key. With this you can instead let it
%   execute \meta{code} if an unknown |NoVal| \key\ was encountered. You can
%   refer to the given \key\ with |#1| in \meta{code}.
%   |\ekvdefunknownNoVal| and |\ekvredirectunknownNoVal| are mutually exclusive,
%   you can't use both.
% \end{function}
% \example Also search |bar| for undefined keys of set |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvdefunknownNoVal{foo}{\ekvset{bar}{#1}}
% \end{lstlisting}
%
% \begin{function}{\ekvletunknown}
%   \begin{syntax}
%     \cs{ekvletunknown}\marg{set}\meta{cs}
%   \end{syntax}
%   This has the same effect as \cs[no-index]{ekvdefunknown} (so suppresses
%   errors) but instead of defining a new macro the unknown handler is let to
%   \meta{cs} which should take two arguments (the first being the \val\ the
%   second the \key).
% \end{function}
% \example Silently ignore unknown keys which were given a value in the set
% |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvletunknown{foo}\@gobbletwo
% \end{lstlisting}
%
% \begin{function}{\ekvletunknownNoVal}
%   \begin{syntax}
%     \cs{ekvletunknownNoVal}\marg{set}\meta{cs}
%   \end{syntax}
%   This will let the unknown handler used when only a \key\ without a \val\ was
%   used to \meta{cs}. \meta{cs} should be a macro taking one argument which
%   will be the \key\ name.
% \end{function}
% \example Treat every unknown \key\ in the set |foo| without a value as if
% |bar=|\key\ was used.
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \expanded
%   {%
%     \unexpanded{\ekvletunknownNoVal{foo}}%
%     \unexpanded\expandafter{\csname\ekv@name{foo}{bar}\endcsname}%
%   }
% \end{lstlisting}
% If you want to redefine the |bar| key at some point the above won't work
% (it'll keep the definition |bar| had when this was used), so you could as well
% use the slightly slower:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvdefunknownNoVal{foo}{\csname\ekv@name{foo}{bar}\endcsname{#1}}
% \end{lstlisting}
% In both cases the \key\ would be |\detokenize|d at this point, so macros
% wouldn't work idiomatically.
%
% \begin{function}{\ekvredirectunknown}
%   \begin{syntax}
%     \cs{ekvredirectunknown}\marg{set}\marg{set-list}
%   \end{syntax}
%   This is a short cut to set up a special |\ekvdefunknown| for \set\ that will
%   check each set in the comma separated \meta{set-list} for the unknown \key.
%   You can't use prefixes (so no |\long| or |\protected|) with this macro, the
%   resulting unknown-key handler will always be |\long|. The first set in the
%   \meta{set-list} has highest priority. Once the \key\ is found the remaining
%   sets are discarded, if the \key\ isn't found in any set an error will be
%   thrown eventually. Note that the error messages are affected by the use of
%   this macro, in particular, it isn't checked whether a |NoVal| key of the
%   same name is defined in order to throw an |unwanted value| error.
%   |\ekvdefunknown| and |\ekvredirectunknown| are mutually exclusive,
%   you can't use both.
% \end{function}
% \example For every key not defined in the set |foo| also search the sets |bar|
% and |baz|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvredirectunknown{foo}{bar, baz}
% \end{lstlisting}
%
% \begin{function}{\ekvredirectunknownNoVal}
%   \begin{syntax}
%     \cs{ekvredirectunknownNoVal}\marg{set}\marg{set-list}
%   \end{syntax}
%   This behaves just like |\ekvredirectunknown| and does the same but for the
%   |NoVal| keys. Again no prefixes are supported. Note that the error messages
%   are affected by the use of this macro, in particular, it isn't checked
%   whether a normal key of the same name is defined in order to throw a
%   |missing value| error.
%   |\ekvdefunknownNoVal| and |\ekvredirectunknownNoVal| are mutually exclusive,
%   you can't use both.
% \end{function}
% \example See above.
%
% \subsection{Parsing Keys}
%
% \begin{function}{\ekvset}
%   \begin{syntax}
%     \cs{ekvset}\marg{set}\{\kv,\ldots\}
%   \end{syntax}
%   Splits \kv\ pairs on commas. From both \key\ and \val\ up to one space is
%   stripped from both ends, if then only a braced group remains the braces are
%   stripped as well. So |\ekvset{foo}{bar=baz}| and
%   |\ekvset{foo}{ {bar}= {baz} }| will both do
%   \texttt{\cs[no-index]{\meta{foobarcode}}\{baz\}}, so you can hide commas,
%   equal signs and spaces at the ends of either \key\ or \val\ by putting
%   braces around them. If you omit the equal sign the code of the key created
%   with the |NoVal| variants described in \autoref{sec:define} will be
%   executed. If \kv\ contains more than a single unhidden equal sign, it will
%   be split at the first one and the others are considered part of the value.
%   |\ekvset| should be nestable.
%
%   |\ekvset| is currently \emph{not} alignment safe.\footnotemark\ As a result,
%   key names and values that contain an |&| must be wrapped in braces when
%   |\ekvset| is used inside an alignment (like \LaTeXe's |tabular| environment)
%   or you have to create a wrapper that ensures an alignment safe context.
% \end{function}
% \footnotetext{This might change in the future, I've not decided yet.}
% \example Parse |key=arg, key| in the set |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvset{foo}{key=arg, key}
% \end{lstlisting}
%
% \begin{function}{\ekvsetSneaked}
%   \begin{syntax}
%     \cs{ekvsetSneaked}\marg{set}\marg{sneak}\{\kv,\ldots\}
%   \end{syntax}
%   Just like \cs[no-index]{ekvset}, this macro parses the \kv\ pairs within the
%   given \set. But \cs[no-index]{ekvsetSneaked} will behave as if
%   \cs[no-index]{ekvsneak} has been called with \meta{sneak} as its argument as
%   the first action.
% \end{function}
% \example Parse |key=arg, key| in the set |foo| with |\afterwards| sneaked out:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvsetSneaked{foo}{\afterwards}{key=arg, key}
% \end{lstlisting}
%
% \begin{function}{\ekvsetdef}
%   \begin{syntax}
%     \cs{ekvsetdef}\meta{cs}\marg{set}
%   \end{syntax}
%   With this function you can define a shorthand macro \meta{cs} to parse keys
%   of a specified \set. It is always defined |\long|, but if you need to you
%   can also prefix it with |\global|. The resulting macro is faster than but
%   else equivalent to the idiomatic definition:\par
%   \texttt
%     {\string\long\string\def\meta{cs}\#1\{\string\ekvset\marg{set}\{\#1\}\}}
% \end{function}
% \example Define the macro |\foosetup| to parse keys in the set |foo| and use
% it to parse |key=arg, key|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvsetdef\foosetup{foo}
% \foosetup{key=arg, key}
% \end{lstlisting}
%
% \begin{function}{\ekvsetSneakeddef}
%   \begin{syntax}
%     \cs{ekvsetSneakeddef}\meta{cs}\marg{set}
%   \end{syntax}
%   Just like \cs[no-index]{ekvsetdef} this defines a shorthand macro \meta{cs},
%   but this macro will make it a shorthand for \cs[no-index]{ekvsetSneaked},
%   meaning that \meta{cs} will take two arguments, the first being stuff that
%   should be given to \cs[no-index]{ekvsneak} and the second the \kv\ list. The
%   resulting macro is faster than but else equivalent to the idiomatic
%   definition:\par
%   \texttt
%     {%
%       \string\long\string\def\meta{cs}\#1\#2\{^^A
%       \string\ekvsetSneaked\marg{set}\{\#1\}\{\#2\}\}^^A
%     }
% \end{function}
% \example Define the macro |\foothings| to parse keys in the set |foo| and
% accept a sneaked argument, then use it to parse |key=arg, key| and sneak
% |\afterwards|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvsetSneakeddef\foothings{foo}
% \foothings{\afterwards}{key=arg, key}
% \end{lstlisting}
%
% \begin{function}{\ekvsetdefSneaked}
%   \begin{syntax}
%     \cs{ekvsetdefSneaked}\meta{cs}\marg{set}\marg{sneaked}
%   \end{syntax}
%   And this one behaves like \cs[no-index]{ekvsetSneakeddef} but with a fixed
%   \meta{sneaked} argument. So the resulting macro is faster than but else
%   equivalent to the idiomatic definition:\par
%   \texttt
%     {%
%       \string\long\string\def\meta{cs}\#1\{^^A
%       \string\ekvsetSneaked\marg{set}\marg{sneaked}\{\#1\}\}^^A
%     }
% \end{function}
% \example Define the macro |\barthing| to parse keys in the set |bar| and
% always execute |\afterwards| afterwards, then use it to parse |key=arg, key|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvsetdefSneaked\barthing{bar}{\afterwards}
% \barthing{key=arg, key}
% \end{lstlisting}
%
% \begin{function}{\ekvparse}
%   \begin{syntax}
%     \cs{ekvparse}\marg{code1}\marg{code2}\{\kv,\ldots\}
%   \end{syntax}
%   This macro parses the \kv\ pairs and provides those list elements which are
%   only keys as an argument to \meta{code1}, and those which are a \kv\ pair
%   to \meta{code2} as two arguments. It is fully expandable as well and returns
%   each element of the parsed list in |\unexpanded|, which has no effect
%   outside of an |\expanded| or |\edef| context.
%   Also |\ekvparse| expands in exactly two steps of expansion.
%   You can use multiple tokens in \meta{code1} and \meta{code2} or just a
%   single control sequence name. In both cases the found \key\ and \val\ are
%   provided as a brace group following them.
%
%   |\ekvparse| is alignment safe, meaning that you don't have to take any
%   precautions if it is used inside an alignment context (like \LaTeXe's
%   |tabular| environment) and any key or value can contain an |&|.
%
%   |\ekvbreak|, |\ekvsneak|, and |\ekvchangeset| and their relatives don't work
%   in |\ekvparse|.  It is analogue to \pkg{expl3}'s |\keyval_parse:NNn|, but
%   not with the same parsing rules -- |\keyval_parse:NNn| throws an error on
%   multiple equal signs per \kv\ pair and on empty \key\ names in a \kv\ pair,
%   both of which |\ekvparse| doesn't deal with.
% \end{function}
% \example
% \begin{lstlisting}
% \ekvparse{\handlekey{S}}{\handlekeyval{S}}{foo = bar, key, baz={zzz}}
% \end{lstlisting}
%   would be equivalent to
% \begin{lstlisting}
% \handlekeyval{S}{foo}{bar}\handlekey{S}{key}\handlekeyval{S}{baz}{zzz}
% \end{lstlisting}
%   and afterwards |\handlekey| and |\handlekeyval| would have to further handle
%   the \key. There are no macros like these two contained in \expkv, you have
%   to set them up yourself if you want to use |\ekvparse| (of course the names
%   might differ). If you need the results of |\ekvparse| as the argument for
%   another macro, you should use |\expanded|, or expand |\ekvparse| twice, as
%   only then the input stream will contain the output above:
% \begin{lstlisting}
% \expandafter\parse\expanded{\ekvparse\k\kv{foo = bar, key, baz={zzz}}}
% \end{lstlisting}
% or
% \begin{lstlisting}
% \expandafter\expandafter\expandafter
% \parse\ekvparse\k\kv{foo = bar, key, baz={zzz}}
% \end{lstlisting}
%   would both expand to
% \begin{lstlisting}
% \parse\kv{foo}{bar}\k{key}\kv{baz}{zzz}
% \end{lstlisting}
%
% \subsection{Other Macros}
%
% \expkv\ provides some other macros which might be of interest.
%
% \begin{function}{\ekvVersion,\ekvDate}
%   These two macros store the version and date of the package.
% \end{function}
%
% \begin{function}{\ekvifdefined,\ekvifdefinedNoVal}
%   \begin{syntax}
%     \cs{ekvifdefined}\marg{set}\marg{key}\marg{true}\marg{false}
%     \cs{ekvifdefinedNoVal}\marg{set}\marg{key}\marg{true}\marg{false}
%   \end{syntax}
%   These two macros test whether there is a \key\ in \set. It is false if
%   either a hash table entry doesn't exist for that key or its meaning is
%   |\relax|.
% \end{function}
% \example Check whether the key |special| is already defined in set |foo|, if
% it isn't input a file that contains more key definitions:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvifdefined{foo}{special}{}{\input{foo.morekeys.tex}}
% \end{lstlisting}
%
% \begin{function}{\ekvifdefinedset}
%   \begin{syntax}
%     \cs{ekvifdefinedset}\marg{set}\marg{true}\marg{false}
%   \end{syntax}
%   This macro tests whether \set\ is defined (which it is if at least one key
%   was defined for it). If it is \meta{true} will be run, else \meta{false}.
% \end{function}
% \example Check whether the set |VeRyUnLiKeLy| is already defined, if so throw
% an error, else do nothing:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvifdefinedset{VeRyUnLiKeLy}
%   {\errmessage{VeRyUnLiKeLy already defined}}{}
% \end{lstlisting}
%
% \begin{function}{\ekvbreak,\ekvbreakPreSneak,\ekvbreakPostSneak}
%   \begin{syntax}
%     \cs{ekvbreak}\marg{after}
%   \end{syntax}
%   Gobbles the remainder of the current |\ekvset| macro and its argument list
%   and reinserts \meta{after}. So this can be used to break out of |\ekvset|.
%   The first variant will also gobble anything that has been sneaked out using
%   |\ekvsneak| or |\ekvsneakPre|, while |\ekvbreakPreSneak| will put
%   \meta{after} before anything that has been smuggled and |\ekvbreakPostSneak|
%   will put \meta{after} after the stuff that has been sneaked out.
% \end{function}
% \example Define a key |abort| that will stop key parsing inside the set |foo|
% and execute |\foo@aborted|, or if it got a value |\foo@aborted@with|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvdefNoVal{foo}{abort}{\ekvbreak{\foo@aborted}}
% \ekvdef{foo}{abort}{\ekvbreak{\foo@aborted@with{#1}}}
% \end{lstlisting}
%
% \begin{function}{\ekvsneak,\ekvsneakPre}
%   \begin{syntax}
%     \cs{ekvsneak}\marg{after}
%   \end{syntax}
%   Puts \meta{after} after the effects of |\ekvset|. The first variant will put
%   \meta{after} after any other tokens which might have been sneaked before,
%   while |\ekvsneakPre| will put \meta{after} before other smuggled stuff.
%   This reads and reinserts the remainder of the current |\ekvset| macro and
%   its argument list to do its job. After |\ekvset| has parsed the entire \kv\
%   list everything that has been |\ekvsneak|ed will be left in the input
%   stream. A small usage example is shown in \autoref{sec:sneakex}.
% \end{function}
% \example Define a key |secret| in the set |foo| that will sneak out
% |\foo@secretly@sneaked|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvdefNoVal{foo}{secret}{\ekvsneak{\foo@secretly@sneaked}}
% \end{lstlisting}
%
% \begin{function}{\ekvchangeset}
%   \begin{syntax}
%     \cs{ekvchangeset}\marg{new-set}
%   \end{syntax}
%   Replaces the current set with \meta{new-set}, so for the rest of the current
%   |\ekvset| call, that call behaves as if it was called with
%   \texttt{\cs[no-index]{ekvset}\marg{new-set}}. It is comparable to using
%   \texttt{\meta{key}/.cd} in \pkg{pgfkeys}.
% \end{function}
% \example Define a key |cd| in set |foo| that will change to another set as
% specified in the value, if the set is undefined it'll stop the parsing and
% throw an error as defined in the macro |\foo@cd@error|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \ekvdef{foo}{cd}
%   {\ekvifdefinedset{#1}{\ekvchangeset{#1}}{\ekvbreak{\foo@cd@error}}}
% \end{lstlisting}
%
% \begin{function}{\ekvoptarg}
%   \begin{syntax}
%     \cs{ekvoptarg}\marg{next}\marg{default}
%   \end{syntax}
%   This macro will check for a following optional argument in brackets (|[]|)
%   expandably. After the optional argument there has to be a mandatory one. The
%   code in \meta{next} should expect two arguments (the processed optional
%   argument and the mandatory one). If there was an optional argument the
%   result will be \meta{next}\marg{optional}\meta{mandatory} (so the optional
%   argument will be wrapped in braces, the mandatory argument will be
%   untouched). If there was no optional argument the result will be
%   \meta{next}\marg{default}\marg{mandatory} (so the default will be used and
%   the mandatory argument will be wrapped in braces after being read once -- if
%   it was already wrapped it is effectively unchanged).
% \end{function}
% |\ekvoptarg| expands in exactly two steps, grabs all the arguments only at the
% second expansion step, and is alignment safe. It has its limitations however.
% It can't tell the difference between |[| and |{[}|, so it doesn't work if the
% mandatory argument is a single bracket. Also if the optional argument should
% contain a nested closing bracket, the optional argument has to use nested
% braces like so: |[{arg]ument}]|.
% \example Say we have a macro that should take an optional argument defaulting
% to 1:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \newcommand\foo{\ekvoptarg\@foo{1}}
% \newcommand\@foo[2]{Mandatory: #2\par Optional: #1}
% \end{lstlisting}
%
% \begin{function}{\ekvoptargTF}
%   \begin{syntax}
%     \cs{ekvoptargTF}\marg{true}\marg{false}
%   \end{syntax}
%   This macro is similar to |\ekvoptarg|, but will result in
%   \meta{true}\marg{optional}\meta{mandatory} or \meta{false}\marg{mandatory}
%   instead of placing a default value.
% \end{function}
% |\ekvoptargTF| expands in exactly two steps, grabs all the arguments only at
% the second expansion step, and is alignment safe. It has the same limitations
% as |\ekvoptarg|.
% \example Say we have a macro that should behave differently depending on
% whether there was an optional argument or not. This could be done with:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \newcommand\foo{\ekvoptargTF\foo@a\foo@b}
% \newcommand\foo@a[2]{Mandatory: #2\par Optional: #1}
% \newcommand\foo@b[1]{Mandatory: #1\par No optional.}
% \end{lstlisting}
%
% \begin{function}{\ekvcsvloop}
%   \begin{syntax}
%     \cs{ekvcsvloop}\marg{code}\marg{csv-list}
%   \end{syntax}
%   This loops over the comma separated items in \meta{csv-list} and, after
%   stripping spaces from either end of \meta{item} and removing at most one set
%   of outer braces, leaves
%   \texttt
%     {^^A
%       \cs[no-index]{unexpanded}\hskip0pt
%       \{\hskip0pt
%         \meta{code}\hskip0pt
%         \marg{item}\hskip0pt
%       \}^^A
%     }
%   for each list item in the input stream. Blank elements are ignored (if you
%   need a blank element it should be given as |{}|). It supports both active
%   commas and commas of category other. You could consider it as a watered down
%   version of |\ekvparse|. However it is not alignment safe, which you could
%   achieve by nesting it in |\expanded| (since the braces around the argument
%   of |\expanded| will hide |&|s from \TeX's alignment parsing).
% \end{function}
% \example The following splits a comma separated list and prints it in a
% typewriter font with parentheses around each element.\\
% \begin{minipage}{.75\linewidth}
% \begin{lstlisting}
% \newcommand*\myprocessor[1]{\texttt{(#1)}}
% \ekvcsvloop\myprocessor{abc,def,ghi}\par
% \ekvcsvloop\myprocessor{1,,2,,3,,4}\par
% \end{lstlisting}
% \end{minipage}^^A
% \begin{exresult}[nobeforeafter,box align=center]{.25\linewidth}
%   \newcommand*\myprocessor[1]{\texttt{(#1)}}
%   \ekvcsvloop\myprocessor{abc,def,ghi}\par
%   \ekvcsvloop\myprocessor{1,,2,,3,,4}\par
% \end{exresult}
%
% \begin{function}{\ekverr}
%   \begin{syntax}
%     \cs{ekverr}\marg{package}\marg{message}
%   \end{syntax}
%   This macro will throw an error fully expandably.\footnotemark\ The error
%   length is limited to a total length of 69~characters, and since ten
%   characters will be added for the formatting (\verb*|! | and
%   \verb*| Error: |) that leaves us with a total length for \meta{package} plus
%   \meta{message} of 59~characters. If the message gets longer \TeX\ will only
%   display the first 69~characters and append |\ETC.| to the end.
%
%   Neither \meta{package} nor \meta{message} expand any further. Also
%   \meta{package} must not contain an explicit |\par| token or the token
%   |\thanks@jfbu|. No such restriction applies to \meta{message}.
%
%   If |^^J| is set up as the |\newlinechar| (which is the case in \LaTeXe\ but
%   not in plain \TeX\ by default) you can use that to introduce line breaks in
%   your error message. However that doesn't change the message length limit.
% \end{function}
% \footnotetext{The used mechanism was to the best of my knowledge first
% implemented by Jean-François Burnol.}
% After your own error message some further text will be placed. The
% formatting of that text will look good if |^^J| is the |\newlinechar|, else
% not so much. That text will read:
% \begin{verbatim}
% ! Paragraph ended before \<an-expandable-macro>
% completed due to above exception.  If the error
% summary is  not comprehensible  see the package
% documentation.
% I will try to recover now.  If you're in inter-
% active mode hit <return>  at the ? prompt and I
% continue hoping recovery was complete.
% \end{verbatim}
% Any clean up has to be done by you, |\ekverr| will expand to nothing after
% throwing the error message.
%
% In \ConTeXt\ this macro works differently. While still being fully expandable,
% it doesn't have the character count limitation and doesn't impose restrictions
% on \meta{package}. It will not display the additional text and adding line
% breaks is not possible.
% \example Say we set up a small calculation which works with user input. In our
% calculation we need a division, so have to watch out for division by zero. If
% we detect such a case we throw an error and do the recovery by using the
% biggest integer allowed in \TeX\ as the result.
% \begin{lstlisting}
% \newcommand*\mydivision[2]
%   {%
%     \the\numexpr
%       \ifnum\numexpr#2=0 % space here on purpose
%         \ekverr{my}{division by 0. Setting result to 2147483647.}%
%         2147483647%
%       \else
%         (#1)/(#2)%
%       \fi
%     \relax
%   }
% $(10+5)/(3-3)\approx\mydivision{10+5}{3-3}$
% \end{lstlisting}
% If that code gets executed the following will be the terminal output
% \begin{verbatim}
% Runaway argument?
% ! my Error: division by 0. Setting result to 2147483647.
% ! Paragraph ended before \<an-expandable-macro>
% completed due to above exception.  If the error
% summary is  not comprehensible  see the package
% documentation.
% I will try to recover now.  If you're in inter-
% active mode hit <return>  at the ? prompt and I
% continue hoping recovery was complete.
% <to be read again>
%                    \par
% l.15 $(10+5)/(3-3)\approx\mydivision{10+5}{3-3}
%                                                $
% ?
% \end{verbatim}
% and the output would contain
% \exres{$(10+5)/(3-3)\approx2147483647$}
% if we continued the \TeX\ run at the prompt.
%
% \bigskip
%
% \begin{function}{\ekv@name,\ekv@name@set,\ekv@name@key}
%   \begin{syntax}
%     \cs{ekv@name}\marg{set}\marg{key}
%     \cs{ekv@name@set}\marg{set}
%     \cs{ekv@name@key}\marg{key}
%   \end{syntax}
%   The names of the macros that correspond to a key in a set are build with
%   these macros. The name is built from two blocks, one that is formatting the
%   \set\ name (|\ekv@name@set|) and one for formatting the \key\ name
%   (|\ekv@name@key|). To get the actual name the argument to |\ekv@name@key|
%   must be |\detokenize|d. Both blocks are put together (with the necessary
%   |\detokenize|) by |\ekv@name|.
%   For |NoVal| keys an additional |N| gets appended irrespective of these
%   macros' definition, so their name is
%   \texttt{\cs[no-index]{ekv@name}\marg{set}\marg{key}N}.\par
%   You can use these macros to implement additional functionality or access key
%   macros outside of \expkv, but \emph{don't} change them! \expkv\ relies on
%   their exact definitions internally.
% \end{function}
% \example Execute the callback of the |NoVal| key |key| in set |foo|:
% \begin{lstlisting}[aboveskip=0pt,belowskip=0pt]
% \csname\ekv@name{foo}{key}N\endcsname
% \end{lstlisting}
%
% \subsection{Examples}
%
% \subsubsection{Standard Use-Case}
%
% Say we have a macro for which we want to create a \kv\ interface. The macro
% has a parameter, which is stored in the dimension |\ourdim| having a default
% value from its initialisation. Now we want to be able to change that dimension
% with the |width| key to some specified value. For that we'd do
% \begin{lstlisting}
% \newdimen\ourdim
% \ourdim=150pt
% \protected\ekvdef{our}{width}{\ourdim=#1\relax}
% \end{lstlisting}
% as you can see, we use the set |our| here. We want the key to behave different
% if no value is specified. In that case the key should not use its initial
% value, but be smart and determine the available space from
% \cs[no-index]{hsize}, so we also define
% \begin{lstlisting}
% \protected\ekvdefNoVal{our}{width}{\ourdim=.9\hsize}
% \end{lstlisting}
% Now we set up our macro to use this \kv\ interface
% \begin{lstlisting}
% \protected\def\ourmacro#1%
%   {\begingroup\ekvset{our}{#1}\the\ourdim\endgroup}
% \end{lstlisting}
% Finally we can use our macro like in the following\\
% \begin{minipage}{.5\linewidth}
% \begin{lstlisting}
% \ourmacro{}\par
% \ourmacro{width}\par
% \ourmacro{width=5pt}\par
% \end{lstlisting}
% \end{minipage}^^A
% \begin{exresult}[nobeforeafter,box align=center]{.5\linewidth}
%   \newdimen\ourdim\ourdim=150pt
%   \protected\ekvdef{our}{width}{\ourdim=#1\relax}^^A
%   \protected\ekvdefNoVal{our}{width}{\ourdim=.9\hsize}^^A
%   \protected\def\ourmacro#1^^A
%     {\begingroup\ekvset{our}{#1}\the\ourdim\endgroup}^^A
%   \ourmacro{}\par
%   \ourmacro{width}\par
%   \ourmacro{width=5pt}\par
% \end{exresult}
%
% \paragraph{The same keys using \protect\expkvd}
% Using \expkvd\ we can set up the equivalent key using a \kv\ interface, after
% the following we could use |\ourmacro| in the same way as above. \expkvd\ will
% allocate and initialise |\ourdim| and define the |width| key |\protected| for
% us, so the result will be exactly the same -- with the exception that the
% default will use |\ourdim=.9\hsize\relax| instead.
% \begin{lstlisting}
% \input expkv-def                 % or \usepackage{expkv-def}
% \ekvdefinekeys{our}
%   {
%     dimen    width = \ourdim,
%     qdefault width = .9\hsize,
%     initial  width = 150pt
%   }
% \end{lstlisting}
%
% \subsubsection{A Macro to Draw Rules}
%
% Another small example could be a \kv\ driven |\rule| alternative, because I
% keep forgetting the correct order of its arguments. First we define the keys
% (and initialize the macros used to store the keys):
% \begin{lstlisting}
% \makeatletter
% \newcommand*\myrule@ht{1ex}
% \newcommand*\myrule@wd{0.1em}
% \newcommand*\myrule@raise{\z@}
% \protected\ekvdef{myrule}{ht}{\def\myrule@ht{#1}}
% \protected\ekvdef{myrule}{wd}{\def\myrule@wd{#1}}
% \protected\ekvdef{myrule}{raise}{\def\myrule@raise{#1}}
% \protected\ekvdef{myrule}{lower}{\def\myrule@raise{-#1}}
% \end{lstlisting}
% Then we define a macro to change the defaults outside of |\myrule| and
% |\myrule| itself:
% \begin{lstlisting}
% \ekvsetdef\myruleset{myrule}
% \newcommand*\myrule[1][]
%   {\begingroup\myruleset{#1}\myrule@out\endgroup}
% \end{lstlisting}
% And finally the output:
% \begin{lstlisting}
% \newcommand*\myrule@out{\rule[\myrule@raise]\myrule@wd\myrule@ht}
% \makeatother
% \end{lstlisting}
% And we can use it:\\
% \begin{minipage}{.5\linewidth}
% \begin{lstlisting}
% a\myrule\par
% a\myrule[ht=2ex,lower=.5ex]\par
% \myruleset{wd=5pt}
% a\myrule
% \end{lstlisting}
% \end{minipage}^^A
% \begin{exresult}[nobeforeafter,box align=center]{.5\linewidth}
%   \makeatletter
%   \newcommand*\myrule@ht{1ex}
%   \newcommand*\myrule@wd{0.1em}
%   \newcommand*\myrule@raise{\z@}
%   \protected\ekvdef{myrule}{ht}{\def\myrule@ht{#1}}
%   \protected\ekvdef{myrule}{wd}{\def\myrule@wd{#1}}
%   \protected\ekvdef{myrule}{raise}{\def\myrule@raise{#1}}
%   \protected\ekvdef{myrule}{lower}{\def\myrule@raise{-#1}}
%   \ekvsetdef\myruleset{myrule}
%   \newcommand*\myrule[1][]{\begingroup\myruleset{#1}\myrule@out\endgroup}
%   \newcommand*\myrule@out{\rule[\myrule@raise]\myrule@wd\myrule@ht}
%   \makeatother
%   a\myrule\par
%   a\myrule[ht=2ex,lower=.5ex]\par
%   \myruleset{wd=5pt}
%   a\myrule
% \end{exresult}
%
%
% \subsubsection{An Expandable \kv\ Macro Using \cs[no-index]{ekvsneak}}
% \label{sec:sneakex}
%
% Let's set up an expandable macro, that uses a \kv\ interface. The problems
% we'll face for this are:
% \begin{enumerate}
%   \item ignoring duplicate keys
%   \item default values for keys which weren't used
%   \item providing the values as the correct argument to a macro (ordered)
% \end{enumerate}
%
% First we need to decide which \kv\ parsing macro we want to do this with,
% |\ekvset| or |\ekvparse|. For this example we also want to show the
% usage of |\ekvsneak|, hence we'll choose |\ekvset|. And we'll have to use
% |\ekvset| such that it builds a parsable list for our macro internals. To
% gain back control after |\ekvset| is done we have to put an internal of our
% macro at the start of that list, so we use an internal key that uses
% |\ekvsneakPre| after any user input.
%
% To ignore duplicates will be easy if the value of the key used last will be
% put first in the list, so the following will use |\ekvsneakPre| for the
% user-level keys. If we wanted some key for which the first usage should be the
% binding one we would use |\ekvsneak| instead for that key.
%
% Providing default values can be done in different ways, we'll use a simple
% approach in which we'll just put the outcome of our keys if they were used
% with default values before the parsing list terminator.
%
% Ordering the keys can be done simply by searching for a specific token for
% each argument which acts like a flag, so our sneaked out values will include
% specific tokens acting as markers.
%
% Now that we have answers for our technical problems, we have to decide what
% our example macro should do. How about we define a macro that calculates the
% sine of a number and rounds that to a specified precision? As a small extra
% this macro should understand input in radian and degree and the used
% trigonometric function should be selectable as well. For the hard part of this
% task (expandably evaluating trigonometric functions) we'll use the \pkg{xfp}
% package.
%
% First we set up our keys according to our earlier considerations and set up
% the user facing macro |\sine|. The end marker of the parsing list will be a
% |\sine@stop| token, which we don't need to define and we put our defaults
% right before it. The user macro |\sine| uses |\ekvoptargTF| to check for the
% optional argument short cutting to the final step if no optional argument was
% found. This way we safe some time in this case, though we have to specify the
% default values twice.
%
% \begin{lstlisting}
% \RequirePackage{xfp}
% \makeatletter
% \ekvdef{expex}{f}{\ekvsneakPre{\f{#1}}}
% \ekvdef{expex}{round}{\ekvsneakPre{\rnd{#1}}}
% \ekvdefNoVal{expex}{degree}{\ekvsneakPre{\deg{d}}}
% \ekvdefNoVal{expex}{radian}{\ekvsneakPre{\deg{}}}
% \ekvdefNoVal{expex}{internal}{\ekvsneakPre{\sine@rnd}}
% \newcommand*\sine{\ekvoptargTF\sine@args{\sine@final{sin}{d}{3}}}
% \newcommand*\sine@args[2]
%   {\ekvset{expex}{#1,internal}\rnd{3}\deg{d}\f{sin}\sine@stop{#2}}
% \end{lstlisting}
%
% Now we need to define some internal macros to extract the value of each key's
% last usage (remember that this will be the group after the first special
% flag-token). For that we use one delimited macro per key.
% \begin{lstlisting}
% \def\sine@rnd#1\rnd#2#3\sine@stop{\sine@deg#1#3\sine@stop{#2}}
% \def\sine@deg#1\deg#2#3\sine@stop{\sine@f#1#3\sine@stop{#2}}
% \def\sine@f#1\f#2#3\sine@stop{\sine@final{#2}}
% \end{lstlisting}
% After the macros |\sine@rnd|, |\sine@deg|, and |\sine@f| the macro
% |\sine@final| will see
% \texttt
%   {^^A
%     \cs[no-index]{sine@final}^^A
%     \marg{f}\marg{degree/radian}\marg{round}\marg{num}^^A
%   }.
% Now |\sine@final| has to expandably deal with those arguments such that the
% |\fpeval| macro of \pkg{xfp} gets the correct input. Luckily this is pretty
% straight forward in this example. In |\fpeval| the trigonometric functions
% have names such as |sin| or |cos| and the degree taking variants |sind| or
% |cosd|. And since the |degree| key puts a |d| in |#2| and the |radian| key
% leaves |#2| empty all we have to do to get the correct function name is stick
% the two together.
% \begin{lstlisting}
% \newcommand*\sine@final[4]{\fpeval{round(#1#2(#4),#3)}}
% \makeatother
% \end{lstlisting}
% Let's test our macro:\\
% \begin{minipage}{.75\linewidth}
%   \begin{lstlisting}[gobble=4]
%   \sine{60}\par
%   \sine[round=10]{60}\par
%   \sine[f=cos,radian]{pi}\par
%   \edef\myval{\sine[f=tan]{1}}\texttt{\meaning\myval}
%   \end{lstlisting}
% \end{minipage}^^A
% \begin{exresult}[nobeforeafter,box align=center]{.25\linewidth}
%   \makeatletter
%   \ekvdef{expex}{f}{\ekvsneakPre{\f{#1}}}^^A
%   \ekvdef{expex}{round}{\ekvsneakPre{\rnd{#1}}}^^A
%   \ekvdefNoVal{expex}{degree}{\ekvsneakPre{\deg{d}}}^^A
%   \ekvdefNoVal{expex}{radian}{\ekvsneakPre{\deg{}}}^^A
%   \ekvdefNoVal{expex}{internal}{\ekvsneakPre{\sine@rnd}}^^A
%   \newcommand*\sine{\ekvoptargTF\sine@args{\sine@final{sin}{d}{3}}}
%   \newcommand*\sine@args[2]
%     {\ekvset{expex}{#1,internal}\rnd{3}\deg{d}\f{sin}\sine@stop{#2}}
%   \def\sine@rnd#1\rnd#2#3\sine@stop{\sine@deg#1#3\sine@stop{#2}}^^A
%   \def\sine@deg#1\deg#2#3\sine@stop{\sine@f#1#3\sine@stop{#2}}^^A
%   \def\sine@f#1\f#2#3\sine@stop{\sine@final{#2}}^^A
%   \newcommand*\sine@final[4]{\fpeval{round(#1#2(#4),#3)}}^^A
%   \makeatother
%   \sine{60}\par
%   \sine[round=10]{60}\par
%   \sine[f=cos,radian]{pi}\par
%   \edef\myval{\sine[f=tan]{1}}\texttt{\meaning\myval}
% \end{exresult}
%
% \paragraph{The same macro using \protect\expkvc}
% Using \expkvc\ we can set up something equivalent with a bit less code. The
% implementation chosen in \expkvc\ is more efficient than the example above and
% way easier to code for the user.
% \begin{lstlisting}
% \makeatletter
% \newcommand*\sine{\ekvoptargTF\sine@a{\sine@b{sin}{d}{3}}}
% \ekvcSplitAndForward\sine@a\sine@b
%   {
%     f=sin,
%     unit=d,
%     round=3,
%   }
% \ekvcSecondaryKeys\sine@a
%   {
%     nmeta degree={unit=d},
%     nmeta radian={unit={}},
%   }
% \newcommand*\sine@b[4]{\fpeval{round(#1#2(#4),#3)}}
% \makeatother
% \end{lstlisting}
% The resulting macro will behave just like the one previously defined, but will
% have an additional |unit| key, since in \expkvc\ every argument must have a
% value taking key which defines it.
%
%
% \subsection{Error Messages}
%
% \expkv\ should only send messages in case of errors, there are no warnings and
% no info messages. In this subsection those errors are listed.
%
% \subsubsection{Load Time}
%
% \file{expkv.tex} checks whether \eTeX\ and the |\expanded| primitive are
% available. If it isn't, an error will be thrown using |\errmessage|:
% \begin{lstlisting}
% ! expkv Error: e-TeX and \expanded required.
% \end{lstlisting}
%
% \subsubsection{Defining Keys}
%
% If you get any error from \expkv\ while you're trying to define a key, the
% definition will be aborted and gobbled.
%
% If you try to define a key with an empty set name you'll get:
% \begin{lstlisting}
% ! expkv Error: empty set name not allowed.
% \end{lstlisting}
%
% Similarly, if you try to define a key with an empty key name:
% \begin{lstlisting}
% ! expkv Error: empty key name not allowed.
% \end{lstlisting}
%
% Both of these messages are done in a way that doesn't throw additional errors
% due to |\global|, |\long|, etc., not being used correctly if you prefixed one
% of the defining macros.
%
% \subsubsection{Using Keys}
%
% This subsubsection contains the errors thrown during |\ekvset|. The errors are
% thrown in an expandable manner using |\ekverr|. In the following messages
% \lstinline|<key>| gets replaced with the problematic key's name, and
% \lstinline|<set>| with the corresponding set. If any errors during \kv\
% handling are encountered, the entry in the comma separated list will be
% omitted after the error is thrown and the next \kv\ pair will be parsed.
%
% If you're using an undefined key you'll get:
% \begin{lstlisting}
% Runaway argument?
% ! expkv Error: unknown key `<key>' in set `<set>'
% \end{lstlisting}
%
% If you're using a key for which only a normal version and no |NoVal| version
% is defined, but don't provide a value, you'll get:
% \begin{lstlisting}
% Runaway argument?
% ! expkv Error: missing value for `<key>' in set `<set>'
% \end{lstlisting}
%
% If you're using a key for which only a |NoVal| version and no normal version
% is defined, but provide a value, you'll get:
% \begin{lstlisting}
% Runaway argument?
% ! expkv Error: unwanted value for `<key>' in set `<set>'
% \end{lstlisting}
%
% If you're using an undefined key in a set for which |\ekvredirectunknown| was
% used, and the key isn't found in any of the other sets as well, you'll get:
% \begin{lstlisting}
% Runaway argument?
% ! expkv Error: no key `<key>' in sets {<set1>}{<set2>}...
% \end{lstlisting}
%
% If you're using an undefined |NoVal| key in a set for which
% |\ekvredirectunknownNoVal| was used, and the key isn't found in any of the
% other sets as well, you'll get:
% \begin{lstlisting}
% Runaway argument?
% ! expkv Error: no NoVal key `<key>' in sets {<set1>}{<set2>}...
% \end{lstlisting}
%
% If you're using a set for which you never executed one of the defining macros
% from \autoref{sec:define} you'll get a low level \TeX\ error, as that isn't
% actively tested by the parser (and hence will lead to undefined behaviour and
% not be gracefully ignored). The error will look like
% \begin{lstlisting}[language={}]
% ! Missing \endcsname inserted.
% <to be read again>
%                    \! expkv Error: Set `<set>' undefined.
% \end{lstlisting}
%
% \subsection{Bugs}
%
% Just like \pkg{keyval}, \expkv\ is bug free. But if you find \pmso{bugs}hidden
% features\footnote{Thanks, David!} you can tell me about them either via mail
% (see the first page) or directly on GitHub if you have an account there:
% \url{https://github.com/Skillmon/tex_expkv}
%
% \subsection{Comparisons}\label{sec:cmp}
%
% This subsection makes some basic comparison between \expkv\ and other \kv\
% packages. The comparisons are really concise, regarding speed, feature range
% (without listing the features of each package), and bugs and misfeatures.
%
% Comparisons of speed are done with a very simple test key and the help of the
% \pkg{l3benchmark} package. The key and its usage should be equivalent to
% \begin{lstlisting}
% \protected\ekvdef{test}{height}{\def\myheight{#1}}
% \ekvsetdef\expkvtest{test}
% \expkvtest{ height = 6 }
% \end{lstlisting}
% and only the usage of the key, not its definition, is benchmarked. For the
% impatient, the essence of these comparisons regarding speed and buggy
% behaviour is contained in \autoref{tab:comp}.
%
% As far as I know \expkv\ is the only fully expandable \kv\ parser. I tried to
% compare \expkv\ to every \kv\ package listed on
% \href{https://ctan.org/topic/keyval}{CTAN}, however, one might notice that
% some of those are missing from this list. That's because I didn't get the
% others to work due to bugs, or because they just provide wrappers around other
% packages in this list.
%
% In this subsection is no benchmark of |\ekvparse| and |\keyval_parse:NNn|
% contained, as most other packages don't provide equivalent features to my
% knowledge. |\ekvparse| is slightly faster than |\ekvset|, but keep in mind
% that it does less. The same is true for |\keyval_parse:NNn| compared to
% |\keys_set:nn| of \pkg{expl3} (where the difference is much bigger). Comparing
% just the two, |\ekvparse| is a tad faster than |\keyval_parse:NNn| because of
% the two tests (for empty key names and only a single equal sign) which are
% omitted.
%
% \paragraph{\pkg{keyval}} is about \SIrange{30}{40}{\percent} faster and has a
% comparable feature set (actually a bit smaller since \expkv\ supports
% unknown-key handlers and redirection to other sets) just a slightly different
% way how it handles keys without values.  That might be considered a drawback,
% as it limits the versatility, but also as an advantage, as it might reduce
% doubled code. Keep in mind that as soon as someone loads \pkg{xkeyval} the
% performance of \pkg{keyval} gets replaced by \pkg{xkeyval}'s.
%
% Also \pkg{keyval} has a bug, which unfortunately can't really be resolved
% without breaking backwards compatibility for \emph{many} documents, namely it
% strips braces from the argument before stripping spaces if the argument isn't
% surrounded by spaces, also it might strip more than one set of braces. Hence
% all of the following are equivalent in their outcome, though the last two
% lines should result in something different than the first two:
% \begin{lstlisting}[belowskip=0pt]
% \setkeys{foo}{bar=baz}
% \setkeys{foo}{bar= {baz}}
% \setkeys{foo}{bar={ baz}}  % should be ` baz'
% \setkeys{foo}{bar={{baz}}} % should be `{baz}'
% \end{lstlisting}
%
% \paragraph{\pkg{xkeyval}} is roughly twenty times slower, but it provides more
% functionality, e.g., it has choice keys, boolean keys, and so on. It contains
% the same bug as \pkg{keyval} as it has to be compatible with it by design (it
% replaces \pkg{keyval}'s frontend), but also adds even more cases in which
% braces are stripped that shouldn't be stripped, worsening the situation.
%
% \paragraph{\pkg{ltxkeys}} is no longer compatible with the \LaTeX\ kernel
% starting with the release 2020-10-01. It is over 380 times slower -- which is
% funny, because it aims to be ``[\ldots] faster [\ldots] than these earlier
% packages [referring to \pkg{keyval} and \pkg{xkeyval}].'' It needs more time
% to parse zero~keys than five of the packages in this comparison need to parse
% 100~keys.  Since it aims to have a bigger feature set than \pkg{xkeyval}, it
% most definitely also has a bigger feature set than \expkv.  Also, it can't
% parse |\long| input, so as soon as your values contain a |\par|, it'll throw
% errors.  Furthermore, \pkg{ltxkeys} doesn't strip outer braces at all by
% design, which, imho, is a weird design choice. In addition \pkg{ltxkeys} loads
% \pkg{catoptions} which is known to introduce bugs (e.g., see
% \url{https://tex.stackexchange.com/questions/461783}). Because it is no longer
% compatible with the kernel, I stop benchmarking it (so the numbers listed here
% and in \autoref{tab:comp} regarding \pkg{ltxkeys} were last updated on
% 2020-10-05).
%
% \paragraph{\pkg{l3keys}} is around four and a half times slower, but has an,
% imho, great interface to define keys. It strips \emph{all} outer spaces, even
% if somehow multiple spaces ended up on either end. It offers more features,
% but is pretty much bound to \pkg{expl3} code. Whether that's a drawback is up
% to you.
%
% \paragraph{\pkg{pgfkeys}} is around \num{2.7} times slower for one key if one
% uses the |/|\meta{path}|/.cd| syntax and almost \SI{20}{\percent} slower if
% one uses |\pgfqkeys|, but has an \emph{enormous} feature set.
% To get the best performance |\pgfqkeys| was used in the benchmark. This
% reduces the overhead for setting the base directory of the benchmark keys by
% about \SI{43}{\ops} (so both $p_0$ and $T_0$ would be about \SI{43}{\ops}
% bigger if |\pgfkeys{|\meta{path}|/.cd,|\meta{keys}|}| was used instead).
% It has the same or a very similar bug \pkg{keyval} has. The brace bug (and
% also the category fragility) can be fixed by \pkg{pgfkeyx}, but this package
% was last updated in 2012 and it slows down |\pgfkeys| by factor~\num{8}. Also
% \pkg{pgfkeyx} is no longer compatible with versions of \pkg{pgfkeys} newer
% than 2020-05-25.
%
% \paragraph{\pkg{kvsetkeys} with \pkg{kvdefinekeys}} is about \num{4.4} times
% slower, but it works even if commas and equals have category codes different
% from 12 (just as some other packages in this list). Else the features of the
% keys are equal to those of \pkg{keyval}, the parser has more features, though.
%
% \paragraph{\pkg{options}} is \num{1.7} times slower for only a single value.
% It has a much bigger feature set. Unfortunately it also suffers from the
% premature unbracing bug \pkg{keyval} has.
%
% \paragraph{\pkg{simplekv}} is hard to compare because I don't speak French (so
% I don't understand the documentation). There was an update released on
% 2020-04-27 which greatly improved the package's performance and adds
% functionality so that it can be used more like most of the other \kv\
% packages. It has problems with stripping braces and spaces in a hard to
% predict manner just like \pkg{keyval}. Also, while it tries to be robust
% against category code changes of commas and equal signs, the used mechanism
% fails if the \kv\ list already got tokenised. Regarding unknown keys it got a
% very interesting behaviour. It doesn't throw an error, but stores the \val\ in
% a new entry accessible with \cs[no-index]{useKV}. Also if you omit \val\ it
% stores |true| for that \key. For up to three keys, \expkv\ is a bit faster,
% for more keys \pkg{simplekv} takes the lead.
%
% \paragraph{\protect\yax} is over twenty times slower. It has a pretty
% strange syntax for the \TeX-world, imho, and again a direct equivalent is hard
% to define (don't understand me wrong, I don't say I don't like the syntax,
% it's just atypical). It has the premature unbracing bug, too. Also somehow
% loading \yax\ broke \pkg{options} for me. The tested definition was:
% \begin{lstlisting}[belowskip=0pt]
% \usepackage{yax}
% \defactiveparameter yax {\storevalue\myheight yax:height } % setup
% \setparameterlist{yax}{ height = 6 }                       % benchmark
% \end{lstlisting}
%
% \begin{table}
%   \def\fnsym{\textcolor{red!80!black}{*}}%
%   \sisetup{round-precision=1, round-mode=places}%
%   \begingroup
%   \centering
%   \newcommand*\yes{\textcolor{red!80!black}  {yes}}^^A
%   \newcommand*\no {\textcolor{green!80!black}{no}}^^A
%   \caption[Comparison of \kv\ packages]
%     {^^A
%       Comparison of \kv\ packages. The packages are ordered from
%       fastest to slowest for one \kv\ pair. Benchmarking was done using
%       \pkg{l3benchmark} and the scripts in the \file{Benchmarks} folder
%       of the \href{https://github.com/Skillmon/tex_expkv}{git repository}.
%       The columns $p_i$ are the polynomial coefficients of a linear fit to the
%       run-time, $p_0$ can be interpreted as the overhead for initialisation
%       and $p_1$ the cost per key. The $T_0$ column is the actual mean ops
%       needed for an empty list argument, as the linear fit doesn't match that
%       point well in general. The column ``BB'' lists whether the
%       parsing is affected by some sort of brace bug, ``CF'' stands for
%       category code fragile and lists whether the parsing breaks with active
%       commas or equal signs.^^A
%       \label{tab:comp}^^A
%     }
%   \begin{tabular}
%       {>{\collectcell\pkg}l<{\endcollectcell}*3{S[table-format=4.1]}ccc}
%     \toprule
%     \rmfamily Package & {$p_1$} & {$p_0$} & {$T_0$}& BB & CF & Date \\
%     \midrule
%     keyval    &   13.742 &    1.486 &    7.254 & \yes & \yes & 2014-10-28 \\
%     \expkv    &   19.701 &    2.169 &    6.592 & \no  & \no  & 2020-10-10 \\
%     simplekv  &   18.334 &    6.971 &   17.710 & \yes & \yes & 2020-04-27 \\
%     pgfkeys   &   24.274 &    1.725 &   10.650 & \yes & \yes & 2020-09-05 \\
%     options   &   23.600 &   15.638 &   20.830 & \yes & \yes & 2015-03-01 \\
%     kvsetkeys & {\fnsym} & {\fnsym} &   40.290 & \no  & \no  & 2019-12-15 \\
%     l3keys    &   71.309 &   33.131 &   31.590 & \no  & \no  & 2020-09-24 \\
%     xkeyval   &  253.563 &  202.246 &  168.300 & \yes & \yes & 2014-12-03 \\
%     \yax      &  421.853 &  157.003 &  114.700 & \yes & \yes & 2010-01-22 \\
%     ltxkeys   & 3400.142 & 4737.958 & 5368.000 & \no  & \no  & 2012-11-17 \\
%     \bottomrule
%   \end{tabular}
%   \par
%   \endgroup
%   \medskip
%   \fnsym For \pkg{kvsetkeys} the linear model used for the other
%   packages is a poor fit, \pkg{kvsetkeys} seems to have approximately
%   quadratic run-time, the coefficients of the second degree polynomial fit are
%   $p_2=\num{8.240}$, $p_1=\num{44.862}$, and $p_0=\num{60.793}$. Of course the
%   other packages might not really have linear run-time, but at least from 1~to
%   20~keys the fits don't seem too bad. If one extrapolates the fits for 100
%   \kv\ pairs one finds that most of them match pretty well, the exception
%   being \pkg{ltxkeys}, which behaves quadratic as well with
%   $p_2=\num{23.500}$, $p_1=\num{2906.634}$, and $p_0=\num{6547.489}$.
% \end{table}
%
% \subsection{License}
%
% Copyright \textcopyright\ 2020\unless\ifnum\year=2020--\the\year\fi\
% Jonathan P. Spratte
%
% \medskip\noindent
% This work 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:
%
% \url{http://www.latex-project.org/lppl.txt}
%
% \noindent
% This work is ``maintained'' (as per LPPL maintenance status) by
%
% \mbox{Jonathan P. Spratte}.
%
% \end{documentation}^^A=<<
%
% \begin{implementation}^^A>>=
%
% \clearpage
%
% \section{Implementation}^^A>>=
%^^A the LaTeX package >>=
% \subsection{The \LaTeX\ Package}
% First we set up the \LaTeX\ package. That one doesn't really do much except
% |\input|ting the generic code and identifying itself as a package.
% \gobbledocstriptag
%<*pkg>
%    \begin{macrocode}
\def\ekv@tmp
  {%
    \ProvidesFile{expkv.tex}%
      [\ekvDate\space v\ekvVersion\space an expandable key=val implementation]%
  }
\input{expkv.tex}
\ProvidesPackage{expkv}%
  [\ekvDate\space v\ekvVersion\space an expandable key=val implementation]
%    \end{macrocode}
% \gobbledocstriptag
%</pkg>
%^^A=<<
%^^A the ConTeXt module >>=
% \subsection{The \ConTeXt\ module}
% This is pretty straight forward, we just have to change the error throwing
% mechanism for \ConTeXt\ (the approach taken for plain and \LaTeX\ breaks in
% \ConTeXt, effectively breaking \ConTeXt, dropping you in an interactive \TeX\
% session with almost no means of escape).
% \gobbledocstriptag
%<*ctx>
%    \begin{macrocode}
\writestatus{loading}{ConTeXt User Module / expkv}
\unprotect
\input expkv.tex
\long\def\ekv@err@collect#1\par#2%
  {\directlua{tex.error[[\detokenize{#2} Error: #1]]}}
\writestatus{loading}
  {ConTeXt User Module / expkv / Version \ekvVersion\space loaded}
\protect\endinput
%    \end{macrocode}
% \gobbledocstriptag
%</ctx>
%^^A=<<
%^^A main file >>=
% \subsection{The Generic Code}
% The rest of this implementation will be the generic code.
% \gobbledocstriptag
%<*tex>
%
% We make sure that it's only input once:
%    \begin{macrocode}
\expandafter\ifx\csname ekvVersion\endcsname\relax
\else
  \expandafter\endinput
\fi
%    \end{macrocode}
%
% Check whether \eTeX\ and |\expanded| are available -- \expkv\ requires \eTeX.
%    \begin{macrocode}
\begingroup
  \edef\ekvtmpa{\string\expanded}
  \edef\ekvtmpb{\meaning\expanded}
  \expandafter
\endgroup
\ifx\ekvtmpa\ekvtmpb
  \expandafter\let\csname ekv@expanded\endcsname\expanded
  \expandafter\let\csname ekv@unexpanded\endcsname\unexpanded
\else
  \begingroup
    \edef\ekvtmpa{\string\expanded}
    \edef\ekvtmpb{\meaning\normalexpanded}
    \expandafter
  \endgroup
  \ifx\ekvtmpa\ekvtmpb
    \expandafter\let\csname ekv@expanded\endcsname\normalexpanded
    \expandafter\let\csname ekv@unexpanded\endcsname\normalunexpanded
  \else
    \errmessage
      {expkv Error: e-TeX and the \noexpand\expanded primitive required}%
    \expandafter\endinput
  \fi
\fi
%    \end{macrocode}
%
% \begin{macro}{\ekvVersion,\ekvDate}
% We're on our first input, so lets store the version and date in a macro.
%    \begin{macrocode}
\def\ekvVersion{1.9a}
\def\ekvDate{2021-09-20}
%    \end{macrocode}
% \end{macro}
%
% If the \LaTeX\ format is loaded we want to be a good file and report back who
% we are, for this the package will have defined |\ekv@tmp| to use
% |\ProvidesFile|, else this will expand to a |\relax| and do no harm.
%    \begin{macrocode}
\csname ekv@tmp\endcsname
%    \end{macrocode}
%
% Store the category code of |@| to later be able to reset it and change it to
% 11 for now.
%    \begin{macrocode}
\expandafter\chardef\csname ekv@tmp\endcsname=\catcode`\@
\catcode`\@=11
%    \end{macrocode}
% |\ekv@tmp| might later be reused to gobble any prefixes which might be
% provided to |\ekvdef| and similar in case the names are invalid, we just
% temporarily use it here as means to store the current category code of |@| to
% restore it at the end of the file, we never care for the actual definition of
% it.
%
% \begin{macro}[internal]{\ekv@if@lastnamedcs}
% If the primitive |\lastnamedcs| is available, we can be a bit faster than
% without it. So we test for this and save the test's result in this macro.
%    \begin{macrocode}
\begingroup
  \edef\ekv@tmpa{\string \lastnamedcs}
  \edef\ekv@tmpb{\meaning\lastnamedcs}
  \ifx\ekv@tmpa\ekv@tmpb
    \def\ekv@if@lastnamedcs{\long\def\ekv@if@lastnamedcs##1##2{##1}}
  \else
    \def\ekv@if@lastnamedcs{\long\def\ekv@if@lastnamedcs##1##2{##2}}
  \fi
  \expandafter
\endgroup
\ekv@if@lastnamedcs
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@empty}
% Sometimes we have to introduce a token to prevent accidental brace stripping.
% This token would then need to be removed by |\@gobble| or similar. Instead we
% can use |\ekv@empty| which will just expand to nothing, that is faster than
% gobbling an argument.
%    \begin{macrocode}
\def\ekv@empty{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]
%   {
%     \@gobble,\@firstofone,\@firstoftwo,\@secondoftwo,
%     \ekv@fi@gobble,\ekv@fi@firstofone,\ekv@fi@firstoftwo,\ekv@fi@secondoftwo,
%     \ekv@gobble@mark,\ekv@gobbleto@stop,\ekv@gobble@from@mark@to@stop
%   }
% Since branching tests are often more versatile than |\if...\else...\fi|
% constructs, we define helpers that are branching pretty fast. Also here are
% some other utility functions that just grab some tokens. The ones that are
% also contained in \LaTeX\ don't use the |ekv| prefix. Not all of the ones
% defined here are really needed by \expkv\ but are provided because packages
% like \expkvd\ or \expkvo\ need them (and I don't want to define them in each
% package which might need them).
%    \begin{macrocode}
\long\def\@gobble#1{}
\long\def\@firstofone#1{#1}
\long\def\@firstoftwo#1#2{#1}
\long\def\@secondoftwo#1#2{#2}
\long\def\ekv@fi@gobble\fi\@firstofone#1{\fi}
\long\def\ekv@fi@firstofone\fi\@gobble#1{\fi#1}
\long\def\ekv@fi@firstoftwo\fi\@secondoftwo#1#2{\fi#1}
\long\def\ekv@fi@secondoftwo\fi\@firstoftwo#1#2{\fi#2}
\def\ekv@gobble@mark\ekv@mark{}
\long\def\ekv@gobbleto@stop#1\ekv@stop{}
\long\def\ekv@gobble@from@mark@to@stop\ekv@mark#1\ekv@stop{}
%    \end{macrocode}
% \end{macro}
% As you can see |\ekv@gobbleto@stop| uses a special marker |\ekv@stop|. The
% package will use three such markers, the one you've seen already, |\ekv@mark|
% and |\ekv@nil|. Contrarily to how for instance \pkg{expl3} does things, we
% don't define them, as we don't need them to have an actual meaning. This has
% the advantage that if they somehow get expanded -- which should never happen
% if things work out -- they'll throw an error directly.
%
% \begin{macro}[internal]
%   {
%     \ekv@ifempty,\ekv@ifempty@,\ekv@ifempty@true,\ekv@ifempty@false,
%     \ekv@ifempty@true@F,\ekv@ifempty@true@F@gobble,
%     \ekv@ifempty@true@F@gobbletwo
%   }
% We can test for a lot of things building on an if-empty test, so lets define a
% really fast one. Since some tests might have reversed logic (true if something
% is not empty) we also set up macros for the reversed branches.
%    \begin{macrocode}
\long\def\ekv@ifempty#1%
  {%
    \ekv@ifempty@\ekv@ifempty@A#1\ekv@ifempty@B\ekv@ifempty@true
      \ekv@ifempty@A\ekv@ifempty@B\@secondoftwo
  }
\long\def\ekv@ifempty@#1\ekv@ifempty@A\ekv@ifempty@B{}
\long\def\ekv@ifempty@true\ekv@ifempty@A\ekv@ifempty@B\@secondoftwo#1#2{#1}
\long\def\ekv@ifempty@false\ekv@ifempty@A\ekv@ifempty@B\@firstoftwo#1#2{#2}
\long\def\ekv@ifempty@true@F\ekv@ifempty@A\ekv@ifempty@B\@firstofone#1{}
\long\def\ekv@ifempty@true@F@gobble\ekv@ifempty@A\ekv@ifempty@B\@firstofone#1#2%
  {}
\long\def\ekv@ifempty@true@F@gobbletwo
    \ekv@ifempty@A\ekv@ifempty@B\@firstofone#1#2#3%
  {}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@ifblank,\ekv@ifblank@}
% The obvious test that can be based on an if-empty is if-blank, meaning a test
% checking whether the argument is empty or consists only of spaces. Our version
% here will be tweaked a bit, as we want to check this, but with one leading
% |\ekv@mark| token that is to be ignored. The wrapper |\ekv@ifblank| will not
% be used by \expkv\ for speed reasons but \expkvo\ uses it.
%    \begin{macrocode}
\long\def\ekv@ifblank#1%
  {%
    \ekv@ifblank@#1\ekv@nil\ekv@ifempty@B\ekv@ifempty@true
      \ekv@ifempty@A\ekv@ifempty@B\@secondoftwo
  }
\long\def\ekv@ifblank@\ekv@mark#1{\ekv@ifempty@\ekv@ifempty@A}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@ifdefined}
% We'll need to check whether something is defined quite frequently, so why not
% define a macro that does this. The following test is expandable and pretty
% fast. The version with |\lastnamedcs| is the fastest version to test for an
% undefined macro I know of (that considers both undefined macros and those with
% the meaning |\relax|).
%    \begin{macrocode}
\ekv@if@lastnamedcs
  {%
    \long\def\ekv@ifdefined#1{\ifcsname#1\endcsname\ekv@ifdef@\fi\@secondoftwo}
    \def\ekv@ifdef@\fi\@secondoftwo
      {%
        \fi
        \expandafter\ifx\lastnamedcs\relax
          \ekv@fi@secondoftwo
        \fi
        \@firstoftwo
      }
  }
  {%
    \long\def\ekv@ifdefined#1%
      {%
        \ifcsname#1\endcsname\ekv@ifdef@\fi\ekv@ifdef@false#1\endcsname\relax
          \ekv@fi@secondoftwo
        \fi
        \@firstoftwo
      }
    \def\ekv@ifdef@\fi\ekv@ifdef@false{\fi\expandafter\ifx\csname}
    \long\def\ekv@ifdef@false
        #1\endcsname\relax\ekv@fi@secondoftwo\fi\@firstoftwo#2#3%
      {#3}
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@strip,\ekv@strip@a,\ekv@strip@b,\ekv@strip@c}
% We borrow some ideas of \pkg{expl3}'s \pkg{l3tl} to strip spaces
% from keys and values. This |\ekv@strip| also strips one level of outer braces
% \emph{after} stripping spaces, so an input of | {abc} | becomes |abc| after
% stripping. It should be used with |#1| prefixed by |\ekv@mark|. Also this
% implementation at most strips \emph{one} space from both sides (which should
% be fine most of the time, since \TeX\ reads consecutive spaces as a single one
% during tokenisation).
%    \begin{macrocode}
\def\ekv@strip#1%
  {%
    \long\def\ekv@strip##1%
      {%
        \ekv@strip@a
          ##1\ekv@nil
          \ekv@mark#1%
          #1\ekv@nil
      }%
    \long\def\ekv@strip@a##1\ekv@mark#1{\ekv@strip@b##1\ekv@mark}%
  }
\ekv@strip{ }
\long\def\ekv@strip@b#1 \ekv@nil{\ekv@strip@c#1\ekv@nil}
\long\def\ekv@strip@c\ekv@mark#1\ekv@nil\ekv@mark#2\ekv@nil#3{#3{#1}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]
%   {\ekv@exparg,\ekv@exparg@,\ekv@expargtwice,\ekv@expargtwice@,\ekv@zero}
% To reduce some code doublets while gaining some speed (and also as convenience
% for other packages in the family), it is often useful to expand the first
% token in a definition once. Let's define a wrapper for this.
%
% Also, to end a |\romannumeral| expansion, we want to use |\z@|, which is
% contained in both plain \TeX\ and \LaTeX, but we use a private name for it to
% make it easier to spot and hence easier to manage.
%    \begin{macrocode}
\let\ekv@zero\z@
\long\def\ekv@exparg#1#2{\expandafter\ekv@exparg@\expandafter{#2}{#1}}
\long\def\ekv@exparg@#1#2{#2{#1}}%
\long\def\ekv@expargtwice#1#2{\expandafter\ekv@expargtwice@\expandafter{#2}{#1}}
\def\ekv@expargtwice@{\expandafter\ekv@exparg@\expandafter}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvcsvloop}
% \begin{macro}[internal]{\ekv@csv@loop@active,\ekv@csv@loop@active@end}
%   An |\ekvcsvloop| will just loop over a csv list in a simple manner. First we
%   split at active commas (gives better performance this way), next we have to
%   check whether we're at the end of the list (checking for |\ekv@stop|). If
%   not we go on splitting at commas of category other.
%    \begin{macrocode}
\begingroup
\def\ekvcsvloop#1{%
\endgroup
\long\def\ekvcsvloop##1##2%
  {\ekv@csv@loop@active{##1}\ekv@mark##2#1\ekv@stop#1}
%    \end{macrocode}
%   This does the same as |\ekv@csv@loop| but for active commas.
%    \begin{macrocode}
\long\def\ekv@csv@loop@active##1##2#1%
  {%
    \ekv@gobble@from@mark@to@stop##2\ekv@csv@loop@active@end\ekv@stop
    \ekv@csv@loop{##1}##2,\ekv@stop,%
  }%
\long\def\ekv@csv@loop@active@end
    \ekv@stop
    \ekv@csv@loop##1\ekv@mark\ekv@stop,\ekv@stop,%
  {}%
}
%    \end{macrocode}
%   Do the definitions with the weird catcode.
%    \begin{macrocode}
\catcode`\,=13
\ekvcsvloop,
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@csv@loop,\ekv@csv@loop@do,\ekv@csv@loop@end}
%   We use temporary macros and an |\expandafter| chain to preexpand
%   |\ekv@strip| here. After splitting at other commas we check again for end
%   the end of the sublist, check for blank elements which should be ignored,
%   and else strip spaces and execute the user code (protecting it from further
%   expanding with |\unexpanded|).
%    \begin{macrocode}
\def\ekv@csv@loop#1%
  {%
    \long\def\ekv@csv@loop##1##2,%
      {%
        \ekv@gobble@from@mark@to@stop##2\ekv@csv@loop@end\ekv@stop
        \ekv@ifblank@##2\ekv@nil\ekv@ifempty@B\ekv@csv@loop@blank
          \ekv@ifempty@A\ekv@ifempty@B
        #1\ekv@csv@loop@do{##1}%
      }%
  }
\expandafter\ekv@csv@loop\expandafter{\ekv@strip{#2}}
\long\def\ekv@csv@loop@do#1#2{\ekv@unexpanded{#2{#1}}\ekv@csv@loop{#2}\ekv@mark}
\def\ekv@csv@loop@end#1%
  {%
    \long\def\ekv@csv@loop@end
        \ekv@stop
        \ekv@ifblank@\ekv@mark\ekv@stop\ekv@nil\ekv@ifempty@B\ekv@csv@loop@blank
        \ekv@ifempty@A\ekv@ifempty@B
        #1\ekv@csv@loop@do##1%
      {\ekv@csv@loop@active{##1}\ekv@mark}%
  }
\expandafter\ekv@csv@loop@end\expandafter{\ekv@strip{\ekv@mark\ekv@stop}}
\long\expandafter\def\expandafter\ekv@csv@loop@blank
    \expandafter\ekv@ifempty@A\expandafter\ekv@ifempty@B
    \ekv@strip{\ekv@mark#1}\ekv@csv@loop@do#2%
  {\ekv@csv@loop{#2}\ekv@mark}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekv@name,\ekv@name@set,\ekv@name@key}
% The keys will all follow the same naming scheme, so we define it here.
%    \begin{macrocode}
\def\ekv@name@set#1{ekv#1(}
\long\def\ekv@name@key#1{#1)}
\edef\ekv@name
  {%
    \ekv@unexpanded\expandafter{\ekv@name@set{#1}}%
    \ekv@unexpanded\expandafter{\ekv@name@key{\detokenize{#2}}}%
  }
\long\ekv@exparg{\def\ekv@name#1#2}{\ekv@name}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@undefined@set}
% We can misuse the macro name we use to expandably store the set-name in a
% single token -- since this increases performance drastically, especially for
% long set-names -- to throw a more meaningful error message in case a set isn't
% defined. The name of |\ekv@undefined@set| is a little bit misleading, as it is
% called in either case inside of |\csname|, but the result will be a control
% sequence with meaning |\relax| if the set is undefined, hence will break the
% |\csname| building the key-macro which will throw the error message.
%    \begin{macrocode}
\def\ekv@undefined@set#1{! expkv Error: Set `#1' undefined.}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@checkvalid}
% We place some restrictions on the allowed names, though, namely sets and
% keys are not allowed to be empty -- blanks are fine (meaning \mbox{set-
% or} key-names consisting of spaces). The |\def\ekv@tmp| gobbles any \TeX\
% prefixes which would otherwise throw errors. This will, however, break the
% package if an |\outer| has been gobbled this way. I consider that good,
% because keys shouldn't be defined |\outer| anyways.
%    \begin{macrocode}
\edef\ekv@checkvalid
  {%
    \ekv@unexpanded\expandafter{\ekv@ifempty{#1}}%
    \ekv@unexpanded
      {{%
        \def\ekv@tmp{}%
        \errmessage{expkv Error: empty set name not allowed}%
      }}%
      {%
        \ekv@unexpanded\expandafter{\ekv@ifempty{#2}}%
        \ekv@unexpanded
          {%
            {%
              \def\ekv@tmp{}%
              \errmessage{expkv Error: empty key name not allowed}%
            }%
            \@secondoftwo
          }%
      }%
    \ekv@unexpanded{\@gobble}%
  }
\ekv@exparg{\protected\def\ekv@checkvalid#1#2}{\ekv@checkvalid}%
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvifdefined,\ekvifdefinedNoVal}
% And provide user-level macros to test whether a key is defined.
%    \begin{macrocode}
\ekv@expargtwice{\long\def\ekvifdefined#1#2}%
  {\expandafter\ekv@ifdefined\expandafter{\ekv@name{#1}{#2}}}
\ekv@expargtwice{\long\def\ekvifdefinedNoVal#1#2}%
  {\expandafter\ekv@ifdefined\expandafter{\ekv@name{#1}{#2}N}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}
%   {
%     \ekvdef,\ekvdefNoVal,\ekvlet,\ekvletNoVal,\ekvletkv,\ekvletkvNoVal,
%     \ekvdefunknown,\ekvdefunknownNoVal,\ekvletunknown,\ekvletunknownNoVal
%   }
% Set up the key defining macros |\ekvdef| etc. We use temporary macros to set
% these up with a few expansions already done.
%    \begin{macrocode}
\def\ekvdef#1#2#3#4#5#6%
  {%
    \protected\long\def\ekvdef##1##2##3%
      {#1{\expandafter\def\csname#2\endcsname####1{##3}#4}}%
    \protected\long\def\ekvdefNoVal##1##2##3%
      {#1{\expandafter\def\csname#2N\endcsname{##3}#4}}%
    \protected\long\def\ekvlet##1##2##3%
      {#1{\expandafter\let\csname#2\endcsname##3#4}}%
    \protected\long\def\ekvletNoVal##1##2##3%
      {#1{\expandafter\let\csname#2N\endcsname##3#4}}%
    \ekv@expargtwice{\protected\long\def\ekv@defunknown##1##2##3##4}%
      {%
        \romannumeral
        \expandafter\ekv@exparg@\expandafter
          {%
            \expandafter\expandafter\expandafter
            \def\expandafter\csname\ekv@name{##3}{}u##1\endcsname##2{##4}%
            #6%
          }%
          {\ekv@zero\ekv@checkvalid{##3}.}%
      }%
    \ekv@expargtwice{\protected\long\def\ekv@letunknown##1##2##3}%
      {%
        \romannumeral
        \expandafter\ekv@exparg@\expandafter
          {%
            \expandafter\expandafter\expandafter
            \let\expandafter\csname\ekv@name{##2}{}u##1\endcsname##3%
            #5%
          }%
          {\ekv@zero\ekv@checkvalid{##2}.}%
      }%
    \protected\long\def\ekvletkv##1##2##3##4%
      {%
        #1%
          {%
            \expandafter\let\csname#2\expandafter\endcsname
            \csname#3\endcsname
            #4%
          }%
      }%
    \protected\long\def\ekvletkvNoVal##1##2##3##4%
      {%
        #1%
          {%
            \expandafter\let\csname#2N\expandafter\endcsname
            \csname#3N\endcsname
            #4%
          }%
      }%
  }
\edef\ekvdefNoVal
  {%
    {\ekv@unexpanded\expandafter{\ekv@checkvalid{#1}{#2}}}%
    {\ekv@unexpanded\expandafter{\ekv@name{#1}{#2}}}%
    {\ekv@unexpanded\expandafter{\ekv@name{#3}{#4}}}%
    {%
      \ekv@unexpanded{\expandafter\ekv@defsetmacro\csname}%
      \ekv@unexpanded\expandafter{\ekv@undefined@set{#1}\endcsname{#1}}%
    }%
    {%
      \ekv@unexpanded{\expandafter\ekv@defsetmacro\csname}%
      \ekv@unexpanded\expandafter{\ekv@undefined@set{#2}\endcsname{#2}}%
    }%
    {%
      \ekv@unexpanded{\expandafter\ekv@defsetmacro\csname}%
      \ekv@unexpanded\expandafter{\ekv@undefined@set{#3}\endcsname{#3}}%
    }%
  }
\expandafter\ekvdef\ekvdefNoVal
\ekv@exparg{\protected\long\def\ekvdefunknown#1#2}%
  {\ekv@defunknown{}{##1##2}{#1}{#2}}
\ekv@exparg{\protected\long\def\ekvdefunknownNoVal#1#2}%
  {\ekv@defunknown{N}{##1}{#1}{#2}}
\ekv@exparg{\protected\long\def\ekvletunknown#1#2}%
  {\ekv@letunknown{}{#1}{#2}}
\ekv@exparg{\protected\long\def\ekvletunknownNoVal#1#2}%
  {\ekv@letunknown{N}{#1}{#2}}
\let\ekv@defunknown\ekv@undefined
\let\ekv@letunknown\ekv@undefined
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvredirectunknown,\ekvredirectunknownNoVal}
% \begin{macro}[internal]
%   {
%     \ekv@defredirectunknown,\ekv@redirectunknown@aux,
%     \ekv@redirectunknownNoVal@aux
%   }
%   The redirection macros prepare the unknown function by looping over the
%   provided list of sets and leaving a |\ekv@redirect@kv| or |\ekv@redirect@k|
%   for each set. Only the first of these internals will receive the \key\ and
%   \val\ as arguments.
%    \begin{macrocode}
\protected\def\ekvredirectunknown
  {%
    \ekv@defredirectunknown
      \ekv@redirect@kv
      \ekv@err@redirect@kv@notfound
      {\long\ekvdefunknown}%
      \ekv@redirectunknown@aux
  }
\protected\def\ekvredirectunknownNoVal
  {%
    \ekv@defredirectunknown
      \ekv@redirect@k
      \ekv@err@redirect@k@notfound
      \ekvdefunknownNoVal
      \ekv@redirectunknownNoVal@aux
  }
\protected\def\ekv@defredirectunknown#1#2#3#4#5#6%
  {%
    \begingroup
    \edef\ekv@tmp
      {%
        \ekvcsvloop#1{#6}%
        \ekv@unexpanded{#2}%
        {\ekvcsvloop{}{#5,#6}}%
      }%
    \ekv@expargtwice
      {\endgroup#3{#5}}%
      {\expandafter#4\ekv@tmp\ekv@stop}%
  }
\def\ekv@redirectunknown@aux#1{#1{##1}{##2}}
\def\ekv@redirectunknownNoVal@aux#1{#1{##1}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[internal]
%   {
%     \ekv@redirect@k,\ekv@redirect@k@a,\ekv@redirect@k@a@,
%     \ekv@redirect@k@b,\ekv@redirect@k@c,\ekv@redirect@k@d,
%     \ekv@redirect@kv,\ekv@redirect@kv@a,\ekv@redirect@kv@a@,
%     \ekv@redirect@kv@b,\ekv@redirect@kv@c,\ekv@redirect@kv@d
%   }
%   The redirect code works by some simple loop over all the sets, which we
%   already preprocessed in |\ekv@defredirectunknown|. For some optimisation we
%   blow this up a bit code wise, essentially, all this does is |\ekvifdefined|
%   or |\ekvifdefinedNoVal| in each set, if there is a match gobble the
%   remainder of the specified sets and execute the key macro, else go on with
%   the next set (to which the \key\ and \val\ are forwarded).
%
%   First we set up some code which is different depending on |\lastnamedcs|
%   being available or not. All this is stored in a temporary macro to have
%   pre-expanded |\ekv@name| constellations ready.
%    \begin{macrocode}
\def\ekv@redirect@k#1#2#3#4%
  {%
    \ekv@if@lastnamedcs
      {%
        \def\ekv@redirect@k##1##2##3%
          {%
            \ifcsname#1\endcsname\ekv@redirect@k@a\fi
            ##3{##1}%
          }%
        \def\ekv@redirect@k@a\fi{\fi\expandafter\ekv@redirect@k@b\lastnamedcs}%
        \long\def\ekv@redirect@kv##1##2##3##4%
          {%
            \ifcsname#2\endcsname\ekv@redirect@kv@a\fi\@gobble{##1}%
            ##4{##1}{##2}%
          }%
        \def\ekv@redirect@kv@a\fi\@gobble
          {\fi\expandafter\ekv@redirect@kv@b\lastnamedcs}%
      }
      {%
        \def\ekv@redirect@k##1##2##3%
          {%
            \ifcsname#1\endcsname\ekv@redirect@k@a\fi\ekv@redirect@k@a@
              #1\endcsname
            ##3{##1}%
          }%
        \def\ekv@redirect@k@a@#3\endcsname{}%
        \def\ekv@redirect@k@a\fi\ekv@redirect@k@a@
          {\fi\expandafter\ekv@redirect@k@b\csname}%
        \long\def\ekv@redirect@kv##1##2##3##4%
          {%
            \ifcsname#2\endcsname\ekv@redirect@kv@a\fi\ekv@redirect@kv@a@
              #2\endcsname{##1}%
            ##4{##1}{##2}%
          }%
        \long\def\ekv@redirect@kv@a@#4\endcsname##3{}%
        \def\ekv@redirect@kv@a\fi\ekv@redirect@kv@a@
          {\fi\expandafter\ekv@redirect@kv@b\csname}%
      }%
  }
%    \end{macrocode}
%   The key name given to this loop will already be |\detokenize|d by |\ekvset|,
%   so we can safely remove the |\detokenize| here for some performance gain.
%    \begin{macrocode}
\def\ekv@redirect@kv#1\detokenize#2#3\ekv@stop{\ekv@unexpanded{#1#2#3}}
\edef\ekv@redirect@kv
  {%
    {\expandafter\ekv@redirect@kv\ekv@name{#2}{#1}N\ekv@stop}%
    {\expandafter\ekv@redirect@kv\ekv@name{#3}{#2}\ekv@stop}%
    {\expandafter\ekv@redirect@kv\ekv@name{#1}{#2}N\ekv@stop}%
    {\expandafter\ekv@redirect@kv\ekv@name{#1}{#2}\ekv@stop}%
  }
%    \end{macrocode}
%   Everything is ready to make the real definitions.
%    \begin{macrocode}
\expandafter\ekv@redirect@k\ekv@redirect@kv
%    \end{macrocode}
%   The remaining macros here are independent on |\lastnamedcs|, starting from
%   the |@b| we know that there is a hash table entry, and get the macro as a
%   parameter. We still have to test whether the macro is |\relax|, depending on
%   the result of that test we have to either remove the remainder of the
%   current test, or the remainder of the set list and invoke the macro.
%    \begin{macrocode}
\def\ekv@redirect@k@b#1%
  {\ifx\relax#1\ekv@redirect@k@c\fi\ekv@redirect@k@d#1}
\def\ekv@redirect@k@c\fi\ekv@redirect@k@d#1{\fi}
\def\ekv@redirect@k@d#1#2\ekv@stop{#1}
\def\ekv@redirect@kv@b#1%
  {\ifx\relax#1\ekv@redirect@kv@c\fi\ekv@redirect@kv@d#1}
\long\def\ekv@redirect@kv@c\fi\ekv@redirect@kv@d#1#2{\fi}
\long\def\ekv@redirect@kv@d#1#2#3\ekv@stop{#1{#2}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@defsetmacro}
%   In order to enhance the speed the set name given to |\ekvset| will be turned
%   into a control sequence pretty early, so we have to define that control
%   sequence.
%    \begin{macrocode}
\edef\ekv@defsetmacro
  {%
    \ekv@unexpanded{\ifx#1\relax\edef#1##1}%
      {%
        \ekv@unexpanded\expandafter{\ekv@name@set{#2}}%
        \ekv@unexpanded\expandafter{\ekv@name@key{##1}}%
      }%
    \ekv@unexpanded{\fi}%
  }
\ekv@exparg{\protected\def\ekv@defsetmacro#1#2}{\ekv@defsetmacro}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvifdefinedset}
%    \begin{macrocode}
\ekv@expargtwice{\def\ekvifdefinedset#1}%
  {\expandafter\ekv@ifdefined\expandafter{\ekv@undefined@set{#1}}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvset}
% Set up |\ekvset|, which should not be affected by active commas and equal
% signs. The equal signs are a bit harder to cope with and we'll do that later,
% but the active commas can be handled by just doing two comma-splitting loops
% one at actives one at others. That's why we define |\ekvset| here with a
% temporary meaning just to set up the things with two different category codes.
% |#1| will be a \texttt{,\textsubscript{13}} and |#2| will be a
% \texttt{=\textsubscript{13}}.
%    \begin{macrocode}
\begingroup
\def\ekvset#1#2{%
\endgroup
\ekv@exparg{\long\def\ekvset##1##2}%
  {%
    \expandafter\expandafter\expandafter
    \ekv@set\expandafter\csname\ekv@undefined@set{##1}\endcsname
      \ekv@mark##2#1\ekv@stop#1{}%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set}
% |\ekv@set| will split the \kv\ list at active commas. Then it has to check
% whether there were unprotected other commas and resplit there.
%    \begin{macrocode}
\long\def\ekv@set##1##2#1%
  {%
%    \end{macrocode}
% Test whether we're at the end, if so invoke |\ekv@endset|,
%    \begin{macrocode}
    \ekv@gobble@from@mark@to@stop##2\ekv@endset\ekv@stop
%    \end{macrocode}
% else go on with other commas.
%    \begin{macrocode}
    \ekv@set@other##1##2,\ekv@stop,%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@endset}
% |\ekv@endset| is a hungry little macro. It will eat everything that remains
% of |\ekv@set| and unbrace the sneaked stuff.
%    \begin{macrocode}
\long\def\ekv@endset
    \ekv@stop\ekv@set@other##1\ekv@mark\ekv@stop,\ekv@stop,##2%
  {##2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@eq@other,\ekv@eq@active}
%   Splitting at equal signs will be done in a way that checks whether there is
%   an equal sign and splits at the same time. This gets quite messy and the
%   code might look complicated, but this is pretty fast (faster than first
%   checking for an equal sign and splitting if one is found). The splitting
%   code will be adapted for |\ekvset| and |\ekvparse| to get the most speed,
%   but some of these macros don't require such adaptions. |\ekv@eq@other| and
%   |\ekv@eq@active| will split the argument at the first equal sign and insert
%   the macro which comes after the first following |\ekv@mark|. This allows for
%   fast branching based on \TeX's argument grabbing rules and we don't have to
%   split after the branching if the equal sign was there.
%    \begin{macrocode}
\long\def\ekv@eq@other##1=##2\ekv@mark##3{##3##1\ekv@stop\ekv@mark##2}
\long\def\ekv@eq@active##1#2##2\ekv@mark##3{##3##1\ekv@stop\ekv@mark##2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set@other}
%   The macro |\ekv@set@other| is guaranteed to get only single \kv\ pairs.
%    \begin{macrocode}
\long\def\ekv@set@other##1##2,%
  {%
%    \end{macrocode}
%   First we test whether we're done.
%    \begin{macrocode}
    \ekv@gobble@from@mark@to@stop##2\ekv@endset@other\ekv@stop
%    \end{macrocode}
%   If not we split at the equal sign of category other.
%    \begin{macrocode}
    \ekv@eq@other##2\ekv@nil\ekv@mark\ekv@set@eq@other@a
      =\ekv@mark\ekv@set@eq@active
%    \end{macrocode}
%   And insert the set name for the next recursion step of |\ekv@set@other|.
%    \begin{macrocode}
    ##1%
    \ekv@mark
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set@eq@other@a, \ekv@set@eq@other@b}
%   The first of these two macros runs the split-test for equal signs of
%   category active. It will only be inserted if the \kv\ pair contained at
%   least one equal sign of category other and |##1| will contain everything up
%   to that equal sign.
%    \begin{macrocode}
\long\def\ekv@set@eq@other@a##1\ekv@stop
  {%
    \ekv@eq@active##1\ekv@nil\ekv@mark\ekv@set@eq@other@active
      #2\ekv@mark\ekv@set@eq@other@b
  }
%    \end{macrocode}
%   The second macro will have been called by |\ekv@eq@active| if no active
%   equal sign was found. All it does is remove the excess tokens of that
%   test and forward the \kv\ pair to |\ekv@set@pair|. Normally we would have to
%   also gobble an additional |\ekv@mark| after |\ekv@stop|, but this mark is
%   needed to delimit |\ekv@set@pair|'s argument anyway, so we just leave it
%   there.
%    \begin{macrocode}
\ekv@exparg
  {%
    \long\def\ekv@set@eq@other@b
        ##1\ekv@nil\ekv@mark\ekv@set@eq@other@active\ekv@stop\ekv@mark
        ##2\ekv@nil=\ekv@mark\ekv@set@eq@active
  }%
  {\ekv@strip{##1}{\expandafter\ekv@set@pair\detokenize}\ekv@mark##2\ekv@nil}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set@eq@other@active}
%   |\ekv@set@eq@other@active| will be called if the \kv\ pair was wrongly
%   split on an equal sign of category other but has an earlier equal sign of
%   category active. |##1| will be the contents up to the active equal sign and
%   |##2| everything that remains until the first found other equal sign. It has
%   to reinsert the equal sign and forward things to |\ekv@set@pair|.
%    \begin{macrocode}
\ekv@exparg
  {%
    \long\def\ekv@set@eq@other@active
        ##1\ekv@stop##2\ekv@nil#2\ekv@mark
        \ekv@set@eq@other@b\ekv@mark##3=\ekv@mark\ekv@set@eq@active
  }%
  {\ekv@strip{##1}{\expandafter\ekv@set@pair\detokenize}\ekv@mark##2=##3}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set@eq@active, \ekv@set@eq@active@}
%   |\ekv@set@eq@active| will be called when there was no equal sign of category
%   other in the \kv\ pair. It removes the excess tokens of the prior test and
%   split-checks for an active equal sign.
%    \begin{macrocode}
\long\def\ekv@set@eq@active
    ##1\ekv@nil\ekv@mark\ekv@set@eq@other@a\ekv@stop\ekv@mark
  {%
    \ekv@eq@active##1\ekv@nil\ekv@mark\ekv@set@eq@active@
      #2\ekv@mark\ekv@set@noeq
  }
%    \end{macrocode}
%   If an active equal sign was found in |\ekv@set@eq@active| we'll have to pass
%   the now split \kv\ pair on to |\ekv@set@pair|.
%    \begin{macrocode}
\ekv@exparg
  {\long\def\ekv@set@eq@active@##1\ekv@stop##2\ekv@nil#2\ekv@mark\ekv@set@noeq}%
  {\ekv@strip{##1}{\expandafter\ekv@set@pair\detokenize}\ekv@mark##2\ekv@nil}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@set@noeq}
%   If no active equal sign was found by |\ekv@set@eq@active| there is no equal
%   sign contained in the parsed list entry. In that case we have to check
%   whether the entry is blank in order to ignore it (in which case we'll have
%   to gobble the set-name which was put after these tests by |\ekv@set@other|).
%   Else this is a |NoVal| key and the entry is passed on to |\ekv@set@key|.
%    \begin{macrocode}
\edef\ekv@set@noeq
  {%
    \ekv@unexpanded
      {%
        \ekv@ifblank@##1\ekv@nil\ekv@ifempty@B\ekv@set@was@blank
          \ekv@ifempty@A\ekv@ifempty@B
      }%
    \ekv@unexpanded\expandafter
      {\ekv@strip{##1}{\expandafter\ekv@set@key\detokenize}\ekv@mark}%
  }
\ekv@exparg
  {%
    \long\def\ekv@set@noeq
        ##1\ekv@nil\ekv@mark\ekv@set@eq@active@\ekv@stop\ekv@mark
  }%
  {\ekv@set@noeq}
\expandafter\def\expandafter\ekv@set@was@blank
    \expandafter\ekv@ifempty@A\expandafter\ekv@ifempty@B
    \ekv@strip{\ekv@mark##1}##2\ekv@mark
  {\ekv@set@other}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@endset@other}
%   All that's left for |\ekv@set@other| is the macro which breaks the recursion
%   loop at the end. This is done by gobbling all the remaining tokens.
%    \begin{macrocode}
\long\def\ekv@endset@other
    \ekv@stop
    \ekv@eq@other\ekv@mark\ekv@stop\ekv@nil\ekv@mark\ekv@set@eq@other@a
    =\ekv@mark\ekv@set@eq@active
  {\ekv@set}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvbreak,\ekvbreakPreSneak,\ekvbreakPostSneak}
% Provide macros that can completely stop the parsing of |\ekvset|, who knows
% what it'll be useful for.
%    \begin{macrocode}
\long\def\ekvbreak##1##2\ekv@stop#1##3{##1}
\long\def\ekvbreakPreSneak ##1##2\ekv@stop#1##3{##1##3}
\long\def\ekvbreakPostSneak##1##2\ekv@stop#1##3{##3##1}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvsneak,\ekvsneakPre}
% One last thing we want to do for |\ekvset| is to provide macros that just
% smuggle stuff after |\ekvset|'s effects.
%    \begin{macrocode}
\long\def\ekvsneak##1##2\ekv@stop#1##3{##2\ekv@stop#1{##3##1}}
\long\def\ekvsneakPre##1##2\ekv@stop#1##3{##2\ekv@stop#1{##1##3}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvparse}
% Additionally to the |\ekvset| macro we also want to provide an |\ekvparse|
% macro, that has the same scope as |\keyval_parse:NNn| from \pkg{expl3}.
% This is pretty analogue to the |\ekvset| implementation, we just put an
% |\unexpanded| here and there instead of other macros to stop the |\expanded|
% on our output. The |\unexpanded\expanded{{...}}| ensures that the material
% is in an alignment safe group at all time, and that it doesn't expand any
% further in an |\edef| or |\expanded| context.
%    \begin{macrocode}
\long\def\ekvparse##1##2##3%
  {%
    \ekv@unexpanded\ekv@expanded
      {{\ekv@parse{##1}{##2}\ekv@mark##3#1\ekv@stop#1}}%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse}
%    \begin{macrocode}
\long\def\ekv@parse##1##2##3#1%
  {%
    \ekv@gobble@from@mark@to@stop##3\ekv@endparse\ekv@stop
    \ekv@parse@other{##1}{##2}##3,\ekv@stop,%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@endparse}
%    \begin{macrocode}
\long\def\ekv@endparse
    \ekv@stop\ekv@parse@other##1\ekv@mark\ekv@stop,\ekv@stop,%
  {}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@other}
%    \begin{macrocode}
\long\def\ekv@parse@other##1##2##3,%
  {%
    \ekv@gobble@from@mark@to@stop##3\ekv@endparse@other\ekv@stop
    \ekv@eq@other##3\ekv@nil\ekv@mark\ekv@parse@eq@other@a
      =\ekv@mark\ekv@parse@eq@active
    {##1}{##2}%
    \ekv@mark
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@eq@other@a,\ekv@parse@eq@other@b}
%    \begin{macrocode}
\long\def\ekv@parse@eq@other@a##1\ekv@stop
  {%
    \ekv@eq@active##1\ekv@nil\ekv@mark\ekv@parse@eq@other@active
      #2\ekv@mark\ekv@parse@eq@other@b
  }
\ekv@exparg
  {%
    \long\def\ekv@parse@eq@other@b
        ##1\ekv@nil\ekv@mark\ekv@parse@eq@other@active\ekv@stop\ekv@mark
        ##2\ekv@nil=\ekv@mark\ekv@parse@eq@active
  }%
  {\ekv@strip{##1}\ekv@parse@pair##2\ekv@nil}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@eq@other@active}
%    \begin{macrocode}
\ekv@exparg
  {%
    \long\def\ekv@parse@eq@other@active
        ##1\ekv@stop##2\ekv@nil#2\ekv@mark
        \ekv@parse@eq@other@b\ekv@mark##3=\ekv@mark\ekv@parse@eq@active
  }%
  {\ekv@strip{##1}\ekv@parse@pair##2=##3}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@eq@active,\ekv@parse@eq@active@}
%    \begin{macrocode}
\long\def\ekv@parse@eq@active
    ##1\ekv@nil\ekv@mark\ekv@parse@eq@other@a\ekv@stop\ekv@mark
  {%
    \ekv@eq@active##1\ekv@nil\ekv@mark\ekv@parse@eq@active@
      #2\ekv@mark\ekv@parse@noeq
  }
\ekv@exparg
  {\long\def\ekv@parse@eq@active@##1\ekv@stop##2#2\ekv@mark\ekv@parse@noeq}%
  {\ekv@strip{##1}\ekv@parse@pair##2}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@noeq}
%    \begin{macrocode}
\edef\ekv@parse@noeq
  {%
    \ekv@unexpanded
      {%
        \ekv@ifblank@##1\ekv@nil\ekv@ifempty@B\ekv@parse@was@blank
          \ekv@ifempty@A\ekv@ifempty@B
      }%
      \ekv@unexpanded\expandafter{\ekv@strip{##1}\ekv@parse@key}%
  }
\ekv@exparg
  {%
    \long\def\ekv@parse@noeq
        ##1\ekv@nil\ekv@mark\ekv@parse@eq@active@\ekv@stop\ekv@mark
  }%
  {\ekv@parse@noeq}
\expandafter\def\expandafter\ekv@parse@was@blank
    \expandafter\ekv@ifempty@A\expandafter\ekv@ifempty@B
    \ekv@strip{\ekv@mark##1}\ekv@parse@key
  {\ekv@parse@other}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@endparse@other}
%    \begin{macrocode}
\long\def\ekv@endparse@other
    \ekv@stop
    \ekv@eq@other\ekv@mark\ekv@stop\ekv@nil\ekv@mark\ekv@parse@eq@other@a
    =\ekv@mark\ekv@parse@eq@active
  {\ekv@parse}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@pair,\ekv@parse@pair@}
%    \begin{macrocode}
\ekv@exparg{\long\def\ekv@parse@pair##1##2\ekv@nil}%
  {\ekv@strip{##2}\ekv@parse@pair@{##1}}
\long\def\ekv@parse@pair@##1##2##3##4%
  {%
    \ekv@unexpanded{##4{##2}{##1}}%
    \ekv@parse@other{##3}{##4}%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@parse@key}
%    \begin{macrocode}
\long\def\ekv@parse@key##1##2%
  {%
    \ekv@unexpanded{##2{##1}}%
    \ekv@parse@other{##2}%
  }
%    \end{macrocode}
% \end{macro}
%
% Finally really setting things up with |\ekvset|'s temporary meaning:
%    \begin{macrocode}
}
\catcode`\,=13
\catcode`\==13
\ekvset,=
%    \end{macrocode}
%
% \begin{macro}{\ekvsetSneaked}
% This macro can be defined just by expanding |\ekvsneak| once after expanding
% |\ekvset|. To expand everything as much as possible early on we use a
% temporary definition.
%    \begin{macrocode}
\edef\ekvsetSneaked
  {%
    \ekv@unexpanded{\ekvsneak{#2}}%
    \ekv@unexpanded\expandafter{\ekvset{#1}{#3}}%
  }
\ekv@expargtwice{\long\def\ekvsetSneaked#1#2#3}{\ekvsetSneaked}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvchangeset}
% Provide a macro that is able to switch out the current \set\ in |\ekvset|.
% This operation allows something similar to \pkg{pgfkeys}'s
% \texttt{\meta{key}/.cd} mechanism. However this operation can be more
% expensive than |/.cd| as we can't just redefine some token to reflect this,
% but have to switch out the set expandably, so this works similar to the
% |\ekvsneak| macros reading and reinserting things, but it only has to read and
% reinsert the remainder of the current key's replacement code.
%    \begin{macrocode}
\ekv@exparg{\def\ekvchangeset#1}%
  {%
    \expandafter\expandafter\expandafter
    \ekv@changeset\expandafter\csname\ekv@undefined@set{#1}\endcsname\ekv@empty
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@changeset}
% This macro does the real change-out of |\ekvchangeset|. |#2| will have a
% leading |\ekv@empty| so that braces aren't stripped accidentally, but that
% will not hurt and just expand to nothing in one step.
%    \begin{macrocode}
\long\def\ekv@changeset#1#2\ekv@set@other#3{#2\ekv@set@other#1}
%    \end{macrocode}
% \end{macro}
%
%
% \begin{macro}[internal]
%   {
%     \ekv@set@pair,\ekv@set@pair@a,\ekv@set@pair@b,\ekv@set@pair@c,
%     \ekv@set@pair@d,\ekv@set@pair@e
%   }
%   |\ekv@set@pair| gets invoked with the space and brace stripped and
%   |\detokenize|d key-name as its first, the value as the second, and the set
%   name as the third argument. It provides tests for the key-macros and
%   everything to be able to throw meaningful error messages if it isn't
%   defined. We have two routes here, one if |\lastnamedcs| is defined and one
%   if it isn't. The big difference is that if it is we can omit a |\csname| and
%   instead just expand |\lastnamedcs| once to get the control sequence.
%   If the macro is defined the value will be space and brace stripped and the
%   key-macro called. Else branch into the error handling provided by
%   |\ekv@set@pair|.
%    \begin{macrocode}
\ekv@if@lastnamedcs
  {%
    \long\def\ekv@set@pair#1\ekv@mark#2\ekv@nil#3%
      {%
        \ifcsname #3{#1}\endcsname\ekv@set@pair@a\fi\@secondoftwo
          {#2}%
          {%
            \ifcsname #3{}u\endcsname\ekv@set@pair@a\fi\@secondoftwo
              {#2}%
              {%
                \ekv@ifdefined{#3{#1}N}%
                  \ekv@err@noarg
                  \ekv@err@unknown
                  #3%
              }%
              {#1}%
          }%
        \ekv@set@other#3%
      }
    \def\ekv@set@pair@a\fi\@secondoftwo
      {\fi\expandafter\ekv@set@pair@b\lastnamedcs}
  }
  {%
    \long\def\ekv@set@pair#1\ekv@mark#2\ekv@nil#3%
      {%
        \ifcsname #3{#1}\endcsname
            \ekv@set@pair@a\fi\ekv@set@pair@c#3{#1}\endcsname
          {#2}%
          {%
            \ifcsname #3{}u\endcsname
                \ekv@set@pair@a\fi\ekv@set@pair@c#3{}u\endcsname
              {#2}%
              {%
                \ekv@ifdefined{#3{#1}N}%
                  \ekv@err@noarg
                  \ekv@err@unknown
                  #3%
              }%
              {#1}%
          }%
        \ekv@set@other#3%
      }
    \def\ekv@set@pair@a\fi\ekv@set@pair@c{\fi\expandafter\ekv@set@pair@b\csname}
    \long\def\ekv@set@pair@c#1\endcsname#2#3{#3}
  }
\long\def\ekv@set@pair@b#1%
  {%
    \ifx#1\relax
      \ekv@set@pair@e
    \fi
    \ekv@set@pair@d#1%
  }
\ekv@exparg{\long\def\ekv@set@pair@d#1#2#3}{\ekv@strip{#2}#1}
\long\def\ekv@set@pair@e\fi\ekv@set@pair@d#1#2#3{\fi#3}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]
%   {\ekv@set@key,\ekv@set@key@a,\ekv@set@key@b,\ekv@set@key@c}
% Analogous to |\ekv@set@pair|, |\ekv@set@key| builds the |NoVal| key-macro and
% provides an error-branch. |\ekv@set@key@| will test whether the key-macro is
% defined and if so call it, else the errors are thrown.
%    \begin{macrocode}
\ekv@if@lastnamedcs
  {%
    \long\def\ekv@set@key#1\ekv@mark#2%
      {%
        \ifcsname #2{#1}N\endcsname\ekv@set@key@a\fi\@firstofone
          {%
            \ifcsname #2{}uN\endcsname\ekv@set@key@a\fi\@firstofone
              {%
                \ekv@ifdefined{#2{#1}}%
                  \ekv@err@reqval
                  \ekv@err@unknown
                  #2%
              }%
              {#1}%
          }%
        \ekv@set@other#2%
      }
    \def\ekv@set@key@a\fi\@firstofone{\fi\expandafter\ekv@set@key@b\lastnamedcs}
  }
  {%
    \long\def\ekv@set@key#1\ekv@mark#2%
      {%
        \ifcsname #2{#1}N\endcsname
            \ekv@set@key@a\fi\ekv@set@key@c#2{#1}N\endcsname
          {%
            \ifcsname #2{}uN\endcsname
                \ekv@set@key@a\fi\ekv@set@key@c#2{}uN\endcsname
              {%
                \ekv@ifdefined{#2{#1}}%
                  \ekv@err@reqval
                  \ekv@err@unknown
                  #2%
              }%
              {#1}%
          }%
        \ekv@set@other#2%
      }
    \def\ekv@set@key@a\fi\ekv@set@key@c{\fi\expandafter\ekv@set@key@b\csname}
    \long\def\ekv@set@key@c#1N\endcsname#2{#2}
  }
\long\def\ekv@set@key@b#1%
  {%
    \ifx#1\relax
      \ekv@fi@secondoftwo
    \fi
    \@firstoftwo#1%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvsetdef}
%   Provide a macro to define a shorthand to use |\ekvset| on a specified \set.
%   To gain the maximum speed |\ekvset| is expanded twice by
%   |\ekv@exparg| so that during runtime the macro storing the set name
%   is already built and one |\expandafter| doesn't have to be used.
%    \begin{macrocode}
\ekv@expargtwice{\protected\def\ekvsetdef#1#2}%
  {%
    \romannumeral
    \ekv@exparg{\ekv@zero\ekv@exparg{\long\def#1##1}}%
      {\ekvset{#2}{##1}}%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvsetSneakeddef,\ekvsetdefSneaked}
% And do the same for |\ekvsetSneaked| in the two possible ways, with a fixed
% sneaked argument and with a flexible one.
%    \begin{macrocode}
\ekv@expargtwice{\protected\def\ekvsetSneakeddef#1#2}%
  {%
    \romannumeral
    \ekv@exparg{\ekv@zero\ekv@exparg{\long\def#1##1##2}}%
      {\ekvsetSneaked{#2}{##1}{##2}}%
  }
\ekv@expargtwice{\protected\def\ekvsetdefSneaked#1#2#3}%
  {%
    \romannumeral
    \ekv@exparg{\ekv@zero\ekv@exparg{\long\def#1##1}}%
      {\ekvsetSneaked{#2}{#3}{##1}}%
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@alignsafe,\ekv@endalignsafe}
%   These macros protect the usage of ampersands inside of alignment contexts.
%    \begin{macrocode}
\begingroup
\catcode`\^^@=2
\@firstofone{\endgroup
  \def\ekv@alignsafe{\romannumeral\iffalse{\fi`^^@ }
}
\def\ekv@endalignsafe{\ifnum`{=\ekv@zero}\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekvoptarg,\ekvoptargTF}
% Provide macros to expandably collect an optional argument in brackets. The
% macros here are pretty simple in nature compared to \pkg{xparse}'s
% possibilities (they don't care for nested bracket levels).
%
% We start with a temporary definition to pre-expand |\ekv@alignsafe| (will be
% |#1|) and |\ekv@endalignsafe| (will be |#2|). As |\ekv@alignsafe| starts with
% a |\romannumeral| we use that to also control the number of steps needed
% instead of adding another |\romannumeral|. For this we have to remove the
% space token from the end of |\ekv@alignsafe|'s definition.
%    \begin{macrocode}
\begingroup
\def\ekvoptarg#1#2{%
\endgroup
%    \end{macrocode}
% The real definition starts an expansion context and afterwards grabs the
% arguments. |#1| will be the next step, |#2| the default value, and |#3| might
% be an opening bracket, or the mandatory argument. We check for the opening
% bracket, if it is found grab the optional argument, else leave |#1{#2}| in the
% input stream after ending the expansion context.
%    \begin{macrocode}
\def\ekvoptarg{#1\ekv@optarg@a}
\long\def\ekv@optarg@a##1##2##3%
  {%
    \ekv@optarg@if\ekv@mark##3\ekv@mark\ekv@optarg@b\ekv@mark[\ekv@mark
    #2%
    \@firstofone{ ##1}{##2}{##3}%
  }%
%    \end{macrocode}
% The other variant of this will do roughly the same. Here, |#1| will be the
% next step if an optional argument is found, |#2| the next step else, and |#3|
% might be the opening bracket or mandatory argument.
%    \begin{macrocode}
\def\ekvoptargTF{#1\ekv@optargTF@a}
\long\def\ekv@optargTF@a##1##2##3%
  {%
    \ekv@optarg@if\ekv@mark##3\ekv@mark\ekv@optargTF@b{##1}\ekv@mark[\ekv@mark
    #2%
    \@firstofone{ ##2}{##3}%
  }
%    \end{macrocode}
% The two macros to grab the optional argument have to remove the remainder of
% the test and the wrong next step as well as grabbing the argument.
%    \begin{macrocode}
\long\def\ekv@optarg@b\ekv@mark[\ekv@mark\ifnum`##1\fi\@firstofone##2##3##4##5]%
  {#2##2{##5}}
\long\def\ekv@optargTF@b
    ##1\ekv@mark[\ekv@mark\ifnum`##2\fi\@firstofone##3##4##5]%
  {#2 ##1{##5}}
}
%    \end{macrocode}
% Do the definitions and add the test macro. We use |\ekv@strip| to remove the
% trailing space from the definition of |\ekv@alignsafe|.
%    \begin{macrocode}
\ekv@exparg
  {%
    \expandafter\ekv@strip\expandafter
      {\expandafter\ekv@mark\ekv@alignsafe}%
      \ekvoptarg
  }%
  \ekv@endalignsafe
\long\def\ekv@optarg@if#1\ekv@mark[\ekv@mark{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\ekverr}
% \begin{macro}[internal]{\ekv@err@collect,\ekv@err@cleanup}
% Since |\ekvset| is fully expandable as long as the code of the keys is (which
% is unlikely) we want to somehow throw expandable errors, in our case via
% a runaway argument (to my knowledge the first version of this method was
% implemented by Jean-François Burnol, many thanks to him). The first step is to
% ensure that the second argument (which might contain user input) doesn't
% contain tokens we use as delimiters (in this case |\par|), this will be done
% by the front facing macro |\ekverr|. But first we set some other things up.
%
% We use a temporary definition for |\ekverr| to get multiple consecutive
% spaces. Then we set up the macro that will collect the error and the macro
% that will throw the error. The latter will have an unreasonable long name.
% This way we can convey more information. Though the information in the macro
% name is static and has to be somewhat general to fit every occurence. The
% important bit is that the long named macro has a delimited argument and is
% short which will throw the error at the |\par| at the end of
% |\ekv@err@collect|. This macro has the drawback that it will only print nicely
% if the |\newlinechar| is |^^J|.
%    \begin{macrocode}
\def\ekv@err@cleanup\par{}
\def\ekv@err@collect#1%
  {%
    \def\ekv@err@collect##1\par##2%
      {%
        \expandafter
        \ekv@err@cleanup
        #1! ##2 Error: ##1\par
      }%
    \def#1##1\thanks@jfbu{}%
  }
\def\ekverr{ }
\expandafter\ekv@err@collect\csname <an-expandable-macro>^^J%
  completed due to above exception. \ekverr If the error^^J%
  summary is \ekverr not comprehensible \ekverr see the package^^J%
  documentation.^^J%
  I will try to recover now. \ekverr If you're in inter-^^J%
  active mode hit <return> \ekverr at the ? prompt and I^^J%
  continue hoping recovery\endcsname
%    \end{macrocode}
%    \begin{macrocode}
\long\def\ekverr#1#2{\expandafter\ekv@err@collect\detokenize{#2}\par{#1}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[internal]{\ekv@err}
% We define a shorthand to throw errors in \expkv.
%    \begin{macrocode}
\ekv@exparg{\long\def\ekv@err#1}{\ekverr{expkv}{#1}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}[internal]
%   {
%     \ekv@err@common,\ekv@err@common@,
%     \ekv@err@unknown,\ekv@err@noarg,\ekv@err@reqval
%   }
% Now we can use |\ekv@err| to set up some error messages so that we can later
% use those instead of the full strings.
%    \begin{macrocode}
\long\def\ekv@err@common #1#2{\expandafter\ekv@err@common@\string#2{#1}}
\ekv@exparg{\long\def\ekv@err@common@#1`#2' #3.#4#5}%
  {\ekv@err{#4 `#5' in set `#2'}}
\ekv@exparg{\long\def\ekv@err@unknown#1}{\ekv@err@common{unknown key}{#1}}
\ekv@exparg{\long\def\ekv@err@noarg  #1}
  {\ekv@err@common{unwanted value for}{#1}}
\ekv@exparg{\long\def\ekv@err@reqval #1}{\ekv@err@common{missing value for}{#1}}
\ekv@exparg{\long\def\ekv@err@redirect@kv@notfound#1#2#3\ekv@stop}%
  {\ekv@err{no key `#2' in sets #3}}
\ekv@exparg{\def\ekv@err@redirect@k@notfound#1#2\ekv@stop}%
  {\ekv@err{no NoVal key `#1' in sets #2}}
%    \end{macrocode}
% \end{macro}
%
% Now everything that's left is to reset the category code of |@|.
%    \begin{macrocode}
\catcode`\@=\ekv@tmp
%    \end{macrocode}
%
% \gobbledocstriptag
%</tex>
%^^A=<<
%
%^^A=<<
%
% \end{implementation}^^A=<<
%
% \clearpage
% \PrintIndex
%
\endinput
%
^^A vim: ft=tex fdm=marker fmr=>>=,=<<