Transparent background in Processing.js

This took me a while to figure out because the documentation on the processing.js is way behind. I wanted to overlay a processing.js element on top of a video canvas, which I already did a while ago, but updating to the newest version of processing.js made the canvas background grey. I searched through the source code and found out that to enable transparent background in your processing.js canvas, you need to add this directive to your javascript code:

You can find a working example in this Github repository.