OurBigBook ships with several commonly used math macros enabled by default.
The full list of built-in macros can be seen at: default.tex.
Here's one example of using \dv from the physics package for derivatives:
\dv{x^2}{x} = 2x
which renders as:
Our goal is to collect the most popular macros from the most popular pre-existing LaTeX packages and make them available with this mechanism.
The built-in macros are currently only available on OurBigBook CLI and OurBigBook Web, not when using the JavaScript API directly. We should likely make that possible as well at some point.