Graphics, Figures & Tables ⇒ overlapped symbols in figure caption

[CoolnessItself]

Using stackrel and stackinset in a figure caption results in the error

! Argument of \@caption has an extra }.
<inserted text>
\par
l.19 ... these two symbols to overlap $\overlap$.}

Am I missing something?

mwe:

Code: Select all

\documentclass{article}

\usepackage{stackengine,scalerel}

\def\useanchorwidth{F}
\def\stackalignment{r}%
\newcommand\overlap{\scalerel*{\hspace{.5mm}\stackinset{c}{-1.5pt}{c}{}{$O$}{$L$}}{+}}

\begin{document}

%works if this is the only \overlap in the document
This is some text with the $\overlap$ symbols.

\begin{figure}[t]
\begin{center}
figure
\end{center}
\caption{I want these two symbols to overlap $\overlap$.} %doesn't work
\end{figure}


\end{document}

[sommerfee]

The command \overlap you have defined is fragile and therefore will not be handled correctly in moving arguments like entries for List of Contents or List of Figure. So either make \overlap robust:

Code: Select all

\DeclareRobustCommand\overlap{\scalerel*{...}{+}}

or use \protect for usage of \overlap within moving arguments:

Code: Select all

\section{...\protect\overlap...}

Code: Select all

\caption{...\protect\overlap...}

[CoolnessItself]

Thanks! I'm not familiar with fragile commands. How can I tell if I'm constructing something fragile? Is it the command I'm declaring or its substitute, i.e., is \newcommand\overlap{} the issue or what's inside the fragile part?