The game engine is structured into two distinct parts. The core engine handles and defines the Entity Component System design, the Messages pattern, and shared resources such as geometry. The standard library provides useful common components and systems, such as rendering to a WebGL2 canvas, an interpolation system, a simple physics movement system, and more.
You can see this structure in the headers for the library, it is structured like this:
As you can see anything that is in the
standard/ directory/path is in the standard library.