Extension development guides

Hello everyone!
I have several modules under my belt now and have become quite comfortable with the process. I have just finished a module that will need an extension to introduce a couple of new damage types and a some languages. I would definitely want to learn the process as well as I know XML. What would you recommend to learn the process from start to finish.
P.S. I started learning full xml module development with the 5E Assets module and a few other guides if that matters.

try this: https://www.youtube.com/watch?v=R_Cu...668LyJXmfk25Yv