# Math/equation keys in pgfkeys and tikz picture

I am using pgfkeys as variables of a newcommand for TikZ pictures. I can transfer numerical values and simple math correctly. However, some math expressions are not transferred to the command. A MWE is provided below.

Why an equality expression and the \unitfrac are not working?

\documentclass[]{standalone}
\usepackage{units}
\usepackage{siunitx}
\usepackage{tikz}

\pgfkeys{/mycom/.is family, /mycom,
default/.style={text = $?$},
text/.estore in = \mytext}

\newcommand{\mycom}[1][]{
\pgfkeys{/mycom, default, #1}
%some tikx command to display the math
\draw (0,0) node{\mytext};
}

\begin{document}

\begin{tikzpicture}

%\mycom[text = aa]                         % Does work
%\mycom[text = $5x$]                       % Does work
%\mycom[text = $5x+6$]                     % Does work
%\mycom[text = $5x=6$]                     % Does not work
%\mycom[text = $\unitfrac[10]{kN}{m}$]     % Does not work
%\mycom[text = $\si{\kilo\newton/\meter}$] % Does work

\end{tikzpicture}

\end{document}

• Unrelated: In general I'd use \per instead of / in \si, and say \sisetup{per-mode=symbol} to get a / in the output. – Torbjørn T. Jun 6 '17 at 7:41

The = needs to be protected to stop PGF trying to parse it. For the second case, you need not to expand it so soon. If you use .store rather than .estore, this all works just fine.

The counter is only for testing because the uncommented code typeset all nodes in the same place.

\documentclass[border=10pt]{standalone}
\usepackage{units}
\usepackage{siunitx}
\usepackage{tikz}
\pgfkeys{/mycom/.is family, /mycom,
default/.style={text = $?$},
text/.store in = \mytext}
\newcounter{foo}
\newcommand{\mycom}[1][]{%
\pgfkeys{/mycom, default, #1}%
%some tikx command to display the math
\draw (\thefoo,0) node {\mytext};%
\stepcounter{foo}%
}

\begin{document}
\begin{tikzpicture}
\mycom[text = aa]                         % Does work
\mycom[text = $5x$]                       % Does work
\mycom[text = $5x+6$]                     % Does work
\mycom[text = {$5x=6$}]                     % Does not work
\mycom[text = {$\unitfrac[10]{kN}{m}$}]     % Does not work
\mycom[text = $\si{\kilo\newton/\meter}$] % Does work
\end{tikzpicture}
\end{document}

• Have you changhe your icon?:-) +1 for your answer. – Sebastiano Jun 6 '17 at 7:04
• @cfr: I have been using .estore for a reason that I do not remember now. There are some discussion about the use of .estore here. Do you have any comments? – berkus Jun 6 '17 at 8:58
• @cfr: Regarding $a=b$. How come the $-signs are ignored? I thought the math enviroment provides the necessary protection. Thoughts? – berkus Jun 6 '17 at 9:00 • @cfr: Seems like we need to add the { } to the $\unitfrac[]{}{}\$ along with the .store. Why do we need the brackets here? – berkus Jun 6 '17 at 9:05
• @cfr: The MWE is actually a package I am working on. To make the code more suitable for end-user, is there any other option without the curly brackets? – berkus Jun 6 '17 at 9:36