\tag + _: Got group of unknown type: 'internal' ```

[nschloe]

In LaTeX, one can start an equation with _ or ^

\documentclass{article}
\begin{document}
\[
\label{2}
_{2}x_{2}
\]
\end{document}

The same works in KaTeX, but not with a \tag{} prepended:

\tag{2}
_{2}x_{2}

KaTeX parse error: Got group of unknown type: 'internal'

I suppose the "fix" is to prefix the underscore with a {}, but it'd be nice if KaTeX could handle these situations itself.

[pzinn]

in a similar vein, I was trying to get cf' right, $cf'$ looked ugly because c and f were too far apart, $\mathit{cf}'$ looked ugly because the ' was too close, finally $\mathit{cf}\,'$ looks perfect in LaTeX but KaTeX will throw KaTeX parse error: Got group of unknown type: 'internal'