From KaTeX documentation:

> throwOnError: boolean.  If true, KaTeX will throw a ParseError when
> it encounters an unsupported command.  If false, KaTeX will render
> the unsupported command as text in the color given by errorColor.
> (default: true)

It's better to render the formula and highlight unsupported commands than
just give up and render whole formula as a code; users are confused and
don't know what's wrong.