I would like to add a placeholder number in my text, to remind me that I still have to look it up, later. I usually just use something like "XYZ" or "???" for this. But when I'm using the \SI notation I get an error that "?" is not a number.
\documentclass{article}
\usepackage{siunitx}
\begin{document}
I don't know yet what number to place here: \SI{???}{\percent}.
\end{document}
The error I get is:
siunitx error: "invalid-token-in-number" Invalid token '?' in numerical input. For immediate help type H <return>. ...at number to place here: \SI{???}{\percent}
What is the best/suggested way to add a placeholder number or symbol in SI-notation?