Demo for Katex.
```math:title=title,macros={"\\f":"#1f(#2)"\,"\\const":"1"},fontSize=16
% \f is defined as #1f(#2) using the macro
\f\relax{x} = \int_{-\infty}^\infty
    \f\hat\xi\,e^{2 \pi i \xi x}
    \,d\xi + \const
```

title