chemformula (9aug14)

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+--------------------------------------------------------------------------
+the CHEMFORMULE package v4.7 2014/08/08
+
+  typeset chemical compounds and reactions
+
+--------------------------------------------------------------------------
+Clemens Niederberger
+Web:    https://github.com/cgnieder/chemformula/
+E-Mail: contact@mychemistry.eu
+--------------------------------------------------------------------------
+Copyright 2011-2014 Clemens Niederberger
+
+This work may be distributed and/or modified under the
+conditions of the LaTeX Project Public License, either version 1.3
+of this license or (at your option) any later version.
+The latest version of this license is in
+  http://www.latex-project.org/lppl.txt
+and version 1.3 or later is part of all distributions of LaTeX
+version 2005/12/01 or later.
+
+This work has the LPPL maintenance status `maintained'.
+
+The Current Maintainer of this work is Clemens Niederberger.
+--------------------------------------------------------------------------
+The chemformula package consists of the following files
+ - chemformula.sty,
+ - chemformula_en.tex, chemformula_en.pdf,
+ - README
+--------------------------------------------------------------------------
+If you have any ideas, questions, suggestions or bugs to report, please
+feel free to contact me.
+--------------------------------------------------------------------------
diff --git a/Master/texmf-dist/doc/latex/chemformula/chemformula_en.pdf b/Master/texmf-dist/doc/latex/chemformula/chemformula_en.pdf
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+% arara: pdflatex
+% !arara: biber
+% !arara: pdflatex
+% arara: pdflatex
+% --------------------------------------------------------------------------
+% the CHEMFORMULA package
+%
+%   typeset chemical compounds and reactions
+%
+% --------------------------------------------------------------------------
+% Clemens Niederberger
+% --------------------------------------------------------------------------
+% https://github.com/cgnieder/chemformula/
+% contact@mychemistry.eu
+% --------------------------------------------------------------------------
+% If you have any ideas, questions, suggestions or bugs to report, please
+% feel free to contact me.
+% --------------------------------------------------------------------------
+% Copyright 2011-2013 Clemens Niederberger
+%
+% This work may be distributed and/or modified under the
+% conditions of the LaTeX Project Public License, either version 1.3
+% of this license or (at your option) any later version.
+% The latest version of this license is in
+%   http://www.latex-project.org/lppl.txt
+% and version 1.3 or later is part of all distributions of LaTeX
+% version 2005/12/01 or later.
+%
+% This work has the LPPL maintenance status `maintained'.
+%
+% The Current Maintainer of this work is Clemens Niederberger.
+% --------------------------------------------------------------------------
+\documentclass[load-preamble+]{cnltx-doc}
+\usepackage[utf8]{inputenc}
+\usepackage[greek=newtx]{chemmacros}
+\setcnltx{
+  package  = {chemformula},
+  url      = https://github.com/cgnieder/chemformula/ ,
+  authors  = Clemens Niederberger ,
+  email    = contact@mychemistry.eu ,
+  abstract = {%
+    \centering
+    \includegraphics{chemmacros-logo.pdf}
+    \par
+  } ,
+  add-cmds = {
+    ce, ch, charrow, chcpd, chemformula@bondlength, chemsetup, chlewis,
+      chname,
+    DeclareChemArrow, DeclareChemBond, DeclareChemBondAlias,
+    mch,
+    NewChemArrow, NewChemBond, NewChemBondAlias,
+    ox, OX,
+    pch,
+    redox, RenewChemArrow, RenewChemBond,
+    setchemformula, ShowChemArrow, ShowChemBond
+  } ,
+  add-silent-cmds = {
+    addplot,
+    chemfig,
+    DeclareInstance, draw,
+    sample, setatomsep,
+    usetikzlibrary
+  }
+}
+
+\usepackage{chemfig,booktabs,cancel,varioref}
+\usepackage[version=3]{mhchem}
+
+\expandafter\def\csname libertine@figurestyle\endcsname{LF}
+\usepackage[libertine]{newtxmath}
+\expandafter\def\csname libertine@figurestyle\endcsname{OsF}
+
+\usepackage[biblatex]{embrac}
+\ChangeEmph{[}[,.02em]{]}[.055em,-.08em]
+\ChangeEmph{(}[-.01em,.04em]{)}[.04em,-.05em]
+
+\usepackage[accsupp]{acro}
+\acsetup{
+  long-format  = \scshape ,
+  short-format = \scshape
+}
+\DeclareAcronym{iupac}{
+  short     = iupac ,
+  long      = International Union of Pure and Applied Chemistry ,
+  pdfstring = IUPAC ,
+  accsupp   = IUPAC
+}
+
+\chemsetup{
+  option/synchronize ,
+  chemformula/format = \libertineLF
+}
+
+\sisetup{
+  detect-mode=false,
+  mode=text,
+  text-rm=\libertineLF
+}
+
+\usepackage{filecontents}
+
+\defbibheading{bibliography}{\addsec{References}}
+\addbibresource{\jobname.bib}
+\begin{filecontents*}{\jobname.bib}
+@book{iupac:greenbook,
+  author    = {E. Richard Cohan and Tomislav Cvita\v{s} and Jeremy G. Frey and
+    Bertil Holmstr\"om and Kozo Kuchitsu and Roberto Marquardt and Ian Mills and
+    Franco Pavese and Martin Quack and J\"urgen Stohner and Herbert L. Strauss and
+    Michio Takami and Anders J Thor} ,
+  title     = {``Quantities, Symbols and Units in Physical Chemistry'', \acs{iupac}
+    Green Book} ,
+  sorttitle = {Quantities, Symbols and Units in Physical Chemistry} ,
+  indexsorttitle = {Quantities, Symbols and Units in Physical Chemistry} ,
+  edition   = {3rd Edition. 2nd Printing} ,
+  year      = {2008} ,
+  publisher = {\acs{iupac} \&\ RSC Publishing, Cambridge}
+}
+\end{filecontents*}
+
+\DeclareInstance{xfrac}{chemformula-text-frac}{text}
+  {
+    scale-factor        = 1 ,
+    denominator-bot-sep = -.2ex ,
+    denominator-format  = \scriptsize #1 ,
+    numerator-top-sep   = -.2ex ,
+    numerator-format    = \scriptsize #1 ,
+    slash-right-kern    = .05em ,
+    slash-left-kern     = .05em
+  }
+
+\newpackagename\chemmacros{chemmacros}
+
+\newidxcmd\manual{\textsf{#1}}[\ (manual)]
+\newidxcmd\arrowtype{\code{#1}}[\ (arrow type)]
+
+\makeatletter
+\newcommand*\cf@arrow{%
+  \@ifstar
+    {\cf@arrow@star}
+    {\cf@arrow@nostar}%
+}
+\newrobustcmd*\cf@arrow@star[1]{%
+  \@ifnextchar[
+    {\cf@arrow@star@opt{#1}}
+    {\cf@arrow@star@opt{#1}[]}%
+}
+\newrobustcmd*\cf@arrow@nostar[1]{%
+  \@ifnextchar[
+    {\cf@arrow@nostar@opt{#1}}
+    {\cf@arrow@nostar@opt{#1}[]}%
+}
+\def\cf@arrow@star@opt#1[#2]{%
+  \ifblank{#2}
+    {\item\arrowtype*{#1}}
+    {\item\arrowtype*{#1}#2}%
+  \cnltx@checkdefault{\hfill\newline}%
+}
+\def\cf@arrow@nostar@opt#1[#2]{%
+  \ifblank{#2}
+    {\item\arrowtype{#1}}
+    {\item\arrowtype{#1}#2}%
+  \cnltx@checkdefault{\hfill\newline}%
+}
+
+\newenvironment{codedesc}
+  {%
+    \def\Code##1{\item\code{##1}\hfill\newline}%
+    \cnltxlist
+  }
+  {\endcnltxlist}
+
+\newenvironment{arrows}
+  {%
+    \let\arrow\cf@arrow
+    \cnltxlist
+  }
+  {\endcnltxlist}
+\makeatother
+
+\renewcommand*\AmS{\hologo{AmS}}
+
+\newcommand*\TikZ{Ti\textit{k}Z}
+
+\newname\hensel{Martin Hensel}
+
+\BeforeBeginEnvironment{example}{\vspace{\baselineskip}}
+\AfterEndEnvironment{example}{\vspace{\baselineskip}}
+\BeforeBeginEnvironment{sourcecode}{\vspace{\baselineskip}}
+\AfterEndEnvironment{sourcecode}{\vspace{\baselineskip}}
+
+\begin{document}
+
+\section{Introduction}
+Probably every chemist using \LaTeXe\ is aware of the great \pkg{mhchem}
+package by \hensel.  There have always been some difficulties intertwining it
+with the \chemmacros{} package, though.  Also, some other minor points in
+\pkg{mhchem} always bothered me, but they hardly seemed enough for a new
+package.  They weren't even enough for a feature request to the \pkg{mhchem}
+author.  The challenge and the fun of creating a new package and the wish for
+a highly customizable alternative led to \chemformula{} after all.
+
+\chemformula{} works very similar to \pkg{mhchem} but is more strict as to how
+compounds, stoichiometric factors and arrows are input.  In the same time
+\chemformula{} offers \emph{many} possibilities to customize the output.
+
+\section{News}
+\subsection{Version 4.0}
+Since version 4.0\sinceversion{4.0}, the \chemformula{} package can be used
+independently from \chemmacros.  This means that if you say
+\begin{sourcecode}
+  \usepackage{chemformula}
+\end{sourcecode}
+then \chemmacros\ will not be loaded.  The \chemmacros\ package, however,
+\emph{will} load \chemformula.
+
+\subsection{Version 4.2}
+\begin{itemize}
+  \item New option \option{arrow-style}.
+  \item New command \cs{chlewis} that allows to add Lewis electrons to an
+    atom, see section~\ref{sec:lewis-formulae}.
+\end{itemize}
+
+\subsection{Version 4.3}
+\begin{itemize}
+  \item New option \option{stoich-print}.
+  \item New command \cs{chstoich}.
+  \item The commands \cs*{DeclareChem\meta{...}} now don't give an error any
+    more if the command already exists.  This is more consistent with \LaTeX's
+    \cs*{DeclareRobustCommand}.  For all those commands a version
+    \cs*{NewChem\meta{...}} is introduced that \emph{does} give an error if
+    the new command is already defined.
+\end{itemize}
+
+\subsection{Version 4.4}
+\begin{itemize}
+  \item A single dash \code{-} in \cs{ch} is now treated as a minus sign.
+  This is consistent with the behaviour of a \code{+}.
+\end{itemize}
+
+\subsection{Version 4.5}
+\begin{itemize}
+  \item New arrow types \arrowtype{>=<}, \arrowtype{>=<<}, \arrowtype{>>=<}
+    and \arrowtype{<==>}.
+  \item Internal changes to \cs{ch} allow usage of optional arguments of
+    \cs*{\textbackslash} and \cs*{label} in \chemmacros' \env*{reactions}
+    environment.
+\end{itemize}
+
+\subsection{Version 4.6}
+\begin{itemize}
+  \item New options \option{circled} and \option{circletype}.  this allows to
+    set the behaviour as described on \chemmacros' manual for a specific usage
+    of \cs{ch}.
+\end{itemize}
+
+\subsection{Version 4.7}
+\begin{itemize}
+  \item Dependency change: \chemformula{} now requires the \TikZ{} library
+    \code{arrows.meta} instead of the library \code{arrows}.  This requires
+    \TikZ{} version~3.0.0.
+\end{itemize}
+
+\subsection{Version 4.8}
+\begin{itemize}
+  \item The \chemformula{} package now is no longer part of the \chemmacros{}
+    bundle but is dirtributed as a package of it's own.
+\end{itemize}
+
+\section{Licence and Requirements}
+\license
+
+The \chemformula{} package needs and thus loads the packages
+\bnd{l3kernel}~\cite{bnd:l3kernel}, \pkg{xparse}, \pkg{l3keys2e} and
+\pkg{xfrac} (all three are part of the \bnd{l3packages}
+bundle~\cite{bnd:l3packages}),
+\pkg{tikz}\footnote{\CTANurl[graphics]{pgf}}~\cite{pkg:pgf},
+\pkg{amsmath}~\cite{pkg:amsmath}, \pkg{nicefrac}~\cite{pkg:nicefrac} and
+\pkg{scrlfile} (from the \KOMAScript\footnote{\CTANurl{koma-script}}
+bundle~\cite{bnd:koma-script}).
+
+\section{Setup}
+All of \chemformula's options belong to \chemmacros' module
+\module{chemformula}.  This means if you load it via \chemmacros{} or in
+addition to \chemmacros{} they can be setup with
+\begin{commands}
+  \command{chemsetup}[\Oarg{chemformula}\marg{options}]
+    Set up options for \chemformula{} exclusively, or
+  \command{chemsetup}[\Marg{chemformula/\meta{option1},chemformula/\meta{option2}}]
+    Set up options for \chemformula{} together with others of \chemmacros'
+    options.
+\end{commands}
+However, if you're using \chemformula{} as a standalone package the command
+\cs{chemsetup} is not available.  This is why \chemformula{} also has its own
+setup command:
+\begin{commands}
+  \command{setchemformula}[\marg{options}]
+    Set up \chemformula{} when using it independently from \chemmacros.
+\end{commands}
+
+\section{The Basic Principle}
+\chemformula{} offers one main command.
+\begin{commands}
+  \command{ch}[\oarg{options}\marg{input}]
+    \chemformula's main command.
+\end{commands}
+The usage will seem very familiar to you if you're familiar with \pkg{mhchem}:
+\begin{example}[side-by-side]
+  \ch{H2O} \par
+  \ch{Sb2O3} \par
+  \ch{H+} \par
+  \ch{CrO4^2-} \par
+  \ch{AgCl2-} \par
+  \ch{[AgCl2]-} \par
+  \ch{Y^{99}+} \par
+  \ch{Y^{99+}} \par
+  \ch{H2_{(aq)}} \par
+  \ch{NO3-} \par
+  \ch{(NH4)2S} \par
+  \ch{^{227}_{90}Th+} \par
+  $V_{\ch{H2O}}$ \par
+  \ch{Ce^{IV}} \par
+  \ch{KCr(SO4)2 * 12 H2O}
+\end{example}
+
+However, there are differences.  The most notable one: \chemformula\
+distinguishes between different types of input.  These different parts
+\emph{have} to be separated with blanks:
+\begin{commands}
+  \command{ch}[\Marg{part1 part2 part3 part4}]
+\end{commands}
+A blank in the input \emph{never} is a blank in the output.  This role of the
+blank strictly holds and disregarding it can have unexpected results and even
+lead to errors.
+
+Another notable difference: \chemformula{} tries to avoid math mode whenever
+possible:
+\begin{example}[side-by-side]
+  \ch{A + B ->[a] C} \par
+  \ce{A + B ->[a] C}
+\end{example}
+
+This means that \cs{ch}\Marg{2H2O} is recognized as a \emph{single} part,
+which in this case is recognized as a compound.
+\begin{example}[side-by-side]
+  \ch{2H2O} \par
+  \ch{2 H2O}
+\end{example}
+This also means, that a part cannot contain a blank since this will
+automatically divide it into two parts.  If you need an extra blank in the
+output you need to use \verbcode+~+.  However, since commands in most cases
+gobble a space after them a input like \cs{ch}\Marg{\cs*{command} ABC} will be
+treated as a single part.  If you want or need to divide them you need to add
+an empty group: \cs{ch}\Marg{\cs*{command}\marg{} ABC}.  The different input
+types are described in the following sections.
+
+% TODO: Module überdenken, Beschreibung anpassen
+There are some options to customize the output of the \cs{ch} command.  They
+can either be applied locally using the optional argument or can be set
+globally using the setup command.  All options of \chemformula{} belong to the
+module \module{chemformula} and can be set in different ways:
+\begin{commands}
+  \command{chemsetup}[\Oarg{chemformula}\marg{options}]
+    when loaded via \chemmacros
+  \command{chemsetup}[\Marg{chemformula/\meta{options}}]
+    when loaded via \chemmacros
+  \command{setchemformula}[\marg{options}]
+    independent from \chemmacros
+\end{commands}
+
+\section{Stoichiometric Factors}
+A stoichiometric factor may only contain of numbers and the signs
+\verbcode+.,_/()+
+\begin{example}[side-by-side]
+  \ch{2} \par
+  \ch{12}
+
+  % decimals:
+  \ch{.5} \par
+  \ch{5,75}
+
+  % fractions:
+  \ch{3/2} \par
+  \ch{1_1/2}
+ 
+  % ``iupac'':
+  \ch{(1/2)}
+\end{example}
+
+As you can see if you input decimal numbers a missing leading zero is added.
+
+You have to be a little bit careful with the right syntax but I believe it is
+rather intuitive.
+\begin{sourcecode}
+  this won't work but will result in an error: \ch{1/1_1}
+\end{sourcecode}
+
+If stoichiometric factors are enclosed with parentheses the fractions are not
+recognized and missing leading zeros are not added.  What's inside the
+parentheses is typeset as is.
+\begin{example}
+  \ch{(1/2) H2O} \ch{1/2 H2O} \ch{0.5 H2O}
+\end{example}
+You can find many examples like the following for stoichiometric factors in
+parentheses in the \acs{iupac} Green Book~\cite{iupac:greenbook}:
+\begin{reaction*}
+ (1/5) K "\ox*{7,Mn}" O4 + (8/5) HCl == (1/5) "\ox*{2,Mn}" Cl2 + (1/2) Cl2 + (1/5) KCl + (4/5) H2O
+\end{reaction*}
+
+There are a few possibilities to customize the output.
+\begin{options}
+  \keyval{decimal-marker}{marker}\Default{.}
+    The symbol to indicate the decimal.
+  \keychoice{frac-style}{math,xfrac,nicefrac}\Default{math}
+    Determines how fractions are displayed.
+  \keyval{frac-math-cmd}{command sequence}\Default{\cs*{frac}}
+    \sinceversion{4.1}Allows you to choose which command is used with
+    \keyis{frac-style}{math}.  This needs to be a command sequence that takes
+    two arguments that are set in math mode.
+  \keyval{stoich-space}{skip}\Default{.1667em plus .0333em minus .0117em}
+    The space that is placed after the stoichiometric factor.  A rubber
+    length.
+  \keybool{stoich-paren-parse}\Default{false}
+    If set to true stoichiometric factors enclosed by parentheses also are
+    parsed.
+  \keyval{stoich-print}{cs}\Default{\cs{chstoich}}
+    This option allows to redefine the macro that prints the stoichiometric
+    factors.  \meta{cs} should be a macro that takes one mandatory argument.
+    \emph{Please note that using this option will disable \chemformula's
+      stoichiometric parsing as that is done by the default command
+      \cs{chstoich}.}
+\end{options}
+
+\begin{example}
+  \ch[decimal-marker={,}]{3.5} \ch[decimal-marker={$\cdot$}]{3,5} 
+\end{example}
+
+The option \keyis{frac-style}{xfrac} uses the \verbcode+\sfrac+ command of the
+\pkg{xfrac} package.  The output strongly depends on the font you use.
+\begin{example}
+  \ch[frac-style=xfrac]{3/2} \ch[frac-style=xfrac]{1_1/2}
+\end{example}
+\chemformula{} defines the instance \verbcode=formula-text-frac= which you can
+redefine to your needs.  See the \pkg{xfrac} documentation for further
+information.  The default definition is this:
+\begin{sourcecode}
+  \DeclareInstance{xfrac}{chemformula-text-frac}{text}
+   {
+     slash-left-kern  = -.15em ,
+     slash-right-kern = -.15em
+   }
+\end{sourcecode}
+This document uses the font Linux Libertine~O and the following definition:
+\begin{sourcecode}
+  \DeclareInstance{xfrac}{chemformula-text-frac}{text}
+   {
+     scale-factor        = 1 ,
+     denominator-bot-sep = -.2ex ,
+     denominator-format  = \scriptsize #1 ,
+     numerator-top-sep   = -.2ex ,
+     numerator-format    = \scriptsize #1 ,
+     slash-right-kern    = .05em ,
+     slash-left-kern     = .05em
+   }
+\end{sourcecode}
+
+The option \keyis{frac-style}{nicefrac} uses the \verbcode+\nicefrac+ command
+of the \pkg{nicefrac} package.
+\begin{example}
+  \ch[frac-style=nicefrac]{3/2} \ch[frac-style=nicefrac]{1_1/2}
+\end{example}
+
+The option \option{stoich-space} allows you to customize the space between
+stoichiometric factor and the group following after it.
+\begin{example}[side-by-side]
+  \ch{2 H2O} \par
+  \ch[stoich-space=.3em]{2 H2O}
+\end{example}
+
+\section{Compounds}\label{ssec:compounds}
+\chemformula{} determines compounds as the type that ``doesn't fit in anywhere
+else.''  This point will become more clear when you know what the other types
+are.
+\begin{example}[side-by-side]
+  \ch{H2SO4} \par
+  \ch{[Cu(NH3)4]^2+}
+\end{example}
+
+\subsection{Adducts}
+\chemformula{} has two identifiers which will create adducts.
+\begin{commands}
+  \command{ch}[\Marg{A.B}] \ch{A.B}
+  \command{ch}[\Marg{A*B}] \ch{A*B}
+\end{commands}
+\begin{example}[side-by-side]
+  \ch{CaSO4.H2O} \par
+  \ch{CaSO4*H2O}
+\end{example}
+Since numbers in a compound always are treated as subscripts (see
+section~\ref{ssec:subscripts}) you sometimes need to introduce stoichiometric
+factors for the right output:
+\begin{example}[side-by-side]
+  \ch{Na3PO4*12H2O} \par
+  \ch{Na3PO4* 12 H2O} \par
+  \ch{Na3PO4 * 12 H2O}
+\end{example}
+
+\subsection{Subscripts}\label{ssec:subscripts}
+\emph{All} numbers in a compound are treated as subscripts.
+\begin{example}[side-by-side]
+  \ch{H2SO4}
+\end{example}
+If you want a letter to be a subscript you can use the math syntax:
+\begin{example}[side-by-side]
+  \ch{A_nB_m}
+\end{example}
+The subscript recognizes groups. You can also use math inside it.
+\begin{example}[side-by-side]
+  \ch{A_{$n$}B_{$m$}} \par
+  \ch{NaCl_{(aq)}}
+\end{example}
+
+\subsection{Commands}
+Commands are allowed in a compound:
+\begin{example}[side-by-side]
+  \ch{\textbf{A2}B3} \ch{A2\color{red}B3}
+\end{example}
+
+However, if the commands demand numbers as argument, \eg, space commands or
+\chemmacros' \verbcode+\ox+ command the direct use will fail.  This is
+because the numbers are treated as subscripts \emph{before} the command
+expands.
+\begin{sourcecode}
+  \ch{A\hspace{2mm}B} will raise an error because \hspace sees something like
+  this: \hspace{$_2$mm}. Actually not at all like it but equally bad\ldots
+\end{sourcecode}
+See section~\ref{ssec:text} for a way around this.
+
+\subsection{Charges and Other Superscripts}
+\paragraph{Basics}
+If a compound \emph{ends} with a plus or minus sign it will be treated as
+charge sign and typeset as superscript.  In other places a plus is treated as
+a triple bond and a dash will be used as a single bond, see
+section~\ref{ssec:bonds}.
+\begin{example}[side-by-side]
+  \ch{A+B} \ch{AB+} \par
+  \ch{A-B} \ch{AB-}
+\end{example}
+
+For longer charge groups or other superscripts you can use the math syntax.
+It recognizes groups and you can use math inside them.  Inside these groups
+neither \code{+} nor \code{-} are treated as bonds.  If a dot \code{.} is
+inside a superscript it is treated as indicator for a radical.  A \code{*}
+gives the excited state.
+\begin{example}[side-by-side]
+  \ch{A^{x-}} \par
+  \ch{A^x-} \par
+  \ch{A^{x}-} \par
+  \ch{A^{$x-$}} \par
+  \ch{RNO2^{-.}} \par
+  \ch{^31H} \par
+  \ch{^{14}6C} \par
+  \ch{^{58}_{26}Fe} \par
+  \ch{NO^*}
+\end{example}
+
+Actually\changedversion{4.5a} a dot \code{.} is not always treated as
+indicator for a radical: if the dot in the superscript is followed by a number
+it is interpreted as a decimal sign.  It is typeset according to the option
+\option{decimal-marker}.  This may be a good place to mention that a comma
+\code{,} in a superscript is also typeset according to
+\option{decimal-marker}.
+
+\begin{example}[side-by-side]
+  \ch{^{22,98}_{11}Na}
+  \ch{^{22.98}_{11}Na}\par
+  \setchemformula{decimal-marker={,}}
+  \ch{^{22,98}_{11}Na}
+  \ch{^{22.98}_{11}Na}
+\end{example}
+
+Ions and ion composites with more than one charge can be typeset quite as
+easy:
+\begin{example}[side-by-side]
+  \ch{SO4^2-} \ch{Ca^2+ SO4^2-}
+\end{example}
+
+\paragraph{Charge Commands}
+You don't need to use \cs{mch} and related commands inside \cs{ch}.  Indeed,
+you \emph{shouldn't} use them as they might mess with the subscript and
+superscript alignment.  The \chemmacros\ option \code{circled} is obeyed by
+\cs{ch}.
+\begin{example}
+  \chemsetup[option]{circled=all}
+  \ch{H+ + OH- <=> H2O}
+\end{example}
+
+\chemformula{} knows the options \option{circled} and \option{circletype} also
+on its own:
+
+There are coupled with \chemmacros{} options, \ie, setting \chemmacros'
+options will also set \chemformula's equivalents.  The other way around the
+options act independently: setting \chemformula's options will \emph{not} set
+\chemmacros' options.
+\begin{options}
+  \keychoice{circled}{formal,\default{all},none}\Default{formal}
+    \chemformula{} uses two different kinds of charges which indicate the usage
+    of real ($+/-$) and formal (\fplus/\fminus) charges.  The choice
+    \code{formal} distinguishes between them, choice \code{none} displays them
+    all without circle, choice \code{all} circles all.
+  % circletype
+  \keychoice{circletype}{\default{chem},math}\Default{chem}
+    This option switches between two kinds of circled charge symbols:
+    \cs{fplus} \fplus\ and \verbcode+$\oplus$+ $\oplus$.
+\end{options}
+
+\paragraph{Behaviour}
+The supercripts behave differently depending on their position in a compound,
+if there are super- and subscripts following each other directly.
+\begin{example}
+  \ch{^33B} \ch{{}^33B} \ch{3^3B} \ch{B^3} \ch{B3^3} \par
+  \ch{^{23}_{123}B} \ch{{}^{23}_{123}B} \ch{_{123}^{23}B}
+  \ch{B^{23}} \ch{B_{123}^{23}} \par
+  \ch{^{123}_{23}B} \ch{{}^{123}_{23}B} \ch{_{23}^{123}B}
+  \ch{B^{123}} \ch{B23^{123}}
+\end{example}
+\begin{itemize}
+  \item If a compound \emph{starts} with a sub- or superscript both sub- and
+    superscript are aligned to the \emph{right} else to the \emph{left}.
+  \item If a compound \emph{does not start} with a sub- or superscript and
+    there is both a sub- and a superscript, the superscript is shifted
+    additionally by a length determined from the option
+    \key{charge-hshift}{dim}, also see page~\pageref{desc:charge-hshift}f.
+\end{itemize}
+The second point follows \ac{iupac}'s recommendations:
+\begin{cnltxquote}[{\acs{iupac} Green Book {\cite[][p.\,51]{iupac:greenbook}}}]
+  In writing the formula for a complex ion, spacing for charge number can be
+  added (staggered arrangement), as well as parentheses:
+  \ch[charge-hshift=full]{SO4^2-}, \ch{(SO4)^2-}.  The staggered arrangement
+  is now recommended.
+\end{cnltxquote}
+
+\subsection{Bonds}\label{ssec:bonds}
+\subsubsection{Native Bonds}
+There are three kinds of what I will call ``native bonds'':
+\begin{example}[side-by-side]
+  single: \ch{CH3-CH3} \par
+  double: \ch{CH2=CH2} \par
+  triple: \ch{CH+CH}
+\end{example}
+
+\subsubsection{Flexible Bonds}
+\paragraph{Predefined Bonds}
+In addition to the three native bonds there are a few more which can be called
+by
+\begin{commands}
+  \command{bond}[\marg{bond name}]
+    Prints the bond type specified by \meta{bond name}.
+\end{commands}
+The predefined bond types are shown in table~\vref{tab:bond_types}.
+
+\begin{table}
+  \centering
+  \caption{Bonds available with \cs*{bond}.}
+  \label{tab:bond_types}
+  \begin{tabular}{lcl}
+    \toprule
+      \bfseries name & \bfseries appearance & \bfseries aliases \\
+    \midrule
+      \code{single}  & \bond{single}        & \code{normal}, \code{sb} \\
+      \code{double}  & \bond{double}        & \code{db} \\
+      \code{triple}  & \bond{triple}        & \code{tp} \\
+      \code{dotted}  & \bond{dotted}        & \code{semisingle} \\
+      \code{deloc}   & \bond{deloc}         & \code{semidouble} \\
+      \code{tdeloc}  & \bond{tdeloc}        & \code{semitriple} \\
+      \code{co>}     & \bond{co>}           & \code{coordright} \\
+      \code{<co}     & \bond{<co}           & \code{coordleft} \\
+    \bottomrule
+  \end{tabular}
+\end{table}
+
+\begin{example}
+  \ch{C\bond{sb}C\bond{db}C\bond{tp}C\bond{deloc}C\bond{tdeloc}C\bond{co>}C\bond{<co}C}
+\end{example}
+
+\paragraph{Own Bonds}
+\chemformula{} offers commands to define own bond types:
+\begin{commands}
+  \command{NewChemBond}[\marg{name}\marg{code}]
+    \sinceversion{4.3}Define the new bond type \meta{name}.  Issue an error if
+    a bond \meta{name} already exists.
+  \command{DeclareChemBond}[\marg{name}\marg{code}]
+    Define the new bond type \meta{name} or overwrite it if it already
+    exists.
+  \command{RenewChemBond}[\marg{name}\marg{code}]
+    Redefine the existing bond type \meta{name}.  Issue an error if a bond
+    \meta{name} doesn't exist.
+  \command{NewChemBondAlias}[\marg{new name}\marg{old name}]
+    \sinceversion{4.3}Declare the bond type \meta{new name} to be an alias of
+    \meta{old name}.  Issue an error if a bond \meta{new name} already
+    exists.
+  \command{DeclareChemBondAlias}[\marg{new name}\marg{old name}]
+    Declare the bond type \meta{new name} to be an alias of \meta{old name}.
+  \command{ShowChemBond}[\marg{name}]
+    Print the definition of bond type \meta{name}.
+\end{commands}
+The usage is best described with an example.  So let's see how the
+\code{single} bond and the \code{co>} bond are defined:
+\begin{sourcecode}
+  \NewChemBond{single}
+    { \draw[chembond] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+  \NewChemBond{coordright}
+    {
+      \draw[chembond,butt cap->]
+        (chemformula-bond-start) -- (chemformula-bond-end) ;
+    }
+  \NewChemBondAlias{co>}{coordright}
+\end{sourcecode}
+Two points are important: the names of the starting and the ending
+coordinates, \code{chemformula-bond-start} and \code{chemformula-bond-end},
+and the \TikZ\ style of the bonds \code{chembond}.
+
+So, let's say you want to define a special kind of dashed bond.  You could do
+this:
+\begin{example}
+  \usetikzlibrary{decorations.pathreplacing}
+  \makeatletter
+  \NewChemBond{dashed}
+    {
+      \draw[
+        chembond,
+        decorate,
+        decoration={
+          ticks,
+          segment length=\chemformula@bondlength/10,amplitude=1.5pt
+        }]
+        (chemformula-bond-start) -- (chemformula-bond-end) ;
+    }
+  \makeatother
+  \chemsetup[chemformula]{bond-length=2ex}
+  \ch{C\bond{dashed}C}
+\end{example}
+
+The last example showed you another macro: \verbcode+\chemformula@bondlength+.
+It only exists so you can use it to access the bond length as set with
+\option{bond-length} directly.
+
+\subsection{Customization}\label{ssec:compounds:customization}
+These options allow you to customize the ouptut of the compounds:
+\begin{options}
+  \keyval{subscript-vshift}{dim}\Default{0pt}
+    Extra vertical shift of the subscripts.
+  \keychoice{subscript-style}{text,math}\Default{text}
+    Style that is used to typeset the subscripts.
+  \keyval{charge-hshift}{dim}\Default{.25em}
+    Shift of superscripts when following a subscript.\label{desc:charge-hshift}
+  \keyval{charge-vshift}{dim}\Default{0pt}
+    Extra vertical shift of the superscripts.
+  \keychoice{charge-style}{text,math}\Default{text}
+    Style that is used to typeset the superscripts.
+  \keychoice{circled}{formal,\default{all},none}\Default{formal}
+    \sinceversion{4.6}Like \chemmacros' package option but local to
+    \chemformula's \cs{ch}.  That is: since \chemmacros' macros use
+    \chemformula's mechanism this is effectively an alias.
+  \keychoice{circletype}{\default{chem},math}\Default{chem}
+    \sinceversion{4.6}Like \chemmacros' package option but local to
+    \chemformula's \cs{ch}.  That is: since \chemmacros' macros use
+    \chemformula's mechanism this is effectively an alias.
+  \keyval{adduct-space}{dim}\Default{.1333em}
+    Space to the left and the right of the adduct point.
+  \keyval{bond-length}{dim}\Default{.5833em}
+    The length of the bonds.
+  \keyval{bond-offset}{dim}\Default{.07em}
+    Space between bond and atoms.
+  \keyval{bond-style}{\TikZ}\Default
+    \TikZ\ options for the bonds.
+  \keyval{bond-penalty}{num}\Default{10000}
+    \sinceversion{4.0a}The penalty that is inserted after a bond for
+    (dis-)allowing line breaks.
+  \keyval{radical-style}{\TikZ}\Default
+    \TikZ\ options for the radical point.
+  \keyval{radical-radius}{dim}\Default{.2ex}
+    The radius of the radical point.
+  \keyval{radical-hshift}{dim}\Default{.15em}
+    Horizontal shift before the radical point is drawn.
+  \keyval{radical-vshift}{dim}\Default{.5ex}
+    Vertical shift relative to the current baseline.
+  \keyval{radical-space}{dim}\Default{.15em}
+    Horizontal shift after the radical point is drawn.
+\end{options}
+
+Maybe you have noticed that charges of certain ions are shifted to the
+right.
+\begin{example}[side-by-side]
+  \ch{SO4^2-} \ch{NH4+} \ch{Na+}
+\end{example}
+They are shifted if they \emph{follow} a subscript which follows \ac{iupac}
+recommendations~\cite[][p.\,51]{iupac:greenbook}.  The amount of the shift can
+be set with the option \option{charge-hshift}.
+\begin{example}
+  \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par
+  \chemsetup[chemformula]{charge-hshift=.5ex}
+  \ch{SO4^2-} \ch{NH4+} \ch{Na+} \par
+  \chemsetup[chemformula]{charge-hshift=.5pt}
+  \ch{SO4^2-} \ch{NH4+} \ch{Na+}
+\end{example}
+
+Despite \ac{iupac}'s recommendation \chemformula{} does not make fully staggered
+arrangements in the default setting as I find it hard to read in some cases
+and ugly in others.  Since this is a subjective decision \chemformula{} not only
+let's you define the absolute amount of the shift but also provides a
+possibility for full staggered arrangements.  For this you have to use
+\keyis{charge-hshift}{full}.
+\begin{example}
+  \ch[charge-hshift=0pt]{C5H11+} \ch[charge-hshift=0pt]{SO4^2-} \par
+  \ch{C5H11+} \ch{SO4^2-} \par
+  \ch[charge-hshift=1ex]{C5H11+} \ch[charge-hshift=1ex]{SO4^2-} \par
+  \ch[charge-hshift=full]{C5H11+} \ch[charge-hshift=full]{SO4^2-}
+\end{example}
+
+If you don't want the charges to be typeset in text mode you can switch to
+math mode:
+\begin{example}
+  \ch{M^x+} \ch{SO4^2-} \par
+  \chemsetup[chemformula]{charge-style = math}
+  \ch{M^x+} \ch{SO4^2-}
+\end{example}
+
+The option \option{subscript-vshift} can be used to adjust the vertical shift
+of the subscripts:
+\begin{example}
+  \ch{H2SO4} \ch{Na3PO4} \par
+  \chemsetup[chemformula]{subscript-vshift=.5ex}
+  \ch{H2SO4} \ch{Na3PO4} \par
+  \chemsetup[chemformula]{subscript-vshift=-.2ex}
+  \ch{H2SO4} \ch{Na3PO4}
+\end{example}
+
+You can choose the mode subscripts are typeset in the same way as it is
+possible for the charges:
+\begin{example}
+  \ch{A_nB_m} \ch{H2SO4} \par
+  \chemsetup[chemformula]{subscript-style = math}
+  \ch{A_nB_m} \ch{H2SO4}
+\end{example}
+
+The option \option{adduct-space} sets the space left and right to the adduct
+symbol $\cdot$.
+\begin{example}
+  \ch{Na3PO3*H2O} \par
+  \chemsetup[chemformula]{adduct-space=.2em}
+  \ch{Na3PO3*H2O}
+\end{example}
+
+Changing the length of the bonds:
+\begin{example}
+  \chemsetup[chemformula]{bond-length=4mm}%
+  single: \ch{CH3-CH3} \par
+  double: \ch{CH2=CH2} \par
+  triple: \ch{CH+CH}
+\end{example}
+
+You can change the distance between bond and atom, too:
+\begin{example}
+  \ch{H-H + N+N + O=O} \par
+  \ch[bond-offset=1pt]{H-H + N+N + O=O}
+\end{example}
+
+\subsection{Standalone Formulae}
+\chemformula\sinceversion{4.0} offers a command that \emph{only accepts} the
+\enquote{compound} input type:
+\begin{commands}
+  \command{chcpd}[\oarg{options}\marg{compound}]
+    Typeset single compounds.
+\end{commands}
+
+\section{Special Input Types}
+There are some \enquote{special type} input groups.
+
+\subsection{Single Token Groups}
+The first kind are groups which consist of only one token, namely of the
+following ones:
+\begin{commands}
+  \command{ch}[\Marg{ + } \ch{ + }]
+    Creates the plus sign between compounds with space around it:\\
+    \cs{ch}\Marg{2 Na + Cl2} \ch{2 Na + Cl2}
+  \command{ch}[\Marg{ - } \ch{ - }]
+    \sinceversion{4.3a}Creates the minus sign between compounds with space
+    around it:\\
+    \cs{ch}\Marg{M - H} \ch{M - H}
+  \command{ch}[\Marg{ v } \ch{ v }]
+    Sign for precipitate: \cs{ch}\Marg{BaSO4 v} \ch{BaSO4 v}
+  \command{ch}[\Marg{ \textasciicircum\ } \ch{ ^ }]
+    Sign for escaping gas\footnotemark: \cs{ch}\Marg{H2 \textasciicircum}
+    \ch{H2 ^}
+\end{commands}
+\footnotetext{Is this the correct English term? Please correct me if it isn't.}
+
+The space left and right of the plus and the minus sign can be set with this
+option:
+\begin{options}
+  \keyval{plus-space}{skip}\Default{.3em plus .1em minus .1em}
+    A rubber length.
+  \keyval{plus-penalty}{num}\Default{700}
+    \sinceversion{4.0a}The penalty that is inserted after the plus and the
+    minus sign for (dis-)allowing line breaks.
+\end{options}
+\begin{example}[side-by-side]
+  \ch{A + B}\par
+  \ch[plus-space=4pt]{A + B}
+\end{example}
+
+\subsection{Option Input}
+Sometimes you might want to apply an option only to a part of a, say,
+reaction.  Of course you have the possibility to use \cs{ch} several times.
+\begin{example}
+  \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par
+  \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-}
+\end{example}
+This, however, interrupts the input in your source and \emph{may} mess with
+the spacing. That's why there is an alternative:
+\begin{commands}
+  \command{ch}[\Marg{ @\marg{options} }]
+    The options specified this way will be valid \emph{only} until the next
+    compound is set.
+\end{commands}
+\begin{example}
+  \ch{H2O +}\textcolor{red}{\ch{H2SO4}}\ch{-> H3O+ + HSO4-} \par
+  \ch{H2O + @{format=\color{red}} H2SO4 -> H3O+ + HSO4-} \par
+  or of course:\par
+  \ch{H2O + \textcolor{red}{H2SO4} -> H3O+ + HSO4-}\par\bigskip
+  \ch{H2O +}\ch[subscript-vshift=2pt]{H2SO4}\ch{-> H3O+ + HSO4-} \par
+  \ch{H2O + @{subscript-vshift=2pt} H2SO4 -> H3O+ + HSO4-}
+\end{example}
+
+\section{Escaped Input}
+In some cases it may be desirable to prevent \chemformula{} from parsing the
+input.  This can be done in two ways.
+
+\subsection{Text}\label{ssec:text}
+If you put something between \verbcode+" "+ or \verbcode+' '+ then the input
+will be treated as normal text, except that spaces are not allowed and have to
+be input with \verbcode+~+.
+\begin{commands}
+  \command{ch}[\Marg{ "\meta{escaped text}" }]
+    One of two possibilities to \emph{escape} \chemformula's parsing.
+  \command{ch}[\Marg{ '\meta{escaped text}' }]
+    The second of two possibilities to \emph{escape} \chemformula's parsing.
+\end{commands}
+\begin{example}
+  \ch{"\ox{2,Ca}" O} \par
+  \ch{"\ldots\," Na + "\ldots\," Cl2 -> "\ldots\," NaCl} \par
+  \ch{'A~->~B'}
+\end{example}
+In many cases you won't need to escape the input.  But when you get into
+trouble when using a command inside \cs{ch} try hiding it.
+
+\subsection{Math}
+If you especially want to input math you just enclose it with \verbcode+$ $+.
+This output is different from the escaped text as it is followed by a space.
+The reasoning behind this is that I assume math will mostly be used to replace
+stoichiometric factors.
+\begin{commands}
+ \command{ch}[\Marg{ \string$\meta{escaped math}\string$ }]
+   One of two possibilities to \emph{escape} \chemformula's parsing into math
+   mode.
+ \command{ch}[\Marg{ \string\(\meta{escaped math}\string\) }]
+   The second of two possibilities to \emph{escape} \chemformula's parsing
+   into math mode.
+\end{commands}
+\begin{example}[side-by-side]
+  escaped text: \ch{"$x$" H2O} \par
+  escaped math: \ch{$x$ H2O} \par
+  also escaped math: \ch{\(x\) H2O} \par
+  \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl}
+\end{example}
+
+The space that is inserted after a math group can be edited:
+\begin{options}
+  \keyval{math-space}{skip}\Default{.1667em plus .0333em minus .0117em}
+   A rubber length.
+\end{options}
+\begin{example}
+  \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par
+  \chemsetup[chemformula]{math-space=.25em}
+  \ch{$2n$ Na + $n$ Cl2 -> $2n$ NaCl} \par
+  \ch{$A->B$}
+\end{example}
+
+\section{Arrows}\label{sec:arrows}
+\subsection{Arrow types}
+Arrows are input in the same intuitive way they are with \pkg{mhchem}.
+There are various different types:
+\begin{arrows}
+  \arrow{->}[ \charrow{->}]
+    standard right arrow
+  \arrow{<-}[ \charrow{<-}]
+    standard left arrow
+  \arrow{-/>}[ \charrow{-/>}]
+    does not react (right)
+  \arrow{</-}[ \charrow{</-}]
+    does not react (left)
+  \arrow{<->}[ \charrow{<->}]
+    resonance arrow
+  \arrow{<>}[ \charrow{<>}]
+    reaction in both directions
+  \arrow{==}[ \charrow{==}]
+    stoichiometric equation
+  \arrow{<=>}[ \charrow{<=>}]
+    equilibrium arrow
+  \arrow{>=<}[ \charrow{>=<}]
+    reversed equilibrium arrow
+  \arrow{<=>>}[ \charrow{<=>>}]
+    unbalanced equilibrium arrow to the right
+  \arrow{>=<<}[ \charrow{>=<<}]
+    reversed unbalanced equilibrium arrow to the right
+  \arrow{<<=>}[ \charrow{<<=>}]
+    unbalanced equilibrium arrow to the left
+  \arrow{>>=<}[ \charrow{>>=<}]
+    reversed unbalanced equilibrium arrow to the left
+  \arrow{<o>}[ \charrow{<o>}]
+    isolobal arrow
+  \arrow{<==>}[ \charrow{<==>}]
+    I've seen this one used. I'm not sure it actually has a meaning in
+    chemical equations.  If you have some official reference for this arrow
+    type please feel free to contact me.
+\end{arrows}
+All these arrows are drawn with \TikZ.
+\begin{example}
+  \ch{H2 + Cl2 -> 2 HCl} \par
+  \ch{H2O + CO3^2- <=> OH- + HCO3-} \par
+  \ch{A <- B} \par
+  \ch{\{[CH2=CH-CH2]- <-> {}[CH2-CH=CH2]- \}} \par
+  \ch{A <> B} \par
+  \ch{H+ + OH- <=>> H2O} \par
+  \ch{2 NO2 <<=> N2O4}
+\end{example}
+
+\subsection{Labels}
+The arrows take two optional arguments to label them.
+\begin{arrows}
+  \arrow*{->\oarg{above}\oarg{below}}
+    Add text above or under an arrow.
+\end{arrows}
+\begin{example}[side-by-side]
+  \ch{A ->[a] B} \par
+  \ch{A ->[a][b] B} \par
+  \ch{A ->[\SI{100}{\celsius}] B}
+\end{example}
+The label text can be parsed seperately from the arrow. The recipe is easy:
+leave blanks.
+\begin{example}[side-by-side]
+  \ch{A ->[H2O] B} \par
+  \ch{A ->[ H2O ] B} \par
+  \ch{A ->[ "\ox{2,Ca}" F2 ] B} \par
+  \ch{A ->[$\Delta$,~ \[H+ \]] B}
+\end{example}
+% TODO: correct info about []
+
+If you leave the blanks \chemformula{} treats the groups inside the square
+brackets as seperated input types.  The arrow reads its arguments
+\emph{afterwards}.  As you can see the arrows \enquote{grow} with the length
+of the labels.  What stays constant is the part that protrudes the labels.  As
+you also can see in the last example square brackets inside the arrow
+arguments can be produced using \cs*{[} and \cs*{]}.  They keep their usual
+meaning outside \cs{ch}.  These commands were necessary since the usual
+grouping (\ie, hiding the brackets inside curly brackets) didn't work due to
+the way \cs{ch} read its argument.  This is no longer true but meanwhile
+\cs*{[} and \cs*{]} are kept for backwards compatibility.
+\begin{example}
+  \ch{A ->[a] B} \par
+  \ch{A ->[ab] B} \par
+  \ch{A ->[abc] B} \par
+  \ch{A ->[abc~abc] B} \par
+  % needs the `chemfig' package:
+  \setatomsep{15pt}
+  \ch{A ->[ "\chemfig{-[:30]-[:-30]OH}" ] B} \par
+  \ch{A ->[[]] B} vs. \ch{A ->[\[\]] B}
+\end{example}
+
+\subsection{Customization}
+These are the options which enable you to customize the arrows:
+\begin{options}
+  \keyval{arrow-offset}{dim}\Default{.75em}
+    This is the length that an arrow protrudes a label on both sides.  This
+    means an empty arrow's length is two times \code{arrow-offset}.
+  \keyval{arrow-min-length}{dim}\Default{0pt}
+    \sinceversion{3.6b}The minimal length an error must have unless two times
+    \key{arrow-offset} plus the width of the label is larger.
+  \keyval{arrow-yshift}{dim}\Default{0pt}
+    Shifts an arrow up (positive value) or down (negative value).
+  \keyval{arrow-ratio}{<factor>}\Default{.6}
+    The ratio of the arrow lengths of the unbalanced equilibrium.  \code{.4}
+    would mean that the length of the shorter arrow is $0.4\times$ the length
+    of the longer arrow.
+  \keyval{compound-sep}{dim}\Default{.5em}
+    The space between compounds and the arrows.
+  \keyval{label-offset}{dim}\Default{2pt}
+    The space between the labels and the arrows.
+  \keyval{label-style}{font command}\Default{\cs*{footnotesize}}
+    The relative font size of the labels.
+  \keyval{arrow-penalty}{num}\Default{0}
+    \sinceversion{4.0a}The penalty that is inserted after an arrow for
+    (dis-)allowing line breaks.
+  \keyval{arrow-style}{\TikZ}\Default
+    \sinceversion{4.1a}Additonal \TikZ\ keys for formatting the arrows.
+\end{options}
+
+The following code shows the effect of the different options on the \verbcode+<=>>+
+arrow:
+\begin{example}
+  standard: \ch{A <=>>[x][y] B} \par
+  longer: \ch[arrow-offset=12pt]{A <=>>[x][y] B} \par
+  higher: \ch[arrow-yshift=2pt]{A <=>>[x][y] B} \par
+  more balanced: \ch[arrow-ratio=.8]{A <=>>[x][y] B} \par
+  labels further away: \ch[label-offset=4pt]{A <=>>[x][y] B} \par
+  larger distance to compounds: \ch[compound-sep=2ex]{A <=>>[x][y] B} \par
+  smaller labels: \ch[label-style=\tiny]{A <=>[x][y] B}
+\end{example}
+
+If you want to have different arrow tips\sinceversion{4.7} there is an easy
+way to use existing arrow tips (as defined by \TikZ).  \chemformula{} uses
+three different arrow tips: \code{cf}, \code{left cf} and \code{right cf}.  If
+you want them to match those of \pkg{chemfig}~\cite{pkg:chemfig} for example
+you could do:
+\begin{sourcecode}
+  \pgfkeys{
+    cf /.tip = {CF@full} ,
+    left cf /.tip = {CF@half}
+  }
+\end{sourcecode}
+\pkg{chemfig} has no equivalent of \code{right cf}.  This mechanism relies on
+\TikZ{} version~3.0.0 and the new \code{arrows.meta} library.
+
+\subsection{Modify Arrow Types}\label{sec:arrows_modify}
+The arrows are defined with the commands
+\begin{commands}
+  \command{NewChemArrow}[\marg{type}\marg{\TikZ}]
+    Define the new arrow type \meta{type}.  Issue an error if an arrow type
+    \meta{type} already exists.
+  \command{DeclareChemArrow}[\marg{type}\marg{\TikZ}]
+    Define the new arrow type \meta{type} or overwrite it if it already
+    exists.
+  \command{RenewChemArrow}[\marg{type}\marg{\TikZ}]
+    Redefine the arrow type \meta{type}.  Issue an error if an arrow type
+    \meta{type} doesn't exist.
+  \command{ShowChemArrow}[\marg{type}]
+    Print out the current definition of the arrow type \meta{type}.
+\end{commands}
+\meta{type} is the sequence of tokens that is replaced with the actual arrow
+code.  For example the basic arrow is defined via
+\begin{sourcecode}
+  \NewChemArrow{->}{
+    \draw[chemarrow,-cf] (cf_arrow_start) -- (cf_arrow_end) ;
+  }
+\end{sourcecode}
+In order to define arrows yourself you need to know the basics of
+\TikZ\footnote{Please see the \manual{pgfmanual} for details.}.  The
+predefined arrows use the arrow tips \code{cf}, \code{left cf} and \code{right
+  cf}.  They also all except the net reaction arrow \code{==} use the
+\TikZ-style \code{chemarrow} that you should use, too, if you want the option
+\option{arrow-style} to have an effect.
+
+There are some predefined coordinates you can and should use.  For
+completeness' sake the arrow tips and the \TikZ-style are also listed:
+\begin{codedesc}
+  \Code{(cf\_arrow\_start)}
+    The beginning of the arrow.
+  \Code{(cf\_arrow\_end)}
+    The end of the arrow.
+  \Code{(cf\_arrow\_mid)}
+    The mid of the arrow.
+  \Code{(cf\_arrow\_mid\_start)}
+    The beginning of the shorter arrow in types like \verbcode+<=>>+.
+  \Code{(cf\_arrow\_mid\_end)}
+    The end of the shorter arrow in types like \verbcode+<=>>+.
+  \Code{cf}
+    A double-sided arrow tip.
+  \Code{left cf}
+    A left-sided arrow tip.
+  \Code{right cf}
+    A right-sided arrow tip.
+  \Code{chemarrow}
+    \chemformula's \TikZ-style that is applied to the arrows and set with
+    \option{arrow-style}
+\end{codedesc}
+\begin{example}
+  \NewChemArrow{.>}{
+    \draw[chemarrow,-cf,dotted,red] (cf_arrow_start) -- (cf_arrow_end);
+  }
+  \NewChemArrow{n>}{
+    \draw[chemarrow,-cf]
+      (cf_arrow_start)
+        .. controls ([yshift=3ex]cf_arrow_mid) ..
+      (cf_arrow_end);
+  }
+  \ch{A .> B} \ch{A .>[a][b] B} \ch{A n> B}
+\end{example}
+
+\begin{example}
+  \texttt{\ShowChemArrow{->}} \par
+  \RenewChemArrow{->}{\draw[chemarrow,->,red] (cf_arrow_start) -- (cf_arrow_end) ;}
+  \texttt{\ShowChemArrow{->}} \par
+  \ch{A -> B}
+\end{example}
+
+\subsection{Standalone Arrows}
+\chemformula{} offers\sinceversion{4.0} a command that \emph{only accepts} the
+\enquote{arrow} input type:
+\begin{commands}
+  \command{charrow}[\marg{type}\oarg{above}\oarg{below}]
+    Print the arrow type \meta{type}.
+\end{commands}
+This command is internally used for the arrows, too, when \cs{ch} is parsed.
+
+\section{Names}
+\subsection{Syntax}
+\chemformula{} has a built-in syntax to write text under a compound.  In a way
+it works very similar to the arrows.
+\begin{commands}
+  \command{ch}[\Marg{ !(\meta{text})( \meta{formula} ) }]
+    Writes \meta{text} below \meta{formula}.
+\end{commands}
+If an exclamation mark is followed by a pair of parentheses \chemformula{} will
+parse it this way:
+\begin{example}
+  \ch{!(ethanol)( CH2CH2OH )}
+\end{example}
+The same what's true for the arrows arguments holds for these arguments: if
+you leave blanks the different parts will be treated according to their input
+type before the text is set below the formula.
+\begin{example}
+  \ch{!(water)(H2O)} \quad
+  \ch{!( "\textcolor{blue}{water}" )( H2O )} \quad
+  \ch{!( $2n-1$ )( H2O )} \quad
+  \ch{!( H2O )( H2O )} \quad
+  \ch{!(oxonium)( H3O+ )}
+\end{example}
+If for some reason you want to insert an exclamation mark \emph{without} it
+creating a name you only have to make sure it isn't followed by parentheses.
+\begin{example}[side-by-side]
+  \ch{H2O~(!)} \par
+  \ch{A!{}()}
+\end{example}
+
+\subsection{Customization}
+\chemformula{} provides two options to customize the output of the names:
+\begin{options}
+ \keyval{name-format}{commands}\Default{\cs*{scriptsize}\cs*{centering}}
+   The format of the name.  This can be arbitrary input.
+ \keychoice{name-width}{\meta{dim},auto}\Default{auto}
+   The width of the box where the label is put into.  \code{auto} will detect
+   the width of the name and set the box to this width.
+\end{options}
+\begin{example}
+  \ch{!(acid)( H2SO4 ) -> B} \par
+  \ch[name-format=\sffamily\small]{!(acid)( H2SO4 ) -> B} \par
+  \ch[name-format=\scriptsize N:~]{!(acid)( H2SO4 ) -> B} \par
+  \ch[name-width=3em,name-format=\scriptsize\raggedright]{!(acid)( H2SO4 ) -> B}
+\end{example}
+
+\subsection{Standalone Names}
+\chemformula{} offers a command\sinceversion{4.0} that allows the usage of the
+\enquote{name} syntax in normal text.  This is the command that a bang is
+replaced with in \chemformula's formulas, actually.  Both arguments are
+mandatory.
+\begin{commands}
+  \command{chname}[\darg{text~1}\darg{text~2}]
+    The command that is useed internally for placing  \meta{text~1} below of
+    \meta{text~2}.
+\end{commands}
+
+\section{Format and Font}\label{sec:format}
+In the standard setting \chemformula{} doesn't make any default changes to the
+font of the formula output.  Let's take a look at a nonsense input which shows
+all features:
+\begin{example}[pre-output={\biolinumLF\libertineLF\chemsetup{chemformula/format=}}]
+  \newcommand*\sample{%
+    \ch{H2C-C+C-CH=CH+ + CrO4^2-
+        <=>[x][y]
+      2.5 Cl^{-.} + 3_1/2 Na*OH_{(aq)} + !(name)( A^n ) "\LaTeXe"}
+  }
+  \sample
+\end{example}
+\newcommand*\sample{%
+  \ch{H2C-C+C-CH=CH+ + CrO4^2-
+      <=>[x][y]
+    2.5 Cl^{-.} + 3_1/2 Na*OH_{(aq)} + !(name)( A^n ) "\LaTeXe"}
+}
+
+Now we're going to change different aspects of the font a look what happens:
+\begin{example}[pre-output={\biolinumLF\libertineLF\chemsetup{chemformula/format=}}]
+  \sffamily Hallo \sample \\
+  \ttfamily Hallo \sample \normalfont \\
+  \bfseries Hallo \sample \normalfont \\
+  \itshape Hallo \sample
+\end{example}
+As you can see most features adapt to the surrounding font.
+
+If you want to change the default format you need to use this option:
+\begin{options}
+  \keyval{format}{anything}\Default
+    Adds arbitrary code before the output of \cs{ch}.
+\end{options}
+\begin{example}[pre-output={\biolinumLF\libertineLF\chemsetup{chemformula/format=}}]
+  \definecolor{newblue}{rgb}{.1,.1,.5}
+  \chemsetup[chemformula]{format=\color{newblue}\sffamily}
+  \sffamily Hallo \sample \\
+  \ttfamily Hallo \sample \normalfont \\
+  \bfseries Hallo \sample \normalfont \\
+  \itshape Hallo \sample
+\end{example}
+
+You can also specifically change the fontfamily, fontseries and fontshape of
+the output.
+\begin{options}
+  \keyval{font-family}{family}\Default
+    Changes the fontfamily of the output with \cs*{fontfamily}\marg{family}.
+  \keyval{font-series}{series}\Default
+    Changes the fontseries of the output with \cs*{fontseries}\marg{series}.
+  \keyval{font-shape}{shape}\Default
+    Changes the fontshape of the output with \cs*{fontshape}\marg{shape}.
+\end{options}
+\begin{example}[pre-output={\biolinumLF\libertineLF\chemsetup{chemformula/format=}}]
+  \chemsetup[chemformula]{font-series=bx}
+  Hallo \sample \par
+  \sffamily Hallo \sample \normalfont \par
+  \chemsetup[chemformula]{font-family=lmss,font-series=m} Hallo \sample
+    \normalfont \par
+  \itshape Hallo \sample
+\end{example}
+
+If you're using \XeLaTeX\ or \LuaLaTeX\ and have loaded \pkg{fontspec} you
+have the possibilty to set the font with it:
+\begin{options}
+  \keyval{font-spec}{font}\Default
+    Use font \meta{font} for \chemformula's formulas.
+\end{options}
+or with options
+\begin{options}
+  \keychoice{font-spec}{\Marg{[\meta{options}]\meta{font}}}
+    Use font \meta{font} with options \meta{options} for \chemformula's
+    formulas.
+\end{options}
+Since this document is typeset with \pdfLaTeX\ the option cannot be
+demonstrated here.
+
+\section{Usage In Math Equations}
+The \cs{ch} command can be used inside math equations.  It recognizes
+\verbcode+\\+ and \verbcode+&+ and passes them on.  However, you can't use the
+optional arguments of \verbcode+\\+ inside \cs{ch}.
+\begin{example}
+  \begin{align}
+   \ch{
+     H2O & ->[a] H2SO4 \\
+     Cl2 & ->[x][y] CH4
+   }
+  \end{align}
+  \begin{align*}
+  \ch{
+    RNO2      &<=>[ + e- ] RNO2^{-.} \\
+    RNO2^{-.} &<=>[ + e- ] RNO2^2-
+  }
+  \end{align*}
+\end{example}
+
+\section{Usage with \TikZ{} or \pkg*{pgfplots} and externalization}
+Since \chemformula{} uses\sinceversion{4.1} \TikZ{} to draw reaction arrows
+and bonds they would be externalized, too, if you use that facility with
+\TikZ{} or \needpackage{pgfplots}~\cite{pkg:pgfplots}.  This may not be
+desirable since they are very small pictures maybe containing of a single
+line.  This is why \chemformula's default behaviour is to disable
+externalization for it's bonds and arrows.  This can be turned on and off
+through the following option:
+\begin{options}
+  \keybool{tikz-external-disable}\Default{true}
+    dis- or enable \TikZ' externalization mechanism for \chemformula's arrows
+    and bonds.
+\end{options}
+
+If you should be using a formula that contains bonds or arrows inside of a
+\code{tikzpicture} that is externalized you should locally enable it for
+\chemformula, too:
+
+\begin{sourcecode}
+  \begin{tikzpicture}
+    \setchemformula{tikz-external-disable=false}
+    \begin{axis}[xlabel={\ch{2 H+ + 2 e- -> H2}}]
+      \addplot ... ;
+    \end{axis}
+  \end{tikzpicture}
+\end{sourcecode}
+
+\section{Lewis Formulae}\label{sec:lewis-formulae}
+\chemformula{} offers\sinceversion{4.2} a command to typeset Lewis formulae.
+This does not mean Lewis structures!  Those can be achieved using the
+\pkg{chemfig} package~\cite{pkg:chemfig}.  \chemformula{} provides the
+possibility to draw electrons as dots and pairs of dots or a line around an
+atom.
+
+\begin{commands}
+  \command{chlewis}[\oarg{options}\marg{electron spec}\marg{atom}]
+    Draws electrons around the \meta{atom} according to \meta{electron spec}.
+\end{commands}
+
+Electrons are specified by the angle to the horizontal in the couter-clockwise
+direction.  The default appearance is a pair of electrons drawn as a pair of
+dots.  Other specifications can be chosen.  The specification follows the
+pattern \meta{angle}\meta{separator}.  \meta{angle} is a positiv or negativ
+integer denoting the angle counter clockwise to the horizontal where the
+electrons should be drawn.  \meta{separator} is either a dot (\code{.}, single
+electron), a colon (\code{:}, electron pair), a vertical line (\code{|},
+electron pair), an o (\code{o}, empty pair), or a comma (\code{,} default
+spec).
+
+\begin{commands}
+  \command{chlewis}[\Marg{\meta{angle1}\meta{type1}\meta{angle2}\meta{type2}}%
+    \marg{atom}]
+    For example: \cs{chlewis}\Marg{0,180}\Marg{O} gives \chlewis{0,180}{O} and
+    \cs{chlewis}\Marg{0.90.180.270.}\Marg{C} gives
+    \chlewis{0.90.180.270.}{C}.
+\end{commands}
+
+The appearance can be influenced by a number of options:
+\begin{options}
+  \keychoice{lewis-default}{.,:,|,o,single,pair,pair (dotted),pair
+    (line),empty}\Default{pair}
+    Sets the default type that is used when no type is given in \meta{electron
+      spec}.
+  \keyval{lewis-distance}{dim}\Default{1ex}
+    The distance of two electrons in a pair.
+  \keyval{lewis-line-length}{dim}\Default{1.5ex}
+    The length of the line representing an electron pair.
+  \keyval{lewis-line-width}{dim}\Default{1pt}
+    The thickness of a line representing an electron pair.
+  \keyval{lewis-offset}{dim}\Default{.5ex}
+    The distance of the symbols from the atom.
+\end{options}
+The dots are drawn according to the \option{radical-radius} option mentioned
+in section~\ref{ssec:compounds:customization}.
+
+The basic usage should be more or less self-explaining:
+\begin{example}[side-by-side]
+  \chlewis{0:90|180.270}{O}
+  \quad
+  \chlewis{45,135}{O}
+  \quad
+  \chlewis{0o}{Na}
+\end{example}
+
+The next example shows the effect of some of the options:
+\begin{example}
+  \chlewis[lewis-default=.]{23,68,113,158,203,248,293,338}{X}
+  \quad
+  \chlewis{0,90,180,270}{X}
+  \quad
+  \chlewis[lewis-distance=1.25ex]{0,90,180,270}{X}
+  \quad
+  \chlewis[lewis-distance=.75ex,radical-radius=.5pt]{0,90,180,270}{X}
+  \quad
+  \chlewis[
+    radical-radius=.5pt,
+    lewis-default=.
+  ]{23,68,113,158,203,248,293,338}{X}
+\end{example}
+
+\begin{example}
+  \ch{
+    !($1s^22s^1$)( "\chlewis{180.}{Li}" ) +
+    !($1s^22s^22p^5$)( "\chlewis{0.90,180,270}{F}" )
+     ->
+    !($1s^2$)( Li+ ) + !($1s^22s^22p^6$)( "\chlewis{0,90,180,270}{F}" {}- )
+  }
+\end{example}
+
+\section{Kröger-Vink Notation}\label{sec:kroger-vink-notation}
+
+\chemformula{} also supports the Kröger-Vink notation\sinceversion{4.5}.
+\begin{options}
+  \keybool{kroeger-vink}\Default{false}
+    Enable the Kröger-Vink notation. As most options this can be enabled
+    globally via the setup command or locally as option to \cs{ch}.
+\end{options}
+
+With this option enabled several changes come into effect: \code{'} prodoces a
+prime, a \code{x} in a superscript produces $\times$, and both a \code{.} and
+a \code{*} produce a little filled circle. In the Kröger-Vink notation a prime
+denotes a negative relative charge, the circle a positive relative charge, and
+the cross denotes a neutral relative charge.
+
+\begin{example}[side-by-side,add-sourcecode-options={literate=}]
+  \setchemformula{kroeger-vink=true}
+  \ch{Al_{Al}^'}
+  \ch{Al_{Al}'}\par
+  \ch{Ni_{Cu}^{x}}\par
+  \ch{V_{Cl}^.}
+  \ch{V_{Cl}^*}\par
+  \ch{Ca_i^{..}}\par
+  \ch{e^'}\par
+  \ch{Cl_i^'}
+  \ch{Cl_i'}\par
+  \ch{O_i^{''}}
+  \ch{O_i''}
+\end{example}
+
+There are a number of options for customizations:
+\begin{options}
+  \keyval{kv-positive-style}{\TikZ}\Default
+    \TikZ\ code for positive charge dot.
+  \keyval{kv-positive-radius}{dim}\Default{.3ex}
+    Radius of positive charge dot
+  \keyval{kv-positive-hshift}{dim}\Default{.15em}
+    Horizontal shift of positive charge dot
+  \keyval{kv-positive-vshift}{dim}\Default{.5ex}
+    Vertical shift positive charge dot
+  \keyval{kv-positive-offset}{dim}\Default{.4em}
+    The offset of two consecutive positive charge dots
+  \keyval{kv-neutral-symbol}{\TeX\ code}\Default{\$\cs*{times}\$}
+    Symbol for neutral particles.
+\end{options}
+
+\end{document}
+
+\section{Further Examples}
+This section presents some examples of a possible usage.
+
+\begin{example}
+  \begin{reaction}[Synthese von Alkanen]
+    !(Synthesegas)( $n$ CO + $(2n+1)$ H2 )
+    ->[\SI{200}{\celsius}][\[CoNi\]]
+    C_{$n$}H_{$2n+2$} + $n$ H2O
+  \end{reaction}
+\end{example}
+
+\begin{example}
+  \begin{reactions*}
+    "a)" && CH4    + Cl2 &-> CH3Cl  + HCl && "{\small Chlormethan/Methylchlorid}" \\
+    "b)" && CH3Cl  + Cl2 &-> CH2Cl2 + HCl && "{\small Dichlormethan/Methylenchlorid}" \\
+    "c)" && CH2Cl2 + Cl2 &-> CHCl3  + HCl && "{\small Trichlormethan/Chloroform}" \\
+    "d)" && CHCl3  + Cl2 &-> CCl4   + HCl && "{\small Tetrachlormethan/Tetrachlorkohlenstoff}"
+  \end{reactions*}
+\end{example}
+
+\begin{example}
+  \chemsetup[ox]{parse=false}
+  \ch{
+    "\ox{\delm,C}" -{} "\ox{\delp,M}" \qquad
+    ( <-> "\ox{\delp,C}" -{} "\ox{\delm,Br}" )
+  } \\
+  \ch[adduct-space=0pt]{X. + .Y <=> X-Y + Bindungsenergie} \\
+  \ch[name-format=\normalsize]{
+    !(\State{H}{f}\qquad)() !(\textcolor{red}{??})( CH4\gas{} ) +
+    !(\num{0})( 2 O2\gas{} )
+    ->
+    !(\num{-94.3})( CO2\gas{} ) +
+    !(\num{-57.9})( H2O\lqd{} ) +
+    !(\num{-192.1})( "\State{H}" )
+  }
+\end{example}
+
+\begin{example}
+  \newcommand\cstack[1]{%
+    \clap{%
+      \begin{tabular}{c}
+        #1
+      \end{tabular}
+    }%
+  }
+  \begin{reactions*}
+    CH3MgBr + "\ox*{1,Cu}" X &
+      -> "\glqq" CH3 "\ox*{1,Cu}\grqq" + MgBrX "\qquad X~$=$~Br,I,CN" \\
+    2 MeLi + CuI &
+      -> !(\cstack{Dimethylcuprat\\(Gilmann-Cuprat)})( Me2CuLi ) + Li
+  \end{reactions*}
+\end{example}
+
+\begin{example}
+  % needs `chemfig'
+  \begin{reactions*}
+    H3C-CH3 + Cl2 &
+      ->[$\Delta$][$h\nu$] H3CCH2Cl + HCl & &
+      "\Enthalpy{-27.1}" \\
+    H3C-CH3 + "\Lewis{0.,Cl}" &
+      -> H3CCH2 "\Lewis{0.,\vphantom{H}}" + HCl & &
+      "\Enthalpy{-5.0}" \\
+    H3C-CH2 "\Lewis{0.,\vphantom{H}}" + Cl2 &
+      -> H3CCH2Cl + "\Lewis{0.,Cl}" & &
+      "\Enthalpy{-23.0}"
+  \end{reactions*}
+\end{example}
+
+The following example shows how the cancelling of compounds could be
+done\footnote{Inspired by a question on TeX.SE:
+  \url{http://tex.stackexchange.com/q/30118/5049}}.
+\begin{example}
+  % needs `cancel'
+  \begin{align*}
+    \ch{\cancel{HCOOH\aq} + H2O\lqd{}  &<=> H3O^+\aq{} + \cancel{HCOO^-\aq}} \\
+    \ch{\cancel{HCOO^-\aq} + H2O\lqd{} &<=> \cancel{HCOOH\aq} + OH^-\aq}\\[-1ex]
+    \cline{1-2}
+    \ch{H2O\lqd{} + H2O\lqd{} &<=> H3O^+\aq{} + OH^-\aq}    
+  \end{align*}
+\end{example}
+
+\end{document}
diff --git a/Master/texmf-dist/tex/latex/chemformula/chemformula.sty b/Master/texmf-dist/tex/latex/chemformula/chemformula.sty
new file mode 100644
index 00000000000..d01d1e79121
--- /dev/null
+++ b/Master/texmf-dist/tex/latex/chemformula/chemformula.sty
@@ -0,0 +1,3116 @@
+% --------------------------------------------------------------------------
+% the CHEMFORMULA package
+%
+%   typeset chemical compounds and reactions
+%
+% --------------------------------------------------------------------------
+% Clemens Niederberger
+% --------------------------------------------------------------------------
+% https://github.com/cgnieder/chemformula/
+% contact@mychemistry.eu
+% --------------------------------------------------------------------------
+% If you have any ideas, questions, suggestions or bugs to report, please
+% feel free to contact me.
+% --------------------------------------------------------------------------
+% Copyright 2011-2014 Clemens Niederberger
+%
+% This work may be distributed and/or modified under the
+% conditions of the LaTeX Project Public License, either version 1.3
+% of this license or (at your option) any later version.
+% The latest version of this license is in
+%   http://www.latex-project.org/lppl.txt
+% and version 1.3 or later is part of all distributions of LaTeX
+% version 2005/12/01 or later.
+%
+% This work has the LPPL maintenance status `maintained'.
+%
+% The Current Maintainer of this work is Clemens Niederberger.
+% --------------------------------------------------------------------------
+\RequirePackage{ expl3 , xparse , l3keys2e , tikz , amsmath , xfrac , nicefrac , scrlfile }
+\usetikzlibrary{arrows.meta}
+\def\chemformula@version{4.7}
+\def\chemformula@date{2014/08/08}
+
+\ProvidesExplPackage
+  {chemformula}
+  {\chemformula@date}
+  {\chemformula@version}
+  {typeset chemical compounds and reactions}
+
+% --------------------------------------------------------------------------
+% check expl3 version:
+\@ifpackagelater { expl3 } { 2012/11/21 }
+  { }
+  {
+    \PackageError { chemformula } { Support~package~expl3~too~old }
+      {
+        You~need~to~update~your~installation~of~the~bundles~'l3kernel'~and~
+        'l3packages'.\MessageBreak
+        Loading~chemformula~will~abort!
+      }
+    \tex_endinput:D
+  }
+
+% --------------------------------------------------------------------------
+% warning and error messages:
+\msg_new:nnnn { chemformula } { missing-argument }
+  { Wrong~name~input~ \msg_line_context: . }
+  {
+    Maybe~you've~forgotten~to~add~the~second~argument~to~name~syntax?~
+    "!(<name>)(<chemformula>)".\\
+    Or~you~have~forgotten~to~add~a~group~between~an~exclamation~mark~and~
+    the~following~parenthesis?~"!~{}()"\\
+    Either~way~-~I~don't~know~what~to~do~ \msg_line_context: .
+  }
+
+\msg_new:nnnn { chemformula } { new-arrow }
+  { The~arrow~type~ \tl_to_str:n { #1 } \c_space_tl is~already~defined. }
+  {
+    You've~tried~to~define~the~arrow~type~\tl_to_str:n { #1 } \c_space_tl with
+    ~\token_to_str:N \NewChemArrow \c_space_tl but~it~already~exists.
+    ~Choose~another~name.
+  }
+
+\msg_new:nnnn { chemformula } { renew-arrow }
+  { The~arrow~type~ \tl_to_str:n { #1 } \c_space_tl is~not~defined. }
+  {
+    You've~tried~to~renew~the~arrow~type~\tl_to_str:n { #1 } ~but~it~doesn't~
+    exist.
+  }
+
+\msg_new:nnnn { chemformula } { new-bond }
+  { The~bond~type~ \tl_to_str:n { #1 } \c_space_tl is~already~defined. }
+  {
+    You've~tried~to~define~the~bond~type~\tl_to_str:n { #1 } \c_space_tl with
+    ~\token_to_str:N \NewChemBond \c_space_tl but~it~already~exists.
+    ~Choose~another~name.
+  }
+
+\msg_new:nnnn { chemformula } { renew-bond }
+  { The~bond~type~ \tl_to_str:n { #1 } \c_space_tl is~not~defined. }
+  {
+    You've~tried~to~renew~the~bond~type~\tl_to_str:n { #1 } ~but~it~doesn't~
+    exist.
+  }
+
+\msg_new:nnnn { chemformula } { stand-alone }
+  {
+    You're~using~`chemformula'~as~a~stand-alone~package~or~have~loaded~it~
+    before~you've~loaded~`chemmacros',~too.~Some~features~might~not~be~
+    provided!~Espacially~you~cannot~use~\token_to_str:N \chemsetup \c_space_tl
+    to~setup~your~formulae.
+  }
+  {
+    You're~using~`chemformula'~as~a~stand-alone~package~or~have~loaded~it~
+    before~you've~loaded~`chemmacros',~too.~Some~features~might~not~be~
+    provided!~Espacially~you~cannot~use~\token_to_str:N \chemsetup \c_space_tl
+    to~setup~your~formulae.
+  }
+
+\msg_new:nnnn { chemformula } { command-deprecated }
+  {
+    The~command~\token_to_str:N #1 \c_space_tl is~deprecated.~Use~
+    \token_to_str:N #2 \c_space_tl instead.
+  }
+  {
+    The~command~\token_to_str:N #1 \c_space_tl is~deprecated.~Use~
+    \token_to_str:N #2 \c_space_tl instead.
+  }
+
+\cs_new_protected:Npn \chemformula_define_deprecated:NNn #1#2#3
+  {
+    \cs_new_protected:Npn #1
+      {
+        \msg_warning:nnnn { chemformula } { command-deprecated }
+          { #1 } { #2 }
+        #3
+      }
+  }
+
+\NewDocumentCommand \DeprecatedFormulaCommand { mmm }
+  { \chemformula_define_deprecated:NNn #1 #2 { #3 } }
+
+% --------------------------------------------------------------------------
+% variants of kernel functions:
+\cs_generate_variant:Nn \keys_set:nn       { nV }
+\cs_generate_variant:Nn \tl_if_blank:nF    { V }
+\cs_generate_variant:Nn \tl_if_in:nnT      { x , nV }
+\cs_generate_variant:Nn \prop_get:Nn       { NV }
+\cs_generate_variant:Nn \tl_set_rescan:Nnn { NnV }
+\cs_generate_variant:Nn \dim_set:Nn        { NV }
+
+% --------------------------------------------------------------------------
+% package options:
+\bool_new:N \l__chemformula_strict_bool
+\keys_define:nn { chemmacros / chemformula }
+  {
+    strict .bool_set:N = \l__chemformula_strict_bool ,
+    strict .default:n  = true
+  }
+
+\ProcessKeysOptions{ chemmacros / chemformula }
+
+\AtBeginDocument
+  {
+    \@ifpackageloaded{ chemmacros }
+      {
+        \bool_if:NT \l_chemmacros_strict_bool
+          { \bool_set_true:N \l__chemformula_strict_bool }
+      }
+      {}
+  }
+
+% --------------------------------------------------------------------------
+% VARIABLES
+% temporary variables:
+\tl_new:N  \l__chemformula_tmpa_tl
+\tl_new:N  \l__chemformula_tmpb_tl
+\tl_new:N  \l__chemformula_tmpc_tl
+
+\dim_new:N \l__chemformula_tmpa_dim
+\dim_new:N \l__chemformula_tmpb_dim
+
+\int_new:N \l__chemformula_tmpa_int
+\int_new:N \l__chemformula_tmpb_int
+
+\box_new:N \l__chemformula_tmpa_box
+\box_new:N \l__chemformula_tmpb_box
+
+\seq_new:N   \l__chemformula_tmpa_seq
+
+% booleans:
+% this one is officially used to detect wether we're in \ch or not:
+\bool_new:N      \l_chemformula_inside_ch_bool
+% those are private:
+\bool_new:N      \l__chemformula_formal_charges_bool
+\bool_new:N      \l__chemformula_formal_chem_bool
+\bool_set_true:N \l__chemformula_formal_chem_bool
+\bool_new:N      \l__chemformula_options_bool
+\bool_new:N      \l__chemformula_is_option_bool
+\bool_new:N      \l__chemformula_stoich_bool
+\bool_new:N      \l__chemformula_no_stoich_bool
+\bool_new:N      \l__chemformula_is_plus_bool
+\bool_new:N      \l__chemformula_is_up_bool
+\bool_new:N      \l__chemformula_is_down_bool
+\bool_new:N      \l__chemformula_is_arrow_bool
+\bool_new:N      \l__chemformula_is_name_bool
+\bool_new:N      \l__chemformula_stoich_is_iupac_bool
+\bool_new:N      \l__chemformula_stoich_parse_iupac_bool
+\bool_new:N      \l__chemformula_first_last_text_bool
+\bool_new:N      \l__chemformula_first_last_double_bool
+\bool_new:N      \l__chemformula_first_last_single_bool
+\bool_new:N      \l__chemformula_first_last_math_bool
+\bool_new:N      \l__chemformula_first_last_dollar_bool
+\bool_new:N      \l__chemformula_first_last_mathbraces_bool
+\bool_new:N      \l__chemformula_number_style_math_bool
+\bool_new:N      \l__chemformula_charge_style_math_bool
+\bool_new:N      \l__chemformula_sub_bool
+\bool_new:N      \l__chemformula_sup_bool
+\bool_new:N      \l__chemformula_is_isotope_bool
+\bool_new:N      \l__chemformula_xfrac_bool
+\bool_new:N      \l__chemformula_nicefrac_bool
+\bool_new:N      \l__chemformula_mathfrac_bool
+\bool_set_true:N \l__chemformula_mathfrac_bool
+\bool_new:N      \l__chemformula_fss_bool
+\bool_new:N      \l__chemformula_fontspec_bool
+\bool_new:N      \l__chemformula_fss_family_bool
+\bool_new:N      \l__chemformula_fss_series_bool
+\bool_new:N      \l__chemformula_fss_shape_bool
+\bool_new:N      \l__chemformula_name_width_bool
+\bool_new:N      \l__chemformula_charge_full_shift_bool
+\bool_new:N      \l__chemformula_tikzexternaldisable_bool
+\bool_set_true:N \l__chemformula_tikzexternaldisable_bool
+\bool_new:N      \l__chemformula_kroegervink_bool
+
+% dimensions:
+\dim_new:N  \l__chemformula_arrow_length_dim
+\dim_new:N  \l__chemformula_arrow_label_height_dim
+\dim_new:N  \l__chemformula_arrow_label_offset_dim
+\dim_set:Nn \l__chemformula_arrow_label_offset_dim { 2pt }
+\dim_new:N  \l__chemformula_arrow_minimum_length_dim
+\dim_new:N  \l__chemformula_arrow_shortage_dim
+\dim_new:N  \l__chemformula_arrow_offset_dim
+\dim_new:N  \l__chemformula_arrow_yshift_dim
+\dim_set:Nn \l__chemformula_arrow_yshift_dim { 0pt }
+\dim_new:N  \l__chemformula_radical_radius_dim
+\dim_set:Nn \l__chemformula_radical_radius_dim { .2ex }
+\dim_new:N  \l__chemformula_radical_hshift_dim
+\dim_set:Nn \l__chemformula_radical_hshift_dim { .15em }
+\dim_new:N  \l__chemformula_radical_vshift_dim
+\dim_set:Nn \l__chemformula_radical_vshift_dim { .5ex }
+\dim_new:N  \l__chemformula_radical_space_dim
+\dim_set:Nn \l__chemformula_radical_space_dim { .3em }
+\dim_new:N  \l__chemformula_arrow_head_dim
+\dim_new:N  \l__chemformula_name_dim
+\dim_new:N  \l__chemformula_adduct_space_dim
+\dim_set:Nn \l__chemformula_adduct_space_dim { .1333em }
+\dim_new:N  \l__chemformula_charge_shift_dim
+\dim_set:Nn \l__chemformula_charge_shift_dim { .5ex }
+\dim_new:N  \l__chemformula_subscript_shift_dim
+\dim_new:N  \l__chemformula_superscript_shift_dim
+\dim_new:N  \l__chemformula_subscript_dim
+\dim_zero:N \l__chemformula_subscript_dim
+\dim_new:N  \l__chemformula_superscript_dim
+\dim_zero:N \l__chemformula_superscript_dim
+\dim_new:N  \l__chemformula_bond_dim
+\dim_set:Nn \l__chemformula_bond_dim { .5833em }
+\dim_new:N  \l__chemformula_bond_space_dim
+\dim_set:Nn \l__chemformula_bond_space_dim { .07em }
+\dim_new:N  \l__chemformula_elspec_pair_distance_dim
+\dim_set:Nn \l__chemformula_elspec_pair_distance_dim { 1ex }
+\dim_new:N  \l__chemformula_elspec_pair_line_length_dim
+\dim_set:Nn \l__chemformula_elspec_pair_line_length_dim { 1.5ex }
+\dim_new:N  \l__chemformula_elspec_pair_width_dim
+\dim_set:Nn \l__chemformula_elspec_pair_width_dim { 1pt }
+\dim_new:N  \l__chemformula_kroegervink_positive_radius_dim
+\dim_set:Nn \l__chemformula_kroegervink_positive_radius_dim { .3ex }
+\dim_new:N  \l__chemformula_kroegervink_positive_hshift_dim
+\dim_set:Nn \l__chemformula_kroegervink_positive_hshift_dim { .15em }
+\dim_new:N  \l__chemformula_kroegervink_positive_vshift_dim
+\dim_set:Nn \l__chemformula_kroegervink_positive_vshift_dim { .5ex }
+\dim_new:N  \l__chemformula_kroegervink_positive_space_dim
+\dim_set:Nn \l__chemformula_kroegervink_positive_space_dim { .4em }
+
+% skips:
+\skip_new:N  \l__chemformula_stoich_space_skip
+\skip_set:Nn \l__chemformula_stoich_space_skip { .1667em plus .0333em minus .0117em }
+\skip_new:N  \l__chemformula_math_space_skip
+\skip_set:Nn \l__chemformula_math_space_skip { .1667em plus .0333em minus .0117em }
+\skip_new:N  \l__chemformula_plus_space_skip
+\skip_set:Nn \l__chemformula_plus_space_skip { .3em plus .1em minus .1em }
+
+
+% integers:
+\int_new:N   \l__chemformula_count_tokens_int
+\int_new:N   \g__chemformula_lewis_int
+
+% token lists:
+\tl_new:N     \l__chemformula_compound_sep_tl
+\tl_set:Nn    \l__chemformula_compound_sep_tl { .5em }
+\tl_new:N     \l__chemformula_arrow_ratio_tl
+\tl_set:Nn    \l__chemformula_arrow_ratio_tl { .6 }
+\tl_new:N     \l__chemformula_radical_style_tl
+\tl_new:N     \l__chemformula_arrow_head_tl
+\tl_set:Nn    \l__chemformula_arrow_head_tl { cf }
+\tl_new:N     \l__chemformula_upper_label_tl
+\tl_new:N     \l__chemformula_lower_label_tl
+\tl_new:N     \l__chemformula_arrow_style_tl
+\tl_new:N     \l__chemformula_arrow_label_style_tl
+\tl_set:Nn    \l__chemformula_arrow_label_style_tl { \footnotesize }
+\tl_new:N     \l__chemformula_arrow_tmp_tl
+\tl_new:N     \l__chemformula_arrow_type_tl
+\tl_new:N     \l__chemformula_arrow_penalty_tl
+\tl_set:Nn    \l__chemformula_arrow_penalty_tl { 0 }
+\tl_new:N     \l__chemformula_arrow_offset_tl
+\tl_set:Nn    \l__chemformula_arrow_offset_tl { .75em }
+\tl_new:N     \l__chemformula_plus_penalty_tl
+\tl_set:Nn    \l__chemformula_plus_penalty_tl { 700 }
+\tl_new:N     \l__chemformula_bond_penalty_tl
+\tl_set:Nn    \l__chemformula_bond_penalty_tl { 10000 }
+\tl_new:N     \l__chemformula_name_tmp_tl
+\tl_new:N     \l__chemformula_chemformula_tmpa_tl
+\tl_new:N     \g__chemformula_options_tl
+\tl_new:N     \g__chemformula_output_tl
+\tl_new:N     \l__chemformula_input_tl
+\tl_new:N     \l__chemformula_stoich_tl
+\tl_new:N     \l__chemformula_decimal_output_tl
+\tl_set:Nn    \l__chemformula_decimal_output_tl { . }
+\tl_new:N     \l__chemformula_font_family_tl
+\tl_set_eq:NN \l__chemformula_font_family_tl \f@family
+\tl_new:N     \l__chemformula_font_series_tl
+\tl_set_eq:NN \l__chemformula_font_series_tl \f@series
+\tl_new:N     \l__chemformula_font_shape_tl
+\tl_set_eq:NN \l__chemformula_font_shape_tl \f@shape
+\tl_new:N     \l__chemformula_format_tl
+\tl_new:N     \l__chemformula_fontspec_options_tl
+\tl_new:N     \l__chemformula_fontspec_argument_tl
+\tl_new:N     \l__chemformula_name_format_tl
+\tl_set:Nn    \l__chemformula_name_format_tl { \scriptsize\centering }
+\tl_new:N     \l_chemormula_sup_super_factor_tl
+\tl_new:N     \l__chemformula_subscript_shift_additional_tl
+\tl_set:Nn    \l__chemformula_subscript_shift_additional_tl { 0pt }
+\tl_new:N     \l__chemformula_superscript_shift_additional_tl
+\tl_set:Nn    \l__chemformula_superscript_shift_additional_tl { 0pt }
+\tl_new:N     \l__chemformula_subscript_tl
+\tl_new:N     \l__chemformula_superscript_tl
+\tl_new:N     \g__chemformula_input_up_tl
+\tl_new:N     \l__chemformula_elspec_angle_tl
+\tl_new:N     \l__chemformula_elspec_radius_tl
+\tl_set:Nn    \l__chemformula_elspec_radius_tl { .5ex }
+\tl_new:N     \l__chemformula_elspec_default_type_tl
+\tl_set:Nn    \l__chemformula_elspec_default_type_tl { pair }
+\tl_const:Nx  \c_chemformula_colon_tl { \token_to_str:N : }
+\tl_new:N     \l__chemformula_kroegervink_positive_style_tl
+\tl_new:N     \l__chemformula_kroegervink_neutral_tl
+\tl_set:Nn    \l__chemformula_kroegervink_neutral_tl { $\times$ }
+
+% property lists:
+\prop_new:N \l__chemformula_arrows_code_prop
+\prop_new:N \l__chemformula_cmpd_prop
+\prop_new:N \l__chemformula_bonds_prop
+\prop_new:N \l__chemformula_stoich_prop
+\prop_new:N \l__chemformula_charge_prop
+\prop_new:N \l__chemformula_numbers_prop
+\prop_new:N \l__chemformula_no_stoich_prop
+\prop_new:N \l__chemformula_lewis_elspec_types_prop
+\prop_new:N \l__chemformula_kroegervink_prop
+
+% sequences:
+\seq_new:N \l__chemformula_arrows_type_seq
+\seq_new:N \l__chemformula_input_seq
+
+% boxes:
+\box_new:N \l__chemformula_arrow_arg_i_box
+\box_new:N \l__chemformula_arrow_arg_ii_box
+\box_new:N \l__chemformula_superscript_box
+\box_new:N \l__chemformula_subscript_box
+
+% --------------------------------------------------------------------------
+% general and helper functions:
+\cs_new:Npn \chemformula_tikz:nn #1#2
+  { \tikz [ #1 ] { #2 } }
+\cs_generate_variant:Nn \chemformula_tikz:nn { xn,nf }
+
+\cs_new:Npn \chemformula_draw:nn #1#2
+  { \draw [ #1 ] #2 ;  }
+\cs_generate_variant:Nn \chemformula_draw:nn { xn,nx,xx,xf,Vn }
+
+\cs_new:Npn \chemformula_node:nn #1#2
+  { \node [ #1 ] { #2 }  ;  }
+\cs_generate_variant:Nn \chemformula_node:nn { x }
+
+\cs_new:Npn \chemformula_node:nnn #1#2#3
+  { \node [ #1 ] ( #2 ) { #3 }  ;  }
+\cs_generate_variant:Nn \chemformula_node:nnn { nx }
+
+\cs_new:Npn \chemformula_allow_break:
+  { \tex_penalty:D \c_zero }
+
+\cs_new_protected:Npn \chemformula_leave_vmode:
+  { \hbox_unpack:N \c_empty_box }
+
+\cs_new:Npn \chemformula_nobreak:
+  { \tex_penalty:D \c_ten_thousand }
+
+\cs_new:Npn \chemformula_skip_nobreak:N #1
+  {
+    \chemformula_nobreak:
+    \skip_horizontal:N #1
+    \chemformula_nobreak:
+  }
+
+\cs_new_protected:Npn \chemformula_skip_nobreak_penalty:Nn #1#2
+  {
+    \chemformula_nobreak:
+    \skip_horizontal:N #1
+    \tex_penalty:D #2 \scan_stop:
+  }
+% \binoppenalty=\maxdimen
+% \relpenalty=\maxdimen
+
+\cs_new_protected:Npn \chemformula_dim_to_width:Nn #1#2
+  {
+    \hbox_set:Nn \l__chemformula_tmpa_box { #2 }
+    \dim_set:Nn #1 { \box_wd:N \l__chemformula_tmpa_box }
+    \box_clear:N \l__chemformula_tmpa_box
+  }
+
+% an l3 conditional that can test 2e's conditionals that go like
+%   \iffoo ... \else ... \fi
+% see http://tex.stackexchange.com/a/119806/5049
+\prg_new_conditional:Npnn \chemformula_latex_if:n #1 {p,T,F,TF}
+  { \use:c { if #1 } \prg_return_true: \else: \prg_return_false: \fi: }
+
+% --------------------------------------------------------------------------
+% prevent externalisation of tikz parts of the formulae:
+\AtBeginDocument { \providecommand \tikzexternaldisable {} }
+
+\keys_define:nn { chemmacros / chemformula }
+  {
+    tikz-external-disable .bool_set:N  =
+      \l__chemformula_tikzexternaldisable_bool
+  }
+
+\cs_new_protected:Npn \chemformula_tikzexternaldisable:
+  {
+    \bool_if:NT \l__chemformula_tikzexternaldisable_bool
+      { \tikzexternaldisable }
+  }
+
+% --------------------------------------------------------------------------
+% circled charge signs:
+\cs_new_protected:Npn \chemformula_fplus:
+  { \ensuremath { \__chemformula_fplus: } }
+
+\cs_new:Npn \__chemformula_fplus:
+  { \mathpalette \__chemformula_fplus_aux: \bigcirc }
+
+\cs_new:Npn \__chemformula_fplus_aux: #1#2
+  {
+    \ooalign
+      {
+        \tex_hfil:D
+        \c_math_toggle_token
+          #1
+          \chemformula_plain_plus:
+        \c_math_toggle_token
+        \tex_hfil:D
+        \tex_cr:D
+        \tex_hfil:D
+        \c_math_toggle_token #1#2 \c_math_toggle_token
+        \tex_hfil:D
+        \tex_cr:D
+      }
+  }
+
+\cs_new_protected:Npn \chemformula_fminus:
+  { \ensuremath { \__chemformula_fminus: } }
+
+\cs_new:Npn \__chemformula_fminus:
+  { \mathpalette \__chemformula_fminus_aux_aux: \bigcirc }
+
+\cs_new:Npn \__chemformula_fminus_aux_aux: #1#2
+  {
+    \ooalign
+      {
+        \tex_hfil:D
+        \c_math_toggle_token
+          #1
+          \chemformula_plain_minus:
+        \c_math_toggle_token
+        \tex_hfil:D
+        \tex_cr:D
+        \tex_hfil:D
+        \c_math_toggle_token #1#2 \c_math_toggle_token
+        \tex_hfil:D
+        \tex_cr:D
+      }
+  }
+
+\AtBeginDocument{
+  \@ifpackageloaded { chemmacros }
+    {
+      \bool_if:nT
+        { \l__chemmacros_circled_bool && !\l__chemmacros_circled_formal_bool }
+        { \bool_set_true:N \l__chemformula_formal_charges_bool }
+      \bool_if:NF \l__chemmacros_circled_chem_bool
+        { \bool_set_false:N \l__chemformula_formal_chem_bool }
+      \keys_define:nn { chemmacros / option }
+        {
+          circletype         .choice: ,
+          circletype / math  .code:n  =
+            {
+              \bool_set_false:N \l__chemmacros_circled_chem_bool
+              \bool_set_false:N \l__chemformula_formal_chem_bool
+            } ,
+          circletype / chem  .code:n  =
+            {
+              \bool_set_true:N \l__chemmacros_circled_chem_bool
+              \bool_set_true:N \l__chemformula_formal_chem_bool
+            } ,
+          circletype         .default:n = chem ,
+          circled            .choice: ,
+          circled / none     .code:n =
+            {
+              \bool_set_false:N \l__chemmacros_circled_bool
+              \bool_set_false:N \l__chemmacros_circled_formal_bool
+              \bool_set_false:N \l__chemformula_formal_charges_bool
+            } ,
+          circled / formal   .code:n =
+            {
+              \bool_set_true:N \l__chemmacros_circled_bool
+              \bool_set_true:N \l__chemmacros_circled_formal_bool
+              \bool_set_false:N \l__chemformula_formal_charges_bool
+            } ,
+          circled / all      .code:n =
+            {
+              \bool_set_true:N \l__chemmacros_circled_bool
+              \bool_set_false:N \l__chemmacros_circled_formal_bool
+              \bool_set_true:N \l__chemformula_formal_charges_bool
+            } ,
+          circled            .default:n  = all
+        }
+    }
+    { }
+}
+
+\cs_new_protected:Npn \chemformula_plain_plus:
+  {
+    \bool_if:NTF \l__chemformula_charge_style_math_bool
+      { \ensuremath { + } }
+      { \mode_if_math:TF { \text { + } } { + } }
+  }
+
+\cs_new_protected:Npn \chemformula_plus:
+  {
+    \bool_if:NTF \l__chemformula_formal_charges_bool
+      {
+        \bool_if:NTF \l__chemformula_formal_chem_bool
+          { \chemformula_fplus: }
+          {
+            \mode_if_math:TF
+              { \oplus }
+              { \c_math_toggle_token \oplus \c_math_toggle_token }
+          }
+      }
+      { \chemformula_plain_plus: }
+  }
+
+\cs_new_protected:Npn \chemformula_plain_minus:
+  {
+    \bool_if:NTF \l__chemformula_charge_style_math_bool
+      { \ensuremath { - } }
+      { \mode_if_math:TF { \text { \textendash } } { \textendash } }
+  }
+
+\cs_new_protected:Npn \chemformula_minus:
+  {
+     \bool_if:NTF \l__chemformula_formal_charges_bool
+      {
+        \bool_if:NTF \l__chemformula_formal_chem_bool
+          { \chemformula_fminus: }
+          {
+            \mode_if_math:TF
+              { \ominus }
+              { \c_math_toggle_token \ominus \c_math_toggle_token }
+          }
+      }
+      { \chemformula_plain_minus: }
+  }
+
+% --------------------------------------------------------------------------
+% Some basic internal commands:
+
+\cs_new_protected:Npn \chemformula_radical_or_decimal:
+  {
+    \peek_meaning:NTF \c_group_begin_token
+      { \chemformula_decimal: }
+      { \chemformula_radical: }
+  }
+
+\cs_new_protected:Npn \chemformula_radical:
+  {
+    \hbox_overlap_right:n
+      {
+        \chemformula_tikz:xn
+          {
+            \l__chemformula_radical_style_tl ,
+            baseline ,
+            minimum~ height = 0pt ,
+            minimum~ width = 0pt ,
+            inner~ sep = 0pt ,
+            outer~ sep = 0pt ,
+            overlay
+          }
+          {
+            \fill (0,0)
+              ++(
+                \l__chemformula_radical_hshift_dim ,
+                \l__chemformula_radical_vshift_dim
+              )
+              circle (\l__chemformula_radical_radius_dim) ;
+          }
+      }
+    \skip_horizontal:N \l__chemformula_radical_space_dim
+  }
+
+\keys_define:nn { chemmacros / chemformula }
+  {
+    % TikZ style:
+    radical-style  .tl_set:N  = \l__chemformula_radical_style_tl ,
+    radical-radius .dim_set:N = \l__chemformula_radical_radius_dim ,
+    % shift before:
+    radical-hshift .dim_set:N = \l__chemformula_radical_hshift_dim ,
+    radical-vshift .dim_set:N = \l__chemformula_radical_vshift_dim ,
+    % space after:
+    radical-space  .dim_set:N = \l__chemformula_radical_space_dim
+  }
+
+\cs_new:Npn \chemformula_adduct:
+  {
+    \skip_horizontal:N \l__chemformula_adduct_space_dim
+    \textperiodcentered
+    \skip_horizontal:N \l__chemformula_adduct_space_dim
+  }
+\cs_new_eq:NN \chemformula_star_adduct: \chemformula_adduct:
+
+% --------------------------------------------------------------------------
+% Kroeger-Vink notation
+\cs_new_protected:Npn \chemformula_kroegervink_negative:
+  { \ensuremath { \prime } }
+
+\cs_new_protected:Npn \chemformula_kroegervink_neutral:
+  { \ensuremath { \text {\l__chemformula_kroegervink_neutral_tl } } }
+
+\cs_new_protected:Npn \chemformula_kroegervink_positive:
+  {
+    \hbox_overlap_right:n
+      {
+        \chemformula_tikz:xn
+          {
+            \l__chemformula_kroegervink_positive_style_tl ,
+            baseline ,
+            minimum~ height = 0pt ,
+            minimum~ width = 0pt ,
+            inner~ sep = 0pt ,
+            outer~ sep = 0pt ,
+            overlay
+          }
+          {
+            \fill (0,0)
+              ++(
+                \l__chemformula_kroegervink_positive_hshift_dim ,
+                \l__chemformula_kroegervink_positive_vshift_dim
+              )
+              circle (\l__chemformula_kroegervink_positive_radius_dim) ;
+          }
+      }
+    \skip_horizontal:N \l__chemformula_kroegervink_positive_space_dim
+  }
+
+\cs_new:Npn \chemformula_prime:
+  {
+    \bool_if:NTF \l__chemformula_kroegervink_bool
+      { \chemformula_kroegervink_negative: }
+      { ' }
+  }
+
+\keys_define:nn { chemmacros / chemformula }
+  {
+    kroeger-vink       .bool_set:N =
+      \l__chemformula_kroegervink_bool ,
+    % TikZ style:
+    kv-positive-style  .tl_set:N   =
+      \l__chemformula_kroegervink_positive_style_tl ,
+    kv-positive-radius .dim_set:N  =
+      \l__chemformula_kroegervink_positive_radius_dim ,
+    % spacing:
+    kv-positive-hshift .dim_set:N  =
+      \l__chemformula_kroegervink_positive_hshift_dim ,
+    kv-positive-vshift .dim_set:N  =
+      \l__chemformula_kroegervink_positive_vshift_dim ,
+    kv-positive-offset .dim_set:N  =
+      \l__chemformula_kroegervink_positive_space_dim ,
+    % symbol:
+    kv-neutral-symbol  .tl_set:N   =
+      \l__chemformula_kroegervink_neutral_tl
+  }
+
+% --------------------------------------------------------------------------
+% ARROW DEFINITION
+% arrow heads:
+
+% full tip for pairs
+\pgfarrowsdeclare { cf~internal } { cf~internal }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfarrowsleftextend { -\l__chemformula_arrow_head_dim }
+    \pgfarrowsrightextend { .5\pgflinewidth }
+  }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfsetdash {} { 0pt }
+    \pgfsetroundjoin
+    \pgfsetroundcap
+    \pgfpathmoveto { \pgfpoint { 0pt } { 0pt } }
+    \pgfpathlineto
+      {
+        \pgfpoint
+          { -\l__chemformula_arrow_head_dim }
+          { .3\l__chemformula_arrow_head_dim }
+      }
+    \pgfpathlineto
+      { \pgfpoint { -.5\l__chemformula_arrow_head_dim } { 0pt } }
+    \pgfpathlineto
+      {
+        \pgfpoint
+          { -\l__chemformula_arrow_head_dim }
+          { -.3\l__chemformula_arrow_head_dim }
+      }
+    \pgfpathlineto { \pgfpoint { 0pt } { 0pt } }
+    \pgfusepathqfillstroke
+  }
+
+% half tip on the left
+\pgfarrowsdeclare { left~cf~internal } { left~cf~internal }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfarrowsleftextend { -\l__chemformula_arrow_head_dim }
+    \pgfarrowsrightextend { .5\pgflinewidth }
+  }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfsetdash {} { 0pt }
+    \pgfsetroundjoin
+    \pgfsetroundcap
+    \pgfpathmoveto { \pgfpoint { 0pt } { 0pt } }
+    \pgfpathlineto
+      {
+        \pgfpoint
+          { -\l__chemformula_arrow_head_dim }
+          { .3\l__chemformula_arrow_head_dim }
+      }
+    \pgfpathlineto { \pgfpoint { -.5\l__chemformula_arrow_head_dim } { 0pt } }
+    \pgfpathlineto { \pgfpoint { 0pt } { 0pt } }
+    \pgfusepathqfillstroke
+  }
+
+% half tip in the right
+\pgfarrowsdeclare { right~cf~internal } { right~cf~internal }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfarrowsleftextend { -\l__chemformula_arrow_head_dim }
+    \pgfarrowsrightextend { .5\pgflinewidth }
+  }
+  {
+    \dim_set:Nn \l__chemformula_arrow_head_dim
+      { 2.5pt + 2.5\pgflinewidth }
+    \pgfsetdash {} { 0pt }
+    \pgfsetroundjoin
+    \pgfsetroundcap
+    \pgfpathmoveto { \pgfpoint { 0pt } { 0pt } }
+    \pgfpathlineto
+      {
+        \pgfpoint
+          { -\l__chemformula_arrow_head_dim }
+          { -.3\l__chemformula_arrow_head_dim }
+      }
+    \pgfpathlineto { \pgfpoint { -.5\l__chemformula_arrow_head_dim } { 0pt } }
+    \pgfpathlineto { \pgfpoint { 0pt } { 0pt } }
+    \pgfusepathqfillstroke
+  }
+
+\pgfkeys{
+  cf~       /.tip = {cf~internal} ,
+  left~cf~  /.tip = {left~cf~internal} ,
+  right~cf~ /.tip = {right~cf~internal}
+}
+
+% --------------------------------------------------------------------------
+% determine length in dependency of labels
+\cs_new_protected:Npn \__chemformula_determine_arrow_length:NN #1#2
+  {
+    \dim_set:NV \l__chemformula_arrow_offset_dim \l__chemformula_arrow_offset_tl
+    \box_set_eq:NN \l__chemformula_tmpa_box #1
+    \dim_set:Nn \l__chemformula_tmpa_dim { \box_wd:N \l__chemformula_tmpa_box }
+    \box_set_eq:NN \l__chemformula_tmpa_box #2
+    \dim_set:Nn \l__chemformula_tmpb_dim { \box_wd:N \l__chemformula_tmpa_box }
+    \box_clear:N \l__chemformula_tmpa_box
+    \dim_compare:nTF { \l__chemformula_tmpa_dim >= \l__chemformula_tmpb_dim }
+      { \dim_set_eq:NN \l__chemformula_arrow_length_dim \l__chemformula_tmpa_dim }
+      { \dim_set_eq:NN \l__chemformula_arrow_length_dim \l__chemformula_tmpb_dim }
+    \dim_add:Nn \l__chemformula_arrow_length_dim
+      { 2\l__chemformula_arrow_offset_dim }
+    \dim_compare:nF
+      { \l__chemformula_arrow_length_dim > \l__chemformula_arrow_minimum_length_dim }
+      {
+        \dim_set_eq:NN
+          \l__chemformula_arrow_length_dim
+          \l__chemformula_arrow_minimum_length_dim
+      }
+    \dim_set:Nn \l__chemformula_arrow_shortage_dim
+      {
+        (
+          \l__chemformula_arrow_length_dim
+          -
+          \l__chemformula_arrow_length_dim *
+          \dim_ratio:nn { \l__chemformula_arrow_ratio_tl pt } { 1pt }
+        ) * 1/2
+      }
+    \box_set_eq:NN \l__chemformula_tmpa_box #1
+    \dim_set:Nn \l__chemformula_tmpa_dim
+      { \box_ht:N \l__chemformula_tmpa_box + \box_dp:N \l__chemformula_tmpa_box }
+    \box_set_eq:NN \l__chemformula_tmpa_box #2
+    \dim_set:Nn \l__chemformula_tmpb_dim
+      { \box_ht:N \l__chemformula_tmpa_box + \box_dp:N \l__chemformula_tmpa_box }
+    \box_clear:N \l__chemformula_tmpa_box
+    \dim_compare:nTF { \l__chemformula_tmpa_dim >= \l__chemformula_tmpb_dim }
+      { \dim_set_eq:NN \l__chemformula_arrow_label_height_dim \l__chemformula_tmpa_dim }
+      { \dim_set_eq:NN \l__chemformula_arrow_label_height_dim \l__chemformula_tmpb_dim }
+  }
+
+% --------------------------------------------------------------------------
+% define arrow types
+
+% read arrow labels:
+
+\cs_new:Npn \chemformula_arrow_labels:nn #1#2
+  {
+    \hbox_set:Nn \l__chemformula_arrow_arg_i_box
+      { \tl_use:N \l__chemformula_arrow_label_style_tl #1 }
+    \hbox_set:Nn \l__chemformula_arrow_arg_ii_box
+      { \tl_use:N \l__chemformula_arrow_label_style_tl #2 }
+    % now that we have both arguments do the actual drawing:
+    \prop_get:NVN \l__chemformula_arrows_code_prop
+      \l__chemformula_arrow_type_tl
+      \l__chemformula_tmpb_tl
+    \__chemformula_arrow_draw:V \l__chemformula_tmpb_tl
+  }
+
+% get arrows (for the use in \ch to replace the symbol)
+%  #1: symbol
+\cs_new_protected:Npn \__chemformula_arrows_get:n #1
+  {
+    % first clear the arguments
+    \box_clear:N \l__chemformula_arrow_arg_i_box
+    \box_clear:N \l__chemformula_arrow_arg_ii_box
+    % then get the arrow type
+    \tl_set:Nn \l__chemformula_arrow_type_tl { #1 }
+  }
+
+% this will be \arrow inside \ch
+\DeclareDocumentCommand \charrow { mO{}O{} }
+  {
+    \group_begin:
+      \chemformula_tikzexternaldisable:
+      \__chemformula_arrows_get:n { #1 }
+      \chemformula_arrow_labels:nn { #2 } { #3 }
+    \group_end:
+  }
+
+% draw the arrows
+\cs_new:Npn \__chemformula_arrow_draw:n #1
+  {
+    \chemformula_nobreak:
+    % prepare arrow code for drawing:
+    \tl_set_rescan:Nnn \l__chemformula_tmpc_tl
+      { \char_set_catcode_letter:N \_ } { #1 }
+    % determine length of the arrow
+    \__chemformula_determine_arrow_length:NN
+      \l__chemformula_arrow_arg_i_box
+      \l__chemformula_arrow_arg_ii_box
+    \chemformula_tikz:nf
+      { inner~sep=0, baseline=(chemformula_arrow_start.base) }
+      {
+        % the coordinates
+        \chemformula_draw:xn
+          { \l__chemformula_arrow_style_tl }
+          {
+            coordinate (chemformula_arrow_start) (0pt,0pt)
+            ++ ( \l__chemformula_compound_sep_tl , .3432em)
+            ++ (0pt,\l__chemformula_arrow_yshift_dim)
+            coordinate (cf_arrow_start)
+            ++ ( .5 * \dim_use:N \l__chemformula_arrow_length_dim , 0pt)
+            coordinate (cf_arrow_mid)
+            ++ ( .5 * \dim_use:N \l__chemformula_arrow_length_dim , 0pt)
+            coordinate (cf_arrow_end)
+            ++ ( \l__chemformula_compound_sep_tl , 0pt )
+            (cf_arrow_start) ++ (\l__chemformula_arrow_shortage_dim , 0pt)
+            coordinate (cf_arrow_mid_start)
+            (cf_arrow_end) ++ (-\l__chemformula_arrow_shortage_dim , 0pt)
+            coordinate (cf_arrow_mid_end)
+          }
+        % the arrow labels:
+        \draw
+            node
+              [ above=\l__chemformula_arrow_label_offset_dim ] at (cf_arrow_mid)
+              { \box_use:N \l__chemformula_arrow_arg_i_box }
+            node
+              [ below=\l__chemformula_arrow_label_offset_dim ] at (cf_arrow_mid)
+              { \box_use:N \l__chemformula_arrow_arg_ii_box }
+          ;
+        \tl_use:N \l__chemformula_tmpc_tl
+      }
+    \chemformula_skip_nobreak_penalty:Nn
+      \c_zero_skip
+      { \l__chemformula_arrow_penalty_tl }
+  }
+\cs_generate_variant:Nn \__chemformula_arrow_draw:n { V }
+
+% commands to declare arrows (can also be used by users):
+%  #1: symbol, #2: code
+\NewDocumentCommand \NewChemArrow { mm }
+  {
+    \prop_if_in:NnTF \l__chemformula_arrows_code_prop { #1 }
+      { \msg_error:nnn { chemformula } { new-arrow } { #1 } }
+      {
+        % store type in the sequence and code in the property list
+        \seq_put_right:Nn \l__chemformula_arrows_type_seq { #1 }
+        \prop_put:Nnn \l__chemformula_arrows_code_prop { #1 } { #2 }
+      }
+  }
+
+\NewDocumentCommand \DeclareChemArrow { mm }
+  {
+    \prop_if_in:NnF \l__chemformula_arrows_code_prop { #1 }
+      { \seq_put_right:Nn \l__chemformula_arrows_type_seq { #1 } }
+    % store type in the sequence and code in the property list
+    \prop_put:Nnn \l__chemformula_arrows_code_prop { #1 } { #2 }
+  }
+
+\NewDocumentCommand \RenewChemArrow { mm }
+  {
+    \prop_if_in:NnTF \l__chemformula_arrows_code_prop { #1 }
+      { \prop_put:Nnn \l__chemformula_arrows_code_prop { #1 } { #2 } }
+      { \msg_error:nnn { chemformula } { renew-arrow } { #1 } }
+  }
+
+\NewDocumentCommand \ShowChemArrow { m }
+  {
+    \prop_get:NnN \l__chemformula_arrows_code_prop { #1 } \l__chemformula_tmpa_tl
+    \tl_to_str:N \l__chemformula_tmpa_tl
+  }
+
+% declare arrows in the right order
+% e.g. <-> must be declared before -> in order to search & replace it first
+% resonance arrow:
+\NewChemArrow { <-> }
+  { \draw[chemarrow,cf-cf] (cf_arrow_start) -- (cf_arrow_end) ; }
+\NewChemArrow { -> }
+  { \draw[chemarrow,-cf] (cf_arrow_start) -- (cf_arrow_end) ; }
+\NewChemArrow { <- }
+  { \draw[chemarrow,cf-] (cf_arrow_start) -- (cf_arrow_end) ; }
+\NewChemArrow { <> }
+  {
+    \draw[chemarrow,-cf]
+      ([yshift=.2ex]cf_arrow_start) -- ([yshift=.2ex]cf_arrow_end) ;
+    \draw[chemarrow,cf-,]
+      ([yshift=-.2ex]cf_arrow_start) -- ([yshift=-.2ex]cf_arrow_end) ;
+  }
+% isolobal arrow:
+\NewChemArrow { <o> }
+  {
+    \draw[chemarrow,cf-cf] (cf_arrow_start) -- (cf_arrow_end) ;
+    \draw[chemarrow]
+      (cf_arrow_mid) .. controls ++(-.9ex,-1.5ex) and
+      ++(.9ex,-1.5ex) .. (cf_arrow_mid) ;
+  }
+\NewChemArrow { <=>> }
+  {
+    \draw[chemarrow,-left~cf]
+      ([yshift=.15ex]cf_arrow_start) -- ([yshift=.15ex]cf_arrow_end) ;
+    \draw[chemarrow,left~cf-]
+      ([yshift=-.15ex]cf_arrow_mid_start) -- ([yshift=-.15ex]cf_arrow_mid_end) ;
+  }
+\NewChemArrow { <<=> }
+  {
+    \draw[chemarrow,-left~cf]
+      ([yshift=.15ex]cf_arrow_mid_start) -- ([yshift=.15ex]cf_arrow_mid_end) ;
+    \draw[chemarrow,left~cf-]
+      ([yshift=-.15ex]cf_arrow_start) -- ([yshift=-.15ex]cf_arrow_end) ;
+  }
+\NewChemArrow { <=> }
+  {
+    \draw[chemarrow,-left~cf]
+      ([yshift=.15ex]cf_arrow_start) -- ([yshift=.15ex]cf_arrow_end) ;
+    \draw[chemarrow,left~cf-]
+      ([yshift=-.15ex]cf_arrow_start) -- ([yshift=-.15ex]cf_arrow_end) ;
+  }
+\NewChemArrow { >>=< }
+  {
+    \draw[chemarrow,right~cf-]
+      ([yshift=.15ex]cf_arrow_start) -- ([yshift=.15ex]cf_arrow_end) ;
+    \draw[chemarrow,-right~cf]
+      ([yshift=-.15ex]cf_arrow_mid_start) -- ([yshift=-.15ex]cf_arrow_mid_end) ;
+  }
+\NewChemArrow { >=<< }
+  {
+    \draw[chemarrow,right~cf-]
+      ([yshift=.15ex]cf_arrow_mid_start) -- ([yshift=.15ex]cf_arrow_mid_end) ;
+    \draw[chemarrow,-right~cf]
+      ([yshift=-.15ex]cf_arrow_start) -- ([yshift=-.15ex]cf_arrow_end) ;
+  }
+\NewChemArrow { >=< }
+  {
+    \draw[chemarrow,right~cf-]
+      ([yshift=.15ex]cf_arrow_start) -- ([yshift=.15ex]cf_arrow_end) ;
+    \draw[chemarrow,-right~cf]
+      ([yshift=-.15ex]cf_arrow_start) -- ([yshift=-.15ex]cf_arrow_end) ;
+  }
+\NewChemArrow { <==> }
+  {
+    \draw[chemarrow,double~ equal~ sign~ distance,double,Implies-Implies]
+      (cf_arrow_start) -- (cf_arrow_end) ;
+    % \node at ([yshift=-.2ex]cf_arrow_mid) { $\Leftrightarrow$ } ;
+  }
+\NewChemArrow { -/> }
+  {
+    \draw[chemarrow,-cf] (cf_arrow_start) -- (cf_arrow_end) ;
+    \draw[chemarrow] (cf_arrow_mid) ++ (.2ex,.4ex) -- ++(-.4ex,-.8ex) ;
+    \draw[chemarrow] (cf_arrow_mid) ++ (-.2ex,.4ex) -- ++(-.4ex,-.8ex) ;
+  }
+\NewChemArrow { </- }
+  {
+    \draw[chemarrow,cf-] (cf_arrow_start) -- (cf_arrow_end) ;
+    \draw[chemarrow] (cf_arrow_mid) ++ (.2ex,.4ex) -- ++(-.4ex,-.8ex) ;
+    \draw[chemarrow] (cf_arrow_mid) ++ (.6ex,.4ex) -- ++(-.4ex,-.8ex) ;
+  }
+% net reaction:
+\NewChemArrow { == } { \node at ([yshift=-.2ex]cf_arrow_mid) { = } ; }
+
+% --------------------------------------------------------------------------
+% arrow customization
+\keys_define:nn { chemmacros / chemformula }
+  {
+    arrow-offset     .tl_set:N  = \l__chemformula_arrow_offset_tl ,
+    arrow-min-length .dim_set:N = \l__chemformula_arrow_minimum_length_dim ,
+    arrow-yshift     .dim_set:N = \l__chemformula_arrow_yshift_dim ,
+    arrow-ratio      .tl_set:N  = \l__chemformula_arrow_ratio_tl ,
+    label-offset     .dim_set:N = \l__chemformula_arrow_label_offset_dim ,
+    compound-sep     .tl_set:N  = \l__chemformula_compound_sep_tl ,
+    arrow-style      .tl_set:N  = \l__chemformula_arrow_style_tl ,
+    label-style      .tl_set:N  = \l__chemformula_arrow_label_style_tl ,
+    arrow-penalty    .tl_set:N  = \l__chemformula_arrow_penalty_tl ,
+    arrow-style      .code:n    =  \tikzset { chemarrow/.style={#1} } ,
+  }
+
+% --------------------------------------------------------------------------
+% MAIN COMMAND
+\cs_new_protected:Npn \__chemformula_ch_main:n #1
+  {
+    \group_begin:
+      \seq_set_split:Nnn \l__chemformula_input_seq { ~ } { #1 }
+      \cs_set_eq:NN \xspace \scan_stop:
+      % the next two aren't necessary any more but shouldn't do harm, too:
+      \cs_set_nopar:Npn \[ { [ }
+      \cs_set_nopar:Npn \] { ] }
+      \bool_set_true:N \l_chemformula_inside_ch_bool
+      \tl_if_blank:VF \g__chemformula_options_tl
+        {
+          \keys_set:nV
+            { chemmacros / chemformula }
+            \g__chemformula_options_tl
+        }
+      \seq_map_function:NN
+        \l__chemformula_input_seq
+        \chemformula_input:n
+      \__chemformula_prepare_output:N \l__chemformula_input_tl
+      \chemformula_write:V \l__chemformula_input_tl
+    \group_end:
+  }
+
+\cs_new:Npn \chemformula_write:n #1
+  {
+    \mode_if_math:TF
+      {
+        \mathchoice
+          { \text { \chemformula_font_inner: #1 } }
+          { \text { \chemformula_font_inner: #1 } }
+          { \text { \scriptsize \chemformula_font_inner: #1 } }
+          { \text { \tiny \chemformula_font_inner: #1 } }
+      }
+      { \chemformula_font_inner: #1 }
+  }
+\cs_generate_variant:Nn \chemformula_write:n { V }
+
+% internal version of \ch command:
+\cs_new_protected:Npn \chemformula_ch:nn #1#2
+  {
+    \group_align_safe_begin:
+      \chemformula_leave_vmode:
+      \tl_if_blank:nTF { #1 }
+        { \tl_gclear:N \g__chemformula_options_tl }
+        { \tl_gset:Nn  \g__chemformula_options_tl { #1 } }
+      \__chemformula_ch_newline:w #2 \\ \q_no_value \q_stop
+    \group_align_safe_end:
+    \tl_use:N    \g__chemformula_output_tl
+    \tl_gclear:N \g__chemformula_output_tl
+  }
+\cs_generate_variant:Nn \chemformula_ch:nn { V , nV , VV }
+
+% Trickery to use \ch inside align environment:
+% bypass \\:
+\cs_new_protected:Npn \__chemformula_ch_newline:w #1 \\ #2 \q_stop
+  {
+    \__chemformula_ch_align:w #1 & \q_no_value \q_stop
+    \quark_if_no_value:nF { #2 }
+      {
+        \tl_gput_right:Nn \g__chemformula_output_tl { \\ }
+        % look for optional argument:
+        \peek_meaning:NTF [
+          { \__chemformula_ch_newline_skip:w }
+          { \__chemformula_ch_newline:w }
+        #2 \q_stop
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_ch_newline_skip:w [ #1 ]
+  {
+    \tl_gput_right:Nn \g__chemformula_output_tl { [#1] }
+    \__chemformula_ch_newline:w
+  }
+
+% bypass &:
+\cs_new_protected:Npn \__chemformula_ch_align:w #1 & #2 \q_stop
+  {
+    \__chemformula_ch_label:w #1 \label \q_no_value \q_stop
+    \quark_if_no_value:nF { #2 }
+      {
+        \tl_gput_right:Nn \g__chemformula_output_tl { & }
+        \__chemformula_ch_align:w #2 \q_stop
+      } 
+  }
+
+% bypass \label:
+\cs_new_protected:Npn \__chemformula_ch_label:w #1 \label #2 \q_stop
+  {
+    \__chemformula_ch_tag:w #1 \tag{} \q_no_value \q_stop
+    \quark_if_no_value:nF { #2 }
+      {
+        \tl_gput_right:Nn \g__chemformula_output_tl { \label }
+        \peek_meaning:NTF [ % ]
+          { \__chemformula_ch_label_opt:w }
+          { \__chemformula_ch_label_no_opt:n }
+        #2 \q_stop
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_ch_label_opt:w [ #1 ] #2
+  {
+    \tl_gput_right:Nn \g__chemformula_output_tl { [{#1}] {#2} }
+    \__chemformula_ch_label:w
+  }
+
+\cs_new_protected:Npn \__chemformula_ch_label_no_opt:n #1
+  {
+    \tl_gput_right:Nn \g__chemformula_output_tl { {#1} }
+    \__chemformula_ch_label:w
+  }
+
+% here's something not working when used together with `hyperref'
+% which seems to be related to \nonumber
+% bypass \tag:
+\cs_new_protected:Npn \__chemformula_ch_tag:w #1 \tag#2 #3 \q_stop
+  {
+    \__chemformula_ch_intertext:w #1 \intertext{} \q_no_value \q_stop
+    \quark_if_no_value:nF { #3 }
+      {
+        \tl_gput_right:Nn \g__chemformula_output_tl { \protect\tag { #2 } }
+        \__chemformula_ch_tag:w #3 \q_stop
+      } 
+  }
+
+% bypass \intertext:
+\cs_new_protected:Npn \__chemformula_ch_intertext:w #1 \intertext#2 #3 \q_stop
+  {
+    \tl_gput_right:Nn \g__chemformula_output_tl
+      { \__chemformula_ch_main:n { #1 } }
+    \quark_if_no_value:nF { #3 }
+      {
+        \tl_gput_right:Nn \g__chemformula_output_tl { \intertext { #2 } }
+        \__chemformula_ch_intertext:w #3 \q_stop
+      }
+  }
+
+% --------------------------------------------------------------------------
+% user commands:
+\NewDocumentCommand \ch { O{}m }
+  { \chemformula_ch:nn { #1 } { #2 } }
+
+\tl_new:N \l__chemformula_compound_tl
+\cs_new_protected:Npn \chemformula_chcpd:nn #1#2
+  {
+    \group_begin:
+      \keys_set:nn { chemmacros / chemformula } { #1 }
+      \__chemformula_save_catcodes:
+      \__chemformula_sanitize:Nn
+        \l__chemformula_chemformula_tmpa_tl
+        { #2 }
+      \chemformula_input_cmpd:VN
+        \l__chemformula_chemformula_tmpa_tl
+        \l__chemformula_compound_tl
+      \__chemformula_prepare_output:N \l__chemformula_compound_tl
+      \chemformula_write:V \l__chemformula_compound_tl
+    \group_end:
+  }
+
+\NewDocumentCommand \chcpd { O{}m }
+  { \chemformula_chcpd:nn { #1 } { #2 } }
+
+% --------------------------------------------------------------------------
+% arrow generation & detection
+\cs_new:Npn \__chemformula_generate_arrows:Nn #1#2
+  {
+    \tl_set_rescan:Nnn \l__chemformula_tmpa_tl
+      {
+        \char_set_catcode_other:N \>
+        \char_set_catcode_other:N \<
+        \char_set_catcode_other:N \-
+        \char_set_catcode_other:N \=
+      }
+      { #2 }
+    \seq_map_inline:Nn \l__chemformula_arrows_type_seq
+      {
+        \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+          { ##1 } { \charrow { ##1 } }
+      }
+    \tl_set_eq:NN #1 \l__chemformula_tmpa_tl
+  }
+\cs_generate_variant:Nn \__chemformula_generate_arrows:Nn { NV }
+
+\cs_new_protected:Npn \__chemformula_detect_arrows:n #1
+  {
+    \bool_set_false:N \l__chemformula_is_arrow_bool
+    \prop_map_inline:Nn \l__chemformula_arrows_code_prop
+      {
+        \__chemformula_sanitize:Nn \l__chemformula_tmpa_tl { ##1 }
+        \tl_if_in:nVT { #1 } \l__chemformula_tmpa_tl
+          { \bool_set_true:N \l__chemformula_is_arrow_bool }
+      }
+  }
+
+% --------------------------------------------------------------------------
+% compound names
+\cs_new:Npn \__chemformula_name_cmpd:w
+  { \peek_meaning:NTF ( { \chname } { ! } }
+
+\NewDocumentCommand \chname { R(){}R(){} }
+  { \chemformula_chwritebelow:nn { #1 } { #2 } }
+
+\cs_new:Npn \chemformula_chwritebelow:nn #1#2
+  {
+%     \group_begin:
+%       \__chemformula_reset:Nn \l__chemformula_tmpa_tl { #1 }
+      \c_math_toggle_token
+      \underset
+        {
+          \bool_if:NF \l__chemformula_name_width_bool
+            {
+              \chemformula_dim_to_width:Nn \l__chemformula_name_dim
+                { \l__chemformula_name_format_tl #1 }
+            }
+          \parbox
+            { \dim_use:N \l__chemformula_name_dim }
+            { \l__chemformula_name_format_tl #1 }
+        }
+        { \text { \strut #2 } }
+      \c_math_toggle_token
+%     \group_end:
+  }
+
+\cs_new_protected:Npn \__chemformula_generate_name:Nn #1#2
+  {
+    \__chemformula_sanitize:Nn \l__chemformula_tmpa_tl { #2 }
+    \tl_if_in:VnT \l__chemformula_tmpa_tl { ! }
+      {
+        \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+          { ! }
+          { \__chemformula_name_cmpd:w }
+      }
+    \tl_set_eq:NN #1 \l__chemformula_tmpa_tl
+  }
+\cs_generate_variant:Nn \__chemformula_generate_name:Nn { NV }
+
+\cs_new_protected:Npn \__chemformula_detect_name:n #1
+  {
+     \bool_set_false:N \l__chemformula_is_name_bool
+     \tl_set:Nn \l__chemformula_tmpa_tl { #1 }
+     \tl_if_in:VnT \l__chemformula_tmpa_tl { ! }
+       { \bool_set_true:N \l__chemformula_is_name_bool }
+  }
+
+% --------------------------------------------------------------------------
+% parsing input
+\prop_put:Nnn \l__chemformula_cmpd_prop { 0 } { \chemformula_subscript:n { 0 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 1 } { \chemformula_subscript:n { 1 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 2 } { \chemformula_subscript:n { 2 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 3 } { \chemformula_subscript:n { 3 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 4 } { \chemformula_subscript:n { 4 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 5 } { \chemformula_subscript:n { 5 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 6 } { \chemformula_subscript:n { 6 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 7 } { \chemformula_subscript:n { 7 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 8 } { \chemformula_subscript:n { 8 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { 9 } { \chemformula_subscript:n { 9 } }
+\prop_put:Nnn \l__chemformula_cmpd_prop { * } { \chemformula_star_adduct: }
+\prop_put:Nnn \l__chemformula_cmpd_prop { . } { \chemformula_adduct: }
+\prop_put:Nnn \l__chemformula_cmpd_prop { - } { \chemformula_single_bond: }
+\prop_put:Nnn \l__chemformula_cmpd_prop { = } { \chemformula_double_bond: }
+\prop_put:Nnn \l__chemformula_cmpd_prop { + } { \chemformula_triple_bond: }
+\prop_put:Nnn \l__chemformula_cmpd_prop { ' } { \chemformula_prime: }
+
+% numbers
+\prop_put:Nnn \l__chemformula_numbers_prop { 0 } { 0 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 1 } { 1 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 2 } { 2 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 3 } { 3 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 4 } { 4 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 5 } { 5 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 6 } { 6 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 7 } { 7 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 8 } { 8 }
+\prop_put:Nnn \l__chemformula_numbers_prop { 9 } { 9 }
+
+% behaviour in a charge
+\prop_put:Nnn \l__chemformula_charge_prop { 0 } { \chemformula_charge_style:n { 0 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 1 } { \chemformula_charge_style:n { 1 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 2 } { \chemformula_charge_style:n { 2 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 3 } { \chemformula_charge_style:n { 3 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 4 } { \chemformula_charge_style:n { 4 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 5 } { \chemformula_charge_style:n { 5 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 6 } { \chemformula_charge_style:n { 6 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 7 } { \chemformula_charge_style:n { 7 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 8 } { \chemformula_charge_style:n { 8 } }
+\prop_put:Nnn \l__chemformula_charge_prop { 9 } { \chemformula_charge_style:n { 9 } }
+\prop_put:Nnn \l__chemformula_charge_prop { + } { \chemformula_plus: }
+\prop_put:Nnn \l__chemformula_charge_prop { - } { \chemformula_minus: }
+\prop_put:Nnn \l__chemformula_charge_prop { . } { \chemformula_radical_or_decimal: }
+\prop_put:Nnn \l__chemformula_charge_prop { , } { \chemformula_decimal: }
+
+% stoichiometric factors
+\prop_put:Nnn \l__chemformula_stoich_prop { 0 } { 0 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 1 } { 1 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 2 } { 2 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 3 } { 3 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 4 } { 4 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 5 } { 5 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 6 } { 6 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 7 } { 7 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 8 } { 8 }
+\prop_put:Nnn \l__chemformula_stoich_prop { 9 } { 9 }
+\prop_put:Nnn \l__chemformula_stoich_prop { . } { \chemformula_decimal: }
+\prop_put:Nnn \l__chemformula_stoich_prop { , } { \chemformula_decimal: }
+\prop_put:Nnn \l__chemformula_stoich_prop { / } { / }
+\prop_put:Nnn \l__chemformula_stoich_prop { _ } { _ }
+\prop_put:Nnn \l__chemformula_stoich_prop { ( } { ( }
+\prop_put:Nnn \l__chemformula_stoich_prop { ) } { ) }
+
+\prop_put:Nnn \l__chemformula_no_stoich_prop { . } { }
+\prop_put:Nnn \l__chemformula_no_stoich_prop { , } { }
+\prop_put:Nnn \l__chemformula_no_stoich_prop { / } { }
+\prop_put:Nnn \l__chemformula_no_stoich_prop { _ } { }
+\prop_put:Nnn \l__chemformula_no_stoich_prop { ( } { }
+\prop_put:Nnn \l__chemformula_no_stoich_prop { ) } { }
+
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 0 } { \chemformula_charge_style:n { 0 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 1 } { \chemformula_charge_style:n { 1 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 2 } { \chemformula_charge_style:n { 2 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 3 } { \chemformula_charge_style:n { 3 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 4 } { \chemformula_charge_style:n { 4 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 5 } { \chemformula_charge_style:n { 5 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 6 } { \chemformula_charge_style:n { 6 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 7 } { \chemformula_charge_style:n { 7 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 8 } { \chemformula_charge_style:n { 8 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { 9 } { \chemformula_charge_style:n { 9 } }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { + } { \chemformula_plus: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { - } { \chemformula_minus: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { . } { \chemformula_radical_or_decimal: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { , } { \chemformula_decimal: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { ' } { \chemformula_kroegervink_negative: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { x } { \chemformula_kroegervink_neutral: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { * } { \chemformula_kroegervink_positive: }
+\prop_put:Nnn \l__chemformula_kroegervink_prop { . } { \chemformula_kroegervink_positive: }
+
+% --------------------------------------------------------------------------
+% bonds:
+\cs_new:Npn \chemformula@bondlength
+  { \l__chemformula_bond_dim }
+
+\cs_new:Npn \chemformula_single_bond:
+  {
+    \bool_if:NTF \l__chemformula_sup_bool
+      { \chemformula_minus: }
+      { \chemformula_bond:n { single } }
+  }
+
+\cs_new:Npn \chemformula_double_bond:
+  { \chemformula_bond:n { double } }
+
+\cs_new:Npn \chemformula_triple_bond:
+  { \chemformula_bond:n { triple } }
+
+\cs_new_protected:Npn \chemformula_bond:n #1
+  {
+    \chemformula_skip_nobreak:N \l__chemformula_bond_space_dim
+    \group_begin:
+    \chemformula_tikzexternaldisable:
+    \chemformula_tikz:nn
+      {
+        inner~sep   = 0pt ,
+        outer~sep   = 0pt ,
+        text~height = 1em ,
+        baseline    = (chemformula-bond-ground.base)
+      }
+      {
+        \draw node[draw=none,minimum~height=1em,minimum~width=0]
+          (chemformula-bond-ground) at (0pt,0pt) {};
+        \draw (chemformula-bond-ground) ++ (0pt,-.1716em)
+          coordinate (chemformula-bond-start) ;
+        \draw (chemformula-bond-start) ++(\l__chemformula_bond_dim ,0pt)
+          coordinate (chemformula-bond-end) ;
+        \tl_if_blank:nTF { #1 }
+          { \__chemformula_bond_draw:n { single } }
+          { \__chemformula_bond_draw:n { #1 } }
+      }
+    \group_end:
+    \chemformula_skip_nobreak_penalty:Nn
+      \l__chemformula_bond_space_dim
+      { \l__chemformula_bond_penalty_tl }
+  }
+
+\cs_new_protected:Npn \__chemformula_bond_draw:n #1
+  {
+    \__chemformula_reset:Nn \l__chemformula_tmpa_tl { #1 }
+    % \tl_set_rescan:Nnn \l__chemformula_tmpa_tl {} { #1 }
+    \prop_get:NV \l__chemformula_bonds_prop
+      \l__chemformula_tmpa_tl
+  }
+
+\NewDocumentCommand \NewChemBond { mm }
+  {
+    \cs_if_exist:cTF { chemformula_bond_type_#1: }
+      { \msg_error:nnn { chemformula } { new-bond } { #1 } }
+      {
+        \cs_new:cpn { chemformula_bond_type_#1: } {}
+        \prop_put:Nnn \l__chemformula_bonds_prop { #1 } { #2 }
+      }
+  }
+
+\NewDocumentCommand \DeclareChemBond { mm }
+  {
+    \cs_if_exist:cF { chemformula_bond_type_#1: }
+      { \cs_new:cpn { chemformula_bond_type_#1: } {} }
+    \prop_put:Nnn \l__chemformula_bonds_prop { #1 } { #2 }
+  }
+
+\NewDocumentCommand \NewChemBondAlias { mm }
+  {
+    \cs_if_exist:cTF { chemformula_bond_type_#2: }
+      {
+        \cs_if_exist:cTF { chemformula_bond_type_#1: }
+          { \msg_error:nnn { chemformula } { new-bond } { #1 } }
+          { \cs_new:cpn { chemformula_bond_type_#1: } {} }
+        \prop_get:NnN \l__chemformula_bonds_prop { #2 } \l__chemformula_tmpa_tl
+        \prop_put:Nno \l__chemformula_bonds_prop { #1 } { \l__chemformula_tmpa_tl }
+      }
+      { \msg_error:nnnn { chemformula } { bond-alias } { #1 } { #2 } }
+  }
+
+\NewDocumentCommand \DeclareChemBondAlias { mm }
+  {
+    \cs_if_exist:cTF { chemformula_bond_type_#2: }
+      {
+        \cs_if_exist:cF { chemformula_bond_type_#1: }
+          { \cs_new:cpn { chemformula_bond_type_#1: } {} }
+        \prop_get:NnN \l__chemformula_bonds_prop { #2 } \l__chemformula_tmpa_tl
+        \prop_put:Nno \l__chemformula_bonds_prop { #1 } { \l__chemformula_tmpa_tl }
+      }
+      { \msg_error:nnnn { chemformula } { bond-alias } { #1 } { #2 } }
+  }
+
+\NewDocumentCommand \RenewChemBond { mm }
+  {
+    \cs_if_exist:cTF { chemformula_bond_type_#1: }
+      { \prop_put:Nnn \l__chemformula_bonds_prop { #1 } { #2 } }
+      { \msg_error:nnn { chemformula } { renew-bond } { #1 } }
+  }
+
+\NewDocumentCommand \ShowChemBond { m }
+  {
+    \prop_get:NnN \l__chemformula_bonds_prop { #1 } \l__chemformula_tmpa_tl
+    \tl_to_str:N \l__chemformula_tmpa_tl
+  }
+
+\NewDocumentCommand \bond { m }
+  { \chemformula_bond:n { #1 } }
+
+% now let's declare some default bonds:
+\NewChemBond{single}
+  { \draw[chembond] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+\NewChemBondAlias{normal}{single}
+\NewChemBondAlias{sb}{single}
+
+\NewChemBond{semisingle}
+  { \draw[chembond,densely~dotted] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+\NewChemBondAlias{dotted}{semisingle}
+
+\NewChemBond{double}
+  {
+    \draw (chemformula-bond-start) ++ (0pt,.0858em) coordinate (double-start-up) ;
+    \draw (chemformula-bond-end) ++ (0pt,.0858em) coordinate (double-end-up) ;
+    \draw (chemformula-bond-start) ++ (0pt,-.0858em) coordinate (double-start-down) ;
+    \draw (chemformula-bond-end) ++ (0pt,-.0858em) coordinate (double-end-down) ;
+    \draw[chembond]
+      (double-start-down) -- (double-end-down)
+      (double-start-up) -- (double-end-up) ;
+  }
+\NewChemBondAlias{db}{double}
+
+\NewChemBond{semidouble}
+  {
+    \draw (chemformula-bond-start) ++ (0pt,.0858em) coordinate (double-start-up) ;
+    \draw (chemformula-bond-end) ++ (0pt,.0858em) coordinate (double-end-up) ;
+    \draw (chemformula-bond-start) ++ (0pt,-.0858em) coordinate (double-start-down) ;
+    \draw (chemformula-bond-end) ++ (0pt,-.0858em) coordinate (double-end-down) ;
+    \draw[chembond] (double-start-down) -- (double-end-down) ;
+    \draw[chembond,densely~dotted] (double-start-up) -- (double-end-up) ;
+  }
+
+\NewChemBondAlias{deloc}{semidouble}
+% \DeclareChemBondAlias{deloc2}{semidouble}
+
+\NewChemBond{triple}
+  {
+    \draw (chemformula-bond-start) ++ (0pt,.1287em) coordinate (triple-start-up) ;
+    \draw (chemformula-bond-end) ++ (0pt,.1287em) coordinate (triple-end-up) ;
+    \draw (chemformula-bond-start) ++ (0pt,-.1287em) coordinate (triple-start-down) ;
+    \draw (chemformula-bond-end) ++ (0pt,-.1287em) coordinate (triple-end-down) ;
+    \draw[chembond]
+      (triple-start-down) -- (triple-end-down)
+      (chemformula-bond-start) -- (chemformula-bond-end)
+      (triple-start-up) -- (triple-end-up) ;
+  }
+\NewChemBondAlias{tp}{triple}
+
+\NewChemBond{semitriple}
+  {
+    \draw (chemformula-bond-start) ++ (0pt,.1287em) coordinate (triple-start-up) ;
+    \draw (chemformula-bond-end) ++ (0pt,.1287em) coordinate (triple-end-up) ;
+    \draw (chemformula-bond-start) ++ (0pt,-.1287em) coordinate (triple-start-down) ;
+    \draw (chemformula-bond-end) ++ (0pt,-.1287em) coordinate (triple-end-down) ;
+    \draw[chembond]
+      (triple-start-down) -- (triple-end-down)
+      (chemformula-bond-start) -- (chemformula-bond-end) ;
+    \draw[chembond,densely~dotted] (triple-start-up) -- (triple-end-up) ;
+  }
+\NewChemBondAlias{tdeloc}{semitriple}
+
+\NewChemBond{coordright}
+  { \draw[chembond,Butt~Cap->] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+\NewChemBondAlias{co>}{coordright}
+
+\NewChemBond{coordleft}
+  { \draw[chembond,<-Butt~Cap] (chemformula-bond-start) -- (chemformula-bond-end) ; }
+\NewChemBondAlias{<co}{coordleft}
+
+% --------------------------------------------------------------------------
+% sub- and superscripts
+\cs_new:Npn \__chemformula_number_style:n #1
+  {
+    \bool_if:NTF \l__chemformula_number_style_math_bool
+      { \ensuremath { #1 } }
+      { \ensuremath { \text { #1 } } }
+  }
+\cs_generate_variant:Nn \__chemformula_number_style:n { V }
+
+\cs_new_protected:Npn \chemformula_charge_style:n #1
+  {
+    \bool_if:NTF \l__chemformula_charge_style_math_bool
+      { \ensuremath { #1 } }
+      { \ensuremath { \text { #1 } } }
+  }
+\cs_generate_variant:Nn \chemformula_charge_style:n { V }
+
+% subscripts
+% remove double or nested sub- and superscripts
+\cs_new_protected:Npn \chemformula_subscript:n #1
+  {
+    \chemformula_nobreak:
+    \tl_if_eq:nnTF { #1 }{ \chemformula_superscript:n }
+      { \__chemformula_subscript:n }
+      {
+        \tl_if_eq:nnTF { #1 }{ \chemformula_subscript:n }
+          { \__chemformula_subscript:n }
+          {
+            \tl_set:Nn \l__chemformula_tmpc_tl { #1 }
+            \tl_if_in:nnT { #1 } { \chemformula_subscript:n }
+              { \tl_remove_all:Nn \l__chemformula_tmpc_tl { \chemformula_subscript:n } }
+            \tl_if_in:nnT { #1 } { \chemformula_superscript:n }
+              { \tl_remove_all:Nn \l__chemformula_tmpc_tl { \chemformula_superscript:n } }
+            \__chemformula_subscript:V \l__chemformula_tmpc_tl
+          }
+      }
+  }
+
+% handle subscripts
+\cs_new_protected:Npn \__chemformula_subscript:n #1
+  {
+    \tl_put_right:Nn \l__chemformula_subscript_tl { #1 }
+    \__chemformula_clean_subscript:
+    % if a subscript follows just store and do nothing else
+    \peek_meaning:NF \chemformula_subscript:n
+      {
+        % if a superscript follows store and do nothing else
+        % if something else follows both sub- and superscript
+        \peek_meaning:NF \chemformula_superscript:n
+          {
+            \__chemformula_measure_subscript:V \l__chemformula_subscript_tl
+            \__chemformula_measure_superscript:V \l__chemformula_superscript_tl
+            \__chemformula_use_sub_and_superscript:
+          }
+      }
+  }
+\cs_generate_variant:Nn \__chemformula_subscript:n { V }
+
+\cs_new_protected:Npn \__chemformula_clean_subscript:
+  {
+    \tl_replace_all:Nnn \l__chemformula_subscript_tl
+      { \chemformula_single_bond: } { \chemformula_minus: }
+    \tl_replace_all:Nnn \l__chemformula_subscript_tl
+      { \chemformula_triple_bond: } {\chemformula_plus: }
+    \tl_replace_all:Nnn \l__chemformula_subscript_tl
+      { \chemformula_adduct: } { . }
+    \tl_replace_all:Nnn \l__chemformula_subscript_tl
+      { \chemformula_star_adduct: } { * }
+  }
+
+\cs_new_protected:Npn \__chemformula_subscript_raise:N #1
+  {
+    \hbox_set:Nn \l__chemformula_tmpa_box
+      { \c_math_toggle_token \scriptstyle Hg \c_math_toggle_token }
+    \hbox_set:Nn \l__chemformula_tmpb_box { Hg }
+    \dim_set:Nn #1
+      {
+        - \box_ht:N \l__chemformula_tmpa_box
+        + .4 \box_ht:N \l__chemformula_tmpb_box
+        + \l__chemformula_subscript_shift_additional_tl
+      }
+    \tex_raise:D #1
+  }
+
+\cs_new_protected:Npn \__chemformula_subscript_write:n #1
+  {
+    \group_begin:
+      \tl_set_eq:NN \chemformula_subscript:n \use:n
+      \tl_set_eq:NN \chemformula_superscript:n \use:n
+      \__chemformula_subscript_raise:N \l__chemformula_subscript_shift_dim
+      \hbox:n
+        {
+          \c_math_toggle_token
+            \scriptstyle
+            \prop_get:NoNTF \l__chemformula_numbers_prop
+              { #1 } \l__chemformula_tmpa_tl
+              { \__chemformula_number_style:V \l__chemformula_tmpa_tl }
+              { \__chemformula_number_style:n { #1 } }
+          \c_math_toggle_token
+        }
+    \group_end:
+  }
+\cs_generate_variant:Nn \__chemformula_subscript_write:n { V }
+
+\cs_new_protected:Npn \__chemformula_measure_subscript:n #1
+  {
+    \hbox_set:Nn \l__chemformula_tmpa_box
+      { \__chemformula_subscript_write:n { #1 } }
+    \dim_set:Nn \l__chemformula_subscript_dim
+      { -\box_wd:N \l__chemformula_tmpa_box }
+    \box_clear:N \l__chemformula_tmpa_box
+  }
+\cs_generate_variant:Nn \__chemformula_measure_subscript:n { V }
+
+% superscripts
+% remove double or nested sub- and superscripts
+\cs_new_protected:Npn \chemformula_superscript:n #1
+  {
+    \chemformula_nobreak:
+    \tl_if_eq:nnTF { #1 } { \chemformula_superscript:n }
+      { \__chemformula_superscript:n }
+      {
+        \tl_if_eq:nnTF { #1 } { \chemformula_subscript:n }
+          { \__chemformula_superscript:n }
+          {
+            \tl_set:Nn \l__chemformula_tmpc_tl { #1 }
+            \tl_if_in:nnT { #1 } { \chemformula_subscript:n }
+              { \tl_remove_all:Nn \l__chemformula_tmpc_tl { \chemformula_subscript:n } }
+            \tl_if_in:nnT { #1 } { \chemformula_superscript:n }
+              { \tl_remove_all:Nn \l__chemformula_tmpc_tl { \chemformula_superscript:n } }
+            \__chemformula_superscript:V \l__chemformula_tmpc_tl
+          }
+      }
+  }
+
+% handle superscripts
+\cs_new_protected:Npn \__chemformula_superscript:n #1
+  {
+    \tl_put_right:Nn \l__chemformula_superscript_tl { #1 }
+    \__chemformula_clean_superscript:
+    \peek_meaning:NF \chemformula_superscript:n
+      {
+        \peek_meaning:NF \chemformula_subscript:n
+          {
+            \__chemformula_measure_subscript:V \l__chemformula_subscript_tl
+            \__chemformula_measure_superscript:V \l__chemformula_superscript_tl
+            \__chemformula_use_sub_and_superscript:
+          }
+      }
+  }
+\cs_generate_variant:Nn \__chemformula_superscript:n { V }
+
+\cs_new_protected:Npn \__chemformula_clean_superscript:
+  {
+    \tl_replace_all:Nnn \l__chemformula_superscript_tl
+      { \chemformula_single_bond: } { \chemformula_minus: }
+    \tl_replace_all:Nnn \l__chemformula_superscript_tl
+      { - } { \chemformula_minus: }
+    \tl_replace_all:Nnn \l__chemformula_superscript_tl
+      { \chemformula_triple_bond: } { \chemformula_plus: }
+    \tl_replace_all:Nnn \l__chemformula_superscript_tl
+      { + } { \chemformula_plus: }
+    \tl_replace_all:Nnn \l__chemformula_superscript_tl
+      { \chemformula_adduct: } { \chemformula_radical_or_decimal: }
+    \bool_if:NTF \l__chemformula_kroegervink_bool
+      {
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { ' } { \chemformula_kroegervink_negative: }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { \chemformula_adduct: } { . }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { \chemformula_star_adduct: } { * }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { \chemformula_radical_or_decimal: } { . }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { \chemformula_prime: } { \chemformula_kroegervink_negative: }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { * } { \chemformula_kroegervink_positive: }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { . } { \chemformula_kroegervink_positive: }
+      }
+      {
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { \chemformula_star_adduct: } { * }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { . } { \chemformula_radical_or_decimal: }
+        \tl_replace_all:Nnn \l__chemformula_superscript_tl
+          { , } { \chemformula_decimal: }
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_superscript_raise:N #1
+  {
+    \hbox_set:Nn \l__chemformula_tmpa_box
+      { \c_math_toggle_token \scriptstyle Hg \c_math_toggle_token }
+    \hbox_set:Nn \l__chemformula_tmpb_box { Hg }
+    \dim_set:Nn #1
+      {
+        + \box_ht:N \l__chemformula_tmpb_box
+        - .5 \box_ht:N \l__chemformula_tmpa_box
+        + \l__chemformula_superscript_shift_additional_tl
+      }
+    \tex_raise:D #1
+  }
+
+\cs_new_protected:Npn \__chemformula_superscript_write:n #1
+  {
+    \group_begin:
+      \tl_set_eq:NN \chemformula_subscript:n \use:n
+      \tl_set_eq:NN \chemformula_superscript:n \use:n
+      \__chemformula_superscript_raise:N \l__chemformula_superscript_shift_dim
+      \hbox:n
+        {
+          \c_math_toggle_token
+            \scriptstyle
+            \bool_if:NTF \l__chemformula_kroegervink_bool
+              {
+                \prop_get:NoNTF \l__chemformula_kroegervink_prop
+                  { #1 } \l__chemformula_tmpa_tl
+                  { \tl_use:N \l__chemformula_tmpa_tl }
+                  { \chemformula_charge_style:n { #1 } }
+              }
+              {
+                \prop_get:NoNTF \l__chemformula_charge_prop
+                  { #1 } \l__chemformula_tmpa_tl
+                  { \tl_use:N \l__chemformula_tmpa_tl }
+                  { \chemformula_charge_style:n { #1 } }
+              }
+          \c_math_toggle_token
+        }
+    \group_end:
+  }
+\cs_generate_variant:Nn \__chemformula_superscript_write:n { V }
+
+\cs_new_protected:Npn \__chemformula_measure_superscript:n #1
+  {
+    \hbox_set:Nn \l__chemformula_tmpa_box
+      { \__chemformula_superscript_write:n { #1 } }
+    \dim_set:Nn \l__chemformula_superscript_dim
+      { -\box_wd:N \l__chemformula_tmpa_box }
+    \box_clear:N \l__chemformula_tmpa_box
+  }
+\cs_generate_variant:Nn \__chemformula_measure_superscript:n { V }
+
+% typeset both sub- and superscripts
+\cs_new_protected:Npn \__chemformula_use_sub_and_superscript:
+  {
+    \group_begin:
+    % No shift for excited state
+    \exp_args:No \tl_if_eq:nnT { \l__chemformula_superscript_tl } { * }
+      {
+        \bool_set_false:N \l__chemformula_charge_full_shift_bool
+        \dim_zero:N \l__chemformula_charge_shift_dim
+      }
+    % no shift for Kroeger Vink notation
+    \bool_if:NT \l__chemformula_kroegervink_bool
+      {
+        \bool_set_false:N \l__chemformula_charge_full_shift_bool
+        \dim_zero:N \l__chemformula_charge_shift_dim
+      }
+    % align to the right if isotope else to the left
+    \bool_if:NTF \l__chemformula_is_isotope_bool
+      {
+        \tl_if_blank:VF \l__chemformula_superscript_tl
+          {
+            \dim_compare:nT
+              { \l__chemformula_subscript_dim < \l__chemformula_superscript_dim }
+              {
+                \skip_horizontal:n { -\l__chemformula_subscript_dim }
+                \skip_horizontal:N \l__chemformula_superscript_dim
+              }
+          }
+      }
+      {
+        % add hshift to the superscript if there also is a subscript
+        \tl_if_blank:VF \l__chemformula_superscript_tl
+          {
+            \tl_if_blank:VF \l__chemformula_subscript_tl
+              {
+                \bool_if:NTF \l__chemformula_charge_full_shift_bool
+                  { \skip_horizontal:n { -\l__chemformula_subscript_dim } }
+                  { \skip_horizontal:N \l__chemformula_charge_shift_dim }
+              }
+          }
+      }
+    % typeset superscript
+    \tl_if_blank:VF \l__chemformula_superscript_tl
+      {
+       \__chemformula_superscript_write:V \l__chemformula_superscript_tl
+        % skip back for the subscript
+        \tl_if_blank:VF \l__chemformula_subscript_tl
+          {
+            \bool_if:NTF \l__chemformula_is_isotope_bool
+              { \skip_horizontal:N \l__chemformula_subscript_dim }
+              {
+                \skip_horizontal:N \l__chemformula_superscript_dim
+                    \bool_if:NTF \l__chemformula_charge_full_shift_bool
+                      { \skip_horizontal:N \l__chemformula_subscript_dim }
+                      {
+                        \skip_horizontal:n
+                          { -\l__chemformula_charge_shift_dim }
+                      }
+              }
+          }
+      }
+    % typeset subscript
+    \tl_if_blank:VF \l__chemformula_subscript_tl
+      { \__chemformula_subscript_write:V \l__chemformula_subscript_tl }
+    \bool_if:NF \l__chemformula_is_isotope_bool
+      {
+        \dim_zero:N \l__chemformula_tmpa_dim
+        \bool_if:NTF \l__chemformula_charge_full_shift_bool
+          {
+            \tl_if_blank:VF \l__chemformula_subscript_tl
+              { \dim_set:Nn \l__chemformula_tmpa_dim
+                { - \l__chemformula_superscript_dim } }
+          }
+          {
+            \tl_if_blank:VF \l__chemformula_superscript_tl
+              {
+                \tl_if_blank:VF \l__chemformula_subscript_tl
+                  {
+                    \dim_set:Nn \l__chemformula_tmpa_dim
+                      {
+                        \l__chemformula_charge_shift_dim
+                        - \l__chemformula_superscript_dim
+                        + \l__chemformula_subscript_dim
+                      }
+                  }
+              }
+          }
+        \dim_compare:nT { \l__chemformula_tmpa_dim > 0pt }
+          { \skip_horizontal:N \l__chemformula_tmpa_dim }
+      }
+    \group_end:
+    % clean up
+    \bool_set_false:N \l__chemformula_is_isotope_bool
+    \tl_clear:N \l__chemformula_subscript_tl
+    \tl_clear:N \l__chemformula_superscript_tl
+  }
+
+% --------------------------------------------------------------------------
+% read the input
+\cs_new_protected:Npn \chemformula_input:n #1
+  {
+    \__chemformula_save_catcodes:
+    \__chemformula_sanitize:Nn \l__chemformula_chemformula_tmpa_tl { #1 }
+    \chemformula_input_escape_text:V \l__chemformula_chemformula_tmpa_tl
+    \chemformula_input_escape_math:n { #1 }
+    \chemformula_input_stoich:n { #1 }
+    \__chemformula_clean_chemmacros:V \l__chemformula_chemformula_tmpa_tl
+    \chemformula_input_cmpd:VN
+      \l__chemformula_chemformula_tmpa_tl \l__chemformula_input_tl
+    \chemformula_input_arrow:n { #1 }
+    \chemformula_input_name:n { #1 }
+    \chemformula_input_plus:n { #1 }
+    \chemformula_input_up:n { #1 }
+    \chemformula_input_down:n { #1 }
+  }
+
+% --------------------------------------------------------------------------
+% set options for next compound:
+\cs_new_protected:Npn \chemformula_input_options:n #1
+  {
+    % \makeatother
+    \char_set_catcode_other:N \@
+    \tl_set_rescan:Nnn \l__chemformula_tmpa_tl
+      { \char_set_catcode_letter:N \@ }
+      { #1 }
+    \tl_if_in:VnTF \l__chemformula_tmpa_tl { @ }
+      {
+        \bool_set_true:N \l__chemformula_options_bool
+        \bool_set_true:N \l__chemformula_is_option_bool
+        \tl_remove_all:Nn \l__chemformula_tmpa_tl { @ }
+        \exp_last_unbraced:Nno
+        \tl_set:Nn \l__chemformula_internal_options_tl
+          { \l__chemformula_tmpa_tl }
+      }
+      { \bool_set_false:N \l__chemformula_is_option_bool }
+  }
+
+% --------------------------------------------------------------------------
+% input stoichiometric factors
+\cs_new:Npn \chemformula_decimal: { { \l__chemformula_decimal_output_tl } }
+
+\cs_new_protected:Npn \chemformula_input_stoich:n #1
+  {
+    \bool_set_true:N \l__chemformula_stoich_bool
+    % the factor consists only of a parenthesis or a decimal marcer:
+    \bool_set_true:N  \l__chemformula_no_stoich_bool
+    \tl_map_inline:nn { #1 }
+      {
+        \prop_get:NnNF \l__chemformula_no_stoich_prop { ##1 } \l__chemformula_tmpa_tl
+          { \bool_set_false:N \l__chemformula_no_stoich_bool }
+      }
+    \bool_if:NF \l__chemformula_no_stoich_bool
+      {
+        \tl_map_inline:nn { #1 }
+          {
+            \prop_get:NnNTF \l__chemformula_stoich_prop { ##1 } \l__chemformula_tmpa_tl
+              {
+                \bool_if:NT \l__chemformula_stoich_bool
+                  { \tl_put_right:NV \l__chemformula_stoich_tl \l__chemformula_tmpa_tl }
+              }
+              { \bool_set_false:N \l__chemformula_stoich_bool }
+          }
+      }
+    \bool_if:NTF \l__chemformula_stoich_bool
+      {
+        \tl_if_blank:VF \l__chemformula_stoich_tl
+          {
+            \tl_put_left:Nn \l__chemformula_stoich_tl { \q_mark }
+            \__chemformula_sanitize:NV
+              \l__chemformula_stoich_tl
+              \l__chemformula_stoich_tl
+            \__chemformula_print_stoich:V
+              \l__chemformula_stoich_tl
+          }
+      }
+      { \tl_clear:N \l__chemformula_stoich_tl }
+  }
+
+\cs_new:Npn \chemformula_bm:n #1 { #1 }
+
+\cs_new:Npn \__chemformula_print_stoich:n #1
+  { \chemformula_parse_stoich:n { #1 } }
+\cs_generate_variant:Nn \__chemformula_print_stoich:n { V }
+
+\cs_new_protected:Npn \chemformula_parse_stoich:n #1
+  { \__chemformula_parse_stoich:w #1 \q_nil }
+
+\NewDocumentCommand \chstoich { m }
+  { \chemformula_parse_stoich:n { #1 } }
+
+\cs_new:Npn \__chemformula_parse_stoich:w \q_mark #1 \q_nil
+  {
+    \__chemformula_bool_set_if_first_last:Nnnn
+      \l__chemformula_stoich_is_iupac_bool { #1 } { ( } { ) }
+    \bool_if:NTF \l__chemformula_stoich_is_iupac_bool
+      { \__chemformula_parse_stoich_iupac:n { #1 } }
+      { \__chemformula_parse_stoich_regular:n { #1 } }
+  }
+
+\DeclareInstance { xfrac } { chemformula-text-frac } { text }
+  {
+    slash-left-kern     = -.15em ,
+    numerator-top-sep   = 0pt ,
+    slash-right-kern    = -.15em
+  }
+
+\cs_new:Npn \__chemformula_parse_stoich_regular:n #1
+  {
+    \tl_if_in:nnTF { #1 } { / }
+      { \__chemformula_parse_stoich_frac:n { #1 } }
+      { \__chemformula_parse_stoich_decimal:n { #1 } }
+  }
+
+\cs_new_protected:Npn \__chemformula_parse_stoich_decimal:n #1
+  {
+    % get head:
+    \tl_set:Nx \l__chemformula_tmpa_tl { \tl_head:n { #1 } }
+    \tl_set:Nn \l__chemformula_tmpb_tl { \chemformula_decimal: }
+    % check if stoich starts with decimal-marker and add leading 0 if so:
+    \tl_if_eq:NNTF \l__chemformula_tmpa_tl \l__chemformula_tmpb_tl
+      { \tl_put_right:Nn \l__chemformula_input_tl { 0#1 } }
+      { \tl_put_right:Nn \l__chemformula_input_tl { #1 } }
+  }
+
+\cs_new:Npn \__chemformula_parse_stoich_frac:n #1
+  {
+    \tl_if_in:nnTF { #1 } { _ }
+      { \__chemformula_parse_stoich_misc_frac:w #1 \q_nil }
+      { \__chemformula_parse_stoich_frac:w #1 \q_nil }
+  }
+
+\cs_new_protected:Npn \__chemformula_parse_stoich_frac:w #1/#2 \q_nil
+  {
+    \tl_put_right:Nn \l__chemformula_input_tl
+      { \__chemformula_frac:nn { #1 } { #2 } }
+  }
+
+\cs_new_protected:Npn \__chemformula_parse_stoich_misc_frac:w #1_#2/#3 \q_nil
+  {
+    \tl_put_right:Nn \l__chemformula_input_tl
+      { \__chemformula_misc_frac:nnn { #1 } { #2 } { #3 } }
+  }
+
+\cs_new_protected:Npn \__chemformula_parse_stoich_iupac:n #1
+  {
+    \bool_if:NTF \l__chemformula_stoich_parse_iupac_bool
+      { \__chemformula_parse_stoich_iupac:w #1 \q_nil }
+      { \tl_put_right:Nn \l__chemformula_input_tl { #1 } }
+  }
+
+\cs_new:Npn \__chemformula_parse_stoich_iupac:w (#1) \q_nil
+  {
+    \tl_put_right:Nn \l__chemformula_input_tl { ( }
+    \__chemformula_parse_stoich_regular:n { #1 }
+    \tl_put_right:Nn \l__chemformula_input_tl { ) }
+  }
+
+\cs_new_eq:NN \chemformula_math_frac:nn \frac
+
+\cs_new:Npn \__chemformula_frac:nn #1#2
+  {
+    \bool_if:NT \l__chemformula_xfrac_bool
+      { \sfrac[chemformula-text-frac]{#1}{#2} }
+    \bool_if:NT \l__chemformula_nicefrac_bool
+      { \nicefrac{#1}{#2} }
+    \bool_if:NT \l__chemformula_mathfrac_bool
+      {
+        \c_math_toggle_token
+          \chemformula_math_frac:nn { \text { #1 } } { \text { #2 } }
+        \c_math_toggle_token
+      }
+  }
+
+\cs_new:Npn \__chemformula_misc_frac:nnn #1#2#3
+  {
+    \bool_if:NT \l__chemformula_xfrac_bool
+      { #1\sfrac[chemformula-text-frac]{#2}{#3} }
+    \bool_if:NT \l__chemformula_nicefrac_bool
+      { #1\nicefrac{#2}{#3} }
+    \bool_if:NT \l__chemformula_mathfrac_bool
+      {
+        #1
+        \c_math_toggle_token
+          \chemformula_math_frac:nn { \text { #2 } } { \text { #3 } }
+        \c_math_toggle_token
+      }
+  }
+
+% --------------------------------------------------------------------------
+% input compounds
+\cs_new_protected:Npn \chemformula_input_cmpd:nN #1#2
+  {
+    \tl_if_blank:VTF \l__chemformula_stoich_tl
+      {
+        \tl_if_eq:nnT { #1 } { + }
+          { \bool_set_true:N \l__chemformula_is_plus_bool }
+        \tl_if_eq:nnT { #1 } { - }
+          { \bool_set_true:N \l__chemformula_is_plus_bool }
+        \tl_if_eq:nnT { #1 } { v }
+          { \bool_set_true:N \l__chemformula_is_down_bool }
+        \tl_if_eq:nnT { #1 } { ^ }
+          { \bool_set_true:N \l__chemformula_is_up_bool }
+        \__chemformula_detect_arrows:n { #1 }
+        \__chemformula_detect_name:n { #1 }
+        \chemformula_input_options:n { #1 }
+        \bool_if:NT \l__chemformula_is_option_bool
+          {
+            \tl_put_right:Nn #2
+              {
+                \group_begin:
+                  \keys_set:nV
+                    { chemmacros / chemformula }
+                    \l__chemformula_internal_options_tl
+              }
+          }
+        \bool_if:nT
+          {
+            !\l__chemformula_is_option_bool &&
+            !\l__chemformula_is_plus_bool &&
+            !\l__chemformula_is_down_bool &&
+            !\l__chemformula_is_up_bool &&
+            !\l__chemformula_is_arrow_bool &&
+            !\l__chemformula_is_name_bool &&
+            !\l__chemformula_first_last_text_bool &&
+            !\l__chemformula_first_last_math_bool
+          }
+          {
+            \__chemformula_handle_sub_and_superscripts:nN { #1 } #2
+            \bool_if:NT \l__chemformula_options_bool
+              {
+                \tl_put_right:Nn #2
+                  {
+                    \group_end:
+                    \tl_clear:N \l__chemformula_internal_options_tl
+                  }
+                \bool_set_false:N \l__chemformula_options_bool
+              }
+          }
+      }
+      {
+        \tl_put_right:Nn #2
+          { \chemformula_skip_nobreak:N \l__chemformula_stoich_space_skip }
+        \tl_clear:N \l__chemformula_stoich_tl
+      }
+  }
+\cs_generate_variant:Nn \chemformula_input_cmpd:nN { V }
+
+\cs_new_protected:Npn \chemformula_font_inner:
+  {
+    \bool_if:NT \l__chemformula_fss_bool
+      {
+        \bool_if:NT \l__chemformula_fss_family_bool
+          { \fontfamily { \l__chemformula_font_family_tl } }
+        \bool_if:NT \l__chemformula_fss_series_bool
+          { \fontseries { \l__chemformula_font_series_tl } }
+        \bool_if:NT \l__chemformula_fss_shape_bool
+          { \fontshape { \l__chemformula_font_shape_tl } }
+        \selectfont
+      }
+    \bool_if:NT \l__chemformula_fontspec_bool
+      { \chemformula_font: }
+    \tl_use:N \l__chemformula_format_tl
+    \exp_args:No \tl_if_eq:nnTF { \f@series } { bx }
+      { \cs_set_eq:NN \chemformula_bm:n \bm }
+      { \cs_set:Nn \chemformula_bm:n { ##1 } }
+  }
+
+\cs_new:Npn \chemformula_font: {}
+\cs_new:Npn \__chemformula_fontspec:n #1
+  {
+    \tl_if_in:nnTF { #1 } { [ }
+      { \__chemformula_fontspec_aux:w #1 \q_stop }
+      { \__chemformula_fontspec_aux:w [] #1 \q_stop }
+  }
+
+\cs_new:Npn \__chemformula_fontspec_aux:w [#1]#2 \q_stop
+  { \newfontfamily \chemformula_font: [ #1 ] { #2 } }
+
+\cs_new_protected:Npn \__chemformula_save_catcodes:
+  {
+    \cs_gset_protected:Npx \__chemformula_restore:
+      {
+        \char_set_catcode:nn {  95 } { \char_value_catcode:n {  95 } }% _
+        \char_set_catcode:nn {  58 } { \char_value_catcode:n {  58 } }% :
+        \char_set_catcode:nn {  94 } { \char_value_catcode:n {  94 } }% ^
+        \char_set_catcode:nn { 123 } { \char_value_catcode:n { 123 } }% {
+        \char_set_catcode:nn { 125 } { \char_value_catcode:n { 125 } }% }
+        \char_set_catcode:nn {  35 } { \char_value_catcode:n {  35 } }% #
+        \char_set_catcode:nn {  33 } { \char_value_catcode:n {  33 } }% !
+        \char_set_catcode:nn {  34 } { \char_value_catcode:n {  34 } }% "
+        \char_set_catcode:nn {  60 } { \char_value_catcode:n {  60 } }% <
+        \char_set_catcode:nn {  62 } { \char_value_catcode:n {  62 } }% >
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_sanitize:Nn #1#2
+  {
+    \tl_set_rescan:Nnn #1
+      {
+        % expl3 catcodes:
+        \char_set_catcode_letter:N \_
+        \char_set_catcode_letter:N \:
+        % I've forgotten why I put this here:
+        \char_set_catcode_math_superscript:N \^
+        % disable some of the specials (needed for sub- and superscripts):
+        \char_set_catcode_letter:N \{
+        \char_set_catcode_letter:N \}
+        % this one seems not necessary any more:
+        % \char_set_catcode_letter:N \\
+        \char_set_catcode_letter:N \#
+        % make the naming work with babel languages like French that make
+        % ! active:
+        \char_set_catcode_other:N  \!
+        % make the naming work with babel languages like Spanish that make
+        % < and > active:
+        \char_set_catcode_other:N \>
+        \char_set_catcode_other:N \<
+        % ensure " is other:
+        \char_set_catcode_other:N \"
+      }
+      { #2 }
+  }
+\cs_generate_variant:Nn \__chemformula_sanitize:Nn { NV }
+
+\cs_new_protected:Npn \__chemformula_prepare_output:N #1
+  {
+    \tl_set_rescan:NnV #1
+      {
+        \__chemformula_restore:
+        \ExplSyntaxOn
+        \makeatletter
+      }
+      #1
+  }
+
+\cs_new_protected:Npn \__chemformula_reset:Nn #1#2
+  { \tl_set_rescan:Nnn #1 { \__chemformula_restore: } { #2 } }
+\cs_generate_variant:Nn \__chemformula_reset:Nn { NV }
+
+\cs_new_protected:Npn \__chemformula_handle_sub_and_superscripts:nN #1#2
+  {
+    \__chemformula_sanitize:Nn \l__chemformula_tmpa_tl { #1 }
+    % let's see if the compound starts with a sub- or superscript:
+    \tl_if_in:xnT { \tl_head:V \l__chemformula_tmpa_tl } { ^ }
+      {
+        \tl_put_left:Nn \l__chemformula_tmpa_tl
+          { \bool_set_true:N \l__chemformula_is_isotope_bool }
+      }
+    \tl_if_in:xnT { \tl_head:V \l__chemformula_tmpa_tl } { _ }
+      {
+        \tl_put_left:Nn \l__chemformula_tmpa_tl
+          { \bool_set_true:N \l__chemformula_is_isotope_bool }
+      }
+    \exp_args:NNx \prop_if_in:NnT \l__chemformula_numbers_prop
+      { \tl_head:V \l__chemformula_tmpa_tl }
+      {
+        \tl_put_left:Nn \l__chemformula_tmpa_tl
+          { \bool_set_true:N \l__chemformula_is_isotope_bool }
+      }
+    \tl_if_in:VnT \l__chemformula_tmpa_tl { ^ }
+      {
+        \tl_replace_all:Nnn \l__chemformula_tmpa_tl { ^ }
+          { \chemformula_superscript:n }
+      }
+    \tl_if_in:VnT \l__chemformula_tmpa_tl { _ }
+      {
+        \tl_replace_all:Nnn \l__chemformula_tmpa_tl { _ }
+          { \chemformula_subscript:n }
+      }
+    \int_zero:N \l__chemformula_count_tokens_int
+    \tl_map_inline:Nn \l__chemformula_tmpa_tl
+      {
+        \int_incr:N \l__chemformula_count_tokens_int
+        \int_compare:nTF
+          { \l__chemformula_count_tokens_int = \tl_count:N \l__chemformula_tmpa_tl }
+          {
+            \tl_if_eq:nnTF { ##1 } { + }
+              {
+                \tl_put_right:Nn #2
+                  { \chemformula_superscript:n { \chemformula_plus: } }
+              }
+              {
+                \tl_if_eq:nnTF { ##1 } { - }
+                  {
+                    \tl_put_right:Nn #2
+                      { \chemformula_superscript:n { \chemformula_minus: } }
+                  }
+                  {
+                    \prop_get:NnNTF \l__chemformula_cmpd_prop { ##1 } \l__chemformula_tmpb_tl
+                      { \tl_put_right:NV #2 \l__chemformula_tmpb_tl }
+                      { \tl_put_right:Nn #2 { ##1 } }
+                  }
+              }
+          }
+          {
+            \prop_get:NnNTF \l__chemformula_cmpd_prop { ##1 } \l__chemformula_tmpb_tl
+              { \tl_put_right:NV #2 \l__chemformula_tmpb_tl }
+              { \tl_put_right:Nn #2 { ##1 } }
+          }
+      }
+    \bool_if:NT \l__chemformula_kroegervink_bool
+      {
+        \tl_replace_all:Nnn #2
+          { \chemformula_prime: }
+          { \chemformula_superscript:n { \chemformula_prime: } }
+      }
+  }
+
+% --------------------------------------------------------------------------
+% clean up chemmacros commands:
+\cs_new_protected:Npn \__chemformula_clean_chemmacros:n #1
+  {
+    \cs_set:Nn \chemmacros_text:n
+      { \mode_if_math:TF { \text { ##1 } } { ##1 } }
+    \cs_set:Npn \chemmacros_xspace: {}
+  }
+\cs_generate_variant:Nn \__chemformula_clean_chemmacros:n { V }
+
+% --------------------------------------------------------------------------
+% input "and" sign
+\cs_new_protected:Npn \chemformula_input_plus:n #1
+  {
+    \tl_if_eq:nnT { #1 } { + }
+      {
+        \tl_put_right:Nn \l__chemformula_input_tl
+          {
+            \chemformula_skip_nobreak:N \l__chemformula_plus_space_skip
+            +
+            \chemformula_skip_nobreak_penalty:Nn
+              \l__chemformula_plus_space_skip
+              { \l__chemformula_plus_penalty_tl }
+          }
+      }
+    \tl_if_eq:nnT { #1 } { - }
+      {
+        \tl_put_right:Nn \l__chemformula_input_tl
+          {
+            \chemformula_skip_nobreak:N \l__chemformula_plus_space_skip
+            \c_math_toggle_token - \c_math_toggle_token
+            \chemformula_skip_nobreak_penalty:Nn
+              \l__chemformula_plus_space_skip
+              { \l__chemformula_plus_penalty_tl }
+          }
+      }
+    \bool_set_false:N \l__chemformula_is_plus_bool
+  }
+
+% --------------------------------------------------------------------------
+% input escaping gas
+\cs_new_protected:Npn \chemformula_input_up:n #1
+  {
+    \group_begin:
+      % ensure ^ has catcode 7
+      % (else chemmacros wouldn't work with e.g. `breqn')
+      \__chemformula_sanitize:Nn \g__chemformula_input_up_tl { #1 }
+      \char_set_catcode_math_superscript:N \^
+      \__chemformula_input_up:V \g__chemformula_input_up_tl
+  }
+
+\cs_new_protected:Npn \__chemformula_input_up:n #1
+  {
+      \tl_gclear:N \g__chemformula_input_up_tl
+      \tl_if_eq:nnT { #1 } { ^ }
+        {
+          \tl_gset:Nn \g__chemformula_input_up_tl
+            { \c_math_toggle_token \uparrow \c_math_toggle_token }
+        }
+    \group_end:
+    \tl_put_right:NV \l__chemformula_input_tl \g__chemformula_input_up_tl
+    \bool_set_false:N \l__chemformula_is_up_bool
+  }
+\cs_generate_variant:Nn \__chemformula_input_up:n { V }
+
+% --------------------------------------------------------------------------
+% input precipitate
+\cs_new_protected:Npn \chemformula_input_down:n #1
+  {
+    \tl_if_eq:nnT { #1 } { v }
+      {
+        \tl_put_right:Nn \l__chemformula_input_tl
+          { \c_math_toggle_token \downarrow \c_math_toggle_token }
+      }
+    \bool_set_false:N \l__chemformula_is_down_bool
+  }
+
+% --------------------------------------------------------------------------
+% input arrow
+\cs_new_protected:Npn \chemformula_input_arrow:n #1
+  {
+    \bool_if:nT
+      {
+        \l__chemformula_is_arrow_bool &&
+        !\l__chemformula_first_last_text_bool &&
+        !\l__chemformula_first_last_math_bool
+      }
+      {
+        \__chemformula_generate_arrows:Nn \l__chemformula_arrow_tmp_tl { #1 }
+        \tl_put_right:NV \l__chemformula_input_tl \l__chemformula_arrow_tmp_tl
+      }
+    \bool_set_false:N \l__chemformula_is_arrow_bool
+  }
+\cs_generate_variant:Nn \chemformula_input_arrow:n { o,V }
+
+% --------------------------------------------------------------------------
+% input compound name
+\cs_new_protected:Npn \chemformula_input_name:n #1
+  {
+    \bool_if:nT
+      {
+        \l__chemformula_is_name_bool &&
+        !\l__chemformula_first_last_text_bool &&
+        !\l__chemformula_first_last_math_bool
+      }
+      {
+        \__chemformula_generate_name:Nn \l__chemformula_name_tmp_tl { #1 }
+        \tl_put_right:NV \l__chemformula_input_tl \l__chemformula_name_tmp_tl
+      }
+    \bool_set_false:N \l__chemformula_is_name_bool
+  }
+
+% --------------------------------------------------------------------------
+% input escaped text
+% #1: <bool> #2: <tl> #3: <first> #4: <last>
+\cs_new_protected:Npn \__chemformula_bool_set_if_first_last:Nnnn #1#2#3#4
+  {
+    \int_zero:N \l__chemformula_tmpa_int
+    \int_zero:N \l__chemformula_tmpb_int
+    \int_set:Nn \l__chemformula_tmpa_int { \tl_count:n { #2 } }
+    \tl_map_inline:nn { #2 }
+      {
+        \int_incr:N \l__chemformula_tmpb_int
+        \int_compare:nT { \l__chemformula_tmpb_int = 1 }
+          {
+            \tl_if_eq:nnT { ##1 } { #3 }
+              { \bool_set_true:N #1 }
+          }
+        \int_compare:nT { \l__chemformula_tmpb_int = \l__chemformula_tmpa_int }
+          {
+            \tl_if_eq:nnF { ##1 } { #4 }
+              { \bool_set_false:N #1 }
+          }
+      }
+  }
+
+\cs_new_protected:Npn \chemformula_input_escape_text:n #1
+  {
+    \__chemformula_first_last_text:n { #1 }
+    \bool_if:NT \l__chemformula_first_last_double_bool
+      {
+        \bool_set_true:N \l__chemformula_first_last_text_bool
+        \__chemformula_read_escape_double:w #1 \q_nil
+      }
+    \bool_if:NT \l__chemformula_first_last_single_bool
+      {
+        \bool_set_true:N \l__chemformula_first_last_text_bool
+        \__chemformula_read_escape_single:w #1 \q_nil
+      }
+  }
+\cs_generate_variant:Nn \chemformula_input_escape_text:n { V }
+
+\cs_new_protected:Npn \__chemformula_read_escape_text:n #1
+  {
+    \tl_set_rescan:Nnn \l__chemformula_tmpa_tl
+      {
+        \char_set_catcode_letter:N \_
+        \char_set_catcode_other:N \:
+        
+      }
+      { #1 }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { \_ } { chemformulaplaceholder }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { _ } { \sb }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { chemformulaplaceholder } { \_ }
+    % TODO: waum ist das auskommentiert
+    % \__chemformula_reset:NV \l__chemformula_tmpa_tl \l__chemformula_tmpa_tl
+    \tl_put_right:NV \l__chemformula_input_tl \l__chemformula_tmpa_tl
+  }
+
+\cs_new:Npn \__chemformula_read_escape_double:w "#1" \q_nil
+  { \__chemformula_read_escape_text:n { #1 } }
+
+\cs_new:Npn \__chemformula_read_escape_single:w '#1' \q_nil
+  { \__chemformula_read_escape_text:n { #1 } }
+
+\cs_new_protected:Npn \__chemformula_first_last_text:n #1
+  {
+    \bool_set_false:N \l__chemformula_first_last_double_bool
+    \bool_set_false:N \l__chemformula_first_last_single_bool
+    \bool_set_false:N \l__chemformula_first_last_text_bool
+    \__chemformula_bool_set_if_first_last:Nnnn
+      \l__chemformula_first_last_double_bool
+      { #1 }
+      { " } { " }
+    \bool_if:NF \l__chemformula_first_last_double_bool
+      {
+        \__chemformula_bool_set_if_first_last:Nnnn
+          \l__chemformula_first_last_single_bool
+          { #1 }
+          { ' } { ' }
+      }
+  }
+
+% --------------------------------------------------------------------------
+% input escaped math
+\cs_new_protected:Npn \chemformula_input_escape_math:n #1
+  {
+    \__chemformula_first_last_math:n { #1 }
+    \bool_if:NT \l__chemformula_first_last_dollar_bool
+      {
+        \bool_set_true:N \l__chemformula_first_last_math_bool
+        \__chemformula_read_escape_dollar:w #1 \q_nil
+      }
+    \bool_if:NT \l__chemformula_first_last_mathbraces_bool
+      {
+        \bool_set_true:N \l__chemformula_first_last_math_bool
+        \__chemformula_read_escape_mathbraces:w #1 \q_nil
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_read_escape_math:n #1
+  {
+    \tl_set_rescan:Nnn \l__chemformula_tmpa_tl
+      {
+        \char_set_catcode_letter:N \_
+        \char_set_catcode_letter:N \:
+      }
+      { \c_math_toggle_token #1 \c_math_toggle_token }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { \_ } { chemformulaplaceholder }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { _ } { \sb }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl
+      { chemformulaplaceholder } { \_ }
+    % \__chemformula_reset:NV \l__chemformula_tmpa_tl \l__chemformula_tmpa_tl
+    \tl_put_right:NV \l__chemformula_input_tl \l__chemformula_tmpa_tl
+    \tl_put_right:Nn \l__chemformula_input_tl
+      { \chemformula_skip_nobreak:N \l__chemformula_math_space_skip }
+  }
+
+\cs_new:Npn \__chemformula_read_escape_dollar:w $#1$ \q_nil
+  { \__chemformula_read_escape_math:n { #1 } }
+
+\cs_new:Npn \__chemformula_read_escape_mathbraces:w \(#1\) \q_nil
+  { \__chemformula_read_escape_math:n { #1 } }
+
+\cs_new_protected:Npn \__chemformula_first_last_math:n #1
+  {
+    \bool_set_false:N \l__chemformula_first_last_math_bool
+    \bool_set_false:N \l__chemformula_first_last_dollar_bool
+    \bool_set_false:N \l__chemformula_first_last_mathbraces_bool
+    \__chemformula_bool_set_if_first_last:Nnnn
+      \l__chemformula_first_last_dollar_bool
+      { #1 }
+      { $ } { $ }
+    \bool_if:NF \l__chemformula_first_last_dollar_bool
+      {
+        \__chemformula_bool_set_if_first_last:Nnnn
+          \l__chemformula_first_last_mathbraces_bool
+          { #1 }
+          { \( } { \) }
+      }
+  }
+
+% --------------------------------------------------------------------------
+% customization of output other than arrows
+\keys_define:nn { chemmacros / chemformula }
+  {
+    circled            .choice: ,
+    circled / none     .code:n =
+      { \bool_set_false:N \l__chemformula_formal_charges_bool } ,
+    circled / formal   .code:n =
+      { \bool_set_false:N \l__chemformula_formal_charges_bool } ,
+    circled / all      .code:n =
+      { \bool_set_true:N \l__chemformula_formal_charges_bool  } ,
+    circled            .default:n  = all ,
+    circletype         .choice: ,
+    circletype / math  .code:n  =
+      { \bool_set_false:N \l__chemformula_formal_chem_bool } ,
+    circletype / chem  .code:n  =
+      { \bool_set_true:N \l__chemformula_formal_chem_bool } ,
+    circletype         .default:n = chem ,
+    charge-hshift         .code:n    =
+      \tl_if_eq:nnTF { #1 } { full }
+        { \bool_set_true:N \l__chemformula_charge_full_shift_bool }
+        {
+          \bool_set_false:N \l__chemformula_charge_full_shift_bool
+          \dim_set:Nn \l__chemformula_charge_shift_dim { #1 }
+        } ,
+    charge-hshift         .default:n = .25em ,
+    charge-vshift         .tl_set:N =
+      \l__chemformula_superscript_shift_additional_tl ,
+    charge-style          .choice: ,
+    charge-style / text   .code:n    =
+      \bool_set_false:N \l__chemformula_charge_style_math_bool ,
+    charge-style / math   .code:n    =
+      \bool_set_true:N \l__chemformula_charge_style_math_bool ,
+    subscript-vshift      .tl_set:N =
+      \l__chemformula_subscript_shift_additional_tl ,
+    subscript-vshift      .default:n = 0pt ,
+    subscript-style       .choice: ,
+    subscript-style / text .code:n   =
+      \bool_set_false:N \l__chemformula_number_style_math_bool ,
+    subscript-style / math .code:n   =
+      \bool_set_true:N \l__chemformula_number_style_math_bool ,
+    decimal-marker        .tl_set:N  = \l__chemformula_decimal_output_tl ,
+    frac-style            .choice: ,
+    frac-style / math     .code:n    =
+      \bool_set_false:N \l__chemformula_xfrac_bool
+      \bool_set_false:N \l__chemformula_nicefrac_bool
+      \bool_set_true:N \l__chemformula_mathfrac_bool ,
+    frac-style / xfrac    .code:n    =
+      \bool_set_true:N \l__chemformula_xfrac_bool
+      \bool_set_false:N \l__chemformula_nicefrac_bool
+      \bool_set_false:N \l__chemformula_mathfrac_bool ,
+    frac-style / nicefrac .code:n    =
+      \bool_set_false:N \l__chemformula_xfrac_bool
+      \bool_set_true:N \l__chemformula_nicefrac_bool
+      \bool_set_false:N \l__chemformula_mathfrac_bool ,
+    frac-math-cmd         .code:n     =
+      { \cs_set_eq:NN \chemformula_math_frac:nn #1 } ,
+    stoich-paren-parse    .bool_set:N = \l__chemformula_stoich_parse_iupac_bool ,
+    stoich-space          .skip_set:N = \l__chemformula_stoich_space_skip ,
+    stoich-print          .code:n     =
+      \cs_set_eq:NN \chemformula_print_stoich:n #1 ,
+    adduct-space          .dim_set:N  = \l__chemformula_adduct_space_dim ,
+    plus-space            .skip_set:N = \l__chemformula_plus_space_skip ,
+    plus-penalty          .tl_set:N   = \l__chemformula_plus_penalty_tl ,
+    math-space            .skip_set:N = \l__chemformula_math_space_skip ,
+    name-format           .tl_set:N   = \l__chemformula_name_format_tl ,
+    name-width            .code:n     =
+      {
+        \tl_if_eq:nnTF { #1 } { auto }
+          { \bool_set_false:N \l__chemformula_name_width_bool }
+          {
+            \bool_set_true:N \l__chemformula_name_width_bool
+            \dim_set:Nn \l__chemformula_name_dim { #1 }
+          }
+      } ,
+    bond-length           .dim_set:N = \l__chemformula_bond_dim ,
+    bond-offset           .dim_set:N = \l__chemformula_bond_space_dim ,
+    bond-style            .code:n    =
+      \tikzset { chembond/.style={Butt~Cap-Butt~Cap,#1} } ,
+    bond-penalty          .tl_set:N  = \l__chemformula_bond_penalty_tl ,
+    font-family           .code:n    =
+      \bool_set_true:N \l__chemformula_fss_bool
+      \bool_set_false:N \l__chemformula_fontspec_bool
+      \bool_set_true:N \l__chemformula_fss_family_bool
+      \tl_set:Nn \l__chemformula_font_family_tl { #1 } ,
+    font-series           .code:n    =
+      \bool_set_true:N \l__chemformula_fss_bool
+      \bool_set_false:N \l__chemformula_fontspec_bool
+      \bool_set_true:N \l__chemformula_fss_series_bool
+      \tl_set:Nn \l__chemformula_font_series_tl { #1 } ,
+    font-shape            .code:n    =
+      \bool_set_true:N \l__chemformula_fss_bool
+      \bool_set_false:N \l__chemformula_fontspec_bool
+      \bool_set_true:N \l__chemformula_fss_shape_bool
+      \tl_set:Nn \l__chemformula_font_shape_tl { #1 } ,
+    font-spec             .code:n    =
+      \bool_set_false:N \l__chemformula_fss_bool
+      \bool_set_true:N \l__chemformula_fontspec_bool
+      \__chemformula_fontspec:n { #1 } ,
+    format                .code:n    =
+      \bool_set_false:N \l__chemformula_fss_bool
+      \bool_set_false:N \l__chemformula_fontspec_bool
+      \tl_set:Nn \l__chemformula_format_tl { #1 }
+  }
+
+% --------------------------------------------------------------------------
+% \chlewis[opions]{el spec}{atom}
+
+\keys_define:nn { chemmacros / chemformula }
+  {
+    lewis-default     .tl_set:N  = \l__chemformula_elspec_default_type_tl ,
+    lewis-distance    .dim_set:N = \l__chemformula_elspec_pair_distance_dim ,
+    lewis-line-length .dim_set:N = \l__chemformula_elspec_pair_line_length_dim ,
+    lewis-line-width  .dim_set:N = \l__chemformula_elspec_pair_width_dim ,
+    lewis-offset      .tl_set:N  = \l__chemformula_elspec_radius_tl
+  }
+
+% #1: options
+% #2- el spec
+% #3: atom
+\cs_new_protected:Npn \chemformula_lewis:nnn #1#2#3
+  {
+    \group_begin:
+      \keys_set:nn { chemmacros / chemformula } { #1 }
+      \int_gincr:N \g__chemformula_lewis_int
+      \chemformula_get_lewis_sequence:n { #2 }
+      \chemformula_tikz:nn { baseline }
+        {
+          \chemformula_node:nxn { anchor=base , inner~sep=0pt }
+            { chlewis-\int_use:N \g__chemformula_lewis_int }
+            {
+              \bool_if:NTF \l_chemformula_inside_ch_bool
+                { #3 }
+                { \chemformula_chcpd:nn {} { #3 } }
+            }
+          \seq_map_inline:Nn \l__chemformula_tmpa_seq
+            { \chemformula_lewis_get_angle_and_spec:n { ##1 } }
+        }
+    \group_end:
+  }
+
+\cs_new_protected:Npn \chemformula_get_lewis_sequence:n #1
+  {
+    \tl_set:Nn \l__chemformula_tmpa_tl { #1  }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl { : } { \scan_stop: : , }
+    \tl_replace_all:NVn \l__chemformula_tmpa_tl \c_chemformula_colon_tl
+      { \scan_stop: : , }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl { . } { \scan_stop: . , }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl { | } { \scan_stop: | , }
+    \tl_replace_all:Nnn \l__chemformula_tmpa_tl { o } { \scan_stop: o , }
+    \seq_set_split:NnV \l__chemformula_tmpa_seq { , } \l__chemformula_tmpa_tl
+  }
+\cs_generate_variant:Nn \tl_replace_all:Nnn { NV }
+
+\cs_new:Npn \chemformula_lewis_get_angle_and_spec:n #1
+  { \__chemformula_lewis_get_angle_and_spec:w #1 \scan_stop: \scan_stop: \q_stop }
+
+\cs_new_protected:Npn
+  \__chemformula_lewis_get_angle_and_spec:w #1 \scan_stop: #2 \scan_stop: #3 \q_stop
+  {
+    \tl_if_blank:nF { #1 }
+      {
+        \tl_set:Nn \l__chemformula_elspec_angle_tl { #1 }
+        \tl_if_blank:nTF { #2 }
+          {
+            \tl_set_eq:NN
+              \l__chemformula_elspec_type_tl
+              \l__chemformula_elspec_default_type_tl
+          }
+          { \tl_set:Nn \l__chemformula_elspec_type_tl { #2 } }
+        \__chemformula_lewis_set_elspec_type:V \l__chemformula_elspec_type_tl
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_lewis_set_elspec_type:n #1
+  {
+    \prop_get:NnNT \l__chemformula_lewis_elspec_types_prop { #1 }
+      \l__chemformula_tmpa_tl
+      { \tl_use:N \l__chemformula_tmpa_tl }
+  }
+\cs_generate_variant:Nn \__chemformula_lewis_set_elspec_type:n { V }
+
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { | }
+  { \__chemformula_lewis_elspec_pair_line: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { : }
+  { \__chemformula_lewis_elspec_pair_dots: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { . }
+  { \__chemformula_lewis_elspec_single: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { o }
+  { \__chemformula_lewis_elspec_empty: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { pair }
+  { \__chemformula_lewis_elspec_pair_dots: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { pair~(dotted) }
+  { \__chemformula_lewis_elspec_pair_dots: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { pair~(line) }
+  { \__chemformula_lewis_elspec_pair_line: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { single }
+  { \__chemformula_lewis_elspec_single: }
+\prop_put:Nnn \l__chemformula_lewis_elspec_types_prop { empty }
+  { \__chemformula_lewis_elspec_empty: }
+
+\cs_new_protected:Npn \__chemformula_lewis_elspec_pair_dots:
+  {
+    \chemformula_draw:nn
+      {
+        fill,
+        inner~sep=0pt,
+        outer~sep=0pt
+      }
+      {
+        (node~cs \c_chemformula_colon_tl
+          name  = chlewis-\int_use:N \g__chemformula_lewis_int ,
+          angle = \l__chemformula_elspec_angle_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_radius_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl +90
+          \c_chemformula_colon_tl
+          .5\l__chemformula_elspec_pair_distance_dim
+        )
+        circle (\l__chemformula_radical_radius_dim)
+        ++
+        (
+          \l__chemformula_elspec_angle_tl -90
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_pair_distance_dim
+        )
+        circle (\l__chemformula_radical_radius_dim)
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_lewis_elspec_pair_line:
+  {
+    \chemformula_draw:nn
+      { line~width = \l__chemformula_elspec_pair_width_dim }
+      {
+        (node~cs \c_chemformula_colon_tl
+          name  = chlewis-\int_use:N \g__chemformula_lewis_int ,
+          angle = \l__chemformula_elspec_angle_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_radius_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl +90
+          \c_chemformula_colon_tl
+          .5\l__chemformula_elspec_pair_line_length_dim
+        )
+        --
+        ++
+        (
+          \l__chemformula_elspec_angle_tl -90
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_pair_line_length_dim
+        )
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_lewis_elspec_single:
+  {
+    \chemformula_draw:nn
+      {
+        fill,
+        inner~sep=0pt,
+        outer~sep=0pt
+      }
+      {
+        (node~cs \c_chemformula_colon_tl
+          name  = chlewis-\int_use:N \g__chemformula_lewis_int ,
+          angle = \l__chemformula_elspec_angle_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_radius_tl
+        )
+        circle (\l__chemformula_radical_radius_dim)
+      }
+  }
+
+\cs_new_protected:Npn \__chemformula_lewis_elspec_empty:
+  {
+    \chemformula_draw:nn { }
+      {
+        (node~cs \c_chemformula_colon_tl
+          name  = chlewis-\int_use:N \g__chemformula_lewis_int ,
+          angle = \l__chemformula_elspec_angle_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_radius_tl
+        )
+        ++
+        (
+          \l__chemformula_elspec_angle_tl +90
+          \c_chemformula_colon_tl
+          .5\l__chemformula_elspec_pair_line_length_dim
+        )
+        coordinate (chlewis-tmp1)
+        ++
+        (
+          \l__chemformula_elspec_angle_tl -90
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_pair_line_length_dim
+        )
+        coordinate (chlewis-tmp2)
+        ++
+        (
+          \l__chemformula_elspec_angle_tl
+          \c_chemformula_colon_tl
+          .25\l__chemformula_elspec_pair_line_length_dim
+        )
+        coordinate (chlewis-tmp3)
+        ++
+        (
+          \l__chemformula_elspec_angle_tl +90
+          \c_chemformula_colon_tl
+          \l__chemformula_elspec_pair_line_length_dim
+        )
+        coordinate (chlewis-tmp4)
+        (chlewis-tmp1) -- (chlewis-tmp2) --
+        (chlewis-tmp3) -- (chlewis-tmp4) --
+        cycle
+      }
+  }
+
+\NewDocumentCommand\chlewis{O{}mm}
+  { \chemformula_lewis:nnn { #1 } { #2 } { #3 } }
+
+% --------------------------------------------------------------------------
+
+\NewDocumentCommand \setchemformula { m }
+  { \keys_set:nn { chemmacros / chemformula } { #1 } }
+
+\setchemformula{
+  bond-style  = {} ,
+  arrow-style = {}
+}
+
+% --------------------------------------------------------------------------
+% hyperref support
+\AfterPackage* { hyperref }
+  {
+    \pdfstringdefDisableCommands
+      {
+        \cs_set:Npn \chcpd #1 { #1 }
+        \cs_set:Npn \charrow #1 { #1 }
+        \cs_set:Npn \chname (#1)(#2) { #2~(#1) }
+        \cs_set:Npn \ch #1 { #1 }
+        \cs_set:Npn \chlewis #1#2 { #2 }
+      }
+  }
+
+\tex_endinput:D
+
+% --------------------------------------------------------------------------
+VERSION HISTORY
+2012/01/28 - version 3.0  - bundled with packages `chemmacros' and `ghs'
+2012/01/30 - version 3.0a - bugfix
+                          - renamed formula => chemformula
+                            (following a request by Karl Berry for TeXlive)
+2012/02/03 - version 3.0b - stepped number with `chemmacros'
+2012/02/05 - version 3.0c - stepped number with `chemmacros'
+2012/02/10 - version 3.0d - several bugfixes
+                          - new arrow type <>
+2012/02/19 - version 3.1  - new arrow types -/>, </- and <o>
+                          - new commands \DeclareChemArrow, \RenewChemArrow and
+                            \ShowChemArrow
+2012/02/26 - version 3.1a - stepped number with `chemmacros'
+2012/03/03 - version 3.1b - arrow types are stored in a sequence to automate the
+                            search and replace in the right order 
+                          - new arrow type ==                                   
+                          - IUPAC compliance for stoichiometric factors
+                          - new handling of super- and subscripts to correct
+                            various flaws: clear distinction between isotope and
+                            formula
+                          - new option charge-vshift
+2012/03/14 - version 3.1c - improved arrow labels
+2012/03/20 - version 3.2  - new: option input via @{<options>}
+2012/05/07 - version 3.3  - \ch now bypasses \ref{}, \label{}, and \intertext{}
+2012/05/13 - version 3.3a - stepped number with `chemmacros'
+2012/05/18 - version 3.3b - stepped number with `chemmacros'
+2012/05/18 - version 3.3c - stepped number with `chemmacros'
+2012/07/24 - version 3.3d - stepped number with `chemmacros'
+                          - default bond length set to 1.1667ex
+                          - bug fix in the bonds
+2012/08/21 - version 3.3e - stepped number with `chemmacros'
+2012/09/11 - version 3.4  - cleaned a little, minor bug fixes
+                          - switched to internal scratch variables
+                          - new command \bond, more bond types
+                          - new commands \DeclareChemBond, \DeclareChemBondAlias,
+                            \RenewChemBond and \ShowChemBond
+                          - radical point thicker, new options `radical-style'
+                            and `radical-radius'
+2012/10/03 - version 3.4a - stepped number with `chemmacros'
+2013/01/04 - version 3.4b - bug fix in the sub- and superscript handling
+2013/01/28 - version 3.5  - disallow breaks at bonds
+                          - allow breaks after arrows
+                          - made some spaces in chemformulas stretch- and
+                            shrinkable
+                          - various internal code improvements
+                          - changed defaults for horizontal spaces that have in
+                            set in ex into corresponding values in em.
+                          - improvements to the placement of sub- and superscripts
+2013/02/19 - version 3.5a - stepped number with `chemmacros'
+2013/02/26 - version 3.6  - support for use with the `breqn' package
+                          - math escaping also via \(\)
+                          - internal: clearer escaping macros
+                          - new options: `radical-vshift', `radical-hshift'
+                            and `radical-space'
+                          - bug fix: `radical-...' options are now correctly set
+                          - stoichiometric factors: add leading 0 if missing
+                          - new option: `stoich-paren-parse'
+                          - internal changes: be way more rigid about protected
+                            and expandable macros
+                          - internal changes: clearer distinction between
+                            private macros and accessable module macros
+                          - internal changes: clearer distinction between
+                            document commands and module level commands
+                          - !()() syntax now also works with babel's French
+2013/02/27 - version 3.6a - bug fix: escaped text and math stays escaped, i.e.
+                            also arrow code like `<=>'
+2013/04/19 - version 3.6b - new option `arrow-min-length'
+                          - bug fix: stoichiometric fractions correctly displayed
+2013/07/06 - version 4.0  - don't need `chemmacros' package any more,
+                            `chemformula' can be used stand-alone;
+                            this has lead to a few definitions that previously
+                            were done by chemmacros; chemmacros will get them
+                            now from chemformula when needed
+                          - bug fix: allow braces in subscripts and superscripts
+                            by disabling superfluous \chemformula_subscript:n
+                            and \chemformula_superscript:n in the scripts write
+                            commands
+                          - remove superfluous rescanning at the begin of the
+                            formula input; this is handled by the sanitize
+                            command later anyway
+                          - changed internal mathshifts from $ ... $ to \( ... \)
+                          - removed superfluous \textstyle from math-frac
+                            definition
+                          - new command \charrow{}[][] that allows direct
+                            access to chemformula's arrows
+                          - new command \chname()() that allows direct access
+                            to chemformula's naming
+                          - new command \chcpd[]{} that allows typesetting a
+                            simple single formula - also not nestable with \ch
+                          - new command \setchemformula
+                          - package option: `strict'
+                          - don't allow a line break before a plus
+                            (`chem-and')
+                          - don't allow a line break between a stoichiometric
+                            factor and a compound
+                          - changed formal charges to match ``plain'' charges
+2013/07/26 - version 4.0a - added options `arrow-penalty' (0), `plus-penalty'
+                            (700) and `bond-penalty' (10000) that determine if
+                            there may be a break after an arrow, a bond or the
+                            plus
+2013/08/24 - version 4.1  - changed `0' values in TikZ coordinates into `0pt'
+                            see http://tex.stackexchange.com/q/128792/5049 and
+                            http://tex.stackexchange.com/q/118467/5049 for
+                            reference
+                          - new option `tikz-external-disable'
+                          - new option `frac-math-cmd'
+2013/10/24 - version 4.2  - \chemformula_font_inner: is only applied /once/ to
+                            a formula, and at the beginning, fixes
+                            https://bitbucket.org/cgnieder/chemmacros/issue/23
+                          - fixed wrong setting of the TikZ bond style
+                          - new option `arrow-style'
+                          - new command \chlewis
+2013/11/04 - version 4.2a - bug fix in \chcpd,
+                          - change sanitizing/restoring of category codes
+2014/01/24 - version 4.3  - changed behaviour of \DeclareChem to match
+                            \DeclareRobustCommand, i.e., no check if command
+                            is defined; added a \NewChem variant to each that
+                            /does/ check; use \NewChem instead of \DeclareChem
+                            for definitions
+                          - new option stoich-print
+                          - new command \chstoich
+2014/01/29 - version 4.4  - treat a single `-' as a minus sign
+2014/04/07 - version 4.5  - make sure that < and > have catcode 12 when read
+                            as parts of arrows
+                          - new arrow types `>=<', `>=<<', `>>=<' and `<==>'
+                          - arrow lengths and compound offset now correctly
+                            adapts to new fontsize if relative lengths (em,ex)
+                            are used
+                          - allow optional arguments to \\ in equation
+                            environments
+                          - allow optional arguments to \label in equation
+                            environments
+                            (credits: http://tex.stackexchange.com/a/166661/5049)
+                          - support for Kröger-Vink notation
+2014/06/30 - version 4.6  - fix: a comma in a superscript is typeset according
+                            to `decimal-marker' again
+                          - fix charge type behaviour: option `circled' and
+                            `circletype' are now obeyed if the option is
+                            changed mid-document
+                          - new option `chemformula/circled' similar to
+                            `chemmacros/circled'
+                          - new option `chemformula/circletype' similar to
+                            `chemmacros/circletype'
+2014/08/04 - version 4.7  - change dependency: pgf library `arrows.meta'
+                            instead of `arrows'
+                          - new arrow tip definition allows redeclaration to
+                            other existing tips by \pgfkeys{cf/.tip=<tip>}
+2014/08/07 - version 4.8  - fix bug introduced in last update: `butt cap' now
+                            needs to be `Butt Cap' with the new `arrows.meta'
+                            library
+                          - split from `chemmacros' bundle as independent
+                            package
+
+% --------------------------------------------------------------------------
+% TODO
+- Addukte: Zahlen nach * und . automatisch erkennen?
+- make escaped text/math /truely/ escaped, i.e., behave as if it's been input
+  /outside/ of \ch