以下 MWE：
\documentclass{article}
\usepackage{siunitx}
\listfiles
\begin{document}
% \SI{a}{\cm} % Invalid token 'a' in numerical input
\SI[parse-numbers = false]{a}{\cm}
\end{document}
a在数学模式下 不会产生。
（一切都从这里开始：正确使用 `siunitx` 方式排版复杂表达式）
有人可以建议siunitx排版这种表达的正确方法是什么吗？
Overleaf 上编译：
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答案1
对于 v2，您将需要强制重置数学模式字体：v3 不需要这样做，因为它有更好的打印方法。
\documentclass{article}
\usepackage{siunitx}[=v2]
\listfiles
\begin{document}
\SI[parse-numbers = false]{\text{\ensuremath{a}}}{\cm}
\end{document}
这也将在 v3 中起作用，但它有点过度：你不需要构造\text{\ensuremath{...}}。