more complex use of tags in xsim

I would like to use the tag level (1,2,3) in xsim, but not only in exclusive manner, but as multiple tags, so that an exercise can have the tag level 1 and 2. So that, collecting later all level 2 exercises of my .tex or the level 1 exercises, I will have the same question in both chapters. (I want to ask some of the basic questions in a later chapter again for revision.)

Is the only possibility, that I create a tag 1 and a tag 2 and a tag 3? Or is there a possibility to write something like

\begin{exercise}[level=1,level=2]


If I do that now 1 is just overwritten by 2, so it will only be printed in chapter 2.

MWE:

\documentclass{article}
\usepackage{xsim}

\DeclareExerciseCollection{foo-easy}
\DeclareExerciseCollection{foo-medium}
\DeclareExerciseTagging{level}

\usepackage{filecontents,lipsum}
\begin{filecontents*}{foo.tex}
\begin{exercise}[level=1]
foo one \lipsum[4]
\end{exercise}
\begin{solution}
foo one \lipsum[4]
\end{solution}
\begin{exercise}[level=2]
foo two \lipsum[4]
\end{exercise}
\begin{solution}
foo two \lipsum[4]
\end{solution}
\begin{exercise}[level=1]
foo three \lipsum[4]
\end{exercise}
\begin{solution}
foo three \lipsum[4]
\end{solution}
\end{filecontents*}

\begin{document}

\collectexercises{foo-easy}
\xsimsetup{level=1}
\input{foo.tex}
\collectexercisesstop{foo-easy}
% collection foo-easy' now contains all exercises of file foo.tex' tagged
% with level=1' but only if I don't add a 'level=2' as suggested above

\collectexercises{foo-medium}
\xsimsetup{level=2}
\input{foo.tex}
\collectexercisesstop{foo-medium}
% collection foo-medium' now contains all exercises of file foo.tex'
% tagged with level=2' and only those, but I would like to add certain level 1 exercises as well

\section{Easy}
\printcollection{foo-easy}

\section{Medium}
\printcollection{foo-medium}

\end{document}


\begin{exercise}[level={1,2}]