How to programmatically draw using DGM.js

I can’t seem to figure out the right combinations of methods/properties/values to draw a simple rectangle into the Editor (I guess onto the canvas) of the DGM.js package.

Is anyone able to provide some example code that will show how to programmatically draw a rectangle (or any shape), that I can use as a starting point?

If it matters, I’d rather the rectangle not be user select-able once it’s drawn, unlike rectangles that a user will draw using their cursor