Source code of libraries in dev versions

How do I access the source code of libraries available only in dev versions (by this time of writing 10.9)? I need to take a look so I could use this as inspiration for potential JavaScript.

Like the 3D beetle library, microworld library, et cetera

I'm not talking about the blocks, I'm talking about the JavaScript code. I want to know how microworlds guide the user.

Find the extesion primitive that loads from a source, like libraries/microworlds/microworld.js. Append that text next to then open that in the browser. Then you could find the source code of it.

To access the source code of the dev libraries, you can go to the Snap! Github repository (jmoenig/Snap), switch to the dev branch, and navigate to the libraries folder. The JavaScript files in that folder are what you're looking for.

@ten_6044's suggestion also works.