Tabularray and bracket in cell

Question

I try to use the tabularray package but I have a error with brackets :

\documentclass{article}
\usepackage{tabularray}
\begin{document}

\begin{tblr}{cells={mode=math}}
 1      &   2   \\
 [1;2]  & [3;4] \\
\end{tblr}

\end{document}

I find a solution without mode math, but it's not very satisfactory :

\documentclass{article}
\usepackage{tabularray}
\begin{document}

\begin{tblr}{}
 $1$        &   $2$    \\
 $[1;2]$    &  $[3;4]$ \\
\end{tblr}

\end{document}

The exercise I'm trying to do is here and it works without math mode :

\begin{tblr}{
hlines,vlines,
colspec={ccQ[c,7em]Q[c,7em]},
}
 $I$ & $J$  &  $I \cap J$ &  $I \cup J$ \\
     $[3;6]$ & $[4,2;7,1]$ &  &  \\
     $[-4;6]$ & $]2;+\infty[$ & & \\
     $]-\infty;1]$ & $]0;+\infty[$ & & \\
     $[-2;8]$ & $[1;3]$ & & \\
         $[-3;1]$ & $[2;4]$ & & 
\end{tblr}

Answer 1

It's a known problem with (almost) all alignment environments: since \\ accepts an optional argument for specifying a vertical separation and ignores spaces when looking for the possible [, your bracket is mistaken for the start of an optional argument.

Math mode or not, it's irrelevant. In your second case, the $ avoids the [ to be mistaken. But the error would happen also in text mode.

Add \relax before a bracket starting a table cell.

\documentclass{article}
\usepackage{tabularray}
\begin{document}

\begin{tblr}{cells={mode=math}}
 1      &   2   \\ \relax
 [1;2]  & [3;4] \\
\end{tblr}

\end{document}