I am using a command that contains more than one cell (containing an & to separate them).

It worked with tabular it does not work with tbrl though. Why?

\documentclass{article} \usepackage{tabularray} \newcommand{\ab}{a & b} \begin{document} \begin{tblr}{c|l} \ab \\ \end{tblr} \end{document} 

The error message is misplaced alignment tab character &