Placeholder number with siunitx

Question

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?

Answer 1

You can pretend that ? is a valid input 'symbol' such as \pi.

\documentclass{article} 
\usepackage{siunitx}
\sisetup{
  input-symbols={?},
}

\begin{document}
    I don't know yet what number to place here: \SI{???}{\percent}.
\end{document}

The same works for XYZ

\documentclass{article}
\usepackage{siunitx}
\sisetup{
  input-symbols={XYZ},
}

\begin{document}
    I don't know yet what number to place here: \SI{XYZ}{\percent}.
\end{document}

---

Alternatively, you could stop siunitx from parsing numbers. Either globally with \sisetup{parse-numbers=false} or locally with \SI[parse-numbers=false]{???}{\percent}.